Soil-plant transfer of radiocaesium in weakly contaminated forest ecosystems

Abstract

During the Chernobyl accident, large areas in Europe, particularly forests, were contaminated by radiocaesium. Soil-plant transfer is often the first step by which ¹37Cs enters to food chains by incorporating the forest biogeochemical cycle. The present work is devoted to assess the soil-plant transfer of radiocaesium in weakly contaminated forest area, in the Franche-Comté region (16 202 km²) in North Eastern France. This region has been markely contaminated after the Chernobyl accident. Twelve sites, with various functional features and high diversity of ecological contexts were selected to sample forests trees. Two species (Picea abies and Fagus sylvatica) and two organs, (leaves or needles and young branches) were sampled for radioactivity measurements. Radiocaesium activities in soils varied between 61 to 280 Bq.kg^-1DW at 0-5 cm depth and between 14 to 224 Bq.kg^-1DW at 10^-15 cm. Radiocaesium activities in leaves, needles and branches displayed high variability. We reported a large variability of Aggregated Transfer Factors (T_ag) values with respect to vegetation type, organ type and soil features. The activity concentration in the leaves and needles were generally higher than those measured in the branches. The T_ag values could be explained by the radiocaesium bioavailability variability in relation to soil type, soil features and environmental parameters.