Toxic Organophosphate Pesticide Research Articles

Potential of Chemical Compounds from Coloring Plants (Stenochlaena palutris) as Competitors for ALK Protein Damage Due To Pesticide Exposure: In Silico Study

Pesticide active ingredients have widespread toxicity effects on target and non-target organisms. Continuous exposure to pesticides causes cancer. Kelakai is thought to have potential cytotoxic activity against the growth of cancer cells. The aim of this research is to examine the potential activity of chemical compounds on Anaplastic Lymphoma Kinase (ALK) proteins exposed to organophosphate pesticides in silico. Protein and ligand preparation with the Chimera program, Docking using SwissDock, as well as virtual screening using the pkCSM web and ProTox. Ethion and neophytadiene have the most negative ∆G values of -8.62 kcal/mol and -8.39 kcal/mol, respectively. The binding site for ethion and neophytadiene compounds with the ALK protein is right at the active site of the ALK protein. Ethion is the most toxic organophosphate pesticide and has the potential to be cytogenic. Neophytadiene from kelakai compounds has the potential to act as a competitor in inhibiting the ALK protein. The similarity in the type and number of binding residues in ethion and neophytadiene in the ALK protein indicates competition between ethion and neophytadiene.

Fibrous Zr-MOF Nanozyme Aerogels with Macro-Nanoporous Structure for Enhanced Catalytic Hydrolysis of Organophosphate Toxins.

Metal-organic frameworks (MOFs) with Lewis acid catalytic sites, such as zirconium-based MOFs (Zr-MOFs), comprise a growing class of phosphatase-like nanozymes that can degrade toxic organophosphate pesticides and nerve agents. Rationally engineering and shaping MOFs from as-synthesized powders into hierarchically porous monoliths is essential for their use in emerging applications, such as filters for air and water purification and personal protection gear. However, several challenges still limit the production of practical MOF composites, including the need for sophisticated reaction conditions, low MOF catalyst loadings in the resulting composites, and poor accessibility to MOF-based active sites. To overcome these limitations, a rapid synthesis method is developed to introduce Zr-MOF nanozyme coating into cellulose nanofibers, resulting in the formation of processable monolithic aerogel composites with high MOF loadings. These composites contain Zr-MOF nanozymes embedded in the structure, and hierarchical macro-micro porosity enables excellent accessibility to catalytic active sites. This multifaceted rational design strategy, including the selection of a MOF with many catalytic sites, fine-tuning the coating morphology, and the fabrication of a hierarchically structured monolithic aerogel, renders synergistic effects toward the efficient continuous hydrolytic detoxification of organophosphorus-based nerve agent simulants and pesticides from contaminated water.

Degradation of parathion methyl by reactive sorption on the cerium oxide surface: The effect of solvent on the degradation efficiency

A simple and easily scalable “wet” procedure was used to prepare nanocrystalline cerium oxide capable of destroying the toxic organophosphate pesticide parathion methyl. The synthetic procedure consists of the direct precipitation of cerous salt with aqueous ammonia in the absence of CO 2 . The prepared cerium oxide was able to decompose the organophosphate compounds both in nonpolar (e.g., heptane) and polar aprotic (e.g., acetonitrile) solvents. However, in solvents with hydrogen-bond donating ability, the –OH groups on the cerium oxide surface were solvated and inactivated. The preferential solvation model was used to express the experimental dependencies of the cerium oxide degradation efficiency on the composition of the water-acetonitrile mixture. In certain solvent systems, some empirical polarity scales, such as the alpha-scale or the Dimrodth-Richardt parameter E T (30), may be correlated with the degradation efficiency of cerium oxide.

A SURVEY BASED ON THE USE OF IMIDACLOPRID ON GREEN LEAFY VEGETABLES IN REMOTELY LOCATED SAGAR, INDIA

The low literacy level of the vegetable growers in the selected region of India is responsible for the use of highly toxic organophosphate pesticides on green leafy vegetables. Although in the Indian market imidacloprid (less toxic) is available but due to its high price and less effectiveness compared to that of organophosphates is not preferred to control pests on green leafy vegetables. The present research is a survey-based study designed to know the insecticide management practice among insecticide dealers, vegetable growers and comparison of obtained information with chromatographic results. The combination of survey and instrumental method (micellar liquid chromatographic technique) was utilized to determine whether the information collected from vegetable growers and insecticide dealers were similar and signicantly correlated with analytical data or not. Among the selected 48 samples of green leafy vegetables, imidacloprid was detected only in 6 samples. The survey of the insecticide dealers and vegetable growers conrmed that the vegetable growers used toxic organophosphates pesticides instead of less toxic imidacloprid. Survey data collected from vegetable growers and pesticide dealers were also tested by chromatographic method and a signicant correlation was found between them, which clearly demonstrates the minimum use of safe insecticide (imidacloprid). Imidacloprid insecticide was detected on green leafy vegetables after a preliminary survey of vegetable growers and pesticide dealers. Survey results revealed the use of potentially harmful pesticides other than imidacloprid which are banned from using in vegetables. Analytical results showed signicantly less use of imidacloprid on green leafy vegetables.

Natural dynamics and residues of pymetrozine for typical rice-growing areas of China

Pymetrozine has replaced toxic organophosphate pesticides previously used for controlling pests of rice crops in China. Existing data on its environmental behavior are usually related to studies on artificial plots that do not adequately address the natural dynamics and residues in actual field conditions. Therefore, studies under field conditions were carried out to investigate the natural dynamics and residues of pymetrozine in two typical rice-growing areas in China – Hunan and Guangxi provinces.Samples of paddy soil and water were collected in relation to spraying events in the study areas. The quick, easy, cheap, effective, rugged and safe (QuEChERS) method was used to extract pymetrozine residues from the samples by a Waters ACQUITY UPLC (Milford, MA, USA) system interfaced with a triple-quadrupole mass spectrometer (Xevo TQ-D, Waters Corp., USA).The initial deposition of pymetrozine in paddy soils was higher than in paddy waters in both areas. The decay of pymetrozine followed an exponential trend consistent with the first order kinetics. The half-life of pymetrozine in paddy water was determined to be 3.0 and 3.8 days, whereas the half-life in soil was 3.8 and 3.5 days in the Guangxi and Hunan samples, respectively. The decline rates of pymetrozine in paddy soil and paddy water in this field study were faster than those conducted under non-field conditions reported in previous studies.Compared to other pesticides used in China as reported in previous studies, the environmental persistence of pymetrozine in both paddy water and soils in Guangxi and Hunan provinces is very low. This has important implications for the use of pymetrozine in agricultural systems globally.

Determination of disulfoton and its metabolites in agricultural products by dispersive soild phase extraction-ultra high performance liquid chromatography-tandem mass spectrometry

基于超高效液相色谱-串联质谱(UHPLC-MS/MS)建立定量分析乙拌磷及其5个代谢物(乙拌磷砜、乙拌磷亚砜、内吸磷-S、内吸磷-S-砜、内吸磷-S-亚砜)的方法,应用该方法分析其在农产品(豌豆、芦笋、小麦、咖啡豆和花生)中的残留量。对样品前处理及色谱条件进行优化,样品经过乙腈涡旋提取(小麦、咖啡豆和花生先加水润湿),经盐析分层,取上清液经50 mg C18、50 mg PSA和50 mg NH2混合分散固相萃取净化后,经Thermo Syncronis C18色谱柱(150 mm×2.1 mm, 5 μm)分离,柱温40 ℃,进样量2 μL,以水和乙腈为流动相梯度洗脱后,采用ESI源,在正离子扫描和多反应监测(MRM)模式下检测,外标法定量。结果表明,乙拌磷及其代谢物在2.0~200.0 μg/L范围内线性关系良好,相关系数(R2)≥0.9981。方法的检出限(LOD)为0.02~2.0 μg/kg,并以最小添加水平5 μg/kg为定量限(LOQ)。乙拌磷及其代谢物在豌豆、芦笋、小麦、咖啡豆和花生中5、100、1000 μg/kg 3个添加水平下的平均回收率为75.0%~110.0%,相对标准偏差(RSD)为0.7%~14.9%,方法的准确度和精密度符合农药残留测定。应用建立的方法对市售的40份小麦样品和40份花生样品进行检测,均低于方法的检出限。该方法具有操作简单、快速、灵敏、准确的特点,适用于谷物、油料、蔬菜等多种农产品中乙拌磷及其代谢物的残留检测。

Enhanced solar light photocatalytic performance of Fe-ZnO in the presence of H2O2, S2O82−, and HSO5− for degradation of chlorpyrifos from agricultural wastes: Toxicities investigation

This study reported Fe doped zinc oxide (Fe-ZnO) synthesis to degrade chlorpyrifos (CPY), a highly toxic organophosphate pesticide and important sources of agricultural wastes. Fourier transform infrared, X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopic analyses showed successful formation of the Fe-ZnO with highly crystalline and amorphous nature. Water collected from agricultural wastes were treated with Fe-ZnO and the results showed 67% degradation of CPY by Fe-ZnO versus 39% by ZnO at 140 min treatment time. Detail mechanism involving reactive oxygen species production from solar light activated Fe-ZnO and their role in degradation of CPY was assessed. Use of H2O2, peroxydisulfate (S2O82−) and peroxymonosulfate (HSO5−) with Fe-ZnO under solar irradiation promoted removal of CPY. The peroxides yielded hydroxyl (OH) and sulfate radical (▪) under solar irradiation mediated by Fe-ZnO. Effects of several parameters including concentration of pollutant and oxidants, pH, co-existing ions, and presence of natural organic matter on CPY degradation were studied. Among peroxides, HSO5− revealed to provide better performance. The prepared Fe-ZnO showed high reusability and greater mineralization of CPY. The GC-MS analysis showed degradation of CPY resulted into several transformation products (TPs). Toxicity analysis of CPY as well as its TPs was performed and the formation of non-toxic acetate imply greater capability of the treatment technology.

A hollow visible-light-responsive surface molecularly imprinted polymer for the detection of chlorpyrifos in vegetables and fruits

A visible-light-responsive azobenzene derivative, 3,5-dichloro-4-((2,6-dichloro-4-(methacryloyloxy)phenyl)diazenyl)benzoic acid, was synthesized and used as the functional monomer to fabricate a visible-light-responsive core-shell structured surface molecularly imprinted polymer (PS-co-PMAA@VSMIP). After removal of the sacrificial PS-co-PMAA core, a hollow structured surface molecularly imprinted polymer (HVSMIP) was obtained. Both the PS-co-PMAA@VSMIP and HVSMIP were used for the detection of chlorpyrifos, a moderately toxic organophosphate pesticide. They exhibited good visible-light-responsive properties (550 nm for trans→cis and 440 nm for cis→trans isomerization for an azobenzene chromophore) in ethanol/water (9:1, v/v). Compared with the PS-co-PMAA@VSMIP, the HVSMIP had a larger surface area, pore volume, binding capacity, imprinting effect, maximum chemical binding capacity, dissociation constant, and photo-isomerization rate. The HVSMIP was applied to detect trace chlorpyrifos in fruit and vegetable samples. This was achieved by measuring the trans→cis rate constant of the HVSMIP in the sample solution, with good recoveries, low relative standard deviations, and a low detection limit.

Room-temperature synthesis of nanoceria for degradation of organophosphate pesticides and its regeneration and reuse.

A simple low-temperature water-based and one-pot synthesis was developed for the preparation of nanocrystalline CeO2 that was used for degradation of the toxic organophosphate pesticide parathion methyl. By changing the reaction temperature in the range from 5 °C to 95 °C, several properties (i.e., crystallinity, grain size and surface area) of nanoceria can be easily controlled. The catalytic decomposition of parathion methyl to its degradation product 4-nitrophenol was highly dependent on the CeO2 preparation temperature. It was demonstrated that at low temperature (i.e. 5 °C), CeO2 with very small crystallites (<2 nm) and high surface area can be obtained. For practical use, it was demonstrated that highly crystalline CeO2 can be prepared at room-temperature (30 °C) in at least 100 g batches. It was shown that precipitated nanoceria had high thermal stability and its post-synthesis annealing up to 400 °C did not significantly alter the material properties and hence the catalytic activity. Furthermore, as shown by the reusability tests, the sorbent can be reactivated by simply washing with water which demonstrated its durability.

Catalytic Chemosensing Assay for Selective Detection of Methyl Parathion Organophosphate Pesticide.

Herein, a catalytic chemosensing assay (CCA), based on a bimetallic complex, [RuII (bpy)2 (CN)2 ]2 (CuI I)2 (bpy=2,2'-bipyridine), is described. This complex integrates a task-specific catalyst (CuI -catalyst) and a signaling unit ([RuII (bpy)2 (CN)2 ]) to specifically hydrolyze methyl parathion, a highly toxic organophosphate (OP) pesticide. The bimetallic complex catalyzed the hydrolysis of the phosphate ester to generate o,o-dimethyl thiophosphate (DTP) anion and 4-nitrophenolate. Intrinsically, 4-nitrophenolate absorbed UV/Vis light at λmax =400 nm, creating the first level of the chemosensing signal. DTP interacted with the original complex to displace the chromophore, [RuII (bpy)2 (CN)2 ], which was monitored by spectrofluorometry; this was classified as the second level of chemosensing signal. By integrating both spectroscopic and spectrofluorometric signals with a simple AND logic gate, only methyl parathion was able to provide a positive response. Other aromatic and aliphatic OP pesticides (diazinon, fenthion, meviphos, terbufos, and phosalone) and 4-nitrophenyl acetate provided negative responses. Furthermore, owing to the metal-catalyzed hydrolysis of methyl parathion, the CCA system led to the detoxification of the pesticide. The CCA system also demonstrated its catalytic chemosensing properties in the detection of methyl parathion in real samples, including tap water, river water, and underground water.

Synthesis of kaolinite/magnetic molecularly imprinted polymers for solid phase extraction of chlorpyrifos

Chlorpyrifos is a highly toxic organophosphate pesticide that is widely used in global agriculture and household applications. It persists in the environment in, for example, rivers, lakes and the soil. A simple way to detect chlorpyrifos is by the use of molecularly imprinted polymers (MIP), but MIPs lack the capacity for phase separation. Magnetic molecularly imprinted polymers (MMIPs) have attracted attention for the detection of organic molecules. In this study, Fe3O4 magnetic nanoparticles, known as superparamagnetic iron oxide nanoparticles, were synthesized with kaolinite. Methacrylic acid is encapsulated as a functional group to obtain a MIP structure for the detection of chlorpyrifos. The crosslinker and initiator used in this work were ethylene glycol dimethacrylate and azobisisobutyronitrile, respectively. The morphology, chemical bonding and crystal structure as well as magnetic properties of the synthesized MMIPs were characterized through field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffractometry and vibrating-sample magnetometry, respectively. Finally, the absorption and removal of chlorpyrifos from the synthesized MMIPs was confirmed by high-performance liquid chromatography.

Graphene oxide encapsulated 3D porous chalcopyrite (CuFeS2) nanocomposite as an emerging electrocatalyst for agro-hazardous (methyl paraoxon) detection in vegetables

Methyl paraoxon (MOX) is a highly toxic organophosphate pesticide. It is recently reported that, MOX can enter the human body through ingestion, inhalation, or by dermal penetration. Due to its high non-degradability, it can bind to the tissues of fruits and vegetables. When it is consumed, it can imposes sub-chronic and chronic diseases, by the inhibition of acetylcholinesterase in human metabolism. Therefore, for the first time, we reported a detection of non-enzymatic electrochemical sensor based on 3D porous phase graphene oxide sheets encapsulated chalcopyrite (GOS@CuFeS2) nanocomposite. Hence, the development of reliable sensors for the real-time detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies. As synthesized GOS@CuFeS2 nanocomposite film screen-printed carbon modified electrode (SPCE) displays excellent electrocatalytic ability towards MOX. Under optimized working conditions, the modified electrode provides linear response range from 0.073 to 801.5 μM. The detection limit was obtained as 4.5 nM. The sensor displayed outstanding sensitivity as 17.97 μA μM−1 cm−2. This composite could be a promising electrode modifier for electrocatalysis. Finally, the GOS@CuFeS2 nanocomposite modified electrode shows greater real-time practicality in vegetable real samples. The obtained moral parameters from the developed method were compared with the authenticated HPLC results.

Enzymatic detoxification: a sustainable means of degrading toxic organophosphate pesticides and chemical warfare nerve agents

AbstractOrganophosphorus (OP) compounds are highly toxic molecules mainly used as pesticides. OP compounds also include nerve gases used in the past as chemical warfare agents and collectively OP pesticides and nerve gases are referred to as nerve agents (NA). An intensive, widespread use of pesticides since the 20th century has resulted in the emergence of an urgent global issue concerning both environment and human health. In addition, past terroristic acts and the recent dramatic events in Syria highlighted more than ever the need to explore applicable strategies for the sensing, decontamination and detoxification of these compounds in stored bulks, on critical surfaces and media (food, water and air) and for in vivo prophylaxes and therapies.OP compounds, act as covalent inhibitors of acetylcholinesterase (AChE) in the nerve system of vertebrates, thus posing a substantial threat to the ecosystem. In order to address a strong demand for the establishment of an environmental monitoring system and remediation process for NA, an increasing number of studies have been focused on the enzymatic degradation in vitro. Use of enzymes for detoxification and decontamination of toxic NA could provide a long‐term benefit as it is environmentally friendly compared with conventional methods such as chemical treatments and incineration. This review presents an overview of the current state of enzymatic detoxification research against NA. This includes the detailed characterization and protein engineering for the improvement in NA‐degrading activities of such enzymes. Research on biosensors for NA detection and identification, although important in the field, has not been treated in this review. Instead special attention has been paid to the Phosphotriesterase‐Like‐Lactonase (PLL) enzyme family. Several PLL enzymes have been isolated from hyperthermophilic Archaea or thermophilic/extremophilic Bacteria, and exhibit exceptional thermal stability. Extremophilic PLLs therefore hold promise for potential industrial application towards NA detoxification. © 2018 Society of Chemical Industry

Toxicological effects of trichlorfon on hematological and biochemical parameters in Cyprinus carpio L. following thermal stress

Trichlorfon is a moderately toxic organophosphate pesticide that is widely used in aquaculture. This study investigated the effects of trichlorfon on hematological parameters, biochemical factors, and stress reaction in Cyprinus carpio L. The fish were exposed to acute concentrations of trichlorfon (0, 0.5, 1.0, 2.0, and 4.0 mg L−1) at 25 °C and 15 °C for 1 and 2 weeks, after which several parameters were evaluated to assess the effects of the pesticide. Significant decreases were observed in red blood cell (RBC) Count, hemoglobin (Hb) level, hematocrit (Ht), and plasma protein levels after each exposure period. In contrast, notable increases in mean corpuscular volume (MCV), mean cell hemoglobin (MCH), calcium, and glucose levels were observed in the trichlorfon-treated groups. Additionally, there were significant increases in the plasma levels of glutamate-oxaloacetate transaminase (GOT), glutamate-pyruvate transaminase (GPT), and alkaline phosphatase (ALP) following the exposure to trichlorfon. Furthermore, the results showed a relationship between toxic stress and increment in HSP70 and cytochrome P450 1A (CYP1A) expression over time. Ht, MCV, MCH, and the value of other biochemical parameters were quite lower at 15 °C than their corresponding values were at 25 °C, which indicated the decreased physical activity at 15 °C. The results of the present work indicate that acute exposure to trichlorfon and thermal stimulus could damage erythropoietic tissue. Additionally, hepatocytes function and physiological mechanisms could be impaired. Ht, glucose, GOT, GPT, HSP70, and CYP1A levels might be useful biomarkers of trichlorfon toxicity in contaminated aquatic ecosystems.

Copper-Containing Catalytic Amyloids Promote Phosphoester Hydrolysis and Tandem Reactions.

Self-assembly of short de novo designed peptides gives rise to catalytic amyloids capable of facilitating multiple chemical transformations. We show that catalytic amyloids can efficiently hydrolyze paraoxon, a widely used, highly toxic organophosphate pesticide. Moreover, these robust and inexpensive metal-containing materials can be easily deposited on various surfaces producing catalytic flow devices. Finally, functional promiscuity of catalytic amyloids promotes tandem hydrolysis/oxidation reactions. High efficiency discovered in a very small library of peptides suggests an enormous potential for further improvement of catalytic properties both in terms of catalytic efficiency and substrate scope.

Fatal poisoning by terbufos following occupational exposure

Context: Terbufos (TBF) is a class Ia (extremely hazardous) organophosphate pesticide (OP) and its distribution in industrialized countries has been severely restricted. Thus, acute occupational poisoning is rather uncommon. However, it still occurs in rural areas of some developing countries, where the sale of TBF is not controlled and its use is thus not properly regulated. We report a case of a 43-year-old female farmer who died after applying TBF granules.Case: The patient died within 3 h after applying 20 bags of 5% TBF granules (900 g per bag). Investigation showed that her personal protective equipment (PPE) did not provide effective protection against dermal and inhalational exposure. Postmortem analysis revealed extremely low red blood cell acetylcholinesterase activity. Toxicological analysis of TBF showed 1.45 × 10−2 μg/ml in the heart blood and 0.17 μg/g in the liver.Discussions: This patient died as a result of toxicity from dermal and inhalational exposure to TBF. Over-application, improper equipment, inadequate and defective PPE, and lack of hygienic precautions were all contributing factors.Conclusions: TBF is a highly toxic OP. Inadequate regulatory control, improper environmental application, and ineffective PPE resulted in a fatal human exposure.

Plasma Cholinesterase Levels of Nepalese Farmers Following Exposure to Organophosphate Pesticides.

Background:Farmers in developing countries use highly toxic organophosphate pesticides. Thus, the aim of this study was to compare plasma cholinesterase (PChE) enzyme activity before and after exposure to organophosphate pesticides in a real-life setting.Methods:This was a prospective study conducted on 25 farmers spraying organophosphate pesticide in their farm. The PChE level was measured and clinical signs and symptoms of toxicity were asked before and immediately after spraying.Results:The mean level of PChE before and after spraying was 1.41 and 1.29 IU/L, respectively (8.51% decreased). Farmers reported more clinical signs and symptoms of intoxication after spraying pesticides.Conclusions:Increase in acute intoxication signs/symptoms and decrease in PChE indicate a serious public health problem among farmers who use organophosphate pesticides. Appropriate training to the farmers is needed to reduce exposure to organophosphate pesticide.

Probiotic Lactobacillus rhamnosus Reduces Organophosphate Pesticide Absorption and Toxicity to Drosophila melanogaster.

The consequences of environmental pesticide pollution due to widespread usage in agriculture and soil leaching are becoming a major societal concern. Although the long-term effects of low-dose pesticide exposure for humans and wildlife remain largely unknown, logic suggests that these chemicals are not aligned with ecosystem health. This observation is most strongly supported by the agricultural losses associated with honeybee population declines, known as colony collapse disorder, in which pesticide usage is a likely trigger. Lactobacilli are bacteria used as beneficial microorganisms in fermented foods and have shown potentials to sequester and degrade environmental toxins. This study demonstrated that commonly used probiotic strains of lactobacilli could sequester, but not metabolize, organophosphate pesticides (parathion and chlorpyrifos). This Lactobacillus-mediated sequestration was associated with decreased intestinal absorption and insect toxicity in appropriate models. These findings hold promise for supplementing human, livestock, or apiary foods with probiotic microorganisms to reduce organophosphate pesticide exposure.

Reproductive toxicity of quinalphos on female albino rats:Effects on ovary and uterus

Quinalphos is a toxic organophosphate pesticide having a wide applicability to control pests in a number of vegetable crops like ladyfinger, brinjal, cauliflower etc. due to its good penetrative properties and long residual action in animals. The present investigation was carried out to determine its toxic effects on reproduction in the female albino rats. Technical quinalphos (2 mg/kg body weight) was administered orally to female albino rats for 15 and 30 days respectively. The weight of ovary decreased significantly in 30 day treated group. In the same group the corpus luteum also decreased significantly. The histologic observations of the ovary revealed the presence of less number of healthy follicles and more number of atretic follicles. There was a non significant decrease in the surface follicles and corpus luteum of treated rats. Gross morphology of uterus had shown significant increase in epithelial cell height and changes in lumen length even. There was a decline in the number of uterine glands with decreased thickness of myometrium. Hence quinalphos at dose concentration of 2mg/kg body weight is toxic for female reproduction.

Kinetics and speciation of paraoxon hydrolysis by zinc(II)–azamacrocyclic catalysts

Four Zn2+–azamacrocyclic complexes were investigated for their ability to catalyze the hydrolysis of the toxic organophosphate (OP) pesticide diethyl paraoxon. Of the four complexes studied, Zn2+–1,5,9-triazacyclododecane (Zn2+–[12]aneN3) was found to be the most effective catalyst with a pseudo-first order reaction rate of k=6.08±0.23×10−4min−1. Using 31P nuclear magnetic resonance (NMR) spectroscopy, the two products diethyl phosphate (DEP) and ethyl (4-nitrophenyl) phosphate (E4NPP) were identified for both catalyzed and background hydrolysis of paraoxon. Reaction rate and selectivity for formation of the non-toxic DEP were observed to correlate with catalyst pKa. The rate of formation of toxic E4NPP, however, was independent of both the presence and nature of the catalyst. The potential roles of buffer concentration and product inhibition were also investigated. Background hydrolysis at elevated reaction temperatures (50°C) displayed no preference for DEP over that of E4NPP despite substantial differences between the characteristics (i.e., pKa values) of the two leaving groups (ethoxide vs. 4-nitrophenoxide anions). As with previous observations of these types of metal-catalyzed hydrolyses, we invoke the formation of a trigonal bipyramidal-like transition state involving a Zn-coordinated phosphate bond, with the leaving group at the apical position and the incoming HO− anion approaching from the opposite end. Kinetic rates for catalytic hydrolysis display an overwhelming propensity for DEP formation, and suggest the importance of steric restrictions on transition state structure, namely a concerted arrangement of the azamacrocycle in opposition to the bulky 4-nitrophenoxy group.