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Hair Samples Used to Trace Movement

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Hair Samples Used to Trace Movement

Science

Hair Samples Used to Trace Movement

Hair Samples Used to Trace Movement

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Scientists have developed a new tool for tracking a person's movements — hair analysis. Researchers have discovered the link between drinking water, which varies from one region to another, and human hair, which acts as a geographic marker.

STEVE INSKEEP, host:

Okay. You already know that scientists can detect DNA in a person's hair. They can even use that piece of hair to detect signs of drug use or heavy metal poisoning. Now, researchers can use hair samples to trace a person's movements in time and space. This has to do with subtle chemical differences in the water they drink.

NPR's Richard Knox reports.

RICHARD KNOX: Detective Todd Park of the Salt Lake Country Sheriff's Department in Utah is one of the first to use the new forensic tool.

Mr. TODD PARK (Detective, Salt Lake County Sheriff's Department): I've got a case where we have a Jane Doe that was found out by the Great Salt Lake back in 2000. We found 28 bones and very little else.

KNOX: The medical examiner estimated her age at 17 to 23, her height at under five foot three and her death date sometime in 1998. Her most distinguishing feature: waist-length reddish-blond hair. Park heard that scientists at the University of Utah had a way of reading people's movements through their hair. He took them some strands of the unknown woman's hair. In the two years before her death, the scientists said, she traveled up and down the West.

Mr. PARK: The hair analysis gave me a geographic area of Salt Lake north up through Idaho and into Montana, the western part of Wyoming and the eastern potions of Oregon and Washington. It's a pretty big area, but it's a heck of a lot of better than the area that I had to work with before.

KNOX: That is the whole country or beyond. The Utah scientists describe their technique in the proceedings of the National Academy of Sciences. James Ehleringer says the idea started with differences found in rain water as clouds move inland from the ocean. Some water contains molecules of hydrogen and oxygen called isotopes that have extra neutrons. That water is literally heavier.

Professor JAMES EHLERINGER (Biology, University of Utah): As the cloud begins to rain out, there's a tendency for the heavier isotopes to fall out first.

KNOX: Ehleringer and his colleagues mapped the differences in rainwater isotopes across the country. These geographic differences show up in drinking water and food. The water that people ingest gets incorporated into their hair.

Professor EHLERINGER: Given that your hair grows at .35 millimeters per day, a history of what you've been eating and where you've been traveling gets recorded through the signals in body water and the food you eat into the hair and that becomes a permanent record.

KNOX: To prove it, Ehleringer sent his wife Edna and a colleague sent his grown children around the country to collect hair from the floors of barber shops.

Professor EHLERINGER: I think almost without exception all the barbers said, Sure, here's a sample, but, boy, that's a wacko idea.

KNOX: Sounds crazy, but it works. The scientists have formed a company to run tests for law enforcement agencies around the country. Ehleringer says they can't yet tell what zip codes a murder victim or a serial killer might've visited, but they can get a pretty good idea of where he or she has been.

Professor EHLERINGER: We might not be able to tell the difference between coastal Los Angeles and interior Los Angeles, but by the time you got the desert at Riverside we could certainly tell a difference.

KNOX: The new technique isn't limited to hair. Todd Park, the Salt Lake Country detective, has sent Ehleringer some of his unidentified woman's teeth. The hope is the isotopes in her teeth will tell a story of where she lived when her permanent teeth grew in.

Richard Knox, NPR News.

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