The Th 228 Decay Series in Adult Beagles: Ra 224 , Ph 212 , and Bi 212 in Blood and Excreta

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The studies to be reported are a part of the long-term studies of the biological effects of Th228 and other radionuclides in adult beagles (1). Since the Th228 decay products, Ra224, Tn220, Pb212, and Bi212, are not completely retained at the sites at which they are formed in the dog, extensive studies of their retention and distribution are needed if estimates of radiation dose rates are to be made. Previously the metabolism in these beagles of the parent nuclide, Th228, over a period of 3.5 years after injection has been described (2). Earlier, Van Dilla et al. (3) reported the translocation of Ra224 during the first few months after injection, and Mays et al. (4) reported the exhalation of Tn220 through 1000 days. This paper gives the results of the measurements of the concentration in blood plasma and the urinary and fecal excretion of Ra224 (3.64-day half-period), and the concentration in blood cells of Pb212 (10.6-hour half-period), through 3.5 years. Also presented are less extensive studies of urinary excretion of Pb212, and urinary excretion and plasma and blood cell concentrations of Bi212 (60.5-minute half-period). From these results estimates of the retentions of these decay products are made.