Abstract:

【Objective】The objective of the experiment was to reveal the residue behavior of imidaclothiz in pakchoi (Brassica chinensis L.), so as to provide a scientific basis for its safety utilization.【Method】Field experiments of 10 % imidaclothiz wettable powder in pakchoi under open field and greenhouse conditions were carried out in winter (between November and December) of 2018 and summer (between July and August) of 2019 at Shanghai. In dissipation experiments, the dosage of imidaclothiz was 90 g (a.i.)·hm^-2(1.5 times recommended dosage) with one-time spray, and the treated samples were collected randomly from several points of each plot at 2 h, 1, 2, 3, 4, 5, 7, 10, 14, 21, and 30 days after spraying of the pesticide to detect the residual concentration. For the study of final residue of imidaclothiz in pakchoi, imidaclothiz was sprayed for 2-3 times at an internal of 7 days at the recommended dosage (60 g (a.i.)·hm^-2) and 1.5 times recommended dosage (90 g (a.i.)·hm^-2), and the treated samples were collected randomly at 3, 5, and 7 days after the final processing to detect the residual concentration. The QuEChERS method coupled with ultra-high performance liquid chromatography-tandem mass spectrum (UPLC-MS/MS) was used to determine imidaclothiz in pakchoi. Dietary intake risk assessments were processed based on the maximal concentration, acceptable daily intake (ADI) of imidaclothiz, and daily consumption of pakchoi. The people involved in the experiment were divided into 8 classes, including underage male and female (subdivided into 3-6 years old infants and 7- 19 years old teenagers), as well as adult male and female (subdivided into 20-59 years old adults and 60-69 years old elder crowed).【Result】The limit of detection (LOD) of imidaclothiz was 0.0002 mg·kg^-1, and the limit of quantitation (LOQ) was 0.01 mg·kg^-1. Recoveries of imidaclothiz in pakchoi ranged from 77.2% to 87.9% at 0.01, 0.10 and 1.0 mg·kg^-1spiked levels, respectively, and the relative standard deviations (RSDs) were in the range of 2.5%-3.0%. The developed analytical method was suitable for the determination of imidaclothiz in pakchoi. Field experiments showed that the dissipation dynamics of imidaclothiz sprayed at the dosage of 90 g (a.i.)·hm^-2in pakchoi exhibited a first-order kinetic decline. The regression equation of imidaclothiz in winter greenhouse, summer greenhouse and summer open fields were C=0.8476e^-0.158t, C=1.6558e^-0.212t and C=4.3069e^-1.197t, and their half-lives were 4.39, 3.27 and 0.58 days, respectively. Both existing time and plant conditions had significant correlation with degradation efficiency of imidaclothiz in pakchoi (P<0.05). The maximal concentrations of imidaclothiz in pakchoi under winter greenhouse were all below 0.5 mg·kg^-1 at 7 days after the final processing, when it was sprayed for 2-3 times at an internal of 7 days at the dosage of 60 or 90 g (a.i.)·hm^-2 in pakchoi, while it just required 3 days to decline below 0.5 mg·kg^-1 for those treated in summer in the same place, regardless of greenhouse and open fields. The final residue concentrations had positive correlation with spraying dosage, but no relationship with spraying number (P>0.05). The risk assessments showed that hazard quotients (HQs) of imidaclothiz for different groups consuming pakchoi were far below 1, and the maximum HQ was 0.2196.【Conclusion】Imidaclothiz was a kind of easily degradable pesticide, and its degradation rate was significantly higher in summer than winter, as well as higher in open fields than greenhouse. The dietary exposure of imidaclothiz only by pakchoi’s consumption was at a relatively low level to the ordinary resident of China. Generally, it’s effective to use imidaclothiz as the pest control method for pakchoi, accompanied with recommended dosage (45-60 g (a.i.)·hm^-2) and appropriate pre- harvest intervals (7 days in winter and 3 days in summer).

Key words: pakchoi, imidaclothiz, residue, greenhouse, open field, risk assessment