Re-evaluation of the biological half-time of caesium in Japanese male adults

After the Chernobyl accident, increased 137Cs body burdens were measured for 22 Japanese male adults. An average biological half-time of 101 days was estimated. In the 1960s, an average Cs biological half-time of 86 days was reported for 23 Japanese male adults under quasi-equilibrium conditions in regard to 137Cs from atmospheric nuclear weapon tests. Comparing the present data with the 1960s results, the difference in the biological half-time of Cs at a confidence level of 90% was not significant but had an increasing tendency. When the two groups of data were combined, the biological half-time for Cs was 93±27 days for the 45 individuals. Thus, the reference biological half-time should be 90 days for Japanese male adults. Four subjects were studied in both the 1960s and the 1980s. A clear relationship was observed between the increase in half-time and increase in age.