Hair Keeps Chemical Record of Where You've Been

Your hair holds clues about where you've been through telltale chemical signs that start out in tap water and end up in your cells.

Even Coke, bottled water and sometimes beer leave a geographic imprint that lasts until you get a trim, because local bottling plants use local water, found a new study.

The research, as it progresses, is helping investigators identify crime victims with hair by showing where people spent time before they died. Along with other forensic strategies, the technique has already been used to help solve at least one mystery.

"Police departments and sheriff departments contact us with cold cases with no leads and say: 'Can you analyze the hair and tell us something about where the victim was from?'" said analytical chemist Lesley Chesson, of IsoForensics, a scientific research company in Salt Lake City.

Scientists know that our bodies use the water we drink to form proteins in our hair, fingernails, muscles and other body tissues. In the last few years, researchers have found that these tissues also record a type of chemical fingerprint in tap water that varies from one geographic region to the next.

The fingerprint takes the form of a unique ratio between heavy and light hydrogen and oxygen atoms. Atoms of different weight are called isotopes, and isotopes end up in different ratios in tap water because of the way water cycles between oceans and clouds -- with heavier atoms less likely to evaporate and more likely to fall out of clouds first.

For the new study, Chesson and colleagues wanted to look beyond tap water to see if other common beverages also reflect their origins.

On three massive road trips around the United States, Chesson bought cans and bottles of Coke, Dasani bottled water and Budweiser beer from 33 cities. She also collected samples of tap water and brought everything back to her lab for testing.

Results, published in the Journal of Agriculture and Food Chemistry, showed a close match in isotope ratios between tap water, soda and bottled water from each area, probably because local bottling plants use local water. The beer showed a weaker match because there are only 12 Budweiser breweries around the country.

In some places, the relationship was murkier because both drinking water and store-bought beverages are often imported from other regions.

As their research continues, Chesson and colleagues are narrowing in on the strengths and weaknesses of hair analyses as a forensic tool.

In one cold case, the team was brought in to help identify the body of a 20-something woman who was found dead of stab wounds in 1971, but whose case remained unsolved. After analyzing the isotopes in her hair, the scientists were able to conclude that the woman had lived (and therefore drunk tap water and other beverages) in Northern California for at least 18 months before she died. That clue helped detectives focus their search.

With the help of missing persons records, DNA and other types of evidence, they were finally able to identify her as Mary Alice Willey -- providing, at least, some finality for family members and opening the possibility that her killer might be found.

In another case, the team was able to say that a particularly long-haired victim had moved every six months or so for the two years before her remains were found near a concert venue along the shores of the Great Salt Lake.

So far, they have not yet figured out who she was.

By showing that the most commonly consumed beverages reflect their location, the new study is "an important step that allows us to remain optimistic about the promise of isotopes to tell us something about human movement," said Jason West, an ecologist at Texas A&M University in College Station.

"What we're learning from this paper is where the strengths are and where some of the limitations are," he added.