Water Quality Standards

Summary information extracted from:  Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. - Geneva, World Health Organization, 1993. pp. 62-63.

Trichloroethene is used mainly in dry cleaning and in metal-degreasing operations. Its use in industrialized countries has declined sharply since 1970. It is released mainly to the atmosphere but may be introduced into surface and ground water in industrial effluents. It is expected that exposure to trichloroethene from air will be greater than that from food or drinking-water. Trichloroethene in anaerobic ground water may degrade to more toxic compounds, including vinyl chloride.

Trichloroethene is rapidly absorbed from the lungs and gastrointestinal tract and distributed to all tissues. Humans metabolize between 40% and 75% of retained trichloroethene. Urinary metabolites include trichloroacetaldehyde, trichloroethanol, and trichloroacetic acid; the reactive epoxide trichloroethene oxide is an essential feature of the metabolic pathway.

Trichloroethene has been classified by IARC in Group 3. It has been shown to induce lung and liver tumours in various strains of mice at toxic doses. However, there are no conclusive data that this chemical causes cancer in other species. Trichloroethene is a weakly active mutagen in bacteria and yeast.

A TDI of 23.8 µg/kg of body weight (including allowance for 5 days per week dosing) was therefore calculated by applying an uncertainty factor of 3000 to a LOAEL of 100 mg/kg of body weight per day for minor effects on relative liver weight in a 6-week study in mice. The uncertainty factor components are 100 for inter- and intraspecies variation, 10 for limited evidence of carcinogenicity, and an additional factor of 3 in view of the short duration of the particular study and the use of a LOAEL rather than a NOAEL. The provisional guideline value derived from this TDI, based on 10% allocation to drinking-water, is 70 µg/litre (rounded figure).