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The Ministers of Environment and Health have released for final publication the assessment report for the priority substance chloroform. Notice concerning the assessment of this substance and a summary of its assessment report was published in the Canada Gazette, Part 1 March 24, 2001. The synopsis of the report is provided below.

A draft of this Assessment Report was made available for a 60-day public comment period (June 3, 2000 - August 2, 2000). No comments were received during this period.

For paper copies of the Full Assessment Report, please contact the Inquiry Centre at Environment Canada:

To obtain an electronic version of the Assessment Report in PDF, please request a copy from the following address: ESB.DSE@ec.gc.ca

Synopsis

Chloroform is used as a solvent and in the production of other chemicals. Its use as the feedstock for polytetrafluoroethylene and other fluoropolymers is increasing at approximately 4–6% per year. Significant releases of chloroform arise indirectly through reactions of chlorine with organic chemicals and as a by-product during the addition of chlorine to drinking water and wastewaters for disinfection. Although no manufacturing occurs in Canada, chloroform may still enter the environment through use and from deliberate and accidental release, as well as from long-range transport.

The majority of environmental releases of chloroform are to the atmosphere. In the troposphere, chloroform may be degraded by reaction with hydroxyl radicals or transported to the surface via washout. Chloroform released to surface waters or soil will be transported to the air because of its high volatility. It does not partition significantly from air to soils, sediments or tissues because of its low affinity for organic carbon and lipids. Chloroform may be quite persistent in groundwater because volatilization is limited, as there is no contact with air, and biodegradation is slow under anaerobic conditions and almost non-existent under most aerobic conditions. Chloroform does not appear to bioconcentrate in aquatic organisms to any significant extent, an observation that is consistent with its octanol/water partition coefficient (log K_ow = 1.97).

Chloroform has been detected in air, surface water, groundwater and drinking water in Canada.

Data on toxicity are available for microorganisms, algae, aquatic invertebrates, fish, amphibians and laboratory mammals. No data on toxicity were identified for birds or wild mammals. Chloroform in Canadian air, surface water and groundwater does not appear to pose significant risks to populations of terrestrial wildlife or aquatic biota.

Chloroform is not an effective agent of stratospheric ozone depletion, since net chlorine loading in the stratosphere from the substance itself and its degradation products is small. Chloroform does not contribute significantly to climate change or to ground-level ozone formation.

The general population in Canada is exposed to chloroform principally through inhalation of indoor air and ingestion of tap water. Estimated intake from a single daily 10-minute shower exceeds that from all other exposure pathways.

Chloroform has induced liver tumours in mice and renal tumours in mice and rats. The weight of evidence, which is strongest for hepatic and renal tumours in mice and more limited for renal tumours in rats, indicates that chloroform may be carcinogenic only at concentrations that induce the obligatory precursor lesions of cytotoxicity and proliferative regenerative response. This cytotoxicity is primarily related to rates of formation of reactive, oxidative metabolites, principally phosgene.

Non-cancer effects observed most consistently at lowest concentrations or doses following repeated exposures of rats and mice to chloroform are sustained cytotoxicity and persistent regenerative proliferation. As for cancer, target organs are the liver (centrilobular region) and kidney (cortical region). In addition, chloroform has induced nasal lesions in rats and mice exposed by both inhalation and ingestion at lowest concentrations or doses.

Modelled tissue dose measures for a 24-hour exposure scenario for the general population of Canada are less than those associated with values considered appropriate as Tolerable Concentrations/Doses for cancer and non-cancer effects. A Tolerable Concentration is the level to which it is believed a person may be exposed daily over a lifetime without deleterious effect.

Based on the information available, it is concluded that chloroform is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity; constitute or may constitute a danger to the environment on which life depends; or constitute or may constitute a danger in Canada to human life or health. Therefore, chloroform is not considered to be "toxic" as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999), and evaluation of options under CEPA 1999 to reduce exposure is not considered a priority at this time. However, this is based on current use patterns; thus, future releases of this compound should continue to be monitored to ensure that exposure does not increase to any significant extent.

In view of the fact that showering is estimated to be the single greatest contributor to total daily intake of chloroform from drinking water, measures to reduce uptake from this source will be most effective in minimizing exposure of the general public.