Size and elemental analyses of nano colloids in deep granitic groundwater; Implications for transport of trace elements

Saito, Takumi*; Suzuki, Yohei*; Mizuno, Takashi   

Nano colloids in granitic groundwater obtained from a borehole located at the -300-m stage of the Mizunami Underground Research Laboratory were studied in terms of their size distributions by flow-field flow fractionation. In order to deal with relatively low concentrations of colloids, colloids were enriched first by ultrafiltration, and then by in-situ enrichment using a large injection loop and the slot flow technique. The size distributions of organic and inorganic constituents of colloids were measured by UV/Vis, fluorescence and inductively coupled plasma mass spectrometry, from which possible association of trace elements with host colloidal phases consisting of major elements and organic materials was discussed. Trace elements, namely, Sr, lanthanides (La, Ce, Eu, Lu), actinide elements (U, Th) and heavy metals (Cu, Zn and W), exhibited distinct size distributions, reflecting their preferential association with certain host colloidal phases.