Environmental mobility of radiocaesium in the Pripyat catchment, Ukraine/Belarus

Evidence from research in the Pripyat catchment, reviewed here, indicates t hat under the ecological conditions prevalent in this area, radiocaesium (C s-137) is highly mobile in both river water and poorly drained organic soil s. Data collected at three different spatial and temporal scales demonstrat e the effects of hydrological events on Cs-137 mobility. During the period 1988-1994, Cs-137 contamination in some poorly drained organic soils in the Pripyat catchment and in the milk from cows grazing on these soils are gen erally declining much faster than the radioactive half life. However, sharp increases in levels of Cs-137 in both floodplain soils and milk to 2-3 tim es that observed immediately after the initial deposition have been measure d immediately after summer floods. The processes causing these observed cha nges have not yet been fully explained but the sites where enhanced Cs-137 mobility has been detected are clearly associated with the spatial patterns of organic soils and river flooding.