158
Pesticides, Organic Contaminants, and Pathogens in Air
condensed phases, such as rain and aerosols. Therefore, the assessments of
TFA toxicity were generally conducted with the ionic form of the molecule.
More detailed reviews of the toxicology of TFA can be found in Boutonnet
et al. (1999) and Solomon et al. (2016).
The toxicity of TFA in animals is low (Table 9.2). The lack of reactivity
of TFA that makes it stable in the environment also makes it unreactive in
the body. In mammals, no toxic effects of the ionic form of TFA have been
reported at 5,000 mg/kg (Blake et al., 1969) and 2.1 mmol/kg (=237 mg/kg)
(Fraser and Kaminsky, 1988). TFA is predominately excreted from mammals
in the urine with half-lives ranging from 16 to 61 hours (Holaday, 1977). Due
to the relatively short half-life of TFA, it will not signifcantly accumulate in
animals. TFA appears to bind to carrier proteins, such as albumin, and other
macromolecules, which may be part of the reason its elimination was slower
than expected. It has been suggested that TFA may form a glucuronide conjugate in the liver only to be excreted in the bile and reabsorbed in the intestine.
This potential enterohepatic circulation might be another reason for the slow
elimination kinetics of TFA (Boutonnet et al., 1999) compared to other small,
unreactive ions. Lastly, TFA is not mutagenic (Waskell, 1978). In essence, TFA
behaves in animals as a small ionic molecule that is relatively inert and easily
excreted in the urine.
The toxicity of TFA in aquatic systems was also fairly low (Table 9.2). The
estimated no observable effect concentration (NOEC) in aquatic microcosms
was 11.8 mg TFA/L (Solomon et al., 2016). A study of TFA toxicity toward a
variety of aquatic organisms, such as algae, diatoms, vascular plants, invertebrates, and fsh, showed the effective concentration-50 (EC 50 ) of all organisms
to be 112 mg/L or higher with the exception of one algae, namely, Selenastrum
capricornutum (Berends et al., 1999). This sensitive species had an EC 50 of
approximately 1.2 mg/L and a NOEC of 0.12 mg/L. The authors conclude
that a concentration of 0.10 mg/L would be safe for the aquatic ecosystem
(Berends et al., 1999). Another microcosm study showed that a mixture of 10
mg/L of trichloroacetic acetic acid (TCA) and TFA did not produce long-term
effects on two aquatic macrophytes (Hanson et al., 2002). Additional studies
of aquatic macrophytes showed the EC 50 for TFA ranged from 221.1 to 10,000
mg/L for three macrophyte species using a variety of indices for potential
impacts on plants (Hanson and Solomon, 2004). Overall, the average NOEC
for aquatic plants and algae was approximately 520 mg/L (Table 9.2), which
makes aquatic plants and algae rather resistant to TFA although some exceptions occur such as that for Selenastrum capricornutum.
The toxicity of TFA in terrestrial plants was expected to be higher than
aquatic plants since terrestrial plants can bioaccumulate TFA. Basically, terrestrial plants can absorb and translocate water and TFA together, but when
the water evaporates from the plant, the TFA is left behind and concentrates
in the leaves (Rollins et al., 1989). The bioconcentration factors (BCF) for TFA
in terrestrial plants were: from 4.9 to 43 over about a 35-day period (data summarized in Boutonnet et al. (1999)); 26 to 295 (Benesch et al., 2002); and 18 to 61
Pesticides, Organic Contaminants, and Pathogens in Air
condensed phases, such as rain and aerosols. Therefore, the assessments of
TFA toxicity were generally conducted with the ionic form of the molecule.
More detailed reviews of the toxicology of TFA can be found in Boutonnet
et al. (1999) and Solomon et al. (2016).
The toxicity of TFA in animals is low (Table 9.2). The lack of reactivity
of TFA that makes it stable in the environment also makes it unreactive in
the body. In mammals, no toxic effects of the ionic form of TFA have been
reported at 5,000 mg/kg (Blake et al., 1969) and 2.1 mmol/kg (=237 mg/kg)
(Fraser and Kaminsky, 1988). TFA is predominately excreted from mammals
in the urine with half-lives ranging from 16 to 61 hours (Holaday, 1977). Due
to the relatively short half-life of TFA, it will not signifcantly accumulate in
animals. TFA appears to bind to carrier proteins, such as albumin, and other
macromolecules, which may be part of the reason its elimination was slower
than expected. It has been suggested that TFA may form a glucuronide conjugate in the liver only to be excreted in the bile and reabsorbed in the intestine.
This potential enterohepatic circulation might be another reason for the slow
elimination kinetics of TFA (Boutonnet et al., 1999) compared to other small,
unreactive ions. Lastly, TFA is not mutagenic (Waskell, 1978). In essence, TFA
behaves in animals as a small ionic molecule that is relatively inert and easily
excreted in the urine.
The toxicity of TFA in aquatic systems was also fairly low (Table 9.2). The
estimated no observable effect concentration (NOEC) in aquatic microcosms
was 11.8 mg TFA/L (Solomon et al., 2016). A study of TFA toxicity toward a
variety of aquatic organisms, such as algae, diatoms, vascular plants, invertebrates, and fsh, showed the effective concentration-50 (EC 50 ) of all organisms
to be 112 mg/L or higher with the exception of one algae, namely, Selenastrum
capricornutum (Berends et al., 1999). This sensitive species had an EC 50 of
approximately 1.2 mg/L and a NOEC of 0.12 mg/L. The authors conclude
that a concentration of 0.10 mg/L would be safe for the aquatic ecosystem
(Berends et al., 1999). Another microcosm study showed that a mixture of 10
mg/L of trichloroacetic acetic acid (TCA) and TFA did not produce long-term
effects on two aquatic macrophytes (Hanson et al., 2002). Additional studies
of aquatic macrophytes showed the EC 50 for TFA ranged from 221.1 to 10,000
mg/L for three macrophyte species using a variety of indices for potential
impacts on plants (Hanson and Solomon, 2004). Overall, the average NOEC
for aquatic plants and algae was approximately 520 mg/L (Table 9.2), which
makes aquatic plants and algae rather resistant to TFA although some exceptions occur such as that for Selenastrum capricornutum.
The toxicity of TFA in terrestrial plants was expected to be higher than
aquatic plants since terrestrial plants can bioaccumulate TFA. Basically, terrestrial plants can absorb and translocate water and TFA together, but when
the water evaporates from the plant, the TFA is left behind and concentrates
in the leaves (Rollins et al., 1989). The bioconcentration factors (BCF) for TFA
in terrestrial plants were: from 4.9 to 43 over about a 35-day period (data summarized in Boutonnet et al. (1999)); 26 to 295 (Benesch et al., 2002); and 18 to 61