Stable isotope analysis of oxygen, carbon, and strontium in modern tooth enamel
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Abstract
This preliminary research analyzes the carbon, oxygen, and strontium stable isotope values in tooth enamel samples from 21 individuals in Boston, Massachusetts. This study provides insights into the diets and geographic characteristics of the participants during childhood. Eligible participants who had a tooth extracted filled out a questionnaire to gather supplemental information to aid in evaluating the stable isotope values. Once the tooth samples were extracted at the Boston Medical Center’s Oral & Maxillofacial Surgery center, enamel was transferred into micro-centrifuge tubes and sent to the Boston University Stable Isotope Laboratory and the University of Utah’s ICP-MS Metals and Strontium facility. Carbon and oxygen analysis subjected the samples to CO2 extraction and composition analysis using a GV IsoPrime Isotope Ratio Mass Spectrometer. Enamel samples were analyzed for strontium concentration using a triple quadrupole ICP-MS instrument for strontium analysis. Isolated strontium was processed using an MC-ICP-MS. Strontium analysis showed that samples clustered according to geographic origins, except for one sample from Carver, Massachusetts, which did not register a strontium signal.
Descriptive statistics were conducted for δ13C‰, δ18O‰, and 87Sr/86Sr values. Puerto Rico had the highest marginal means for δ13C‰ and δ18O‰, while the Dominican Republic had the lowest for δ13C‰ and El Salvador had the lowest for δ18O‰. The lowest standard deviation was associated with Massachusetts individuals who drank tap water, while the highest standard deviation was associated with Massachusetts individuals who consumed tap and bottled water. When city-specific origin analysis was applied, Plymouth and Weymouth, Massachusetts, encompassed δ13C‰ values of other regions, while Weymouth, Massachusetts, and Espírito Santo, Brazil, encompassed δ18O‰ values of other regions. Plymouth, Massachusetts, also encompassed other regions' 87Sr/86Sr values. This preliminary research provided valuable insights into the isotopic characteristics and supplementary diet and geographic origin information for Bostonian samples. The differences in δ13C‰ values indicate variations in the consumption of C3 and C4 plants, with some individuals having diets richer in one compared to the other. This dietary information can be significant in understanding cultural practices, subsistence patterns, and potential health conditions such as diabetes. This information is valuable for forensic investigations where identifying the geographic origin of unidentified individuals is crucial. However, this study also emphasizes the limitations of using single-isotopic analysis, as some samples did not register a signal or registered a signal that was an outlier for comparable geographic origins.
Furthermore, distinguishing signatures can be complicated due to overlapping isotopic values across different regions. Therefore, gathering supplementary information and human tissue samples is encouraged to establish a reliable baseline for forensic comparisons. The small sample size restricts the generalizability of the findings and prevents them from being used to analyze a larger population. More extensive datasets are necessary to establish robust isotopic ranges for geographic regions worldwide that can enhance the accuracy and applicability of stable isotope analysis in contexts of forensic anthropology. The globalization of foods and water sources are a limitation within the research. Globalization causes overlapping elemental isotopic signatures as food and water sources are distributed from one region to another. Future research suggests exploring the influence of water sources on isotopic values to improve the interpretation of data. Overall, this preliminary research provides a valuable foundation for future studies in stable isotope analysis, highlighting the need for comprehensive data and interdisciplinary collaborations to advance our understanding of isotopes regarding human populations to improve forensic investigation.