From ENE News
February 20, 2017
The Aviationist, Feb 19 2017 (emphasis added): U.S. Air Force deploys WC-135 nuclear sniffer aircraft to UK as spike of radioactive Iodine levels is detected in Europe… Along with monitoring nuke testing, the WC-135 is used to track radioactive activity as happened after the Chernobyl nuclear plant disaster in the Soviet Union in 1986 and Fukushima incident back in 2011… As of yet, there has been no official statement from the U.S. military about the reasons why such nuclear research aircraft was deployed there. However, many sources suggest the aircraft was tasked with investigating the spike in Iodine levels detected in northern Europe since the beginning of January… no one seems to know the reason behind the released Iodine-131…
Barents Observer, Feb 19, 2017: … radioactive Iodine-131 of unknown origin was in January detected over large areas in Europe. Since the isotope has a half-life of only eight days, the detection is a proof of a rather recent release. Where the radioactivity is coming from is still a mystery… Iodine-131 in the air could come from an incident with a nuclear reactor… Someone out there knows why the radioactivity was spread over larger areas of Europe… Nuclear installations [where] radioactivity was first discovered, includes nuclear power plants in Finland, Sweden and Russia… The source could as well come from even further away installations.
IRSN (France’s Radioprotection and Nuclear Safety Institute), Feb 13, 2017: Iodine-131 (131I), 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. Iodine-131 is a radionuclide with a short half-life (T1/2 = 8.04 day). The detection of this radionuclide is proof of a rather recent release… the origin of which is still unknown… Lead-210 [concentration detected by IRSN peaked at 1600 µBq/m3 in January, four times higher than the usual mean value]… It must be pointed out that only particulate iodine was reported. When detectable, gaseous iodine is usually dominant and can be estimated to be 3 to 5 times higher than the fraction of particulate iodine. In France, particulate 131I reached 0.31 µBq/m3 and thus the total (gaseous + particulate fractions) can be estimated at about 1.5 µBq/m3.
See map of 131I detections here