"You are what you eat and drink - and that is recorded in your hair," says geochemist Thure Cerling, who led University of Utah research with ecologist Jim Ehleringer. The scientists developed a new crime-fighting tool by showing that human hair reveals the general location where a person drank water, helping police track past movements of criminal suspects or unidentified murder victims.
"We have found significant variations in hydrogen and oxygen isotopes in hair and water that relate to where a person lives in the United States," Ehleringer says. Isotopes are forms of the same chemical element with different atomic weights and stable isotopes are those that do not decay radioactively. The new technique analyzes stable isotopes of hydrogen and oxygen incorporated in growing hair from the water and food that a person consumes and from air they breathe.
Eighty-five percent of the variation in isotope levels in a person's hair was explained by variations in drinking water isotope levels in areas where they spent time. So, a single hair can help determine a person's location during recent weeks to years, depending on the length of the hair sample. The scientists used the method to produce color-coded maps showing how ratios of hydrogen and oxygen isotopes in scalp hair vary in different areas of the United States.
