Assessment of 2,4-Dinitroanisole Transformation Using Compound-Specific Isotope Analysis after In Situ Chemical Reduction of Iron Oxides

Abstract

A study of isotope fractionation upon reaction of the insensitive munitions compounds 2,4-dintroanisole with natural minerals in the presence of ferrous iron or treated with dithionite to produce reducing equivalents. File list (2) download file view on ChemRxiv NtlMats_ms_20191212-submitted for chemRxiv.docx (1.05 MiB) download file view on ChemRxiv NtlMats_SI_20191212-submitted.docx (2.90 MiB)

Exploring the Utility of Compound-Specific Isotope Analysis for Assessing Ferrous Iron-Mediated Reduction of RDX in the Subsurface

“…To minimize particle release/transport during the column experiments, the ionic strength of all further feed solutions was adjusted by adding 10 mM NaCl. 20 A sequence of three experiments at constant volumetric flow of 0.5 mL/min was conducted unless indicated otherwise. First, a 0.115 M NaBr tracer solution was introduced in a step input to determine hydraulic properties of the column (Table S2).…”

“…14,15,33 From a mechanistic perspective, it is also unclear if any isotope fractionation associated with Fe(II)-catalyzed processes is caused by the reduction of the NO2 functional groups of nitramines, which would cause isotope effects comparable to the abiotic reduction of aromatic NO2 moieties. 16,19,20,22,23,[37][38][39][40] Alternatively, denitration and ring cleavage reactions could also contribute to observable stable isotope fractionation, as has been hypothesized for anaerobic RDX biodegradation. 17 The goal of this work was to assess the utility of CSIA for evaluating abiotic reduction of RDX in anaerobic environments.…”

“…14,15 CSIA is used to characterize changes to the stable isotope ratios of elements in nitro-containing munition compounds. [14][15][16][17][18][19][20] These changes are associated with a particular (bio)chemical degradation pathway based on the assumption that kinetic isotope effects for the reacting bonds cause the observable stable isotope fractionation. 16,[19][20][21][22][23][24][25] For RDX, variations of 15 N/ 14 N, 13 C/ 12 C, and 18 O/ 16 O have been associated with biodegradation under aerobic and anaerobic conditions and with abiotic alkaline hydrolysis reactions in both laboratory and field observations.…”

“…[14][15][16][17][18][19][20] These changes are associated with a particular (bio)chemical degradation pathway based on the assumption that kinetic isotope effects for the reacting bonds cause the observable stable isotope fractionation. 16,[19][20][21][22][23][24][25] For RDX, variations of 15 N/ 14 N, 13 C/ 12 C, and 18 O/ 16 O have been associated with biodegradation under aerobic and anaerobic conditions and with abiotic alkaline hydrolysis reactions in both laboratory and field observations. 14,15,17,18,26 Assignment of the initial bond cleavage reactions in RDX to the different transformation pathways, however, is particularly challenging regardless of whether transformation occurs biologically or abiotically.…”

“…In a second application, we used the CSIA-based approach to monitor RDX transformation in laboratory column reactors where reactive Fe(II) for RDX reduction was generated in situ through iron mineral reduction with dithionite. 20,41…”