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Multi‐isotope approaches for region‐of‐origin predictions of undocumented border crossers from the US–Mexico border
Abstract
This chapter presents stable isotope analysis (SIA) results for bone‐tooth pairs from undocumented border crossers (UBC) from Brooks County, Texas. Bone and tooth samples were prepared for SIA, including carbon and nitrogen isotope analysis of bone collagen, carbon and oxygen isotope analysis of bone bioapatite and enamel bioapatite, and strontium isotope analysis of tooth enamel. Using a multi‐isotope approach, the likely region‐of‐origin is narrowed down for these individuals. The chapter presents preliminary interpretations of isotope results for two case studies to illustrate the use of SIA as an investigative tool for deceased UBC cases from Texas. The case studies highlight the value of a multi‐isotope approach for predicting region‐of‐origin and some of the complexities involved with reconstructing the life and travel history of UBCs. For migrants who cross the US‐Mexico border, it is assumed that food and water were most likely consumed at their place of origin.
... To this point, promising new work is emerging. Machine learning models are being developed that merge relative estimates of tripartite ancestry, case year, and geospatial data for the location of recovery to infer place of origin and subsequently map immigration pathways from home region to the Arizona border (Algee-Hewitt et al. 2020b), while research focusing on the utility of stable isotopes in the context of unidentified remains is demonstrating the potential for excluding geographic regions when isotopic values are inconsistent with the remains in question (Ammer et al. 2020;Bartelink et al. 2020;Kramer et al. 2020). However, these isotopic methods are still developing and have yet to be comprehensively compared to individuals of known origin with consideration for water stress and resource globalization (Juarez et al. 2020), and the biogeographic models require the integration of data representing cases across multiple border states. ...
... Similarly, Wang et al. (2008) extended this notion into the modern HEA groups by individual level. Information on ancestry increases as we increase the number of forensic STRs, and different markers and systems, including other kinds of biological or cultural data, not only support but differently enrich results (Algee-Hewitt et al. 2016, 2018, 2020aAmmer et al. 2020;Bartelink et al. 2020;Hughes et al. 2017;Kramer et al. 2020;Soler et al. 2019). It is likely, then, that our best solutions will use a broad set of genomic (STR, single-nucleotide polymorphisms, mitochondrial and Y-STR haplogroups), skeletal, morphological, isotopic, and case-context data. ...
... To this point, there is promising new work emerging. Machine learning models are being developed that merge relative estimates of triparental ancestry, case year, and geospacial data for the location of recovery to infer place of origin and subsequently map immigration pathways from home region to the Arizona border ; while research focusing on the utility of stable isotopes in the context of unidentified remains is demonstrating the potential for excluding geographic regions when isotopic values are inconsistent with the remains in question (Ammer et al. 2020;Bartelink et al. 2020;Kramer et al. 2020). However, these isotopic methods are still developing and have yet to be comprehensively compared to individuals of known origin with consideration for water stress and resource globalization (Juarez et al. 2020), and the biogeographic models require the integration of data representing cases across multiple Border states. ...
... There is still considerable exploration to be done to identify the most appropriate methods, the optimal set of genetic markers, and the best parental/reference samples for making predictions on the individual level. It has already been shown that information on ancestry increases as we increase the number of forensic STRs, and that different markers and systems, including other kinds of biological or cultural data, not only support but differently enrich results Algee-Hewitt et al. 2018;Ammer et al. 2020;Bartelink et al. 2020;Hughes et al. 2017;Kramer et al. 2020;Soler et al. 2019). It is likely, then, that our best solutions will utilize a broadened set of genomic (STR, single nucleotide polymorphisms, mitochondrial and Y-STR haplogroups), skeletal, morphological, isotopic, and case context data. ...
The humanitarian crisis on the US-Mexico border is a long-standing and evolving crisis in which nearly 8,000 deaths have been reported in the last two decades. These deaths are largely distributed across the Arizona-Mexico and Texas-Mexico border regions, where demographic trends for immigrants attempting to cross into the United States have shifted dramatically. The demographic change and volume of immigrants seeking shelter in the United States present new challenges for the forensic practitioners entrusted with the identification of individuals who lose their lives during the final segment of their journey. Within this border context, this study investigated how genetic variation inferred from forensically significant microsatellites can provide valuable information on regions of origin for unidentified remains at the group level. To explore how to mobilize these genetic data to inform identification strategies, the authors conducted a comparative genetic analysis of identified and unidentified immigrant cases from the Arizona- and Texas-Mexico contexts, as well as 27 other Latin American groups. Allele frequencies were utilized to calculate FST, and relationships were visually depicted in a multidimensional scaling plot. A Spearman correlation coefficient analysis assessed the strength and significance of population relationships, and an agglomerative clustering analysis assessed population clusters. Results indicate that Arizona-Mexico immigrants have the strongest relationship (>80%) with groups from El Salvador, Guatemala, Mexico, and an indigenous group from southern Mexico. Texas-Mexico immigrants have the strongest relationships (>80%) with groups from Belize, Colombia, Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua. These findings agree with, and are discussed in comparison with, previously reported demographic trends, population genetics research, and population history analyses. The authors emphasize the utility and necessity of coupling genetic variation research with a nuanced anthropological perspective for identification processes in the US-Mexico border context.
... To date, this investigative tool has not been used in DVI, as only recently have applications in more long-term victim identification events been demonstrated (e.g., [10][11][12][13][14][15]). ...
Within the complex world of disaster victim identification, or DVI, forensic science practitioners use a variety of investigative techniques to work toward a common goal: identification of the decedents, bringing closure to the affected communities. Identification is a complex undertaking; the event (disaster) also can be extraordinarily complex, as it may be an acute event, or one that spans months or years. Compounding this time issue, remains may be heavily fragmented, dispersed, commingled, or otherwise disrupted by either the perpetrators or the disaster itself. To help solve these complexities, we explore the use of stable isotope analysis (SIA) in DVI events. SIA can be used with a variety of body tissues (hair, nail, bone, and teeth), and each represents different time depths in a decedent's life. Bone collagen and tooth enamel carbonate are useful to reconstruct an individual's diet and source water intakes, respectively, leading to likely population or geographic origin determinations. Additionally, the carbon and nitrogen isotopic signatures of bone collagen have calculated intraperson ranges. These facts allow investigators to determine likely origin of remains using isotopic data and can be used to link skeletal elements (to an individual), or perhaps more importantly, show that remains are not linked. Application of SIA can thus speed remains identification by eliminating individuals from short lists for identification, linking or decoupling remains, and reducing the need for some DNA testing. These strategies and hypothesis tests should commence early in the DVI process to achieve maximum effectiveness.
... Furthermore, law enforcement agencies could use the isoscape to predict the region of 'growing areas' or determine country of origin using bioavailable 87 Sr/ 86 Sr from confiscated illicit drugs, like marijuana or heroin [132,133]. Additionally, although Aotearoa does not encounter many unidentified human remains, if they were recovered and traditional identification methods failed to produce a positive identification, 87 Sr/ 86 Sr values from the unidentified person's teeth could help predict their region or country of origin [19,25,26,37,65,74,77,134,135]. ...
As people, animals and materials are transported across increasingly large distances in a globalized world, threats to our biosecurity and food security are rising. Aotearoa New Zealand is an island nation with many endemic species, a strong local agricultural industry, and a need to protect these from pest threats, as well as the economy from fraudulent commodities. Mitigation of such threats is much more effective if their origins and pathways for entry are understood. We propose that this may be addressed in Aotearoa using strontium isotope analysis of both pests and products. Bioavailable radiogenic isotopes of strontium are ubiquitous markers of provenance that are increasingly used to trace the origin of animals and plants as well as products, but currently a baseline map across Aotearoa is lacking, preventing use of this technique. Here, we have improved an existing methodology to develop a regional bioavailable strontium isoscape using the best available geospatial datasets for Aotearoa. The isoscape explains 53% of the variation (R² = 0.53 and RMSE = 0.00098) across the region, for which the primary drivers are the underlying geology, soil pH, and aerosol deposition (dust and sea salt). We tested the potential of this model to determine the origin of cow milk produced across Aotearoa. Predictions for cow milk (n = 33) highlighted all potential origin locations that share similar ⁸⁷Sr/⁸⁶Sr values, with the closest predictions averaging 7.05 km away from their true place of origin. These results demonstrate that this bioavailable strontium isoscape is effective for tracing locally produced agricultural products in Aotearoa. Accordingly, it could be used to certify the origin of Aotearoa’s products, while also helping to determine if new pest detections were of locally breeding populations or not, or to raise awareness of imported illegal agricultural products.
... La aplicación del análisis de los isótopos (tanto estables como radiogénicos) constituye una herramienta que aporta elementos para la identificación humana, puede ser útil para orientar los procesos de identificación y de búsqueda de personas desaparecidas, ya que genera información de inclusión o exclusión, lo cual permite reducir el universo de posibles coincidencias Bartelink & Chesson, 2019;Bartelink et al., 2014Bartelink et al., , 2016Bartelink et al., , 2020Chesson et al., 2014Chesson et al., , 2018Eck et al., 2019;Ehleringer et al., 2010;Juárez, 2008;Kamenov & Curtis, 2017;Kramer et al., 2020;McLean et al., 2013McLean et al., , 2014Meier-Augenstein, 2010;Meier-Augenstein & Fraser, 2008;Philp, 2007;Rauch et al., 2007). ...
El artículo presenta una revisión de las investigaciones realizadas a la fecha en Colombia relacionadas con la aplicación de los análisis de isótopos en la identificación humana. En especial, hace énfasis en la utilidad de las relaciones isotópicas de estroncio (87Sr/86Sr) para rastrear el lugar de origen de un cuerpo en condición no identificada (CNI). Dentro de la revisión se resalta la importancia de la variabilidad geológica colombiana, la cual puede incidir en la diversidad del estroncio biodisponible, en un espacio y un periodo determinados. Esta diversidad del estroncio biodisponible puede verse reflejada en la distribución espacial de la composición isotópica de estroncio en diferentes tejidos humanos (dientes, huesos, cabello y uñas) de los pobladores del territorio colombiano. Esto es debido a la transferencia de la señal isotópica del estroncio biodisponible a los tejidos humanos. Dentro de las conclusiones de la revisión bibliográfica realizada se menciona la importancia del uso del estroncio (Sr) en la identificación humana en el contexto colombiano, su aplicación forense y sus posibles limitantes respecto al uso de esta metodología en el país.
... More recently, Ammer, Kootker, et al. (2020) measured 87 Sr/ 86 Sr ratios of hair (n = 101) and tap water collected in Mexico and found that they were strongly correlated. This has led investigators to use Sr in combination with C and/or O to predict the likely origin of recovered UBC remains (e.g., Bartelink et al., 2018Bartelink et al., , 2020Kramer et al., 2020). Mapping products (isoscapes) needed for these geolocation efforts are being rapidly created-that is, for Mexico (Ammer, Kootker, et al., 2020;Juarez et al., 2018; see Figure 2), and the circum-Caribbean region Laffoon et al., 2017; see Figure 3) as well as other parts of the world (Adams et al., 2019;Bataille et al., 2018Bataille et al., , 2020Daux et al., 2021;Gautam et al., 2020;Shin et al., 2020;Wang & Tang, 2020;Zieli nski et al., 2021). ...
Stable isotope ratio analysis is becoming an extremely important tool for the forensic investigator. It can be particularly useful in missing persons investigations to help establish an unknown's identity by potentially reconstructing an individual's geolocational history, determining the number of individuals present in a case, and linking/separating remains from commingled assemblages. In this review article, we explore several main themes related to the use of stable isotopes in postconflict forensic identification. First, we describe what stable isotopes are and how global isotopic variation arises in human tissues via natural processes and cultural practices. Next, we discuss the selection of appropriate human tissue samples for examination based on testable hypotheses. We provide guidance on the options that exist for isotope sample preparation, analysis, and data handling; and finally, we examine which sample quality measures and quality assurance approaches should be used in isotope data reporting and interpretation. These themes are primarily presented to help the isotope data consumer understand the benefits and limitations of the technique that might not be apparent when sending samples to and receiving results from a high throughput, contract isotope testing laboratory. Real world examples of forensic stable isotope ratio analysis are provided within the article to highlight many of the concepts, particularly in regard to identification applications.
This article is categorized under: Forensic Anthropology > Anthropology in Mass Disaster & War Crime Contexts
Forensic Biology > Interpretation of Biological Evidence
Forensic Chemistry and Trace Evidence > Emerging Technologies and Methods
... Recent additions in the technical armamentarium of forensic anthropology has facilitated the application of anthropological knowledge to medico-legal investigations. Different molecular and chemical approaches like stable isotope and portable kit-based DNA analyses have remarkably helped in identification of migration-related undocumented border-crossers and their geographical origins [4][5]. Facial imaging and facial approximation techniques have helped in recognition and identification of the missing or suspect persons [6]. ...
Forensic anthropology involves diverse applications of anthropological knowledge to medico-legal problems like human identification based on sex determination, age estimation, stature reconstruction, and deciphering ancestry of unknown living individuals or skeletal remains. Sex can be determined by using different body parts such as extremities (legs and arms) parameters, head, face, clavicle, and other parameters. In present cross-sectional study, cephalometric dimensions of 800 Ladakhi subjects (431 males and 369 females) of Purigpas and Brokpas ancestry were taken. Descriptive statistics of cumulative cephalometrics in two sexes revealed that all the measurements were significantly larger in males than females (p<0.001). Statistically, significant sex differences were found in the various anthropometric, cephalometric, and morphological features of Brokpas and Purigpas of Kargil (Ladakh, UT). Univariate discriminant function analysis found head length as the best cephalofacial variable to estimate the sex of 73.4% of individuals; followed by physiognomic facial length to estimate the sex of 71% of subjects. From multivariate discriminant function analysis, the physiological facial length, head length, nasal breadth, head circumference, nasal height, bizygomatic breadth, length of right ear, and left ear breadth were selected as the best variables to correctly classify the sex of 83.8% of individuals to their category (81.9% males and 85.9% females). The present study results are the only cephalometric standards that have been suggested for Purigpas and Brokpas of Ladakh (Jammu and Kashmir) which can be used for medico-legal sex determination of unknown individuals of the studied population.
... Future research should focus on assembling and sharing large scale reference databases, and the provision of a framework for the analysis, interpretation and presentation of the evidential value of anthropological findings [80]. Another way forward is the exploration of interdisciplinary approaches for identification purposes, as shown by emerging publications concerning the use of stable isotope analysis in forensic anthropology for narrowing down of the provenance of human remains, and thus helping search for antemortem data [81][82][83][84][85]. ...
In this position statement, the Board members of the Forensic Anthropology Society of Europe (FASE) argue that forensic anthropology methods can be used as means of personal identification, particularly in situations with limited availability of traditional identification methods (i.e. dactyloscopy, odontology, and molecular genetic analysis). This statement has been issued taking into account the international migration crises related to thousands of deaths worldwide, in which the utility of these traditional means of identification has been sporadic to non-existent. The statement is however not limited to deaths related to the migration crises, as similar problems may occur in fatalities en masse such as in natural disasters and armed conflicts, and on a smaller scale in cases of homeless or otherwise socioeconomically disadvantaged persons. The number of reports on personal identification based on sound anthropological methodology is increasing in the scientific literature. However, more research is needed to develop evidence-based standard operating procedures and statistical frameworks. It remains essential to raise awareness among forensic practitioners, law enforcement, and judiciary professionals on the utility of forensic anthropology in cases where it can provide sufficient information for identification.
Según el informe publicado entre la Procuraduría de Trata y Explotación y la Colectiva
de Intervención Ante las Violencias en el año 2015, la cantidad de personas fallecidas
sin identidad conocida (NN) registradas en la República Argentina para el periodo
desde el año 1995 al 2013 asciende a un total de 5329. Adicionalmente, la información
reunida sobre personas NN y desaparecidas carece en muchos casos de datos específicos
sobre sexo, edad, huellas dactilares, etc., lo cual dificulta las tareas de identificación.
Considerando esta situación, en este trabajo presentamos una revisión sobre la utilización de isótopos estables en contextos forenses de identificación de personas. Esta permite proponer el uso del análisis de isótopos estables de carbono (13C/12C), nitrógeno (15N/14N) y oxígeno (18O/16O) como una herramienta que puede ayudar en las
investigaciones para establecer la identificación de restos humanos correspondientes al
contexto democrático argentino. Esta técnica puede aportar información antemortem y
circunscribir el área de búsqueda al estimar hábitos alimentarios, origen y/o residencia
de las personas que se busca identificar, a partir de analizar sus restos óseos y dentales.
En suma, en este trabajo presentamos una breve revisión del estado de la cuestión
respecto a los análisis de isótopos estables en el marco de investigaciones de antropología
forense y en base a esta revisión introducimos una propuesta de trabajo futura para
aplicar en la República Argentina con individuos sin identidad conocida, asignables al
período democrático (desde el año 1983 hasta la actualidad). Dicha propuesta tiene el
propósito específico de producir un marco de referencia sobre la población actual de
la Ciudad de Buenos Aires (CABA) y Áreas Metropolitana de Buenos Aires (AMBA), a
partir del estudio de los isótopos estables del carbono (13C/12C), nitrógeno (15N/14N) y
oxigeno (18O/16O) en tejido óseo y dental.
Strontium and oxygen isotope values are used in conjunction with a maximum likelihood assignment model to predict the childhood and adulthood geographic residences of 20 deceased migrants recovered along the México-U.S. border in south Texas. The objectives of this research are to determine (1) if the childhood and adulthood residency assignments predict the same geographic region, (2) if using the predicted residential history/nationality as a filter on the National Missing and Unidentified Persons System (NamUs) reduces the number of potential matching missing person reports, and (3) if we should target teeth or bone as the optimal hard tissue to sample. We found that 12 of the 20 cases (60%) predict similar regions of residency using isotopes derived from bone bioapatite (adulthood residency) and tooth bioapatite (childhood residency). When predicted residential history/nationality data were used as a filter in NamUs, there was a significant reduction in the mean number of case searches (mean = 1568.5 ± 505.3 [1 SD] vs. 107.9 ± 142.6 [1 SD]; t = 12.441, df = 22, p < 0.001, unequal variances assumed). These results demonstrate the utility of isotope data for narrowing down the region of origin and in turn the number of missing persons records to review. Finally, we recommend that death investigators at minimum collect dental samples (premolars or molars) for future unidentified migrant cases to aid in identification efforts utilizing isotope analytical methods. Bone bioapatite samples can provide more recent residential history information but should be used in conjunction with tooth enamel data.
Over its fifty years of established existence beginning in 1967, the Association of Southeast Asian Nations (ASEAN) has expounded its consolidated and integrated model in political relations, economic developments, and cultural values. However, confronted by threats to global security, ASEAN has also faced the complex impacts of transnational narcotics trafficking (TransNT). The study uses grey literature as secondary data to illustrate the current situations of TransNT in Southeast Asia by way of examining drug trafficking starting from the original countries (Myanmar) through the transit points (Vietnam) to final destination countries (Malaysia). Besides reviewing more than four decades of collaboration, the paper analyses ASEAN’s milestones in building its cooperative mechanism and assesses its institutional framework for combatting TransNT with specific initiatives. The study notes the main barriers and practical challenges that constrain the process of regional cooperation. Some brief recommendations are also suggested for further research in the near future to enhance regional cooperation in combatting transnational crimes.
Building on applications in anthropology, the use of stable isotope ratio analysis of human bone collagen to investigate an individual’s life history is becoming more commonplace in the forensic science community. Careful consideration of the resultant isotope delta (δ) values, particularly in regard to their accuracy and reliability, is paramount when introducing isotope data into the U.S. court system. In this study, we use a simple framework to calculate real interpretative difference (RID) values for collagen (“col”) and assess isotope data comparability for sample analysis (RIDanalysis) as well as sample preparation/analysis combined (RIDcombined). The RIDcombined values of 0.59‰ for δ13Ccol and 0.91‰ for δ15Ncol are similar to more complex, published calculations of inter-laboratory variability in the stable isotope analysis of skeletal remains, but they are easier to calculate and intuitively elegant. The RIDcombined as well as RIDanalysis values presented here allow users to examine multiple sources of inter-laboratory isotopic variation (preparation, analysis, and both together) in a two-step process whereby a RID value is constructed and then tested. Implementation of this RID approach will provide surety for the legal and research communities in forensic applications of stable isotope ratio analysis.
Objectives:
Thousands of migrants have died along the United States/Mexico border and many remain unidentified. The purpose of this research is to test whether estimations of population affinity, derived from craniometric data, can facilitate identification of migrant remains and provide a geographic region of origin rather than the broad label Hispanic. The appropriateness of current forensic reference data will also be assessed.
Methods:
A case study combined with craniometric data from positively identified and unidentified migrants from the Pima County Office of the Medical Examiner (n = 489) in Arizona and operation identification (n = 201) in Texas were compared to skeletal data representing Guatemalan (n = 87) and Mexican (n = 65) Mayans. Biological distance and discriminant function analyses were used to assess overall population relationships and classificatory models for forensic anthropological application.
Results:
The majority of evidence indicates that estimations of population affinity can assist in the facilitation identification of migrant remains, even when a broad classification is used. Biological distances among the groups suggest that positively identified Guatemalan and Mexican migrants are similar to one another but differ from Guatemalan and Mexican Mayans.
Conclusions:
Population affinity estimations can aid migrant identification, and current reference data used in forensic anthropological practice should be replaced with data from positive identifications. Estimates of geographic origin may be more useful than the broad generic term Hispanic for narrowing down the search for a missing person, but more data and research is needed to achieve this goal. Although, the utility of geographic origin estimates relies on transnational data centralization and sharing, which is not always the case.
Isotope analysis has become an increasingly valuable tool in forensic anthropology casework over the past decade. Modern-day isotopic investigations on human remains have integrated the use of multi-isotope profiles (e.g. C, N, O, H, S, Sr, and Pb) as well as isotopic landscapes (“isoscapes”) from multiple body tissues (e.g. teeth, bone, hair, and nails) to predict possible region-of-origin of unidentified human remains. Together, data from various isotope analyses provide additional lines of evidence for human identification, including a decedent’s possible region-of-birth, long-term adult residence, recent travel history, and dietary choices. Here, we present the basic principles of isotope analysis and provide a brief overview of instrumentation, analytical standards, sample selection, and sample quality measures. Finally, we present case studies that reflect the diverse applications of isotope analysis to the medicolegal system before describing some future research directions. As shown herein, isotope analysis is a flexible and powerful geolocation tool that can provide new investigative leads for unidentified human remains cases.
In 2012, Texas surpassed Arizona in migrant deaths. The majority of deaths occurred in the Rio Grande Valley, specifically in Brooks County, Texas. Brooks County is one of the poorest in the state and was overwhelmed with deaths, without appropriate resources to follow the state laws pertaining to the investigation of unidentified human remains. Until 2013, most remains that were not immediately identified were buried without collecting DNA samples and the location of burials was not recorded. Our paper outlines the difficulties searching for these burials, the struggles of the families of the missing, and the collaborative approaches to facilitating identifications in South Texas. Community outreach combined with geophysical surveys guide which cemeteries are in need of exhumations. Once cemeteries are surveyed, archaeological methods are employed to exhume remains and document burials. Remains are taken to the Forensic Anthropology Center at Texas State for processing, analysis, and identification efforts. Undergraduate and graduate students clean remains and wash clothing and personal effects.
After skeletal analysis, all information regarding the remains, including photographs of personal effects, are uploaded to the National Missing and Unidentified Persons System (NamUs) and a DNA sample is submitted to the University of North Texas for inclusion in the Combined DNA Index System (CODIS) DNA database. However, CODIS lacks DNA family reference samples from many families of the missing due to families living outside the US or because they do not feel comfortable providing a DNA sample in the presence of law enforcement. Therefore, it is necessary to work with non-governmental organizations who specialize in collecting missing persons reports and DNA samples from the families of the missing. Working collaboratively with multiple agencies, identification of migrant remains is possible.
This book provides the first comprehensive, overview and guide to forensic isotope analysis, an exciting new application of stable isotope analytical techniques. Topics are introduced using examples and real-life case studies such as food quality control where isotope analysis has already had a major impact, in terms of consumer protection, These examples illustrate the underlying principles of isotope profiling or fingerprinting. A section comprising actual criminal case work is used to build a bridge between the introduction and the technical section to encourage students to engage with this novel departure for analytical sciences while at the same time providing hands-on examples for the experienced researcher and forensic practitioner to match problems and success stories encountered with the topics discussed in the technical section.
What little information is available on the subject in book form so far, has been published as individual chapters in books dealing either with mass spectrometry, forensic geoscience or environmental forensics, this is the first book to focus on the entire spectrum of forensic isotope analysis and will be an invaluable reference to both researchers in the field and forensic practitioners.
This chapter traces the movement of deceased migrants in South Texas through the system of identification and repatriation. Given significant differences in funding, resources, labor power, institutional support, and time, the timing and movement of bodies through the process are highly variable. In many ways, the fragmentation and differential support for volunteer forensic scientists have produced particular systems-level nodes where bodies may wait “in limbo” for years. This chapter considers constraints faced by forensic scientists and the systemic implications of those individual constraints.
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.
Recent forensic applications of stable isotope analysis (SIA) have demonstrated its value as an investigative tool in the identification of unknown decedents. Stable isotope ratios measured in bones, teeth, hair, and nails provide a record of a person’s dietary preferences, travel history, and residence patterns. Stable carbon, nitrogen, and sulfur isotopes of human tissues provide information regarding a decedent’s dietary preferences, which in turn may reflect a person’s geographic region of origin. Additionally, stable oxygen and strontium isotopes in body tissues can be used to provenance human remains, because these isotopes reflect the source of drinking water and local geology, respectively. When combined, a multi-isotope approach provides a powerful geolocation tool for predicting a region of origin or recent travel history for unidentified human remains. In this study, we present on two forensic cases that used SIA to predict the travel history and region of origin of unknown decedents.
Stable isotopes are being used for forensic science studies, with applications to both natural and manufactured products. In this review we discuss how scientific evidence can be used in the legal context and where the scientific progress of hypothesis revisions can be in tension with the legal expectations of widely used methods for measurements. Although this review is written in the context of US law, many of the considerations of scientific reproducibility and acceptance of relevant scientific data span other legal systems that might apply different legal principles and therefore reach different conclusions. Stable isotopes are used in legal situations for comparing samples for authenticity or evidentiary considerations, in understanding trade patterns of illegal materials, and in understanding the origins of unknown decedents. Isotope evidence is particularly useful when considered in the broad framework of physiochemical processes and in recognizing regional to global patterns found in many materials, including foods and food products, drugs, and humans. Stable isotopes considered in the larger spatial context add an important dimension to forensic science.
The present chapter on strontium isotopes from human dental enamel aims at presenting four archaeological case studies to illustrate the anthropological significance and range of applications of this technique: a northern Maya origin for the founder of Copan, a local king from Tikal, and the regional origin of two of Palenque’s rulers. The results show that isotopic variation within the various culturally important regions of Mesoamerica is generally much less than variation among the different regions. Thus analysis of strontium isotope ratios in dental enamel, which retains the ratio of the place of childhood residence, can be used not only to indicate mobility but also on occasion to determine the geographic origin of the individual.
RationaleNatural stable carbon (δ13C) and nitrogen isotope ratios (δ15N) of humans are related to individual dietary habits and environmental and physiological factors. In forensic science the stable isotope ratios of human remains such as hair and nail are used for geographical allocation. Thus, knowledge of the global spatial distribution of human δ13C and δ15N values is an essential component in the interpretation of stable isotope analytical results.Methods
No substantial global datasets of human stable isotope ratios are currently available, although the amount of available (published) data has increased within recent years. We have herein summarised the published data on human global δ13C andδ15N values (around 3600 samples) and added experimental values of more than 400 additional worldwide human hair and nail samples. In order to summarise isotope ratios for hair and nail samples correction factors were determined.ResultsThe current available dataset of human stable isotope ratios is biased towards Europe and North America with only limited data for countries in Africa, Central and South America and Southeast Asia. The global spatial distribution of carbon isotopes is related to latitude and supports the fact that human δ13C values are dominated by the amount of C4 plants in the diet, either due to direct ingestion as plant food, or by its use as animal feed. In contrast, the global spatial distribution of human δ15N values is apparently not exclusively related to the amount of fish or meat ingested, but also to environmental factors that influence agricultural production.Conclusions
There are still a large proportion of countries, especially in Africa, where there are no available data for human carbon and nitrogen isotope ratios. Although the interpretation of modern human carbon isotope ratios at the global scale is quite possible, and correlates with the latitude, the potential influences of extrinsic and/or intrinsic factors on human nitrogen isotope ratios have to be taken into consideration. Copyright © 2015 John Wiley & Sons, Ltd.
The application of stable isotope analysis has provided novel approaches for provenancing unidentified human remains from forensic contexts. Stable isotope ratios measured in human tissues provide a record of the foods consumed during life as well as the geographic location where drinking water or food was obtained. This study begins with an overview of the application of stable isotope analysis for provenancing human remains, followed by three cases that illustrate how chemical signatures in bone reflect a probable region of origin. Using stable carbon and nitrogen isotopes of human bone, we test whether human skeletal remains recovered by the Joint POW/MIA Accounting Command-Central Identification Laboratory (JPAC-CIL, or CIL) reflect a geographic origin within North America or Asia. Stable carbon and nitrogen isotopes of human bone collagen and stable carbon isotopes of bone apatite reflect consumption of food resources that are expected to vary between world regions due to cultural dietary differences. Based on the isotopic differences, a testable hypothesis of geographic origin can be applied, determining if the remains are more likely of a U.S. service person or of an indigenous local. We believe that this approach can provide useful information for narrowing search parameters in unidentified persons cases; can contribute to human rights cases where an unknown individual is thought to originate from a different geographic area; and, in human remains cases of unknown geographic provenience, can determine whether a person is local or nonlocal.
Stable isotope methods can be used to determine the provenance of unidentified corpses. Body tissue materials such as teeth, bone, hair and nail taken from mortal remains provide information of different time periods of an individuals' life from childhood to death. Tissues of newborns contain provenance information of different time periods during pregnancy of the child's mother.The results of stable isotope analyses of body residues of two adults and a newborn found in Germany between 2010 and 2012 are presented. To determine the geographic origin and movements of unknown individuals, stable isotopes of hydrogen, carbon, nitrogen and sulphur were analysed in hair and bone collagen samples. Amino acid composition and, as a consequence, δ2H, δ13C, δ15N, and δ34S values in human keratin and bone collagen are different. Consequently correction factors were determined to compare isotopic data of bone collagen with those of an extensive worldwide reference hair collection. The isotopic signatures in hair and in bone collagen samples were compared to geographical groups of reference hair samples by canonical discriminant analysis. The results served as the basis for providing provenance constraints for the unidentified persons as requested by the police and prosecution. Ultimately the individuals were identified; hence the isotopic provenance interpretations can be critically evaluated and are shown to be successful.
Although variation in 87Sr/86Sr has been widely pursued as a tracer of provenance in environmental studies, forensics, archeology and food traceability, accurate methods for mapping variations in environmental 87Sr/86Sr at regional scale are not available. In this paper, we build upon earlier efforts to model 87Sr/86Sr in bedrock by developing GIS-based models for Sr isotopes in rock and water that include the combined effects of lithology and time. Using published data, we fit lithology-specific model parameters for generalized equations describing the concentration of radiogenic Sr in silicate and carbonate rocks. The new model explained more than 50% of the observed variance in measured Sr isotope values from independent global databases of igneous, metaigneous, and carbonate rocks, but performed more poorly (explaining 33% of the variance) for sedimentary and metasedimentary rocks. In comparison, a previously applied model formulation that did not include lithology-specific parameters explained only 20% and 8% of the observed variance for igneous and sedimentary rocks, respectively, and exhibited an inverse relationship with measured carbonate rock values. Building upon the bedrock model, we also developed and applied equations to predict the contribution of different rock types to 87Sr/86Sr variations in water as a function of their weathering rates and strontium content. The resulting water model was compared to data from 68 catchments and shown to give more accurate predictions of stream water 87Sr/86Sr (R2 = 0.70) than models that did not include lithological weathering parameters. We applied these models to produce maps (“isoscapes”) predicting 87Sr/86Sr in bedrock and water across the contiguous USA, and compared the mapped Sr isotope distributions to data on Sr isotope ratios of US marijuana crops. Although the maps produced here are demonstrably imperfect and leave significant scope for further refinement, they provide an enhanced framework for lithology-based Sr isotope modeling and offer a baseline for provenance studies by constraining the 87Sr/86Sr in strontium sources at regional scales.
Strontium isotope analysis of archaeological skeletons has provided useful and exciting results in archaeology in the last 20 years, particularly by characterizing past human migration and mobility. This review covers the biogeochemical background, including the origin of strontium isotope compositions in rocks, weathering and hydrologic cycles that transport strontium, and biopurification of strontium from to soils, to plants, to animals and finally into the human skeleton, which is subject to diagenesis after burial. Spatial heterogeneity and mixing relations must often be accounted for, rather than simply ``matching'' a measured strontium isotope value to a presumed single-valued geologic source. The successes, limitations and future potential of the strontium isotope technique are illustrated through case studies from geochemistry, biogeochemistry, ecology and archaeology.
We present data on the carbon (δ(13)C), nitrogen (δ(15)N) and sulfur (δ(34)S) isotope ratios of human hair collected in the central portions of the USA. These elements are incorporated into hair from the diet and thus provide a record of dietary inputs that may also document geospatial patterns. We detected regional differences in hair δ(34)S values across the USA, with the lowest values in the northern Great Plains and increasing values towards the east, west and south. In contrast, no statistically significant patterns were detected in the spatial variation of human hair δ(13)C and δ(15)N values. Using δ(34)S values and a Geographic Information System approach, we created a map ('sulfur isoscape'). The accuracy of the map was tested using hair samples not included in its generation. We conclude that sulfur isotope analysis may represent a new tool to investigate the movements and/or region-of-origin of humans.
This study investigated the impact of purchase location on the stable isotope ratios of beverages by measuring the delta(2)H and delta(18)O values of bottled water, soda, beer, and tap water collected across the contiguous United States. Measured beverage delta(2)H and delta(18)O values generally fit the Global Meteoric Water Line (GMWL), suggesting region-of-origin information is recorded in beverage water. Tap water delta(2)H and delta(18)O values were strongly correlated with the stable isotope ratios of bottled water and soda purchased in the same location. Beer water delta(2)H and delta(18)O values were also correlated with tap water, although not as strongly. Variability in delta(2)H and delta(18)O values among beverages purchased at a single location ranged from 2 to 41 per thousand and from 0.3 to 5.2 per thousand, respectively, but was generally moderate in most locations. It was concluded that the isotopic composition of local tap water is a reasonable proxy for consumers' fluid intake in most U.S. cities.
We develop and test a model to predict the geographic region-of-origin of humans based on the stable isotope composition of their scalp hair. This model incorporates exchangeable and nonexchangeable hydrogen and oxygen atoms in amino acids to predict the δ²H and δ¹⁸O values of scalp hair (primarily keratin). We evaluated model predictions with stable isotope analyses of human hair from 65 cities across the United States. The model, which predicts hair isotopic composition as a function of drinking water, bulk diet, and dietary protein isotope ratios, explains >85% of the observed variation and reproduces the observed slopes relating the isotopic composition of hair samples to that of local drinking water. Based on the geographical distributions of the isotope ratios of tap waters and the assumption of a “continental supermarket” dietary input, we constructed maps of the expected average H and O isotope ratios in human hair across the contiguous 48 states. Applications of this model and these observations are extensive and include detection of dietary information, reconstruction of historic movements of individuals, and provision of region-of-origin information for unidentified human remains.
• stable isotopes
• water
• anthropology
• forensics
• meteoric water
This article analyzes numeric trends and demographic characteristics of undocumented border crossers (UBCs) who have perished in southern Arizona between 1990 and 2013 in the area covered by the Pima County Office of the Medical Examiner (PCOME) in Tucson, Arizona. Of 2,413 UBC decedents investigated during this period, 95 percent died after 1999 and 65 percent after 2005. The rate of UBC deaths in the Tucson Border Patrol Sector has been consistently high, with an average of nearly 163 deaths investigated per year between 1999 and 2013. The increase in border enforcement during the mid-to-late 1990s, which led to a shifting of unauthorized migration flows into more desolate areas, coincided with an increase in migrant remains investigated by the PCOME. Despite a decrease in the number of unauthorized crossers traversing the area as measured by the number of Border Patrol apprehensions in the Tucson Sector, the number of remains examined for every 100,000 apprehensions nearly doubled between 2009 and 2011. These findings suggest that migrants are being forced to travel for longer periods of time through remote areas in an attempt to avoid detection by US authorities, thus increasing the probability of death.
The typical UBC decedent can be described as a male near the age of 30 from central or southern Mexico who perished in a remote area of southern Arizona after attempting to cross into the United States. Nevertheless, the share of non-Mexican UBCs in the region has increased notably over time. The findings show other important differences in UBC decedent characteristics across time periods, which speak to the dynamic nature of unauthorized migration as a social process. The authors contend that these deaths and demographic changes are the result of structural and political transformations over the past two decades. They argue that the tragic, yet mostly preventable, migrant deaths in southern Arizona constitute a form of structural violence.
Here, we discuss a relatively new investigative technique useful for identification of human skeletal remains—forensic isotope analysis. Many elements exist in multiple isotope forms, distinguished by differing numbers of neutrons. Stable isotopes contained within human tissues are related to the isotopes in drinking water and food, which can vary based on geography, environment, cultural practices, etc. It's thus possible to analyze the stable isotopes contained within tissues and collect information about someone's life history: where he/she lived, what he/she ate. This chapter presents a brief history of isotope analysis, reviewing foundational research in the fields of ecology, geology, and anthropology that set the stage for the application of stable isotopes in modern forensic investigations of unidentified human remains. It also presents a series of success stories in which forensic isotope analysis helped lead to the identification of an unknown decedent.
Forensic archeology employs a systematic approach to the recovery of human remains and associated evidentiary items. Employing archeological technique to the exhumation of human remains takes a substantial amount of planning and expertise. For exhumations of unidentified migrants, additional political and cultural factors must be considered. This chapter explores the efforts of university volunteers before, during, and after the large-scale exhumations that took place in 2013 and 2014 in Brooks County, TX, and places their work within a broader sociopolitical framework. It positions the forensic scientist within a complex set of interactions where they are both a commodity producer and consumer and therefore an actor in the political economy of forensic science in the Texas borderlands. Additionally, it introduces readers to the skills and planning required to conduct these complex exhumations while exploring unique outside factors like funding and media involvement that impact these exhumations.
Thousands of Mexican and Central American migrants have died in their journey toward the United States in the past two decades. In both the United States and Mexico, many of the dead remain unidentified due to a lack of standardized DNA testing and the lack of political will to identify migrant remains. US immigration policies as well as neoliberal economic policies in Mexico and Central America which have displaced rural and urban workers have produced the current “disappeared” along the US-Mexico border and along Mexico’s vertical border, extending over 1,000 miles from Central America to the United States. A focus on the individual responsibility of coyotes and narco-traffickers and even on the supposed recklessness and ignorance of migrants themselves cover up the fact that these deaths are state crimes – the deaths are known outcomes of state policies that criminalize the working poor and militarize borders. This chapter explores the reasons state-driven violence may be “missed,” ignored, or simply dismissed as the fault of migrants themselves. Finally, it examines the ways migrants, their families and loved ones, and other members of civil society seek to identify and remember the dead, protest violence against migrants, and demand the defense of immigrant rights.
Methods of forensic identification are complex, diverse, and fluid. While theoretically there is a broad-ranging toolkit of identification methods, the realities of this work include limited resources and limited opportunities for applying the full range of techniques to any one case. Using these realities as a departure point, this chapter traces the strategy and pragmatism involved with case load and assignment and considers in this methodological context why some bodies may have a greater chance of being identified than others. Further, this chapter discusses the complexities associated with the identification of deceased undocumented border crossers (UBCs) from south Texas and presents case studies to highlight novel applications of stable isotope analysis as an investigative tool for identifying the dead.
This article focuses on the role of the forensic anthropologist in the identification of migrant remains in the American Southwest. These migrant cases present a unique set of circumstances that necessitate a regional approach to identification. The Pima County Office of the Medical Examiner (PCOME), located in Tucson, Arizona has developed best practices that facilitate high identification rates of migrant deaths. These best practices have provided a foundation for other agencies that are faced with similar issues; namely, developing specific protocols for migrant deaths, working with nongovernmental humanitarian organizations, and sharing information have maximized identification efforts. In 2012, Texas surpassed Arizona in the number of migrant deaths. The Forensic Anthropology Center at Texas State (FACTS) began identification efforts for migrant remains found in Brooks County, Texas in 2013. Informed by best practices from the PCOME, FACTS has made successful identifications. Descriptions of the processes at both the PCOME and FACTS are described in detail.
The recent increase in the number of missing persons and unidentified dead in the United States, which has resulted in an increase in the total count of cold cases around the country, has triggered multiple requests from medical examiner's offices and law enforcement agencies to reevaluate the original biological profiles derived from these unsolved cases. The general misconception that a positive DNA match can always be provided in conjunction with questionable, mostly outdated methodology used for profiling, and an incorrect understanding of geographic origins of deceased individuals, has led to many erroneous assessments of biological parameters. This chapter illustrates how these cases can be approached using a complex multifactorial analysis relying on more than a single strategy. In the present study, a geometric morphometric landmark-based approach was combined with an analysis of strontium, oxygen, and carbon isotopes and applied to a North Carolina cold case. Although official reports indicate that the geographic origin of Hispanics in North Carolina is approximately 61% Mexican, the region of provenance for deceased immigrants found in North Carolina is less straightforward. The analyzed indicators suggest that the reexamined cold cases (including the one highlighted) are morphologically closer to samples from Panama and Guatemala than Mexican individuals. The combined approach also shows that although the point of entry for the undocumented immigrants is most likely the US/Mexico border, other regions of origin such as South America (eg, Peru, Chile) and Central America (eg, Honduras, El Salvador) should be considered as possible places of origin.
Geospatially distributed isotopes (isoscapes) from biogeochemically fractionated processes have been applied in many forensic investigations, such as authentication of food and sourcing of drugs. Provenancing of human remains using isotopes has been hindered by a lack of appropriate isoscapes, by changes in these isoscapes over time, and by various homogenization processes. In this study we create spatiotemporal isoscapes for anthropogenic lead (Pb) for the contiguous United States and Europe using literature data from dated sediments, soils and biological tissues. We compare 206Pb/207Pb isoscapes with isoscapes of δ13C, δ18O and 87Sr/86Sr to determine their relative efficacy for the forensic identification of human remains. We do this comparison using third molar enamel data from 22 United States Air Force Academy cadets with known life trajectories born between 1983 and 1985. We use these spatiotemporal isoscapes with osteologic analyses, hospital records and isotopic analyses of tooth enamel carbonate from permanent teeth to help identify 32 individuals from unmarked graves found in a forgotten 19th century mental asylum cemetery.
Stable isotope analysis has undergone rapid development in recent years and yielded significant results in the field of forensic sciences. In particular, carbon and oxygen isotopic ratios in tooth enamel obtained from human remains can provide useful information for the crosschecking of morphological and DNA analyses and facilitate rapid on-site prescreening for the identification of remains. This study analyzes carbon and oxygen isotopic ratios in the tooth enamel of Japanese people born between 1878 and 1930, in order to obtain data for methodological differentiation of Japanese and American remains from the Second World War. The carbon and oxygen isotopic ratios in the tooth enamel of the examined Japanese individuals is compared to previously reported data for American individuals (born post WWII), and statistical analysis is conducted using a discrimination method based on a logistic regression analysis. The discrimination between the Japanese and US populations, including Alaska and Hawaii, is found to be highly accurate. Thus, the present method has potential as a discrimination technique for both populations for use in the examination of mixed remains comprising Japanese and American fallen soldiers.
Stable isotope analysis has a lengthy application history in the fields of biology, ecology, and geology but its application in forensic investigations is relatively new. A recent report by the National Research Council on the strength of the forensic sciences in the United States highlighted areas of weakness, including the lack of a tested scientific foundation for many of the analytical techniques used in examinations. Stable isotope analysis has a strong scientific foundation developed in the academic community and could thus play a major role in the forensic community as a powerful tool in the investigator's toolbox.This chapter presents a framework for applying the stable isotope analysis techniques commonly employed by isotope geochemists in forensics settings. The utility of this framework lies in its ability to address a range of questions from relatively simple sample comparisons to more complex region or origin predictions. The forensic application of stable isotope analysis within this framework is discussed at both a nonspatial and spatial scale, examples of applications include the analysis of nonorganic and organic materials. The chapter concludes with a discussion detailing how the stable isotope analysis techniques developed in scientific settings can be extremely useful in legal settings as well.
The isotopic ratios of common light elements often provide useful information about past geologic, environmental, or biologic history. Bender’s (1968) clear identification of two distinct isotopic values for carbon from C3 and C4 plant organic matter led to the experiments which showed that animal δ13C values were closely related to dietary values (DeNiro and Epstein 1978a; Tieszen et al. 1983). Results from field applications (DeNiro and Epstein 1978b; Vogel 1978; Tieszen et al. 1979; Tieszen and Imbamba 1980) established the usefulness of these tracers and soon led to numerous archaeological studies. C and N, both present in bone collagen, have been most useful to suggest marine versus terrestrial dependence, to establish maize utilization or dependence on legumes, and to identify relative trophic-level positions or carnivory versus herbivory. Recently, attention has been focused on the use of bioapatite CO3 (Lee-Thorp et al. 1989a, 1989b; Lee-Thorp and van der Merwe 1991) as a supplement to collagen, especially in bones older than 10000 years, and as an adjunct to collagen for estimates of carnivory. The 180 signal in bioapatite also has the potential to provide information on the water status of the individual or the environment. Sulfur isotopes δ
34
S), when present in sufficient quantities, as in hair or skin, are also useful and in some cases can distinguish clearly between marine and terrestrial dietary sources (Krouse and Herbert 1988).
Stable isotopes are valuable biogeochemical markers for solving problems faced by society today, such as distinguishing authentic from adulterated foods and beverages or tracing the origins of illicit drugs. Hydrogen and oxygen isotopes in water exhibit distinct continental patterns (isoscapes), which provide useful region-of-origin information. We ourselves refl ect the stable isotope ratios of the water we drink and the food we eat: our hair records any isotopic changes to our diets, which can often be related to location. This latter aspect can be of interest to law enforcement in determining the origins and travel histories of unidentifi ed murder victims.
This article analyzes numeric trends and demographic characteristics of undocumented border crossers (UBCs) who have perished in southern Arizona between 1990 and 2013 in the area covered by the Pima County Office of the Medical Examiner (PCOME) in Tucson, Arizona. Of 2,413 UBC decedents investigated during this period, 95 percent died after 1999 and 65 percent after 2005. The rate of UBC deaths in the Tucson Border Patrol Sector has been consistently high, with an average of nearly 163 deaths investigated per year between 1999 and 2013. The increase in border enforcement during the mid-to-late 1990s, which led to a shifting of unauthorized migration flows into more desolate areas, coincided with an increase in migrant remains investigated by the PCOME. Despite a decrease in the number of unauthorized crossers traversing the area as measured by the number of Border Patrol apprehensions in the Tucson Sector, the number of remains examined for every 100,000 apprehensions nearly doubled between 2009 and 2011. These findings suggest that migrants are being forced to travel for longer periods of time through remote areas in an attempt to avoid detection by US authorities, thus increasing the probability of death.
The typical UBC decedent can be described as a male near the age of 30 from central or southern Mexico who perished in a remote area of southern Arizona after attempting to cross into the United States. Nevertheless, the share of non-Mexican UBCs in the region has increased notably over time. The findings show other important differences in UBC decedent characteristics across time periods, which speak to the dynamic nature of unauthorized migration as a social process. The authors contend that these deaths and demographic changes are the result of structural and political transformations over the past two decades. They argue that the tragic, yet mostly preventable, migrant deaths in southern Arizona constitute a form of structural violence.
The use of stable carbon isotopes for diet reconstruction is predicated on the assumption that you are what you eat. In other words, the carbon isotopic composition of animal tissues is assumed to be a direct and constant function of the diet. Is this assumption valid? Precise dietary reconstruction requires as accurate knowledge of the isotopic composition of locally available dietary resources, as well as an adequate understanding of the effects of nutrition, environment, and physiology on the diet-tissue function (van der Merwe 1982, 1989; Chisholm 1989; Norr 1990; Matson and Chisholm 1991; Tieszen 1991; Ambrose 1992). There is a systematic but poorly defined difference between the isotopic composition of the consumer tissues and that of the diet (an enrichment factor, expressed as Δ diet-tissue). Given the isotopic composition of a specific tissue, that of the diet or of other tissues may be calculated if the Δ diet-tissue difference factors are known. The dietary proportions of isotopically distinct food resources (e.g., C3 vs C4, or C3 vs marine) have thus been calculated from the δ
13C value of bone collagen (Δ13Cd-co) and bone apatite carbonate (Δ13Cd-ca). Deviations from actual or assumed average δ
13C values for dietary endmembers, and incorrect values for diet-to-tissue isotopic relationships, will lead to errors in the estimation of consumption of specific classes of resources. Experiments and observations designed to determine the diet-to-collagen stable isotope functions (Δ13Cd-co) however, have provided widely different values.
Two men walking across a bridge along highway I-75 found a young woman's body floating in the water below. This 1971 case has since become known as the “Little Miss Panasofkee” case. It is still an open homicide, for which neither the victim nor the perpetrator have been identified. Throughout the United States, thousands of similar cases remain open. The medicolegal communities work on these cases, as the years pass, applying new scientific methods and following new leads as they can be developed. As the years pass, the priorities of the investigations often shift. In any homicide investigation the goal is to solve the murder and bring the perpetrator to justice. While this is still true for long-term open or cold cases, the needs of families to know the truth, find and bury remains, and find closure outside of criminal trials become increasingly important. In the case study presented here, we reanalyzed the biological profile of the decedent, created a new facial approximation and imaging for visualization of personal evidence, and analyzed samples of hair, bone, and enamel for Sr, Pb, C, N, and O isotopes to decipher a geographical place of origin for the decedent. Hair data show a shift from lighter to heavier C isotopic values indicating a diet change from more grain-based (hair tip) to more corn-based (hair root) diet. Oxygen isotopes in teeth show relatively heavy isotopic values suggesting southern geographical origin near a major water basin. Lead isotopic data for teeth and bone samples show relatively low-radiogenic values suggesting that the victim was born and raised in Europe. There is shift to low 87Sr/86Sr from first to third molar and bone indicating possible migration and dietary change. Taken together, the radiogenic and stable isotope data indicate that the decedent was foreign born. The shift in the hair C isotopes suggests that the victim arrived in Florida/United States between 2 and 12 months before she was murdered. The Pb isotope data suggest European origin. Considering all of the chemical data, including Pb concentrations and Pb, Sr, O, and C isotope analyses on teeth, rib, and hair samples, we can suggest that the victim was most likely a foreigner from southeastern Europe, possibly Greece. The methods used here and the impact of these methods for developing new leads for investigators decades later are discussed and provide new avenues of investigation for other unsolved cases.
Stable strontium isotopes have been used to identify the skeletons of migrants in several recent archaeological studies, in which local 87Sr/86Sr values have been inferred through statistical parameters of human 87Sr/86Sr data, or by reference to local fauna or other environmental samples. This paper compares these approaches using data from the ancient Maya city of Tikal, Guatemala. The skeletons of eight migrants from distant geological zones are readily apparent among the 83 Tikal skeletons sampled. Three additional non-local skeletons can be eliminated to obtain a normally distributed “local” Tikal sample. The mean of this sample is higher than the available data for local fauna and for lime that may have been used to treat maize at Tikal. It is possible that imported sea salt with a high 87Sr/86Sr ratio could account for this elevated mean for Tikal humans. Modeling demonstrates that dietary 87Sr/86Sr may be raised to the level found at Tikal by a daily intake of only 6 g of sea salt.
This study is novel in that it is the first of its kind to compile a reference sample of isotopic values associated with known natal regions to be utilized in forensic work. Stable isotopes of carbon, oxygen, strontium, and lead were examined to determine if natal origins could be assessed isotopically between Southeast Asian and American dental remains as well as regionally within the United States. Teeth believed to be of East Asian origin were compared to the extracted third molars of recent American dental patients. Living subjects completed surveys detailing physiological, behavioral, and residential information that affect isotope values. The least squares means for all isotope values examined exhibited significant differences between the East Asian and American cohorts. Based on this information, a discriminant function was created that correctly classified individuals, through resubstitution and cross-validation, as belonging to one of these two groups by 95% or better. American strontium values displayed a distinct trend toward homogenization, with the mean value for Sr87/Sr86 varying only slightly from that of seawater. In order to identify natal origin among Americans, nine regions were created within the United States based on O18 values. Good discrimination was noted between the mountain states and the southern states. A discriminant function analysis proved disappointing though, and additional sampling from most states is needed to improve the statistical robusticity of the model. The results of this study will have wide-reaching effects across the medico-legal spectrum. This body of research will serve as the foundation for a database of modern, human, geolocational isotope values that will assist not only in the identification of fallen servicemen and women, but in the identification of victims of mass fatality incidents, undocumented aliens who perish attempting entry into the U.S., and local skeletal "Jane and John Doe" cases.
Isotopes are forms of an element that differ in the number of neutrons. Isotopes function as natural dyes or colors, generally tracking the circulation of elements. Isotopes trace ecological connections at many levels, from individual microbes to whole landscapes. Isotope colors mix when source materials combine, and in a cyclic process that ecologists can appreciate, the process of isotope fractionation takes the mixed material and regenerates the sources by splitting or fractionating the mixtures. Elements and their isotopes circulate in the biosphere at large, but also in all smaller ecological plant, animal, or soil systems. Chapter 3 reviews this circulation for each of the HCNOS elements, then gives four short reviews that may stimulate you to think about how you could use isotopes in your own ecological research.
1] Understanding links between water consumers and climatological (precipitation) sources is essential for developing strategies to ensure the long-term sustainability of water supplies. In pursing this understanding a need exists for tools to study and monitor complex human-hydrological systems that involve high levels of spatial connectivity and supply problems that are regional, rather than local, in nature. Here we report the first national-level survey of stable isotope ratios in tap water, including spatially and temporally explicit samples from a large number of cities and towns across the contiguous United States. We show that intra-annual ranges of tap water isotope ratios are relatively small (e.g., <10% for d 2 H) at most sites. In contrast, spatial variation in tap water isotope ratios is very large, spanning ranges of 163% for d 2 H and 23.6% for d 18 O. The spatial distribution of tap water isotope ratios at the national level is similar to that of stable isotope ratios of precipitation. At the regional level, however, pervasive differences between tap water and precipitation isotope ratios can be attributed to hydrological factors in the water source to consumer chain. These patterns highlight the potential for monitoring of tap water isotope ratios to contribute to the study of regional water supply stability and provide warning signals for impending water resource changes. We present the first published maps of predicted tap water isotope ratios for the contiguous United States, which will be useful in guiding future research on human-hydrological systems and as a tool for applied forensics and traceability studies.
What Are Stable Isotopes?What Are the Units for Expressing the Abundance of Stable Isotopes?What Is the Basis for Variations in Stable Isotope Abundances?What Instrumentation Is Needed for High-Precision Stable Isotope Measurements?How Can Stable Isotope Analyses Assist Forensics Cases?Stable Isotope Abundances in Forensic EvidenceReferences
A field that will likely benefit from the developments of isoscapes is forensic sciences, where there is an interest in understanding
where evidentiary material might have originated from. This chapter focuses on one small aspect of this large field through
exploration of how analyses of hydrogen and oxygen isotopes in water and in human body tissues may be applied to forensic
applications where spatially relevant information is required as part of an investigation. The applications of isocapes to
forensic sciences are broad, including wildlife, food sourcing, and murder investigations. While the focus of this chapter
is on hydrogen and oxygen isotopes, the analyses of heavy elements are an equally important component that can be scaled to
include broad geo-spatial patterns.
Strontium isotope ratios (87Sr/86Sr) in human bones and teeth have become a useful tool to study migration and sedentism of individuals from archaeological contexts. Here we analyzed 87Sr/86Sr of water, bedrock, soils, and plants across a broad geographic region to test the potential of this method in the ancient Maya area. Our aims were two-fold: first to test if the sources of dietary strontium (i.e., plants and water) in humans reflect the 87Sr/86Sr ratio of exposed bedrock, and second, to determine whether the ranges of 87Sr/86Sr values were sufficiently distinct among the principal Maya geocultural areas to infer past migration. We identified five distinct subregions on the basis of geologic maps and evaluated the variability of 87Sr/86Sr values (values given as mean 87Sr/86Sr ±2 standard deviations; number of samples): (1) Northern Lowlands (0.70888±0.00066; n=16); (2) Southern Lowlands (0.70770±0.00052; n=86); (3) Volcanic Highlands and Pacific Coast (0.70415±0.00023; n=34); (4) Metamorphic Province (0.70743±0.00572; n=50); and (5) the Maya Mountains of Belize (0.71327±0.00167; n=3). Although the sample size is small and overlap exists in 87Sr/86Sr values among some subregions, most areas can be readily distinguished from one another on the basis of strontium isotopes. These subregional 87Sr/86Sr differences provide archaeologists with a powerful tool to recognize geographic “outliers” in ancient Maya burials and thereby test hypotheses concerning the origin of specific individuals, inferred population migration patterns, and the possibility of outside cultural influences in the Maya region.
Carbon and nitrogen isotope ratios of human fingernails were measured in 490 individuals in the western US and 273 individuals in southeastern Brazil living in urban areas, and 53 individuals living in a moderately isolated area in the central Amazon region of Brazil and consuming mostly locally grown foods. In addition, we measured the carbon and nitrogen isotope ratios of common food items to assess the extent to which these isotopic signatures remain distinct for people eating both omnivorous and vegetarian diets and living in different parts of the world, and the extent to which dietary information can be interpreted from these analyses. Fingernail delta13C values (mean +/- standard deviation) were -15.4 +/- 1.0 and -18.8 +/- 0.8 per thousand and delta15N values were 10.4 +/- 0.7 and 9.4 +/- 0.6 per thousand for southeastern Brazil and western US populations, respectively. Despite opportunities for a "global supermarket" effect to swamp out carbon and nitrogen isotope ratios in these two urbanized regions of the world, differences in the fingernail isotope ratios between southeastern Brazil and western US populations persisted, and appeared to be more associated with regional agricultural and animal production practices. Omnivores and vegetarians from Brazil and the US were isotopically distinct, both within and between regions. In a comparison of fingernails of individuals from an urban city and isolated communities in the Amazonian region, the urban region was similar to southeastern Brazil, whereas individuals from isolated nonurban communities showed distinctive isotopic values consistent with their diets and with the isotopic values of local foods. Although there is a tendency for a "global supermarket" diet, carbon and nitrogen isotopes of human fingernails hold dietary information directly related to both food sources and dietary practices in a region.
Much of the difficulty associated with identifying and repatriating deceased undocumented border-crossers stems from an inability to narrow down the search area to more probable options. Analysis of the isotopic variation in the tooth enamel of modern Mexican populations is currently underway at the University of California Santa Cruz. Using Thermo Ionization Mass Spectrometry, the pilot research analyzed strontium isotopes located in the donated permanent teeth of Mexican-born individuals of known origin from four states. The preliminary results reveal the formation of three distinctly significant regions in the data set. Using the technology outlined here, a map documenting the isotopic variation in modern Mexican tooth enamel is being complied to use for cross comparison with deceased border crossers of unknown origin.
Sociopolitics of Migrant Death and Repatriation
- E.J. Bartelink