Radiation Protection Dosimetry (2014), Vol. 162, No. 3, pp. 375 –381 Advance Access publication 27 November 2013
doi:10.1093/rpd/nct308
MEASUREMENTS OF RADON CONCENTRATIONS IN WATERS AND SOIL GAS OF ZONGULDAK, TURKEY Abdullah Koray1,*, Gizem Akkaya2, Ays¸egu¨l Kahraman2 and Go¨kay Kaynak2 1 Ereg˘li Education Faculty, Bu¨lent Ecevit University, 67300 Kdz. Ereg˘li, Zonguldak, Turkey 2 Physics Department, Faculty of Arts and Sciences, Uludag University, Gorukle Campus, Bursa 16059, Turkey *Corresponding author: [email protected]
The radon concentrations in soil-gas and water samples (in the form of springs, catchment, tap, thermal) used as drinking water or thermal were measured using a professional radon monitor AlphaGUARD PQ 2000PRO. The measured radon concentrations in water samples ranged from 0.32 to 88.22 Bq l21. Most of radon levels in potable water samples are below the maximum contaminant level of 11 Bq l21 recommended by the US Environmental Protection Agency. The calculated annual effective doses due to radon intake through water consumption varied from 0.07 to 18.53 mSv y21. The radon concentrations in soil gas varied from 295.67 to 70 852.92 Bq m23. The radon level in soil gas was found to be higher in the area close to the formation boundary thrust and faults. No correlation was observed between radon concentrations in groundwater and soil gas. Also, no significant correlation was observed between soil-gas radon and temperature, pressure and humidity. The emanation of radon from groundwater and soil gas is controlled by the geological formation and by the tectonic structure of the area.
INTRODUCTION Radon is a radioactive, water-soluble noble gas produced by the natural decay of 226Ra (radium) and is widespread in soil and rock(1). Radon has a half-life of roughly 3.8 d and decays by alpha-particle emission to the solid daughter product 218Po ( polonium). Radon is introduced into ground water from a radium source primarily by diffusion along microcrystalline imperfections within the rock(2, 3). The migration of radon through a porous material or fractured rock occurs primarily by advective transport (4). The migration and concentration of radon in an anisotropic medium, such as bedrock, is highly variable and dependent upon the rock type, the physical condition of the rock (i.e. fractures, joints and porosity), the aquifer parameters and the aquifer geochemistry(5, 6). Another source of radon-rich water is the build up of radium-rich material on the surface of cracks and fissures from which radon emanates directly into water through cracks(7). Radon emission from soil, rocks and degassing from water are of significant interest due to the source of radon in houses and geological mapping(8). Terrestrial radiation is emitted from the natural radionuclides present in varying amounts in soil, air, water and other environmental materials(9). The levels of radioactivity in water and soil are important because of their radiological effects. The internal irradiation of lungs by alpha-emitting short-lived decay products of radon and thoron causes lung cancer. Cothern et al.(10) estimated that 1–7 % of lung cancer fatalities in the USA related to indoor radon levels derive from groundwater use.
Radon concentration measurements were previously performed in some mines and caves in Zonguldak by Aytekin et al.(11) and Baldık et al.(12). The aims of this study are to draw a general picture of the natural radioactivity of waters and soil in Zonguldak. Measurement of 222Rn has been performed on 30 water samples taken from different sources. Measurement of radon (222Rn) concentration in soil gas was performed using the active method at 21 sites. In the same locations thoron (220Rn) concentrations were measured with the AlphaGUARD gauge. As far as is known, this is the first study to determine the radon concentrations in waters and soil in Zonguldak basin.
Study area Zonguldak province is situated between 4180000 and 4183500 N latitude and between 3181800 and 3281900 E longitude and has an area of 3309 km2, and had a population of 619 703 as of December 2012. The Zonguldak Basin, which contains a thick Carboniferous clastic sequence with several coal seams, is located in the northwestern Turkey on the Black Sea coast. It has two orogenesis histories: the pre-Cretaceous Hercynian and the late-Cretaceous Alpine. In the basin, stratigraphy includes Paleozoic, Mesozoic, Tertiary and crystalline units. Rock units are found as volcanic, volcano–sedimentary and sedimentary of origin(13). Both northern and southern margins of the basin have tectonic characteristics. Turkish seismic code defines northern of the basin as being in the second-degree and southern of the basin in the first-degree earthquake zone(14). These features
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Received 15 May 2013; revised 5 November 2013; accepted 6 November 2013
A. KORAY ET AL.
make Zonguldak an interesting candidate for radiological studies. MATERIALS AND METHODS Measurement of radon (222Rn and 220Rn) activity in soil gas
Measurement of radon (222Rn) activity in water An experimental technique described in detail by Kochowska et al.(15) was employed. The radon concentration in water was measured using the professional radon monitor AlphaGUARD PQ2000 PRO. For water measurements the additional equipment AquaKIT was used. Figure 2 shows the set-up for radon in water measurements. In a close gas cycle, radon was expelled from the water samples ( placed in degassing vessel) using the pump. The security vessel was connected with the degassing vessel. All drops would deposit in it if they had got into the gas cycle during the degassing process. This way the stress of the water vapour was minimised for the radon monitor. The background of empty set-up was measured for a few minutes before every water-sample measurement. After that the water was injected into the degassing vessel, and the AlphaGUARD and AlphaPUMP were switched on. After 10 min the pump was switched off and the AlphaGUARD remained switched on for another 20 min and so the radon measurement was continued. This cycle was repeated three times in order to obtain a better precision. The AlphaGUARD monitor worked in a ‘flow’ mode and the radon concentration was recorded every
Figure 1. Schematic view of the experimental set-up for radon measurements in soil gas.
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AlphaGUARD PQ2000 PRO can measure a range of radon concentrations from 2 to 2 000 000 Bq m23. The system allows for spot measurements as well as for continuous soil-gas monitoring (Fig. 1). Stitz soil gas probe consisting of capillary probe and drilling rod with an air-lock and rivet was installed at 1 m depth in soil with the aid of a heavy hammer. The soil gas was pumped into the ionisation chamber of the AlphaGUARD (in flow mode) with AlphaPUMP. AlphaPUMP was set to perform 1 l min21. To guarantee and to check a complete exchange of the soil gas in the 0.6-l ionisation chamber, 1-l capacity air bag was used. A tube connection between the soil-gas probe and AlphaPUMP includes filter cartridge against radon progeny products and water break-in. The chamber was filled with soil gas. The measuring mode of AlphaGUARD was selected as ‘1 min FLOW’. The total concentration of both isotopes [222Rn (t1/2 ¼ 3.82 d) and 220Rn (t1/2 ¼ 55 s)] were measured during pumping for 10 min. In order to measure the radon (222Rn) concentration only, AlphaGUARD and probe were separated and the chamber was kept tightly closed from all sides for 10 min—the time needed for thoron (220Rn) to decay. AlphaGUARD remained switched on for about another 10 min and so radon measurement was continued. Afterwards, the average total concentration from the first 10 single, 1-min measurements and
average radon concentration from the last 10 single, 1-min measurements recorded by the AlphaGUARD were obtained. The meteorological parameters, which are temperature, pressure and the humidity, were also recorded in the same cycle. This method gave information about the temporary thoron and radon concentrations in soil gas. One measurement was taken from each sampling location.
RADON IN WATERS AND SOIL GAS, ZONGULDAK
minute. The flow rate of the pump was 0.3 l min21. The radon concentration in the system was determined with the AlphaGUARD, whose ionisation chamber was also a part of the gas cycle. The determination of radon concentration in water samples was based on the radon concentration indicated by the AlphaGUARD. This value was not the radon concentration in the water sample yet because radon driven out had been diluted in the air within the measurement set-up and a small part of the radon remained diluted in the watery phase. The following equation served to determine the radon concentration in the measured water samples: Vsystem Vsample þ k C0 Cwater ¼ Cair Vsample Cwater is the radon concentration in the water sample (Bq m23); Cair the radon concentration in the set-up after expelling radon from the water sample (Bq m23); C0, background (Bq m23); Vsystem the interior volume of the measurement set-up (ml) and Vsample the volume of the water sample (ml) and k the radon distribution coefficient.
RESULTS AND DISCUSSION The results of thoron and radon measurements in soil gas and radon in water in Zonguldak basin are given in Table 1. The sample locations on a geological map are shown in Figure 3. In soil gas, the maximum (59 885.06 Bq m23) and minimum (4299.56 Bq m23) thoron concentrations were recorded in Ormanlı and Tu¨rkali areas, respectively. An average thoron value in
soil gas was found to be 29 708.16 Bq m23. In soil gas, the maximum radon concentration (70 852.92 Bq m23) was recorded in I˙sabeyli area, on formation boundary thrust, and close to the faults. The minimum radon concentration (295.67 Bq m23) was recorded from the Gu¨rbu¨zler area. An average radon value for all locations in soil gas was found to be 25 853.62 Bq m23. The second and third highest values were recorded in Buruncuk (56 328.0 Bq m23) and Kokaksu (45 490.53 Bq m23) areas, respectively. The reason for this may be the proximity to the fault lines(16). As a geological tool radon monitoring technique can be used in earthquake prediction. With this technique fault zones have been recognised worldwide with fairly good precision(17). The fourth highest value was recorded in Alpaslan (46 455.61 Bq m23). The higher value of radon in the soil gas from Alpaslan may be due to the fact this location is close to faults and river Yenice and that the moisture content may enhance the radon level in the sample(18). Also, all samples with .25 853.62 Bq m23 (average value) were collected at sites located close to the faults (location 1, 2, 3, 8, 9, 22 and 24). The average radon values for northern (locations 1, 2, 3, 4, 5, 6, 9, 11, 12, 13, 14, 15 and 16) and southern (locations 7, 8, 10, 17, 18, 19, 20, 21, 23 and 24) parts of the basin in soil gas were found to be 27 823.35 and 23 227.32 Bq m23, respectively. The results from both parts were found close to each other. A total of 30 water samples were sampled and analysed. For each site, two measurements were taken and then averaged. The radon concentration in the drinking water was found to vary from 0.32 to 21.30 Bq l21 with a mean value of 6.77 Bq l21. The radon
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Figure 2. Schematic view of the experimental set-up for radon measurements in water.
Table 1. Levels of radon and thoron in soil gas with temperature (T ), pressure (P) and humidity rate (H ) and groundwater with ingestion dose (ID) in different locations. Loc. no.
Location
Soil-gas thoron concentration (Bq m23)
Soil-gas radon concentration (Bq m23)
49 058.7+1684.76
56 328.0 +1227.65
26.7
995
68.8
T (8C) P (mbar) H. (%)
Buruncuk
2
Ilıksu
17 824.57+1893.96
39 044.0+731.98
33.8
1014
38.2
3
Kokaksu
49 798.36+5548.27
45 490.53+1037.78
32.1
1012
43.1
4 5 6
Tu¨rkali Çamlık Sog˘anlıyo¨ru¨k
4299.56+384.98 — 49 513.59+2403.21
3828.44+149.71 — 24 349.94+511.16
25.1 — 33
1011 — 978
58.7 — 36.6
7
Du¨zpelit
14 166.99+698.05
6733.58+288.73
32.1
983
40.2
8
I˙sabeyli
15 803.08+4013.75
70 852.92+1353.16
32.5
977
32.2
9
Alpaslan
28 056.39+2691.8
46 455.61+835.55
35.6
1001
27.1
10
Gaziler
28 445.81+1780.04
21 159.11+849.28
32.8
1005
31.8
11 12 13
Geris¸ Kerimler Dag˘lıca
22 898.73+2743.98 12 957.09+2121.37 20 683.64+1203.79
28 378.07+1084.58 21 986.91+991.36 10 356.36+234.54
26.1 25 31.3
1007 1007 964
45.3 51.6 34.3
14
Balc¸ıklı
39 214.48+3435.16
19 267.30+299.91
33.3
985
34.5
15 16
Sofular Beycuma
29 358.55+1365.76 31 565.26+2184.92
14 737.45+513.3 23 657.60+519.97
33.6 31.4
977 983
31.2 32.1
17 18
Gu¨rbu¨zler Eg˘erci-1
10 112.33+701.08 —
26.4 —
982 —
48.7 —
19
Eg˘erci-2
20 21 22 23
Fındıklı Hu¨seyinli Is¸ıklı Uludag˘
33 602.84+2797.91 35 809.66+3091.72 45 029.57+2724.4 25 787.2+1873.53
7229.16+197.21 24 580.74+580.47 31 444.61+628.67 15 019.20+414.85
28.9 32.4 30.6 27.9
24
Ormanlı
59 885.06+6461.59
31 730.94+818.86
27
—
295.67+22.78 — —
—
—
—
998 987 978 975
43.5 41.3 35.2 59
1005
63.6
Radon concentration in water (Bq l21)
ID (mSv y21)
1.14+0.23 15.34+0.75
0.24 3.22
46.22+3.44
9.71
88.22+5.71
18.53
3.57+0.47 0.71+0.30 9.25+0.92 21.30+0.98 9.24+0.79 12.87+0.65
0.75 0.15 1.94 4.47 1.94 2.70
4.31+0.71
0.91
5.64+0.11
1.18
13.88+0.49
2.91
5.18+0.45 5.60+0.54 2.82+0.20 0.82+0.15 1.88+0.03 1.66+0.22 4.52+0.33 3.63+0.35 15.44+0.59
1.09 1.18 0.59 0.17 0.39 0.35 0.95 0.76 3.24
6.05+0.51 7.82+0.63
1.27 1.64
5.16+0.43
1.08
0.66+0.01 0.32+0.01 10.16+0.82 6.77+0.42
0.14 0.07 2.13 1.42
13.75+0.58
2.89
Tap water Natural spring Thermal water Thermal water Catchment Catchment Catchment Tap water Catchment Natural spring Natural spring Natural spring Natural spring Catchment Catchment Tap water Catchment Catchment Catchment Catchment Catchment Natural spring Catchment Natural spring Natural spring Catchment Tap water Well water Natural spring Tap water
A. KORAY ET AL.
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378
1
Water type
RADON IN WATERS AND SOIL GAS, ZONGULDAK
Figure 4. Contour maps of radon concentration in (a) water and (b) soil gas.
concentrations in thermal water were found to be 46.22 and 88.22 Bq l21. All radon concentration results for thermal waters are ,100 Bq l21, which is the limit proposed by the Commission of the European Communities(19). The high radon concentration in thermal waters compared with the drinking water is an expected result due to the effects of geothermal systems. In the surface waters such as lakes and rivers, the radon concentrations are generally in the range of a few Bq l21, while in groundwaters occurring in sedimentary rock aquifers, the levels range
from 1 to 50 Bq l21. Some geothermal waters have considerably higher radon levels, e.g. values up to 1868 Bq l21 were reported for some thermal springs(20). The samples collected from springs display generally higher values (mean ¼ 9.69 Bq l21) than those coming from the catchments (5.29 Bq l21) and taps (4.5 Bq l21). The catchments allow a long contact of the water with the atmosphere inducing the transfer of radon from the liquid to the gas phase. Although some authors demonstrated some radon increase in
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Figure 3. Study area and sampling sites.
A. KORAY ET AL. Table 2. Statistical results for radon concentrations in soil gas and water samples. Statistics Median Arithmetic mean+SE
Correlation with soil gas Correlation with water
Water
21 986.91 25 853.62 + 4123.276 17 972.94 16 091.08 295.67– 70 852.92 1.189 1.495 Normal p ¼ 0.062 1
5.64 6.70 + 1.09 4.73 4.67 0.32– 15.44 0.579 20.669 Normal p ¼ 0.193 0.136
0.136
1
Table 3. Correlation of radon concentration in soil gas with meteorological parameters. Parameter
Radon and temperature Radon and pressure Radon and humidity
Correlation coefficient
Significance level
0.267
0.242
0.184 20.059
0.426 0.798
CONCLUSION
waters flowing in old distribution networks due to radium adsorption, the overall water radon activity in tap waters will be significantly reduced during transport from captation to the point of use(21). On the basis of the results, contour maps of radon concentration in soil gas and water in Zonguldak basin are shown in Figure 4. The statistical summary of the data located in Table 1 is given in Table 2. The frequency distributions of radon concentration in soil gas and water were determined. Whether the data comply with the normal distribution was tested with Shapiro –Wilk or Kolmogorov– Smirnov tests. The Shapiro–Wilk test is more appropriate for small sample sizes (,50 samples) and therefore, when the number of sample is ,50, Shapiro–Wilk normality test is used. In cases where the value of p (significance level) is .0.05, the distribution of data complies with the normal distribution. As a result of the test, it was found that the frequency distributions obtained for soil gas and water can be fitted to a normal distribution. Although a weak positive correlation between the radon concentration in soil gas and water was observed, a statistically significant correlation was not found. The correlation between the radon concentration in soil gas and the meteorological parameters, which are temperature, pressure and humidity for the values
The first measurements of radon concentrations in soil gas and water in Zonguldak were carried out. It can be concluded that radon emanation from the ground is a function of the tectonic structure of the investigated area. The radon level in soil-gas was found higher in the area close to the faults. With few exceptions, the levels of radon in the water in Zonguldak are below the recommended radon level(23). The results showed that the radon concentrations in the tap and catchment water in Zonguldak are lower than that in spring water. No correlation was observed between the radon concentrations in groundwater and soil gas. Finally, radon is still a big concern for public health, especially where sources with high radon concentrations are used for water supply. It is possible that consumers of water from these sources may take up elevated quantities of radon through ingestion. This study contributes to the database of the radioactivity level in the Zonguldak province. The results may also be used to evaluate any radioactivity change in the future. ACKNOWLEDGEMENTS ¨ zkan DEKA The authors are thankful to Mr. Kemal O Mining Topographer for his cooperation in preparing the map of the study area. REFERENCES
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1. Evans, R. D. Engineers guide to the elementary behavior of radon daughters. Health Phys. 17, 229–252 (1969).
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SD Geometric mean Range Skewness Kurtosis Frequency distribution
Soil gas
in Table 1, is evaluated (Table 3). The negative correlation (20.059) has been observed between radon concentration and humidity, whereas positive correlations 0.267 and 0.184 have been observed between the radon concentration and temperature and pressure, respectively. On the basis of radon concentration in each water sample (see in Table 1), the annual weighted estimate of consumption rate and the dose coefficient of the concerned radon isotope per unit intake, which is equal to 3.5 nSv Bq21, the annual mean ingestion dose values were calculated(22). The consumption rate of 60 l y21, which was taken from United Nations Scientific Committee on the Effects of Atomic Radiation(22), has been considered. The expected dose due to 222Rn varies from 0.07 to 18.53 mSv y21. The inhalation dose for thermal springs per treatment session of 0.5 h was also calculated. The equilibrium factor of radon indoors, dose conversion factor and air-water concentration ratio were taken as 0.4, 9 nSv h21 per Bq m23 and 1024, respectively(22). The expected inhalation dose rates for 222Rn levels in Ilıksu and Kokaksu are 8.32 and 15.88 nSv respectively.
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RADON IN WATERS AND SOIL GAS, ZONGULDAK ¨ . and Okandan, E. Fracture/cleat analysis 13. Karacan, C. O of coals from Zonguldak Basin_(northwestern Turkey) relative to the potential of coalbed methane production. Int. J. Coal Geol. 44, 109–125 (2000). 14. Republic of Turkey Prime Disaster and Emergency Management Presidency. Tu¨rkiye Deprem Bo¨geleri Haritası. Available on http://www.deprem.gov.tr/sarbis/ depbolge/zonguldak.gif (accessed on 8 May 2013). 15. Kochowska, E., Mazur, J., Kozak, K. and Janik, M. Radon in well waters in the Krako´w area. Isot. Environ. Health Stud. 40, 207– 212 (2004). 16. Singh, B., Singh, S., Bajwa, B. S., Singh, J. and Kumar, A. Soil gas radon analysis in some areas of Northern Punjab, India. Environ. Monit. Assess. 174, 209–217 (2011). 17. Khattak, N. U., Khan, M. A., Nawab, A. and Muntazir, S. A. Radon monitoring for geological exploration: a review. J. Himalayan Earth Sci. 44(2), 91– 102 (2011). 18. Singh, B. and Virk, H. S. Effect of soil and sand moisture content on radon diffusion using plastic track etched detector. Radiat. Meas. 26(1), 49–50 (1996). 19. Commission of the European Communities (CEC). Commission recommendation of 20 December 2001 on the protection of the public against exposure to radon in drinking water supplies. Official Journal of the European Communities, C(2001)/4580/01/928/EURATOM (2001). 20. Roba, C. A., Codrea, V., Moldovan, M., Bacıu, C. and Cosma, C. Radon and radium content of some cold and thermal aquifers from Bihor County (northwestern Romania). Geofluids 10, 571– 585 (2010). 21. D’Alessandro, W. and Vita, F. Groundwater radon measurements in the Mt. Etna area. J. Environ. Radioact. 65, 187–201 (2003). 22. UNSCEAR, United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation. Annex B. United Nations (2000). 23. USEPA (U.S. Environmental Protection Agency). National primary drinking water regulations for radionuclides. EPA/ 570/9-91/700. U.S. Environmental Protection Agency (1991).
2. Tanner, A. B. Radon Migration in the Ground—A Review. The Natural Radiation Environment. Chicago University Press, pp. 253– 276 (1964). 3. Andrews, J. N. and Wood, D. F. Mechanisms of radon release in rock matrices and entry into groundwaters. Inst. Min. Metall. 81, B198–B209 (1972). 4. Wanty, R. B. and Gundersen, L. C. Groundwater geochemistry and radon-222 distribution in two sites on the Reading Prong, Eastern Pennsylvania. Missouri Department of Natural Resources Special Publication 4 (1998). 5. Michel, J. Relationship of Radium and Radon with geological formations, Radon, Radium and Uranium in Drinking Water. Lewis Publishers, Inc., pp. 83–95 (1990). 6. Harris, S. A., Billmeyer, E. R. and Robinson, M. A. Evaluation of repeated measurements of radon-222 concentrations in well water sampled from bedrock aquifers of the Piedmont near Richmond, Virginia, USA: Effects of lithology and well characteristics. Environ. Res. 101, 323 –333 (2006). 7. Voronov, A. N. Radon-rich waters in Russia. Environ. Geol. 46, 630–634 (2004). 8. Iskandar, D. et al. The transport mechanisms of 222Rn in soil at Tateishi as an anomaly spot in Japan. Appl. Radiat. Isot. 63, 401– 408 (2005). 9. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiations). Sources, effects and risks of ionizing radiation. United Nations (2000). 10. Cothern, C. R., Lappenbusch, W. L. and Michel, J. Drinking water contribution to natural background. Health Phys. 50, 33–39 (1986). 11. Aytekin, H., Baldık, R., Celebi, N., Ataksor, B., Tas¸delen, M. and Kopuz, G. Radon measurements ın the caves of Zonguldak (Turkey). Radiat. Prot. Dosim. 118(1), 117– 121 (2006). 12. Baldık, R., Aytekin, H., Celebi, N., Ataksor, B. and Tas¸delen, M. Radon concentration measurements in the Amasra coal mine, Turkey. Radiat. Prot. Dosim. 118(1), 122 –125 (2006).
doi:10.1093/rpd/nct308
MEASUREMENTS OF RADON CONCENTRATIONS IN WATERS AND SOIL GAS OF ZONGULDAK, TURKEY Abdullah Koray1,*, Gizem Akkaya2, Ays¸egu¨l Kahraman2 and Go¨kay Kaynak2 1 Ereg˘li Education Faculty, Bu¨lent Ecevit University, 67300 Kdz. Ereg˘li, Zonguldak, Turkey 2 Physics Department, Faculty of Arts and Sciences, Uludag University, Gorukle Campus, Bursa 16059, Turkey *Corresponding author: [email protected]
The radon concentrations in soil-gas and water samples (in the form of springs, catchment, tap, thermal) used as drinking water or thermal were measured using a professional radon monitor AlphaGUARD PQ 2000PRO. The measured radon concentrations in water samples ranged from 0.32 to 88.22 Bq l21. Most of radon levels in potable water samples are below the maximum contaminant level of 11 Bq l21 recommended by the US Environmental Protection Agency. The calculated annual effective doses due to radon intake through water consumption varied from 0.07 to 18.53 mSv y21. The radon concentrations in soil gas varied from 295.67 to 70 852.92 Bq m23. The radon level in soil gas was found to be higher in the area close to the formation boundary thrust and faults. No correlation was observed between radon concentrations in groundwater and soil gas. Also, no significant correlation was observed between soil-gas radon and temperature, pressure and humidity. The emanation of radon from groundwater and soil gas is controlled by the geological formation and by the tectonic structure of the area.
INTRODUCTION Radon is a radioactive, water-soluble noble gas produced by the natural decay of 226Ra (radium) and is widespread in soil and rock(1). Radon has a half-life of roughly 3.8 d and decays by alpha-particle emission to the solid daughter product 218Po ( polonium). Radon is introduced into ground water from a radium source primarily by diffusion along microcrystalline imperfections within the rock(2, 3). The migration of radon through a porous material or fractured rock occurs primarily by advective transport (4). The migration and concentration of radon in an anisotropic medium, such as bedrock, is highly variable and dependent upon the rock type, the physical condition of the rock (i.e. fractures, joints and porosity), the aquifer parameters and the aquifer geochemistry(5, 6). Another source of radon-rich water is the build up of radium-rich material on the surface of cracks and fissures from which radon emanates directly into water through cracks(7). Radon emission from soil, rocks and degassing from water are of significant interest due to the source of radon in houses and geological mapping(8). Terrestrial radiation is emitted from the natural radionuclides present in varying amounts in soil, air, water and other environmental materials(9). The levels of radioactivity in water and soil are important because of their radiological effects. The internal irradiation of lungs by alpha-emitting short-lived decay products of radon and thoron causes lung cancer. Cothern et al.(10) estimated that 1–7 % of lung cancer fatalities in the USA related to indoor radon levels derive from groundwater use.
Radon concentration measurements were previously performed in some mines and caves in Zonguldak by Aytekin et al.(11) and Baldık et al.(12). The aims of this study are to draw a general picture of the natural radioactivity of waters and soil in Zonguldak. Measurement of 222Rn has been performed on 30 water samples taken from different sources. Measurement of radon (222Rn) concentration in soil gas was performed using the active method at 21 sites. In the same locations thoron (220Rn) concentrations were measured with the AlphaGUARD gauge. As far as is known, this is the first study to determine the radon concentrations in waters and soil in Zonguldak basin.
Study area Zonguldak province is situated between 4180000 and 4183500 N latitude and between 3181800 and 3281900 E longitude and has an area of 3309 km2, and had a population of 619 703 as of December 2012. The Zonguldak Basin, which contains a thick Carboniferous clastic sequence with several coal seams, is located in the northwestern Turkey on the Black Sea coast. It has two orogenesis histories: the pre-Cretaceous Hercynian and the late-Cretaceous Alpine. In the basin, stratigraphy includes Paleozoic, Mesozoic, Tertiary and crystalline units. Rock units are found as volcanic, volcano–sedimentary and sedimentary of origin(13). Both northern and southern margins of the basin have tectonic characteristics. Turkish seismic code defines northern of the basin as being in the second-degree and southern of the basin in the first-degree earthquake zone(14). These features
# The Author 2013. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at The Univesity of Calgary on February 2, 2015
Received 15 May 2013; revised 5 November 2013; accepted 6 November 2013
A. KORAY ET AL.
make Zonguldak an interesting candidate for radiological studies. MATERIALS AND METHODS Measurement of radon (222Rn and 220Rn) activity in soil gas
Measurement of radon (222Rn) activity in water An experimental technique described in detail by Kochowska et al.(15) was employed. The radon concentration in water was measured using the professional radon monitor AlphaGUARD PQ2000 PRO. For water measurements the additional equipment AquaKIT was used. Figure 2 shows the set-up for radon in water measurements. In a close gas cycle, radon was expelled from the water samples ( placed in degassing vessel) using the pump. The security vessel was connected with the degassing vessel. All drops would deposit in it if they had got into the gas cycle during the degassing process. This way the stress of the water vapour was minimised for the radon monitor. The background of empty set-up was measured for a few minutes before every water-sample measurement. After that the water was injected into the degassing vessel, and the AlphaGUARD and AlphaPUMP were switched on. After 10 min the pump was switched off and the AlphaGUARD remained switched on for another 20 min and so the radon measurement was continued. This cycle was repeated three times in order to obtain a better precision. The AlphaGUARD monitor worked in a ‘flow’ mode and the radon concentration was recorded every
Figure 1. Schematic view of the experimental set-up for radon measurements in soil gas.
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AlphaGUARD PQ2000 PRO can measure a range of radon concentrations from 2 to 2 000 000 Bq m23. The system allows for spot measurements as well as for continuous soil-gas monitoring (Fig. 1). Stitz soil gas probe consisting of capillary probe and drilling rod with an air-lock and rivet was installed at 1 m depth in soil with the aid of a heavy hammer. The soil gas was pumped into the ionisation chamber of the AlphaGUARD (in flow mode) with AlphaPUMP. AlphaPUMP was set to perform 1 l min21. To guarantee and to check a complete exchange of the soil gas in the 0.6-l ionisation chamber, 1-l capacity air bag was used. A tube connection between the soil-gas probe and AlphaPUMP includes filter cartridge against radon progeny products and water break-in. The chamber was filled with soil gas. The measuring mode of AlphaGUARD was selected as ‘1 min FLOW’. The total concentration of both isotopes [222Rn (t1/2 ¼ 3.82 d) and 220Rn (t1/2 ¼ 55 s)] were measured during pumping for 10 min. In order to measure the radon (222Rn) concentration only, AlphaGUARD and probe were separated and the chamber was kept tightly closed from all sides for 10 min—the time needed for thoron (220Rn) to decay. AlphaGUARD remained switched on for about another 10 min and so radon measurement was continued. Afterwards, the average total concentration from the first 10 single, 1-min measurements and
average radon concentration from the last 10 single, 1-min measurements recorded by the AlphaGUARD were obtained. The meteorological parameters, which are temperature, pressure and the humidity, were also recorded in the same cycle. This method gave information about the temporary thoron and radon concentrations in soil gas. One measurement was taken from each sampling location.
RADON IN WATERS AND SOIL GAS, ZONGULDAK
minute. The flow rate of the pump was 0.3 l min21. The radon concentration in the system was determined with the AlphaGUARD, whose ionisation chamber was also a part of the gas cycle. The determination of radon concentration in water samples was based on the radon concentration indicated by the AlphaGUARD. This value was not the radon concentration in the water sample yet because radon driven out had been diluted in the air within the measurement set-up and a small part of the radon remained diluted in the watery phase. The following equation served to determine the radon concentration in the measured water samples: Vsystem Vsample þ k C0 Cwater ¼ Cair Vsample Cwater is the radon concentration in the water sample (Bq m23); Cair the radon concentration in the set-up after expelling radon from the water sample (Bq m23); C0, background (Bq m23); Vsystem the interior volume of the measurement set-up (ml) and Vsample the volume of the water sample (ml) and k the radon distribution coefficient.
RESULTS AND DISCUSSION The results of thoron and radon measurements in soil gas and radon in water in Zonguldak basin are given in Table 1. The sample locations on a geological map are shown in Figure 3. In soil gas, the maximum (59 885.06 Bq m23) and minimum (4299.56 Bq m23) thoron concentrations were recorded in Ormanlı and Tu¨rkali areas, respectively. An average thoron value in
soil gas was found to be 29 708.16 Bq m23. In soil gas, the maximum radon concentration (70 852.92 Bq m23) was recorded in I˙sabeyli area, on formation boundary thrust, and close to the faults. The minimum radon concentration (295.67 Bq m23) was recorded from the Gu¨rbu¨zler area. An average radon value for all locations in soil gas was found to be 25 853.62 Bq m23. The second and third highest values were recorded in Buruncuk (56 328.0 Bq m23) and Kokaksu (45 490.53 Bq m23) areas, respectively. The reason for this may be the proximity to the fault lines(16). As a geological tool radon monitoring technique can be used in earthquake prediction. With this technique fault zones have been recognised worldwide with fairly good precision(17). The fourth highest value was recorded in Alpaslan (46 455.61 Bq m23). The higher value of radon in the soil gas from Alpaslan may be due to the fact this location is close to faults and river Yenice and that the moisture content may enhance the radon level in the sample(18). Also, all samples with .25 853.62 Bq m23 (average value) were collected at sites located close to the faults (location 1, 2, 3, 8, 9, 22 and 24). The average radon values for northern (locations 1, 2, 3, 4, 5, 6, 9, 11, 12, 13, 14, 15 and 16) and southern (locations 7, 8, 10, 17, 18, 19, 20, 21, 23 and 24) parts of the basin in soil gas were found to be 27 823.35 and 23 227.32 Bq m23, respectively. The results from both parts were found close to each other. A total of 30 water samples were sampled and analysed. For each site, two measurements were taken and then averaged. The radon concentration in the drinking water was found to vary from 0.32 to 21.30 Bq l21 with a mean value of 6.77 Bq l21. The radon
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Figure 2. Schematic view of the experimental set-up for radon measurements in water.
Table 1. Levels of radon and thoron in soil gas with temperature (T ), pressure (P) and humidity rate (H ) and groundwater with ingestion dose (ID) in different locations. Loc. no.
Location
Soil-gas thoron concentration (Bq m23)
Soil-gas radon concentration (Bq m23)
49 058.7+1684.76
56 328.0 +1227.65
26.7
995
68.8
T (8C) P (mbar) H. (%)
Buruncuk
2
Ilıksu
17 824.57+1893.96
39 044.0+731.98
33.8
1014
38.2
3
Kokaksu
49 798.36+5548.27
45 490.53+1037.78
32.1
1012
43.1
4 5 6
Tu¨rkali Çamlık Sog˘anlıyo¨ru¨k
4299.56+384.98 — 49 513.59+2403.21
3828.44+149.71 — 24 349.94+511.16
25.1 — 33
1011 — 978
58.7 — 36.6
7
Du¨zpelit
14 166.99+698.05
6733.58+288.73
32.1
983
40.2
8
I˙sabeyli
15 803.08+4013.75
70 852.92+1353.16
32.5
977
32.2
9
Alpaslan
28 056.39+2691.8
46 455.61+835.55
35.6
1001
27.1
10
Gaziler
28 445.81+1780.04
21 159.11+849.28
32.8
1005
31.8
11 12 13
Geris¸ Kerimler Dag˘lıca
22 898.73+2743.98 12 957.09+2121.37 20 683.64+1203.79
28 378.07+1084.58 21 986.91+991.36 10 356.36+234.54
26.1 25 31.3
1007 1007 964
45.3 51.6 34.3
14
Balc¸ıklı
39 214.48+3435.16
19 267.30+299.91
33.3
985
34.5
15 16
Sofular Beycuma
29 358.55+1365.76 31 565.26+2184.92
14 737.45+513.3 23 657.60+519.97
33.6 31.4
977 983
31.2 32.1
17 18
Gu¨rbu¨zler Eg˘erci-1
10 112.33+701.08 —
26.4 —
982 —
48.7 —
19
Eg˘erci-2
20 21 22 23
Fındıklı Hu¨seyinli Is¸ıklı Uludag˘
33 602.84+2797.91 35 809.66+3091.72 45 029.57+2724.4 25 787.2+1873.53
7229.16+197.21 24 580.74+580.47 31 444.61+628.67 15 019.20+414.85
28.9 32.4 30.6 27.9
24
Ormanlı
59 885.06+6461.59
31 730.94+818.86
27
—
295.67+22.78 — —
—
—
—
998 987 978 975
43.5 41.3 35.2 59
1005
63.6
Radon concentration in water (Bq l21)
ID (mSv y21)
1.14+0.23 15.34+0.75
0.24 3.22
46.22+3.44
9.71
88.22+5.71
18.53
3.57+0.47 0.71+0.30 9.25+0.92 21.30+0.98 9.24+0.79 12.87+0.65
0.75 0.15 1.94 4.47 1.94 2.70
4.31+0.71
0.91
5.64+0.11
1.18
13.88+0.49
2.91
5.18+0.45 5.60+0.54 2.82+0.20 0.82+0.15 1.88+0.03 1.66+0.22 4.52+0.33 3.63+0.35 15.44+0.59
1.09 1.18 0.59 0.17 0.39 0.35 0.95 0.76 3.24
6.05+0.51 7.82+0.63
1.27 1.64
5.16+0.43
1.08
0.66+0.01 0.32+0.01 10.16+0.82 6.77+0.42
0.14 0.07 2.13 1.42
13.75+0.58
2.89
Tap water Natural spring Thermal water Thermal water Catchment Catchment Catchment Tap water Catchment Natural spring Natural spring Natural spring Natural spring Catchment Catchment Tap water Catchment Catchment Catchment Catchment Catchment Natural spring Catchment Natural spring Natural spring Catchment Tap water Well water Natural spring Tap water
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378
1
Water type
RADON IN WATERS AND SOIL GAS, ZONGULDAK
Figure 4. Contour maps of radon concentration in (a) water and (b) soil gas.
concentrations in thermal water were found to be 46.22 and 88.22 Bq l21. All radon concentration results for thermal waters are ,100 Bq l21, which is the limit proposed by the Commission of the European Communities(19). The high radon concentration in thermal waters compared with the drinking water is an expected result due to the effects of geothermal systems. In the surface waters such as lakes and rivers, the radon concentrations are generally in the range of a few Bq l21, while in groundwaters occurring in sedimentary rock aquifers, the levels range
from 1 to 50 Bq l21. Some geothermal waters have considerably higher radon levels, e.g. values up to 1868 Bq l21 were reported for some thermal springs(20). The samples collected from springs display generally higher values (mean ¼ 9.69 Bq l21) than those coming from the catchments (5.29 Bq l21) and taps (4.5 Bq l21). The catchments allow a long contact of the water with the atmosphere inducing the transfer of radon from the liquid to the gas phase. Although some authors demonstrated some radon increase in
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Figure 3. Study area and sampling sites.
A. KORAY ET AL. Table 2. Statistical results for radon concentrations in soil gas and water samples. Statistics Median Arithmetic mean+SE
Correlation with soil gas Correlation with water
Water
21 986.91 25 853.62 + 4123.276 17 972.94 16 091.08 295.67– 70 852.92 1.189 1.495 Normal p ¼ 0.062 1
5.64 6.70 + 1.09 4.73 4.67 0.32– 15.44 0.579 20.669 Normal p ¼ 0.193 0.136
0.136
1
Table 3. Correlation of radon concentration in soil gas with meteorological parameters. Parameter
Radon and temperature Radon and pressure Radon and humidity
Correlation coefficient
Significance level
0.267
0.242
0.184 20.059
0.426 0.798
CONCLUSION
waters flowing in old distribution networks due to radium adsorption, the overall water radon activity in tap waters will be significantly reduced during transport from captation to the point of use(21). On the basis of the results, contour maps of radon concentration in soil gas and water in Zonguldak basin are shown in Figure 4. The statistical summary of the data located in Table 1 is given in Table 2. The frequency distributions of radon concentration in soil gas and water were determined. Whether the data comply with the normal distribution was tested with Shapiro –Wilk or Kolmogorov– Smirnov tests. The Shapiro–Wilk test is more appropriate for small sample sizes (,50 samples) and therefore, when the number of sample is ,50, Shapiro–Wilk normality test is used. In cases where the value of p (significance level) is .0.05, the distribution of data complies with the normal distribution. As a result of the test, it was found that the frequency distributions obtained for soil gas and water can be fitted to a normal distribution. Although a weak positive correlation between the radon concentration in soil gas and water was observed, a statistically significant correlation was not found. The correlation between the radon concentration in soil gas and the meteorological parameters, which are temperature, pressure and humidity for the values
The first measurements of radon concentrations in soil gas and water in Zonguldak were carried out. It can be concluded that radon emanation from the ground is a function of the tectonic structure of the investigated area. The radon level in soil-gas was found higher in the area close to the faults. With few exceptions, the levels of radon in the water in Zonguldak are below the recommended radon level(23). The results showed that the radon concentrations in the tap and catchment water in Zonguldak are lower than that in spring water. No correlation was observed between the radon concentrations in groundwater and soil gas. Finally, radon is still a big concern for public health, especially where sources with high radon concentrations are used for water supply. It is possible that consumers of water from these sources may take up elevated quantities of radon through ingestion. This study contributes to the database of the radioactivity level in the Zonguldak province. The results may also be used to evaluate any radioactivity change in the future. ACKNOWLEDGEMENTS ¨ zkan DEKA The authors are thankful to Mr. Kemal O Mining Topographer for his cooperation in preparing the map of the study area. REFERENCES
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SD Geometric mean Range Skewness Kurtosis Frequency distribution
Soil gas
in Table 1, is evaluated (Table 3). The negative correlation (20.059) has been observed between radon concentration and humidity, whereas positive correlations 0.267 and 0.184 have been observed between the radon concentration and temperature and pressure, respectively. On the basis of radon concentration in each water sample (see in Table 1), the annual weighted estimate of consumption rate and the dose coefficient of the concerned radon isotope per unit intake, which is equal to 3.5 nSv Bq21, the annual mean ingestion dose values were calculated(22). The consumption rate of 60 l y21, which was taken from United Nations Scientific Committee on the Effects of Atomic Radiation(22), has been considered. The expected dose due to 222Rn varies from 0.07 to 18.53 mSv y21. The inhalation dose for thermal springs per treatment session of 0.5 h was also calculated. The equilibrium factor of radon indoors, dose conversion factor and air-water concentration ratio were taken as 0.4, 9 nSv h21 per Bq m23 and 1024, respectively(22). The expected inhalation dose rates for 222Rn levels in Ilıksu and Kokaksu are 8.32 and 15.88 nSv respectively.
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