Trifluoroacetic Acid and Other PFAS in Groundwater: the Role of Plant Protection Products
Photo: Peter Bormann, AI-generated with Reve Image 1.0 (Reve AI Inc., 2025)
The occurrence of per- and polyfluoroalkyl substances (PFAS) is widely documented in soils, water bodies, drinking water and foods. An analysis by Agroscope ranks the contribution made by plant-protection products and other sources to groundwater contamination with PFAS.
Scarcely a day goes by without a report in the media on the occurrence of PFAS in soils and water bodies, foods and the human body. Today, the use of a number of ‘classic” PFAS – i.e. longer-chain, highly fluorinated PFAS – is strictly regulated. Main reasons for this are the persistence of these substances in the environment and their toxicological properties.
Effects not yet fully explained
While we do not know enough about the effects of numerous other types of PFAS on human health or the environment, work is being done at the European level to bridge these knowledge gaps and improve regulation. Part of this involves determining maximum levels for PFAS in drinking water and groundwater.
The definition has evolved
The term ‘PFAS’ was long taken to mean only long-chain, highly fluorinated ‘per- and polyfluorinated alkyl substances’, encompassing around 1000 chemicals. Since 2021, however, a new and much broader OECD definition has been applied according to which over 10,000 polyfluorinated compounds now qualify as PFAS.
Plant protection product (PPP) active substances not part of ‘classic’ PFAS
There are no longer-chain, highly fluorinated PFAS that are approved as PPP active substances. There are, however, various fluorinated active substances that, according to the current broad definition, are now considered PFAS. The fluorine in the molecular structure of these active substances improves their stability and effectiveness. Conversely, fluorinated compounds often degrade more slowly in the environment.
TFA – a special PFAS compound
A breakdown product of most of these fluorinated active substances, trifluoroacetic acid (TFA) is also considered a PFAS according to the new definition and is found in groundwater throughout Switzerland. As with other PFAS, the effects of TFA on humans and the environment are not yet sufficiently understood.
Refrigerants and PPPs contribute to TFA in groundwater
Fluorinated refrigerants from air-conditioning units and cooling appliances that degrade in the atmosphere into TFA and enter the water cycle through rainfall are considered the main source of TFA in the environment, followed by fluorinated PPP active substances which break down into TFA in the soil. The share of groundwater contamination with TFA for which each of these two sources is actually responsible is influenced by various factors, and can therefore not be estimated at present. Whilst TFA is evenly deposited over all of a surface area with the rain, PPPs are only applied over part of an area. TFA concentration in rain has significantly increased since the 1990s, unlike the amount of TFA potentially produced from PPPs, which has remained around the same over the last 15 years.
PFAS-containing co-formulants in PPPs are very rare
In addition to active substances, PPPs also contain so-called co-formulants, which are occasionally named as a potential source of PFAS in the environment. Our analysis has shown that PFAS-containing co-formulants only occur in a very small number of PPPs. One product contains small amounts of a long-chain, highly fluorinated antifoaming agent; three products contain fluorinated propellants. Compared to other sources, the amounts sold with PPPs are small. Co-formulants do not contribute appreciably to the occurrence of PFAS in the environment, whether they be ‘classic’ PFAS or TFA.
PFAS: ‘per- and polyfluorinated alkyl substances’
Until a few years ago, the acronym ‘PFAS’ primarily meant long-chain and fully- or highly fluorinated substances (‘classic’ PFAS). Since 2021, however, a far broader definition from the OECD is used: ‘PFAS’ is now the umbrella term for all chemical compounds having at least one perfluorinated methyl group (-CF3) or methylene group (-CF2-), covering a total of over 10,000 different substances with widely differing physical, chemical and biological characteristics.
TFA: ‘trifluoroacetic acid’
TFA is the smallest carboxylic acid among the PFAS. It can potentially be produced by degradation of any PFAS containing a -C- CF3 unit in their molecular structure and that are not themselves persistent in the environment. TFA is readily water-soluble, hardly retained in the soil, and – according to the current state of knowledge – does not further degrade under environmental conditions. The effects that TFA has on human health and the environment are not yet conclusively understood.
Conclusions
- The term ‘PFAS’ is usually taken to mean longer-chain, fully- or highly fluorinated alkyl substances. As a whole, PPPs are not a significant source of these ‘classic’ PFAS.
- PFAS-containing co-formulants are very rarely present in PPPs. In Switzerland, between 1-6 kg of PFAS-containing antifoaming agents and around 100-1000 kg of fluorinated propellants were sold annually with PPPs from 2014 to 2023. Compared to other sources, these quantities are negligible.
- According to the latest, very broad OECD definition, 20 PPP active substances currently approved in Switzerland are also categorised as PFAS. Among these are 18 potential TFA precursors. From 2008 to 2023, a total of around 30 to 45 tonnes of these active substances were sold per year.
- Fluorinated refrigerants from air-conditioning and cooling systems that are released into the atmosphere where they degrade into TFA are considered to be the group of chemicals with the highest quantitative TFA-formation potential, followed by fluorinated PPP active substances which degrade in the soil to produce TFA.
- Atmospheric deposition of TFA is estimated at 24.5 tonnes per year for the whole of Switzerland, mainly from the degradation of fluorinated refrigerants. The maximum TFA-formation potential from the PPP active substances sold in Switzerland averaged 11.5 tonnes of TFA per year.
- Whilst the amount of PFAS sold with PPPs is known and the maximum amount of TFA produced in the environment can be estimated relatively accurately, there is very little comparable information for other areas of application.
- TFA is documented in groundwater and drinking water throughout Switzerland. The share accounted for by refrigerants and PPPs respectively varies between sites, and depends on various factors.
- It is not yet sufficiently understood how contamination with TFA affects the environment and human health.
Bibliographical reference
Trifluoressigsäure und andere PFAS im Grundwasser – was tragen Pflanzenschutzmittel bei?.
