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WIREs Forensic Sci

The use of stable isotopes in postconflict forensic identification

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Abstract Stable isotope ratio analysis is becoming an extremely important tool for the forensic investigator. It can be particularly useful in missing persons investigations to help establish an unknown's identity by potentially reconstructing an individual's geolocational history, determining the number of individuals present in a case, and linking/separating remains from commingled assemblages. In this review article, we explore several main themes related to the use of stable isotopes in postconflict forensic identification. First, we describe what stable isotopes are and how global isotopic variation arises in human tissues via natural processes and cultural practices. Next, we discuss the selection of appropriate human tissue samples for examination based on testable hypotheses. We provide guidance on the options that exist for isotope sample preparation, analysis, and data handling; and finally, we examine which sample quality measures and quality assurance approaches should be used in isotope data reporting and interpretation. These themes are primarily presented to help the isotope data consumer understand the benefits and limitations of the technique that might not be apparent when sending samples to and receiving results from a high throughput, contract isotope testing laboratory. Real world examples of forensic stable isotope ratio analysis are provided within the article to highlight many of the concepts, particularly in regard to identification applications. This article is categorized under: Forensic Anthropology > Anthropology in Mass Disaster & War Crime Contexts Forensic Biology > Interpretation of Biological Evidence Forensic Chemistry and Trace Evidence > Emerging Technologies and Methods
Spatial variations in the δ18O values of water are an effect of the hydrological cycle and the processes of evaporation and condensation. Water molecules containing the heavier isotope 18O evaporate more slowly and condense more readily than water molecules containing the lighter isotope 16O, leading to higher δ18O values in warmer, coastal areas and lower δ18O values in colder, inland areas. Illustration reprinted from Earth‐Science Reviews, Vol. 188, Sarah Pederzani and Kate Britton, Oxygen isotopes in bioarchaeology: Principles and applications, challenges and opportunities, 77–107, Copyright (2019), with permission from Elsevier
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The process of stretching and shifting raw δ values to the accepted isotope scale is presented graphically, redrawn from (Sharp, 2017). First, the measured difference between two reference materials is stretched (or compressed) to match the accepted difference between the materials. Then, the stretched (or compressed) data are shifted so that the measured δ values of the reference material agree with their accepted δ values. The factors calculated in this process are finally applied to the raw δ values of samples to scale them
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Distribution of δ13C and δ18O values of tooth enamel carbonate for East Asian (red circles), U.S. American (yellow triangles), and Japanese (plus signs) individuals, demonstrating that populations can isotopically differ. Data are compiled from Regan (2006) and Someda et al. (2016) and redrawn for this article. Labels for select East Asian and U.S. American data points reflect information provided in fig. 5‐1 of Regan (2006)
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The predicted origin of an individual from Caracas, Venezuela, (A) V1, based on the measurement of O and Sr isotope ratios in tooth enamel. Measured δ18O values and 87Sr/86Sr ratios were plotted on separate maps and combined, using a given margin of error. The resulting prediction included the known natal origin of the individual (starred). Image © 2017 Laffoon et al. and reprinted under the terms of the Creative Commons Attribution License
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Isoscapes of δ18O values (a) and 87Sr/86Sr ratios (b) expected for human tooth enamel in the Circum‐Caribbean region. Individuals born and raised in the three indicated locations would have recorded different combinations of O and Sr isotopic signatures in their enamel. While not necessarily unique or “zip code” specific, the signatures can be used to eliminate many potential regions‐of‐origin from consideration and provide investigative leads into the source of an individual. Image © 2017 Laffoon et al. and reprinted under the terms of the Creative Commons Attribution License
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An isotope landscape (isoscape) map of tap water δ18O values, given in parts per thousand (‰) vs. the internationally agreed standard Vienna Standard Mean Ocean Water (VSMOW). The isoscape shows spatial variation across Mexico, with lower δ18O values observed in mountainous regions (interior and southwestern coast), and higher δ18O values observed in eastern coastal and drier desert regions. Map reprinted from Ammer, Bartelink, et al. (2020), with permission
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Forensic Chemistry and Trace Evidence > Emerging Technologies and Methods
Forensic Biology > Interpretation of Biological Evidence
Forensic Anthropology > Anthropology in Mass Disaster & War Crime Contexts

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