Investigation of pesticide residues level on commonly consumed leafy vegetables picked from the central market in Jeddah, Saudi Arabia.

This study aimed to investigate the presence of pesticide residues in a variety of commonly consumed leafy vegetables, including Grape leaves, Lettuce, Arugula, Spinach, Purslane, Ocimum, Parsley, Jew's mallow, Celery, Coriander, and Mint. A total of 100 samples were collected from the Central Market of Jeddah, Kingdom of Saudi Arabia. Our methodology involved employing the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) extraction method in combination with Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) to analyze a comprehensive database of 237 distinct pesticides. The range for limit of detection (LOD) and limit of quantification (LOQ) of the method were 0.0001 to 0.0014 mg. Kg-1 and 0.0010 to 0.0064 mg. Kg-1 for tested pesticides, respectively. The recoveries were in the range of 70-172.9%, with a relative standard deviation (RSD) of less than 19.0% for all tested pesticides. The results revealed that 60% of the analyzed samples were free from pesticide residues, while 40% exhibited contamination with 17 different pesticide residues. Notably, the most prevalent pesticide detected was Triallate in the Ocimum samples, followed by Metalaxyl in Grape leaves, Mint, and Spinach, and Methomyl in Celery. Approximately 45% of the samples contained pesticide residues that fell below or were equal to the European Union Maximum Residue Levels (EU MRLs), while the remaining 55% exceeded these MRLs. Remarkably, high pesticide concentrations were observed in all Ocimum samples (Triallate, Pyridaben, Hexythiazox, Imidacloprid), 67% of Grape leaves (Metalaxyl, Azoxystrobin, Difenoconazole Isomer), and 40% of Celery (Azoxystrobin, Methomyl). In conclusion, this study sheds light on the contamination levels of commonly consumed domestically produced and purchased leafy vegetables in the Central Market of Jeddah. To ensure food safety and the well-being of consumers, we strongly recommend enhanced scientific assessments and continued monitoring of pesticide usage in agricultural practices.

A microwave-induced plasma jet for efficient degradation of methomyl in aqueous solution.

As a typical carbamate pesticide, methomyl was once widely used in agriculture for its excellent broad-spectrum insecticidal effect. However, due to its high toxicity, long half-life, and difficult degradation properties, it poses a serious challenge to water environment pollution. In this study, an electrode-free discharge microwave-induced plasma technology was used to rapidly and efficiently degrade methomyl in aqueous solution. In this experiment, the statistical design of experiments (DOE) was adopted to optimize the plasma degradation parameters. Under the optimized parameters (P = 140 W, D = 0 mm, R = 0.5 L/min), 78.4% removal of 50 mg/L of methomyl was achieved after 8 min. The optical emission spectrometry and free radical detection experiments showed that the active substances generated by the collision reaction between plasma and water molecules occurring at the gas-liquid interface were the key factors to exert the degradation effect. The degradation rate of methomyl decreased by 73.2% after the addition of tert-butanol (OH burster), while it decreased by only about 12.0% after the addition of peroxidase. These implied that ∙OH was largely responsible for methomyl degradation. In addition, based on the detected intermediates, possible degradation mechanisms and pathways were analyzed.

Signal optimized rough silver nanoparticle for rapid SERS sensing of pesticide residues in tea.

Trace detection of toxic chemicals in foodstuffs is of great concern in recent years. Surface-enhanced Raman scattering (SERS) has drawn significant attention in the monitoring of food safety due to its high sensitivity. This study synthesized signal optimized flower-like silver nanoparticle-(AgNP) with EF at 25 °C of 1.39 × 106 to extend the SERS application for pesticide sensing in foodstuffs. The synthesized AgNP was deployed as SERS based sensing platform to detect methomyl, acetamiprid-(AC) and 2,4-dichlorophenoxyacetic acid-(2,4-D) residue levels in green tea via solid-phase extraction. A linear correlation was twigged between the SERS signal and the concentration for methomyl, AC and 2,4-D with regression coefficient of 0.9974, 0.9956 and 0.9982 and limit of detection of 5.58 × 10-4, 1.88 × 10-4 and 4.72 × 10-3 µg/mL, respectively; the RSD value < 5% was recorded for accuracy and precision analysis suggesting that proposed method could be deployed for the monitoring of methomyl, AC and 2,4-D residue levels in green tea.

Qualitative enzymatic detection of organophosphate and carbamate insecticides.

In this study, new polymers containing amides (TrisPS-Ntaa, and TrisPS-Ntaa-Fc) were synthesized by condensation reaction for qualitative identification of insecticides. The synthesized polymers, including amides were investigated by infrared spectroscopy (IR), scanning electron microscopy-energy dispersion X- ray spectrometry (SEM-EDX), and gel permeation chromatography (GPC). Then, acetylcholinesterase enzyme (AChE) was covalently immobilized on these polymers to improve properties (including activity, reusability, and storage stability). Accordingly, organophosphate (malathion, acephate, chlorpyrifos methyl) and carbamate (carbofuran, methiocarb, methomyl), which are used to prevent harmful organisms in some agricultural products were enzymatically determined based on their inhibitory activity on AChE.

Simple Colorimetric Method for Cholinesterase-inhibitor Screening in Gastric Content by Using Phytoesterase Enzyme from Kidney Bean.

BACKGROUND AND OBJECTIVE: Diagnosis of cholinesterase inhibitor insecticide ingestion is based on clinical suspicious and should be confirmed by cholinesterase essay. However, serum cholinesterase activity test requires specific instruments and procedure. This study aimed to develop simple colorimetric test to detect cholinesterase inhibitors in the gastric content, using phytoesterase and alpha naphthyl acetate as a chromogenic substrate. MATERIALS AND METHODS: Methomyl and chlorpyrifos were selected for the phytoesterase enzyme inhibition assay. The experiment was conducted using pooled insecticide-free gastric content sample from ten cadavers. The gastric content samples were prepared by simple filtration procedure or liquid-liquid extraction procedure with dichloromethane or ethyl acetate. The inhibitor concentrations measured by the developed phytoesterase enzyme inhibition assay were compared with those analyzed by the LC-MS/MS and the GC-FPD. RESULTS: Different sample preparation procedures, sensitivity and specificity and specificity of the test were investigated. Sample extracted with dichloromethane reduced the effect of matrix in gastric content as same as ethyl acetate. The developed color test method of detection showed 56.52% sensitivity and 100% specificity for methomyl, 100% sensitivity and 96.30% specificity for chlorpyrifos. The limit of detection of the assay was 422.6 ng mL-1 for methomyl and was 339.8 ng mL-1 for chlorpyrifos. CONCLUSION: This developed method could be used an alternative diagnostic test for methomyl and chlorpyrifos self-ingestion.

Tracing the source of methomyl using stable isotope analysis.

RATIONALE: Pesticide self-poisoning is a major method of suicide in many agricultural communities worldwide. In addition, there are a number of known crime cases related to people being harmed by insecticides. Methomyl, a prohibited insecticide in the Republic of Korea, has high toxicity and is frequently used for self-poisoning. In this study, we investigated the source of origin of methamyl in a fatal poisoning case using stable isotope ratio analysis. METHODS: Two bottles of Soju from a crime scene were seized and nine different brands of methomyl products were collected from the neighborhood for analysis. In addition, the gastric contents and energy drink from the person who had committed suicide were analyzed. Isotope analysis using GC/Isolink/IRMS was conducted to determine the source of the methomyl by comparing their carbon and nitrogen isotope ratios. Linear discriminant analysis was utilized to verify the results. RESULTS: Isotope ratio analysis showed that the isotope ratio ranges of methomyl found in the Soju, the gastric contents of the suicide victim, and the energy drink bottle were similar to those of a seized methomyl product, Samgong methomyl 2011 (SG11). Thus, it was assumed that SG11 was used in this fatal poisoning case. CONCLUSIONS: This study demonstrates the potential of stable isotope ratio analysis for the determination of insecticide origin in fatal poisoning cases.

An experimental study of postmortem decomposition of methomyl in blood.

Methomyl (S-methyl-1-N-[(methylcarbamoyl)oxy]thioacetimidate) is a carbamate pesticide. It has been noted that in some cases of methomyl poisoning, methomyl is either not detected or detected only in low concentrations in the blood of the victims. However, in such cases, methomyl is detected at higher concentrations in the vitreous humor than in the blood. This indicates that methomyl in the blood is possibly decomposed after death. However, the reasons for this phenomenon have been unclear. We have previously reported that methomyl is decomposed to dimethyl disulfide (DMDS) in the livers and kidneys of pigs but not in their blood. In addition, in the field of forensic toxicology, it is known that some compounds are decomposed or produced by internal bacteria in biological samples after death. This indicates that there is a possibility that methomyl in blood may be decomposed by bacteria after death. The aim of this study was therefore to investigate whether methomyl in blood is decomposed by bacteria isolated from human stool. Our findings demonstrated that methomyl was decomposed in human stool homogenates, resulting in the generation of DMDS. In addition, it was observed that three bacterial species isolated from the stool homogenates, Bacillus cereus, Pseudomonas aeruginosa, and Bacillus sp., showed methomyl-decomposing activity. The results therefore indicated that one reason for the difficulty in detecting methomyl in postmortem blood from methomyl-poisoning victims is the decomposition of methomyl by internal bacteria such as B. cereus, P. aeruginosa, and Bacillus sp.

Simultaneous determination and identity confirmation of thiodicarb and its degradation product methomyl in animal-derived foodstuffs using high-performance liquid chromatography with fluorescence detection and tandem mass spectrometry.

A high-performance liquid chromatography-fluorescence detection method was developed for the simultaneous determination of thiodicarb and its degradation product methomyl in animal-derived food products, including chicken muscle, beef, pork, table eggs, and milk. Thiodicarb is known to degrade during analysis; therefore, a thorough investigation was carried out, revealing that thiodicarb degrades to methomyl immediately after spiking into a matrix of animal-derived food products. Consequently, thiodicarb was determined as the sum of the parent compound and methomyl. Samples were extracted with acetonitrile and sodium salts, and purified using solid-phase extraction (SPE). The limits of detection (LODs) and quantification (LOQs) were 0.0013 and 0.004mg/kg, respectively, for both analytes in various matrices. Seven-point external calibration curves were obtained, and they showed excellent linearity with determination coefficients (R2)≥0.999 for all tested matrices. The method was validated at three fortification levels (LOQ, LOQ×2, and LOQ×10) in triplicate with average recoveries ranging from 84.24 to 112.8% (for methomyl) and relative standard deviations (RSDs)≤6.5% in all matrices. The converted recoveries of thiodicarb in various matrices ranged from 74.80 to 107.80% with RSDs≤4.5%. The identities of both compounds in standard solutions and for recovery were confirmed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The developed method was further validated by accurate reproduction at another laboratory. Finally, the method was applied to market samples collected from different areas (and, in the case of milk, different brands), and none of the samples tested positive for thiodicarb or methomyl. In conclusion, the developed method can be successfully applied for a single-run analysis of thiodicarb and methomyl in livestock products.

Aging of biomixtures: Effects on carbofuran removal and microbial community structure.

The aim of this work was to determine the efficiency of a straw/compost/soil biomixture for pesticide depuration during its aging and continuous use, for a period of over a year, based on its capacity to remove carbofuran (CFN), while simultaneously monitoring the variations in microbial community structure. Successive CFN spikings were applied in the biomixture at 6-week intervals, and the removal efficiency was determined 48 h post-application. Initially, only a discrete degradation performance was observed (9.9%), but one CFN application was sufficient to induce efficient elimination (>88.5%) of the pesticide at subsequent influxes for a period of over 6 months. A statistically significant reduction on CFN removal efficiency after this time was detected, reaching levels similar to the fresh-prepared biomixture (14.8%) at the end of the experiment. Simultaneous DGGE analyses showed only modest changes on microbial community patterns through time for both, bacteria and fungi. The clustering of genetic fingerprints in chronological groups corresponding to significantly different CFN degradation efficiencies indicates that biomixture aging changes not only the composition of microbial communities, but also their suitability to engage in pesticide degradation. Periodic substitution of straw/compost/soil biomixture in biopurification systems or regular provision of easily-degradable organic substrates should be considered to maintain an adequate depuration capacity on this system.

Fate of thiodicarb and its metabolite methomyl in sandy loam soil under laboratory conditions.

Fate of thiodicarb and its major metabolite in sandy loam soil were studied by applying thiodicarb (Larvin 75 WP) at 500 and 1000 g a. i. ha(-1) under laboratory conditions. Samples drawn periodically were analysed on GC-FTD equipped with capillary column. The average initial deposits of total thiodicarb (thiodicarb and methomyl) were 0.025 and 0.035 mg kg(-1) at single and double dosages, respectively. Residues of thiodicarb reached below the determination level (BDL) of 0.005 mg kg(-1) after 15 days. Half-life periods for total thiodicarb were calculated to be 5.90 and 8.29 days at two doses, respectively, following first-order kinetics.

Effective photodegradation of methomyl pesticide in concentrated solutions by novel enhancement of the photocatalytic activity of TiO2 using CdSO4 nanoparticles.

Annihilation of electrons-holes recombination process is the main remedy to enhance the photocatalytic activity of the semiconductors photocatalysts. Doping of this class of photocatalysts by foreign nanoparticles is usually utilized to create high Schottky barrier that facilitates electron capture. In the literature, because nonpolar nanoparticles (usually pristine metals, e.g., Ag, Pt, Au, etc.) were utilized in the doping process, the corresponding improvement was relatively low. In this study, CdSO4-doped TiO2 nanoparticles are introduced as a powerful and reusable photocatalyst for the photocatalytic degradation of methomyl pesticide in concentrated aqueous solutions. The utilized CdSO4 nanoparticles form polar grains in the TiO2 matrix due to the electrons leaving characteristic of the sulfate anion. The introduced nanoparticles could successfully eliminate the harmful pesticide under the sunlight radiation within a very short time (less than 1 h), with a removal capacity reaching 1,000 mg pesticide per gram of the introduced photocatalyst. Moreover, increase in the initial concentration of the methomyl did not affect the photocatalytic performance; typically 300, 500, 1,000, and 2,000 mg/l solutions were completely treated within 30, 30, 40, and 60 min, respectively, using 100 mg catalyst. Interestingly, the photocatalytic efficiency was not affected upon multiple use of the photocatalyst. Moreover, negative activation energy was obtained which reveals super activity of the introduced photocatalyst. The distinct photocatalytic activity indicates the complete annihilation of the electrons-holes recombination process and abundant existence of electrons on the catalyst surfaces due to strong electrons capturing the operation of the utilized polar CdSO4 nanoparticles. The introduced photocatalyst has been prepared using the sol-gel technique. Overall, the simplicity of the synthesizing procedure and the obtained featured photocatalytic activity strongly recommend the introduced nanoparticles to treat the methomyl-containing polluted water.

Determination of methomyl in the stomach contents of baited wildlife by gas chromatography-mass spectrometry.

The poisoning of wildlife with fly-bait containing the active ingredient methomyl is an intentional and illegal act in many jurisdictions. A case of 2 animals poisoned by methomyl through consumption of tainted bait at multiple stations is described. Although thermally and ultraviolet-labile, methomyl can be identified by gas chromatography-mass spectrometry and is detected in abundance in bait samples; however, it is not readily observed in tissues, owing to its rapid metabolism and elimination. The application of derivatizing functionalities, such as trimethylsilyl groups, stabilizes the methomyl-oxime metabolite to facilitate its detectability during exposure to the relatively harsh conditions of gas chromatography. This brief communication reports on the analytical detection of methomyl in baits and biological samples from poisoned wildlife. Essential to the case were the added determination of a fly-bait coactive ingredient, (Z)-9-tricosene, and identification of a chemical indicator, caffeine, to confirm both the type of pesticide product involved in the poisoning incident and the vehicle used to perpetrate its delivery.

Online microchannel preconcentrator for carbofuran detection.

A simple and rapid online microchannel preconcentrator coupled with an amperometric detection for the analysis of carbofuran using polyethylene glycol coated onto magnetic particle (PEG-magnetic particles) sorbents was developed. This simple-to-prepare microchannel preconcentrator used an external magnet to retain the PEG-magnetic particle sorbents inside the microchannel. Under optimum conditions, the system provided two linear ranges, from 0.01 to 10.0 mg L(-1) and from 10.0 to 130.0 mg L(-1) with a limit of detection of 8.7 ± 0.1 µg L(-1). The microchannel preconcentrator provided very good stability; it can be used for up to 326 consecutive injections of 5.0 mg L(-1) carbofuran with a relative standard deviation of less than 3%. The developed system provided a good microchannel-to-microchannel and a good electrode-to-electrode reproducibility (n = 6, %RSD < 1). It also provided an excellent selectivity when it was tested with two other carbamate pesticides, carbaryl and methomyl, with a 43 and 256 times higher detection sensitivity for carbofuran, respectively. The developed system was successfully applied to detect carbofuran in surface water samples obtained near vegetable plantation areas. The concentrations of carbofuran in these samples were found to be in the range of non-detectable to 0.047 ± 0.001 mg L(-1). The developed system is easy to operate and easy to couple with other analytical instruments and it could be easily adapted for the analysis of other polar organic contaminants.

Measurement of the pesticide methomyl by modified quartz crystal nanobalance with molecularly imprinted polymer.

A simple and cost-effective analysis method based on quartz crystal nanobalance (QCN) coated with a molecularly imprinted polymer (MIP) for measurement of methomyl was investigated. In the first part of this study, a sensitive, selective and reliable quartz crystal nanobalance (QCN) sensor was designed for the selective determination of methomyl in aqueous solutions. In the second part, in order to demonstrate the applicability and performance of the fabricated sensor in the real world situation, it was successfully applied for the determination of methomyl residual in photo catalytic degradation by ZnO powders in aqueous solutions. The fabricated sensor presents a high selectivity and sensitivity (4.56 Hz per mg L(-1)) for methomyl and it can be used for determination of methomyl concentration ranged between 1 to 45 mg L(-1). Furthermore, good reproducibility, R.S.D. = 2.14% (n = 5) was observed. To investigate the performance of the sensor, the change in the insecticide concentration during the photocatalytic degradation of methomyl by ZnO was investigated by QCN and UV/Vis spectroscopy. Results obtained from QCN sensor and UV/Vis spectroscopy measurement are in good mutual agreement. So the fabricated sensor may provide an efficient, low cost, easy-to-use method for the in-field evaluation of specific targeted analytes in aqueous solutions which in turn may lead to improved food and water safety.

Application of energy dispersive X-ray fluorescence spectrometry (EDX) in a case of methomyl ingestion.

We applied energy dispersive X-ray fluorescence spectrometry (EDX) in a case of poisoning by methomyl, a carbamate pesticide. Quantitative GC/MS analysis showed that the concentration of methomyl-oxime in the femoral blood was 4.0 µg/ml. The elemental analysis by EDX identified the high peak of silicon and sulfur in the stomach contents. We concluded that the cause of his death was methomyl poisoning. This indicates that screening of stomach contents by EDX provides useful information for the forensic diagnosis.

Environmental fate and toxicology of methomyl.

The insecticide methomyl, an oxime carbamate, was first introduced in 1968 for broad spectrum control of several insect classes, including Lepidoptera, Hemiptera, Homoptera, Diptera, and Coleoptera. Like other carbamates, it inhibits AChE activity, resulting in nerve and/or tissue failure and possibly death. Considered highly toxic to insects (larval and adult stages), methomyl is thought to be metabolically degraded via mixed-function oxidase(s). Methomyl has both a low vapor pressure and Henry's law constant; hence, volatilization is not a major dissipation route from either water or moist or dry soils. Photolysis represents a minor dissipation pathway; however, under catalytic conditions, degradation via photolysis does occur. Methomyl possesses a moderate-to-high water solubility; thus hydrolysis, under alkaline conditions, represents a major degradation pathway. Methomyl has a low-to-moderate sorption capacity to soil. Although results may vary with soil type and organic matter content, methomyl is unlikely to persist in complex soils. Methomyl is more rapidly degraded by microbes, and bacterial species have been identified that are capable of using methomyl as a carbon and/or nitrogen source. The main degradation products of methomyl from both abiotic and biotic processes are methomyl oxime, acetonitrile, and CO2. Methomyl is moderately to highly toxic to fishes and very highly toxic to aquatic invertebrates. Methomyl is highly toxic orally to birds and mammals. Methomyl is classed as being highly toxic to humans via oral exposures, moderately toxic via inhalation, and slightly toxic via dermal exposure. At relatively high doses, it can be fatal to humans. Although methomyl has been widely used to treat field crops and has high water solubility, it has only infrequently been detected as a contaminant of water bodies in the USA. It is classified as a restricted-use insecticide because of its toxicity to multiple nontarget species. To prevent nontarget species toxicity or the possibility of contamination, as with all pesticides, great care should be taken when applying methomyl-containing products for agricultural, residential, or other uses.

A novel luminescent terbium-3-carboxycoumarin probe for time-resolved fluorescence sensing of pesticides methomyl, aldicarb and prometryne.

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (µs-ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A time-resolved (gated) luminescence-based method for determination of pesticides methomyl, aldicarb and prometryne in microtiterplate format using the long-lived terbium-3-carboxycoumarin in 1:3 metal:ligand ratio has been developed. The limit of detection is 1.20×10(6), 5.19×10(5) and 2.74×10(6)ng L(-1) for methomyl, prometryne and aldicarb, respectively. The quantum yield (QY=0.08) of Tb(III)-3-carboxycoumarin was determined using 3-(2-benzothiazolyl)-7-diethylamino-coumarin (coumarin 6). Stern-volmer studies at different temperatures indicate that collisional quenching dominates for methomyl, aldicarb and prometryne. Binding constants were determined at 303, 308 and 313 K by using Lineweaver-Burk equation. A thermodynamic analysis showed that the reaction is spontaneous with negative ΔG. Effect of some relevant interferents on the detection of pesticides has been investigated.

[Determination of 132 pesticide residues in tobacco by gas chromatography-tandem mass spectrometry].

A simple method for the determination of 132 pesticide residues in tobacco by gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) was established. The influences of different extraction solvents, different buffer systems and different purifying agents on the recoveries of pesticides were investigated. The tobacco sample was extracted with acetonitrile, then cleaned up by the mixed sorbents of primary secondary amine (PSA) and octadecylsilane (C18E). After dried by nitrogen, the extract residue was reconstituted with n-hexane-acetone (9:1, v/v). GC-MS/MS in multi-reaction monitoring (MRM) mode was used as the detection method and triphenyl phosphate (TPP) as the internal standard. All of the 132 pesticides had good linear relationships (r2 > 0.99) between 20 microg/kg and 2 000 microg/kg. At the three spiked levels of 50, 200 and 500 microg/kg in the tobacco extract, the average recoveries of all the pesticides were in the range of 68.10% to 123.15% except for mirex and hexachlorobenzene; moreover, the relative standard deviations (RSDs) of them were between 1.79% and 19.88%. We participated in the CORESTA (Cooperation Centre for Scientific Research Relative to Tobacco) 2012's co-experiment. The results of our method and the existed standard methods had good consistency. The accurate, reliable and sensitive method can be applied to the determination of the 132 pesticide residues in tobacco for rapid screening and quantitative analysis.

Inhibition of cholinesterase activity by soil extracts and predicted environmental concentrations (PEC) to select relevant pesticides in polluted soils.

The correlation of predicted environmental concentrations (PEC) with cholinesterase activity inhibition detected in soil extracts was determined. PEC was derived from organophosphate (OP) and carbamate (CA) compounds applied to a flower crop area. Samples of surface soil (0 - 30 cm in depth) and subsurface soil (30 to 60 cm in depth) were taken from a flower crop area in which OP pesticides such as acephate ((RS)-N-[methoxy(methylthio)phosphinoyl]acetamide), dimethoate (2-dimethoxyphosphinothioylthio-N-methylacetamide) and methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate), and CA pesticides such as carbendazim (methyl benzimidazol-2-ylcarbamate), carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) and methomyl (S-methyl (EZ)-N-(methylcarbamoyloxy) thioacetimidate) were applied for two years. Weekly loads of these pesticides were registered to estimate the annual load of each compound. Physicochemical analysis and relative inhibition of cholinesterasic activity were measured for each soil sample. PEC values were estimated with Pesticide Analytical Model (PESTAN), a leach model, for each pesticide using soil sample data obtained from physicochemical analysis. From all pesticides tested, only acephate and methomyl showed a significant correlation (p < 0.01) between PEC values and inhibition cholinesterase activity of soil extracts. These results suggest that inhibition of cholinesterase activity observed in soil extracts is produced mainly by these two pesticides. Further studies could be developed to measure acephate and methomyl concentrations to reduce their environmental impact.

Measurement of acetylcholinesterase inhibition using bienzymes immobilized monolith micro-reactor with integrated electrochemical detection.

This paper reports a simple micro-FIA based method for the rapid evaluation of acetylcholinesterase inhibition based on bienzymes immobilized monolith micro-reactor, with integrated electrochemical detection. The monolith was prepared inside a micro-fluidic device from two precursors TMOS and MTMOS using a sol-gel method, followed by PEI polymer functionalization and subsequent enzyme immobilization via electrostatic attraction between electronegative enzymes and electropositive PEI polymers. A bienzyme system containing co-immobilized acetylcholinesterase and choline oxidase was used for the evaluation of enzyme inhibition induced by malaoxon, eserine and methomyl analytes. The proposed method, which gave a LOD of 0.5, 0.2 and 1.0 microM for malaoxon, eserine and methomyl repeatedly, was found to offer several advantages over existing systems including efficient enzyme immobilization, minimal reagent consumption and rapid analysis capability.