September 15, 2005. Copyright 2005, Graphic News. All rights reserved

Nuclear tests leave signature in teeth to reveal age

The above-ground testing of nuclear bombs in the 1950s and 1960s may have an unexpectedly useful legacy -- helping forensic scientists to improve the estimation of an individual's age at the time of their death. Tooth enamel preserves a permanent record of the amount of radioactive fallout present in the atmosphere when the tooth was formed. By determining the amount of radioactive carbon-14 in the tooth, scientists can then calculate the age of the tooth, and its owner, according to research reported in this weeks edition of the journal Nature.

The method is accurate to within roughly 1.6 years -- better than current methods of evaluating skeletal remains and tooth wear, which are accurate to within only 5-10 years in adults, report researchers from the Karolinska Institute in Stockholm and the Lawrence Livermore National Laboratory in California. But as nuclear testing only began in 1955, the technique does not work for individuals born before 1943 because all of their teeth would already have been formed by this time. 

When nuclear testing began, it dramatically increased the amount of radioactive carbon-14 in the atmosphere, the researchers explain. This found its way into human teeth after being incorporated into plants during photosynthesis and thus entering the food chain. In this way, carbon-14 levels in the human body closely parallel those in the atmosphere at any given time.

The enamel of individual teeth is formed at distinct times during childhood and contains 0.4% carbon. As there is no turnover of enamel once laid down, the carbon-14 concentration in the enamel reflects that of the atmosphere. Levels began to drop off again when above-ground nuclear testing was stopped in 1963 -- so comparing the amount of carbon-14 in tooth enamel to the records of the decline in atmospheric levels gives an accurate picture of when the tooth in question was formed.

The method, which the scientists say is no more difficult than doing a blood test, has already been used to help identify people who died in the Indian Ocean tsunami last year and American researchers are also offering to determine the age of unidentified victims of Hurricane Katrina with the technique.
/ENDS

CONTACT:
Jonas Frisˇn (Karolinska Institute, Stockholm, Sweden)
Tel: +46 8 5248 7562; E-mail: jonas.frisen@cmb.ki.se