LIFE-SPAN STUDIES IN RATS EXPOSED TO (PUO2)-PU-239 AEROSOL .3. SURVIVAL AND LUNG-TUMORS

Female, young adult, Wistar rat were given a single inhalation exposur e to a submicron sized aerosol of high-fired (PuO2)-Pu-239 and observe d during their lifespan for primary lung tumours. Rats were distribute d among sham-control (n = 1052) and exposed (n = 2105) groups. Surviva l was significantly reduced only in rat with lung doses > 30 Gy. A tot al of 99 primary lung tumours were found, of which 92% were malignant and 80% were carcinomas. Of malignant lung tumours, 49 were squamous c ell carcinoma, 23 adenocarcinoma, nine hemangiosarcoma, seven adenosqu amous carcinoma, and three fibrosarcoma. One adenocarcinoma was found in controls and only four adenomas were seen in the exposed rat at lun g doses < 1.5 Gy. The lowest doses at which lung tumours appeared in e xposed rats were 1.5 Gy for squamous cell carcinoma, 3.1 Gy for adenoc arcinoma. 4.1 Gy for hemangiosarcoma, and about 9 Gy for adenosquamous carcinoma and fibrosarcoma. Pulmonary squamous metaplasia was not see n in controls and was first seen in exposed rats only at lung doses > 1 Gy. Primary lung tumours were the presumed cause of death (fatal) in 60% of rats with malignant lung tumours; causes of death were equally distributed among all tumour types and doses. The incidence of all lu ng tumours was 0.095% in control rats, 0.21% in 1877 rats with lung do ses < 1 Gy, and 41% in 228 rats with doses > 1 Gy. Lung tumour inciden ce increased in a linear manner from 6.9% at 2.3 Gy to an incidence of 64-88% at 16-44 Gy. Absolute malignant lung tumour risk averaged 270 lung tumours per 10(4) rat-Gy above a lung dose of 1 Gy. All types of malignant lung tumours induced by inhaled (PuO2)-Pu-239 exhibited a th reshold at a lung dose > 1 Gy.