FACTORS CONTROLLING THE STABILITY OF SUBMICRON COLLOIDS IN NATURAL-WATERS

Particles are ubiquitous in all natural systems and play an important role in the control and fate of nutrients and pollutants. Submicron pa rticles are especially important because they have large specific surf ace areas and high surface free energies which facilitate sorption of significant quantities of substances. Currently, only limited informat ion is available on particle number and size distributions of natural submicron particles, owing to the significant problems involved in the ir experimental determination. In the present paper, existing data are discussed and compared with theoretical predictions based on a classi cal coagulation/sedimentation model where the kinetics of coagulation is described by Smoluchowski's equations and sedimentation is characte rized by Stokes' law. Model predictions agree well with reported parti cle behaviour for particles larger than 100 nm. While classical theory does not explain the presence of colloids smaller than 100 nm in surf ace waters, the existence of such small colloids, embedded in large or ganic matrices, has been-observed recently by high resolution transmis sion electron Microscopy. Improvements in the measurement techniques a vailable as well as development of the necessary theory to describe th ese organic/inorganic associations would be most welcome.