Enantioselective monitoring chiral fungicide mefentrifluconazole in tomato, cucumber, pepper and its pickled products by supercritical fluid chromatography tandem mass spectrometry.

A fast, effective, and environmental-friendly method was developed for enantioseparation and analysis of mefentrifluconazole in vegetables based on supercritical fluid chromatography tandem mass spectrometry. The enantioselective behaviors of mefentrifluconazole enantiomers in tomato, cucumber, and pepper in the greenhouse, and pickled cucumber and pepper during processing were investigated. Mefentrifluconazole enantiomers could obtain baseline separation within 2 min. The average recoveries of all matrices ranged from 78.4% to 119.0%, with relative standard deviations less than 16.8% for two enantiomers. S-(+)-mefentrifluconazole was preferentially degraded in pepper, while there was no enantioselectivity in tomato and cucumber under field conditions. During processing, S-(+)-mefentrifluconazole was reduced preferentially than R-(-)-mefentrifluconazole in pickled cucumber and cucumber brine. Inversely, R-(-)-mefentrifluconazole degraded faster than S-(+)-mefentrifluconazole in pepper brine. But, no obvious enantioselectivity was observed in pickled pepper. The result of this study could contribute to a more accurate dietary risk assessment of mefentrifluconazole in vegetables and processed products.

Occurrences of eight common-used pesticide adjuvants in ten vegetable species and implications for dietary intake in North China.

Pesticide adjuvants (PAs) are important components of pesticide products. However, limited information is available regarding their occurrences in foodstuffs. Herein, eight common-used PAs were investigated in vegetables in North China in 2014-2016. The residue levels of total PAs in vegetables from markets and farms were 500 and 661 µg/kg, respectively. The highest residues of total PAs were found in cauliflowers (average: 1.53 × 103 µg/kg, market vegetables) and spinaches (average: 3.72 × 103 µg/kg, farm vegetables), respectively. In addition, Tristyrylphenol ethoxylates (TPE) dominated the total 8 PAs concentrations in most vegetable species. Moreover, the risk assessment showed that the human health risks associated with TPE and nonylphenol (NP) exposure via vegetables for adults were acceptable, and the estimated daily intakes (EDIs) of other six PAs were in the range of <0.010-0.89 µg/kg bw/day, which were less likely to pose a threat to human health.

Enantioseparation and dissipation monitoring of oxathiapiprolin in grape using supercritical fluid chromatography tandem mass spectrometry.

Oxathiapiprolin is a chiral fungicide used in China for the prevention and treatment of grape downy mildew, but its potential risk could be inaccurately assessed without distinguishing its enantiomers. In this study, an effective and sensitive chiral analytical method was first established for quantification of oxathiapiprolin enantiomers using supercritical fluid chromatography tandem mass spectrometry. Baseline separation for oxathiapiprolin enantiomers was achieved for less than 3 min by using a Lux Cellulose-2 chiral column with the resolution of 1.51. The elution order of the eluting enantiomers was identified as (-)-oxathiapiprolin and (+)-oxathiapiprolin by an optical rotation detector. The grape samples were extracted by QuEChERS method, with the average recoveries of each enantiomer in grapes were in the range of 88.1-111.8% and the relative standard deviations were less than 18.9%. The enantioselective analysis of the dissipation of oxathiapiprolin in field grape samples showed that (-)-oxathiapiprolin was dissipated faster than (+)-oxathiapiprolin. The results indicate that this proposed method could provide data support for the risk assessment of oxathiapiprolin in agricultural produces in a more accurate way.

Development of S-Fluxametamide for Bioactivity Improvement and Risk Reduction: Systemic Evaluation of the Novel Insecticide Fluxametamide at the Enantiomeric Level.

Increasing numbers of novel pesticides have been applied in agriculture. However, traditional evaluation of pesticides does not distinguish between their enantiomers, which may lead to inaccurate results. In this study, systematic research on the chiral insecticide fluxametamide was conducted at the enantiomeric level. The methods for enantioseparation and semipreparative separation of fluxametamide enantiomers were developed. The optical rotation and absolute configuration of two enantiomers were determined, and their stability was verified in solvents and soils. Enantioselective bioactivities against four target pests (Plutella xylostella, Spodoptera exigua, Aphis gossypii, and Tetranychus cinnabarinus) were tested. Acute toxicities of fluxametamide enantiomers toward honeybees were also evaluated. S-(+)-Isomer exhibited 52.1-304.4 times and 2.5-3.7 times higher bioactivity than R-(-)-isomer and rac-fluxametamide, respectively. Meanwhile, rac-fluxametamide was more toxic than S/R-isomer, and S-(+)-isomer showed >30-fold higher acute toxicity than R-(-)-isomer. Molecular docking studies were performed with γ-aminobutyric acid receptor (GABAR) to monitor the mechanism of stereoselective bioactivity. The better Grid score of S-(+)-fluxametamide (-60.12 kcal/mol) than R-(-)-enantiomer (-56.59 kcal/mol) indicated higher bioactivity of S-(+)-isomer than of R-(-)-isomer. The dissipation of fluxametamide in cabbage, Chinese cabbage, and soil was nonenantioselective under field conditions. Development of S-(+)-fluxametamide could maintain the high-efficacy and low-risk properties, which should attract attention of producers, applicators, and managers of pesticides.

Systematic Evaluation of Chiral Fungicide Imazalil and Its Major Metabolite R14821 (Imazalil-M): Stability of Enantiomers, Enantioselective Bioactivity, Aquatic Toxicity, and Dissipation in Greenhouse Vegetables and Soil.

Chiral pesticides are often produced and applied without distinguishing the difference of enantiomers, which sometimes leads to overuse and inaccurate risk assessment. Imazalil is a widely used chiral fungicide; its parent and major metabolite R14821 (imazalil-M) are usually detected in environmental and plant samples. The enantioselective bioactivity of imazalil enantiomers to seven typical pathogens (e.g., Fulvia fulva) was explored. S-(+)-Imazalil showed 3.00-6.59 times higher bioactivity than its antipode for selected pathogens. Molecular docking partly explained the mechanism of enantioselectivity in bioactivity. S-(+)-Imazalil had a stronger hydrophobic interaction and lower energy conformation with binding sites than R-(-)-imazalil. The acute toxicity of S-(+)-imazalil was 1.23-fold and 2.25-fold more than R-(-)-imazalil to P. subcapitata and D. magna, respectively. And, S-(+)-imazalil-M had 2.21-fold and 1.70-fold higher toxicity than R-(-)-imazalil-M to P. subcapitata and D. magna, respectively. However, R-(-)-imazalil was 1.21 times more toxic than S-(+)-imazalil to D. rerio. The enantioselective dissipation of imazalil and imazalil-M was explored under greenhouse conditions. High-effective S-(+)-imazalil preferentially enriched in leaf and fruit of tomato and cucumber, and no enantioselective degradation was found in soil. Imazalil-M enantiomers formed in cucumber, leaf of cucumber, and tomato, and the EF values fluctuated between 0.332 and 0.499. The results could provide information for more accurate assessment of imazalil; they implicated that using S-(+)-imazalil could reduce pesticide input and the risk to D. rerio.

Enantioselective Separation and Dissipation of Prothioconazole and Its Major Metabolite Prothioconazole-desthio Enantiomers in Tomato, Cucumber, and Pepper.

In this study, a simple and effective chiral analytical method was developed to monitor prothioconazole and prothioconazole-desthio at the enantiomeric level using supercritical fluid chromatography-tandem triple quadrupole mass spectrometry. The baseline enantioseparation for prothioconazole and prothioconazole-desthio was achieved within 2 min on a Chiralcel OD-3 column with CO2/0.2% acetic acid-5 mmol/L ammonium acetate 2-propanol (85:15, v/v) as the mobile phase at a flow rate of 1.5 mL/min and column temperature of 25 °C. The limit of quantitation for each enantiomer was 5 µg/kg, with a baseline resolution of >3.0. The results of enantioselective dissipation showed that R-(-)-prothioconazole was preferentially degraded in tomato, cucumber, and pepper under greenhouse conditions. S-(-)-prothioconazole-desthio was preferentially degraded in tomato and cucumber; however, R-(+)-prothioconazole-desthio was preferentially degraded in pepper. Results of this study may help to facilitate more accurate risk assessment of prothioconazole and its major metabolite in agricultural products.

Evaluation of the safe application of copper nonylphenolsulfonate and hexaconazole in wax gourd under field conditions.

Wax gourd is a popular vegetable and the new organic copper pesticide product of copper nonylphenolsulfonate and hexaconazole was firstly recommended to control the serious disease powdery mildew frequently occurred in wax gourd. However, it is still a concern for data deficiency of residue amounts of these two pesticides in edible portion of wax gourd and the persistence in environment. In this study, the dissipation and residue of copper nonylphenolsulfonate and hexaconazole in wax gourd and soil were investigated. The experiment results demonstrated that the dissipation half-lives of copper nonylphenolsulfonate and hexaconazole in wax gourd and soil were 4.6-5.8 days and 7.1-21.7 days, respectively. After 3 days from the last treatment, the residues of copper nonylphenolsulfonate were below 0.38 mg kg-1 in wax gourd and were below 0.21 mg kg-1 in soil, and the residues of hexaconazole ranged from < 0.01 to 0.19 mg kg-1 in wax gourd and from 0.01 to 0.63 mg kg-1 in soil. The long-term dietary risk assessment was done based on the supervised trial median residue and Chinese dietary pattern combining corresponding standards, by comparing with national estimated daily intake, the results showed that it was safe to use copper nonylphenolsulfonate·hexaconazole 20% microemulsion (ME) at the dosage of 420 g a.i. ha-1 with the pre-harvest interval of 3 days in China. And it also supplied authorities with important data for establishing MRL standards of copper nonylphenolsulfonate and hexaconazole in wax gourd in China.