The 1986 Chornobyl nuclear disaster left behind a trail of environmental destruction. Over 50,000 people left the nearby settlements, fleeing the radiation. But other animals weren’t so lucky. Among them, were the domestic dogs abandoned by evacuated residents. These dogs have since established free-ranging populations within the exclusion zone (CEZ).

For years, researchers have studied these dogs, intrigued by their survival in a radioactive environment. In particular, they were curious about two dog populations that seem distinct even though they live very close to each other: one is around the nuclear power plant in Prypiat, and one lives in the nearby abandoned town of Chornobyl.

“We have been working with two dog populations that, while separated by just 16 kilometers, or about 10 miles, are genetically distinct,” says Matthew Breen, a Professor of Comparative Oncology Genetics at NC State. “We are trying to determine if low-level exposure over many years to environmental toxins such as radiation, lead, etcetera, could explain some of those differences.”

According to the results of the study, it’s not the radiation that’s causing the differences.

A nuclear legacy

The Chornobyl nuclear accident (“Chornobyl” reflects the Ukrainian spelling while “Chernobyl” follows the Russian transliteration) was the world’s largest uncontrolled release of radioactive materials. Efforts to contain the disaster led to the creation of a 30-kilometer exclusion zone and the entire area is now uninhabitable for humans. Rather surprisingly, wildlife has flourished in the area, including the descendants of domestic dogs.

These animals face multi-generational exposure to radiation, heavy metals, and other mutagenic environmental contaminants. So researchers thought it would make sense if they have a higher mutation rate. If this were the case, it would lead to distinct genetic differences between groups within the CEZ.

It’s not the first time scientists have looked at these differences. Previously, they identified 391 outlier genetic regions among the two populations, some of them containing genes associated with repairing DNA damage. Now, they wanted to see whether the mutations were building up in these regions, which is what you’d expect in the case of radioactivity.

“First, we contextualized the level of genetic differences between two dog populations, which indicated that the genetics of Chornobyl City dogs were very similar to dog populations in Russia, Poland, and the surrounding areas,” says Megan Dillon, Ph.D. candidate at NC State and lead author of the study.

That way, we were able to use the Chornobyl City dogs as a representative control population to compare with the nuclear power plant dogs.

Collecting blood from radioactive dogs

The research focused on two dog populations: one near the heavily contaminated power plant and another 16 kilometers away in Chornobyl City. Blood samples from 171 dogs were collected and subjected to whole-genome sequencing, complemented by an analysis technique called short tandem repeat (STR), which measures microsatellite diversity, a measure of genetic variation in a population.

Initially, the researchers looked at chromosomal differences. Then, they looked at small genome intervals, and ultimately, differences in single nucleotides — essentially looking at smaller and smaller genetic differences.

"Think of it like using the zoom function on your phone's camera to get more details — we start with a wide view of a subject and then zoom in," Breen says.

"We know that, for example, exposure to high doses of radiation can introduce instability from the chromosomal level on down. While this dog population is 30 or more generations removed from the one present during the 1986 disaster, mutations would likely still be detectable if they conferred a survival advantage to those original dogs. But we didn't find any such evidence in these dogs."

Contrary to expectations, the study found no evidence of increased mutation rates in either population. Despite the power plant population's proximity to higher contamination levels, their genomic profiles showed no significant differences in mutation accumulation compared to the Chornobyl City dogs. In other words, it's not the radiation exposure that's causing it.

What does this mean?

The absence of increased mutations raises questions about the long-term genetic effects of chronic radiation exposure. Previous studies in other species within the CEZ, such as insects and rodents, have reported mixed results. For example, while some studies identified radiation-linked genetic damage, others, including this canine study, suggest that low-dose exposure may not lead to measurable increases in mutation rates.

Instead, it seems like other selective pressures are the ones affecting the populations and causing the observed differences.

This doesn't necessarily mean that the radiation isn't affecting the dogs, however.

"It's possible that the dogs that survived long enough to breed already had genetic traits that increased their ability to survive. So perhaps there was extreme selective pressure at the start, and then the dogs at the power plant just remained separate from the city population. Investigating that question is an important next step that we are now working on."

The dogs of Chornobyl serve as a valuable model for understanding radiation's impact on mammals, offering insights that may extend to human populations exposed to environmental contaminants.

"While no one lives at the NPP or in Pripyat anymore, up until the Russian invasion many thousands of people continued to work there every day on remediation and construction projects nearby," Kleiman says. "Studying companion animals like these dogs offers a window into the kinds of adverse health risks that people may face."

The shadow of a disaster

Chornobyl's exclusion zone has become an unintended wildlife refuge. Populations of species like wolves, boars, and birds have thrived in the absence of human interference. It's damning that a nuclear radiation site is not as harmful to animals as human interference, but that's all the more reason to study the animals in the area.

The importance of continuing to study the environmental health aspects of large-scale disasters like this cannot be overemphasized," Kleiman said, "as it is certain, given our increasingly technological and industrial societies, there will invariably be other such disasters in the future, and we need to understand the potential health risks and how best to protect people.

The dogs, as sentinel species, highlight how animals can adapt to contaminated environments. Their health and genetic stability offer hope for other species facing similar challenges.

Journal Reference: Megan N. Dillon et al, Is increased mutation driving genetic diversity in dogs within the Chornobyl exclusion zone?, PLOS ONE (2024). DOI: 10.1371/journal.pone.0315244