Determination of residues of two organophosphates and their dissipation pattern by QuEChERS method

An experiment was carried out at the main farm of Bangladesh Tea Research Institute (BTRI) to find the residue levels of commonly used two organophosphate insecticides, namely chlorpyrifos and quinalphos in green leaf and black tea, at various plucking intervals after spraying during 2017-2018. The safe harvest interval was also calculated based on the degradation of pesticide residue from green leaf to processed tea. Pesticides were applied in the experimental plots following BTRI recommended dose (Chlorpyrifos 48 EC @ 1.0 L ha-1 and Quinalphos 25 EC @ 0.5 L ha-1). Green leaf and black tea samples were analyzed for pesticide residue of the above insecticides at the pesticide analytical laboratory (ISO/IEC 17025 accredited lab) of Bangladesh Agricultural Research Institute (BARI). The samples were extracted and cleaned up using the QuEChERS extraction method. Flame Thermionic Detector (FTD) with ATTM-1 capillary column (30 m x 0.25 mm x 0.25 µm) was used to determine the pesticide residue. The initial (0 days) pesticide residue of chlorpyrifos was 7.822 mg kg-1 in green leaf and 0.893 mg kg-1 in black tea, respectively. These were reduced to an undetectable level in the green leaf on the 10th day and 0.013 mg kg-1 in the black tea on the 7th day. On the other hand, quinalphos residue levels were initially (0 day) detected in green leaf and black tea at 4.973 and 0.193 mg kg-1, respectively. It decreased to undetectable levels on the 5 and 10 days in both cases. The result showed that pesticide residue decreased considerably in the process stage. Chlorpyrifos and quinalphos had pesticide residue degradation rates ranges from 70.70-92.07% and 94.21-96.12%, respectively