Many studies have been carried out since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Here, we would like to introduce the special issue on the FDNPP accident which includes contributions from various fields covering aerosols, soil, forest, river, ocean and application of new analytical technique to samples collected in Fukushima.
Huge amounts of radionuclides were released into the atmosphere and ocean from the Fuku shima Dai-ichi Nuclear Power Plant (FDNPP), as a result of the reactor accident after the magnitude 9.0 Great East Japan Earthquake and subsequent gigantic tsunami on March 11, 2011. This paper summarizes our research activities on measurements of actinide elements (236U, 238,239,240,241Pu, 241Am and 242,243,244Cm) in the environmental samples.
Water-insoluble radioactive materials emitted during an early stage of the Fukushima Dai-ichi Nuclear Power Plant accident in 2011 were identified, and their chemical and physical properties were characterized as particulate matters. In this report, studies on radioactive particles collected from filter samples in Tsukuba on March 14–15, 2011 are summarized. Their compositions, chemical states, sizes, shapes, crystallinity, and hygroscopicity were analyzed using microscopic analyses such as electron microscopy and synchrotron with a micro-beam. The results indicate that they include Cs, Fe, and Zn as well as elements from fission products and are water insoluble, spherical-glassy particles with ca. 2 micrometer in size. Understanding of their detailed properties is significant to improve the numerical models during the accident and to understand their occurrences in soil as well as the accident itself. In addition to the water-insoluble radioactive materials, water-soluble radioactive materials, which were likely emitted in different events during the accident, should be investigated to have comprehensive understanding of the accident and its environmental effects. More samples from various environments such as soil will be needed, and more detailed chemical and physical analyses will help to understand their formation process, influences on human health, and long term decrements in ambient conditions.
Mineral species that really retain radioactive cesium in Fukushima soil have been investigated by analyzing actual contaminated soil samples in Fukushima using IP autoradiography, electron microscopy and X-ray diffraction. Weathered biotite originated from granitic body in Fukushima was frequently found as radioactive fine particles. The weathered biotite is mineralogically a biotite-vermiculite mixed-layer mineral. Besides, smectite-like clay mineral was identified in biotite-free particles using X-ray diffraction. A new cesium-sorption experiment was conducted, in which various clay minerals were immersed together in dilute 137Cs radioisotope solutions and the amount of 137Cs adsorbed in each mineral was measured by IP autoradiography to reproduce the sorption at actual concentration level in the radioactive particles. It was found that 137Cs was sorbed predominantly by the weathered biotite collected in Fuku shima, confirming the results from the investigation of the actual contaminated soil mentioned above.
The Fukushima Dai-ichi Nuclear Power Plant accident led to the release of various and huge amount of radionuclides into the environment, and contamination of wide area of eastern Japan, mainly Fukushima prefecture. More than 70% of radioactive cesium, which dominates the exposure dose, was deposited in forest far from our living sphere and is considered to be remobilized with time by water flow and strong wind caused by natural events such as typhoons. Numerous researches on the behavior of radionuclides in the environment have been performed not only by observation in the contaminated regions but also by model analysis so far. This paper overviewed results of understanding and modeling of transport behavior of radiocesium from forests through river systems.
This paper reviewed the transport behavior of 137Cs in river systems of Fukushima Prefecture, Japan after the Fukushima Dai-ichi Nuclear Power Plant accident during 2011–2014. Total radioactivity of 137Cs in water samples from the Abukuma River and small watershed river systems in eastern Fukushima, Hama-dori region, decreases exponentially with increasing time after the accident at normal flow condition. Higher radioactivity was found at higher flow condition caused by rain events. Particulate phase of 137Cs in river waters ranged from 60 to 99% to total radioactivity. Apparent distribution coefficient (Kd value) of 137Cs was 102 to 103 l g-1. The annual export of 137Cs from land to coastal ocean was estimated as 1010 to 1013 Bq in the river basins on the basis of field research data. These results indicate that major part of 137Cs is exported as particulate forms associated with suspended solids in the river waters.
Settling particle collector, sediment trap, has played an important role in the study of spatiotemporal variability in biogeochemical particles' cycle in the ocean. This report reviews the observational study of behavior (such as dispersion, distribution and existence form) of particulate artificial radionuclides in the ocean emitted from severe accidents of two nuclear power plants (Chernobyl NPP and Tokyo Electric Power Corporation Fukushima Dai-ichi NPP) by using time-series sediment trap.
Inductively coupled plasma (ICP) is characterized by high ionization efficiency for almost all elements. Recently, a triple quadrupole ICP-MS (ICP-MS/MS) has been applied to the measurements of isotope ratios for ultra-low level radioisotopes. The ICP-MS/MS features an additional quadrupole mass filter situated in front of the octopole reaction cell and quadrupole mass filter, which allows only the analyte ion to enter the cell by rejecting all the other ions. In this manuscript, we review recent studies on environmental radioactivity in Fukushima achieved by ICP-MS/MS techniques.
Amino acids, necessary to form life body, are present in greater abundances in natural seafloor hydrothermal fluids over 200℃ than in ambient seawater, although these are unstable and decomposed rapidly under simulated hydrothermal conditions. Serine and aspartic acid, which are thermally labile amino acids, are detected in the high temperature fluids. Inorganic matters such as metal ions and minerals could protect these labile amino acids in the fluids. Most of the dissolved amino acids are combined form and L form, suggesting that these are derived from organisms around hydrothermal vents. In addition, low levels of non-protein amino acids content indicate that amino acids are fresh and not experienced thermal alteration for long time. Amino acids are important as common sources of carbon and nitrogen for heterotrophic marine microbes. The release of biogenic amino acids along circulation paths of hydrothermal fluids could be effective for the development of hydrothermal vent fauna. In this paper, I review the origins and characteristics of dissolved amino acids in the natural hydrothermal fluids and implicates importance of the biogeochemical cycle of nitrogen and carbon around hydrothermal venting in detail.