Determination of 129I/127I in environmental waterbefore and after the 2011 Fukushima Daiichi nuclearpower plant accident with a solid extraction disk

Shigeru Bamba • Kosei E. Yamaguchi •

Hikaru Amano

Received: 5 September 2013 / Published online: 30 May 2014

� Akademiai Kiado, Budapest, Hungary 2014

Abstract A method that combines solid extraction with

accelerator mass spectrometry was applied to determine129I in terrestrial environmental water samples. To validate

the method, water samples were spiked with diluted NIST

SRM 3231 129I isotopic standard (high level). Then129I/127I ratios in river and pond waters in Fukushima and

Ibaraki prefectures were measured in samples obtained

both before and after the Fukushima Daiichi nuclear power

plant accident caused by the great earthquake and tsunami

of 11 March 2011. Before the accident, 129I/127I was

1.1–3.5 9 10-9 in the river waters and 6.0–6.6 9 10-9 in

the pond waters, and afterwards it was 3.3–8.4 9 10-9 in

the river waters and 3.7–6.5 9 10-8 in the pond waters,

reflecting the large amounts of radionuclides that were

released into the environment by the accident. In the

samples collected in April 2011, 129I/127I ratios were about

one order of magnitude larger in pond water, and several

times higher in river water, compared with the samples

collected before the accident.

Keywords 129I � Isotopic ratio � Solid extraction �Accelerator mass spectrometry � River � Pond �Fukushima Daiichi NPP accident

Introduction

Iodine-129 is a long-lived (T1/2 = 1.57 9 107 years)

isotope produced by cosmic ray-induced spallation of Xe

in the atmosphere and spontaneous fission of U in the

geosphere. Most 129I in the environment is from nuclear

weapons testing, fuel reprocessing, and nuclear accidents.

Iodine-129 has been used as a tracer in both geologic [1–

3] and oceanographic [4–6] studies. The analysis of 129I

in environmental samples has usually involved sample

pretreatment (e.g., sample combustion) and separation

and purification of iodine by, for example, solvent

extraction [7, 8]. If the concentration is rather high, a

method using an ICP-MS with an octopole reaction

system can be used [9]. A recently developed analytical

method uses a solid extraction disk and accelerator mass

spectrometry (AMS) to determine 129I/127I ratio [10].

Analysis results for solid samples analyzed by this

method agree well with the results obtained by the

conventional method (solvent extraction and neutron

activation analysis). This new method is not only rapid

and easy but can also separate and purify iodine from

soil samples with high precision.

Analysis of radionuclides in environmental water sam-

ples is important for assessing radionuclide levels and for

estimating the public dose. The solvent extraction method

is usually used to extract iodine from water samples for 129I

analysis, but because of the low level of 129I in the natural

environment, large samples are required and the procedure

is very time consuming. In this study, we used a solid

extraction disk method to extract iodine from terrestrial

(river and pond) waters for measurement of 129I/127I iso-

topic ratios. We found this to be a very simple and rapid

method for iodine extraction from terrestrial environmental

water samples.

S. Bamba (&) � H. Amano

Japan Chemical Analysis Center, 295-3 Sanno-cho,

Inage Ward, Chiba, Chiba 262-0033, Japan

e-mail: s-bamba@jcac.or.jp

S. Bamba � K. E. Yamaguchi � H. Amano

Department of Chemistry, Toho University, 2-2-1 Miyama,

Funabashi, Chiba 274-8510, Japan

123

J Radioanal Nucl Chem (2014) 301:75–80

DOI 10.1007/s10967-014-3055-8

Iodine-129 is the optimum proxy for 131I which is one of

the most harmful radionuclides released from the Fuku-

shima Daiichi NPP accident. From this point of view,

isotopic ratio of 129I/131I has been measured in traditional

method for the purpose of dose reconstruction [11].

Experimental

Reagents and apparatus

All reagents used were analytical grade. The iodine carrier

was prepared from KI reagent (Wako Pure Chemical,

Osaka, Japan). Niobium powder (Sigma Aldrich, MO,

USA) was used for AMS sample preparation.

Solid extraction disk

The 3 M EmporeTM anion exchange-SR disk (radius,

47 mm; thickness, 1 mm) was used for separation and

purification of iodine. The disk is composed of a

poly(styrenedivinylbenzene) copolymer that has been

modified with quaternary ammonium groups. The disk was

conditioned (described below) prior to being used for the

extraction.

AMS measurement

The 129I/127I isotopic ratio was measured at the AMS

facility of the Japan atomic energy agency (JAEA) in

Mutsu, Japan. Details of the measurement procedures used

at this facility have been described previously [12]. To

confirm the AMS measurement precision, aliquots of river

water samples (from points 1 and 4) with volumes of 5 and

10 L were extracted and measured. With the 5 L sample

volume, the error was reasonable. Thus, we decided that a

sample volume of 5 L was suitable for AMS measurement.

Analytical method

Disk conditioning

The extraction disk was centered on the base of the filtra-

tion apparatus and clamped to the filtering reservoir. The

disk was washed with 15 mL of acetone, vacuum dried,

and placed in 15 mL of methanol. About 5 mL of methanol

was pulled through the disk by applying a vacuum, then the

vacuum was vented, and the disk was left to soak for 30 s.

Most of the remaining methanol was then pulled through

the disk under vacuum, leaving a small amount above the

surface of the disk.

This procedure was then repeated with water, 1 M

sodium hydroxide, and water. In each case, a small amount

of the liquid was always left above the disk so that the disk

was kept wet.

Solid phase extraction of iodine

Usually, the maximum volume of water sample that can be

extracted by a single solid extraction disk is 1 L. However,

the 129I/127I isotopic ratio in environmental water in Japan

is very low, so more than 1 L of water had to be extracted

for precise measurement of the isotopic ratio. To determine

the effect of the water volume on iodine recovery by the

extraction disk, a pure water sample and a sample of river

water to which a stable iodine carrier had been added were

extracted with one disk and the recovery of iodine carrier

was determined by ICP-MS.

After determining the maximum water sample volume for

quantitative extraction with a solid phase extraction disk, we

analyzed samples spiked with a high-level 129I standard to

validate this analysis method for iodine and to show the

reproducibility of the results. We used the NIST SRM 3231

high-level 129I isotopic standard for spiking. Both the low-

level (129I/127I = 0.981 9 10-6 ± 0.012 9 10-6) and

high-level (0.982 9 10-8 ± 0.012 9 10-8) SRM 3231

standards were available, but the isotopic ratios of both were

too high to be measured with the JAEA AMS system. To

prevent contamination of the spectrometer from measure-

ment of the high isotopic SRM, the high-level SRM was

diluted by adding iodine carrier. Then, we spiked river and

pond water samples collected before the Fukushima accident

with the diluted standard before analysis. The detailed

extraction procedures are as follows.

Water samples were filtered through a 0.1 lm membrane

filter (TOYO ADVANTEC, Tokyo, Japan) into a beaker

before the analysis. Then, 2.5 mL of 10 w/v % sodium sul-

fate (Na2SO3) and 1 mg of iodine carrier were added to 5 or

10 L of water and the mixture was stirred well. The sample

was poured into the filtering reservoir and a vacuum was

applied. The sample flow rate was about 200 mL/min. After

the sample had been completely transferred into the filtering

reservoir, the beaker was washed with a small amount of pure

water and the wash water was also transferred to the reser-

voir. After the sample extraction, the disk was washed with

15 mL of water. Then, a disposable centrifuge tube (50 mL)

was placed under the filtration apparatus and 20 mL of 1 M

HNO3 was added to the reservoir to elute the iodine. After

5 mL of HNO3 had been pulled through the extraction disk

under vacuum, the vacuum was vented and the disk was left

for 1 min. Then, the vacuum was applied again and the

HNO3 was aspirated at a rate of 10 mL/min. After the aspi-

ration, more vacuum was applied to collect the residual

HNO3. The extraction disk was then discarded, and the fil-

tering reservoir was washed with water to transfer the

residual HNO3 into the centrifuge tube.

76 J Radioanal Nucl Chem (2014) 301:75–80

123

After all the HNO3 was collected in the centrifuge tube,

an Ag? carrier was added to precipitate silver iodide (AgI).

To prevent AgI decomposition by light, the tube was kept

wrapped with aluminum foil. The tube containing the AgI

was centrifuged at 1,0009g for 5 min and the supernatant

was discarded. The AgI precipitate was washed three times

with water, one time with 28 % ammonium hydroxide, and

another three times with water. Then, the washed AgI was

transferred to a microtube and dried in a desiccator.

AMS sample preparation

The dried AgI was weighed to the nearest 0.001 mg, and

then niobium powder (2.59 the AgI weight) was added to

the dried precipitate. The mixture of AgI and Nb powder

was transferred to an agate mortar and ground thoroughly to

homogenize it. Then, the homogenized powder was pressed

into a target for use as the measurement sample [10].

Study area

Samples measured for this study were collected from the

Kuji river, which flows through Fukushima and Ibaraki

prefectures, and from Ichinoseki pond in Ibaraki prefecture

(Fig. 1). The Kuji river drains central Honshu; the main

stream is 124 km long and the total length of the river

system, including tributaries, is 527 km [13]. The Kuji

river begins on Mt. Yamizo (Yamizo-san; elevation,

1,022 m), where Fukushima, Ibaraki, and Tochigi prefec-

tures meet, which is 90 km southwest of Fukushima

Daiichi nuclear power plant (NPP). Samples were collected

along the river at points 1–4, from upstream to down-

stream. Point 1 is in Fukushima prefecture and points 2–4

are in Ibaraki prefecture. Samples were collected from

November 2010 to July 2011. River and pond water sam-

ples collected 3 or 4 months before the Fukushima accident

(Table 1) were analyzed to show the background level of129I/127I in those waters.

The concentration of iodine in the river and pond water

samples was measured by using ICP-MS (Yokogawa HP-

4500). Before the accident, the iodine concentration in the

river water sample collected at point 1 was 1.1–2.2 ng/mL

and that in the pond water was 4.7 ng/mL. The river water

iodine concentrations agree well with values reported by

Kushita et al. [14].

Results and discussion

Effect of the amount of sample on iodine recovery

Quantitative extraction of the iodine carrier was successful

from volumes of up to 10 L of both the pure water and

river water, but the recovery of iodine decreased from

samples larger than 10 L. Thus, the maximum sample

volume usable for quantitative analysis is 10 L (Table 2).

Fig. 1 Sampling locations

Table 1 Sample collection dates

Sample Location ID Collection dates (dd/mm/yy)

River water Point 1 22/11/10 17/04/11 02/07/11

Point 2 11/12/10 17/04/11 02/07/11

Point 3 11/12/10 17/04/11 02/07/11

Point 4 22/11/10 17/04/11 02/07/11

Pond water – 11/12/10 17/04/11 02/07/11

J Radioanal Nucl Chem (2014) 301:75–80 77

123

Validation of the analytical method

We analyzed three spiked samples each of river water and

pond water (three replications) (Table 3). The 129I/127I

isotopic ratio in the diluted SRM was calculated to be

4.7 9 10-10. To confirm this calculated ratio, AgI prepared

directly from the diluted SRM solution, without extraction,

was also measured. The result of this analysis agreed with

the ratio calculated by using the certified ratio of the SRM.

The ratios in the spiked samples extracted with the

extraction disk agreed well with calculated ratios, thus

showing the validity and reproducibility of the results of

this analytical extraction method.

Background levels of 129I/127I in river water

near the Fukushima Daiichi NPP before the accident

At point 4, the most downstream point, the 129I/127I ratio

was slightly higher than at the other sampling points on the

river. The isotopic ratio in the pond water was higher than

the ratios in the river water, a trend consistent with the

results reported by Snyder et al. [15].

In the previous section, we described how the repro-

ducibility of the results obtained with this extraction

method was confirmed by analysis of samples spiked with

an NIST SRM. To confirm the reproducibility of the ana-

lytical method with real, non-spiked environmental sam-

ples, three aliquots each of a river water sample (from point

3) and the pond water sample collected before the accident

were analyzed. The isotopic ratios determined for the three

replicates agreed well, confirming the reproducibility of

results by this method (Table 4).

Results of 129I/127I measurements of river and pond

water

The changes in the 129I/127I ratios from before to after the

Fukushima accident are shown in Fig. 2. After the acci-

dent, the 129I/127I ratios in river water gradually increased

to several times the background ratios, measured in sam-

ples collected 3 or 4 months before the accident. Moreover,

the discrepancies of 129I/127I among the four river collec-

tion points were smaller than before the accident. The129I/127I ratio in the pond water sample collected in April

2011 was about 10 times the background ratio. Iodine-129

that fell into the pond would remain there longer, compared

with 129I deposited in the river, because the turnover rate of

the pond water is slow. As a result, 129I/127I was higher in

the pond water.

Very few studies on the 129I in terrestrial water samples

were carried out after the NPP accident. Matsuzaki et al.

measured the 129I concentration in terrestrial water samples

collected in Fukushima Prefecture. These concentrations

show both an increasing and decreasing trends. However,

the reason of decreasing 129I/127I ratio had not been

clear [16].

Table 2 Iodine recovery test results

Sample Analyzed

volume (L)

Recovery (%)

#1 #2 #3 Mean

Pure water 1 95 94 93 94

3 94 97 92 94

5 96 95 96 96

10 91 95 90 92

15 80 85 82 82

River water 1 98 93 94 95

3 96 95 92 94

5 94 93 93 93

10 90 92 90 91

15 81 76 84 80

Table 3 Results for samples spiked with NIST SRM 3231

Sample Replication no. 129I/127I Differences from

the spiked value (%)

River water #1 4.5 9 10-10 ± 6.0 9 10-12 -4.2

#2 4.7 9 10-10 ± 6.4 9 10-12 0

#3 4.7 9 10-10 ± 6.5 9 10-12 0

Pond water #1 4.6 9 10-10 ± 6.2 9 10-12 -2.1

#2 4.7 9 10-10 ± 6.1 9 10-12 0

#3 5.0 9 10-10 ± 6.5 9 10-12 ?6.4

NIST SRM 3231* 4.8 9 10-10 ± 6.3 9 10-12 ?2.1

Spiked NIST SRM 3231 4.7 9 10-10 –

* AgI was prepared directly, without extraction, from the diluted SRM solution

78 J Radioanal Nucl Chem (2014) 301:75–80

123

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J Radioanal Nucl Chem (2014) 301:75–80 79

123

Conclusions

A simple and rapid solid extraction method was used to

extract iodine for isotopic analysis from terrestrial water

samples. The method was validated and the reproducibility

of the results was confirmed by spiking tests with the NIST

SRM. River and pond water samples collected before and

after the Fukushima Daiichi NPP accident were analyzed

and the iodine isotopic ratio was found to have increased

after the accident, and the increase was largest in the pond

water sample, because of the slow turnover rate of the pond

water compared with the river water. Examination of

changes in the 129I/127I ratio over time in samples collected

at the same point improves our understanding of iodine

migration in the environment.

Acknowledgments This work was performed under the Common-

Use Facility Program of JAEA. The authors acknowledge the staff

members of the Mutsu AMS facility of JAEA for providing isotope

data of excellent quality.

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Big Earthquake in Japan

(11 March, 2011)

1.0E-10

1.0E-09

1.0E-08

1.0E-07

01 Nov, 2010 01 Jan, 2011 01 Mar, 2011 01 May, 2011 01 Jul, 2011

129 I

/127 I

rat

io

Sampling date

River Point 1River Point 2River Point 3River Point 4Pond

Big Earthquake in Japan(11 March, 2011)

Fig. 2 129I/127I ratios before and after the Fukushima NPP accident.

All error bars are smaller than the symbol

80 J Radioanal Nucl Chem (2014) 301:75–80

123