Shioka Hamamatsu

Exchangeable Cs/K ratio in soil is an index to estimate accumulation of radioactive and stable Cs in rice plant

Abstract Pot and field experiments were conducted to clarify the effect of soil exchangeable potassium (K) and cesium-137 (137Cs) on 137Cs accumulation and to establish soil index in rice (Oryza sativa L.). Four paddy soils in Fukushima Prefecture, Japan, showing different transfer factors for radioactive Cs derived from the accident of Fukushima Daiichi Nuclear Power Station in the field were compared in terms of 137Cs accumulation in rice in a pot experiment. 137Cs accumulation in shoots and brown rice widely varied among soils with the transfer factor ranging from 0.018 to 0.068 for shoots and 0.004 to 0.065 for brown rice. 137Cs concentration in brown rice and shoots tended to decrease with higher levels of soil exchangeable K, and they were more closely related to the exchangeable Cs/K ratio. Similar relationships between the Cs/K ratio and Cs accumulation in plants were obtained for the stable isotope cesium-133 (133Cs). The distributions of 137Cs and 133Cs in grains were also similar and variable among soils. The transfer factors obtained in pot experiments mostly agreed with field observations. The results imply that the exchangeable 137Cs/K can be a potential soil index to estimate 137Cs accumulation in rice.

Distribution of Radioactive Cesium (134Cs plus 137Cs) in Rice Fractions during Polishing and Cooking

We investigated the distribution of cesium-134 ((134)Cs) and cesium-137 ((137)Cs) during polishing and cooking of rice to obtain their processing factors (Pf) and food processing retention factors (Fr) to make the information available for an adequate understanding of radioactive Cs dynamics. Polishing brown rice resulted in a decreased radioactive Cs concentration of the polished rice, but the bran and germ (outer layers) exhibited higher concentrations than brown rice. The Pf values for 100% polished rice and outer layers ranged from 0.47 to 0.48 and 6.5 to 7.8, respectively. The Fr values for 100% polished rice and outer layers were 0.43 and 0.58 to 0.60, respectively. The distribution of radioactive Cs in polished rice and outer layers was estimated at approximately 40 and 60%, respectively. On the other hand, cooked rice showed significantly lower levels of radioactive Cs than polished rice, and transfer of radioactive Cs into wash water was observed. The Pf and Fr values for cooked rice were 0.28 and 0.65 to 0.66, respectively. From these results, we can calculate that if the radioactive Cs concentration in brown rice is 100 Bq/kg, the concentrations of Cs in polished rice and cooked rice will be 47 to 48 Bq/kg and 13 Bq/kg, respectively.

Characterization of brown rice as a certified reference material for Fukushima accident-related radioactivity measurements.

We developed a certified reference material of brown rice to measure radioactivity from the Fukushima Daiichi Nuclear Power Plant accident. The rice was planted in the spring of 2011, just after the Fukushima accident occurred, and it was harvested in the autumn of 2011. The certified value of radioactivity concentration in the rice was 33.6 Bq kg(-1) of Cs-134 and 51.8 Bq kg(-1) of Cs-137 on August 1, 2012. The reference material is being widely distributed by the National Metrology Institute of Japan. To determine the radioactivity and its uncertainties in the brown rice, we employed gamma-ray spectrometry with a high-purity germanium detector and Monte Carlo simulation.

Distribution of radioactive cesium ((134)Cs Plus(137)Cs) in a contaminated Japanese soybean cultivar during the preparation of tofu, natto, and nimame (Boiled Soybean).

We investigated the fate of radioactive cesium ((134)Cs plus (137)Cs) during the production of tofu, natto, and nimame (boiled soybean) from a contaminated Japanese soybean cultivar harvested in FY2011. Tofu, natto, and nimame were made from soybean grains containing radioactive cesium (240 to 340 Bq/kg [dry weight]), and the radioactive cesium in the processed soybean foods and in by-product fractions such as okara, broth, and waste water was measured with a germanium semiconductor detector. The processing factor is the ratio of radioactive cesium concentration of a product before and after processing. For tofu, natto, nimame, and for the by-product okara, processing factors were 0.12, 0.40, 0.20, and 0.18, respectively; this suggested that these three soybean foods and okara, used mainly as an animal feed, can be considered safe for human and animal consumption according to the standard limit for radioactive cesium of soybean grains. Furthermore, the ratio of radioactive cesium concentrations in the cotyledon, hypocotyl, and seed coat portions of the soybean grain was found to be approximately 1:1:0.4.

Homogeneity of wheat flour in 5 ml containers for certified reference materials

We aimed to develop certified reference materials that could be used for well-type HPGe detector. We chose wheat flour as a sample and evaluated the homogeneity of the sample in well-type container (5ml). Results showed that inhomogeneity was sufficiently small for validation checks of well-type HPGe detector (uhom = 0.44%).