TY - JOUR
AU1 - M, Kamenova-Totzeva, R
AU2 - V, Totzev, A
AU3 - M, Kotova, R
AU4 - R, Ivanova-Teneva, G
AB - Abstract This study presents the results of 222Rn in 24 sources of mineral water, 54 samples from different captured natural springs and drillings. 222Rn determination was performed by direct measurement using Alpha Guard with Aqua Kit. The results for the TDS, anions (F−, Cl−, SO42−), cations (Na+, Ca2+, Mg2+), pH and temperature of the investigated mineral waters were correlated with radon content by statistical software tool IBM SPSS. In the paper are shown the results of investigated correlations between the 222Rn content and gross alpha activity, gross beta activity and specific activity of 226Ra. The received results show that the 222Rn activities range from 0.40 to 476 Bq/l with a median value of 16 Bq/l. The Spearman’s rho coefficients demonstrate a strong positive correlation between SO42− and F− anions and 222Rn (r, 0.731 and r, 0.784 respectively). Correlations between226Ra/222Rn, gross alpha activity/222Rn, gross beta activity/222Rn were investigated but not observed. INTRODUCTION Radon (222Rn, half-life = 3.8 d) is an alpha-emitting radioactive gas produced naturally in the environment by the decay of 226Ra. Its nature as Nobel gas is determined by the physical processes and not by the chemical interactions, and it reflects the presence of its parental radionuclide. Because of its gaseous physical state and inert chemical nature, radon is very mobile and can migrate either as a distinct gas or dissolved in geofluids (e.g. groundwater)(1) It is well-known that the specific activity of 222Rn depends on the geological structure of the aquifer and distribution of its parent element in the rock matrix.(2, 3) During its migration within the earth’s crust, mineral waters may come in contact with the surfaces of radioactive eruptive rocks such as granites, quartz porphyry, basalt which contain radium.(3) The concentration of the radon in the water also depends on the solubility of the parent element and its own solubility in waters.(4) The solubility of radionuclides is affected by chemical and physical composition of the aquifer.(2) For example, the solubility of 222Rn is varied with the physical conditions and it decreases with the increase of temperature.(5) Some geothermal waters have high concentrations of 222Rn which may cause damage to the health of individuals.(6, 7, 8) Radon and its long-lived daughters 210Po and 210Pb contribute to a significant radiation dose on the human body.(9, 10) Exposure of person to high concentration of radon and its short-lived progeny for long periods of time leads to health problems, particularly lung cancer, resulting from inhalation of radon.(8, 11, 12) The motivation for this work stems from the high radiological impact of the radon content concerning human health and from the need to provide data for the radon content in Bulgarian mineral waters. To identify possible additional mechanisms, the main hydrochemical properties such as pH, temperature (T), total dissolved solids (TDS), anions (F−, Cl−, SO42−), cations (Na+, Ca2+, Mg2+) and the activity of radon were also determined. The results for pH, TDS, anions and cations have been taken from the State Certificates of mineral waters, published in the public registry of the official web page of the Ministry of Health.(13) In addition, our team tried to find the correlations between the 222Rn content and the gross alpha activity, gross beta activity and the specific activity of the 226Ra in investigated waters. Because of the available data for 226Ra, gross alpha activity and gross beta activity, in the case of established good correlation we could be able to make a better decision concerning optimisation of measurements for 222Rn in all investigated mineral waters. DESCRIPTION OF THE STUDY SITE Bulgaria is divided into three major hydrogeological units—Low Danubian basin, Intermediate region and Rila-Rhodopes region. Three types of reservoirs are found in the country—stratified, fractured and mixed. The three major hydrogeological units are well described in Ref.(14) Bulgaria has a total of more than 225 hydrothermal sources of mineral waters with a total capacity of 5000 l/s. In South Bulgaria, they are 148 and in Northern Bulgaria are 77. Based on their temperature, mineral waters are cold (up to 37°C), warm (from 37 to 60°C) and hot (over 60°C). The majority of them have the temperature between 37 and 50°C. MATERIAL AND METHODS Sampling was done in the period of 3 y (2014–17). In this study, we present the results for 54 mineral waters from 24 sources, represented a different degree of mineralisation and different hydrogeological units. We investigated four drillings of mineral water from three sources in Low Danubian basin, 33, samples from different captured natural springs and drillings from twelve sources in the Intermediate region and 17 samples from different captured natural springs and drillings in Rila-Rhodopes region. For radon measurements, we collected water in plastic syringes and sampled 100 ml. The syringes were filled fully and under the water to prevent losses of radon. The radon determination was performed by Alpha Guard with Aqua Kit. The measurements were done within three h after sampling.(15) The 226Ra determination was done by measurement of its daughter 222Rn after equilibrium in an ionising chamber using Alpha Guard with Aqua Kit. Gross alpha activity was determined following BS ISO 9696:2007.(16) Measurements were performed with Thermo FHT-770T. Calibration for self-absorption was done using a natural uranium certified solution. Gross beta activity was measured using an internal laboratory method based on the evaporation of water sample to dryness and measurement of an aliquot in a low-level scintillation counter.(17) Efficiency calibration was done with a potassium chloride certified source. Physicochemical analyses were done by the Accredited Laboratory from the National Specialized Hospital for Physical Therapy and Rehabilitation. The results have been taken from the State Certificates of mineral waters, published in the public registry of the official web page of the Ministry of Health.(13) The results for the TDS, anions (F−, Cl−, SO42−), cations (Na+, Ca2+, Mg2+), pH, T, gross alpha activity, gross beta activity and 226Ra of the investigated mineral waters were correlated with radon content by statistical software tool IBM SPSS. RESULTS AND DISCUSSION The results for 222Rn specific activities of 54 analysed Bulgarian mineral waters from 24 sources, range from 0.40 ± 0.19 to 476 ± 15 Bq/l with a median value of 16 Bq/l. The mean value of 85 ± 17 Bq/l with standard deviation of 124 Bq/l demonstrates the wide range of the results. The results represent ~24% of all mineral waters in Bulgaria. The distribution of the results is shown in Figure 1. Figure 1. View largeDownload slide Histogram with the distribution of the 222Rn content in Bulgarian mineral waters. Figure 1. View largeDownload slide Histogram with the distribution of the 222Rn content in Bulgarian mineral waters. The highest values were obtained for the waters where hydrothermal circulation takes place in the fractured massif of granite and metamorphic rocks and in the Upper Cretaceous volcano-sedimentary deposits. The values for 222Rn content varied from 40.0 ± 2.8 to 476 ± 15 Bq/l. The lowest concentrations of 222Rn were detected in mineral waters originating from geothermal reservoirs built in effusive rocks and sediments as a dominant geological structure. The values are from 0.71 ± 0.17 to 15.38 ± 1.43 Bq/l. Using statistical analyses, we found that the value of the Kurtosis was 1.9 which is an indication for the platykurtic distribution of the results. The data from the Figure 1 show bimodal distribution. This could suggest the origin of the investigated waters from two sources. Probably, this hypothesis is not approved because the investigated mineral water sources belonged to a different geological origin. This could be disprove also from the results received for one mineral water source, named Hisaria. The source has 22 captured natural springs and drillings with completely different radiological and hydrochemical properties. We investigated eight of them and found values for the 222Rn content between 40 and 450 Bq/l. Up to now, it is not clear the genesis and forming of the radon waters. When compared the radon specific activity values received in the present study with similar results reported in other countries (Table 1), we found that these results are of the same order of magnitude of those reported for Italy, are less than those in Hungary and are higher than those determined in waters from Romania, Spain and Turkey. Table 1. The comparison of 222Rn content in mineral waters from different countries. Country 222Rn [Bq/l] Literature source Italy 7.7–506.2 (18) Hungary 1.8–962.8 (19) Romania 4.5–110.8 (2) Spain 0.225–130 (20) Turkey 0.14–82.6 (21) Bulgaria 0.4–476 This study Country 222Rn [Bq/l] Literature source Italy 7.7–506.2 (18) Hungary 1.8–962.8 (19) Romania 4.5–110.8 (2) Spain 0.225–130 (20) Turkey 0.14–82.6 (21) Bulgaria 0.4–476 This study Table 1. The comparison of 222Rn content in mineral waters from different countries. Country 222Rn [Bq/l] Literature source Italy 7.7–506.2 (18) Hungary 1.8–962.8 (19) Romania 4.5–110.8 (2) Spain 0.225–130 (20) Turkey 0.14–82.6 (21) Bulgaria 0.4–476 This study Country 222Rn [Bq/l] Literature source Italy 7.7–506.2 (18) Hungary 1.8–962.8 (19) Romania 4.5–110.8 (2) Spain 0.225–130 (20) Turkey 0.14–82.6 (21) Bulgaria 0.4–476 This study Correlations between physicochemical parameters and 222Rn The chemical compositions and specific activities of 222Rn in the mineral waters analysed indicate a broad variation for all parameters. The TDS ranged from a few mg/l to 10 g/l. The results of pH, temperature, anions and cations confirm the difference in the mineral waters composition. The concentration of 222Rn in water could be influenced by a number of factors, such as geological compositions of the water table, hydrochemical composition of the aquifer and chemical behaviour of the parent nuclide. Spearman correlation coefficients (two-tailed) between physicochemical parameters and 222Rn content quantified in the investigated mineral waters were estimated and presented in Table 2. The Spearman’s rho coefficients indicate a strong positive correlation between SO42− and F− anions and 222Rn (r, 0.731 and r, 0.784, respectively). No correlation was observed between 222Rn and temperature, pH, Cl−, Na+, Ca2+, Mg2+and F−. Knowing the inert chemical properties of radon, we could suggest that the high positive impact of the SO42− and F− anions is on the solubility of the parent radionuclide radium in water, resulting in radon mentioned above correlations. Table 2. Spearman correlation coefficients (r), related to particular physicochemical parameters and 222Rn content. T [oC] pH TDS [mg/l] Cl− [μg/l] F− [μg/l] Na+ [μg/l] Ca2+ [μg/l] Mg2+ [μg/l] SO42− [μg/l] 222Rn [mBq/l]  Spearman’s rho 0.094 −0.330 0.600* 0.534 0.784** 0.396 0.377 −0.051 0.731**  Sig. (2-tailed) 0.761 0.271 0.006 0.060 0.002 0.181 0.204 0.897 0.005 T [oC] pH TDS [mg/l] Cl− [μg/l] F− [μg/l] Na+ [μg/l] Ca2+ [μg/l] Mg2+ [μg/l] SO42− [μg/l] 222Rn [mBq/l]  Spearman’s rho 0.094 −0.330 0.600* 0.534 0.784** 0.396 0.377 −0.051 0.731**  Sig. (2-tailed) 0.761 0.271 0.006 0.060 0.002 0.181 0.204 0.897 0.005 **Correlation is significant at the 0.01 level (two-tailed). *Correlation is significant at the 0.05 level (two-tailed). Table 2. Spearman correlation coefficients (r), related to particular physicochemical parameters and 222Rn content. T [oC] pH TDS [mg/l] Cl− [μg/l] F− [μg/l] Na+ [μg/l] Ca2+ [μg/l] Mg2+ [μg/l] SO42− [μg/l] 222Rn [mBq/l]  Spearman’s rho 0.094 −0.330 0.600* 0.534 0.784** 0.396 0.377 −0.051 0.731**  Sig. (2-tailed) 0.761 0.271 0.006 0.060 0.002 0.181 0.204 0.897 0.005 T [oC] pH TDS [mg/l] Cl− [μg/l] F− [μg/l] Na+ [μg/l] Ca2+ [μg/l] Mg2+ [μg/l] SO42− [μg/l] 222Rn [mBq/l]  Spearman’s rho 0.094 −0.330 0.600* 0.534 0.784** 0.396 0.377 −0.051 0.731**  Sig. (2-tailed) 0.761 0.271 0.006 0.060 0.002 0.181 0.204 0.897 0.005 **Correlation is significant at the 0.01 level (two-tailed). *Correlation is significant at the 0.05 level (two-tailed). Relationship between the radon, radium and gross activities With the thought of optimising the monitoring strategy, it was interesting to investigate the relationships between the investigated radionuclides (222Rn and 226Ra), gross alpha and gross beta activity. Applying Spearman’s rank correlation test to the data set of the radon, 226Ra, gross alpha and gross beta activity concentrations measured, no correlations have been found to be significant at the 1% level. The particular correlation coefficients (r) are given in Table 3. Table 3. Spearman correlation coefficients (r), related to 226Ra, gross alpha and gross beta activity and 222Rn content. Gross beta activity [mBq/l] Gross alpha activity [mBq/l] 226Ra [mBq/l] 222Rn [mBq/l]  Spearman’s rho 0.100 0.168 0.172  Sig. (two-tailed) 0.470 0.229 0.337 Gross beta activity [mBq/l] Gross alpha activity [mBq/l] 226Ra [mBq/l] 222Rn [mBq/l]  Spearman’s rho 0.100 0.168 0.172  Sig. (two-tailed) 0.470 0.229 0.337 Table 3. Spearman correlation coefficients (r), related to 226Ra, gross alpha and gross beta activity and 222Rn content. Gross beta activity [mBq/l] Gross alpha activity [mBq/l] 226Ra [mBq/l] 222Rn [mBq/l]  Spearman’s rho 0.100 0.168 0.172  Sig. (two-tailed) 0.470 0.229 0.337 Gross beta activity [mBq/l] Gross alpha activity [mBq/l] 226Ra [mBq/l] 222Rn [mBq/l]  Spearman’s rho 0.100 0.168 0.172  Sig. (two-tailed) 0.470 0.229 0.337 CONCLUSIONS The diversity of the geological origin of Bulgarian mineral waters constitutes the main factors for the different physicochemical parameters of the waters. The highest values were obtained for the waters where hydrothermal circulation takes place in the fractured massif of granite and metamorphic rocks and in the Upper Cretaceous volcano-sedimentary deposits. The lowest concentrations of 222Rn were registered in mineral waters originating from geothermal reservoirs built in effusive rocks and sediments as a dominant geological structure. The received results show that the 222Rn activities range from 0.40 to 476 Bq/l with a median value of 16 Bq/l. The Spearman’s rho coefficients demonstrate strong positive correlation between SO42− and F− anions and 222Rn (r, 0.731 and r, 0.784, respectively). We consider that, given the inert chemical properties of radon, these correlation dependencies are related to the influence on solubility of the parent radionuclide. Correlations between226Ra/222Rn, gross alpha activity/222Rn, gross beta activity/222Rn were not observed. 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TI - QUANTITATIVE AND QUALITATIVE STUDY OF RADON CONTENT IN BULGARIAN MINERAL WATERS
JF - Radiation Protection Dosimetry
DO - 10.1093/rpd/ncy089
DA - 2018-09-01
UR - https://www.deepdyve.com/lp/oxford-university-press/quantitative-and-qualitative-study-of-radon-content-in-bulgarian-v0LV3u3bXF
SP - 48
VL - 181
IS - 1
DP - DeepDyve
ER -