Plutonium and Cesium inventories in European topsoils

Global nuclear weapon testing and the Chernobyl accident have released large amounts of radionuclides into the environment. However, to date, the spatial patterns of these fallout sources remain poorly constrained. Fallout radionuclides (137Cs, 239Pu, 240Pu) were measured in soil samples (n = 160) collected at flat, undisturbed grasslands in Western Europe in the framework of a harmonised European soil survey. We show that both fallout sources left a specific radionuclide imprint in European soils. Accordingly, we used plutonium to quantify contributions of global versus Chernobyl fallout to 137Cs found in European soils. Spatial prediction models allowed for a first assessment of the global versus Chernobyl fallout pattern across national boundaries. Understanding the magnitude of these fallout sources is crucial not only to establish a baseline in case of future radionuclide fallout but also to define a baseline for geomorphological reconstructions of soil redistribution due to soil erosion processes.

An international group of scientists, including he Joint Research Centre (JRC), the Laboratoire des Sciences du Climat et de l'Environnement (LSCE - CEA/CNRS/UVSQ, Université Paris-Saclay), the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL/ETHZ), the University of Basel (Switzerland), the Metropolitan State University of Denver (Colorado, USA), Earth and Life Institute, UCLouvain, Louvain‑La‑Neuve (Belgium) and the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture (Austria) used a new method to refine the map of caesium and plutonium radionuclide concentrations in soils in Western Europe. Using the LUCAS topsoil, the scientists traced the sources of the deposition of these radionuclides between 1960 and 2009, based on the isotopic signature of their fallout and in particular the caesium/plutonium ratio. This study was published in Scientific Reports inJuly 2020. This group has developed a new reference map of caesium and plutonium inventory levels in France and several neighbouring countries (Switzerland, Italy, Germany, Belgium). These two radionuclides were released during the global nuclear weapon testing, particularly in the 1960s, but also during the Chernobyl accident in 1986. 

The data collected, made available to the scientific community and the public, are useful for establishing a reference base in the event of possible future fallout of radionuclides, but also for use in new studies, particularly in geomorphology. They will, for example, allow the reconstruction of soil erosion rates since the 1960s in areas of Europe where there have been major landscape changes. These maps are based on a new calculation method, namely the use of the caesium/plutonium ratio. It also has a better spatial resolution (one value every 500 metres) than previous reference maps, thanks to the use of spatial multi-parameter models (GAM) to calculate the value at any point in the study area.

The researchers used 160 samples from a LUCAS-topsoil database (survey: 2009). These samples were taken from soils under grassland, which have remained stable since the 1960s (absence of erosion and accumulation) and are representative of the variability of rainfall conditions observed in the countries covered by the study. The radionuclides found in these samples, caesium and plutonium (137Cs, 239Pu, 240Pu), left a specific footprint in European soils. Indeed, in the countries covered by the study, the plutonium came exclusively from nuclear weapon tests. As for caesium, it is the result of both nuclear tests and the 1986 Chernobyl accident. The relationship between caesium and plutonium is therefore different depending on whether it originates from nuclear weapon tests or the Chernobyl accident. It is this relationship that has enabled researchers to trace the origin of these artificial radionuclides deposited on European soils.

 

Baseline inventories of Caesium 137 (0-20 cm) topsoil (Bq m-2) - corrected for radioactive decay as of August 1, 2009, estimated using a generalized additive model with 500 m resolution. In the study area, areas above 1000 m were masked out (white). Baseline stocks of Plutonium 239+240 in the topsoil (0-20 cm) (Bq m-2) are estimated with an additive model with a resolution of 500 m. In the study area, areas above 1000 m elevation were masked out (white). 

 

Publication - References

Reference: Meusburger, K., Evrard, O., Alewell, C., Borrelli, P., Cinelli, G., Ketterer, M., Mabit, L., Panagos, P., van Oost, K., Ballabio, C. 2020. Plutonium aided reconstruction of caesium atmospheric fallout in European topsoils. Scientific Reports 10: 11858. https://doi.org/10.1038/s41598-020-68736-2

Data

The data of this study are available here

 

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Title: Caesium-137 and Plutonium-239+240 in European topsoils
Resource Type: Datasets, Soil Threats Data
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Country: Italy
Year: 2020
Publisher: European Commission, Joint Research Centre (JRC)
Language: en
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