An Analytical and Statistical Toolbox for Per- and Polyfluoroalkyl Substances Biogeochemistry and Source Attribution

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a class of thousands of anthropogenic chemicals that contain one fully fluorinated methyl (-CF3) or methylene (-CF2-) carbon. Their unique chemistry includes thermal stability, low polarizability, and amphipathic properties. Health and safety studies were not required prior to widespread use of proprietary mixtures of PFAS in everyday life. Exposure to some perfluoroalkyl acids (PFAA) at levels measured in the drinking water supply of hundreds of millions of Americans has been associated with compromised immune health in children. The use of PFAS in aqueous film forming foams (AFFF) for firefighting and training is one of the biggest sources of drinking water contamination. The majority of PFAS in AFFF are PFAA precursors that lack analytical standards and therefore cannot currently be measured using standard methods. As a result, little is known about environmental chemistry, prevalence, and risks of precursors downstream of AFFF use. This thesis develops a quantitative analytical and statistical toolbox for measuring precursors to better understand the biogeochemistry of PFAS originating from AFFF. Chapter 1 of this thesis presents and applies the toolbox to measure the concentration and composition of PFAS in legacy and contemporary AFFF. Results reveal the predominance of precursors with six or fewer perfluorinated carbons in AFFF and establishes endmember data for understanding environmental AFFF contamination. Chapters 2 and 3 of this thesis apply the toolbox to AFFF-contaminated surface water and groundwater in a well-studied watershed on Cape Cod, Massachusetts, United States. In Chapter 2, the toolbox is used to evaluate the temporal dynamics and hydro-biogeochemistry of PFAS in soil and groundwater beneath a former fire training area from the first multidecadal record of PFAS in groundwater. Field measurements and modeling results suggest retention at the soil air-water interface sustains high concentration of PFAS for decades after AFFF was last used at the site and that saturation flushes these PFAS through the vadose zone into groundwater. The mobilization and slow biological transformation of precursors into PFAA is a substantial contributor to ongoing contamination. Without remediation of the soil, groundwater beneath the fire training area is projected to exceed statewide maximum contaminant levels for centuries. In Chapter 3, the toolbox is used to distinguish the fingerprint of upstream AFFF use at the fire training area (enriched in PFAS with six and eight perfluorinated carbons) from other diffuse sources and uncover large additional sources of organofluorine to surface waters. My dissertation provides new insights into the magnitude and biogeochemistry of PFAS at AFFF-contaminated sites and shows that precursor chemistry controls the fate of PFAA with six or fewer perfluorinated carbons. These findings are critical to inform regulatory and remedial strategies to manage risks of PFAS exposure.