MS Thesis Defense : Margaret Siao

Margaret Siao, M.S. Student

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Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals commonly used in consumer and industrial products. For over 60 years, PFAS have contaminated water supplies; however, long-term, average concentrations in most water resources remain unknown. The objective of this thesis was to develop and validate the performance of a novel passive sampling device that employs anion-exchange membranes to measure time-averaged concentrations of over 20 PFAS in water. We evaluated the impacts of pH, salinity, and dissolved organic matter content on the selective uptake of PFAS with variable physicochemical properties (e.g., chain length, head group) using batch reactors. Selectivity coefficients, the key calibration parameter for the passive samplers, were calculated by measuring PFAS and chloride concentrations in water and membrane phases. Trends between selectivity coefficients and PFAS properties were identified. Selectivity coefficients varied with pH for PFAS with sulfonamide moieties, but a speciation-based model was successfully fit to the experimental data. Dissolved organic matter served as a competing anion but did not affect measured selectivity coefficients, suggesting negligible impacts on passive sampler calibration. Samplers were field-validated at four locations in and around Baltimore Harbor. They were deployed for two, three, and four weeks, with grab samples collected at deployment and retrieval. Using the universal calibration, selectivity coefficients were derived from site-specific water quality parameters to determine PFAS concentrations in the water. The back-calculated PFAS concentrations demonstrated reasonable agreement with grab samples. The outcomes of this study highlight the development of passive samplers with universal calibrations for PFAS measurement in diverse water sources.

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