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Pesticides, Organic Contaminants, and Pathogens in Air
anthropogenic/industrial origin” (Jordan and Frank, 1999). This result was
reinforced by Nielsen et al. (2001), who studied ancient fresh water, from both
groundwater and Greenland ice cores, and found undetectable concentrations of TFA. In another study, ancient spring water also had no detectable
TFA in it (<5 ng/L) (Berg et al., 2000). However, Von Sydow et al. (2000) measured Antarctic ice cores and detected relatively high concentrations of TFA
in ice that predates the industrial age, so they concluded that there must be a
natural source of TFA. Additionally, studies of ocean water columns showed
consistent concentrations of TFA near 200 ng/L even in deep seawater greater
than 60 years old (Frank et al., 2002). The authors conclude that the freshwater
TFA is predominately anthropogenic in origin while the TFA in seawater
arises from some natural source that concentrates in the ocean due to TFA’s
great stability. Additional ocean research has confrmed relatively high TFA
concentrations in deep ocean water that predated the industrial age (Scott
et al., 2005). This research also sampled water over deep-sea geothermal
vents that showed elevated TFA, which suggests that deep-sea geothermal
vents are a source of TFA. Some fuorinated organics have been detected in
fuorite and volcanic rocks (Harnisch et al., 2000), but the fuorinated compounds identifed so far have been limited to single carbon or single sulfur
molecules that lack the ability to form TFA.
9.4 Chemistry of TFA
As with all chemicals, the physicochemical properties of TFA dictate its fate
and transport in organisms and the environment.
9.4.1 Acidity
The frst and most important characteristic of TFA is its strong acidity that
causes it to be an ion under environmental conditions. This strong acidity, as
quantifed by the low pK a of TFA (Table 9.1), is due to the electron-withdrawing
fuorines in the molecule. When comparing acetic acid to the TFA series of
compounds, it is clear that each fuorine addition lowers the pK a and therefore makes a stronger acid.
The low pK a for TFA means that it will readily ionize in water under
almost any environmental condition to become the trifuoroacetate ion,
which has several implications for its environmental fate and transport.
If TFA is generated in the atmosphere, it will partition to water (rain,
fog), ionize, and be washed out of the atmosphere. Bowden et al. (1996)
measured the Henry’s law constant for TFA (K H = 8,950 ± 100 mol/kg/atm
at 298 K) and determined that the ionization of TFA was the main property that causes TFA to partition into atmospheric water where it could be
Pesticides, Organic Contaminants, and Pathogens in Air
anthropogenic/industrial origin” (Jordan and Frank, 1999). This result was
reinforced by Nielsen et al. (2001), who studied ancient fresh water, from both
groundwater and Greenland ice cores, and found undetectable concentrations of TFA. In another study, ancient spring water also had no detectable
TFA in it (<5 ng/L) (Berg et al., 2000). However, Von Sydow et al. (2000) measured Antarctic ice cores and detected relatively high concentrations of TFA
in ice that predates the industrial age, so they concluded that there must be a
natural source of TFA. Additionally, studies of ocean water columns showed
consistent concentrations of TFA near 200 ng/L even in deep seawater greater
than 60 years old (Frank et al., 2002). The authors conclude that the freshwater
TFA is predominately anthropogenic in origin while the TFA in seawater
arises from some natural source that concentrates in the ocean due to TFA’s
great stability. Additional ocean research has confrmed relatively high TFA
concentrations in deep ocean water that predated the industrial age (Scott
et al., 2005). This research also sampled water over deep-sea geothermal
vents that showed elevated TFA, which suggests that deep-sea geothermal
vents are a source of TFA. Some fuorinated organics have been detected in
fuorite and volcanic rocks (Harnisch et al., 2000), but the fuorinated compounds identifed so far have been limited to single carbon or single sulfur
molecules that lack the ability to form TFA.
9.4 Chemistry of TFA
As with all chemicals, the physicochemical properties of TFA dictate its fate
and transport in organisms and the environment.
9.4.1 Acidity
The frst and most important characteristic of TFA is its strong acidity that
causes it to be an ion under environmental conditions. This strong acidity, as
quantifed by the low pK a of TFA (Table 9.1), is due to the electron-withdrawing
fuorines in the molecule. When comparing acetic acid to the TFA series of
compounds, it is clear that each fuorine addition lowers the pK a and therefore makes a stronger acid.
The low pK a for TFA means that it will readily ionize in water under
almost any environmental condition to become the trifuoroacetate ion,
which has several implications for its environmental fate and transport.
If TFA is generated in the atmosphere, it will partition to water (rain,
fog), ionize, and be washed out of the atmosphere. Bowden et al. (1996)
measured the Henry’s law constant for TFA (K H = 8,950 ± 100 mol/kg/atm
at 298 K) and determined that the ionization of TFA was the main property that causes TFA to partition into atmospheric water where it could be