An international consortium of scientists has specified a map of concentrations of cesium and plutonium radionuclides in soils in Switzerland and several neighboring countries. Using an archive of European soil samples, a team of researchers led by Catherine Meisburger from the University of Basel was able to track down the sources of radioactive fallout between 1960 and 2009. This study was published in the journal Scientific Reports.
On the new map of radioactive contamination of the soil, there are not only Switzerland but also several neighboring countries – France, Italy, Germany and Belgium. The map is based on a new calculation method, namely the use of the ratio of cesium to plutonium. These two radionuclides were released during military nuclear tests in the 1960s. Additional cesium fell into some countries during the Chernobyl accident in 1986.
Scientists have created a new map to provide a basis for assessing soil loss after anthropogenic release of radionuclides. For this, it is important to know the proportion of radioactive fallout from Chernobyl.
The collected data provided to the scientific community and the public is useful for creating a reference base in case of possible future fallout of radionuclides. They are also useful for use in new research, especially in geomorphology. Data, for example, will restore soil erosion rates since the 1960s in areas of Europe where major landscape changes have occurred.
Researchers at the consortium have used 160 samples from a bank of European soil since 2009.
The radionuclides found in these samples – cesium and plutonium (137 Cs, 239 Pu, 240 Pu) – have left a special mark in European soils.
In the countries that participated in the study, plutonium was obtained solely from nuclear tests. As for cesium, this is the result of both nuclear tests, especially in the 1960s, and the accident at the Chernobyl nuclear power plant in 1986. Therefore, the relationship between cesium and plutonium is different depending on whether it is a nuclear test or an accident in Chernobyl. It was this relationship that allowed researchers to trace the origin of these artificial radionuclides deposited on European soils. Unlike the previous map, now scientists can distinguish between sources of radioactive fallout.