interactions between different pharmaceuticals but also pharmaceuticals and heavy
metals could be observed, which are not always favouring an increased or decreased
accumulation in plants. This uptake is rather influenced by additional parameters like
physicochemical properties of the compound, plant physiology or soil composition.
Biodegradation is considered the most important process for eliminating the
majority of xenobiotics (e.g. pharmaceuticals), where microorganisms – as important degraders – provide products to other organisms in the food web. However,
these processes are only significant when the molecules’ toxicity does not inhibit
microbial activity. Although, known for a long time, the biodegradation of drugs and
their effects on ecological processes driven by microorganisms is quite scarce but
may be also too complex to be fully addressed in this book chapter [13]. Besides the
potential transformation of pharmaceuticals by soil organisms, their bioavailability
might also be reduced by the microbial communities at root surfaces – so-called
rhizobacteria – which can act as enhancers of phytoremediation efficiency; the same
concept has been proposed for endophytic bacteria inhabiting root tissue. Moreover,
the latter can interact closely with their host plant boosting the degradation pathways
and metabolic activities and then decreasing both phytotoxicity and evapotranspiration of volatile organic compounds [14–16].
Various microbial species and strains may perform differently under different
environmental and growth conditions, determining their efficiency and hence their
usefulness [17, 18]. Although many microbial species are still unidentified, Agrawal
and co-authors [17] listed a wide range of pollutant-degrading microorganisms that
have been spotted by culture-independent techniques and could be harboured in the
root environment of various plant species. The full metabolic capacity of the plant
associated bacteria (plant endophytes and rhizosphere bacteria) has not been
completely resolved yet, although first experiments indicate that microbial activities
can have a strong influence on biotransformation processes of pharmaceuticals
[15, 19] (more details are provided in chapter “Impact of PhACs on Soil
Microorganisms”).
Another factor that has been mostly neglected is the direct availability of active
metabolites that may be excreted from animals or humans. Generally, it is assumed
that 90% of an active compound are metabolized from a mammalian body within
48 h, after treatment. In any case, the availability of parent compounds and major
metabolites will be decisive for their further fate in plants.
2.1 Compounds Properties
One of the primary criteria that influences uptake into roots and translocation in plant
tissue is the molar mass of the pharmaceuticals [20]. Low-molar mass organic
compounds can easily enter the soft rhizodermis and move through the porous
mesh of the cell wall. Hence, organic substances with molar mass <1,000 g/mol
are easily absorbed by the apical sections of plant roots [21]. However according to
Chuang and co-workers [20], only molecules below 300 g/mol can, in general, enter
Uptake and Translocation of Pharmaceuticals in Plants:. . .
107
metals could be observed, which are not always favouring an increased or decreased
accumulation in plants. This uptake is rather influenced by additional parameters like
physicochemical properties of the compound, plant physiology or soil composition.
Biodegradation is considered the most important process for eliminating the
majority of xenobiotics (e.g. pharmaceuticals), where microorganisms – as important degraders – provide products to other organisms in the food web. However,
these processes are only significant when the molecules’ toxicity does not inhibit
microbial activity. Although, known for a long time, the biodegradation of drugs and
their effects on ecological processes driven by microorganisms is quite scarce but
may be also too complex to be fully addressed in this book chapter [13]. Besides the
potential transformation of pharmaceuticals by soil organisms, their bioavailability
might also be reduced by the microbial communities at root surfaces – so-called
rhizobacteria – which can act as enhancers of phytoremediation efficiency; the same
concept has been proposed for endophytic bacteria inhabiting root tissue. Moreover,
the latter can interact closely with their host plant boosting the degradation pathways
and metabolic activities and then decreasing both phytotoxicity and evapotranspiration of volatile organic compounds [14–16].
Various microbial species and strains may perform differently under different
environmental and growth conditions, determining their efficiency and hence their
usefulness [17, 18]. Although many microbial species are still unidentified, Agrawal
and co-authors [17] listed a wide range of pollutant-degrading microorganisms that
have been spotted by culture-independent techniques and could be harboured in the
root environment of various plant species. The full metabolic capacity of the plant
associated bacteria (plant endophytes and rhizosphere bacteria) has not been
completely resolved yet, although first experiments indicate that microbial activities
can have a strong influence on biotransformation processes of pharmaceuticals
[15, 19] (more details are provided in chapter “Impact of PhACs on Soil
Microorganisms”).
Another factor that has been mostly neglected is the direct availability of active
metabolites that may be excreted from animals or humans. Generally, it is assumed
that 90% of an active compound are metabolized from a mammalian body within
48 h, after treatment. In any case, the availability of parent compounds and major
metabolites will be decisive for their further fate in plants.
2.1 Compounds Properties
One of the primary criteria that influences uptake into roots and translocation in plant
tissue is the molar mass of the pharmaceuticals [20]. Low-molar mass organic
compounds can easily enter the soft rhizodermis and move through the porous
mesh of the cell wall. Hence, organic substances with molar mass <1,000 g/mol
are easily absorbed by the apical sections of plant roots [21]. However according to
Chuang and co-workers [20], only molecules below 300 g/mol can, in general, enter
Uptake and Translocation of Pharmaceuticals in Plants:. . .
107