Some Recent Developments in the Characterization of Estuarine Particulates

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Abstract
Estuaries and coastal zones are characterised by very varied chemical and physical environments. As a result, heterogenous reactions predominate between dissolved and mineral phases, and with the biota. These reactions primarily affect elements and compounds located at the particulate surface. Thus the determination of surface properties of particles is an important key to understanding interactions of trace elements and organic compounds between particulate and dissolved phases in estuarine and coastal systems. Specific surface area (SSA), cationic exchange capacity (CEC) and heat of immersion (∆H) have been measured on native untreated suspended sediment and after oxidation with 15% H2O2. SSA and ∆H have also been measured on samples Leached with NaOH and Na-dithionite in order to remove amorphous aluminosilicates. Results indicated that SSA is controlled by amorphous oxides and is related to the Al content of samples and their granulometry, suggesting an almost uniform coating of the detrital core by amorphous oxides. On the other hand, CEC and ∆H, which appear to be highly correlated, are controlled by both organic matter and amorphous oxides. Studies on electrophoretic mobility have provided additional data on the excess of charge at the interface between suspended matter and electrolytic medium. Particles in suspension in fresh, sea, and estuarine waters appear ubiquitously to exhibit a small range of negative surface charge. This uniformity is attributed to the presence of organic surface coatings on the particles (Loder and Liss, 1985). Finally, the significance of organic and oxide coatings as carriers of trace metal pollutants is discussed. It is shown that their importance in terms of flux is usually Low despite their major role in controlling solid-liquid interactions.

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