- Per- and polyfluoroalkyl substances (PFAS) are a group of anthropogenic compounds gaining notoriety as contaminants of emerging concern. With the frequent detection of PFAS in the environment, drinking water, and consumer products, awareness and concern from the public regarding PFAS is increasing. The two most notorious PFAS are perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS), which belong to the perfluorinated carboxylate (PFCAs) and perfluorinated sulfonate (PFSAs) classes respectively. While attention to the PFCA and PFSA classes are increasing, PFAS are a structurally diverse family of molecules. In addition to the concern of ionic PFAS, like PFCAs and PFSAs, volatile polyfluorinated alkyl substances (volatile PFAS) have been gaining attention in research communities across the globe. While the health effects of volatile PFAS are relatively under studied, the ability for volatile PFAS to act as indirect sources of PFCAs and PFSAs has also been of increasing concern. Thus, when thinking about the total amount of PFAS discharged into the environment, the quantification of volatile PFAS is an important factor to consider.
Chapter 2 discusses a new analytical method for the analysis of consumer products for volatile PFAS, as well as the first non-targeted analysis efforts of volatile PFAS by GC-MS. A low waste, rapid method, with comparable sensitivity to previously published methods was created by combining an in-vial extraction with a novel injection technique: Concurrent Solvent Recondensation- Large Volume Splitless Injection (CSR-LVSI). For purposes of method demonstration, 16 samples of convenience (seven papers and nine textiles) were analyzed through in vial extraction GC-CSR-LVSI-MS. A subset of samples was subjected to non-targeted analysis by GC-QTOF-MS, followed by a Kendrick mass defect analysis to identify additional, previously unknown volatile PFAS homologs. Careful inspection of Kendrick mass defect plots yielded the discovery of 13 additional homologues of known volatile PFAS classes, accounting for 14-18% of the total volatile PFAS signature present on three textiles.
Because of the discharge of PFAS into the environment, ecotoxicological assessments of PFAS are becoming increasingly important in order to understand the risks to organisms from environmental PFAS contamination. While there are toxicity reference values (TRVs) for select PFAS in the literature, careful inspection between studies (using the same model organism) yields drastically different, inconsistent TRVs. In order to avoid conflicting TRVs in the literature, identifying and controlling for potential sources of experimental error is crucial. Thus, experimental data to inform best practices in the ecotoxicological assessments of PFAS is vital in controlling potential error.
Chapter 3 presents a set of experimentally derived best practices to be used in the preparation of PFAS stock and exposure solutions, for use in the toxicological assessments of PFAS. The overarching hypothesis for the study presented in Chapter 3 was that a discrepancy between nominal concentration and actual exposure concentration accounts for the variability observed in toxicity reference values for PFAS. Key factors, such as purchased solid PFAS purity, time to dissolution of solid, stratification, and storage container material, were investigated. The largest contribution to the disagreement between nominal and actual concentrations was in the preparation of highly concentrated PFAS stocks. Specifically, the dissolution time for each PFAS solid differed as a function of carbon fluorine chain-length which in turn impacted homogeneity of the stock used to create exposure solutions. Mixing times for the PFAS studied varied between 2-5 depending on carbon fluorine chain-length.
When considering human exposure to PFAS, the majority of research efforts has focused on ingestion or inhalation of PFAS. However, dermal has been neglected as a major route of human exposure to PFAS. The reason for the lack of dermal research is due to conventional knowledge that if chemical compounds are ionic (like PFCAs or PFSAs), that dermal absorption is unlikely to occur, due to the low permeability associated with ionic compounds. However, it has been recently discovered that dermal exposure to PFAS may induce negative health outcomes typically associated with ingestion of PFAS. In light of recent research, dermal exposure to PFAS is becoming a new topic of concern. Thus, data on the fundamental dermal absorption behavior is needed for PFAS in order to understand the magnitude and importance of dermal exposure, once and for all.
The aim of Chapter 4 was to investigate percutaneous absorption of select PFAS. While dermal exposure to PFAS is inevitable given the ubiquitous nature of PFAS, only two papers have attempted to quantify the rate at which PFOA (a single PFAS) absorbs. Chapter 4 presents the first data obtained regarding the dermal uptake of a homologous distribution of select PFCAs. Silicone rubber was used as a surrogate for human skin in diffusion experiments meant to simulate flux of PFAS through skin. Findings indicate that short-chained PFAS (containing three fluorinated carbon atoms) and long chain PFAS (containing eight fluorinated carbon atoms) have low permeability to silicone, and thus low permeability to skin. Select PFAS with medium chain-length (4-7 fluorinated carbon atoms) are a factor or 2-3 times more permeable, depending on chain-length.