(lincomycin, sulfamethoxazole) by two different lettuce cultivars. By sampling at
three points throughout the growth stage, they also demonstrated how the rate of
plant growth during the maturation process can exceed the rate of uptake, resulting in
decreasing concentrations in lettuce leaves. Azanu et al. [76] showed similar relative
concentrations of amoxicillin and tetracycline uptake in the edible portions of lettuce
and carrot with average concentrations of amoxicillin 27.1 ng/g and tetracycline
20.2 ng/g.
Such results have contributed to prioritisation efforts, like that of Christou et al.
[77], who ranked different crop species based on potential risk resulting from the
accumulation of pharmaceuticals. They show that leafy green vegetables and root
edible vegetables pose the most significant human exposure risk due to the consumption of pharmaceuticals in fresh produce.
4.1.2 Impacts of Soil Type
Unlike hydroponic systems, the soil-plant system introduces both the relevance and
complexities of chemical-soil-plant interactions. A few studies using
pharmaceutical-fortified irrigation water have been conducted using soils of differing properties in an effort to determine how soil-pharmaceutical interactions impact
uptake. In addition to four plant species, Kodesova et al. [29] also investigated three
soil types (loess, paragneiss and sand). Interestingly, they showed that differences in
transformation processes of the compounds in the different soils had a more significant impact on uptake than the sorption affinity of the compounds to the different
soils. Sallach et al. [78] utilised a manipulated soil system, whereby sand and
Sharpsburg silt clay were mixed at varying proportions to provide a low organic
sand, sandy loam and loam soil. Uptake into lettuce of three antibiotic compounds
(lincomycin, oxytetracycline and sulfamethoxazole) was compared with their sorption coefficient (K d ) values in each of the three soils. Results showed that only the
uptake of sulfamethoxazole in lettuce shoots followed the expected trend of increasing uptake resulting from decreasing soil sorption (K d ), whereas oxytetracycline,
with a K d value three orders of magnitude greater than sulfamethoxazole, was not
detected in lettuce shoots.
4.1.3 Impacts of Environmental Conditions
Whereas the hydroponic system has been used to show the significance of transpiration rate on pharmaceutical uptake [45, 46], the fortified irrigation system has been
used to evaluate how environmental processes, namely, soil moisture conditions,
impact the uptake of pharmaceuticals. Santiago et al. [79] used varied volumetric soil
moisture depletion thresholds of 14% (À4.26 kPa), 10% (À8.66 kPa) and 7%
(À18.37 kPa) to investigate the uptake of atenolol, diclofenac and ofloxacin in
cowpea (Vigna unguiculata), Swiss chard (Beta vulgaris var. cicla), turnip (Brassica
rapa var. rapa), whole collards, basil (Ocimum basilicum), lettuce and cilantro
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three points throughout the growth stage, they also demonstrated how the rate of
plant growth during the maturation process can exceed the rate of uptake, resulting in
decreasing concentrations in lettuce leaves. Azanu et al. [76] showed similar relative
concentrations of amoxicillin and tetracycline uptake in the edible portions of lettuce
and carrot with average concentrations of amoxicillin 27.1 ng/g and tetracycline
20.2 ng/g.
Such results have contributed to prioritisation efforts, like that of Christou et al.
[77], who ranked different crop species based on potential risk resulting from the
accumulation of pharmaceuticals. They show that leafy green vegetables and root
edible vegetables pose the most significant human exposure risk due to the consumption of pharmaceuticals in fresh produce.
4.1.2 Impacts of Soil Type
Unlike hydroponic systems, the soil-plant system introduces both the relevance and
complexities of chemical-soil-plant interactions. A few studies using
pharmaceutical-fortified irrigation water have been conducted using soils of differing properties in an effort to determine how soil-pharmaceutical interactions impact
uptake. In addition to four plant species, Kodesova et al. [29] also investigated three
soil types (loess, paragneiss and sand). Interestingly, they showed that differences in
transformation processes of the compounds in the different soils had a more significant impact on uptake than the sorption affinity of the compounds to the different
soils. Sallach et al. [78] utilised a manipulated soil system, whereby sand and
Sharpsburg silt clay were mixed at varying proportions to provide a low organic
sand, sandy loam and loam soil. Uptake into lettuce of three antibiotic compounds
(lincomycin, oxytetracycline and sulfamethoxazole) was compared with their sorption coefficient (K d ) values in each of the three soils. Results showed that only the
uptake of sulfamethoxazole in lettuce shoots followed the expected trend of increasing uptake resulting from decreasing soil sorption (K d ), whereas oxytetracycline,
with a K d value three orders of magnitude greater than sulfamethoxazole, was not
detected in lettuce shoots.
4.1.3 Impacts of Environmental Conditions
Whereas the hydroponic system has been used to show the significance of transpiration rate on pharmaceutical uptake [45, 46], the fortified irrigation system has been
used to evaluate how environmental processes, namely, soil moisture conditions,
impact the uptake of pharmaceuticals. Santiago et al. [79] used varied volumetric soil
moisture depletion thresholds of 14% (À4.26 kPa), 10% (À8.66 kPa) and 7%
(À18.37 kPa) to investigate the uptake of atenolol, diclofenac and ofloxacin in
cowpea (Vigna unguiculata), Swiss chard (Beta vulgaris var. cicla), turnip (Brassica
rapa var. rapa), whole collards, basil (Ocimum basilicum), lettuce and cilantro
194
L. J. Carter et al.