The effects of perfluorooctanoic acid, perfluorobutanesulfonic acid, and perfluorooctanesulfonic acid on model biological membranes and monolayers

Abstract

Poly- and perfluoroalkyl substances (PFAS) are synthetic chemicals used in industrial and consumer products for their water, grease, and stain-resistant properties. Despite their widespread use, PFAS persist in the environment for decades and pose significant public health threats. This dissertation investigates the surface and bulk solution behavior of legacy PFAS and PFAS effects on lipid bilayers and monolayers. Surface tension, conductivity, and dynamic light scattering (DLS) were used to examine the behavior of perfluorooctanoic acid (PFOA), perfluorobutanesulfonic acid (PFBS), and perfluorooctanesulfonic acid (PFOS). Results showed that surface activity is pH-dependent. Furthermore, these surfactants form aggregates in solution rather than micelles. These aggregates continue to grow with increasing solute concentration in contrast to traditional surfactant behavior. Cryo-EM images confirm a broad distribution of aggregates in solution. Differential scanning calorimetry (DSC) and DLS studies examining the effects of PFOA on DPPC lipid bilayers showed that sub-micromolar PFOA concentrations lowered the gel-liquid crystalline transition enthalpy without affecting transition temperature. DLS measurements also revealed the formation of smaller objects resembling niosomes. Again, cryo-EM images confirmed multilamellar vesicle and niosome formation. Vibrational sum frequency generation (VSFG) and Langmuir isotherms quantified the effects of PFOA on DPPC monolayers adsorbed to the air-water interface. PFOA had minimal impact on lipid structure in tightly packed monolayers but significantly affected moderately packed films. Furthermore, data from the -OH stretching region demonstrated that PFOA adsorption to moderately and tightly packed films created a charged surface whose electric double layer that oriented interfacial water molecules. Langmuir isotherms showed that PFOA shifted the transition surface area and decreased collapse pressure, indicating PFOA interacts with DPPC monolayers without disrupting the lipid film's integrity. The final chapter details efforts to identify PFAS concentrations in private wells in rural Montana. Shallow wells and smaller properties had higher PFAS levels, with elevated health risks in a quarter of the tested wells. These findings highlight the importance of using advanced methods to assess PFAS contamination and associated health risks in drinking water.