uptake, metabolism and accumulation of recalcitrant micropollutants such as ketamine and carbamazepine [92].
There are, therefore, also evidences of pharmaceutical’s metabolization within the
plant tissue. That biotransformation can occur either through phytodegradation
(or phytotransformation) or endophytic degradation. Phytodegradation
(or phytotransformation) is defined in this context as the metabolic degradation or
breakdown of organic contaminants by plant enzymes [77]. In this process,
micropollutants may be mineralized but are most often partially transformed into
stable intermediates and stored in the plants [50]. He et al. [93] found that P. australis
can metabolize ibuprofen to hydroxyibuprofen, 1,2-dihydroxyibuprofen,
carboxyibuprofen and glucopyranosyloxy-hydroxyibuprofen. In addition, cytochrome
P450 monooxygenase was found to be involved in the production of the two hydroxy
intermediates. A few more examples of phytodegradation of pharmaceuticals by
CWs plants are provided by Vo et al. [57]. Endophytic degradation of pharmaceuticals has also been reported in the literature. Endophytic bacteria isolated from
P. australis were shown to promote growth of their host and to contribute to
carbendazim metabolism. Sauvêtre et al. [94] presented strong evidence that
xenobiotic metabolism and degradation pathways in plants can be modulated by
interactions with their endophytic community. A few more examples of this plantbacteria synergism can be found in Nguyen et al. [60].
In spite of the recent advances, studies on the metabolic transformation of
pharmaceuticals in plant tissues and their intermediate transformation products are
rather limited. Apart from a very recent and interesting study that used mass
spectrometry imaging to identify xenobiotics, including pharmaceuticals and respective transformation products in plant leaves from a CW [95], the usage of advanced
mass spectrometry in studies with CWs is scarce. Moreover, there is little quantitative evaluation of the contribution of uptake, translocation, accumulation and
metabolization for the overall removal efficiency of pharmaceuticals in CWs
[50, 57].
3.5 Microbial Degradation (or Rhizosphere Remediation)
Removal efficiency for pharmaceuticals, as for other pollutants, is higher in planted
than unplanted CWs [62]. Hijosa-Valsero et al. [96] found that root-related biofilms,
plant exudates and microenvironment modifications near plant tissues could play a
role in the removal of tetracycline. Moreover, the presence of plants improved the
degradation of naproxen, ibuprofen, diclofenac and caffeine, while P. australis
displayed better performance than T. angustifolia [97]. Tai et al. [98] reported that
root sorption and rhizobacterial activities made the most important contribution in
macrolide removal. However, some exceptions are also known, for instance,
clarithromycin and trimethoprim exhibit higher removal in non-planted systems
[96]. Overall, it is well established that rhizosphere remediation, through microbial
degradation, is of major importance for pharmaceutical removal in CWs. However,
Constructed Wetlands and Phytoremediation as a Tool for Pharmaceutical Removal
403
There are, therefore, also evidences of pharmaceutical’s metabolization within the
plant tissue. That biotransformation can occur either through phytodegradation
(or phytotransformation) or endophytic degradation. Phytodegradation
(or phytotransformation) is defined in this context as the metabolic degradation or
breakdown of organic contaminants by plant enzymes [77]. In this process,
micropollutants may be mineralized but are most often partially transformed into
stable intermediates and stored in the plants [50]. He et al. [93] found that P. australis
can metabolize ibuprofen to hydroxyibuprofen, 1,2-dihydroxyibuprofen,
carboxyibuprofen and glucopyranosyloxy-hydroxyibuprofen. In addition, cytochrome
P450 monooxygenase was found to be involved in the production of the two hydroxy
intermediates. A few more examples of phytodegradation of pharmaceuticals by
CWs plants are provided by Vo et al. [57]. Endophytic degradation of pharmaceuticals has also been reported in the literature. Endophytic bacteria isolated from
P. australis were shown to promote growth of their host and to contribute to
carbendazim metabolism. Sauvêtre et al. [94] presented strong evidence that
xenobiotic metabolism and degradation pathways in plants can be modulated by
interactions with their endophytic community. A few more examples of this plantbacteria synergism can be found in Nguyen et al. [60].
In spite of the recent advances, studies on the metabolic transformation of
pharmaceuticals in plant tissues and their intermediate transformation products are
rather limited. Apart from a very recent and interesting study that used mass
spectrometry imaging to identify xenobiotics, including pharmaceuticals and respective transformation products in plant leaves from a CW [95], the usage of advanced
mass spectrometry in studies with CWs is scarce. Moreover, there is little quantitative evaluation of the contribution of uptake, translocation, accumulation and
metabolization for the overall removal efficiency of pharmaceuticals in CWs
[50, 57].
3.5 Microbial Degradation (or Rhizosphere Remediation)
Removal efficiency for pharmaceuticals, as for other pollutants, is higher in planted
than unplanted CWs [62]. Hijosa-Valsero et al. [96] found that root-related biofilms,
plant exudates and microenvironment modifications near plant tissues could play a
role in the removal of tetracycline. Moreover, the presence of plants improved the
degradation of naproxen, ibuprofen, diclofenac and caffeine, while P. australis
displayed better performance than T. angustifolia [97]. Tai et al. [98] reported that
root sorption and rhizobacterial activities made the most important contribution in
macrolide removal. However, some exceptions are also known, for instance,
clarithromycin and trimethoprim exhibit higher removal in non-planted systems
[96]. Overall, it is well established that rhizosphere remediation, through microbial
degradation, is of major importance for pharmaceutical removal in CWs. However,
Constructed Wetlands and Phytoremediation as a Tool for Pharmaceutical Removal
403