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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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Environmental Science & Technology

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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,§

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†

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8F 1-29, Okitama-cho, Fukushima-shi, Fukushima 960-8034, Japan

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‡

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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]

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ACS Paragon Plus Environment

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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

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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

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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

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coefficient suggests that paddy fields play a major role in radiocesium migration through the

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water system. An understanding of the decrease rate of the entrainment coefficient of paddy

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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

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physical processes such as soil erosion. It was then mainly transported in particulate form

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through the river system.6-9 The migration of particulate 137Cs from terrestrial fields to the water

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system is a serious issue when predicting changes in environmental contamination levels and for

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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

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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

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the catchment area to model the rate of

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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-

69

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

100

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

102 103

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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128 129

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

133

ArcGIS 10 software. The prefectural border and shore-lines were obtained from Geospatial

134

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.

141 142

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.

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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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156 157

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.

172 173

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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137

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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

189

137

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deposition density in both the 2012 and 2013 samples. This suggests that the initial surface

191

deposition density is an important factor in the particulate

192

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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196 137

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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

199

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

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and compared with the initial surface deposition density (shown by the open circles in Figure 4).

211

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

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size dependency of the particulate

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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

224

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.

233

234 235

Figure 5. Boxplot of entrainment coefficients calculated from particulate 137Cs concentrations in

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turbid paddy water corrected for particle size dependency. The box and the error bars show the

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ranges from the first to third quartiles and from the minimum to the maximum values,

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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

240

water sample collected on June 13, 2013 in previous study11 is shown as an open circle.


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241 242

Figure 6 shows the temporal decrease in entrainment coefficient taken from Tables 1 and 2. The

243

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

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came from only site 1, and the coefficients may be biased by the first one data of June 13, 2011.

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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

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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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279 280

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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302

water system is consistent with the results of studies monitoring the SS flux from paddy fields.11-

303

13

304

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

320


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321

TABLES.

322

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 －


19


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


20

Page 21 of 29


342 343

Author Contributions

344

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

353

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.

360

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


21


364

Page 22 of 29

FDNPP, Fukushima Daiichi Nuclear Power Plant; SS, Suspended solid.

365 366

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