UC Berkeley

Per- and polyfluoroalkyl substances (PFASs) are a class of anthropogenic organic chemicals characterized by the presence of a single perfluorinated carbon (-CF2- or -CF3). The strength and low polarizability of carbon-fluorine bonds make PFASs desirable for hydrocarbon fire suppression and other applications where oleophobic and hydrophobic properties are desired. These same properties make PFASs extremely stable in the environment and can lead to adverse health outcomes in people and wildlife. After decades of use, PFASs are detected in blood serum of 97% of the U.S. population, contaminate the drinking water of hundreds of millions of people, and pose risks to ecosystems worldwide.

Despite the magnitude and importance of PFAS contamination, the ubiquitous nature of the compounds and their recalcitrance makes it difficult to identify their sources and to understand the extent of contamination of difficult-to-measure polyfluoroalkyl compounds. This dissertation focuses on the application of the total oxidizable precursor (TOP) assay— a chemical oxidation process that indirectly quantifies difficult to measure polyfluoroalkyl compounds (precursors)—as a tool for PFAS source apportionment.

In Chapter 1, background is provided on the motivations for developing PFAS source apportionment tools and ways in which the TOP assay might be adapted to provide better information on precursor sources and fate. In Chapter 2, I develop a data analysis tool that can be used to separate PFAS sources related to the use of aqueous film-forming foams (AFFF), municipal wastewater, and municipal solid waste landfill leachate. The use of dimension-reducing algorithms, such as principal component analysis (PCA), improved separation among sources compared to existing forensic approaches and the use of targeted PFAS analysis. In Chapter 3, I modified the TOP assay using solid-phase extraction (SPE) to separate precursors into different fractions related to their behavior in the presence of ion exchange resins prior to TOP assay oxidation. This modification provides previously unavailable information on the composition of precursors and their behavior in the environment. In Chapter 4, I applied the modified TOP assay in a forensic study of a large urban sewershed by characterizing and quantifying major sources of PFASs that contribute to PFAS release to surface waters from the municipal wastewater treatment plant. In chapter five, I describe how the computational and laboratory tools developed in this dissertation can provide a simple means of elucidating sources of PFAS contamination and suggest future research directions to enable better management of PFASs.