Inspections of radiocesium concentration levels in rice from Fukushima Prefecture after the Fukushima Dai-ichi Nuclear Power Plant accident

On-Site Ratiometric Analysis of UO22+ with High Selectivity

Uranyl ions (UO22+) are recognized as important indicators for monitoring sudden nuclear accidents. However, the interferences coexisting in the complicated environmental matrices impart serious constraints on the reliability of current on-site monitoring methods. Herein, a novel ratiometric method for the highly sensitive and selective detection of UO22+ is reported based on a [Eu(diaminoterephthalic acid)] (Eu-DATP) metal-organic framework. Benefiting from the unique chemical structure of Eu-DATP, energy transfer from DATP to UO22+ was enabled, resulting in the up-regulated fluorescence of UO22+ and the simultaneous down-regulated fluorescence of Eu3+. The limit of detection reached as low as 2.7 nM, which was almost 2 orders of magnitude below the restricted limit in drinking water set by the United States Environmental Protection Agency (130 nM). The Eu-DATP probe showed excellent specificity to UO22+ over numerous interfering species, as the intrinsic emissions of UO22+ were triggered. This unprecedentedly high selectivity is especially beneficial for monitoring UO22+ in complicated environmental matrices with no need for tedious sample pretreatment, such as filtration and digestion. Then, by facilely equipping a Eu-DATP-based sampler on a drone, remotely controlled sampling and on-site analysis in real water samples were realized. The concentrations of UO22+ were determined to be from 16.5 to 23.5 nM in the river water of the Guangzhou downtown area, which was consistent with the results determined by the gold-standard inductively coupled plasma mass spectrometry. This study presents a reliable and convenient method for the on-site analysis of UO22+.

Conceptualization of the comprehensive phyto-radiotoxicity incurred by radiocesium and strategies to expunge the metal using biotechnological and phytoremediative approaches

Agricultural pollution with 137Cs is an ecological threat due to its sustained half-life and radioactivity. Release of radiocesium isotopes after major nuclear power plant accidents like the Fukushima Dai-ichi and the Chernobyl nuclear power plant disasters have severely affected the surrounding growth of agricultural crops and vegetables cultivated across extensive areas. Even years after the nuclear accidents, biosafety in these agricultural fields is still questionable. Due to similarity in charge and ionic radius between radiocesium and K+, the radionuclides are promiscuously uptaken via K+ channels expressed in plants. Bioaccumulation of radiocesium reportedly promotes physiological and anatomical anomalies in crops due to radiation and also affects the rhizospheric architecture. Due to radiation hazard, the ecological balance and quality are compromised and ingestion of such contaminated food results in irreversible health hazards. Recently, strategies like exogenous supplementation of K+ or genetic engineering of K+ channels were able to reduce radiocesium bioaccumulation in plants taking the advantage of competition between radiocesium and K+ translocation. Furthermore, bioremediation strategies like phycoremediation, mycoremediation, phytoremediation and rhizofiltration have also showed promising results for removing radiocesium from polluted sites. It has been proposed that these eco-friendly ways can be adopted to de-pollute the contaminated sites prior to subsequent cultivation of crops and vegetables. Hence it is essential to: 1) understand the basic radiotoxic effects of radiocesium on agricultural crops and surrounding vegetation and, 2) design sustainable ameliorative strategies to promote radiocesium tolerance for ensuring food and social security of the affected population.

Change in sense of food safety associated with social connectedness and information sources-A 10-year longitudinal survey before and after the Fukushima nuclear power plant accident

OBJECTIVES

This study analyzes the change in the sense of food safety over time, from 2 years before to 8 years after the Fukushima accident in 2011, and its association with social connectedness using cohort data, taking into account regional differences in Fukushima Prefecture.

STUDY DESIGN

Repeated cross-sectional data from Fukushima Prefectural Government from 2009 to 2018 were used.

METHODS

We randomly selected 1300 people every fiscal year (FY). The survey gathered data on age, gender, occupation, residential region, and the explanatory variables 'sense of social connectedness' and 'recovery-related information source' (information source). The prefecture was divided into three regions for the survey-Hamadori region, where the nuclear power plant is located, Nakadori region, where the air dose rate after the earthquake was high, and in Aizu, far from the nuclear power station but has suffered from harmful rumors.

RESULTS

Focusing on FY 2014, when the sense of safety first showed recovery, we performed a binominal logistic regression analysis with 'sense of safety' as the outcome and 'sense of social connectedness' and 'information source' as the explanatory variables. The sense of safety significantly decreased in all regions in 2011 relative to earlier years. The sense of food safety decreased markedly in Hamadori and Nakadori but started to improve 3 years after the earthquake and reached the pre-earthquake level in 2018. The effect sizes were larger in the Hamadori region and in Nakadori than in Aizu. In FY 2014, multivariate analysis found that a sense of food safety was significantly positively associated with a sense of social connectedness, whereas the use of information from newspapers and TV and word of mouth was negatively associated.

CONCLUSION

Although the recovery of a sense of food safety may take some time, a focus on social connectedness during recovery and scrutiny of information sources may facilitate recovery. Health communication has an important role when the provider sends information intelligibly and the recipient can distinguish good news from bad and link it to self-determination. It is necessary to improve literacy.

Influence of irrigation water intake on local increase of radiocesium activity concentration in rice plants near a water inlet

To identify the cause of the phenomenon that rice plants close to the water inlet contain relatively higher radiocesium within a paddy field plot, we conducted a field experiment by establishing experimental channel using polypropylene corrugated sheets, and sampling surface water, paddy soil and rice plants according to the distance from the water inlet in 2014 and 2015. It was found that the ¹³⁷Cs activity concentrations in both dissolved and particulate forms in paddy surface water presented a declining trend from the water inlet towards the outlet. The ¹³⁷Cs activity concentration in paddy soil in the harvesting season and those of brown rice and rice straws were highest at 1-2 m from the water inlet. Balance calculation suggests that destination of the lost ¹³⁷Cs from the surface water was likely to be adsorption of the dissolved form and sedimentation of particulate form onto the soil. The concentration of exchangeable potassium ion in paddy soil was below the recommended standard of 250 mg kg^-1 (as K₂O in dry soil) near the water inlet at the harvesting period both years．These findings suggested that the possible crucial factors to induce rice plant uptake of radiocesium near the water inlet were either (1) direct absorption of dissolved ¹³⁷Cs in surface water by rice plants, (2) absorption of ¹³⁷Cs, which was originally retained in particulate matter and released by ion exchange and/or by organic matter decomposition in combination with (3) loss of soil exchangeable potassium caused due partly to transportation of soil particles with exchangeable potassium by the rapid water flow near the water inlet and/or leaching by ion exchange onto the soil of other cations such as calcium ion flowing into the paddy field. These findings will contribute to providing possible measures for producing safe rice in highly contaminated areas in which agricultural production will resume in the near future. We propose providing a non-planting zone for the area closer than about 5 m from the water intake to avoid the occurrence of high ¹³⁷Cs concentrations in rice crops.

Effects of cesium accumulation on chlorophyll content and fluorescence of Brassica juncea L

The aim of our study was to investigate the toxicological mechanism of cesium on Indian mustard (Brassica juncea L.). The impact of cesium toxicity to plants was evaluated using phytophysiology and genetic methods. In this study, Brassica juncea was grown on Cs-contaminated Hoagland's nutrient solution, and chlorophyll content, chlorophyll fluorescence, and Cs bioaccumulation were measured. Transcriptome data was used to perform an in-depth analysis of the molecular mechanisms underlying the effects of Cs accumulation. The results showed that Cs accumulated up to 3586.70 mg kg^-1 in B. juncea treated with 100 mg L^-1 Cs. The chlorophyll content and several chlorophyll fluorescence parameters (F_v/F₀, F_v/F_m, ΦPS II, qP, and NPQ) significantly decreased under Cs exposure. The starting process of PSII was also inhibited under higher Cs conditions. These results indicate that excessive Cs can damage PS II in leaves, decreasing photochemical activity and the energy conversion rate. Further analysis revealed that Cs interfered with the expression of chloroplastic metabolic genes (25 up and 36 down) and inhibited the expression of PsaB, psbC, PetF, LHCA1, and LHCB5. The results indicate that stable Cs leads to abnormal expression of genes related to photosynthesis pathway, blocking the electron transport process from plastoquinone-QA to plastoquinone-QB, resulting in abnormal photosynthesis, which leads to abnormal growth of B. juncea.

Source evaluation of 137Cs in foodstuffs based on trace 134Cs radioactivity measurements following the Fukushima nuclear accident

We performed gamma-ray analysis to determine the amount of radioactive cesium-134 (¹³⁴Cs) and cesium-137 (¹³⁷Cs) in 259 foodstuffs five years after the Fukushima nuclear accident of 2011. Using measurements of trace ¹³⁴Cs radioactivity, we investigated the contribution ratio of ¹³⁷Cs derived from the Fukushima accident on 2011 and pre-Fukushima. The median detected concentration of radiocesium (¹³⁴Cs + ¹³⁷Cs) in foodstuffs was 0.33 Bq/kg-raw, a much lower radioactivity than the Japanese regulatory limit. However, a few samples had particularly high radioactivity, including some dried mushrooms sold in Iwate Prefecture that had a ¹³⁷Cs radioactivity concentration as high as 441 Bq/kg. Our analysis showed that 75.5% of the ¹³⁷Cs detected in these mushrooms originated from the Fukushima accident, and 24.5% was originated before the Fukushima event. Our study clarified the ¹³⁷Cs contamination in 75 of all 259 food samples before and after the Fukushima nuclear accident, showing that not only mushrooms but also fish had been contaminated before the Fukushima accident.

The Knowledge and Awareness for Radiocesium Food Monitoring after the Fukushima Daiichi Nuclear Accident in Nihonmatsu City, Fukushima Prefecture

On 11 March 2011, Japan experienced a massive earthquake and tsunami that triggered the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, resulting in the release of large amounts of cesium-134 and -137 into the atmosphere. In addition to the food radioactivity control in the markets throughout the country, radiocesium concentrations in locally grown foods were voluntarily inspected and the results were shown to the residents by the local government to raise their awareness of the internal radiation contamination risk from low knowledge in Nihonmatsu City, Fukushima Prefecture. In this longitudinal study, local food products for in-home consumption were evaluated by seven different food radioactivity measuring devices in Nihonmatsu City from 2011–2017. Radiocesium was detected in local foods in Nihonmatsu City even six years after the FDNPP accident. The highest number of products tested was in 2012, with the number steadily decreasing thereafter. Most foods had contamination levels that were within the provisional regulation limits. As edible wild plants and mushrooms continue to possess high radiocesium concentrations, new trends in radioactivity in foods like seeds were discovered. This study highlights that the increased risk of radiation exposure could possibly be due to declining radiation awareness among citizens and food distributors. We recommend the continuation of food monitoring procedures at various points in the food processing line under the responsibility of the government to raise awareness for the reduction of future risks of internal exposure.

Assessment of Instructions on Protection Against Food Contaminated with Radiocesium in Japan in 2011

The Japan Ministry of Health, Labour and Welfare (MHLW) has published instructions for radiological protection against food after the Fukushima Daiichi nuclear power plant accident in 2011. Following the instructions, the export and consumption of food items identified as being contaminated were restricted for a certain period. We assessed the validity of the imposed restriction periods for two representative vegetables (spinach and cabbage) grown in Fukushima Prefecture from two perspectives: effectiveness for reducing dietary dose and economic efficiency. To assess effectiveness, we estimated the restriction period required to maintain consumers' dose below the guidance dose levels. To assess economic efficiency, we estimated the restriction period that maximizes the net benefit to taxpayers. All estimated restriction periods were shorter than the actual restriction periods imposed on spinach and cabbage from Fukushima in 2011, which indicates that the food restriction effectively maintained consumers' dietary dose below the guidance dose level, but in an economically inefficient manner. We also evaluated the response of the restriction period to the sample size for each weekly food safety test and the instructions for when to remove the restriction. Stringent MHLW instructions seemed to sufficiently reduce consumers' health risk even when the sample size for the weekly food safety test was small, but tended to increase the economic cost to taxpayers.

Agricultural aspects of radiocontamination induced by the Fukushima nuclear accident - A survey of studies by the Univ. of Tokyo Agricultural Dept. (2011-2016)

Immediately after the Fukushima nuclear power plant accident, a team of 40-50 researchers at the Graduate School of Agricultural and Life Sciences at the University of Tokyo began to analyze the behavior of radioactive materials in the fallout regions. The fallout has remained in situ and become strongly adsorbed within the soil over time. 137Cs was found to bind strongly to the fine clay, weathered biotite, and organic matter in the soil; therefore, it has not mobilized from mountainous regions, even after heavy rainfall. In farmland, the quantity of 137Cs in the soil absorbed by crop plants was small. The downward migration of 137Cs in soil is now estimated at 1-2 mm/year. The intake of 137Cs by trees occurred through the bark and not from the roots. This report summarizes the findings of research across a wide variety of agricultural specialties.

Characteristics of radiocesium contaminations in mushrooms after the Fukushima nuclear accident: evaluation of the food monitoring data from March 2011 to March 2016

The monitoring inspection of food after the Fukushima nuclear accident (2011) was essential for ensuring food safety in Japan and reducing the adverse health effects due to incorporation of inacceptable amounts of radionuclides, in particular radiocesium (¹³⁴Cs and ¹³⁷Cs). In this study, the mushroom fraction of the governmental data set of the first 5 years after the accident has been analyzed for contamination levels in mushrooms, in particular time trends and radioecological characteristics as well as associated health risks. The analyses show that mycorrhiza mushrooms are much more sensitive for radionuclide uptake than saprobiontic mushrooms (the latter of which include the very popular shiitake mushrooms (Lentinula edodes)). The maximum value reached 31,000 Bq/kg in a sample of apricot milkcaps in 2012. Analysis of the origin of the samples revealed that the origin (in terms of prefecture) of the mushrooms was a less determining factor for the contamination level than the type of mushrooms, as most exceedances in 2012 and thereafter were found outside Fukushima Prefecture. Several dose models were applied to the data to evaluate both worst case and realistic effective committed dose scenarios. The doses were generally rather low due to low consumption rates in the Japanese food basket. In any case, the analysis proved that the food monitoring campaign was highly effective in cutting doses to the public by more than a factor of 10 compared with a hypothetical scenario in which no monitoring had been conducted.

Time trends in radiocaesium in the Japanese diet following nuclear weapons testing and Chernobyl: Implications for long term contamination post-Fukushima

Estimation of time changes in radiocaesium in foodstuffs is key to predicting the long term impact of the Fukushima accident on the Japanese diet. We have modelled >4000 measurements, spanning 50 years, of ¹³⁷Cs in foodstuffs and whole diet in Japan after nuclear weapons testing (NWT) and the Chernobyl accident. Broadly consistent long term trends in ¹³⁷Cs activity concentrations are seen between different agricultural foodstuffs; whole diet follows this general trend with remarkably little variation between averages for different regions of Japan. Model blind tests against post-NWT data for the Fukushima Prefecture showed good predictions for radiocaesium in whole diet, spinach and Japanese radish (for which good long term test data were available). For the post-Fukushima period to 2015, radiocaesium in the average diet followed a declining time trend consistent with that seen after NWT and Chernobyl. Data for different regions post-Fukushima show a high degree of mixing of dietary foodstuffs between regions: significant over-estimates of average dietary ¹³⁷Cs were made when it was assumed that only regionally-produced food was consumed. Predictions of mean committed effective internal doses from dietary ¹³⁷Cs (2011 to 2061) in non-evacuated parts of the Fukushima Prefecture show that average internal dose is relatively low. This study focused on average regional ingestion dose rates and does not attempt to make site specific predictions. However, temporal trends identified could form a basis for site specific predictions of long term activity concentrations in agricultural products and diet both outside and (to assess potential re-use) inside currently evacuated areas.

Production of low-Cs+ rice plants by inactivation of the K+ transporter OsHAK1 with the CRISPR-Cas system

The occurrence of radiocesium in food has raised sharp health concerns after nuclear accidents. Despite being present at low concentrations in contaminated soils (below μm), cesium (Cs⁺ ) can be taken up by crops and transported to their edible parts. This plant capacity to take up Cs⁺ from low concentrations has notably affected the production of rice (Oryza sativa L.) in Japan after the nuclear accident at Fukushima in 2011. Several strategies have been put into practice to reduce Cs⁺ content in this crop species such as contaminated soil removal or adaptation of agricultural practices, including dedicated fertilizer management, with limited impact or pernicious side-effects. Conversely, the development of biotechnological approaches aimed at reducing Cs⁺ accumulation in rice remain challenging. Here, we show that inactivation of the Cs⁺ -permeable K⁺ transporter OsHAK1 with the CRISPR-Cas system dramatically reduced Cs⁺ uptake by rice plants. Cs⁺ uptake in rice roots and in transformed yeast cells that expressed OsHAK1 displayed very similar kinetics parameters. In rice, Cs⁺ uptake is dependent on two functional properties of OsHAK1: (i) a poor capacity of this system to discriminate between Cs⁺ and K⁺ ; and (ii) a high capacity to transport Cs⁺ from very low external concentrations that is likely to involve an active transport mechanism. In an experiment with a Fukushima soil highly contaminated with ¹³⁷ Cs⁺ , plants lacking OsHAK1 function displayed strikingly reduced levels of ¹³⁷ Cs⁺ in roots and shoots. These results open stimulating perspectives to smartly produce safe food in regions contaminated by nuclear accidents.

Japanese Food Data Challenge the Claimed Link between Fukushima's Releases and Recently Observed Thyroid Cancer Increase in Japan

Internal, high-dose exposure with radioiodine is known to increase the risk for thyroid cancer in children and adolescents. Ingestion of contaminated food is generally regarded a dominant route of internal exposure. We analyzed the huge data set of the post-Fukushima food monitoring campaign and deployed a conservative model for the estimation of the doses to the general public in a worst-case scenario. Our data suggest that the committed equivalent ingestion doses to the thyroids of the affected Japanese public, even in the utmost conservative approach, remained below the limit on ingestion of radioiodine in foodstuffs and beverages of 50 mSv (as thyroid equivalent dose). This level of 50 mSv is also the intervention level for the administration of stable iodine, mainly after inhalation. Our study hence suggests that, based on the food data, the internal exposure of Japanese residents was too low to cause a statistically discernible increase in thyroid cancer, even if the contribution from inhalation is taken into account. The data also indicate that the governmental efforts in the food monitoring campaign were successful and cut the thyroid doses to the public by a factor of approximately 3 compared to a scenario without any monitoring.

Low-cesium rice: mutation in OsSOS2 reduces radiocesium in rice grains

In Japan, radiocesium contamination in foods has become of great concern and it is a primary issue to reduce grain radiocesium concentration in rice (Oryza sativa L.). Here, we report a low-cesium rice mutant 1 (lcs1) with the radiocesium concentration in grain about half that in the wild-type cultivar. Genetic analyses revealed that a mutation in OsSOS2, which encodes a serine/threonine-protein kinase required for the salt overly sensitive (SOS) pathway in plants, is responsible for the decreased cesium (Cs) concentrations in lcs1. Physiological analyses showed that Cs+ uptake by lcs1 roots was significantly decreased under low-potassium (K+) conditions in the presence of sodium (Na+) (low K+/Na+). The transcript levels of several K+ and Na+ transporter genes, such as OsHAK1, OsHAK5, OsAKT1, and OsHKT2;1 were significantly down-regulated in lcs1 grown at low K+/Na+. The decreased Cs+ uptake in lcs1 might be closely related to the lower expression of these genes due to the K+/Na+ imbalance in the lcs1 roots caused by the OsSOS2 mutation. Since the lcs1 plant had no significant negative effects on agronomic traits when grown in radiocesium-contaminated paddy fields, this mutant could be used directly in agriculture for reducing radiocesium in rice grains.

Monitoring and radioecological characteristics of radiocesium in Japanese beef after the Fukushima nuclear accident

After the Fukushima nuclear accident, beef proved to be a problematic food item with several exceedances entering the market. The reason was contaminated rice straw that was fed to cattle. Japanese authorities responded quickly to the exceedances and made beef one of the most-monitored food items after the Fukushima accident with more than a million samples within 5 years. Activity levels dropped quickly and are now considerably below the regulatory limit. No exceedance of the regulatory limit was observed after October 2012. The monitoring campaign focuses on the pre-market to catch any exceedances before they reach the consumer. The analysis also showed that some late beef samples exhibited an unusually high ¹³⁴Cs/¹³⁷Cs activity ratio. The reason for this is unknown.

Research with radiation and radioisotopes to better understand plant physiology and agricultural consequences of radioactive contamination from the Fukushima Daiichi nuclear accident

Research carried out by me and my group over the last almost four decades are summarized here. The main emphasis of my work was and continues to be on plant physiology using radiation and radioisotopes. Plants live on water and inorganic elements. In the case of water, we developed neutron imaging methods and produced 15O-labeled water (half-life 2 min) and applied them to understand water circulation pattern in the plant. In the case of elements, we developed neutron activation analysis methods to analyze a large number of plant tissues to follow element specific distribution. Then, we developed real-time imaging system using conventional radioisotopes for the macroscopic and microscopic observation of element movement. After the accident in Fukushima Daiichi nuclear power plant, we, the academic staff of Graduate School, have been studying agricultural effects of radioactive fallout; the main results are summarized in two books published by Springer.

A comparison of the dose from natural radionuclides and artificial radionuclides after the Fukushima nuclear accident

Due to the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the evacuees from Namie Town still cannot reside in the town, and some continue to live in temporary housing units. In this study, the radon activity concentrations were measured at temporary housing facilities, apartments and detached houses in Fukushima Prefecture in order to estimate the annual internal exposure dose of residents. A passive radon-thoron monitor (using a CR-39) and a pulse-type ionization chamber were used to evaluate the radon activity concentration. The average radon activity concentrations at temporary housing units, including a medical clinic, apartments and detached houses, were 5, 7 and 9 Bq m(-3), respectively. Assuming the residents lived in these facilities for one year, the average annual effective doses due to indoor radon in each housing type were evaluated as 0.18, 0.22 and 0.29 mSv, respectively. The average effective doses to all residents in Fukushima Prefecture due to natural and artificial sources were estimated using the results of the indoor radon measurements and published data. The average effective dose due to natural sources for the evacuees from Namie Town was estimated to be 1.9 mSv. In comparison, for the first year after the FDNPP accident, the average effective dose for the evacuees due to artificial sources from the accident was 5.0 mSv. Although residents' internal and external exposures due to natural radionuclides cannot be avoided, it might be possible to lower external exposure due to the artificial radionuclides by changing some behaviors of residents.

Scientification and Social Control: Defining Radiation Contamination in Food and Farms

Issues related to the existence of low-level radiation in the environment, in food and on farms have added significant problems to the already problem-ridden reconstruction efforts that Japan faces after the crisis in March 2011. Radiation-related issues have brought to the surface hitherto hidden fault lines within society, especially the rifts in the varied interpretations of risk. Despite the deepseated concerns that some people have about the presence of ionised radiation, overt public objections are rarely seen nor heard. Against this backdrop, this article asks the question why the lay public, particularly victims of the disaster, is not more vocal in objecting and expressing concerns. The analysis sheds light on the social conditions that tend to suppress the expression of concern. The data are drawn from in-depth interviews with farmers and consumers in Fukushima and participant observations in public forums and seminars that concern radiation of food and farms. The study indicates that various forms of social control exist within the phenomenon which the author calls ‘scientification of food and agriculture’.

Evaluation of the cause of unexplained radiocaesium contamination of brown rice in Fukushima in 2013 using autoradiography and gamma-ray spectrometry

The Great East Japan Earthquake on 11 March 2011, caused the release of radioactive materials from the Fukushima Daiichi Nuclear Power Plant (FDNPP), contaminating eastern Japan, particularly in part of Fukushima Prefecture. In 2012 and 2014, the radiocaesium concentration in brown rice did not exceed regulatory levels in Minamisoma City, Fukushima. However, in 2013, some radiocaesium concentrations in brown rice exceeded regulatory levels. In this work, autoradiograms showed that high radioactivity was present as contaminated spots on the panicles of rice and in brown rice in 2013. We evaluate the contribution of direct contamination to the radiocaesium concentration in brown rice and discuss the origin of radiocaesium contamination in brown rice using the ¹³⁴Cs/¹³⁷Cs radioactivity ratio. Here, we show that the main cause of the unexplained radiocaesium contamination of brown rice in Minamisoma City in 2013 is the adherence of radioactive materials to the rice panicles, and these radioactive materials are associated with reactor units 2 or 3 of FDNPP.

Assessment of the effectiveness of the post-Fukushima food monitoring campaign in the first year after the nuclear accident: A hypothesis

The purpose of this study was to assess whether or not the food monitoring campaign after the Fukushima nuclear accident has been successful in reducing the number of above-limit-food from reaching the consumers. The hypothesis of this study is that the fraction of "post-market" food can be used for this purpose, when the post-market fraction in the above-limit (p') items is compared to the post-market fraction in the entity of food items (p) that have been screened for radionuclides ((134)Cs and (137)Cs). Indeed the post-market fraction in most vegetarian produce decreased significantly in the above-limit food items (p'/p < 1), indicating a high efficiency of the monitoring campaign. For tea, however, the analysis reveals a low efficiency of the campaign (p'/p ≈ 1). For beef, the fraction of post-market-foods within the above-limit samples was much higher than the respective fraction in the entity of measured samples (p'/p > 1), indicating a much lower effectiveness of the monitoring action for beef. The author speculates that, by following the governmental monitoring manual (which gives "meat" only second priority), the sudden exceedances caught the monitoring agencies unprepared and triggered a much higher density monitoring of beef with the delay of several weeks. Even then, many above limit items reached the market (mainly because the monitoring during this period had focused on the post-market). Therefore, it is likely that some above-limit beef has been consumed by the public. For other meat products, the fraction of post-market samples was very low, which does not allow for the validation of the effectiveness of the monitoring campaign. Overall, the monitoring seemed to have been more effective for vegetarian produce than for meat.

137Cs in the meat of wild boars: a comparison of the impacts of Chernobyl and Fukushima

The impact of Chernobyl on the ¹³⁷Cs activities found in wild boars in Europe, even in remote locations from the NPP, has been much greater than the impact of Fukushima on boars in Japan. Although there is great variability within the ¹³⁷Cs concentrations throughout the wild boar populations, some boars in southern Germany in recent years exhibit higher activity concentrations (up to 10,000 Bq/kg and higher) than the highest ¹³⁷Cs levels found in boars in the governmental food monitoring campaign (7900 Bq/kg) in Fukushima prefecture in Japan. The levels of radiocesium in boar appear to be more persistent than would be indicated by the constantly decreasing ¹³⁷Cs inventory observed in the soil which points to a food source that is highly retentive to ¹³⁷Cs contamination or to other radioecological anomalies that are not yet fully understood.

Effective and ecological half-lives of 90Sr and 137Cs observed in wheat and rice in Japan

Published pre-Fukushima food monitoring data from 1963 to 1995 were used to study the long-term presence of ¹³⁷Cs and ⁹⁰Sr in rice and wheat. Effective half-lives (T_eff) were calculated for rice (¹³⁷Cs: 5.6 years; ⁹⁰Sr: 6.7 years) and wheat (¹³⁷Cs: 3.5 years; ⁹⁰Sr: 6.2 years), respectively. In rice, ¹³⁷Cs exhibits a longer T_eff because putrefaction processes will lead to the formation of NH₄⁺ ions that are efficient ion exchangers for mineral-adsorbed cesium ions, hence making it more readily available to the plant. Knowledge on the long-term behavior of radiocesium and radiostrontium will be important for Japanese food-safety campaigns after the Fukushima nuclear accident.