Bromodichloromethane Environmental Exposures

Bromodichloromethane Environmental Exposures


The most important exposure route for the general public is ingesting chlorinated water.[1] Both dermal and inhalation exposure are also important routes when showering[1] and engaging in competitive swimming.[2] CAREX Canada’s environmental estimates indicate that bromodichloromethane (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.[3] 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.[3]

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.[3] 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.[3] 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).

Cancer Risk Estimates

Potential lifetime excess cancer risk (LECR) is an indicator of Canadians’ exposure to known or suspected carcinogens in the environment. When potential LECR is more than 1 per million in a single pathway, a more detailed risk assessment may be useful for confirming the need to reduce individual exposure. If measured levels of BDCM in relevant exposure pathways (drinking water, and food and beverages) decrease, the risk will also decrease.

Potential LECR is calculated by multiplying lifetime average daily intake (the amount inhaled or ingested) by a cancer potency factor or unit risk factor. More than one cancer potency factor may be available, because agencies interpret the underlying health studies differently, or use a more precautionary approach. Our results use cancer potency factors from Health Canada, the US Environmental Protection Agency (US EPA), and/or the California Office of Environmental Health Hazard Assessment (OEHHA).

The calculated lifetime daily intake and LECR results for BDCM are provided in the tables below. For more information on supporting data and sources, click on the Methods and Data tab below.

Calculated Lifetime Daily Intake

Lifetime Excess Cancer Risk (per million people)

*LECR based on average intake x cancer potency factor from each agency

Compare substances: Canadian Potential Lifetime Excess Cancer Risk, 2011

The data in this table are based on average intake and Health Canada’s cancer potency factor, assuming no change in measured levels. When Health Canada values are not available, United States Environmental Protection Agency values are used.
Click the second tab to view LECR data. 

**Exposure not applicable: For indicated pathways, substance not present, not carcinogenic, or exposure is negligible
**Gap in data: No cancer potency factor or unit risk factor, or no data available
IARC Group 1 = Carcinogenic to humans, IARC Group 2A = Probably carcinogenic to humans, IARC Group 2B = Possibly carcinogenic to humans
NOTE: Chromium (hexavalent) estimates assume that 5% of total chromium measured in outdoor air is hexavalent and 8% total chromium measured in indoor dust is hexavalent. 

Potential LECR assumes exposure occurs at the same level, 24 hours per day, for 70 years. This is rarely true for any single individual, but using a standard set of assumptions allows us to provide a relative ranking for known and suspected carcinogens across different exposure routes. While ongoing research continually provides new evidence about cancer potency and whether there is a safe threshold of exposure, our approach assumes there are no safe exposure levels.

Methods and Data

Our Environmental Approach page outlines the general approach used to calculate lifetime excess cancer risk estimates.

Data sources and data quality for bromodichloromethane can be found in the PDF below.

Supplemental data – Bromodichloromethane [PDF]


1. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for bromodichloromethane (1989) (PDF)
2. Lindstrom, AB et al. “Alveolar breath sampling and analysis to assess trihalomethane exposures during competitive swimming training.” Environmental Health Perspectives, 1997;105(6):636-642.(PDF)

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As a national organization, our work extends across borders into many Indigenous lands throughout Canada. We gratefully acknowledge that our host institution, the University of British Columbia Point Grey campus, is located on the traditional, ancestral and unceded territories of the xʷməθkʷəy̓əm (Musqueam) people.