Degradation Dynamics and Final Residue of Bifenthrin in Tea

[Objective] The study aimed to understand the degradation dynamics and final residue of bifenthrin in tea and confirm its safe application plastochron and times.[Method] In the field test,with tea selected from 916 tea farm in Shucheng County of Anhui Province as the tested material,it was applied by 2.5% bifenthrin EC at 2 times of its recommended rate.The applied tea were sampled after application for 1 h and 1,2,3,5,7,14,21,30 and 45 d resp.and the samples were extracted by acetone and petroleum ether and then measured by gas chromatogram(GC),with the adding recovery of test being 77.0%.[Result] The bifenthrin was dissipated rapidly in tea.When bifenthrin was applied to the tea according to twice of recommended rate,the degradation ratio of bifenthrin from the samples after application for 1 d was 44.7%,and the half-life was 3.83 d.When the recommended dosage of bifenthrin was 90 g a.i/hm2 for applying 4 times,the residue of bifenthrin in tea was less then 5 mg/kg after final application for 3,7,14 d,specially,that in tea was 0.08mg/kg after final application for 14 d.[Conclusion] If taking the bifenthrin residue in tea of 5 mg/kg as the reference index,it was suggested that the safe application plastochron of bifenthrin was confirmed as 3 d and the application times didn't exceed 4 times.