APPLICATION OF STABLE ISOTOPE FORENSICS FOR PREDICTING REGION OF ORIGIN OF HUMAN REMAINS FROM PAST WARS AND CONFLICTS

Disaster victim identification: Stable isotope analysis and the identification of unknown decedents

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.

Forensic application of isotope ratio mass spectrometry (IRMS) for human identification

Application of isotope ratio mass spectrometry (IRMS) to skeletal remains has become an important tool to investigate human behavior and history. Isotopic variations in collagen, enamel, and keratin reflect variations in an individual's diet and drinking water. Since food and water sources typically are geographically linked, isotope testing can assist in forensic identification by classifying remains to a likely geographic or population origin. If remains are commingled, differences in diet or geographic origin also can support their separation. The usefulness of IRMS in forensic science is dependent on the underlying quality and surety of the isotope test results; in other words, we need to understand their reliability in interpretations. To take ownership of isotopic data quality, we recommend asking a series of questions:Here, we use data collected during the buildout and accreditation of an isotope testing program at the Defense POW/MIA Accounting Agency (DPAA) to answer the above questions for the forensic application of IRMS for human identification. While our primary focus is on the preparation and analysis of bone collagen, the questions above should be considered whenever isotope testing is used in forensic casework. Whether the populations of interest are drugs or humans, olives or explosives, users need to evaluate their isotopic data and interpretations to ensure they are scientifically sound and legally defensible.

Assessment of carbon, oxygen, strontium, and lead isotopic variation in modern Colombian teeth: An application to human identification

Colombia faces the complex humanitarian challenges of locating approximately 100,000 missing persons and identifying thousands who are deceased. Identification is a difficult task in many cases, because the skeletonized bodies are deteriorated, missing person data are unavailable for comparison, and the provenance of the remains is often totally unknown. Isotopic analysis of human tissues (e.g., bone, hair, nails, and teeth) aid in the identification process of unknown individuals because they can provide valuable information on possible geographic origin. This project evaluated the isotopic variability of carbon (C), oxygen (O), strontium (Sr), and lead (Pb) in modern Colombian teeth according to city, department (a political designation similar to "state" in the US or Mexico), and one of four geographically determined regions of origin; and assessed its utility for human identification in Colombia. Isotopic data (O-C-Sr-Pb) were analyzed from modern Colombians originating from the cities of Bogotá, Cali, and Neiva (n = 95); and these data were compiled with published Colombian data of individuals mainly from the city of Medellín (n = 61). Results indicate a wide range and overlap of O-C-Sr-Pb isotopic distribution according to the defined categories. However, differences between coastal and lowland individuals are observed when using δ18 O values, and differences between mountainous regions are observed when using 87 Sr/86 Sr values. In addition, this study suggests that the usefulness of isotopic analysis for unidentified individuals in Colombia would be with assigning them geographically using the designations of North, Central Andes, Eastern Andes, or Southwest Andes versus making classifications at a city or department level.

Stable Isotope Provenance of Unidentified Deceased Migrants-A Pilot Study

In the global migration crisis, one of the challenges in the effort to identify deceased migrants is establishing their region of origin, which facilitates the search for ante mortem data to be compared with the post mortem information. This pilot study explores the potential of using stable isotope analysis to distinguish between individuals coming from West Africa and the Horn of Africa. Six individuals (four of known origin and two of unknown origin) were sampled. δ13CVPDB(keratin), δ15NVPDB(keratin) and δ18OVSMOW(keratin) of hair were analysed using Elemental Analyzers coupled with Isotope Ratio Mass Spectrometry (IRMS). δ18OVSMOW(carbonate) and δ13CVPDB(carbonate) of bone were analysed using GasBench II with IRMS, while 87Sr/86Sr composition was determined in bone and dental enamel using laser ablation multi-collector inductively coupled plasma mass spectrometry. The stable isotope compositions of the individual from the Horn of Africa differed from the other individuals. The differences found between 87Sr/86Sr of enamel and bone and between δ18O and δ13C in bone and hair reflect changes in sources of food and water in accordance with regionally typical migration journeys. The analysis of multiple stable isotopes delivered promising results, allowing us to narrow down the region of origin of deceased migrants and corroborate the information about the migration journey.

Paired stable carbon and oxygen isotope analyses of human enamel for forensic human geolocation: An exploratory study

Stable carbon isotope analysis has proven utility for reconstructing dietary information in humans in past populations. The usefulness of stable carbon for forensic geolocation has been little investigated, largely because of the globalization of the human diet seemingly rendering it inconsequential. This study queried this assumption at a country-wide level on a known sample group. Stable carbon isotope values were obtained from human enamel with known biographical and geographical information to determine whether stable carbon, when paired with stable oxygen isotope values, could differentiate Canadians from non-Canadians. Samples originating outside of Canada were separated into three regions, and a linear discriminant analysis was used to generate discriminant functions that best separate the regions according to the stable carbon and oxygen isotope values. The results revealed two functions, where the first function explained 92.1% and the second 7.9% of the variance. Although some overlap in stable carbon and oxygen values was observed for individuals from both the United States and Canada, differences were observed between those from Canada and other geographical regions. This study demonstrated that pairing the dietary isotope carbon with the geolocator stable oxygen isotope, produced an interesting separation geographically, one that might well be helpful when attempting a geolocation query on unknown human remains.

Examination of amino acid hydrogen isotope measurements of scalp hair for region-of-origin studies

RATIONALE

Hydrogen isotope (δ2 H) analysis of keratinaceous bulk tissues has been used in forensic science to reconstruct an individual's travel history or determine their region-of-origin. Here, we use a compound-specific approach to examine patterns of individual amino acid δ2 H values in relation to those of local tap water, bulk scalp hair tissues, and region-of-origin.

METHODS

We measured δ2 H values of amino acids in anonymously collected scalp hair (n = 67) and tap water from 28 locations in the United States. Samples were hydrolyzed into their constituent amino acids, derivatized alongside in-house reference materials, and analyzed in triplicate using a GC-C-IRMS system.

RESULTS

Non-essential amino acid (AANESS ) δ2 H values and their corresponding tap water samples varied systematically across continental regions. Hydrogen isotope values of alanine, glutamic acid, and glycine were significantly correlated with tap water and an estimated 42%-51% of the hydrogen atoms in these AANESS were derived from tap water. We used linear discriminate analysis (LDA) to explore regional patterns in scalp hair bulk tissue and amino acid δ2 H values. For the model that included AANESS data, 87% of the variance was explained by the first linear discriminant axis (LD1), and was driven by bulk hair tissue, alanine, and proline. This model had an overall 72% successful reclassification with samples from the south and northwest regions reclassifying correctly 92% and 78% of the time, respectively. For the model that included AAESS data, LD1 explained 81% of the variation and was driven bulk hair, threonine, valine, phenylalanine, and isoleucine. The overall reclassification rate for the model that included AAESS was 70%.

CONCLUSIONS

Our findings suggest that δ2 H analyses of AANESS and AAESS could help improve geolocation models for human and wildlife forensics by simultaneously providing information about both dietary and tap water inputs of hydrogen to tissue synthesis.

Multi-isotopes in human hair: A tool to initiate cross-border collaboration in international cold-cases

Unidentified human remains have historically been investigated nationally by law enforcement authorities. However, this approach is outdated in a globalized world with rapid transportation means, where humans easily move long distances across borders. Cross-border cooperation in solving cold-cases is rare due to political, administrative or technical challenges. It is fundamental to develop new tools to provide rapid and cost-effective leads for international cooperation. In this work, we demonstrate that isotopic measurements are effective screening tools to help identify cold-cases with potential international ramifications. We first complete existing databases of hydrogen and sulfur isotopes in human hair from residents across North America by compiling or analyzing hair from Canada, the United States (US) and Mexico. Using these databases, we develop maps predicting isotope variations in human hair across North America. We demonstrate that both δ2H and δ34S values of human hair are highly predictable and display strong spatial patterns. Multi-isotope analysis combined with dual δ2H and δ34S geographic probability maps provide evidence for international travel in two case studies. In the first, we demonstrate that multi-isotope analysis in bulk hair of deceased border crossers found in the US, close to the Mexico-US border, help trace their last place of residence or travel back to specific regions of Mexico. These findings were validated by the subsequent identification of these individuals through the Pima County Office of the Medical Examiner in Tucson, Arizona. In the second case study, we demonstrate that sequential multi-isotope analysis along the hair strands of an unidentified individual found in Canada provides detailed insights into the international mobility of this individual during the last year of life. In both cases, isotope data provide strong leads towards international travel.

A global carbon and nitrogen isotope perspective on modern and ancient human diet

Stable carbon and nitrogen isotope analyses are widely used to infer diet and mobility in ancient and modern human populations, potentially providing a means to situate humans in global food webs. We collated 13,666 globally distributed analyses of ancient and modern human collagen and keratin samples. We converted all data to a common "Modern Diet Equivalent" reference frame to enable direct comparison among modern human diets, human diets prior to the advent of industrial agriculture, and the natural environment. This approach reveals a broad diet prior to industrialized agriculture and continued in modern subsistence populations, consistent with the human ability to consume opportunistically as extreme omnivores within complex natural food webs and across multiple trophic levels in every terrestrial and many marine ecosystems on the planet. In stark contrast, isotope dietary breadth across modern nonsubsistence populations has compressed by two-thirds as a result of the rise of industrialized agriculture and animal husbandry practices and the globalization of food distribution networks.

Application of Trace Elemental Profile of Known Teeth for Sex and Age Estimation of Ajnala Skeletal Remains: a Forensic Anthropological Cross-Validation Study

Teeth store crucial information needed for medical, environmental, genomics, public health, and forensic anthropological research work. The prolonged forensic utility of teeth is ensured by their extended postmortem longevity as they can resist almost all sorts of chemical, biological, and physical degradations or destructions. The main aim of the present investigation was to utilize the discriminant functions and regression equations generated from the elemental profile of known teeth for estimating sex and age of unknown human skeletal remains excavated from an abandoned well at Ajnala (Amritsar, India). The written records mentioned that 282 Indian mutineer soldiers were killed in July 1857, their cadavers were dumped in the disused well, and then a religious structure was built over the periphery of the said well. These human remains, along with some contextual items, were excavated non-scientifically in April 2014. Preliminary results obtained from application of different forensic anthropological techniques like stable isotope, pulp-tooth area ratio, and mtDNA analyses have indicated that these remains belonged to adult males. In present study, the elemental concentrations of 100 mandibular molars of known age and sex were estimated from wavelength-dispersive X-ray fluorescence spectrophotometer (WD-XRF) analyzer. The statistical equations so generated from elemental concentrations of known teeth were applied to estimate the probable age and the sex of unknown mandibular teeth (N = 100) collected from Ajnala skeletal assemblage. The elements Pb and As were detected in ancient teeth only whereas the detection of elements like Ba, Se, and Te was limited to modern teeth samples only. When the statistical equations so generated were applied to elemental concentrations of Ajnala teeth, it was found that 96% teeth belonged to adult males and the remaining ones were classified to be that of females. Though sexual differences were observed in concentrations of majority of elements, statistically significant differences were found in elemental concentrations of very few teeth. Age estimates of unknown teeth were found in the age ranges of 19 to 48 years. Thus, the trace elemental analysis results supported the written records that the victims were adult males. The cross-validated application of elemental profiles of known teeth for establishing the identity of unknown teeth is the first forensic anthropological study reported from India. Though the obtained accuracy levels were not found within acceptable forensic threshold limits, the present study results may guide future researches involving human hard tissues. It may be concluded that trace elemental concentrations of teeth may be influenced by the factors like age and sex of an individual and thus cannot be used for accurate and reliable forensic sex or age estimations. Dental trace elemental composition can be used as a forensic tool only if used in conjunction with other morphological or molecular analysis of the unknown dental remains.

Assessing the efficacy of isotopic provenancing of human remains in Colombia

We report isotopic ratios for δ¹⁸O and ⁸⁷Sr/⁸⁶Sr from 71 individual human permanent teeth, obtained from 61 individuals with known regions of origins from eight of the 32 departments in Colombia. This survey of the applicability of isotopic provenancing is a vital addition to the ongoing identification efforts within Colombia concerning unidentified decedents recovered from clandestine and cemetery burials. At this time, only median isotopic values are reported due to heterogeneity of inter- and intra-departmental variance among the obtained isotopic values. The use of department of origin as a regional assignment schema is inadequate to effectively georeference unidentified human remains, given the wide-ranging topography and climatic diversity within Colombia. Therefore, a critical need for additional isotopic sampling of individual reference material exists, in order to improve the accuracy of potential region of origin estimates of unknown decedents originating from forensic contexts within Colombia.

Recent applications of isotope analysis to forensic anthropology

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.

Applying the principles of isotope analysis in plant and animal ecology to forensic science in the Americas

The heart of forensic science is application of the scientific method and analytical approaches to answer questions central to solving a crime: Who, What, When, Where, and How. Forensic practitioners use fundamentals of chemistry and physics to examine evidence and infer its origin. In this regard, ecological researchers have had a significant impact on forensic science through the development and application of a specialized measurement technique-isotope analysis-for examining evidence. Here, we review the utility of isotope analysis in forensic settings from an ecological perspective, concentrating on work from the Americas completed within the last three decades. Our primary focus is on combining plant and animal physiological models with isotope analyses for source inference. Examples of the forensic application of isotopes-including stable isotopes, radiogenic isotopes, and radioisotopes-span from cotton used in counterfeit bills to anthrax shipped through the U.S. Postal Service and from beer adulterated with cheap adjuncts to human remains discovered in shallow graves. Recent methodological developments and the generation of isotope landscapes, or isoscapes, for data interpretation promise that isotope analysis will be a useful tool in ecological and forensic studies for decades to come.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

Role of stable isotope analyses in reconstructing past life-histories and the provenancing human skeletal remains: a review

This article reviews the present scenario of use of stable isotopes (mainly δ13C, δ15N, δ18O, 87Sr) to trace past life behaviours like breast feeding and weaning practices, the geographic origin, migration history, paleodiet and subsistence patterns of past populations from the chemical signatures of isotopes imprinted in human skeletal remains. This approach is based on the state that food-web isotopic signatures are seen in the human bones and teeth and such signatures can change parallely with a variety of biogeochemical processes. By measuring δ13C and δ15N isotopic values of subadult tissues of different ages, the level of breast milk ingestion at particular ages and the components of the complementary foods can be assessed. Strontium and oxygen isotopic analyses have been used for determining the geographic origins and reconstructing the way of life of past populations as these isotopes can map the isotopic outline of the area from where the person acquired water and food during initial lifetime. The isotopic values of strontium and oxygen values are considered specific to geographical areas and serve as reliable chemical signatures of migration history of past human populations (local or non-local to the site). Previous isotopic studies show that the subsistence patterns of the past human populations underwent extensive changes from nomadic to complete agricultural dependence strategies. The carbon and nitrogen isotopic values of local fauna of any archaeological site can be used to elucidate the prominence of freshwater resources in the diet of the past human populations found near the site. More extensive research covering isotopic descriptions of various prehistoric, historic and modern populations is needed to explore the role of stable isotope analysis for provenancing human skeletal remains and assessing human migration patterns/routes, geographic origins, paleodiet and subsistence practices of past populations.

Using Carbon, Oxygen, Strontium, and Lead Isotopes in Modern Human Teeth for Forensic Investigations: A Critical Overview Based on Data from Bulgaria

Isotopic data obtained from human remains can provide information about an individual's origin, migration, and diet. We evaluate the usefulness of carbon, oxygen, strontium, and lead isotopes for forensic investigations by comparing data from Bulgarian teeth with data from other regions. Geo-referencing based on oxygen or strontium isotopes can be misleading due to overlap with other countries in Europe and other continents. Carbon and lead isotopes, in combination with oxygen and strontium isotopes, provide the most useful information for identification of local vs foreigner status. In particular, high-precision Pb isotopes show a distinct "Bulgarian" range; however, it is possible that individuals from other countries in Eastern Europe and/or central to western Asia could have overlapping isotopic values. Additional high-precision multi-isotope data from modern humans from different regions in the world are required to transition from speculative to more quantitative estimation of a geographical place of origin for unidentified human remains.

Trial application of oxygen and carbon isotope analysis in tooth enamel for identification of past-war victims for discriminating between Japanese and US soldiers

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 are 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.