Extractability of radiocesium from processed green tea leaves with hot water: the first emergent tea leaves harvested after the TEPCO’s Fukushima Daiichi Nuclear Power Plant accident

Comparisons of effective half-lives of radiocesium in Japanese tea plants after two nuclear accidents, Chernobyl and Fukushima

The time-dependence of ¹³⁷Cs in new shoots of tea (Camellia sinensis (L.) Kuntze) following a¹³⁷Cs-deposition was analyzed and quantified in terms of effective half-lives. The underlying monitoring studies were performed after the accidents in the Chernobyl and the Fukushima Daiichi nuclear power plants for tea plants growing in Japan. The major transfer route for atmospherically deposited radiocaesium to the first new shoots sampled after the accidents were different: for the Fukushima accident, it was mainly translocation of radiocaesium deposited onto old leaves and twigs to the new growth, while direct deposition on the new leaves was the major source after the Chernobyl accident. The effective half-lives in new tea leaves representing the fast and slow components of the decline did not significantly differ between these accidents. Geometric means (ranges) of fast and slow effective half-lives of ¹³⁷Cs after the Chernobyl accident were 66 d (25-125 d) and 902 d (342-15900 d), respectively, and those after the Fukushima accident were 50 d (26-105 d) and 416 d (222-1540 d), respectively. From these results, ¹³⁷Cs declines in new tea leaves were similar although contamination conditions were different for these two accidents.

Radionuclides in tea and their behaviour in the brewing process

Tea plantations may be strongly affected by radioactive fallout. Tea plantations on the Turkish coast of the Black Sea were heavily contaminated by the fallout from the reactor fire at the Chernobyl nuclear power plant in 1986. Two years later, the contamination level was reduced by about 90%. When tea is brewed, the original contamination in the tea leaves is more or less leached into the tea water. While most of the radiocaesium (60-80%) is washed out by brewing, most of the radiostrontium remains in the leaves (70-80%). In food laws, a dilution factor of 40-50 is considered for tea brewing. Most laws only define limit values for radiocaesium. Radiostrontium is not specially regulated, even though its dose coefficients for ingestion are higher than the corresponding coefficients for radiocaesium. Radiostrontium in tea occurs primarily from global fallout (bomb tests from 1945-1965).

The determination of Fukushima-derived cesium-134 and cesium-137 in Japanese green tea samples and their distribution subsequent to simulated beverage preparation

Health Canada's Radiation Protection Bureau has identified trace quantities of (134)Cs and (137)Cs in commercially available green tea products of Japanese origin. Referenced to March 11, 2011, the activity ratio ((134)Cs/(137)Cs) has been determined to be 1:1, which supports an origin from the Fukushima Dai-ichi Nuclear Power Plant accident. The upper limits of typical tea beverage preparation conditions were applied to the most contaminated of these green tea samples to determine the proportion of radiocesium contamination that would be available for human consumption. The distribution of radiocesium among the components of the extraction experiments (water, residual tea solid, and filter media) was determined by both conventional and Compton-suppressed gamma spectroscopy. The latter aided tremendously in providing a more complete radiocesium distribution profile, particularly for the shorter-lived (134)Cs. Cesium extraction efficiencies of 64 ± 7% and 64 ± 5% were determined based on (134)Cs and (137)Cs, respectively. Annual, effective dose estimates from ingestion of (137)Cs and (134)Cs (1.8-3.7 μSv), arising from the consumption of tea beverages prepared from the most contaminated of these samples, are insignificant relative to both total (∼ 2.4 mSv) and ingested (∼ 0.28 mSv) annual effective doses received from naturally occurring radioactive sources. As such, there is no health concern arising from the consumption of green tea beverages contaminated with radiocesium at the levels encountered in this study.

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.

Activity concentrations of environmental samples collected in Fukushima Prefecture immediately after the Fukushima nuclear accident

Radionuclide concentrations in environmental samples such as surface soils, plants and water were evaluated by high purity germanium detector measurements. The contribution rate of short half-life radionuclides such as ¹³²I to the exposure dose to residents was discussed from the measured values. The highest values of the ¹³¹I/¹³⁷Cs activity ratio ranged from 49 to 70 in the environmental samples collected at Iwaki City which is located to the south of the F1-NPS. On the other hand, the ¹³²I/¹³¹I activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the ¹³²I/¹³¹I activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by ¹³²I was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by ¹³²I might be negligible if ¹³²I contamination was restricted to Iwaki City.

The transfer of radioactive cesium and potassium from rice to sake

Using rice grains contaminated with radioactive cesium ((134)Cs and (137)Cs) that was released by the Fukushima Daiichi Nuclear Power Plant Accident in March of 2011, we investigated the behaviors of the radioactive cesium and potassium (total K and (40)K) during sake brewing. Cesiumis a congener of K, and yeast cells have the ability to take up Cs using known K transporters. During rice polishing, the concentrations of radioactive Cs and K in the polished rice grains decreased gradually until a milling ratio (polished rice weight/brown rice weight) of 70% was reached. No significant changes were observed below this milling ratio. Sake was brewed on a small scale using the 70% polished rice. The transfer ratio of radioactive Cs to sake and to the sake cake was significantly different than the ratio of K. Approximately 36% and 23% of radioactive Cs in the polished rice was transferred to the sake and sake cake, respectively; however, 40% was removed by washing and steeping the rice grains. On the other hand, 25% and 40% of K in the polished rice was recovered in the sake and sake cake, respectively, and 35% was removed by washing and steeping the rice grains. From the present results, the concentration of radioactive Cs in sake would be 4 Bq/kg fresh weight, which is well below the regulation values (100 Bq/kg), even using brown rice containing 100 Bq/kg of radioactive Cs.

Anthropogenic radionuclides in Japanese food: environmental and legal implications

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 ((134)Cs/(137)Cs) 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 (134)Cs/(137)Cs 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.