Concentrations of Radiocesium in Local Foods Collected in Kawauchi Village after the Accident at the Fukushima Dai-ichi Nuclear Power Station

Abstract

We evaluated the current concentrations of radiocesium in local foods collected in Kawauchi Village, which is located less than 30 km from Fukushima Daiichi Nuclear Power Station, to minimize public anxiety regarding internal radiation exposure through the consumption of locally produced foods after the 2011 Fukushima accident. The number of samples exceeding the regulatory radiocesium limit (100 Bq/kg for general foods) was five out of 4,080 vegetables (0.1%), 652 of 1,986 (32.8%) among edible wild plants and fungi, and eight of 647 (1.2%) in fruits. Our study confirmed that the internal radiation doses of ingesting these foods are acceptably low compared to the public dose limit, ranging from 24.4 to 42.7 μSv for males and from 21.7 to 43.4 μSv for females, although the potential for radiation exposure still exists. Long-term comprehensive follow-up should take place to clarify trends in radiocesium concentrations in local foods and the committed effective doses found in Fukushima-area residents. By constructing a system that allows residents to access information on radiocesium concentration in foods, a risk communication model between specialists and residents could be developed in the recovery phase after the Fukushima accident.

Concentrations of Radiocesium in Local Foods Collected in Kawauchi Village after the Accident at the Fukushima Dai-ichi Nuclear Power Station

OPEN

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Makiko Orita, Kanami Nakashima, Naomi Hayashida, Yuuko Endo, ShunichiYamashita &

NoboruTakamura

We evaluated the current concentrations of radiocesium in local foods collected in Kawauchi Village,

On March 11, 2011, a massive earthquake struck the east coast of Japan. The earthquake, combined with the resulting tsunami, triggered a severe nuclear accident at the Fukushima Daiichi Nuclear Power Station (FDNPS)1.

As a result, large amounts of radionuclides, including iodine-131 (131I), cesium-134 (134Cs) and cesium-137 (137Cs) were released into the atmosphere2. The United Nations Scientic Committee on the Eects of Atomic Radiation estimated the total release of 131I, 134Cs, and 137Cs at 120.0, 9.0, and 8.8 petabecqueral (PBq), respectively2.

Radiocesium (mainly 134Cs and 137Cs) is the predominant contributor to radiation exposure aer the FDNPS accident because it has a relatively long half-life134Cs has a half-life of 2.06 years and 137Cs 30.2 yearshigh transferability, and wide distribution in the environment3. Because of these relatively long half-lives, residents have expressed concerns about whether 134Cs and 137Cs may remain on the surface of soils in the fields for extended period time, and consequently be found in the plants growing on that land. Cesium (Cs) is an alkaline with chemical properties similar to potassium (K), which is an essential element for plants. Higher levels of K in the growth media are known to reduce plants uptake of Cs4.

Kawauchi Village, Fukushima Prefecture, is located within a 30km-radius from FDNPS. Aer the May 2011 accident at FDNPS, almost all residents were evacuated outside the village (Fig.1). On January 31, 2012, the mayor of the village declared that residents who lived at least 20 km away from FDNPS could return to their homes because the Japanese Prime Minister had declared that the reactors had achieved a state of cold shutdown

Department of Global Health, Medicine, and Welfare, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki Division of Strategic Collaborative Research, Center for Promotion of Collaborative Research on Department of Radiation Medical Sciences,

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Figure 1. Location of Kawauchi Village, Fukushima Prefecture. The rst author (M.O.) created the map using the soware (Zenrin Electric Map Z i17, ZENRIN CO., LTD., Tokyo, Japan. http://www.zenrin.co.jp/

product/gis/zmap/zmaptown.html).

Percentage

above the

regulatory limit

for radiocesium

Vegetables 4,080 5 0.1 Edible wild

pants and

mushrooms

in December 2011 and that radiation doses were found to be at comparatively low levels5. Since this declaration, the village office has been working steadily towards reconstruction. However, even though four years have now passed since return was authorized (and ve since the accident), only about 60% of pre-accident population has returned. One reason that some residents have chosen not to return to the village is anxiety regarding radiation exposure6, especially the risks of internal exposure through the consumption of locally produced foods7. Recently, we evaluated the radiocesium concentrations in wild fungi collected at Kawauchi Village and found that radiocesium is oen detectable8. On the other hand, radiocesium concentrations in other local samples should be also evaluated for food safety policy in Fukushima. Therefore, we examined the current concentrations of radiocesium in local food samples collected in the village and evaluated the internal eective doses of local residents.

Results

The summary of radioactive contaminants in the surveyed foods is shown in Table1. The number of samples exceeding the radiocesium regulatory limit (100Bq/kg for general foods) is ve (0.1%) for vegetables, 652 (32.8%) for edible wild plants and fungi, and eight (1.2%) for fruits.

The distribution of radiocesium in vegetables, edible wild plants and fungi, and fruits in Kawauchi Village is shown in Table2. The radiocesium concentrations for all the samples reected an extremely wide range in every

Number of

samples in

the analysis

Number in excess of

the regulatory limit for

radiocesium (100Bq/kg for

general foods)

Food type

1,986

652

32.8

Fruits 647 8 1.2 Fisha 36 14 38.9 Gameb 172 155 90.1 Cropsc 296 32 10.8 Othersd 451 106 23.5 N 7,668 972 12.7

Table 1. Summary of the radioactive contaminants survey for foods. aRiver sh, mainly char. bMainly wild boar (93.0%), pheasant, and rabbit. cMainly chestnuts (55.4%), beans, and buckwheat. dMainly wild honey (22.5%) and produced foods combined with fungi.

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Median (mini-max) (Bq/kg fresh)

Geometric

meansgeometric standard

deviations (Bq/kg fresh)

134Cs 137Cs 134Cs 137Cs

Spring 300 5 (<5181) 5 (<5331) 5.81.5 6.41.8 Summer 2,186 5 (<567) 5 (<5103) 5.11.1 5.11.2 Autumn 1,430 5 (<549) 5 (<586) 5.11.2 5.31.3 Winter 164 5 (<563) 5 (<5206) 5.11.2 5.21.4

Spring 1,032 20 (<201,939) 20 (<204,788) 30.22.3 38.93.0 Summer 336 20 (<201,232) 20 (<202,612) 22.21.6 24.81.9 Autumn 609 62 (<202,754) 149 (<208,487) 70.93.4 140.34.8 Winter 9 59 (<20307) 166 (<20716) 56.12.3 130.03.2

Spring 1 n.d.b n.d. n.d. n.d. Summer 284 5 (<517) 5 (<<530) 5.21.2 5.91.4 Autumn 329 5 (<5149) 5 (<5457) 5.41.5 6.21.9 Winter 33 5 (<557) 5 (<5204) 5.71.7 7.12.2 Fish All seasons 36 23 (<10169) 60 (<10397) 35.72.1 60.62.6 Game All seasons 172 210 (<205,248) 513 (<2016,585) 192.13.3 460.33.8 Crops All seasons 296 5 (<5225) 5 (<5522) 23.21.6 27.62.1 Others All seasons 451 20 (<20584) 20 (<201,818) 27.21.9 41.42.9

Table 2. Distribution of radiocesium in three items. aFrom April 2013 to December 2014: Spring is March to May, summer June to August, autumn September to November, and winter from December to January. bn.d.; Not detected.

season. In autumn, for example, concentrations of radiocesium in edible wild plants and fungi ranged from <20

to 2,754Bq/kg for 134Cs and <23 to 8,487Bq/kg for 137Cs.

The committed eective doses from these agricultural products are summarized in Table3. The committed eective doses ranged from 2.61 to 7.08 Sv for males and from 2.94 to 7.61 Sv for females, and from 1.88 to 5.75 Sv for male children and from 1.95 to 5.15Sv for female children due to the ingestion of vegetables. The ingestion of edible wild plants and fungi led to ranges from 0.12 to 11.94 Sv for males and from 0.17 to 10.15 Sv for females and from 0.04 to 4.57Sv for male children and from 0.50 to 7.77Sv for female children. Finally, eating fruits led to a range of 0.25 to 1.65 Sv for males and from 0.50 to 1.65 Sv for females and from 0.55 to 1.64 Sv for male children and from 0.59 to 1.61 Sv for female children. The committed eective doses ranged from 24.4 to 42.7 Sv for all males and from 21.7 to 43.4 Sv for all females due to ingestion of the three food groups combined (Fig.2).

Discussion

The present study shows that radiocesium exceeding the current regulation value of radionuclides for foods (>100Bq/kg) was detected in ve of 4,080 (0.1%) vegetables and eight of 647 (1.2%) fruits collected in Kawauchi Village. Immediately aer the accident, the Government of Japan established provisional regulation values for 131I

(300Bq/kg for drinking water and milk and 2,000Bq/kg for vegetables) and 134Cs and 137Cs (200Bq/kg for drinking water and milk and 500Bq/kg for vegetables, grains, meats, sh, and eggs), and issued an order to restrict the shipment of food products exceeding these provisional values. Soon aer, 131I exceeding provisional levels was detected in fresh cow milk, cultivated green leafy vegetables, and tapwater9, and foods that exceeded the provisional values were removed from the market8,10,11.

Five years have passed since the accident, and the concentration of radionuclides in food has decreased overall12. The Ministry of Health, Labour and Welfare (MHLW) has monitored radiocesium in foods since March 2011, using Ge semiconductor detectors or NaI scintillation detectors. They collected 16,712 vegetables and 3,302 fruits in Fukushima and its surrounding prefecture between April 2014 and March 2015, demonstrating that radiocesium exceeding the regulation values was not detected13.

In Kawauchi Village, the decontamination of residential areas and agricultural land has been underway since mid-2011, in accordance with the technical guidelines for decontamination developed by the Ministry of the Environment14. The top 5cm of soil in which radiocesium was concentrated has either been completely removed or mixed with non-contaminated subsurface soil during tillage of agricultural lands. Forests within a 20-m radius from residential houses and agricultural lands have been decontaminated though the removal of branches, fallen leaves, and leaf mold14. Owing to these steps, substantial amounts of radiocesium have been removed from the area, contributing to the decrease of ambient dose rates. The current ambient dose of Kawauchi Village is 0.085Sv/hour (May 5, 2016), whereas the highest ambient dose during the accident was 1.5Sv/hour (March 15, 2011). Previously, we had evaluated the external radiation doses of residents who had temporally stayed in areas within a 20-km zone of the village and had estimated that the median annual dose was 1350Sv/year15. These results suggest that the external exposure from living in Kawauchi Village is limited.

Our results showed that the radiocesium concentrations in edible wild plants and fungi were notably higher than in fruits and vegetables. Hoshi et al. reported that children consuming fungi showed a high 137Cs body burden near the plant16. It is well known that aer the accident at the Chernobyl Nuclear Power Plant, wild fungi

Food Type Seasona

Number of

samples

Vegetables

Edible wild

plants and fungi

Fruits

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Food Type Seasonsa Gender Age 019 2029 3039 4049 5059 6069 >70

Vegetables

Edible wild

plants and

fungi

Spring Male 0.551.10 0.25 0.48 0.66 0.82 0.96 0.64

Female 0.591.19 0.50 0.48 0.61 0.78 1.15 0.72

Summer Male 0.821.64 0.80 0.96 1.04 1.15 1.12 1.43

Female 0.771.55 0.85 0.96 0.90 1.33 1.57 1.22

Autumn Male 0.711.43 0.91 0.43 1.33 1.11 1.65 1.29

Female 0.801.61 0.99 0.77 1.03 1.30 1.12 1.22

Winter Male 0.701.41 0.49 1.02 0.75 1.36 1.57 1.27

Female 0.691.39 0.64 1.12 1.15 1.32 1.52 1.65

Table 3. Committed Eective Doses from Three Food Typesb. aFrom April 2013 to December 2014: Spring is March to May, summer June to August, autumn September to November, and winter from December to January. bCommitted eective doses from vegetables, edible wild plants and mushrooms, and fruits due to radiocesium in Kawauchi Village (Sv/3 months). The range of average intake for vegetables is 179517g (minimum maximum), for edible wild plants and fungi is 140g, and for fruits is 1178g based on the information issued by the Environmental Radioactivity Monitoring Center of Fukushima, Fukushima Prefecture, Japan, for all age categories.

Spring Male 2.114.34 2.91 2.96 3.48 4.11 3.07 3.58

Female 2.064.26 3.35 2.96 4.12 4.34 5.10 3.29

Summer Male 2.795.75 4.20 4.99 4.75 5.73 7.08 6.99

Female 2.505.15 4.58 4.99 5.87 5.61 7.61 6.05

Autumn Male 1.883.87 3.96 2.61 3.38 4.11 5.29 4.09

Female 1.954.02 3.45 3.38 3.42 4.15 5.62 3.81

Winter Male 2.284.70 4.88 3.73 3.13 5.49 4.69 4.08

Female 2.064.26 4.24 2.94 3.01 4.76 4.54 3.60

Spring Male 0.250.51 0.23 0.41 0.23 0.82 0.58 0.70

Female 0.501.03 0.29 0.41 0.17 0.64 0.70 0.70

Summer Male 0.040.09 0.12 0.12 0.47 0.47 0.18 0.41

Female 0.340.69 0.41 0.21 0.29 0.47 0.35 0.71

Autumn Male 1.443.02 1.98 2.55 5.67 5.67 6.80 7.65

Female 3.096.47 9.64 1.70 6.52 6.52 4.25 5.67

Winter Male 2.184.57 3.58 3.88 5.67 11.94 6.56 6.86

Female 3.707.77 3.28 1.79 4.18 10.15 9.85 5.37

Fruits

Figure 2. Internal eective doses due to radiocesium in Kawauchi Village, Fukushima Prefecture.

could be an important contributor to 137Cs body burdens, due to their capacity to accumulate 137Cs, and that certain population groups showed relatively high internal exposure due to intakes of such foodstus17. Since the accident at FDNPS, decontamination in the forests beyond a 20-m radius from residential houses has not been conducted10, leading to the relatively high concentrations of radiocesium in edible wild plants and fungi.

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In this study, we showed that the lifetime committed eective doses ranged from 24.4 to 42.7Sv for all males and from 21.7 to 43.4 Sv for all females, indicating that the health risk from internal exposure in residents through ingesting agricultural produce is extremely low. We had previously evaluated the committed eective doses from local agricultural samples in Kawauchi Village from May 2012 to March 2013, showing that the estimated doses ranged from 18 to 44Sv/y for males and from 20 to 48Sv/y for females, respectively6. Harada et al. also evaluated dietary exposure to radiocesium from a food-duplicate survey in three areasKawauchi Village, Tamano, and Haramachilocated between 20 and 50 km from FDNPS in 2012, reporting that the estimated internal dose rates from dietary intake of radiocesium averaged 5.8, 9.0, and 8.8 Sv/y in Kawauchi, Tamano, and Haramachi, respectively, while the estimated committed eective doses did not exceed the regulation values (<103Sv/y)18. These results show that the risk of internal exposure in Kawauchi Village residents is low since the initial phase of the accident.

Following the Chernobyl accident, it is well known that there was a seasonal dierence in Cs body burden due to the seasonal change in diet and that the concentration of Cs body burden was higher in autumn; these results suggest that residents may have consumed products derived from the contaminated forests17. In this study, the seasonal change of radiocesium concentrations was observed only in Edible wild plants and fungi (Table2). In spring and summer, most samples of this category are edible wild plants, but in autumn and winter, most samples are fungi. This dierence in sample types causes the seasonal change in this category.

Although relatively high proportions of sh (mainly char), game (mainly wild boars), and crops (mainly chestnut) were above the regulatory limit, we excluded them from the analysis for committed eective doses since they were not actually consumed in the village.

Although residents who returned to the area aer the accident had a higher likelihood of consuming locally produced vegetables than the general Japanese population, the food supply in those farming areas did not increase exposure to radiocesium because municipalities in Fukushima Prefecture routinely screen food products intended for human consumption.

The present study has several limitations. Our study was conducted only in Kawauchi Village, which might have led to sampling bias. Also, we could not evaluate analytical uncertainties since we had measured each sample only once. We used the average daily intake data of fungi and other foods issued before the accident (20092010), but the intake amount of such foods might decrease due to anxiety about the internal radiation exposure in Fukushima. Further comprehensive analyses with detailed reports on all areas around FDNPS are needed.

In conclusion, our study conrmed that the internal radiation doses of ingesting foods are acceptably low compared to the public dose limit, although the potential for radiation exposure still exists. Attention should be paid when consuming foods harvested from forests in order to avoid unnecessary chronic internal exposure. Moreover, long-term comprehensive follow-up should be undertaken to clarify trends in radiocesium concentrations in locally produced foods and the committed eective doses of residents in areas around FDNPS. By constructing a system that enables residents to access information on radiocesium concentration in foods, a risk communication model between specialists and residents could be developed in the recovery phase aer the Fukushima accident.

Materials and Methods

Local food samples were collected in Kawauchi Village. A radioactive contaminant survey for foods produced or collected in the village has been carried out by personnel at the village office since May 1, 2012. For this survey, 7,668 food samples produced or collected in the village were collected between April 2013 and December 2014. Of the total collected, 6,713 samples (4,080 vegetables, 1,986 edible wild plants and fungi, and 647 fruit samples) were selected for the current study, because these three items are major dietary components consumed by the residents and thus can be expected to contribute substantially to their internal radiation exposure. In this study, vegetables was dened as being grown and harvested from elds, and wild plants and fungi were natively grown in the wild. Wild fungi samples collected in this study were completely dierent samples from which we analyzed in the previous study8. The others, such as wild boars, chestnut, pheasants, and river sh, were also collected mainly for the investigation of radioactivity levels, but these samples were excluded from the analysis for committed eective doses because they were not actually consumed.

Aer preparation, local food samples (approximately 1000 g fresh) were put into plastic containers made of acrylic acid resin to measure the concentrations of 134Cs and 137Cs concentrations using an NaI detector (Canberra, CAN-OSP-NAI, AREVA NC Inc., Meridien) coupled to a multichannel analyzer (Genie 2000, Canberra Japan KK., Tokyo, Japan) for 1,800 s. The resolution of the instrument was <7.5% on 661.64 keV for

137Cs. ICRP.

The committed eective doses caused by the consumption of vegetables, edible wild plants and fungi and fruits were estimated from the radioactive ssion product concentration, using the following formula:

=

H C D e,

int int

where C is the median activity concentration of detected radiocesium (Bq/kg fresh), Dint is the dose conversion coefficient for childrens intake (ages 0 to 19, 1.3 1053.0 105 mSv/Bq for 134Cs and 9.6 1062.2 105 mSv/Bq for 137Cs) and for adult intake (age 20 and older, 1.9 105 mSv/Bq for 134Cs and 1.4 105 mSv/Bq for 137Cs19, and e is the average daily intake data (g/day) for age, gender, and season in areas around FDNPS, as issued by the Environmental Radioactivity Monitoring Center of Fukushima, Fukushima Prefecture, Japan in 2009201020. We evaluated the committed eective doses using the following age groups: ages 0 to 12 months, 1 year to 3 years, 3 years to 8 years, 8 years to 13 years, 13 years to 18 years, and adults. In adults, we performed the calculation depending on the age classication and based on the average intake of food for every 10-year division. However, in children, we calculated the minimum and maximum values of the committed

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eective dose based on the average intake of 20 years to cover all age categories of children because we did not have the data for the average intake of food groups in the 19-years-or-less category.

In this study, we applied the recommendation of the Global Environment Monitoring System-Food Contamination Monitoring and Assessment Programme from the World Health Organization (GEMS/food of WHO), which the Japanese Ministry of Health, Labour and Welfare applied for the establishment of new standard limits for radionuclides in food21,22. In this recommendation, it is outlined that when the detection limit is not shown, 5Bq/kg should be applied to food groups for which the ratio of ND (not detected) is not less than 80%; 10Bq/kg should be applied to food groups for which the ratio of ND is 60% to 80%; and 20Bq/kg should be applied to all others. Based on this recommendation, we calculated the committed eective doses, and the values under the radiocesium detection limits were assumed to have activity concentrations corresponding to 5Bq/kg for vegetables and fruits and the detection limit itself (20Bq/kg) for edible wild plants and fungi.

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Author Contributions

Conceived and designed the experiments: M.O., K.N. and N.H. Performed the experiments: M.O., Y.E., S.Y. and N.T. Analyzed the data: M.O., N.H. and N.T. Contributed reagents/ materials/ analysis tools: M.O. and N.T. Wrote the paper: M.O., S.Y. and N.T.

Additional Information

Competing nancial interests: The authors declare no competing nancial interests.

How to cite this article: Orita, M. et al. Concentrations of Radiocesium in Local Foods Collected in Kawauchi Village aer the Accident at the Fukushima Dai-ichi Nuclear Power Station. Sci. Rep. 6, 28470; doi: 10.1038/ srep28470 (2016).

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