Abiotic reduction is an important process that governs the fate of munitions compounds (MCs) in reducing environments and represents a potential approach to remediate MC-contaminated soil and groundwater. Organic carbon in soils contains redox-active functional groups that can behave like rechargeable electron reservoirs which, when reduced, can react with MCs. To understand the kinetics and mechanism of MC transformation by carbonaceous reductants, we investigated the reactivity of dithionite-reduced anthraquinone-2,6-disulfonate (AQDS, a model quinone and surrogate of dissolved organic carbon), Leonardite humic acid (LHA), and two carbon-rich soils, Pocomoke and Rhydtalog, toward 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN), insensitive munitions constituents in the IMX-101 and IMX-104 formulations. NTO was reduced to 3-amino-1,2,4-triazol-5-one (ATO), and DNAN was reduced to 2,4-diaminoansiole (DAAN) through 2-amino-4-nitroanisole as the predominant intermediate. DAAN formation was transient, particularly in the presence of LHA, presumably due to further transformation. LHA exhibited measurable reactivity toward NTO and DNAN only when reduced above a threshold percent of its electron storage capacity (ESC), beyond which the reduction rates and extents of both MCs increased with LHA electron content. The reaction rates generally increased with pH, presumably due to the speciation of NTO and hydroquinone functional groups. The pseudo-first-order rate constant for NTO varied by ~2 orders of magnitude from pH 2 to 9.5 and increased by about 3 orders of magnitude for DNAN between pH 6 and 8.5. While the rates of MCs transformation increased with the extent of Pocomoke and Rhydtalog reduction (i.e., chemical enhancement), the mass balances worsen indicative of side reactions between reduced species in soils and the MCs. This study illustrates the reactivity and potentially important role of soil organic carbon in influencing the natural and enhanced attenuation of NTO and DNAN in munitions constituent-impacted sites.

Abiotic reduction of the munitions compounds DNAN and NTO by carbonaceous reductants and carbon-rich soils

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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