Americium-241 Studies in Beagles

Abstract

Forty-eight adult beagles were injected with 0.00179 to 4.49 μCi 241A/kg body mass. Retained activity in the living animals was evaluated via the 60 keV gamma-ray using a combination of total-body and partial-body counting to determine the proportion in the liver and in non-liver tissue. Soon after injection, about 50% and 40%, respectively, of the administered 241Am was deposited in the liver and non-liver tissue (mainly skeleton). In the animals injected with 0.00179–0.305 μCi/kg the liver and non-liver burdens decreased slowly each with a biological half time of about 10 yr during the first 850 days. Two dogs injected with about 2.80 μCi/kg exhibited a sharp decrease in liver retention beginning about 100 days after injection accompanied by an increase in non-liver 241Am. Both showed extreme degenerative liver changes at death 401 and 448 days after injection. Similar but more slowly progressing effects were observed in the retention of 241Am by two animals injected with about 0.904 μCi/kg. Excreta collections from four dogs during the first 3 weeks after injection showed that 7/8 of the excretion was urinary and that nearly 4 of the total 241Am excreted during this period appeared in the first day's collection. Evaluation of the activity of individual bones, organs, and tissues of six animals autopsied 1–448 days after injection showed that although 241Am was distributed in many soft tissues, the liver and skeleton were the principal deposition sites; however, americium concentration in the thyroid gland was higher than in the skeleton and was higher than in any other soft tissue except the liver. Autoradiography showed that 241Am was deposited close to the location of the functioning thyroid cells. The kidney also had a relatively high concentration of activity, selectively deposited in the glomerull.