Environmental Behavior of Metals and Radionuclides

Metals can be present in a number of forms within environmental systems, such as aqueous ions, complexes, nanoparticles, colloids, minerals and coatings on minerals. A range of processes affects the distribution and bioavailability of metals in these systems, including aqueous complexation of metals, dissolution of minerals, aggregation of colloids, and adsorption of aqueous ions or complexes onto mineral surfaces or biological surfaces. The research presented in this dissertation focuses on several of these processes in order to improve our ability to model heavy metal and radionuclide behavior in the environment and to predict heavy metal bioavailability in complex geologic systems. Chapter 2 focuses on the creation of an advanced biotic ligand model that uses a surface complexation modeling approach to predict metal bioavailability. Chapter 3 focuses on the aqueous behavior of the isolated U60 uranyl peroxide nanocluster. Chapter 4 examines the aqueous behavior of a second isolated uranyl peroxide nanocluster, U24Py, to determine the effect of nanocluster size, composition and morphology on nanocluster aqueous behavior. The results of this dissertation research provide insight into the toxicity of heavy metals and the nature of the aqueous behavior of uranyl peroxide nanoclusters. Chapter 1 shows that advanced biotic ligand models (ABLM) that incorporate surface complexation modeling yield flexible and accurate bioavailability models. ABLM can dramatically improve our understanding and ability to predict toxicity and other reactions linked to metal bioavailability in complex geologic systems. The results presented in Chapters 3 and 4 indicate that aqueous behavior of both the U24Py and the U60 uranyl peroxide nanoclusters is best described as that of aqueous complexes. These findings provide a better understanding of the thermodynamic stability and behavior of uranyl peroxide nanoclusters in aqueous systems, which can be used to estimate the dissociation behavior of nanoclusters under a range of aqueous conditions.