Browsing by Author "Damian Shea, Committee Chair"

Now showing 1 - 4 of 4

Bioavailability of Polycyclic Aromatic Hydrocarbons in the Aquatic Environment.
(2006-03-06) White, Katrina Elizabeth; Chris Hofelt, Committee Member; Elizabeth Guthrie Nichols, Committee Member; W. Gregory Cope, Committee Member; Damian Shea, Committee Chair
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and have been shown to elicit toxicity in humans and other organisms. Therefore, it is important to monitor environmental concentrations of PAHs. Toxicologically, we are concerned not only with the total PAH concentration but, with that fraction available to partition into an organism (bioavailable fraction). This research fits within three areas concerning bioavailability of PAHs including; 1) development of methods to measure bioavailability in the field, 2) identification and characterization of mechanisms controlling bioavailability and, 3) development of models to predict bioavailability in the natural environment. In the first phase of this research, the role of black carbon (BC) in the bioavailability of PAHs in soil and sediment was examined by measuring sorption in systems containing BC, natural organic matter (NOM), and microorganisms. A model was developed to predict the bioavailable fraction of PAHs and factors that may alter sorption in the natural environment from that predicted by laboratory models were examined. In the second phase of this research, a novel passive sampling device was developed to monitor truly dissolved PAH concentrations in water. Sorption isotherms of pyrene-d10 were measured for diesel soot (DS), Suwannee River NOM, Leonardite humic acids (HA), DS previously exposed to NOM and HA, in binary systems containing both DS and NOM, and to DS exposed to lake water. When DS was previously exposed to NOM, competition for sorption sites was observed. However, when both pyrene-d10 and NOM were introduced to DS simultaneously, less competition occurred and sorption was predicted within 92% of observed values using additive sorption models (based on the unit-normalized Freundlich model and Polyani-Dubinin-Manes model). Weathering of DS significantly reduced adsorption capacity but many strong sorption sites still remained, possibly due to renewal of sorption sites by microorganisms. This research demonstrated that sorption in the natural environment may be altered from that predicted by laboratory models due to 1) competition of linear organic carbon for sorption sites on DS, and 2) the presence of microorganisms. This research has important implications for predicting bioavailability and ecotoxicological risk of organic contaminants in soils and sediments. In the second phase of this research, I evaluated a novel passive sampling device, the polydimethyl(siloxane) (PDMS) integrative sampler, by 1) measuring the uptake and release kinetics of 48 PAHs from water into PDMS 2) comparing methods of loading performance reference compounds and 3) verifying the uptake kinetics by comparing PAH concentrations predicted by samplers to measured concentrations. Polycyclic aromatic hydrocarbons with a log K[subscript ow] 4.90 remained in the linear uptake phase for the duration of the exposure. Standard deployments of two weeks could be used for time-integrative monitoring of these compounds. Compounds with a log K[subscript ow] 4.38 reach equilibrium rapidly (T₅₀ 9 d) and the linear uptake model could not be used to predict analyte concentrations. Decreasing the surface area to volume ratio of the sampler would easily solve this issue. Surface area normalized sampling rates of PDMS samplers and semi-permeable membrane devices (SPMDs), the most commonly used passive sampling device, were similar, indicating that PDMS samplers are comparable to the SPMD. Concentrations of PAHs in the PDMS samplers predicted concentrations in water within a factor of two and on average within 30% of the actual concentration. Poly(dimethylsiloxane) samplers offer great potential for monitoring PAH exposure in the aquatic environment.
Development and Population Divergence
(2009-11-30) Bozinovic, Goran; Mac Law, Committee Member; Trudy Mackay, Committee Member; David Hinton, Committee Member; Margie Oleksiak, Committee Co-Chair; Damian Shea, Committee Chair
GORAN, BOZINOVIC. Development and Population Divergence. (Under the Direction of Damian Shea and Marjorie F. Oleksiak.) Changes in gene expression, coupled by biochemical, physiological, and behavioral alterations play a critical role in adaptation to environmental stress. To explore the ways natural populations may have adapted to local polluted environments, we took advantage on natural populations of the teleost fish Fundulus heteroclitus, one of the few studied fish species in North America that has established resistant populations in highly contaminated urban estuaries. We quantified expression of about one-fourth of Fundulus genes in all 40 stages of Fundulus embryogenesis . Waves of differential gene expression are associated with the different hallmarks of development (e.g., gastrula, vascular and organ development). Contrasting developmental patterns of gene expression and phenotypic variation among populations indicate that individuals from heavily polluted sites have an altered developmental program during critical developmental stages. Exposure to polluted sediment during development has a greater effect on individuals from Ã¢â‚¬Å“cleanÃ¢â‚¬Â sites, suggesting that individuals from polluted sites have evolved mechanisms to enhance developmental canalization.
Mechanisms of Toxicity of Polybrominated Diphenyl Ethers
(2006-05-25) Sanders, Johnny Michael; Damian Shea, Committee Chair
Lower molecular weight polybrominated diphenyl ethers (PBDEs) including 2,2',4,4'-tetraBDE (BDE47), 2,2',4,4',5-pentaBDE (BDE99), and 2,2',4,4',5,5'-hexaBDE (BDE153) have accumulated in the abiotic and biotic environment and are detected in human tissues and fluids. All three PBDEs are components of commercial pentaBDE mixtures primarily used as flame retardants in polyurethane foams. PentaBDE mixtures are both dioxin- and phenobarbital-like enzyme inducers and cause toxicity in rodents. Therefore, studies were designed to correlate biological effects with specific components of a pentaBDE mixture, as well as search for congener-specific differences in metabolic fates that could influence their toxic potentials. Quantitative RT-PCR analysis demonstrated that BDE47, BDE99, and BDE153 had little or no ability to up-regulate CYP1A1 gene expression in rat liver; therefore, are not dioxin-like. GC-MS analysis indicated that polybrominated dibenzodioxins and furans (PBDD⁄Fs) were present in the pentaBDE mixture and individual PBDEs. PBDD⁄Fs appear to be responsible for dioxin-like effects in rodents exposed to pentaBDE mixtures. Conversely, PBDEs up-regulated CYP2B and CYP3A gene expression in rats within the same order of magnitude as noncoplanar PCB153; therefore, are apparent CAR and PXR agonists. 14C-Labeled BDE47, BDE99, or BDE153 were readily absorbed, retained in lipid, accumulated in tissues, and were slowly excreted. BDE99 was metabolized to the greatest extent; whereas, BDE153 underwent minimal metabolism. BDE47 and BDE99 apparently induced their own metabolism following repeated exposure and are probable substrates of CYP2B. Metabolism of BDE47 and BDE99 resulted in formation of reactive intermediates in rats. Conjugates derived from arene oxides are excreted in urine and bile of BDE47-treated rats and conjugated bromophenols are excreted in urine as a result of oxidative cleavage of the molecule. BDE99 forms reactive metabolite(s) capable of binding liver protein. In summary, these studies have shown that toxic response in rodents exposed to pentaBDE mixtures may correlate with PBDE induction of CYP2B and CYP3A, congener-specific formation of reactive metabolites, and the presence of contaminants capable of inducing CYP1A1.
Signatures of Selection in Natural Populations Exposed to Chronic Pollution.
(2010-07-30) Williams, Larissa; Damian Shea, Committee Chair; Marjorie Oleksiak, Committee Chair; Robert Smart, Committee Member; Patricia McClellan-Green, Committee Member; William McMillan, Committee Member