What Are Per- and polyfluoroalkyl substances (PFAS)
- Tommaso A. Dragani
- 29 minutes ago
- 4 min read
Per- and polyfluoroalkyl substances (PFAS) are a broad class of synthetic compounds widely used in industrial applications and consumer products due to their unique properties, namely, their resistance to heat, water, and oil.
These characteristics derive from the strength of the carbon–fluorine bond, one of the most durable in organic chemistry, which makes PFAS remarkably persistent in the environment and the human body. For this reason, PFAS are often referred to as “forever chemicals.”
While some PFAS, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), are well-known for their toxicity and environmental persistence, the broader class includes over 12,000 structurally diverse compounds with varying properties, toxicological profiles, and environmental behaviors. This chemical diversity has led to a critical regulatory challenge: how to define PFAS accurately and consistently, without compromising environmental protection or scientific integrity.
The OECD Definition of PFAS
In 2021, the Organisation for Economic Co-operation and Development (OECD) introduced a revised working definition of PFAS that significantly broadened the substances included in this category. According to this definition, PFAS are: “Fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (i.e., –CF₃ or –CF₂–) without any hydrogen, chlorine, bromine, or iodine atoms attached to it” [OECD 2021; Wang et al. 2021].
The revised OECD guidance clarified that PFAS encompass both fully (per-) and partially (poly-) fluorinated alkyl substances connected to various functional groups. This definition aims to provide a pragmatic and functional framework for chemical screening, risk assessment, and regulatory decision-making [OECD 2021].
Importantly, the OECD acknowledges that PFAS are not a chemically homogeneous class. Instead, they represent a structurally diverse group of substances with different physicochemical, environmental, and biological properties. Some PFAS have well-documented health effects, while others, such as certain fluoropolymers, have not demonstrated the same levels of toxicity or bioaccumulation potential [Améduri 2023; Spyrakis & Dragani 2023].
The IUPAC Redefinition Effort and Scientific Backlash
In June 2024, the International Union of Pure and Applied Chemistry (IUPAC) announced the start of a project to redefine PFAS. The stated goal is to improve clarity and scientific communication [IUPAC 2024]. However, this initiative has already drawn strong criticism from the scientific community.
A group of 20 PFAS experts published a letter expressing concern that the IUPAC initiative could lead to a significantly narrower definition, potentially excluding important classes of PFAS from regulatory scrutiny [Sigmund et al. 2025].
The concern is that a revised, narrower definition may:
Exclude emerging PFAS of concern from future regulation,
Obscure the true scale of contamination,
Undermine existing environmental and public health protections, particularly in jurisdictions like the EU and UK where broad regulatory frameworks are under development.
Critics argue that the current OECD definition, while broad, is scientifically defensible and functionally effective for regulatory and environmental purposes. They caution that narrowing the definition may serve specific industrial interests by removing substances from oversight before adequate toxicological characterization has been completed.
Substance-Specific Risk vs Blanket Classification
At ASPIDIA, we recognize that not all PFAS pose the same risk. For instance, some fluoropolymers, due to their large molecular weight and low solubility, are not expected to exhibit the same bioavailability or toxicity as smaller, mobile PFAS [Spyrakis & Dragani 2023]. Nevertheless, there is a compelling argument for maintaining a broad definitional umbrella until sufficient data
are available to support individual exemptions based on robust scientific evidence.
Regulatory frameworks must balance two principles:
Precautionary Inclusion – Ensuring that substances of potential concern are not prematurely excluded from oversight.
Substance-Specific Evaluation – Recognizing that risk varies widely among PFAS, and refining regulatory strategies accordingly.
Blanket exclusion of subgroups, especially before independent risk assessments are completed, undermines this balance and could delay meaningful regulatory and remediation efforts.
Implications for Remediation and Technology Development
From a technological standpoint, a consistent and inclusive PFAS definition is essential for developing effective environmental remediation strategies. At ASPIDIA, we are advancing enzyme-based and microbial bioremediation technologies that rely on clear classification to identify target molecules and design degradative pathways.
Fragmented or inconsistent definitions hinder innovation by creating uncertainty around which compounds need to be addressed. Moreover, narrowing the regulatory scope may incentivize the use of novel PFAS with similar persistence and unknown health impacts, rather than promoting true
chemical substitution or elimination.
The Way Forward: Science, Transparency, and Collaboration
The PFAS definitional debate is not just academic. It has direct implications for environmental policy, public health, and technological innovation.
We urge all stakeholders, regulators, scientists, industry, and civil society, to engage with this issue in a manner that prioritizes:
Scientific integrity: Decisions should be based on robust, transparent data, not political agendas or economic expedience.
Regulatory coherence: Definitions should support enforceable and practical policy tools.
Public trust: Maintaining clarity and transparency is essential to preserve public confidence in environmental governance.
At ASPIDIA, while we acknowledge the practical utility of broad definitions like the one proposed by the OECD, we do not endorse any single classification system as sufficient for guiding regulation or remediation.
For risk assessment, we advocate for a compound-specific approach grounded in toxicological evidence and environmental behavior. Regulatory definitions should serve as starting points, not endpoints, for scientific assessment. Any revisions or frameworks must be informed by open,
transparent, and peer-reviewed analysis, not by industrial or political interests.
Join the Conversation
At ASPIDIA, we are committed to advancing rigorous, science-based solutions for PFAS remediation, including enzyme-driven and microbial technologies that target pollutants with precision. We believe meaningful progress begins with accurate definitions, robust data, and open dialogue.
We invite you to explore our research, contribute to the discussion, and collaborate toward a cleaner, more transparent future.
Contact us to learn more or share your perspective. Together, we can turn scientific insight into environmental impact.
References
Améduri B.
Fluoropolymers as Unique and Irreplaceable Materials: Challenges and Future Trends in These Specific Per or Poly-Fluoroalkyl Substances. Molecules.2023;28(22):7564. Published 2023 Nov 13. doi:10.3390/molecules28227564
IUPAC
Terminology and Classification of Per- and Poly-Fluoroalkyl Substances (PFAS). 2024. Available at: https://iupac.org/project/2024-006-3-100/
OECD
Reconciling Terminology of the Universe of Per- and Polyfluoroalkyl Substances. 2021. Available at: https://www.oecd.org/en/publications/reconciling-terminology-of-the-universe-of-per-and-polyfluoroalkyl-substances_e458e796-en.
Sigmund G, Venier M, Ågerstrand M, et al.
Scientists’ statement on the chemical definition of PFASs. Environ Sci Technol Lett. 2025.
Spyrakis F, Dragani TA.
The EU's Per- and Polyfluoroalkyl Substances (PFAS) Ban: A Case of Policy over Science. Toxics. 2023;11(9):721. Published 2023 Aug 22. doi:10.3390/toxics11090721
Wang Z, Buser AM, Cousins IT, et al.
A New OECD Definition for Per- and Polyfluoroalkyl Substances. Environ Sci Technol. 2021;55(23):15575-15578. doi:10.1021/acs.est.1c06896