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As the third most abundant transition metal in the Earth’s crust, manganese (Mn) is often found in various forms of (oxyhydr)oxides in the environment (hereafter, Mn-oxides). Mn-oxides possess a high sorption capacity and are a powerful oxidizer, and thus, play critical roles in regulating nutrient cycles and the speciation and distribution of trace metals and metalloids in the environment. The structure and geochemical behaviors of Mn-oxides have been extensively studied using birnessite minerals that contain mainly Mn(IV) and variable concentrations of Mn(II) and Mn(III) in layered structures. However, relatively little research has been done on the more common lower valent Mn(II/III) oxides, such as hausmannite and manganite, presenting a lack of knowledge on the reactivity and transformation process in those Mn minerals. Thus, this dissertation focuses on accurately reflecting natural environments to measure the adsorption and oxidation ability of lower valent Mn-oxides towards a toxic metalloid of concern, namely, arsenic (As). That is, conditions, such as the presence of metal impurities in the mineral’s structure and the co-existence of the secondary mineral phases, are simulated to examine how and to what extent these variations affect the geochemical reactivity and transformation processes of hausmannite and manganite. Furthermore, examination of the fate of metal impurities when the minerals undergo dissolution reactions is of critical importance to better understand the environmental behavior and cycling of trace metals that are associated with the minerals. Chapter 1 and Chapter 2 examine the impact of various quantities of the structural impurities nickel (Ni) and cobalt (Co), the most common metal impurities in lower valent Mn-oxides on the stability and reactivity of hausmannite and/or of manganite toward As. Chapter 3 investigates the surficial interaction modes of hausmannite and manganite and their synergistic reactivity toward As oxidation and removal processes when they co-present. To probe the changes in the structural and surficial properties, as well as in the size and morphology of Mn-oxides induced by the metal substitution, As(III) oxidation to As(V), and the formation of other Mn oxide phases, these research activities utilize an array of state-of-the-art instrumentations, including X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and scanning and transmission electron microscopy. Metal substitutions at higher loadings induce greater structural changes in hausmannite and significantly enhances the As(III) oxidizing ability of hausmannite, but is at a lesser extent in manganite. As(III) oxidation by both oxides leads to the formation of multiple surface complexes, but binuclear bidentate As(V) surface complexes are dominant on oxides. Both Ni(II) and Co(III) occupy the octahedral Mn(III) sites in hausmannite, but only redox-active Co(III) is involved with the As(III) oxidation, while redox-inactive Ni(II) is not. In contrast, when Co(II) occupies the octahedral Mn(III) sites in manganite, the oxidizing ability of manganite is not affected. Therefore, both Co coordination chemistry and structural quantity are critical to determining the extent of structural Co effects in Mn(II/III)-oxides. In both oxides, a greater mineral dissolution is observed with metal substitution in the presence of As. Even when the oxides undergo accelerated mineral dissolution, releasing significant levels of structural Mn, the majority of structurally-incorporated Ni and Co remain in the mineral/solid phases, showing the limited solubility and mobility of these metal substituents. Furthermore, mixtures of manganite and hausmannite show a higher As(V) production and As(III) removal rate when comparing that of the individual mineral phase. Such synergistic effects arise from aggregation structures of these oxides, where manganite limits the aggregation of hausmannite, resulting in more highly reactive hausmannite being available/exposed for the surface-mediated As(III) oxidation reactions. Thus, it is important to consider the presence, property, and relative quantity of structural impurities and presence of secondary Mn oxides to better predict the oxidative and adsorptive capacity of Mn oxides toward As in the environment. The present work helps recognize such important, but overlooked, effects on the mineral’s properties and reactivity and hence, improve our understanding of the geochemical behaviors of natural Mn(II/III) oxides and their interaction with associated metals and metalloids in the environment. / Geoscience

The potential utility of in situ cosmogenic ¹⁴C (in situ ¹⁴C) in surficial process studies is widely recognized, yet a reliable means of isolating it has proved difficult to develop. Here we present a new method for isolating in situ ¹⁴C in quartz that yields more precise estimates of production rates than achieved by previously published extraction techniques. The new technique involves resistance heating of samples, and collection of all evolved carbon as CO₂ between 500°C and 1500°C. Our improved technique holds three distinct advantages over other extraction methods: (1) we can identify and quantitatively eliminate atmospheric/organic ¹⁴C contamination, (2) we can identify the in situ ¹⁴C component unambiguously without assumptions of ¹⁴CO/¹⁴CO₂ production proportions within the rock or equilibria on extraction, and (3) background ¹⁴C levels are consistently low. To develop our new procedures, we identified and sampled wave-cut quartzite benches associated with Lake Bonneville's two highest shorelines, as well as basalts that erupted into the late Pleistocene lake at Tabernacle Hill. Comparison of ¹⁴C thermal release patterns from the shoreline quartzites to well-shielded quartzite samples showed that contaminant ¹⁴C is released at ≤ 500°C, and that ¹⁴C released from 500 to 1500°C is essentially all in situ-produced. Two replicate analyses yield a sampling site production rate of 59.8 ± 4.6 (¹⁴C atoms/g SiO₂)/yr. Uncertainties in altitude and latitude scaling factors yield a 2σ range of sea-level, >60° geomagnetic latitude ¹⁴C production rate estimates consistent with an independent estimate based on an experimental ¹⁴C/¹⁰Be production ratio (Reedy et al., 1994) and ¹⁰Be production rate estimates from similar Lake Bonneville shoreline sites (Gosse and Klein, 1996). Our preferred production rate estimate is thus 18.2 ± 2.0 (¹⁴C atoms/g SiO₂)/yr. This estimate is also consistent with revised in situ ¹⁴C production rate estimates based on our previously published data, but is lower and more precise--indicating that we have successfully reduced contaminant ¹⁴C and other sources of variability in our data. After we have replicated these Lake Bonneville results, our new extraction procedures should bring in situ ¹⁴C into the mainstream of process-oriented cosmogenic nuclide surface studies.

<p>The overall goal of this research project was to examine the occurrence and fate of S(II-) and associated trace metals in aqueous systems under oxidizing conditions, specifically freshwater sediments and surface waters. Three studies were conducted that examined the following: (a) the fate of Ag(I) sorbed to FeS(s) and the stabilization of S(II-) by Ni(II), Mn(II), Cu(II) and Zn(II) upon oxidation of an FeS(s) suspension, (b) the stabilization of S(II-) in oxic solution by Zn(II), Fe(II), Fe(III), Cu(II) and Ag(I) in association with Suwannee River fulvic acid (SRFA), and (c) the applicability of the colourimetric methylene blue-sulfide (MBS) method to the determination of trace S(II-) in oxic freshwaters. Silver(I) added to an aqueous FeS(s) suspension was scavenged from solution by the solid phase. Upon oxidation of the Ag-FeS(s) suspension, S(II-) concentration in solution rapidly decreased while Ag(I) was released back into solution. Similar experiments were repeated with added amounts of Ni(II), Mn(II), Cu(II) and Zn(II) to examine the effect of these metals on S(II-) in solution during FeS(s) oxidation. Zinc(II) in the presence of FeS(s) retarded the loss of S(II-) from solution, suggesting the stabilization of S(II-) by Zn(II) under oxic conditions. Sulfide did not appear to be stabilized by the other metals as concentrations decreased below detectable levels. In the case of Cu(II) and Ni(II) however, stable metal sulfide species may have formed and persisted under oxic conditions, but were not reacted and detected in the MBS analysis. Sulfide in aqueous solution in the absence of metals, with and without SRFA, decreased over time under oxic conditions due to reaction with oxygen and/or NOM. Zinc(II) was able to bind and stabilize S(II-) in the presence of NOM under oxic conditions, and this effect was attained even when other S(II-) binding metals, Fe(III) or Ag(I), were added to the sample. It was not, however, clear whether the association of Zn(II) with SRFA offered more stability to S(II-) than the Zn(II) alone. Iron in either oxidation state (II, III) did not stabilize S(II-) under oxic conditions regardless of whether NOM was present. Although Ag(I) and Cu(II) were both able to bind S(II-), even in the presence of NOM, it was not possible to assess whether these metals stabilized S(II-) under oxic conditions. In the presence of Ag(I) and Cu(II), MBS formation was inhibited in the acidic colourimetric reagent (MDR) and S(II-) could not be determined. Using the methylene blue method of S(II-) determination (MBS), S(II-) was measured at low nanomolar concentrations in a number of natural freshwater samples of varying organic carbon content. This study revealed a number of limitations in the application of the MBS method to the measurement of S(II-) in natural samples. Most significantly, total S(II-) concentration was underestimated by this method, as S(II-) bound to Ag(I) and Cu(II) and possibly other metals, was not readily reactive in the colourimetric reagent to form the methylene blue complex. Pretreatment of the sample with Cr(II) to reduce such metal sulfide species, resulted in higher S(II-) recoveries relative to MBS. Particulates and NOM contained in samples interfered with absorbance measurements, while adsorption of metal sulfide species to container surfaces caused S(II-) concentrations to be underestimated.</p> / Doctor of Philosophy (PhD)

<p>metal fate, transport and toxicity are speciation dependent. Natural organic matter (NOM) is a complex mixture of many potential metal binding sites and it is ubiquitous in the environment. Therefore, a site-specific, non-invasive, sensitive method is required to investigate metal interactions with NOM. This thesis considers the development and application of a multiresponse fluorescence method to determine site-specific binding of Al, Cu and H to model NOM ligands, fulvic acid and isolated NOM samples. Natural organic matter is treaed as a mixture of average binding sites. The minimum number of sites along with their excitation and emission wavelengths are determined from deconvolution of fluorescence surfaces using SIMPLISMA (Windig and Guilment, Anal. Chem. 1991, 63, 1425-1432). Fluorescence at wavelengths corresponding to these components is measured during metal titration and the multiresponse data are fit to a multi-site speciation model for the metal-NOM system. This multiresponse fluorescence method is validated in that it recovers known values for Al with two model ligands simultaneously and predicts free copper during a titration of Suwannee River fulvic acid within 0.1 log units when compared to the model of Cabaniss and Schuman (Geochim. Cosmochim. Acta 1988, 52, 185-193). A total of seven different fluorophores were identified in NOM isolated from nine different watersheds in Norway. Each sample contained four to six of the seven identified fluorophores. On average, at pH 4, the fluorophores bind Al with a strength similar to salicylic acid (logK'≈5.5), although there are stronger and weaker sites with logK'≈7 and logK'≈3, respectively. The speciation results are dependent on the isolation method used to obtain the NOM sample. For the NOM samples, the difference between reverse osmosis and low-pressure-low-temperature evaporative isolates are as large as the differences between sampling sites. Suwannee River fulvic acid is represented by five fluorescent binding sites for Cu, Al and H binding. The constants for Al and Cu are consistent with salicylic acid-like sites and the H binding can only be explained if diprotic sites are used. Thus, multiresponse fluorescence methods allow discrimination between monoprotic and polyprotic models. Finally, a protocol is proposed for multiresponse fluorescence determination of metal interactions with NOM.</p> / Doctor of Philosophy (PhD)

<p>Recently, background silver concentrations in freshwater have been shown to be only 0.001-0.01 nanomolar. However, locations with significant sewage input have concentrations at least two orders of magnitude greater. Although geochemical processes appear to regulate background silver at picomolar levels, there is concern that point-discharges of silver may produce acute and/or chronic toxic responses in aquatic organisms. How silver speciates in these waters will largely determine its bioavailability and toxicity. This thesis project investigated silver(I) speciation in freshwater. Silver binds much more strongly to sulfide, S(-II), containing ligands compared with ligands containing nitrogen and oxygen. Determinations of silver-sulfide formation constants gave log K values of 11.0 to 13.0 compared with log K values of <6.0 for ligands containing nitrogen and oxygen. Thermodynamic calculations suggest that silver in freshwaters is over-saturated relative to Ag₂S(s) solubility (Ksp = 35.94, 25℃, μ = 0.0) and that predominant silver species in freshwater should be AgHS〫and Ag-thiolates. However, field studies at a sewage treatment plant, Dundas, Ontario and at an old mining camp, Cobalt, Ontario, demonstrated that silver is 90%-100% colloidally bound, which explains silver's apparent over-saturation in natural waters. Concentrations of aquo silver species (AgHS〫and Ag-thiolates) represent <10% of total silver in these waters. The field studies also demonstrated that inorganic sulfide is present in oxic waters at 10-200 nM (80-100% colloidally bound) while thiol concentrations are below 1 nM. Using a competitive ligand equilibration-solvent extraction technique we showed that silver is bound to the inorganic sulfide. This inorganic sulfide is likely present as metal sulfide clusters that are bound to natural organic matter (NOM). The complexation of sulfide by metals would explain its persistence even in oxic waters. In sediments silver likely forms Ag₂-S(s) as long as the silver to sulfide ratio is <1. A laboratory study demonstrated that silver reacts rapidly with sedimentary FeS and behaves thermodynamically like a distinct acanthite, Ag₂S(s), phase. Silver measurable in the porewaters is probably associated with colloidal metal sulfides, as was observed for the surface waters and sewage treatment plant effluents. In summary, the findings of this thesis research showed for the first time that sulfides are important to the speciation of silver not only in anoxic sediments but also in oxic surface waters and sewage treatment plant effluents. Based on these findings, we recommend that the SEM/AVS approach, developed as a sediment quality criterion, could also be used as a water quality criterion for silver. However, before adopting this approach, toxicity studies need to be carried out using well-characterized silver-sulfide species to verify that sulfide protects aquatic organisms from silver bioaccumulation and toxicity.</p> / Doctor of Philosophy (PhD)

<p>Gross Ontario rain and snow chemistry and heavy metal speciation was determined on samples collected from a precipitation sampling network established in Hamilton and Northern Ontario. Relative to surface waters, precipitation is normally a low conductivity (mean value = 34 μmho/ cm (25°)), low pH (4.3) system with elevated heavy metal (10 - 100 μg/l) and nutrient (50 - 100 μg/l P; 400 - 2000 μg/l N) concentrations. Anodic stripping voltammetry (ASV) was employed to determine "soluble" heavy metal speciation. ASV peak potential shifts and current measurements were used as criteria in making this determination. Unusual anodically shifted Cu peaks common to many precipitation samples suggested a Cu-colloid association. Duplication of polarographic behaviour observed for natural precipitation samples was obtained with synthetically prepared Fe-Mn colloids. In terms of "soluble" Cu speciation, Northern Ontario could be divided into two distinct regions; near Sudbury rain and snow contained aquo-Cu⁺⁺ ion at elevated concentrations, while in the remainder of the province, precipitation contained colloidally associated copper. Zn, Cd, and Pb were generally present as the aquo-species. Rain-out of colloidally associated copper into the higher ionic strength environment of lakes will probably result in metal desorption and colloid flocculation. Copper would then be available as a biologically toxic species.</p> / Doctor of Philosophy (PhD)