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

Human tissue oxygen and strontium isotope values in North America: A data compilation and assessment for forensic geolocation

The use of isotopic analysis for human mobility, geolocation, and forensic identification has become common over the past two decades, yet its effectiveness depends on the availability of well-documented reference data. Many reference data exist in the literature, but the suitability of these data for forensic applications has not been critically assessed. Here, we compile oxygen and strontium isotope data for North American human tissues (hair, nails, bone, and tooth enamel). We review the geographic distribution of these data, evaluate their relationship with the predicted geographic variation, and assess potential sources of bias that may limit the comparability of different datasets in the compilation. A substantial number of data are available for some of these substrates and isotope systems, but in most cases, their geographic distribution is patchy with many areas under sampled. Except for hair Sr isotopes, a robust relationship occurs between human tissue values and modeled local environmental values, suggesting theoretically expected relationships between human tissues and local sources of O and Sr are expressed. These relationships are noisy; we identify several methodological differences that produce systematic biases across the compiled data. Based on these findings, we suggest interpreting forensic isotope data using currently published reference data is problematic. We propose the adoption of consistent metadata reporting and standardized laboratory protocols to enhance the utility of data gathered in future research as these practices could lead to measurable improvements in the strength of forensic interpretations derived from human tissue isotope data.

Segmental analysis of human hair reveals intra-annual variation in 25(OH)D3 concentrations in modern and archaeological individuals

Vitamin D is essential for healthy skeletal growth and is increasingly recognised for its role in chronic disease development, inflammation and immunity. 25-hydroxyvitamin D3 (25(OH)D3) concentrations are an indicator of vitamin D status and are normally analysed in plasma or serum samples in clinical settings, while archaeological studies rely on the identification of skeletal markers of vitamin D deficiency, such as rickets. Here, we determined 25(OH)D3 concentrations in hair specimens ('locks') that had been sampled close to the root, aligned by cut end, and sliced into sequential segments from participants (n = 16), from Aberdeen, Scotland, using a modified protocol designed to minimise sample size. Concentrations were above detectable levels in 14 of 16 individuals, generating a (~ monthly) time-series of 25(OH)D3 concentrations, with fluctuating intra-hair trends consistent with the bioaccumulation of 25(OH)D3. In three participants, fluctuations in intra-hair 25(OH)D3 appear linked to recent significant weight loss, potentially due to the release of stored 25(OH)D3 from adipose tissue and subsequent uptake in hair. For the remaining participants, no statistically-significant correlations were determined between mean hair 25(OH)D3 levels and self-reported data, including age, sex, BMI, vitamin D supplementation, frequency of oily fish consumption, and hours spent outside. For a subset of our cohort (n = 4) isotope analysis highlighted potential relationships between elevated δ18O values (which can indicate season of hair growth) and 25(OH)D3 concentrations in some individuals, which may reflect seasonally-increased UVB exposure. We also present data from an archaeological individual from the same city, with the addition of further isotope analysis (carbon, nitrogen, sulphur) to characterise diet. Results suggest possible positive correspondence of 25(OH)D3 levels with season in this archaeological individual, and possibly with marine protein consumption, highlighting the potential use of this approach in characterising the relationship between past vitamin D levels and diet. While results are promising, we recognise the limits of this study in terms of sample size and use of self-reported data, and further work is needed to better understand the relationship between serum and hair 25(OH)D3 before this approach can further be developed as either a non-invasive medical test or an archaeo-investigative technique.

Trans-Saharan migratory patterns in Vanessa cardui and evidence for a southward leapfrog migration

Some insects, such as the painted lady butterfly Vanessa cardui, exhibit complex annual migratory cycles spanning multiple generations. Traversing extensive seas or deserts is often a required segment of these migratory journeys. We develop a bioavailable strontium isoscape for Europe and Africa and then use isotope geolocation combining hydrogen and strontium isotopes to estimate the natal origins of painted ladies captured north and south of the Sahara during spring and autumn, respectively. Our findings reveal moderate migratory connectivity across the Sahara characterized by a broad-front, parallel migration. We also report evidence of a leapfrog migration, wherein early autumn migrants from higher latitudes cover greater distances southward than their late autumn counterparts. This work represents a major advancement in understanding insect migratory patterns and connectivity, particularly across extensive barriers, which is essential for understanding population dynamics and predicting the impacts of global change on insect-mediated ecosystem services.

Isotopic heterogeneity in U.S. Urban water supply systems reflects climatic, environmental, and sociodemographic factors: Implications for forensic identification

The forensic application of stable oxygen isotope data from human tissues depends on naturally occurring isotopic variation in drinking water across geographic areas. One factor which complicates interpretation of forensic data is local variability: if a wide range of drinking water values is in a small geographic region it may be difficult to identify or rule out that region as a location of origin. We examine data from community collection programs documenting tap water isotope variation within 30 cities\developed areas throughout the United States. Isotopic variation within individual developed areas ranged widely, from essentially nil to greater than 9‰ (δ18O interdecile range). Many (14/30) of the study areas exhibited multi-modal isotope distributions, even in cases where the isotopic range was very small (e.g., <2.0‰), suggesting that the use of multiple, isotopically different sources was common. Most variation was attributed to differences in the source-region altitude or degree of evaporation for different water sources, and we observe limited variation in areas where contrasts in these variables are small. Variation tended to be largest in cities across the western USA. We explored correlations between the magnitude of local isotopic variation and climatic, environmental, and socioeconomic variables. We found that higher levels of variation occurred at sites where local water resources were likely to be more isotopically heterogeneous and in lower supply, consistent with the development of supply systems in these areas that access diverse and isotopically heterogeneous water resources. We also found that variation was positively correlated with larger developed areas, suggesting that pressures related to city growth may affect the degree to which infrastructure tapping diverse water resources is developed. Collectively, our results suggest that the influence of local tap water isotope heterogeneity on the precision of forensic geolocation is systematic and somewhat predictable, information to be factored into future applications.

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.

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.

Procedures from samples to sulfur isotopic data: A review

RATIONALE

Sulfur isotopes have been widely used to solve some key scientific questions, especially in the last two decades with advanced instruments and analytical schemes. Different sulfur speciation and multiple isotopes analyzed in laboratories worldwide and in situ microanalysis have also been reported in many articles. However, methods of sampling to measurements are multifarious, and occasionally some inaccuracies are present in published papers. Vague methods may mislead newcomers to the field, puzzle readers, or lead to incorrect data-based correlations.

METHODS

We have reviewed multiple methods on sulfur isotopic analyses from the perspectives of sampling, laboratory work, and instrumental analysis in order to help reduce operational inhomogeneity and ensure the fidelity of sulfur isotopic data. We do not deem our proposed solutions as the ultimate standard methods but as a lead-in to the overall introduction and summary of the current methods used.

RESULTS

It has been shown that external contamination and transformation of different sulfur species should be avoided during the sampling, pretreatment, storage, and chemical treatment processes. Conversion rates and sulfur isotopic fractionations during sulfur extraction, purification, and conversion processes must be verified by researchers using standard or known samples. The unification of absence of isotopic fractionation is needed during all steps, and long-term monitoring of standard samples is recommended.

CONCLUSION

This review compiles more details on different methods in sampling, laboratory operation, and measurement of sulfur isotopes, which is beneficial for researchers' better practice in laboratories. Microanalyses and molecular studies are the frontier techniques that compare the bulk sample with the elemental analysis/continuous flow-gas source stable isotope ratio mass spectrometry method, but the latter is widely used. The development of sulfur isotopic measurements will lead to the innovation in scientific issues with sulfur proxies.

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.

BITACORA: An isotopic database of modern human tissues (keratin, teeth) for Argentina

As a consequence of the recent history of Argentina related to crimes against humanity, the country has positioned itself as a leader on Forensic Anthropology in human rights contexts. To some extent it can even be argued that Forensic Genetics for human identification had its origins in human rights work in the early 1980s in Argentina. However, there are still hundreds of unidentified human remains recovered from the dictatorial regimes' crimes. Additionally, every year there are dozens of unidentified deceased buried in public cemeteries. Thus, there is an urgent need to adopt new techniques that could increase the biological profile of a person, and therefore increase the chances of positive identifications. One of such initiatives is the development of isotopic databases and models that can provide information on the population and region of origin of unidentified victims. We present the development of an isotopic database of modern human tissues named BITACORA (from its name in Spanish: Base de Información Isotópica de Tejidos Actuales Como Referencia Argentina). BITACORA holds isotopic data (δ18O, δ2H, δ13C, δ15N and δ34S values) from teeth (enamel and dentine) and keratin tissues (scalp hair, beard and fingernails) obtained from volunteers of known origin, as well as individual information of the donors (age, gender, biometrics, dietary preferences, and relocation history). BITACORA is associated with a tap water isotope database. Currently, we have 345 keratin, 273 teeth and 287 tap water samples gathered from across the country. We present preliminary analyses on the geographic distribution of these isotopic markers, and provide an overall discussion of the current status and future development of the databases.