Assessing Iron-Mediated Oxidation of Toluene and Reduction of Nitroaromatic Contaminants in Anoxic Environments Using Compound-Specific Isotope Analysis

Tobler, Nicole B.; Hofstetter, Thomas B.; Schwarzenbach, René P.

doi:10.1021/es071129c

Cited by 51 publications

(69 citation statements)

References 39 publications

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“…Biotic and abiotic degradation mechanisms involving nitro reduction have indicated intrinsic (reaction site) ε 15 N values in the range of Ϫ25‰ to Ϫ42‰ (54)(55)(56)(57)(58). In contrast, our bulk ε 15 N value attributed to anaerobic pathway A, presumably reflecting the first nitro reduction step, corresponds to an apparent intrinsic ε 15 N value of around Ϫ59‰.…”

Section: Discussioncontrasting

confidence: 54%

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Fuller

Heraty

Condee

et al. 2016

Appl Environ Microbiol

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Kinetic isotopic fractionation of carbon and nitrogen during RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) biodegradation was investigated with pure bacterial cultures under aerobic and anaerobic conditions. Relatively large bulk enrichments in 15 ؊ production were much larger than, but systematically related to, the bulk RDX N isotope effects with different bacteria. Apparent intrinsic 15 N-NO 2 ؊ values were consistent with an initial denitration pathway in the aerobic experiments and more complex processes of NO 2 ؊ formation associated with anaerobic ring cleavage. These results indicate the potential for isotopic analysis of residual RDX for the differentiation of degradation pathways and indicate that further efforts to examine the isotopic composition of potential RDX degradation products (e.g., NO x ) in the environment are warranted. IMPORTANCEThis work provides the first systematic evaluation of the isotopic fractionation of carbon and nitrogen in the organic explosive RDX during degradation by different pathways. It also provides data on the isotopic effects observed in the nitrite produced during RDX biodegradation. Both of these results could lead to better understanding of the fate of RDX in the environment and help improve monitoring and remediation technologies. Explosives manufacturing, testing, and training range activities have resulted in the release of explosive compounds, including the nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), in soils at numerous U.S. Department of Defense (DoD) installations. Because RDX is mobile in soils and persistent, it has also been detected in groundwater or drinking water at some of these sites (1, 2).There has been extensive research examining the biological degradation of explosive compounds by pure cultures of bacteria as well as mixed consortia (for a review, see reference 3). RDX biodegradation has been observed under a range of redox conditions (4-9), and at least three predominant degradation pathways have been elucidated (Fig. 1). Typically, RDX is degraded anaerobically as an electron acceptor, requiring a carbon source as an electron donor, and entails either successive reduction of the three nitro groups via successive two-electron (2e Ϫ ) transfers followed by ring cleavage (pathway A) or an earlier opening of the ring structure (pathway B1), with or without initial denitration (pathway B2). The specific mechanism of ring destabilization and the steps that lead to ring cleavage may be variable and remain subject to debate (6,7,10). A denitration reaction that converts hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) (in pathway A) through multiple intermediates to methylenedinitramine (MEDINA) (in pathway B) under anaerobic conditions has also been proposed (7,11,12). Aerobic degradation proceeds via two single-electron transfer steps resulting in sequential denitration (2 NO 2 Ϫ removed) followed by ring cleavage and production of 4-nitro-2,4-diazabutanal (NDAB) (pathway C) (7). Some bacteria are able to utilize R...

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Section: Discussioncontrasting

confidence: 54%

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Fuller

Heraty

Condee

et al. 2016

Appl Environ Microbiol

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“…Pathway-specific C isotope enrichment factors, ϵ C j , were obtained from product δ 13 C-values using two procedures adapted from previous studies 5,47,48 as demonstrated in eqs 8 and 9, and eq 10, respectively. (9) where δ 13 C P, j is the measured isotope signature of a product of reaction j, δ 13 C 0 is the initial isotope signature of the substrate, f is the fraction of remaining substrate, and ϵ C bulk is the C isotope enrichment factor reflecting the combined isotope fractionation of all reaction pathways. D j (δ 13 C) is the deviation of a particular product isotope signature from the weighted average of all products.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Isotope Effects of Enzymatic Dioxygenation of Nitrobenzene and 2-Nitrotoluene by Nitrobenzene Dioxygenase

Pati

Köhler

Bolotin

et al. 2014

Environ. Sci. Technol.

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Oxygenation of aromatic rings is a frequent initial step in the biodegradation of persistent contaminants, and the accompanying isotope fractionation is increasingly used to assess the extent of transformation in the environment. Here, we systematically investigated the dioxygenation of two nitroaromatic compounds (nitrobenzene and 2-nitrotoluene) by nitrobenzene dioxygenase (NBDO) to obtain insights into the factors governing its C, H, and N isotope fractionation. Experiments were carried out at different levels of biological complexity from whole bacterial cells to pure enzyme. C, H, and N isotope enrichment factors and kinetic isotope effects (KIEs) were derived from the compound-specific isotope analysis of nitroarenes, whereas C isotope fractionation was also quantified in the oxygenated reaction products. Dioxygenation of nitrobenzene to catechol and 2-nitrotoluene to 3-methylcatechol showed large C isotope enrichment factors, ϵC, of -4.1 ± 0.2‰ and -2.5 ± 0.2‰, respectively, and was observed consistently in the substrates and dioxygenation products. ϵH- and ϵN-values were smaller, that is -5.7 ± 1.3‰ and -1.0 ± 0.3‰, respectively. C isotope fractionation was also identical in experiments with whole bacterial cells and pure enzymes. The corresponding (13)C-KIEs for the dioxygenation of nitrobenzene and 2-nitrotoluene were 1.025 ± 0.001 and 1.018 ± 0.001 and suggest a moderate substrate specificity. Our study illustrates that dioxygenation of nitroaromatic contaminants exhibits a large C isotope fractionation, which is not masked by substrate transport and uptake processes and larger than dioxygenation of other aromatic hydrocarbons.

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“…Example for anaerobic enzymatic oxidation of toluene coupled to the microbial reduction of a solid iron mineral (19,35) C …”

Section: Box 3 From Bulk Isotope Enrichment Factors To Bond-specific mentioning

confidence: 99%

Assessing Transformation Processes of Organic Compounds Using Stable Isotope Fractionation

Hofstetter

Schwarzenbach

Bernasconi

2008

Environ. Sci. Technol.

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Quantifying the transformation processes of organic compounds in the environment using conventional methods is a major challenge due to the effects of dilution, volatilization, or sorption to the environmental matrix. Assessing these processes is key to addressing the risks of soil and water contamination. Hofstetter et al. illustrate how changes in isotope signatures provide unique information on reaction pathways and open new avenues to assess the sources and transformation processes of organic compounds.

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Assessing Iron-Mediated Oxidation of Toluene and Reduction of Nitroaromatic Contaminants in Anoxic Environments Using Compound-Specific Isotope Analysis

Cited by 51 publications

References 39 publications

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Relating Carbon and Nitrogen Isotope Effects to Reaction Mechanisms during Aerobic or Anaerobic Degradation of RDX (Hexahydro-1,3,5-Trinitro-1,3,5-Triazine) by Pure Bacterial Cultures

Isotope Effects of Enzymatic Dioxygenation of Nitrobenzene and 2-Nitrotoluene by Nitrobenzene Dioxygenase

Assessing Transformation Processes of Organic Compounds Using Stable Isotope Fractionation

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