Saito's group webpage

Natural organic matters (NOMs) such as humic substances (HSs) are known to play important roles in mobilities and bio-availabiliities of actinide elements and heavy metals. Most of researches on NOMs have been performed with NOMs isolated from surface environments such as soil and river water. The properties and roles of NOMs in deep groundwater has been largely unknown. In this research we have investigated the physiochemical and ion binding properties of HSs isolated from sedimentary groundwater collected at a borehole at the -150 m experimental stage of the Horonobe underground research laboratory, JAEA. It was the first attempt to clarify details of ion binding to deep groundwater HSs over a wide range of conditions. Horonobe HSs consist of relatively small organic molecules rich in aliphatic C and S, which are rather distinctive, compared with structures and compositions of HSs with surface origins. Although the densities of carboxylic groups, which are supposedly responsible for metal ion binding in HSs, are similar to or even larger than those of surface HSs, the binding of copper ion (Cu2+) is smaller for Horonobe HSs. This can be explained by mono-dentate coordination of the carboxylic groups which are sparsely distributed on aliphatic chains of the HSs. Extended X-ray absorption fine structure analyses have revealed involvement of S in binding of Cu2+ to Horonobe HSs at relatively low pH, […]