3 Natural Attenuation of Pharmaceuticals in the Aquatic …
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phototransformation only at high pH (Baena-nogueras et al. 2017). However, natural
attenuation of these pharmaceuticals via phototransformation is highly unlikely in
the freshwater aquatic environment (Yang et al. 2017).
Indirect photolysis plays an important role in the phototransformation of carbamazepine in natural waters. Presence of nitrate ions and humic constituents of
DOM were reported to enhance the transformation of carbamazepine into readily
degradable photoproducts in surface water (Lam and Mabury 2005), while under
direct photolytic conditions, carbamazepine was found to be extremely persistent.
At environmentally relevant concentration at neutral pH, ambient temperature, and
sufficient dissolved oxygen, carbamazepine showed a half-life of over 25 days under
direct photolysis, while the same was reduced to 4.5 days in the presence of humic
substances, acidic pH, and ample dissolved oxygen (Calisto et al. 2011). Gabapentin
is another commonly used antiepileptic drug. It is known to be eliminated almost
entirely in its native form such that it is present in surface water and even in potable
water (Herrmann et al. 2015). The major issue with this pharmaceutical is that under
UV treatment in drinking water plants, it forms a large number of persistent and
toxic photoproducts. These products are more toxic than the parent compound (Herrmann et al. 2015). These dead-end photoproducts end up in surface water, and they
have been reported to be present even after prolonged photolysis. A similar case,
wherein more toxic transformation by-products were discharged and detected in surface water, was those of the antidepressant, trimipramine (Khaleel et al. 2017) and
antipsychotic drug, quetiapine (Herrmann et al. 2016).
The case of fluoxetine, a selective serotonin uptake inhibitor, is somewhat different. Fluoxetine is extremely photostable under UVA (320–400 nm) irradiation in the
presence of humic substances and dissolved organic carbon photosensitizers. However, significant degradation of the compound is observed in the presence of a variety
of cations, such as Cu (II), Fe (II), Fe (III), and Al (III) ions (Maalanka et al. 2013).
Phototransformation of fluoxetine with metal ions is consistent with the kinetics of
a first-order reaction, and the reaction rate constant is the highest in the presence of
Cu(II) ions and the slowest in the presence of Al(III) ions. Desipramine was also
shown to undergo significantly higher photolytic removal under solar simulator via
the indirect pathway, owing to the presence of humic substances (half-life of 12 h,
as opposed to 36 h via direct pathway) (Gros et al. 2015; Khaleel et al. 2016). On the
other hand, another less commonly prescribed antidepressant, amisulpride was readily degraded through the direct photolysis under simulated sunlight in ultrapure water
(half-life of 3 h). Nevertheless, amisulpride was the only pharmaceutical belonging
to this class of drugs that underwent complete degradation without the generation of
toxic by-products (Gros et al. 2015).
Steroid and Hormones
The similar issue regarding the removal of steroidal pharmaceuticals and hormones
is their ability to cause endocrine disruption in aquatic life (Archer et al. 2017). Most
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phototransformation only at high pH (Baena-nogueras et al. 2017). However, natural
attenuation of these pharmaceuticals via phototransformation is highly unlikely in
the freshwater aquatic environment (Yang et al. 2017).
Indirect photolysis plays an important role in the phototransformation of carbamazepine in natural waters. Presence of nitrate ions and humic constituents of
DOM were reported to enhance the transformation of carbamazepine into readily
degradable photoproducts in surface water (Lam and Mabury 2005), while under
direct photolytic conditions, carbamazepine was found to be extremely persistent.
At environmentally relevant concentration at neutral pH, ambient temperature, and
sufficient dissolved oxygen, carbamazepine showed a half-life of over 25 days under
direct photolysis, while the same was reduced to 4.5 days in the presence of humic
substances, acidic pH, and ample dissolved oxygen (Calisto et al. 2011). Gabapentin
is another commonly used antiepileptic drug. It is known to be eliminated almost
entirely in its native form such that it is present in surface water and even in potable
water (Herrmann et al. 2015). The major issue with this pharmaceutical is that under
UV treatment in drinking water plants, it forms a large number of persistent and
toxic photoproducts. These products are more toxic than the parent compound (Herrmann et al. 2015). These dead-end photoproducts end up in surface water, and they
have been reported to be present even after prolonged photolysis. A similar case,
wherein more toxic transformation by-products were discharged and detected in surface water, was those of the antidepressant, trimipramine (Khaleel et al. 2017) and
antipsychotic drug, quetiapine (Herrmann et al. 2016).
The case of fluoxetine, a selective serotonin uptake inhibitor, is somewhat different. Fluoxetine is extremely photostable under UVA (320–400 nm) irradiation in the
presence of humic substances and dissolved organic carbon photosensitizers. However, significant degradation of the compound is observed in the presence of a variety
of cations, such as Cu (II), Fe (II), Fe (III), and Al (III) ions (Maalanka et al. 2013).
Phototransformation of fluoxetine with metal ions is consistent with the kinetics of
a first-order reaction, and the reaction rate constant is the highest in the presence of
Cu(II) ions and the slowest in the presence of Al(III) ions. Desipramine was also
shown to undergo significantly higher photolytic removal under solar simulator via
the indirect pathway, owing to the presence of humic substances (half-life of 12 h,
as opposed to 36 h via direct pathway) (Gros et al. 2015; Khaleel et al. 2016). On the
other hand, another less commonly prescribed antidepressant, amisulpride was readily degraded through the direct photolysis under simulated sunlight in ultrapure water
(half-life of 3 h). Nevertheless, amisulpride was the only pharmaceutical belonging
to this class of drugs that underwent complete degradation without the generation of
toxic by-products (Gros et al. 2015).
Steroid and Hormones
The similar issue regarding the removal of steroidal pharmaceuticals and hormones
is their ability to cause endocrine disruption in aquatic life (Archer et al. 2017). Most