Document OEe5mp174aLMjwq97XJ2rdZ9j

Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Environmental Science Processes & Impacts CRITICAL REVIEW O R* ROYAL SOCIETY 400 OF CHEMISTRY View Article Online View Journal I View Issue I -sr Check for updates -a Cite this: Environ. Sci.: Processes Impacts, 2021, 23, 1641 Received 22nd July 2021 Accepted 1st October 2021 DOI: 10.1039/d1em00306b rsc.li/espi Insufficient evidence for the existence of natural trifluoroacetic acid Shira ea Joudan, Amila O. De eb Silva and Cora J. Young *a Trifluoroacetic acid (TFA) is a persistent and mobile pollutant that is present ubiquitously in the environment. As a result of a few studies reporting its presence in pre-industrial samples and a purported unaccounted source, TFA is often claimed to exist naturally. Here, we examine the evidence for natural TFA by: (i) critically evaluating measurements of TFA in pre-industrial samples; (ii) examining the likelihood of TFA formation by hypothesized mechanisms; (iii) exploring other potential TFA sources to the deep ocean; and (iv) examining global budgets of TFA. We conclude that the presence of TFA in the deep ocean and lack of closed TFA budget is not sufficient evidence that TFA occurs naturally, especially without a reasonable mechanism of formation. We argue the paradigm of natural TFA should no longer be carried forward. Environmental significance Trifluoroacetic acid (TFA) is an environmental contaminant that arises from multiple sources, including the degradation of several regulated chemicals. Earlier studies proposed a natural source of TFA to explain the presence of TFA in some environmental samples and the lack of a balanced global budget. This paradigm has been propagated without sufficient evidence. This critical review fully explores the literature and determines that there are no compelling scientific arguments to support the existence of naturally formed TFA. Thus, in the absence of new evidence, natural TFA should not be invoked in any discussions about the production and/or regulation of TFA. Introduction Trifluoroacetic acid (TFA; CF3COOH) has been measured in the environment since the 1990s,' but recent advances in analytical techniques are renewing interest in the global ubiquity of TFA.' Heightened concerns over per- and polyfluoroalkyl substances (PFAS) have brought TFA into the forefront, with debate on whether or not TFA should be considered a part of the PFAS class.8-7 What remains irrefutable is that TFA is a very persistent, very mobile (vPvM) contaminant because of its extremely low reactivity and high water solubility. The vPvM chemicals are subject to increased attention because they can readily move throughout the environment and accumulate, even though their chemical properties (e.g. octanol-water partitioning coefficients) differ from those of traditional persistent organic pollutants.8 The bioaccumulation potential of TFA in mammals and fish is typically thought to be lower than more scrutinized PFAS that contain a continuous chain of four of more perfluorinated carbon atoms."'" Nevertheless, the detection of high TFA levels in human blood and their association with health issues indicate that TFA is bioavailable and has non- 'Department of Chemistry, York University, Toronto, Ontario, Canada E-mail: . @yorku.ca 'Aquatic Contaminants Research Division, Environment and Climate Change Canada, Burlington, Ontario, Canada negligible residence time in biota." Although TFA is not bioaccumulative in the traditional sense, the high levels in humans are cause for concern (and suggest higher exposure). TFA is phytoaccumulative12 and has been found in food and beverages.' The TFA paradigm includes the long-held concept that it exists naturally, and only some of its sources are anthropogenic in origin. For example, the European Fluorocarbon Technical Committee (EFCTC) says "the evidence is clear and irrefutable that TFA occurs naturally in large quantities in the environment".13 Similar statements have propagated in academic literature that natural TFA exists, and is widely accepted (e.g. ref. 14-19) but questioned by few (e.g. ref. 20-22). In an effort to better understand the scientific basis for this statement, we sought its origin and corresponding data. The outcome of this objective is that there is inadequate scientific evidence of naturally derived TFA and that the natural TFA paradigm represents a vast overstatement without data to back it up. The question of natural TFA occurrences has not previously been examined in detail, and thus the objective of this work is to critically assess the evidence that TFA occurs naturally. Here, we address some common misinterpretations and limitations of the older TFA research that is often considered the benchmark in newer publications, with the aim to prevent their propagation through new manuscripts. Specifically, we: (i) evaluate published TFA measurements in pre-industrial and other This journal is The Royal Society of Chemistry 2021 Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 1 1641 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Environmental Science: Processes & Impacts environmental samples; (ii) examine the evidence for the proposed natural source; (iii) explore potential sources of TFA to the deep ocean; and (iv) examine the basis for global TFA budgets. Evaluation of published TFA concentrations in old natural systems The purported presence of TFA in pre-industrial water samples has been used to suggest TFA is naturally derived. To this end, freshwater and oceanwater samples have been collected, dated, and analyzed for TFA. A major challenge in evaluating the reported measurements is the limited analytical detail provided in these manuscripts, which oen did not have Electronic Supplementary Information associated with them. When evaluating quantitative environmental measurements, we require standard gures of merit including limits of detection (LOD) and quantication (LOQ), accuracy, and precision. These are usually developed by determining concentrations in eld and laboratory blanks, method recovery efficiency, replicate analysis, standard reference materials and clear data handling methods such as correcting for recovery or background contamination. Our own research using ultra trace analysis of TFA in high Arctic ice caps has underscored the importance of rigorous reporting and efforts to constrain as well as report analytical artefacts.23 Specically, we want to know how the sampling was performed, and if any uorinated materials were used during sample collection, storage, or processing. Four studies report TFA in pre-industrial freshwater and are summarized in Table 1. The rst study was by Jordan and Frank, in which TFA in old groundwater was below LOD whereas TFA in newer groundwater and surface water was 70-320 ng L1.23 Berg et al. used 15 000 year-old groundwater as a method blank for their measurements of TFA in rainwater and surface waters and did not observe TFA above the detection limit of 5 ng L1.24 Similarly, Nielsen et al. reported no detectable TFA in 2000 year-old groundwater and ice cores dated to 4191 20 years, with a detection limit of 2 ng L1.25 Unlike these three papers, Von Sydow et al. reported TFA concentrations of 6-56 ng L1 in 190 year-old Antarctic rn and 5 ng L1 in glacier ice from Sweden that formed 500 years ago.26 No obvious relationship was observed between concentration and depth in the rn core. Furthermore, the anthropogenic organochlorine insecticide lindane, and alkyl phosphate ame retardants were noted in the same glacier samples which presents signicant concern regarding data quality. Collectively these data suggest that the data quality was hampered by modern contamination or that there were problems in the dating methods used to assign age. Despite these limitations, the authors conclude that based on these data, TFA must have a natural source. Closer scrutiny of the reported analytical methods indicates aws based on the rst principles of quantitative analysis. All sample concentrations were extrapolated below their lowest calibration standard, which was 100 ng TFA into 10 mL water, resulting in a nal concentration of 1000 ng mL1 aer sample processing.26 There was no apparent effort to determine whether the linear range of 1642 | Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 Table 1 Critical assessment of TFA reporting in pre-industrial freshwater samples Sample type Groundwater23 Groundwater24 Location Antonien, Kondrau (Bavaria, Germany) Bayern, Kondrau (Bavaria, Germany) Thuringer Wald, Kondrau (Bavaria, Germany) Rennsteig, Kondrau (Bavaria, Germany) Small aquifer in N Switzerland Age (from sample collection) >700 200 400 60 185 15 000 1800 Dated year of samples Pre-1300 CE 1800 CE 1596 60 CE 1811 CE 13 000 1800 BCE TFA (n)a ND (3) 23 3 ng L1 (5) ND (3) 13 3 ng L1 (3) ND (3) 6-56 ng L1 (11) 5 ng L1 ND (3) ND (2) LOD 10 ng L1 5 ng L1 1 ng or 1 ng L1b 2 ng L1 Notes No information provided about methods for sample collection Details about sample collection and dating in ref. 27 Fluoropolymer used in sample preparation. LODs and sample concentrations reported below calibration standards Dated using radiocarbon in dissolved CO2 Chemical analysis of ice core from well documented standard archive Firn26 Glacier26 Various depths, Maud Land, East Antarctica Marmaglaciaren, Sweden 190 to present >500 1806-1997 CE Pre-1500 CE View Article Online Critical Review This journal is The Royal Society of Chemistry 2021 Groundwater25 Grundfoer, Denmark 2000 0 CE Ice core25 Summit, Greenland 4191 20 2199 20 BCE a n sample replicates; ND not detected above LOD. b The LOD in this paper was unclear, as described in the text. Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Critical Review View Article Online Environmental Science: Processes & Impacts the calibration curve extended below this calibration standard. The authors dene their LOD and LOQ based on their laboratory blanks, but the limited range of calibration standards indicate extrapolation was employed to quantify TFA in the blanks (as well as the samples).26 Overall, our conclusion from these reports is that there is no defensible evidence of any freshwater TFA in the pre-industrial period. Deep ocean samples that were presumed to be uninuenced by anthropogenic pollution have been analyzed for TFA and are summarized in Fig. 2. Frank et al. reported TFA concentrations consistently 200 ng L1 regardless of location or depth, down to 4150 m in the mid-Atlantic Ocean, and down to 2000 m in the Southern Ocean (Antarctica).28 The authors were very thorough in quality control measures during their sampling, wherein eld blanks of 400 year-old mineral water were transported throughout the sampling campaign during one year of sampling, and articial seawater during the next year. The old mineral water, purchased from a commercial supplier, con- tained the same amount of TFA as both the articial seawater and deionized water stored in the laboratory (35 5 ng L1, 34 1 ng L1, 33 3 ng L1, respectively). These concentrations are high, and higher than the pre-industrial freshwater in Table 1. The authors corrected the measured TFA concentrations in ocean water by subtracting the eld blank corresponding to the sample, whether it was the 1998 old mineral water, or the 1999 articial seawater in glass or polypropylene bottles. The authors dene their LOD (20 ng L1) and LOQ (32 ng L1) as the mean concentration of TFA in deionized water laboratory blanks of (8 ng L1) plus three times the standard deviation (4 ng L1) for LOD or plus 6 the standard deviation for LOQ. It would be more correct to dene LOD and LOD based on the concentrations of TFA in the eld blanks because this accounts for the entire sample handling process. The lowest calibration standard was 28 ng L1, suggesting they reported concentrations in their quality control blanks below their lowest calibration standard; however, the samples were above the lowest calibra- tion standard. In this study, the oldest samples were aged as >60 years old. Their dating was limited by the use of chlorouorocarbon (CFC) levels in the water, which has a lower limit of 1940, approximately 60 years before the samples were collected. The authors concluded that only a pre-industrial TFA source (i.e. natural source) could explain the consistent TFA concen- trations measured in waters > 60 years old. Scott et al. collected depth proles from several oceans to provide a more comprehensive picture of global oceanic TFA.29 They observed different trends in TFA depth proles in different locations, as shown in Fig. 2, with much more variable concentrations than Frank et al.,28 including multiple sites with much lower concentrations. For example, in the Atlantic Ocean, TFA ranged from 20 to 200 ng L1 from 23 N, 20 W to 38 N, 73 W. This variability is consistent with more recent analysis of PFAS proles in ocean sampling across extensive latitudinal gradients.30-32 Similar to the work of Frank et al.,28 Scott et al. reported relatively high concentrations of TFA (>100 ng L1) deep into the South Atlantic.29 An additional objective of Scott et al. was to test the hypothesis that deep sea vents could be a source of TFA into the ocean, and these results will be discussed below.29 The works of Frank et al.28 and Scott et al.29 demonstrate that TFA can be found in the deep ocean. A limitation of these studies was that they did not consider plausible TFA delivery mechanisms from ocean depths representing modern times to the deep ocean. These same two studies were summarized in a 2016 review paper on TFA that stated "What is clear from these data is that a large amount of the TFA salts in the ocean is from natural rather than human-made sources. However, salts of TFA in surface fresh waters are more likely of anthropogenic origins".16 The review paper has been cited for the statement that TFA has some natural origins by scientists,33 including by those working in the uorocarbon industry.6,13 However, similar to Frank et al. and Scott et al.,28,29 the review did not consider other explanations for the observation of TFA in deep ocean, did not critically assess the analytical methods in those papers, and did not discern the plausibility of the natural mechanism for producing TFA.16 Another line of evidence for natural TFA used by the uorocarbon industry13 is measurements of TFA from four archived soil samples from Rothamsted Agricultural Research Station, dating from 1865, 1881, 1944, and 1956, which reported concentrations of 0.51, 0.55, <0.1 and 0.35 ng g1 TFA (dry weight), respectively.34 Here, the method details are incongruous whereby the authors report a method limit of detection of 1 ng g1 based on a 10 g sample, suggesting either all of the sample results are below the limit of detection, or they extracted upwards of 100 g of sample. The inconsistency and ambiguity underscore the responsibility of researchers to report rigorous methods, which we have highlighted as a limitation for many early TFA studies. Peer reviewers and journal editors also share a responsibility to insist on the inclusion of rigorous and reproducible methodologies in publications. Additionally, the oldest sample from 1865 contained unexpectantly high concentrations of other haloacetic acids, notably 315 ng g1 dichloroacetic acid, suggesting it was likely contaminated. As demonstrated by early research analyzing TFA in aqueous samples, lab blanks tended to have high TFA concentrations. As such, additional skepticism is incurred by the absence of any reported blanks in this study. Taken together, this stand-alone paper purporting a natural source of TFA in old soil is not supported by sufficient evidence. Overall, the origins of the natural TFA source paradigm are largely based on the observation of TFA in pre-industrial samples, but no studies present a plausible mechanism for formation of TFA from natural sources. Proposed natural source to deep ocean Of the thousands of organouorine molecules found in the environment, the vast majority are solely anthropogenic. Harnisch et al.35 observed that several uorine-containing gases were liberated from the mineral uorite (CaF2) upon grinding. The uorinated gases observed were CF4, NF3, and SF6, along with several CFCs. The presence of CF4 and other uorinated gases has been observed in a few studies examining tectonically active areas on the continents.36-39 Evidence of enrichment of This journal is The Royal Society of Chemistry 2021 Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 | 1643 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Environmental Science: Processes & Impacts View Article Online Critical Review uorinated gases has been sought but not found in other studies of volcanic emissions,40-42 indicating the heterogeneous nature of their emission. This heterogeneity has been attributed to the natural variability in uorine content,41,42 which is found primarily in the form of the mineral uorite. Fluorite is found on continents in deposits typically near major faults or as an accessory mineral in granites,41 and is not found in the deep ocean. Although CF4 has been observed to be released from geologic processes, evidence of this occurring in the deep Pacic Ocean was sought but not found.43 Instead, all observed CF4 could be attributed to dissolution from the atmosphere.43 In the same study in which uorine-containing gases were measured from crushed uorite, the authors cite conference presentations of deep ocean observations of TFA (early version of ref. 29) and propose that uorite "is a source of natural TFA analogous to natural CF4". There have been no experimental or observational reports of uorite being a source of TFA under environmental conditions. In addition, the parallel drawn between TFA and CF4 ignores basic chemistry. Whereas CF4, NF3, and SF6 can all be formed under the anoxic conditions common in magmatic and hydrothermal uids, production of TFA from uorite would require an oxygen source for its formation. Observations of CF4 production solely from continental uorite does not provide a convincing foundation for TFA production in the deep ocean from anoxic hydrothermal vents. The deep ocean TFA measurements by Scott et al. included measurements of four proles over geologically active areas (Fig. 2) based on the hypothesis that deep sea vents or underwater volcanoes could act as a natural source of TFA.29 Here, we delve into this data and the plausibility of their implications. Three vent proles were collected in the Pacic Ocean and one in the Mediterranean Sea (Fig. 2). All vent proles have TFA concentrations within the range reported from depth proles without vents in the Atlantic, Arctic, and Southern Oceans (Fig. 1). For most vent locations, no measurements exist in a similar location in the absence of vents for direct comparison. One exception is the South Pacic, where a single non-vent depth prole was collected (Fig. 2). The South Pacic non-vent depth prole is distinct from all other ocean proles (Fig. 1) emphasizing the importance of potential spatial heterogeneity on the interpretation of the data. The South Pacic vent and non-vent depth proles are shown together in Fig. 2b. If the vents were a signicant source of TFA, we might expect higher concentrations of TFA at the deepest depths near the vents, but the proles do not show this. Overall, the TFA Fig. 1 Ocean depth profiles of TFA concentrations redrawn from Frank et al. (left)28 and Scott et al. (right).29 For the Scott et al.29 data, only profiles with a depth of 1500 m or greater were included. Line colours correspond to sampling locations shown in the top panel, and line styles correspond to year of sample collection. Fig. 2 Profiles measured above vents redrawn from Scott et al.29 left panel shows all four vents (note that Mediterranean site is quite shallow). Right panel shows S Pacific vent site vs. S Pacific non-vent site. For all other vent locations, we do not have a non-vent profile for comparison. 1644 | Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 This journal is The Royal Society of Chemistry 2021 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Critical Review View Article Online Environmental Science: Processes & Impacts depth proles measured above active vents reported in this single study are not persuasive of a natural TFA source. Other possible sources to deep ocean Many anthropogenic pollutants have been found in the deep ocean since the measurement of TFA, including radionuclides,44,45 persistent organic pollutants,33,46-49 heavy metals,50 and microplastics.51 Other PFAS have also been observed in the deep ocean,52,53 including peruorooctanoic acid (PFOA) and peruorooctane sulfonate (PFOS). Deep ocean observations of pollutants with disparate physical properties indicate multiple mechanisms can transport chemicals to the deep ocean on decadal timescales or faster. Three mechanisms, each of which may contribute to TFA in the deep ocean, will be discussed here: (i) meridional overturning circulation; (ii) shelf water cascading; and (iii) sinking of solids. The rst potential transport mechanism relates to deep ocean water formation through the meridional overturning circulation, also known as the global conveyer belt. This is well established to carry dissolved gases (e.g. CFCs54) to the deep ocean and has been suggested to contribute to deep-ocean observations of POPs (e.g. polychlorinated biphenyls (PCBs),48 Fig. 3). Measurements and models have also shown that meridional overturning circulation delivers PFAS to the deep ocean (Fig. 3).52,53 The second potential transport mechanism is through dense water formed on continental shelves that descends along continental slopes or through submarine canyons to deep waters in a process called shelf water cascading.55 These intermittent transport events can occur in all the world's oceans55 and have been shown to efficiently deliver contaminants, including persistent organic pollutants56 and several PFAS,57 from coastal regions to the deep sea.58 The third potential transport mechanism involves sinking of particles and organisms, which can account for the presence of numerous anthropogenic pollutants in the deepest parts of the ocean. These chemicals include persistent organic pollutants46 (e.g. PCBs,33,47,49 polybrominated diphenyl ethers,33,47 organochlorine pesticides33), heavy metals,50 radionuclides,45 and microplastics.51 Studies have shown that PFAS can accumulate in plankton59 and that sinking of plankton can transport PFAS from the surface ocean.32 These proposed mechanisms are all plausible pathways by which TFA could reach the ocean, and thus, the presence of TFA in deep ocean waters does not in itself necessitate invoking a natural source. More marine measurements of TFA, including deep ocean measurements, will help to increase our understanding of potential transport mechanisms. Fig. 3 North Atlantic Ocean depth profiles of persistent compound concentrations. PFAAs (perfluorobutane sulfonate (PFBS), perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA)) measured at 56.6 N, 52.8 W in 2004 and reported in Yamashita et al.53 PCBs (PCB-18, -28, -52, -101, -153) measured at 79 N, 4 E for 1 year from July 2012-2013 and reported in Sun et al.48. Large fraction of TFA remains unexplained Finally, arguments have been made that TFA must have a natural source because there is no other explanation for some estimated global burdens. However, until a clear source of natural TFA has been identied and all anthropogenic sources have been completely constrained, an unknown fraction does not itself prove the presence of a natural source. Based on their average reported marine TFA concentrations, Frank et al. roughly estimated the total ocean TFA burden using 200 ng L1 and an ocean volume of 1.34 1021 L, resulting in a total of 268 106 tonnes of TFA in oceans.28 The authors assumed homogeneity of the oceans, which is a vast oversimplication, as shown by other papers discussed herein. This approximation is oen used as evidence of natural TFA. Scott et al. based their calculated ocean burden on more comprehensive TFA measurements, which divided global waters into different depth proles and assessed Pacic, Atlantic and Indian Oceans separately, in addition to the Canadian Basin of the Arctic Ocean.29 The authors calculated the total TFA burden using high and low values for Atlantic and Pacic deep water, ultimately reporting a lower total oceanic TFA burden than Frank et al. of (61-205) 106 tonnes. Such estimates are speculative as the calculated TFA burdens are based on extrapolation of uncertain concentrations using unrealistic assumptions of spatial homogeneity throughout the ocean, and that their limited measurements are the most representative. The propagation of error in this workow results in a highly uncertain burden. This journal is The Royal Society of Chemistry 2021 Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 | 1645 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Environmental Science: Processes & Impacts View Article Online Critical Review Poor source apportionment of TFA does not specically support or refute the presence of a natural source. Most anthropogenic contaminants do not have comprehensively characterized budgets, including those with more widespread and simpler measurements. From a wider perspective, the global biogeochemical cycle of elemental uorine was only rst published in 2020.60 TFA is released both directly into the environment and indirectly via reactive precursors.23,61 Some reactive precursors are emitted into the gas phase, where they are oxidized predominantly by hydroxyl radicals to form TFA.62 Like other strong acids, TFA is primarily removed by wet and dry deposition.14,24 Other precursors are emitted into surface waters, where they are oxidized via hydrolysis or via biological processes.61 The long-range transport potential and reactivity of different precursors impact the quantity and location of TFA production, in addition to TFA being transported itself.22,62,63 Among the most important atmospheric precursors to TFA are heat transfer uids, such as hydrochlorouorocarbons (HCFCs) and hydrouorocarbons (HFCs), that have been introduced as replacements for CFCs through the Montreal Protocol and subsequent amendments.23,64 The atmospheric formation of TFA from these chemicals has been the subject of many studies and the resulting environmental burden is reasonably well constrained.16,62 However, more sources are being identied, such as recently, when a surprising amount of HCFC-133a (CH2ClCF3) was found in East Asia, likely as a byproduct of chemical production processes, updating the global emissions of this TFA precursor to 2300 tonnes per year from 2016-2019.65 A 2021 paper used a global three-dimensional chemical transport model to investigate the changes in global TFA from the transition of HFC134a (CF3CH2F) to a hydrouoroolen, HFO-1234yf (CF3CFCH2), and found that this change resulted in a 33-fold increase in the global burden of TFA when the 2015 emissions were used (i.e. 65 tons per year for HFC-134a vs. 2200 tons per year for HFO-1234yf).22 Fast reaction of HFO-1234yf to TFA was observed to result in a 250-fold increase of urban surface level TFA concentrations across Europe.22 Zhai et al. reported a 17fold increase of TFA in Beijing's landscape waters over recent years,66 and Wu et al. suggested there are additional sources of TFA that are not well constrained.49 The increase observed in Beijing from 2002 to 2012 ref. 66 was much larger than the increase observed by Pickard et al. in remote Arctic ice cores,23 suggesting local sources and short-lived TFA precursors play an important role. The authors suggested the rapid increase in Beijing was caused by increased usage of the TFA precursor HFC-134a in local automobile air conditioners.66 Many other chemicals form TFA in small quantities as byproducts of their synthesis or as degradation products. Fluorotelomer-based chemicals can form small yields of TFA depending on their peruoroalkyl chain length,67 and directly uorinated high density polyethylene plastic can leach TFA as well as other uorinated chemicals.68 High concentrations of TFA have been reported in Sweden near reghter training sites, landlls and hazardous waste management facilities, which show the impact of point sources into waterways.2 In that study, Bjornsdotter et al. reported the highest concentration of 14 000 ng L1 TFA near a re ghter training facility, where aqueous lm forming foams were used.2 Although TFA is not an active ingredient in aqueous lm forming foams, and to the best of our knowledge, has not been identied in a commercial foam product, this work shows that TFA is coming from aqueous lm forming foam contamination either from its presence as a synthetic byproduct and/or the presence of TFAprecursors. Another source of TFA to the environment is the thermolysis of plastics including polytetrauoroethylene (PTFE).69,70 Additionally, many common pesticides and pharmaceuticals contain CF3-substituted aromatic groups, which can be precursors to TFA. As of 2020, 18% of pharmaceuticals on the market contain organouorine for a total of 340 molecules, and 54 of them contain a CF3-substituted aromatic group.71 Also as of 2020, 16% of agrochemicals that have ever been on the market contain organouorine, for a total of 424 molecules, and 117 of them contain an aCF3-substituted aromatic group.72 Environmental transformation reactions oen result in deuorination of the CF3 group (i.e. F is observed), but sometimes TFA forms instead - these two products occur via two different reaction mechanism, that are impacted by pH and other conditions.73 Scheurer et al. tested the biotransformation of a few suspected TFA-precursors and reported 30-40% conversion to TFA aer 60 minutes from three drugs containing CF3-substituted aromatic groups: uoxetine, urtamone, uopyram.20 They also reported TFA formation of these three molecules upon ozonation, whereas other pesticides and pharmaceuticals tested whose CF3 moiety was not on a benzene ring either produced no TFA or small amounts of TFA.20 Another way TFA-precursors have been identied in landll leachate is by using the total oxidizable precursor (TOP) assay, which identies TFA-precursors using extreme oxidative conditions in the laboratory.74 A mass balance approach to estimate the fraction of TFA in environmental samples that can be traced to anthropogenic sources is not reasonable given the wide range of TFA precursors. Much more work is necessary to fully understand the sources of TFA, which is more possible now with improved analytical techniques. The budgets determined in the late 1990s and early 2000s must be revisited in light of the recent experimental and observational evidence of additional TFA precursors. Conclusions Here, we have summarized the ubiquity of TFA throughout the environment, a lack of rigour in TFA measurements highlighting uncertainty on absolute concentrations in older studies, and have proposed plausible mechanisms that can transport TFA into "old" samples. Irrespective of analytical data quality, the presence of TFA in the deep ocean cannot itself be considered evidence of a naturally derived source. There is no data to support a natural geological source of TFA. Recent reports suggest we will continue to nd additional novel TFA sources, and we must better constrain known sources to effectively understand its global burden. As scientists, it is our responsibility to ensure the foundation for scientic discussion 1646 | Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 This journal is The Royal Society of Chemistry 2021 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Critical Review View Article Online Environmental Science: Processes & Impacts is supported by sound science. As discussion about TFA in the environment becomes popular, it is crucial to use correct language based on the most advanced scientic understanding. In probing the natural TFA paradigm, we conclude that based on the current available research, the notion of a natural source of TFA should not be invoked. Conflicts of interest There are no conicts of interest to declare. References 1 H. Frank, D. Renschen, A. Klein and H. Scholl, Trace Analysis of Airborne Haloacetates, J. High Resolut. Chromatogr., 1995, 18, 83-88. 2 M. K. Bjornsdotter, L. W. Y. Yeung, A. Karrman and I. E. Jogsten, Ultra-Short-Chain Peruoroalkyl Acids including Triuoromethane Sulfonic Acid in Water Connected to Known and Suspected Point Sources in Sweden, Environ. Sci. Technol., 2019, 53(19), 11093-11101. 3 H. M. Pickard, A. S. Criscitiello, D. Persaud, C. Spencer, D. C. G. Muir, I. Lehnherr, M. J. Sharp, A. O. De Silva and C. J. Young, Ice core record of persistent short-chain uorinated alkyl acids: Evidence of the impact from global environmental regulations, Geophys. Res. Lett., 2020, 47, e2020GL087535. 4 M. Scheurer and K. Nodler, Ultrashort-chain peruoroalkyl substance triuoroacetate (TFA) in beer and tea - An unintended aqueous extraction, Food Chem., 2021, 351, 129304. 5 C. F. Kwiatkowski, D. Q. Andrews, L. S. Birnbaum, T. A. Bruton, J. C. Dewitt, D. R. U. Knappe, M. V. Maffini, M. F. Miller, K. E. Pelch, A. Reade, et al., Scientic Basis for Managing PFAS as a Chemical Class, Environ. Sci. Technol. Lett., 2020, 7(8), 532-543. 6 R. R. Singh and D. K. Papanastasiou, Comment on "Scientic Basis for Managing PFAS as a Chemical Class, Environ. Sci. Technol. Lett., 2021, 8(2), 192-194. 7 C. F. Kwiatkowski, D. Q. Andrews, L. S. Birnbaum, T. A. Bruton, J. C. Dewitt, D. R. U. Knappe, M. V. Maffini, M. F. Miller, K. E. Pelch, A. Reade, et al., Response to "comment on Scientic Basis for Managing PFAS as a Chemical Class, Environ. Sci. Technol. Lett., 2021, 8(2), 195-197. 8 S. E. Hale, H. P. H. Arp, I. Schliebner and M. Neumann, Persistent, mobile and toxic (PMT) and very persistent and very mobile (vPvM) substances pose an equivalent level of concern to persistent, bioaccumulative and toxic (PBT) and very persistent and very bioaccumulative (vPvB) substances under REACH, Environ. Sci. Eur., 2020, 32(1), 155. 9 D. A. Holaday, Absorption, Biotransformation, and Storage of Halothane, Environ. Health Perspect., 1977, 21, 165-169. 10 J. W. Martin, S. A. Mabury, K. R. Solomon and D. C. G. Muir, Dietary accumulation of peruorinated acids in juvenile rainbow trout (Oncorhynchus mykiss), Environ. Toxicol. Chem., 2003, 22(1), 189-195. 11 Y. Duan, H. Sun, Y. Yao, Y. Meng and Y. Li, Distribution of novel and legacy per-/polyuoroalkyl substances in serum and its associations with two glycemic biomarkers among Chinese adult men and women with normal blood glucose levels, Environ. Int., 2020, 134, 105295. 12 J. A. Benesch, M. S. Gustin, G. R. Cramer and T. M. Cahill, Investigation of effects of triuoroacetate on vernal pool ecosystems, Environ. Toxicol. Chem., 2002, 21(3), 640-647. 13 EFCTC, Naturally Occurring TFA, https:// www.uorocarbons.org/wp-content/uploads/2020/08/ EFCTC-TheEvidenceThatTFAoccursNaturally_A4.pdf, accessed May 6, 2021. 14 D. J. Luecken, R. L. Waterland, S. Papasavva, K. N. Taddonio, W. T. Hutzell, J. P. Rugh and S. O. Andersen, Ozone and TFA impacts in North America from degradation of 2,3,3,3tetrauoropropene (HFO-1234yf), a potential greenhouse gas replacement, Environ. Sci. Technol., 2010, 44(1), 343-348. 15 S. A. Montzka, G. J. M. Velders (lead authors), P. B. Krummel, J. Muhle, V. L. Orkin, S. Park, N. Shah and H. WalterTerrinoni, Hydrouorocarbons (HFCs), in World Meteorological Organization Global Ozone Research and Monitoring Project - Report No. 58: Scientic Assessment of Ozone Depletion: 2018, World Meteorological Organization (WMO), Geneva, Switzerland, 2018. 16 K. R. Solomon, G. J. M. Velders, S. R. Wilson, S. Madronich, J. Longstreth, P. J. Aucamp and J. F. Bornman, Sources, fates, toxicity, and risks of triuoroacetic acid and its salts: Relevance to substances regulated under the Montreal and Kyoto Protocols, J. Toxicol. Environ. Health, Part B, 2016, 19(7), 289-304. 17 J. Kazil, S. McKeen, S.-W. Kim, R. Ahmadov, G. A. Grell, R. K. Talukdar and A. R. Ravishankara, Deposition and rainwater concentrations of triuoroacetic acid in the United States from the use of HFO-1234yf, J. Geophys. Res.: Atmos., 2014, 119(24), 14059-14079. 18 M. Sun, J. Guo, Z. Zhai, P. Zuo and J. Zhang, Fluorochemicals biodegradation as a potential source of triuoroacetic acid (TFA) to the environment, Chemosphere, 2020, 254, 126894. 19 F. Freeling, D. Behringer, F. Heydel, M. Scheurer, T. A. Ternes and K. Nodler, Triuoroacetate in Precipitation: Deriving a Benchmark Data Set, Environ. Sci. Technol. Lett., 2020, 54(18), 11210-11219. 20 M. Scheurer, K. Nodler, F. Freeling, J. Janda, O. Happel, M. Riegel, U. Muller, F. R. Storck, M. Fleig, F. T. Lange, et al., Small, mobile, persistent: Triuoroacetate in the water cycle - Overlooked sources, pathways, and consequences for drinking water supply, Water Res., 2017, 126, 460-471. 21 I. T. Cousins, J. C. Dewitt, J. Gluge, G. Goldenman, D. Herzke, R. Lohmann, C. A. Ng, M. Scheringer and Z. Wang, The high persistence of PFAS is sufficient for their management as a chemical class, Environ. Sci.: Processes Impacts, 2020, 22(12), 2307-2312. 22 R. Holland, M. A. H. Khan, I. Driscoll, R. Chhantyal-Pun, R. G. Derwent, C. A. Taatjes, A. J. Orr-Ewing, C. J. Percival and D. E. Shallcross, Investigation of the Production of Triuoroacetic Acid from Two Halocarbons, HFC-134a and This journal is The Royal Society of Chemistry 2021 Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 | 1647 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Environmental Science: Processes & Impacts View Article Online Critical Review HFO-1234yf and Its Fates Using a Global Three-Dimensional Chemical Transport Model, ACS Earth Space Chem., 2021, 5, 849-857. 23 A. Jordan and H. Frank, Triuoroacetate in the environment. Evidence for sources other than HFC/HCFCs, Environ. Sci. Technol., 1999, 33(4), 522-527. 24 M. Berg, S. R. Muller, J. Muhlemann, A. Wiedmer and R. P. Schwarzenbach, Concentrations and mass uxes of chloroacetic acids and triuoroacetic acid in rain and natural waters in Switzerland, Environ. Sci. Technol., 2000, 34(13), 2675-2683. 25 O. J. Nielsen, B. F. Scott, C. Spencer, T. J. Wallington and J. C. Ball, Triuoroacetic acid in ancient freshwater, Atmos. Environ., 2001, 35(16), 2799-2801. 26 L. M. Von Sydow, A. B. Grimvall, H. B. Boren, K. Laniewski and A. T. Nielsen, Natural background levels of triuoroacetate in rain and snow, Environ. Sci. Technol., 2000, 34(15), 3115-3118. 27 U. Beyerle, R. Purtschert, W. Aeschbach-Hertig, D. M. Imboden, H. H. Loosli, R. Wieler and R. Kipfer, Climate and groundwater recharge during the last glaciation in an ice- covered region, Science, 1998, 282(5389), 731-734. 28 H. Frank, E. H. Christoph, O. Holm-Hansen and J. L. Bullister, Triuoroacetate in ocean waters, Environ. Sci. Technol., 2002, 36(1), 12-15. 29 B. F. Scott, R. W. Macdonald, K. Kannan, A. Fisk, A. Witter, N. Yamashita, L. Durham, C. Spencer and D. C. G. Muir, Triuoroacetate proles in the Arctic, Atlantic, and Pacic Oceans, Environ. Sci. Technol., 2005, 39(17), 6555-6560. 30 N. Yamashita, K. Kannan, S. Taniyasu, Y. Horii, G. Petrick and T. Gamo, A global survey of peruorinated acids in oceans, Mar. Pollut. Bull., 2005, 51, 658-668. 31 J. P. Benskin, D. C. G. Muir, B. F. Scott, C. Spencer, A. O. De Silva, H. Kylin, J. W. Martin, A. Morris, R. Lohmann and G. Tomy, Peruoroalkyl Acids in the Atlantic and Canadian Arctic Oceans, Environ. Sci. Technol., 2012, 46(11), 5815- 5823. 32 B. Gonzalez-Gaya, P. Casal, E. Jurado, J. Dachs and B. Jimenez, Vertical transport and sinks of peruoroalkyl substances in the global open ocean, Environ. Sci.: Processes Impacts, 2019, 21, 1957-1969. 33 J. Cui, Z. Yu, M. Mi, L. He, Z. Sha, P. Yao, J. Fang and W. Sun, Occurrence of Halogenated Organic Pollutants in Hadal Trenches of the Western Pacic Ocean, Environ. Sci. Technol., 2020, 54(24), 15821-15828. 34 B. F. Scott, C. Spencer, J. W. Martin, R. Barra, H. A. Bootsma, K. C. Jones, A. E. Johnston and D. C. G. Muir, Comparison of haloacetic acids in the environment of the Northern and Southern Hemispheres, Environ. Sci. Technol., 2005, 39(22), 8664-8670. 35 J. Harnisch, M. Frische, R. Borchers, A. Eisenhauer and A. Jordan, Natural uorinated organics in uorite and rocks, Geophys. Res. Lett., 2000, 27(13), 1883-1886. 36 A. Jordan, J. Harnisch, R. Borchers, F. Le Guern and H. Shinohara, Volcanogenic halocarbons, Environ. Sci. Technol., 2000, 34(6), 1122-1124. 37 D. C. Koh, L. N. Plummer, E. Busenberg and Y. Kim, Evidence for terrigenic SF6 in groundwater from basaltic aquifers, Jeju Island, Korea: Implications for groundwater dating, J. Hydrol., 2007, 339(1-2), 93-104. 38 D. A. Deeds, M. K. Vollmer, J. T. Kulongoski, B. R. Miller, J. Muhle, C. M. Harth, J. A. Izbicki, D. R. Hilton and R. F. Weiss, Evidence for crustal degassing of CF4 and SF6 in Mojave Desert groundwaters, Geochim. Cosmochim. Acta, 2008, 72(4), 999-1013. 39 D. A. Deeds, J. T. Kulongoski, J. Muhle and R. F. Weiss, Tectonic activity as a signicant source of crustal tetrauoromethane emissions to the atmosphere: Observations in groundwaters along the San Andreas Fault, Earth Planet. Sci. Lett., 2015, 412, 163-172. 40 S. A. Penkett and D. Prosser, Atmospheric measurements of CF4 and other uorocarbons containing the CF3 grouping, J. Geophys. Res., 1981, 86(80), 5172-5178. 41 J. Harnisch and A. Eisenhauer, Natural CF4 and SF6 on Earth, Geophys. Res. Lett., 1998, 25(13), 2401-2404. 42 M. Frische, K. Garofalo, T. H. Hansteen, R. Borchers and J. Harnisch, The origin of stable halogenated compounds in volcanic gases, Environ. Sci. Pollut. Res., 2006, 13(6), 406-413. 43 D. A. Deeds, J. Mu and R. F. Weiss, Tetrauoromethane in the deep North Pacic Ocean, Geophys. Res. Lett., 2008, 35, L14606. 44 N. Wang, C. Shen, W. Sun, P. Ding, S. Zhu, W. Yi, Z. Yu, Z. Sha, M. Mi, L. He, et al.,Penetration of Bomb 14C Into the Deepest Ocean Trench, Geophys. Res. Lett., 2019, 46(10), 5413-5419. 45 K. Oguri, K. Kawamura, A. Sakaguchi, T. Toyofuku, T. Kasaya, M. Murayama, K. Fujikura, R. N. Glud and H. Kitazato, Hadal disturbance in the Japan Trench induced by the 2011 Tohoku-Oki earthquake, Sci. Rep., 2013, 3, 1-6. 46 J. Dachs, R. Lohmann, W. A. Ockenden, L. Mejanelle, S. J. Eisenreich and K. C. Jones, Oceanic biogeochemical controls on global dynamics of persistent organic pollutants, Environ. Sci. Technol., 2002, 36(20), 4229-4237. 47 A. J. Jamieson, T. Malkocs, S. B. Piertney, T. Fujii and Z. Zhang, Bioaccumulation of persistent organic pollutants in the deepest ocean fauna, Nat. Ecol. Evol., 2017, 1(3), 24-27. 48 C. Sun, T. Soltwedel, E. Bauerfeind, D. A. Adelman and R. Lohmann, Depth proles of persistent organic pollutants in the North and Tropical Atlantic Ocean, Environ. Sci. Technol., 2016, 50(12), 6172-6179. 49 A. Sobek and O. Gustafsson, Deep water masses and sediments are main compartments for polychlorinated biphenyls in the Arctic Ocean, Environ. Sci. Technol., 2014, 48, 6719-6725. 50 M. Liu, W. Xiao, Q. Zhang, L. Shi, X. Wang and Y. Xu, Methylmercury bioaccumulation in deepest ocean fauna: Implications for ocean mercury biotransport through food webs, Environ. Sci. Technol. Lett., 2020, 7(7), 469-476. 51 L. C. Woodall, A. Sanchez-Vidal, M. Canals, G. L. J. Paterson, R. Coppock, V. Sleight, A. Calafat, A. D. Rogers, B. E. Narayanaswamy and R. C. Thompson, The deep sea 1648 | Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 This journal is The Royal Society of Chemistry 2021 Published on 04 October 2021. Downloaded by University of Groningen on 7/7/2023 1:40:51 PM. Critical Review View Article Online Environmental Science: Processes & Impacts is a major sink for microplastic debris, R. Soc. Open Sci., 2014, 1, 140317. 52 X. Zhang, Y. Zhang, C. Dassuncao, R. Lohmann and E. M. Sunderland, North Atlantic Deep Water formation inhibits high Arctic contamination by continental peruorooctane sulfonate discharges, Global Biogeochem. Cycles, 2017, 31(8), 1332-1343. 53 N. Yamashita, S. Taniyasu, G. Petrick, S. Wei, T. Gamo, P. K. S. Lam and K. Kannan, Peruorinated acids as novel chemical tracers of global circulation of ocean waters, Chemosphere, 2008, 70, 11589-11609. 54 S. C. Doney, W. J. Jenkins and J. L. Bullister, A comparison of ocean tracer dating techniques on a meridional section in the eastern North Atlantic, Deep Sea Res., Part I, 1997, 44(4), 603-626. 55 V. V. Ivanov, G. I. Shapiro, J. M. Huthnance and D. L. Aleynik, Cascades of dense water around the world ocean, Prog. Oceanogr., 2004, 60(1), 47-98. 56 J. A. Salvado, J. O. Grimalt, J. F. Lopez, A. Palanques, S. Heussner, C. Pasqual, A. Sanchez-Vidal and M. Canals, Role of dense shelf water cascading in the transfer of organochlorine compounds to open marine waters, Environ. Sci. Technol., 2012, 46(5), 2624-2632. 57 A. Sanchez-Vidal, M. Llorca, M. Farre, M. Canals, D. Barcelo, P. Puig and A. Calafat, Delivery of unprecedented amounts of peruoroalkyl substances towards the deep-sea, Sci. Total Environ., 2015, 526, 41-48. 58 S. Tamburrino, S. Passaro, M. Barsanti, A. Schirone, I. Delbono, F. Conte, R. Delfanti, M. Bonsignore, M. Del Core, S. Gherardi, et al., Pathways of inorganic and organic contaminants from land to deep sea: The case study of the Gulf of Cagliari (W Tyrrhenian Sea), Sci. Total Environ., 2019, 647, 334-341. 59 X. Zhang, R. Lohmann and E. M. Sunderland, Poly- And Peruoroalkyl Substances in Seawater and Plankton from the Northwestern Atlantic Margin, Environ. Sci. Technol., 2019, 53(21), 12348-12356. 60 W. H. Schlesinger, E. M. Klein and A. Vengosh, Global Biogeochemical Cycle of Fluorine, Global Biogeochem. Cycles, 2020, 34(12), 1-18. 61 M. Scheurer, K. Nodler, F. Freeling, J. Janda, O. Happel, M. Riegel, U. Muller, F. R. Storck, M. Fleig, F. T. Lange, et al., Small, mobile, persistent: Triuoroacetate in the water cycle - Overlooked sources, pathways, and consequences for drinking water supply, Water Res., 2017, 126, 460-471. 62 C. J. Young and S. A. Mabury, Atmospheric Peruorinated Acid Precursors: Chemistry, Occurence, and Impacts. in, Reviews of Environmental Contamination and Toxicology, Volume 208: Peruorinated Alkyl Substances, ed. P. de Voogt, Springer, New York, 2010, pp. 1-109. 63 V. R. Kotamarthi, J. M. Rodriguez, M. K. W. Ko, T. K. Tromp, N. D. Sze and M. J. Prather, Triuoroacetic acid from degradation of HCFCs and HFCs: A three-dimensional modeling study, J. Geophys. Res.: Atmos., 1998, 103(D5), 5747-5758. 64 J. Wu, J. W. Martin, Z. Zhai, K. Lu, L. Li, X. Fang, H. Jin, J. Hu and J. Zhang, Airborne triuoroacetic acid and its fraction from the degradation of HFC-134a in Beijing, China, Environ. Sci. Technol., 2014, 48(7), 3675-3681. 65 M. K. Vollmer, J. Muhle, S. Henne, D. Young, M. Rigby, B. Mitrevski, S. Park, C. R. Lunder, T. S. Rhee, C. M. Harth, et al., Unexpected nascent atmospheric emissions of three ozone-depleting hydrochlorouorocarbons, Proc. Natl. Acad. Sci. U. S. A., 2021, 118(5), e2010914118. 66 Z. Zhai, J. Wu, X. Hu, L. Li, J. Guo, B. Zhang, J. Hu and J. Zhang, A 17-fold increase of triuoroacetic acid in landscape waters of Beijing, China during the last decade, Chemosphere, 2015, 129, 110-117. 67 D. A. Ellis, J. W. Martin, A. O. De Silva, S. A. Mabury, M. D. Hurley, M. P. Sulbaek Andersen and T. J. Wallington, Degradation of uorotelomer alcohols: A likely atmospheric source of peruorinated carboxylic acids, Environ. Sci. Technol., 2004, 38(12), 3316-3321. 68 A. A. Rand and S. A. Mabury, Peruorinated carboxylic acids in directly uorinated high-density polyethylene material, Environ. Sci. Technol., 2011, 45(19), 8053-8059. 69 J. Cui, J. Guo, Z. Zhai and J. Zhang, The contribution of uoropolymer thermolysis to triuoroacetic acid (TFA) in environmental media, Chemosphere, 2019, 222, 637-644. 70 D. A. Ellis, S. A. Mabury, J. W. Martin and D. C. G. Muir, Thermolysis of uoropolymers as a potential source of halogenated organic acids in the environment, Nature, 2001, 412, 321-324. 71 M. Inoue, Y. Sumii and N. Shibata, Contribution of Organouorine Compounds to Pharmaceuticals, ACS Omega, 2020, 5(19), 10633-10640. 72 Y. Ogawa, E. Tokunaga, O. Kobayashi, K. Hirai and N. Shibata, Current Contributions of Organouorine Compounds to the Agrochemical Industry, iScience, 2020, 23, 101467. 73 D. A. Ellis and S. A. Mabury, The aqueous photolysis of TFM and related triuoromethylphenols. An alternate source of triuoroacetic acid in the environment, Environ. Sci. Technol., 2000, 34(4), 632-637. 74 B. Wang, Y. Yao, H. Chen, S. Chang, Y. Tian and H. Sun, Perand polyuoroalkyl substances and the contribution of unknown precursors and short-chain (C2-C3) peruoroalkyl carboxylic acids at solid waste disposal facilities, Sci. Total Environ., 2020, 705, 1358321-1358410. This journal is The Royal Society of Chemistry 2021 Environ. Sci.: Processes Impacts, 2021, 23, 1641-1649 | 1649