Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a potential human carcinogen, and its contamination of subsurface environments is a significant threat to public health. This study investigated abiotic and biological degradation of RDX in contaminated aquifer material. Anoxic batch systems were started with and without pre-aeration of aquifer material to distinguish initial biological RDX reduction from abiotic RDX reduction. Aerating the sediment eliminated chemical reductants in the native aquifer sediment, primarily Fe(II) sorbed to mineral surfaces. RDX (50 μM) was completely reduced and transformed to ring cleavage products when excess concentrations (2. mM) of acetate or lactate were provided as the electron donor for aerated sediment. RDX was reduced concurrently with Fe(III) when acetate was provided, while RDX, Fe(III), and sulfate were reduced simultaneously with lactate amendment. Betaproteobacteria were the dominant microorganisms associated with RDX and Fe(III)/sulfate reduction. In particular, Rhodoferax spp. increased from 21% to 35% and from 28% to 60% after biostimulation by acetate and lactate, respectively. Rarefaction analyses demonstrated that microbial diversity decreased in electron-donor-amended systems with active RDX degradation. Although significant amounts of Fe(III) and/or sulfate were reduced after biostimulation, solid-phase reactive minerals such as magnetite or ferrous sulfides were not observed, suggesting that RDX reduction in the aquifer sediment is due to Fe(II) adsorbed to solid surfaces as a result of Fe(III)-reducing microbial activity. These results suggest that both biotic and abiotic processes play an important role in RDX reduction under in situ conditions.
Bibliographical noteFunding Information:
We thank Karen Haugen and the anonymous reviewers for their thoughtful reviews of the manuscript. We thank Kelly Skinner, Brandon Bates, Aaron Garoutte, Jennifer Brulc (Argonne National Laboratory), Kay Millerick, and Jovan Popovic (Clemson University) for laboratory assistance. This work was supported in part by the US Department of Defense Strategic Environmental Research and Development Program (SERDP) Project Number ER-1377. Microbial community analyses work was supported by Argonne National Laboratory LDRD Funds. M.J.K. was supported by Argonne Director’s Fellowship Program and KIST – Gangneung Institute (Grant No. 2E22100).
- Abiotic reduction
- Electron donor
- Iron reduction
ASJC Scopus subject areas
- Public Health, Environmental and Occupational Health
- General Chemistry
- Health, Toxicology and Mutagenesis
- Environmental Engineering
- Environmental Chemistry