compounds as well as matrix effects inherent in traditional mass spectrometric
instruments [41]. Dodgen et al. [42] investigated the uptake of diclofenac and
naproxen and found limited translocation of these anionic compounds in plant edible
portions of lettuce (Lactuca sativa) and collards (Brassica oleracea). Interestingly,
they found that the vast majority of
14 C was not extractable from plant tissues.
Meanwhile, the development of multi-residue methods for the analysis of pharmaceuticals with varied physiochemical properties was used to elicit associations
between compound properties and distribution within plants. In experiments using
20 frequently occurring pharmaceuticals and personal care products (PPCPs), the
root uptake of neutral compounds was shown to positively correlate with the
pH-adjusted octanol-water partition coefficient (K OW ) adjusted for pH (D ow ), whilst
the inverse correlation governed translocation from roots to leaves [43]. These trends
suggest the importance of fat solubility (lipophilicity) in root uptake and water
solubility (hydrophilicity) in xylem-mediated translocation. This work builds upon
the results of Tanoue et al. [44] who associated plant uptake with octanol-water
partitioning and translocation with chemical polarity using a suite of 13 pharmaceutical compounds.
Recently, the uptake of 13 other commonly used pharmaceuticals selected to
represent the wide range of physicochemical properties inherent to these compounds
was investigated in lettuce [34]. This study investigated the multiple inter- and
intracellular pathways by which pharmaceuticals can enter and translocate within
plants. These were the symplast pathway, utilising either passive diffusion across the
lipid bilayer membranes or transport utilising integral protein transport in cell walls,
and the apoplast pathway as well as the role of the casparian strip in controlling
which compounds enter the xylem. The study suggests that there is a molecular
weight cut-off around 300 g/mol where physical limitation controlled the pathway
that a compound could utilise. Furthermore, using a traditional sorption isotherm
system with freeze-dried plants roots, the sorption affinity of these compounds was
shown to be a strong indicator of root accumulation and predicted limited translocation to other plant parts [34].
Protein-mediated transport was demonstrated for the psychoactive pharmaceutical amitriptyline by Nason et al. [45]. Investigating the uptake of four psychoactive
drugs (carbamazepine, amitriptyline, fluoxetine and lamotrigine), the authors found
that the uptake strongly followed transpiration-based accumulation and suggested
that underestimation by the model could be the result of a lack of consideration of
transporter protein-facilitated uptake. Furthermore, this work also showed that the
co-occurrence of psychoactive compounds affected both uptake and metabolism of
these compounds and highlights the need for more studies investigating mixture
effects. Nason et al.’s study confirmed the earlier work of Dodgen et al. [46],
whereby the hydroponic system was used to show that increased transpiration
resulted in increased uptake for ionised compounds.
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L. J. Carter et al.
instruments [41]. Dodgen et al. [42] investigated the uptake of diclofenac and
naproxen and found limited translocation of these anionic compounds in plant edible
portions of lettuce (Lactuca sativa) and collards (Brassica oleracea). Interestingly,
they found that the vast majority of
14 C was not extractable from plant tissues.
Meanwhile, the development of multi-residue methods for the analysis of pharmaceuticals with varied physiochemical properties was used to elicit associations
between compound properties and distribution within plants. In experiments using
20 frequently occurring pharmaceuticals and personal care products (PPCPs), the
root uptake of neutral compounds was shown to positively correlate with the
pH-adjusted octanol-water partition coefficient (K OW ) adjusted for pH (D ow ), whilst
the inverse correlation governed translocation from roots to leaves [43]. These trends
suggest the importance of fat solubility (lipophilicity) in root uptake and water
solubility (hydrophilicity) in xylem-mediated translocation. This work builds upon
the results of Tanoue et al. [44] who associated plant uptake with octanol-water
partitioning and translocation with chemical polarity using a suite of 13 pharmaceutical compounds.
Recently, the uptake of 13 other commonly used pharmaceuticals selected to
represent the wide range of physicochemical properties inherent to these compounds
was investigated in lettuce [34]. This study investigated the multiple inter- and
intracellular pathways by which pharmaceuticals can enter and translocate within
plants. These were the symplast pathway, utilising either passive diffusion across the
lipid bilayer membranes or transport utilising integral protein transport in cell walls,
and the apoplast pathway as well as the role of the casparian strip in controlling
which compounds enter the xylem. The study suggests that there is a molecular
weight cut-off around 300 g/mol where physical limitation controlled the pathway
that a compound could utilise. Furthermore, using a traditional sorption isotherm
system with freeze-dried plants roots, the sorption affinity of these compounds was
shown to be a strong indicator of root accumulation and predicted limited translocation to other plant parts [34].
Protein-mediated transport was demonstrated for the psychoactive pharmaceutical amitriptyline by Nason et al. [45]. Investigating the uptake of four psychoactive
drugs (carbamazepine, amitriptyline, fluoxetine and lamotrigine), the authors found
that the uptake strongly followed transpiration-based accumulation and suggested
that underestimation by the model could be the result of a lack of consideration of
transporter protein-facilitated uptake. Furthermore, this work also showed that the
co-occurrence of psychoactive compounds affected both uptake and metabolism of
these compounds and highlights the need for more studies investigating mixture
effects. Nason et al.’s study confirmed the earlier work of Dodgen et al. [46],
whereby the hydroponic system was used to show that increased transpiration
resulted in increased uptake for ionised compounds.
186
L. J. Carter et al.