11.2 Challenges and Restrictions of Currently Applied
Methods
Approximately 33% anthropogenic pollutants released into the environment are
chiral. However, the enantioselective kinetics, bioaccumulation, biotransformation
and enantiomerisation profiles are only scarcely investigated to date. A particularly
challenging question to be addressed includes enantioselective bioaccumulation: Is
one enantiomer preferentially bioaccumulated over the other? Which one of the two
enantiomers (R- or S-) is preferentially bioaccumulated at the expense of the other?
Do these enantiomers racemise or transform into each other in the presence of
biocatalysts (such as enzymes or other cellular tools) inside the metabolic systems
of organisms?
These questions are quite challenging for all scientists investigating those compounds globally. Therefore, serious measures and research priorities are needed for
ensuring a safe environment for the healthy livelihood of potentially exposed human
populations and environments (Hussain et al. 2015; Zhou et al. 2018).
The most serious challenge in enantiomer-selective analyses is the sample preparation. It separates the enantiomers of chiral pollutants from the impurities and other
species. The presence of the other species and low concentrations of the chiral
pollutants in the real-world samples are the major hurdles. Some chiral pollutants
have reached even the Polar region of our globe (Jantunen and Bidleman 1998;
Bidleman et al. 2002; Hoekstra et al. 2003; Warner et al. 2005; Ross et al. 2008;
Terry et al. 2013; Carlsson et al. 2014; Lu et al. 2014; Jin et al. 2017). They are
contaminating glaciers and other remote environments (MacLeod and Wong 2010;
Terry et al. 2013; Carlsson et al. 2014). It is a scientific challenge to detect and
quantify them in expected trace amounts (pg–ng level) with conventional analytical
methods due to the high degree of selectivity and sensitivity required for quantitative
enantiomer-selective trace-level analysis. The sampling is very costly and not easy to
perform in a validated way (Wang et al. 2008; Kasprzyk-Hordern et al. 2010;
Bagnall et al. 2012; Wang et al. 2016). The various techniques of sample preparation
include liquid–liquid extraction, solid-phase extraction, micro-wave-assisted extraction, ultrasonic extraction, molecularly imprinted solid-phase extraction, empty fibre
liquid-phase micro-extraction, pressurised liquid extraction, supercritical fluid
extraction, dispersive liquid–liquid micro-extraction and pressurised hot water
extraction. Some of these have been used for the sample preparations for the chiral
pollutants. Sometimes, these sample handling methods are not effective, especially
at low volume of the samples and low concentrations of the chiral pollutants (Ali
et al. 2008a, b; Ali 2009; Malagueno de Santana et al. 2009; Dolowy and Pyka 2014;
Lipka and Vaccher 2015).
Additionally, the detection of the chiral pollutants is difficult as many pesticide
residues are photosensitive (Hühnerfuss et al. 1993; Hühnerfuss 2000; Pal et al.
2003; Ding et al. 2020). Sometimes, the reproducibility of analytical results is a
challenge due to high detection limits or inappropriate enantioselective chromatographic resolution (Wang et al. 2008; Zhong et al. 2014; Caballo et al. 2015; Maia
308
11 Perspectives
Methods
Approximately 33% anthropogenic pollutants released into the environment are
chiral. However, the enantioselective kinetics, bioaccumulation, biotransformation
and enantiomerisation profiles are only scarcely investigated to date. A particularly
challenging question to be addressed includes enantioselective bioaccumulation: Is
one enantiomer preferentially bioaccumulated over the other? Which one of the two
enantiomers (R- or S-) is preferentially bioaccumulated at the expense of the other?
Do these enantiomers racemise or transform into each other in the presence of
biocatalysts (such as enzymes or other cellular tools) inside the metabolic systems
of organisms?
These questions are quite challenging for all scientists investigating those compounds globally. Therefore, serious measures and research priorities are needed for
ensuring a safe environment for the healthy livelihood of potentially exposed human
populations and environments (Hussain et al. 2015; Zhou et al. 2018).
The most serious challenge in enantiomer-selective analyses is the sample preparation. It separates the enantiomers of chiral pollutants from the impurities and other
species. The presence of the other species and low concentrations of the chiral
pollutants in the real-world samples are the major hurdles. Some chiral pollutants
have reached even the Polar region of our globe (Jantunen and Bidleman 1998;
Bidleman et al. 2002; Hoekstra et al. 2003; Warner et al. 2005; Ross et al. 2008;
Terry et al. 2013; Carlsson et al. 2014; Lu et al. 2014; Jin et al. 2017). They are
contaminating glaciers and other remote environments (MacLeod and Wong 2010;
Terry et al. 2013; Carlsson et al. 2014). It is a scientific challenge to detect and
quantify them in expected trace amounts (pg–ng level) with conventional analytical
methods due to the high degree of selectivity and sensitivity required for quantitative
enantiomer-selective trace-level analysis. The sampling is very costly and not easy to
perform in a validated way (Wang et al. 2008; Kasprzyk-Hordern et al. 2010;
Bagnall et al. 2012; Wang et al. 2016). The various techniques of sample preparation
include liquid–liquid extraction, solid-phase extraction, micro-wave-assisted extraction, ultrasonic extraction, molecularly imprinted solid-phase extraction, empty fibre
liquid-phase micro-extraction, pressurised liquid extraction, supercritical fluid
extraction, dispersive liquid–liquid micro-extraction and pressurised hot water
extraction. Some of these have been used for the sample preparations for the chiral
pollutants. Sometimes, these sample handling methods are not effective, especially
at low volume of the samples and low concentrations of the chiral pollutants (Ali
et al. 2008a, b; Ali 2009; Malagueno de Santana et al. 2009; Dolowy and Pyka 2014;
Lipka and Vaccher 2015).
Additionally, the detection of the chiral pollutants is difficult as many pesticide
residues are photosensitive (Hühnerfuss et al. 1993; Hühnerfuss 2000; Pal et al.
2003; Ding et al. 2020). Sometimes, the reproducibility of analytical results is a
challenge due to high detection limits or inappropriate enantioselective chromatographic resolution (Wang et al. 2008; Zhong et al. 2014; Caballo et al. 2015; Maia
308
11 Perspectives