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

Yiran Tong, Matthew J Berens, Bridget A. Ulrich, Jakov Bolotin, Jennifer H Strehlau, Thomas B. Hofstetter, William A. Arnold

Research output: Contribution to journalArticlepeer-review

Abstract

Subsurface contamination with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) at ordnance production and testing sites is a problem because of the persistence, mobility, and toxicity of RDX and the formation of toxic products under anoxic conditions. While the utility of compound-specific isotope analysis for inferring natural attenuation pathways from stable isotope ratios has been demonstrated, the stable isotope fractionation for RDX reduction by iron-bearing minerals remains unknown. Here, we evaluated N and C isotope fractionation of RDX during reduction by Fe(II) associated with Fe minerals and natural sediments and applied N isotope ratios to the assessment of mineral-catalyzed RDX reduction in a contaminant plume and in sediment columns treated by in situ chemical reduction. Laboratory studies revealed that RDX was reduced to nitroso compounds without denitration and the concomitant ring cleavage. Fe(II)/iron oxide mineral-catalyzed reactions exhibited N isotope enrichment factors, ϵN, between -6.3±0.3‰ and -8.2±0.2‰, corresponding to an apparent 15N kinetic isotope effect of 1.04-1.05. The observed variations of the δ15N of μ15‰ in RDX from groundwater samples suggested an extent of reductive transformation of 85% at an ammunition plant. Conversely, we observed masking of N isotope fractionation after RDX reduction in laboratory flow-through systems, which was presumably due to limited accessibility to reactive Fe(II).

Original languageEnglish (US)
Pages (from-to)6752-6763
Number of pages12
JournalEnvironmental Science and Technology
Volume55
Issue number10
DOIs
StatePublished - May 18 2021

Bibliographical note

Funding Information:
This work was supported by the Strategic Environmental Research and Development Program (SERDP, Project No. ER 2618). We thank Stephanie Park and Kim-Lee Yarberry at Jacobs Engineering for coordinating groundwater sampling at IAAAP and providing the relevant data for these samples.

Publisher Copyright:
© 2021 American Chemical Society.

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't

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