Temporal change in fallout Cs-137 in terrestrial and aquatic systems: A whole ecosystem approach

During the years after a nuclear accident, the bioavailability and environm ental mobility of radiocesium declines markedly, resulting in large changes in contamination of foodstuffs, vegetation, and surface waters. Predicting such changes is crucial to the determination of potential doses to affecte d populations and therefore to the implementation of radiological counterme asures. We have analyzed 77 data sets of radiocesium (Cr-137) activity conc entrations in milk, vegetation, and surface waters after the Chernobyl acci dent Our results show that the rate of decline in Cs-137 during the years a fter Chernobyl is remarkably consistent in all three ecosystem components, having a mean effective half-life, T-eff approximate to 2 years. By compari ng changes in Cs-137 availability with rates of diffusion of K-40 (a close analogue) into the lattice of an illitic clay (1) we have, for the first ti me, directly linked changes in the environmental availability of Cs-137 to fixation processes at a mechanistic level. These changes are consistent wit h declines in the exchangeable fraction of Cs-137 in soils (2, 3).