| Exianliumi is a novel bisthioether derivative containing a 1,3,4-oxadiazole ring,which has antibacterial and nematocidal activities.It is a new micromolecular pesticide designed and synthesised by Guizhou University.There are few studies on the migration,degradation and metabolites of exianliumi in the environment because of novelty of exianliumi.It is necessary to comprehensively understand the migration,residue and degradation of exianliumi in the soil environment,and correctly evaluate the impact of exianliumi on environmental safety,so that exianliumi can be put into production and application better.In this paper,the research was mainly established on the migration,adsorption-desorption,degradation and its metabolic pathway of exianliumi in soil.In the first part,the detection methods of exianliumi residues in water and soil were established.Nanjing field water,Nanjing yellow brown sandy loam,Heilongjiang black heavy loam and Jiangxi red loam were selected as research objects.High performance liquid chromatography(HPLC)and gas chromatography(GC)were used as the quantitative methods of exianliumi.Exianliumi was detected by HPLC,the linearity was good in the concentration range of 0.01 mg/L～10 mg/L with the correlation coefficient(R2)being 0.9998.Exianliumi was detected by GC,the linearity was good in the concentration range of 0.05 mg/L～0.8 mg/L with the correlation coefficient(R2)being 0.9998.LC-18 solid phase extraction(SPE)column was used for water extraction and enrichment,and exianliumi content was detected by HPLC.The result showed that the average recovery for exianliumi in the water was in a range of 97.38%～100.3%.The exianliumi residue in Nanjing soil was extracted with the mixture solution of acetone and water at a volume ratio of 3:1,purified by LC-18 solid-phase extraction and detected by HPLC.The average recovery for exianliumi in Nanjing soil was 92.73%～112.0%.The exianliumi residue in Heilongjiang soil was extracted with the mixture solution of acetone and petroleum ether by volume ratio of 4:1,purified by Florisil solid-phase extraction and detected by GC.The average recovery for exianliumi in Heilongjiang soil was 92.73%～97.17%.The exianliumi residue in Jiangxi soil was extracted by the mixture solution of acetone and water in the ratio of 4:1 by volume,purified by the extraction of petroleum ether,and detected by HPLC.The average recovery for exianliumi in Jiangxi soil was 91.20%～105.3%.The accuracy and precision of the above methods meet the requirement of pesticide residue analysis.The above established detection methods were applied to study the horizontal migration,vertical leaching,adsorption-desorption and degradation of exianliumi in Nanjing yellow brown sandy loam,Heilongjiang black heavy loam and Jiangxi red loam.The horizontal migration of exianliumi was explored by thin layer chromatography(TLC).It was found that exianliumi was moderate movement in Jiangxi soil(0.393±0.0271),difficult movement in Nanjing soil(0.145±0.0101),and non movement in Heilongjiang soil(0.0861±0.00230)by comparing the specific migration values(Rf)of exianliumi in the three soils.The vertical migration of exianliumi in the three soils was studied by the soil column leaching experiment.The results showed that exianliumi was not detected in the percolating solution of Heilongjiang soil and Nanjing soil,but formed a slightly asymmetric breakthrough curve in Jiangxi soil.Therefore,the migration ability of exianliumi was the weakest in Heilongjiang soil,the second in Nanjing soil,and the strongest in Jiangxi soil.After that,the adsorption and desorption characteristics of exianliumi in the three kinds of soil were studied by using the standard batch equilibration.The water to soil ratio was 5:1 and the equilibrium time was 24 h.The concentration gradient of exianliumi in the system was set as 0.1 mg/L,0.2 mg/L,0.5 mg/L,1 mg/L and 2 mg/L.The experiment was carried out at 25±1℃.The results showed that Freundlich model could better explain the adsorption and desorption behavior of exianliumi in the three soils.Heilongjiang soil had the strongest adsorption capacity for exianliumi,followed by Nanjing soil,and Jiangxi soil,according to its adsorption coefficient(Kf-ads).According to the empirical constant(1/nf-ads)of Freundlich model,the adsorption process of exianliumi in the three soils was nonlinear.It was found that the desorption of exianliumi in Heilongjiang soil and Jiangxi soil is enhanced and negative hysteresis occurs,which can not be defined in Nanjing soil,through the desorption hysteresis(H).Then the degradation behavior of exianliumi in the three soils was studied.The results showed that the degradation rate of exianliumi in the three soils was from large to small,which was Nanjing soil,Heilongjiang soil and Jiangxi soil,with half lives of 3.26 d,5.54 d and 13.1 d respectively.The effect of microorganism and soil organic matter on the degradation of exianliumi in the three soils was studied by means of sterilization and removal of the organic matter.The effect of microorganism on the degradation of exianliumi in the three soils was more obvious according to the results of minitab main effect analysis.Then,Nanjing soil was selected as the research object.And the effect of four environmental factors,such as light intensity,temperature,soil moisture and microorganism,on the degradation of exianliumi were further investigated.The degradation rate of exianliumi was 1.21 times as fast as that of dark culture when using 350 W xenon lamp and 1.42 times as fast as that of dark culture when using 500 W xenon lamp.The degradation rate of exianliumi in the soil increased first and then decreased when the soil moisture increased gradually.The half-life of exianliumi was 5.85 d,3.26 d and 3.47 d respectively when the soil moisture was 40%,60%and 80%of the maximum field water capacity.The increase of temperature could accelerate the degradation of exianliumi in the three soils.The degradation rate of exianliumi at 35℃ was 2.38 times of that at 15℃.The degradation rate of exianliumi slowed down when the soil was sterilized to exclude the degradation of microorganisms.The degradation rate of exianliumi in the non sterilized soil was 2.43 times,2.15 times and 1.81 times of that in sterilized soil at 15℃,25℃ and 35℃,respectively.The degradation rate of exianliumi in the sterilized soil at 35℃ was 3.19 times of that at 15℃.There was no significant difference in the effect of light intensity on the degradation of exianliumi,and there was significant difference in the effect of soil moisture,temperature and microorganism on the degradation of exianliumi,and the effect of temperature was the most obvious,according to minitab’s analysis of the effect of the four factors.Finally,the degradation products and degradation pathway of exianliumi in Nanjing soil were further explored by HRLC-Q-TOF-MS/MS.Eight degradation products and three conjugates of exianliumi were identified in the dark culture.Six degradation products and one conjugate of exianliumi were identified in the sterilized soil of Nanjing under the illumination of 500 W xenon lamp.The possible degradation pathways of exianliumi under the above two environmental conditions were speculated,mainly hydrolysis hydroxylation and dealkylation. |
PDF Full Text Request