Multi-isotope analysis refers to the identification of isotopic signature, which is the abundance of stable isotopes of certain chemical elements (e.g., C or Pb) located within inorganic or organic compounds. Multi-isotope analysis has the potential to provide insights into various scientific disciplines, such as the elucidation of environmental processes, understanding of human populations of the past, and identification of individuals in mass graves.
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Modern-day isotopic investigations on human remains are fully utilizing multi-isotope profiles (such as C, N, O, H, S, Sr, Pb) as well as isotopic landscapes originating from a range of body tissues (i.e., teeth, bone, hair, and nails) to predict possible region-of-origin of the unidentified human remains.
Collating the data from various isotope analyses can provide additional evidence for human identification, including a decedent’s approximate birth region, long-term adult residence, travel history, and dietary information.
Isotopes as Historical Archives
An example of how multi-isotope analysis of teeth can shed light on prehistoric (neolithic) populations can be observed in an article by T. Fernández-Crespo et al. Their analysis of fine-grained isotope data for the early lives of 32 individuals has served to confirm different burial locations (caves or megalithic graves) and paint an even more complete picture.
Significant cave and megalithic grave differences in 13C collagen values were documented across all age categories except those younger than five years and those aged between 10 and 12 years. Physiological processes and/or social age-related dietary differences may explain these exceptions to what can otherwise be considered a very robust trend.
All the observed differences in juvenile dietary patterns, subsistence practices, landscape use, and, possibly even residence systems between people buried in caves and in megalithic graves in the Iberian region provide enough evidence to suggest that there were permanent socioeconomic and cultural (perhaps even ethnic) differences which the distinct funerary practices can also infer.
Analytical Techniques in Multi-isotope Analysis
Two widely used analytical techniques within multi-isotope analysis are stable and radiogenic isotope analysis. Stable isotope analysis is used in geochemistry when exploring isotopes that are almost unaffected by radioactive decay, such as the isotopes of oxygen (O16, O17, O18), which are very commonly found within a sample of rock or water. Their stability facilitates tracing processes like biogeochemical cycling and climate change over a certain time span.
A radiogenic isotope is a daughter isotope that comes from the decay of a radioactive parent isotope. The differences observed in radiogenic isotopes can add stand-alone and/or complementary information to stable isotope variations in sedimentary environments.
In sedimentary geology and environmental science, radiogenic isotopes are useful for tracing the sources and transport of dissolved and detrital constituents in the sedimentary hydrologic cycles and ecosystems. Radiogenic isotope ratios (such as sulfates or phosphates) can be measured in ancient marine authigenic sediments and can be used to reconstruct the chemistry of the oceans back in time.
A relevant example of a radiogenic isotope record of temporal change in ocean chemistry is the Sr isotope curve of Burke et al. The “Burke curve” provides information for the Phanerozoic eon and is based on analyses of carbonates and evaporites.
Applications in Archaeology and Anthropology
A unique opportunity arose when the remains of King Richard the Third were discovered. Multi-isotope analysis could be used, and its results could be compared with the information found in historical literature or even enriched it.
Indeed, in a study by Angela Lamb et al. Analysis was performed on a range of materials of Kind Richard’s skeleton. Dental enamel and dentine (which contains Sr, Pb, and O isotopes), a part of the right femur, and a section of a left rib were included. The idea behind the choice of the particular parts was that they vary greatly in terms (parts of teeth may not remodel at all). Therefore, they could provide information on different life segments of the individual.
Since King Richard was the twelfth child of Richard, the Duke of York, he was never projected to become a monarch, so his early life was not documented in detail. The Sr and O data from his remains enabled hypotheses regarding his early life, which appeared to have taken place in the east of England, consistent with his known birthplace in Northamptonshire.
Low d18 Op is usually found in populations that resided in the low rainfall zone of eastern England at that time. Additionally, this was the first time that the intake of wine was observed to have an impact on the oxygen isotope composition of an individual, which, when assessed against historical data, appears to be the time when Richard was at the peak of his reign.
Forensic Science and Broader Modern Applications
Multi-isotope analysis has only been employed in other forensically relevant areas without necessarily including teeth or other bones: Glass evidence is forensically examined by comparing the physical, optical, and chemical properties of glass fragments recovered from the scene of a crime to a source of the glass of known origin. Glass fragments recovered from the clothing of an individual suspected to be the driver (or passenger) in a vehicle involved in a hit-and-run accident can be compared to the glass recovered from a broken windshield.
The gold standard method for the comparison of the trace elemental composition of very small glass fragments is Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), which essentially is a multi-element and a multi-isotope analysis and, throughout the years, has become more and more reliable, producing interlaboratory results that are very consistent.
Nuclear Forensic Science, more commonly known as Nuclear Forensics, has been defined as a discipline of forensic science involving the examination of nuclear and other radioactive material or of other evidence that is radio-contaminated in a legal context.
Nuclear Forensics is an important facet of a country’s nuclear security infrastructure and can deal with the threats of nuclear smuggling, nuclear expansion, and nuclear terrorism. A nuclear forensic examination aims to obtain information on the history of the material (for example, the method and date of production) and its utility. Information regarding its place of production and the last legal owner can also be acquired.
It should be noted, however, that a single parameter(e.g., element or isotope) is insufficient to reach a conclusion about the history of the material of interest. This discipline largely relies on methods of radio-analytical chemistry, including multi-isotope analysis.
Sources
- Eric J. Bartelink and Lesley A. Chesson 2019 Recent Applications of Isotope Analysis to Forensic Anthropology Forensic Sci Res.; 4(1): 29–44. doi: 10.1080/20961790.2018.1549527
- Jay L. Banner 2004 Radiogenic isotopes: systematics and applications to earth surface processes and chemical stratigraphy; Earth-Science Reviews 65(3–4):141-194 doi: https://doi.org/10.1016/S0012-8252(03)00086-2
- Tian et al.2022 Simultaneous multi-element and multi-isotope detection in single-particle ICP-MS analysis: Principles and applications; Trends in Analytical Chemistry 157:116746 doi: https://doi.org/10.1016/j.trac.2022.116746
- Varga et al. 2022 Trends and perspectives in Nuclear Forensic Science; Trends in Analytical Chemistry 146:116503 doi: https://doi.org/10.1016/j.trac.2021.116503
- Lambert et al. 2022 An interlaboratory study to evaluate the forensic analysis and interpretation of glass evidence; Forensic Chemistry 27: 100378 doi:https://doi.org/10.1016/j.forc.2021.100378
- Crespo et al. 2020 Multi-isotope evidence for the emergence of cultural alterity in Late Neolithic Europe; Sci.Adv;6;eeay2169 doi: 10.1126/sciadv.aay2169
Further Reading