Nobuharu Kihou

Potassium fertilizer and other materials as countermeasures to reduce radiocesium levels in rice: Results of urgent experiments in 2011 responding to the Fukushima Daiichi Nuclear Power Plant accident

Abstract Huge amounts of radionuclides, particularly radiocesium, were discharged from the Fukushima Daiichi Nuclear Power Plant (FDNPP), and widespread of contamination of the land, including paddy fields, was observed. Because rice is a staple food in Japan, contamination of paddy fields is a serious problem, and practical countermeasures to reduce radiocesium contamination of rice are urgently required. Potassium (K) fertilization was previously shown to be an effective countermeasure in fields contaminated by the Chernobyl accident, but researchers did not study the effects on rice (Oryza sativa L.). In the present study, we performed urgent field experiments to test the use of K fertilization, as well as other soil amendments, to reduce radiocesium contamination of rice. We found that K fertilization was an effective and practical countermeasure to reduce radiocesium uptake by rice from several soil types in Japanese paddy rice culture. Other treatments, including the application of expanded vermiculite or manure, were effective, and the effect appears to be explained by their K content. Based on these results, the recommended level of exchangeable soil potassium to lower the radiocesium content of rice to acceptable levels is about 200 mg K kg–1 soil before the usual fertilization. This K fertilizer application criterion was applied in a wide, low-contaminated area from the 2012 cropping season, and satisfactory results have been obtained generally.

Introduction of fiber plants to plant bed filter systems for wastewater treatment in relation to resource recycling

Abstract In order to develop a low-cost and energy-saving technique for wastewater treatment in combination with a resource recycling function, we constructed a plant bed filter ditch in which terrestrial and aquatic plants can be utilized for nitrogen and phosphorus removal from wastewater. The experimental ditch (4.0×0.4×0.4Hm) contained baskets filled with bed filter material (zeolite) and were planted with higher plants. Depending on the ability of the plant species to endure saturation, the height of the zeolite packed in baskets was changed. Kenaf (Hibiscus Cannabinus L.), sunn hemp (Crotalaria juncea L.), and papyrus (Cyperus papyrus L.), which are useful fiber materials, and reed (Phragmites communis Trin.) were tested to evaluate their suitability for use as plant bed filter systems. Phosphorus and nitrogen loading rate to the system during the experiment was 0.24-0.28 and 1.4-1,8 g m−2 d−1, respectively. The addition of higher plants to the ditches enhanced the removal of nitrogen and phosphorus...

Behavior of Iodine in a Forest Plot, an Upland Field and a Paddy Field in the Upland Area of Tsukuba, Japan. Iodine Concentration in Precipitation, Irrigation Water, Ponding Water and Soil Water to a Depth of 2.5 m

In the course of a series of studies conducted to investigate the long-term behavior of 129I (which has a half-life of 16 million years) in the environment, the concentration of stable iodine (127I) in precipitation, irrigation water and soil water to a depth of 2.5 m in a forest plot, an upland field and a paddy field in the upland area of Tsukuba, Japan, was determined. In the forest plot, the mean iodine concentrations in soil water at all the depths ranged from 0.13 to 0.21 μg L−1, about one-tenth of the values recorded in precipitation (weighted mean 2.1 μg L−1). This finding suggests that the major part of iodine in precipitation was sorbed onto the surface soil horizon under oxidative conditions. In the upland field, the mean iodine concentration in soil water was 2.2 μg L−1 at a depth of 0.2 m and it decreased to 0.34–0.44 μg L−1 at a depth of 0.5 m or more; these concentrations were about one-fifth of that in precipitation. This suggested that the major part of the iodine derived from precipitation was sorbed onto the subsurface soil horizon (at depths between 0.2 and 0.5 m). In the paddy field, during the non-irrigation period, the mean iodine concentrations in soil water at all the depths ranged from 1.8 to 4.8 μg L−1, almost the same values as those recorded in precipitation. During the irrigation period, the mean iodine concentrations at depths of 0.2 and 0.5 m were 18.8 and 16.7 μg L−1, values higher than the 10.9 μg L−1 value recorded in irrigation water and the 11.8 μg L−1 value recorded in ponding water. However, at a depth of 1.0 m or more, the mean iodine concentrations in soil water rapidly decreased from 7.3 to 1.8 μg L−1. These data suggested that a significant amount of iodine flowed out from the paddy field by surface runoff and a considerable amount of iodine that leached to a depth of 0.5 m was retained onto the mildly oxidative soil horizon (2Bw) that lay at depths between 0.5 and 1.0 m. At a depth of 2.5 m in the paddy field, the mean iodine concentration in soil water decreased to 1.8 μg L−1, but this level was much higher than those in the forest plot and upland field at the same depth, which suggested that a significant amount of iodine had leached into the groundwater-bearing layer. There was a negative correlation (r=-0.889) between the Eh of soil and the iodine concentration in soil water (0.2 m depth) of the paddy field. Particularly, when the Eh of soil fell below approximately 150 mV, the iodine concentration rapidly increased to above 10μg L−1. As for the chemical forms of iodine in precipitation, irrigation water, ponding water and soil water during the winter irrigation period in the paddy field with oxidative conditions, 58–82% of iodine consisted of IO− 3 and 17–42% of iodine consisted of I−. In the soil water during the summer irrigation period in the paddy field under reductive conditions, 52–58% of iodine consisted of I−, and 42–47% consisted of IO− 3.

Use of higher plants and bed filter materials for domestic wastewater treatment in relation to resource recycling

Abstract A bench scale experiment was conducted to compare the effectiveness of three kinds of bed filters (zeolite, zeolite + shell fossils, charcoal chips) and five plant species (Chinese water spinach (Ipomea aquatica Forskal), rice (Oryza sativa L. cv. Takanari), zinnia (Zinnia elegance L.), watercress (Nasturtium officinale R. Br.), stock (Matthiona incana R. Br.)) for use as plant-bed filter systems in order to develop low cost and energy-saving devices for wastewater treatment combined with resource recycling and amenity functions. Pots (0.05 m2) filled with bed filter materials were prepared as experimental systems. The addition of higher plants to the bed filters enhanced the nitrogen and phosphorus removal from wastewater as plant species considerably affected the P and N removal efficiency. In the summer-autumn season (June-December), Chinese water spinach and rice were more effective than zinnia. In the winter-spring season (January-May), watercress was more effective than stock. Although the ...

Changes in radiocesium concentration in a Japanese chestnut (Castanea crenata Sieold & Zucc.) orchard following radioactive fallout

Abstract We investigated changes in radiocesium concentrations in a Japanese chestnut (Castanea crenata Sieold & Zucc.) orchard in Ibaraki prefecture for 3 years after the Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant accident in March 2011. The radiocesium concentrations in the aboveground organs of Japanese chestnut trees were almost the same, while the concentration in the roots was the lowest among all the organs investigated. The concentration of radiocesium decreased exponentially for 3 years in nuts, leaves and current shoots. The radiocesium concentrations in soils were higher in the surface layer, and the trend of an annual decrease in radiocesium in the soils was similar to that of the natural decay of radiocesium. The transfer factor of radiocesium from soils to nuts of Japanese chestnut decreased annually. These results suggest that radiocesium adhered directly to the aboveground organs of Japanese chestnut trees in March 2011, and that the accumulation of radiocesium in nuts is mainly due to radiocesium transfer from the branches and trunk to nuts several years after the nuclear power plant accident.

Changes in radiocesium concentration in a blueberry (Vaccinium virgatum Aiton) orchard resulting from radioactive fallout

Abstract We investigated changes in the radiocesium concentration in a blueberry (Vaccinium virgatum Aiton) orchard in Fukushima prefecture to clarify the radiocesium contamination for 3 years after the Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant accident occurred in mid-March 2011. In the aboveground part of blueberry bushes, the concentrations of radiocesium in branches that were directly affected by radioactive fallout were the highest among the samples investigated, and the concentrations in fruits were the lowest. The concentration of radiocesium decreased exponentially in the fruits and leaves over 3 years. The radiocesium concentrations in soils were higher in the surface layer. The amount of radiocesium in organic matter on the soil surface under the canopy greatly decreased from 2011 to 2012. The transfer factor of the radiocesium from soil to blueberry fruits decreased annually. These results suggest that radiocesium adhered directly to the aboveground organs of blueberry bushes in March 2011, and it is possible that the accumulation of radiocesium in fruits is mainly due to radiocesium transfer from the branches and trunk to fruits for several years after the nuclear power plant accident.

Radiostrontium monitoring of bivalves from the Pacific coast of eastern Japan

In early April 2011, radiostrontium was accidentally released from the Fukushima Daiichi Nuclear Power Plant to the Pacific coast of eastern Japan. We developed a simple procedure to analyze radiostrontium levels in marine mussels (Septifer virgatus) and seawater using crown ether (Sr Resin; Eichrom). Then, we used our method to describe the spatial and temporal distribution of radiostrontium in mussels and seawater on the Pacific coast of eastern Japan from 2011 to 2013 and for 2015. Activity of 90Sr in mussels and seawater decreased with distance from the Fukushima Daiichi Nuclear Power Plant and between 2011 and 2013 tended to be higher in areas south of the Fukushima Daiichi Nuclear Power Plant than to the north of it. Activity in mussels and seawater also tended to decrease from 2011 to 2013 and by 2015 had reached levels experienced prior to the Fukushima accident. Our results suggest that radiostrontium discharged from the Fukushima Daiichi Nuclear Power Plant was dispersed by coastal currents in a southerly direction along the Pacific coast of eastern Japan from 2011 to 2013, following which its activity decreased to background levels by 2015.

Bromine and iodine in Japanese soils determined with polarizing energy dispersive X-ray fluorescence spectrometry

Abstract The bromine (Br) and iodine (I) status of Japanese soils was investigated by analyzing around 900 soil samples and related materials with polarizing energy dispersive X-ray fluorescence spectrometry (EDXRF). The samples consisted of the following five groups: (1) 468 soil samples collected from 70 sites in the mainland of Japan (mainland soils); (2) 139 agricultural soils collected nationwide; (3) 93 samples taken from the southwestern island (island soils); (4) 52 coastal marine sediments; and (5) 137 tsunami deposits by the 2011 off the Pacific coast of Tohoku Earthquake. The geometric mean of Br was highest in marine sediments (30.6 mg kg−1), followed by that in island soils (24.8 mg kg−1), although the difference between these two groups was not significant. The values for the other three groups were significantly lower at p < 0.05 by Welch’s t test, and were in the following order: mainland soils (10.4 mg kg−1) > tsunami deposits (8.52 mg kg−1) > agricultural soils (7.86 mg kg−1). For I, the geometric mean of island soils (31.9 mg kg−1) was significantly higher than that of other soils at p < 0.05 by Welch’s t test, and was more than three times higher than that of mainland soils (9.11 mg kg−1), which was the second highest group. The values for the other three groups were in the following order: marine sediments (5.68 mg kg−1) > tsunami deposits (4.66 mg kg−1) > agricultural soils (3.50 mg kg−1). The contents of I were higher than those of Br for around two thirds of the island samples. As a result, the geometric mean of the Br/I ratio was less than 1.0 only in this group. The contents of both elements were significantly higher in upland soils than in paddy fields soils. These differences could be partly attributed to the higher ratio of Andosols containing higher amounts of Br and I in upland samples, in addition to the difference in the chemical forms of both elements in paddy field and upland samples. The correlation coefficients among rare earth elements, for example, were more than 0.9 for a considerable number of combinations, whereas more than 80% of the absolute values of correlation coefficients for Br and I against 60 other elements were less than 0.4. These results strongly suggest that the behavior of Br and I in the terrestrial environments differs considerably from that of most other metallic elements.

Changes in concentrations of 131I, 134Cs and 137Cs in leafy vegetables, soil and precipitation in Tsukuba city, Ibaraki, Japan, in the first 4 months after the Fukushima Daiichi nuclear power plant accident

Abstract Concentrations of 131I: iodine-131, 134Cs: cesium-134 and 137Cs: cesium-137 in leafy vegetables, soil and precipitation after the Fukushima Daiichi nuclear power plant accident were investigated at Tsukuba city, approximately 170 km from the nuclear power plant. The first precipitation after the accident was on March 21–23, 2011, and contained an amount of radionuclides. The concentration of 131I in leafy vegetables, particularly spinach (Spinacia oleracea L.), was significantly increased because of dry deposition of the first radioactive plume. The concentrations of 131I, 134Cs and 137Cs in soil were significantly increased by the first precipitation on March 21–23; however, the contribution of precipitation to the concentrations of 131I, 134Cs and 137Cs in leafy vegetables was smaller than that in soil. Changes in the concentrations of 131I, 134Cs and 137Cs differed between spinach and komatsuna (Japanese mustard; Brassica campestris var. peruviridis).