National Agriculture and Food Research Organization

Dynamics of radioactive cesium behavior in agro-environment

Noriko Yamaguchi, Kazunori Kohyama, Yusuke Takata, Sadao Eguchi

National Institute for Agro-environmental Sciences, NARO

RCs concentration in farmland soils

Plant uptake

Criterion to decide whether or not decontamination is necessary

Soil to water distribution

What causes changes in RCsconcentration infarmland soils?

3. Radiocesium Interception Potential (RIP) of farmland soils

1. Changes in RCsconcentration of farmlandsoils for 5 years

2. Loss of RCs from paddy fields

Radioactive cesium (RCs): 134Cs+137Cs

Three topics in this presentation

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2. Loss of radiocesium from paddy fields3. Radiocesium Interception Potential of farmland soils

Contents1. Changes in radiocesium concentration of farmland soils over 5 years

RCs deposition

Plough

15 cm

composite sample from 5 plots in each field

0-15cm

Ge detector 134Cs and 137Cs

activity

Yamaguchi et al., J. Environ. Radioactiv. (2012) 2/15

RCs level in soil (Bq / kg)

Technology

～ 5,000

Inverting plow, reduction of RCs uptake by crop,topsoil removal (uncultivated field)

5,000 ～10,000

Topsoil removal, inverting plow, removal of soil after paddling with water

10,000 ～25,000 Topsoil removal

25,000 ～Topsoil removal after solidification

RCs distribution map of farmland soils in Fukushima

8900 ha(2011)

2015

2200 ha(2015)

Kohyama, Takata, unpublished

0-500500-10001000-50005000-1000010000-2500025000-5000050000<

(Bq kg-1)

Farmlands over 5000 Bq/kg

Technologies sorted by RCs levels in soil2011

DecontaminationRadioactive decayErosion

3/15

Rates of RCs decrease were typically faster than radioactive decay

RCs decrease over 5 years without decontaminationPaddy fields (average of 16 fields)

Upland fields (average of 14 fields)

Rel

ativ

e R

Cs

acti

vity

year

RCs concentration (Bq/kg)RCs concentration in 2012

4/15

Wind erosion

Surface run-off Downward migration

Accelerated by soil perturbation due to agricultural practices

Loss of RCs-bearing soil particles

17 y (9-24 y) 17 y (8-26 y)

Paddy field Upland field (wheat)

Effective half life of 137Cs in ploughed layerMonitoring of 137Cs concentration in farmland soils for 25 years(Komamura et al., 1999, 2004)

Global fall-out by atmospheric nuclear weapons test1

37C

s (B

q/k

g D

W)

Rates of decrease were faster than radioactive decay (T1/2=30.1yr)

Radioactive decay

Average of 15 paddy fields

1960 1970 1980 1990 2000 2010

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1. Changes in radiocesium concentration of farmland soils for 5 years2.3. Radiocesium Interception Potential of farmland soils

Contents

2. Loss of radiocesium from paddy fields

Soil perturbation event by soil puddling with irrigation water before transplanting rice seedlings

Irrigation waterAtmospheric deposition

Surface drainageTile drainage

Input

Output

Surface drainage

during puddling

Surface drainage before

transplanting

(5 days after puddling)SS: 65000 mg/L

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0.001

0.01

0.1

1

10

100

1000

0.1 1 10 100 1000 10000 100000

日和田 降下物日和田 灌漑水日和田 表面排水 慣行日和田 表面排水 節水日和田 暗渠排水小浜 降下物小浜 灌漑水小浜 表面排水小浜 湧水大波 降下物大波 灌漑水大波 表面排水大波 暗渠排水月舘 降下物月舘 灌漑水月舘 表面排水月舘 暗渠排水日和田・畑 表面排水猪苗代・草地 降下物猪苗代・草地 表面排水比曽 降下物比曽 表面排水比曽 河川水樋渡 降下物樋渡 河川水南相馬 灌漑水

SS (>0.025 μm) concentration (mg/L)

Total RCs vs suspended solids (SS)

Tota

l RC

s（B

q/L）

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

RC

s b

alan

ce/i

nve

nto

ry (%

)

RCs Inventory (Bq/km2)500 103 to 104

Input and output of RCs was associated with those of suspended solids. RCs was lost from paddy fields at rates of less than a few % per year of the soil

RCs inventory

RCs balance/Inventory

RCs inventory (Bq/m2)R

Cs

bal

ance

/in

ven

tory

(%

)

8

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1.E+2

1.E+3

1.E+4

1.E+5

1.E+6

1.E+7

0.001 0.01 0.1 1

日和田 降下物日和田 灌漑水日和田 表面排水 慣行日和田 表面排水 節水日和田 暗渠排水小浜 降下物小浜 灌漑水小浜 表面排水小浜 湧水大波 降下物大波 灌漑水大波 表面排水大波 暗渠排水月舘 降下物月舘 灌漑水月舘 表面排水月舘 暗渠排水日和田・畑 表面排水日和田・果樹 表面排水日和田・果樹 浸透水猪苗代・草地 降下物猪苗代・草地 表面排水比曽 降下物比曽 表面排水比曽 河川水樋渡 降下物樋渡 河川水南相馬 灌漑水

Electrical conductivity (EC) (dS/m)

Kd

(L/k

g)

Kd 103～107 L/kg

Decrease with increasing EC

Bq/Lfi l trate in conc Cs

Bq/kgSS in conc CsL/kgK

137

137

d

1 10 100 1000 10000

103

104

105

106

107

Kd

RIP (mmol kg-1

)

Distribution coefficient

Source of plant uptake

Kd

(L/k

g)

103

104

105

106

107

10.10.01102

0.001

9

8/15

Intrinsic parameter describing RCs mobility in soil independent of various environmental factors

1. Changes in radiocesium concentration of farmland soils for 5 years2. Loss of radiocesium from paddy fields

Contents

Reflect the soil characteristics of RCs adsorption

Variable depending on water quality/plant type, growing & nutrient condition

=RCs in plant

RCs in soil

Transfer factor (TF)

Simple and Important parameters to describe/predict RCs behavior

SoilWater

Plant

RIP

TF

Kd

=RCs in soil

RCs inwater

Distribution coefficient

3. Radiocesium Interception Potential (RIP) of farmland soils

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Radiocesium interception potential (RIP)

Parameter to evaluate selectivity and quantity of highly selective sites for Cs sorption

Cation exchange sites except FESmasked by Ca2+

FES saturated by K+

Spiked 137Cs is exchanged with K on FES

COO-

OO

COO

HO －－

－

－

－ －

－ －

－

－

－ － －

－

－

－ －

－

－

－ －

－ －

－

－

Experimental method137Cs

10/15

Geometric mean: 1280 ± 2.16 mmol/kgMinimum: 73 mmol/kgMaximum: 12700 mmol/kgMedian: 1300 mmol/kg

RIP distribution map

11/15

<500

500 - 1000

1000 - 1500

1500 - 2000

2000 - 2500

2500 - 3000

3000 - 3500

>3500

RIP (mmol kg-1)

Fluvisols

Cambisols

Andosols

Soil Group

Values within a column followed by different letters are significantly different according to Steel-Dwasstest at p≦0.01 for soil group and p≦0.005 for clay mineral composition

Mica × × 〇Sm × 〇 〇Ave 625 1530 1560N 37 28 487

a b b

Andosols Fluvisols Cambisols

TC % >6% 3~6％ <3% >3% <3%Average 486 812 1360 1260 1870 2410

N 52 69 96 79 486 143a b c c d e

Mica: vermiculite, illiteSm: smectite

Soil Group Clay mineral composition

Low RIP Andosols, High TC, w/o crystalline clay minerals12/15

RCs distribution map RIP map

Prediction of RCs uptake by crop

+

RCs concentration of farmland soil changes over time

Loss of Cs-bearing soil particles by erosion

Summary

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Acknowledgement

This work was performed under a contract with the Agriculture, Forestry and Fisheries Research Council, MAFF, Japan.

We wish to thank the staff at prefectural institutes and farmers in Fukushima, Ibaraki, Tochigi, Miyagi for their cooperation with sample collections.

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