Degradation, Adsorption-desorption Characteristics Of A Novel Herbicide Pinoxaden In Soil And Its Degradation In Water

This paper established the pretreatment method of pinoxaden and its analysis and detection method on LC-MS/MS to determine its content in soil and water.The degradation behavior of pinoxaden in soil and its influencing factors were simulated indoors,the metabolites of pinoxaden in soil were identified,and the degradation mechanism was speculated.The adsorption and desorption characteristics of pinoxaden on soil were explored,and the hydrolysis and photolysis behaviors of pinoxaden in water were also studied.(1)The QuEchERS method has been improved,and the extraction solvent,extraction method,extraction time and purification agent have been optimized to obtain the best extraction conditions.A method for the analysis and detection of pinoxaden on liquid chromatography-mass spectrometry/mass spectrometry(LC-MS/MS)has been established.The standard curve of the solvent and matrix of pinoxaden(with a concentration of 0.0002 to0.5000?g/m L)has a good Linear relationship,R~2is 0.9969-0.9996,limit of detection(LOD)and limit of quantification(LOQ)are 0.00012 mg/kg and 0.0004 mg/kg,matrix effect ME is between 0.4 and 1.6;The average daily recovery rate of pinoxaden on the four types of soils of Anhui,Guizhou,Hainan and Heilongjiang is 85.50%-115.71%,and the relative standard deviation(RSD)was 0.72%-5.04%;the average daily recovery rate is 74.79%-116.40%,and the RSD is 1.64%-6.13%,the analysis method meets the testing requirements.(2)The degradation experiments of pinoxaden in the soil under different temperature,different water content,sterilization and deorganization conditions were studied.The results showed that there was a positive correlation between the degradation rate of azolinoxate and the temperature in the temperature range of 15?to 35?.In the range of 16%-32%water content,the degradation rate of zolinoxate in the four soils was positively correlated with soil water content.After sterilization,the degradation half-life of pinoxaden in the four soils was extended by 0.6,0.9,7.4 and 10.6 h,respectively,compared with that before sterilization,indicating that biodegradation was one of the main degradation pathways of pinoxaden.The half-life of pinoxaden in the deorganized soils of Guizhou,Anhui,Hainan and Heilongjiang was extended by 0.2-3.2 times,indicating that organic matter is an important factor affecting the degradation of pinoxaden.Pinoxaden is easily degradable pesticide in four different soils,and the order of degradation rate is Guizhou>Anhui>Hainan>Heilongjiang,indicating that soil type is also the main factor affecting the degradation of pinoxaden.A total of five possible metabolites of pinoxaden were detected in the soil.According to the possible structure of the metabolites,it is speculated that pinoxaden may have undergone processes such as hydrolysis,oxidation,substitution,electron rearrangement,and ring opening in the soil.(3)The oscillation equilibrium method was used to explore the adsorption kinetics,desorption kinetics,isothermal adsorption test and isothermal desorption test of pinoxaden in the soil.The results showed that the adsorption and desorption equilibrium time of pinoxaden in four soils was 12 hours.The adsorption isotherm test showed that the adsorption of pinoxaden in the soil is a spontaneous process,mainly physical adsorption,and the Freundlich adsorption empirical coefficient is in the range of 0.864-0.998,indicating that the adsorption capacity of pinoxaden decreases with the increase of concentration.There is no hysteresis of pinoxaden in the four soils,and the desorption constant Kf is positively correlated with the clay content and cation exchange capacity of the soil.The adsorption capacity of pinoxaden in the soil is Heilongjiang>Guizhou>Anhui>Hainan.It belongs to the medium adsorption grade in Heilongjiang soil,and belongs to the difficult adsorption grade in the other three soils,although the pinoxaden is not easy to adsorb in the soil.Although pinoxaden was not easily adsorbed in soil,it could not possibly pollute groundwater due to its short half-life.(4)The hydrolysis law of pinoxaden in different temperature and different p H buffer solutions was investigated.The results showed that the hydrolysis trend of pinoxaden in water conforms to the first-order kinetic equation,and the hydrolysis rate of pinoxaden is related to temperature and p H.The value is positively correlated.When the temperature is constant,the stronger the alkalinity is,the faster the hydrolysis rate of pinoxaden;when the p H value of the buffer is 5,the value of pinoxaden is more easily hydrolyzed at 15°C.Buffers at other temperatures and p H values of 7 and 9 are all easily hydrolyzed pesticides.In addition,using a xenon lamp as a light source,the effects of different light intensity,p H buffer solution,and initial concentration conditions on the photodegradation behavior of pinoxaden were investigated.The results showed that pinoxaden was exposed to light intensity of 200,400 and 600 W.,Its half-lives are 3.54 d,1.54 d,and 1.53 d,respectively;the half-lives of pinoxaden in buffer solutions at p H=5,7,and 9 are 5.59 d,1.52 d,and 0.10d,respectively,and its degradation rate is proportional to the p H value.Negative correlation;four initial concentrations of 10,40,100,and 400 ng/m L were set to explore the influence of the concentration on the photolysis of pinoxaden.The degradation half-lives of pinoxaden were 1.53,1.54,2.51,and 3.36 d,respectively.The results showed that the initial concentration of pinoxaden was negatively correlated with the degradation rate.