Adsorption On Soils And Enantioselectivity In Aquatic Toxicity To Green Algae Of The Chrial Fugicide Metalaxyl

As the selective biodegradation and bioaccumulation,chiral pesticides have special fates in environment.The research on the enantioselectivity of pesticides leads to the precise assessment of ecosystem and human health.Metalaxyl is a chiral compound and important fungicide,mostly entering into market in the form of racemic metalaxyl.Assessing the ecotoxicology and environmental fate of chiral metalaxyl and its transformation products is necessary to accurately evaluate environmental risk of pesticides.Adsorption of several acetanilide pesticides including metalaxyl was investigated firstly.Then eco-toxicology of chiral metalaxyl and its metabolite on Scenedesmus obliquus,was maily studied.Adsorption of these acetanilide pesticides on the typical soils collected from Baiyang Lake farmland followed Freundlich equation with r² being more than 0.966,and decreased in an order of butachlor＞alachlor＞acetochlor＞metochlor＞metalaxyl.Due to lower organic matter content and adsorption capacity,acetanilide pesticides readily transported from Fu River soils to Baiyang Lake Wetland.There was a good linear correlation between logK_oc and logK_ow of acetanilide pesticides,which revealed that their adsorption was driven predominately by partition.Adsorption of the acetanilide pesticides could be largely attributed to physical adsorption.Toxicology of chiral fungicide metalaxyl and metalaxyl acid is enantioselective to Scenedesmus obliquus solutions.The EC₅₀ values of metalaxyl and its metabolite indicated that the toxicity of R-metalaxyl was 3 times as much as that of Rac-metalaxyl.The transformation products metalaxyl acids were lower toxicic than the parent compounds,and Rac-metalaxyl acid was least toxic.Minor metalaxyl could be degraded to metalaxyl acid by the algae.The degradation of the R-enantiomer was faster than the Rac-metalaxyl at the low concentration.The algae accumulated more Rac-metalaxyl under the same conditions. Metalaxyl stimulated the cell permeability while metalaxyl acid weakened the cell permeability.The study on metalaxyl showed evidences of enantioselective toxicity, degradation,accumulation and cell permeability in Scenedesmus obliquus cultures.