Enantioselective toxic effects of hexaconazole enantiomers against Scenedesmus obliquus

Enantioselectivity in ecotoxicity of chiral pesticides in the aquatic environment has been a subject of growing interest. In this study, the toxicological impacts of hexaconazole enantiomers were investigated with freshwater algae Scenedesmus obliquus. After 96 h of exposure, the EC(50) values for rac-hexaconazole, (+)-hexaconazole, and (-)-hexaconazole were 0.178, 0.355, and 0.065 mg l(-1) , respectively. Therefore, the acute toxicities of hexaconazole enantiomers were enantioselective. In addition, the different toxic effects were evaluated when S. obliquus were exposed to 0.2, 0.5, and 1.0 mg l(-1) of rac-hexaconazole, (+)-hexaconazole, and (-)-hexaconazole during 96 h, respectively. The chlorophyll a and chlorophyll b contents of S. obliquus treated by (-)-hexaconazole were lower than those exposed to (+)-hexaconazole, whereas the malondialdehyde contents of S. obliquus treated by (-)-form were higher than those exposed to (+)-form at higher concentrations. In general, catalase activities were significantly upregulated by exposure to (-)-enantiomer than (+)-enantiomer at all three concentrations. However, superoxide dismutase activities exposed to (-)-hexaconazole were lower than that exposed to (+)-hexaconazole at 0.2 mg l(-1) and 0.5 mg l(-1) . On the basis of these data, the acute toxicity and toxic effects of hexaconazole against S. obliquus were enantioselective, and such enantiomeric differences must be taken into consideration in pesticide risk assessment.