STRONGLY COMPLEXED CU AND NI IN WASTE-WATER EFFLUENTS AND SURFACE RUNOFF

Although a variety of analytical techniques have been developed to cha racterize metal speciation, few have been used successfully in the com plicated matrices encountered in wastewater effluents and surface runo ff. In this study, competitive ligand equilibrium-cathodic stripping v oltammetry (CLE-CSV) and chelating resin column partitioning graphite furnace atomic absorption spectroscopy (CRCP-GFAAS) are used to determ ine the speciation of Cu and Ni in point and non-point pollutant sourc es discharging into South San Francisco Bay. As expected, most of the dissolved Gu and Ni in wastewater effluents and surface runoff are com plexed. Moderately strong; metal-complexing ligands, which likely cons ist of activated sludge biopolymers and humic substances, are responsi ble for the complexation of only about 20% of the Ni and 5-50% of the Cu. The remaining Cu and Ni is complexed by ligands with apparent stab ility constants comparable to those of synthetic chelating agents. Str ongly complexed Cu is present at concentrations below 40 nM and accoun ts for 5-60% of the Cu discharged by these sources. Strongly complexed Ni is present at concentrations ranging from approximately 10 to 200 nM and accounts for >75% of the Ni discharged by wastewater treatment plants and approximately 25% of the Ni in surface runoff, Strong Ni co mplexes, which are not removed during wastewater treatment, are extrem ely stable in seawater. The existence of strong metal-complexing ligan ds in wastewater effluent and, to a lesser degree, in surface runoff m ust be accounted for when evaluating metal treatability and biogeochem istry.