de Arruda Leite_2025_Comp.Biochem.Physiol.C.Toxicol.Pharmacol_296_110236

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 microg/L) at different developmental stages (24, 48, 72, 120, and 144 hpf). Morphological, behavioral, and biochemical endpoints were assessed. Exposure to concentrations <=125 microg/L significantly reduced swim bladder inflation (up to 100 % inhibition at <=250 microg/L) and induced spinal curvature in over 60 % of larvae. Survival decreased progressively with increasing concentrations, reaching 100 % mortality at 1000 microg/L. Larvae exposed to 125 microg/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.