Mitigation of VX Effluents in Thorough Decontamination Operations

Research Note pubs.acs.org/IECR

Mitigation of VX Effluents in Thorough Decontamination Operations George W. Wagner* and Roberta Xega U.S. Army Edgewood Chemical Biological Center, Attn: RDCB-DRP-F, Aberdeen Proving Ground, Maryland 21010-5424, United States S Supporting Information *

ABSTRACT: Effluents resulting from the decontamination of VX from CARC-painted panels using DF200 have been studied to determine the presence of toxic species. The effect of concrete and sand (two possible sump materials) on the effluents is also examined. Wash-effluents, generated by washing the panel with hot soapy water prior to decontamination, contain high levels of VX which slowly hydrolyze to nontoxic EMPTA, EMPA, and toxic EA-2192, with concrete tending to minimize formation of the latter. Rinse-effluents, generated following decontamination, contain lower levels of VX which tend to fall below acceptable levels (20 ppb) within several hours in contact with sand. VX in rinse-effluents in contact with concrete persists for up to a week, consistent with the decomposition by concrete of active H2O2 in any residual DF200. EA-2192 persists for at least a week in rinse-effluentsin contact with either sand or concrete. Lining sump pits with HTH is a possible mitigation strategy as this decontaminant readily oxidizes residual VX, EA-2192, and even EMPTA to nontoxic EMPA and MPA.

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INTRODUCTION U.S. Army Field Manual 3-5 (FM 3-5)1 details the procedures to be used for the thorough decontamination of military vehicles in the field. Four stations are specified: (1) initial wash; (2) decontaminant application; (3) contact time (to allow applied decontamination to effect neutralization); and (4) final rinse. Each vehicle requires about 250 gallons of water for washing, 15 gallons of decontaminant, and 200 gallons of water for the final rinse; thus, the volume of effluent during decontamination operations is quite large, being contained in ditches and sumps constructed on site. Sumps are typically dug next to stations 1 and 4, catching the effluents resulting from washing and rinsing operations separately. To enable safe operations within the vicinity of the sumps, knowledge of the persistence of any toxic constituents contained in the effluents is required. In addition, the mitigation of any toxic constituents would facilitate the safe handling and environmentally responsible disposal of decontamination effluents. In this preliminary study, effluents resulting from the decontamination of VX [S-2-(diisopropylamino)ethyl O-ethyl methylphosphonothioate]and the persistence and mitigation of any toxic byproductsare examined in lab-scale experiments. Many strategies exist to decontaminate VX.2 The newest decontaminants are those formulated with hydrogen peroxide (H2O2), such as DF2003 which was supplied to U.S. troops during the recently ended Iraq War (2003−2011).4 Scheme 1 shows the reaction of VX with H2O2-based decontaminants,5 which are typically rendered basic to generate the peroxyanion (OOH−)a powerful nucleophile for VX.6 Besides fast reaction rates, perhydrolysis of VX also avoids formation of toxic EA-2192 [S-2-(diisopropylamino)ethyl methylphosphonothioic acid, Scheme 1], exclusively generating nontoxic ethyl methylphosophonic acid (EMPA) and dissopropylaminoethanethiol (DESH). Under simple basic hydrolysis (OH−), as much as 13% EA-2192 has been shown to form.6 Adding equimolar, or less, amounts of water to VX also avoids formation of toxic EA-2192 as a slow, selective This article not subject to U.S. Copyright. Published 2012 by the American Chemical Society

Scheme 1. Perhydrolysis of VX

hydrolysis to nontoxic EMPA ensues.7 However, the reverse is not true: When small amounts of VX are added to water, the major product is, in fact, EA-2192 (Scheme 2),8 along with Scheme 2. VX Hydrolysis in Excess Neutral Water

lesser amounts of EMPA and the perhaps higher-profile,9−11 but still nontoxic, EMPTA (O-ethyl methylphosphonothioic acid). Thus, VX in excess water tends to react via cleavage of P−O, P−S, and S−C bonds12 to form EA-2192, EMPA, and EMPTA, respectively. This undesired behavior of VX in water Received: Revised: Accepted: Published: 16146

July 11, 2012 October 31, 2012 November 23, 2012 November 23, 2012 dx.doi.org/10.1021/ie301836q | Ind. Eng. Chem. Res. 2012, 51, 16146−16150

Industrial & Engineering Chemistry Research

Research Note

Figure 1. Degradation profiles for VX wash-effluent samples in contact with glass (control), concrete, and sand as determined by 31P NMR.

decontaminant to 20 mL rinsewater is proportional to field conditions1). These rinse-effluent vials were removed and capped for analysis. The effect of concrete on DF200 was assessed using a 100ppm stock solution of VX in water which was allowed to partially degrade to EA-2192 and EMPA. Three samples were then prepared in 10-mm NMR tubes using the degraded stock solution: (1) 1.75 mL of stock solution, 1.75 mL of water (control); (2) 1.75 mL of stock solution, 1.65 mL of water, 0.1 mL of DF200 (added in this order); and (3) 0.088 g of concrete, 1.65 mL of water, 0.1 mL of DF200, 1.75 mL of stock solution (added in this order). The samples were then analyzed by 31P NMR to determine the extent of reaction for VX and EA-2192. 31 P NMR was employed to analyze the more concentrated wash-effluent samples using a Varian 300 Unityplus NMR spectrometer fitted with a standard 5 mm NMR probe. To analyze the more dilute samples of the VX/DF200/concrete decontamination test, a 10 mm NMR probe was used on the same instrument. 31P NMR spectra were referenced to an external sample of H3PO4, the standard 31P NMR shift reference; its value is assigned to 0 ppm on the 31P NMR chemical shift reference scale. The separation of VX and EA2192 was carried out using an UPLC system (consisting of vacuum degasser, autosampler, and binary pump) (Acquity, Waters, MA, USA) equipped with a reversed phase Pinnacle DB IBD biphenyl column of 50 × 2.1 mm with particle size 1.9 μm (Restek, Corp, USA). Column temperature was maintained at 40 °C. Mobile phases A and B were water and methanol. The mobile phase was prepared by adding 2 mL of 1 M ammonium formate and 2 mL of 1 M formic acid in 1 L of water (A) or methanol (B). A gradient elution was made using the binary gradient of UPLC pump as follows: 0−0.38 min, 90% A/10% B; 0.38−3.5 min 100% B; 4− 5 min, 90% A/10% B. The flow rate was kept constant at 0.4 mL/min. Total run time was 5 min, and injection volume was 2.0 μL. The UPLC system was coupled with a Quattro Premier triple quadrupole mass spectrometer (Waters, MA, USA) equipped with an electrospray ionization (ESI) interface and Mass Lynx software (Version 4.1). The tandem mass spectrometer was operated at positive electrospray ionization mode for VX and EA-2192 detection. Data acquisition was performed working in multiple reaction monitoring (MRM) mode. Capillary voltage was 3.0 kV; nitrogen was used as spray gas. Source temperature was set at 120 °C. The optimized setting for cone voltage (CV) was 30 V. Collision energy (CE) was varied between (8−30 V). The collision gas was argon. The transition which corresponds to most abundant product ion was used for quantitation, and the second one for identification

will manifest itself during thorough decontamination operations, impacting especially the wash station effluent. Another factor affecting the formation and persistence of toxic byproducts of VX is the material of construction of the sumps themselves. In this preliminary paper, contact of decontamination effluents with concrete and sand are examined. The fate of VX on concrete and sand is rather well-understood.13−19 On concrete, the desired degradation of VX to nontoxic EMPA is observed.13−19 On dry sand, VX also primarily yields EMPA, with some EMPTA forming, depending on the type of sand.18,19 However, on wet sand VX is observed to yield ca. 10% EA-2192,19 presumably owing to the mechanism in Scheme 2. Thus, use of a concrete surface to receive decontamination effluents may offer an advantage over that of sand in avoiding formation of the toxic byproduct EA2192 during VX decontamination operations. In this communication, effluents are generated from the decontamination of VX-contaminated CARC panels using DF200 in a manner described previously,20 with residual VX and EA-2192 being monitored to 20 ppbthe drinking water standard for VX.21

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EXPERIMENTAL SECTION DF200 was provided by Mr. Lawrence Procell, ECBC. Samples of the concrete and sand, “AFS-50 Fine Sand”19 and “C04″,22 were provided by Dr. Carol Brevett, SAIC. VX and CARCpainted aluminum panels were obtained locally at ECBC. The soap utilized for the hot soapy water wash1 was Baum’s Product Kleenrinse Car Wash (Rome, NY). Using a slightly modified procedure1 from that previously described,20 three 2 in. diameter CARC panels were contaminated with 10 2 μL drops of VX (10 g/m2), covered, and allowed to stand for 1 h. The panels were then held over 4 in. glass funnels and washed, without agitation or scrubbing, with 20 mL of hot (60 °C) soapy water1, the “wash effluents” being caught in 40 mL glass vials placed under the funnels. These wash-effluent vials were removed and capped for analysis. Besides an empty glass vial for the control, two other vials containing 0.5 g of crushed C04 concrete and AFS50 Fine Sand were used to simulate effluent in contact with sumps comprising these materials. Following the wash procedure, the CARC panels were placed in fresh 4 in. funnels fitted with fresh 40 mL vials (one empty and two containing 0.5 g of crushed concrete and sand), and 1 mL of DF200 was applied as a liquid (foam was not used) to the panels, evenly distributed with the pipet tip; the panels were allowed to stand, covered, for 30 min. Following the 30 min decontamination time the three panels were rinsed over the same funnels/40 mL vials with 20 mL of room temperature water (the ratio of 1 mL 16147

dx.doi.org/10.1021/ie301836q | Ind. Eng. Chem. Res. 2012, 51, 16146−16150


Research Note

Table 1. Degradation of VX Rinse-Effluents As Determined by LC−MS VX glass concrete sand a

EA-2192

3h

5h

1 day

1 week

2h

6h

1 day

1 week

300 ppb 2600 ppb 230 ppb

a 680 ppb a

a 110 ppb a

a a a

48 ppb 150 ppb 41 ppb


25 ppb 130 ppb a


Below 20 ppb threshold.

of DF200 by the concrete. Thus although the C04 concrete is considered “low iron”,25 0.58 wt % Fe,26 it still contains enough, apparently, to effect H2O2 decomposition as confirmed by results for VX/EA-2192 decontamination by DF200 with and without the presence of concrete (Table 2; see

purposes. The calibration range for EA-2192 was 4−100 ng/ mL, while the VX calibration range was 4−120 ng/mL.

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RESULTS AND DISCUSSION Wash-Effluent. Degradation profiles for VX wash-effluent in contact with glass (control), concrete, and sand as measured by 31P NMR are shown in Figure 1. In agreement with the anticipated behavior of VX,8 substantial amounts of toxic EA2192 are observed to form for the wash-effluent in contact with glass. Similar results are seen for the wash-effluent in contact with sand, where large amounts of EA-2192 also form, consistent with the results of Brevett et al.19 for VX deposited on wet sand. For the wash-effluent in contact with concrete, however, the formation of EA-2192 is diminished. Although EA-2192 was not previously observed to form for VX deposited on concrete,13−18 it can form for water solutions in contact with concrete, and, presumably, on wet concrete as well (analogous to the case of dry18,19 vs wet19 sand). The enhanced reactivity exhibited by the concrete requires additional comments. For convenience, crushed concrete was used which, compared to uncrushed monoliths, has been shown14 to afford faster VX degradation. Crushing does perhaps expose more basic reactive surfaces than that afforded by monoliths, yet degradation of EA-2192 has been observed on concrete monoliths.23 The pH of the wash-water in contact with the crushed concrete was not measured, but it can reasonably be expected to be higher than that of either the glass control or sand. For normal (uncrushed) concrete surfaces, then, somewhat slower degradation rates would reasonably be anticipated. Clearly, further experimentation is required to better define the beneficial reactivity of concrete observed in this initial study. Rinse-Effluent. Degradation profiles for the VX rinseeffluent in contact with glass (control), concrete, and sand as determined by LC−MS are shown in Table 1. It should be stressed that DF200 was merely used as the vehicle to generate the effluent. As CARC paint is sorptive for VX,20 any decontamination with any decontaminant would result in the presence of residual VX (and EA-219224). Thus, no firm conclusions can be drawn regarding the relative effectiveness of DF200 for the decontamination of VX on CARC paint simply from these experiments. Direct comparison with other decontaminants is required, which is beyond the scope of the current study. For the rinse samples, only the toxic species of concern, residual VX and EA-2192, were monitored for experimental expediency (NMR detects other degradation products directly; LC−MS requires additional calibration samples and curves to detect the other less-important, nontoxic products). The first striking result is the large, initial amounts of both VX and EA219224 for the rinse-effluents in contact with concrete, compared to either the glass control or sand. This difference is attributed to decomposition of the reactive H2O2 component

Table 2. Decontamination of VX and EA2192 by DF200 in the Absence and Presence of Concrete As Determined by 31 P NMR starting amounts DF200/no concrete DF200/with concrete a

VX

EA-2192

EMPA

13 ppm a 3.7 ppm

15 ppm 6.0 ppm 12 ppm

10 ppm 21 ppm 16 ppm

Below detection limit of 1 ppm.

Experimental Section). (Vigorous bubbling of the DF200 solution in contact with the concrete confirmed H 2O 2 decomposition was indeed occurring.) Industrially, various additives are employed to stabilize H2O2 for storage,27 but it is beyond the scope of the current work to assess the effectiveness of these stabilizers in decontaminants such as DF200. VX in the rinse-effluents showed rather quick degradation within the first several hours, with the samples in contact with glass and sand falling below the 20 ppb threshold. And although the sample in contact with concrete was initially more concentrated, it also showed steady decay, falling below the 20 ppb threshold within 1 week. EA-2192, however, as in the case of the wash-effluents, persisted for samples in contact with all three materials during the week-long monitoring period. Additional work would be required to compare the degradation rates of EA-2192 observed in these experiments to that of EA2192 in water alone. Mitigation of Toxic Effluents. That the presence of toxic VX and/or EA-2912 has been established in thorough decontamination effluents, mitigation of the material is desired to enable safe operations within the vicinity of the sump pits and to ease restrictions on the handling, transportation, and eventual disposal of the waste. One possible mitigation strategy would be to use a common battlefield decontaminant, solid HTH powder1 (an effective decontaminant for VX2), to line the sump pits prior to commencing decontamination operations. As shown by the 31P NMR spectra in Figure 2, adding HTH to a VX wash-effluent containing EMPTA, VX, EA-2192, and EMPA, readily converts the species with oxidizable sulfur groups,2 VX, EA-2192, EMPTA, to nontoxic EMPA (in the cases of VX and EMPTA) and nontoxic methylphosphonic acid (MPA, in the case of EA-2192). The reaction mechanism2 is depicted in Scheme 3. Thus, the addition of HTH to the sump pits during decontamination operations is one viable option for mitigating the toxic hazards of VX and EA-2192 in wash- and rinse-effluents. Additional work is needed to determine the longevity of HTH in sumps 16148



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Research Note

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Carol A. S. Brevett for many helpful discussions on the fate of VX in sand. Support of this work was provided through the Defense Threat Reduction Agency (DTRA) under Project No. BB11PHM154.

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Figure 2. 31P NMR spectra obtained for VX wash-effluent with (top) and without (bottom) added HTH.

Scheme 3. Reactions of Effluent Species with HTH

during decontamination operations and how often it would need replenishment.

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CONCLUSIONS VX produces toxic effluents in thorough decontamination operations. In wash-effluents (generated prior to decontamination) residual VX persists for more than a month and hydrolyzes to toxic EA-2192, although contact with a concrete sump surface should tend to minimize its formation. For rinseeffluents, generated following decontamination, residual VX should quickly fall to below acceptable limits (20 ppb) within several hours when in contact with a sand sump surface; yet, residual VX could persist for up to a week when in contact with concretean observation consistent with the observed decomposition of the employed decontaminant’s active H2O2 by concrete. EA-2912 persists for at least a week in rinseeffluents, regardless of the sump material. One possible mitigation strategy for ridding wash- and rinse-effluents of toxic VX and EA-2192 is lining the sump pits with HTH as this decontaminant oxidizes VX, EA-2912, and even EMPTA, to nontoxic EMPA and MPA.

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REFERENCES

(1) NBC Decontamination, Field Manual 3-5; Department of the Army: Washington, DC, July 2000 (unclassified). (2) Yang, Y.-C.; Baker, J. A.; Ward, J. R. Decontamination of Chemical Warfare Agents. Chem. Rev. 1992, 92, 1729−1743. (3) See http://www.easydecon.com/easydecon/FactSheet69ca.html (accessed October 9, 2012). DF200 utilizes 7.95% H2O2; the concentration of H2O2 is about half this in the final, mixed decontaminant. (4) See http://www.easydecon.com/news/Lynch.pdf (accessed April 6, 2012). (5) A reviewer of this manuscript pointed out that N-chloroamines also decontaminate VX.2 A major advantage of using H2O2 rather than these types of reactive materials is the lack of any persistent residue: H2O2 decomposes to water and oxygen, whereas the amine compound remains following action of its N−Cl groups. (6) Yang, Y.-C.; Berg, F. J.; Szafraniec, L. L.; Beaudry, W. T.; Bunton, C. A.; Kumar, A. Perhydrolysis of Nerve Agent VX and Model Compounds and Related Nucleophlic Reactions. J. Chem. Soc., Perkin Trans. 2 1997, 607−613. (7) Yang, Y.-C.; Szafraniec, L. L.; Beaudry, W. T.; Procell, L. R.; Rohrbaugh, D. K.; Samuel, J. B. Autocatalytic Hydrolysis of V-Type Nerve Agents. J. Org. Chem. 1996, 61, 8407−8413. (8) Szafraniec, L. J.; Szafraniec, L. L.; Beaudry, W. T.; Ward, J. R. On the Stoichiometry of Phosphonthiolate Ester Hydrolysis. CRDEC-TR212. Aberdeen Proving Ground, MD, July 1990; unclassified report. (9) Ember, L. Soil Sample Key to U.S. Missile Strike in Sudan. Chem. Eng. News 1998, 76 (35), 6−7. (10) Rouhi, M. No Trace of Nerve Gas Precursor Found at Bombed Sudan Plant. Chem. Eng. News 1999, 77 (7), 11−12. (11) Rouhi, M. Analytical Credibility. Chem. Eng. News 1999, 77 (8), 37. (12) Yang, Y.-C. Chemical Detoxification of Nerve Agent VX. Acc. Chem. Res. 1999, 32, 109−115. (13) Groenewold, G. S.; Appelhans, A. D.; Gresham, G. L.; Olson, J. E.; Jeffery, M.; Weibel, M. Characterization of VX on Concrete Using Ion Trap Secondary Ion Mass Spectrometry. J. Am. Soc. Mass. Spectrom. 2000, 11, 69−77. (14) Wagner, G. W.; O’Connor, R. J.; Procell, L. R. Preliminary Study on the Fate of VX in Concrete. Langmuir 2001, 17, 4336−4341. (15) Groenewold, G. S.; Williams, J. M.; Appelhans, A. D.; Gresham, G. L.; Olson, J. E.; Jeffery, M. T.; Rowland, B. Hydrolysis of VX on Concrete: Rate of Degradation by Direct Surface Interrogation Using an Ion Trap Secondary Ion Mass Spectrometer. Environ. Sci. Technol. 2002, 36, 4790−4794. (16) Wagner, G. W.; O’Connor, R. J.; Edwards, J. L.; Brevett, C. A. S. Effect of Drop Size on the Degradation of VX in Concrete. Langmuir 2004, 20, 7146−7150. (17) Williams, J. M.; Rowland, B.; Jeffery, M. T.; Groenewold, G. S.; Appelhans, A. D.; Gresham, G. L.; Olson, J. E. Degradation Kinetics of VX on Concrete by Secondary Ion Mass Spectrometry. Langmuir 2005, 21, 2386−2390. (18) Mizrahi, D. M.; Columbus, I. 31P MAS NMR: A Useful Tool for the Evaluation of VX Natural Weathering in Various Urban Matrixes. Environ. Sci. Technol. 2005, 39, 8931−8935.

ASSOCIATED CONTENT

S Supporting Information *

Additional 31P NMR spectra and LC/MS/MS chromatograms. This material is available free of charge via the Internet at http://pubs.acs.org. 16149



Research Note

(19) Brevett, C. A. S.; Sumpter, K. B.; Pence, 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. (20) Wagner, G. W.; Procell, L. R.; Sorrick, D. C.; Lawson, G. E.; Wells, C. M.; Reynolds, C. M.; Ringelberg, D. B.; Foley, K. L.; Lumetta, G. J.; Blanchard, D. L., Jr. All-Weather Hydrogen PeroxideBased Decontamination of CBRN Contaminants. Ind. Eng. Chem. Res. 2010, 49, 3099−3105. (21) Subcommittee on Guidelines for Military Field Drinking Water Quality, Committee on Toxicology, Board on Environmental Studies and Toxicology, National Research Council. In Guidelines for Chemical Warfare Agents in Military Field Drinking Water; National Academy Press: Washington, DC, 1995. (22) Brevett, C. A. S.; Sumpter, K. B.; Nickol, R. G. Kinetics of the Degradation of Sulfur Mustard on Ambient and Moist Concrete. J. Hazard. Mater. 2009, 162, 281−291. (23) Wagner, G. W.; O’Connor, R. J.; Edwards, J. L.; Brevett, C. A. S. Degradation and Decontamination of VX in Concrete. In Proc. 2004 Chem. Bio. Def. Res. ECBC-SP-020. Aberdeen Proving Ground, MD, Dec. 2005; unclassified report. (24) Although a ca. 3× higher EA-2192 concentration is observed over concrete, such low-level ppb amounts form from either residual, unreacted20 VX being rinsed from the CARC panels or via hydrolysis of the well-known VX impurity CH3P(O)(SCH2CH2NiPr2)2.7 H2O2based decontaminants do not form EA-2192 directly from VX itself.20 (25) Brevett, C. A. S.; Sumpter, K. B. Degradation of the Chemical Warfare Agents HD, GD, Thickened GD, and VX on Ambient and Moist Environmental Substrates. Main Group Chem. 2010, 9, 205−219 and references therein.. (26) Dr. Carol Brevett, SAIC, personal communication. (27) See http://h2o2.evonik.com/product/h2o2/en/about/stabilitydecomposition/pages/default.aspx (accessed October 31, 2012).

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Mitigation of VX Effluents in Thorough Decontamination Operations

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