For several years, forensic scientists have been able to use isotopes found in human hair as markers that can indicate a region of the country where a person was living because many water supplies have unique isotopic signatures that are captured in hair. A person drinks the local water, and an isotopic record of that water is recorded in the individual's hair. Such water-based isotopic information has assisted investigators in identifying the "region of origin" of several skeletal remains, leading to the eventual identification of the individuals.
Isotopes are different forms of the same chemical element that can be measured accurately and compared. For forensic purposes, isotope ratios of different elements like carbon, nitrogen, oxygen, and hydrogen will vary based on a person's exposure to environmental factors such as drinking water and nutrients in food. Therefore, isotope ratios can be used as a molecular signature to reflect an individual's habits and daily exposure to the environment.
In this NIJ-supported project, researchers from West Virginia University wanted to increase the forensic value of hair as an investigative tool by studying the isotopic signature of specific molecular components of that hair, which might produce a more detailed forensic profile of a person. Analyzing the chemical signatures in hair is fundamentally different than the traditional, but limited, forensic practice of comparing hairs through examination under a microscope.
The isotopes, which are in the DNA-free keratin protein shaft of a hair, contain "a chronological record of dietary and metabolic activities of the donor, thus providing insight into the biochemical processes in the body as a function of time [and] distance," the researchers said. By conducting isotope analysis of hair, the researchers said, they can provide "elemental, proteomic (protein), and isotopic information about human hair samples which, because of their objectivity, scientific foundation, and statistical nature, offer many advantages over forensic hair microscopy."
"The criminal justice system could benefit enormously from an objective, instrumental method of analysis of human hair that could provide investigative leads such as the age, sex, race, dietary habits, region-of-origin, genetic disorders, disease state, or body mass index of the donor in the absence of a comparison sample," the researchers said in their report.
To develop that method, the researchers collected hair samples from 97 U.S. and 94 Jordanian subjects. Each of the participants completed a questionnaire on biometrics, nutritional habits, lifestyle, health, and region of origin. The samples were studied through bulk isotope-ratio mass spectrometry (IRMS), the traditional method of analyzing the whole hair sample, and then a portion of those samples were used for more detailed isotopic analysis of the individual types of amino acids that make up the hair. The results of the analysis were then incorporated into an already-existing global database of approximately 3,500 individual isotope samples. Geographic analysis of the U.S. subjects' data is pending.
Carbon isotopes were also studied, as they are correlated to the plants that serve as primary dietary sources (wheat and rice vs. corn). Scientists can roughly determine human regions of origin or residence by measuring carbon isotope ratios in relation to dietary plants and other foods.
Using various combinations of isotope measurements, the researchers tried to identify body mass index, age, and diet of members of the sample group. They also tried to predict the presence of Type II diabetes from the amino acids in the hair samples.
The sex of an individual was predicted with 94 percent accuracy; age group with 83 percent accuracy; and region of origin with 61 percent accuracy. They also said that they were able to detect Type II diabetes with 100 percent accuracy, for the sample studied.
The researchers noted that isotopic analysis of human hair for forensic investigations remains in the experimental stage. "At this time, we do not expect these fundamental research findings to affect public policy or routine casework in crime laboratories. However, we have made significant strides towards the development of novel investigative leads that law enforcement could use in the future to help solve crimes."
Learn about other NIJ-supported projects regarding isotope ratios:
A Comprehensive Test of the Methods and Models Used to Assign Geographic Origin to Human Skeletal Remains With Stable Isotope Data
Isotope Analyses of Hair as a Trace Evidence Tool to Reconstruct Human Movements: Establishing the Effects of the "Human Ecosystem" On Strontium and Oxygen Isotope Ratios
About This Article
The research described in this article was funded by NIJ award 2013-DN-BX-K007, awarded to West Virginia University. This article is based on the grantee report "Biometrics from the Isotopic Analysis of Amino Acids in Human Hair" (pdf, 46 pages) by Glen P. Jackson, principal investigator, West Virginia University.
This research is part of a broader portfolio of trace evidence projects managed by NIJ Physical Scientist, Gregory Dutton, Ph.D. Learn more about NIJ's trace evidence research portfolio.