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Issue 11, 2010
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Stable isotope fractionation to investigate natural transformation mechanisms of organic contaminants: principles, prospects and limitations

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Abstract

Gas chromatographyisotope ratio mass spectrometry (GC-IRMS) has made it possible to analyze natural stable isotope ratios (e.g., 13C/12C, 15N/14N, 2H/1H) of individual organic contaminants in environmental samples. They may be used as fingerprints to infer contamination sources, and may demonstrate, and even quantify, the occurrence of natural contaminant transformation by the enrichment of heavy isotopes that arises from degradation-induced isotope fractionation. This review highlights an additional powerful feature of stable isotope fractionation: the study of environmental transformation mechanisms. Isotope effects reflect the energy difference of isotopologues (i.e., molecules carrying a light versus a heavy isotope in a particular molecular position) when moving from reactant to transition state. Measuring isotope fractionation, therefore, essentially allows a glimpse at transition states! It is shown how such position-specific isotope effects are “diluted out” in the compound average measured by GC-IRMS, and how a careful evaluation in mechanistic scenarios and by dual isotope plots can recover the underlying mechanistic information. The mathematical framework for multistep isotope fractionation in environmental transformations is reviewed. Case studies demonstrate how isotope fractionation changes in the presence of mass transfer, enzymatic commitment to catalysis, multiple chemical reaction steps or limited bioavailability, and how this gives information about the individual process steps. Finally, it is discussed how isotope ratios of individual products evolve in sequential or parallel transformations, and what mechanistic insight they contain. A concluding session gives an outlook on current developments, future research directions and the potential for bridging the gap between laboratory and real world systems.

Graphical abstract: Stable isotope fractionation to investigate natural transformation mechanisms of organic contaminants: principles, prospects and limitations

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Publication details

The article was received on 08 Jun 2010, accepted on 27 Aug 2010 and first published on 29 Oct 2010


Article type: Critical Review
DOI: 10.1039/C0EM00277A
Citation: J. Environ. Monit., 2010,12, 2005-2031
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    Stable isotope fractionation to investigate natural transformation mechanisms of organic contaminants: principles, prospects and limitations

    M. Elsner, J. Environ. Monit., 2010, 12, 2005
    DOI: 10.1039/C0EM00277A

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