Genetic analysis of the dogs near the Chernobyl nuclear power plant in Ukraine shows they are different. But there is no evidence that it is due to radiation. A study of more than 300 wild dogs suggests that genetic relationships change with distance from reactor number 4, which exploded in 1986. However, these differences could be due to causes unrelated to the release of radioactive material or that are harmful in the long run. In fact, the area witnesses a brutal explosion of wildlife.
On April 26, 1986, reactor number 4 of the Vladimir Ilich Lenin power plant, located 17 kilometers from Chernobyl (in the north of the country), suffered the largest nuclear accident in history. For days, large amounts of radioactive material, including cesium-137, iodine-131 and other radionuclides that emit ionizing radiation, were burned and released into the atmosphere. Weeks later, the Chernobyl Exclusion Zone (ZEC) was established in a radius of 2,600 km², from which all residents were evacuated. As part of the containment program, Ukraine’s Interior Ministry, then within the Soviet Union, ordered the euthanasia of all pets. But some dogs escaped the purge.
How did the dogs fare in such an initially adverse environment? As for the number, it seems so good. There are currently more than 800 wild dogs in the region, according to the Chernobyl Dog Research Initiative census. For Tim Mousseau, a biologist at the University of South Carolina (USA) and senior author of this new study, “everything we learn about how they survive in this environment is of direct relevance to people in Chernobyl and other radioactive environments.” . To do this, they took blood samples from 302 samples. Almost half live around the power station and Prípiat, the nearest town, which has now become a ghost town. Another 150 are from Chernobyl itself, 17 kilometers from ground zero. And the remaining 16 roam Slavutich, also a Ukrainian population, but 45 kilometers away, already outside the exclusion zone.
The blood from the samples allowed them to map genetic similarities. The results of this work, published in the journal Science Advances, indicate that these dogs are genetically different from other dogs from different countries analyzed for comparison. They also come from stray dogs caught in Vinnitsa, a Ukrainian city located 350 kilometers southwest of Chernobyl. The study goes even further: the studied animals are divided into three large populations from a genetic point of view, and belonging to one or another group depends on the distance from the plant. This suggests that radiation exposure may have affected the genes of some more than others. But for the time being there is no data that this happened.
In principle, ionizing radiation causes, among other things, oxidative stress, cell and DNA damage, which is strongly dependent on the dose and duration of exposure. However, the authors of the work did not publish data on changes in dogs, especially when they observed changes in mutation rate. Mousseau had been going to Chernobyl for twenty years (until war broke out), almost as long as he had been warning of the damage the radiation would do. “We have conducted preliminary studies on the external and internal doses of these dogs, and we have an article under review that covers part of this question,” Mousseau clarified in an email.
One of the problems with this biologist’s thesis, an expert on the effects of the environment on genes, is that it spills over into reality. After the catastrophe of 1986, which must have cost the lives of countless creatures, the exclusion zone has almost become a paradise on earth. After the evacuation of the Adams and Eves and the abandonment of the fields, flora and fauna in the entire area around the power plant have developed magnificently. High-impact work published in 2015 showed that while the presence of large mammals decreased in the first few years after the accident, it recovered immediately. Aerial surveys conducted since the 1990s show that moose, deer, roe deer and wild boar populations were similar to those in other regions. And without humans, the wolf population had increased sevenfold, with the highest population density in Europe.
“Most research clearly shows that many organisms living in the most radioactive regions of the Exclusion Zone have serious injuries of many kinds.”
Tim Mousseau, biologist at the University of South Carolina, USA
“A lot of studies are now suggesting that in the parts of the Exclusion Zone that aren’t particularly radioactive, many animals did very well, particularly those hunted in other areas outside the zone,” Mousseau concedes. “However, most research clearly shows that many organisms living in the most radioactive regions of the exclusion zone have serious injuries of many kinds,” he adds. So we have to wait for the second part of his investigation, already with the data on the radioactive load, to find out how the dogs are doing.
Jim Smith is a biologist at the University of Portsmouth (UK) and, like Mousseau, has been traveling to Chernobyl for several years. He is the lead author of this work on wolves and other large mammals and has participated in various censuses of wildlife in the region. “In our 2015 study, we could not find evidence linking mammalian populations to radiation dose and found mammal population densities similar to other nature reserves in Belarus,” whose border is less than 20 kilometers away. “I haven’t investigated their situation since, but other scientists have found similar results,” he adds.
“In the absence of human pressure, wildlife thrives despite the potential impact of chronic low-level radiation”
Jim Smith, Biologist at the University of Portsmouth, UK
For Smith, the genetic part of Mousseau’s research is impeccable, but he denies that it can be linked to radiation exposure. “Any radiation (including natural radiation from rocks, X-ray scanners, cosmic rays…) can damage DNA, so radiation at some Chernobyl hotspots certainly affects animal genetics. . But the question is to what extent it’s happening and whether it’s having a significant impact on the population,” he says. The problem is that there are many other environmental factors, so “even in the most heavily contaminated areas, it’s difficult to clearly determine the effects of radiation on individuals,” he adds. And he concludes: “I realize that without human pressure, wildlife thrives despite the potential impact of chronic low-level radiation.”
Like Mousseau and Smith, many other scientists of various disciplines from around the world frequently visit Chernobyl, unfortunately the largest experiment to study the effects of radiation on life. One of them is the biologist Germán Orizaola from the University of Oviedo, who has a laboratory in the city thanks to a collaboration with the Chernobyl Center for Nuclear Safety, Radioactive Waste and Radioecology. A few years ago he published a paper on Przewalski’s horses. About 30 of these wild horses were initially released into the exclusion zone in 1998, 12 years after the explosion, without much ecological logic. In the article, Orizaola wrote: “Initial predictions indicated that the area would be uninhabitable for more than 20,000 years due to radioactive contamination. It was assumed that Chernobyl would become a desert for life. However, there are currently around 200.
At right, a San Antonio frog caught outside the restricted zone. On the left a frog of the same species (‘Hyla orientalis’) from a pond near reactor number 4. Germán Orizaola
The goal of Orizaola is actually the study of amphibians, in particular the San Antonio frog, a small frog with an intense light green color. In a study published in 2020 along with his colleague Pablo Burraco, they found that there the closer the frogs are to the power plant, the darker the frogs are, to the point of those in nearby ponds being almost black. Like Mousseau in his study with the dogs, Orizaola and Burraco measured ambient radiation. But what Mousseau didn’t do (at least he didn’t publish it), and they did, was measure the radiation present inside the animals, specifically the presence of cesium in the muscles and strontium in the bones. They found no connection between the coloration of the frogs and the currently absorbed radiation dose.
In a statement from the University of Oviedo, they explain the apparent puzzle: “These results suggest that the differences in coloration are not due to current radiation exposure and point to the effects of historical exposure on these populations.” In other words, the dark coloring of the Chernobyl frogs would be because they were initially exposed to very high levels of radiation, not from contemporary frogs but from those living there in 1986. The more or less strong melanin protects against radiation, so the darker amphibians would have suffered less from the radiation released by the accident and would have a greater chance of survival.
“In dogs or other animals, it is crucial to determine the radiation exposure,” Orizaola recalls, and is one of the critics he voices of the study of the Chernobyl dogs. But it has others. “The original number of those who survived the hunt that began after the explosion is unknown, which introduces the bias of the founding dogs,” adds the biologist. A very small initial population favors genetic differentiation. “Furthermore, the 1986 irradiation has nothing to do with the current one. It has been reduced by 90% and the most dangerous compounds have disappeared”. His final verdict on the study of dogs can be summed up in one sentence: “They are as different as the dogs of Warsaw are from those of Kraków,” he says. Both Polish cities are relatively far from the center.
The ecologist at the National Museum of Natural Sciences, Ismael Galván, worked with Mousseau on the study of the Chernobyl birds. This resulted in a paper published in 2014 with such interesting conclusions that it caused quite a stir at the time. They studied the effects of radiation on 16 species of birds. Literally, their conclusion is this: “Birds improve their antioxidant levels and body condition, and decrease their levels of oxidative stress and DNA damage with the increase in background radiation they are exposed to at Chernobyl.” That is, the birds shine from the radiation exposure not to be affected. As Orizaola also said, “Chernobyl is experiencing an explosion of life,” says Galván now.
Regarding the dogs, Galván concedes that the data shows that they are genetically different, so he doesn’t see the radiation hypothesis as problematic. “Genetic differentiation could be the basis for the adaptations we’ve seen in birds,” he says. “It is likely that the animals adapted to low but chronic levels of radiation over time, leading to physiological adaptation,” he adds. The problem is that there is a lack of data on canine physiology.
The key might lie in a word you need to look up in the dictionary: hormesis. “When an organism is exposed to something harmful that the metabolism needs to fight or process [un agente químico, un daño ambiental, la radiación…], the final state can be better than the initial state,” explains Galván. It’s the scientific version of what doesn’t kill, but makes you fat. “It’s obvious that radiation isn’t good, but animals have the ability to adapt over generations,” says this researcher.
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