What Are PFAS?
Generally speaking, “PFAS” stands for “per- and poly- fluoroalkyl substances”.
Within this broad group of substances, there are roughly 12 thousand that have been assigned a chemical abstracts service number (i.e., a CAS No.), and many more that have not.
The following might help explain the term more completely:
- An alkyl substance has one or more molecular portions (‘moieties’) with a general carbon and hydrogen formula of CnH2n+1 where n is any integer.
- In a per-fluoroalkyl substance, all the hydrogen atoms in the alkyl moiety(ies) are replaced with fluorine.
- In a poly-fluoroalkyl substance, at least one alkyl moiety is fully fluorinated (i.e., all the hydrogen atoms are replaced with fluorine) and at least one alkyl moiety is not fully fluorinated.
- Though not explicitly referenced in the acronym, many PFAS definitions also admit substances with a single fully fluorinated methylene moiety with a general formula of CnH2n
|
A perfluoro alkyl substance |
A perfluoro alkene substance that is considered to be a PFAS |
A polyfluoro alkyl substance |
CAS No. 116-15-4 |
CAS No. 24210-45-5 |
CAS No. 678-39-7 |
|
In these molecular structure diagrams the red features are what make the molecule a PFAS. Carbon atoms are presumed at each line intersection. Each carbon atom will make four bonds. Hydrogen atoms are not shown, and fill a single bond location for all the carbon bonds not otherwise shown. Thus, CAS No. 678-39-7 could also be depicted as shown here. |
||
However, for any particular regulation, the term PFAS will have a slightly narrower meaning (refer to “PFAS Definitions” section, below).
PFAS should not be confused with “perfluoroalkoxy alkanes” (PFAs) which are a subset of PFAS.
PFAS should not be confused with “perfluorinated sulfonic acids” (PFSAs) nor with “perfluoroalkylsulfonates” (which regrettably have been referred to in literature from around 2009 with the acronym “PFAS”). Both chemical species are subsets of PFAS.
Fluoropolymers (such as PTFE, PVDF, and PFA) are substances with long chains of repeating molecular blocks that are all the same type, or a mix of two or three types, and which have a portion of the block that includes carbon atoms bonded to fluorine atoms. All fluoropolymers are PFAS.
A few of the non-polymer PFAS such as PFOA (perfluorooctanoic acid – C7F15-CO2H), PFHxS (perfluorohexane-1-sulphonic acid – C6F13-SO3H) and PFOS (perfluorooctanesulfonic acid – C8F17-SO3H) have brought attention to the larger PFAS chemical family because of their persistence in the environment and hazard to human health.
Many of the PFAS have a “backbone” of carbon atoms bonded together, each of which is bonded to one or more fluorine atoms – this structure has given rise to terms such as “long-chain” and “short-chain.”
Why are PFAS being regulated as a group?
Early PFAS regulations focused on single PFAS or small groups of PFAS such as the EU POPs regulation PFOA restriction. More recently, however, jurisdictions are developing regulations that have the entire PFAS family in scope (with varying definitions). The reasons that authors have given for this large expansion of scope includes the following points:
Note: SEMI and the members of the SEMI PFAS working group have not confirmed whether these assertions are true, nor taken a position on whether they are sufficient to warrant broad-spectrum PFAS restriction.
- PFAS are persistent (PFAs have lifetimes in the thousands of years) and bio-accumulative. Long term accumulation increases the risk of harm. Top predators in the food chain (including humans, whales, bald eagles) have highest PFAS levels in their blood and tissues.
- PFAAs (perfluoroalkyl acids and perfluoroalkyl-ether acids such as PFOA), a subset of PFAS, are well absorbed in animals and transport to organs with high blood flow. They can occupy sites on multiple receptors, proteins, and cell interfaces – resulting in cancers, changes in hormone and immune system function, and adverse developmental effects. Approximately 85% of PFAS are PFAA precursors.
- The early control on well-known PFAS “bad-actors” (such as PFOS) has resulted in regrettable substitution with shorter chain PFAS. In other words, the alternative substances used to replace the targeted bad substance turned out have just as many (or more) negative impacts as the original substance.
- Shorter chain PFAS are quite mobile in the environment, permeating through the soil, and more easily accumulate in plants than longer chain PFAS.
- Fluoropolymers are believed to release low molecular weight PFAS and other hazardous substances throughout their lifecycle. Low molecular weight PFAS are used as raw materials or additives in fluoropolymer production and can (and are known to have) been released into the environment and human water supplies. Further, greenhouse gases can be formed during some types of FP production, contributing to global warming.
- Although incineration can destroy PFAS, it has been found that incineration is often performed at temperatures that are too low or for durations that are too short for complete destruction of PFAS.
- Fluoropolymers are generally comprised of very long molecules that cannot interact with biological systems, but some molecules that are technically fluoropolymers are very short (e.g. having fewer than 10 monomers) and so are biologically active.
- Fluoropolymers can be a source of microplastics. (Note: this is true of most polymers, whether they are PFAS or not)
- Perfluoroalkanes and perfluoroalkylamines (subsets of PFAS) are generally biologically inert, but they can be very potent greenhouse gases.
- Less than 1% of all PFAS have been tested for their hazardous effects. Testing one chemical at a time will cause substantial delays in the effort to protect health and the environment.
Sources for this information:
[1] record of the Hearing of the ASSEMBLY COMMITTEE ON ENVIRONMENTAL SAFETY AND TOXIC MATERIALS, Bill Quirk, Chair – Date of Hearing: April 26, 2022, LINK
[2] “Scientific Basis for Managing PFAS as a Chemical Class”, Carol F. Kwiatkowski, et al., : Environ. Sci. Technol. Lett. 2020, 7, 532−543, LINK
[3] “Are Fluoropolymers Really of Low Concern for Human and Environmental Health and Separate from Other PFAS?”, Rainer Lohmann, et al., Environ. Sci. Technol. 2020, 54, 12820−12828, LINK
Other discussions of PFAS:
[4] “Commission Staff Working Document / Poly- and Perfluoroalkyl Substances (PFAS)”, European Commission SWD (2020) 249 Final, Brussels, 14.10.2020, LINK
[5] “Fluorinated polymers in a low carbon, circular and toxic-free economy / Technical report”, Wahlström, M. & Pohjalainen, E. (editors) et al., European Environment Agency – European Topic Centre on Waste and Materials in a Green Economy (ETC/WMGE) & European Environment Agency – European Topic Centre on Climate Change Mitigation and Energy (ETC/CME), Eionet Report – ETC/WMGE 2021/9, LINK
[6] “Reconciling Terminology of the Universe of Per- and Polyfluoroalkyl Substances: Recommendations and Practical Guidance Series on Risk Management No.61”, Organisation for Economic Co-operation and Development (OECD), ENV/CBC/MONO(2021)25, 9 July 2021, LINK
Please note: SEMI makes no warranties or representation to the accuracy or usefulness of the information contained on this webpage. Accuracy is solely the responsibility of the user. Users are cautioned to refer to other relevant literature of the subject matter herein. This information is subject to change without notice. This "explainer" was developed by members of the SEMI PFAS Working Group. Please send suggestions for improvement to ehs@semi.org.