Single and binary-combined toxic effects of acetochlor and Cu²⁺ on goldfish (Carassius auratus) larvae

Acetochlor and copper are common freshwater pollutants and pose a severe threat to aquatic animals. The toxicity of acetochlor (Ac) and Cu²⁺ toward goldfish larvae was investigated by subjecting the larvae to different concentrations of acetochlor, Cu²⁺, and mixed solutions for 1, 3, and 7 days. The length of goldfish larvae exposed to the 100 μg/L Ac + 100 μg/L Cu²⁺ mixed solution was considerably lower than that of the control on day 3, but there were no significant differences among the other groups. The heart rates of the larvae in 100 μg/L Ac + 100 μg/L Cu²⁺ mixed solution were higher than those of the control group on days 3 and 7. Acetochlor and Cu²⁺ also caused severe damage to the liver and intestine of the larvae, especially in the 100 μg/L Ac + 100 μg/L Cu²⁺ mixed solution group. Indicators related to oxidative stress (hydrogen peroxide, catalase, glutathione peroxidase, and total superoxide dismutase) that could potentially be induced by acetochlor or Cu²⁺ began to increase on day 7, and the enzyme activities of the larvae in the mixed groups were significantly lower than those in the control group. In contrast, the expression levels of the genes related to antioxidant stress were rapidly down-regulated in all groups on the 7th day after exposure. Briefly, the combined toxicity of acetochlor and Cu²⁺ was stronger than that of the single toxicity treatments. Furthermore, toxicity toward larvae in the mixed solution group (100 μg/L Ac + 100 μg/L Cu²⁺) was more obvious.