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The degree of insecticide resistance, synergism effects, acetylcholinesterase (AChE) activity kinetics, specific activities of detoxification enzymes and cross-resistance were investigated in omethoate resistant and relatively susceptible strains of Aphis gossypii Glover. The resistant cotton aphid strain (ORR) exhibited 231.3-fold resistance to omethoate compared to the susceptible strain (OSS). Synergist piperonyl butoxide (PBO) dramatically increased the toxicity of omethoate in the resistant strain, while triphenyl phosphate (TPP) and diethyl maleate (DEM) did not exhibit synergism effects. The calculated AChE activity, V max and K m ratios of ORR to OSS were 0.1, 0.2 and 0.4, respectively. Based on analysis of IC 50 indices, enzyme inhibition experiments showed that AChE from the ORR strain was 10.6-, 3.2-, 6.2-, 10.5- and 4.4-fold more insensitive to inhibition by eserine, omethoate, paraoxon, paraoxon-methyl and malaoxon, respectively, than that from the OSS strain. The cytochrome P450-mediated O-demethylation activity (3.7-fold) and ethoxycoumarin-O-deethylase activity (2.6-fold) in the ORR strain were significantly higher than in the OSS strain. Specific activity of carboxylesterase (CarE) and glutathione S-transferase (GST) were not significantly different in both the ORR and OSS strains. Bioassay results indicated the ORR strain had developed high levels of cross-resistance to chlorpyrifos (24.2-fold), malathion (21.1-fold), acephate (10.2-fold), esfenvalerate (30.6-fold), methomyl (22.4-fold), carbofuran (33.2-fold), but had negative cross-resistance to bifenthrin (0.4-fold). Overall, these results demonstrate that reduced AChE sensitivity, combined with increased cytochrome P450 monooxygenase detoxification, plays an important role in the high levels of omethoate resistance and can cause cross-resistance to other insecticides in the ORR strain.

The study aimed mainly to assess effects of omethoate on certain oxidative stress biomarkers in various tissues of frogs ( Rana ridibunda). Biomarkers selected for stress monitoring were malondialdehyde (MDA) and antioxidant defense system (ADS) constituent such as reduced glutathione (GSH) level, glutathione peroxidase (GSH-Px), glutathione-S-transferase (GST) and superoxide dismutase (SOD) activities in the liver, brain, heart and kidney tissues of frogs exposed to 10 and 20 ppm dosages of omethoate for 24, 48, 72 and 96 hours. Results showed that the administrations of omethoate promote MDA content in the tissues of the frogs treated with both dosages of omethoate. With regard to the ADS, GSH-Px, GST, SOD activities and GSH levels decreased after 24, 48, 72 and 96 hours in the tissues of treatment groups compared with controls. Collective results demonstrated that the exposures to omethoate of frogs induced an increase in MDA joined with fluctuated ADS. This may reflect the potential role of these parameters as useful biomarkers for assessment of aquatic pollution.

The aim of this study was to investigate the effect of an organophosphorus insecticide omethoate (OM), on certain oxidative stress biomarkers (malondialdehyde (MDA), reduced glutathione (GSH), glutathione- S-transferase (GST), glutathione reductase (GR), catalase (CAT)) in tongue, lung, stomach and muscle tissues of adult frogs ( Rana ridibunda Pallas). Animals were exposed to 10 and 20 parts per million dosages of OM for 24, 48, 72 or 96 h. According to the results, MDA level increased significantly in lung and stomach tissues. GSH content fluctuated in lung and muscle while it elevated in tongue and stomach tissues. With regard to antioxidant enzymes (GST, GR and CAT), their activities reduced in tongue, while they increased in lung and fluctuated in stomach and muscle tissues. It can be concluded that exposure of frogs to OM are characterized by increased MDA levels and fluctuated enzyme activities and GSH contents. This may reflect the potential role of these parameters as useful biomarkers for assessment of OM toxicity.

A simple and effective analytical procedure has been developed for the determination of dimethoate (DIM) residues and its metabolite, omethoate, in serum samples of pesticide operators. For the sel...

Omethoate is one of the most powerful insecticides in China. Despite its high risks of human health and environmental safety, omethoate is still hard to be replaced because of its low price and high efficiency. To better understand physiological and biochemical responses to omethoate, we examined plant growth and antioxidative defense responses as well as omethoate uptake in wheat seedlings grown hydroponically with omethoate. Fresh and dry shoot weights were significantly higher at low concentrations (e.g. 0.1 g/L) than at high concentrations (e.g. 5.0 g/L). The same is true for the soluble protein content. On the contrary, contents of malondialdehyde, proline and omethoate, and activities of superoxide dismutase, peroxidase and ascorbate peroxidase in shoots increased linearly with increasing concentration of omethoate and with exposure time as well. However, catalase activity was increased dramatically at 0.1 g/L but sharply decreased by omethoate added at 1.0 g/L and above compared with that of the control. Taken together, these results support our hypothesis that antioxidative defense response is an important component of plant responses to omethoate and oxidative damage is the major cause for growth reduction of wheat exposed to higher concentrations of omethoate.

In the present study an effort has been made to evaluate the residues of selected insecticides (organophosphorous and pyrethroid) and fungicides (triazoles and chloronitriles) in fruits and vegetables collected from Xiamen, China, during the October 2006 to March 2009 monitoring campaign. Gas chromatography with electron capture detector (GC-ECD) was used to determine the concentrations of 22 pesticide residues among those recommended for pest treatment. Of 1135 samples (37.7%) that contained pesticide residues, pakchoi cabbage, legumes, and leaf mustard were the commodities in which pesticide residues were most frequently detected, with 17.2%, 18.9% and 17.2% of the samples exceeding the maximum residue limits (MRLs), respectively. Concerning the most frequently detected pesticide residues, cypermethrin was found in 18.7% of the samples analyzed. Data obtained were then used for estimating the potential health risks associated with the exposures to these pesticides. The estimated daily intakes (EDIs) range from 0.1% of the ADI for cyfluthrin to 2.61% of the ADI for omethoate and 0.1% of the ADI for omethoate. The most critical commodity is legumes, contributing 2.61% to the hazard index (HI). The results show that despite a high occurrence of pesticide residues in fruits and vegetables from this region, it could not be considered a serious public health problem. Nevertheless, an investigation into continuous monitoring and tighter regulation of pesticide residues in fruits and vegetables is recommended.

Omethoate (OMT), a typical organophosphorus pesticide and also an oxidation byproduct of dimethoate, is very difficult to remove from water due to its hydrophilic nature and relatively low reactivity towards ozone. In this work, Fe(III)-loaded activated carbon (Fe@AC) was prepared and used as catalyst to promote OMT degradation by ozone. The catalytic activity of Fe@AC was investigated under various experiment conditions. Results indicate that the OMT removal was significantly enhanced in O3/Fe@AC through effective generation of hydroxyl radicals (·OH), as compared to ozonation alone and O3/AC. The Fe(III) deposited on AC mainly existed in the form of ferrihydrite (FHD) particles which provided the main active sites promoting ozone decomposition. The optimal pH ranged from 7.0 to 8.0 for catalytic ozonation, which corresponded to a nearly neutral surface charge of the catalyst. The apparent rate constant of OMT degradation was almost linearly correlated with the aqueous ozone concentration. The acute toxicity of the reaction solution was substantially reduced by catalytic ozonation with Fe@AC.

The carmine spider mite Tetranychus cinnabarinus is the most serious of crop mite pests in China. Their ability to rapidly develop resistance to acaricides has caused difficulty in controlling this mite. In this study, the molecular mechanism of acaricide resistance associated with esterase genes TCE1 and TCE2 was investigated in susceptible and acaricide-resistant strains of T. cinnabarinus. The quantitative real-time PCR (qrtPCR) method was adopted to compare the expression level of two esterase genes TCE1 and TCE2 among four different strains (abamectin-resistant, AbR; fenpropathrin-resistant, FeR; omethoate-resistant, OmR and susceptible strains, S) of T. cinnabarinus. The relative expression level of TCE2 was 1.39–2.47 fold in the three resistant strains compared with the S strain. And after inducing with abamectin, fenpropathrin, and omethoate the highest expression level of TCE2 in the S was 1.64-, 2.92- and 2.24-fold compared with the control, respectively, and this difference was found to be significant. However, there was no obvious difference of the mRNA relative expression levels of TCE1 genes among the four strains, and those of TCE1 were not higher than the control throughout the study. Furthermore, the expression modes of TCE1 and TCE2 in AbR and FeR were similar with that in the S after being treated with abamectin and fenpropathrin, respectively. These results indicated that the enhanced expression of esterase gene TCE2 was associated with acaricide-resistance in T. cinnabarinus.

Degradation of the 3 pesticides (acephate, omethoate, and dimethyl dichloroviny phosphate [DDVP]) by electrolyzed water was investigated. These pesticides were commonly used as broad-spectrum insecticides in pest control and high-residual levels had been detected in vegetables. Our research showed that the electrolyzed oxidizing (EO) water (pH 2.3, available chlorine concentration:70 ppm, oxidation-reduction potential [ORP]: 1170 mV) and the electrolyzed reducing (ER) water (pH 11.6, ORP: -860 mV) can reduce the pesticide residues effectively. Pesticide residues on fresh spinach after 30 min of immersion in electrolyzed water reduced acephate by 74% (EO) and 86% (ER), omethoate by 62% (EO) and 75% (ER), DDVP by 59% (EO) and 46% (ER), respectively. The efficacy of using EO water or ER water was found to be better than that of using tap water or detergent (both were reduced by more than 25%). Besides spinach, the cabbage and leek polluted by DDVP were also investigated and the degradation efficacies were similar to the spinach. Moreover, we found that the residual level of pesticide residue decreased with prolonged immersion time. Using EO or ER water to wash the vegetables did not affect the contents of Vitamin C, which inferred that the applications of EO or ER water to wash the vegetables would not result in loss of nutrition.

Based on Support Vector Machine (SVM) and genetic algorithm (GA), this paper intends to search for the characteristic spectral ranges and wavelengths of near infrared spectroscopy of navel oranges contaminated by different pesticides, and set up recognition models. The pesticides in the experiment were Lannate®L insecticide, fenvalerate and omethoate, and three different concentrations were given to each pesticide. Preparing ten groups of navel oranges, each group was sprayed with a different pesticide and the 10th group without pesticide spraying was used for comparison. Searching the whole spectral range through GA, 5 best spectral ranges (165 wavelengths) were obtained and the recognition rate reached 98.86%. Then based on the chosen spectral ranges, 85 feature wavelengths were extracted with continual GA-SVM optimization, and the recognition rate was 99.14%. Experiment results showed that the application of SVM combining with GA can not only improve recognition accuracy, but also simplify the model effectively

Although pesticides are widely used in agriculture, they and in particular the relative residues in foodstuffs, water and atmosphere, may cause remarkable sanitary problems due to the harmful effects (carcinogenic and mutagenic effects) on the human health. In fact, their spread in waters and atmosphere can produce undesired effects on various organisms and/or water contamination.This paper shows an analytical approach based on XAD-2 adsorbent and GC analysis for evaluating the pesticide trend in atmosphere: in particular, the pesticides investigated are omethoate, dicrotofos, disulfoton, dimethoate, parathion methyl, formothion, paraoxon ethyl, malaoxon, parathion ethyl, iodofenfos and triazofos. For the analytical methodology a linearity response was obtained (r^2 = 0.9988) in GC-NPD whereas the limits of detection range between 2 and 5 pg/μL in GC-NPD with a Relative Standard Deviation below 9.5. Finally, this approach has been successfully applied to real samples: the results show that dimethoate concentration decreases with increasing distance from the sampling site but it is still persistent in atmosphere after few days from the pesticide spraying.

We have investigated surface-enhanced Raman spectroscopy (SERS) spectrum of Omethoate (O,O-dimethyl-S-methylcarbamoylmethylthiophosphate). It is found significant signals in the ordinary Raman spectrum for solid-state Omethoate as well as strong vibrational signals absorbed on the silver sol surface which is prepared by γ-irradiation technique at a very low concentration. Effects of pH and anions (Cl-, Br-, I-) on the adsorption orientation are investigated as well. Two different adsorption mechanisms are deduced, depending on the experimental conditions. The sulfur atom or the sulfur and two oxygen atoms are adsorbed onto the silver sol surface. Among halide ions, Br- and I- are more strongly adsorbed onto the silver sol surface. As a result, the adsorption of Omethoate is less effective due to their steric hindrance.

Cyclodextrin played an important role in environmental protection in recent years.Application of cyclodextrins in enviroment science upon aspects;enrichment and removal of organic pollutants and heavy metals from soil,water,and atmosphere. β-cyclodextrin (β-CD) can be linked when it was sulfonation-modified.A convenient method of photocatalytic degradation of pesticide in lab by self-designed photocatalytic equipment was proposed based on analysis and comparison of different methods used to determine pesticide. The effects of illumination,reaction time,and pesticide concentration were analyzed. The results showed that the photodegradation of monocrotophes increased 2.08-2.86 times in the presence of 20g/L and 40g/L sulfonated β-cyclodextrin.In addition,the photodegradation of omethoate increased 1.8-2.2 times in the presence of 40g/L sulfonated β-cyclodextrin. The light activation were caused by the formaton of inclusion complexes of monocrotophes with sulfonated β-cyclodextrin. It was found that the method was simple and paid lower costs; and it could be used in lab for the photo-catalytic degradation of pesticide.

The degree of insecticide resistance, acetylcholinesterase (AChE) activity kinetics, AChE gene expression and the cDNA sequence of AChE gene were investigated in resistant and relatively susceptible strains of the cotton aphids, Aphis gossypii (Glover). The resistant strain (ORR) exhibited 53.28-fold resistance to omethoate compared to the relatively susceptible strain (OSS) in cotton aphids. AChE activity, V(max) and K(m) were significantly lower in the ORR strain than in the OSS strain (0.13-, 0.04- and 0.31-fold, respectively). Based on analysis of IC(50) indices, enzyme inhibition experiments showed that AChE from the ORR strain was 7.99-, 4.12-, 4.27-, 8.71- and 4.57-fold insensitive to inhibition by eserine, omethoate, paraoxon, paraoxon-methyl and malaoxon than the OSS strain. Sequence analysis indicated that there were no amino acid substitutions in AChEI (Ace1) and AChEII (Ace2) between the OSS and ORR strain. However, when compared with the 81-171B strain (GenBank No. AF502081), we detected two site mutations (S146N and L532P) in Ace1 with high frequency in both the ORR and OSS strains. One conserved mutation (S431F) in Ace2 was also found in both strains when compared with the 171B strain (GenBank No. AJ748114). Measurements of the levels of gene expression for Ace1 and Ace2 in ORR and OSS, as determined by real-time quantitative PCRs, revealed that the relative transcription levels of Ace1 and Ace2 were 0.26- and 1.07-fold, respectively, in the ORR strain as compared to the OSS strain. These results indicate that the altered AChE sensitivity brought about by a decreased transcriptional level of Ace1 mRNA and combined with the site mutants in both Ace1 and Ace2 might be related to omethoate resistance in cotton aphids.

The authors thank SGAI-CSIC for the allocation of computational resources, the Spanish Ministerio de Ciencia e Innovacion´ for the FIS2007-63065 grant, Comunidad de Madrid through the MICROSERES network (grant S-2009/TIC-1476), and the 2005 Italy–Spain integrated cooperation project (Ministerio de Educacion y Ciencia, ref. HI2004-0373, and MIUR, ref. IT2050).

A simple, rapid and sensitive method is described for the determination of omethoate, dimethoate, diazinon, chlorpyrifos, parathion-ethyl, chlorfenvinphos, quinalphos and azinphos-ethyl in postmortem whole blood samples. The analytes and internal standard (ethion) were isolated from the matrix by solid-phase extraction, and were analysed by gas chromatography/mass spectrometry in the selected ion monitoring mode. The method has shown to be selective after analysis of postmortem samples of 40 different origins. Calibration curves were established between 0.05 (0.1 for omethoate) and 25 µg/mL, and the values obtained for intra- and interday precision and accuracy were within the criteria usually accepted for bioanalytical method validation. Lower limits of quantitation were 50 ng/mL for all compounds, except for omethoate (100 ng/mL); the limits of identification of the method were 25 ng/mL for all analytes, except for omethoate, for which 50 ng/mL was obtained. Absolute recovery was determined at three concentration levels, and ranged from 31 to 108%. The proposed method is simple and fast, and can be routinely applied in the determination of these compounds in postmortem whole blood samples within the scope of forensic toxicology. In addition, mass spectrometry has demonstrated to be a powerful and indispensable tool for the unequivocal identification of the analytes, since the acceptance criteria were accomplished even at very low levels, thus allowing obtaining forensically valid and sound results.

This study was to evaluate the protective effects of Danshensu on liver injury induced by omethoate in Sprague Dawley rats. The acute omethoate poisoning model was established by administrating subcutaneously with omethoate at a single dose of 60 mg/kg. Danshensu treatment markedly inhibited the increases of aspartate aminotransferase, alanine aminotransferase, cyclooxygenase-2, tumor necrosis factor-alpha, thromboxane B(2), and thromboxane B(2)/6-keto-PGF1alpha ratio induced by omethoate. The histopathological examination further confirmed that administration with Denshensu ameliorated liver injury. The results demonstrated that Danshensu possesses protective action on hepatic injury induced by omethoate and the pharmacological mechanism was related to the anti-inflammatory effect and circulation improvement of Danshensu, at least in part.

Several organophosphorus (OP) insecticides can selectively kill the silkworm maggot, Exorista sorbillans (Es) (Diptera: Tachinidae), while not obviously affecting the host (Bombyx mori) larvae, but the mechanism is not yet clear. In this study, the cDNA encoding an acetylcholinesterase (AChE) from the field Es was isolated. One point mutation (Gly353Ala) was identified. The Es-353G AChE and Es-353A AChE were expressed in baculovirus- insect cell system, respectively. The inhibition results showed that for eserine and Chlorpyrifos, Es-353A AChE was significantly less sensitive than Es-353G AChE. Meanwhile, comparison of the I(50) values of eserine, dichlorvos, Chlorpyrifos and omethoate of recombinant Es AChEs with its host (Bombyx mori) AChEs indicated that, both Es AChEs are more sensitive than B. mori AChEs. The results give an insight of the mechanism that some OP insecticides can selectively kills Es while without distinct effect on its host, B. mori.

In this study, the oxygen consumption, ammonia excretion, and filtration rate were monitored in Mytilus edulis in response to administration of the two pesticides, methamidophos and omethoate. Five sublethal concentrations (1, 10, 50, 100, and 200 µgL−1) were administered over 96 h. Oxygen consumption rates increased following administration of all concentrations of methamidophos for 96 h and to the lower concentrations of omethoate (1, 10, and 50 µg L−1) from 6 to 24 h. Over 24 h, oxygen consumption decreased significantly. Ammonia excretion rates were higher than the control after 36 h of exposure to methamidophos, while reduction was observed when M. edulis was exposed to omethoate. The O:N ratios increased when the animals were first exposed to these two pesticides and then decreased at all the concentrations. At the concentrations of 100 and 200 µgL−1, the O:N ratio was below 30 after 72 h. The filtration rate of M. edulis decreased with the increasing concentration of pesticide exposure.

Dimethoate, a systemic insecticide, has been used extensively in vegetable production. Insecticide residues in treated vegetables, however, pose a potential risk to consumers. Photocatalytic degradation is a new alternative to managing pesticide residues. In this study, the degradation of dimethoate in Bok choy was investigated under the field conditions using cerium-doped nano titanium dioxide (TiO2/Ce) hydrosol as a photocatalyst. The results show that TiO2/Ce hydrosol can accelerate the degradation of dimethoate in Bok choy. Specifically, the application of TiO2/Ce hydrosol significantly increased the reactive oxygen species (ROS) contents in the treated Bok choy, which speeds up the degradation of dimethoate. Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) analysis detected three major degradation products, including omethoate, O,O,S-trimethyl thiophosphorothioate, and 1,2-Bis (acetyl-N-methyl-) methane disulfide. Two potential photodegradation pathways have been proposed based on the intermediate products. To understand the relationship between photodegradation and the molecular structure of target insecticides, we investigated the bond length, Mulliken atomic charge and frontier electron density of dimethoate using ab initio quantum analysis. These results suggest the P = S, P-S and S-C of dimethoate are the initiation sites for the photocatalytic reaction in Bok choy, which is consistent with our empirical data.

A method for the determination of 50 pesticides in fruits by gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed. The three QuEChERS methods (the original one without buffer, the one with acetate buffer and the one with citrate buffer) were compared. The purification effects of primary secondary amine (PSA) and SinChERS-Nano column were also investigated. The results showed that the acetate buffer and the citrate buffer had positive influence on the extraction compared to the original method without buffer, and there was no significant difference between the two methods using buffers. Finally, the QuEChERS method using acetate buffer was chosen as the extraction method. By comparing the purification effect images and the total ion current (TIC) chromatograms, SinChERS-Nano column was revealed to have a better cleaning effect, and was chosen for cleanup. The recoveries of methamidophos, acephate, omethoate, chlorothalonil and dicofol were in ranged of 71.2%-129.2%, the other 45 pesticides were ranged from 79.1% to 122.3%. The limits of detection (LODs) were 0.3-3.0 μ g/kg and the limits of quantification (LOQs) were 1.0-10.0 μ g/kg. The method is rapid and suitable for the screening of the 50 pesticide residues in citrus, grapes and other fruit samples.

BACKROUND: In Tetranychus urticae Koch, acetylcholinesterase insensitivity is often involved in organophosphate (OP) and carbamate (CARB) resistance. By combining toxicological, biochemical and molecular data from three reference laboratory and three OP selected strains (OP strains), the AChE1 mutations associated with resistance in T. urticae were characterised. RESULTS: The resistance ratios of the OP strains varied from 9 to 43 for pirimiphos-methyl, from 78 to 586 for chlorpyrifos, from 8 to 333 for methomyl and from 137 to 4164 for dimethoate. The insecticide concentration needed to inhibit 50% of the AChE1 activity was, in the OP strains, at least 2.7, 55, 58 and 31 times higher for the OP pirimiphos-methyl, chlorpyrifos oxon, paraoxon and omethoate respectively, and 87 times higher for the CARB carbaryl. By comparing the AChE1 sequence, four amino acid substitutions were detected in the OP strains: (1) F331W (Torpedo numbering) in all the three OP strains; (2) T280A found in the three OP strains but not in all clones; (3) G328A, found in two OP strains; (4) A201S found in only one OP strain. CONCLUSIONS: Four AChE1 mutations were found in resistant strains of T. urticae, and three of them, F331W, G328A and A201S, are possibly involved in resistance to OP and CARB insecticides. Among them, F331W is probably the most important and the most common in T. urticae. It can be easily detected by the diagnostic PCR-RLFP assay developed in this study. Copyright © 2009 Society of Chemical Industry

The aim of this work was to investigate whether reduced glutathione (GSH) could protect rats from the respiratory muscle injury induced by omethoate. Three groups named as control, OM (omethoate poisoning) and OM + GSH (omethoate poisoning treated with GSH) were arranged. The cholinesterase (ChE) activity was assayed and the pathological observation of respiratory muscles was carried out. Furthermore, activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and the free organophosphate (FOP) remained in the respiratory muscles were measured. The results indicated that ChE activity was significantly inhibited by omethoate and not be changed by GSH. GSH could attenuate the respiratory muscle injury after omethoate poisoning. No changes of SOD, GPx, CAT and FOP were found after GSH was given. The findings suggested that GSH could protect the respiratory muscle against injury induced by omethoate, which was not the result of GSH to reactivate ChE or regulate the antioxidant enzymes.

Sminthurus viridis (lucerne flea) is a major crop and pasture pest throughout southern regions of Australia that experience a Mediterranean type climate. It is particularly problematic at the establish- ment phase, and chemicals are currently the main option available to farmers for their control. Few studies have assessed the currently registered pesticides for the control of S. viridis, and rates of application are generally similar to the frequently co-occurring red-legged earth mite, Halotydeus destructor, despite few comparisons between species for their susceptibility being made. Here, we examine the response of S. viridis to six pesticides (a-cypermethrin, bifenthrin, omethoate, methi- dathion, chlorpyrifos and phosmet) and then directly compare them with H. destructor. S. viridis displayed similar dose-response curves for bifenthrin, omethoate, chlorpyrifos and phosmet. It had greater sensitivity to methidathion and greater tolerance to a-cypermethrin. S. viridis was found to be significantly more tolerant than H. destructor to all pesticides tested, with the exception of chlorpyrifos. This indicates that rates of application for control of S. viridis should be greater than H. destructor and that the organophosphates are likely to provide the most effective control of this pest.

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.

The degradation of omethoate was conducted using H2O2 as oxidant, TiO2 supported on NaY zeolite as photocatalyst and a 300W lamp as light source. The effect of the calcination temperature of the photocatalyst, the amount of TiO2 loaded on NaY zeolite, the photocatalyst amount, the pH value and the radiation time on the degradation ratio of omethoate were investigated. The results show that TiO2/NaY zeolite photocatalyst prepared by sol-gel method had good photocatalysis. The photocatalytic optimum oxidation conditions of omethoate are as follows: the calcination temperature of the photocatalyst is 550°C,the amount of TiO2 loaded on NaY zeolite is 35.2 wt-%, the amount of photocatalyst is 5 g/L, pH = 8 and the radiation time is 180 min. Under these conditions, the removal ratio of omethoate is up to 93%.

Diethylphosphono acetic acid (DPA) was used as a current hapten to generate broad specificity polycolonal antibodies against a group of organophosphorus pesticides. Six New Zealand white rabbits were immunized with immunogens synthesized by the active ester method (AEM) or 1-ethyl-3-(3-dimethylaminopropyl)-carbodimide method (EDC). The titers of antisera reached 25 600 by AEM and 6 400 by EDC, respectively. Polyclonal antibodies raised against DPA were screened and selected for the competitive indirect enzyme-linked immunosorbent assay (CI-ELISA). A CI-ELISA for DPA was developed with a detection limit of 3.536 ng mL−1 and an I50 value of 0.182 μg mL−1. The assay specificity was evaluated by obtaining competitive curves for several structurally related compounds as competitors. The antiserum showed high affinities to chlorpyrifos, diazinon, omethoate, parathion-ethyl and profenofos with I50 of 0.12, 0.15, 0.21, 0.88, 0.97 and 2.5 μg mL−1, respectively. The results indicate that the assay could be a screening tool for quantitation and semi- quantitation determination of the above former five organophosphorus pesticides.

Onion thrips, Thrips tabaci Lindeman, is a major pest of Australian field onion Allium cepa Linnaeus with their control heavily reliant on a few insecticides. An earlier study after grower complaints of control failures did not detect resistance in three populations. After testing an additional nine populations via a Potter spray tower laboratory bioassay unequally against α-cypermethrin, diazinon, dimethoate, λ-cyhalothrin, malathion and methidathion, we document resistance in T. tabaci for the first time in Australia. The maximum difference in response (resistance) for each insecticide was detected by dividing the most resistant LC50 response by the least resistant LC50 response. Comparison of the most susceptible to the least susceptible population tested produced α-cypermethrin and λ-cyhalothrin resistance at 164- and 606-fold, respectively. Diazinon and dimethoate resistance was also detected at 27-fold and 5.2-fold respectively although omethoate, malathion and methidathion resistance were not detected.

The toxicity of 10 organophophorus (OP) insecticides-acephate, dimethoate, dichlorvos, dicrotophos, monocrotophos, methamidophos, phosphamidon, omethoate, phosdrin, and trichlorfon-was evaluated in Caenorhabditis elegans using lethality, movement, and acetylcholinesterase (AChE) activity as the endpoints after a 4-hr- exposure period. The OP insecticides tested showed LC50 values ranging from 0.039 mM (for dichlorovs) to 472.8 mM (for methamidophos). The order of toxicity for lethality and movement was not significantly different when tested using the rank order correlation coefficient. AChE activity was markedly affected by all the OP insecticide exposures that caused significant inhibition in movement, indicating that the mechanism of toxicity of OP insecticides in C. elegans is the same as in higher animals. All OP insecticides induced greater than 50% inhibition of AChE at the lowest tested OP insecticide concentration resulting in inhibition in movement. While a significant correlation was evident between LC50 values in C. elegans and the LD50 values in rats for the 10 OP insecticides studied, a correlation was not evident between EC50 values in C. elegans and LD50 values in rats. Overall, the two endpoints, LC50 and movement, were more reliable and easier to perform than measurement of AChE activity in C. elegans for determining the toxicity of OP insecticides. Further, ranking of these endpoints with respect to the OP insecticides studied indicates that these parameters in C. elegans are predictive of OP insecticides mammalian neurotoxicity.

Levels of insecticide resistance, carboxylesterase activity, and carboxylesterase expression were investigated in both omethoate-selected resistant and susceptible strains of cotton aphids, Aphis gossypii (Glover). The resistant strain exhibited 21.72-fold resistance to omethoate based on comparison LC 50 values with the susceptible strain in cotton aphids. Five substrates, α-naphthyl acetate (α-NA), β-naphthyl acetate (β-NA), α-naphthyl butyrate (α-NB), α-Naphthyl propionate (α-NPr), and α-naphthyl phosphate (α-NP) were used to determine carboxylesterase activity in both resistant and susceptible strains of cotton aphids. Carboxylesterase activity was significantly higher in resistant strain than in susceptible strain, 11-fold for α-NA and β-NA, 12-fold for α-NB and 10-fold for α-NPr and α-NP. The levels of gene expression for carboxylesterase of both resistant and susceptible strains were determined by real-time quantitative PCRs. Compared with the susceptible strain, the relative transcription levels and gene copy numbers of the carboxylesterase were 4.54- and 0.97-fold in the resistant strain, respectively. These results indicated that the increased expression of the carboxylesterase resulted from the increased transcription levels of carboxylesterase mRNA was related to omethoate resistance in cotton aphids.

Dimethoate (DIM) is an organophosphorothionate (OPT) pesticide used worldwide as a systemic insecticide and acaricide. It is characterized by low-to-moderate acute mammalian toxicity; similarly to the other OPT pesticides, its mode of action is mediated by the inhibition of acetylcholinesterase (AChE), exerted by its toxic metabolite dimethoate-oxon or omethoate (OME), which is also used as a direct acting pesticide. Human hepatic DIM bioactivation to the toxic metabolite OME has been characterized by using c-DNA expressed human CYPs and human liver microsomes (HLM) also in the presence of CYP-specific chemical inhibitors, with a method based on AChE inhibition. The obtained kinetic parameters and AChE IC(50) have been compared with those previously obtained with other OPTs, indicating a lower efficiency in DIM desulfuration reaction and a lower potency in inhibiting AChE. Results showed that, similarly to the other OPTs tested so far, at low DIM concentration OME formation is mainly catalysed by CYP1A2, while the role of 3A4 is relevant at high DIM levels. Differently from the other OPTs, DIM desulfuration reaction showed an atypical kinetic profile, likely due to CYP3A4 autoactivation. The sigmoidicity degree of the activity curve increased with the level of CYP3A4 in HLM or disappeared in the presence of a CYP3A4 chemical inhibitor. This atypical kinetic behaviour can be considered one of the possible explanations for the recent findings that among patients hospitalized following OPT intoxication, DIM ingestion gave different symptoms and more severe poisoning (23.1% of fatal cases versus total) than chlorpyrifos (8% of deaths), which has a lower LD(50) value. Since DIM-poisoned patients poorly responded to pralidoxime, the possibility to use CYP3A4 inhibitors could be considered as a complementary treatment.

Wheat aphid, Sitobion avenae (fabricius), is one of the most important wheat pests and has been reported to be resistant to commonly used insecticides in China. To determine the resistance mechanism, the resistant and susceptible strains were developed in laboratory and comparably studied. A bioassay revealed that the resistant strain showed high resistance to pirimicarb (RR: 161.8), moderate reistance to omethoate (32.5) and monocrotophos (33.5), and low resistance to deltamethrin (6.3) and thiodicarb (5.5). A biochemistry analysis showed that both strains had similar glutathione- S -transferase (GST) activity, but the resistant strain had 3.8-fold higher esterase activity, and its AChE was insensitive to this treatment. The I 50 increased by 25.8-, 10.7-, and 10.4-folds for pirimicarb, omethoate, and monocrotophos, respectively, demonstrating that GST had not been involved in the resistance of S. avenae . The enhanced esterase contributed to low level resistance to all the insecticides tested, whereas higher resistance to pirimicarb, omethoate, and monocrotophos mainly depended on AChE insensitivity. However, the AChE of the resistant strain was still sensitive to thiodicarb (1.7-fold). Thus, thiodicarb could be used as substitute for control of the resistant S. avenae in this case. Furthermore, the two different AChE genes cloned from different resistant and susceptible individuals were also compared. Two mutations, L436(336)S in Sa.Ace1 and W516(435)R in Sa.Ace2, were found consistently associated with the insensitivity of AChE. They were thought to be the possible resistance mutations, but further work is needed to confirm this hypothesis.

On the basis of several experiments carried out in China, it was proved that both seaweed liquid fertilizer and rare earth (RE) could promote the growth of crops and increase their yield. The effects of extraction from seaweed and its complex with RE on the degradation of organophosphorous pesticides and the yield of vegetables were investigated. The results showed that the extract and its complex with RE could degrade organophosphorous pesticides in neutral solvent. The residues of the pesticides treated by the extract decreased by 96.88%, 52.30%, 49.52%, and 22.88%, respectively, for chlorpyrifos, dichlorvos, omethoate, and dimethoate, and those by the complex decreased by 95.99%, 54.23%, 48.79%, and 25.66%, respectively, when compared with the control. The residues of chlorpyrifos and dimethoate in spinach sprayed with the complex were decreased by 90.64% and 76.56%, respectively, compared with those in spinach from control plots when the interval between spraying and sampling was 8 d. The fresh weight of brassica chinensis and cabbage increased by 28.62% and 18.72%, and their dry weight increased by 44.49% and 14.74%, respectively, compared with those of the controls. The chlorpyrifos and dimethoate residues in brasscia chinese were decreased by 36.36% and 50.00%, respectively, and their rate of decrease in cabbage was 40.00% and 75.00%, respectively, on 5th day after spraying with the complex, when compared with those in the vegetable from control. These results suggest that this complex can increase the agricultural productivity and reduce the use of pesticide residues in the production of vegetables.

Resistance of cotton aphid (Aphis gossypii Glover) collected from four leading cotton producing regions and one non-cotton producing region in Shandong Province, China, in 1985, 1999, and 2004 to fenvalerate, omethoate, imidacloprid, acetamiprid, carbosulfan, and endosulfan, was determined on cotton (Gossypium hirsutum L.). Dose-response results indicate that A. gossypii became highly resistant to fenvalerate, and the resistance ratios (RRs) increased from 30–370-fold in 1985 to 370–2150-fold from different regions as compared with the susceptible population (S). A. gossypii also exhibited strong resistance to imidacloprid and acetamiprid with RRs of 17- to 97-fold in 2004. Resistance of A. gossypii to omethoate varied greatly among the five geographical regions, and the RRs ranged from 5- to 80-fold. In contrast, the resistance to carbosulfan did not significantly increase from 1999 to 2004 in all regions. The information from this study would be helpful for management of A. gossypii on cotton in those regions.

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.

There is an ongoing debate about the benefit of fresh frozen plasma (FFP) infusion in organophosphorus (OP) pesticide-poisoned patients. This prompted us to investigate the kinetics of OP pesticide degradation by FFP with an enzymatic assay in vitro. Degradation was rapid with shortest half-lives of 19.5s for chlorpyrifos-oxon, 6.3min for paraoxon-ethyl and 17.9min for dichlorvos. Heptenophos (78.0min), mevinphos (101.8min), profenofos (162.3min) and malaoxon (179.7min) showed half-lives of up to 3h. Substantial longer degradation half-lives of 69.7-80.8h were determined with chlorfenvinphos and bromfenvinphos. Methamidophos and omethoate showed no degradation by FFP indicated by half-lives similar to spontaneous hydrolysis. In conclusion, degradation by FFP depends on the particular OP pesticide and the used FFP batch.

Three types of chitosan with high (3.40 × 10(6)), medium (2.11 × 10(5)), and low (5.89 × 10(4)) molecular weights were chosen as ligands to synthesize chitosan magnesium, calcium, iron(III), and zinc coordination complexes. Degradation of four organophosphorous pesticides (dichlorvos, omethoate, dimethoate, and chlorpyrifos) by the above complexes in a heterogeneous system was studied using solid-phase extraction (SPE) and gas chromatography (GC). The degradation effect is related to the different types of chitosan, metal, and organophosphorus pesticides (OPs). Complexes of transition metals and the low molecular weight chitosan showed high hydrolytic activity. The chitosan-iron(III) complex was further used to study its catalytic kinetics on the hydrolysis of OPs. At pH 7.0 and 20 °C, the half-life of dichlorvos hydrolyzed by chitosan iron(III) was 52 h, whereas that of spontaneous dichlorvos hydrolysis was 105 h. The degradation ratio of omethoate and dimethoate increased to 38 and 52 %, respectively, which were 34 and 48 % higher than the control after 6 days at pH 7.0 and 20 °C. For all tested conditions, an increase of pH and temperature resulted in a higher degradation rate.

Resins of complexes made from agarose-Ce4+ (RCA-Ce) and chitosan-Ce4+ (RCC-Ce) were prepared. Hydrolysis rates of methamidophos, omethoate and chlorpyrifos treated by RCA-Ce were 32.39%, 27.12% and 46.62%, respectively, those of chlorpyrifos and methamidophos in mung bean sprout juice 38.28% and 35.45%, and that of chlorpyrifos in tea extract 59.76%. Hydrolysis rates of protein in tea extract treated by RCA-Ce increased by 86.46%. RCC-Ce could be employed in the apple juice production. The contents of methamidophos and parathion-methyl in the juice treated by RCC-Ce decreased 58.76% and 71.92%. Furthermore, RCC-Ce was used to clarification for beer by the ways of a column. RCC-Ce could hydrolyze sensitive protein and increase contents of free amino acid in the beer. Therefore, the beer treated by RCC-Ce could stay oxidation and aging procedure due to some metal ions being absorbed by RCC-Ce.

Some of the pesticides listed in the European 76/464/EC Directive and in the Directive 2000/60/ EC are very polar and require special analytical methodology with respect to their extraction from water. The extraction of the organophosphorus pesticides methamidophos, omethoate, oxydemeton-methyl, mevinphos and trichlorfon with lg P OW below 1 was investigated using 21 different solid-phase materials. Each material was tested on spiked natural water at 4 different pH values, adjusted prior to extraction. The following range of materials were tested: octadecyl silica, polymers, modified silica, ion exchange and carbon. Extraction of the above compounds from water is possible. A relationship between the octanol-water partition coefficient and recovery rates was obtained not only for octadecyl solid phases but also for some polymeric materials. General conclusions about the use of solid-phase materials and specific conclusions about the extraction of particular compounds were made. An optimized extraction procedure was deduced and confirmed.

This work is focused on the effectiveness of headspace solid-phase microextraction (HS-SPME) for the analysis of nine organophosphorus (OPs) insecticides (dimethoate, diazinon, fenitrothion, malathion, fenthion, parathion ethyl, methyl bromophos, methidathion, ethion) and four metabolites (omethoate, malaoxon, fenthion sulfoxide and fenthion sulfone) residues in olive oil samples. The efficiency of six fibre types with different film thickness was compared. PDMS (100 mu m) was found to be the most suitable fibre for the analysis of OPs in olive oils. Optimization of SPME conditions (stirring rate, extraction time, temperature, salt addition) was based on previous developed method in the laboratory that was enriched with additional analytes including major metabolites. In addition, the effect of the oil matrix on the pesticide recoveries was evaluated using spiked oil samples of different composition (acidity, fatty acids, triglycerides, sterols). It was found that only acidity and total amount of sterols are the main factors influencing the SPME efficiency. Matrix effects were compensated for, by using the internal standard method for the quantification of pesticides. The recoveries at three spiking levels were between 80% and 106% with R.S.D. (%) values below 10% in most cases. Good linearity (R-2 > 0.985) was observed in the 0.025-0.50 mg kg(-1) concentration range with satisfactory R.S.D. (%) values of 4.5-10.4%. The method allowed detection of the tested compounds at concentrations below 0.010 mg kg(-1) with GC-FTD detection. In addition, intra- and inter-day precision was satisfactory (R.S.D. (%) < 10%). The performance results confirm the usefulness of the proposed methodology for the analysis of OPs in olive oils. Moreover, the maximum residue limits required by European and international regulations can be attained without difficulty. Finally, the method was applied to 30 virgin olive oil samples from major olive production areas of Greece in the framework of an extended monitoring survey of OPs residues in olive oil. The most commonly found pesticides were fenthion, dimethoate and ethion in levels that did not exceed the MRLs. (c) 2006 Elsevier B.V. All rights reserved. Analytica Chimica Acta

Anti-cholinesterase resistance is in many cases caused by modified acetylcholinesterase (MACE). A comparison was made of toxicological data and AChE activity gathered from 21 field populations and nine laboratory strains of houseflies, Musca domestica L., to elucidate the best way of generating data to provide advice for management strategies and gathering information for resistance risk assessment on the organophosphates azamethiphos and dimethoate and the carbamate methomyl, which have been the primary insecticides used against adult houseflies in Denmark. Cluster analysis was performed and > 2000 houseflies were assigned to one of three phenotypes based on total acetylcholinesterase activity as well as inhibition by azamethiphos, methomyl or omethoate. A cluster, i.e. a phenotype, with high total AChE activity and high sensitivity to azamethiphos and less sensitivity to inhibition by methomyl and omethoate was shown to be linked to methomyl resistance. It was not possible to define any clusters that could be linked to azamethiphos or dimethoate resistance. The five mutations V180L, G262A, G262V, F327Y and G365A causing anticholinesterase resistance in houseflies were all identified in the Danish housefly strains. The data are very heterogeneous, and a correlation of molecular genetic background and resistance of phenotypes is not obvious with the available data. Copyright © 2006 Society of Chemical Industry

Solid-phase micro extraction (SPME) coupled with GC enables rapid and simple analysis of organophosphorus pesticides in a range of complex matrices. Investigations were made into the extraction efficiencies from water of six organophosphorus insecticides (methamidophos, omethoate, dimethoate, parathion methyl, malathion, and parathion ethyl) showing a wide range of polarities. Three SPME fibres coated with different stationary phases, polydimethylsiloxane, polyacrylate, and carbowax-divinylbenzene (CW-DVB), were investigated. Water was spiked with the pesticides at concentrations from 1 to 0.01 µg mL-1, and the solutions used for optimization of the procedure. The CW-DVB fibre, with a 65 µm coating, gave the best performance. The optimized experimental conditions were sample volume 10 mL at 20°C, equilibration time 16 min, pH 5, and presence of 10% w/v NaCl. SPME analyses were performed on solutions obtained by equilibrating aqueous pesticide solutions with six certified soils with various physico-chemical characteristics. SPME data were also assessed by comparison with analyses performed by using conventional solid-phase extraction. Results indicate the suitability of SPME for analysis of pesticides in environmental water samples.

Hydrolysis activities of PACC (particle of agarose-Ce4+ complex, newly made through double emulsification) for compounds containing phosphodiester or peptide bonds were studied. The results showed that PACC could hydrolyze organophosphorous pesticides not only in water but also in vegetable juice or tea extract. Hydrolysis rates of methamidophos, omethoate and chlorpyrifos in water are 32.39%, 27.12% and 46.62% respectively, those of chlorpyrifos and methamidophos in mung sprout juice 38.28% and 35.45% respectively, and that of chlorpyrifos in tea extract 59.76%. Hydrolysis rates of BSA (bovine serum albumin) in water and protein in tea extract by PACC increase by 54.30% and 86.46% respectively as compared with the control.

This work presents an automatic method able to identify the presence of neurotoxic insecticides using omethoate as a model compound. The acetylcholinesterase (AChE)-based biosensors used to detect the neurotoxic insecticides present two shortcomings: the weak limit of detection (LOD) and the lack of selectivity. An appropriate LOD is obtained in our work by using two sensitive AChEs from Drosophila melanogaster ( Dm ): the wild type (wt- Dm ) and the E69W mutant. To discriminate between the insecticides and all other interferences, we use a FIA system that provides analytical information acquired from two enzymes: (i) the sensitive Dm- AChEs and (ii) an omethoate-resistant AChE from Electric Eel (Eel), which is equally affected by the matrix. The enzymes were immobilised on screen-printed electrodes by entrapment in a photocrosslinkable PVA-SbQ polymer used with a FIA system with three channels, each one of them simultaneously analysing the same sample using biosensors based on different AChEs. The biosensor based on the wt- Dm had a LOD of 2 × 10 −6 M omethoate, while the one based on the E69W mutant permitted to lower the LOD to 1 × 10 −7 M. Interferences produced by mercury and hypocloryte were successfully discriminated. Environmental water samples were also analysed.

The acute toxicities of two organophosphorodithioate (dimethoate and disulfoton) and two organophosphorothioate (omethoate and demeton-S-methyl) insecticides were evaluated individually and in binary combination with the herbicide atrazine using fourth-instar larvae of the aquatic midge, Chironomus tentans. Atrazine alone up to 1000 μg/L did not show significant toxicity to the midges in a 48-h bioassay. However, atrazine concentrations as low as 1 μg/L in combination with dimethoate at EC25 (concentration to affect 25% of tested midges), 100 μg/L in combination with disulfoton (EC25), and 10 μg/L in combination with demeton-S-methyl (EC25) significantly enhanced the toxicity of each organophosphate insecticide. In contrast, atrazine concentrations of 10 μg/L and above in combination with omethoate (EC25) significantly decreased the toxicity of the insecticide. Biochemical analysis indicated that increased toxicity of dimethoate, disulfoton, and demeton-S-methyl in binary combination with atrazine correlated to the increased inhibition of acetylcholinesterase. Furthermore, cytochrome P450-dependent O-deethylation activity in the midges exposed to atrazine at 1000 μg/L was 1.5-fold higher than that in the control midges. Thus, atrazine appeared to induce cytochrome P450 monooxygenases in the midges. Elevated cytochrome P450 monooxygenase activity may increase the toxicities of dimethoate, disulfoton, and demeton-S-methyl by enhancing the oxidative activation of dimethoate into omethoate, and disulfoton and demeton-S-methyl into their sulfoxide analogs with increased anticholinesterase activity. In contrast, atrazine reduced the toxicity of omethoate possibly by enhancing the oxidative metabolic detoxification since omethoate does not require oxidative activation.