The faults of Etna represent a triple danger for the populations: they generate earthquakes, fracture the soil and give off radon, a carcinogenic gas which can accumulate in houses making them unhealthy. The study, signed by INGV, was published in the international journal "Frontiers in Public Health"
For many years, the National Institute of Geophysics and Volcanology (INGV) has been analyzing radon throughout the country, a carcinogenic gas that the World Health Organization (WHO) places in "group 1", i.e. among the most dangerous for human health.
A particular territory is that of Etna, on whose flanks numerous faults emerge which have a peculiarity: they intensely fracture the surrounding rocks, significantly increasing their permeability. This allows fluids and gases present in the subsurface to move more freely in those fractured areas, reaching the surface more easily. Among these gases, radon also emerges on the surface.
INGV monitors radon on Etna 24 hours a day through a network of sensors located in the ground in key areas to interpret volcanic and seismic activity, comparing this data with the numerous other signals coming from the dense monitoring networks of the Etna Observatory (INGV -OE).
Since 2015, however, radon analyzes have also been performed in the air and, in particular, "indoor", i.e. inside homes to verify whether the gas, which is not perceptible to our senses since it is odourless, colorless and tasteless, assumes concentrations dangerous to human health.
The first results of indoor radon measurements have just been published in the international journal Frontiers in Public Health - Environmental Health, in a scientific article entitled "Preliminary Indoor Radon Measurements Near Faults Crossing Urban Areas of Mt. Etna Volcano (Italy)", signed by Marco Neri, Salvatore Giammanco and Anna Leonardi.
For three years, continuous measurements were recorded by twelve sensors located in seven buildings located on the southern and eastern slopes of the volcano, in the territories of Giarre, Zafferana Etnea, Aci Catena, Aci Castello and Paternò.
Continuous long-term monitoring of indoor radon has allowed researchers to "purify" the radon concentration signals from the variations induced by environmental conditions, which are in turn linked to the changing seasons.
The sensors have detected average annual concentrations often exceeding 100 Bq/m3 (Bequerel per cubic meter), which corresponds to the first level of concern for average annual exposure recommended by the WHO. In some cases, this average concentration was greater than 300 Bq/m3, with peaks exceeding 1000 Bq/m3 recorded for many consecutive months. These data complete the surveys of radon concentrations measured in the soils of Etna in past years, which have shown values ranging from a few thousand to over 70.000 Bq/m3.
The study also documents that the houses with the highest presence of radon inside them are located near active faults. In other words, the closer the monitored houses were located to the faults, the higher the concentration of radon inside them was.
This data confirms, once again, that the danger of the Etna faults is given not only by their seismogenicity but also by their permeability to gases, allowing the ascent of radon.
Ultimately, the article published in Frontiers in Public Health documents a first continuous and multi-year sampling of indoor radon, even if it concerns a limited number of homes. However, the collected data highlight a potential problem for the health of the Etna population, which amounts to almost one million people, and therefore it seems appropriate and useful to deepen and extend this monitoring to a larger sample of buildings.
Overall, therefore, a general picture that deserves the attention of researchers who are concerned with assessing the healthiness of inhabited environments, also considering that the recent earthquake of December 26, 2018, heavily affecting the south-eastern slope of Etna, has highlighted once again the vulnerability of the Etna area and its exposure to natural phenomena of various types.
picture 1 – Schematic structural map of Etna, with the main urban areas highlighted (in light grey). The small blue circles indicate the radon measurement sites. Contour lines are represented in metres. Top left, one of the radar meters used to measure indoor radon.
picture 2 – Fracture of the soil (co-seismic faulting) formed during the earthquake of 26 December 2018 in Fleri, in the territory of Zafferana Etnea (CT). The blue arrows schematize the behavior of radon (Rn), which rises more easily from the subsoil to the surface through rock fractures.
picture 3 – Fracture of the soil at the point where the Pernicana Fault cuts the road linking the towns of Milo and Linguaglossa, on the eastern side of Etna. The photo was taken on the morning of 27 October 2002, a few hours after the start of the lateral eruption which would have destroyed the tourist resort of Piano Provenzana. The blue arrows schematize the behavior of radon (Rn), which rises more easily from the subsoil to the surface through rock fractures.
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