the roots than the leaves of the pinto bean, up to 31 μg/g and 6.4 μg/g, respectively.
Unlike most published research where plant samples are taken on the final day of
harvest for chemical analysis, samples in this experiment were taken every 7 days for
a period of 28 days which enabled the kinetics of plant uptake to be evaluated. In the
soil exposure, maximum accumulation in the roots was reached after 14 days for
both chemicals, after which there was little to no further increase. In fact, the
distribution of EE2 to roots decreased over time from 1.5% in the first week to
0.8% in the fourth week. Conversely, for the sand exposure, accumulation was much
larger on the whole and continued to increase in a linear fashion in the roots for both
EE2 and triclosan. Comparatively, the distribution of EE2 in leaves from the sand
exposure was very low (0–0.7%) during the first 3 weeks, although it did increase
over time, whereas it was very low in leaves (0.1–0.7%) over the entire study period.
3.2 Differences in Accumulation Amongst Different Plant
Species
Studies previously discussed highlight differences in the uptake and accumulation of
pharmaceuticals not only within various plant organs but also across a wide range of
plant species. Differences may be explained by factors such as degree of root growth,
transpiration rates and the size and shape of the leaf material. Differences in plant
lipid contents may also be important as this can affect the sorption of hydrophobic
chemicals [67]. For example, the lipid content of perennial ryegrass is higher than for
radish bulbs, which only contain trace amounts of lipid. Carter et al. [5] suggested
this may, in part, explain the lower uptake of carbamazepine, diclofenac and
propranolol in radish. Differences in plant uptake behaviour, however, could not
be solely attributable to differences in lipid content between plants, which was
supported by findings in a study by Wu et al. [68].
The role of species traits in plant uptake has been comprehensively addressed in a
greenhouse study by Eggen et al. [63] who investigated the accumulation of the
antidiabetic medication, metformin, in nine edible plant species encompassing fruits,
cereals, leaves and roots. The species included barley (Hordeum vulgare cv. Edel),
wheat (Triticum aestivum cv. Bjarne), oat (Avena sativa cv. Berlinda), carrot
(Daucus carota cvs. Napoli and Amagar), potato (Solanum tuberosum cv. Astrix),
tomato (Solanum lycopersicum cv. Suzanne), zucchini (Cucurbita pepo cv. Black
Beauty), bean (Vicia faba cv. Red Epicure) and rape (Brassica rapa cv. Valo,
Brassica napus cv. Sheik and Brassica napus cv. Sola). High uptake and translocation of metformin in oily seeds of rape B. napus and B. rapa were measured with
BCFs up to 21.72. Comparatively, the BCFs for the cereals were 15–70 times lower,
0.29, 0.91 and 1.35 for wheat, barley and oat, respectively, and accumulation factors
of metformin in tomato and squash fruits were even less. The authors suggested this
might be a result of metformin being able to mimic natural nitrogen compounds
which are easily carried across membranes via transporters in high allocation
Uptake and Effects of Pharmaceuticals in the Soil-Plant-Earthworm System
191
Unlike most published research where plant samples are taken on the final day of
harvest for chemical analysis, samples in this experiment were taken every 7 days for
a period of 28 days which enabled the kinetics of plant uptake to be evaluated. In the
soil exposure, maximum accumulation in the roots was reached after 14 days for
both chemicals, after which there was little to no further increase. In fact, the
distribution of EE2 to roots decreased over time from 1.5% in the first week to
0.8% in the fourth week. Conversely, for the sand exposure, accumulation was much
larger on the whole and continued to increase in a linear fashion in the roots for both
EE2 and triclosan. Comparatively, the distribution of EE2 in leaves from the sand
exposure was very low (0–0.7%) during the first 3 weeks, although it did increase
over time, whereas it was very low in leaves (0.1–0.7%) over the entire study period.
3.2 Differences in Accumulation Amongst Different Plant
Species
Studies previously discussed highlight differences in the uptake and accumulation of
pharmaceuticals not only within various plant organs but also across a wide range of
plant species. Differences may be explained by factors such as degree of root growth,
transpiration rates and the size and shape of the leaf material. Differences in plant
lipid contents may also be important as this can affect the sorption of hydrophobic
chemicals [67]. For example, the lipid content of perennial ryegrass is higher than for
radish bulbs, which only contain trace amounts of lipid. Carter et al. [5] suggested
this may, in part, explain the lower uptake of carbamazepine, diclofenac and
propranolol in radish. Differences in plant uptake behaviour, however, could not
be solely attributable to differences in lipid content between plants, which was
supported by findings in a study by Wu et al. [68].
The role of species traits in plant uptake has been comprehensively addressed in a
greenhouse study by Eggen et al. [63] who investigated the accumulation of the
antidiabetic medication, metformin, in nine edible plant species encompassing fruits,
cereals, leaves and roots. The species included barley (Hordeum vulgare cv. Edel),
wheat (Triticum aestivum cv. Bjarne), oat (Avena sativa cv. Berlinda), carrot
(Daucus carota cvs. Napoli and Amagar), potato (Solanum tuberosum cv. Astrix),
tomato (Solanum lycopersicum cv. Suzanne), zucchini (Cucurbita pepo cv. Black
Beauty), bean (Vicia faba cv. Red Epicure) and rape (Brassica rapa cv. Valo,
Brassica napus cv. Sheik and Brassica napus cv. Sola). High uptake and translocation of metformin in oily seeds of rape B. napus and B. rapa were measured with
BCFs up to 21.72. Comparatively, the BCFs for the cereals were 15–70 times lower,
0.29, 0.91 and 1.35 for wheat, barley and oat, respectively, and accumulation factors
of metformin in tomato and squash fruits were even less. The authors suggested this
might be a result of metformin being able to mimic natural nitrogen compounds
which are easily carried across membranes via transporters in high allocation
Uptake and Effects of Pharmaceuticals in the Soil-Plant-Earthworm System
191