On the formation of organic coatings on marine particles: Interactions of organic matter at hydrous alumina/seawater interfaces

Abstract

The interaction mechanism between aquatic organic matter (AOM) and mineral particles in seawater has been studied using hydrous alumina as a model mineral phase. The electrochemical methodology allowed direct measurements in oxide suspensions and distinction between ‘dissolved’ and ‘particulate’ organic matter. Adsorption of small organic molecules, such as salicylic acid, was found to be negligible at natural concentration levels. Unsaturated lipids are the most reactive surface-active constituents of AOM leading to multilayer formation. For humic materials an inverse relationship has been established between absorbed densities and particle concentration and it is interpreted as the fractionation effect of a polydisperse solute. A new, highly surface-active fraction of AOM has been identified as fluid surface-active aggregates, ubiquitous in productive surface waters, sea surface microlayers and in mixing zones in estuaries. Hydrophobic attraction is the most important force governing AOM—particle interaction in seawater. Reversible adsorption of organic molecules at charged marine interfaces is only the initial step in the process of organic coating formation that involves complex structural organization phenomena well known in membrane sciences and biophysics.