The concentrations of indium (In), thallium (Tl) and bismuth (Bi) in rivers and lakes in Hokkaido, Kanto area, Tokai area, Shinetsu area and Kyusyu area of Japan were analyzed by ICP-MS. Five hundreds mL of samples were filtrated with 0.45μm membrane filter. The concentrations of the three elements in the filtrate were shown as soluble In, Tl and Bi. The concentrations of the three elements in the residue on the membrane filter of 0.45μm pore size were shown as filtration residue In, Tl and Bi. The averages and standard deviations (unit:ng/L) of the soluble elements were In 2.3±5.1 (n=195), Tl 8.4±17. 1 (n=195), and Bi 1.2±4.2 (n=159). Those for filtration residues were In 9.3±36. 1 (n=177), Tl 30.0±112.3(n=177), and Bi 31.0±118.7 (n=159), respectively. Although, these samples were collected in various seasons and sampling dates, the average concentration might indicate the representative concentrations of In, Tl and Bi in rivers and lakes in Japan. The results for Japanese samples were compared with the results of foreign countries.

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火山地域を含む流域では，噴火による噴出物や湧水中の溶存成分の増減が，流域の水環境に影響を及ぼすことが考えられる。箱根山では2015年6月29日に大涌谷で噴火が発生し，噴火後，大涌沢や早川で強い濁りがみられた。このため，大涌沢や早川等の周辺河川や降水を継続して1～3か月ごとに採取し，溶存成分の変化を把握した。大涌沢では，噴火後に高ECが観測されたものの，その後，値は徐々に下がった。大涌沢の陰イオン中に含まれるCl-の割合を求めた結果，噴火直後は高かったものが1年後には低下する傾向がみられた。また，降水の水質組成には火山ガスの影響が認められ，主な噴気孔である大涌谷との距離が近い観測地点の降水ほど，溶存成分量が多いことが明確となった。

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