Metal-organic framework-based multienzyme cascade bioreactor for sensitive detection of methyl parathion

In this study, a cascade nanobioreactor was developed for the highly sensitive detection of methyl parathion (MP) in food samples. The simultaneous encapsulation of acetylcholinesterase (AChE) and choline oxidase (CHO) in a zeolitic imidazole ester backbone (ZIF-8) effectively improved the stability and cascade catalytic efficiency of the enzymes. In addition, glutathione-stabilized gold nanoclusters (GSH-AuNCs) were encapsulated in ZIF-8 by ligand self-assembly, conferring excellent fluorescence properties. Acetylcholine (ATCh) is catalyzed by a cascade of AChE/CHO@ZIF-8 as well as Fe(II) to generate hydroxyl radicals (·OH) with strong oxidizing properties. The ·OH radicals then oxidize Au(0) in GSH-AuNCs@ZIF-8 to Au(I), resulting in fluorescence quenching. MP, as an inhibitor of AChE, hinders the cascade reaction and thus restores the fluorescence emission, enabling its quantitative detection. The limit of detection of the constructed nanobioreactor for MP was 0.23 µg/L. This MOF-based cascade nanobioreactor has great potential for the detection of trace hazards.

Pesticides in surface water of the Ondas river watershed, western Bahia, Brazil: Spatial-seasonal distribution and risk assessment

This study investigated the occurrence and seasonal distribution of different classes of pesticides in surface waters of the Ondas River Watershed, as well as potential risks to the aquatic health and human water consumption in the western region of Bahia state, Brazil. Two gas chromatography-mass spectrometry analytical methods were applied to monitor 34 pesticides in water samples collected during both the dry and rainy seasons at 17 sites. Upon individual analysis, only γ-HCH, methoxychlor, demeton-S, methyl parathion, fenitrothion, chlorpyrifos, and azoxystrobin exhibited statistically significant differences between seasons. During rainy season, concentration medians of residues were higher for γ-HCH (74.7 ng L-1), methoxychlor (25.1 ng L-1), and azoxystrobin (47.2 ng L-1), potentially linked to historical contamination or illegal use. Conversely, pesticides like methyl parathion, fenitrothion, and chlorpyrifos, belonging to the organophosphate class, showed higher concentration medians in the dry period, measuring 75.1, 5.50, and 10.8 ng L-1, respectively, probably due to region crop activities. The risk quotient (RQ) assessment for aquatic life indicated that 59.0% of the samples in the dry season and 76.0% in the rainy season had RQ values greater than one, signifying a critical scenario for species conservation. Regarding human consumption, elevated risks were observed for heptachlor in both sampling periods and for azoxystrobin during the rainy season, surpassing RQ levels above 1, indicating danger in untreated water ingestion. Additionally, 24.0% and 53.0% of the samples in the dry and rainy seasons, respectively, contained at least one pesticide exceeding the EU resolution limit (100 ng L-1). Therefore, considering this information, implementing mitigation measures to avoid the river's contamination becomes imperative.

Core-shell ZnO@CoO nitrogen doped nano-composites as highly sensitive electrochemical sensor for organophosphate pesticides detection

Core-shell ZIF-8@ZIF-67 was synthesized by growing a cobalt-based ZIF-67 on a ZIF-8 seed particle. Herein, through selective etching of the ZIF-8@ZIF-67 core and subsequent direct carbonization, core-shell hollow ZnO@CoO nitrogen-doped nanoporous carbon (HZnO@CoO-NPC) nanocomposites were prepared. HZnO@CoO-NPCs possessed a high nitrogen content, large surface area, high degree of graphitization and excellent electrical conductivity, all of which were attributed to successfully integrating the unique advantages of ZIF-8 and ZIF-67. HZnO@CoO-NPCs were used to assemble acetylcholinesterase (AChE) biosensors for organophosphorus pesticides (OPs) detection. The low detection limit of 2.74 × 10-13 M for chlorpyrifos and 7.6 × 10-15 M for parathion-methyl demonstrated the superior sensing performance. The results showed that the electrochemical biosensor constructed by HZnO@CoO-NPC provided a sensitive and efficient electrochemical strategy for OPs detection.

Ecological risk assessment for typical organophosphorus pesticides in surface water of China based on a species sensitivity distribution model

The ecological risks posed by widespread organophosphorus pesticide (OPs) pollution in the surface waters of China remain unclear. In this study, species sensitivity distribution (SSD) parametric statistical approaches were coupled with fully acute and chronic toxicity data to fit the sensitivity distributions of different aquatic species to five typical OPs: dimethoate, malathion, parathion-methyl, trichlorfon, and dichlorvos. Crustaceans exhibit the highest sensitivity to OPs, whereas algae are the least sensitive. The acute hazardous concentrations that affected 5 % of the species (HC5) were 0.112, 0.001, 0.001, 0.001, and 0.001 mg/L for dimethoate, malathion, parathion-methyl, trichlorfon, and dichlorvos, respectively, whereas their chronic HC5 values were 0.004, 0.004, 0.053, 0.001, and 0.0005 mg/L, respectively. Hence, dichlorvos is highly toxic and poses greater risk to non-target aquatic species. The evaluation data revealed varying geographical distribution characteristics of the ecological risks from OPs in 15 freshwater aquatic systems across different regions of China. Dichlorvos posed the highest risk in the basins of Zhejiang and Guangdong Provinces, with the highest chronic Risk Quotient (RQ) and Hazard Index (HI) at 9.34 and 9.92, respectively. This is much higher than what was collected and evaluated for foreign rivers (the highest chronic RQ and HI in foreign rivers were 1.65 and 2.24, respectively). Thus, dichlorvos in the surface waters of China poses a substantial ecological risk to aquatic organisms, and may endanger human health.

Development of a bioluminescence resonance energy transfer Quenchbody sensor for the detection of organophosphorus pesticides in water bodies

Rapid and precise quantification of organophosphorus pesticides (OPPs) in environmental water bodies is crucial for evaluating ecological risks and safeguarding human health. Traditional instrumental methods are complex, time-consuming, and expensive, while enzyme-based biosensors suffer from instability and require a constant supply of substrates. Hence, there is an urgent need for a fast, simple, and sensitive biosensor for OPPs. In this study, we developed a novel non-enzymatic biosensor for the detection of methyl parathion (MP) by employing the bioluminescence resonance energy transfer (BRET) Q-body strategy. Optimizing the spacer arm and screening fluorescent dyes identified the R6G BRET MP Q-body sensor with the best performance. Key parameters affecting the sensor's detection performance were optimized by using single-factor experiments. Under optimal conditions, the detection exhibited a detection limit of 5.09 ng·mL-1 and a linear range of 16.21-848.81 ng·mL-1. The sensor's accuracy was validated using standard recovery experiments, yielding a recovery rate of 84.47 %-102.08 % with a standard deviation of 1.93 %-9.25 %. The detection results of actual water samples demonstrate that this fast, simple, and highly sensitive BRET Q-body sensor holds great promise for practical water quality monitoring.

Recombinant Organophosphorus acid anhydrolase (OPAA) enzyme-carbon quantum dot (CQDs)-immobilized thin film biosensors for the specific detection of Ethyl Paraoxon and Methyl Parathion in water resources

Organophosphates pesticide (OP) toxicity through water resources is a large concern globally among all the emerging pollutants. Detection of OPs is a challenge which needs to be addressed considering the hazardous effects on the health of human beings. In the current research thin film biosensors of recombinant, Organophosphorus acid anhydrolase (OPAA) enzyme along with carbon quantum dots (CQDs) immobilized in thin films were developed. OPAA-CQDs thin film biosensors were used for the specific detection of two OPs Ethyl Paraoxon (EP) and Methyl Parathion (MP) in river water and household water supply. Recombinant OPAA enzyme was expressed in E. Coli, purified and immobilized on the CQD containing chitosan thin films. The CQDs used for this purpose were developed by a one-pot hydrothermal method from phthalic acid and Tri ethylene diamine. The properties of CQDs, OPAA and thin films were characterized using techniques like XPS, TEM, XRD, enzyme activity and CLSM measurements. Biosensing studies of EP and MP were performed by taking fluorescence measurements using a fiber optic spectrometer. The analytical parameters of biosensing were compared against an estimation carried out using the HPLC method. The biosensing performance indicates that the OPAA-CQDs thin film-based biosensors were able to detect both EP and MP in a range of 0-100 μM having a detection limit of 0.18 ppm/0.69 ppm for EP/MP, respectively with a response time of 5 min. The accuracy of estimation of EP/MP when spiked in water resources lie in the range of ∼100-102% which clearly indicates the OPAA-CQD based thin film biosensors can function as a point-of-use method for the detection of OP pesticides in complex water resources.

Boosted electrocatalytic oxidation of organophosphorus pesticides by a novel high-efficiency CeO2-Doped PbO2 anode: An electrochemical study, parameter optimization and degradation mechanisms

This article presents a novel and highly efficient electrocatalytic degradation method for two significant organophosphorus pesticides, fenitrothion (FEN), and methyl parathion (MPN), using a Ti/β-PbO2-CeO2 modified anode (indirect oxidation). A comprehensive electrochemical investigation was also carried out to gain new insight into the redox behavior and destruction pathway of these pesticides (direct oxidation). The study also explores the effects of various operating parameters, such as initial solution pH, applied current density, and initial pesticides concentration, on the conversion-paired electrocatalytic removal process. To further enhance the degradation efficiency, a new configuration of the electrochemical cell was designed, employing two types of electrodes and two independent power supply devices. The conversion paired electrocatalytic degradation process of these pesticides involves first the direct reduction of FEN (or MPN) on a graphite cathode and then the indirect oxidation of reduced FEN (or MPN) by hydroxyl radicals electro generated on the Ti/β-PbO2-CeO2 anode. The synergism of these two processes together will effectively lead to FEN (or MPN) degradation. The degradation percentages of 98% for FEN and 95% for MPN at the optimal conditions for the electrochemical degradation of these pesticides were achieved at pH = 7, initial concentration 50 mg L-1, with a current density of 90 mA cm-2 for direct reduction and 11 mA cm-2 for indirect oxidation. Overall, this study presents a promising and efficient approach for the remediation of organophosphorus pesticide-contaminated environments, offering valuable insights into the electrochemical degradation process and highlighting the potential for practical application in wastewater treatment and environmental protection.

Attention guided learnable time-domain filterbanks for speech depression detection

Depression, as a global mental health problem, is lacking effective screening methods that can help with early detection and treatment. This paper aims to facilitate the large-scale screening of depression by focusing on the speech depression detection (SDD) task. Currently, direct modeling on the raw signal yields a large number of parameters, and the existing deep learning-based SDD models mainly use the fixed Mel-scale spectral features as input. However, these features are not designed for depression detection, and the manual settings limit the exploration of fine-grained feature representations. In this paper, we learn the effective representations of the raw signals from an interpretable perspective. Specifically, we present a joint learning framework with attention-guided learnable time-domain filterbanks for depression classification (DALF), which collaborates with the depression filterbanks features learning (DFBL) module and multi-scale spectral attention learning (MSSA) module. DFBL is capable of producing biologically meaningful acoustic features by employing learnable time-domain filters, and MSSA is used to guide the learnable filters to better retain the useful frequency sub-bands. We collect a new dataset, the Neutral Reading-based Audio Corpus (NRAC), to facilitate the research in depression analysis, and we evaluate the performance of DALF on the NRAC and the public DAIC-woz datasets. The experimental results demonstrate that our method outperforms the state-of-the-art SDD methods with an F1 of 78.4% on the DAIC-woz dataset. In particular, DALF achieves F1 scores of 87.3% and 81.7% on two parts of the NRAC dataset. By analyzing the filter coefficients, we find that the most important frequency range identified by our method is 600-700Hz, which corresponds to the Mandarin vowels /e/ and /eˆ/ and can be considered as an effective biomarker for the SDD task. Taken together, our DALF model provides a promising approach to depression detection.

Improved charge-transfer resonance in graphene oxide/ZrO2 substrates for plasmonic-free SERS determination of methyl parathion

This work reports a sensitive SERS substrate based on graphene oxide (GO) and quantum-sized ZrO₂ nanoparticles (GO/ZrO₂) for label-free determination of the organophosphate pesticide methyl parathion (MP). The enhanced light-matter interactions and the consequent SERS effect in these substrates resulted from the effective charge transfer (CT) mechanism attributed to synergistic contributions of three main factors: i) the strong molecular adherence of the MP molecules and the ZrO₂ surface which allows the first layer-effect, ii) the relatively abundant surface defects in low dimensional ZrO₂ semiconductor NPs, which act as intermediate electronic states that reduce the large bandgap barrier, and iii) the hindered charge recombination derived from the transference of the photoinduced holes to the GO layer. This mechanism allowed an enhancement factor of 8.78 × 10⁴ for GO/ZrO₂-based substrates, which is more than 5-fold higher than the enhancement observed for platforms without GO. A detection limit of 0.12 μM was achieved with an outstanding repeatability (variation ≤4.5%) and a linear range up to 10 μM, which is sensitive enough to determine the maximal MP concentration permissible in drinking water according to international regulations. Furthermore, recovery rates between 97.4 and 102.1% were determined in irrigation water runoffs, strawberry and black tea extracts, demonstrating the reliability of the hybrid GO/ZrO₂ substrate for the organophosphate pesticides quantification in samples related to agri-food sectors and environmental monitoring.

Rapid and reliable detection and quantification of organophosphorus pesticides using SERS combined with dispersive liquid-liquid microextraction

Rapid and reliable detection and quantification of pesticide residues in complex matrices by surface enhanced Raman spectroscopy (SERS) remain challenging due to the low level of target molecules and the interference of nontarget components. In this study, SERS was combined with dispersive liquid-liquid microextraction (DLLME) to develop a rapid and reliable method for the detection of organophosphorus pesticides (OPPs). In this method, DLLME was used to extract and enrich two representative OPPs (triazophos and parathion-methyl) from a liquid sample, and a portable Raman spectrometer was used to analyze the separated sediment using homemade gold nanoparticles colloids as enhancing substrates. The results showed that the developed method displayed good sensitivity and stability for the detection and quantification of triazophos and parathion-methyl with R² ≥ 0.98. The calculated limits of detection (LODs) in the simultaneous detection of triazophos and parathion-methyl were 2.17 × 10^-9 M (0.679 ppb) and 2.28 × 10^-8 M (5.998 ppb), and the calculated limits of quantification (LOQs) were 7.23 × 10^-9 M (2.26 ppb) and 7.62 × 10^-8 M (19.098 ppb), respectively. Furthermore, the developed SERS method was successfully applied to the detection of triazophos and parathion-methyl in apple juice with recoveries between 78.07% and 110.87% and relative standard deviations (RSDs) ≤ 2.06%. Therefore, the developed DLLME facilitated liquid SERS method exhibited good sensitivity and stability for the rapid detection and quantification of OPPs and had the potential to be applied to the rapid detection of OPPs in complex matrices.

Anchoring Cu Nanoclusters on Melamine-Formaldehyde Microspheres: A New Strategy for Triggering Aggregation-Induced Emission toward Specific Enzyme-Free Methyl Parathion Sensing

Methyl parathion (MP) residues have aroused extensive attention on account of their significant threat to the environment and food safety. Currently reported fluorescent methods used for MP sensing largely depend upon an enzyme. Designing a facile and specific enzyme-free MP fluorescent sensor is in great demand, which remains a challenge. Here, negatively charged Cu nanoclusters (CuNCs) anchored on positively charged melamine-formaldehyde (MF) microspheres (MF@CuNCs) through an electrostatic interaction were prepared. MF microspheres triggered aggregation-induced emission (AIE) of CuNCs and successfully circumvented the shortcomings of poor stability and low luminescence of CuNCs. The fluorescence intensity of MF@CuNCs can be quenched by p-nitrophenol produced by MP under alkaline conditions. Accordingly, a specific enzyme-free MP sensing method was constructed with MF@CuNCs. In combination with a smartphone, visually quantitative analysis of MP in a fast and portable way was also achieved. For the first time, AIE of CuNCs used for enzyme-free MP sensing was successfully explored in this work, and it is believed that this method will open a new pathway for AIE of CuNCs to be applied in various applications.

Urinary para-nitrophenol levels of pregnant women and cognitive and motor function of their children aged 2 years: Evidence from the SMBCS (China)

BACKGROUND

Urinary para-nitrophenol (PNP), an exposure biomarker of ethyl parathion (EP) and methyl parathion (MP) pesticides, was still pervasively detected in the general population even after global restriction for years. And the concern whether there is an association of PNP level with child development of the nervous system is increasing. The current study aimed to evaluate the maternal urinary PNP concentrations during late pregnancy and the associations of PNP levels with cognitive and motor function of their children at the age of 2 years.

METHODS

323 mother-child pairs from the Sheyang Mini Birth Cohort Study were included in the current study. Gas chromatography-tandem mass spectrometry was used to measure concentrations of PNP, the specific metabolite of EP and MP, in maternal urine samples during pregnancy. Developmental quotients (DQs) scores measured with Gesell Developmental Scales were employed to evaluate cognitive and motor function of children aged 2 years. Generalized linear models were performed to analyze the associations of PNP concentrations in pregnant women's urine samples with cognitive and motor function of their children.

RESULTS

Maternal PNP was detected in all urine samples with a median of 4.11 μg/L and a range from 0.57 μg/L to 109.13 μg/L, respectively. Maternal urinary PNP concentrations showed a negative trend with DQ of motor area [regression coefficient (β) = - 1.35; 95 % confidence interval (95 %CI): - 2.37, - 0.33; P < 0.01], and the children whose mothers were in the fourth quartile exposure group performed significantly worse compared to the reference group (β = - 1.11; 95 %CI: - 1.80, - 0.42; P < 0.01). As for average DQ score, children with their mothers' urinary PNP concentrations in the third quartile group had higher scores than those in the first quartile group (β = 0.39; 95 %CI: 0.03, 0.75; P = 0.04). In sex-stratified analyses, a negative trend between maternal urinary PNP concentrations and DQ scores in motor area of children was only observed in boys (β = - 1.62; 95 %CI: - 2.80, - 0.43; P < 0.01). Boys in the third quartile group had higher DQ average scores than those in the lowest quartile as reference (β = 0.53; 95 %CI: 0.02, 1.04; P = 0.04).

CONCLUSIONS

The mothers from SMBCS may be widely exposed to EP and/or MP, which were associated with the cognitive and motor function of their children aged 2 years in a sex-specific manner. Our results might provide epidemiology evidence on the potential effects of prenatal exposure to EP and/or MP on children's cognitive and motor function.

AuNPs and graphdiyne nanocomposite as robust electrocatalyst for methyl parathion detection in real samples

The present work describes a simple and rapid synthesis method of gold nanoparticles and graphdiyne (AuNPs@GDY) nanocomposites including porous structure. Moreover, the synthesized AuNPs@GDY material was decorated on the glassy carbon electrode (GCE) with a drop coating method to construct a non-enzymatic electrochemical pesticides sensor. The micro-morphology and elemental composition of the materials were characterized by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The electrocatalysis and conductivity of the material were studied with cyclic voltammetry (CV) and impedance method, respectively. The properties of the sensor were investigated by CV and differential pulse voltammetry (DPV). The results showed that AuNPs@GDY exhibited excellent electrocatalytic ability for methyl parathion in a wide linear range (from 0.25 ng/mL to 24.43 μg/mL) and low limit of detection value (6.2 pg/mL). Furthermore, the DPV method used in this paper was accurate and sensitive, and could be used for routine quality control of methyl parathion in kiwi fruit and tomato samples.

Graphene/g-carbon nitride (GO/g-C3N4) nanohybrids as a sensor material for the detection of methyl parathion and carbendazim

The widespread use of methyl parathion (MP) and carbendazim (CBZ) as pesticide molecules for controlling pests and protect crops has added pollution issues; excess usage of these can lead to atmospheric pollution through contaminating water and soil sources. In the present study, detection of these compounds at the trace level was achieved by employing graphene oxide (GO) and graphitic carbon nitride (g-C₃N₄) nanohybrid electrode assembly (GO/g-C₃N₄/GCE). The X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM) techniques were also used to characterize the materials developed to reveal their purity, crystal structure, and morphology. The complete voltammetric behavior of these analytes was investigated using cyclic voltammetic (CV) and square wave voltammetry (SWV) techniques. The influence of pH was studied and it was noticed that electrochemical response was the highest at pH 7.0 for MP and at pH 4.2 for CBZ. Density Functional Theory (DFT) calculations could help us to understand the adsorption behavior of MP and CBZ onto the GO and g-C₃N₄ before their degradation due to the electrochemical reactions. SWV technique was helpful in the trace level detection of MP and CBZ. Linearity plots were obtained in the range of concentration from 8.0 × 10^-8 M to 1.0 × 10^-4 M with a limit of detection 0.824 nM for MP and 1.0 × 10^-8 M to 2.5 × 10^-4 M for CBZ with the detection limit of 2.82 nM. Significance of the developed method in the field of agricultural and environmental domains was successfully investigated by monitoring MP and CBZ in water and soil samples, and the obtained results suggested the selectivity, stability, and reproducibility of the newly developed GO/g-C₃N₄/GCE electrode assembly.

Monitoring of parathion methyl using a colorimetric gold nanoparticle-based acetylcholinesterase assay

A colorimetric gold nanoparticles (AuNPs)-based acetylcholinesterase (AChE) assay was designed for the first time to measure the concentration of parathion-methyl (PM) in lake water samples. In this assay, the analyte PM inhibited the hydrolysis of acetylthiocholine (ATCh) by AChE, preventing the formation of thiocholine (TCh) that would otherwise react with the AuNPs catalyst and deactivate the catalyst. Therefore, in the presence of PM, the AuNPs catalyzed the oxidation of the 3,3',5,5'-tetramethylbenzidine (TMB) colorimetric indicator to oxTMB, inducing a visual color change from colorless to blue. However, in the absence of PM, AChE hydrolyzed ATCh to TCh, which then reacted with the AuNPs, preventing the oxidation of TMB to oxTMB and rendering the solution colorless. Therefore, the change in the color of the analyte solution indicated the presence of PM, and the absorbance of the resulting solution was measured by UV-Vis spectroscopy to calculate the concentration of PM after generation of a calibration curve. This method was then employed using the smartphone app Color Picker, which converted the color information from the photos of the solution into digital red (R), green (G), and blue (B) values. The ratio of green (G) to blue (B) (G/B) was then plotted against the corresponding concentration to calculate the standard curve, whose regression equation was expressed by y = -0.012x + 1.02 (ng/mL), and the coefficient of determination (R²) was 0.97. In addition, this method was also used to determine the amount of PM in real lake water samples with recovery of 90.2-133.3%.

A hybrid nanobiocatalyst with in situ encapsulated enzyme and exsolved Co nanoclusters for complete chemoenzymatic conversion of methyl parathion to 4-aminophenol

Combination of enzymatic and chemical reactions provides tremendous possibilities for chemoenzymatic cascade processes. However, constructing efficient hybrid catalysts still faces great challenges. Herein, we develop a hybrid catalyst by in situ encapsulating organophosphorus hydrolase (OPH) into a Zn-doped Co-based ZIF (0.8CoZIF) via biomimetic mineralization for the chemoenzymatic cascade conversion of methyl parathion to 4-nitrophenol and then 4-aminophenol. The exsolved Co nanoclusters in Zn/Co-ZIF are found to catalyze 4-nitrophenol reduction into 4-aminophenol in the presence of sodium borohydride (NaBH₄). The as-synthesized OPH@0.8CoZIF catalyzes the complete conversion of 95 μM methyl parathion at nearly 100% 4-aminophenol production in the presence of 50 mM NaBH₄ within 15 min, which is 1/4 that of the physical mixture of OPH and 0.8CoZIF, benefiting from the MP accumulation and substrate channeling in the hybrid catalyst. The maximum cascade conversion rate of MP to 4-AP reaches 8.07 μmol·min^-1·g-catalyst^-1, which is higher than most of the reported chemoenzymatic cascade catalysts. Therefore, the hybrid nanocatalyst containing Co-ZIF-based catalyst and OPH is successfully fabricated and enables to catalyze the complete conversion of a toxic pollutant like methyl parathion into a non-toxic resource like 4-aminophenol for recycling in useful chemical synthesis through efficient one-pot cascade reactions.

Mechanism of unactivated peroxymonosulfate-induced degradation of methyl parathion: Kinetics and transformation pathway

Although various activated peroxymonosulfate (PMS) processes have been applied widely for the destruction of recalcitrant organics due to its high generation potential of various electrophiles reactive oxygen species (e.g., sulfate and hydroxyl radicals and singlet oxygen), non-radical-based PMS reactions with pollutants are poorly understood. Especially, relatively little information exists on the reactivity of PMS towards organic ester compounds such an organophosphorus pesticides (OPPs). Herein, we systematically studied the unactivated PMS-induced transformation of methyl parathion, a stubborn and toxic OPP. Specifically, direct reaction rather than electrophile radical-based oxidation was responsible for the rapid degradation of methyl parathion. The contribution of the produced singlet oxygen (¹O₂) from the self-decomposition of PMS to methyl parathion degradation can be neglected. The degradation rate constant (k_obs) was strongly dependent on PMS loading and solution pH. The implication of the PMS reaction with methyl parathion for environment treatment was further evaluated by investigating the effects of common water matrices such as sediment humic acids, Cl^-, and natural water. The identified metabolic products revealed that exposure to PMS resulted in hydrolysis and oxidation to methyl parathion. Further study demonstrated that PMS was also capable of effectively oxidizing other typical OPPs without explicit activation. This study provides novel insights into the reaction of methyl parathion with PMS, which indicate feasibility for the decontamination of OPP-contaminated environments.

Transcriptomic analysis of Burkholderia cenocepacia CEIB S5-2 during methyl parathion degradation

Methyl parathion (MP) is a highly toxic organophosphorus pesticide associated with water, soil, and air pollution events. The identification and characterization of microorganisms capable of biodegrading pollutants are an important environmental task for bioremediation of pesticide impacted sites. The strain Burkholderia cenocepacia CEIB S5-2 is a bacterium capable of efficiently hydrolyzing MP and biodegrade p-nitrophenol (PNP), the main MP hydrolysis product. Due to the high PNP toxicity over microbial living forms, the reports on bacterial PNP biodegradation are scarce. According to the genomic data, the MP- and PNP-degrading ability observed in B. cenocepacia CEIB S5-2 is related to the presence of the methyl parathion-degrading gene (mpd) and the gene cluster pnpABA'E1E2FDC, which include the genes implicated in the PNP degradation. In this work, the transcriptomic analysis of the strain in the presence of MP revealed the differential expression of 257 genes, including all genes implicated in the PNP degradation, as well as a set of genes related to the sensing of environmental changes, the response to stress, and the degradation of aromatic compounds, such as translational regulators, membrane transporters, efflux pumps, and oxidative stress response genes. These findings suggest that these genes play an important role in the defense against toxic effects derived from the MP and PNP exposure. Therefore, B. cenocepacia CEIB S5-2 has a great potential for application in pesticide bioremediation approaches due to its biodegradation capabilities and the differential expression of genes for resistance to MP and PNP.

Magnetic Fe3O4@SiO2@β-cyclodextrin for solid phase extraction of methyl parathion and fenthion in lettuce samples

In this study, magnetic Fe3O4@SiO2@β-cyclodextrin copolymerized microparticles were synthesized and applied for the extraction of methyl parathion and fenthion in lettuce samples followed by HPLC-UV detection. The magnetic β-cyclodextrin copolymerized microparticles were prepared by dispersion polymerization with acryloyl β-cyclodextrin as the functional monomer and ethylene glycol dimethyacrylate as the crosslinker. The composite magnetic microparticles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, magnetic measurement, and thermogravimetric analysis, and used as the adsorbent of magnetic solid-phase extraction (MSPE) for methyl parathion and fenthion. The extraction conditions including sample pH and ionic strength, desorption solvent type and volume, and adsorption and desorption times were optimized. Under the optimal extraction conditions, an MSPE-HPLC-UV method was developed for the detection of methyl parathion and fenthion in lettuce. Wide linear ranges of 1.0-200 μg kg-1 (R2 = 0.9998) for methyl parathion and 1.5-200 μg kg-1 (R2 = 0.9978) for fenthion were obtained and the limits of detection were 0.3 μg kg-1 for methyl parathion and 0.5 μg kg-1 for fenthion in lettuce, respectively. The proposed method was applied for the determination of methyl parathion and fenthion in lettuce with satisfactory recoveries between 89.2-101.2%, and relative standard deviations were less than 9.1%. Thus, the MSPE-HPLC-UV method has high accuracy and sensitivity for the analysis of methyl parathion and fenthion in lettuce samples.

Biodegradation pathway of the organophosphate pesticides chlorpyrifos, methyl parathion and profenofos by the marine-derived fungus Aspergillus sydowii CBMAI 935 and its potential for methylation reactions of phenolic compounds

The indiscriminate use of organophosphate pesticides causes serious environmental and human health problems. This study aims the biodegradation of chlorpyrifos, methyl parathion and profenofos with the proposal of new biodegradation pathways employing marine-derived fungi as biocatalysts. Firstly, a growth screening was carried out with seven fungi strains and Aspergillus sydowii CBMAI 935 was selected. For chlorpyrifos, 32% biodegradation was observed and the metabolites tetraethyl dithiodiphosphate, 3,5,6-trichloropyridin-2-ol, 2,3,5-trichloro-6-methoxypyridine, and 3,5,6-trichloro-1-methylpyridin-2(1H)-one were identified. Whereas 80% methyl parathion was biodegraded with the identification of isoparathion, methyl paraoxon, trimethyl phosphate, O,O,O-trimethyl phosphorothioate, O,O,S-trimethyl phosphorothioate, 1-methoxy-4-nitrobenzene, and 4-nitrophenol. For profenofos, 52% biodegradation was determined and the identified metabolites were 4-bromo-2-chlorophenol, 4-bromo-2-chloro-1-methoxybenzene and O,O-diethyl S-propylphosphorothioate. Moreover, A. sydowii CBMAI 935 methylated different phenolic substrates (phenol, 2-chlorophenol, 6-chloropyridin-3-ol, and pentachlorophenol). Therefore, the knowledge about the fate of these compounds in the sea was expanded, and the marine-derived fungus A. sydowii CBMAI 935 showed potential for biotransformation reactions.

Phenol driven changes onto MnO2 surface for efficient removal of methyl parathion: The role of adsorption

Manganese oxides (MnO₂), important environmental oxides, have drawn significant attention in areas such as detoxification of micro-hazardous organic contaminants with electron-donating functional groups such as -OH. However, studies on whether these oxidized processes might further impact the fate of some esters like organophosphorus pesticide (OPPs) remain poorly understood. Herein, we propose a new mechanism involved in the enhanced removal of methyl parathion in mixtures of MnO₂ and phenol. Specifically, the removal of methyl parathion (up to 73.7%) was significantly higher for a binary system than for MnO₂ alone (approximately 9.3%) and was primarily due to adsorption rather than degradation. The extent of methyl parathion adsorption was dependent significantly on pH, reactant loading and metal ion co-solutes (such as Ca²⁺, Mg²⁺, Fe³⁺ and Mn²⁺). Both spectroscopic (FT-IR, SEM-EDX and XPS) and chromatographic (LC/HRMS) analyses showed that the remarkable increase in the number of organics (e.g., polymers) onto the MnO₂ surface dominated methyl parathion adsorption via hydrogen bonding, n-π and π-π interactions, van der Waals forces and pore-diffusion. The results from this study provided evidence for the role of manganese oxides in adsorption of methyl parathion in soil-aquatic environments involving phenolic compounds.

In-depth biochemical identification of a novel methyl parathion hydrolase from Azohydromonas australica and its high effectiveness in the degradation of various organophosphorus pesticides

Organophosphorus pesticides are highly toxic phosphate compounds with the general structure of O = P(OR)₃ and threaten human health seriously. Methyl parathion hydrolase from microbial is an important enzyme to degrade organophosphorus pesticides (OPs) into less toxic or nontoxic compounds like. p-nitrophenol and diethyl phosphate. Here, a gene encoding methyl parathion hydrolase from Azohydromonas australica was firstly cloned and expressed in Escherichia coli. The recombinant hydrolase showed its optimal pH and temperature at pH 9.5 and 50 °C. Leveraging 1 mM Mn²⁺, the enzyme activity was significantly enhanced by 29.3-fold, and the thermostability at 40 and 50 °C was also improved. The recombinant MPH showed the specific activity of 4.94 and 16.0 U/mg towards methyl parathion and paraoxon, respectively. Moreover, A. australica MPH could effectively degrade various of OPs pesticides including methyl parathion, paraoxon, dichlorvos and chlorpyrifos in a few minutes, suggesting a great potential in the bioremediation of OPs pesticides.

Mechanism of interactions between organophosphorus insecticides and human serum albumin: Solid-phase microextraction, thermodynamics and computational approach

Organophosphates insecticides (OPs) are one of the major environmental pollutants and their interaction with human serum albumin (HSA) has been shown to have significant effects on their bioavailability which is related to toxicokinetics and toxicodynamics in human body. In this research, solid-phase microextraction methods were developed to analyse the free concentrations of three OPs (chlorpyrifos, parathion-methyl and malathion) in buffered HSA solution and that provide a useful method for the determination of binding affinity constants (K_a), binding forces and binding location. Polydimethylsiloxane fibers were selected for analysing the free concentrations of OPs, with an external calibration approach. Good linearities conducted in PBS solution were observed in the range of 0.0025-1.7 μmol L^-1 (R² = 0.9975) for chlorpyrifos, 1.0-27 μmol L^-1 (R² = 0.9974) for parathion-methyl, and 0.5-70 μmol L^-1 (R² = 0.9973)for malathion, respectively. The LODs for instrument response were 1 ng, 5 ng and 10 ng for chlorpyrifos, parathion-methyl and malathion, respectively. The K_a values for chlorpyrifos, parathion-methyl and malathion showed that they were positively correlated with hydrophobicity and negatively correlated with temperature. The OP binding sites on HSA were confirmed by site marker competition test and further proven by computational approaches. The recognition region of parathion-methyl was situated within residues 199-292 in subdomain IIA. Malathion bonded to residues 404-558 in subdomain IIIA. The mode of action between HSA-parathion-methyl and HSA-malathion is found to involve mainly by H-bonds, π-π stacking and hydrophobic effects. These results clearly demonstrate the noncovalent binding of OPs with HSA and provide new insight into solid-phase microextraction, thermodynamics and computational approaches.

Epigallocatechin-3-gallate (EGCG) protects the oocytes from methyl parathion-induced cytoplasmic deformities by suppressing oxidative and endoplasmic reticulum stress

Methyl parathion (MP) is a commonly used organophosphorus insecticide in commercial farming. It is well known that MP exposure can affect the function of nervous, respiratory, cardiovascular and reproductive systems. In our previous report we have demonstrated that MP exposure results in poor oocyte maturation and defective embryo development which is mainly mediated through oxidative stress. The present investigation was designed to explore whether using a potent free radical scavenger like Epigallocatechin-3-gallate (EGCG) can help in reducing the detrimental effects of MP on the oocytes. For the study, germinal vesicle (GV) stage oocytes collected from the ovaries of adult Swiss albino mice were subjected to in vitro maturation (IVM) in the presence or absence of MP (100 μg/mL) and/or EGCG (0.25 μM). MP significantly reduced the nuclear maturation rate, and resulted in poor cytoplasmic organization which was evident from the altered distribution pattern of mitochondria, endoplasmic reticulum and abnormal spindle organization. These changes were associated with significant elevation in oxidative stress and expression of ER stress markers such as 78 kDa Glucose regulated protein (GRP78) as well as X-box binding protein-1 (XBP1) in the oocytes. Further, the oocytes exposed to MP had lower activation rate and developmental potential. Supplementation of EGCG during IVM not only improved the nuclear maturation rate but also reduced the cytoplasmic abnormalities. These beneficial effects appear to be due to mitigation of oxidative and ER stress in oocytes. In conclusion, results of our study indicate that EGCG can help in alleviating MP-induced oocyte abnormalities.

Fabrication of Pt-Pd@ITO grown heterogeneous nanocatalyst as efficient remediator for toxic methyl parathion in aqueous media

In this study, nano-sized ITO supported Pt-Pd bimetallic catalyst was synthesized for the degradation of methyl parathion pesticide, a common extremely toxic contaminant in aqueous solution. On the characterization with different techniques, a beautiful scenario of honeycomb architecture composed of ultra-small nanoneedles or fine hairs was found. Average size of nanocatalyst also confirmed which was in the range of 3-5 nm. High percent degradation (94%) was obtained in 30 s using 1.5 × 10^- 1 mg of synthesized nanocatalyst, 0.5 mM NaBH₄, and 110 W microwave radiations power. Recyclability of nanocatalyst was efficient till 4th cycle observed during study of reusability. The supported Pt-Pd bimetallic nanocatalyst on ITO displayed many advantages over conventional methods for degradation of methyl parathion pesticide, such as high percent degradation, short reaction time, small amount of nanocatalyst, and multitime reusability. Graphical abstract Schematic illustration of reaction for degradation of methyl parathion.

Solubility and reactivity of surfactant-enhanced alkaline hydrolysis of organophosphorus pesticide DNAPL

The study presented in this paper evaluated the effectiveness of surfactants in enhancing mass removal of organophosphorus pesticides (OPPs) from soil under highly alkaline conditions and potential for enhancing in situ alkaline hydrolysis for treatment of OPPs, particularly parathion (EP3) and methyl parathion (MP3). In control and surfactant experiments, hydrolysis products EP2 acid, MP2 acid, and PNP were formed in non-stoichiometric amounts indicating instability of these compounds. MP3 and malathion were found to have faster hydrolysis rates than EP3 under the conditions studied. All surfactants evaluated increased solubility of OPPs under alkaline conditions with four nonionic alcohol ethoxylate products providing the greater affect over the polyglucosides, sulfonate, and propionate surfactants evaluated. The alcohol ethoxylates were shown to provide substantial mass removal of OPPs from soil. Hydrolysis rates were typically slower in the presence of surfactant, despite the relatively higher aqueous concentrations of OPPs; this was likely due to micellar solubilization of the OPPs which were therefore less accessible for hydrolysis. The results of this study support the use of surfactants for contaminant mass removal from soil, particularly under alkaline conditions, and may have implications for use of some surfactants in combination with other technologies for treatment of OPPs.

BHUS-5

A new isolate of genus Scytonema distinct from its closest relative cyanobacterium, Scytonema hofmanni was found efficient in the removal and degradation of organophosphorus (OP) pesticide, methyl parathion (MP). The cyanobacterial isolate was also capable of utilizing the phosphorus present in the MP following its degradation, which was evident from the increase in growth (chlorophyll content), biomass, protein content, and total phosphorus in comparison to cyanobacterium grown in phosphate-deficient cultures. The rapid removal of MP by the cyanobacterium during initial 6 hours of incubation was defined by the pseudo-second-order biosorption kinetics model, which indicated the involvement of chemosorption in initial removal of pesticide. Further, degradation of MP was also confirmed by the appearance of p-nitrophenol in the medium after 24 hours of incubation. Thus, the cyanobacterial isolate of Scytonema sp. BHUS-5 seems to be a potential bioremediation agent for the removal of OP pesticide, MP from the habitat.

Enhanced cholinergic transmission promotes recall in honeybees

The involvement of the cholinergic system in learning and memory in honeybees has been well established using olfactory conditioning. We examined the effect of Methyl Parathion (MeP), an acetylcholinesterase inhibitor of the organo-phosphate family, on the learning and recall of visual and olfactory discrimination tasks in honeybees. One of our expectations was to observe the effects induced by both the nicotinic and muscarinic systems, as the blocking of acetylcholinesterase should induce an increase in the activity of both systems. We were also interested in knowing whether the type of tasks could influence the results. The visual tasks involved learning to discriminate the orientation of gratings in a Y-maze; the olfactory task involved learning to discriminate odours in a proboscis extension reflex (PER) paradigm. The results indicate that MeP treatment enhances recall of learned tasks in the visual and olfactory domains, but it does not affect the acquisition phase in either domain. Surprisingly, MeP treatment led to muscarinic-like effects but failed to mimic the nicotinic-like effects already described in relation to learning phases in honeybees. Implications for the role of cholinergic pathways in learning and memory and the nature of their involvement are discussed, and a hypothesis relating to the organisation of the cholinergic system and the relationship between the nicotinic and muscarinic systems in honeybees is proposed. The results are also discussed in terms of their ecotoxicological consequences.

Biological detection and analysis of toxicity of organophosphate- and azadirachtin-based insecticides in Lathyrus sativus L

In this study, attention was paid to investigate the effect of organophosphate insecticides, profenofos 40% EC, methyl parathion (metacid) 50% EC, and neem-based product nimbecidine 0.03% EC (from Azadirachta indica) on somatic chromosomal behavior, level of leaf protein, and activity of antioxidant enzymes in Lathyrus sativus L., the leguminous herb. The experiments on somatic chromosomes of root tip cells of L. sativus L. revealed that most common type of abnormalities were anaphase bridge, chromosome fragment, breaks, giant interphase, etc. Also, the mitotic index reduced and abnormality index enhanced, which were directly proportional to the rise in concentration as well as time period of exposure of chemicals. The profenofos and metacid induced drastic changes in mitotic index when compared with nimbecidine. The electrophoretic studies of leaf protein of L. sativus L. showed alteration of some major and minor protein bands subjected to spraying of organophosphate insecticides and induced to synthesize additional high molecular mass protein compared to untreated control. Analysis of SOD, EST, and POD activity by non-denaturing polyacrylamide gel electrophoresis showed different patterns of the isoforms. Complete inhibition of EST was observed in profenofos-treated plants, while with metacid- and nimbecidine-treated plants EST was suppressed. Induction and/or increased activities of SOD and POD were generally enhanced. Our present study not only provides the important information for better understanding of the toxic and tolerance mechanisms, but as well can be used as a bio-indicator for contamination by pesticides, which could cause genetic instabilities of natural plant populations and in crop varieties.

Parameters affecting microwave-assisted extraction of organophosphorus pesticides from agricultural soil

This work describes an optimised method for the determination of six representative organophosphorus pesticides (OPPs) (diazinon, parathion, methyl pirimiphos, methyl parathion, ethoprophos, and fenitrothion) in agricultural soils. The method is based on microwave-assisted extraction using a water-methanol modified mixture for desorption and simultaneous partitioning on n-hexane (MAEP), together with gas chromatography-flame photometric detection (GC-FPD). To improve GC-FPD signals (peak intensity and shape) olive oil was used effectively as a "matrix mimic". The optimisation of the extraction method was achieved in two steps: an initial approach through experimental design and principal component analysis where recovery of compounds using a water-methanol mixture ranged from 54 to 77%, and the second one by studying the addition of KH2PO4 to the extracting solution where recoveries were significantly increased, molecular replacing of OPPs from adsorption sites by phosphate being the probable extraction mechanism. Under optimised conditions, recoveries of pesticides from different soils were higher than 73%, except for methyl parathion in some soils, with SD equal or lower than 11% and detection limits ranging from 0.004 to 0.012 microg g(-1). The proposed method was used to determine OPPs in soil samples from different agricultural zones of Chile.

Children's exposure to pesticides used in homes and farms

Commercial and residential use of pesticides is common in El Paso, Texas, especially in agricultural areas. Recently, concerns have arisen about the type of pesticides used by residents because of the ease with which methyl parathion can be obtained from the neighboring border city of Juarez in Chihuahua, Mexico. Survey data were collected regarding residents' perceptions about pesticide safety and use of pesticides, and their preferred source of health information. The authors assessed the number of respondents who were using the illegal pesticide methyl parathion, known locally as polvo de avion (airplane dust) as well as their beliefs concerning the safety and efficacy of pesticides. The study found that 88.7 percent (133 of 150) used some type of pesticide, and of these, 9.8 percent (13 of 133) reported using methyl parathion. Biological/environmental testing would be useful to assess use of methyl parathion and to determine the types of pesticides used by local farmers.

Lack of cross-resistance to indoxacarb in insecticide-resistant Spodoptera frugiperda (Lepidoptera: Noctuidae) and Plutella xylostella (Lepidoptera: Yponomeutidae)

Two field strains of the fall armyworm, Spodoptera frugiperda (JE Smith), collected from corn in north Florida showed high resistance to carbaryl (626- and 1159-fold) and moderate resistance to parathion-methyl (30- and 39-fold) as compared with a laboratory susceptible strain. A field strain of the diamondback moth, Plutella xylostella (L.) collected from cabbage in north Florida and selected for 20 generations with permethrin showed high resistance to permethrin (987-fold) as compared with a susceptible strain. However, in all instances, no cross-resistance to indoxacarb, a novel oxidiazine insecticide, was observed in these two species. Biochemical studies revealed that, in S. frugiperda, activities of detoxification enzymes (microsomal oxidase, glutathione S-transferase and general esterase) were significantly higher in the field strains than in the susceptible strain, indicating that these detoxification enzymes were not actively involved in the resistance to indoxacarb. The lack of cross-resistance between indoxacarb and permethrin in P. xylostella further supports the notion that the mode of action of these insecticides on the insect sodium channel is different.

Functional effects of amino acid substitutions within the large binding pocket of the phosphotriesterase OpdA fromAgrobacteriumsp. P230

The phosphotriesterase OpdA from Agrobacterium sp. P230 has about 10-fold higher activity for dimethyl organophosphate (OP) insecticides, than its homologue from Flavobacterium sp. ATCC27551, organophosphate hydrolase (OPH). OpdA shows about 10% amino acid sequence divergence from OPH and also has a 20 residue C-terminal extension. Here we show that the difference in kinetics is largely explained by just two amino acid differences between the two proteins. A truncated form of OpdA demonstrated that the C-terminal extension has no effect on its preference for dimethyl organophosphate substrates. Chimeric proteins of OPH and OpdA were then analysed to show that replacement of a central region of OpdA sequence, which encodes the residues in the large subsite of the active site, with the homologous region in OPH decreased the activity of OpdA towards dimethyl OPs, to values close to those for OPH. Site-directed mutagenesis in this region identified two differences between the proteins, Y257H and F272L (with the OpdA residues first) as being responsible for this reduction. These two differences were also responsible for the increased activity of OpdA towards the diisopropyl organophosphate, diisopropyl fluorophosphate, relative to OPH. Molecular modelling of triethyl phosphate in the active site of OpdA confirmed a reduction in the size of the large subsite relative to OPH.

Flight behavior of methyl-parathion-resistant and -susceptible western corn rootworm (Coleoptera: Chrysomelidae) populations from Nebraska

Relative flight behavior of methyl-parathion-resistant and -susceptible western corn rootworm, Diabrotica virgifera virgifera LeConte populations, was studied as part of a larger effort to characterize the potential impact of insecticide resistance on adult life history traits and to understand the evolution and spread of resistance. A computer interfaced actograph was used to compare flight of resistant and susceptible individuals, and flight of resistant individuals with and without prior exposure to methyl-parathion. In each case, mean trivial and sustained flight durations were compared among treatments. In general, there were few differences in trivial or sustained flight characteristics as affected by beetle population, insecticide exposure, sex, or age and there were few significant interactions among variables. Tethered flight activity was highly variable and distributions of flight duration were skewed toward flights of short duration. Tethered flight activity was similar among resistant and susceptible beetles with the exception that susceptible beetles initiated more flights per beetle than resistant beetles. After sublethal exposure to methyl-parathion, total flight time, total trivial flight time, and mean number of flights per resistant beetle declined significantly. Because long-range flight was uncommon, short- to medium-duration flights may play an important role in determining gene flow and population spread of resistant D. v. virgifera. These results suggest that organophosphate-resistant beetles can readily move and colonize new areas, but localized selection pressure (e.g., management practices) and exposure to methyl-parathion may contribute to the small-scale differences in resistance intensity often seen in the field.

Immunological assessment of an insecticide resistance-associated esterase in the Western corn rootworm

In previous investigations, we have determined that organophosphate resistance in the western corn rootworm, Diabrotica virgifera virgifera, is at least partially attributed to a group of non-specific carboxylesterases referred to as group II. Antiserum raised against a purified 66-kDa group II esterase is specific for the denatured enzyme. This antiserum reacts similarly with both beetle homogenates from resistant and susceptible populations, although there is much higher signal intensity in immunoblots of resistant relative to susceptible beetles. These results suggest that overproduction of group II esterases is the underlying basis of esterase-mediated resistance in D. v. virgifera by demonstrating that (1) group II esterases are immunologically indistinguishable between the resistant and susceptible populations, and (2) the intensity differences are due to increased group II esterase proteins in the resistant population. The diagnostic potential of immunological-based assays was tested with a traditional diagnostic concentration bioassay and a biochemical-based native PAGE assay. Significant correlations were observed among all three diagnostic assays (regression coefficients ranging from 0.95 to 0.96). These results demonstrate the importance of the 66-kDa protein as a resistance-associated biochemical marker, thus emphasizing the potential for 66-kDa protein-targeted immunoassays in resistance monitoring programs.

Detoxification of organophosphorus compounds by recombinant carboxylesterase from an insecticide-resistant mosquito and oxime-induced amplification of enzyme activity

Currently, bioremediation is a promising approach to the degradation of environmental pollutants. Here we describe the application of the recombinant insecticide-resistant mosquito carboxylesterase B1 to detoxify organophosphorous compounds. However, this approach has a major limitation: 1:1 stoichiometry of the enzyme detoxification of those organophosphorous compounds containing no carboxyl ester bonds, such as paraoxon, chlorpyrifos etc. To improve the effectiveness of the enzymatic detoxification of organophosphorous compounds, we used a combination of carboxylesterase B1 with the uncharged oxime diacetylmonoxime. It was demonstrated that the repeated addition of 20 times the molar concentration of paraoxon to carboxylesterase B1 every 2 h in the presence of 4 mM diacetylmonoxime did not result in significant inhibition of the enzyme. The stoichiometry of enzyme detoxification was higher than 45:1 and 20:1 for paraoxon and chlorpyrifos, respectively. The kinetic experiments on reactivation of organophosphorus compound-inhibited carboxylesterase B1 showed that the half-life for paraoxon- and chlorpyrifos-inhibited carboxylesterase reactivation is 0.75 and 0.88 h, respectively. Using the recombinant insecticide-resistant mosquito carboxylesterase with oxime is an effective approach for detoxification of organophosphorous compounds.

Characterization of general esterases from methyl parathion-resistant and -susceptible populations of western corn rootworm (Coleoptera: Chrysomelidae)

A consistent correlation between elevated esterase activity and methyl parathion resistance among Nebraska western corn rootworm, Diabrotica virgifera virgifera LeConte, populations has previously been documented. Characterization of general esterase activity using naphtholic esters as model substrates indicated that differences between resistant and susceptible strains could be maximized by optimizing assay conditions. The optimal conditions identified here were similar to those reported for other insect species. The majority of general esterase activity was found in the cytosolic fractions of resistant populations, whereas the activity was more evenly distributed between cytosolic and mitochondrial/nuclear fractions in the susceptible population. General esterase activity was predominately located in the adult thorax and abdomen. Although there were significant differences in general esterase activities between resistant and susceptible populations, the differences exhibited in single beetle activity assays did not provide sufficient discrimination to identify resistant individuals. In contrast, single larva activity assays provided greater discrimination and could be considered as an alternative to traditional bioassay techniques.

Detoxification of methyl-parathion pesticide in aqueous solutions by electrochemical oxidation

Commercial methyl-parathion (MeP) was detoxified using an electrochemical method that employed a Ti/Pt anode and stainless steel 304 as cathode. Sodium chloride was added as electrolyte and the mixture was passed through an electrolytic cell for 2 h. Due to the strong oxidizing potential of the produced chemicals, the organic pollutants were wet oxidized to carbon dioxide and water. A number of experiments were run at laboratory scale. Reductions of COD and BOD(5) were both over 80% and the mean energy consumption was 18-8 kWh per kg(-1) COD reduced (COD(r)). The degradation of MeP was more effective when the pH of the brine solution was in the acid range than when it was in the alkaline range. From the results it can be concluded that electrolysis could be used as an oxidation pre-treatment stage for detoxification of toxic wastes with MeP.

Inheritance of methyl-parathion resistance in Nebraska western corn rootworm populations (Coleoptera: Chrysomelidae)

Field populations of western corn rootworm, Diabrotica virgifera virgifera LeConte, were collected from three different sites (York Co., Phelps Co., and Saunders Co.) in Nebraska during 1996. Adult bioassays of these three populations were conducted with different concentrations of methyl-parathion and at a diagnostic concentration (1.0 microg/ml) to determine resistance levels among these populations. Self and reciprocal crosses were made between the two resistant and one susceptible laboratory-reared populations. Dose-responses and dominance ratios calculated for the four reciprocal crosses indicated that resistance was incompletely dominant in both strains, although in one of the strains there was an indication of sex linkage. However, evaluation of native polyacrylamide gels stained for nonspecific esterases and nonspecific esterase activity of parents and F1 progeny of the crosses suggested that esterase inheritance was completely dominant and autosomal. The results of this study were inconclusive with regard to the precise nature of inheritance, because the bioassays and esterase assays could not discriminate between heterozygotes and homozygotes. However, they do provide insight into the potential for developing simple diagnostic assays to assess resistance frequencies. Based on the inheritance studies described in this investigation, we can begin to generate information on specific genetic factors that dictate the evolutionary divergence of discrete resistant populations and facilitate modeling efforts designed to approximate the movement of genes for resistance among populations.

Diagnostic assays based on esterase-mediated resistance mechanisms in western corn rootworms (Coleoptera: Chrysomelidae)

Resistance to methyl-parathion among Nebraska western corn rootworm, Diabrotica virgifera virgifera LeConte, populations is associated with increased hydrolytic metabolism of an organophosphate insecticide substrate. An electrophoretic method to identify resistant individuals based on the staining intensity of esterase isozymes on nondenaturing polyacrylamide gels was developed. Three groups of esterases (I, II, and III) were visible on the gels, but only group II esterase isozymes were intensified in resistant populations. A total of 26 and 31 field populations of western corn rootworms from Nebraska (in 1998 and 1999, respectively) were assessed with nondenaturing polyacrylamide gel electrophoresis (PAGE) assays and diagnostic concentration bioassays. Significant correlations were observed between the two diagnostic assays. Group II esterase isozymes provide a reliable biochemical marker for detection of methyl-parathion resistance in individual western corn rootworms and a tool for monitoring the frequency of resistant individuals in field populations.

The role of glutathione S-transferases in the detoxification of some organophosphorus insecticides in larvae and pupae of the yellow mealworm, Tenebrio molitor (Coleoptera: Tenebrionidae)

The correlation between the natural levels of glutathione S-transferase (GST) and the tolerance to the organophosphorus insecticides parathion-methyl and paraoxon-methyl, as well as the interaction of affinity-purified enzyme and the insecticides were investigated in order to collect further information on the role of the glutathione S-transferase system as a mechanism of defence against insecticides in insects. The studies were carried out on the larvae and pupae of the coleopteran Tenebrio molitor L, which exhibit varying natural levels of GST activity. Stage-dependent susceptibility of the insect against insecticides was observed during the first 24 h. However, 48 h after treatment, the KD50 value increased significantly due to the recovery of some individuals. Simultaneous injection of insecticide with compounds which inhibit GST activity in vitro caused an alteration in susceptibility of insects 24 or 48 h post-treatment, depending on stage and insecticide used. Inhibition studies combined with competitive fluorescence spectroscopy revealed that the insecticides probably bind to the active site of the enzyme, thus inhibiting its activity towards 1-chloro-2,4-dinitrobenzene in a competitive manner. High-performance liquid chromatography and gas chromatography revealed that T molitor GST catalyses the conjugation of the insecticides studied to a reduced form of glutathione (GSH). From the above experimental results, it is considered that GST offers a protection against the organophosphorus insecticides studied by active site binding and subsequent conjugation with GSH.

Treatment thresholds for stink bugs (Hemiptera: Pentatomidae) in cotton

The green stink bug, Acrosternum hilare (Say), the southern green stink bug, Nezara viridula (L), and the brown stink bug, Euschistus servus (Say), were predominant phytophagous Pentatomidae detected during 1995-1997 in cotton in South Carolina. These species occurred in similar numbers in conventional and transgenic cotton 'NuCOTN33B', containing the gene for expression of CryIA(c) delta-endotoxin of Bacillus thuringiensis Berliner variety kurstaki. Adult stink bugs moved into cotton from wild and cultivated alternate hosts during July, and reproducing populations usually were detected in cotton from late July into September. Applications of either methyl parathion (0.56 kg [AI]/ha) directed for stink bugs or lambda-cyhalothrin (0.037 kg [AI]/ha) or cyfluthrin (0.056 kg [AI]/ha) for control of cotton bollworm, Helicoverpa zea (Boddie), provided effective control of pentatomids in NuCOTN33B or conventional 'DP5415' and increased yields compared with untreated plots. Fiber quality did not differ among treated or untreated plots of NuCOTN33B. The ground-cloth technique was used to estimate populations of stink bugs, and data indicated that treatment at one bug per 2 m of row adequately protected cotton from yield loss due to stink bug damage. Observations on boll damage indicated that treatment might be necessary if >20-25% reveal internal symptoms of feeding injury during mid- to late season. More detailed damage thresholds should be developed to complement an approach based on population monitoring. This study validated current recommendations for management of pentatomids in cotton, demonstrated the necessity of threshold use for stink bugs in transgenic cultivars expressing endotoxin from B. thuringiensis, and provided insight into further development of management options for pentatomids in the crop.

Comparison of pheromone-mediated mating disruption and conventional insecticides for management of tufted apple bud moth (Lepidoptera: Tortricidae)

Large-plot studies were used to compare pheromone-mediated mating disruption and conventional insecticide applications for management of tufted apple bud moth, Platynota idaeusalis (Walker), in North Carolina in 1993 and 1994. Pheromone trap catches were reduced in mating disruption blocks, and traps placed in the lower stratum of the canopy had a higher level of trap capture reduction compared with traps placed in the upper stratum. First-generation tufted apple bud moth exposure to either pheromones for mating disruption or insecticides affected second generation pheromone trap catches in the lower and upper canopy. More second generation male moths were caught in pheromone traps placed in the upper compared with the lower canopy in blocks treated with pheromones for mating disruption during the first generation, whereas the opposite was true in blocks treated with insecticides during the first generation. Despite reduced trap catches in pheromone-treated blocks, egg mass densities were not reduced in these blocks compared with insecticide-treated blocks. Furthermore, fruit damage was not significantly different between mating disruption blocks and conventionally treated blocks in orchards with relatively low populations of tufted apple bud moth, but damage was greater in mating disruption blocks in orchards with higher moth densities.

New esterase enzymes involved in organophosphate resistance in Culex pipiens (Diptera: Culicidae) from Guang Zhou, China

Organophosphate (OP) insecticides have been used widely to control Culex pipiens L. populations and this has led to the emergence of OP-resistance. Predominantly, resistance in Cx. pipiens is caused by over-production of nonspecific esterases, such as Est beta 1(1) and Est alpha 2(1)/beta 2(1). These esterases confer multiple resistance to organophosphorus and carbamate insecticides. To define the esterases in Chinese Cx. pipiens, restriction fragment-length polymorphism analysis was performed at the esterase beta locus. A new esterase haplotype (Est beta 8) was found. Starch gel electrophoresis indicated that Est beta 8 was coelevated with a novel Est alpha 8. This article reports Est alpha 8/beta 8 esterase-mediated resistance in Cx. pipiens complex.

Linkage of acetylcholinesterase insensitivity to methyl parathion resistance in Heliothis virescens

Resistance to methyl parathion insecticide has evolved in the tobacco budworm, Heliothis virescens, and several biochemical mechanisms have been identified in various strains. Reduced sensitivity of acetylcholinesterase to inhibition by methyl paraoxon, the active metabolite of the insecticide, is controlled by a single autosomal locus, AceIn. We report that AceIn is genetically linked to methyl parathion resistance, which is expressed as a dominant gene. Methyl parathion-resistant and -susceptible strains were intercrossed and the resulting mixed colony was heterozygous at AceIn. Pair matings from the mixed colony were chosen, on the basis of AceIn genotype only, to establish strains Ace-S and Ace-R, homozygous for AceInSS and AceInRR, respectively. The Ace-R strain was 15.9-fold resistant compared to AceInSS, while hybrid progeny expressed 24.6-fold resistance, demonstrating dominant inheritance of resistance. When progeny of the backcross (Ace-S x Ace-R) to Ace-S were exposed to a discriminating dose of methyl parathion, 24.5% survived as predicted by the model of a single resistance gene. Survivors displayed only the AceInRS genotype, demonstrating a linkage disequilibrium which was highly significant. Assuming that no other resistance genes are linked closely to AceIn, it would appear that AceIn is a powerful gene for resistance, conferring a resistance proportional to the slower rate of inhibition in the resistant enzyme. The contribution of AceIn to resistance relative to detoxicative genes and the possible interaction of resistance genes are discussed.

[Summaries on the first draft of the EHC monographs in 1990]

The first drafts of the EHC monographs in 1990 were summarized into Japanese. The chemicals consist of hexachlorocyclopentadiene, trichlorfon, fenitrothion, methylparathion, trichloroethane, platinum and selected platinum salts, di(2-ethylhexyl)phthalate, partially halogenated chlorofluorocarbons, methyl ethyl ketone, and propachlor.

Response of nuclear polyhedrosis virus-resistant Spodoptera frugiperda larvae to other pathogens and to chemical insecticides

Selection in the laboratory for Spodoptera frugiperda (Sf) resistant to nuclear polyhedrosis virus (NPV) affected the susceptibility of the insect to certain other mortality agents, including a chemical insecticide. Median lethal concentrations (LC50S) and associated statistics were compared for several mortality agents between colonies of NPV-resistant and -susceptible (control) insects. Compared to the susceptible insects, the NPV-resistant insects were cross-resistant to the S. frugiperda granulosis virus and to the Autographa californica NPV based on nonoverlap of 95% fiducial limits of the LC50S. The NPV-resistant insects were significantly more susceptible to methyl parathion than the control insects. The two colonies of S. frugiperda did not differ significantly in their response to Bacillus thuringiensis, Vairimorpha necatrix, or carbaryl. The cross-resistance experiments were based on per os exposure of the insects to the pathogens and insecticides; the susceptibility of the resistant and control insects did not differ significantly when the Sf NPV was injected into the hemocoel or when methyl parathion was applied topically.

Field disposal of methyl parathion using acidified powdered zinc

The degradation of methyl parathion in soil with various amounts of acidified powdered zinc under field conditions was studied. Treatment was progressively more effective with increasing amounts of zinc. Disappearance of parent compound was followed for 2 1/2 years. The expected conversion product aminomethyl parathion and its N-methyl derivative were formed. In addition, N,N-dimethylamino, and the azo and azoxy condensation products were characterized by high resolution mass spectrometry. Aminomethyl parathion was shown to be identical to an authentic standard. The other specific positional isomers were considered likely, but were not proven by mass spectrometry. Structure elucidation was made with high resolution mass spectrometry, using the direct insertion probe, and with gas chromatography/low resolution mass spectrometry.