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  • Author or Editor: M. Yamada x
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Abstract  

Salmon (Oncorhynchus keta) samples were collected on the Pacific coast of Japan and analyzed for their239+240Pu and137Cs concentrations in six places, i.e., muscle, viscera, gill, gonad, skin and spine. The239+240Pu concentrations in muscle ranged from 0.07 to 0.14 mBq/kg (wet) and had the lowest value among the six regions. The mean239+240Pu concentrations in viscera, gonad and spine were more than 1 mBq/kg (wet_ while those in muscle and skin were one order of magnitude lower. The largest amounts of239+240Pu were accumulated in gonad. The239+240Pu/137Cs activity ratios in all positions were lower than that of the global fallout ratio of 0.022, suggesting that137Cs could be accumulated with greater ease than239+240Pu in all positions and ratios of uptake differed remarkably from position to position. The total accumulations of239+240Pu and137Cs in salmon were 1.32 and 328 mBq/individual, respectively.

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Summary  

Studies on the environmental behavior of plutonium in the marine environment require an analytical method with high sensitivity and capability to provide the isotopic composition of Pu in marine samples. In this work, as part of our on-going project on Pu environmental behavior in the Pacific Ocean, a sector field ICP-MS method combined with an off-line anion-exchange chromatography system was optimized for the determination of Pu and its atomic ratio of 240Pu/239Pu in sediment core samples. Using a conical concentric nebulizer and 150-second counting time, we were able to lower the detection limit of Pu down to 0.35 fg. The mass discrimination effect was evaluated using a mixed Pu isotope standard solution with certified a 240Pu/239Pu isotope ratio (NBS-947). The overall performance of the analytical method was validated by the determination of Pu and its isotope composition in an ocean sediment reference material (IAEA-368). Both the 239+240Pu activity and 240Pu/239Pu atomic ratio were found to be in good agreement with the certified and/or literature values. As an important application, we employed the analytical method to investigate the vertical profiles of 239+240Pu activity and 240Pu/239Pu atomic ratio in sediment cores in the Sea of Okhotsk and the NW Pacific. It was found that the Bikini close-in fallout Pu could be transported as far as the Sea of Okhotsk. The results provided evidence to support our hypothesis on the oceanic current transportation of Bikini close-in fallout Pu in the NW Pacific and its marginal seas.

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Abstract  

The surface seawater and marine organisms were collected on the Japanese coast and analyzed for their137Cs concentrations during the 1980's. The137Cs concentrations in surface seawater decreased almost exponentially with time and the137Cs removal rate constant was estimated to be 0.0445 y−1. The137Cs concentrations in marine organisms also decreased almost exponentially with time. The environmental half-lives of137Cs in muscle and viscera of fish, crustacea, and seaweed were estimated from the measured decreases of137Cs concentrations.

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Abstract  

Four sediment cores were collected from Tokyo Bay and analyzed for their 239+240Pu and 137Cs concentrations. Shallow nearshore sediments from Tokyo Bay have 239+240Pu inventories which average 214±14 MBq/km2. They are five times greater than the supply expected from the atmospheric global fallout at the same latitude of 42 MBq/km2. The measured mean 137Cs inventory of 433±93 MBq/km2 is approximately one fifth the value expected from global fallout. Furthermore, the 239+240Pu/137Cs activity ratios, with a mean ratio of 0.50±0.14, are significantly greater than the ratio expected from the global fallout of 0.021. Excess 239+240Pu inventories can be considered to have been introduced into Tokyo Bay as weathering products by soil erosion, transported via rivers and winds, and to be much more efficiently scavenged from seawater by particles resuspended at the sediment-water interface.

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Abstract  

Seawater samples were collected from the East China Sea continental shelf and analyzed for 239+240Pu activities. The vertical profiles of 239+240Pu had a similarity for all three stations in the East China Sea. 239+240Pu concentrations were low in the surface layer (3-4 mBq/m3) and increased gradually with depth to become high in the near-bottom layer (7-10 mBq/m3). 239+240Pu concentrations in seawater and the concentrations of suspended particles showed almost the same vertical profiles in the East China Sea continental shelf. The maximum value of 239+240Pu found in the near-bottom layer may be due to the contribution of Pu-rich suspended particles.

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Abstract  

Marine sediment cores were taken from Sagami Bay of the western Northwest Pacific and analyzed for 239+240Pu and 137Cs activities. A significant correlation was observed between 239+240Pu and 137Cs activities in sediment cores, i.e., their vertical profiles. The measured activities which were used to obtain the inventories of 239+240Pu and 137Cs in the sediment column, showed large variations, ranging from 36 to 474 MBq/km2 for 239+240Pu and 49 to 652 MBq/km2 for 137Cs. 239+240Pu inventories in the sediment from one region in the Bay, Sagami Nada were 5–10 times greater than those predicted from atmospheric global fallout 42 MBq/km2 at the same latitude. On the other hand, 137Cs inventories, with a mean value of 297±168 MBq/km2, were much less than predicted, 2040 MBq/km2. The activity ratios of 239+240Pu/137Cs obtained, with a mean of 0.65±0.17, were significantly greater than the ratio predicted from fallout, 0.021. Furthermore, there was a clear relationship between both 239+240Pu and 137Cs inventories and the water content, indicating that higher inventories may be attributed principally to concentration in, and scavenging by, fine-grained particles.

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To understand the molecular mechanism of hyperglucocorticoidism in obese Zucker rats, this study investigated glucocorticoid synthesis-related factors and their transcription factors in the adrenals. glucocorticoid synthesis-related factors and their transcription factors in the adrenals. The serum corticosterone level after foot shock stress was higher in obese Zucker rats than in lean Zucker rats. after foot shock stress was higher in obese Zucker rats than in lean Zucker rats. In the adrenals from obese Zucker rats, the mRNA and protein levels of steroidogenic acute regulatory protein were higher than those from lean Zucker rats. rats. However, the mRNA level of steroidogenic factor-1(SF-1), an important transcription factor for these glucocorticoid synthesis-related factors, did not differ between lean and obese Zucker rats. glucocorticoid synthesis-related factors, did not differ between lean and obese Zucker rats. Focusing on leptin signal transduction, Akt phosphorylation, which was known to inhibit glucocorticoid secretion, decreased in the adrenals from obese Zucker rats. from obese Zucker rats. We found that the stress-induced glucocorticoid secretion and the glucocorticoid synthesisrelated factors in the adrenals were increased in obese Zucker rats. factors in the adrenals were increased in obese Zucker rats. The decrease of Akt phosphorylation in the adrenals might induce these increases in obese Zucker rats.adrenals might induce these increases in obese Zucker rats.

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Abstract  

Seawater samples were collected from the Yamato Basin and the Tsushima Basin in the Japan Sea and analyzed for their239+240Pu and137Cs concentrations. The concentration of239+240Pu was 7.4 mBq/m3 in the surface water and increased with depth to a maximum value of 38.6 mBq/m3 at 500 m at the Yamato Basin station. The subsurface maximum may be produced by scavenging of239+240Pu in surface water and release of239+240Pu from settling particles. The239+240Pu inventories in the water column were 86.6 and 85.2 Bq/m2 at the two basin stations, suggesting that 90% of239+240Pu delivered to the Japan Sea is still present in the water column.

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Summary  

From the viewpoint of environmental radioactivity monitoring, the determination of uranium and its isotope ratio is important for identifying and assessing the environmental impact of any unexpected release from nuclear facilities. In this work, a survey was conducted to determine 238U concentrations and 235U/238U atom ratios in coastal waters off Rokkasho Village, Aomori, Japan, where several uranium-related nuclear facilities have been operating since 1992, and a newly constructed nuclear fuel reprocessing plant is scheduled to be commissioned in 2006. Seawater samples were analyzed directly after a 10-fold dilution using isotope dilution sector-field ICP-MS. Based on the results, we concluded that there is no observable uranium contamination in the investigated sites. In addition, for the first time, a correlation between uranium concentration and salinity was established in coastal waters using the SF-ICP-MS technique.

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Abstract  

A technique to determine concentrations of 32P, 33P and 7Be in dissolved and particulate forms, in the upper ocean was developed. By using a large volume in situ filtration and concentration system (LV-FiCS), several tons of seawater at different depths were filtered concurrently through two kinds of filters. The dissolved radionuclides were concentrated onto adsorbents in the LV-FiCS. The radionuclides obtained were further purified by precipitation and ion-exchange chromatography, and quantified by gamma-spectrometry and ultra-low level liquid scintillation counter measurements. The technique was used with good results in a coastal area of Ibaraki, Japan.

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