A new study published in PLOS ONE suggests that radiation-induced mutations are unlikely to account for the genetic differences observed between two populations of dogs living in Chornobyl City and the nearby Chornobyl Nuclear Power Plant (NPP). Conducted by researchers from North Carolina State University (NC State) and the Columbia University Mailman School of Public Health, the study has significant implications for understanding the long-term effects of environmental contamination, including radiation exposure, on populations over time.
Genetic Differences in Canine Populations
The research focused on two dog populations that, despite being separated by just 16 kilometers (about 10 miles), show genetic distinctiveness. The first group of dogs resides in Chornobyl City, while the second is found near the Chornobyl NPP. Matthew Breen, the Oscar J. Fletcher Distinguished Professor of Comparative Oncology Genetics at NC State and the corresponding author of the study, emphasized that while the populations are geographically close, they are genetically distinct, prompting the researchers to explore whether low-level environmental toxins such as radiation, lead, and other contaminants could explain this genetic divergence.
The initial phase of the study revealed that the genetic makeup of the dogs in Chornobyl City was remarkably similar to dog populations in Russia, Poland, and other surrounding areas. This similarity allowed the researchers to use the Chornobyl City dogs as a representative control population when comparing them with the dogs living near the power plant.
Understanding Genetic Variants
Earlier research by the team had identified 391 outlier regions across the dogs’ genomes, which revealed significant differences between the two populations. These regions included genes associated with DNA repair, a process potentially influenced by radiation exposure. However, the new study aimed to dig deeper into the genomic data, searching for signs of mutations that could have accumulated over generations as a result of the environmental contaminants in the area.
Megan Dillon, a Ph.D. candidate at NC State and the study’s lead author, explained the approach used to investigate these genetic differences. The team began by analyzing the genetic variations at a broad chromosomal level and then gradually zoomed in, examining smaller genome intervals and even single nucleotide changes. Their primary focus was to uncover any evidence of mutations in the germ line DNA—changes that occur in the DNA of reproductive cells and are passed on to future generations.
The analogy of “zooming in” on a photo helps to understand their methodology: starting with a broad view and gradually narrowing down to capture more detailed information. Breen noted that while high doses of radiation are known to cause instability in the chromosomes, it was unlikely that the dogs’ populations—now 30 or more generations removed from the original dogs present during the 1986 disaster—would show such mutations, unless they provided a survival advantage to the dogs that first survived the radiation exposure. However, the researchers found no such evidence of radiation-induced genetic mutations.
The Role of Selective Pressures
Although the study did not find genetic mutations linked to radiation, it does not rule out the possibility that selective pressures played a role in the differences observed between the two dog populations. Dillon suggested that the genetic traits enabling survival in the aftermath of the disaster may have already been present in the population at the time, and it is possible that these dogs had some inherent resistance to the environmental stresses of the area.
“In human terms, this would be like studying a population that is centuries removed from the one present at the time of the disaster,” Dillon noted. She further speculated that the dogs that survived the initial waves of contamination likely had genetic traits that enabled them to withstand the harsh conditions. Over time, these dogs may have remained genetically distinct from the city population due to extreme selective pressure during the early years after the disaster.
Breen and Dillon emphasized that this hypothesis requires further investigation. The team is now working on exploring how selective pressures, rather than genetic mutations, might explain the differences observed between the two populations of dogs.
Broader Implications for Environmental Contamination
While the study’s primary focus was on radiation and genetic mutations in dogs, it also sheds light on the broader environmental impacts of large-scale disasters, particularly in terms of long-term exposure to a range of toxins. As Norman Kleiman, co-author and professor of environmental health sciences at Columbia University, pointed out, the Chornobyl nuclear disaster did not only release radiation but also many other harmful substances such as heavy metals, lead powder, pesticides, and asbestos. These toxins were spread during the cleanup and remediation efforts over the subsequent three decades.
Although the human population in Pripyat and the immediate vicinity of the NPP was evacuated, thousands of workers continued to engage in the cleanup process and other tasks related to the power plant until the Russian invasion of Ukraine in 2022. Therefore, the potential for environmental toxins to affect both human and animal health remains an important area of research.
By studying the health and genetics of animals such as these dogs, Kleiman argued, scientists can gain valuable insights into the environmental risks faced by people living and working near contaminated areas. The dogs offer a unique opportunity to investigate the effects of prolonged exposure to environmental hazards without the confounding variables associated with human behavior and intervention.
Tick-Borne Pathogens and Environmental Health
In addition to studying genetic mutations, the research team also explored differences in tick populations found on the dogs in Chornobyl City and those near the power plant. Their findings, published separately in Parasites and Vectors, identified variations in the types of ticks and the prevalence of pathogens they carry. These differences likely reflect the different environmental exposures at the two locations, providing further insight into the environmental health risks in the region.
The team’s research on ticks and pathogens highlights the complexity of studying environmental contamination. While radiation is often the focus when discussing the Chornobyl disaster, it is clear that many other toxins, including those found in the biological systems of ticks, can also play a significant role in the health of local wildlife, domesticated animals, and humans.
The Need for Continued Research
Kleiman emphasized the importance of continued research into the environmental health effects of large-scale disasters. “As our societies continue to advance technologically and industrially, it is inevitable that future disasters will occur,” he said. Understanding the long-term health risks of these events, especially when it comes to radiation, heavy metals, and other toxic substances, will be crucial to protecting both human and animal populations in the aftermath of such incidents.
The Chornobyl disaster, which took place nearly four decades ago, continues to be a poignant reminder of the enduring environmental consequences of human activities. This study, along with others on the health of animals and people in the region, underscores the need for more research into the long-term impacts of exposure to radiation and other pollutants. The researchers are hopeful that their findings will inform future strategies for mitigating the health risks of large-scale environmental contamination and provide insights that can help safeguard vulnerable populations worldwide.
References: 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
Megan N. Dillon et al, Contrasting pathogen prevalence between tick and dog populations at Chornobyl, Parasites & Vectors (2024). DOI: 10.1186/s13071-024-06563-4