PFAS panel
The PFAS panel at ATMO America 2024 in Washington, D.C. (from left): Richie Kaur, NRDC; Michael Garry, ATMOsphere; Mindi Messmer, MedStar Health; and Gabriel Salierno, Toxics Use Reduction Institute.

ATMO America: Scientists Address PFAS Implications of HFOs, TFA

TFA is linked to potential health impacts, though the U.S. EPA relies on assurances from NOAA and the Montreal Protocol.

Three scientists considered the potential health and environmental risks of HFOs and their trifluoroacetic acid (TFA) degradation product during a panel discussion of PFAS (per- and polyfluoroalkyl substances) at the ATMOsphere (ATMO) America Summit 2024 in Washington, D.C.

The conference, which ran June 10–11, was organized by ATMOsphere, publisher of

The panel discussion, held on June 10, followed a keynote by Robert Bilott, the well-known environmental attorney whose lawsuits over a two-decade period first exposed the environmental and health threat of PFAS. He said that he sees “history repeating itself” in the way the chemical industry is characterizing refrigerants.

The panel agreed with Bilott that the potential hazards associated with refrigerants and TFA are being underplayed, but in a policy discussion on June 11 an Environmental Protection Agency (EPA) representative deferred to a less concerning characterization of TFA by the Montreal Protocol and the National Oceanic and Atmospheric Administration (NOAA).

Known as “forever chemicals” for their persistence in nature, PFAS encompass more than 14,000 synthetic fluorinated chemicals that have been used in a variety of applications, such as nonstick cookware and packaging, stain-resistant clothing and carpets, and firefighting foam. Bilott’s work uncovered links between a common type of PFAS called PFOA (perfluorooctanoic acid) and kidney cancer, testicular cancer, thyroid disease, high cholesterol, pre-eclampsia and ulcerative colitis.

PFOA contains eight carbon atoms, but health issues have been found for shorter chain PFAS such as GenX; concerns are now being directed at the ultra-short chain, two-carbon TFA, considered a PFAS by the scientific community. TFA, which is formed by the breakdown of HFO-1234yf in the atmosphere, is structurally the same as PFOA except with fewer carbon atoms.

TFA, formed by the 100% oxidation of HFO-1234yf in the atmosphere, is well-known to be very persistent and mobile (vPvM), and the German government has linked it to reproductive toxicity. A study of Indiana households states that TFA’s presence in human blood suggests bioaccumulative properties. TFA has been found in drinking water in Europe, also attributed to pesticide breakdown and other sources.

One of the panelists, Mindi Messmer, Senior Research Scientist for MedStar Health and former Member of the New Hampshire House of Representatives, said she saw a parallel between the health findings for PFOA and the potential health effects of TFA. “We are seeing a repeat of the PFOA and the GenX issue with respect to TFA,” she said.

Bilott’s first PFAS client, the West Virginia farmer Wilbur Earl Tennant, complained about the devastating health impact on his cows of what turned out to be PFOA. Messmer noted that  German authorities found “almost identical health effects in rabbits associated with TFA exposure: they saw fetal abnormalities. They saw the same eye defects that Mr. Tennant’s cows had. They see fertility issues, and they see reproductive and child development issues. So it’s history repeating itself again. Do we really want to continue down this road again and in another 40 years understand that we’ve made a huge mistake?”

Ultrashort-chain PFAS like TFA are often cited as not being very bioaccumulative, though in the Indiana study TFA was reported to bind to protein fractions and lipids. “I absolutely think [TFA] could be bioaccumulative,” said Messmer. “I think there’s enough information to show that your body is not going to discriminate between how many [carbon–fluorine] bonds there are, whether it’s a PFOA or a TFA. As long as it has that C–F bond, it appears that the health effects are similar.”

The EPA currently excludes f-gases and TFA from its definition and takes a piecemeal approach to regulating PFAS. Messmer was one of more than 150 PFAS scientists who recently signed a statement calling for a broader definition of PFAS that includes f-gases and TFA and for government agencies to regulate PFAS chemicals as a class rather than one by one. “There is precedent for this; we did do this in 1980s with PCBs [polychlorinated biphenyls],” she said. “So it’s not like it’s an outlandish request.”

By contrast, the chemical industry prefers to carve out certain types of PFAS so that they are not subject to regulation. When Messmer was working on getting her PFAS bills passed in the New Hampshire legislature, she said, “the American Chemistry Council came and told us that these PFAS chemicals are like berries – some are good for you, and some are bad for you – and we really need to limit that definition down, which is an absurd thing to say.” (The American Chemistry Council declined to comment for this article.)

But New Hampshire regulators are not sampling for TFA yet in any water systems, despite the state “[leading] the way in understanding how widespread PFAS was in our water systems.”

The essential-use approach

Another PFAS panelist, Richie Kaur, Non-CO2 Climate Pollution Reduction Advocate, Climate & Energy for the Natural Resources Defense Council (NRDC), recommended the “essential-use approach” to HFOs in applications like residential heat pumps and air conditioners in the U.S. The HFOs would be used only as long as it took for standards groups like ASHRAE and UL, the EPA and building codes to approve higher charge limits for propane (R290) in those applications. R290 heat pump and ACs are already being used in Europe.

“There is a need for getting to sustainable refrigerant alternatives now, and it’s more urgent now than it has ever been because the trade-off shouldn’t be that I get cooling, but then I get exposed to this toxic chemical that’s going to stay in my body forever as that science becomes clearer and clearer,” said Kaur.

However, the transition to non-PFAS refrigerants “is not easy, particularly not for air conditioners and heat pumps, and particularly not here in the U.S.,” she noted.

This is where the essential-use approach comes in, dealing with PFAS as a class and not chasing “one compound after the other until we fully elucidated all the effects over a period of 30 years because we’ll never get there with 14,000 or potentially 7 million compounds,” said Kaur. The essential-use approach would also “expedite the [standards] process and help prevent undue delays.”

The essential-use framework offers a time-limited exemptions for refrigerants that are deemed critical and essential when no other technically or economically feasible alternatives are available. “Except the burden of proof is on the industry, noted Kaur. “It’s not on the government to point out with certainty that something is causing harm. It says we have enough evidence of harm with this class of chemicals that we will put the burden of proof on industry to demonstrate that they can come up with nothing better. It flips the script.” The industry has to prove every five years or so that that exemption should still stand.

Kaur also called for more research, development and deployment of the most sustainable alternatives, “without arguing what the definition of PFAS is or why something should be forever exempted from regulations.” Also critical is training the workforce on how to safely handle flammable refrigerants like propane in heat pumps and ACs. In the U.S. “the one thing that equipment manufacturers are afraid of is the liability risk of propane,” she said.

Kaur pointed out the effort underway by the U.S. Department of Energy regarding the future of refrigerants. “It is talking about looking at the coefficient of performance, analyzing various refrigerant alternatives and figuring out where we need to update the codes and standards and how quickly we can get there,” she said.

A third PFAS panelist, Gabriel Salierno, Green Chemist for the Toxics Use Reduction Institute at the University of Massachusetts, Lowell, explained research he conducted showing that under certain conditions TFA – and another HFO degradation product called TFE (trifluoroacetaldehyde) – can degrade into HFC-23, a potent global warming gas with a 100-year GWP of 14,600 (IPCC, AR6). He also rejected the claim often made by the chemical industry that TFA is naturally occurring. “if anyone tells you that it is naturally occurring, don’t believe them,” he said.

While TFA is extremely stable, “what I found is if we start factoring in some environmental factors such as visible light and some biological process, we can produce HFC-23,” Salierno said. “Actually, if TFA degrades, the product is going to be HFC-23.” On the other hand, TFE – formed from the complete atmospheric breakdown of HFO-1234ze(Z) and HFO-1336mzz(Z) – is very reactive and short lived and can either become TFA, the most likely pathway, or through photolysis generate HFC-23.

Because of the high GWP of HFC-23, it only takes a 1.1% HFO conversion into HFC-23 for the effective GWP of the HFO to jump from around 1 to more than 150, the regulatory threshold for most applications in Europe and the U.S., said Salierno.


Cindy Newberg, EPA
Cindy Newberg, U.S. EPA

In the policy panel discussion at ATMO America on June 11, Cindy Newberg, Director of the Stratospheric Protection Division at the EPA’s Office of Atmospheric Programs, provided an update on the agency’s rollout of the U.S. AIM Act regulating HFCs.

 Asked about concerns regarding HFOs’ transformation into TFA, she said the EPA has worked closely with NOAA, which monitors the chemical for the U.S., and the Montreal Protocol to determine its stance on TFA. “And every assessment I’ve seen from them, and the most recent was the 2022 assessment report, they have basically said this is not of concern from their perspective, though we need to continue to monitor and keep a watch on TFA and bioaccumulation.”

The EPA is open to new information on TFA when it becomes available, Newberg added. “It’s not like we’ve never changed our minds about something. HFCs is a good example. Because we all know, 30 years ago, that’s where we thought everybody was going to go.”

“I think there’s enough information to show that your body is not going to discriminate between how many [carbon–fluorine] bonds there are, whether it’s a PFOA or a TFA. As long as it has that C–F bond, it appears that the health effects are similar.”

Mindi Messmer, Senior Research Scientist for MedStar Health

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