Abstract: To evaluate the toxicity of chlorpyrifos and chlorothalonil in single dose and combinations, zebrafish was taken as biological subjects. By using the static method and real-time fluorescent quantitative PCR, the acute toxicity of chlorpyrifos or/and chlorothalonil on zebrafish embryos and their influence on the related genes of zebrafish larvae gonadal axis were studied. It was shown that chlorpyrifos and chlorothalonil were moderately and highly toxic to zebrafish embryos, respectively, as the 96 h-LC₅₀ (lethal concentration 50) was 2.139 mg·L^-1 and 0.353 mg·L^-1, respectively. The toxicivy of chlorpyrifos and chlorothalonil were synergistic to zebrafish embryos. In the joint exposure of chlorpyrifos and chlorothalonil, the 96 h-LC₅₀ was 0.38 mg·L^-1 and 0.063 mg·L^-1, respectively. Moderate concentration (26.7 μg·L^-1) and high concentration (106.7 μg·L^-1) of chlorpyrifos led to upregulation of the gene expression of the aromatase (CYP19α), vitellogenin (VTG1, VTG2), and estrogen receptor (ERα, ERβ1 and ERβ2). Low concentration of 1.1 μg·L^-1 chlorothalonil led to the upregulation of gene expression of VTG1, VTG2, ERβ1 and ERβ2. Combination of 6.7 μg·L^-1 chlorpyrifos+1.1 μg·L^-1 chlorothalonil led to the downregulation of gene expression of VTG1, ERβ1, ERβ2 and ERα in zebrafish compared with the control. The results indicated that chlorpyrifos and chlorothalonil had an estrogenic effect on zebrafish, while the combination reduced the effect of estrogenic interference. Therefore, the effects of combined pollution should be fully considered for harm assessment of pesticides to aquatic organisms.

Key words: pesticides, water pollution, environmental toxicity