Multiple European nuclear monitoring agencies have detected higher than normal levels of radioactive isotopes in the atmosphere above Scandinavia and western Russia.
From June 22 to 23, The Comprehensive Test Ban Treaty Organization (CTBTO)—a watchdog group that operates monitoring stations to help enforce nuclear treaties—noticed elevated levels of caesium-134, caesium-137, and ruthenium-103 from its monitoring station in Sweden.
CTBTO Executive Secretary Lassina Zerbo shared a map of the affected region in a tweet and said the isotopes are “associated w/Nuclear fission @ higher than usual levels (but not harmful for human health...these isotopes are most likely from a civil source. We are able to indicate the likely region of the source, but it’s outside the CTBTO’s mandate to identify the exact origin.”
CTBTO did not immediately respond to VICE’s request for comment.
The closest nuclear power plants to the affected area are both in Russia, near its western border. The Leningrad plant operates in St. Petersburg and the Kola plant in Murmansk. A spokesperson for the Rosenergoatom power company, which operates both plants, told Russian news agency TASS that both plants are operating normally and that no leak has been detected on its end.
"Both stations are working in normal regime,” the company told TASS. “There have been no complaints about the equipment’s work."
The CTBTO wasn’t the only monitoring station that picked up on elevated levels of nuclear material in the air. Radiation and nuclear safety authorities in Sweden, Finland, Norway, and the Netherlands all detected radioactive isotopes in the air around the same time in June.
“The detected radioactive substances are artificial. The combination of radionuclides may be explained by an anomaly in the fuel elements of a nuclear power plant,” RVIM, the Netherlands nuclear monitoring agency, said on its website. “The radionuclides travelled from the direction of western Russia to Scandinavia, but no specific country of origin can be pointed out at this moment.”
Nuclear monitoring stations constantly take air, water, and soil samples to check the levels of radioactive material in the environment. What makes this incident so striking is that so many agencies are all reporting the same thing at the same time.
A similar incident happened in 2017 when a large cloud of ruthenium moved across Eurasia. Many separate agencies all came to the same conclusion—that a nuclear accident in Russia released a cloud of radiation which traveled west. At first, Moscow denied that the cloud existed, then switched course and said it existed, but that Russia wasn’t responsible.
The monitoring agencies said there’s no immediate danger from the radioactive isotopes they are currently tracking and that the most likely cause is a contaminated fuel source at a nuclear power plant.
There is no proof that Russian power plants are to blame, but Russia has a history of occluding the truth when it comes to nuclear issues. In August of last year, a nuclear accident at a Russian missile facility killed seven Russians and released nuclear materials into the air. Moscow didn’t publicly acknowledge the incident for two days.
This article originally appeared on VICE US.