Study On The Difference In Degradation Of Glufosinate-ammonium Enantiomers In Citrus Orchard Soil And Weeds

In this paper,a crown ether chiral stationary phase was used to establish a method for the analysis of glufosinate enantiomers and three metabolites in weeds,soils using ultra-high-performance liquid tandem high-resolution mass spectrometers?UPLC-HRMS?.Field experiments were conducted in Guiyang,Guizhou,and Changsha,Hunan,from May to July 2019 to investigate the stereoselectivity of the degradation of glufosinate enantiomers in weeds and soils in the field environment,and compare the degradation of glufosinate in soils in indoor and field environments.Formation trends of 3-?methylphosphino?propionic acid?MPP?,N-acetyl-glufosinate?NAG?and 2-?methylphosphino?acetic acid?MPA?were clarified.The deposition distribution of glufosinate in citrus orchards was also investigated.Soil and weed samples were extracted with pure water by shaking at constant temperature,purified with dichloromethane,the water phase was filtered and directly tested on the machine.Linearity of peak area and mass concentration in soil and weed matrix when D-glufosinate,L-glufosinate,MPP,NAG,MPA mass concentrations are0.00125,0.005,0.05,0.5,5 mg/L,respectively.The relationship was good with a correlation coefficient greater than 0.998.D-glufosinate and L-glufosinate both showed matrix inhibitory effects in two soil matrices and two weed matrices.In soil,the average recoveries of D-glufosinate and L-glufosinate at three different levels of 0.4,4,40mg/kg were 77.3-84.3%,RSD was 5.55-7.83%.The average recovery of NAG and MPA at three different levels of 0.08,0.8,and 8 mg/kg was 78.6-85.8%,and the RSD was 5.63-8.37%.In the weeds,the average recovery rates of D-glufosinate and L-glufosinate at three different levels of 0.4,4,40 mg/kg were 86.3-92.4%,and the RSD was 4.38-6.72%.The average recovery of MPP,NAG,and MPA at three different levels of 0.08,0.8,and 8 mg/kg was 80.4-86.0%,and the RSD was 6.50-1.13%.In soil and weed,the limit of quantification?LOQ?of D-glufosinate,L-glufosinate,MPP,MPA,NAG was 0.4,0.4,0.08,0.08,0.08 mg/kg,respectively.The limits of detection?LOD?were 0.04,0.04,0.01,001,and 0.01 mg/kg,respectively.This method meets the requirements of pesticide residue analysis and can be used to detect samples.Based on field experiments of 200 g/L glufosinate in Guizhou and Hunan citrus orchards,the selective degradation of glufosinate enantiomers in weeds and soils in the field environment and its deposition and distribution after application were studied.The experimental results showed that the glufosinate was mainly deposited in the weeds at the recommended dosage,and only a small amount?about 2%?of the glufosinate was lost to the soil.Rainfall and dew on the weeds affected total glufosinate residues in weeds.In the field environment,D-glufosinate and L-glufosinate were rapidly degraded in soil and weeds.At 1 day,the degradation rate of D-glufosinate and L-glufosinate in the weeds of the two places exceeded 70%.The half-life T_1/2 of D-glufosinate and L-glufosinate in Guizhou weeds were 1.3 days and 0.7 days,respectively,and the half-life T_1/2 in Hunan weeds were 2.4 days and 1.1 days,respectively.The degradation of glufosinate enantiomers in the weeds in the two places showed obvious selectivity,L-glufosinate were preferentially degraded.The major metabolites of glufosinate enantiomers on weeds in both places were MPP?MPP in Guizhou weeds up to 15.66%of the parent,and MPP in Hunan weeds up to 14.28%of the parent?,NAG was a secondary product,only a small amount of glufosinate?<1%?was metabolized to MPA.In the field environment,the half-lives T_1/2 of D-glufosinate and L-glufosinate in Guizhou soil were 1.3 days and 1.1 days,respectively.The half-life T_1/2 in Hunan soil was 3.1 days and 3.1 days,respectively.The degradation of glufosinate enantiomers in the field soils of the two places did not show obvious selectivity,the degradation rate of glufosinate enantiomers was basically the same;Under laboratory conditions,the half-lives T_1/2 of D-glufosinate and L-glufosinate in Guizhou soil were respectively 3.9days,2.4 days.The half-life T_1/2 in Hunan soil was 11.4 days and 4.4 days,respectively.The degradation of glufosinate enantiomers in the two soils was selective under laboratory conditions,L-glufosinate was preferentially degraded.Under field conditions,the MPP produced by the glufosinate enantiomer in soil was 1.52-8.3%,the NAG produced was 1.74-2.15%,and only a small amount of glufosinate?about0.69%?was metabolized to MPA.Under laboratory conditions,the MPP produced by the glufosinate enantiomer in the soil was 43.07-52.78%,the NAG produced was 5.89-7.30%,and the MPA produced was 11.38-20.37%.