Very low levels of radioactive iodine-131 have been detected in the Czech Republic and elsewhere in Europe but the particles are not believed to pose a public health risk, the UN nuclear agency said on Friday.
The International Atomic Energy Agency (IAEA), the Vienna-based UN watchdog, said it was seeking to determine the source but that it was not believed to come from Japan's stricken Fukushima plant after its nuclear emergency in March.
The Czech Republic nuclear security authority said the source was not believed to be in the country and was not believed to be from a nuclear power plant. It said it could possibly be from the production of radiopharamceuticals.
Iodine-131, linked to cancer if found in high doses, can contaminate products such as milk and vegetables.
The IAEA said the Czech Republic's nuclear safety body had informed it that "very low levels" of iodine-131 had been measured in the atmosphere over the central European country in recent days.
"The IAEA has learned about similar measurements in other locations across Europe," the brief statement said.
"The IAEA believes the current trace levels of iodine-131 that have been measured do not pose a public health risk and are not caused by the Fukushima Daiichi nuclear accident in Japan," it added. "The IAEA is working with its counterparts to determine the cause and origin of the iodine-131."
Iodine-131 is a short-lived radioisotope that has a radioactive decay half-life of about eight days, the IAEA said.
The Czech watchdog said it had detected iodine-131 at a number of monitoring stations since late October. It said there was no health risk from the iodine. "It was detected by our radiation monitoring network, with probability bordering on certainty the source is abroad. It is iodine-131 and we have asked the IAEA if they know what the source could be," Czech State Office for Nuclear Safety chief Dana Drabova told Reuters.
The IAEA said it did not know the source of the iodine-131 and would give more details when available. It did not give details of the other locations in Europe where levels had been detected.
Officials in Spain and Ukraine said they had not detected any abnormal radiation levels and Romania's watchdog said there had been no incident at the country's sole nuclear plant.
In the world's worst nuclear accident since Chernobyl in 1986, a huge earthquake followed by a massive tsunami overwhelmed the Fukushima plant in Japan, causing a reactor meltdown and leakage of radiation, including of iodine.
In the days and weeks after the accident, minuscule numbers of iodine-131 believed to have come from Fukushima were detected as far away as Iceland and other parts of Europe, as well as in the United States.