Influence of age on the tumorigenicity of plutonium-239 in rats

The study was designed to examine the influence of age at the time of exposure on the incidence of tumors following administration of plutonium (239Pu) to Wistar rats. Adult and weanling rats were intravenously and newborns intracardially injected with monomeric 239Pu and prenatal animals exposed by intravenous injection of the dam. Dose levels selected resulted in similar 10-day radiation doses to the femur of all ages although cumulative doses over the 30-month observation period showed age-dependent differences. Bone tumor incidence in the adults increased with increasing dose. The dose-response relationships were less clear in the younger age groups; the younger rats were less sensitive on an administered dose basis but more sensitive when radiation dose was considered. The extremities were the preferential site of bone tumor development in the adults but tumors of the head predominated in the newborn and prenatal groups. Mammary tumors developed at earlier times in the females at the higher dose levels although differences in final incidence were less clear. These studies demonstrate that incidence and pattern of tumor induction are clearly dependent on the age of the rat at the time of administration and are related to both metabolic differences and differences in radiosensitivity