Measurement of longer chain PFAS in rainfall, surface water, soil and the Antarctic
The measurement and quantification of PFAS in the environment is critical to understanding their potential environmental and health effects. While there are already extensive studies on Trifluoroacetic acid (TFA) which is highly relevant to the use and emissions of some HFCs and HFOs, two recent papers have reported on the measurement of longer chain PFAS acids in rainfall, surface water, soil and the Antarctic. The longer chain PFAS acids studied are not relevant to the HFCs, HFOs and HCFOs used as refrigerants and foam blowing agents. In addition, TFA, which is a breakdown product of some HFCs and HFOs, occurs naturally in the oceans in large quantities and has different properties to the longer chain PFAS acids.
The paper “Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS)” [1] compares the levels of four selected perfluoroalkyl acids (PFAAs), perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), and perfluorononanoic acid (PFNA)) in various global environmental media (i.e., rainwater, soils, and surface waters) with recently proposed guideline levels. The paper, on the basis of the four PFAAs considered, as one of its conclusions that levels of PFOA and PFOS in rainwater often exceeded drinking water advisory or limit values. The paper noted that although the global emissions of these 4 PFAAs have been reduced in recent years in most countries, these substances continue to remain in the environment due to their high persistence and will continually cycle in the hydrosphere. Another paper, “Increasing Accumulation of Perfluorocarboxylate Contaminants Revealed in an Antarctic Firn Core (1958−2017)”, [2], reports the measurement of six perfluorocarboxylates (PFCA, C4−C9; note TFA is C2) in a firn (granular compressed snow) core collected from a non-coastal, high-altitude site in Eastern Antarctica. The paper found increasing PFCA accumulation in snow over this time period and states that the study illustrates that firn cores are useful tools that can provide multidecadal records that enable us to better understand the sources and deposition of chemical pollution in the global environment.
TFA (trifluoroacetic acid and its salts) occurs naturally in the oceans, estimated at 61-205 million tonnes [3], formed over millions of years. It is well established that TFA is a ubiquitous natural component in rivers, lakes, and other surface water bodies. It is found in the environment as a salt. Natural sources are thought to include undersea volcanic vents. Most PFAS have different properties from TFA [4]. As TFA is highly water soluble, poorly absorbed and therefore very mobile, it can very rapidly enter the natural water cycle through the atmosphere, soil and wastewater. It is virtually impossible to lock TFA into the soil. TFA’s toxicity has been tested on various aquatic and terrestrial species and can be assessed as low. Based on the available studies, TFA is of no health concern at the measured concentrations and at these concentrations is not harmful to ecosystems [5].
The German Federal Environment Agency (UBA) guidance value for TFA in drinking water is based on available toxicological studies for TFA salts. This sets a drinking water health guidance value of 60 μg/L and a target value of 10 μg/L. The health guidance value is based on the life-long tolerable daily intake of TFA via the drinking water (assumption: 2 L per day), in which no harm to human health is to be expected [6]. The study “Future emissions and atmospheric fate of HFC-1234yf from mobile air conditioners in Europe” [7], concluded that the contribution of TFA from HFO-1234yf to European mean TFA concentrations in rainwater were estimated at 0.6 μg/L to 0.8 μg/L. Within the EU annual mean concentrations were predicted to be highest in the Czech Republic and Southern Germany (1.7 μg/L), with a European maxima of 2.2 μg/L. Analysis of 1187 samples of rainwater collected in eight locations across Germany in 2018–2019 showed median and a precipitation-weighted mean concentration of TFA of 0.210 μg/L and 0.335 μg/L, respectively. [4] Some concentrations of TFA measured in the oceans are similar to rainwater concentrations: 0.19 to 0.21 μg/L in the mid-Atlantic at 8 different depths [8] and 0.16 μg/L in the deep Arctic Ocean [3] where the average age of the Canadian Basin Deep Waters is comparably high at perhaps 400 years.
In its Summary Update 2020 for Policymakers [9], the UNEP Environmental Effects Assessment Panel has these scientific conclusions for TFA: The current low concentration of trifluoroacetic acid (TFA) produced by the degradation of several hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs), is currently judged not to pose a risk to human health or to the environment. Trifluoroacetic acid continues to be found in the environment, including in remote regions, although concentrations are currently very unlikely to have adverse toxicological consequences for humans and ecosystems.
EFCTC has published on its website a new short leaflet TFA: what is it, how much is formed from F-gases, and what are its environmental effects.
References
[1] Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS), I. T. Cousins, J. H. Johansson, M. E. Salter, B. Sha, and M. Scheringer, Environmental Science & Technology 2022 56 (16), 11172-11179, https://doi.org/10.1021/acs.est.2c02765
[2] Increasing Accumulation of Perfluorocarboxylate Contaminants Revealed in an Antarctic Firn Core (1958−2017), J. Garnett, C. Halsall, H. Winton, H. Joerss, R. Mulvaney, R. Ebinghaus, M. Frey, A. Jones, A. Leeson, and P. Wynn, Environmental Science & Technology 2022 56 (16), 11246-11255, https://doi.org/10.1021/acs.est.2c02592
[3] B. F. Scott, R. W. Macdonald, K. Kannan, A. Fisk, A. Witter, N. Yamashita, L. Durham, C. Spencer and D. C. G. Muir, Trifluoroacetate profiles in the Arctic, Atlantic, and Pacific Oceans, Environ. Sci. Technol., 2005, 39(17), 6555–6560.
[4] Neale, R. E., Barnes, P. W., Robson, T. M., Neale, P. J., Williamson, C. E., Zepp, R. G., et al. (2021). Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020. Photochemical & Photobiological Sciences. https://doi.org/10.1007/s43630-020-00001-x. See sections 7.8 to 7.11 for Trifluoroacetic acid (TFA).
[5] Reducing chemical input into water bodies – trifluoroacetate (TFA) as a persistent and mobile substance from many sources, K. Adlunder et al, 2021, German Environment Agency, www.umweltbundesamt.de/en.
[6] Trifluoressigsäure (TFA)–Gewässerschutz im Spannungsfeld von toxikologischem Leitwert, Trinkwasserhygiene und Eintragsminimierung. Erläuterungen zur Einordnung des neuen Trinkwasserleitwerts von 60 μg/L. 20. Oktober 2020. Umweltbundesamt www.umweltbundesamt.de
[8] H. Frank, E. H. Christoph, O. Holm-Hansen and J. L. Bullister, Trifluoroacetate in ocean waters, Environ.Sci. Technol., 2002, 36(1), 12–15.
[9] Available at Environmental Effects Assessment Panel (EEAP) | Ozone Secretariat (unep.org)