1) The document analyzes radioactive contamination of aquatic ecosystems following the Chernobyl nuclear accident, focusing on accumulation of radionuclides in aquatic biota. 2) Radionuclide levels remained highly elevated in the Chernobyl cooling pond ecosystem for years after the accident, with bottom sediments, aquatic plants, and mollusks showing particularly high contamination. 3) Predatory fish species in the cooling pond and other water bodies accumulated much higher levels of radiocesium than non-predatory species, demonstrating the effect of trophic transfer.

1. J. Environ. Radioactivity. Vol. 27 No. 3, pp. 207-219, 1995
Copyright 0 1995Elsevier Science Limited
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ELSEVIER 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

2. 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.

3. 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

4. 210 I. I. Kryshev
*,
0 1
L-l---l
2
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

5. 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 6+4 2.3 f 1.0 50 f 20
330 * 200 50 f 30 54 f 20 1200 zt 450
410 f 210 70+40 50f 18 1100zt400
270 f 100 40f 15 32f 16 700 f 360
13oi70 20f 10 lOf5 220 f 100
1700 f 400 250 f 60 1.4 f 0.4 30f 10
200 k 100 30f 15 2.7 f 1.8 60 f 40
400 f 200 60 zt 30 5.0 f 2.3 llOf50
800 f 500 120 It 70 18f6 400 f 140
530 f 270 80 f 40 13f6 280 f 120
330 f. 200 50 f 30 30f 14 640 f 280
200 * 130 30 f 20 40 zk 20 860 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, 137Csand ‘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,

6. 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 ‘(‘Sr concentration
Water 0.02 l 0.013 (0.04)
Bottom sediments 6Oi25 (140)
Algae 15f9 (40)
Molluscs 40f 10 (60)
Fish 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

7. 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+40 110*40 140*30 180+40 30f I3
(260) (240) (180) (220) (50)
1987 50 It 30 100 i 50 100 f 50 200 f 100 170*90
(320) (280) (240) (410) (420)
1988 40f 14 401t 18 40f 18 160 f 100 1501t80
(60) (100) (100) (360) (360)
1989 25 & 6 403 13 82% 10
(40) (90) (100)
1990 15&5 8f3 12f8 60 + 20 80 i 40
(25) (15) (70) (90) (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

8. 214 1. I. Kryshev
4;20 5/l 5/10 5/20 5130 WlO 6120
Fig. 3. The 13r1content 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*
2100f600 100 f 30 14ozt40 80 f 25
132
I 750 f 300 240 f 100 60 k 20 220 k 80
14*Ba 1400*400 18Oi70 240 i 100
99Mo 670 It 200 70 f 25 200 f 70
lo3Ru 550 f 200 230 f 90 l5f6 310 f 120
“Ye 380 f 150 l60f60 200 f 80
14’Ce 400 f 140 260 f 100 250 f 80
95Zr 400 f 150 270 f 100 7*4 250 f 100
“Nb 420 i 160 250 f 100 614 230 f 90
239N~ 360 50
’34cs 130f50 lOf6 4f2 lOzt6
I37cs 250 f 100 20f 10 lOf5 20f 10
“Sr (water and 30 f 20 5f2
suspended matter)

9. 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 6000 f 3800 190 f 80 120 It 50
y5Nb 800 + 500 200 zt 80 170 f 70
‘03RLl 3 600 l 2000 90 f 50 100 f 60
131
1 800 III 500 2oxt 12 30 f 20
‘34cs 900 f 500 6f3 8f4
137Cs
1500 f 800 12 f 5 16 f 7
14’Ba 2400 zt 1700 30 f 20 60 f 38
14’La 2600 it 1800 70 f 46 85 f 50
14’Ce 4500 + 1600 100 f 40 100 * 30
‘44Ce 6200 f 2400 120 f 50 120 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

10. 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 * 1.0 670 f 160 960 f 400 220 f 100
1987 o-5 i 0.2 110*30 480 f 160 590 + 170
1988 0.4 + 0.1 70 x?T
20 440 zt 100 1 040 f 360
1989 0.4hO.l 70% 16 370 i 80 440 i 150
Kanev reservoir
1986 0.1 f 0.04 100&40 190 f 100 60 i 20
1987 0.1 f 0.03 100 % 30 90 f 20 280 i! 60
1988 0.2 i 0.05 5oi IO 30f 14 170*50
1989 0.2 f 0.04 30 f 4 26xt IO 80f 16
Kremenchug reservoir
1986 0.05 + 0.02 lOf4 -.
1987 0.03 zt 0.01 30 f 8 180&50 260 f 80
1988 0.04 i 0.01 40 It 5 23 f 4 3Ozt 16
i989 0.05 i 0.0 1 3066 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

11. 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 Bottom sedi- Algae Perch Sprat
fmBqll) ments (Bqjkg) (Bqlkg) (Bq1kg.f.w.i (Bqlkg.1:rv.j
1985 10&3 I .2 f 0.6 3.9 l 1.4 3.5 f 1.0 1.4 It 0.5
1986 1 050 i 500 40 f 20 175 + 120 22 + 8 54 * 30
(185)* (2 770)*
1987 230 f 110 19f4 30f 12 120f40 60 f 20
1988 120f40 lOzt.5 30% 10 130f40 25 f 8
1989 56f II IO-f5 24 zt 8 120 f 30 26i IO
1990 50+ 10 5It-3 141t6 116f30 36i IO
*The maximum observed concentration.

12. 218 I. I. Kryshev
This water body could be used as a model for assessing extreme
consequences of an accident for aquatic ecosystems.,
(ii) 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.
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