This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Your hair contains a record of everywhere you've been. That's because your body uses the hydrogen and oxygen from water (and other beverages and foods) to make proteins—like the keratin in your hair. Because the ratio of the exact isotopes of hydrogen and oxygen varies depending on location—for instance, Denver's isotopic signature in liquids is quite different from Dallas's—forensic scientists may have a new way to piece together your past travels.
Technician Lesley Chesson of IsoForensics in Salt Lake City and her colleagues analyzed the isotope signatures of beer (Budweiser), bottled water (Dasani) and soda (Coke) from 33 U.S. cities in a bid to see whether local beverages generally matched the local water's isotope ratio. They found that the majority of said beverages bore the same "iso-footprint," suggesting that local bottlers were using, for the most part, local water. Each of the cities had a relatively unique ratio of isotopes as well, the researchers report in the May 26 Journal of Agricultural and Food Chemistry.
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In addition to potentially providing a method to ensure that your next bottle of Fiji Water in fact came from the authoritarian island chain rather than a local tap, such isotope signatures might help the police piece together the whereabouts and travels of crime suspects from a simple strand of hair. It's already being used to help reveal the geographic origins of unidentified murder victims.
Of course, there are all kinds of potential problems: This won't help with local criminals too much—it's difficult to distinguish Chicago from Milwaukee, for example—and a stray bottle of true Fiji Water—or a bottle of Bud trucked across the state of Texas, for that matter—could throw the whole trail off. And that's before an accomplished criminal takes the savvy step of shaving his or her head. Plus, the isotope signature was stronger for tap water and soda than it was for beer, suggesting this might be a concern primarily for sober evildoers. In fact, the variation in a given city's isotope ratio among different kinds of beverages varied as much as 41 percent for levels of the rare, heavy isotope of hydrogen.
The variation was most extreme in states including Colorado, Utah and Wyoming, and cities such as El Paso, Tex. and Chula Vista, Calif., suggesting folks in these areas might get their water from elsewhere. A deeper investigation of the latter city (home to a Budweiser brewery) reveals that its water comes from at least four different sources. And that makes for a hairy (isotopic ratio) mess.
Image: A map of the isotope ratios of water throughout the U.S. Courtesy of the University of Utah