that can vary over small spatial areas. Background soils from woodland and grassland areas were sampled to compare chiral signatures and determine the spatial
variability within a few square meters. The enantiomer fractions, EF ¼ areas of the
(+)/[(+)+(À)]-enantiomers, showed variability between and within ecosystems. For
example, the EF of cis-chlordane varied between 0.272 and 0.558 in nine samples
taken over a few square meters, and a range of 0.431–0.506 was found within depths
of a few centimetres. Woodland and grassland soils were spiked with α-HCH,
chlordanes and o,p'-DDT for laboratory experiments. Of the spiked α-HCH,
20–32% remained after 209 days and 4–7% after 445 days. For the two chlordanes,
47–76% of the spiked amounts were present after 209 days and 46–73% after
445 days. In the case of α-HCH, the loss was accompanied by significant
enantiomer-selective degradation, which was not observed for the chlordanes and
chiral DDT. In general, the enantiomer transformation preferences in the controlled
laboratory experiment were similar to those in the field. Soil organic matter content
and pH exerted a minor influence on this variability. The results of this study have
implications for the use of chiral compounds to make inferences about air–soil
exchange and for the mechanisms of biodegradation/biotransformation of anthropogenic compounds in soils.
Source elucidation was also the main focus for another study, where enantiomeric
profiling was applied to the identification of emission history from agricultural soils
in Canada (Bidleman et al. 2006). Air samples were collected above farmed lands in
the Fraser Valley and orchards in the Okanagan Valley, British Columbia, Canada.
The volatilisation of past-used organochlorine pesticides was investigated in detail.
Concentrations of pesticides in the air were elevated over soils that contained higher
residues. Soil/air fugacity ratios at sites with the higher soil residues were calculated
relative to air sampled at 40 cm height and background air. The enantiomer fraction
(EF) of the chiral compounds α -HCH, trans-chlordane, cis-chlordane and o,p'-DDT
were determined in overlying air samples and soils. EFs in air corresponded nicely to
those in soils at fields in which soil concentrations were high, but were decoupled
from soil signatures at fields with low soil residues. Mean EFs in air sampled over
soils were significantly non-racemic for α-HCH and chlordanes and agreed with
published EFs in regional ambient air. The mean EF of o,p'-DDT for all air samples
did not show a significant deviation from racemic EFs ( p > 0.2).
Daly et al. performed a similar study from Costa Rica where enantiomeric profiles
were used for the identification of atmospheric pollution sources (Daly et al. 2007).
Air samples and soil from 23 stations across the country were collected and analysed
in 2004. Average annual air concentrations, determined with XAD-based passive
samplers, and surface soil concentrations were generally low when compared to
values reported for North and Central America, which is consistent with relatively
low historical domestic use and little atmospheric inflow from neighbouring countries. Statistical analysis and concentration maps reveal three types of spatial distribution: α-HCH and p,p'-DDD had a relatively uniform distribution across the
country; other DDT-related species were greatly elevated over the national average
at Manuel Antonio, a National Park on the Pacific coast; and dieldrin-, lindane- and
chlordane-related species had higher concentrations in Costa Rica’s populated
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
197
variability within a few square meters. The enantiomer fractions, EF ¼ areas of the
(+)/[(+)+(À)]-enantiomers, showed variability between and within ecosystems. For
example, the EF of cis-chlordane varied between 0.272 and 0.558 in nine samples
taken over a few square meters, and a range of 0.431–0.506 was found within depths
of a few centimetres. Woodland and grassland soils were spiked with α-HCH,
chlordanes and o,p'-DDT for laboratory experiments. Of the spiked α-HCH,
20–32% remained after 209 days and 4–7% after 445 days. For the two chlordanes,
47–76% of the spiked amounts were present after 209 days and 46–73% after
445 days. In the case of α-HCH, the loss was accompanied by significant
enantiomer-selective degradation, which was not observed for the chlordanes and
chiral DDT. In general, the enantiomer transformation preferences in the controlled
laboratory experiment were similar to those in the field. Soil organic matter content
and pH exerted a minor influence on this variability. The results of this study have
implications for the use of chiral compounds to make inferences about air–soil
exchange and for the mechanisms of biodegradation/biotransformation of anthropogenic compounds in soils.
Source elucidation was also the main focus for another study, where enantiomeric
profiling was applied to the identification of emission history from agricultural soils
in Canada (Bidleman et al. 2006). Air samples were collected above farmed lands in
the Fraser Valley and orchards in the Okanagan Valley, British Columbia, Canada.
The volatilisation of past-used organochlorine pesticides was investigated in detail.
Concentrations of pesticides in the air were elevated over soils that contained higher
residues. Soil/air fugacity ratios at sites with the higher soil residues were calculated
relative to air sampled at 40 cm height and background air. The enantiomer fraction
(EF) of the chiral compounds α -HCH, trans-chlordane, cis-chlordane and o,p'-DDT
were determined in overlying air samples and soils. EFs in air corresponded nicely to
those in soils at fields in which soil concentrations were high, but were decoupled
from soil signatures at fields with low soil residues. Mean EFs in air sampled over
soils were significantly non-racemic for α-HCH and chlordanes and agreed with
published EFs in regional ambient air. The mean EF of o,p'-DDT for all air samples
did not show a significant deviation from racemic EFs ( p > 0.2).
Daly et al. performed a similar study from Costa Rica where enantiomeric profiles
were used for the identification of atmospheric pollution sources (Daly et al. 2007).
Air samples and soil from 23 stations across the country were collected and analysed
in 2004. Average annual air concentrations, determined with XAD-based passive
samplers, and surface soil concentrations were generally low when compared to
values reported for North and Central America, which is consistent with relatively
low historical domestic use and little atmospheric inflow from neighbouring countries. Statistical analysis and concentration maps reveal three types of spatial distribution: α-HCH and p,p'-DDD had a relatively uniform distribution across the
country; other DDT-related species were greatly elevated over the national average
at Manuel Antonio, a National Park on the Pacific coast; and dieldrin-, lindane- and
chlordane-related species had higher concentrations in Costa Rica’s populated
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
197