Trifluoroacetic acid (TFA) is the smallest molecule in the PFAS family – this acid is also one of the “forever chemicals” that are harmful to the environment and health. However, it has only been partially clarified from which precursor substances this PFAS molecule in air and water is formed. A study from Switzerland now shows that the concentrations of this acid in precipitation and rivers have increased four to six times over the last 25 years. But so far only around two thirds of this contamination can be attributed to known sources and precursors.
PFAS, short for per- and polyfluorinated alkyl compounds, are not called eternal chemicals for nothing: These fluorine-containing organic molecules are difficult to break down and remain in the environment for decades or even centuries. They can accumulate in people and animals and can be harmful to health. However, the PFAS class of substances includes thousands of different compounds and how they are formed, how widespread they are and how they affect the environment and health are not known for all of them.
Smallest PFAS molecule in focus
This also applies to trifluoroacetic acid (C2HF3O2), TFA for short, the smallest molecule in the PFAS family. The strong acid is created as a breakdown product of various precursor substances, including coolants and blowing agents such as hydrofluoroolefins. These fluorinated gases now replace the climate-damaging hydrofluorocarbons (HFCs). In contrast to these, these substitute gases decompose quickly in the atmosphere – but are converted into TFA, among other things. “Trifluoroacetic acid, which is formed in the atmosphere, quickly enters precipitation and from there into surface water and then into groundwater,” says senior author Stefan Reimann from the Swiss Federal Materials Testing and Research Institute (Empa).
Another important source of trifluoroacetic acid is the breakdown of pesticides in the soil. The TFA formed there usually ends up directly in the water. The final place of accumulation for the persistent fluorinated acid is therefore the ocean. However, this PFAS molecule is harmful to aquatic organisms and, like other PFAS, is hardly broken down in the environment. In high doses, the acid is harmful when inhaled and causes chemical burns. However, how harmful the environmentally relevant TFA concentrations are for living beings and also for humans has not yet been conclusively researched. Some new studies provide evidence of possible long-term toxicity. “TFA is very persistent, accumulates more and more in our water and is difficult to remove,” says Reimann. “We should therefore act according to the precautionary principle and limit the use of precursor substances as much as possible.”
Strong increase in rain and water
It is therefore important to determine as precisely as possible how and from what TFA is formed in the atmosphere and in what quantities the substance enters the water. The team led by Reimann and first author Stephan Henne from Empa therefore investigated this question together with the Swiss Federal Office for the Environment (FOEN). The team evaluated the TFA content of samples from precipitation and surface water in Switzerland over a period of three years. Archived water samples dating back to 1984 were also included. At the same time, the researchers created a detailed model of the atmospheric input of trifluoroacetic acid. “We model the known precursors of TFA, their degradation pathways and intermediate products, as well as the deposition of the TFA formed in this way, both via precipitation and directly on surfaces,” explains Henne. “We can use this to calculate for every place in Europe how much TFA ends up in the environment there in a certain month.”
The measurements showed: The concentrations of trifluoroacetic acid in precipitation and surface water have increased many times over in the last few decades. “During 2021 to 2023, mean measured TFA levels were 0.33 to 0.96 micrograms per liter in precipitation and 0.33 to 0.88 micrograms per liter in nine river samples,” the team reports. “This represents a four to six-fold increase since 1996/1997.” According to the model, around 60 to 70 percent of this PFAS contamination can be explained by hydrofluoroolefins and other fluorinated blowing and coolants. “As the use of HFO in refrigeration and air conditioning systems continues to increase, we assume that these TFA entries will also increase in the future,” says Reimann.
However, the comparison with the model also raises questions. “Our model explains around two thirds of the total measured atmospheric input from TFA,” reports Henne. “Therefore, there are probably other precursor substances and pathways that we don’t yet know.” This is also supported by the fact that even historical precipitation samples contain TFA, albeit in much lower concentrations than today. However, the known precursor substances have only been in use since the 1990s. In the future, the researchers want to take a closer look at these still unknown precursors and incorporate them into their atmospheric model.
Source: Empa – Federal Materials Testing and Research Institute; Specialist article: Atmospheric Chemistry and Physics, doi: 10.5194/acp-25-18157-2025