Washington, Feb 26 : A new study has shown that a single strand of your hair is enough for forensic scientists to discover where you live or the places you have been to.
University of Utah scientists have developed a new crime-fighting tool by showing that human hair reveals the general location where a person drank water, and thus could prove invaluable for criminal investigations.
"You are what you eat and drink - and that is recorded in your hair," said geochemist Thure Cerling, who led the research effort with ecologist Jim Ehleringer.
The technique shows that the ratio of oxygen and hydrogen isotopes in a person's hair typically match those found in their local water supply.
Cerling said that apart from helping police track past movements of criminal suspects or unidentified murder victims, the technique could also prove useful to anthropologists, archaeologists and medical doctors.
"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. Police are already using this to reconstruct the possible origins of unidentified murder victims," Ehleringer. Said.
To make the discovery, Cerling's team visited 65 towns across 18 U.S. states, collecting barbershop clippings and water samples along the way.
They analysed both, and observed roughly an 85 per cent correlation between their isotopic ratios, strongly linking the drinking water, and thus geographical locale, to hair composition.
Cerling said that even in the face of imported foods, made from differing water supplies, the local water remains fairly prominently recorded in the timeline of the hair.
The team also used the information collected to develop a predictive map of the U.S., illustrating the expected hydrogen and oxygen isotope ratios in the hair of people across 48 states. This map itself may be an important future tool, the researchers said.
"Drinking water from any area has an isotope signature that is incorporated into growing hair. That signature is not complicated by other beverages because "a significant fraction of beer, soft drinks and milk is local in its origin," Ehleringer said.
"It's a phenomenal method," said detective Todd Park, who is using the new type of hair analysis in an effort to identify a murdered woman whose partial remains were found in Salt Lake County, Utah in October 2000.
The hair sample told Park that the woman had spent the last two years of her life moving around within the Idaho-Montana-Wyoming area and possibly into Oregon and Washington state.
"Every little bit helps. You put pieces of the puzzle together to get a whole picture. And this is definitely something that will give us a piece of the puzzle," Park said.
The authors said that the technique could also prove useful for doctors trying to track to worsening symptoms of a dietary disease, and anthropologists or archaeologists trying to trace migratory patterns of long-dead peoples or animals.
The study appears in the Proceedings of the National Academy of Sciences.