Page 3: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Carbon Tetrachloride

Part I. Overview and Application - Continued

2.0 Executive summary

Carbon tetrachloride is an ozone-depleting substance, and its production and consumption are controlled following an international agreement (the Montreal Protocol). It was phased out in Canada in 1996, but can still be imported for limited use in chemical production. In the environment, it is found mainly in air, primarily from direct releases to the atmosphere.

Health Canada recently completed its review of the health risks associated with carbon tetrachloride in drinking water. This Guideline Technical Document reviews and assesses all identified health risks associated with carbon tetrachloride in drinking water, incorporating multiple routes of exposure from drinking water, including ingestion and both inhalation and skin absorption from showering and bathing. It assesses new studies and approaches, and takes into consideration the availability of appropriate treatment technology. From this review, a guideline for carbon tetrachloride in drinking water is established as a maximum acceptable concentration (MAC) of 0.002 mg/L (2 µg/L).

2.1 Health effects

Carbon tetrachloride is classified as a possible human carcinogen, based on inadequate evidence of carcinogenicity in humans, but sufficient evidence in animals. However, there are major deficiencies in the available cancer studies. Animal studies suggest that the carcinogenicity of carbon tetrachloride is secondary to its hepatotoxic effects, indicating a possible threshold. As a result the MAC was established based on liver toxicity, and incorporating an additional uncertainty factor of 10 to accommodate for a lack of adequate chronic studies and evidence regarding the carcinogenic mode of action.

2.2 Exposure

Canadians can be exposed to carbon tetrachloride through its presence in air and drinking water. In addition, certain segments of the population may be exposed through the use of specific consumer products or in occupational settings. Because of its high volatility, concentrations of carbon tetrachloride are expected to be higher in drinking water from groundwater sources than in drinking water from surface water. Carbon tetrachloride is present in ambient air due to past and present releases resulting from production, disposal, or use. Recent surveys conducted on carbon tetrachloride in indoor and outdoor air in Canada have shown that mean levels are below 1 µg/m³. Exposure to carbon tetrachloride from food is not of concern because it is no longer used for grain fumigation in Canada, and its use in other countries is limited.

2.3 Treatment

Municipal treatment plants can reduce the levels of carbon tetrachloride in drinking water through granular activated carbon adsorption and air stripping. Oxidation and reverse osmosis membrane filtration may also be effective in the reduction of volatile organic compounds such as carbon tetrachloride from drinking water. At the residential scale, certified treatment devices (primarily point-of-use, some point-of-entry) are currently available for the reduction of volatile organic compounds such as carbon tetrachloride. Point-of-entry systems are preferred because they provide treated water for bathing and laundry as well as for cooking and drinking.

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