Enantioselective Toxic Effects and Degradation of Myclobutanil Enantiomers in Scenedesmus obliquus

Research on the enantioselective environmental behavior of chiral pesticides has been a hot spot of environmental chemistry recently. In this study, the acute toxicity of myclobutanil enantiomers was investigated with the aquatic algae Scendesmus obliquus. After exposure for 96h, the EC50 values for (-)-myclobutanil, rac-myclobutanil and (+)-myclobutanil were 3.951, 2.760, and 2.128mg/L, respectively. The photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoids) and antioxidant enzyme activities catalase (CAT) were determined to evaluate the different toxic effects when S. obliquus were exposed to 1.5, 5 and 15mg/L of rac-myclobutanil, (-)-myclobutanil, and (+)-myclobutanil for 96h, respectively. In addition, the degradation of myclobutanil enantiomers in S. obliquus was also studied. Myclobutanil in the medium inoculated with algae degraded faster than in the uninoculated medium. The degradation of (-)-myclobutanil was faster than that of (+)-myclobutanil at a concentration of 3mg/L. On the basis of these data, the acute toxicity and toxic effects of myclobutanil against S. obliquus were concluded to be enantioselective, and such enantiomeric differences should be taken into consideration in pesticide risk assessment. Chirality 25:858-864, 2013. (c) 2013 Wiley Periodicals, Inc.