Extending the Biological Profile: Using Stable Isotope Analysis as an Exclusionary Tool in Region-of-Origin Investigations of Unidentified Remains

BEASLEY, MELANIE M; CHESSON, LESLEY A; VALENZUELA, LUCIANO O; BARTELINK, ERIC J

Washington

Encuentro; 65th Anniversary Meeting of the American Academy of Forensic Sciences; 2013

American Academy of Forensic Sciences

Afterattending this presentation, attendees will understand the application of hydrogenand oxygen stable isotope analysis in forensic anthropology. We highlight howstable isotope analysis can contribute to the biological profile ofunidentified remains by tracking the movement of a victim prior to death. Thispresentation will impact the forensic community by demonstrating how anextended biological profile that includes stable isotope data has enormous potentialfor aiding in the positive identification of unknown individuals. Althoughanthropologists have used stable isotope analysis extensively since the 1970sto examine diet, weaning, and migration in prehistory, the technique has hadlimited application in forensic anthropology demonstrated by the paucity of stableisotope presentations and publications. Stable isotope analysis offers another toolto the medico-legal community to reconstruct the movement prior to death ofunidentified decedents and to exclude possible matches and narrow search areas. Stableisotope analysis is most beneficial to forensic anthropologists in cases where standardmethods of identification are unsuccessful. Although the biological profiletypically consists of sex, age, ancestry, stature, and antemortemcharacteristics, stable isotope analysis of biological tissues can provideadditional information regarding migration history, including birthplace, thelast decade of life, or the weeks and months before death depending on thetissue sampled. Previous research has demonstrated the utility of usingmultiple stable isotopes to identify region of origin and/or dietary patternsin broader-crossers deaths from Mexico (Juarez, AAFS Proceedings, 2005), U.S.soldier war-dead from the Vietnam conflict (Regan et al., AAFS Proceedings,2006), unidentified individuals from California (Bartelink et al., AAFSProceedings, 2008), and the identification of a U.S. airman?s remains recoveredin Laos (Holland et al., AAFS Proceedings, 2012). Theapplication of stable hydrogen and oxygen isotope analysis of biologicaltissues to investigate origin is possible because stable isotope ratios ofwater vary systematically and predictably across landscapes due to environmentalfactors. These isotope distributions can be visualized using GIS mapshighlighting distinct isotopic regions, or isotope landscapes (isoscapes). Inturn, the isotopes of biological tissues record the isotopic composition oflocally available water. For example,human hair records the isotopic composition of drinking water consumed by anindividual throughout the duration of hair growth. Ehleringer et al.1demonstrated that predictive models relating human hair stable isotope ratiosto drinking water ? and thus, geography ? achieved an overall 86% success ratebetween observed and predicted region of origin within the continental USA.However,the success of origin predictions based on the analysis of stable isotopes in tissues is dependent upon the quality of water isotope data used in building the foundational predictive isoscapes. Here, we investigated the impact of a fine scale tap water collection scheme within two U.S. states on the performance of a continental USA tap water isoscape model originally developed by Bowen et al.2 The collected sample set consisted of 186 tap water samples from several cities throughout California and Oregon. These samples were then used to develop a tap water isoscape specifically for the two coastal states. The new model was then used to predict the isotopic composition of 20 validation samples randomly selected from the dataset that were not used in model generation. The agreement between measured isotope ratios and those predicted using the new isoscape was compared to agreement between measured isotope ratios and those predicted using the previous Bowen et al.2isoscape to judge the accuracy of tap water predictions in the new model generated from samples collected at a finer spatial resolution.This project highlights the utility of stable isotope analysis in forensic anthropology investigations by demonstrating the application of the technique to tissues that record geographic information and by presenting methods fori ncreasing the reliability of region of origin interpretations based on measured stable isotope data.References:1Ehleringer JR, Bowen GJ, Chesson LA, West DW, Podlesak DW, Cerling TE. Hydrogen and oxygen isotope ratios in human hair are related to geography. PNAS 2008;105(8):2788-93.2Bowen G, Ehleringer J, Chesson L,Stange E, Cerling T. Stable isotope ratios of tap water in the contiguousUnited States. Water Resour Res. 2007;43(W03419):1?12.