78
S. Mohapatra et al.
2017). However, when sufficient reaction time is provided, direct photolysis in surface waters has the potential to degrade many pharmaceuticals. Typically, it has been
reported that the degradation time of most pharmaceuticals in surface water may
vary from a few hours to months depending on various environmental parameters
(Chowdhury et al. 2011). The specific rate of direct photolysis may vary according
to the type of pharmaceutical and surface water quality.
For the sake of understanding the underlying principles of phototransformation
of pharmaceuticals, researchers have published results for experiments conducted
using various types of irradiation sources with varying intensity. For instance, most
bench-scale laboratory experiments conducted with filtered surface water have been
irradiated with light sources emitting light over a specific wavelength range, and
both monochromatic or polychromatic light sources have been used (Mazellier et al.
2008). The most common irradiation sources include UVC, UVB, UVA, simulated
solar light and irradiation using natural sunlight. A rise in light intensity (I) generally
increases removal efficiency although the change in pseudo-first-order rate constant
varies depending on the pharmaceutical and the light intensity (Sornalingam et al.
2016). Increased rate constants were explained by the higher photon flux, resulting
from the increasing intensity.
3.2.4.2 Phototransformation of Specific Pharmaceuticals
Analgesics
Analgesics constitute an important category of pharmaceuticals, which are frequently
sold over the counter. Additionally, many medications have these in combination with
other pharmaceuticals. Hence, analgesics, including non-steroidal anti-inflammatory
drugs (NSAIDs), are frequently detected in wastewater effluents and surface water
around the world (Archer et al., 2017; Lee et al. 2003a, b; Shanmugam et al. 2014).
These are characterized by extremely low biodegradability index, due to which they
pass through the conventional wastewater treatment systems with negligible change
in concentration and eventually contaminate surface water bodies (Kim et al. 2007;
Valcárcel et al. 2011). Typically, most analgesics and particularly NSAIDs are effectively removed in surface water exposed to sunlight (Matamoros et al. 2009). For
most analgesics, photochemical degradation is reported to follow the indirect pathway, and they have much shorter half-lives compared to steroids and other phenolics.
Direct photolysis is reported to play an essential role in water exposed to UV radiation, owing to the characteristic UV absorbance of analgesics (Chen et al. 2017).
In the natural environment, direct photolysis of analgesics exposed to sunlight is
negligible with a few exceptions, such as ketoprofen.
Multiple studies are available on the photochemical degradation of analgesics,
such as diclofenac, naproxen, ibuprofen, acetaminophen, and aspirin in sunlit surface waters. For a lake in Singapore exposed to natural sunlight and a solar simulator, Xu et al. (2011) studied the effect of direct and indirect photolytic pathway
on degradation of the NSAID, ibuprofen (initial concentration of 100 μg/L). While
S. Mohapatra et al.
2017). However, when sufficient reaction time is provided, direct photolysis in surface waters has the potential to degrade many pharmaceuticals. Typically, it has been
reported that the degradation time of most pharmaceuticals in surface water may
vary from a few hours to months depending on various environmental parameters
(Chowdhury et al. 2011). The specific rate of direct photolysis may vary according
to the type of pharmaceutical and surface water quality.
For the sake of understanding the underlying principles of phototransformation
of pharmaceuticals, researchers have published results for experiments conducted
using various types of irradiation sources with varying intensity. For instance, most
bench-scale laboratory experiments conducted with filtered surface water have been
irradiated with light sources emitting light over a specific wavelength range, and
both monochromatic or polychromatic light sources have been used (Mazellier et al.
2008). The most common irradiation sources include UVC, UVB, UVA, simulated
solar light and irradiation using natural sunlight. A rise in light intensity (I) generally
increases removal efficiency although the change in pseudo-first-order rate constant
varies depending on the pharmaceutical and the light intensity (Sornalingam et al.
2016). Increased rate constants were explained by the higher photon flux, resulting
from the increasing intensity.
3.2.4.2 Phototransformation of Specific Pharmaceuticals
Analgesics
Analgesics constitute an important category of pharmaceuticals, which are frequently
sold over the counter. Additionally, many medications have these in combination with
other pharmaceuticals. Hence, analgesics, including non-steroidal anti-inflammatory
drugs (NSAIDs), are frequently detected in wastewater effluents and surface water
around the world (Archer et al., 2017; Lee et al. 2003a, b; Shanmugam et al. 2014).
These are characterized by extremely low biodegradability index, due to which they
pass through the conventional wastewater treatment systems with negligible change
in concentration and eventually contaminate surface water bodies (Kim et al. 2007;
Valcárcel et al. 2011). Typically, most analgesics and particularly NSAIDs are effectively removed in surface water exposed to sunlight (Matamoros et al. 2009). For
most analgesics, photochemical degradation is reported to follow the indirect pathway, and they have much shorter half-lives compared to steroids and other phenolics.
Direct photolysis is reported to play an essential role in water exposed to UV radiation, owing to the characteristic UV absorbance of analgesics (Chen et al. 2017).
In the natural environment, direct photolysis of analgesics exposed to sunlight is
negligible with a few exceptions, such as ketoprofen.
Multiple studies are available on the photochemical degradation of analgesics,
such as diclofenac, naproxen, ibuprofen, acetaminophen, and aspirin in sunlit surface waters. For a lake in Singapore exposed to natural sunlight and a solar simulator, Xu et al. (2011) studied the effect of direct and indirect photolytic pathway
on degradation of the NSAID, ibuprofen (initial concentration of 100 μg/L). While