Polysaccharide-Thickened Aqueous Fluoride Solutions for Rapid

Feb 11, 2014 - Yoon Jeong Jang , Kibong Kim , Olga G. Tsay , David A. Atwood , and David G. Churchill. Chemical Reviews 2015 115 (24), PR1-PR76...
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Polysaccharide-Thickened Aqueous Fluoride Solutions for Rapid Destruction of the Nerve Agent VX. Introducing the Opportunity for Extensive Decontamination Scenarios Shlomi Elias, Sigal Saphier, Ishay Columbus,* and Yossi Zafrani* Department of Organic Chemistry, Israel Institute for Biological Research, Ness-Ziona, 74100, Israel S Supporting Information *

ABSTRACT: Among the chemical warfare agents, the ext rem ely t oxic n er ve ag en t V X (O-ethyl S-2(diisopropylamino)ethyl methylphosphonothioate) is a target of high importance in the development of decontamination methods, due to its indefinite persistence on common environmental surfaces. Liquid decontaminants are mostly characterized by high corrosivity, usually offer poor coverage, and tend to flow and accumulate in low areas. Therefore, the development of a noncorrosive decontaminant, sufficiently viscous to resist dripping from the contaminated surface, is necessary. In the present paper we studied different polysaccharides-thickened fluoride aqueous solutions as noncorrosive decontaminants for rapid and efficient VX degradation to the nontoxic product EMPA (ethyl methylphosphonic acid). Polysaccharides are environmentally benign, natural, and inexpensive. Other known decontaminants cannot be thickened by polysaccharides, due to the sensitivity of the latter toward basic or oxidizing agents. We found that the efficiency of VX degradation in these viscous solutions in terms of kinetics and product identity is similar to that of KF aqueous solutions. Guar gum (1.5 wt %) with 4 wt % KF was chosen for further evaluation. The benign nature, rheological properties, adhering capabilities to different surfaces, and decontamination from a porous matrix were examined. This formulation showed promising properties for implementation as a spray decontaminant for common and sensitive environmental surfaces.

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INTRODUCTION Detoxification of extremely toxic chemical warfare agents (CWAs) such as VX and GB (sarin) is a current concern not only due to the obvious military scenario but also owing to the fact that chemical terror is becoming more relevant than ever.1,2 During the past decade, the fate of CWAs in environmental matrices has been the focus of extensive research made by others and us.3−9 These studies led to the conclusion that rapid removal and preferably destruction of CWAs (in particular, the exceedingly persistent nerve agent VX) from diverse urban and environmental surfaces is required, in order to regain use of the affected area and equipment. Dealing with the remediation of a civilian area requires one to consider a population much more diverse and sensitive than the military one. As a result, the recommended thresholds for hazardous materials are lower by orders of magnitude for civilian population, as compared to the military thresholds. Considering the broad and complicated decontamination scenarios, various methods have been developed for the detoxification of CWAs.10,11 Simultaneously, there has been an ongoing effort to implement laboratory decontamination methods according to the field requirements.11b These include, for example, the liquid ‘Decon Green’ decontaminant, based on hydrogen peroxide,12 or SX3413,14 and FAST ACT15 systems, based on solid powder adsorbents. Liquid decontaminants usually offer poor coverage and tend to flow and © 2014 American Chemical Society

accumulate in low areas. Once applied, the desired decontaminant should flow sufficiently to avoid blockage of the dissemination equipment; however, it should be simultaneously adequately viscous and adhere to the contaminated surface for a prolonged contact time without dripping off. A few years ago, a formulation that utilizes potassium peroxymonosulfate (Oxone) gelled with fumed silica was developed for CWA oxidative degradation.16 In addition, a hypochlorite bleach gel patent was also published.17 The desired rheological characteristics were achieved using thickening agents. However, the intrinsic corrosivity problem still exists. Recently, following our ongoing studies regarding the fluoride ion reactivity toward organophosphorus compounds, we found that VX is catalytically degraded to the nontoxic product EMPA by water-swelled polymer-supported ammonium fluorides in heterogeneous solutions.18 Moreover, it is exclusively and rapidly degraded to EMPA even in dilute noncorrosive aqueous fluoride solutions.19 In most cases, the “G-analogue” (O-ethyl methylphosphonofluoridate, Et-G) was observed as an unstable intermediate (Scheme 1). Noteworthy is the fact that the Received: Revised: Accepted: Published: 2893

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(1), hydroxypropylmethyl cellulose (2), guar gum carboxy methylether 2-hydroxypropylether, sodium salt (3), guar gum 2hydroxy 3-(trimethylammonium)-propyl ether chloride (4), guar gum (5), and chitosan (6). Solutions were prepared by dissolving the appropriate amount of polysaccharide powder (1 or 1.5 wt %) in distilled water followed by vortex or mechanical stirring. For pH controlled experiments carbonate or Tris buffers were used instead of water. The buffered solutions (0.1 M each) were prepared by standard procedures, carbonate/bicarbonate buffer for pH 10.5 and 9.65, and Tris buffer for pH 8.64 and 7.45. KF was added directly as a solid, and the mixture was vortexed or stirred. KF was added in different amounts to give different percentages between 1 wt % and up to 7.5 wt %. For kinetic degradation experiments, 1 and 4 wt % KF were used, resulting in 5 or 18 mol equiv of salt per VX, respectively. Decontamination Kinetics and Product Determination. Caution: These experiments should only be performed by trained personnel using applicable safety procedures. An amount of 10 μL (0.037 mmol) of VX was added to 1 g of the total polysaccharide solution, and the mixture was vortexed and transferred to a Teflon NMR tube via a syringe. The tube was sealed with a Teflon cap and inserted into a glass NMR tube. 31P NMR spectra were measured periodically to determine the residual starting material amount and identify the degradation products. In cases where Tris buffer was used, the buffer component 3-amino-3-(2-hydroxy-ethyl)-pentane-1,5-diol reacted with Et-G to give the corresponding ester. It was assumed that this does not affect dramatically the outcome of the processes. The half-life times of the CWAs (VX and Et-G) were calculated from the slope of the plot of ln[%CWA] as a function of time. Due to the excess use and the catalytic nature of the fluoride in this reaction, the KF concentration is kept relatively constant. Therefore a pseudo-first-order reaction may be assumed. Viscosity Studies. Initial viscosity evaluations were performed by the tube inversion test. More precise measurements were performed using a Brookfield digital Viscometer Model LVDV-E, equipped with a LV4 cylindrical spindle. The effect of shear rate on the viscosity of selected samples was evaluated at ambient temperature using different spindle rates. Readings of viscosity were taken after two minutes at each spindle rate. Spraying. A Schlick device (Model 942/5, 1.8 mm droplets size) spray was used. A constant pressure of 2 bar dried compressed air was introduced to a syringe containing the solution. This allowed an absolute coverage of the desired surfaces. Corrosivity Evaluation. Iron, painted metal, and copper plates were cut to 1.5 × 2 cm pieces and immersed in different decontamination solutions. After three days, the plates were taken out, washed with distilled water, and dried. Wind Tunnel Experiments. The evaporation experiment was performed in a wind tunnel, situated in a chamber capable of determining and monitoring temperature, relative humidity, and air velocity. A detailed description of this laboratory setup was reported recently.5,8 Briefly, the contaminated surface was located in an inner chamber. Two sets of collecting vessels allowed continuous air sampling into a buffered solution. The analysis of VX concentration was based on Ellmann’s enzymatic method, utilizing various choline esterases. The typical protocol limitation in the evaporation studies was 0.15−0.35 ng/mL VX. The determination of VX concentration in the buffer solutions

Scheme 1

substantial formation of the toxic side product desethyl-VX ((diisopropylamino)ethyl methylphosphonothioic acid) in nonbuffered water (only slightly less toxic than VX)20 is completely avoided in the presence of fluoride ions. We have found both experimentally and using theoretical calculations that the facile degradation, even in dilute fluoride solutions, resulted from the increased fluoride reactivity toward the phosphorus atom. The fact that dilute fluoride solutions are both environmentally benign and noncorrosive, but still sufficiently effective in destroying organophosphorus CWAs, encouraged us to thicken these solutions using thickening agents. Polysaccharides (such as hydroxypropylmethyl cellulose, chitosan, and different types of guar gum) are well-known as very eco-friendly thickening agents and vastly used for various applications in pharmaceutics, cosmetics, and the food industry.21−23 Polysaccharides (naturally occurring or chemically modified) are the most common organic compounds on earth, and many of them can serve as excellent viscosity-increasing agents at very low concentrations. Herein, we wish to disclose our results on the preparation of various polysaccharide-based aqueous fluoride highly viscous solutions. Their ability to decontaminate VX was examined, both in terms of kinetics and product identity. In addition, the physical properties leading to easy dissemination and adhering capabilities to various surfaces and the corrosivity of a sample solution (guar gum 5) was studied. Finally, a preliminary decontamination simulation using a challenging matrix was conducted in our wind tunnel system.

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EXPERIMENTAL SECTION Reagents and Materials. VX was obtained locally at IIBR (>99% purity). KF was obtained from Merck. Carboxymethylcellulose sodium salt (1) was obtained from BDH Laboratory reagents. Hydroxypropylmethyl cellulose (2), guar gum carboxy methylether, 2-hydroxypropylether sodium salt (3), guar gum 2hydroxy 3-(trimethylammonium)-propyl ether chloride (4), guar gum (5), and chitosan (6) were obtained from SigmaAldrich. NMR. 31P and 19F NMR spectra were obtained at 202 and 471 MHz, respectively, on a 11.7 T (500 MHz) spectrometer. Chemical shifts for 31P and 19F were referenced to external trimethyl phosphate (TMP) and CFCl3, respectively, as 0 ppm. For 31P spectra the pulse delay was 2 s. The frequency offset was set between the signals of VX and EMPA. For comparison purposes, spectra were recorded under identical conditions. The chemical shifts (ppm, δ) for the organophosphorus compounds were as follows: VX: 57.7, desethyl-VX: 38.4, Et-G: 30.8 (d, J = 1053 Hz), EMPA: 22.4, EMPTA: 71.4. Preparation of Polysaccharide Solutions. Six polysaccharides were examined: carboxymethylcellulose, sodium salt 2894

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Figure 1. A. Selected 31P NMR spectra depicting the degradation profile of VX in polysaccharide 5 solution in the presence of 18 equivalents KF (run 9) after (I) 19 min, (II) 82 min, (III) 313 min. B. Selected 31P NMR spectra depicting the degradation profile of VX in polysaccharide 5 solution in the absence of KF (run 10) after (I) 18 min, (II) 1770 min, (III) 5.9 × 104 min.

after the dispersion, the surface was introduced into the wind tunnel for evaporation measurements.

enabled the calculation of VX concentration in the air during a certain sampling period. The environmental parameters were as follows: temperature (20 °C), relative humidity (20%), and wind speed (1.7 m/s). The contamination droplet size was 0.2 μL, and the surface concentration was 1 g/m2. Fifteen mg of VX was dispersed as small droplets over a 10 × 16 cm2 piece of a commercial red sidewalk brick.8 The gel solution (1.5% guar gum, 4% KF, in water) was dispersed (35 mL, 2.2 L/m2) on the contaminated surface 0.5 h after the VX contamination. Three h

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RESULTS AND DISCUSSION Solution Preparation and Kinetic Study of VX Degradation. An optimal formulation should consist of minimal concentrations of both polysaccharide and KF and be characterized by highly efficient decontamination. A variety of six polysaccharides (1−6), known among other functionalities as 2895

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Table 1. pH and VX Degradation Rates Using Various Polysaccharides with and without Fluoride in Nonbuffered Solutions run

polysaccharideb

polysaccaride concn [wt %]

KF concn [wt %]

pH

t(1/2) VX [min]

t(1/2) Et-G [min]

1 2 3 4 5 6 7 8 9 10 11 12 13

1 1 2 2 3 3 4 4 5 5 5 -

1.5 1.5 1.5 1.5 1 1 1 1 1.5 1.5 1.5 -

4 4 4 4 4 1 4 1

7.57 6.74 7.72 5.16 9.10 10.02 6.69 4.07 7.26 5.50 6.41 7.84 7.31

5.6 1.2 × 104a 5.7 1.4 × 104a 8.6 1.4 × 104a 3.9 1.7 × 104a 5.2 1.7 × 104a 20.8 6.9 19.6

82.5 108.3 119.5 88.9 93.7 433.2 111.8 216.6

a

Carboxymethylcellulose, sodium salt (1), hydroxypropylmethyl cellulose (2), guar gum carboxy methylether 2-hydroxypropylether, sodium salt (3), guar gum 2-hydroxy 3-(trimethylammonium)-propyl ether chloride (4), guar gum (5). bObtained rates without KF addition (in addition to EMPA, desethyl-VX was mainly formed).

Et-G) it can be concluded that only a few hours are required to obtain a total detoxification of the toxic ingredients. The polysaccharide solutions without KF showed very sluggish degradation rates (t1/2 = 1.2 × 104−1.7 × 104 min), and desethylVX formation emphasizes the necessity of KF in the degradation process (runs 2, 4, 6, 8, 10). pH Effect. Obviously, the fact that the intermediate Et-G (sarin analogue) is degraded to EMPA indicates that this formulation is appropriate for decontamination of both V and G nerve agent’s families. In order to facilitate even further the degradation of the G group we proceeded to study the pH effect considering both the kinetics and products of this process. Accordingly, the pH of the different thickened solutions was measured (Table 1). We found that the pH range was relatively similar to the aqueous solutions in the absence of the polysaccharide, excluding polysaccharide 3 which initially exhibited a basic pH. It is expected that a more acidic pH will accelerate the degradation rate of VX, whereas a more basic pH will enhance the Et-G degradation rate.19 However, such a linear correlation between the initial pH values to the degradation rates was not observed. This may result from a pH increase (10.5) upon VX addition.19 Consequently, in an additional set of experiments, VX was added to KF/polysaccharide 5 solutions prepared in buffered solutions with pH values ranging from 7.3 to 10.5. It is worth noting that the viscosity of the formulations did not seem to be impaired by the buffer components (Tris or carbonate/bicarbonate), and, therefore, it may serve as a potential decontamination formulation. The degradation rates are summarized in Table 2. As expected, at a constant mild basic pH value (∼10.5), any Et-G formed was immediately hydrolyzed

thickening agents, were used for initial evaluation. Most preparations containing 1 wt % polysaccharide (prior the addition of KF) gave viscous solutions except for hydroxypropylmethyl cellulose (2). In general, increasing the polysaccharide concentration to 1.5 wt % gave more viscous solutions with gellike characteristics. A complete dissolution of chitosan (6) required a slight addition of HCl lowering the pH value to 5. Therefore, the last solution was not further examined. Addition of 4 wt % KF to all solutions did not seem to impair the solution’s viscosity and enabled us to further perform the decontamination assays effectively. VX degradation (1 wt %, 37.5 mM) and product formation were followed using 31P NMR for polysaccharides 1−5 aqueous fluoride solutions (1 or 4 wt % KF, 5 equiv or 18 equiv relative to VX, respectively). As a control, for each polysaccharide, VX degradation in the polysaccharide solution lacking KF was examined (see for example Figure 1A,B). Degradation of VX in a KF solution using distilled water (in the absence of polysaccharide) was used as an additional control. Polysaccharide solutions containing KF gave immediately a mixture of Et-G and EMPA. As the reaction progressed, the only phosphorus containing product remaining was EMPA. The halflife times (t1/2, pseudo- first-order) of VX and Et-G in nonbuffered solutions were calculated and are summarized in Table 1. Even though the various polysaccharides led to different pH values of the solutions, the fluoride ion efficiently catalyzed VX degradation in all cases. The results are similar to our previous kinetics study on VX degradation in aqueous fluoride solutions.19 Initially, a substitution of the aminoethylthiol group occurs via a rapid nucleophilic fluoride ion attack on the phosphorus, followed by hydrolysis of the formed intermediate Et-G to form EMPA. Significantly, according to these results, it is demonstrated that the presence of the polysaccharides did not impair the rapid degradation process. The corresponding data (Figures S1−S17 in the Supporting Information) show that the VX degradation profiles for all 1−5 polysaccharides fluoride solutions exhibited an exponential decay. Higher KF concentrations (18 vs 5 equiv relative to VX) shortened the half-life times of VX (runs 11 vs 9). Also, it should be noted that this process does not involve the generation of the undesired toxic product desethyl-VX, which was formed (ca. 40%) in polysaccharide solutions without KF. According to calculation of the total time for degradation by polysaccharide/KF solutions (>99.5%, 8 half-life times of VX and

Table 2. VX and Et-G Degradation Rates in Different Buffered Solutions Containing Polysaccharide 5 (1.5 wt %) and 18 equiv of KF run

buffered solution pH

final pH solution (after KF addition)

t(1/2) VX [min]

t(1/2) Et-G [min]

14 15 16 17

7.29a 8.67a 9.66b 10.5b

7.50 9.00 9.56 10.40

5.3 5.1 4.7 13.3

51.3 26 9.3 -

a

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to EMPA (run 17). Once again, it should be noted that the formation of desethyl-VX was avoided during this process. Viscosity Studies and Surface Adhering Assay. An optimal formulation for the decontaminant, in addition to highly efficient decontamination, should be characterized by good sprayability and adhesion to surfaces. Polysaccharide 5 was chosen to demonstrate the applicability of the formulation due to its high availability, low cost, and relatively rapid VX degradation rate. The desired physical properties of the solution would obviously be influenced by the concentration of both components, namely, polysaccharide and KF. Following preliminary results, it seemed that the desired viscosity would be achieved in the range of 1−1.5 wt % of guar gum. It has been shown that the mixing conditions may affect the rheological properties of polysaccharide hydrocolloids.24 Indeed, more vigorous stirring of small volumes by vortex led to enhanced viscosity and gel-like properties in the 1.5 wt % solutions. This was exemplified by the preparation of a 1 wt % and 1.5 wt % guar gum solutions, followed by the addition of 4 wt % KF and a 0.5 wt % green coloring agent. After each step, the solutions were vigorously stirred by vortex. The resultant solutions were subjected to the tube inversion test, and the 1.5 wt % solution showed flow resistance, as shown in Figure 2. The

Figure 3. Viscosity of guar gum solutions with different concentrations of KF.

viscosity and avoid draining from the inclined surface once deposited.28 The pseudoplasticity and thixotropy of the guar gum solution containing KF was investigated and compared to a solution without KF. In Figure 4a, the expected performance of the guar gum solution can be observed. First, the viscosity was measured with periodic (2 min) increase of shear rate up to 100 rpm. The viscosity decreased upon increase of shear rate (blue arrow pointing down). This demonstrates the shear thinning characteristic of the solution. The ramp direction was reversed, and measurements were taken at decreasing shear rates back to the starting point (blue arrow pointing up). The “up” and “down” curves did not fully coincide. This hysteresis loop illustrates that the solution is thixotropic. The hysteresis loop formed for both solutions showed that the KF addition did not reduce the thixothropic property of the solution; on the contrary, the gap between the “down” curve and “up” curve increased, meaning that the thixotopic properties are greater in the KF containing solution. Next, we examined the solution’s ability to adhere to different types of surfaces at a roughly perpendicular position. For this purpose the 1.5 wt % guar gum containing 4 wt % KF formulation was sprayed over different types of surfaces (left to right): A rough metal, B - commercial red sidewalk brick (a concrete brick containing added iron oxide as a red pigment), C - smooth white painted metal, D - stainless steel, E - glass (Figure 5a). The solutions were shaken prior to spraying for reducing the viscosity (pseudoplastic behavior). The sprayed solution adhered well to the different surfaces, and dripping was not observed. For surfaces A and B there was some penetration of the solution inside the bulk material leading to an observed thinner layer. The dried formulation was also examined the subsequent day (Figure 5b), demonstrating efficient and stable adherence to the surfaces. Corrosivity Evaluation. As mentioned, the KF thickened solution based on the polysaccharide guar gum is expected to be environmentally benign and noncorrosive. Illustration of this point was performed on some representative surfaces in comparison to other common solution based decontaminants. Sodium hypochlorite and potassium peroxymonosulfate (Oxone) were taken as representative oxidizing agents. Oxone is the active ingredient in the L-gel decontaminant formulation.16 The commercial strongly basic decontamination solutions DS2 and GDS2000 were also examined. Three types of representative sensitive surfaces were chosen for corrosivity assessment: iron, painted coated metal, and copper. The plates were immersed in the solutions for three days. These extreme conditions were used in order to observe the maximal harmful effect that might occur from the KF/guar gum solution. As could be expected the oxidizing agents bleach and Oxone were the most corrosive,

Figure 2. Tube Inversion tests for 1 (left) and 1.5 (right) wt % solutions of guar gum (5).

1 wt % polysaccharide solution displayed a lower viscosity compared to the 1.5 wt % solution and showed an immediate flow upon inversion. As indicated in Figure 2, the 1.5 wt % solution also demonstrates good adherence to the glass vial. Yet, this high viscosity did not prevent efficient dissemination, as will be further discussed. Thus, this polysaccharide concentration was chosen as a suitable candidate for further examination. The addition of salts may strongly influence the properties of polysaccharide solutions.25−27 Either mono- or divalent cations can lead to precipitation or to enhancement/reduction of the viscosity. The viscosity of a series of guar gum solutions with increasing concentrations of KF was measured under the same shear rate and time to measurement for all samples. A small decline in viscosity was observed as the amount of KF was increased (Figure 3). The changes in viscosity were found to be relatively small. At the highest KF concentration prepared (7.5 wt %), the viscosity decrease was around 20%, relative to the polysaccharide solution without KF. Considering these results combined with the kinetic data, a concentration of 4 wt % KF was chosen for further characterization. Guar gum forms solutions in water, which are both pseudoplastic (decreasing viscosity with an increasing shear rate − shear thining) and thixotropic (decreasing viscosity with time while subjected to constant shear rate). These properties are important for enabling thinning of the solution upon stirring or shaking. The shaken solution can easily be sprayed and will gain 2897

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Figure 4. Viscosity changes as a function of spindle rate. A: 1.5 wt % guar gum. B: 1.5 wt % guar gum +4 wt % KF (• measurements at increasing shear rates, ○ measurements at decreasing shear rates).

closer results to those observed in situ. A more challenging situation occurs with porous surfaces where VX is known to be adsorbed and preserved. Aiming to address this issue, we performed a decontamination scenario selecting concrete (commercial red sidewalk bricks) as a porous surface contaminated with VX. Our leading thickened formulation, KF/polysaccharide 5 gel solution, was implemented on the contaminated surface, which was then introduced into the wind tunnel. Figure 7 shows VX volatilization profiles from the concrete surfaces, with and without decontamination. We have found that in spite of the very low concentration of this formulation (only 4 wt % of fluoride) one-day long evaporation was sufficient to reduce VX concentration by 2−3 orders of magnitude relative to the nondecontaminated surface. Initially, a rapid reduction in VX concentration was observed. After one day, a distortion from linearity occurred and the degradation rate diminished. At this point we assume that extensive water evaporation has taken place, and this led to quenching of the degradation process. One should note that these conditions, in which a high wind speed is implemented (1.7 m/s), might slow down the degradation process (the fluoride-promoted hydrolysis) due to water evaporation from the formulation. Further experiments, using water addition or less evaporative conditions, may show an improved performance regarding the American threshold (see dashed line). In conclusion, the ability to form viscous aqueous fluoride solutions with different polysaccharides was examined, and the efficiency of VX degradation was explored. It was shown that these formulations exhibited fast VX degradation rates initially forming Et-G by a fluoride substitution (t1/2 = 3.9−20.8 min), which was eventually hydrolyzed to the nontoxic EMPA product. Based on control experiments, it was established that thickening the solutions using polysaccharides does not interfere with the degradation efficiency. From a toxicological point of view, in spite of the fact that these noncorrosive thickened solutions contain ca. 95 wt % of water, the toxic side-product desethyl-VX was not generated, which emphasizes the importance of this formulation. In the absence of KF, very sluggish degradation rates were obtained, forming the toxic desethyl-VX byproduct. The pH value of the solution plays a significant role in the degradation kinetics and products distribution, specifically important is the absence of Et-G intermediate under the action of slightly basic (pH 10.5) buffered solutions. According to the presented results, we can conclude that low cost environmentally benign polysaccharides, commonly used in

Figure 5. 1.5 wt % solution of guar gum (5) (+4% KF) sprayed over different types of surfaces (a) a few minutes after spraying and (b) 1 day after spraying.

harming all types of surfaces (Figure 6). Basic nucleophiles also damaged the surfaces, although to a lower extent. Regarding the painted metal, the paint was pilled-off, and some corrosivity was found on the metal surfaces. In contrast, no differences could be observed between plates exposed to KF/guar gum solution and control plates with no treatment at all. These results exemplify the gentle nature of our new decontaminant formulation, even at long exposure times. Decontamination Experiment on a Porous Surface. The high efficiency of the above-mentioned gel formulation in situ (tube tests) led us to perform a preliminary evaluation of its performance in simulated contamination experiments in our wind tunnel.8 We assume that the decontamination of most surfaces presented in Figure 5, mainly inert and nonporous surfaces (known to be nonconserving of VX), would lead to 2898

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Figure 6. Corrosivity of different decontaminants on different surfaces.

Figure 7. Volatilization of 15 mg of VX from commercial red bricks (1 g/m2) at 20 °C with (green) and without (red) treatment of KF/polysaccharide 5 solution. The dashed line represents a possible extrapolation assuming no water evaporation from the surface.

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the pharmaceutical, cosmetics, and food industries, were found to be very compatible and efficient as additives to fluoride solutions. Thickened solutions were obtained with favorable rheological properties. The shear thinning effects enabled easy spraying of these solutions that can adhere to sensitive and perpendicular surfaces and accomplish a gentle, noncorrosive decontamination process. In this way, we introduce the opportunity for broad decontamination scenarios where spraying the decontaminant is required, enabling an efficient and extended covering of the toxic CWA (V and G types) which is subsequently chemically destructed.

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(1) Okumura, T.; Takasu, N.; Ishimatsu, S.; Miyanoki, S.; Mitsuhashi, A.; Kumada, K.; Tanaka, K.; Hinohara, S. Report on 640 victims of the Tokyo subway sarin attack. Ann. Emer. Med. 1996, 28 (2), 129−135. (2) Forensic aspects of chemical and biological terrorism. Wecht, C. H., Ed.; Lawyers and Judges Publishing Co, Inc.: Tucson, AZ, 2004; pp 41−42. (3) Mount, C.; Begos, A.; Bellier, B. Extraction of nerve agent VX from soils. Anal. Chem. 2004, 76, 2791−2797. (4) Love, A. H.; Vance, A. L.; Reynolds, J. G.; Davisson, M. L. Investigating the affinity and persistence of VX nerve agent in environmental matrices. Chemosphere 2004, 57, 1257−1264. (5) Waysbort, D.; Manisterski, E.; Leader, H.; Manisterski, B.; Ashani, Y. Laboratory setup for long-term monitoring of the volatilization of hazardous materials: preliminary tests of O-ethyl S-2-(N,Ndiisopropylamino)ethyl methylphosphonothiolate on asphalt. Environ. Sci. Technol. 2004, 38, 2217−2223. (6) Mizrahi, D. M. Columbus I. 31P MAS NMR: A useful tool for the evaluation of VX natural weathering on various urban matrixes. Environ. Sci. Technol. 2005, 39, 8931−8395. (7) Mizrahi, D. M.; Goldvaser, M.; Columbus, I. Long term evaluation of the fate of sulfur mustard on dry and humid soils, asphalt, and concrete. Environ. Sci. Technol. 2011, 45, 3466−3472. (8) Columbus, I.; Waysbort, D.; Marcovitch, I.; Yehezkel, L.; Mizrahi, D. M. VX fate on common matrices: evaporation versus degradation. Environ. Sci. Technol. 2012, 46, 3921−3927. (9) Brevett, C.; Sumpter, K. B.; Pence, J. J.; Nickol, R. G.; King, B. E.; Giannaras, C. V.; Durst, H. D. Evaporation and degradation of VX on silica sand. J. Phys. Chem. C 2009, 113, 6622−6633.

ASSOCIATED CONTENT

S Supporting Information *

Figures S1−S17 provide VX degradation profiles for polysaccharides 1−5 in aqueous or buffered solutions, with and without the addition of KF and control experiments in the absence of the polysaccharide. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*Phone: 972 8 9381711. Fax: 972 8 9381548. E-mail: yossiz@ iibr.gov.il (Y.Z.). *E-mail: [email protected] (I.C.). Notes

The authors declare no competing financial interest. 2899

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dx.doi.org/10.1021/es4056388 | Environ. Sci. Technol. 2014, 48, 2893−2900