U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Toxicology

Halogenated Alkanes

Dibromochloromethane

Human Health Toxicity

Dibromochloromethane (DBCM) is a byproduct of chlorine disinfection of raw source water before domestic use. This compound is not manufactured in the United States. The general population is exposed to DBCM via the ingestion of drinking water, from inhalation of the volatilized compound from shower and bath water, and by dermal contact when bathing or showering (ATSDR 2005).

DBCM is readily absorbed through the gastrointestinal tract and also can be absorbed through the skin and respiratory tract. After absorption, it is distributed throughout the body. The compound is metabolized in the liver by the cytochrome P 450 mixed-function oxidase enzymes, resulting in the generation of a highly reactive intermediate metabolite. The ultimate metabolic products of DBCM metabolism include carbon dioxide and carbon monoxide (ATSDR 2005).

Short- and long-term laboratory animal studies strongly suggest that the liver is the critical target organ for DBCM toxicity. Fatty changes are seen in the liver, and at a sufficient dose, necrosis. DBCM has been reported as causing kidney damage in mice. Several studies suggest a positive association between the consumption of chlorinated drinking water containing disinfection by-products and the incidence of human cancers of the colon, rectum, and bladder; however, the presence of several trihalomethanes (THMs) in chlorinated water prevents the assessment of the carcinogenicity of a single compound, such as DBCM, in this medium. Animal studies show that a strain of mice dosed with the chemical developed liver cancers, but this effect was not seen in rats. EPA's Integrated Risk Information System (IRIS) classifies the compound as "C; possible human carcinogen, based on inadequate human data, limited evidence of carcinogenicity in animals, positive mutagenicity data and structural similarity to THMs that are known to be animal carcinogens."

Existing epidemiological studies of the pregnancy outcomes of women exposed to THMs in drinking water are inadequate to establish a causal relationship between DBCM and reproductive and/or developmental toxicity. Animal studies suggest that high dose exposure to could reduce fertility and might be toxic to the developing fetus, but the data are insufficient to make firm conclusions (ATSDR 2005).

DBCM shows positive results for genotoxicity in both in vitro and in vivo assays (ATSDR 2005).

As of 2010, EPA has not developed a maximum contaminant level (MCL) for DBCM alone, but the total annual average trihalomethane amount for bromoform, chloroform, bromodichloromethane, and dibromochloromethane together should not exceed 80 mg/L for safe drinking water. The non-enforceable maximum contaminant level goal (MCLG, i.e., the level of a contaminant in drinking water below which there is no known or expected risk to health) for DBCM is 0.06 mg/L.

References

Toxicological Profile for Bromoform and Chlorodibromomethane
Agency for Toxic Substances and Disease Registry (ATSDR), 273 pp, 2005

Stage 1 Disinfectants and Disinfection Byproducts Rule
U.S. EPA, Office of Water. EPA 816-F-01-014, 4 pp, 2001

Ecological Toxicity

The Pesticide Action Network Pesticides Database cites studies of the effects of DBCM on various life stages of amphibians and zooplankton. In addition, the database reports that the compound is slightly toxic to one species of fish (Kegley et al 2010).

No information is available regarding the toxicity of DBCM to terrestrial species; however, DOE (1999) provides a toxicity reference value.

References

Chlorodibromomethane: 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, 2010

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.



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