Ecotoxicological Difference Of Two Typical Chiral Pesticides

About 25% of currently used pesticides are chiral, and this ratio is increasing with the introduction of more structure-complex pesticides. A chiral pesticide has two or more enantiomers that share the same physicochemical properties and behaviors in achiral environment. However, as biochemical receptors and enzymes generally distinguish chirality, enantiomers of the same pesticide may behave differently in biological activities and in biologically mediated environmental processes. The worldwide research on the enantioselective behavior of chiral contaminants in the environment is still at its early stage, especially in China. Because of the bioactivities of enantiomers being so different, they are selectively degraded and interacted in the environmental media. More attentions have been given to environmental behavior of enantiomers.Racemic product of metolachlor contains two R-enantiomers and two S-enantiomers. S-metolachlor is now widely used instead of rac-metolachlor for the former is more effective in herbicidal activity than the latter. A comparative toxicity assessment of rac- and S-metolachlor was discussed through their effects on some enzyme activities of the fifth-instar silkworm, Bombyx mori L. The results showed that rac-metolachlor and S-metolachlor have different effects on enzyme activities of 5th instar silkworm larvae. The LDH activity and the catalase activity in hemolymph treated with rac-metolachlor were much lower than that of S-metolachlor treatment. The ACP activity in hemolymph was 44~73% higher in larvae of control than that of rac-metolachlor treatment, but there were no big difference between S-metolachlor treatment and control. The ALKP activity of midgut treated with rac-metolachlor was 46% lower than that of control, and the effect of S-metolachlor on ALKP activity of mid-gut was minor. The difference of the two herbicides existed maining in the beginning 5 days of the 5th instar, and then recovered after 5 days of the 5th instar. It is showed that rac-metolachlor has induced more toxicity on economically important silkworms by disturbing some of the enzymes and the metabolism than S-metolachlor did.Metalaxyl, a chiral fungicide, has been widely used throughout the world, its enantioselective toxicity to Daphnia magna.was investigated in this research. The48h-LCs0 of Metalaxyl and Metalaxyl-M were 51.5 (45.5, 58.3) mg/L and 41.9 (35.2, 49.8) mg/L, respectively. These were both low toxicant according to classification standard of toxicity. Parameters such as length, the number of broods per female were significantly (P<0.05) affected when Metalaxyl-M concentrations were higher than 1 mg/L, but these parameters were not significantly affected until at Metalaxyl concentrations higher than 2 mg/L. The result showed that Metalaxyl-M was more toxic than Metalaxyl to hydrobiont from long-term effect.