The detective knows what water you've been drinking
Researchers say isotopes found in hair reveal subtle regional differences based on the tap water people consume
A sample of someone's hair can reveal where they have been living, says a team of U.S. researchers who are hoping their new technique will help police solve crimes.
We are what we drink, and subtle regional differences in tap water show up in our hair, says University of Utah environmental scientist James Ehleringer, lead author of a paper to be published today in the Proceedings of the National Academy of Sciences.
The hair analysis method he and his colleagues developed is already being used by police in Utah in an attempt to identify a female murder victim whose remains were found in October, 2000, near Great Salt Lake.
The technique can't identify the city or town where someone has been living, but it can tell the general geographic areas where they stayed and drank local water.
The Great Salt Lake murder victim's hair showed that she probably spent the two years before she died in the Idaho-Montana-Wyoming area, says Salt Lake County Sheriff's detective Todd Park, a member of the cold case homicide unit.
Dr. Ehleringer and his colleagues analyzed hair samples from the floors of barber shops in 65 cities across the United States, choosing places with populations of 100,000 or less to reduce the chance of getting hair from tourists rather than local customers. They also took samples of tap water.
They found significant variations of hydrogen and oxygen isotopes in hair and water that relate to where a person lives, Dr. Ehleringer says.
Isotopes are forms of the same element with different atomic weights. The isotopes in water - hydrogen and oxygen - vary with geography, says University of Utah geochemist Thure Cerling.
As clouds move inland from the ocean, raindrops with heavier forms of oxygen and hydrogen tend to fall first. Cloud temperature and the amount of water that evaporates from soil and plants also have an effect.
Dr. Ehleringer and his colleagues have created colour-coded maps showing how the isotopes found in hair varied across the country.
Canadian drinking water has similar regional differences, Dr. Cerling says. "It would be the same phenomenon."
For the technique to work here, he says, someone would have to collect hair and water samples and make a similar map.
What about people who drink bottled water? They still tend to consume coffee and tea made with tap water, Dr. Ehleringer says. They also boil pasta, potatoes and other foods in regular drinking water. Unless people drink only bottled water or imported beer, and cook with it, he says, the local water affects their hair in ways that shampooing, dying or bleaching can't change.
Scalp hair grows about a centimetre a month, so a single strand could help scientists piece together past movements of a person or an animal, Dr. Cerling says.
The method could help police check alibis.
"You can tell the difference between Utah and Texas," Dr. Ehleringer says.
The test is 85 per cent accurate, because about 15 per cent of the differences between people's hair are due to other factors, like diet, not the water they drink.
It may also have medical applications, or help anthropologists track migrations of Native Americans by analyzing ancient hair samples.
Dr. Ehleringer and his colleagues are exploring what other personal information they can extract from a strand of hair, including whether someone is a vegetarian or eats a lot of fast food.CTVglobemedia
