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Environmental fate & pathways

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Trifluoroacetic acid (TFA) is a strong organic acid with a pKa of around 0.43 so it will be under dissociated form in all environmental compartments.

The possible reductive and oxidative degradation of TFA has been investigated by photocatalytic experiments conducted with aqueous suspensions of semiconducting materials. TFA proved to be a rather inert compound under practically all conditions and from these experiments it can be postulated that direct and indirect photolysis are not expected to be an important transformation process for TFA in water and air. No standard test is available to assess the decomposition or degradation of TFA by reaction with water. However the hydrolysis potential of TFA is expected to be very low based on its chemical structure, the preliminary results of non standard tests and the concentrations stability observed during analytical measurements of standard biodegradation and ecotox tests. The results of standard respiration tests with activated sludge showed that trifluoroacetic acid is not readily nor inherently biodegradable and non standard tests on several bacterial stains and different substrates showed that trifluoroacetic acid is not biodegradable under aerobic conditions. Moreover, one field study investigated the degradation of TFA in field aquatic microcosms and laboratory sediment water systems. Trifluoroacetic acid was extremely persistent and showed no degradation during one-year field studies and 2880h in laboratory microsoms. Only a non assignable test showed some potential of biodegradation under anaerobic conditions.

In conclusion, TFA was found to be highly resistant to abiotic and biotic degradation and, coupled with its extreme chemical stability, these results suggest a very long lifetime for TFA in the environment.

No bioaccumulation studies obtained from established experimental protocols are available for TFA. The substance is expected to have a low potential for bioaccumulation according to its log Kow of 0.79 at 25°C. However, because of the structural similarity of TFA to acetate it was suspected that organisms might use the fluorinated compound to synthesize biomolecules and several non standard experimental studies were conducted on aquatic and terrestrial organisms. The results indicate a low level of incorporation of TFA by aquatic (microbial communities, phytoplancton, oligochaetes, macroinvertebrates,Callitriche sp., Lemna sp. and Impatiens capensis) and terrestrial (Pines, Lycopersicon esculentum, wheat and sunflower) organisms spanning a range of trophic levels. In some aquatic species, TFA was incorporated into their biomolecule fractions and thus was metabolically transformed and in some terrestrial species some evidence of TFA depuration was found on transfer to clean medium.

In conclusion, these results show that TFA does not accumulate significantly in lower aquatic life forms such as bacteria, algae, small invertebrates, oligochaete worms and some aquatic and terrestrial plants.

The Henry's Law constant (KH) for trifluoroacetic acid, 0.009 Pa.m3.mol-1, was calculated by the average of two measured values 8950 and 5800 mol.kg-1.atm-1 at 25°C reported in two valid peer reviewed studies. Standard and non standard adsortion/desorption tests results show that TFA is poorly absorbed to the soil and is considered as a mobile organic compound at the majority of soils investigated. The Kd ranged between 0.19 to 20 L/kg for organic and mineral soils (the organic horizon exhibiting greater retention) giving a geometric mean of 0.94 L/kg (SD= 4.86, n= 20). Further, TFA was added experimentally to upland and wetland forest in two field studies. More than 70% of the added TFA was exported from the upland forest in drainage water while the reminder was retained in the surface organic soil (10-20%) and vegetation (5-20%). In contrast, probably <5% of the added TFA flowed out of the forest wetland in drainage water. Considerable TFA was retained in the forest wetland soil (20 -60%) and vegetation (20-50%). With such results and because trifluoroacetic acid is totally miscible with water and has a log Kow value of 0.79 at 25°C, the preferred environmental compartment will be water, rather than air, ground or biota.

Several monitoring studies of good quality report widespreaded TFA concentrations in several environmental matrix including air, freshwaters and marine waters all around the world and tend to establish its sources. Analytical techniques for TFA have been successfully employed in several environmental matrices and at various concentrations. In Europe, TFA has been measured in samples of rainwater (<0.2-850 ng/L), surface waters (<0.2-280 ng/L), fog condensate (2154 ng/L), drinking water (<0.2-450 ng/L) and air (<3.3-3230 ng/L). In water samples from other continents (South Africa, Australia, Brasil, Israel, Siberia) concentrations ranged from 20 to 500 ng/l and in two samples, TFA could not be detected. Ocean waters contained TFA concentrations ranging from 0.5 ng/L to 250 ng/L. In one study, TFA level was independent of depth and in another study, the sampling at low depth (up to 700 -800 m) exhibited variable TFA concentrations but below this depth, the TFA concentration was constant. Supporting data obtained from several locations in North America and China give similar concentration ranges in the different environmental matrix than in Europe. Further, results indicated that washout of TFA from the lower atmosphere was observed in both rain and fog samples and that precipitation concentrations can be successfully predicted by the Henry's law constant.

Known sources of TFA include the termolysis of perfluorinated chemicals, the atmospheric oxidation of hydrochlorofluorocarbons and hydrofluorocarbons and fluorotelomer alcohols. For some authors, TFA has only recently entered the environment and arises from anthropogenic sources. The pattern of high TFA concentration values observed in industrialized countries of Europe, coupled with very low concentrations near blank values found in remote regions suggests that a significant part of TFA is produced from precursor molecules with lifetimes of less than two weeks. TFA is present in the global environment in quantities exceeding what can be explained by industrial processes and/or chemicals hitherto considered, and is far more than may be expected from a few years of HFC production. All this information suggests that there are unknown sources of TFA. However, whether anthropogenic processes such as combustion of fossil fuels have contributed to the present-day levels, or whether natural geogenic or biogenic processes are also involved remains to be clarified.