Scientists defend widely used definition of PFASs
In a new paper published today in Environmental Science & Technology Letters, 22 scientists—including Professor Ian Cousins and Associate Professor Marlene Ågerstrand from the Department of Environmental Science—defend the current definition of PFASs established by the Organisation for Economic Co-operation and Development (OECD).
The scientists assert that the 2021 OECD definition, developed through a transparent, peer-reviewed process involving academia, regulators, and industry, is chemically unambiguous and well-suited to PFASs. It is based on molecular structure and does not prescribe how these chemicals should be regulated.
“The OECD definition identifies PFASs based solely on intrinsic molecular features,” the authors write, “and provides a clear scientific basis for determining which substances belong in this group.”
The commentary addresses proposals—particularly one supported by the International Union of Pure and Applied Chemistry (IUPAC), a global authority on chemical terminology—to redefine PFASs more narrowly. This approach could exclude certain subgroups such as fluorinated gases, polymers, and trifluoroacetic acid (TFA), which are included under the OECD definition based on their molecular structure. The authors caution that narrowing the scope in this way—potentially based on use or toxicity rather than chemical structure—may be politically or economically motivated and could lead to regulatory confusion and weaker protections.
Professor Ian Cousins. Photo: Stockholm University
“The current OCED definition of PFASs is simple and elegant: any chemical which has a fully fluorinated carbon is qualified as a PFAS,” says Professor Cousins. “Those advocating redefinition of PFASs under IUPAC’s authority are intentionally blurring the line between the OECD’s clear chemical definition and the varied regulatory scopes and definitions around the world.”
The scientists emphasize that if decision-makers wish to exempt certain PFASs from regulation for specific applications, this should be done transparently without altering the general chemical definition.
Associate Professor Marlene Ågerstrand. Photo: Stella Papadopoulou
"Conflicting definitions create confusion, erode trust, and hinder action. And contrary to claims by some interest groups, the OECD definition does not prevent regulation of a subset of PFAS — as clearly demonstrated in the EU and elsewhere," says Ågerstrand.
The article concludes that there is no scientific basis for replacing the OECD’s chemical definition of PFASs and warns that doing so could hinder progress in protecting human and environmental health from PFAS pollution.
Last updated: 2025-06-11
Source: Department of Environmental Science