Environmentalists say the latest flooding may have sent radioactive substances into the river, potentially affecting hundreds of thousands of people living near the banks of the Tobol downstream. State nuclear agency Rosatom, whose subsidiary operates the mines at the Dobrovolnoye uranium deposit, denied that its mining facilities were impacted by the flood.

The isotope measured in air in Tromsø for now is unknown. The isotope comes from a nuclear reactor, and is used in medial diagnostic.

Finland says the low concentrations of radioactive material found in air samples pose no danger.

Invisible for humans, but detectable for radiation-filters. A cloud with tiny levels of radioactivity, believed to originate from western Russia, has been detected over Scandinavia and European Arctic.

Japan was filled with scenes of desperation a day after an 8.9-magnitude quake, as survivors called for help and rescuers looked for people buried in rubble.