Enantiomer-specific effects of metconazole disrupt soil microbiota, gut homeostasis, and genomic responses of Eisenia fetida.

The selective use of highly active, low-risk enantiomers in place of racemic fungicides represents a sustainable approach to balancing agricultural productivity with environmental safety. Little is known about the enantioselective toxicity and environmental disturbances of the chiral triazole fungicide metconazole (MEZ) on the soil ecosystem. This study revealed that rac-MEZ dissipated faster than cis-MEZs in soil, but rac-MEZ induced a greater decrease in bacterial diversity and network complexity. The longer persistence of cis-MEZs possibly led to greater bioaccumulation in earthworms (Eisenia fetida). Enantioselectivity was observed for two cis-MEZs; cis-1R,5S-MEZ exhibited more severe acute toxicity in earthworms than cis-1S,5R-MEZ. This may be attributed to the potential detoxifying protein (CYP4V), which binds weakly with cis-1R, 5S-MEZ. This weaker detoxification capacity potentially resulted in oxidative stress response system collapse in earthworms, leading to excess reactive oxygen species (ROS) accumulation and disturbance of antioxidant and detoxification enzymes (such as CAT, SOD, and GST). The ROS dysregulation caused by cis-1R, 5S-MEZ induced severe ecotoxicity, including DNA damage, heme metabolism disruption, and downregulation of transcriptional ovo-spermathecal apparatus development and genomic diversification, possibly resulting in higher ipotoxicity, genotoxicity, and reproductive toxicity. Therefore, cis-1R,5S-MEZ is more toxic to earthworms and their ecological functions, suggesting a less favorable environmental risk profile for potential agricultural use.