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Over 150 Scientists Urge Adoption of PFAS Definition that Includes F-Gases and TFA

The broader definition, featuring ‘at least one fully fluorinated carbon atom,’ is aimed at the U.S. EPA and some states.

More than 150 scientists from around the world with expertise in per- and polyfluoroalkyl substances (PFAS) have co-signed a new statement urging governmental bodies to adopt a science-based “at least one fully fluorinated carbon atom” definition of PFAS that includes fluorinated (f)-gases and trifluoroacetic acid (TFA), an atmospheric byproduct of certain f-gases.

The statement, which is still open to additional signatures from PFAS scientists, underscores “the necessity for government agencies and legislatures to adopt complete PFAS definitions grounded in science without political interference.” It is targeting agencies such as the U.S. Environmental Protection Agency (EPA) and states such as Delaware and West Virginia, which use a narrower definition of PFAS not aligned with the scientists’ recommendation; this definition requires at least two fully fluorinated carbon atoms and excludes f-gases.

The statement reportedly added weight to testimony by scientists who opposed the adoption of a bill by the Indiana State Senate that sought to adopt the narrower definition, which would have reversed current state regulations. The bill, recently passed by the Indiana House of Representatives, was rejected on February 26 by the Indiana Environmental Affairs Committee. “The consequences of weak PFAS policies can reverberate for generations,” said Lydia Jahl, a senior scientist at the Green Science Policy Institute who helped organize the statement. “It is great news for people and the planet that at least one such policy was blocked this week.”

PFAS, dubbed “forever chemicals” for their durability in nature, encompass thousands of substances and are known for enabling oil and water repellency, temperature resistance and friction reduction; the better-studied long-chain PFAS like PFOA and PFOS have been linked to cancer and other adverse health effects.

Many f-gases “persist in the environment” or decay into TFA, the scientists’ statement reads. (Notably, HFO-1234yf decomposes completely into TFA in the atmosphere within weeks.) “We are concerned that TFA has been increasingly detected in people and drinking water worldwide.” Last year, a study of households in the U.S. state of Indiana found ultrashort-chain TFA in samples of dust, drinking water, human blood serum, and recommended further research on potential adverse health effects of these exposures.

PFAS definitions that exclude gases and polymers “are overlooking the most widely used PFAS,” the statement says, adding that claims that these PFAS are needed to fulfill climate and infrastructure goals are “irrelevant” to the definition of PFAS and are “continuing to be refuted through the development of safer alternatives.”

The low global warming potential of some fluorinated gases “does not justify their exclusion from the definition of PFAS,” say the scientists.

F-gas manufacturers Chemours and Honeywell did not immediately respond to a request for comment on the scientists’ statement. The American Chemistry Council declined to comment.

At least one fluorinated carbon vs. two

The definition supported by the scientists states that PFAS contain “at least one fully fluorinated carbon atom.” This definition has been used by at least 23 U.S. states (notably Maine and Minnesota), the U.S. Department of Defense and the U.S. Congress. If any exemptions are needed to this definition “then those can be given without changing the definition of PFAS,” said the scientists.

“Having this single widely adopted definition creates important consistency for manufacturers, retailers and regulators; this definition has been used in state and federal legislation since 2018,” said Safer States, an alliance of U.S. state-based environmental health organizations.

The “at least one fully fluorinated carbon atom” definition, noted the scientists, is nearly identical to one developed for the OECD (Organisation for Economic Co-operation and Development) in 2021 by a panel of international PFAS experts, including those representing the chemical industry and U.S. Environmental Protection Agency (EPA); the OECD definition is also close to the one being employed by the EU as it considers comprehensive new PFAS regulations.

However, the broader definition is not being used by the U.S. EPA’s Office of Pollution Prevention and Toxics (OPPT), which has taken a number of approaches in recent years. In 2021 it announced a “working definition of PFAS” as chemicals with at least two adjacent carbon atoms, where one carbon is fully fluorinated and the other is at least partially fluorinated; this definition specifically excludes TFA. Last year the EPA said it would take a “case-by-case” approach to what the agency considers a PFAS. Then, last October, the EPA announced a new rule requiring reporting by manufacturers of more than 1,400 PFAS; the definition of PFAS that applies to this rule includes one of the following structures:

  • R-(CF2)-CF(R’)R”, where both the CF2 and CF moieties are saturated carbons;
  • R-CF2OCF2-R’, where R and R’ can either be F, O or saturated carbons; and
  • CF3C(CF3)R’R”, where R’ and R” can either be F or saturated carbons.

The EPA acknowledged that its latest definition “does not include substances that only have a single fluorinated carbon, or unsaturated fluorinated moieties (e.g., fluorinated aromatic rings and olefins).” As such it excludes f-gases and TFA. The EPA did not immediately respond to a request for comment on the scientists’ statement.

Public Employees for Environmental Responsibility (PEER) has sued the EPA to gain better clarity on how it developed its PFAS definition. To date, the suit has revealed that the EPA “didn’t really have a well-developed scientific justification for choosing any of the definitions it has thrown out there,” said Tim Whitehouse, Executive Director for PEER.

“Having a non-comprehensive and inaccurate definition for PFAS can result in regrettable substitutions by encouraging a shift to PFAS not covered by the definition,” said Safer States. “This also shields some of the most widely used ‘forever’ chemicals from restrictions and clean-up.”

Some U.S. states have also adopted the narrower PFAS definition, requiring at least two fully fluorinated carbon atoms and excluding gases, including Delaware and West Virginia.

In defending the broader definition of PFAS, the scientists’ statement pointed out that the carbon-fluorine bond is “the strongest single bond in organic chemistry, giving all PFAS the shared trait of persistence, leading to their accumulation in our bodies and ecosystems.” As a result, they added, PFAS “requires a class-based approach and a definition that reflects that.”

The notion that PFAS should be regulated as a class and not as individual chemicals was defended last year by Robert Sussman, a Deputy Administrator at the EPA during the Clinton administration, at the ATMOsphere America conference in Washington, D.C.; the conference was organized by ATMOsphere, publisher of Taking a contrary view, the Sustainable PFAS Action Network (SPAN), an industry group representing AHRI, Arkema, Honeywell, Daikin and others, states on its website, “Creating regulations that treat all PFAS compounds the same, or impose blanket restrictions on uses, would have devastating economic and safety consequences for the U.S. refrigeration and air conditioning industry.”

Even if policy makers choose to take action on certain PFAS chemicals, “the definition of PFAS should be science-based and not based on the preferences of PFAS manufacturers and users,” says Katie Pelch, Scientist, Environmental Health, for the Natural Resources Defense Council (NRDC), in a recent blog post. She is one of the scientists who signed the new statement.

Essential use approach

Pelch notes in her blog post that there is no scientific reason that f-gases should not be considered PFAS. “We can still be exposed to these PFAS and they can still cause harm,” she says, referring to the Indiana study on TFA.

Another blog post co-authored by Pelch states that, while phasing down HFCs is necessary for climate protection, “this does not justify blanket exemptions from PFAS regulations for the next generation of alternatives,” such as HFOs. Other authors of this post include Pelch’s NRDC colleagues Anna Reade, Director, PFAS Advocacy, Environmental Health (and another signatory of the new scientists’ statement); Alex Hillbrand, Technical Director, Industry & Emerging Technologies, Climate & Energy and Richie Kaur, Non-CO2 Climate Pollution Reduction Advocate, Climate & Energy.

The NRDC post advocates for the use of “the essential use approach,” adopted in the Maine and Minnesota PFAS regulations. This holds that chemicals of concern should not be used in products or processes unless they are critical for health, safety or the functioning of society; time-limited exceptions would be made for essential chemicals for which there are no safer alternatives. But there are safer non-PFAS alternatives in f-gas-using sectors such as natural refrigerants CO2 and hydrocarbons, points out the NRDC blog. Meanwhile,  it adds, “PFAS pollution is incredibly difficult to contain and clean up; therefore continued use of PFAS-based refrigerants will further exacerbate the already high levels of PFAS being detected in homes and people.”

This is not the first time scientists and others have challenged the EPA’s definition of PFAS. In 2021, 15 scientists – most of whom, including Pelch and Reade, are listed in the current statement – co-signed a letter to EPA Administrator Michael Regan urging the agency to use the OECD’s definition of PFAS. In 2023, three scientists along with three attorneys and a legislative associate co-signed a similar letter to Regan.

“We are concerned that TFA has been increasingly detected in people and drinking water worldwide.”

Statement by PFAS scientists

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