Valency five, similarities between plutonium and neptunium in gastrointestinal uptakes

The gastrointestinal uptake of neptunium has been shown to be dependent on mass ingested in rats and in baboons. Among possible explanations, Sullivan has suggested a gastrointestinal reduction of the neptunyl ion (NpO2+) to Np4+ ion, which is less readily absorbed. With plutonium, we have shown that for a high ingested mass (5.104 μg.kg-1) of the 5 valency state which is stable and administered without added oxidants, the gastrointestinal uptake is high and close to Np values obtained in the same conditions (1.10-2). When the mass ingested is decreased to 10 μg.kg-1, the G.I. uptake decreases to 1.10-4. The two curves, G.I. transfer versus ingested mass, obtained with the two actinides in baboons were compared. Similarities and differences were explained by physiochemistry of the elements. (author)