Enantioselective toxicity of lactofen and its metabolites in Scenedesmus obliquus

In this study, the acute toxicity of lactofen and its two metabolites desethyl lactofen and acifluorfen was determined in the aquatic algae Scenedesmus obliquus. After exposure for 96 h, the EC50 values for S-(+)-, rac-, and R-(-)-lactofen were 0.896, 0.784, and 0.649 mu g/L, respectively; the EC50 values for S-(+)-, rac-, and R-(-)-desethyl lactofen were 0.837, 0.822, and 0.696 mu g/L, respectively; and the EC50 value for acifluorfen was 340.838 mu g/L. The results indicate that the toxicities of the transformation products are lower than that of the parent compound and that the acute toxicity (96 h EC50) of these compounds is enantioselective. The photosynthetic pigment content (Chl a, Chl b, total chlorophyll and carotenoids), antioxidant enzyme activity (CAT, SOD), and malondialdehyde content (MDA) were investigated to assess the different toxic effects when S. obliquus was exposed to lactofen and its two metabolites for 96 h. On the basis of these data, the acute toxicity and toxic effects of lactofen and its two metabolites against S. obliquus were concluded to be enantioselective, indicating that such enantiomeric differences should be taken into consideration in the study of pesticide risk assessment. (C) 2015 Elsevier B.V. All rights reserved.