Strontium Isotope Ratios of Hair for Human Provenancing

TIPPLE, BRETT; CHAU, TH; CHESSON, LESLEY A; EHLERINGER, JAMES R; MANCUSO, CHRISTY; VALENZUELA, LUCIANO O

Orlando

Encuentro; 67th Annual Scientific Meeting of the American Academy of Forensic Sciences; 2015

American Academy of Forensic Sciences,

In this presentation,attendees will gain an understanding of how strontium isotopes in human hairrelate to geography and can be used to answer questions regarding human originsand movement. This work will impact the forensic anthropology and toxicology communitiesby demonstrating how the innate chemical composition of human tissues reflectsan individual?s origin and travel history. Attendees will gain specific knowledgeon how strontium is incorporated into hair, how strontium isotope profiles withinhair can be used to reconstruct regions-of-residence and travel movements, andhow strontium isotopes can be combined with other isotopes to refine human movementhistories. This presentation focuseson the application of strontium isotope analysis to human hair to aid in theidentification of individuals of unknown origin or history. Reconstructing thetravel-movement history of individuals can be important to many forensicinvestigations, spanning from nation-wide homeland security issues to investigationsof unidentified decedents by local agencies. Analysis of stable isotopes inhuman scalp hair has shown to be a useful tool for reconstructing the recentgeographic-movement histories of individuals because hair proteins (i.e.,keratin), and the stable isotopes contained within keratin, are recorders of anindividual?s geographical environment. As an example, the oxygen(O) isotope values (d18O) ofhuman hair keratin can provide travel/geographic origin information and guidecriminal investigations. This is due to the well-established relationshipbetween the d18O valuesof human hair and an individual?s drinking water. Since the d18O valuesof drinking water vary predictably across landscapes, the d18O valuesof human hair correlate to specific geographic regions. These geographicprojections of isotope values across landscapes are termed an ?isoscape.? Whiled18Oisoscapes provide a valuable tool for describing geographical spaces where anindividual may have originated, the estimated geographical regions can bebroad. To refine these broad region-of-origin predictions, investigators need acomplementary isotopic approach that reflects different geographic information. Strontium (Sr) isotoperatios (87Sr/86Sr) of human hair have attracted interestas a complement to d18O valuesdue geographic variations in 87Sr/86Sr within theenvironment based on local geology. It has been previously established that the87Sr/86Sr ratios of human tissues composed ofhydroxyapatite (e.g., bones and teeth) relate to geography. However,application of Sr isotope analysis to keratinous human tissues (e.g., hair andfingernails) has been avoided to date due to low strontium concentrationswithin these tissues. Recent technological advances have made analysis ofkeratin-based tissues possible, which have proven useful in reconstructingnon-human animal geospatial histories. As human hair is structurally similar tonon-human keratinous tissues, 87Sr/86Sr values of humanhair should also provide geospatial information. Tounderstand the linkages between the Sr in keratinous tissues and anindividual?s geographical environment, human hair and tap waters were collectedfrom 55 cities throughout the contiguous United States and the 87Sr/86Sr ratios were measured on pairedhair-water samples. We found paired tapwater and hair 87Sr/86Sr ratios were strongly correlatedand displayed a 1:1 relationship, indicating little to no fractionation betweenSr isotope ratios in water and hair. Our findings indicate Sr isotope signals from water are reflected in the isotope ratios ofthe hair of individuals, and in turn, the 87Sr/86Sr ratiosof human hair provide unique geographic information relating to the localitywhere an individual resides. As O and Sr isotope ratios within human hair are bothgeographically controlled, but reflect different physical and chemicalenvironmental processes, the paired analyses of both O and Sr isotope ratios wouldallow for a finer resolution reconstruction of the travel-movement history of an individual than analysisof either O or Sr alone.