Biological availability of americium-241 in oligotrophic and mesotrophic surface waters: Combined effects of acidity and phosphate

The influence of pH (between pH 5 to 8) and PO43- (0.2 mg/l) in three oligo to mesotrophic surface waters on the biological availability of the transuranic element 241Am for the fresh water snail Lymnaea stagnalis L. was investigated. Concentration factors (CF) were determined in the whole animal, the shell, the shell margin and three internal organs after a short-time experiment of 5 days. The results show that the uptake of 241Am by L. stagnalis could occur by separate processes, namely by adsorption on the external structures (CF between 180 and 7800) and by direct uptake of 241Am from the water or with the food. Compared with the CF in the hepatopancreas (37-580) the CF in the blood remain at relatively low values (0.4-15). Moreover, the biological availability of 241Am for L. stagnalis is influenced by external parameters. The presence of algae, the indirect effect of the presence of PO43-, has a pronounced effect on the accumulation of 241Am by L. stagnalis and yields higher CF. This could mean that the biological fixation of americium is strongly enhanced by its presence in the foodchain. The uptake of 241Am is most significantly affected by the physico-chemical composition of the water. Small differences in the characteristics of fresh waters may thus cause differences of an order of magnitude in the biological availability of 241Am for aquatic organisms. (author)