Effect of chemical pollution on forms of Cs-137, Sr-90 and Pu-239,Pu-240 in Arctic soil studied by sequential extraction

The aim of the present study was to determine the forms of Cs-137, Sr-90 an d Pu-239.240 occurring in different soil horizons using sequential extracti on of samples taken from four sites located along a pollution gradient from the copper-nickel smelter at Monchegorsk in the Kola Peninsula, Russia, an d from a reference site in Finnish Lapland in 1997. A selective sequential- leaching procedure was employed using a modification of the method of Tessi er, Cambell and Bisson ((1979). Analytical Chemistry, 51, 844-851). For Cs- 137 organic (O) and uppermost mineral (E1) layer were studied, for Sr-90 an d Pu-239.240 only the uppermost organic layer (Of). The fraction of Cs-137 occurring in readily exchangeable form in the organic layer was about 50% a t the reference site and decreased as a function of pollution, being 15% at the most polluted site in the Kola Peninsula. There was a clear positive c orrelation in the O layer between the distance from the smelter and the per centage of Cs-137 extracted in the readily exchangeable fraction (Spearman correlation r(sp) = 0.7805, p = 0.0001), whereas in the El layer no correla tion was evident. The distribution of Sr-90 in the Of layer was similar at all sites, with the highest amounts occurring in exchangeable form and boun d to organic matter, whereas stable Sr showed a somewhat different distribu tion with the highest amount in the oxide fraction. Most of the Pu-239.240 was bound to organic matter. Chemical pollution affected the exchangeable f raction of Pu-239.240, which was about 1% at the most polluted site and 4-6 % at the other sites. (C) 2000 Elsevier Science Ltd. All rights reserved.