as Arabidopsis thaliana [28, 60, 79], Lemna gibba [77, 81], Phragmites australis
[69], Typha angustifolia/latifolia [75], poplar [82] (the latter three plant types are
commonly used in the realization of constructed wetlands), and the edible plants
barley [58] and garden cress [35, 40, 53] upon uptake from water. In the following, a
few selected papers on this topic will be discussed in detail.
The first report on the metabolization of DCF in plants was by Huber et al. [58]. In
an experiment with barley, they could prove the formation of a phase I metabolite
(hydroxylated DCF) in the plant that was subsequently transformed into a phase II
metabolite by conjugation with glucose. This analytical work was based on HPLC
with low-resolution MS (ion trap) whereby the formation of the glucose conjugate
was further bolstered by enzymatic cleavage. In 2017 Fu et al. proposed a degradation/transformation pathway for DCF in Arabidopsis cells. The strategy employed to
detect and further identify DCF-related metabolites was the use of data from HPLCHR-MS, whereby the characteristic isotopic pattern resulting from the two chlorine
atoms in DCF was employed as a first hint, and subsequently comparison with
standard substances. This approach resulted in an unambiguous identification of a
number of phase I + II metabolites [60]. A special asset of this work and a second
one published by the same group [28] (focusing on IBU and naproxen) was that
additional experiments with
14 C-labeled drugs allowed a judgment on the
non-extractable phase III metabolites integrated in cell walls (a portion that is not
considered in the majority of works within this field).
Mlynek et al. presented an interesting workflow with respect to the use of drifttube ion-mobility (DT-IM) coupled to HR-MS for the detection of DCF-related
metabolites in hydroponically grown garden cress (see Fig. 3) [40]. In this approach,
drift times were recorded for the peaks eluting from HPLC, and, as a QTOF/MS
instrument was used, all analytes were subsequently fragmented with low collision
energies to yield significant fragments. This allowed to assign these signals to
DCF-related drug metabolites (all in all 30 DCF metabolites formed in the plant
could be identified).
As already stated in the previous section, to facilitate the detection and (at least
tentative) identification of the drug metabolites formed within the plant, most studies
employ relatively high concentrations of the parent drug (commonly in mg L
À1 to
high μg L
À1 range). Nonetheless, in several papers the authors tried to approximate
the drug concentrations used to those expected in real environmental waters. Examples for such a practice have been published by Emhofer et al. (employing DCF,
NPX, KPF, and mefenamic acid at concentrations of 1 μg L
À1 each) [35] or Di
Baccio et al. [81] and He et al. [69] with IBU concentrations of 20 μg L
À1 and
60 μg L
À1 , respectively.
4.3 Antibiotics
Many antibiotics are applied for the treatment of humans as well as animals. For this
reason they can enter the environment either via the sewage system or via the use of
512
F. Mlynek et al.
[69], Typha angustifolia/latifolia [75], poplar [82] (the latter three plant types are
commonly used in the realization of constructed wetlands), and the edible plants
barley [58] and garden cress [35, 40, 53] upon uptake from water. In the following, a
few selected papers on this topic will be discussed in detail.
The first report on the metabolization of DCF in plants was by Huber et al. [58]. In
an experiment with barley, they could prove the formation of a phase I metabolite
(hydroxylated DCF) in the plant that was subsequently transformed into a phase II
metabolite by conjugation with glucose. This analytical work was based on HPLC
with low-resolution MS (ion trap) whereby the formation of the glucose conjugate
was further bolstered by enzymatic cleavage. In 2017 Fu et al. proposed a degradation/transformation pathway for DCF in Arabidopsis cells. The strategy employed to
detect and further identify DCF-related metabolites was the use of data from HPLCHR-MS, whereby the characteristic isotopic pattern resulting from the two chlorine
atoms in DCF was employed as a first hint, and subsequently comparison with
standard substances. This approach resulted in an unambiguous identification of a
number of phase I + II metabolites [60]. A special asset of this work and a second
one published by the same group [28] (focusing on IBU and naproxen) was that
additional experiments with
14 C-labeled drugs allowed a judgment on the
non-extractable phase III metabolites integrated in cell walls (a portion that is not
considered in the majority of works within this field).
Mlynek et al. presented an interesting workflow with respect to the use of drifttube ion-mobility (DT-IM) coupled to HR-MS for the detection of DCF-related
metabolites in hydroponically grown garden cress (see Fig. 3) [40]. In this approach,
drift times were recorded for the peaks eluting from HPLC, and, as a QTOF/MS
instrument was used, all analytes were subsequently fragmented with low collision
energies to yield significant fragments. This allowed to assign these signals to
DCF-related drug metabolites (all in all 30 DCF metabolites formed in the plant
could be identified).
As already stated in the previous section, to facilitate the detection and (at least
tentative) identification of the drug metabolites formed within the plant, most studies
employ relatively high concentrations of the parent drug (commonly in mg L
À1 to
high μg L
À1 range). Nonetheless, in several papers the authors tried to approximate
the drug concentrations used to those expected in real environmental waters. Examples for such a practice have been published by Emhofer et al. (employing DCF,
NPX, KPF, and mefenamic acid at concentrations of 1 μg L
À1 each) [35] or Di
Baccio et al. [81] and He et al. [69] with IBU concentrations of 20 μg L
À1 and
60 μg L
À1 , respectively.
4.3 Antibiotics
Many antibiotics are applied for the treatment of humans as well as animals. For this
reason they can enter the environment either via the sewage system or via the use of
512
F. Mlynek et al.