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A study was carried out to evaluate the dissipation kinetics of field-applied omethoate during wheat storage. Both the identification and metabolic dynamics of omethoate metabolites were analyzed using UPLC-QTOF/MS. The presence of the metabolite dimethyl phosphate (DMP) was confirmed in wheat samples with applied omethoate. This might be because the group attached to the P atom of omethoate is replaced by a hydroxyl group through hydrolysis, thus leading to the formation of the specific metabolite DMP during wheat storage. Although the initial concentrations of DMP in different doses were considerably lower than those of omethoate, the half-life values of DMP were 11.87–31.50 days, which were close to the half-life of the parent omethoate (11.85–30.94 days). This indicates that potential health risks might be caused by dietary exposure to DMP and omethoate. Therefore, more importance should be given to the risk assessment for omethoate and its metabolite DMP in wheat.

The use of an in vitro cell suspension to study insecticide metabolism is a simpler strategy compared to using intact plants, especially for a difficult matrix such as tea. In this study, a sterile tea leaf callus was inoculated into B5 liquid media with 2,4-dichlorophenoxyacetic acid (2,4-D, 1.0 mg L-1) and Kinetin (KT, 0.1 mg L-1). After 3-4 subcultures (28 days each), a good cell suspension was established. Utilizing these cultures, the metabolic behaviors of six insecticides, including two organophosphates (dimethoate, omethoate) and four neonicotinoids (thiamethoxam, imidacloprid, acetamiprid, and imidaclothiz) were compared. The results showed that thiamethoxam, dimethoate, and omethoate were easily metabolized by tea cells, with degradation ratios after 75 days of 55.3%, 90.4%, and 100%, respectively. Seven metabolites of thiamethoxan and two metabolites of dimethoate were found in treated cell cultures using mass-spectrometry, compared to only two metabolites for thiamethoxam and one for dimethoate in treated intact plants.

Omethoate is a frequently used organophosphorus pesticide, and the establishment of a sensitive, selective, and simple method to determine omethoate is very important for food safety. In this paper, a dual strategy was applied to improve the detection sensitivity of omethoate. In the first strategy, graphene quantum dots (GQDs) were doped with nitrogen to increase the fluorescence quantum yield to 30%. By coupling N-GQDs with omethoate aptamer, an N-GQDs-aptamer probe was synthesized. The fluorescence of the N-GQDs-aptamer probe was turned off by graphene oxide (GO), but recovered by omethoate. Based on this principle, the fluorescence method for detecting omethoate was established with a detection limit of 0.041 nM. To further improve the detection sensitivity, the fluorescence polarization analysis method was applied as another strategy based on the polarization signal of GQDs. The detection limit was decreased to 0.029 pM by using the fluorescence polarization method. The detection limits in this paper were lower than those in other reports. The imaging of omethoate on plant leaves showed that the probe could be used for visual semiquantitative determination of omethoate.

A practical, inexpensive, and green chemical process is greatly needed for degrading pesticides in food and environmental water. In this work, the impact of O(2) plasma treatment on reduction of dichlorvos (DDVP) and omethoate in maize was determined by gas chromatography (GC). The main plasma-induced degradation mechanisms were investigated through identification of intermediates or products during O(2) plasma treatment for DDVP and omethoate on solid surfaces by gas chromatography/mass spectrometry (GC/MS). The results clearly demonstrate that O(2) plasma treatment is significantly effective in the degradation of original DDVP and omethoate, and the degradation efficiency mainly depends upon related operating parameters and chemical structures of pesticides. Moreover, GC/MS analyses show that DDVP and omethoate molecules are degraded into less-toxic compounds, and the plasma degradation mechanisms for pesticides can be dominated by a free-radical reaction. It is concluded that O(2) plasma has the potential to reduce pesticide residues in agricultural products.

We describe here a colorimetric and phosphorimetric dual-signaling strategy for sensitive assay of organophosphorus pesticides (OPPs). The principle for assay depends on the phenomenon that the phosphorescence of Mn-ZnS quantum dots (QDs) can be dramatically quenched by Au nanoparticles (AuNPs) through the inner filter effect (IFE) and the activity of acetylcholinesterase (AChE), an enzyme that catalytically hydrolyzes acetylthiocholine to thiocholine that can be inhibited by OPPs. By virtue of the variations of absorbance and phosphorescence of the analytical system, a dual-readout assay for OPPs has been proposed. The limits of detection for different OPPs including paraoxon, parathion, omethoate, and dimethyl dichlorovinyl phosphate (DDVP) are found to be 0.29, 0.59, 0.67, and 0.44 ng/L, respectively. The proposed assay was allowed to detect pesticides in real spiked samples and authentic contaminated apples with satisfactory results, suggesting its potential applications to detect pesticides in complicated samples.

Comparative toxicity of selected organophosphate (OP) insecticides against resistant and susceptible clones of the greenbug, Schizaphis graminum, were studied both in vitro and in vivo. Two resistant (OR-1 and OR-2) clones of the greenbug showed marginal to high levels of resistance to all seven OPs tested, ranging from 11- to 327-fold greater than those of a susceptible (OSS) clone. The OR-1 clone showed lower levels of resistance to phenyl (parathion and parathion-methyl) and heterocyclic (chlorpyrifos) OPs than to aliphatic OPs (dimethoate, omethoate, disulfoton, and demeton-S-methyl), whereas the OR-2 clone showed a rather broad spectrum of resistance to nearly all OP insecticides examined. In vitro inhibition of acetylcholinesterase (AChE) using six selected OP oxon analogues showed that alterations of AChE were involved in resistance to all OP compounds examined in both the OR-1 and OR-2 clones. Although the levels of insensitivity of AChE to these OPs were relatively low, ranging from 1.1- to 3.8-fold, the insensitivity spectrum of AChE to different OPs was rather broad. The general esterase activity in the OR-1 and OR-2 clones was 1.3-8. 4-fold higher than that in the OSS clone, depending on the substrates used. The AChE activity in both the OR-1 and OR-2 clones was 1.8-fold higher than that in the OSS clone. High resistance levels of the OR-2 clone to phenyl and heterocyclic OPs appeared to be associated with the ability of the esterases to hydrolyze beta-naphthyl acetate and more hydrophobic substrates.

Supercritical fluid extraction (SFE) was evaluated for the extraction of organophosphate and carbamate insecticides in honeybees. Extracts were analyzed by gas chromatography (GC) with nitrogen−phosphorus detection or flame-photometric detection with confirmation by GC with ion-trap mass spectrometry. Samples were mixed with diatomaceous earth and optimal extraction conditions were: (1) CO2 density of 0.7 g/mL, (2) 60 °C, (3) 2 min equilibration time, (4) 40 mL of CO2, and (5) 1.6 mL/min flow rate. Analytes were trapped on octadecyl silane (ODS) and eluted with acetonitrile. No further cleanup was necessary and chromatographic interferences in SFE extracts were comparable to those in solvent extracts that had undergone extensive cleanup procedures. Recoveries from honeybees fortified at 1 and 0.1 μg/g were greater than 75% for all pesticides studied except omethoate. Samples containing residues were also extracted by SFE, and there was good quantitative agreement with results from analyses based on solve...

This article presents a novel application of dispersive microextraction based on "magnetic water" (m-water) for the purification of organophosphorus pesticides (methamidophos, omethoate, monocrotophos) from cold-pressed vegetable oils. In the present study, a trace amount of water (extractant) was adsorbed on bare Fe₃O₄ by hydrophilic interaction to form m-water. Rapid extraction can be achieved while the m-water is dispersed in the sample solution with the aid of a vigorous vortex. After extraction, the analyte-adsorbed m-water can be readily isolated from the sample solution by a magnet, which could greatly simplify the operation and reduce the whole pretreatment time. Several parameters affecting the extraction efficiency were investigated, and under the optimized conditions, a simple and effective method for pesticide analysis was established by coupling with gas chromatography/mass spectrometry (GC/MS). The linearity range of the proposed method was 2-100 ng/g with satisfactory correlation coefficients (R) of 0.9997-0.9998, and the limits of quantification (LOQ) for the target compounds were in the range of 0.70-1.27 ng/g. In addition, the reproducibility was obtained by evaluating the intra- and interday precisions with relative standard deviations (RSDs) less than 7.2% and 6.5%, respectively. Finally, the established "magnetic water" microextraction method was successfully applied for the determination of pesticide residues in several kinds of cold-pressed vegetable oils.

How to determine trace multipesticide residues in fruits is an important problem. This paper reports a molecularly imprinted polymer (MIP) that was prepared using 4-(dimethoxyphosphorothioylamino)butanoic acid as the template, acrylamide as the functional monomer, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. The novel imprinted polymer was characterized by static and kinetic adsorption experiments, and it exhibited good recognition ability and fast adsorption-desorption dynamicd toward trichlorfon, malathion, acephate, methamidophos, omethoate, dimethoate, phosphamidon, monocrotophos, and methyl parathion. Using this imprinted polymer as sorbent, matrix solid-phase dispersion coupled to gas chromatography for simultaneous determination of nine trace organophosphorus pesticide residues was first presented. Under the optimized conditions, the LOD (S/N = 3) of this method for the nine organophosphorus was 0.3-1.6 μg kg(-1); the RSD for three replicate extractions ranged from 1.2 to 4.8%. The apple and pear samples spiked with nine organophosphate pesticides at levels of 20 and 100 μg kg(-1) were determined according to this method with good recoveries ranging from 81 to 105%. Moreover, this developed method was successfully applied to the quantitative detection of the nine organophosphorus pesticide residues in orange samples.

In this study, the occurrence of 15 organophosphorus pesticide residues in Greek virgin olive oil was investigated. Analysis was carried out using capillary gas chromatography with specific detectors (FPD and NPD), after sample extraction with n-hexane and cleanup by partitioning between n-hexane and acetonitrile. Sixty-two samples of virgin olive oil were taken from the major production areas and packing companies of Greece during 1992-1994. In 46 samples, 9 organophosphorus pesticides, namely dimethoate, fenthion, omethoate, chlorpyrifos, methamidophos, parathion-methyl, parathion, methidathion, and malathion, were found, in concentrations ranging from 0.0005 to 0.1800 mg/kg. Diazinon, pirimiphos-methyl, paraoxon-methyl, malaoxon, carbophenothion, and azinphos-ethyl were not detected in any sample. In most samples pesticide residues were below the detection limits (0.0001 and 0.001 mg/kg), and most of the positive findings were a fraction (i.e.

The persistence of three pesticides (fenitrothion, dimethoate, and ziram) in apricots in field conditions and their fate during the drying process were studied. After the treatments, the pesticides showed fast decay rates with pseudo-first-order kinetics and half-lives ranging from 6.9 to 9.9 days. The drying process showed a different effect on residue concentrations in dried apricots: omethoate (metabolite of dimethoate) and ziram residues had almost doubled, while fenitrothion disappeared and dimethoate remained constant. Keywords: Residues; pesticides; apricot; dried apricot