A strand of hair offers clues
Scientists have devised a way to determine roughly where a person has lived using a strand of hair, a technique that could help track the movements of criminal suspects or unidentified murder victims.
The method relies on measuring how chemical variations in drinking water around the country show up in the hair of people who drink the water.
“You are what you eat and drink, and that is recorded in your hair,” said Thure Cerling, a geologist at the University of Utah and lead author of the study published this week in the Proceedings of the National Academy of Sciences.
Though the U.S. diet is relatively homogenous, water supplies vary. The differences are a result of weather patterns. The chemical composition of rainfall changes slightly as rain clouds move.
Most of the hydrogen and oxygen atoms in water are stable, but traces of both elements are also present as heavier isotopes. The heaviest rain falls first. As a result, storms that form over the Pacific Ocean deliver heavier water to California than to Utah. Similar patterns exist throughout the country.
By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair, scientists can construct a geographic timeline. Each inch of hair corresponds to about two months, Cerling said.
Cerling’s team collected tap water samples from 600 U.S. cities and constructed a map of the regional differences. The researchers checked the accuracy of their map by testing 200 hair samples collected from 65 small-town barber shops.
They were able to accurately place the hair samples in broad regions roughly corresponding to the movement of rain systems across the country.
“It’s not good for pinpointing,” Cerling said. “It’s good for eliminating a lot of possibilities.”
Todd Park, a cold-case detective at the Salt Lake County Sheriff’s Office, said the method had already helped him learn more about an unidentified woman whose partial skeleton was discovered in 2000 off Interstate 80 at the south end of Great Salt Lake.
The woman was about 5 feet tall and between 17 and 22 when she died. Police recovered 26 bones, a T-shirt, a necklace and several strands of hair. “The victim had really long hair, halfway down her back,” Park said.
When he heard about the research at a forensics conference, he gave the hair samples to the researchers.
Chemical testing showed that in the two years before her death she moved about every two months.
She stayed in the Northwest, though the test could not be more specific than somewhere between eastern Washington and Oregon and western Wyoming.
“It’s still a substantial area,” Park said. “But it narrows it way down for me.”
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