This book, which I have had the pleasure to edit, deals with regulations for, the synthesis of and applications of per- and polyfluoroalkyl substances (PFASs). PFASs are aliphatic compounds and, owing to the strong electronegativity and small atomic size of the fluorine atom, the perfluoroalkyl moiety (C_nF_2n+1) imparts enhanced properties to molecules (e.g. stability, stronger acidity, higher surface activity at very low concentrations and/or oil and water repellency) compared with their hydrocarbon counterparts. PFASs are important because they have been widely used in industry and manufacturing owing to their unique chemical properties – properties that make them heat resistant, able to repel water and oil and close to indestructible. Hence, based on the desired functionality and production capability, a large number of PFASs (there are over 4700 compounds) have been developed by different companies over time for a wide variety of industrial and consumer applications such as cosmetics, bioactive molecules, pharmaceuticals and drugs, ionic liquids, aqueous firefighting foams, food contact materials, household products, inks, medical devices, hoses and liners in oil production, mining, pesticide formulations, textiles, fabrics and leather coatings, apparel and specific and durable items in high-tech domains (e.g. aerospace, electronics, automotive, cable and wire industries and optics).

For many years, PFASs were thought to be inert and non-toxic, and were extensively used with just a few constraints regarding environmental disposal and ecological impact. It was not until early this century that the extent of global contamination by PFASs was first realised: research on PFASs identified them as being persistent, toxic and bioaccumulative, and their widespread use led to them being almost ubiquitous in the environment. Hence many academic and industrial researchers have spent much energy, resources and money to find alternatives and to overcome the dangers, although there is still some hope that these chemicals may be really useful for future generations. However, during the last couple of decades, severe issues with PFASs have arisen because they can be detected in trace amounts (i.e. ppb levels) in wildlife and also in human serum as people can be exposed to low levels of PFASs through consumer products that may contain them (e.g. carpets, textiles, paper and packaging materials and non-stick cookware).

Two recent books (Perfluoroalkyl Substances in the Environment; Theory, Practice and Innovation and Forever Chemicals. Environmental, Economic and Social Equity Concerns with PFAS in the Environment, published in 2019 and 2021, respectively) were aimed at highlighting rather negative aspects of such fluorochemicals. However, recent guidelines on regulations for these compounds and PFASs, and also alternatives and the huge potential of fluorinated compounds and bioactive molecules involved in medicine, pharmacy, agrochemistry and materials sciences (aeronautics, automobile industries, internet of things, 5G etc.), may suggest a more encouraging future.

In addition, facing the planned obsolescence of such compounds, society is searching for more stable and durable materials that are resistant to aggressive conditions (such as thermal, climatic, ageing and corrosive conditions) to reduce excessive costs involved in changing and fixing items after only a few months or years of use. For example, fluoropolymers (FPs) are unique materials that can preserve their outstanding properties over a wide range of temperatures. They are irreplaceable products for many essential technologies that manufacture clean energy, smart mobility and sustainable industry – all of which are required to meet the EU's Green Deal objectives. From delivering on the EU's Hydrogen Strategy to its Strategic Action Plan for Batteries, FPs have a key role to play in the transition to an integrated and decarbonised energy system. Furthermore, the durability of FPs can be an issue but recycling of commodity polymers (in addition to the environmental issues with microplastics) is a real challenge that is still far from being solved.

This book tackles the position and uses of PFASs, in some cases demonstrating optimistic trends and indispensable applications. The chapters provide in-depth perspectives into various features, including the regulation of PFASs, their detection, quantification, synthesis, properties and applications, and also the key areas in which they are applied. Taken together, or as readers' interests guide them, the variety of topics covered in the book present balanced and optimistic reviews of the complexity of PFASs. It addresses the current state of PFASs and the indicators pointing to future developments.

The authors have summarized many important areas, from fluorinated bioactive compounds to materials, and collectively the chapters highlight the vibrancy and high potential of PFASs, hence contributing in a unique way to innovation and performance in the development of functional molecules and materials. These contributions were prepared and submitted during the Covid-19 virus pandemic, which impacted many universities and research laboratories across the world, so I warmly thank all contributors for maintaining their commitment to provide very interesting reviews based on their expertise.

Bruno Améduri

CNRS Research Director