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Uranium isotopes in well water samples as drinking sources in some settlements around the Semipalatinsk Nuclear Test Site, Kazakhstan

  • Masayoshi Yamamoto
  • Junpei Tomita
  • Aya Sakaguchi
  • Yoshihito Ohtsuka
  • Masaharu Hoshi
  • Kazbek N. Apsalikov
Open Access
Article

Abstract

Radiochemical results of U isotopes (234U, 235U and 238U) and their activity ratios are reported for well waters as local sources of drinking waters collected from the ten settlements around the Semipalatinsk Nuclear Test Site (SNTS), Kazakhstan. The results show that 238U varies widely from 3.6 to 356 mBq/L (0.3–28.7 μg/L), with a factor of about 100. The 238U concentrations in some water samples from Dolon, Tailan, Sarzhal and Karaul settlements are comparable to or higher than the World Health Organization’s restrictive proposed guideline of 15 μg (U)/L. The 234U/238U activity ratios in the measured water samples are higher than 1, and vary between 1.1 and 7.9, being mostly from 1.5 to 3. The measured 235U/238U activity ratios are around 0.046, indicating that U in these well waters is of natural origin. It is probable that the elevated concentration of 238U found in some settlements around the SNTS is not due to the close-in fallout from nuclear explosions at the SNTS, but rather to the intensive weathering of rocks including U there. The calculated effective doses to adults resulting from consumption of the investigated waters are in the range 1.0–18.7 μSv/y. Those doses are lower than WHO and IAEA reference value (100 μSv/y) for drinking water.

Keywords

Semipalatinsk nuclear test site Kazakhstan Well waters Uranium isotopes Annual effective dose 

Introduction

Over a period of 40 years from 1949 to 1989, the former Union of Soviet Socialistic Republics (USSR) conducted more than 450 nuclear explosions at the Semipalatinsk Nuclear Test Site (SNTS), Kazakhstan; 26 of them were above ground, 87 in the atmosphere and 346 underground [1, 2]. Considerable efforts have been devoted to investigate the consequences of radiation exposures to the residents living in the area, particularly in villages contaminated heavily by fallout of the radioactive cloud [1, 2, 3].

We have also investigated the present situation of radioecology in and around the SNTS since 1994, and measured long-lived radionuclides 137Cs and Pu isotopes in large number of soil samples from various areas [4, 5, 6, 7]. From these measurements, settlements around the SNTS we visited were found to be contaminated by 239,240Pu with levels from several to a few hundred times higher than those (40–120 Bq/m2) for global fallout observed in Japan, while 137Cs contamination is not so high [8]. Furthermore, as for an external radiation dose in the air, it has been gradually clarified that residents of Dolon, where is well known to have been highly contaminated by radioactive fallout due to the first USSR nuclear detonation on 29 August 1949, received around 0.5 Gy [9].

On the other hand, information concerning internal doses experienced by village residents is still very limited around the SNTS. Recently, Tanaka et al. [10] reported that frequencies of unstable-type chromosome aberrations and micronucleus in lymphocytes were higher in residents of contaminated areas such as Dolon, Sarzhal and Kainar than those of the non-contaminated area. They point out that such a higher incidence may be caused mainly by internal exposure, although factors such as age, habitation, smoking, drinking water, medical exposure, life style and so on must be further considered in the interpretation of data from contaminated area.

To serve as an aid to resolve such problem, the present work was aimed at clarifying the present situation of radionuclide levels in well waters as local sources of drinking waters. Among naturally occurring radionuclides, uranium belongs to the most chemical and radiological toxicity of elements for human. Here, we report the present U isotope (234U, 235U and 238U) levels in well waters collected mainly from the settlements around the SNTS and the associated annual effective doses to adults resulting from consumption of the investigated waters.

Experimental

Samples

The settlements where well waters were collected are shown in Fig. 1. These areas are semiarid plains with a low mean annual precipitation (200–300 mm). Total of 35 well water samples was collected from the contaminated settlements such as Dolon, Sarzhal and Karaul around the SNTS. The pH measurement in the water was carried out on a potable pH meter (Model-D-24, Horiba Ltd.) that was calibrated in situ before each set of measurement. The samples were taken in two 200 mL polyethylene bottles without filtration. In addition, about 100 mL of water was collected in light-tight glass bottle for measuring alkalinity; diluted mercuric chloride solution was added to the bottle to prevent decomposition of dissolved organic matter and then the bottle was tightly sealed. For comparison, river surface water sample was also collected from the Irtysh River, which is the largest one among them and flows into the Ob River after leaving this area.
Fig. 1

Map showing sampling locations of well waters around Semipalatinsk Nuclear Test Site, Kazakhstan

Measurement of uranium

Uranium isotopes were determined by α-particle spectrometry after radiochemical separation [11]. The sample water was at first acidified to less than pH 1 by adding a small amount of HNO3. After shaking and standing for overnight, the water was transferred into a 500 mL beaker with the addition of known amount of 232U as a yield tracer, and evaporated to dryness. The obtained residue was dissolved in 10 M HCl and the solution was passed through an anion-exchange resin column (Dowex 1 × 8 of 100–200 mesh, Cl form, 0.8 cmϕ × 5 cm). The column was washed with a small amount of 8 M HNO3 to remove adsorbed iron and then by a sufficient amount of 10 M HCl to remove most of the other elements. Uranium was eluted from the column with 2 M HCl and the solution was evaporated to dryness. The separated U was electroplated onto a polished stainless steel disc (2 cmϕ), and its activity was measured by α-particle spectrometer with measuring time of 3–4 days (Tennelec TC256 spectrometer coupled to a 1k-channel pulse height analyzer). The counting efficiency is about 30% and the lowest limit of detection is about 0.2 mBq for 238U.

Analysis of major chemical compositions

Major dissolved ions (Na+, K+, Mg2+, Ca2+, Cl, NO3 and SO4 2−) of water samples were determined by ion chromatograph (Dionex ICS-1000). The alkalinity was measured by titration method with 0.1 M HCl down to pH 4.8 [12].

Results and discussion

Chemical composition

The chemical composition of 35 investigated waters is listed in Table 1. The pH of water samples ranges from 7.0 to 8.1, and is mostly neutral. The cation/anion balance ((Σcation − Σanion)/(Σcation + Σanion) in meq/L) for most of samples measured is smaller than 5%, although some samples have values over 10%. Total dissolved salt (TDS) concentrations are in the range 189–936 mg/L. As a whole, the TDS seems to be higher in Dolon, Mostik, Budene, Znamenka, Salzhal and Karaul than in other settlements. Those water samples contain large amounts of Na+, Ca2+, Mg2+, HCO3 and SO4 2−.
Table 1

Chemical composition of the investigated well and river waters

Settlement

Sampling date

Ion concentration (mg/L)

Ion balance (%)a

pH

Na

K

Mg

Ca

Cl

NO3

SO4

HCO3

TDS

Kanoneruka

 00Y71

08.11.00

8.1

4.77

n.d.

6.7

53.23

51.1

0.75

38.1

73

228

−0.4

Dolon

 05D1

09.20.05

7.7

93.6

19.3

24.2

62.7

33.9

71.2

114

260

679

5.1

 05D2

09.20.05

7.4

120

4.0

28.4

76.7

48.6

114

132

293

817

3.2

 04D1

11.11.04

7.6

92.7

4.6

21.8

66.0

39.7

55.7

116

273

670

1.7

 04D2

11.11.04

7.2

116

3.7

26.9

81.7

66.0

104

138

236

773

5.2

 04D3

11.11.04

7.2

93.1

17.3

22.9

61.3

46.5

70.2

119

269

699

0.5

 04D4

11.11.04

7.4

81.5

2.7

17.5

51.0

28.5

48.8

97.1

242

569

0.0

 04D5

11.11.04

7.5

73.6

4.0

16.7

49.7

19.9

10.3

65.2

301

541

0.9

 00D1

08.11.00

7.4

61.5

n.d.

23.2

107

100

11.5

129

266

699

−0.8

 00D2

08.11.00

7.4

134

n.d.

30.9

121

94.1

15.5

253

294

942

5.2

Mostik

 Y69

08.12.04

7.8

14.3

n.d.

17.4

122

95.2

17.4

62.4

199

528

4.2

Cheryomocyki

 03CH1

10.20.03

7.4

14.3

0.3

10.8

21.2

7.1

5.0

17.2

113

189

1.8

 03CH2

10.20.03

7.5

37.0

29.5

21.5

38.3

34.7

25.6

48.2

129

363

14.6

 03CH3

10.20.03

7.5

20.8

6.3

18.9

37.2

15.9

17.1

29.5

117

262

15.8

 03CH4

10.20.03

7.6

29.1

6.5

12.1

22.9

11.1

5.3

21.3

121

229

11.8

Bodene

 03BW1

10.22.03

7.5

201

1.9

61.1

47.6

111

39.5

211

174

847

19.0

 03BW2

10.22.03

7.9

231

1.3

38.0

30.0

121

13.0

261

180

874

10.1

 03BW3

10.22.03

8.1

219

1.4

38.0

19.1

109

7.2

280

176

851

6.8

Znamenka

 05Z1

09.22.05

7.0

111

1.4

37.5

41.7

50.4

106

130

208

686

4.1

Tailan

 W-7

10.10.99

n.a.

226

8.8

35.7

130

118

n.d.

399

n.a.

  

Sarzhal

 05S1

09.22.05

7.6

114

2.4

29.9

70.3

59.2

18.7

228

214

736

3.6

 05S2

09.22.05

7.8

117

2.3

40.7

92.9

84.6

65.5

222

271

896

2.4

 99S1

10.10.99

n.a.

131

n.d.

40.8

142

102

3.5

252

n.a.

  

 99S2

10.10.99

n.a.

102

10.8

35.2

119

72.5

n.d.

189

n.a.

  

 95S1

10.05.95

n.a.

95.5

5.3

40.1

131

104

36.2

203

n.a.

  

 95S2

10.05.95

n.a.

140

5.2

58.8

147

162

81.6

272

n.a.

  

Kainar

 99KA1

10.11.99

n.a.

16.3

4.6

7.1

73.7

10.5

n.d.

50.4

n.a.

  

 99KA2

10.11.99

n.a.

25.6

10.4

10.7

87.8

25.4

2.4

53.1

n.a.

  

Karaul

 04K1

11.12.04

7.9

84.3

6.1

37.6

132

84.2

177

198

216

936

2.4

 04K2

11.12.04

7.7

62.9

2.3

31.4

110

44.6

69.0

185

262

767

1.5

 04K3

11.12.04

8.0

23.7

2.1

16.2

76.4

9.1

7.9

111

203

450

1.6

 04K4

11.12.04

7.2

35.7

3.2

22.3

101

28.1

47.1

109

223

569

6.5

 04K5

11.12.04

7.5

30.8

2.6

20.1

86.0

16.6

18.6

114

242

531

1.7

 04K6

11.12.04

7.9

23.7

2.1

16.1

76.2

9.2

8.0

112

210

457

0.5

 99K1

10.10.99

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

n.a.

  

Irtysh River

 05R1

09.20.05

8.0

20.0

1.5

7.3

31.9

21.2

1.3

20.7

140

244

−4.4

 04R1

08.12.04

8.3

11.6

n.d.

8.2

58.9

24.7

n.d.

52.0

110

266

6.9

Error shows 1σ standard deviation from counting statistics

a(Σcation − Σanion)/(Σcation + Σanion) × 100

n.d. not detected, n.a. not analyzed

Uranium levels and isotopic ratios

The result of the uranium analysis of well water samples is summarized in Table 2, together with those of river water samples from the Irtysh River. It is apparent from Table 2 that concentrations of 238U in the investigated waters vary in a wide range 3.6–356 mBq/L (0.3–28.7 μg/L), with a factor of about 100. The lowest concentration (3.6 mBq/L) of 238U was detected in the well water from Kainar and the highest concentration (356 mBq/L) of 238U was observed in the well water samples from Karaul. In Dolon and Karaul, the 238U contents change widely even within the area of each settlement. For waters from other settlements, the concentrations of 238U do not change largely. Such variation of 238U concentrations may be connected with the different local, geological and hydrological conditions of the original places of the investigated waters, although the 238U levels seem to increase with increasing mineralization as a whole. Literature values of 238U in freshwater have been reported in the range 0.002–5 μg/L, and the median was 0.4 μg/L [13]. Global means, 0.04 and 2.0 μg/L, were reported [14]. The 238U contents found here are several to several tens of times higher than the reported values. Kawabata et al. [15, 16] have also observed similarly high 238U concentrations for well water samples collected from some areas in Kazakhstan and Uzbekistan. It is worth noting that the 238U concentrations in some well samples from Dolon, Tailan, Sarzhal and Karaul settlements are comparable to or higher than the World Health Organization’s restrictive proposed guideline of 15 μg (U)/L [17]. Most of the measured 234U/238U activity ratios are higher than 1, and vary from 1.5 to 7.9, with most from 1.5 to 3. Those higher ratios of 234U/238U may be explained by preferential leaching of 234U due to the α-recoil effect [11, 18]. No clear relationship is observed between 238U concentration and 234U/238U activity ratio. On the other hand, all of the measured 235U/238U activity ratios show the value of around 0.046 with a relatively large counting error of about 10%. It is probable that the elevated concentration of 238U found in some settlements around the SNTS is not due to the close-in fallout from nuclear explosions at the SNTS, but rather to the intensive weathering of rocks including U there.
Table 2

Results of uranium measurements of the investigated well and river waters

Settlement

238U concentration

Activity ratio

 

(mBq/L)

(μg/L)

234U/238U

235U/238U

Kanoneruka

 00Y71

11.4 ± 0.7

0.92

1.63 ± 0.12

0.047 ± 0.008

Dolon

 05D1

189.9 ± 6.8

15.3

1.63 ± 0.03

0.044 ± 0.002

 05D2

157.2 ± 8.7

12.6

1.64 ± 0.06

0.043 ± 0.002

 04D1

99.8 ± 5.0

8.03

1.44 ± 0.05

 

 04D2

194.6 ± 12.1

15.7

1.54 ± 0.06

 

 04D3

197.9 ± 11.4

15.9

1.48 ± 0.05

 

 04D4

45.1 ± 1.4

3.62

1.65 ± 0.05

 

 04D5

51.4 ± 2.8

4.13

1.51 ± 0.07

 

 00D1

135.6 ± 6.3

10.9

1.42 ± 0.06

0.040 ± 0.005

 00D2

117.1 ± 5.4

9.42

1.36 ± 0.06

0.048 ± 0.004

Mostik

 Y69

49.2 ± 2.2

3.96

1.54 ± 0.07

0.050 ± 0.010

Cheryomocyki

 03CH1

42.3 ± 1.9

3.40

1.36 ± 0.06

0.047 ± 0.006

 03CH2

25.1 ± 0.7

2.02

1.44 ± 0.05

 

 03CH3

22.6 ± 0.7

1.81

1.38 ± 0.05

0.043 ± 0.006

 03CH4

28.9 ± 0.7

2.33

1.53 ± 0.04

 

Bodene

 03BW1

144.3 ± 4.8

11.6

2.93 ± 0.06

0.048 ± 0.005

 03BW2

114.2 ± 4.9

9.19

2.98 ± 0.08

0.043 ± 0.005

 03BW3

139.9 ± 5.2

11.2

2.67 ± 0.06

0.049 ± 0.006

Znamenka

 05Z1

36.5 ± 2.5

2.94

6.80 ± 0.38

0.045 ± 0.005

Tailan

 W-7

274.0 ± 10.9

22.0

1.97 ± 0.06

0.049 ± 0.003

Sarzhal

 05S1

144.4 ± 6.1

11.6

2.42 ± 0.06

0.044 ± 0.003

 05S2

213.9 ± 12.0

17.2

2.41 ± 0.07

0.043 ± 0.003

 99S1

206.4 ± 14.1

16.6

2.35 ± 0.13

0.048 ± 0.003

 99S2

127.8 ± 6.9

10.3

2.19 ± 0.11

0.052 ± 0.006

 95S1

156.1 ± 8.3

12.6

2.15 ± 0.10

0.050 ± 0.006

 95S2

172.4 ± 10.0

13.9

2.26 ± 0.12

0.045 ± 0.005

Kainar

 99KA1

3.56 ± 0.59

0.29

7.88 ± 1.28

 

 99KA2

4.14 ± 0.67

0.33

5.51 ± 0.87

 

Karaul

 04K1

82.8 ± 4.9

6.66

2.34 ± 0.10

 

 04K2

90.8 ± 6.6

7.30

2.16 ± 0.11

0.048 ± 0.005

 04K3

52.1 ± 3.6

4.19

2.53 ± 0.14

 

 04K4

116.8 ± 7.4

9.39

1.51 ± 0.07

0.045 ± 0.004

 04K5

97.6 ± 5.1

7.85

1.73 ± 0.07

0.048 ± 0.005

 04K6

48.6 ± 2.8

3.91

2.35 ± 0.11

 

 99K1

355.6 ± 23.4

28.6

1.09 ± 0.06

0.047 ± 0.009

Irtysh River

 05R1

31.0 ± 1.3

2.49

1.77 ± 0.07

0.044 ± 0.005

 04R1

37.0 ± 1.5

2.98

1.65 ± 0.06

 

Error shows 1σ standard deviation from counting statistics

The 238U concentrations for river water samples collected from the Irtysh River are 31–37 mBq/L (2.5–3.0 μg/L). The levels in the Irtysh River are close to the values in well water samples from Mostik and Cheryomocyki. The 234U/238U activity ratios (1.7–1.8) are nearly the same as those found at settlements around the Irtysh River.

Radiological annual dose

Assuming that a man drinks 2 L of water per day, the annual effective doses (D) resulting from consumption of the investigated waters can be calculated using the following formula:
$$ D\,\left( {\upmu {\text{S}}\upnu/{\text{y}}} \right) = \sum Ii \cdot Fi \cdot 365 $$
where Ii is the concentration of the given U isotopes (Bq/day), and geometric mean values of 238U and 234U concentrations were used as representative values for each settlement. The 235U contents were estimated by using the value (0.046) of 235U/238U activity ratio for natural uranium. The values of Fi are the ingestion dose coefficients (dose equivalent per intake of unit activity, Sv/Bq) reported by the International Commission on Radiological Protection [19]; 4.4 × 10−8 for 238U, 4.9 × 10−8 for 234U and 4.9 × 10−8 for 235U. In this case, fractional transfer to blood is assumed to be 0.02 for all uranium isotopes. The effective dose for adults caused by ingestion of uranium isotopes of the investigated well waters are presented in Table 3, except the settlements where only one well water sample was measured. The calculated effective doses vary from 1.0 to 18.7 μSv/y. The dose (18.7 μSv/y) estimated for the adults living in the Sarzhal region is comparable to the value of 16 μSv/y (range 9–20 μSv/y) reported recently by Vintró et al. [20]. Those doses are lower than WHO and IAEA reference value (100 μSv/y) for drinking water [21, 22].
Table 3

Annual effective dose to adult arising from U ingestion (consuming 2 L of water daily) through well water in each settlement

Settlement

Analyzed number of samples

Range

Geometric mean

Effective dose (mSv/y)

238U (mBq/L)

238U (mBq/L)

234U (mBq/L)

235Ua (mBq/L)

Dolon

9

45.1–197.9

117.3

177.9

5.4

10.3

Cheryomocyki

4

22.6–42.3

28.9

41.1

1.3

2.4

Bodene

3

114.2–144.3

132.1

377.4

6.1

18.0

Sarzhal

6

127.8–213.9

167.3

365.4

7.7

18.7

Kainar

2

3.56–4.14

3.8

25.3

0.2

1.0

Karaul

7

48.6–355.6

94.6

181.9

4.4

9.8

aContents of 235U were calculated by using the value (0.046) of 235U/238U for natural U

Conclusion

The concentrations of 238U in the well water samples from some settlements around the SNTS vary in a wide range 3.6–356 mBq/L (0.3–28.7 μg/L). The 238U concentrations in some samples from Dolon, Tailan, Sarzhal and Karaul settlements are comparable to or higher than the World Health Organization’s restrictive proposed guideline of 15 μg (U)/L. The measured 234U/238U activity ratios are higher than 1, and are mostly from 1.5 to 3. The 235U/238U activity ratios show the value of around 0.046, indicating that U in the wells is of natural origin. It is probable that the higher 238U concentrations are not due to the close-in fallout from nuclear explosions at the SNTS, but rather to the intensive weathering of rocks including U there. The calculated annual effective doses arising from the ingestion of U isotopes (234U, 235U and 238U) are in the range 1.0–18.7 μSv/y, and are lower than the recommended value of 100 μSv/y for drinking water.

Notes

Acknowledgments

We would like to express our gratitude to the research staff of the Kazakh Scientific Research Institute of Radiation Medicine and Ecology for their help with sampling. This work was supported by a Grand-in-Aid (M. Y. and M. H.: 1995–2005) for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Open Access

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Copyright information

© The Author(s) 2010

Authors and Affiliations

  • Masayoshi Yamamoto
    • 1
  • Junpei Tomita
    • 1
  • Aya Sakaguchi
    • 2
  • Yoshihito Ohtsuka
    • 3
  • Masaharu Hoshi
    • 4
  • Kazbek N. Apsalikov
    • 5
  1. 1.Low Level Radioactivity Laboratory, K-INETKanazawa UniversityWake, Nomi-shiJapan
  2. 2.Faculty of ScienceHiroshima UniversityHiroshimaJapan
  3. 3.Institute of Environmental SciencesAomoriJapan
  4. 4.International Radiation Information Center, Research Institute for Radiation Biology and MedicineHiroshima UniversityHiroshimaJapan
  5. 5.Kazakh Scientific Research Institute for Radiation Medicine and EcologySemipalatinskThe Kazakhstan Republic

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