recently published reviews (Bidleman et al. 2002; Asad et al. 2017; Basheer 2018;
Jeschke 2018). Earlier, organochlorine (OC) pesticides were heavily used on farmlands in the U.S. and Canada during the 1960s and 1970s. As OC pesticides and their
metabolites are highly persistent, residues remained in many soils. For example,
chlordane and heptachlor have not been used in agriculture since 1983, but before
that time 65% of chlordane applications were for crops, home lawns, turf and
ornamentals (Wiberg et al. 2001a, b; Bidleman et al. 2002). From 1983 until their
ban in 1988, chlordane and hepachlor were used exclusively for structural termite
control, resulting in greatly elevated levels in home air. Based on this background, an
interdisciplinary international working group started an investigation which focused
on the question whether or not sources of chlordane and heptachlor to ambient air
still include volatilisation from agricultural soils and/or emissions from house
foundations or are largely caused by long range transport from countries still using
these OC pesticides such as Mexico and other Latin American countries (Bidleman
et al. 1998a, b, c, d, 2002, 2006, 2012, 2013a, b; Wiberg et al. 2001a, b; Bidleman
and Leone 2004; Kurt-Karakus et al. 2007; Jantunen et al. 2015). Furthermore, the
authors addressed the problem of whether heptachlor exoepoxide in the air arises
mainly from photolysis of heptachlor or by volatilisation of this compound as
produced by metabolism of heptachlor in soils.
In the course of this study, enantioselective gas chromatography played a major
role, because it was conjectured that the chiral pesticides chlordane and heptachlor,
which were and still are being applied as racemic mixtures, are being emitted from
houses, as well as from actual long-distant application sites as racemates. Once in the
air, photolysis may yield oxychlordane, photoheptachlor, heptachlorepoxide and
other oxidation products, which in all cases will form racemates. By contrast,
Aigner et al. showed that selective enzymatic degradation of chlordane enantiomers
by micro-organisms did occur in soils from the midwestern U.S. resulting in
non-racemic signatures of the chiral pesticides in soils (Bidleman and Falconer
1999; Leone et al. 2001; Bidleman et al. 2002). The same is assumed to be valid
for heptachlor. This result formed the basis for the application of non-racemic
enantiomeric signatures to distinguish between releases of chlordane and heptachlor
from agricultural soils vs. termiticide emissions.
Soil and air samples were collected in four states in the U.S. Corn Belt region:
Ohio, Pennsylvania, Indiana and Illinois, at different times from 1995 to 1997. At
38 farms, eight soil cores (% 15 cm depth) were taken and pooled to obtain a
representative sample for each field (Wiberg et al. 2001a, b; Bidleman et al. 2002).
Three types of air samples were collected: ambient, above soil and indoor, using
polyurethane foam (PUF) traps (Falconer et al. 1998). Ambient and indoor samples
were also collected around Muscle Shoals, Alabama, and ambient and indoor air in
Columbia, South Carolina (Wiberg et al. 1997a, b).
Chlordane residues (sum of cis- and trans-chlordane) in Corn Belt soils were, on
average, ten times higher than levels found in soils from Alabama (geometric meansCorn Belt 1.4 ng/g; Alabama 0.17 ng/g; (Wiberg et al. 1997a, b, 2001a, b; Bidleman
et al. 1998a, b, c, d, 2002; Bidleman and Leone 2004)). Average concentrations of
chlordanes in ambient air in the Corn Belt (0.041 ng/m
3 , n ¼ 4) were similar to
188
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants
Jeschke 2018). Earlier, organochlorine (OC) pesticides were heavily used on farmlands in the U.S. and Canada during the 1960s and 1970s. As OC pesticides and their
metabolites are highly persistent, residues remained in many soils. For example,
chlordane and heptachlor have not been used in agriculture since 1983, but before
that time 65% of chlordane applications were for crops, home lawns, turf and
ornamentals (Wiberg et al. 2001a, b; Bidleman et al. 2002). From 1983 until their
ban in 1988, chlordane and hepachlor were used exclusively for structural termite
control, resulting in greatly elevated levels in home air. Based on this background, an
interdisciplinary international working group started an investigation which focused
on the question whether or not sources of chlordane and heptachlor to ambient air
still include volatilisation from agricultural soils and/or emissions from house
foundations or are largely caused by long range transport from countries still using
these OC pesticides such as Mexico and other Latin American countries (Bidleman
et al. 1998a, b, c, d, 2002, 2006, 2012, 2013a, b; Wiberg et al. 2001a, b; Bidleman
and Leone 2004; Kurt-Karakus et al. 2007; Jantunen et al. 2015). Furthermore, the
authors addressed the problem of whether heptachlor exoepoxide in the air arises
mainly from photolysis of heptachlor or by volatilisation of this compound as
produced by metabolism of heptachlor in soils.
In the course of this study, enantioselective gas chromatography played a major
role, because it was conjectured that the chiral pesticides chlordane and heptachlor,
which were and still are being applied as racemic mixtures, are being emitted from
houses, as well as from actual long-distant application sites as racemates. Once in the
air, photolysis may yield oxychlordane, photoheptachlor, heptachlorepoxide and
other oxidation products, which in all cases will form racemates. By contrast,
Aigner et al. showed that selective enzymatic degradation of chlordane enantiomers
by micro-organisms did occur in soils from the midwestern U.S. resulting in
non-racemic signatures of the chiral pesticides in soils (Bidleman and Falconer
1999; Leone et al. 2001; Bidleman et al. 2002). The same is assumed to be valid
for heptachlor. This result formed the basis for the application of non-racemic
enantiomeric signatures to distinguish between releases of chlordane and heptachlor
from agricultural soils vs. termiticide emissions.
Soil and air samples were collected in four states in the U.S. Corn Belt region:
Ohio, Pennsylvania, Indiana and Illinois, at different times from 1995 to 1997. At
38 farms, eight soil cores (% 15 cm depth) were taken and pooled to obtain a
representative sample for each field (Wiberg et al. 2001a, b; Bidleman et al. 2002).
Three types of air samples were collected: ambient, above soil and indoor, using
polyurethane foam (PUF) traps (Falconer et al. 1998). Ambient and indoor samples
were also collected around Muscle Shoals, Alabama, and ambient and indoor air in
Columbia, South Carolina (Wiberg et al. 1997a, b).
Chlordane residues (sum of cis- and trans-chlordane) in Corn Belt soils were, on
average, ten times higher than levels found in soils from Alabama (geometric meansCorn Belt 1.4 ng/g; Alabama 0.17 ng/g; (Wiberg et al. 1997a, b, 2001a, b; Bidleman
et al. 1998a, b, c, d, 2002; Bidleman and Leone 2004)). Average concentrations of
chlordanes in ambient air in the Corn Belt (0.041 ng/m
3 , n ¼ 4) were similar to
188
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants