# Random-Specific Activity in Drinking Water and Radiological Health Risk Assessment: A Case Study
## 1 Introduction  
The natural radioactivity in the environment, due to the presence of cosmogenic and primordial radioisotopes in the Earth's crust, contributes the highest percentage to the dose received by the population [1; 2; 3]. Although environmental aspects of natural radioactivity have been widely discussed in the literature [4; 5; 6], the presence of natural radioisotopes in drinking water has not been sufficiently addressed up to now, despite the fact that water represents a critical component of the surrounding environment. In fact, it is worthy of note that the health protection of the population cannot be separated from ensuring the quality of water for human consumption, as drinking water should not pose a health risk over a lifetime [7; 8; 9]. In particular, as water is a critical component of the environment, its quality can be harmed by increased pollution, human activity and a high concentration of naturally occurring radioactive elements [10; 11].  
As widely reported in the literature, drinking water has a natural radioactivity content that is strictly dependent on its origin [12]. In particular, among the naturally occurring radioisotopes, radon is one of the most remarkable, since, as is well known, its ionizing radiation provides the major contribution of internal human exposure compared with other natural sources [13; 14]. Radon exhalates from rocks and easily migrates and entersfracturing groundwater bodies [15]. Each rock type has a characteristic radon content, with the highest values for granitic and metamorphic rocks, phosphate rocks, black shales and some carbonate rocks [16]. Although the solubility of radon in water is relatively low [17], its specific activity in this environmental matrix may instead be several orders of magnitude higher than that of other natural radionuclides [18]. This could also lead to an increase in indoor airborne radon activity concentration, since it was estimated that the transfer coefficient of radon from water to indoor air is \(10^{-4}\)[19]. Therefore, a very high concentration of radon in drinking water poses a serious public health hazard because it can lead, in the long term, to the development of diseases of internal organs, i.e., stomach cancer from ingestion and lung cancer from inhalation [19,20].  
In light of this, in order to protect the public from possible health consequences, it is necessary to investigate radon levels in drinking water [21,22]. This is usually achieved by using reliable measuring devices with reasonably low detection limits, affordable price and simple operation, now available in many laboratories [2,23].  
The results of a campaign to measure the specific activity of radon in groundwater samples for human use coming from civic springs of the Reggio Calabria district, an aquifer system located in the Calabria region, southern Italy, are reported in this article in order to (i) increase the available experimental data with respect to the presence of Rn-22 in groundwater samples for human use from the area under investigation and (ii) to ascertain the relative health risk to members of the population. The overall approach consisted of an initial screening to assess if activity concentration values (in Bq L\({}^{-1}\)) were below the parameter value (100 Bq L\({}^{-1}\)) reported in the Italian D.Lgs. 28/2016 [24], and a second, deeper investigation, based on the assessment of radiological risk to public health by computing the total annual effective dose associated with ingestion and inhalation of the investigated radionuclide, only in those cases where the parameter value was exceeded [25].