[Studies on dichlorvos (DDVP). II. Testing of dichlorvos for carcinogenic activity in rats].

The question has remained open, whether or not the pesticide Dichlorvos (DDVP) should be classified as a carcinogen. The results of a long-term experiment of testing DDVP in male and female C57Bl/6/Bln mice, recently published by us in this journal did not indicate the development of neoplastic lesions due to the administration of the compound. Now we report on results of long-term administration of DDVP to male and female BD IX/Bln rats. In the groups of male rats a increased incidence of proliferations of bile duct cells and of oval cells of the liver was observed, which was statistically significant (p less than 0.05) in the group of the higher dosed animals when compared with the group of the vehicle control male rats. Among the DDVP-treated female rats a significantly decreased incidence of tumors of the adrenal glands and of mammary tumors was observed as compared to the vehicle control group. Similar results were obtained in earlier experiments, when rats were treated with Trichlorfon, which easily convert to DDVP. In comparison to the corresponding control group DDVP-treated male rats showed a higher incidence of focal, hyperplasias of the urinary bladder, of focal hyperplasias of the pelvis and of transitional cell carcinomas of the renal pelvis. DDVP-treated female rats showed the opposite, namely lower incidences of these types of tumors, when compared with the control group. In our study on rats there were no neoplastic lesions found which could be attributed to the treatment of the animals with DDVP.