- Email: [email protected]
Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment
Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment Izabela Chmielewska n, Stanisław Chałupnik, Michal Bonczyk Silesian Centre for Environmental Radioactivity, Central Mining Institute, Pl. Gwarków 1, 40-166 Katowice, Poland
H I G H L I G H T S
Analyses of water samples collected from underground wells usually show elevated natural radioactivity. The most crucial radionuclides are 226Ra and 228Ra. Attention should be focused on the fate of solid waste after water treatment. Radon in the air at water treatment plants should be monitored and to ensure compliance.
art ic l e i nf o
a b s t r a c t
Keywords: Drinking waters Annual effective dose Solid waste materials BCR procedure
Content of 226Ra, 228Ra and uranium isotopes in waters from subsurface aquifers was studied. The sampling points were chosen for having the elevated natural content of iron and manganese. Measurements of radium were made by LSC, while uranium was measured by alpha spectrometry. Waste sludge was measured by gamma spectrometry and three-stage BCR sequential extraction was performed. Radon activity concentration in the air at water treatment plants was determined and dose adsorbed by staff was calculated. & 2014 Elsevier Ltd. All rights reserved.
1. Introduction In the most cases radionuclides present in water are of natural origin, mainly associated with uranium or thorium-bearing soils, mineral rocks. The occurrence of natural radioactivity in waters severely depends on the local geological structure of source, geochemistry of certain element and as well geochemical conditions in particular places (Ajayi and Achuka, 2009). The quality of drinking waters must be strictly controlled. For this reason drinking waters supplies, especially underground one, need to be monitored in terms of the among others natural radioactivity (Jobbagy et al., 2009). The most studied radionuclides are 226Ra, 228Ra, 238U, 234U and 222 Rn because they may deliver the highest doses to people due to the consumption of waters. Radium enters groundwater by direct recoil across the liquid–solid interface between soil and water. After ingestion about 20% is initially distributed via blood to soft tissue, but finally it is retained in bone (de Oliviera et al., 2001). In case of uranium only 5% of ingested amount retains in human body, mainly in lungs and bone tissue. But rather the chemical
n
Corresponding author. Tel.: þ 48 32 259 27 14. E-mail address: [email protected] (I. Chmielewska).
toxicity of uranium as a heavy metal is emphasized, than risk arising from radioactive properties. It may cause kidney damage and problems with procreation. Radon is water-soluble inert gas. Its high activity concentration is connected usually with granite rocks but also with karstic zones. Radon transported with water may lead to public exposure rather from transfer into the air in dwellings than from direct water consumption. The other places where increased radon exposure can be expected are water treatment plants (WTPs). Therefore special concern should be put on operators of WTPs. Due to the occurrence of natural radioactivity in drinking water and the need for evaluation of potential exposure of the public, many international standards and guidelines have been issued. The World Health Organization (WHO) in “Guidelines for Drinking Water Quality” prior to qualitative water surveys recommends screening methods, namely measurement of gross alpha and beta activities. In the latest, 4th edition, these values were set 0.5 Bq/L and 1 Bq/L for alpha and beta activity respectively (WHO, 2011). The European Commission published in 1998 Directive 98/83/ EC on the quality of water intended for human consumption. In terms of radioactivity, only direct maximum acceptable value for tritium was set in that Directive. Content of the rest of radioisotopes is expressed as total indicative dose (TID) and should not exceed annual dose 0.1 mSv. TID excludes tritium, 40K, 14C, radon
0969-8043/$ - see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2014.01.017
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
and its decay products (European Commission (EC), 1998) and should be calculated accordingly to Council Directive 96/29 Euratom (European Commission (EC), 1996).
2. Materials and methods Upper Silesia is located in the southern Poland (Fig. 1), covers about 7250 km2. It is a large metropolitan area which consists of 37 towns, where 3.5 million of inhabitants live. Region is rich in mineral resources, mainly hard coal. Upper Silesian Coal Basin (USCB) is one from the largest in Europe. As a result of mining activity the region became highly industrialized and urbanized what in turn caused a large need for drinking waters. The primary surface water sources are Goczałkowice and Dzieckowice reservoirs. Research of those waters done in 2009 indicated that the level of natural and man-made radioactivity is very low and does not cause any radiological hazard for people (Chmielewska et al., 2011). However, the vast majority of the region is supplied by drinking water from underground aquifers. Waters are drawn from depths range from 10 up to 300 m. Very often they contain considerable amount of iron and manganese and elevated level of natural radioisotopes. The most critical natural alpha and beta emitters in terms of internal contamination, 226Ra, 228Ra, 238U, 234U and 222 Rn are considered. Treatment is provided at the water treatment plants, using aeration, filtration and disinfection. Sporadically, coagulation by means of aluminium sulphate is included. This may cause the increase of radon activity concentration in air in closed rooms of WTPs. Therefore in this work attention was focused on underground sources and the above mentioned radioisotopes. Water samples were collected within 2011–2012 years. Raw and treated waters were taken simultaneously. The radiochemical procedure for 226Ra and 228Ra is exactly described by Chalupnik and Lebecka (1993). Radium isotopes were coprecipitated with barium carrier as Ba(Ra)SO4, later on precipitate was dissolved in EDTA/NH4OH in order to purify from other radionuclides (including 210Pb). At pH 4.5 adjusted by glacial acetic acid, radium was reprecipitated with barium, whereas lead remained in solution as strong complex with EDTA. Ba(Ra)SO4
was then mixed with gelling scintillator and measured 30 days later by means of LS spectrometer Quantulus. Uranium was concentrated and isolated from waters by precipitation with Fe(OH)3. Samples were spiked with a known amount of 232 U. Later the precipitate was centrifuged and dissolved in 9 M HCl. Soon after two columns were employed. The first one with anion exchanger (Dowex 1 8, 200–400 mesh) in order to remove thorium and other disturbing isotopes. The second column containing extraction chromatographic resin UTEVA was used for elimination of iron. Eventually, uranium was eluted with 0.02 M HCl and the alpha source was prepared by means of electroplating. The more detailed procedure for uranium separation is presented in Warwick (Warwick et al., 1999). Than alpha source was measured using high-resolution alpha spectrometry. Track-etch detectors were used for measuring radon activity concentration in air of WTPs. They are CR-39 type detector foils in diffusion chamber. They were placed for 3 months in different WTP buildings in order to obtain mean radon activity in rooms, where water plant operators spent the most of their working time. Later on, CR39 foils were etched in 25% NaOH. And finally, the computer controlled optical evaluation system which counts the tracks on the detector foil corresponding to concentration of radon was used (Fisher et al., 1996). As it was mentioned previously, in the most cases the sole applied method for water treatment turned out to be aeration in order to precipitate Fe(OH)3 and MnO2, accordingly with the following chemical reaction: 4Fe2 þ þ O2 þ 10H2 O-4FeðOHÞ3 þ 8H þ 2Mn2 þ þ O2 þ 2H2 O-2MnO2 þ 4H þ Sludge obtained during aeration and filtration processes adsorbs radionuclides on their surface and disposed in uncontrolled way could pose a serious problem for surrounding environment. In our study we collected sludge samples and after drying they were determined by gamma spectrometry. Finally in order to assess the potential negative impact of that sludge on natural environment the 3-stage sequential extraction according to BCR procedure (Ure et al., 1993) was performed. Scheme of that procedure is depicted in the figure below (Fig. 2).
3. Results and discussion
Fig. 1. Map of Poland, with marked Upper Silesia region, where drinking waters were monitored.
Water samples were taken from 9 underground sources being within boundary of Upper Silesia region. Each time about 15 L of water was sampled, later on they were concentrated by evaporation and activity of certain isotopes were determined according to protocols mentioned before. Results are reported in Table 1. The impact of radionuclides derived from drinking water can be assessed by determining the effective dose to each age group in population. The doses were calculated based on obtained activity concentration of radioisotopes for various water sources, assumed amount of water consumption for each age group (Table 2) as well dose coefficient recommended by Council Directive 96/29/Euratom (European Commission (EC), 1996). Outcomes with the highest estimated annual dose are depicted below (Fig. 3). In many cases for raw waters the recommended dose 0.1 mSv/year was exceeded. Generally aeration used for removing iron and manganese caused decreasing of radioactivity. Nonetheless still are some treated waters, where despite of treatment process, annual dose 0.1 mSv is exceeded. The most crucial age groups are small babies, below 1 year and teenagers within 12–17 years. In the next figure (Fig. 4) contribution of individual nuclides to total dose is shown. As an example we decided to present dose
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
30 g solid waste sample (gamma spectrometry)
stage 1 sample + 0,11M HOAc overnight shaking
exchangeable fraction and bound to carbonates
supernatant
solid
centrifuging 10min, 2000rpm
stage 2 0,1M NH2 OH.HCL overnight shaking
solid
reducible fraction and bound to Fe/Mn oxides
centrifuging 10min, 2000rpm
stage 3 8,8M H2O2 heating up to 85°C (2x), 1M NH4 Ac (pH=2, HNO3) overnight shaking
supernatant
Oxidisable fraction bound to organic matter and sulfides
centrifuging 10min, 2000rpm
supernatant
solid Dry residuals
(gamma spectrometry)
extractants were analysed for Ra-226 i Ra-228 by means of LSC
Fig. 2. Scheme of 3-stage sequential extraction according to BCR.
Table 1 Activity concentration of radionuclides in underground waters used for human consumption. 226
Water treatment plant
Ra (mBq/dm3)
228
Ra (mBq/dm3)
238
U (mBq/dm3)
234
U (mBq/dm3)
WTP 1
Raw Potable
158.4 7 5.8 95.2 7 2.6
27.0 714.6 24.7712.7
0.76 70.09 1.14 70.13
3.2 7 0.3 3.2 7 0.3
WTP 2
Raw Potable
10.6 7 2.0 7.5 7 1.5
11.4 75.2 7.8 75.2
14.4 70.9 6.5 70.4
24.8 7 1.4 16.9 7 0.9
WTP 3
Raw Potable
13.2 7 1.2 12.0 7 1.0
10.2 74.8 7.3 74.1
11.8 70.7 6.4 70.4
31.4 7 1.7 17.2 7 0.9
WTP 4
Raw Potable
16.0 7 2.3 13.6 7 3.0
6.6 74.5 6.6 74.5
3.2 70.3 5.2 70.4
4.0 7 0.4 6.6 7 0.5
WTP 5
Raw Potable
11.4 7 1.3 6.9 7 0.9
16.2 76.3 3.4 71.7
1.09 70.14 1.58 70.12
2.17 0.3 1.85 7 0.14
WTP 6
Raw Potable
26.2 7 1.9 16.17 1.5
48.4 79.3 33.777.9
12.0 70.7 13.0 70.9
29.17 1.4 27.2 7 1.9
WTP 7
Raw Potable
66.47 3.1 7.17 1.1
64.8 711.7 15.3 76.1
1.3 70.5 0.16 70.04
2.5 7 0.8 0.277 0.05
WTP 8
Raw Potable
20.9 7 1.7 15.2 7 1.4
38.9 78.4 26.3 77.2
0.0770.02 0.08 70.02
0.127 0.03 0.107 0.03
WTP 9
Raw Potable
11.9 7 1.2 8.9 7 1.1
21.6 76.7 14.9 76.1
0.10 70.02 0.10 70.02
0.157 0.02 0.187 0.02
derived from waters processed in WTP1 for age group below 1 year. As it can be clearly seen the main contributors are both 226Ra and 228Ra isotopes.
In order to evaluate the potential risk, resulting from radon inhalation by people working in water treatment plants (especially those working in closed rooms) we placed solid state track detectors to be exposed for 3–6 months. To assess dose for
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
water-plant operators, it was necessary to compute potential alpha energy concentration (PAEC). To obtain this value, the following assumptions were made:
Having known radon activity concentration (CR) in certain places, PAEC may be calculated with application of the formula:
Equilibrium factor (F) equals 0.4. PAEC (Cα) in equilibrium (k) with 100 Bq/m3 of radon is equal 0.56 μJ/m3.
Subsequently, having Cα value, annual effective dose can be calculated as follows:
Table 2 Rate of water ingestion per year for different age groups (Risica and Grande, 2000). Age group l/Year
o1 1–2 2–7 year years years Annual water consumption 250 350 350
7–12 years
12–17 years
417 years
350
540
730
Fig. 3. Estimated annual effective dose after consumption of underground waters.
Cα ¼ CR=100Fk
E ¼ 0:0014Cαt where: t [h] – estimated working time of the staff; 0.0014 [mSv/ h μJ/m3] – PAEC conversion factor to dose for working places, accordingly to Euratom Directive 96/26 (European Commission (EC), 1996). Doses caused by exposure to radon are in most of the cases relatively low (Fig. 5). Nevertheless, in one case estimated dose was higher than 1 mSv/year. On the other hand, there is only a small number of investigated plants till now. Therefore in whole country the problem of occupational exposure of water plants staff to radon cannot be neglected and there is still a need for more survey of water treatment plants. Radionuclides concentration in solid wastes generated by the water treatment plants is given in Table 3. In case of WTP 8 and 9 there was no possibility to take sludge therefore results are not included in the below table. According to Basic Safety Standard proposed by IAEA (IAEA, 2010), if sum of activity concentration both isotopes 226Ra and 228Ra in solid waste materials is higher than 1000 Bq/kg, they should be treated as waste with elevated radioactivity. In our study such situation appears in case of WTP 2 and WTP 3, where total activity both isotopes amounts to 4091 Bq/kg and 1369 Bq/kg for WTP 2 and WTP 3, respectively. Moreover, it must be emphasized that in few cases of sludge samples, total activity admittedly does not exceed 1 Bq/g, but those activities are undoubtedly higher than typical values for the Earth crust. As it was mentioned above, from selected solid wastes (with the highest radioactivity) sequential extraction was carried out. During research attention was focused on the two most dominant Table 3 Radioactivity concentration in solid wastes from water treatment plants.
Fig. 4. Contribution of individual nuclides to the total dose in case of waters from plant 1.
Location
226
WTP1 WTP2 WTP3 WTP4 WTP5 WTP6 WTP7
1727 9 4377 12 296 7 7 3327 17 2977 12 48 7 1 1267 3
Ra [Bq/kg]
228
210
238
3367 24 3654 7 142 10747 41 4707 34 5727 32 807 3 977 4
697 7 177 15 517 11 1597 33 o 49 48 7 4 367 9
49 7 22 o 15 o 23 o 51 o 57 297 13 247 17
Ra [Bq/kg]
Pb [Bq/kg]
U [Bq/kg]
Fig.5. Effective annual dose from exposure to radon for water treatment plant operators.
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
5
Fig.6. Results for sequential extraction of radionuclides from solid waste after water treatment.
radionuclides, accumulated in the sludge, namely 226Ra and 228Ra. Taking into account the results (Fig. 6), it can be easily noticed that leachability of both radionuclides is pretty high and ranges between 10% and 90%. Significant amounts of isotopes were extracted at the 2nd and 3rd stage, while pH and redox conditions are changing. It means, that under such conditions mobility and bioavailability in natural environment arises, too. 4. Conclusions Analyses of water samples collected from underground wells usually show elevated natural radioactivity. The most crucial radionuclides are 226Ra and 228Ra. The obtained data may provide basic and at once useful information for water consumers and authority. More attention should be focused on the fate of solid waste after water treatment, since very often they are disposed without any control and may cause serious environmental contamination. Additionally, radon in the air in closed places, where underground waters are treated for human consumption, should be monitored and mitigated to ensure compliance. References Ajayi, O.S., Achuka, J., 2009. Radioactivity in drilled and dug well drinking water of Ogun state southwestern Nigeria and consequent dose estimates. Radiat. Prot. Dosimetry 135, 54–63. Chalupnik, S., Lebecka, J., 1993. Determination of 226Ra, 228Ra, 224Ra in water and aqueous solutions by liquid scintillation counting. In: Noakes, J.E., Schonhofer, F., Polach, H.A. (Eds.), Liquid Scintillation Spectrometry, 1992. Radiocarbon, Tuscon, pp. 397–403.
Chmielewska, I., Chalupnik, S., Michalik, B., Mielnikow, A., 2011. Methods for determination of natural radioactivity in drinking water samples. In: P., Cassette (Ed.), LSC 2010, Advances in Liquid Scsintillation Spectrometry. Radiocarbon, Tuscon, pp. 107–113 De Oliviera, J., Mazilli, B.P., De Oliviera Sampa, M.H., Bambalas, E., 2001. Natural radionuclides in drinking water supplies of Sao Paulo, Brazil and consequent population doses. J. Environ. Radioact. 53, 99–109. European Commission (EC), 1998. Council Drinking Water Directive 98/83/EC on the quality of water intended for human consumption. European Commission (EC), 1996. Council Directive 96/29/Euratom laying down basic safety standards for the protection of the health of workers and the general public against the danger arising from ionizing radiation. Fisher, E.L., Fuortes, L.J., Field, R.W., 1996. Occupational exposure of water operators to high concentration of radon-222 gas. J. Occup. Environ. Med. 38, 759–764. IAEA 2010, 2011. Radiation Protection and Safety of Radiation Sources. International Basic Safety Standards, GSR Part 3, Vienna. Jobbagy, V., Chmielewska, I., Kovacs, T., Chałupnik, S., 2009. Uranium determination in water samples with elevated salinity from Southern Poland by micro coprecipitation using alpha spectrometry. Microchem. J. 93 (2009), 200–205. Risica, S., Grande, S., 2000. Council Directive 98/83/EC on the Quality of Water Intended for Human Consumption: Calculation of Derived Activity Concentrations. Rapporti ISTISAN 00/16 (2000). Ure, A.M., Quevauviller, P., Muntau, H., Griepink, B., 1993. Speciation of heavy metals in soils and sediments. An account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission of the European Communities. Int. J. Environ. Anal. Chem. 51, 135–151. Warwick, P.E., Croudance, I.W., Dale, A.A., 1999. An optimized and roboust method for the determination of uranim and plutonium in aqueous samples. Appl. Radiat. Isot. 50, 579–583. World Health Organization (WHO), 2011. Guidelines for Drinking Water Quality, fourth ed., Geneva.
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment Izabela Chmielewska n, Stanisław Chałupnik, Michal Bonczyk Silesian Centre for Environmental Radioactivity, Central Mining Institute, Pl. Gwarków 1, 40-166 Katowice, Poland
H I G H L I G H T S
Analyses of water samples collected from underground wells usually show elevated natural radioactivity. The most crucial radionuclides are 226Ra and 228Ra. Attention should be focused on the fate of solid waste after water treatment. Radon in the air at water treatment plants should be monitored and to ensure compliance.
art ic l e i nf o
a b s t r a c t
Keywords: Drinking waters Annual effective dose Solid waste materials BCR procedure
Content of 226Ra, 228Ra and uranium isotopes in waters from subsurface aquifers was studied. The sampling points were chosen for having the elevated natural content of iron and manganese. Measurements of radium were made by LSC, while uranium was measured by alpha spectrometry. Waste sludge was measured by gamma spectrometry and three-stage BCR sequential extraction was performed. Radon activity concentration in the air at water treatment plants was determined and dose adsorbed by staff was calculated. & 2014 Elsevier Ltd. All rights reserved.
1. Introduction In the most cases radionuclides present in water are of natural origin, mainly associated with uranium or thorium-bearing soils, mineral rocks. The occurrence of natural radioactivity in waters severely depends on the local geological structure of source, geochemistry of certain element and as well geochemical conditions in particular places (Ajayi and Achuka, 2009). The quality of drinking waters must be strictly controlled. For this reason drinking waters supplies, especially underground one, need to be monitored in terms of the among others natural radioactivity (Jobbagy et al., 2009). The most studied radionuclides are 226Ra, 228Ra, 238U, 234U and 222 Rn because they may deliver the highest doses to people due to the consumption of waters. Radium enters groundwater by direct recoil across the liquid–solid interface between soil and water. After ingestion about 20% is initially distributed via blood to soft tissue, but finally it is retained in bone (de Oliviera et al., 2001). In case of uranium only 5% of ingested amount retains in human body, mainly in lungs and bone tissue. But rather the chemical
n
Corresponding author. Tel.: þ 48 32 259 27 14. E-mail address: [email protected] (I. Chmielewska).
toxicity of uranium as a heavy metal is emphasized, than risk arising from radioactive properties. It may cause kidney damage and problems with procreation. Radon is water-soluble inert gas. Its high activity concentration is connected usually with granite rocks but also with karstic zones. Radon transported with water may lead to public exposure rather from transfer into the air in dwellings than from direct water consumption. The other places where increased radon exposure can be expected are water treatment plants (WTPs). Therefore special concern should be put on operators of WTPs. Due to the occurrence of natural radioactivity in drinking water and the need for evaluation of potential exposure of the public, many international standards and guidelines have been issued. The World Health Organization (WHO) in “Guidelines for Drinking Water Quality” prior to qualitative water surveys recommends screening methods, namely measurement of gross alpha and beta activities. In the latest, 4th edition, these values were set 0.5 Bq/L and 1 Bq/L for alpha and beta activity respectively (WHO, 2011). The European Commission published in 1998 Directive 98/83/ EC on the quality of water intended for human consumption. In terms of radioactivity, only direct maximum acceptable value for tritium was set in that Directive. Content of the rest of radioisotopes is expressed as total indicative dose (TID) and should not exceed annual dose 0.1 mSv. TID excludes tritium, 40K, 14C, radon
0969-8043/$ - see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2014.01.017
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
and its decay products (European Commission (EC), 1998) and should be calculated accordingly to Council Directive 96/29 Euratom (European Commission (EC), 1996).
2. Materials and methods Upper Silesia is located in the southern Poland (Fig. 1), covers about 7250 km2. It is a large metropolitan area which consists of 37 towns, where 3.5 million of inhabitants live. Region is rich in mineral resources, mainly hard coal. Upper Silesian Coal Basin (USCB) is one from the largest in Europe. As a result of mining activity the region became highly industrialized and urbanized what in turn caused a large need for drinking waters. The primary surface water sources are Goczałkowice and Dzieckowice reservoirs. Research of those waters done in 2009 indicated that the level of natural and man-made radioactivity is very low and does not cause any radiological hazard for people (Chmielewska et al., 2011). However, the vast majority of the region is supplied by drinking water from underground aquifers. Waters are drawn from depths range from 10 up to 300 m. Very often they contain considerable amount of iron and manganese and elevated level of natural radioisotopes. The most critical natural alpha and beta emitters in terms of internal contamination, 226Ra, 228Ra, 238U, 234U and 222 Rn are considered. Treatment is provided at the water treatment plants, using aeration, filtration and disinfection. Sporadically, coagulation by means of aluminium sulphate is included. This may cause the increase of radon activity concentration in air in closed rooms of WTPs. Therefore in this work attention was focused on underground sources and the above mentioned radioisotopes. Water samples were collected within 2011–2012 years. Raw and treated waters were taken simultaneously. The radiochemical procedure for 226Ra and 228Ra is exactly described by Chalupnik and Lebecka (1993). Radium isotopes were coprecipitated with barium carrier as Ba(Ra)SO4, later on precipitate was dissolved in EDTA/NH4OH in order to purify from other radionuclides (including 210Pb). At pH 4.5 adjusted by glacial acetic acid, radium was reprecipitated with barium, whereas lead remained in solution as strong complex with EDTA. Ba(Ra)SO4
was then mixed with gelling scintillator and measured 30 days later by means of LS spectrometer Quantulus. Uranium was concentrated and isolated from waters by precipitation with Fe(OH)3. Samples were spiked with a known amount of 232 U. Later the precipitate was centrifuged and dissolved in 9 M HCl. Soon after two columns were employed. The first one with anion exchanger (Dowex 1 8, 200–400 mesh) in order to remove thorium and other disturbing isotopes. The second column containing extraction chromatographic resin UTEVA was used for elimination of iron. Eventually, uranium was eluted with 0.02 M HCl and the alpha source was prepared by means of electroplating. The more detailed procedure for uranium separation is presented in Warwick (Warwick et al., 1999). Than alpha source was measured using high-resolution alpha spectrometry. Track-etch detectors were used for measuring radon activity concentration in air of WTPs. They are CR-39 type detector foils in diffusion chamber. They were placed for 3 months in different WTP buildings in order to obtain mean radon activity in rooms, where water plant operators spent the most of their working time. Later on, CR39 foils were etched in 25% NaOH. And finally, the computer controlled optical evaluation system which counts the tracks on the detector foil corresponding to concentration of radon was used (Fisher et al., 1996). As it was mentioned previously, in the most cases the sole applied method for water treatment turned out to be aeration in order to precipitate Fe(OH)3 and MnO2, accordingly with the following chemical reaction: 4Fe2 þ þ O2 þ 10H2 O-4FeðOHÞ3 þ 8H þ 2Mn2 þ þ O2 þ 2H2 O-2MnO2 þ 4H þ Sludge obtained during aeration and filtration processes adsorbs radionuclides on their surface and disposed in uncontrolled way could pose a serious problem for surrounding environment. In our study we collected sludge samples and after drying they were determined by gamma spectrometry. Finally in order to assess the potential negative impact of that sludge on natural environment the 3-stage sequential extraction according to BCR procedure (Ure et al., 1993) was performed. Scheme of that procedure is depicted in the figure below (Fig. 2).
3. Results and discussion
Fig. 1. Map of Poland, with marked Upper Silesia region, where drinking waters were monitored.
Water samples were taken from 9 underground sources being within boundary of Upper Silesia region. Each time about 15 L of water was sampled, later on they were concentrated by evaporation and activity of certain isotopes were determined according to protocols mentioned before. Results are reported in Table 1. The impact of radionuclides derived from drinking water can be assessed by determining the effective dose to each age group in population. The doses were calculated based on obtained activity concentration of radioisotopes for various water sources, assumed amount of water consumption for each age group (Table 2) as well dose coefficient recommended by Council Directive 96/29/Euratom (European Commission (EC), 1996). Outcomes with the highest estimated annual dose are depicted below (Fig. 3). In many cases for raw waters the recommended dose 0.1 mSv/year was exceeded. Generally aeration used for removing iron and manganese caused decreasing of radioactivity. Nonetheless still are some treated waters, where despite of treatment process, annual dose 0.1 mSv is exceeded. The most crucial age groups are small babies, below 1 year and teenagers within 12–17 years. In the next figure (Fig. 4) contribution of individual nuclides to total dose is shown. As an example we decided to present dose
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
30 g solid waste sample (gamma spectrometry)
stage 1 sample + 0,11M HOAc overnight shaking
exchangeable fraction and bound to carbonates
supernatant
solid
centrifuging 10min, 2000rpm
stage 2 0,1M NH2 OH.HCL overnight shaking
solid
reducible fraction and bound to Fe/Mn oxides
centrifuging 10min, 2000rpm
stage 3 8,8M H2O2 heating up to 85°C (2x), 1M NH4 Ac (pH=2, HNO3) overnight shaking
supernatant
Oxidisable fraction bound to organic matter and sulfides
centrifuging 10min, 2000rpm
supernatant
solid Dry residuals
(gamma spectrometry)
extractants were analysed for Ra-226 i Ra-228 by means of LSC
Fig. 2. Scheme of 3-stage sequential extraction according to BCR.
Table 1 Activity concentration of radionuclides in underground waters used for human consumption. 226
Water treatment plant
Ra (mBq/dm3)
228
Ra (mBq/dm3)
238
U (mBq/dm3)
234
U (mBq/dm3)
WTP 1
Raw Potable
158.4 7 5.8 95.2 7 2.6
27.0 714.6 24.7712.7
0.76 70.09 1.14 70.13
3.2 7 0.3 3.2 7 0.3
WTP 2
Raw Potable
10.6 7 2.0 7.5 7 1.5
11.4 75.2 7.8 75.2
14.4 70.9 6.5 70.4
24.8 7 1.4 16.9 7 0.9
WTP 3
Raw Potable
13.2 7 1.2 12.0 7 1.0
10.2 74.8 7.3 74.1
11.8 70.7 6.4 70.4
31.4 7 1.7 17.2 7 0.9
WTP 4
Raw Potable
16.0 7 2.3 13.6 7 3.0
6.6 74.5 6.6 74.5
3.2 70.3 5.2 70.4
4.0 7 0.4 6.6 7 0.5
WTP 5
Raw Potable
11.4 7 1.3 6.9 7 0.9
16.2 76.3 3.4 71.7
1.09 70.14 1.58 70.12
2.17 0.3 1.85 7 0.14
WTP 6
Raw Potable
26.2 7 1.9 16.17 1.5
48.4 79.3 33.777.9
12.0 70.7 13.0 70.9
29.17 1.4 27.2 7 1.9
WTP 7
Raw Potable
66.47 3.1 7.17 1.1
64.8 711.7 15.3 76.1
1.3 70.5 0.16 70.04
2.5 7 0.8 0.277 0.05
WTP 8
Raw Potable
20.9 7 1.7 15.2 7 1.4
38.9 78.4 26.3 77.2
0.0770.02 0.08 70.02
0.127 0.03 0.107 0.03
WTP 9
Raw Potable
11.9 7 1.2 8.9 7 1.1
21.6 76.7 14.9 76.1
0.10 70.02 0.10 70.02
0.157 0.02 0.187 0.02
derived from waters processed in WTP1 for age group below 1 year. As it can be clearly seen the main contributors are both 226Ra and 228Ra isotopes.
In order to evaluate the potential risk, resulting from radon inhalation by people working in water treatment plants (especially those working in closed rooms) we placed solid state track detectors to be exposed for 3–6 months. To assess dose for
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
water-plant operators, it was necessary to compute potential alpha energy concentration (PAEC). To obtain this value, the following assumptions were made:
Having known radon activity concentration (CR) in certain places, PAEC may be calculated with application of the formula:
Equilibrium factor (F) equals 0.4. PAEC (Cα) in equilibrium (k) with 100 Bq/m3 of radon is equal 0.56 μJ/m3.
Subsequently, having Cα value, annual effective dose can be calculated as follows:
Table 2 Rate of water ingestion per year for different age groups (Risica and Grande, 2000). Age group l/Year
o1 1–2 2–7 year years years Annual water consumption 250 350 350
7–12 years
12–17 years
417 years
350
540
730
Fig. 3. Estimated annual effective dose after consumption of underground waters.
Cα ¼ CR=100Fk
E ¼ 0:0014Cαt where: t [h] – estimated working time of the staff; 0.0014 [mSv/ h μJ/m3] – PAEC conversion factor to dose for working places, accordingly to Euratom Directive 96/26 (European Commission (EC), 1996). Doses caused by exposure to radon are in most of the cases relatively low (Fig. 5). Nevertheless, in one case estimated dose was higher than 1 mSv/year. On the other hand, there is only a small number of investigated plants till now. Therefore in whole country the problem of occupational exposure of water plants staff to radon cannot be neglected and there is still a need for more survey of water treatment plants. Radionuclides concentration in solid wastes generated by the water treatment plants is given in Table 3. In case of WTP 8 and 9 there was no possibility to take sludge therefore results are not included in the below table. According to Basic Safety Standard proposed by IAEA (IAEA, 2010), if sum of activity concentration both isotopes 226Ra and 228Ra in solid waste materials is higher than 1000 Bq/kg, they should be treated as waste with elevated radioactivity. In our study such situation appears in case of WTP 2 and WTP 3, where total activity both isotopes amounts to 4091 Bq/kg and 1369 Bq/kg for WTP 2 and WTP 3, respectively. Moreover, it must be emphasized that in few cases of sludge samples, total activity admittedly does not exceed 1 Bq/g, but those activities are undoubtedly higher than typical values for the Earth crust. As it was mentioned above, from selected solid wastes (with the highest radioactivity) sequential extraction was carried out. During research attention was focused on the two most dominant Table 3 Radioactivity concentration in solid wastes from water treatment plants.
Fig. 4. Contribution of individual nuclides to the total dose in case of waters from plant 1.
Location
226
WTP1 WTP2 WTP3 WTP4 WTP5 WTP6 WTP7
1727 9 4377 12 296 7 7 3327 17 2977 12 48 7 1 1267 3
Ra [Bq/kg]
228
210
238
3367 24 3654 7 142 10747 41 4707 34 5727 32 807 3 977 4
697 7 177 15 517 11 1597 33 o 49 48 7 4 367 9
49 7 22 o 15 o 23 o 51 o 57 297 13 247 17
Ra [Bq/kg]
Pb [Bq/kg]
U [Bq/kg]
Fig.5. Effective annual dose from exposure to radon for water treatment plant operators.
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i
I. Chmielewska et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
5
Fig.6. Results for sequential extraction of radionuclides from solid waste after water treatment.
radionuclides, accumulated in the sludge, namely 226Ra and 228Ra. Taking into account the results (Fig. 6), it can be easily noticed that leachability of both radionuclides is pretty high and ranges between 10% and 90%. Significant amounts of isotopes were extracted at the 2nd and 3rd stage, while pH and redox conditions are changing. It means, that under such conditions mobility and bioavailability in natural environment arises, too. 4. Conclusions Analyses of water samples collected from underground wells usually show elevated natural radioactivity. The most crucial radionuclides are 226Ra and 228Ra. The obtained data may provide basic and at once useful information for water consumers and authority. More attention should be focused on the fate of solid waste after water treatment, since very often they are disposed without any control and may cause serious environmental contamination. Additionally, radon in the air in closed places, where underground waters are treated for human consumption, should be monitored and mitigated to ensure compliance. References Ajayi, O.S., Achuka, J., 2009. Radioactivity in drilled and dug well drinking water of Ogun state southwestern Nigeria and consequent dose estimates. Radiat. Prot. Dosimetry 135, 54–63. Chalupnik, S., Lebecka, J., 1993. Determination of 226Ra, 228Ra, 224Ra in water and aqueous solutions by liquid scintillation counting. In: Noakes, J.E., Schonhofer, F., Polach, H.A. (Eds.), Liquid Scintillation Spectrometry, 1992. Radiocarbon, Tuscon, pp. 397–403.
Chmielewska, I., Chalupnik, S., Michalik, B., Mielnikow, A., 2011. Methods for determination of natural radioactivity in drinking water samples. In: P., Cassette (Ed.), LSC 2010, Advances in Liquid Scsintillation Spectrometry. Radiocarbon, Tuscon, pp. 107–113 De Oliviera, J., Mazilli, B.P., De Oliviera Sampa, M.H., Bambalas, E., 2001. Natural radionuclides in drinking water supplies of Sao Paulo, Brazil and consequent population doses. J. Environ. Radioact. 53, 99–109. European Commission (EC), 1998. Council Drinking Water Directive 98/83/EC on the quality of water intended for human consumption. European Commission (EC), 1996. Council Directive 96/29/Euratom laying down basic safety standards for the protection of the health of workers and the general public against the danger arising from ionizing radiation. Fisher, E.L., Fuortes, L.J., Field, R.W., 1996. Occupational exposure of water operators to high concentration of radon-222 gas. J. Occup. Environ. Med. 38, 759–764. IAEA 2010, 2011. Radiation Protection and Safety of Radiation Sources. International Basic Safety Standards, GSR Part 3, Vienna. Jobbagy, V., Chmielewska, I., Kovacs, T., Chałupnik, S., 2009. Uranium determination in water samples with elevated salinity from Southern Poland by micro coprecipitation using alpha spectrometry. Microchem. J. 93 (2009), 200–205. Risica, S., Grande, S., 2000. Council Directive 98/83/EC on the Quality of Water Intended for Human Consumption: Calculation of Derived Activity Concentrations. Rapporti ISTISAN 00/16 (2000). Ure, A.M., Quevauviller, P., Muntau, H., Griepink, B., 1993. Speciation of heavy metals in soils and sediments. An account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission of the European Communities. Int. J. Environ. Anal. Chem. 51, 135–151. Warwick, P.E., Croudance, I.W., Dale, A.A., 1999. An optimized and roboust method for the determination of uranim and plutonium in aqueous samples. Appl. Radiat. Isot. 50, 579–583. World Health Organization (WHO), 2011. Guidelines for Drinking Water Quality, fourth ed., Geneva.
Please cite this article as: Chmielewska, I., et al., Natural radioactivity in drinking underground waters in Upper Silesia and solid wastes produced during treatment. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.01.017i