Degradation Of Chiral Triazole Fungicide Prothioconazole And Its Metabolite In Water

Chiral triazole fungicide prothioconazole has been widely used in the fungal control of cereal crops.Pesticide could enter water body through surface runoff after the application,which affects the balance of aquatic ecosystem.Prohiocoanzole and its major mentabolite prothioconazole-desthio possessed highly toxicity against aquatic organisms.To better understand the fate of prothioconazole in aquatic ecosystems and develop a treatment strategy,the biodegradation and abiotic degradation of prothioconazole was investigated at enantiomer level and the metabolic pathway of the prothioconazole was indentified.In addition,the removel method of highly toxicity metabolite prothioconazole-desthio in water was also proposed.The main research results are as follows:1、The stereoselective toxicity of prothioconazole against Chlorella pyrenoidosa was determined at the enantiomer level.The results of acute toxicity experiment showed that prothioconazole possessed stereoselective acute toxicity and the order of toxicity was S-prothioconazole>rac-prothioconazole>R-prothioconazole.The EC₅₀ of S-prothioconazole,rac-prothioconazole,R-prothioconazole were 12.207、9.640、14.779mg/L,respectively.2、The non-biodegradation experiment results showed that prothioconazole could be slowly degraded in water under dark conditions with a half-life of 17.77～34.65 d.Light could promote the degradation rate of prothioconazole in water,and the half-life was13.08～16.50 d.The degradation of prothioconazole in water showed no stereoselectivity,the highly toxic metabolite prothioconazole-desthio was formed with the degradation of prothioconazole and could be persisted in water.3、Biodegradation experiment results showed that C.pyrenoidosa could promote the degradation of prothioconazole in water with a degradation half-life of 2.09-3.81 d and there was obvious stereoselectivity with preferentially degradation of S-prothioconazole.EF values were 0.5-0.7,and stereoselectivity was more remarkable under low concentration exposure than that of high concentration exposure.With the degradation of prothioconazole,the metabolite was generated and the concentration increased gradually,indicating that degradation ability of C.pyrenoidosa on prothioconazole-desthio was weak.The bioconcentration factors（BCF）of prothioconazole enantiomers were less than 10,suggesting that prothioconazole was not easily accumulated in C.pyrenoidosa.4、The potential degradation pathway of prothioconazole in water-algae system was determined by liquid chromatography quadrupole time of flight mass spectrometry（LC-TOF/MS）.Fourteen metabolites of phaseⅠand two metabolites of phaseⅡwere found,including hydroxylation,dehydration,dechlorination,desulfuration,glucuronic acid conjugation and glutathione conjugation.5、Advanced oxidation processes was used to removed the prothioconazole-desthio in water.About 96%of prothioconazole-desthio removed from water within 90 min.About22.8%of the highly toxic metabolite was mineralized to carbon dioxide and water.