During June, small levels of several radioisotopes were measured in the air above Europe. Stations in Estonia, Finland, and Sweden detected cesium-134, cesium-137, cobalt-60, and ruthenium-103. The concentrations were only a few microbecquerels per cubic meter of air and posed no danger to people or the environment, according to local officials. The isotope mix suggests that the source was a nuclear power plant, and the release could have happened during normal operations rather than in an accident, says Georg Steinhauser of Leibniz University Hannover. On June 27, the International Atomic Energy Agency contacted other countries in the region for more information. So far, no other countries have measured elevated radioisotope levels or reported releases from their plants. Using the data from the Scandinavian stations, researchers at the Dutch National Institute for Public Health and the Environment calculated that the radionuclides entered northern Europe from the southeast, but they did not make any final conclusions about the origin of the nuclides. In 2017, radioactive ruthenium-106 was detected in the air across Europe. The radioisotope was present at high enough levels that scientists were able to reconstruct the origin of that plume, but the smaller amounts measured this time may make that impossible.