Seasonal Variations in Interstitial Water Transuranium Element Concentrations

Abstract

The porewater concentrations of the transuranium elements Np, Pu, and Am have been measured over time at a salt marsh in west Cumbria, U.K., and all three show seasonal variations. Pu follows the pattern previously observed at this site very closely, with concentrations reaching a maximum of 3.2 mBq L-1 and a minimum of 0.8 mBq L-1 in 1996, compared with 3.5 mBq L-1 and 1.1 mBq L-1, respectively, in 1994. However, no relationship with dissolved Fe and Mn concentrations was observed in this study. Plutonium and Am concentrations follow similar patterns from April to September, but there are fluctuations in the Am concentration in February which are not observed for Pu. Neptunium concentrations, measured by accelerator mass spectrometry, follow a less clear pattern, although they are at a marked maximum of 0.56 mBq L-1 in February. Changes in Pu and Am concentrations between April and September can be related to changes in the microbial community and suggest that these elements are taken up in biosorption processes. When biomass is low, no relationship is observed between Pu and Am concentrations. There is no correlation between the microbiological data and Np concentrations at any time of year.