Assessment of trichloroethylene as an occupational carcinogen.

The reaction is described of the National Institute for Occupational Safety and Health (NIOSH) in the US to the results of experimental studies which showed that tetrachlorethylene is carcinogenic. Parallels are given with vinyl chloride, which it resembles structurally. The main occupational exposure to trichloroethylene is in the vapour degreasing of metal parts. The machine used for this activity is described, and it is shown that there is a high potential exposure. Possible control measures are outlined. The main evidence for the potential carcinogenicity of trichloroethylene is the occurrence of its epoxide as an intermediate in its metabolism to chloroethanol; species differences have been observed. Epdemiological studies have so far been inconclusive. NIOSH decided that trichloroethylene is potentially carcinogenic in the workplace, but only weakly so. No new standard has been recommended, although a lowering of the present standard is recommended.