LUNG CANCER FOLLOWING POLONIUM-210 INHALATION IN RATS

Inhalation by 3 groups of rats of NaCl aerosols with small amounts of Po2l0 added produced initial lung burdens of 0.15, 0.05, and 0.02 [mu]Ci. After 280 days, resulting accumulated lung doses were 538, 202, and 71 rads, respectively. life span of the highest dose group was shortened, with 87% of animals dying within 1 year after exposure, compared to 35% for controls and the other 2 experimental groups. Increased incidence and severity of acute pneumonia was the chief cause of the high mortality. Radiation changes in the lung were seen only in animals exposed to the highest level of radioactivity. No primary lung tumors developed in control rats, but 41 were found in 288 exposed rats dying spontaneously during the 96-week experiment. Squamous cell carcinoma was the commonest tumor type, accounting for 55% of the total number found. Over 70% of the squamous cell tumors occurred in rats exposed to the highest dose of Po210, and many were early lesions associated with radiation injury. Pulmonary adenomas were seen only in rats exposed to low and medium doses. The highest dose appeared to be effective in preventing mediastinal lymphomas.