Graduate Theses & Dissertations

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Relationships between Dissolved Organic Matter and Vanadium Speciation in the Churchill River, MB and the Mackenzie River Basin, NWT using diffusive gradients in thin films (DGT)
This study examines the influence of dissolved organic matter (DOM) on dissolved vanadium (V) speciation in the Churchill River and Great Slave Lake using diffusive gradients in thin film (DGT). Vanadium is commonly found in natural environments such as rivers, lakes and oceans. It regulates normal cell growth, but in excessive amounts, it can have toxic effects on human and aquatic organisms. The use of in situ, time integrated DGT devices allows to better (1) monitor the most bioavailable fraction of V, the DGT-labile V, in Arctic Rivers and (2) assess the influence of DOM on dissolved V speciation. Higher DGT-labile V was found in the the central regions of the Mackenzie River (MR), with an average of 7.7 ± 2.3 nM, likely due to sediment leaching and permafrost thawing. The Churchill River and Great Slave Lake (GSL) showed lower DGT-labile V levels (2.2 ± 1.6 nM and 3.6 ± 2.7 nM, respectively), compared to central regions in MR. The CR DGT-labile V concentrations was positively correlated to protein-like DOM concentration and abundance (r = 0.3, p < 0.05). The data collected from this study will help in developing new strategies regarding environmental health and impact assessments of environmentally hazardous waste that consist of potentially high levels of toxic vanadium species. Developments in the use of DGT devices as a sampling method will also aid in future studies involved in analyzing environmental health and specifically dissolved V species in natural waters. Author Keywords: diffusive gradients in thin-films, dissolved organic matter, fluorescence, mass spectrometry, UV-Vis, vanadium
Effect of Water Surface Simulated Rain Drop Impacts on Water to Air Chemical Transfers of Perfluorinated Carboxylic Acids (PFCAs)
Perfluorinated carboxylic acids (PFCAs) are anthropogenic environmentally ubiquitous surfactants that tend to concentrate on water surfaces. This investigation looked at the effect of simulated rain on the atmospheric concentration of a suite of PFCAs (C2 - C12) above the bulk water system. Increased air concentrations of all PFCAs were detected during simulated rain events. Long chain PFCAs (>C8) were found to be much more concentrated in the air above the bulk water system than their short chain counter parts (
Development and Use of Passive Samplers for Monitoring Dissolved and Nanoparticulate Silver in the Aquatic Environment
Silver nanoparticles (nAg) are the largest and fastest growing class of nanomaterials, and are a concern when released into aquatic environments even at low μg L-1+). Diffusive gradient in thin films (DGT) with a thiol-modified resin were used to detect labile silver and carbon nanotubes (CNT-sampler) were used to measure nAg. Laboratory uptake experiments in lake water provided an Ag+ DGT diffusion coefficient of 3.09 x 10 -7 cm2s-1 and CNT sampling rates of 24.73, 5.63, 7.31 mL day-1, for Ag+, citrate-nAg and PVP-nAg, respectively. The optimized passive samplers were deployed in mesocosms dosed with nAg. DGT samplers provided estimated Ag+ concentrations ranging from 0.15 to 0.98 μg L-1 and CNT-samplers provided nAg concentrations that closely matched measured concentrations in water filtered at 0.22 μm. Author Keywords: ICP-MS, mesocosms, nanoparticles, nanosilver, passive sampling
Models of partitioning, uptake, and toxicity of neutral organic chemicals in fish
Models of partitioning, uptake, and toxicity of neutral organic chemicals in fish Alena Kathryn Davidson Celsie A novel dynamic fugacity model is developed that simulates the uptake of chemicals in fish by respiration as applies in aquatic toxicity tests. A physiologically based toxicokinetic model was developed which calculates the time-course of chemical distribution in four tissue compartments in fish, including metabolic biotransformation in the liver. Toxic endpoints are defined by fugacity reaching a 50% mortality value. The model is tested against empirical data for the uptake of pentachloroethane in rainbow trout and from naphthalene and trichlorobenzene in fathead minnows. The model was able to predict bioconcentration and toxicity within a factor of 2 of empirical data. The sensitivity to partition coefficients of computed whole-body concentration was also investigated. In addition to this model development three methods for predicting partition coefficients were evaluated: lipid-fraction, COSMOtherm estimation, and using Abraham parameters. The lipid fraction method produced accurate tissue-water partitioning values consistently for all tissues tested and is recommended for estimating these values. Results also suggest that quantum chemical methods hold promise for predicting the aquatic toxicity of chemicals based only on molecular structure. Author Keywords: COSMOtherm, fish model, fugacity, Partition coefficient, tissue-water, toxicokinetics

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