Nitro explosives such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 3-Nitro-1,2,4-triazole-5-one (NTO) are potential contaminants at munition training, storage, and disposal sites. Under anoxic conditions, iron-bearing minerals mediate abiotic reduction of nitro-contaminants, and these processes may be important in the natural attenuation of these compounds. If natural attenuation is to be used as a remedial strategy, the kinetics and mechanisms of these reactions with different minerals and aquifer materials need to be understood. Besides directly determining intermediates and products, compound specific isotope analysis (CSIA) is a robust approach to indicate chemical transformation of nitro contaminants in groundwater and assessing reaction pathways. In this study, the reduction kinetics for the attenuation of RDX and NTO with synthetic iron-bearing minerals, including goethite, magnetite and mackinawite, as well as natural minerals extracted from military installations are measured. GC/LC-Isotope ratio mass spectrometry (IRMS) is used to determine the N and C isotope fractionation associated with abiotic reduction. For RDX reduction, results show that mineral identity and pH are both critical variables. For pH, the reaction rate and accumulation of reaction intermediates is highly pH dependent. CSIA shows greater enrichment of 15N compared to 13C as RDX being reduced, regardless the phase of mineral. This result and the reaction product analysis suggests that reduction at –NO<sub>2</sub> group is the rate-limiting step. For NTO reduction, kinetics and CSIA data are also collected.

Reduction of nitro explosives RDX and NTO by iron-bearing minerals: A study on the kinetics and using compound specific isotope analysis to assess mechanisms

2019 Spring National Meeting

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