Turtle shells carry a record of radiation exposure.
September 1, 2022
Researchers at Los Alamos have a new way to study the presence of radioactive materials in the environment. The key to their research may seem unusual, but the scientists believe they have found the ideal recorder of nuclear events. It’s a turtle.
“Turtles are useful in tracing nuclear activities because of the specific characteristics of how their shells grow,” says Los Alamos archaeologist Cyler Conrad, who is leading the study. “This work has the potential to provide insight into historical radiological operations or releases into the environment.”
As a turtle or tortoise grows, each year its shell produces a thin layer of keratin that then becomes inert. Layers build up, like rings of a tree, and elements from the environment are trapped within the layers. In this way, the shell maintains a time-constrained record of all the environmental conditions in which the animal lived.
Among various kinds of environmental signatures, turtle shells can pick up very small concentrations of radionuclides. These are radioactive forms of elements, some of which form naturally while others are formed anthropogenically. Conrad and his team are looking specifically at anthropogenic uranium, plutonium, strontium, and others.
Jez Inglis, a Laboratory geochemist on the team, says at first the idea behind the study struck him as “a little bit out there.” He recalls, “When Cyler came to me and suggested that we could use turtle shells to do the same thing that people have attempted with tree rings, I thought, ‘that’s kind of interesting, we could give it a go’.”
Inglis points out that tree rings do not become inert with time, and thereby allow the migration of radionuclides throughout the tissues of the tree. Turtle shells, by contrast, are excellent recorders of the pollutants in their environment because the elements are locked in the inert keratin layer in which they were first deposited. He says, “I think our ability to look at the ecology of areas with turtles and see how the isotopes in that particular region change over time is going to open up new understanding of how uranium and other isotopes impact the environment.”
The team began by using shells of deceased turtles from museums and other natural-history collections. Conrad notes that the turtle samples show no evidence of any detrimental health effects from environmental radiation. “One of the samples was a box turtle collected in 1962 from Oak Ridge. We found a clear record of anthropogenic uranium contamination,” he says. Oak Ridge, Tennessee, is home to Oak Ridge National Laboratory, which has been a major center of nuclear energy research since 1942.
Another turtle sample was collected south of the Trinity Site at White Sands Missile Range in 1947. “It was born in the late 1930s and lived through the Manhattan Project,” Inglis says. “I’m excited to see if we find a signature associated with the Trinity test.”
Two advantages of using turtles and tortoises for the study is that they can be found just about everywhere, and they have long lives. “Long-lived animals provide a way of concentrating past exposures over time and therefore can tell us about which radionuclides, and how much of them, may be in a particular location or time period,” says Jeanne Fair, a Lab biologist and co-investigator on the study. “Often, long-lived tortoise species live in the same dry desert regions where nuclear testing was done, both in the U.S. and abroad. Measuring radionuclides in animals at different ages can be a way of assessing how much radiation is still being picked up from these environments.”
The researchers say they aren’t certain whether radioactive signatures in turtle shells come from the animals having ingested isotopes in food or water or just from environmental exposure. “Turtles are passive collectors of information,” explains Inglis. “They’re just out there foraging in the environment and collecting this information without even knowing it.”
Now that the Los Alamos team has proven that the approach works with archival samples, the next step is to collect live samples including box turtles from around the Trinity Site, desert tortoises from the Nevada National Security Site, and sea turtles from the Marshall Islands. “Taking a sample doesn’t hurt the turtle,” assures Conrad. He compares the process to people cutting their fingernails and notes that the shells regrow.
This research will identify patterns of radiation exposure and examine the long-term impact of low-level radiation exposure over time on organisms and ecosystems. “Understanding exposure to radiation in the environment and using animals for surveillance takes a true multidisciplinary research team,” says Fair. “Scientists with many different backgrounds make up this team; we complement each other’s skills and expertise, as we work to put the pieces of the puzzle together.”