Industrial Chemicals– Possible Carcinogen (IARC 2B)
CAS No. 75-27-4
Photo: Wikimedia Commons
IARC Monograph Vol. 71, 1999 (Group 2B)
Bromodichloromethane (BDCM) is a colourless, non-flammable liquid. BDCM is one of a group of compounds called trihalomethanes (THMs) commonly found as by-products of drinking water chlorination. BDCM is formed when chlorine reacts with organic matter in the presence of bromine. It is also naturally produced in small amounts by marine algae.
Other trihalomethanes include chloroform, dibromochloromethane, and bromoform. CAREX Canada reviewed Canadian exposure to chloroform as well as chlorination disinfection by-products as a group; please see the specific carcinogen profiles for more information.
Bromodichloromethane may also be referred to as dichlorobromomethane. There are numerous other synonyms and product names; see the Hazardous Substances Data Bank (HSDB) for more information.
Bromodichloromethane is classified by the International Agency for Research on Cancer (IARC) as Group 2B, possibly carcinogenic to humans, based on data in experimental animals. BDCM is an intestinal and kidney carcinogen in rats and mice. The incidence of liver tumours was also elevated in female mice.
Although several epidemiological studies suggest an association between chlorinated water containing BDCM and increased cancer rates, none have been able to control sufficiently for confounding variables such as other chlorination by-products.
There is some indication from animal studies that BDCM and other THMs containing bromine may be more toxic than those containing chlorine. Further study is needed to confirm these additional health outcomes. Similarly, exposures to high levels of BDCM have been linked to increases in adverse reproductive effects including spontaneous abortion or stillbirth, however evidence is insufficient to determine causality. High doses of BDCM are also linked to central nervous system disturbances.
No American Conference of Governmental Industrial Hygienists (ACGIH) TLVs (threshold limit values) or Occupational Exposure Limits (OELs) are available for BDCM. Nunavut and Saskatchewan list BDCM as a designated substance.
Bromodichloromethane was not included in other Canadian government environmental guidelines reviewed.[10,11,12,13,14]
NDSL* - Included
National Classification System for Contaminated Sites
Rank = "High hazard"
* The Non-Domestic Substances List (NDSL) is an inventory of substances included in the EPA's Toxic Substances Control Act (TSCA), but not on Canada's DSL. The substances are acknowledged to be in use internationally but requirements for information are less rigorous than those of the DSL.
Bromodichloromethane was not included in other Canadian government chemical listings reviewed.[18,19,20,21]
BDCM is typically produced in small quantities and used primarily to produce organic chemicals and to act as a reagent in laboratory research. It has also been used to separate minerals and salts because of its solvent properties.
Canadian Production and Trade
No data regarding production or trade of bromodichloromethane in Canada was identified.
CAREX Canada assessed BDCM as a low priority agent for occupational settings due to limited exposure circumstances in workplaces. Because BDCM is a chlorination by-product, there is potential for exposure for lifeguards, swim instructors, and maintenance workers who are exposed via chlorinated swimming pools and hot tubs. Some research workers may also be exposed to BDCM when it is used to synthesize organic chemicals.
CAREX Canada has not prioritized BDCM for exposure estimate development. This is because the likelihood of exposure in Canadian workers is very low.
The most important exposure route for the general public is ingesting chlorinated water. Both dermal and inhalation exposure are also important routes when showering and engaging in competitive swimming. CAREX Canada's environmental estimates indicate that BDCM levels in indoor air result in increased risks of cancer (moderate data quality).
BDCM levels are usually higher in treated surface water compared to treated groundwater because there is more organic matter in surface water. Concentrations of BDCM are also higher in summer months as warm temperatures contribute to increased organic matter and thus increased formation of disinfection by-products in surface water.
Most water treatment plants across Canada are able to uphold the maximum allowable concentration (MAC, listed above) for BDCM in drinking water, with concentrations well below the national guidelines. A few small community systems (providing water to <4% of Canadians), however, have average levels above the Canadian guidelines. Smaller treatment systems have limited ability to remove organic matter before treating with chlorine, which increases the production of BDCM. CAREX Canada's environmental estimates indicate that BDCM levels in Canadian drinking water result in higher risks of cancer (moderate data quality).
No Canadian data on concentrations of BDCM in foods or beverages were identified. However, using data from the US Food and Drug Administration (FDA), CAREX Canada estimates that BDCM levels in food and beverages do not result in elevated cancer risk (very low data quality).
Our team has performed a detailed scan of exposure control resources and assembled a compilation of key publications and resources. These are organized by type of exposure (environmental or occupational) and by specificity (general or carcinogen-specific). Please visit our Exposures Reduction Resources page to view. We have also developed a series of resources on environmental health with and for First Nations groups, and one of these is entitled "Drinking water chlorination - What are the risks?". This resource is available via our Environmental Health Resources for First Nations page.
We also recommend exploring the Prevention Policies Directory, a freely-accessible online tool offering information on policies related to cancer and chronic disease prevention. Providing summaries of the policies and direct access to the policy documents, the Directory allows users to search by carcinogen, risk factor, jurisdiction, geographical location, and document type. Click here to learn more about policies specific to BDCM in the Directory. For questions about this resource, please contact a member of the Prevention Team at the Canadian Partnership Against Cancer at firstname.lastname@example.org.