Uranium, radium and radon isotopes in selected brines of Poland

ORIGINAL PAPER NUKLEONIKA 2010;55(4):519−522 Uranium, radium and radon isotopes in selected brines of Poland Beata Kozłowska, Agata Walencik, Tadeusz A. Przylibski, Jerzy Dorda, Wiktor Zipper Abstract. Natural radioactive isotopes were studied in nine different types of brines from four locations in Poland. Investigated brines are exploited from various geological structures composed of the rocks of different chemical and mineral composition as well as different age and depth. All investigated brines are used in balneotherapy (i.e. baths, inhalations, showers). The main goal of this study was to obtain some basic knowledge on the activity range of natural elements such as uranium, radium and radon in different brine types in Poland and their variability depending on their location in certain geological structures. Activities of 234,238U, 226,228Ra and 222Rn isotopes were measured with the use of two nuclear spectrometry techniques: liquid scintillation and alpha spectrometry. The activity concentrations of 222Rn vary from below 1 to 76.1±3.7 Bq/l, for the 226Ra isotope from 0.19±0.01 to 85.5±0.4 Bq/l and for 228Ra from below 0.03 to 2.17±0.09 Bq/l. For uranium isotopes, the concentrations are in the range from below 0.5 to 5.1±0.4 mBq/l for 238 U and from 1.6±0.4 to 45.6±2.0 mBq/l for 234U. The obtained results indicate high radium activity concentrations corresponding to high mineralization of waters. Key words: uranium • radium • radon • brines Introduction B. Kozłowska , A. Walencik, J. Dorda, W. Zipper Department of Nuclear Physics and Its Applications, Institute of Physics, University of Silesia, 4 Uniwersytecka Str., 40-007 Katowice, Poland, Tel.: +48 32 359 1308, Fax: +48 32 258 8431, E-mail: [email protected] T. A. Przylibski Division of Geology and Mineral Waters, Institute of Mining, Faculty of Geoengineering, Mining and Geology, Wrocław University of Technology, 27 Wybrzeże S. Wyspiańskiego, 50-370 Wrocław, Poland Received: 30 June 2009 Accepted: 30 December 2009 Brine is a highly mineralized groundwater (total dissolved solids, TDS > 30 g/l) often containing also higher amounts of natural radioactive isotopes. Concentration of Cl– ions and some other hydrochemical indicators together with the isotopic data of brines from the studied Upper Silesia Basin (USB) region indicate that their salinity has its origin in leaching the Miocene sediments [6, 7]. Another evidence come from the considerable differences in Cl– concentrations accompanying the constant isotopic composition. Thus, the salinity of deep Carboniferous brines from the USB has its origin in leaching with possible secondary enrichment in infiltration processes. Brines studied in this work are exploited from various geological structures composed of the rocks of different chemical and mineral composition. Investigated brines are not natural springs, but they are obtained from boreholes at a depth of 500–1800 m. Water drillings at Ustroń were performed in 1962–1992. Brines from U-3 and U-3a intakes are of Cl-Na-Ca, Br, I, Fe, Sr type with temperatures of 50°C and 22°C, respectively. They were obtained from the Upper and Middle Devonian layers. Borehole C-1 was drilled for secondary forced water and brine from this intake has a similar chemical type as from U-3 and U-3a and the temperature about 20°C. Podbasenie is the place for water usage. Qualities 520 Fig. 1. Localization of the investigated regions on the map of Poland. 1 – Ustroń health resort (U-3, U-3a, Podbasenie, C-1 brines); 2 – Dębowiec health resort (D-2, ST-5, Thermal Brine Zabłocka); 3 – Grudziądz (IG-1); 4 – Sopot (Zdrój Św. Wojciecha). and values of brines from Dębowiec were discovered in the year 1912 when the investigations performed by Chemisch-Mikroskopische Laboratorium from Vienna showed that they contain the highest concentrations of I and Br in Europe. The exploited brines led to the production of specific, for human health, thermal brine Zabłocka with very rich mineral composition. Therapeutic water of chemical type Cl-Na, Br, I, Fe, B was found in the borehole Grudziądz IG-1. This is the “old” water of the pre-Quaternary infiltration which contains an admixture of other waters, e.g. probably relict marine waters. The brine Zdrój Św. Wojciecha from Sopot is of Cl-Na, Br, I type. Investigated brines represent different chemical types and mineralization and are used in balneotherapy in baths, inhalations, showers, etc. Their localization on the map of Poland is presented in Fig. 1. Experimental procedures Studies of natural radioactivity in nine brines from four resorts in Poland were performed with the use of two different nuclear spectrometry techniques. The measurement of radon 222Rn and radium 226,228Ra activity concentrations in investigated samples were performed with the use of a 1414 WinSpectral α/β liquid scintillation counter (LSC) from Wallac. 222Rn concentration in water samples was determined according to the procedure worked out by Suomela [12]. A sample of 10 ml of water was drawn by a disposable syringe and transferred to a scintillation vial filled with 10 ml of a scintillation cocktail Insta-Fluor (Canberra, Packard). 222Rn activity concentration was calculated from the α part of the spectrum originating from this isotope and its α-radioactive daughters. The minimum detectable activity (MDA) was calculated according to Curie’s publication [3] and was equal to 1 Bq/l at 1 h counting time. B. Kozłowska et al. The procedure for radium 226,228Ra determination was based on radiochemical preconcentration by coprecipitation with BaSO4 and purification of its derivatives. This method is based on the Polish Norm [8]. The measurements were performed once a day (1 h counting time) over the period of a month, until the secular equilibrium between radium and its derivatives is reached. 226Ra was calculated from the α part of the spectrum. 228Ra content was estimated from a high-energy β daughter 228Ac in the radioactive equilibrium state with 228Ra. Theoretical calculations were based on Bateman’s equations [1]. The MDA was equal to 0.01 Bq/l for 226Ra and 0.03 Bq/l for 228Ra for 1 h counting time and 3 l of water sample. The uranium 234,238U determination was performed with the use of a α-spectrometer 7401VR (Canberra, Packard, USA) and a silicon surface barrier detector with a surface area of 300 mm2 (Ortec Instruments). Prior to the radiochemical treatment of samples, the standard of 232U National Institute of Standards and Technology (NIST), USA of well known activity was added to each 0.5 l water sample. Uranium was separated on the anion-exchange resin Dowex 1×8 (Cl–, 200–400 mesh) on the basis of a slightly modified procedure worked out by Soumela [13]. A thin α-spectrometry source was prepared from a uranium fraction by coprecipitation with NdF3 [11]. The MDA was equal to 0.5 mBq/l for 234,238U for a measurement lasting two days. Samples from Ustroń and Dębowiec Health Resorts were collected four times over the period of 3 years (2005–2007). Sampling at Grudziądz and Sopot was performed once in 2007. The samples were collected in polyethylene bottles and acidified in order to avoid radionuclide precipitation and adsorption on the walls of the containers. Results and discussion Brines from eight intakes and one bottle from four different spas were investigated for radon, radium and uranium isotopes (Table 1). Concerning their high mineralization up to 120 g/l, special care was needed during radiochemical procedures. As can be seen in Table 1, activity concentrations of the radon isotope 222Rn (from below 1 to 76.1±3.7 Bq/l) are always close to that of its parent radionuclide radium 226Ra. For investigated brines from Ustroń and from Dębowiec health resorts, the 222Rn activity concentrations are equal to or a little lower than 226Ra. For the remaining brines (IG-1, Zdrój Św. Wojciecha) from Grudziądz and Sopot, the 222Rn values are a little higher than 226Ra, but still of the same order of magnitude. The correlation coefficient between these two isotopes is equal to r = +0.98 (Table 2) what indicates a strong positive correlation. It seems that in all investigated brines radon originates from radium dissolved in water, not from surrounding reservoir rocks. The opposite result was obtained previously for mineral and spring groundwaters of different origin in Poland [4, 9, 10]. The activity concentrations for uranium isotopes varied from below 0.5 mBq/l to 5.1±0.4 mBq/l and from 1.6±0.4 mBq/l to 45.6±2.0 mBq/l for 238U and 234U, 45.6 ± 2.0 (1) Correlated elements Rn-226Ra Ra-228Ra 226 Ra-238U TDS-Ratotal TDS-226Ra TDS-228Ra 222 5.1 ± 0.4 (1) 226 1.02 ± 0.05 (1) 0.47 ± 0.02 (1) 6.80 ± 0.60 (1) 44 Number of correlated pairs Correlation coefficient 8 5 6 7 7 5 0.98 0.95 –0.30 0.91 0.91 0.61 respectively. For radium isotopes, the concentrations ranged from 0.19±0.01 Bq/l to 85.5±0.4 Bq/l for 226Ra and from below 0.03 to 2.17±0.9 Bq/l for 228Ra. The isotopic ratio of 234U/238U in the investigated samples varied from 3±1 to 9±1, which means that 234U isotope is more easily leached from a solid matrix to water than 238U. The 234U excess in water is caused by the direct transfer of 234U across the crystalline matrix by alpha recoil or by increased vulnerability to waters related to the oxidation of uranium from the valence state +4 to +6. The correlation coefficient between two radium isotopes was equal to r = +0.95 (Table 2), which indicates a statistically strong positive correlation. This may mean that chemical properties of radium are responsible for its content in the investigated water and, therefore, independent of the mass of the isotope and its attachment to the radioactive decay series. Low negative correlation (r = –0.30) was observed between 226Ra and its parent nuclide 238U. Thus, different chemical properties of radium and uranium are the reason for their different behaviour in the environment of brine water. Although the TDS values are incomplete, it can be observed that the higher TDS of the water, the higher activity concentration of the measured radium (r = +0.91), Table 2. Previous investigations showed similar dependences, especially for 226 Ra [4] r = +0.6 for the Sudety Mts and r = +0.71 for the Outer Carpathians groundwaters, [5] r = +0.82, [14] r = +0.72, [2] r = +0.97. The data presented here are only preliminary indicating an important role of chemical type of studied brines and probably also the lithology of its reservoir rocks on the wide concentrations of investigated radionuclides. Obtained results indicated the necessity of further and more detailed research on this scope. NA – not available. Zdrój Św. Wojciecha Sopot 521 Table 2. Correlation coefficients and the number of correlated pairs * (n) – number of individuals. NA NA 2.17 ± 0.09 (1) 4.90 ± 0.50 (1) 79 IG-1 Grudziądz 2.16 ± 0.07 (1) 2.6 ± 0.4 (1) 1.6 ± 0.4 (1) NA 0.8 ± 0.2 (1) < MDA NA 1.16 ± 0.04 (1) 1.18 ± 0.10 (1) < MDA 32 36 44 D-2 ST-5 Thermal Brine Zabłocka Ustroń Dębowiec 1.07 ± 0.01 (3) 1.27 ± 0.04 (2) 0.19 ± 0.01 (1) 1.20 ± 0.04 (1) 1.32 ± 0.06 (1) 0.11 ± 0.03 (1) 14.0 ± 1.9 (1) 3.2 ± 0.4 (1) 4.8 ± 0.5 (1) 4.2 ± 0.5 (1) 2.7 ± 0.9 (1) 0.5 ± 0.2 (1) 0.9 ± 0.3 (1) 0.5 ± 0.2 (1) < MDA < MDA < MDA < MDA 47.2 ± 10.1 (4) 76.1 ± 3.7 (4) 25.3 ± 0.5 (4) 24.8 ± 0.4 (4) 101 122 NA NA U-3 U-3a Podbasenie C-1 68.6 ± 3.0 (4) 85.5 ± 0.4 (4) 25.9 ± 0.6 (4) 25.2 ± 0.7 (4) U (mBq/l) 234 U (mBq/l) 238 Ra (Bq/l) 228 Ra (Bq/l) 226 Ra (Bq/l) 222 TDS (g/l) Brand name of brine Health resort Table 1. Mineralization and activity concentration of 222Rn and 226,228Ra in Bq/l and of 234,238U in mBq/l for studied brines. For 222Rn, 226,228Ra and 234,238U values ± SD (n)*. The uncertainty of a single measurement was calculated as a square root of the sum of uncertainties in all quantities in quadrate Uranium, radium and radon isotopes in selected brines of Poland Conclusions The main goal of this research was to contribute to the knowledge about the distribution of radioactive isotopes in brines in Poland. Studied brines represent different localities and were obtained from different geological structures from the depths of 500–1800 m. The obtained results indicate high radium activity concentrations corresponding to high mineralization of waters (TDS). As the natural radioactivity of brines seems to be related to the brine chemical type and its total mineralization, its identification may be useful for the general prediction of radiological hazards to miners and patients. It is also necessary to carry out more detailed geochemical investigations due to lithology of the reservoir rocks of brines. 522 Obtained interesting results point out the necessity of undertaking wider and more complex research on the natural radionuclides present in different chemical types of brines exploited from various geological structures in Poland. It is important concerning both the practical point of view (radiation protection) and scientific one (geochemistry of U, Ra and Rn isotopes). B. Kozłowska et al. 6. 7. 8. Acknowledgment. One of the authors (A.W.) would like to thank the Polish Ministry of Science and Higher Education for financial support (project: 1010/B/P01/2008/35, PhD grant). 9. 10. References 1. Bateman H (1910) Solution of a system of differential equations occurring in the theory of radioactive transformations. Proc of the Cambridge Philosophical Society. Mathematical and Physical Sciences 15:423–427 2. 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