Incorporation of trivalent chromium into riverine and estuarine colloidal material

The binding of dissolved trivalent chromium by dissolved and colloidal substrates at the riverestuary interface was studied using a combination of product and reactant mode experiments, at concentrations of materials typical of estuarine conditions. Using spikes of 1–20 μg/l Cr3+, about one third of the Cr3+ was scavenged by that fraction of riverine colloidal material which flocculated upon mixing of river water and seawater. Reactant mode experiments, using chemiluminescence as a speciation technique, showed that virtually all of the spiked Cr3+ was bound by dissolved or colloidal substrates, but that the higher molecular weight fractions were able to kinetically outcompete the lower molecular weight fractions. There was no effect of salinity or the flocculation process on the binding of Cr by riverine substrates at natural concentrations. However, salinity did produce a strong kinetic inhibition of binding if the river water was first diluted. This salinity response is likely a result of a wide variety of Cr binding site energies on the substrates.