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USE OF STABLE ISOTOPES IN ENVIRONMENTAL AND FORENSIC GEOCHEMISTRY STUDIES
Citation:
Philip, P. AND J T. Wilson*. USE OF STABLE ISOTOPES IN ENVIRONMENTAL AND FORENSIC GEOCHEMISTRY STUDIES. Presented at 4th Int'l. Battelle Conf, Monterey, CA, May 24 - 27, 2004.
Impact/Purpose:
To inform the public.
Description:
Stable carbon and hydrogen isotopes have been used for many decades in the petroleum industry, but the development of combined gas chromatography-isotope ratio mass spectrometry (GCIRMS) has led to a virtual explosion in application of this technique not only in petroleum exploration but also in the environmental and forensic geochemical fields. This workshop will present an introduction to stable isotope geochemistry and discuss applications of stable isotopes to various environmental problems. Topics to be covered will include an introduction to the concept of stable isotopes, with particular attention to carbon, hydrogen, and to a lesser degree, chlorine. Techniques for determination of bulk isotope values will be describe along with the advantages and disadvantages of the GCIRMS approach. Examples will be given of the use of bulk isotope data combined with other techniques such as GC or GCMS for the purpose of determining whether or not contaminants are related to each other. This is particularly important where there might be multiple sources potentially responsible for a particular spill. In cases where the contaminant has multiple components and the GC and GCMS data are not particularly useful for correlation purposes, relationships between source and product might be determined only through the stable isotopes of individual compounds. GCIRMS is also extremely valuable for single-component contaminants, such as MTBE or PCE, where GC and GCMS will be of no use for correlation. Particular emphasis will be given to the interpretation of stable carbon and hydrogen isotope ratios of MTBE in contaminated ground water. In particular, course participants will learn how to predict the fraction of MTBE originally present in contaminated ground water and removed through biological transformation to TBA. They will also learn how to predict the concentration of TBA that should be expected from biotransformation of MTBE. Data will be presented from the sites in California and on the East Coast to illustrate the effect of biological transformations on the SCIR and SHIR ratio in MTBE and to illustrate the calculations.