Radon gas is being described as a “silent killer” due to its colourless, odourless and tasteless nature, and it is the second leading cause of lung cancer worldwide. The Canary Islands are not exempt from this threat, particularly because of their volcanic soils.
The Nuclear Safety Council (CSN) estimates that 19% of the Canary Islands has a high potential for this radioactive gas, which originates from the breakdown of uranium in the ground and rocks. While regions like Galicia and Extremadura face risks from granite, in the Canaries, the danger is linked to volcanic origins, especially in Tenerife and Gran Canaria, according to Candelaria Martín, a researcher at the University of La Laguna.
One factor is geological; these two islands have volcanic rocks with higher concentrations of uranium and radon compared to the basalt typical of other islands. Additional factors include soil permeability, construction types, and home ventilation.
The Tajogaite eruption on La Palma in 2021 disrupted radon emission levels. Martín, along with Pedro Salazar from the Department of Medical Physics and Pharmacology at the university, leads a programme monitoring radon in La Palma. Their results show significant increases in radon concentrations near the volcanic site, although the radiation dose for the population did not pose a major public health risk.
During the eruption, emissions from the crater reached around 30 million becquerels per square metre per day—160 times higher than other active volcanoes in calm periods and up to a million times greater than natural soil levels. The study attributes these spikes to the dynamics of the eruption, new fractures, and increased soil permeability.
In the areas closest to the eruption, about a quarter of the measurements inside buildings exceeded the reference level of 300 becquerels per cubic metre set by health regulations. However, the study’s authors note that weather factors, like weak winds and low thermal inversions, hindered gas dispersion and increased its concentration indoors.
Following the eruption, monitoring will continue until December 2025 at 131 sites between El Remo and Tazacorte. Only five have shown levels above the recommended threshold, all located in Puerto Naos and La Bombilla, except for one in Tajuya. The researchers plan to add more measurement points in the area.
To mitigate radon concentrations, Martín says the most basic measure is to ventilate affected properties. In Puerto Naos, experimental measures are in place that draw out CO2, which also helps reduce radon levels. Experts recommend sealing cracks, using special paints for waterproofing, applying radon barrier membranes, or creating an air gap between the ground and the building’s foundation.
“Radon is everywhere; in varying concentrations, it can be found wherever you measure,” says Martín. Due to this risk, 65 areas in their academic institution are closed. Typically, radon concentrations in the open air reach 10-15 becquerels per cubic metre, but they are higher indoors, particularly in basements, ground floors, and locations like mines or caves.
In addition to monitoring La Palma, Martín is involved with colleagues from the Medical Physics and Environmental Radioactivity Laboratory at the university in a campaign measuring radon in the Cueva del Viento, one of the world’s largest volcanic tubes, located in Icod de los Vinos. Findings suggest that the cave is safe for tourists and that radon levels vary by area and season, with the lowest levels occurring from October to April and the highest from July to October.
