Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 142, No. 2, (1990) 531-538 A STUDY ON RADIONUCLIDE ASSOCIATION WITH SOIL COMPONENTS USING A SEQUENTIAL EXTRACTION PROCEDURE G. RIISE*, H. E. BJORNSTAD*, H. N. LIEN*, D. H. OUGHTON**, B. SALBU* *Isotope and Electron Microscopy Laboratories, Agriculture University of Norway, P.O. Box 26, N-1432 Aas-NLH (Norway] **Department o f Chemistry, University o f Manchester, Manchester (England] (Received February 8, 1990) Measurements performed in 1986-1988 demonstrate that most of the radiocesium iso- topes (13~Cs and i a4Cs ) deposited after the Chemobyl accident are still located in the upper soil layers (0-2 em). The vertical migration appears to be slow, and only a small fraction of the radiocesium has been transferred into the biological cycle. Sequential extraction tech- niques have been utilized in order to investigate the degree of binding or association be- tween deposited radionuclides (137Cs, 134Cs and 9o Sr) and components in soil. "lhe results indicate that a major fraction of the radiocesium is associated strongly with organic and mineral materials in the litter or upper soil layers: less than 10% is easily leachable. The dis- tribution of 137Cs throughout the fractions was similar to that determined for naturally occurring stable cesium (133Cs), implying that isotopic exchange had been extensive. For 9oSt, the results show a relatively high leachable fraction. Therefore, present results indicate that radiocesium should be less mobile, and less available for root uptake, than 9oSr in soil. Introduction Following the Chernobyl accident, radionuclides were deposited in Central Norway (April 28 - May 2, 1986). Hot particles containing radioisotopes ofCs, Ru, Ce, Nb, Zr and Sr have been reported from several countries in Europe, 1,2 and have been identified in Norway, 3 Furthermore,hot colloids containing different radionuclides, including 13 7Cs and 134Cs, were identified in rainwater collected in Norway (4). Three years after the deposition, radiocesium is still retained in the upper soil layer, with a relatively small fraction being transferred to vegetation, implying a strong association of Cs-isotopes with soil components. However, transformation processes taking place in the environment (e.g. weathering) may influence the mobility both of the radiocesium isotopes and of other radionuclides (i.e. 9~ Information on the binding mechanisms of trace metals and radionuclides with soil components, i.e. primary ad/absorption processes, can be obtained from desorption experiments. Elsevier Sequoia S. A., Lausanne Akaddmiai Kiad6, Budapest