Using Strontium Isotope Data in Hair Analysis

Through the National Criminal Justice Reference Service, NIJ has made available the following final technical report (this report is the result of an NIJ-funded project but was not published by the U.S. Department of Justice):

Isotope Analyses of Hair as a Trace Evidence Tool to Reconstruct Human Movements: Combining Strontium Isotope with Hydrogen/Oxygen Isotope Data (pdf, 51 pages)


Brett J. Tipple


Reconstructing the travel-movement of individuals can be important to many forensic investigations, spanning from homeland security issues at the national level to cold-case investigations at the local level. Analysis of stable isotopes recorded in human scalp hair at natural abundance levels has shown to be a useful tool to law enforcement and has assisted in the reconstruction of the recent geographic-movement histories of individuals.

This is because hair proteins (i.e., keratin), and the stable isotopes contained within keratin, are recorders of an individual’s geographical environment. For example, the oxygen (O) isotope values (δ18O) of human hair keratin have provided novel travel/geographic origin information that helped guide local, national, and international criminal investigations. This is because of the well-established relationship between the δ18O values of human hair and drinking water. Since the δ18O values of drinking water vary predictably across landscapes, the δ18O values of human hair correlate to specific geographic regions.

The author hypothesized that Strontium (Sr) isotope ratios (87Sr/86Sr) of human hair could be an additional estimator of geographic region independent of O isotopes, as Sr is not a structural component of hair and the 87Sr/86Sr ratio of a geographic area is largely controlled by regional geology. The 87Sr/86Sr ratios of biological materials have been successfully applied to many region-of-origin questions in the fields of archaeology, ecology, food science, and forensic science.

The author was able to isolate the exogenous and endogenous Sr isotope signals to hair and show that the exogenous Sr isotope signal is most informative for forensic questions. In addition, the author determined that the most important exogenous Sr to hair is the Sr contained in bathing water. The findings permit the development of the application of Sr isotope ratios of modern human hair as a novel forensic tool. The combination of δ18O values and 87Sr/86Sr ratios of hair constitute a distinct isotope signature, which could allow for greater specificity for region-of-origin assignment during criminal investigations than the use of one isotope measurement alone.

Click here to download the full paper.

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