--- that radioactive Iodine-131 had been observed across much of northern and central Europe. Since the isotope has a half-life of only eight days, the detection was an indication of a rather recent release. As the Barents Observer added, "where the radioactivity is coming from is still a mystery."
The emission was rumored to have originated close to the Arctic circle, with some speculating that a nuclear test of emergency had taken place in Russia in January and the fallout then spread to Norway and onward to Europe:
"Iodine-131 a radionuclide of anthropogenic origin, has recently been detected in tiny amounts in the ground-level atmosphere in Europe. The preliminary report states it was first found during week 2 of January 2017 in northern Norway. Iodine-131 was also detected in Finland, Poland, Czech Republic, Germany, France and Spain, until the end of January", the French Institute de Radioprotection et de Süreté Nucléaire wrote in a press release.