For its part, the Swiss Federal Office of Public Health (FOPH) gave its first results of measurements indicating "low levels of radioactivity in the air". These measurements "revealed traces of ruthenium-106, a radioactive element with a half-life of 373.6 days, in aerosols taken from Cadenazzo, Ticino, between 25 September and 2 October 2017. The concentration of ruthenium 106 amounts to about 40 micro-Bq / m3, which is 17 000 times lower than the limit of air emissions set for this radionuclide in the Radiation Protection Ordinance." Since October 3, 2017, IRSN has mobilized all its measurement stations for atmospheric monitoring and undertook the analysis of their filter samples [1]. Analysis of the filters at the Orsay (91) and Grenoble (38) stations gives results of less than 50 micro-Bq / m3. It should be noted that the weather conditions of the last 48 hours did not favor the transfer of air masses from Eastern Europe to Western Europe. On the basis of the weather conditions of the last days, retro-trajectory calculations are under way, to try to determine the origin of this air pollution. The very low levels of atmospheric contamination of ruthenium 106 observed to date by European monitoring networks have no environmental or health consequences. Nevertheless, IRSN maintains a watchful vigilance on this presence of ruthenium in the air.