European researchers have concluded that a radioactive cloud that drifted over Europe in 2017 likely originated in Russia, possibly from a plant that was the site of an infamous nuclear disaster.
Meteorologists and researchers detected the burst of radioactive isotopes in October 2017, and have struggled to determine its origins.
At the time, prevailing winds and other evidence pointed to Russia, but authorities denied responsibility for the release of the ruthenium-106 isotopes. The dispersed isotopes were harmless to human health, but noticeable by monitoring equipment.
In a paper published on July 26 in the journal PNAS, a team of more than seven dozen researchers said they had concluded that the origins of the "sizable, yet undeclared nuclear accident" appeared to be a nuclear reprocessing facility located in the Urals region.
The researchers also said ruthenium isotopes had not been detected in the global atmosphere since the 1986 Chernobyl disaster. They also said that, while the threat to human health in Europe was minimal, there may have been a more serious fallout closer to the origin of the release.
"The Mayak nuclear complex in southern Urals should be considered as a likely candidate for the release," they wrote.
There were no immediate responses to the paper from Russian authorities, and the state-run nuclear company Rosatom did not respond to an e-mail seeking comment.
Mayak was once a major site for processing nuclear fuel for the Soviet Union’s nuclear arsenal, as well as civilian reactors. In 1957, a storage unit at the site containing radioactive waste exploded, sending radioactive waste spewing into the environment.
At the time, the incident was largely covered up by Soviet authorities, but around 10,000 people were ultimately evacuated. Some studies have said hundreds of people may have died from cancer caused by the accident.