Stereoisomeric developmental toxicity of orysastrobin and its isomeric metabolite in zebrafish (Danio rerio) embryos: Cardiac abnormal development by orysastrobin.

Orysastrobin (OSB), a strobilurin fungicide, inhibits the normal redox reactions of cytochrome bc1 at the Qo site of target phytopathogenic fungal species. Its frequent detection and high concentrations in natural wetlands and rivers have raised concerns regarding its acute toxicity and potential effects on fish. Therefore, this study examined the acute toxicities of OSB and its stereoisomeric metabolite F001 on zebrafish (Danio rerio) embryos, an animal model. OSB and F001 did not induce substantial mortality or inhibit hatching in the treated embryos. However, OSB exhibited acute toxicities, including pericardial and yolk sac edemas, spine curvature, and bleeding, at 5.0 mg/L concentration. In contrast, F001 did not induce such abnormalities in zebrafish embryos within the tested concentration ranges. Additionally, OSB induced abnormal cardiac development and significantly impaired heart function in embryos, likely due to the up-regulation of key heart development genes, such as kcnn6a and amhc. In OSB-treated embryos, a developmental delay in liver formation was observed. OSB-induced reactive oxygen species in zebrafish embryos. Overall, this study underscores the importance of gathering comprehensive toxicological data on OSB and F001 in fish to fully understand their environmental impacts, emphasizing the urgent need for repeated periodic monitoring to mitigate the environmental risks posed in agricultural waters, reservoirs, and other aquatic ecosystems.