DETERMINATION AND DOSE CONTRIBUTION OF URANIUM ISOTOPES AND 210Po ACTIVITY CONCENTRATIONS OF NATURAL SPRING WATERS IN THE PROVINCE OF GRANADA, SPAIN

DETERMINATION AND DOSE CONTRIBUTION OF URANIUM ISOTOPES AND 210Po ACTIVITY CONCENTRATIONS OF... Abstract The activity concentrations of alpha-emitters comprising isotopes of uranium (238, 234, 235U) and polonium (210Po) were measured using alpha-particle spectrometry in natural spring waters in the province of Granada, Spain. These water are consumed by the population of the zone who live in villages. This is almost half of the population of the whole region. Mean values of activity concentrations found are 42.61 ± 2.66; 49.55 ± 3.03; 1.64 ± 0.28 and 1.74 ± 0.15 mBq L−1 for 238U, 234U, 235U and 210Po, respectively. Finally, the radiological impact of the analysed waters has been determined, in terms of the estimation of the committed annual effective dose due to the ingestion of the water. The assessment has been carried out for five age groups with the aim to cover all the population. The calculated annual effective doses are observed to be below the prescribed dose limit of 100 μSv y−1 recommended by WHO. INTRODUCTION Nowadays, there is an increasing tendency in a lot of European countries to replace tap water with commercially available natural waters(1, 2). Although these mineral waters pass through exhaustive purification processes before they get bottled, in many cases they are directly consumed from its original source by the population, and therefore they do not suffer any treatment. The main reason is that there is an important fraction of the population that lives surrounding the aquifers (i.e. a city fountain) and they have consumed it over the years, as for drinking as for other purposes (irrigating, bathing, cooking, health treatments, household needs, etc.). This increased consumption of spring waters is added to the fact that exposure to natural radiation sources contributes more than 86% of the total exposure. In particular, radiological control of water is necessary due to its huge importance in human life. Water plays a very important role in the majority of aspects of industry and commercial sectors, whether treated or not. Because of that, the monitoring of radioactivity levels in water is mandatory. This monitoring has been carried out since 1993, when the World Health Organisation published the first guidelines for drinking water quality(3). Later on, guidelines have been updated and reference levels of individual radionuclides have been included(4). In Europe, the first regulation was established by the European Council in 1980, in the regulation 80/778/EEC(5), although no mention about radioactivity levels was made. It was in 1998 when in directive 98/83/EC(6) firstly mentioned a dose level due to the consumption of drinking water of 0.1 mSv y−1. Spanish regulation has followed the same line than international standards, applying the same criteria in all over the national territory(7). Inside the monitoring of radioactivity levels in water, one can highlight natural alpha emitters, which are the most hazardous for human being, considering their particular biological effectiveness when they enter into the body(8). Particularly, primordial radionuclides, belonging to the natural decay series, should be considered, given their long half-lives (the order of the age of the Earth) and its highly radioactive progeny. These radionuclides can easily enter the human body mainly through food and water. In this work the focus will be on uranium natural isotopes and 210Po, due to its internal dose impact. Uranium is a widely distributed element in the Earth’s crust, given its primordial nature. This element consists of three radioactive isotopes 238U, 235U and 234U, with a mass ratio of 99.2843:0.711: 0.0054%. These three isotopes are all of them alpha emitters, with emission energies: Eα ≈ 4.2 MeV; Eα ≈ 4.3–4.6 MeV and Eα ≈ 4.7 MeV, respectively. In addition, their long half-lives (4.47 × 109, 7.04 × 108 and 2.45 × 105 y, respectively), make these isotopes long-term hazardous. The concentrations of all of them and of their descendants can be significant in different reservoirs in the environment. Consequently, taking into account both chemical toxicity and radiotoxicity of uranium(9); its determination in low concentrations levels, especially in water samples, is really important(9). On the other hand, polonium is also a natural metal element of high atomic weight that can be found at trace levels in the majority of compartments in the environment. Natural polonium consists of several radioactive isotopes, all of them belong to the natural decay series. Among them, the most important one is 210Po (t1/2 = 138 d), because it is the longest-lived polonium isotopes. It belongs to the natural uranium series, and its fate depends on the further members of this decay series. This radionuclide is an alpha emitter (99.999%) of high energetic radiation (Eα = 5.305 MeV) and decaying in 206Pb (stable), which together with its easy incorporation to the human body, where the compounds of polonium are strongly accumulated, makes it an important hazard for human health, even in extremely small quantities at trace levels(10). In general, it is very difficult to forecast the amount of these natural radionuclides in a particular spring water supply due to the strong influence of local geologic, geochemical and hydrogeological conditions of the zone. Therefore, many factors are responsible of the presence and concentration of U isotopes and 210Po in these waters, as the leaching process of uranium and polonium in the rock material composing the aquifer, as well as its retention in the different reservoirs, depending of pH, temperature (T), oxidation–reduction potential (Eh) and other factors. The aim of this article is the determination of the activity concentrations of natural uranium isotopes and 210Po in some natural waters in the Southeastern of Spain; and to calculate the associated committed effective doses by ingestion. Nowadays, the consumption of these waters is continuously growing in most regions in Europe, and they are also often used for farming and stock rearing, so both in a direct and an indirect way, these radionuclides can enter the human body through the food chain. The importance of this work is justified by the normal consumption of these waters by the population, both directly and indirectly, and by the need for monitoring radioactivity levels in the region, being the first time a radiological study of this kind is carried out in this region. MATERIALS AND METHODS Study area The study area is the province of Granada, in the Southeastern region of Spain. The mean altitude of the province is ~1070 m (3510 ft) above mean sea level, although it includes both high-mountain zones, including Mulhacen peak, the highest one of the Iberian Peninsula (3478 m, 11 411 ft) and beach zones. The province lies between North latitude 36°41′ to 38°5′ and Western longitude 4°20′ to 2°12′, and the catchment area of the entire province is 12 531 km2. From a geological standpoint, the study area largely corresponds to the Granada Intramontane Basin within the Betic Cordillera. Its basement and borders, of a Palaeozoic to Tertiary age, belong to the External (Northern) and Internal (Southern) Zones of this cordillera. There is a majority of carbonate rocks in both zones around the basin, although in its Southeastern sector siliceous materials (micaschists and quartzites) crop out extensively(11, 12). Important faults affect the basement; some of them are still tectonically active resulting in relatively frequent seismic events. This fact could lead to radionuclides to appear in groundwaters in the zone(13). The population of this zone is nearly 1 million people, based on the 2016 census. Of this population, almost 50% live in cities, while the other half live in villages. In both urban and rural zones, the majority of the natural water resources are used for human consumption, both for drinking and other purposes. In this context, 37 natural spring waters were sampled. The selection was based on their use by the population nearby. Their locations are shown in Figure 1. Figure 1. View largeDownload slide Map of the location of the sampling sites in Granada province, Southern Spain (taken from Google Earth®). Figure 1. View largeDownload slide Map of the location of the sampling sites in Granada province, Southern Spain (taken from Google Earth®). Sampling Except three samples taken from the two main rivers of the area (samples 7, 9 and 15), the rest of the samples correspond to both springs and wells. A number of significant springs are included among the samples; two of them range between the ones with the biggest outflow in the province: points 2 and 27 have an average discharge in the range of 250–500 L s−1. In the other hand, points 3, 10 and 26 have lesser, although significant, values: between 100 and 200 L s−1. In the principal river of the region we have sampled in two sections, one at the end of its headwater sector (sample 15) and the other ~20 km downstream (sample 7). As mentioned above, water samples correspond to springs and wells, and they are used for (a) domestic and urban supply; (b) irrigation; and (c) medical and spa services. Three of the wells exhibit flowing artesianism (samples 6, 22 and 25), and they have been sampled as the springs: directly from their outflow. The rest of the sampled wells were equipped with electrical submersible pumps. The sample in these cases was considered representative of the aquifer discharge after purging the well water. This was done by pumping after the stabilisation of the values of temperature, pH and electrical conductivity (EC) of the extracted water (from 10 to 20 min, usually). Spring water samples taken from the locations shown in Figure 1 were collected in 5 L polyethylene bottles during December 2016 and January 2017. The bottles were rinsed with concentrated HNO3, and then washed out with distilled water(14). The collected water samples were immediately acidified with concentrated HNO3 to pH <2 to break down organic materials and prevent loss of ions whether by precipitation or binding to the container. In order to determine pH and conductivity in the laboratory, 150 mL of each water sample was collected in a plastic can and not acidified. The determination of alpha emitters by alpha-particle spectrometry in the laboratory was made in a range of time varying from 1 week to a maximum of 2 months from the sampling date. Temperature, pH and EC of the water samples were measured ‘in situ’ using a portable equipment Hanna Instruments HI 9829. These measurements have been carried out in some samples, including the thermal group (samples 1, 6, 11, 19, 23, 24 and 26), and several of the most important springs sampled (samples 2–5, 13–15 and 27–37). The ranges obtained in these measurements will be discussed in the Results and Discussion. Determination of U and Po isotope activity concentrations Alpha particles from these radionuclides were measured by alpha spectrometry after its isolation from the matrix. In order to determine the activity concentration of natural radioisotopes of U and Po, a radiochemical separation procedure was applied to the water samples. A 1 L of each acidified sample was first filtered through a 0.45 μm cellulose nitrate filter. Radioactive tracers of known activity (232U-tracer (t1/2 = 68.9 y) and 209Po-tracer (t1/2 = 102 y), ≈50 mBq each) were added to the samples and mixed with magnetic stirrer for homogenisation. 232U tracer was supplied by CIEMAT (P3721/LMRI/RN/2174), whereas 209Po tracer was supplied by Eckert & Ziegler® Isotope Products (1895-42). Both 232U and 209Po tracers are provided as solutions with certified activity concentration. Later on, 10 mg Fe3+ carrier (in the form of FeCl3 solution, 5 mg mL−1) were added and the temperature rose to ~50°C. Co-precipitation of radionuclides was done at pH = 9 with addition of concentrated NH4OH. The samples were left overnight to settle. The resulting precipitate was decanted from the solution, centrifuged at 4200 rpm for 10 min and dried under infra-red lamp until total dryness. Then, it was dissolved with 8 M HNO3 and transferred to a separation funnel where a liquid–liquid solvent extraction method was carried out for selective separation of U and Po nuclides(15), using tributyl phosphate as the organic phase and both 8 M HNO3 and distilled water as aqueous phases to extract Po and U isotopes, respectively. Preparation of U and Po sources for alpha spectrometry measurement The purified U fraction was evaporated to dryness and then redissolved with 0.3 mL of concentrated H2SO4 and 4 mL of distilled water. The solution was transferred to an electrodeposition cell, pH was adjusted to 2.2 using dilute NH4OH and electrodeposition of U on a stainless steel planchet (25 mm diameter) was complete after 1 h at a current of 1.2 A(16). On the other hand, the Po fraction was evaporated to dryness (under temperature-controlled process without exceeding 80°C to avoid losses of Po), redissolved with 20 mL of concentrated HCl, evaporated to dryness again, and then redissolved with 50 mL of 2 M HCl. The preparation method was spontaneous deposition on copper discs(17). A few mg of ascorbic acid was added in order to reduce Fe3+ ions present in the sample, so they do not interfere in the deposition of Po. Finally, the copper disc was added to the solution and it was stirred at 80°C for 4 h. After deposition, the disc was rinsed with both distilled water and acetone, and dried under an infra-red lamp. Alpha-spectrometric system The measurements of uranium isotope and 210Po activity concentrations were carried out in a CANBERRA Alpha Analyst spectrometer (Canberra–Packard, USA), equipped with Passivated Implanted Planar Silicon (PIPS) detectors, model A450-18AM with an active area of 450 mm2 and resolution of 18 keV FWHM at 5.486 MeV. The system consists of six independent chambers where detectors are placed. Two of these chambers are devoted exclusively to U measurements, two devoted to the measurements of Po and the remaining two to Th measurements. The U and Po sources prepared by applying the radiochemical method were placed at 5.5 mm distance from the detector. This distance was determinate by the efficiency calibration of the instrument, taking into account the optimisation of counting efficiency without any resolution loss. In addition, an energy calibration was performed to ensure the precision of the results. For both efficiency and energy calibration, a certified activity alpha cocktail supplied by CIEMAT (P3525/LMRI/RN/2013) was used. The cocktail contains 233U, 239Pu and 241Am with activity ratio 1:(0.808 ± 0.014):(0.947 ± 0.016) (k = 2). Finally, for the analysis of the alpha spectra the software Genie 2000 has been used. Counting times vary from 2 to 4 days, finding minimum detectable activities (MDA) in the range 0.5–4 mBq L−1. The specific MDA for each analysed isotope is indicated in Table 1 for those samples with activity concentrations lower than this MDA. More details about this instrument have been given by Milena-Pérez(18). Table 1. Activity concentrations (mBq L−1) of the alpha emitters analysed in this study. Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 Table 1. Activity concentrations (mBq L−1) of the alpha emitters analysed in this study. Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 RESULTS AND DISCUSSION Quality analysis and validation of results The radiochemical method applied to the samples has been validated both for Po and U isotope determination. Specifically, water reference samples provided by the Spanish Nuclear Safety Council (CSN) in several intercomparison exercises have been used in the validation process, giving satisfactory results in all of them. In addition, one can mention mean radiochemical yields obtained from the analysis of the water samples, calculated from the integral of the tracer peak in the alpha spectrum. In the case of the analysis of uranium isotopes, the mean yield of the process is ~80 ± 10%, whereas for polonium isotopes, it is ~60 ± 6%, leading to the MDA of 0.5–4 mBq L−1, mentioned above. Results for the ‘in situ’ measurements The range of temperature values registered in the samples which this measurement has been carried out varies from ~10°C to slightly more than 40°C. The lesser values—between 10 and 14°C—were found in the river samples and in springs located above 1000 m altitude. Some of the springs and artesian wells sampled present water that can be classified as thermal (samples 1, 6, 11, 19, 23, 24 and 26). The criterion is that their temperature exceeds in 4°C or more the average value of that of the air (19°C in the study area). This thermal character is not due to recent magmatic influence, does not exist in this region; but to the fact that they follow relatively deep flow paths along the aquifer up to the surface in a short period of time, before thermal equilibrium is reached. The range of EC values in the sampled waters is from ~250 to nearly 20 000 μS cm−1. The sampled with lower values (250–650 μS cm−1) are of the calcium bicarbonate type. They correspond to the rivers and to springs draining siliceous materials and carbonate aquifers (limestones and dolostones). EC values from 1000 to 3000 μS cm−1 have been registered in aquifers with important agricultural occupation based on irrigation practices. Finally, higher values of EC are found in the thermal artesian wells, indicating a complex origin of mineral dissolution favoured by a long residence time within the host rocks. The pH values registered are in the 6.0–8.0 range, although most of the samples show values between 6.5 and 7.5, due to the buffering effect induced by the dissolution of the abundant carbonate minerals. Results for the alpha emitters analysed In this study, a total of 37 spring water samples were analysed in order to determine the activity concentrations of 238U, 234U, 235U and 210Po. These results can be seen in Table 1. Uncertainties have been expressed with the criterion two sigma. In this Table, the activity concentrations of the U isotopes for almost all spring water samples collected show that 234U > 238U > 235U. As can be seen in Table 1, the activity of 238U varies in the range between 2.20 ± 0.33 and 178.25 ± 8.63 mBq L−1; the activity concentration of 234U ranges between 3.87 ± 0.33 and 208.18 ± 9.65 mBq L−1; and the activity concentration of 235U lies between 0.15 ± 0.06 and 6.93 ± 0.51 mBq L−1. For these three uranium isotopes, mean activity concentrations are 42.61 ± 2.66; 49.55 ± 3.03 and 1.64 ± 0.28 mBq L−1, respectively, although 235U activity concentrations are higher than the limit of detection only in 57% of the samples. Finally, the activity concentration of 210Po in the water samples was found to be in the range between 0.26 ± 0.04 and 17.65 ± 0.59 mBq L−1, with a mean value of 1.74 ± 0.15 mBq L−1, for those samples with higher values than the limit of detection (76% of the cases). A further analysis of results shown in Table 1 shows that activity concentrations of natural U isotopes (except 235U) are in the majority of the cases in the range between <10 and 50 mBq L−1 (Figure 2a). These values are in concordance with the results obtained in similar samples analysed in other European countries. This comparison can be seen in Table 2. On the other hand, activity concentrations of 210Po found in the water samples shows that in the majority of the samples studied the value is below 4 mBq L−1, as shown in the frequency distribution plotted in Figure 2b. Table 2 also shows a comparison to data of 210Po activity concentrations taken from the literature, and as seen, in most cases the values are similar for different types of water. Therefore, regarding both Table 1 and Figure 2, it is easy to see that the activity concentrations of the main U isotopes (234U and 238U) cover a wider range than the 210Po activity concentrations, and in the majority of the samples, concentrations of 234, 238U are higher than the activity concentrations of 210Po. This is expected, taking into account the well-known, higher solubility in water of U relative to Po(19, 20). Figure 2. View largeDownload slide (a) Frequency distribution of the 238U activity concentrations found in the water samples. (b) Frequency distribution of the 210Po activity concentrations found in the water samples. Figure 2. View largeDownload slide (a) Frequency distribution of the 238U activity concentrations found in the water samples. (b) Frequency distribution of the 210Po activity concentrations found in the water samples. Table 2. Range of activity concentrations (mBq L−1) of the alpha emitters analysed in this study and their comparison to data from the literature. Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study View Large Table 2. Range of activity concentrations (mBq L−1) of the alpha emitters analysed in this study and their comparison to data from the literature. Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study View Large However, in this study there are several samples with activity concentrations higher than the normal ranges(21), as can be seen in Table 2. This is case of samples 19, 24 and 31 for U isotopes (Table 1) and sample 13 for 210Po (Table 1). Nevertheless, in any case these values are lower than the guidance levels given by the World Health Organisation,(4) which for the radionuclides studied are as follows: for 238U, 10 000 mBq L−1; for 234U, 1000 mBq L−1; for 235U, 1000 mBq L−1; and for 210Po, 100 mBq L−1. Finally, in Table 1 it is also possible to observe that the activity concentration of 238U is much higher than the activity concentration of 235U in the water samples collected. These results are quite logical since the 235U concentrations are much lower in environmental samples than those of 238U, because of its lower abundance. Moreover, the activity ratio 235U/238U in the spring water samples ranged between 0.027 ± 0.007 and 0.053 ± 0.016, with a mean value of 0.038 ± 0.016. This value coincides approximately with the 235U/238U ratio value of 0.045 for natural sources. Finally, both radionuclides are well correlated, as expected (r2 = 0.978). At the same time, some of these waters appear to be slightly enriched in 234U compared with 238U, as the 234U/238U activity ratios vary in the range 0.81–3.91. A strong correlation exists between them (r2 = 0.978). A linear regression between these isotopes shows this tendency ([234U] = 1.05 [238U] + 4.81), where the slope is slightly higher than 1 (1.05), confirming the slight enrichment in 234U compared with 238U. A more accurate plot is presented in Figure 3, where 234U/238U activity ratio vs 238U activity concentration is shown. In this Figure, it can be seen that 89% of the spring water samples present a 234U/238U activity ratio higher than one, therefore they are not in secular equilibrium, while in 11% of the water samples the uranium isotopic secular equilibrium was found. The lack of uranium isotopic equilibrium in waters is a well-known phenomenon, due to the nuclear recoil of 238U during the α-decay of 238U to 234Th, and also due to the nuclear recoil of 234U, so damage is occasioned to crystal lattices by radiation emitted in these decay processes. For these reasons, a preferential lixiviation of 234U relative to 238U in the rock/water interaction is produced; this process of solubility of 234U is accentuated under certain environmental conditions (pH, HCO3−, Eh)(22). Normally the disequilibrium of the U isotopes is greater in minerals containing small amounts of uranium element, whereas uranium rich minerals present activity ratios closer to one(23). This tendency is clearly confirmed by Figure 3. Figure 3. View largeDownload slide 234U/238U activity ratio vs 238U activity concentration in the water samples analysed. Figure 3. View largeDownload slide 234U/238U activity ratio vs 238U activity concentration in the water samples analysed. Estimation of dose due to water consumption In order to evaluate the radiological impact arising from human consumption of these waters, the committed effective dose was estimated by applying the following equation(24, 25). Ding=∑iAiIA⋅(CF)i, wherei=U238,U234,U235,P210o where Ding is the committed effective dose of a person due to ingestion of radionuclides (given in units Sv y−1), Ai is the activity concentration of each radionuclide ingested (Bq L−1), IA is the annual intake of drinking water (L y−1) and (CF)i is the effective dose conversion for the ingestion of each radionuclide (Sv Bq−1). The value of CF depends on the radionuclide under consideration and on the age of the considered population. In this article, the committed effective dose has been calculated for the four radionuclides and the five age groups shown in Table 3. In these five age groups, the effective doses are assessed considering a yearly intake of 730 L y−1 for adults; 350 L y−1 for population between 7 and 17 years old; and 250 L y−1 for population between 1 and 7 years old(26, 27). In Table 3, the values of CF used in the calculations are given, as taken from the standard regulation(7, 28). Table 3. Values of CF (committed effective dose per unit of activity incorporated by ingestion), expressed in Sv Bq−1, for radionuclides and groups of age considered in this work(7, 28), and highest dose found in the samples analysed. 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) Table 3. Values of CF (committed effective dose per unit of activity incorporated by ingestion), expressed in Sv Bq−1, for radionuclides and groups of age considered in this work(7, 28), and highest dose found in the samples analysed. 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) The maximum values of the calculated effective dose for the five age groups are also given in Table 3. As can be seen, the maximum value is obtained for babies and then it decreases with age. A secondary increase is observed in adults, because of their higher water consumption. In all cases, the values are much lower than the WHO recommended reference level of 100 μSv y−1 for all water samples(4). Therefore, the acceptable radiological quality of the water samples analysed in this work is confirmed. A full view of the calculated effective doses on a logarithmic scale is plotted in Figure 4. It is observed that the highest values of the committed effective doses due to the consumption of water are obtained for the younger age groups, especially for babies, despite their annual intake of water being the lowest (250 L y−1). In general, the tendency observed is a reduction of the dose when age increases, until the adult age when dose increases because of an increased annual intake (730 L y−1)(26, 27). Figure 4. View largeDownload slide The calculated committed effective dose (in logarithmic scale), in μSv y1, of the different age groups based on the ingestion dose conversion coefficients given by ICRP(28). Figure 4. View largeDownload slide The calculated committed effective dose (in logarithmic scale), in μSv y1, of the different age groups based on the ingestion dose conversion coefficients given by ICRP(28). From a further analysis of the data, it can be seen that, despite the fact that in the majority of the samples the activity concentration of 210Po is much lower than the activity concentration of 238U (or 234U, considering similar values for both of them, in this discussion 235U will not be considered), it is clear that its contribution to the committed effective dose is higher than that of the uranium isotopes. This can be observed in Figure 5. This fact can lead one to think that 210Po is the main contributor to the committed effective doses by ingestion due to the consumption of these natural waters. However, more analysis needs to be done with others alpha emitters (especially regarding of radium isotopes) to confirm this hypothesis. Figure 5. View largeDownload slide Contributions of 238U, 234U and 210Po to the committed effective doses by ingestion determined for the water samples analysed in this work for the lactation age group (1–2 years). Figure 5. View largeDownload slide Contributions of 238U, 234U and 210Po to the committed effective doses by ingestion determined for the water samples analysed in this work for the lactation age group (1–2 years). CONCLUSIONS Radiological measurements, in terms of natural alpha-emitters isotopes of uranium (238U, 234U and 235U) and polonium (210Po) have been carried out in 37 spring waters of the province of Granada, in the Southeastern region of Spain. This study has determined the radiological quality of the analysed water samples, showing that the majority of them satisfy the recommendations of both Spanish and international regulations. As these water are used by the population of the zone, both for drinking or for other purposes (bathing, cooking, irrigation, etc.), the committed effective dose by ingestion has been calculated. The results show that there are no samples representing a health risk for the population, in any group, since the dose values from all measured radionuclides are much lower than the recommended reference level of 100 μSv y−1 for consumption of water. ACKNOWLEDGEMENTS We wish to thank the Spanish Nuclear Safety Council (CSN), giving its support to the Radiochemistry and Environmental Radiology Laboratory of the University of Granada since 1993 as a member of the laboratories of the Spanish Sparse Network for Environmental Surveillance. REFERENCES 1 Benedik , L. and Jeran , Z. Natural alpha emitting radionuclides in bottled drinking water, mineral water and tap water. Proceedings of Third European IRPA Congress. Helsinki, pp. 1–8 ( 2010 ). 2 Nuhanovic , M. , Mulic , M. , Mujezinovic , A. , Grgic , Z. and Bajic , I. Determination of gross alpha and beta activity and uranium isotope content in commercially available, bottled, natural spring waters . B. Chem. Tech. Bosnia Herzegovina 45 , 31 – 34 ( 2015 ). 3 WHO . Guidelines for Drinking Water Quality ( Geneva : WHO, ) ( 1993 ). 4 WHO . Guidelines for Drinking Water Quality ( Geneva : WHO ) ( 2011 ). 5 EC Council Directive of 15th July 1980 relating to the quality of water intended for human consumption. Official Journal of the European Communities 229, pp. 11–29 ( 1980 ). 6 EC Council Directive of 3rd November 1998 relating to the quality of water intended for human consumption. Official Journal of the European Communities 530, pp. 32–54 ( 1998 ). 7 Real Decreto 314/2016 , de 29 de julio, por el que se establencen los criterios sanitarios de la calidad del agua de consumo humano, Madrid ( 2016 ). 8 Pimpl , M. , Yoo , B. and Yordanova , I. Optimization of a radioanalytical procedure for the determination of uranium isotopes in environmental samples . J. Radioanal. Nucl. Chem. 161 , 437 – 441 ( 1992 ). Google Scholar CrossRef Search ADS 9 Merkel , B. J. and Hasche-Berger , A. Uranium in the Environment—Mining Impact and Consequences ( Berlin : Springer-Verlag ) ( 2006 ). 10 Díaz-Francés , I. , Mantero , J. , Manjón , G. , Díaz , J. and García-Tenorio , R. 210Po and 238U isotope concentration in commercial bottled mineral water samples in Spain and their dose contribution . Radiat. Prot. Dosim. 156 , 336 – 342 ( 2013 ). Google Scholar CrossRef Search ADS 11 DPG-ITGE . Hydrogeolocial atlas of Granada province ( 1990 ). 12 DPG-ITGE . 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Recommendations of the International Commission on Radiological Protection ( Oxford : Pergamon Press ) ( 1991 ). 29 Desideri , D. , Meli , M. A. , Feduzi , L. , Roselli , C. , Rongoni , A. and Saetta , D. 238U, 234U, 226Ra, 210Po concentration of bottled mineral waters in Italy and their dose contribution . J. Environ. Radioact. 94 , 86 – 97 ( 2006 ). Google Scholar CrossRef Search ADS 30 Vasile , M. , Loots , H. , Jacobs , K. , Verheyen , L. , Sneyers , F. , Verrezen , F. and Bruggeman , M. Determination of 210Pb, 210Po, 226Ra, 228Ra and uranium isotopes in drinking water in order to comply with the requirements of the EU 'Drinking Water Directive . Appl. Radiat. Isot. 109 , 465 – 469 ( 2016 ). Google Scholar CrossRef Search ADS PubMed 31 Kovacs , T. , Bodrogi , E. , Dombovari , P. , Somlai , J. , Nemeth , C. , Capote , A. and Tarjan , S. 238U, 226Ra and 210Po concentrations of bottled mineral waters in Hungary and their commited effective dose . Radiat. Prot. 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DETERMINATION AND DOSE CONTRIBUTION OF URANIUM ISOTOPES AND 210Po ACTIVITY CONCENTRATIONS OF NATURAL SPRING WATERS IN THE PROVINCE OF GRANADA, SPAIN

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Abstract

Abstract The activity concentrations of alpha-emitters comprising isotopes of uranium (238, 234, 235U) and polonium (210Po) were measured using alpha-particle spectrometry in natural spring waters in the province of Granada, Spain. These water are consumed by the population of the zone who live in villages. This is almost half of the population of the whole region. Mean values of activity concentrations found are 42.61 ± 2.66; 49.55 ± 3.03; 1.64 ± 0.28 and 1.74 ± 0.15 mBq L−1 for 238U, 234U, 235U and 210Po, respectively. Finally, the radiological impact of the analysed waters has been determined, in terms of the estimation of the committed annual effective dose due to the ingestion of the water. The assessment has been carried out for five age groups with the aim to cover all the population. The calculated annual effective doses are observed to be below the prescribed dose limit of 100 μSv y−1 recommended by WHO. INTRODUCTION Nowadays, there is an increasing tendency in a lot of European countries to replace tap water with commercially available natural waters(1, 2). Although these mineral waters pass through exhaustive purification processes before they get bottled, in many cases they are directly consumed from its original source by the population, and therefore they do not suffer any treatment. The main reason is that there is an important fraction of the population that lives surrounding the aquifers (i.e. a city fountain) and they have consumed it over the years, as for drinking as for other purposes (irrigating, bathing, cooking, health treatments, household needs, etc.). This increased consumption of spring waters is added to the fact that exposure to natural radiation sources contributes more than 86% of the total exposure. In particular, radiological control of water is necessary due to its huge importance in human life. Water plays a very important role in the majority of aspects of industry and commercial sectors, whether treated or not. Because of that, the monitoring of radioactivity levels in water is mandatory. This monitoring has been carried out since 1993, when the World Health Organisation published the first guidelines for drinking water quality(3). Later on, guidelines have been updated and reference levels of individual radionuclides have been included(4). In Europe, the first regulation was established by the European Council in 1980, in the regulation 80/778/EEC(5), although no mention about radioactivity levels was made. It was in 1998 when in directive 98/83/EC(6) firstly mentioned a dose level due to the consumption of drinking water of 0.1 mSv y−1. Spanish regulation has followed the same line than international standards, applying the same criteria in all over the national territory(7). Inside the monitoring of radioactivity levels in water, one can highlight natural alpha emitters, which are the most hazardous for human being, considering their particular biological effectiveness when they enter into the body(8). Particularly, primordial radionuclides, belonging to the natural decay series, should be considered, given their long half-lives (the order of the age of the Earth) and its highly radioactive progeny. These radionuclides can easily enter the human body mainly through food and water. In this work the focus will be on uranium natural isotopes and 210Po, due to its internal dose impact. Uranium is a widely distributed element in the Earth’s crust, given its primordial nature. This element consists of three radioactive isotopes 238U, 235U and 234U, with a mass ratio of 99.2843:0.711: 0.0054%. These three isotopes are all of them alpha emitters, with emission energies: Eα ≈ 4.2 MeV; Eα ≈ 4.3–4.6 MeV and Eα ≈ 4.7 MeV, respectively. In addition, their long half-lives (4.47 × 109, 7.04 × 108 and 2.45 × 105 y, respectively), make these isotopes long-term hazardous. The concentrations of all of them and of their descendants can be significant in different reservoirs in the environment. Consequently, taking into account both chemical toxicity and radiotoxicity of uranium(9); its determination in low concentrations levels, especially in water samples, is really important(9). On the other hand, polonium is also a natural metal element of high atomic weight that can be found at trace levels in the majority of compartments in the environment. Natural polonium consists of several radioactive isotopes, all of them belong to the natural decay series. Among them, the most important one is 210Po (t1/2 = 138 d), because it is the longest-lived polonium isotopes. It belongs to the natural uranium series, and its fate depends on the further members of this decay series. This radionuclide is an alpha emitter (99.999%) of high energetic radiation (Eα = 5.305 MeV) and decaying in 206Pb (stable), which together with its easy incorporation to the human body, where the compounds of polonium are strongly accumulated, makes it an important hazard for human health, even in extremely small quantities at trace levels(10). In general, it is very difficult to forecast the amount of these natural radionuclides in a particular spring water supply due to the strong influence of local geologic, geochemical and hydrogeological conditions of the zone. Therefore, many factors are responsible of the presence and concentration of U isotopes and 210Po in these waters, as the leaching process of uranium and polonium in the rock material composing the aquifer, as well as its retention in the different reservoirs, depending of pH, temperature (T), oxidation–reduction potential (Eh) and other factors. The aim of this article is the determination of the activity concentrations of natural uranium isotopes and 210Po in some natural waters in the Southeastern of Spain; and to calculate the associated committed effective doses by ingestion. Nowadays, the consumption of these waters is continuously growing in most regions in Europe, and they are also often used for farming and stock rearing, so both in a direct and an indirect way, these radionuclides can enter the human body through the food chain. The importance of this work is justified by the normal consumption of these waters by the population, both directly and indirectly, and by the need for monitoring radioactivity levels in the region, being the first time a radiological study of this kind is carried out in this region. MATERIALS AND METHODS Study area The study area is the province of Granada, in the Southeastern region of Spain. The mean altitude of the province is ~1070 m (3510 ft) above mean sea level, although it includes both high-mountain zones, including Mulhacen peak, the highest one of the Iberian Peninsula (3478 m, 11 411 ft) and beach zones. The province lies between North latitude 36°41′ to 38°5′ and Western longitude 4°20′ to 2°12′, and the catchment area of the entire province is 12 531 km2. From a geological standpoint, the study area largely corresponds to the Granada Intramontane Basin within the Betic Cordillera. Its basement and borders, of a Palaeozoic to Tertiary age, belong to the External (Northern) and Internal (Southern) Zones of this cordillera. There is a majority of carbonate rocks in both zones around the basin, although in its Southeastern sector siliceous materials (micaschists and quartzites) crop out extensively(11, 12). Important faults affect the basement; some of them are still tectonically active resulting in relatively frequent seismic events. This fact could lead to radionuclides to appear in groundwaters in the zone(13). The population of this zone is nearly 1 million people, based on the 2016 census. Of this population, almost 50% live in cities, while the other half live in villages. In both urban and rural zones, the majority of the natural water resources are used for human consumption, both for drinking and other purposes. In this context, 37 natural spring waters were sampled. The selection was based on their use by the population nearby. Their locations are shown in Figure 1. Figure 1. View largeDownload slide Map of the location of the sampling sites in Granada province, Southern Spain (taken from Google Earth®). Figure 1. View largeDownload slide Map of the location of the sampling sites in Granada province, Southern Spain (taken from Google Earth®). Sampling Except three samples taken from the two main rivers of the area (samples 7, 9 and 15), the rest of the samples correspond to both springs and wells. A number of significant springs are included among the samples; two of them range between the ones with the biggest outflow in the province: points 2 and 27 have an average discharge in the range of 250–500 L s−1. In the other hand, points 3, 10 and 26 have lesser, although significant, values: between 100 and 200 L s−1. In the principal river of the region we have sampled in two sections, one at the end of its headwater sector (sample 15) and the other ~20 km downstream (sample 7). As mentioned above, water samples correspond to springs and wells, and they are used for (a) domestic and urban supply; (b) irrigation; and (c) medical and spa services. Three of the wells exhibit flowing artesianism (samples 6, 22 and 25), and they have been sampled as the springs: directly from their outflow. The rest of the sampled wells were equipped with electrical submersible pumps. The sample in these cases was considered representative of the aquifer discharge after purging the well water. This was done by pumping after the stabilisation of the values of temperature, pH and electrical conductivity (EC) of the extracted water (from 10 to 20 min, usually). Spring water samples taken from the locations shown in Figure 1 were collected in 5 L polyethylene bottles during December 2016 and January 2017. The bottles were rinsed with concentrated HNO3, and then washed out with distilled water(14). The collected water samples were immediately acidified with concentrated HNO3 to pH <2 to break down organic materials and prevent loss of ions whether by precipitation or binding to the container. In order to determine pH and conductivity in the laboratory, 150 mL of each water sample was collected in a plastic can and not acidified. The determination of alpha emitters by alpha-particle spectrometry in the laboratory was made in a range of time varying from 1 week to a maximum of 2 months from the sampling date. Temperature, pH and EC of the water samples were measured ‘in situ’ using a portable equipment Hanna Instruments HI 9829. These measurements have been carried out in some samples, including the thermal group (samples 1, 6, 11, 19, 23, 24 and 26), and several of the most important springs sampled (samples 2–5, 13–15 and 27–37). The ranges obtained in these measurements will be discussed in the Results and Discussion. Determination of U and Po isotope activity concentrations Alpha particles from these radionuclides were measured by alpha spectrometry after its isolation from the matrix. In order to determine the activity concentration of natural radioisotopes of U and Po, a radiochemical separation procedure was applied to the water samples. A 1 L of each acidified sample was first filtered through a 0.45 μm cellulose nitrate filter. Radioactive tracers of known activity (232U-tracer (t1/2 = 68.9 y) and 209Po-tracer (t1/2 = 102 y), ≈50 mBq each) were added to the samples and mixed with magnetic stirrer for homogenisation. 232U tracer was supplied by CIEMAT (P3721/LMRI/RN/2174), whereas 209Po tracer was supplied by Eckert & Ziegler® Isotope Products (1895-42). Both 232U and 209Po tracers are provided as solutions with certified activity concentration. Later on, 10 mg Fe3+ carrier (in the form of FeCl3 solution, 5 mg mL−1) were added and the temperature rose to ~50°C. Co-precipitation of radionuclides was done at pH = 9 with addition of concentrated NH4OH. The samples were left overnight to settle. The resulting precipitate was decanted from the solution, centrifuged at 4200 rpm for 10 min and dried under infra-red lamp until total dryness. Then, it was dissolved with 8 M HNO3 and transferred to a separation funnel where a liquid–liquid solvent extraction method was carried out for selective separation of U and Po nuclides(15), using tributyl phosphate as the organic phase and both 8 M HNO3 and distilled water as aqueous phases to extract Po and U isotopes, respectively. Preparation of U and Po sources for alpha spectrometry measurement The purified U fraction was evaporated to dryness and then redissolved with 0.3 mL of concentrated H2SO4 and 4 mL of distilled water. The solution was transferred to an electrodeposition cell, pH was adjusted to 2.2 using dilute NH4OH and electrodeposition of U on a stainless steel planchet (25 mm diameter) was complete after 1 h at a current of 1.2 A(16). On the other hand, the Po fraction was evaporated to dryness (under temperature-controlled process without exceeding 80°C to avoid losses of Po), redissolved with 20 mL of concentrated HCl, evaporated to dryness again, and then redissolved with 50 mL of 2 M HCl. The preparation method was spontaneous deposition on copper discs(17). A few mg of ascorbic acid was added in order to reduce Fe3+ ions present in the sample, so they do not interfere in the deposition of Po. Finally, the copper disc was added to the solution and it was stirred at 80°C for 4 h. After deposition, the disc was rinsed with both distilled water and acetone, and dried under an infra-red lamp. Alpha-spectrometric system The measurements of uranium isotope and 210Po activity concentrations were carried out in a CANBERRA Alpha Analyst spectrometer (Canberra–Packard, USA), equipped with Passivated Implanted Planar Silicon (PIPS) detectors, model A450-18AM with an active area of 450 mm2 and resolution of 18 keV FWHM at 5.486 MeV. The system consists of six independent chambers where detectors are placed. Two of these chambers are devoted exclusively to U measurements, two devoted to the measurements of Po and the remaining two to Th measurements. The U and Po sources prepared by applying the radiochemical method were placed at 5.5 mm distance from the detector. This distance was determinate by the efficiency calibration of the instrument, taking into account the optimisation of counting efficiency without any resolution loss. In addition, an energy calibration was performed to ensure the precision of the results. For both efficiency and energy calibration, a certified activity alpha cocktail supplied by CIEMAT (P3525/LMRI/RN/2013) was used. The cocktail contains 233U, 239Pu and 241Am with activity ratio 1:(0.808 ± 0.014):(0.947 ± 0.016) (k = 2). Finally, for the analysis of the alpha spectra the software Genie 2000 has been used. Counting times vary from 2 to 4 days, finding minimum detectable activities (MDA) in the range 0.5–4 mBq L−1. The specific MDA for each analysed isotope is indicated in Table 1 for those samples with activity concentrations lower than this MDA. More details about this instrument have been given by Milena-Pérez(18). Table 1. Activity concentrations (mBq L−1) of the alpha emitters analysed in this study. Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 Table 1. Activity concentrations (mBq L−1) of the alpha emitters analysed in this study. Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 Sample 238U 234U 235U 210Po 1 18.9 ± 2.6 29.4 ± 1.9 <2.7 <4.0 2 10.6 ± 0.8 20.5 ± 1.3 <0.2 1.24 ± 0.13 3 14.7 ± 1.0 20.8 ± 1.3 0.47 ± 0.14 <2.0 4 7.4 ± 1.4 9.2 ± 1.6 <1.7 0.84 ± 0.11 5 42.9 ± 2.5 48.4 ± 2.7 1.43 ± 0.26 1.35 ± 0.10 6 2.2 ± 0.3 4.38 ± 0.49 <0.3 0.61 ± 0.08 7 38.0 ± 1.7 45.4 ± 2.2 1.62 ± 0.19 1.03 ± 0.14 8 65.5 ± 6.9 74.4 ± 7.7 <2.3 <1.6 9 23.4 ± 1.7 25.6 ± 1.8 1.23 ± 0.28 0.88 ± 0.13 10 6.6 ± 0.5 7.27 ± 0.57 <0.2 0.40 ± 0.06 11 32.5 ± 3.1 53.9 ± 4.6 <0.5 4.48 ± 0.47 12 36.1 ± 3.3 40.2 ± 3.6 <1.3 2.19 ± 0.19 13 4.9 ± 0.4 4.52 ± 0.36 0.15 ± 0.06 17.65 ± 0.59 14 56.6 ± 3.1 81.8 ± 4.3 1.99 ± 0.30 0.79 ± 0.08 15 20.5 ± 1.8 23.5 ± 2.0 0.87 ± 0.29 1.09 ± 0.11 16 8.6 ± 1.1 12.1 ± 1.3 <0.9 <1.8 17 8.5 ± 1.7 18.6 ± 2.7 <2.9 0.68 ± 0.08 18 13.8 ± 2.0 23.0 ± 2.9 <1.7 0.99 ± 0.17 19 175 ± 8 208 ± 10 7.01 ± 0.53 8.50 ± 0.33 20 12.5 ± 1.3 14.8 ± 1.5 <0.7 0.37 ± 0.04 21 11.4 ± 1.2 19.8 ± 1.8 <0.7 <1.6 22 31.6 ± 3.9 35.7 ± 4.3 <3.0 0.39 ± 0.06 23 4.0 ± 0.5 15.7 ± 1.2 <0.4 0.73 ± 0.10 24 112 ± 7 128 ± 8 3.94 ± 0.61 1.45 ± 0.11 25 3.0 ± 0.3 3.87 ± 0.33 <0.2 0.26 ± 0.04 26 10.9 ± 0.8 14.1 ± 0.9 0.29 ± 0.09 <0.4 27 8.5 ± 0.5 6.86 ± 0.41 0.23 ± 0.05 0.62 ± 0.07 28 50.4 ± 2.4 64.3 ± 3.1 1.94 ± 0.19 1.30 ± 0.11 29 41.4 ± 2.0 48.0 ± 2.3 1.42 ± 0.16 <0.4 30 79.7 ± 3.8 88.5 ± 4.2 2.84 ± 0.26 1.73 ± 0.13 31 178 ± 9 172 ± 8 6.93 ± 0.51 2.49 ± 0.15 32 27.4 ± 1.4 30.9 ± 1.6 1.26 ± 0.15 <3.7 33 78.3 ± 3.8 83.3 ± 4.1 3.06 ± 0.28 0.79 ± 0.08 34 73.6 ± 3.7 73.5 ± 3.7 2.55 ± 0.27 0.95 ± 0.10 35 33.9 ± 2.0 36.1 ± 2.1 1.27 ± 0.22 0.58 ± 0.07 36 135 ± 6 142 ± 7 5.57 ± 0.38 <0.4 37 97 ± 5 105 ± 5 3.83 ± 0.32 2.21 ± 0.15 RESULTS AND DISCUSSION Quality analysis and validation of results The radiochemical method applied to the samples has been validated both for Po and U isotope determination. Specifically, water reference samples provided by the Spanish Nuclear Safety Council (CSN) in several intercomparison exercises have been used in the validation process, giving satisfactory results in all of them. In addition, one can mention mean radiochemical yields obtained from the analysis of the water samples, calculated from the integral of the tracer peak in the alpha spectrum. In the case of the analysis of uranium isotopes, the mean yield of the process is ~80 ± 10%, whereas for polonium isotopes, it is ~60 ± 6%, leading to the MDA of 0.5–4 mBq L−1, mentioned above. Results for the ‘in situ’ measurements The range of temperature values registered in the samples which this measurement has been carried out varies from ~10°C to slightly more than 40°C. The lesser values—between 10 and 14°C—were found in the river samples and in springs located above 1000 m altitude. Some of the springs and artesian wells sampled present water that can be classified as thermal (samples 1, 6, 11, 19, 23, 24 and 26). The criterion is that their temperature exceeds in 4°C or more the average value of that of the air (19°C in the study area). This thermal character is not due to recent magmatic influence, does not exist in this region; but to the fact that they follow relatively deep flow paths along the aquifer up to the surface in a short period of time, before thermal equilibrium is reached. The range of EC values in the sampled waters is from ~250 to nearly 20 000 μS cm−1. The sampled with lower values (250–650 μS cm−1) are of the calcium bicarbonate type. They correspond to the rivers and to springs draining siliceous materials and carbonate aquifers (limestones and dolostones). EC values from 1000 to 3000 μS cm−1 have been registered in aquifers with important agricultural occupation based on irrigation practices. Finally, higher values of EC are found in the thermal artesian wells, indicating a complex origin of mineral dissolution favoured by a long residence time within the host rocks. The pH values registered are in the 6.0–8.0 range, although most of the samples show values between 6.5 and 7.5, due to the buffering effect induced by the dissolution of the abundant carbonate minerals. Results for the alpha emitters analysed In this study, a total of 37 spring water samples were analysed in order to determine the activity concentrations of 238U, 234U, 235U and 210Po. These results can be seen in Table 1. Uncertainties have been expressed with the criterion two sigma. In this Table, the activity concentrations of the U isotopes for almost all spring water samples collected show that 234U > 238U > 235U. As can be seen in Table 1, the activity of 238U varies in the range between 2.20 ± 0.33 and 178.25 ± 8.63 mBq L−1; the activity concentration of 234U ranges between 3.87 ± 0.33 and 208.18 ± 9.65 mBq L−1; and the activity concentration of 235U lies between 0.15 ± 0.06 and 6.93 ± 0.51 mBq L−1. For these three uranium isotopes, mean activity concentrations are 42.61 ± 2.66; 49.55 ± 3.03 and 1.64 ± 0.28 mBq L−1, respectively, although 235U activity concentrations are higher than the limit of detection only in 57% of the samples. Finally, the activity concentration of 210Po in the water samples was found to be in the range between 0.26 ± 0.04 and 17.65 ± 0.59 mBq L−1, with a mean value of 1.74 ± 0.15 mBq L−1, for those samples with higher values than the limit of detection (76% of the cases). A further analysis of results shown in Table 1 shows that activity concentrations of natural U isotopes (except 235U) are in the majority of the cases in the range between <10 and 50 mBq L−1 (Figure 2a). These values are in concordance with the results obtained in similar samples analysed in other European countries. This comparison can be seen in Table 2. On the other hand, activity concentrations of 210Po found in the water samples shows that in the majority of the samples studied the value is below 4 mBq L−1, as shown in the frequency distribution plotted in Figure 2b. Table 2 also shows a comparison to data of 210Po activity concentrations taken from the literature, and as seen, in most cases the values are similar for different types of water. Therefore, regarding both Table 1 and Figure 2, it is easy to see that the activity concentrations of the main U isotopes (234U and 238U) cover a wider range than the 210Po activity concentrations, and in the majority of the samples, concentrations of 234, 238U are higher than the activity concentrations of 210Po. This is expected, taking into account the well-known, higher solubility in water of U relative to Po(19, 20). Figure 2. View largeDownload slide (a) Frequency distribution of the 238U activity concentrations found in the water samples. (b) Frequency distribution of the 210Po activity concentrations found in the water samples. Figure 2. View largeDownload slide (a) Frequency distribution of the 238U activity concentrations found in the water samples. (b) Frequency distribution of the 210Po activity concentrations found in the water samples. Table 2. Range of activity concentrations (mBq L−1) of the alpha emitters analysed in this study and their comparison to data from the literature. Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study View Large Table 2. Range of activity concentrations (mBq L−1) of the alpha emitters analysed in this study and their comparison to data from the literature. Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study Country Type of water 238U 234U 235U 210Po Reference Belgium Drinking water <0.1–25.3 <0.1–54.4 — <0.1–3.1 (30) Hungary Drinking water <2–98 <2–92 — 2–20 (31) Bosnia and Herzegovina Spring water <0.4–6 <0.1–40 <0.02–0.4 — (2) Serbia Spring water 0.2–9.4 <0.2–18.9 <0.02–1.8 — (32) Italy (1) Mineral water <0.2–89 <0.2–79 — <0.04–21 (29) Italy (2) Spring water 2.0–57 1.6–60 — — (33) Poland River water — — — 0.6–5.5 (34) Granada (Spain) Spring water 2.2–180 3.9–210 <0.05–7 <0.2–17 Present study View Large However, in this study there are several samples with activity concentrations higher than the normal ranges(21), as can be seen in Table 2. This is case of samples 19, 24 and 31 for U isotopes (Table 1) and sample 13 for 210Po (Table 1). Nevertheless, in any case these values are lower than the guidance levels given by the World Health Organisation,(4) which for the radionuclides studied are as follows: for 238U, 10 000 mBq L−1; for 234U, 1000 mBq L−1; for 235U, 1000 mBq L−1; and for 210Po, 100 mBq L−1. Finally, in Table 1 it is also possible to observe that the activity concentration of 238U is much higher than the activity concentration of 235U in the water samples collected. These results are quite logical since the 235U concentrations are much lower in environmental samples than those of 238U, because of its lower abundance. Moreover, the activity ratio 235U/238U in the spring water samples ranged between 0.027 ± 0.007 and 0.053 ± 0.016, with a mean value of 0.038 ± 0.016. This value coincides approximately with the 235U/238U ratio value of 0.045 for natural sources. Finally, both radionuclides are well correlated, as expected (r2 = 0.978). At the same time, some of these waters appear to be slightly enriched in 234U compared with 238U, as the 234U/238U activity ratios vary in the range 0.81–3.91. A strong correlation exists between them (r2 = 0.978). A linear regression between these isotopes shows this tendency ([234U] = 1.05 [238U] + 4.81), where the slope is slightly higher than 1 (1.05), confirming the slight enrichment in 234U compared with 238U. A more accurate plot is presented in Figure 3, where 234U/238U activity ratio vs 238U activity concentration is shown. In this Figure, it can be seen that 89% of the spring water samples present a 234U/238U activity ratio higher than one, therefore they are not in secular equilibrium, while in 11% of the water samples the uranium isotopic secular equilibrium was found. The lack of uranium isotopic equilibrium in waters is a well-known phenomenon, due to the nuclear recoil of 238U during the α-decay of 238U to 234Th, and also due to the nuclear recoil of 234U, so damage is occasioned to crystal lattices by radiation emitted in these decay processes. For these reasons, a preferential lixiviation of 234U relative to 238U in the rock/water interaction is produced; this process of solubility of 234U is accentuated under certain environmental conditions (pH, HCO3−, Eh)(22). Normally the disequilibrium of the U isotopes is greater in minerals containing small amounts of uranium element, whereas uranium rich minerals present activity ratios closer to one(23). This tendency is clearly confirmed by Figure 3. Figure 3. View largeDownload slide 234U/238U activity ratio vs 238U activity concentration in the water samples analysed. Figure 3. View largeDownload slide 234U/238U activity ratio vs 238U activity concentration in the water samples analysed. Estimation of dose due to water consumption In order to evaluate the radiological impact arising from human consumption of these waters, the committed effective dose was estimated by applying the following equation(24, 25). Ding=∑iAiIA⋅(CF)i, wherei=U238,U234,U235,P210o where Ding is the committed effective dose of a person due to ingestion of radionuclides (given in units Sv y−1), Ai is the activity concentration of each radionuclide ingested (Bq L−1), IA is the annual intake of drinking water (L y−1) and (CF)i is the effective dose conversion for the ingestion of each radionuclide (Sv Bq−1). The value of CF depends on the radionuclide under consideration and on the age of the considered population. In this article, the committed effective dose has been calculated for the four radionuclides and the five age groups shown in Table 3. In these five age groups, the effective doses are assessed considering a yearly intake of 730 L y−1 for adults; 350 L y−1 for population between 7 and 17 years old; and 250 L y−1 for population between 1 and 7 years old(26, 27). In Table 3, the values of CF used in the calculations are given, as taken from the standard regulation(7, 28). Table 3. Values of CF (committed effective dose per unit of activity incorporated by ingestion), expressed in Sv Bq−1, for radionuclides and groups of age considered in this work(7, 28), and highest dose found in the samples analysed. 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) Table 3. Values of CF (committed effective dose per unit of activity incorporated by ingestion), expressed in Sv Bq−1, for radionuclides and groups of age considered in this work(7, 28), and highest dose found in the samples analysed. 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) 1–2 Years 2–7 Years 7–12 Years 12–17 Years Adult 238U 1.2 × 10−7 8.0 × 10−8 6.8 × 10−8 6.7 × 10−8 4.5 × 10−8 234U 1.3 × 10−7 8.8 × 10−8 7.4 × 10−8 7.4 × 10−8 4.9 × 10−8 235U 1.3 × 10−7 8.5 × 10−8 7.1 × 10−8 7.0 × 10−8 4.7 × 10−8 210Po 8.8 × 10−6 4.4 × 10−6 2.6 × 10−6 1.6 × 10−6 1.2 × 10−6 Maximum 39.1 ± 1.3 19.6 ± 0.7 17.5 ± 0.8 14.4 ± 0.6 20.9 ± 0.9  Value (μSv y−1) The maximum values of the calculated effective dose for the five age groups are also given in Table 3. As can be seen, the maximum value is obtained for babies and then it decreases with age. A secondary increase is observed in adults, because of their higher water consumption. In all cases, the values are much lower than the WHO recommended reference level of 100 μSv y−1 for all water samples(4). Therefore, the acceptable radiological quality of the water samples analysed in this work is confirmed. A full view of the calculated effective doses on a logarithmic scale is plotted in Figure 4. It is observed that the highest values of the committed effective doses due to the consumption of water are obtained for the younger age groups, especially for babies, despite their annual intake of water being the lowest (250 L y−1). In general, the tendency observed is a reduction of the dose when age increases, until the adult age when dose increases because of an increased annual intake (730 L y−1)(26, 27). Figure 4. View largeDownload slide The calculated committed effective dose (in logarithmic scale), in μSv y1, of the different age groups based on the ingestion dose conversion coefficients given by ICRP(28). Figure 4. View largeDownload slide The calculated committed effective dose (in logarithmic scale), in μSv y1, of the different age groups based on the ingestion dose conversion coefficients given by ICRP(28). From a further analysis of the data, it can be seen that, despite the fact that in the majority of the samples the activity concentration of 210Po is much lower than the activity concentration of 238U (or 234U, considering similar values for both of them, in this discussion 235U will not be considered), it is clear that its contribution to the committed effective dose is higher than that of the uranium isotopes. This can be observed in Figure 5. This fact can lead one to think that 210Po is the main contributor to the committed effective doses by ingestion due to the consumption of these natural waters. However, more analysis needs to be done with others alpha emitters (especially regarding of radium isotopes) to confirm this hypothesis. Figure 5. View largeDownload slide Contributions of 238U, 234U and 210Po to the committed effective doses by ingestion determined for the water samples analysed in this work for the lactation age group (1–2 years). Figure 5. View largeDownload slide Contributions of 238U, 234U and 210Po to the committed effective doses by ingestion determined for the water samples analysed in this work for the lactation age group (1–2 years). CONCLUSIONS Radiological measurements, in terms of natural alpha-emitters isotopes of uranium (238U, 234U and 235U) and polonium (210Po) have been carried out in 37 spring waters of the province of Granada, in the Southeastern region of Spain. This study has determined the radiological quality of the analysed water samples, showing that the majority of them satisfy the recommendations of both Spanish and international regulations. As these water are used by the population of the zone, both for drinking or for other purposes (bathing, cooking, irrigation, etc.), the committed effective dose by ingestion has been calculated. The results show that there are no samples representing a health risk for the population, in any group, since the dose values from all measured radionuclides are much lower than the recommended reference level of 100 μSv y−1 for consumption of water. ACKNOWLEDGEMENTS We wish to thank the Spanish Nuclear Safety Council (CSN), giving its support to the Radiochemistry and Environmental Radiology Laboratory of the University of Granada since 1993 as a member of the laboratories of the Spanish Sparse Network for Environmental Surveillance. REFERENCES 1 Benedik , L. and Jeran , Z. 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Radiation Protection DosimetryOxford University Press

Published: Mar 1, 2018

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