A New Concept Linking Observable Stable Isotope Fractionation to Transformation Pathways of Organic Pollutants
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- 作者：Martin Elsner ; Luc Zwank ; Daniel Hunkeler ; and René ; P. Schwarzenbach
- 刊名：Environmental Science & Technology
- 出版年：2005
- 出版时间：September 15, 2005
- 年：2005
- 卷：39
- 期：18
- 页码：6896 - 6916
- 全文大小：482K
- 年卷期：v.39,no.18(September 15, 2005)
- ISSN：1520-5851
文摘
Measuring stable isotope fractionation of carbon, hydrogen,and other elements by Compound Specific IsotopeAnalysis (CSIA) is a new, innovative approach to assessorganic pollutant degradation in the environment. Central tothis concept is the Rayleigh equation which relatesdegradation-induced decreases in concentrations directlyto concomitant changes in bulk (= average over thewhole compound) isotope ratios. The extent of in situtransformation may therefore be inferred from measuredisotope ratios in field samples, provided that an appropriateenrichment factor (
bulk) is known. This bulk value,however, is usually only valid for a specific compoundand for specific degradation conditions. Therefore, a directcomparison of bulk values for different compounds andfor different types of reactions has in general not beenfeasible. In addition, it is often uncertain how robust andreproducible bulk values are and how confidently they canbe used to quantify contaminant degradation in the field.To improve this situation and to achieve a more in-depthunderstanding, this critical review aims to relate fundamentalinsight about kinetic isotope effects (KIE) found in thephysico(bio)chemical literature to apparent kinetic isotopeeffects (AKIE) derived from bulk values reported inenvironmentally oriented studies. Starting from basic ratelaws, a quite general derivation of the Rayleigh equationis given, resulting in a novel set of simple equations that takeinto account the effects of (1) nonreacting positions and(2) intramolecular competition and that lead to position-specificAKIE values rather than bulk enrichment factors.Reevaluation of existing bulk literature values result inconsistent ranges of AKIE values that generally are in goodagreement with previously published data in the (bio)chemical literature and are typical of certain degradationreactions (subscripts C and H indicate values for carbonand hydrogen): AKIEC = 1.01-1.03 and AKIEH = 2-23 foroxidation of C-H bonds; AKIEC = 1.03-1.07 for SN2-reactions; AKIEC = 1.02-1.03 for reductive cleavage ofC-Cl bonds; AKIEC = 1.00-1.01 for C=C bond epoxidation;AKIEC = 1.02-1.03 for C=C bond oxidation by permanganate.Hence, the evaluation scheme presented bridges a gapbetween basic and environmental (bio)chemistry and providesinsight into factors that control the magnitude of bulkisotope fractionation factors. It also serves as a basis toidentify degradation pathways using isotope data. It is shownhow such an analysis may be even possible in complexfield situations and/or in cases where AKIE values are smallerthan intrinsic KIE values, provided that isotope fractionationis measured for two elements simultaneously ("two-dimensional isotope analysis"). Finally, the procedure isused (1) to point out the possibility of estimating approximatebulk values for new compounds and (2) to discuss themoderate, but non-negligible variability that may quitegenerally be associated with bulk values. Future researchis suggested to better understand and take into accountthe various factors that may cause such variability.
bulk) is known. This bulk value,however, is usually only valid for a specific compoundand for specific degradation conditions. Therefore, a directcomparison of bulk values for different compounds andfor different types of reactions has in general not beenfeasible. In addition, it is often uncertain how robust andreproducible bulk values are and how confidently they canbe used to quantify contaminant degradation in the field.To improve this situation and to achieve a more in-depthunderstanding, this critical review aims to relate fundamentalinsight about kinetic isotope effects (KIE) found in thephysico(bio)chemical literature to apparent kinetic isotopeeffects (AKIE) derived from bulk values reported inenvironmentally oriented studies. Starting from basic ratelaws, a quite general derivation of the Rayleigh equationis given, resulting in a novel set of simple equations that takeinto account the effects of (1) nonreacting positions and(2) intramolecular competition and that lead to position-specificAKIE values rather than bulk enrichment factors.Reevaluation of existing bulk literature values result inconsistent ranges of AKIE values that generally are in goodagreement with previously published data in the (bio)chemical literature and are typical of certain degradationreactions (subscripts C and H indicate values for carbonand hydrogen): AKIEC = 1.01-1.03 and AKIEH = 2-23 foroxidation of C-H bonds; AKIEC = 1.03-1.07 for SN2-reactions; AKIEC = 1.02-1.03 for reductive cleavage ofC-Cl bonds; AKIEC = 1.00-1.01 for C=C bond epoxidation;AKIEC = 1.02-1.03 for C=C bond oxidation by permanganate.Hence, the evaluation scheme presented bridges a gapbetween basic and environmental (bio)chemistry and providesinsight into factors that control the magnitude of bulkisotope fractionation factors. It also serves as a basis toidentify degradation pathways using isotope data. It is shownhow such an analysis may be even possible in complexfield situations and/or in cases where AKIE values are smallerthan intrinsic KIE values, provided that isotope fractionationis measured for two elements simultaneously ("two-dimensional isotope analysis"). Finally, the procedure isused (1) to point out the possibility of estimating approximatebulk values for new compounds and (2) to discuss themoderate, but non-negligible variability that may quitegenerally be associated with bulk values. Future researchis suggested to better understand and take into accountthe various factors that may cause such variability.