木川田 喜一

The gases dissolved in the waters of volcanic lakes can present a serious hazard if the physical-chemical conditions change due to variations in the supply of magmatic gases. The monitoring of gases such as CO₂ and He help us understand the degassing process and their connection with magmatic/hydrothermal system. One of the most acidic volcanic lakes on the planet is the Yugama, on Kusatsu Shirane volcano (Japan). We report the results of an interdisciplinary study carried out in August 2013 at Yugama consisting of the first estimation of rate of diffuse CO₂ emission, the chemical and isotopic analysis of water and dissolved gases in samples from vertical lake profiles, and an echo-sounding survey. The lake water has an average temperature of 24-25°C, pH 1.01, concentrations of SO₄^2- between 1,227 and 1,654 mgL⁻¹ and Cl⁻ between 1,506 and 2,562 mgL⁻¹, with gas bubbling at several locations and floating sulfur globules with sulfide inclusions. A total of 66 CO₂ efflux measurements were taken at the lake surface by means of the floating accumulation chamber method to estimate the diffuse CO₂ output from the studied area. CO₂ efflux values ranged from 82 up to 25,800 g m⁻² d⁻¹. Estimation of the diffuse CO₂ emission at Yaguma Crater Lake was 30 ± 12 t d⁻¹. Normalized CO₂ emission rate (assuming an area of 0.066 km²) was 454 t km⁻² d⁻¹, a value within the range of acid volcanic lakes. Vertical profiles of major ions and dissolved gases showed variations with increases in ion content and dissolved CO₂ and He with depth. Acoustic imaging shows the presence of intense bubbling and provides important information on the bathymetry of the lake. The 50–200 kHz echograms exhibit frequent vertical plumes of rising gas bubbles. Within the crater-lake, three circular submarine vents have been identified showing flares due to a significant activity of sublacustrine emissions. This work shows the first data of diffuse CO₂ degassing, dissolved gases in water and echosounding (ES) from Yugama Crater Lake. Periodic hydrogeochemical and hydroacoustic surveys at Yugama Crater Lakemay thus help to document changes in the state of activity of this high-risk volcanic area.

Plutonium (Pu-238 and Pu-239,Pu-240), (CS)-C-137 and plutonium activity ratios (Pu-238/Pu-239,Pu-240) as did uranium isotope ratio (U-235/U-238) were measured in surface soil samples collected in southeast Mongolia. The Pu-239,Pu-240 and Cs-137 concentrations in Mongolian surface soils (<53 mu m of particle size) ranged from 0.42 +/- 0.03 to 3.53 +/- 0.09 mBq g(-1), and from 11.6 +/- 0.7 to 102 +/- 1 mBq g(-1), respectively. The Pu-238/Pu-239,Pu-240 activity ratios in the surface soils (0.013-0.06) coincided with that of global fallout. The U-235/U-238 atom ratios in the surface soil show the natural one. There was a good correlation between the Pu-239,Pu-240 and Cs-137 concentrations in the surface soils. We introduce the migration depth to have better understanding of migration behaviors of anthropogenic radionuclides in surface soil. We found a difference of the migration behavior between Pu-239,Pu-240 and Cs-137 from Cs-137/Pu-239,Pu-240-Cs-137 plots for the Mongolian and Tsukuba surface soils; plutonium in surface soil is migrated easier than Cs-137. (C) 2016 Elsevier Ltd. All rights reserved.

Changes in temperatures in shallow geothermal systems beneath the Manza area in the Kusatsu-Shirane volcano region, Japan with time, were reconstructed by using chemical geothermometers derived from long-term data on the water chemistry of three typical hot springs in the area from almost the last fifty years. The calculated equilibrium temperatures for quartz, anhydrite and alunite were helpful in understanding the state of the hydrothermal systems in the area. Although the measured water temperatures of the hot springs at their vents have decreased gradually since the 1970s, the temperatures of the geothermal systems in the area do not seem to be in a downward trend based on the geothermometry. The temperatures of the geothermal systems have probably fluctuated in response to changes in the volcanic activity of the Kusatsu-Shirane volcano. The changes in the estimated equilibrium temperatures for appropriate minerals give us helpful information on the volcanic activity that we cannot obtain directly, by monitoring of water chemistry of hot springs in the volcanic area. (C) 2017 The Authors. Published by Elsevier B. V.

Mixtures of cesium nitrate and ammonium-ion type zirconium phosphate, NH4Zr2(PO4)(3), with varying molar ratios were thermally treated at 600 or 750 degrees C, yielding partial cesium-ion type zirconium phosphates, CsxH1-xZr2(PO4)(3) (x = 0.4, 0.6, 0.8). Immobilization of cesium on the CsxH1-xZr2(PO4)(3) was examined. Leaching tests at 90 degrees C using pseudo-seawater as leachant revealed that the cesium leach rates of the materials with x = 0.4 and 0.6 were in the order of 10(-2) g m(-2) day(-1), smaller than those reported for borosilicate glasses, the generally accepted first-generation waste form. This indicated the materials examined were better cesium immobilizers than borosilicate glasses.

Extraction experiments on soil radioactively contaminated by the Fukushima Daiichi Nuclear Power Plant accident were conducted by using a variety of extractants to acquire knowledge on the mobility of radioactive cesium in soil. The experimental results revealed that cesium is tightly bound with soil particles and that radioactive cesium newly deposited on soil due to the accident had apparently a higher mobility than stable cesium commonly existing in soil. The results suggested that radioactive cesium deposited on soil hardly migrates via aqueous processes, although chemical and mineralogical conditions of soil affect their mobility.

We performed three-step sequential extraction experiments, with Milli-Q water, 1 M ammonium acetate solution and 0.11 M acetic acid as extractants of Cs, on soils radiologically contaminated by Fukushima Dai-ichi Nuclear Power Plant accident. Though aqueous solutions containing ammonium salts are effective to extract Cs from soils, the obtained overall extracted fractions of radioactive Cs by the three-step sequential extraction process were less than 30 %. Thus, the most of the radioactive Cs deposited on soils is probably incorporated in the non- or hardly exchangeable site of clay minerals, components of the soils.

The U-235/U-238 ratios in the monthly atmospheric deposition samples in Akita, located at west side of northern part of the main island of Japan, in 1977 and 1978 were determined. The anomalous uranium slightly depleted in U-235 has been found in the some deposition samples collected in mid-1977. The uranium depleted in U-235 had probably been injected into the atmosphere with plutonium by the largest Chinese nuclear tests conducted on 17th November, 1976 and transported directly throughout the atmosphere. (C) 2015 Published by Elsevier B.V.

Lead and lithium isotope ratios in the monthly atmospheric deposits in Fukuoka, located on the southwestern part of the Japanese Islands, in 1964 and 1965 were determined. The Pb isotope ratios in the deposits suggest the atmospheric environment in the 1960s in Japan had been strongly affected by automobile pollution in those days. The Li isotope ratio in the deposits shows the seasonal variation. This variation could be attributed to mixing of sea salt aerosols with mineral dust. (C) 2015 The Authors. Published by Elsevier B.V.

Concentrations of rare earth elements (REEs) in acidic spring waters collected from sulfurous alteration zones in the Manza area belonging to the Kusatsu-Shirane volcano region, Japan were investigated. Based on the correlation in concentrations between REEs and major dissolved components, the common convex shape found in the heavy REEs in their REE patterns probably reflects the hydrothermal reservoir beneath the Manza area. Moreover, the varying distribution patterns in the light REEs presumably resulted from precipitation and/or dissolution of secondary sulfate minerals, such as alunite and anhydrite. (C) 2012 The Authors. Published by Elsevier B.V.

Temporal variations of monthly thorium (Th) deposition observed at Tsukuba, Japan during the period 1990-2007, comparing with plutonium deposition, was studied. The monthly Th-232 deposition as did Pu-239,Pu-240, varied according to season and inter-annually. In particular, Th-232 deposition increased significantly in spring coinciding with Asian dust (Kosa) events. The Th-230/Th-232 activity ratios vary according to sources and can therefore be used to differentiate between locally derived and remotely derived Th-232. The Th-230/Th-232 activity ratios in deposition samples showed large variability with high ratios occurring in early spring. These high Th-230/Th-232 ratios in deposition can be attributed to local dust storms, especially in,early spring, that cause resuspension of soils from cultivated fields which are characterized by high Th-230/Th-232 activity ratios. The results reveal that both locally and remotely derived Th-232 deposition showed seasonal variations with maxima in spring, although the remotely derived fraction is dominant rather than the locally derived one. The Th-232 deposition maxima later in spring is attributable to the remotely derived fraction, corresponding to the Kosa events. Annual Th-232 deposition exhibited an increasing trend, suggesting the presence of sources other than soil dust such as fly ash from increasing coal burning. (C) 2011 Elsevier Ltd. All rights reserved.

草津白根火山地域の温泉水ならびに硫黄鉱山排水が周辺河川の水質に与える影響の見積

大気降下物試料の化学組成分析の前処理としてのマイクロ波分解の適用条件に関する検討

In order to better understand the behavior of Pb-210 deposition in Far East Asia, comprehensive data of monthly Pb-210 deposition, which includes several time-series and spatial distribution data at 14 stations in Japan and 2 stations in Taiwan, were analyzed. Pb-210 deposition at most of the sites exhibited a typical seasonal change with higher values in winter and lower values in summer; especially, the greatest Pb-210 deposition in the world occurred in winter at sites beside the Japan Sea. The deposition behavior of Pb-210 in Far East Asia differed between winter and summer. The meteorological phenomenon peculiar to winter of the Japan Sea side, i.e., formation of the Japan Sea convergence zone, might cause the high Pb-210 concentration in rainwater, as may heavy snowfall. The Pb-210 concentration in rainwater showed long-term variability, although this differed between winter and summer. This long-term variability may be related to climatological factors such as El Nino. (C) 2010 Elsevier Ltd. All rights reserved.

2008年を通して川崎市で採取した大気粒子状物質の水溶性成分から，川崎市北西部の大気環境の現状を評価した．

The contents of arsenic in soils collected in the Kusatsu hot spring area, Gunma, Japan, were determined by INAA, with the average content of 36 mg/kg, which was obviously higher than that reported for the Japanese crust. The remarkably high contents of arsenic, 170 and 130 mg/kg, were observed in the soils collected near the discharge point of the surplus hot spring water. The distribution of arsenic in the ground suggests that arsenic originated from hot springs has been diffusing into the ground accompanying the penetration of the hot spring water.

A total of 19 elements in the samples of atmospheric deposition collected in Kawasaki, Japan, were determined by neutron activation analysis, ICP-AES and flame photometry. The amounts of soil dust depositions were larger in springs and those of Sb and Zn depositions were larger in summers than in the other seasons. The values of the enrichment factors were higher for Sb and Zn than for the other elements determined throughout the sampling period. A factor analysis showed that the two elements were characterized as industrial components. Rubber products like tires that contain noncombustibles and rubber accelerators were a possible origin of high concentrations of Sb and Zn in the present samples.

The concentrations of As(III) and As(V) in natural hot spring and river waters collected in the Kusatsu-Shirane volcano area, Gunma, Japan, were determined by neutron activation analysis (NAA) preceded by the pyrrolidinedithiocarbamate (PDC) coprecipitation. The PDC coprecipitation technique using Pb(PDC)(2) as a collector of As(III) was applicable to the determination of As(III) at mu g/L to mg/L levels. It was found important that the sufficient amount of PDC must be added to sample waters to accomplish the quantitative coprecipitation of As(III), taking the amounts of coexisting metal ions into consideration.

鹿児島湾の若尊カルデラ海底熱水活動地域, 静岡県伊東沖手石海丘 (海底噴火地点) の底質試料を対象に, 火山性海底堆積物に対する逐次溶解法の適用性を検討した. 若尊カルデラ底質試料におけるヒ素およびアンチモンの抽出挙動は, 火山性の海底噴気あるいは熱水を介して海水中に供給されたヒ素, アンチモンの一部が鉄水酸化物に吸着し, また一部が硫化物として周辺堆積物中に固定されていることを示すものであった. 一方, 手石海丘底質試料における抽出挙動からは硫化物態アンチモンの存在は見出されたものの, 硫化物態ヒ素の存在は見出されず, ヒ素の全てが鉄水酸化物等による吸着捕集によるものと見なされた, 硫化物態としてのヒ素の固定は, 若尊カルデラに特徴的な硫化水素を含む噴気・熱水の存在に起因していると思われ, 火山性海底堆積物への逐次溶解法の適用が, 海底噴気および海底熱水の化学的特徴を読み解くための有効なツールとなり得ることが示唆された.

A series of experiments was conducted in which boron minerals were precipitated by water evaporation from solutions containing boron and potassium, sodium or lithium at 25 degrees C, and boron isotope fractionation accompanying such mineral precipitation was investigated. In the boron-potassium ion system, K-2[B4O5(OH)(4)]-2H(2)O, santite (K[B5O6(OH)(4)]-2H(2)O), KBO2.1.33H(2)O, KBO2-1.25H(2)O and sassolite (B(OH)(3)) were found deposited as boron minerals. Borax (Na-2[B4O5(OH)(4).H2O) was found deposited in the boron-sodium ion system, and Li2B2O4.16H(2)O, Li2B4O7.5H(2)O, Li2B10O16. 10H(2)O, LiB2O3(OH).H2O and sassolite in the boron-lithium ion system. The boron isotopic analysis was conducted for santite, K-2[B4O5(OH)(4)].2H(2)O, borax and Li2B2O4.16H(2)O. The separation factor, S, defined as the B-11/B-10 isotopic ratio of the precipitate divided by that of the solution, ranged from 0.991 to 1.012. Computer simulations for modeling boron mineral formations, in which polyborates were decomposed into three coordinated BO3 unit and four coordinated BO4 unit for the purpose of calculation of their boron isotopic reduced partition function ratios, were attempted to estimate the equilibrium constant, KB, of the boron isotope exchange between the boric acid molecule (B(OH)(3)) and the monoborate anion (B(OH)(4)(-)). As a result, the K-B value of 1.015 to 1.029 was obtained. The simulations indicated that the K-B value might be dependent on the kind of boron minerals, which qualitatively agreed with molecular orbital calculations independently carried out.

Long-term changes in the concentration of arsenic in these 40 years were investigated for four hot springs, Kusatsu-Yubatake, Bandaiko and Kagusa No. 3 and No. 8, located in the Kusatsu hot springs area in the eastern foot of Kusatsu-Shirane volcano, Gunma, Japan. The drastic increase in arsenic content was observed only in Bandaiko between 1985 and 1998. The concentration of arsenic in Bandaiko water showed good positive correlations with those of iron and sulfate ions during that period. In addition, the arsenic content has fluctuated equimolecularly with that of iron through the period. This suggests the major origin of the dissolved arsenic in Bandaiko water is arsenopyrite. The drastic increase in the concentration of arsenic probably have been caused by the accelerating oxidation-dissolution of arsenopyrite present in and around underground hydrothermal reservoir, which started in 1970 since the hot spring issued out, associating with the continuous intrusion of meteoric water containing a considerable amount of dissolved oxygen. The concentration of arsenic in Bandaiko water is now around 10 mg dm^-3, meaning that the annual supply of arsenic from Bandaiko water is about 49 ton y^-1. Bandaiko is by far the largest arsenic supplier in the Kusatsu hot springs area.

We compared two analytical values for sulfur species in water samples of Yugama, a crater lake of the Kusatsu-Shirane volcano, collected between 1966 and 1995. One analytical method was ion chromatograph, by which concentrations of the sulfate ion (SO_4^<2->) were determined. The other was gravimetric analysis preceded by oxidation of the samples, by which total concentrations of sulfur species (T-SO_4^<2->) were determined. The concentration differences between the two were in good accordance with the total concentration of poly-thionates reported by Takano and Watanuki (1990) through the whole period studied. This suggested that the concentration difference between SO_4^<2-> and T-SO_4^<2-> can be used to estimate the concentrations of dissolved poly-thionates. In this way we can grasp very easily the secular change of the total concentration of poly-thionates without any special analytical conditions and/or instruments.