80
S. Mohapatra et al.
the degradation rate of diclofenac in purified water, deionized water, and Mississippi
river water as reported by Packer et al. (2003). The authors proposed that addition of
the quencher possibly led to the generation of other radicals or led to photoreduction
of the carboxyl group (–COOH) containing diclofenac, with isopropanol serving
as the H-source. Such reactions are commonly observed for acidic pharmaceuticals,
such as naproxen, ibuprofen, aspirin, and clofibric acid (Packer et al. 2003). Typically,
in the case of diclofenac, the presence of humic substances was found to act more as
an inner filter, limiting the light reaching the parent compound (Zhang et al. 2008a,
b). On the other hand, contradictory results regarding the role of photosensitizers
and indirect photolytic pathway have been reported for other NSAIDs.
Acetaminophen or paracetamol was also reported to undergo around 27% removal
in surface waters in the summer season by phototransformation for studies conducted
in the River Aire, UK (Ebele et al. 2017). In surface waters, the mechanism of
phototransformation of acetaminophen was deduced to be via the indirect pathway
with a half-life of 29 h (Baena-nogueras et al. 2017). However, similar to the case
with naproxen and diclofenac, photoproducts of acetaminophen have been reported
to be more complex and more recalcitrant than the parent compound. For instance,
13 photoproducts of acetaminophen were identified in a study. These products were
structurally different from microbial biodegradation products or human metabolites
(Yin et al. 2017). Studies by Kawabata et al. (2012) also showed that upon exposure to
UV light, acetaminophen dimerizes, leading to the formation of a toxic photoproduct
as revealed by the bioluminescence inhibition assay.
Antiepileptic and Antidepressants
Antiepileptic drugs and psychoactive drugs are by design highly hydrophobic as they
have to cross the blood–brain barrier of the human body. Carbamazepine, a widely
used antiepileptic drug, has been most commonly detected at relatively high concentrations in surface waters around the world, along with its metabolites, trans-10,11dihydro-10,11- dihydroxycarbamazepine (Zhang et al. 2008a, b). These are among
the most persistent and recalcitrant pharmaceuticals occurring in surface waters.
Negligible removal by direct phototransformation was reported for carbamazepine,
fluoxetine, caffeine, and amitriptyline in distilled water exposed to the solar simulator by Baena-nogueras et al. (2017). However, Matamoros et al. (2009) reported
degradation at 45 °C with a half-life of 35 h. This was attributed to the thermal
disintegration of carbamazepine to iminostilbene. Additionally, carbamazepine was
also reported to undergo some removal when spiked water samples were exposed to
500 W Xe lamps, as opposed to 300 W Xenon lamps, usually used in solar simulators
(Baena-nogueras et al. 2017). High acidity or salinity can also increase phototransformation rates. For experiments in seawater, tenfold decrease in half-life was observed
as compared to that in freshwater (Matamoros et al. 2009). This increase in removal
rate was possibly due to photosensitizers that initiated the indirect phototransformation pathway. Similar results were reported for caffeine and amitriptyline, where
the former underwent phototransformation only in seawater and the latter showed
S. Mohapatra et al.
the degradation rate of diclofenac in purified water, deionized water, and Mississippi
river water as reported by Packer et al. (2003). The authors proposed that addition of
the quencher possibly led to the generation of other radicals or led to photoreduction
of the carboxyl group (–COOH) containing diclofenac, with isopropanol serving
as the H-source. Such reactions are commonly observed for acidic pharmaceuticals,
such as naproxen, ibuprofen, aspirin, and clofibric acid (Packer et al. 2003). Typically,
in the case of diclofenac, the presence of humic substances was found to act more as
an inner filter, limiting the light reaching the parent compound (Zhang et al. 2008a,
b). On the other hand, contradictory results regarding the role of photosensitizers
and indirect photolytic pathway have been reported for other NSAIDs.
Acetaminophen or paracetamol was also reported to undergo around 27% removal
in surface waters in the summer season by phototransformation for studies conducted
in the River Aire, UK (Ebele et al. 2017). In surface waters, the mechanism of
phototransformation of acetaminophen was deduced to be via the indirect pathway
with a half-life of 29 h (Baena-nogueras et al. 2017). However, similar to the case
with naproxen and diclofenac, photoproducts of acetaminophen have been reported
to be more complex and more recalcitrant than the parent compound. For instance,
13 photoproducts of acetaminophen were identified in a study. These products were
structurally different from microbial biodegradation products or human metabolites
(Yin et al. 2017). Studies by Kawabata et al. (2012) also showed that upon exposure to
UV light, acetaminophen dimerizes, leading to the formation of a toxic photoproduct
as revealed by the bioluminescence inhibition assay.
Antiepileptic and Antidepressants
Antiepileptic drugs and psychoactive drugs are by design highly hydrophobic as they
have to cross the blood–brain barrier of the human body. Carbamazepine, a widely
used antiepileptic drug, has been most commonly detected at relatively high concentrations in surface waters around the world, along with its metabolites, trans-10,11dihydro-10,11- dihydroxycarbamazepine (Zhang et al. 2008a, b). These are among
the most persistent and recalcitrant pharmaceuticals occurring in surface waters.
Negligible removal by direct phototransformation was reported for carbamazepine,
fluoxetine, caffeine, and amitriptyline in distilled water exposed to the solar simulator by Baena-nogueras et al. (2017). However, Matamoros et al. (2009) reported
degradation at 45 °C with a half-life of 35 h. This was attributed to the thermal
disintegration of carbamazepine to iminostilbene. Additionally, carbamazepine was
also reported to undergo some removal when spiked water samples were exposed to
500 W Xe lamps, as opposed to 300 W Xenon lamps, usually used in solar simulators
(Baena-nogueras et al. 2017). High acidity or salinity can also increase phototransformation rates. For experiments in seawater, tenfold decrease in half-life was observed
as compared to that in freshwater (Matamoros et al. 2009). This increase in removal
rate was possibly due to photosensitizers that initiated the indirect phototransformation pathway. Similar results were reported for caffeine and amitriptyline, where
the former underwent phototransformation only in seawater and the latter showed