The Validation and Application of a Chemical Equilibrium Model for Interpreting the Interdependence between Free Copper Ion Activity and Sedimentary Copper-Organic Carbon Ratio in the Coastal Marine Environment

This research studied the relationship between marine sediment composition and the chemical speciation of copper in the overlying water from the point of view that sediment and the overlying water are dynamically and synergistically interacting phases of the same ecosystem and that free copper ion activity ({Cu2+}) plays a key role in understanding the speciation and bioavailability of metals in marine ecosystems. The main objective of this research was the validation and application of the sediment chemical equilibrium model (SCEM). The SCEM was developed to interpret the interdependence between surface sediment composition and {Cu2+ } in the overlying water column. The SCEM was validated for the case of Cu by isotherm adsorption titration of slurries of surface (0-1 cm) sediment, collected from various geographic locations and characterized by a range of OCsed and metal concentrations. The SCEM was used to predict {Cu2+} in Chesapeake Bay waters based on the observed sediment composition. Within this research, a prototype of a Vibrating in-situ free Ion Recorder (VIR) was developed. VIR consists of a commercially available polystyrene solid phase, whose surface has been modified to contain functional groups with metal binding properties. By mechanically assisted thinning of the surface boundary layer, the probe rapidly equilibrates with ambient free copper ion activity. The metal adsorbed on the active surface is successively measured by inductively coupled plasma spectroscopy (ICP-MS) and related to the ambient {Cu2+} using previously defined adsorption isotherms for calibration. VIR reaches equilibrium with ambient {Cu2+} in about 150 minutes. It provides reproducible results over a dynamic range of {Cu2+} (10-15-10-9 M) and agrees well with independent assessments of {Cu2+} in natural samples by competitive ligand equilibration-cathodic stripping voltammetry (CLE-CSV). It provides a potential tool for monitoring {Cu2+} at greater spatial and temporal resolutions than is currently possible with available laboratory-based methods