Cycling of Pu, Sr, Cs, and other longliving radionuclides in forest ecosystems of the 30-km zone around Chernobyl

Abstract In the framework of the EC-coordinated research program of ECP-5, the behaviour of radionuclides in natural and seminatural ecosystems was investigated. The main work is focussed on the transfer of radionuclides from soil to plants of the understorey vegetation. Therefore soil and plant samples from three sites in the 30-km zone around Chernobyl were analysed radiochemically for Pu and Sr and by γ-spectrometry for Cs, Ce, Ru, Eu, Sb and other longliving radionuclides. Based on these data, transfer factors of the above-mentioned radionuclides by different 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 activities of plutonium in plants are generally low with transfer factors in the range of 0.001 –.02, but increase to 0.3 in berries. Radiostrontium shows an average transfer factor of 0.2 and is about the same for all plants and sites, whereas the greatest variance in transfer factors is observed for radiocaesium. Depending upon soil type and plant species, 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, unexpectedly high values ranging up to a transfer factor of 0.43 were measured. For other fission products such as ruthenium, antimony, europium and the activation product, cobalt, low transfer factors in the range of 0.001 – 0.01 were determined. These radionuclides are obviously not accumulated by plants.