Pure trichloroethylene (tri), stabilized by an amine base, was administered by inhalation at 0, 100, and 500 ppm for 6 h/day, 5 days/week, for 18 months to mice, rats and Syrian hamsters of both sexes. No significant increase in tumor formation was observed in any species or dosing group, except in malignant lymphomas, which were increased in female mice in the following incidence rates: 9/29 (controls), 17/30 (100 ppm), and 18/28 (500 ppm). Whether or not this high occurrence of lymphomas, which is peculiar to this strain of mice (NMRI) has any relationship to tri-exposure, cannot be decided upon by the present experiment. It is concluded that from these findings no indication for a carcinogenic potential of pure trichloroethylene can be deduced.

Previous analytical studies of industrial samples of trichloroethylene (TRI) have revealed the presence of mutagenic and carcinogenic epoxides which, it was proposed, might be responsible for the carcinogenicity of such samples, as demonstrated with mice in other laboratories. To test this hypothesis, Swiss mice (ICR/HA) of both sexes, bred and kept in SPF conditions, were dosed daily with TRI in corn oil by gavage (males: 2.4 g/kg, females: 1.8 g/kg) with or without the addition of epichlorohydrin (EPC, 0.8%, w/w), 1,2-epoxybutane (BO, 0,8%), or EPC + BO (0.25% + 0,25%) for 18 months. The ensuing observation period terminated at 106 weeks (from start of experiment). Gross and microscopic examination of all organs revealed a statistically significant increase in the incidence of forestomach papillomas and carcinomas after EPC-, BO-, and (EPC + BO)-stabilized samples of TRI, but not after pure, amine base-stabilized TRI. This type of tumor is believed to be induced by the direct alkylating epoxides epichlorohydrin and epoxybutane, whose industrial use in stabilizing chlorinated aliphatic hydrocarbons should be discontinued. No other significant increase in tumor incidences was found. Again, this study does not support the suggestion that trichloroethylene itself is carcinogenic under realistic exposure conditions.