Dense nonaqueous phase liquids (dnapls)

1,2-Dichlorobenzene

Human Health Toxicity

1,2-Dichlorobenzene (1,2-DCB) does not occur naturally, but is synthesized for use in the manufacture of a variety of oils, waxes, rubbers dyes, and asphalts. It is also generated as a byproduct of the manufacture of its more widely used isomer, 1,4-dichlorobenzene. 1,2-DCB is released to the environment via fugitive emissions during manufacture, industrial use, and disposal as an unwanted byproduct. The general population is exposed to 1,2-DCB via the inhalation of ambient air. Ingestion of 1,2-DCB via drinking water and food is not thought to be an important route of exposure for the general population. Occupational exposure to the compound is assumed to be via inhalation and dermal contact (ATSDR 2006).

It can be assumed that 1,2-DCB is absorbed as it has been found in human tissue after oral or inhalation exposure. Animal studies indicate rapid absorption via the lung and gastrointestinal tract. No studies are available that describe dermal absorption in either humans or laboratory animals. A rodent study suggests that once absorbed, 1,2-DCB achieves its highest concentrations in fat, kidney, bladder, and liver. 1,2-DCB is metabolized by cytochrome P450 enzymes to an epoxide that might react with cellular components or be metabolized further. Most 1,2-DCB metabolites are excreted in urine (ATSDR 2006).

Little information is available on the human health effects of 1,2-DCB, apart from reports of eye and respiratory tract irritation resulting from exposure to the vapor. Lesions of the nasal cavity and olfactory epithelium have been reported in rodents exposed to the chemical in vapor form. Acute and chronic laboratory rodent studies suggest that the liver is the primary target for 1,2-DCB toxicity, with high levels of exposure resulting in histological changes and necrosis. EPA's Integrated Risk Information System (IRIS) record for 1,2-DCB offers the following classification: "D; not classifiable as to human carcinogenicity; Based on no human data and evidence of both negative and positive trends for carcinogenic responses in rats and mice."

There are no human studies reporting developmental or reproductive toxicity of 1,2-DCB; however, laboratory rodent studies suggest that this compound does not exert adverse effects on reproduction or development. The compound gives both positive and negative results in standard genotoxicity tests; in three in vivo tests the compound yielded positive results, but negative results in the majority of mammalian and microbial in vitro assays.

EPA's maximum contaminant level (MCL) for 1,2-DCB in drinking water is 0.6 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	1.9 E+03 mg/kg
Industrial soil	9.8 E+03 mg/kg
Residential air	2.1 E+02 ug/m3
Industrial air	8.8 E+02 ug/m3
Tapwater	3.7 E+02 ug/L

References

1,2-Dichlorobenzene (CASRN 95-50-1)
U.S. EPA, Integrated Risk Information System (IRIS)

Toxicological Profile for Dichlorobenzenes
Agency for Toxic Substances and Disease Registry (ATSDR), 493 pp, 2006

This profile provides information on human health effects, fate and transport, production, and uses of all three dichlorobenzenes: 1,2-, 1,3-, and 1,4-DCB.

For Further Information

Update of the Public Health Goal (PHG) for 1,2-Dichlorobenzene, 08/13/09
CalEPA, Office of Environmental Health Hazard Assessment, 2009

1,2-Dichlorobenzene CAS No: 95-50-2
United Nations Environment Programme, OECD SIDS, 203 pp, 2001

Ecological Toxicity

Summaries of acute toxicity tests performed on aquatic species are presented in the Pesticides Action Network North America Pesticide Database. Ten species of fish were tested to determine the acute toxicity of 1,2-DCB. The compound was slightly toxic to four species (LC₅₀ values in the range 13 to 57.4 mg/L) and moderately toxic to the remaining six test species (LC₅₀ values in the range 1.7 to 9.6 mg/L) (Kegley et al. 2009).

No studies of the toxicity of 1,2-DCB to terrestrial ecological receptors were found, but a terrestrial toxicity reference value (TRV) for the rat has been derived (DOE 1999).

References

Ortho-dichlorobenzene: 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

Terrestrial Toxicity Reference Values
U.S. DOE
Manual ERD-AG-003 Revision 0 (TRVs), 1999

This 13-page Department of Energy manual provides toxicity reference values for earthworms, various mammals, and various bird species.