Effects of long-term oral administration of DDT on nonhuman primates

Because of reports on tumorigenic activity in different animal species expo sed to DDT a decision was made in 1969 to evaluate the long-term effects of DDT on 24 cynomolgus and rhesus monkeys. DDT (20 mg/kg) was given in the d iet for 130 months, followed by an observation period that ended in 1994. T he two cases of malignant tumor detected in the DDT group included a metast atic hepatocellular carcinoma in a 233-month-old male and a well-differenti ated adenocarcinoma of the prostate in a 212-month-old monkey. Benign tumor s detected in the DDT group included three cases of leiomyoma, two of which were uterine and one, esophageal. No tumor was detected in the control gro up of 17 monkeys. Fatty changes in the liver were observed in 52.9% of the DDT group and 29.4% of the control group. More specific signs of hepatotoxi city were documented microscopically in seven DDT monkeys. Severe tremors a nd histological evidence of CNS and spinal cord abnormalities were observed in six DDT monkeys. The present findings show clear evidence of hepatic an d CNS toxicity following long-term DDT administration to cynomolgus and rhe sus monkeys. However, the two cases involving malignant tumors of different types are inconclusive with respect to a carcinogenic effect of DDT in non human primates.