Effects of Protraction of the α Dose to the Lungs of Mice by Repeated Inhalation Exposure to Aerosols of239PuO2

To determine the long-term biological effects of protracted α irradiation of the lung, 84-day-old C57BL/6J mice were repeatedly exposed by inhalation to aerosols of239PuO2every other month for up to six exposures in 10 months to reestablish lung burdens of 20, 90, or 460 Bq. Other mice were exposed only once when either 84 or 460 days of age to achieve desired initial lung burdens of 20, 90, 460, or 2300 Bq. Suitable control groups were maintained. Groups of mice with similar cumulative α doses to the lung had 3.4 to 4.4 times greater incidence of pulmonary tumors (adenomas and adenocarcinomas) when the dose to the lung was protracted by the repeated inhalation exposures compared to mice that received a single inhalation exposure. Excess pulmonary tumors per unit dose to the lung were also greater in groups of repeatedly exposed mice compared to those exposed only once. Repeatedly exposed mice also died earlier with pulmonary tumors than did those exposed once. It appears that protraction of an α dose to lungs increases the carcinogenic risk of inhaled239PuO2in mice.