Agricultural Practices Explain Pesticide Residues in Soil and Earthworms

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 earthworm samples derived from farmlands in southwest Friesland, the Netherlands. In June-July 2020, twenty-six fields representing a gradient from intensive to extensive management were sampled (four bulb, seven corn, eight grassland and seven old-grassland). Historic land-use and management practices were reconstructed through interviews. 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 their long-term persistence in soil. Bulb field soils 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 profiles in earthworms were generally consistent with those observed in soil. A strong positive relationship between soil concentrations and the likelihood of earthworm pesticide detection indicates that soil exposure is a key driver of pesticide concentrations in earthworms. These results demonstrate that crop type and management practices structure pesticide profiles in soil and earthworms, indicating that earthworm-consuming wildlife may consequently be exposed to these compounds through their diet.