The stable form of TFA in the environment is the trifluoroacetate ion (CF3COO-) which will be combined with counter-ions such as sodium, in seawater, or calcium or ammonium inland, to form neutral salts. However, "TFA" is used as generic shorthand for trifluoroacetic acid and its salts.

TFA is a naturally occurring chemical. Over 200,000,000 tonnes is present in the oceans, having apparently accumulated over many million years from chemical reactions in or around sub-sea volcanic vents.[1][2]

TFA is not confined to the oceans. Samples of fog, rain, river and lake water analysed during the 1990s contained concentrations ranging from tens to tens of thousands of ng litre-1, with a typical European level of 100 ng litre-1 (found in German rainwater) in 1995.[3] At that time, the only man-made precursor present in the atmosphere was HFC-134a, at a concentration which would have sustained a global average concentration of TFA in precipitation of only 2 ng litre-1. There were no other significant man-made potential sources.

A probable global natural cycle for TFA would involve transport from the oceans in the sea-salt aerosol, subsequent evaporation (as trifluoroacetic acid) and long range transport before deposition in rainwater. The concentrations measured in the 1990s indicate that some 36,000 tonnes/year are transported into the atmosphere from the ocean surface. Most of this is directly returned to the ocean in precipitation but about 4000 tonnes/year is transported over land and returned to the seas in river water.

Atmospheric breakdown of some of the fluorocarbons already in wide use - HCFC-123 (CF3CHCl2), HCFC-124 (CF3CHFCl), HFC-134a (CF3CH2F) and HFC-227ea (CF3CHFCF3) - and some that may be used in the future - HFO-1234yf (CF3CF=CH2) - may produce traces of trifluoroacetyl halides (CF3COCl or CF3COF) in the atmosphere. The trifluoroacetyl halides will hydrolyse in environmental water to augment the existing TFA burden.

There are no recent reports of determinations of environmental concentrations of TFA. If emissions of the fluorocarbons are actually making a contribution to the global flux, TFA levels might be expected to be greater over a wide area than those seen in the 1990s.

The processes of TFA transport or formation make a negligible contribution to acid rain. There is no significant addition to the chloride and fluoride already present in the biosphere from natural sources.

Based on current knowledge, the very low concentrations of TFA from the combination of the natural flux and alternative fluorocarbons are not likely to have an impact on any of the wide range of organisms studied to date, which includes humans, animals, plants and microorganisms.

TFA appears to be resistant to biodegradation by the majority of natural or laboratory microbial systems that have been tested. However, laboratory study has shown that certain bacteria, under special conditions, can degrade TFA.

An overall environmental risk assessment has been conducted on the basis of the data generated by the TFA studies. The results are published in Human and Ecological Risk Assessment[3].

Does trifluoroacetate break down in the environment?

        TFA appears to be very resistant to degradation by non-biological physicochemical processes. Its light-absorption properties make it resistant to photochemical breakdown. Other physicochemical loss processes that have been studied are extremely slow under environmental conditions. TFA salts are highly soluble and will not precipitate from solution at concentrations expected in the environment. Thus, the stability and solubility of TFA suggest that it will tend to remain dissolved in water. The bulk of existing data suggests that TFA is resistant to biodegradation in natural environments. However, certain bacterial strains maintained in the laboratory have been shown to degrade TFA with release of carbon dioxide. The fate of the fluorine atoms in this process is unknown.

Are living organisms affected by environmental trifluoroacetate?

        Tests have shown that mammals are not affected by TFA at concentrations many thousands of times higher than expected in the environment. With humans, some fluorinated drugs break down in the human body to form trifluoroacetate, which is rapidly excreted. Tests with fish and crustaceans show these organisms are also highly resistant to TFA. Because TFA has very low affinity for lipids (fatty materials), there is no potential for passive accumulation in fatty tissues, even after long exposure at low levels.

        Microorganisms that have been tested do not actively concentrate TFA from the environment. TFA does not inhibit the growth of bacteria and most of the algae tested, even at high concentrations. The growth of one species of alga was inhibited by TFA at concentrations about 1000 times above those expected in rain and snow.

        AFEAS-sponsored research has shown that plants take up TFA through the roots as well as through leaf surfaces. Trifluoroacetate has no known toxicity to plants at the concentrations at which it is expected to be deposited in rain and snow. In prolonged exposure, however, at concentrations several thousands of times greater than these levels, TFA inhibits plant growth and development.

        These findings were recently confirmed by the Environmental Effects Panel of the Montreal Protocol which concluded: "[T]he decomposition of substitutes for ozone-depleting substances can lead to a range of chemical species, however with little relevance expected for human health and the environment. The hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) used as substitutes for ozone-depleting CFCs can break down into trifluoroacetic acid (TFA), which is very stable and will accumulate in the oceans, salt lakes, and playas. However, based on historical use and projections of future uses, including new products entering the market such as the fluoro-olefins, increased loadings of TFA and monofluoracetic acid (MFA) in these environmental sinks will be small. Even when added to existing amounts from natural sources, risks from TFA (and the more toxic MFA) to humans and organisms in the aquatic environment are judged to be negligible.^[4]

TFA Risk Assessment

An overall environmental risk assessment has been conducted on the basis of the data generated by studies in the 1990s. A summary is provided below. The results of the risk assessment and several review articles are published in the peer-reviewed literature.

Trifluoroacetic acid is a strong organic acid with a pKa of 0.23. It is miscible with water and its low octanol/water partition coefficient (log Pow = -2.1) indicates no potential to bioaccumulate.

When the risk assessment was conducted, the natural reservoir of TFA had not been discovered and the reported environmental concentrations were not considered to be natural. Consequently the assessment was based on the assumption that all TFA would be from man- made precursors.

Industrial use of TFA is limited and environmental releases are very low. In addition to the natural flux, some TFA will be formed from the breakdown of a few halogenated hydrocarbons, most notably HFC-134a (CF3CH2F), HCFC-124 (CF3CHFCl) and HCFC-123 (CF3CHCl2). When the assessment was carried out, these substances had been produced only in limited commercial quantities and their contribution to environmental levels was minimal. Surprisingly, environmental measurements at that time in diverse locations showed existing levels of 100 to 300 ng.l-1 in water with one site (Dead Sea) having a level of 6400 ng.l-1. These levels could not be accounted for based on current atmospheric sources and implied the long-term, pre-industrial source that was subsequently found.

Generally, soil retention of TFA is poor although soils with high levels of organic matter have been shown to have a greater affinity for TFA when contrasted to soils with low levels of organic matter. This appears to be an adsorption phenomenon, not irreversible binding. Therefore, TFA will not be retained in soil, but will ultimately enter the aqueous compartment.

Modeling of emission rates and subsequent conversion rates for precursors led to estimates of additional levels of TFA in rain water in the region of 0.1 g.l-1 in the year 2020. Subsequently, the natural flux was identified as being similar in size.

There do not seem to be any recent determinations of environmental TFA concentrations over a large enough geographical area to be able to link release of fluorocarbons to changes in the TFA flux. Nevertheless, the calculated current and future concentrations are within the range of effects studied in the risk assessment.

TFA is resistant to both oxidative and reductive degradation. While there had been speculation regarding the possibility of TFA being degraded into monofluoroacetic acid (MFA), the rate of breakdown of MFA is so much higher than for TFA that any MFA formed would rapidly degrade. Thus, there would be no buildup of MFA regardless of the levels of TFA present in the environment.

Although highly resistant to microbial degradation, there have been reports of TFA degradation under anaerobic conditions. In one study, natural sediments reduced TFA. However, even though this work was done in replicate, the investigators and others were unable to reproduce it in subsequent studies. In another, radiolabeled TFA was removed from a mixed anaerobic in vitro microcosm. Limited evidence of decarboxylation has also been reported for two strains of bacteria grown under highly specific conditions. TFA was not biodegraded in a semi-continuous activated sludge test even with prolonged incubation (up to 84 days). A third study, reported after the risk assessment, showed anaerobic degradation by methanogenic bacteria in a laboratory reaction system.

TFA does not accumulate significantly in lower aquatic life forms such as bacteria, small invertebrates, oligochaete worms and some aquatic plants including Lemna gibba (duckweed). Some bioaccumulation was observed in terrestrial higher plants, such as sunflower and wheat. This result appeared to be related to uptake with water and then concentration due to transpiration water loss. When transferred to clean hydroponic media, some elimination of TFA was seen. Also, more than 80% of the TFA in leaves was found to be water extractable, suggesting that no significant metabolism of TFA had occurred.

At an exposure level of 1200 mg.l-1 of sodium trifluoroacetate (NaTFA) - corresponding to 1000 mg.l-1 HTFA - no effects were seen on either Brachydanio rerio (a fish) or Daphnia magna (a water flea). With duckweed, mild effects were seen on frond increase and weight increase at the same exposure level. At a concentration of 300 mg.l-1 no effects were observed. Toxicity tests were conducted with 11 species of algae. For ten of these species the EC50 was greater than 100 mg.l-1. In Selenastrum capricornutum the no-effect level was 0.12 mg.l-1. At higher levels the effect was reversible. The reason for the unique sensitivity of this strain is unknown, but a recovery of the growth rate was seen when citric acid was added. This could imply a competitive inhibition of the citric acid cycle.

The effect of TFA on seed germination and plant growth has been evaluated with a wide variety of plants. Application of NaTFA at 1000 mg.l-1 to seeds of sunflower, cabbage, lettuce, tomato, mung bean, soy bean, wheat, corn, oats and rice did not affect germination. Foliar application of a solution of 100 mg.l-1 of NaTFA to field grown plants did not affect growth of sunflower, soya, wheat, maize, oilseed rape, rice and plantain. When plantain, wheat (varieties Katepwa and Hanno) and soya were grown in hydroponic systems containing NaTFA, no effects were seen on plantain at 32 mg.l-1, on wheat (Katepwa) and soya at 1 mg.l-1, or on wheat (Hanno) at 10 mg.l-1; some effects on growth were seen at, respectively, 100 mg.l-1, 5 mg.l-1, 5 mg.l-1 and 10 mg.l-1 and above.

TFA is not metabolized in mammalian systems to any great extent. It is the major final metabolite of halothane, HCFC-123 and HCFC-124. The half-life of TFA in humans is 16 hours. As expected, the acute oral toxicity of the free acid is higher than that of its sodium salt. The inhalation LC50 (2 hour exposure) for mice was 13.5 mg.l-1 (2900 ppm) and for rats it was 10 mg.l-1 (2140 ppm). Thus, TFA is considered to have low inhalation toxicity. The irritation threshold for humans was 54 ppm.

As one would expect of a strong acid, it is a severe irritant to the skin and eye. When conjugated with protein, it has been shown to elicit an immunological reaction; however, it is unlikely that TFA itself would elicit a sensitization response. Repeat administration of aqueous solutions have shown that TFA can cause increased liver weight and induction of peroxisomes. Relative to the doses (0.5% in diet or 150 mg.kg-1.day-1 by gavage) the effects are mild.

In a series of Ames assays, TFA was reported to be non-mutagenic. Its carcinogenic potential has not been evaluated. Although TFA was shown to accumulate in amniotic fluid following exposure of pregnant animals to high levels of halothane (1200 ppm), no fetal effects were seen. Likewise, a reproduction study that involved exposure of animals to halothane at levels up to 4000 ppm for 4 hours per day, 7 days per week, resulted in no adverse effects. Given the high levels of halothane exposure, it is unlikely that environmental TFA is a reproductive or developmental hazard.

        Overall the toxicity of TFA has been evaluated in stream mesocosms, algae, higher plants, fish, animals and humans. It has been found to be of very low toxicity in all of these systems. The lowest threshold for any effects was the reversible effect on growth of one strain of algae, Selenastrum capricornutum, which was seen at 0.12 mg.l^-1. There is a 1000-fold difference between the no-effect concentration and the projected environmental levels of TFA from HFCs and HCFCs (0.0001 mg.l^-1). Based on available data, one can conclude that environmental levels of TFA resulting from the breakdown of alternative fluorocarbons do not pose a threat to the environment.

TFA and Seasonal Wetlands

        Studies of enclosed river and lake systems, where the main loss of water is by evaporation from the terminal lake have shown significant enhancement of TFA concentrations in the receiving water body^1 2. In this, TFA is no different from other ionic and relatively involatile species and, if the only loss is by evaporation, as in the Dead Sea, the receiving water becomes saturated with salts.

        However, it was hypothesised that accumulation due to evaporation might be problematic in seasonal wetlands, such as vernal pools, where the same patch of ground is flooded in the winter and spring and then evaporates to dryness in summer³. The theory was that TFA would be preserved in this area and that the concentration would ratchet upwards as each year's dose from the atmosphere was incorporated into the ecosystem. There is no evidence that this happens with, for example, chloride ion which has similar physical properties to TFA and is present in much larger amounts.

        The hypothesis has been shown to be unfounded. Studies of vernal pool systems in California over two years showed that there was an increase in concentration as the pool dried out but, although there was also an increase in concentration from one year to the next, it was well within the range of normal variability for this region⁴. Furthermore, field microcosm studies in Guelph (Canada) did not show the same year-on-year enhancement in TFA concentration and also that this fell at cooler temperatures, perhaps indicating partitioning into a non-aqueous compartment of the ecosystem⁵. Neither of these studies found any adverse effects on the ecosystems and this was replicated by Benesch and colleagues⁶, who studied the effects of concentrations up to 10,000,000 ng litre^-1, or many thousand times the typical environmental concentrations reported.

        AFEAS sponsored the studies that led to the original hypothesis^3 7 8 but had no involvement in the work that disproved it.

AFEAS Research on Trifluoroacetic Acid

        The Alternative Fluorocarbons Environmental Acceptability Study (AFEAS) committed more than 1 million U.S. dollars to study the environmental fate and potential effects of trifluoroacetic acid, which may be formed when certain fluorocarbons (HFC-134a, HCFC-123 or HCFC-124) decompose in the atmosphere. Based on current knowledge, TFA derived from these compounds is expected to occur in rain and snow in very low concentrations. At these concentrations, TFA is not likely to have an impact on any of the wide range of organisms studied to date, which includes humans, animals, plants and microorganisms. Because TFA has very low affinity for lipids (fatty materials), there is no potential for passive accumulation in fatty tissues, even after long exposure at low levels, thus precluding bioconcentration in the food chain.

        The results of the AFEAS program on TFA have been reviewed with academic experts at two scientific workshops and the proceedings were published by AFEAS^7 8. A final risk assessment was conducted and published in Human and Ecological Risk Assessment⁹. Independent experts were involved in the review process.