Water Qual Expo Health (2011) 3:149–155 DOI 10.1007/s12403-011-0052-9
Contributions of Natural Radionuclides in the Domestic Water of Two Critical Gold Mining Communities in Ghana J.K. Gbadago · A. Faanhof · C. Schandorf · E.O. Darko · M.A. Addo
Received: 1 September 2011 / Revised: 12 November 2011 / Accepted: 17 November 2011 / Published online: 8 December 2011 © Springer Science+Business Media B.V. 2011
Abstract A study of the possible radiological impact as a result of usage of water in two critical mining communities of Dumasi and Chujah at Bogoso in the Western Region of Ghana was carried out. Water samples collected from boreholes and treated water supplied by a gold mining company were analyzed for important radionuclides such as 238 U, 234 U, 226 Ra, 210 Po, 230 Th, 232 Th and 224 Ra, using extractive techniques in the RadioAnalytical Laboratory of the South African Nuclear Energy Corporation. None of the radionuclide concentrations found exceeded the world averages in drinking water. The 238 U/235 U ratios were also found to fall within those for natural environmental materials. The dose contributions of the radionuclides for different age groups were evaluated using the IAEA recommended dose conversion factors. The lifetime average dose for all the communities are lower than 0.1 mSv/a as recommended by WHO; however, if age group classification is considered, infants less than 1 year old in Chujah are exposed to 0.11 mSv/a when the treated water is used.
J.K. Gbadago () · E.O. Darko · M.A. Addo Ghana Atomic Energy Commission, P.O. Box LG 80, Legon, Accra, Ghana e-mail:
[email protected] A. Faanhof South African Nuclear Energy Corporation, P.O. Box 582, Pretoria 0001, South Africa J.K. Gbadago · C. Schandorf · E.O. Darko · M.A. Addo School of Nuclear and Allied Sciences, University of Ghana, Legon, Accra, Ghana A. Faanhof Centre of Applied Radiation Science and Technology, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho, South Africa
Keywords Radiological impacts · Water usage · Age groups · Infants · Average dose
Introduction Dumasi and Chujah are two critical mining communities located at Bogoso in the Western Region of Ghana. Dumasi straddles the road linking the towns of Bogoso and Prestea and is about 2 km north of the mine site entrance. The population is estimated at 3,000 people (GSR 2008). The livelihood activities of the inhabitants include farming and fishing. Basic schools are also located in the community. It is the closest critical community to the mining activities. The Dumasi mining pit is located about 200 m east of the Dumasi community, and it is the intention of the mining company to expand this pit; as a result negotiations for resettlement are currently ongoing. There has been reported spillage of tailings and flooding on farms near tailings dams (GSR 2008). The source of domestic water is treated water supplied by the Bogoso-Prestea mine in about 3000-gallon capacity polytank and a few water boreholes located in the community. Chujah lies directly west of the mine’s entrance and located further from the disposal facility than Dumasi. It is sparsely populated at about 30 persons per km2 . The source of domestic water is also treated water supplied by the mines and a water borehole is also located in the community. The numerous potential transport mechanisms and pathways of natural radioactivity make it difficult to assess, and in most studies (DWAF 1999; Faanhof and Louw 2001; Desideri et al. 2007; Palomo et al. 2007), two main pathways are considered to give rise to significant exposures. These are (a) direct ingestion resulting from regular and continuous use of the water for drinking purposes, and (b) regular
150 Table 1 Dose conversion factors, E(g), for ingestion by various age groups of the Public, in Sv/Bq (IAEA 1996)
J.K. Gbadago et al. Radionuclide
<1a
1–2a
2–7a
7–12a
12–17a
>17a
E(g)
E(g)
E(g)
E(g)
E(g)
E(g)
238 U
3.4E−07
1.2E−07
8.0E−08
6.8E−08
6.7E−08
4.5E−08
234 Th
4.0E−08
2.5E−08
1.3E−08
7.4E−09
4.2E−09
3.4E−09
234 U
3.7E−07
1.3E−07
8.8E−08
7.4E−08
7.4E−08
4.9E−08
230 Th
4.1E−06
4.1E−07
3.1E−07
2.4E−07
2.2E−07
2.1E−07
226 Ra
4.7E−06
9.6E−07
6.2E−07
8.0E−07
1.5E−06
2.8E−07
214 Pb
2.7E−09
1.0E−09
5.2E−10
3.1E−10
2.0E−10
1.4E−10
214 Bi
1.4E−09
7.4E−10
3.6E−10
2.1E−10
1.4E−10
1.1E−10
210 Pb
8.4E−06
3.6E−06
2.2E−06
1.9E−06
1.9E−06
6.9E−07
210 Bi
1.5E−08
9.7E−09
4.8E−09
2.9E−09
1.6E−09
1.3E−09
210 Po
2.6E−05
8.8E−06
4.4E−06
2.6E−06
1.6E−06
1.2E−06
235 U
3.5E−07
1.3E−07
8.5E−08
7.1E−08
7.0E−08
4.7E−08
231 Pa
1.3E−05
1.3E−06
1.1E−06
9.2E−07
8.0E−07
7.1E−07
227 Ac
3.3E−05
3.1E−06
2.2E−06
1.5E−06
1.2E−06
1.1E−06
227 Th
3.0E−07
7.0E−08
3.6E−08
2.3E−08
1.5E−08
8.8E−09
223 Ra
5.3E−06
1.1E−06
5.7E−07
4.5E−07
3.7E−07
1.0E−07
232 Th
4.6E−06
4.5E−07
3.5E−07
2.9E−07
2.5E−07
2.3E−07
228 Ra
3.0E−05
5.7E−06
3.4E−06
3.9E−06
5.3E−06
6.9E−07
228 Th
3.7E−06
3.7E−07
2.2E−07
1.5E−07
9.4E−08
7.2E−08
224 Ra
2.7E−06
6.6E−07
3.5E−07
2.6E−07
2.0E−07
6.5E−08
consumption of fish obtained from contaminated water bodies. In the present study, the drinking water pathway required more and urgent research due to the consumption rate, proximity to disposal facility and geological factors. Public water supply systems derive their water from both surface and underground water bodies, as such, a number of countries and international institutions have established concentration levels at which radioactivity must be controlled (EC, 1996, 1998; DWAF 1999; Canadian GD 2000; NHMRC/ANZECC/ARMCANZ 2000; WHO 2004; South African National Nuclear Regulator 2005). From radioactivity monitoring studies of drinking water resources, it was established that measurement of 238 U, 234 U, 226 Ra, 210 Po, 230 Th, 232 Th, and 224 Ra from the 3decay chains are necessary to calculate the estimated annual dose with a high degree of certainty (DWAF 1999; Faanhof and Louw 2001; Desideri et al. 2007). This is because measurement of the activity concentration of every single radionuclide in the uranium and thorium decay series is neither economically feasible nor necessary in order to obtain a reasonable estimate of the ingestion dose. Certain radionuclides will contribute very little to the overall radiation dose, because they have very small dose coefficient factors (DCFs), Table 1, and/or their parents may be present only at very low activity concentrations (IAEA 1996;
DWAF 1999). Also, due to the high degree of disequilibrium in water, assumptions of equilibrium are no longer valid. The relatively high DCFs of the selected radionuclides (238 U, 234 U, 226 Ra, 210 Po, 230 Th, 232 Th, 228 Th, 224 Ra, 235 U, 227 Th, 223 Ra) coupled with their radio-toxicological importance made them the appropriate choice in the estimation of the annual dose with a high degree of certainty. The amount and duration of exposure to radiation may cause short- or long-term health effects. The ability of ionizing radiation to break chemical bonds in atoms and molecules makes it a potent carcinogen. Damage occurring at the cellular or molecular level can disrupt natural processes which control the rates of cells growth and replacement of damaged tissues, permitting the uncontrolled growth of cells resulting in cancer. Unlike cancer, health effects such as nausea, weakness, hair loss, skin burns as well as diminished organ function emanate from acute exposure to radiation (USEPA 2004). The objectives of the present study, therefore, are to measure the activity concentration levels of important natural radionuclides in the domestic water of the two critical communities and estimate the average radiation exposures as a result of usage. Extractive methods have been employed.
Contributions of Natural Radionuclides in the Domestic Water of two Critical Gold Mining Communities
151
Fig. 1 The geological map of Ghana showing the study area (Bogoso) and major mining towns
The Geology, Topographic and Climatic Factors of the Study Area The geological formations of the gold mine concession are metasedimentary and volcanic rocks of the Tarkwaian and Birimian sequences, which hosts the Prestea (Ps), Bogoso (Bog), Obuasi (Obs) and Konongo (Kon) gold deposits, Fig. 1 (van Bart 2008). The transition between volcanic belts and sedimentary basins is marked by chemical sediments including cherts, manganese and carbon-rich sediments. The mineral reserves are contained within open pits at an elevation of approximately 150 m below sea level. Gold occurs in two primary ore types; principally, as re-
fractory sulphide ores in the host rocks where arsenopyrite is the main ore mineral (sub-types of this include graphitic shear zones, siliceous ores, carbonate alteration zones and wall rock hosts), and as a mixture of quartz, sulphide and carbonate veins with free-milling gold. The resource base, while substantial, is limited to generally refractory sulphide. The project area is characterized by gently rolling hills incised by an extensive drainage network. The area is wet, with low-lying swampy areas. Extensive subsistence farming occurs throughout the area with plantain, pineapple, coconut, cassava, maize, yam and some oil palm and coffee being the principal crops (GSR 2001). The topographic and
152
climatic factors coupled with the geological settings make the study of radionuclides highly relevant.
Experimental Sampling Water samples were collected from boreholes and treated water supplied by the gold mine company in about 3000gallon capacity polytank to the two communities. The samples were first filtered using 8 μm 47 mm diameter cellulose ester membrane filters. A second filtration was carried out using 0.45 μm 47 mm diameter cellulose ester membrane filters which were counted on a Tennelec 5X gas proportional counter. About 2 ml of nitric acid (63%) was added to every 1 l of residual liquid collected in order to preserve radionuclides and desorb possible nuclides adsorbed to the wall of the original container. Radiochemical Separation of Natural Radionuclides in Water The radiochemical separation of uranium and thorium was based on solid phase extra-action and the isotopes were detected by alpha spectrometry. TRU*Spec® extraction columns and cation exchange resin, BIO-RAD AG® 50 W-X8 were used to separate the uranium and thorium. Determination of 210 Po was by spontaneous deposition on silver followed by alpha spectrometry. The activity concentrations of radium were determined by co-precipitation with barium sulphate and alpha spectrometry. Radium was separated from the bulk by adding lead and barium carriers to the sample, and then precipitating together as a mixed sulphate using a complexing agent, ethylene diamine tetraacetic acid (EDTA). The fraction of barium (and radium) in the sample was determined by adding a known activity of 133 Ba tracer to the sample, and measuring the precipitate by gross αβ-counting. The radiotracers used for the determination of uranium, thorium, and 210 Po were 232 U, 229 Th, and 209 Po, respectively. The radiochemical yields for the determinations were in the range of 88% to 97%. The alpha spectrometer used consists of Passivated Implanted Planar Silicon (PIPS) semiconductor detectors of 450 mm2 active area (Canberra, Alpha Analyst), coupled to low-noise preamplifiers, amplifiers and a multichannel analyzer. Water Consumption and Dose Calculation The total doses due to the water consumption by the Dumasi and Chujah communities were calculated using the IAEA
J.K. Gbadago et al. Table 2 Water consumption (WC ) in litres per annum for different age groups (IAEA 1996) Age group
<1a
1–2a
2–7a
7–12a
12–17a
>17a
WC
200
260
300
350
600
730
BSS dose conversion factors and water consumption rates from Tables 1 and 2, respectively (IAEA 1996; Faanhof and Louw 2001). The doses were calculated from the formula D = WC CE(g) where D is the yearly dose in mSv/a, WC is water consumption per annum for each age group, C is the concentration of a specific radionuclide from the decay chain (mBql−1 ), and E(g) is the ingesting dose conversion factor for the specific radionuclide.
Results and Discussions No detectable amount of alpha and beta were found on the 45 μm 47 mm diameter cellulose ester membrane filters, which represent the suspended solids in the liquid samples. The activity concentrations of individual radionuclides of the three decay chains measured in the domestic water of the critical communities, Dumasi and Chujah are shown in Tables 3, 4 and 5. The arithmetic mean of the 238 U-series is about 24 ± 5 mBql−1 , and that of 235 U and 232 Th are, respectively, about 5 ± 2.3 and 8 ± 3.8 mBql−1 . Clearly, any possible radiological impact as a result of usage of water in these communities might likely come from the 238 U-series. It can also be seen that apart from the Chujah treated water, 234 U is relatively enriched compared to 238 U (Table 3). The reason for the higher 234 U concentrations is due to alpha recoil process, which enhances the mobilization and solubility of the decay product (234 U) relative to the parent (238 U). After the alpha particle has been emitted, the uranium is often stabilized in solution as a very mobile uranyl carbonate complex (IAEA 2003; Global Security 2005). The enrichment in 234 U is accordingly related to the crystal damage and leaching, which are the main mechanisms for the 234 U/238 U disequilibrium in environmental water (Kronfeld et al. 2004). The 234 U/238 U activity ratios obtained in Table 3 are within the ranges, 1 to 2, and 0.52 to 9.02, analyzed for natural water and groundwater, respectively (Goldstein 1997; Awudu and Darko 2011). Most of the values fall within that for natural water except that for DA School treated water, which falls within the range analyzed for groundwater. The 234 U/238 U activity ratios obtained for DA School treated water agreed with the observations, made by Awudu and Darko in 2011, that the largest disequilibrium occurred in treated water. Also, the ratios between 238 U and 235 U (Table 3) are within that for natural environmental materials (Goldstein 1997).
Contributions of Natural Radionuclides in the Domestic Water of two Critical Gold Mining Communities Table 3
238 U-series
153
activity concentrations (mBql−1 ) in domestic water samples from Dumasi and Chujah 238 U
Location
234 U
230 Th
226 Ra
210 Po
234 U/238 U
238 U/235 U
Chujah borehole
27 ± 5
38 ± 6
13.1 ± 3.4
8.0 ± 3.8
6.20 ± 3.11
1.39 ± 0.34
22.5 ± 5.6
Chujah treated water
34 ± 4
25 ± 3
22 ± 6
12.0 ± 5.1
10 ± 4.09
0.74 ± 0.12
21.3 ± 3.3
Dumasi borehole
17 ± 4
24 ± 5
25.4 ± 8.0
<21
4.12 ± 2.38
1.42 ± 0.44
21.3 ± 7.3
Dumasi treated water
70 ± 7
72 ± 7
23 ± 6
9.6 ± 6.8
7.83 ± 3.52
1.03 ± 0.14
22 ± 3.0
DA-school treated water
14 ± 4
40 ± 6
47 ± 10
11 ± 4
4.71 ± 2.36
2.86 ± 0.92
20 ± 8.1
Critical limits
1200
1100
98
85
15
0.52–9.02
21.7
Table 4 235 U-series activity concentrations (mBql−1 ) in domestic water samples from Dumasi and Chujah 235 U
227 Th
Chujah borehole
1.2 ± 0.2
<10
<19
Chujah treated water
1.6 ± 0.2
6.4 ± 3.9
<30
Dumasi borehole
0.8 ± 0.2
16.3 ± 6.8
<28
Dumasi treated water
3.2 ± 0.3
12.5 ± 5.4
<37
DA-school treated water
0.7 ± 0.2
2.0 ± 3.3
<25
Critical limits
1100
1300
75
Location
223 Ra
228 Th
224 Ra
Chujah borehole
1.7 ± 1.0
1.2 ± 1.1
9.3 ± 5.3
Chujah treated water
3.9 ± 2.2
1.2 ± 1.9
16 ± 8
Location
Dumasi borehole
23.2 ± 6.7
17.3 ± 5.8
9.1 ± 5.3
Dumasi treated water
0.9 ± 0.9
4.3 ± 3.1
7.4 ± 5.3
DA-school treated water
2.6 ± 1.8
7.6 ± 3.1
12.3 ± 6.2
Critical limits
87
110
150
In general, the radionuclides of concern in groundwater are 226 Ra and its progeny (IAEA 2003). Concentrations of 226 Ra are known to vary in the USA from 0.4 to 40 mBql−1 in surface water and from 20 to 930 mBql−1 in groundwater (IAEA 2003). The activity concentrations measured for 226 Ra in both Dumasi and Chujah boreholes are far below the USA range. The mean activity concentration of 226 Ra in tap water in Turkey reported by Cevik et al. (2005) was 19.2 mBql−1 . This value is relatively higher than the value obtained for Dumasi and Chujah treated water. 210 Po is noted as a radionuclide with high radiotoxicity and it is the main source of internal alpha dose to humans, its concentration in water is therefore very important from a radiological point of view. Presently, none of the 210 Po concentrations measured exceeded the EU limit of 15 mBql−1 for drinking
water for infants reported by Desideri et al. (2007); however, the closeness to this limit of the 210 Po concentrations measured in the treated water of Chujah might suggest the need for re-evaluation of the treatment process. It is possible that the treatment process might be a contributory factor to the relatively high 210 Po activity concentration. Thorium isotopes were detected in almost all the measurements; however, their contribution to the radioactivity of water is negligible due to their high insolubility. This observation agrees with that reported by Pujol and Sanchez-Cabeza (2000). The 1996 water quality guidelines of the Department of Water Affairs and Forestry (DWAF 1996) of South Africa gave criteria for uranium-238 concentrations. These criteria were based on the chemical toxicity of uranium to the kidney rather than its radiological toxicity. Activity concentration range of 0–890 mBql−1 has no significant effects, and the annual cancer risk was said to be less than 1 in 4 × 106 . The water quality is ideal for <0.25 mBql−1 and a color code of blue is assigned. For good water quality, green was assigned to activity concentration range of 0.25–890 mBql−1 . In the present measurement, 238 U activity concentration ranges from 10–77 mBql−1 and therefore falls within green according to the classification. Furthermore, none of the radionuclide concentrations exceeded the critical limits for children at age ≤1 year for the various radionuclides in drinking water, Tables 3, 4 and 5 (CD96/29/EURATOM 1996; Risica and Grande 2000; Desideri et al. 2007). The estimated total equivalent doses for the various age groups of Dumasi and Chujah as a result of water consumption are shown in Table 6. The present DWAF (2005) guidelines assigned ≤0.10 mSv/a to blue and >0.10–1 mSv/a to green. For the present estimated doses, the lifetime average doses for all the communities fall within blue. However, if age group classification is considered, infants less than 1 year fall within the green classification. The WHO (2004) limit of 0.1 mSv/a also confirms the quality of the water in exception of infants under age 1. This is about 10% more than the WHO reference limit. This confirms the possible contribution to the dose by the observed 210 Po concentration in the Chujah treated water.
154 Table 6 Radiation exposure for water consumption in Dumasi and Chujah
J.K. Gbadago et al. Location
Age group exposure/(mSv/a) <1a
1–2a
2–7a
7–12a
Average lifetime 12–17a
>17a
Exposure/(mSv/a)
Chujah borehole
0.07
0.02
0.01
0.01
0.02
0.01
0.01
Chujah treated water
0.11
0.04
0.02
0.02
0.03
0..02
0.02
Dum borehole
0.09
0.02
0.01
0.01
0.02
0.02
0.02
Dum treated water
0.09
0.03
0.02
0.02
0.03
0.02
0.02
DASchool treated water
0.09
0.02
0.02
0.02
0.03
0.02
0.02
Cells division in children corresponds to their rapid growth, and as such, exposure to radiation may disrupt the process. The resulting effects depend on which systems are developing at the time of exposure (USEPA 2004). Any increment above the limits set for children, and in particular infants, must therefore raise a concern. Every reasonable effort must be made to keep the source of exposure as low as reasonably achievable (ALARA). Protecting infants from associated health risks of radiation exposure therefore provides justification for any additional costs that might be incurred in the re-examination of the water treatment process.
Conclusion Measurement of radioactivity in drinking water of two critical communities of a gold mining company has been carried out. None of the radionuclides concentrations exceeded the world maximum allowable averages in drinking water. The 238 U/235 U ratios are within those for natural environmental materials. The estimated lifetime average doses for all the communities also fall within recommended world limits. However, if age group classification is considered, infants less than 1 year receive doses about 10% more than the 0.1 mSv/a recommended by the WHO. Acknowledgements The authors would like to express their gratitude to the International Atomic Energy Agency (IAEA), for providing the fellowship under which this work was done at the RadioAnalysis Department of the South African Nuclear Energy Corporation (Necsa). Our gratitude also goes to the National Nuclear Research Institute of the Ghana Atomic Energy Commission for providing the local support.
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