Ecotoxicological impacts of fipronil sulfone: Developmental and behavioral disruptions in zebrafish embryos and larvae

Abstract

Fipronil sulfone is a persistent oxidative metabolite of the insecticide fipronil, frequently detected in aquatic systems and known to exert neurotoxic effects on non-target organisms. Despite its environmental relevance, the developmental impacts of fipronil sulfone remain underexplored. In this study, zebrafish embryos and larvae were exposed to environmentally relevant concentrations of fipronil sulfone (12.5–1000 μg/L) at different developmental stages (24, 48, 72, 120, and 144 hpf). Morphological, behavioral, and biochemical endpoints were assessed. Exposure to concentrations ≥125 μg/L significantly reduced swim bladder inflation (up to 100 % inhibition at ≥250 μg/L) and induced spinal curvature in over 60 % of larvae. Survival decreased progressively with increasing concentrations, reaching 100 % mortality at 1000 μg/L. Larvae exposed to 125 μg/L also exhibited hyperactivity followed by reduced locomotion, likely due to blocked GABAergic receptors and acetylcholinesterase inhibition. Moreover, oxidative stress was confirmed by increased reactive oxygen species and glutathione S-transferase activity. These findings demonstrate that even low concentrations of fipronil sulfone can compromise neurodevelopment and survival in zebrafish, underscoring the need for its inclusion in environmental monitoring and risk assessment frameworks.