Environmental Behavior And Residual Characteristics Of Fluazifop-P-Butyl In Panax Ginseng Cultivation System

Based on a systematic review of the available relevant literatures for fluazifop–P–butyl（FPB）,in order to systematically investigate the environmental behaviors and the residual characteristics of FPB in the Panax ginseng cultivation system,a series of hydrolytic and photolytic experiments and the supervised residual field trials of FPB were performed.Furthermore,the dietary risk for FPB was also evaluated.The following results were obtained:1.The test results of the effects of different reaction temperatures and p H buffer solutions on the hydrolysis of FPB showed that the FPB hydrolytic reaction rate had a positive correlation with the p H value of the reaction medium and the temperature of the reaction system.And at25℃,the half–lives of FPB hydrolyzed in three p H buffer solutions at p H 4.0,p H 7.0 and p H9.0 were 6931.47,1732.87 and 28.88 hours,respectively.The half–lives of FPB hydrolyzed at50℃were 2310.49,693.15 and 16.50 hours,respectively.Furthermore,from the perspectives of temperature effect coefficient and reaction activation energy,the rules of the effects of buffer solution p H value and reaction temperature on the FPB hydrolysis were revealed.The changes of temperature had the smallest effect on the hydrolysis rate of FPB in alkaline buffer solution,and the effect was the greatest in the acidic buffer solution,indicating that alkaline was a favorable condition for FPB hydrolysis.According to the standards in“Test Guidelines on Environmental Safety Assessment for Chemical Pesticides—Part 2:Hydrolysis”,FPB was classified as the degradable pesticide in alkaline buffer system,but it was difficult to degrade in an acidic system.Considering that the Panax ginseng field soil belongs to the slightly acidic“synthetic soil”,it was inferred that the hydrolysis rate of FPB in it was lower than that in the neutral or weakly alkaline ordinary soils.The trimethylsilane derivatives of hydrolysates of FPB in alkaline buffer solution were separated and identified by GC–MS.From the identified hydrolysates,it was concluded that the alkaline hydrolysis of FPB mainly included such chemical processes as ester hydrolysis,hydroxylation,molecular rearrangement,ether bond cleavage and isomerization.2.Under the low pressure mercury lamp irradiation,the photodegradation kinetics of FPB in buffer solutions at 25℃showed that there was a positive correlation between the photolysis rate of FPB and the p H value of reaction medium.And the half–lives of FPB in p H 4.0,7.0 and9.0 buffer solutions were 40.77,22.36,and 13.33 minutes,respectively.According to the standards in“Test Guidelines on Environmental Safety Assessment for Chemical Pesticides—Part 3:Phototransformation”,FPB was a susceptible pesticide to photolysis in alkaline buffer system.The experimental results,which was nano–Ti O₂ mediated photocatalytic degradation of FPB,showed that nano–Ti O₂ exhibit ED effective photosensitization on FPB photodegradation under low pressure mercury lamp（main emission lines are 254 nm）or xenon light source（full wavelength spectrum）irradiation.Although the photolysis rate of FPB under xenon lamp irradiation was far lower than that under low pressure mercury lamp,the photosensitivity of nano–Ti O₂ to FPB photodegradation under xenon lamp irradiation was about 8.8 times that of low pressure mercury lamp.This study provides a low–cost and environmentally friendly methodology or idea for FPB degradation in the environment to reduce their hazards.Furthermore,the possible photolysis pathways of FPB by nano–Ti O₂ mediated were deduced through the systematic analysis of 12 photocatalytic degradation products isolated and identified.The simulated sunlight photolysis of FPB on the surface of air–dry or wet（20%water content）Panax ginseng field soil showed that excluding the microbial degradation factor,more than 60%of the degradation of FPB on the soil surface was contributed by hydrolysis,and the degradation by photolysis was only less than 30%.In order to clarify the effects of the main characteristic elements,humus and the commonest biopesticides in Panax ginseng field soil on the photolysis of FPB under ultraviolet light,a series of photolysis experiments were designed and carried out.The results showed that Li⁺and Co²⁺quenched the photolysis of FPB,low concentrations of VO₃⁺and Mo⁶⁺sensitized the photolysis of FPB,Sn⁺and Mn²⁺strongly sensitized the photolysis of FPB,and humic acid,polymycin and Ningnanmycin were all quenching agents to the ultraviolet photolysis of FPB.3.The carboxylated multi–walled carbon nanotubes were introduced into the Qu ECh ERS sample pretreatment process together with conventional adsorption materials(PSA,C₁₈,and GCB),and a simple and efficient sample preparation method and specific and sensitive HPLC–MS/MS analysis method for FPB and its relevant metabolites fluazifop acid（FP）and 2–hydroxy–5–trifluoromethylpyridin（TFMP）residues in the matriices of fresh Panax ginseng,dried Panax ginseng,Panax ginseng plants and Panax ginseng field soil were established.The performance indices of the analytical method showed that under the optimized HPLC–MS/MS conditions,FPB,FP and TFMP at the concentrations ranging from 5μg/L to 1000μg/L all presented good linearity responses in the four sample matrices（R²>0.9980）.The fortified recovery was 75.8～97.8%,the relative standard deviation was less than 16%,the detection limit of FPB in the four sample matrices was 2.0～8.6μg/kg,FP was 3.9～5.7μg/kg,and TFMP was 3.5～11.3μg/kg.On this basic,the frozen storage stability of FPB and its main metabolites in fresh Panax ginseng,Panax ginseng plants and Panax ginseng field soil samples were studied.And the results showed that the frozen storage stability period of FPB in fresh Panax ginseng,Panax ginseng plants and Panax ginseng field soil samples could reach at least 9 months,while the frozen storage stability period of the metabolites FP and TFMP in fresh Panax ginseng,Panax ginseng plants and Panax ginseng field soil samples could be at least 12 months,and the data are of great significance in the registration of FPB in the Panax ginseng cultivation.4.The results of supervised residue field trials of FPB in the Panax ginseng field indicated that FPB was rapidly degraded in Panax ginseng plants（the residual half–life is about 3 days）,while the metabolite FP was relatively stable（the half–life is about 1 month）.The residual half–life of FPB in the Panax ginseng field soil was about 1 week,and the half–life of metabolite FP was about 2～3 weeks.In addition,the detection amount of metabolite TFMP in the Panax ginseng field soil was about twice that of Panax ginseng plants,however,whether the detected TFMP in Panax ginseng plants came from the metabolism system of Panax ginseng plants or Panax ginseng field soil was temporarily uncertain.It can be confirmed that TFMP was mainly derived from the Panax ginseng field soil metabolic system.The terminal residue values of the two metabolites FP and TFMP of FPB in fresh Panax ginseng were converted into the total residue（total FP）together with the residue value of FPB in fresh Panax ginseng,and the supervised trials median residue（0.20 mg/kg）and supervised trials high residue（0.27 mg/kg）were statistically calculated from terminal residue values.The dietary safety risk assessment of FPB was performed by incorporating Panax ginseng into the Chinese traditional medicine and health food,the calculated NEDI,RQ and the ratio of RDI to TDI of FPB were 0.011mg/（kg?bw?d）,2.01%and 6.40%,respectively.It indicated that,in the practice of using FPB by foliar application at the dose of 150 g ai/ha,in Panax ginseng field to control the annual or perennial grass weeds in the broad–leaved crop field,the produced agricultural products usually do not cause unacceptable health risks to the general population.And the recommended MRL of 4 mg/kg by the European Union for FPB in fresh Panax ginseng can ensure consumer safety.