The gastrointestinal absorption and urinary excretion of plutonium in male volunteers

The gastrointestinal absorption and urinary excretion of ²⁴⁴Pu have been measured in five healthy adult males in a two-stage study. Firstly, the volunteers ingested about 10¹⁴ atoms of ²⁴⁴Pu in citrate solution with a mid-day meal and urinary excretion was measured for the following 7-9 days. After a period of at least six months, the same volunteers were given an intravenous injection of 2 x 10¹² atoms of ²⁴⁴Pu in citrate solution. Urinary excretion was then measured for the following 79 days and subsequently at intervals over periods up to 5-6 years. Fractional absorption of Pu from the gastrointestinal tract, calculated by comparing excretion for the two routes of administration, averaged 6 x 10^-4, consistent with the ICRP value of 5 x 10^-4. The results show a positive correlation between increasing age of the subjects, between 36 and 64 years of age, and increasing absorption of ingested Pu from 10^-4 to 10^-3. In general, results for urinary excretion after injection are consistent with predictions of the current ICRP model although daily excretion after 5-6 years (3 subjects) averaged 0.005% of the administered amount, about twice the predicted value.