137Cs and 40K soil-to-plant relationship in a seminatural grassland of the Giulia Alps, Italy

To examine the soil-to-plant transfer of Cs-137 and K-40, we performed a study based on sampling of natural soil and plants from an alpine pasture site situated in the Giulia Alps, Italy, during July 1997. High Cs-137 activity was present in the upper most soil layer, and decreased one order of magnitude at a depth of 10 cm. An opposite gradient was observed for K-40. Simultaneous sampling of soil and plant material was performed in order to analyse transfer factor (TF) values. In spite of homogeneous Cs-137 activities in soil, grass samples showed a high variability. A negative correlation was detected between K-40- and Cs-137-activities in plants. TF values for Cs-137 were highly variable, thus suggesting that this parameter would be independent of Cs-137 soil activity. Lower variability was observed for K-40 TFs values. Our results suggest that TFs are highly variable parameters that appear to be independent on radionuclide soil activity. Because soil and plant characteristics strongly affect TF values, caution is necessary when TF values are used as the sole parameter to predict radionuclide uptake by plants in semi-natural ecosystems. (C) 2002 Elsevier Science B.V. All rights reserved.