Water Quality Standards

Summary information extracted from: Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. -Geneva, World Health Organization, 1993. pp. 59-60.

1,1,1-Trichloroethane has been found in only a small proportion of surface and ground waters, usually at concentrations of less than 20 µg/litre. In a few instances, much higher concentrations have been observed. There appears to be increasing exposure to 1,1,1-trichloroethane.

1,1,1-Trichloroethane is rapidly absorbed from the lungs and gastrointestinal tract, but only small amounts — about 6% in humans and 3% in experimental animals — are metabolized. Exposure to high concentrations can lead to hepatic steatosis (fatty liver) in both humans and laboratory animals.

IARC has placed 1,1,1-trichloroethane in Group 3. Available studies of oral administration were considered inadequate for calculation of a TDI. As there is an increasing need for guidance on this compound, a 14-week inhalation study in male mice was selected for use in calculating the guideline value. Based on a NOAEL of 1365 mg/m3, a TDI of 580 µg/kg of body weight was calculated from a total absorbed dose of 580 mg/kg of body weight per day (assuming an average mouse body weight of 30 g, breathing rate of 0.043 m3/day, and absorption of 30% of the air concentration), applying an uncertainty factor of 1000 (100 for inter- and intraspecies variation and 10 for the short duration of the study). A provisional guideline value of 2000 µg/litre (rounded value) is proposed, allocating 10% of the TDI to drinking-water.

This value is provisional because of the use of an inhalation study rather than an oral study. It is strongly recommended that an adequate oral toxicity study be conducted to provide more acceptable data for the derivation of a guideline value.