Scientists criticise IUPAC attempts to redefine PFAS as deregulation

Leading chemists have warned against efforts to narrow the scientific definition of PFAS. 

In a statement published by the American Chemical Society, they defend the current OECD definition as scientifically robust and fit for purpose. 

They express concern that those redefinitions endorsed the International Union of Pure and Applied Chemistry (IUPAC) may erode the foundations of PFAS monitoring.

Their message is clear: these revisions threaten to confuse international regulation and therefore, weaken public health protections.

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How are PFAS defined?

PFAS are a vast class of fluorinated chemicals, widely used for their non-stick, water-repellent and stain-resistant properties. 

Their chemical hallmark is the presence of strong carbon-fluorine bonds, which confer extreme environmental persistence, hence the term "forever chemicals".

In 2021, the Organisation for Economic Co-operation and Development (OECD) defined PFAS as any substance containing at least one fully fluorinated methyl (–CF₃) or methylene (–CF₂–) group, with no hydrogen, chlorine, bromine or iodine atoms attached. 

This structural definition captures both legacy contaminants like PFOS and PFOA, and less well-known but environmentally relevant substances such as fluorinated gases, fluoropolymers and precursors that degrade into persistent compounds like trifluoroacetic acid (TFA).

Crucially, the OECD definition is based on intrinsic molecular features alone. It does not attempt to categorise PFAS by use, risk, or regulatory status, only by structure.

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Are IUPAC pushing for redefinition?

IUPAC, the international authority on chemical nomenclature, is currently reviewing its terminology around PFASs. While this effort is framed as a scientific clarification, the timing and context have alarmed many experts.

Several industry groups and stakeholders have lobbied for a narrower definition, one that would exclude fluorinated gases used in refrigeration and medical devices, short-chain PFAS, fluoropolymers used in coatings and textiles, and even some fluorinated pharmaceuticals and pesticides. 

These substances are valuable commercially and widely used, and their inclusion under a broad PFAS umbrella could trigger costly regulatory consequences.

The concern raised by the scientists is that a narrower IUPAC definition, if endorsed, would carry disproportionate weight.

It could influence governments, delay regulation, complicate litigation, and grant cover to sectors seeking to avoid PFAS-related restrictions. 

In effect, they argue, this is not a scientific redefinition but a politically motivated retreat from the realities of PFAS persistence.

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Implications for monitoring and regulation

The consequences of altering the definition are particularly acute for environmental monitoring professionals and compliance officers.

A narrower PFAS definition would undermine the growing use of "total PFAS" screening methods, such as combustion ion chromatography or total oxidisable precursor (TOP) assays, which depend on a broad chemical scope. 

Laboratories might find their existing methods incompatible with revised regulatory targets. 

Monitoring programs designed to assess total fluorine burdens in water, soil or air could be rendered less effective or even legally contested.

Moreover, a restricted definition would likely exclude PFAS precursors and degradation products, despite their known environmental transformations. 

This risks missing critical exposure pathways and underestimating risk. 

Inconsistencies between jurisdictions could emerge, frustrating efforts to harmonise regulation and slowing down joint initiatives such as international drinking water standards or trade-related chemical disclosures.

In short, redefinition would not merely affect terminology, it would reverberate through the infrastructure of PFAS monitoring.

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Are there legitimate exemptions?

The scientists acknowledge that not all PFASs need to be regulated in the same way. Indeed, many jurisdictions already apply context-specific exemptions. 

For example, Canada's group-based PFAS restriction currently excludes fluoropolymers, while the European Union's proposed PFAS restriction includes time-limited derogations for medical devices and critical uses.

However, the authors argue strongly that such exemptions should be made transparently and politically, not by altering the foundational chemical definition. 

Redefining PFAS to suit industrial or regulatory preferences, they warn, opens the door to confusion and abuse.

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A call for scientific integrity

The statement concludes with a clear appeal: retain the OECD definition as the scientific baseline for identifying PFASs, and resist pressure to dilute it. 

Regulatory bodies can and should decide how to act on this definition, granting exemptions, setting priorities and managing risk but they should not distort the chemistry itself.

Introducing a new, narrower definition that incorporates non-chemical considerations would, the scientists argue, invite ambiguity, hinder harmonisation, and ultimately delay the mitigation of PFAS contamination.

In the face of mounting environmental and public health challenges, the authors insist that clarity, consistency, and structural integrity in chemical classification are more important than ever.