The colloidal fraction of trace metals is ubiquitous in seawater. The interaction between marine colloids and trace metals strongly controls the speciation, bioavailability, toxicity and the ultimate fate of metals in the ocean. The significance of colloidal trace metals and the role that colloidal particles play in the behavior of metals during the estuarine mixing is overviewed in this paper. A brief discussion was finally made on the potential role of colloids in the determination of distribution coefficients between particulate and dissolved phases, [WTBX]i.e.[WT], the role of colloids in the solid-liquid partitioning.
The available literature data have shown a quite variation of colloidal trace metals in the total dissolved fraction. For example, colloidal Fe, Cu, Cd, Zn, Al and Pb represent 4%~100%, 1%~78%, 0%~76%, 1%~14%, 3%~100%, 12%~100% of the total dissolved metal respectively. The fundamental reasons that caused such large variations in different estuarine settings are unclear yet, which may partially be related to the different techniques and/or protocols that have been applied in separating marine colloids.
The behavior of estuarine colloidal metals is rather complex, which is primarily controlled by the association of metals and the surface of organic matter or particles. Prior research has manifested a positive correlation between certain colloidal trace metals such as Cu and colloidal organic carbon, suggesting there exist strong organic ligands for certain metals.
The role of colloid in the interaction of metals between different phases has been claimed to be important, and the occurrence of colloids may explain the so called “particle concentration effect” on the apparent distribution coefficient.