The US EPA has confirmed it will not pursue a single uniform definition of PFAS across its programmes. Instead, the agency told Chemical Watch News & Insight that it will maintain its case-by-case approach, tailoring the definition to each regulatory action.
The agency’s position continues a "fit-for-purpose" approach adopted under the Biden administration. It comes as the EPA reviews stakeholder comments on the proper scope of substances that should be subject to its TSCA 8(a)(7) PFAS reporting rule.
The confirmation means that the PFAS definition applicable to any regulation could theoretically shift. To date, the EPA’s Office of Pollution Prevention and Toxics (OPPT) appears to rely largely on the same structural definition used during the latter half of the Biden administration.
According to the EPA, taking a fit-for-purpose approach allows the agency to promote "gold standard science" by tailoring its PFAS definition to a particular regulatory purpose.
For example, the agency said, when the goal is to ensure potentially risky new substances do not enter commerce unchecked, using a broader definition can "capture more chemistries early, help prevent poor substitutions and let EPA evaluate new PFAS-like substances before they are in wide use".
By contrast, when the agency needs high-quality data on chemicals already in commerce, a tighter definition "focused on well-characterised PFAS that laboratories can reliably measure can keep reporting accurate, comparable and manageable", it said.
A single uniform definition "could undercut both the protectiveness and the practicality that the tailored approach is designed to deliver", the agency said.
The EPA acknowledged that the regulated community needs clarity and said that each of its rules specifies the PFAS definition that applies to it. The agency also noted that it supports compliance through guidance and lists identifying covered substances.
Nonetheless, defining what constitutes a PFAS on a case-by-case basis is a deliberate choice, not "an inconsistency to be resolved", the EPA said.
Shifting definitions
The agency’s current fit-for-purpose approach emerged in 2023, after the EPA quietly abandoned a working definition that OPPT had applied across its TSCA activities since at least 2021.
The working definition was a single-structure definition covering substances with at least two adjacent fluorinated carbons, capturing at least 1,364 substances. The definition underpinned the agency’s 2021 PFAS roadmap, its national testing strategy, and its June 2021 proposed PFAS reporting rule under TSCA section 8(a)(7).
After the EPA moved away from the working definition concept, however, the agency began relying on a broader three-part definition.
The final version of the TSCA 8(a)(7) reporting rule, adopted in October 2023, shifted to that broader definition, adding 41 substances and bringing the total subject to reporting to at least 1,462.
Later rules – including the January 2024 inactive PFAS SNUR and the December 2024 new chemicals procedural rule – followed suit, each applying the same three-structure definition.
Trump administration stays the course
Now, the Trump administration appears to rely on that same three-part definition within OPPT, even as it revisits Biden-era PFAS regulations.
The EPA proposed in November 2025 to substantially narrow the reach of the TSCA section 8(a)(7) PFAS reporting rule, adding exemptions for imported articles, de minimis quantities, certain byproducts and other categories.
In that proposal, however, the EPA left the existing PFAS definition intact.
The EPA’s pesticide programme also cited the same three-structure definition in defending its registration of pesticides containing a single fluorinated carbon in November 2025.
Future shifts?
The lack of a single PFAS definition leaves open the possibility that OPPT could deploy a new description for the persistent compounds, including for the closely watched TSCA 8(a)(7) reporting rule.
In its November proposal to overhaul the PFAS reporting rule, the EPA specifically invited comment on whether the agency "should amend the scope of reportable chemicals".
In response, several industry groups said the EPA should focus on a smaller universe of substances.
A coalition of 19 industry groups, spearheaded by the US Chamber of Commerce, urged the EPA to exempt fluoropolymers and "chemistries of low concern," such as hydrofluorocarbons (HFCs) and fluorinated gases (F-gases).
In separate comments, the American Chemistry Council (ACC) urged the EPA to exempt fluoropolymers from the PFAS reporting rule, arguing the agency should apply the same rationale it uses to exclude most polymers from the TSCA Chemical Data Reporting (CDR) rule.
More broadly, the ACC said it supports regulations that rely on a discrete list of substances rather than a structural definition, given the uncertainty about which chemicals are covered by the latter.
Nonetheless, due to the "sheer amount of work" that companies have already put into complying with the TSCA section 8(a)(7) rule, the ACC said it "must, unfortunately, support the continued use of the structural definition" for the PFAS reporting exercise.
Path forward for PFAS reporting
The EPA said it has received thousands of comments on the November 2025 proposed revisions and is reviewing them.
Any change to the scope of reportable PFAS, the agency said, would be made through the rulemaking process and explained in the final rule.
A final rule is expected later in 2026, with the submission window set to open 60 days after its effective date, or by 31 January 2027 at the latest.
For now, the agency said it is "not in a position to characterise a final result while that review is underway".