The key role of submicrometer sized colloids and biopolymers in the transport of trace metals and organic pollutants in waters and soils is now welldocumented. Through covalent, electrostatic or hydrophobic interactions [12.1,12.2], a large proportion (often 40–90%) of trace compounds may be adsorbed on aquatic colloids [12.3,12.4]. Subsequently, trace compounds can be transported long distances on stable colloids, or quickly sedimented on flocculating colloids and biopolymers. In order to thoroughly understand these processes, information on the exact nature of the colloids and biopolymers is required.