Use of Otolith for Detecting Strontium-90 in Fish from the Harbor of

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Use of otolith for detecting strontium-90 in fish from the harbor of Fukushima Dai-ichi Nuclear Power Plant Ken Fujimoto, Shizuho Miki, Hideki Kaeriyama, Yuya Shigenobu, Kaori Takagi, Daisuke Ambe, Tsuneo Ono, Tomowo Watanabe, Kenji Morinaga, Kaoru Nakata, and Takami Morita Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es5051315 • Publication Date (Web): 22 May 2015 Downloaded from http://pubs.acs.org on May 27, 2015

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Environmental Science & Technology

Use of otolith for detecting strontium-90 in fish from the harbor of Fukushima Dai-ichi Nuclear Power Plant Ken Fujimoto1*, Shizuho Miki1, Hideki Kaeriyama1, Yuya Shigenobu1, Kaori Takagi2, Daisuke Ambe1, Tsuneo Ono1, Tomowo Watanabe1 Kenji Morinaga1, Kaoru Nakata3 and Takami Morita1 1

Research Center for Fisheries Oceanography and Marine Ecosystem, National Research

Institute of Fisheries Science, Fisheries Research Agency, 2-12-4, Fuku-ura, Kanazawa-ku, Yokohama, Kanagawa, 236-8648, Japan 2

National Research Institute of Aquaculture, Fisheries Research Agency, 2482-3, Chuguji,

Nikko, Tochigi 321-1661, Japan 3

Head office of Fisheries Research Agency, Queen’s Tower B 15F, 2-3-3, Minato Mirai, Nishi-

ku, Yokohama, Kanagawa, 220-6115, Japan

*

Corresponding auther: 2-12-4, Fuku-ura, Kanazawa-ku, Yokohama, Kanagawa, 236-8648,

Japan, Phone: +81-45-788-7654, Fax: +81-45-788-5001, e-mail: [email protected]

ACS Paragon Plus Environment

1


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KEYWORDS Fukushima Dai-ichi Nuclear Power Plant Accident, radiocesium, strontium-90, otolith

1

ABSTRACT

2

To clarify the level of contamination with radioactive cesium (radiocesium) discharged from

3

Fukushima Dai-ichi Nuclear Power Plant (FDNPP), three fish species caught in the main harbor

4

of FDNPP were subjected to gamma-ray analysis. The concentration of radiocesium in muscle

5

differed among individual fish, even those of similar size of the same species, and showed little

6

relation to the standard length of fish. The maximum concentration of radiocesium (202 kBq/kg-

7

wet) was detected from fat greenling samples. Comparison with data from outside the port

8

indicated that the level of radiocesium contamination inside the port was higher than that outside.

9

We found that beta-rays were emitted from otoliths of fishes caught in the port of FDNPP. Beta-

10

ray intensities were correlated with the concentrations of radiocesium in muscles of the three fish

11

species. In Japanese rockfish, the beta-ray count rates from otoliths were significantly correlated

12

with the concentration of radiocesium and

13

Japanese rockfish. However, no beta-rays were detected from brown hakeling samples collected

14

around FDNPP, suggesting that the detection of beta-rays from otoliths may indicate living in the

15

main harbor of FDNPP.

90

Sr in whole body without internal organs of

16 17

TEXT

18

Introduction


2

Page 3 of 24


19

An earthquake and the subsequent tsunami on March 11, 2011 resulted in severe damage to

20

nature and people around north-east Japan and the Tokyo Electric Power Company (TEPCO)

21

Fukushima Dai-ichi Nuclear Power Plant (FDNPP). A large amount of radioactive nuclides, such

22

131

23

damage (5). Given their long half-lives, two cesium isotopes (134Cs: 2.07 y; 137Cs: 30.1 y) are of

24

great concern to consumers.

25

The total quantity of 137Cs discharged into the atmosphere between March 12 and April 6, 2011

26

was estimated to be approximately 1.3 × 1016 Bq (5). The quantities of

27

atmosphere between March 12 and May 1, 2011 and deposited on the land and ocean surfaces

28

were estimated as 5.8 × 1015 Bq and 7.6 × 1015 Bq, respectively (10). In addition, the direct

29

release of 137Cs into the ocean near FDNPP by the end of May 2011 was estimated as 3.5 × 1015

30

Bq (22).

31

The Ministry of Agriculture, Forestry and Fisheries (MAFF), Fukushima Prefecture, and the

32

Fisheries Research Agency (FRA) started monitoring marine organisms to ensure the safety of

33

fishery products immediately after the FDNPP accident (12). Although approximately 40% of

34

samples collected at the coast of Fukushima Prefecture had radiocesium (134Cs +

35

above the Japanese regulatory limit (100 Bq/kg-wet) at 1 year after the accident (1), the ratio had

36

decreased to 1.9% at the end of 2013 (12). Wada et al. showed the temporal change of

37

radiocesium concentration in numerous species of marine organisms collected around Fukushima

38

Prefecture, and clarified the difference of the decreased rate of radiocesium among species (23).

39

In contrast to the intensive monitoring for fishery products, sufficient data regarding radionuclide

40

contamination of fish in the main harbor of FDNPP, where highly contaminated water was

I,

134

Cs, and

137

Cs, were released into the atmosphere and sea from FDNPP as result of the

137

Cs released into the

137

Cs) levels


3


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41

directly released, are not available. TEPCO conducts daily monitoring at several stations in the

42

main harbor of FDNPP and publishes the results on its website (21). Unfortunately, their report

43

shows insufficient information, and does not include biological information, e.g., fish size.

44

Additionally, the contamination level of fish in the main harbor was not statistically analyzed

45

because they did not collect sufficient fish samples in a short period.

46

Compared with radiocesium, there are fewer reports dealing with radioactive strontium (89Sr:

47

50.5 d; 90Sr: 28.8 y) released from FDNPP, because the measurement of radioactive strontium is

48

more complicated and time-consuming than that of radiocesium (19). Strontium is less volatile

49

than cesium at the reactor temperature, and the amount of strontium-90 released into the

50

atmosphere was estimated at 1/1000 of the

51

estimated to range from 9.0 × 1013 Bq to 1.0 × 1015 Bq by calculating the

52

seawater (4, 15). Although TEPCO did not publish data on 90Sr in fish samples collected inside

53

the FDNPP harbor, they monitored the concentrations of

54

from FDNPP, which showed that the concentration was less than 1.5 Bq/kg-wet after May 2012

55

(21). This may be because of the strontium released into the marine system is highly soluble and

56

the fact that radioactive strontium is easily diluted in seawater (8). Radioactive strontium is

57

known to accumulate in bone tissues, because the chemical properties of strontium are similar to

58

that of calcium. Calcium carbonate is the main component of the otolith, and thus

59

accumulate in the otolith (2). The structure aids in maintaining balance of fish and the daily and

60

seasonal rings that form on the otolith over time are used for estimating fish age (3). In addition,

61

the otolith is used as a means to investigate the environmental conditions experienced by fish

62

because it remains metabolically unchanged once formed (3). Therefore, fish that had lived in an

137

Cs released (18). The total amount of

90

90

90

Sr was

Sr/137Cs ratio in

Sr in fish samples collected 20 km

90

Sr would


4

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63

environment with high concentrations of radioactive strontium are likely to have measurable

64

quantities of the nuclide in their otoliths.

65

In this study, three fish species, Japanese rockfish (Sebastes cheni), brown hakeling (Physiculus

66

maximowiczi), and fat greenling (Hexagrammos otakii), collected in the main harbor of FDNPP,

67

were examined to assess the level of contamination with radiocesium and strontium-90. In

68

addition, beta-rays from otolith were measured and correlated with radioactive strontium levels.

69

Materials and methods

70

Fish samples were collected using small cages and gill nets at the FDNPP harbor from January

71

18 to February 12, 2013 by TEPCO (Fig. 1). In total, 84 Japanese rockfish, 42 brown hakeling,

72

and 14 fat greenling were obtained (Table 1). Samples were frozen at TEPCO’s laboratory near

73

Hirono thermal power plant of TEPCO (21 km south of FDNPP), and stored at −20 °C for

74

transportation to the National Research Institute of Fisheries Science (NRIFS). Brown hakeling

75

were also obtained using small cages (110 × 65 × 40 cm, L/W/H) by R/V SOYO-maru belonging

76

to FRA from December 14 to 19, 2012 around FDNPP (Fig. 1). After the standard lengths of the

77

fish had been measured, muscle and otolith were taken from the dorsal parts and cranial bones,

78

respectively. Muscle and otolith samples were prepared from individual fish and handled

79

independently in further treatment. Muscle samples (2.4–31 g) isolated from each individual fish

80

caught in the FDNPP harbor were minced using a knife and placed in gamma-ray measuring

81

container A (diameter: 50 mm; height: 60 mm) and stored at −20 °C until gamma-ray

82

measurement. Similarly, a few hundred grams of muscle sample from brown hakeling caught

83

around FDNPP was individually packed into gamma-ray measuring container B (diameter: 95

84

mm; height: 57 mm) and stored. Otoliths were washed with water to remove blood and other

85

tissues, and stored at room temperature. Otoliths (left side) removed from Japanese rockfish,


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86

brown hakeling, and fat greenling ranged in weight from 43.3–241, 32.9–105, and 5.30–11.3 mg,

87

respectively. Dissection and measurement of fish samples were conducted in the radiation

88

controlled area of NRIFS.

89

Gamma-rays emitted from muscle samples were measured using a highly purified germanium

90

semiconductor detector equipped with multichannel spectroscope (GEM series and MCA-7600,

91

Seiko EG & G, ORTEC, USA). The energy-dependent efficiency calibration was conducted with

92

activity standard gamma volume sources made with the same measuring containers (A:

93

MX033U8PP; B: MX033SPS) with different heights (5, 10, 20, 30, and 50 mm) purchased from

94

Japan Radioisotope Association. These reference sources contained quantified concentrations of

95

nine gamma-ray radionuclides:

96

Coincidence summing effects of

97

purchased from Japan Radioisotope Association. The gamma-ray measurement time for each

98

sample prepared from fish caught at FDNPP was typically 1200 seconds, but was increased to

99

16,000 seconds for samples with low concentration under ca. 500 Bq/kg-wet as

51

Cr,

134

54

Mn,

57

Co,

60

Co,

85

Cs were corrected with

Sr, 134

88

Y,

109

Cd,

137

Cs, and

139

Ce.

Cs standard solutions (CZ005)

137

Cs. The

100

measurement time for samples from outside FDNPP was set to 7200 seconds. The triplicate

101

value of counting error was defined as the detection limit for gamma-ray spectrometry. The

102

detection limits of 137Cs for 1200 seconds measurement with 20 g and for 16,000 seconds with a

103

2.4-g muscle sample in container A were ca. 250 and 70 Bq/kg-wet, respectively. In the

104

conditions applied to samples from outside FDNPP (ca. 100 g muscle sample in container B), the

105

detection limit of

106

134

107

concentration refers to the sum of the 134Cs and 137Cs concentrations.

Cs and

137

Cs for 7200 seconds measurement was 3.0 Bq/kg-wet. Concentrations of

137

Cs were corrected for the decay to the date of sampling. In this paper, radiocesium


6

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90

108

Nine individuals of Japanese rockfish were chosen for the measurement of

109

concentration of radiocesium in muscle samples. After removal of internal organs, the fishes

110

were dried at 105 °C for 48 hours, then ashed at 500 °C using an electric furnace for a further 48

111

hours. A 20 g sample of fish ash was dissolved in 6 mL nitric acid, and organic matter was

112

decomposed under high temperature and pressure using a microwave apparatus (Multiwave

113

3000, Agilent Technologies Japan, Ltd.). Divalent cations including strontium were separated

114

from other ions with carbohydrate precipitation and the oxalic acid precipitation method (13).

115

The precipitate containing strontium was dissolved in 200 mL of 0.5 M HCl and loaded to a

116

cation ion exchange resin column (Dowex 50W-X8, dia. 3 cm × 26 cm, Dow Chemical, USA).

117

Calcium and lead were removed using 1100 mL of ammonium acetate solution (15.4 w/v%) /

118

ethanol (1:1, v/v). Finally, strontium was eluted with 600 mL of ammonium acetate solution

119

(15.4 w/v%). Strontium-90 was measured by its progeny nuclide (yttrium-90,

120

hours) 2 weeks after the scavenging period (13). Beta-rays emitted from

121

using a low background gas flow beta counter (LBC-471Q, HITACHI-Aloka Medical, Ltd.

122

Japan) for 60 minutes. Concentrations of

123

sampling. All reagents used for preparation of radioactive strontium were of the highest purity

124

available and were purchased from WAKO Pure Chemicals (Japan).

125

Total beta-rays emitted from an intact otolith were measured with a low background gas flow

126

beta counter (LBC-471Q, HITACHI-Aloka Medical, Ltd. Japan). An otolith was placed on the

127

measuring dish (diameter 25 mm) and measured for 60 minutes, repeated three times. The

128

background count with a blank dish for 60 min was 0.3 counts per minute. To elucidate the

129

radionuclide emitting beta-ray from otolith, otoliths of Japanese rockfish caught in and outside

130

the FDNPP main harbor were subjected to 90Sr analysis. Otoliths were individually dissolved in

90

90

Sr based on the

90

Y, T1/2 = 64.1

Y were measured

Sr were corrected for the decay to the date of


7


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131

3 mL of 12 M HCl. The contents of stable calcium and strontium in otolith were measured with

132

inductively coupled plasma atomic emission spectroscopy (ICP-AES; Optima 7300 DV,

133

PerkinElmer, Inc., USA). Two mL Sr Resin column (SR-C50-A, Eichrom, USA) were used to

134

purify 90Sr from otolith sample solutions. The concentrations of 90Sr were then calculated from

135

beta-ray emitted from 90Y, 2 weeks after the scavenging period described previously (13).

136 137

Results

138

Radiocesium concentrations in fish obtained from the FDNPP main harbor

139

Figure 2 shows the relationship between the standard length and concentration of radiocesium in

140

the muscle of fish. There was no difference in the standard length among sampling points. There

141

were slight correlations between standard length and concentrations of radiocesium in muscles in

142

Japanese rockfish (Fig. 2a, r = 0.217, p < 0.05), brown hakeling (Fig. 2b, r = 0.363, p < 0.05),

143

and fat greenling (Fig. 2c, r = 0.476, p < 0.05). Concentrations of radiocesium differed even

144

among individuals of similar size from the same species. The highest concentration of

145

radiocesium (202 ± 0.532 kBq/kg-wet) was detected from a fat greenling caught at the entrance

146

of the main harbor on February 12, 2013, and the lowest concentration of radiocesium (104 ±

147

5.35 Bq/kg-wet) was detected from a brown hakeling caught at the south jetty on January 30,

148

2013. The average concentration of radiocesium among the three species was different

149

(ANOVA, p < 0.001). The concentration in brown hakeling was clearly lower than that in the

150

other species (Scheffe, p < 0.01). The average concentration of radiocesium in the muscle of fat

151

greenling was significantly higher than that of Japanese rockfish (Scheffe, p < 0.01).

152

Detection of beta-ray from fish otoliths and nuclide identification


8

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153

Beta-rays were detected in almost all otoliths isolated from the three fish species caught in the

154

FDNPP harbor, and the variation in beta-ray count rates did not significantly differ among

155

sampling points. In a measurement time of 80,000 seconds, no gamma-rays, including those

156

from

157

radionuclide in the otolith was deduced to be a pure beta-emitting radionuclide, such as 90Sr and

158

its progeny nuclide

159

weight of the otoliths collected from three Japanese rockfish caught in the FDNPP harbor. In two

160

of three fish, the concentrations of 90Sr in the otoliths of two Japanese rockfish were 4.13 ± 0.19

161

and 4.38 ± 0.13 Bq/g-dry, and the beta-ray count rates of the otolith were 9.85 and 9.89 cpm,

162

respectively. However, the concentration of

163

rate = 9.16 cpm) was lower than the others (2.75 ± 0.19 Bq/g-dry). The beta-ray count rates

164

from otoliths differed even among fish of similar weight from the same species (Fig. 3). There

165

was no difference in the variation in otolith weight across sampling points. Although the

166

correlation between total beta-ray count rates of the otolith and the weight of otolith weight was

167

not statistically significant in Japanese rockfish (Fig. 3a, p > 0.05) and fat greenling (Fig. 3c, p >

168

0.05), it was significant in brown hakeling (Fig. 3b, r = 0.782, p < 0.001).

169

Figure 4 shows the relationship between radiocesium concentrations in muscles of fish and total

170

beta-ray count rates of otoliths. Correlation coefficients for Japanese rockfish, brown hakeling,

171

and fat greenling were 0.567 (p < 0.001), 0.569 (p < 0.001), and 0.755 (p < 0.005), respectively.

172

The ratios between concentrations of radiocesium and total beta-ray count rates were not

173

identical among the three species because the volumes of otoliths varied by fish species.

174

Sampling point did not affect the ratio between concentrations of radiocesium and total beta-ray

175

counts.

40

K, could be detected in any otolith samples. From these results, the beta-ray-emitting

90

Y. Stable strontium contents ranged in weight from 0.18 to 0.20% of dry

90

Sr in the third Japanese rockfish (beta-ray count


9


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176

Relationships between 90Sr and radiocesium concentrations in fish

177

The concentration of

178

without internal organs of Japanese rockfish (Fig. 5, r = 0.893, p < 0.005). Furthermore, the

179

concentration of

180

from the otoliths (Fig. 6, r = 0.904, p < 0.005).

181

Comparison of radiocesium concentrations between inside and outside of FDNPP

182

Our results for the three species collected inside the main harbor and the results of monitoring

183

outside the main harbor by Fukushima Prefecture from January to February 2013 are

184

summarized in Fig. 7. The concentrations of radiocesium in samples from the three study species

185

within the main harbor were higher than those measured in the same species outside the harbor (t

186

test, p < 0.0001). Furthermore, the lower quartiles of radiocesium concentrations in the harbor

187

exceeded the upper quartile of the concentrations measured from outside samples.

188

Figure 8 shows the results of an investigation intended for brown hakeling by R/V Soyo-maru in

189

December 2012 around FDNPP. The highest concentration of radiocesium in the muscle of

190

brown hakeling was detected at St. Pod 7 (1450 ± 14.1 Bq/kg-wet), followed by 924 ± 8.69

191

Bq/kg-wet at the same point. On the other hand, all samples caught at other sites had radiocesium

192

concentrations of less than 500 Bq/kg-wet. In this investigation, beta-rays were not detected in

193

otoliths from any samples, including fish samples with radiocesium concentrations greater than

194

1000 Bq/kg-wet.

195

Discussion

90

Sr was directly proportional to that of radiocesium in the whole body

90

Sr in Japanese rockfish was correlated with the counts of beta-rays emitted


10

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196

This study revealed the radiocesium contamination levels by radiocesium in three fish species

197

from the main harbor of FDNPP. In freshwater, the radiocesium concentration in fish depends on

198

the fish size (11). In this study, there were also slight correlations between standard length and

199

concentrations of radiocesium in the muscles of each species in the main harbor. However, large

200

variations in the concentration were observed even in fish of similar size in each species (Fig. 2).

201

According to daily monitoring of surface seawater in the main harbor by TEPCO, the

202

concentration of radiocesium at the unloading deck had a maximum value of 1.3 × 106 Bq/L on

203

April 6, 2011, and exponentially decreased to ca. 1000 Bq/L at the end of April 2011 (21). The

204

concentration subsequently decreased from ca. 50 Bq/L in early February 2012 to ca. 5.0 Bq/L at

205

the end of February 2013 (21). The concentration factor (CF, ratio of the radiocesium

206

concentration in fish [Bq/kg-wet] to the radiocesium concentration in seawater [Bq/kg]) of

207

cesium between fish and seawater is estimated to be between 5 and 100 (6); therefore, it was not

208

reasonable to detect very high concentrations, such as an order of 105 Bq/kg-wet radiocesium in

209

fish from the main harbor. Although the CF concept has been widely applied for evaluation of

210

steady state contamination of marine ecosystems, it is not applicable to the evaluation of

211

temporal changes in radiocesium under non-steady state (or transition state) conditions. The

212

dynamic biological compartment model is useful under transition state conditions (20).

213

Furthermore, to evaluate the radiocesium concentration of fish collected in the main harbor, it

214

would be necessary to consider the highly contaminated bottom sediments in the main harbor.

215

The heterogeneous contamination of bottom sediments would produce the large variations we

216

observed in the radiocesium concentration in fish species.

217

Another possibility to generate the large variations in the radiocesium concentration is the timing

218

for the fish to encounter seawater containing high radiocesium levels. At the very early stage of


11


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219

leakage, the concentration of radiocesium (in the order of 104 to 106 Bq/L) was sufficient to

220

produce a very high concentration (on the order of 105 Bq/kg-wet) in fish species. However, the

221

radiocesium concentration exponentially decreased because leaked water would be rapidly

222

diluted by seawater coming from outside the port. Fish accidentally encountering the highly

223

contaminated water earlier would incorporate more radiocesium. In addition, the different

224

radiocesium concentrations in seawater could also produce the large variations in the

225

radiocesium concentration between individuals of similar body size in the same species. In other

226

words, there could be fish, of the same species and the same size, contaminated at different

227

periods in the main harbor. The main harbor has been isolated from the outer ocean with several

228

nets at the entrance, but the nets are temporarily removed when ships enter and leave the main

229

harbor. Therefore, fish would be able to enter and leave the main harbor. In addition to the

230

timing of contamination, the area of the main harbor where the fish are present is also important

231

for producing the different levels of contamination. However, there was no difference in the

232

concentrations among sampling points in the main harbor (Fig.2). This could be due to the

233

migration of fish within the main harbor.

234

Feeding habitat is thought to be one reason for the difference in radiocesium concentration

235

among fish species (16). In the main harbor, the mean radiocesium concentration in muscles of

236

brown hakeling was clearly lower than that of Japanese rockfish and fat greenling (Fig. 7). The

237

same tendency was observed in the monitoring data obtained for the area outside the main harbor

238

by Fukushima Prefecture (Fig. 7 and 23).

239

Beta-rays were detected in almost all otolith samples from fish collected in the main harbor (Fig.

240

3). Interestingly, a correlation between the otolith weight and total beta-ray count rate from the

241

otolith was observed in only brown hakeling (Fig. 3b). A definite difference among the three


12

Page 13 of 24


242

species’ otoliths is the shape: that of brown hakeling is a rod type, whereas the other species have

243

a plate type. However, the relationship between total beta-ray counts from the otolith and the

244

otolith shape is unclear. Self-shielding effects of different otolith shapes may be a possible

245

source of the differences in beta-ray counting rates among different fish species.

246

We could not detect beta-rays from otolith samples of brown hakeling caught near FDNPP (14 to

247

86 km distance) between December 16 and 19, 2012, by R/V SOYO-maru, even in fish with

248

high muscle radiocesium concentrations (Fig. 8). Thus, the detection of beta-rays from the otolith

249

indicated the possibility that the fish lived in the main harbor. The beta-rays (total beta: 3.68

250

cpm) were also detected from otoliths of the fat greenling having high muscle concentrations of

251

radiocesium (23 kBq/kg-wet for

252

FDNPP on August 1, 2012. Because this unique fat greenling was apparently different in its

253

radiocesium concentration from other fat greenling samples caught in the same area, the

254

possibility of migration from FDNPP had been discussed by Shigenobu et al. (17). The beta-ray

255

count rates from the otolith and the concentration of radiocesium in muscle of the unique fat

256

greenling were in good agreement with the deduced relationship observed in the fat greenlings

257

caught in the main harbor (Fig. 4c, asterisk). Our results also show that the unique fat greenling

258

had lived in the main harbor before swimming to the sampling point 20 km north of FDNPP.

259

In this study, the concentration of

260

ray count rates from the otoliths (Fig. 6). The results of the 90Sr purification analysis confirmed

261

that the beta-ray emitting nuclide in the otolith was indeed

262

affinity to lead as well as strontium, the effect of radioactive lead (210Pb) was negligible in this

263

case, because the lead content in the otolith is extremely low, generally less than 1.0 ppm (3).

264

We were also able to confirm that the half-life times of the purified nuclide were identical to that

137

Cs, 15 kBq/kg-wet for

90

134

Cs) and caught 20 km north of

Sr in Japanese rockfish was correlated to the beta-ray beta

90

Sr. Although Sr Resin has some


13


Page 14 of 24

265

of 90Y with repeated beta-ray measurements. Importantly, the concentration of 90Sr in the otolith

266

(2.75–4.83 Bq/g-dry) was only slightly higher than that in the whole body without internal

267

organs of fish (0.15–2.0 Bq/g-ash). This result suggests that the measuring beta-ray in the otolith

268

can potentially be applied to estimate the concentration of

269

concentrations of 90Sr in the otolith were identical to the beta-ray counting rates of intact otoliths

270

in two cases, there was an exception in Japanese rockfish. As stated earlier in the discussion, this

271

may be due to the differences in otolith geometry. Thus, the self-shielding effect of otolith

272

shapes should be investigated in future work.

273

There were significant relationships between the concentrations of radiocesium in muscles and

274

total beta-ray beta ray count rates from otoliths of each species. Ratio The ratio between

275

radiocesium concentration in muscle and the beta-ray count rate of otoliths did not differ by

276

sampling point or period (Fig.4, p > 0.05). On the other hand, the ratio of radiocesium and 90Sr in

277

seawater of the harbor was not constant (21). Those results indicated that the three species in the

278

main harbor were contaminated for a limited time, although the large variation in the

279

concentration of radiocesium in each species with the same body size suggested that fish

280

contaminated at different periods coexisted, as described above. Ages of the Japanese rockfish,

281

brown hakeling, and fat greenling used in this study were estimated to be 3-6, 2-3 and 2-4 years

282

from their standard length, respectively. One 157 mm Japanese rockfish was considered a year

283

old (7, 9, 14). Considering that our samples were collected between January 18 to February 12,

284

2013 (679-704 days after March 11, 2011), it is highly likely that almost all of the sampled fish

285

in this study experienced the earlier highly contaminated water containing radiocesium and 90Sr,

286

assuming the fishes were inhabiting the harbor at that time.

90

Sr in the entire fish. However the


14

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287

This study is the first to show the concentration of 90Sr in fish in the main harbor (Fig. 5). The

288

maximum concentration of

289

caught before the FDNPP accident (ca. 0.02 Bq/kg-wet in whole body without internal organs of

290

benthic fish collected around Japan, FRA unpublished data). According to TEPCO’s report, the

291

maximum 90Sr concentration in seawater in the main harbor was 720 Bq/L (September 2013 at

292

the north side of the Unit 1–4 water intake channel) from June 2012 to February 2014.

293

Additionally, the

294

330 Bq/L even in February 2014 (21). Considering that the CF of strontium between fish and

295

seawater had been estimated as 1 to 3 (6), it was reasonable to detect high concentrations such as

296

170 Bq/kg-wet of radioactive strontium in fish from the main harbor.

297

Because measuring

298

time-consuming and difficult, alternative methods using inductively coupled plasma mass

299

spectroscopy (ICP-MS) have been gradually applied to survey the presence of

300

samples (19). Our result demonstrated that the detection of beta-rays emitted from otoliths of

301

Japanese rockfish in the main harbor was correlated to the concentration of

302

rockfish. Additionally, because the otolith is easily isolated from the fish head, the measurement

303

of beta-rays emitted from otoliths of fish would be simpler than purification of other bone

304

tissues. Therefore, we examined whether the measurement of beta-rays from otoliths can

305

substitute for that of 90Sr in fish. For Japanese rockfish, the detected minimum values were 0.76

306

± 0.21 cpm for beta-ray count rate in the otolith and 11 ± 0.23 Bq/kg-wet for 90Sr in the whole

307

body without internal organs (Fig. 6). However, the concentrations of

308

out of the main harbor of FDNPP were almost all less than 1.0 Bq/kg-wet (12). Consequently,

309

the use of otoliths as a biomonitor for

90

90

Sr (170 ± 1.2 Bq/kg-wet) was four orders higher than that in fish

Sr concentration at the north side of the Unit 1–4 water intake channel was

90

Sr concentrations in organisms by chemical separation method is both

90

90

Sr in several

90

Sr in Japanese

Sr in the fish samples

90

Sr is not feasible for fish outside the main harbor,


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310

because the beta-ray intensity is too low to detect. Nevertheless, the measurement of beta-rays

311

from otoliths will be a useful tool to estimate the concentration of

312

exposed to water with high levels of environmental

313

main harbor of FDNPP.

90

Sr in fish that have been

90

Sr, such as the samples obtained in the

314 315

FIGURES

316 317

Figure 1. Map of monitoring area around/in Fukushima Dai-ichi Nuclear Power Plant. 1–4:

318

Reactor unit of 1–4, IC: Intake canal of unit 1–4, a: sampling point with cage at unloading deck,

319

b: sampling point with cage at north jetty, c: sampling point with cage at south jetty, d: sampling

320

point with gill net at entrance of harbor. The sampling station by R/V SOYO-maru is in the left

321

map.

322


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323 324

Figure 2. Relationships between standard length and concentration of radiocesium: (a) Japanese

325

rockfish, (b) brown hakeling, and (c) fat greenling. Symbols represent sampling point of fish:

326

triangles, entrance of the harbor; diamonds, north jetty; squares, south jetty; circles, unloading

327

deck. Error bars indicate 1σ value derived from counting errors of gamma-ray measurements.

328

329 330

Figure 3. Relationships between weight of otolith and total beta-ray count rates emitted from

331

otolith: (a) Japanese rockfish, (b) brown hakeling, and (c) fat greenling. Error bars indicate

332

standard deviations for three independent beta-ray measurements. Symbols represent sampling

333

point of fish: triangles, entrance of the harbor; diamonds, north jetty; squares, south jetty; circles,

334

unloading deck. Not detection data (N.D.) are plotted on the X axis and shown by filled symbols.

335


17


Page 18 of 24

336 337

Figure 4. Relationships between concentration of radiocesium in muscle and total beta-ray count

338

rates of otolith in each individual: (a) Japanese rockfish, (b) brown hakeling, and (c) fat

339

greenling. X-axis error bars indicate 1σ value derived from counting errors of gamma-ray

340

measurements and Y-axis error bars indicate standard deviation for three independent beta-ray

341

measurements.

342

343 344

Figure 5. Relationship between concentration of radiocesium and 90Sr in whole body without

345

internal organs of Japanese rockfish. Error bars indicate 1σ value derived from counting errors

346

of each measurement, but the error was too small to be visible.


18

Page 19 of 24


347 348

Figure 6. Relationship between concentration of 90Sr in whole body without internal organs and

349

the count rates of beta-rays emitted from otolith of Japanese rockfish. X-axis error bars indicate

350

1σ value derived from counting errors of beta-ray measurement and Y-axis error bars indicate

351

standard deviation for three independent beta-ray measurements.

352

353 354

Figure 7. Box plots of concentration of radiocesium in muscles of fish caught in the main harbor

355

of FDNPP and around Fukushima Prefecture. Each box indicates the range between first and

356

third quartile. A band inside the box indicates the median. Whiskers show the minimum and

357

maximum concentration observed. Open circles indicate outliers. Data set of Fukushima

358

Prefecture was obtained from web site (http://www.pref.fukushima.lg.jp/).


19


Page 20 of 24

359

360 361

Figure 8. Box plots of concentration of radiocesium in muscles of brown hakeling caught around

362

FDNPP. Each box indicates the range between first and third quartile. A band inside the box

363

indicates the median. Whiskers show the minimum and maximum concentration observed. Open

364

circles indicate outliers. The sampling sites are shown in the left map in Fig.1.

365 366

TABLES.

367

Table 1. The information of sampling for fish caught in the harbor of FDNPP.


20

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368

369 370 371

AUTHOR INFORMATION

372

Corresponding Author

373

National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4, Fuku-ura,

374

Kanazawa-ku, Yokohama, Kanagawa, 236-8648, Japan

375

Tel: +81-45-788-7654

376

E-mail: [email protected]

377 378

ACKNOWLEDGMENT

379

We would like to thank Mr. Teruyuki Masai for his support in preparation of samples, and staff

380

of Tokyo Electric Power Environmental Engineering Co., Inc. for transport of samples. We also

381

appreciate the captain and crews of the R/V SOYO-maru belonging to FRA for their kind work


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382

to collect fish samples around FDNPP. This study was supported by Fisheries Agency, Ministry

383

of Agriculture, Forestry and Fisheries, JAPAN.

384 385

REFERENCES

386 1.

Buesseler, K. O. Fishing for answers off Fukushima. Science 2012, 338, 480–482.

387 2.

Campania, S. E.; Neilson, J. D. Microstructure of fish otolith. Can. J. Fish. Aqua. Sci. 1985, 42,

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1014–1032.

389 3.

Campana, S. E. Chemistry and composition of fish otoliths: pathways, mechanisms and

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applications. Mar. Ecol. Prog. Ser. 1999, 188, 263-297.

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Casacuberta, N.; Masque, P.; Carcia-Orellana, J.; Garcia-Tenorio, R.; Bessemer, K. O. 90Sr and

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Biogeoscience, 2013, 10, 3649–3659.

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Chino, M.; Nakayama, H.; Nagai, H.; Terada, H.; Katata, G.; Yamazawa, H. Preliminary

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Fukushima Pref. Fish. Exp. Stat. 1999, 8, 41–49. (in Japanese)

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Nishinihon-Sokouobukaihou. 1996, 23, 119–129. (in Japanese)

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dispersion simulations. J. Nuc. Sci. Technol. 2013, 50(3), 255–264.

409 11. Koulikov, A. O.; Ryabov, I. N. Specific cesium activity in freshwater fish and the size effect. Sci. 410

Total Environ. 1992, 112, 125–142.

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coast of Fukushima. Bull. Fukushima Pref. Fish. Stat. 2006, 13, 63–76. (in Japanese)

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Abstract Art


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Use of Otolith for Detecting Strontium-90 in Fish from the Harbor of

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