Minuscule traces of uranium have been found in the outer shells of turtles and tortoises, providing a new way of tracking radioactive contamination over time.
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. He added that the nuclear exposure was unlikely to have affected the turtle’s health for the same reason.
“When we consider the legacies of 20th-century nuclear deployment, testing, and production, we must now also consider chelonians and their lived experience in areas where these activities occurred,” the research stated.
One of the turtles came from Enewetak Atoll in the Pacific, the site of 43 nuclear tests. Although the animal was probably not yet born at the time of the testing, the presence of uranium may have come through legacy contamination 20 years after testing ended.
Another turtle that took part in the study was an eastern box turtle from Oak Ridge, Tennessee, in the US. Oak Ridge houses a nuclear facility that has been producing and processing uranium since 1943.
In addition to detecting the presence of uranium, Conrad and his team were also able to pinpoint the specific isotopes found, and link them to different types of nuclear activity.
The team hopes that the technique can help scientists understand where and when nuclear activity occurred and how radioactive materials move from soil and water into plants and animals.
“We anticipate that combining analyses of historically collected and modern specimens will significantly expand our environmental monitoring abilities as they relate to ongoing nuclear contamination questions,” the authors said.
The study was published in PNAS Nexus.
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