J Radioanal Nucl Chem (2014) 299:311–319 DOI 10.1007/s10967-013-2845-8
Radon measurements in water samples from the thermal springs of Yalova basin, Turkey E. Tabar • H. Yakut
Received: 13 June 2013 / Published online: 20 November 2013 Ó Akade´miai Kiado´, Budapest, Hungary 2013
Abstract The radon concentration has been measured in thermal waters used for medical therapy and drinking purposes in Yalova basin, Turkey. Radon activity measurements in water samples were performed using RAD 7 radon detector equipped with RAD H2O (radon in water) accessory and following a protocol proposed by the manufacturer. The results show that the concentration of 222Rn in thermal waters ranges from 0.21 to 5.82 Bql-1 with an average value of 2.4 Bql-1. In addition to radon concentration, physicochemical parameters of water such as temperature (T), electrical conductivity, pH and redox potential (Eh) were also measured. The annual effective doses from radon in water due to its ingestion and inhalation were also estimated. The annual effective doses range from 0.2 to 0.75 lSvy-1 for ingestion of radon in water and from 2.44 to 9 lSvy-1 for inhalation of radon released from the water. Keywords
Radon Thermal water Yalova
Introduction Among the radioisotopes that contribute to natural background radiation the great attention is dedicated to radon since it presents the largest risk to human health [1, 2]. It is already known that radon and its short-lived decay products are responsible for 50 % of the effective dose received by the general public from the natural radiation sources [3]. E. Tabar (&) H. Yakut Department of Physics, Faculty of Science and Art, Sakarya University, Sakarya, Turkey e-mail:
[email protected]
Radon has three natural isotopes: 219Rn (actinon) in the U series; 220Rn (thoron) in the 232Th series and 222Rn (radon) in the 238U series. Because of the low activity concentrations of 235U and the short half-life (3.96 s) of 219 Rn, this isotope is not significant for human exposure. In addition, the risk due to the exposure of 220Rn is neglected because of its short half-life (55.6 s). Therefore, owing to its relatively long half-life (3.82 days), 222Rn is the most important isotope and it is of special interest all over the world [3, 4]. 222 Rn is a naturally occurring, chemically inert radioactive gas. It is odourless, colourless and tasteless [5]. 222 Rn is continuously produced within the rock strata by the radioactive decay of 226Ra in 238U radioactive chains [6]. When 226Ra decays, the resulting atoms of 222Rn must first escape from the soil and enter the air or water filled pores and move through the atmosphere [3]. Where the pores are saturated with water, radon is dissolved and then transported by it [6]. When the temperature and the pressure become high enough some of this water travels back up through faults and cracks and reaches the earth’s surface as thermal springs or geysers [7]. During their long passage within the earth’s crust, the thermal waters come in contact with large surfaces of igneous rocks like granites, quartz porphyry, basalt etc. which contain radium [8]. Therefore, thermal waters are usually found containing obviously high concentration of radon [7]. Thermal waters are used in thermal baths where therapy is carried out. Generally 70 % of radon in water is released to the indoor air [9]. Thus, especially in spas, the exposure to radon and its short-life decay products can reach elevated values [2]. Exposure of person to high concentration of 222Rn and its short-lived progeny for a long period leads to health problems, particularly lung cancer, resulting from inhalation of radon [10]. In addition, a very high level of radon in drinking 235
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Fig. 1 Map of the study area (Modified from Google Maps). The sampling sites are located in Termal district (yellow part on map). (Color figure online)
water can lead to a significant risk of stomach cancer [11]. Therefore, monitoring of radon levels in thermal waters is necessary to protect the public from consequences of excessive exposure to radiation. Radon in thermal spring systems and associated health risks have been recognised and documented in many regions worldwide for decades [12–19] and also led to extensive surveys in various locations of Turkey [20–24]. Yalova basin is a well-known geothermal area in Turkey. The hot springs in the area are used for therapy and drinking
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purposes by visitors. However, there is not yet radon dose assessment from hot springs for tourists and people living in this area. In this paper, the first results of radon measurements in thermal springs of Yalova basin were presented. The annual effective doses from ingestion and inhalation of radon were also estimated and the contributions of radon isotope to the exposure of people who use the spa waters for therapeutic purpose were assessed. In addition, the correlation analyses between radon and physical parameters were presented.
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Fig. 2 Schematic diagram of RAD H2O assembly (modified from Ref. [30])
Materials and methods Study area Yalova is located in north-western Turkey, on the eastern coast of the Sea of Marmara. It is situated at latitude N 29°160 3000 and longitude E 49°390 2000 (Fig. 1) [25]. Yalova has a city population of 92,166, while the population of the Yalova Province is 202,531 [26]. In terms of geography, a large part of the region consists of flat areas in the coastal sides of the city. There are also hilly areas in Armutlu district including Daz Mountain with 921 m height [27]. Geologically the study area is characterised by very large Quaternary deposits and the Miocene Kilic Formation. The Kilic Formation is situated in the south of the study area and shows a sedimentary stratigraphy consisting of clay stone, sandstone, siltstone, conglomerate and marl. This Formation forms the ridges which are perpendicular to the Marmara Sea. Quaternary deposits overlie the Kilic Formation. Quaternary deposits consist of stratified materials having varied grain sizes, and are derived from the various geological units in the vicinity. The region lies on the North Anatolian Fault Zone [27]. An earthquake in 1999 has damaged drastically this city. The effects of tectonic movements in the region have formed faults and fractures. The area is characterized by NW–SE and NE–SW trending faults. There are normal and reverse faults along the valleys where thermal sources originate. The distribution of thermal springs is controlled by these fracture patterns and most of them formed by normal faults [28]. Sampling Radon concentration measurements were performed in selected five thermal waters during a period of time
between March 2013 and August 2013. Before the sampling, approximately 15 l of water was let out. After that, the water samples were collected in special glass bottles (40 and 250 ml capacity). All the samples were taken from the respective locations with great care since sampling technique is generally the major source of error in the radon measurements. Measurement technique 222
Rn concentrations in thermal waters were measured using RAD 7, an electronic radon detector manufactured by Durridge Company Inc., connected to a RAD H2O (radon in water) accessory [29]. RAD 7 can measure radon levels in air, water and soil. The schematic diagram of RAD 7 with RAD H2O accessory is presented in Fig. 2. The RAD 7 can compute the energy of each alpha particle which can partially distinguish the sample pulse from the noise, and makes it possible to recognize to which isotopes (218Po, 214Po, etc.) a radioactive reading belongs. Therefore, one can immediately distinguish old radon from new radon, radon from thoron, and signal from noise [29]. A sample spectrum of RAD 7 was given in Fig. 3. In the setup, the sampling bottles (40 or 250 ml) are connected to the RAD 7 detector and the test is started using selected protocols (Wat-40 or Wat-250). The internal air pump of RAD 7 runs for 5 min, re-circulating a closed air-loop through the water sample, purging radon from the water into the RAD 7. The system waits a further 5 min for reaching a state of equilibrium. After reaching equilibrium between water, air, and radon progeny attached to the detector, the system starts counting the radon activity concentration of the sample. After 5 min it prints out a short-form report. The same process runs again 5 min later, and for two more 5 min periods after that. At the end of the run (30 min after the start), the RAD 7 prints out a
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The presence of 220Rn in ground waters would indicate that the reservoir of water is located near a source [33].
Results and discussion The results of 222Rn measurements in thermal waters of Yalova basin have been represented in Fig. 4. The 222Rn activity concentrations range from 0.21 to 5.82 Bql-1 with an average value of 2.4 Bql-1. The radon activity concentration levels reported in this study are much lower than the WHO recommended level of 100 Bql-1 [34]. In addition, the recorded values of radon concentration do not exceed the safe limit of 11 Bql-1 proposed by the US Environmental Protection Agency (USEPA) [35]. Therefore, it can be concluded that the analysed thermal waters in this study are safe for drinking purpose. As can be seen from Fig. 4, the radon activity in thermal waters varies over a wide range. One reason for the radon changes can be the seismic processes accompanying the earthquake events in the region. Geologically, the Yalova province is located on North Anatolian Active fault which was the site of the most recent major earthquake in the country in 1999 [28]. It has been shown in several studies that there is a relation between the variations of radon concentration in water and the seismic activities [36–38]. Another reason for variation of radon concentration may be the different geological structure of the aquifer where these waters originate [39]. It is already known that granitic rock aquifers show higher radon concentrations than sedimentary rock aquifers [39]. The statistic of 222Rn contents in five thermal waters monitored in Yalova geothermal area have been presented in Table 1. As can be seen from Table 1 the mean values of
Fig. 3 Sample spectrum of RAD 7. The windows, A: 6 MeV from 218 Po 6.05 MeV from 212Bi, B: 6.78 MeV from 216Po, C: 7.69 MeV from 214Po, D: 8.78 MeV from 212Po [29]
summary, showing the average radon reading from the four cycles counted, a bar chart of the four readings, and a cumulative spectrum [29]. The details of the system and measurement technique can be found elsewhere [4, 5, 31, 32]. The background level was determined from the measurement of a radon free water sample. The distilled water sample kept sealed for 4 weeks was used as radon free water sample. The minimum detectable concentration (MDA) was found to be 0.074 Bql-1. In the analysed water samples there was no detectable thoron. Natural waters may be enriched in both the radon isotopes if there is a source but their distributions are influenced by their half-lives and mixing of waters. The half-life of 222Rn (3.82 days) is long enough so that its concentration could be maintained during its transport over long distance, whereas 220Rn (55 s) dissipates very quickly. Fig. 4 222Rn concentrations in thermal waters of Yalova basin during the study period
Mide Goz Ayak Kursunlu Valide
222
-1
Rn(Bql )
6
4
2
13
A
13
ug
20
20
13
3 5
A
ug
l2
01
3 Ju 29
l2 Ju
25
Date
123
01
20 1 n
Ju
M
3
20 13
ay
20
A
pr 15
11
13
3 20 1 22
8
A
pr
ar M 16
4
M
ar
20
20
13
13
0
J Radioanal Nucl Chem (2014) 299:311–319
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Table 1 Statistic of
222
Sampling station
Number of Samples
AM (Bql-1)
GM (Bql-1)
Median (Bql-1)
Maximum (Bql-1)
Minimum (Bql-1)
Mide water Go¨z water
10
1.24
0.97
1.17
3.27
0.28
10
3.57
3.44
3.45
5.82
2.26
Ayak water
10
0.97
0.70
0.88
3.29
0.21
Kurs¸ unlu Spa
10
3.20
3.00
3.05
4.70
1.71
Valide Spa
10
3.00
2.66
3.06
4.75
0.78
Rn content in thermal waters of Yalova basin
Table 2 The comparison of 222 Rn activities observed in this study with the results of other studies
Water type
Rn activity (Bql-1)
Study
Country
Thermal water
53.4–292.5
Song et al. 12]
China
Thermal water Thermal water
7.7–506.2 3.18–46.9
Bertolo et al. [2] Chaudhuri et al. [8]
Italy India
Thermal water
0.225–130
Thermal water
1.8–98
Thermal water
1–560
Thermal water
4.5–110.8
Duenas et al. [14]
Spain
Eross et al. [15]
Hungary
Horvath et al. [16]
Venezuela
Roba et al. [17]
Romania
Thermal water
145–2,731
Beitollahi et al. [18]
Iran
Thermal water
24.5–648
Nikolov et al. [19]
0.51–8.5
Bolca et al. [20] Gu¨rler et al. [21]
Serbia ˙Izmir, Turkey Bursa, Turkey Amasya, Turkey
Thermal water Thermal water
222
222
2.513–82.553
Thermal water
0.3–31
Thermal water
0.11–0.71
Tabar et al. [22] ¨ ner et al. [23] O
Thermal water
0.14–5.77
Erees et al. [24]
West Anatolia, Turkey
Thermal water
0.21–5.82
This study
Yalova, Turkey
Rn ranges from 0.97 to 3.57 Bql-1. The lowest 222Rn concentration (0.21 Bql-1) was recorded in Ayak Water, whereas the highest concentration (5.82 Bql-1) was measured in Goz Spa. The high value of radon measured in a water sample from Goz Spa may be due to the seismic or the meteorological events. Especially seismic events cause rise in the emanation coefficient of radon from the rocks [40]. On the other hand, the low values of 222Rn concentrations observed in water samples from Ayak and Mide waters are probably associated with the very low amounts of the mother nuclide, 226Ra, in the reservoir of these waters [41]. In the Table 2 values of radon concentration obtained during this study have been compared with those reported by other works. As can be seen from Table 2, our results are comparable with those reported for geothermal springs in West Anatolia [24] and in Izmir [20], but higher than the values reported for geothermal springs in Amasya [23]. On the other hand, there are thermal waters where 222Rn activity can reach higher levels [2, 8, 12, 14–22]. In addition to radon concentration, physicochemical parameters of thermal water such as temperature (T), pH, electrical conductivity (EC) and redox potential (Eh) were measured in order to evaluate the impact of these parameters on radon concentration. The details of the
Dikili, Turkey
physicochemical measurements of hot waters are given in Table 3. The mean pH values of the waters are very similar and change between 7.19 and 7.54. It can be said that thermal waters in the area are slightly acidic. This may be related to the contact with the carbonate rocks such as limestone and dolomite [17]. In the analysed thermal waters, the average EC range from 1.42 to 2.15 mS cm-1. The EC is directly correlated with the amount of the salts dissolved in the water [17]. Therefore, it can be said that Ayak and Valide waters are poor in terms of dissolved salts. The ranges of the other parameters are from 33.7 to 96.1 °C for temperature and from 18.94 to 27.54 mV for redox potential. In Fig. 5 222Rn concentrations plotted as functions of water temperature, pH, EC and redox potential are given. The data indicate that there is no significant relation between radon and pH (Fig. 5a). The variation of 222Rn content with increasing temperature (Fig. 5b) shows a negative correlation (r = -0.54) compatible with the law of dissolution of gasses in liquids. It has been reported that there is a direct relationship between the radon concentration and the temperature of the water [39]. Radon is highly soluble, especially in cold water, but its solubility decreases with the increase in temperature. As a result, high radon levels correspond to low water
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Table 3 Physico-chemical characteristics of thermal waters of Yalova basin Sampling station
Temp. (°C)
EC (mScm-1)
pH
Eh (mV)
Range
Mean
Range
Mean
Range
Mean
Range
Mean
Mide water
30–38
33.7
6.15–7.95
7.45
1.95–2.32
2.14
1.4–69.2
24.30
Goz water
55–60
57.3
5.90–7.70
7.19
1.95–2.34
2.15
5.1–80
23.91
Ayak water
94–98
96.1
6.50–8.10
7.45
0.13–2.54
1.42
6.4–34.8
18.94
Kursunlu Spa
56–61
60
6.39–7.85
7.54
0.15–2.32
1.69
8.9–71.7
22.25
Valide Spa
60–65
62.4
6.50–7.80
7.44
0.40–2.19
1.43
1.6–60
27.54
a
b
10
10
8
8
6
6
Rn ( Bql -1)
Rn ( Bql -1)
Mide
r=-0.54
r=0.19
4
222
222
4
Goz Ayak Kursunlu Valide
2
2
0 5,5
0 6,0
6,5
7,0
7,5
8,0
8,5
9,0
30
40
50
c
d 10
10
70
80
90
100
r=-0.28
r=0.31 8
6
6
Rn ( Bql -1)
8
4
4
222
222
Rn ( Bql -1)
60
T ( 0C)
pH
2
2
0
0 0
0,5
1,0
1,5
2,0
2,5
3,0
0
10
20
30
EC (mScm -1)
Fig. 5
40
50
60
70
80
Eh (mV)
222
Rn activity versus pH, temperature (T), electrical conductivity (EC) and redox potential (Eh)
temperatures [42]. A positive correlation has been observed between the 222Rn concentrations and EC (Fig. 5c), but the correlation coefficient is weak (r = 0.31). Low redox potential conditions decrease the adsorption of radium onto aquifer surfaces. This leads to increase of radium concentration in water [17]. It is already known that there is a direct correlation between radon and radium activities because of their parent daughter relationship [17]. Therefore, it is expected that
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the radon concentration in water increases with decreasing redox potential. Although a negative trend is observed between the radon and redox potential, the correlation coefficient is weak (r = -0.28). Therefore, this behaviour has not been observed clearly in thermal waters of Yalova basin. It can be inferred from the results illustrated in Fig. 5 that there is no significant correlation between the radon activities and the analysed physicochemical parameters.
J Radioanal Nucl Chem (2014) 299:311–319 Table 4 Dose contribution from
317
222
Rn
Ingestion of 222Rn (lSvy-1)
*Dose to Stomach (lSvy-1)
Inhalation of 222Rn (lSvy-1)
Total Effective Dose (lSvy-1)
Mide water Go¨z water
0.26
0.009
3.12
3.38
0.75
0.027
9
9.75
Ayak water
0.20
0.007
2.44
2.64
Kurs¸ unlu Spa
0.68
0.025
8.06
8.74
Sampling station
Valide Spa
0.63
0.023
7.56
8.19
Mean
0.50
0.018
6.05
6.55
The annual effective dose to an individual consumer due to intake of radon from water is calculated using the relation [43]: DRn ing: ¼ CRn Ia Df
here CRn is the radon concentration of ingested water in terms of Bql-1, Ia describes the annual intake of drinking water (60 ly-1) and Df refers to dose conversion factor, 3.5 9 10-3 lSvBql-1. The dose contribution arising from the release of 222Rn in water to the air is calculated using the relation [43]: Rn DRn inh: ¼ Cw Rw F T Df
* Dose conversion factor was taken from Ref [44]
ð1Þ
ð2Þ
-3
Table 5 Comparison of the annual effective doses estimated in this study with those reported worldwide Water type
Annual effective dose (lSvy-1)
Study
Country
Ingestion
Inhalation
Thermal water
0–4,200
–
Horvath et al. [16]
Venezuela
Thermal water
3,230
–
Beitollahi et al. [18]
Iran
Thermal water
450–4,700
–
Nikolov et al. [19]
Serbia
Thermal water
1.75
–
Tabar et al. [22]
Dikili, Turkey
Thermal water
–
0.28–1.78
Oner et al. [23]
Amasya, Turkey
Thermal water
0.20–0.75
2.44–9
This study
Yalova, Turkey
Estimation of doses from ingestion and inhalation The radon in water can be taken by human in two ways: by ingestion of dissolved radon in drinking water and by inhalation of radon released from water to the air [43]. In the case of ingestion, radon and its daughters present in the drinking water can impart a radiation dose mainly to the stomach. However, radon gas present in the drinking water can also escape into the indoor air during showering and other domestic uses and can cause a significant increase in the risk of lung cancer due to the radon inhaled [5]. It is known that 70 % of radon in water is released to the indoor air [10]. Thermal waters in Yalova basin are frequently used by visitors for drinking purpose. Besides, these thermal waters are used in thermal baths where thermal therapy is carried out. Therefore, in order to evaluate the radiological risk from exposure, the annual mean effective doses from ingestion and inhalation of 222Rn in water were estimated.
where CwRn (in Bqm ) is the radon concentration in water, Rw is the ratio of radon in air to the radon in water (10-4), T is the average indoor occupancy time per person (7,000 hy-1), F is the equilibrium factor between radon and its progenies (0.4), and Df is a dose conversion factor (9 nSv h1 Bq1 m3 ) [43]. The results of dose estimations for thermal waters of Yalova basin have been given in the Table 4. The World Health Organization (WHO) recommends the safe limit of the annual effective dose received from drinking water consumption to be 100 lSvy-1 [34]. According to WHO [34], if dose is lower (or equal) than 100 lSvy-1, then, the water is suitable for drinking purpose and no further action is necessary, however, if dose is higher than 100 lSvy-1, then remedial measures are needed to reduce it [5]. In this study mean annual effective doses for ingestion and inhalation from drinking water were computed to be 0.50 and 6.05 lSvy-1, respectively. In addition, the total average annual effective dose was estimated to be 6.55 lSvy-1. These values are well below the reference level of 100 lSvy-1 recommended by WHO [34]. It may be evident from these results that radon poses no threat to the people who use the spa waters for medical purposes. In the Table 5 the estimated annual effective doses from radon in thermal waters of Yalova basin due to its ingestion and inhalation have been compared with the results of similar studies. As can be seen from table our annual effective doses due to the ingestion of dissolved radon in thermal water are lower than the annual effective doses for Venezuela [16], Iran [18], Serbia [19] and Dikili geothermal area of Turkey [22]. Especially, the doses for Venezuela [16], Iran [18] and Serbia [19] are significantly higher than the other results reported in Table 5. Our annual effective doses for inhalation are higher than those reported for geothermal springs in Amasya [23], Turkey.
Conclusion In this study, the 222Rn concentrations in water samples from the thermal springs of Yalova basin have been
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determined using commercially available radon measuring device RAD 7 of Durridge. The results obtained from this study reveal the fact that dissolved 222Rn levels are generally low. The activities presented in this study are less than the reference levels proposed by international agencies. The measured radon concentration values are also lower than those reported in other studies from Turkey [20–24]. The calculated doses for ingestion and inhalation are also well below the total indicative dose of 100 lSvy-1 suggested by WHO [34]. Thus, 222Rn present in the hot waters of the area of this study do not pose any significant health risk to the public. In addition to 222Rn measurements, physicochemical parameters of thermal waters such as temperature (T), pH, EC and redox potential (Eh) were also measured in order to evaluate the impact of these parameters on radon concentration. From the results of these measurements, a negative correlation was observed between 222Rn level and temperature (T) of the hot waters. More data on 222Rn level in thermal waters will be needed for a deeper understanding of the influence of geological and hydro-chemical factors in Yalova. Acknowledgments The authors thank Prof Ibrahim OKUR and Assoc Prof B. Tamer TONGUC for their careful reading of the manuscript. The authors also wish to express their graduate to Miss Melek SANKUR for her valuable contribution during the sampling and to Fatih ARICI for providing the map of the study area. This work was supported by Research Fund of the Sakarya University. Project Number: 2012-02-02-007.
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