Molecular to tissue-level perspective: Evaluating the toxicity and ecological risk of fluopyram to Eisenia fetida

Fluopyram, a succinate dehydrogenase inhibitor (SDHI) fungicide, is applied to soil for the control of nematode diseases. However, its toxicity to non-target soil organisms such as earthworms remains poorly understood. We hypothesized that fluopyram exposure would induce multi-level toxicity in Eisenia fetida through the activation of oxidative stress and disruption of gut microbial homeostasis. To test this hypothesis, we investigated the ecotoxicological effects of fluopyram on E. fetida. Results showed significant accumulation of fluopyram (2.73 mg kg^-1) in the gut of E. fetida, leading to suppressed growth and reproduction. Furthermore, it induced a significant increase in reactive oxygen species, activating oxidative stress and altering related enzyme activities and gene expression. Transcriptome analysis confirmed that the oxidative stress was induced via the c-Jun N-terminal kinase (JNK) signaling pathway. Concurrently, the digestive function of earthworms was impaired, characterized by reduced digestive enzyme activities and an altered gut microbial community structure. Furthermore, molecular ecological network analysis revealed that fluopyram disrupted the complexity and stability of the gut microbial network. In conclusion, fluopyram induces multi-toxicity in E. fetida by triggering JNK pathway-mediated oxidative stress and disturbing gut microbiota balance, which corroborates our initial hypothesis. This study enriches the toxicological database for E. fetida and provides a more comprehensive theoretical basis for the scientific assessment of the soil ecological risks of fluopyram.