Radon (222Rn) in volcanic islands (Azores): Implications for public health

Radon (²²²Rn) is a noble gas that results from the radioactive decay chain of ²³⁸U. As the only gaseous element of this decay chain is the element with more mobility and can be released from the rocks and soils into the atmosphere. In outdoor environments the presence of this gas normally does not pose a problem for public health, however when it accumulates inside buildings it can represent a threat for human health. Being a radioactive gas, the radiation released can damage the lung cells and, in certain conditions, the damage can be so severe that can lead to the development of lung cancer.

The studied areas are located at S. Miguel and S. Jorge volcanic island located in the Azores archipelago. Two different volcanic environments were considered in this study, namely, a trachytic polygenetic volcano and basaltic rift zones. The trachytic polygenetic volcano selected was Furnas Volcano located at S. Miguel Island. Furnas Volcano is well known by its important soil diffuse degassing (CO₂ and ²²²Rn), fumarolic fields, thermal and CO₂-rich waters. Two basaltic rift systems were selected, the Picos Volcanic System located in S. Miguel Island and the Manadas Volcanic System located at S. Jorge Island. No important visible degassing was known in both volcanic systems.

At Furnas Volcano, the radon measurements were performed in buildings located at Furnas Village with maximum values of 14864 Bq/m³. In the basaltic rift zones, measurements were performed at Ponta Delgada City located at Picos Volcanic System and at Velas, Toledo, and Santo Amaro villages located at Manadas Volcanic System. In Ponta Delgada the maximum value reached 3717 Bq/m³ and in the Manadas Volcanic System the maximum value was measured at Velas reaching 1885 Bq/m³. Spectral Analysis and Multivariate Regression Analysis were applied to the data obtained to evaluate variables that may interfere with the radon emission as well as cyclic behaviour.

Despite the geological differences between the two volcanic environments considered in this study, the maximum values measured in all the volcanic systems were above the 300 Bq/m³, limit proposed by the Portuguese law for human exposure.  As so, this work enhances the importance of performing indoor measurements in volcanic environments, even in areas where lower values would be expected.