Degradation of the blister agent sulfur mustard, bis(2-chloroethyl) sulfide, on concrete
Introduction
Knowledge of when a Chemical Warfare Agent (CWA) no longer poses a hazard – that is, when a contaminated area is safe to enter without protective clothing – is of major concern for battlefield commanders. Decisions must be made whether to decontaminate an area, or allow resumption of normal operations after an acceptable waiting period. The correct assessment of the amount of agent in the air, in nearby water, on equipment, and on the ground (substrates such as soil, grass, concrete and asphalt) is critical to making correct decisions about the need for decontamination. Therefore, testing methods that detect both the CWA and its degradation products, some of which may be toxic, are needed.
The chemistry of decontamination has been studied and reviewed [1]. Bleach and other decontamination solutions and mixtures containing the hypochlorite ion, OCl−, reacted with sulfur mustard to form sulfoxide derivatives, which then formed sulfone derivatives, which then formed the corresponding elimination products. The elimination products 2-chloroethyl vinyl sulfide (CEVS) and divinyl sulfide (DVS) [2] were seen immediately with the use of DS2, an alternative decontamination solution containing CH3-OCH2CH2O−, that was developed to avoid the corrosiveness of bleach.
Although sulfur mustard exhibited low solubility in water, forming droplets within it, reactions occurred at the water–sulfur mustard interface to form the hydrolysis products chlorohydrin (CH) and thiodiglycol (TDG), which subsequently formed the toxic sulfonium ions H-2TG and CH-TG [1].
Environmentally, sulfur mustard has been observed to persist for 4 years in soil [3]. Wagner and MacIver [4] used 13C SSMAS (solid state magic angle spinning) NMR to show that sulfur mustard persisted for several weeks on dry soil, but hydrolyzed and polymerized to form toxic CH-TG and H-2TG sulfonium ions within 1 week when water was added. Liquid chromatography followed by electrospray ionization mass spectrometry of acetonitrile extracts was used to confirm the presence of the sulfonium ions.
Similarly, when sulfur mustard was placed on MgO or CaO, the products thiodiglycol (TDG), CEVS and DVS were formed [5]. Degradation of sulfur mustard on CaO also led to minor amounts of sulfonium ions [6]. On the surface of ambient alumina, sulfur mustard reacted to give mostly thiodiglycol with minor amounts of CEVS and DVS. When excess water was added, the sulfonium ions H-2TG and CH-TG were formed, and Al(H2O)63+ was liberated from the surface [7].
CWAs and their degradation products have been removed from solid matrices using solvents and then analyzed by Hooijschuur, Kientz and Brinkman [8]. Davis, Jensen, McGuire, Skoumal and Fagan [9] extracted sulfur mustard from concrete after a 30-min contact time using isopropanol and acetonitrile; GC/MS analysis of the solvent showed 2–68% recovery of sulfur mustard when isopropanol was used and 7–21% recovery of sulfur mustard when acetonitrile was used. Decomposition products were not detected. Tomkins, Sega and Mcnaughton [10] developed an extraction and GC method for analyzing the breakdown products of sulfur mustard on soil and concrete. The substrates were spiked and extracted immediately, yielding a total recovery of the analyte. Wils, Hulst, and de Jong [11] used thermal desorption followed by headspace analysis to monitor the recovery of sulfur mustard from rubber over a period of 6 weeks. The 30 min recovery was 86%; the six week recovery was 57%.
In the current study, both extraction and SSMAS techniques were employed to study the persistence and reactivity of sulfur mustard on concrete quantitatively. The sulfur mustard and its degradation products were extracted from concrete monoliths with chloroform and analyzed using both GC/MSD and liquids NMR. For the SSMAS studies, a sample of sulfur mustard on the same concrete was sealed in a SSMAS rotor and monitored over a period of 12 weeks. In addition, sulfur mustard was placed onto concrete, which was then crushed, studied using SSMAS, and subsequently extracted for GC/MSD; this procedure enabled side-by-side comparison of the SSMAS and extraction methods.
Section snippets
Substrates
The concrete was made in the year 2000 using Portland cement, ∼3 mm silicate filler, and a 0.32 water-to-concrete ratio. All samples were used under ambient conditions (about 21 °C and 20% RH). The concrete had a surface area of 7.8 m2/g and 17% porosity (four samples) as measured by mercury intrusion porosimetry (MIP). Nitrogen gas adsorption with BET surface area (SA) calculations gave a value of 9.0 m2/g for a small monolith; a sample of the concrete that was finely ground with a mortar and
Contact time
When the samples were extracted after 1 h, the percentages of sulfur mustard recovered were 90–100%. The NMR and GC percent recoveries were generally within 10% of each other for any given extract; sample-to-sample variation of the duplicates was also generally within 10%. As the contact time of sulfur mustard on concrete was increased, the percent sulfur mustard extracted decreased; about 40% of the sulfur mustard was extractable after 24 h (Fig. 1). The concrete:sulfur mustard ratio for these
Discussion
The observed decline in the extraction efficiency of sulfur mustard from concrete as the contact time increased was similar to the trends seen in prior investigations [9], [10], [11]. Beck, Carrick, Cooper and Muir [12] used pressurized liquid extraction to remove thiodiglycol from two soils and one type of sand; their percentage recovery ranged from 56 to 89 after 24 h depending upon the substrate, and declined over a period of 1–28 days.
The concrete:sulfur mustard ratio affected the rate of
Conclusions
After 200 h very little mustard was extracted from the concrete monoliths, but the SSMAS spectra of crushed samples showed clearly that it was still present. This difference suggested that the mustard existed in the concrete in a non-extractable form prior to its degradation.
The degradation of the sulfur mustard as observed via 13C SSMAS NMR progressed similarly to that in water or on wet soil, yielding mostly sulfonium ion products, with a minor component of the reaction yielding elimination
Acknowledgements
We thank Drs. Jeffrey Rice and Vicky Bevilacqua for many fruitful discussions, and Ms. Monicia Hall for assistance with the agent operations. We also thank Drs. James Savage, H. Dupont Durst and Mark Brickhouse for programmatic support.
References (17)
- et al.
Analytical separation techniques for the determination of chemical warfare agents
J. Chromatogr. A
(2002) - et al.
Determination of mustard gas and related vesicants in rubber and paint by gas chromatography–mass spectrometry
J. Chromatogr.
(1992) - et al.
Extraction of thiodiglycol from soil using pressurized liquid extraction
J. Chromatogr. A
(2001) - et al.
Application of headspace analysis, solvent extraction, thermal desorption and gas chromatography–mass spectrometry to the analysis of chemical warfare samples containing sulphur mustard and related compounds
J. Chromatogr.
(1993) - et al.
Decontamination of chemical warfare agents
Chem. Rev.
(1992) - et al.
Kinetics and mechanism of the hydrolysis of 2-chlrorethyl sulfides
J. Org. Chem.
(1988) - et al.
Identification of nerve agent and sulphur mustard residues in soil samples collected 4 years after a chemical attack
- et al.
Degradation and fate of mustard in soil as determined by 13C MAS NMR
Langmuir
(1998)