Journal of Environmental Radioactivity 139 (2015) 344e350
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Analysis of 129I in the soils of Fukushima Prefecture: preliminary reconstruction of 131I deposition related to the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) Yasuyuki Muramatsu a, *, Hiroyuki Matsuzaki b, Chiaki Toyama a, Takeshi Ohno a a b
Faculty of Science, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-0032, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 December 2013 Received in revised form 3 May 2014 Accepted 11 May 2014 Available online 13 June 2014
Iodine-131 is one of the most critical radionuclides to be monitored after release from reactor accidents due to the tendency for this nuclide to accumulate in the human thyroid gland. However, there are not enough data related to the reactor accident in Fukushima, Japan to provide regional information on the deposition of this short-lived nuclide (half-life ¼ 8.02 d). In this study we have focused on the long-lived iodine isotope, 129I (half-life of 1.57 107 y), and analyzed it by accelerator mass spectrometry (AMS) for surface soil samples collected at various locations in Fukushima Prefecture. In order to obtain information on the 131I/129I ratio released from the accident, we have determined 129I concentrations in 82 soil samples in which 131I concentrations were previously determined. There was a strong correlation (R2 ¼ 0.84) between the two nuclides, suggesting that the 131I levels in soil samples following the accident can be estimated through the analysis of 129I. We have also examined the possible influence from 129m Te on 129I, and found no significant effect. In order to construct a deposition map of 131I, we determined the 129I concentrations (Bq/kg) in 388 soil samples collected from different locations in Fukushima Prefecture and the deposition densities (Bq/m2) of 131I were reconstructed from the results. © 2014 Elsevier Ltd. All rights reserved.
Keywords: 129 I 131 I Fukushima Soil Deposition density Reconstruction
1. Introduction Large quantities of radioactivity were released during March 2011 following the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) which is operated by Tokyo Electronic Power Company (TEPCO) (Chino et al., 2011; Yoshida and Takahashi, 2012; Terada et al., 2012). The amounts of radionuclides released are ranked in the following order: 133Xe (half-life: 5.2 d), 131I (halflife: 8.0 d), 132Te (half-life: 3.2 d), 133I (half-life: 20.8 h), 134Cs (halflife: 2.1 y) and 137Cs (half-life: 30 y), (NISA, 2011). Following the accident, we have carried out intensive studies on the distribution and behaviour of these nuclides in the environment (e.g. Ohno et al., 2012; Muramatsu et al., 2014). Although the activity of 133 Xe showed the highest value, radiation effects on humans are expected to be low due to the non-reactivity of this noble gas. On the other hand, radioiodine and radiocesium are two of the most important radionuclides to be considered following the accident,
* Corresponding author. E-mail address: [email protected] (Y. Muramatsu). http://dx.doi.org/10.1016/j.jenvrad.2014.05.007 0265-931X/© 2014 Elsevier Ltd. All rights reserved.
in terms of radiation health. The total amount of 131I and 137Cs discharged into the atmosphere were estimated to be approximately 2.0 1017and 1.3 1016 Bq, respectively (Kobayashi et al., 2013). Special attention must be paid to 131I because of its affinity for the thyroid gland. Although the amount of 131I released from FDNPP was about one tenth of that released from the Chernobyl accident (UNSCEAR, 2000), it is necessary to obtain information regarding the deposition of this nuclide in different locations in Fukushima Prefecture. In order to understand the dispersion of radionuclides emitted from FDNPP, a large-scale soil sampling campaign was organized in June 2011 by MEXT (Ministry of Education, Culture, Sports, Science and Technology) with the cooperation of many researchers from a variety of universities and institutes (MEXT, 2011a; MEXT, 2011b; Yoshida and Takahashi, 2012; Saito et al., 2014). Surface soil samples (0e5 cm in depth) were collected systematically from about 2200 locations roughly within an 80 km zone surrounding FDNPP. Five samples were collected, in most cases, from each location so the overall number of the collected samples exceeded 10,000. Immediately after the sampling, all samples were analyzed for the concentrations of radionuclides by
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
gamma-spectrometry at different laboratories. From the measured results, an average value was calculated from five samples to obtain a representative deposition density (Bq/m2) for each location (reference date: June 14, 2011). Radiocesium (134Cs and 137Cs) was detected at all locations and deposition maps for these nuclides were constructed (MEXT, 2011a; Saito et al., 2014). These maps are useful in understanding the dispersion of radiocesium and the spatial distribution of the two radiocesium isotopes following the accident. In the case of 131I, however, its short halflife (8 d) made it impossible to obtain adequate sample coverage that would permit direct determination of the regional deposition patterns within the prefecture and surrounding areas. Only about 400 locations had detectable 131I, comprising less than 20% of the measured 2200 locations. A map for 131I was also constructed by MEXT (MEXT, 2011b, Fig. 3 in Saito et al., 2014), although the resolution was not sufficient. On the other hand, small amounts of 129I (half-life of 1.57 107 y) produced in the reactor were also released during the accident (Miyake et al., 2012; Xu et al., 2013). It is known that iodine (both as iodide and iodate) has a high distribution coefficient (Kd) in most Japanese soils (Muramatsu et al., 1990; Yoshida et al., 1992, 1995). Therefore, radioiodine deposited on the ground is expected to be retained tightly in surface soil. In a previous study (Ohno et al., 2012), the vertical profile of radionuclides in soil showed that more than 90% of 131I was found to be distributed within about 5 cm of the surface in soil from four different places studied in Koriyama, Fukushima Prefecture, following the accident. Due to the long halflife of 129I and high adsorbability on soil particles as mentioned above, analysis of 129I in surface soil should provide useful information on the 131I deposited on soil. Following the Chernobyl accident, one of the authors (Y. M.) cooperated on measurements of 129I in soil by neutron activation analysis (NAA) in order to estimate the deposition of 131I in Poland (Pietrzak-Flis et al., 2003). Since NAA for 129I is a time consuming method and requires a research reactor for analysis, number of places where 131I deposition density was reconstructed are limited. Thereafter, we developed a highly sensitive method for the determination of ultra-low levels of 129I in soil by accelerator mass spectrometry (AMS) (Matsuzaki et al., 2007; Muramatsu et al., 2008). We applied this method successfully for the determination of 129I in Chernobyl soil samples (Sahoo et al., 2009) and have shown the feasibility of this method for reconstructing 131I deposition densities following nuclear accidents. In this study, we use AMS to determine 129I in the soil samples collected in different locations of Fukushima Prefecture (MEXT, 2011a) in order to reconstruct a 131I deposition map for Fukushima Prefecture. For the reconstruction of 131I deposition densities, it is essential to know the ratio of 131I/129I deposited on soil surfaces. For this purpose, we initially selected soil samples in which 131I had already been measured, and analyzed them for 129I. We also examined a possible additional source of 129I due to the decay of 129m Te released from the accident, which might affect the observed 131 129 I/ I ratios. In this paper we report our preliminary results on the 131I/129I ratio released at the accident and on the 131I deposition densities reconstructed for 388 locations with no 131I deposition data. 2. Samples and methods 2.1. Sample collection and preparation We have used samples that were collected during the abovementioned soil sampling campaign of MEXT performed in June 2011 (MEXT, 2011a; MEXT, 2011b; Yoshida and Takahashi, 2012; Saito et al., 2014). Sampling sites were selected systematically to
345
fall within a 2 km grid space covering an 80 km zone and within a 10 km grid space for the surrounding areas (80e100 km zone). There were altogether about 2200 locations where samples were collected by the MEXT sampling campaign, except for locations where soil sampling was difficult (e.g. ravines, cliffs, etc.). Altogether, 340 people from 24 organizations (universities and institutions) participated in the sampling. Samples were collected at up to five points per grid location. Uncultivated soils were collected from a depth of 0e5 cm and were at first put in a plastic bag and mixed manually by simply crumpling the bag. Then the sample was placed in a 100 mL plastic vessel (U-8 vessel, Sekiya-Rika Co., Tokyo), which is in common use in Japan as a sample container for measurements using a Ge-detector. In this study of radioiodine, we were able to use samples from the above-mentioned collection. In order to obtain information on the 131I/129I ratio released from the accident, we selected 82 samples in which 131I concentrations were previously determined (MEXT, 2011b). About half of them were collected from north of the FDNPP and the other half were from south of the FDNPP. In addition to these samples, we have selected 388 soil samples from the areas where 131I data were lacking. The soil samples, which were stored in the above-mentioned vessels, were put into a plastic bag and homogenised by hand. About one third of the homogenised sample was moved into a glass vessel and dried at 90 C over night. The dried sample was powdered using a ball mill, and was then subjected to iodine separation. 2.2. Separation of iodine from soil samples and determination of stable iodine Separation of iodine was carried out utilizing a pyrohydrolysis procedure based on the method developed by Schnetger and Muramatsu (1996). The powdered sample (usually 0.2e0.5 g) was weighed in a ceramic boat and mixed with V2O5. Then it was placed in a quartz tube and heated at 1000 C for about 30 min under a flow of oxygen gas. The iodine released by heating was collected with a trap containing 1% TMAH (tetramethyl ammonium hydroxide) and 0.1% Na2SO3 solutions. For the analysis of stable iodine, a 0.5 ml aliquot of the trap solution was taken and diluted with de-ionized water to an iodine concentration between 2 and 100 ppb, into which 0.5% TMAH was added. In order to compensate for drift during the pulse measurement, an internal standard (Te2þ or Csþ) was added. The diluted sample solution was measured for iodine by ICP-MS (Agilent 7700 or Agilent 8800). Standard solutions containing different concentrations of iodide were prepared to make a calibration curve. 2.3. Purification of iodine by solvent extraction In order to prepare samples for 129I determination by AMS, iodide (I) carrier (4 mg I), in which the 129I/127I ratio is known, and Na2SO3 solution (1 ml of 2% solution) were added to convert all iodine species to I. In order to purify the iodine fraction, a 0.1 ml of 1% NaNO2 solution was added under acidic condition to form elemental iodine (I2) and extracted into an organic solvent (CCl4). Then it was back-extracted into an aqueous Na2SO3 solution as I. A silver nitrate solution was added to precipitate iodide as AgI. The precipitate, which was separated by centrifuging, was washed with ammonia solution to dissolve impurities such as AgCl. Details on the separation procedures were described in a previous paper (Muramatsu et al., 2008). Finally, the AgI precipitate was freezedried, and then mixed with Nb powder and pressed into a cathode cone to prepare the AMS target. The standard used for the
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determination of 129I/127I ratio was Z94-0596 prepared by Prime Lab., University Purdue. We also determined the 129I/127I ratio of the KI solution (Kanto Chemicals Co.) in order to examine the carrier blank value (129I/127I ratio: 1.8 1013). Measurements of 129I/127I ratio were performed at the MALTAMS facility at the University of Tokyo. Details on the method and the measurement conditions by AMS were described by Matsuzaki et al. (2007). 3. Results and discussion 3.1. Relationship between
129
I and
131
I in soil
Deposition density of 131I (Bq/m2)
Results obtained for 129I in 82 soil samples are listed in Appendix together with 131I data compiled by MEXT (2011b). Stable iodine concentrations (127I) and 129I/127I ratios are also listed in the table. To normalize the data, all samples were decay corrected to 14 June 2011, the end of the sampling campaign. Since it is necessary to distinguish measurement uncertainties from spatial variability in the deposition density, we have estimated both the analytical uncertainty and the variability among samples from a given grid cell. Analytical uncertainty from the AMS measurements of 129I is in most cases about 3%, showing good precision for the AMS analyses in this study. On the other hand, uncertainties in the gamma spectrometry for the 131I measurements were 5e30% (mainly 20% or higher). Larger relative errors are related mainly to decreased 131I activity (due to its short half-life) by the time of the measurement in June 2011. Variability in the deposition density observed for 131I in 5 samples from a 2 2 km mesh was on average about 30% (standard deviation of 5 samples). Concentrations of both 129I and 131I are plotted in Fig. 1. A close correlation (R2 ¼ 0.84) was found between the concentrations of the two nuclides. This finding suggests that the 131I levels in soil samples following the accident can be estimated through the analysis of 129I, although there is some uncertainty (about 30e40%). The 131I/129I ratio obtained from the slope of the linear regression (Fig. 2) was 9.37 103 at the sampling end date (14 June 2011). If we make a decay correction to 11 March 2011 (at accident), the atom
x
ratio of 131I/129I is estimated to be 0.048 (or 21 as the 129I/131I atom ratio). Nishihara et al. (2012) carried out a model calculation for many nuclides (including iodine isotopes) produced in the reactors of FDNPP (Reactor-1, Reactor-2 and Reactor-3) at the time of the accident using ORIGEN2 code (Nishihara et al., 2012). They obtained a 129I/131I atom ratio of 31.4 for Reactor-1, 21.9 for Reactor-2 and 20.8 for Reactor-3. Our estimated atom ratio of 129I/131I (20.8) is therefore close to the values obtained from the ORIGEN2 calculation, especially for Reactor-2 and Reactor-3. Miyake et al. (2012) determined both 131I and 129I in 27 soil samples collected from Fukushima Prefecture in late April 2011 in a separate study. They also found a good correlation between 131I and 129 I. The atom ratio of 129I/131I reported in Miyake et al. (2012) was 31.6 ± 8.9 (decay corrected to 11 March 2011). This value is also similar to our measured ratio. There are several factors that might influence the 129I/131I ratio. The proportion of these nuclides produced in the three reactors is not always constant because of the different burn time of the nuclear fuel in the reactors. The transport direction of the radioactive plume released from the different reactors may also influence the ratio at different locations. There exist also errors caused by gamma-spectrometry for the determination of 131I. In order to validate the analytical quality, the detectors were calibrated using the standard sources provided by the International Atomic Energy Agency (IAEA) and the Japan Chemical Analysis Center (JCAC), as mentioned by Saito et al. (2014). Therefore, the values obtained should be reasonable. High concentrations of 137Cs in the samples also may cause interference with the 131I peak due to Compton scattering. In contrast to the relatively large errors for gammaspectrometry, errors related to the AMS measurement are considerably smaller, as mentioned above. 3.2. Effect of
129
I produced from
131
I via
129
I in soil
131
I deposition density using the analytical
Apart from the above-mentioned 82 samples, we have analyzed I concentrations (Bq/kg) in an additional 388 soil samples in which 131I was not detected by gamma-spectrometry. Concentrations of 131I (Bq/kg) were calculated based on the measured 129I concentrations (Bq/kg) in soil samples by multiplying by the obtained 131I/129I ratio (9.37 103) mentioned above. The deposition density of 131I (Bq/m2) was calculated from the amount of 131I (Bq) in a U8 vessel and sampling area (F50 mm). Since the analysis of 129
Fig. 1. Relationship between the deposition density (Bq/m2) of samples collected from Fukushima Prefecture.
Te deposited on soil
Iodine-129 is also produced by the decay of 129mTe (half-life: 33.6 d) that was present in the reactor due to the fission of uranium fuel. This nuclide was released into the atmosphere during the accident, and subsequently was deposited on soil (MEXT, 2011c). We have calculated the amount of 129I produced from the 129mTe deposited on soil surfaces. We selected four soil samples collected from four different locations, two from north and two from south of the plant (see Table 1). Concentrations of 129mTe for these samples were determined with a Ge-detector (MEXT, 2011c). Amounts of 129 I atoms produced from the decay of 129mTe have been calculated for each soil. From the measured activity concentrations of 129I, the numbers of 129I atoms have been calculated. The proportion of 129I atoms (%) produced from 129mTe was calculated (see Table 1). As can be seen from the table, the proportion of the 129I produced from the deposited 129mTe is only about 0.2% at the time of the sampling (June 14, 2011). If we make a decay correction of 129mTe to the date of the accident, the proportion of 129I derived from 129mTe was estimated to be about 1%. Therefore, there is no appreciable contribution to the 129I concentration from the deposited 129mTe. 3.3. Reconstruction of results of 129I in soil
Deposition density of 129I (Bq/m2)
129m
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
Fig. 2. Deposition map (Bq/m2) of
131
I reconstructed from
129
I analysis in Fukushima Prefecture.
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Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
Table 1 Estimation of
129
I atoms produced from
129m
Te deposited on soil.
Sample No. (aMesh ID)
129m Te deposition density (Bq/m2)
129
I deposition density (Bq/m2)
Proportion of 129I atoms produced from129mTe (%)
23 32 47 93
6.73Eþ05 5.56Eþ04 2.31Eþ05 2.20Eþ04
2.12 0.20 1.12 0.077
0.18 0.16 0.12 0.17
(38N36) (30S06) (40N38) (50S16)
Deposition density (Bq/m2) of 129mTe is from the data of MEXT (2011c) and that of 129 I is from this study. Proportion of 129I produced from the deposited 129mTe was calculated as number of atoms. a Mesh ID: Indication of sampling location related to the distance (km) and direction (N: north or S: south) from FDNPP. For example, “38N36” indicates the location 38 km north and 36 km west from FDNPP. 129
I is time consuming, it is not practical to determine this nuclide in all five samples for every location. Therefore, we selected one representative sample for the 129I determination, in most cases using the sample with the median 137Cs deposition density value for each location. In order to estimate the average 131I deposition density (Bq/m2) for a location, we used the average of the 137Cs data for the five samples from the respective location. For each location, a ratio of the 137Cs deposition density between the “selected sample” and the “average of five samples” was calculated. Finally, the mean deposition density (Bq/m2) of 131I for each location was estimated by multiplying this ratio by the 131I value for the selected sample. The deposition densities (Bq/m2) of 131I reconstructed from the 129 I analysis for 388 locations were plotted to make a preliminary deposition map for 131I (see Fig. 2). Compared to the previous map, Fig. 3 of Saito et al. (2014) constructed from the direct measurement of 131I by gamma-spectrometry, we obtained data that filled in some areas where 131I values were lacking, specifically in the 20 km zone and in the south-west direction. There are a few discrepancies between the 131I deposition in Fig. 3 of Saito's paper (Saito et al., 2014) and that in the newly reconstructed map (Fig. 2 of this paper), such as the point just outside of 30 km line south-southwest from FDNPP, and the point just inside of 20 km line northnorthwest from FDNPP. Due to the lack of 131I deposition data in these locations in our study, the cause of the discrepancies cannot be clearly ascertained. Since only one sample from five samples exceeded the detection limit in these sampling locations, heterogeneity of the deposition may partly explain the high values (or high variation). In this paper we have not merged the values obtained from the direct measurements of 131I and the reconstructed values to plot a map. In order to combine the results obtained by gammaspectrometry and those reconstructed from 129I measurements, several other variables must be factored in, e.g. background 129I levels, variation of 131I/129I ratios. As we continue to analyze l129I in additional samples in the future, we plan to further improve on the accuracy of the reconstruction and compare it with the initial gamma-spectrometry results. From these maps a high level deposition of 131I was observed in the north-west direction, similar to the radiocesium deposition map (MEXT, 2011a). However, the spatial distribution of 131I differs from that of radiocesium (Fig. 2 of Saito et al., 2014). The reconstructed map shows dispersion of 131I in the southern direction, which is not visible on the radiocesium deposition map. The proportion of 131I compared to 137Cs is thus considerably higher in the southern direction, suggesting the plume containing higher 131 137 I/ Cs ratios moved in a southerly direction. The method of using 129I to reconstruct 131I deposition density seems to be very useful in understanding the dispersion and
distribution of radioiodine in the environment. The reconstructed data for 131I deposition could be used in the validation of dispersion models of radioiodine from FDNPP and also in the estimation of radiation dose for inhabitants due to the released 131I. Since there is considerable variation in the 131I/129I ratio between soil samples, we will determine the ratio in additional samples in which 131I values are known, to improve the estimation of 131I deposition density. There is a potential influence due to the deposition of 129I from global fallout (Toyama et al., 2012). However, the influence of 129I levels from global fallout and reprocessing emissions that existed before the Fukushima accident is smaller in comparison to the deposition density of 129I in the studied area (mostly in 60 km zone from FDNPP). For remote areas where 131I depositions were low, we will consider the background value of the 129I deposition in our future estimation to improve the accuracy. In order to understand the distribution of radioiodine in Fukushima Prefecture and surrounding areas, we are analyzing 129I in more samples for constructing a more detailed 131I deposition map. 4. Conclusions In order to understand the spatial distribution of 131I released from the accident at FDNPP, we analyzed the concentration of longlived 129I in surface soils. This nuclide was successfully detected by AMS in soils collected in Fukushima Prefecture. We have analyzed 129 I concentrations in 82 soil samples in which 131I concentrations were previously determined. Our results showed that there is a close relationship between the concentrations of 129I and 131I. The 131 129 I/ I ratio obtained from the slope of the linear regression was 9.37 103 at the sampling end date (14 June 2011). This value is comparable to the model ratio obtained using ORIGEN2 code (Nishihara et al., 2012). A negligibly small influence from 129mTe released during the accident on the 129I deposition density was found. These results indicate that the 131I deposition density following the accident can be estimated through the analysis of 129I in soil. We have used soil samples which were collected during the soil sampling campaign organized by MEXT in June 2011 and analyzed for 129I. As a result, deposition densities (Bq/m2) of 131I were reconstructed for 388 locations in Fukushima Prefecture. It is observed that the special distribution of 131I is different from that of radiocesium. Since we found variations in the 131I/129I ratios in the soil samples, we are planning to analyze more samples in which 131I values were known and re-evaluate the 131I/129I ratio released from the accident. We expect that we will be able to construct a more detailed and reliable 131I deposition map by determining more samples for 129I in the future. Acknowledgements We would like to thank Dr. Kimiaki Saito (JAEA), Dr. Satoshi Yoshida (NIRS) and Mr. Daichi Saito (MEXT) for their useful comments to initiate this study. Thanks are also due to Dr. Glen Snyder (Rice University), Dr. Jean Moran (California State University), Dr. Shun-ichi Hisamatsu (IES) and reviewers for their critical readings and improvement of English in the manuscript. We also thank Mr. Shinichiro Matsumoto (JAEA), Mr. Shigetomo Hagiwara (JAEA),Mr. Hiroshi Takemiya (JAEA), Mr. Yoshihiro Ikeuchi (JCAC), Mr. Kei Tanaka (Japan Map Center) for their technical cooperation, and Ms. Maki Honda, Mr. Nobuaki Okabe, Mr. Yasuto Miyake for their help in sample preparation and analyses. This study was supported from Ministry of Education, Culture, Sport, Science, and Technology, Japan (MEXT).
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
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Appendix Values of
131
I, 129I and
Sample no.
Mesh ID
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-
42N40 42N44 38N22 38N36 38N44 36N40 36N44 26N24 24N18 22N10 18N18 18N24 18N26 18N38 16N18 16N22 14N20 22S02 22S06 24S04 24S06 26S06 28S02 30S06 32S04 34S06 46S06 48S10 50S04 52S08 52S12 58S08 60S28 52N42 48N36 46N48 44N40 42N48 40N38 38N24 38N28 36N24 34N26 34N36 32N26 32N48 30N22 30N44 30N48 24N10 24N20 24N32 24N38 22N18 22N26 16N26 14N44 12N18 12N22 12N40 28S60 36S06 36S08 38S04 40S04 42S06 42S10 44S40 44S06 44S10
1 2 3 4 5 6 7 9 13 15 18 19 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 54 55 56 58 59 64 65 66 68 69 70 72 73 74 75 76 77 79 80 81 82 83 84 85 86 87
127
I (stable iodine) in soil samples used for the determination of
1 4 4 3 4 5 5 5 5 2 5 4 3 5 3 2 3 2 3 4 5 4 3 2 3 4 2 5 5 5 5 1 4 1 3 3 1 1 2 5 1 4 2 3 5 2 3 4 2 4 2 5 3 3 5 5 3 5 2 1 5 5 3 4 2 4 4 2 4 2
City/town name
131
I deposition (Bq/m2)
Date-shi Fukushima-shi Iidate-mura Date-shi Fukushima-shi Fukushima-shi Fukushima-shi Iidate-mura Iidate-mura Minamisoma-shi Namie-machi Namie-machi Namie-machi Nihonmatsu-shi Namie-machi Namie-machi Katsurao-mura Hirono-machi Naraha-machi Hirono-machi Hirono-machi Hirono-machi Hirono-machi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Kori-machi Date-shi Fukushima-shi Date-shi Fukushima-shi Fukushima-shi Iidate-mura Iidate-mura Iidate-mura Iidate-mura Date-shi Iidate-mura Fukushima-shi Iidate-mura Fukushima-shi Fukushima-shi Minamisoma-shi Iidate-mura Kawamata-machi Nihonmatsu-shi Iidate-mura Iidate-mura Namie-machi Nihonmatsu-shi Katsurao-mura Katsurao-mura Nihonmatsu-shi Hirono-machi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi
2.17Eþ03 2.07Eþ03 1.79Eþ03 2.29Eþ03 3.39Eþ03 1.75Eþ03 2.21Eþ03 4.61Eþ03 4.30Eþ03 3.51Eþ03 1.32Eþ04 5.14Eþ03 5.84Eþ03 8.92Eþ02 2.48Eþ04 7.28Eþ03 1.05Eþ04 2.25Eþ03 5.47Eþ03 1.87Eþ03 2.91Eþ03 1.67Eþ03 4.65Eþ03 1.76Eþ03 1.06Eþ03 7.03Eþ02 1.41Eþ03 1.12Eþ03 2.47Eþ03 1.17Eþ03 2.43Eþ03 1.33Eþ03 8.97Eþ02 2.33Eþ03 1.31Eþ03 1.95Eþ03 2.90Eþ03 2.31Eþ03 5.49Eþ03 3.43Eþ03 3.58Eþ03 4.46Eþ03 3.27Eþ03 2.93Eþ03 4.56Eþ03 1.55Eþ03 3.54Eþ03 1.29Eþ03 1.33Eþ03 2.17Eþ03 4.21Eþ03 1.55Eþ03 1.45Eþ03 3.64Eþ03 4.98Eþ03 1.62Eþ03 1.99Eþ03 5.65Eþ03 2.36Eþ03 9.57Eþ02 3.92Eþ03 4.82Eþ02 1.55Eþ03 1.18Eþ03 1.03Eþ03 9.75Eþ02 2.42Eþ03 1.03Eþ03 1.96Eþ03 1.11Eþ03
131 129
I/
I ratio.
Iodine in soil (mg/g, dry)
129
3.59Eþ00 6.10E-01 4.24Eþ00 5.90E-01 3.27Eþ00 5.20E-01 4.80E-01 2.89Eþ00 1.89Eþ00 2.12Eþ01 3.63Eþ00 2.57Eþ00 1.35Eþ00 6.90E-01 1.27Eþ01 2.26Eþ00 4.19Eþ00 5.39Eþ00 1.97Eþ01 2.27Eþ00 3.45Eþ01 5.95Eþ00 5.59Eþ00 1.26Eþ00 7.90E-01 2.47Eþ00 1.65Eþ00 6.60E-01 2.49Eþ00 4.90E-01 8.60E-01 8.00E-01 2.27Eþ01 2.86Eþ00 2.76Eþ00 2.86Eþ00 2.19Eþ00 2.71Eþ00 1.24Eþ00 5.61Eþ00 4.10E-01 2.14Eþ00 2.23Eþ00 4.28Eþ00 5.70E-01 6.91Eþ00 5.66Eþ00 3.12Eþ00 3.15Eþ00 5.42Eþ00 1.89Eþ01 1.84Eþ00 8.90E-01 2.08Eþ00 6.04Eþ00 6.00E-01 1.57Eþ00 1.38Eþ00 4.80Eþ00 6.40E-01 4.90E-01 1.84Eþ00 7.40E-01 2.42Eþ00 5.00E-01 1.45Eþ00 6.40Eþ00 5.80E-01 8.90E-01 5.26Eþ00
9.63Eþ00 2.66Eþ00 3.58Eþ00 7.67Eþ00 6.17Eþ00 2.46Eþ00 2.45Eþ00 7.12Eþ00 2.06Eþ01 6.71Eþ00 3.23Eþ01 1.28Eþ01 4.37Eþ00 1.78Eþ00 5.71Eþ01 9.41Eþ00 3.05Eþ01 9.17Eþ00 1.85Eþ01 2.42Eþ00 8.57Eþ00 1.08Eþ01 1.10Eþ01 3.38Eþ00 2.99Eþ00 2.24Eþ00 1.14Eþ00 1.24Eþ00 5.89Eþ00 1.25Eþ00 4.55Eþ00 1.16Eþ00 3.17Eþ00 1.91Eþ00 2.17Eþ00 5.06Eþ00 3.21Eþ00 3.26Eþ00 3.95Eþ01 6.06Eþ00 4.71Eþ00 4.43Eþ00 6.28Eþ00 7.92Eþ00 6.32Eþ00 3.57Eþ00 6.17Eþ00 2.69Eþ00 2.07Eþ00 3.13Eþ00 1.28Eþ01 2.74Eþ00 2.58Eþ00 7.52Eþ00 1.87Eþ01 1.99Eþ00 4.63Eþ00 1.36Eþ01 6.14Eþ00 1.63Eþ00 4.71Eþ00 1.47Eþ00 5.02Eþ00 4.21Eþ00 1.90Eþ00 1.87Eþ00 7.85Eþ00 1.62Eþ00 2.93Eþ00 2.40Eþ00
I in soil (mBq/kg)
129 127
I/
I ratio in soil
4.43E-07 6.68E-07 1.29E-07 2.00E-06 2.89E-07 7.17E-07 7.83E-07 3.77E-07 1.67E-06 4.86E-08 1.36E-06 7.64E-07 4.63E-07 3.95E-07 6.22E-07 6.38E-07 9.41E-07 2.61E-07 1.44E-07 1.63E-07 3.81E-08 2.80E-07 3.01E-07 4.12E-07 5.79E-07 1.39E-07 1.06E-07 2.85E-07 3.63E-07 3.90E-07 8.15E-07 2.23E-07 2.15E-08 1.02E-07 1.20E-07 2.71E-07 2.25E-07 1.85E-07 4.43E-06 1.65E-07 1.74E-06 3.17E-07 4.31E-07 2.83E-07 1.70E-06 7.91E-08 1.67E-07 1.32E-07 1.00E-07 8.85E-08 1.03E-07 2.27E-07 4.46E-07 5.53E-07 4.73E-07 5.11E-07 4.52E-07 1.51E-06 1.96E-07 3.92E-07 1.46E-06 1.23E-07 1.04E-06 2.66E-07 5.89E-07 1.97E-07 1.88E-07 4.29E-07 5.02E-07 6.99E-08
129
I deposition (Bq/m2)
2.10E-01 1.50E-01 1.32E-01 2.95E-01 3.13E-01 1.54E-01 1.77E-01 3.29E-01 6.08E-01 2.75E-01 1.34Eþ00 6.27E-01 2.24E-01 6.50E-02 2.39Eþ00 5.10E-01 7.46E-01 3.41E-01 6.74E-01 1.82E-01 3.37E-01 7.04E-01 5.06E-01 2.08E-01 1.20E-01 9.50E-02 5.50E-02 8.10E-02 2.63E-01 7.10E-02 2.52E-01 7.80E-02 1.16E-01 9.80E-02 9.60E-02 1.93E-01 1.81E-01 1.61E-01 1.25Eþ00 3.15E-01 2.71E-01 2.83E-01 3.49E-01 2.40E-01 3.84E-01 1.09E-01 2.64E-01 1.22E-01 1.10E-01 1.60E-01 5.21E-01 1.37E-01 1.50E-01 4.16E-01 7.06E-01 1.17E-01 1.74E-01 6.52E-01 2.78E-01 6.50E-02 2.91E-01 8.20E-02 2.51E-01 1.05E-01 1.47E-01 9.00E-02 3.47E-01 1.16E-01 1.66E-01 1.49E-01 (continued on next page)
350
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
(continued ) Sample no.
Mesh ID
AAAAAAAAAAAA-
46S12 46S14 46S16 48S06 48S16 50S16 52S04 52S10 52S14 54S06 58S10 58S28
88 89 90 91 92 93 94 95 96 97 98 99
3 2 1 1 5 2 2 1 2 2 4 5
City/town name
131
I deposition (Bq/m2)
Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi
1.04Eþ03 1.12Eþ03 8.67Eþ02 2.55Eþ03 1.41Eþ03 7.88Eþ02 1.90Eþ03 1.02Eþ03 1.30Eþ03 1.77Eþ03 1.28Eþ03 9.34Eþ02
Iodine in soil (mg/g, dry)
129
3.03Eþ00 2.16Eþ00 1.44Eþ00 2.50E-01 5.70E-01 1.48Eþ00 9.82Eþ00 7.60E-01 2.48Eþ00 2.58Eþ00 8.86Eþ00 4.53Eþ00
2.67Eþ00 2.15Eþ00 3.07Eþ00 2.79Eþ00 1.36Eþ00 1.57Eþ00 5.46Eþ00 1.04Eþ00 4.47Eþ00 2.64Eþ00 1.80Eþ00 1.46Eþ00
I in soil (mBq/kg)
129 127
I/
I ratio in soil
1.35E-07 1.52E-07 3.27E-07 1.70E-06 3.66E-07 1.62E-07 8.52E-08 2.11E-07 2.76E-07 1.57E-07 3.12E-08 4.92E-08
129
I deposition (Bq/m2)
1.69E-01 7.80E-02 1.11E-01 1.93E-01 7.70E-02 7.90E-02 1.66E-01 5.80E-02 1.31E-01 1.28E-01 9.10E-02 7.10E-02
(Note) 129I deposition (mBq/m2) was converted from the measured 129I concentration (Bq/kg) based on the amount of soil collected from 0 to 5 cm using a U8 vessel (5 cm diameter). 131 I deposition (Bq/m2) was calculated from the estimated 129I deposition (mBq/m2) data. Decay correction was made to 14 June 2011. Mesh ID: Indication of sampling location related to the distance (km) and direction (N: north or S: south) from FDNPP. For example, “42N40” indicates the location 42 km north and 40 km west from FDNPP, “22S02” indicates the location 22 km north and 2 km west from FDNPP.
References Chino, M., Nakayama, H., Nagai, H., Terada, H., Katata, G., Yamazawa, H., 2011. Preliminary estimation of release amounts of 131I and 137Cs accidentally discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphere. J. Nucl. Sci. Technol. 48, 1129e1134. Kobayashi, T., Nagai, H., Chino, M., Kawamura, H., 2013. Source term estimation of atmospheric release due to the Fukushima Dai-ichi nuclear power plant accident by atmospheric and oceanic dispersion simulations. J. Nucl. Sci. Technol. 50, 255e264. Matsuzaki, H., Muramatsu, Y., Kato, K., Yasumoto, M., Nakano, C., 2007. Development of 129I-AMS system at MALT and measurements of 129I concentrations in several Japanese soils. Nucl. Instrum. Methods Phys. Res. Sect. B 259, 721e726. MEXT, 2011a. Preparation of Distribution Map of Radiation Doses, etc. (Map of Radioactive Cesium Concentration in Soil), Organized by MEXT. August 30, 2011, in Japanese. http://radioactivity.nsr.go.jp/ja/contents/6000/5043/24/11555_0830.pdf. MEXT, 2011b. Preparation of Distribution Map of Radiation Doses, etc. (Map of Iodine 131 Concentration in Soil), Organized by MEXT. September 21, 2011, in Japanese. http://radioactivity.nsr.go.jp/ja/contents/6000/5047/view.html. MEXT, 2011c. Preparation of Distribution Map of Radiation Doses, etc. (Maps of Concentration of Tellurium 129m and Silver 110m in Soil), Organized by MEXT. October 31, 2011, in Japanese. http://radioactivity.nsr.go.jp/ja/contents/6000/ 5050/24/5600_111031_rev130701.pdf. Miyake, Y., Matsuzaki, H., Fujiwara, T., Saito, T., Yamagata, T., Honda, M., Muramatsu, Y., 2012. Isotopic ratio of radioactive iodine (129I/131I) released from Fukushima Daiichi NPP accident. Geochem. J. 46, 327e333. Muramatsu, Y., Takada, Y., Matsuzaki, H., Yoshida, S., 2008. AMS analysis of 129I in Japanese soil samples collected from background areas far from nuclear facilities. Quat. Geochronol. 3, 291e297. Muramatsu, Y., Uchida, S., Sriyotha, P., Sriyotha, K., 1990. Some considerations on the sorption and desorption phenomena of iodide and iodate on soil. Water, Air Soil. Pollut. 49, 125e138. Muramatsu, Y., Sugiyama, M., Ohno, T., Sato, Mutsuto, Sato, Mamoru, 2014. Transfer of radiocesium to forest products (in Japanese). J. Soil. Sci. Plant Nutri. Jpn. 85 (2), 117e120. NISA, 2011. Amounts of Radioactivity Released from the Accident (Errata), News Release. Nuclear and Industrial Safety Agency (NISA) (October 20, 2011, in Japanese). http://www.meti.go.jp/press/2011/10/20111020001/20111020001. pdf.
Nishihara, K., Iwamoto, H., Suyama, K., 2012. Estimation of Fuel Compositions in Fukushima-Daiichi Nuclear Power Plant. September 2012, JAEA-Data/Code 012e018 (in Japanese). Ohno, T., Muramatsu, Y., Miura, Y., Oda, K., Inagawa, N., Ogawa, H., Yamazaki, A., Toyama, C., Sato, M., 2012. Depth profiles of radioactive cesium and iodine released from the Fukushima Daiichi Nuclear Power Plant in different agricultural fields and forests. Geochem. J. 46, 287e295. Pietrzak-Flis, Z., Krajewski, P., Radwan, I., Muramatsu, Y., 2003. Retrospective evaluation of 131I deposition density and thyroid doses in Poland after the Chernobyl accident. Health Phys. 84, 698e708. Sahoo, S.K., Muramatsu, Y., Yoshida, S., Matsuzaki, H., Rühm, W., 2009. Determination of 129I and 127I concentration in soil samples from the Chernobyl 30-km zone by AMS and ICP-MS. J. Radiat. Res. 50, 325e332. Saito, K., Tanihata, I., Fujiwara, M., Saito, T., Shimoura, S., Otsuka, T., Onda, Y., Hoshi, M., Ikeuchi, Y., Takahashi, F., Kinouchi, K., Saegusa, J., Seki, S., Takemiya, H., Shibata, T., 2014. Detailed deposition density maps constructed by large-scale soil sampling for gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident. J. Environ. Radioact. submitted for publication. Schnetger, B., Muramatsu, Y., 1996. Determination of halogens, with a special reference to I, in geological and biological samples using pyrohydrolysis for preparation and ICP-MS and IC for measurement. Analyst. 121, 1627e1631. Terada, H., Katata, G., Chino, M., Nagai, H., 2012. Atmospheric discharge and dispersion of radionuclides during the Fukushima Dai-ichi nuclear power plant accident. Part II: verification of the source term and analysis of regional-scale atmospheric dispersion. J. Environ. Radioact. 112, 141e154. Toyama, C., Muramatsu, Y., Uchida, Y., Igarashi, Y., Aoyama, M., Matsuzaki, H., 2012. Variations of 129I in the atmospheric fallout of Tokyo, Japan: 1963e2003. J. Environ. Radioact. 113, 116e122. UNSCEAR Report, 2000. Effects of Ionizing Radiation, Annex J: Exposures and Effects of the Chernobyl Accident. http://www.unscear.org/docs/reports/annexj.pdf. Xu, S., Freeman, S.P., Hou, X., Watanabe, A., Yamaguchi, K., Zhang, L., 2013. Iodine isotopes in precipitation: temporal responses to 129I emissions from the Fukushima nuclear accident. Environ. Sci. Technol. 47, 10851e10859. Yoshida, S., Muramatsu, Y., Uchida, S., 1992. Studies on the sorption of I (iodide) and IO 3 (iodate) onto Andosols. Water, Air Soil. Pollut. 63, 321e329. Yoshida, S., Muramatsu, Y., Uchida, S., 1995. Adsorption of I and IO 3 onto 63 Japanese soils. Radioisotopes 44, 837e845. Yoshida, N., Takahashi, Y., 2012. Land-surface contamination by radionuclides from the Fukushima Daiichi Nuclear Power Plant accident. Elements 8, 201e206.
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Analysis of 129I in the soils of Fukushima Prefecture: preliminary reconstruction of 131I deposition related to the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) Yasuyuki Muramatsu a, *, Hiroyuki Matsuzaki b, Chiaki Toyama a, Takeshi Ohno a a b
Faculty of Science, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-0032, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 December 2013 Received in revised form 3 May 2014 Accepted 11 May 2014 Available online 13 June 2014
Iodine-131 is one of the most critical radionuclides to be monitored after release from reactor accidents due to the tendency for this nuclide to accumulate in the human thyroid gland. However, there are not enough data related to the reactor accident in Fukushima, Japan to provide regional information on the deposition of this short-lived nuclide (half-life ¼ 8.02 d). In this study we have focused on the long-lived iodine isotope, 129I (half-life of 1.57 107 y), and analyzed it by accelerator mass spectrometry (AMS) for surface soil samples collected at various locations in Fukushima Prefecture. In order to obtain information on the 131I/129I ratio released from the accident, we have determined 129I concentrations in 82 soil samples in which 131I concentrations were previously determined. There was a strong correlation (R2 ¼ 0.84) between the two nuclides, suggesting that the 131I levels in soil samples following the accident can be estimated through the analysis of 129I. We have also examined the possible influence from 129m Te on 129I, and found no significant effect. In order to construct a deposition map of 131I, we determined the 129I concentrations (Bq/kg) in 388 soil samples collected from different locations in Fukushima Prefecture and the deposition densities (Bq/m2) of 131I were reconstructed from the results. © 2014 Elsevier Ltd. All rights reserved.
Keywords: 129 I 131 I Fukushima Soil Deposition density Reconstruction
1. Introduction Large quantities of radioactivity were released during March 2011 following the accident at Fukushima Daiichi Nuclear Power Plant (FDNPP) which is operated by Tokyo Electronic Power Company (TEPCO) (Chino et al., 2011; Yoshida and Takahashi, 2012; Terada et al., 2012). The amounts of radionuclides released are ranked in the following order: 133Xe (half-life: 5.2 d), 131I (halflife: 8.0 d), 132Te (half-life: 3.2 d), 133I (half-life: 20.8 h), 134Cs (halflife: 2.1 y) and 137Cs (half-life: 30 y), (NISA, 2011). Following the accident, we have carried out intensive studies on the distribution and behaviour of these nuclides in the environment (e.g. Ohno et al., 2012; Muramatsu et al., 2014). Although the activity of 133 Xe showed the highest value, radiation effects on humans are expected to be low due to the non-reactivity of this noble gas. On the other hand, radioiodine and radiocesium are two of the most important radionuclides to be considered following the accident,
* Corresponding author. E-mail address: [email protected] (Y. Muramatsu). http://dx.doi.org/10.1016/j.jenvrad.2014.05.007 0265-931X/© 2014 Elsevier Ltd. All rights reserved.
in terms of radiation health. The total amount of 131I and 137Cs discharged into the atmosphere were estimated to be approximately 2.0 1017and 1.3 1016 Bq, respectively (Kobayashi et al., 2013). Special attention must be paid to 131I because of its affinity for the thyroid gland. Although the amount of 131I released from FDNPP was about one tenth of that released from the Chernobyl accident (UNSCEAR, 2000), it is necessary to obtain information regarding the deposition of this nuclide in different locations in Fukushima Prefecture. In order to understand the dispersion of radionuclides emitted from FDNPP, a large-scale soil sampling campaign was organized in June 2011 by MEXT (Ministry of Education, Culture, Sports, Science and Technology) with the cooperation of many researchers from a variety of universities and institutes (MEXT, 2011a; MEXT, 2011b; Yoshida and Takahashi, 2012; Saito et al., 2014). Surface soil samples (0e5 cm in depth) were collected systematically from about 2200 locations roughly within an 80 km zone surrounding FDNPP. Five samples were collected, in most cases, from each location so the overall number of the collected samples exceeded 10,000. Immediately after the sampling, all samples were analyzed for the concentrations of radionuclides by
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
gamma-spectrometry at different laboratories. From the measured results, an average value was calculated from five samples to obtain a representative deposition density (Bq/m2) for each location (reference date: June 14, 2011). Radiocesium (134Cs and 137Cs) was detected at all locations and deposition maps for these nuclides were constructed (MEXT, 2011a; Saito et al., 2014). These maps are useful in understanding the dispersion of radiocesium and the spatial distribution of the two radiocesium isotopes following the accident. In the case of 131I, however, its short halflife (8 d) made it impossible to obtain adequate sample coverage that would permit direct determination of the regional deposition patterns within the prefecture and surrounding areas. Only about 400 locations had detectable 131I, comprising less than 20% of the measured 2200 locations. A map for 131I was also constructed by MEXT (MEXT, 2011b, Fig. 3 in Saito et al., 2014), although the resolution was not sufficient. On the other hand, small amounts of 129I (half-life of 1.57 107 y) produced in the reactor were also released during the accident (Miyake et al., 2012; Xu et al., 2013). It is known that iodine (both as iodide and iodate) has a high distribution coefficient (Kd) in most Japanese soils (Muramatsu et al., 1990; Yoshida et al., 1992, 1995). Therefore, radioiodine deposited on the ground is expected to be retained tightly in surface soil. In a previous study (Ohno et al., 2012), the vertical profile of radionuclides in soil showed that more than 90% of 131I was found to be distributed within about 5 cm of the surface in soil from four different places studied in Koriyama, Fukushima Prefecture, following the accident. Due to the long halflife of 129I and high adsorbability on soil particles as mentioned above, analysis of 129I in surface soil should provide useful information on the 131I deposited on soil. Following the Chernobyl accident, one of the authors (Y. M.) cooperated on measurements of 129I in soil by neutron activation analysis (NAA) in order to estimate the deposition of 131I in Poland (Pietrzak-Flis et al., 2003). Since NAA for 129I is a time consuming method and requires a research reactor for analysis, number of places where 131I deposition density was reconstructed are limited. Thereafter, we developed a highly sensitive method for the determination of ultra-low levels of 129I in soil by accelerator mass spectrometry (AMS) (Matsuzaki et al., 2007; Muramatsu et al., 2008). We applied this method successfully for the determination of 129I in Chernobyl soil samples (Sahoo et al., 2009) and have shown the feasibility of this method for reconstructing 131I deposition densities following nuclear accidents. In this study, we use AMS to determine 129I in the soil samples collected in different locations of Fukushima Prefecture (MEXT, 2011a) in order to reconstruct a 131I deposition map for Fukushima Prefecture. For the reconstruction of 131I deposition densities, it is essential to know the ratio of 131I/129I deposited on soil surfaces. For this purpose, we initially selected soil samples in which 131I had already been measured, and analyzed them for 129I. We also examined a possible additional source of 129I due to the decay of 129m Te released from the accident, which might affect the observed 131 129 I/ I ratios. In this paper we report our preliminary results on the 131I/129I ratio released at the accident and on the 131I deposition densities reconstructed for 388 locations with no 131I deposition data. 2. Samples and methods 2.1. Sample collection and preparation We have used samples that were collected during the abovementioned soil sampling campaign of MEXT performed in June 2011 (MEXT, 2011a; MEXT, 2011b; Yoshida and Takahashi, 2012; Saito et al., 2014). Sampling sites were selected systematically to
345
fall within a 2 km grid space covering an 80 km zone and within a 10 km grid space for the surrounding areas (80e100 km zone). There were altogether about 2200 locations where samples were collected by the MEXT sampling campaign, except for locations where soil sampling was difficult (e.g. ravines, cliffs, etc.). Altogether, 340 people from 24 organizations (universities and institutions) participated in the sampling. Samples were collected at up to five points per grid location. Uncultivated soils were collected from a depth of 0e5 cm and were at first put in a plastic bag and mixed manually by simply crumpling the bag. Then the sample was placed in a 100 mL plastic vessel (U-8 vessel, Sekiya-Rika Co., Tokyo), which is in common use in Japan as a sample container for measurements using a Ge-detector. In this study of radioiodine, we were able to use samples from the above-mentioned collection. In order to obtain information on the 131I/129I ratio released from the accident, we selected 82 samples in which 131I concentrations were previously determined (MEXT, 2011b). About half of them were collected from north of the FDNPP and the other half were from south of the FDNPP. In addition to these samples, we have selected 388 soil samples from the areas where 131I data were lacking. The soil samples, which were stored in the above-mentioned vessels, were put into a plastic bag and homogenised by hand. About one third of the homogenised sample was moved into a glass vessel and dried at 90 C over night. The dried sample was powdered using a ball mill, and was then subjected to iodine separation. 2.2. Separation of iodine from soil samples and determination of stable iodine Separation of iodine was carried out utilizing a pyrohydrolysis procedure based on the method developed by Schnetger and Muramatsu (1996). The powdered sample (usually 0.2e0.5 g) was weighed in a ceramic boat and mixed with V2O5. Then it was placed in a quartz tube and heated at 1000 C for about 30 min under a flow of oxygen gas. The iodine released by heating was collected with a trap containing 1% TMAH (tetramethyl ammonium hydroxide) and 0.1% Na2SO3 solutions. For the analysis of stable iodine, a 0.5 ml aliquot of the trap solution was taken and diluted with de-ionized water to an iodine concentration between 2 and 100 ppb, into which 0.5% TMAH was added. In order to compensate for drift during the pulse measurement, an internal standard (Te2þ or Csþ) was added. The diluted sample solution was measured for iodine by ICP-MS (Agilent 7700 or Agilent 8800). Standard solutions containing different concentrations of iodide were prepared to make a calibration curve. 2.3. Purification of iodine by solvent extraction In order to prepare samples for 129I determination by AMS, iodide (I) carrier (4 mg I), in which the 129I/127I ratio is known, and Na2SO3 solution (1 ml of 2% solution) were added to convert all iodine species to I. In order to purify the iodine fraction, a 0.1 ml of 1% NaNO2 solution was added under acidic condition to form elemental iodine (I2) and extracted into an organic solvent (CCl4). Then it was back-extracted into an aqueous Na2SO3 solution as I. A silver nitrate solution was added to precipitate iodide as AgI. The precipitate, which was separated by centrifuging, was washed with ammonia solution to dissolve impurities such as AgCl. Details on the separation procedures were described in a previous paper (Muramatsu et al., 2008). Finally, the AgI precipitate was freezedried, and then mixed with Nb powder and pressed into a cathode cone to prepare the AMS target. The standard used for the
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determination of 129I/127I ratio was Z94-0596 prepared by Prime Lab., University Purdue. We also determined the 129I/127I ratio of the KI solution (Kanto Chemicals Co.) in order to examine the carrier blank value (129I/127I ratio: 1.8 1013). Measurements of 129I/127I ratio were performed at the MALTAMS facility at the University of Tokyo. Details on the method and the measurement conditions by AMS were described by Matsuzaki et al. (2007). 3. Results and discussion 3.1. Relationship between
129
I and
131
I in soil
Deposition density of 131I (Bq/m2)
Results obtained for 129I in 82 soil samples are listed in Appendix together with 131I data compiled by MEXT (2011b). Stable iodine concentrations (127I) and 129I/127I ratios are also listed in the table. To normalize the data, all samples were decay corrected to 14 June 2011, the end of the sampling campaign. Since it is necessary to distinguish measurement uncertainties from spatial variability in the deposition density, we have estimated both the analytical uncertainty and the variability among samples from a given grid cell. Analytical uncertainty from the AMS measurements of 129I is in most cases about 3%, showing good precision for the AMS analyses in this study. On the other hand, uncertainties in the gamma spectrometry for the 131I measurements were 5e30% (mainly 20% or higher). Larger relative errors are related mainly to decreased 131I activity (due to its short half-life) by the time of the measurement in June 2011. Variability in the deposition density observed for 131I in 5 samples from a 2 2 km mesh was on average about 30% (standard deviation of 5 samples). Concentrations of both 129I and 131I are plotted in Fig. 1. A close correlation (R2 ¼ 0.84) was found between the concentrations of the two nuclides. This finding suggests that the 131I levels in soil samples following the accident can be estimated through the analysis of 129I, although there is some uncertainty (about 30e40%). The 131I/129I ratio obtained from the slope of the linear regression (Fig. 2) was 9.37 103 at the sampling end date (14 June 2011). If we make a decay correction to 11 March 2011 (at accident), the atom
x
ratio of 131I/129I is estimated to be 0.048 (or 21 as the 129I/131I atom ratio). Nishihara et al. (2012) carried out a model calculation for many nuclides (including iodine isotopes) produced in the reactors of FDNPP (Reactor-1, Reactor-2 and Reactor-3) at the time of the accident using ORIGEN2 code (Nishihara et al., 2012). They obtained a 129I/131I atom ratio of 31.4 for Reactor-1, 21.9 for Reactor-2 and 20.8 for Reactor-3. Our estimated atom ratio of 129I/131I (20.8) is therefore close to the values obtained from the ORIGEN2 calculation, especially for Reactor-2 and Reactor-3. Miyake et al. (2012) determined both 131I and 129I in 27 soil samples collected from Fukushima Prefecture in late April 2011 in a separate study. They also found a good correlation between 131I and 129 I. The atom ratio of 129I/131I reported in Miyake et al. (2012) was 31.6 ± 8.9 (decay corrected to 11 March 2011). This value is also similar to our measured ratio. There are several factors that might influence the 129I/131I ratio. The proportion of these nuclides produced in the three reactors is not always constant because of the different burn time of the nuclear fuel in the reactors. The transport direction of the radioactive plume released from the different reactors may also influence the ratio at different locations. There exist also errors caused by gamma-spectrometry for the determination of 131I. In order to validate the analytical quality, the detectors were calibrated using the standard sources provided by the International Atomic Energy Agency (IAEA) and the Japan Chemical Analysis Center (JCAC), as mentioned by Saito et al. (2014). Therefore, the values obtained should be reasonable. High concentrations of 137Cs in the samples also may cause interference with the 131I peak due to Compton scattering. In contrast to the relatively large errors for gammaspectrometry, errors related to the AMS measurement are considerably smaller, as mentioned above. 3.2. Effect of
129
I produced from
131
I via
129
I in soil
131
I deposition density using the analytical
Apart from the above-mentioned 82 samples, we have analyzed I concentrations (Bq/kg) in an additional 388 soil samples in which 131I was not detected by gamma-spectrometry. Concentrations of 131I (Bq/kg) were calculated based on the measured 129I concentrations (Bq/kg) in soil samples by multiplying by the obtained 131I/129I ratio (9.37 103) mentioned above. The deposition density of 131I (Bq/m2) was calculated from the amount of 131I (Bq) in a U8 vessel and sampling area (F50 mm). Since the analysis of 129
Fig. 1. Relationship between the deposition density (Bq/m2) of samples collected from Fukushima Prefecture.
Te deposited on soil
Iodine-129 is also produced by the decay of 129mTe (half-life: 33.6 d) that was present in the reactor due to the fission of uranium fuel. This nuclide was released into the atmosphere during the accident, and subsequently was deposited on soil (MEXT, 2011c). We have calculated the amount of 129I produced from the 129mTe deposited on soil surfaces. We selected four soil samples collected from four different locations, two from north and two from south of the plant (see Table 1). Concentrations of 129mTe for these samples were determined with a Ge-detector (MEXT, 2011c). Amounts of 129 I atoms produced from the decay of 129mTe have been calculated for each soil. From the measured activity concentrations of 129I, the numbers of 129I atoms have been calculated. The proportion of 129I atoms (%) produced from 129mTe was calculated (see Table 1). As can be seen from the table, the proportion of the 129I produced from the deposited 129mTe is only about 0.2% at the time of the sampling (June 14, 2011). If we make a decay correction of 129mTe to the date of the accident, the proportion of 129I derived from 129mTe was estimated to be about 1%. Therefore, there is no appreciable contribution to the 129I concentration from the deposited 129mTe. 3.3. Reconstruction of results of 129I in soil
Deposition density of 129I (Bq/m2)
129m
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
Fig. 2. Deposition map (Bq/m2) of
131
I reconstructed from
129
I analysis in Fukushima Prefecture.
347
348
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
Table 1 Estimation of
129
I atoms produced from
129m
Te deposited on soil.
Sample No. (aMesh ID)
129m Te deposition density (Bq/m2)
129
I deposition density (Bq/m2)
Proportion of 129I atoms produced from129mTe (%)
23 32 47 93
6.73Eþ05 5.56Eþ04 2.31Eþ05 2.20Eþ04
2.12 0.20 1.12 0.077
0.18 0.16 0.12 0.17
(38N36) (30S06) (40N38) (50S16)
Deposition density (Bq/m2) of 129mTe is from the data of MEXT (2011c) and that of 129 I is from this study. Proportion of 129I produced from the deposited 129mTe was calculated as number of atoms. a Mesh ID: Indication of sampling location related to the distance (km) and direction (N: north or S: south) from FDNPP. For example, “38N36” indicates the location 38 km north and 36 km west from FDNPP. 129
I is time consuming, it is not practical to determine this nuclide in all five samples for every location. Therefore, we selected one representative sample for the 129I determination, in most cases using the sample with the median 137Cs deposition density value for each location. In order to estimate the average 131I deposition density (Bq/m2) for a location, we used the average of the 137Cs data for the five samples from the respective location. For each location, a ratio of the 137Cs deposition density between the “selected sample” and the “average of five samples” was calculated. Finally, the mean deposition density (Bq/m2) of 131I for each location was estimated by multiplying this ratio by the 131I value for the selected sample. The deposition densities (Bq/m2) of 131I reconstructed from the 129 I analysis for 388 locations were plotted to make a preliminary deposition map for 131I (see Fig. 2). Compared to the previous map, Fig. 3 of Saito et al. (2014) constructed from the direct measurement of 131I by gamma-spectrometry, we obtained data that filled in some areas where 131I values were lacking, specifically in the 20 km zone and in the south-west direction. There are a few discrepancies between the 131I deposition in Fig. 3 of Saito's paper (Saito et al., 2014) and that in the newly reconstructed map (Fig. 2 of this paper), such as the point just outside of 30 km line south-southwest from FDNPP, and the point just inside of 20 km line northnorthwest from FDNPP. Due to the lack of 131I deposition data in these locations in our study, the cause of the discrepancies cannot be clearly ascertained. Since only one sample from five samples exceeded the detection limit in these sampling locations, heterogeneity of the deposition may partly explain the high values (or high variation). In this paper we have not merged the values obtained from the direct measurements of 131I and the reconstructed values to plot a map. In order to combine the results obtained by gammaspectrometry and those reconstructed from 129I measurements, several other variables must be factored in, e.g. background 129I levels, variation of 131I/129I ratios. As we continue to analyze l129I in additional samples in the future, we plan to further improve on the accuracy of the reconstruction and compare it with the initial gamma-spectrometry results. From these maps a high level deposition of 131I was observed in the north-west direction, similar to the radiocesium deposition map (MEXT, 2011a). However, the spatial distribution of 131I differs from that of radiocesium (Fig. 2 of Saito et al., 2014). The reconstructed map shows dispersion of 131I in the southern direction, which is not visible on the radiocesium deposition map. The proportion of 131I compared to 137Cs is thus considerably higher in the southern direction, suggesting the plume containing higher 131 137 I/ Cs ratios moved in a southerly direction. The method of using 129I to reconstruct 131I deposition density seems to be very useful in understanding the dispersion and
distribution of radioiodine in the environment. The reconstructed data for 131I deposition could be used in the validation of dispersion models of radioiodine from FDNPP and also in the estimation of radiation dose for inhabitants due to the released 131I. Since there is considerable variation in the 131I/129I ratio between soil samples, we will determine the ratio in additional samples in which 131I values are known, to improve the estimation of 131I deposition density. There is a potential influence due to the deposition of 129I from global fallout (Toyama et al., 2012). However, the influence of 129I levels from global fallout and reprocessing emissions that existed before the Fukushima accident is smaller in comparison to the deposition density of 129I in the studied area (mostly in 60 km zone from FDNPP). For remote areas where 131I depositions were low, we will consider the background value of the 129I deposition in our future estimation to improve the accuracy. In order to understand the distribution of radioiodine in Fukushima Prefecture and surrounding areas, we are analyzing 129I in more samples for constructing a more detailed 131I deposition map. 4. Conclusions In order to understand the spatial distribution of 131I released from the accident at FDNPP, we analyzed the concentration of longlived 129I in surface soils. This nuclide was successfully detected by AMS in soils collected in Fukushima Prefecture. We have analyzed 129 I concentrations in 82 soil samples in which 131I concentrations were previously determined. Our results showed that there is a close relationship between the concentrations of 129I and 131I. The 131 129 I/ I ratio obtained from the slope of the linear regression was 9.37 103 at the sampling end date (14 June 2011). This value is comparable to the model ratio obtained using ORIGEN2 code (Nishihara et al., 2012). A negligibly small influence from 129mTe released during the accident on the 129I deposition density was found. These results indicate that the 131I deposition density following the accident can be estimated through the analysis of 129I in soil. We have used soil samples which were collected during the soil sampling campaign organized by MEXT in June 2011 and analyzed for 129I. As a result, deposition densities (Bq/m2) of 131I were reconstructed for 388 locations in Fukushima Prefecture. It is observed that the special distribution of 131I is different from that of radiocesium. Since we found variations in the 131I/129I ratios in the soil samples, we are planning to analyze more samples in which 131I values were known and re-evaluate the 131I/129I ratio released from the accident. We expect that we will be able to construct a more detailed and reliable 131I deposition map by determining more samples for 129I in the future. Acknowledgements We would like to thank Dr. Kimiaki Saito (JAEA), Dr. Satoshi Yoshida (NIRS) and Mr. Daichi Saito (MEXT) for their useful comments to initiate this study. Thanks are also due to Dr. Glen Snyder (Rice University), Dr. Jean Moran (California State University), Dr. Shun-ichi Hisamatsu (IES) and reviewers for their critical readings and improvement of English in the manuscript. We also thank Mr. Shinichiro Matsumoto (JAEA), Mr. Shigetomo Hagiwara (JAEA),Mr. Hiroshi Takemiya (JAEA), Mr. Yoshihiro Ikeuchi (JCAC), Mr. Kei Tanaka (Japan Map Center) for their technical cooperation, and Ms. Maki Honda, Mr. Nobuaki Okabe, Mr. Yasuto Miyake for their help in sample preparation and analyses. This study was supported from Ministry of Education, Culture, Sport, Science, and Technology, Japan (MEXT).
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
349
Appendix Values of
131
I, 129I and
Sample no.
Mesh ID
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-
42N40 42N44 38N22 38N36 38N44 36N40 36N44 26N24 24N18 22N10 18N18 18N24 18N26 18N38 16N18 16N22 14N20 22S02 22S06 24S04 24S06 26S06 28S02 30S06 32S04 34S06 46S06 48S10 50S04 52S08 52S12 58S08 60S28 52N42 48N36 46N48 44N40 42N48 40N38 38N24 38N28 36N24 34N26 34N36 32N26 32N48 30N22 30N44 30N48 24N10 24N20 24N32 24N38 22N18 22N26 16N26 14N44 12N18 12N22 12N40 28S60 36S06 36S08 38S04 40S04 42S06 42S10 44S40 44S06 44S10
1 2 3 4 5 6 7 9 13 15 18 19 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 54 55 56 58 59 64 65 66 68 69 70 72 73 74 75 76 77 79 80 81 82 83 84 85 86 87
127
I (stable iodine) in soil samples used for the determination of
1 4 4 3 4 5 5 5 5 2 5 4 3 5 3 2 3 2 3 4 5 4 3 2 3 4 2 5 5 5 5 1 4 1 3 3 1 1 2 5 1 4 2 3 5 2 3 4 2 4 2 5 3 3 5 5 3 5 2 1 5 5 3 4 2 4 4 2 4 2
City/town name
131
I deposition (Bq/m2)
Date-shi Fukushima-shi Iidate-mura Date-shi Fukushima-shi Fukushima-shi Fukushima-shi Iidate-mura Iidate-mura Minamisoma-shi Namie-machi Namie-machi Namie-machi Nihonmatsu-shi Namie-machi Namie-machi Katsurao-mura Hirono-machi Naraha-machi Hirono-machi Hirono-machi Hirono-machi Hirono-machi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Kori-machi Date-shi Fukushima-shi Date-shi Fukushima-shi Fukushima-shi Iidate-mura Iidate-mura Iidate-mura Iidate-mura Date-shi Iidate-mura Fukushima-shi Iidate-mura Fukushima-shi Fukushima-shi Minamisoma-shi Iidate-mura Kawamata-machi Nihonmatsu-shi Iidate-mura Iidate-mura Namie-machi Nihonmatsu-shi Katsurao-mura Katsurao-mura Nihonmatsu-shi Hirono-machi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi
2.17Eþ03 2.07Eþ03 1.79Eþ03 2.29Eþ03 3.39Eþ03 1.75Eþ03 2.21Eþ03 4.61Eþ03 4.30Eþ03 3.51Eþ03 1.32Eþ04 5.14Eþ03 5.84Eþ03 8.92Eþ02 2.48Eþ04 7.28Eþ03 1.05Eþ04 2.25Eþ03 5.47Eþ03 1.87Eþ03 2.91Eþ03 1.67Eþ03 4.65Eþ03 1.76Eþ03 1.06Eþ03 7.03Eþ02 1.41Eþ03 1.12Eþ03 2.47Eþ03 1.17Eþ03 2.43Eþ03 1.33Eþ03 8.97Eþ02 2.33Eþ03 1.31Eþ03 1.95Eþ03 2.90Eþ03 2.31Eþ03 5.49Eþ03 3.43Eþ03 3.58Eþ03 4.46Eþ03 3.27Eþ03 2.93Eþ03 4.56Eþ03 1.55Eþ03 3.54Eþ03 1.29Eþ03 1.33Eþ03 2.17Eþ03 4.21Eþ03 1.55Eþ03 1.45Eþ03 3.64Eþ03 4.98Eþ03 1.62Eþ03 1.99Eþ03 5.65Eþ03 2.36Eþ03 9.57Eþ02 3.92Eþ03 4.82Eþ02 1.55Eþ03 1.18Eþ03 1.03Eþ03 9.75Eþ02 2.42Eþ03 1.03Eþ03 1.96Eþ03 1.11Eþ03
131 129
I/
I ratio.
Iodine in soil (mg/g, dry)
129
3.59Eþ00 6.10E-01 4.24Eþ00 5.90E-01 3.27Eþ00 5.20E-01 4.80E-01 2.89Eþ00 1.89Eþ00 2.12Eþ01 3.63Eþ00 2.57Eþ00 1.35Eþ00 6.90E-01 1.27Eþ01 2.26Eþ00 4.19Eþ00 5.39Eþ00 1.97Eþ01 2.27Eþ00 3.45Eþ01 5.95Eþ00 5.59Eþ00 1.26Eþ00 7.90E-01 2.47Eþ00 1.65Eþ00 6.60E-01 2.49Eþ00 4.90E-01 8.60E-01 8.00E-01 2.27Eþ01 2.86Eþ00 2.76Eþ00 2.86Eþ00 2.19Eþ00 2.71Eþ00 1.24Eþ00 5.61Eþ00 4.10E-01 2.14Eþ00 2.23Eþ00 4.28Eþ00 5.70E-01 6.91Eþ00 5.66Eþ00 3.12Eþ00 3.15Eþ00 5.42Eþ00 1.89Eþ01 1.84Eþ00 8.90E-01 2.08Eþ00 6.04Eþ00 6.00E-01 1.57Eþ00 1.38Eþ00 4.80Eþ00 6.40E-01 4.90E-01 1.84Eþ00 7.40E-01 2.42Eþ00 5.00E-01 1.45Eþ00 6.40Eþ00 5.80E-01 8.90E-01 5.26Eþ00
9.63Eþ00 2.66Eþ00 3.58Eþ00 7.67Eþ00 6.17Eþ00 2.46Eþ00 2.45Eþ00 7.12Eþ00 2.06Eþ01 6.71Eþ00 3.23Eþ01 1.28Eþ01 4.37Eþ00 1.78Eþ00 5.71Eþ01 9.41Eþ00 3.05Eþ01 9.17Eþ00 1.85Eþ01 2.42Eþ00 8.57Eþ00 1.08Eþ01 1.10Eþ01 3.38Eþ00 2.99Eþ00 2.24Eþ00 1.14Eþ00 1.24Eþ00 5.89Eþ00 1.25Eþ00 4.55Eþ00 1.16Eþ00 3.17Eþ00 1.91Eþ00 2.17Eþ00 5.06Eþ00 3.21Eþ00 3.26Eþ00 3.95Eþ01 6.06Eþ00 4.71Eþ00 4.43Eþ00 6.28Eþ00 7.92Eþ00 6.32Eþ00 3.57Eþ00 6.17Eþ00 2.69Eþ00 2.07Eþ00 3.13Eþ00 1.28Eþ01 2.74Eþ00 2.58Eþ00 7.52Eþ00 1.87Eþ01 1.99Eþ00 4.63Eþ00 1.36Eþ01 6.14Eþ00 1.63Eþ00 4.71Eþ00 1.47Eþ00 5.02Eþ00 4.21Eþ00 1.90Eþ00 1.87Eþ00 7.85Eþ00 1.62Eþ00 2.93Eþ00 2.40Eþ00
I in soil (mBq/kg)
129 127
I/
I ratio in soil
4.43E-07 6.68E-07 1.29E-07 2.00E-06 2.89E-07 7.17E-07 7.83E-07 3.77E-07 1.67E-06 4.86E-08 1.36E-06 7.64E-07 4.63E-07 3.95E-07 6.22E-07 6.38E-07 9.41E-07 2.61E-07 1.44E-07 1.63E-07 3.81E-08 2.80E-07 3.01E-07 4.12E-07 5.79E-07 1.39E-07 1.06E-07 2.85E-07 3.63E-07 3.90E-07 8.15E-07 2.23E-07 2.15E-08 1.02E-07 1.20E-07 2.71E-07 2.25E-07 1.85E-07 4.43E-06 1.65E-07 1.74E-06 3.17E-07 4.31E-07 2.83E-07 1.70E-06 7.91E-08 1.67E-07 1.32E-07 1.00E-07 8.85E-08 1.03E-07 2.27E-07 4.46E-07 5.53E-07 4.73E-07 5.11E-07 4.52E-07 1.51E-06 1.96E-07 3.92E-07 1.46E-06 1.23E-07 1.04E-06 2.66E-07 5.89E-07 1.97E-07 1.88E-07 4.29E-07 5.02E-07 6.99E-08
129
I deposition (Bq/m2)
2.10E-01 1.50E-01 1.32E-01 2.95E-01 3.13E-01 1.54E-01 1.77E-01 3.29E-01 6.08E-01 2.75E-01 1.34Eþ00 6.27E-01 2.24E-01 6.50E-02 2.39Eþ00 5.10E-01 7.46E-01 3.41E-01 6.74E-01 1.82E-01 3.37E-01 7.04E-01 5.06E-01 2.08E-01 1.20E-01 9.50E-02 5.50E-02 8.10E-02 2.63E-01 7.10E-02 2.52E-01 7.80E-02 1.16E-01 9.80E-02 9.60E-02 1.93E-01 1.81E-01 1.61E-01 1.25Eþ00 3.15E-01 2.71E-01 2.83E-01 3.49E-01 2.40E-01 3.84E-01 1.09E-01 2.64E-01 1.22E-01 1.10E-01 1.60E-01 5.21E-01 1.37E-01 1.50E-01 4.16E-01 7.06E-01 1.17E-01 1.74E-01 6.52E-01 2.78E-01 6.50E-02 2.91E-01 8.20E-02 2.51E-01 1.05E-01 1.47E-01 9.00E-02 3.47E-01 1.16E-01 1.66E-01 1.49E-01 (continued on next page)
350
Y. Muramatsu et al. / Journal of Environmental Radioactivity 139 (2015) 344e350
(continued ) Sample no.
Mesh ID
AAAAAAAAAAAA-
46S12 46S14 46S16 48S06 48S16 50S16 52S04 52S10 52S14 54S06 58S10 58S28
88 89 90 91 92 93 94 95 96 97 98 99
3 2 1 1 5 2 2 1 2 2 4 5
City/town name
131
I deposition (Bq/m2)
Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi Iwaki-shi
1.04Eþ03 1.12Eþ03 8.67Eþ02 2.55Eþ03 1.41Eþ03 7.88Eþ02 1.90Eþ03 1.02Eþ03 1.30Eþ03 1.77Eþ03 1.28Eþ03 9.34Eþ02
Iodine in soil (mg/g, dry)
129
3.03Eþ00 2.16Eþ00 1.44Eþ00 2.50E-01 5.70E-01 1.48Eþ00 9.82Eþ00 7.60E-01 2.48Eþ00 2.58Eþ00 8.86Eþ00 4.53Eþ00
2.67Eþ00 2.15Eþ00 3.07Eþ00 2.79Eþ00 1.36Eþ00 1.57Eþ00 5.46Eþ00 1.04Eþ00 4.47Eþ00 2.64Eþ00 1.80Eþ00 1.46Eþ00
I in soil (mBq/kg)
129 127
I/
I ratio in soil
1.35E-07 1.52E-07 3.27E-07 1.70E-06 3.66E-07 1.62E-07 8.52E-08 2.11E-07 2.76E-07 1.57E-07 3.12E-08 4.92E-08
129
I deposition (Bq/m2)
1.69E-01 7.80E-02 1.11E-01 1.93E-01 7.70E-02 7.90E-02 1.66E-01 5.80E-02 1.31E-01 1.28E-01 9.10E-02 7.10E-02
(Note) 129I deposition (mBq/m2) was converted from the measured 129I concentration (Bq/kg) based on the amount of soil collected from 0 to 5 cm using a U8 vessel (5 cm diameter). 131 I deposition (Bq/m2) was calculated from the estimated 129I deposition (mBq/m2) data. Decay correction was made to 14 June 2011. Mesh ID: Indication of sampling location related to the distance (km) and direction (N: north or S: south) from FDNPP. For example, “42N40” indicates the location 42 km north and 40 km west from FDNPP, “22S02” indicates the location 22 km north and 2 km west from FDNPP.
References Chino, M., Nakayama, H., Nagai, H., Terada, H., Katata, G., Yamazawa, H., 2011. Preliminary estimation of release amounts of 131I and 137Cs accidentally discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphere. J. Nucl. Sci. Technol. 48, 1129e1134. Kobayashi, T., Nagai, H., Chino, M., Kawamura, H., 2013. Source term estimation of atmospheric release due to the Fukushima Dai-ichi nuclear power plant accident by atmospheric and oceanic dispersion simulations. J. Nucl. Sci. Technol. 50, 255e264. Matsuzaki, H., Muramatsu, Y., Kato, K., Yasumoto, M., Nakano, C., 2007. Development of 129I-AMS system at MALT and measurements of 129I concentrations in several Japanese soils. Nucl. Instrum. Methods Phys. Res. Sect. B 259, 721e726. MEXT, 2011a. Preparation of Distribution Map of Radiation Doses, etc. (Map of Radioactive Cesium Concentration in Soil), Organized by MEXT. August 30, 2011, in Japanese. http://radioactivity.nsr.go.jp/ja/contents/6000/5043/24/11555_0830.pdf. MEXT, 2011b. Preparation of Distribution Map of Radiation Doses, etc. (Map of Iodine 131 Concentration in Soil), Organized by MEXT. September 21, 2011, in Japanese. http://radioactivity.nsr.go.jp/ja/contents/6000/5047/view.html. MEXT, 2011c. Preparation of Distribution Map of Radiation Doses, etc. (Maps of Concentration of Tellurium 129m and Silver 110m in Soil), Organized by MEXT. October 31, 2011, in Japanese. http://radioactivity.nsr.go.jp/ja/contents/6000/ 5050/24/5600_111031_rev130701.pdf. Miyake, Y., Matsuzaki, H., Fujiwara, T., Saito, T., Yamagata, T., Honda, M., Muramatsu, Y., 2012. Isotopic ratio of radioactive iodine (129I/131I) released from Fukushima Daiichi NPP accident. Geochem. J. 46, 327e333. Muramatsu, Y., Takada, Y., Matsuzaki, H., Yoshida, S., 2008. AMS analysis of 129I in Japanese soil samples collected from background areas far from nuclear facilities. Quat. Geochronol. 3, 291e297. Muramatsu, Y., Uchida, S., Sriyotha, P., Sriyotha, K., 1990. Some considerations on the sorption and desorption phenomena of iodide and iodate on soil. Water, Air Soil. Pollut. 49, 125e138. Muramatsu, Y., Sugiyama, M., Ohno, T., Sato, Mutsuto, Sato, Mamoru, 2014. Transfer of radiocesium to forest products (in Japanese). J. Soil. Sci. Plant Nutri. Jpn. 85 (2), 117e120. NISA, 2011. Amounts of Radioactivity Released from the Accident (Errata), News Release. Nuclear and Industrial Safety Agency (NISA) (October 20, 2011, in Japanese). http://www.meti.go.jp/press/2011/10/20111020001/20111020001. pdf.
Nishihara, K., Iwamoto, H., Suyama, K., 2012. Estimation of Fuel Compositions in Fukushima-Daiichi Nuclear Power Plant. September 2012, JAEA-Data/Code 012e018 (in Japanese). Ohno, T., Muramatsu, Y., Miura, Y., Oda, K., Inagawa, N., Ogawa, H., Yamazaki, A., Toyama, C., Sato, M., 2012. Depth profiles of radioactive cesium and iodine released from the Fukushima Daiichi Nuclear Power Plant in different agricultural fields and forests. Geochem. J. 46, 287e295. Pietrzak-Flis, Z., Krajewski, P., Radwan, I., Muramatsu, Y., 2003. Retrospective evaluation of 131I deposition density and thyroid doses in Poland after the Chernobyl accident. Health Phys. 84, 698e708. Sahoo, S.K., Muramatsu, Y., Yoshida, S., Matsuzaki, H., Rühm, W., 2009. Determination of 129I and 127I concentration in soil samples from the Chernobyl 30-km zone by AMS and ICP-MS. J. Radiat. Res. 50, 325e332. Saito, K., Tanihata, I., Fujiwara, M., Saito, T., Shimoura, S., Otsuka, T., Onda, Y., Hoshi, M., Ikeuchi, Y., Takahashi, F., Kinouchi, K., Saegusa, J., Seki, S., Takemiya, H., Shibata, T., 2014. Detailed deposition density maps constructed by large-scale soil sampling for gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident. J. Environ. Radioact. submitted for publication. Schnetger, B., Muramatsu, Y., 1996. Determination of halogens, with a special reference to I, in geological and biological samples using pyrohydrolysis for preparation and ICP-MS and IC for measurement. Analyst. 121, 1627e1631. Terada, H., Katata, G., Chino, M., Nagai, H., 2012. Atmospheric discharge and dispersion of radionuclides during the Fukushima Dai-ichi nuclear power plant accident. Part II: verification of the source term and analysis of regional-scale atmospheric dispersion. J. Environ. Radioact. 112, 141e154. Toyama, C., Muramatsu, Y., Uchida, Y., Igarashi, Y., Aoyama, M., Matsuzaki, H., 2012. Variations of 129I in the atmospheric fallout of Tokyo, Japan: 1963e2003. J. Environ. Radioact. 113, 116e122. UNSCEAR Report, 2000. Effects of Ionizing Radiation, Annex J: Exposures and Effects of the Chernobyl Accident. http://www.unscear.org/docs/reports/annexj.pdf. Xu, S., Freeman, S.P., Hou, X., Watanabe, A., Yamaguchi, K., Zhang, L., 2013. Iodine isotopes in precipitation: temporal responses to 129I emissions from the Fukushima nuclear accident. Environ. Sci. Technol. 47, 10851e10859. Yoshida, S., Muramatsu, Y., Uchida, S., 1992. Studies on the sorption of I (iodide) and IO 3 (iodate) onto Andosols. Water, Air Soil. Pollut. 63, 321e329. Yoshida, S., Muramatsu, Y., Uchida, S., 1995. Adsorption of I and IO 3 onto 63 Japanese soils. Radioisotopes 44, 837e845. Yoshida, N., Takahashi, Y., 2012. Land-surface contamination by radionuclides from the Fukushima Daiichi Nuclear Power Plant accident. Elements 8, 201e206.
