Dense Nonaqueous Phase Liquids (DNAPLs)

Halogenated Monoaromatics

Chlorobenzene

Human Health Toxicity

Chlorobenzene, also known as monochlorobenzene, is a synthetic chemical used as a feedstock for the production of other chlorinated compounds and as an industrial use solvent. The compound has use as a pesticide carrier and formerly had use as a carrier for PCBs.

Chlorobenzene is released to the atmosphere during its manufacture, industrial use, and agricultural applications. A small amount is also discharged to surface water. The compound has a moderate ability to bioaccumulate in tissue, but less than that of more highly chlorinated benzenes, such as the dichloro- or trichlorobenzenes (Malcolm et al. 2004, ATSDR 1990).

The general population can be exposed to chlorobenzene via inhalation of urban air and possibly from the ingestion of contaminated drinking water. Industrial use of the chemical provides potential for high exposure (ATSDR 1990).

Chlorobenzene is absorbed from the lung and intestinal tract of humans and laboratory animals. No studies of either humans or animals are available that describe dermal exposure to chlorobenzene and subsequent absorption through the skin. One laboratory rodent study indicates that the chemical is distributed to all tissues after inhalation exposure, but is preferentially distributed to fat. Human and animal studies suggest absorbed chlorobenzene can be eliminated from the body unchanged in expired air, and/or metabolized in liver by either oxidative pathways or conjugation reactions. Chlorobenzene-derived metabolites are excreted in urine (ATSDR 1990).

There are no reports that chlorobenzene has caused the death of humans by any route of administration, although studies are available that describe the lethality of high doses of the compound to laboratory animals. Case reports of chlorobenzene inhalation toxicity in human subjects describe neurological effects, including headache, dizziness, and sleepiness. Laboratory animal studies support the observation that chlorobenzene is neurotoxic. Although animal investigations have found that the compound exerts kidney and liver toxicity, no human studies are available that address these issues; however, based on animal investigations, liver and kidney toxicity could be a concern in humans (ATSDR 1990).

EPA's Integrated Risk Information System (IRIS) database classifies chlorobenzene as "D; not classifiable as to human carcinogenicity."

There are no case reports that identify chlorobenzene as a human developmental or reproductive toxicant, and results from animal studies appear to support this conclusion; however, animal fertility studies may be insufficiently sensitive to predict reproductive injury to humans (ATSDR 1990).

A majority of bacterial, yeast, and mouse lymphoma genotoxicity studies are negative for chlorobenzene, suggesting genotoxicity may not be a concern for humans exposed to this compound (IRIS, ATSDR 1990).

EPA's maximum contaminant level (MCL) for chlorobenzene in drinking water is 0.1 mg/L.

The Regional Screening Levels (formerly Preliminary Remediation Goals) posted by EPA Region 9 identify risk-based concentrations for 1,2-DCB for the following common exposure pathways:

Residential soil	2.9 E+02 mg/kg
Industrial soil	1.4 E+03 mg/kg
Residential air	5.2 E+01 ug/m3
Industrial air	2.2 E+02 ug/m3
Tapwater	9.1 E+01 ug/L

References

Chlorobenzene (CASRN 108-90-7)
U.S. EPA, Integrated Risk Information System (IRIS)

Chlorobenzenes Other Than Hexachlorobenzene: Environmental Aspects
Malcolm, H.M., P.D. Howe, and S. Dobson.
World Health Organization, Concise International Chemical Assessment Document 60, 2004

Toxicological Profile for Chlorobenzene
Agency for Toxic Substances and Disease Registry (ATSDR), 100 pp, 1990

Ecological Toxicity

Chlorobenzene is moderately toxic to an aquatic crustacean, the fleshy prawn, as well as moderately toxic to three zooplankton species: the opossum shrimp, and the water fleas Ceriodaphnia dubia and Daphnia magna. Of 11 fish species used to assess the acute toxicity of chlorobenzene, the compound was slightly toxic to seven, moderately toxic to three, and highly toxic to a single species (Kegley et al. 2009).

Very few studies are available that describe the toxicity of MCB to terrestrial organisms; however, the results of acute toxicity studies using four species of earthworms as test subjects are summarized in Malcolm et al. (2004).

References

Chlorobenzene: Identification, Toxicity, Use, Water Pollution Potential, Ecological Toxicity and Regulatory Information
Kegley, S.E., B.R. Hill, S. Orme, and A.H. Choi.
PAN Pesticide Database. Pesticide Action Network, San Francisco, CA, 2009

Chlorobenzenes Other Than Hexachlorobenzene: Environmental Aspects
Malcolm, H.M., P.D. Howe, and S. Dobson.
World Health Organization, Concise International Chemical Assessment Document 60, 2004