137Cs and 90Sr mobility in soils and transfer in soil–plant systems in the Novozybkov district affected by the Chernobyl accident

The Chernobyl radionuclides distribution and mobility in soils and uptake by plants have been studied in seminatural and agricultural moraine and in fluvioglacial landscapes typical for the areas of the Bryansk region affected by the accident. The major part of the Chernobyl 137Cs accumulated in the topsoil is insoluble in water, 40 to 93% of this radionuclide is strongly fixed by soil, while 70 to 90% of the 90Sr is present in water soluble, exchangeable and weak-acid soluble forms. Radionuclide vertical migration is most pronounced in local depressions with organic and gley soils in which both radionuclides are detected to the depth of 30–40 cm. In woodlands, most of the 137Cs is still fixed in litter and the upper mineral soil layer. The concentration peak in litter has moved to the lower AOF layer. Concentration in topsoil leads to high radionuclide uptake by forest species with shallow root systems (bilberry, mushrooms, fern). Contaminated forest products may contribute considerably to the internal irradiation doses of the local population. On flood plain grasslands traditionally used by local populations for haycrops and grazing, radionuclides are more strongly fixed in soils with fine texture. Radioisotope uptake by plants decreases in the order: legumes>herbs>grasses. Transfer to grasses in local depressions is usually higher compared with the dry levees. Observed exclusions are assumed to be due to comparatively low mobility of 137Cs and relatively high K content in soil. 137Cs accumulation in potato tubers grown on sandy soddy podzolic watershed soils mainly corresponds to its total amount in soils; uptake of 90Sr depends upon the percentage of its most mobile fraction. Pronounced relief is proved to cause different patterns in distribution and migration of radionuclides in soils and local food chains. The study showed it to be true for private farms situated in different landscape positions within the same settlement. The forest litter, topsoil and products, and flood plain pastures, especially localities in depressions are critical materials for the long-term radioecological monitoring of the contaminated landscapes of the study area and those of similar conditions. Population of the areas within the zone of contamination exceeding 15Ci/km2 (555kBq/m2) should be recommended to exclude local forest products from their diets and to avoid cattle grazing on wet flood plain meadows without remediation.