Per- and Polyfluoroalkyl Substances (PFAS)

The objective of these pages is to provide an overview of the current understanding of per- and polyfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), regarding their major historical and current uses; scientific information about their sources, chemistry and analysis, potential human exposure and associative adverse health outcomes, and environmental fate and transport; and progress in site investigation techniques and cleanup alternatives for environmental media affected by PFAS at levels of concern.

Many PFAS precursors (such as alcohols, amides) can be degraded to perfluroroalkyl acids (PFAA) (OECD 2007, Buck et al. 2011, and Suthersan et al. 2016). The most studied PFAAs to date are PFOA and PFOS (OECD 2013); hence, PFOS and PFOA are the primary focus of these pages.

There are variations in terminology, names, and abbreviations to describe PFAS. As a result, researching and reviewing the scientific literature for these substances can be confusing. Buck et al. (2011) discusses the need for harmonized terminology, names, and abbreviations that describe each PFAS compound clearly and specifically. A fact sheet (NIEHS 2012) notes some commonly used terms for PFAS:

• Perfluorinated chemicals (PFCs).
• Perfluorochemicals (PFCs).
• Perfluoroalkyls (PFAs).
• Perfluorinated alkyl acids (PFAAs).
• Polyfluorinated chemicals (PFCs).
• Polyfluorinated compounds (PFCs).

Buck et al. (2011) recommends that PFAS be adopted as the name of choice because it more specifically addresses this class of chemicals. Buck et al. (2011) also notes that the abbreviation PFC has been used in official Kyoto Protocol documents since its adoption in 1997, specifically to designate greenhouse gas perfluorocarbons (United Nations 1998) as another reason for preferring PFAS to PFC. Greenhouse gas perfluorocarbons have very different chemistry and behaviors compared to PFASs discussed here.

Many PFASs are acids and can exist in a protonated or anionic state. The same abbreviation is generally used to represent either state. For example, PFOA can represent the protonated state [(C₇F₁₅COOH) CAS number 335-67-1] or the anionic state [(C₇F₁₅COO-) CAS number 45285-51-6].

By convention among all nonpolymeric PFASs, "long-chain PFASs" refers to (i) PFCAs with 7 and more perfluoroalkyl carbons, such as PFOA (with 8 carbons, or C8 PFCA) and PFNA (with 9 carbons or C9 PFCA); (ii) perfluoroalkyl sulfonic acids (PFSAs) with 6 and more perfluoroalkyl carbons, such as PFHxS (with 6 perfluoroalkyl carbons, or C6 PFSA) and PFOS (with 8 perfluoroalkyl carbons or C8 PFSA); and (iii) substances that have the potential to degrade to long-chain PFCAs or PFSAs, i.e., precursors such as PASF- and fluorotelomer-based compounds (OECD 2013).

Fluorotelomer-based substances have their own naming protocol. C₈F₁₇CH₂CH₂OH, for example would be named 8:2 fluorotelomer alcohol where the 8 represents the number of carbons in the perfluorinated backbone and the 2 is the number of carbons in the functional group, which in this case is an alcohol.

PFAS fluorine-carbon bonds are very stable and give these substances high thermal and chemical stability and are therefore persistent in the environment (Buck et al. 2011). Many PFASs are found worldwide in the environment, wildlife, and humans (Houde et al. 2006 and 2007, Lau et al. 2007, Lindstrom et al. 2011, and USEPA 2016a).

PFAS applications have made use of their unique surfactant properties. Their alkyl tails make these substances both hydrophobic (water-repelling) and oleophobic/lipophobic (oil/fat-repelling). Because of these properties, PFASs have been used extensively in surface coating and protectant formulations. Major applications have included protectants that enhance water, grease, and soil repellency for paper and cardboard packaging products, carpets, leather products, and textiles. The compounds also have been widely used in industrial surfactants, emulsifiers, wetting agents, additives, and coatings. PFASs have been used in fire-fighting foams because they are effective in extinguishing hydrocarbon-fueled fires. They are also used as processing aids in the manufacture of fluoropolymers, such as nonstick coatings on cookware, membranes for clothing that are both waterproof and breathable, electrical wire casing, fire- and chemical-resistant tubing, and plumbing thread seal tape (OECD 2013 and Buck et al. 2011).

The manufacture and import of PFOA was phased out in the United States as part of the PFOA Stewardship program (USEPA 2016b). In 2002 the only major U.S. manufacturer voluntarily agreed to phase out production of PFOS. Exposure to PFOS in the United States remains possible due to its legacy uses, existing and legacy uses on imported goods, degradation of precursors, and extremely high persistence in the environment and the human body. PFOS and related compounds continue to be produced in other countries and could enter the U.S. as imported products (USEPA 2016c).

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Additional Resources

Aqueous Film-Forming Foam
Interstate Technology and Regulatory Council (ITRC), 4 pp, 2022

Aqueous film-forming foam (AFFF) is highly effective foam intended for fighting high-hazard flammable-liquid fires. AFFF products typically are formed by combining hydrocarbon foaming agents with fluorinated surfactants. The purpose of this fact sheet is to outline how to properly identify, handle, store, capture, collect, manage, and dispose of AFFF. The fact sheet is not intended to replace manufacturer specifications or industry guidance for AFFF use, or to discuss alternatives in detail. It is only intended to educate users on AFFF use to reduce and eliminate potential harm to human health and the environment.

EPA's Per- and Polyfluoroalkyl Substances (PFAS) Action Plan
U.S. EPA, Washington, DC. EPA 823-R-18-004, 72 pp, 2019

This Action Plan describes EPA's approach to identifying and understanding PFASs, addressing current PFAS contamination, preventing future contamination, and effectively communicating with the public about PFASs. The Action Plan describes broad actions underway to address challenges with PFASs in the environment as well as other short- and long-term actions currently being implemented.

Fact Sheets: PFOS and PFOA
Emerging Contaminants Website, commissioned by Rijkswaterstaat Environment (the Netherlands) and OVAM (Public Waste Agency of Flanders), 2016

The following web-based factsheets about PFOS and PFOA are available in English: introduction to the properties; production, use, and sources; international developments and policy; toxicology; and behavior in soil and water.

Groundwater and PFAS: State of Knowledge and Practice
National Ground Water Association (NGWA) Press, Westerville, OH. ISBN: 1-56034-037-1, 114 pp, 2017

NGWA published this PFAS document to assist members and other groundwater professionals who may be tasked with investigating the transport pathways and PFAS extent in groundwater and surface water, assessing potential risks to receptors, or designing and constructing engineering controls to manage subsurface PFAS contamination. The main purpose of this document is to summarize the current state of knowledge and practice regarding PFAS fate, transport, remediation, and treatment, recognizing that knowledge in this field continues to advance. This document also summarizes current technologies, methods, and field procedures being used to characterize sites and test remediation and treatment technologies.

History and Use of Per- and Polyfluoroalkyl Substances (PFAS) found in the Environment
Interstate Technology and Regulatory Council (ITRC), 4 pp, 2022

Following an overview of PFAS discovery and development and subsequent detection in the environment, this fact sheet describes emerging concerns of potential adverse human health effects and efforts to reduce PFAS use or replace with alternate formulations, or both. Major sources of PFAS in the environment are identified.

Lists of PFOS, PFAS, PFOA, PFCA Related Compounds and Chemicals That May Degrade to PFCA
OECD (Organisation for Economic Co-operation and Development). Environment, Health and Safety Publications Series on Risk Management No. 21, ENV/JM/MONO(2006)15, 157 pp, 2007

The annexed lists of PFOS, PFAS, PFOA, their related chemical substances, and chemicals that may degrade to PFCA are based on member country responses to the OECD surveys; OECD member country inventories; reviews by international agencies or regulatory bodies; and published literature. In this document, PFAS is a generic term used to describe any fully fluorinated carbon chain length sulfonate compound, including higher and lower homologues as well as PFOS. PFAS-related substances may be salts of PFAS, or polymers that contain PFAS as a portion of the entire structure.

Naming Conventions for Per- and Polyfluoroalkyl Substances (PFAS)
Interstate Technology and Regulatory Council (ITRC), 4 pp, 2022

This fact sheet provides an overview of terminology, names, and abbreviations for PFASs, focusing on those most commonly reported in the environment and those most commonly tested for by current analytical methods, but also describing other important PFAS classes. Common PFAS physical and chemical properties are summarized, along with a discussion of properties for which no data are currently available.

On Per- And Polyfluoroalkyl Substances: Suggested Resources and Considerations for Groundwater Professionals
Frankel, A.J. | Groundwater 59(4):481-487(2021) [Abstract]

Resources and key considerations are suggested in this article for groundwater professionals wishing to familiarize themselves with PFAS compounds. The article discusses background information, current groundwater-related regulations, risk considerations, and mitigation options. It also compares PFAS to other groundwater contaminants and provides a broad selection of references.

Perfluorinated Chemicals (PFCs) — Perfluorooctanoic Acid (PFOA) & Perfluorooctane Sulfonate (PFOS) — Information Paper
ASTSWMO (Association of State and Territorial Solid Waste Management Officials), 68 pp, 2015

This introduction to PFOA and PFOS contains brief discussions of manufacturing and uses, environmental fate and transport, health and environmental effects, and analytical and treatment methods.

Perfluoroalkyl and Polyfluoroalkyl Substances in the Environment: Terminology, Classification, and Origins
Buck, R.C., J. Franklin, U. Berger, J.M. Conder, I.T. Cousins, P. de Voogt, A. Astrup, et al.
Integrated Environmental Assessment & Management 7(4):513-541(2011)

This paper provides an overview of PFASs and recommends clear, specific, and descriptive terminology, names, and abbreviations for the compounds. Particular emphasis is placed on long-chain perfluoroalkyl acids, substances related to the long-chain perfluoroalkyl acids, and substances intended as alternatives to the use of the long-chain perfluoroalkyl acids or their precursors. The text contains a brief description of the two main PFAS production processes—electrochemical fluorination and telomerization (important for compound branching and chemical analysis)—and shows how the principal families of PFASs are interrelated as industrial, environmental, or metabolic precursors or transformation products. The Supplemental Data Table lists 42 families and subfamilies of PFASs and 268 selected individual compounds, providing recommended names and abbreviations, structural formulas, and Chemical Abstracts Service registry numbers.

Polyfluorinated Compounds: Past, Present, and Future
Lindstrom, A.B., M.J. Strynar, and E.L. Libelo.
Environmental Science & Technology 45(19):7954-7961(2011)

This overview highlights recent interest in PFASs and briefly explores the history of PFAS production, occurrence in the environment, human exposure, refining of analytical approaches to enable PFAS detection at very low levels, and PFAS studies that might be undertaken in the near future.

Potential Designated Chemicals: Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs)
California Environmental Contaminant Biomonitoring Program, 22 pp, 2015.

This summary covers chemical identity and example structures, exposure or potential exposure to the public or specific subgroups, known or suspected health effects, and results of biomonitoring studies of some PFAS subclasses.

Synthesis Paper on Per- and Polyfluorinated Chemicals (PFCs)
OECD/UNEP Global PFC Group, Environment, Health and Safety, Environment Directorate, 60 pp, 2013

Separate chapters provide overviews of (1) historical and current major uses of PFASs; (2) scientific evidence on sources to the environment, environmental fate, human exposure, and potential adverse effects; (3) recent developments on alternatives to long-chain PFASs; and (4) European regulatory approaches with respect to PFASs.

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