4.2 Wastewater Exposure
Hydroponic, spiked soil and fortified water irrigation studies have provided significant insights into the processes that underlie the uptake and translocation of
pharmaceuticals in plants. However, these systems only simulate the agricultural
practices by which pharmaceuticals enter the agroecosystem. These studies simplify
the issue by removing the complexity of finished wastewater that is also composed
of levels of organics, salts and nutrients as well as microbiological activity. Whilst
some studies have made efforts to artificially include these complexities with abiotic
synthetic wastewater [75], work over the past 10 years has sought to approach and
even evaluate pharmaceutical uptake from actual reclaimed wastewater in greenhouse, semi-field and field studies.
One of the challenges of using treated wastewater is that the levels of particular
pharmaceuticals fluctuate day-to-day and even intra-day depending on usage practices [83]. Therefore, gaining insights into the mechanisms of uptake is challenging.
However, fortifying wastewater with a known concentration of one or more pharmaceuticals ensures a minimum exposure concentration, in addition to the background levels in the wastewater, and allows for the study of uptake with all the
additional complexity of the wastewater matrix. Although not field-based studies,
studies using actual wastewater described below are limited in number of studies,
region of the world studied and compounds investigated (Table 1).
4.2.1 Greenhouse Studies: Israel
Shenker et al. [23] were one of the first to apply this approach of fortifying
wastewater to study the uptake and accumulation of carbamazepine in cucumber
plants. Greenhouse studies with wastewater fortified with carbamazepine at 1 μg/L
showed that BCFs in plant leaves ranged from 17 to 20, whilst root BCFs were far
less at 0.8–1. This approach has been used to show the distribution of both neutral
compounds (carbamazepine, lamotrigine and caffeine) and ionic compounds (metoprolol, bezafibrate, clofibric acid, diclofenac, gemfibrozil, ibuprofen, ketoprofen,
naproxen, sulfamethoxazole and sildenafil) in plant portions of two root vegetables,
carrots and sweet potatoes (Ipomoea batatas) [20]. Using treated wastewater from a
conventional activated sludge system in Israel fortified with the select pharmaceuticals at environmentally measured concentrations, it was shown that neutral compounds lamotrigine, carbamazepine and the carbamazepine metabolite 10,11epoxycarbamazepine were accumulated at the highest concentrations, as high as
25 ng/g fresh weight. Using a threshold of toxicological concern (TTC) approach,
lamotrigine in carrots consumed by children could exceed the TTC threshold and
thus be characterised as an emerging concern. Building on this work, Paz et al. [84]
showed that sorption of lamotrigine and carbamazepine and its major metabolites in
wastewater to soils was governed by soil organic matter content. When the soils
produced by the experiments in Malchi et al. [20] were then used for wheat
196
L. J. Carter et al.
Hydroponic, spiked soil and fortified water irrigation studies have provided significant insights into the processes that underlie the uptake and translocation of
pharmaceuticals in plants. However, these systems only simulate the agricultural
practices by which pharmaceuticals enter the agroecosystem. These studies simplify
the issue by removing the complexity of finished wastewater that is also composed
of levels of organics, salts and nutrients as well as microbiological activity. Whilst
some studies have made efforts to artificially include these complexities with abiotic
synthetic wastewater [75], work over the past 10 years has sought to approach and
even evaluate pharmaceutical uptake from actual reclaimed wastewater in greenhouse, semi-field and field studies.
One of the challenges of using treated wastewater is that the levels of particular
pharmaceuticals fluctuate day-to-day and even intra-day depending on usage practices [83]. Therefore, gaining insights into the mechanisms of uptake is challenging.
However, fortifying wastewater with a known concentration of one or more pharmaceuticals ensures a minimum exposure concentration, in addition to the background levels in the wastewater, and allows for the study of uptake with all the
additional complexity of the wastewater matrix. Although not field-based studies,
studies using actual wastewater described below are limited in number of studies,
region of the world studied and compounds investigated (Table 1).
4.2.1 Greenhouse Studies: Israel
Shenker et al. [23] were one of the first to apply this approach of fortifying
wastewater to study the uptake and accumulation of carbamazepine in cucumber
plants. Greenhouse studies with wastewater fortified with carbamazepine at 1 μg/L
showed that BCFs in plant leaves ranged from 17 to 20, whilst root BCFs were far
less at 0.8–1. This approach has been used to show the distribution of both neutral
compounds (carbamazepine, lamotrigine and caffeine) and ionic compounds (metoprolol, bezafibrate, clofibric acid, diclofenac, gemfibrozil, ibuprofen, ketoprofen,
naproxen, sulfamethoxazole and sildenafil) in plant portions of two root vegetables,
carrots and sweet potatoes (Ipomoea batatas) [20]. Using treated wastewater from a
conventional activated sludge system in Israel fortified with the select pharmaceuticals at environmentally measured concentrations, it was shown that neutral compounds lamotrigine, carbamazepine and the carbamazepine metabolite 10,11epoxycarbamazepine were accumulated at the highest concentrations, as high as
25 ng/g fresh weight. Using a threshold of toxicological concern (TTC) approach,
lamotrigine in carrots consumed by children could exceed the TTC threshold and
thus be characterised as an emerging concern. Building on this work, Paz et al. [84]
showed that sorption of lamotrigine and carbamazepine and its major metabolites in
wastewater to soils was governed by soil organic matter content. When the soils
produced by the experiments in Malchi et al. [20] were then used for wheat
196
L. J. Carter et al.