Inhalation Carcinogenesis of High-Fired 238 PuO 2 in Rats

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Abstract
Wistar rats were given a single, nose only exposure to freshly prepared high fired 238PuO2 particles (activity median aerodynamic diameter of 238PuO2, 1.8 .+-. 0.6 .mu.m), and the rats were observed over their life span. A total of 344 rats were examined: 294 exposed to 238PuO2 and 50 unexposed controls. A significantly increased incidence of malignant tumors was found only in the lung. Most of the lung tumors were adenocarcinomas followed in abundance by squamous cell carcinomas. The incidences of lung tumors were 0 in unexposed controls, 0.8% at an initial alveolar deposition of 0.14 nCi 238Pu, 7.5% at 11 nCi, 60% at 220 nCi and 19% at 890 nCi. High fired 238PuO2 appeared less effective in producing lung tumors in the Wistar rat than 239PuO2 possibly due to the smaller amount of lung tissue irradiated by 238PuO2 particles than by 239PuO2 particles.