Residue reduction and risk evaluation of chlorfenapyr residue in tea planting, tea processing, and tea brewing

The chlorfenapyr residues in the entire tea chain, i.e., in tea planting, tea processing, and tea brewing, were systematically investigated. The degradation rate constants of chlorfenapyr in the tea plants ranged from 0.2460 to 0.2870 with the half-life of 2.4-3.0 days, and 87.5-89.9% of the chlorfenapyr in tea shoots dissipated in the interval of 7 days. In the processing process of both black tea and green tea, the chlorfenapyr residue decreased by 59.1-67.6% compared with the residue in tea shoots due to high vapor pressure (1.2 × 10^-2 mPa 25 °C), and drying was the key step that dissipated the chlorfenapyr. A low leaching efficiency of 2.2-3.4% from tea leaves to tea infusion, resulted in low water solubility (0.14 mg L^-1 25 °C), indicated that >90% of the residual chlorfenapyr was eliminated before the intake of tea infusion. On the basis of these results, an extremely large proportion of the chlorfenapyr deposited on tea shoots was degraded during tea planting, tea processing, and tea brewing, and the health risk was reduced primarily in the first and the last step rather than during tea processing. The remaining 0.2% chlorfenapyr sprayed on the tea shoots represents a negligible health risk based on the RQ assessment. The pesticides with high vapor pressure and low water solubility were more recommended in tea garden for pest control.