INDUSTRIAL CHEMICALS – POSSIBLE CARCINOGEN (IARC 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 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.
Regulations and Guidelines
No American Conference of Governmental Industrial Hygienists (ACGIH) TLVs (threshold limit values) or Occupational Exposure Limits (OELs) are available for BDCM.[6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] Nunavut and Saskatchewan list BDCM as a designated substance.[19,20]
Canadian Environmental Guidelines
|Canadian Drinking Water Guidelines||0.1 mg/L
(MAC for all THMs)
|Quebec’s Drinking Water Standards||MAC = 80 µg/L||2014|
|BC’s Contaminated Sites Regulation, BC Reg 375/96||
Sets soil standards for the protection of human health:
Drinking water: 100 μg/L*
Sets vapour standards for the protection of human health:
THMs = trihalomethanes
MAC = maximum allowable concentration
*Standard is specific for total trihalomethanes. Sum of the concentrations of bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (tribromomethane), and chloroform (trichloromethane) must not exceed the standard specified.
|Health Canada||NDSL* – Included||2005|
|National Classification System for Contaminated Sites||Rank = “High hazard”||2008|
* 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.
Canadian Production and Trade
No data regarding production or trade of bromodichloromethane in Canada was identified.
Environmental Exposures Overview
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).
For more information, see the environmental exposure estimate for BDCM.
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.
- Agency for Toxic Substance and Disease Registry (ATSDR). ToxFAQ Sheet for bromodichloromethane (PDF)
- International Programme on Chemical Safety (IPCS) INCHEM. Environmental Health Criteria 216. Disinfectants and Disinfectant By-Products (2000)
- International Agency for Research on Cancer (IARC). Monograph, Volume 52: Chlorinated Drinking Water (1991) (PDF)
- Health Canada. It’s Your Health: Drinking Water Chlorination (PDF)
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