Post on 19-Jun-2020
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Kohyama, Takata, unpublished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
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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
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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
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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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