Copper speciation in estuaries and coastal waters

Abstract

The goals of this dissertation are to better understand the sources and the Cu binding ability of ligands that control Cu toxicity in estuaries and harbors, where elevated Cu concentrations have caused documented toxic effects on microorganisms, fish, and benthic fauna. I modified and improved a commonly used approach to determine metal speciation (competitive ligand exchange adsorptive cathodic stripping voltammetry, CLE-ACSV). Using this new approach to chemical Cu speciation and an old approach to physical Cu speciation (filtration), I show that riverine humic substances, filtrable, recalcitrant and light absorbing molecules from degraded plant material, can account for all of the Cu binding in the Saco River estuary. This finding directly supports the hypothesis that terrestrial humic substances might be the most important source of Cu ligands for buffering Cu toxicity in coastal locations with freshwater inputs. However, fieldwork in coastal waters with large inputs of both Cu and suspended colloids (Boston Harbor, Narragansett Bay, and two ponds on Cape Cod) shows that some Cu present in these samples is inert to our competitive ligand exchange method for at least 48 hours. These results support the hypothesis that a significant fraction of the Cu present in these samples is physically sequestered in colloidal material, with the remaining fraction complexed by humic substances. Previous studies of Cu speciation were not able to distinguish between strongly complexed Cu and inert Cu, and our analytical approach should be used further to determine the role of colloids in Cu speciation in all natural waters.