Accepted Manuscript Pu isotopes in the seawater off Fukushima Daiichi Nuclear Power Plant site within two months after the severe nuclear accident Wu Men, Jian Zheng, Hai Wang, Youyi Ni, Yuichiro Kumamoto, Masatoshi Yamada, Shigeo Uchida PII:
S0269-7491(18)33413-4
DOI:
https://doi.org/10.1016/j.envpol.2018.12.007
Reference:
ENPO 11947
To appear in:
Environmental Pollution
Received Date: 25 July 2018 Revised Date:
3 December 2018
Accepted Date: 3 December 2018
Please cite this article as: Men, W., Zheng, J., Wang, H., Ni, Y., Kumamoto, Y., Yamada, M., Uchida, S., Pu isotopes in the seawater off Fukushima Daiichi Nuclear Power Plant site within two months after the severe nuclear accident, Environmental Pollution (2019), doi: https://doi.org/10.1016/ j.envpol.2018.12.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
Pu isotopes in the seawater off Fukushima Daiichi Nuclear Power
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Plant site within two months after the severe nuclear accident
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Wu Mena,b, Jian Zhenga,*, Hai Wanga,c, Youyi Nia, Yuichiro Kumamotod
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Masatoshi Yamadae, Shigeo Uchidaa,
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a
National Institute of Radiological Sciences, National Institutes for Quantum and
Radiological Science and Technology, 491 Anagawa, Inage, Chiba 263-8555, Japan b
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Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, State Oceanic Administration,
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184 Daxue Road, Xiamen 361005, China c
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School of Nuclear Science and Technology, University of South China, Hengyang 421001, China
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Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061, Japan,
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Department of Radiation Chemistry, Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Hon-cho, Hirosaki, Aomori 036-8564, Japan
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e
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Research and Development Center for Global Change, Japan Agency for
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______________________________________________________________________
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* Corresponding author. E-mail:
[email protected] 1
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Abstract The marine environment is complex, and it is desirable to have measurements for
31
seawater samples collected at the early stage after the Fukushima Daiichi Nuclear
32
Power Plant (FDNPP) accident to determine the impact of Fukushima-derived
33
radionuclides on this environment. Here Pu isotopes in seawater collected 33-163 km
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from the FDNPP site at the very early stage after the accident were determined (May
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2011, within two months after the accident). The distribution and temporal variation
36
of
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concentrations (from 0.81±0.16 to 11.18±1.28 mBq/m3) and
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(from 0.216±0.032 to 0.308±0.036) in these seawater samples were within the
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corresponding background ranges before the accident, and this suggested that
40
Fukushima-derived Pu isotopes, if any, were in too limited amount to be distinguished
41
from the background level in the seawater. The analysis of Pu isotopic composition
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indicated that the major sources of Pu in the seawater after the accident were still
43
global fallout and the Pacific Proving Ground close-in fallout. The contribution
44
analysis showed that the contributions of the Pacific Proving Ground close-in fallout
45
in the water column of the study area ranged from 26% to 77% with the average being
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48%.
Pu and
240
Pu were studied. The results indicated that both
239+240
Pu activity
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Pu/239Pu atom ratios
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240
atom ratio
0.3
240Pu/239Pu
0.4
0.2
May 2011
Before FDNPP accident
Pacific Proving Grounds (0.30-0.36)
Global fallout (0.176±0.014) 0.1 0
47 48 49
5
10
15 239+240Pu
20 (mBq/m3)
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30
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Graphical abstract Keywords:239+240Pu; 240Pu/239Pu atom ratio; Fukushima accident; seawater; ICP-MS 2
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A capsule that summarizes the main finding of the work
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The analysis of Pu isotopes in seawater samples within two months after the
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Fukushima accident indicated the accident-derived Pu contamination was negligible.
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1. Introduction
Plutonium isotopes are a health concern due to their radiotoxicity and chemical
57
toxicity. After the FDNPP accident, several studies confirmed that the FDNPP-derived
58
Pu isotopes had been released into the terrestrial environment due to atmospheric
59
deposition (Zheng et al., 2012a; MEXT 2011; Imanaka et al., 2012; Yamamoto et al.,
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2012; Lujaniene et al., 2012a, b) and the 239+240Pu amount was estimated to be 1.0-2.4
61
GBq (Zheng et al., 2013). Since the marine environment received not only the
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atmospheric deposition but also the direct discharge of highly contaminated liquid
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wastes as well as the runoff input, it was unavoidable for the FDNPP derived Pu
64
isotopes entering into the marine environment. It also caused concerns due especially
65
to seafood safety, and studies that focused on marine sediments sampled within (Bu et
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al., 2013; 2014a; 2015; Wendel et al., 2017), and outside (Wendel et al., 2017; Zheng
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et al.,2012b; Bu et al., 2014b) a 30 km zone from the FDNPP site indicated negligible
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Pu contamination from the accident. For seawater, several studies have been
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conducted for samples collected within the 30 km zone from the FDNPP site in
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October 2014 (Casacuberta et al., 2017) and outside that zone in August 2011
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(Sakaguchi et al., 2012), August 2012 (Hain et al., 2017), January, May and July 2013
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(Bu et al., 2014c; 2015b; Men et al., 2018), and October 2014 (Casacuberta et al.,
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2017). However, the results obtained in these studies were inadequate to verify
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whether the FDNPP accident raised marine Pu contamination due to the delayed
75
sampling period. The temporal variations of radio-cesium concentrations in seawater
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are shown in Fig. 1 (Takata et al., 2017). It was obvious that the Fukushima-derived
78
cesium decreased sharply with the time after undergoing marine processes such as
79
water mass dilution, mixing and transportation in the coastal environment. Similarly,
80
the FDNNP-derived Pu activities or atom ratios could have been decreased with time
81
by these marine processes after being released into the marine environment. The
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sampling times in the reported seawater Pu studies were ~4 to ~41 months after the
83
accident, and hence the resulting Pu signals might not be definitive. By contrast, the
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seawater samples collected in the early stage of the accident are much more promising
85
to illustrate the contaminations of Pu isotopes. In this study,
86
concentrations and
87
months after the FDNPP accident were measured to provide the evidence for the
88
contamination extent of Fukushima-derived Pu isotopes in the marine environment.
240
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239+240
Pu activity
Pu/239Pu atom ratios of seawater samples collected within two
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2. Methodology
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2.1. Study area and seawater sampling
Seawater samples were collected during two oceanographic expeditions
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YK11-E02 and NT11-E01, which were done in May 2011 by the Japan Agency for
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Marine-Earth Science and Technology (JAMSTEC). Activity concentrations of
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radiocesium and radioiodine in seawater samples from these cruises have been
96
published (Oikawa et al., 2013). JAMSTEC also collected replicate seawater samples
97
as spares and shared them with us. The map with the sampling station is shown in Fig.
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2.
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2.2. Analytical procedure for 239Pu and 240Pu analysis 4
ACCEPTED MANUSCRIPT All the seawater samples were filtered using a 0.20 µm pore size cartridge filter to
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remove suspended particles and were acidified to pH~2 by adding HNO3 for storage
103
and transport to prevent Pu isotopes from adsorbing onto the wall of container. Pu
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isotopes were analyzed using a method which involved Fe(OH)2 primary
105
co-precipitation, CaF2/LaF3 secondary co-precipitation, extraction chromatographic
106
(TEVA, UTEVA, and DGA resins) separations and SF-ICP-MS detection (Men et al.,
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2018). Briefly, Pu isotopes in the pre-filtered seawater was reduced by TiCl3 and
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co-precipitated by Fe(OH)2 at pH = 8.8 - 9.0. Concentrated HNO3 was used to
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dissolve the Fe(OH)2 co-precipitate and 0.57 pg of 242Pu spike (CRM 130, plutonium
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spike assay and isotopic standard, New Brunswick Laboratory, USA) was added as a
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yield tracer. Ca2+, La3+ and concentrated HF were added to form the CaF2/LaF3
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co-precipitate. Then the CaF2/LaF3 precipitate was dissolved in 3 M HNO3 with the
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addition of H3BO3. The Pu (III) in the solution was adjusted to Pu (IV) by the addition
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of NaNO2 and heated at 40 °C for 0.5 h. The sample solution was loaded onto a
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TEVA resin cartridge, and the TEVA resin cartridge was washed with 3 M HNO3 to
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remove Ca, Fe, and rare earth elements, followed by 1 M HNO3 to remove U, Pb, and
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Tl, and 9 M HCl to remove Th and Bi. Before the elution of Pu, an UTEVA+DGA
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resin cartridge was connected under the TEVA resin cartridge. Then 3 M HNO3−0.1
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M ascorbic acid−0.02 M Fe2+ was employed to reduce Pu (IV) to Pu (III) and elute Pu
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(III) from TEVA resin to the DGA resin. The DGA resin cartridge was rinsed by 0.1
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M HNO3 to remove U, Tl, Pb, and Fe. Next, the plutonium on the DGA resin was
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eluted by 0.5 M HCl−0.1 M NH2OH·HCl. The eluted sample solution was evaporated
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to dryness at 250 oC and dissolved with aqua regia. After heating the dissolved sample
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solution to dryness at 200 oC, 1 mL of ultrapure HNO3 was added and heated to near
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dryness at 200 °C. Finally, the sample was dissolved in 0.7 mL 4% HNO3 and
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ACCEPTED MANUSCRIPT detected by a highly sensitive APEX/SF-ICP-MS analytical system. For each batch of
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seawater samples, the operation blanks were determined simultaneously. The Pu
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recovery was ~70% - ~90%. Detection limits of this method for 239Pu and 240Pu were
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both 0.08 fg/mL, corresponding to 0.01 mBq/m3 for 239Pu and 0.05 mBq/m3 for 240Pu
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(Men et al., 2018). A serial of IAEA-443(seawater standard reference material of
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IAEA) spiked seawater samples were used to illustrate the validation of the method.
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The results of 240Pu/239Pu atom ratios ranged from 0.225 ± 0.009 to 0.241 ± 0.040,
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which agreed well with the certificate values of 0.229 ± 0.006 within the range of
134
error. In order to accurately measure
135
atom ratios, some samples of different layers collected at the same station were
136
combined into one sample. Ten stations were involved in this kind of combination and
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their detailed information is given in the column marked “Depth” in Table 1.
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Pu/239Pu
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Pu activity concentrations and
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3. Results and Discussion
The results of the activity concentrations of 239+240Pu and 240Pu/239Pu atom ratios as
141
well as the relevant sampling information are listed in Table 1. The activities of
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239+240
143
ranged from 0.216±0.032 - 0.308±0.036, with an average of 0.254 ±0.023 (average
144
uncertainty 9.2%). The data of 137Cs activities provided by Takahata et al. (2018) and
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Kumamoto et al. were listed in Table 1. The extremely high values of
146
(13.7-13800 Bq/m3) demonstrated that they were FDNPP-derived and the waterbody
147
in the coastal areas near the FDNPP was highly polluted by the FDNPP accident
148
(Aoyama et al., 2016a,b; Buesseler et al., 2017).
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Pu ranged from 0.81±0.16 - 11.18±1.28 mBq/m3. The
240
Pu/239Pu atom ratios
137
Cs activity
149 150
3.1. Vertical distribution of
239+240
Pu in the water column of the coastal area off the 6
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FDNPP site Under simple dispersion conditions, the activities of radionuclides generally
153
decrease with distance from their sources. For example, for the natural occurring
154
radium isotopes, the river and the sediment are their sources, they always decreased
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with the increasing distance off the estuary horizontally or off the sediment vertically
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(Moore, 2000; Liu et al., 2010; Men et al., 2011). This is a general feature that can be
157
utilized to distinguish the sources. In addition, comparing the distributions of target
158
nuclides with those of other nuclides which have known sources is another way. The vertical distributions of
239+240
Pu and
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Cs activities are shown in Fig. 3. 137
Except for station A, it shows that the distribution pattern of
161
water column had obviously higher 137Cs activities in surface water than in deep water,
162
which suggested that
163
Unlike the distribution of 137Cs, the 239+240Pu activities in bottom water layer were all
164
obviously higher than the intermediate layer. There were two patterns for the vertical
165
distribution of Pu. One was that
166
bottom layers than the intermediate layer, as shown by Stations A, S-1 and S-2. The
167
other one was that
168
Station S-3. In addition, for the stations with combined samples Stations 1, 3 and B
169
(Table 1), the 239+240Pu activities in the bottom water layer were obviously higher than
170
those of upper layers. Plutonium is a typical particle-reactive element. The boundary
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scavenging effect makes continental sediments relatively enriched in Pu. During this
172
process, Pu is transported downward into the sediments with sinking biogenic
173
particles and partially released into near-bottom nepheloid layer through the repeated
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resuspensions of fine particles (Lindahl et al., 2010; Hirose, 2009; Zheng and Yamada,
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2006; Yamada and Aono, 2002; 2003; 2006). Therefore, this kind of geochemical
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137
Cs activities in the
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Cs was transported from the surface water to the deep water.
Pu had higher activities at the surface and
Pu activities increased with increasing depth, as shown by
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239+240
239+240
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behavior of Pu isotopes resulted in the distributions in this work. The difference of
177
vertical distributions between Pu isotopes and
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from different sources, i.e. Pu isotopes were from sediment and
179
surface water. Fig. 4 shows the distribution of
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bottom water as well as
181
well negatively correlate with the increasing distance off the FDNPP both in surface
182
water and bottom seawater. It implied that there was complicated mixing and
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transport system in the study area as 137Cs was mainly controlled by water mixing and
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current transport in the ocean. As for
185
distance off the FDNPP. Except for the complicated mixing and transport system, the
186
sediment property and the source were the other influence factors for the distributions
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of 239+240Pu.
239+240
Pu and
137
137
137
Cs was from the
Cs activities in the
Cs activities did not
Pu, it had also no correlativity with the
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239+240
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Cs distribution in surface water.
3.2. The impact of Pu isotopes on the seawater
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Cs might suggest that they came
137
188 189
137
The variation of 239+240Pu activities is the most direct indicator for a new source of 239+240
Pu isotopes. Before the FDNPP accident,
Pu activities in seawater of the
192
Northwest Pacific and its marginal seas changed with a large variation (i.e. not
193
detected -32.0 mBq/m3) (Bertine et al., 1986; Kim et al., 2004; Norisuye et al., 2005;
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Yamada et al., 2006; Yamada and Zheng, 2008; 2010; 2011; Oikawa et al., 2015;
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Oikawa et al., 2011; Wu et al., 2017). Our study found that the
196
0.81-11.18 mBq/m3 in the sea area 33-163 km from the FDNPP site within 60 days
197
after the accident. The
198
accident. One reasonable explanation for this was that contribution of the
199
FDNPP-derived Pu was covered by the background in the seawater and the amount
200
released from the FDNPP accident was too small to change the Pu activity level in the
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239+240
239+240
Pu activity was
Pu activities were still within the background before the
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seawater.
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The
240
Pu/239Pu atom ratio is another indicator for a new source. The
240
Pu/239Pu
atom ratio has been well characterized for various sources and applied widely as a
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fingerprint to identify radioactive contamination sources (Zheng and Yamada, 2006;
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Yamada and Zheng, 2012). The worldwide integrated global fallout sourced Pu is
206
characterized by
207
(Krey et al., 1976). Additionally, the Pacific Proving Ground (PPG) close-in fallout is
208
another source with the
209
shown in Fig. 5, the PPG sourced Pu is transported mainly by the North Equatorial
210
Current and Kuroshio Current to the Northwest Pacific and its marginal seas (Bu et al.,
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2014b; 2015; Wu et al., 2014; Zheng and Yamada, 2004), which includes the study
212
area of this work, and the
213
global fallout and PPG close-in fallout (Bertine et al., 1986; Kim et al., 2004;
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Norisuye et al., 2005; Yamada et al., 2006; Yamada and Zheng, 2008; 2010; 2011;
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Oikawa et al., 2015; Oikawa et al., 2011; Wu et al., 2017; Zheng et al., 2012b). The
216
240
217
Pacific (Bertine et al., 1986; Yamada et al., 2006; Buesseler, 1997), from 0.18 to 0.33
218
in the marginal seas including the Yellow Sea, Japan Sea, Tsushima Strait and the
219
coastal area of Japan (Kim et al., 2004; Norisuye et al., 2005; Yamada et al., 2006;
220
Yamada and Zheng, 2008; 2010; 2011; Oikawa et al., 2015; Oikawa et al., 2011),
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from 0.184 to 0.263 in the marginal sea including the South China Sea, East China
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Sea and Kuroshio current area (Yamada et al., 2006; Yamada and Zheng, 2011; Wu et
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al., 2017). In this study, the highest atom ratio of 0.308 was close to the PPG value.
224
However, the wide range of the PPG ratios (0.30-0.36) and the overlap with the atom
225
ratio range of the FDNPP reactors (0.320-0.356) (Nishihara et al., 2012) prevent us
Pu/239Pu ratios of 0.17-0.19 with the average of 0.176±0.014
240
Pu/239Pu atom ratio of >0.30 (Lindahl et al., 2012). As
Pu/239Pu atom ratio in this sea area falls between that of
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AC C
EP
Pu/239Pu atom ratio was reported to vary from 0.178 to 0.26 in the Northwest
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from stating that this is evidence of Fukushima-derived Pu in seawater. The same as
227
for the
228
also in the background range before the FDNPP accident, suggesting that the amount
229
of FDNPP-derived Pu was too small to increase the 240Pu/239Pu atom ratio level in the
230
seawater.
Pu activity, the
More reasonably, the
240
Pu/239Pu atom ratio in this study (0.216 - 0.308) was
239+240
240
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239+240
Pu/239Pu atom ratios in this study
Pu activities and
232
should be compared with the coastal area of Japan to eliminate any possible regional
233
difference. Oikawa et al. (2015) reported
234
240
235
coastal areas during 3 years (2008-2010) just before the FDNPP accident, which could
236
be used as a much more specific background level for Pu isotopes off the FDNPP site.
237
Values for
238
(2008-2010) and this study were plotted in Fig. 6. It was obvious that neither 239+240Pu
239
activities nor
240
FDNPP accident. Therefore, it can be concluded conservatively that there were no
241
notable amounts of Pu isotopes released into the marine environment from the
242
accident. This conclusion has been supported by previously reported findings (Bu et
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al., 2013; 2014a; 2015; Wendel et al., 2017; Zheng et al.,2012b; Bu et al., 2014b;
244
Casacuberta et al., 2017; Sakaguchi et al., 2012; Hain et al., 2017; Bu et al., 2014c;
245
2015b; Men et al., 2018).
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Pu activities (2.8-32.0 mBq/m3) and
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Pu/239Pu atom ratios (0.173-0.322) in surface and bottom seawater layers of Japan
239+240
240
Pu/239Pu atom ratios from Oikawa et al. (2015)
Pu activities and
Pu/239Pu atom ratios exceeded the corresponding ranges before the
EP
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240
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239+240
The relationship between
239+240
Pu and
137
Cs activities is shown in Fig.7. It shows
247
that there was no correlation between them. 239+240Pu/137Cs activity ratios ranged from
248
9.91 × 10-8-3.00 × 10-4 (Table 1). Table S1 (in Supplementary data) shows the
249
239+240
250
litter, soil and black substances) and the seawater in the North Pacific before the
Pu/137Cs activity ratios of reactor units of FDNPP, terrestrial samples (including
10
ACCEPTED MANUSCRIPT 239+240
Pu/137Cs activity ratios between
251
FDNPP accident. The large differences of
252
reactor units of the FDNPP and seawater samples could be attributed to the different
253
sources.
254
FDNPP accident, while the FDNPP accident-derived 239+240Pu was too limited to raise
255
the seawater
256
global fallout and PPG. Unlike the Cs which is highly volatile, Pu is nonvolatile. In
257
addition, Cs is dissolved in the seawater while Pu is easily adsorbed on the
258
suspending particles. As we know, the radionuclides released from the FNNPP
259
through the explosion to the atmosphere and the direct discharge of radioactive liquids
260
as well as uncontrolled leaking of the heavily contaminated coolant water (Buesseler
261
et al., 2017; Kaeriyama, 2017). Therefore, no matter what way that the radionuclides
262
were released into the marine environment by the FDNPP accident, the fractionation
263
between
264
239+240
265
derived Pu.
239+240
137
Cs were not from the same source.
239+240
Pu was mainly from
Pu and
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239+240
137
Cs was unavoidable. Due to the unconservative property of
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Pu/137Cs activity ratios, it cannot be an indicator for tracing the Fukushima
266
3.3. Temporal variation of
268
FDNPP accident
239+240
AC C
EP
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269
239+240
Cs was from the
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Pu activity level after the accident;
137
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Pu and
The temporal variation of
Pu activities and
239+240
240
Pu/239Pu atom ratios after the
Pu activities and
240
Pu/239Pu atom ratios in
270
seawater within 100km from the FDNPP site after the accident (May 2011-August
271
2014) were plotted as a box plot in Fig. 8. Unlike Fukushima-derived cesium, which
272
decreased sharply with time after entering into the coastal environment (30-90km off
273
FDNPP site) (Fig. 1),
274
Most of the data every year were all below 10 mBq/m3 and the median values were all
275
below 5 mBq/m3. The maximum
239+240
Pu had no obvious interannual variation in the seawater.
239+240
Pu activity (15.30 mBq/m3) observed in
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October 2014 (Casacuberta et al., 2017) did not exceed the background level before
277
the FDNPP accident (ND-32.0 mBq/m3). As for
278
fell between that of PPG close-in fallout and global fallout, within the background
279
level before the FDNPP accident (0.173-0.322) (Oikawa et al., 2015). There was also
280
no obvious interannual variation except for August 2012, which had lower 240Pu/239Pu
281
atom ratios. From these temporal variations of both
282
atom ratio, it is obvious that the release of Pu into the marine environment from
283
FDNPP even at the early stage of the accident was negligible.
3.4. Contribution of the PPG close-in fallout
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239+240
Pu activity and
240
Pu/239Pu
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Pu/239Pu atom ratios, all the data
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240
As the abovementioned work proved that the amount of Pu isotopes released into
287
the marine environment from the FDNPP accident was too small to be distinguished
288
from the background level in the seawater, the major sources of Pu were still global
289
fallout and PPG close-in fallout. The contributions of global fallout and PPG close-in
290
fallout Pu were estimated using the two end-member mixing model proposed by Krey
291
et al. (1976).
EP =
.
(1)
.
AC C
292
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286
293
where R refers to 240Pu/239Pu ratio, subscripts P, G and S refer the PPG close-in fallout,
294
and the global stratospheric fallout and the sample, respectively. The value 3.674 is
295
the ratio of the specific activity of 240Pu to 239Pu, by which the atom ratio is converted
296
to the activity ratio. The contributions of the PPG close-in fallout of our study ranged
297
from 26% to 77%, with a mean of 48% (Supplementary data, Table S2). Buesseler
298
(1997) suggested that fallout Pu derived from the PPG would be preferentially
299
removed from the water column, compared with global stratospheric fallout Pu which 12
ACCEPTED MANUSCRIPT is more soluble. However, up to 77% of the PPG close-in fallout Pu was still retained
301
in the seawater columns. In our previous study (Men et al., 2018), there was also a
302
much higher 240Pu/239Pu atom ratio (0.322) with the high contribution of PPG close-in
303
fallout Pu of 84% in Northwest Pacific 905 km from the FDNPP site. This might
304
suggest that the PPG is still an important source even more than 60 years after the
305
1950s (Wu et al., 2014) and the North Equatorial Current systems continuously
306
transport the remobilized Pu from the Marshall Islands area to the Northwest Pacific
307
Ocean.
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308
Acknowledgements
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We thank JAMSTEC for providing us the spare samples collected during the
311
coastal monitoring done by the Japanese Government in 2011. This work was
312
supported by the Grant of Fukushima Prefecture related to Research and Development
313
in Radiological Sciences, the Interdisciplinary Project on Environmental Transfer of
314
Radionuclides, the Agency for Natural Resources and Energy, the Ministry of
315
Economy, Trade and Industry (METI), Japan, and the JSPS KAKENHI (Grant
316
number JP17k00537). W. Men thanks the China Scholarship Council for financial
317
support to carry out research abroad. We sincerely thank for the patience and valuable
318
suggestions of the reviewers which improves this work a lot.
320
EP
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321
Supplementary data
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Supplementary table. Table S1: 239+240Pu/137Cs activity ratios of different items. Table
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S2: Contribution of the PPG close-in fallout.
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References
327
Aoyama, M., Hamajima, Y., Hult, M., Uematsu, M., Oka, E., Tsumune, D., 134
Cs in the North Pacific Ocean derived from
329
the March 2011 TEPCO Fukushima Dai-Ichi Nuclear Power Plant accident,
330
Japan. Part one: surface pathway and vertical distributions. J. Oceanogr. 72,
331
53–65.
RI PT
Kumamoto, Y., 2016a.
332
Cs and
137
328
Aoyama, M., Kajino, M., Tanaka, T. Y., Thomas T. S., Tsumune D., Tsubono, T., 134
Hamajima, Y., Inomata, Y., Toshitaka, G., 2016b.
Cs in the North
334
Pacific Ocean derived from the March 2011 TEPCO Fukushima Dai-Ichi
335
Nuclear Power Plant accident, Japan. Part two: estimation of
336
inventories in the North Pacific Ocean. J. Oceanogr. 72, 67–76.
134
Cs and
137
Cs
SC
Cs and
137
333
Bertine, K. K., Chow, T. J., Koide, M., Goldberg, E.D.,1986. Plutonium isotopes in
338
the environment: some existing problems and some new ocean results. J. Environ.
339
Radioactivity. 3(3), 189-201.
M AN U
337
Bu, W., Zheng, J., Aono, T., Tagami, K., Uchida, S., Zhang, J., Honda, M. C., Guo, Q.
341
J., Yamada. M., 2013. Vertical distributions of plutonium isotopes in marine
342
sediment cores off the Fukushima coast after the Fukushima Dai-ichi Nuclear
343
Power Plant accident. Biogeosciences, 10, 2497–2511.
TE D
340
Bu, W., Fukuda, M., Zheng, J., Aono, T., Ishimaru,T., Kanda, J., Yang, G., Tagami,
345
K., Uchida, S., Guo Q., Yamada. M., 2014a. Release of Pu isotopes from the
346
Fukushima Daiichi Nuclear Power Plant accident to the marine environment was
347
negligible. Environ. Sci. Technol. 48 (16), 9070-9078.
EP
344
Bu, W., Zheng, J., Guo Q., Aono, T., Otosaka S., Tagami, K., Uchida, S., 2015a.
349
Temporal distribution of plutonium isotopes in marine sediments off Fukushima
350 351
AC C
348
after the Fukushima Dai-ichi Nuclear Power Plant accident. J. Radioanal. Nucl. Chem. 303, 1151-1154.
352
Bu, W., Zheng, J., Guo Q., Aono, T., Tazoe, H., Tagami, K., Uchida, S., Yamada. M.,
353
2014b. A method of measurement of 239Pu, 240Pu, 241Pu in high U content marine
354
sediments by sector field ICP–MS and its application to Fukushima sediment
355
samples. Environ. Sci. Technol. 48(1), 534-541.
356
Bu, W., Zheng, J., Guo, Q., Aono, T., Tagami, K., Uchida, S., Tazoe, H., Yamada, M.,
357
2014c. Ultra-trace plutonium determination in small volume seawater by sector
358
field inductively coupled plasma mass spectrometry with application to 14
ACCEPTED MANUSCRIPT 359
Fukushima seawater samples, J. Chromatogr. A. 1337, 171–178.
360
Bu, W., Zheng, J., Aono, T., Wu, J., Tagami, K., Uchida, S., Guo, Q., Yamada, M.,
361
2015b. Pu distribution in seawater in the near coastal area off Fukushima after
362
the Fukushima Daiichi Nuclear Power Plant accident. J. Nucl. Radiochem. Sci.
363
15(1), 1-6.
365
Buesseler, K. O., 1997. The isotopic signature of fallout plutonium in the North
RI PT
364
Pacific. J. Environ. Radioact. 36, 69–83.
Buesseler, K., Dai, M., Aoyama, M., Benitez-Nelson, C., Charmasson, S., Higley, K.,
367
Maderich, V., Masque, P., Oughton, D., Smith, J., 2017. Fukushima Daiichi
368
derived radionuclides in the ocean: transport, fate, and impacts. Annu. Rev. Mar.
369
Sci. 9, 173−203.
370
SC
366
Casacuberta, N., Christl, M., Buesseler, K. O., Lau, Y., Vockenhuber, C., Castrillejo, 129
M., Synal, H.-A., Masqué, P., 2017. Potential releases of
372
Isotopes from the Fukushima Dai-ichi Nuclear Power Plants to the ocean from
373
2013 to 2015. Environ. Sci. Technol. 51(17), 9826-9835.
M AN U
I,
236
371
U, and Pu
Hain, K., Faestermann, T., Fimiani, L., Golser, R., Gómez-Guzmán, J. M., Korschinek,
375
G., Kortmann, F., von Gostomski C. L., Ludwig, P., Steier, P., Tazoe, H., Yamada,
376
M., 2017. Plutonium isotopes (239–241Pu) dissolved in Pacific Ocean waters
377
detected by Accelerator Mass Spectrometry: no effects of the Fukushima
378
Accident observed. Environ. Sci. Technol. 51(4), 2031–2037.
381 382 383
Nucl. Radiochem. Sci. 10, R7-R16. IAEA-443
EP
380
Hirose, K., 2009. Plutonium in the ocean environment: its distribution and behavior. J.
reference
material.
(https://nucleus.iaea.org/rpst/referenceproducts/referencematerials/radionuclides/
AC C
379
TE D
374
IAEA-443/RS_IAEA_443_final.pdf.) (accessed January 2, 2018).
384
Imanaka, T., Endo, S., Sugai, M., Ozawa, S., Shizuma, K., Yamamoto, M., 2012.
385
Early radiation survey of the Iitate village heavily contaminated by the
386 387 388 389
Fukushima Daiichi accident, conducted on March 28th, 2011. Health Phys. 102, 680−686.
Kaeriyama, H. 2017. Oceanic dispersion of Fukushima-derived radioactive cesium: a review. Fish. Oceanogr. 26(2), 99–113.
390
Kim, C. K., Kim, C. S., Chang, B. U., Choi, S. W., Chung, C. S., Hong, G. H., Hirose,
391
K., Igarashi, Y., 2004. Plutonium isotopes in seas around the Korean Peninsula.
392
Sci. Total Environ. 318(1-3), 197-209. 15
ACCEPTED MANUSCRIPT 393
Krey, P. W., Pachucki, C., Rourke, F., Coluzza, J.,Benson, W. K., 1976. Mass
394
isotopic composition of global fall-out plutonium in soil. In Horn, W. ed.,
395
Transuranium Nuclides in the Environment. IAEA, PP: 671-678. Kumamoto, Y., Yamada M., Aoyama, M., Hamajima, Y., Kaeriyama H., Nagai, H.,
397
Yamagata, T., Murata, A., Masumoto Y. Radiocesium in North Pacific coastal
398
and offshore areas within several months after the Fukushima Accident. J.
399
Environ. Radioact. Submitted.
RI PT
396
Lindahl, P., Keith-Roach, M., Worsfold, P., Choi, M. S., Shin, H. S., Lee, S. H., 2010.
401
Ultra-trace determination of plutonium in marine samples using multi-collector
402
inductively coupled plasma mass spectrometry. Anal. Chim. Acta. 671, 61-69.
SC
400
Lindahl, P., Andersen, M. B., Keith-Roach, M., Worsfold, P., Hyeong, K., Choi, M. S.,
404
Lee, S. H., 2012. Spatial and temporal distribution of Pu in the Northwest Pacific
405
Ocean using modern coral archives. Environ. Int. 40, 196-201.
M AN U
403
406
Liu, G. S., Men, W., Ji, L. H., 2010. Vertical mixing rate evaluation based on radium
407
isotope distributions of Yellow Sea and East China Sea. Chin. J. Geophys. 53(8),
408
1976–1984.
Lujaniene, G., Bycenkiene, S., Povinec, P. P., Gera, M., 2012a. Radionuclides from
410
the Fukushima accident in the air over Lithuania: measurement and modeling
411
approaches. J. Environ. Radioact. 114, 71−80.
412
TE D
409
Lujaniene, G., Valiulis, D., Bycenkiene, S., Sakalys, J., Povinec, P. P., 2012b. 241
Plutonium isotopes and
414
different source terms. Atmos. Environ. 61, 419−427.
416
Men, W., Wang, F. F., Liu, G. S., 2011.
224
Ra and its implications in the East China
Sea. J. Radioanal. Nucl. Chem. 288, 189–195.
AC C
415
Am in the atmosphere of Lithuania: a comparison of
EP
413
417
Men, W., Zheng, J., Wang, H., Ni, Y., Aono, T., Maxwell, S. L., Tagami, K., Uchida,
418
S., Yamada, M., 2018. Establishing rapid analysis of Pu isotopes in seawater to
419 420 421
study the impact of Fukushima nuclear accident in the Northwest Pacific. Sci. Rep. 8, 1892. DOI:10.1038/s41598-018-20151-4.
MEXT (Ministry of Education, Culture, Space, Science, and Technology, Japan). Distribution
423
(http://radioactivity.mext.go.jp/ja/distribution_map_around_FukushimaNPP/)
424
(accessed October 28, 2012).
425
map
of
Plutonium
and
90
422
Sr,
2011.
Moore, W. S., 2000. Determining coastal mixing rates using radium isotopes. Cont. 16
ACCEPTED MANUSCRIPT 426
Shelf Res. 20, 1993–2007.
427
Nishihara, K., Iwamoto, K., Kenya, S., 2012. Estimation of fuel compositions in
428
Fukushima-Daiichi nuclear power plant, Japan Atomic Energy Agency.
429
JAEA-Data/Code No. 2012-018. Norisuye, K., Okamura, K., Sohrin, Y., Hasegawa, H., Nakanishi, T., 2005. Large
431
volume preconcentration and purification for determining the240Pu/239Pu isotopic
432
ratio and
433
Chem. 267(1), 183–193.
RI PT
430
238
Pu/239+240Pu alpha-activity ratio in seawater. J. Radioanal. Nucl.
Oikawa, S., Watabe, T., Inatomi, N., Isoyama, N., Misonoo, J., Suzuki, C, Nakahara,
435
M., Nakamura, R., Morizono, S., Fujii, S., Hara, T., Kido, K., 2011. Plutonium
436
isotopes concentration in seawater and bottom sediment off the Pacific coast of
437
Aomori sea area during 1991-2005. J. Environ. Radioact.
SC
434
102, 302-310.
Oikawa, S., Takata, H., Watabe, T., Misonoo, J., Kusakabe, M., 2013. Distribution of
439
the Fukushima-derived radionuclides in seawater in the Pacific off the coast of
440
Miyagi, Fukushima, and Ibaraki Prefectures, Japan. Biogeosciences 10,
441
5031–5047.
M AN U
438
Oikawa, S., Watabe, T, Takata, H., 2015. Distributions of Pu isotopes in seawater and
443
bottom sediments in the coast of the Japanese archipelago before and soon after
444
the Fukushima Dai-ichi Nuclear Power Station accident, J. Environ. Radioact.
445
142, 113–123.
TE D
442
Sakaguchi, A., Kadokura, A., Steier, P., Tanaka, K., Takahashi, Y., Chiga, H.,
447
Matsushima, A., Nakashima, S., Onda, Y., 2012. Isotopic determination of U, Pu
448
and Cs in environmental waters following the Fukushima Daiichi Nuclear Power
449
Plant accident. Geochem. J. 46, 355−360.
AC C
EP
446
450
Takahata, N., Tomonaga, Y., Kumamoto, Y., Yamada, M., Sano, Y., 2018. Direct
451
tritium emissions to the ocean from the Fukushima Dai-ichi nuclear accident.
452
Geochem. J. 51, 211–217.
453
Takata, H., Kusakabe, M., Inatomi, N., Hasegawa, K., Ikenoue, T., Watanabe, Y.,
454
Watabe, T., Suzuki, C., Misonoo, J., Morizono S., 2017. Long-term Distribution
455
of Radioactive Cesium in the Coastal Seawater and Sediments of Japan. in
456
Special Report: “Radioactivity in the Marine Environment and in Fisheries
457
Products during the Five Years after the Fukushima Dai-ichi Nuclear Power
458
Plant Accident. Rep. Mar. Ecol. Res. Inst., 22 (Supplement), 17-25.
459
Wendel, C. C. S., Lind, O. C., Fifield, L. K., Tims, S. G., Salbu, B, Oughton, D. H., 17
ACCEPTED MANUSCRIPT 460
2017. No Fukushima Dai-ichi derived plutonium signal in marine sediments
461
collected 1.5-57km from the reactors. Appl Radiat Isot. 129, 180-184.
462
Wu, J., Dai, M., Xu, Y., Zheng, J., 2017. Sources and accumulation of plutonium in a
463
large Western Pacific marginal sea: The South China Sea. Sci Total Environ.
464
610/611, 200-211. Wu, J., Zheng, J., Dai, M., Huh, C. A., Chen, W., Tagami, K., Uchida, S., 2014.
466
Isotopic composition and distribution of plutonium in Northern South China Sea
467
sediments revealed continuous release and transport of Pu from the Marshall
468
Islands. Environ. Sci. Technol. 48(6), 3136–3144.
471 472 473
SC
470
Yamada, M., Aono, T., 2002. Large particle flux of 239+240Pu on the continental margin of the East China Sea. Sci Total Environ. 287, 97-105. Yamada, M., Aono, T., 2003. Vertical profiles of
239+240
Pu in seawater from the East
China Sea. J. Radioanal. Nucl. Chem. 256(3), 399-402. Yamada, M., Aono, T., 2006.
M AN U
469
RI PT
465
238
U, Th isotopes,
210
Pb and
239+240
Pu in settling
474
particles on the continental margin of the East China Sea: Fluxes and particle
475
transport processes. Mar. Geol.
227, 1–12.
Yamada, M., Zheng, J., Wang, Z. L., 2006. 137Cs, 239+240Pu and 240Pu/239Pu atom ratios
477
in the surface waters of the western North Pacific Ocean, eastern Indian Ocean
478
and their adjacent seas. Sci. Total Environ. 366, 242–252.
479
TE D
476
Yamada, M., Zheng, J., 2008. Determination of
240
Pu/239Pu atom ratio in coastal
480
surface seawaters from the western North Pacific Ocean and Japan Sea. Appl.
481
Radiat. Isot.
484 485 486 487
EP
483
Yamada, M., Zheng, J., 2010. Temporal variation of 239+240
240
Pu/239Pu atom ratio and
Pu inventory in water column of the Japan Sea. Sci. Total Environ.
AC C
482
66, 103-107.
408,
5951–5957.
Yamada, M., Zheng, J., 2011. Determination of
240
Pu/239Pu atom ratio in seawaters
from the East China Sea. Radiat. Prot. Dosim. 146, 311–313.
Yamada, M., Zheng, J., 2012.
239
Pu and 240Pu inventories and
240
Pu/239Pu atom ratios
488
in the equatorial Pacific Ocean water column. Sci. Total Environ. 430, 20–27.
489
Yamamoto, M., Sakaguchi, A., Ochiai, S., Takada, T., Hamataka, K., Murakami, T.,
490
Nagao, S. 2014. Isotopic Pu, Am and Cm signatures in environmental samples
491
contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident. J.
492
Environ. Radioact. 132, 31−46.
493
Yamamoto, M., Takada, T., Nagao, S., Koike, T., Shimada, K.,Hoshi, M., Zhumadiov, 18
ACCEPTED MANUSCRIPT 494
K., Shima, T., Fukuoka, M., Imanaka, T., Endo,S., Sakaguchi, A., Kimura, S.,
495
2012. An early survey of the radioactive contamination of soil due to the
496
Fukushima Dai-ichi Nuclear Power Plant accident, with emphasis on plutonium
497
analysis. Geochem. J. 46, 341−353. Zheng, J., Tagami, K., Watanabe, Y., Uchida, S., Aono, T., Ishii, N., Yoshida, S.,
499
Kubota, Y., Fuma, S., Ihara, S., 2012a. Isotopic evidence of plutonium release
500
into the environment from the Fukushima DNPP accident. Sci. Rep. 2, 304.
501
Doi:10.1038/srep00304.
RI PT
498
Zheng, J., Tagami, K., Uchida, S., 2013. Release of plutonium isotopes into the
503
environment from the Fukushima Daiichi Nuclear Power Plant Accident: what is
504
known and what needs to be known. Environ. Sci. Technol. 47(17), 9584−9595.
SC
502
Zheng, J., Aono, T., Uchida, S., Zhang, J. & Honda, M.C. 2012b. Distribution of Pu
506
isotopes in marine sediments in the Pacific 30km off Fukushima after the
507
Fukushima Daiichi nuclear power plant accident. Geochem. J. 46, 361-369.
508
Zheng, J., Yamada, M., 2006. Plutonium isotopes in settling particles: transport and
509
scavenging of Pu in the western Northwest Pacific. Environ. Sci. Technol.
510
40(13), 4103–4108.
M AN U
505
Zheng, J., Yamada, M., 2004. Sediment core record of global fallout and Bikini
512
close-in fallout Pu in Sagami Bay, Western Northwest Pacific Margin. Sci. Total
513
Environ. 38 (13), 3498-3504.
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141°24.0′
37°39.9′
42
2
141°23.9′
37°35.0′
37
3
141°24.1′
37°30.0′
34
4 5 6 7 8 9 10
141°23.9′ 141°23.9′ 141°24.0′ 141°24.0′ 141°24.1′ 141°15.0′ 141°04.9′
37°22.9′ 37°15.9′ 37°11.9′ 37°05.9′ 36°59.9′ 37°00.0′ 37°00.0′
33 37 41 48 57 51 47
A
141°05.0′
37°45.0′
37
B
141°15.0′
37°42.4′
37
S-1
141°05.0′
37°48.3′
43
S-2
141°15.1′
37°48.2′
47
Sampling time
2+61 114 119 2+64 122 3+71 136 4+76 85+160 172 132 82 3 14 20 3+30 50 3 16 20 20 4 30
Cruise YK11-E02 2011/5/3 17.1 2011/5/3 8.5 2011/5/5 8.9 2011/5/3 17.0 2011/5/3 8.6 2011/5/5 17.1 2011/5/3 8.5 2011/5/5 17.7 2011/5/3 16.3 2011/5/5 8.9 2011/5/7 9.0 2011/5/5 8.9 2011/5/3 7.9 2011/5/3 9.0 2011/5/3 9.1 2011/5/5 17.5 2011/5/5 8.7 2011/5/7 9.0 2011/5/7 8.6 2011/5/7 8.8 2011/5/3 8.4 2011/5/5 8.7 2011/5/5 9.0
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Depth* m
Volume L
240
Pu/239Pu atom ratio
0.261±0.050 0.308±0.036 0.270±0.034 / 0.256±0.036 / 0.260±0.032 0.256±0.040 0.262±0.041 / 0.235±0.031 0.289±0.038 0.269±0.049 0.216±0.032 0.234±0.038 / 0.271±0.035 0.279±0.040 0.245±0.028 0.222±0.018 0.278±0.038 0.233±0.040 0.243±0.030
20
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Distance from the site km
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Table 1 239+240Pu, 137Cs activity concentrations and 240Pu/239Pu atom ratios in seawater collected 30-163 km from the FDNPP site during May 2011 Pu activity mBq/m3
1.58±0.30 3.29±0.42 6.15±0.79 1.00±0.23 3.60±0.52 1.12±0.20 3.64±0.47 1.46±0.23 2.48±0.42 1.84±0.38 2.52±0.34 3.88±0.54 7.02±1.30 2.98±0.42 6.74±1.08 0.81±0.16 3.69±0.49 4.30±0.63 2.47±0.29 8.67±0.70 5.77±0.84 4.30±0.72 3.42±0.43
137
Cs activity Bq/m3
2010±80 27.4±1.0 20.3±0.8 178±10 25.3±1.0 136±10 25.6±1.1 505±29 19.7±0.5 14.0±0.6 24.0±0.9 444±37 1470±70 1490±80 1620±90 8170±270 8880±390** 13800±500** 5140±220** 10300±400** 3380±150 7670±340** 7190±290
239+240
Pu/137Cs activity ratio 7.88×10-7 1.19×10-4 3.00×10-4 5.61×10-6 1.41×10-4 8.28×10-6 1.05×10-4 2.89×10-6 1.25×10-4 1.34×10-4 6.32×10-5 8.76×10-6 4.71×10-6 2.00×10-6 4.16×10-6 9.91×10-8 4.16×10-7 3.12×10-7 4.81×10-7 8.42×10-7 1.71×10-6 5.61×10-7 4.76×10-7
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Distance from the site km
S-3
141°19.0′
36°56.5′
59
S-4
141°05.0′
36°56.5′
54
2 3 4 5 8
142°00.0′ 141°59.8′ 142°29.7′ 142°29.8′ 141°30.0′
38°00.1′ 37°20.0′ 37°19.7′ 36°40.1′ 36°00.0′
107 86 130 155 163
Depth* m
Sampling time
47 3 84 163 3 54
Volume L
2011/5/5 8.6 2011/5/3 8.2 2011/5/3 9.0 2011/5/3 8.6 2011/5/5 8.9 2011/5/5 9.0 Cruise NT11-E01 2011/5/12 20 2011/5/10 10 2011/5/10 20 2011/5/11 20 2011/5/11 20
240
Pu/239Pu atom ratio
3+101 100 3+99 3+100 3+100
239+240
Pu activity mBq/m3
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Latitude N
0.269±0.049 0.241±0.034 0.218±0.028 0.230±0.024 0.262±0.029 /
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Longitude E
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Station
/ 0.231±0.041 / / /
137
Cs activity Bq/m3
5.76±1.06 2.57±0.36 2.89±0.36 6.29±0.70 11.18±1.28 1.81±0.52
4710±210 4450±180** 37.1±1.3 30.2±1.2 811±43** 585±31
0.97±0.20 1.09±0.19 0.95±0.25 1.13±0.23 0.85±0.18
36.1±1.1 15.0±0.7 97.5±2.6 2.63±0.11 1.56±0.07
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* “number + number” means the seawater sample at the depth of the corresponding number (m) were combined together, for example, “2+61” means the samples at the depth of 2 m and 61 m were combined. ** Takahata et al. (2018) “/” no data
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239+240
Pu/137Cs activity ratio 1.22×10-6 5.78×10-7 7.73×10-5 2.07×10-4 1.38×10-5 3.09×10-6
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Fig. 1 Temporal variations of radio-cesium concentrations in seawater within 30-90km from the FDNPP site over the period March 2011 to
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Fig. 3 Vertical distributions of 239+240Pu and 137Cs activity concentrations at Stations A, S-1, S-2 and S-3.
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Fig. 4 The distribution of 239+240Pu and 137Cs activity concentrations in the surface and bottom water layers. Fig. 5 Distribution of 240Pu/239Pu atom ratio in water columns in the Northwest Pacific and its marginal sea before the FDNPP accident (Bertine
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Fig. 6 239+240Pu activities vs 240Pu/239Pu atom ratio in seawater off the coast of the FDNPP site. Data compiled from Oikawa et al. (2015) and this study.
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Fig. 7 The relationship between 239+240Pu and 137Cs activity concentrations.
Fig. 8 Box plot showing the time evolution of the 239+240Pu activities and 240Pu/239Pu atom ratios in the seawater. The data (within 100 km from the FDNPP site) were plotted: May 2011 (this study), August 2012 (Bu et al., 2014a), May 2013 (Hain et al., 2017) and October 2014
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(Casacuberta et al., 2017). The box plot displays the distribution of data based on the five-number summary: minimum (MIN), first
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Fig. 7
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Fig. 8
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Highlights Plutonium isotopes in seawater at the very early stage of Fukushima accident were determined.
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Pu activities and atom ratios of the seawater samples 33-163 km off FDNPP site were provided.
Fukushima-derived plutonium isotopes were too limited to be distinguished from the background.
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Contributions of the PPG Pu in the water column of the study area ranged from 26 % to 77 %.