Diffusive gradients in thin films (DGT) for measuring potentially bioavailable pesticide residues in soil systems: Current challenges and perspectives

Pesticide residues in terrestrial ecosystems may cause unintended toxicity toward soil micro- and macro-fauna and plants leading to detrimental effects on environmental quality and crop productivity. However, conventional methods for measuring pesticide residues only quantify the total pesticide concentration in soil, which may in some cases be higher than the portion to which organisms are actually exposed (i.e., the bioavailable fraction). To measure potentially bioavailable pesticide residues and/or other organic pollutants (OPs), the diffusive gradients in thin films (DGT) technique has been proposed. DGT is an <i>in situ</i> passive sampling technique that mimics the diffusional flux of a target compound toward plant roots under a diffusion-limited system, typically present in the soil. In other words, DGT measures the analyte present in the soil solution and analyte fractions that are resupplied from the solid phase. Due to this benefit, DGT has been designed and tested for measuring the potential bioavailability of various OPs but with less focus to date on soil pesticide residues. This paper reviews recent advances in the application of the DGT technique, focussing on pesticides in soil system, and provides perspectives on using this method to accurately assess the potential bioavailability of soil pesticide residues to plants. Research to date suggests that the DGT technique can predict the concentration of bioavailable pesticide residues more accurately than conventional solvent extraction techniques or soil pore water analyses. This presents many opportunities for the development of DGT-based standard methods for supporting soil pesticide management and risk assessments.