finnish studies on radioactivity in the baltic sea in 1987

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STUK-A82 May 1988

FINNISH STUDIES ON RADIOACTIVITY IN THE BALTIC SEA IN 1987

STUK-A82 May 1988

FINNISH STUDIES ON RADIOACTIVITY IN THE BALTIC SEA IN 1987 Supplement 8 to Annual Report 1987 (STUK-A74) Tarja K. Ikäheimonen, Erkki Hus and Ritva Saxen

Finnish Centre for Radiation and Nuclear Safety P.O.Box 268, SF-00101 HELSINKI FINLAND

ISBN 951-47-1473-7 ISSN 0781-1705 Helsinki 1988. Valtion painatuskeskus

3

ABSTRACT Monitoring of radioactive substances in the Baltic Sea was continued within the framework of the Finnish national monitoring programme. Samples of sea water, bottom sediment and fish were collected for radionuclide analyses. All samples were analysed for gamma-emitting radionuclides and partly also for 9 0 Sr and transuranic elements. The only regularly detected gamma nuclides in sea water were 40 K, 1 3 2 *°Pu and 2 3 8 P u varied from 0.01 to 9.9 and from 0 to 0.35 Bq kg-1 dry weight, respectively (Table VII). Traces of 2 3 6 Pu were also detected in some surface layer samples. The ratio 238 Pu/239'240 Pu varied in the box corer samples from 0.035 to 0.082.

14 The samples taken by the Niemistö corer at the Teili-1 station were sectioned to 1-cm-thick slices to 5 cm depth and further to 5-cm-thick slices to 30 cm depth. The gamma nuclides originating from the Chernobyl fallout were found only in the uppermost 2-3 centimetres. Therefore the nuclide rations differed markedly from other sediment samples, which were sectioned to 5-cm-thick slices. 137 Cs was detected to a dypth of 10-15 cm. 3.3

Fish

The results of our preceding report are completed in Table IX, where the activity concentrations of 89 Sr and 90 Sr are given for fish samples in 1986. Table X shows the contents of 90 Sr, 134 Cs and 137 Cs in fish samples caught in 1987. In the Baltic herring the 137 Cs values varied from 18 to 41 Bq kg-1 fresh weight and in pike and cod from 15 to 30 Bq kg*1 fresh weight (Table X ) . In all samples the activity concentrations of 134 Cs varied from 4 to 14 Bq kg-1 fresh weight and those of 90 Sr from 0.024 to 0.11 Bq kg-1 fresh weight. The 90 Sr values were at the same level as in 1986 (cf. Tables IX and X).

15

4

DISCUSSION

The considerably scattered nature of areal distribution was characteristic of the Chernobyl fallout. This was a distinctive feature for all of our 1986 results.2 Over the period of one year the values have became considerably more evenly distributed, at least in sea water. Owing to vertical and horizontal mixing in the water phase and sedimentation the high concentrations of radionuclides in coastal waters have decreased and no clear differences were found between coastal and offshore stations. In 1987 the surface water concentrations of 1 3 7 C s were about 100-200 Bq nr3 in the Baltic Proper, 200-300 Bq nr3 in the Gulf of Finland, 300-400 Bq nr3 in the Bothnian Sea and about 100 Bq nr3 in the Bothnian Bay (cf. also Ref. 3 ) . The * 37 Cs concentrations have decreased in the surface layers of the Bothnian Sea and the Gulf of Finland by about 20-60 % from 1986 to 1987. However, at the C VI station in the Bothnian Bay the 137 Cs content of surface water has clearly increased, which is obviously due to the river inflow. Also in the Baltic Proper our results in general show a slight increase from the values of 1986. This could be an indication of outflowing fresh surface water originating from the northern parts of the Baltic Sea. With the exception of 4 0 K , 1 3 4 C s and * 37 Cs were the only regularly detected gamma nuclides in sea water. The ratio of 134 Cs/137 Cs was 0.36 +_ 0.01 in all of our surface water samples in 1987. In the few samples of near-bottom water the ratio was clearly lower, indicating a larger proportion of old 137 Cs. A marked difference still existed in the radiocesi-.Ti contents between the surface layer and the bottom water of the Baltic Proper. In the Gotland Deep (station BY 15, depth 230m) the activity concentrations of 13*Cs and 137Ca were 2.6 and 26 Bq nr3 , respectively. In 1986 the corresponding values were 13

16 and 49 Bq m*3 . The detection of 1 3 4 C s in the bottom water of the Gotland Deep in 1986 supplied the main argument for our contention, that the fallout nuclides were sinking quite rapidly and also below the primary halocline.2 Before 1986 we had not detected 134Cs from our regular water samples (30 litres) taken from the Baltic Sea. The deposition of 9 0 Sr has been less significant than that of 137 C s (Fig. 2 ). The activity concentrations of M S r were both in sea water and in fish at about the same level in 1987 as before the Chernobyl accident. Likewise, the levels of 2 3 9 - 2* ° Pu have remained unchanged in the surface water. The sedimentation of the fresh fallout nuclides into the bottom sediments of the open sea basins only began to increase in 1987. With the exception of the results from the EB 1 station in the Bothnian Sea, the sedimentation of fallout nuclides was very low in 1986 (Fig. 3, Table I V ) . The faster sinking of radionuclides at the EB 1 station may be due to the weak salinity stratification in the Bothnian Sea. The addition of 1 3 7 Cs and other fallout nuclides in sediments in 1987 was strongest at the XV 1 station in the eastern part of the Gulf of Finland (Fig. 3, Table V ) . The total deposition of 1 3 7 C s was about 18 kBq m~2 during the last year (Fig. 4, Table V I I ) . Most of the cesium certainly originates from particulate material transported to the area by rivers. Another reason for the strong deposition is probably the high sedimentation rate at the station. The distinct 1 3 7 C s peak in 1987 is a useful sign for future sedimentation studies. At the EB 1 station the total deposition of 137 Cs since 1985 is about 11 kBq m-2 (Fig. 4 ) . The bulk of the nuclides from the Chernobyl fallout occurred in a thin surface layer of the sediment. At the Teili-1 station, where sediment samples were sectioned to 1-cm-thick slices, the occurrence of these nuclides was restricted to the uppermost 2-3 centimetres (Fig. 5). The apparent transportation of the

17 fresh fallout nuclides to the deeper layers may be a reflection of difficulties in sampling soft sediments and, at some stations, also the mixing effect of benthic animals (e.g. EB 1 and XV 1). As a whole the additions of 2 3 8 Pu and 239 - 2 *°Pu have been low in sediments. However, an addition of 2 3 9 - 2 4 0 P u is visible in the total amounts calculated per unit area (Table VII). At the Teili-1 station the ratio 23ePu/239.240 P u w a s 0.15-0.17 in the surface layers of the sediment, while it was earlier clearly below O.l.10"16 The increase is due to the higher amount of 238 Pu in the Chernobyl fallout. No areal differences were found in the 9 0 Sr, 1 3 4 C s and 1 3 7 Cs contents of fish samples caught from the coastal waters of Finland in 1987. Also the differences between the three fish species were insignificant. In pike and cod the 1 3 7 C s values have slightly increased since 1986, being now about five times those before the Chernobyl accident. The ratio 134 Cs/137 Cs was 0.32 +_ 0.02 in all fish samples. The activity concentrations of 9 0 Sr were at the same level as in 1985 and the preceding years. The consumption of Baltic Sea fish contributes only insignificantly to internal radiation doses in Finnish people.2

18

ACKNOWLEDGEMENTS The authors are indebted to all the individuals and institutions that helped us in our sampling. Our special thanks are due to the Finnish Institute of Marine Research for their excellent cooperation over many years. Me are also grateful to Hannele Aaltonen, who made the ganmaspectrometric analyses and to Maarit Keino, Ulla Koskelainen and Virpi Kymäläinen, who assisted in radiochemical analyses and pre-treatment of the samples. Taina Ilus helped in the preparation of the figures. We would also like to thank the Director of the Department, Anneli Salo, for valuable comments on the manuscript.

19

REFERENCES 1.

Bryant FJ, Morgan A, Spicer GS. The determination of radiostrontium in biological material. AERE-R 3030. Harwell, 1959.

2.

U u s E, Sjöblom K-L, Saxen R, Aaltonen H and Taipale TK. Finnish studies on radioactivity in the Baltic Sea after the Chernobyl accident in 1986. Report STUKA66. Supplement 11 to Annual Report 1986 STUK-A55. Helsinki: Finnish Centre for Radiation and Nuclear Safety, 1987.

3.

U u s E, Klemola S, Sjöblom K-L and Ikäheimonen TK. Radioactivity of Fucus vesiculosus along the Finnish coast in 1987. Report STUK-A83. Supplement 9 to Annual Report 1987 STUK A74. Helsinki: Finnish Centre for Radiation and Nuclear Safety, 1988.

4.

Niemistö L. A gravity corer for studies of soft sediments. Merentutkimuslait. Julk./Havsforskningsinst. Skr. 1974; 238: 33-38.

5.

Paakkola O, Voipio A. Strontium-90 in the Baltic Sea. Suomen Kemistilehti 1965; B38: 11-17.

6.

Sinkko K. Computer Analysis of Gamma-Ray Spectra in Sample Measurements (in Finnish). Licentiate Thesis. Helsinki: University of Helsinki, Department of Physics, 1981.

7.

Sinkko K, Aaltonen H. Calculation of the True Coincidence Summing Correction for Different Sample Geometries in Gamma-Ray Spectroscopy. Report STUK-BVALO 40. Helsinki: Finnish Centre for Radiation and Nuclear Safety, 1985.

20

Studies on environmental radioactivity in Finland 19711975. Annual Report STL-A21. Helsinki: Institute of Radiation Protection, 1977. Studies on environmental radioactivity in Finland 19761977. Annual Report STL-A26. Helsinki: Institute of Radiation Protection, 1979. Studies on environmental radioactivity in Finland 1978. Annual Report STL-A32. Helsinki: Institute of Radiation Protection, 1980. Studies on environmental radioactivity in Finland 1979. Annual Report STL-A34. Helsinki: Institute of Radiation Protection, 1980. Studies on environmental radioactivity in Finland 1980. Annual Report STL-A38. Helsinki: Institute of Radiation Protection, 1982. Studies on environmental radioactivity in Finland 1981. Annual Report STL-A40. Helsinki: Institute of Radiation Protection, 1982. Studies on environmental radioactivity in Finland 1982. Annual Report STL-A47. Helsinki: Institute of Radiation Protection, 1983. Studies on environmental radioactivity in Finland 1983. Annual Report STL-A48. Helsinki: Institute of Radiation Protection, 1984. Studies on environmental radioactivity in Finland 19841985. Annual Report STUK-A54. Helsinki: Finnish Centre for Radiation and Nuclear Safety, 1987.

21 Study of radioactive materials in the Baltic Sea. IAEATECDOC-362. A technical document issued by the International Atomic Energy Agency, Vienna, 1986. Taipale TK, Tuomainen K. Radiochemical Determination of Plutonium and Americium from Seawater, Sediment and Biota Samples. Report STUK-B-VALO 26. Helsinki: Finnish Centre for Radiation and Nuclear Safety, 1985.

22

Fig. 1. Sampling stations for sea water (W), bottom sediment (S), fish (F) and biolndicators (B). 1.Station C VI (W + S), 2. Hailuoto (F), 3. Vaasa (F), 4. The Olkiluoto area (W + S + B ) , 5. Station EB 1 (W+S), 6. Selli (F), 7. Tvärminne (F), 8. Station Pernaja Rl (W + S), 9. The Loviisa area (W + S + B ) , 10. Station XV 1 (S), 11. Station LL 3a (w + S), 12. Station Teili-1 (W + S), o. Station BY 28 (W), 13. Station BY 15 (W + S), 14. Station 3Y 2 (W). The BY 28 station has been excluded froru the revised Finnish monitoring programme.

23

Bq/i*3 700-

137

500-

•» •» *

B a l t i c Proper (BY I S )

«-•o-o

B o t h n l a n Bay (C VI)

S-Q-B

B o t h n l a n Saa (EB 1)

M-x-x

Gulf o f F i n l a n d (LL 3 a )

Cs

300 -j

200

100-

—I • 1 1974 197S

T

1976

1977

1979

T

1980

1961

1982

1983

1964

1965

1 • T 19B6 1987

Ytar

Ba/m3 700-T 90 600-

500-

« « *

Sr

B a l t i c Propar (BY 1 5 )

«-•*•-»

B o t h n l a n Bay (C VI)

B-O-B

B o t h n l a n Saa (EB 1)

H-X-x

Gulf o f F i n l a n d (LL 3 a )

300-

200-

o-L

~-«— i — 1976

1 1977

1 1978

1 1979

"T"

**

T"

1980

1981

19B4

1965

1986

Y««r

Fig. 2. Cesium-137 and strontium-90 contents (Bq nrJ ) of uea water < four sampling stations in the 3altic Sea in 1971-1907.- ""

24

CVI ä e p t h cm

cm

CA

Oi

O-i

o-i

I X

1?

ia

u

I

s

Hi 1986

1909

10

/

i/

I

15-

i i i i i [ i i i

SOO

1

' ' I ' •'

i • I » i i J i i i • • 1

•" I 1000

SOO

SOP

1000

BQ

BqA«

BqAg

Ag

EB1 d«pth

»

CM

0-»

O

1906

10

1/

20-

/ IS

I i i i i i i i i i I • * i i i i i i i I

O

SOO

20

1000

o

soo

BflA»

looo

° Bo/k s

M/kg

XVI cm 0

cm

0-

O

3[ 5-

/

3r 198S

1C

1987

19BS

10

10

;

[

15-

15-

> t

20-

201 ' ' •

M

1 looo

Bo A g

1 1 1 1 1 1 i i i i 111 i

o

soo BaAg

i i i r i f

1000

i

O

•

1

1000

'

1

2000

1

1

300?

1

r

4000

60/K 9

Fig. 3. Vertical distributions of cesium-137 concentrations (Bq kg-1 dry wt.) in sediment samples from three basins of the Baltic Sea in 1985, 1986 and 1987."

25

JCOOO 1

*

n

XV 1

.TJ

CVI

E

V I

• zoooo -

r

_&.

is7«

i«7*

^

,„, ,

SMO

,

,n,

|

i»«s

KSlsa F^ar

JSE

,.,,,„, ,

tMa

i«»

ia«4

sal:

n

r l«a>7

if

rt»»

Fig. 4. Total amounts of cesium-137 (Bq mr2 ) in sediments of three basins of the Baltic Sea in 1978-1987.21°-"

depth cm

aeotn cm

0

J-

2-

17.6.66

3-t

4.8.87

3-

5J —1 100

'

1—

—i

200 Bq/kg

300

r—-1 100

1

— I —

r 500

100

200

— I — 300

100

-I

f

500

Ba/kg

Fig. 5. Vertical distribution of cesium-137 concentrations (Bq kg-1 dry wt.) in surface layers of sediment at the Teili-1 station in 1986 and 1987.2

26

Table 1.

Gamma-emitting radionuclides and 9 0 Sr i n sea water samples taken from the Baltic Sea stations i n 1987 (Bq nr3 ) . For sampling stations see Fig. 1. Sr

125

Sb

134

Cs

137

Cs

144

CVI 65°14,2*N, 23°33,7'E

18.8.87

0

2.86

1100

14

0»

37

98

0

Olkiluoto 2 61° 13,9'N, 21° 24,1'E

13.8.87

0

5.71

2200

22

10

110

310

0

EB 1 61° 04,0'N, 19°44,0*E

1.8.87

0

6.00

2300

25

0

160

42C

0

Loviisa 3 60D22,2'N, 26°23,lfE

14.7.87

0

4.51

1700

25

11

100

280

0

Pernaja Rl 60°21,9'N, 26°06,2'E

14.7.87

0

5.57

1700

28

0

73

200

0

LL 3a 60°04,4'N, 26°20,2'E

5.8.87

0

4.81

1700

23

0

85

230

0

Teili-1 59°26,0'N, 21°30,0'E

4.8.87

0 150

6.75 9.54

2200 3300

21 20

0 0

53 7.5

150 35

0 0

BY 28 59°02,0'N, 21° 05,0'E

27.8.87

0

7.09

2700

21

0

49

130

24

BY 15 57°19,9'N, 20D02,9*E

29.7.87

0 230

7.47 12.30

2900 4100

22 22

0 0

42 2.6

120 26

0 0

BY 2 55°00,0'N, 14° 05,0* E

2.9.87

0

7.76

2900

20

0

39

110

0

below the detection limit

K

90

Date

8

Depth S ° / M m

40

Sailing station

Ge

27 Table II. S9 Sr and 9 0 Sr in sea water samples taken from the Baltic Sea stations in 1986 (Bq m~3 ). For sampling stations see Fig. 1.

Sampling station

Date

Depth m

S° / „ ,

89

Sr

90

Sr

C VI 65°14,3'N, 23°33,7'E

2.9.86

0

3.2

120"

16

Olkiluoto 2 61°13,9'N, 21°24,1'E

13.8.86

0

5.90

180

24

EB 1 61°04,0'N, 19°44,0'E

27.8.86

0

5.0

140

28

Loviisa 3 60°22,2'N, 26°23,1'E

16.7.86

0

4.95

280

26

Pernaja R 1 60°21,9'N, 26°06,2'E

16.7.86

0

5.20

40

20

LL 3a 60°04,4'N, 26°20,0'E

20.8.86

0

5.00

550

27

Teili-1 59°25,4*N, 21°30,1'E

17.6.86

0 60 153

6.83 8.57 10.24

460 500 340

22 19 22

BY 28 59°01,9'N, 21°01,1'E

19.8.86

0

6.40

160

27

BY 15 57°20,6'N, 20°01,8'E

17.8.86

0

6.61

120

22

BY 2 54°59,9*N, 14°05,1'E

13.8.86

0

7.60

160

21

a

The uncertainty of a l l the 8 9 Sr concentrations i s greater than usual, being about 30 %. This i s due to the excessive amount of s t r o n t i u m c a r r i e r added t o t h e samples, compared with the calibration samples.

Table ill. Transuranic elements in sea water samples (mBqnr3 ) in 1986 and 1987. For sampling stations see Fig. 1. The coordinates are given in Tables I and II.

Sampling ste tion

Activity concentrations mBqnr3

Depth m

2 38pu

2.09.86 18.08.87

0 0

0« 2.8

3.7 5.9

2.6

LL 3a

20.08.86 5.08.87

0 0

0 0

4.8 4.2

Teili-1

17.06.86

0 153

0 0

2.1 2.2

C VI

BY 15

Date

27.10.86

0 150

0 1.7

4.08.87

0 150

0 0

17.08.86 29.07.87

0 0

• Below the detection limit, Not analysed.

b

0 3.9

239 . 240 p

u

2 4 1 An,

242

C m

2 4 3 . 24 4

0 -

0 -

0 6.5

0 23

0 0

3.0 6.0

0 0

0 0

~b

4.4 1.3

2.0 -

3.4 17

3.1 13

7. 2 63

4.5 0

2.9 3.0

14 5.7

4. 6 3. 8

6.4 3.6

0 -

0 -

C m

to 00

Table IV. Vertical distribution of gamma-emitting radionuclides in sediment samples taken from the Baltic Sea stations in 1986 (Bq kg-1 dry wt.). For sampling stations see Ref. 2.

Sanpling station

C VI

Date

2.09.86

Depth

Sample depth

m

cm

40K

70

0-5

720 830

5-10 ro 1

27.08.86

128

0-5 5-10 10-15

Ga 63

26.10.86

139

0-5 5-10 10-15 15-20

XV 1

28.10.86

55

0-5 5-10 10-15 15-20

LL 3a

BY 15

20.08.86

17.08.86

65

236

0-5 5-10 0-5 5-10 10-15 15-17

a

Below the detection limit.

95

Zr

0» 0

95

Nb

1