Feasibility of Detecting Byproducts of Chemical Weapons Manufacturing in Environmental Media: A Preliminary Evaluation
Quantitative information on the environmental transport and fate of organophosphorus nerve agents has been limited to studies conducted at high concentration representative of acute doses (Munroe et al. 1999). Nerve agents have relatively rapidly degradation rates at acute levels, and first order degradation pathways and half-lives have been characterized. However, similar knowledge is lacking in the open literature on the long-term environmental persistence of nerve agents, their manufacturing precursors and byproducts, and their degradation products, particularly at sub-acute or chronic health levels. Although many recent publications reflect low-level detection methods for chemical weapons signature compounds extracted from a variety of different media (e.g. D'Agostino et al., 2001; Kataoka et al., 2001), little of this work answers questions regarding their adsorptive character and chemical persistence. However, these questions are a central theme to both the detection of illegal chemical weapons manufacturing, as well as determining long-term cleanup needs and health risks associated with potential terrorist acts using such agents. Adsorption onto environmental surfaces can enhance the persistence of organophosphorus compounds, particularly with strong chelators like phosphonic acids. In particular, organophosphorus compound adsorption can lead to irreversible binding (e.g. Aubin and Smith, 1992), and current methods of chemical extraction and solid-state detection are challenged to detect them. This may be particularly true if the adsorbed compound is of a low initial concentration because it may be that the most preferred adsorption sites form the strongest bonds. This is particularly true in mixed media having various adsorption domains that adsorb at different rates (e.g. Weber and Huang, 1996). For high enough initial concentrations, sorption sites become saturated and solvent extraction has a relatively high efficiency. It is no surprise that many CW fate studies can report findings using traditional extraction or solid-state methods of detection, since release concentration exceed the capacity of environmental media to adsorb or degrade them. This report documents a test using solid-state {sup 31}P-NMR and GC/MS methods to delineate two adsorbed phosphonates on a uniform silica gel substrate at different concentrations. The test sought to determine the sensitivity of {sup 31}P-NMR detection, delineate adsorption character of the phosphonates, quantify their extraction efficiency using different solvents, and test the phosphonate mobility and photodegradability under short-term idealized conditions. The results show that solid-state detection at the experimental conditions can detect individual phosphonate species down to the 100 ppm level. Sensitivity could be further increased using larger samples and longer collection times. Solvent extraction of the phosphonates from the silica gel showed that a chlorinated solvent (methylene chloride) produced poor recovery for phosphonic acids from the silica gel, whereas methanol used as a solvent achieved high extraction efficiency. The phosphonates used showed strong aqueous mobility in a silica gel column experiment, with a small but significant amount left adsorbed to the substrate. A 96 hour photo-degradation experiment showed no degradation of the compounds.
- Research Organization:
- Lawrence Livermore National Laboratory, CA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15008096
- Report Number(s):
- UCRL-ID-153208; TRN: US200425%%259
- Resource Relation:
- Other Information: PBD: 1 Mar 2003
- Country of Publication:
- United States
- Language:
- English
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