Nitroaromatic compounds pose serious threats to environmental quality. Large groundwater plumes of RDX, HMX, TNT, and DNT are associated with sources on Department of Defense (DoD) live fire ranges, as well as explosives manufacturing facilities. Development of chemical "fingerprints" for nitroaromatic compounds would allow their fate in field sites to be quantitatively and qualitatively measured, thereby providing a sound scientific and technological basis for managing site cleanup.
This project sought to build on existing knowledge of the chemical and microbiological processes that influence nitroaromatic compounds in the laboratory and at field sites. The objective was to implement a novel assay that would provide new information about relationships between attenuation and geochemical conditions that may prevail or be established at contaminated sites. The resultant information was designed to answer whether attenuation of nitroaromatics occurs and how it can be converted into an effective, reliable site-remediation technology.
The mechanisms of contaminant attenuation expected to operate naturally and in engineered settings for TNT, RDX, and HMX include microbial cometabolism and chemical processes that reduce, polymerize, and bind the contaminant. The reasons for field persistence and hence plume migration for the above 3 co-metabolized explosives is likely one or a combination of the following: toxicity; insufficient organic carbon to drive co-metabolism; insufficient carbon in sediment matrix to bind reduced products; improper redox potential to cause irreversible binding to soil; and nutrient limitations. This project focused on TNT and developed a means to characterize type and degree of TNT binding to soil organic matter. A later goal was to devise ways to engineer site conditions to enhance polymerization reactions and explain why and how nitroaromatics have attenuated naturally in some sites and persisted in others. Key assays for discerning the extent of nitroaromatic humification include High-Performance Liquid Chromatography (HPLC) analysis of the reduced monomers or oligomers, assessment of leachability from site soils, and assessment of the degree of incorporation into soil organic matter by pyrolysis Gas Chromatograph/Mass Spectrometer (GC/MS).
Clear criteria do not yet exist to seek field evidence for attenuation of nitroaromatics or enhancement of the process. This project endeavored to develop attenuation criteria (i.e., chemical “fingerprints”) via a novel suite of chemical and microbiological measures applied to laboratory experiments and field samples.
The pyrolysis-GC/MS procedures successfully identified soil-bound polymeric chemicals derived from TNT in a highly contaminated soil sample from the Louisiana Army Ammunition Plant. The scientific advances of the project were published in Environmental Science & Technology (Weiss et al., 2004). Despite proof of principle, the project's technological success was limited because the analytical technique was unable to detect TNT and its derivatives in the majority of contaminated DoD soils tested. Inadequate sensitivity in the assay led to early project termination. (Project Completed - 2003)