The Coke-Zero I drank today was made in Toronto. The beer I drank this afternoon was made in Halifax Nova Scotia. Some of the beer I frequently buy comes from England, Belgium and I drink wines from Niagara, Australia and France.
Not to mention a large proportion of the water I get daily comes from my food. Much of which can come from far of places like Chile and South Africa, and for my Kiwi's New Zealand.
Yes beverages may leave geographic signatures, but by what I eat and drink in a single meal I can be receiving water from a half-dozen places around the world.
Very good point, I hadn't considered that source until I read this comment. Given that they're measuring the ratio of the isotopes, this kind of "pollution" could probably cause significant noise in any sample. I wouldn't be surprised it it were enough to make pinpointing nearly impossible for many people.
It'd be interesting to see an actual study of a few hundred people, and see how accurately it can pinpoint travelers (and their destinations) as opposed to global-munchers.
Someone who eats 'healthily' is going to be much harder to geolocate than someone who eats 'carnivore' style.
I suppose you would look for the strongest source and use that. However I can't help but feel that they're measuring differences in identical isotopes and not relying on unique isotopes (IE of a different mineral) to do the locating. More potassium might mean the North American east coast and more calcium could mean the west is how their method reads to me. This means that they're calculating from the sum of the isotopes.
Scientifically, it's fair enough - hair testing can be used to detect drug use, for example. But people generally drink many different kinds of liquid per day, and only the most consistent and unusual intake patterns would be much actual use. Great for CSI-style plots like 'it's said he will only drink wine made in the village where he grew up...start staking out high-end barbershops.' If you're trying to match a hair found at a crime scene to a particular suspect, you just compare his DNA with that at the root of the hair sample.
