Skeletal retention and distribution of 226Ra and 239Pu in beagles injected at ages ranging from 2 days to 5 years.

The age at exposure significantly affects the retention and distribution of 226Ra and 239Pu, both of which deposit in the skeleton although in somewhat different patterns. Beagles aged 2 days (neonates), 90 days (juveniles), 18 months (young adults), or 5 yrs (mature) received a single subacute injection of one of these nuclides and were sacrificed serially during a 2-yr interval. Nuclide concentrations in plasma, the skeleton, individual bones and bone sections were determined and retention equations were calculated. The microanatomical skeletal nuclide distribution was studied after fission track or conventional autoradiography. Elimination of 239Pu and its translocation from bone surfaces to the bone volume caused by bone growth and turnover processes were measured. Average radiation doses and dose rates as a function of age at exposure were determined. Initial uptake and retention, skeletal nuclide concentration, proliferative activity of local cell populations and residence time of the nuclide on skeletal surfaces were affected significantly by age at exposure. The effect of these parameters on tumor induction is discussed. This study has provided early retention and distribution data which together with data from a chronic toxicity study will be used to estimate the risk of Pu exposure relative to that of Ra to humans of all ages.