Saharan dust: the radioactivity does not come from France’s nuclear tests


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, due to the scale of the associated dust deposits on the ground, covering a large part of Western Europe.

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 this event in March 2022. 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 CNRS Terre & Univers laboratories, the University of Oviedo and the laboratory of the Swiss Federal Office for Civil Protection in Spiez, 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 arrive at these results, various types of complementary analysis 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 some 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.

 

Exemple d’échantillon de poussière collecté dans le Nord de la France dans le cadre de l’approche de science participative menée en mars 2022. © LSCE

Example of a dust sample collected in the North of France as part of the participatory science approach carried out in March 2022. © LSCE

 

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 mark expected from French nuclear testing. On the contrary, the dust bears the signature of the global fallout largely dominated by the nuclear tests conducted by the United States and the Soviet Union in the late 1950s and early 1960s, which still leave their mark on soils around the world today.

What’s more, 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 rate1.

At a time when the recurrence of this type of event in Europe is being impacted by 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.

 

More

1 Several orders of magnitude lower than the levels authorised in the European Union.

CNRS Labs

Laboratoire des sciences du climat et de l’environnement (LSCE-OVSQ, CNRS/CEA/CNRS/UVSQ/Université Paris-Saclay)

Géosciences Paris-Saclay (GEOPS-OSUPS, Univ Paris-Saclay/CNRS/Observatoire de Paris-PSL)

Reference

Yangjunjie Xu-Yang et al., Radioactive contamination transported to Western Europe with Saharan dust. Sci. Adv.11, eadr9192(2025).

Contacts

 

Source : CNRS Terre & Univers.

 

Olivier Evrard, Charlotte Skonieczny et Yangjunjie Xu


Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL)