Chemical availability of Cs-137 and Sr-90 in undisturbed lysimeter soils maintained under controlled and close-to-real conditions

Chemical availability of Cs-137 and Sr-90 was determined in four undisturbe d soils in a lysimeter study three and four years after deposition to the s oil surface. The study was part of a larger project on radionuclide soil-pl ant interactions under well-defined conditions. The soil types were loam, s ilt loam. sandy loam and loamy sand, and were representatives of important European soil and climatic conditions. The lysimeters were installed in gre enhouses with climatic and hydrological control, and were contaminated with Cs-137 and Sr-90 in an aerosol mixture simulating fallout from a nuclear a ccident. Soil samples were taken from several depths in each soil in 1997 a nd 1998 and the samples were sequentially extracted with H2O, NH4Ac, NH2OH . HCl, H2O2 and HNO3. Extractability of Cs-137 decreased in the order: HNO3 > Residual greater than or equal to NH4Ac > H2O2 greater than or equal to NH2OH . HCl greater than or equal to H2O. More than 80% was found in the ac id digestible or residual fractions, and 11-17% in labile fractions. Soil t ype differences were small. Extractability of Sr-90 decreased in the order: NH4Ac > NH2OH . HCl > HNO3 > H2O2 approximate to H2O. 31-58% was found in easily available fractions. Differences between soil types were quite small . The results suggest that availability of Cs-137 for plant uptake and migr ation is low, whereas availability of Sr-90 is rather high. (C) 2001 Elsevi er Science Ltd. All rights reserved.