In a recent joint ACS/CAS webinar, experts from CAS and the Swiss Federal Laboratories for Materials Science and Technology (Empa) explored the evolving landscape of PFAS regulation. The session focused on how structural definitions, rather than individual compound lists, are reshaping how regulators and industries approach these persistent chemicals.
Why PFAS definitions matter
Dr. Jeremy Krogman, Information Scientist at CAS, opened the discussion by explaining why PFAS structural definitions are central to future regulation. He noted that the carbon–fluorine bond is one of the strongest in organic chemistry. This gives PFAS unique properties like chemical inertness, thermal stability, and resistance to degradation.
These properties make PFAS useful across industries, but also difficult to manage environmentally. Dr. Krogman emphasized that broader structural definitions are now being adopted to capture the full scope of PFAS compounds:
"The OECD definition from 2021 is quite broad… trifluoroacetic acid is captured by this definition, but it is excluded from the three EPA definitions."
He also highlighted the scale of the challenge:
“The OECD definition captures approximately 24 million unique PFAS structures in our registry… while the U.S. EPA’s three definitions together capture about 1.8 million substances.”
Data from the CAS Content Collection reveals widespread industrial use
Using our curated database, Dr. Krogman showed how PFAS compounds, defined structurally, are embedded across nearly every major industrial sector. He explained that CAS scientists manually index literature and patents to connect chemical structures with real-world applications to find molecules that match a pattern and understand what those molecules do when used. In pharmaceuticals alone, CAS identified over 500,000 documents involving PFAS compounds. Other sectors with significant PFAS use include plastics, agrochemicals, electronics, and energy storage.
OECD's rationale for redefining PFAS
Dr. Zhanyun Wang, Scientist at Empa and contributor to the OECD PFAS definition, provided historical context and scientific rationale for the revised definition:
"We were tasked to update the OECD list of PFAS… and identified that a lot of chemicals share very similar structures to those in the Buck et al. paper, but do not necessarily meet its exact definition."
He outlined four cases where previous definitions fell short, including cyclic compounds and molecules with functional groups on both ends, and emphasized that the OECD definition is chemistry-based and designed to be implementable by non-experts. He also clarified that the definition excludes substances with only one fluorine atom or those halogenated by chlorine, bromine, or iodine.
Implications for regulation and innovation
Both speakers stressed that the complexity of the PFAS universe should not deter action. Wang noted:
"We shouldn't be scared by these large numbers… we should understand the scope and origin of this inclusion."
He introduced the concept of essential use, dividing PFAS applications into three categories:
- Non-essential: Uses driven by marketing, such as PFAS in bike lubricants or ski waxes.
- Substitutable: Uses with viable alternatives, like water-resistant textiles.
- Essential: Uses with no current alternatives, such as certain medical devices or semiconductor applications.
Dr. Krogman noted that for certain categories like pharmaceuticals, batteries, or semiconductor fabrication, the immediate ban of these substances would have a significant impact on the economy.
Both speakers agreed that essential uses should not be considered permanent, and innovation must continue to find safer alternatives.
Final thoughts: Data-driven decisions for a complex challenge
As the webinar concluded, Dr. Angela Zhou of CAS, Dr. Wang, and Dr. Krogman encouraged attendees to explore the full CAS report and consider how structural definitions can support more effective regulation. Even though these may be "forever chemicals," Dr. Wang noted "we will make this problem 'not forever.'"
To hear directly from the experts and explore these insights in more depth, watch the full webinar. The session includes detailed examples, data visualizations, commentary on the future of PFAS regulation, and a lively Q&A session.
