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Journal of Environmental Radioactivity 110 (2012) 84e89

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Journal of Environmental Radioactivity

journal homepage: www.elsevier .com/locate / jenvrad

Radiation doses among residents living 37 km northwest of the FukushimaDai-ichi Nuclear Power Plant

Nanao Kamada a, Osamu Saito b, Satoru Endo c, Akirou Kimura d, Kiyoshi Shizuma c,*

aHiroshima Atomic Bomb Survivors Relief Foundation, 3-50-1 Kurakake, Asa-kitaku, Hiroshima 739-1743, JapanbWatari Hospital, 34 Watari-nakae-cho, Fukushima 960-8141, JapancGraduate school of Engineering, Hiroshima University 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, JapandResearch Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3 Kasumi, Minamiku, Hiroshima 734-8553, Japan

a r t i c l e i n f o

Article history:Received 15 July 2011Received in revised form20 January 2012Accepted 15 February 2012Available online 16 March 2012

Keywords:Fukushima Dai-ichi Nuclear Power PlantExternal radiation doseInternal radiation doseUrinary bioassayTohoku disaster

* Corresponding author. Tel.: þ81 824 7614; fax: þE-mail address: shizuma@hiroshima-u.ac.jp (K. Sh

0265-931X/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.jenvrad.2012.02.007

a b s t r a c t

External and internal radiation doses were estimated for 15 residents who lived approximately 37 kmnorthwest of the Fukushima Dai-ichi Nuclear Power Plant, which released radioactive plumes on March11, 2011 as the result of the Tohoku earthquake and subsequent tsunami damage. Residents wereinterviewed on where they stayed and what they ate after the incident. To estimate external dose, the airdose rate around each person’s home was measured, and cumulative effective doses up to 54 d after thedeposition were calculated. To estimate committed effective dose, urinary bioassays were performedusing a low-background Ge spectrometer on 54 d and 78e85 d after the deposition. The averagecumulative effective dose was 8.4 mSv for adults and 5.1 mSv for children. The average committedeffective dose from 134Cs and 137Cs was 0.055 mSv for adults and 0.029 mSv for children. Iodine-131 wasobserved from urinary samples of five residents, the equivalent doses for thyroid gland were 27e66 mSvat maximum. We discuss the necessity of reducing the risk of further exposure.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

A catastrophic nuclear accident occurred on March 11, 2011, atthe Fukushima Dai-ichi Nuclear Power Plant in Japan, which wasrun by the Tokyo Electric Power Company (TEPCO). Monitoring ofair and sampling of soils have been performed and are still inprogress. The external and internal radiation doses of employees ofthe damaged reactors have been reported from TEPCO (2011),however, internal radiation doses for the residents in FukushimaPrefecture were not investigated in detail despite the fact thatradioactive fallout was detected within and beyond the prefecture.In particular, radioactive plumes were not distributed uniformly,but in various directions from the power plant mainly due to wind.

Iitate Village and Kawamata Town lie about 37 km northwest ofthe power plant and is known to be one of the highly contami-nated areas (MEXT, 2011a). To date, investigation of nucleardisasters, such as the Chernobyl Nuclear Power Plant accident inthe former Soviet Union (Svendsen et al., 2010), nuclear weaponfacility accident at Mayak (Ostroumova et al., 2008) and theSemipalatinsk nuclear weapon tests (Bauer et al., 2005) has

81 824 2453.izuma).

All rights reserved.

revealed that radiation from leaked radionuclides caused a varietyof diseases. Therefore, to clarify the epidemiology of health statusof residents, internal and external doses must be investigated inthe above areas.

The purpose of this study was to estimate cumulative effec-tive doses and committed effective doses of residents in theIitate Village and Kawamata Town area. The maximum dose forthyroid gland was also estimated through urinary bioassaymethod.

2. Materials and methods

2.1. Samples

The locations of Iitate Village and Kawamata Town are shown inFig. 1. Surveyed persons were five residents (G1eG5) in KawamataTown and 10 residents in Iitate Village (G6eG15) (10 males and fivefemales; age range of 4e77 years). We interviewed the residentsabout where they stayed, what kind of food they ate and what kindof structures (Japanese-style wooden houses or concrete buildings)they lived in from March 11 to May 5. To measure internal dose,urine samples were collected twice; on May 5 (first sample, 54 dafter deposition) and from May 29 to June 6 (second sample,78e85 d after deposition).

Fig. 1. Locations of Iitate Village and Kawamata Town in Fukushima Prefecture.

a

b

Fig. 2. (a) Air dose rate (mSv/h) over time after deposition. (b) Examples of cumulativeeffective doses for residents G1 in Kawamata Twon and G7 in Iitate Village up to 54 dfrom the deposition.

N. Kamada et al. / Journal of Environmental Radioactivity 110 (2012) 84e89 85

2.2. Air dose rate

To estimate the external exposure of residents, air dose ratesover time are needed. Such data are available frommonitoring postdata at the Iitate Village and Kawamata Town offices through thehome page of Fukushima Prefecture (Fukushima, 2011). Themonitoring data are shown in Fig. 2(a). Based on the monitoringdata, the deposition date was assumed to be March 15, 2011. The airdose rate in Kawamata Town was lower than that in Iitate Village.Moreover, the air dose rates outside the homes of each residentwere measured 1 m above the ground with a scintillation surveymeter (TCS-161 Aloka Co. Ltd., Tokyo, Japan) on May 5. The surveymeter was calibrated with a standard gamma-ray field according tomanufacturer instructions. Shielding coefficients weremeasured tocorrect the external dose rate for where each resident had beenstaying. Coefficients were determined as 1, 0.8, 0.4 and 0.1 foroutside, inside a car, inside a Japanese wooden house and insidea concrete building, respectively. The coefficient of Japanesewooden house was measured for two houses at Kawamata Townand 4 houses at Iitate Village on May 5 and May 29, 2011. Thecoefficient of a car was measured for four cars. The coefficient ofconcrete building was applied for children staying at schools. Theassociated variations are about 10e30%.

Fig. 3. Typical gamma-ray spectra of 100-ml urine sample. Iodine-131, 134Cs and 137Cswere released from the accident and others are natural radionuclides.

2.3. Bioassay of urine samples

Urine samples were poured directly into a 100 ml Teflon vial(4.5 cm diameter� 6.5 cm long; inner volume, 110 ml), and a screwcap was tightly closed. Gamma-ray measurement was performedwith a low-background Ge detector (Seiko EG&G ORTEC GWL-120230-S, Tokyo, Japan) with a relative detection efficiency of 23%,which was shielded with lead of 20 cm thickness and was equippedwith an anticoincidence system (Shizuma et al., 1992). Urinesamples were measured for 20,000e50,000 s. A typical gamma-rayspectrum is shown in Fig. 3. Fission products 131I, 134Cs and 137Cs

Table 1Concentration of radionuclides in urine at the time of sampling. Samples G1eG5 areresidents in Kawamata Town and others are in Iitate Village.

Subject Age Bodyweight(kg)

131I (Bq/l) 134Cs (Bq/l) 137Cs (Bq/l)

(1st sampling)a

G1 77 57 1.80 � 0.50 4.25 � 0.68 5.12 � 0.65G2 76 53 1.70 � 0.79 9.14 � 0.93 7.17 � 1.20G3 10 48 0.61 � 0.33 2.47 � 0.42 2.05 � 0.42G4 12 40 NDc 3.48 � 0.89 2.21 � 0.84G5 14 30 ND 6.37 � 1.02 5.04 � 2.00G6 61 68 ND 3.78 � 0.77 3.49 � 0.70G7 59 63 ND 1.23 � 0.65 3.23 � 0.77G8 68 53 ND 2.04 � 0.50 2.57 � 0.48G9 54 65 ND 1.56 � 0.45 0.95 � 0.42G10 36 75 ND 2.00 � 0.45 1.04 � 0.42G11 29 49 ND 1.19 � 0.41 0.52 � 0.43G12 4 17 ND 2.10 � 0.59 2.00 � 0.54G13 54 61 ND 0.32 � 0.32 0.13 � 0.38G14 65 55 1.42 � 1.03 5.26 � 0.96 6.22 � 0.96G15 59 61 0.69 � 0.60 3.97 � 0.55 5.94 � 0.56(2nd sampling)b

G1 77 57 ND 9.44 � 0.64 7.18 � 0.71G2 76 53 ND 1.89 � 0.46 2.30 � 0.46G3 10 48 ND 4.05 � 0.69 4.56 � 0.71G4 12 40 ND 5.24 � 0.66 5.24 � 0.60G5 14 30 ND 3.03 � 0.63 2.50 � 0.60G6 61 68 ND 5.56 � 0.74 4.64 � 0.65G7 59 63 ND 0.24 � 0.51 1.51 � 0.49G8 68 53 ND 2.54 � 0.50 2.27 � 0.54G9 54 65 ND 2.21 � 0.60 0.92 � 0.65G10 36 75 ND 0.89 � 0.38 0.45 � 0.29G11 29 49 ND 1.16 � 0.46 1.95 � 0.44G12 4 17 ND 1.39 � 0.51 2.10 � 0.54G13 54 61 ND 2.00 � 0.38 2.17 � 0.41G14 65 55 ND 7.30 � 0.74 6.17 � 0.71G15 59 61 ND 2.85 � 0.55 3.12 � 0.60

a May 5, 2011.b May 30eJune 5.c ND means lower than detection limit (<0.33 Bq/l).

N. Kamada et al. / Journal of Environmental Radioactivity 110 (2012) 84e8986

were detected. Efficiency calibration is described in detail byShizuma et al. (1998). The radioactivity of each fission product wasobtained in Bq/l, and the radioactivity at the time of sampling wasdetermined by correcting the elapsed time from sampling tomeasurement. Concentrations of 131I, 134Cs and 137Cs are given inTable 1.

Table 2Cumulative effective dose up to 54 d, committed effective dose from 134Cs and 137Cs and

Subject M/F Age Bodyweight (kg) Cumulative effective dosea (mSv)

(Adult Group)G1 M 77 57 8.7G2 F 76 53 7.9G6 F 61 68 7.0G7 M 59 63 11.2G8 M 68 53 8.4G9 M 54 65 6.6G10 M 36 75 7.6G11 F 29 49 8.2G13 M 54 61 10.0G14 F 65 55 7.0G15 M 59 61 10.3Average 8.4(Child group)G3 M 14 48 5.4G4 F 12 40 5.4G5 M 10 30 5.6G12 M 4 17 3.9Average 5.1

a Errors to be 10%.b Errors to be 12%.

3. Results

3.1. Estimation of cumulative effective doses

The cumulative air dose (DMPcum) at the location of monitoring

post can be obtained by integrating the air dose rate of monitoring

post ( _DMP

) over time. Effective dose (EIndcum) can be calculated from

the air dose (DMPcum) scaled by a factor of _E

Ind=a _D

MP, where _E(1)Ind is

the effective dose rate at 1 cm depth measured outside the indi-vidual home of each resident 1 m height above the ground with thesurvey meter and a is a conversion factor from air dose to effectivedose rate at 1 cm depth,

EIndcum ¼ b DMPcum

_EInd

a _DMP$

�εo

to24

þ εiti24

þ εctc24

�; (1)

where b is a conversion factor from air dose to effective dose, andεi is the shielding factor (i ¼ outdoor (o), inside Japanese woodenhouse or concrete building (i), and inside a car (c); specifically, 1,0.8 or 0.4, and 0.1, respectively). We assume here that the effectivedose rate at 1 cm depth is equal to effective dose, therefore a ¼ b.The period corresponding i, o and c is given with to, ti and tc inhour, respectively. For example, to, ti and tc were assigned to be8 h, 12 h and 4 h for the resident G1 in Kawamata Town and 16 h,8 h and 0 h for the resident G7 in Iitate Village, respectively,according to the results of interview. External effective doses forG1 and G7 are shown in Fig. 2(b) up to 54 d from the deposition.The estimated cumulative effective doses for 15 residents aregiven in Table 2. The results are also shown in Fig. 4. Effectivedoses for adults were 6.6e11.2 mSv, with an average of 8.4 mSv,and those for children were 3.9e5.6 mSv, with an average of5.1 mSv.

3.1.1. Estimation of committed effective doses from radiocesiumThe radioactivity concentration of 131I, 134Cs and 137Cs in urine

samples collected at both samplings are given in Table 1. Iodine-131was observed in the first sampling but not in the second sampling.Because the short-lived 131I was observed in only five residents,internal radioactive contamination was considered to occurthrough ingestion of contaminated foods.

equivalent dose for thyroid gland from 131I.

Committed effective doseb Equivalent dose (thyroid)

134Cs (mSv) 137Cs (mSv) Cs total (mSv) 131I (mSv)

0.065 0.044 0.110 660.044 0.033 0.077 580.051 0.036 0.087 ND0.026 0.005 0.032 ND0.023 0.014 0.037 ND0.011 0.014 0.025 ND0.010 0.012 0.022 ND0.012 0.007 0.018 ND0.014 0.008 0.022 ND0.062 0.039 0.101 500.049 0.024 0.073 270.033 0.021 0.055 50

0.022 0.014 0.036 440.021 0.015 0.036 ND0.020 0.016 0.037 ND0.004 0.003 0.007 ND0.017 0.012 0.029 44

Fig. 5. Retention function and urine excretion rate for 137Cs (PNNL-15614, ICRPPublication 78).

Fig. 6. Committed effective doses from 137Cs and 134Cs. G3eG5 and G12 are children,and the others are adults.

Fig. 4. Cumulative effective doses for 15 residents up to 54 d from the deposition.G3eG5 and G12 are children, and the others are adults.

N. Kamada et al. / Journal of Environmental Radioactivity 110 (2012) 84e89 87

After the Fukushima accident, a radioactive plume was releasedmainly from March 12 to 15 and was deposited northwest of theplant over Iitate Village and Kawamata Town onMarch 15. Drinkingwater and vegetables grown in this area were controlled on March20, but residents took foods grown in their yard and natural waterbeforehand. Thus, intake of radioactive contamination might havecontinued for at least one week. In this study, the representativeintake date was assumed to be March 20.

Total excretion of radioactivity per day is expressed by radio-nuclide concentration in urine Au (Bq/l), total urinary volume perday Mu (l) and ratio of radionuclide in urine to total excretion F asfollows,

Xt ¼ AuMu=F: (2)

The total amount of urine volume per day was reported asnormal range 0.8e2 l for adults (Landry and Bazari, 2011). Acevedoet al. (2007) reported an average total urine volume for childrenaged 3e5 y as 426 ml from collection of 24 h urine sample for 63children. In the present study, total urine volume was assumed tobe 3% of bodyweight. The ratio F was taken to be 0.8 from ICRPPublication 54 (1989), which was replaced with ICRP Publication78 (1997).

The retaining radioactivity in the whole body at t days I(t) aftersingle intake I0 (Bq) is expressed with retention functionRðtÞ asfollows,

IðtÞ ¼ I0RðtÞ: (3)

The total excretion of radioactivity from thewhole body at t daysafter the intake is expressed as the time differential of I(t) asfollows,

XðtÞ ¼ dI=dt ¼ I0YðtÞ; (4)

where Y(t) is the excretion rate for individual radionuclides. Thus,the initial intake radioactivity, I0 (Bq) is expressed as follows,

I0 ¼ AuMu=fFYðtÞg (5)

The retention function of Cs is described with two componentsin Pacific Northwest National Laboratory (PNNL) report (PNNL-15614, 2009) and also ICRP Publication 78 (1997); the first one is10% with a clearance half-time of 2 d and the second one is 90%with a half-time of 110 d as,

RðtÞ ¼ 0:1expð�0:693t=2Þ þ 0:9expð�0:693t=110Þ: (6)

The excretion rate function is represented as the time differ-ential of R(t) as follows.

YðtÞ ¼ 0:035expð�0:693t=2Þ þ 0:0057expð�0:693t=110Þ:(7)

Whole body retention function and urine excretion rate in thecase of ingestion are shown in Fig. 5. Normally, 80% of excretionoccurs in urine and 20% in feces (Fig. 6).

As a result, the committed effective dose is evaluated as follows:

Eð70Þ ¼ I eð70Þ; (8)

where, e(70) (mSv/Bq) is an effective dose conversion coefficient forthe general public until 70 y old. We assume here that all radio-cesium intake was from ingestion route, and the age-dependenteffective dose coefficients for ingestion of 137Cs and 134Cs arecited from ICRP Publication 72 (1996). Committed effective doses of134Cs, 137Cs and total radiocesium for individuals and the ratio ofexternal to internal total radiocesium doses are given inTable 2. Committed effective doses from radiocesium were0.022e0.110 mSv for adults and 0.007e0.036 mSv for children.

3.2. Estimation of equivalent dose of thyroid gland from 131I

Generally, 30% of iodine is concentrated in the thyroid gland and70% is excreted in urine at 1 d after intake in reference to ICRPPublication 78 (1997). Kim and Whang (2009) reported that onaverage 19.7% of iodine is concentrated in the thyroid gland 1 d

Fig. 7. Retention function and urine excretion rate for 131I (PNNL-15614, ICRP Publi-cation 78).

N. Kamada et al. / Journal of Environmental Radioactivity 110 (2012) 84e8988

after intake and 71.1% is excreted in urine. The retention functionand urine excretion rate of 131I ingestion are given in Fig. 7 based onPNNL-15614 (2009) and ICRP Publication 78 (1997). The urineexcretion rate at 46 dwas graphically obtained as 1.9� 10�5 (Fig. 8).

The equivalent organ dose was evaluated using Eq. (8). The age-dependent effective dose coefficient e(70) for 131I is given in ICRPPublication 56 (1989). The coefficients in the case of ingestion forthyroid gland are 0.0036 (1e2 y), 0.0021 (2e7 y), 0.0010 (7e12 y),0.00068 (12e17 y) and 0.00043 (>17 y) in units of mSv/Bq. Esti-mated effective doses are given in Table 2. The equivalent doses ofthyroid gland are 27e66 mSv for adults and 44 mSv for children.

4. Discussion

4.1. Cumulative effective dose

The cumulative effective doses up to 54 d from the deposition ofresidents living about 37 km from the power plant were6.6e11.2 mSv for adults and 3.9e5.6 mSv for children. The reasonwhy external doses for children are lower than those for adults inthe present study is that G12 spent most time indoors, and G3, G4and G5 spent their time at elementary schools or junior highschools that are concrete buildings.

In this study, we used the air dose rates 1 m above the ground tocalculate the effective doses for children. However, air dose rates50 cm above the ground would have been more suitable for chil-dren because who are generally shorter than adults and air doses atthis height were 30% higher than at 1 m (MEXT, 2011b). Thus, theactual effective dose for children might be 30% higher than

Fig. 8. Effective organ doses of thyroid gland for 15 residents. G3eG5 and G12 arechildren, and others are adults.

reported (3.9e5.6mSv). In addition, children are known to be aboutthree times more sensitive than adults to radiation (Preston et al.,2003). Taking these factors into consideration and neglectingdose rate effect if any, children’s doses could be 15e22 mSv. Thegovernment of Japan announced 20 mSv/y as the maximumpermissive level of radiation exposure in the case of an emergency(Web Site of Prime Minister of Japan and His Cabinet, http://www.kantei.go.jp/saigai/faq/20110502genpatsu_faq.html). Since resi-dents about 37 km from the power plant were already reaching thislevel at 54 d after the deposition, they should have been evacuatedat that time.

4.2. Committed effective dose

In this study, 134Cs and 137Cs were detected from urine samplesof all residents and 131I from five residents in the first sampling onMay 5, 2011. The total committed effective dose of radiocesiumwasless than about 0.11 mSv for all residents. If doses from short-livedradionuclides such as 129mTe, 129Te, 132I, 136Cs and 140La were alsoaccounted for, the total dose might have increased. From theinterviews, we found that three residents (G3, G4 and G5) hadeaten mushrooms from contaminated areas and four (G1, G2, G7and G8) had eaten vegetables from their gardens around the end ofApril (about 45 d after the deposition), which seemed to be oneroute of intake. Equivalent organ dose for thyroid gland in thisstudy 27e66 mSv gives an estimation of maximum dose. To esti-mate thyroid concentration, an additional radioactive survey usinga thyroid monitor or human counter is necessary.

The present findings revealed that the committed effectivedoses from radiocesium were considerably lower (0.22e1.4%) thanthe external effective dosed up to 54 d after deposition. However,the ratio was comparable to the Chernobyl accident (Thomberget al., 2002). From now on, residents should pay attention to radi-ation monitoring of foods conducted by the government as well asto the radiation levels in their living environment to avoid the riskof internal exposure as much as possible.

5. Conclusion

The average cumulative effective dose of 15 residents about37 km northwest of the Fukushima Dai-ichi Nuclear Power Plantwas about 8.4 mSv for adults and about 5.1 mSv for children up to54 d after deposition. The committed effective dose from radio-cesiumwas less than 0.11mSv for all residents surveyed, which wasconsiderably lower than external effective dose. Equivalent dose forthyroid gland was estimated 27e66 mSv at maximum.

Acknowledgement

The authors appreciate the cooperation of the 15 surveyedresidents and related persons in Fukushima. This research has beenapproved by the ethics committee of Hiroshima University(Epidemiological Study No. 425).

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