Physiological and Biochemical Responses of Soil‐Dwelling Organism, Earthworm Exposed to Succinate Dehydrogenase Inhibitor (SDHI) Fungicides

Succinate dehydrogenase inhibitor (SDHI) fungicide use in agriculture is steadily increasing, raising concerns about their negative effects on non-target soil organisms. This study evaluated the short-term (14-day) effects of fluxapyroxad (FLU) and boscalid (BOS) on Eisenia fetida, including studies of survival, growth, and biochemical biomarkers. Acute toxicity testing according to OECD 207 showed no significant mortality. Earthworm biomass decreased in a concentration-dependent manner, with average reductions of 19.9% and 41.3% at the highest FLU and BOS doses (12.2 and 12.0 mg/kg, respectively) relative to the solvent control after 14 days of exposure. Biochemical analysis revealed oxidative stress responses, with average 1.07-2.62-fold increases in the production of reactive oxygen species (ROS) under FLU exposure (0.12-12.2 mg/kg) and 0.96-1.75-fold increases under BOS exposure (0.12-12.0 mg/kg). Elevated ROS levels were accompanied by altered activities of antioxidant enzymes (SOD and CAT) and increased lipid peroxidation (LPO). Detoxification enzymes (GST and CES) also showed increased activity, indicating enhanced metabolic stress. Integrated biomarker response version 2 (IBRv2) values increased significantly (> 3) with increasing concentrations, indicating cumulative physiological disruption. Risk quotient (RQ) analysis indicated low risk based on survival and growth endpoints, whereas selected biochemical endpoints produced RQ values > 1, indicating potential ecological concern. These findings indicate the importance of incorporating sublethal endpoints into ecological risk assessment. Future studies should focus on long-term exposure at low concentrations and reproductive endpoints to better understand the long-term effects of SDHI fungicides in soil ecosystems.