34 years have passed since the accident at the Chernobyl nuclear power plant (Ukraine). This accident, the largest in history in a nuclear installation, led to the creation of a 4 700 square kilometer Exclusion Zone between Ukraine and Belarus. A total of 350,000 people were evacuated from that area.
Initial predictions indicated that, due to radioactive contamination, the area was to be uninhabitable for more than 20,000 years. Chernobyl was thought to become a desert for life.
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- Life makes its way in the Chernobyl radioactive ecosystem
Three decades later, numerous studies have indicated that Chernobyl lives a diverse and abundant animal community. A large number of threatened species at national and European level today have their refuge in the Chernobyl Exclusion Zone.
A clear example of the fauna situation in Chernobyl is that of Przewalski's horses.
The existence of wild horses in the steppes of Asia was known in the west since the 15th century. But it was not until 1881 when the species was formally described to science from a skull and skin collected by Russian colonel Nikolai Przewalski. This is how the horses known as takhi ("sacred") in Mongolia were renamed Przewalski's horses ( Equus ferus przewalski ).
For a long time they were considered the only wild horse in the world. However, recent studies have indicated that they are feral forms descended from the first horses domesticated by the Botai people in northern Kazakhstan 5,500 years ago.
In Colonel Przewalski's time these wild horses were already rare in the steppes of Mongolia and China. Overgrazing and hunting for consumption by human populations caused its final decline. The last wild specimen was observed in the Gobi desert in 1969.
The captive population did not go through a very positive situation either. In the 1950s, only 12 individuals survived in European zoos. However, from them a captive breeding program began that has managed to rescue the species from extinction.
Today the population reaches 2,000 individuals. Several hundred live in freedom in the steppes of Asia and different areas of Europe. Among them, to the surprise of many, in Chernobyl.
At the time of the accident at the nuclear power plant there were no Przewalski horses in Chernobyl. It was not until 1998 when the first 31 individuals arrived in the Exclusion Zone. They were 10 males and 18 females from the Askania Nova nature reserve in southern Ukraine, and 3 males from a local zoo.
After high mortality associated with transfer and release, the high birth rate brought the population to 65 individuals in just five years. The intense poaching between 2004 and 2006 decimated the population. Only 50 individuals survived in 2007.
Intense protection measures have meant that just 20 years after his arrival in Chernobyl his number has multiplied by five. The most current census, carried out by local scientists in 2018, revealed that about 150 animals live in the Ukrainian part of the Exclusion Zone. Horses are grouped into 10 to 12 family herds, plus two groups of males and some solitary individuals. In 2018 at least 22 foals were born in the Exclusion Zone. Some have moved further north and have already settled in Belarus.
The photo-trapping cameras installed throughout the Exclusion Zone have shown that, despite being a species associated with the steppes, in Chernobyl these horses use the forest with great frequency. This includes the famous "red forest", one of the most radioactive areas on the planet.
Recent fires in Chernobyl have severely affected some of the locations used by horses in the Exclusion Zone. It will now be necessary to evaluate the effect that these fires will have on the conservation of the species in the area.
The lessons of the Chernobyl horses
The introduction of Przewalski's horses to Chernobyl has been a success. Several lessons can be drawn from this success.
The case of Przewalski's horses reflects once again that, in the absence of humans, Chernobyl has become a haven for wildlife. This should lead us to reflect on the impact of human presence on natural ecosystems. With no human activity around, even with radioactive contamination, the great fauna thrives.
Other areas affected by radioactive contamination, such as that derived from the accident at the Fukushima plant (Japan) and from the tests of atomic bombs on the Pacific atolls, also maintain a high diversity of fauna. Perhaps we should reconsider our vision of the medium and long-term impact of radioactivity on the environment.
In any case, we need to better understand the mechanisms that allow fauna to live in areas with radioactive contamination. Many questions remain to be answered. Are living Chernobyl organisms exposed to less radiation than expected? Does this exposure cause less harm? Do organisms have more effective than expected mechanisms for repairing cellular damage caused by radiation?
To answer these questions we need more science. In September, we hope to start working with Przewalski's horses in Chernobyl, trying to unravel the mysteries that make this species and many others thrive in the Exclusion Zone.
Germán Orizaola is a researcher at the Ramón y Cajal Program, University of Oviedo
