The goal of this thesis was to advance our understanding of the aqueous geochemistry of trace metals such as Cd, Zn and Cu, in an urban river (Don River, Toronto, Ontario, Canada). My objectives address questions concerning trace metal partitioning among suspended particulate and solution phases;​ and factors that influence partitioning, in this system.

In general, my results are consistent with the predominantly laboratory derived, theoretical framework for metal complexation. However, one of the more important results, was the demonstration that synergistic effects of a combined suite of variables in a natural system can have far greater effects than those observed or predicted by well controlled laboratory studies.

In this well buffered system, environmental parameters other than pH, were most important in influencing trace metal partitioning. Relatively less Cd, Cu and Zn partitioned to the particulate phase with decreasing water temperature;​ resulting in a relatively higher proportion of metals in the more bioavailable, dissolved phase. Increasing NaCI concentration associated with roadsalt runoff, also favoured the partitioning of metals to the dissolved phase.

My results provide a field based, empirical validation of current trace metal surface complexation theory. They demonstrate that Fe oxides dominate the surface of suspended particulates in the Don River, with a limited co-occurrence of organic matter. These two geochemical fractions are the major suspended particulate trace metal sinks in the Don River.

My results did not provide evidence for a dominant role of particle size in determining either particulate metal concentrations or their geochemical associations in this system. Rather, they suggest that the major influence of grain size is related to the particle surface area available for oxides and organics to coat.

Calculated distribution coefficients (particulate metal / dissolved metal) demonstrated that sorption affinities of Cd, Zn and Cu, varied among 3 operationally defined, particulate geochemical fractions. Cd and Zn affinities were highest for the leachable (exchangeable/carbonates) and reducible (oxides) fractions of the suspended particulate pool, while Cu affinities were highest for the oxidizable (organics) particulate fraction.