[Characteristics of the occurrence and development of tumors in rats depending on age and the nature of the strontium-90 exposure].

In chronic strontium-90 administration into rats aged 8--10 months osteosarcomas did not develop, while in animals at the age of 3--4 months osteosarcomas incidence was 6.7%. In single injection of the radionuclide in 8--10 months old animals osteosarcomas developed in 2.2% of observations, whereas in 3--4 months old animals--in 45.7%. The most early appearance of osteosarcomas (at the 193d--316th day) was noted in 3--4 months old animals subjected to a single exposure to strontium-90.