In March 2022, the skies over Granada, Almería, Murcia, and Alicante turned an eerie orange as an intense calima spread Sahara dust across large parts of Spain and Europe.
This phenomenon prompted scientists to collect dust samples to investigate the potential presence of radioactive particles.
How a calima occurs
A calima is a weather phenomenon characterised by the presence of dust and sand particles in the atmosphere, often originating from the Sahara Desert. It occurs when strong, dry winds—such as the sirocco or harmattan—lift fine desert dust high into the atmosphere. These winds can carry the dust over long distances, sometimes reaching as far as southern Europe. The suspended particles reduce visibility and often tint the sky in shades of orange or reddish-brown. Calimas are more common in the Canary Islands and southern Spain but can affect large parts of Europe under specific atmospheric conditions.
Findings of radioactive elements
A study published in Science Advances and reported by El País revealed that the dust contained traces of cesium and plutonium—elements associated with nuclear tests. Typically, dust particle concentrations remain below 100 micrograms per cubic metre, but during the 2022 calima, levels soared to 3,100 micrograms in Almería. Given these unprecedented levels, scientists from across Europe gathered samples to assess potential health risks.
The dust was found to contain significant amounts of palygorskite, a clay mineral primarily found in the northern Sahara and commonly used in industrial materials. More notably, isotopes of cesium-137, plutonium-239, and plutonium-240 were detected. Despite these findings, the radiation levels were low enough that the risk to human health was considered negligible.
Investigating the source of radioactivity
The discovery raised questions about the origin of the radioactive particles. Between 1960 and 1961, France conducted four nuclear tests in Reggane, southern Algeria, alongside thirteen underground explosions in the region. These tests have historically caused concern whenever calima events carried dust towards France. However, the particles detected in the 2022 calima were not linked to these French tests.
Germán Orizaola, co-author of the study, explained that each country used distinct “recipes” for their nuclear bombs, allowing scientists to trace the origin of radioactive particles by analysing isotope ratios. The results indicated that the particles likely originated from large-scale nuclear tests conducted by the United States and the Soviet Union, rather than the French tests in Algeria. Despite being carried out far from the Sahara, these tests contributed radioactive particles to the atmosphere that have persisted for over three decades.
Implications for future research
While the immediate health risks are minimal, the findings highlight the long-lasting environmental impact of nuclear testing and the far-reaching effects of atmospheric conditions like calima. Scientists stress the importance of continued monitoring to understand how historical nuclear activity continues to influence current environmental conditions across Europe.