A COMPARATIVE-STUDY OF RADIOCESIUM MOBILITY MEASUREMENTS IN SOILS ANDSEDIMENTS FROM THE CATCHMENT OF A SMALL UPLAND OLIGOTROPHIC LAKE (DEVOKE-WATER, UK)

The mobility of radiocesium was studied in a number of soil and sedime nt cores collected from the Devoke Water catchment. Samples were subje cted to a range of techniques, which are currently used in countries f rom western Europe and the former Soviet Union and which were develope d on the premise that radionuclides are present in different forms whi ch influence their mobility in the environment. The techniques were fo und to provide complimentary information and are very useful in the pr ediction of the mobility of post-Chernobyl radionuclides in the aquati c environment. Radiocesium was found to be much more mobile in the org anic soils of the Devoke Water catchment than in the mineral soils. A simple model, based on the similarities in the ion-exchange behavior o f radiocesium and potassium, was successfully used to predict the conc entration of radiocesium in runoff water and in the lake. The results suggest radiocesium in the peat soils to be mainly bound to organic ex change sites. In-situ K-D values for radiocesium in Devoke Water sedim ents, which varied over one order of magnitude with depth in the sedim ent, were accurately predicted using an ion-exchange model based on th e premise that radiocesium was sorbed exclusively on the frayed edges of clay minerals. It is shown that ''exchangeable''-K-D's more accurat ely reflect the fraction of particulate radiocesium that is available for exchange with the solution and most closely correspond to the assu mptions of the ion-exchange theory. Therefore, this parameter is recom mended for use in radionuclide transport models. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.