Water-Regulated Mechanisms for Degradation of Pesticides Paraoxon and Parathion by Phosphotriesterase: Insight from QM/MM and MD Simulations.

The enzymatic degradation of pesticides paraoxon (PON) and parathion (PIN) by phosphotriesterase (PTE) has been investigated by QM/MM calculations and MD simulations. In the PTE-PON complex, Znα and Znß in the active site are five- and six-coordinated, respectively, while both zinc ions are six coordinated with the Znα -bound water molecule (WT1) for the PTE-PIN system. The hydrolytic reactions for PON and PIN are respectively driven by the nucleophilic attack of the bridging-OH- and the Znα -bound water molecule on the phosphorus center of substrate, and the two-step hydrolytic process is predicted to be the rate-limiting step with the energy spans of 13.8 and 14.4 kcal/mol for PON and PIN, respectively. The computational studies reveal that the presence of the Znα -bound water molecule depends on the structural feature of substrates characterized by P=O and P=S, which determines the hydrolytic mechanism and efficiency for the degradation of organophosphorus pesticides by PTE.

Ag(I) Pyridine-Amidoxime Complex as the Catalysis Activity Domain for the Rapid Hydrolysis of Organothiophosphate-Based Nerve Agents: Mechanistic Evaluation and Application.

Two novel Ag(I) complexes containing synergistic pyridine and amidoxime ligands (Ag-DPAAO and Ag-PAAO) were first designed as complex monomers. Taking advantage of the molecular imprinting technique and solvothermal method, molecular imprinted porous cross-linked polymers (MIPCPs) were developed as a robust platform for the first time to incorporate Ag-PAAO into a polymer material as a recyclable catalyst. Advantageously, the observed pseudo first-order rate constant (kobs) of MIPCP-Ag-PAAO-20% for ethyl-parathion (EP) hydrolysis is about 1.2 × 104-fold higher than that of self-hydrolysis (30 °C, pH = 9). Furthermore, the reaction mechanism of the MIPCP-containing Ag-PAAO-catalyzed organothiophosphate was analyzed in detail using density functional theory and experimental spectra, indicating that the amidoxime can display dual roles for both the key coordination with the silver ion and nucleophilic attack to weaken the P-OAr bond in the catalytic active site.

Activation of persulfate and removal of ethyl-parathion from soil: Effect of microwave irradiation.

Advanced persulfate oxidation technology is widely used in organic pollution control of super fund sites. In recent years, microwave radiation has been proven a promising method for persulfate activation. However, most of the prior works were focused on the treatment of polluted water, but there are few reports aiming at contaminated sites, especially the knowledge of using microwave activated persulfate technology to repair pesticide-contaminated sites. In this study, an effective activation/oxidation method for the remediation of pesticide-contaminated soil, i.e., microwave/persulfate, was developed to treat soil containing ethyl-parathion. The concentration of persulfate, reaction temperature, and time were optimised. The results showed that up to 77.32% of ethyl-parathion was removed with the addition of 0.1 mmol·persulfate·g-1 soil under the microwave temperature of 60 °C. In comparison, 19.43% of ethyl-parathion was removed at the same reaction temperature under the condition of water bath activated persulfate. Electron paramagnetic resonance (EPR) spectroscopy combined with spin-trapping technology was used to detect reactive oxidation species, and OH and SO4- were observed in the microwave/persulfate system. Quenching experiments suggested that ethyl-parathion was degraded by the generated OH and SO4-. Paraoxon, phenylphosphoric acid, 4-nitrophenol, dimethyl ester phosphate, and some alkanes were the dominant oxidative products identified by gas chromatography-mass spectrometry (GC-MS) analysis. A possible pathway for ethyl-parathion degradation was proposed in this study. The results obtained serve as the guidance to the development of remediation technologies involving persulfate and microwave for soil contaminated by organic contaminants such as pesticides.

Impact of Pesticide Type and Emulsion Fat Content on the Bioaccessibility of Pesticides in Natural Products.

There is interest in incorporating nanoemulsions into certain foods and beverages, including dips, dressings, drinks, spreads, and sauces, due to their potentially beneficial attributes. In particular, excipient nanoemulsions can enhance the bioavailability of nutraceuticals in fruit- and vegetable-containing products consumed with them. There is, however, potential for them to also raise the bioavailability of undesirable substances found in these products, such as pesticides. In this research, we studied the impact of excipient nanoemulsions on the bioaccessibility of pesticide-treated tomatoes. We hypothesized that the propensity for nanoemulsions to raise pesticide bioaccessibility would depend on the polarity of the pesticide molecules. Bendiocarb, parathion, and chlorpyrifos were therefore selected because they have Log P values of 1.7, 3.8, and 5.3, respectively. Nanoemulsions with different oil contents (0%, 4%, and 8%) were fabricated to study their impact on pesticide uptake. In the absence of oil, the bioaccessibility increased with increasing pesticide polarity (decreasing Log P): bendiocarb (92.9%) > parathion (16.4%) > chlorpyrifos (2.8%). Bendiocarb bioaccessibility did not depend on the oil content of the nanoemulsions, which was attributed to its relatively high water-solubility. Conversely, the bioaccessibility of the more hydrophobic pesticides (parathion and chlorpyrifos) increased with increasing oil content. For instance, for chlorpyrifos, the bioaccessibility was 2.8%, 47.0%, and 70.7% at 0%, 4%, and 8% oil content, respectively. Our findings have repercussions for the utilization of nanoemulsions as excipient foods in products that may have high levels of undesirable non-polar substances, such as pesticides.

In vivo efficacy of the Reactive Skin Decontamination Lotion (RSDL®) kit against organophosphate and carbamate pesticides.

In this study, we assessed the efficacy of the Reactive Skin Decontamination Lotion (RSDL®) Kit against parathion and aldicarb pesticide dermal exposure in a guinea pig model. The pesticides inhibit acetylcholinesterase (AChE) leading to signs and symptoms of hyperactivity of organs due to accumulation of acetylcholine. The RSDL Kit has been shown to physically remove and chemically degrade chemical warfare agents. Degradation occurs from a nucleophilic substitution reaction between an active ingredient in the RSDL lotion, potassium 2,3-butanedione monoximate (KBDO), with susceptible sites in these compounds. In the present study, guinea pigs dermally exposed to parathion and aldicarb were decontaminated with RSDL to mitigate the toxic effects of the pesticides. It is observed that animals exposed to 749 mg/kg of parathion (n = 3) died within 24 h without RSDL decontamination; however, RSDL-treated animals (n = 3) showed only mild signs of neurotoxicity. The RSDL-treated animals had an AChE inhibition of 0-58% while the untreated animals had up to 86% inhibition. Similarly, RSDL has been demostrated to prevent aldicarb neurotoxicity effects. The percent inhibition of AChE activity during the 24 h post challenge of 9 mg aldicarb/kg of animal weight ranged from 25% to 61% with severe signs of intoxication while only up to 5% with mild or no signs of intoxication in the case of RSDL-decontaminated animals. Generally, it has been shown that the toxic effects of the organophosphate and carbamate pesticides can be prevented via decontamination using the RSDL Kit.

An integrated nanocatalyst combining enzymatic and metal-organic framework catalysts for cascade degradation of organophosphate nerve agents.

An integrated nanocatalyst (INC), denoted OPH@MIL-100(Fe), was synthesized by immobilizing a biocatalyst onto a metal-organic framework (MOF)-based catalyst, which can cascadingly degrade organophosphate nerve agents to 4-aminophenol (4-AP) and result in a sharp decrease of their toxicity up to 208-fold.

Carbon and hydrogen isotope analysis of parathion for characterizing its natural attenuation by hydrolysis at a contaminated site.

The applicability of compound-specific isotope analysis (CSIA) for assessing in situ hydrolysis of parathion was investigated in a contaminated aquifer at a former pesticide wastes landfill site. Stable isotope analysis of parathion extracted from groundwater taken from different monitoring wells revealed a maximum enrichment in carbon isotope ratio of +4.9‰ compared to the source of parathion, providing evidence that in situ hydrolysis took place. Calculations based on the Rayleigh-equation approach indicated that the natural attenuation of parathion was up to 8.6% by hydrolysis under neutral and acidic conditions. In degradation experiments with aerobic and anaerobic parathion-degrading microbes, no carbon and hydrogen isotope fractionation of parathion were observed. For the first time, CSIA has been applied for the exclusive assessment of the hydrolysis of phosphorothioate-containing organophosphorus pesticides at a contaminated field site.

Kinetic studies of the AOP radical-based oxidative and reductive destruction of pesticides and model compounds in water.

Absolute second-order rate constants for hydroxyl radical (HO) reaction with four organophosphorus pesticides, malathion, parathion, fenthion and ethion, and a suite of model compounds of structure (EtO)2P(S)-X (where X = Cl, F, SH, SEt, OCH2CF3, OEt, NH2, and CH3) were measured using electron pulse radiolysis and transient absorption techniques. Specific values were determined for these four pesticides as k = (3.89 ±â€¯0.28) x 109, (2.20 ±â€¯0.15) x 109, (2.02 ±â€¯0.15) x 109 and (2.93 ±â€¯0.10) x 109 M-1 s-1, respectively, at 20 ±â€¯2 °C. The corresponding Brönsted plot for all these compounds demonstrated that the HO oxidation reaction mechanism for the pesticides was consistent with the model compounds, attributed to initial HO-adduct formation at the P(S) moiety. For malathion, steady-state 60Co radiolysis and 31P NMR analyses showed that hydroxyl radical-induced oxidation produces the far more potent isomalathion, but only with an efficiency of 4.9 ±â€¯0.3%. Analogous kinetic measurements for the hydrated electron induced reduction of these pesticides gave specific rate constants of k = (3.38 ±â€¯0.14) x 109, (1.38 ±â€¯0.10) x 109, (1.19 ±â€¯0.12) x 109 and (1.20 ±â€¯0.06) x 109 M-1 s-1, respectively, for malathion, parathion, fenthion and ethion. Model compound measurements again supported a single reduction reaction mechanism, proposed to be electron addition at the PS bond to form the radical anion. These results demonstrate, for the first time, that the radical-based treatment of organophosphorus contaminated waters may present a potential toxicological risk if advanced oxidative processes are used.

A sensitive chemiluminescence enzyme immunoassay based on molecularly imprinted polymers solid-phase extraction of parathion.

The chemiluminescence enzyme immunoassay (CLEIA) method responds differently to various sample matrices because of the matrix effect. In this work, the CLEIA method was coupled with molecularly imprinted polymers (MIPs) synthesized by precipitation polymerization to study the matrix effect. The sample recoveries ranged from 72.62% to 121.89%, with a relative standard deviation (RSD) of 3.74-18.14%.The ratio of the sample matrix-matched standard curve slope rate to the solvent standard curve slope was 1.21, 1.12, 1.17, and 0.85 for apple, rice, orange and cabbage in samples pretreated with the mixture of PSA and C18. However, the ratio of sample (apple, rice, orange, and cabbage) matrix-matched standard-MIPs curve slope rate to the solvent standard curve was 1.05, 0.92, 1.09, and 1.05 in samples pretreated with MIPs, respectively. The results demonstrated that the matrices of the samples greatly interfered with the detection of parathion residues by CLEIA. The MIPs bound specifically to the parathion in the samples and eliminated the matrix interference effect. Therefore, the CLEIA method have successfully applied MIPs in sample pretreatment to eliminate matrix interference effects and provided a new sensitive assay for agro-products.

Environmentally-friendly in situ plated bismuth-film electrode for the quantification of the endocrine disruptor parathion in skimmed milk.

An in situ bismuth-film electrode (BiFE) together with square-wave cathodic voltammetry (SWCV) was used to determine the concentration of the endocrine disruptor parathion in skimmed milk. The experimental conditions (deposition time, deposition potential and Bi (III) concentration) were optimized for the preparation of the BiFE. A glassy carbon electrode was used as the substrate. The selection of the chemical composition of the supporting electrolyte and the solution pH was aimed at improving the reduction of parathion at the BiFE surface. In addition, the parameters of the square-wave cathodic voltammetry were adjusted to improve the sensor performance. A cathodic current identified at -0.523 V increased linearly with the parathion concentration in the range of 0.2-2.0 µmol L(-1) (R=0.999). The sensitivity of the calibration curve obtained was 4.09 µA L µmol(-1), and the limits of detection (LOD) and quantification (LOQ) were 55.7 nmol L(-1) and 169.0 nmol L(-1), respectively. The performance of the sensor was tested using a sample of skimmed milk with parathion added. The same determination was carried out by UV-vis spectroscopy and the results obtained were used for the statistical evaluation of the data obtained.

Simultaneous detection of imidacloprid and parathion by the dual-labeled time-resolved fluoroimmunoassay.

A highly sensitive direct dual-labeled time-resolved fluoroimmunoassay (TRFIA) to detect parathion and imidacloprid simultaneously in food and environmental matrices was developed. Europium (Eu(3+)) and samarium (Sm(3+)) were used as fluorescent labels by coupling separately with L1-Ab and A1P1-Ab. Under optimal assay conditions, the half-maximal inhibition concentration (IC50) and limit of detection (LOD, IC10) were 10.87 and 0.025 µg/L for parathion and 7.08 and 0.028 µg/L for imidacloprid, respectively. The cross-reactivities (CR) were negligible except for methyl-parathion (42.4 %) and imidaclothiz (103.4 %). The average recoveries of imidacloprid ranged from 78.9 to 104.2 % in water, soil, rice, tomato, and Chinese cabbage with a relative standard deviation (RSD) of 2.4 to 11.6 %, and those of parathion were from 81.5 to 110.9 % with the RSD of 3.2 to 10.5 %. The results of TRFIA for the authentic samples were validated by comparison with gas chromatography (GC) analyses, and satisfactory correlations (parathion: R (2) = 0.9918; imidacloprid: R (2) = 0.9908) were obtained. The results indicate that the dual-labeled TRFIA is convenient and reliable to detect parathion and imidacloprid simultaneously in food and environmental matrices.

Altering the substrate specificity of methyl parathion hydrolase with directed evolution.

Many organophosphates (OPs) are used as pesticides in agriculture. They pose a severe health hazard due to their inhibitory effect on acetylcholinesterase. Therefore, detoxification of water and soil contaminated by OPs is important. Metalloenzymes such as methyl parathion hydrolase (MPH) from Pseudomonas sp. WBC-3 hold great promise as bioremediators as they are able to hydrolyze a wide range of OPs. MPH is highly efficient towards methyl parathion (1 × 10(6) s(-1) M(-1)), but its activity towards other OPs is more modest. Thus, site saturation mutagenesis (SSM) and DNA shuffling were performed to find mutants with improved activities on ethyl paraxon (6.1 × 10(3) s(-1) M(-1)). SSM was performed on nine residues lining the active site. Several mutants with modest activity enhancement towards ethyl paraoxon were isolated and used as templates for DNA shuffling. Ultimately, 14 multiple-site mutants with enhanced activity were isolated. One mutant, R2F3, exhibited a nearly 100-fold increase in the kcat/Km value for ethyl paraoxon (5.9 × 10(5) s(-1) M(-1)). These studies highlight the 'plasticity' of the MPH active site that facilitates the fine-tuning of its active site towards specific substrates with only minor changes required. MPH is thus an ideal candidate for the development of an enzyme-based bioremediation system.

Kinetic studies of heterogeneous reactions of particulate phosmet and parathion with NO3 radicals.

Organophosphorous pesticides (OPPs) are ubiquitous pollutants in the atmospheric environment with adverse effects on human health. In this study, heterogeneous kinetics of particulate phosmet and parathion with NO3 radicals were investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer were used to monitor online the decays of particulate OPPs and reference compound, respectively. Reactive uptake coefficients of NO3 radicals on phosmet and parathion particles were (0.12±0.03) and (0.14±0.04), respectively, calculated according to the measured OPPs loss ratios and the average NO3 concentrations. Additionally, the average effective rate constants for heterogeneous reactions of particulate phosmet and parathion with NO3 radicals measured under experimental conditions were (2.80±0.16)×10(-12) and (2.97±0.13)×10(-12) cm(3) molecule(-1) s(-1), respectively. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne OPPs particles.

Chemodynamics of methyl parathion and ethyl parathion: adsorption models for sustainable agriculture.

The toxicity of organophosphate insecticides for nontarget organism has been the subject of extensive research for sustainable agriculture. Pakistan has banned the use of methyl/ethyl parathions, but they are still illegally used. The present study is an attempt to estimate the residual concentration and to suggest remedial solution of adsorption by different types of soils collected and characterized for physicochemical parameters. Sorption of pesticides in soil or other porous media is an important process regulating pesticide transport and degradation. The percentage removal of methyl parathion and ethyl parathion was determined through UV-Visible spectrophotometer at 276 nm and 277 nm, respectively. The results indicate that agricultural soil as compared to barren soil is more efficient adsorbent for both insecticides, at optimum batch condition of pH 7. The equilibrium between adsorbate and adsorbent was attained in 12 hours. Methyl parathion is removed more efficiently (by seven orders of magnitude) than ethyl parathion. It may be attributed to more available binding sites and less steric hindrance of methyl parathion. Adsorption kinetics indicates that a good correlation exists between distribution coefficient (Kd) and soil organic carbon. A general increase in Kd is noted with increase in induced concentration due to the formation of bound or aged residue.

Construction of genetically engineered bacteria that degrades organophosphorus pesticide residues and can be easily detected by the fluorescence.

Organophosphorus compounds (OPs) are widely used in agriculture and industry and there is increased concern about their toxicological effects in the environment. Bioremediation can offer an efficient and cost-effective option for the removal of OPs. Herein, we describe the construction of a genetically engineered microorganism (GEM) that can degrade OPs and be directly detected and monitored in the environment using an enhanced green fluorescent protein (EGFP) fusion strategy. The coding regions of EGFP, a reporter protein that can fluoresce by itself, and organophosphorus hydrolase (OPH), which has a broad substrate specificity and is able to hydrolyse a number of organophosphorus pesticides, were cloned into the expression vector pET-28b. The fusion protein of EGFP-OPH was expressed in E. coli BL21 (DE3) and the protein expression reached the highest level at 11 h after isopropyl beta-D-thiogalactopyranoside induction. The fluorescence of the GEM was detected by fluorescence spectrophotometry and microscopy, and its ability to degrade OPs was determined by OPH activity assay. Those GEM that express the fusion protein (EGFP and OPH) exhibited strong fluorescence intensity and also potent hydrolase activity, which could be used to degrade organophosphorus pesticide residues in the environment and can also be directly monitored by fluorescence.

Parathion hydrolysis revisited: in situ aqueous kinetics by (1)h NMR.

The kinetics of parathion (PTH) decomposition into para-nitrophenolate (pNP) and O,O-diethylthiophosphate (DETP) were measured in high-pH aqueous solutions at 20 °C by proton nuclear magnetic resonance spectroscopy ((1)H NMR). Reaction rates were determined over a 16 h observation time, in solutions with NaOD concentrations of 5.33 mM, 33.33 mM, and 100 mM, with NaCl added to fix ionicity. The pseudo-first-order rate constants for these systems were determined to be 1.9 × 10(-4) min(-1), 1.4 × 10(-3) min(-1), and 3.8 × 10(-3) min(-1) respectively. The slope of the linear plot of these rates against OD(-) concentration yielded the second-order hydrolysis rate constant 3.90 × 10(-5) mM(-1) min(-1), valid over this pH range from 10.5 to 13. The data agree with some, and contradict other, earlier work. Our fitting procedure included background levels and allowed us to not only obtain reliable kinetic results but also to measure residual pNP and DETP impurity levels.

Effect of ionising radiation on polyphenolic content and antioxidant potential of parathion-treated sage (Salvia officinalis) leaves.

The γ-irradiation effects on polyphenolic content and antioxidant capacity of parathion-pretreated leaves of Salvia officinalis plant were investigated. The analysis of phenolic extracts of sage without parathion showed that irradiation decreased polyphenolic content significantly (p<0.05) by 30% and 45% at 2 and 4kGy, respectively, compared to non-irradiated samples. The same trend was observed for the Trolox equivalent antioxidant capacity (TEAC), as assessed by the anionic DPPH and cationic ABTS radical-scavenging assays. The antioxidant potential decreased significantly (p<0.01) at 2 and 4kGy, by 11-20% and 40-44%, respectively. The results obtained with a pure chlorogenic acid solution confirmed the degradation of phenols; however, its TEAC was significantly (p<0.01) increased following irradiation. Degradation products of parathion formed by irradiation seem to protect against a decline of antioxidant capacity and reduce polyphenolic loss. Ionising radiation was found to be useful in breaking down pesticide residues without inducing significant losses in polyphenols.

Structural requirements of organophosphorus insecticides (OPI) to inhibit chicken yolk sac membrane kynurenine formamidase related to OPI teratogenesis.

This paper provides new information related to the mechanism of OPI (organophosphorus insecticides) teratogenesis. The COMFA (comparative molecular field analysis) and COMSIA (comparative molecular similarity indices analysis) suggest that the electrostatic and steric fields are the best predictors of OPI structural requirements to inhibit in ovo chicken embryo yolk sac membrane kynurenine formamidase, the proposed target for OPI teratogens. The dominant electrostatic interactions are localized at nitrogen-1, nitrogen-3, nitrogen of 2-amino substituent of the pyrimidinyl of pyrimidinyl phosphorothioates, and the oxygen of crotonamide carbonyl in crotonamide phosphates. Bulkiness of the substituents at carbon-2 and carbon-6 of the pyrimidinyls and/or N-substituents and carbon-3 substituents of crotonamides are the steric structural components that contribute to superiority of those OPI as in ovo inhibitors of kynurenine formamidase.

Analytical and toxicological studies of decomposition of insecticide parathion after gamma-irradiation and ozonation.

The decomposition of the widely used organophosphorus pesticide parathion was carried out in aqueous solutions by the use of gamma-irradiation from a 60Co source or ozonation by means of an ozone generator, and by combined processes of ozonation and radiolysis. Factors affecting the parathion decomposition as well formation and decomposition of the main by-products, including irradiation dose, length of ozonation time, and presence of common scavengers, were investigated. The most efficient was found to be the gamma-irradiation process combined with a short ozonation period; about 1 kGy irradiation dose was sufficient to decompose the pesticide in 15 mg/L solutions. Chemical studies of the decomposition of parathion were accompanied by monitoring of toxicity changes of irradiated solutions with the Microtox test.

Partitioning and diffusion of parathion in human dermis.

A previously developed method employing the use of a dialysis membrane in series with human dermis tissue mounted in side-by-side diffusion cells was utilized to observe the effects of the presence of soluble proteins in the donor compartment on the measured transport parameters of parathion. In the presence of the dialysis membrane the partition coefficient was significantly lower and the diffusion coefficient significantly higher than those determined in its absence; however, the difference was less than that previously determined for the more highly protein bound compound, diclofenac. The result suggests the dialysis membrane method is important for studying permeants that are more than about 87% bound to soluble proteins in the dermis. The results are discussed in the context of a predictive model for partitioning and transport of low molecular weight solutes in human dermis.