Chemical speciation of copper, lead, cadmium, and zinc in estuarine and coastal waters: Investigating organic complexation in size fractionated samples.

摘要

This dissertation focuses on the chemical speciation of trace metals in estuarine and coastal waters. Complexation of Cu, Pb, Cd, and Zn by natural organic ligands was determined using previously developed techniques to detect electrochemically labile inorganic metal species as kinetically distinct from non-labile metal organic complexes. Differential pulse anodic stripping voltammetry with a thin mercury film at a rotating glassy carbon disk electrode (DPASV/TMF-RGCDE), has exceptional sensitivity and sufficiently low detection limit to measure inorganic concentrations of these trace metals in ambient conditions. Results from research in Narragansett Bay and South S.F. Bay determined metal organic chelates are the dominant species in these estuarine waters (90-99% Cu; 70-95% Pb; 50-97% Zn; 70-80% Cd).;Metal titration data was modeled by a single class of ligands for Zn and Cd, whereas Pb and Cu results were interpreted as organic complexation by multiple ligand classes with each class having a unique conditional stability constant. Concentrations of these metal-specific organic ligands were typically in excess of the total dissolved metal; consequently, free metal ion concentrations were reduced to picomolar levels--below toxic levels cited in laboratory reports on marine phytoplankton growth.;Further characterization of these metal binding organic ligands was achieved by combining the DPASV technique with size fractionated samples. Colloids were removed from the dissolved phase by ultrafiltration with operationally defined membranes (;A different segment investigated the contrast in upwelling systems near the Monterey Bay. Dissolved cadmium was not drawn down relative to nitrate at sites where high chlorophyll was measured as part of phytoplankton blooms. Presumably this is due to preferential uptake of Zn ions over Cd ions when sufficient Zn