Dissipation kinetics and residues of triazolopyrimidine herbicides flumetsulam and florasulam in corn ecosystem

Herbicidal Activity of Beflubutamid Analogues as PDS Inhibitors and SAR Analysis and Degradation Dynamics in Wheat

In this work, a series of beflubutamid (BF) analogues' postemergent herbicidal activity was evaluated, and the structure-activity relationship (SAR) was discussed. At a dosage of 300 g ai/ha, compounds (Rac)-6h and (Rac)-6q showed excellent herbicidal activity against Amaranthus retroflexus, Abutilon theophrasti, and Medicago sativa, with inhibition rates of 90, 100, and 80% and 100, 100, and 100%, respectively, comparable to that of commercial herbicide BF, which showed inhibition rates of 90, 100, and 100%, respectively. Notably, at dosages of 150 and 300 g ai/ha, the chiral compounds (S)-6h and (S)-6q exhibited higher herbicidal activities than their racemates. Molecular docking results indicated that compounds (S)-BF and (S)-6h have stronger binding affinities with Oryza sativa phytoene desaturase (OsPDS), resulting in a higher herbicidal activity. Additionally, the degradation dynamics half-life of (S)-BF in wheat was determined to be 77.02 h. Consequently, compounds (S)-6h and (S)-6q are promising lead candidates for the development of highly effective herbicides.

Terminal Residue and Dietary Risk Assessment of Atrazine and Isoxaflutole in Corn Using High-Performance Liquid Chromatography-Tandem Mass Spectrometry

Isoxaflutole and atrazine are representative pesticides for weed control in corn fields. Formulations containing these two pesticides have been registered in China, and their residues may threaten food safety and human health. In this study, a method for simultaneous determination of isoxaflutole, atrazine, and their metabolites in fresh corn, corn kernels, and corn straw was established based on modified QuEChERS pre-treatment and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The linearity of seven compounds was good (R2 ≥ 0.9912), and the matrix effect was 48.5-77.1%. At four spiked levels of 0.01, 0.02, 0.05, and 0.5 mg kg-1, all compounds' average recovery was 76% to 116%, with relative standard deviation (RSD) less than 18.9%. Field experiments were conducted in Liaoning, Heilongjiang, Inner Mongolia, Shanxi, Beijing, and Yunnan provinces to study the terminal residues. The terminal residues of all compounds were below the LOQ (0.01 mg kg-1) in fresh corn and corn kernels, and atrazine residues in corn straw ranged from <0.05 mg kg-1 to 0.17 mg kg-1. Finally, a dietary risk assessment was conducted based on residues from field trials, food consumption, and acceptable daily intake (ADI). For all populations, the chronic dietary risk probability (RQc) of atrazine was between 0.0185% and 0.0739%, while that of isoxaflutole was 0.0074-0.0296%, much lower than 100%. The results may provide scientific guidance for using isoxaflutole and atrazine in corn field ecosystems.

Effect of flumetsulam alone and coexistence with polyethylene microplastics on soil microbial carbon and nitrogen cycles: Elucidation of bacterial community structure, functional gene expression, and enzyme activity

Flumetsulam (FLU) is a new class of broad-spectrum herbicides. With the widespread use of plastic products, polyethylene (PE) microplastics (MPs) may remain in the soil. It is possible for these two novel contaminants to co-exist in the soil environment. In the present study, we used brown soil as the test soil and determined the toxicity of FLU at 0.05, 0.5 and 2.5 mg kg-1 alone and in combination with PE MPs (1%) on soil microorganisms. The obtained results demonstrated that the exposure of FLU and FLU+MPs had an inhibitory effect on the numbers of bacteria and fungi. In addition, FLU and FLU+MPs caused changes in the relevant functional bacterial genera, favored nitrogen fixation and denitrification, and promoted soil carbon fixation, but inhibited nitrification. Compared to FLU exposure alone, exposure to FLU+MPs gave rise to significant differences in soil bacterial community composition, but did not affect carbon and nitrogen cycling. The integrated biomarker response results indicated that the toxicity of FLU and FLU+MPs to soil microorganisms increased with increasing concentrations of FLU. The present experiment clarified the toxicological effects of co-exposure of FLU and MPs on microorganisms and filled the toxicological data gap of FLU.

Ultrasound-assisted synthesis of pyrimidines and their fused derivatives: A review

The pyrimidine scaffold is present in many bioactive drugs; therefore, efficient synthetic routes that provide shorter reaction times, higher yields, and site-selective reactions are constantly being sought. Ultrasound (US) irradiation has emerged as an alternative energy source in the synthesis of these heterocyclic scaffolds, and over the last ten years there has been a significant increase in the number of publications mentioning US in either the construction or derivatization of the pyrimidine core. This review presents a detailed summary (with 140 references) of the effects of US (synergic or not) on the construction and derivatization of the pyrimidine core through classical reactions (e.g., multicomponent, cyclocondensation, cycloaddition, and alkylation reactions). The main points that were taken into consideration are as follows: chemo- and regioselectivity issues, and the results of conventional heating methods compared to US and mechanistic insights that are also presented and discussed for key reactions.

Recent developments in sample preparation techniques combined with high-performance liquid chromatography: A critical review

This review article compares and contrasts sample preparation techniques coupled with high-performance liquid chromatography (HPLC) and describes applications developed in biomedical, forensics, and environmental/industrial hygiene in the last two decades. The proper sample preparation technique can offer valued data for a targeted application when coupled to HPLC and a suitable detector. Improvements in sample preparation techniques in the last two decades have resulted in efficient extraction, cleanup, and preconcentration in a single step, thus providing a pathway to tackle complex matrix applications. Applications such as biological therapeutics, proteomics, lipidomics, metabolomics, environmental/industrial hygiene, forensics, glycan cleanup, etc., have been significantly enhanced due to improved sample preparation techniques. This review looks at the early sample preparation techniques. Further, it describes eight sample preparation technique coupled to HPLC that has gained prominence in the last two decades. They are (1) solid-phase extraction (SPE), (2) liquid-liquid extraction (LLE), (3) gel permeation chromatography (GPC), (4) Quick Easy Cheap Effective Rugged, Safe (QuEChERS), (5) solid-phase microextraction (SPME), (6) ultrasonic-assisted solvent extraction (UASE), and (7) microwave-assisted solvent extraction (MWASE). SPE, LLE, GPC, QuEChERS, and SPME can be used offline and online with HPLC. UASE and MWASE can be used offline with HPLC but have also been combined with the online automated techniques of SPE, LLE, GPC, or QuEChERS for targeted analysis. Three application areas of biomedical, forensics, and environmental/industrial hygiene are reviewed for the eight sample preparation techniques. Three hundred and twenty references on the eight sample preparation techniques published over the last two decades (2001-2021) are provided. Other older references were included to illustrate the historical development of sample preparation techniques.

Fast and Low-Cost Surface-Enhanced Raman Scattering (SERS) Method for On-Site Detection of Flumetsulam in Wheat

The pesticide residues in agri-foods are threatening people’s health. This study aims to establish a fast and low-cost surface-enhanced Raman scattering (SERS) method for the on-site detection of flumetsulam in wheat. The two-step modified concentrated gold nanoparticles (AuNPs) acted as the SERS substrate with the aid of NaCl and MgSO₄. NaCl is served as the activator to modify AuNPs, while MgSO₄ is served as the aggregating agent to form high-density hot spots. The activation and aggregation are two essential collaborative procedures to generate remarkable SERS enhancement and achieve the trace-level detection of flumetsulam. This method exhibits good enhancement effect with an enhancement factor of 10⁶ and wide linear range (5–1000 μg/L). With simple pretreatment, the flumetsulam residue in real wheat samples can be successfully detected with the limit of detection (LOD) down to 0.01 μg/g, which is below the maximum residue limit of flumetsulam in wheat (0.05 μg/g) set in China. The recovery of flumetsulam residue in wheat ranges from 88.3% to 95.6%. These results demonstrate that the proposed SERS method is a powerful technique for the detection of flumetsulam in wheat, which implies the great application potential in the rapid detection of other pesticide residues in various agri-foods.

Residue behavior and dietary risk assessment of chlorothalonil and its metabolite SDS-3701 in water spinach to propose maximum residue limit (MRL)

Dietary risk assessment generally combines food consumption data and the concentration of pesticide by using the risk quotient (RQ) method. Chlorothalonil is the second popular fungicide in the world, and its residue and risk assessment in water spinach remain unknown. In this paper, the field trials of chlorothalonil in water spinach were operated under good agricultural practice (GAP) in China to human health protective. The dissipation experiments demonstrated that chlorothalonil was rapidly degraded in water spinach, with the half-lives of 1.8-3.2 days, and the amount of its metabolite SDS-3701 (4-hydroxy-2,5,6-trichloroisophthalonitrile) taken up through the water spinach roots from the soil was minor. The terminal experiments disclosed that the average residues of chlorothalonil and SDS-3701 in water spinach were below 6.59 mg/kg and 0.01 mg/kg, respectively. The results suggested the chronic dietary risk probability of chlorothalonil was 51.95-59.15% in terms of all registered crops, and the acute dietary risk probability of chlorothalonil was 12.30%-63.01% in water spinach, highlighting that the dietary risk of chlorothalonil in water spinach under GAP was acceptable. MRL of chlorothalonil was proposed as 7 mg/kg for water spinach and 5 days was recommended as a safe pre-harvest interval (PHI) for chlorothalonil application in water spinach field.

Identification of photoproducts of florasulam in water using UPLC-QTOF-MS

Here, we aimed to investigate florasulam photodegradation in aquatic environments under UV-visible irradiation. LC-MS/MS was used to explore the photolysis kinetics of florasulam degradation with respect to different light source types, florasulam concentrations, water sources, and pH. We also tested whether the addition of the nitrate ions, Fe³⁺, or I^- to the reaction solution influences florasulam photolysis kinetics. NO₃^- accelerates florasulam degradation at low concentrations (0.01-1 mg L^-1), but decreases the process at higher concentrations. At low concentrations (≤ 0.1 mg L^-1), Fe³⁺ enhanced florasulam photodegradation obviously. However, the addition of 0.01-10 mg L^-1 I^- decreased the degradation rate linearly. The florasulam photolysis rates in alkaline and neutral solutions were higher than that in acidic solutions. The florasulam degradation rate under mercury light irradiation was greater than that under xenon light. The rate of florasulam degradation in distilled water was greater than in tap water, lake water, and rice paddy water. As the concentration of florasulam increased, the photodegradation rate decreased. Six kinds of transformation products (TPs) were isolated and identified using UPLC/Q-TOF-MS. Based on these TPs and their evolutionary processes, we inferred the florasulam degradation mechanisms, identifying four possible florasulam degradation pathways. Cleavage of the florasulam sulfonamide bond yielded TPs2. TPs2 was intermolecularly rearranged to form a SO₂ extrusion compound, TPs3. Cleavage of the [C-F] bonds led to the formation of TPsl, TPs4, and TPs5, while hydroxylation led to the formation of TPs6. We then predicted the stability of each of the florasulam TPs in water. TPs2 and TPs3 rapidly degraded after reaching maximum concentration due to poor light stability. TPs4 and TPs6 were more photostable than florasulam (the parent compound) and may be important contributors to water pollution.

Influence of various parts of sweet corn ears on pesticide residue levels

Pesticide residue levels in various parts of sweet corn ears were analyzed. For this purpose, five pesticides were sprayed on corn in two different fields, and the harvested samples were separated into four portions, namely kernels, cobs, silks, and husks. Each of these portions was then separately analyzed. Pesticide residues were predominantly distributed in the silk and husk portions, which constituted ≥91% of the whole crop, whereas relatively minimal residues remained in the kernel and cob portions. Further, residue distributions in the silks and husks were found to differ between the two fields. The calculated residue levels in kernels with the cob and silk were obviously higher than the residue levels in the kernel alone (max. >62 times different). This result suggests that the silk portion could greatly affect pesticide residue levels in the edible portion of corn.

Effect of Environmental Conditions on the Degradation of Florasulam in Typical Soils of Northern China

The widespread use of florasulam in China makes residues from this herbicide in soil a serious concern due to their potential to pollute the soil environment and groundwater. Accelerating the degradation of these residues will reduce their pollution potential. In this study, we investigated the degradation and adsorption of florasulam in four typical soils in northern China and examined the degradation of florasulam in Inceptisols at different temperatures, soil moisture contents, and pH values, as well as the influence of microorganisms and the use of organic matter and biogas slurry as soil amendments. The half-lives of florasulam in the four soils were 13.6 d (Ultisols), 13.9 d (Vertisols), 15.1 d (Alfisols), and 19.3 d (Inceptisols), and the adsorption ability of the four soils followed the order Inceptisols > Alfisols > Vertisols > Ultisols. Florasulam degradation rates increased as temperature and soil moisture increased and as soil pH decreased (from 8.0 to 6.0). Adding a small amount of organic matter to the soil increased the florasulam degradation rates. The use of biogas slurry also increased the degradation rates. Florasulam half-life in unsterilized soil ( = 19.3 d) was significantly shorter than in sterilized soil ( = 113.4 d). These results provide agricultural producers and environmental managers useful information for reducing the environmental risk associated with florasulam use.