Enantioselective toxicological response of the green alga Scenedesmus obliquus to isocarbophos

Chiral compounds usually behave enantioselectively in phyto-biochemical processes. Isocarbophos (ICP) is a chiral pesticide that is widely used. To evaluate the toxicological response of ICP and its enantiomers to Scenedesmus obliquus, algal growth, total chlorophyll, total soluble protein, and the superoxide anion radicals (O(2)(•-)) were investigated. The microalgae were treated with ICP and its enantiomers at 0.01-10 mg/l for 96 h. The growth of S. obliquus was stimulated at low levels of ICP and its enantiomers (0.01-1 mg/l), but all were inhibited at high concentrations (10 mg/l). The total soluble protein content and total chlorophyll content of the tested green alga S. obliquus gradually increased, depending on the growth of algal cells in the medium. Meanwhile, the content of O(2)(•-) was decreased. Interestingly, the cell number and content of the chlorophylls and protein decreased with increasing levels of concentration, whereas O(2)(•-) increased. Our results indicated that enantioselectivity was observed in the dose-response of ICP and its enantiomers in S. obliquus. The high O(2)(•-) level might lead to the death of S. obliquus. The stimulation of growth suggests a regulatory mechanism that is related to the capability of the algae to adapt to the O(2)(•-).