Metabolomics insights into the combined effects of boscalid and polystyrene microplastics on earthworms (Eisenia fetida): The critical role of pesticide dose and microplastics size

The extensive use of pesticides and agricultural plastic films has created emerging environmental challenges, with accumulating evidence showing their co-occurrence in soils. This coexistence raises serious concerns about their combined ecological impacts, particularly their potential synergistic effects that remain poorly understood and require urgent investigation. In this study, we evaluated the ecological toxicity effects of boscalid (BOS, 1.0 and 5.0 mg/kg) and polystyrene microplastics (PE MPs, 15 and 150 μm) combined exposure on earthworms ( Eisenia fetida ) from changes in oxidative defense system, intestinal structural function, and metabolic phenotypes. Our findings demonstrated that co-exposure to BOS and PE MPs significantly inhibited earthworm growth and induced oxidative stress. Furthermore, the combined treatment disrupted intestinal barrier integrity. Metabolomics analysis revealed substantial perturbations in earthworm metabolic profiles, suggesting systemic physiological dysregulation. Notably, the toxicological interactions between BOS and PE MPs were dose- and size-dependent, with higher pesticide concentrations and greater MPs exacerbating adverse effects. Collectively, this study highlights that agricultural plastic residues could synergistically enhance the toxicity of co-occurring pesticides, underscoring the need for greater environmental and regulatory scrutiny of such combined pollutants.