BioEd Online

Cold War nuclear-bomb testing may have a beneficial legacy: helping forensic experts to estimate more accurately the age of dead bodies. Radioactive remains from the many blasts detonated during the 1950s and 60s are present in the tooth enamel of people all over the world, allowing examiners to work out when the teeth were formed.

The method, developed by researchers at the Karolinska Institute in Stockholm, Sweden, has already helped Swedish police to identify six of that country's victims from last year's Asian tsunami. And it may help with the task of putting names to the victims of Hurricane Katrina.

The technique works because a burst of nuclear testing in the 1950s, chiefly by the United States and Russia, released huge amounts of the radioactive isotope carbon-14 into the atmosphere. This was subsequently taken up by crops and other plants, thus entering the food chain. This bomb carbon is not dangerous, but it is traceable.

Since the signing of the Partial Test Ban Treaty in 1963, which banned above-ground nuclear detonations, atmospheric levels of C-14 have been dropping at a known rate. And because tooth enamel is not replenished after a certain age, the carbon in that enamel bears the hallmarks of the time when it was made, explains Jonas Frisén, who led the research team.

Someone in middle age, whose teeth were formed in the 1960s, will for example have higher levels of C-14 in their enamel than a teenager, whose teeth were made when there was less carbon-14 around.

Age detector

The dating method can judge a person's age to within 1.6 years, the researchers report in Nature¹. This is an improvement on existing methods, such as examining skeletal remains, which is thought to be accurate to only 5-10 years. What's more, the new method gives an actual birth date for the body, rather than simply an age at death. This could be helpful in situations when it is unclear how long the victim in question has been deceased.

An accurate estimate of a body's birth date could be a great help in identifying victims of disasters such as the Asian tsunami or the genocide in the former Yugoslavia, Frisén says. The alternative method of DNA profiling requires exhaustive analysis of tissue samples, many of which simply no longer exist. Teeth are far easier to preserve for later examination.

Investigators struggling to identify bodies left behind by Hurricane Katrina may also adopt the method. Victims of drowning can sometimes be hard to identify thanks to water damage, and the flooding may have destroyed some records traditionally used for identification. "In situations like New Orleans they will be having huge problems," Frisén says. "In many cases dental records will have been washed away."

As the flurry of Cold War testing recedes into the past, atmospheric carbon-14 levels will eventually tail off to a level where the method will no longer work. "But that is several decades away," Frisén says.