Pleural mesothelioma in the rat following exposure to 239PuO2

Pleural mesothelioma was an infrequent observation following deposition of 239PuO2 in the lung or pleural cavity. Only five tumors were found in 2,105 rats exposed to 239PuO2 aerosols in the present study, while four tumors were found in 527 rats that inhaled 239PuO2 in previously published lifespan studies. Risk of pleural mesothelioma was not significantly increased by intrapleural injection of 30 kBq 239PuO2. In contrast, a much higher incidence of peritoneal mesothelioma was seen following intraperitoneal injection of 239PuO2 due to aggregation of 239PuO2 particles on mesothelial surfaces. It was concluded that the lack of 239PuO2 aggregation on pleural surfaces is responsible for small numbers of pleural mesothelioma observed following deposition of 239PuO2.