MOSCOW-Russian scientists have said radioactive pollution detected in Europe in September was not linked to one of the country’s nuclear facilities and speculated that a satellite could be the cause. Russia’s Rosatom nuclear agency in November asked scientists at the Nuclear Safety Institute to look into the origin of “extremely high” readings of radioactive ruthenium reported in some parts of Russia by the meteorological service. Results shown to journalists in Moscow on Friday did not pinpoint the source of the pollution, but scientists dismissed suggestions that Mayak, a facility in the Russian Urals that processes spent nuclear fuel, was the origin. “Our conclusion is that Mayak could not be the source of the radioactive ruthenium-106,” said Vladimir Boltunov, who headed the investigation.

He said medical tests showed no changes in the bodies of the Mayak staff and added that “between August 1 and November 30, there was no accident or problem” at the facility.

“While we still cannot say with certainty what caused the release, we cannot rule out that a space object such as a satellite or a fragment of one containing Ruthenium-106 re-entering the atmosphere could have been such a source,” a statement by the scientists said.

France’s Institute for Radiological Protection and Nuclear Safety (IRSN) issued a report in November saying the isotope Ruthenium-106 had been detected in France between September 27 and October 13.

The institute declined to comment on Russia’s findings on Friday but its deputy director Jean-Marc Peres previously told AFP that the satellite version is “very unlikely.”

Russia’s meteorological service said in late November that “extremely high” levels of Ru-106 were detected by weather stations near Mayak, in Russia’s Chelyabinsk region.

Ruthenium-106 is a product of splitting atoms in a reactor, and is also used in certain medical treatments. It does not occur naturally.

The commission on Friday said the pollution was not caused by a nuclear power plant or a medical facility, reiterating that the levels detected in Russia were not dangerous to human health.

Russian Greenpeace however said in a statement that the authorities “must investigate the incident so that in the future it does not lead to more serious consequences and to the covering-up of important information.”

The commission’s report “does not look like an investigation into the source of pollution,” it said.

Greenpeace also launched a petition to Russia’s prosecutor general demanding a “comprehensive” probe into the incident.