Sole and co-exposure toxicity of commercial formulations ethoprophos and bispyribac-sodium to Oreochromis niloticus: Assessment of oxidative stress, genotoxicity, and gill ultrastructure.

Aquatic organisms are simultaneously exposed to multiple hazardous chemicals that can be released into water bodies. The current study aimed to evaluate the effect of sublethal concentration (1/50 96 h-LC₅₀) of two formulated pesticides: ethoprophos, bispyribac-sodium, and their combination for 1, 2, 3, and 4 weeks on oxidative stress, genotoxic response, and gill morphology in Nile tilapia. This study is the first to demonstrate the toxic effects of ethoprophos and bispyribac-sodium mixture on the commercial important species, Oreochromis niloticus. The results showed that the 96 h-LC₅₀ values of ethoprophos and bispyribac-sodium were 4.8 and 0.064 mg/L, respectively. Additionally, exposure to individual or combined pesticides induced a significant increase in the level of malondialdehyde (MDA), glutathione S-transferase (GST), and 8-hydroxy-2-deoxyguanosine (8-OHdG), as well as a notable decline in reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) levels at all time of exposure. Furthermore, there were alterations in ultrastructure of the gill samples, including erosive lesions on the primary and secondary lamellae, fusion of microridges, and excessive mucus secretions on the epithelium. The data clearly demonstrate that the negative effects of the tested compounds are time-dependent and are more severe in combination than in a single compound. Collectively, our results indicated that the interaction of ethoprophos and bispyribac-sodium might be largely synergistic and provide new insights into the molecular mechanisms of fish confronting these substances.