Geochemical and microbiological processes contributing to the transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated aquifer material
- Geochemical and microbiological processes contributing to the transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated aquifer material
- 권만재; Edward J. O; D. A. Antonopoulos; Kevin T. Finneran
- RDX; Biodegradation; Electron donor; Abiotic reduction; Iron reduction
- Issue Date
- VOL 84, NO 9, 1223-1230
- 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.
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