The effect of lead on chemical- and viral-induced tumor production in mice.

Female Swiss mice were exposed to lead in the drinking water at concentrations ranging from 0 to 1000 ppm for 105 or 280 day periods of time. The effect of lead on urethan-induced pulmonary adenoma formation was evaluated in the 105 day study. Urethan-induced sleeping times observed following ip injection of urethan (1.5 mg/g) after 3 weeks of lead exposure were not altered by lead indicating that lead did not affect the rate of urethan elimination. Pulmonary adenoma formation was evaluated 84 days later. Lead exposure did not affect the number of tumors produced, nor did it alter the mean tumor diameter in the lead treatment groups. This suggests that the immunosuppressive activity of lead does not enhance urethan-induced adenoma formation. In the 280 day study, the incidence of spontaneous murine lymphocytic leukemia was evaluated. Leukemia was observed in all treatment groups. Mortality was greater in the lead-exposed mice. Mice exposed to 50 or 1000 ppm lead had 41.6% and 58.3% more deaths associated with the virus. The median survival time was also reduced in the lead-exposed mice. It appears that the immunosuppressive effects of lead allow for increased expression of the murine lymphocytic leukemia virus.