The total, methyl and dissolved gaseous mercury (Hg) in the marine surface microlayer, for which there have been few data, were investigated in the eastern Seto Inland Sea. The results showed that the concentrations of total and methyl Hg in the microlayer layer were higher than those in the surface seawater below, but in some cases the concentrations in the surface seawater at other sites were higher. On the other hand, dissolved gaseous Hg concentrations in the microlayer layer were found to be 2.6 to 29 times higher than in the surface seawater below and in other surface waters. Dissolved gaseous Hg is an important parameter for Hg exchange between atmosphere and sea surfaces. Thus, further investigation data should be necessary.

In this study, we analyze the seasonal and annual changes in the chemical composition of rainwater collected continuously at the summit of Mt. Sefuri since 2013, and consider the behavior of elements in the atmosphere.The concentration of inorganic elements in precipitation increased from winter to spring and decreased from summer to autumn. The elements with high concentrations and clear seasonal changes were Cl and Na, and their v was almost the same as that of seawater. It is thought that the Na and Cl contained in rainwater are strongly influenced by seawater. The Mg concentration also shows a roughly positive correlation with Cl, but its Mg/Cl ratio is generally slightly higher than that of seawater.

Tropospheric ozone is not only the third largest greenhouse gas in terms of radiative forcing, but it also acts as a photochemical oxidant, controlling the oxidative capacity of the atmosphere, and has a significant impact on the atmospheric environment and ecosystems. Tropospheric ozone is produced primarily through the photodissociation of nitrogen dioxide, which is produced by the reaction of nitric oxide with peroxy radicals. Therefore, without understanding the process by which nitrogen dioxide is produced, it is impossible to quantitatively understand where and how tropospheric ozone is produced and consumed. In this study, we used the triple oxygen isotopic compositions as an indicator to directly quantify the contribution of peroxy radicals to the overall nitrogen dioxide production reactions in the atmosphere, and attempted to estimate the net ozone production.

We developed a highly sensitive method for precise boron isotope ratio analysis and quantification at the sub-nanogram level using isotope dilution-total evaporation (ID-TE) combined with negative thermal ionization mass spectrometry (NTI-MS). Boron isotope ratios were measured by detecting BO2- ions with a TRITON NTI-MS, yielding results consistent with certified standards and excellent reproducibility (RSD = 0.44%, n = 24). Strong correlations confirmed the accuracy of this method, which demonstrated a detection limit of 0.09 pg. This approach shows great potential for accurate boron isotope and concentration analyses in geological, biological, environmental, and nuclear-related samples.

We developed a sensitive analytical method for precise quantification of radioactive 36Cl in nuclear power plant wastewater using total evaporation and isotope dilution combined with negative thermal ionization mass spectrometry (NTI-MS). To ensure accuracy, stable chlorine isotope ratios (35Cl/37Cl) were measured using a total evaporation approach on a NIST standard solution, minimizing isotope fractionation. Ba was loaded onto a degassed rhenium filament to enhance ionization, and multi-collector NTI-MS measured 35Cl, 36Cl, and 37Cl simultaneously. The method achieved consistent detection of 36Cl with high reproducibility, demonstrating its suitability for nanogram-level isotope analysis in complex environmental samples.

In the geological disposal of high-level radioactive waste, bentonite plays a crucial role in retarding radionuclide migration by adsorbing cationic species. Cesium ions (Cs⁺), in particular, are strongly adsorbed by montmorillonite, the main component of bentonite. However, the detailed adsorption states and mechanisms remain unclear. We employed classical molecular dynamics simulations to investigate the adsorption behavior of Cs⁺ and sodium ions (Na⁺) from bulk water into the interlayer of Na-montmorillonite, by evaluating free energy profiles. Our results revealed that Cs⁺ adsorbs more strongly into the interlayer than Na⁺ due to the formation of the inner- and outer-sphere complexes of Cs⁺ and Na⁺, respectively. In the presentation, we will also discuss the fundamentals of classical molecular dynamics, the physical origin of the free energy profiles, detailed adsorption mechanisms, and comparisons with experimental data.

Atmospheric mercury is deposited on land and in the ocean through both wet and dry deposition. In recent years, the role of rivers in transporting mercury from terrestrial to marine environments has received increasing attention, with estimates suggesting that annual riverine transport may be comparable to atmospheric deposition (Liu et al., 2021a, b). However, observational data on mercury concentrations in Japanese rivers remain limited to the Hokuriku region (Ohno et al., 2020), leaving many aspects of mercury cycling at the island arc scale unresolved. Furthermore, the mercury speciation in river water is essential for assessing the contribution of terrestrial sources to methylmercury input into the ocean. In this study, we collected samples from major rivers across eastern Japan to quantify concentrations of dissolved mercury (DHg), particulate mercury (PHg), total mercury (THg), and dissolved monomethylmercury (MeHg), and to estimate mercury budgets and riverine fluxes to the ocean.The mean (± standard deviation) concentrations of each mercury species in river water were: DHg, 0.68 ± 0.40 ng/L; PHg, 1.78 ± 2.78 ng/L; THg, 2.48 ± 2.93 ng/L; and MeHg, 6.1 ± 4.4 pg/L. PHg was suggested to be the dominant mercury species in river water (PHg/THg: 57.4 ± 18.5%). The estimated riverine mercury flux was 1.9 ± 2.2 µg/m²/yr, accounting for 12.6 ± 10.9% of atmospheric deposition. The total annual mercury export from the Japanese archipelago via rivers was estimated to be 0.95 ± 0.15 t/yr for THg and 2.0 x 10^-3 t/yr for MeHg. The THg flux accounted for approximately 14% of atmospheric deposition to land (wet deposition: 3.8 ± 0.11 t/yr; dry deposition: 3.0 ± 1.0 t/yr). The discrepancy between atmospheric deposition and riverine export is likely due to the reemission of deposited mercury and retention in vegetation and soils. The THg flux estimated in this study was approximately one order of magnitude lower than the previous estimate of 8.3 ± 6.0 t/yr by Liu et al. (2021b). Liu et al. estimated PHg and the solid-liquid partition coefficient (K_d) using an empirical equation in which suspended solids concentration (SS) was the explanatory variable. DHg was then calculated from PHg and K_d. However, SS in Chinese rivers are generally higher than those in Japanese rivers and K_d values tend to be lower (estimated from Ohno et al., 2020). Therefore, Liu et al.'s method may have led to an overestimation of mercury fluxes from Japanese rivers to the ocean.

The water quality of observation wells, which were settled at coastal area of Sendai City, observation well of 10 m and 15 m deep was Na-Cl, and that of 30 m deep was Na-HCO₃. The influence of seawater intrusion was observed at depths of 10 to 15 m, and there were slight differences in the Na⁺ and Ca²⁺ concentrations between the 10 m and 15 m deep well. To elucidate the detailed condition of seawater intrusion and the formation process of groundwater quality, undisturbed boring cores with 30 m deep were sampled near the observation sites. Half of the boring core was cut into 5 cm depth sections, and pore water was extracted by centrifugation method to measure EC, pH, ion concentration, and oxygen and hydrogen stable isotope ratios. In this presentation, we will report on the characteristics of vertical distribution of soil moisture and EC value, and dissolved inorganic ions in the pore water.

Clay minerals control the environmental behaviors of various elements because they are widely distributed in the Earth's surface layer and adsorb many cations. One such element is radioactive cesium (Cs) released from the Fukushima Daiichi Nuclear Power Plant accident, which was fixed in the soil surface layer due to its strong adsorption on clay minerals. However, the details of the adsorption reaction of clay minerals remain unclear due to the complex structure.In this study, we focused on the fact that the adsorption site changes with the concentration of Cs adsorbed on clay minerals, aiming to systematically clarify the microstructural changes and Cs binding properties over a wide range of adsorption concentrations through a combination of experiments and simulations. The results showed that the adsorption structure changes with increasing Cs concentration and that Cs forms ionic bonds regardless of these changes.

Cerium (Ce) anomalies and oxidation state distributions in marine sediments are important redox indicators in ocean geochemistry, owing to Ce's unique redox behavior compared to other rare earth elements. In oxic seawater, Ce(III) is typically oxidized to insoluble Ce(IV), resulting in characteristic positive Ce anomalies in sediments. This oxidation process has traditionally been attributed to the catalytic action of manganese oxides. Consequently, the potential role of other minerals in Ce redox transformation has been largely overlooked.This study reveals that natural montmorillonite (SWy-3) can oxidize Ce(III) to Ce(IV) in artificial seawater. In batch experiments containing 50 mg SWy-3 and 0.5 uM Ce(III), we observed the oxidation of approximately 30% of the Ce(III) within 24 hours. Analysis using Ce L3-edge XANES and EXAFS spectroscopy confirmed the formation of Ce(IV) species on the mineral surface. In contrast, no oxidation occurred in identical experiments conducted under freshwater conditions.These results indicate that clay minerals, which have traditionally been regarded as redox-inert, may also participate in Ce oxidation under specific geochemical conditions. The input of clay minerals into marine systems through hydrothermal or tectonic activity could contribute to the formation of Ce anomalies, potentially affecting interpretations of past marine environments.

The ingestion of microplastics(MPs) by various aquatic organisms -ranging from zooplankton to marine mammals across trophic levels-has been widely reported. Among fish species, filter-feeding fish are particularly noteworthy, as they capture phytoplankton and suspended particles in the water through the movement of cilia or bristles, thus posing a risk of simultaneously ingesting MPs.Among MPs, tire and road wear particles (TRWP) are especially notable, with an estimated annual global emission of approximately 6 million tons. It has been suggested that ingestion on TRWPs themselves or their leachates may exert toxic effects on certain aquatic organisms. These TRWPs are believed to primarily enter rivers-and eventually oceans-via urban drainage systems, particularly during rainfall events. However, the actual status of TRWPs in environmental waters remains largely unknown.Therefore, this study was conducted with the aim of elucidating the types and abundance of TRWPs present in aquatic environments.

The use of MC-ICP-MS for the measurement of uranium isotope ratios is now commonplace in both geochemical (e.g. geochronology) and nuclear science (e.g. non-proliferation) applications. It is typically faster and less demanding of sample preparation time than comparable techniques such as Thermal Ionization MS (TIMS).However, the ultimate performance in terms of precision and accuracy still cannot match TIMS, mostly due to the inherent instabilities in the ionization technique. The performance of the current generation of instruments is also constrained by detector limitations, including the regular requirement to cross-calibrate between different detector technologies.We show uranium isotope ratio data taken with a totally new MC-ICP-MS platform. This prototype instrument exhibits excellent mass bias stability and abundance sensitivity. It also uses the unique ATONA technology from Isotopx, a system known for extremely low Faraday detector noise couple to very high dynamic range. These factors combine to produce precise, reproducible uranium isotope ratios for a range of sample sizes, potentially improving the future analytical capabilities of MC-ICP-MS for the analysis of uranium and other actinides.

In this study, to clarify the current status and causes of nitrate-nitrogen increase, we analyzed groundwater at 7 sites and river water at 3 sites (Kamo, Nakayama, and Takamatsu Rivers) in Saijo City for major cations and anions, nutrients, and stable isotope ratios of NO₃^-. The average NO₃^- concentrations (umol/L) in the Kamo River, Nakayama River, and Takamatsu River were 28.8, 47.0, and 134, respectively, and were higher in the Takamatsu River, which has a catchment area on the western hillside of the city where fruit trees are planted. On the other hand, the groundwater showed a large variation from 17.8 to 536, with lower values in groundwater with low water temperature and higher values in groundwater near the hills on the west side of the city. The average Si concentrations (umol/L) in the three rivers were 98.9, 151, and 258, respectively, and those in groundwater were 116-354, showing a similar trend to that of NO₃^-. The Kamo River system and low-temperature groundwater are thought to have their sources at higher elevations, resulting in lower concentrations of various ions and Si. The high NO₃^- concentrations in the river water and groundwater on the west side of the city are considered to be largely influenced by fertilizer application, especially ammonium sulfate, in fruit tree cultivation.

Japan has been positioned as a model region for weathering research. However, despite this historical background, studies applying non-traditional stable isotopes, which have advanced since the 2000s, for quantifying weathering fluxes have not been actively pursued. In this study, as a preliminary step toward analyses using silicon and magnesium stable isotopes as tracers, we investigated the controlling factors of magnesium concentration in river water. Using data from multiple rounds of comprehensive river sampling conducted between 2022 and 2024, we conducted (1) a comparison with major ion concentration in river water data from the 1950s, (2) an estimation of area-normalized magnesium fluxes by watershed, and (3) a statistical analysis of geological composition in upstream catchments using GIS.

Trace elements in seawater and defined as those present at concentrations below 1 mg/L. Many of these elements as essential for sustaining functions. It is well established that several essential trace elements serve as catalytic in enzymes. For example, selenium acts as the active site element in glutathione peroxidase. Unlike major components such as chloride and sodium, the concentrations of these essential trace elements vary significantly among the world's oceans and even with depth, making their accurate analysis historically detection limits of analytical instruments, and development of desalination and concentration methods have enabled more reliable measurements to be reported. This study discusses the marine distributions and controlling factors of selenium which exists in three dissolved species, as well as GEOTRACES key parameters including aluminum, manganese, iron, cobalt, nickel, zinc, copper, cadmium, and lead.

Among the trace components found in seawater, metals that serve as the active centers of metalloenzymes involved in metabolism within organisms are referred to as bioactive trace metals. To date, investigations into the distribution of bioactive trace metals have primarily been conducted in open ocean areas, with relatively few analytical studies focusing on coastal regions that are more susceptible to the influence of river water. Therefore, this study examined the distribution of nine bioactive trace metal elements (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) in Osaka Bay. Dissolved metals exhibited a significant negative correlation with salinity and a significant positive correlation with nutrients, suggesting influences from riverine sources and planktonic activity. Among exchangeable particulate metals, Mn, Co, Ni, Cu, Zn, and Cd showed significant positive correlations with one another, indicating a common supply source. Al and Fe showed strong positive correlations in both the exchangeable particulate metals and total dissolved metals, suggesting that Fe, like Al, originates primarily from crustal sources.

This study proposes a solid-phase extraction method using InertSep ME-2 resin that enables one-step preconcentration of trace metals and rare earth elements (REEs) across a wide salinity range. Developed as an alternative following the discontinuation of Nobias Chelate PA-1, the method uses a custom system with eight resin columns to process 40-50 mL samples in parallel within 20 minutes. Analysis by ICP-MS, employing matrix-matched bracketing standards along with Y and Lu spikes, achieved high precision (relative standard deviation below 5%) and high recovery rates (trace metals 99 ± 5%, REEs 103 ± 2%). Application to Toyama Bay revealed clear distribution patterns of trace metals and REEs in river water, groundwater, submarine groundwater discharge (SGD), and seawater, demonstrating that SGD plays a significant role in transporting terrestrial metals to coastal areas. This method provides a reliable and efficient approach for trace element analysis in diverse aquatic environments.

Cesium-135 (¹³⁵Cs) is a radioactive nuclide released into the environment from nuclear tests and nuclear facilities. As an alternative to ¹³⁷Cs, it has potential applications as a tracer for oceanic circulation and for monitoring around nuclear-related sites, necessitating the development of reliable analytical methods. However, the typical concentration of ¹³⁵Cs in seawater is extremely low (estimated at 1.6 fg/kg), requiring separation and preconcentration from approximately 50 liters of seawater for mass spectrometric analysis. In this study, an insoluble cobalt ferrocyanide (Co-FC)-loaded adsorbent was synthesized via graft polymerization, and the adsorption and desorption conditions for Cs in seawater were investigated. In addition, a chemical separation method suitable for mass spectrometric determination was also examined.

To establish a mass spectrometric method for determining²³⁷Np in seawater water, we investigated (1) a preconcentration technique of Np from seawater using an amidoxime adsorbent, and (2) the construction of the excitation functions of Np isotope via the ²³²Th+⁷Li reaction for spike production. Under optimized conditions, approximately 90% of Np in seawater was adsorbed onto the amidoxime adsorbent, and about 80% of the adsorbed Np was successfully eluted by treating the ashed adsorbent with 3 M nitric acid. In the ²³²Th+⁷Li reaction, ^236gNp was successfully synthesized and its excitation function was obtained. It was also revealed that ²³⁷Np is concurrently produced in this reaction.

Changes in global climate have accelerated ice loss in Antarctica, where the highest melt rates are found in the Amundsen Sea (AS), West Antarctica. Ice mass loss results from the incursion of relatively warm modified Circumpolar Deep Water (mCDW), which flows under the fringing ice shelves, including the Dotson Ice Shelf (DIS). Here, we report dissolved REE concentrations, with an emphasis on Nd, and Nd isotopes from nine stations located off of the DIS. We show REE enrichment near between ~ 300-400 meters, within the depth range of maximum outflow velocities and meltwater fractions. This implications has significance in the context of REE contribution from Antarctic glacial melting.

Fish otoliths and eye lenses retain the isotopic and trace elemental composition of the food consumed and the surrounding seawater at the time of their formation. The method called iso-logging that reconstructs the migration history of organisms between regions with different isotopic compositions by utilizing the time-series isotopic information preserved in such accumulative tissues has recently attracted attention. In this study, we conducted the estimation of nitrogen stable isotope ratios and the measurement of radiocarbon isotope ratios from lens samples of adult chub mackerel (Scomber japonicus) reported by Harada et al. (2022). For the spatial distribution of marine nitrogen isotope ratios, we used the monthly isoscape data by Yoshikawa et al. (2024) to construct a spatiotemporally continuous nitrogen stable isotope dataset. We developed a state-space model that integrates these isotopic data, and estimated the migratory pathways of chub mackerel. Radiocarbon measurements showed distinct changes during the later growth stages, when variations in nitrogen isotope ratios become smaller, suggesting that multi-elemental constraints may contribute to improving the accuracy of migration path estimation.

This study aims to develop a new analytical method for the rapid and simultaneous quantification of both salinity and carbonate species (CO₂, HCO₃^-, CO₃^2-) in aqueous solutions such as seawater, hot spring water, and fluid inclusions. Conventional approaches require complex procedures involving chemical equilibrium calculations to determine carbonate species concentrations. In contrast, the proposed method employs near-infrared and infrared absorption spectroscopy to directly quantify component concentrations without relying on equilibrium assumptions.Using NaHCO₃solutions with a total carbonate concentration set to approximately 10 times that of seawater, spectral measurements were conducted while varying the pH. The intensities of peaks corresponding to HCO₃^- (1303 and 1364 cm^-1) and CO₃^2- (1396 cm^-1) changed in response to pH. At low pH, the asymmetric stretching vibration of CO₂(aq) (2350 cm^-1) was observed, and a correlation was obtained between estimated concentrations and absorbance variations. Moreover, spectra of carbonate species were also successfully observed in more dilute carbonate solutions.