Effect Of Distilled Bamboo Vinegar On Pesticide Photodegradation

Bamboo vinegar is a byproduct in the production of bamboo charcoal.The original bamboo vinegar include unfavorable components,such as bamboo tar that have attracted attention due to the harmful influence on crops.The tar has been reported to include benzo[a]pyrene,a well-known carcinogen.The evaporation method is a effective method for removal of bamboo tar components.Thus,the distilled bamboo vinegar shows a good application prospect.However,the distilled bamboo vinegar remains unexploited.Bamboo vinegar has been used as natural fungicide,pesticide synergist and so on.Based on the published studies,the bamboo vinegar shows a synergistic effect when combined with azadirachtin A on the insect pests in vegetable plants.Combination of the bamboo vinegar associated with chemical preservative can produce a synergistic effect.However,the mechanism of synergistic effect is still unknown.Photolysis is an important degradation process to consider when evaluating the persistence of a pesticide in the field.In this study,photodegradation of azadirachtin A and thiamethoxam in aqueous solution and on the glass surface with distilled bamboo vinegar was investigated.Liquid chromatography/quadrupole time-of-flight mass spectrometry(LC-Q-TOF-MS)methods were optimized for the determination of azadirachtins and thiamethoxam.Furthermore,volatile compounds of the original bamboo vinegar and distilled bamboo vinegar were enriched and analyzed by purge and trap thermal desorption-gas chromatography-mass spectrometry(P&T-TD-GC-MS).The effect of phenol and guaiacol were evaluated on photodegradation of azadirachtin A.The main results are given as follows:(1)A simple LC-Q-TOF-MS methods were developed for the determination of azadirachtin A and thiamethoxam in the tested samples.The separation was performed using a C18 column(150×2.1 mm i.d.,1.8 μm)at 30 ℃.The solvent system consisted of a mixture of water acid and acetonitrile at a flow rate of 0.25 m L/min with gradient elution.The injectionvolume was 2 μL.The detection wavelength were set at 215 nm and 254 nm for azadirachtin A and thiamethoxam,respectively.(2)A fully automated SPE-LC-Q-TOF-MS method was developed and validated for simultaneous quantification of five azadirachtins(azadirachtins A,B,D,H and I)in the neem extracts.The azadirachtins were extracted from neem samples with acetonitrile(70%).The optimized SPE-LC-Q-TOF-MS method showed good recovery(82.0~102.8%),linearity(R2 ≥0.9991)and precision(0.83~4.83%).The limit of detections(LODs)for the five analytes ranged from 0.34 to 0.76 ng/m L.The validated method has been successfully applied for determination of the analytes in different neem leaves,seeds and a neem formulation.(3)The effect of bamboo vinegar on photodegradation of azadirachtin A was studied in water and on glass surface under high pressure mercury lamp(HPML).Results showed that bamboo vinegar exhibited photo-quenching effect on photolysis of azadirachtin A.In the presence of the 10 times diluted solution of bamboo vinegar,the half-life of the azadirachtin A on the glass surface was 4.13 min.The half-life was significantly prolonged compared to the control groups.Additionally,the photolysis of azadirachtin A was lowered 2.4-fold in diluted bamboo vinegar compared to that in distilled water.Overall,bamboo vinegar can improve the photostability of pesticides in aqueous solution or on the glass surface.There was a good dose-effect relationship between the half-lives of azadirachtin A and concentrations of the distilled bamboo vinegar.(4)Effect of bamboo vinegar with different concentrations on the photoprotection of thiamethoxam was studied in water under high pressure mercury lamp(HPML)and xeon lamp.Results showed that bamboo vinegar could inhibit the photolysis of thiamethoxam in aqueous solution.In the presence of the 30 times diluted solution of bamboo vinegar,the thiamethoxam was photodegraded with a half-life of 7.37 min under high pressure mercury lamp irradiation.The photolysis of thiamethoxam was lowered 6.5-fold in the diluted bamboo vinegar compared to distilled water.In the presence of the 30 times diluted solution of bamboo vinegar,the thiamethoxam was photodegraded with a half-life of 3.38 h under xeon lamp irradiation.Thehalf-life was significantly prolonged compared to the control test.Thus,bamboo vinegar can improve the photostability of thiamethoxam in aqueous solution.(5)Chemical components of bamboo vinegars were analyzed by purge and trap thermal desorption-gas chromatography-mass spectrometry(P&T-TD-GC-MS).A total of 26 compounds were identified in distilled bamboo vinegar.The major components with a relative content of more than 2% were acetic acid methyl ester,acetic acid,furfural,phenol,2-methoxy-phenol.(6)Photo-quenching mechanism of the distilled bamboo vinegar.Chemical components of distilled bamboo vinegar before and after UV irradiation were analyzed by GC-MS.The results showed that an obvious decrease in relative contents of phenolics.The main compounds phenol and guaiacol showed photo-quenching effect on photolysis of azadirachtin A.In conclusion,validated LC-Q-TOF-MS methods were developed for quantification of five azadirachtins and thiamethoxam.The distilled bamboo vinegar exhibited photo-quenching effect on photolysis of azadirachtin A and thiamethoxam.Thus,bamboo vinegar could be a promising candidate as a light stabilizer agent in pesticide formulations.