Determination of degradation of pyrethroid pesticides

The pyrethroid pesticides fenpropathrin, permethrin, and tetramethrin were used to study the degradation activity of pyrethroid pesticides by BL21AI-GBS, and the degradation rate was determined by the residual amount of pesticides after 5- h reaction. The degradation reaction systems were set as follows: 0.5 mL of CPS and 0.5 mL of 1 mg/mL pesticide (dissolved in acetone) were added into the test tube containing 4 mL of 0.05 M Tris–HCl buffer (pH 7.2). After mixing, 2 mL of the mixture was taken out, and 0.5 mL of 50% TCA was added as a reaction terminator, mixed, and temporarily stored in a refrigerator at 4 °C, which was used as a “0-h sample”. After the remaining mixture reacted in a water bath at 37 °C for 5 h, 2 mL of the reaction solution was taken up, and 0.5 mL of 50% TCA was added thereto, which was used as a “5-h sample”. Two milliliters (2 mL) of n-hexane was separately added to the 0-h sample and 5-h sample for extraction, and the upper organic phase was taken for measurement. The pyrethroid pesticides in the extracting solutions were analyzed by an Agilent 6890 gas chromatograph-5976 N mass selective detector (GC–MSD) system (Agilent Technologies Inc., Santa Clara, CA, USA) equipped with a DB-5 capillary column (30 m × 0.25 mm × 0.25 μm, J & W Scientific, CA, USA). The carrier gas was helium at a constant flow rate of 1.2 mL min⁻¹. The column temperature was programmed to rise from 100 to 200 °C at 16 °C min⁻¹ and then to 300 °C at 8 °C min⁻¹ and held for 5 min at 300 °C. One microliter (1.0 μL) of the sample was injected in splitless mode. The injection port, GC-MS interface, and ion source temperatures were maintained at 250, 300, and 200 °C, respectively. The ionization was carried out in the electron impact mode at 70 eV and the data were acquired under selected ion monitoring (SIM) mode.