RESUMO
Deceased undocumented border crossers are some of the most difficult individuals to identify due to the inability to narrow down the region of origin and therefore to obtain family reference samples for DNA comparison. The isotopic compositions of various body tissues have been demonstrated to be useful biomarkers for tracking locations and movements to aid in the identification of human remains. This study closes the large spatial gap of available 87Sr/86Sr ratios from North America in tap water and presents the first 87Sr/86Sr human tissue-based ratios from Mexico. The 101 hair samples from 32 locations in Mexico range in 87Sr/86Sr ratios from 0.70424 to 0.71613 (ΔSrmax-min=0.01189). Furthermore, 151 tap water samples from 51 locations range between 0.70404 to 0.71385 (ΔSrmax-min=0.00981). Overall, small variations in the hair and tap water samples collected from individual locations were recorded (ΔSrmax-min=0.00041 and 0.00034 respectively). Despite the fact that Mexico is one of the largest bottled water consumers in the world, the 87Sr/86Sr ratios of human hair and tap water correlated strongly (R2=0.87 for location averages and R2=0.80 when using individual data points). These data represent a valuable resource for identifying the provenance of human remains.
Assuntos
Água Potável/química , Cabelo/química , Isótopos de Estrôncio/análise , Biomarcadores/análise , Ciências Forenses , Humanos , México/epidemiologia , Valores de Referência , Análise EspacialRESUMO
Substantial progress in the application of multiple isotope analyses has greatly improved the ability to identify nonlocal individuals amongst archaeological populations over the past decades. More recently the development of large scale models of spatial isotopic variation (isoscapes) has contributed to improved geographic assignments of human and animal origins. Persistent challenges remain, however, in the accurate identification of individual geographic origins from skeletal isotope data in studies of human (and animal) migration and provenance. In an attempt to develop and test more standardized and quantitative approaches to geographic assignment of individual origins using isotopic data two methods, combining 87Sr/86Sr and δ18O isoscapes, are examined for the Circum-Caribbean region: 1) an Interval approach using a defined range of fixed isotopic variation per location; and 2) a Likelihood assignment approach using univariate and bivariate probability density functions. These two methods are tested with enamel isotope data from a modern sample of known origin from Caracas, Venezuela and further explored with two archaeological samples of unknown origin recovered from Cuba and Trinidad. The results emphasize both the potential and limitation of the different approaches. Validation tests on the known origin sample exclude most areas of the Circum-Caribbean region and correctly highlight Caracas as a possible place of origin with both approaches. The positive validation results clearly demonstrate the overall efficacy of a dual-isotope approach to geoprovenance. The accuracy and precision of geographic assignments may be further improved by better understanding of the relationships between environmental and biological isotope variation; continued development and refinement of relevant isoscapes; and the eventual incorporation of a broader array of isotope proxy data.