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As a link in the pre-operational research program for the establishment of the first fuel reprocessing plant in Japan, the metabolism in man ofruthenium was studied in experiments involving the oral administration of metabolized tracer in shellfish. A whole body counter-scanner could trace in vivo the movement of ingested tracer from stomach to rectum through the large intestine within 24 hr. Whole body retention was best fitted by a three-component exponential function with time, the fastest component being caused by a large fecal excretion which amounted to about 95% ofadministered dose within 2 days. The second component could be attributable to the prolonged retention of radioruthenium inside the gastrointestinal tract, the biological half-life being 2.3 days. The slowest component, about 1 % of the administered dose, retained in the body with a half-life of 30 days, and this fraction was considered to be absorbed from the gastrointestinal tract.Successive experiments with non-metabolized tracer in the chemical forms of the chloro complexes of nitrosylruthenium(II1) and ruthenium(II1 and 1V)resulted in ahighergastrointestinal absorption of the former by a factor of about 3 than the latter. It is suggested that changes in the chemical and physical states of ruthenium, of p H and of different periods of time following preparation until administration, as well as changes in residence time in the gastrointestinal tract may cause variability in absorption.

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