SUMMARY OF DATA FOR CHEMICAL SELECTION
Dibenzofuran
132-64-9
BASIS OF NOMINATION TO CSWG
Dibenzofuran is presented to CSWG for consideration based on the potential for widespread
human exposure and a lack of information on toxicity.
Worker exposure to dibenzofuran may occur through inhalation and dermal contact at sites
where coal tar, coal tar derivatives, or creosote are handled. The general population may be
exposed to dibenzofuran through contact with creosote-treated wood or inhalation of fly ash
particulates and emissions from municipal waste incinerators. Since dibenzofuran is a
contaminant often found in waste dumps and in water supplies, exposure through ingestion of
contaminated food products, e.g., fish, may also occur.
Despite significant human exposure, very little information on the toxicity of dibenzofuran was
found in the available literature. This limited information suggests that dibenzofuran may not
exhibit "dioxin-like" behavior.
INPUT FROM GOVERNMENT AGENCIES/INDUSTRY
Dibenzofuran was originally presented to the CSWG as a result of the Furans Class Study. In
August 1978, dibenzofuran was dropped as a candidate chemical for testing because it was being
studied by Litton Bionetics under contract to the Environmental Protection Agency (EPA). The
CSWG members felt that the Litton protocol was sufficient to meet the NCI standards since it
addressed both carcinogenicity and reproductive effects via the oral route of administration with
an adequate number of animals. Unfortunately, the Litton study was terminated several months
after exposure was initiated due to lack of funds (Beliles, 2000).
SELECTION STATUS
ACTION BY CSWG: 12/12/00
Studies requested:
Carcinogenicity
Short-term tests for chromosome aberrations
Priority: High
Rationale/Remarks:
Widespread human exposure as an environmental pollutant
Exposure as a contaminant of several products handled in the occupational setting
Human exposure occurs via multiple routes
Potential for carcinogenicity via epigenetic mechanisms not related to TCDD toxicity
CSWG suggested skin painting studies using the TGAC mouse, with the recommendation that
the FVB/N strain also be added
NCI will conduct the mouse lymphoma assay
Dibenzofuran
132-64-9
CHEMICAL IDENTIFICATION
CAS Registry Number: 132-64-9
Chemical Abstract Service Name: Dibenzofuran (8CI; 9CI)
Synonyms: 2,2-Biphenylene oxide, dibenzo(b,d)furan, diphenyl-
ene oxide
Structural Class: Polycyclic aromatic hydrocarbon (PAH); cyclic
ether
Structure, Molecular Formula and Molecular Weight:
O
C12H8O Mol. wt.: 168.19
Chemical and Physical Properties:
Description: White solid (Sigma-Aldrich, 2000)
86.5 癈 (Lide, 1995)
Melting Point:
287 癈 (Lide, 1995)
Boiling Point:
Solubility: Slightly soluble in water; soluble in ethanol and
acetone; very soluble in ether, benzene, and acetic
acid; sublimable (Elvers, 1989; Lide, 1995)
Density: 1.0886 at 99癈 (Lide, 1995)
Reactivity: Strong oxidation agent; stable at room temperature
in closed container (Fisher Scientific Canada, 1999)
Octanol/Water Partition Coefficient: Log Ko/w = 4.12 (NLM, 2000a)
0.0044 mm Hg at 25 癈 (NLM, 2000a)
Vapor Pressure:
Technical Products and Impurities: Dibenzofuran is available at 99+% purity from Sigma-
Aldrich (Sigma-Aldrich, 2000). Research grade dibenzofuran is also available from Acros,
Alfa Aesar, and TCI America (Alfa Aesar, 1999; Fisher Scientific, 2000; TCI America,
1998).
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EXPOSURE INFORMATION
Production and Producers: Dibenzofuran is recovered from a wash oil fraction of coal tar
that boils between 275 癈 and 290 癈. Redistillation separates dibenzofuran from
acenaphthene, which boils at a lower temperature. Crystallization of the redistilled
fraction then produces technically pure dibenzofuran (Elvers et al., 1989).
Dibenzofuran is supplied by twelve companies within the United States (Chemical
Sources International, 2000).
Dibenzofuran is listed in the EPA's Toxic Substances Control Act (TSCA) Inventory
(NLM, 1999).
Use Pattern: Dibenzofuran is found in various percentages in coal tars and coal tar
creosotes. Coal tar creosote is a complex mixture typically composed of 85% PAHs
and 2-17% phenolics. Typical wood preservative creosote is approximately 3.5%
dibenzofuran. Dibenzofuran occurs at levels of 0.19-1.50 wt % of dry tar in
commercial coal tars (ATSDR, 1990; NLM, 2000a).
Due to its high heat resistance, dibenzofuran, together with biphenyl, is a component of
heat-transfer oils. When combined with methylnaphthalenes, it is suitable as a carrier
for dyeing and printing textiles. A range of polymers can be produced from
dibenzofuran, e.g., heat-resistant polyarylacetylene and quinoxaline polymers or
photoconductive polymers for electrophotography (Elvers et al., 1989).
As a combustion product, dibenzofuran may be released from the incomplete
combustion of coal biomass, refuse, diesel fuel and residual oil, as well as from
tobacco smoke (NLM, 2000a).
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Human Exposure: Humans are exposed to dibenzofuran through inhalation of contaminated
air, ingestion of contaminated food, or dermal contact with some treated wood
products (NLM, 2000a).
Occupational Exposure. The National Occupational Exposure Survey (NOES), which
was conducted by the National Institute for Occupational Safety and Health (NIOSH)
between 1981-1983, estimated that 3,292 workers were potentially exposed to
dibenzofuran in the workplace. (NLM, 1999). Occupational exposure to dibenzofuran
may occur through dermal contact and inhalation, particularly at sites where coal tar
and coal tar derivatives, especially creosote, are used (NLM, 2000a).
General Population Exposure. The general population may be exposed to
dibenzofuran through inhalation of air which has been contaminated by a variety of
combustion sources. Assuming an average ambient air concentration of 19 ng/m3, the
average daily air intake of dibenzofuran is 380 ng (NLM, 2000a).
There should be very little exposure of the average homeowner to creosote solutions
[containing dibenzofuran] used for wood treatment because they can only be sold to
certified applicators. However, homeowners can be exposed to creosote-treated
products (ATSDR, 1990).
In the EPA's National Human Adipose Tissue Survey, 46 composite samples of human
adipose tissue representing various age groups and locations were analyzed. Three
percent of these samples contained dibenzofuran (NLM, 2000a).
Environmental Exposure. Exposure to dibenzofuran may occur through consumption
of contaminated food and drinking water. Dibenzofuran was qualitatively detected in
catfish from the Black River near Lorain, Ohio, and in Potomac River bass.
Dibenzofuran was qualitatively identified in drinking water collected from Cincinnati,
Ohio in October 1978 and Philadelphia, Pennsylvania in February 1976 (NLM, 2000a).
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The concentration of dibenzofuran detected in Finnish margarines and vegetable oils
ranged from 0.08 to 0.64 礸/kg. The mean concentration in various Finnish cereal
products ranged from 1.0 (wheat) to 4.7 礸/kg (bran) (NLM, 2000a).
Environmental Occurrence:
Dibenzofuran is a common component of environmental pollutants, and has been
identified in air, ground water, fuel gas, fly ash from municipal incinerators, and diesel
exhaust gas particulates, and cigarette smoke (Watanabe, 1992).
Water. Dibenzofuran has been detected in the surface waters of Lake Erie and is one of
28 aromatic compounds regularly detected in surface sediments from the Elizabeth
River, which flows into the Chesapeake Bay. Dibenzofuran (1.70 and 9.50 ppm) was
found in sediment from two of five Great Lakes tributaries. Dibenzofuran has also
been found in sediments collected from Lake Pontchartrain, Eagle Harbor (Puget
Sound area), the Black River, the Martha's Vineyard area, and in sediment cores in
various northern New Jersey waterways (NLM, 2000a; Padma et al., 1999).
Dibenzofuran was also found in tissue of snails obtained from two different sites in
Pensacola, Florida as well as in sediment taken from the Black River (Rostad &
Pereira, 1987; West et al., 1988).
Concentrations of dibenzofuran ranging 0.008 - 0.42 ppm were detected in ground
water beneath an abandoned creosote plant in Texas. Dibenzofuran was also found at
concentrations of 0.01 - 0.49 ppm beneath a wood preserving facility in Florida and
was detected qualitatively in ground water beneath a coal-tar distillation facility in
Minnesota (NLM, 2000a).
Hazardous waste sites. Dibenzofuran is a component of coal tar. Prior to the
development of a nationwide gas pipeline system, gas was produced locally by coal
distillation. The coal tar residue not sold for roofing and road surfacing materials was
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disposed of at sites near the gasification plants. There are approximately 1,500 coal tar
waste sites in the United States (Culp et al., 1998).
Air. The total releases and transfers of dibenzofuran listed in EPA's Toxic Release
Inventory for 1994 were reported as 26,116 pounds and 53,744 pounds, respectively
(EPA, 1994). In 1998, the Toxic Release Inventory reported that total on-site releases
of dibenzofuran were 150,929 pounds (air emissions - 94,230 pounds; releases to land -
56,670 pounds; surface water discharges - 29 pounds) and total off-site releases were
13,304 pounds. For creosote, total on-site releases in 1998 were 3,072,169 pounds
and total offsite releases were 1,263,532 pounds (EPA, 1998).
Atmospheric sampling of dibenzofuran was performed between November 1988 and
February 1989 in Minneapolis and Salt Lake City. Levels ranged from 6.5 - 31 ng/m3
in Minneapolis and 10 -76 ng/m3 in Salt Lake City. The concentration of dibenzofuran
in the gas-phase in the ambient air of Portland, Oregon in February to April 1984 was
13 - 25 ng/m3 (mean 19 ng/m3) but the concentration in the particulate phase was only
0 - 0.35 ng/m3 (mean 0.1 ng/m3) (NLM, 2000a).
Regulatory Status: Dibenzofuran is cited in the Clean Air Act 1990 Amendments -
Hazardous Air Pollutants as a volatile hazardous air pollutant of potential concern.
The Superfund Amendment Reauthorization Act (SARA) Section 110 placed
dibenzofuran on the revised Agency for Toxic Substances and Disease Registry
(ATSDR) priority list of hazardous substances to be the subject of a toxicological
profile. The listing was based on the substance's frequency of occurrence at
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)
National Priorities List sites, its toxicity, and/or its potential for human exposure.
Dibenzofuran is also listed in the Massachusetts Substance List for Right-to-Know
Law, the New Jersey Department of Health Hazard Right-to-Know Program
Hazardous Substance List, and the Pennsylvania Department of Labor and Industry
Hazardous Substance List. California's Air Toxics "Hot Spots" List (Assembly Bill
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2588) and EPA's Toxic Release Inventory Chemicals also list dibenzofuran as a
hazardous air pollutant (EDF, 1998; EPA, 1998; STN, 2000).
No standards or guidelines have been set by NIOSH or the Occupational Safety and
Health Administration (OSHA) for occupational exposure to or workplace allowable
levels of dibenzofuran. Dibenzofuran was not on the American Conference of
Governmental Industrial Hygienists (ACGIH) list of compounds for which
recommendations for a Threshold Limit Value (TLV) or Biological Exposure Index
(BEI) are made. The OSHA standard for coal-tar pitch volatiles (which contain a small
amount of dibenzofuran) in workroom air is a 0.2 mg/m3 time-weighted average
(ATSDR, 1990).
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EVIDENCE FOR POSSIBLE CARCINOGENIC ACTIVITY
Human Data: No epidemiological studies or case reports investigating the association of
exposure to dibenzofuran and cancer risks in humans were identified in the available
literature.
Animal Data: No 2-year carcinogenicity studies of dibenzofuran in animals were identified
in the available literature.
According to the International Agency for Research on Cancer (IARC), the available
data indicate that coal-tars and coal-tar pitches are causally associated with cancer in
humans and that creosotes derived from coal-tars are probably carcinogenic to humans
(IARC, 1984).
To determine the contribution of benzo[a]pyrene to the carcinogenicity of coal tar,
mice were fed two coal tar mixtures or benzo[a]pyrene in a 2-year bioassay. The coal
tar diets induced a dose related increase in tumors at multiple sites. Although the
benzo[a]pyrene present in the two coal tar mixtures could have accounted for the
forestomach tumors observed, the lung and liver tumors appeared to be due to other
components in the coal tar mixture and the small intestine tumors may have resulted
from chemically-induced cell proliferation that occurred at high doses of coal tar.
Although the coal tar mixtures contained 1,504 or 1,810 mg/kg of dibenzofuran,
respectively, they also contained mutagenic PAHs which could have accounted for the
observed lung and liver tumors (Culp et al., 1998; Goldstein et al., 1998).
Short-Term Tests:
Dibenzofuran has been evaluated for mutagenic activity in the Ames
assay. Dibenzofuran did not induce genotoxicity with or without metabolic activation
in Salmonella TA98 at concentrations from 0.025-1.6 祄ol/plate and TA100 at
concentrations from 0.05- 4.0 祄ol/plate (Matsumoto et al., 1988). In a separate
study by Mortelmans and coworkers (1984), dibenzofuran did not induce
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mutagenicity in Salmonella strains TA98, TA100, TA1535, or TA1537 in the
absence and presence of S-9. These results are consistent with the results reported
by Uno and coworkers (1991), as well as Schoeny (1982).
Metabolism: No information on the metabolism of dibenzofuran in mammalian organisms
was found in the available literature. The bacteria Sphingomonas, Brevibacterium,
Terrabacter, and Staphylococcus auricularis degrade dibenzofuran to 2,2',3-
trihydroxybiphenyl via dibenzofuran 4,4a-dioxygenase (Bunz & Cook, 1993; Ouelette
& McLeish, 2000).
Other Biological Effects:
Enzyme Induction. The P450 superfamily contains the principal enzymes responsible
for the metabolic activation of carcinogens. In the P4501A family, CYP1A1 and
CYP1B1 metabolize and participate in the metabolic activation of PAHs. CYP1A2
catalyzes aromatic and heterocyclic amine N-oxidation, and has been implicated as a
risk factor in urinary bladder and colorectal cancer (Gonzalez & Kimura, 1999;
MacLeod et al., 1997).
Chaloupka and coworkers investigated manufactured gas plant PAH mixtures in
B6C3F1 mice. This residue contained a complex mixture of 2-ring, 3-ring and 4-ring
PAHs which induced hepatic CYP1A1 and CYP1A2 gene expression. However, the
3-ring mixture, which contained dibenzofuran and five other PAHs induced only
CYP1A2. All six tricyclic PAHs significantly induced hepatic microsomal
methoxyresorufin O-de-ethylase (MROD) activity, a more specific indicator of
CYP1A2 activity than ethoxyresorufin O-de-ethylase (EROD) activity, although
acenaphthylene and anthracene were more active than dibenzofuran (Chaloupka et al.,
1994; Chaloupka et al., 1995).
Aryl Hydrocarbon (Ah) Receptor Binding Studies. An important criterion to define
whether dibenzofurans and dibenzodioxins exhibit "dioxin-like" toxicity is Ah receptor
binding (EPA, 2000).
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In competitive binding studies using mouse hepatic cytosol, the tricyclic PAHs,
including dibenzofuran, did not displace TCDD from the Ah receptor or
benzo[a]pyrene from the 4S carcinogen binding protein. Thus, tricyclic PAHs appear
to induce hepatic CYP1A2 gene expression in mice by an Ah receptor-independent
pathway (Chaloupka et al., 1994; Chaloupka et al.,1995).
Immunotoxicity. A reconstituted PAH mixture containing 17 congeners, including
dibenzofuran, and the 2-, 3-, and 4-ring PAH fractions all caused a dose-dependent
decrease in the splenic plaque-forming cell response of B6C3F1 mice to sheep red
blood cells or trinitrophenyl-lipopolysaccharide antigens (Harper et al., 1996). While
this response may occur with "dioxin-like" PAHs, it cannot be attributed to
dibenzofuran because of the other PAHs present in the mixtures.
Structure-Activity Relationship: Chemicals structurally similar to dibenzofuran were
screened for relevant information associating these chemicals with mutagenic or
carcinogenic effects. Dibenzo-p-dioxin was found to be the most structurally related
compound to dibenzofuran. The structure of dibenzo-p-dioxin is shown below:
O
O
A bioassay of unsubstituted dibenzo-p-dioxin was conducted in Osborne-Mendel rats
and B6C3F 1 mice. Groups of 35 rats of each sex were administered dibenzo-p-dioxin
at 5,000 or 10,000 ppm in feed for 110 weeks. Groups of 50 mice of each sex were
administered the same doses in feed for 87 or 90 weeks. Controls consisted of groups
of 35 untreated rats of each sex and 50 untreated mice of each sex. No tumors were
induced in rats or mice of either sex at incidences that were significantly higher in the
dosed groups than in the corresponding control groups. Thus, it was concluded that
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under the conditions of the bioassay, dibenzo-p-dioxin was not carcinogenic (NTP,
1979).
Dibenzo-p-dioxin was negative in the Ames Salmonella strains TA98 and TA100 with
or without S-9 activation (NLM, 2000b).
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3-nitrodibenzofuran and 3-aminodibenzofuran. Toxicol. Lett., 55, 31-37
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