Graduate Thesis Or Dissertation

 

‘Tis a Gift to be Simple : On Passive Sampling and Compatible Techniques for Reducing the Complexity of Environmental Mixtures Public Deposited

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  • Assessing the risk from exposure to a chemical mixture in the environment can seem prohibitively challenging. Most components of the mixture are not readily identifiable, chemicals may interact to cause other-than-additive toxicity, and the number of potential combinations of environmental contaminants is enormous. These challenges can make it seem impossible to accuractely assess risks associated with chemical mixtures. In reality, not all chemicals in the environment are accessible for organismal uptake, there are a limited number of predictable combinations of chemicals in the environment, and a minority of chemicals are likely responsible for the majority of toxicity in any given sample. This dissertation addresses the seemingly daunting challenge of assessing mixture toxicity by strategically adapting and implementing a collection of sampling and analytical methods to reduce complex environmental mixtures into manageable components. In the first study, personal exposure to chemical mixtures in rural Peru was assessed with silicone wristbands. The samples naturally clustered into groups that were defined by distinct classes of chemicals and were associated with broad demographics of the study participants. The results revealed chemical patterns in wristbands that are possibly indicative of common mixtures in the personal environment and suggest regional sources and routes of chemical exposure. The second study simplified environmental mixtures from a contaminated urban waterway into the most hazardous components. Effect-directed analysis of passive sampling device extracts using a zebrafish bioassay, chromatographic fractionation, and various chemical analyses, eliminated priority pollutants as suspect toxicants and identified responsible toxicants. Specifically, fatty acids and possibly dithiocarbamates were previously unrecorded components of LDPE extracts that likely drive the toxicity of the whole mixtures. Indeed, a minority of chemicals in the whole mixture was responsible for the majority of effects. In total, this dissertation demonstrates that complex mixtures are not unsolvable by applying passive sampling and compatible techniques for simplifying exposure to, and effects of, environmental mixtures.
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