A 17-fold increase of trifluoroacetic acid in landscape waters of Beijing, China during the last decade

Spatial heterogeneity of per- and polyfluoroalkyl substances caused by glacial melting in Tibetan Lake Nam Co due to global warming

Per- and polyfluoroalkyl substances (PFASs) in high-latitude polar regions and the Tibetan Plateau have received widespread international attention. Here, we measured 18 PFASs and 11 major isomers in the lake water, sediment, and surrounding runoff of Lake Nam Co in 2020. The concentrations of ultrashort-chain trifluoroacetic acid (TFA) and perfluoropropanoic acid (PFPrA) and major isomers of perfluoooctanoic acid (PFOA) and perfluoooctane sulfonate acid (PFOS) in water bodies in high-latitude polar regions and the Tibetan Plateau are reported for the first time. The results showed that the concentration of ∑PFASs in glacial runoff was approximately 139 % greater than that in nonglacial runoff. The concentrations of ∑PFASs in the lake water and sediment in the southern lake with multiple glacial runoff events were approximately 113 % and 108 % higher, respectively, than those in the northern lake. The concentrations of short-chain perfluorobutanoic acid (PFBA) and ultrashort-chain TFA and PFPrA, which may be indicators of ice and snow melt, exhibited significant spatial heterogeneity. Overall, the spatial heterogeneity of PFAS concentrations in the water, sediment and surrounding runoff of Lake Nam Co may be caused mainly by glacial melting.

Atmospheric fate and impacts of HFO-1234yf from mobile air conditioners in East Asia

HFO-1234yf (2,3,3,3-tetrafluoropropene) is being used as refrigerant to replace HFC-134a (1,1,1,2-tetrafluoroethane), a potent greenhouse gas, in mobile air conditioners. However, the environmental impacts of HFO-1234yf, which is quickly and almost completely transformed to the persistent and phytotoxic trifluoroacetic acid (TFA), is of great concern. Here, we used the nested-grid chemical transport model, GEOS-Chem, to assess the fate and environmental impacts of HFO-1234yf emissions from mobile air conditioners in East Asia. With total emissions of 30.3 Gg yr-1, the annual mean concentrations of HFO-1234yf in China, Japan, and South Korea were 4.00, 3.23, and 5.54 pptv (parts per trillion volume), respectively, and the annual deposition fluxes (dry plus wet) of TFA in these regions were 0.35, 0.48, and 0.53 kg km-2 yr-1, dominated by wet deposition. About 14 %, 13 % and 11 % of HFO-1234yf emissions were deposited as TFA in China, Japan and South Korea, respectively, i.e. a large portion of TFA was deposited in areas outside of the emission boundary regions. The TFA characteristics in Japan and South Korea was significantly influenced by emission from China, which contributions ranged from 43 % to 94 % for the TFA concentrations and 44 % to 98 % for the TFA depositions across the four seasons. This suggests that the influence of neighboring emission sources cannot be ignored when assessing the impact of HFO-1234yf emissions in individual countries.

Assessment of Potential Accumulation of Trifluoroacetate in Terminal Lakes

Trifluoroacetate (TFA) is the anionic form of the shortest perfluorocarboxylic acid (PFCA) and is ubiquitous in the environment at concentrations that are typically much higher than those of other PFCAs. As a stable and nonvolatile anion, it is expected to accumulate in terminal lakes in endorheic basins. This research sampled eight terminal lakes in the Western United States to determine the degree to which TFA is concentrating in these lakes and compare the data to samples collected from three of these lakes 25 years ago. The first observation was that three of the six terminal lakes sampled had higher TFA concentrations than their input streams, while the last two lakes lacked surface water inputs at the sampling time. The TFA concentrations in Mono Lake effectively remained constant over 25 years despite the input stream concentrations increasing 6.5-fold. In contrast, Pyramid Lake concentrations increased approximately the expected amount based on a simplistic analysis of input flows and concentrations. An additional observation was that lakes in basins with agricultural activity appeared to have higher TFA concentrations, which suggests an agricultural input.

Elevated Levels of Ultrashort- and Short-Chain Perfluoroalkyl Acids in US Homes and People

Per- and polyfluoroalkyl substances (PFAS) make up a large group of fluorinated organic compounds extensively used in consumer products and industrial applications. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), the two perfluoroalkyl acids (PFAAs) with 8 carbons in their structure, have been phased out on a global scale because of their high environmental persistence and toxicity. As a result, shorter-chain PFAAs with less than 8 carbons in their structure are being used as their replacements and are now widely detected in the environment, raising concerns about their effects on human health. In this study, 47 PFAAs and their precursors were measured in paired samples of dust and drinking water collected from residential homes in Indiana, United States, and in blood and urine samples collected from the residents of these homes. Ultrashort- (with 2 or 3 carbons [C2-C3]) and short-chain (with 4-7 carbons [C4-C7]) PFAAs were the most abundant in all four matrices and constituted on average 69-100% of the total PFAA concentrations. Specifically, trifluoroacetic acid (TFA, C2) and perfluoropropanoic acid (PFPrA, C3) were the predominant PFAAs in most of the samples. Significant positive correlations (n = 81; r = 0.23-0.42; p < 0.05) were found between TFA, perfluorobutanoic acid (PFBA, C4), and perfluoroheptanoic acid (PFHpA, C7) concentrations in dust or water and those in serum, suggesting dust ingestion and/or drinking water consumption as important exposure pathways for these compounds. This study demonstrates that ultrashort- and short-chain PFAAs are now abundant in the indoor environment and in humans and warrants further research on potential adverse health effects of these exposures.

Projections of National-Gridded Emissions of Hydrofluoroolefins (HFOs) in China

Hydrofluoroolefins (HFOs) are being used as substitutes for potent greenhouse gas hydrofluorocarbons (HFCs). However, the use and environmental impacts of HFOs are of great concern due to the rapid degradation of HFOs to produce persistent and phytotoxic trifluoroacetic acid (TFA). Here, we provide a comprehensive projection of HFO emissions in China during 2024-2060 for the first time. Under the Kigali Amendment to the Montreal Protocol, China's HFO emissions are estimated to increase from 1.7 (1.3-2.3) to 148.8 (111.4-185.4) kt in 2024-2060 with cumulative emissions of 2.8 (2.0-3.5) Gt, and cumulative reduced HFCs emissions are evaluated to be 5.4 Gt CO2-equivalent. High HFO emissions would be distributed mainly in the North China Plain and the eastern and coastal areas. HFO-1234yf (2,3,3,3-tetrafluoropropene) contributes most of HFO emissions with a cumulative emission of 1.7 Gt in 2024-2060, while the cumulative increment of TFA deposition from HFO-1234yf emissions would reach 0.4-1.0 Gt. The long-term national-gridded HFO emission inventories can provide scientific support for evaluating the environmental risks of HFOs and developing HFC phase-out pathways for addressing climate change.

Mammalian toxicity of trifluoroacetate and assessment of human health risks due to environmental exposures

While trifluoroacetic acid has limited technical uses, the highly water-soluble trifluoroacetate (TFA) is reported to be present in water bodies at low concentrations. Most of the TFA in the environment is discussed to arise from natural processes, but also with the contribution from decomposition of environmental chemicals. The presence of TFA may result in human exposures. For hazard and risk assessment, the mammalian toxicity of TFA and human exposures are reviewed to assess the margin of exposures (MoE). The potential of TFA to induce acute toxicity is very low and oral repeated dose studies in rats have identified the liver as the target organ with mild liver hypertrophy as the lead effect. Biomarker analyses indicate that TFA is a weak peroxisome proliferator in rats. TFA administered to rats did not induce adverse effects in an extended one-generation study and in a developmental toxicity study or induce genotoxic responses. Based on recent levels of TFA in water and diet, MoEs for human exposures to TFA are well above 100 and do not indicate health risks.

Trace Analysis Method Based on UPLC-MS/MS for the Determination of (C2-C18) Per-and Polyfluoroalkyl Substances and Its Application to Tap Water and Bottled Water

As the usage of long-chain perfluoroalkyl and polyfluoroalkyl substances (PFASs) may be gradually restricted, short-chain and even ultra-short-chain PFASs have been widely produced and used, which has put forward new requirements for the simultaneous analysis of the above substances. Using solid phase extraction two-fraction elution and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), an experimental method was established for the simultaneous analysis of ultrashort-chain, short-chain, and long-chain PFASs and the precursor perfluorohexanesulfonamide (FHxSA) in low-concentration water, such as tap water and bottled water. By optimizing the volume of methanol in the first-fraction elution, the concentration of ammonia in the second-fraction elution, and the concentration of ammonium acetate in the mobile phase, the high recovery and low detection limit (0.01-3 ng/L) were obtained. In addition, this method was used to measure nine tap water samples and six bottled water samples for validation, and the results showed that the concentration of PFASs in bottled water was lower than that in tap water. This study first reported the trifluoroacetic acid concentration in bottled water (6.61 ± 9.60 ng/L), which was lower than that in tap water (1712 ± 174 ng/L). The main substances in tap water and bottled water are both ultrashort-chain PFASs (C2-C3), accounting for more than 50%. There are few reports on the simultaneous analysis of ultrashort-chain, short-chain, and long-chain PFASs (C2-C18) and the precursor FHxSA in low-concentration water samples, and the new method can be further developed for different environmental media.

Unravelling the occurrence of trace contaminants in surface waters using semi-quantitative suspected non-target screening analyses

Several classes of anthropogenic chemicals such as pesticides and pharmaceuticals are frequently used in human-related life activities and are discharged into the aquatic environment. These compounds can exert an unknown effect on aquatic life and humans if the water is used for human consumption. Thus, unravelling their occurrence in the aquatic system is crucial for the well-being of life and monitoring purposes. To this end, we used nanoflow-liquid and ion-exchange chromatography hyphenated with orbitrap high-resolution tandem mass spectrometry to detect several thousands of features (chemical entities) in surface water. Later, the features were narrowed down to a few focused lists using a stepwise filtering strategy, for which the structural elucidation was made. Accordingly, the chemical structure was confirmed for 83 compounds from different application areas, mainly being pharmaceuticals, pesticides, and other multiple application industrial compounds and xenobiotic degradation products. The compounds with the highest concentration were lamotrigine (27.6 μg/L), valsartan (14.4 μg/L), and ibuprofen (12.7 μg/L). Some compounds such as prosulfocarb, fluopyram, and tris(3-chloropropyl) phosphate were found to be the most abundant and widespread contaminants. Of the 32 sampling sites, nearly half of the sites (47%) contained more than 30 different compounds. Two sampling sites were far more contaminated than other sites based on the estimated concentration and the number of identified contaminants they contained. Our triplicate analysis revealed a low relative standard deviation between replicates, advocating for the added value in analysing more sampling sites instead of sample repetition. Overall, our study elucidated the occurrence of organic contaminants from a variety of sources in the aquatic environment. Furthermore, our findings highlighted the role of suspected non-target screening in exposing a snapshot of the chemical composition of surface water and the localized possible contamination sources.

Comprehensive investigation of persistent and mobile chemicals and per- and polyfluoroalkyl substances in urine of flemish adolescents using a suspect screening approach

Persistent and mobile chemicals (PMs) and per- and polyfluoroalkyl substances (PFAS) are groups of chemicals that have received recent global attention due to their potential health effects on the environment and humans. In this study, exposure to a broad range of PMs and PFAS was investigated in Flemish adolescents' urine samples (n = 83) using a suspect screening approach. For this purpose, three sample preparation methods were evaluated, and a basic liquid-liquid extraction was optimized for urine analysis based on the extraction efficiency of PMs (53-80%) and PFAS (>70%). In total, 9 PMs were identified in urine samples at confidence levels (CL) 1-3 and, among them, acetaminophen, 4-aminophenol, 2,2,6,6-tetramethyl-4-piperidone, trifluoroacetic acid (TFAA), sulisobenzone, ethyl sulfate, and 1,2-benzisothiazol-3(2H)-one 1,1-dioxide were confirmed at CL 1 and 2. In addition, the detection and identification of 2,2,6,6-tetramethyl-4-piperidone, 4-aminophenol, TFAA, and m-(2,3-epoxypropoxy)-N,N-bis(2,3-epoxypropyl) aniline (CL 3), has been reported for the first time in human urine in this study. For PFAS, only 2 compounds were identified at CL 4, implying that urine is not a suitable matrix for suspect screening of such compounds. A significant difference between sexes was observed in the detection rate of identified PMs, in particular for acetaminophen, 4-aminophenol, and sulisobenzone. The findings of this study can be used in future human biomonitoring programs, such as by including the newly identified compounds in quantitative methods or monitoring in other human matrices (e.g., serum).

A pilot study on extractable organofluorine and per- and polyfluoroalkyl substances (PFAS) in water from drinking water treatment plants around Taihu Lake, China: what is missed by target PFAS analysis?

Per- and polyfluoroalkyl substances (PFAS) have raised concerns due to their worldwide occurrence and adverse effects on both the environment and humans as well as posing challenges for monitoring. Further collection of information is required for a better understanding of their occurrence and the unknown fractions of the extractable organofluorine (EOF) not explained by commonly monitored target PFAS. In this study, eight pairs of raw and treated water were collected from drinking water treatment plants (DWTPs) around Taihu Lake in China and analyzed for EOF and 34 target PFAS. Mass balance analysis of organofluorine revealed that at least 68% of EOF could not be explained by target PFAS. Relatively higher total target concentrations were observed in 4 DWTPs (D1 to D4) when compared to other samples with the highest sum concentration up to 189 ng L^-1. PFOA, PFOS and PFHxS were the abundant compounds. Suspect screening analysis identified 10 emerging PFAS (e.g., H-PFAAs, H-PFESAs and OBS) in addition to target PFAS in raw or treated water. The ratios PFBA/PFOA and PFBS/PFOS between previous and current studies showed significant replacements of short-chain to long-chain PFAS. The ratios of the measured PFAS concentrations to the guideline values showed that some of the treated drinking water exceeds guideline values, appealing for efforts on drinking water safety guarantee.

Increases in Trifluoroacetate Concentrations in Surface Waters over Two Decades

Trifluoroacetate (TFA) is a persistent perfluorinated alkanoic acid anion that has many anthropogenic sources, with fluorocarbon refrigerants being a major one. After an initial burst of research in the late 1990s and early 2000s, research on this ubiquitous pollutant declined as atmospheric emissions of the precursor compounds grew rapidly. Thus, there is little contemporaneous information about the concentrations of TFA in the environment and how they have changed over time. This research determined the change in TFA concentrations in streams by resampling a transect that was originally sampled in 1998. The transect was designed to determine the regional distribution of TFA both upwind and downwind of major metropolitan areas in Northern California as well as a set of globally remote sites in Alaska. The results showed that TFA concentrations increased by an average of 6-fold over the intervening 23 years, which resulted in a median concentration of 180 ng/L (range 21.3-2790). The highest concentrations were found in streams immediately downwind of the San Francisco Bay Area, while substantially lower concentrations were found in the upwind, regionally remote, and globally remote sites. The C3 to C5 perfluorinated alkanoic acids were also investigated, but they were rarely detected with this methodology.

Per- and Polyfluoroalkyl Substances in Outdoor and Indoor Dust from Mainland China: Contributions of Unknown Precursors and Implications for Human Exposure

Per- and polyfluoroalkyl substances (PFASs) were analyzed in outdoor (n = 101) and indoor dust (n = 43, 38 paired with outdoors) samples across mainland China. From 2013 to 2017, the median concentration of ∑PFASs in outdoor dust tripled from 63 to 164 ng/g with an elevated contribution of trifluoroacetic acid and 6:2 fluorotelomer alcohol. In 2017, the indoor dust levels of ∑PFASs were in the range 185-913 ng/g, which were generally higher than the outdoor dust levels (105-321 ng/g). Emerging PFASs were found at high median levels of 5.7-97 ng/g in both indoor and outdoor dust samples. As first revealed by the total oxidized precursors assay, unknown perfluoroalkyl acid (PFAA)-precursors contributed 37-67 mol % to the PFAS profiles in indoor dust samples. A great proportion of C8 PFAA-precursors were precursors for perfluorooctanesulfonic acid, while C6 and C4 PFAA-precursors were mostly fluorotelomer based. Furthermore, daily perfluorooctanoic acid (PFOA) equivalent intakes of PFAAs (C4-C12) mixtures via indoor dust were first estimated at 1.3-1.5 ng/kg b.w./d for toddlers at high scenarios, which exceeds the derived daily threshold of 0.63 ng/kg b.w./d. from the European Food Safety Authority (EFSA). On this basis, an underestimation of 56%-69% likely remains without considering potential risks due to the biotransformation of unknown PFAA-precursors.

Per- and polyfluoroalkyl substances in the environment

Over the past several years, the term PFAS (per- and polyfluoroalkyl substances) has grown to be emblematic of environmental contamination, garnering public, scientific, and regulatory concern. PFAS are synthesized by two processes, direct fluorination (e.g., electrochemical fluorination) and oligomerization (e.g., fluorotelomerization). More than a megatonne of PFAS is produced yearly, and thousands of PFAS wind up in end-use products. Atmospheric and aqueous fugitive releases during manufacturing, use, and disposal have resulted in the global distribution of these compounds. Volatile PFAS facilitate long-range transport, commonly followed by complex transformation schemes to recalcitrant terminal PFAS, which do not degrade under environmental conditions and thus migrate through the environment and accumulate in biota through multiple pathways. Efforts to remediate PFAS-contaminated matrices still are in their infancy, with much current research targeting drinking water.

Mass Balance of Perfluoroalkyl Acids, Including Trifluoroacetic Acid, in a Freshwater Lake

Perfluoroalkyl acids (PFAAs) are highly persistent chemicals that are ubiquitously found in the environment. The atmospheric degradation of precursor compounds has been identified as a source of PFAAs and might be an important pathway for contamination. Lake Vättern is one of Sweden's largest lakes and is an important source for drinking water. In addition to contamination via atmospheric deposition, the lake is subject to several potential contamination sources via surface water inflow. The relevance of different sources is not well understood. A mass balance of selected PFAAs was assembled based on measured concentrations in atmospheric deposition, surface water from streams that constitute the main inflow and outflow, and surface water in the lake. The largest input was seen for trifluoroacetic acid (150 kg/year), perfluoropropanoic acid (1.6 kg/year), perfluorobutanoic acid (4.0 kg/year), and perfluoro-octanoic acid (1.5 kg/year). Both atmospheric deposition and surface water inflow was found to be important input pathways. There was a positive correlation between the input of most perfluoroalkyl carboxylic acids via atmospheric deposition and global radiation and between the input via surface water inflow and catchment area. These findings highlight the importance of atmospheric oxidation of volatile precursor compounds for contamination in surface waters.

Levels and Seasonal Trends of C1-C4 Perfluoroalkyl Acids and the Discovery of Trifluoromethane Sulfonic Acid in Surface Snow in the Arctic

C1-C4 perfluoroalkyl acids (PFAAs) are highly persistent chemicals that have been found in the environment. To date, much uncertainty still exists about their sources and fate. The importance of the atmospheric degradation of volatile precursors to C1-C4 PFAAs were investigated by studying their distribution and seasonal variation in remote Arctic locations. C1-C4 PFAAs were measured in surface snow on the island of Spitsbergen in the Norwegian Arctic during January-August 2019. Trifluoroacetic acid (TFA), perfluoropropanoic acid (PFPrA), perfluorobutanoic acid (PFBA), and trifluoromethane sulfonic acid (TFMS) were detected in most samples, including samples collected at locations presumably receiving PFAA input solely from long-range processes. The flux of TFA, PFPrA, PFBA, and TFMS per precipitation event was in the ranges of 22-1800, 0.79-16, 0.19-170, and 1.5-57 ng/m2, respectively. A positive correlation between the flux of TFA, PFPrA, and PFBA with downward short-wave solar radiation was observed. No correlation was observed between the flux of TFMS and solar radiation. These findings suggest that atmospheric transport of volatile precursors and their subsequent degradation plays a major role in the global distribution of C2-C4 perfluoroalkyl carboxylic acids and their consequential deposition in Arctic environments. The discovery of TFMS in surface snow at these remote Arctic locations suggests that TFMS is globally distributed. However, the transport mechanism to the Arctic environment remains unknown.

Insufficient evidence for the existence of natural trifluoroacetic acid

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.

Trifluoroacetate in Precipitation: Deriving a Benchmark Data Set

Although precipitation is considered to be the most important diffuse source of trifluoroacetate (TFA) to the nonmarine environment, information regarding the wet deposition of TFA as well as general data on the spatial and temporal variations in TFA concentration in precipitation is scarce. This is the first study to provide a comprehensive overview of the occurrence of TFA in precipitation by a systematic and nation-wide field monitoring campaign. In total, 1187 precipitation samples, which were collected over the course of 12 consecutive months at eight locations across Germany, were analyzed. The median, the estimated average, and the precipitation-weighted average TFA concentration of all analyzed wet deposition samples were 0.210, 0.703, and 0.335 μg/L, respectively. For Germany, an annual wet deposition flux of 190 μg/m² or approximately 68 t was calculated for the sampling period from February 2018 to January 2019. The campaign revealed a pronounced seasonality of the TFA concentration and wet deposition flux of collected samples. Correlation analysis suggested an enhanced transformation of TFA precursors in the troposphere in the summertime due to higher concentrations of photochemically generated oxidants such as hydroxyl radicals, ultimately leading to an enhanced atmospheric deposition of TFA during summer.

Fluorochemicals biodegradation as a potential source of trifluoroacetic acid (TFA) to the environment

The anthropogenic release of trifluoroacetic acid (TFA) into the environmental media is not limited to photochemical oxidation of CFC alternatives and industrial emissions. Biological degradation of some fluorochemicals is expected to be a potential TFA source. For the first time, we assess if the potential precursors [6:2 fluorotelomer alcohol (6:2 FTOH), 4:2 fluorotelomer alcohol (4:2 FTOH), acrinathrin, trifluralin, and 2-(trifluoromethyl)acrylic acid (TFMAA)] can be biologically degraded to TFA. Results show that 6:2 FTOH was terminally transformed to 5:3 polyfluorinated acid (5:3 FTCA; 12.5 mol%), perfluorohexanoic acid (PFHxA; 2.0 mol%), perfluoropentanoic acid (PFPeA; 1.6 mol%), perfluorobutyric acid (PFBA; 1.7 mol%), and TFA (2.3 mol%) by day 32 in the landfill soil microbial culture system. 4:2 FTOH could remove multiple -CF₂ groups by microorganisms and produce PFPeA (2.6 mol%), PFBA (17.4 mol%), TFA (7.8 mol%). We also quantified the degradation products of TFMAA as PFBA (1.3 mol%) and TFA (6.3 mol%). Furthermore, we basically analyzed the biodegradation contribution of short-chain FTOH as raw material residuals in commercial products to the TFA burden in the environmental media. We estimate global emission of 3.9-47.3 tonnes of TFA in the period from 1961 to 2019, and project 3.8-46.4 tonnes to be emitted from 2020 to 2040 via the pathway of 4:2 and 6:2 FTOH biodegradation (0.6-7.1 and 0.6-7.0 tonnes in China, respectively). Direct evidence of the experiments indicates that biodegradation of fluorochemicals is an overlooked source of TFA and there are still some unspecified mechanisms of TFA production pathways.

Phototransformation of perfluorooctane sulfonamide on natural clay minerals: A likely source of short chain perfluorocarboxylic acids

In this study, a new phototransformation pathway for perfluorooctane sulfonamide (FOSA) and underlying degradation mechanisms are described. Phototransformation of FOSA in a natural clay mineral (montmorillonite) suspension was compared to that in an aqueous solution. Results showed that the presence of montmorillonite can significantly promote the transformation of FOSA to perfluocarboxylic acids (increasing rate). The phototransformation reaction was found to be initiated by the activation of adsorbed oxygen molecules on the surface of montmorillonite, which generate superoxide anion and hydroxyl radicals. Hydroxyl radicals can then attack FOSA adsorbed onto the surface of montmorillonite, promoting the transformation process. In this reaction, clay minerals played a dual role: providing hydroxyl radicals and concentrating FOSA on their surfaces. This helped to promote the contact and reaction between FOSA and hydroxyl radicals. This study provides the first evidence that heterogeneous oxidation of FOSA at the surface of natural clay minerals may act as an important source of perfluocarboxylic acids (PFCAs), especially short chain PFCAs (i.e. trifluoroacetic acid, TFA).

Challenges in the analytical determination of ultra-short-chain perfluoroalkyl acids and implications for environmental and human health

Ultra-short-chain perfluoroalkyl acids have recently gained attention due to increasing environmental concentrations being observed. The most well-known ultra-short-chain perfluoroalkyl acid is trifluoroacetic acid (TFA) which has been studied since the 1990s. Potential sources and the fate of ultra-short-chain perfluoroalkyl acids other than TFA are not well studied and data reporting their environmental occurrence is scarce. The analytical determination of ultra-short-chain perfluoroalkyl acids is challenging due to their high polarity resulting in low retention using reversed-phase liquid chromatography. Furthermore, recent studies have reported varying extraction recoveries in water samples depending on the water matrix and different methods have been suggested to increase the extraction recovery. The present review gives an overview of the currently used analytical methods and summarizes the findings regarding potential analytical challenges. In addition, the current state of knowledge regarding TFA and other ultra-short-chain perfluoroalkyl acids, namely perfluoropropanoic acid, trifluoromethane sulfonic acid, perfluoroethane sulfonic acid, and perfluoropropane sulfonic acid‚ are reviewed. Both known and potential sources as well as environmental concentrations are summarized and discussed together with their fate and the environmental and human implications.

Distribution characteristics of trifluoroacetic acid in the environments surrounding fluorochemical production plants in Jinan, China

Trifluoroacetic acid (TFA) is a ubiquitous and extremely stable contaminant in the ambient environment and may be discharged during fluorochemical production processes. However, the impacts of fluorochemical production on surrounding areas have seldom been evaluated. We focused on Jinan, the capital of Shandong Province, China, and measured TFA levels in water, soil, and air samples. Our results showed that the average TFA concentrations in flowing water bodies were lower than those in landscape water bodies. The average TFA concentrations in soils were significantly higher than the background concentration. As for atmospheric TFA levels, the mean concentrations in the gas phase were higher than those in the particle phase, and average daytime levels were slightly higher than nighttime levels. In addition, the quotient method was used to assess the ecological risk of TFA in water in Jinan. The ratio of pollutant environmental concentration to predicted no-effect concentration (PEC/PNEC) for TFA was greater than 1, indicating that TFA does potentially damage the aquatic ecosystem of Jinan. Our findings suggest that TFA pollution around fluoride production plants is a serious problem and that actions are required to avoid exacerbating the local ecological and environmental risks of TFA.

Ultra-Short-Chain Perfluoroalkyl Acids Including Trifluoromethane Sulfonic Acid in Water Connected to Known and Suspected Point Sources in Sweden

Data presenting the environmental occurrence of ultra-short-chain perfluoroalkyl acids (PFAAs) are scarce and little is known about the potential sources. In this study, ultra-short-chain PFAAs were analyzed in water connected to potential point sources using supercritical fluid chromatography coupled with tandem mass spectrometry. Samples (n = 34) were collected in connection with firefighting training sites, landfills, and a hazardous waste management facility. Ultra-short-chain PFAAs were detected in all samples at concentrations up to 84 000 ng/L (∑C1-C3), representing up to 69% of the concentration of 29 per- and polyfluoroalkyl substances (PFASs). Trifluoroacetic acid (TFA), perfluoropropanoic acid (PFPrA), trifluoromethane sulfonic acid (TFMS), perfluoroethane sulfonic acid (PFEtS), and perfluoropropane sulfonic acid (PFPrS) were detected at concentrations up to 14 000, 53 000, 940, 1700, and 15 000 ng/L, respectively. Principal component analysis suggests that TFA is associated with landfills. PFPrS was associated with samples collected close to the source at all types of sites included in this study. These findings reveal the presence of high concentrations of ultra-short-chain PFAAs released into the environment from various sources and emphasize the large fraction of ultra-short-chain PFAAs to the total concentration of PFASs in water.

The contribution of fluoropolymer thermolysis to trifluoroacetic acid (TFA) in environmental media

The source of trifluoroacetic acid (TFA) has long been a controversial issue. Fluoropolymer thermolysis is expected to be a potential anthropogenic source except for CFC alternatives. However, its TFA yield and contributions have rarely been reported more recently. In this study, we investigated the thermal properties of three kinds of fluoropolymers, including poly (vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP), poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) and poly (tetrafluoroethylene) (PTFE). A laboratory simulation experiment was then performed to analyze the TFA levels in the thermolysis products and hence to examine the TFA yields of these fluoropolymers. Thermolysis of these fluoropolymers occurred in the temperature ranges from ∼400 °C to ∼650 °C, with the peak weight loss rate at around 550-600 °C. TFA could be produced through fluoropolymer thermolysis when being heated to 500 °C and above. Average TFA yields of PTFE, PVDF-HFP and PVDF-CTFE were 1.2%, 0.9% and 0.3%, respectively. Furthermore, the contribution of fluoropolymer thermolysis and CFC alternatives to rainwater TFA in Beijing, China was evaluated by using a Two-Box model. The degradation of fluoropolymers and HCFCs/HFCs could explain 37.9-43.4 ng L^-1 rainwater TFA in Beijing in 2014. The thermolysis of fluoropolymers contributed 0.6-6.1 ng L^-1 of rainwater TFA, accounting for 1.6-14.0% of the TFA burden from all the precursors which were considered here.

Per- and polyfluoroalkyl substances (PFASs) in precipitation from mainland China: Contributions of unknown precursors and short-chain (C2C3) perfluoroalkyl carboxylic acids

A nationwide survey was conducted on per- and polyfluoroalkyl substances (PFASs) in precipitation across mainland China. Twenty-two PFASs, including precursors to perfluoroalkyl acids (pre-PFAAs), were investigated in thirty-nine precipitation samples collected from twenty-eight cities. Trifluoroacetate (TFA), perfluorooctanoic acid, and perfluorooctane sulfonic acid (PFOS) were ubiquitous in precipitation. TFA displayed the highest concentrations (8.8-1.8 × 10³ ng/L), which were particularly elevated in coastal cities. 6:2 chlorinated polyfluorinated ether sulfonic acid, an alternative to PFOS, was detected for the first time in precipitation at a frequency of 43%. Polyfluoroalkyl phosphoric acid diesters and 6:2 fluorotelomer sulfonic acid were also occasionally detected. PFAS fluxes in the northeastern area (C4C12; 2.0 × 10²-3.4 × 10³ ng/m²/d) with major PFAS manufacturing facilities were higher than those in the southwestern area (63-1.7 × 10³ ng/m²/d). Using total oxidizable precursor (TOP) assay, the occurrence of unknown pre-PFAAs was for the first time uncovered in precipitation with maximum estimated fluxes of C6 and C8 pre-PFAAs at 3.1 × 10³ and 4.3 × 10³ ng/m²/d, respectively. The relative contribution of ultrashort-chain PFCAs (C2C3) ranged from 22% to 91% of ∑PFASs, while unknown pre-PFAAs accounted for 6%-56% of the total molar concentrations of PFASs. This bears critical concerns on underestimation of PFAS mass load from precipitation to surface environment ascribed to monitoring data solely on known PFASs. Unknown precursors of PFAAs in the atmosphere are yet to be identified for their chemical structures and relevant environmental risks as well.

Uptake mechanisms of perfluoroalkyl acids with different carbon chain lengths (C2-C8) by wheat (Triticum acstivnm L.)

Organic compounds could be taken up by plants via different pathways, depending on chemical properties and biological species, which is important for the risk assessment and risk control. To investigate the transport pathways of perfluoroalkyl acids (PFAAs) by wheat (Triticum acstivnm L.), the uptake of five perfluoroalkyl carboxylic acids (PFCAs): TFA (C2), PFPrA (C3), PFBA (C4), PFHxA (C6), PFOA (C8), and a perfluoroalkyl sulfonic acid: PFOS (C8)) were studied using hydroponic experiments. Various inhibitors including a metabolic inhibitor (Na₃VO₄), two anion channel blockers (9-AC, DIDS), and two aquaporin inhibitors (AgNO₃, glycerol) were examined. The wheat root and shoot showed different concentration trends with the carbon chain length of PFAAs. The uptake of TFA was inhibited by Na₃VO₄ and 9-AC whereas PFPrA was inhibited by Na₃VO₄, AgNO₃ and 9-AC. For the other four PFAAs, only Na₃VO₄ was effective. These results together with the result of concentration-dependent uptake, which followed the Michaelis-Menten model, indicate that the uptake of PFAAs by wheat is mainly an energy-dependent active process mediated by carriers. For the ultra-short chain PFCAs (C2 and C3), aquaporins and anion channels may also be involved. A competition between TFA and PFPrA was determined during the plant uptake but no competition was observed between these two shorter chain analogues with other analogues, neither between PFBA and PFHxA, PFBA and PFBS, PFOA and PFOS.

Robust trace analysis of polar (C2-C8) perfluorinated carboxylic acids by liquid chromatography-tandem mass spectrometry: method development and application to surface water, groundwater and drinking water

A simple and robust analytical method for the determination of perfluorinated carboxylic acids (PFCAs) with C₂ to C₈ chains, based on solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), was developed, validated and applied to tap water, groundwater and surface water. Two stationary phases for LC (Obelisc N and Kinetex C₁₈) and two materials with weak anion-exchange properties for SPE (Strata X-AW and Oasis WAX) were evaluated. Robust separation and retention was achieved with the reversed phase column and an acidic eluent. Quantitative extraction recoveries were generally achieved for PFCAs with C > 3, but extraction efficiencies were different for the two shortest chained analytes: 36 to 114% of perfluoropropanoate (PFPrA) and 14 to 99% of trifluoroacetate (TFA) were recovered with Strata X-AW, while 93 to 103% of PFPrA and 40 to 103% of TFA were recovered with Oasis WAX. The sample pH was identified as a key parameter in the extraction process. One-step elution-filtration was introduced in the workflow, in order to remove sorbent particles and minimise sample preparation steps. Validation resulted in limits of quantification for all PFCAs between 0.6 and 26 ng/L. Precision was between 0.7 and 15% and mean recoveries ranged from 83 to 107%. In groundwater samples from sites impacted by per- and polyfluoroalkyl substances (PFASs), PFCA concentrations ranged from 0.056 to 2.2 μg/L. TFA and perfluorooctanoate were the predominant analytes. TFA, however, revealed a more ubiquitous occurrence and was found in concentrations between 0.045 and 17 μg/L in drinking water, groundwater and surface water, which were not impacted by PFASs.

Distribution of trifluoroacetic acid in gas and particulate phases in Beijing from 2013 to 2016

Trifluoroacetic acid (TFA) was measured at an urban site in Beijing from April 2013 to April 2016 and examined its characteristics and particle/gas distributions. The average monthly atmospheric TFA concentration fluctuated significantly and presented marked seasonal variations. The concentration levels of gas-phase TFA were significantly higher in spring and summer than in fall and winter. The PM_2.5 mass concentration and ambient temperature were important factors affecting the concentration of particulate-phase TFA. Hence, at higher PM_2.5 concentrations and lower temperatures, atmospheric TFA tended to be enriched in particulate matter. Our findings suggest that the percentage of gas-phase TFA in Beijing is higher than that in the steady state; thus, gas-phase TFA can still be transformed to the particulate phase and increase the contribution of TFA to haze formation.

Multimedia Distribution and Transfer of Per- and Polyfluoroalkyl Substances (PFASs) Surrounding Two Fluorochemical Manufacturing Facilities in Fuxin, China

Industrial facilities can be point sources of per- and polyfluoroalkyl substances (PFASs) emission to the surrounding environment. In this study, 25 neutral and ionizable PFASs were analyzed in 94 multimedia samples including air, rain, outdoor settled dust, soil, plant leaves, river water, surface sediment, and shallow groundwater from two fluorochemical manufacturing parks (FMPs) in Fuxin, China, to elucidate the multimedia distribution and transfer pattern of PFASs from a point source. The concentrations of individual PFASs in air, outdoor settled dust, and surface river water decreased exponentially as the distance increases from the FMPs, whereas the concentrations of short-chain (C2-C4) perfluoroalkyl carboxylic acids (PFCAs) remained high (3000 ng/L) in the surface water 38 km away. At FMPs, air concentrations of fluorotelomer alcohols and iodides were found dominant with levels of up to 7900 pg/m³ and 920 pg/m³, respectively. Trifluoroacetic acid was directly released from FMPs and occurred in all the environmental matrices at levels 1-2 orders of magnitude higher than other PFCAs. Higher air-water concentration ratios of short-chain PFCAs (C2-C4) suggested their transfer tendency from air to water. Both short-chain (C2) and long-chain (>C6) PFCAs have greater sediment-water distribution coefficients and deposit dust-air coefficients, which have great influences on the long-range transport potential of different analogues.

Occurrence and Phase Distribution of Neutral and Ionizable Per- and Polyfluoroalkyl Substances (PFASs) in the Atmosphere and Plant Leaves around Landfills: A Case Study in Tianjin, China

A total of 23 per- and polyfluoroalkyl substances (PFASs) were investigated in the air, dry deposition, and plant leaves at two different landfills and one suburban reference site in Tianjin, China. The potential of landfills as sources of PFASs to the atmosphere and the phase distribution therein were evaluated. The maximum concentrations of ∑PFASs in the two landfills were up to 9.5 ng/m³ in the air, 4.1 μg/g in dry deposition, and 48 μg/g lipid in leaves with trifluoroacetic acid and perfluoropropionic acid being dominant (71%-94%). Spatially, the distribution trend of ionizable and neutral PFASs in all three kinds of media consistently showed the central landfill > the downwind > the upwind > the reference sites, indicating that landfills are important sources to PFASs in the environment. Plant leaves were found effective in uptake of a variety of airborne PFASs including polyfluoroalkyl phosphoric acid diesters, thus capable of acting as a passive air sampling approach for air monitoring.

Dynamic and thermodynamic mechanisms of TFA adsorption by particulate matter

Trifluoroacetic acid (TFA) in the atmosphere is produced by degradation of hydrochlorofluorocarbons and hydrofluorocarbons. In recent years, TFA has attracted global attention because of increased environmental concentrations, biological toxicity and accumulation in aqueous environments. This study focused on the mechanisms underlying the adsorption of TFA by particulate matter to identify the appropriate descriptive model for this process and thus improve estimation of TFA adsorption in future environmental monitoring. Onsite gas and particle phase sampling in Beijing, China, and subsequent measurement of TFA concentrations indicated that the TFA concentration in the gas phase (1396 ± 225 pg m^-3) was much higher than that in the particle phase (62 ± 8 pg m^-3) and that monthly concentrations varied seasonally with temperature. Based on the field results and analysis, an adsorption experiment of TFA on soot was then conducted at three different temperatures (293, 303, and 313 K) to provide parameters for kinetic and thermodynamic modelling. The proportion of atmospheric TFA concentration in the gas phase increased with temperature, indicating that temperature affected the phase distribution of TFA. The subsequent kinetic and thermodynamic modelling showed that the adsorption of TFA by soot could be described well by the Bangham kinetic model. The adsorption was controlled by diffusion, and the key mechanism was physical adsorption. The adsorption behavior can be well described by the Langmuir isotherm model. The calculated thermodynamic parameters ΔG° (-2.34, -1.25, and -0.15 kJ mol^-1 at 293, 303, and 313 K, respectively), ΔH° (-34.34 kJ mol^-1), and ΔS° (-109.22 J mol^-1 K^-1) for TFA adsorption by soot were negative, indicating that adsorption was a spontaneous, exothermic process.

Sources, fates, toxicity, and risks of trifluoroacetic acid and its salts: Relevance to substances regulated under the Montreal and Kyoto Protocols

Trifluoroacetic acid (TFA) is a breakdown product of several hydrochlorofluorocarbons (HCFC), regulated under the Montreal Protocol (MP), and hydrofluorocarbons (HFC) used mainly as refrigerants. Trifluoroacetic acid is (1) produced naturally and synthetically, (2) used in the chemical industry, and (3) a potential environmental breakdown product of a large number (>1 million) chemicals, including pharmaceuticals, pesticides, and polymers. The contribution of these chemicals to global amounts of TFA is uncertain, in contrast to that from HCFC and HFC regulated under the MP. TFA salts are stable in the environment and accumulate in terminal sinks such as playas, salt lakes, and oceans, where the only process for loss of water is evaporation. Total contribution to existing amounts of TFA in the oceans as a result of the continued use of HCFCs, HFCs, and hydrofluoroolefines (HFOs) up to 2050 is estimated to be a small fraction (<7.5%) of the approximately 0.2 μg acid equivalents/L estimated to be present at the start of the millennium. As an acid or as a salt TFA is low to moderately toxic to a range of organisms. Based on current projections of future use of HCFCs and HFCs, the amount of TFA formed in the troposphere from substances regulated under the MP is too small to be a risk to the health of humans and environment. However, the formation of TFA derived from degradation of HCFC and HFC warrants continued attention, in part because of a long environmental lifetime and due many other potential but highly uncertain sources.