Arsenic Originating in Kusatsu Hot Springs, Gunma, Japan, and Arsenic Pollution Status of Kusatsu Rivers

Kusatsu hot springs at the eastern foot of the Kusatsu-Shirane volcano is a famous spa area in Japan. Its hot springs are strongly acidic making local rivers acidic, requiring lime water neutralization. We determined the arsenic concentration in hot springs, rivers, and neutralization products, to calculate the mass balance of arsenic in river systems. Hot springs supply a total of 45 tons a year in arsenic to local rivers, which transport some 28 tons a year — most of which is accounted for by Bandaiko hot spring and the Yu River. After neutralization, these flow into the Shinaki Dam reservoir, which accumulates large amounts of suspended neutralization products. Mass balance calculation suggests that arsenic dissolved in river water is nearly completely coprecipitated with or adsorbed by neutralization products, so that Shinaki Dam reservoir accumulates some 25 tons of arsenic yearly.