The gastrointestinal absorption of protactinium, uranium, and neptunium in the hamster

The gastrointestinal absorption of protactinium, uranium, and neptunium in adult hamsters was measured. The actinide preparations were administered intragastrically and animals were kept 2-4 weeks prior to the radiochemical analysis of selected tissue samples. Total absorption was estimated using data for the distribution of the actinides after intravenous injection in soluble form. The values obtained were 3.9 and 0.22% for ²³¹U Pa citrate and ²³¹Pa fluoride, respectively; 0.77 and 0.11% for ²³³U (uranyl) nitrate and ²³³U dioxide, respectively; and 0.06 and 0.05% for ²³⁷Np citrate and ²³⁷Np nitrate, respectively. The absorption factors recommended by the International Commission on Radiological Protection for use in calculating annual limits on intake for occupationally exposed workers are: 0.1% for all compounds of Pa; 5 and 0.2% for soluble hexavalent and relatively insoluble tetravalent forms of U, respectively; and 1.0% for all chemical forms of Np. The experimental basis for these values is discussed.