PFAS science and regulation should be reconsidered using fluorine-specific physical chemistry

Poly- and perfluoroalkyl substances (PFAS) have been widely used due to their unique properties, such as water and oil repellence, chemical and physical resistance, and surfactant nature. However, many studies have revealed unfavourable properties of PFAS, especially their long-range transport potential, environmental persistence and harmful effects on human health and ecosystems. Production and use of a few PFAS are restricted. Many alternatives have been introduced to the market, but some are as problematic as the original PFAS (i.e., regrettable substitution). This has led to discussions about regulation of PFAS as a chemical class, but a lack of PFAS-specific scientific knowledge on their physical properties prevents a detailed discussion on PFAS regulation. The Stratified Dipole-Arrays (SDA) theory provides fluorine-specific science to understand the unique properties of PFAS. It decisively reveals that the material properties of a single molecule and molecular aggregates are intrinsically different and therefore must be strictly discriminated. In addition, PFAS with longer fluoroalkyl chains containing seven or more carbon–fluorine (CF2) groups can self-aggregate due to the combinatorial effect of the dipole moment along the carbon–fluorine bond and the helical conformation around the molecular axis, which determines the properties of PFAS. The SDA theory also shows that shorter PFAS do not self-aggregate and act as single molecules with dipoles on their surfaces, which can interact with biological molecules. Expanding the SDA theory to incorporate the interaction between PFAS and biomolecules will improve understanding of the biological effects of PFAS. Comprehensive understanding of the nature of PFAS is required for their sound regulation, production and use.