Study On The Degradation Behavior Of Flonicamid In Tea

In this paper,a method for the determination of flonicamid and its metabolites residues in tea was established.In 2017 and 2018,the field experiments were conducted and the residues of flonicamid and its metabolites were studied in tea.The collected dynamic tea samples in 2017 were processed to green tea in the laboratory.The contents of flonicamid and its metabolites in fresh tea and green tea were studied,and the effects of machining process on flonicamid and its metabolites were also discussed.The optimal combination of leaching rate of flonicamid and its metabolites was obtained using the orthogonal experimental design with four factors and three conditions[L₉?3⁴?],and the method in tea infusion was established.The residues of flonicamid and its metabolites were determined in tea infusion.The risk assessment of dietary intake of flonicamid was evaluated based on risk quotient?RQ?method.It may provide a reference for the safe use of flonicamid and the establishment of a reasonable maximum residue level value?MRL?in tea.The research results were as follow:1.A QuEChERS–LC–MS/MS analytical method was established.The samples were extracted with acetonitrile?containing 1%acetic acid?and were purified by graphitized carbon black?GCB?.The method showed good linearity and sensitivity.The linearity of the method was excellent in the concentration range of 0.01–10?g/mL and the correlation coefficients?R²?was greater than 0.9993.The limit of quantification?LOQ?and the limit of detection?LOD?was 0.004–0.040 mg/kg and 0.0013–0.013mg/kg,respectively.The average recoveries in tea were 76.86%–91.52%for flonicamid,75.14%–90.38%for 4-Trifluoromethylnicotinic acid?TFNA?,77.08%–83.87%for N-?4-trifluoromethylnicotinoyl?glycine?TFNG?,and 77.70%–89.76%for 4-trifluoromethylnicotinamide?TFNA-AM?,with the relative standard deviation was ranged from 1.07%–6.32%.The method can meet the analytical requirement of flonicamid and its metabolites in tea.2.The established method was applied to detect tea samples in field experiments.The results showed that the half-lives of flonicamid on tea were 2.78–4.05 d in 2017.The residues of flonicamid and its metabolites were 0.005–0.360 mg/kg.The total terminal residues of flonicamid from tea samples collected 10 days after the last application were 0.023–0.046 mg/kg,which were below the maximum residue limit set by the European Union?MRL:0.1 mg/kg?.The half-lives of flonicamid on tea were3.63–3.98 d in 2018.The residues of flonicamid and its metabolites were 0.005–2.332mg/kg.The total terminal residue concentrations of flonicamid 7 days after the last application were 0.173–0.471 mg/kg,which were lower than the maximum residue limit set by Japan?MRL:8 mg/kg?.3.The optimal combination of tea leaching rate was obtained based on the orthogonal experimental design,and the method in tea infusion was established.The effects of machining process on flonicamid and its metabolites were discussed and the residues in tea infusion were determined.The results showed that the processing factor of flonicamid was ranged from 0.36 to 5.50.The residues of TFNA and TFNA-AM were not detected in green tea,the residue level of TFNG was also not detected in Guizhou green tea,and the processing factor was 0.44–1.75 in Anhui and Zhejiang green tea.In tea infusion,the residue of flonicamid was 0.011–1.127 mg/kg.The residues of TFNA and TFNA-AM at all three sites were not detected,the residue level of TFNG was also not detected in Guizhou tea infusion,and the residue concentration in Anhui and Zhejiang tea infusion was 0.002–0.024 mg/kg.The total residues of flonicamid were 0.002–1.140 mg/kg and the infusion factor ranged 0.169–0.935.The residue and leaching rate of flonicamid and its metabolites in tea infusion decreased gradually with the increase of soaking times.4.The dietary risk assessment was carried out by combining the median and maximum total terminal residual values of flonicamid on tea with the infusion factor obtained from tea soaking.The results showed that the chronic risk quotient?RQ_c?and the acute risk quotient?RQ_a?value were far less than 1,according to the recommended dose and the tea brewing method adopted in the field experiment,the potential dietary intake risk of flonicamid on tea is acceptable and tea drinking is safe.