February 27, 2008 DNA contained in hair is currently used in crime fighting to determine the identity of those who commit illicit acts. Thanks to new research, hair may now also help police track past movements of criminal suspects or unidentified murder victims by revealing the general location where a person drank water.
The breakthrough comes from scientist at the University of Utah led by geochemist Thure Cerling with ecologist Jim Ehleringer. Basing the work on the premise that “you are what you eat and drink – and that is recorded in your hair”, the research team found significant variations in hydrogen and oxygen isotopes in human hair and water that relate to where a person lives. The study found a strong correlation between hydrogen and oxygen isotope levels in hair and drinking water; 85 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. The technique they developed as a result, analyzes stable isotopes of hydrogen and oxygen incorporated in growing hair from water and food that a person consumes and from air they breathe.
A single hair can help determine a person’s location during recent weeks to years, depending on the length of the hair sample and thus how much time it took to grow. Several factors cause isotope concentrations in water to change according to geography including the fact that heavier rainwater (containing oxygen-18 and hydrogen-2) tends to fall nearer to the coast. Cloud temperatures, the season during which rain falls and the amount of water that evaporates from soil and plants are also key parts of the puzzle.
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. Based on the analysis of hair and water samples collected from 65 cities in 18 states, the maps cannot pinpoint a person’s exact locations in the past, but identifies general geographic areas where they stayed and drank local water. According to researchers, they would be able to tell the difference between Utah and Texas but possible not between Chicago and Kansas City. Further research showed that drinking water from any area has a unique isotope signature that is incorporated into growing hair that is not complicated by other beverages because “a significant fraction of beer, soft drinks and milk is local in its origin,” Ehleringer says.
Cerling and Ehleringer co-founded IsoForensics three years ago, a company that uses stable isotope analysis of forensic substances to find slight variations in a chemical element’s various isotopes. The technique has practical applications for crime fighters as is can be used to check an accused criminal’s alibi when claiming they have not been in a region where a crime has occurred. The method has already been implemented by Utah police to reconstruct the possible origins of unidentified murder victims. Salt Lake County Sheriff’s Detective Todd Park is one such officer and said the new type of hair analysis is being used to try and identify a murdered woman whose remains were found near the Great Salt Lake in October 2000. “It’s a phenomenal method…I think it will help the law enforcement community a great deal.”
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