Historical reconstruction of Plutonium contamination in the Swiss-Italian Alps

¹ Institute for the Dynamics of Environmental Processes IDPA-CNR, 30123 Venice, Italy
² Department of Environmental Sciences, Informatics and Statistics, University Ca’ Foscari of Venice, 30123 Venice, Italy
³ Paul Scherrer Institut, 5232 Villigen (PSI), Switzerland
⁴ Laboratoire de Glaciologie et Géophysique de I’Environnement (LGGE), University Joseph Fourier of Grenoble, 38402 St Martin d’Hères Cedex, France
⁵ Centre for Ice and Climate - Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark

^a jacopo.gabrieli@idpa.cnr.it

Abstract

Plutonium is present in the environment as a consequence of atmospheric nuclear tests carried out in the 1960s, nuclear weapons production and releases by the nuclear industry over the past 50 years. Approximately 6 tons of ²³⁹Pu have been released into the environment as a result of 541 atmospheric weapon tests Nuclear Pu fallout has been studied in various environmental archives, such as sediments, soil and herbarium grass. Mid-latitude ice cores have been studied as well, on Mont Blanc, the Western Alps and on Belukha Glacier, Siberian Altai. We present a Pu record obtained by analyzing 52 discrete samples of an alpine firn/ice core from Colle Gnifetti (M. Rosa, 4450 m a.s.l.), dating from 1945 to 1991. The ²³⁹Pu signal was recorded directly, without preliminary cleaning or preconcentration steps, using an high resolution inductively plasma mass spectrometer equipped with a desolvation system. The ²³⁹Pu profile reflects the three main periods of atmospheric nuclear weapons testing: the earliest peak lasted from 1954/55 to 1958 and was caused by the first testing period reaching a maximum in 1958. Despite a temporary halt of testing in 1959/60, the Pu concentration decreased only by half with respect to the 1958 peak due to long atmospheric residence times. In 1961/62 Pu concentrations rapidly increased reaching a maximum in 1963. After the signing of the “Limited Test Ban Treaty” between USA and USSR in 1964, Pu deposition decreased very sharply reaching a minimum in 1967. The third period (1967-1975) is characterized by irregular Pu concentrations with smaller peaks which might be related to the deposition of Saharan dust contaminated by the French nuclear tests of the 1960s.