Comparison of strontium isotope ratios in Mexican human hair and tap water as provenance indicators

The response of the forensic anthropology scientific community to migrant deaths: Where are we at and where do we stand?

Migrant deaths have persistently intensified in the last 30 years, followed by inconsistent engagement of official policies to tackle the lack of identifications. Forensic anthropologists have been increasingly involved in the recovery, analysis and identification of human remains associated with migrants, and are therefore the most well-versed practitioners in raising awareness of policy makers about this plight. This review describes the current state-of-the-art of the forensic anthropological practice and research on unidentified migrants. The focus of the review is twofold: one section explores the current legal, logistical, and administrative issues related to management and identification activities, primarily in Europe and North America. The second section addresses the scientific contributions and new challenges that forensic anthropologists face when analyzing skeletal remains from underrepresented and unreferenced population groups. According to this literature review, forensic anthropologists are the professionals most actively involved in addressing the issue of unidentified migrants. Despite significant efforts, several challenges still hinder identifications in this context, including the inability to create comprehensive databases for collecting postmortem and antemortem data. Recently, scientific research in forensic anthropology has begun to address the limitations in developing reliable biological profiles for deceased migrants, as these groups are often inadequately represented in existing skeletal reference populations. Finally, this review highlights the global efforts of the scientific community to integrate these victims into a well-established identification system, aiming to foster public responsibility and promote the adoption of unified and innovative strategies to comprehensively address and resolve this social, scientific, and humanitarian crisis.

Enhancing the contemporary human and water isotope reference database for the Netherlands: New insights from Sr-O-C-N-H isotope data

The determination of an individual's geographic origin is an essential aspect of forensic investigations. When primary identifiers cannot be used to make a positive identification, isotope analysis can be utilized to provide new leads. Modern reference data are essential for accurate interpretation of human isotopic data in terms of diet and origin. This article presents Sr-O-C-N-H isotope data of modern individuals (hair, dental enamel, and dentine collagen) and drinking water from the Netherlands. The δ15N values of human hair fall within the range of values observed worldwide and cannot be utilized to differentiate from other countries. Distinct disparities in the hair δ13C are evident between European countries and other regions, making it possible to exclude the Netherlands as a region of origin. Comparing Dutch dental isotope data to those of other nations has proven difficult due to the limited availability of reference data. The same limitation applies to tap water δ2H data.

Isotopic analysis of formula milk reveals potential challenges in geolocating bottle-fed babies

In forensic investigations involving the identification of unknown deceased individuals, isotope analysis can provide valuable provenance information. This is especially pertinent when primary identifiers (i.e., DNA, dactyloscopy, etc.) fail to yield matches. The isotopic composition of human tissues is linked to that of the food consumed, potentially allowing the identification of regions of origin. However, the isotopic composition of deceased newborns and infants fed with milk formula may be influenced by that of the prepared milk. The findings contribute towards the possibility to isotopically identify bottle-fed infants. More importantly, the data convincingly show that the Sr isotope composition of the prepared milk is determined by that of the formula and not the (local) tap water, thereby limiting the potential of Sr isotope analysis for determining the geological or geographical origin in formula-fed babies in medico-legal cases.

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.

The effects of dyes and bleaches on the sorption and desorption of trace elements in human hair

Trace element concentrations and isotope ratios of hair reflect the blood levels at the time of hair formation, but can be affected by external factors such as dyeing, bleaching, and bathing. To investigate the effect of dyeing, bleaching, and bathing on hair, hair was immersed in tap water, and changes in trace element concentrations and the Sr isotope ratio were observed over time. During soaking, alkaline earth metals (Ca, Mg, and Sr) from tap water were gradually absorbed into the hair over time. After about one day, the adsorption capacity of hair reached a maximum and the reverse reaction started to occur. In contrast, alkaline metals (Na and K) behaved in reverse. In dyed and bleached hair, Na was significantly desorbed from the hair and gradually migrated to the water over time. The adsorption and desorption of trace elements were minimal in untreated original hair, but much higher in dyed and bleached hair. Thus, dyeing and bleaching appear to damage the hair surface structure and greatly promote the exchange of trace elements. The rapid exchange of trace elements, including Sr, between hair and tap water observed in this study indicates that hair samples can be easily contaminated during bathing.

Use of strontium isotope ratios in geolocation of Guatemalan population: Potential role in identification of remains

Within post‐conflict communities, attempts to identify and repatriate unidentified and missing individuals poses a difficult task. As current forensic strategies commonly lack the capacity to provide region of origin assessments, forensic anthropologists/investigators are often unable to identify sources of DNA for kinship analysis. Using Thermal Ionization Mass Spectrometry (TIMS), hair samples from 10 volunteers were used to assess the variation in strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) between extant people in Guatemala City and Coban; with a leach (external) and digest (dietary) signal analyzed for each sample. A two‐way anova demonstrated that the difference between ⁸⁷Sr/⁸⁶Sr of Guatemala City and Coban was statistically significant (F [1, 16] = 259.839, p < 0.05), with no statistically significant differences observed between leach and digest ⁸⁷Sr/⁸⁶Sr (F [1,16] = 4.319, p = 0.054). Overall, individuals from Coban demonstrate ⁸⁷Sr/⁸⁶Sr comparable to previously recorded baseline values, demonstrating a minimal change in diet which is reflected in associated surveys. Volunteers from Guatemala City, however, show a marked shift in ⁸⁷Sr/⁸⁶Sr away from predicted values highlighting the potential influence of imported goods. The results here highlight the applicability of ⁸⁷Sr/⁸⁶Sr in hair to serve as a potential tool to support the identification of unknown individuals in Guatemala in a forensic context.

Spatial distributions of strontium isotope ratios in human hair and tap water from South Korea

Natural variations of ⁸⁷Sr/⁸⁶Sr ratios in biological samples, such as human hair, provide a biological record of provenance. Spatial distribution maps reflecting heterogeneity in isotopic signatures across large geographical regions are helpful for discerning the provenance and mobility of organisms. In this national-scale study conducted across South Korea, we investigated the spatial distribution patterns of ⁸⁷Sr/⁸⁶Sr ratios in human hair and tap water samples to determine their spatial variabilities and the relationships of isotopic signatures between hair and tap water. The strontium isoscapes of tap water and hair showed similar spatial distribution patterns. Non-parametric comparison indicated no significant differences in isotopic ratios between the two sample types. The ⁸⁷Sr/⁸⁶Sr ratios in human hair showed a significant and strong correlation with the ratios in tap water in eastern Korea, suggesting potential use of ⁸⁷Sr/⁸⁶Sr ratios in provenance studies. However, tap water and hair samples from western Korea did not show significant correlation between them, overall reducing the predictive power of the hair ⁸⁷Sr/⁸⁶Sr ratios for provenance studies. The deviation between ⁸⁷Sr/⁸⁶Sr_{tap water} and ⁸⁷Sr/⁸⁶Sr_hair was much larger in western coastal areas than in eastern Korea. Relatively high utilization of groundwater or exogenous materials, such as Asian dust, may have been responsible for this pattern. To fully utilize the potential of the strontium isotope signature as a biorecorder in provenance studies, it is essential to evaluate the effects of groundwater and other exogenous materials on the isotope signatures of hair and other biological samples. In this study, only hair samples from males were used to develop ⁸⁷Sr/⁸⁶Sr isoscapes. Therefore, further studies are required to examine the applicability of ⁸⁷Sr/⁸⁶Sr hair isoscapes based solely on human hair samples from males to forensic and provenance studies of human hair samples from females.

Mapping the Chemistry of Hair Strands by Mass Spectrometry Imaging-A Review

Hair can record chemical information reflecting our living conditions, and, therefore, strands of hair have become a potent analytical target within the biological and forensic sciences. While early efforts focused on analyzing complete hair strands in bulk, high spatial resolution mass spectrometry imaging (MSI) has recently come to the forefront of chemical hair-strand analysis. MSI techniques offer a localized analysis, requiring fewer de-contamination procedures per default and making it possible to map the distribution of analytes on and within individual hair strands. Applying the techniques to hair samples has proven particularly useful in investigations quantifying the exposure to, and uptake of, toxins or drugs. Overall, MSI, combined with optimized sample preparation protocols, has improved precision and accuracy for identifying several elemental and molecular species in single strands of hair. Here, we review different sample preparation protocols and use cases with a view to make the methodology more accessible to researchers outside of the field of forensic science. We conclude that—although some challenges remain, including contamination issues and matrix effects—MSI offers unique opportunities for obtaining highly resolved spatial information of several compounds simultaneously across hair surfaces.

Uncloaking a Lost Cause: Decolonizing ancestry estimation in the United States

Since the professionalization of US‐based forensic anthropology in the 1970s, ancestry estimation has been included as a standard part of the biological profile, because practitioners have assumed it necessary to achieve identifications in medicolegal contexts. Simultaneously, forensic anthropologists have not fully considered the racist context of the criminal justice system in the United States related to the treatment of Black, Indigenous, and People of Color; nor have we considered that ancestry estimation might actually hinder identification efforts because of entrenched racial biases. Despite ongoing criticisms from mainstream biological anthropology that ancestry estimation perpetuates race science, forensic anthropologists have continued the practice. Recent years have seen the prolific development of retooled typological approaches with 21st century statistical prowess to include methods for estimating ancestry from cranial morphoscopic traits, despite no evidence that these traits reflect microevolutionary processes or are suitable genetic proxies for population structure; and such approaches have failed to critically evaluate the societal consequences for perpetuating the biological race concept. Around the country, these methods are enculturated in every aspect of the discipline ranging from university classrooms, to the board‐certification examination marking the culmination of training, to standard operating procedures adopted by forensic anthropology laboratories. Here, we use critical race theory to interrogate the approaches utilized to estimate ancestry to include a critique of the continued use of morphoscopic traits, and we assert that the practice of ancestry estimation contributes to white supremacy. Based on the lack of scientific support that these traits reflect evolutionary history, and the inability to disentangle skeletal‐based ancestry estimates from supporting the biological validity of race, we urge all forensic anthropologists to abolish the practice of ancestry estimation.