Background Indoxacarb is a chiral insecticide with excellent insecticidal activity against lepidopterous insects. Because of their enantioselectivity, chiral pesticides' environmental behavior at the enantiomeric level has been highlighted. The chiral stability, enantioselective bioaccumulation, biotransformation behavior of indoxacarb to a non‐target insect silkworm are still unclear. Results A chiral analysis method for indoxacarb and its metabolite DCJW in silkworm was developed using liquid chromatography and high‐resolution mass spectrometry (HPLC/HRMS). In silkworms, the recoveries of indoxacarb and DCJW were 86.06%‐104.52% with relative standard deviation (RSD) < 9.01%. The 96‐h lethal concentration (LC50) values of R‐indoxacarb, S‐indoxacarb, and enriched S‐indoxacarb (2.333 S/1R) were 1.08 × 102, 1.92, and 6.89 mg a.i. L−1, respectively, according to the acute toxicity test results. When silkworm larvae were exposed to 1/50 of the LC50 concentration, the bioconcentration factor (BCF) of R‐indoxacarb was 0.0296–0.318, and the BCF of S‐indoxacarb was 0.0125–0.211. In silkworm larvae, the amount of R‐DCJW produced by R‐indoxacarb was 0.00610 to 2.34 times that of the parent R‐indoxacarb, and the amount of S‐DCJW produced by S‐indoxacarb was 0.125–36.9 times that of the parent S‐indoxacarb. Conclusion There was no chiral transition from S‐indoxacarb to R‐indoxacarb or a transformation from R‐indoxacarb to S‐indoxacarb. Indoxacarb was preferentially bioaccumulated in silkworm larva, while S‐indoxacarb bioconversion into the metabolite S‐DCJW was much greater than R‐indoxacarb bioconversion into R‐DCJW. This study could improve understanding of the indoxacarb accumulation and transformation process in insects, as well as provide more scientific data for indoxacarb environmental and ecological risk assessment. © 2023 Society of Chemical Industry.
In this study, high-performance liquid chromatography−high-resolution mass spectrometry (HPLC−HRMS, Q-Exactive Orbitrap) and Compound Discoverer 3.3 were used to screen dimethachlon degradation products in soils. Four metabolites 4-(3,5-dichloroanilino)-4-oxobutanoic acid (DCBAA), 3,5-dichloroaniline (3,5-DCA), succinic acid, and muconic acid were confirmed by primary and secondary ion mass spectrometry comparisons between standards and samples. A quantitative analysis method of dimethachlon residues and four metabolites in soils was developed using HPLC−HRMS. Dimethachlon degradation in agricultural soil indoor unsterilized, sterilized, and field environments in three typical areas was measured. Dimethachlon degraded fast with a half-life of less than 1 day in three nonsterile soils. The maximum DCBAA and 3,5-DCA residues during degradation could reach 22.5−35.2% of the initial concentration of the parent dimethachlon. The metabolite DCBAA had a greater impact on soil enzyme activity than the parent dimethachlon.
Herein, an accurate and sensitive method was developed for detecting four stereoisomers of propiconazole in “Fengtang” plum by LC-MS/MS. The mean recovery of four propiconazole stereoisomers ranged from 79.42 to 104.10% at three adding levels with reasonable RSD of 1.54–11.68%, and the LOD and LOQ of the four stereoisomers was 0.0005 mg/kg and 0.004 mg/kg, respectively. In addition, the residue and selective degradation of propiconazole stereoisomers in plums were investigated by storage at 20 °C and 4 °C. The half-lives of propiconazole stereoisomeric during storage were 9.49–15.40 d at 20 °C, and 21.00–28.88 d at 4 °C. The degradation of (2R,4R)-propiconazole and (2R,4S)-propiconazole in stored plums was slightly slower than that of the corresponding enantiomers (2S,4S)-propiconazole and (2S,4R)-propiconazole. The total residues of propiconazole were 0.026–0.487 mg/kg in the plum storage period, and the water washing could remove 49.35% to 54.65% of the propiconazole residue in plum. The hardness of plums treated with propiconazole was generally higher than that of control in the middle and late stages of storage. The effects of propiconazole on the total soluble solid content of plums were different at 20 °C and 4 °C. This study provides a scientific reference for the food safety evaluation of the “Fengtang” plum after the application of propiconazole during the storage period.
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