Hideki Arae

Strontium-90 activity concentration in soil samples from the exclusion zone of the Fukushima daiichi nuclear power plant

The radioactive fission product 90Sr has a long biological half-life (˜18 y) in the human body. Due to its chemical similarity to calcium it accumulates in bones and irradiates the bone marrow, causing its high radio-toxicity. Assessing 90Sr is therefore extremely important in case of a nuclear disaster. In this work 16 soil samples were collected from the exclusion zone (<30 km) of the earthquake-damaged Fukushima Daiichi nuclear power plant, to measure 90Sr activity concentration using liquid scintillation counting. 137Cs activity concentration was also measured with gamma-spectroscopy in order to investigate correlation with 90Sr. The 90Sr activity concentrations ranged from 3.0 ± 0.3 to 23.3 ± 1.5 Bq kg−1 while the 137Cs from 0.7 ± 0.1 to 110.8 ± 0.3 kBq kg−1. The fact that radioactive contamination originated from the Fukushima nuclear accident was obvious due to the presence of 134Cs. However, 90Sr contamination was not confirmed in all samples although detectable amounts of 90Sr can be expected in Japanese soils, as a background, stemming from global fallout due to the atmospheric nuclear weapon tests. Correlation analysis between 90Sr and 137Cs activity concentrations provides a potentially powerful tool to discriminate background 90Sr level from its Fukushima contribution.

Distribution and retention of Cs radioisotopes in soil affected by Fukushima nuclear plant accident

PurposeThere was a large release of radio-cesium (134Cs and 137Cs) to the atmosphere during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, and contaminated the soil, over a vast area, due to fallout activity. Therefore, studies on the behaviour of radio-cesium especially migration in soil and its retention on soil particles is very important for external dose assessment and root uptake.Materials and methodsWe have determined the sorption coefficient (Kd) for Cs using the laboratory batch method in soil samples collected from a contaminated area affected by the FDNPP accident, and the effect of various soil parameters on the Kd value has been studied.Results and discussionWe have noticed that Cs sorption is mostly influenced by cation exchange process and Cs is sorbed on the surface of clay particles. From vertical depth profile of Cs in soil, it is found that most of it is retained on the top layer within a 5-cm thickness.ConclusionsSequential extraction of soil using various reagents may be helpful to understand better the mechanism of Cs retention.

Dose effect for Japanese due to 232Th and 238U in imported drinking water.

Abstract— The consumption rate of bottled mineral water in Japan has increased due to changes in eating habits and contamination of water sources. Radioactivity levels of 238U and 232Th in imported mineral water were checked from the viewpoint of internal radiation for Japanese subjects. Concentration ranges of 238U and 232Th in imported bottled mineral water, domestic bottled mineral water, domestic tap water, and domestic soft drinks were as follows: for 238U, N.D to 7.48 × 103, 1.07 to 344, 0.66 to 104, and 3.04 to 46.2 ng dm−3 (ppt); for 232Th, 0.60 to 5.12, 0.65 to 22.4, 0.64 to 22.1, and 11.0 to 48.5 ng dm−3, respectively. In some brands of imported bottled mineral water, 238U concentration was sometimes much higher than domestic bottled mineral water and domestic tap water. The annual effective dose (1.5 × 10−3 mSv y−1) estimated from intake of 238U was approximately 7 times higher than that through dietary intake in Japanese. However, the internal dose added by drinking the imported portable water is negligible compared with total annual internal dose. Concentrations of non-radioactive elements were also compared between imported and domestic bottled water. Geometric means of cobalt, arsenic, strontium, cesium, phosphorous, and calcium in imported bottled water were higher compared with those of domestic bottled mineral water and domestic tap water. Maximum values of 11 elements (arsenic, rubidium, strontium, cesium, barium, sodium, magnesium, potassium, calcium, and manganese) were also found in imported bottled water.

Measurement of 90Sr in contaminated Fukushima soils using liquid scintillation counter

A method based on liquid scintillation counting system has been developed for the measurement of (90)Sr in Fukushima soil samples due to contamination of (134)Cs and (137)Cs. Three soil samples were collected within 30 km radius from the Fukushima Daiichi Nuclear Power Plant (FDNPP). Activity concentration of (134)Cs and (137)Cs were measured using a gamma spectroscopy system with high-purity germanium detector. (90)Sr contamination is little elevated but comparable with the background contamination level that originated from atmospheric nuclear weapon tests, whereas radiocesium contamination has increased significantly. Activity concentration of (90)Sr in the soil samples varied in the range of 10.4±0.6-22.0±1.2 Bq kg(-1). Activity concentrations of (134)Cs and (137)Cs in the soil samples were in the range of 28.2±0.2-56.3±0.2 kBq kg(-1) and 35.2±0.1-70.2±0.2 kBq kg(-1), respectively (reference date for decay correction is 1 December 2011).

Distribution of uranium and some selected trace metals in human scalp hair from Balkans

The possible consequences of the use of depleted uranium (DU) used in Balkan conflicts in 1995 and 1999 for the people and the environment of this reason need attention. The heavy metal content in human hair may serve as a good indicator of dietary, environmental and occupational exposures to the metal compounds. The present work summarises the distribution of uranium and some selected trace metals such as Mn, Ni, Cu, Zn, Sr, Cd and Cs in the scalp hair of inhabitants from Balkans exposed to DU directly and indirectly, i.e. Han Pijesak, Bratoselce and Gornja Stubla areas. Except U and Cs, all other metals were compared with the worldwide reported values of occupationally unexposed persons. Uranium concentrations show a wide variation ranging from 0.9 ± 0.05 to 449 ± 12 µg kg(-1). Although hair samples were collected from Balkan conflict zones, uranium isotopic measurement ((235)U/(238)U) shows a natural origin rather than DU.

Variability of radiocaesium inventory in Fukushima soil cores from one site measured at different times

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the deposition of radioactive contamination of soils mainly by (134)Cs and (137)Cs. The contaminated areas are of a great concern since external radiation may lead to significant long-term doses to humans and animals. External dose rate above ground will decrease with physical decay of the radionuclides and as they migrate deeper into the soil with time. In the present study, depth profiles of Cs radioisotopes have been studied at different times over a period of 1 y. Radiocaesium inventories for (134)Cs and (137)Cs down to a depth of 10 cm at the four measurement times varied from 2.09 to 4.14 MBq m(-2) with coefficient of variation (CV): 27.4 %, n = 4 and from 2.13 to 4.23 MBq m(-2) with CV: 27.3 %, n = 4, respectively. The activity ratio for (134)Cs/(137)Cs decreased from 0.62 to 0.46 during 1 y of measurement i.e. July 2012 to June 2013. However, the ratio with decay correction (15 March 2011) was found to be constant ∼1, indicating contamination from FDNPP origin. In order to understand the radiocaesium distribution in soil profile, physico-chemical characterisation of soil has been carried out.