Rice-Driven Formation and Transport of Highly Toxic Ethiprole Metabolites in Water–Sediment–Animal–Plant Continuum

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Ethiprole, a phenylpyrazole insecticide widely used as a fipronil alternative, raises emerging ecological concerns due to its poorly characterized metabolic fate in paddy fields. This study systematically explored the environmental behavior, metabolic mechanisms, and metabolite-specific risks of ethiprole across a water–sediment–animal–plant (WSAP) continuum. Rice cultivation markedly accelerated ethiprole degradation by 4.33-fold (half-life of 2.22 days) compared to nonvegetated systems. A sulfide metabolite (E-R) was exclusively detected in plant-containing continuums and exhibited a 15-fold higher acute toxicity to benthic loach (LC 50 of 0.07 mg/L). Crucially, E-R was endogenously generated and preferentially accumulated in rice roots, while oxidative metabolism in aerial tissues produced ethiprole sulfone (E-O). Root-derived E-R subsequently migrated to sediments, persisted for over 50 days, and posed extreme ecological risk (RQ >2000). This work reveals a previously unrecognized rice-driven pathway generating highly toxic metabolites and highlights the need for metabolite-specific risk assessment.