Biomedical subjects

Katsumi Hirose

Publications and source records attributed to Katsumi Hirose.

12 recordsLinked to original sources

PubMed2006

Re-construction and updating our understanding on the global weapons tests 137Cs fallout.

Global nuclear weapons tests fallout of 137Cs in the northern hemisphere has been documented in the UNSCEAR (United Nations Scientific Committee on the Effect of Atomic Radiation) reports. However, many questions have arisen during the past three to four decades; e.g. the water column inventory of 137Cs in the North Pacific Ocean was two to three time higher than the cumulative decay corrected fallout at the same latitude as stated in the UNSCEAR reports. Here we show more precise spatial distribution of global 137Cs fallout primarily on the basis of global measurements in rain, seawater and soil, as data from 10 degrees x 10 degrees grids. A typical feature of geographical distribution is that two high global 137Cs fallout areas exist in the northern hemisphere, where the highest 137Cs fallout was observed in the globe. These areas correspond to crossovers of areas where larger precipitation amounts were expected and where higher stratosphere-troposphere exchange was expected. Our new estimate of 765 +/- 79 PBq as global 137Cs fallout for the northern hemisphere is 1.4 times higher than that of 545 PBq in the UNSCEAR reports.

Cesium Radioisotopes↗

PubMed2006

Chemical speciation of trace metals in seawater: a review.

The recent development of the chemical speciation of trace metals in seawater is described. The speciation studies reveal that metal ion complexation is one of the most important processes in seawater; especially, most bioactive trace metals, such as Fe(III) and Cu, exist as complexes with ligands in dissolved organic matter. The organic ligands in seawater are characterized with metal ions selected by the HSAB concept. A strong organic ligand, which originates from marine microorganisms, is classified as a hard base including carboxylates. The free organic ligand concentrations in seawater are buffered by complexation with excess amounts of Ca and Mg in seawater. The chemical equilibrium model suggested that the concentrations of bioactive free metal ions are at an optimal level to activities of marine microorganisms. For chemical speciation, it is important to have a better understanding of the ecological roles of trace metals in seawater.

Journal Article↗

PubMed2005

Seasonal and spatial variation of atmospheric 210Pb and 7Be deposition: features of the Japan Sea side of Japan.

Monthly depositional fluxes of (210)Pb and (7)Be at Tatsunokuchi, Japan which faces the Japan Sea were studied over a 12-year period from 1991 to 2002. The data were compared with the spatial variability of these fluxes at Taejon in Korea and at 11 other sites in Japan from Ishigaki of the southern islands of Okinawa to Wakkanai of the northern end of Hokkaido over a 2-year period from 2000 to 2001. The monthly depositions of both (210)Pb and (7)Be at Tatsunokuchi revealed very similar seasonal variations with a single peak; both depositions were high in winter and low in summer. This phenomenon was found to be not transient but stationary. The deposition of these nuclides was much greater on the Japan Sea side of Japan than on the Pacific Ocean side. The cause for high deposition of (210)Pb and (7)Be in winter might be explained by a combination of a series of the following processes: blowing out of air masses with a high (210)Pb concentration near the surface layer over the continent by strong winter monsoons, additional flow of cold air masses with high (7)Be concentration at high latitude, well-mixing with generation of ascending current and convection clouds over the Japan Sea, and heavy snowfalls accompanying them.

Air Pollutants, Radioactive↗

PubMed2005

90Sr, 137Cs and (239,240)Pu concentration surface water time series in the Pacific and Indian Oceans--WOMARS results.

Under an IAEA's Co-ordinated Research Project "Worldwide Marine Radioactivity Studies (WOMARS)" 90Sr, 137Cs and (239,240)Pu concentration surface water time series in the Pacific and Indian Oceans have been investigated. The Pacific and Indian Oceans were divided into 17 latitudinal boxes according to ocean circulation, global fallout patterns and the location of nuclear weapons test sites. The present levels and time trends in radionuclide concentrations in surface water for each box were studied and the corresponding effective half-lives were estimated. For the year 2000, the estimated average 90Sr, 137Cs and (239,240)Pu concentrations in surface waters of the Pacific and Indian Oceans varied from 0.1 to 1.5 mBq/L, 0.1 to 2.8 mBq/L, and 0.1 to 5.2 microBq/L, respectively. The mean effective half-lives for 90Sr and 137Cs in surface water were 12+/-1 years for the North, 20+/-1 years for the South and 21+/-2 years for the Equatorial Pacific. For (239,240)Pu the corresponding mean effective half-lives were 7+/-1 years for the North, 12+/-4 years for the South and 10+/-2 years for the Equatorial Pacific. For the Indian Ocean the mean effective half-lives of 137Cs and (239,240)Pu were 21+/-2 years and 9+/-1 years, respectively. There is evidence that fallout removal rates before 1970 were faster than those observed during recent decades. The estimated surface water concentrations of 90Sr, 137Cs and (239,240)Pu in latitudinal belts of the Pacific and Indian Oceans for the year 2000 may be used as the average levels so that any new contribution from nuclear facilities, nuclear weapons test sites, radioactive waste dumping sites and from possible nuclear accidents can be identified.

Cesium Radioisotopes↗

PubMed2004

Artificial radionuclides database in the Pacific Ocean: HAM database.

The database "Historical Artificial Radionuclides in the Pacific Ocean and its Marginal Seas", or HAM database, has been created. The database includes 90Sr, 137Cs, and 239,240Pu concentration data from the seawater of the Pacific Ocean and its marginal seas with some measurements from the sea surface to the bottom. The data in the HAM database were collected from about 90 literature citations, which include published papers; annual reports by the Hydrographic Department, Maritime Safety Agency, Japan; and unpublished data provided by individuals. The data of concentrations of 90Sr, 137Cs, and 239,240Pu have been accumulating since 1957-1998. The present HAM database includes 7737 records for 137Cs concentration data, 3972 records for 90Sr concentration data, and 2666 records for 239,240Pu concentration data. The spatial variation of sampling stations in the HAM database is heterogeneous, namely, more than 80% of the data for each radionuclide is from the Pacific Ocean and the Sea of Japan, while a relatively small portion of data is from the South Pacific. This HAM database will allow us to use these radionuclides as significant chemical tracers for oceanographic study as well as the assessment of environmental affects of anthropogenic radionuclides for these 5 decades. Furthermore, these radionuclides can be used to verify the oceanic general circulation models in the time scale of several decades.

Cesium Radioisotopes↗

PubMed2004

Chemical speciation of thorium in marine biogenic particulate matter.

Concentrations of particulate thorium in seawater were determined together with the strong organic ligand (SOL) and uranium in particulate matter (PM). The concentrations of particulate Th in surface waters of the western North Pacific and the Sea of Japan ranged from 0.05 to 1.5 pM (1 x 10(-12) M), and showed relatively large temporal and spatial variations. In order to chemically characterize the particulate Th in seawater, the relationship between particulate Th and SOL concentrations in surface PM was examined. The result reveals that particulate Th in surface PM was well correlated with the SOL concentration in PM. The concentrations of particulate Th in surface water were linearly related to those of particulate U. Mass balance analysis suggests that the dominant chemical form of Th(IV), as well as of U, in surface PM is a surface complex with the SOL in PM. Our findings suggest that the SOL in PM is a nonmetal-specific chelator originating from the cell surface of microorganisms.

Particle Size↗

PubMed2004

Spatial distribution of 3H, 90Sr, 137Cs and (239,240)Pu in surface waters of the Pacific and Indian Oceans--GLOMARD database.

The data stored in the IAEA's Global Marine Radioactivity Database (GLOMARD) developed in the framework of the IAEA's project "Worldwide Marine Radioactivity Studies (WOMARS)" have been evaluated for Pacific and Indian Ocean surface waters. Four anthropogenic radionuclides-- 3H, 90Sr, 137Cs and (239,240)Pu --have been chosen as the most representative of anthropogenic radioactivity in the marine environment, comprising beta, gamma and alpha-emitters which are the most frequently analysed in the marine environment and which have (with the exception of tritium) the highest potential contribution to radiation doses to humans via seafood consumption. For the purposes of this study, the Pacific and Indian Oceans were divided into latitudinal boxes for which average radionuclide concentrations were estimated for the year 2000. The highest concentrations have been observed in the Japan Sea/East Sea and the North-West Pacific Ocean, the lowest in the Southern Ocean.

Databases, Factual↗

PubMed2004

Spatial and temporal variations of atmospheric 85Kr observed during 1995-2001 in Japan: estimation of atmospheric 85Kr inventory in the Northern Hemisphere.

Atmospheric 85Kr concentrations have been continuously monitored since 1995 at the Meteorological Research Institute (MRI) in Tsukuba, Japan. They have also been observed once a year at several stations over the Japanese islands since 1995. The annual growth rate of the background atmospheric 85Kr concentrations in Tsukuba was 0.03 Bq x m(-3) x yr(-1) during 1996-2001. The atmospheric 85Kr concentrations at several stations over Japan were within the range of the annual variations in Tsukuba. However, higher and lower 85Kr concentrations in early winter, compared with those in Tsukuba (36.1 degrees N, 140.1 degrees E), occurred in Sapporo (43.1 degrees N, 141.3 degrees E) and Ishigaki (24.3 degrees N, 124.2 degrees E), respectively. The reason for this is that Sapporo is covered by a continental air mass, some from European sources, whereas Ishigaki is still covered by a subtropical air mass. The Northern Hemispheric background 85Kr concentrations from 1994 to 2001 was calculated from the 85Kr inventory and the release rate of 85Kr from the nuclear fuel reprocessing plants in Europe. Calculated 85Kr concentrations in surface air were in good agreement with annual average observed values at the MRI, Tsukuba. The global atmospheric inventory of 85Kr in December 2001 was also estimated to be approximately 5 EBq by using observed data in Tsukuba.

Air Pollutants, Radioactive↗

PubMed2003

Present background levels of surface 137Cs and (239,240)Pu concentrations in the Pacific.

The present levels of anthropogenic radionuclides, 137Cs and (239,240)Pu, in surface waters of the Pacific are estimated using the HAM database, which is a comprehensive data set of 137Cs, (239,240)Pu and other anthropogenic radionuclides. The time-series data of surface 137Cs and (239,240)Pu suggests that surface 137Cs and (239,240)Pu concentrations in the Pacific since 1971 decrease exponentially in each sea area, although the temporal changes of surface 137Cs and (239,240)Pu differed between sea areas of the Pacific. The calculated 137Cs concentrations in the Pacific surface waters in 2000 are homogeneous in the Pacific, comparing with that in the 1960s and 1970s, although they are still high in the North Pacific and low in the South Pacific. The biogeochemical and physical processes are significant factors to control present levels of surface (239,240)Pu concentrations, which are high in the Subarctic and equatorial Pacific and low in the mid-latitude region of the eastern North Pacific.

Cesium↗

PubMed2003

Numerical simulation of 137Cs and (239,240)Pu concentrations by an ocean general circulation model.

We simulated the spatial distributions and the temporal variations of 137Cs and (239,240)Pu concentrations in the ocean by using the ocean general circulation model which was developed by National Center of Atmospheric Research. These nuclides are introduced into seawaters from global fallout due to atmospheric nuclear weapons tests. The distribution of radioactive deposition on the world ocean is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute in Japan and several observed points in New Zealand. Radionuclides from global fallout have been transported by advection, diffusion and scavenging, and this concentration reduces by radioactive decay in the ocean. We verified the results of the model calculations by comparing simulated values of 137Cs and (239,240)Pu in seawater with the observed values included in the Historical Artificial Radionuclides in the HAM database, which has been constructed by the Meteorological Research Institute. The vertical distributions of the calculated 137Cs concentrations were in good agreement and are in good agreement with the observed profiles in the 1960s up to 250 m, in the 1970s up to 500 m, in the 1980s up to 750 m and in the 1990s up to 750 m. However, the calculated 137Cs concentrations were underestimated compared with the observed 137Cs at the deeper layer. This may suggest other transport processes of 137Cs to deep waters. The horizontal distributions of 137Cs concentrations in surface water could be simulated. A numerical tracer release experiment was performed to explain the horizontal distribution pattern. A maximum (239,240)Pu concentration layer occurs at an intermediate depth for both observed and calculated values, which is formed by particle scavenging. The horizontal distributions of the calculated (239,240)Pu concentrations in surface water could be simulated by considering the scavenging effect.

Cesium↗

PubMed2003

Recent trends of plutonium fallout observed in Japan: plutonium as a proxy for desertification.

Plutonium in monthly deposition samples collected in Tsukuba (the Meteorological Research Institute), Japan from 1990 to end of 2001 is reported, together with monthly plutonium deposition in Nagasaki and Yonaguni in 2000. The annual deposition of (239,240)Pu during the period from 1990 to 2001 shows no systematic interannual variation. However, monthly (239,240)Pu depositions show a typical seasonal variation with a maximum in spring season (March to April), which corresponds to seasonal cycle of soil dusts originating from the East Asian arid area. Plutonium isotopic ratios in the deposition samples suggest that significant amounts of the recent (239,240)Pu deposition observed in Japan are attributed to the resuspension of plutonium-bearing surface soil particles; resuspended plutonium originates from the East Asian arid areas. The recent increased tendency of (239,240)Pu content in residues in deposition samples may reflect desertification in the East Asian continent.

Asia↗

PubMed2003

Resuspension: decadal monitoring time series of the anthropogenic radioactivity deposition in Japan.

Monthly atmospheric depositions of (90)Sr and (137)Cs have been observed at the Meteorological Research Institute (MRI), Tsukuba, Japan. This study reports temporal trends and levels of (90)Sr and (137)Cs depositions in the 1990s. Although the current (90)Sr and (137)Cs concentrations declined dramatically, they have been found continuously in the deposition samples throughout the 1990s. During this period, the annual (90)Sr ((137)Cs) deposits at MRI ranged from 70-180 (140-350) mBq/m(2)/year. With a sufficiently long time series, the decreasing trend of the deposition evidently differs from the past stratospheric fallout; it is far slower. Thus, reservoirs other than the stratosphere provide small amounts of (90)Sr and (137)Cs to the atmosphere. A simple calculation clearly refutes the significance of the ocean as a potential source of airborne anthropogenic radioactivity. We will demonstrate that these radionuclides in the deposited materials originate from resuspension processes (soil dust suspension processes). The temporal trends of the time series monitoring reveal differences from those in the UNSCEAR Report 2000, which were predicted by a model that disregarded resuspension. The specific activity of (90)Sr ((137)Cs) in the annual depositions exhibited a 10-year (20-year) half-life. Those data were comparable with values reported in the literature for the half-residence time (HRT) of (90)Sr and (137)Cs in Japanese surface soils. They were also comparable to those calculated from nationwide data of (90)Sr and (137)Cs concentrations in the surface soil (0-10 cm) obtained from the Ministry of Education, Culture, Sports, Science and Technology Environmental Radiation Database (the MEXT Database). Regarding the activity ratio of (137)Cs/(90)Sr, the Japanese nationwide surface soil data collected during the 1990s in the MEXT Database (median: 5.3, n = 584) did not accord with that in the deposition samples (average: 2.1, n = 82) at MRI. This supports our previous hypothesis that Asian dust may transport a large fraction of anthropogenic radioactivity into the Japanese atmosphere. We need to study the fate of long-lived anthropogenic radioactivity dispersed in the environment over greater spatial and temporal scales.

Air Pollutants, Radioactive↗