2.1 Instruments and reagents
The following materials were used: 1260-6470 HPLC-MS/MS (Agilent Technologies, USA), SHMADIU Model AUY220 Balance (Shmadiu Corporation, Japan), HUAPUDA Model YXJ-A Centrifugal Machines (Changzhou Huapuda Educational Instrument Corporation, China), Kunshan KQ-500 Ultrasonicator (Kunshan Ultrasonics Corporation, China), and a digital high-speed dispersive homogeniser (IKA T25, IKA Company, Germany).
Analytical standards of mandipropamid (Dr. Ehrenstorfer GmbH, Germany) were used. Acetonitrile and methanol were of HPLC grade (MREDA Technology Inc., USA), formic acid was of 96% HPLC grade (TEDIA Company, USA), ammonium acetate was of 98% analysis grade (SIGMA, Germany), both sodium chloride and magnesium sulphate were of analytical grade (Beijing Chemical Plant, China), and Cleanert PSA was of PR grade (Agela Technology, China).
2.2 Field trial
From August to September 2020, field trials were conducted at five locations over one year. The trial locations were Fusong County in Jilin Province, Huanren Manchu Autonomous County in Liaoning Province, Baishan City in Jilin Province, Ji'an City in Jilin Province, and Yanbian City in Jilin Province. The final residue experiment was carried out in all five locations, and the degradation experiment of the ginseng plant and soil was carried out simultaneously in Fusong, Huanren, and Baishan, and the experiments were designed according to NY/788-2018 (Pesticide Residue Test Guidelines) (Ministry of Agriculture and Rural Affairs of the People's Republic of China, 2018).
The area of the experimental plots was 50 m2. At the initial stage of the onset of ginseng disease, the spraying dose was 210.6 g a.i./ha of stem and leaf spray, dynamic soil application was soil spray mixed with water at 600 kg/ha, and the number of sprays was one. After one application, the ginseng plant and soil samples were collected at intervals of 0, 1, 3, 5, 7, 14, 21, 28, 35, 45, and 60 d. Residual samples of fresh ginseng, ginseng plant, and soil were collected at 14, 21, and 28 d.
2.2.1 Preparation of samples
Fresh ginseng samples were gently washed using cool water, and the surfaces of the samples were dried indoors. Fresh ginseng samples were baked at 55°C for 24 h to prepare dried ginseng, and fresh ginseng samples were placed in a cage on a pot filled with water at 80°C and heated to boiling for 2.5–3 h. Then, the heated ginseng was cooled and dried at 70°C for 6 h with a dryer. Next, the ginseng was infiltrated with water, and the ginseng was dried again at 55°C for 24 h. Ginseng plant samples were placed in a tissue masher, and mashed for 5 min, and then passed through a 40-mesh sieve.
2.3 Extraction and purification
Next, 5.0 (±0.05) g of the homogenised fresh ginseng, dried ginseng, red ginseng, ginseng plant, and ginseng soil samples were added to 50-mL centrifuge tube, and then, 5 mL of distilled water and 10 mL of acetonitrile were added to the tube. After standing immersion for 5 min, vortex extraction was performed for 2 min, and the samples were centrifuged at 5,000 g for 5 min.
An aliquot of 1 mL of the upper layer of fresh ginseng, dried ginseng, red ginseng, and ginseng soil was transferred to a centrifuge tube containing 50 mg PSA and 100 mg anhydrous magnesium sulphate. An aliquot of 1 mL of the upper layer of the ginseng plant was transferred to a centrifuge tube containing 50 mg PSA, 25 mg GCB, and 100 mg anhydrous magnesium sulphate. The mixture was shaken vigorously 100 times and centrifuged for 5 min at 5,000 rpm. The upper layer was filtered through a 0.22-μm nylon syringe filter disc and analysed by HPLC-MS/MS.
2.4 Instrumental parameters
2.4.1 Chromatographic conditions
The chromatographic column used was an Agilent Zorbax RRHD Eclipse Plus C18 (3.0 ×100 mm, 1.8 μm at 30°C) column. The mobile phase was composed of acetonitrile (A) and water containing 0.1% formic acid and 5 mmol ammonium acetate (B) with a linear gradient. The linear mobile phase gradient was 0–2 min, 90–80% A; 2–3 min, 80–70% A; 3–5.5 min, 70–10% A; 5.5–7 min, 10% A; 7–9 min, 10%–30% A; 9–9.5 min, 30–60% A; 9.5–10 min, 60–90% A; and 10–15 min, 90% A. The flow rate was 0.3 mL/min, and the injection volume was 5 µL.
2.4.2 Mass spectrometry conditions
The ionisation source mode was electrospray ionisation, ionisation source polarity was positive ion mode (ESI+), scanning mode was multiple reaction monitoring, atomising gas was nitrogen, nebuliser gas pressure was 45 psi, ion spray voltage was 4,000 V, sheath gas temperature was 350°C, sheath gas was 12 L/min, quantitative ion of mandipropamid was 412/328.1, qualitative ion of mandipropamid was 412/328.1 and 412/124.8, fragmentor was 60 V, and collision energy was 412/328.1 (13 V) and 412/124.8 (35 V).
2.5 Statistical analysis
In this study, the standard curve and matrix standard curve of the same concentration were detected under the same chromatographic conditions, and the matrix effect was calculated according to the slope of the two standard solutions. When the matrix effect was within 100% (± 20), it was ignored; when it was greater than 120%, it showed enhancement, and when this was less than 80%, it showed inhibition. The calculation formula is as follows (Fang et al., 2019):
where KS is the slope of the standard curve and Km is the slope of the matrix standard curve.
The dissipation dynamics of mandipropamid in ginseng plants and soil were evaluated using first-order kinetics as follows (Fang et al., 2019; Vargas‐Pérez et al., 2020):
where Ct (mg/kg) is the residual concentration of mandipropamid in the ginseng plant or soil, C0 (mg/kg) is the initial concentration of mandipropamid in the ginseng plant or soil, k (day−1) is the dissipation rate constant, and T1/2 is the pesticide half-life of pesticide degradation.
2.6 Dietary intake risk assessment
Dietary exposure and risk assessments were performed to ensure the rational use of mandipropamid. RQ>100% indicated that there was an unacceptable risk to human health; the larger the value, the greater the risk. RQ<100% indicated that the risk to human health was acceptable; the smaller the value, the smaller the risk.
The chronic dietary risk assessment was undertaken by calculating RQ as follows (Fang et al., 2019):
where NEDI (mg/kg, bw) is the national estimated daily intake, STMRi (mg/kg) is the supervised trial median residue level, Fi (kg/d) is the average daily food intake, bw (kg) is the average Chinese body weight (63 kg), and ADI (mg/kg, bw) is the acceptable daily intake.