PEC 11 & 12 Assessment
para-Dichlorobenzene
____________________________
Priority Existing Chemical
Assessment Report No. 13
December 2000
Commonwealth of Australia 2000
ISBN 0 642 43266 X
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ii Priority Existing Chemical Number 13
Preface
This assessment was carried out under the National Industrial Chemicals Notification and
Assessment Scheme (NICNAS). This Scheme was established by the Industrial Chemicals
(Notification and Assessment) Act 1989 (the Act), which came into operation on 17 July
1990.
The principal aim of NICNAS is to aid in the protection of people at work, the public and the
environment from the harmful effects of industrial chemicals.
NICNAS assessments are carried out in conjunction with Environment Australia (EA) and
the Therapeutic Goods Administration (TGA), which carry out the environmental and public
health assessments, respectively.
NICNAS has two major programs: the assessment of the health and environmental effects of
new industrial chemicals prior to importation or manufacture; and the other focussing on the
assessment of chemicals already in use in Australia in response to specific concerns about
their health/or environmental effects.
There is an established mechanism within NICNAS for prioritising and assessing the many
thousands of existing chemicals in use in Australia. Chemicals selected for assessment are
referred to as Priority Existing Chemicals.
This Priority Existing Chemical report has been prepared by the Director (Chemicals
Notification and Assessment) in accordance with the Act. Under the Act manufacturers and
importers of Priority Existing Chemicals are required to apply for assessment. Applicants for
assessment are given a draft copy of the report and 28 days to advise the Director of any
errors. Following the correction of any errors, the Director provides applicants and other
interested parties with a copy of the draft assessment report for consideration. This is a period
of public comment lasting for 28 days during which requests for variation of the report may
be made. Where variations are requested the Director's decision concerning each request is
made available to each respondent and to other interested parties (for a further period of 28
days). Notices in relation to public comment and decisions made appear in the
Commonwealth Chemical Gazette.
In accordance with the Act, publication of this report revokes the declaration of this chemical
as a Priority Existing Chemical, therefore manufacturers and importers wishing to introduce
this chemical in the future need not apply for assessment. However, manufacturers and
importers need to be aware of their duty to provide any new information to NICNAS, as
required under section 64 of the Act.
For the purposes of Section 78(1) of the Act, copies of Assessment Reports for New and
Existing Chemical assessments may be inspected by the public at the Library, NOHSC, 92-
94 Parramatta Road, Camperdown, Sydney, NSW 2050 (between 10 am and 12 noon and 2
pm and 4 pm each weekday). Summary Reports are published in the Commonwealth
Chemical Gazette, which are also available to the public at the above address.
iii
para-Dichlorobenzene
Copies of this and other Priority Existing Chemical reports are available from NICNAS either
by using the prescribed application form at the back of this report, or directly from the
following address:
GPO Box 58
Sydney
NSW 2001
AUSTRALIA
Tel: +61 (02) 9577 9437
Fax: +61 (02) 9577 9465 or +61 (02) 9577 9465 9244
Other information about NICNAS (also available on request) includes:
NICNAS Service Charter;
information sheets on NICNAS Company Registration;
information sheets on PEC and New Chemical assessment programs;
subscription details for the NICNAS Handbook for Notifiers; and
subscription details for the Commonwealth Chemical Gazette.
Information on NICNAS, together with other information on the management of workplace
chemicals can be found on the NICNAS Web site:
http://www.nicnas.gov.au
iv Priority Existing Chemical Number 13
Overview
Para-dichlorobenzene (p-DCB; CAS No. 106-46-7) was declared a Priority Existing
Chemical on 7 April 1998. The declaration of p-DCB was in response to concerns relating to
possible human health risks and environmental hazards associated with the widespread use of
the material in school and public toilet blocks and urinals and as an air freshener.
Up to 1000 tonnes of p-DCB are imported and used annually in Australia. p-DCB is primarily
used as a deodoriser in toilet blocks, in household toilet bowls and as a room freshener. It has
some minor uses in the agricultural and pharmaceutical industries.
Occupational exposure to p-DCB in Australia is primarily due to operations involved in the
handling and processing of imported material. Exposure during such procedures may result
from inhalation of dust when opening bags of raw material and of vapour, produced by
sublimation or during melting and recasting operations. Exposure of the general public to p-
DCB is from the use of several consumer products that contain p-DCB.
p-DCB is absorbed well by inhalation and oral routes and less well by dermal contact. Target
organs for p-DCB are adipose tissue, liver, kidneys and lungs. Metabolism of p-DCB is by
aromatic hydroxylation and, depending on the species involved, results in the formation of
epoxides which are converted to their corresponding dichlorophenols. Further metabolism by
conjugation with sulfate or glucuronate can occur. The parent compound and its derivatives
are rapidly excreted in the urine. There is no evidence that p-DCB bioaccumulates in any
tissue.
Acute exposure to p-DCB vapour within the range of 30 to 60 ppm in air is associated with
irritation to the nose, eyes and upper respiratory tract. Exposure to vapour of 80 to 160 ppm
results in acute discomfort, painful irritation of the nose and eyes and may induce breathing
difficulties. Ingestion of large doses of p-DCB have been associated with vomiting, vertigo,
disorientation, tiredness and oedema. Chronic exposure to large doses of p-DCB may result in
headache, nausea, vertigo, ataxia, dysarthria, hyporeflexia, paresthesia, behavioural and
haematological changes including anaemia.
Genotoxicity studies of p-DCB have produced negative results. However, p-DCB does induce
the formation of kidney tumours in male rats and liver tumours in both sexes of mice after
prolonged exposure. The formation of kidney tumours in male rats is thought to be due to the
presence of the protein, 2?globulin. As 2?globulin is specific to the mature male rat, p-
DCB is not considered to present a carcinogenic risk to humans by this mechanism. The
tumours observed in mice after prolonged exposure to p-DCB are also considered to be
irrelevant to humans. There are significant differences in the metabolism of p-DCB in the
liver of mice and humans and it has been further observed that the mouse strains used
demonstrate a high natural rate for liver tumour formation.
Exposure of pregnant rats to p-DCB vapour produced no evidence of maternal toxicity or
embryo- or foetotoxicity. There have been no teratogenic effects observed in animals or
humans as a result of acute or chronic exposure.
v
para-Dichlorobenzene
Environmental exposure to p-DCB can occur due to the use of the product in toilets from
which it may be washed into the sewer system or enter the atmosphere by virtue of its volatile
nature. p-DCB does not persist in air or surface water but accumulates in anaerobic
sediments. p-DCB has a medium acute toxicity for aquatic life and may impair the
reproduction of aquatic life. However, based on current patterns of p-DCB use within
Australia, the risk to the environment is expected to be low.
The occupational risk assessment for p-DCB concluded that, for known Australian work
situations, potential atmospheric concentrations of p-DCB are unlikely to reach levels likely
to cause acute effects, including eye or respiratory irritation. In addition, it is unlikely that
workers in these occupations will be at risk from chronic adverse health effects related to p-
DCB exposure, as margins of exposure are generally high for inhalation exposure. In the
absence of any monitoring data for workers involved in the hygiene sector estimates for p-
DCB exposure were obtained using the UK EASE model. Results from this modelling
indicate that the risk to workers is expected to be low.
Recommendations for reducing potential occupational health and safety risks for p-DCB
include the monitoring of airborne p-DCB to be undertaken and a review of the current
occupational exposure standard for p-DCB by the National Occupational Health and Safety
Commission.
The hazard classification should be amended to include the follows safety phrases, S23 ( Do
not breath vapour), S24 (Avoid contact with skin), S25 (Avoid contact with eyes) and S51
(Use only in well ventilated areas).
vi Priority Existing Chemical Number 13
Contents
PREFACE iii
OVERVIEW v
ACRONYMS AND ABBREVIATIONS xiii
1. INTRODUCTION 1
1.1 Declaration 1
1.2 Objectives 1
1.3 Australian perspective 1
1.4 International perspective 2
1.5 Sources of information 2
1.6 Peer-review 3
2. APPLICANTS 4
2.1 List of applicants 4
3. CHEMICAL IDENTITY AND COMPOSITION 5
3.1 Chemical identity 5
3.2 Chemical composition 5
4. PHYSICAL AND CHEMICAL PROPERTIES 6
4.1 Physical properties 6
4.2 Chemical properties 7
5. METHODS OF DETECTION AND ANALYSIS 8
5.1 Identification 8
5.2 Atmospheric monitoring 8
5.3 Water monitoring 8
5.4 Soil and sediments analysis 9
5.5 Biological monitoring 9
6. MANUFACTURE, IMPORTATION AND USE 10
6.1 Manufacture and importation 10
6.1.1 Manufacture 10
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para-Dichlorobenzene
6.1.2 Importation 10
6.2 Use 10
6.3 Manufacture of air freshener/deodoriser blocks 12
6.4 Export 12
7. ENVIRONMENTAL EXPOSURE 13
7.1 Environmental exposure 13
7.1.1 Release 13
7.1.2 Fate 14
7.2 Predicted environmental concentrations 23
7.2.1 Local predicted environmental concentration in air 23
7.2.2 Local PEC in water 24
7.2.3 Continental PEC in water 25
7.2.4 Local PEC in soil 25
7.2.5 Comparison with measured environmental concentrations 26
8. OCCUPATIONAL EXPOSURE 28
8.1 Routes of exposure 28
8.2 Methodology for estimating exposure 28
8.3 Processing and formulation 28
8.4 Hygiene sector 30
8.5 Automotive/Marine Sector 31
9. TOXICOKINETICS AND METABOLISM 32
9.1 Absorption 32
9.1.1 Animals 32
9.1.2 Humans 33
9.2 Distribution 33
9.2.1 Animals 33
9.2.2 Humans 34
9.3 Metabolism 35
9.3.1 Animals 35
9.3.2 Humans 37
9.3.3 In vitro studies 37
9.4 Elimination and excretion 39
9.4.1 Animals 39
9.4.2 Humans 41
viii Priority Existing Chemical Number 13
9.5 Other studies 42
10. EFFECTS ON LABORATORY MAMMALS AND OTHER TEST SYSTEMS 45
10.1 Acute toxicity 45
10.1.1 Lethality 45
10.1.2 Systemic effects 45
10.1.3 Metabolites of p-DCB 47
10.2 Irritation and corrosivity 47
10.3 Sensitisation 48
10.4 Immunotoxicity 48
10.5 Repeated dose toxicity 48
10.5.1 Oral administration 48
10.5.2 Inhalation 52
10.5.3 Dermal 53
10.6 Reproductive and developmental toxicity 54
10.6.1 Reproductive toxicity 54
10.6.2 Developmental toxicity 55
10.7 Genotoxicity 57
10.8 Carcinogenicity 60
10.8.1 Oral exposure 60
10.8.2 Inhalation exposure 61
11. HUMAN HEALTH EFFECTS 63
11.1 Acute toxicity 63
11.2 Irritation and sensitisation 63
11.3 Repeated exposure 63
11.3.1 Case reports 63
11.4 Epidemiological studies 65
12. HEALTH HAZARD ASSESSMENT AND CLASSIFICATION 67
12.1 Physicochemical hazards 67
12.2 Kinetics, metabolism and mechanisms 67
12.3 Health hazards 69
12.3.1 Acute effects 69
12.3.2 Irritant effects 69
12.3.3 Sensitisation 71
12.3.4 Severe effects (non-carcinogenic) after repeated or
prolonged exposure 71
ix
para-Dichlorobenzene
12.3.5 Reproductive effects 72
12.3.6 Genotoxicity 73
12.3.7 Carcinogenicity 73
13. ENVIRONMENTAL EFFECTS 80
13.1 Aquatic toxicity 80
13.1.1 Toxicity to fish 80
13.1.2 Toxicity to aquatic invertebrates 81
13.1.3 Toxicity to aquatic plants 82
13.1.4 Toxicity to micro-organisms 82
13.1.5 Predicted no effect concentration for the aquatic
environment 83
13.2 Terrestrial toxicity 83
13.2.1 Terrestrial plants 84
13.2.2 PNEC for soil 85
14. OCCUPATIONAL RISK CHARACTERISATION 86
14.1 Methodology 86
14.2 Critical health effects and exposures 87
14.2.1 Acute effects 87
14.2.2 Chronic effects 87
14.3 Occupational health and safety risks 88
14.3.1 Risk from physicochemical hazards 88
14.3.2 Acute health risks 88
14.3.3 Chronic health risks 88
14.3.4 Uncertainties in the calculation of margins of exposure 89
15. ENVIRONMENTAL RISK CHARACTERISATION 90
15.1 Atmospheric risk 90
15.2 Aquatic risk 90
15.3 Terrestrial risk through agricultural use 91
16. PUBLIC HEALTH ASSESSMENT 92
17. RISK MANAGEMENT 94
17.1 Workplace control measures 94
17.1.1 Elimination and substitution 95
17.1.2 Isolation 95
x Priority Existing Chemical Number 13
17.1.3 Engineering controls 95
17.1.4 Safe work practices 95
17.1.5 Personal protective equipment 95
17.2 Emergency procedures 96
17.3 Hazard communication 96
17.3.1 Assessment of material safety data sheets (MSDS) 96
17.3.2 Assessment of labels 98
17.3.3 Standard for the Uniform Scheduling of Drugs and Poisons
(SUSDP) 99
17.3.4 Education and training 100
17.4 Other regulatory controls 100
17.4.1 Atmospheric monitoring 100
17.4.2 Occupational exposure standard 100
17.4.3 Health surveillance 101
17.4.4 Australian Code for the Transport of Dangerous Goods by
Road and Rail 102
18. DISCUSSION AND CONCLUSIONS 103
19. RECOMMENDATIONS 107
19.1 Hazard classification 107
19.2 Hazard communication 107
19.2.1 Material safety data sheets (MSDS) 107
19.2.2 Occupational health and safety 108
19.2.3 Occupational exposure standard 108
19.3 Public health 108
20. SECONDARY NOTIFICATION 109
Appendix 1 List of products containing p-DCB 110
Appendix 2 - Excerpt from the Approved Criteria (NOHSC, 1999a) 111
Appendix 3 Sample Material Safety Data Sheet for 1,4-Dichlorobenzene 116
REFERENCES 122
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para-Dichlorobenzene
LIST OF FIGURES
Figure 1 - Uses of p-DCB in Australia 11
Figure 2 - Metabolic pathways for the metabolism of p-DCB in humans, rats and mice 40
Figure 3 - Metabolism of 1,4-dichlorobenzene (p-DCB) by rat, mouse and human
hepatic microsomes 68
LIST OF TABLES
Table 1 - Chemical identity 5
Table 2 - Physical properties 6
Table 3 - Worst case environmental release estimates 14
Table 4 - Soil characteristics 16
Table 5 - Aerobic degradation test results 17
Table 6 - Anaerobic degradation test results 20
Table 7 - Bioaccumulation results (modified from SIAR, 1999) 22
Table 8 - Handling of p-DCB in Australia 29
Table 9 - Metabolites formed by hepatic microsomal metabolism of p-DCB 38
Table 10 - Summary of p-DCB acute lethality studies 45
Table 11 ?Summary of acute systemic effects due to p-DCB 46
Table 12 ?Summary of NOAEL and LOAEL values for p-DCB 56
Table 13 - Acute and chronic toxicity of p-DCB to Fish 81
Table 14 - Toxicity of p-DCB to aquatic invertebrates 81
Table 15 - Toxicity of p-DCB to aquatic plants 82
Table 16 - Toxicity of p-DCB to micro-organisms 83
Table 17 - Characteristics of soil types 83
Table 18 - Findings of the MSDS Assessment 97
Table 19 - Findings of the label assessment 99
Table 20 - Occupational exposure limits for p-DCB (ACGIH, 1998 ) 101
Table 21 - List of products containing p-DCB 110
xii Priority Existing Chemical Number 13
Acronyms and Abbreviations
8-oxodG 8-oxo-7,8-dihydro-2'-deoxyguanosine
ACGIH American Conference of Governmental Industrial Hygienists
ADE aldrin epoxidase
ADG Australian Dangerous Goods
AICS Australian Inventory of Chemical Substances
ALT alanine aminotransferase
APHA American Public Health Association
AST aspartate aminotransferase
ASTM American Standard Test Method
BCF bioconcentration factor
BOD biochemical oxygen demand
BrdU 5-bromo-2'-deoxyuridine
BSO buthionine sulfoximine
BUA Beratergremium f黵 Umweltrelevante Altstoffe
BUN blood urea nitrogen
bw body weight
CAS Chemical Abstracts Service
cDNA complementary deoxyribonucleic acid
CNS central nervous system
CYP cytochrome P450
DCB dichlorobenzene
DCBQ dichlorobenzoquinone
DCP dichlorophenol
DNA deoxyribonucleic acid
dw dry weight
EA Environment Australia
EASE Estimation and Assessment of Substance Exposure
EC50 concentration leading to a 50% reduction in biomass
EC European Commission
concentration at which an effect is produced in 50% of test organisms
EC50
ECD electron capture detection
ECOD 7-ethoxycoumarin O-deethylase
EH epoxide hydrolase
EINECS European Inventory of Existing Commercial Chemical Substances
ELS early life stage
concentration leading to a 50% reduction in growth rate
E礐50
EPA Environmental Protection Agency (USA)
EROD 7-ethoxyresorufin O-deethylase
EU European Union
F344 Fisher-344
FID flame ionisation detection
GC gas chromatography
GLP good laboratory practice
GLT glucuronyl transferase
-GT -glutamyl transferase
xiii
para-Dichlorobenzene
GSH glutathione
GST glutathione S-transferase
HPLC high performance liquid chromatography
IUCLID International Uniform Chemical Information Database
IARC International Agency for Research on Cancer
IUPAC International Union of Pure and Applied Chemistry
i.p. intraperitoneal
i.v. intravenous
LBB lethal body burden
LC lethal concentration
LD lethal dose
LDH lactate dehydrogenase
LOAEL lowest observed adverse effect level
m-DCB meta-dichlorobenzene (1,3-dichlorobenzene)
MLD minimum lethal dose
MOE margin of exposure
MS mass spectroscopy
MSDS Material Safety Data Sheet
NADH nicotinamide adenine dinucleotide (reduced)
NADPH nicotinamide adenine dinucleotide phosphate (reduced)
NDPSC National Drugs and Poisons Schedule Committee
NICNAS National Industrial Chemicals Notification and Assessment Scheme
NIOSH National Institute for Occupational Safety and Health (USA)
NOAEL no observed adverse effect level
NOEC no observed effect concentration
NOHSC National Occupational Health and Safety Commission
NTP National Toxicology Program (USA)
OECD Organization for Economic Cooperation and Development
o-DCB ortho-dichlorobenzene (1,2-dichlorobenzene)
p-DCB para-dichlorobenzene (1,4-dichlorobenzene)
PEC predicted environmental concentration
PID photoionization detection
PNEC predicted no effect concentration
PPE Personal protective equipment
ppm parts per million
QSAR Quantitative Structure-Activity Relationship
RNA ribonucleic acid
RTECS Registry of Toxic Effects of Chemical Substances
S-D Sprague-Dawley
SDH sorbitol dehydrogenase
STEL short-term exposure limit
STP sewage treatment plant
SUSDP Standard for the Uniform Scheduling of Drugs and Poisons
TGA Therapeutic Goods Administration
TOC total oxygen concentration
TWA time-weighted average
UDS unscheduled DNA synthesis
UK United Kingdom
UN United Nations
xiv Priority Existing Chemical Number 13
1. Introduction
1.1 Declaration
The chemical para-dichlorobenzene (p-DCB), Chemical Abstracts Service (CAS)
number 106-46-7, was declared a priority existing chemical for full assessment under
the Industrial Chemicals (Notification and Assessment) Act 1989 (the Act), as
amended, by notice in the Chemical Gazette on 7 April 1998.
The declaration was made on the basis that there were reasonable grounds for
believing that the handling and use of p-DCB may give rise to a risk of adverse
health effects. In summary, these grounds were:
? the potential for occupational and environmental exposure and potential adverse
health effects and in particular, possible carcinogenic effects;
? lack of publicly available information on the health and environmental effects of
p-DCB which is of concern in view of their widespread use and potential for
exposure; and
? a need for characterisation of exposure and associated health and environmental
risks.
In accordance with the Act, persons who wished to manufacture or import p-DCB
into Australia were required to apply for assessment whilst p-DCB remained a
priority existing chemical. As p-DCB is not manufactured in Australia, applications
were limited to importers. A list of applicants is included in Section 2.
1.2 Objectives
The objectives of this assessment were to:
? characterise the hazards of p-DCB to human health (particularly carcinogenicity)
and the environment;
? characterise current and potential occupational, public and environmental
exposure to p-DCB;
? characterise the risk of adverse effects resulting from exposure to workers, the
general public, and the environment; and
? make appropriate recommendations to control exposures and/or reduce potential
health and environmental risks.
1.3 Australian perspective
The primary use of p-DCB in Australia is as a deodoriser for use in public toilet
facilities. Domestically, p-DCB is used in households as a deodorant and a room
1
para-Dichlorobenzene
freshener. It has some minor use as a moth repellent and mildew control agent and in
the agricultural and pharmaceutical industries.
Due to the widespread use of p-DCB in Australia there has been concern over
possible health effects, including eye and upper respiratory tract irritation and
concern that it may be a possible human carcinogen.
The declaration of p-DCB as a Priority Existing Chemical (Chemical Gazette 7 April
1998) indicated that it was to be assessed with ortho-dichlorobenzene. While under
investigation it became apparent that the use and toxicological profiles of these two
chemicals were substantially different. Consequently, the two chemicals have been
assessed and published separately. The ortho-dichlorobenzene report may be
obtained from NICNAS.
1.4 International perspective
Historically, p-DCB has been manufactured and used internationally on a large scale
for several decades. p-DCB has been used extensively in industrial and domestic
situations as a space deodorant, toilet deodoriser, moth repellent and mildew control
agent. It has been used as an insecticide for the control of termites and other
organisms in soil and as a fungicide agent for the control of plant diseases. Other uses
of p-DCB have included the manufacture of dyes, polyphenylene sulfide resin and
1,2,4-trichlorobenzene and in the pharmaceutical and agricultural industries.
1.5 Sources of information
Information required for assessment was supplied by applicants and notifiers and
located through comprehensive database and literature searches.
Reviews on health effects of p-DCB by other national or international organisations
have been carried out by Environment Canada (1993), the UK Health and Safety
Executive (1994), the United States Department of Health and Human Services
(1998) and the OECD (SIAR, 1999).
Due to the availability of a number of overseas assessment reports, not all primary
sources of data were evaluated. All critical studies, that is, those which contribute
significantly to an understanding of the metabolism, toxicity, clinical effects and
hazard evaluation of p-DCB, have been evaluated for this report and their content
have been taken into consideration in making the recommendations stemming from
this assessment. Sources referred to but not sighted are acknowledged in the body of
this report and in the Reference Section. All relevant studies published since these
reports became available have been evaluated. The last literature search for this
assessment was conducted on 14 March 2000.
In addition, surveys were conducted by NICNAS. Questionnaires were designed and
sent to importers, re-sellers, re-packers, formulators, and end users of p-DCB to
obtain information on amounts of p-DCB imported, uses, formulation process,
Material Safety Data Sheets (MSDS), labels, worker and environmental exposure,
2 Priority Existing Chemical Number 13
and control measures. Workplace site visits were also carried out to obtain
information to assist in the assessment.
1.6 Peer-review
During all stages of preparation, this report has been subject to internal peer review
by NICNAS, Environment Australia and the Therapeutic Goods Administration. The
toxicology/hazard assessment component of this report was peer reviewed by Dr
Michael Davies of the Heart Research Institute, Camperdown, NSW, Australia. Dr
George Nossar of Royal Prince Alfred Hospital provided advice on respiratory
irritation and Dr Gene McConnell of ToxPath Inc. provided advice on
carcinogenicity.
3
para-Dichlorobenzene
2. Applicants
2.1 List of applicants
Following the declaration of p-DCB as a Priority Existing Chemical, 7 companies
responded as either importers or potential importers of p-DCB into Australia for use
as air freshener/deodorant blocks or research use. The applicants supplied
information on the properties, import quantities and uses of the chemical. In
accordance with the Industrial Chemicals (Notification and Assessment) Act 1989,
NICNAS provided the applicants with a draft copy of the report for comment during
the corrections/variation phase of the assessment. Data for the assessment were also
provided by 4 notifiers, that is, companies which purchase p-DCB in Australia and
formulate it into various products.
The applicants were, as follows:
Amtrade International P/L Redox Chemicals P/L
PO Box 6421 30-32 Redfern Street
St. Kilda Road Central PO Locked Bag No. 60
Melbourne Wetherill Park
Victoria 3004 NSW 2164
Bio-Scientific Pty Ltd Sigma-Aldrich
PO Box 78 PO Box 970
Gymea Castle Hill
NSW 2227 NSW 2154
Crown Scientific Pty Ltd Unipuns International Pty Ltd
144 Moorebank Avenue PO Box 1109
Private Mail Bag 4 Ferntree Gully
Moorebank Victoria 3128
NSW 2170
Recochem Inc
PO Box 478
Wynnum
Queensland 4178
4 Priority Existing Chemical Number 13
3. Chemical Identity and
Composition
3.1 Chemical identity
Table 1 - Chemical identity
Chemical name (IUPAC) 1,4-Dichlorobenzene
Other names para-dichlorobenzene
p-Dichlorobenzene
p-DCB
1,4-DCB
CAS Number 106-46-7
EINECS Number 203-400-5
RTECS Number CZ4550000
C6H4Cl2
Empirical formula
Cl
Structural formula
Cl
Molecular weight 147.00
Trade and product names are listed at Appendix 1.
3.2 Chemical composition
Commercially available p-DCB in Australia is typically more than 99.8% pure and
contains the following impurities:
0.1% 1,2- and 1,3-dichlorobenzene
0.05% chlorobenzene and trichlorobenzenes
5
para-Dichlorobenzene
4. Physical and Chemical Properties
4.1 Physical properties
p-DCB is a volatile solid, present as colourless or white crystals at ambient
temperature and pressure (Merck, 1989). It has an aromatic, camphor-like odour with
an odour threshold in air of 0.18 ppm and an odour threshold in water of 0.011 mg/L
(Amoore and Hautala, 1983).
Conversion factors
1 ppm = 6.01 mg/m3 and 1 mg/m3 = 0.17 ppm (at 20oC and 1013 hPa; Verschueren,
1996).
The physical properties of p-DCB are given in Table 2.
Table 2 - Physical properties
Property Value Reference
53.1oC
Melting point Lide, 1994
174.55oC
Boiling point Lide, 1994
Flash point
66oC NFPA 1994
(closed cup)
> 5000C
Ignition Temperature Rathjen, 1975
Density (20oC) 1.2475 g/cm3 Lide, 1994
Vapour pressure (20oC) 0.84 hPa Verschueren, 1983
Water solubility (25oC) 79 mg/l Verschueren, 1996
Soluble in alcohol, ether,
Solubility in organic solvents Lide, 1994
acetone, benzene
Henry's Law constant (25oC) 321.1 Pa.m3/mol BUA, 1994
Banerjee et al., 1980
Partition coefficient (25oC) Log Pow = 3.37
Miller et al., 1985
6 Priority Existing Chemical Number 13
4.2 Chemical properties
Hydrolysis
Hydrolysis of p-DCB to p-chlorophenol and hydroquinone proceeds only under
drastic conditions (days at > 200oC).
Combustion products
Oxides of carbon, hydrogen chloride gas and some phosgene may form on
combustion of p-DCB.
Reactivity
p-DCB may react vigorously with oxidising materials (Sax, 1996). p-DCB may react
with some plastics, particularly styrene, acrylonitrile, and acrylonitrile-butadiene-
styrene based plastics, rubber and coatings.
Polymerisation
p-DCB does not polymerise.
Explosivity
p-DCB does not form explosive mixtures with air.
7
para-Dichlorobenzene
5. Methods of Detection and Analysis
5.1 Identification
The isomers of dichlorobenzene are quantitatively determined by gas
chromatography (GC) and, if required for definitive analysis, gas
chromatography/mass spectroscopy (GC-MS). Sample preparation is based on
concentration techniques utilising adsorption onto porous resins or activated charcoal
with thermal or extractive desorption techniques followed by electron capture (ECD),
flame-ionisation (FID) or photoionization (PID) detection. The use of capillary
columns has been found to provide better resolution and sensitivity than packed
columns (Washall and Wampler, 1988).
The analytical accuracy for p-DCB can be influenced by several factors such as
sampling flow rates, temperature and humidity. These factors can influence the
adsorption of p-DCB onto various sorbants (APHA, 1995). Separation of all isomers
of dichlorobenzene can be achieved using Carbowax 20M coated glass capillary
columns with isothermal or temperature gradient methods (Korhonen, 1983).
The purity of bulk dichlorobenzenes can be determined by melting point analysis.
5.2 Atmospheric monitoring
NIOSH method 1003, for the determination of occupational airborne p-DCB
(NIOSH, 1994) entails the passage of 10 litres of sample volume over activated
charcoal at a rate of 50 to 200 mL/min. Desorption is achieved with carbon disulfide
followed by GC-FID. The detection limit is 0.1 mg/m3.
The determination of dichlorobenzenes in ambient air can be achieved by either
passive or active means. Passive sampling involves adsorption onto activated
charcoal with desorption by carbon disulfide followed by capillary GC. Active
methods include adsorption onto Tenax (a porous polymer) using an air flow rate of
23 L/hr. Thermal desorption at 200o to 250oC is followed by GC/MS (Wallace,
1987). The limit of detection is within the ng/m3 range.
Information provided by an industry survey indicated that, within Australia, detection
of airborne p-DCB at one workplace is achieved by the use of Dr鋑er short term
sampling tubes (type: chlorobenzene 5/a; qualitative). The method is not specific for
p-DCB and the range and accuracy of the tube was stated to be 5 to 200 ppm ?15%.
5.3 Water monitoring
Determination of dichlorobenzenes in water samples can be achieved using several
methods. Older methods utilise liquid/liquid partitioning. The UK Department of the
Environment (1986) method requires a 2-litre sample of water to be extracted with
8 Priority Existing Chemical Number 13
hexane and an aliquot subjected to capillary column analysis with GC-ECD or GC-
FID. If wastewater is to be analysed clean up of the sample will be required. The
detection limit for p-DCB is stated to be in the range of 9 ng/mL for surface water
and 420 ng/mL for wastewater.
Recent techniques depend on purging the sample with an inert gas, usually helium or
nitrogen, which is then passed through a sorbent. Final analysis is achieved by
thermal desorption followed by GC or GC/MS techniques. The detection limit varies
depending on the quality of water sampled and can range from 0.1 to 100 ng/mL. For
wastewater, an intermediate clean-up procedure is required.
5.4 Soil and sediments analysis
The determination of p-DCB in soil or sediment samples according to the method of
Oliver and Bothen (1982) involves the extraction of 30 g wet weight (or 10 to 15 g
dry weight) of sample with hexane/acetone. GC-ECD is proceeded by extraction and
column chromatography. The detection limit is given as 5 礸/kg.
5.5 Biological monitoring
The presence of dichlorobenzenes in biological samples including urine, blood,
tissues, milk and breath can be detected by various techniques, however, many of the
techniques have not been validated. Generally, extraction of dichlorobenzenes from
biological samples requires liquid/liquid partitioning or, for blood, urine and human
milk, purge techniques using an inert gas can be used.
The presence of p-DCB in breath can be detected without the need for prior clean-up
by the use of a spirometer to provide pure air and an adsorbent cartridge or canister
for collection of the breath samples (Thomas et al., 1991). Analyates are then
concentrated or thermally desorbed prior to detection by GC/MS. The detection limit
using Tenax cartridges is approximately 1 礸/m3.
9
para-Dichlorobenzene
6. Manufacture, Importation and Use
6.1 Manufacture and importation
6.1.1 Manufacture
The manufacture of p-DCB does not occur in Australia but is undertaken in the USA,
Canada, Europe and Japan. In 1989, it was estimated that the world-wide production
capacity (excluding the former USSR) for p-DCB was 165,000 tonnes while world-
wide consumption for the same year was estimated to be 113,000 tonnes (BUA,
1994).
The manufacture of p-DCB is accomplished by the fluid phase chlorination of
benzene in the presence of a catalyst, usually ferric chloride, aluminium chloride or
stannous tetrachloride, at atmospheric pressure between 20 to 80oC (Beck, 1986). By
adjusting the temperature of the process and the molar ratio of benzene to chlorine,
the percentage of final chlorinated products can be determined. The process typically
yields a mixture of chlorobenzene, isomers of dichlorobenzene and small quantities
of higher chlorinated benzenes. Subsequent purification is achieved by distillation
and fractional crystallisation. The resulting p-DCB contains less than 0.5% each of
1,2- and 1,3-dichlorobenzene and less than 0.1% monochlorobenzene and
trichlorobenzene.
6.1.2 Importation
Based on Customs import data and industry information, for the past 5 years the
amount of p-DCB imported into Australia typically ranges between 500 to 1000
tonnes per annum.
In 1998, five companies imported p-DCB into Australia. Imported raw material
arrives in shipping containers, packaged in 4 ply paper bags each containing 25 kg
net weight of p-DCB. Imported material is typically 99.8% pure. Only one company
was identified as an importer of a finished product (a pharmaceutical) containing p-
DCB. The imported raw material is used in the formulation of air freshener and toilet
deodorant blocks and, to a lesser extent, insect repellent blocks and veterinary
products.
6.2 Use
Within Australia, p-DCB is used almost exclusively for the production of air
freshener and toilet deodorant blocks, where the chemical acts mainly to disguise
odours.
A survey of the handling and uses of dichlorobenzenes was undertaken by NICNAS.
The survey identified the following areas and sectors of industry in which p-DCB is
10 Priority Existing Chemical Number 13
regularly used, mostly as an air freshener/deodoriser and predominantly in toilet
facilities:
? State Government (public buildings, police stations, correctional institutions);
? Council buildings (public toilet facilities);
? Schools (public and private);
? Motels/Inns/Caravan Parks/Resorts;
? Hotels/Leagues Clubs/Service Clubs/Night Clubs;
? Sporting Clubs and Sporting Facilities (e.g. bowls clubs);
? Industry (company toilets, transport, packaging, automotive and marine sector);
? Cleaning industry (associated with cleaning the facilities provided in the above
areas); and
? Household use (as an air freshener/deodorant and moth/silverfish repellent).
To use an air freshener/deodoriser or repellent disk, the cellophane wrapping is
punctured and the disk is left in a suitable location. The p-DCB undergoes
sublimation and the vapour disperses. Where use in urinals is required, the blocks or
disks are unwrapped and placed directly in the urinal. A breakdown of the uses of p-
DCB is presented in Figure 1.
Figure 1 - Uses of p-DCB in Australia
Toilet blocks
85%
Insect Repellent
Pharmaceutical &
<1%
Veterinary
Air freshener
<1%
13%
An estimated 5 tonnes per year (less than 1%) of p-DCB are used in the agricultural
sector. The National Registration Authority for Agricultural and Veterinary
Chemicals has 7 products registered with p-DCB listed as an active constituent.
Three are for moth repellency for home use, e.g. in candles or coils. The
concentration of p-DCB in these products is 990 to 1000 g/kg. The other
11
para-Dichlorobenzene
formulations are classified as veterinary products. These are topical dressings and are
registered for use as blowfly strike treatments (p-DCB present at 50 to 400 g/kg) or
mulesing fluids (p-DCB present at 10 g/kg).
A small quantity, approximately 30 kg, is imported as a finished product for
pharmaceutical use.
Further consideration of non-industrial uses (agricultural/veterinary and
pharmaceutical) is not included in this assessment.
Approximately 10 kg of analytical grade material was identified for use in Australia
for teaching and research purposes in schools and universities.
6.3 Manufacture of air freshener/deodoriser blocks
The major process involved in the manufacture of air freshener and toilet deodorant
blocks is the addition of dye and perfume to p-DCB and then compression of flaked
or granular p-DCB into disks or blocks. Due to a tendency for the imported material
to become fused whilst in transit prior processing of the material is required, either
melting/recrystallising and flaking or milling. The p-DCB is added to a hopper from
which it enters an enclosed tank and reduced to a molten state by heating to 60oC. A
small quantity of dye and perfume are added prior to spreading the liquefied material
onto a stainless steel conveyer belt which results in the formation of a thin layer of
blended material suitable for flaking. Alternatively, the solid material is milled and
then mixed with dye and perfume. The next step involves the pressing of the blended
material into blocks of the required weight, typically 25, 50 or 100 g blocks.
Subsequently, the blocks are wrapped in cellophane, labelled and boxed for
distribution.
One importer also supplies blended p-DCB (containing dye and perfume) in flake
form in 600 kg bags for sale to other processors who press and wrap the product.
The amount of p-DCB in finished commercially available air freshener/deodorant
products ranges from 988 to 992 g/kg.
6.4 Export
A small quantity of p-DCB products (air freshener and toilet deodorant blocks) for
export was identified. The amount of material exported accounted for less than 1% of
all raw material imported into Australia.
12 Priority Existing Chemical Number 13
7. Environmental Exposure
7.1 Environmental exposure
No studies with respect to environmental fate and toxicity were provided by
applicants. As such, international reports and summary data have been relied upon.
Reports available include the German BUA Report (BUA, 1994), the Canadian
Environmental Protection Act report (1993), and the OECD draft report (SIAR,
1999). Data within these reports are largely the same and appears in the IUCLID
datasheet (International Uniform Chemical Information Database), which has also
been used where appropriate, predominantly to obtain fate and toxicity data. Results
from this datasheet are non-confidential data supplied to the European Commission
by European industry. Where IUCLID results appear in the SIAR (1999), original
reports have been validated by the French authorities.
7.1.1 Release
Less than 1000 tonnes/year are used in the formulation and end use of air
freshener/toilet blocks.
Reformulation
The manufacture/reformulation of p-DCB into air freshener/deodoriser blocks is
described above in Section 6.3. There are no actual figures on release estimates
during this process, but melting of the imported product is conducted in an enclosed
tank, where releases to air and water are expected to be minimal. Generally, it would
be expected that, compared to the end use of the product, release to water will be
negligible through this process, with any release being predominantly to the
atmosphere. While no specific data on releases to the atmosphere are available, a
default release factor of 1% will be used based on the Technical Guidance Document
(European Commission, 1996). Up to 10 tonnes may be expected to be released
annually. Assuming reformulation processes are conducted on 200 days of the year,
this results in estimated release to the atmosphere of up to 50 kg per day.
End use
Figure 1 shows in the order of 13% p-DCB used in air fresheners and 85% used in
toilet blocks.
When used in air fresheners, release is assumed to be primarily to air, while use in
toilet blocks will see release to both the atmospheric and aquatic compartments.
In the SIAR report (1999) on p-DCB, it was estimated based on a literature report
that 67% of the toilet block evaporated during use. In the absence of other
information, for the purposes of this assessment, this estimation will also be used,
13
para-Dichlorobenzene
with the remainder assumed to go to the sewer system. Therefore, annual releases of
p-DCB when used in toilet blocks will consist of up to 570 tonnes evaporating to air,
and up to 280 tonnes per annum being released to sewer.
Releases of p-DCB are summarised in Table 3. These are worst case calculations
based on a maximum use of 1000 tonnes per annum.
Table 3 - Worst case environmental release estimates
Quantity of Release Annual Days
Daily release (kg)
use (%) release per year
(kg) (kg) Air Water Soil
Reformulation 1000000 1 10000 200 50 - -
End use
Air freshener 130000 100 130000 365 356 - -
Toilet Blocks 850000
- Air 67 570000 365 1560 - -
- Water 33 280000 365 - 770 -
Total Daily Releases 1966 770 0
7.1.2 Fate
Modelling predicts that at equilibrium, in the order of 99% of this chemical will
partition to air, with 0.22% and 0.66% partitioning to water and soil respectively
(Trent University, 1998). Negligible amounts are expected to partition to sediments,
suspended sediment, biota and aerosols.
Equilibrium was determined using the Australian Capital Territory as a model inland
environment with Lake Burley Griffin as the water body, and using environmental
inputs for volumes of air, soil, water etc. as described in Connell and Hawker (1986).
Atmospheric fate
p-DCB is expected to partition predominantly to the atmosphere at equilibrium. The
chemical absorbs radiation weakly at wavelengths greater than 300 nm, so direct
photolysis in the atmosphere is not likely (Government of Canada, 1993). However,
reaction with photochemically produced hydroxyl radicals in the atmosphere will
occur. Howard et al. (1991) has estimated the photo-oxidation half-life to range
between 8.4 to 83.6 days.
The hydroxyl radical reaction rate constant for p-DCB in the atmosphere was
determined experimentally at 270C as 4.8 x 10-13 cm3/molecule/s, and at 220C as 3.2 x
10-13 cm3/molecule/s using different methods (BUA, 1994). Assuming a global mean
hydroxyl radical concentration of 5x105 molecule/cm3, this corresponds to half-lives
of 33 and 50 days, which is within the range reported above.
14 Priority Existing Chemical Number 13
The presence of p-DCB in rainwater indicates that it persists long enough to be
returned to the earth's surface by atmospheric wash out (Government of Canada,
1993).
Aquatic fate
Experimental Henry's Law Constants have been reported in BUA (1994), and range
from 214.8 Pa.m3/mol (10oC) to 394.1 Pa.m3/mol (30oC). The experimental result at
25oC was 321.1 Pa.m3/mol. According to the scale of Mensink (1995), these results
suggest p-DCB is readily volatile from aqueous solution. Wang and Jones (1994)
state that volatilisation has been found to be the predominant removal process for
chlorobenzenes from lakes and coastal seawater.
Howard (1989) reported an estimated half-life of 4.3 hours from a model river one
metre deep flowing at 1 m/s with a wind velocity of 3 m/s at 200C. Other
volatilisation half-lives ranging between <1 and 31 days have been reported
(Government of Canada, 1993).
An experiment conducted to investigate the fate of p-DCB in coastal water by means
of a mesocosmic plant is described in BUA (1994). In open water tanks, with a
height of 5.5 m and diameter of 1.8 m, environmentally relevant concentrations of a
mixture of test substances were added to 13 m3 of unfiltered seawater (no sediment
was present). The water was stirred four times per day for two hours, to simulate
tides and water currents. The experiment was conducted in spring, summer and
winter, and reported half lives of 18, 10 and 13 days respectively. Further, in
summer, the experiment was conducted with and without addition of the microbicide
HgCl2, and resulted in similar half lives of 10.6 and 11 days respectively. This ruled
out the possibility that biodegradation by plankton and microorganisms may
contribute to total elimination.
In contrast to modelling predictions, monitoring data conducted in the Great Lakes
area of North America indicate that adsorption to sediment is a major environmental
fate process. Its detection in Lake Ontario sediment cores indicates that the chemical
has persisted in these sediments for decades. Adsorption to sediment in water will
attenuate volatilisation. p-DCB may biodegrade in aerobic water after microbial
adaptation; however it is not expected to biodegrade under anaerobic conditions
which may exist in lake sediments or various ground waters (Howard, 1989).
Similarly, extensive monitoring data tabulated in the SIAR (1999) report shows
sediment readings from rivers in Germany, France, the Netherlands, Denmark and
Japan. Sediment measurements tended to greatly exceed those found in the surface
waters, with concentrations in sediments ranging from <0.01 to >103 礸/kg dw.
Reported concentrations in surface waters ranged from <0.01 to 4.05 礸/L. For a
more detailed discussion of monitoring data, see Section 7.2.5.
If groundwater is exposed to p-DCB, due to the low bacterial density, low oxygen
content, and generally very low organic matter content, a long residence time is
expected which may last for decades (BUA, 1994).
15
para-Dichlorobenzene
Terrestrial fate
The IUCLID data sheet provides several results (with test reports validated in the
SIAR (1999) though conditions are not available in detail for all the tests) in a wide
range of soils and sediment with Koc values ranging from 155 to 1375 (mean 584).
The highest Koc of 1375 was reported for a sediment and no other characteristics are
available.
The SIAR (1999) states that some tests were performed with very low contents of
organic carbon thereby increasing the possible error of the result. The OECD Test
Guideline 106 suggests an organic carbon content of 0.6 to 3.5%. Results obtained
from soils with an organic carbon content in this range are reported in Table 4.
1
Table 4 - Soil characteristics
2
Soil % Sand % Silt % Clay % OC pH Koc
Sandy soil 90 8 2 2.6 4 155
Silty loam 9 68 21 1.1 - 273
Dormont 2 38 60 1.2 4.2 280
Sandy agricultural soil 86.5 7.5 1.4 2.2 4.8 364
Podsol 81.5 10 7.2 3.56 3.88 744
Rendzina 8.5 68.3 20.6 1.11 7.9 748
1
(data from SIAR 1999); 2 OC = organic carbon.
These results are suggestive of medium to low mobility. From these data, Koc
appears independent of the various soil characteristics including pH. The less reliable
results obtained with very low contents of organic carbon (<0.76% and not reported
in the above table) which are typical of many parts of Australia, tended to show
higher Koc values (>595).
Leaching from hazardous waste disposal areas in Niagara Falls to adjacent surface
waters has been reported and the detection of p-DCB in ground water indicates that
leaching can occur (Howard, 1989). Findings of leaching are supported by Robertson
(1994) where a tracer experiment was conducted in which 450 mL of a plumbing line
cleaner containing dichlorobenzene and 1 kg sodium bromide were injected into a
septic system. Dichlorobenzene concentrations of up to 3460 礸/L were observed in
the septic tank effluent, up to 650 礸/L in the unsaturated zone 0.45 m below the tile
bed, and up to 13 礸/L at the water table at 2 m depth.
However, Wang and Jones (1994) suggest that while dichlorobenzenes may have
some potential to leach in soils due to the convective mobility, because of the high
volatility of these chemicals, dissipation to the atmosphere will be very rapid, except
in those cases where continuous downward movement or a soil cover prevents escape
through the soil surface. They further claim that chlorobenzenes in soil have a low
potential to leach downward to groundwater. Results from one experiment (details
not provided) showed p-DCB did not leach through large Dutch soil columns with a
water table at a metre depth (Wang and Jones, 1994).
16 Priority Existing Chemical Number 13
Volatilisation from soil surfaces may be an important transport mechanism; however,
this may be mitigated by absorption or leaching. It is possible that the chemical can
be slowly biodegraded in soil under aerobic conditions. Chemical transformation
processes such as hydrolysis, oxidation, or direct photolysis on soil surfaces are not
expected to occur (Howard, 1989).
Biodegradation
Results within the IUCLID data sheet have been assessed, but none of the original
reports have been provided. The discussion in the SIAR (1999) with respect to
biodegradation is brief, and does not contain many of the results provided in
IUCLID. These are limited only to a couple of results from standard test systems (see
Tests 1 and 3 in Table 5), where mineralisation is determined.
There appear to be no results from standard tests for soil and sediment.
Aerobic Degradation
Table 5 summarises results from the IUCLID data sheet and the BUA (1994) report.
There are some discrepancies between results listed in the IUCLID data sheet and the
discussion from the BUA report. Where these discrepancies occur, the results from
the BUA report have been used as these have been validated.
Table 5 - Aerobic degradation test results
Test Inoculum Method Result
1 Activated sludge OECD 301D 67% after 28 days
2 Activated sludge OECD Confirmatory Test 30% after 21 days
3 Activated sludge. MITI Test 100% after 28 days (8
ppm)
4 Activated sludge Respirometric (EU) 20% after 21 days
(unpublished)
5 Sewage plant effluent Biofilm column test 61-79% (time not
reported)
6 Primary sewage sludge Biofilm column test 98% degraded (2 years)
7 Primary sewage sludge Biofilm column test 40-52% (1.5 hours)
8 Microorganisms from upper Batch test 100% after 5 days
layer of slow sand filter
9 Microorganisms from upper Biofilm column test 0-49% depending on flow
layer of slow sand filter rate (7 days).
10 Aquifer material from the Soil column 90->99.9% (6 d flooding;
interface of a river/ground 16 d drying; 3 cycles)
water infiltration site
Test 1 was based on oxygen consumption and showed 1.4% of the original
concentration (1.9 ppm) was degraded after 8 days, 49.5% after 15 days and 67%
after 28 days. Complete degradation of the transformation products was confirmed
17
para-Dichlorobenzene
through HPLC analysis. In addition to this test, the author further investigated the
degradability of the chemical in a continuous OECD confirmatory test after a 15 day
adaptation period (Test 2). While an elimination rate of 97% was determined, 31% of
this was attributed to biodegradation with the remainder attributed to volatilisation
and adsorption to sewage sludge.
Test 3 determined degradation of p-DCB at 8 and 40 ppm in primary sludge with the
test medium supplemented by nutrient substances. After 14 days, no degradation was
observed at any concentration. In both replicates for the 8 ppm concentration, 100%
degradation was observed after 28 days, while 0 and 38% were observed in the 40
ppm test. The mineralisation of p-DCB was determined by oxygen consumption,
which reached about 80% of the theoretical oxygen demand. The authors assumed
the initial concentration of 40 ppm had a toxic effect on the sewage sludge.
Test 4 is unpublished and no details are available.
Biofilm experiments are carried out as a model for trickling filter sewage plants, and
several are reported. Test 5 used inoculum from the outlet of a sewage plant
nitrification tank, and investigated the degradation of chlorinated benzenes and
phenols. At initial concentrations of 1 and 5 ppb degradation of 69 to 79% and 61 to
72% respectively is reported. The duration of the experiment is unclear. The system
was closed so losses through other means are excluded.
Test 6 was a two year experiment investigating degradation of approximately 10 ppb
p-DCB in a mixture of several other chlorinated compounds in a closed system
comprising a column filled with glass beads and charged from below, and a biofilm
of primary sludge of unknown origin. Sodium acetate (1.39 ppm) was used as the
primary substrate and added to the mineral medium. The reaction time in the column
was approximately 20 minutes, and organisms adapted to the p-DCB within about 10
days. An average p-DCB biodegradation of 98% was observed. The authors found no
intermediate metabolites in the efflux of the control column.
A 4.5 year biofilm degradation test in a 1 m long column filled with glass beads is
described (Test 7). The column was inoculated with municipal primary sludge and
charged with an oxygen-saturated solution by a continuous flow through method. The
addition of electron acceptors facilitated the formation of aerobic, denitrifying and
sulfate-reducing zones with correspondingly different redox potentials. The
degradation appeared to be between 40 and 52% for the duration of the experiment.
A very limited aerobic zone and large supply of acetate (60 ppm) which is more
readily metabolised, led the authors to predict a lower utilisation of p-DCB which
provides less energy.
Test 8 determined the biodegradation of p-DCB through a mixed population of
microorganisms originating directly from the upper layer of former slow sand filters
in a water processing plant. Bottle tests were performed in glass flasks on shaking
apparatuses containing a bacterial suspension and p-DCB at concentrations of 3 and
15 ppb. Concentration reductions of 30% and 100% were reported after 1.5 and 5
days respectively. Experiments under sterile conditions showed the decrease of p-
DCB to be due to biological effects.
18 Priority Existing Chemical Number 13
The authors of the above study also conducted a biofilm investigation with four glass
columns filled with sintered glass material (Test 9). Three columns operated on a
flow through system, with one operating by recirculation. Flow rates were either 1 or
5 litres per hour, and degradation rates obtained at 7 days after commencement. The
results where the flow rate was 1 litre per hour showed 25 to 40% degradation in the
flow through columns and 49% degradation in the recirculation column. With a flow
rate of 5 litres per hour, the flow through columns showed degradation of 0 to 32%
with 41% degradation reported in the recirculation column. These results indicate
that the flow through conditions lead to lower degradation, and degradation is
reduced with faster rates of flow.
A flooding/drying schedule was used to investigate the degradation of organic trace
substances in sandy soil from a rapid infiltration area for waste water and crude waste
water (Test 10). Three cycles, consisting of 6 days of flow through (infiltration rate
of 34 cm per day) and 16 days of drying, were conducted both aerobically and then
anaerobically. Concentrations tested were 5, 10, 70 and 500 ppb. The aerobic column
flowoff showed between 0.03 and 10% of the initial concentration in eluate. No real
inferences on biodegradation can be drawn from this as no comment is made on the
adsorption processes, and it appears this was not tested.
Experiments not reported in IUCLID that have been summarised in the
BUA report.
In one test, biodegradation was determined by means of the biological oxygen
demand (BOD) and total oxygen concentration (TOC) content of the test batches in a
static enrichment degradation test with microorganisms from settled municipal waste
water. Three parallel experiments were mixed after 7 days, separated again, and
spiked with new chemical. The initial and additional concentrations of p-DCB were 5
and 10 ppm respectively. Degradation was higher in the 5 ppm concentration,
ranging from 16 to 55% after 7 days, while for the 10 ppm concentration, it ranged
from 0 to 54%. The authors attributed the reduced degradation rate to poisoning
effects. It was also highlighted that the concentrations were excessive for
environmental conditions, and the static conditions were unrealistic.
A column test detected p-DCB degradation of greater than 90%. The columns were
charged with material from a river/groundwater infiltration area. Evaluation of the
tests showed nearly the same results for the uninoculated columns as for a column
inoculated with a xylene enrichment culture. In the flow through method, the
columns were protected against volatilisation and charged with synthetic
groundwater with p-DCB at a concentration of 29.4 ppb. After an initial
breakthrough, the concentration in the outflow after 10 days was only 50% of the
starting concentration and after approximately 3 weeks, less than 10% was detected.
Approximately 80% of the starting concentration was already removed within the
first 4.7 cm of the column, although it is not apparent how much of this was through
degradation and how much through adsorption.
In a follow up study, 58.8 ppb p-DCB in synthetic river water was also degraded to a
remainder of about 10%. After the oxygen had been removed from this column, the
19
para-Dichlorobenzene
chemical was only degraded for a few more hours. During the following 90 days
under anoxic conditions, no further degradation was observed.
Conclusion
Tests reported with respect to aerobic degradation generally appeared to follow non-
standard conditions. The two results following standard guidelines for ready
biodegradability show the chemical to be readily biodegradable although it is not
certain if the 10 day window criterion was met in one of these tests.
While other tests seem to be non-standard and hard to interpret due to a lack of
details, they generally show p-DCB may be expected to degrade relatively quickly
under aerobic conditions.
Anaerobic/Anoxic Degradation
Table 6 summarises results from the IUCLID data sheet, with the discussion below
outlining further information summarised from the BUA (1994) report.
Test 1 considered primary degradation of 710 ppb under anaerobic conditions in a
bottle test with settled, digested sewage sludge. Sodium acetate and sodium
propionate were added as nutrients. To determine the proportion of elimination not
due to biodegradation, one experiment contained 1% sodium azide. In the digested
sewage sludge without sodium azide, elimination steadily increased from 12% at 2
days to 80% at 32 days. This compared with 5% at 2 days with sodium azide to 8% at
32 days, although the 4 day measurement showed 18% elimination. Statistical
evaluation of the elimination results of the experiments with and without sodium
azide show that, in this investigation, p-DCB was degraded anaerobically.
Table 6 - Anaerobic degradation test results
Test Inoculum Method Result
Anaerobic 1 Co-settled digested sludge Batch test 80% after 32 days
2 Methanogenic mixed culture Not given 0% after 84 days
3 Primary effluent sludge Batch test No significant degradation
after 11 weeks.
4 Soil microorganisms from a Soil column 80-96% (6 d flooding; 16 d
rapid infiltration field drying; 3 cycles)
Anoxic Aquifer material from the Soil column 0% after 90 days.
interface of a river/groundwater
infiltration site
This result contrasts to two other anaerobic bottle experiments. The first used
methanogenic sludge from an experimental sewage plant (Test 2). The tests were
conducted in the dark at 350C with a mineral medium. Three concentrations of p-
DCB were tested, 74, 29 and 7.4 ppb. No degradation was detected at any
concentration after 84 days.
20 Priority Existing Chemical Number 13
The second contrasting result found no significant degradation after 11 weeks (Test
3). To initial primary (aerobic) sewage sludge, a mixture of various halogenated,
aliphatic and aromatic hydrocarbons, at concentrations of 40 and 114 ppb per
substance, and a mineral medium were added and tested under denitrifying
conditions. From the absence of biological degradation under the denitrifying
conditions and the previous result using methanogenic sludge, it was concluded that
molecular oxygen is necessary for the degradation of p-DCB.
Following the aerobic column tests described above which employed a flooding-
drying schedule to investigate sandy soil from a rapid infiltration area for waste water
and crude waste water (aerobic Test 10), an investigation was carried out on the
anaerobic degradation of p-DCB and other compounds, under other similar
conditions (Test 4). At the three concentrations of 5, 50 and 700 ppb, between 4 and
20% of the initial concentration was found in eluate. As with the aerobic test, no
comment has been made with respect to the adsorption of the chemical to the column.
However, the concentrations found in the eluate in the anaerobic test are significantly
higher than in the aerobic test suggesting that degradation is not as significant under
the anaerobic conditions.
As described in Section 7.1.2.5, the anoxic test followed on from an aerobic soil
column study where 58.8 ppb p-DCB in synthetic river water was degraded. After the
oxygen had been removed from this column, the chemical was only degraded for a
few more hours. During the following 90 days under anoxic conditions, no further
degradation was observed.
Experiments not reported in IUCLID that have been summarised in the
BUA report.
Two anaerobic tests are reported in the BUA report which do not appear in the
IUCLID data sheet. Column tests with anaerobic Rhine sediment indicate that
microorganisms capable of degradation prefer certain chlorinated hydrocarbons.
When environmentally relevant concentrations of several chlorinated hydrocarbons
were mixed, only dichlorobenzenes were still detectable after 2-6 months in the
efflux of a column of only 20 cm in length.
In a follow up experiment, it was demonstrated that under anaerobic conditions, p-
DCB was formed from 1,2,4-trichlorobenzene (TCB). It was further shown that after
450 days operation of the experimental plant, under various conditions TCB was
already dechlorinated to p-DCB in the first 0.5 cm of the column, while in the lower
10 cm, a slight decline in the p-DCB concentration was accompanied by the
formation of monochlorobenzene. 1,3-dichlorobenzene and p-DCB were only
dechlorinated after the complete removal of 1,2-dichlorobenzene. It was concluded
that, under reducing conditions, TCB can be degraded via dichlorobenzene to
chlorobenzene and chloride.
Conclusion
As with the aerobic tests, the experiments were largely of a non-standard nature.
While two experiments indicate a significant degree of degradation, the rate appears
21
para-Dichlorobenzene
slower than rates for aerobic degradation. Other results show p-DCB to be relatively
resistant to degradation under anaerobic conditions.
Bioaccumulation
Several bioaccumulation studies have been reported in the SIAR (1999) (Table 7).
As stated in the SIAR (1999) report, test conditions were not available in detail for all
the tests. However, with the exception of the 7 day rainbow trout larvae test and the
60 day flow through test on rainbow trout, the rest appear to have been derived from
fairly standard guidelines.
Table 7 - Bioaccumulation results (modified from SIAR, 1999)
Conc. Elimination a
Species Test Fat (%) BCF
( 礸/L) Half-life (d)
b c
O. mykiss (eggs) 2 d flow through 13.4 See below 45-220
L. macrochirus 14 d flow through - 10.1 <1 60
O. mykiss (larvae) 7d- - 3 <1 112
O. mykiss (larvae) 7 d- - 15 <1 40
O. mykiss (larvae) 7d- - 73 <1 85
P. promelas 28 d flow through 3.2-4.1 570-1000 - 110
J. floridae 28 d flow through 8.5 5 0.7 296
P. reticulata 20 d flow through 6.5 - - 98
d
O. mykiss (eggs) 60 d flow through - 3 - 100-1400
a) BCF = bioconcentration factor; b) Elimination half lives of > 1 day are reported for egg, eyed egg and
hatchlings, while < 1 day is reported for adsorbed half yolk, partially adsorbed yolk and alevin; c) The
lowest BCF was found in the alevin stage, while the highest was reported for adsorbed half yolk; d) The
highest BCF of 1400 was only observed at hatching. It fell to approximately 100 at the end of the test.
These results are indicative of low to medium accumulation potential at all lifestages
of the fish, although it generally appears the chemical was readily eliminated from
the animals, mostly in the order of less than 24 hours.
Mortimer and Connell (1995) undertook work on the effect of exposure to
chlorobenzenes on growth rates of the crab Portunus pelagicus (L). In this work,
critical body residue concentrations in lipid associated with a growth rate reduction
of 50% was determined, and Quantitative Structure-Activity Relationships (QSARs)
relating to this concentration were developed including bioconcentration factors
(BCF). A BCF of 1445 was reported which is approximately the same as the highest
value determined in the above studies.
When considering the general characteristics of organic chemicals which exhibit
bioaccumulation, the molecular weight, log Pow and solubility are all suggestive of
bioaccumulative compounds. However, the chemical structure and limited expected
persistence of p-DCB do not indicate bioaccumulation (Connell, 1990).
22 Priority Existing Chemical Number 13
Summary of Environmental Fate
p-DCB is expected to predominantly partition to the atmospheric compartment of the
environment. While it is not expected to undergo direct photolysis to a significant
degree, reaction with photochemically produced hydroxyl radicals in the atmosphere
will occur. Estimated half-lives in the atmosphere range from a few days to a little
under three months.
Experimentally determined Henry's Law Constants for p-DCB suggest it is readily
volatile in aqueous solution. Aqueous half-lives ranging from <1 to 31 days have
been reported in the literature for surface waters. These are similar to those expected
for marine waters where mesocosmic experimentation showed half-lives of 10 to18
days for three seasons. Microbial degradation was shown to not be a factor in the
elimination of p-DCB from this system.
Where p-DCB becomes associated with soils or sediment, it can be expected to
exhibit medium to low mobility. However, monitoring data from North America,
Europe and Japan indicate that adsorption to sediment is a major environmental fate
process with significantly higher concentrations found in sediments than surface
waters.
Tests reported with respect to degradation generally appeared to follow non-standard
conditions. The two aerobic results following standard guidelines for ready
biodegradability show the chemical to be readily biodegradable although it is not
certain if the 10 day window criterion was met in one of these tests. While other tests
seem to be non-standard and difficult to interpret due to a lack of details, they
generally show p-DCB may be expected to degrade relatively quickly under aerobic
conditions.
As with the aerobic tests, the anaerobic experiments were largely of a non-standard
nature. While two experiments indicate a significant degree of degradation, the rate
appears slower than rates for aerobic degradation. Other results show p-DCB to be
relatively resistant to degradation under anaerobic conditions.
Based on 7 tests with a maximum measured BCF of approximately 300 (except for
1440 in eggs and a literature calculation of 1445), the chemical is not expected to be
highly bioaccumulative.
7.2 Predicted environmental concentrations
7.2.1 Local predicted environmental concentration in air
The local predicted environmental concentration (PEC) in air at 100 m from a point
source can be estimated as follows:
Cair = Emission x Cstdair
where:
concentration in air at 100 m from a point source (kg/m3)
=
Cair
23
para-Dichlorobenzene
Emission = emission rate to air (kg/s)
Cstdair = standard concentration in air at source strength of 1 kg/s
24 x 10-6 kg/m3.
=
Assuming as worst case that all reformulation occurs at the one plant, 50 kg can be
expected to be released to the atmosphere per day (see Section 7.1.1). This results in
emission of 5.8 x 10-4 kg/s to the atmosphere giving a concentration of p-DCB at 100
m from the point source of 13.9 礸/m3 (2.3 ppb based on the conversion factor
provided in Section 4.1).
A crude calculation can be used to determine concentrations in air from end use.
Using figures from Connell and Hawker, 1986, the atmospheric component in
Canberra can be estimated as 2.21 x 1011 m3. Canberra has less than 2% of
Australia's population. Assuming that 2% of annual release to air occurs in Canberra,
then 39 kg per day is expected to be released through use as an air freshener or in
toilet blocks. This equates to an air concentration of 0.176 礸/m3, or 0.029 ppb per
day. With no degradation, this suggests an annual concentration in air of 10.7 ppb.
This is clearly an overestimation as removal processes such as degradation through
reaction with hydroxyl radicals will reduce the expected concentration. The
atmospheric half-life of p-DCB is expected to be between 33 and 50 days, so the
equilibrium concentration in the atmosphere is expected to be significantly less than
that calculated above.
7.2.2 Local PEC in water
To determine a local PEC in water it will be assumed that the use of p-DCB will be
more concentrated in urban centres where facilities such as those outlined in Section
6.2 are likely to be in greater supply. As a worst case scenario, it will be assumed that
20% of the predicted release to water occurs in an urban area of 1.5 million people
serviced by one sewage treatment plant (STP) with a daily output of 250 ML. Table 3
estimates up to 770 kg of p-DCB released to water per day. Therefore, this
calculation will assume 154 kg (20%) daily to the STP.
p-DCB can be considered biodegradable under aerobic conditions. This, and its high
level of volatility, indicate a significant degree of removal through the sewage
treatment plant (STP). The SIAR (1999) provides results from both pilot sewage
plants and full scale STPs regarding elimination of p-DCB. Pilot plants showed
removal of 95% and 90%, with the latter being due to 68% removal from stripping,
22% from degradation and 0.8% from adsorption. An OECD confirmatory test
(described in Section 7.1.2.4) provided elimination of 97% which was attributed to
67% volatilisation and 30% degradation. Elimination in full scale STPs was
significantly less, varying from 60 to 74%.
The SIAR (1999) hypothesises that the difference in removal from the pilot plants
and full scale STPs may be explained by the very low influent concentrations in the
full-scale STPs (2.2 to 4.2 ppb) compared to the spiked influents in the pilot plants
and confirmatory test of 17.7 to 1000 ppb.
24 Priority Existing Chemical Number 13
The fate of p-DCB has been modelled by Clark et al., 1995. This model predicted
removal of 72% being through 19% volatilisation, 46% degradation and 7% bound to
sludge. Within this paper, the modelling results were compared to removal
efficiencies reported in a second paper. In this report (not obtained), removal was
measured at 57 to 80% with a medium of 70%, being by 40% volatilisation, 10%
biodegradation and 20% bound to sludge.
No test reports have been validated within this assessment. The assumptions for
elimination provided in the SIAR (1999) were removal of 70% attributed to 50% to
air, 19% through degradation and 1% through adsorption. Total removal seems in
general agreement with the literature and modelled results. The separation between
volatilisation, degradation and adsorption to sludge appear quite variable but are not
essential for this part of the assessment, and 30% of the chemical going through the
STP will be assumed to be released to receiving waters. Therefore, the local PEC can
be calculated as follows:
Inflow of p-DCB per day 154 kg
Quantity after 70% removal 46.2 kg
185 礸/L (ppb)
Concentration in STP
Concentration in receiving waters (10% dilution) 18.5 ppb
7.2.3 Continental PEC in water
The continental PEC can be determined using the same assumptions above with
respect to removal from STPs. Based on an Australia population of 18 million
people, sewer discharge of 2.7 x 103 ML per day can be expected (150 L per person).
A daily release of 770 kg per day to sewer will leave 231 kg in effluent after removal
processes. This gives a concentration in an STP of 86 ppb, and leads to a prediction
of a concentration of 8.6 ppb in receiving waters.
7.2.4 Local PEC in soil
The full extent of application of sewage sludge to land is not known in Australia.
However, it is understood that Sydney Water sends in excess of 90% of their sludge
(equating to up to 200,000 tonnes per annum) to beneficial use. Some goes to
agricultural use and is soil incorporated while some goes to compost and horticulture
where surface application may occur. No local measurements of p-DCB in sewage
sludge, or its subsequent soil concentration after application to land are available, so
data obtained from the literature will be relied upon. Wang and Jones (1994b)
measured mean concentrations of 1.12 mg/kg in UK sewage sludge, with mean soil
concentrations after application of 1.38 礸/L. In another paper, p-DCB
concentrations in soil of sludge amended plots ranged from 0.02 to 16.6 礸/kg (Wang
et al., 1995). In the absence of other information, the highest value of 16.6 礸/kg will
be used as a PEC in soil in Australia in the event of sewage sludge application to
land.
25
para-Dichlorobenzene
7.2.5 Comparison with measured environmental concentrations
Effluent
Within Australia, in 1994/95, 320 effluent samples taken from 16 sewage treatment
plants discharging effluent to the Hawkesbury-Nepean River system in NSW found
no p-DCB in excess of the detection limit of 5 ppb (Sydney Water, 1996).
The SIAR (1999) has given measured levels of p-DCB within sewage treatment plant
effluents in France, Sweden, USA and Canada. The highest reading was 756 礸/L.
However, the majority of samples did not detect the chemical. Three STPs in Canada
showed levels of 0.9 to 1.4 ppb with effluents from three STPs in the USA showing
levels below detection to 53 礸/L.
Surface water
Within Australia, no p-DCB was detected in the receiving waters (detection limit 0.5
ppb) when effluent was discharged from 16 sewage treatment plants to the
Hawkesbury-Nepean River system in NSW (Sydney Water, 1996).
Several surface water measurements in Germany from 1985-1994 showed p-DCB
concentrations to be less than 0.1 ppb with only a few exceptions where the
concentrations ranged from 0.12 to 2.9 ppb (BUA, 1994). The SIAR (1999) provides
levels from several hundred sample sites in Europe, mainly Germany and France.
Readings for the majority tend to be less than 0.5 ppb, although several levels are in
excess of this with measured levels of up to 4.05 ppb in the Rhine River in France.
One set of results indicates levels less than 50 ppb, although it appears this was the
detection limit so actual levels are not known.
The IUCLID data sheet provides several measurements within Japanese surface
waters. Between 1986 and 1994, 166 samples were taken with p-DCB found in 82 of
these. Maximum concentrations ranged from 2.5 礸/L in 1989 to 0.18 礸/L in 1991.
While no p-DCB was detected in Australian receiving waters, the continental PEC of
8.6 ppb above is higher than the worst case range based on international readings,
with the highest measured value of 4.05 ppb in the Rhine River.
Sediment
Sediment studies around the diffuser of a relatively untreated major marine municipal
sewage discharge in Canada showed p-DCB levels at 1710 礸/kg dw at the point of
outfall, and 277 礸/kg dw at 100 metres from the outfall (Chapman et al., 1996).
The SIAR (1999) provides sediment concentrations from Japanese rivers from 1986
to 1994 with maximum concentrations found ranging from 27 礸/kg dw in 1986 to
150 礸/kg dw in 1991 and 1993.
Also, concentrations in sediment and suspended matter are provided for European
samples where suspended matter levels of up to 58 礸/kg dw were found in
Germany in 1994 and up to 77 礸/kg dw in 1992. In 128 samples in France between
1993/96, no p-DCB was detected in suspended matter with the detection limit being
26 Priority Existing Chemical Number 13
either 50 or 200 礸/kg dw. Sediment readings from rivers in Germany, France, the
Netherlands, and Denmark showed concentrations sediments ranging from less than
0.01 to greater than 104 礸/kg dw. The highest level of 10540 礸/kg dw appears to be
an outlier and was measured in the Elbe in Germany. The next highest reading was
2980 礸/kg dw also from a German river.
Air
The IUCLID data sheet and SIAR (1999) have given background concentrations in
air from municipal areas of Europe. In Hamburg, 300 measurements obtained during
1986/87 provided a mean concentration of 0.14 礸/m3. In the area of Essen, 50
measurements during 1987/88 gave a range in levels of 0.147 to 0.269 礸/m3. At
three unnamed garbage incineration plants (2 samples each), p-DCB was found in
concentrations of 0.03 to 0.15 礸/m3. Gaseous effluents from a garbage dump (stated
as an anaerobic dump) had p-DCB measured at 0.44 礸/m3. Measurements taken at
the border of the Hoechst factory at Frankfurt between 1987/88 gave a maximum
value of 4 礸/m3, although out of 224 measurements around 97% were below the
detection limit of 1 礸/m3.
Further monitoring data are included in the SIAR (1999). Rain samples in 1984 in
Portland, Oregon showed a mean concentration of 0.120 礸/m3 in air and
0.0048 礸/L in rain. As noted in Section 7.1.2.1, p-DCB has been detected in
rainwater in Canada, although levels are not provided.
The PEC for air calculated above resulted in a daily concentration of 0.176 礸/m3
which appears within the range of the measured data.
Soil
As noted above, soil concentrations of p-DCB after application of sewage sludge are
given by Wang and Jones, 1994. Within the sludge, the chemical was present at
1120 礸/kg. After application of wet solid at 69 g/kg soil (following centrifuging and
discarding of the supernatant), the soil concentration of p-DCB was measured at 1.38
礸/kg.
27
para-Dichlorobenzene
8. Occupational Exposure
8.1 Routes of exposure
Occupational exposure is likely to occur due to vapour emitted from the volatile solid
or from molten material during processing and formulation of imported material into
blocks or tablets. Exposure to vapour and dust can occur during handling of the solid
material, particularly during the opening, filling or sealing of bags used to transport
p-DCB, and during milling of the solid. After initial processing of imported p-DCB,
the product is wrapped in cellophane, which minimises subsequent exposure.
The major routes for occupational exposure to p-DCB are by inhalation and dermal
contact. Absorption by the oral route is unlikely to be a significant source of exposure
under normal occupational use conditions. As p-DCB is not manufactured within
Australia there is no occupational exposure related to its production in this country.
8.2 Methodology for estimating exposure
The assessment of occupational exposure is ideally based on workplace monitoring
data. Where such data is inadequate or unavailable, reliance must be placed on
knowledge-based mathematical models that can estimate exposure when the various
patterns of use and the physical properties of the substance under investigation are
known. Due to a lack of monitoring data for p-DCB exposure estimates were made
using the UK EASE (Estimation and Assessment of Substance Exposure) model,
developed by the UK Health and Safety Executive. The estimates presented are
considered to be feasible worst-case scenarios in that they determine exposure at the
high-end or maximum concentration of the substance likely to be encountered in the
workplace. They do not take into consideration exposures due to accidents, spills or
other unusual situations. The information input into the EASE model was derived
from industry through survey results and site visits. Monitoring data from overseas
situations has also been included, where appropriate, to supplement the modelled
data.
8.3 Processing and formulation
In Australia, between 500 and 1000 tonnes of p-DCB were processed, formulated
and/or handled by at least 19 companies, for either industrial or domestic use, in
1998. Due to the failure of some companies involved in the packaging and
distribution of p-DCB products to supply adequate information, the number of
workers involved in the industry and the numbers hours worked could not be
determined accurately. However, the processes are generally semi-automated and
typically involve 1 or 2 workers per company.
28 Priority Existing Chemical Number 13
The manufacture of air freshener and toilet blocks composed of p-DCB is a simple
process, involving either the milling or melting of the imported material at 60oC
followed by blending with small quantities of dye and perfume and then pressing into
moulds. Variations of the process are as follows:
? The p-DCB is removed from 25 kg bags and milled. The milled material is
placed in a mixer where dye and perfume are added. This mixture is then placed
into a hopper, which feeds into a press to produce blocks or tablets of the desired
weight, typically 25, 50 or 100 g. The blocks are wrapped in cellophane, labelled
and boxed.
? The p-DCB is removed from 25 kg bags and melted down after which a small
quantity of dye and perfume are added. The molten material is poured into
moulds and allowed to solidify. The solid material is removed from the mould,
wrapped in cellophane, labelled and boxed.
? The contents of 600 kg bags of p-DCB flakes (purchased from the major
importer/processor and containing pre-mixed p-DCB, dye and perfume) are
loaded into a hopper, which feeds into a press producing blocks of the required
size. The blocks are then wrapped in cellophane, labelled and boxed.
Duration of exposure
From a survey, 7 companies were identified that formulate and or tabulate products
containing p-DCB. Generally, production is intermittent with consumer demand
regulating production activities. Consequently, few workers are involved in the
production process, typically 1 to 2 operators per company. Exposure duration for
workers in Australia (obtained by survey) are shown in Table 8.
Table 8 - Handling of p-DCB in Australia
1
Hours/day [Days/year]
Number of Number of Workers
Activity
(range) (range)
Companies
Formulation/
4 1-5 2 [30] - 8 [100]
pressing/wrapping
Pressing/wrapping only 3 1-2 6 [12] - 7 [48]
Re-packing only 3 1 - 15 0.5 [1] - 3 [150]
Distribution only 9 NA NA
1
Workers handling p-DCB; NA, data not available.
29
para-Dichlorobenzene
Re-packing typically involves the removal of wrapped p-DCB from drums or pails
and packaging into plastic bags or boxes for distribution. Companies only involved in
the distribution of p-DCB products generally purchase sealed containers of the
material and re-sell it without opening the container.
Levels of exposure
Only one company provided monitoring data. This company is the major importer
and formulator of p-DCB products in Australia. The company recorded an airborne
concentration of 19 ppm of p-DCB in the general work area, 34 ppm near a feed
hopper and the maximum concentration reached was 59 ppm of p-DCB in the
bagging area; the data were for April, 1981. More recent data were provided by the
company for August, 1998 which indicated an upper concentration range during
processing of 10 to 15 ppm near a discharge chute and a position near an exhaust
chute in the bagging area gave a level of 6 to 8 ppm. The data were obtained with an
air temperature of 22oC and using Dr鋑er tubes (Chlorobenzene 5/a ) which provides
an approximate measurement only. These exposure levels are in general agreement
with data predicted by the UK EASE model which estimated airborne concentrations
of 10 to 50 ppm (8 hour TWA) under conditions of 25oC with a non-dispersive
pattern of use and with dilution ventilation. The EASE model predicted the same
concentration range under conditions where p-DCB is handled in the molten state
(60oC) with a non-dispersive pattern of use and local exhaust ventilation.
8.4 Hygiene sector
As the greatest use of p-DCB in Australia occurs in the hygiene sector where the
compound is used extensively as an air freshener and deodorant for toilet facilities,
occupational exposure is likely to be greatest amongst cleaners. Cleaners of toilet
facilities are likely to be exposed for periods during their work routine by inhalation.
Dermal and oral exposure is expected to be negligible under these conditions,
particularly if gloves are worn. As much of the cleaning routine is performed after
normal daytime working hours when the facilities are not in use, and hence less air
flow would be expected, the concentration of p-DCB in the air within toilet facilities
is likely to be higher than during daytime working hours. No monitoring data were
available for Australian conditions. The following basic studies have been conducted
in Germany to determine the airborne concentration of p-DCB in two public toilet
facilities (Globol Werke GmbH, 1986):
? Two toilet facilities were used, toilet 1 contained two urinals and toilet 2
contained 1 urinal. Three p-DCB blocks (41.3 g/block) were placed in each
urinal. The volumes of toilets 1 and 2 were 39.56 m3 and 15.42 m3 respectively.
Ventilation was not controlled during the experiment and was dependent on the
number of users. The temperature varied from 16 to 22oC. A total of 67 and 57
days were required for the blocks to fully dissipate for toilets 1 and 2
respectively. Measurements taken from toilets 1 and 2 prior to the experiment
indicated a concentration of 0.2 ppm (1 mg/m3) and 0.1 ppm (0.6 mg/m3) of p-
DCB respectively (no information about prior recent usage of p-DCB in the
toilets was provided). Readings taken in the morning and at midday for up to 47
30 Priority Existing Chemical Number 13
days showed maximal readings of 1.7 ppm (10.1 mg/m3) for toilet 1 and 2.2 ppm
(13.3 mg/m3) for toilet 2.
? In a further experiment, an air freshener tablet (77.44 g) was placed in a toilet
facility 1.6 m above a urinal. The volume of the room was 15.42 m3. Ventilation
was not controlled and was dependent on users. The temperature range was from
16 to 22oC. The duration of the experiment was 30 days although the p-DCB
block required 67 days to dissipate completely. A background measurement
taken prior to the study gave a reading of 0.1 ppm (0.7 mg/m3) of p-DCB. After
placement of the p-DCB tablet, the morning air concentration of p-DCB ranged
from 0.5 to 3.8 ppm (3.0 to 23.0 mg/m3) for the first week and gave a mean of 0.6
ppm (3.6 mg/m3) for days 12 to 30. The midday concentration of p-DCB ranged
from 1.1 to 3.7 ppm (6.4 to 22.4 mg/m3) for the first week with a mean of 0.7
ppm (4.2 mg/m3) for days 12 to 30. Concentrations in the evening ranged from
0.2 to 4.0 ppm (1.5 to 23.8 mg/m3) during the first week with a mean of 1.2 ppm
(7.5 mg/m3) for days 12 to 30.
8.5 Automotive/Marine Sector
The car detailing/cleaning and transport sectors were identified as users of p-DCB
although no monitoring data were available. Use of p-DCB was also identified in the
marine industry, generally confined to small pleasure craft. It may be expected that
the airborne concentrations of p-DCB are likely to be higher under these conditions
due to the limited and confined air space, limited ventilation and higher than average
temperatures found within vehicles and boats. However, the duration of exposure is
likely to be short and intermittent.
31
para-Dichlorobenzene
9. Toxicokinetics and Metabolism
9.1 Absorption
9.1.1 Animals
There have been few studies conducted that address the issue of absorption of p-DCB
by the oral and inhalation routes.
The absorption of radiolabel after oral administration of p-[14C]-DCB (250 mg/day)
for 5 days was examined in female rats (strain CFY). Urinalysis revealed that 91 to
97% of the radiolabel was excreted in the urine with approximately 2 to 5%
appearing in the faeces and less then 1% in expired breath (Hawkins et al., 1980). As
the amount appearing in bile after a single dose amounted to 46 to 63% of radiolabel
recovered, indicating considerable enterohepatic circulation of radiolabel, the data
suggest that absorption by the oral route is substantially complete at this dose level.
An investigation of the distribution of p-[14C]-DCB after oral administration to male
and female rats (strain F344; 149 or 305 mg/kg bw) and mice (strain B6C3F1; 310 or
638 mg/kg bw) showed peak blood levels to occur at 1 hour after dosing while peak
tissue levels occurred at 6 hours (Wilson, 1990; cited in SIAR 1999).
The kinetics of p-DCB absorption was examined by oral administration of p-[14C]-
DCB (10, 50, or 250 mg/kg bw) dissolved in corn oil to male Wistar rats. At the
lowest dose the maximal concentration of the parent compound in the blood
(Cmax[DCB]; determined by gas chromatography) was reached at 4 hours (6.75
祄ol/l) while the maximal concentration of radioactivity (Cmax[Ra]) in the blood
occurred at 2 hours. For the mid-dose, Cmax[DCB] was reached at 6 hours (21.3
祄ol/l) and Cmax[Ra] at 3 hours. At 250 mg/kg bw, Cmax[DCB] and Cmax[Ra] both
occurred at 6 hours (104 祄ol/l). Clearance values for p-DCB at 10, 50, or 250
mg/kg bw were 24.1, 23.7 and 22.7 mL/min/kg respectively while the half-life values
for the same doses were 8.1, 7.1 and 7.6 hours respectively (Hissink et al., 1997a).
The data indicate that rate-limiting conditions, with respect to absorption, had not
been reached and that absorption appears to be rapid.
The kinetics of p-[14C]-DCB absorption were investigated in male and female rats
(strain F344) and mice (strain B6C3F1) following exposure by inhalation. Exposures
were conducted in male rats at 160 and 502 ppm and in female rats at 161 and 496
ppm; in mice, exposures at 158 and 501 ppm were used. Absorption via the
respiratory system was rapid but not complete. Absorption after inhalation exposure
was poor compared to oral exposure. Mice demonstrated increased absorption
relative to F344 rats after inhalation (59% in mice versus 25-33% in rats) (Wilson,
1990; cited in SIAR 1999).
No studies have been carried out to specifically address dermal absorption in animals.
32 Priority Existing Chemical Number 13
9.1.2 Humans
There are no reliable data for the absorption of p-DCB by humans.
9.2 Distribution
9.2.1 Animals
The concentration of p-DCB in male rats, after a single dose (200 mg/kg bw) by
gavage, was found to be highest in adipose tissue with lesser amounts in blood, liver,
kidneys, heart, lung and brain tissue (Kimura et al., 1979).
Charbonneau et al. (1989) studied the distribution of radiolabel 24 hours after
administering a single oral dose of p-[14C]-DCB (500 mg/kg bw) to male rats (strain
F344). The greatest deposition of radiolabel occurred in the adipose tissue (13,617
nmol/g) followed by the kidneys (535 nmol/g) and liver (458 nmol/g). The plasma
accounted for 201 nmol/mL of radiolabel. Within the kidney 266 nmol/g was bound
to cytosolic components with 3.3 nmol of p-DCB equivalents bound to 2?globulin-
containing fractions. The radiolabel bound to the fractions was not removed by
dialysis unless sodium dodecyl sulfate (0.1%) was present, demonstrating the non-
covalent nature of the binding.
Klos and Dekant (1994) investigated the distribution of p-[14C]-DCB (900 mg/kg bw)
and its metabolites in male and female rats (strain F344) after administration by
gavage. The highest content of radiolabel, 72 hours after dosing, occurred in the
adipose tissue followed by the liver, kidney, lung, adrenal gland and spleen. The
distribution of radiolabel between the tissues of the two sexes was not substantially
different.
Administration of p-[14C]-DCB (1000 ppm) by inhalation (3 hours/day for up to 10
days; whole-body) to female rats (strain CFY) revealed that 24 hours after the final
dose the greatest concentration of radiolabel was found in the adipose tissue with
lower concentrations in the kidneys and liver. Levels of radiolabel in lungs and
muscle were comparable to plasma levels. Tissue concentrations of radiolabel
increased with exposure duration within the first 6 days but reached a plateau or
decreased slightly at 8 to 10 days, possibly due to the induction of P450 enzymes.
When p-[14C]-DCB (250 mg/kg bw per day) was administered for up to 10 days by
gavage or by subcutaneous injection a similar distribution of radiolabel occurred
(Hawkins et al., 1980).
The distribution of p-DCB in rats (strain F344/DuCrj) after inhalation (whole-body)
of the vapour (500 ppm) for 24 hours was assessed by determining the level of p-
DCB in serum, liver, kidneys and adipose tissue at intervals up to 24 hours during
and after exposure. Peak serum levels of p-DCB for both male and female rats
occurred 3 hours after exposure ceased. The level of p-DCB in the livers of females
increased markedly at 24 hours peaking at 3 hours post exposure and reached
significantly higher levels than male livers. Conversely, male rat kidneys took up
more of the compound than their female counterparts though the difference was not
as marked as with the livers. No significant differences in plasma or adipose tissue
33
para-Dichlorobenzene
levels were evident between the two genders. For all tissues examined, 24 hours after
exposure ceased the level of p-DCB declined to below the level detected after the
initial 6-hour exposure (Umemura, 1990).
When p-DCB was administered as a single oral dose (100 or 1000 mg/kg bw
dissolved in polyethylene glycol) to male rats (strain Wistar TNO W47) peak plasma
concentrations of p-DCB and its metabolite, 2,5-dichlorophenol, occurred at 24 hours
for each dose. Similarly, maximal amounts of p-DCB and 2,5-dichlorophenol
occurred in adipose, hepatic and renal tissue at 24 hours after treatment with 1000
mg/kg bw p-DCB. At the 100 mg/kg bw dose, only trace amounts of p-DCB or 2,5-
dichlorophenol could be detected in hepatic and renal tissue (Bomhard et al., 1998).
In a further series of experiments by Bomhard et al., (1998) rats (strain Wistar TNO
W47) were fed a diet containing 100 or 1000 ppm (equivalent to approximately 10
and 100 mg/kg bw respectively) p-DCB daily for 4 weeks. At 100 ppm, neither p-
DCB nor 2,5-dichlorophenol were detectable in the plasma at any time point. After
feeding 1000 ppm and measured at day 3, p-DCB and 2,5-dichlorophenol levels were
at their highest and subsequently declined to give steady-state concentrations from
day 6 to day 14. Thereafter, plasma concentrations of both compounds declined to
undetectable levels for p-DCB and less than 0.5 礸/mL for 2,5-dichlorophenol.
Adipose, hepatic and renal tissue levels of p-DCB and 2,5-dichlorophenol were also
determined. At 100 ppm, adipose tissue levels were constant at low levels (< 5
礸/mL) over the experimental period. Both compounds in the 100 ppm group were
undetectable in hepatic and renal tissue over the corresponding period. Within the
1000 ppm group, maximal levels of p-DCB occurred at day 3 in hepatic and renal
tissue with both tissues exhibiting a rapid decline by day 6. Low steady-state levels of
p-DCB existed from day 6 to day 28 in hepatic (< 0.5 礸/g) and renal (< 1.0 礸/g)
tissue. Hepatic levels of 2,5-dichlorophenol remained constant at low levels (< 0.25
礸/g tissue) during the experimental period while renal levels displayed a biphasic
response with maxima occurring at days 3 and 21.
9.2.2 Humans
There are no detailed studies of the distribution of p-DCB in humans. Analyses of
human samples of adipose tissue, blood and milk have all shown the presence of p-
DCB.
In a study of Tokyo residents, 34 samples of adipose tissues obtained from local
hospitals all had detectable levels of p-DCB with an average level of 2.3 礸/g tissue
(range 0.2 to 11.7 礸/g). Analysis of six blood samples showed an average level of p-
DCB of 9.5 ng/mL (range 4 to 16 ng/mL) (Morita and Ohi 1975).
In another report, analysis by mass fragmentography for chlorinated benzenes in a
mixture of 15 samples of human adipose tissues obtained from the Tokyo area
showed that the main component present was p-DCB. The detection level was 0.010
礸/g tissue (Morita et al., 1975).
Mes et al., (1986) reported traces of p-DCB in all of 210 human milk samples tested
from 5 different regions across Canada.
34 Priority Existing Chemical Number 13
A survey of 1000 adults in the United States revealed 98% had detectable levels of
2,5-dichlorophenol in their urine (up to 8.7 mg/l) and detectable levels of p-DCB in
their blood (up to 49 礸/l) (Hill et al., 1995).
9.3 Metabolism
9.3.1 Animals
The oral administration of p-DCB (0.5 g/kg) to rabbits resulted in the formation of
urinary metabolites consisting of 2,5-dichlorophenol (35%), present as the glucuronic
and sulfate conjugates, and 2,5-dichloroquinol (6%) (Azouz et al., 1955).
Administration of p-[14C]-DCB (1000 ppm) by inhalation (whole-body) or by oral
administration (250 mg/day) to female rats (strain CFY) revealed that the major
urinary metabolites were sulfate and glucuronide conjugates of 2,5-dichlorophenol
comprising 46 to 54% and 31 to 34% of total radiolabel respectively. Two minor
metabolites were dihydroxydichlorobenzene and a mercapturic acid of p-DCB
(Hawkins et al., 1980).
Administration of p-[14C]-DCB (0.9 mmol/kg) to male rats (strain F344) by
intraperitoneal (i.p.) injection revealed that the highest concentration of radiolabel in
the liver occurred within the first 4 hours with less than 35% of the radiolabel
remaining by 12 hours. Analysis of aqueous soluble metabolites indicated that
soluble products of p-DCB did not exceed 34% of total radiolabel at any time point.
The presence of aqueous soluble metabolites correlated with the covalent binding of
radiolabel to hepatic proteins which remained within the range 31 to 52 pmol/mg
protein bound over a 24 hour period. The role of hepatic glutathione was determined
by estimating the total non-protein sulfhydryl content over a period of 5 hours after
i.p. injection of p-DCB (1.8 mmol/kg), however, no significant difference in
glutathione content compared with controls was noted. Depletion of hepatic
glutathione by pre-treatment of the animals with phorone resulted in a significant
increase in plasma alanine aminotransferase (ALT) levels 24 hours after the
administration of p-DCB demonstrating a role for glutathione in modulating the
hepatotoxicity of p-DCB (Stine et al., 1991).
The in vivo metabolic fate of p-DCB was examined in male rats (strain Wistar) by the
administration of p-[14C]-DCB (10, 50 or 250 mg/kg bw) by gavage. Metabolites
detected in the urine were 2,5-dichlorophenol (8.4 to 9.3%), 2,5-dichlorophenol
glucuronide (19.3 to 25.4%), 2,5-dichlorophenol sulfate (56.7 to 62.2%) and
mercapturic acids (8.6 to 10.2%). Minor metabolites accounting for the remaining
radiolabel (10%) were N-acetyl-cysteine-S-dihydro-hydroxy-1,4-dichlorobenzene and
N-acetyl-cysteine-S-1,4-dichlorobenzene. No hydroquinone metabolites were
detected. The main effect of increasing the dose was a decrease in the amount of
sulfate conjugates and an increase in the glucuronide conjugates. Induction of
CYP2E1 by prior treatment with isoniazid resulted in an elevated urinary excretion of
p-DCB metabolites providing evidence for the role of this cytochrome in the in vivo
metabolism of p-DCB (Hissink et al., 1997a).
35
para-Dichlorobenzene
In a study by Lake et al. (1997) male rats (strain F344) were treated daily with p-
DCB at 0, 25, 75, 150 or 300 mg/kg bw and male mice (strain B6C3F1) at 0, 300 or
600 mg/kg bw by gavage, 5 days/week. The cytochrome P450 content of rat livers
increased at all time periods with doses of 75 mg/kg bw or greater. Mouse hepatic
cytochrome P450 content increased during all time points only for the 600 mg/kg bw
treatment. The identity of the p-DCB-induced cytochromes was investigated in the
rat and mouse using an immunoblotting technique with antibodies to CYP2B1/2 and
CYP3A. A marked induction of CYP2B1/2 in both rat and mouse was detected and a
lesser induction of CYP3A occurred in the rat. The authors concluded that p-DCB is
an inducer of CYP2B in the rat and mouse.
Analysis of urinary metabolites collected from male and female rats (strain F344) 24
to 36 hours after administration of p-DCB (900 mg/kg bw) as a single oral dose
revealed the presence of conjugates of 2,5-dichlorophenol as the major metabolites.
2-(N-acetyl-cysteine-S-yl)-1,4-dichlorobenzene was also present, as were conjugates
of 2,5-dichlorohydroquinone. In the organs tested, protein-bound radiolabel was
below the limit of detection (Klos and Dekant 1994).
The time course of induction of hepatic and renal enzymes was studied in male and
female rats (strain F344) by the administration of p-DCB (0, 150 or 600 mg/kg bw; 7
days/week for 4 weeks) by gavage. On days 3, 9, 15 and 28 the activities of the phase
I enzymes, 7-ethoxycoumarin O-deethylase (ECOD; corresponding to cytochrome
isoforms CYP1A1, CYP2B1 and CYP2D1), 7-ethoxyresorufin O-deethylase (EROD;
CYP1A1) and aldrin epoxidase (ADE) and the phase II enzymes, epoxide hydrolase
(EH), glutathione S-transferase (GST) and glucuronyl transferase (GLT) were
studied. Maximal induction of ECOD in the liver occurred at the highest dose on day
9 at which time a 7 and 10-fold increase in enzyme activity occurred for male and
females respectively compared to control animals. At this dose level induction of
ECOD was characterised by a biphasic response with a second peak in activity
occurring on day 28. At 150 mg/kg bw, p-DCB induced ECOD activity was maximal
at day 9 for males, although not biphasic, and absent in the female liver. The
maximal response to EROD induction by p-DCB (600 mg/kg bw) was less than
ECOD and occurred in the liver at days 15 and 28 for males and females
respectively. Males did not show an increase in hepatic ADE activity at either dose
while females demonstrated a 5 and 10-fold increase on day 9 at 150 and 600 mg/kg
bw respectively but which subsequently declined towards the end of the study period.
The hepatic phase II enzymes, EH, GST and GLT, showed similar patterns of
induction in response to p-DCB (600 mg/kg bw). Maximal activity occurred on day 9
with a subsequent decrease in activity on succeeding days. Compared to control
animals, EH activities increased 6 and 4-fold for males and females, GS-T activities
increased 4-fold and 2-fold for males and females and GLT activities increased 8-
fold and 4-fold for males and females respectively. At 150 mg/kg bw, only marginal
increases in the phase II enzyme activities were recorded. The renal response to p-
DCB (600 mg/kg bw) was a maximal induction of ECOD activity for both sexes on
day 15, 7-fold for females and 3.5-fold for males compared to control animals. Of the
other enzymes studied, only EH exhibited a slight induction of less than 2-fold on
day 15. No renal induction was seen for any enzyme at 150 mg/kg bw (Bomhard
1998).
36 Priority Existing Chemical Number 13
9.3.2 Humans
The metabolism of p-DCB has not been extensively investigated in humans.
In an early study, Pagnotto and Walkley (1965) reported the presence of
dichlorophenol in the urine of workers exposed to p-DCB vapour in the range 10 to
233 ppm.
9.3.3 In vitro studies
In a study of the metabolism of p-DCB by rat liver microsomes (derived from male
Wistar rats) the main metabolites produced were 2,5-dichlorophenol with lesser
amount of 2,4-dichlorophenol detected. 2,5-Dichlorophenol was further metabolised
to 2,5-dichlorohydroquinone and 2,4-dichlorophenol was metabolised to 3,5-
dichlorocatechol and, to a lesser extent, 1-chlorobenzoquinone. Subsequent oxidation
of the dichlorohydroquinone/dichlorocatechol species produced reactive
dichlorobenzoquinones. These reactive species were capable of protein binding
although they demonstrated less affinity for DNA. Significantly less protein binding
was observed when the reductant, ascorbic acid, was added to the incubation medium
(Den Besten et al., 1992).
The metabolism of p-DCB (1 mM) by rat liver slices (strains Sprague-Dawley and
F344) was examined. After 2 and 6 hours of incubation, the amount of metabolites
derived from p-DCB were comparable between the two strains giving 2.1 to 2.7
nmol/mg protein. The metabolites formed were also comparable in terms of chemical
species produced with glutathione/cysteine conjugates being the major metabolites.
Covalent binding of reactive p-DCB metabolites to liver slices was assessed and
revealed comparable levels of binding for F344 and Sprague-Dawley tissues (0.471
and 0.359 nmol bound/mg protein respectively) after 6 hours incubation (Fisher et
al., 1995).
To further delineate the species and strain differences in hepatic microsomal
cytochrome P450-mediated metabolism of p-DCB, Hissink et al. (1997b) undertook
a comparative study of male rats (strains Wistar, Sprague-Dawley, and F344) and
male mice (strain B6C3F1). Conversion of p-[14C]-DCB by microsomes ranged from
16% for mice to 1.3% for Wistar and F344 rats while Sprague-Dawley rats gave
0.6% conversion. Prior treatment of Wistar rats with phenobarbital increased the
conversion of p-DCB by 4-fold. The main metabolites identified are listed in Table 9.
In all cases, 2,5-dichlorophenol accounted for more than 50% of converted material.
In the absence of ascorbic acid, hydroquinone metabolites accounted for 10.2 to
27.1% of the total conversion. Addition of ascorbic acid significantly increased the
recovery of hydroquinone metabolites while decreasing covalent binding. Covalent
binding of p-DCB metabolites to microsomal protein was highest for mouse
microsomes (20.9% bound) with rat microsomes ranging between 6.8% to 10.1%
bound. Prior treatment of Wistar rats with phenobarbital significantly increased the
response from 8.1% to 13.4% bound. In all cases, the addition of ascorbic acid or
glutathione reduced microsomal covalent binding. In the absence of exogenous
glutathione, mouse microsomes produced no detectable glutathione-epoxide
conjugates whereas rat microsomes produced detectable levels (range 5.0 to 15.0% of
37
para-Dichlorobenzene
total conversion) for each strain. Addition of glutathione to microsomal preparations
resulted in undetectable levels of glutathione-epoxide conjugates from mouse
preparations and a significant increase (range 39.7 to 52.2%) for all rat strains.
Further studies of the metabolism of p-DCB were undertaken using hepatic
microsomes derived from male and female rats (strain Wistar) and mice (strain
B6C3F1) with or without induction of CYP3A or CYP2E1. The formation of soluble
metabolites after the addition of p-[14C]-DCB (0.1 mM) to microsomal preparations
was 3-fold greater for male than for female mice. Treatment of animals with
pregnenolone 16-carbonitrile to induce CYP3A resulted in a 7-fold increase in
covalently bound metabolites in male rats and a 5-fold decrease in the formation of
soluble metabolites by male and female mice compared to controls. Induction of
CYP2E1 (by benzene inhalation) did not result in any significant change in soluble or
covalently bound metabolite formation by rats or mice. Inhibition of CYP2E1 by
diethyldithiocarbamate resulted in significantly less p-DCB oxidation by rat and
mouse microsomes (Nedelcheva et al., 1998).
Table 9 - Metabolites formed by hepatic microsomal metabolism of p-DCB
Species Conversion
(strain) (% of total Metabolite (% of total conversion)
radioactivity)
1
Hydroquinone 2,5-DCP GS-quinone
GS-epoxide
Mouse 15 ND 16.1 50.5 3
Rat
1.1 5.0 27.1 56.8 6.0
(F344)
Rat
0.6 7.3 10.2 70.7 ND
(S-D)
Rat
1.3 15.0 10.5 50.0 ND
(Wistar)
Human 0.3 ND 16.8 66.2 ND
1
derived from endogenous GSH; ND, not detected in the absence of exogenous GSH; S-D, Sprague-
Dawley; GS, glutathione conjugate; DCP, dichlorophenol (Hissink et al., 1997b).
Incubation of human liver slices (from 10 individuals; 5 male, 5 female; 7 from head
injury victims and 3 from resections with metastatic colon cancer) with p-DCB (1 or
2 mM) for up to 6 hours resulted in a decrease in protein synthesis and an increase in
leakage of the cytosolic enzyme, lactate dehydrogenase (LDH), only at the higher
concentration. The effect was time-dependent with statistically significant (p<0.05)
results occurring at 4 hours (Fisher et al., 1991).
In another study by Fisher et al. (1995), the metabolism of p-DCB (1 mM) by human
liver slices (from 7 individuals) was examined after 2 and 6 hours of incubation. p-
DCB metabolites amounted to 2.6 and 3.3 nmol/mg protein respectively. Covalent
binding of reactive metabolites to liver slices was assessed and amounted to 0.482
nmol bound/mg protein after 6 hours.
38 Priority Existing Chemical Number 13
Comparative studies undertaken with microsomes derived from human cell lines
transfected with cDNA expressing specific cytochrome P450 isoforms have
demonstrated that p-DCB is metabolised predominantly by CYP2E1 to 2,5-
dichlorophenol. CYP1A2 demonstrated the next highest activity, which amounted to
6.0% of the CYP2E1 activity. CYP1A1, CYP3A4 and CYP2D6 possessed little
activity towards p-DCB (Bogaards et al., 1995).
The role of hepatic microsomal cytochrome P450-mediated metabolism of p-DCB
(150 礛) was further investigated by Hissink et al. (1997b). Human cell lines
expressing specific cytochrome P450 isoforms (from 5 individuals) were utilised.
Total conversion of p-[14C]-DCB by microsomes was 0.3%. 2,5-Dichlorophenol
accounted for 66.2% of the metabolites produced with hydroquinone species
accounting for a further 16.8%. Addition of ascorbic acid increased the recovery of
hydroquinone metabolites to 27.9%. Covalent binding comprised 5.8% of the total
conversion.
Nedelcheva et al. (1998) found that inhibition of CYP2E1 by diethyldithiocarbamate
and CYP3A by triacetyloleandomycine resulted in substantial inhibition of the
metabolism of p-[14C]-DCB by human microsomes derived from the livers of male
brain injury victims. No correlation could be found, using immunoblotting
techniques, for an association between cytochrome type and rate of metabolism.
The major metabolic routes for the metabolism of p-DCB by hepatic microsomes
derived from humans, rats and mice and the proposed bio-reactive metabolites are
shown in Figure 2. The metabolism of p-DCB by humans is limited and proceeds by
aromatic hydroxylation by CYP2E1 to give the 2,3-epoxide (Bogaards et al., 1995).
The epoxide, in a non-enzymatic process, converts to 2,5-dichlorophenol which is
excreted or conjugated with sulfate or glucuronic acid prior to excretion. Lesser
amounts are converted by -glutamyl transferase which results in excretion of
mercapturic acid derivatives. In the rat and mouse aromatic hydroxylation involves
other P450 enzymes in addition to CYP2E1 so that 1,2-epoxide and 2,3-epoxide
derivatives are formed, both of which form 2,4- and 2,5-dichlorophenols
respectively. By secondary oxidation hydroquinone derivatives are produced which
may autoxidise to their corresponding benzoquinone forms (Den Besten et al., 1992).
The 1,2-epoxide can conjugate with glutathione and be excreted as a mercapturic
acid. Alternatively, both epoxides can form glutathionyl, sulfate or glucuronide
derivatives prior to excretion (Hissink et al., 1997a,b).
9.4 Elimination and excretion
9.4.1 Animals
In rabbits, the excretion of p-DCB metabolites occurred predominantly in the urine
when p-DCB was administered by gavage (1.5 g/animal). Only glucuronides and
sulfates of 2,5-dichlorophenol were detected, which peaked two days after
administration of the parent compound. Detectable levels of metabolites continued to
be found in the urine six days after dosing. Analysis over six days failed to detect p-
DCB or its metabolites in the faeces (Azouz et al., 1955).
39
para-Dichlorobenzene
Hawkins et al. (1980) found that p-[14C]-DCB (1000 ppm) administered by inhalation
(3 hours/day for up to 10 days; whole-body) to female rats (strain CFY) was rapidly
eliminated after termination of exposure. Analysis of excreta collected over 4 days
post-exposure showed 97.4% of the radiolabel to be in the urine, 2.5% in the faeces
and 0.2% in expired air. Similarly, when administered by gavage, p-DCB (250 mg/kg
bw per day) was excreted predominately in the urine with less than 10% in the
faeces.
Cl OH
H
SM SM
Cl
H
SG
OH
H
Cl
Cl
-GT OH
H
Cl
Cl
GSH
H
Human Sulfate and glucuronide
Human
O conjugates of
Mouse Mouse 2,5-DCP
& Rat H
& Rat
Cl
Cl
Cl
Conjugates
OH of
2,3-epoxide
2,5-DCHQ
Cl
OH
Mouse
Cl
Cl Cl
& Rat
O HO
2,5-DCP
1,4-DCB Cl
H Cl
Cl
Mouse OH
O
2,5-DCHQ
& Rat OH O
Cl HO
Cl O GSH
Cl
SG
Cl
Cl
1,2-epoxide
2,5-DCBQ 2,5-DCGHQ
Cl O
GSH 2-CBQ
2,4-DCP
OH O
OH OH HO O
Cl Cl
SM
SG
Cl Cl
Cl Cl 3,5-DCBQ
3,5-DCC
Figure 2 - Metabolic pathways for the metabolism of p-DCB in humans, rats and mice.
The major urinary products are depicted in boxes. CBQ, chlorobenzoquinone; DCB,
dichlorobenzene; DCBQ, dichlorobenzoquinone; DCC, dichlorocatechol; DCGHQ,
dichlorogluthionyl-hydroquinone; DCHQ, dichlorohydroquinone; DCP, dichlorophenol;
DCBQ, dichloro-1,2-benzoquinone; -GT, gamma glutamyl transferase; GSH, reduced
glutathione; SG, glutathione-S-yl-metabolite, SM, N-acetyl-cysteine-S-yl-metabolite. Dashed
arrows represent multi-step pathways (After Den Besten et al., 1992, Klos and Dekant 1994
and Hissink et al., 1997).
40 Priority Existing Chemical Number 13
Umemura et al. (1990) observed that tissue levels of p-DCB in male and female rats
(strain F344; 3 animals/group) exposed to p-DCB vapour (500 ppm) for 6, 12, and 24
hours fell approximately 90% within the following 24-hour period.
The excretion of p-[14C]-DCB (900 mg/kg bw) by male and female rats (strain F344)
was determined over 72 hours after a single oral dose. Urine was collected over 12-
hour intervals. The results indicated that 72 hours after dosing 41.3% and 37.8% of
the radiolabel was excreted in the urine by males and females respectively. Faeces
accounted for 3.6% of the radiolabel from males and 2.5% from females. Peak
excretion for both sexes occurred during the 24 to 36 hour interval. No treatment-
related changes in urine volume were observed. At the end of the study only 0.05%
and 0.04% of the total radiolabel remained in the pooled tissues from males and
females respectively. Similar results were obtained with unlabelled p-DCB. The
major excretion products were conjugates of 2,5-dichlorophenol. These were higher
in the male although females excreted higher amounts of 2-(N-acetyl-cysteine-S-yl)-
1,4-dichloro-benzene than males. Males also excreted more conjugates of 2,5-
dichlorohydroquinone than females (Klos and Dekant 1994).
The elimination of p-DCB by male rats (strain Wistar) was studied following the
administration of a single dose of p-[14C]-DCB (10, 50 or 250 mg/kg bw) by gavage.
Less than 1% of all dose levels was eliminated by the lungs. Examination of all
organs for radiolabel after 168 hours accounted for less than 0.05% of the dose.
Elimination in urine accounted for 80% of the dose while the faeces contained 4% of
radiolabel with changes in dose levels having no significant effect on these values.
Most of the radiolabel was excreted between 8 and 24 hours after dosing. Metabolites
detected in the urine were 2,5-dichlorophenol (5-10%), the 2,5-dichlorophenol
glucuronide (20-30%) and 2,5-dichlorophenol sulfate (50-60%). Minor metabolites
including mercapturic acids (10%) accounted for the remaining radiolabel. Excretion
in bile was dose-dependent with 4% of total radiolabel excreted in the first 12 hours
after administering 10 mg/kg bw; faeces contained less than 2.5% of the dose. At 250
mg/kg bw, 10 to 30% of total radiolabel appeared in the bile with less than 5% in the
faeces suggesting that enterohepatic circulation of p-DCB and its metabolites is
significant with reabsorption by the intestinal route high (Hissink et al., 1997a).
9.4.2 Humans
A study of workers exposed to dichlorobenzenes (predominantly p-DCB) by
inhalation found that urinary excretion of the major metabolite, 2,5-dichlorophenol,
commenced soon after initial exposure with maximal excretion occurring at the end
of the exposure period. Air sampling indicated a range of concentrations from 8 to 49
ppm of dichlorobenzene and urinary dichlorophenol formed from 10 to 233 mg/l. The
excretion of metabolites was found to be biphasic with an initial rapid decrease in
urinary metabolites followed by a prolonged reduction over several days (Pagnotto
and Walkley, 1965).
In a controlled experiment using human volunteers it was determined that the
biological residence time of p-DCB in humans, based on exhaled breath
measurements and using a least-squares fit to a one compartment pharmacokinetic
model, to be 20 to 30 hours (Wallace et al., 1989).
41
para-Dichlorobenzene
Hill et al., (1995), in a study of 1000 adults in the United States, demonstrated a
significant correlation (p<0.0001) between the concentration of p-DCB in the blood
and urinary p-dichlorophenol concentration.
9.5 Other studies
In vivo studies
Covalent binding of radiolabel to DNA, RNA and protein 22 hours after i.p.
administration of p-[14C]-DCB to male rats (strain Wistar) and mice (strain BALB/c)
was examined. Covalent binding of radiolabel to DNA extracted from rat liver,
kidney, lung and stomach was not detected whereas binding for the corresponding
mouse DNA samples were 0.14, 0.09, 0.60 and 0.08 pmol/mg respectively. Covalent
binding of radiolabel to RNA from rat and mouse was: liver (0.60 and 1.83
pmol/mg), kidney (2.28 and 1.60 pmol/mg), lung (0.95 and 4.28 pmol/mg) and
stomach (0.08 and the mouse was not determined). Covalent binding of radiolabel to
protein from rat and mouse tissue was: liver (0.12 and 0.75 pmol/mg), kidney (0.63
and 0.74 pmol/mg), lung (0.60 and 0.73 pmol/mg) and stomach (0.54 and 0.38
pmol/mg) (Lattanzi et al., 1989).
Renal cell proliferation in response to the oral administration of p-DCB (0, 118 or
294 mg/kg bw) to male rats (strain F344) for 7 days was examined. A significant
increase (p<0.05) was observed in treated animals (Charbonneau et al., 1989).
Eldridge et al. (1992) investigated hepatocellular proliferation in female rats (strain
F344) and mice (strain B6C3F1) of both sexes after administration of a single oral
dose of p-DCB (600 mg/kg bw). Cell proliferation increased (as determined by
incorporation of 5-bromo-2'-deoxyuridine (BrdU)) reaching a maximum for female
mice and rats at 24 hours and declined thereafter. For male mice, no increase was
observed during the first 24 hours but a maximal response was observed at 48 hours.
Cell proliferation returned to control levels 4 days after treatment. Further
experiments over 13 weeks with doses of 0, 300 or 600 mg/kg bw per day for mice
and 0 or 600 mg/kg bw per day for rats were performed. Hepatocellular proliferation
was observed during the first week at 600 mg/kg bw per day in both sexes of mice
and in female rats. Cell proliferation was not observed at the lower 300 mg/kg bw
dose in mice.
Cell proliferation in response to p-DCB exposure was investigated in male and
female rats (strain F344) and mice (strain B6C3F1) using the BrdU technique. Male
rats were administered p-DCB by gavage for 4 days at 0, 150 or 300 mg/kg bw.
Another group, composed of male and female rats and female mice were
administered doses of 0, 300 or 600 mg/kg bw. Increased cell proliferation was
observed in the proximal convoluted tubules and to a lesser extent the proximal
straight tubules but not distal tubules of treated male rats. Female rats or mice of
either sex did not exhibit increased cell proliferation of the renal tubules. Increased
cell proliferation was noted in the livers of both sexes of rats and mice at 300 mg/kg
bw (Umemura et al., 1992).
42 Priority Existing Chemical Number 13
The role of endogenous glutathione in protecting against p-DCB-induced
hepatotoxicity was demonstrated in male mice (strain ddY). The mice were pre-
treated by i.p. injection with buthionine sulfoximine (BSO; 2 mmol/kg) to deplete
glutathione prior to the oral administration of p-DCB (100 to 400 mg/kg).
Hepatotoxicity was demonstrated by an increase in serum ALT and hepatic calcium
levels which both peaked 24 hours after the administration of p-DCB (300 mg/kg);
histopathology showed microvacuolar lipid accumulation of the periportal and
midzonal areas within 4 hours of exposure. By 24 to 30 hours necrosis of the
centrilobular and midzonal regions was evident. Control animals not treated with
BSO and receiving p-DCB (1200 mg/kg) had serum ALT levels of 37.5 units/mL 30
hours after treatment while BSO treated animals exposed to p-DCB (100 to 400
mg/kg) had ALT levels of 342 to 3820 units/mL (Mizutani et al., 1994).
The role of p-DCB as an inducer of DNA synthesis was assessed using hepatocytes
derived from male B6C3F1 mice. Mice where administered p-DCB (0, 750 or 1500
mg/kg bw) by the oral route and hepatocytes prepared 24, 39 or 48 hours later.
Replicative DNA synthesis was assessed after the addition of [methyl-3H]thymidine
followed by autoradiography. A positive result was obtained with the lower dose at
48 hours while the higher dose gave positive results at 39 and 48 hours (Miyagawa et
al., 1995).
In a study by Lake et al. (1997) male rats (strain F344) were treated daily with p-
DCB at 0, 25, 75, 150 or 300 mg/kg bw and male mice (strain B6C3F1) at 0, 300 or
600 mg/kg bw by gavage 5 days/week. Replicative DNA synthesis in hepatocytes
and renal proximal tube cells was assessed in vivo at weeks 0 to 1, 3 to 4 and 12 to13
(i.e., for six-day periods). Histological examination showed that a dose of 150 mg/kg
bw or less did not increase the hepatocyte labelling index for rats whereas 300 mg/kg
bw resulted in an increase of 255% of the control value at week one. No increases
were observed for the same parameter for weeks 4 and 13. In the mouse, the
hepatocyte-labelling index increased for all doses for weeks 1 and 4 with no
significant differences observed at week 13. Replicative DNA synthesis in renal
proximal tubule cells labelling increased at weeks 1, 4 and 13 in rats while the mouse
kidney labelling index increased only during the 4 week period.
The relationship between the expression of the immediate-early genes, c-fos, c-jun
and c-myc to hepatocyte proliferation after exposure to p-DCB has been investigated.
Male rats (strain F344) were given a single oral dose of p-DCB (300 mg/kg bw).
Examination of liver sections 48 hours after dosing revealed an increase of 4- to 5-
fold in the hepatic labelling index (S-phase; as determined by BrdU labelling)
compared to controls. The increase in labelling index was proceeded by an increase
in the expression, in some cells, of c-fos, c-jun and c-myc at one hour post-dosing.
Considerable inter-animal variation was observed in the expression of the immediate-
early genes. A direct correlation between the expression of c-myc, but not c-fos or c-
jun, with the hepatocyte labelling index was observed. In situ hybridization analysis
indicated that cells expressing c-jun and c-fos were randomly distributed across the
liver lobules while cells expressing c-myc were mainly midzonal and, to a lesser
extent, periportal (Hasmall et al., 1997a).
43
para-Dichlorobenzene
To further delineate the relationship between p-DCB-induced cell proliferation and
hepatocarcinogenesis, Umemura et al. (1998) treated male rats (strain F344) and
male mice (strain B6C3F1) with p-DCB (0, 75, 150 or 300 mg/kg bw or 0, 150, 300
or 600 mg/kg bw respectively) by gavage for 1 and 4 weeks. Relative liver weights
increased at both time points in mice at 600 mg/kg bw and in rats at 150 and 300
mg/kg bw. At week 4 a significant decrease (p<0.01) was noted in glutamine
synthetase-expressing hepatocytes, a marker of hepatocyte injury, in mice at 150
mg/kg bw but not at week 1 or either time point for rats. The hepatic cumulative
replicating fraction, determined by BrdU labelling, of mice increased at 300 and 600
mg/kg bw at week 1 with the response declining at week 4 to reach significance
(p<0.05) only at 600 mg/kg bw. The cumulative replicating fraction in rat livers
increased at 150 and 300 mg/kg bw at week 1 but returned to control levels at week
4. The absence of any hepatotoxic effect in the rat at 75 mg/kg bw and the mouse at
150 mg/kg bw suggests that a threshold level is required for hepatocarcinogenesis.
The relationship between cell proliferation and apoptosis in the maintenance of
hepatic homeostasis after the oral administration of p-DCB to male rats (strain F344)
and mice (strain B6C3F1) at 300 and 600 mg/kg bw respectively, was investigated.
After 2 days of treatment, DNA synthesis was significantly elevated (p<0.05) in both
species while the percentage of apoptotic hepatocytes, both spontaneous and
transforming growth factor 1-induced, was significantly (p<0.05) decreased. In all
mice and 4 out of 5 rats apoptosis decreased to undetectable levels. Using Western
blot analysis, an increase in the expression of mouse hepatic CYP2B1/2 was detected
in response to treatment with p-DCB (James et al., 1998).
In vitro studies
DNA synthesis by isolated rat (strain F344) and mouse (strain B6C3F1) hepatocytes
exposed to p-DCB (500 礛) for 40 hours was significantly elevated (p<0.05) in cells
of both species while the percentage of apoptotic cells, both spontaneous and
transforming growth factor 1-induced, was significantly (p<0.05) decreased (James
et al., 1998).
44 Priority Existing Chemical Number 13
10. Effects on Laboratory Mammals
and Other Test Systems
Toxicological studies made available for assessment by applicants and notifiers and
relevant studies identified after extensive literature searches have been evaluated and
are summarised in this section. Use was also made of international assessment reports
for p-DCB (BUA 1994, ATSDR 1998 (draft) and SIAR 1999 (draft)). In certain
cases, studies cited in such reports, but not accessible for evaluation for this
assessment, were utilised and have been acknowledged as such in the appropriate
place.
10.1 Acute toxicity
10.1.1 Lethality
Lethality studies have demonstrated that p-DCB presents a low level of toxicity by
the oral, dermal and inhalation routes. The LD50 and LC50 values from several
published studies are presented in Table 10.
Table 10 - Summary of p-DCB acute lethality studies
Route Species Result Reference
LD100 4000 mg/kg bw Hollingsworth et al., 1956
Oral Rat
Rat LD50 = 2512 mg/kg bw Varshavskaja, 1967
Rat LD50 = 3790 to 3863 mg/kg bw Gaines and Linder, 1986
LD100 2800 mg/kg bw Hollingsworth et al., 1956
Guinea pig
Dermal Rat LD50 > 6000 mg/kg bw Gaines and Linder, 1986
Inhalation Rat LC50 > 5.07 mg/L/4 hours Hardy, 1987
Intraperitoneal Rat LD50 = 2562 mg/kg bw Zupko and Edwards, 1949
10.1.2 Systemic effects
Acute toxic effects reported in animals due to p-DCB are generally nephrotoxicity in
male rats and hepatotoxicity in both sexes of mice. A summary of the acute toxic
effects is presented in Table 11.
45
para-Dichlorobenzene
46 Priority Existing Chemical Number 13
Charbonneau et al. (1989) reported the formation of protein droplets in the renal
tissue of male, but not female rats (strain F344), 24 hours after a single oral dose of
p-DCB (500 mg/kg bw).
Eldridge et al. (1992) found no increase in plasma enzyme levels, indicative of
cellular injury, (alanine aminotransferase (ALT), aspartate amino-transferase (AST)
or lactate dehydrogenase (LDH)), from male and female mice (strain B6C3F1) and
female rats (strain F344) which were administered a single dose of p-DCB (600
mg/kg bw). However, an increase in the liver weights of mice and rats was observed
and an increase in the hepatocellular labelling index, (as determined by incorporation
of 5-bromo-2'-deoxyuridine (BrdU)), a measure of cell proliferation, occurring at 24
and 48 hours after exposure for mice and rats respectively. The labelling index
returned to normal 4 days after treatment. Histological examination of the livers
revealed vacuolation of periportal hepatocytes and granulated cytoplasm of
centrilobular hepatocytes of male mice and to a lesser degree in female mice. Rats
developed slight vacuolation of the centrilobular hepatocytes although necrosis was
not evident. Further experiments over 13 weeks with doses of 0, 300 or 600 mg/kg
bw per day for mice and 0 or 600 mg/kg bw per day for rats were performed.
Hepatocellular proliferation was observed during the first week at 600 mg/kg bw per
day in both sexes of mice and in female rats. Cell proliferation was not observed at
the lower 300 mg/kg bw dose in mice.
Similar effects were observed in another study of rats (strain F344) above 450 mg/kg
bw in which hepatocellular degeneration was observed (Allis et al., 1992).
10.1.3 Metabolites of p-DCB
The administration of 2,5-dichloro-3-(glutathion-S-yl)-1,4-benzoquinone (DCGBQ;
0, 50, 100, 150 or 200 祄ol/kg), a metabolite of p-DCB, to male rats (Sprague-
Dawley strain) by i.v. injection resulted in the development of a dose-dependent renal
proximal tubular necrosis. The condition was characterised at 19 hours post
administration by an increase in blood urea nitrogen (BUN) at the highest dose and
elevated excretion of glucose, LDH and -glutamyl transferase (-GT) at 100
祄ol/kg and above. Histopathological examination of the kidneys demonstrated
extensive necrosis of the proximal tubules at 19 hours post exposure. The
investigators concluded that DCGBQ derived from the hepatic metabolism of p-DCB
is responsible for the early onset of nephrotoxicity in the male rat (Mertens et al.,
1991).
10.2 Irritation and corrosivity
There is little published information relating to skin and eye irritation in animals due
to acute exposure to p-DCB. Hollingsworth et al. (1956) reported that solid p-DCB
has a negligible irritating action on intact uncovered human skin but can produce a
burning sensation when in close contact for an excessive period. Eye irritation due to
p-DCB vapour (798 ppm) was also reported in rabbits, rats and guinea pigs.
47
para-Dichlorobenzene
In an unpublished study, it was reported that p-DCB (500 mg in paraffin oil) was
slightly irritating to rabbit skin (erythema but no oedema) after exposure for 4 hours.
Similarly, when the same preparation was applied to the eyes of rabbits for 24 hours
slight irritation was observed as judged by the presence of isolated damage to the
conjunctiva (erythema and oedema) (Maertins 1988, cited in SIAR 1999).
There have been no studies reporting p-DCB as being corrosive.
10.3 Sensitisation
A Magnusson and Kligman test was conducted on guinea pigs to examine the
sensitisation potential of p-DCB. Animals were tested at induction concentrations of
0.1% intradermally, 25% topically and a challenge concentration of 25% in
petrolatum. Irritation was slight after 0.1% intradermal application. All animals were
negative for sensitisation at 24 hours and 21% of animals were positive at 48 hours
(Bornatowicz et al., 1995, cited in SIAR 1999).
Two non-validated sensitisation studies have also been reported in which the results
were negative (Leung et al., 1990 and Suzuki et al., 1991).
10.4 Immunotoxicity
Human lymphocytes exposed for 4 hours to p-DCB (100 礛 to 10 mM) proved to
be cytotoxic only at the highest concentration as judged by the trypan blue dye
exclusion assay (Perocco et al., 1983).
Total thyroxine (T4) and total triiodothyronine (T3) plasma levels of male rats (strain
Wistar) at 24 hours after a single intraperitoneal injection of p-DCB (1 or 2 mmol/kg)
were examined. p-DCB decreased T4 levels at 2 mmol/kg but not at the lower dose
and T3 levels were not altered (Den Besten et al., 1991).
10.5 Repeated dose toxicity
10.5.1 Oral administration
Male and female rats (strain F344) were administered p-DCB (0, 60, 125, 250, 500 or
1000 mg/kg bw) by gavage for 14 days. All treated animals survived with the
exception of one male (125 mg/kg bw), the death being attributed to gavage error.
The final average body weights for males were decreased relative to controls; female
body weights were not affected (NTP, 1987).
A second 14-day study of male and female rats (strain F344) was conducted with
increased doses of p-DCB (0, 500, 1000, 2000, 4000 or 8000 mg/kg bw) by gavage.
A dose of 1000 mg/kg bw resulted in the death of 4 of 5 females and one male
(attributed to gavage error). Doses of 2000 mg/kg bw or greater proved fatal for all
animals within 14 days (NTP, 1987). The results of the two 14 day studies in rats are
inconsistent and both sets of results were confounded by a high incidence of gavage
errors that may have contributed to the deaths of some animals.
48 Priority Existing Chemical Number 13
Male and female mice (strain B6C3F1) were administered p-DCB (0, 250, 500, 1000,
2000 or 4000 mg/kg bw) by gavage for 14 days. All mice dosed at 4000 mg/kg bw
died by day 4. Two male and one female control animals died due to gavage errors.
The final mean body weight of male mice at 2000 mg/kg bw was 15% lower than
controls. No dose-related histopathological results were observed (NTP, 1987).
In a second 14-day study, male and female mice (strain B6C3F1) were administered
p-DCB (0, 250, 500, 1000, 2000 or 4000 mg/kg bw) by gavage. No p-DCB-related
deaths were observed. One treated male (125 mg/kg bw) and 2 male and 1 female
control animals died due to gavage errors. Final mean body weights were not
different from control animals (NTP, 1987).
Renal cell proliferation in response to the oral administration of p-DCB (0, 118 or
294 mg/kg bw) to male rats (strain F344) for 7 days was examined. A significant
increase (p<0.05) was observed in treated animals (Charbonneau et al., 1989).
A 1-year oral study in which p-DCB was administered via capsule was conducted
with Beagle dogs (5 male and 5 female dogs/group) using doses of 0, 10, 50 or 150
mg/kg/day. Due to severe toxicity at the highest dose, the maximum dose was
adjusted to 100 mg/kg/day for males at 3 weeks and subsequently decreased to 75
mg/kg/day for both sexes. Two males and 1 female died within the first 4 weeks of
the study and 1 male control died at a later date. The effects at 150 mg/kg (and for the
deceased control male) included hypoactivity, dehydration, decreased defecation,
blood-like faecal colour, emesis, emaciation and pale oral mucosa. Cumulative body
weight gain was decreased at 150 mg/kg/day although, after the reduced dosage
regimen was introduced, final body weights were comparable at the conclusion of
the study. High-dose animals exhibited a mild anaemia, characterised by decreased
erythrocyte and haematocrit levels at 6 months, but returned to normal due to a
compensatory hemopoietic response. Doses of 50 mg/kg/day or greater resulted in an
increase in hepatic enzymes (ALT, AST and GGT) and were associated with
increases in liver weights compared to control animals. Histopathological findings
included hepatocellular hypertrophy, hepatocellular pigment deposition, bile duct
hyperplasia and hepatic portal inflammation. Renal effects observed included
collecting duct epithelial vacuolation in a high-dose male and at all dose levels in
females and, at 50 mg/kg/day or greater, was associated with increased renal weights
with renal discolouration (Naylor and Stout, 1996). The NOAEL was 10 mg/kg/day
and a LOAEL of 50 mg/kg/day based on hepatotoxicity.
The effect of p-DCB (300 mg/kg bw) on male rat (strain F344) hepatocyte ploidy and
nuclearity were examined after 7 days following daily administration of the
compound by gavage. Examination of isolated untreated hepatocytes showed the
dominant cell population to be tetraploid cells with lesser populations of diploid and
octoploid cells. Following p-DCB treatment the number of octoploid cells increased
by 18% and a decrease in the tetraploid and diploid cell populations resulted. p-DCB
also caused an 11% increase in the population of mononucleated octoploid cells but
not of binucleated octoploid or mononucleated and binucleated tetraploid cells. It was
further shown that p-DCB treatment resulted in a 12-fold increase in the hepatic
labelling index as determined by BrdU labelling. The distribution of BrdU labelling
within each ploidy and nuclearity class showed significant increases in the labelling
49
para-Dichlorobenzene
index of diploid, mononucleated tetraploid and mono- and binucleated octoploid
cells. The labelling index of binucleated tetraploid cells was not increased by p-DCB
(Hasmall et al., 1997b).
Oral administration of p-DCB to male rats (strain not specified) and delivered by
gavage, five days/week for four weeks at doses of 10, 100 and 500 mg/kg bw,
resulted in the development of liver necrosis and swelling of the renal tubular
epithelium at the highest dose. No adverse effects were observed with the lower
doses (Hollingsworth et al., 1956).
A long term study was performed with female rats given p-DCB (0, 18.8, 188, or 376
mg/kg bw) by gavage for 5 days/week over 192 days (138 doses). The results
demonstrated an increase in average liver weight and a slight increase in kidney
weight at 188 and 376 mg/kg bw. At the higher dose histopathological findings
indicated slight cirrhosis and focal necrosis of the liver. There were no adverse
haematological findings. The NOAEL for this study was 18.8 mg/kg bw
(Hollingsworth et al., 1956).
A 13-week study investigated the effect of p-DCB on male and female rats (strain
F344). Rats were administered p-DCB (0, 300, 600, 900, 1200 or 1500 mg/kg bw) 5
days/week by gavage. Examination of the animals revealed that p-DCB at all doses
induced histopathological changes in the kidneys of all male rats; the changes where
characterised by renal tubular cell alterations with hyaline droplet formation. At
1,200 and 1,500 mg/kg bw survival of male rats decreased and female survival
decreased at 1,500 mg/kg bw. Weight gain decreased for male rats at 300 mg/kg bw
or greater and for females at 1,200 and 1,500 mg/kg bw. A statistically significant
increase in liver weights was observed at 900 mg/kg bw for both sexes. At doses of
1,200 and 1,500 mg/kg bw pathological conditions were seen in both sexes including
degeneration and necrosis of hepatocytes, bone marrow hypoplasia, lymphoid
depletion of the thymus and spleen and epithelial necrosis of the nasal turbinates.
Haematological changes observed in male rats at doses of 300 to 1,200 mg/kg bw
included statistically significant decreases in haematocrit, erythrocyte count and
haemoglobin level. No significant changes in female blood parameters were observed
(NTP, 1987). The NOAEL for females was 600 mg/kg bw while a NOAEL was not
identified for males.
A second 13-week NTP study examined the effect of lower doses of p-DCB (0, 37.5,
75, 150, 300 or 600 mg/kg bw) on male and female F344 rats when administered by
gavage. The findings indicated that the NOAEL for female rats was 600 mg/kg bw
per day and for male rats the NOAEL was 300 mg/kg bw per day where renal cortical
degeneration was observed at 600 mg/kg bw (NTP, 1987).
A 13-week study of male and female mice (strain B6C3F1) dosed with p-DCB (0,
600, 900, 1000, 1500 or 1800 mg/kg bw) by gavage 5 days/week resulted in
hepatocellular degeneration in all treatment groups. The survival of males and
females at 1,500 and 1,800 mg/kg bw was decreased compared to control groups.
Administration of p-DCB to male mice at 600 mg/kg bw or more resulted in
leukopenia and females at 1,000 mg/kg bw or more displayed a similar condition. No
renal pathologies were observed in any treatment group (NTP, 1987). A LOAEL of
600 mg/kg bw for both sexes of mice was determined.
50 Priority Existing Chemical Number 13
A second 13-week gavage study of mice (strain B6C3F1) treated with lower doses of
p-DCB (0, 85, 338, 675 or 900 mg/kg bw) for 5 days/week. Both sexes developed
hepatocellular cytomegaly at 675 mg/kg bw or greater but was not observed at lower
doses. No renal pathologies were observed in any treatment group (NTP, 1987). The
NOAEL was 338 mg/kg bw.
A study of the nephrotoxic effects of p-DCB for male and female rats (strain F344)
was conducted. Animals received oral doses of p-DCB (0, 75, 150, 300 or 600 mg/kg
bw per day), 7 days/week for 4 or 13 weeks. No treatment-related effects were
observed for food consumption, growth or haematocrit. Urinalysis showed a dose-
dependent shift to acidic values and an increase in the presence of epithelial cells in
the males at 4 and 13 weeks. The presence of LDH was elevated in the urine of males
at day 9 and was dose-dependent from 75 to 300 mg/kg bw. LDH was similarly
elevated at 4 and 13 weeks. Gross pathology of the kidneys at 4 weeks showed an
increase in absolute and relative weights for the males at 300 mg/kg bw and females
at 600 mg/kg bw. At week 13 the increase occurred at 150 mg/kg bw for males while
the female weight increase was significant at 600 mg/kg bw. Histopathological
changes were evident in the male kidneys after 4 weeks of exposure to p-DCB at
doses of 150 and 600 mg/kg bw and consisted of dilated tubules, cellular
degeneration and hyaline droplet formation. The kidneys of the 75 mg/kg bw group
showed no sign of structural alterations. At 13 weeks male kidneys in the 150 to 600
mg/kg bw groups showed signs of epithelial regeneration and chronic nephropathy
with extensive hyaline droplet formation in the proximal tubular epithelial cells. The
female kidneys showed no sign of hyaline droplet formation and no structural
alterations due to p-DCB (Bomhard et al., 1988). The LOAEL for males was 75
mg/kg bw for both the 4 and 13 week studies while the NOAEL for females was 300
mg/kg bw for both time periods.
A 13-week study was undertaken to determine the effects of p-DCB on male and
female mice (strain B6C3F1) and female rats (strain F344) (5 animals/group) in
which the mice received 0, 300 or 600 mg/kg bw per day and the rats 0 or 600 mg/kg
bw per day by gavage. One experimental group from each species was given p-DCB
up to week 5 and for the remainder of the study received the vehicle (corn oil). At the
highest dose, liver weights increased in all treated animals. Hepatocellular
proliferation was observed during the first week at 600 mg/kg bw per day in both
sexes of mice and in female rats but not in mice at 300 mg/kg bw per day. There were
no changes in liver-associated plasma enzymes for any treatment group compared to
control animals. In the groups in which the treatment with p-DCB ceased at 5 weeks
the increase in liver weight halted and reverted to normal weight by the end of the
study demonstrating the reversible nature of the effect. These results indicate that,
under the experimental conditions described, p-DCB can induce a mitogenic response
in the liver in the absence of a necrotic response (Eldridge et al., 1992). The LOAEL
was 600 mg/kg bw for each species due to hepatocellular proliferation.
In a study by Lake et al. (1997) male rats (strain F344) were treated daily with p-
DCB at 0, 25, 75 150 or 300 mg/kg bw and male mice (strain B6C3F1) at 0, 300 or
600 mg/kg bw by gavage, 5 days/week. The animals were sacrificed at weeks 1, 4
and 13. Treatment of rats with p-DCB at 300 mg/kg bw resulted in a marked increase
in relative liver weights at weeks 1, 4 and 13 and became significant at 150 mg/kg bw
51
para-Dichlorobenzene
at week 4. A significant increase in kidney weight in rats at weeks 4 and 13 was
noted at a dose of 150 and 300 mg/kg bw. Relative liver weights for mice were
increased at weeks 1, 4 and 13 at 300 mg/kg bw but kidney weights were not
significantly different from controls. Histological examination of liver sections
revealed no pathological changes in response to 300 mg/kg bw in the rat for 1 week
and slight centrilobular hypertrophy in the mouse. At 300 mg/kg bw rats developed a
mild centrilobular hypertrophy after 13 weeks exposure while mice receiving 600
mg/kg bw showed a marked centrilobular hypertrophy. The NOAEL for rats was 75
mg/kg bw and for mice the NOAEL was 300 mg/kg bw.
A 2-year study of the effects of oral administration of p-DCB on both sexes of rats
(strain F344) and mice (strain B6C3F1) was conducted. Male rats were dosed at 0,
150 or 300 mg/kg bw and female rats and male and female mice at 0, 300 or 600
mg/kg bw for 5 days/week. Survival of high dose male rats was significantly lower
than controls. Male rats exhibited nephropathy due to epithelial hyperplasia of the
renal pelvis, mineralisation of the collecting tubules of the renal medulla and focal
hyperplasia of the renal tubular epithelium at both doses. Female rats showed
increased nephropathy at either dose compared to controls. Both sexes of mice
exposed to p-DCB developed hepatic lesions characterised by cytomegaly,
karyomegaly, cellular degeneration and individual cell necrosis. Male mice displayed
an increase in nephropathy while females exhibited renal tubular regeneration. The
LOAEL for male and female rats were 150 and 300 mg/kg bw respectively. The
LOAEL for both sexes of mice was 300 mg/kg bw (NTP, 1987). Male rats developed
renal tumours while both sexes of mice developed hepatic tumours which are
described in further detail in Section 10.8.
10.5.2 Inhalation
Male and female rats (strain not specified), guinea pigs and rabbits were exposed to
p-DCB vapour (0, 96, 158, 173, 341 or 798 ppm) 7 hours/day (8 hours/day for 798
ppm), 5 days/week from 1 to 69 exposures. At the highest dose the animals displayed
tremors, weakness, an unkempt appearance and unconsciousness. Histological
findings included slight to moderate cloudy swelling and central necrosis of the liver
of all animals and swelling of the tubular epithelium of female rat kidneys. Rabbits,
but not rats or guinea pigs, exhibited reversible eye ground changes and 2 exhibited
pulmonary congestion with emphysema. One group of animals were treated at 341
ppm p-DCB for 6 months. Male rats developed a slight increase in liver and kidney
weights and the growth of male guinea pigs was depressed. Histological findings in
male guinea pigs included cloudy swelling of the liver with fatty degeneration, focal
necrosis and slight cirrhosis in some animals. Exposure to 173 ppm p-DCB for 16
days produced a moderate increase in the average weights of livers and kidneys of
rats and degeneration of the central areas of female rat livers. The average weight of
the spleen in male guinea pigs was depressed. Histological examination of lung tissue
revealed slight interstitial oedema and congestion in male rats and female rabbits and
guinea pigs while some animals developed alveolar haemorrhages and oedema.
Similarly, treatment with 158 ppm produced an increase in the average weights of
male livers and kidneys and female rat and guinea pig livers but no other adverse
effects. Exposure to p-DCB at 96 ppm for six months produced no adverse effects
52 Priority Existing Chemical Number 13
(Hollingsworth et al., 1956). A NOAEL of 96 ppm and a LOAEL of 158 ppm were
identified for rats.
In a study reviewed by Loeser and Litchfield (1983), exposed rats (strain Wistar-
derived) and mice (strain Swiss) to long term exposure of p-DCB vapour (0, 75 and
500 ppm), 5 hours/day, 5 days/week for 76 and 57 weeks for rats and mice
respectively. They found no treatment-related changes to the rats with respect to
mortality, changes in body weight, or food and water intake. At 500 ppm, urinary
coproporphyrin was elevated with the authors concluding that this may be related to
an observed increase in liver and kidney weights of this group. There was no change
in hepatic aminopyrine demethylase. It was concluded that while long-term exposure
of rats to p-DCB at 500 ppm induced some changes in liver function there was no
toxicological effect at 75 ppm. Mice exposed to p-DCB under identical conditions as
the rats did not demonstrate any signs of toxicity giving a NOAEL of 500 ppm,
however, due to recurrent respiratory infections the results reported are of
questionable value.
In the 2-year JBRC (1995) study, to determine the carcinogenicity of p-DCB, rats
(strain F344) were exposed to the vapour at 0, 20, 75 or 300 ppm 6 hours/day, 5
days/week. Treatment of male rats at 300 ppm resulted in an increase in kidney
weight with mineralisation of the of the papilla collecting tubule and urothelial
hyperplasia. Respiratory effects were observed (respiratory metaplasia in nasal cavity
gland and eosinophilic changes in respiratory epithelium) in females at 300 ppm and
eosinophilic changes in olfactory epithelium in both sexes of control and treated
animals at 300 ppm and females at 75 ppm. The apparent presence of an underlying
respiratory pathology in control and test animals makes the interpretation of
treatment-related respiratory effects difficult. Based on renal pathology alone a
NOAEL of 75 ppm was determined.
A 2-year study was undertaken to determine the carcinogenicity of p-DCB for mice
(strain BDF1) exposed to the vapour of p-DCB at 0, 20, 75 or 300 ppm 6 hours/day,
5 days/week. Liver weights were increased at 300 ppm for both sexes and an increase
in hepatic enzymes (AST, ALT, LDH and alkaline phosphatase) was observed.
Histological examination revealed slight local necrosis in both sexes and
hepatocellular hypertrophy in males. Kidney weights of both sexes was increased at
300 ppm (JBRC, 1995). A NOAEL of 75 ppm was determined.
The carcinogenic effects observed in the above 2-year studies are discussed in
Section 10.8
10.5.3 Dermal
A dermal toxicity study was conducted with male and female rats (strain Sprague-
Dawley) by application of p-DCB (0 to 300 mg/kg bw per day) in mineral oil, 5
days/week for 3 weeks. No evidence of any toxicity or significant dermal effect was
observed (Arletta, 1990; cited in SIAR 1999).
53
para-Dichlorobenzene
10.6 Reproductive and developmental toxicity
10.6.1 Reproductive toxicity
A two-generation reproductive study was conducted with Sprague-Dawley rats.
Weanling rats (F0) were exposed to p-DCB vapour (0, 66, 211 or 538 ppm) for 6 hr/d
for 10 weeks before mating and during mating, gestation and lactation. F1 weanlings
were then exposed for 11 weeks and mated under the conditions described above.
Exposure to p-DCB at 538 ppm resulted in a decrease in body weight for both sexes
and a reduction in body weight gain along with reduced food consumption. Body
weights for F0 and F1 females during gestation and F1 females during lactation were
decreased at 538 ppm. No reproductive effects were observed for either generation.
The F1 and F2 litter body weights were decreased and an increase in perinatal deaths
occurred at 538 ppm. All levels of exposure to p-DCB resulted in F0 and F1 male
nephrotoxicity (hyaline droplet nephropathy) with increases in kidney weights. Doses
of 211 or 538 ppm resulted in increased male and female liver weights with
hepatocellular hypertrophy at 538 ppm in both F0 and F1 sexes (Neeper-Bradley et
al., 1989). No NOAEL could be determined for males. A NOAEL for females of 66
ppm was determined based on hepatotoxicity observed at 211 ppm and for
reproductive effects a NOAEL of 211 ppm was determined.
In a two-generation study of the effects of p-DCB on reproduction (OECD guideline
416) rats (strain Sprague-Dawley) were administered p-DCB (0, 30, 90 or 270 mg/kg
bw per day) by gavage. Treatment was initiated 77 days prior to mating for male (F0)
rats and for F0 females 14 days before mating and continued during mating, gestation,
and lactation and for 21 days postnatal. In parents, in both generations at 270 mg/kg
bw, the organ weights of male rat livers and kidneys (associated with nephrotoxicity)
were increased while spleen weights decreased. Parameters examined were time
between beginning of mating and evidence of copulation, time of gestation, fertility
index, gestational index, percentage of dams with dead pups, total number of pups at
birth, percentage of pups with positive ear reflex, grasping and orientation reflex,
absolute and relative weights of testes, epididymides and ovaries, absolute and
relative weights of female livers, kidneys and spleens. Treatment with p-DCB at 270
mg/kg bw per day resulted in both generations in a reduction in the number of live
pups at birth and mean body weights of pups only at birth and an increased pup
mortality between days 1 to 4 and 5 to 21 of lactation. Developmental effects
included retardation of the erection of ears and opening of eyes, a statistically
significant (p<0.05) reduction in the number of pups with a positive draw up reflex
and an increase incidence of dry skin. At 90 mg/kg bw per day, reversible reduced
mean body weight at birth in the F0/F1 generation and a statistically significant
increase in the number of deceased pups between days 1 to 4 only in F1/F2 generation
was noted. The NOAEL for fertility was estimated to be 270 mg/kg bw per day while
the NOAEL for parents F0 and F1 was 90 mg/kg bw per day. The NOAEL for
developmental effects was 30 mg/kg bw per day with reversible reduced mean body
weight at birth in F0/F1 pups, increased number of deceased pups in 1 time period in 1
generation and slight behavioural anomalies in 1 generation (Bornatowicz et al.,
1994, cited in SIAR 1999).
54 Priority Existing Chemical Number 13
10.6.2 Developmental toxicity
The developmental toxicity of p-DCB in New Zealand rabbits has been investigated.
Inseminated rabbits were exposed to p-DCB (0, 100, 300 or 800 ppm) for 6 hr/day on
days 6 to 18 of gestation. Maternal toxicity was observed, described as slight and
based on a decrease in body weight gain during the first three day of exposure, at 800
ppm. No significant differences were observed when animals were examined for
number of pregnancies, number of litters, corpora lutea/dam, foetuses/litter, litters
totally resorbed, resorptions/litters with resorptions, sex ratio and foetal body weight.
A significant, but non dose-dependent, increase in the percent implantations resorbed
and percent litters with resorptions at 300 ppm was observed. At 800 ppm a
significant increase in retro-oesophageal right subclavian artery development was
observed (controls, 1/115; 800 ppm, 6/119; historical controls for the laboratory, 5%)
but was not considered to be a teratogenic response to treatment. No other significant
treatment-related changes in offspring were observed (Hayes, 1985). A NOAEL of
300 ppm for maternal toxicity was determined. The NOAEL for developmental
toxicity was 800 ppm.
Pregnant female rats (strain CD) were treated from day 6 to day 15 of gestation with
p-DCB (0, 250, 500, 750 or 1000 mg/kg bw per day) by gavage. A dose of 500
mg/kg bw or higher resulted in a decrease in maternal weight gain. No significant
change was observed in the number of implantations, corpora lutea/dam, number of
live foetuses, percent pre-implantation and post-implantation loss or percent
resorptions compared to control animals. At the highest dose foetal weights were
significantly lower (p<0.01) than control or other treated groups. No abnormalities
were observed with the exception of the 750 and 1000 mg/kg bw groups where
skeletal variations were detected and a dose-related incidence of extra rib formation
at 500 to 1000 mg/kg bw (Giavini et al., 1986). The NOAEL for maternal toxicity
and developmental toxicity was 250 mg/kg bw per day.
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para-Dichlorobenzene
56 Priority Existing Chemical Number 13
57
para-Dichlorobenzene
10.7 Genotoxicity
In vitro
A series of Ames tests were conducted with several strains of Salmonella
typhimurium (TA98, TA100, TA1535 and TA1538), with or without metabolic
activation by the S9 system. In one experiment, p-DCB was used in the gas phase (0,
94, 299 or 682 ppm) and in two other experiments the plate incorporation method (4,
20, 100, 500 or 2500 礸 p-DCB/plate) was used. All strains gave negative results
with the exception of the TA1535 strain which was positive at 500 礸/plate in one
experiment only (Anderson, 1976, cited by Loeser and Litchfield, 1983).
Other Ames tests by Shimizu et al., (1983) using Salmonella typhimurium strains
TA98, TA100, TA1535, TA1537, and TA1538 and Haworth et al., (1983) using
strains TA98, TA100, TA1535 and TA1537 produced negative results with or
without metabolic activation.
Tests with p-DCB using other species of bacteria (Bacillus subtilis and Escherichia
coli) have reported negative results (Waters 1982). However, a mutagenic effect due
to p-DCB was found in the eukaryotic Aspergillus nidulans assay (Prasad, 1970).
Human lymphocytes exposed for 4 hours to p-DCB (0.01 to 1 mM) failed to induce
unscheduled DNA synthesis by a [3H]-thymidine uptake assay (Perocco et al., 1983).
Studies of unscheduled DNA synthesis in the HeLa cell line proved to be negative
with or without metabolic activation (Instituto di Recerche Biomediche 1986a) as did
gene mutation assays involving Chinese hamster lung cells (Instituto di Recerche
Biomediche 1986b; cited in SIAR, 1999).
The mutagenic potential of p-DCB was assessed in the L5178Y mouse lymphoma
forward mutation assay, however, the results proved to be inconclusive due to one
metabolic activation test giving a negative result and two other tests giving positive
results, one positive at high doses, the other at an intermediate dose. The test was
negative without metabolic activation (McGregor et al., 1988).
Human lymphocytes from 2 donors, when incubated for 48 hours with 0.05, 0.1 or
0.2 礸/mL p-DCB and without metabolic activation, resulted in a significant increase
in the sister-chromatid exchange rate at the two highest doses. At 0.1 and 0.2 礸/mL,
p-DCB was cytotoxic as judged by a decrease in third and second metaphases. The
lowest tested concentration of p-DCB (0.05 礸/mL) was without effect (Carbonell et
al., 1991).
Treatment of rat hepatocyte primary cultures with p-DCB (0.56 to 3.2 mM) resulted
in a biphasic response with a significant increase (p = 0.05) in micronuclei at 1.0 to
1.8 mM and a return to control levels at 3.2 mM. The frequency of DNA strand
breaks did not alter in response to treatment with p-DCB. Human hepatocytes, from 2
donors, under the same conditions did not exhibit clastogenic effects (Canonero et
al., 1997).
58 Priority Existing Chemical Number 13
The binding of radiolabel to calf thymus DNA after the addition of p-[14C]-DCB was
mediated by rat and mouse microsomes (from liver and lung) and was enhanced by
the addition of glutathione suggesting that activation of p-DCB by cytochromes P450
and microsomal glutathione transferases are important for DNA binding to occur
(Lattanzi et al., 1989).
In vivo
A dominant lethal assay using male CD-1 mice exposed to p-DCB (0, 75, 225 or 450
ppm) 6 hr/day for 5 days found p-DCB to be non-mutagenic at any maturation stage
of the 8-week spermatogenic cycle. No significant increases in post implantation
early foetal deaths, early foetal deaths or percentage of early foetal deaths per total
implants per pregnancy were detected which could be attributed to p-DCB (Anderson
and Hodge, 1976, cited in Loeser and Litchfield, 1983).
A micronucleus assay performed on male and female mice (strain B6C3F1) after oral
administration of p-DCB (0, 600, 900, 1000, 1500 and 1800 mg/kg bw) in corn oil
for 13 weeks produced no evidence of peripheral micronucleated erythrocytes at any
dose (NTP, 1987).
The clastogenic activity of p-DCB was assessed using an in vivo bone marrow
micronucleus test. The p-DCB (0, 355, 710, 1065 or 1420 mg/kg bw) was
administered in two doses 24 hours apart by i.p. injection to male NMRI mice and the
animals sacrificed 6 hours after the final injection. At 30 hours after first exposure, a
dose-dependent increase in micronuclei was observed in the femoral bone marrow of
treated mice compared to control animals. Data on cytotoxicity were not presented
(Mohtashamipur, 1987).
The covalent binding of radiolabel to DNA has been investigated in male Wistar rats
and BALB/c mice after intraperitoneal injection of p-[14C]-DCB (0.4 mg/kg bw). The
amount of radioactivity covalently bound to DNA in the liver, kidneys, lungs and
stomach was determined 22 hours later. The results demonstrated no DNA binding in
the rat and low level binding to the DNA of all organs tested in the mouse.
Examination of mice 72 hours after injection revealed no detectable binding of
radiolabel to DNA (Lattanzi et al., 1989).
In another micronucleus assay, i.p. doses of p-DCB at 355 and 710 mg/kg bw
produced negative test results. Cytotoxicity was noted at the highest dose based on a
change in the polychromatic/normochromatic erythrocyte ratio (Herbold, 1988, cited
in SIAR 1999).
No evidence of micronucleus formation was found in male mice (strain CD-1) after
double i.p. injections of up to 75% of the LD50 or double oral doses of up to 2000
mg/kg bw by gavage (Morita et al., 1997).
Damage to the DNA of male mice (strain CD-1) after treatment with p-DCB (2000
mg/kg bw, suspended in 2% Tween-80) by i.p. injection was assessed by the single-
cell gel electrophoresis (Comet) assay. At 3 hours post-injection DNA damage was
evident in the liver and, to a lesser extent, in the spleen but absent in both organs at
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para-Dichlorobenzene
24 hours. Kidney, lung and bone marrow were negative for DNA damage at all time
points. The frequency of apoptotic cells was not recorded (Sasaki et al., 1997).
Hepatocytes derived from male and female rats (strain F344) and female mice (strain
B6C3F1) were examined for unscheduled DNA synthesis (UDS) and replicative DNA
synthesis after administration by gavage of p-DCB (0, 300, 600 or 1,000 mg/kg bw)
dissolved in corn oil. The mouse liver and rat kidney were negative for UDS.
Hepatocytes from both sexes of mice showed a dose-dependent increase in S-phase
cells. Renal tissue from male rats also showed an increase in S-phase cells but not
females (Sherman et al., 1998).
Exposure of Drosophila to p-DCB vapour produced no mutagenic effect in a sex-
linked recessive lethal test. Significant mortality of flies occurred from 6000 to 15600
ppm. (Bioassay Systems Corp. 1982; cited in SIAR, 1999).
Metabolites
When calf thymus DNA was incubated in the presence of the p-DCB metabolites,
2,5-dichlorohydroquinone (DCHQ) or 2,5-dichlorobenzoquinone (DCBQ), an
increase in the oxidation product, 8-oxo-7,8-dihydro-2'-deoxyguanosine, was
observed. In addition, DCHQ and DCBQ induced dose-dependent increases in single
and double strand DNA breaks. DCHQ required the presence of Cu(II) ions while
DCBQ required Cu(II) and NADH for the observed effects to occur. Analysis of
DNA fragments showed site specificity for thymine residues. Inhibitor studies
indicated that formation of the semiquinone radical reduces molecular oxygen to
superoxide which, by dismutation, produces hydrogen peroxide. The observed DNA
changes resulted from the combined action of copper and hydrogen peroxide
(Oikawa and Kawanishi, 1996).
10.8 Carcinogenicity
10.8.1 Oral exposure
A 2-year study by the National Toxicology Program was conducted in which rats
(strain F344) and mice (strain B6C3F1) were administered p-DCB by gavage (5
days/week). Male rats received 0, 150 or 300 mg/kg bw per day and female rats and
both sexes of mice received 0, 300 or 600 mg/kg bw per day. The survival of female
rats and both sexes of mice treated with p-DCB was comparable to the control groups
while high dose male rats had a significantly lower survival rate (40%). Male and
high dose female rats showed a dose-dependent increase in nephropathy. The non-
carcinogenic effects are summarised in Section 10.5 Treated male rats showed an
increased incidence (not significant and within the range of the laboratory historical
controls) of mononuclear cell leukaemia and a dose-dependent increase (statistically
significant at 300 mg/kg bw per day, p = 0.011 by life table test) in the formation of
renal tubular cell adenocarcinoma (controls 1/50; low-dose, 3/50; high-dose, 7/50).
One case of tubular cell adenoma was also recorded in a high-dose male rat. An
increase in hyperplasia of the parathyroid gland was observed in male rats (control,
4/42; low-dose, 13/42; high-dose 20/38) but not females.
60 Priority Existing Chemical Number 13
In mice, there was no was no significant difference in survival time between the three
dosage groups for either gender. Males and females showed an increase, which was
statistically significant in the high-dose animals, in the incidence of hepatocellular
carcinoma (males: controls, 14/50; low-dose, 11/49; high-dose, 32/50; females:
controls, 5/50; low-dose, 5/48; high-dose, 19/50), hepatocellular adenoma (males:
controls, 5/50; low-dose, 13/49; high-dose, 16/50; females: controls, 10/50; low-dose,
6/48; high-dose, 21/50) and hepatocellular carcinoma and adenoma (combined)
(males: controls, 17/50; low-dose, 22/49; high-dose, 40/50; females: controls, 15/50;
low-dose, 10/48; high-dose 36/50). Four high-dose males developed rare
hepatoblastomas although statistical significance was not reached. A high incidence
of spontaneous hepatic adenomas and carcinomas were observed in control animals
and in historical controls. An increase (not significant) in pheochromocytomas in
male mice (controls, 0/47; low-dose, 2/48; high-dose, 4/49) and thyroid gland
follicular cell hyperplasia was also evident (NTP, 1987).
An investigation of the hepatocarcinogenic activity of p-DCB in male rats (strain
F344), when administered by gavage at doses up to 58.8 mg/kg bw per day gave
negative results in an initiation/promotion assay (Gustafson et al., 1998).
10.8.2 Inhalation exposure
A study involving the inhalation of p-DCB vapour (0, 75 and 500 ppm) for 5
hours/day, 5 days/week for 76 weeks by rats (strain Wistar-derived) and 56 weeks by
mice (strain Swiss) found no evidence for increased tumour or multiple tumour
formation. However, the study in mice was compromised by the presence of
respiratory infections and both studies were of limited duration. See Section 10.5.2
for further details (Loesser and Litchfield, 1983).
In a two-year study to determine the carcinogenicity of p-DCB, rats (strain F344)
were exposed to the vapour at 0, 20, 75 or 300 ppm 6 hours/day, 5 days/week. The
non-carcinogenic treatment effects are summarised in section 10.5.2. No treatment-
related tumours were observed (JBRC, 1995).
A two-year study was undertaken to determine the carcinogenicity of p-DCB for
mice (strain BDF1) exposed to the vapour of p-DCB at 0, 20, 75 or 300 ppm 6
hours/day, 5 days/week. An increase in the incidence of hepatocellular carcinoma
was observed which was statistically significant at 300 ppm (p<0.01) (males: control
12/49, low-dose 17/49, mid-dose 16/50, high-dose 38/49; females: control 2/50, low-
dose 4/50, mid-dose 2/49, high-dose 41/50). Females showed an increase in
hepatocellular adenomas which became significant at 300 ppm (control 2/50, low-
dose 10/50, mid-dose 6/49, high-dose 20/50). A statistically significant (p<0.05)
increase in hepatic histiocytosarcomas was observed at 300 ppm (control 0/49, 3/49,
1/50, 6/49) only in males with hepatocellular carcinomas. Hepatoblastoma-like
tumours were observed in animals with hepatocarcinoma (males: control 0/12, low-
dose 2/17, mid-dose 1/16, high-dose 8/38; females: high-dose 6/41). As with the oral
study (NTP, 1987) a high spontaneous incidence of hepatic adenomas and
carcinomas were observed in control animals, despite this, statistical significance was
achieved. High-dose females exhibited a statistically significant increase (p = 0.0430)
in combined bronchiolar-alveolar adenomas and bronchiolar-alveolar carcinomas
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para-Dichlorobenzene
(experimental controls, 1/50; high-dose females, 7/50). However, the combined
incidence of bronchiolar-alveolar adenomas and bronchiolar-alveolar carcinomas for
historical controls for the laboratory was 7.6% (range 0/50 to 9/50). There were no
increases in bronchiolar-alveolar adenomas or bronchiolar-alveolar carcinomas in
male mice (JBRC, 1995).
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11. Human Health Effects
There are few reports concerning the effects of p-DCB on humans and no clinical
studies on human volunteers. In cases of occupational and accidental exposure or
misuse the extent of exposure is not known and the involvement of other chemicals
uncertain.
11.1 Acute toxicity
Only one case report describing the acute effects after p-DCB ingestion is reported in
the literature. Following ingestion of an unknown quantity of moth crystals
containing p-DCB, a 3-year-old male was hospitalised with acute haemolytic
anaemia. He became listless, jaundiced and his haemoglobin fell to 36%. Urinalysis
revealed methemoglobinuria and a compound stated to be 2,5-dichloroquinol
(Hallowell, 1959).
11.2 Irritation and sensitisation
Occupational exposure to the vapour of p-DCB in the range 50 to 80 ppm was
associated with irritation to the eyes and nose and severe irritation apparent in the
range 80 to 160 ppm. It was reported that due to respiratory irritant effects workers
required the use of a respirator at concentrations above 160 ppm although some
workers, who had became acclimated to the effects of p-DCB, did not require their
use (Hollingsworth et al., 1956).
Hollingsworth et al. (1956) reported that solid p-DCB has a negligible irritating
action on intact uncovered human skin but can produce a burning sensation if held in
close contact for an excessive period.
A 69-year-old male developed allergic purpura attributed to dermal contact with an
armchair that had been treated with p-DCB crystals and in which he had sat the same
day. The symptoms appeared 24 to 48 hours later. An indirect basophil degranulation
test was positive for p-DCB. The level and duration of exposure to p-DCB were
unknown (Nalbandian and Pearce, 1965).
11.3 Repeated exposure
11.3.1 Case reports
There are a number of case reports of long-term occupational or domestic exposure to
p-DCB. In addition, several cases are known of deliberate long-term ingestion or
inhalation of p-DCB.
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para-Dichlorobenzene
In an older report, five cases of poisoning following exposure to preparations
containing p-DCB used for moth killing were described (Cotter, 1953). However, no
clear cause-effect relationship was established. The cases are as follows:
? A 36-year-old female developed symptoms of periorbital swelling, headache and
profuse rhinitis after domestic exposure to a p-DCB preparation (purity and
duration of exposure not given) for killing moths. The symptoms resolved
themselves within 24 hours without treatment.
? A 34-year-old female with a history of demonstrating p-DCB preparations (while
enclosed in a glass cabinet) for a department store reported a long period of
general malaise. After returning to work from a break, she subsequently
developed acute symptoms of headache, nausea and vomiting and showed signs
of jaundice after renewed handling of p-DCB. She was diagnosed with subacute
yellow atrophy and cirrhosis of the liver.
? A 60-year-old male domestically exposed to mothball vapour for 3 to 4 months
developed a persistent headache, weight loss and irregular bowel movements. In
addition, he suffered an unsteady gait and paresthesia of the lower extremities.
On admission to hospital he was found to have slurred speech and anaemia; the
patient subsequently died. A diagnosis of acute yellow atrophy of the liver was
made.
? The wife (age not stated) of the above male also died within a year and following
"persistent and severe" exposure to p-DCB. She was diagnosed with acute yellow
atrophy of the liver, Laennec's cirrhosis and splenomegaly.
? A 52-year-old male who had used p-DCB for two years began to suffer weakness
and nausea and became jaundiced. He was found to be anaemic and neutropenic.
A diagnosis of subacute yellow atrophy of the liver was made.
Other cases include:
? A 19-year-old female consumed 4 to 5 mothballs (composed of p-DCB, purity
unknown) daily for 2.5 years which resulted in a fixed drug eruption
characterised by symmetrical, well demarcated areas of increased skin
pigmentation ranging from 3 to 7 cm in diameter. The symptoms disappeared
within 4 months once consumption of the mothballs ceased (Frank and Cohen,
1961).
? Two cases of acute myeloblastic lymphoid leukaemia and a chronic lymphoid
leukaemia, related to the use of a cleaning fluid containing p-DCB were
described (Girard, 1969). A cause-effect relationship could not be demonstrated
due to a lack of information on the duration and level of exposure and to the
presence of other substances in the product and lack of information on exposure
to other chemicals.
? A 21-year-old pregnant female consumed 1 to 2 toilet air-freshener blocks
(predominantly p-DCB) per week throughout her pregnancy. The patient
developed hypochromic, microcytic anaemia with polychromasia and marginal
nuclear hypersegmentation of the neutrophils. Liver function and urinalysis
64 Priority Existing Chemical Number 13
findings were normal. A complete recovery was made upon removal of the
chemical from her diet. The neonate was reported to display no abnormalities
(Cambell and Davidson, 1970).
? A 68-year-old female was admitted to hospital following an epistaxis episode and
the presence of ecchymoses and petechiae. On examination, she complained of
recent tiredness, asthenia, dyspnea and palpitations on exertion, oedema of the
lower limbs and a nasal discharge. Haematological examination revealed aplastic
anaemia with a haematocrit of 22%. Prior to her admission, the woman had been
working at a clothing shop and had spent the previous three weeks in a poorly
ventilated room packing clothing. She had handled 5.5 kg of p-DCB and 7 kg
naphthalene during that time; the average outdoor temperature was 27oC (Harden
and Baetjer, 1978). The role of p-DCB in this case is not clear due to the
confounding presence of naphthalene.
? A 25-year-old female presented with symptoms of severe cerebral ataxia,
dysarthria, weakness of the limbs and hyporeflexia. A comprehensive clinical
examination produced negative results with the exception of delayed brainstem
auditory evoked potentials. The woman had been exposed to p-DCB for
approximately 6 years due to a phobia relating to ticks, which resulted in
excessive household use of mothballs including grinding the mothballs to powder
and spreading it amongst her bed clothes and clothing. The symptoms
disappeared within 6 months after her exposure to p-DCB ended (Miyai et al.,
1988).
? A 16-year-old female who regularly inhaled p-DCB vapour from a toilet bowl for
several months developed encephalopathy with bilateral reduction of visual
acuity, ataxia, behavioural disturbances, asthenia, impaired memory, apathy and
sleepiness. Haematological symptoms included anaemia. After discontinuing the
practice of inhaling p-DCB vapour the symptoms disappeared within 6 months
(Reygagne et al., 1992).
11.4 Epidemiological studies
No well-controlled epidemiological studies have been conducted. Confounding
factors in epidemiological studies of chemical exposure are concomitant exposure to
other agents and inadequate details of exposure conditions, previous or existing
medical conditions, medication or substance abuse.
Hollingsworth et al., (1956) conducted a study of 58 men employed in a plant
producing p-DCB continuously or intermittently for 8 hours/day, 5 days/week. The
average work time at the plant was 4.75 years (range 0.7 to 25 years). During an
initial survey, the average airborne p-DCB concentration was 85 ppm (range of 10 to
550 ppm). A second, later survey of the same plant found two sets of working
conditions: those uncomfortable to employees (due to irritation of the eyes and nose)
with an average concentration of 380 ppm (range 100 to 725 ppm) and tolerable
conditions with an average of 90 ppm (range 5 to 275 ppm). A third survey was
conducted after extensive plant modifications. Areas where there were continued
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para-Dichlorobenzene
complaints from employees gave average p-DCB concentrations of 105 ppm (range
50 to 170 ppm) while other areas of the plant which received no complaints recorded
an average of 45 ppm (range 15 to 85 ppm). Medical examination of the employees,
including a comprehensive haematological examination, found no evidence that
could be attributed to a p-DCB-related effect on health other than eye and nose
irritation.
Nine males with a mean age of 54.1 years (range 32 to 66 years) and a mean working
time of 24.1 years (range 13 to 35 years) in a factory using chlorobenzenes (mono-,
para- and ortho-dichlorobenzene) were identified as having chloracne based on the
presence of polymorphic dermatosis, predominately comedones and cysts. All
patients had conjunctivitis and reported gastrointestinal complaints including nausea
with occasional vomiting and as having paresthesia of the lower extremities. Five of
the workers had developed a diffuse melanotic discolouration and four developed
hyperpigmentation of the face. Liver function tests were abnormal and radiology
indicated enlargement of the liver. The symptoms described were present for at least
two years after leaving the company. Analysis of water from the work site gave 15
ppm of chloracne inducing substances. Analysis of air samples were recorded as
being inconclusive (Vazquez et al., 1996). Due to the inadequacy of the data on
exposure levels and the absence of data relating to other work related compounds or
other substances including medication, a causal relationship cannot be demonstrated.
66 Priority Existing Chemical Number 13
12. Health Hazard Assessment and
Classification
The purpose of this section is to evaluate the physicochemical data, kinetic and
metabolism studies, human and animal experimental studies (including in vivo and in
vitro data) in order to determine the potential hazard to human health that exposure to
p-DCB might entail.
Workplace substances are classified as `hazardous' to health if they meet the NOHSC
Approved Criteria for Classifying Hazardous Substances (the Approved Criteria)
[NOHSC:1008(1999a)], and `dangerous' in terms of physicochemical hazards, if they
satisfy the criteria of the Australian Code for the Transport of Dangerous Goods by
Road and Rail (ADG Code) (Federal Office of Road Safety, 1998).
The classifications for p-DCB are incorporated in the following assessment of
physicochemical and health hazards.
12.1 Physicochemical hazards
p-DCB is a white crystalline solid which undergoes sublimation (vapour pressure
1.35 hPa at 25oC) resulting in dissipation of the solid over time. The melting point is
53.5oC and the flash point (closed crucible) is 65oC. The flammability limit is 2.5%.
Classification status:
p-DCB is not classified under the ADG Code.
12.2 Kinetics, metabolism and mechanisms
Absorption of p-DCB is rapid by inhalation and the oral route in animals. Dermal
absorption is considered to be low based on acute dermal and repeated dose toxicity
studies. In animals, p-DCB is distributed to all tissues although principally in adipose
tissue, the kidneys and liver. Due to the lipophilic nature of p-DCB it is likely that the
major mechanism for the transport of this compound across cellular membranes is by
passive diffusion. The biological residence time is short with almost complete
excretion of the metabolised compound occurring in the urine by 24 to 48 hours.
Minor amounts are lost by the faeces and breath. There appears to be considerable
enterohepatic circulation of p-DCB and its metabolites in the rat.
In vitro studies indicate that p-DCB is metabolised by hepatic cytochrome P450
enzymes in animals and humans. A substantial number of metabolic studies,
including comparative studies with mice, rats and humans, have been undertaken. In
all mammal species thus far examined, the metabolism of p-DCB proceeds by
hydroxylation of the aromatic ring resulting in the formation of an intermediate
epoxide. The subsequent metabolic fate of the epoxide is species-dependent. The
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para-Dichlorobenzene
epoxide may form a conjugate with glutathione, undergo catalysis by epoxide
hydrolase to yield a dichlorophenol or dihydrodiol, or undergo secondary metabolism
to form a hydroquinone derivative. In the rat and mouse the major metabolites are
dichlorophenols, dichlorohydroquinones and glutathione-epoxide and glutathione-
quinone conjugates. Covalent binding to the tissues of the liver and kidneys in the rat
and mouse has been reported and is linked to the formation of reactive epoxides and
benzoquinones, the latter being derived from oxidation of hydroquinones.
In contrast to the rat and mouse, human metabolism of p-DCB, in vitro, results in a
non-reactive epoxide which is converted to one major metabolite, 2,5-
dichlorophenol. In humans, excreted metabolites consist predominately of 2,5-
dichlorophenol and its conjugated sulfate and glucuronide derivatives.
The metabolism of p-DCB by rat, mouse and human microsomes and proposed toxic
effects are summarised in Figure 3.
Conjugation and
Excretion in Nephrotoxicity/Carcinogenicity
Humans
Cl
in Rats
H Cl
O OH
Human
H
Mouse
& Rat Cl HO
Cl
Cl
Cl
Cl OH
2,3-epoxide
2,5-DCHQ
OH
HO
Protein binding SG
Cl
Cl
Cl Cl
2,5-DCGHQ
GSH
O
2,5-DCP
1,4-DCB Cl
O
Mouse H O
& Rat
Cl
2,5-DCBQ Covalent Binding
Hepatotoxicity/Carcinogenicity
Cl in Mice
OH O
Cl Cl
1,2-epoxide
2-CBQ
Cl O
2,4-DCP OH O
HO O
Cl Cl
Cl Cl
3,5-DCBQ
3,5-DCC
Figure 3 - Metabolism of 1,4-dichlorobenzene (p-DCB) by rat, mouse and human hepatic
microsomes. Pathways for the formation of bioactive metabolites in rats, mice and humans
are shown. CBQ, chlorobenzoquinone; DCB, dichlorobenzene; DCBQ,
dichlorobenzoquinone; DCC, dichlorocatechol; DCGHQ, dichlorogluthionyl-hydroquinone;
DCHQ, dichlorohydroquinone; DCP, dichlorophenol; DCBQ, dichloro-1,2-benzoquinone;
GSH, reduced glutathione; SG, glutathione-S-yl-metabolite (After Den Besten et al., 1992;
Klos and Dekant, 1994 and Hissink et al., 1997).
68 Priority Existing Chemical Number 13
12.3 Health hazards
12.3.1 Acute effects
Animal studies with rats and mice have shown p-DCB to induce reversible, acute
nephrotoxic and hepatotoxic effects. In acute studies the oral LD50 for the rat was in
the range 3790 to 3863 mg/kg bw. The LD50 for the rat due to dermal exposure was
>6000 mg/kg bw. The LC50 in rats by inhalation is given as >5.07 mg/L/4 hours (845
ppm).
Only one case report of acute toxicity has been described involving a 3-year old male
who ingested an unknown quantity of p-DCB, which resulted in haemolytic anaemia
with methemoglobinuria and jaundice.
Classification status:
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for acute lethal effects
by oral, inhalation or dermal exposure.
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for non-lethal
(irreversible) effects after a single exposure.
12.3.2 Irritant effects
Skin irritation
Few data are available from animal studies addressing the irritant potential of p-DCB.
Hollingsworth et al. (1956) reported that solid p-DCB has a negligible irritating
action on intact uncovered human skin but can produce a burning sensation if held in
close contact for an excessive period. Maertins (1988, unpublished) indicated that p-
DCB was slightly irritating to rabbit skin producing erythema but no oedema. A case
study of a woman exposed to p-DCB crystals and powder for approximately 6 years
as a result of a neurosis showed no sign of skin irritation. Despite the widespread use
of p-DCB over many years there are no convincing reports of skin irritation effects in
the literature.
Classification status:
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for skin irritation.
Although p-DCB does not meet the criteria for classification as a skin irritant, due to
concerns that prolonged exposure may produce irritation, the notation `Avoid contact
with skin (S24)' should be retained.
Eye irritation
Hollingsworth (1956) reported that occupational exposure to p-DCB vapour (above
50 ppm; 300 mg/m3) led to increased complaints of eye irritation which was
described as painful at concentrations greater than 80 ppm (481mg/m3). It was further
reported that rabbits, rats and guinea pigs experienced eye irritation when exposed to
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para-Dichlorobenzene
p-DCB vapour at 798 ppm. In a case study, a woman was reported to develop
periorbital oedema after domestic use of p-DCB (Cotter, 1953).
Maertins (1988, unpublished) reported that rabbits (3 only) appeared to experience
only slight ocular irritation, characterised by slight erythema and oedema of the
conjunctivae which was reversible by the third day.
The Hollingsworth (1956) study is insufficiently detailed with respect to the nature of
the eye irritation for purposes of classification. Similarly, the only animal study is
inadequate for the purpose of classification.
Classification status:
Insufficient data exists to classify p-DCB for eye irritation (R36). However, based on
limited human data, sufficient evidence exists for precaution to be exercised in the
use of p-DCB under industrial conditions and for which the following safety phrases
are recommended: Avoid contact with eyes (S25) and Use only in well ventilated
areas (S51).
Respiratory irritation
Hollingsworth (1956) reported that occupational exposure to p-DCB vapour (above
50 ppm; 300 mg/m3) has been reported to cause irritation to the nose and upper
respiratory tract. Irritation to the nose was reported as painful at concentrations of 80
to 160 ppm (481 to 962 mg/m3) while higher concentrations were irrespirable. The
development of profuse rhinitis after p-DCB exposure was reported in one case study
although the level of exposure was not known (Cotter, 1953). Another case study
reported a woman experiencing an epistaxis episode and dyspnea due to persistent
exposure to p-DCB, however, the presence of naphthalene was a confounding factor
(Harden and Baetjer, 1978).
The effects of p-DCB exposure on animals during a 2-year inhalation study included
histopathological changes to the olfactory epithelium (eosinophilic changes) in male
rats at 300 ppm (1803 mg/m3) and female rats at 75 ppm (451 mg/m3) and 300 ppm
(1803 mg/m3). Female rats were also observed to develop eosinophilic changes to the
respiratory epithelium and metaplasia of the nasal cavity gland at 300 ppm (1803
mg/m3). Under identical conditions, mice did not develop any upper respiratory tract
lesions (JBRC, 1995). In a study of 16 days duration at an exposure level of 173 ppm
(1040mg/m3) with rats, guinea pigs and rabbits, slight pulmonary interstitial oedema
and congestion were observed in all male rats and female guinea pigs and rabbits
with alveolar haemorrhage and oedema observed in some animals (Hollingsworth et
al., 1956).
The case reports (Cotter, 1953) are insufficiently detailed for purposes of
classification as the vapour concentrations were not available and potential
confounding factors, such as allergy or co-existing infections, were not discussed.
Other cases of p-DCB exposure reported by Cotter (1953) and others do not include
adverse respiratory symptoms. Similarly, the Hollingsworth (1956) study is
considered inadequate as the use of other chemicals was not described nor were co-
existing medical conditions of the workers. The animal studies do not provide
70 Priority Existing Chemical Number 13
sufficient evidence for upper respiratory tract irritation. While female rats developed
marked changes to the olfactory epithelium at 75 ppm (451 mg/m3) the control
animals displayed a high incidence (98%) of slight to moderate olfactory lesions.
Such lesions were not observed in mice.
Classification status:
Insufficient data exists to classify p-DCB for irritation to the respiratory system
(R37). However, based on limited human data, sufficient evidence exists for
precaution to be exercised in the use of p-DCB under industrial conditions and for
which the following safety phrases are recommended: Do not breath vapour (S23)
and Use only in well ventilated areas (S51).
12.3.3 Sensitisation
Few studies have been conducted addressing the issue of sensitisation as a result of
exposure to p-DCB. A case of acute petechial purpura attributed to p-DCB has been
reported although insufficient details were provided by the study to establish a causal
relationship (Nalbandian and Pearce, 1965). Extensive industrial experience with p-
DCB has not resulted in reports of sensitisation.
A study of guinea pigs indicated that exposure by dermal contact causes weak
sensitisation (Bornatowicz et al., 1995, cited in SIAR 1999).
Classification status:
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for sensitising effects
(skin or inhalation).
12.3.4 Severe effects (non-carcinogenic) after repeated or prolonged exposure
Cases involving prolonged human exposure to p-DCB have indicated the
development of neurological symptoms all of which appear to be reversible following
cessation of exposure. Haematological disorders have also been noted, particularly
anaemia. There have been two deaths (related individuals) attributed to p-DCB
exposure, however, other factors which may have contributed to mortality were not
discussed in the case report. Adverse liver effects have been noted in some case
studies. In all case reports of repeated exposure the cause-effect relationship with
respect to p-DCB has not been clearly established. Repeated ingestion of p-DCB or
inhalation of its vapour, due to intentional misuse, may result in drowsiness,
incoordination and anaemia.
Several repeated dose studies, of up to 2 years duration, via inhalation and oral routes
have been conducted in mice and rats. A 1-year oral study in dogs has also been
conducted. Only 1 dermal study, of 3 weeks duration, has been reported.
Prolonged exposure of animals to p-DCB results in neurological disturbances
including tremor, unsteady gait and an unkempt appearance. Severe effects include
increases in liver and kidney weights and the development of hepatic lesions, an
increase in hepatocellular proliferation in rats and mice and death at high doses. The
71
para-Dichlorobenzene
most relevant studies are the 2-year inhalation and oral studies in mice and rats and
the NOAELs and critical effects are described below.
A NOAEL in male rats by the oral route was not identified and for females was 300
mg/kg. A LOAEL was 75 mg/kg bw for male rats for nephropathy and 600 mg/kg bw
for females for nephropathy and increased liver weights (NTP, 1987; Bomhard, 1998;
Eldridge et al., 1992).
A NOAEL by inhalation for the rat (both sexes) was 75 ppm (451 mg/m3 or 0.451
mg/L) and a LOAEL of 300 ppm (1803 mg/m3 or 1.803 mg/L) identified for
nephropathy in males and hepatotoxicity in both sexes.
In the mouse, by the oral route, a NOAEL was not identified and a LOAEL of 300
mg/kg bw for both sexes was determined based on hepatocellular degeneration and
increased kidney weight. By inhalation, a NOAEL of 75 ppm (451 mg/m3 or 0.451
mg/L) was determined for both sexes of mice and a LOAEL of 300 ppm for
hepatotoxicity and increased kidney weights.
For dogs exposed to p-DCB by the oral route a NOAEL of 10 mg/kg bw was
determined and a LOAEL of 50 mg/kg bw for hepatic toxicity and increased kidney
weights with some epithelial cell degeneration.
Classification status:
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for severe effects after
repeated/prolonged exposure.
12.3.5 Reproductive effects
There have been no reports of reproductive effects in humans described in the
literature. A neonate delivered to a woman who regularly ate toilet air-freshener
blocks composed of p-DCB throughout her pregnancy showed no developmental
problems or other adverse effects.
The effects of p-DCB on reproductive and developmental toxicity have been studied
in rats and rabbits. In oral and inhalation 2-generation reproductive studies no fertility
effects were observed at or below exposure levels which did not induce maternal
toxicity. Slight developmental effects (reversible reduced mean body weight at birth
in F0/F1 pups, increased number of deceased pups in 1 time period in 1 generation
and slight behavioural anomalies in 1 generation) were observed in rats in a 2-
generation oral reproductive study. The effects were observed at 90 mg/kg bw per
day. These slight developmental effects occurred at doses where no parental toxicity
was evident (NOAEL maternal toxicity was 90 mg/kg bw per day). However, similar
effects were not observed in a 2-generation inhalation study or in two well-conducted
developmental studies (oral and inhalation).
Classification status:
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for reproductive
effects.
72 Priority Existing Chemical Number 13
12.3.6 Genotoxicity
Several test systems including the Ames test (with or without metabolic activation),
gene mutation, chromosomal aberration and DNA effect assays have given negative
results for p-DCB.
In vitro, unscheduled DNA synthesis tests with human lymphocytes have given
negative results while a mouse lymphoma forward mutation assay proved to be
inconclusive. Positive results have been obtained for human lymphocytes showing an
increase in the sister-chromatid exchange rate.
Under in vivo conditions using several test methods, including dominant lethal,
micronucleus and unscheduled DNA synthesis assays, p-DCB was found to give
negative genotoxic responses. Using the alkaline Comet assay, damage to DNA
occurred in the liver and spleen, but not other tissues tested, of male mice exposed to
p-DCB while a sex-linked recessive lethal test with Drosophila produced negative
results.
Classification status:
From the results of in vitro and in vivo studies, p-DCB does not meet the Approved
Criteria (NOHSC, 1999a) for mutagenic effects.
12.3.7 Carcinogenicity
Investigations of the carcinogenic potential of p-DCB are limited to two well-
conducted 2-year studies in rats and mice, the US NTP (1987) oral study and the
JBRC (1995) inhalation study. An older inhalation study with a duration of 76 weeks
for rats and 56 weeks for mice was also conducted (Loeser and Litchfield, 1983),
however, this study is of limited value due to its short duration.
The effects of oral exposure to p-DCB over 2 years were characterised by the
development of renal tumours in male rats (LOAEL 150 mg/kg bw per day) and
hepatic tumours in both sexes of mice (LOAEL 600 mg/kg bw per day; NOAEL 300
mg/kg bw per day). The inhalation studies showed no evidence of treatment-related
neoplasia in rats of either gender while both sexes of mice developed hepatic tumours
(LOAEL 300 ppm) in the 2-year study.
Available evidence from in vitro and in vivo genotoxicity testing indicate that p-DCB
itself does not appear to induce DNA alterations and, consequently, separate
epigenetic mechanisms have been proposed to account for the observed sex- and
species-dependent renal and hepatic tumours.
Renal carcinogenesis
Exposure of mature male rats to oral doses of p-DCB results in the development of
nephrotoxicity and ultimately renal tumour formation (adenocarcinoma). Extensive
investigations of the mechanisms involved in renal carcinogenesis have revealed two
apparently separate pathologies; a proximal tubular necrosis due to hyaline droplet
formation and a second nephropathy associated with reactive metabolites of p-DCB.
73
para-Dichlorobenzene
Role of 2?Globulin in renal carcinogenesis
Several studies in which p-DCB was administered orally to rats resulted in a male-
specific pathology characterised by the formation of hyaline droplets in proximal
tubule epithelial cells (NTP, 1987; Bomhard, 1989). Early studies of the effects of p-
DCB on male rat kidneys considered the development of hyaline droplet nephropathy
to be the prelude to the formation of kidney tumours. It has been proposed that p-
DCB forms a reversible complex with the male rat-specific protein, 2?globulin. In
untreated rats, 2?globulin is catabolised by lysosomal proteases thus preventing its
accumulation. In p-DCB-treated rats the modified protein appears to be resistant to
degradation and accumulates as a precipitate within phagolysosomes of the proximal
convoluted tubule epithelial cells thus producing the hyaline droplet pathology
(Charbonneau et al., 1989). Subsequent studies, in vitro, have demonstrated that the
p-DCB metabolite, 2,5-dichlorophenol, is responsible for inhibiting the degradation
of 2?globulin and not the parent compound (Lehman-McKeeman et al., 1990). The
role of modified 2?globulin in hyaline droplet nephropathy is supported by the
observation that immature male rats, which do not produce significant amounts of
2?globulin, do not develop renal lesions when exposed to chemicals which induce
hyaline droplet formation. Similarly, old male rats which are deficient in the protein
failed to develop renal lesions in response to chemical induction (reviewed in
Melnick, 1992; Hard et al., 1993).
The presence of p-DCB-induced intracellular hyaline droplets ultimately induce cell
death and a proliferative response in adjacent cells which subsequently leads to the
development of a low incidence of renal tubular cell tumours in male rats
(Charbonneau et al., 1989). Further studies of cell proliferation in response to p-DCB
exposure have been undertaken in male and female rats and mice using
immunohistochemical techniques. Increased cell proliferation was observed in the
proximal convoluted tubules and to a lesser extent the proximal straight tubules but
not distal tubules of treated male rats. Female rats or mice of either sex did not
exhibit increased cell proliferation of the renal tubules (Umemura et al., 1992).
However, in a 2-year oral study by Dominick et al. (1991), it was demonstrated that a
direct cause-and-effect relationship between chemically induced 2?globulin-
dependent hyaline droplet formation and renal carcinogenesis could not be
established. In support of this, exposure of male rats to p-DCB by inhalation for 76
weeks did not result in renal carcinogenesis (Loeser and Litchfield, 1983) despite
several studies demonstrating the presence of hyaline droplets after short term p-DCB
exposure (Bomhard et al., 1988; Charbonneau et al., 1989; Den Besten et al., 1991).
It has been suggested that the failure of male rats to develop renal tumours during the
inhalation studies was due to differences in tissue concentrations of p-DCB as they
were not comparable to concentrations achieved by oral administration of the
compound (Barter et al., 1999). Thus a threshold effect may be required for the
development of p-DCB-induced renal carcinogenesis in male rats.
The relevance of 2?globulin-dependent hyaline droplet formation as a potential
cause of human carcinogenesis has been extensively examined. Synthesis of 2?
globulin occurs only in the liver of the mature male rat under hormonal, particularly
androgenic, control. The protein is filtered from the blood by the kidneys with
74 Priority Existing Chemical Number 13
approximately 60% being resorbed and the remainder excreted in the urine. The
physiological function of 2?globulin in the rat remains speculative although it has
been postulated that the protein may function as a carrier for lipophilic ligands,
possibly pheromones. The 2?globulin protein has been sequenced and belongs to a
superfamily of low molecular weight proteins, the lipocalin family. With the
exception of the mouse major urinary proteins, the sequence homology of 2?
globulin with other members of the superfamily is low and in vitro studies have
shown that their affinities for various ligands appear to be unrelated (Cavaggioni et
al., 1990). It has been proposed that 2?globulin can transport p-DCB (or its
metabolites) to the kidneys where reactive metabolites form due to renal metabolism
with the consequent development of nephrotoxicity and carcinogenesis in addition to
hyaline droplet formation (Melnick, 1992). Support for this hypothesis has been
provided by Charbonneau et al. (1989) who have shown that, after adipose tissue, the
male rat kidney accumulated the highest amount of radiolabel after oral dosing with
p-DCB. It was further shown that male rat kidneys acquire more radiolabel that
female kidneys (Umemura, 1990).
The mechanism of 2?globulin-mediated nephropathy and carcinogenesis has been
generally adopted by the scientific community as not predictive of carcinogenic risk
in humans and in particular for p-DCB (Rice et al., 1999).
Metabolite-induced nephropathy
A second renal pathology is associated with reactive metabolites of p-DCB. In the rat
liver, p-DCB is metabolised to a number of compounds including 2,5-dichloro-1,4-
benzoquinone, that can react with glutathione to give 2,5-dichloro-3-(glutathion-S-
yl)-1,4-benzoquinone (DCGBQ). The administration of DCGBQ to male rats by i.v.
injection resulted in the development of a dose-dependent renal proximal tubular
necrosis. Histopathological examination of the kidneys demonstrated extensive single
cell necrosis (with pyknotic nuclei) of the proximal tubules, however, there was no
evidence of hyaline droplet formation. Co-administration of ascorbic acid to reduce
the DCGBQ to the corresponding hydroquinone enhanced the nephrotoxic effect.
These findings suggest that DCGBQ and its parent hydroquinone derived from the
hepatic metabolism of p-DCB can contribute to the early onset of nephrotoxicity in
the rat (Mertens et al., 1991). In p-DCB-treated rats this condition is likely to be
independent of, although concurrent with, the above-described hyaline droplet
nephropathy and supports the hypothesis of Melnick (1992). At present, it is not
known if DCGBQ binds to 2?globulin and, if so, the extent of renal accumulation
of the compound. Similarly, the relationship between DCGBQ-induced nephropathy
and renal carcinogenesis is uncertain. However, this mechanism is considered not to
be relevant to humans as the metabolites involved are not produced to the same
extent during human metabolism of p-DCB.
Hepatocarcinogenesis
Exposure of rats and mice to p-DCB resulted in the development of hepatotoxicity in
both species and hepatocarcinogenicity in mice. Rats exhibited a reversible increase
in liver weight but no increase in serum levels of hepatic enzymes while histological
findings revealed mild centrilobular hypertrophy. Mice, when exposed to p-DCB by
75
para-Dichlorobenzene
the oral route, exhibited non-neoplastic hepatic lesions characterised by cytomegaly,
karyomegaly, hepatocellular degeneration and individual cell necrosis (NTP 1987)
while exposure via the inhalation route resulted in centrilobular hepatocellular
hypertrophy in high-dose males (JBRC 1995). Neoplastic lesions consisted of
hepatocellular adenoma and carcinoma and a limited number of rare
hepatoblastomas. Of significance was the high spontaneous incidence of
hepatocellular adenoma and carcinoma in control mice and in historical control
animals for the two testing laboratories suggesting the presence of pre-neoplastic cell
populations in the animals involved. The experimental data for the NTP testing
laboratory (NTP, 1987) were: male controls (adenoma, 15.0%; carcinoma, 37.5%;
combined adenoma and carcinoma, 43.4%) and female controls (adenoma, 27.4%;
carcinoma, 13.2%; combined adenoma and carcinoma, 39.0%). The experimental
data for the JBRC testing laboratory (JBRC, 1995) were: male controls (adenoma
28.9%; carcinoma, 25.6%; combined adenoma and carcinoma, 43.6%) and female
controls (adenoma, 4.8%; carcinoma, 7.1%; combined adenoma and
carcinoma,10.7%). The B6C3F1 mouse is considered to be a sensitive strain based on
its tumour response to chemical testing (Tennant et al., 1986; Gold et al., 1989). Less
data are available for the Crj:BDF1 mouse, however, as this strain is genetically
similar to the B6C3F1 mouse, in that they share the same maternal lineage, it is
expected that a similar sensitivity towards chemicals would be observed.
A number of studies have failed to demonstrate, either in vitro or in vivo, a genotoxic
mechanism by which p-DCB could induce a carcinogenic response, consequently,
alternative mechanisms must be evaluated. It has been shown, by several in vivo
studies, that p-DCB is an inducer of hepatocellular proliferation and that the response
is mitogenic in nature. Eldridge et al., (1992) observed that p-DCB produced a
mitogenic response in rats and mice characterised by an increase in hepatocellular
proliferation and which occurred in the absence of hepatocellular necrosis. Other
studies have concluded that p-DCB-induced cell proliferation is not sufficient to
induce hepatic carcinogenesis as rats showed increased hepatocellular proliferation
without developing tumours in long-term studies and that the cumulative replicative
fraction of rat hepatocytes is significantly greater than that of mouse hepatocytes
(Umemura et al., 1992). These data suggest that, in order to maintain hepatic
homeostasis, a higher rate of hepatocyte apoptosis would be required in the rat. James
et al. (1998) have confirmed that the basal apoptotic rate of rat hepatocytes is
substantially higher than that of their murine counterparts. It was further
demonstrated that p-DCB suppresses the apoptotic response in both species, in vitro
and in vivo. The proliferative response in the rat liver was shown to be proceeded by
the expression of the immediate-early genes c-fos, c-jun and c-myc and the
localisation of c-Myc protein with areas of proliferation was demonstrated (Hasmall
et al., 1997). The products of these proto-oncogenes (c-Fos and c-Jun) form a
heterodimer, activator protein-1 (AP-1), which recognises a DNA specific sequence
motif, the AP-1 binding site. AP-1-induced gene transcription is associated with
increased cell proliferation (Chiu et al., 1988). Umemura et al. (1998) established a
threshold effect for p-DCB-induced cell proliferation (75 mg/kg bw for rats and 150
mg/kg bw for mice) below which a proliferative response was not observed. It was
further demonstrated that, above the threshold dose, the proliferative response in the
rat liver was transient whereas the response in the mouse liver, while attenuated, was
76 Priority Existing Chemical Number 13
prolonged. A prolonged response is considered to be predictive of carcinogenesis
(Melnick and Huff 1993). However, the lack of concordance in the responses
between species and between doses of p-DCB which induce cell proliferation and
carcinogenesis suggest that additional factors are involved in the development of
hepatic tumours in mice.
Several lines of evidence indicate that the differences in species-related
hepatotoxicity of p-DCB would appear to be due to differences in the metabolism of
the compound by hepatic cytochromes P450. Lake et al. (1997) observed, in vivo, a
marked induction of CYP2B1/2 in both the rat and the mouse in response to p-DCB
exposure. CYP2E1 is also involved in the metabolism of p-DCB and results in the
formation of the 2,3-epoxide whereas metabolism by CYP2B1/2 produces the 1,2-
epoxide. Subsequent metabolism of the 1,2-epoxide results in the formation of mono-
and dichlorohydroquinones (Klos and Dekant 1994). Studies with human cell lines
transfected with cDNA expressing specific cytochrome P450 isoforms revealed that
only CYP2E1 participated in the metabolism of p-DCB (Hissink et al., 1997b).
Hissink et al. (1997b) demonstrated the existence of substantial interspecies
differences between mice, rats and humans with respect to the hepatic microsomal
metabolism of p-DCB. The rank order for hepatic microsomal metabolism was
determined to be (as a percentage of total conversion): mice (16%) >> rats (0.6% to
1.3%) > humans (0.3%). Covalent binding of p-DCB metabolites to microsomal
protein was demonstrated to have the following rank order (as a percentage of total
conversion): mice (21%) > rats (10%) > humans (6%). In all cases, the addition of
ascorbic acid reduced microsomal covalent binding indicating that benzoquinone
species, derived from hydroquinones, rather than epoxides are primarily involved.
For mice, the ascorbate-dependent reduction was 92% compared to 25% for humans
from which it may be concluded that quinone/protein binding is not extensive for
human microsomes. Addition of glutathione to microsomal preparations and analysis
for glutathione-epoxide conjugates resulted in undetectable levels from mouse
preparations, a 6% increase from human preparations and a significant increase
(range 40 to 52%) for all rat strains.
It has been established that the metabolism of p-DCB in mice proceeds by the action
of CYP2E1 and CYP2B1/2 with substantial hydroquinone formation whereas with
humans, metabolism proceeds by the action of CYP2E1 only with relatively minor
amounts of hydroquinones produced. As humans do not express CYP2B1/2, the 1,2-
epoxide and subsequent hydroquinones are not produced in the human liver. Total
hydroquinone formation (as a percentage of total hepatic microsomal metabolites and
in the presence of ascorbate as reductant) was 8.86% for mice while rat and human
microsomal metabolism resulted in a maximum conversion of 0.4% and 0.08%
respectively.
A number of studies have provided evidence implicating redox cycling of
hydroquinone species, derived from p-DCB, in murine hepatocarcinogenesis.
Lattanzi et al. (1989) demonstrated, in vivo, the binding of radiolabeled metabolites
of p-DCB to the DNA of mouse liver but found no evidence for binding to rat liver
DNA. Sasaki et al. (1997) also showed, in vivo, lesions to DNA derived from the
liver and spleen of mice treated with p-DCB but no damage to the DNA of other
77
para-Dichlorobenzene
organs. Under in vitro conditions, 2,5-dichlorohydroquinone (2,5-DCHQ) induced
single and double strand breaks in DNA and DNA base alterations including the
formation 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) when incubated with
native DNA. The effect was enhanced when 2,5-DCHQ was able to redox cycle in
the presence of the intracellular reductant, nicotinamide adenine dinucleotide
(NADH) (Oikawa and Kawanishi, 1996). Inhibitor studies revealed a direct role for
reactive oxygen species (superoxide and hydrogen peroxide) in 2,5-DCHQ-mediated
DNA damage. The formation of DNA lesions were completely prevented when
catalase, a scavenger of hydrogen peroxide, was present. The hydrogen peroxide
arises by dismutation of superoxide which is produced by the autoxidation of
hydroquinone species. Oxidative modification of DNA bases, particularly the 8-
oxodG base alteration, has been shown to result in DNA misreplication (Shibutani, et
al., 1991) and has been implicated in mutations leading to cancer formation (Floyd
1990). It is recognised that hydroquinone species and hydrogen peroxide can act as
tumour promoters. Tumour promotion can arise from the ability of these substances
to alter intracellular redox status, mediate immediate-early gene expression, disrupt
intercellular gap junction communication and promote cell proliferation
(Gopalakrishna et al., 1994; Joseph et al., 1998; Huang et al., 1999).
While the modulation of cellular function by hydroquinone species provides a
plausible mechanism for the increased numbers of hepatic tumours observed in long
term carcinogenicity studies of mice after exposure to p-DCB, the mechanism, at
present, is not generally accepted by the scientific community.
Classification
As the rat renal tumours are not considered relevant to humans the only evidence for
carcinogenicity is the occurrence of liver tumours in mice.
The Approved Criteria (NOHSC, 1999a) for classifying carcinogenic effects are
provided in full in Appendix 2.
It is clear from the available data that p-DCB does not fall into either Category 1 or 2
of the criteria. In considering whether p-DCB should be classified in Category 3 or
`no classification' based on increased liver tumour formation in mice, the following
were taken into consideration:
? there was no evidence of liver tumours of any type from the rat studies;
? increases in hepatic adenoma and carcinoma formation in male and female mice
occurred only at doses above or close to the maximum tolerated dose;
? there was no evidence for a genotoxic mechanism;
? the strains of mice used (B6C3F1 and Crj:BDF1) exhibited a high spontaneous
incidence of hepatocellular adenoma and carcinoma;
? the B6C3F1 and Crj:BDF1 mice are considered to be a sensitive strains based on
their tumour responses to chemical testing; and
? there are substantial differences in the hepatic metabolism of p-DCB by mice in
comparison to rats and humans.
78 Priority Existing Chemical Number 13
Classification status:
p-DCB does not meet the Approved Criteria (NOHSC, 1999a) for carcinogenicity.
Review of carcinogenicity by other countries/agencies
The renal tumours induced by p-DCB in male rats are considered by IARC not to be
predictive of a human carcinogenic hazard due to the role of 2?globulin in the
formation of these tumour. However, on the bases of the mouse liver tumours, for
which a satisfactory mechanism of tumour formation is considered lacking, IARC
has classified p-DCB as Group 2B: possibly carcinogenic to humans on the basis of
IARC criteria (Rice et al., 1999).
The SIAR (1999) concluded that the available data do not justify the classification of
p-DCB as a carcinogen (Category 3) on the assumption that the liver tumours were
probably not relevant to humans and that they were likely to occur as a consequence
of chronic liver damage, despite the hypothesis not being clearly demonstrated.
Based on the conclusions of the SIAR, France recommended to the European
Commission Working Group on the Classification and Labelling of Dangerous
Substances (October, 1998) that classification of p-DCB as a carcinogen was not
warranted. This was on the basis that the rat kidney and mouse liver tumours induced
by p-DCB were species-specific and the mechanisms not relevant for humans.
Agreement was reached by the Working Group in 1998 that the p-DCB-related
carcinogenic events in animals were not relevant to humans. The Australian
classification criteria are the same as those used by the European Union.
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para-Dichlorobenzene
13. Environmental Effects
No ecotoxicity tests were provided by applicants. In the following tables, results have
been taken from the SIAR (1999). Additional studies not included in that report have
been taken from the IUCLID datasheet although these results can not be assumed to
be valid.
No QSAR results are reported here due to the large amount of experimental results
available. Comments relating to tests are provided from the SIAR report (1999)
where available.
13.1 Aquatic toxicity
13.1.1 Toxicity to fish
Based on the scale of Mensink (1995) p-DCB can be considered slightly to
moderately toxic to fish when tested acutely, and when subject to chronic exposure,
the chemical can be classed as slightly toxic to fish. The acute and chronic data are
summarised in Table 13.
No observations regarding sublethal effects are made about the acute tests in either
the SIAR (1999) or BUA (1994) reports. They followed OECD, American Standard
Test Method (ASTM) or US EPA guidelines. Early life stage (ELS) testing on P.
promelas followed a flow-through methodology and was conducted during
development from egg to larvae. Each test was initiated by placing 30 embryos, 4 to
12 hours old, into the aquarium with the percentage of normal larvae hatching and
surviving (abnormal developing fish included) used as endpoints.
ELS testing on J. floridae was similar to that for fathead minnow. Water samples
were analysed 5 days per week during 28 day exposure. Two age groups were used
simultaneously: eggs/embryo/larval fish with data collected on hatching success 4 to
6 days after exposure and 10 day larval survival; and one week old fry with data
generated on survival and growth over 28 days. No influence was demonstrated on
hatching rate while significant effects with respect to survival of larvae up to 10 days
of age in two parallel tests were observed at 0.31 and 0.32 mg/L.
ELS testing on rainbow trout appeared to be conducted with 1000 eggs and 25
embryos per test concentration. No morphological and histological effects at any
tested concentration were observed. A cumulative mortality of 30% for all the
treatments as well as the controls is reported.
80 Priority Existing Chemical Number 13
Table 13 - Acute and chronic toxicity of p-DCB to Fish
Species Test Duration Result (mg/L) Reference
Acute
Brachydanio rerio (zebra fish) 96 hours LC50 = 2.1 SIAR, 1999
Pimephales promelas SIAR, 1999
96 hours LC50 = 3.6 (larvae)
(fathead minnow) LC50 = 14.2 (juveniles)
LC50 = 11.7 (subadults)
Pimephales promelas 96 hours LC50 = 4.2 SIAR, 1999
Jordanella floridae 96 hours LC50 = 4.5 (semi static) SIAR, 1999
(American flagfish) LC50 = 2.1 (flow through)
Oncorhynchus mykiss 96 hours LC50 = 1.12 SIAR, 1999
(Rainbow trout)
Cyprinodon variegatus 96 hours LC50 = 7.4 SIAR, 1999
(Sheepshead minnow) NOEC = 5.6
Lepomis macrochirus 96 hours LC50 = 4.28 IUCLID
Chronic
Brachydanio rerio 14 days NOEC = 0.44 SIAR, 1999
LOEC = 0.7
Poecilia reticulata 14 days LC50 = 4 IUCLID
Pimephales promelas 28 days NOEC = 0.57 SIAR, 1999
(early life stage) LOEC = 1
Jordanella floridae 14 days NOEC = 0.2 SIAR, 1999
(early life stage) 28 days NOEC = 0.35
Oncorhynchyus mykiss 60 days NOEC = 0.12 SIAR, 1999
(early life stage)
13.1.2 Toxicity to aquatic invertebrates
Using the scale described in Mensink (1995), p-DCB can be said to be moderately to
highly toxic to aquatic invertebrates under acute exposure, and slightly toxic under
chronic exposure. Toxicity data for representative aquatic invertebrates are given in
Table 14.
Table 14 - Toxicity of p-DCB to aquatic invertebrates
Species Test Duration Result (mg/L) Reference
Acute
Daphnia magna 24 hours EC50 = 1.6 SIAR, 1999
EC50 = 3.2
48 hours LC50 = 2.2 SIAR, 1999
EC50 = 0.7
Mysidopsis bahia 96 hours EC50 = 1.99 IUCLID
Tanytarsis dissimilis (midge) 48 hours EC50 = 13 IUCLID
Chronic
Daphnia magna 21 days NOEC = 0.4 SIAR, 1999
28 days NOEC = 0.22 SIAR, 1999
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para-Dichlorobenzene
No observations are made regarding sublethal effects for the acute tests in either the
SIAR (1999) or BUA (1994) reports. The 21 day chronic Daphnia test used the most
sensitive parameter stated as the time of the first birth. Animals were transferred
every second day to new, closed test bottles and the test concentration was observed
to decrease from 0.5 to 0.3 mg/L before renewal. No observed effects were noticed,
and the mean nominal concentration of 0.4 mg/L was used as a NOEC. The 28 day
fertility tests used 25 new born animals exposed to different concentrations for 28
days. Toxic and alimentation solutions were changed daily and at the same time the
number of dead and new-born animals were observed. Concentration loss never
exceeded 15% of the initial concentration.
In addition to these tests, Mortimer and Connell (1995) investigated the effects of p-
DCB on the crab Portunus pelagicus (L). Juvenile crabs were exposed to aqueous
concentrations, and the end point was growth rate. Concentrations tested were 31, 62,
125 and 250 ppb. The result is expressed as a 96 hour LC50 of 1.37 祄ol/L which has
been equated to 201 礸/L making this species the most sensitive aquatic invertebrate
tested both acutely and chronically.
13.1.3 Toxicity to aquatic plants
Using the scale described in Mensink (1995), p-DCB can be said to be toxic to
slightly toxic to algae and aquatic plants. No observations from the tests are
available. The data for aquatic plant toxicity tests are presented in Table 15.
Table 15 - Toxicity of p-DCB to aquatic plants
Species Test Result (mg/L) Reference
Duration
Wong et al.,
Ankistrodesmus falcatus 4 hours EC50 = 20 (photosynthesis)
(algae) 1984
Scenedesmus pannonicus SIAR, 1999
72 hours E礐50 = 31
Scenedesmus subspicatus 48 hours SIAR, 1999
EC50 = 28
E礐50 = 38
Selenastrum capricornutum SIAR, 1999
96 hours E礐50 = 1.6
Cyclotella meneghiniana SIAR, 1999
48 hours E礐50 = 34.3
Selenastrum capricornutum 3 hours EC50 = 5.2 (photosynthesis) IUCLID
EC50 is based on inhibition of reproduction. E礐50 is based on inhibition of growth rate.
13.1.4 Toxicity to micro-organisms
p-DCB can be described as slightly to practically non-toxic to micro-organisms
(Table 16). Specifically, sewage sludge and methanogenic sewage sludge only
showed slight to practically no toxic effects when exposed to the chemical. No
observations from the tests are available.
82 Priority Existing Chemical Number 13
Table 16 - Toxicity of p-DCB to micro-organisms
Species Test Duration Result (mg/L) Reference
Nitrosomonas sp (Bacteria) 12 hours IC50 = 86 SIAR, 1999
Photobacterium phosphorem 5 minutes IC50 = 4.3 IUCLID
(Bacteria)
IC50 = 330 SIAR, 1999
Active sludge 12 hours
IC50 = 86 SIAR, 1999
Methanogenic sewage sludge 48 hours
13.1.5 Predicted no effect concentration for the aquatic environment
There are a significant number of experimental test results for this chemical to the
aquatic compartment, covering all trophic levels. A number of chronic results are
available for both fish and aquatic invertebrates.
The predicted no effect concentration (PNEC) can therefore be determined by taking
the lowest chronic value (14-day NOEC for J. floridae = 0.2 ppm), and using an
assessment factor of 10 to reflect the large amount of data. The outcome would be the
same if the most sensitive acute effect (96h LC50 = 200 礸/L for P. pelagicus (L)) is
used.
The resulting PNEC is 20 礸/L (ppb) in water.
13.2 Terrestrial toxicity
The SIAR (1999) has provided toxicity results for two worm species, Eisenia andrei
and Lumbricus rubellus. In both tests, at least five concentrations and a control were
used with 20 adults per test concentration. The tests were carried out in an open static
system in two soils, one a natural sand soil (KOBG) and the other an artificial soil
(OECD). The characteristics of the soils are presented in Table 17.
Table 17 - Characteristics of soil types
1
Soil type pH % OM % sand % silt % clay
KOBG 4.8 3.7 86.5 1.4 7.5
OECD 5.9 8.1 72.1 8.1 7.4
1
OM = organic matter
The p-DCB was first combined with a small amount of dry soil, and this mixture was
combined with the remaining soil. With mortality as an endpoint the LC50 for E.
andrei and L. rubellus was 128 (KOBG soil) to 229 (OECD soil) and 184 (KOBG
soil) to 615 (OECD soil) mg/kg soil dw respectively. When results were based on
calculated concentrations in soil porewater, the LC50 was lower, ranging from 17.8 to
51 and 26.2 to 229 mg/L respectively. Tests in the KOBG soil appeared to result in
higher toxicity. This may be due to higher removal of the chemical through
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para-Dichlorobenzene
adsorption in the OECD soil as there is a significantly higher concentration of
organic matter.
The SIAR (1999) has normalised the results to an organic matter content of 3.4% in
line with the EU TGD which resulted in recalculated LC50 of 118 (KOBG soil) to 96
(OECD soil) and 169 (KOBG soil) to 258 (OECD soil) mg/kg soil dw for E. andrei
and L. rubellus respectively.
Based on these results, p-DCB can be considered only slightly toxic to earthworms.
In a published report, the lethal body burden (LBB) of p-DCB was determined for the
earthworm (E. andrei) with the contact paper toxicity test method (Belfroid et al.,
1993). Exposure to 735 and 220 礸/cm2 of p-DCB resulted in death within 8 hours.
The LBB was measured at 0.33 祄ol/g (approximately 48.5 mg/kg). This is not
comparable with an LC50. This paper showed that the LBB of p-DCB was lower than
four other chlorobenzenes (by up to an order of magnitude). It is stated that this
observation has been made in other research, citing another paper where LBBs of p-
DCB for midge larvae were 0.14 祄ol/g and for other chlorobenzenes ranged from
0.29 to 1.24 祄ol/g. An hypothesis for this apparent higher toxicity of p-DCB is
given in that it may be expected there is a higher possibility of transformation for a
lower chlorinated benzene than higher chlorinated benzenes such as those tested (eg
penta-chlorobenzene and hexa-chlorobenzene). The appearance of toxic metabolites
would result in death at lower internal concentrations, and therefore in lower LBBs.
13.2.1 Terrestrial plants
The SIAR (1999) summarises a 7 to 14 day growth test on the dicotyledon Lactuca
sativa, and a second 16 to 21 day growth test on the same plant is described in the
IUCLID data sheet.
The 7 to 14 day test followed OECD Test Guideline 208. Soil from two collections in
an orchard were used, with pH 7.5; percent organic matter (%OM) 1.4 to 1.8; clay 12
to 24% with moisture at 80% of water holding capacity. Concentrations were spaced
by a factor of 3.2 with at least 3 concentrations and a control. Ten seeds per tray were
used with two replicates. Only the 5 first germinated seedlings were kept. The 7 day
EC50 was 213 mg/kg soil dw (although it is stated that this result may be
underestimated). The 14 day EC50 was 248 mg/kg soil dw (based on nominal
concentrations).
The second test followed older (1968) methodology. The test was conducted under
semi-static conditions with renewal three times a week. The structure used 5
seedlings (1 week old with minimum root length of 3 cm) per pot with two replicates.
Concentrations were spaced by a factor of 3.2. The test reports an EC50 was 5.1
mg/kg soil dw.
The phytotoxicity of p-DCB was tested using soybean, carrot and tomato cell cultures
during their periods of fast growth (Wang et al., 1996). The cells were grown under
standard conditions until day 4, 5 and 6 for soybean, tomato and carrot respectively
when the cultures were transferred into sealed flasks and incubated for 1 day with 6
different concentrations of p-DCB. Preliminary experiments showed that the standard
84 Priority Existing Chemical Number 13
cultivation method is not suitable due to the volatility of the compound. Sealing the
culture flasks during the whole growth period affected the growth of cells more than
the chemical itself. However, when cell cultures were incubated during the period of
their fastest growth, an incubation time of 1 day proved sufficient to determine the
differences in the growth rates in relation to the concentration of the chemical. The
results showed that p-DCB is toxic to plant cells. A 50% inhibition in growth was
produced by 0.05 mM for tomato and 0.5 mM for soybean and carrot cultures. This
does not appear to be a standard phytotoxicity test.
13.2.2 PNEC for soil
Only short term toxicity tests for soil are available for p-DCB. The most sensitive
result was LC50 for E. andrei of 128 mg/kg soil dw. Due to the lack of data available,
an assessment factor of 1000 will be used, giving a PNEC in soil of 0.128 mg/kg soil
dw (ppm).
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para-Dichlorobenzene
14. Occupational Risk
Characterisation
In this section, the results of the health hazard and occupational exposure assessments
have been integrated to characterise the risk of adverse effects to workers potentially
exposed to p-DCB.
Results from the risk characterisation process provide the basis for health risk
management strategies (i.e., methods to reduce exposure and/or increase worker
awareness of potential hazards and safe handling of p-DCB).
14.1 Methodology
The risk to human health from exposure to p-DCB has been characterised using
margin of exposure methodology commonly adopted in international assessments
(EC, 1994; OECD 1994).
For health effects caused by repeated or prolonged exposure, risk(s) have been
characterised as follows:
1. Identification of the critical effect(s).
2. Identification of the most appropriate/reliable NOAEL (if available) for the
critical effect(s).
3. Where appropriate, comparison of the NOAEL with the estimated human dose
or exposure (EHD), to provide a margin of exposure (MOE), that is:
NOAEL
=
MOE
EHD
Where actual exposure monitoring data are unavailable or insufficient, the
EHD may be determined using exposure assessment models, such as the UK
EASE model.
4. Characterisation of risk, by evaluating whether the MOE indicates a concern
for the human population under consideration.
The MOE provides a measure of the likelihood that a particular adverse health effect
will occur under the conditions of exposure. As the MOE increases, the risk of
potential adverse effects decreases. In deciding whether the MOE is of sufficient
magnitude, expert judgement is required. Such judgements are usually made on a
86 Priority Existing Chemical Number 13
case-by-case basis, and should take into account uncertainties arising in the risk
assessment process, such as the completeness and quality of the database, the nature
and severity of effect(s) and intra/inter species variability.
14.2 Critical health effects and exposures
14.2.1 Acute effects
The critical effects from acute exposure to p-DCB vapour to humans are eye and
respiratory irritation. Eye and nose irritation has been reported at atmospheric levels
as low as 50 to 80 ppm with severe discomfort experienced in the range 80 to 160
ppm. Severe respiratory irritation has been observed at 160 ppm and above.
Acute oral toxicity may present as haemolytic anaemia with methaemoglobinuria
following ingestion of p-DCB. No deaths directly attributable to acute p-DCB
toxicity have been reported.
14.2.2 Chronic effects
Effects from long-term, repeated (chronic) exposures are not well characterised in
human populations. Therefore, the risk characterisation is based upon the critical
health effect in animals. A number of chronic studies have been carried out in a
variety of animal species (by different routes of exposure). p-DCB elicits kidney
tumours in male rats and liver tumours in both sexes of mice. The results of
genotoxicity testing, both in vitro and in vivo, have yielded negative results and
therefore threshold based risk assessment has been conducted.
Consistent findings associated with repeated human exposure to p-DCB include
reversible neurological and haematological disorders.
Oral exposure
Chronic oral studies have been conducted with rats, mice and dogs. In rats the critical
non-neoplastic endpoints were renal and hepatic toxicity and the critical neoplastic
endpoint was renal tumour formation. In mice the critical non-neoplastic and
neoplastic endpoints were hepatic effects. For dogs, the critical endpoint was
hepatotoxicity.
For the most sensitive species, the dog, the NOAEL(oral) was 10 mg/kg bw per day
and a LOAEL(oral) of 50 mg/kg bw per day was observed which produced
hepatotoxicity.
Inhalation
Inhalation effects were observed in chronic (2-year) inhalation studies with rats and
mice. Both species exhibited hepatotoxicity and increased kidney weights. The
NOAEL(inhalation) was 75 ppm and the LOAEL(inhalation) was 300 ppm for rats and mice.
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para-Dichlorobenzene
Dermal exposure
No treatment-related effects were seen in a 3-week dermal study with rats.
14.3 Occupational health and safety risks
Occupational health risks may result from acute and/or chronic exposure to p-DCB
via inhalation exposure (the most relevant route of exposure). Other occupational
safety risks may arise from physicochemical hazards.
14.3.1 Risk from physicochemical hazards
Risks of fire and/or explosion during handling and use of p-DCB are low.
14.3.2 Acute health risks
While p-DCB has a high vapour pressure (0.84 hPa at 20oC) which results in
sublimation of the compound, it is considered unlikely that, for uses identified in
Australia, vapour levels would reach those required to elicit acute systemic effects
(from inhalation). Based on old monitoring data from one Australian company and
the UK EASE model, levels could reach above 50 ppm. Thus, irritation to the eyes
and upper respiratory tract may occur where ventilation is inadequate, such as during
bagging operations.
14.3.3 Chronic health risks
Despite the fact that exposures are not well characterised for occupational scenarios
with potential exposure to p-DCB either in Australia or overseas, information on
known use profiles and data obtained from the UK EASE model have enabled broad
estimates of risk to be made. Dermal exposure is unlikely to contribute significantly
to body burden due to the solid nature of p-DCB and the use of gloves in the
workplace. Consequently, only exposure via inhalation has been assessed in the
following occupational scenarios. The critical effects are liver and kidney effects in
rats and mice via inhalation. Margins of exposure (MOE) were calculated using the
NOAEL(inhalation) of 75 ppm (450 mg/m3) reported in the JBRC (1995) study.
Formulation p-DCB products
The formulation of p-DCB products is basically an open process involving either the
milling or melting at 60oC of p-DCB followed by blending with dyes and perfume.
Monitoring data from 1981 indicated exposures of 10 to 60 ppm, with the highest
exposures in the bagging area. Similar levels were predicted by EASE. However,
more recent but not very accurate monitoring data suggest that levels are more likely
to be 5 to 15 ppm giving a MOE of 15 to 5. Taking into account the intermittent
exposure (approximately 100 days per year) and the LOAEL of 300 ppm, the risk of
chronic effects are likely to be low. However, the poor basis of the exposure data
must be acknowledged.
88 Priority Existing Chemical Number 13
Pressing and wrapping p-DCB products
The pressing and wrapping of air freshener and deodorant products composed of p-
DCB occurs at ambient temperatures and, based on survey results, is generally an
intermittent process occupying approximately 50 days per year. Monitoring data for
these activities are not available. However, as the exposure levels are likely to be
lower than during formulation and exposure frequency much less, it is likely that the
risk of chronic effects will be low.
Hygiene sector
Due to the extensive use of p-DCB as an air freshener/deodorant in public and
workplace toilet facilities, cleaners are regularly exposed to the vapour of p-DCB by
inhalation. No Australian workplace monitoring data are available for these
conditions. Two experimental studies conducted in Germany found the highest
airborne concentrations of p-DCB to be 1.8 ppm in one facility and 3.8 ppm in
another giving MOE of 41.7 and 19.7 respectively. However, the values can only be
considered as rough approximations of toilet facilities in general as the concentration
of p-DCB vapour will depend on several variables including the number of p-DCB
blocks used, the internal volume of the facility, the type of ventilation, the
temperature and whether the blocks are wrapped or unwrapped. Due to the
intermittent nature of exposure and the low levels of p-DCB likely to be encountered,
the risk of chronic effects to workers in the hygiene sector from exposure to p-DCB
is likely to be low.
14.3.4 Uncertainties in the calculation of margins of exposure
A consideration of uncertainties in the risk characterisation process is necessary when
discussing the acceptability and implications of estimated MOE. Examples of
uncertainties inherent in the assessment of risk for p-DCB are as follows:
Inadequate data
? lack of exposure monitoring data;
? lack of representative worker exposure profiles (i.e., degree of worker exposure
may vary from factory to factory); and
? inadequate data on human health effects following chronic exposure.
Assumptions in the assessment process
? that occupational dermal absorption (of vapour) is minimal;
? that absorption and bioavailability of p-DCB via inhalation is similar in humans
and rats;
? that dose-response relationships are likely to be similar (on a ppm in air basis) in
rats and humans.
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para-Dichlorobenzene
15. Environmental Risk
Characterisation
p-DCB is a volatile and water soluble chemical with its major use in Australia being
as an air freshener, and toilet blocks. This leads to widespread release to the
atmosphere and aquatic compartment through direct release to the sewer. Monitoring
data from around the world confirms the widespread transport of this chemical with
substantial detection obtained in air, surface water and sediments overseas. While
monitoring in Australia has tended to not detect p-DCB, the level of monitoring has
not been substantial, and not all environmental compartments have been tested.
15.1 Atmospheric risk
No experimental data on environmental organisms exposed through the gas phase are
available, so it is not possible to conduct a hazard assessment for those residing in the
atmosphere. However, abiotic effects can be assessed. While direct photolysis is not
considered likely, the atmospheric half-life is relatively short (expected to be <50
days) due to reaction with photochemically produced hydroxyl radicals. The
chemical contains chlorine substituents which suggests it may have a potential effect
on stratospheric ozone. However, with half-lives for migration to the stratosphere of
3 to 10 years (Bunce, 1994), this chemical would not be expected to persist long
enough in the troposphere to be of concern.
Nonetheless, Webster et al. (1998) state that transport times to the Arctic can be
measured in weeks. Therefore, with a half-life of 5 to 7 weeks for p-DCB, it can be
expected that the chemical could undergo significant transport in the atmosphere and
may migrate to the poles. No measurements appear to be available from these
regions.
For chemicals to be considered persistent organic pollutants (POPs), they need to
meet certain criteria with respect to persistence, bioaccumulation and the potential for
long range transport. p-DCB meets the draft UNEP criteria for persistence in air
(half life > 2 days), and therefore, possibly the draft criterion for long range transport.
The draft criteria indicate half-lives in soil and sediments need to be greater than six
months, but there are no measurements in this area so no conclusions can be drawn.
However, p-DCB fails the draft persistence in water criterion of either two or six
months, and also fails the draft bioaccumulation criterion of BCF>5000. Therefore,
p-DCB is unlikely to be considered a POP.
15.2 Aquatic risk
PEC/PNEC ratios for the aquatic compartment can be calculated using the worst-case
local scenario, in this instance, the PEClocal of 18.5 礸/L and PECcontinental of 8.6
90 Priority Existing Chemical Number 13
礸/L. The ratio of PEC/PNEC has been calculated for local and continental
compartments as follows:
PEC/PNEClocal = 0.925
= 0.43
PEC/PNECcontinental
In order to predict a low potential for an environmental hazard, the PEC/PNEC ratio
must be less than 1. The PNEC has been conservatively determined by taking the
lowest effect from a large data source, and applying a further safety factor of 10.
In determining the PEC/PNEC ratio, the PEC is clearly an overestimate using worst-
case assumptions. Where surface waters were monitored in Australia, p-DCB failed
to be detected at 0.5 礸/L. While the estimated continental PEC is above the highest
monitored surface water level in the Northern Hemisphere (4.05 礸/L), the majority
of monitoring samples in surface waters from around the world were significantly
less than this, and often involved no chemical being detected.
Within sediments, evidence suggests p-DCB will be present at higher concentrations
than receiving waters where exposed. However, no benthic tests are available in
which to conduct a meaningful risk assessment for sediments. It is reasonable to
assume that p-DCB associated with the sediments is in fact adsorbed and so not
bioavailable. If this were not the case, the chemical would be expected to volatilise.
Based on this, the hazard to benthic organisms is anticipated to be low. However,
anaerobic degradation studies indicate that p-DCB is relatively resistant to
biodegradation under the conditions expected in sediments. Additionally, the much
higher levels found in sediments (see Section 7.2.5) than surface waters indicate
possible accumulation in this compartment, which may be an area of concern.
p-DCB is classified under the International Maritime Dangerous Goods code as a
UN3077 Class 9 Environmentally Hazardous Substance. However, based on current
usage patterns, the evidence supports a conclusion of a low expected risk to the
aquatic environment in Australia.
15.3 Terrestrial risk through agricultural use
In the event of application of sewage sludge to land, a PEC of 16.6 礸/kg has been
determined with a PNEC of 128 礸/kg. These values give a PEC/PNEC ratio of 0.13.
Data for terrestrial organisms were only limited to earthworms and one plant species,
and there is a possibility other terrestrial organisms may be more sensitive. However,
an assessment factor of 1000 was used to reflect this scenario.
In summary, the use of p-DCB is expected to present a low terrestrial environmental
risk.
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para-Dichlorobenzene
16. Public Health Assessment
Public exposure will arise from the use of p-DCB in toilet deodorant blocks and air
fresheners. When used as air freshener/deodoriser the cellophane wrapping is
punctured and the p-DCB block or disk undergoes sublimation and the vapour
disperses. Blocks or disks are unwrapped and placed into urinals. Consequently,
public exposure will occur principally by inhalation, with the potential for dermal
exposure reduced by the containment of p-DCB in cellophane wrapping during
handling. There have been no reports of skin irritation or sensitisation in widespread
human use, except for one case of acute petechial purpura in a 69-year old man.
Consequently the hazard of dermal irritation or sensitisation is considered to be low.
Several products are available in disk form for domestic use as air deodorisers with
insect repellent activity and are used to protect clothes in cupboards and wardrobes
from silverfish and moths. The sublimation of such p-DCB products may lead to a
concentration of p-DCB vapour in an enclosed space.
A study undertaken to establish a baseline for the trace compound composition of
expired human breath was conducted by Conkle et al., (1975). The condensate from
the breaths of 8 male volunteers at an airforce base were collected by cryogenic
trapping and subjected to GC/MS analysis. Morning samples were collected for 60
minutes after a nine-hour fast prior to analysis. A total of ten determinations were
made and samples were corrected for supply air contaminants. Of the ten samples
analysed, seven contained traces of dichlorobenzene (mean 4.6 礸/hr, range 0.001 to
26.0 礸/hr; isomer not stated). The authors concluded that the dichlorobenzene was
p-DCB and was present as a result of the men using the toilet facilities, where it was
present in block form, prior to the commencement of the experiment. The airborne
levels of p-DCB in public toilet facilities have been discussed previously in Section
8.2.4.
Studies in Japan measured airborne concentrations and personal exposure levels by
means of passive samplers while the inhabitants lived their daily lives. Maximal
p-DCB concentrations were 5.9 mg/m3 (1 ppm) for airborne concentration and 0.5
ppm (3.3 mg/m3) for personal exposure (SIAR, 1999).
Occupational exposure to vapour can cause irritation to the nose and upper
respiratory tract at levels at or above 50 ppm (300 mg/m3), including such symptoms
as coughing, chest pains and difficulty in breathing at around 160 ppm (962 mg/m3).
NOAEL's from chronic, repeat-exposure inhalation studies in rats and mice of
75 ppm (451 mg/m3) are well in excess of measured personal exposure levels from
household products. Medical examinations of 58 workers exposed for up to 25 years
(average exposure approximately 5 years) to average airborne concentrations of
45-380 ppm, measured in 3 separate surveys, showed no evidence of p-DCB-related
effects on health, except for eye and nose irritation. However, the study was not
controlled for such things as concentration and type of chemical exposure and pre-
existing medical conditions (Hollingsworth et al., 1956). Consequently, the risk from
92 Priority Existing Chemical Number 13
the use of p-DCB products in the household and public toilets is considered to be
low.
It should be noted that public exposure could occur during non-industrial use of p-
DCB, that is, when used as an insect repellent or a pharmaceutical.
Experiments were conducted to determine the air-borne levels of p-DCB in two
unfurnished rooms where the chemical was used as an insect repellent in two
identically sized wardrobes (volume 0.58 m3). Room 1 had a volume of 25.66 m3 and
room 2 was 30.28 m3. Approximately 90 g of p-DCB were placed between clothes in
each wardrobe. The wardrobe in room 1 was never opened while the other was
opened for 2 minutes each day. The rooms were aerated daily, with the exception of
weekends, for 15 minutes after air samples were taken. Room temperature was
maintained at 20oC. Complete dissipation of the p-DCB took 80 days. Maximum
airborne levels of p-DCB in rooms 1 and 2 over 80 days and before aeration were 1.7
ppm (10.0 mg/m3) and 1.3 ppm (8.0 mg/m3) respectively. The average levels over 73
days before aeration were 1 ppm (5.8 mg/m3) for room 1 and 0.7 ppm (4.0 mg/m3)
for room 2 (Globol GmbH, 1986).
Pharmaceutical exposure will principally arise from the use of p-DCB in a finished
product (Cerumol Ear Drops containing 2% w/v p-DCB). Exposure will be via the
dermal route, with the possibility of accidental oral and ocular exposure. The hazards
associated with the intended use of this product are likely to be low for the following
reasons. This product is only available in a small volume (10 ml dropper bottle), and
if used as directed, a very small volume (5 drops) should be administered up to twice
per day for a few days. It exists in Schedule 2 (S2) of the Standard for the Uniform
Scheduling of Drugs and Poisons (SUSDP), and therefore it is available from
pharmacies without prescription. The National Drugs and Poisons Schedule
Committee Guidelines (NDPSCG, 1997) describe S2 chemicals as "substantially safe
in use but where advice or counselling is available if necessary" and "for minor
ailments or symptoms which can be easily recognised by the consumer and/or do not
require medical diagnosis or management". Characteristics of preparations in S2
include an "extremely low abuse potential" and "a low potential for harm from
inappropriate use".
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para-Dichlorobenzene
17. Risk Management
In this section, measures currently employed in the management of human health
risks from occupational and consumer exposure to p-DCB are discussed. The
information reviewed includes national and international standards, together with
relevant guidance material, MSDS and labels. Due to the low environmental risk
associated with current patterns of use, there are no specific environmental regulatory
controls for p-DCB.
Relevant information was provided by importers of p-DCB and formulators of
products in which p-DCB is an ingredient. Information was also obtained from site
visits.
The key elements in the management of risks discussed in this section include:
? workplace control measures;
? hazard communication (including training and education);
? monitoring and regulatory controls; and
? emergency procedures.
17.1 Workplace control measures
According to the NOHSC National Model Regulations for the Control of Workplace
Substances (NOHSC, 1994c), exposure to hazardous substances should be prevented
or, where this is not practicable, adequately controlled, so as to minimise risks to
health and safety. p-DCB is classified as a hazardous substance in accordance with
the NOHSC Approved Criteria. A National Code of Practice for the Control of
Workplace Hazardous Substances, lists the hierarchy of controls measures, in priority
order, that should be implemented to eliminate or minimise exposure to hazardous
substances. These are:
? elimination;
? substitution;
? isolation;
? engineering controls;
? safe work practices; and
? personal protective equipment.
Control measures are not mutually exclusive and effective control usually requires a
combination of these measures. Particular attention needs to be given to control
measures that minimise inhalation of p-DCB.
94 Priority Existing Chemical Number 13
17.1.1 Elimination and substitution
Elimination is the removal of a chemical from a process and should be the first option
considered when minimising risks to health.
In situations where it is not feasible or practicable to eliminate the use of a chemical,
substitution should be considered. Substitution includes replacing the chemical with
a less hazardous substance or the same substance in a less hazardous form.
17.1.2 Isolation
Isolation as a control measure aims to separate employees, as far as practicable, from
the chemical hazard. This can be achieved by distance or enclosure.
The formulation of p-DCB, by the addition of additives in a melting or mixing
process, is predominantly an open process. For example, at one site visited, melting
of p-DCB is achieved by loading manually the raw material into a tank which is
sealed during the melting process. Liquid p-DCB is then transferred from the tank to
the processing area by a system of pipes. Prior to spreading the molten p-DCB onto a
stainless steel conveyer belt a small quantity of dye and perfume are added. All
subsequent operations which include crystallisation of molten material on the
conveyer belt, flaking into a hopper and transfer into bags take place under open
conditions.
The pressing and wrapping of p-DCB products is a simple and open process and
generally the equipment is of older manufacture. The operation of hoppers and
presses results in the formation of dust particles composed of p-DCB. This dust was
observed at all sites visited. The survey and site visits revealed that open containers,
for temporary storage of p-DCB, were common to many companies.
17.1.3 Engineering controls
Two of 3 formulators have exhaust ventilation during formulation. But on one site
visit an air extraction system used to reduce airborne levels of p-DCB was of
uncertain efficiency due to tears in the ducting material and the presence of p-DCB
dust on the ducting itself. One company pressing and wrapping end products reported
use of ventilation.
17.1.4 Safe work practices
No safe work practices were identified that can be characterised as unique to p-DCB.
Common safe work practices employed include storage in closed containers in well
ventilated areas, and away from incompatible materials and immediate clean-up of
spills.
17.1.5 Personal protective equipment
Where other control measures are not practicable or adequate to control exposure,
personal protective equipment (PPE) should be used. In practice, PPE used for
handling p-DCB includes the following:
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para-Dichlorobenzene
? overalls;
? safety glasses; and
? gloves
Three companies (2 formulators and 1 pressing end products) reported that workers
used respirators during processing of p-DCB.
17.2 Emergency procedures
The availability of an emergency response plan to deal with unexpected releases of p-
DCB, such as large spills, is good practice. All employees need to be trained in
accident and emergency procedures.
All plans/procedures should be fully documented and available to all workers. Local
emergency services should be consulted on the appropriateness of emergency
procedures developed. No emergency plans for p-DCB were submitted for
assessment.
17.3 Hazard communication
17.3.1 Assessment of material safety data sheets (MSDS)
MSDS are the primary source of information for workers involved in the handling of
chemical substances. Under the NOHSC National Model Regulations for the Control
of Workplace Hazardous Substances (NOHSC, 1994c) and the corresponding State
and Territory legislation, manufactures and suppliers are obliged to provide an
MSDS to their customers for all hazardous substances. Due to its inclusion on the
List of Designated Hazardous Substances (NOHSC, 1999b), p-DCB is considered to
be a hazardous substance.
A sample MSDS for p-DCB, prepared in accordance with the MSDS Code, is
provided at Appendix 3. The sample MSDS, prepared from information obtained for
the assessment of p-DCB, is for guidance purposes only. Under the National Model
Regulations, manufactures and suppliers have the responsibility to compile their own
MSDS and ensure that the information is up-to-date and accurate.
Of 20 companies handling p-DCB to which survey forms were sent, 5 did not submit
a MSDS for assessment. A total of 7 MSDS for commercial grade p-DCB (purity
99%) were provided for assessment and an additional 8 for p-DCB-containing
products (purity > 95%) intended for industrial use. The 15 MSDS were assessed
against the NOHSC National Code of Practice for the Preparation of Material Safety
Data Sheets (NOHSC, 1994d). The results of the MSDS assessment are presented in
Table 18.
A significant number of MSDS were deficient on information which adequately
describes the health hazards associated with p-DCB. Particularly noticeable was the
lack of information pertaining to the effects associated with ingestion of the chemical
and effects on the central nervous system. Several MSDS contained advice that the
96 Priority Existing Chemical Number 13
administration of adrenaline is contra-indicated in the event of p-DCB exposure,
however, this assessment found no evidence to support this direction.
Table 18 - Findings of the MSDS Assessment
Type of Information Number of MSDS
Statement of hazardous nature 12/15
Product Identification
Correct CAS number 13/15
Physical description/properties 15/15
Health Hazard Information
Acute effects
Harmful if swallowed 14/15
Ingestion effects (headache, nausea, vomiting, anaemia) 5/15
Irritating to the eye 15/15
Irritating to the upper respiratory tract 15/15
Effects on central nervous system (confusion, incoordination,
7/15
narcosis, paresthesia)
Chronic effects
Ingestion effects (anaemia) 5/15
MSDS stated `no data available' for health effects 1/15
1
First Aid Advice
If more than 15 minutes from medical attention induce
12/15
vomiting
Do not give milk or oils 11/15
Advice to physician 14/15
If poisoning occurs, contact a doctor or Poisons Information
15/15
Centre
Instruction that adrenaline is contra-indicated 9/15
Precautions For Use
Correct value for TWA and STEL exposure standard 10/15
Adequate ventilation 14/15
Eye protection 14/15
Gloves protection 12/15
Respirator 11/15
Safe Handling Information
Statement of combustible nature 13/15
Statement that hydrogen chloride or phosgene form on
12/15
combustion
Adequate information on extinguishing media (CO2, foam, dry
14/15
chemical, water fog)
Contact Point
Contact person nominated 10/15
Direct phone number for contact person 9/15
Emergency telephone number provided 6/15
1
First aid statement as recommended by SUSDP; TWA, time weighted average; STEL = short term
exposure limit.
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para-Dichlorobenzene
One third of companies did not provide full exposure standard values, in particular,
the STEL value was not reported by these companies. A number of MSDS did not
convey sufficient information for the contact point in the event of an emergency. A
general deficiency was the absence of an emergency or direct contact telephone
number for an appropriate contact person.
The MSDS supplied by two major importers were the least comprehensive of all
submitted. Of the 6 MSDS issued by suppliers, 2 were of recent issue date (1998), 2
issued in 1997 and 1 each issued in 1996 and 1994. All companies, with the
exception of one, provided good advice concerning personal protective equipment.
17.3.2 Assessment of labels
Under the NOHSC National Model Regulations and Code of Practice for the Control
of Workplace Hazardous Substances (NOHSC, 1994c) and the corresponding State
and Territory legislation, suppliers of industrial chemicals are obliged to provide
labels in accordance with the NOHSC Code of Practice for the Labelling of
Hazardous Substances (Labelling Code) (NOHSC, 1994e).
The information needed on labels for containers with a capacity of more than 500 g
of p-DCB include:
? Signal word `Hazardous';
? Identification information
? product name
? chemical name
? Directions for use (where appropriate);
? Safety phrases;
? First aid instructions;
? Emergency procedures;
? Supplier details; and
? Reference to MSDS.
Nine labels were provided for assessment, comprising 3 labels for industrial grade p-
DCB and 6 for products containing p-DCB (greater than 90% p-DCB) for industrial
use. As all the products are intended for industrial use they should be labelled in
accordance with the Labelling Code (NOHSC, 1994e). The findings of the
assessment of labels issued for commercial grade material are summarised in Table
19.
The risk phrase required prior to this Assessment (from the List of Designated
Hazardous Substances [NOHSC: 10005(1994)]) was `Harmful if swallowed' (R22).
98 Priority Existing Chemical Number 13
Of the 9 labels submitted for assessment only 3 contained reference to the harmful
nature of the product.
Generally, the labels assessed failed to convey the necessary information required in
the event of an emergency. Specifically, information relating to health risks and first
aid procedures were either absent or insufficient.
Table 19 - Findings of the label assessment
Number of
Information provided
Labels
Signal word
HAZARDOUS 3/9
Identification information
8/9
Chemical name
Safety phrases
Avoid contact with skin and eyes (S24/25) 6/9
First aid instructions (or similar statement)
If poisoning occurs contact a doctor or Poisons
7/9
Information Centre
In case of contact with eyes, rinse immediately with plenty
of water for 15 minutes. Contact a doctor or Poisons
4/9
Information Centre if irritation persists
If swallowed, and more than 15 minutes from medical
6/9
attention induce vomiting, preferably using Ipecac Syrup
APF
Do not give milk or oils 6/9
Information on emergency procedures 3/9
Reference to MSDS 4/9
17.3.3 Standard for the Uniform Scheduling of Drugs and Poisons (SUSDP)
Where products containing p-DCB are intended for domestic end-use, they need only
comply with the SUSDP labelling requirements (Australian Health Ministers'
Advisory Council, 1997). p-DCB is listed (as `Paradichlorobenzene') in Schedule 5
of the Drugs and Poisons Schedule (SUSDP, Australian Health Ministers' Advisory
Council, 1997). Its availability is not restricted, but it must be labelled with the
signal words `KEEP OUT OF THE REACH OF CHILDREN' together with the
following safety directions (SD) and first aid instructions, if it is likely to be used in
the public domain:
Safety directions:
? Avoid contact with eyes (SD1);
? Avoid contact with skin (SD4).
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para-Dichlorobenzene
First aid instructions:
? If poisoning occurs, contact a doctor or Poisons Information Centre;
? If swallowed and more than 15 minutes from a hospital, induce vomiting,
preferably using Ipecac Syrup AFP;
? Avoid giving milk or oils.
Of 13 labels from 2 companies assessed for compliance with the SUSDP Code, 2 did
not contain the general safety precautions.
17.3.4 Education and training
Guidelines for the induction and training of workers potentially exposed to hazardous
substances are provided in the NOHSC Model Regulations and Code of Practice for
the Control of Workplace Hazardous Substances (NOHSC, 1994c). Specifically,
matters that need to be addressed for p-DCB include:
? the potential adverse health effects of p-DCB;
? specific protective equipment to be worn; and
? explanation of data contained in MSDS and labels.
17.4 Other regulatory controls
The following sections comprise regulations/standards promulgated with the aim of
protecting workers from adverse exposures to p-DCB in Australia.
17.4.1 Atmospheric monitoring
Under the NOHSC Model Regulations and Code of Practice for the Control of
Workplace Hazardous Substances (NOHSC, 1994c), employees are required to carry
out an assessment of the workplace for all hazardous substances, the methodology of
which is provided in the NOHSC Guidance Note for the Assessment of Health Risks
Arising from the Use of Hazardous Substances in the Workplace (NOHSC, 1994f).
When the assessment indicates that the risk of exposure via inhalation is significant,
atmospheric monitoring should be conducted to measure p-DCB levels in the
workplace as a precursor to the implementation of suitable control measures to
reduce exposure. Subsequent monitoring will be required to ensure that such
measures are effective.
17.4.2 Occupational exposure standard
The current national occupational exposure standard for p-DCB is 75 ppm (451
mg/m3) TWA, 110 ppm (661 mg/m3) STEL (NOHSC, 1995g).
Overseas occupational exposure limits for p-DCB are listed in Table 20.
The adopted Australian occupational exposure standard of 75 ppm is consistent with
the standard in several other countries, however, some countries have a lower
100 Priority Existing Chemical Number 13
exposure standard, including the United Kingdom, Germany, Ireland, the Netherlands
and Japan.
The current occupational exposure standard for p-DCB in Australia was adopted
from the ACGIH standard of 1961 to 1992. This standard was set on the basis that p-
DCB is less toxic than the ortho isomer (which had a ceiling limit value of 50 ppm)
and that the TLV and STEL should be `sufficiently low to prevent acute and chronic
poisoning'.
Table 20 - Occupational exposure limits for p-DCB (ACGIH, 1998 )
TWA STEL
Year
Country
adopted
3 3
ppm mg/m
ppm mg/m
Belgium 75 450 110 660 1993
Denmark 75 450 - - 1993
Finland 75 450 115 690 1993
France 75 450 110 675 1993
Germany 50 300 100 600 1995
Ireland 25 150 50 300 1997
Japan 50 300 - - 1998
Netherlands 25 153 50 300 1997
United Kingdom 25 153 50 306 1995
United States
10 60 - - 1996
(ACGIH)
United States (OSHA) 75 450 - - 1996
Sweden 75 450 110 660 1993
Switzerland 75 450 150 900 1993
TWA = time weighted average; STEL = short term exposure limit.
In 1993, the ACGIH adopted a TWA (8 hrs) of 10 ppm (plus A3, animal carcinogen).
The TWA was aimed to protect against eye irritation reported in humans (effects
observed at 17 ppm in an unpublished study) and renal toxicity in rats (LOAEL of 25
ppm in male rats (NTP, 1987)).
The UK Health and Safety Executive adopted occupational exposure standards of 25
ppm TWA and 50 ppm STEL (15 minutes) in 1993. The STEL is aimed to prevent
nose and eye irritation which occurs in humans at about 50 ppm or above. The TWA
was set at 25 ppm (8 hrs) to `allow for possible differences in response between
animals and man' (based on a NOAEL of about 100 ppm for repeated exposures in
animals).
17.4.3 Health surveillance
In accordance with NOHSC Model Regulations for the Control of Workplace
Hazardous Substances (NOHSC, 1994c), employers have a responsibility to provide
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para-Dichlorobenzene
health surveillance in those workplaces where the workplace assessment indicates
that exposure to a hazardous substance may lead to an identifiable substance-related
disease or adverse health effect. p-DCB is not listed in Schedule 3 (list of substances
requiring health surveillance) and as such there are no formal requirements for health
surveillance programs for exposed workers.
17.4.4 Australian Code for the Transport of Dangerous Goods by Road and
Rail
Currently, p-DCB is not classified in the 6th Edition of the Australian Code for the
Transport of Dangerous Goods (ADG) (FORS 1998). However, the current
International Maritime Dangerous Goods code classifies p-DCB as a UN3077 Class 9
Environmentally Hazardous Substance, Solid, N.O.S. and this classification is
expected to be adopted in the 7th Edition of the ADG code.
102 Priority Existing Chemical Number 13
18. Discussion and Conclusions
The manufacture of p-DCB does not occur in Australia and up to 1000 tonnes are
imported annually. Almost all of this material is used in the production of toilet
deodorant (approximately 85%) and air freshener blocks (approximately 13%). The
remaining p-DCB is used in non-industrial activities, that is, pharmaceutical and
agricultural uses.
p-DCB is used extensively in the public and private sectors mostly as an air
freshener/deodoriser and predominantly in toilet facilities. Due to the high vapour
pressure of p-DCB it slowly sublimates to the atmosphere. Use of this property is
made by wrapping disks of the material (typically 99% p-DCB) with cellophane
which, when punctured, allows the vapour to slowly disperse where it can act to
disguise odours. Alternatively, and because of its insoluble nature, where use in
urinals is required the blocks or disks are unwrapped and placed directly in the urinal.
Health effects
Animal studies have shown p-DCB to be of low acute toxicity by either oral, dermal
or the inhalation route. Acute toxic effects reported in animals are nephrotoxicity in
male rats and hepatotoxicity in both sexes of mice. Limited data indicate that p-DCB
is not corrosive or irritating to the skin but can cause eye and respiratory tract
irritation in animals and humans.
The systemic health effects of p-DCB in humans are poorly characterised and based
on cases of accidental or intentional exposure. The effects reported from case studies
include the development of neurological and haematological symptoms, all of which
appear to be reversible following cessation of exposure. There have been two deaths
attributed to p-DCB exposure, however, other factors which may have contributed to
mortality were not discussed in the case report and a causal relationship can not be
established. In humans, ingestion of p-DCB or inhalation of its vapour, by accidental
or intentional means, may result in drowsiness, nausea, incoordination, unconscious,
hypotension and anaemia. Exposure to vapour may cause coughing, chest pains and
difficulty in breathing.
There have been no adverse reports of reproductive effects in humans or animals
described in the literature and investigations of the genotoxic effect of p-DCB using
several test systems have yielded negative results.
p-DCB has been found to be carcinogenic in the rat and mouse in two well-conducted
studies. In an oral study, renal tumours were found in the kidneys of male rats and in
oral and inhalation studies livers tumours were observed in both sexes of mice. Due
to the negative results of genotoxicity testing the tumours are considered to be
epigenetic in nature. The renal tumours in the male rat are not considered to be
relevant to humans. There have been no well conducted epidemiological studies of
the effects of p-DCB on humans.
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para-Dichlorobenzene
Occupational health and safety
In Australia, between 500 and 1000 tonnes of p-DCB were processed, formulated or
handled by at least 23 companies into products for industrial or domestic use in 1998.
The processing of p-DCB is generally semi-automated and usually involves 1 or 2
workers per company. Production is intermittent with consumer demand regulating
production activities. The duration of exposure varies from 6 to 7 hours/day for
approximately 12 to 150 days/year.
The major route for occupational exposure to p-DCB is by inhalation. Occupational
exposure in Australia can occur during the formulation of products or from use of
finished products containing p-DCB. Absorption by the oral and dermal routes is
unlikely to be a significant source of exposure under normal occupational use.
Occupational exposure is likely to occur due to vapour emitted from the volatile solid
or from molten material during reforming of imported material into blocks or tablets.
Exposure to vapour and dust can occur during handling of the solid material although
once processed into finished products a cellophane wrapping minimises subsequent
exposure. Monitoring data for workplace airborne concentrations of p-DCB in
Australia are inadequate. However, based on data supplied and modelling estimates,
exposure levels are likely to range from 5 to 15 ppm giving an expected MOE of 15
to 5. In practice, the MOE will be larger due to intermittent exposure.
There is the potential for workers involved in the hygiene sector, particularly those
involved in cleaning toilet facilities, to be exposed to p-DCB. Due to the relatively
small amount of p-DCB used per facility, the use of ventilation and the
comparatively short exposure times involved, the risk to these workers is expected to
be low.
Based on current knowledge concerning the use of p-DCB in Australia, it is
concluded that, due to intermittent exposure and its relatively low toxicity, the risk to
workers engaged in the manufacture of products containing p-DCB or in the use of p-
DCB products is expected to be low.
A survey of workplace control measures indicated that the provision of adequate
ventilation is not a routine procedure. In particular, the provision of exhaust
ventilation in areas where p-DCB products are re-packaged appeared to be deficient.
An assessment of submitted MSDS and labels revealed a number deficiencies. The
most common deficiency for MSDS was generally poor information on human health
effects, both acute and chronic. A number of MSDS (60%) did not include an
emergency contact number. For labels, the appropriate signal word (66%), safety
phrases (33%) and information on emergency procedures (66%) were absent from
several labels.
The hazard assessment identified an adverse effect in animals that was observed at a
concentration equivalent to the body burden achievable at the current occupational
exposure level for p-DCB, therefore, the occupational exposure standard should be
reviewed.
104 Priority Existing Chemical Number 13
Under the National Model Regulations for the Control of Workplace Hazardous
Substances (NOHSC, 1994c), a hazardous substance means a substance which is on
the List of Designated Hazadous Substances (NOHSC, 1999b). Consequently, as p-
DCB appears on the List of Designated Hazadous Substances (NOHSC, 1999b) it
must be considered to be a hazardous substance.
Public health
Public exposure will principally arise from the use of p-DCB in toilet deodorant
blocks and air fresheners. Public exposure will occur principally by inhalation, with
the potential for dermal exposure reduced by the containment of p-DCB in
cellophane wrapping during handling. There have been no confirmed reports of skin
irritation or sensitisation in widespread human use. Consequently the risk of dermal
irritation or sensitisation is considered to be low.
Several products in tablet and button form are sold as household insect repellents
and/or air deodorisers with insect repellent activity and are used to protect clothes in
cupboards and wardrobes from silverfish and moths. The sublimation of such p-DCB
products may lead to a concentration of p-DCB vapour in an enclosed space.
Investigations of the airborne concentrations resulting from the use of p-DCB as an
insect repellent in wardrobes or as a household air freshener indicate that
concentrations are likely to be well below those where irritation or chronic effects
may be observed. Consequently, the risk to the public from the intended use of
p-DCB blocks or buttons in the household or public toilets is considered to be low.
As the lowest reported oral LD50 value for the rat is 2512 mg/kg (Varshavskaja,
1967), a T-value of 250 would be expected. Currently, the T-value listed in the
SUSDP for p-DCB is 50.
Environment
The chemical is biodegradable and relatively soluble in water. Its removal from
aqueous systems occurs significantly from volatilisation, and at equilibrium, over
98% of the chemical would be expected to partition to the atmosphere where it will
break down through reaction with hydroxy radicals. Concentrations likely to occur in
aquatic systems are expected to be far lower than those of concern, and this
expectation is supported by monitoring data from Australia and around the world. A
low aquatic risk is predicted.
Additionally, the short atmospheric lifetime of p-DCB indicates concentrations will
not occur at levels harmful to the atmosphere. While widespread transport within the
troposphere is likely, the chemical is not expected to reach the stratosphere and
therefore not expected to have an influence on global warming or ozone depletion.
No risks have been identified for the environment due to the use of p-DCB. However,
there appears to be the potential for accumulation of p-DCB in sediments. No
Australian data exists for this compartment, and levels should be monitored where
possible to determine whether accumulation is a factor. It is noted that use levels of
p-DCB in Australia have been declining over the last few years, and the trend appears
to be for a continuing decline, which may negate this issue.
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para-Dichlorobenzene
Data gaps
Generally, the toxicity of p-DCB has been extensively investigated using a number of
critical endpoints. Consequently, further testing is not required. Within Australia the
major data gap is a need for further workplace monitoring data.
106 Priority Existing Chemical Number 13
19. Recommendations
19.1 Hazard classification
The recommended classification for p-DCB based on the health hazard assessment of
currently available data and in accordance with the National Occupational Health and
Safety Commission's Approved Criteria for Classifying Hazardous Substances
(NOHSC, 1999a), is:
? Do not breath vapour (Safety phrase S23)
? Avoid contact with skin (Safety phrase S24)
? Avoid contact with eyes (Safety phrase S25)
? Use only in well ventilated areas (Safety phrase S51)
MSDS, labels and training materials should be amended to provide appropriate
information.
Due to its inclusion on the List of Designated Hazardous Substances (NOHSC,
1999b), p-DCB is considered to be a hazardous substance.
19.2 Hazard communication
19.2.1 Material safety data sheets (MSDS)
The NOHSC National Code of Practice for the Preparation of Material Safety Data
Sheets (NOHSC, 1994d) provides guidance for the preparation of MSDS.
It is recommended that Australian suppliers of p-DCB amend their MSDS taking into
account the classification recommended in Section 19.1 and, where necessary, rectify
the deficiencies identified by this assessment with particular attention being given to
the following:
? inclusion of a statement of hazardous nature;
? inclusion of appropriate risk and safety phrases;
? inclusion of acute and chronic health effects;
? inclusion of appropriate first-aid advice;
? inclusion of appropriate advice to doctor;
? inclusion of Australian exposure standard;
? inclusion of appropriate engineering controls, such as exhaust ventilation in areas
where vapours are likely to occur; and
? inclusion of an Australian emergency contact number.
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para-Dichlorobenzene
A sample MSDS for p-DCB is provided at Appendix 3.
19.2.2 Occupational health and safety
The following recommendations are made:
? monitoring data for p-DCB are of either poor quality or non-existent.
Consequently, it is recommended that quantitative monitoring of workplace p-
DCB levels should be undertaken to determine actual worker exposure levels and
to identify whether improvements in control measures are warranted;
? adequate ventilation should be provided to minimise worker exposure to p-DCB
vapour;
? containers used for the temporary storage of p-DCB should be provided with lids
when not in use; and
? regular removal of p-DCB dust from work areas should be undertaken.
19.2.3 Occupational exposure standard
It is recommended to NOHSC that the present occupational exposure standard for p-
DCB of 75 ppm TWA (8 hr) be reviewed noting:
? eye and nose irritation in humans at 50 ppm; and
? the NOAEL of 75 ppm (inhalation) and a LOAEL of 300 ppm (inhalation) for
increases in liver weight.
19.3 Public health
The requirements for the first aid instruction and general safety precautions for
products in the public domain should be strictly adhered to. There are no changes
recommended to the first aid instructions or general safety precautions for p-DCB.
The lowest oral rat LD50 value quoted as a single value is 2512 mg/kg. Consequently,
it is recommended that SUSDP consider re-assigning the T-value from 50 to 250.
108 Priority Existing Chemical Number 13
20. Secondary Notification
Under Section 65 of the Act, the secondary notification of p-DCB may be required,
where an applicant or other introducer (importer) of p-DCB, becomes aware of any
circumstances which may warrant a reassessment of its hazards and risks. Specific
circumstances include:
a) The function or use of p-DCB has increased, or is likely to change, significantly;
b) The amount of p-DCB introduced into Australia has increased, or is likely to
increase significantly;
c) Manufacture of p-DCB has begun in Australia; or
d) Additional information has become available to the applicant/notifier as to the
adverse health and/or environmental effects of p-DCB.
The Director must be notified within 28 days of the applicant/notifier becoming
aware of any of the above circumstances.
109
para-Dichlorobenzene
Appendix 1
List of products containing p-DCB
This appendix provides a list of products containing p-DCB (Table 21) that were marketed in
Australia in 1998/99. The list includes the trade name of each product, the use and the
amount (in % w/w) of p-DCB in the product.
This list is not intended to be exhaustive but is considered to be representative of current p-
DCB usage in Australia as indicated by information provided by manufactures and
distributors of p-DCB products. Formulations may have changed since the preparation of the
list and some products may no longer be commercially available.
Table 21 - List of products containing p-DCB
Product Use p-DCB (% w/w)
Air Freshener Blocks Air freshener/Deodorant 98.8
Blue Bell Blocks Deodorant - Toilets 100
Brickettes Deodorant - Toilets 99.0
Dellas Air Freshener Tablet Air freshener/Deodorant 99.0
De-Odo-Air Deodorant - Toilets 99.0
Deodorant Buttons Deodorant - Toilets 99.0
Fragrasan Air freshener/Deodorant 99.2
Fresha Air freshener/Deodorant 99.0
Fresh Air Air freshener/Deodorant 99.2
Masquerades - Blue Deodorant - Toilets 99.0
Masquerades - Lemon Deodorant - Toilets 99.0
Parry's Fresh Air Air freshener/Deodorant 99.2
Parry's Fresh Guard Household Fumigant 99.2
1,4-Dichlorobenzene Chemical reagent 100
Para-dichlorobenzene Chemical reagent 97.5
Para-dichlorobenzene Chemical reagent 99.9
Rainbow Blue Air freshener/Deodorant 98.8
110 Priority Existing Chemical Number 13
Appendix 2
Excerpt from the Approved Criteria (NOHSC, 1999a)
CARCINOGENIC SUBSTANCES
4.76 Substances are determined to be hazardous due to carcinogenic effects
if they fall into one of the following categories:
Substances known to be carcinogenic to humans.
Category 1
Category 2 Substances which should be regarded as if they are
carcinogenic to humans.
Category 3 Substances which cause concern for humans owing to
possible carcinogenic effects but in respect of which the
available information is not adequate for making a
satisfactory assessment.
EXPLANATORY NOTES REGARDING THE
CATEGORISATION OF CARCINOGENIC SUBSTANCES
4.77 The placing of a substance into Category 1 is done on the basis of
epidemiological data; placing into Categories 2 and 3 is based
primarily on animal experiments.
CATEGORY 1
4.78 Substances are determined to be hazardous and classified as
Toxic (T) and assigned risk phrase R45 or R49 in accordance with the
criteria given below.
R45 MAY CAUSE CANCER
R49 MAY CAUSE CANCER BY INHALATION2
2
For substances which present a carcinogenic risk only when inhaled, for example, dust, vapour or
fumes (and where other routes of exposure, for example, by swallowing or in contact with the skin do
not present any carcinogenic risk) the specific risk phrase R49 should be used.
111
para-Dichlorobenzene
4.79 A substance is included in Category 1 if there is sufficient evidence to
establish a causal association between human exposure and the
development of cancer on the basis of epidemiological data. The
existence of a causal relationship would be any of the following:
? an increased incidence of one or more cancer types in an exposed
population in comparison with a non-exposed population,
? evidence of dose-time-response relationships, that is, an increased
cancer incidence associated with higher exposure levels or with
increasing exposure duration,
? an association between exposure and increased risk observed in more
than one study,
? demonstration of a decline in risk after reduction of exposure, and
? specificity of any association, defined as an increased occurrence of
cancer at one target organ or of one morphological type.
CATEGORY 2
4.80.1 Substances are determined to be hazardous and classified as
Toxic (T) and assigned risk phrase R45 or R49 in accordance
with the criteria given below.
R45 MAY CAUSE CANCER
R49 MAY CAUSE CANCER BY INHALATION2
4.81 A substance is included in Category 2 if there is sufficient evidence, on
the basis of appropriate long term animal studies or other relevant
information, to provide a strong presumption that human exposure to
that substance may result in the development of cancer.
4.82 For classification as a Category 2 carcinogen either positive results in
two animal species should be available or clear positive evidence in
one species, together with supporting evidence such as genotoxicity
data, metabolic or biochemical studies, induction of benign tumours,
structural relationship with other known carcinogens, or data from
epidemiological studies suggesting an association.
2
For substances which present a carcinogenic risk only when inhaled, for example, dust, vapour or
fumes (and where other routes of exposure, for example, by swallowing or in contact with the skin do
not present any carcinogenic risk) the specific risk phrase R49 should be used.
112 Priority Existing Chemical Number 13
4.83 Human data providing suspicions of carcinogenic potential may
warrant a Category 2 classification irrespective of the nature of any
animal data. Increased confidence in the credibility of a causal
relationship would be provided by evidence of carcinogenicity in
animals and/or of genotoxic potential in short term screening tests.
CATEGORY 3
4.84 Substances are determined to be hazardous and classified as Harmful
(Xn) and assigned risk phrase R40 in accordance with the criteria
given below.
R40 POSSIBLE RISK OF IRREVERSIBLE EFFECTS
4.85 A substance is included in Category 3 if there is some evidence from
appropriate animal studies that human exposure can result in the
development of cancer, but this evidence is insufficient to place the
substance in Category 2.
Category 3 actually comprises 2 sub-categories
(a) substances which are well investigated but for which the
evidence of a tumour-inducing effect is insufficient for
classification in Category 2. Additional experiments would not
be expected to yield further relevant information with respect
to classification;
(b) substances which are insufficiently investigated. The available
data are inadequate, but they raise concern for humans. This
classification is provisional; further experiments are necessary
before a final decision can be made.
4.86 For a distinction between Categories 2 and 3 the arguments listed
below are relevant which reduce the significance of experimental
tumour induction in view of possible human exposure. These
arguments especially in combination, would lead in most cases to
classification in Category 3, even though tumours have been induced
in animals:
113
para-Dichlorobenzene
? carcinogenic effects only at very high dose levels exceeding the
'maximal tolerated dose'. The maximal tolerated dose is
characterised by toxic effects which, although not yet reducing
lifespan, go along with physical changes such as about 10%
retardation in weight gain,
? appearance of tumours, especially at high dose levels, only in
particular organs of certain species known to be susceptible to a
high spontaneous tumour formation,
? appearance of tumours, only at the site of application, in very
sensitive test systems (e.g. intraperitoneal, or subcutaneous
application of certain locally active compounds), if the particular
target is not relevant to humans,
? lack of genotoxicity in short-term tests in vivo and in vitro,
? existence of a secondary mechanism of action with the implication
of a practical threshold above a certain dose level (e.g. hormonal
effects on target organs or on mechanisms of physiological
regulation, chronic stimulation of cell proliferation),
? existence of a species-specific mechanism of tumour formation
(e.g. by specific metabolic pathways) irrelevant for humans.
NO CARCINOGEN CLASSIFICATION
4.87 For a distinction between Category 3 and no classification
arguments are relevant which exclude a concern for humans:
? a substance should not be classified in any of the categories if the
mechanism(s) of experimental tumour formation is/are clearly
identified, with good evidence that such mechanism(s) cannot be
extrapolated to humans for each tumour,
? if the only available tumour data are liver tumours in certain
sensitive strains of mice, without any other supplementary
evidence, the substance may not be classified in any of the
categories,
? particular attention should be paid to cases where the only
available tumour data are the occurrence of neoplasms at sites and
114 Priority Existing Chemical Number 13
in strains where they are well known to occur spontaneously with a
high incidence.
115
para-Dichlorobenzene
Appendix 3
Sample Material Safety Data Sheet for 1,4-Dichlorobenzene
Date of issue Page of Total
08 December 2000 1 6
1,4-Dichlorobenzene is classified as Hazardous according to the National Occupational Health
and Safety Commission's Approved Criteria for Classifying Hazardous Substances
[NOHSC:1008(1999)]
Company details
Company name
Address
State Postcode
Telephone number Emergency telephone number
Facsimile number Telex number
Identification
Product name
1,4-Dichlorobenzene
Other names
para-dichlorobenzene; p-dichlorobenzene; p-DCB; Di-Chloricide; Evola; Globol; NCI-C54955;
Para Crystals; Paracide; Paradow; Paramoth
Manufacturer's product code
UN number
3077
Dangerous goods class and subsidiary risk
Class 9 Environmentally Hazardous Substance
Hazchem code
None allocated
Poisons Schedule number
Schedule 5
Use
Air freshener, deodorant blocks, moth repellent
116 Priority Existing Chemical Number 13
Page of Total
2 6
Physical description and properties
Appearance
White or colourless crystalline solid with penetrating aromatic odour.
Melting point Boiling point
174.6oC
53.1癈 (127.4癋)
Vapour pressure
0.84 hPa at 20oC
Specific gravity
1.248 (water = 1)
Flashpoint
66oC (150癋) (closed cup)
Flammability limits
Not available
Solubility in water
60 to 70 mg/l (at 20oC)
Other properties
Odour: Aromatic odour.
Odour threshold: 0.18 ppm
Density: 1.248 g/cm3 (at 20癈)
Ignition temperature: >500oC
Ingredients
Chemical Name: 1,4-dichlorobenzene CAS Number: 106-46-7 Proportion:
117
para-Dichlorobenzene
Page of Total
3 6
Health hazard information
HEALTH EFFECTS
Acute
Inhalation: Low acute inhalation toxicity. Vapour may be irritating to the nose at 50 ppm or greater.
May cause headache, dizziness, nausea, vomiting and breathing difficulties. High doses may cause
depression of the central nervous system.
Skin: Low acute dermal toxicity in animal studies. May cause burning sensation on prolonged
contact with solid material.
Eye: Vapour irritating to the eyes at 50 ppm or greater.
Swallowed: Low acute oral toxicity. Symptoms may include, headache, nausea, vomiting and
anaemia.
Chronic
Skin: No evidence of sensitisation in animals or humans.
Systemic: In humans, ingestion over prolonged periods may cause reversible neurological
symptoms including unsteady gait, incoordination and paresthesia (tingling) of the limbs.
Haematological disorders can include anaemia. Has been shown to cause kidney tumours in rats by
ingestion and liver tumours in mice by ingestion and inhalation.
FIRST AID
Inhalation: Remove from exposure to fresh air immediately. Victim may appear intoxicated. Keep
warm and at rest until fully recovered. If breathing is laboured and patient cyanotic (bluish
colouration of skin and mucus membranes) give oxygen. If the victim is not breathing, clear airway
and apply artificial respiration. Call a doctor.
Skin: Remove contaminated clothing. Wash affected area immediately with copious quantities of
water and non-abrasive soap (at least 15 minutes). Seek medical attention if irritation develops.
Eye: Irrigate immediately with copious quantities of water or normal saline for at least 15 minutes.
Seek medical attention.
Swallowed: Do not give anything by mouth if victim is losing consciousness, unconscious or
convulsing. If more than 15 minutes from medical attention induce vomiting, preferable with
Ipecac Syrup APF. Do not give milk or oils. Seek medical attention.
Alcohol consumption may accelerate the onset and severity of symptoms caused by ingestion of p-
DCB.
Contact a Poisons Information Centre for further information.
ADVICE TO DOCTOR
Treatment is symptomatic and supportive. No specific antidote.
118 Priority Existing Chemical Number 13
Page of Total
4 6
Precautions for use
EXPOSURE STANDARD
Australian Exposure Standard: 75 ppm (451 mg/m3) TWA (8 hr), 110 ppm (661 mg/m3) STEL
ENGINEERING CONTROLS
Control airborne concentrations below the exposure standard.
Use only with adequate ventilation.
Local exhaust ventilation may be necessary for some operations.
PERSONAL PROTECTION
Wear overalls, rubber footwear, safety glasses and gloves in accordance with manufacturer's
recommendations. A respirator with full-face protection may be required where engineering
controls are inadequate, such as during clean-up of large spills.
An emergency eye wash station should be available in the immediate work area.
Self contained breathing apparatus (SCBA) and complete protective clothing should be worn during
fire fighting.
FLAMMABILITY
Combustible solid.
119
para-Dichlorobenzene
Page of Total
5 6
Safe handling information
STORAGE and TRANSPORT
Non-regulated goods. Store in a cool, dry place and out of direct sunlight and away from naked
flame and sources of ignition. Ensure adequate ventilation.
Store away from incompatible materials (see FIRE/EXPLOSION HAZARD).
SPILLS and DISPOSAL
Evacuate unprotected personnel from spillage area.
Shut off all possible sources of ignition following spillage.
Increase ventilation in contaminated area.
Clean-up personnel should wear self-contained breathing apparatus and full protective clothing.
Place collected material into metal or plastic containers and dispose of in accordance with all Local,
State and Federal regulations at an approved waste disposal facility.
FIRE/EXPLOSION HAZARD
Incompatible materials: organic peroxides and strong oxidising agents.
Vapour is heavier than air.
Toxic and irritant vapours and gases, including oxides of carbon, hydrogen chloride and phosgene,
may be formed on combustion.
Fire fighting:
? wear SCBA and complete protective clothing.
? Water fog, foam, alcohol foam, carbon dioxide or dry chemical extinguishing media may be
used.
120 Priority Existing Chemical Number 13
Page of Total
6 6
Other information
Animal toxicity data:
Acute (inhalation) LD50 (4hr): LC50 > 5.07 mg/litre (rat).
Acute (oral) LD50 : 3863 to 3790 mg/kg bw (rat).
Acute (dermal) LD50: >6000 mg/kg (rat).
Reproductive and developmental data: Negative results.
Mutagenic data: Negative results for mutagenicity by several test systems.
Environmental data:
1,4-Dichlorobenzene is moderately toxic to aquatic life.
Acute:
Daphnia magna 48h EC50 0.7 mg/L
Mysidopsis bahia 96h EC50 1.99 mg/L
Brachydanio rerio (Zebra fish) 96h LC50 2.1 mg/L
Pimephales promelas (Fathead minnow) 96h LC50 4.2 mg/L
Oncorhynchus mykiss (Rainbow trout) 96h LC50 1.12 mg/L
Further information:
National Industrial Chemicals Notification and Assessment Scheme, para-Dichlorobenzene -
Priority Existing Chemical Assessment Report No. 13 , NICNAS, Sydney, 2000.
Contact point
Contact name Telephone number
Position title
Address
State Postcode Country
121
para-Dichlorobenzene
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