Combined acute toxic effects of fenbuconazole and copper on zebrafish (Danio rerio) at different life stages

In order to clarify the combined acute toxic effects of the fungicide fenbuconazole and copper to zebrafish, the acute toxicity of fenbuconazole and copper alone, as well as their combination at equaltoxicity ratio or at different mass concentration ratios to zebrafish during different life stages were determined. The combined acute toxic effects were evaluated using the additional index (AI) method and co-toxicity coefficient (CTC) method. The results showed that the 96 h-LC₅₀ values of fenbuconazole for adults, embryos, and larvae of zebrafish were 2.615, 4.121 and 4.140 mg/L, respectively, while that of copper were 0.235, 0.353, and 0.429 mg/L, respectively. The order of the acute toxicity was adult > embryo > larvae. The toxic effects of the mixtures on both zebrafish larvae and embryos showed an enhancement tendency. At equitoxicity ratio, the 96 h-LC₅₀ of the mixed fenbuconazole and copper for larvae and embryos was 2.051 and 2.207 mg/L, respectively, and the evaluation results with AI and CTC methods were both additive; while the 96 h-LC₅₀ of the mixture for adults was 1.755 mg/L, and the evaluation results of the two methods were different, which were antagonistic and additive effects, respectively. At different mass concentration ratios, the 96 h-LC₅₀ values of fenbuconazole and copper mixed at 2 : 8, 5 : 5, and 8 : 2 were 0.272, 0.378 and 0.785 mg/L for embryos, respectively, which showed synergistic effects; the 96 h-LC₅₀ values were 0.532, 0.621 and 0.934 mg/L for larvae, respectively, which showed either synergistic or additive effects. The results of the two methods were consistent for the embryos and larvae. As for the adults zebrafish, the 96 h-LC₅₀ values were 0.434、0.653 and 1.053 mg/L, respectively, and the mixtures showed antagonistic effects except that it showed antagonistic and additive effects at 8:2 ratio with the two different methods. The results suggested that the acute toxicity of the mixture of fenbuconazole and copper was stronger to zebrafish at early life stages. This finding will help us to better evaluate the impact of contamination of fenbuconazole and copper on aquatic organisms.