DICHLORVOS - 2-YEAR INHALATION CARCINOGENESIS STUDY IN RATS

To determine the effects of dichlorvos vapor on the tumor incidence in rats, 5 wk old Carworth Farm E strain rats weighing between 94 and 150 g were exposed to 0, 0.05, 0.5 and 5.0 mg/m3 in a 2 yr inhalation study. The growth rate of all treated rats was depressed, particularly in the males. There was increased survival of the rats exposed to 5 mg/m3. There were no consistent differences in food intake, organ weights, hematological or blood chemistry estimations, except in cholinesterase activities, among the various groups of rats. No compound related differences were seen in acetylcholine and choline estimations done in a small number of female rats'' brain tissues after 2 yr exposure. There were no gross or microscopic compound related changes in the rats'' tissues. Ultrastructural examination of the respiratory tissues of the rats from the control and 5 mg/m3 group showed no changes attributable to dichlorvos. The results of a relative risk analysis of the tumor data showed that no dose-related increase in tumor risk was established for rats of either sex. These data confirm the results of earlier studies supporting the safety of insecticidal uses of dichlorvos.