Multiplicative effect of inhaled plutonium oxide and benzo (a) pyrene on lung carcinogenesis in rats.

This study describes the effect of intratracheal instillations (2 X 5 mg) of benzo(a)pyrene (B(a)P) on lung carcinogenesis in rats which had previously inhaled different levels of 239 plutonium oxide (220, 630, 6300 Bq, initial lung burden). Survival decreased with increasing PuO2 exposure and additional B(a)P exposure. The incidence of malignant lung tumours, adjusted for differences in survival, increased in a dose-related fashion with PuO2 dose and was elevated in the presence of additional B(a)P exposure. A multiplicative relative risk model was found to describe reasonably well the observed joint effect. The practical implications of these findings are discussed.