Pesticide residue patterns in soil and earthworms across agricultural land uses and their relevance to earthworm-consuming wildlife

Pesticides are integral to mainstream agriculture. Consequently, many non-target organisms that rely on agricultural landscapes may be exposed to them. Vertebrate non-target species can be exposed to pesticides via their food webs that may include soil and soil-dwelling organisms, like earthworms. Despite long-term and widespread use, direct links between agricultural practices and pesticide exposure in soil organisms remain understudied. This study screened for 648 current-use pesticides and quantified their presence in soils and whole-earthworm samples derived from farmlands in southwest Friesland, the Netherlands. In June-July 2020, 26 fields differing in crop type and agricultural management practices were sampled (4 bulb, 7 corn, 8 grass, and 7 old grass fields). Historical land-use and management practices were reconstructed through interviews and farmer data collection. Sampling revealed that insecticides were rarely detected. Fungicide concentrations were highest in bulb field soils, while the herbicide metabolite terbuthylazine-2-hydroxy dominated corn field soils. Grassland soils revealed elevated fungicide levels corresponding with past bulb cultivation, indicating long-term persistence in soil. Soils from bulb fields were associated with prothioconazole-desthio, metolachlor, and metamitron, whereas corn-field soils were associated with foramsulfuron, fluroxypyr-1-methylheptylester, and fluroxypyr. Bixafen was associated with old-grassland soils. Pesticide residues in whole-earthworm samples were generally consistent with the pesticide profiles observed in soil. These results demonstrate that crop type and management practice structure pesticide residue profiles in soil and earthworms, indicating that earthworm-consuming wildlife may be exposed to these compounds through their diet.