Isotope Analyses of Hair as a Trace Evidence Tool to Reconstruct Human Movements: Establishing the Effects of the "Human Ecosystem" On Strontium and Oxygen Isotope Ratios

Critical advances in isotope mass spectrometry technologies, laboratory methodologies, and spatial modeling have allowed for increased application of oxygen (18O/16O) and strontium (87Sr/86Sr) isotope analysis of human hair to determine an individuals travel histories and probable region-of-origin. We have established that the 18O/16O and 87Sr/86Sr ratios of human
hair relate to geography, where human hair isotope values are primarily influenced by isotope ratios of municipal waters in that an individual imbibes (18O/16O) and bathes (87Sr/86Sr). Both the 18O/16O and 87Sr/86Sr ratios of municipal waters are governed by geography and by the water distribution system in a specific locality. Many major metropolitan areas within the Western
United States acquire their municipal waters from a mix of local groundwater and distant regions(i.e., transported water). The proportions of each water source used depend on water ownership by different municipality-specific water utilities. Thus, adjacent municipal water districts in a single metropolitan area can provide residents with waters that are isotopically distinct from one another, from other nearby metropolitan areas, and from local water sources. These geospatial disconnections imparted on municipal water supplies are transferred to individuals hair and invalidate simple regional isotopic relationships in Western U.S. population centers. However,after a basic understanding of municipal water usage and isotopic variation is incorporated into
spatial models and maps (i.e., isoscapes), these once-complexities may provide a unique
municipal-level (i.e., near zip code) isotopic fingerprint for individuals living within these large metropolitan areas. These isoscapes have the potential to be an ideal forensic tool to assist
in the reconstruction of an individuals geographic-movement histories from trace evidence materials, especially in cases where establishing residency of an individual can be a challenge and travel histories of an individual remain unknown.
In our initial study supported by NIJ, we discovered the 87Sr/86Sr ratios of human hair are controlled by the 87Sr/86Sr ratios of tap water in that an individual bathes and that the 87Sr/86Sr ratios of tap water are defined by the water management practices employed by municipalities.
Here, we propose to expand on initial work and to demonstrate that (a) residence versus nonresident status can be determined, (b) the recent travel histories of suspects and deceased individuals can be established using the combination of 18O/16O and 87Sr/86Sr ratios of human hairs, and (c) a model and isoscape product can be developed that incorporates municipal water
management practices. We propose a study that, if successful, would allow us to distinguish residents from non-residents within six metropolitan test areas of the Western US: Los Angeles-Long Beach-Santa Ana, San Francisco-Oakland-Fremont, Riverside-San Bernardino-Ontario,
Phoenix-Mesa-Glendale, San Diego-Carlsbad-San Marcos, and San Jose-Sunnyvale-Santa Clara.
To complete this objective, we will require analysis of oxygen and strontium isotope ratios of 600+ hair and 800+ water samples collected from these metropolitan regions. We will then collect and analyze hair and water at a high-resolution spatial and temporal resolution within one metropolitan area [Salt Lake City] to confirm and model the water distribution system controls on strontium contributions to water and hair. We will then build a water distribution-modulated geospatial model and isoscape of water and hair oxygen and strontium isotope values across the Western U.S. Applications of this product are diverse and include reconstructing travel histories of unidentified murder victims, reconstructing movements of trans-nationals associated with
crimes, and reconstructing the region-of-origin of exploited individuals transported across state and/or national boundaries.
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