Chloroform Environmental Exposures

Chloroform Environmental Exposures


The primary source of environmental exposure to chloroform is ingestion via chlorinated drinking water.[1] Chloroform is produced during drinking water treatment through the reaction between chlorine and decomposing organic material.[2] Typical concentrations of chloroform in Canadian chlorinated water range from 10 to 90 µg/litre (or parts per billion, ppb).[3,4]


Chlorinated water can also release aerated chloroform (e.g. during showering), creating an inhalation risk.[1,5] Dermal absorption of chloroform from water can also occur.[1,5] Once present, chloroform may persist in groundwater for many years,[6] but it does not bioaccumulate in aquatic animals.[4] CAREX Canada’s environmental estimates indicate that chloroform levels in Canadian drinking water and indoor air result in higher risks of cancer (moderate data quality). Estimates for outdoor air show that chloroform levels likely do not result in lifetime excess cancer risks higher than 10 cases per million people (high data quality).

Most chloroform in the environment is released by industrial sources, including pulp and paper mills, municipal wastewater treatment plants, chemical manufacturing plants, and waste incinerators.[3] Although chloroform is not produced in Canada, it enters the environment through industrial releases and long range atmospheric transport from other non-Canadian cities.[3] Chloroform has been detected in Canadian air, surface water, and groundwater samples.[2] Indoor air concentrations tend to be higher than outdoor air concentrations.[7] Nationwide testing of indoor chloroform levels have not been conducted since 1996.[2] However, a study conducted in Quebec City in 2005 found that of 96 homes tested, all had detectable levels of chloroform with a mean level of 3.2 µg/m3in the winter.[8] Another study conducted in Windsor, Ontario, in 2005 monitored approximately 50 homes and found slightly lower average indoor levels of chloroform in the winter (1.1 µg/m3).[7]

In 2001, it was estimated that the average Canadian daily exposure to chloroform was between 0.6 and 10.3 µg/kg (by weight) per day; the highest exposure based on body weight was calculated for infants who were formula fed.[2]

Searches of Environment Canada’s National Pollutant Release Inventory (NPRI) and the US Household Products Database yielded the following results on current potential for exposure to chloroform in Canada:

NPRI and US Household Products Database

NPRI 2015[9]
Search term: ‘chloroform’
Category Quantity Industry
Released into Environment 55 t Pulp & paper mills, chemical manufacturers,
and water and waste treatment
facilities (9 facilities)
Disposed of 6.1 t
Sent to off-site recycling None t
t = tonne
US Household Products 2016[10]
Search Term Quantity Product Type
‘chloroform’ 1 adhesive remover


This map shows predicted levels of chloroform in outdoor air at residential locations by health region in Canada as of 2011. The average (median) concentration of chloroform within the health regions measured in outdoor air for 2011 was 0.085 µg/m3, but concentrations of chloroform can be higher or lower than average in many locations. Concentrations should be compared to the applicable jurisdictional guidelines and standards for ambient air quality based on chronic, carcinogenic effects (or non-carcinogenic effects, if cancer is not the point of interest).

Predicted annual average chloroform concentrations in outdoor air at residential locations by health region, 2011


*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011

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 chloroform in relevant exposure pathways (outdoor air, indoor air, 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 chloroform 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 and includes documentation on our mapping methods.

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

Supplemental data – Chloroform [PDF]


1. National Toxicology Program (NTP). 14th report on carcinogens for Chloroform (2016) (PDF)
4. World Health Organization (WHO). CICAD 58: Chloroform. Geneva (2004) (PDF)
6. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Chloroform (1997) (PDF)
7. Khanchi A, Hebbern CA, Zhu J, Cakmak S.“Exposure to volatile organic compounds and associated health risks in Windsor, Canada.” Atmospheric Environment 2015;120:152-9.
8. Héroux MÈ, Gauvin D, Gilbert NL, Guay M, Dupuis G, Legris M, Lévesque B.“Housing characteristics and indoor concentrations of selected volatile organic compounds (VOCs) in Quebec City, Canada.” Indoor and Built Environ 2008;17(2):128-37.
9. Environment and Climate Change Canada. National Pollutant Release Inventory Facility Search (Substance name: ‘Chloroform’)
10. US Household Products Database (HPD). Household Products (Search term: ‘Chloroform’)

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