Trace elements are chemical elements present in low concentrations in the environment, including: (1) essential elements for plants and/or animals (such as Cu, Mn, and Zn), which sometimes cause human deficiency (frequent for Mo and Se) and toxicity when concentrations are below or above certain thresholds, respectively; and (2) elements with no identified biological role, which only cause toxicity to human health above a specific threshold value (cases of As, Cd, and Pb). These elements in soils can be transferred to plant through different processes that depend on the element speciation, resulting in distinct bioavailabilities. Agricultural practices can influence the transfer of trace elements, constituting a potential lever on environmental and health issues. Indeed, exogenous organic matter constitutes a reactive surface that controls the retention and bioavailability of trace elements in soils. Quantifying its role is therefore essential for a better agricultural management.

In this context, we aimed to evaluate the influence of organic matter application on the chemical transfer from soil to plant in uncontaminated and gradually contaminated agricultural soils considering various trace elements. To better track the fate of these trace elements, we considered stable isotopes (Cu, Zn, Pb and Fe) and rare earth elements as geochemical tracers. Specifically, organic matter application (manure, compost, and crop residues) was studied on maize growing on four Belgian agricultural soils with contrasting contamination levels and origins in a greenhouse experiment. We measured trace element content and used geochemical tracers in soil, soil solution, and plant samples to follow the element fate between compartments.