RESUMO
Results are presented from studies concerning the behavior of the Chernobyl-derived radionuclides 137Cs and 90Sr 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 137Cs 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 90Sr, activity levels ranged from 1.4-40 kBq m-2, and the highest 90Sr deposition was observed in the Gomel Region, Belarus. The highest 90Sr: 137Cs 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 137Cs was found to be strongly bound to soil components. In the Russian and Ukrainian soils, between 40 and 98% of the 90Sr was found in the easily extractable fractions, and the distribution of 137Cs and 90Sr followed that of the naturally occurring stable isotopes of cesium and strontium. However, in the Gomel soils, between 20 and 50% of the 90Sr was easily extractable and the distribution of 90Sr within the extraction fractions did not follow that observed for stable strontium. These results are thought to reflect the association of 90Sr with fuel particles deposited in the Gomel Region. The mobility of 90Sr is expected to increase with time (as the particles weather) in these soils.
