Genotoxicity of the pesticide Dichlorvos and herbicide Butachlor in Rhacophorus megacephalus tadpoles

Dichlorvos and Butachlor are,respectively,the most commonly used pesticide and herbicide in Chinese agriculture.Run-off from fields treated with these agricultural chemicals contaminates various bodies of water,from ditches to lakes and rivers,and could have a negative impact on indigenous aquatic fauna.In this report,the alkaline single-cell gel electrophoresis assay or comet assay was performed on erythrocytes from Rhacophorus megacephalus tadpoles following whole-body exposure to increasing concentrations of the tested substances.The animal is common in the agricultural regions of South China.Tadpoles treated for 24 h in the laboratory with different concentrations of the test agents,2.08,4.16,6.24,8.32,10.40 mg/L for Dichlorvos and 0.1025,0.205,0.410,0.820,1.230 mg/L for Butachlor,had significant,dose-responsive increases in the levels of DNA damage,as measured by the mean DNA length:width ratio.Concentrations as low as 2.08 mg/L Dichlorvos and 0.41 mg/L Butachlor resulted in significant increases in DNA damage in the tadpoles.There was a strong linear correlation between the mean DNA length-to-width ratios and the concentrations of the two test substances:Dichlorvos,y=1.136±0.0083x,r=0.957,P0.01;Butachlor,y=0.968±0.0093x,r=0.964,P0.01.The results of this study indicate that these two commonly used agricultural chemicals produce DNA damage in an indigenous Chinese amphibian,and that using the Comet assay may be useful for measuring DNA damage in tadpoles exposed in the field.