Anthropogenic Radionuclides in Japanese Food - ACS Publications

Dec 19, 2012 - Anthropogenic Radionuclides in Japanese Food: Environmental and. Legal Implications. Stefan Merz,. †. Georg Steinhauser,*. ,‡,† a...
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Anthropogenic Radionuclides in Japanese Food: Environmental and Legal Implications Stefan Merz,† Georg Steinhauser,*,‡,† and Nobuyuki Hamada§ †

Vienna University of Technology, Atominstitut, Stadionallee 2, 1020 Wien, Austria Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, United States § Radiation Safety Research Center, Nuclear Technology Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 2-11-1 Iwado-kita, Komae, Tokyo 201-8511, Japan ‡

S Supporting Information *

ABSTRACT: The Japanese government ordered the analysis of thousands of foods after the Fukushima nuclear accident to ascertain compliance with regulatory limits for anthropogenic radionuclides in food. Four hundred and forty-five samples obtained until 31 December 2011 from 11 prefectures exceeded the regulatory limits that were in force until 31 March 2012. The possibility of these 445 samples representing localized areas of high radiocesium concentration was investigated. The objective of this study was to determine the radiocesium activity ratio (134Cs/137Cs) in foods from each geographic area to possibly identify the radioactive signature of the four different reactors (i.e., four independent sources) in the distinct regions. The average 134Cs/137Cs activity ratio was 0.98 ± 0.01 for all samples. However, no statistically significant deviations from this value could be confirmed in the various regions. Therefore, we conclude that the releases from reactor No. 4 (carrying a significantly smaller activity ratio) are assumed to be small when compared with the other three reactor releases. The individual radioisotopic signatures of reactors No. 1, 2, and 3 could not be identified in various Japanese regions using the food samples, indicating integral radiocesium contamination from these sources. Subsequent releases of fission products from the reactors (e.g., after possible criticalities reported in October 2011) proved to have no impact on the radiocesium activity ratio. A discussion of the development of the regulatory limits in Japan and Europe with regard to the current limits and radiological food safety are also included.

1. INTRODUCTION The Fukushima nuclear accident will remain in the public memory as one of the greatest environmental disasters in recent years. Four of six reactors at the Fukushima Daiichi Nuclear Power Plant site (referred hereinafter to as Fukushima NPP) were severely damaged after a tsunami destroyed the emergency power supply and left the nuclear fuel cooling system inoperable, causing nuclear fuel damage or meltdown. Massive hydrogen explosions occurred in the course of pressure release measures and destroyed three reactor buildings. During the accident large amounts of volatile radionuclides were released into the environment from the damaged reactors between 12 March and the beginning of April 2011 (minor releases continued much longer), resulting in significant contamination across various regions of Japan (see e.g. refs 1 and 2). Radionuclides released from a nuclear reactor may impact human health in several ways. Three types of exposure are most important: one, external exposure; two, internal exposure due to inhalation of contaminated air; and three, internal exposure upon ingestion of contaminated food and water. External exposure in the Fukushima nuclear accident is relevant only for relatively small areas such as the site of the Fukushima NPP, its © 2012 American Chemical Society

immediate vicinity, and selected local hotspots in more remote areas. Since the population of areas at risk were efficiently evacuated, external exposure was limited to workers at the power plant site. Internal exposure due to inhalation of radionuclides was relevant primarily during the initial phase of the accident. Several mechanisms, such as precipitation washout, and atmospheric dilution, together with the physical decay of short-lived radionuclides, decreased the radioactivity levels in air within a relatively short time span. Lastly, the ingestion of contaminated food and water remains a potential hazard for a large group of people; potentially the entire Japanese population. Contaminated food can be exported into areas where radionuclides were not deposited directly. Radioactive decay and removal of nuclides through environmental factors are only significant removal mechanisms for physically short-lived nuclides or nuclides with a short ecological half-life. Hence, after the initial phase, ingestion of contaminated food is the most significant route of radionuclide Received: Revised: Accepted: Published: 1248

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samples were measured immediately upon receipt to avoid unnecessary decay. Food handling manuals recommend washing and preparing the food for cooking prior to radioanalytical testing so that realistic and relevant results may be obtained.12,13 All samples were inspected, washed (if necessary), and prepared following good food handling practices prior to any analysis.3 The 18 supermarket food samples appeared fresh, free of soil, and edible, so no further action in washing or preparing the samples for measurement was undertaken, so that the worst case for radioactive contamination could be determined. See the Supporting Information for the radioanalytical methodology (γ-spectrometry). Dose Aspects. The committed effective dose was determined for each food based on the measured activity in each sample. The committed effective dose is the dose to an individual evaluated over the 50 year period following ingestion or inhalation (eq 1).14

uptake and remains the most relevant source for internal dose to members of the public.3 Surveillance of contamination levels of food and potable water have been prioritized by the Japanese authorities. No regulations were in place in Japan regarding radionuclide concentration in food until after the accident occurred. The Japanese government ordered local governments of each prefecture to perform the necessary radioactivity monitoring − including food. The measurements were conducted by several institutions using all available radioanalytical resources, including detectors at universities and research institutes. The monitoring of radionuclides in Japanese food has been the topic of previous studies.3−7 This paper focuses on two aspects: first, the abundance of radionuclides in food, their radioactive signature, and potential attribution to their source; second, legal aspects with a focus on the development of the regulatory limits in Japan and Europe and resulting health policy implications as well as future aspects of this legislation.

2. MATERIALS AND METHODS Target Radionuclides. Volatile radionuclides comprised the majority of the activity released from the Fukushima accident (Kr, Xe, I, Cs, Te), whereas less volatile elements (e.g., actinides, Sr, Ba, Nb, and others) were mostly retained inside the reactors during venting.3,8 The target nuclides for this study were 131I (T1/2= 8.03 d), 134Cs (T1/2= 2.07 y), and 137Cs (T1/2= 30.08 y). Although 131I has a short half-life it bioconcentrates in the thyroid gland9 and can deliver a significant dose in adults and especially children. The activity ratio of the radiocesium isotopes 134Cs and 137Cs was used to study possible local differences in deposition and if possible determine signatures that may be attributed to one of the four reactors. One advantage of measuring the 134Cs/137Cs ratio is that, once released into the environment, no chemical fractionation occurs as they are isotopes of the same element. The applicability of this approach has been shown in recent studies.8,10 Samples. Radioactivity monitoring by local Japanese government agencies revealed that 445 food samples (vegetables, beef, fruit, tea, and others, for details see the Supporting Information) obtained until December 2011 exceeded the maximum permissible limit stipulated as the "provisional regulation value" (that was in place until 31 March 2012) for radiocesium. All the samples were analyzed as a part of the ongoing Japanese food monitoring program and were representative of the Japanese diet. Measurements were performed by local governments, universities, or research institutes as required by the Nuclear Emergency Response Headquarters (NERHQ) or the Ministry of Health, Labour and Welfare (MHLW).3,11 The samples originated from eleven Japanese prefectures (Figure S-1, Supporting Information). Food sampling was performed over several months starting on 21 March 2011. An abbreviated set of data (until June 2011) were briefly discussed in ref 3. The data utilized in this work encompass 21 March 2011 to December 2011. It is important to note that of the many thousands of food samples measured, only 445 samples exceeded the regulatory limits in force at the time of measurement. Samples with measured radioactivity below the regulatory limit were not evaluated any further, in order to optimize the use of limited detector and human resources. An additional 18 food items were purchased privately at supermarkets in several Japanese prefectures for analysis and submitted to the Atominstitut for analysis. All submitted

E=

∑ h(g )j ,ing ·Aj ,ing j

(1)

The variables in eq 1 are as follows: E is the committed effective dose (Sv); h(g)j,ing is the dose conversion factor for ingestion (Sv Bq1−) of radionuclide j and the age group g, for which values were taken from ref 14; and Aj,ing is the activity (Bq) of the ingested amount of the radionuclide j. The term “annual daily consumption” better illustrates the concept of committed effective dose. The annual daily consumption represents the amount of food that is consumed daily over the time span of a year resulting in the maximum permissible dose (to the public) of 1 mSv. According to European law, which follows the recommendations of the International Commission on Radiological Protection (ICRP),15 1 mSv is an acceptable dose for members of the public. Formally, this dose would be obtained during the 51 years following the first ingestion or inhalation (taking into account the different dates of uptake over a year). For radionuclides with a short physical (131I) or biological half-life (134 Cs, 137Cs),16 almost the entire dose will be conveyed within the first year. For these nuclides, the value of the overall dose (E) hence will almost equal an annual dose. Accordingly, Aj,ing is assumed to be the product of the annual consumption rate of a food (kg) and the activity concentration (Bq kg−1) of the ingested radionuclide j. The possible long-term effects on food contamination (for 137Cs and 134Cs) for subsequent crops depend almost entirely on the effective ecological half-life (the soil’s potential to retain radiocesium in bioavailable form and at the level of the roots).17,18

3. RESULTS AND DISCUSSION Possible Source Identification Using Radiocesium Activity Ratios. Sampling food provides an indication of the concentration and availability of radionuclides in areas under cultivation. The sampling of food, instead of soil, allows sampling over a wide geographic area and reduces the amount of soil sampling required to isolate radionuclide concentrations that could impact human health. Additionally, determining the source of the food and isotopic ratio could potentially lead to identification of the source of the radioactivity. Identification of the sources of contamination in certain areas may provide valuable insight into the radionuclide release patterns from each reactor. Such knowledge is crucial for 1249

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Figure 1. Ratio of the activity concentrations of 134Cs/137Cs in food vs the activity concentration of 137Cs (as an indicator of possible “old” Samples submitted to the Atominstitut and from Fukushima Prefecture. All data were decay corrected to 11 March 2011.

137

Cs).

Background Influences on the Radiocesium Activity Ratio. Before utilizing the radiocesium ratio to ascertain the source of contamination, one must first exclude any possible interference from environmental radioactivity unrelated to the Fukushima accident, such as 137Cs fallout. The sample set was split into two parts for analysis. The first set contained samples from Fukushima Prefecture together with the 18 samples submitted to the Atominstitut (Figure 1). The second set of samples was from the remaining ten Japanese prefectures (Figure 2). Some scattering of the 134Cs/137Cs ratio is observed in Figures 1 and 2, especially for low activity concentrations. Statistical uncertainties associated with low concentrations of radioactivity are possibly responsible for the increased scatter of data at low count rates. A second possible explanation for the increased scatter of data at low radioactivity concentrations could be the contribution of 137Cs from (atmospheric) nuclear explosions in the past as well as previous nuclear accidents leading to a decreased ratio. The shorter half-life 134Cs (2.07 y) from other reactor accidents has undergone significant decay, and, after 25−30 years, is essentially undetectable in comparison to 137Cs (30.08 y half-life). High activity samples which contain some measurable 134Cs are thus expected to best reflect the Fukushima radiocesium signature. The arithmetic mean of the lowest 50% of the samples with respect to increasing activity concentration of 137Cs (low contamination) is 0.979 ± 0.015 (on 11 March 2011). The arithmetic mean of the higher 50% of samples is slightly greater (0.987 ± 0.010) but not statistically significant at the 99.9% confidence interval. The decay corrected mean 134Cs/137Cs activity ratio of all data in this study is 0.98 ± 0.01.

learning lessons from the accident. Radionuclides were not released simultaneously from all four reactors but sequentially over the time-span of several days. It is likely that radionuclides deposited in the various regions were from different reactors, due to different weather conditions (wind directions, precipitation) that prevailed during the releases. The hypothesis behind this study was that certain radionuclides in foods may act as indicators of a particular type of reactor accident and may be used to determine the reactor which was the source of the contamination based upon isotopic ratios. While 137Cs is a typical fission product (cumulative fission yield 6.18% for thermal fission of 235U), 134Cs is produced only through nuclear fission as a low yield fission fragment (7.698 × 10−8 cumulative fractional yield),19,20 and mainly via neutron absorption of 133Cs. The decay chain of the 134-isobar ends with stable 134Xe, so 134Cs is a “blocked” nuclide, and is not produced via decay of its isobar fission fragments or significantly from fission. With increasing duration of operation, reactors produce 134Cs via neutron capture of stable 133Cs, which is the end of the decay chain of the 133-isobar. The radiocesium activity ratio 134Cs/137Cs can be related to the age of the fuel but it can vary due to the different ages of nuclear fuel in a reactor as well as physical decay after shutdown.21 The radiocesium activity ratio may be useful as a “radioactive fingerprint” to identify sources of contamination. The activity ratio of 134Cs/137Cs 0.5 d after shutdown of a pressurized water reactor (burn-up of 30 GWd/t; 3% initial enrichment) was simulated and reported in a previous study22 (as cited in ref 3) to be in the range of 1.2. A radiocesium ratio of 1.2 is indicative of nuclear fuel in the (late) middle of its lifetime (usually 40−55 GWd/t). 1250

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Figure 2. Ratio of the activity concentrations of 134Cs/137Cs in food vs the activity concentration of 137Cs (as an indicator of possible “old” Samples from ten Japanese prefectures. All data were decay corrected to 11 March 2011.

137

Cs).

decreased activity ratio of 134Cs/137Cs of approximately 0.1 for reactor No. 4 releases, a difference which can be determined with radiometric methods. A goal of this study was to identify samples with a radiocesium activity ratio corresponding to that for reactor No. 4. The investigation of the different sources of contamination was done by plotting the ratio against the average distance of each prefecture to the Fukushima NPP, representing the region of cultivation of the crops (Figure 3). No clear clustering or trends can be observed in Figure 3 (perhaps with exception of samples from Miyagi Prefecture, showing a slightly lower average ratio, but the data density is low and not conclusive). The approximate average of the radiocesium ratios is in the range of 1. Thus, the contribution of reactor No. 4 to the total radiocesium contamination was small compared with the other three sources. If it exists, any unique signature from the other three reactors would only manifest a short distance from the each. Since all samples utilized in this study were taken many kilometers from the Fukushima NPP, atmospheric mixing is assumed to preclude any analysis which would allow identification of a specific reactor source of radiocesium. Also, some crops may have been contaminated with radiocesium from more than one source. Consequently, the ratios measured in our samples are likely to represent the integral radiocesium deposition in the course of the Fukushima nuclear accident. Radiocesium Activity Ratios Over Time. The influence of decay on samples was eliminated by applying decay correction to the date of the accident in the previous

Fallout deposition may not have been distributed equally over the years, due to factors such as rainfall or different ability of soil types to adsorb cesium. Hence the relative contribution of old radiocesium (where 134Cs activity is undetectable or nearly undetectable) may differ from the current contamination patterns (e.g., due to rainfall) and alter the measured radiocesium ratios. Soils with a silica-rich volcanic ash matrix 23 or certain humus types or compositions,24 for example, may act as effective cesium absorbers, whereas other humus types may allow rainfall to wash out any superficial cesium beneath the levels of the roots. 25 Other factors such as the presence of fungal communities also affect cesium fixing in soil,26 causing large fluctuations in concentration.18 In any case, the contribution from old radiocesium to the total activity in the sample appears negligible for the attempted source identification study, because the ratio scatters in the range of 1 for all samples. Radiocesium Activity Ratios in Distinct Regions. In contrast to the Chernobyl accident, the Fukushima accident involved four different reactors (four different source terms) that released their radioactivity sequentially over a period of time. As illustrated above, the activity ratio of 134Cs/137Cs can act as a measure for the age of nuclear fuel and hence as a fingerprint for a certain source. Since reactor No. 4 of the Fukushima NPP was shut down for three and a half months prior to the accident, any releases from its fuel in the spent fuel pool carried a signature corresponding to at least this decay time. A physical decay period of three months resulted in a 1251

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Figure 3. Ratio of the activity concentrations of 134Cs/137Cs in food vs distance to Fukushima NPP. Southern directions are indicated with positive values; northern directions with negative values. All data were decay corrected to 11 March 2011.

consideration. Figure 4 shows the 134Cs/137Cs activity ratios, decay corrected to the time of purchase. The red line in Figure 4 represents physical decay of the radiocesium ratio expected for fuel in mid to late life according to the simulated value (see ref 22 as cited in ref 3), starting at a ratio of 1.2. The black radiocesium ratio trend line was obtained by taking into account all of the measured data points (observed data). A ratio of 0.98 (for the black line) was calculated as the starting point, from which radioactive decay effects can be observed. The observed ratio trend line (black) is virtually parallel to the line (red) produced by assuming that the ratio is 1.2 (fuel in mid to late life). Comparing the decayed ratio values of radiocesium observed and the ratio expected for fuel that is in the middle or late in life, Figure 4 shows the ratios remain parallel. Thus it seems highly unlikely that the source term had a 134/137Cs ratio of 1.2.27 Figure 4 also allows the assessment of later releases of radioactivity from the reactors. Following the major releases in mid-March of 2011, minor atmospheric releases of radionuclides have been reported until approximately the beginning of April (even less significant releases continued until at least the end of 2011). Any releases after March 2011 either exhibited the identical radiocesium ratio, or, what is more likely, the activity release was insignificant compared to the releases between 12 March and the beginning of April. Later reports on the release of volatile short-lived radionuclides (October 2011) raised concern with respect to a possible continuation of a nuclear chain reaction, which would have raised the ratio again,

but no increase in the ratio can be seen in Figure 4. Ultimately, spontaneous fission of heavy nuclides was thought as the source of the reported short-lived radionuclides.28 Later contributions to the environmental radiocesium inventory were insignificant compared with the early releases and thus did not affect the monitored radiocesium ratio, because the monitoring data do not show any sudden increase in the ratio during the time after the accident. Any large releases due to a criticality post-March 2011 would be expected to alter the radiocesium ratio such that it would be apparent in Figure 4. Contamination Levels of Food from the Supermarkets. Food contamination levels can be utilized to provide an estimate of long-term internal radiation dose. The main use of available radiation detection capabilities in Japan is to identify food that is above the regulatory contamination limits, and analysis of detectable, but below the regulatory limit contamination receives less attention. The activity concentrations of anthropogenic radionuclides in the food samples submitted to the Atominstitut in Vienna are tabulated in Table S-1. The vegetables listed in Table S-1 include typical Japanese cuisine such as chingensai (qing-gengcai; spinach-like green vegetable), shungiku (garland chrysanthemum), mizuna (potherb mustard), and onigiri (tuna inside rice ball wrapped in seaweed). The radiation dose to members of the public (>17 years of age) was calculated based on consumption of the items in Table S-1 using eq 1. With the exception of tap water, 131I activities had fallen below the 1252

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Figure 4. Ratio of the activity concentrations of 134Cs/137Cs vs date of purchase. The red decay curve (labeled simulation) is based on an expected 1.2 134/137Cs ratio from middle to late life fuel and the black line is the decay corrected ratio of all samples analyzed (observed). Decay correction was to the individual dates of purchase of samples.

1990 of 1990 designating the maximum permitted levels of radioactive contamination of animal feed following a nuclear accident. The DG for Health and Consumers basically resurrected the “Chernobyl regulatory limits” by enacting these regulations. European regulatory limits were aligned with the Japanese limits on 11 April 2011, and the stricter Japanese regulatory limits were adopted for the EU.32 After minor adaptions (Regulation Nos. 506/2011 and 657/2011) a consolidation of the regulations resulted in Regulation No. 961/2011. Later modifications (Regulation Nos. 1371/2011 and 250/2012) were finally followed by Regulation No. 284/2012 that is in force at present.33 Again, the stricter Japanese limits were incorporated into European legislation. It is interesting to note that the European limits (Regulation No. 351/2011) reinstituted values from Chernobyl Regulation No. 3954/1987 for radiostrontium although no such limits were adopted by Japanese authorities (where radiostrontium was considered to coexist together with radiocesium, assuming one tenth of the 137Cs activity for 90Sr, see ref 3). This resulted in a bizarre discrepancy of stricter limits for radiocesium and less restrictive limits for bone-seeking radiostrontium in water and food (see Table 1). Regulation No. 284/2012 noted that, since there were no significant releases of strontium, plutonium, and americium following the accident, control for the presence of these radionuclides in food or feed from Japan was not

detection limit due to physical decay at the time of purchase and measurement. Development of the Regulatory Limits. The regulatory limits for radioactivity in food are in place to prevent potential health hazards that might occur due to the consumption of contaminated food by the public. Table 1 lists the regulatory limits set by the Japanese government and by the European Union (EU), respectively, both of which are effective since April 2012, as well as previous limits. The Japanese “provisional regulation values”, based on index values,13 were stipulated on 17 March (general food) and 5 April 2011 (radioiodine in seafood).3 Japanese regulatory limits for radiocesium were reduced on 1 April 2012 by a factor between 4 and 20.29 European regulatory limits after the Fukushima accident were topic of intense discussions and modifications in the EU. The European Directorate General (DG) for Health and Consumers enacted limits on radionuclide concentration in food for imports from Japan on 25 March 2011 (Commission Implementing Regulation No. 297/2011).30 These regulations included the Council Regulation (Euratom) No. 3954/1987 of 198731 designating the maximum permitted levels of radioactive contamination of food and animal feed following a nuclear accident; Commission Regulation (Euratom) No. 944/ 1989 of 1989 designating the maximum permitted levels of radioactive contamination in minor foods following a nuclear accident; and Commission Regulation (Euratom) No. 770/ 1253

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necessary. As a consequence these radionuclides were not addressed in Regulation No. 284/2012.33 Further, European limits only apply for imports from Japan. Agricultural products originating in countries adjacent to the accident at the Chernobyl nuclear power station still have much higher limits (e.g., 600 Bq·kg−1 for radiocesium in other than infant food),34 which once again illustrates inconsistency in European limits. Categorization of the Samples from the Supermarkets. An analysis of the 18 samples obtained at supermarkets was performed by the Atominstitut in Vienna to ascertain compliance with regulatory limits and to calculate internal dose to a member of the public. The activity concentrations in the food listed in Table S-1 together with the regulatory limits according to the European or Japanese regulations (Table 1) demonstrate that none of the limits in force at the time of analysis were exceeded. Note that the small, random sample utilized here may not necessarily reflect the overall levels of activity in Japanese food. The highest activities of 134Cs and 137Cs were found in a sample of plums from Fukushima Prefecture (32 and 36 Bq·kg−1, respectively). A member of the public would receive a dose of 1 mSv only by consuming as much as 2.6 kg of plums every day over a period of one year. All other samples in Table S-1 were less contaminated than the plums. Consequently, the consumption levels required for a member of the public to obtain an annual dose of 1 mSv would be ridiculously high. In any case, according to the data of ref 35, radiocesium concentrations in the rice sample from the Fukushima Prefecture was approximately 100 times higher than before the Fukushima accident. A hypothetical one-time intake of 1 L of radiocesium contaminated water at the initial maximum level of the regulatory limits (1000 Bq·kg−1 in Europe; 200 Bq·kg−1 in Japan; see Table 1) would deliver to an adult a committed effective dose of 0.016 mSv (Europe) or 0.0032 mSv (Japan), respectively (assuming an activity ratio of 134Cs/137Cs of 1). The corresponding acceptable annual daily consumption leading to a dose of 1 mSv after one year is 171 or 856 mL, respectively, illustrating the conservative approach behind the concept of the annual daily consumption. Assuming a daily consumption of 2 L of water contaminated with radiocesium at the maximum level of the above-mentioned regulatory limits theoretically would result in a dose of 12 mSv (Europe) and 2.3 mSv (Japan) after one year (adults). In an inverted approach, assuming a consumption of 2 L per day would result in a dose of 1 mSv after 1 year, at the maximum constant activity of radiocesium of 89 Bq·L−1. Stricter Regulatory Limits: Necessary Adjustment or Lipstick on a Pig? After any nuclear accident, stricter regulatory limits are naturally appreciated by the public, because they imply increased safety. In any case, under which circumstances are stricter regulatory actions justified from a radiological point of view? The original philosophy behind the European regulatory limit values that were issued after the Chernobyl accident31 was that the consumer should not receive a dose exceeding the maximum permissible additional annual dose of 1 mSv under the assumption that 10% of the entire amount of foodstuffs ingested by the consumer is contaminated at the maximum permissible level, whereas the other 90% are assumed to be completely uncontaminated (M. Ditto, Austrian Federal Ministry of Health, personal communication). In the authors’ opinion, this approach was quite reasonable. Since the

Valid from 25 March 2011 until 10 April 2011. bValid from 11 April 2011 until 31 March 2012. cValid from 1 April 2012. dValid from 17 March 2011 until 31 March 2012. eValid from 1 April 2012. fBaby foods are defined as those foodstuffs intended for the feeding of infants during the first four to six months of life, which meet, in themselves, the nutritional requirements of this category of person and are put up for retail sale in packages which are clearly identified and labeled ″food preparation for infants″. gLiquid foodstuffs as defined in the heading 2009 and in chapter 22 of the combined nomenclature. Values are calculated taking into account consumption of tap water, and the same values should be applied to drinking water supplies at the discretion of competent authorities in Member States. hCarbon14, tritium, and potassium-40 are not included in this group. IAll values were in Bq·kg −1 at the time of consumption (ingestion).

20d/−e 20d/ −e uranium 125a/125b/ −c 750a/750b/ −c 125a/125b/ −c 75a/75b/ −c

alpha-emitting isotopes of plutonium and transplutonium elements, notably Pu-239, Am-241 isotopes of strontium, notably Sr-90

400a/ 200b/ 50c a b 1 /1 /−c all other nuclides of half-life greater than 10 daysh, notably Cs-134, Cs-137

Article

a

20d/−e 100d/−e

1d/−e 1d/−e plutonium and other transuranic α emitters

1d / −e

10d/−e

200d/ 10e 200d/ 50e radiocesium

−d/ 50e

500d/ 100e

300d/−e 2000d/−e 300d/ −e

2000a/ 2000b/ −c 1250a/ 500b/ 100c 80a/10b/−c 500a/ 300b/ −c 1000a/ 200b/ 50c 20a/1b/−c 150a/ 100b/−c isotopes of iodine, notably I-131

dairy produce

500a/ 300b/ −c 1000a/ 200b/ 10c 20a/1b/−c

radioiodine

100d/ −e

drinking water vegetables, cereals, meats, eggs, seafood and other foodstuffs milk

Japan

infant foods liquid foodstuffsg other foodstuffs except minor foodstuffs baby foodsf

European Union

Table 1. Regulatory Limits for Radioactivity in Foodstuffs (Selected Data) Listed for Different Radionuclide-Groups and Compared for Japan and the EU Member States and Their Historical EvolutionI

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radionuclides in certain foods (e.g., radiocesium in mushrooms or fish) will be of importance as well as the determination of the ecological half-life in affected areas. Concerning legislation on a European level, we hope that the current regulatory limits will be reviewed in-depth (especially with respect to any future nuclear accidents), leading to regulatory limits that not only satisfy the population’s desire for utmost food safety but also comply with current scientific standards.

Fukushima accident, the regulatory limits have become much stricter in Japan and Europe (down to 12.5% for baby food or even 1% for liquid food calculated from the initial European value; see Table 1). We assume that the average adult consumes approximately 1.5−1.7 kg of food excluding water and beverages daily (estimation based on data from ref 36). Based on the calculations above, one would need to eat 1.7 kg of food contaminated at a concentration of 100 Bq·kg−1 radiocesium (the current regulatory limit) every day to reach the 1 mSv threshold for public dose. In other words, the current regulatory limits assume that 100% (or theoretically even more) of the food consumed in one year could be contaminated at the maximum level allowed by regulatory limits. In this scenario, food contamination levels had to remain constant at the regulatory limit over a period of one year, and all food would have to originate in Japan and be from areas which were contaminated. These regulatory assumptions neglect both physical decay and any governmental efforts and actions toward replacing highly contaminated foods by less contaminated ones. In the authors’ opinion, the recently passed regulations probably represent an overly conservative approach. Food Safety after a Possible Future Accident. Thanks to enormous efforts, the Japanese Government seems to have secured both general food safety and ample availability of below-limit food in Japan (and have even been able to implement stricter limits). This situation, however, disguises the real problem: What happens after a future nuclear accident. In such scenario, governments will possibly immediately issue new regulatory limits. The most likely scenario is that the regulatory limits used on previous occasions will be reused for the presumably unforeseeable new situation (for radioiodine older limits had to be used because these are no longer included in the current regulatory limits); just as it happened in Europe after the Fukushima nuclear accident, when the Chernobyl limits were resurrected. Consequently, one can assume that the current (very low) values will be reissued after a future nuclear emergency. The lower limits may cause impacted countries a dilemma, because suddenly a large fraction of food may be contaminated beyond the very low regulatory limits and hence must not be sold in supermarkets − irrespective of posing any manifest health hazard. Note that regulatory limits are all based on the assumption that the public will consume the contaminated food at the regulatory limit for a year. Regulatory limits do not make any provision for food to be contaminated over a short-term. Since protective measures are typically put into place rapidly, and short-lived nuclides deliver the bulk of dose to the public, it is worthwhile to consider these factors when designating limits for food. Overly restrictive limits could leave the governments with two inconvenient options: either raising the limits again (presumably a very unpopular action) or potentially jeopardizing the availability of food by staying with the strict limits. In the authors’ opinion, legislation should follow the ALARAprinciple, as described by the ICRP, which states that dose and the hazards of ionizing radiation should be As Low As Reasonably Achievable. Fortunately, some member states of the EU have already suggested an in-depth revision of the entire EU legislation with respect to food safety after a nuclear accident. We hope that the outcome of this debate will provide not only food safety but also a sense of proportion regarding the hazards of ionizing radiation. Outlook. The efforts toward food safety in Japan must and will continue. In particular, the possible enrichment of

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ASSOCIATED CONTENT

S Supporting Information *

Methodological information, activity concentrations of each sample (Table S-1 as well as separate list), a map of their origin (prefecture) (Figure S-1), a discussion of low dose effects and of internal exposure as well as the temporal evolution of the committed effective dose (Figure S-2). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +43 1 58801 141389. Fax: +43 1 58801 14199. E-mail: [email protected]; [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank K. Nemoto, B. Munro, S. Takenoshita, A. Mengoni, and M. Pietraszkiewicz for providing the foodstuff samples investigated herein as well as D. Hainz (Atominstitut, Austria) for technical assistance. We are also indebted to M. Ditto (Austrian Federal Ministry of Health) for valuable discussion of the regulatory limits and T. E. Johnson (Colorado State University, United States) for critical reading of the manuscript. Further we would like to gratefully acknowledge financial support to this study by the Austrian Federal Ministry for Agriculture, Forestry, Environment and Water Management (BMLFUW) and the Dr. Michael-Häupl-Fonds.

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