[en] A methodology based on large volume ultrafiltration (>1000 l) is developed in order to characterize the artificial radionuclides associated with the colloidal populations in natural waters. 'Inorganic elements' and organic carbon sinks or sources due to sorption or post desorption within the ultrafiltration assembly/membranes of the Sartorius system are underlined and discussed from methodological step experiments as well as recoveries obtained for artificial radionuclides such as ¹⁰⁶Ru, ¹²⁵Sb, ¹³⁷Cs and ^239+240Pu fractionating natural waters from the Rhone River (France), its estuary and the Mediterranean Sea (Gulf of Lions)