Shigeyoshi Otosaka

Collection of Lanthanides and Actinides from Natural Waters with Conventional and Nanoporous Sorbents

Effective collection of trace-level lanthanides and actinides is advantageous for recovery and recycling of valuable resources, environmental remediation, chemical separations, and in situ monitoring. Using isotopic tracers, we have evaluated a number of conventional and nanoporous sorbent materials for their ability to capture and remove selected lanthanides (Ce and Eu) and actinides (Th, Pa, U, and Np) from fresh and salt water systems. In general, the nanostructured materials demonstrated a higher level of performance and consistency. Nanoporous silica surface modified with 3,4-hydroxypyridinone provided excellent collection and consistency in both river water and seawater. The MnO(2) materials, in particular the high surface area small particle material, also demonstrated good performance. Other conventional sorbents typically performed at levels below the nanostructured sorbents and demonstrate a larger variability and matrix dependency.

Bacterial Production of Organic Acids Enhances H2O2-Dependent Iodide Oxidation

To develop an understanding of the role that microorganisms play in the transport of (129)I in soil-water systems, bacteria isolated from subsurface sediments were assessed for iodide oxidizing activity. Spent liquid medium from 27/84 bacterial cultures enhanced iodide oxidation 2-10 fold in the presence of H(2)O(2). Organic acids secreted by the bacteria were found to enhance iodide oxidation by (1) lowering the pH of the spent medium, and (2) reacting with H(2)O(2) to form peroxy carboxylic acids, which are extremely strong oxidizing agents. H(2)O(2)-dependent iodide oxidation increased exponentially from 8.4 to 825.9 μM with decreasing pH from 9 to 4. Organic acids with ≥2 carboxy groups enhanced H(2)O(2)-dependent iodide oxidation (1.5-15-fold) as a function of increasing pH above pH 6.0, but had no effect at pH ≤ 5.0. The results indicate that as pH decreases (≤5.0), increasing H(2)O(2) hydrolysis is the driving force behind iodide oxidation. However, at pH ≥ 6.0, spontaneous decomposition of peroxy carboxylic acids, generated from H(2)O(2) and organic acids, contributes significantly to iodide oxidation. The results reveal an indirect microbial mechanism, organic acid secretion coupled to H(2)O(2) production, that could enhance iodide oxidation and organo-iodine formation in soils and sediments.

Anthropogenic radionuclides in the Japan Sea: their distributions and transport processes

The anthropogenic radionuclides, (90)Sr, (137)Cs and (239+240)Pu, were measured in the water column of the Japan Sea/East Sea during 1997-2000. The vertical profiles of radionuclide concentrations showed: exponential decrease with depth for (90)Sr and (137)Cs, and surface minimum/subsurface maximum for (239+240)Pu. These results do not differ substantially from results reported previously. The area-averaged concentrations of radionuclides in the Japan Sea are higher than those found in the Northwest Pacific Ocean below surface layer showing the accumulation of the radionuclides in the deep waters in the Japan Sea. Concerning spatial distributions, the area of high (137)Cs inventory extends from the Japan Basin into the Yamato Basin. It is suggested that wintertime convection of water, occurring mainly in the Japan Basin, causes the radionuclides to sink. The nuclides then advect into the Yamato Basin after detouring around the Yamato Rise.

Development of a Non-conservative Radionuclides Dispersion Model in the Ocean and its Application to Surface Cesium-137 Dispersion in the Irish Sea

A numerical simulation model system that consists of an ocean current model, Princeton Ocean Model (POM), and a particle random-walk model, SEA-GEARN, has been developed to describe the migration behavior of non-conservative radionuclides in a shallow water region. Radionuclides in the ocean are modeled in three phases, i.e., the dissolved phase in seawater, the adsorbed with large particulate matter (LPM) and the adsorbed with active bottom sediment. The adsorption and desorption processes between the dissolved and solid phases are solved by the stochastic method with the kinetic transfer coefficients. Deposition of the LPM and re-suspension from bottom sediment are also considered. The system was applied to simulate the long-term (24-year) dispersion of 137Cs actually released from the BNFL spent nuclear fuel reprocessing plant at Sellafield in United Kingdom. The calculation well reproduced the main characteristics of migration of dissolved 137Cs concentration in the Irish Sea.

Anthropogenic Radionuclides in Seawater of the Japan Sea The Results of Recent Observations and the Temporal Change of Concentrations

Between 1996 and 2002, a wide-area research project on anthropogenic radionuclides was carried out in an area covering the Japanese and Russian Exclusive Economic Zones of the Japan Sea, through a collaboration of Japanese and Russian institutes. The aim was to investigate the migration behavior of anthropogenic radionuclides (90Sr, 137Cs, and 239+240Pu) in the sea. Four expeditions conducted in the Japan Sea between 2001 and 2002 found that the observed concentrations and distributions of radionuclides were similar to those found in previous investigations. Inventories estimated from the concentration data indicate that larger amounts of these radionuclides accumulate in the Japan Sea seawater (by a factor of 1.5–2.1) than are supplied by global fallout in the same latitude belt. Further, we found that the 90Sr and 137Cs concentrations in the intermediate layer show temporal variations with time scales of 1 to several years. The results of cross-analysis using the data of 137Cs and dissolved oxygen suggest that the distribution and variation of radionuclide concentrations in the intermediate layer may reflect water mass movement in the upper part of the Japan Sea.

Vertical and lateral transport of particulate radiocesium off Fukushima.

Transport processes of particulate radiocesium were investigated using a sediment trap deployed at about 100 km east of the Fukushima Daiichi Nuclear Power Plant. A sediment trap was installed at 873 m depth of the station (119 m above the bottom), and time-series sampling of sinking particles was carried out from August, 2011 to June, 2013. The accident-derived radiocesium was detected from sinking particles over two years after the accident. Observed 137Cs flux was highest in September 2011 (98 mBq m(-2) day(-1): decay-corrected to March 11, 2011), and decreased over time with seasonal fluctuations. Particulate fluxes of radiocesium were mainly affected by two principal processes. One was the rapid sinking of radiocesium-bound particles (moderate mode). This mode was dominant especially in the early postaccident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another mode was observed in winter, and secondary transport of particles attributed to turbulence near the seabed increased fluxes of particulate radiocesium (turbulence mode). Although the latter process would not drastically change the distribution of sedimentary radiocesium in the short term, attention should be paid as this key process redistributing the accident-derived radiocesium may cumulatively affect the long-term distribution.

Estimation of Total Amounts of Anthropogenic Radionuclides in the Japan Sea

We estimated the total amounts of anthropogenic radionuclides, consisting of 90Sr, 137Cs, and 239+240 Pu, in the Japan Sea for the first time based on experimental data on their concentrations in seawater and seabed sediment. The radionuclide inventories in seawater and seabed sediment at each sampling site varied depending on the water depth, with total inventories for 90Sr, 137Cs, and 239+240Pu in the range of 0.52–2.8 kBq m−2, 0.64--4.1 kBqm−2, and 27-122Bqm−2, respectively. Based on the relationship between the inventories and the water depths, the total amounts in the Japan Sea were estimated to be about 1:2 ± 0:4PBq for 90Sr, 1:8 ± 0:7PBq for 137Cs, and 69 ± 14TBq for 239+240Pu, respectively; the amount ratio, 90Sr:137Cs:239+240Pu, was 1.0:1.6:0.059. The amounts of 90Sr and 137Cs in the Japan Sea were in balance with those supplied from global fallout, whereas the amount of 239+240Pu exceeded that supplied by fallout by nearly 40%. These results suggest a preferential accumulation of the plutonium isotopes. The data used in this study were obtained through a wide-area research project, named the “Japan Sea expeditions (phase I),” covering the Japanese and Russian exclusive economic zones.

Circulation in the Northern Japan Sea Studied Chiefly with Radiocarbon

Radiocarbon concentrations in the northernmost region of the Japan Sea were observed during the summer of 2002. The averaged surface ?14C (above 100 m depth) was 52 ± 8‰, which is significantly higher compared with the values of the Pacific Ocean and Okhotsk Sea. The Δ14C in the deep water decreased with density, and the minimum value was 70‰ By analyzing 14C and other hydrographic data, we found that i) the Tsushima Warm Current Water reaches to the surface layer in the southern Tatarskiy Strait; ii) deep convection did not occur in the northernmost region, at least not after the winter of 20012002; and iii) the bottom water that was previously formed in this region may step down southward along the bottom slope and mix with the Japan Sea Bottom Water. Furthermore, a new water mass characterized by high salinity (>34.09 psu) was found in the subsurface layer in the area north of 46°N.

Dependence of Lanthanide-Ion Binding Performance on HDEHP Concentration in HDEHP Impregnation to Porous Sheet

An octadecylamino-group-introduced polymer chain grafted onto a porous sheet was impregnated with bis(2-ethylhexyl)hydrogen phosphate (HDEHP). A mixture of HDEHP and ethanol of various HDEHP concentrations was used for the impregnation. The porous sheet into which a C18H37NH group was introduced was immersed in HDEHP/ethanol solution before ethanol evaporation. The liquid permeability of a cartridge charged with the HDEHP-impregnated porous sheet in disk form prepared in 50 (v/v)% HDEHP/ethanol solution was 96% that of the starting-porous-disk-packed cartridge. The equilibrium binding capacity of the HDEHP-impregnated porous disk for yttrium ions was 0.32 mol per kg of the disk. In addition, the HDEHP-impregnated-porous-disc-packed cartridge was found to be applicable to the preconcentration of trace amounts of lanthanides in a multielement solution prior to their measurement by inductively coupled plasma mass spectrometry.

A passive collection system for whole size fractions in river suspended solids

In order to solve difficulties in collection of river suspended solids (SS) such as frequent observations during stochastic rainfall events, a simple passive collection system of SS has been developed. It is composed of sequentially connected two large-scale filter vessels. A portion of river water flows down into the filter vessels utilizing a natural drop of streambed. The system enable us to carry out long-term, unmanned SS collection. It is also compatible with dissolved component collection. Its performance was validated in a forested catchment by applying to radiocesium and stable carbon transport.