FRACTIONATION OF CESIUM (CS-137) IN CONIFEROUS FOREST SOIL IN CENTRAL SWEDEN

Sequential extraction procedure (SEP) was applied for fractionation of Chernobyl fallout Cs-137 bound onto soils of a coniferous forest ecosystem located in central Sweden. Results of sequentially extracted Cs-137 fractions demonstrated that 8% (mean value) of the total deposited Cs-137 was water soluble (F1) and 13% was NH4OAc extractable (F2). Oxidation of F2 residuals by H2O2, led to a release of 15% of soil-bound Cs-137 (F3). Acid digestion of F3 residuals showed a possibility of releasing an extra amount of soil-bound Cs-137, 22% of the total soil Cs-137 inventory (F4). These two fractions (F3 and F4) include strongly bound Cs-137 that seems to require longer biodegradation processes by soil microflora and microfauna before becoming available for uptake by plants and fungi. More than 37% of the total soil Cs-137 inventory was bound onto soil residuals in a non-extractable form that includes slowly degradable organic matter and other soil residual compartments. The distribution coefficient (K-d) was rather low and shows an inverse relation with the increase of percentage of soil organic matter, which indicates a week binding of Cs-137 onto forest soil. In contrast, chemical fractionation of soil bound Cs-137 showed a substantial fraction of Cs-137 was strongly bound onto soil as organically bound Cs-137. Apparently, the binding processes of radiocaesium onto forest soil seems to be time dependent.