Translocation of radiocesium from stems and leaves of plants and the effect on radiocesium concentrations in newly emerged plant tissues

Radioactive pollution and accumulation of radionuclides in wild plants in Fukushima

The radionuclide status of wild plants and soil in the Fukushima area was investigated during the period May 2011 to October 2012, using an imaging plate (autoradiograms) or a high purity germanium detector. Analyses of autoradiograms showed that wild plants grown in March 2011 were strongly polluted with fallout released from the Fukushima 1 Nuclear Power Plant. The radioactivity was mostly due to fallout adsorbed on the surface of the plants. On the other hand, a number of herbaceous plants were regularly collected in the Fukushima area and their radionuclide concentrations were measured with a high-purity germanium detector. Plants grown in March 2011 showed very high levels of ¹³⁴Cs and ¹³⁷Cs, but these radioactivity levels decreased rapidly after July 2011 and eventually became lower than that of endogenous ⁴⁰K. During this period, the radioactivity of the soil remained high. We therefore suppose that a significant proportion of the radioactivity detected from plants harvested after July 2011 was most likely derived from soil dust attached on the plant surface. Autoradiograms of rice plants were virtually identical between plants cultivated in Fukushima and Osaka area, reflecting the background radiation due to ⁴⁰K.

Radiocesium concentrations in the bark, sapwood and heartwood of three tree species collected at Fukushima forests half a year after the Fukushima Dai-ichi nuclear accident

Radiocesium ((134)Cs and (137)Cs) distribution in tree stems of Japanese cedar (aged 40-56 y), red pine (42 y), and oak (42 y) grown in Fukushima Prefecture were investigated approximately half a year after the Fukushima Dai-ichi nuclear accident. Japanese cedar, red pine, and oak were selected from five sites, one site, and one site, respectively. Three trees at each site were felled, and bark, sapwood (the outer layer of wood in the stem), and heartwood (the inner layer of wood in the stem) separately collected to study radiocesium concentrations measured by gamma-ray spectrometry. The radiocesium deposition densities at the five sites were within the range of 16-1020 kBq m(-2). The radiocesium was distributed in bark, sapwood, and heartwood in three tree species, indicating that very rapid translocation of radiocesium into the wood. The concentration of radiocesium in oak (deciduous angiosperm) bark was higher than that in the bark of Japanese cedar and red pine (evergreen gymnosperms). Both sapwood and heartwood contained radiocesium, and the values were much lower than that in the bark samples. The results suggest that radiocesium contamination half a year after the accident was mainly attributable to the direct radioactive deposition. The radiocesium concentrations in the Japanese cedar samples taken from five sites rose with the density of radiocesium accumulation on the ground surface. To predict the future dynamics of radiocesium in tree stems, the present results taken half a year after the accident are important, and continuous study of radiocesium in tree stems is necessary.

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.

Radiocesium fallout in the grasslands on Sakhalin, Kunashir and Shikotan Islands due to Fukushima accident: the radioactive contamination of soil and plants in 2011

The accident at the Fukushima Dai-ichi Nuclear Power Plant has resulted in radioactive contamination of environmental media and food in the Far East of Russia, particularly in the Sakhalin Region. To obtain the knowledge about the (134)Cs and (137)Cs spatial distribution in the Sakhalin Region, soil samples were collected at 31 representative grassland sites on Sakhalin, Kunashir and Shikotan islands (43.80°-46.40° N and 142.73°-146.84° E) in the middle of May and around the end of September to early October 2011. In the autumn, vegetation samples (mixed grass/forb crop and bamboo, Sasa sp.) were collected together with soil samples. Maximum measured activity concentrations (on dry weight) of (134)Cs and (137)Cs in soil were 30 Bq kg(-1) and 210 Bq kg(-1), respectively. Within soil profile, (134)Cs activity concentrations declined rapidly with depth. Although for both sampling occasions (in the spring and autumn) the radionuclide was completely retained in the upper 3-4 cm of soil, a deeper penetration of the contaminant into the ground was observed in the autumn. In contrast with (134)Cs, activity concentrations of (137)Cs demonstrated a broad range of the vertical distribution in soil; at most sites, the radionuclide was found down to a depth of 20 cm. This resulted from interfering the aged pre-accidental (137)Cs and the new Fukushima-borne (137)Cs. To calculate contribution of these sources to the inventory of (137)Cs, the (134)Cs:(137)Cs activity ratio of 1:1 in Fukushima fallout (the reference date 15 March 2011) was used. The maximum deposition density of Fukushima-derived (137)Cs was found on Shikotan and Kunashir Islands with average density of 0.124 ± 0.018 kBq m(-2) and 0.086 ± 0.026 kBq m(-2), respectively. Sakhalin Island was less contaminated by Fukushima-derived (137)Cs of 0.021 ± 0.018 kBq m(-2). For the south of Sakhalin Island, the reference inventory of pre-Fukushima (137)Cs was calculated as 1.93 ± 0.25 kBq m(-2) (reference date 15 March 2011). For Shikotan and Kunashir Islands, the pre-Fukushima reference levels of (137)Cs ground contamination appeared to be higher: on average, 2.81 ± 0.35 kBq m(-2). Maximum measured activity concentrations (on wet weight) of (134)Cs and (137)Cs in the vegetation were 5 Bq kg(-1) and 18 Bq kg(-1), respectively. Soil-to-plant aggregated transfer factors, T(ag)s, for (134)Cs were more than an order of magnitude higher than those for (137)Cs. For the above-ground biomass density of 1 kg per m(2) (wet weight), plant contamination may contribute approximately 2% and 0.1% to the ground deposition of Fukushima-derived and pre-accidental (137)Cs, respectively.

Radionuclide analysis on bamboos following the Fukushima nuclear accident

In response to contamination from the recent Fukushima nuclear accident, we conducted radionuclide analysis on bamboos sampled from six sites within a 25 to 980 km radius of the Fukushima Daiichi nuclear power plant. Maximum activity concentrations of radiocesium (134)Cs and (137)Cs in samples from Fukushima city, 65 km away from the Fukushima Daiichi plant, were in excess of 71 and 79 kBq/kg, dry weight (DW), respectively. In Kashiwa city, 195 km away from the Fukushima Daiichi, the sample concentrations were in excess of 3.4 and 4.3 kBq/kg DW, respectively. In Toyohashi city, 440 km away from the Fukushima Daiichi, the concentrations were below the measurable limits of up to 4.5 Bq/kg DW. In the radiocesium contaminated samples, the radiocesium activity was higher in mature and fallen leaves than in young leaves, branches and culms.