UBA report “Analysis of current seawater samples for trifluoroacetic acid”

The UBA report “Analysis of current seawater samples for trifluoroacetic acid” is an important new study on current concentrations of TFA in the Atlantic Ocean [1]. A validated analytical method was applied to surface water and deep-sea water samples of the Atlantic Ocean collected in 2022 and 2023 during two independent sampling campaigns. During the expeditions, a total of 33 surface water samples were taken in the Atlantic Ocean at 31 measuring points between latitudes 47° south to 50° north. The surface water samples had TFA concentrations between 260 ng/L and 306 ng/L. A total of seven depth profiles of the Atlantic Ocean were obtained, at maximum extraction depths of 3800 m and 4590 m. The TFA concentrations of samples from seven depth profiles ranged from 237 ng/L to 294 ng/L. All depth profiles, with the exception of one, showed a slight decrease in TFA concentration with increasing ocean depth.

The UBA report comments that, compared with sampling campaigns in the Atlantic from 1998 (Frank et al. [2]) and 1998/2002 (Scott et al. [3]), the TFA contents of depth profiles determined in the UBA report work are at a higher level. Frank et al. found a median TFA content of 202 ng/L (range: 190–210 ng/L) for a depth profile in the mid-Atlantic, while the median content of all seawater samples obtained in the UBA study was 273 ng/L (range: 237–294 ng/L; n=41). Taking into account the near-surface seawater samples collected, the median TFA content of the depth profile samples in the UBA study is 278.5 ng/L (range: 237–306 ng/L; n= 48). The Frank et al. results for the Southern Ocean [4] were similar to those of the depth profile in the mid-Atlantic [5]. The small fluctuation range of the TFA contents within a depth profile and between the UBA depth profiles is similar to that observed by Frank et al., who also found no pronounced spatial heterogeneity in TFA content.

The UBA report prompts two interesting points which are discussed in detail in separate items in this newsletter:

• Do the UBA results indicate a significant TFA content in the Atlantic Ocean, and if there is a significant TFA content in the Atlantic Ocean, can it all result from industrial sources or does it imply there must be a natural source?

 

Conclusion: The UBA reported TFA concentration measurements indicate a TFA content of about 43 million tonnes in the Atlantic Ocean to a depth of 4000 m. Industrial sources, estimated from inventories for 1930 to 1999 [6] and preliminary results (not yet published) from an updated inventory for 2000 to 2020 [7] can perhaps only account for about a maximum 1.2 million tonnes of TFA in the Atlantic Ocean. This would imply that there is a large natural content of TFA in the Atlantic Ocean.

• Has there been a significant increase in TFA concentration since around 2000 (previous oceanic concentration measurements) or is it a result of the uncertain quality and robustness of the TFA data determined in previous studies and the differences in the sampling sites?

Conclusion: It appears that most of the difference in TFA concentrations measured by Frank/Scott and UBA are more likely explained by differences in analytical method accuracy rather than due to anthropogenic emissions of TFA. There are two pieces of supporting evidence for this: (1) An estimate of industrial TFA emissions in the period 2000 to 2020; (2) the TFA concentrations required in precipitation and surface water (rivers) to result in the apparent increase in TFA concentration in the Atlantic Ocean are in far excess of those measured.

The UBA report explains that comparing the seawater content of TFA with the content of other PFAS can provide important information about the origin of the detected TFA and the anthropogenic influence of a seawater sample. It is planned to correlate the generated measured values for TFA with the levels of other PFAS in the samples examined. The UBA stated that at the time of writing its report, measurements for other PFAS representatives were not available, so they could not be used to interpret the TFA findings. In the current UBA measurement campaign, no significant difference could be determined in the mean TFA contents of samples from the northern and southern hemisphere.

References and Notes

[1] Examination of current seawater samples for trifluoroacetic acid | Federal Environment Agency (umweltbundesamt.de), Texte 35/2024, F. Freeling, and A Mangels

[2] Trifluoroacetates in Ocean Waters. Frank, H., Christoph, E. H., Holm-Hansen, O., & Bullister, J. L., Environmental Science & Technology, 2002, 36(1), 12–15. https://doi.org/10.1021/es0101532

[3] Trifluoroacetate Profiles in the Arctic, Atlantic, and Pacific Oceans, Scott, B. F., Macdonald, R. W., Kannan, K., Fisk, A., Witter, A., & Yamashita, N., et al., Environmental Science & Technology, 2005, 39(17), 6555–6560. https://doi.org/10.1021/es047975u

[4] The depths (m) and concentrations (ng/L) measured in the Southern Ocean were 10 m, 195 ng/L and 195 ng/L ; 50 m, 185 and 200 ng/L; 100 m, 195 and 200 ng/L ; 200 m, 195 ng/L; 500 m, 205 and 200 ng/L ; 750 m, 195 and 200 ng/L ; 1000 m, 205ng/L ; 1500 m, 220 ng/L; 2000 m, 210 ng/L.

[5] The depths (m) and concentrations (ng/L) measured in the Mid-Atlantic Ocean were 0 m, 190 ng/L ; 2m, 200 ng/L ; 40 m, 210 ng/L ; 120 m, 205 ng/L ; 380 m, 210 ng/L ; 1000 m, 205 ng/L ; 4000 m, 195 ng/L ; 4150 m, 200 ng/L

[6] An Inventory of Fluorspar Production, Industrial Use, and Emissions of Trifluoroacetic Acid (TFA) in the Period 1930 to 1999, A.A. Lindley, Journal of Geoscience and Environment Protection > Vol.11 No.3, March 2023, https://doi.org/10.4236/gep.2023.113001

[7] 2020 was selected as the end date for the updated inventory because emission estimates for fluorocarbons derived from atmospheric monitoring are currently available up to 2020