Study on the residue and degradation of fluorine-containing pesticides in Oolong tea by using gas chromatography–mass spectrometry

Abstract

The natural degradation of pyrethroids pesticides (bifenthrin and cyhalothrin) and benzoylurea pesticides (teflubenzuron, flufenoxuron and chlorfluazuron) in the leaves of Oolong tea trees and the effect of processing steps and pesticide's dose on the residue of above five pesticides in dried Oolong tea leaf samples were studied in detail by farm experiment and gas chromatography–mass spectrometry. The experimental results showed that: 1) Higher pesticide's dose used in tea planting will result in higher residue of pesticides in dried Oolong tea leaf samples, but the dose did not affect the degradation rate of pesticide. 2) The degradation of bifenthrin, cyhalothrin, teflubenzuron, flufenoxuron and chlorfluazuron in the leaves of tea trees follows zero-order kinetics with a half-life of 9.3–9.4, 10.2–10.4, 9.2–9.6, 12.1–13.5 and 7.0–8.2 days respectively, suggested that the pesticide's dose and the interval between tea picking and pesticide spraying are two key factors on the residue of fluorine-containing pesticides in dried Oolong tea leaf samples. 3) In comparison with bifenthrin, cyhalothrin, teflubenzuron and flufenoxuron, chlorfluazuron is more difficult to be remained in dried Oolong tea leaf samples. 4) The pesticide residue was not affected by the processing steps except the fermentation step in which the benzoylurea insecticides and bifentrin were partially lost or degraded. The results of this study are helpful for farmer to safely use fluorine-containing pesticides in Oolong tea planting.