Organic compounds in soils 45
column so that the ethynyloestradiol fraction can be analysed by gas chromatography. The mestranol fraction is again cleaned up by a gel separation and a Florisil
column. Thin-layer chromatography was used to confirm the results obtained by gas
chromatography. Recoveries in soil samples averaged less than 50%, even after corrections. This may have been due to degradation of the compounds by soil microorganisms
or to chemical and physical interactions with the soil. Mestranol recoveries averaged
26–30% from soils at the 0.1 ppm level. Recoveries of ethynyloestradiol were even
lower, presumably because of its greater chemical reactivity due to the slightly acidic
hydrogen in the 3-hydroxy position.
2.8.3 Trifluoroacetic acid
In the early 1990s chlorofluorocarbon refrigerants and propellants were largely
replaced by hydrofluorocarbons and hydrochlorofluorocarbons in order to reduce
stratospheric ozone depletion. The hydrochlorofluorocarbons and hydrofluorocarbons, unlike the older chlorofluorocarbons are unstable in the troposphere and can
degrade to trifluoroacetic acid as a by-product [279]. As a result of its high water
solubility and low Henry’s constant, trifluoroacetic acid is removed from the atmosphere primarily through wet disposition [280, 281] were it tends to accumulate at
near toxic levels in amounts between 100 and 500 ng/l and in aquatic ecosystems with
little outflow or seepage and high evaporation rates [282, 283].
Cahill et al [237] have developed a simple and sensitive analytical procedure for
determining the concentration of trifluoroacetic acid in plant, soil, and water samples.
The analysis involves extraction of trifluoroacetic acid by sulphuric acid and methanol
followed by derivatisation to the methyl ester of trifluoroacetic acid. This is accomplished within a single vial without complex extraction procedures. The highly volatile
methyl ester is then analysed using headspace gas chromatography. The spike recovery
trials from all media ranged from a low of 86.7% to a high of 121.4%. The relative
standard deviations were typically below 10%. The minimum detectable limit for the
method was 34 ng/g for dry plant material, 0.20 ng/g for soil and 6.5 ng/l for water.
2.8.4 Flame retardants
A new potential source of environmental contamination is the use of flame retardants
composed of brominated aromatics, many of which have close structural relationships
to polychlorobiphenyls and other known persistent organic pollutants.
Incubation in soils showed that polybrominated biphenyls were resistant to
degradation, but were apparently not taken up by plants or leached into groundwater [284, 285]. Commercial formulations or brominated aromatic flame retardants
had variable composition; some contained highly brominated phenols, but no evidence
of contamination with dibenzodioxins and dibenzofurans was found [286].
2.8.5 Polystyrene
A Curie Point flash evaporation-pyrolysis gas chromatography-mass spectrometric
method [287] has been applied to the determination of polystyrenes in soil via identification and determination of their unzipping pyrolysis products, such as styrene
column so that the ethynyloestradiol fraction can be analysed by gas chromatography. The mestranol fraction is again cleaned up by a gel separation and a Florisil
column. Thin-layer chromatography was used to confirm the results obtained by gas
chromatography. Recoveries in soil samples averaged less than 50%, even after corrections. This may have been due to degradation of the compounds by soil microorganisms
or to chemical and physical interactions with the soil. Mestranol recoveries averaged
26–30% from soils at the 0.1 ppm level. Recoveries of ethynyloestradiol were even
lower, presumably because of its greater chemical reactivity due to the slightly acidic
hydrogen in the 3-hydroxy position.
2.8.3 Trifluoroacetic acid
In the early 1990s chlorofluorocarbon refrigerants and propellants were largely
replaced by hydrofluorocarbons and hydrochlorofluorocarbons in order to reduce
stratospheric ozone depletion. The hydrochlorofluorocarbons and hydrofluorocarbons, unlike the older chlorofluorocarbons are unstable in the troposphere and can
degrade to trifluoroacetic acid as a by-product [279]. As a result of its high water
solubility and low Henry’s constant, trifluoroacetic acid is removed from the atmosphere primarily through wet disposition [280, 281] were it tends to accumulate at
near toxic levels in amounts between 100 and 500 ng/l and in aquatic ecosystems with
little outflow or seepage and high evaporation rates [282, 283].
Cahill et al [237] have developed a simple and sensitive analytical procedure for
determining the concentration of trifluoroacetic acid in plant, soil, and water samples.
The analysis involves extraction of trifluoroacetic acid by sulphuric acid and methanol
followed by derivatisation to the methyl ester of trifluoroacetic acid. This is accomplished within a single vial without complex extraction procedures. The highly volatile
methyl ester is then analysed using headspace gas chromatography. The spike recovery
trials from all media ranged from a low of 86.7% to a high of 121.4%. The relative
standard deviations were typically below 10%. The minimum detectable limit for the
method was 34 ng/g for dry plant material, 0.20 ng/g for soil and 6.5 ng/l for water.
2.8.4 Flame retardants
A new potential source of environmental contamination is the use of flame retardants
composed of brominated aromatics, many of which have close structural relationships
to polychlorobiphenyls and other known persistent organic pollutants.
Incubation in soils showed that polybrominated biphenyls were resistant to
degradation, but were apparently not taken up by plants or leached into groundwater [284, 285]. Commercial formulations or brominated aromatic flame retardants
had variable composition; some contained highly brominated phenols, but no evidence
of contamination with dibenzodioxins and dibenzofurans was found [286].
2.8.5 Polystyrene
A Curie Point flash evaporation-pyrolysis gas chromatography-mass spectrometric
method [287] has been applied to the determination of polystyrenes in soil via identification and determination of their unzipping pyrolysis products, such as styrene