Chlorination By-Products Environmental Exposures

Chlorination By-Products Environmental Exposures


Ingestion, inhalation and dermal absorption are all routes of exposure for the general public.[1] Canadians are exposed to Chlorination disinfection by-products (DBPs) by drinking treated water. People who drink treated water from above-ground reservoirs, lakes, or streams with no pre-treatment filtration of organic matter may be exposed to higher levels of DBPs.

Environmental estimates are available for the following chlorination by-products:

*Separate profiles are available for bromodichloromethane and chloroform and therefore are not included on this page.

Summaries of environmental concentration data are available for chlorination by-products 2,4,6-Trichlorophenol [PDF] and N-Nitrosomethylethylamine [PDF].


Exposure may also occur by breathing air while bathing or showering or using chlorinated pools and hot tubs. It is also possible via dermal absorption during these activities. Inhalation is reported to be a more significant route of exposure for swimmers, while exposure via dermal absorption is more important for hot tub users due to higher water temperatures.[2]

Health Canada conducted a national survey of DBP levels in treatment plants and distribution systems in 1993.[3] A more recent analysis of data from 1990 to 2004 looked at 135 large (> 5,000 people served) and 312 small (< 5,000 people served) water treatment plants in Canada. It found 12% of large systems and 44% of small systems had total HAAs above the guideline of 80 µg/L.[4]

The Municipal Water and Wastewater Survey is conducted annually by Environment Canada.[5] Responding is voluntary, so the data are limited.

In 2009, Statistics Canada completed a survey of DBP levels in approximately 2,600 drinking water plants in Canada for the years 2005, 2006 and 2007. Levels of total haloacetic acids, total trihalomethanes, and bromodichloromethane were reported by all surveyed facilities. Drinking water plants that serve fewer than 300 people were not included.[6]

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 chlorination by-products 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 dichloroacetic acid are provided below. Estimates for bromodichloromethane and chloroform are available on their substance profiles. For more information on supporting data and sources, click on the Methods and Data tab below.

Calculated Lifetime Daily Intake – Dichloroacetic acid

Lifetime Excess Cancer Risk (per million people) – Dichloroacetic acid

*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.


A national map on predicted annual average chloroform concentrations in outdoor air at residential locations is available on the chloroform profile.


Methods and Data

Our Environmental Approach page outlines the general approach used to calculate lifetime excess cancer risk estimates and includes documentation on our mapping methods.

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

Supplemental data – Dichloroacetic acid [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.