Marine Colloids

Abstract

Aquatic colloids, nanoparticles and macromolecules in the 1 nm to 1 µm size range, are characterized by large interfacial energies and scatter light. Colloids are most often separated from seawater through ultrafiltration. They are characterized by physical techniques, such as diffusion, permeation, or light scattering, and can be imaged by atomic force and electron microscopy. Chemically, they are composed mostly of organic macromolecules, which make up 20–30% of marine dissolved organic carbon (DOC). Marine colloidal organic matter (COM) contains biologically resistant heteropolycondensations, such as humic‐type molecules (geopolymers), and products of carbon fixation and consumption such as exopolymeric substances (EPS) excreted by microorganisms. Both geopolymers and biopolymers are amphiphilic with charged and uncharged groups, and contain strong metal‐binding ligands, rendering them metal‐ and radionuclide sequestering agents. Therefore, colloids in the ocean can act as vectors of metal and radionuclide removal and of solubilization, depending on the biomolecule, as well as modifiers of metal bioavailability in delicately balanced marine ecosystems. In addition, marine colloids are also important in their response to global change, as they enhance the sinking flux of carbon, and thus, play a role in global carbon cycling.

Marine Microgels

“…Most studies of the sizes and shapes of SCOM have been conducted by scanning electron microscopy or transmission electron microscopy (TEM) (Santschi et al 1998, Santschi 2005. Koike et al (1990) were among the first to report the presence of 0.4-1.0 μm "particles" in the ocean.…”

Direct and Indirect Toxic Effects of Engineered Nanoparticles on Algae: Role of Natural Organic Matter

“…Buffle et al distinguished three groups of NOM compounds based on their biophysical properties: (i) rigid biopolymers, including the polysaccharides and peptidoglycans produced by algae or bacteria, (ii) fulvic compounds mostly from terrestrial sources, originating from the decomposition products of plants, and (iii) flexible biopolymers composed of aquagenic refractory organic matter from a recombination of microbial degradation products. While it is thought that rigid biopolymers can induce aggregation/deposition through gel formation, ,, the latter two groups may work by modifying the particle or its surface charge due to their high surface charge density . While dispersed particles will be destabilized when their surface charge is nearly neutralized, their stability can also be increased due to electrostatic or steric repulsion. ,, The interactions between ENPs and NOM will most likely determine the fate of ENPs in aquatic systems.…”