Stuart Black and his colleagues at the University of Reading are testing a new method of determining where people have lived by measuring the ratios of oxygen and hydrogen isotopes in their tissues or fluids. They presented their results at the British Association for the Advancement of Science Festival in Exeter, UK.

The isotopes, absorbed into the body from water, have predictable values for different local areas and leave a telltale signature in tissues. “Hair is particularly good because it grows about a centimetre a month,” says Black. “So it actually grows a record of not only where you have been but what you have been eating and drinking.”

He says the technology could assist police investigations and potentially help immigration officials to decide whether people seeking asylum are arriving from appropriate countries. “We’re not going to get a postcode,” says Black. “It will only get as far as a regional level, but that may be good enough for some cases.”

Distinct local patterns

The method is based on the ratio of two sets of naturally occurring isotopes, oxygen-16 and oxygen-18, and hydrogen and deuterium. Plants and animals alike absorb a distinct local pattern of isotopes from the water and food they consume.