Traces of particulate radioactive iodine (131I) were detected in the European atmosphere in January/February 2017. Concentrations of this nuclear fission product were very low, ranging 0.1 to 10 μBq m-3 except at one location in western Russia where they reached up to several mBq m-3. Detections have been reported continuously over an 8-week period by about 30 monitoring stations. We examine possible emission source apportionments and rank them considering their expected contribution in terms of orders of magnitude from typical routine releases: radiopharmaceutical production units > sewage sludge incinerators > nuclear power plants > spontaneous fission of uranium in soil. Inverse modeling simulations indicate that the widespread detections of 131I resulted from the combination of multiple source releases. Among them, those from radiopharmaceutical production units remain the most likely. One of them is located in Western Russia and its estimated source term complies with authorized limits. Other existing sources related to 131I use (medical purposes or sewage sludge incineration) can explain detections on a rather local scale. As an enhancing factor, the prevailing wintertime meteorological situations marked by strong temperature inversions led to poor dispersion conditions that resulted in higher concentrations exceeding usual detection limits in use within the informal Ring of Five (Ro5) monitoring network.

″Frédéric Joliot Curie National Research Institute for Radiobiology and Radiohygiene POB 101 Budapest H 1775 Hungary

Agenzia Regionale per la Protezione dell'Ambiente Milan 20129 Italy

Bundesamt für Strahlenschutz Freiburg 79098 Germany

Central Laboratory for Radiological Protection Warsaw PL 03 134 Poland

Centro de Investigaciones Energéticas Medioambientales y Tecnológicas Madrid 28040 Spain

Comenius University Department of Nuclear Physics and Biophysics Bratislava 84248 Slovakia

Deutscher Wetterdienst Offenbach 63067 Germany

Health Canada Radiation Protection Bureau Ottawa A L 6302A Ontario K1A 1C1 Canada

Helmholtz Zentrum München German Research Center for Environmental Health Neuherberg 85764 Germany

Institut de Radioprotection et de Sûreté Nucléaire Fontenay aux Roses 92262 France

Institute of Nuclear and Radiological Sciences and Technology Energy and Safety NCSR Demokritos Environmental Radioactivity Laboratory Ag Paraskevi Attiki 15310 Greece

Jozef Stefan Institute Ljubljana 1000 Slovenia

Leibniz Universität Hannover Institute of Radioecology and Radiation Protection Hannover 30419 Germany

National Radiation Protection Institute Prague 140 00 Czech Republic

Norwegian Radiation Protection Authority Svanvik NO 9925 Norway

Pacific Northwest National Laboratory P O Box 999 Richland Washington 99352 United States

Physikalisch Technische Bundesanstalt Braunschweig 38116 Germany

Radiation and Nuclear Safety Authority P O Box 14 Helsinki 00811 Finland

Radiation Protection and Radiochemistry Austrian Agency for Health and Food Safety Wien 1220 Austria

Radioecology and Radon Austrian Agency for Health and Food Safety Linz 4020 Austria

The Henryk Nievodniczanski Institute of Nuclear Physics Polish Academy of Sciences Kraków 31 342 Poland

University of Bremen Institute of Environmental Physics Bremen 28359 Germany

Vinča Institute of Nuclear Sciences Belgrade 11001 Serbia

References provided by Crossref.org

Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017