Distribution and Short-Term Effects of Intratracheally Instilled Neutron-Irradiated UO2 Particles in the Rat

In the present study we investigated the radionuclide distribution and histopathological effects of neutron-irradiated UO2, particles in the rat after intratracheal instillation. The kinetics and short-term effects of uranium fission products (95Zr, 95Nb, 103Ru and 141Ce) were examined during a 3-month follow-up period. A rapid clearance (about 21%) of particles occurred via the gastrointestinal tract within 24 hr after the instillation. Autoradiographic and histological examinations revealed that the retained particles were nonuniformly distributed in the lungs. Translocation of the fission products from the lung to various other tissues was slow; 3 months after the instillation, the activity of the total body burden was below 1% in the liver, kidney, and spleen, whereas in the lungs it was 83%. Clearance of particles appeared to be mainly due to tracheobronchial mucociliary mechanisms. Translocation of the fission products to the bone and liver was significantly less than that reported by the ICRP, indicating that the clearance of uranium-matrix-associated fission products is preferably dependent on the physical characteristics of the particulate material. The cumulative lung doses ranging from 170 to 550 mSv caused slight or moderate local inflammatory reactions in the lungs, but at smaller dose levels there were no histopathological changes observed