An investigation into the toxicity, bioconcentration, and risk of perfluoroalkyl substances in aquatic taxa
Olson, Adric D.
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Perfluorinated compounds (PFASs) such as perfluorooctane sulfonate (PFOS) and pefluorohexane sulfonate (PFHxS) are surfactants that were discovered to be persistent and potentially toxic in the environment and to humans. They were used in Aqueous Film Forming Foams (AFFFs) and in some household products due to their flame-retardant nature. As part of AFFF formulations they were used to fight fires, but the large volume required and their mobility as a liquid led them to be detected in a large number of waterways and animal tissues. They were voluntarily phased out by the manufacturer between 2000 and 2002 over concerns about their persistence and health effects. These same concerns have led to them being listed as a contaminant of emerging concern by the U.S. Environmental Protection Agency (US EPA) and the Organisation for Economic Co-operation and Development (OECD). This project presents work with PFOS, and to a lesser extent PFHxS, on a variety of aquatic taxa, spanning a large section of the food web. Initially, my work involved figuring out an experimental setup to use with these chemicals, as they have been shown to sorb to glass. In the second chapter, I report a study using the Western mosquitofish (Gambusia affinis) in the laboratory, field collection of other fish species, and a literature review to develop a physiologically based pharmacokinetic (PBPK) model to predict the uptake of and depuration of PFOS into and out of several fish tissues. In that chapter, I also developed a spatially-explicit bioconcentration model that can be used to simulate the variability inherent in environmental exposures. Then, I present the result of toxicity tests over both an acute and sub-chronic exposure period with a snail, the great pond snail (Lymnaea stagnalis), and an insect, the yellow fever mosquito (Aedes aegypti). These tests are crucial for improving scientific understanding for a variety of reasons: acute toxicity tests are generally used by risk assessors to estimate the risk due to a chemical while chronic tests more closely approximate the environmentally relevant exposure length, due to the persistence of the chemicals. I found that none of the species evaluated exhibited toxic effects at environmentally relevant concentrations of PFOS. However, different life stages of L. stagnalis were affected differently by exposure. Further, I discovered that combining PFOS and PFHxS into a mixture increased the toxicity to A. aegypti in a manner greater than would be predicted by additivity. Finally, I present an analysis of the PFOS burdens of a marine invertebrate, the Eastern oyster (Crassostrea virginica), collected along the Texas coastline. The amount of PFOS found in these samples suggest that the phase-out of PFASs has been successful in decreasing environmental concentrations found worldwide. These results provide further insight for the scientific community about the behavior of PFOS and may allow risk managers to make more informed decisions relating to PFASs.