Migration of Cs-137, Sr-90, and Pu239+240 in Mediterranean forests: influence of bioavailability and association with organic acids in soil

摘要

The understanding of downward migration of anthropogenic radionuclides in soil is a key factor in the assessment of their environmental behavior. There are several factors that can affect this process, such as the radionuclide source, their chemical form, soil and environmental characteristics, etc. Two Mediterranean pinewood ecosystems in Spain, which were affected mainly by global fallout, were selected to assess the migration of Cs-137, Sr-90, and Pu239+240. Using auxiliary modeling (diffusion-convection equation and compartmental model), it followed from field observations that the migration velocities of Sr-90 and Pu239+240 were similar and higher than that of Cs-137. The downward migration of radionuclides can be considered a consequence of their association with soil particles. A sequential speciation procedure also confirmed that Sr-90 was the most bioavailable radionuclide followed by Pu239+240 and Cs-137. Although this can explain the different velocity of Sr-90 and Cs-137, bioavailability could not explain by itself the similar velocities of Pu239+240 and Sr-90. The presence of organic acids in the soil can also influence the migration of radionuclides attached to them, which decreased in the order: Pu239+240 > Sr-90 > Cs-137. Thus, the joint consideration of bioavailable and humic + fulvic acid fractions can explain the observed differences in the downward velocities. (C) 2015 Elsevier Ltd. All rights reserved.