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Behavior of Arsenic in Yukawa River of the Kusatsu
Hot Spring Resource Area, Gunma Prefecture, Japan
Yoshikazu KIKAWADA+, Ken-ichi KYOMEN, and Takao OI+Abstract
Concentrations of trivalent inorganic arsenic and pentavalent inorganic arsenic dissolved in hot spring and river waters in the Kusatsu hot spring area, Gunma, Japan were
determined to discuss the inﬂuence of the river water neutralization system working in
the area on the mobility of arsenic originated from the hot springs. The water of YukawaRiver, into which the hot springs in the Kusatsu spa resort ﬂow, contained a remarkableamount of pentavalent arsenic. By contrast, the dissolved arsenic in the hot springs was
mostly trivalent arsenic just after the hot spring gushed out. These observations indicatethat trivalent arsenic originated from the hot springs was gradually oxidized to pentavalent arsenic as the river ﬂowed down. Pentavalent arsenic in the river was almost completely coprecipitated probably with ferric hydroxide as neutralization products after theriver water was subjected to the neutralization treatment. The remaining arsenic, mostly
trivalent arsenic, having escaped the coprecipitation, was oxidized to pentavalent arsenic
with the water ﬂowing down, and eventually adsorbed on neutralization products.
Key words : arsenic, river water neutralization system, Kusatsu hot spring, suspended
substances, pyrrolidinedithiocarbamate῏῍)*+,-'(./(01 /(02304567. As ῌ 891 As ῍ 89:;
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Chiyodo-ku, Tokyo +*,῎2//., Japan.
,% +*,῎2//.  !"#$ 1῎+ , Department of Chemistry,
Faculty of Science and Technology, Sophia University, 1῎+ Kioi-cho, Chiyodo-ku, Tokyo +*,῎
2//., Japan.

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Fig. + Map of the river system around the Kusatsu hot spring area with sampling locations.
Sampling locations are marked with closed circles for hot springs and open circles forriver waters. Neutralization points are marked with stars.

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The analytical results for the hot spring and river waters collected in the Kusatsu hot spring area.

Water
Sampling Temp.
Sampling location Location
No.
date
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Table +

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Fig. , The plots of (a) concentrations of iron (open circle) and arsenic (closed circle), (b) molar proportions of Fe (III) (open circle) and As (V) (closed circle) to T-Fe and T-As, respectively, and (c) pH in
Yukawa River waters before and after neutralization.

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BCD!' Fig. ,b!)EF1%>? As ῎ )EFG>AH':#I(!'8 CJK Pierce and Moore, +32,  CL".BC Fe ῍ )%>?)M " As ῎ AN+OPJ!' &C*" As ῍

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Kikawada, Y., Fuji, H., Ohno, Y. and Oi, T. (,**2a) : Mobility of arsenic in hot spring water accompanying its penetration into the ground. J. Radioanal. Nucl. Chem., ,12, -,-ῌ-,0.
Kikawada, Y., Kawai, S. and Oi, T. (,**.) : Determination of arsenic and bromine in hot springwaters by neutron activation analysis. J. Radioanal. Nucl. Chem., ,0+, -2+ῌ-20.

 

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012 34 56.7 .* +,/ῌ+-0.
Kikawada, Y., Kawai, S., Shimada, K. and Oi, T. (,**2b) : Arsenic originating in Kusatsu hot
springs, Gunma, Japan, and arsenic pollution status of Kusatsu rivers. J. Disaster Res., -,,0+ῌ,03.
Pierce, M.L. and Moore, C.B. (+32,) : Adsorption of arsenite and arsenate on amorphous ironhydroxide, Water Res., +0, +,.1ῌ+,/-.
Sano, J., Kikawada, Y. and Oi, T. (,**2) : Determination of As (III) and As (V) in hot spring andriver waters by neutron activation analysis with pyrrolidinedithiocarbamate coprecipitation technique. J. Radioanal. Nucl. Chem., ,12, +++ῌ++0.
Stiller, M., Mantel, M. and Rapaport, M.S. (+32.) : The determination of trace elements (Co, Cu
and Hg) in the dead sea by neutron activation followed by X-ray spectrometry and magnetic deﬂection of beta ray interference. J. Radioanal. Nucl. Chem., 2-, -./ῌ-/,.
Sun, Y.C. and Yang, J.Y. (+333) : Simultaneous determination of arsenic (III, V), selenium (IV,VI), and antimony (III, V) in natural water by coprecipitation and neutron activation
analysis. Anal. Chim. Acta, -3/, ,3-ῌ-**.

87