A high-resolution spatial map reveals the distribution of soil contamination in Europe by Caesium 137 from nuclear tests and the Chernobyl accident. It’s a radio-element harmful to health but also useful for geological tracing.
Nuclear, radioactivity … words that produce chills in the context of war or environmental disasters. However, radioactivity is naturally present on our planet. We’re all more or less exposed to natural radiation, which poses no risks for the environment, our well-being or our health. It’s exposure to abnormally high radiation that’s the problem, such as in the aftermath of nuclear accidents at Fukushima in 2011 and Chernobyl in 1986.
Nuclear tests and accidents: a question of altitude
What about nuclear testing? In the 1950s and 1960s, many nuclear tests were carried out by France, England, the United States, and Russia. ‘These tests were carried out in a very high layer of the atmosphere and the radioactive elements, like caesium, travelled around the world and fell to the ground with rain in different parts of the world. This isn’t a problem because such fallout isn’t highly radioactive,’ explains Kristof Van Oost, professor and researcher at the UCLouvain Earth and Life Institute. On the other hand, on 26 April 1986, when the Chernobyl nuclear power plant exploded, radioactive elements were propelled into the lowest atmosphere, the troposphere, under the clouds, and fell quickly with the local rains. Thus areas close to the accident were much more affected and contaminated by the radioactive fallout. ‘Caesium, which was present at low altitude, moved with air mass movements immediately after the accident and contaminated the soils in the areas where it rained immediately after. This is what our analyses, published in Scientific Reports, demonstrated, by using maps with greater spatial resolution than previously available
To each its own radioactive signature
Using 12,000 soil samples provided by the European Union Joint Research Centre, Prof. Van Oost and his team looked into the monitoring of the Chernobyl nuclear accident to understand the distribution of radioactive fallout across Europe. The work, funded in part by the FNRS, serves public health, of course, because caesium is toxic, but also research in geomorphology and dating geological strata. ‘Caesium is a tracer that tracks sediment transport, soil erosion, etc.,’ Prof. Van Oost says. ‘For this type of research, it’s important to have good knowledge of radio-elements in the soil. Each nuclear event (nuclear tests, accidents, etc.) has its radioactive signature, which makes it possible to identify the sources of soil radio-elements.
Belgium in the green
Caesium 137 has a fairly short half-life: 30 years. This means that it loses half of its radioactivity after 30 years. The Chernobyl accident therefore reintroduced this tracer into the environment some 30 years after the 1950s and 1960s nuclear tests. In the Scientific Reports study, Prof. Van Oost and his colleagues show that of the Caesium 137 in Europe’s soils, on average, 50% came from nuclear tests and 50% from the Chernobyl accident. The contamination distribution maps show that the data vary greatly from one region to another, with Belgium being in the green and eastern Germany and northern Italy in the red, i.e. highly contaminated. Regarding health monitoring in terms of contamination/exposure/risk level, the radioactive fallout associated with nuclear tests and the Chernobyl accident currently contributes less than 1% of the average exposure dose of a person in France (more information on the IRSN and AFCN websites).