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Tracing the radioactive fallouts back to global nuclear weapon testing and the Chernobyl nuclear power plant disaster, an international group of scientists has mapped their residual presence in Western European soils.
These maps of Caesium and Plutonium radionuclides serve both as a reference to model fallout patterns and to help reconstruct soil erosion rates since the 1960s in areas of Europe that have seen to major landscape changes.
The first artificial fallout radionuclides were released into the environment almost 80 years ago, with the explosion of the first atomic bomb in New Mexico in July 1945.
Almost 80 years on, traces of fallout radionuclides from the atmospheric nuclear weapons tests of the mid-1950s to 1980, and the Chernobyl disaster of 1986, can still be detected in measurable quantities in the upper layers of soil in Europe.
These mostly concern the main long-lasting radionuclides, i.e. caesium-137 (137Cs) and plutonium isotopes such as plutonium-239 (239Pu) and plutonium-240 (240Pu).
Their distribution is based on the patterns of precipitation (rain and snow) that brought the fallout from the stratosphere to Earth.
This study, published in Scientific Reports, set out make an inventory of radioactive fallout at the continental scale, by estimating and analysing the patterns of global fallout, Chernobyl and total 137Cs and 239+240Pu fallout across national boundaries.
It focused on a selection of soil samples collected in France, Belgium, Southern Germany, Switzerland and Northern Italy, to cover regions assumed to have received variable levels of Chernobyl radionuclide fallout.
The authors used gamma- and mass spectrometry to measure the radionuclide activities of the fallout radionuclides 137Cs, 239Pu, 240Pu in 160 topsoil samples that had been collected from flat, undisturbed grassland areas in Western Europe as part of the Land Use/Cover Area frame Survey (LUCAS) - a pan-European topsoil survey managed by the JRC.
Plutonium was found to originate exclusively from the nuclear tests, while caesium was the result of both nuclear tests (particularly from the 1960s) and the 1986 Chernobyl disaster.
As the global and Chernobyl fallout sources were found to leave a specific radionuclide imprint in European soils, the authors used plutonium to quantify how much each contributed to the 137Cs found in European soils.
This new methodology, based on new laboratory analysis of soil samples and advanced modelling techniques, allowed the authors to refine the earlier maps of caesium and plutonium radionuclide concentrations in soils in Western Europe, and make it possible to evaluate global fallout patterns and study soil erosion.
Caesium (137Cs ) is a well-established tracer of soil erosion.
However, given its short half-life of 30 years, it may in the future be replaced by plutonium-239 (239Pu) and plutonium-240 (240Pu), which have half-lives of 24,100 and 6,560 respectively.
The expanding use of this tracer would give the 239+240Pu baseline further relevance.
The current research therefore provides a unique database for reconciling local investigations such as soil erosion studies conducted on individual hillslopes or catchments with European-wide homogeneous sample banks.
 E.g. Atlas of caesium deposition on Europe after the Chernobyl accident, Published: 2001-05-17,
Radioactivity measurements in Europe after the Chernobyl accident. Part II, Fallout and deposition, Published: 1992-09-24;
Atlas on caesium contamination of Europe after the Chernobyl nuclear plant accident, Published: 1996-01-16