ELSEVIER

J. Environ. Radioactivity. Vol. 27 No. 3, pp. 207-219, 1995

Copyright 0 1995Elsevier Science Limited Printed in Ireland. All rights reserved

0265-93 I X/95 $9.50 + 0.00

0265-931 X(94)00042-5

Radioactive Contamination of Aquatic Ecosystems Following the Chernobyl Accident

I. I. Kryshev

Institute of Experimental Meteorology, SPA ‘Typhoon’, 82 Lenin Avenue, Obninsk, Kaluga Region, 249020 Russia

(Received 9 February 1993; accepted 25 July 1994)

ABSTRACT

The dynamics of radioactive contamination of aquatic ecosystems (1986

1990) is considered on the basis of observational data in the near and

distant zones of the Chernobylfallout (the Chernobyl Nuclear Power Plant

(CNPP) cooling pond, the Pripyat River, the Dnieper reservoirs, and the

Kopor inlet of the Gulf of Finland). Radionuclide accumulation in aquatic

biota is analyzed.

The results obtained indicate that the radioecological conditions in the water bodies under investigation were in a state of non-equilibrium over a

long period of time following the Chernobyl accident. Reduction in the

‘37Cs concentration proceeded slowly in most of the aquatic ecosystems.

The effect of trophic levels which consisted of increased accumulation of

radiocaesium by predatory fish was observed in various parts of the

contaminated area.

INTRODUCTION

The aquatic environment plays a special role in evaluation of the possible consequences of the nuclear accident for people as well as for ecosystems. The radioactive substances enter water bodies not only as a result of atmospheric fallout and direct discharge but also due to radionuclide washoff from the water-catchment areas. In contaminated water bodies, radionuclides are quickly redistributed and accumulated in such compo-

207

208 I. I. Kryshev

nents as bottom sediments, benthos, aquatic plants, and fish. This is of particular concern from the viewpoint of radiation exposure of aquatic organisms and humans connected by food-chains within the hydrosphere. Monitoring data on radioactive contamination of surface water and sedi- ments following the Chernobyl NPP accident have been reported (Izrael et al., 1990; Vakulovsky et al., 1990).

This paper emphasizes the accumulation of radionuclides in aquatic biota based on radioactive contamination of aquatic ecosystems in various areas of the emergency zone that differed significantly in contamination levels (Fig. 1): in the CNPP cooling pond, rivers of the Dnieper catchment area, the Dnieper reservoirs, etc. (Kryshev, 1991, 1992; Kryshev et al., 1993; Kuzmenko et al., 1991).

EXPERIMENTAL

Samples of water, bottom sediments and aquatic biota were taken from the Chernobyl cooling pond, the Pripyat River, the Dnieper cascade reservoirs and others. Radionuclide contents were determined by using the

Dniepropetrovsk

Fig. 1. The Dnieper reservoir system.

Radiouctive contamination of aquatic ecos~stt~m.s,follo,c~ing Chernoh~~l 209

radiochemical, radiometric or gamma-spectrometric method. 90Sr was determined through its daughter, 9oY. Gamma-spectrometric measure- ments were carried out using the AI-1024 or AI-4096 gamma analyzer with a semiconductor detector.

RADIOACTIVE CONTAMINATION OF THE CHERNOBYL COOLING POND ECOSYSTEM

The CNPP cooling pond is the most contaminated water body in the Chernobyl emergency zone (Fig. 2). Therefore it can serve as a model to be used for estimation and forecasting of potential consequences of radioactive contamination of aquatic systems.

The CNPP cooling pond located to the southeast of the NPP site was formed by cutting off part of the Pripyat River plain with a dike. The area of the cooling pond is 22 km2, its average depth is 6.6 m, and volume is 0.15 km”. The cooling pond is characterized by moderate values of mineraliza- tion (260-430 mg/l). Transparency of water in autumn and spring is 1.2-1.3 m and in summer it is 0.6 m. The content of suspended matter ranges from 10 to 30 mg/l. The distribution of nutrients across the water body is relatively uniform. The ranges of time dependent parameters of hydrochemical regime are: ammonia nitrogen, 0.15-3.46 mg N/l; nitrites, 0.0 1-O. 17 mg N/l; nitrates, 0.1-2.3 mg N/l; organic nitrogen, 0.01-3.28 mg N/l; phosphates, 0.01-0.51 mg P/l; organic phosphorus, O@lO.55 mg P/l; iron, 0.01-0.82 mg/l; silicon, 0.1-5.4 mg/l; oxygen, -2612.2 mg/l; pH, 7.487 (Kaftan- nikova et al., 1987). According to monitoring data from May 1986, the radioactivity in the cooling pond water was mainly characterized by ‘j’1 and other short-lived radionuclides (Table 1). In the following months water activity decreased considerably as a result of radioactive decay and radionuclide deposition to bottom sediments. Since then the radioisotopes of caesium made a principal contribution to water radioactivity. The concentration of 90Sr in the cooling pond in August 1986 did not exceed 2- 3% of the ‘37Cs concentration.

The radionuclide distribution in bottom sediments of the cooling pond was characterized by a pronounced nonuniformity. Very high radio- nuclide concentrations were registered in silts that comprised 27% of the reservoir bottom area. The maximum total activity concentration levels in silts were 8-10 MBq/kg, fresh weight. Other radionuclides made the following contributions to the total activity of bottom sediments: 95Zr and 95Nb, 54-70%; ‘44Ce, 7-20%; ‘06Ru, 4%; ‘37Cs, 2-5%; 134Cs l-2%. The concentration of 90Sr in bottom sediments in 1986 was 60 kBq/kg, or about 35% of ‘37Cs. In 1987-1988 the total activity in bottom sediments

210 I. I. Kryshev

0 1 2

L-l---l km

*, 1

Fig. 2. Scheme of the Chernobyl NPP cooling pond (with isolines of contamination with 13’Cs, MBq/m*).

decreased as a result of radioactive decay. The contribution of long-lived *37Cs to the total activity amounted to 20-60% in 1988, and its concen- tration in silts was 0.4 MBq/kg on average.

Radioactive contamination of aquatic plants (algae, mainly Cladophora glomerata Kuetz) in the cooling pond was characterized by different radionuclides. According to the average data, 95Zr and 95Nb (35%) lUCe (32%) ‘06Ru (4%), ‘37Cs (2-5%) and ‘34Cs (l-2%) contributed primarily to the total activity of aquatic plants in summer and autumn of 1986. The

Radioactive contamination of aquatic ecosystems following Chernobyl 211

TABLE 1 The Estimated Activity of Water and Sediments in the Chernobyl Cooling Pond (30 May

1986)

Radionuclide Water Sediments

Activity Total amount Activity Total amount

(Bqll) ( TBq) (MBqim’1 ( TBq)

40 * 21 330 * 200 410 f 210 270 f 100 13oi70

1700 f 400 200 k 100 400 f 200 800 f 500 530 f 270 330 f. 200 200 * 130

6+4 50 f 30 70+40 40f 15 20f 10

250 f 60 30f 15 60 zt 30

120 It 70 80 f 40 50 f 30 30 f 20

2.3 f 1.0 54 f 20 50f 18 32f 16 lOf5

1.4 f 0.4 2.7 f 1.8 5.0 f 2.3 18f6 13f6 30f 14 40 zk 20

50 f 20 1200 zt 450 1100zt400 700 f 360 220 f 100

30f 10 60 f 40

llOf50 400 f 140 280 f 120 640 f 280 860 f 400

average contribution of 90Sr amounted to about 2%. The maximum observed levels of activity concentration in aquatic plants in 1986 were 2.4 MBq/kg, fresh weight.

In 19861987 the radioactive contamination of molluscs in the cooling pond was mainly governed by 90Sr, ‘44Ce, ‘06Ru, 137Cs and ‘34Cs. In 1986 the maximum total activity concentration in molluscs was O-4 MBq/kg, with the concentration of 90Sr being 5.0 x lo4 Bq/kg, and lUCe being 1.8 x 10’ Bq/kg. The mean concentration of ‘37Cs in molluscs was about 2.6 x lo4 Bq/kg in 1986 and 1.9 x lo4 Bq/kg in 1987.

The estimated average concentrations of long-lived ‘37Cs and 90Sr in ecosystem components of the cooling pond are presented in Tables 2 and 3.

For most fish species, radioisotopes of caesium occurred in muscle tissue (Table 4). In 19861987 the concentration of caesium radioisotopes in gills, scale, skin and fins decreased as compared to muscles. For exam- ple, for a pike-perch of 60&700 g, the ratio of the ‘37Cs content in muscles, gills and skin was: 1-O : 0.8 : 1.0 in 1987; 1.0 : 0.5 : O-3 in 1988 and 1-O : 0.4 : 0.2 in 1990. Fatty tissues were contaminated by caesium radioisotopes to a lesser extent. Radionuclides such as lWCe, lo6Ru, 95Zr and 95Nb were mainly contained in the GI tract, gills and skin and were rarely detected in fish muscles. Analysis of the dynamics of the 137Cs content in muscles of various species of fish shows the difference in the processes of radiocaesium accumulation for ‘predatory’ and ‘non-preda- tory’ species (Table 4). For ‘non-predatory’ species (carp, silver carp,

212 I. I. Kryshev

TABLE 2 The Estimated “‘Cs Content in the Ecosystem Components of the Chernobyl NPP Cool-

ing Pond (1986-1990)

Year Water (Bqll) Bottom sediments Algae MONUSCS

IkBq/kgj:w) CkBq1kg.f.w.) (kBqlkgf1w.j

1986 210f80 170 i 100 90 i 40 26i 7 (I 700) (440) (160) (36)

1987 60 f- 40 60 i 30 16f 10

(700) (170) (30) 1988 19f7 160f90 25f 10

(240) (460) (40) 1990 14&6 140 f 100 19f8

(23) (380) (40)

Presented are the average annual concentrations (June-December 1986). Figures in brackets are the maximum observed “‘Cs concentrations in the ecosystem components.

TABLE 3 The Estimated 90Sr Content in the Ecosystem Components of the Chernobyl NPP Cooling

Pond (July-December 1986), kBq/kg Fresh Weight

Ecosystem components

Water Bottom sediments

Algae Molluscs

Fish

‘(‘Sr concentration

0.02 l 0.013 (0.04) 6Oi25 (140) 15f9 (40) 40f 10 (60)

2.0 f 1.2 (4)

Presented are the average concentrations. Figures in brackets are the maximum observed concentrations of 90Sr in the ecosystem components.

silver bream) the highest contamination by radiocaesium was reported in 1986. For ‘predatory’ species (pike, pike-perch, perch) the maximum levels of radiocaesium were observed in 1987-1988. It should be noted that the maximum ‘s7Cs contamination level for predatory species exceeded that of nonpredatory ones by 3-10 times, i.e. the effect of trophic levels in radiocaesium accumulation was clearly reflected.

According to monitoring data of 1986, the 90Sr content in fish was about 2 kBq/kg fresh weight on average, or about 1% of the ‘37Cs content (Table 3).

RADIOACTIVE CONTAMINATION OF RIVER ECOSYSTEMS

Radioactive contamination of river ecosystems was noted early after the accident: late April-early May 1986. The total activity of water in

Rudioactive contamination of aquatic ecosystems following Chernobyl 213

TABLE 4 The Average Values of the 13’Cs Content in Muscles of Various Fish Species in the Cher-

nobyl NPP Cooling Pond (19861990), kBq/kg Fresh Weight

Year Carp Silver bream Silver carp Perch Pike-perch

1986 loo+40

(260) 1987 50 It 30

(320) 1988 40f 14

(60) 1989 25 & 6

(40) 1990 15&5

(25)

110*40

(240) 100 i 50

(280) 401t 18

(100)

8f3

(15)

140*30

(180) 100 f 50

(240) 40f 18

(100) 403 13

(90) 12f8

(70)

180+40

(220) 200 f 100

(410) 160 f 100

(360)

60 + 20

(90)

30f I3

(50) 170*90

(420) 1501t80

(360) 82% 10

(100) 80 i 40

(170)

Presented are the average annual concentrations. Figures in brackets are the maximum

observed ‘37Cs concentrations in fish muscles.

this period amounted to 10 kBq/l in the Pripyat River (the Chernobyl region), 5 kBq/l in the Uzh River and 4 kBq/l in the Dnieper River. In this period the short-lived nuclides, primarily 1311, were of princi- pal radio-ecological importance. The dynamics of the ‘st1 content in water and fish of the Kiev reservoir in May-June 1986 is presented in Fig. 3.

In the same period, such radionuclides as 13*Te, 14’Ba, 14’La, 99Mo, lo3Ru, ‘44Ce, 14’Ce, 95Zr, 95Nb, 239Np, 137Cs, 134Cs, etc., were also detec- ted. The activity of short-lived radionuclides exceeded that of long-lived caesium radioisotopes by an order of magnitude (Table 5). The activity of 90Sr in the Pripyat River on 1 May 1986 was 30 f 20 Bq/l. The ratio of 89Sr/90Sr ranged from 7 to 14. From the end of May to June, the 90Sr content in the Pripyat River was l-2 Bq/l. The maximum concentration of 239,240Pu observed in the Pripyat River water in the first few days of May (0.4 Bq/l) fell to 7.4 mBq/l by August 1986 (Izrael et al., 1990). The activity of suspended matter contaminated by the 13*Te, 14’Ba, 99M~, 95Zr, 95Nb, 144ce, 141c,, 239 Np exceeded that of the water fraction. The activity of water decreased significantly as the short-lived nuclides decayed and deposited with particles into bottom sediments. Even in June 1986 it had decreased by 100 times as compared to the early period of emergency contamination and was mainly characterized by 134Cs, ‘37Cs and 90Sr. 95Zr, 95Nb, ‘44Ce, 14’Ce, lo3Ru and ‘06Ru settled on the bottom with particles and made a principal contribution to the contamination of bottom sediments in May 1986 (Table 6). The contribution of caesium radioisotopes to the total activity in bottom sediments of the Pripyat

214 1. I. Kryshev

4;20 5/l 5/10 5/20 5130 WlO 6120

Fig. 3. The 13r1 content in water and fish muscles of the Kiev reservoir in May-June 1986.

TABLE 5 The Radionuclide Content in River Waters in the Early Period After the Accident (I May

1986), Bq/l

Radionuclide Pripyat River (Chernobyl) Kiev Reservoir (Lyutezh)

Water Suspended matter Water Suspended matter

131*

132 I

14*Ba 99Mo

lo3Ru “Ye 14’Ce 95Zr “Nb

239N~ ’ 34cs I 37cs

“Sr (water and suspended matter)

2100f600 100 f 30 750 f 300 240 f 100

1400*400 18Oi70 670 It 200 70 f 25 550 f 200 230 f 90 380 f 150 l60f60 400 f 140 260 f 100 400 f 150 270 f 100 420 i 160 250 f 100

360 130f50 lOf6 250 f 100 20f 10

30 f 20

14ozt40 60 k 20

l5f6

7*4 614

4f2 lOf5

80 f 25 220 k 80 240 i 100 200 f 70 310 f 120 200 f 80 250 f 80 250 f 100 230 f 90

50 lOzt6 20f 10

5f2

Radioactive contamination of aquatic ecosystems,fofiowing Chernobyl 215

TABLE 6

The Estimated Content of Radionuclides in the Bottom Sediments of the Dnieper Reser-

voirs and the Pripyat river (kBq/m2)

Radionucfide Pripyat River (mouth) Kiev reservoir Kanev reservoir

95Zr y5Nb

‘03RLl 131 1 ‘34cs 137Cs

14’Ba

14’La 14’Ce ‘44Ce

6000 f 3800 800 + 500

3 600 l 2000 800 III 500

900 f 500 1500 f 800 2400 zt 1700 2600 it 1800 4500 + 1600 6200 f 2400

190 f 80 200 zt 80

90 f 50 2oxt 12

6f3 12 f 5 30 f 20

70 f 46 100 f 40 120 f 50

120 It 50 170 f 70 100 f 60

30 f 20 8f4

16 f 7

60 f 38 85 f 50

100 * 30 120 f 40

River, Dnieper River, Kiev and Kanev reservoirs in that period was about 2-7%. For other reservoirs (Kremenchug, Dneprodzerzhinsk, Kakhovka) located downstream in the Dnieper River, the contribution of caesium radioisotopes to the total activity of bottom sediments was somewhat higher, i.e. lO--30%. Distribution of radionuclides in bottom sediments was characterized by notable inhomogeneity (‘spottiness’). Very high levels of radioactive contamination were registered in the upper layer of silts (Vakulovsky et al., 1990; Kryshev, 1992).

The long-term radioecological consequences of the Chernobyl acci- dent are largely estimated from contamination of the affected territory by long-lived radionuclides ( ‘37Cs, ‘34Cs, 90Sr). As noted above, in the first period following the accident the contribution of long-lived radio- nuclides in the rivers of the Dnieper catchment area and its reservoirs amounted to 10% of the total activity. But as short-lived radionuclides decayed, the contribution of caesium and strontium radioisotopes to the exposure dose of organisms increased and then prevailed. Tables 7 and 8 show estimates of the annual mean content of ‘37Cs and 90Sr in water, molluscs and fish based on observational data for 1986-1989 (Pankov, 1990; Volkova, 1990; Kryshev, 1992; Kryshev et al., 1993). Highest levels of contamination by ‘37Cs occurred for all ecosystem components of the Kiev reservoir. The Kanev reservoir, which is downstream in the Dnieper River showed concentrations of ‘37Cs in fish and molluscs 3-4 times lower than those in the Kiev reservoir. Downstream along the cascade of reservoirs (the Kremenchug reservoir and others), the ‘37Cs levels were increasingly lower. Mean levels of 90Sr concentration in water for the Kiev reservoir in 1987-1989 practically did not differ from the annual mean concentration in 1986. For

216 I. I. Kryshev

TABLE 7 The Estimated 13’Cs Content in the Ecosystem Components of the Dnieper Reservoirs

Yeur Water (Bqllj Mollusc Dreissena Fish (Bq1kgf.w.j bugensis (Bq1kg.f.w.)

Bream Pike-perch

Kiev reservoir 1986 2.0 * 1.0 1987 o-5 i 0.2 1988 0.4 + 0.1 1989 0.4hO.l

Kanev reservoir 1986 0.1 f 0.04 1987 0.1 f 0.03 1988 0.2 i 0.05 1989 0.2 f 0.04

Kremenchug reservoir 1986 0.05 + 0.02 1987 0.03 zt 0.01 1988 0.04 i 0.01 i989 0.05 i 0.0 1

670 f 160 110*30 70 x?T 20 70% 16

100&40 100 % 30 5oi IO 30 f 4

lOf4 30 f 8 40 It 5 3066

960 f 400 220 f 100 480 f 160 590 + 170

440 zt 100 1 040 f 360 370 i 80 440 i 150

190 f 100 60 i 20 90 f 20 280 i! 60 30f 14 170*50 26xt IO 80f 16

-.

180&50 260 f 80

23 f 4 3Ozt 16 IO&6 30 * 7

The data presented in Tables 7 and 8 are taken from the following publications: water

(Kryshev, 1992); biota, 1986 (Ibid.); molluscs, 1987-1989 (Pankov, 1990); fish, 1987-1989 (Volkova, 1990).

molluscs accumulating 90Sr in their shells, the contamination by 90Sr significantly exceeded that of ‘37Cs.

RADIOACTIVE CONTAMINATION OF SEA ECOSYSTEMS

The Chernobyl accident resulted in radioactive contamination of some regions distant from the Chernobyl site. Some coastal regions of the Baltic Sea, in particular, were affected by the CNPP radioactive release.

TABLE 8 The Estimated “Sr Content in the Ecosystem Components of the Kiev Reservoir (1986

1989)

Year Water (Bqll) Mollusc Dreissena Fish (Bq/kgf.w.) bugensis (Bq1kgf.w.)

Bream Pike-perch

1986 0.85 f 0.30 1000 f 400 60 f 30 1987 0.56 xt 0.18 700 f 200 16f3 10+4 1988 0.78 f 0.23 1 100 f 300 30 * 5 70 f 20 1989 0.37 f 0.10 1 200 f 300 20 f 6 40* 15

Radioactive contamination qf‘aquatic ecos~stems,fi)lloM,ing Chernobyl 217

According to the monitoring data from Sosnovy Bor (Leningrad region), located on the coast of the Gulf of Finland, atmospheric fallout and radionuclide washoff from the catchment areas were responsible for radioactive contamination of sea and river ecosystems (Kryshev, 1991, 1992). By 1 May 1986 the concentration of ‘j’1 in the river water in Sosnovy Bor amounted to 130-150 Bq/l. The concentration of “‘I in fish muscles in the coastal waters of the Gulf of Finland from 2 May to 22 May 1986 was 40-50 Bq/kg. After the decay of iodine and other short- lived radionuclides, radioisotopes of caesium were of particular radio- ecological concern for aquatic biota. Table 9 shows the dynamics of “‘Cs content in aquatic ecosystem components of the Kopor inlet of the Gulf of Finland. From the monitoring data obtained in 1989-1990 the concen- tration of ‘37Cs in components of aquatic ecosystems exceed the back- ground levels of contamination for 1985. A distinct effect of trophic levels on radiocaesium accumulation was observed for predatory species of fish. For example, the concentration of ‘37Cs in perch was growing after the Chernobyl accident and since 1987, it is 2-5 times higher than that of sprat.

CONCLUSION

The studies of radioactive contamination of aquatic ecosystems carried out in the areas affected by the Chernobyl contamination in 1986-1990 show:

(i) One of the most contaminated water bodies in the zone of the Chernobyl accident is the cooling pond of the Chernobyl NPP.

TABLE 9 The “‘Cs Content in the Ecosystem Components of the Kopor Inlet, the Gulf of Finland

(1985-1990)

Year Sea water

fmBqll)

Bottom sedi-

ments (Bqjkg)

Algae Perch Sprat

(Bqlkg) (Bq1kg.f.w.i (Bqlkg.1:rv.j

1985 10&3

1986 1 050 i 500

1987 230 f 110 1988 120f40 1989 56f II 1990 50+ 10

I .2 f 0.6

40 f 20

(185)* 19f4

lOzt.5 IO-f5 5It-3

3.9 l 1.4 175 + 120 (2 770)* 30f 12 30% 10 24 zt 8 141t6

3.5 f 1.0 1.4 It 0.5

22 + 8 54 * 30

120f40 60 f 20 130f40 25 f 8 120 f 30 26i IO 116f30 36i IO

*The maximum observed concentration.

218 I. I. Kryshev

(ii)

This water body could be used as a model for assessing extreme consequences of an accident for aquatic ecosystems., As a result of the processes of radioactive decay and settling of radionuclides on the bottom of water bodies, the radioactive contamination was notably reduced for most components of aquatic ecosystems beyond the nearest zone affected by the Cher- nobyl accident. However, in future the reduction of radioactive contamination levels will, most likely, go more slowly since the radiation situation in water bodies at the present time is largely determined by long-lived radionuclides of 13’Cs and 90Sr. For most of the surveyed water bodies the effect of trophic levels was clearly seen in radiocaesium uptake by predatory fish.

The results of this investigation indicate that the processes involved in the formation of the current radioecological situation in water bodies caused non-equilibrium for a long period after the Chernobyl accident. Further studies on radioecological processes in the Chernobyl contami- nated areas should, probably, focus on the role of aquatic biota in biogenic migration and possible transformation of migration character- istics of long-lived radionuclides. Serious attention should also be given to the problems of radionuclide migration and accumulation in trophic chains of aquatic ecosystems, assessment and prediction of long-term irradiation dose for man through the aquatic food chain.

ACKNOWLEDGMENT

The author would like to express his gratitude to Dr William L. Temple- ton for his suggestions, discussions and valuable comments.

REFERENCES

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Kaftannikova, 0. G., Protasov, A. A., Sergeeva, 0. A., Kahnichenko, R. A., Vinogradskaya, T. A., Lenchina, L. G., Kosheleva, S. I., Novikov, B. I., Afanasiev, S. A., Sinitsina, 0. O., Movchan, N. B. & Pankov, N. G. (1987). The Ecology of NPP’s Cooling Pond. Ukraine Academy of Sciences, Kiev, pp. 1-97 (in Russian).

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Radioactive contamination of aquatic ecosystems fotIowing Chernobyl 219

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Kuzmenko, M. I., Pankov, I. V., Volkova, E. N. & Shirokaya, Z. 0. (1991). Artificial radionuclides in aquatic biota of major European rivers. In Seminar on Comparative Assessment of the Environmental Impact of Radionuclides Released during Three Major Nuclear Accidents: Kyshtym, Windscale, Cher- nobyl. Proc. Seminar, Luxembourg, I-5 October 1990, Vol 2. CEC, EUR 13574, Brussels, Belgium, pp. 665-77.

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Vakulovsky, S. M., Voitsekhovich, 0. V., Katrich, I. Yu., Medinets, V. I., Niki- tin, A. I. & Chumichev, V. B. (1990). Radioactive contamination of river systems in the area affected by releases from the Chernobyl nuclear power plant accident. In Environmental Contamination Following a Major Nuclear Accident, Proc. Int. Symp., Vienna, 16-20 October 1989, Vol 1. IAEA-SM- 306/l 15, IAEA, Vienna, Austria, pp. 23146.

Volkova, E. N. (1990). Radioactive Contamination of Fish Fauna in the Dnieper Reservoirs after the Chernobyl Accident. Ukraine Academy of Sciences, Kiev, pp, l-25 (in Russian).