Page 12: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Tetrachloroethylene

11.0 Rationale

Tetrachloroethylene is primarily used as a solvent in the dry cleaning industry and as a chemical intermediate, with exposures of the general public primarily coming from indoor and outdoor air. Entry into the environment is primarily from anthropogenic sources, and tetrachloroethylene's presence in drinking water can result from spills.

The effects of tetrachloroethylene have been studied in humans and experimental animals, with neurological effects being observed in all species. The cancers repeatedly observed in animals (hepatocellular adenomas and carcinomas in mice and mononuclear cell leukaemia in rats) have not been observed in humans with occupational or environmental exposure to tetrachloroethylene. The weight of evidence for the MOA for these animal tumours suggests that they do not likely result from mutagenic activity.

Given the volatility of tetrachloroethylene, a multiroute exposure assessment was performed using PBPK modelling in order to determine any additional exposure by dermal or inhalation exposure during showering or bathing. This multiroute exposure was used in both the cancer and non-cancer risk assessments.

PBPK modelling was used to calculate the BMD for neurological effects based on the internal dose of tetrachloroethylene in humans occupationally exposed to the compound in air. The HBV for tetrachloroethylene obtained from this approach was 0.01 mg/L (10 µg/L). This value is lower than the HBV for hepatocellular tumours of 0.015 mg/L (15 µg/L), which was calculated based on the rate of tetrachloroethylene metabolism in the liver. The HBV for neurological effects is therefore sufficiently protective of both potential cancer and non-cancer effects resulting from exposure to tetrachloroethylene in drinking water.

A MAC of 0.010 mg/L (10 µg/L) is established for tetrachloroethylene in drinking water, as it is protective of potential health effects, can be reliably measured by available analytical methods and is achievable by municipal and residential scale treatment technologies.

As part of its ongoing guideline review process, Health Canada will continue to monitor new research in this area and recommend any change to the guideline that is deemed necessary.

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