Chemical speciation of dissolved copper, lead and zinc in a ria coastal system: the role of resuspended sediments

Abstract

The chemical speciation of dissolved Cu, Pb and Zn was studied in a ria coastal system applying differential pulse anodic stripping voltammetry using a hanging mercury dropping electrode. Cu and Pb were found to be strongly complexed with organic ligands in solution: inorganic Pb was not detected in the samples, whereas inorganic Cu only accounted for <3% of total dissolved metal. Organic complexation of Zn was weaker, ranging from 48 to 72% of total dissolved metal. Sediment resuspension experiments were carried out in order to study the desorption of organic ligands to the water column. Results from the sediment resuspension study showed a desorption of organic ligands (together with metals) presenting similar complexing abilities of those found in the water column. This has important implications from an ecotoxicological point of view, since the potential danger to the aquatic biota from significant concentrations of desorbed metals – which is critical when contaminated sediments are considered – is in part buffered by the in situ desorption of organic ligands.