Copper speciation in San Francisco Bay: A novel approach using multiple analytical windows

Abstract

Dissolved copper speciation and total dissolved copper concentrations were determined at six San Francisco Bay sites in January and March of 2003. Multiple analytical windows were incorporated into an established competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) method, which employs salicylaldoxime (SA) as the added competitive ligand for speciation analyses. The titration results were integrated into [Cu T *] versus log [Cu 2+] plots, combining data from each of the different competing ligand concentrations and providing a powerful approach to visually interpret the variation in [Cu 2+] as the natural Cu-binding ligands in the sample are titrated over a wide range of [Cu T]. In addition, the data for different analytical windows were interpreted with Langmuir and Scatchard linearization techniques to estimate natural Cu-binding ligand concentrations [ L i ] and conditional stability constants K CuL i,Cu 2+ cond. All results indicate that ambient ligand concentrations exceed total dissolved copper concentrations at each site, with dissolved copper greater than 99.9% complexed by the strong copper-binding L 1 ligand class. The [Cu 2+] does not exceed 10 −13 M at any site, a concentration sufficiently below the toxicity threshold for microorganisms. Thus, the excess of strong Cu-binding ligands appears to effectively buffer free Cu 2+ at low concentrations and the existing levels of copper do not impair San Francisco Bay.