The present radiological situation at the nuclear weapons test site at Semipalatinsk in Kazakhstan with regard to plutonium contamination

PLUTONIUM IN THE ENVIRONMENT A. Kudo (Editor) 9 Elsevier Science Ltd. All rights reserved

The present radiological situation at the nuclear weapons test site at Semipalatinsk in Kazakhstan with regard to plutonium contamination G. M. Voigt a, N. Semiochkina a, B. Dodd c, B. J. Howard c, B. Karabalinb M. Mukuschewab G Rosner a, A. S a n c h e z c D. L. Singleton c, E Strand d 9

*

9

aGSF-lnstitutfar Strahlenschutz, D-85764 Neuherberg, Germany bNNC Institute of Radiation Protection and Ecology, Kurchawv, Republic of Kazakhstan CITE Institute of Terrestrial Ecology, Grange-Over-Sands, UK dNRPA Norwegian Radiation Protection Agency, Osteras, Norway

Abstract

The preliminary results of measurements of plutonium and other radioisotopes in soil and vegetation samples originating from the former Soviet Union's nuclear test site of Semipalatinsk (STS) in Kazakhstan are presented. Sampling sites were chosen to cover agriculturally used land to receive information on contamination levels of products foreseen for human consumption and to estimate doses to the population. Here the measured activity concentrations of 5238pu and 239'240pu in selected samples are given and their impact on humans is discussed. In most cases (67 and 75%, respectively) at the two highly contaminated sites of the STS, the activity concentrations in soil samples were below 30 Bqkg-1(239,240pu) and 5 Bqkg -1 (238pu) for Lake Balapan and below 25 Bqkg -1 (239,240pu) or 6 Bqkg -1 (238pu) for Ground Zero. Crown Copyright 9 2001 Published by Elsevier Science Ltd.

Keywords: Americium; Environment; GIS; Nuclear weapons testing; Plutonium; Radioecology; Radionuclides; Restoration; Semipalatinsk nuclear test site; Soils; Vegetation

364

G. M. Voigt et al.

Introduction

The Semipalatinsk test site (STS) in Kazakhstan was one of the major sites for testing nuclear weapons used by the former Soviet Union. At this 18 500 km 2 site, 456 atomic tests (this number differs in the literature depending on the source of information and the definition of "nuclear test" and ranges from a 456 to 498) comprising aboveground, atmospheric and underground tests have been performed between 1949 and 1989, constituting 64% of the total estimated Soviet bomb yield (Michailov, 1996). Whilst the tests were being conducted, access to the site was strictly controlled by the Soviet military and no civilian use of the area was permitted. Since the early 1990s, responsibility for the site has passed to the Kazakh authorities and there has been a gradual re-establishment of agricultural use (horse and sheep farming), largely by Kazakh nationals. It has therefore become important to evaluate the current and future risk to people living on and using the contaminated area. One of the objectives of the EC-supported international project RESTORE (restoration of radioactive contaminated ecosystems) and Kazakh ISTC conversion project (International Science Technology Center) was the evaluation of the present radiological situation in the STS, i.e. the identification of radioecologically sensitive areas due to fluxes of radionuclides and the derivation of recommendations for appropriate countermeasures or remediation actions if considered necessary. The major radionuclide addressed due to its long-term impact on humans and the environment in these investigations was radiocaesium (137Cs); for this the RESTORE-Environmental Decision Support System (EDSS) combining GIS (geographical information systems) and appropriate radioecological transfer models has been adapted and applied to the STS conditions (Van der Perk et al., 1998; Voigt et al., 1999). However, because of the diverse nature of the various explosions at the STS, exposures due to radionuclides other than 137Cs need to be considered. The available data for beta-emitters such as 9~ or alpha-emitters such as 238,239,24~ and 235'238U are in general sparse, because of the resource-demanding nature of the analyses. There is some evidence that these radionuclides may occur in rather high quantifies in some areas of the STS (IAEA, 1998). Even though external exposures in this case can be neglected, internal exposures after ingestion of contaminated foodstuff and inhalation of resuspended material have the potential to lead to local internal doses representing a risk to the affected population. In order to estimate such doses, there is a need for an adequate number of measurements of 9~ Pu isotopes and 241Am radionuclides in soil, vegetation and relevant food samples, and to understand their distributions in space and time. This paper reports some of the results of 241 Am and Pu measurements in soils and plants obtained during field campaigns in the last few years.

Materials and methods

Three particularly heavily contaminated areas were identified to be the experimental sites of Ground Zero, Lake Balapan and the Degelen mountains (see also IAEA, 1998; Voigt & Semiochkina, 1998). Undisturbed soil and vegetation samples were taken from

The present radiological situation at the nuclear weapons test site at Semipalatinsk

77 ~

77,J~,~-'-~,~_T&,

365

79 ~

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7

7

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0

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60

0

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Fig. 1. Sampling sites at the Semipalatinsk test site (isolines indicate contamination levels as determined by aerial gamma-spectrometry; dots represent the sampling sites and squares the locations of investigated winter huts).

plots close to Ground Zero, where winter huts are used by Kazakhs for horse and sheep breeding, from one sheep farm close to Lake Balapan and at several sites in the Degelen mountains. Dose rate measurements (1 m above ground) and geographical co-ordinates were also recorded. The sampling sites are shown in Fig. 1. Soils were sampled with a soil corer using the standard envelope technique coveting an area of one m 2 (five samples) up to a depth of 30 cm. Cored soil layers (0-5 cm, 5 10 cm, 10-20 cm, 20--30 cm) were bulked, weighed and transferred to the laboratory.

366

G. M. Voigtet al.

Soils were sieved through a 2 mm mesh, stones, root and plant material removed, and dried at room temperature, the dry weight being recorded. Corresponding plant samples were clipped from the plots where the soil samples were taken but coveting an area greater than 1 m 2 to generate a minimum of 1 kg of sample. The extent of the area was recorded to obtain the yield and fresh samples were weighed. In the laboratory, the samples were washed under running water and air-dried. Leaves and straw were cut to 1 cm pieces, cut vegetation was dried for 5 to 18 hours at 80~ dried material was weighed and milled. All samples were incinerated and at 300 ~ to 400~ before radiochemical analysis. Samples were split and distributed to the different laboratories in ITE, NRPA and GSF and in NNC-Kazakhstan where laboratory intercalibration had been performed and showed to be in reasonable agreement. The alpha and beta analyses of samples were performed according to standard radiochemical procedures. For a detailed description of chemical procedures and alpha- and beta-spectrometric measurements see Rosner et al. (1990), Sanchez & Singleton (1996) and Kazachevskii et al. (1999). Gammaspectrometric and 241Am measurements were performed at GSF; for a detailed description of the measurement and counting technologies and statistics see Voigt et al. (1996).

Results

Vegetation growth at the STS in general is rather sparse. Thus yields of less than 1 kg m -2, with a mean value of about 300 g m -2, were obtained. The most characteristic plant communities represent cereal shrubs (Caragana spirea) and feather grass or fescue grass and sedge (Carex). The grassy vegetation consists mainly of Stipa, Festuca, Artemesia and Poa species; lichen (Parmelia) and halophytes are observed at sites where vascular plants are suppressed or on salty areas, respectively. Soil types on the STS consist mainly of light chestnut, solonchak and solonez soils. A description of the characteristics of the different major soil types is given in Table 1. Transfer to plant species and migration of radionuclides for these soils and how they can be influenced has rarely been investigated or made available in the international published literature and are presently the subject of further study (ISTC project K-52). For radiocaesium, the transfer models used for the EC and the CIS countries affected by the Chernobyl accident (Absalom et al., 1999) have been applied and resulted in an underestimate of transfer factors to vegetation and consequently predicted activity concentrations in pasture grass and corresponding sheep meat underestimated by a factor of almost ten. However, parameters needed as model input such as exchangeable K, RIP (Radiocaesium Interception Potential) (Smolders et al., 1997), pH and organic matter were not yet quantitatively available for the whole STS to guarantee an appropriate application of the models. In addition, the models have been developed for rye grass only which is not the predominant vegetation species at the STS, as outlined above. Furthermore, the inhomogenous vertical and horizontal distributions of the radionuclides in the STS in general make predictions possible only on a very local scale if all the necessary information is available.

367

The present radiological situation at thenuclear weapons test site at Semipalatinsk

Table 1 Soil characteristics of the major soil types of the Semipalatinsk test site Depth

pH,

CO 2

Humus

Total N

Exchangeable form

Adsorbed bases (meq/100 g of soil)

(cm)

water

(%)

(%)

(%)

P205

K20

Ca

Mg

Na

CEC

Light chestnut (average of 9 samples) 0-20 8.1 0.8 3.0 0.24 20-40 8.7 4.4 2.4 0.19

28 12

466 259

10.2 11.2

2.1 2.7

0.12 0.14

13.8 12.9

Dark chestnut (average of 9 samples) 0-20 8.2 3.5 3.8 20-40 8.5 4.4 2.4

15 8

974 717

21.5 20.1

4.1 5.7

0.32 0.28

28.6 27.1

Meadow chestnut carbonate (average of 10 samples) 0-20 8.4 2.4 4.8 0.26 12 20-40 8.5 4.4 2.2 0.13 7

489 337

21.5 17.1

3.2 2.8

0.24 0.17

26.5 19.9

216

6.6 3.5

1.9 6.2

3.3 0.5

11.8 10.7

0.27 0.18

Solonez (average of 4 samples)

0-20 20--40

8.0 8.7

n 4.6

1.1 .

.

0.10 .

26 .

Yet no models on the transfer of Sr, Am or Pu have been applied for the STS since further work is presently being performed on the behaviour of these radionuclides in representative STS soils and vegetation in controlled lysimeter experiments and the results will be incorporated and the models developed when available. Therefore, as a first step, activity concentrations in soil (96 samples) and vegetation (61 samples) collected in the last few years were measured. As an example, the results of the measured activities of 137Cs, 238pu, 239'240pu, 241Am and 9~ in soils from close to Ground Zero and Lake Balapan which are used for agricultural production are presented in Table 2. The frequency distributions of plutonium in the soil samples measured until now for the two identified agricultural areas located in the restricted area of the STS are given in Figs 2 and 3. The activity concentrations generally (in more than two thirds of the cases) were below 30 Bqkg -1 (239'240pu) and 5 Bq kg -1 (238pu) at Lake Balapan and below 25 Bqkg -1 (239'240pll) a n d 6 Bqkg -1 (238pu) at Ground Zero, respectively. Depth profiles of the radionuclides are given for one exemplary soil sample taken at Ground Zero (Fig. 4). Further analyses of depth profiles of radionuclides in soils are ongoing. Vegetation samples of Lake Balapan were bulked according to their 137Cs activity concentrations and their geographical co-ordinates and the results of the bulk samples are presented in Table 3 and range from 3.4 to 0.5 Bq kg -1 (239'240pu) and from 1.3 to below the detection limit of 0.03 Bq kg -1 (238pu), respectively. The distributions of the radionuclides in six individual vegetation samples of Ground Zero are shown in Fig. 5. Food samples were collected from the locals but are still in the process of activity determination. However, the preliminary results have shown rather low activities of less than 1 Bq kg -1.

368

G. M. Voigt et al.

Table 2 Measured activity concentrations (4- measurement error) of 137Cs, 238pu and 239'240pu, 90St and 241Am in soil samples collected at Ground Zero and Lake Balapan Number

Activity concentration (Bq/kg) 137Cs

90 Sr

239.240 Pu

238 Pu

241 Am

Balapan 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

47.21 4- 0.5 39204-6 4318 -+-8 132.7 4-1.8 4173+8 19884-5 7.17 4-1.12 424.7 4- 2.2 33774-6 80.234-0.5 122.3 4-1.8 10.41 4-0.4 31.17 4-0.7 66.034-0.5 60.55 4-0.5 62.634-0.5 34.98 4- 0.3 34.91 4- 0.3 43.71 4- 0.5 26.53 4- 0.4

1310 906 166 4373 829 14 693 2779 33 74

4- 37 4- 67 + 28 4- 40 4- 4 4- 2 4- 20 4- 15 4- 1 4- 3

11 4- 10 9 4- 8 16 4- 4 9 4- 1

10.22 4- 0.6 1664-6 202 4- 6 3.24-0.3 964-3 54 4-2 1.45 4-0.07 19.7 4- 0.6 1014-3 9.04-0.3 11.9 4- 0.6 1.84-0.11 8.14 4-0.46 26.24-0.8 21.34-0.6 63+2 6.72 4- 0.41 8.2 4- 0.4 7.39 4- 0.64 2.26 4- 0.13

0.15 4- 0.01 724-3 86 + 3 0.834-0.16 404-1 22.1 4-0.9 0.094-0.02 7.7 4- 0.2 424-1 3.84-0.1 4.8 4- 0.3 0.034-0.01 0.1 4-0.01 0.424-0.05 0.524-0.04 0.834-0.07 0.07 4- 0.01 0.22 4- 0.03 0.08 4- 0.03 0.03 4- 0.01

2700 + 250 800 + 80 2200 4- 200 4000 4- 300 1100 4-120 300 4- 40 41.534-2.45 1.5 4- 0.13 2.61 4- 0.28 1.34 4- 0.12 19.11 4-1.11 2.33 4- 0.2 18.134-1.18 1.324-0.17 0.424-0.07 0.22 + 0.05 2.23 4-0.21 2.92 4- 0.25 114.084-6.42 0.7 4- 0.09 1.32 4- 0.12

100.00 -t- 10 16.00 4- 6 83.00 4-10 220.00 4- 20 36.00 4-12 6.00 4- 3 2.91 4-0.22 0.03 4- 0.02 0.06 4- 0.02 0.03 4- 0.02 0.284-0.05 0.06 4- 0.03 0.324-0.06 0.034-0.02 <0.01 0.04-t- 0.03 0.05 4-0.03 0.04 4- 0.03 1.454-0.18 0.03 4- 0.02 0.02 4- 0.02

0.74 + 0.05 68.00 + 8 51.00+5 2.80• 3 6 2 + 14 27 5:15 8.2-t- 1.6 99+ 7 6.9 q- 1.4 6.4+2.4 0.13+0.01 0.52-t-0.04 13.0+3.6 10-t-3.4 5.10+1.1 1.00+0.04 0.19+0.02

Ground Zero 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

2300 + 140 275 -1-25 300 4- 25 290 4- 30 1300 4-10 240 4-10 4004-1.8 33 4- 0.3 42 4- 0.5 32 4- 0.4 684-0.5 35 4- 0.5 624-0.5 17 4-0.4 94-0.3 4 4- 0.3 27 4-0.7 32 4- 0.5 394-0.5 17 + 0.6 27 4- 0.6

200 + 40 2300 4- 300 890 4- 80 2100 4- 200 540 4- 50 38 4- 3 7 4- 3 12 4- 3 7 4- 2 7 4- 2 15 -1- 5 10 4- 2 12 4- 2 9 4- 2 7• 2 40 4- 4 120 4- 8 11 4- 2 15 4- 5 9 4- 5

340.00 • 20 125.004-10 85.00+ 10 80.00 + 10 65.00 • 5 20.00 • 5

The present radiological situation at the nuclear weapons test site at Semipalatinsk

369

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100

Activity concentration, Bq/kg Fig. 2. Frequencydistributionsof 238pu and 239'240pu in soil samples collected at LakeBalapan.

Discussion and conclusions The distribution of the measured activities of a variety of radionuclides at different locations and the highly variable isotopic ratios have again demonstrated the nonhomogenous character of the releases and of the distribution of radionuclides in the STS environment. Currently available information together with the results obtained during the reported studies suggest that radioactive contamination by Pu in soils and vegetation (as compared to radiocaesium) is in general rather low, with the exception of very localised 'hot spots'. The activity concentrations in biota and foodstuffs are in most cases below recorded values of 0.6-2 Bqkg -1 (239,24~ and 84 Bqkg -1 (241Am) in vegetation measured in the coastal zones of the Irish Sea (Hallastadius et al., 1986) or 375 Bq kg -1

370

G. M. Voigt et al.

///// / / / / /

/////

238Pu, soil, GZ]

/ / / / / / / / / /

15

/ / / / /

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~J

E 10

/ / / / / / / /

/ / / / / / / /

/ / / / / / / /

/ / / / / / / /

/////, / / / / / . . . . .

/ / / / /

0

/ / / / / / / / / / / / / / / /

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E Z 5

/ 1 / / / / / / / / / / / / / /

/ / / / / / / / / / / / / / / ,

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.

.

.

.

! 25

! 50

,1I ~ ~' / ~ 1 . "/'5 100

125

1 150

I 175

,'~1 200 225

I 250

Activity concentration, Bq/kg

7"77.. r r

'239.240pu,soil, GZ ]

r r

10

~'//, .../I.

~//~

~..

8

r

0

r r

E Z 4

///. r

~'i/, r///

0

250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000

Activity concentration, Bq/kg Fig. 3. Frequency distributions of 238pu and 239,240pu ill soil samples collected at Ground Zero.

239pu in clover of the Nevada test site (Romney et al., 1970). For foodstuffs, Bennet (1976) recorded levels of 0.37-3.7 Bq kg -1 of 239'240pu due to global fallout in the US. For cumulative deposition in the year 2000, values of 30 Bq m -2 (241Am) and 82 Bq m -2 (239'24~ were estimated for the US (Bennet, 1978) for global fallout. Most of the values measured at the STS are either in that range or smaller. At the STS, most of the plutonium has been found in or below the 10 cm soil layers and thus is unavailable to plant uptake which is additionally in general very low with a transfer

371

The present radiological situation at the nuclear weapons test site at Semipalatinsk

I1 11000

[7-/~ 6oco

1OOOO

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9OOO

238pu 9~

8OOO 0

137Cs 241Am ]52Eu 154Eu

7OOO 6OOO 5OOO 4OOO 3OOO

< t000t0

5

20

t5

25

Depth, cm Fig. 4. Example of the distributions of radionuclides with depth in a soil core of Ground Zero.

137Cs

[

8OOO

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..

6 0 0 0

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~

o

...

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4OOO

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O o.,.

._~ 2ooo-

< .

t

2

3

4

$

j

,

6

Sample Fig. 5. Distribution of radionuclides in six individual soil samples taken at Ground Zero.

factor of ca. 0.0001 (Bq k g - 1 per Bq k g - 1 dry soil (Ramikov, 1997)). Resuspension might lead to inhalation of Pu particles. This has, however, been recorded as negligible and in the range of 3.7 x 10 -8 to 7.4 x 10 -9 Bq 1-1 (Dubasov et al., 1993). The best recommendation

372

G. M. Voigt et al.

Table 3 Measured activity concentrations of 137Cs, 238pu and 239,24~ in bulked vegetation samples collected at Ground Zero and Lake Balapan (mean • standard deviation) Sample

1 (n = 2 (n = 3 (n = 4 (n =

8) 7) 6) 3)

Activity concentration, Bq/kg dry weight 137Cs 239,240pu

238pu

401.8 + 419.8 12.1 4- 14.3 7.8 • 3.7 6.5 • 3.1

1.3 • 0.02 ~<0.3 0.1 • 0.1 ~<0.06

3.4 • 1.8 • 1.0 • 0.5 •

0.03 0.5 0.1 0.3

therefore to prevent any radiological hazard due to plutonium contamination is not to disturb the soil layers, e.g. by ploughing or digging, to prevent dust, resuspension and redistribution into the upper soil layers. For dose estimation due to g a m m a radionuclides, in addition to evaluating consumption habit questionnaires, whole body measurements have been performed recently. For 137Cs, most of the measured people were below the detection limit of 100 Bq and were thus comparable to the contents in EC human bodies, e.g. in Bavaria, due to the Chernobyl accident (Berg, 1999). In order to estimate doses due to Pu contamination, it would be necessary to perform urinary excretion measurements for the population and measurements in lung or other tissues if available. However, their internal contribution to the internal dose via ingestion or inhalation is expected to be small because of the low gastrointestinal absorption of transuranic elements. The state of hygiene, the general pollution of the STS and behavioural factors may contribute to, and play a m o r e important role in, the observed increased cancer incidence rates of the population (Gusev et al., 1997) than the current radioactive exposures due to the nuclear tests performed in the past. However, to draw a complete picture of the contamination of the STS and to estimate realistically the exposures and health effects, the creation of a comprehensive data base summarising and describing historic and current information on the releases and actual contamination levels and coveting all possible exposure pathways as well as health records, and using m o d e m technologies such as the application of GIS and geostatistics, is urgently required.

Acknowledgements This project was funded by the European Commission under contract number FI4P-Cq95-0021c. In addition, the authors are grateful for the support of the ISTC (International Science and Technology Center) Brussels and Moscow within the ISTC projects K-54 and K-52.

References Absalom, J. P., Young, S. D., Crout, N. M. J., Nisbet, A. E, Woodman, R. E M., Smolders, E. & Gillet A. G. (1999). Predicting soil to plant transfer of radiocaesium using soil characteristics. Environ. Sci. Technolol., 33, 1218-1223.

The present radiological situation at the nuclear weapons test site at Semipalatinsk

373

Bennet, B. G. (1976). Fallout in 239/240pu in diet. Report no. HASL-306, Washington, D.C., USA. Bennet, B. G. (1978). Environmental measurements laboratory: Environmental aspect of Americium, December 1978. Department of Energy, EML-348, New York, N.Y., USA. Berg, D. (1999). GSF-Institute of Radiation Biology, personnel communication. Dubasov, Yu. V., Krivokhatski, A. S., Filonov, N. E & Kharitonov, K. V. (1993). Radiation situation around the Semipalatinsk test site. Bulletin of the Centre of Public Information in the Field of Nuclear Energy, N9 (in Russian). Gusev, B. I., Rosenson, R. I. & Abylkassimova, Zh. N. (1997). Tumour incidence among inhabitants of some rayons in the Semipalatinsk region exposed after nuclear testings on the test ground. In Hoshi, Takada, Kim & Nitta (Eds), Proceedings of the 2nd Hiroshima International Symposium: 'Effects of Low Level Radiation for Residents near Semipalatinsk Nuclear Test Site', Hiroshima, Japan 23-25.7.96 (pp. 153-193). Research Institute for Radiation Biology and Medicine, Hiroshima University, Daigaku Letterpress Co., Ltd, Hiroshirna, Japan. Hallastadius, L., Aarkrog, A., Dahlgaard, H., Holm, E., Boelskifte, S., Duniec, S. & Persson, B. (1986). Plutonium and americium in Arctic waters, the North Sea and Scottish and Irish coastal zones. J. Environ. Radioact., 4, 11-30.

IAEA (1998). Radiological conditions at the Semipalatinsk test site, Kazakhstan: Preliminary assessment and recommendations for further studies. Radiological Assessment Reports Series. Vienna, Austria: International Atomic Energy Agency. Kazachevskii, I. V., Lukachenko, S. N., Chumikov, G. N., Chakrova, E. T., Smirin, L. N., Solodukhin, V. E, Khayekber, S., Beredinova, N. M., Ryazanova, L. A., Bannyh, V. I. & Muratova, V. M. (1999). Combined radiochemical procedure for determination of Plutonium, Americium and Strontium-90 in the soil samples from SNTS. Czech. J. Phys., 49, 445-460. Michailov, V. N. (Ed.) (1996). USSR Nuclear Weapon Tests and Peaceful Nuclear Explosions. 1949 through 1990. RFNC-VNIIEF Report Series. Sarov, Russia (in Russian). Ramikov, A. (1997). Subcontract report to RESTORE on transfer of radionuclides for STS conditions, personnel communication. Romney, E. M., Mork, M. & Larsen, K. H. (1970). Persistence of plutonium in soil, plants and small mammals. Health Phys., 19, 487-491. Rosner, G., Hoetzel, H. & Winlder, R. (1990). Simultaneous radiochemical determination of Pu, St, U and Fe nuclides and application to atmospheric deposition and aerosol samples. Fresenius J. Analyt. Chem., 383, 606-609. Sanchez, A. & Singelton, D. L. (1996). A radioanalytical scheme for determining transuranic nuclides and Sr-90 in environmental samples. J. Radioanalyt. and Nucl. Chem., 209, 41-50. Smolders, E., Van Den Brande, K. & Merckx, R. (1997). The concentrations of 137Cs and K in soil solution predict the plant availability of 137Cs in softs. Environ. Sci. & Tecnol., 31, 3432-3438. Van tier Perk, M., Burrough, E A. & Voigt, G. (1998). GIS based modelling to identify regions of Ukraine, Belarus, and Russia affected by residues of the Chernobyl nuclear power plant accident. J. Hazardous Materials, 61, 85-90. Voigt, G., Rauch, E & Paretzke, H. G. (1996). Long-term behavior of radiocesium in dairy herds in the years following the Chernobyl accident. Health Phys., 71,370-373. Voigt, G. & Semiochkina, N. (Eds) (1998). Preliminary evaluation of the radioecological situation on the Semipalatinsk test site in the Republic of Kazakhstan. GSF-report 10/98. Neuherberg, Germany. Voigt, G. & Semiochkina, N. (Eds) (1999). Restoration strategies for radioactive contaminated ecosystems (RESTORE). Final Report of the Association contract No. FI4P-ffI95-0021c. Neuherberg, Germany.