The enantioselective toxicity and oxidative stress of beta-cypermethrin on zebrafish

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Although the toxicity of beta-cypermethrin (beta-CYP) to aquatic organisms has become a significant concern in recent years, its enantioselective effects on non-target organisms is poorly understood. To investigate the enantioselective toxicity of beta-CYP on zebrafish, adult zebrafish were exposed to a series of isometric concentrations of four beta-CYP enantiomers and the beta-CYP racemate for 96 h. In addition, the activities of four antioxidant enzymes and the malondialdehyde (MDA) content in zebrafish liver and brain were tested after 15 and 30 days beta-CYP enantiomers and racemate exposure under environmentally relevant dosages (0.01 and 0.1 μg/L). According to the acute toxicity results, the 1R-cis-αS and 1R-trans-αS enantiomers were more lethal than 1S-cis-αR and 1S-trans-αR. At 0.1 μg/L, the 1R-cis-αS and 1R-trans-αS enantiomers, and the beta-CYP racemate could significantly induce a hepatic MDA content at 30 days post exposure (dpe), while only 1R-cis-αS caused brain lipid peroxidation. An apparent regulation of antioxidase levels was observed in zebrafish liver and brain after exposure to the 1R-cis-αS and 1R-trans-αS enantiomers, and the beta-CYP racemate. In contrast, no significant oxidative stress was observed in zebrafish exposed to 1S-cis-αR and 1S-trans-αR enantiomers under the test concentrations. This work demonstrated the occurrence of enantioselectivity in toxicity and oxidative stress of beta-CYP to adult zebrafish, which should be considered in environmental risk assessments.