The sources, fate, and toxicity of chemical warfare agent degradation products

All-Weather Dry Decontaminant Polymer-H2O2 Complex for HD Degradation

Hydrogen peroxide (H2O2) is a highly effective decontaminant against chemical warfare agents (CWAs) when present both in a liquid and as a solid powder. For the latter, this can be in the form of H2O2 being complexed to a polymer, such as polyvinylpyrrolidone (PVP). While a H2O2-PVP complex is indeed effective at decontaminating CWAs, it is vulnerable to environmental conditions such as high relative humidities (RH), which can dissociate the H2O2 from the complex before it is given the opportunity to react with CWAs. In this paper, we demonstrate that the cross-linked version of PVP forms a highly stable complex with H2O2, which can withstand both high (40 °C) and low (-20 °C) temperatures as well as maintain stability at high RH up to 90% over several days. Collectively, this lays the framework for processing the H2O2-PVP complex in a variety of form factors that can maintain efficacy under a wide range of real-world environmental conditions.

A Miniaturized Method for Evaluating the Dynamic Gas-Phase Adsorption and Degradation of Sarin on Porous Adsorbents at Different Humidity Levels

Metal organic frameworks based on zirconium nodes (Zr-MOFs) have impressive adsorption capacities, and many can rapidly hydrolyze toxic organophosphorus nerve agents. They could thus potentially replace commonly used adsorbents in respiratory filters. However, current test methodologies are poorly adapted to screen the large number of available MOFs, and data for nerve agent adsorption by MOFs are scarce. This paper presents a miniaturized method for assessing the capacity of Zr-MOFs for dynamic gas phase adsorption and degradation of sarin (GB) into the primary hydrolysis product isopropyl methyl phosphonic acid (IMPA). The method was validated by comparing the dynamic adsorption capacities of activated carbon (AC) and NU-1000 for GB under dry and humid conditions. Under dry conditions, unimpregnated AC had a greater capacity for GB uptake (0.68 ± 0.06 g/g) than pelletized NU-1000 (0.36 ± 0.03 g/g). At 55% relative humidity (RH), the capacity of AC was largely unchanged (0.72 ± 0.10 g/g) but that of NU-1000 increased slightly, to 0.46 ± 0.10 g/g. However, NU-1000 exhibited poor water retention at 55% RH. For both adsorbents, the degree of hydrolysis of GB into IMPA was significantly greater at 55% RH than under dry conditions, but the overall degree of hydrolysis was limited in both cases. Further tests at higher relative humidities are needed to fully evaluate the ability of NU-1000 to degrade GB after adsorption from the gas phase. The proposed experimental setup uses very small amounts of both adsorbent material (20 mg) and toxic agent, making it ideal for assessing new MOFs. However, future methodological challenges are reliable generation of sarin at higher RH and exploring sensitive methods to monitor degradation products from nerve agents in real-time.

Determination of tissue distribution of VX and its metabolites EMPA and EA-2192 in various rat tissues by LC-ESI-MS/MS after phosphotriesterase treatment

Phosphotriesterases (PTE) are a new and promising approach for the treatment of organophosphate poisoning, since the current therapy of such intoxications shows some limitations. A previous rat in vivo study confirmed the therapeutic effect of PTE, which were specifically designed for VX breakdown, and demonstrated rapid degradation of VX in whole blood samples. The present study now focuses on the degradation of VX and its distribution in organ tissues of the animals used in the aforementioned study. In order to gain a broader overview, we have extended the investigations to the VX metabolites EA-2192 and EMPA by using methods developed for an LC-ESI-MS/MS system. Applying these methods, we were able to verify the effectiveness of the PTE treatment and gained an overview of VX tissue distribution in poisoned but untreated rats.

In Vitro Characterization and Rescue of VX Metabolism in Human Liver Microsomes

Venomous agent X (VX) is an organophosphate acetylcholinesterase (AChE) inhibitor, and although it is one of the most toxic AChE inhibitors known, the extent of metabolism in humans is not currently well understood. The known metabolism in humans is limited to the metabolite identification from a single victim of the Osaka poisoning in 1994, which allowed for the identification of several metabolic products. VX has been reported to be metabolized in vitro by paraoxonase-1 and phosphotriesterase, although their binding constants are many orders of magnitude above the LD50, suggesting limited physiologic relevance. Using incubation with human liver microsomes (HLMs), we have now characterized the metabolism of VX and the formation of multiple metabolites as well as identified a Food and Drug Administration-approved drug [ethylenediaminetetraacetic acid (EDTA)] that enhances the metabolic rate. HLM incubation alone shows a pronounced increase in the metabolism of VX compared with buffer, suggesting that cytochrome P450-mediated metabolism of VX is occurring. We identified a biphasic decay with two distinct rates of metabolism. The enhancement of VX metabolism in multiple buffers was assessed to attempt to mitigate the effect of hydrolysis rates. The formation of VX metabolites was shown to be shifted with HLMs, suggesting a pathway enhancement over simple hydrolysis. Additionally, our investigation of hydrolysis rates in various common buffers used in biologic assays discovered dramatic differences in VX stability. The new human in vitro VX metabolic data reported points to a potential in vivo treatment strategy (EDTA) for rescue in individuals that are poisoned though enhancement of metabolism alongside existing treatments. SIGNIFICANCE STATEMENT: Venomous agent X (VX) is a potent acetylcholinesterase inhibitor and chemical weapon. To date, we do not possess a clear understanding of its metabolism in humans that would assist us in treating those exposed to it. This study now describes the human liver microsomal metabolism of VX and identifies ethylenediaminetetraacetic acid, which appears to enhance the rate of metabolism. This may provide a potential treatment option for human VX poisoning.

Recent advances in cotton fabric-based photocatalytic composites for the degradation of organic contaminants

Cotton is one of the oldest and most widely used natural fibers in the world. It enables a wide range of applications due to its excellent moisture absorption, thermal insulation, heat resistance, and durability. Benefiting from current developments in textile technology and materials science, people are constantly seeking more comfortable, more beautiful and more versatile cotton fabrics. As the second skin of body, clothing not only provides the basic needs of wear but also increases the protection of body against different environmental stimuli. In this article, a comprehensive review is proposed regarding research activities of systematically summarise the development and research of cotton fabric-based photocatalytic composites for the degradation of organic contaminants in the area of self-cleaning, degradation of gaseous contaminants, pathogenic bacteria or viruses, and chemical warfare agents. Specifically, we begin with a brief exposition of the background and significance of cotton fabric-based photocatalytic composites. Next, a systematical review on cotton fabric-based photocatalytic composites is provided according to their mechanisms and advanced applications. Finally, a simple summary and analysis concludes the current limitations and future directions in these composites for the degradation of organic contaminants.

Treatment of Organophosphorus Poisoning with 6-Alkoxypyridin-3-ol Quinone Methide Precursors: Resurrection of Methylphosphonate-Aged Acetylcholinesterase

Organophosphorus (OP) nerve agents inhibit acetylcholinesterase (AChE), creating a cholinergic crisis in which death can occur. The phosphylated serine residue spontaneously dealkylates to the OP-aged form, which current therapeutics cannot reverse. Soman's aging half-life is 4.2 min, so immediate recovery (resurrection) of OP-aged AChE is needed. In 2018, we showed pyridin-3-ol-based quinone methide precursors (QMPs) can resurrect OP-aged electric eel AChE in vitro, achieving 2% resurrection after 24 h of incubation (pH 7, 4 mM). We prepared 50 unique 6-alkoxypyridin-3-ol QMPs with 10 alkoxy groups and five amine leaving groups to improve AChE resurrection. These compounds are predicted in silico to cross the blood-brain barrier and treat AChE in the central nervous system. This library resurrected 7.9% activity of OP-aged recombinant human AChE after 24 h at 250 μM, a 4-fold increase from our 2018 report. The best QMP (1b), with a 6-methoxypyridin-3-ol core and a diethylamine leaving group, recovered 20.8% (1 mM), 34% (4 mM), and 42.5% (predicted maximum) of methylphosphonate-aged AChE activity over 24 h. Seven QMPs recovered activity from AChE aged with Soman and a VX degradation product (EA-2192). We hypothesize that QMPs form the quinone methide (QM) to realkylate the phosphylated serine residue as the first step of resurrection. We calculated thermodynamic energetics for QM formation, but there was no trend with the experimental biochemical data. Molecular docking studies revealed that QMP binding to OP-aged AChE is not the determining factor for the observed biochemical trends; thus, QM formation may be enzyme-mediated.

Highly sensitive chemiluminescence sensors for the detection and differentiation of chemical warfare agents

Highly sensitive chemiluminescence-based probes that effectively detect and differentiate between the extremely toxic real G- and V-type organophosphorus chemical warfare agents (OPCWAs) are presented. This straightforward approach does not require any instrumentation or light source; hence, it appears ideal for the future development of field colorimetric detectors.

Ethanolysis of nitrogen mustards: A novel strategy for nitrogen mustard identification in environmental matrices by liquid chromatography-electrospray ionization-tandem mass spectrometry

RATIONALE

Nitrogen mustards (NMs) are blistering chemical warfare agents. The ability to detect NMs in environmental samples is very important for obtaining forensic evidence. The most common analytical techniques for NM detection are gas chromatography-mass spectrometry, which detects NMs in their intact form but is disadvantaged by high limits of detection (LODs), and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) of their hydrolysis products, which do not provide robust evidence to support NM use.

METHODS

We developed a novel approach to detect and identify NMs using LC/ESI-MS/MS after chemical derivatization. The method is based on ethoxide-promoted ethanolysis prior to analysis. The effects of reaction time, temperature, ethoxide concentration and chromatography behavior were studied and optimized. In the developed procedure, 0.1% (v/v) sodium ethoxide solution is added to the NMs in ethanol and agitated for 2 h at 50°C, followed by LC/ESI-MS/MS, without any other pretreatment.

RESULTS

The ethanolysis reaction efficiencies were evaluated in ethanolic extracts from soil, asphalt, and ethanol contaminated with 0.5% (v/v) diesel fortified with NMs at a five-point calibration curve. The calibration curves showed good linearity in the range of 0.05-1 ng/mL, with an R2 value of 0.99, and were similar to those of LC/MS-grade ethanol, with almost no observable matrix effects. The derivatization products were stable at room temperature, with LODs of 10 pg/mL, in all investigated extracts.

CONCLUSIONS

Through this newly developed strategy, the derivatization of active NMs by ethanolysis was achieved for the first time, and these derivatization products can serve as specific indicators for the use and presence of NMs. The methodology can also verify trace levels of NM chemical warfare agents collected in war or terror scenarios in forensic investigations.

Recent Advances in Real-Time Label-Free Detection of Small Molecules

The detection and analysis of small molecules, typically defined as molecules under 1000 Da, is of growing interest ranging from the development of small-molecule drugs and inhibitors to the sensing of toxins and biomarkers. However, due to challenges such as their small size and low mass, many biosensing technologies struggle to have the sensitivity and selectivity for the detection of small molecules. Notably, their small size limits the usage of labeled techniques that can change the properties of small-molecule analytes. Furthermore, the capability of real-time detection is highly desired for small-molecule biosensors' application in diagnostics or screening. This review highlights recent advances in label-free real-time biosensing technologies utilizing different types of transducers to meet the growing demand for small-molecule detection.

Discriminative detection of soman or VX exposure using europium chelated microparticle-based immunofluorescence microfluidic chip

The retrospective detection of organophosphorus nerve agents (OPNAs) exposure has been achieved by the off-site analysis of OPNA-human serum albumin (HSA) adducts using mass spectrometry-based detection approaches. However, few specific methods are accessible for on-site detection. To address this, a novel immunofluorescence microfluidic chip (IFMC) testing system combining europium chelated microparticle (EuCM) with self-driven microfluidic chip assay has been established to unambiguously determine soman (GD) and VX exposure within 20 min, respectively. The detection system was based on the principle of indirect competitive enzyme-linked immunosorbent assay. The specific monoclonal antibodies that respectively recognized the phosphonylated tyrosine 411 of GD-HSA and VX-HSA adducts were labeled by EuCM to capture corresponding adducts in the exposed samples. The phosphonylated peptides in the test line and goat-anti-rabbit antibody in the control line were utilized to bind the EuCM-labeled antibodies for signal exhibition. The developed IFMC chip could discriminatively detect exposed HSA adducts with high specificity, demonstrating a low limit of detection at exposure concentrations of 0.5 × 10-6 mol/L VX and 1.0 × 10-6 mol/L GD. The exposed serum samples can be qualitatively detected following an additional pretreatment procedure. This is a novel rapid detection system capable of discriminating GD and VX exposure, providing an alternative method for rapidly identifying OPNA exposure.

Underestimations in the In Silico-Predicted Toxicities of V-Agents

V-agents are exceedingly toxic nerve agents. Recently, it was highlighted that V-agents constitute a diverse subclass of compounds with most of them not extensively studied. Although chemical weapons have been banned under the Chemical Weapons Convention (CWC), there is an increased concern for chemical terrorism. Thus, it is important to understand their properties and toxicities, especially since some of these agents are not included in the CWC list. Nonetheless, to achieve this goal, the testing of a huge number of compounds is needed. Alternatively, in silico toxicology offers a great advantage for the rapid assessment of toxic compounds. Here, various in silico tools (TEST, VEGA, pkCSM ProTox-II) were used to estimate the acute oral toxicity (LD50) of different V-agents and compare them with experimental values. These programs underestimated the toxicity of V-agents, and certain V-agents were estimated to be relatively non-toxic. TEST was also used to estimate the physical properties and found to provide good approximations for densities, surface tensions and vapor pressures but not for viscosities. Thus, attention should be paid when interpreting and estimating the toxicities of V-agents in silico, and it is necessary to conduct future detailed experiments to understand their properties and develop effective countermeasures.

The suitability of a polydimethylsiloxane-based (PDMS) microfluidic two compartment system for the toxicokinetic analysis of organophosphorus compounds

Organ-on-a-chip platforms are an emerging technology in experimental and regulatory toxicology (species-specific differences, ethical considerations). They address gaps between in vivo and in vitro models. However, there are still certain limitations considering material, setup and applicability. The current study examined the suitability of a commercially available polydimethylsiloxane-based (PDMS) organ-chip for the toxicokinetic characterization of the highly toxic nerve agent VX and the organophosphate pesticide parathion. The respective concentrations of 1000 µmol/L and 100 µmol/L VX and parathion were chosen deliberately high in order to study concentrations even if high compound absorption by PDMS might occur. Neuronal and liver spheroids, totaling 2 × 106 cells were used to study concentration changes of VX and parathion. In addition, VX enantiomers were quantified. The current study suggests a significant absorption of VX, respectively parathion by PDMS. This might require future investigation of alternative materials or coatings to limit absorption for organophosphorus compounds in toxicokinetic studies.

Enhanced LC-ESI-MS/MS Sensitivity by Cationic Derivatization of Organophosphorus Acids

The chemical derivatization to enhance the signal intensity and signal-to-noise (S/N) of several organophosphorus (OP) acids in liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS) is illustrated. The OP class of compounds represents the environmental degradants of OP nerve agents and pesticides. N-(2-(bromomethyl)benzyl)-N,N-diethylethanaminium bromide (CAX-B) was utilized to derivatize a panel of eight acids consisting of five alkyl methylphosphonic acids (ethyl-, isopropyl-, isobutyl-, cyclohexyl-, and pinacolyl-methylphosphonic acid) along with three dialkylphosphate analogs (diethyl-, dibutyl-, and diethyl thio-phosphate). The derivatization reaction with CAX-B was conducted in acetonitrile in the presence of potassium carbonate at 70 °C for 1 h. The resulting acid derivatives were analyzed with an LC-Orbitrap-ESI-MS/MS, and their dissociation processes were investigated. It was found that the derivatization procedure increased the limits of identification (LOIs) by one to over two orders of magnitude from the range of 1 to 10 ng/mL for the intact OP-acids to the range of 0.02-0.2 ng/mL for the derivatized acids utilizing an LC-MS(QqQ) in MRM mode, regardless of the sample matrix (hair, concrete, or plant extracts). The interpretation of the corresponding ESI-MS/MS spectra for each type of derivatized sub-OP family revealed the formation of characteristic neutral losses and a characteristic ion for the organophosphorus core. This derivatization is beneficial and useful for screening and identifying target and "unknown" OP acids.

Evidence of nerve agent VX exposure in rat plasma by detection of albumin-adducts in vitro and in vivo

VX is a highly toxic organophosphorus nerve agent that reacts with a variety of endogenous proteins such as serum albumin under formation of adducts that can be targeted by analytical methods for biomedical verification of exposure. Albumin is phosphonylated by the ethyl methylphosphonic acid moiety (EMP) of VX at various tyrosine residues. Additionally, the released leaving group of VX, 2-(diisopropylamino)ethanethiol (DPAET), may react with cysteine residues in diverse proteins. We developed and validated a microbore liquid chromatography-electrospray ionization high-resolution tandem mass spectrometry (µLC-ESI MS/HR MS) method enabling simultaneous detection of three albumin-derived biomarkers for the analysis of rat plasma. After pronase-catalyzed cleavage of rat plasma proteins single phosphonylated tyrosine residues (Tyr-EMP), the Cys34(-DPAET)Pro dipeptide as well as the rat-specific LeuProCys448(-DPAET) tripeptide were obtained. The time-dependent adduct formation in rat plasma was investigated in vitro and biomarker formation during proteolysis was optimized. Biomarkers were shown to be stable for a minimum of four freeze-and-thaw cycles and for at least 24 h in the autosampler at 15 °C thus making the adducts highly suited for bioanalysis. Cys34(-DPAET)Pro was superior compared to the other serum biomarkers considering the limit of identification and stability in plasma at 37 °C. For the first time, Cys34(-DPAET)Pro was detected in in vivo specimens showing a time-dependent concentration increase after subcutaneous exposure of rats underlining the benefit of the dipeptide disulfide biomarker for sensitive analysis.

Degradation of Chemical Warfare Agent Nitrogen Mustard Using Ferrate (VI)

Chemical warfare agents (CWAs) are one of the most toxic compounds. Degradation of CWAs using decontamination agents is one of the few ways to protect human health against the harmful effects of CWAs. A ferrate (VI)-based potential chemical warfare agent decontaminant was studied for the degradation of persistent nitrogen mustard (tris(2-chloroethyl)amine, HN3). By optimizing the reaction conditions, the complete degradation of HN3 was achieved in 4 min. The degradation products contained mostly reduced Fe species, which confirmed the environmental friendliness of the proposed decontamination solution.

Evaluation of Malathion, DIMP, and Strawberry Furanone as CWA Simulants for Consideration in Field-Level Interior Building Remediation Exercises

Field-level exercises with the purpose to assess remediation following the deliberate release of a highly toxic chemical in an indoor environment can be conducted using low(er) toxicity simulants if they are closely linked to the behavior of the toxic chemical itself. Chemical warfare agent (CWA) simulants have been identified on their suitability based on chemical structural similarities and associated physical and chemical properties. However, there are no reported studies that combine measurement of simulant parameters like persistence on surfaces, ability to sample for, and capability to degrade during the decontamination phase such that the level of success of a field-level exercise can be quantified. Experimental research was conducted to assess these gaps using a select number of CWA simulants. The organophosphate pesticide malathion was found to be a suitable simulant for use in field-level exercises that simulate the release of the highly persistent nerve agent VX based on its high persistence, effective surface sampling and analysis using standard analytical equipment, and the in situ degradation in the presence of different oxidizing decontaminants.

Elimination of A-234 from the environment: Effect of different decontaminants

With the fact that there are Novichoks in the list of toxic chemicals by the Chemical Weapons Convention parties, it is necessary to develop methods of effective neutralization of the agents as well as for other organophosphorus toxic substances. However, experimental studies on their persistence in the environment and effective decontamination measures remain scarce. Therefore, here, we investigated the persistence behavior and decontamination methods of A-234 (ethyl N-[1-(diethylamino)ethylidene]phosphoramidofluoridate), a Novichok series, A-type nerve agent to assess its potential risk to the environment. Different analytical methods were implemented, including ³¹P solid-state magic angle spinning nuclear magnetic resonance (NMR), liquid ³¹P NMR, gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry, and vapor-emission screening using a microchamber/thermal extractor with GC-MS. Our results showed that A-234 is extremely stable in sand and poses a long-lasting risk to the environment even when released in trace quantities. Moreover, the agent is not easily decomposed by water, dichloroisocyanuric acid sodium salt, sodium persulfate, and chlorine-based water-soluble decontaminants. However, it is efficiently decontaminated by Oxone® monopersulfate, calcium hypochlorite, KOH, NaOH, and HCl within 30 min. Our findings provide valuable insights for eliminating the highly dangerous Novichok agents from the environment.

Toxic effects and bioaccumulation of pinacolyl methylphosphonate acid in zebrafish following soman exposure to a water environment

Soman has been shown to be highly neurotoxic and can be easily degraded to produce pinacolyl methylphosphonate acid (PMPA). Thus, the perniciousness of PMPA deserved serious attention after soman was exposed to the environment. However, the toxicity of PMPA was not clearly elucidated to date. In this regard, the objective of this study was to determine if PMPA could pose an environmental risk after soman exposure to a water environment. In this study, the toxicity and bioaccumulation assessments of PMPA were carried out on zebrafish. Histological examination was used to assess the toxicity of PMPA in zebrafish and revealed that PMPA has chronic toxicity in view of tissue injury. The contents of PMPA in whole zebrafish and tissues were determined after soman exposure. The result showed that PMPA bioaccumulated in the whole zebrafish and tissue, especially the liver and intestinal tissues. This is the first report showing that the hydrolyzate of a G-series chemical nerve agent could accumulate in organisms. This study offers novel insights into the environmental risk assessments associated with soman exposure to a water environment.

Activation of the human TRPA1 channel by different alkylating sulfur and nitrogen mustards and structurally related chemotherapeutic drugs

An important target in toxicology is the ion channel known as human transient receptor potential ankyrin 1 (hTRPA1). It is triggered by a variety of chemicals, including the alkylating chemical warfare agent sulfur mustard (SM). The activation potentials of structural analogs including O- and sesquimustard, nitrogen mustards (HN1, HN2, and HN3), and related chemotherapeutic drugs (bendamustine, cycylophosphamide, and ifosfamide) were examined in the current study. The aequorin assay was used to measure changes in intracellular calcium levels in human hTRPA1 overexpressing HEK293 cells. The XTT assay was used to determine cytotoxicity. The data presented here highlight that all investigated alkylating substances, with the exception of cyclophosphamide and ifosfamide, cause the activation of hTRPA1. Cytotoxicity and activation of hTRPA1 were found to be related. Compounds with high reactivity had higher cytotoxicity and vice versa. However, inhibiting hTRPA1 with the specific inhibitor AP18 could not reduce the cytotoxicity induced by alkylating agents. As a result, hTRPA1 does not play a significant role in the cytotoxicity of alkylating agents.

Environmental degradation of human metabolites of cyclophosphamide leads to toxic and non-biodegradable transformation products

The present study assessed the ready biodegradability of the prodrug cyclophosphamide (CPA) and its stable human metabolites in the closed bottle test (CBT). The results of the CBT showed that only the main human metabolite, carboxyphosphamide (CXP), was biodegradable to a certain extent (23 ± 2.4 % ThOD_NH3). All other metabolites showed neither biodegradation under these conditions nor were any toxic effects on the inoculum observed. Yet, HRMSⁿ results revealed partial primary elimination of all human metabolites and formation of 25 new transformation products. Abiotic degradation via S_Ni and S_N2 reactions was proposed as the main degradation pathway during the CBT. The main degradation products were assigned as 3-(2-chloroethyl)oxazolidin-2-one (COAZ), cytotoxic N-2-chloroethylaziridine (CEZ) and nor‑nitrogen mustard (NNM), an analogue of the chemical warfare agent HN2. While the acute ecotoxicity of the detected products is widely unknown, many have already been reported in medical literature to be either mutagenic, genotoxic, cytotoxic or carcinogenic and may therefore cause a greater risk than their precursors. QSAR models predicted that 16 of them are mutagenic and genotoxic, thus classifying the majority of the chemicals as potential environmental hazards. The central intermediates during the degradation process were proposed as CEZ and its corresponding aziridinium ion. However, other degradation products may occur depending on the type and strength of nucleophiles present in the matrices. Overall, the results demonstrated the importance to include human metabolites in the evaluation of the environmental fate of pharmaceuticals and their risk assessment especially when investigating prodrugs. The results underline the importance of identifying possible degradation products of metabolites, as they can be more toxic than related parent compounds and metabolites and can cause a greater risk to the environment and humans.

Functionalized reactive polymers for the removal of chemical warfare agents: A review

Protection from and removal of chemical warfare agents (CWAs) from the environment remains a global goal. Activated charcoal, metal oxides, metal organic frameworks (MOFs), polyoxometalates (POMs) and reactive polymers have all been investigated for CWA removal. Composite polymeric materials are rapidly gaining traction as versatile building blocks for personal protective equipment (PPE) and catalytic devices. Polymers are inexpensive to produce and easily engineered into a wide range of materials including films, electro-spun fibers, mixed-matrix membranes/reactors, and other forms. When containing reactive side-chains, hydrolysis catalysts, and/or oxidative catalysts polymeric devices are primed for CWA decontamination. In this review, recent advances in reactive polymeric materials for CWA removal are summarized. To aid in comparing the effectiveness of the different solid catalysts, particular attention is paid to the stoichiometric ratio of reactive species to toxic substrate (CWA or CWA simulant).

Analysis of degradation products of nerve agents in biological fluids by ion chromatography-tandem mass spectrometry

PURPOSE

The detection of hydrolysis products of nerve agents (alkyl methylphosphonic acids; RMPAs) in biological samples from victims is important to confirm exposure to nerve agents. However, analysis of RMPAs is difficult due to their high hydrophilicity. The aim of this study was to develop ion chromatography-tandem mass spectrometry (IC-MS/MS) methods using commercially available equipment and columns to analyze RMPAs in human urine and serum with high sensitivity and without using complicate techniques.

METHODS

A Dionex IonPac AS11-HC anion-exchange column was used to analyze six RMPAs (MPA, EMPA, IMPA, ⁱBuMPA, CHMPA, and PMPA). For pretreatments of biological fluids, we developed two pretreatment methods (Method 1: dilution and ultrafiltration; Method 2: removal of chloride ions with Ag cartridges).

RESULTS

Six RMPAs including highly hydrophilic methylphosphonic acid and ethyl methylphosphonic acid could be analyzed with sufficient retention times and peak shape. The detection limits of RMPAs were improved using Dionex OnGuard II Ba/Ag/H cartridges and MetaSEP IC-Ag cartridges (urine: 0.5-5 ng/mL; serum: 1-5 ng/mL). These methods were also applied to the test samples for the Organisation for the Prohibition of Chemical Weapons Biomedical Proficiency Tests.

CONCLUSIONS

RMPAs could be sufficiently analyzed by IC-MS/MS. In addition, the limits of detection were superior to those obtained in our previous study involving LC-MS/MS or derivatization-LC-MS/MS method. For analysis of biological samples, an appropriate pretreatment method can be chosen according to the amount of sample available for analysis and expected RMPA concentrations.

Toxicokinetics of plasmatic VX in a swine model: comparison of a simple enzymatic titration method with a mass spectrometry method

Recent events have shown that organophosphorus nerve agents (OPNAs) are a serious threat. Cholinesterase inhibition by OPNAs results in acetylcholine accumulation, a cholinergic crisis leading to death if untreated. Efficacy assessment of new medical countermeasures against OPNAs relies on translational animal models. We developed a swine model of percutaneous VX intoxication and a simple plate reader-based enzymatic method to quantify plasmatic VX over time. Juvenile pigs anesthetized with sevoflurane were poisoned with a single supralethal (n = 5; 1200 μg/kg) or sublethal (n = 6; 320 μg/kg) percutaneous dose of VX. These intoxicated animals were compared to 7 control animals. Repeated blood sampling was performed up to 6 h post-intoxication. Blood cholinesterase activities were measured using the Ellman assay. Nanomolar plasma concentrations of VX were measured by exogenous butyrylcholinesterase added to an aliquot of plasma. As expected, we observed a steady increase in plasma concentration of VX over time concomitant to a decrease in blood cholinesterase activities for all intoxicated pigs. Despite the simplicity of the enzymatic method, the results obtained are in good agreement with those of the liquid chromatography-mass spectrometry method. This method is also applicable to other OPNAs such as novichoks with minor adaptations.

Pretreatment Method for Chloramine-T Decon Sample Before GC Analysis of HD and VX

Chloramine-T, especially its solution in weak acidity, is one of the decontaminants for chemical warfare agents (CWAs), HD, and VX. A high CWAs recovery from decontamination (decon) sample via pretreatment was essential for evaluating decontamination effects. This paper performed experiments to optimize pretreatment methods to extract residual CWAs from chloramine-T decon samples before GC analysis. Effects of two neutralization methods, destroying decon activity by 15% Na₂SO₃ or decreasing decon activity by 3% NH₃·H₂O or 4% NaOH, were studied. Results showed they were all suitable for the HD decon sample, but only 4% NaOH was ideal for the VX decon sample. As for extractant, compared with dichloromethane, petroleum ether was more suitable for recovering CWAs from decon samples. A high recovery above 80% could be obtained for HD and VX samples ranging from 10 mg/L to 10,000 mg/L when optimized neutralization and extraction methods were simultaneously carried out.

Catalytic degradation of CWAs with MOF-808 and PCN-222: Toward practical application

Chemical warfare agents, such as nerve agents (GD and VX) and blister agents (HD), have strong toxicities to mankind. In recent years, zirconium-based metal-organic frameworks have been found to be attractive materials for chemical warfare agent degradation. Among them, metal-organic framework-808 (MOF-808) and porous coordination network-222 (PCN-222) were the best. However, few papers pay attention to their practical application. In this work, we prepared MOF-808 and PCN-222 using water phase and organic solvothermal methods, respectively. Their performance for the catalytic degradation of chemical warfare agents under practical decontamination conditions was studied. The results showed that MOF-808 displayed a high potency for catalytic hydrolysis of VX (10,000 mg L−1) in unbuffered solution. PCN-222 exhibited weaker reactivity with a half-life ( t1/2) of 28.8 min. Their different performances might stem from the different connectivity of the Zr6 nodes and framework structures. The results illustrated that the hydrolysis of high-concentration GD required a strong alkaline buffer to neutralize the hydrolysis product of hydrofluoric acid (HF) to avoid catalyst poisoning. When H2O2 was used as the oxidant instead of O2, both zirconium-based metal-organic frameworks performed with effective catalytic potency for HD degradation without any special lighting and so was suitable for practical application, whereas the products obtained from HD, such as HDO2 and V-HDO2, still possessed vesicant toxicity. Overall, MOF-808 prepared via a water-phase synthesis performed with effective catalysis for the degradation of high-concentration VX, GD, and HD with t1/2 of < 0.5, 3.1 and 2.2 min, respectively, exhibiting its potential for practical applications.

Nature-based approaches to reducing the environmental risk of organic contaminants resulting from military activities

As is the case with many other industrial activities, the organic contaminants at military-impacted sites may pose significant hazards to the environment and human health. Given the expected increase in defense investments globally, there is a need to make society aware of the risks of emissions of organic contaminants generated by military activities and to advance risk minimization approaches. The most recent advances in environmental analytical chemistry, persistence, bioavailability and risk assessment of organic contaminants indicate that efficient risk reductions through biological means are possible. This review debates the organic contaminants of interest associated with military activities, the methodology used to extract and analyze these contaminants, and the nature-based remediation technologies available to recover these sites. In addition, we revise the military environmental regulatory frameworks designed to sustain such actions. Military activities that potentially release organic contaminants on land could be classified as infrastructure and base operations, training exercises and armed conflicts; additionally, chemicals may include potentially toxic compounds, energetic compounds, chemical warfare agents and military chemical compounds. Fuel components, PFASs, TNT, RDX and dyphenylcyanoarsine are examples of organic contaminants of environmental concern. Particularly in the case of potentially toxic and energetic compounds, bioremediation and phytoremediation are considered eco-friendly and low-cost technologies that can be used to remediate these contaminated sites. In addition, this article identifies implementing the bioavailability of organic contaminants as a justifiable approach to facilitate the application of these nature-based approaches and to reduce remediation costs. More realistic risk assessment in combination with new and economically feasible remediation methods that reduce risk by reducing bioavailability (instead of lowering the total contaminant concentration) will serve as an incentive for the military and regulators to accept nature-based approaches.

Cation-Exchangeable Pralidoxime Chloride@bio-MOF-1 as a Treatment for Nerve Agent Poisoning and Sulfur Mustard Skin Poisoning in Animals

A 2-PAM@bio-MOF-1 composite was prepared by cationic exchange of counter N,N-dimethylammonium cations in the pores of the anionic, biocompatible metal-organic framework (bio-MOF-1) with pralidoxime chloride (2-PAM-Cl) by impregnation. In vitro drug release measurements revealed that the release rate of 2-PAM from 2-PAM@bio-MOF-1 in simulated body fluid (SBF) was more than four-fold higher than that in deionized water, indicating that the presence of endogenous cations in SBF triggered the release of 2-PAM through cation exchange. The release of 2-PAM was rapid within the first 10 h but was much slower over the period of 10-50 h. At room temperature, the maximum release rate of 2-PAM was 88.5% (15 mg of 2-PAM@bio-MOF-1 in 1 mL of SBF), indicating that the drug was efficiently released from the composite MOF in SBF. In simulated gastric fluid, 64.3% of 2-PAM was released from bio-MOF-1 into the simulated gastric fluid after 50h. This suggested that 2-PAM@bio-MOF-1 might be effective for enabling the slow release of 2-PAM in the human body. Indeed, the maximum reactivation rate of acetylcholinesterase in sarin-poisoned mice reached 82.5%. In addition, 2-PAM@bio-MOF-1 demonstrated the ability to adsorb and remove sulfur mustard (HD) in solution and from the skin of guinea pigs.

Research models of sulfur mustard- and nitrogen mustard-induced ocular injuries and potential therapeutics

Sulfur mustard (SM) is a notorious, bifunctional alkylating vesicant that was first used in warfare during World War I in 1917 and since then has been deployed in numerous skirmishes with its most recent documented use being during the Middle Eastern conflicts. Apart from its use in combat and terrorist activities, continual threat of accidental exposure from old stockpiles and improperly discarded munitions is ever present, especially to the innocent and unassuming civilian populations. SM can cause devastating injuries, depending on the dosage of SM exposure, route of exposure, as well as the physiological conditions of the individuals exposed. The most common routes of exposure are ocular, dermal, and exposure to the lungs and respiratory tissues through inhalation. Eyes are the most susceptible organ to SM-induced toxicities owing to their high moisture content and rapidly dividing cells. Additionally, ocular injury causes the most expeditious disablement of individuals even upon whole-body exposures. Therefore, it is imperative to understand the mechanisms underlying SM-induced ocular toxicity and design therapeutic interventions to prevent/mitigate ocular injuries. Ocular SM exposure may cause a wide range of symptoms such as inflammation, lacrimation, itching, dryness, photophobia, edema of the cornea/sclera/retina/iris, conjunctivitis, degradation of the corneal layer, fusion of two or more ocular layers, neovascularization, fibrosis, and temporary or permanent structural damage to one or more ocular layers. These symptoms may lead to vision impairments, resulting in partial or complete blindness that may be permanent. The highly toxic and exceedingly notorious nature of SM makes it a highly regulated chemical, requiring very expensive licensing, security, and safety requirements; thus, the more easily accessible analogue, nitrogen mustard (NM) that mimics SM-induced toxicity and injuries is employed in plethora of studies conducted in different animal models and culture systems. This review provides a comprehensive account of the injuries and symptoms that occur upon ocular SM exposures in human patients as well as studies in animal (in vivo, ex vivo) and cell (in vitro) models of SM and NM ocular exposures. Special emphasis has been laid on highlighting the strengths and lacunae in the research as well as the possible unexplored avenues of mechanisms underlying mustard-induced ocular injury that can be explored in future research endeavors. Furthermore, development of therapeutic interventions and targets of interest in the ocular system exposed to SM and NM, based on studies in human patients as well as in vivo, ex vivo, and in vitro models has been discussed in great depth, providing a valuable knowledge database to delineate pathways associated with vesicant-induced toxicity, and strategies/diagnostic tools against SM-induced toxicity.

Evaluating risk, exposure, and detection capabilities for chemical threats in water

The unexpected release of chemicals into the environment requires estimation of human health risks, followed by risk management decisions. When environmental concentrations of toxicants are associated with adverse health risks, the limit for analytical measurement needs to be at or below the risk threshold. The aim of this study was to assess chemical contaminants that have the potential to produce acute adverse human health impacts following oral consumption of contaminated drinking water. The U.S. Environmental Protection Agency's (EPA) Candidate Contaminant List, version 4 (CCL4) and EPA's Selected Analytical Methods (SAM) document were screened to identify 24 chemicals that exist as a solid or liquid at room temperature, with acute oral LD₅₀ (lethal dose in 50% of the test population) values < 500 mg/kg-d and water solubility > 500 mg/L at ambient temperature. While these screening criteria were used to identify prioritized needs for targeted research, it does not imply that other chemicals on the CCL4 and SAM lists are not issues in acute and chronic exposures. Of these 24 most toxic and most soluble chemicals, this evaluation identified 6 chemicals (2-chlorovinylarsonous acid, lewisite, N-nitrosopyrrolidine, N-nitrosodiethylamine, 3-hydroxycarbofuran, and triethylamine) lacking either sufficient toxicity value information or analytical sensitivity required to detect at levels protective against adverse effects in adults for acute exposures. This assessment provides an approach for gap identification and highlights research needs related to water contamination incident involving these six priority chemicals.

Efficient Decontamination of HD by an Electrophilic Iodine/Carboxylate Composite as an Active Sorbent

The development of new and efficient decontamination methods has become more relevant in recent years, especially with regard to solid-based decontamination and detoxification systems. The majority of powders used today are dealing with the physical adsorption of chemical warfare agents (CWAs) and their removal from sites without actively destroying them. In this work, we have designed and developed an active solid composite matrix combining organic carboxylate salts and N-iodosuccinimide (NIS) for HD decontamination via oxidation. All the reactions and mechanistic studies for the sorption and degradation of CWAs were conducted using direct polarization and cross polarization solid-state magic-angle spinning nuclear magnetic resonance techniques. Performance toward the sorption and detoxification of HD was tested, exhibiting oxidation within minutes in a mild and selective manner to the nontoxic sulfoxide derivative followed by visible formation of iodine. The results indicate that carboxylate moieties in the matrix are important for stabilizing the positively charged sulfonium ion intermediate and for supplying oxygen for hydrolysis in a water-deficient environment. The NaOBz/NIS composite was shown to be the most efficient in sorbing and converting the water-insoluble agent HD to its nontoxic, water-soluble sulfoxide, which could then be removed from the site with mere water, resulting in less environmental damage and quick remediation.

Enhancing the quantum yield of singlet oxygen: photocatalytic degradation of mustard gas simulant 2-chloroethyl ethyl sulfide catalyzed by a hybrid of polyhydroxyl aluminum cations and porphyrin anions

By combining the anionic salt meso-tetra(4-carboxyphenyl)porphyrin (TCPP4-) and the Keggin polyoxometalate cation cluster [Al13O4(OH)24(H2O)12]7+ via a simple ion-exchange method, a hybrid (C48H26N4O8)[Al13O4(OH)24(H2O)12]2(OH)10·18H2O (Al13-TCPP) was prepared and thoroughly characterized as a prototype of polyoxometalate-porphyrin hybrids for the photocatalytic degradation of the mustard gas simulant 2-chloroethyl ethyl sulfide (CEES). The experimental results showed that the catalytic degradation rate of CEES in the presence of Al13-TCPP reached 96.16 and 99.01% in 180 and 90 min in methanol and methanol-water solvent mixture (v/v = 1 : 1), respectively. The reaction followed first-order reaction kinetics, and the half-life and kinetic constant in methanol and solvent mixture were 39.8 min, -0.017 min-1 and 14.7 min, -0.047 min-1. Mechanism analysis indicated that under visible light irradiation in air, CEES was degraded through a combination of oxidation and alcoholysis/hydrolysis in methanol and the methanol-water solvent mixture. The superoxide radical (O2˙-) and singlet molecular oxygen (1O2) generated by Al13-TCPP selectively oxidized CEES into a non-toxic sulfoxide. The singlet oxygen capture experiments showed that Al13-TCPP (Φ = 0.236) had a higher quantum yield of singlet oxygen generation than H4TCPP (Φ = 0.135) under visible light irradiation in air. The material Al13-TCPP has good reusability, and the degradation rate of CEES can still reach 98.37% after being recycled five times.

Metagenomic Analysis of the Gastrointestinal Microbiota of Gadus morhua callarias L. Originating from a Chemical Munition Dump Site

Several hundred thousand tonnes of munitions containing chemical warfare agents (CWAs) are lying on the seafloor worldwide. CWAs have started leaking from corroded munitions, and their presence in the environment and in organisms inhabiting dump sites has been detected. The presence of CWAs in the water negatively affects fish, macrobenthos and free-living bacteria. It can be expected that the presence of CWAs would also affect the gut-associated bacteria in fish, which are vital for their condition. The main aim of this study was to test if the microbiota of cod collected in the Baltic Bornholm Deep (highly polluted with CWAs) is dysregulated. To investigate this, we conducted metagenomic studies based on 16S rRNA gene sequencing. We found that the microbiota of cod inhabiting the dump site was significantly less taxonomically diverse compared to those from a non-polluted reference site. Moreover, taxa associated with fish diseases (e.g., Vibrionaceae, Aeromonadaceae) were more prevalent, and probiotic taxa (e.g., Actinobacteriota, Rhodobacteraceae) were less frequent in the guts of individuals from the dump site, than those from the reference site. The differences in vulnerability of various bacterial taxa inhabiting cod gastrointestinal tracts to CWAs were hypothesised to be responsible for the observed microbiota dysregulation.

Insects as Chemical Sensors: Detection of Chemical Warfare Agent Simulants and Hydrolysis Products in the Blow Fly Using LC-MS/MS

In this work, blow flies were investigated as environmental chemical sample collectors following a chemical warfare attack (CWA). Blow flies sample the environment as they search for water and food sources and can be trapped from kilometers away using baited traps. Three species of blow flies were exposed to CWA simulants to determine the persistence and detectability of these compounds under varying environmental conditions. A liquid chromatography mass spectrometry (LC-MS/MS) method was developed to detect CWA simulants and hydrolysis products from fly guts. Flies were exposed to the CWA simulants dimethyl methylphosphonate and diethyl phosphoramidate as well as the pesticide dichlorvos, followed by treatment-dependent temperature and humidity conditions. Flies were sacrificed at intervals within a 14 day postexposure period. Fly guts were extracted and analyzed with the LC-MS/MS method. The amount of CWA simulant in fly guts decreased with time following exposure but were detectable 14 days following exposure, giving a long window of detectability. In addition to the analysis of CWA simulants, isopropyl methylphosphonic acid, the hydrolysis product of sarin, was also detected in blow flies 14 days post exposure. This work demonstrates the potential to obtain valuable samples from remote or access-restricted areas without risking lives.

Dimethoxytriadinylation LC-MS/MS of Novichok A-Series Degradation Products in Human Urine

Novichok A-series compounds, novel nerve agents, pose an increasing threat to citizens worldwide; however, no analytical methods have been reported for detecting their hydrolysis products. Herein, a screening method was developed to detect and identify Novichok A-series degradation products (hydrolysates of A230, A232, A234, A262, and one related compound) and alkyl methylphosphonic acids (RMPAs, conventional nerve agent hydrolysates) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We identified a suitable derivatization reagent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM), and optimized the reaction conditions. The derivatized esters of Novichok A-series degradation products were stable and easily detected. We used this derivatization to achieve the first analytical method for Novichok hydrolysis products in urine (0.40-4.0 ng/mL). The detection limits of the RMPAs (0.1-0.4 ng/mL) were comparable to those presented in previous reports involving pentafluorobenzylation or direct LC-MS/MS. The applicability of the newly developed method was evaluated by analyzing urine samples from the OPCW Fifth Biomedical Proficiency Test.

Effective Degradation of Novichok Nerve Agents by the Zirconium Metal-Organic Framework MOF-808

Novichoks are a novel class of nerve agents (also referred to as the A-series) that were employed in several poisonings over the last few years. This calls for the development of novel countermeasures that can be applied in protective concepts (e.g., protective clothing) or in decontamination methods. The Zr metal-organic framework MOF-808 has recently emerged as a promising catalyst in the hydrolysis of the V- and G-series of nerve agents as well as their simulants. In this paper, we report a detailed study of the degradation of three Novichok agents by MOF-808 in buffers with varying pH. MOF-808 is revealed to be a highly efficient and regenerable catalyst for Novichok agent hydrolysis under basic conditions. In contrast to the V- and G-series of agents, degradation of Novichoks is demonstrated to proceed in two consecutive hydrolysis steps. Initial extremely rapid P-F bond breaking is followed by MOF-catalyzed removal of the amidine group from the intermediate product. The intermediate thus acted as a competitive substrate that was rate-determining for the whole two-step degradation route. Under acidic conditions, the amidine group in Novichok A-230 is more rapidly hydrolyzed than the P-F bond, giving rise to another moderately toxic intermediate. This intermediate could in turn be efficiently hydrolyzed by MOF-808 under basic conditions. These experimental observations were corroborated by density functional theory calculations to shed light on molecular mechanisms.

Screening of monoclonal antibodies against specific phosphonylation sites and analysis of serum samples exposed to soman and VX using an indirect competitive enzyme-linked immunosorbent assay

Organophosphorus nerve agents (OPNAs) covalently bind to tyrosine 411 of human serum albumin (HSA) and the formed adducts are stable biomarkers of OPNA exposure. The detection of these adducts has been limited to mass spectrometry techniques combined with protein digestion. Here, we developed indirect competitive ELISA (icELISA) methods to verify OPNA exposure by the detection of OPNA-phosphonylated adducts at tyrosine 411 residue (OPNA-HSA adducts), in which monoclonal antibodies (mAbs) against phosphonylation sites at tyrosine 411 were introduced. The two mAbs were prepared by the fourth generation of rabbit mAb technology using the phosphonylated peptides of LVRY^{(GD or VX)}TKKVPQC as the haptens. These mAbs were screened using our developed competitive ELISA method and then selected based on their individual affinity and selectivity. As a result, we obtained two mAbs that recognized the HSA Tyr 411 adduct of GD (mAb-5G2) or VX (mAb-12B9), respectively. They shared the highest affinity exhibiting a Kd value of about 10^-6 mol/L of the OPNA exposure concentration. They also had remarkable selectivity, which could especially recognize their individual OPNA-HSA adducts in a native state but did not recognize other OPNA-HSAs and unadducted HSAs. Especially for mAb-12B9, it could clearly distinguish VX-HSA and GB-HSA between which there was only one alkyl difference in their phosphonyl portion of the adducted sites. The two mAbs were then used to build the icELISA method for analysis of the serum samples exposed to OPNA. It was found that the detectable lowest GD- and VX-exposed concentrations in serum samples were respectively 1.0 × 10^-6 mol/L and 10.0 × 10^-6 mol/L. This study provides one novel approach and strategy for the retrospective detection of OPNA exposure, and the two mAbs have great potential to be extended for point-of-care testing of OPNA intoxication.

Advice on assistance and protection provided by the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons: Part 3. On medical care and treatment of injuries from sulfur mustard

Blister agents damage the skin, eyes, mucous membranes and subcutaneous tissues. Other toxic effects may occur after absorption. The response of the Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) to a request from the OPCW Director-General in 2013 on the status of medical countermeasures and treatments to blister agents is updated through the incorporation of the latest information. The physical and toxicological properties of sulfur mustard and clinical effects and treatments are summarised. The information should assist medics and emergency responders who may be unfamiliar with the toxidrome of sulfur mustard and its treatment.

Hydrolysis of methylphosphonic anhydride solid to methylphosphonic acid probed by Raman and infrared reflectance spectroscopies

Much is still unknown about the mechanisms and rates of environmental degradation of organophosphorous pesticides and agents. In this study we focus on the degradation of one organophosphorous compound, namely solid methylphosphonic anhydride [CH₃P(O)OHOP(O)OHCH₃, MPAN] and its rate of conversion to methylphosphonic acid (MPA) via heterogeneous hydrolysis. Pure MPAN was synthesized and loaded in open sample cups placed inside exposure chambers containing saturated salt solutions to control the relative humidity (RH). The reaction was monitored in the sample cup at various times using both infrared hemispherical reflectance (HRF) spectroscopy and Raman spectroscopy. Calibrated HRF and Raman spectra of both pure reagents as well as gravimetrically prepared mixtures were used to quantify the concentrations of MPAN and MPA throughout the reaction. Results show both HRF and Raman spectroscopies are convenient non-invasive methods for detection of solid chemicals as long as a large area is sampled to average out any spatial inhomogeneities that occur on the sample surface and minimal phase changes occur during the course of the reaction. The samples for the 54 and 75% RH studies showed significant deliquescence, and the liquid water had to be removed prior to measurement; this effect led to differences in the sample form, such that the calibration spectra were no longer valid for quantitative analysis using HRF spectroscopy. Raman spectroscopy, on the other hand, proved to be less sensitive to these effects and provided better estimation of the MPAN and MPA concentrations. The MPAN degradation rate displayed a very strong dependence on relative humidity: at room temperature the reaction showed 50% conversion of the MPAN in 761 ± 54 h at 33% RH, 33 ± 4 h at 43% RH, 17 ± 2 h at 54% RH and just 7 ± 1 h at 75% RH.

Paper-Based Analytical Device for the On-Site Detection of Nerve Agents

We report a colorimetric paper-based microfluidic device based on an enzyme inhibition assay that allows the on-site detection of nerve agents by sampling and wicking. The sample and reagents are automatically transported through the channel where an enzyme inhibition reaction is conducted, followed by an enzyme-substrate reaction and a color reaction. This device can detect 0.1 μg/mL of the nerve agent VX in a 2.5 μL drop and is nerve agent selective and robust against temperature, pH, and several liquids. We confirmed that sampling procedures (dilution and wiping) are applicable to this device. Furthermore, the fabrication procedure is easy, and the cost is at most a few tens of cents. Thus, the present device provides a practical method for the urgent detection of nerve agents in suspected chemical terrorism incidents.