Colloids and Nanoparticles in Aquatic Systems

Abstract Colloids in the ocean are mainly composed of natural organic matter (NOM), with trace amounts of metals, nutrients, radionuclides, pollutants, and variable amounts of anthropogenically produced engineered nanoparticles and nanoplastics. Thus, state‐of‐the‐art instrumental techniques are required to unravel the chemical composition of colloids. Such studies revealed that colloidal macromolecular organic matter (COM) contain aquagenic substances (composed of microbially produced exopolymeric substances, EPS, gels, transparent exopolymer particles, TEP, and TEP precursors) and pedogenic substances (humic and fulvic matter). COM can act as glue or as soap; can be bioavailable and biodegradable or refractory; and contain different moieties that act as metal chelators, antioxidants, or absorber of hydrophobic pollutants. EPS in aquatic systems, mostly composed of polysaccharides and proteins, can form not only biofilms but also marine snow (MS) or marine oil snow (MOS), and are important in initiating and maintaining aggregation and sedimentation processes. These processes can also be traced by natural radionuclides that have colloidal fractions. These aggregation processes lead to “colloidal pumping” (aggregation to form larger particles) of trace substances bound to EPS and other macromolecular NOM compounds that counteract the prevailing pathway of degradation of macromolecular NOM to low‐molecular‐weight molecules.