Saharan dust storms in Europe do not carry radioactivity from France’s Sahara nuclear tests

Saharan dust storms in Europe do not carry radioactivity from France’s Sahara nuclear tests

The Reggane region, where the first four French atmospheric nuclear tests were carried out in southern Algeria in the 1960s, is located in one of the most active dust source regions, responsible for recurrent episodes of massive Saharan dust that reach Western Europe and have a significant impact on air quality. Following a major episode, a participatory scientific campaign was launched using social networks. More than 100 samples were collected in six Western European countries. The results show that the plutonium isotopic signatures of the samples analysed coincide with the signatures of global fallout, largely dominated by nuclear tests conducted by the USA and the former USSR, and are significantly different from those attributed to the French tests. Although radioactive contamination was detected in all the dust samples taken across Europe, their radiocaesium activity did not present a risk to public health in terms of exposure to radioactivity.

Sentinel-3 visible imagery showing Saharan dust over southwest Europe on 15 March 2022. Source: European Union, Copernicus Sentinel-3 imagery

Desert dust is the world’s largest source of aerosols in the atmosphere. These fine earth particles emitted by the wind can be transported over varying distances. Each year, the Sahara and the Sahel provide most of the mineral dust emitted on a global scale, some of which is transported to Europe, mainly in the form of sporadic episodes, generally in early spring. These episodes of Saharan dust darken the sky and have an impact on air quality, which can lead to respiratory problems. In March 2022, an exceptional event occurred, covering a large part of Western Europe, due to the scale of the associated dust deposits on the ground.

Cesium-137 (an artificial radioactive substance emitted by atmospheric nuclear tests and nuclear accidents) was detected by an association in dust deposits collected in France during the March 2022 event. The origin of this substance had been attributed to the French nuclear tests carried out in the Reggane region of southern Algeria in the early 1960s. However, the results of a study conducted by the LSCE, GEOPS, the University of Oviedo and the Spiez laboratory of the Swiss Federal Office for Civil Protection, based on the analysis of samples (110 in all) taken as part of a participatory science approach, show that this is not the case.

To obtain these results, various types of complementary analyses were carried out (analysis of air mass retro-trajectories, elemental geochemistry, granulometry, clay mineralogy and radionuclide activities and their isotopic signature). These were carried out on all or part of the 110 samples collected from the south of Spain to Austria following a call to collect event deposits via social networks during the event and the following days.

The results show that, although the dusts come from a region that partly coincides with that of southern Algeria where France carried out atmospheric nuclear tests in 1960 and 1961, they do not display the radioactive labelling expected from French nuclear testing. On the contrary, the dust shows the signature of the global fallout largely dominated by the nuclear tests carried out by the United States and the Soviet Union in the late 1950s and in the early 1960s, which still leave their mark on soils around the world today.

In addition, the levels of radioactive caesium detected in all the dust samples collected (median of 14 Bq/kg) are well below those permitted in most foodstuffs in the European Union (generally 1000 Bq/kg). In addition, inhalation of this dust exposes people to a negligible radioactive dose rate (several orders of magnitude lower than the levels permitted in the European Union).

While the recurrence of this type of event in Europe is impacted by current climate change, these results are reassuring from a health point of view. This study also highlights the unique opportunity offered by participatory science. In fact, such a large number of samples spread across Europe could not have been collected by research teams alone.

Link to download the article in ‘open access’

Contacts: Olivier Evrard and Yang Xu (LSCE)