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

Importance of the Topic

Stable isotope fingerprinting of hydrogen and oxygen in human tissues offers forensic and anthropological insights into individual movement patterns and regional origin. Traditional evidence in criminal investigations can be supplemented by isotope data locked in hair keratin, providing a chemical “tape recorder” of water sources consumed by an individual.

Study Objectives and Overview

The primary goal of the study by Ehleringer et al. (2008) was to evaluate the relationship between δ2H and δ18O values in human scalp hair and local tap drinking water across the United States. Samples from 65 cities in 18 states were analyzed to establish a predictive framework for human provenance based on isotope fingerprints in keratin.

Methodology

• Sample Collection: Discarded hair clippings gathered from barbershops and corresponding 25 ml tap water samples from each location.
• Isotope Analysis: Measurement of nonexchangeable δ2H and δ18O in hair and water via elemental analysis pyrolysis coupled to isotope ratio mass spectrometry (EA-IRMS) at 1400 °C.
• Data Quality: Bracketing with internal standards (keratin from Florida and Utah) to achieve precisions of ±4 ‰ for δ2H and ±0.4 ‰ for δ18O in hair, and ±0.9 ‰ / ±0.2 ‰ for water.

Instrumentation Used

The study employed an elemental analysis–isotope ratio mass spectrometry system (EA-IRMS) equipped with a high-temperature pyrolysis reactor, similar to the Thermo Scientific™ EA IsoLink™ IRMS System.

Main Findings and Discussion

• Geographic Variation: δ2H and δ18O values in hair mirror local precipitation and tap water isoscapes, with predictable inland and altitude trends.
• Isoscape Modeling: Predicted maps based on nearly 500 locations demonstrated consistent regional patterns across the USA.
• Correlation: Strong linear relationship between hair keratin isotopes and local tap water confirms drinking water as the dominant influence over dietary water from food.
• Temporal Resolution: Hair growth (~1 cm per month) allows reconstruction of individual travel history over time.

Benefits and Practical Applications of the Method

• Forensic Support: Provides ancillary evidence of an individual’s recent geographic history in criminal investigations.
• Case Resolution: Assists in unresolved cases, including homicides, where conventional clues are insufficient.
• Anthropology: Traces origin and mobility of ancient and modern populations in migration studies.

Future Trends and Potential Applications

• Multi-Isotopic Integration: Combining hydrogen and oxygen with other tracers (strontium, sulfur) for enhanced geographic resolution.
• High-Throughput EA-IRMS: Development of faster workflows for large-scale screening in forensic and environmental studies.
• Public Health: Mapping water intake patterns to explore links between regional water sources and health outcomes.
• Advanced Modeling: Use of machine learning to refine isoscape predictions and improve provenance assignments.

Conclusion

The study by Ehleringer et al. demonstrates that hydrogen and oxygen isotope analysis of hair keratin reliably reflects local tap water signatures, enabling reconstruction of human movements for forensic and anthropological applications. The established correlation framework and isoscape models provide a robust basis for future high-resolution provenance analysis.

References

1. Ehleringer JR, Bowen GJ, Chesson LA, West AG, Podlesak DW, Cerling TE. PNAS. 2008;105(8):2788-2793.
2. Rodrigues C, Brunner M, Steiman S, Bowen GJ, Nogueira JMF, Gautz L, Prohaska T, Máguas C. J Agric Food Chem. 2011;59:10239-10246.
3. Bowen GJ. Annu Rev Earth Planet Sci. 2010;38:161-187.
4. Cerling TE, Barnette JE, Bowen GJ, Chesson LA, Ehleringer JR, Remien CH, Patrick S, Tipple B, West JB. Annu Rev Earth Planet Sci. 2016;44:175-206.