Chemosphere 163 (2016) 234e241

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Simpliﬁed measurement method for dissolved radio-Cs in litter andsoil seepage water using copper-substituted Prussian blue
Momo Takada a, Tetsuo Yasutaka b, *, Toshinori Okuda aab

Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan
National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japanh i g h l i g h t s

g r a p h i c a l a b s t r a c t

 We developed a simpliﬁed methodfor detecting dissolved radio-Cs inseepage water.
 99% of dissolved 137Cs from litter wascollected in the ﬁeld experiment.
 More than 90% of dissolved 137Csfrom soil seepage water wascollected.
 This method reduces preparationtime
relative
toconventional
methods.
 The method can also separate theparticulate and dissolved radio-Cs insitu.

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 17 February 2016
Received in revised form
21 July 2016
Accepted 1 August 2016
Available online 16 August 2016

We developed a simple and rapid method for detecting dissolved radio-Cs in litter and/or soil seepage
water using nonwoven fabrics impregnated with copper-substituted Prussian blue (Cu-NF). In laboratory
and ﬁeld experiments, litter and/or soil seepage water including dissolved radio-Cs were passed throughtraditional lysimeter systems combined with seven sheets of the Cu-NF. We then examined the recovery
ratios of dissolved 137Cs in the Cu-NF. In the laboratory experiments with faster ﬂow rates (11e2200 mm h1), over 86% of the total dissolved 137Cs in litter seepage water was detected in the Cu-NF
and over 82% of the collected 137Cs was present in the ﬁrst three sheets. In the ﬁeld experiments, 99% of
the total dissolved 137Cs litter seepage water was collected in the Cu-NF and more than 96% of thecollected 137Cs was present in the ﬁrst three sheets. Furthermore, the recovery ratio of dissolved 137Cs
increased with increasing installation Cu-NF length, probably because the packed soil in the Cu-NF
lysimeter become more stable over time. Finally, because only the Cu-NF is measured, it is not necessary to undertake traditional measurement preparations such as ﬁltration to remove particulate radio-Cs
materials and evaporative concentration for low concentration of radio-Cs. As a result, we can save timeand effort in measurement preparation by using the Cu-NF lysimeter method.
© 2016 Elsevier Ltd. All rights reserved.

Handling Editor: Martine Leermakers
Keywords:
Cesium-137
Environmental monitoring
Forest soil
LitterLysimeter

1. Introduction* Corresponding author.
E-mail address: t.yasutaka@aist.go.jp (T. Yasutaka).
http://dx.doi.org/10.1016/j.chemosphere.2016.08.010
0045-6535/© 2016 Elsevier Ltd. All rights reserved.

Large amounts of radionuclides were released into the environment during the Fukushima Daiichi Nuclear Power Plant(FDNPP) accident in 2011 (Endo et al., 2012) and were widely

M. Takada et al. / Chemosphere 163 (2016) 234e241

dispersed on the surrounding terrain. As forest areas account for
more than 70% of land in the Fukushima Prefecture, radioactive
cesium (radio-Cs), especially 137Cs, will remain in the areas for aconsiderable period of time because 137Cs has the long half-life of
30.17 years. Therefore, the radioactive contamination of forests andforest products will be a matter of serious concern for some time tocome (Kuroda et al., 2013).
Soon after the FDNPP accident, radio-Cs deposited on the forest
ﬂoors was estimated to migrate into soil by becoming dissolved inwater; however, the transported amounts of dissolved radio-Cs
rapidly decreased with time after the accident (Matsunaga et al.,2013). Dissolved radio-Cs can move rapidly from the litter layer
into soil and then from the soil to plants (Nakanishi et al., 2013).
Therefore, studies of the migration of the radio-Cs among thesecomponents (e.g. plants, litter layer and soil) are important over the
coming decades, rather than focusing only on radio-Cs accumulation within each component (Hashimoto et al., 2012). In addition,clariﬁcation of radio-Cs dynamics in forest ecosystems will play animportant role in applications such as forest management and radiation protection, taking account of the various uses of forest resources (Fujii et al., 2014).
Two different methods have been employed to evaluate verticalmigration of radio-Cs in forest soil: the soil proﬁle method and thelysimeter method. Many studies have investigated vertical migration of radio-Cs by using the soil proﬁle method (e.g. Straume et al.,2006; Takahashi et al., 2015), in which migration rates were estimated from changes of radio-Cs in soil depth proﬁles during periods from 1 year to several years. Although this method isrelatively simple, sampling point must be shifted slightly at eachsampling period. As it was well known that radio-Cs in forest soil
shows extensive spatial heterogeneity (Onda et al., 2015), the soil
proﬁle results may be affected by the spatial variation of radio-Cs insoil. There is also a possibility that evaluation over short periods is
associated with substantial uncertainty.
In contrast, a lysimeter method directly monitors migrating ionsin the soil (Rasmussen et al., 1986). Several types of lysimeter, suchas a zero-tention lysimeter (Giesler et al., 1996) and suction
lysimeter (Kosugi and Katsuyama, 2004) stainless steel lysimeter€ rr, 1996), had been developed for forest soil moni(Tegen and Do
toring. Although these method was used after the Chernobyl acci€ rr, 1996) and the FDNPP accident in 2011
dent in 1986 (Tegen and Do(Nakanishi et al., 2014), it has not been widely adopted for radio-Cs
monitoring because of its complex procedure and a huge amount ofeffort for pretreatment and analysis of collected drainage water. For
example, to employ the lysimeter method, we need to excavate soil
deeply (tens of centimeters) to install a large sized lysimeter.
Therefore, multi-point monitoring with lysimeters in a forest
ecosystem is not practical. In addition, using the lysimeter method,
we need to collect drainage water once in several weeks or a monthand bring the water sample to a laboratory for radio-Cs measurement because the activity concentration of radio-Cs is typically low(Nakanishi et al., 2014). Determination of the radio-Cs concentration in the water sample requires ﬁltration and evaporative concentration prior to measurement or a long period for a small
volume of collected water or a very low concentration of radio-Cs.
Furthermore, the conventional lysimeter method separates dissolved radio-Cs from particulate radio-Cs not in-situ but in thelaboratory by ﬁltration. Therefore, development of a simple, rapid
and easy monitoring method for radio-Cs in litter and soil seepage
water is required to concentrate dissolved radio-Cs on-site to beeasily measured.
After the FDNPP accident, a rapid method was developed for thedetection of dissolved radio-Cs in fresh water using nonwoven
fabric impregnated with Prussian blue (Yasutaka et al., 2013) orpotassium zinc ferrocyanide (Yasutaka et al., 2015). Prussian blue

235

(potassium ferrocyanide (II) potassium oxide iron (II), KFe[Fe(CN)6]3$xH2O) is known to speciﬁcally adsorb dissolved radio-Cs(IAEA, 1997). Yasutaka et al. (2016) also developed the nonwoven
fabrics impregnated with copper-substituted Prussian blue (hereafter, Cu-NF) for detecting radio-Cs in seawater. The Cu-NF canabsorb the radio-Cs in the water sample with high concentration ofco-existing ions.
In this study, we aimed to develop a simple, rapid and in-situ
separation method for examining the migration of dissolved
radio-Cs from soil and/or litter in forest using Cu-NF. We introduced
the Cu-NF to a conventional lysimeter, which can adsorb dissolved
radio-Cs in the seepage water in-situ. We also examined the recovery ratio of dissolved radio-Cs with the Cu-NF method in bothlaboratory and ﬁeld experiments.
2. Materials and methods
We conducted two experiments using Cu-NF combined with alysimeter (hereafter termed the Cu-NF lysimeter): laboratory experiments and ﬁeld experiments. First, we conﬁrmed the absorption ability of dissolved radio-Cs in litter seepage water using the
Cu-NF in laboratory experiments. Next, we conducted ﬁeld experiments to examine the applicability of this method to litter and/or
soil seepage water in the forest environment.
2.1. Experimental materials
The Cu-NF lysimeters for the laboratory and the ﬁeld experiments consisted of PVC pipes (90 cm2), nonwoven fabric ﬁlters anda polypropylene bottle (I-Boy, As ONE Corporation, Japan), as
shown in Fig. 1. Litter and/or soil were packed as packing materials
in the PVC pipes, followed by two or three sheets of 26 mm pore size
nonwoven fabric sheets (ELV-130 for the laboratory experiment, H8010 for the ﬁeld experiment, Japan Vilene Co., Ltd., Japan) andseven sheets of Cu-NF (volumetric density 0.03 g cm3, thickness
0.01 cm, Japan Vilene Co., Ltd., Japan). The 26 mm pore size
nonwoven fabric sheets were used to collect soil particles to avoid
contamination of the Cu-NF. Both the Cu-NF and the 26 mm poresize nonwoven fabric were cut to a diameter of 113 mm. The water,
passed through litter and/or soil, the 26 mm pore size nonwoven
fabric sheets and the Cu-NF, was collected with 2 L polypropylene
bottles.
2.2. Laboratory experiments
In the laboratory experiments, we evaluated the recovery ratioof dissolved radio-Cs in water passed through the litter in the Cu-NF
lysimeter. The litter was separately collected from the L layer and FH layer at a Japanese cedar forest (Cryptomeria japonica) in Kawamata, Yamakiya District, 40 km north-west of the FDNPP(37 360 2900 N, 140 380 5700 E; 583 m asl). Litter from the L layer(400 g) and the F-H layer (160 g) was mixed well after being cut to2 cm in length. Next, the pipe was ﬁlled with litter (approximately
800 Bq/65 g wet weight) to a height of 5 cm in three of the Cu-NF
lysimeters (Nos. 1-1, 1-2 and 1-3) and a control lysimeter (No. 1-41). In three of the Cu-NF lysimeters (Nos. 1-1, 1-2 and 1-3), two
sheets of 26 mm pore size nonwoven fabric and seven sheets of CuNF were combined, and in the remaining lysimeter (No. 1-4-1), only
three sheets of 26 mm pore size nonwoven fabric without Cu-NF
was used as the control.
Table S1 and Fig. S1 show the experimental conditions andprocedures. Ten liters of ion exchange water, which was approximately 1100 mm of throughfall volume and nearly the same as
annual precipitation in Fukushima Prefecture (1166 mm,
1981e2010), was passed through each the Cu-NF lysimeter (Nos. 1-

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M. Takada et al. / Chemosphere 163 (2016) 234e241

Fig. 1. Schematic of the Cu-NF lysimeter sets for the laboratory experiment (a) and ﬁeld experiment (b).

1, 1-2, 1-3) and the control lysimeter (No.1-4-1; Fig. 1a). Water ﬂow
rates (L hour1) through the packing materials in the four lysimeters decreased with time because of the clogging of 26 mm pore size
nonwoven fabric. The average ﬂow rate was approximately
0.2 L h1 (i.e. 22 mm h1), and initial and ﬁnal rates were 8.0 and
0.1 L h1(i.e. 880 mm h1 and 11 mm h1), respectively. Accordingly, ﬂow rates of the water through the Cu-NF of No. 1-1, 1-2 and1-3 agreed with the ﬂow rates shown above.
For the control lysimeter (No. 1-4-2), the water passed throughthe lysimeter No. 1-4-1 was initially ﬁltered with 0.45 mm membrane ﬁlters (mixed cellulose ester, Advantech, Tokyo, Japan) to
remove particulate radio-Cs, and passed through seven sheets of
Cu-NF (No. 1-4-2). The ﬂow rate through No. 1-4-2 was constant,about 20 L h1(i.e. 2200 mm h1), which is rapid compared with

M. Takada et al. / Chemosphere 163 (2016) 234e241

the other three Cu-NF lysimeters (No. 1-1, 1-2 and 1-3).
To measure the 137Cs concentration in the water, the collectedwater passed through the Cu-NF lysimeter was ﬁrst ﬁltered using a
0.45 mm membrane ﬁlter to remove suspended solids, except forthe samples of No. 1-4-2. Next, 1 L of ﬁltered water was evaporated
on a Teﬂon sheet (250  250 mm) that was kept at 120  C by a hot
plate. Thereafter, g-ray measurements were performed with a lowbackground, well-type Ge detector (Seiko EG&G, GWL 120230-S,
Shizuma et al., 2010). The measurement time for each sample was
10,000 s.
To measure the 137Cs concentration in the Cu-NF, the Cu-NF(seven sheets in total) was separated to the ﬁrst three sheets andthe latter four sheets, which were separately cut into 2-cm pieces.
The Cu-NF were washed with an ultrasonic washing machine for
15 min before the radio-Cs measurement to remove particulate
radio-Cs (under 26 mm diameter) attached to the Cu-NF. We conducted preliminary repeated experiments of this washing process
to check the effectiveness of this washing process. We found thatthe difference in the radio-Cs concentration between the Cu-NF
after the 1st and 2nd washing process was negligible. Therefore,
the Cu-NF was treated with ultrasonic washing for 15 min before
measurements. The concentration of 137Cs in the Cu-NF wasdetermined by g-ray spectrometry using a coaxial type, low background Ge detector (GEM Series HPGe Coaxial Detector System,
GEM-110225, Seiko EG&G, Shizuma et al., 2016). The measurement
time was 30,000 s.
2.3. Field experiments
Field experiments were conducted in a Japanese cedar forest(Cryptomeria japonica) in Kawamata, Yamakiya District (37 360 2900
N, 140 380 5700 E; 583 m asl). Annual precipitation was 1342 mm(Tsushima weather station, Japan Meteorological Agency (JMA))
and average temperature was 11.9  C (Nihonmatsu weather station,
JMA). The experimental site has not been subjected to any decontamination work. The thickness of the litter layer in the site wasapproximately 4 cm.
Six Cu-NF lysimeters were used in the ﬁeld experiments(Fig. 1b). Three Cu-NF lysimeters were ﬁlled with 4 cm of litter, andinstalled under the litter layer (Nos. 2-1, 2-2 and 2-3), and threefurther Cu-NF lysimeters were ﬁlled with 4 cm of litter and 5 cm ofsoil, and installed at 5 cm depth below the soil surface (Nos. 3-1, 3-2
and 3-3). Intact litter and soil cores were collected by pounding apipe with 10.7 cm diameter into the litter and soil to 5 cm depth
and ﬁlled in Cu-NF lysimeters without further compaction. There
were 10-cm blank/void spaces between the ﬁlled litter/soils and the
Cu-NF (Fig. 1b). Seepage water was passed through the 26 mm NF
and the Cu-NF, and ﬁnally collected in 2 L polypropylene bottles. As
the installation site was sloping, approximately 15 cm height of
enclosures from the ground surface were combined with the Cu-NF
lysimeters to avoid the direct inﬂux of surface runoff into the Cu-NF
lysimeters.
Lysimeters under the litter layer (Nos. 2-1, 2-2 and 2-3) were
installed from 24 May to 27 August 2015, and those at 5 cm depth
below the soil surface (Nos. 3-1, 3-2 and 3-3) from 3 July to 27
August 2015. Sample collection of the Cu-NF and water in thebottles was conducted three times for litter ﬁlled Cu-NF lysimeters(No. 2-1, 2-2 and 2-3 on 3 July, 30 July, and 27 August 2015) andtwice for litter and soil ﬁlled Cu-NF lysimeters (Nos. 3-1, 3-2 and 33, on 30 July and 27 August 2015) during the experimental periods.
The Cu-NF was exchanged without disturbance of litter/soils(Fig. 1b) because this equipment can be separate two parts, litter/soils with 26 mm pore size nonwoven fabric sheet part and Cu-NF
part. The volume of the collected water in the bottles was determined on each sample collection date. On the last sample collection

237(27 August), the litter and soil in the Cu-NF lysimeters were alsocollected. The soil and litter in the Cu-NF lysimeters Nos. 3-1 and 32 were collected separately, but litter and soil of No. 3-3 could not
be collected separately because the soil and litter had been
disturbed and mixed together (probably by heavy precipitation
events).
Measurement procedures for 137Cs activities in collected water
samples and the Cu-NF were the same as those in the laboratory
experiments. The packing materials (litter and soil) were dried at
80  C for 48 h for analyzing 137Cs activity. The samples were ﬁlled
into 100 mL plastic polystyrene containers (U-8) and the concentrations of 137Cs were determined by the low background Ge detector same as the measurement of Cu-NF (600 s of themeasurement time).
3. Results and discussion
3.1. Laboratory experiments
Fig. 2 shows the results of the laboratory experiments.
Approximately 86e93% of dissolved 137Cs was collected in the CuNF and over 95% of the collected 137Cs was present in the ﬁrst
three of the total seven sheets. This indicated that most of the
dissolved radio-Cs was collected by the Cu-NF and 86e93% of dissolved radio-Cs in the seepage water was in ionic form.
The recovery ratio of dissolved 137Cs in the Cu-NF for No. 1-4-2(average ﬂow rate: 2200 mm h1) presented the same pattern as
those for No. 1-1, 1-2 and 1-3 (average ﬂow rate 22 mm h1), eventhough the ﬂow rate for No. 1-4 was 100 times faster than theothers. The gravity-dependent ﬂow rate range in the present study(11e2200 mm h1) is thought to be acceptable for a good recovery
rate, even though the recovery rate of 137Cs in the Cu-NF decreases
with the increasing ﬂow rate (Yasutaka et al., 2016).
In contrast, about 7e14% of 137Cs was also detected in the water
passed through the Cu-NF and the 0.45 mm membrane ﬁlter. Cu-NF
adsorbed only ionic radio-Cs. As mentioned in the laboratory test,
over 95% of the collected 137Cs was present in the ﬁrst three of theFig. 2. Recovery ratios of 137Cs detected in the Cu-NF and the water passed through the
Cu-NF. The 137Cs concentrations in the water are shown after ﬁltration with 0.45 mm
membrane ﬁlters. The error bars indicate the measurement error.

238

M. Takada et al. / Chemosphere 163 (2016) 234e241

Table 1
Collecting volume of the water samples during monitoring period.
Monitoring period (year/
month/day)

Days

1st

2015/5/24e2015/7/2

40

2nd

2015/7/3e2015/7/29

27

3rd

2015/7/30e2015/8/27

28

a

a

Collecting water volume (ml) (calculated precipitation [mm])No. 2-1

No. 2-2

No. 2-3

No. 3-1

No. 3-2

No. 3-3

353
(39)
615
(68)
620
(69)

510
(57)
480
(53)
522
(58)

620
(69)
969
(108)
967
(107)

e

e

e

637
(71)
748
(83)

814
(90)
927
(103)

722
(80)
836
(93)

Precipitation (mm) (maximum [mm h1])

144
(29)
148
(15)
137
(13)

Data at Tsushima meteorological station, 10 km south-east of the monitoring site (Japan Meteorological Agency database, http://www.jma.go.jp/jma/index.html).

total seven sheets and under 5% of 137Cs was remain later four
sheets. This result indicated that almost all ionic radio-Cs wereadsorbed Cu-NF.
In this term, there is the possibility that other existing forms of
the radio-Cs (except for the dissolved form in the water; particulate
radio-Cs with radius of less than 0.45 mm and/or colloid radio-Cs),
may pass through 0.45 mm membrane ﬁlters but not become
adsorbed to the Cu-NF. The contribution of the undetermined formsof radio-Cs is estimated at about 7e14% in our laboratory experiments and thus clearly cannot be ignored. However, the ﬂow rates(No.1-1 e No.1-3 initial 2200 mm h1, average 22 mm h1 and No.14-2 initial 2200 mm h1, average 22 mm h1) in the laboratory
experiments are far higher than those encountered when precipitation penetrates into forest soil in the environment. This ﬂow
condition may cause that some radio-Cs, which adsorbed soil particle, organic matter, dissolve organic carbon and/or colloid withradius of less than 0.45 mm, were drove in the collected water
because of these abnormally high ﬂow rates. As a result, 7e14% of
the undetermined forms of radio-Cs may be measured. This hypothesis will reinforcement at the result of ﬁeld experiment.
3.2. Field experiments
3.2.1. 137Cs activity of the packing materials and collected water
volumeTable S2 shows the 137Cs activities in the packing materials ineach Cu-NF lysimeter. The average 137Cs activities of the lysimeters
installed under litter layer and in soil at 5 cm depth were 779e1006
and 1665e2181 Bq, respectively, which is consistent with the results of spatial heterogeneity of radio-Cs in forest soil after the
FDNPP accident (Onda et al., 2015).

Table 1 shows the collected volumes of water samples of the CuNF lysimeters and precipitation (mm) with hourly maximum precipitation (mm h1) at the Tsushima weather station (JMA), thenearest meteorological station, during the experimental periods.
Monitored precipitations by the JMA during three experimental
periods were 137e148 mm, while the collected water were
39e108 mm (77 mm on average, calculated by collected water
volumes). The difference between the lowest and highest volumesof the collected water depended on neither the installed depths of
the Cu-NF lysimeters nor the location of installation in the forest
stand. Our results were consistent with a previous study on large
spatial variation in throughfall and soil water (Kobayashi et al.,2000).
3.2.2. Recovery ratios of dissolved 137Cs with the Cu-NF
Table 2 shows the results from the lysimeters ﬁlled with litter(Nos. 2-1, 2-2 and 2-3). More than 99% of the total dissolved 137Cs
was collected by the Cu-NF, and 96% of the collected 137Cs was
located in the ﬁrst three sheets (Table 2). Dissolved 137Cs was
detected in the collected water but the ratio is much lower (under1%). This result may be mainly owing to the slow ﬂow rate
(maximum 29 mm h1) compared with the laboratory experiments(11e2200 mm h1). However, the high concentration of 137Cs in the
Cu-NF also indicates that the radio-Cs in the seepage water was
mainly in an ionic form. Based on these results, we conclude that
the Cu-NF lysimeter method is suitable for detecting dissolved
radio-Cs in litter seepage water in the forest environment in placeof traditional lysimeter methods.
The recovery ratios of dissolved radio-Cs in the litter and soil
seepage water (Nos. 3-1, 3-2 and 3-3) were over 90% for the second
experimental period, and were over 97% for the third experimental

Table 2
Recovery ratios of dissolved 137Cs with the Cu-NF and 137Cs activities of the collected water.
Lysimeter no. and monitoring period

2e1

2e2

2e3

3e1
3e2
3e3
a 137
b 137

1st 2015/5/24e7/2
2nd 2015/7/3e7/29
3rd 2015/7/30e8/27
1st 2015/5/24e7/2
2nd 2015/7/3e7/29
3rd 2015/7/30e8/27
1st 2015/5/24e7/2
2nd 2015/7/3e7/29
3rd 2015/7/30e8/27
2nd 2015/7/3e7/29
3rd 2015/7/30e8/27
2nd 2015/7/3e7/29
3rd 2015/7/30e8/27
2nd 2015/7/3e7/29
3rd 2015/7/30e8/27

Cu-NFa (%)

Collected waterb (%)

First three sheets

Latter four sheets

Total

98.9
99.6
96.1
97.6
98.6
99.2
98.6
99.4
98.2
74.9
95.9
80.7
94.9
89.3
98.4

0.7
0.3
3.4
2.2
0.8
0.5
1.2
0.4
1.4
19.2
2.8
10.0
2.8
5.7
0.9

99.6
99.9
99.5
99.8
99.3
99.7
99.8
99.7
99.5
94.1
98.8
90.7
97.7
95.0
99.3

Cs activity after ultrasonic washing.
Cs activity after ﬁltration with 0.45 mm membrane ﬁlters.

0.4
0.1
0.5
0.2
0.7
0.3
0.2
0.3
0.5
5.9
1.2
9.3
2.3
5.0
0.7

M. Takada et al. / Chemosphere 163 (2016) 234e241239

Fig. 3. Dissolved 137Cs concentrations in litter and soil seepage water (137Cs in Cu-NF and collected water after 0.45 mm MF ﬁltration) during the monitoring periods. Cu-NF lysimeterNos. 2-1, 2-2 and 2-3 were installed under the litter layer, and Nos. 3-1, 3-2 and 3-3 were installed at 5 cm soil depth. The error bars indicate the measurement error.

period (Table 2; note that no data of Nos. 3-1, 3-2 and 3-3). The
recovery ratio in the second experimental period was lower thanthat in the third experimental period for all three samples. In
addition, the recovery ratio of 137Cs in the ﬁrst three sheets of the
Cu-NF in the secondary experimental period (74.9e89.3%) was
lower than that in the third experimental period (94.9e98.9%). In
both laboratory and ﬁeld experiments, the precipitation volume,
maximum precipitation rate, collected volume and the radioactivity of soil and litter in the second experimental period were thesame as those in the third experimental period (Table 1 and Fig. 3).
The reason for the relatively low recovery ratio of Nos. 3-1, 3-2
and 3-3 in the second monitoring period is not clear. However, soil
disturbance probably occurred in the second experimental period,
perhaps because of the soil packing in the Cu-NF lysimeters and/or
spaces between the packed soil and the PVC pipes. After a certain
amount of time (~approximately one month), spaces among thesoil particles are inﬁlled and soil cores gradually became stable. In
the third measurement period, over 98% of the dissolved 137Cs wascollected in the Cu-NF and over 95% of the 137Cs was present in theﬁrst three sheets, showing a similar pattern to the results of thelitter seepage water. The Cu-NF lysimeter can be considered suitable for soil seepage water; however, we suggest that sample
collection to be conducted after the lysimeter has been installed fora certain amount of time (~approximately one month).
3.2.3. Concentration and migration rate of radio-Cs from litter or
soil
Fig. 3 shows the 137Cs concentrations in litter and/or soil seepage
water in the Cu-NF and collected water in each Cu-NF lysimeter
during the experimental periods. Average 137Cs concentrationcollected under litter layer (Nos. 2-1, 2-2, 2-3) was approximately
15 Bq L1, while that in soil at 5 cm depth (Nos. 3-1, 3-2, 3-3) was 1.5
Bq L1. The 137Cs concentration in seepage water from each Cu-NF
lysimeter showed temporal variation. Although the temporal variation was observed,, the range of in 137Cs migration among lysimeters were larger than the temporal variation in each Cu-NF
lysimeter. Longer monitoring period (e.g. one year) than that of thepresent study is required to discuss a temporal trend of 137Cs

Table 3Flux and migration rate of dissolved 137Cs during the monitoring period.
Cs ﬂux (Bq m2 day1)

Migration rate of investigated period (% day1)

Lysimeter no.

137

2015/5/24e2015/7/2

2015/7/3e2015/7/29

2015/7/30e2015/8/27

S2-1
2e2
2e3
3e1
3e2
3e3

14.9
29.6
25.4
e
e
e

29.9
38.0
44.7
2.1
2.0
15.8

29.1
38.0
35.0
10.2
3.6
28.5

0.023
0.027
0.034
0.001
0.001
0.006

240

M. Takada et al. / Chemosphere 163 (2016) 234e241

migration.
Table 3 shows the 137Cs ﬂuxes during the experimental periods.
Daily migration rates of 137Cs at 5 cm depth in litter or soil were also
calculated. We observed that approximately 0.03% of 137Cs in thelitter layer migrated to the surface soil over a day in the dissolved
form, while annual 137Cs migration at 5 cm depth accounted forapproximately 0.003%. This indicates that radio-Cs migrating fromthe litter layer to the soil remains in the surface layer of soil(<5 cm), which is consistent with previous studies in the Fukushima region (Takahashi et al., 2015).
However, the migration of 137Cs at 5 cm depth for lysimeter No.
3-3 was larger than those of the other two Cu-NF lysimeters,
probably because of the disturbed packing material in No. 3-3. For
lysimeter Nos. 3-1 and 3-2, dissolved 137Cs leached from litter layer
stopped at the surface part of soils, while for lysimeter No. 3-3,
dissolved 137Cs may be leached from litter mixed in soils locatednear Cu-NF, the and dissolved 137Cs was collected by Cu-NF.
Although the water volumes collected and the 137Cs concentration varied between Cu-NF lysimeters and sampling periods(Table 1 and Fig. 3), the annual 137Cs ﬂux and the migration rates
were spatially homogeneous. Based on these results, we can also
use the Cu-NF lysimeter to calculate the ﬂux of dissolved 137Cs only
by measuring the radio-Cs activity of the Cu-NF without water
sample collection, and to monitor radio-Cs in the ﬁeld over the longterm.
4. Conclusion
In this study, we developed a simple, rapid and easy install andmonitoring method for radio-Cs in litter and/or soil seepage water.
The Cu-NF lysimeter method was showed to be able to collectdissolved radio-Cs in seepage water. By introducing the Cu-NF to a
traditional lysimeter method, the concentration of dissolved radioCs in litter or soil seepage water can be evaluated by measuring the
Cu-NF after ultrasonic washing. Accordingly, this method can
reduce the time required for measurement preparation.
Furthermore, this method also has potentials of several advantages for the long-term monitoring. If we only focus on 137Cs ﬂuxes,
bottles for water collection need not be prepared, and consequently
we do not pay attention to the overﬂowing of seepage water fromwater bottles. Although the Cu-NF lysimeters were installed for up
to 40 days in the environment, seven sheets of Cu-NF collecteddissolved radio-Cs in 10 L (annual throughfall in Fukushima region)of litter passed water in the laboratory experiment. This means thatCu-NF have a potential adsorption ability of radio-Cs and stable-Cs,
which exist higher concentration compared with radio-Cs in theenvironment. In addition, the Cu-NF lysimeter can be installed at ashallower position below the soil surface than traditional lysimeters. However, this research does not conﬁrm the durability of CuNF and condition of clogging of 26 mm-NF in the long-term monitoring. For using long term-monitoring over 3 months, further researches such as actual long term experiment are needed. However,this method have a potential that can be monitored radio-Cs inseepage water by not only the one month but also long-term
installation (e.g. several months ~ a year) of the Cu-NF lysimeters,
and thus reduce the time and effort needed to collect sample water.
Acknowledgments
We thank the authorities of Kawamata and Genkatsu Kanno for
their assistance during our research. We also thank Profs. K. Shizuma and S. Endo at the Graduate School of Engineering, Hiroshima
University for their support and useful comments regarding sample
measurements and analysis. We thank Profs. Y. Onda at the Center
for Research in Isotopes and Environmental Dynamics, University of

TSUKUBA for useful comments for ﬁeld monitoring. The work was
ﬁnanced in part by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) / Japan Society for the Promotion of
Science (JSPS) KAKENHI Grant No. 26241023, 40178322 and
15J03548. The work was also supported by the Hiroshima University Phoenix Leader Education Program (Hiroshima Initiative) for
the “Renaissance from Radiation Disaster”, funded by the Ministryof Education, Culture, Sports, Science and Technology.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.chemosphere.2016.08.010.
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