Residue Analysis And Stereoselective Degradation Of Chiral Fungicide Dipropamidil In Soil

Mandipropamid(a novel fungicide)was developed by Swiss Syngenta.The patent protection of mandipropamid in China will expire in 2021,and it will be mass-produced and put on the market.The enantioselective degradation of mandipropamid and factors affecting the degradation in Chinese soil and water were investigated for the first time in this paper.The results could provide some accurate data to evaluate the environmental risk and safety.The enantioselective degradation data of mandipropamid in four types of Chinese soil under different conditions showed that:(1)The half-lives of R-(-)-enantiomer and S-(+)-enantiomer in four types of Chinese soil were18.2-110.0 d and 22.8-144.4 d.Mandipropamid degradation could be attributed to p H,microbial activity,OM,temperature and soil moisture of soil,and the degradation rate of mandipropamid enantiomers increased with p H,OM,temperature or soil moisture increasing.(2)The half-lives of R-(-)-enantiomer and S-(+)-enantiomer decreased 1.07-1.95 times and1.08-1.79 times with incubation temperature increasing 10,and the half-lives of R-(-)-mandipropamid and S-(+)-mandipropamid decreased 1.09-1.43 times and 1.06-1.50 times with soil moisture increasing 20%,respectively.(3)The ES values ranged from0.025 to 0.170 indicating that the enantioselectivity was observed in the degradation process of rac-mandipropamid in soil,and R-(-)-enantiomer preferentially degraded.(4)Enantiopure mandipropamid enantiomers were configurationally stable in soil,and no interconversion was observed during the degradation process.(5)Four major metabolites and three minor metabolites of mandipropamid were detected in soil.The enantioselective hydrolysis data of mandipropamid in water showed that:(1)The half-lives of R-(-)-enantiomer and S-(+)-enantiomer in water samples were 230.9-495.1 d and 216.6-462.1 d,respectively.(2)The degradation rate of mandipropamid increased with the p H increasing,and the degradation rate order of R-(-)-enantiomer and S-(+)-enantiomer in sterilized buffer solution was p H 9.10 > p H 7.18 > p H 5.05.(3)The degradation rate of mandipropamid increased with the incubation temperature increasing in p H 5.05 and p H 7.18 buffer solution,and the degradation rate of mandipropamid first increased and then maintained in p H 9.10 buffer solution.The influence order of incubation temperature on hydrolysis of mandipropamid in buffer solutions was p H 5.05 > p H 7.18 > p H 9.10.(4)Weak enantioselective degradation of mandipropamid was observed in p H 5.05 and p H 7.18 buffer solutions at 15 °C,25 °C and 35 °C,and in p H 9.10 buffer solution at 35 °C,and S-(+)-enantiomer preferentially degraded.(5)The degradation rate order of R-(-)-enantiomer and S-(+)-enantiomer in the three natural water matrices was pond water = rain water > tap water and pond water > rain water > tap water,respectively.Enantioselective hydrolysis of mandipropamid was weak,and S-(+)-enantiomer hydrolyzed preferentially.The enantioselectivity order of mandipropamid hydrolysis in three natural water matrices was pond water > rain water > tap water.(6)Enantiopure mandipropamid enantiomers were configurationally stable in water,and no interconversion was found during the hydrolysis process.(7)Two transformation products of mandipropamid,CGA 380778 and NOA 458422 were detected in water.