change increases the pressure on freshwater resources in many regions where precipitations are scarce and subject to large seasonal and annual fluctuations. Concentrations of human pharmaceuticals and their metabolites are detected continuously in
wastewaters. Since the use of treated wastewater to irrigate crops is getting widespread in regions where freshwater is limited, drugs are released in the agrosystems
by wastewater irrigation. Then soils are exposed to drugs, and crops can take up and
translocate them becoming this fact a food safety issue. Many of the reported plant
uptake studies have been performed in hydroponic settings; the information on the
fate of these compounds in soil-plant system is not always available. Only through
field experiments can the actual potential uptake of drugs by crops be fully assessed
and integrated into a database for risk assessment. The chemical uptake by plant
roots in soil-root-leaves system depends largely on sorption and desorption of
contaminants in soils and their physicochemical properties.
In general, organic chemicals with logP >4 are expected to have a high potential
for root retention and low translocation capacity. Moderately hydrophobic compounds are most likely to be translocated by plants, as observed in previous research
with the most translocatable compounds exhibiting a logP between 1 and 4. The
molecular mass histogram demonstrates that translocatable compounds generally
have a molecular mass of <350 Da, below Lipinski’s cutoff of 500 Da. Hydrogen
bond donor and acceptor histograms appear to have cutoffs around 4 and 7, respectively. Carbamazepine as a neutral compound is expected to show high mobility in
plants because of its low molecular weight (236 Da), a moderate logP (2.8), and low
hydrogen bonding capacity (1 donor and 1 acceptor). Other compounds that can
potentially be translocated are expected to be identified by considering the balance
between water solubility, passive membrane permeability, and size. Once they are
translocated the compounds can covalently bound to vacuoles. There are a few
studies evaluating the formation of non-extractable residues of drugs, the most
informative experimental approach being the use of radiolabeled
14 C compounds.
Recently, in a study using
14 C-labeled diclofenac and naproxen, a large fraction of
these compounds was observed to be converted into not extractable material in plant
tissues. There is the need to conduct more studies with radiolabeled drugs to
facilitate quantitative assessment of covalent binding, in order to evaluate which
compounds are most prone to be bound. At the last step prior to human consumption
are studies to determine the relevance of the release of bound-residues upon cooking
or other forms of food processing.
4 Toxicity in the Environment and Humans
Few studies have evaluated the exposure of drugs through the intake of vegetables.
Some studies have demonstrated that health threat due to the consumption of
vegetables irrigated with treated wastewater is low. However, it has been detected
that in root crops for two compounds (lamotrigine and 10,11-epoxycarbamazepine)
detected in carrot roots, carrot leaves, and sweet potato leaves, a health risk was
528
S. Pérez et al.
wastewaters. Since the use of treated wastewater to irrigate crops is getting widespread in regions where freshwater is limited, drugs are released in the agrosystems
by wastewater irrigation. Then soils are exposed to drugs, and crops can take up and
translocate them becoming this fact a food safety issue. Many of the reported plant
uptake studies have been performed in hydroponic settings; the information on the
fate of these compounds in soil-plant system is not always available. Only through
field experiments can the actual potential uptake of drugs by crops be fully assessed
and integrated into a database for risk assessment. The chemical uptake by plant
roots in soil-root-leaves system depends largely on sorption and desorption of
contaminants in soils and their physicochemical properties.
In general, organic chemicals with logP >4 are expected to have a high potential
for root retention and low translocation capacity. Moderately hydrophobic compounds are most likely to be translocated by plants, as observed in previous research
with the most translocatable compounds exhibiting a logP between 1 and 4. The
molecular mass histogram demonstrates that translocatable compounds generally
have a molecular mass of <350 Da, below Lipinski’s cutoff of 500 Da. Hydrogen
bond donor and acceptor histograms appear to have cutoffs around 4 and 7, respectively. Carbamazepine as a neutral compound is expected to show high mobility in
plants because of its low molecular weight (236 Da), a moderate logP (2.8), and low
hydrogen bonding capacity (1 donor and 1 acceptor). Other compounds that can
potentially be translocated are expected to be identified by considering the balance
between water solubility, passive membrane permeability, and size. Once they are
translocated the compounds can covalently bound to vacuoles. There are a few
studies evaluating the formation of non-extractable residues of drugs, the most
informative experimental approach being the use of radiolabeled
14 C compounds.
Recently, in a study using
14 C-labeled diclofenac and naproxen, a large fraction of
these compounds was observed to be converted into not extractable material in plant
tissues. There is the need to conduct more studies with radiolabeled drugs to
facilitate quantitative assessment of covalent binding, in order to evaluate which
compounds are most prone to be bound. At the last step prior to human consumption
are studies to determine the relevance of the release of bound-residues upon cooking
or other forms of food processing.
4 Toxicity in the Environment and Humans
Few studies have evaluated the exposure of drugs through the intake of vegetables.
Some studies have demonstrated that health threat due to the consumption of
vegetables irrigated with treated wastewater is low. However, it has been detected
that in root crops for two compounds (lamotrigine and 10,11-epoxycarbamazepine)
detected in carrot roots, carrot leaves, and sweet potato leaves, a health risk was
528
S. Pérez et al.