Large-volume liquid-scintillation counters were used to measure in vivo the biological half-time (BT1/2), wholebody retention, and excretion of several gamma-emitting alkali-metal radionuclides in five species of animals. Tracer amounts of the radionuclides were administered to mice, rats, monkeys, dogs and men by oral, intraperitoneal or intravenous administration. Radioactivity levels in the excreta were determined at subsequent intervals and the whole-body retention was followed, where possible, until the retained body burden fell to 1.0±0.1% of the administered dose. The logarithms of the retention and excretion levels were plotted as functions of time after administration, and standard first-order kinetics were applied to determine the biological half-times and retention equations. Whole-body retention curves were best fitted by a single or multiple-component exponential function of the form R=a1e −k1t+a2e −k2t+…+ane−knt where a1, a2 …. an are the intercept constants; k1, k2 … kn are the rate constants; and R is the whole-body retention at time t. Values for the BT1/2 of K42 in the mouse, rat and dog were 13, 4.0 and 8.0 days, respectively. Respective values for Na22 in the mouse, rat, monkey, dog and man were 1.7, 2.9, 7.5, 9.5 and 11.0 days; and Rb86, 3.8, 8.6, 15.0, 20.0 and 80.0 days; and for Cs134 and Cs137, 1.2, 6.5, 19.0, 25.0 and 110.0 days. Calculations based on these data suggest a reduction in the maximum permissible concentrations of radiocesium and radiorubidium in air, food and water. A first approximation for an interspecies correlation between BT1/2 and body surface area of the form BT1/2 = k(SA)b, where k and b are constants was demonstrated for the radionuclides investigated. Data on the naturally occurring K42 in laboratory animals and on the distribution of Group I radionuclides in various tissues of the rat were also obtained.
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Chester R. Richmond (1980) studied this question.