CYCLING OF PU, SR, CS, AND OTHER LONGLIVING RADIONUCLIDES IN FOREST ECOSYSTEMS OF THE 30-KM ZONE AROUND CHERNOBYL

In the framework of the EC-coordinated research program of ECP-5, the behaviour of radionuclides in natural and seminatural ecosystems was i nvestigated. The main work is focussed on the transfer of radionuclide s from soil to plants of the understorey vegetation. Therefore soil an d plant samples from three sites in the 30-km zone around Chernobyl we re analysed radiochemically for Pu and Sr and by gamma-spectrometry fo r Cs, Ce, Ru, Eu, Sb and other longliving radionuclides. Based on thes e data, transfer factors of the above-mentioned radionuclides by diffe rent plants on different soils with varying properties were determined . The transfer factor is defined as ratio of the specific activity in plants to the specific activity in organic horizons. The specific acti vities of plutonium in plants are generally low with transfer factors in the range of 0.001-0.02, but increase to 0.3 in berries. Radiostron tium shows an average transfer factor of 0.2 and is about the same for all plants and sites, whereas the greatest variance in transfer facto rs is observed for radiocaesium. Depending upon soil type and plant sp ecies, the values range from 0.03 in a fern up to 16.7 in a mushroom. For cerium, a 3-valent ion with generally low uptake by plants, unexpe ctedly high values ranging up to a transfer factor of 0.43 were measur ed. For other fission products such as ruthenium, antimony, europium a nd the activation product, cobalt, low transfer factors in the range o f 0.001-0.01 were determined. These radionuclides are obviously not ac cumulated by plants.