Genotoxicity of the Pesticide Dichlorvos and Herbicide Butachlor on Rana zhenhaiensis Tadpoles

Genotoxicity of dichlorvos and butachlor on erythrocytes of Rana zhenhaiensis tadpoles was investigated by the alkaline single-cell gel electrophoresis assay or comet assay. Tadpoles were treated for 24 h in the laboratory with different concentrations of the testing agents, 2.256, 4.512, 6.768, 9.024, 11.280 mg/L for dichlorvos and 0.292, 0.584, 0.876, 1.168, 1.460 mg/L for butachlor, to use the comet Assay to test for the significance of dosage responsiveness to an increase in DNA damage, as measured by the mean DNA tail length-to-width ratio. The concentrations of 4.512 mg/L dichlorvos and 0.876 mg/L butachlor resulted in highly significant increases in DNA damage of the tadpoles. There were linear correlations between the mean DNA tail length-to-width ratio and the concentrations of the two test substances. Our results showed that the two commonly used agricultural chemicals caused dose dependent DNA damage of amphibians, and that comet assay might be a useful tool for measuring DNA damage of tadpoles exposed in the field.