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Monitoring of uranium concentrations in water samples collected near potentially hazardous objects in North-West Tajikistan
Journal of Environmental Radioactivity 181 (2018) 109–117
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Monitoring of uranium concentrations in water samples collected near potentially hazardous objects in North-West Tajikistan
MARK
P. Zoriya,∗, M. Schlägera, K. Murtazaevb, J. Pillatha, M. Zoriya, B. Heuel-Fabianeka a b
Forschungszentrum Jülich, Department of Safety and Radiation Protection 52425 Jülich, Germany Khujand State University, Department of Physics 735700 Khujand, Tajikistan
A B S T R A C T The water contamination near ecologically problematic objects was investigated between 2009 and 2014 in North-West Tajikistan as a part of a joint project between Forschungszentrum Jülich and Khujand State University. The main part of this work was the determination of uranium in water samples collected near the Degmay tailings dump, the Taboshar pit lake and the Syr Darya river. More than 130 water samples were collected and analyzed to monitor the uranium concentration near the investigated areas. Two different mass spectrometers and an ion chromatograph were used for element concentration measurements. Based on the results obtained, the uranium influence of the Degmay tailings on the rivers Khoja-Bakyrgan-Say and Syr Darya and surrounding water was not found. The uranium concentration in water samples was monitored for a lengthy period at seven locations Great differences in the uranium concentration in waters collected in 2010, 2011, 2012, 2013 for each location were not observed. Drinking water samples from the region of North-West Tajikistan were analyzed and compared with the World Health Organization's guidelines. Seven out of nine drinking water samples near Taboshar exceeded the WHO guideline value for uranium concentrations (30 μg/L). The average uranium concentration of water samples from Syr Darya for the period from 2009 to 2014 was determined to be 20.1 ( ± 5.2) μg/L. The uranium contamination of the Syr Darya was determined from the western border to the eastern border and the results are shown in this paper.
1. Introduction In the middle of the last century, uranium mining and processing in Central Asia was important for the nuclear weapons and nuclear energy program of the former Soviet Union. During the Soviet period and a few years after its collapse, uranium production left behind a huge legacy of uranium mining and processing waste. About 1 billion tonnes of waste from mining and processing radioactive ore is stored at the tailings sites of operational and abandoned uranium mines in Central Asia. Considerable amounts of uranium ore were also exported to Central Asia for processing from other countries (Assessment of national experts, 2009; Corcho Alvarado et al., 2014; IAEA, 2012; Kassenova, 2010; Lind et al., 2013). More than 20% of the uranium produced in the USSR was supplied by Tajikistan. In northern Tajikistan, uranium ores were mainly processed at three isolated sites: the towns of Chkalovsk (now known as Buston), Taboshar (now Istiqlol) and Adrasman. The present state of the waste containment and the radiological situation is a potential hazard for local residents and a risk of environment contamination for the Fergana valley (IAEA, 2011; Ministry of Energy and Industry of the
∗
Republic of Tajikistan, 2009; Mirsaidov, 2012). Several international projects and studies were initiated in the last years to assess the condition of the uranium tailings and their impact on the environment and public (Lespukh et al., 2013; Skipperud et al., 2013a, 2013b; Stegnar et al., 2013; Stromman et al., 2013; Zoriy et al., 2010). The main factors of the estimated contamination risk are dust and radon released from uncovered tailings dumps. In addition, contamination of the ground water which is used for drinking and irrigation increases the potential radiological risk for the population. On this basis, the major part of the radiological investigations is focused on measurements of ground water as well as drinking water contamination. The determination of the uranium concentration in the surrounding water resources is important for understanding and evaluating environment contamination. In July 2011, the World Health Organization (WHO) released the fourth edition of its guidelines for drinking-water quality (Frisbie et al., 2013; World Health Organization, 2011). In this edition, the drinkingwater guidance level for uranium was increased to 30 μg/L (Ansoborlo et al., 2015; Frisbie et al., 2013).
Corresponding author. Wilhelm-Johnen-Straße, 52428 Jülich, Germany. E-mail address: [email protected] (P. Zoriy).
https://doi.org/10.1016/j.jenvrad.2017.11.010 Received 9 May 2017; Received in revised form 3 November 2017; Accepted 7 November 2017 Available online 12 November 2017 0265-931X/ © 2017 Elsevier Ltd. All rights reserved.
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Fig. 1. Central Asia - a) (map data: 2017 Google, Scale 1:20000000). Water sampling points for the period 2009–2014 in North-West Tajikistan - b) (map data: Google, Copernicus; Scale 1:1300000).
The Taboshar radium/uranium mine was opened in 1936 (largescale production: 1949–1965) and is one of the oldest uranium mines on the territory of the former USSR. Today, the area of over 0,54 km2 with 10 million tonnes of uranium ore waste is occupied by open cast mines, a pit lake and areas with crushed rock and uranium ore processing waste. A few kilometers from the disposal sites, the town of Taboshar is located with a population of about 12,000. The artificial pit lake (600 m length x 240 m width x 60 m depth) represents a water reservoir in this region and domestic animals such as cows, sheep and goats feed nearby and also use the pit water for drinking (Skipperud et al., 2013b). Approximately 400 m south-west of the pit lake there is a small stream, which supplies water along the valley over several kilometers towards the Utkan-Sue river, a tributary of the Syr Darya. The Syr Darya river originates in the Tian Shan Mountains in Kyrgyzstan and eastern Uzbekistan and flows for 2200 km west and north-west to the remains of the Aral Sea. The Syr Darya river basin is located in the Republic of Kazakhstan, the Kyrgyz Republic, the Republic of Uzbekistan and the Republic of Tajikistan. In Tajikistan, the Syr Darya flows over 105 km and is used to supply water to its surroundings as well as to the city of Khujand. Moreover, the waters of the Syr Darya are used for irrigating the important cotton-growing and agricultural areas along its course as well as for producing hydroelectric power (Kairakkum hydropower plant). Due to the relative proximity of the Syr Darya to legacy sites and its international significance, the analysis and monitoring of river water is an important factor from both the environmental and political points of view.
The present paper presents the results obtained from the collaborative project between the Department of Safety and Radiation Protection of Forschungszentrum Jülich (FZJ) and the Khujand State University (KSU). This part of the project focuses on the monitoring of uranium concentration in water samples collected near uranium tailings in North-West Tajikistan and on comparison of obtained results with values of WHO guidelines. The analysis of the collected water samples could explain the kind of contamination and its origin. Results on the radon exhalation of the uranium tailings dump Degmay also carried out in this project have been published by Schläger et al. (2016). 2. Material and methods 2.1. Study sites in North-West Tajikistan Based on our interest in the ecologically problematic objects in North-West Tajikistan, three main sampling areas surrounding these objects were chosen for investigation: Degmay tailings, the town of Taboshar and the Syr Darya river. Degmay is one of the largest uranium tailings dumps located in the Gafurov region about 1 km to the south of the nearest settlement Goziyan and approximately 10 km from Khujand, the second largest city in Tajikistan. The Degmay tailings dump was in operation in the period from 1963 to 1993. Currently it contains about 36 million tonnes of uranium ore processing waste with a surface area of approximately 1 km2 (Assessment of national experts, 2009; Mirsaidov, 2012; Skipperud et al., 2013b). The tailings are not covered, thus allowing a significant radon exhalation (Schläger et al., 2016). The areas of potential contamination impact from the Degmay tailings include the Syr Darya river, the longest river in Central Asia, which is located 4.6 km from the dump. One of the tributaries of the Syr Darya is the KhojaBakyrgan-Say (Ходжа-Бакырган-Сай) river, which flows near the Degmay tailings. There are several monitoring wells for observing the contamination of underground water around the Degmay tailings. However, no appreciable ground water monitoring has been carried out around Degmay in more than 10 years.
2.2. Water sampling More than 130 water samples were collected to monitor the uranium concentration near the investigated areas. The first field expedition was undertaken in November 2009 and then each subsequent year till 2014(June–July). The locations of the sites investigated and water sampling points in the joint project are shown in Fig. 1. Water samples were mostly collected from water sources such as rivers, lakes, wells and drinking water points (in depth from 0 to 20 cm). There is free access to almost all water sources for both humans and animals. 110
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technical water samples collected near the tailings and their surroundings were found to be 7.2 and 8.6 μg/L, respectively. However, the average uranium concentration in water samples from the Degmay wells, located directly at or close to the tailings, was 0.4 μg/L. These differences between the three categories of water samples could be explained by the fact that both technical and drinking water is sourced from the Syr Darya while water from the Degmay wells is ground water, which is not influenced by uranium contamination from the Syr Darya. In order to further evaluate the influence of the Degmay tailings on the surrounding waters, the Khoja-Bakyrgan-Say river nearest to the tailings was investigated (Fig. 3). No correlation was found between the uranium concentration in the water and the distance to the Degmay tailings (Fig. 4a). However, a correlation (R2 = 0.78) was observed between the uranium concentration in the water and the distance to the Syr Darya river (Fig. 4b). All measured uranium concentrations in water samples from the Khoja-Bakyrgan-Say were found to be in the range from 3.4 to 9.6 μg/L, which is less than the average uranium concentration of water from the Syr Darya. All these results demonstrate that the Degmay tailings have no uranium influence on the surrounding waters or that this influence is negligible and could not be determined due to the relatively high uranium concentration in the water of the Syr Darya. Nevertheless, all uranium concentrations in water samples were found to be lower than those recommended by WHO for uranium in drinking water (30 μg/L).
Particularly near the Degmay tailings, approximately 60 water samples were collected; near the town of Taboshar ∼30 samples; in the basin of the Syr Darya river from one border to the other ∼30 samples. To establish a typical value of the uranium concentration in water samples from this region, approximately 20 water samples were collected in different areas far away from the potentially contaminating objects. Moreover, several locations of water sources were chosen for long-term monitoring where water samples were collected during each field campaign. The water samples were collected in 50 mL polyethylene tubes, acidified with 65% nitric acid (Suprapur Merck), given a field name, packed and transported to the laboratory at Forschungszentrum Jülich, Germany, for analysis. After acidification, no turbidity was visible in any of the samples. The samples were stored at 4 °C in darkness until they were measured. 2.3. Preparation and measurements Water samples were filtered through a 0.45 μm Millipore filter (Millipore Corporation) in the laboratory. Due to the relatively high concentration of uranium in the analyzed samples and to avoid contaminating the equipment, diluted sample aliquots were measured. A quadrupole inductively coupled plasma mass spectrometer (ICPQMS, Bruker 810-MS) and a Neptune Plus Multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Thermo Fisher Scientific) were used for the determination of the elements of interest, such as Mn, Co, Ni, Pb, Th and U, as well as for uranium isotope ratio measurements. Both instruments provide exceptionally low background noise and high sensitivity. For instance, limits of detection for U-238 and Th-232 were found to be 0.2 ppt and 0.5 ppt, respectively. An ion chromatograph (IC-790, Metrohm) was applied to measure elements such as Na, K, Ca and Mg. For calibration and quality control purposes, the standard reference material river water SLRS-4 and uranium isotope standard NIST U020 were prepared and analyzed parallel to the analyzed samples. Relatively good precision of the measurements in terms of relative standard deviations (RSD) was obtained for all elements and ranged from 1.3 to 5.2%. All measurements were performed in the analytical laboratory of the Safety and Radiation Protection Department at Jülich, which is accredited with a flexible scope, covering amongst others the test area of water analysis.
3.2. Long-term uranium monitoring in water One of the main tasks of the current project was to monitor the uranium concentration of water samples for a lengthy period. For this reason, seven locations were chosen to monitor the uranium concentration. The measurements were performed during the period 2009–2014. The locations were divided into two regions - in the surroundings of the city of Khujand: lake Kairakkum, Syr Darya river near a new bridge, Syr Darya river near the western border, near Degmay tailings and drinking water from Khujand; and near the town of Taboshar: Taboshar pit lake and the uranium mine adit. The samples near the town of Taboshar were collected in 2009, 2010 and 2014. The results of the uranium concentrations in the analyzed water samples are summarized in Fig. 5a (for the surroundings of the city of Khujand) and Fig. 5b (near the town of Taboshar). The analysis of the data obtained for water samples from the surroundings of Khujand showed that there were no great differences in uranium concentrations in 2010, 2011, 2012, 2013 for each location. However, relatively high uranium concentrations in waters from each location were found in 2009 and 2014. For instance, in 2009 the uranium content in lake Kairakkum was found to be approximately 3 times as high as in 2010. An up to 60% increase in uranium concentrations was found for all locations in 2014 in comparison to 2013. The high uranium concentration in 2009 could be explained due to the late sample collection, which was performed at the beginning of November (rainy season for this region) when a lot of water comes down from the mountains. Because five of the sampling sites are located in the Syr Darya basin, the concentrations of uranium in water samples from each location obviously depend on the uranium content in the Syr Darya. A slight increase in uranium concentrations from 1.8 to 2.1 mg/L and from 1.0 to 1.1 mg/L in the period 2009–2014 was observed for the locations Taboshar and the uranium mine adit, respectively (see Fig. 5b). The lowest uranium concentrations in water from both locations near Taboshar, in contrast to water samples from the surroundings of Khujand, were measured in 2009.
3. Results and discussion 3.1. Degmay The study of the influence of the Degmay tailings (reported uranium concentration from 427 to 4760 Bq/kg (Skipperud et al., 2013b)) on the surrounding ground water is important to estimate the radiation risk for the population in this region. Therefore, contaminations of the ground water and surrounding water sources from the Degmay tailings were investigated during the current project. Water samples from drilled wells near the tailings (Degmay wells), the Khoja-Bakyrgan-Say river as well as drinking and technical water in surroundings up to 8 km in different directions from Degmay collected during expeditions from 2009 to 2014 were analyzed (Fig. 2a). The measured data show some increase in uranium contamination in a northern direction from the Degmay tailings in comparison to the other directions. This increase (up to 20 μg/L) could be explained by the use of water for irrigation and technical water from the Syr Darya river, which is located to the north of the Degmay tailings (average concentration of uranium in Syr Darya was found to be 19.8 μg/L). The data obtained on the uranium concentration in water samples was divided into three categories corresponding to drinking water, technical water and water samples from the Degmay wells (Fig. 2b). The average values of the uranium concentration for drinking and
3.3. Syr Darya Results concerning the water quality of the Syr Darya river in Central Asia have already been presented by several authors 111
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Fig. 2. Uranium concentrations in water samples collected near the Degmay tailings in the period 2009–2014: a) depending on sampling directions to Degmay tailings; b) depending on the category of samples (drinking, well and technical water).
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Fig. 3. Sample locations and uranium concentration in water samples from the Khoja-Bakyrgan-Say river, near the Degmay tailings (map data: Google, DigitalGlobe; Scale 1:110000).
(Abdushukurov et al., 2014; Kawabata et al., 2008; Yuldashev et al., 2004). During the current project, water samples collected along the Syr Darya in North-West Tajikistan in the period from 2009 to 2014
were analyzed. In Fig. 6, all the measured uranium concentrations in water samples for each year from the eastern to the western border are shown. The highest and lowest uranium concentrations in the water 113
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Fig. 4. Dependence of the uranium concentration in water samples from river Khoja-Bakyrgan-Say on the distance to: a) Degmay tailings; b) Syr-Darya river.
samples (43 μg/L and 12 μg/L) were found in November 2009 and June 2010, respectively. The average uranium concentration of water samples for the period from 2009 to 2014 was determined to be 20.1 ( ± 5.2) μg/L, which is lower than the values in the WHO guidance level for drinking water. The results in the figure in the direction of flow of the river show that there are no significant changes of uranium concentration in water samples collected in locations from eastern border to the western border. The same tendencies were observed for each year. In addition, as mentioned above, the relatively high uranium concentrations found in 2009 could be due to sample collection in the rainy season.
downstream are summarized in Fig. 7. The highest uranium concentration (2000 μg/L) was obtained in Taboshar pit lake. As can be observed, the uranium contamination in water samples decreased with increasing distance from the pit lake. A slightly increased uranium concentration was identified near the “Yellow” tailings dump, which is located approximately 1 km from the pit lake, and very probably also influences the downstream waters. Uranium concentrations in water samples below the values of the WHO guideline were measured only in the water samples which were collected downstream at a distance of 9 km and more from the pit lake. In order to evaluate a typical background value of uranium in waters for the region of North-West Tajikistan, samples were collected and analyzed in the village of Vorukh and the town of Isfara. The results were found to be in the range from 1.8 to 2.9 μg/L for Vorukh and from 5.6 to 8.7 μg/L for Isfara.
3.4. Other sampling sites As mentioned above, water samples were also collected at other locations in North-West Tajikistan. Depending on water sampling locations, the concentrations of U-238 in the surroundings of the town of Taboshar were found to be in the range from 25.7 μg/L to 2.1 mg/L. All water samples in the surroundings of Taboshar were divided into two types: drinking water (9 samples) and water collected near Taboshar pit lake (25 samples). The uranium concentrations in drinking water samples varied from 17 to 124 μg/L (see Table 1). Seven out of nine drinking water samples analyzed exceeded the WHO guideline value for uranium concentrations (30 μg/L), some of them by a factor of 4. The results of uranium concentrations in water samples collected in 2010 from the Taboshar pit lake, from mine adits as well as
3.5. Other measured elements The concentrations of Th-232 as well as the U-235/U-238 ratios were measured for all water samples collected in 2009–2014. The concentrations of Th-232 were found to be in the range from 0.01 to 0.1 μg/L, which can be regarded as insignificant. The U-235/U-238 concentration ratios in the analyzed samples were found to be in a range from 0.0068 to 0.0076, natural abundance ratio of uranium 0,0072 (Cowan and Adler, 1976). Five selected samples from different sites were also measured for Na, K, Ca, Mg, Mn, Co, Ni, and Pb content.
Fig. 5. Monitoring of uranium concentration in water samples in the period 2009–2014 at seven different locations (a - in the surroundings of Khujand; b - near Taboshar).
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Fig. 6. Uranium concentrations of water from the Syr Darya river collected at different sampling points (from western to eastern borders) during 2009–2014.
• No uranium influence of the Degmay tailings on the surrounding
Table 1 Uranium concentrations in drinking water collected near the town of Taboshar (bold uranium concentration exceed the WHO guideline for uranium in drinking water). Sample name
Sampling site description
U-238, μg/L
T-W-2010-29 T-W-2010-6 T-W-2010-7 T-W-2010-9 T-W-2014-2
Drinking water from Old Taboshar Drinking water from village Shurbulok, Taboshar Drinking water from Hukumat,Taboshar Drinking water from Old Taboshar Drinking water from water pipe, village Gornjatskoe Drinking water from water pipe, Old Taboshar Drinking water. ∼1200 m down from mine lake. Drinking water. ∼1400 m down from mine lake. Drinking water from town open water pipe, Taboshar
87.1 124.1 98.3 91.2 54.2
T-W-2014-4 T-W-2014-5a T-W-2014-5b T-W-2014-7
•
•
61.3 17.3 17.1 120.8
• The results are presented in Table 2 and some of the elements are compared with the WHO guidelines, as well as with the data reported by Skipperud (Skipperud et al., 2013b). As can be seen from Table 2, obtained results for Taboshar pit lake were found to be in good agreement with published results by Skipperud for all compared elements. From all measured elements only uranium has exceeded WHO guidelines in some water samples, such as Taboshar pit lake, Taboshar mine adit, etc.
• •
4. Conclusions To estimate the impact of environmental pollution arising from potentially hazardous objects in North-West Tajikistan, the uranium concentration in water samples was determined during a joint project in 2009–2014. Level of water contamination with uranium was evaluated based on a comparison of obtained results with WHO guideline. Based on the results obtained and reported in the present paper, several conclusions can be drawn:
water, and in particular on the Syr Darya and Khoja-Bakyrgan-Say rivers was found. Uranium concentrations in drinking water collected in the surroundings of Khujand were found to be in the range from 2 to 13 μg/ L, which is lower than the WHO guideline value. However seven out of nine drinking water samples analyzed from the surroundings of Taboshar exceeded the WHO guideline value for uranium concentrations (30 μg/L), some of them even by a factor of 4. Monitoring data from seven different locations in North-West Tajikistan shows that there are no great differences in the uranium concentration in waters collected in 2010, 2011, 2012, 2013 for each location. Increased uranium concentrations in water samples were found in 2009 and 2014 in the surroundings of the city of Khujand and depend on the uranium content in the Syr Darya. The water samples most heavily contaminated with uranium were found in the town of Taboshar and its surroundings. The Taboshar pit lake and “Yellow” tailings dump have a great influence on downstream (up to 9 km) waters, which are used for irrigation and as technical water by local inhabitants. The increased concentration of uranium in the Syr Darya river in North-West Tajikistan could be due to the high concentration of uranium upstream in the countries of Uzbekistan and Kyrgyzstan, which requires further confirmation. In addition, for some measured elements the results obtained were found to be in good agreement with the data reported by other authors.
The work carried out during 2009–2014 emphasizes the importance of the project. Further investigations of water pollution, especially in the town of Taboshar and its surroundings as well as waters from the Syr Darya in Kyrgyzstan and Uzbekistan would be an essential step for estimating, safeguarding and quickly responding to the hazardous impact of radiation contamination on humans and the environment.
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Fig. 7. Uranium concentrations in water samples collected downstream from Taboshar pit lake (map data: Google, CNES/Astrium; Scales: a)1:50000 and b)-1:110000).
Table 2 Concentrations of selected elements ( ± 5% uncertainty) in water samples from different sites in North-West Tajikistan (bold - concentration of element exceed the WHO guideline). Source of water
Na
K
Ca
Mg
103 94 83 101 84 111 –
Co
Ni
Pb
Th-232
U-238
U-235/ U-238
0.4 0.1 0.4 0.7 0.5 – –
4.4 3.1 2.4 2.6 3.1 3.8 70
0.2 0.1 0.2 0.5 0.1 – 10
0.069 0.010 0.002 0.056 0.009 0.07 1Bq/L (245 μg/L)
1980 1050 15.6 18.5 10.7 2000 30
0.0072 0.0071 0.0069 0.0074 0.0071 0.0072 –
μg/L
mg/L Taboshar pit lake Taboshar mine adit Syr Darya river Lake Kairakkum Near Degmay tailings Skipperud, pit lake(Skipperud et al., 2013b) WHO guidelines, 2011 (World Health Organization, 2011)
Mn
3.8 3.0 4.7 6.2 5.3 3.6 –
111 124 119 142 100 126 –
Acknowledgments
44.0 52.2 57.3 68.0 48.2 36.0 –
12.7 1.0 5.2 15.2 0.9 13.0 400
support. The authors thank J. Höbig, H. Dederichs, M. Gorgels (FZJ) A. Murtazaev, S. Azizov, S. Rakhimberdiev and B. Rakhmatuloev (KSU) for their assistance and outstanding efforts during data collection in Tajikistan.
This work was made possible thanks to funding provided by the Dr. Erich Schmitt-Stiftung. We would like to express our gratitude for this 116
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Monitoring of uranium concentrations in water samples collected near potentially hazardous objects in North-West Tajikistan
MARK
P. Zoriya,∗, M. Schlägera, K. Murtazaevb, J. Pillatha, M. Zoriya, B. Heuel-Fabianeka a b
Forschungszentrum Jülich, Department of Safety and Radiation Protection 52425 Jülich, Germany Khujand State University, Department of Physics 735700 Khujand, Tajikistan
A B S T R A C T The water contamination near ecologically problematic objects was investigated between 2009 and 2014 in North-West Tajikistan as a part of a joint project between Forschungszentrum Jülich and Khujand State University. The main part of this work was the determination of uranium in water samples collected near the Degmay tailings dump, the Taboshar pit lake and the Syr Darya river. More than 130 water samples were collected and analyzed to monitor the uranium concentration near the investigated areas. Two different mass spectrometers and an ion chromatograph were used for element concentration measurements. Based on the results obtained, the uranium influence of the Degmay tailings on the rivers Khoja-Bakyrgan-Say and Syr Darya and surrounding water was not found. The uranium concentration in water samples was monitored for a lengthy period at seven locations Great differences in the uranium concentration in waters collected in 2010, 2011, 2012, 2013 for each location were not observed. Drinking water samples from the region of North-West Tajikistan were analyzed and compared with the World Health Organization's guidelines. Seven out of nine drinking water samples near Taboshar exceeded the WHO guideline value for uranium concentrations (30 μg/L). The average uranium concentration of water samples from Syr Darya for the period from 2009 to 2014 was determined to be 20.1 ( ± 5.2) μg/L. The uranium contamination of the Syr Darya was determined from the western border to the eastern border and the results are shown in this paper.
1. Introduction In the middle of the last century, uranium mining and processing in Central Asia was important for the nuclear weapons and nuclear energy program of the former Soviet Union. During the Soviet period and a few years after its collapse, uranium production left behind a huge legacy of uranium mining and processing waste. About 1 billion tonnes of waste from mining and processing radioactive ore is stored at the tailings sites of operational and abandoned uranium mines in Central Asia. Considerable amounts of uranium ore were also exported to Central Asia for processing from other countries (Assessment of national experts, 2009; Corcho Alvarado et al., 2014; IAEA, 2012; Kassenova, 2010; Lind et al., 2013). More than 20% of the uranium produced in the USSR was supplied by Tajikistan. In northern Tajikistan, uranium ores were mainly processed at three isolated sites: the towns of Chkalovsk (now known as Buston), Taboshar (now Istiqlol) and Adrasman. The present state of the waste containment and the radiological situation is a potential hazard for local residents and a risk of environment contamination for the Fergana valley (IAEA, 2011; Ministry of Energy and Industry of the
∗
Republic of Tajikistan, 2009; Mirsaidov, 2012). Several international projects and studies were initiated in the last years to assess the condition of the uranium tailings and their impact on the environment and public (Lespukh et al., 2013; Skipperud et al., 2013a, 2013b; Stegnar et al., 2013; Stromman et al., 2013; Zoriy et al., 2010). The main factors of the estimated contamination risk are dust and radon released from uncovered tailings dumps. In addition, contamination of the ground water which is used for drinking and irrigation increases the potential radiological risk for the population. On this basis, the major part of the radiological investigations is focused on measurements of ground water as well as drinking water contamination. The determination of the uranium concentration in the surrounding water resources is important for understanding and evaluating environment contamination. In July 2011, the World Health Organization (WHO) released the fourth edition of its guidelines for drinking-water quality (Frisbie et al., 2013; World Health Organization, 2011). In this edition, the drinkingwater guidance level for uranium was increased to 30 μg/L (Ansoborlo et al., 2015; Frisbie et al., 2013).
Corresponding author. Wilhelm-Johnen-Straße, 52428 Jülich, Germany. E-mail address: [email protected] (P. Zoriy).
https://doi.org/10.1016/j.jenvrad.2017.11.010 Received 9 May 2017; Received in revised form 3 November 2017; Accepted 7 November 2017 Available online 12 November 2017 0265-931X/ © 2017 Elsevier Ltd. All rights reserved.
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Fig. 1. Central Asia - a) (map data: 2017 Google, Scale 1:20000000). Water sampling points for the period 2009–2014 in North-West Tajikistan - b) (map data: Google, Copernicus; Scale 1:1300000).
The Taboshar radium/uranium mine was opened in 1936 (largescale production: 1949–1965) and is one of the oldest uranium mines on the territory of the former USSR. Today, the area of over 0,54 km2 with 10 million tonnes of uranium ore waste is occupied by open cast mines, a pit lake and areas with crushed rock and uranium ore processing waste. A few kilometers from the disposal sites, the town of Taboshar is located with a population of about 12,000. The artificial pit lake (600 m length x 240 m width x 60 m depth) represents a water reservoir in this region and domestic animals such as cows, sheep and goats feed nearby and also use the pit water for drinking (Skipperud et al., 2013b). Approximately 400 m south-west of the pit lake there is a small stream, which supplies water along the valley over several kilometers towards the Utkan-Sue river, a tributary of the Syr Darya. The Syr Darya river originates in the Tian Shan Mountains in Kyrgyzstan and eastern Uzbekistan and flows for 2200 km west and north-west to the remains of the Aral Sea. The Syr Darya river basin is located in the Republic of Kazakhstan, the Kyrgyz Republic, the Republic of Uzbekistan and the Republic of Tajikistan. In Tajikistan, the Syr Darya flows over 105 km and is used to supply water to its surroundings as well as to the city of Khujand. Moreover, the waters of the Syr Darya are used for irrigating the important cotton-growing and agricultural areas along its course as well as for producing hydroelectric power (Kairakkum hydropower plant). Due to the relative proximity of the Syr Darya to legacy sites and its international significance, the analysis and monitoring of river water is an important factor from both the environmental and political points of view.
The present paper presents the results obtained from the collaborative project between the Department of Safety and Radiation Protection of Forschungszentrum Jülich (FZJ) and the Khujand State University (KSU). This part of the project focuses on the monitoring of uranium concentration in water samples collected near uranium tailings in North-West Tajikistan and on comparison of obtained results with values of WHO guidelines. The analysis of the collected water samples could explain the kind of contamination and its origin. Results on the radon exhalation of the uranium tailings dump Degmay also carried out in this project have been published by Schläger et al. (2016). 2. Material and methods 2.1. Study sites in North-West Tajikistan Based on our interest in the ecologically problematic objects in North-West Tajikistan, three main sampling areas surrounding these objects were chosen for investigation: Degmay tailings, the town of Taboshar and the Syr Darya river. Degmay is one of the largest uranium tailings dumps located in the Gafurov region about 1 km to the south of the nearest settlement Goziyan and approximately 10 km from Khujand, the second largest city in Tajikistan. The Degmay tailings dump was in operation in the period from 1963 to 1993. Currently it contains about 36 million tonnes of uranium ore processing waste with a surface area of approximately 1 km2 (Assessment of national experts, 2009; Mirsaidov, 2012; Skipperud et al., 2013b). The tailings are not covered, thus allowing a significant radon exhalation (Schläger et al., 2016). The areas of potential contamination impact from the Degmay tailings include the Syr Darya river, the longest river in Central Asia, which is located 4.6 km from the dump. One of the tributaries of the Syr Darya is the KhojaBakyrgan-Say (Ходжа-Бакырган-Сай) river, which flows near the Degmay tailings. There are several monitoring wells for observing the contamination of underground water around the Degmay tailings. However, no appreciable ground water monitoring has been carried out around Degmay in more than 10 years.
2.2. Water sampling More than 130 water samples were collected to monitor the uranium concentration near the investigated areas. The first field expedition was undertaken in November 2009 and then each subsequent year till 2014(June–July). The locations of the sites investigated and water sampling points in the joint project are shown in Fig. 1. Water samples were mostly collected from water sources such as rivers, lakes, wells and drinking water points (in depth from 0 to 20 cm). There is free access to almost all water sources for both humans and animals. 110
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technical water samples collected near the tailings and their surroundings were found to be 7.2 and 8.6 μg/L, respectively. However, the average uranium concentration in water samples from the Degmay wells, located directly at or close to the tailings, was 0.4 μg/L. These differences between the three categories of water samples could be explained by the fact that both technical and drinking water is sourced from the Syr Darya while water from the Degmay wells is ground water, which is not influenced by uranium contamination from the Syr Darya. In order to further evaluate the influence of the Degmay tailings on the surrounding waters, the Khoja-Bakyrgan-Say river nearest to the tailings was investigated (Fig. 3). No correlation was found between the uranium concentration in the water and the distance to the Degmay tailings (Fig. 4a). However, a correlation (R2 = 0.78) was observed between the uranium concentration in the water and the distance to the Syr Darya river (Fig. 4b). All measured uranium concentrations in water samples from the Khoja-Bakyrgan-Say were found to be in the range from 3.4 to 9.6 μg/L, which is less than the average uranium concentration of water from the Syr Darya. All these results demonstrate that the Degmay tailings have no uranium influence on the surrounding waters or that this influence is negligible and could not be determined due to the relatively high uranium concentration in the water of the Syr Darya. Nevertheless, all uranium concentrations in water samples were found to be lower than those recommended by WHO for uranium in drinking water (30 μg/L).
Particularly near the Degmay tailings, approximately 60 water samples were collected; near the town of Taboshar ∼30 samples; in the basin of the Syr Darya river from one border to the other ∼30 samples. To establish a typical value of the uranium concentration in water samples from this region, approximately 20 water samples were collected in different areas far away from the potentially contaminating objects. Moreover, several locations of water sources were chosen for long-term monitoring where water samples were collected during each field campaign. The water samples were collected in 50 mL polyethylene tubes, acidified with 65% nitric acid (Suprapur Merck), given a field name, packed and transported to the laboratory at Forschungszentrum Jülich, Germany, for analysis. After acidification, no turbidity was visible in any of the samples. The samples were stored at 4 °C in darkness until they were measured. 2.3. Preparation and measurements Water samples were filtered through a 0.45 μm Millipore filter (Millipore Corporation) in the laboratory. Due to the relatively high concentration of uranium in the analyzed samples and to avoid contaminating the equipment, diluted sample aliquots were measured. A quadrupole inductively coupled plasma mass spectrometer (ICPQMS, Bruker 810-MS) and a Neptune Plus Multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Thermo Fisher Scientific) were used for the determination of the elements of interest, such as Mn, Co, Ni, Pb, Th and U, as well as for uranium isotope ratio measurements. Both instruments provide exceptionally low background noise and high sensitivity. For instance, limits of detection for U-238 and Th-232 were found to be 0.2 ppt and 0.5 ppt, respectively. An ion chromatograph (IC-790, Metrohm) was applied to measure elements such as Na, K, Ca and Mg. For calibration and quality control purposes, the standard reference material river water SLRS-4 and uranium isotope standard NIST U020 were prepared and analyzed parallel to the analyzed samples. Relatively good precision of the measurements in terms of relative standard deviations (RSD) was obtained for all elements and ranged from 1.3 to 5.2%. All measurements were performed in the analytical laboratory of the Safety and Radiation Protection Department at Jülich, which is accredited with a flexible scope, covering amongst others the test area of water analysis.
3.2. Long-term uranium monitoring in water One of the main tasks of the current project was to monitor the uranium concentration of water samples for a lengthy period. For this reason, seven locations were chosen to monitor the uranium concentration. The measurements were performed during the period 2009–2014. The locations were divided into two regions - in the surroundings of the city of Khujand: lake Kairakkum, Syr Darya river near a new bridge, Syr Darya river near the western border, near Degmay tailings and drinking water from Khujand; and near the town of Taboshar: Taboshar pit lake and the uranium mine adit. The samples near the town of Taboshar were collected in 2009, 2010 and 2014. The results of the uranium concentrations in the analyzed water samples are summarized in Fig. 5a (for the surroundings of the city of Khujand) and Fig. 5b (near the town of Taboshar). The analysis of the data obtained for water samples from the surroundings of Khujand showed that there were no great differences in uranium concentrations in 2010, 2011, 2012, 2013 for each location. However, relatively high uranium concentrations in waters from each location were found in 2009 and 2014. For instance, in 2009 the uranium content in lake Kairakkum was found to be approximately 3 times as high as in 2010. An up to 60% increase in uranium concentrations was found for all locations in 2014 in comparison to 2013. The high uranium concentration in 2009 could be explained due to the late sample collection, which was performed at the beginning of November (rainy season for this region) when a lot of water comes down from the mountains. Because five of the sampling sites are located in the Syr Darya basin, the concentrations of uranium in water samples from each location obviously depend on the uranium content in the Syr Darya. A slight increase in uranium concentrations from 1.8 to 2.1 mg/L and from 1.0 to 1.1 mg/L in the period 2009–2014 was observed for the locations Taboshar and the uranium mine adit, respectively (see Fig. 5b). The lowest uranium concentrations in water from both locations near Taboshar, in contrast to water samples from the surroundings of Khujand, were measured in 2009.
3. Results and discussion 3.1. Degmay The study of the influence of the Degmay tailings (reported uranium concentration from 427 to 4760 Bq/kg (Skipperud et al., 2013b)) on the surrounding ground water is important to estimate the radiation risk for the population in this region. Therefore, contaminations of the ground water and surrounding water sources from the Degmay tailings were investigated during the current project. Water samples from drilled wells near the tailings (Degmay wells), the Khoja-Bakyrgan-Say river as well as drinking and technical water in surroundings up to 8 km in different directions from Degmay collected during expeditions from 2009 to 2014 were analyzed (Fig. 2a). The measured data show some increase in uranium contamination in a northern direction from the Degmay tailings in comparison to the other directions. This increase (up to 20 μg/L) could be explained by the use of water for irrigation and technical water from the Syr Darya river, which is located to the north of the Degmay tailings (average concentration of uranium in Syr Darya was found to be 19.8 μg/L). The data obtained on the uranium concentration in water samples was divided into three categories corresponding to drinking water, technical water and water samples from the Degmay wells (Fig. 2b). The average values of the uranium concentration for drinking and
3.3. Syr Darya Results concerning the water quality of the Syr Darya river in Central Asia have already been presented by several authors 111
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Fig. 2. Uranium concentrations in water samples collected near the Degmay tailings in the period 2009–2014: a) depending on sampling directions to Degmay tailings; b) depending on the category of samples (drinking, well and technical water).
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Fig. 3. Sample locations and uranium concentration in water samples from the Khoja-Bakyrgan-Say river, near the Degmay tailings (map data: Google, DigitalGlobe; Scale 1:110000).
(Abdushukurov et al., 2014; Kawabata et al., 2008; Yuldashev et al., 2004). During the current project, water samples collected along the Syr Darya in North-West Tajikistan in the period from 2009 to 2014
were analyzed. In Fig. 6, all the measured uranium concentrations in water samples for each year from the eastern to the western border are shown. The highest and lowest uranium concentrations in the water 113
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Fig. 4. Dependence of the uranium concentration in water samples from river Khoja-Bakyrgan-Say on the distance to: a) Degmay tailings; b) Syr-Darya river.
samples (43 μg/L and 12 μg/L) were found in November 2009 and June 2010, respectively. The average uranium concentration of water samples for the period from 2009 to 2014 was determined to be 20.1 ( ± 5.2) μg/L, which is lower than the values in the WHO guidance level for drinking water. The results in the figure in the direction of flow of the river show that there are no significant changes of uranium concentration in water samples collected in locations from eastern border to the western border. The same tendencies were observed for each year. In addition, as mentioned above, the relatively high uranium concentrations found in 2009 could be due to sample collection in the rainy season.
downstream are summarized in Fig. 7. The highest uranium concentration (2000 μg/L) was obtained in Taboshar pit lake. As can be observed, the uranium contamination in water samples decreased with increasing distance from the pit lake. A slightly increased uranium concentration was identified near the “Yellow” tailings dump, which is located approximately 1 km from the pit lake, and very probably also influences the downstream waters. Uranium concentrations in water samples below the values of the WHO guideline were measured only in the water samples which were collected downstream at a distance of 9 km and more from the pit lake. In order to evaluate a typical background value of uranium in waters for the region of North-West Tajikistan, samples were collected and analyzed in the village of Vorukh and the town of Isfara. The results were found to be in the range from 1.8 to 2.9 μg/L for Vorukh and from 5.6 to 8.7 μg/L for Isfara.
3.4. Other sampling sites As mentioned above, water samples were also collected at other locations in North-West Tajikistan. Depending on water sampling locations, the concentrations of U-238 in the surroundings of the town of Taboshar were found to be in the range from 25.7 μg/L to 2.1 mg/L. All water samples in the surroundings of Taboshar were divided into two types: drinking water (9 samples) and water collected near Taboshar pit lake (25 samples). The uranium concentrations in drinking water samples varied from 17 to 124 μg/L (see Table 1). Seven out of nine drinking water samples analyzed exceeded the WHO guideline value for uranium concentrations (30 μg/L), some of them by a factor of 4. The results of uranium concentrations in water samples collected in 2010 from the Taboshar pit lake, from mine adits as well as
3.5. Other measured elements The concentrations of Th-232 as well as the U-235/U-238 ratios were measured for all water samples collected in 2009–2014. The concentrations of Th-232 were found to be in the range from 0.01 to 0.1 μg/L, which can be regarded as insignificant. The U-235/U-238 concentration ratios in the analyzed samples were found to be in a range from 0.0068 to 0.0076, natural abundance ratio of uranium 0,0072 (Cowan and Adler, 1976). Five selected samples from different sites were also measured for Na, K, Ca, Mg, Mn, Co, Ni, and Pb content.
Fig. 5. Monitoring of uranium concentration in water samples in the period 2009–2014 at seven different locations (a - in the surroundings of Khujand; b - near Taboshar).
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Fig. 6. Uranium concentrations of water from the Syr Darya river collected at different sampling points (from western to eastern borders) during 2009–2014.
• No uranium influence of the Degmay tailings on the surrounding
Table 1 Uranium concentrations in drinking water collected near the town of Taboshar (bold uranium concentration exceed the WHO guideline for uranium in drinking water). Sample name
Sampling site description
U-238, μg/L
T-W-2010-29 T-W-2010-6 T-W-2010-7 T-W-2010-9 T-W-2014-2
Drinking water from Old Taboshar Drinking water from village Shurbulok, Taboshar Drinking water from Hukumat,Taboshar Drinking water from Old Taboshar Drinking water from water pipe, village Gornjatskoe Drinking water from water pipe, Old Taboshar Drinking water. ∼1200 m down from mine lake. Drinking water. ∼1400 m down from mine lake. Drinking water from town open water pipe, Taboshar
87.1 124.1 98.3 91.2 54.2
T-W-2014-4 T-W-2014-5a T-W-2014-5b T-W-2014-7
•
•
61.3 17.3 17.1 120.8
• The results are presented in Table 2 and some of the elements are compared with the WHO guidelines, as well as with the data reported by Skipperud (Skipperud et al., 2013b). As can be seen from Table 2, obtained results for Taboshar pit lake were found to be in good agreement with published results by Skipperud for all compared elements. From all measured elements only uranium has exceeded WHO guidelines in some water samples, such as Taboshar pit lake, Taboshar mine adit, etc.
• •
4. Conclusions To estimate the impact of environmental pollution arising from potentially hazardous objects in North-West Tajikistan, the uranium concentration in water samples was determined during a joint project in 2009–2014. Level of water contamination with uranium was evaluated based on a comparison of obtained results with WHO guideline. Based on the results obtained and reported in the present paper, several conclusions can be drawn:
water, and in particular on the Syr Darya and Khoja-Bakyrgan-Say rivers was found. Uranium concentrations in drinking water collected in the surroundings of Khujand were found to be in the range from 2 to 13 μg/ L, which is lower than the WHO guideline value. However seven out of nine drinking water samples analyzed from the surroundings of Taboshar exceeded the WHO guideline value for uranium concentrations (30 μg/L), some of them even by a factor of 4. Monitoring data from seven different locations in North-West Tajikistan shows that there are no great differences in the uranium concentration in waters collected in 2010, 2011, 2012, 2013 for each location. Increased uranium concentrations in water samples were found in 2009 and 2014 in the surroundings of the city of Khujand and depend on the uranium content in the Syr Darya. The water samples most heavily contaminated with uranium were found in the town of Taboshar and its surroundings. The Taboshar pit lake and “Yellow” tailings dump have a great influence on downstream (up to 9 km) waters, which are used for irrigation and as technical water by local inhabitants. The increased concentration of uranium in the Syr Darya river in North-West Tajikistan could be due to the high concentration of uranium upstream in the countries of Uzbekistan and Kyrgyzstan, which requires further confirmation. In addition, for some measured elements the results obtained were found to be in good agreement with the data reported by other authors.
The work carried out during 2009–2014 emphasizes the importance of the project. Further investigations of water pollution, especially in the town of Taboshar and its surroundings as well as waters from the Syr Darya in Kyrgyzstan and Uzbekistan would be an essential step for estimating, safeguarding and quickly responding to the hazardous impact of radiation contamination on humans and the environment.
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Fig. 7. Uranium concentrations in water samples collected downstream from Taboshar pit lake (map data: Google, CNES/Astrium; Scales: a)1:50000 and b)-1:110000).
Table 2 Concentrations of selected elements ( ± 5% uncertainty) in water samples from different sites in North-West Tajikistan (bold - concentration of element exceed the WHO guideline). Source of water
Na
K
Ca
Mg
103 94 83 101 84 111 –
Co
Ni
Pb
Th-232
U-238
U-235/ U-238
0.4 0.1 0.4 0.7 0.5 – –
4.4 3.1 2.4 2.6 3.1 3.8 70
0.2 0.1 0.2 0.5 0.1 – 10
0.069 0.010 0.002 0.056 0.009 0.07 1Bq/L (245 μg/L)
1980 1050 15.6 18.5 10.7 2000 30
0.0072 0.0071 0.0069 0.0074 0.0071 0.0072 –
μg/L
mg/L Taboshar pit lake Taboshar mine adit Syr Darya river Lake Kairakkum Near Degmay tailings Skipperud, pit lake(Skipperud et al., 2013b) WHO guidelines, 2011 (World Health Organization, 2011)
Mn
3.8 3.0 4.7 6.2 5.3 3.6 –
111 124 119 142 100 126 –
Acknowledgments
44.0 52.2 57.3 68.0 48.2 36.0 –
12.7 1.0 5.2 15.2 0.9 13.0 400
support. The authors thank J. Höbig, H. Dederichs, M. Gorgels (FZJ) A. Murtazaev, S. Azizov, S. Rakhimberdiev and B. Rakhmatuloev (KSU) for their assistance and outstanding efforts during data collection in Tajikistan.
This work was made possible thanks to funding provided by the Dr. Erich Schmitt-Stiftung. We would like to express our gratitude for this 116
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