Comparative study of granitic and sedimentary groundwater colloids by flow-field flow fractionation coupled with ICP-MS

Colloids in deep underground water play an important role in the migration of radionuclides and are of great concern in the safety assessment of the geological disposal of nuclear wastes. Size distribution and elemental compositions of colloids in granitic and sedimentary deep groundwater were determined by flow-field flow fractionation (Fl-FFF) combined with inductively coupled plasma mass spectrometry (ICP-MS). Great care was taken to examine colloids over a wide range of size and to detect trace elements associated with them. In the granitic groundwater organic colloids and various inorganic elements were found in limited size ranges. The presence of different types of organic colloids was suggested in this groundwater. Most of the inorganic elements exhibited similar size distributions at <10 nm, which largely overlapped with organic colloids rich in fluorophores. In the sedimentary groundwater small organic and probably inorganic colloids were found at <5 nm together with larger inorganic colloids. Organic colloids in this groundwater were homogeneous in terms of their sizes and the compositions of chromophores and fluorophores. The size distribution of inorganic elements at <10 nm depended on their types, indicating the presence of different host colloidal phases.