Radon monitoring in a volcanic cave: El Viento Cave (Canary Islands, Spain)
Authors: Martín-Luis M. Candelaria , Salazar-Carballo Pedro A. , López-Pérez María , Duarte-Rodríguez Xiomara , Martín González María Esther 
Published: March 2022

&lt;p&gt;Radon (&lt;sup&gt;222&lt;/sup&gt;Rn, t &lt;sub&gt;1/2&lt;/sub&gt; = 3.82 days) is by far the dominant radionuclide in indoor air and constitutes a health hazard in poorly ventilated environments, such as caves, mines or tunnels. In these contexts, radon gas can accumulate, reaching harmful concentrations due to the ionizing radiation from &lt;sup&gt;222&lt;/sup&gt;Rn and its progeny. To minimize the exposure risk, a radon monitoring program is required to adopt mitigation measures for the radiological protection of workers, cavers and visitors. The Directive 2013/59/EURATOM sets the recommended occupational and public effective dose limits being 20 and 1 mSv/year, respectively.&lt;/p&gt;&lt;p&gt;El Viento Cave is a volcanic lava tube located in the northern flank of Pico-Viejo volcano, in the Icod Valley, (Tenerife, Canary Islands, Spain). It was formed during the early eruptions of the Pico Viejo volcano, 27,030 &amp;#177; 430 years ago, from basaltic, plagioclase-rich pahoehoe lavas. The cave has an extraordinary complexity, with several sinuous tubes and branches in three superimposed and interconnected levels and is considered the 5&lt;sup&gt;th&lt;/sup&gt; longest volcanic cavity on Earth (Carracedo and Troll, 2013). A 200 m long segment of this lava tube, named &amp;#8220;El Sobrado Cave&amp;#8221;, is enabled for touristic visits. Only in 2019 the cave received more than 28000 visitors.&lt;/p&gt;&lt;p&gt;Monthly radon profiles were obtained during one year (from 2020/10/01 to 2021/09/30) in the touristic section of the cave by using SSNTD (CR-39), installed approximately every 35 m. Besides, a RadonScout monitor (SARAD GmbH) was set up at about 100 m from the cave entrance, for continuous monitoring (integration time of 1 hour) of radon and environmental parameters (air temperature, relative humidity, and barometric pressure).&lt;/p&gt;&lt;p&gt;&lt;sup&gt;222&lt;/sup&gt;Rn levels inside the cave ranged from 0-5.000 Bq/m&lt;sup&gt;3&lt;/sup&gt;, exhibiting seasonal, diurnal and semidiurnal fluctuations. Short-period radon variations (24 and 12 h frequencies) are related to air temperature and humidity. Long-period radon fluctuations (annual-seasonal) are correlated with rainfall, with lower radon levels in winter (rainy season) and higher in summer (dry season).&lt;/p&gt;&lt;p&gt;Annual mean effective dose due to &lt;sup&gt;222&lt;/sup&gt;Rn gas exposure was estimated from the geometric mean of radon concentration during the studied period, assuming an average indoor occupancy of 10 working hours/week during 48 weeks/year for guides and a punctual visit of 1 hour for tourists. In these conditions, the resulting annual effective dose computed for guides is below 2mSv/year.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&lt;em&gt;References:&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Carracedo, J.C. &amp; Troll, V.R. (Eds.). (2013). Teide Volcano: Geology and Eruptions of a Highly Differentiated Oceanic Stratovolcano. Active Volcanoes of the World, Springer Berlin Heidelberg, 296 pp.&lt;/p&gt;