Introduction

Natural radioactivity in the environment is due to the presence of cosmogenic and primordial radionuclides in the Earth’s crust and it provides the greatest contribution to the dose received by the population (Torrisi et al. 2010; Caridi et al. 2016a; Tzortzis et al. 2003). Cosmogenic radioisotopes are produced by the interaction of cosmic-rays with atomic nuclei in the atmosphere; the origin of primordial radionuclides goes back to the formation of the Earth, when they were formed by the process of nucleo-synthesis (Torrisi et al. 2008; Caridi et al. 2016b; Von Gunten 1995).

Although environmental aspects of natural radioactivity were discussed in numerous publications (Cooper et al. 2003; Caridi et al. 2016c, 2021) the presence of natural radioisotopes in drinking water as a hazard factor to the public was not addressed in sufficient detail (Atwood 2010; Vallejos et al. 2015). Water-quality assurance is one of the most important issues in environmental programs to protect public health, because safe drinking water must not represent any significant risk to health over a lifetime consumption, including different sensitivities that may occur between life stages (Alabdula’aly et al. 2010; Kansaana et al. 2012). Drinking waters contain natural radionuclides in various concentrations depending on their origin (Moreno et al. 2014; Baeza et al. 1995); the activity concentrations of gross alpha or beta in drinking water, in particular, could guide in determining whether the water can be used for human consumption (AOAC 1990; Oluyide et al. 2019). This led to an increased demand for data, with the aim of addressing public concern pertaining to the quality of drinking water since most of Italian people use groundwater as fetched directly from wells for domestic use (Caridi et al. 2019; Velis et al. 2017). Gross alpha is more of a concern than gross beta for natural radioactivity in water as it refers to the radioactivity of Th, U, Ra as well as Rn and its descendants (EML 1990; Ashton et al. 2012; Osmond et al. 1976).

The Italian Legislative Decree n. 28/2016 constitutes the current national legislative reference regarding the quality of drinking water, in relation to radioactivity. In particular, it regulates the methods of controlling radioactive substances by means of indicator parameters and indicates the related parameter values: Indicative Dose (DI), 0.1 mSv year−1; activity concentration of radon, 100 Bq L−1 and tritium-specific activity, 100 Bq L−1. The Legislative Decree n. 28/2016 also establishes that the determination of the Indicative Dose (ID) is consequent to a preliminary screening, based on the measurement of the gross alpha and beta activity concentration: if the values of 0.1 Bq L−1 for the gross alpha and 0.5 Bq L−1 for the gross beta-specific activities, respectively, are not exceeded, it can reasonably be assumed that the Indicative Dose value of 0.1 mSv year−1 is also respected. If this is not the case, an analytical study must be carried out which allows the dose to be calculated on the basis of the activity concentration of the radionuclides present in the investigated sample (Caridi et al. 2020).

In the present study, a campaign of measurements to control the gross alpha and beta activity concentration in drinking water from public supplies in the Calabria region, southern Italy, is reported. The purpose was to contribute to data compilation concerning the presence of α- and β-emitting radionuclides in drinking waters in the investigated region and to determine the associated radiological health risk for the population.

Therefore, the data reported in this paper were compared with the abovementioned reference values and the associated health risk was calculated.

Materials and Methods

The investigated area is located in the southern part of Italy (Fig. 1). In particular, in the Calabrian districts of Reggio Calabria, Catanzaro, Crotone and Vibo Valentia, 54 municipalities, with springs, wells and related fountains and tanks were identified and monitored, as reported in Table 1, for a total of 250 drinking water samples collected during the 2019. The sampling collection was done for different seasons of the year, according to the local weather conditions, that in some periods put severe limitations on access to the monitoring stations.

Fig. 1
figure 1

A map of the investigated zone

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Table 1 The investigated municipalities
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All samples were collected into 1 L of acidified polyethylene holders, tightly sealed and labeled, to avoid radionuclide precipitation and adsorption on walls of the containers.

For the measurements, a Perkin-Elmer Tricarb 4910 TR Liquid Scintillation Counter (LSC) was employed (Perkin-Elmer Tri-Carb 4910 Manual 2009). Its energy range was 0–2 meV (β particles) and 0–10 meV (α particles). Its minimum acceptable efficiency was 60% for 3H (0–18.6 keV) and 95% for 14C (0–156 keV). Its average Background was 17 CPM for 3H and 26 CPM for 14C. It worked in Normal Count Mode/Low activity—High Sensitivity Mode, with the external standard 133Ba to take into account chemical and optical quenches and to determine the counting efficiency through the Transformed Spectral Index of the External Standard with Automated Efficiency Control (TSIE/AEC) (Caridi et al. 2016d).

For gross alpha and beta assessment, the activity concentration was measured as follows: 200 mL of sample, acidified with 20 µL of ultra-pure HNO3 (67–69%), were preconcentrated at a volume of 20 mL and pH about of 1.85. Of this total volume only 8 mL were taken and mixed with 12 mL of Perkin Elmer ULTIMA GOLD AB scintillating cocktail, stored in a 20 mL plastic vial and, after a rest time of 3 h, counted for 1000 min together with a background (UNI EN ISO 9696–9697 2019).

The activity concentration (Bq L−1) was calculated using the following formula (Caridi et al. 2016e, 2017):

$$ C = \frac{N}{\varepsilon tV} $$
(1)

where N indicates net counts, ε the counting efficiency, V the sample volume (L) and t the live time (s).

In the case of exceeding gross alpha or beta, an analytical study must be carried to calculate the ID parameter (Caridi F. et al. 2020). The Indicative Dose is a measure of the effect on the body of the radioactivity taken by ingestion: it was obtained by qualitative and quantitative analysis of the radionuclides present in the sample and was calculated using the dose coefficients reported in the Italian Legislation D.Lgs. n. 230 and s.m.i. 1995. These coefficients, together with the assumption of an annual ingestion of water of 730 L, allow to calculate the derived activity concentrations for the individual radionuclides, corresponding to an effective committed dose of 0.1 mSv per year (Italian Legislation D. Lgs. n. 28 2016).

The ID parameter was therefore determined by:

$$ ID \left( {{\text{mSv}}} \right) = \mathop \sum \limits_{i = 1}^{n} \frac{{C_{i} \left( {{\text{mis}}.} \right)}}{{C_{i} \left( {{\text{der}}.} \right)}}x\left( {0.1 {\text{mSv}}} \right) $$
(2)

where n indicates the number of radionuclides that contributed at the ID, Ci(mis.) and Ci(der.) the measured and derived specific activities of the i-th radionuclide, respectively.

The ID was less than or equal to the parameter value of 0.1 mSv if the following condition was satisfied:

$$ \mathop \sum \limits_{i = 1}^{n} \frac{{C_{i} \left( {{\text{mis}}.} \right)}}{{C_{i} \left( {{\text{der}}.} \right)}} \le 0.1 $$
(3)

Results and Discussion

Figure 2 shows the average value of the gross alpha and beta activity concentrations in the analyzed samples, for each sampling site. Values lower than the minimum detectable activity (MDA) (0.04 Bq L−1 and 0.20 Bq L−1 for gross alpha and gross beta, respectively) were not reported (UNI EN ISO 9696–9697 2019).

Fig. 2
figure 2

The average value of the gross alpha and beta activity concentrations in the analyzed samples, for each sampling site

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It is evident that both specific activities in the investigated drinking waters varies widely. In particular, for gross alpha, the activity concentration ranges from a minimum value lower than the LSC MDA for the site IDs 13, 28, 34, 35, 38, 44, 53, to a maximum of (0.16 ± 0.03) Bq L−1 for the site ID 22; for gross beta, the specific activity varies from a minimum value lower than the LSC MDA for all the sampling sites except for the site IDs 5, 6, 9, 13, 15, 18, 19, 25, 27, 29, 33, 34, 40, to a maximum of (0.34 ± 0.07) Bq L−1 for the site ID 15.

This variation indicates that the origin of these drinking waters is not the same and that they come from different depths and pass through different geological layers. This irregular distribution of the activity concentration may depend on the U and Th content in rocks or solid aquifers in the areas where are located and the residence time of waters/rocks-soils in contact as well. In particular, the maximum values were obtained for municipalities located in an area where the geological setting is the “Calabrian-Peloritan arc” (Atzori et al. 1984). Its rocks are acidic intrusive igneous and metamorphic, characterized by the highest natural radioactivity.

Obtained results are in good agreement with those reported in the literature from other parts of world (Davila Rangel et al. 2001; Turhan 2020; Ogundare et al. 2015; Ho et al. 2020), on the basis of similar geological considerations.

All the gross alpha and beta activity concentration values turn out to be lower than 0.1 Bq L−1 and 0.5 Bq L−1, respectively, except for the gross alpha-specific activity in the sampling site ID 22 (see Fig. 2). Thus, in this case an analytical study was carried out to calculate the Indicative Dose through the Eq. (2) on the basis of the activity concentration of the radionuclides present in the investigated sample (Caridi et al. 2020).

In particular, we measured an activity concentration of (0.07 ± 0.02) Bq L−1, (0.09 ± 0.03) Bq L−1 and lower than 0.04 Bq L−1 for 238U, 234U and 226Ra, respectively, and then an Indicative Dose of 0.005 mSv year−1, much lower than the parameter value of 0.1 mSv year−1 (Italian Legislation D. Lgs. n. 28 2016).

All obtained values, due to ingestion of α- and β-emitting radionuclides in drinking water to any individual in the population living in the Calabria region, are then lower than the screening and parameter values reported by the Italian Legislative Decree n. 28/2016, thus excluding any possible radiological health risk.

Conclusions

In this article, results from the gross alpha- and beta-specific activity measurements, performed during the 2019, to preliminarily assess the radiological health risk due to the presence of α- and β-emitting radionuclides in drinking water of the Calabria region, are reported. Reported results have a more immediate and easy-to-comment graphic layout, even for evaluations.

The gross alpha and beta activity concentrations were measured by means of the Perkin-Elmer Tricarb 4910 TR Liquid Scintillation Counter (LSC). Obtained results show that the specific activities in drinking water in the investigated 54 municipalities are well below the screening levels indicated by the current Italian legislation (0.1 Bq L−1 for the gross alpha and 0.5 Bq L−1 for the gross beta, respectively) except for the gross alpha-specific activity in the sampling site ID 22. In this case, an analytical study was carried out and the calculated Indicative Dose was of 0.005 mSv year−1, fully compliant with the parameter value set by the current Italian legislation (0.1 mSv year−1). Therefore, it can be argued that the water examined is safe for drinking and other domestic purposes, and no remedial actions are demanded.

However, even though these results show low values of gross alpha and beta activity concentrations and doses in perfect compliance with the official institutional indications, it has to be underlined that periodical screening could be necessary to guarantee the safety of drinking water. Therefore, more measurements and investigations are needed, for the sake of public health.