In a new study funded by the German Environment Agency (UBA), growing concentrations of trifluoroacetate (TFA) were found in archived leaf samples of various tree species, with a two-to-five-fold increase between 1995 and 2018.

The study attributed the TFA growth to “increasing emissions of gaseous TFA precursors” such as certain HFC and HFO refrigerants.

The study –  “Levels and Temporal Trends of Trifluoroacetate (TFA) in Archived Plants: Evidence for Increasing Emissions of Gaseous TFA Precursors over the Last Decades” – was published April 18 in Environmental Science & Technology. Its authors are Finnian Freeling, Marco Scheurer, Jan Koschorreck, Gabriele Hoffmann, Thomas A. Ternes, and Karsten Nödler.

Scheurer and Nödler also participated in another recent German TFA study that found TFA, among other similar chemicals, “widespread and dominant” in 46 water samples collected from 13 different sources of German drinking water.

In its acid form (trifluoroacetic acid), TFA is produced in the atmosphere by the 100% breakdown of HFO-1234yf, and is carried in rainfall to the earth, where it is found in acetate form. Between 7% and 20% of HFC-134a breaks down into TFA in the atmosphere.

According to the leaf-study authors, this is the first study to describe the “concentrations and temporal trends of TFA in biota by analyzing archived leaf samples of various tree species from the German Environmental Specimen Bank [ESB].” They regard plants as “an efficient biomonitoring tool” to evaluate the presence of TFA in the environment over time.

In total, 55 tree leaf samples from the German ESB were analyzed for TFA. Samples of the same leaf species from different locations each had a similar concentration range of TFA. The highest concentrations (up to about 1,000μg/kg dry weight) were found in Lombardy poplar leaves.

A “statistically significant positive trend” in the TFA concentration within the study period was found for most species and sites. This trend, the study says, is “likely the result of both bioaccumulation as well as increasing emissions of gaseous TFA precursors over the last three decades.”

Widespread contamination

Since TFA was detected in all analyzed plant samples, these results show that “the ubiquitous presence of TFA in dry and wet deposition leads to a widespread contamination of terrestrial ecosystems, even at near-natural and remote locations,” says the study.

While the study authors do not know of any “ecotoxicological effect data” for the tree species at higher TFA levels, they see the study results contributing to the “current discussion on the regulation of per- and polyfluoroalkyl substances (PFAS) to protect human and environmental health.” TFA is considered an ultra-short-chain PFAS, according to the Organisation for Economic Co-operation and Development (OECD).

The study noted that TFA manifests a very high persistence and mobility in the environment, which means it has “a much higher likelihood for long-lasting and widespread adverse effects.” Consequently, the study says, TFA and its precursors “should be considered for regulation to reduce the risk of potentially irreversible harm in the future.” 

TFA sources include industrial discharges and the degradation of many pesticides and pharmaceuticals. However, the study assumed that the predominant source of TFA in the studied plant matrices was atmospheric deposition from f-gas degradation.

The leaf study encompassed the species European beech, Lombardy poplar, Norway spruce, and Scots pine. The TFA concentrations of investigated tree leaf samples generally ranged from tens to hundreds of μg/kg of dry weight (dw).

TFA concentrations ranged between 24.6μg/kg dw in 1989 and 312μg/kg dw in 2019 in the European beech leaf samples; between 42.8μg/kg dw (1992) and 538 μg/kg dw (2020) in the Norway spruce leaves; between 98.5μg/kg dw (1992) to 453μg/kg dw (2018) in the Scots pine samples; and between 156μg/kg dw (1991) and 1,060μg/kg dw (2020) in leaves of the Lombardy poplar.

The high levels of TFA in recent tree leaf samples in Germany are comparable to the observations made by two studies in China, which reported TFA concentrations between approximately 280 and 3,000μg/kg dw for similar plant matrices, the study says.

Other TFA studies

The leaf studies and the recent German drinking water study add to the growing body of work looking at the growth of TFA in the environment.

For example, a two-year study published in 2020 measured the concentration of TFA in rainwater across eight locations in Germany. Compared to earlier studies done in 1995-1996 and 1996-1997, the amount of TFA has increased by three-to-five times.

Denmark has also been studying the presence of TFA in water supplies. In 2021, the Danish Environmental Protection Agency reported finding TFA in 219 out of 247 groundwater wells, as well as in some drinking water supplies. In the vast majority of groundwater wells, the concentration of TFA is lower than 1 µg/L.

Canadian researchers have also studied the presence of TFA in the environment. Other recent studies of current and projected TFA levels were reviewed at the ATMOsphere Europe conference last year.

In response to concerns about the growth of HFO and TFA levels in the environment, five European countries announced last year their intention to submit a joint proposal to restrict per- and polyfluorinated alkyl substances (PFAS), including some HFC and HFO refrigerants, to the European Chemicals Agency (ECHA) under the REACH regulation by July 2022 (which has been postponed to January 2023).

The chemical industry has addressed the deposition of TFA in an October 2021 study funded by the Global Forum for Advanced Climate Technologies (globalFACT), which represents f-gas producers Chemours, Honeywell, Arkema and Koura (and equipment manufacturer Daikin). The study concluded that “with the current knowledge of the effects of TFA on humans and ecosystems, the projected emissions through 2040 would not be detrimental.”

But the study also acknowledged that “the major uncertainty in the knowledge of the TFA concentrations and their spatial distributions is due to uncertainties in the future projected emissions.”

TFA and its precursors “should be considered for regulation to reduce the risk of potentially irreversible harm in the future.” 

Research study “Levels and Temporal Trends of Trifluoroacetate (TFA) in Archived Plants: Evidence for Increasing Emissions of Gaseous TFA Precursors over the Last Decades”

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