Bioassay of 1,1-dichloroethane for possible carcinogenicity.

A bioassay of technical-grade 1,1-dichloroethane for possible carcinogenicity was conducted using Osborne-Mendel rats and B6C3F1 mice. 1,1-Dichloroethane in corn oil was administered by gavage, at either of two dosages, to groups of 50 male and 50 female animals of each species, 5 days a week for a period of 78 weeks, followed by an observation period of 33 weeks for rats and 13 weeks for mice. A preliminary subchronic toxicity test, consisting of 6 weeks of 1,1-dichloroethane administration at five dosage levels followed by 2 weeks of observation, was performed for the purpose of selecting initial dosages. Subsequent dosage adjustments were made during the course of the study. The high and low time-weighted average dosages of 1,1-dichloroethane were, respectively, 764 and 382 mg/kg/day for male rats; 950 and 475 mg/kg/day for female rats; 2,885 and 1,442 mg/kg/day for male mice; and 3,331 and 1,665 mg/kg/day for female mice. For each species, 20 animals of each sex were placed on test as vehicle controls. These animals were gavaged with corn oil at the same times that dosed animals were gavaged with 1,1-dichloroethane mixtures. Twenty animals of each sex were placed on test as untreated controls for each species. These animals were not intubated. Survival was poor in all rat groups and several mouse groups. Survival at the end of the study in the untreated control, vehicle control, low dose, and high dose groups was, respectively, 30, 5, 4, and 8 percent in male rats; 40, 20, 16 and 18 percent in female rats; 35, 55, 62 and 32 percent in male mice; and 80, 80, 80 and 50 percent in female mice. Pneumonia was observed in 80 percent of the rats in this bioassay. There were dose-related marginal increases in mammary adenocarcinomas and in hemangiosarcomas among female rats and there was a statistically significant increase in the incidence of endometrial stromal polyps among dosed female mice as compared to controls. These findings are indicative of the possible carcinogenic potential of the test compound. However, it must be recognized that under the conditions of this bioassay there was no conclusive evidence for the carcinogenicity of 1,1-dichloroethane in Osborne-Mendel rats or B6C3F1 mice.