Photocatalytic degradation of the pesticide pyridaben: Identification of degradation pathways using SERS and GC–MS

Abstract

Degradation pathways of the pesticide pyridaben in tea caused by ultraviolet photocatalytic degradation were identified using SERS and GC–MS. Pyridaben in tea decreased from 4.50 mg/kg to 3.46 mg/kg after 2 h and to 0.62 mg/kg after 5 h, with a degradation rate of 86.22 % and a recovery rate of 90.00 %. The pyridaben degradation process involved C–S cleavage, with a SERS band of ν(C–S) at 710 cm⁻¹ disappearing in the first hour. This was followed by cleavage of the N atom and the attached tert butyl group, resulting in the cleavage of the C-N bond in the ring, causing ring opening degradation. The presence of residual pyridaben was not necessarily related to the content of tea polyphenols; however, the UV light significantly reduced the content of theobromine, EGC, EC, and ECG but increased the content of EGCG. Ultraviolet irradiation slightly reduced the moisture content of oolong tea samples and did not significantly affect the total ash content. The content of water extract increaseing irradiation time due to the influence of moisture. UV irradiation time at the range of 60–360 min could degrade pyridaben while reducing its impact on tea quality.