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A retention-excretion model for americium in humans.

This paper discusses current information on the biological behavior of americium and describes a biokinetic model for americium in humans. Emphasis is on the time-dependent distribution and excretion of systemic americium in the adult, but potential differences with age in parameter values are addressed, and predictive models of absorption of americium to blood from the respiratory and gastrointestinal (GI) tracts are provided in an appendix. The analysis builds on the author's previous biokinetic model for plutonium in humans and recent analyses and/or models of other authors regarding the behavior of americium and related elements in humans and laboratory animals. Compared with the retention model for americium implied in ICRP Publication No. 48, the present model, as applied to adults, yields reasonably similar whole-body retention of americium at all times, much less retention in the liver after a few months, somewhat greater retention in the total skeleton after a few years, and very similar long-term integrated activities of long-lived americium isotopes on bone surfaces. Compared with a previous model of Durbin and Schmidt, the present model, as applied to adults, predicts very similar retention in the liver at all times, somewhat smaller retention in the total skeleton after a few years, and somewhat greater urinary excretion rates at all times after acute uptake to blood.