Comparative Studies of 132Cs and 86Rb Turn-over in Man using a Double-tracer Method

Comparative studies of Cs and Rb metabolism were made with an adult male of human subject using 132Cs and 86Rb double-tracer method. Whole body retention and distribution after single oral administration were investigated by a whole body counter-scanner at the National Institute of Radiological Sciences, and total excreta in urine and feces that were collected for 9 days after the administration were measured separately by the same detector. Marked differences were found in the biological half-lives, excretion patterns and distributions in the whole body between the two radionuclides. Whole body retention could be expressed by two-component exponential function of time for the both nuclides, but short-term component had a shorter half-life (1.0 day) for 132Cs than that for 86Rb (6.0 days) and long-term component had a longer-life (72 days) for 132Cs than that for 86Rb (53 days). Total excretion of 132Cs for the first 5 days after the administration was correspondingly larger than that of 86Rb, but fecal excretion of 86Rb was slightly larger than that of 132Cs which resulted in a large disagreement in values of urinary-to-fecal excretion ratio between the two. Whole body distributions obtained with the elapse of time since the administration indicated that 86Rb was transferred to its final compartments within 3 days, but 132Cs needed more than 10 days. At the equilibrium in distribution 132Cs concentrated in muscular tissues more specifically than did 86Rb, but 86Rb was present more in liver, heart, and brain etc. , than 132Cs. These results suggest that Cs must have a different metabolic pathway to that of Rb, and that effective elimination of 137Cs from the human body can be made by some means when applied before 3 days after accidental 137Cs intake.