Sex-Related Differences in the Human Metabolism of Plutonium

Data are reported on the clearance from blood and excretion of 237 Pu injected intravenously as Pu(IV) citrate into healthy subjects. Large inter-subject differences developed in the retention in blood (range 0.4-4.5% at 14 d), the higher values generally occurring in females. Except during the first 24 h, no important systematic differences were found between the early (<21 d) urinary excretion and the losses indicated in ICRP Publication 54, while after 6 and 12 wk the ICRP's prediction accorded roughly with excretion in the men but underestimated it in the women by up to a factor of 3. The renal clearance rate fell sharply to a minimum after 6-24 h, consistent with rapid binding of the tracer to transferrin, but a subsequent partial recovery up to 14-21d indicated a further change in the speciation of plutonium in the blood; lower rates in the women suggested possible sex-related differences in the balance of metabolites in the circulation. The relevant function in ICRP Publication 54 tended to exaggerate faecal excretion in the males at all times, but was more appropriate for the females.