Spatial Distributions of Isotope Ratios in Tap Water, Hair, and Teeth from Latin America for Region-of- Origin Predictions of Unidentified Border Crossers

In this article, we present and summarize reference stable isotope data useful in the identification efforts of deceased undocumented border crossers (UBCs) found in southern Arizona and South Texas. In addition, we discuss the use of reference baseline data to refine predictions of region-of-origin of unidentified UBC remains. Overall, Mexican reference hair samples reflect significant consumption of C4 resources, indicating a diet dominated by corn and corn products. Even though meat consumption in the United States is almost twofold that of Mexico, the Mexican δ15N values were elevated over U.S. values, suggesting differences in nitrogen isotope baselines. The comparison of isotope data collected from deceased UBCs recovered from south Texas versus Arizona suggests only small differences in dietary isotopes between the two groups. Geolocation isotopes showed significant differences in δ18O values of both bone and tooth enamel bioapatite, suggesting differences in the sources of drinking water. However, no significant differences were identified between 87Sr/86Sr ratios for the two groups. Further, we present a case application of successful region-of-originpredictions using the δ18O values and 87Sr/86Sr ratios and also discuss some of the inherent limitations and challenges of applying reference data sets to large-scalehumanitarian identification projects.