Strontium isotope ratios (87 Sr/86 Sr) of human fingernail clippings reveal multiple location signals

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.

Longitudinal isotope ratio variations in human hair and nails

Due to the straightforward and non-invasive sampling, ease of transport and long-term storage and access to time-resolved information, determination of element concentrations and isotope ratios in hair and nails finds increasing use. Multi-isotopic information preserved in keratinous tissues allows one to reveal dietary, physiological and environmental influences, but progress in this area is still limited by complicated and time-consuming analytical procedures and challenges in accuracy assessment. In this study, longitudinal distributions of δ³⁴S, ⁸⁷Sr/⁸⁶Sr, ^207,208Pb/²⁰⁶Pb, δ⁶⁶Zn, δ⁵⁶Fe, δ⁶⁵Cu, δ²⁶Mg, and δ¹¹⁴Cd were obtained for hair and nails collected from nine subjects with different age, biological sex, diet and/or place of residence. For S and Zn, the distribution along hair strands revealed a trend towards a heavier isotopic signature from the proximal to the distal end, with a maximum difference within the hair of a single subject of 1.2‰ (Δ³⁴S) and 0.4‰ (Δ⁶⁶Zn). For Fe, Cu, Mg and Cd, a shift towards either a lighter (Cu) or heavier (Fe, Mg and Cd) isotopic composition is accompanied by increasing concentration towards the distal hair end, indicating possible isotope fractionation during deposition or external contamination with a different isotopic composition. Pb and Sr isotope ratios are relatively stable throughout the hair strands despite notable concentration increases towards the distal end, likely reflecting external contamination. The isotopic composition of Sr points to tap water as a probable main source, explaining the relative stability of the ratio for individuals from the same geographical location. For Pb, isotopic compositions suggest tap water and/or indoor dust as possible sources. Similar δ³⁴S, ⁸⁷Sr/⁸⁶Sr, ^207,208Pb/²⁰⁶Pb, δ⁶⁶Zn, δ⁵⁶Fe, and δ⁶⁵Cu observed for hair, fingernails and toenails sampled from the same individual suggest that keratinous tissues are conservative receivers of internal and external inputs and can be used complementary. Seasonal variation in δ³⁴S, ^207,208Pb/²⁰⁶Pb, and δ⁶⁵Cu was observed for fingernails.

The Use of Intrinsic Markers for Studying the Migratory Movements of Bats

Mortality of migratory bat species at wind energy facilities is a well-documented phenomenon, and mitigation and management are partially constrained by the current limited knowledge of bat migratory movements. Analyses of biochemical signatures in bat tissues ("intrinsic markers") can provide information about the migratory origins of individual bats. Many tissue samples for intrinsic marker analysis may be collected from living and dead bats, including carcasses collected at wind energy facilities. In this paper, we review the full suite of available intrinsic marker analysis techniques that may be used to study bat migration, with the goal of summarizing the current literature and highlighting knowledge gaps and opportunities. We discuss applications of the stable isotopes of hydrogen, oxygen, nitrogen, carbon, sulfur; radiogenic strontium isotopes; trace elements and contaminants; and the combination of these markers with each other and with other extrinsic markers. We further discuss the tissue types that may be analyzed for each and provide a synthesis of the generalized workflow required to link bats to origins using intrinsic markers. While stable hydrogen isotope techniques have clearly been the leading approach to infer migratory bat movement patterns across the landscape, here we emphasize a variety of lesser used intrinsic markers (i.e., strontium, trace elements, contaminants) that may address new study areas or answer novel research questions.

Fast exchange of strontium between hair and ambient water: Implication for isotopic analysis in provenance and forensic studies

Trace elements in hair originate from intake (e.g., diet, inhalation, skin absorption), are transported in the bloodstream, and then incorporated during hair formation. However, the trace element abundance and isotopic compositions may be altered by post-eruption environmental processes. Such alterations must be addressed to obtain a meaningful interpretation of hair analysis for biomonitoring. In this study, we used strontium (Sr) isotopic analysis together with sorption kinetics of ionic Sr to quantify the rate and extent of replacement of endogenous Sr in hair by exogenous Sr from ambient water. We found that with only 10 minutes of exposure at room temperature (22°C), more than 30% of original endogenous Sr in hair was replaced with exogenous Sr from the solution. After 16 days of exposure to the solution, more than 90% of endogenous Sr was replaced, with a warmer temperature (60°C) accelerating the exchange substantially. We also found that acid leaching of exposed hair did not remove or isolate the exogenous Sr; therefore, neither the original endogenous nor the exogenous 87Sr/86Sr signal could be separated. Nonetheless, these findings illustrated that the quantitative correlation between the fraction of exogenous Sr and the soaking time, if established, could be used to estimate the length of water contact time for hair in forensic studies. Even if such time since initial contact cannot be established, the combination of acid leaching and 87Sr/86Sr analysis of hair samples may still be valuable in provenance studies to identify recent changes in the exogenous Sr pool, including movements or changes in water source.

Trace element concentrations in horn: Endogenous levels in keratin and susceptibility to exogenous contamination

As a recorder containing both physiological and environmental information, keratinized tissues, such as hair and feather, can be used to reveal geographical information, to monitor the exposure to pollutants, and to reconstruct dietary history. However, trace element analysis of keratinized tissues is complicated by the lack of reference endogenous ranges of trace element and the lack of understanding of the susceptibility of each element to exogenous contamination. The interior of animal horn is the cleanest of all keratinized tissues with minimum exogenous contamination because of its large size. Thus, the trace element concentrations in horn interior samples can provide reliable endogenous concentration ranges. Here we measured the concentrations of trace elements in horn interior samples of cattle and wild animals, which we propose to be used as the reference ranges for endogenous levels of trace elements in keratin. We calculated the enrichment factors of 30 trace elements in horn interior samples relative to the continental crust, which we considered the average exogenous contamination. We compared the ranges of elemental concentrations measured in horn interior samples, in the order of decreasing enrichment factor, to their reference ranges in hair, fingernails, and toenails, as well as their concentrations in caprine horns. Such comparison validates the use of the enrichment factor as an indicator of the susceptibility of an element to contamination: an element with a high enrichment factor is generally less likely to be affected by contamination and vice versa.

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.

Strontium isotope ratios of human hair from the United States: Patterns and aberrations

RATIONALE

Strontium isotope ratios (⁸⁷ Sr/⁸⁶ Sr) of hair may be a valuable tool to estimate human provenance. However, the systematics and mechanisms controlling spatial variation in ⁸⁷ Sr/⁸⁶ Sr of modern human hair remain unclear. Here, we measure ⁸⁷ Sr/⁸⁶ Sr of hair specimens from across the USA to assess the presence of geospatial relationships.

METHODS

Ninety-eight human hair specimens were collected from salon/barbershop floors in 48 municipalities throughout the conterminous USA. [Sr] and ⁸⁷ Sr/⁸⁶ Sr ratios were measured from hair using quadrupole and multi-collector inductively coupled plasma mass spectrometers, respectively. The [Sr] and ⁸⁷ Sr/⁸⁶ Sr ratios of hair were compared with the measured [Sr] and ⁸⁷ Sr/⁸⁶ Sr ratios of tap waters from the collection locations. In addition, the ⁸⁷ Sr/⁸⁶ Sr ratio of hair was compared with the modeled ratios of bedrock and surface waters.

RESULTS

Hair color was independent of the ⁸⁷ Sr/⁸⁶ Sr ratio, but related to [Sr]. The ⁸⁷ Sr/⁸⁶ Sr ratios of hair and leachate were not statistically different and were positively correlated; however, in several hair-leachate pairs, the ratios were conspicuously different. The ⁸⁷ Sr/⁸⁶ Sr ratios of both hair and leachate were linearly correlated with tap water. The ⁸⁷ Sr/⁸⁶ Sr ratio of hair was also significantly correlated with the modeled ratio of bedrock and surface waters, although the ⁸⁷ Sr/⁸⁶ Sr ratio of hair was most strongly correlated with the measured ratio of tap water.

CONCLUSIONS

The ⁸⁷ Sr/⁸⁶ Sr ratio of hair is related to the ratio of tap water, which varied geographically. The ratio of hair provided geographic information about an individual's recent residence. Differences in the ⁸⁷ Sr/⁸⁶ Sr ratios of hair and hair leachate may be concomitant with travel and could potentially be used as a screening tool to identify recent movements.