Safety Analysis Of Bifenthrin Used In Tea Prouduction

Bifenthrin is a broad spectrum insecticide, which with low toxicity and residues. It is widely used in Tea Garden. Because of this, bifenthrin have a high detection rate in tea. To reduce the residues of bifenthrin in tea, this study do search for how the production affect the residues. The factors including the determination method, pesticide concentration, applied amount of liquid, spraying direction, rainfall, picking standard and drying conditions.1. The study determinated the bifenthrin by solid phase extraction gas chromatography (SPE-GC). Comparing the chromatograms of the bifenthrin, which were divided by different adsorbents. The results showed that, if anhydrous sodium sulfate is added or not, or Florisil be activated or not, have no effect on the measurement results. When the column was added with 0.1g activated carbon, the baseline of the chromatograms was more stable. Therefore, extract the befenthrin in tea with 1g Florisil(not activated),and 0.1g of activated carbon, without anhydrous sodium sulfate, can operate more energy-efficient and time-saving. Under this condition the average recovery was in the range of 84.26 ± 8.24%～108.23± 3.05%(n=10), RSD≤8.24%, the detection limit was 0.001mg/L. The method can be use in befenthrin determination.2. The effects of pesticide concentration and spray volume on befenthrin residues were studied in this experiment. The results showed that different concentrations of pesticide had a significant impact on the residues of bifenthrin. Sprayed by constant volume, the initial residues of double-recommended concentration were 2.5times as recommended concentration’s.7 days after, the befenthrin residues of the tea sprayed by recommended concentration were lower than the max residues limit (MRL,5mg/kg); the tea sprayed by double-recommended concentration had the risk of excessing the MRL. Spray volume had a significant influence on the residues of bifenthrin. Sprayed by recommended concentration, the initial residues of 4 times-constant volume were 1.11 times as constant volume spraying. Sprayed by double-recommended concentration, the initial residues of 4 times-constant volume were 1.54 times as constant volume. Pesticide concentrations affected the bifenthrin residues greater than spray volume.3. Detected the residues of bifenthrin in tea after spraying or painting the bifenthrin on leaf abaxial and adaxial surfaces. When using manual sprayers spray toward the leaf abaxial surfaces., the pesticide could be blocked by the branches; just a few pesticide could arrive at the leaf. The Initial residues were 13.78% of the bifenthrin in tea which was sprayed on the adaxial surface. When daubing bifenthrin on leaf abaxial and adaxial surface,the Initial residues of the former were 121.42% of the latter. This meant if the pesticide liquid can be uniformly arrive at the leaf abaxial and adaxial surfaces, the former one had the stronger adhesion.7 days after the pesticide degradation of the bifenthrin painted the on leaf abaxial and adaxial surfaces were 59.68% and 58.74%, both of the residues were lower than the MRL.4. Different tea plucking standards significantly affected the amount of bifenthrin residues.7 days after bifenthrin application, single bud, a bud with one leaf, a bud and two leaves and a bud three leaves have significant difference in pesticide content.7 days after sprayed by recommended concentration, the bifenthrin residues of one bud three leaves were 9.53%,76.92%,447.61% higher than the residues in one bud two leaves, one bud one leaf, single bud.3 days after recommended concentrations spraying, picking single bud and one bud with one leaf could compliance with the safety standards. Improved picking criteria could reduce the risk of excessive pesticide residues standard. Leaves in different positions had different growth rates, and had different growth dilute, thus affected the bifenthrin residues between the tea picking by differences tea plucking standards.5. The interval between rainfall and bifenthrin application affected the residues significantly. Simulated moderate rain when 4h,8h,17h,24h after pesticide spraying, the degradation rates were 48.02%,21.84%,8.98%,-2.10%,the shorter the interval, the higher bifenthrin degradation rate. When it was raining short time after bifenthrin application, whether the pesticide should be spraying again or not, need according to the pest control efficiency.24h after bifenthrin application, rainfall had no significant effect on the residual amount of the bifenthr in tea.24h after the application, light rain, moderate rain, heavy rain, had no influence on the bifenthrin residues in tea, the residues were 4.71±0.17mg/kg,4.92±0.024mg/kg,4.84±0.37mg/kg, all had no significant difference with the CK (4.82±0.22 mg/kg). According to the existing reports,24h after bifenthrin application, pest control efficiency was ranged from 82.93% to 100%. Therefore, if the rain occurs 24h after bifenthrin application, there is no need to spray again.6 The drying temperature and duration had a significant impact on tea bifenthrin reducing. When the drying temperature at 90℃,110℃,130℃, drying time during Omin～60min, the higher the temperature and the longer the duration, the less the bifenthrin residues. The former 10min had the biggest degradation, ranged from 10.52% to 15.44%, then as the duration be longer the duration, the degradation was lower. Under the same drying duration(longer than 10min),the degradation of the 130℃’s was significantly higher than 90℃’s and 110℃’s. in order to keep the quality of the tea while reducing the bifenthrin residues, the drying temperature of the former 10min can be 90℃, then increased to 130℃.