Methane (CH₄) is typically generated in anaerobic environments and is known to be oxidatively decomposed in aerobic environments. However, seawater, particularly surface water, often contains excess dissolved CH₄ compared to atmospheric equilibrium. This phenomenon is known as the 'methane paradox.'This study aimed to elucidate the sources of excess CH₄ in seawater by measuring d¹³C and d²H. It was confirmed that many samples from subsurface seawater exhibited CH₄ supersaturation compared to atmospheric equilibrium. The d¹³C value of excess CH₄in seawater was determined to be an average of -54.7(per mille). Furthermore, this study revealed the d²H values of excess CH₄, averaging -29.4(per mille) for the first time in the world.The high d²H values observed in this study are believed to result from residual effects of oxidative decomposition during the release of methane generated under reduction environments within sinking particles into oxidative seawater.

Fixed-point observations were conducted to determine the latitudinal and altitudinal distribution and long-term variations of N₂O isotopocule ratios in the Northern mid- and high-latitudes, and to analyze the dynamics of N₂O production and consumption. The bulk nitrogen isotope ratio (d¹⁵N^bulk) increased by about 0.05 permil/year and the oxygen isotope ratio (d¹⁸O) increased by about 0.03 permil/year, corresponding to the increase in concentration, from 2005 to 2022 at Hateruma Island, Okinawa (47 m altitude) and over Novosibirsk, Russia (500 m and 7000 m altitudes). On the other hand, ¹⁵N-site preference (SP, the difference of d¹⁵N between central and edge N in NNO molecules) showed no significant long-term change. Detailed analysis of the long-term trends showed an increase in the altitudinal difference in N₂O concentrations and short-term variations in isotopocule ratios at each altitude during 2010-2016 in Novosibirsk, suggesting a change in the contribution of surface sources and stratospheric N₂O.

The chemical properties of aerosols reflect changes in anthropogenic activities and natural environments, with past aerosols preserved in ice cores. In this study, we aimed to elucidate the relationship between modern anthropogenic activities and aerosol chemical properties by examining zinc speciation and stable isotope ratios in past aerosols from the SE-Dome II ice core, which provides a high-resolution record from 1800. In terms of Zn speciation, we identified Zn sulfate and other species that have reacted with anthropogenic gases. Additionally, we will present the progress of our zinc isotope measurement.

Since the industrial revolution, trace metals, such as iron (Fe) and zinc, have been emitted to the atmosphere due to anthropogenic activities, affecting cloud formation processes, phytoplankton growth following their deposition to the ocean. In this study, we reconstructed the concentrations, chemical forms, and solubilities of Fe in aerosols preserved in the Southeastern Greenland Dome II (SE-Dome II) ice core in order to understand the changes in deposition flux and chemical properties of Fe in the atmosphere from the pre-industrial times to the present. Iron solubility increased until the 1970s and subsequently decreased until the present. This trend is likely associated with changes in the degree of Fe dissolution in the atmosphere, which can be attributed to changes in the flux of acidic materials and/or changes in the iron emission sources.

In East Asia, emissions of air pollutants have been decreasing, but the decreasing rates depend on the composition of the pollutants, and in recent years the relative importance of transboundary pollution originating from nitrogen oxides has been increasing. We have been conducting continuous observations of total odd nitrogen species, total inorganic nitrate (the sum of gaseous nitric acid and particulate nitrate), ozone, carbon monoxide, and so on at Suzu, Noto Peninsula for about 15 years. In this presentation, we report the results of the long-term continuous observations of these transboundary air pollutants at Suzu.

Airborne microorganisms in bioaerosols are thought to effect on the cloud formation as ice nuclei and, after deposition, they would support the organic cycles in oceanic ecosystems. The survey and investigation suggesting the global dynamics by bioaerosols will be introduced here.

Fatty alcohols (FAs) are major components of surface lipids in plant leaves and serve as surface-active organic aerosols, which can act as primary biological aerosol particles. This study aims to elucidate the specific plant species as a dominant source of secondary FAs (SFAs) in aerosols, based on simultaneous samplings of size-segregated aerosols and plant leaves at Tomakomai experimental forest in different seasons. Among five SFAs identified, n-nonacosan-10-ol was the most abundant compound in aerosols. The concentrations of n-nonacosan-10-ol were the highest in spring, with its peak diameter > 7.2 micrometer. n-nonacosan-10-ol was also identified in the needle leaf samples of Abies sachalinensis (conifer), mainly in the non-esterified form. The overall results suggest that plant waxes in the needle leaves can act as source of aerosol SFAs, and that the emission strength is controlled by the phenology of the leaf and the local wind speeds.

As one of the most important reservoirs of mercury (Hg) on earth, ocean plays a crucial role in mediating the global cycling of Hg. Mercury undergoes complex migration and transformation processes (e.g., adsorption/desorption, deposition/resuspension, oxidation/reduction, and methylation/demethylation) between multiple interfaces (e.g., atmosphere-seawater, land-seawater, seawater-sediment, and seawater/sediment-biota) of the ocean. Recently, Hg stable isotope approach has shown great advantages in studying the biogeochemical cycling of oceanic Hg, from tracing sources and processes to reconstructing paleoenvironment and paleoclimate. Here, we overviewed the accurate analytical methods for measuring Hg isotopes in different marine samples, summarized the reported Hg isotope dataset in seawater, sediment/particulate, and biological samples, and comprehensively analyzed the fractionation mechanisms of Hg isotopes and their potential applications in tracing marine Hg cycling. We found that 1) Hg isotope data in seawater and marine particles are very limited, 2) marine Hg isotope fractionation mechanisms, especially mass-independent fractionation mechanisms remain unclear, (3) studies on Hg transfer in marine food chain and Hg exchange amongst reservoirs are constricted only by limited Hg isotope data in single Hg species (e.g., Hg of different chemical forms in sediment and methylmercury in seawater/sediment/biota), thus with great uncertainity, and (4) reconstruction of paleo-marine environment using Hg isotopes is still in its infancy. As a result, the systematics of Hg in oceanic environment and the global Hg cycling model could not be accurately established using current marine Hg isotope data, requiring further systematic study to precisely verify and restrict the key processes and corresponding fluxes of marine and even global Hg cycling. This work includes, but not limited to 1) establish and/or improve isotope analysis method for single Hg species and in-situ or real-time measurement of seawater and important input sources like marine volcanic hydrothermal and submarine groundwater, 2) well investigate the mechanisms of Hg isotope fractionation in seawater matrix (e.g., organic and inorganic media, particulate matter, microorganism), 3) deeply explore Hg (especially MeHg) enrichment and transfer in marine food chain, and 4) Hg exchange between ocean-atmosphere and seawater-sediment, and further reconstruct ancient ocean evolution, in order to provide basic data and theoretical support for controlling marine Hg pollution and understanding global Hg cycling.

In anaerobic environments, dissolved Fe(II) can accelerate the transformation of metastable iron oxides, such as ferrihydrite and lepidocrocite, to more thermodynamically stable mineral phases. As one of the widely existed substances in the environment, organic matters can strongly interact with Fe(II) ions and iron oxides through different functional groups, and then change the type and relative proportion of secondary minerals in metastable iron minerals phase transformation. Based on the theory of reactive intermediate Fe(III) (labile Fe(III)), some low molecular weight organic ligands were selected as the models to investigate their role in the Fe(II)-catalyzed ferrihydrite transformation process, the results showed that organic ligands had an impact at multiple stages throughout the whole transformation process: i) changing the reductive potential of Fe(II) ions by complexation, and occupying the adsorption sites on the surface of ferrihydrite to affect the electron transfer process of Fe(II)-ferrihydrite; ii) complexing with the intermediate labile Fe(III) and reducing the effective supersaturation of the system, which is not conducive to the nucleation of the secondary mineral; iii) adsorbing on the surface of secondary mineral crystal nuclei, changing the surface energy and nucleation barrier. These effects of organic ligands are directly related to the number of carrying functional groups and the adsorption structures on the surface of secondary minerals. The results provide a new perspective and method for understanding the metastable iron (oxyhydr)oxides transformation in the more complex natural environment.

The purpose of this research is to understand the redox reaction between structural Fe in clay minerals and concomitant elements in environments. Then, we are investigating redox properties of Fe in clay minerals over a large range of redox potentials (Eh) and pH. Redox state of the Fe-bearing clay mineral sample (nontronite) was controlled by potential electrolysis at various Eh-pH conditions. From this experiment, we obtained information about the dependence of the redox state of structural Fe in clay minerals on Eh and pH conditions.

The nuclear disaster at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011 resulted in partial meltdowns of three reactors. During the meltdowns, a type of condensed particle, a cesium-rich micro-particle (CsMP), formed inside the reactors through unknown processes. This presentation provides an overview of a series of articles that encompass the elucidation of meltdown processes, including the evolution of debris. CsMPs are associated with various nanoparticles derived from irradiated fuel assembly and structural materials, including U dioxide and U-Zr oxide eutectic nanoparticles, Pu, and B isotopes. The studies conducted in the last decade showcase that, despite their small size, radioactive microparticles released during severe accidents can be a crucial source of information when state-of-the-art analytical techniques are applied.

Due to the accident at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant on March 11, 2011, a large amount of radiocesium was released into the atmosphere and the ocean. It has been reported that the concentration of total radiocesium in the lake water of Lake Akagi in Gunma Prefecture is decreasing more slowly compared to other lake and pond water systems. The cause of this is considered to be the low water exchange ability due to the closed nature of the lake and the elution of radiocesium from the bottom sediments during the summer. Previous studies have suggested the increase in radiocesium concentration in the bottom water during the summer is caused by elution of radiocesium from the sediments. In this study, we investigated the concentration of radiocesium in the bottom water of Lake Akagi during the winter season of 2022 to 2024, when stratification progresses similarly to the summer.

Because mercury has the high volatility and the capability of bioaccumulation, it behaves similarly to bio-elements. Given these properties, it is important to understand mercury dynamics during land-ocean aquatic continuum. However there are many reported cases of mercury concentrations in rivers worldwide, they are unevenly distributed and there are very few examples in Japan. In this study, we collected water samples from 26 major rivers in the Hokuriku, Sanriku-Hitachi, and Tokaido regions. The concentrations of dissolved mercury were determined. Statistical analyses of the factors controlling their variations of were also conducted using the National Land Information System of the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) have been used in a wide range of industrial applications due to their excellent chemical and thermal stability. However, their high persistence in the aquatic environment and their impact on human health and ecosystems have become problematic, leading to worldwide regulation. Previous studies have shown that general water treatment is largely ineffective for PFAS removal, and advanced water purification technologies, such as activated carbon adsorption, anion exchange, or high-pressure membrane filtration, are essential. In recent years, progress has been made in developing membranes specifically designed for PFAS removal. Good PFAS removal has been reported using membranes with enhanced adsorption performance by incorporating highly hydrophobic materials, such as carbon nanotubes, or upcycled membranes, where waste membranes are chlorinated to improve permeability. Furthermore, research on simple and rapid measurement methods for PFAS has revealed PFAS-specific biological responses through the application of omics technology, which is expected to be used in biosensors.

Oxidative dissolution of sulfide minerals by the atmosphere generates toxic metal-containing drainage in Active and abandoned mines. Ferrous and manganese ions in the drainage can be precipitated through an oxidation reaction; however, the actual technique of manganese removal is not contracted yet because its reaction is significantly complex rather than ferrous ion. This presentation shows the kinetic effects of autocatalytic reaction by MnO₂ and complex ion formation by anions on the manganese oxidation rate, based on results obtained by experiments using actual drainages in Japanese mines.

The migration of arsenic and uranium at the Ningyo-Toge environments was studied. Laboratory experiments and synchrotron XAFS analysis showed that in natural sedimentary environments, arsenic is adsorbed and coprecipitated on iron (hydr)oxides, such as ferrihydrite and goethite, limiting their behavior in the hydrosphere.

Concentration and stable isotope ratios of mercury were analyzed for the soils taken from Kii Peninsula to Shikoku. Mercury concentrations of more than 600 soil samples, including those of soils taken from surroundings of Osaka Plain, were mapped, and zonal distribution of highly concentrated mercury occurrence appeared in the south of Median Tectonic Line of Kii Peninsula and Shikoku (Median: 198 µg/kg; Average: 275 µg/kg). Mercury stable isotope ratios of 10 samples were within the same range of those of groundwaters taken near the faults in the surrounding Osaka Plain or smaller than those (delta²⁰²Hg: -2.5 - -0.4 pamil). Mass-independent fractionation was not observed for those isotope values. Thus, the geogenic mercury is presumed to emit in association with vapor-fluid fractionation to the surface.

At Lake Kiba in Komatsu City, Ishikawa Prefecture, COD, an indicator of water pollution, consistently exceeds the standard value of 3 mg/L, and in 1995 was the second highest in Japan. Previous studies have suggested that there is a correlation between COD and DOC and POC concentrations. The eight regular observations were made at Lake Kiba from June to October 2023 to measure water quality. In particular, DOC and POC concentrations increased significantly in August and September, suggesting an increase in phytoplankton. 2023 summer recorded the highest temperature ever recorded in Komatsu City (40 degrees), and August precipitation was the lowest in the past 10 years. Compared to summer season with the heavy rainfall of 2022, DOC and POC concentrations are higher approximately twofold in August 2023, which was both light rain and extremely hot, suggesting that temperature and rainfall had an effect on dynamics of dissolved and particular organic matter.

In January 2020, the International Maritime Organisation (IMO) established a regulation (the Marine Fuel Regulation) that requires the sulphur (S) content of marine fuels used in general marine areas to be below 0.5%. V and Ni are known metallic elements generated in heavy oil combustion, and the heavy oil regulation is expected to reduce emissions of these elements into the environment. In addition, the voluntary restraint of industrial activities due to the spread of new coronavirus infections (COVID-19) since April 2020 may have been observed, reducing the emission of anthropogenic substances. In this study, S concentrations and trace metal element concentrations in TSP samples from Nagoya in 2018 before the corona were analysed, and the relationship between these concentrations in TSP and each element for the three years from 2018 to 2020 suggests that the 2020 fuel oil regulation for marine fuel and changes in industrial activities, etc. during the corona disaster may have The aim was to investigate changes in the impact of fossil fuel origin substances in the TSP. The results of the study will be presented in this presentation.

The Yamato River, flowing from Nara Prefecture to Osaka Prefecture, was once considered the most polluted river in Japan. From 2002 to 2005, the Osaka Museum of Natural History led Project Y: Yamato River Edition, a river system survey project that investigated the river's biology and water quality. In 2023, Project Y: Yamato River Edition was relaunched. In addition to reporting on the long-term changes in major ionic components first reported in the early 2000s, the project now includes new survey items such as trace heavy metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) and humic substances (humic and fulvic acids) supplied from soil to the river. This study reports on the changes and current status of the Yamato River's water quality.Comparing concentrations between the early 2000s and 2023-2024, nitrate and phosphate ions showed increased concentrations at almost all sampling points in 2023-2024. The increase in nitrate ions is likely due to changes in wastewater treatment methods since 1995, where effluent previously discharged as NH₄ is now released as NO₃. Sulfate ion concentrations decreased at most sampling points.

Since the early 2000s, various studies on Si stable isotope ratios have been conducted worldwide, while there are very few examples in Japan. The effectiveness of combined analyses of Ge/Si ratios has also been recommended as pseudo stable isotope ratio. Hence, it is important to establish an analytical platform in Japan where both indicators can be analyzed for applying these analyses to environmental samples. In this study, we developed a method for analyzing Si stable isotope ratios using MC-ICP-MS and for trace Ge analysis using isotope dilution hydride generation ICP-MS. We report an overview of these methods and present measurement results for several natural samples.

we present spatiotemporal distributions of Cs-137 in the Baltic Sea, the North Sea, and the Norwegian Sea, for which a large quantity of data are available, and those in the Japanese coastal waters. The effective half-lives 1 to 9 years after each accident were shortest (1.6-4.7 y) in Japanese coastal waters, 4.9 y in the North Sea, and 14.4 y in the Baltic Sea, suggesting that decreases in Cs-137 concentrations are largely dependent on the local geography, and that the dilution-diffusion effect of seawater was greater in the Japanese coastal waters. The effective half-lives of Cs-137 in the surface waters of European seas, based on 30 years of data after the CNPP accident, became longer, ranging from 8.4 to 11.9 y. This may be due to the influence of rivers, and a delay in the decrease in Cs-137 levels caused by the small difference in radioactivity concentrations between the seas and diluting waters.

To understand the regional characteristics of the atmospheric environment, we have observed the atmospheric concentration and deposition flux of both beryllium-7 and lead-210 in Toki City, Gifu Prefecture, Japan, since 2014. In this study, we focused on the atmospheric behavior of lead-210. The concentrations of lead-210 after the summer of 2022 were higher than those before summer 2022. Atmospheric concentrations of lead-210 were observed as double peaks in spring and fall and showed low in summer. Deposition fluxes of lead-210 tended to be low in winter. Comparing the monthly average concentration of lead-210 until 2021 with the monthly average concentration of lead-210 after 2022, it increased from 0.77 mBq/m³ to 1.2 mBq/m³ for atmosphere and from 19 Bq/m² to 34 Bq/m² for deposition. We discuss the causes of the increase in lead-210 concentrations, including the results of backward trajectory analysis, measurements of trace element concentrations, and weather data.

The aim of this study was to establish a method for the selective recovery and quantification of iodide ions (I^-) from environmental water using electrochemical methods, and to investigate the optimization of measurement conditions and the effects of interfering ions. The method was also applied to actual environmental samples for practical use. First, the applied potential, electrode surface area and reaction time were optimized. A linear relationship was observed between the logarithm of the I^- concentration in solution and the amount of I^- accumulated to the electrode. The interference of Cl^- was also confirmed, while there is no interference of IO₃^-. Furthermore, comparison with HPLC-ICP-MS showed that the I^- concentrations in the actual environmental samples were within the error range, confirming the validity of this method.

The ^239+240Pu concentrations in seawater from the North Pacific Ocean were determined to estimate its Pu mean residence time. In the western North Pacific, the ^239+240Pu concentration increased with depth; a subsurface maximum was identified at 500 m depth and then decreased with depth. Its water column inventory was was 1.6 times more ^239+240Pu in the entire water column than would be expected from atmospheric global fallout. The decreasing rate and mean residence time were estimated from water column inventory between surface and 1000 m depth.