Trifluoroacetic acid – TFA – is present everywhere in groundwater. However, concentrations differ clearly depending on the location: TFA pollution is significantly higher under arable land. TFA enters groundwater on a large scale due to the use of plant protection products. At lower concentrations, TFA is also transferred to groundwater by precipitation. TFA found in precipitation originates primarily from gas refrigerants and propellant gases. In particular cases, the discharge of treated industrial wastewater into watercourses can lead to considerable contamination of groundwater with TFA.
Trifluoroacetic acid (TFA) is a highly mobile and yet persistent substance. It is completely fluorinated and therefore considered a per- and polyfluorinated alkylated substance, or PFAS. TFA is formed as degradation product of PFAS containing at least one trifluoromethyl group (CF3). These PFAS are used in large quantities primarily as plant protection products and as gaseous refrigerants and propellants. TFA can also be released from biocides, pharmaceuticals and numerous industrial chemicals.
TFA was analysed in groundwater in 2022 and 2023 as part of a pilote study of the NAQUA National Groundwater Monitoring. Samples were taken at all NAQUA monitoring sites – of which there are almost 550. The limit of quantification was 0.2 micrograms of TFA per litre (µg/l).
TFA in groundwater everywhere
TFA is present everywhere in groundwater. Concentrations are around 100 to 1,000 times higher than concentrations of other PFASs that have been detected in groundwater to date. TFA is a persistent artificial substance that pollutes groundwater throughout the country and, according to current knowledge, is by far the most widespread artificial chemical in groundwater.
Concentrations of TFA differ clearly from one location to the next. Values are lowest – consistently below 0.6 µg/l – at over 1,000m a.s.l. in the Alps, Prealps and Southern Alps. In regions with a lot of farmland they are significantly above average: at over 60% of the NAQUA monitoring sites with a catchment area largely affected by arable farmland TFA concentration are between 1 and 5 µg/l. Exceptionally high peak values of over 10 µg/l were recorded at two neighbouring monitoring sites located near a watercourse that also contains treated industrial wastewater.
Different sources
TFA enters groundwater from different sources. The main sources of TFA in groundwater are pesticides and gaseous refrigerants and propellants. While TFA from pesticides is leached directly from the soil into the groundwater, TFA-forming gases from refrigerants and propellants are first released into the atmosphere and from there TFA enters soil and groundwater via precipitation. Industrial wastewater can also play a significant role in certain areas.
TFA as a metabolite of plant protection products
In regions with a lot of arable land, the concentrations of TFA are markedly higher because of the use of plant protection products. At these monitoring sites, concentrations in groundwater are on average about two times higher than in recent years' precipitation, i.e. around 1.2 µg/l, and can even reach values of up to 5 µg/l.
A total of 28 active substances of plant protection products are currently authorised that contain at least one CF3 group in their molecular structure and thus potentially degrade to TFA. These are primarily herbicides and fungicides, as well as some insecticides. They are used in field and vegetable cultivation, in fruit growing and viticulture, as well as for ornamental plants and occasionally in forestry nurseries. In 2022, more than 40 tonnes of these plant protection products were applied. In Switzerland, flufenacet and fluazinam were used in the largest quantities: up to 10 tonnes in each case. Flufenacet is authorised as a herbicide for the cultivation of several crops, including maize, cereals and potatoes. Fluazinam is used in the cultivation of potatoes and is also authorised for use in viticulture and for various ornamental plants.
Documentation as part of the authorization procedure
In manufacturers' laboratory tests, which serve as the basis for authorisation of individual plant protection products, TFA has so far been rarely identified or documented as a metabolite. This is probably because TFA is a very small molecule which cannot be traced using the usual standardised radioactive labelling of active ingredients in laboratory tests, or only to a limited extent. In addition, the prescribed duration of laboratory tests may be too short.
As part of the EU’s ongoing re-evaluation of the active substance flufenacet, TFA has, for the first time, been officially documented as a metabolite of this active substance. TFA concentrations of over 10μg/l in the leachate one metre below treated areas were simulated in modelling of certain applications and crops.
TFA from refrigerants and propellants
The use of TFA-forming refrigerant and propellant gases has increased considerably in recent years. As a result, TFA concentrations in precipitation have risen in the last 10 years and averaged around 0.6 µg/l in the last years in Central Europe. This roughly corresponds to the values in groundwater at the NAQUA monitoring sites above 1,000m where no arable farming is carried out in the catchment areas. At these sites, TFA most likely enters the groundwater in rain. Concentrations there are therefore relatively low.
TFA concentrations in groundwater tend to reflect the TFA concentrations in the rain that fell a few years previously. It takes several years, even decades, for precipitation – and thus the rising TFA concentrations – to seep through the soil and subsoil.
TFA from industrial wastewater
At some NAQUA sites, the TFA in the groundwater originates from industrial sources, which can significantly pollute the groundwater in particular cases. Infiltration of contaminated river water is responsible for the peak values of 14 and 23 µg/l at two monitoring sites in north-west Switzerland. Both monitoring sites are located in the immediate vicinity of the River Ergolz.
Kanton Basel-Landschaft: Zustandsbericht Grundwasserqualität 2024
Auswertung Grundwasserdaten 2010 bis 2022 des Kantons Basel-Landschaft
Groundwater quality on site
All data gathered as part of the NAQUA National Groundwater Monitoring is available to the cantonal authorities. The water companies concerned have also been informed about the results. The cantonal authorities are responsible for providing detailed information about groundwater quality of a specific region or location. Consumers can obtain information on drinking water quality directly from their water companies.
Further Informationen
Documents
Quellen, Eintragspfade, Umweltkonzentrationen von TFA und regulatorische Ansätze. Hintergrund - November 2021
Last modification 18.11.2024
