Hydrolysis of VX on concrete: rate of degradation by direct surface interrogation using an ion trap secondary ion mass spectrometer

Detoxification of V-Nerve Agents Assisted by a Microperoxidase: New Pathway Revealed by the Use of a Relevant VX Simulant

The biocatalyzed oxidative detoxification of the V-series simulant PhX, by mean of the microperoxidase AcMP11, affords the corresponding phosphonothioate as the prominent product instead of the classical P-S and P-O bond cleavage. While PhX is structurally very close to the live agent VX (the methyl group is replaced by a phenyl), assessment with other surrogates missing the nucleophilic amino function displayed more resistance under the same conditions with no phosphonothioate observed. These encouraging results highlight 1) the efficacy of AcMP11 microperoxidase to efficiently detoxify V-series organophosphorus nerve agents (OPNA), and 2) the necessity to use representative alkyl or aryl phosphonothioates simulants such as PhX bearing the appropriate side chain as well as the P-O and P-S cleavable bond to mimic accurately the V-series OPNA to prevent false positive or false negative results.

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.

Influence of cyclic and acyclic cucurbiturils on the degradation pathways of the chemical warfare agent VX

The highly toxic nerve agent VX is a methylphosphonothioate that degrades via three pathways in aqueous solution, namely through the hydrolysis of the P-O or P-S bonds, or the cleavage of the C-S bond at the 2-aminoethyl residue. In the latter case, an aziridinium ion and a phosphonothioate is formed. Here it is shown that acyclic or cyclic cucurbiturils inhibit these reactions in phosphate buffer at physiological pH and thus stabilise the nerve agent. When using unbuffered basic solutions as the reaction medium, however, in which the P-S or P-O bonds are normally hydrolysed preferentially, cucurbiturils turned out to strongly shift VX degradation towards the cleavage of the C-S bond. Cucurbit[7]uril, in particular, has a so pronounced effect under suitable conditions that it almost completely suppresses the formation of products resulting from the other degradation pathways. Investigations involving VX analogues in combination with computational methods suggest that one reason for the reaction control exerted by the cucurbiturils is the preorganisation of VX for aziridinium ion formation. In addition, cucurbit[7]uril also lowers the transition state of the reaction by stabilising the positive charge developing on the way to the product. Cucurbiturils thus have a marked effect on the reactivity of a highly toxic nerve agent, which potentially allows using them for decontamination purposes.

Photoexcitation effect on the adsorption of hazardous gases on silica surface

There is very little scientific understanding of photoexcitation effect on the adsorption properties of adsorbent. The adsorption of four hazardous gases (SARIN (propan-2-ylmethylphospho-nofluoridate), methyl dichlorophosphate (MDCP), trimethyl phosphate (TMP) and hydrogen sulfide (H₂S)) on silica surface is taken as target sample in this work. The adsorption energy order (MDCP<SARIN<TMP) in the ground state is consistent with the strength order of intermolecular hydrogen bond (inter-HB) between hydroxyl group of silica surface and hazardous gas, and the desorption order of the three gases in previous reports. However, with the adsorption energy increase of MDCP and the decrease of SARIN and TMP, this order changes remarkably to SARIN<TMP<MDCP after photoexcitation to excited state by absorbing shortwave ultraviolet irradiation. This change is opposite to the inter-HB weakening of MDCP in the first excited (S₁) state and the strengthening of TMP and SARIN in the second excited (S₂) state. This opposite change is caused by formation of intermolecular charge transfer state of MDCP and local excitation of SARIN and TMP. The H₂S is dissociated after photoexcitation to the S₁ state. This work presents photoexcitation as a new standard for the design and detection of adsorption properties of adsorbent for its striking effect on adsorption behaviors.

Comparison of latex body paint with wetted gauze wipes for sampling the chemical warfare agents VX and sulfur mustard from common indoor surfaces

Comparison of solvent-wetted gauze with body paint, a peelable surface sampling media, for the sampling of the chemical warfare agents VX and sulfur mustard from nine surfaces was performed. The nine surfaces sampled are those typical of interior public venues and include smooth, rough, porous, and non-porous surfaces. Overall, solvent-wetted gauze (wipes) performed better for the recovery of VX from non-porous surfaces while body paint (BP) performed better for the porous surfaces. The average percent VX recoveries using wipes and BP, respectively, are: finished wood flooring, 86.2%, 71.4%; escalator handrail, 47.3%, 26.7%; stainless steel, 80.5%, 56.1%; glazed ceramic tile, 81.8%, 44.9%; ceiling tile, 1.77%, 13.1%; painted drywall 7.83%, 21.1%; smooth cement, 0.64%, 10.3%; upholstery fabric, 24.6%, 23.1%; unfinished wood flooring, 9.37%, 13.1%. Solvent-wetted gauze performed better for the recovery of sulfur mustard from three of the relatively non-porous surfaces while body paint performed better for the more porous surfaces. The average percent sulfur mustard recoveries using wipes and BP, respectively, are: finished wood flooring, 30.2%, 2.97%; escalator handrail, 4.40%, 4.09%; stainless steel, 21.2%, 3.30%; glazed ceramic tile, 49.7%, 16.7%; ceiling tile, 0.33%, 11.1%; painted drywall 2.05%, 10.6%; smooth cement, 1.20%, 35.2%; upholstery fabric, 7.63%, 6.03%; unfinished wood flooring, 0.90%, 1.74%.

VX fate on common matrices: evaporation versus degradation

A study of the volatilization rate of the nerve agent VX (O-ethyl S-2-(N,N-diisopropylamino)ethyl methylphosphonothiolate) from various urban matrices in a specially designed climatic chamber (model system) is described. The performance of the model system combined with the analytical procedure produced profiles of vapor concentration obtained from samples of VX dispersed as small droplets on the surfaces of the matrices. The results indicated that the bitumen-containing surfaces such as asphalt blocks and bitumen sheets conserve VX and slow-release part of it over a long period of time. No complete mass balance could be obtained for these surfaces. Influence of environmental and experimental parameters as well as the efficacy of decontamination procedure were also measured. From smooth surface tiles a fast release of VX was measured and almost a complete mass balance was obtained, which characterizes the behavior of inert surfaces. Experiments carried out on concrete blocks showed fast decay of the concentration profile along with a very poor reconstruction of the initial quantity of VX, implying that this matrix degraded VX actively due to its multiple basic catalytic sites. To complement this study, solid-state NMR measurements were compared to add data concerning agent-fate within the matrices.

Long-term evaluation of the fate of sulfur mustard on dry and humid soils, asphalt, and concrete

The long-term fate of the blister agent sulfur mustard (HD, bis(2-chloroethyl)sulfide) was determined in a variety of commercial and natural matrices. HD was found to be extremely stable in dry matrices for over a year. The addition of 5% water to the matrices induced slow degradation of HD, which lasted several months. The major degradation product in sands and asphalt was found to be a sulfonium salt, S[CH(2)CH(2)S(+)(CH(2)CH(2)OH)(2)](2) (H-2TG). Red loam soil, which has not been examined before, exhibited strong interaction with HD, both in dry form and in the presence of water. Humid red loam soil gave rise to unique oxidative degradation products. On humid concrete HD degraded to a complex mixture of products, including vinyls. This may be attributed to the basic sites incorporated in concrete.

Repeated, intermittent exposures to diisopropylfluorophosphate in rats: protracted effects on cholinergic markers, nerve growth factor-related proteins, and cognitive function

Organophosphates (OPs) pose a constant threat to human health due to their widespread use as pesticides and their potential employment in military and terrorist attacks. The acute toxicity of OPs has been extensively studied; however, the consequences of prolonged or repeated exposure to levels of OPs that produce no overt signs of acute toxicity (i.e. subthreshold levels) are poorly understood. Further, there is clinical evidence that such repeated exposures to OPs lead to prolonged deficits in cognition, although the mechanism for this effect is unknown. In this study, the behavioral and neurochemical effects of repeated, intermittent, and subthreshold exposures to the alkyl OP, diisopropylfluorophosphate (DFP) were investigated. Rats were injected with DFP s.c. (dose range, 0.25-1.0 mg/kg) every other day over the course of 30 days, and then given a 2 week, DFP-free washout period. In behavioral experiments conducted at various times during the washout period, dose dependent decrements in a water maze hidden platform task and a spontaneous novel object recognition (NOR) procedure were observed, while prepulse inhibition of the acoustic startle response was unaffected. There were modest decreases in open field locomotor activity and grip strength (particularly during the DFP exposure period); however, rotarod performance and water maze swim speeds were not affected. After washout, DFP concentrations were minimal in plasma and brain, however, cholinesterase inhibition was still detectable in the brain. Moreover, the 1.0 mg/kg dose of DFP was associated with (brain region-dependent) alterations in nerve growth factor-related proteins and cholinergic markers. The results of this prospective animal study thus provide evidence to support two novel hypotheses: (1) that intermittent, subthreshold exposures to alkyl OPs can lead to protracted deficits in specific domains of cognition and (2) that such cognitive deficits may be related to persistent functional changes in brain neurotrophin and cholinergic pathways.

Fate of the chemical warfare agent VX in asphalt: a novel approach for the quantitation of VX in organic surfaces

VX is one of the most toxic chemical warfare agents. Its low volatility and its persistence in the environment raise the issue of long-term exposure risks, either by inhalation or by transdermal penetration. Therefore, a topic of acute interest is the fate of VX in preservative environmental surfaces. In this work, the fate of VX in asphalt pavement, a suspected preservative matrix, was explored, by applying a novel quantitative method for the extraction of trapped VX from "digested" asphalt. It is based on dissolution of asphalt in toluene, precipitation of the heavy components by basic methanol followed by GC-NPD analysis. This method is complementary to methanol extraction of VX from the outer surface of asphalt, and enabled us to explore the total amount of viable VX both on and inside the matrix. Using this method, bis-diisopropylaminoethyl-disulfide [(DES)2], a degradation product of VX, was also assayed. Small chunks of Asphalt were spiked with VX, sealed and analyzed after various aging periods up to 425 days. The level of VX on the outer surface of the asphalt was found to be diminishing with time following a single-exponential decay. The level inside the asphalt increases during the first day, decays steeply to a level of about 5% during the following two weeks, and declines moderately during all the period up to 425 days following a bi-exponential decay. The total recovery of VX from the asphalt declined from almost 100% after 30 minutes to about 2% after 425 days, with a half-life of about 14 days.

Ab initio molecular orbital and density functional studies on the solvolysis of sarin and O,S-dimethyl methylphosphonothiolate, a VX-like compound

[reaction: see text] Potential energy surfaces for the alkaline hydrolysis of sarin and O,S-dimethyl methylphosphonothiolate, a VX model compound, and the perhydrolysis of the latter have been computed at the MP2/6-31+G(d)//mPW1K/MIDI! level of theory. The effect of aqueous solvation was accounted for via the integral equation formalism polarizable continuum model (IEF-PCM) at the HF/6-31+G(d) level. Excellent agreement with the experimental enthalpy of activation for alkaline hydrolysis of sarin was found. For the alkaline hydrolysis of O,S-dimethyl methylphosphonothiolate, it was found that the P-O and P-S bond cleavage processes are kinetically competitive but that the products of P-S bond cleavage are thermodynamically favored. For the perhydrolysis of O,S-dimethyl methylphosphonothiolate, it was found that P-O bond cleavage is not kinetically competitive with P-S bond cleavage. In both cases, the data support initial formation of trigonal bipyramidal intermediates and demonstrate kinetic selectivity for nucleophilic attack on the face opposite the more apicophilic methoxide ligand.

31P MAS NMR: a useful tool for the evaluation of VX natural weathering in various urban matrixes

The fate of chemical warfare agent VX (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate) in various urban matrixes was monitored utilizing 31P MAS NMR. Chosen matrixes represent buildings, roads, pavement, and earth found in urban environments. In view of the high toxicity of VX, solid state NMR afforded a fairly safe experimental mode, omitting any chance for evaporation. Moreover, due to the nondestructive nature of these experiments, measurements could be repeated over and over using the same samples. Degradation rates of VX were obtained and compared to provide a list of relative reactivity toward VX: concrete >> desert sand > beach sand > asphalt approximately to bitumen sheet. Chemical interactions between VX, its degradation products, and the matrixes were often expressed by widening of the peaks to the extent that mass balance could not be achieved. It is noteworthy that these experiments were usually carried out on crushed or milled specimens, allowing high reactivity and rapid reactions.

Photoassisted Reaction of Chemical Warfare Agent VX Droplets under UV Light Irradiation

A photoassisted reaction of O-ethyl S-[2-(diisopropylamino) ethyl] methylphosphonothioate (VX) droplets in air was carried out. The experimental results indicated that VX droplets could be easily and chemically transformed into other compounds under irradiation of a germicidal lamp over sufficient time. Quantum chemical calculation results demonstrated that UV light less than 278 nm wavelength could possibly initiate photoreaction of VX and that both P-S and P=O bonds in the VX molecule were lengthened. The identification of reaction products by gas and liquid chromatography mass spectroscopy and NMR revealed that the VX molecule in air under UV light irradiation could undergo isomerization of S-esters to O-esters, cleavage of P-S, S-C, and C-N bonds, and ozonation of tertiary amines.

Degradation kinetics of VX on concrete by secondary ion mass spectrometry

At trace coverages on concrete surfaces, the nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) degrades by cleavage of the P-S and S-C bonds, as revealed by periodic secondary ion mass spectrometry (SIMS). The observed kinetics were (pseudo-) first-order, with a half-life of 2-3 h at room temperature. The rate increased with surface pH and temperature, with an apparent second-order constant of k(OH) = 0.64 M(-1) min(-1) at 25 degrees C and an activation energy of 50-60 kJ mol(-1). These values are consistent with a degradation mechanism of alkaline hydrolysis within the adventitious water film on the concrete surface. Degradation of bulk VX on concrete would proceed more slowly.

Investigating the affinities and persistence of VX nerve agent in environmental matrices

Laboratory experiments were conducted to determine environmental variables that affect the affinities and persistence of the nerve agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) at dilute concentrations in environmental matrices. Quantitative analyses of VX and its degradation products were performed using LC-MS. Batch hydrolysis experiments demonstrated an increasing hydrolysis rate as pH increased, as shown in previous studies, but also indicated that dissolved aqueous constituents can cause significant differences in the absolute hydrolysis rate. Adsorption isotherms from batch aqueous experiments revealed that VX has a high affinity for hydrophobic organics, a moderate affinity for montmorillonite clay, and a very low affinity for an iron-oxyhydroxide soil mineral, goethite. The adsorption on goethite was increased with the presence of dissolved organic matter in solution. VX degraded rapidly when dried onto goethite, when specific adsorption was forced. No enhanced degradation occurred with goethite in small amounts of water. These results suggest that aqueous conditions have important controls on VX adsorption and degradation in the environment and a more mechanistic understanding of these controls is needed in order to enable accurate predictions of its long-term fate and persistence.

Effect of drop size on the degradation of VX in concrete

The effect of drop size on the degradation rate of VX, O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate, in fresh concrete has been examined using (31)P NMR. Drops of neat VX, ranging in size from 4 microL to 0.2 microL, applied to small concrete coupons (8 mm x 15 mm) were observed to degrade at different rates, with the 1 microL and smaller drops reacting in less than 4 days, and the larger droplets reacting in less than 11 days. Additionally, 4 microL VX predissolved in hexane to evenly spread it over the concrete coupon likewise reacted faster, degrading in less than 5 days. The fresh concrete, less than 2 months old, exhibited significantly faster VX degradation for all drop sizes than that observed for "aged" concrete in a previous study where VX persisted for months. The enhanced reactivity of the "fresh" concrete for VX was maintained for at least a 1-year period. The pH of water containing crushed "fresh" and "aged" concrete was 10.0 and 9.0, respectively. The higher pH of the "fresh" concrete is one reason for its enhanced reactivity toward VX. An additional contribution to the enhanced reactivity of the "fresh" concrete is suggested by the increased mobility of its sorbed VX as evidenced by its significantly narrower peak in (31)P NMR spectra.

Extraction of Nerve Agent VX from Soils

The development and optimization of a method allowing the extraction of intact organophosphorus chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) from several types of soils are presented here. This involved the selection of an appropriate buffer to bring the sample to a pH close to the pK(a) of VX but sufficiently low to avoid its basic hydrolysis. Buffering with Tris (pH 9) and subsequent extraction of the aqueous layer by a 85:15 (v/v) hexane/dichloromethane mixture allows rapid and sensitive flame photometric detection of VX at spiking levels lower than 10 microg x g(-1), even after 3 months of aging. Extraction yields were close to 60% in complex matrixes. This method also allows recovery and identification of a characteristic degradation product of VX, bis(2-diisopropylaminoethyl) disulfide, which appears to be formed during the aging process. The performance of this method is far better than that of OPCW reference operating procedure, which does not allow extraction of detectable amounts of VX (spiked at 10 microg x g(-1)) in one of the soils used for this study.