3 Natural Attenuation of Pharmaceuticals in the Aquatic …
79
direct photolytic removal of ibuprofen was negligible, the indirect photolysis rate was
reported to increase with an increase in dissolved organic carbon content (DOC), and
DOC was predicted to be the most important photosensitizer for ibuprofen degradation. However, a detrimental effect was observed in water containing high amounts
of nitrate and nitrite. With an increase in the concentration of nitrate, the formation of nitrated intermediates was found to increase, and these intermediates were
resistant to further transformation. Similar observations were made by Winkler et al.
(2001) for ibuprofen in German rivers, Elbe and Saale. In the case of naproxen,
photosensitization was reported in the presence of fulvic acid-like substances, such
that the photolytic removal rate increased in its presence. On the other hand, the
presence of humic acids led to a substantial inner filter effect, adversely affecting
photolysis (Chen et al. 2017). Chen et al. (2017) reported that the apparent quantum
yields for indirect photolytic removal of naproxen in the presence of fulvic acids
and humic acids were 2.3 × 10
−4 and 2.6 × 10
−5 , respectively, whereas the direct
photolysis yield (studied in ultrapure water) was 2.1 × 10
−2 . The direct photolytic
removal was attributed to the decomposition of the excited triplet state of naproxen
(
3 NP
* ) and self-sensitization involving
1 O 2 . The mechanism of fulvic acid-mediated
photolysis was not completely elucidated as photolytic removal of naproxen was
influenced by fulvic acids only at a lower light intensity, ample aeration, and low
pollutant concentration. Additionally, a study by la Farré et al. (2008) indicated that
some phototransformation by-products of naproxen showed higher toxicity in bacteria, algae, rotifers, and microcrustaceans compared to the parent compound. Similar
results were also obtained by Yin et al. (2017), where they found that photoproducts of naproxen exhibited tenfold higher toxicity in Ceriodaphnia compared to the
parent compound.
Another NSAID viz. ketoprofen has been reported to undergo pseudo-first-order
direct photolytic removal in experiments conducted in distilled water irradiated under
natural sunlight (half-life of 2.4 min) as well as under a 300 W Xe lamp solar simulator (half-life of 0.54 min) (Matamoros et al. 2009). The short half-lives of ketoprofen
can be attributed to its simpler structure; ketoprofen does not have a fused ring structure. However, an inspection of photoproducts of ketoprofen by the researchers also
indicated the possibility of the persistence of (3-(1-hydroxyethyl)phenyl)(phenyl)
methanone and benzophenone in river waters at the end of 24 days when irradiated under natural sunlight. Under similar conditions, ibuprofen exhibited moderate
removal rates with a half-life of about one day (Matamoros et al. 2009).
Phototransformation has been reported as the primary mechanism for the removal
of diclofenac in surface waters (Zhang et al. 2008a, b). Diclofenac is also characterized by negligible chemical and biological degradation rates (Baena-nogueras et al.
2017), while almost 90% of it was observed to undergo transformation during exposure to sunlight with a half-life of less than 1 h, at an initial concentration of 100 ng/L
(Ebele et al. 2017). Several photoproducts of diclofenac have also been identified.
Unlike ketoprofen, none of the photoproducts of diclofenac was persistent although
a particular product, i.e., chlorocarbazole was reported to cause cell lysis in red blood
cells with significantly higher efficiency than diclofenac itself (Encinas et al. 1998).
Surprisingly, the addition of an OH radical quencher (isopropyl alcohol) increased
79
direct photolytic removal of ibuprofen was negligible, the indirect photolysis rate was
reported to increase with an increase in dissolved organic carbon content (DOC), and
DOC was predicted to be the most important photosensitizer for ibuprofen degradation. However, a detrimental effect was observed in water containing high amounts
of nitrate and nitrite. With an increase in the concentration of nitrate, the formation of nitrated intermediates was found to increase, and these intermediates were
resistant to further transformation. Similar observations were made by Winkler et al.
(2001) for ibuprofen in German rivers, Elbe and Saale. In the case of naproxen,
photosensitization was reported in the presence of fulvic acid-like substances, such
that the photolytic removal rate increased in its presence. On the other hand, the
presence of humic acids led to a substantial inner filter effect, adversely affecting
photolysis (Chen et al. 2017). Chen et al. (2017) reported that the apparent quantum
yields for indirect photolytic removal of naproxen in the presence of fulvic acids
and humic acids were 2.3 × 10
−4 and 2.6 × 10
−5 , respectively, whereas the direct
photolysis yield (studied in ultrapure water) was 2.1 × 10
−2 . The direct photolytic
removal was attributed to the decomposition of the excited triplet state of naproxen
(
3 NP
* ) and self-sensitization involving
1 O 2 . The mechanism of fulvic acid-mediated
photolysis was not completely elucidated as photolytic removal of naproxen was
influenced by fulvic acids only at a lower light intensity, ample aeration, and low
pollutant concentration. Additionally, a study by la Farré et al. (2008) indicated that
some phototransformation by-products of naproxen showed higher toxicity in bacteria, algae, rotifers, and microcrustaceans compared to the parent compound. Similar
results were also obtained by Yin et al. (2017), where they found that photoproducts of naproxen exhibited tenfold higher toxicity in Ceriodaphnia compared to the
parent compound.
Another NSAID viz. ketoprofen has been reported to undergo pseudo-first-order
direct photolytic removal in experiments conducted in distilled water irradiated under
natural sunlight (half-life of 2.4 min) as well as under a 300 W Xe lamp solar simulator (half-life of 0.54 min) (Matamoros et al. 2009). The short half-lives of ketoprofen
can be attributed to its simpler structure; ketoprofen does not have a fused ring structure. However, an inspection of photoproducts of ketoprofen by the researchers also
indicated the possibility of the persistence of (3-(1-hydroxyethyl)phenyl)(phenyl)
methanone and benzophenone in river waters at the end of 24 days when irradiated under natural sunlight. Under similar conditions, ibuprofen exhibited moderate
removal rates with a half-life of about one day (Matamoros et al. 2009).
Phototransformation has been reported as the primary mechanism for the removal
of diclofenac in surface waters (Zhang et al. 2008a, b). Diclofenac is also characterized by negligible chemical and biological degradation rates (Baena-nogueras et al.
2017), while almost 90% of it was observed to undergo transformation during exposure to sunlight with a half-life of less than 1 h, at an initial concentration of 100 ng/L
(Ebele et al. 2017). Several photoproducts of diclofenac have also been identified.
Unlike ketoprofen, none of the photoproducts of diclofenac was persistent although
a particular product, i.e., chlorocarbazole was reported to cause cell lysis in red blood
cells with significantly higher efficiency than diclofenac itself (Encinas et al. 1998).
Surprisingly, the addition of an OH radical quencher (isopropyl alcohol) increased