Longevity of modern pesticides in Swiss agricultural soils: distribution, drivers, and potential environmental implications.

Abstract

The widespread use of pesticides in crop protection leads to their release into soil, where their occurrence is shaped by multiple factors, including land use, management practices, and pedoclimatic conditions. However, their long-term behavior and effects on beneficial soil organisms remain poorly understood. Here, we investigated the drivers of pesticide residue occurrence in agricultural soils, their persistence beyond the period in which ≥90% of the applied substance is expected to dissipate from the soil according to regulatory data (DT90), and potential ecotoxicological effects on soil invertebrates. We analyzed 146 substances (127 active ingredients and 19 transformation products) in topsoil from 126 Swiss sites across different land uses (arable and vegetable fields, orchards, and vineyards) using a sensitive analytical method. In addition to pesticide application intensity, pedoclimatic factors - particularly soil organic carbon and 30-year mean precipitation - emerged as key drivers of residue occurrence. Observed field persistence exceeded regulatory maximum field half-lives in about 60% of cases, especially for residues remaining in soil well beyond the DT90 period. While most pesticide concentrations declined to below 10% of the applied amount after this period, several remained above this threshold for extended periods and at concentrations potentially relevant for ecotoxicological effects on soil invertebrates. Among these, difenoconazole, epoxiconazole, and chlorpyrifos contributed most strongly to the potential ecotoxicological impact across land uses, with overall concerns higher in Switzerland than in the European LUCAS soil monitoring survey. Our findings indicate that regulatory prospective persistence estimates frequently fail to capture field longevity and associated potential ecotoxicological effects of multiple pesticides.