Lung carcinogenesis in rats after inhalation exposure to (NpO2)-Np-237

The results of several studies of experimental carcinogenesis suggest that, after inhalation of alpha-particle emitters, lung tumor incidence varies d epending on the exposure rate and dose distribution in the tissue. In the c ase of transuranics, the main influencing factor would be the specific alph a-particle activity of the inhaled actinide. To confirm these results, long -term studies were performed using male Sprague-Dawley rats exposed to (NpO 2)-Np-237 by inhalation. The initial lung burdens of the animals ranged fro m 0.1 to about 7 kBq. The rats were followed during their life span and wei ghed regularly, and their lung burdens were determined in vivo and at death to estimate the lung dose. At death, the incidence of lung tumors and thei r malignancy and histological types were analyzed. The analysis revealed a typically linear-quadratic dose response for incidence of malignant lung ne oplasm and a differential dose response for various types of tumors. Althou gh these results confirm the influence of the activity of the inhaled actin ide oxide, further experiments are needed to be able to compare a more homo geneous population of animals, (C) 1999 by Radiation Research Society.