Fomesafen induced ecotoxicological responses, bioaccumulation, and implications for soil ecosystems remediation in three ecotypes earthworms

Fomesafen (FSA) is a herbicide commonly used in soybean fields, but its long half-life in the soil can pose pollution risks to the soil ecosystem. Earthworms, which have an indicative function for soil health and play a vital role in maintaining soil ecological functions, have not been fully studied in terms of their susceptibility to FSA. This study examined the effects of different concentrations of FSA on three ecotypes of earthworms (Eisenia fetida (epigeic), Metaphire guillelmi (anecic), and Aporrectodea caliginosa (endogeic)) and found varying trade-off strategy of their growth and reproduction. When subjected to FSA stress, E. fetida prioritized reproduction, A. caliginosa prioritized growth, while M. guillelmi maintained consistent growth and reproduction, effectively allocating the acquired biomass to reproduction. The study also analyzed the oxidative stress response, gene expression, and an integrated biomarker response. The strongest induction performance of the three ecotypes of earthworms was in the expression of antioxidant enzymes such as CAT, POD, SOD, and P450 expression, while the performance was significantly different in AChE activity, AChE and HSP70 expression, which may lead to differences in toxicity and detoxification mechanisms of earthworms in different ecotypes. The partial least squares-path model (PLS-PM) also showed that the three ecotypes of earthworms exhibited different toxicity, detoxification and regulatory pathways under FSA stress. M. guillelmi had the highest IBRv2 index (28.67–42.90). At the same time, the FSA bioaccumulation tended to be stable with increasing concentration, and its main detoxification ability (GST activity and P450 expression) could still maintain the same level as CK at high concentrations, indicating that it is very likely to be a potential earthworm type for FSA remediation. This study firstly provides a comprehensive assessment of FSA's toxic effects on different ecotypes of earthworms and highlights the importance of identifying potential resistant species for soil remediation.