木川田 喜一

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

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．

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.

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.