Spatial Distributions of Oxygen Stable Isotope Ratios in Tap Water From Mexico for Region of Origin Predictions of Unidentified Border Crossers.

One of the many difficulties associated with identifying undocumented border crossers stems from an inability to narrow down the search area for the region of origin and family members to obtain family reference samples for DNA comparison. While the geography of regions of origins is wide, the biological profiles of the undocumented border crossers often show strong similarities, young and male. The isotopic composition of human bones, teeth, and hair has been demonstrated to be useful biomarkers for tracing locations and movements of individuals and for aiding in the identification of human remains. Data obtained from human remains can be compared to and aligned with various reference sources, such as soils and bedrock, archaeological remains, or cultural data. Here, the spatial deficiency in isotopic reference data for Mexico, specifically for oxygen (δ18 O) isotopes in tap water, is being addressed through the collection and analysis of over 150 water samples and explored with tooth enamel isotopic values from recently identified Mexican nationals. The isoscape was developed using a Spine with Barriers interpolation method and shows sufficient detail to narrow down the regions where specific isotopic values are represented. The individuals were plotted on the developed isoscape using conditional correlations. The methodology was successful in assigning the correct regions of origin for the two individuals, which shows the tremendous potential of the developed isoscape. Nonetheless, there is more research needed to further improve upon this geolocation method, including analysis of multiple isotopes in different tissues, and the development of new isotopic methods.

Age at death estimation using bone densitometry: testing the Fernández Castillo and López Ruiz method in two documented skeletal samples from Portugal.

This study aims to evaluate the accuracy, precision and bias of a method for age at death estimation based in bone mineral density values assessed by dual X-ray absorptiometry at Ward's area (proximal femur). Estimated age at death was contrasted with documented age at death in two Portuguese reference samples (Coimbra Identified Skeletal Collection - CISC, and Identified Skeletal Collection of the 21st Century - Santarém XXI). Mean absolute error (accuracy) varies between 10.5 years (females) and 11.6 years (males) in the CISC sample; and between 11.9 years (males) and 12.7 years (females) in the Santarém XXI study base. The precision of the method varies between 13.0 years (females) and 14.5 years (males), in the CISC sample, and between 8.4 years (females) and 9.5 years (males), in the Santarém XXI sample. Mean error values (bias) suggest that this method tends to overestimate age in younger individuals, and to underestimate it in older individuals, regardless of sex or sample. Nonetheless, the method seems to perform as well as, or better than, other widely tested age estimation techniques, making it a suitable option when more accurate tests are not feasible in any given situation.