Surface Properties Characterization of Suspended Matter in the Ebro Delta (Spain); With an Application to Trace Metal Sorption

The potential interactions between suspended matter (SM) and estuarine waters have been investigated in the Ebro River Delta. The potential particulate reactivity has been estimated using several operational indices: the specific surface area (SSA) determined through N2 (SSABET) and ethylene glycol mono ethyl (SSAEGME) adsorption; the heat of immersion (HI) in water and in amphipatic solvent (octanol); and the ammonium saturation index (ASI). Comparisons were made with pure oxides (Al2O3 and SiO2) and one peat sample. Particulate SSA determination is subject to operational bias which is discussed in relation to the particulate organic/inorganic matter abundance and association. Comparison of the HI obtained with each solvent shows that the two methods give similar results for organic-free oxides but tend to differ when the particulate organic carbon (POC) increases (SM, peat), suggesting a strong POC control on wetting processes. Similarly, the SM cation exchange properties (ASI) are closely related to POC. Despite the overall large salinity and redox gradients characterizing this estuarine environment, the SM surface properties do not appear to be significantly altered during the transit of particles from the river to the sea. An attempt to relate the result of in-situ sorption of stable trace elements, and their radioactive equivalents, to HI (in water) and ASI shows that significant relationships can be obtained between these reactivity indices and the amount of sorbed metals in the case of a highly labile element such as manganese. Contrariwise, these indices cannot be considered as representative of the cobalt and 137Cs sorption.