Environmental contamination from anthropogenic activities is often defined by the presence of either legacy or emerging contaminants.  Superfund sites associated with legacy contaminants were the focus of environmental remediation activities in the twentieth century.  Now, "emerging contaminants" have captured the focus of the environmental community.  However the distinction between legacy and merging contaminants is often blurred, especially for metals and metalloids, because once these species enter the environment, they cannot be destroyed and often re-emerge.  The unique properties of elements such as Pb, Hg, Ra, Cd, Zn, Cr, As, Se, B, Li and rare earth elements make them valuable economic resources; demand is growing rapidly and will continue to grow throughout the world.  Their toxicity, fate and transport depend on their concentration and speciation.  The context specific nature of metal ion contamination can also be viewed from an evolutionary perspective. While emerging organic contaminants often derive from the synthesis of novel compounds that provide unique marketable properties, emerging inorganic contaminants often arise from natural resource extraction that yields environmental concentrations above their natural cycles established during evolutionary timeframes. The inability of ecosystems and humans to rapidly adapt to these increased concentrations suggests that caution is needed whenever new elements or higher concentrations of more common metals are introduced or re-introduced into the environment, especially when they are combined with other elements that alter their speciation, electronic structure, or bioavailability.

Significant advances have been made over the past few decades, toward understanding the complex reaction chemistry that controls speciation and ultimately dictates potential treatment and remediation options. Advanced spectroscopic, computational and molecular level tools have been key to identifying speciation and quantifying thermodynamic and kinetic processes. Using tools such as x-ray and vibrational spectroscopy, the structure of ions and interfacial water at interfaces has been revealed. Computational tools have provided validation of molecular structures observed via spectroscopy, confirmed the presence of complexes and ion-pairs at surfaces and within pores, and allowed quantification of thermodynamic parameters of processes such as sorption and precipitation. The translation of these results to predict contaminant fate and transport in natural systems has relied on macroscopic or thermodynamic based models such as surface complexation models for oxide minerals or the Donnan-Manning model for membrane systems. The continual refinement of these models is often guided by molecular level insights that provide more accurate descriptions of sorption, ion exchange and precipitation processes and more detailed descriptions of the electrical double layers present at charged interfaces. In this seminar, we will explore several examples in which molecular level insights from spectroscopic and/or computational studies have been used to guide modeling of metal ion sorption in water treatment processes, predict ion-pairing in membrane systems, and describe metal(oid) processes in contaminated sediments in mining impacted lakes. Through these examples, we will demonstrate how increased understanding at the molecular level can guide contaminant remediation and treatment options.