A two-year drinking-water study of dichloromethane in rodents. II. Mice.

To investigate its carcinogenic potential, dichloromethane (DCM) was administered at levels of 0, 0, 60, 125, 185 and 250 mg/kg body weight/day to a total of 1000 B6C3F1 mice in deionized drinking-water for 104 wk. The high-dose male and female mice showed a transitory increase in mean leucocyte counts. Treatment-related toxic changes were noted in both male and female livers at the highest dose. There was a slight elevation of proliferative hepatocellular lesions in the treated males but no dose-related trend was apparent and the effect was absent in the females. Neoplastic lesions observed in the study were homogeneous among all groups and were within the range of incidence in historical controls. The results of this study demonstrated a toxicological no-observable-effect level (NOEL) for DCM of 185 mg/kg body weight/day in both sexes.