Turtles and tortoises have been found to store decades-long records of exposure to radioactive contamination on their backs.

A team of scientists at the Pacific Northwest National Laboratory used a special mass spectrometer to detect uranium in the shells of four chelonians (the order of reptiles that include turtles and tortoises), that lived near radioactive sites in the past. 

The researchers discovered that turtles exposed to radioactive material, such as fallout from nuclear weapons testing or accidental waste releases, accumulated uranium isotopes in their shell scales.

Each layer of shell equates to one year of the turtle’s life. In one of the shells, the researchers traced varying levels of uranium in individual concentric layers that formed like tree rings and tracked the animal’s uranium uptake over time. 

The amount of uranium found was so small – around one part in one billion – that co-author Cyler Conrad could confirm it was not radioactive...