Enantioselective toxic effects of cyproconazole enantiomers against Rana nigromaculata.

The environmental contaminant, especially pesticides, threatened the amphibian population. In this assay, the enantioselective behavior of cyproconazole on Rana nigromaculata was studied. We found LC50 (lethal concentration causing 50% mortality) of 4-enantiomers was nearly twice as 3-enantiomers in 96 h acute toxicity test. Besides, the significant considerable variation of oxidative stress and LDH (lactic dehydrogenase) induced by the four enantiomers indicated that cyproconazole could enantioselectively affect enzymes in tadpoles. Bioaccumulation experiments showed the order of cyproconazole in the tadpoles was 4-enantiomers>3- enantiomers>2- enantiomers>1- enantiomers during the exposure for 28d. In tissue distribution test, cyproconazole was formed and accumulated in order of 4-enantiomers>2-enantiomers>3- enantiomers>1- enantiomers, except that in the gut. During the elimination experiment, cyproconazole was rapidly eliminated by 95% within the only 24 h. These results suggested that the influence of enantioselective behavior should consider when assessing ecological risk of chiral pesticides to amphibians.