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Article 137
Time dependence of the Cs concentration in particles discharged from rice paddies to freshwater bodies after the Fukushima Daiichi NPP accident Kazuya Yoshimura, Yuichi Onda, and Taeko Wakahara Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b05513 • Publication Date (Web): 21 Mar 2016 Downloaded from http://pubs.acs.org on March 24, 2016
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Time dependence of the 137Cs concentration in
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particles discharged from rice paddies to freshwater
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bodies after the Fukushima Daiichi NPP accident
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Kazuya Yoshimura,*,†,‡ Yuichi Onda,‡ Taeko Wakahara,§
6
†
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8F 1-29, Okitama-cho, Fukushima-shi, Fukushima 960-8034, Japan
8
‡
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Tennodai, Tsukuba, Ibaraki 305-8572, Japan
Sector of Fukushima Research and Development, Japan Atomic Energy Agency, Sahei Building
Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1
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§
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Technology, 3-5-8, Saiwai-cho, Fuchu, Tokyo 183-8509, Japan
Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and
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*Corresponding author (Kazuya Yoshimura)
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Phone: +81-24-529-5560; e-mail address:
[email protected] 15
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ABSTRACT
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The concentration of particulate
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entering the water system, was studied following the Fukushima Daiichi Nuclear Power Plant
19
accident. To parameterize the concentration and to estimate the time dependence, paddy fields
20
covering various levels of
21
121). The particulate 137Cs concentration (kBq kg-SS−1) showed a significant correlation with the
22
initial surface deposition density (kBq m-2). This suggests that the entrainment coefficient (m2
23
kg-SS−1), defined as the ratio between the particulate
24
deposition density, is an important parameter when modeling
25
The entrainment coefficient decreased with time following a double exponential function. The
26
decrease rate constant of the entrainment coefficient was clearly higher than that reported for
27
other land uses and for river water. The difference in the decrease rates of the entrainment
28
coefficient suggests that paddy fields play a major role in radiocesium migration through the
29
water system. An understanding of the decrease rate of the entrainment coefficient of paddy
30
fields is therefore crucial to understand the migration of radiocesium in the water system.
137
137
Cs in paddy fields, which can be a major source of
137
Cs
Cs deposition were investigated over the period 2011–2013 (n =
137
Cs concentration and the initial surface 137
Cs wash-off from paddy fields.
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1. INTRODUCTION
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Large amounts of radiocesium, especially
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Nuclear Power Plant (FDNPP) accident and deposited on the ground over the North Kanto and
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the South Tohoku regions of Japan.1-3 Most of the
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soil particles,4,5 and a part of this
37
physical processes such as soil erosion. It was then mainly transported in particulate form
38
through the river system.6-9 The migration of particulate 137Cs from terrestrial fields to the water
39
system is a serious issue when predicting changes in environmental contamination levels and for
40
evaluating the effect on water utilization in downstream region.
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Paddy fields for growing rice are a major land use in South, East, and Southeast Asia. In
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Fukushima prefecture, paddy fields cover an area of 1053 km2, accounting for 70% of
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agricultural capacity.10 Large areas of the paddy in Fukushima prefecture have been affected by
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137
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rice have been confirmed to be within safety margins, a major proportion of the radiocesium
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inventory in paddy fields might still be in place.11 Paddy fields have been shown to be one of the
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most sensitive land uses to soil erosion in the region.9,11-13 Accordingly, they constitute the main
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source of particle-bound radiocesium entering the rivers. The typical paddy cultivation cycle in
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Japan and the corresponding field conditions are as follows. In spring, the dry field is flooded
50
with irrigation water, followed by soil puddling, which mixes the paddy soil to a depth of around
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15 cm. This produces a muddy soil surface covered by highly turbid water with a 5–10 cm depth.
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The field is then left fallow for 2–5 days as to allow the water level to adjust to 0–5 cm and for
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soil compaction appropriate for rice planting to take place. The rice seedlings are then planted.
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The paddy field is kept flooded throughout the irrigation period at a water depth varying
137
137
Cs, were released from the Fukushima Daiichi
137
Cs deposited over ground bound tightly to
Cs subsequently migrates to the water system through
Cs deposition following the FDNPP accident (Fig. 1). While the contamination levels of the
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approximately 0–10 cm. The irrigation water is drained off in early autumn, followed by
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harvesting. There is then a period from the end of autumn to early spring in which the fields are
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not irrigated. The major causes of soil wash-off from paddy fields are runoff of turbid paddy
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water during puddling, enforced drainage after puddling, runoff of paddy water during heavy
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rainfall, and soil erosion during the non-irrigation period. Many studies have used monitoring
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and modeling to evaluate the soil wash-off from paddy field.11,13,14-17 However, to estimate the
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particulate
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concentration in the discharged suspended solid (SS) is essential.
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The
64
the catchment area to model the rate of
65
between the particulate
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density in the catchment area have been reported.9,20 An entrainment coefficient (m2 kg-SS−1),
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defined as the ratio of 137Cs concentration in the eroded soil (kBq kg-SS−1) and the initial surface
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deposition density (kBq m-2), has been used to model the concentration of 137Cs in eroded soil.21-
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23
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surface deposition density can be used to estimate the particulate 137Cs concentration discharged
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from paddy fields into the water system. Entrainment coefficients were investigated from
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experimental runoff plots in land uses such as farmland, grassland, bare ground, and forests,
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following the Chernobyl Nuclear Power Plant accident21-23 and the FDNPP accident,24 but the
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coefficient has never been established for paddy fields. A decrease in
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river and lake waters was reported in the period following the Chernobyl Nuclear Power Plant
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accident,18,19,25,26 suggesting that the entrainment coefficient decreases with time. This decrease
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is thought to reflect factors affecting radiocesium wash-off, such as susceptibility to soil erosion,
137
137
Cs wash-off from paddy fields, parameterization of the particulate
137
Cs
Cs concentration in river water has been normalized by the surface deposition density in 137
Cs transfer in the river.18,19 Significant correlations
137
Cs concentration in the SS in river water and the surface deposition
These studies suggest that the relationship between the
137
Cs concentration and the initial
137
Cs concentrations in
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the chemical/physical properties of the soil (i.e., adsorption and desorption of radiocesium), and
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progressive vertical migration of radiocesium. These factors in turn depended on the uses to
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which the land is put. It is therefore important to evaluate the entrainment coefficient of paddy
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fields.
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The entrainment coefficient should vary with the particle size of the matrix, such as soil and SS,
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because the specific surface area of the matrix directly affects the 137Cs adsorption capacity. The
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fine fractions of soil and SS in river water and the sediment in river beds show higher
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concentrations than those of coarser fractions.7-8, 27-30 The entrainment coefficient has also been
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shown to vary depending on the particle size of SS in the river water.24 These findings suggest
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that particle size needs to be considered to parameterize the entrainment coefficient.
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This study monitored particulate
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covering various deposition levels in the Fukushima prefecture. The aim of the study was to
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provide a parameter that can be used to model the wash-off of
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improve our understanding of the migration of
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system.
137
137
Cs
Cs concentration in paddy fields extensively in the area
137
Cs from paddy fields and to
137
Cs from agricultural fields into the water
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Figure 1. Distributions of 137Cs inventory and paddy fields in Fukushima prefecture. This map
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was generated by ArcGIS 10 software. The prefectural border and shore-lines were obtained
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from Geospatial Information Authority of Japan. The 137Cs distribution was derived from the
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Third Airborne Monitoring Survey by Ministry of Education, Culture, Sports, Science and
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Technology, Japan.37 The distribution of paddy field in 2009 was based on the National Land
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Numerical Information service of the Ministry of Land, Infrastructure, Transport and Tourism.39
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2. MATERIALS AND METHODS
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2-1. Study sites and sampling
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To estimate the entrainment coefficient in paddy fields at various deposition levels of
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turbid paddy water was collected 0–2 days after puddling from 14 sites between May 6 and June
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22, 2012, and from 27 sites between April 29 and May 23, 2013, including 12 of the sites
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selected in 2012 (Fig. 2). At all sites, cultivation had been carried out continuously, including
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2011. Sampling was carried out before seedling planting and while sedimentation of SS was in
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progress. Coarse soil fractions, which are sedimented within 0–2 days of puddling, were not
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sampled. Although puddling causes vertical and horizontal mixing of the paddy soil, the
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concentration and inventory have been found to be heterogeneous.31,32 In this study, we therefore
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collected turbid paddy water at four points in a paddy field and combined these samples.
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In addition to the extensive sampling of turbid paddy water, particulate
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the discharged SS due to puddling or rainfall were monitored at six experimental paddy fields to
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evaluate the sequential decrease in the entrainment coefficient (Fig. 2). Monitoring at site 1 was
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conducted between September 1 and October 24, 2011 and from May 14, 2012 to September 14,
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2013. Monitoring at sites 2–6 was carried out from August 19, 2012 to September 23, 2013. The
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monitoring at site 1 was a continuation of a previous study,11 which monitored two paddy fields,
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one of which had been decontaminated, while the other one was not. In this study, we analyzed
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only the data from the un-decontaminated paddy field. The SS discharged from paddy fields by
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heavy rainfall and puddling was trapped using a time-integrated SS sampler33 installed at an
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outlet of the paddy field, as shown in Figure 3. The trapped SS was collected in suspension at
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intervals of 2–4 weeks. The monitoring system was based on the previous study of in site 1.11
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Samples of turbid paddy water and the suspension were kept still for 2–3 days, and the
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supernatant was removed. Next, the residue was dried at 105 °C for 24 h for analysis.
137
Cs,
137
Cs
137
Cs concentrations in
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Figure 2. Sites where turbid paddy water was collected after puddling (open circles and double
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circles) and SS discharge from paddy fields was monitored (open squares). A double circle
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indicates that the site was used to collect turbid paddy water in both 2012 and 2013, while an
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open circle denotes a site used only once in either 2012 or 2013. This map was generated by
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ArcGIS 10 software. The prefectural border and shore-lines were obtained from Geospatial
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Information Authority of Japan. The 137Cs distribution was derived from the Third Airborne
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Monitoring Survey by Ministry of Education, Culture, Sports, Science and Technology, Japan.37
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Figure 3. Cross-section of paddy field and location of the time-integrated SS sampler. The water
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level ranged approximately 0–10 cm because of evaporation, weeping, and withdrawal of
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irrigation water during the irrigation period.
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2-2. Analysis of 137Cs
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The particulate
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germanium gamma-ray well detector (GCW2022S, Canberra–Eurisys, Meriden, U.S.A.)
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equipped with an amplifier (PSC822, Canberra, Meriden, U.S.A.), and a multichannel analyzer
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(DSA1000, Canberra, Meriden, U.S.A.). Gamma-ray emissions were measured at an energy of
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662 keV. Analytical accuracy was certified by the World-Wide Proficiency Test using standard
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soil samples from IAEA.34 Measurement was continued until the counting error in the
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measurement of 137Cs activity was less than 10%. This required a measurement period of 1–24 h,
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depending on the sample weight.
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There were time lags in the date of sampling of turbid irrigation water after puddling in the 2012
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and 2013 samples. Therefore, the particulate
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first date of each sampling period. The
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experimental paddy fields was also decay-corrected from the first date of sampling for each
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period.
137
Cs concentration (kBq m2 kg-SS−1) was measured using a high-purity
137
137
Cs concentration was decay-corrected from the
Cs concentration in the SS samples from the six
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2-3. Correction of particle size dependency
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The particle size dependency of the
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correction factor (P) based on specific surface area.9,35,36 We measured the particle size
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distribution using a laser diffraction particle size analyzer (SALD-3100, Shimadzu Co., Ltd.,
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Kyoto, Japan), and the specific surface area was estimated using a spherical approximation of
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particles in each size class. To normalize the particle size dependency of the 137Cs concentration
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in the SS, the concentration was divided by P, which was calculated as follows:
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137
Cs concentration was corrected using a particle-size
P = (Sr/Ss)v, (1)
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where Ss is the specific surface area of the criterial sample. In this study, Ss was 0.386 m2 g-dry−1,
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determined from the SS discharge from the experimental paddy field during puddling at site 1 on
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June 13, 2011. Sr denotes the specific surface area of each soil sample (tables S1-S2), and v is a
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constant coefficient with the value 0.65.9,30
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To ensure valid correction, a typical Ss should be applied. The average P obtained in this study
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was 1.0 (standard deviation (SD) = 0.41, n = 121), indicating that the Ss value applied was
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typical for correcting the 137Cs concentration in the SS discharged from the paddy fields.
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2-4. Entrainment coefficient
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The entrainment coefficient (Sc, m2 kg-SS−1) of 137Cs was calculated as follows:
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Sc = Ct/A0,
(2)
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where Ct is the particulate
Cs concentration with or without correction for particle size
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dependency at time t (kBq m2 kg-SS−1), and A0 is the initial surface deposition density of
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(kBq m−2). The initial surface deposition densities were based on the results of the Third
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Airborne Monitoring Survey37 as the value on July 2, 2011. These were calibrated using a
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proportional relationship between air dose rates estimated by the survey and the deposition
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density of
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The initial surface deposition density ranged 13–415 kBq m−2 in the paddy fields used to collect
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turbid paddy water and 61–391 kBq m−2 in the six experimental paddy fields.
137
Cs
137
Cs on the ground surface measured from soil core samples taken at 2,200 points.
184 185
3. RESULTS AND DISCUSSION
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3-1. Variation in particulate 137Cs concentrations
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Figure 4 shows the variations in particulate
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2012 and 2013 with the initial surface deposition density. The increase in uncorrected particulate
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137
190
deposition density in both the 2012 and 2013 samples. This suggests that the initial surface
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deposition density is an important factor in the particulate
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and that the entrainment coefficient is an appropriate metric for estimating the particulate
137
Cs
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concentration in the discharged SS. This is in line with reports of the particulate
137
Cs
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concentration of SS in river water.9,20
137
Cs concentration in the turbid paddy waters in
Cs concentrations showed a statistically significant relationship with the initial surface
137
Cs concentration in paddy fields,
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Figure 4. Relationship between initial surface deposition densities of
Cs obtained from the
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Third Airborne Monitoring Survey37 and the particulate
137
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turbid paddy water in 2012 and 2013. The particulate
137
200
particle size dependency is shown by the closed circles with a solid regression line, and the
201
corrected data is shown by the open circles with a dashed regression line. The particulate
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concentrations collected from May 6 to June 22, 2012 and from April 29 to May 23, 2013 were
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corrected for decay from the first date of each sampling period.
Cs concentrations found in the SS of
Cs concentration uncorrected for the
137
Cs
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The particle size dependency of particulate 137Cs concentration of eroded soil, SS in river water,
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and sediments in riverbeds have been well documented.7-8, 27-30 Particle size varies depending on
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the location, processes and intensity of soil erosion. Difference in particulate size distribution
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between the samples were therefore assumed to be reflected in variation in the entrainment
209
coefficient. The particulate size dependency of the particulate 137Cs concentration was corrected
210
and compared with the initial surface deposition density (shown by the open circles in Figure 4).
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The corrected particulate 137Cs concentration also significantly correlated with the initial surface
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deposition density. The determination coefficients were higher than those of un-corrected data.
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The average entrainment coefficient and its standard deviation are given in Table 1. The standard
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deviation decreased after correcting for the particle size dependency, which has also been
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reported to improve the correlation between particulate
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and the initial surface deposition density in the catchment area.9 This suggests that the particulate
217
size dependency of the particulate
218
considered in the parameterization of the entrainment coefficient in terrestrial environments.
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The averaged entrainment coefficients calculated for the eroded soil samples from the six
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experimental paddy fields are given in Table 2. The entrainment coefficient of the samples
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collected at site 1 in the 2011 study11 was also calculated. The particulate
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corrected for particle size dependency using the particle size distribution re-analyzed in this
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study, and the initial surface deposition density (310 kBq m-2) estimated by the Third Airborne
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Monitoring Survey37 were used for the calculation. The entrainment coefficients obtained in this
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study (after September 23, 2011) varied by almost the same order of magnitude.
137
137
Cs concentration of SS in river water
Cs concentration is an important factor that should be
137
Cs concentration,11
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3-2. Temporal decrease in entrainment coefficient
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Figure 5 shows the distributions of the entrainment coefficient measured from turbid paddy
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water in 2012 and 2013. The entrainment coefficient from the previous study, measured at site 1
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on June 13, 2011 (0.184), is also plotted. The range, median, and averaged values decreased
231
between 2012 and 2013. The entrainment coefficient in 2011 was higher than those in 2012 and
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2013. These results demonstrate a temporal decrease in the entrainment coefficient.
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234 235
Figure 5. Boxplot of entrainment coefficients calculated from particulate 137Cs concentrations in
236
turbid paddy water corrected for particle size dependency. The box and the error bars show the
237
ranges from the first to third quartiles and from the minimum to the maximum values,
238
respectively. The line identified the median value, and the averaged entrainment coefficient is
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represented by the closed circle. The entrainment coefficient calculated for the turbid paddy
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water sample collected on June 13, 2013 in previous study11 is shown as an open circle.
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Figure 6 shows the temporal decrease in entrainment coefficient taken from Tables 1 and 2. The
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decrease occurred in two phases: a steep decrease in the first half year after the FDNPP accident,
244
followed by a slower decrease. Although the data 2011 data covered only site 1, the decrease in
245
the entrainment coefficient of
246
function as follows:
247
ܵ௧ = ܣ × ݁ ିభ ௧ + ܤ × ݁ ିమ ௧
248
where Sct is the entrainment coefficient at time t (yr), and A0 and B0 (m2 kg-SS−1) are constants
249
denoting the initial fractions of the entrainment coefficient that decreased steeply and slowly
250
over time with decrease rate constants of –k1 and –k2 (yr−1), respectively. The decrease rate
251
constants include the decay constant of 137Cs (0.023 yr−1). The data used to calculate A0 and –k1
252
came from only site 1, and the coefficients may be biased by the first one data of June 13, 2011.
253
This adds large uncertainties to the coefficient. The data were included in the analysis, however,
254
because the initial period after the accident is crucially important, and data on this period is
255
scarce. Assuming that the decrease half a year after the accident was represented by the −k2
256
obtained using the results of this study, the parameters of the paddy field were calculated as an
257
A0 of 1.7 m2 kg-SS−1 (σ range from 0.19 to 15 m2 kg-SS−1), a B0 of 0.051 m2 kg-SS−1 (σ range from
258
0.041 to 0.065 m2 kg-SS−1), a −k1 of −14 yr−1 (σ range from −20 to −7.5 yr−1), and a −k2 of −0.48
259
yr−1 (σ range from −0.60 to −0.35 yr−1).
260
The decreases in the
261
represented using a double or triple exponential function.19, 25−26 The results suggest that the
262
decrease in
137
137
Cs over time was derived by fitting a double exponential
(3)
137
Cs concentrations in European and Asian river waters were also
Cs concentration in a water system is characterized by both fast and slow phases.
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Smith and coworkers used the triple exponential function to represent the decrease based on data
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from the long-term monitoring over a period of 10 years following the Chernobyl Nuclear Power
265
Plant accident.19 The third decrease rate (i.e. -k3 in their report) was one order of magnitude
266
lower than the -k2 values in our study and in their own report, suggesting that the radiocesium
267
wash-off from paddy field will decrease with time. Therefore, long-term monitoring data is
268
needed to evaluate the rate of decrease in the entrainment coefficient in paddy fields and to
269
predict the migration of 137Cs through paddy fields.
270
271 137
272
Figure 6. Temporal decrease in entrainment coefficients obtained from the particulate
Cs
273
concentration corrected for the particle size dependency. Closed and open circles show the
274
averaged entrainment coefficients obtained from the turbid paddy water after puddling and from
275
the SS discharged from the six experimental paddy fields, respectively. Error bars represents
276
standard deviations. Gray circles and crosses represent the entrainment coefficient obtained at
277
site 1 from June to July 2012 and from the previous 2011 study.11 The double exponential
278
function fitted to the data is shown as a solid line.
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While the temporal trends in the concentration of dissolved and total (dissolved and particulate)
281
137
282
accident,18,19,25,26 the decrease in particulate
283
Furthermore, the decreasing rate constant of the 137Cs concentration depends strongly on the time
284
span over which the constant is calculated.26 As a result, only limited information is available to
285
compare with our results. Temporal variation in the entrainment coefficient has been reported for
286
the eroded soil from experimental plots of farmland, grassland, and forest in the two years after
287
the FDNPP accident.24 The results showed no temporal decrease in the entrainment coefficient,
288
while the coefficient of the paddy fields decreased by approximately one order of magnitude
289
over the same period. The decrease in 137Cs concentration in river water has been observed after
290
the FDNPP accident.7 The entrainment coefficient of SS in water from the Abukuma River,
291
which is the largest river in Fukushima prefecture, has been evaluated from the ratio between the
292
particulate
293
rate of decrease in the entrainment coefficient of SS observed from one to three years after the
294
accident was 0.27 yr-1, or 56% of that obtained for paddy fields. These results suggest a rapid
295
decrease in particulate
296
those in land under other uses and in river water.
297
SS in river water is derived from a diversity of land uses. The entrainment coefficient of SS in
298
the river water decreased with time, while the decrease in the entrainment coefficient has only
299
been observed for paddy fields. This suggests that the paddy field is an important source of SS
300
and particulate radiocesium in river water, accounting for the decrease in the entrainment
301
coefficient of SS in river water. This large contribution by paddy fields to SS migration in the
Cs in river and lake waters were well documented after the Chernobyl Nuclear Power Plant
137
137
Cs concentrations were less precisely evaluated.
Cs concentration and the initial surface deposition density in the catchment.38 The
137
Cs concentrations in SS discharged from paddy fields, compared with
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water system is consistent with the results of studies monitoring the SS flux from paddy fields.11-
303
13
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therefore crucial for understanding the migration of radiocesium through the water system.
305
The paddy fields studied, with the exception of site 1, are located outside the evacuation zone,
306
and all the sites, including site 1, have been cultivated, every year including 2011. The
307
countermeasures used against radiocesium contamination of the paddy fields mainly comprised
308
fertilizer management and deep tillage to inhibit the migration of radiocesium into the rice plants.
309
The role of decontamination in the decrease in the entrainment coefficient has therefore been
310
limited. As the paddy fields were kept flooded for several days after puddling, the fine soil
311
fractions, which settle slowly, are assumed to form the surface layer and to be discharged
312
preferentially. Fine soil is well known to contain higher concentrations of 137Cs than coarse soil.7-
313
8, 27-30
314
paddy fields preferentially during the period immediately after the FDNPP accident. Annual
315
puddling would lead to mixing with deeper and less-contaminated soil, further decreasing the
316
particulate 137Cs concentration of the surface soil.31,32 Although additional research is necessary,
317
the preferential discharge of highly contaminated fine soil, and the physical mixing with deeper
318
and less-contaminated soil, can explain the faster rate of decrease in the particulate
319
concentration of paddy fields than that recorded for other land uses.
An understanding of the time dependence of the entrainment coefficient of paddy fields is
Highly contaminated fine soil was therefore assumed to have been removed from the
137
Cs
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TABLES.
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Table 1. Averaged entrainment coefficient obtained from turbid paddy water and their standard
323
deviation (SD). Both of the uncorrected and corrected data for the particle size dependency are
324
shown.
Sampling dates May 6, 2012 Apr. 29, 2013
Entrainment coefficient (uncorrected) m2 kg-SS-1 Ave SD 0.050 0.062 0.026 0.020
Entrainment coefficient (corrected) m2 kg-SS-1 Ave SD 0.037 0.023 0.023 0.013
325 326
Table 2. Entrainment coefficients obtained from SS discharged from paddy fields and their
327
standard deviation (SD). Both of the uncorrected and corrected data for the particle size
328
dependency are shown. The data from June 13, 2011 to July 27, 2012 was obtained from site 1
329
only. Italics indicate the data calculated for the
330
campaign at site 1.
Sampling dates Jun. 13, 2011 Jun. 20, 2011 Jul. 3, 2011 Jul. 4, 2011 Jul. 15, 2011 Jul. 22, 2011 Jul. 31, 2011 Aug. 6, 2011 Aug. 9, 2011 Aug. 18, 2011 Aug. 19, 2011 Aug. 28 2011 Sep. 23, 2011
Entrainment coefficient (uncorrected) m2 kg-SS-1 Ave SD 0.184 0.036 0.046 0.058 0.041 0.030 0.044 0.034 0.031 0.024 0.039 0.029 0.030
137
Cs concentration obtained in previous
Entrainment coefficient (corrected) m2 kg-SS-1 Ave SD 0.184 - 0.069 - 0.062 - 0.074 - 0.057 - 0.047 - 0.062 - 0.056 - 0.043 - 0.041 - 0.057 - 0.038 - 0.050 -
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Oct. 24, 2011 Jun. 1, 2012 Jun. 22, 2012 Jul. 6, 2012 Jul. 18, 2012 Jul. 27, 2012 Sep. 4, 2012 Sep. 17, 2012 Sep. 30, 2012 Oct. 15, 2012 Nov. 10, 2012 Dec. 9, 2012 Jan. 1, 2013 Feb. 5, 2013 May 9, 2013 Jun. 12, 2013 Jul. 14, 2013 Aug. 20, 2013 Sep. 14, 2013
0.021 0.011 0.023 0.017 0.017 0.004 0.027 0.029 0.037 0.029 0.026 0.025 0.034 0.033 0.029 0.022 0.022 0.015 0.015
- - - - - 0.017 0.019 0.027 0.021 0.018 0.016 0.022 0.016 0.025 0.012 0.013 0.012 0.012
0.038 0.017 0.028 0.021 0.021 0.008 0.028 0.031 0.036 0.029 0.027 0.022 0.027 0.025 0.029 0.021 0.022 0.016 0.014
Page 20 of 29
- - - - - - 0.016 0.019 0.023 0.022 0.021 0.014 0.014 0.008 0.018 0.010 0.013 0.010 0.011
331 332 333 334
AUTHOR INFORMATION
335
Corresponding Author
336
* Kazuya Yoshimura
337
Phone: +81-3-3592-2177
338
e-mail address:
[email protected] 339
Present Addresses
340
§
341
8F 1-29, Okitama-cho, Fukushima-shi, Fukushima 960-8034, Japan
Sector of Fukushima Research and Development, Japan Atomic Energy Agency, Sahei Building
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Author Contributions
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K.Y. and J.T. carried out the collections of sample and data and measurement. K.Y. performed
345
analysis. K.Y. and Y.O. discussed the results and contributed to the manuscript preparation.
346 347
Notes
348
The authors declare no competing financial interest.
349 350
ACKNOWLEDGMENT
351
This work was conducted as a part of project entitled the Establishment of grasp method of long-
352
term effects caused by radioactive materials from the Fukushima Daiichi Nuclear Power Plant
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accident, financially supported by the Ministry of Education, Culture, Sports, Science and
354
Technology and by the Nuclear Regulation Authority, Japan. We are grateful to reviewers for
355
their valuable comments to improve this article.
356 357
ASSOCIATED CONTENT
358
Supporting Information Available
359
Table S1. Specific surface area of SS in the turbid paddy water collected after puddling.
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Table S2. Specific surface area of SS discharged from six monitoring paddy fields.
361
These materials are available free of charge via the Internet at http://pubs.acs.org.
362 363
ABBREVIATIONS
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FDNPP, Fukushima Daiichi Nuclear Power Plant; SS, Suspended solid.
365 366
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