(Table 3). These results are mainly represented by Wu and co-workers [110], where
the highest translocations were observed for pepper plants (Capsicum annuum) even
when exposed to different concentrations (0.5 and 5 μg/L), which might indicate a
favoured translocation because of the plant species. Moreover, dilantin displays only
a slightly negative pKa (À0.003), which could mean that its behaviour is more
similar to a neutral compound, like carbamazepine, than to an anionic one.
The uptake of the psychotropic drug diazepam was studied in a radish experiment
in soil [130]. As for all studied compounds on this crop, TF values were higher than
the ones for BCF (Table 4, Fig. 5b), however according to its log D OW (4.73), it
would be expected the opposite, which might indicate the important role of this
specific plant species [11, 102, 112, 121, 124]. This hypothesis is also supported by
the higher BCF > TF values of diazepam in different other plants (cucumber, lettuce,
pepper, spinach), which was tested in hydroponic experiments [109, 110].
Lastly, average TF values of ibuprofen (anti-inflammatory) were higher than
average BCF values in hydroponic studies [109, 110, 126, 127, 135]. However,
these differences are mainly caused by the presence of an outlier in TF observations
(see Fig. 5a).
3.2.3 Cationic Compounds
In hydroponic studies with cationic compounds, generally higher BCFs>TFs were
obtained (Tables 5 and 6, Fig. 6). The main reason behind this observation might be
the fact that plant cell walls are negatively charged, due to their high concentration in
uronic acids [142]. The electrostatic attraction between the root cell wall and the
cationic compounds may facilitate adsorption to the root epidermis. Compounds that
are positively charged at pH 4–6 can be trapped in the apoplast or root vacuoles
(pH 5) [63]. Consequently, a reduced concentration can enter the vascular system for
the translocation to aerial parts.
Among these cases, atenolol (beta-blocker) and trazodone (psychotropic drug)
presented TFs > BCFs. For both compounds, this might be related to the high
concentrations applied (830–1,000 and 10,000 μg/L, respectively) and to the plant
species used [11, 139]. Kedosová and colleagues [11] registered higher atenolol
concentrations in leaves of radish and spinach than in arugula and lamb’s lettuce.
Additionally, in the study of Reichl et al. [139], high amounts of trazodone in cress
aerial tissues (Lepidium sativum) were registered, showing that uptake efficiency is
dependent of the plant species used, and therefore, for studies of human health risk
assessment, different plant species should be tested to estimate more reliable risks.
For soil data, when compared to BCFs values, higher TFs were calculated
(Table 6). According to Miller and co-workers [9], some evidences were already
demonstrated, that cationic compounds applied to soil have higher TF values than,
for example, anionic ones. However, in our studies no correlation was found
between TFs and the respective log D OW , suggesting that other factors might be
more relevant for the translocation of cationic compounds.
Uptake and Translocation of Pharmaceuticals in Plants:. . .
129
the highest translocations were observed for pepper plants (Capsicum annuum) even
when exposed to different concentrations (0.5 and 5 μg/L), which might indicate a
favoured translocation because of the plant species. Moreover, dilantin displays only
a slightly negative pKa (À0.003), which could mean that its behaviour is more
similar to a neutral compound, like carbamazepine, than to an anionic one.
The uptake of the psychotropic drug diazepam was studied in a radish experiment
in soil [130]. As for all studied compounds on this crop, TF values were higher than
the ones for BCF (Table 4, Fig. 5b), however according to its log D OW (4.73), it
would be expected the opposite, which might indicate the important role of this
specific plant species [11, 102, 112, 121, 124]. This hypothesis is also supported by
the higher BCF > TF values of diazepam in different other plants (cucumber, lettuce,
pepper, spinach), which was tested in hydroponic experiments [109, 110].
Lastly, average TF values of ibuprofen (anti-inflammatory) were higher than
average BCF values in hydroponic studies [109, 110, 126, 127, 135]. However,
these differences are mainly caused by the presence of an outlier in TF observations
(see Fig. 5a).
3.2.3 Cationic Compounds
In hydroponic studies with cationic compounds, generally higher BCFs>TFs were
obtained (Tables 5 and 6, Fig. 6). The main reason behind this observation might be
the fact that plant cell walls are negatively charged, due to their high concentration in
uronic acids [142]. The electrostatic attraction between the root cell wall and the
cationic compounds may facilitate adsorption to the root epidermis. Compounds that
are positively charged at pH 4–6 can be trapped in the apoplast or root vacuoles
(pH 5) [63]. Consequently, a reduced concentration can enter the vascular system for
the translocation to aerial parts.
Among these cases, atenolol (beta-blocker) and trazodone (psychotropic drug)
presented TFs > BCFs. For both compounds, this might be related to the high
concentrations applied (830–1,000 and 10,000 μg/L, respectively) and to the plant
species used [11, 139]. Kedosová and colleagues [11] registered higher atenolol
concentrations in leaves of radish and spinach than in arugula and lamb’s lettuce.
Additionally, in the study of Reichl et al. [139], high amounts of trazodone in cress
aerial tissues (Lepidium sativum) were registered, showing that uptake efficiency is
dependent of the plant species used, and therefore, for studies of human health risk
assessment, different plant species should be tested to estimate more reliable risks.
For soil data, when compared to BCFs values, higher TFs were calculated
(Table 6). According to Miller and co-workers [9], some evidences were already
demonstrated, that cationic compounds applied to soil have higher TF values than,
for example, anionic ones. However, in our studies no correlation was found
between TFs and the respective log D OW , suggesting that other factors might be
more relevant for the translocation of cationic compounds.
Uptake and Translocation of Pharmaceuticals in Plants:. . .
129