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Resistance to pesticides is typically identified via laboratory bioassays after field control failures are observed, but the results of such assays are rarely validated through experiments under field conditions. Such validation is particularly important when only a low-to-moderate level of resistance is detected in the laboratory. Here we undertake such a validation for organophosphate resistance in the agricultural pest mite Halotydeus destructor, in which low-to-moderate levels of resistance to organophosphorus pesticides have evolved in Australia. Using data from laboratory bioassays, we show that resistance to the organophosphate chlorpyrifos is higher (around 100-fold) than resistance to another organophosphate, omethoate (around 7-fold). In field trials, both these chemicals were found to effectively control pesticide-susceptible populations of H. destructor. However, when applied to a resistant mite population in the field, the effectiveness of chlorpyrifos was substantially decreased. In contrast, omethoate remained effective when tested alone or as a mixture with chlorpyrifos. We also show that two novel (non-pesticide) treatments, molasses and wood vinegar, are ineffective in controlling H. destructor when sprayed to pasture fields at rates of 4 L/ha. These findings suggest a close link between levels of resistance quantified through laboratory bioassays and the field effectiveness of pesticides; however, in the case of H. destructor, this does not necessarily mean all field populations possessing organophosphate resistance will respond similarly given the potentially complex nature of the underlying resistance mechanism(s). [ABSTRACT FROM AUTHOR]

A simple homogeneous photoelectrochemical (PEC) sensing platform based on an alkaline phosphatase (ALP)–mediated pesticide assay was established for the sensitive detection of omethoate (OM). The Bi2S3@Bi2Sn2O7 heterojunction was used as a photoactive material to provide stable background photocurrent signals. The inhibition of OM on ALP and PEC determination was carried out in the homogeneous system. In the absence of OM, dephosphorylation of L-ascorbic acid 2-phosphate trisodium salt (AAP) was catalyzed by ALP to produce the enzyme-catalyzed product (L-ascorbic acid, AA). AA, as an electron donor, could capture photogenerated holes on the Bi2S3@Bi2Sn2O7 heterojunction, thus inhibiting the recombination of electron holes to achieve an increase of the photocurrent signal. When the OM was introduced, the enzyme activity of ALP was reduced due to the organophosphorus pesticides (OPs)–based enzyme inhibition, and the AA produced by catalytic hydrolysis was also reduced, thus reducing the photocurrent signal. Compared with the traditional PEC sensor for OPs, this homogeneous PEC sensor avoided immobilization procedures, covalent labeling, separation, and the steric hindrance effect caused by immobilized biomolecules, which achieved high recognition efficiency and caused a reduction in analysis time. Additionally, an ALP-mediated pesticide assay for the determination of OPs with a simplified experimental process further improved the stability and reproducibility of the PEC sensor. The PEC sensor showed high sensitivity to the target OM within a dynamic range of 0.05 ~ 500 ng mL−1, and the detection limit was 0.0146 ng mL−1. Additionally, the PEC biosensing system showed good selectivity and anti-interference ability, and exhibited a satisfactory result in spinach and mustard samples. A homogeneous PEC biosensor based on ALP inhibition strategy was constructed for OM detection in vegetable samples via Bi2S3@Bi2Sn2O7 heterojunction as the photoactive substrate material [ABSTRACT FROM AUTHOR]

Organophosphate pesticides are used in large quantities. Once accumulated in the environment, they exhibit toxic effects on non-target organisms. Dimethoate, a frequently used insecticide, and its oxo-analog omethoate inhibit acetylcholinesterase and are toxic for mammals. However, under environmental conditions, they also undergo chemical transformations and decomposition. Nevertheless, the systematic data about dimethoate and omethoate decomposition are missing. We performed a systematic analysis of dimethoate and omethoate decomposition under different pH conditions and estimated their long-term eco-neurotoxic effects. Dimethoate and omethoate decompose rapidly in alkaline aqueous solutions (half-lives 5.7 ± 1.4 and 0.89 ± 0.21 days) but are highly stable in acidic solutions (half-lives 124 ± 18 and 104 ± 9 days). These differences are explained using quantum chemical calculations, indicating that a weaker P–S bond in omethoate is more susceptible to hydrolysis, particularly at a high pH. The toxicity of these pesticide solutions decreases over time, indicating that no or very little of highly more toxic omethoate is formed during hydrolysis of dimethoate, pointing to the advantage of alkaline hydrolysis over other techniques for dimethoate removal. Presented data are used to benchmark dimethoate and omethoate concentrations and toxicity in contaminated water in the pH range 3 to 9 for up to 70 days upon the release in the environment. [ABSTRACT FROM AUTHOR]

In this work, surface-enhanced Raman spectroscopy (SERS) was used with silver colloid substrate for rapid detection of omethoate (an organophosphate pesticide) in standard solution and peach extract. The findings demonstrated that the characteristic wavenumber of the pesticide could be precisely identified using the SERS method. The calibration curve was plotted between concentrations and Raman intensities of the target peak at 1649 cm−1 for the peach extract and at 1647 cm−1 for the standard solution. The coefficients of determination (R2) of 0.9829 and 0.98 were obtained for standard solution and for peach extract, respectively. The calculated limits of detection for omethoate in standard solution and in peach extracts were 0.001 mg L−1 and 0.01 mg kg−1, respectively. This study revealed that the proposed method could be used for the analysis of trace contaminants like omethoate in multifaceted food matrices. [ABSTRACT FROM AUTHOR]

Organophosphorous pesticide (OP) contamination could have serious adverse effects on human health and the environment. Due to the toxicity of OPs and the threat presented by their accidental or intentional release in populated areas, the determination and monitoring of these OPs in food products and environment is of great importance. OPs are present in very small quantities and therefore, methods for their detection need to be highly sensitive and selective. Here, we aimed to develop a simple and selective aptamer-based colorimetric assay for the detection of omethoate, which is one of the commonly used OPs. The principle of the assay is that single-stranded DNA (ssDNA)-wrapped gold nanoparticles (AuNPs) are resistant to salt-induced aggregation. By employing an 'artificial antibody' organophosphorous pesticide-binding aptamer (OBA) as the recognition element, aptamer-wrapped AuNPs (Au-apta) show high selectivity towards omethoate, resulting in the disconnection of aptamers from AuNPs and the aggregation of AuNPs. As there is a significant color change from the interparticle plasmon coupling during the aggregation of AuNPs, the established assay showed good linearity between 0.1 and 10 μmol/L, with a low detection limit of 0.1 μmol/L. Other OPs such as profenofos, phorate, and isocarbophos would not interfere with the detection of omethoate despite having similar structures. Thus, the colorimetric method shows potential for use in the detection of omethoate in real soil samples. [ABSTRACT FROM AUTHOR]

Three types of chitosan with high (3.40 × 10), medium (2.11 × 10), and low (5.89 × 10) 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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

A capillary electrophoresis method has been developed for the analysis of omethoate and dichlorvos. Response surface methodology (RSM) was used to optimize the separate conditions for simultaneous detection of omethoate and dichlorvos. The results indicated that the optimal conditions for omethoate and dichlorvos determination were; pH 7.64, SDS concentration 67.5 mM, separation voltage 19.0 KV. Quantitative linear ranges were 1.0–300 μg/mL for omethoate and dichlorvos with correlation of 0.9967 and 0.9965, respectively. The limits of detection were 0.046 μg/mL and 0.031 μg/mL for omethoate and dichlorvos, with relative standard deviations (R.S.D.) <3.6%. The value of recoveries for omethoate and dichlorvos were arranged from 94.1% to 106.0%. [ABSTRACT FROM AUTHOR]

Levels of acetylcholinesterase and neurotoxic esterase were measured in brain autopsy material. In tissue from a fatal human poisoning and from hens given 4-8 × unprotected LD AChE was highly inhibited and neurotoxic esterase uninhibited. The findings correlate with the inhibitory power of omethoate against these enzymes in vitro. It is concluded that omethoate has negligible potential to cause delayed neuropathy and a published report of human neuropathy due to omethoate is criticised. [ABSTRACT FROM AUTHOR]