THE MOBILITY OF CS-137 AND SR-90 IN AGRICULTURAL SOILS IN THE UKRAINE, BYELARUS, AND RUSSIA, 1991

Results are presented from studies concerning the behavior of the Chernobyl-derived radionuclides Cs-137 and Sr-90 in soil-plant agricultural systems in the Ukraine, Belarus, and Russia during 1991. The sites, representing ploughed and natural pastures, were located at varying distances between 50 and 650 km and varying directions from the Chernobyl reactor site. The Cs-137 activity concentrations in the upper 0-5 cm soil layer ranged from 25-1,000 kBq m(-2) and were higher in natural pastures as compared to ploughed pastures. For Sr-90, activity levels ranged from 1.4-40 kBq m(-2), and the highest Sr-90 deposition was observed in the Gomel Region, Belarus. The highest Sr-90:Cs-137 ratio was also observed in the Gomel soils, i.e., 15% as compared to between 0.72 and 7.4% in the other soils. The mobility of radionuclides was studied by means of sequential extraction. For all soils, between 60 and 95% of the Cs-137 was found to be strongly bound to soil components. In the Russian and Ukrainian soils, between 40 and 98% of the Sr-90 was found in the easily extractable fractions, and the distribution of Cs-137 and Sr-90 followed that of the naturally occurring stable isotopes of cesium and strontium. However, in the Gomel soils, between 20 and 50% of the Sr-90 was easily extractable and the distribution of Sr-90 within the extraction fractions did not follow that observed for stable strontium. These results are thought to reflect the association of Sr-90 with fuel particles deposited in the Gomel Region. The mobility of Sr-90 is expected to increase with time (as the particles weather) in these soils.