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Stable isotope tools provide a powerful line of evidence in civil and criminal forensic investigations. Some of the most notable cases in America that utilized stable isotope evidence include the 2001 anthrax attacks case and the 2001/2003 shoe bomber case. The U.S. Department of Justice, Amerithrax Investigative Summary, February 19, 2010; Sarah Benson et al., Forensic Analysis of Explosives Using Isotope Ratio Mass Spectrometry (IRMS)-Preliminary study on TATP and PETN, 49 Sei. &. Justice 81-86 (2009). Stable isotope forensics has been practiced for decades with applications in food authenticity, assessing geographic origins of explosives and narcotics, as well as the geographic origins of unidentified human remains.
Over the past 20 years, stable isotope tools, specifically compound-specific isotope analysis (CSIA), have been extended to environmental forensics for contaminated groundwater applications to address questions such as: are there multiple sources of contamination at a site; are there multiple responsible parties; what is the fate of the contamination? Through extensive research and publication of peer-reviewed literature, including proof-of-concept field applications, CSIA has been demonstrated to provide a valuable line of evidence for differentiating groundwater contaminant sources, estimating contaminant degradation rates, and distinguishing natural attenuation by degradation pathways compared to physical processes at contaminated sites. As a result, CSIA is receiving more attention and scrutiny in the courts, particularly in litigation matters involving claims of multiple contaminant sources.
This article discusses the principles of CSIA and the capabilities and limitations of this tool, as well as the reliability and admissibility of stable isotope evidence under Federal Rule of Evidence 702 (Rule 702). Existing case law supports a determination that CSIA, when properly used, adheres to the requirements of Rule 702. Our discussion here provides an overview of considerations to appropriately apply CSIA in legal matters.
The practice of CSIA in environmental forensics is based on straightforward scientific principles, building on a foundation of applications spanning more than 50 years in the petroleum exploration industry. Stable isotopes are atoms of the same chemical element (e.g., carbon) that do not decay and have the same atomic makeup, with the exception of a different atomic mass due to a difference in the number of neutrons. This results in light and heavy isotopes of the same element. CSIA measures the stable isotopic...