Wed. Apr 24th, 2019

Life makes its way into the radioactive ecosystem of Chernobyl | Science

Life makes its way into the radioactive ecosystem of Chernobyl | Science


It was the second time that a fish had eluded its jaws, but the agile otter did not give up. I kept swimming and looking for the fish trail. The smell of a new dam took her to the shore, where a dead fish lay. An easy snack for the otter, who did not hesitate to give an account of the carrion. He did not notice, but while enjoying his luck, a camera immortalized the moment. Days later, far from there, a scientist nodded satisfied to see the images. Life proliferates in the polluted waters of the Prípiat river.

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The fish had been placed on the river bank by a team of scientists who wanted to see which animals came to the buffet. Otters, American minks and white-tailed eagles They came to eat the fish offered, while the cameras spied on them. Unknowingly, they have become part of an increasingly broad list: the species that live in the Chernobyl Exclusion Zone (ZEC).

After the disaster of April 26, 1986, the USSR established a 30-kilometer security zone around the Chernobyl Nuclear Power Plant. Thousands of people were forced to leave their homes, leaving more than 4,200 kmtwo free of direct human influence. Of those kilometers, slightly more than half belong to Ukraine. The rest are managed by Belarus, which has converted them into the State Radioecological Reserve of Polesia, one of the largest nature reserves in Europe.


One of the otters caught by the trap cameras placed in the Chernobyl Exclusion Zone.see photo gallery
One of the otters caught by the trap cameras placed in the Chernobyl Exclusion Zone.

James Beasley, an ecologist at the University of Georgia, is one of the researchers who is studying how life proliferates in Chernobyl. Together with an international team, he began documenting the animals that inhabit the Radioecological Reserve by studying traces and counting from helicopters. The results were promising and this led them to install trap cameras with odors to attract animals. In 2016 they published their findings: 30 years after the disaster, wildlife abound in the Belarusian Exclusion Zone. The cameras had captured 14 species of mammals, including moose, roe deer, boar, gray wolves, foxes and raccoon dogs. According to Beasley, the data is "the testimony of the resistance of wildlife when they are freed from direct human pressures."

The Ukrainian side is not far behind either. The project TREE (TRansfer - Exposure - Effects) is an initiative of the British program Radioactivity And The Environment. Its main objective is to reduce the uncertainty that exists in estimating the risk to humans and wildlife when exposed to radioactivity. With the help of Ukrainian scientists, between 2014 and 2015, the TREE project installed 42 trap cameras at different points in the ZEC. Birds, deer, squirrels, lynx or wolves were some of the animals that they paraded before the cameras. Also, European bison and Przewalski horses, both species introduced in other areas for their conservation. Even the presence of brown bears was documented in the Ukrainian territory. The Bears have returned to these forests after having been eliminated by humans 100 years ago.

The Bears have returned to these forests after having been eliminated by humans 100 years ago

Looking at the catalog of species, it is tempting to argue that radiation could be a shield to protect wildlife. The animals even seem to develop all their splendor. The rivers around Chernobyl harbor what some qualify as monstrous mutant fish for its large size. But the reality is that these fish are not the result of radioactivity nor will they ever be part of the script of a B-movie. The explanation is very simple: without human pressure the species grow by developing their true sizes. In the words of Jim Smith, professor of environmental sciences at the University of Portsmouth, "this does not mean that radiation is good for wildlife, only that the effects of human life, including hunting, agriculture and forestry, are much worse. "


Wild boars in an abandoned village in the Chernobyl Exclusion Zone.see photo gallery
Wild boars in an abandoned village in the Chernobyl Exclusion Zone.

Science has a good repertoire of papers to show that living exposed to cesium-137 also takes its toll on the fauna. A meta-analysis published in 2016 showed that the radiation in Chernobyl increases the frequency and the degree of cataracts in eyes, decreases the size of the brain, increases the incidence of tumors, affects fertility and promotes the appearance of development anomalies in birds. This study was carried out by researchers from Chernobyl + Fukushima Research Initiative, a research group that uses a multidisciplinary approach to understand the effects of radiation on human health and the environment. Its director is Tim Mousseau, of the University of Carolina of the South; and, together with Anders Møller, of the University of Paris-South, they have directed more than 35 expeditions to Chernobyl and another 16 to Fukushima.

This does not mean that radiation is good for wildlife, only that the effects of human life, including hunting, agriculture and forestry, are much worse

In one of these expeditions, they observed that trees in the ZEC forests can still be found that died on the day of the disaster. After so many years, its trunks seem to stand the test of time. To understand what was happening, they placed hundreds of samples of uncontaminated litter at different points in the ZEC. After nine months outdoors, they collected the samples and measured the weight they had lost. Their results showed that, in the most polluted areas, the decomposition of the leaves was 40% lower than in the one registered in uncontaminated forests.

That is to say, the radiation is preventing the microorganisms from decomposing the dead remains of the plants. This means that the nutrient cycle slows down, making a large part of the nutrients inaccessible to plants and the rest of the food chain. But the lack of decomposition has another, more sinister facet. The accumulation of dead plant material favors forest fires, which in the case of the SAC can spread, through smoke, radiation to other areas. To date, the worst fire that was recorded was in April 2015, when about 400 hectares were burned about 20 km from the nuclear power plant.

The central Chernobyl seen from Pripyat.
The central Chernobyl seen from Pripyat.

The accumulation of dead plant material favors forest fires, which in the case of the SAC can spread, through smoke, radiation to other areas

So, if radioactivity is also primed with animals, plants and microorganisms, why does life claim Chernobyl? The answer must be sought in the capacity that some species have to survive. In the 90s, a team of American researchers analyzed the mitochondrial genes of field mice captured in the ZEC. The rate of mitochondrial DNA mutation in mice living in the contaminated area was higher than in those living in other regions. But even so, walking on the edge of what their species can stand, the mice multiply and survive. In other cases, we must look at the dynamics of the populations that make up a species. For example, the swallows practically disappeared after the accident. It has been the constant drip of new individuals, who arrived migrating from other areas, which has allowed the establishment of new populations. The recolonization would explain the presence of large animals, such as moose or wolves. However, it remains to be seen how the accumulation of cesium-137 particles throughout the trophic chain is affecting them.

But in addition to the capacity for survival and recolonization, we can include in the equation the adaptation of the species. Let's go back to the swallows. In one of the expeditions of Mousseau and Møller, they collected feathers from these birds and sent them to the Spanish researcher Mario Ruiz-González. They wanted to see what kind of bacteria lived in them and, after isolating them, put them to grow under different doses of radiation. The experiments showed that the colonies that grew best were those whose bacteria came from sites with intermediate radiation levels. While bacteria from places with higher or lower levels of radiation had lower growth. In other words, the intermediate doses of radiation seemed to be a selective pressure, which was giving the bacteria the ability to survive in contaminated environments.

The radiation can also alter the mutation rate of the bacteria and make them more virulent, promoting the adaptation of the swallows they live on. In 2017, the Spanish researcher Magdalena Ruiz-Rodríguez published in PLOS ONE, together with Mousseau and Møller, a study showing that the Chernobyl swallows have a greater capacity to defend themselves against bacteria. In this research, the blood plasma of swallows was exposed to twelve species of bacteria. The results showed that individuals living in the most contaminated areas had a greater capacity to defend against bacteria. This adaptation is explained by the natural selection that has been taking place in Chernobyl since the disaster. For years, the mortality of swallows has been high, leaving only individuals who could cope with the most virulent bacteria. According to Magdalena Ruiz-Rodríguez, "there was probably a very intense selection process, and only those individuals who were able to survive the new conditions could stay alive and reproduce."

That life survives a nuclear disaster may seem incredible. But this is how species work: they survive on the basis of trial and error.

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