Chapter 1: Why Aim Toward a PFAS-free Future?

As global consumption continues to grow and society runs up against planetary boundaries,¹  there has never been a greater need for green chemistry. The intersecting global crises of climate change, pollution, and biodiversity loss highlight the need for safe- and sustainable-by-design chemicals and materials²  that can enable the decarbonization of energy systems and the transition to a circular economy while minimizing the adverse impacts on human and ecological health. A sustainable future cannot be built with unsustainable chemicals.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) constitute a large class of synthetic chemicals that have become widespread environmental pollutants. They have been detected in indoor and outdoor environments, humans, and biota, including remote mountaintops,³  the deep sea,^4,5  rainwater,⁶  and umbilical cord blood.^7–9  They have even been called “forever chemicals” since they will likely outlast humanity. But despite their widely documented hazards (see Chapter 2), PFASs are still used in hundreds of consumer and industrial products^10,11  due to their unique and lucrative properties. It is difficult to name a manufacturing sector that has not benefited from the use of PFASs. These chemicals have become ingrained in a wide range of industries and applications, including surface treatments for textiles and food packaging, pharmaceuticals, pesticides, aqueous film-forming firefighting foams (AFFFs), metal plating fume suppressants, aerospace components, automotive parts and interiors, paints and other architectural coatings, flooring, roofing, semiconductors, touchscreens, lithium-ion batteries, and many more.^10–14 

Depending on whom you ask, a PFAS-free future might seem both unattainable and inevitable. On one hand, scientists around the world have been raising concerns and advocating for the regulation of the entire class of PFASs,^15–20  policymakers have been banning PFASs from a growing list of non-essential uses, consumers are increasingly demanding PFAS-free products, and leading companies are finding innovative safer replacements. On the other hand, the use of PFASs is still mandated by government standards such as the United States (U.S.) Navy’s specification for AFFF²¹  and the Japanese National Specification for Steel Bridge Coatings.²²  Moreover, the use of PFASs continues to grow in applications promoted for climate change mitigation, such as electric vehicle batteries, solar panels, and wind turbines.

We are now at an inflection point, where policymakers and the public are becoming increasingly aware of the dangers associated with continued PFAS use, triggering widespread changes in the market. This represents an opportunity for businesses of all sizes who incorporate the principles of green and sustainable chemistry into their research and development to emerge as leaders. Replacing PFASs in their diverse applications will require creative thinking and perseverance. There are no prior examples where efforts have been made to find safer alternatives for such a large class of chemicals across such a wide range of products. This transition presents both challenges and opportunities.

To aid in this effort, this book showcases case studies of identifying safer substitutes for PFASs in select consumer products. Most of these case studies were conducted by students of the Greener Solutions course at the University of California Berkeley. The framework employed in these case studies can be applied to other settings and products, with a few modifications.

This chapter provides key definitions and background information on PFASs and their many functional applications. Chapter 2 delves deeper into why PFASs are chemicals of concern, highlighting their health and environmental hazards as well as current and proposed policies at the state, federal, and international levels to address the use of PFASs in consumer products. Chapters 3 through 5 present case studies for identifying safer alternatives to PFASs for food packaging, household packaging, and floor polishes, respectively. Chapter 6 discusses strategies for removing PFASs from carpet fibers during the recycling process, and Chapter 7 addresses how the green building industry is searching for safer alternatives to PFASs for building products. Chapters 8 and 9 present case studies for identifying safer alternatives to PFASs in textiles, for outdoor gear and firefighting turnout gear, respectively. Chapter 10 examines the key factors that are powering the shift toward a PFAS-free future and concludes with recommendations for those willing to embark on this journey.

In a landmark 2011 paper, Buck et al. first introduced the term perfluoroalkyl and polyfluoroalkyl substances (PFASs), differentiating these chemicals from other members of the broader fluorochemicals family.²³  According to their definition, perfluoroalkyl substances are “aliphatic substances for which all of the H atoms attached to C atoms in the nonfluorinated substance from which they are notionally derived have been replaced by F atoms, except for those H atoms whose substitution would modify the nature of any functional groups present”, and polyfluoroalkyl substances are “aliphatic substances in which all H atoms attached to at least one (but not all) C atom have been replaced by F atoms, in such a manner that they contain the perfluoroalkyl moiety C_nF_2n+1”.²³  This definition covers a wide range of substances that vary in terms of their chemical structure and molecular weight.

In 2015, the Swedish Chemicals Agency published a list of over 3000 chemicals that align with the Buck et al. PFAS definition.¹²  Subsequently, various organizations and authoritative bodies have developed their own working definition and understanding of this class. For instance, in 2018 the Organisation for Economic Cooperation and Development (OECD) published a list of 4730 Chemical Abstracts Service (CAS) registry numbers related to individual PFASs or commercial PFAS mixtures available on the global market that “contain a perfluoroalkyl moiety with three or more carbons (i.e., –C_nF_2n–, n ≥ 3) or a perfluoroalkyl ether moiety with two or more carbons (i.e., –C_nF_2nOC_mF_2m–, n and m ≥ 1)”.²⁴  In 2021, OECD proposed the following revised definition to address gaps in the original Buck et al. definition: “PFASs are defined as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it), i.e., with a few noted exceptions, any chemical with at least a perfluorinated methyl group (–CF₃) or a perfluorinated methylene group (–CF₂–) is a PFAS”.²⁵ 

Meanwhile, the U.S. Environmental Protection Agency (EPA)’s Office of Pollution Prevention and Toxics, which administers the U.S. Toxic Substances Control Act, adopted a more restrictive PFAS working definition that “includes perfluorinated and polyfluorinated substances that structurally contain a R–CF₂–C(F)(R′)(R″) unit. Both the CF₂ and CF moieties are saturated and none of the R groups (R, R′ or R″) can be hydrogen”.²⁶  In contrast, several laws in U.S. states limiting the presence of PFASs in certain consumer products broadly define PFASs as “a class of fluorinated organic chemicals containing at least one fully fluorinated carbon atom”.^27–35  Some community health advocates are pushing for an even broader definition that would encompass all fluorinated organic chemicals as PFASs, while some industry representatives are arguing that fluoropolymers should not be considered PFASs because they align with the definition of polymers of low concern as outlined by the OECD.^14,36 

Regardless of the specifics of the definition used, a few key subclasses of PFASs can be identified: perfluoroalkyl acids (PFAAs), PFAA precursors, perfluoropolyethers (PFPEs), and fluoropolymers. While PFAAs constitute a small subset (approximately 1%) of PFASs, they are terminal degradation products, manufacturing aids, feedstocks, or impurities of other PFAS class members, which makes their hazard traits relevant to the entire class (Figure 1.1). PFAAs are extremely persistent and mobile in the environment, and the ones which have been studied were found to be toxic (see Chapter 2). This subgroup includes:

• Perfluoroalkyl carboxylic acids (PFCAs) such as perfluorooctanoate (PFOA);^†

• Perfluoroalkane sulfonic acids (PFSAs) such as perfluorooctane sulfonate (PFOS)^†

• Perfluoroalkane sulfinic acids (PFSiAs)

• Perfluoroalkyl phosphonic acids (PFPAs)

• Perfluoroalkyl phosphinic acids (PFPiAs)

• Perfluoroether carboxylic acids (PFECAs)

• Perfluoroether sulfonic acids (PFESAs).

PFASs that can degrade into PFAAs are termed PFAA precursors and provide a significant indirect source of PFAAs to the environment (see examples of PFAA precursors in Figure 1.2). Most polyfluoroalkyl substances are PFAA precursors. Of the 4730 individual PFASs or commercial PFAS mixtures identified by OECD on the global market, 4186 likely degrade to PFAAs in the environment or biota.²⁴  Degradation to PFAAs can occur, for instance, in the atmosphere, wastewater treatment plants, landfills, or consumer products, mainly via biodegradation, hydrolysis, or photo-oxidation.^37–39  The degradation half-life of PFAA precursors can range from days to centuries.^37,40,41  PFAAs and some of their precursors are frequently subdivided into longer- and shorter-chain compounds. The longer-chain PFSAs have six or more perfluorinated carbons; longer-chain PFCAs, PFPAs, and PFPiAs have seven or more perfluorinated carbons.

PFPEs and fluoropolymers are characterized by fluorine atoms embedded in the backbone of a polymeric structure. PFPEs are perfluoroalkyl substances with large molecular weight (oligomers, polymers, and copolymers) and ether linkages. They are highly persistent in the environment and unlikely to degrade to PFAAs under typical environmental conditions, but may contain non-polymeric impurities and may release hazardous products during combustion.⁴²  Fluoropolymers are characterized by F atoms directly attached to a carbon-only chain, and are also highly persistent in the environment. They do not degrade to PFAAs under typical environmental conditions, but will eventually break down into microplastics by weathering and physical stress, enabling further dispersion and enhanced bioavailability.⁴³  PFAA manufacturing aids and other low molecular weight intermediaries can occur as impurities in the final fluoropolymer product.⁴³  Moreover, fluoropolymers may release PFCAs, including PFOA, during combustion at temperatures between 180 and 800 °C.^44,45  Examples of fluoropolymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF).

Fluorine (F) stands out among the elements in the periodic table because it forms the strongest single bond with carbon.⁴⁶  Due to its high electronegativity, the F atom pulls the shared electrons of the covalent C–F bond toward itself. This renders it partially negative and the C atom partially positive, creating a polar covalent bond. This bond requires high energy to dissociate, up to 544 kJ mol⁻¹,⁴⁷  compared to the 337 kJ mol⁻¹ needed to separate carbon and hydrogen.⁴⁸  This means PFASs, which have multiple carbon–fluorine bonds, tend to be thermally, chemically, and biologically stable.⁴⁹  The PFASs that can degrade in the environment typically transform into smaller PFASs that do not degrade further under environmental conditions, such as PFAAs.^{23,41,50–53} 

When added to products and materials, PFASs confer increased stability at extreme temperatures, antistatic properties, and resistance to wettability, staining, and corrosion.^23,54  Some PFASs are inert to solvents, hydrocarbons, acids, and bases.⁵⁵  Of note, PFASs are the only chemicals known to date to repel both oil and water.⁵⁶  The oleophobic and hydrophobic characteristics of PFASs are a result of the bonds between the carbon–fluorine (CF₃ and CF₂) groups, which create very low critical surface energy. Their oleophobicity, hydrophobicity, and ability to lower surface tension makes PFASs useful in a variety of materials and products, such as textiles, leathers, food packaging, photovoltaic cells, architectural membranes, paints, and glass.¹⁰  Their ability to lower surface tension also makes PFASs useful in applications such as toner and printer inks, polymer extrusion aids, metal plating, oil and gas drilling fluids, photographic processing solutions, semiconductor industry, textile dyeing, paints and coatings, and AFFF.¹⁰  Glüge et al. provided a comprehensive overview of the various industries that employ PFASs, and the properties that make PFASs useful in those applications.¹⁰ 

These versatile chemicals have a plethora of functional applications. For instance, these are some of the functional uses identified for PFASs in cosmetics:^12,57–62 

• Adsorbent

• Anticaking

• Antistatic

• Binding

• Brightening

• Bulking

• Cleansing

• Detacktifier

• Detangling

• Durability

• Emollient

• Emulsifying

• Emulsion stabilizing

• Epilating agent

• Film forming

• Hair conditioning

• Hair lamination

• Increasing oxygen absorption of skin

• Increasing skin penetration

• Oil repellency

• Opacifying

• Pore strip

• Protectant

• Skin conditioning

• Skin feel modifier

• Slip modifier

• Solvent

• Surface modifier

• Surfactant

• Surfactant dispersing

• Viscosity controlling

• Water repellency

• Weather resistance

The unique properties of PFASs contribute to their environmental persistence, global distribution, and accumulation in water, soils, plants, and animals. In addition to being persistent, some PFASs are known to be toxic, and some are also bioaccumulative. However, unlike other persistent, bioaccumulative, and toxic contaminants, these and many other PFASs are highly water soluble,⁶³  which means that drinking water can be a significant route of human exposure to these compounds.

Many of the problematic uses of PFASs have resulted from attempts to solve other problems. In many cases, today’s problems are yesterday’s solutions. In the field of chemical management, the term “regrettable substitution” describes instances where a chemical of known concern is phased out and replaced with a similar chemical with little or no data about its safety. Such replacement chemicals, after years of use in consumer products or industrial applications, are often found to be just as bad, or even worse, than the chemicals they replaced.

An example of regrettable substitution is the case of AFFF. Originally developed by the U.S. Navy and 3M as a way to quickly extinguish liquid fuel fires on ships, this product has been used widely at military installations, airports, and industrial facilities.⁶⁴  The surface-active properties of PFASs make them especially suited for use in AFFF, as they allow the product to form a film that spreads on top of the fuel and limits oxygen flow to the fire.⁶⁵ 

From the 1960s until the early 2000s, the majority of AFFF formulations contained long-chain PFASs.⁶⁶  When concerns emerged regarding the adverse impacts of long-chain PFASs, AFFF manufacturers began replacing them with short-chain PFASs that were presumed to have an improved health and safety profile. In the two decades since this switch occurred, further research has shown that the short-chain PFASs used in AFFF are also persistent and can be toxic. Like their long-chain predecessors, use of these chemicals in AFFF contributes to the contamination of water resources.⁶⁷ 

Governments around the world are now restricting the use of AFFF containing any PFASs. AFFF users who only recently switched from formulations based on long-chain PFASs to those based on short-chain PFASs must now replace their inventories once again and find a method to safely dispose of these foams. The increased regulatory scrutiny on firefighting foams has spurred the development of new PFAS-free formulations and even new frameworks for assessing the environmental profile of these products.⁶⁸ 

In contrast to regrettable substitutions, informed substitution considers the inherent trade-offs that are involved in replacing a chemical of concern with another chemical or redesigning a product to provide the same function without the need of a chemical. Alternatives assessment is a tool that provides a structured framework for identifying these trade-offs and managing them.

Understanding and mitigating the trade-offs of new products, processes, and technologies are critical for a truly sustainable PFAS-free future. For example, molded fiber food packaging such as clamshell takeout food containers, food bowls, and egg trays was developed as a sustainable alternative to plastic food packaging. Molded fibers are typically derived from agricultural waste products, thus enhancing their value and reducing waste. Moreover, molded fiber products can be composted at the end-of-their-life unlike most plastic packaging, which is typically landfilled. However, molded fibers are not inherently grease- and liquid-proof. To enable this packaging to hold foods such as soup, french fries, salads, etc., PFASs are mixed into the molded fiber slurry during manufacturing. Several studies found PFASs, including PFAAs and their precursors, in molded fiber food packaging products.^69–71  The problem? These PFASs can migrate from packaging products into food,^69,72  resulting in human exposures. Additionally, the presence of highly persistent PFASs conflicts with product compostability claims. Compost derived from PFAS-containing food packaging contains PFASs,⁷³  which can be taken up by plants from the soil^74–76  and subsequently enter the food chain, impacting both humans and other biota.

Back in 2018, all molded fiber food packaging products on the U.S. market contained PFASs.⁷⁷  Since then, pressure from customers, compostability certifiers, and policymakers has motivated some manufacturers to develop PFAS-free molded fiber food packaging products, demonstrating that it is possible to find functionally acceptable alternatives. Based on an alternatives assessment, Washington State concluded that some of these alternatives are safer than PFASs.^78,79  However, these alternatives include coating the molded fiber with a layer of plastic or replacing the molded fiber altogether with certain types of plastic. Most of these plastics are not compostable, so they negate one of the main purported benefits of molded fiber food packaging, i.e., its compostability. Trade-offs such as these are common. Exploring them through an alternatives assessment can guide innovation toward truly sustainable alternatives.

We will revisit this example in more detail in Chapter 3, which provides a framework for identifying safer alternatives to PFASs in plant fiber-based food packaging products. This and the other case studies presented in this book illustrate the benefits of understanding chemical hazards and seeking inspiration from nature for bio-inspired designs. Nature’s infinite creativity may be the ultimate ally in the quest toward a PFAS-free future.

The authors would like to thank David Grealish for developing the graphical illustrations, and Anne Cooper Doherty and Chris Leonetti for their helpful comments on the manuscript.