| Metals are ubiquitous in surface waters, however their fate, transport, and effects are dependent on source characteristics and local chemical conditions including particles, dissolved organic matter (DOM), and pH. The interactions among the phases has short and long term implications. This dissertation adds to the body of literature on metal interactions and distribution in surface waters through the following three components. Three studies were pursued in the metal interactions and distributions are in surface waters, and are outlined below, but the broader objective for the dissertation was to investigate the size dependence nature and implications of the interactions, and secondarily to consider the interactions rates.;A synthetic surface water, in a controlled laboratory setting, was used to investigate zinc oxide nanoparticles (ZnO NPs) interactions with dissolved and colloidal natural organic matter (DOM and COM); aggregation and dissolution were monitored using varied techniques. DOM and COM both sorbed quickly onto the NPs, resulting in a reduction in zeta potential (&zgr;). Substantial sedimentation was observed only at pH 8 in the absence of OM (isoelectric point pH ZPC=8.3). The most influential factor governing dissolution was pH, where rapid and extensive dissolution occurred at pH 6 and 7 (50%), while dissolution was minimal at pH 8 (<10%). DOM and COM (0.5 ppm) reduced dissolved Zn concentration through OM mediated re-adsorption (NP-OM-Zn), and DOM appeared to suppress ZnO dissolution. In the absence of OM, evidence of aggregate compaction was observed, possibly due to Ostwald ripening.;Interactions among phases were examined using environmentally collected samples. In-stream and stormwater runoff samples were collected from four land use types: highway, urban, agricultural, and natural. A novel fractionation method, based on both particle size and settling characteristics, was employed to examine differences in metal distributions among fractions. Highway samples contained the highest dissolved concentrations for most metals, and freshwater ambient water quality criteria were exceeded for Zn, Cd, and Pb for the first storm of the water year. Anthropogenic sources were indicated for Cu, Zn, Cd, and Pb in highway and urban samples. Agricultural samples contained the highest dissolved concentrations of Se and As. The storm event agricultural sample contained ∼10-fold higher suspended solids concentration than any other sample, and had correspondingly elevated suspended solids-associated metals. Distribution coefficients revealed the following affinities: Zn, Ni, Cd, and Pb to large dense particles; Se to particulate organic matter; and Cu, Zn, Cr, Ni, and Pb to colloidal organic matter.;Metal-NOM complexation and the dependence on molecular size were explored using size exclusion chromatography (SEC) with online inductively coupled plasma mass spectrometer (ICP-MS), where SEC is used to separate NOM based on molecular size. Samples from four land-uses were analyzed and interestingly, many of the metals exhibited similar metal-OM size distributions. Fe and Pb were associated with molecules >10 kDa. Absorbance (254 nm), as a measure of conjugated NOM, was typically observed for molecules 3--6 kDa; Cu, Ni, Pb, and Zn were also commonly detected for this size range. Cr, Mn, Co, and Ni were commonly detected as dissolved constituents (<100 Da). |
