to measure the soil-air partition coefficient (K SA ). K SA of some spiked BFRs and
OCPs increased from day 10 to 60 or 90 and levelled off afterwards. This suggests
that the volatility of BFRs and OCPs decreases over time as the chemicals become
more strongly bound to the soil. Transformation of alternative BFRs (α- and βTBECH, β-TBCO, DPTE), BDE-17 and α-HCH was evident in soils over 360 days,
but no transformation was observed for the BDE-28, -47, -99 and trans-chlordane. A
newly developed method for the enantiomer separation of α-TBECH and β-TBCO
was applied. This method was also used for the enantiomer separation of α-HCH.
Discrepancies between the enantiomer fraction (EF) of chemicals extracted from the
soil by dichloromethane (DCM) and air were found. It is suggested that DCM
removes both the sequestered and loosely bound fractions of chemicals in soil,
whereas air accesses only the loosely bound fraction, and these two pools are subject
to different degrees of enantioselective transformation. This calls for caution when
interpreting EFs obtained from DCM extraction of soil with EFs in ambient air.
8.2.3.1 Air/Water Gas Exchange Studies in Freshwater Environments
Air–water gas transfer involves both absorption and volatilisation; the direction of
net exchange is usually determined by the difference between the concentrations of
the gaseous and dissolved compound in air and surface water. The magnitude of the
exchange depends on this difference and the mass transfer coefficient that involves
the temperature-dependent Henry’s law constant. This latter aspect may be
oversimplified because of uncertainties in the Henry’s law constant and the mass
transfer coefficient. Furthermore, on an undulating water surface, the presence of
capillary waves, wave-breaking processes, as well as slick-induced modifications of
these processes may strongly influence air-water exchange processes (Hühnerfuss
and Garrett 1981). In addition, such methods are subject to analytical errors in
measuring the concentrations of the compound(s) in air and water. Together, these
uncertainties are substantial and may sum up to several hundred percent (see
Chap. 4). Enantioselective gas chromatography of chiral pollutants helped to circumvent the latter analytical errors and provided new insights into the environmental
transport of toxic compounds, as well as information pertaining to the environmental
transformation of these compounds. As an advantage, the relative peak areas of
enantiomers or enantiomeric ratios can be determined with high precision (relative
standard deviations generally better than Æ 4%) by enantioselective cGC, whereas
the precision in measuring concentrations of trace organic compounds is typically
15–20% (Ridal et al. 1997), and computing the difference of two concentrations thus
yields an even greater error. Therefore, enantioselective cGC can be used to examine
environmental processes difficult to resolve by comparing concentration data alone.
One chiral pollutant that is prevalent in the environment and partitions readily
between the atmosphere and surface waters of lakes and the oceans because of its
relatively low Henry’s law constant is α-HCH. As a result of gas-phase absorption, it
is estimated that about 20% of the global environmental burden of HCHs is held
within the upper 200 m of the world’s oceans (Ridal et al. 1997). Therefore, very
extensive investigations have been carried out by Bidleman and co-workers
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
201
OCPs increased from day 10 to 60 or 90 and levelled off afterwards. This suggests
that the volatility of BFRs and OCPs decreases over time as the chemicals become
more strongly bound to the soil. Transformation of alternative BFRs (α- and βTBECH, β-TBCO, DPTE), BDE-17 and α-HCH was evident in soils over 360 days,
but no transformation was observed for the BDE-28, -47, -99 and trans-chlordane. A
newly developed method for the enantiomer separation of α-TBECH and β-TBCO
was applied. This method was also used for the enantiomer separation of α-HCH.
Discrepancies between the enantiomer fraction (EF) of chemicals extracted from the
soil by dichloromethane (DCM) and air were found. It is suggested that DCM
removes both the sequestered and loosely bound fractions of chemicals in soil,
whereas air accesses only the loosely bound fraction, and these two pools are subject
to different degrees of enantioselective transformation. This calls for caution when
interpreting EFs obtained from DCM extraction of soil with EFs in ambient air.
8.2.3.1 Air/Water Gas Exchange Studies in Freshwater Environments
Air–water gas transfer involves both absorption and volatilisation; the direction of
net exchange is usually determined by the difference between the concentrations of
the gaseous and dissolved compound in air and surface water. The magnitude of the
exchange depends on this difference and the mass transfer coefficient that involves
the temperature-dependent Henry’s law constant. This latter aspect may be
oversimplified because of uncertainties in the Henry’s law constant and the mass
transfer coefficient. Furthermore, on an undulating water surface, the presence of
capillary waves, wave-breaking processes, as well as slick-induced modifications of
these processes may strongly influence air-water exchange processes (Hühnerfuss
and Garrett 1981). In addition, such methods are subject to analytical errors in
measuring the concentrations of the compound(s) in air and water. Together, these
uncertainties are substantial and may sum up to several hundred percent (see
Chap. 4). Enantioselective gas chromatography of chiral pollutants helped to circumvent the latter analytical errors and provided new insights into the environmental
transport of toxic compounds, as well as information pertaining to the environmental
transformation of these compounds. As an advantage, the relative peak areas of
enantiomers or enantiomeric ratios can be determined with high precision (relative
standard deviations generally better than Æ 4%) by enantioselective cGC, whereas
the precision in measuring concentrations of trace organic compounds is typically
15–20% (Ridal et al. 1997), and computing the difference of two concentrations thus
yields an even greater error. Therefore, enantioselective cGC can be used to examine
environmental processes difficult to resolve by comparing concentration data alone.
One chiral pollutant that is prevalent in the environment and partitions readily
between the atmosphere and surface waters of lakes and the oceans because of its
relatively low Henry’s law constant is α-HCH. As a result of gas-phase absorption, it
is estimated that about 20% of the global environmental burden of HCHs is held
within the upper 200 m of the world’s oceans (Ridal et al. 1997). Therefore, very
extensive investigations have been carried out by Bidleman and co-workers
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
201