Lithogenic and pyrogenic aerosols supply potentially bioavailable iron to the open ocean where increases in the supply could result in a decrease in atmospheric carbon dioxide concentrations. This paper reviews recent progresses in observations, laboratory simulations, aerosol modelling and ocean biogeochemical modelling, focusing on pyrogenic iron. New data on emission, chemistry and dissolution kinetics confirmed a considerably higher iron solubility of pyrogenic aerosol than natural dust. State-of-the-art aerosol models highlighted that pyrogenic sources contribute to the total atmospheric supply of dissolved iron about 20% into the global ocean (Ito et al., Science Advances, 2019). The fertilizing effect of this “new” iron source has been increasingly examined in ocean models, some of which reported higher efficiency of pyrogenic iron to enhance marine productivity than lithogenic sources. It is, however, still a major challenge in future research to quantitatively understand and predict the high variability, complex aerosol and seawater chemistry of this iron source and diverse marine responses.

Association of local governmental environment research institutes are conducting national wide acid rain monitoring survey since 1991. Precipitation samples were collected at more than 50 locations nationwide for net 19 year in the period of 1991-2015. Cations and anions concentrations are analyzed and monthly values are available from the database maintained by Center for Global Environmental Research, National Institute for Environmental Studies. Outliers such as pollution, probably by sample handling, and the influence of strong local emission sources are removed from this data set. A piper plot following the data representation of groundwater observation was suitable for characterization of the precipitation samples. The plots for cations and anions aligned along lines having sea salts end member and nationwide uniform slopes for magnesium to calcium and for nitrate to sulfate. The regionality, seasonality and secular trends are analyzed, mainly by the ratios of components. Since December 2018, we have collected daily precipitation and snowfall samples in Hirosaki and Goshogawara, Aomori. Cations and anions have been analyzed by ion chromatography. The observational data are compared with the national database and are analyzed focusing the information given by the daily sampling.

We measured alkalinity and dissolved inorganic components in mountainous river waters located in western Aomori Prefecture to evaluate rock weathering during the ground water processes and run off. Surveyed rivers, Asai River and Biwata River, are small tributaries of the class A River Hirakawa and volcanic deposit and tuffaceous rock are the major geological feature of the drainage. We started the observation from January 2019, and 1 or 2 times of samplings per month have been continued so far. Increasing concentration gradients toward downstream were observed for major inorganic constituents throughout the year, suggesting the supplies from the river basin. Owing to the weathering of volcanic deposit, concentrations of dissolved silica in Asai and Biwata rivers are much higher than these in Hirakawa river main stream and rivers having drainage basin in adjacent mountainous area, Shirakami Mountains, which consists of old sedimentary rock. Sodium concentration ratio to sea salt calculated, under assumption that all chloride is originated from sea salt, was decreased in the snow melt season, because the sodium concentration ratio in the wet depositions is very close to the sea water. In the summer season, sodium concentration ratio increased. The increasing groundwater ratio to the total river flow and the promotion of silicate mineral weathering due to the increasing temperature are suggested.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released the largest quantity of radiocaesium into the terrestrial environment since the Chernobyl nuclear accident. We will discuss the deposition and distribution of radionuclides, especially radiocaesium, in the terrestrial environment as a result of the FDNPP accident. Anthropogenic activities such as rice and vegetable cultivation and residential activities in the upstream area have led to a rapid decline in the activity concertation of Cs-137 of suspended sediment (SS) transport in the river network, and these decline directly controls the dissolved Cs-137 concentration in the river water. We outline the environmental and anthropogenic factors that influenced the subsequent transport and impacts of the radionuclides through the environment. The environmental aftermath of the accident at Fukushima is compared to Chernobyl, and the relatively rapid remediation of the Fukushima region relative to the region surrounding Chernobyl will be discussed.

While river water flows from mountainous region to flatlands, the concentration of dissolved inorganic components in river water changes due to the influence of the basin. In this study, we investigated the concentrations of dissolved silica and inorganic ions in small rivers in Hirakawa City, Aomori Prefecture, and their seasonal changes. Dissolved silica decreased significantly within the short period after planting rice, and then increased in concentration but fluctuated at a fairly lower concentration than that of irrigation water.There became no concentration difference in irrigation water and paddy water by the rice harvest season.From the time series change, it was found that the silica absorption by the rice was most active in the early stages of rice growth, when paddy water silica was depleted.The growing rice continued to use silica in irrigation water, but paddy water silica was not be depleted. In the rice agriculture area, dissolved silica concentration in small rivers used for paddy field irrigation showed significant decrease in downstream area than that in the upstream area, indicating the influence of rice cultivation on the river water quality.

Hydrogen peroxide (H₂O₂) is the most stable reactive oxygen species formed in river water. At high concentration, it can be toxic to aquatic organisms. It is therefore important to monitor its concentration in order to establish potential toxicity concerns in the water body. In this study, H₂O₂ concentration in selected rivers across Japan was investigated. In addition, the factors responsible for its formation were considered. Twelve rivers were sampled over different seasons of the year and their H₂O₂ concentration was determined by the Fenton method using benzene as a probe. The DOM optical properties were investigated via UV absorption properties and fluorescence measurement with parallel factor (PARAFAC) analysis. The results showed that the H₂O₂ concentration ranged from 21 – 2929 nM. Kokubu river had the highest concentration which was consistently higher than the PNEC value regardless of the sampling season. This suggests potential H₂O₂-mediated toxicity in the river. PARAFAC analysis showed Kokubu river had some fluorescence whitening agents, which have a high H₂O₂ photoformation rate.

The Oklo uranium deposit yielded in the Francevillian sedimentary group at east part of the Republic of Gabon, central Africa is known as a fossil of natural fission reactors. In this talk, I review the recent studies of the Oklo natural fission reactors in the last decade.

Estimating the formation mechanisms of insoluble radioactive cesium particles (Type A) released into the environment at the time of the Fukushima Daiichi NPS accident is useful for clarifying the accident progression. The authors pointed out that the origin of Type A may be that the Unit 3 HEPA filter (glass fiber: GF) was melted and atomized during a hydrogen explosion. In that case, carbon in the activated carbon filter or GF binder is likely to be present with the Type A particles. However, in conventional observations, it has been difficult to identify carbon because carbon tape has been used for fixing particles. In this study, carbon was tried to be identified using an electron probe microanalyzer (EPMA) and a sample table other than carbon tape. As a result, the carbon content of Type A was similar to that of GF, which is considered to be of binder origin. This is consistent with the hypothesis by the authors. While paying close attention to the relationship between carbon information and other constituent elements, we will work on further elucidation of the formation process.

Heavy metals are very important due to their association with ecological environment issues, especially human health. Core sediments can serve as an unique sink to record historical and current environment contaminations. To assess heavy metal pollution, their concentrations in core sediments collected from Tokyo Palace Moat were measured coupled with sedimentation age determination using 210Pb activity concentrations and chemical speciation to confirm secondary migration of the elements within the sediment column. As a result, a record of metal contamination in Tokyo mainly via atmosphere is developed in core sediments during the period of 1832-2019. The average sedimentation rate was estimated to be 0.38 cm/yr. All the elements showed low concentrations during Edo period, but concentrations of V, Cr, Mn, Cu, Zn, As, Cd, Sn, Sb, and Pb in core sediments abruptly increased after 1870 as contaminants possibly due to the industrial revolution in Japan in Meiji Period. These elements are basically volatile elements, which supports the fact that most of the elements were supplied via air. Most of the elements showed peaks during 1900-1920 and 1940-1950, but became low around 1925 possibly due to the influence by the Great Kanto earthquake in 1923. Quantitative analysis of Zn K-edge XANES indicated that Zn was mainly present as ZnS after 1930s, but as ZnCO3 before 1930s, possibly because sulfur concentration was not sufficient to form ZnS before 1930s. The formation of these insoluble minerals such as ZnS and ZnCO3 assures that the secondary migration of Zn within the core has been minimal. Anthropogenic Mn accumulation in sediments peaked around 1975 in accordance with the period of high economic growth in Japan, but further discussion in needed to identify the source. For the period of 1980-2019, the data of core sediments reflected the result of stricter environment regulations, which lowered the emission of most of the elements. However, heavy metal concentrations in the surface sediments were still greater than the levels at the bottom of the core. It suggests that some anthropogenic depositions via air are still present in Tokyo at present, which are greater than those in Edo Period recorded in the core (1830-1867).

Estuary plays an essential role in the transformation processes and fate of riverine substances, such as trace metals. Therefore, it is important to reveal the distributions of trace metals in estuarine to understand their biogeochemical cycle. In this study, we determined the concentration of dissolved trace metals; manganese (d-Mn), iron (d-Fe), copper (d-Cu), and cobalt (d-Co), and macronutrients in Ariake Sea, a shallow semi-enclosed inlet bay in western Japan. This study aims to investigate possible sources and transport of these metals.The seawater samples were taken by clean sampling method on board Kakuyo-maru (Nagasaki Univ.) in May during 2018 cruise. By using a single preconcentration system with chelating resin column and inductively couple plasma mass spectrometry (ICP-MS), we determined d-Mn, d-Fe, and d-Cu concentration in the samples. On the other hand, d-Co concentration in seawater was measured by cathodic stripping voltammetry (CSV) with nioxime.The concentration of all analyzed trace metals and macronutrients showed higher values in river waters compared to those in seawaters. The highest concentration of trace metals and macronutrients were detected in the surface waters of the innermost station of Ariake Sea and decreased gradually from the nearshore region to the East China Sea (ECS).During estuarine mixing, all trace metals showed non-conservative patterns, suggesting the distributions of all analyzed trace metals were not simply controlled by physical mixing between rivers and ECS waters. The deviation of trace metals concentration relative to the mixing line indicated either removal or addition. The metal removal was pronounced for d-Fe due to the flocculation; d-Mn was also scavenged from the water column during estuarine mixing. D-Cu and d-Co exhibited a similar pattern in our study, implying that a similar mechanism governs their distributions. Moreover, the upward deviations of d-Cu and d-Co relative to the mixing line highlighted the importance of their benthic input from the seafloor sediments within the embayment system. By applying the estuary mixing model, we estimated their internal fluxes were slightly higher than those of riverine fluxes.

Average of Σ14DPAHs concentration was 3.64 ng L^-1 (1.67-5.15 ng L^-1) in 2017 and 3.97 ng L^-1 (1.98-6.48 ng L^-1) in 2019. In 2017, higher DPAHs concentrations were observed at higher latitudes, while in 2019 the trend was reversed. Salinity and temperature profiles indicates an eastward surface mixing of Liman Current water (salinity 32.5-33.0, temp. ＜16℃) within the subarctic gyre in 2017 and a purer transport of Tsushima Warm Current (salinity 33.7-34.5, temp. >17℃) in 2019. Such results were contrasted with the DREAMS model. From the diagnostic ratios [Flu] / [Flu + Pyr] (0.49-0.69) and [BaA] / [BaA + Chr] (0.33-1.0), sources of DPAHs were inferred to be majorly pyrolytic at all points. In conclusion, the DPAHs distribution along northeastern Japan Sea is related to both surface currents.

The mean total 14 PAHs (particulate plus dissolved) concentrations were highest in summer and lowest in winter. Correspondingly, 8.50 ng L⁻¹, 14.44 ng L⁻¹, 10.31 ng L⁻¹, and 7.01 ng L⁻¹, respectively for the 4 sampling surveys. Particulate-dissolved phase distribution had discrepancies among seasons, tightly related with rainfall amounts, days before sampling. Highest particulate PAHs in the west area, decreasing towards the east area was the general trend. Riverine runoffs were a major transportation pathway of particulate-PAHs towards the bay. The risk quoefficient for ∑14 PAHs varied from 0 to 82.49 in 60 surface seawater samples, representing a very low to low risks to marine life.