EA-IRMS: Tracing human provenance using hydrogen and oxygen isotope fingerprints

Significance of the Topic

Human provenance and movement tracking are critical in forensic investigations and anthropological research. Stable isotope fingerprinting leverages the relationship between environmental water isotopes and human tissues to provide evidence that complements traditional forensic data. This approach can clarify migratory patterns and support criminal casework.

Objectives and Study Overview

This study by Ehleringer et al. examined correlations between δ2H and δ18O values in human hair keratin and local drinking water across the United States. Hair and tap water samples were collected from 65 cities in 18 states to test whether geographic variations in precipitation isotopes are recorded in human hair, enabling provenance analysis.

Methodology and Instrumentation

Sample collection involved discarded hair clippings and 25 ml of tap water from each site. Hair samples (≈150 µg) were loaded into silver capsules, and water (40 µl) was injected separately. Both types underwent pyrolysis at 1400 °C in an EA-IRMS system to produce H2 and CO for isotope ratio measurements. In-house hair standards and water end-member standards ensured data quality, with precision of ±0.9‰ for δ2H and ±0.2‰ for δ18O in water, and ±4‰ and ±0.4‰ respectively in hair.

• Elemental Analyzer–Isotope Ratio Mass Spectrometry (EA-IRMS) with pyrolysis reactor
• Silver capsules for hair keratin analysis
• In-house isotopic standards: Florida (heavy) and Utah (light) hair, “zero” water and deionized tap water

Key Results and Discussion

Modeled isoscapes derived from nearly 500 locations showed clear δ2H and δ18O gradients corresponding to latitude, altitude, and distance from the coast. Hair isotope values were strongly correlated with local tap water, indicating that the primary determinant of hair keratin isotopic composition is drinking water consumption. Hair growth rates (~1 cm/month) allow temporal reconstruction of movement across isotopic landscapes.

Benefits and Practical Applications

• Forensic casework: Adds objective evidence for determining an individual’s geographic history, aiding investigations such as homicide.
• Anthropological research: Supports studies into ancient migration by analyzing preserved hair or keratinous tissues.
• Quality assurance in provenance studies: Provides reproducible, quantitative data on human movement.

Future Trends and Potential Applications

Advances may include compound-specific isotope analyses for finer resolution, integration with other isotopes (e.g., carbon, nitrogen), and development of global isoscapes for broader provenance studies. Emerging portable IRMS technologies could enable on-site forensic assessments.

Conclusion

The correlation between hydrogen and oxygen isotopic signatures in human hair and local drinking water offers a robust framework for tracing human provenance. EA-IRMS analysis of keratin provides reliable, quantitative evidence that enhances both forensic and anthropological investigations.

References

1. Ehleringer JR, Bowen GJ, Chesson LA, West AG, Podlesak DW, Cerling TE. Hydrogen and oxygen isotope ratios in human hair and potential environmental influences. PNAS. 2008;105(8):2788–2793.
2. Rodrigues C, Brunner M, Steiman S, et al. Agricultural and Food Chemistry. 2011;59:10239–10246.
3. Bowen GJ. Annual Review of Earth and Planetary Sciences. 2010;38:161–187.
4. Cerling TE, Barnette JE, Bowen GJ, et al. Annual Review of Earth and Planetary Sciences. 2016;44:175–206.