2.2 Plant Metabolism
Hydroponic studies have also been used to reveal the mechanisms used by plants to
metabolise pharmaceuticals and identify the metabolites. Emhofer et al. [47] used
high-resolution mass spectrometry to reveal the metabolites of four non-steroidal
anti-inflammatory drugs (ketoprofen, mefenamic acid, naproxen and diclofenac).
Using the model species cress (Lepidium sativum), they identified 16 metabolites
formed by hydroxylation of the parent compound or conjugation with polar plant
metabolites like glucose, amino acids and small organic acids. They then followed
this up by studying the in-plant metabolism of lipid-lowering statin drugs, including
atorvastatin, fluvastatin and simvastatin. These studies revealed nearly 40 metabolites and confirmed hydroxylation and conjugation with sugars and amino acids as
major metabolic pathways [48]. Importantly, at near environmentally relevant exposures (1–10 μg/L), 50% of the metabolites identified could be detected. Hydroxylation of diclofenac has been shown to occur within 3 h of exposure, whereby the
resulting 4
0 OH-diclofenac metabolite is conjugated with glucose [49].
Recently, Chuang et al. [34] investigated the metabolism of caffeine in lettuce.
Their studies revealed the significance of demethylation reactions in the metabolism
of caffeine in lettuce roots with oxidation and hydroxylation providing other metabolic pathways. Using authentic standards for eight metabolites, this study revealed
that 20% of the initially applied caffeine was transformed into demethylated
metabolites.
2.3 Environmental Phytoremediation: Uptake in Aquatic
Plants
The environmentally relevant implications of hydroponic exposure are demonstrated
by studies investigating the suitability of aquatic plants, often referred to as hydrophytes or macrophytes, for phytoremediation in wetlands. Whilst addressed in detail
in chapter “Conclusions and Future Perspectives”, it should be noted that an
extensive amount of work has been done investigating the plant uptake of pharmaceuticals in these systems including veterinary medicines [50, 51], triclosan [52],
metformin [53], ibuprofen [54] and diclofenac [55]. More generally, the efficacy of
constructed wetlands in the removal of 137 pharmaceuticals was reviewed by
Verlicci and Zambello [56].
3 Plant Uptake from Spiked Soil
Following identification of potential pathways by which pharmaceuticals, from both
human and veterinary origin, can accumulate in soils, work started to evaluate the
potential for uptake and accumulation of these chemicals in plants. This was
Uptake and Effects of Pharmaceuticals in the Soil-Plant-Earthworm System
187
Hydroponic studies have also been used to reveal the mechanisms used by plants to
metabolise pharmaceuticals and identify the metabolites. Emhofer et al. [47] used
high-resolution mass spectrometry to reveal the metabolites of four non-steroidal
anti-inflammatory drugs (ketoprofen, mefenamic acid, naproxen and diclofenac).
Using the model species cress (Lepidium sativum), they identified 16 metabolites
formed by hydroxylation of the parent compound or conjugation with polar plant
metabolites like glucose, amino acids and small organic acids. They then followed
this up by studying the in-plant metabolism of lipid-lowering statin drugs, including
atorvastatin, fluvastatin and simvastatin. These studies revealed nearly 40 metabolites and confirmed hydroxylation and conjugation with sugars and amino acids as
major metabolic pathways [48]. Importantly, at near environmentally relevant exposures (1–10 μg/L), 50% of the metabolites identified could be detected. Hydroxylation of diclofenac has been shown to occur within 3 h of exposure, whereby the
resulting 4
0 OH-diclofenac metabolite is conjugated with glucose [49].
Recently, Chuang et al. [34] investigated the metabolism of caffeine in lettuce.
Their studies revealed the significance of demethylation reactions in the metabolism
of caffeine in lettuce roots with oxidation and hydroxylation providing other metabolic pathways. Using authentic standards for eight metabolites, this study revealed
that 20% of the initially applied caffeine was transformed into demethylated
metabolites.
2.3 Environmental Phytoremediation: Uptake in Aquatic
Plants
The environmentally relevant implications of hydroponic exposure are demonstrated
by studies investigating the suitability of aquatic plants, often referred to as hydrophytes or macrophytes, for phytoremediation in wetlands. Whilst addressed in detail
in chapter “Conclusions and Future Perspectives”, it should be noted that an
extensive amount of work has been done investigating the plant uptake of pharmaceuticals in these systems including veterinary medicines [50, 51], triclosan [52],
metformin [53], ibuprofen [54] and diclofenac [55]. More generally, the efficacy of
constructed wetlands in the removal of 137 pharmaceuticals was reviewed by
Verlicci and Zambello [56].
3 Plant Uptake from Spiked Soil
Following identification of potential pathways by which pharmaceuticals, from both
human and veterinary origin, can accumulate in soils, work started to evaluate the
potential for uptake and accumulation of these chemicals in plants. This was
Uptake and Effects of Pharmaceuticals in the Soil-Plant-Earthworm System
187