Use of rare earth elements as tracers for soil–plant transfer of trace elements

Transfer of trace elements from soil to plant is a corner stone for risk assessment. Rare earth elements (REE) are frequently used as geochemical tracers for element transfer to plant. In this study, we evaluated biogeochemical behaviors of trace elements and REE in the soil–plant continuum to assess to what extend the REE monitoring allows identifying preferential pathway from soil to plant. We quantified 11 trace elements and 14 REE in soil, root, shoot, soil solution, and soil water-extract samples of an intercropping cover crop. Evaluation of the element mobility was performed using both soil extractability and transfer factors. Results showed distinct soil–plant transfer of trace elements according to their biological roles or substitution potential. Soil, root, and shoot REE patterns were similar, indicating a large influence of soil REE composition on plant one. Compared to light REE (LREE), heavy REE (HREE) were more extractable and thus transferred to plants. We also observed differences in Ce and Eu behavior concerning soil extractability and transfer from root to shoot. Soil solution and soil water-extract samples are not chemically representative of the fraction that can be uptaken by plants. However, LREE/HREE and Ce/Eu ratios in soil solution and soil water-extract samples can be used as indicators of environmental conditions