Bioassay of 1,1,2,2-tetrachloroethane for possible carcinogenicity.

A bioassay for possible carcinogenicity of technical-grade 1,1,2,2-tetrachloroethane was conducted using Osborne-Mendel rats and B6C3F1 mice. At initiation of the study the rats were approximately 7 weeks old, and the mice were approximately 5 weeks old. 1,1,2,2-Tetrachloroethane in corn oil was administered by gavage, at either of two dosages, to two groups of 50 male and 50 female animals of each species, 5 days a week. Treatment was over a period of 78 weeks, followed by observation periods of 32 weeks for the rats and 12 weeks for the mice. The high and low time-weighted average dosages were, respectively, 108 and 62 mg/kg/day for male rats, 76 and 43 mg/kg/day for female rats, and 282 and 142 mg/kg/day for the mice of both sexes. For each species, 20 animals of each sex were placed on test as vehicle controls. These animals were intubated with corn oil at the same rate as the high dose animals. Twenty animals of each sex were placed on test as untreated controls for each species. These animals were not intubated. Among mice, hepatocellular carcinomas were observed in 2/16 (13 percent) male untreated controls, 1/18 (6 percent) male vehicle controls, 13/50 (26 percent) low dose males, 44/49 (90 percent) high dose males, 0/18 female untreated controls, 0/20 female vehicle controls, 30/48 (63 percent) low dose females, and 43/47 (91 percent) of the high dose females. This incidence of hepatocellular carcinoma indicated a highly significant (P<0.001) positive dose-related trend in mice of both sexes. No statistically significant incidence of neoplastic lesions was observed in male or female rats. However, two hepatocellular carcinomas and one neoplastic nodule, which are rare tumors in the male Osborne-Mendel rat, were observed in the high dose males. Under the conditions of this study, orally administered 1,1,2,2-tetrachloroethane is a liver carcinogen in B6C3F1 mice of both sexes. The results do not provide conclusive evidence for the carcinogenicity of 1,1,2,2-tetrachloroethane in Osborne-Mendel rats.