Isotope Effects as New Proxies for Organic Pollutant Transformation

Hofstetter, Thomas B.; Bolotin, Jakov; Pati, Sarah G.; Skarpeli-Liati, Marita; Spahr, Stephanie; Wijker, Reto S.

doi:10.2533/chimia.2014.788

Cited by 15 publications

(10 citation statements)

References 34 publications

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“…[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.…”

Section: Introductionmentioning

confidence: 99%

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

Tong

Berens

Ulrich

et al. 2021

Environ. Sci. Technol.

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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 ironbearing minerals remains unknown. Here, the N isotope fractionation of RDX during reduction by Fe(II) associated with Fe minerals and natural sediments was evaluated and applied 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‰ to -8.2±0.2‰ corresponding to an apparent 15 N kinetic isotope effect of 1.04-1.05.The observed variations of the δ 15 N of ~15‰ 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 a limited accessibility to reactive Fe(II).

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Section: Introductionmentioning

confidence: 99%

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

Tong

Berens

Ulrich

et al. 2021

Environ. Sci. Technol.

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“…The analysis of stable isotope ratios in organic soil and water contaminants has become a widely used approach to identify the sources of pollution and to identify (bio)degradation pathways. − Whereas constant ratios of 13 C/ 12 C, 2 H/ 1 H, 15 N/ 14 N, and of other elements in a compound enable one to infer precursor materials, synthesis routes, and formation pathways of pollutants, − changes of isotope ratios lead to stable isotope fractionation patterns that reveal the (bio)chemical reaction by which a pollutant is degraded. − However, because of the poor sensitivity of gas and liquid chromatography used in combination with isotope-ratio mass spectrometry, − the applications of compound-specific isotope analysis (CSIA) have largely focused on so-called legacy contaminants such as halogenated solvents, nitroaromatic explosives, and fuel constituents − Those compounds are often found in the high μg/L to mg/L concentration range and can be extracted from the environmental matrices in straightforward procedures, for example, through transfer of the analytes into the gas phase and enrichment onto solid sorbents. − Unfortunately, such procedures are not necessarily applicable for CSIA of polar organic micropollutants of current interest, such as pesticides, pharmaceuticals, consumer chemicals, and personal care products. Their sub-μg/L concentrations in natural and treated waters require the processing of large sample volumes greater than 5 L by solid-phase extractions (SPE, e.g., ref ) to obtain the necessary analyte mass for isotope-ratio mass spectrometry.…”

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confidence: 99%

Molecularly Imprinted Polymers for Compound-Specific Isotope Analysis of Polar Organic Micropollutants in Aquatic Environments

et al. 2018

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Compound-specific isotope analysis (CSIA) of polar organic micropollutants in environmental waters requires a processing of large sample volumes to obtain the required analyte masses for analysis by gas chromatography/isotope-ratio mass spectrometry (GC/IRMS). However, the accumulation of organic matter of unknown isotopic composition in standard enrichment procedures currently compromises the accurate determination of isotope ratios. We explored the use of molecularly imprinted polymers (MIPs) for selective analyte enrichment for C/C and N/N ratio measurements by GC/IRMS using 1 H-benzotriazole, a typical corrosion inhibitor in dishwashing detergents, as example of a widely detected polar organic micropollutant. We developed procedures for the treatment of >10 L of water samples, in which custom-made MIPs enabled the selective cleanup of enriched analytes in organic solvents obtained through conventional solid-phase extractions. Hydrogen bonding interactions between the triazole moiety of 1 H-benzotriazole, and the MIP were responsible for selective interactions through an assessment of interaction enthalpies and N isotope effects. The procedure was applied successfully without causing isotope fractionation to river water samples, as well as in- and effluents of wastewater treatment plants containing μg/L concentrations of 1 H-benzotriazole and dissolved organic carbon (DOC) loads of up to 28 mg C/L. MIP-based treatments offer new perspectives for CSIA of organic micropollutants through the reduction of the DOC-to-micropollutant ratios.

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“…Because 18 O-KIEs were sensitive to the 2 H label, the authors concluded that the initial H atom abstraction from 2-hydroxyethylphosphonate happened either prior to or concomitant with O 2 reduction to the Fe III -superoxo species. This example suggests that the study of isotope effects in oxygenation reactions, which are done to elucidate contaminant biodegradation, [59] could also provide valuable information on the kinetic mechanisms of organic contaminant oxygenations.…”

Section: Rate-determining Steps and O 2 Uncoupling In Reactions Of Ot...mentioning

confidence: 99%

Enzyme Kinetics of Organic Contaminant Oxygenations

Bopp

Köhler

Hofstetter

2020

Chimia

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Enzymatic oxygenations initiate biodegradation processes of many organic soil and water contaminants. Even though many biochemical aspects of oxygenation reactions are well-known, quantifying rates of oxidative contaminant removal as well as the extent of oxygenation remains a major challenge. Because enzymes use different strategies to activate O2, reactions leading to substrate oxygenation are not necessarily limiting the rate of contaminant removal. Moreover, oxygenases react along unproductive pathways without substrate metabolism leading to O2 uncoupling. Here, we identify the critical features of the catalytic cycles of selected oxygenases that determine rates and extents of biodegradation. We focus most specifically on Rieske dioxygenases, a subfamily of mononuclear non-heme ferrous iron oxygenases, because of their ability to hydroxylate unactivated aromatic structures and thus initiate the transformation of the most persistent organic contaminants. We illustrate that the rate-determining steps in their catalytic cycles range from O2 activation to substrate hydroxylation, depending on the extent of O–O cleavage that is required for generating the reactive Fe-oxygen species. The extent of O2 uncoupling, on the other hand, is highly substrate-specific and potentially modulated by adaptive responses to oxidative stress. Understanding the kinetic mechanisms of oxygenases will be key to assess organic contaminant biotransformation quantitatively.

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Isotope Effects as New Proxies for Organic Pollutant Transformation

Cited by 15 publications

References 34 publications

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

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

Molecularly Imprinted Polymers for Compound-Specific Isotope Analysis of Polar Organic Micropollutants in Aquatic Environments

Enzyme Kinetics of Organic Contaminant Oxygenations

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