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Observation of Radionuclides in Marine Biota off the Coast of Fukushima Prefecture After TEPCO’s Fukushima Daiichi Nuclear Power Station Accident

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Abstract

Monitoring and surveying of radioactivity in seawater and biota in the marine environment off the coast of Fukushima Prefecture in the Pacific Ocean are important for understanding the dispersion of artificial radionuclides after the TEPCO Fukushima Daiichi Nuclear Power Station (FD1NPS) accident. Marine biota were collected in the coastal area off Fukushima Prefecture after this accident to investigate the radioactivity of 134Cs, 137Cs, and 110mAg in marine biota, including not only fish and shellfish but also benthos. It is well known that 108mAg, one of the radioactive isotopes of Ag, was observed in some kinds of squid and octopus before this accident. As a result, 110mAg was observed in many kinds of marine biota off the coastal area of Fukushima. It is suggested that rapid change in the radioactivity in seawater, resuspension of particles from sediments, and food chain effects led to high radionuclide activities in the marine biota after this accident.

Keywords

110mAg 134Cs 137Cs Marine organisms 
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11.1 Introduction

Monitoring and surveying of radioactivity in seawater, sediments, and biota in the marine environment in the Pacific Ocean around Eastern Japan are important for understanding the dispersion of artificial radionuclides after the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Station (FD1NPS) accident. The activities of 134Cs + 137Cs in seawater were observed to be more than 10 kBq/L around FD1NPS at the end of March 2011 and have recently decreased gradually to 1–2 mBq/L, approaching the pre-accident levels [1]. On the other hand, higher activities of 134Cs + 137Cs in sediments have been reported off the coast area of Fukushima Prefecture in the Pacific Ocean [2]. It is necessary that radioactivity in marine biota, including not only fish and shellfish but also the benthos, be monitored continuously as it is well known that marine biota accumulate and concentrate elements and radionuclides in their bodies [3]. The activities of radionuclides in marine biota off Fukushima, including plankton and benthos, are investigated to determine the variation in radioactivity. The observed artificial gamma-emitting radionuclides in marine biota include not only 134Cs and 137Cs but also 110mAg. Artificial radionuclides such as 134Cs, 137Cs, 141Ce, 144Ce, 103Ru, 106Ru, and 110mAg were reported in Mediterranean seagrass after the Chernobyl accident [4]. However, 141Ce, 144Ce, 103Ru, and 106Ru were not observed in the fallout after this accident [5]. Most marine biota, aside from benthos, contained no observable 110mAg a year after the accident, as the activities of the short half-life radionuclide decrease with time, rather than being discharged by metabolic activity in the biota. 134Cs + 137Cs activity in marine biota was classified into three types, either tending to gradually decrease with time, or showing considerable variation, or being less than the detection limit of activity [6]. The aims of the present study were to examine the temporal and spatial changes in radioactivity in marine biota and to survey the contamination after this accident.

11.2 Materials and Methods

Marine biota samples were collected with a plankton net, dredge sampler, and trawl during cruises of T/S Umitaka-maru, T/S Shinyo-maru, and some research and fishing vessels. After being classified into species and weighed, each sample was dried with a vacuum drying machine, homogenized, and packed into a plastic container (U-8). Radioactivity was determined by gamma-ray spectrometry using a HPGe detector (GX-2019; Canberra). The radionuclide activities of biota in the sampling date were calculated with the correction of the decay and the coincidence-summing of 134Cs. Detection limits of 134Cs, 137Cs, and 110mAg were estimated within 1 and 0.5 Bq/kg [wet weight (wet wt)], respectively.

11.3 Results and Discussion

Radionuclide activity in the marine biota off Onahama (Fukushima) that are used as foodstuffs, measured on June 21, 2011 and December 20, 2011, is shown in Tables 11.1 and 11.2. Radionuclide activity in marine biota (plankton and benthos, etc.) off Fukushima in the Pacific Ocean is shown in Table 11.3. The radioactivity of 134Cs + 137Cs in marine products ranged from 15 to 132 Bq/kg (wet wt) in June 2011 and from less than 1 to 135 Bq/kg (wet wt) in December 2011. 110mAg activity was not detected in fishes collected in December 2011, although this activity was observed in the viscera of squid, crab, and fish collected in June 2011. It is considered that the activity of 110mAg in fish and plankton gradually decreased with time because the half-life of 110mAg is 249.8 days. However, no cesium radioactivity was observed in squid and crab. It is well known that Mollusca and Crustacea concentrate silver in their visceral parts. After the accident, 110mAg was observed from fallout in the eastern area of Japan in April and May 2011 [2]. 110mAg added to seawater tends to be rapidly scavenged to the sediments because the solubility of silver in seawater is extremely low. The bottom-dwelling biota such as shellfish and benthos had high activities of Cs and Ag 1 year after the accident. Comparison of weight and radioactivity in each part of the marine organisms is shown in Fig. 11.1. The ratios of cesium activity in the various parts of marine organisms are similar to their weight ratios. The average cesium activity in seawater was 0.20 Bq/L in June 2011, which gradually decreased to 0.03 Bq/L in December 2011 around the sampling area [7]. Cesium activity in seawater decreased to a low ten times during 6 months, and then activity in marine organisms was also reduced. On the other hand, the decrease of 110mAg activity in mollusks could be observed to be almost that of the physical half-life time. It is thought the decrease of activity of these radionuclides in marine organisms depends on differences in the mechanisms of accumulation and metabolism.
Table 11.1

Activities of radionuclides in marine organisms used as foodstuffs off Onahama (Fukushima) on June 21, 2011

Name of biota

Measured parts

134Cs (Bq/kg-wet wt)

137Cs (Bq/kg-wet wt)

110mAg (Bq/kg-wet wt)

Marine products

English name

Genus, species

Fish

Japanese anchovy

Engraulis japonica

Whole body

10.1 ± 0.1

10.8 ± 0.1

<0.5

Fish

Pacific cod

Gadus macrocephalus

Whole bodya

Muscle (edible portion)

27.5 ± 0.3

30.2 ± 0.5

<0.5

    

37.9 ± 0.2

41.8 ± 0.3

<0.5

   

Viscera

15.1 ± 0.1

16.3 ± 0.2

1.2 ± 0.1

   

Bony parts

24.9 ± 0.2

27.2 ± 0.4

<0.5

Fish

Fat greenling

Physiculus maximowiczi

Whole bodya

Muscle (edible ortion)

30.5 ± 0.4

33.4 ± 0.5

<0.5

    

42.3 ± 0.2

46.2 ± 0.3

<0.5

   

Viscera

11.0 ± 0.1

11.8 ± 0.1

0.6 ± 0.03

   

Bony parts

35.3 ± 0.3

39.0 ± 0.4

<0.5

Fish

Pointhead flounder

Hippoglossoides dubius

Whole bodya

Muscle (edible portion)

63.3 ± 0.9

68.8 ± 1.3

<0.5

    

137.0 ± 0.9

148.9 ± 1.2

<0.5

   

Viscera

22.5 ± 0.2

24.3 ± 0.3

<0.5

   

Bony parts

18.4 ± 0.1

20.2 ± 0.2

<0.5

Fish

Rikuzen sole

Dexistes rikuzenius

Whole bodya

Muscle (edible portion)

13.2 ± 0.2

14.1 ± 0.3

0.8 ± 0.1

    

13.5 ± 0.1

14.7 ± 0.2

<0.5

   

Viscera

17.6 ± 0.2

18.8 ± 0.2

5.3 ± 0.1

   

Bony parts

11.6 ± 0.1

12.2 ± 0.2

<0.5

Squid

Bobtail squid

Sepioida

Whole bodya

Muscle (edible portion)

5.4 ± 0.1

5.7 ± 0.1

37.6 ± 0.2

    

2.5 ± 0.1

2.7 ± 0.1

2.9 ± 0.1

   

Viscera

8.0 ± 0.1

8.6 ± 0.1

70.7 ± 0.2

Squid

Japanese common squid

Todarodes pacificus

Whole bodya

Muscle (edible portion)

10.6 ± 0.1

11.5 ± 0.2

24.9 ± 0.3

    

10.6 ± 0.1

11.5 ± 0.1

1.5 ± 0.03

   

Viscera

10.6 ± 0.1

11.3 ± 0.1

92.8 ± 0.3

Crab

Snow crab

Chionoecetes opilio

Soft tissueb

7.2 ± 0.1

7.8 ± 0.2

3.4 ± 0.1

aWhole-body activity was weighted as average with that in all parts

bActivity was calculated with those in muscle and viscera parts because that in the shell part of crab was not determined

Table 11.2

Radionuclide activity in marine organisms used as foodstuffs off Onahama (Fukushima) on December 20, 2011

Name of biota

Measured parts

134Cs (Bq/kg-wet wt)

137Cs (Bq/kg-wet wt)

110mAg (Bq/kg-wet wt)

Marine products

English name

Genus, species

Algae

Arame

Eisenia bicyclis

Whole body

16.4 ± 0.3

20.9 ± 0.4

1.9 ± 0.1

Fish

Greeneyes

Chlorophthalmus albatrossis

Whole bodya

Muscle (edible portion)

11.9 ± 0.3

15.1 ± 0.4

<0.5

    

12.1 ± 0.3

15.2 ± 0.5

<0.5

   

Viscera

14.0 ± 0.4

18.2 ± 0.7

<0.5

   

Bony parts

10.9 ± 0.2

14.5 ± 0.3

<0.5

Fish

Slime flounder

Microstomus achne

Whole bodya

Muscle (edible portion)

1.7 ± 0.1

2.3 ± 0.2

<0.5

    

1.5 ± 0.1

2.1 ± 0.2

<0.5

   

Viscera

2.9 ± 0.1

3.8 ± 0.2

<0.5

   

Bony parts

1.4 ± 0.1

1.7 ± 0.1

<0.5

Squid

Japanese squid

Loliolus (Nipponololigo) japonica

Whole bodya

Muscle (edible portion)

<1

<1

4.2 ± 0.1

    

<1

<1

4.6 ± 0.1

   

Viscera

<1

<1

43.3 ± 0.7

   

Eyeball

<1

<1

6.9 ± 0.1

   

Cartilage

<1

<1

15.1 ± 0.9

Squid

Spear squid

Loligo bleekeri

Whole bodya

<1

<1

2.4 ± 0.2

   

Muscle (edible portion)

<1

<1

<0.5

   

Viscera

<1

<1

12.4 ± 0.4

   

Eyeball

<1

<1

1.7 ± 0.1

   

Cartilage

<1

1.1 ± 0.1

<0.5

Crab

Snow crab

Chionoecetes opilio

Whole bodyb

Muscle (edible portion)

<1

<1

3.1 ± 0.1

    

<1

<1

2.2 ± 0.1

   

Viscera

<1

<1

11.1 ± 0.2

Shellfish

Sakhalin surf clam

Pseudocardium sachalinense

Whole bodyc

Muscle (edible portion)

58.9 ± 1.1

76.3 ± 1.8

19.0 ± 0.7

    

16.8 ± 0.3

20.5 ± 0.5

4.8 ± 0.2

   

Mantle

108.4 ± 1.6

142.1 ± 2.6

29.7 ± 1.0

   

Viscera

23.7 ± 0.5

29.5 ± 0.8

31.7 ± 0.6

aWhole-body activity was weighted as average with that in all parts

bWhole-body activity was calculated with those in muscle and viscera parts, as that in the shell part of crab was not determined

cWhole-body activity was calculated with those in muscle, mantle, and visceral parts, as that in the shell parts of shellfish was not determined

Table 11.3

Radionuclide activity in marine biota (plankton and benthos) off Fukushima in the Pacific Ocean

Date

Location

Depth (m)

Name of biota

Measured part

134Cs (Bq/kg-wet wt)

137Cs (Bq/kg-wet wt)

110mAg (Bq/kg-wet wt)

Latitude

Longitude

Marine products

English name

Genus, species

2011/7/6

36

55

2

N

141

0

0

E

 

Plankton

  

Whole

2.7 ± 0.2

2.9 ± 0.2

1.6 ± 0.1

2011/7/6

36

55

2

N

141

25

92

E

 

Plankton

  

Whole

2.2 ± 0.9

2.4 ± 1.2

0.9 ± 0.1

2011/7/14

37

5

0

N

140

59

10

E

7

Crustacea

Mysidacea

 

Whole

24.1 ± 0.4

26.4 ± 0.6

15.5 ± 0.3

2011/8/17

37

4

58

N

140

59

19

E

7

Crustacea

Mysidacea

 

Whole

41.3 ± 0.5

46.7 ± 0.7

7.0 ± 0.2

2011/9/5

37

5

8

N

140

59

56

E

10

Crustacea

Mysidacea

 

Whole

31.0 ± 0.5

34.8 ± 0.7

15.0 ± 0.3

2011/11/1

37

4

30

N

141

9

18

E

26

Plankton (mesh size of net, 330 μm)

  

Whole

32.2 ± 0.8

37.1 ± 1.1

<1

2012/4/25

37

50

0

N

141

6

0

E

28

Plankton (mesh size of net, 330 μm)

  

Whole

22.2 ± 1.1

31.5 ± 1.3

<1

2011/10/22

36

55

2

N

141

0

0

E

40

Polychaeta

Polychaetes

 

Whole

146.8 ± 3.8

181.5 ± 5.7

11.6 ± 1.5

2011/10/22

36

55

2

N

141

0

0

E

40

Sea urchin

 

Echinocardium cordatum

Whole

271.0 ± 5.6

311.4 ± 8.5

<1

2011/10/22

36

55

2

N

141

0

0

E

40

Starfish

 

Distolasterias nipon

Whole

5.6 ± 0.3

7.0 ± 0.4

8.3 ± 0.3

2011/10/22

36

55

2

N

141

0

0

E

40

Starfish

Northern Pacific seastar

Asterias amurensis

Whole

3.4 ± 0.3

4.7 ± 0.4

16.0 ± 0.4

2011/10/22

36

55

2

N

141

0

0

E

40

Sea slug

Opisthobranchia Spengel

Philine argentata

Whole

17.2 ± 0.4

20.6 ± 0.5

21.8 ± 0.4

Open image in new windowFig. 11.1
Fig. 11.1

Comparison of weight and radioactivity in each part of the marine organisms. Black bars, whole body; gray bars, muscle (edible parts); open bars, viscera; light gray bars, bony parts. Samples were collected in June (a) and December (b), 2011

The CR [concentration ratio = activity in biota (Bq/kg (wet wt))/activity in seawater (Bq/kg or Bq/L)] is usually represented in term of the concentration in biota relative to that of seawater for modeling purposes. This value of cesium in marine organisms was calculated with the activity of cesium in seawater (Fig. 11.2). CR of cesium (CR-Cs) in marine organisms ranged from 2.6E+1 in the muscle part of squid to 1.0E+4 in clam viscera. Large differences in CR-Cs in different parts of marine organisms were not observed. These values were higher than the reported CR of fish, crustaceans, mollusks, and macroalgae in TRS-422, 1.0E+2, 5.0E+1, 6.0E+1, and 5.0E+1, respectively [8]. CR in plankton was also calculated with the activity of cesium in seawater collected around the sampling area during this monitoring period. These resulting values ranged from 5.8E+1 to 7.8E+2, and were higher than the Cs-CR values (2.0E+1–4.0E+1), but also similar to the Cs-K d value in TRS-422 [8]. It was suggested that the rapid change in radioactivity in seawater and the resuspension of particles from the sediments led to high CRs of Cs after the accident.
Open image in new windowFig. 11.2
Fig. 11.2

Concentration ratio of cesium (CR-Cs) in each part of the marine organisms. Black squares, whole body; gray squares, muscle (edible parts); open squares, viscera; open circles, bony parts

11.4 Conclusion

The activities of 134Cs, 137Cs, and 110mAg in marine biota off the coast of Fukushima Prefecture in the Pacific Ocean were investigated a year after the FD1NPS accident. 110mAg could be observed in many marine biota after this accident, although it is well known that Mollusca and Crustacea concentrate silver in the visceral parts. Finally, it was suggested that the CR fluctuations in plankton is a result of both radioactivity in seawater and sediment resuspension.

Notes

Acknowledgements

Sampling would not have been possible without the field support provided by the T/S Umitaka-maru, T/S Shinyo-maru, and some research and fishing vessels. Part of the sample treatment support was provided by staff members of the National Research Institute of Fisheries Science, Fisheries Research Agency. This work was partly supported by Health Labour Sciences Research Grant and MEXT Grant-in-Aid for Scientific Research on Innovative Areas (24110004).

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Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Authors and Affiliations

  1. 1.Fukushima Project HeadquartersNational Institute of Radiological SciencesChibaJapan
  2. 2.Department of Ocean SciencesTokyo University of Marine Science and TechnologyTokyoJapan
  3. 3.Fukushima Prefecture Fisheries Experimental StationIwakiJapan
  4. 4.Fukushima Prefecture Sea-Farming AssociationIwakiJapan

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