Method validation and residue analysis of methoxyfenozide and metaflumizone in Chinese broccoli under field conditions by liquid chromatography with tandem mass spectrometry.

Methoxyfenozide and metaflumizone are insecticides used on Chinese broccoli to prevent insects and increase yield. However, the residues are potentially harmful to the environment and consumers. In this study, the quick, easy, cheap, effective, rugged, safe method with high-performance liquid chromatography with tandem mass spectrometry was modified and validated for determination of methoxyfenozide and metaflumizone in Chinese broccoli. The clean-up efficiency of different sorbents including C18 , primary secondary amine, graphitized carbon black, and carbon nanofiber was compared. Recoveries of the validated method were 71.8-94.6% with relative standard deviations of 1.5-3.2% and the limits of quantification were 0.01 and 0.005 mg/kg for methoxyfenozide and metaflumizone, respectively. A storage stability test showed almost no degradation of methoxyfenozide in Chinese broccoli, however, the degradation rate of metaflumizone was 22.9% after 10-wk storage at -20°C. In field trials in four producing regions, the dissipation of both methoxyfenozide and metaflumizone in Chinese broccoli was fast, with half-lives of only 1.0-5.1 and 0.7-2.5 days, respectively. Terminal residues after application of the two pesticides were all below 1.0 mg/kg after 5 days.

Dissipation and residues of picoxystrobin in peanut and field soil by QuEChERS and HPLC-MS/MS.

The dissipation and final residues of picoxystrobin in peanut and soil were determined by a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The dissipation and final residue of picoxystrobin at three different provinces (Hebei, Hubei, and Shandong) in China were studied. The fortification experiments at three different spiking levels of 0.01, 0.05, and 0.5 mg kg(-1) in all matrices (soil, peanut seedling, shell, stalk, and kernels) were conducted, and the recoveries were 79-114% with relative standard deviations of 3-12 (n = 5). The dissipation half-lives of picoxystrobin were 1.5-8.6 days in soil, and 2.1-2.8 days in seedlings. The final residues of picoxystrobin in supervised field trials were 0.05-6.82 mg kg(-1) in stalk, ≤0.381 mg kg(-1) in soil, ≤0.069 mg kg(-1) in shells, and ≤0.005 mg kg(-1) in peanut kernels. Considering the final residue levels and the maximum residue limits (MRLs), the pre-harvest interval of 14 days was recommended for the safe use of picoxystrobin in peanut crop.

One-Step construction of Polyimide/NH2-UiO-66 heterojunction for enhanced photocatalytic degradation of sulfonamides.

Photocatalysis treatment is a promising technology to eliminate water pollutants. Herein, we constructed polyimide/NH2-UiO-66 composites (PUs) through a facile one-step solvothermal method for the photocatalytic degradation of sulfonamides. The optimized photocatalyst PU1.5 was superior to the photocatalysts prepared through multi-step methods due to the more exposed (001) facets of polyimide and the better distribution of small NH2-UiO-66 particles. PU1.5 showed the highest photocatalytic activity, which was 9.5 and 92.0 times higher than that of polyimide and NH2-UiO-66. Such improvement was attributed to the improved carrier separation efficiency resulted from direct Z-scheme heterojunction. The probable degradation pathway of sulfathiazole was proposed by the LC-MS/MS and Density Functional Theory (DFT) calculation. Furthermore, the reduced toxicity and the little antibacterial activity of intermediates was investigated by the Quantitative Structure-Activity Relationship (QSAR) analysis and the residual antibiotic activity experiment. The study might provide a new strategy for designing composite photocatalyst to achieve efficient removal of pollutants.

Development and application of a numerical dynamic model for pesticide residues in apple orchards.

BACKGROUND: Limited understanding of the fate of pesticides in apple orchards may lead to recurring pests or pose risks to food safety. In this study, through a field experiment conducted in an apple orchard, a dynamic plant uptake model, coupled with a soil water model, was developed to simulate measured pesticide concentrations in soil and different plant compartments. RESULTS: Results showed that the overall model could adequately describe the data set of four pesticides in the apple orchard. An estimated 15%-24.7% of applied pesticides were deposited on leaves and 0.37%-0.58% on fruits. Decreasing pesticide concentrations in fruits were observed after pesticide application, with 9.6%-64.8% of this decrease explained by biodegradation, 29.8%-75.8% by fruit growth dilution and 11.3%-47.6% by wash-off. Furthermore, a first estimation of dietary risks indicated that ingestion of the apples may not represent an acute or chronic risk to human health. CONCLUSION: The dynamic plant uptake model, coupled with the tipping buckets soil water model, could successfully be fitted to describe to the data set for the fate of four pesticides applied in an apple orchard. The contribution of different pathways to pesticide concentration was highly influenced by precipitation, fruit growth dilution and the characteristics of different pesticides. This model can improve our understanding of pesticide fate in apple orchards and has great potential for supporting food safety assessment and decision-making to minimize impacts arising from pesticide applications. © 2022 Society of Chemical Industry.

Dissipative behavior, residual pattern, and risk assessment of four pesticides and their metabolites during tea cultivation, processing and infusion.

BACKGROUND: In recent years, metabolic products of pesticides have gained much attention due to their substantial characteristics as organic pollutants. So far, the behavior and metabolite levels of pesticide metabolites in crops have not been characterized well. In the present study, four registered pesticides (imidacloprid, diafenthiuron, malathion and chlorothalonil) were applied on tea plants in Fujian and Sichuan to characterize their metabolites residue pattern and dietary risk. RESULTS: Four pesticides dissipated first-order kinetics in the fresh tea leaves with the half-lives of 1.4-3.8 days. Nine metabolites were detected in the fresh tea leaves and green tea after processing. The metabolites residues showed an increasing trend first and then declined after treatment, and reached the maximum near the half-lives of pesticide. Compared with the parent pesticide, the total residue and acute risk (included the metabolites) increased by 1.7-105.2 times. Some metabolites, especially those whose parent pesticides have high water solubility and low Log Kow, will be more easily transferred to tea infusion. CONCLUSION: Pesticides were metabolized rapidly on tea plants after application, but the production of metabolites increased the health risk of tea consumption. These results could provide insights to use the pesticides in tea gardens and risk monitoring after application. © 2022 Society of Chemical Industry.

Multiview behavior and neurotransmitter analysis of zebrafish dyskinesia induced by 6PPD and its metabolites.

The typical tire manufacturing additive 6PPD, its metabolites 6PPDQ and 4-Hydroxy should be monitored because of their ubiquitous presence in the environment and the high toxicity of 6PPDQ to coho salmon. The toxic effect of 6PPD and its metabolites have been revealed superficially, especially on behavioral characteristics. However, the behavioral indicators explored so far are relatively simple and the toxic causes are poorly understood. With this in mind, our work investigated the toxic effects of 6PPD, 6PPDQ and 4-Hydroxy on adult zebrafish penetratingly through machine vision, and the meandering, body angle, top time and 3D trajectory are used for the first time to show the abnormal behaviors induced by 6PPD and its metabolites. Moreover, neurotransmitter changes in the zebrafish brain were measured to explore the causes of abnormal behavior. The results showed that high-dose treatment of 6PPD reduced the velocity by 42.4% and decreased the time at the top of the tank by 91.0%, suggesting significant activity inhibition and anxiety. In addition, γ-aminobutyric acid and acetylcholine were significantly impacted by 6PPD, while dopamine exhibited a slight variation, which can explain the bradykinesia, unbalance and anxiety of zebrafish and presented similar symptoms as Huntingdon's disease. Our study explored new abnormal behaviors of zebrafish induced by 6PPD and its metabolites in detail, and the toxic causes were revealed for the first time by studying the changes of neurotransmitters, thus providing an important reference for further studies of the biological toxicity of 6PPD and its metabolites.

Chemisorption of CO and mechanism of CO oxidation on supported platinum nanoclusters.

Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O(2) pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O(2) activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C(16)O-(18)O(2)-(16)O(2) reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevant O(2) activation steps involve direct O(2)* (or O(2)) reactions with CO* to form reactive O*-O-C*=O intermediates that decompose to form CO(2) and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O(2). These CO-assisted O(2) dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassisted O(2) dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O(2) reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with (12)CO-(13)CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at saturation coverages do not depend on Pt cluster size in a range that strongly affects the coordination of Pt atoms exposed at cluster surfaces. These data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size. Theoretical estimates of rate and equilibrium constants for surface reactions and CO adsorption show that both parameters increase as the coordination of exposed Pt atoms decreases in Pt(201) cluster surfaces; such compensation dampens but does not eliminate coordination and cluster size effects on measured rate constants. The structural features and intrinsic non-uniformity of cluster surfaces weaken when CO forms saturated monolayers on such surfaces, apparently because surfaces and adsorbates restructure to balance CO surface binding and CO-CO interaction energies.

Copper/Lewis base cooperatively catalyzed asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates with azomethine ylides.

In this paper, an asymmetric allylic alkylation of easily available azomethine ylides with Morita-Baylis-Hillman (MBH) carbonates through a copper (i)/Lewis base cooperative catalysis strategy has been realized. The co-catalyzed asymmetric allylic alkylation provided the corresponding amino acid derivatives in up to 90% yields with up to 99% ee as well as good to excellent regioselectivity.

[Rapid detection of dichlorvos in chlorpyrifos by mid-infrared and near-infrared spectroscopy].

In the present study, the content of dichlorvos in chlorpyrifos was rapidly determined by mid-infrared and near-infrared spectroscopy. The quantitative models were established by partial least squares (PLS) method and optimized. The independent validation sets and 7 test samples were used to evaluate the model accuracy. The results showed that mid-infrared and near-infrared spectroscopy can accurately determine the content of dichlorvos in chlorpyrifos. The RMSEC (the root mean square error of calibration) of the mid-infrared model and near-infrared model was 0.013 and 0.020, respectively. R2 (determination coefficient) both were 1.000. For 7 test samples, RMSEP before model recalibration is 0.22 (MIRS) and 0.09 (NIRS). The adaptability of the near-infrared model was much better and model updating was unnecessary. To sum up, MIR and NIR are both rapid and easy-operation method with simple pretreatment.

Evaluation of cleanup procedures in pesticide multi-residue analysis with QuEChERS in cinnamon bark.

Cinnamon bark is a very complex spices matrix for pesticide residue analysis. In this study, two cleanup procedures, dispersive solid-phase extraction (d-SPE) and repetitive d-SPE, combined with Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction were both investigated and applied for the determination of 60 pesticide residues in cinnamon bark by liquid chromatography - tandem mass spectrometry (LC-MS/MS) detection. The extraction solvents, phase partition salts, and cleanup sorbents were optimized. The results showed that 150 mg MgSO4 + 50 mg C18 showed the best performance in d-SPE. The repetitive d-SPE achieved less matrix effects than d-SPE, but several high water-solubility analytes were lost during the cleanup, and also the 10 fold dilution compromised the sensitivities of analytes. With the validated QuEChERS-d-SPE method, 44 of 60 pesticides obtained satisfactory recoveries (71%-118%) and RSDs (2%-27%) at three to five spiking levels. The method was applied to monitor 15 market cinnamon samples.

Photodegradation of Imidacloprid in Aqueous Solution by the Metal-Free Catalyst Graphitic Carbon Nitride using an Energy-Saving Lamp.

Imidacloprid has become a research hotspot, due to its high toxicity to bees and other nontarget organisms. Photodegradation is a common method for removing imidacloprid in an aquatic environment. Traditional methods of pesticide photodegradation have generally been confined by many factors, such as response to only high-energy ultraviolet light. Herein, the visible-light-driven photocatalyst graphitic carbon nitride (g-C3N4) was applied to the photodegradation of imidacloprid. Visible-light illumination (λ >400 nm) resulted in nearly 90% substrate transformation in 5 h. With the illumination of an energy-saving lamp, imidacloprid has also been mostly removed. 1-((6-chloropyridin-3-yl)methylhydroxy)imidazolidin-2-ylidene nitramide) and 4,5-dihydro-N-nitro-1-(3-pyridinylmethyl)-1H-imidazol-2-amine were the main photoproducts identified by LC-MS analysis. The photocatalytic mechanism has also been discussed. This work could provide new perspective that g-C3N4, as a good visible-light photocatalyst could be applied to the cleanup of environmental pesticide pollution.

Systematic qualitative and quantitative assessment of fatty acids in the seeds of 60 tree peony (Paeonia section Moutan DC.) cultivars by GC-MS.

Seeds from Paeonia ostii and Paeoniarockii have been recently identified as novel resources of α-linolenic acid (ALA) in China. To assess whether tree peony cultivars can be used as oil resource, fatty acids (FAs) in 60 cultivars were monitored and evaluated in this study. The results indicated that the composition and content of FAs varied dramatically among different cultivars, in which ALA, linoleic acid, oleic acid, palmitic acid, and stearic acid were the dominant. The 60 cultivars were classified into six clusters by hierarchical cluster analysis, and they were quite distinct from each other. Finally, six cultivars with high yield and high quality were screened out, comprising of 'Liuliguanzhu', 'Hongguanyupei', 'LSS-2', 'LSS-1', 'Jingshenhuanfa' and 'LSS-11'. These cultivars were appropriately applied in practical oil production. Overall, tree peony oil with abundant unsaturated fatty acids especially ALA was proved to be a top-grade source for edible oil and nutritional supplements.

Assessment of flavonoids and volatile compounds in tea infusions of water lily flowers and their antioxidant activities.

Water lily, a member of the Nymphaeaceae family, can be made into tea on the basis of outstanding fragrance characteristics and health care functions. In this study, 16 flavonoids were identified and quantified in tea infusions prepared from the petals of 33 water lily cultivars using HPLC-DAD and HPLC-ESI-MS/MS. The infusions were analyzed with HS-SPME coupled with GC-MS; 29 volatile compounds were detected, of which nine were found to be scent components. The cultivars were clustered into three clusters characterized according to scent components. The 'Conqueror' and 'Virginia' cultivars had the highest antioxidant activities. The concentrations of polyphenols and flavonoids showed significant positive correlations with antioxidant activity as measured by DPPH, ABTS(+), and FRAP assays. This study is valuable for a fuller understanding of this important tea and can also be used for the development of water lily.

Dissipation and residues of trifloxystrobin and its metabolite in rice under field conditions.

Residue analysis of trifloxystrobin and its metabolite (CGA 321113) in rice matrices, paddy water, and soil was developed using the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and high-performance liquid chromatography-tandem mass spectrometry. The method was used to evaluate the dissipation rate of trifloxystrobin and CGA 321113 in rice seedling, soil, and paddy water as well as the residual level in harvest rice (grain, hull, straw) and soil. The results demonstrated that the dissipation half-lives of trifloxystrobin in rice seedling, soil, and water were 1.9 d to 4.7 d, 0.35 d to 0.54 d, and 0.28 d to 0.51 d, respectively. The final total residue of trifloxystrobin and CGA 321113 was highest in rice hull and lowest in paddy soil. The highest total residues in husked rice, rice hull, straw, and paddy soil at 28 d after spraying were 0.39 mg kg(-1), 3.82 mg kg(-1), 0.29 mg kg(-1), and 0.15 mg kg(-1), respectively. According to the final residue data and the maximum residue limits of trifloxystrobin in rice grain and straw (Codex Alimentarius) and in rice hull (US Environmental Protection Agency), 28 d could be recommended as the preharvest interval for trifloxystrobin application in the rice field. The data show that CGA 321113 constitutes a small amount of the final total residues in rice matrices, whereas it is much higher than its parent compound in soil samples.

Determination of halosulfuron-methyl residues and dissipation in wheat by QuEChERS and LC-MS/MS.

A sensitive and rapid analytical method based on QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation and LC-MS/MS detection was developed for the analysis of halosulfuron-methyl residues in wheat. The recoveries of halosulfuron-methyl in both the wheat plant and grain ranged from 87% to 119% and from 75% to 97%, respectively, with relative standard deviations (RSDs) of 3-9%. The limit of quantification (LOQ) was 0.005 mg kg(-1) for wheat plant and 0.001 mg kg(-1) for wheat grain. The half-life of halosulfuron-methyl in the wheat plant was 0.9-9.5 days. The terminal residue levels of halosulfuron-methyl in wheat grain were below 0.01 mg kg(-1) at harvest.

Mixed-phase oxide catalyst based on Mn-mullite (Sm, Gd)Mn2O5 for NO oxidation in diesel exhaust.

Oxidation of nitric oxide (NO) for subsequent efficient reduction in selective catalytic reduction or lean NO(x) trap devices continues to be a challenge in diesel engines because of the low efficiency and high cost of the currently used platinum (Pt)-based catalysts. We show that mixed-phase oxide materials based on Mn-mullite (Sm, Gd)Mn(2)O(5) are an efficient substitute for the current commercial Pt-based catalysts. Under laboratory-simulated diesel exhaust conditions, this mixed-phase oxide material was superior to Pt in terms of cost, thermal durability, and catalytic activity for NO oxidation. This oxide material is active at temperatures as low as 120°C with conversion maxima of ~45% higher than that achieved with Pt. Density functional theory and diffuse reflectance infrared Fourier transform spectroscopy provide insights into the NO-to-NO(2) reaction mechanism on catalytically active Mn-Mn sites via the intermediate nitrate species.