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Pesticides, Organic Contaminants, and Pathogens in Air
is highly water soluble, stable, and does not form any signifcant precipitates
or complexes.
The predominately ionic character also affects the fate of TFA within
organisms. Since TFA is a small, unreactive, ionic molecule, it will preferentially stay in the aqueous phases in animals where it can be readily excreted
by the kidneys. The easy excretion of TFA in urine prevents it from bioaccumulating in animals like PFOS or PFOA. In plants, TFA can be acquired by
direct deposition on foliage or TFA can be taken up in water and transported
to plant tissues by the xylem. When the water evaporates from a plant, or is
otherwise consumed during photosynthesis, TFA is left behind in the plant
tissues. This could lead to a steady increase in tissue concentrations over time
in the leaves. The TFA might be lost from plants by leaching into rainfall and
some plants can excrete water by guttation.
9.4.2 Stability
The second physicochemical property of TFA is that it is exceptionally stable
under most environmental conditions. Since TFA is a highly oxidized molecule, it is expected to be resistant to degradation by oxidation. Additionally,
the carbon–fuorine bond is one of the strongest single bonds found in organic
molecules, which makes it more diffcult to break. It also lacks any hydrogen
atoms that are vulnerable to hydrogen abstraction. Therefore, degradation in
the environment is expected to be very slow.
Oxidation reactions are a common means to degrade organic chemicals, but
their usefulness in degrading the highly oxidized TFA was uncertain. In the
atmosphere, the gas-phase protonated form of TFA can react with hydroxyl
radicals (OH•). The atmospheric lifetime of TFA due to the reaction with OH•
has been estimated to be about 230 days (Hurley et al., 2004), 68 days (Mogelberg
et al., 1994), and 100 days (Carr et al., 1994). Gas-phase reaction with TFA was
slower than that of other perfuorinated carboxylic acids (PFCAs) (Hurley et al.,
2004), so TFA is even more stable than other longer chain PFCAs. However,
the researchers noted that TFA would most likely be removed from the atmosphere by wet or dry deposition with a lifetime of roughly 10 days, so atmospheric oxidation of TFA is a relatively minor loss process.
TFA degradation in aqueous systems under environmental conditions is
expected to be very slow. Hydroxyl radicals in aqueous solutions are not
very reactive toward TFA; TFA was the least reactive of the haloacetic acids
(Maruthamuthu et al., 1995). Additionally, degradation of TFA in natural surface waters is likely to be slow due to the presence of other dissolved organic
matter that would more readily react with hydroxyl radicals. In microcosm
studies, there was no observed TFA degradation over 49 days, so a half-life
could not be calculated (Hanson et al., 2002). A longer, 1-year study also did
not detect any TFA degradation in pond water (Ellis et al., 2001a).
Thermal decomposition of TFA in water is likewise slow at ambient temperatures. There was no observed degradation of TFA at 90°C over 100 days
Pesticides, Organic Contaminants, and Pathogens in Air
is highly water soluble, stable, and does not form any signifcant precipitates
or complexes.
The predominately ionic character also affects the fate of TFA within
organisms. Since TFA is a small, unreactive, ionic molecule, it will preferentially stay in the aqueous phases in animals where it can be readily excreted
by the kidneys. The easy excretion of TFA in urine prevents it from bioaccumulating in animals like PFOS or PFOA. In plants, TFA can be acquired by
direct deposition on foliage or TFA can be taken up in water and transported
to plant tissues by the xylem. When the water evaporates from a plant, or is
otherwise consumed during photosynthesis, TFA is left behind in the plant
tissues. This could lead to a steady increase in tissue concentrations over time
in the leaves. The TFA might be lost from plants by leaching into rainfall and
some plants can excrete water by guttation.
9.4.2 Stability
The second physicochemical property of TFA is that it is exceptionally stable
under most environmental conditions. Since TFA is a highly oxidized molecule, it is expected to be resistant to degradation by oxidation. Additionally,
the carbon–fuorine bond is one of the strongest single bonds found in organic
molecules, which makes it more diffcult to break. It also lacks any hydrogen
atoms that are vulnerable to hydrogen abstraction. Therefore, degradation in
the environment is expected to be very slow.
Oxidation reactions are a common means to degrade organic chemicals, but
their usefulness in degrading the highly oxidized TFA was uncertain. In the
atmosphere, the gas-phase protonated form of TFA can react with hydroxyl
radicals (OH•). The atmospheric lifetime of TFA due to the reaction with OH•
has been estimated to be about 230 days (Hurley et al., 2004), 68 days (Mogelberg
et al., 1994), and 100 days (Carr et al., 1994). Gas-phase reaction with TFA was
slower than that of other perfuorinated carboxylic acids (PFCAs) (Hurley et al.,
2004), so TFA is even more stable than other longer chain PFCAs. However,
the researchers noted that TFA would most likely be removed from the atmosphere by wet or dry deposition with a lifetime of roughly 10 days, so atmospheric oxidation of TFA is a relatively minor loss process.
TFA degradation in aqueous systems under environmental conditions is
expected to be very slow. Hydroxyl radicals in aqueous solutions are not
very reactive toward TFA; TFA was the least reactive of the haloacetic acids
(Maruthamuthu et al., 1995). Additionally, degradation of TFA in natural surface waters is likely to be slow due to the presence of other dissolved organic
matter that would more readily react with hydroxyl radicals. In microcosm
studies, there was no observed TFA degradation over 49 days, so a half-life
could not be calculated (Hanson et al., 2002). A longer, 1-year study also did
not detect any TFA degradation in pond water (Ellis et al., 2001a).
Thermal decomposition of TFA in water is likewise slow at ambient temperatures. There was no observed degradation of TFA at 90°C over 100 days