Study of the transfer of radionuclides in trees at a forest site

The transfer of radionuclides such as 137Cs and 90Sr from soil to trees (conifers) was studied in a forest area, the Boréon massif, 30 km north of Nice in South Eastern France. This area has been highly contaminated after the Chernobyl accident. Besides the γ-emitting fission products, the α-emitters 238Pu and 239+240Pu and the pure β-emitter 90Sr were measured in different parts of the studied trees (roots, branches, twigs, etc.). As has already been reported by other authors, the radionuclide activities in the tree rings are not correlated with the fallout deposition. They were found varying according to the sap flux in the tree and higher in sapwood than in heartwood. For cesium the root absorption was found to be lower than the atmospheric deposition. Soil-to-plant concentration factors were calculated for 137Cs, 90Sr and 239+240Pu.