74
S. Mohapatra et al.
and ibuprofen were reported to be biotransformed by in-stream biofilms growing
on submerged macrophytes, and the hyporheic zone had a minimal role to play due
to its low hydraulic conductivity (Kunkel and Radke 2011). Additionally, phototransformation and sorption could not contribute to the natural attenuation of these
pharmaceuticals. No attenuation was noticed for bezafibrate, diclofenac, metoprolol, and naproxen. Among the antibiotics, biotransformation of sulfamethoxazole was
affected by its initial concentration, water temperature, and concentration of humic
acid. The biotransformation rate of this compound was significantly increased with
increase in temperature from 4 to 25 °C in the water-sediment system. Similarly, with
an increase in humic acid concentration from 5 to 30 mg/L, the biotransformation rate
was increased from 82.9 to 90.1%, respectively (Xu et al. 2011). Biotransformation of
β-blockers in surface water-sediment systems is quite slow. For pindolol and atenolol,
90% removal could be achieved within 0.4–10 days, while more than 100 days were
required to eliminate sotalol, propranolol, or celiprolol. However, biotransformation was the primary removal mechanism for such pharmaceuticals compared to
sorption (Ramil et al. 2010). In another study, atenolol, acetaminophen, ifenprodil,
ibuprofen, carbamazepine, indomethacin, mefenamic acid, and propranolol exhibited low biotransformation in river water (half-life > 24 h), whereas they were more
susceptible to phototrasnformation with half-life < 24 h and sorption (Yamamoto
et al. 2009). However, biotransformation of ibuprofen along with diclofenac, bezafibrate, and naproxen was significantly increased in the deeper anoxic sediment layer
(Fono et al. 2006; Kunkel and Radke 2008). River regions with low flow velocity
and flat river beds are more susceptible to the development of anaerobic conditions.
Koumaki et al. (2017) studied biotransformation of naproxen, ibuprofen, diclofenac,
and ketoprofen under four different redox conditions, i.e., aerobic, anoxic, anaerobic
and sulfate-reducing conditions in a lab-scale river water/sediment system. All the
pharmaceuticals were significantly biotransformed under aerobic conditions. Biotransformation of naproxen and ketoprofen was enhanced by a factor of two in the
absence of oxygen, whereas diclofenac was the most stable pharmaceuticals.
The biotransformation fate of anti-influenza drugs in real surface water samples
was studied by Azuma et al. (2017). Among the drugs studied, the biodegradability
of laninamivir octanoate and oseltamivir was high followed by laninamivir, amantadine, favipiravir, octanoate, peramivir, and zanamivir. Oseltamivir exhibited slower
biotransformation than that of laninamivir with a half-life of 112–139 days, which further reduced to about 80% after one month. Phototransformation for such compounds
may be neglected in the water-sediment system.
3.2.4 Phototransformation
In the photolytic process, as the name suggests, one of the most important factors is
light. In an engineered system, light is often used artificially. However, for natural
attenuation in surface waters, solar radiation serves as the light source. The process
of photolysis is catalyzed by light of a specific wavelength or energy, which acts as
S. Mohapatra et al.
and ibuprofen were reported to be biotransformed by in-stream biofilms growing
on submerged macrophytes, and the hyporheic zone had a minimal role to play due
to its low hydraulic conductivity (Kunkel and Radke 2011). Additionally, phototransformation and sorption could not contribute to the natural attenuation of these
pharmaceuticals. No attenuation was noticed for bezafibrate, diclofenac, metoprolol, and naproxen. Among the antibiotics, biotransformation of sulfamethoxazole was
affected by its initial concentration, water temperature, and concentration of humic
acid. The biotransformation rate of this compound was significantly increased with
increase in temperature from 4 to 25 °C in the water-sediment system. Similarly, with
an increase in humic acid concentration from 5 to 30 mg/L, the biotransformation rate
was increased from 82.9 to 90.1%, respectively (Xu et al. 2011). Biotransformation of
β-blockers in surface water-sediment systems is quite slow. For pindolol and atenolol,
90% removal could be achieved within 0.4–10 days, while more than 100 days were
required to eliminate sotalol, propranolol, or celiprolol. However, biotransformation was the primary removal mechanism for such pharmaceuticals compared to
sorption (Ramil et al. 2010). In another study, atenolol, acetaminophen, ifenprodil,
ibuprofen, carbamazepine, indomethacin, mefenamic acid, and propranolol exhibited low biotransformation in river water (half-life > 24 h), whereas they were more
susceptible to phototrasnformation with half-life < 24 h and sorption (Yamamoto
et al. 2009). However, biotransformation of ibuprofen along with diclofenac, bezafibrate, and naproxen was significantly increased in the deeper anoxic sediment layer
(Fono et al. 2006; Kunkel and Radke 2008). River regions with low flow velocity
and flat river beds are more susceptible to the development of anaerobic conditions.
Koumaki et al. (2017) studied biotransformation of naproxen, ibuprofen, diclofenac,
and ketoprofen under four different redox conditions, i.e., aerobic, anoxic, anaerobic
and sulfate-reducing conditions in a lab-scale river water/sediment system. All the
pharmaceuticals were significantly biotransformed under aerobic conditions. Biotransformation of naproxen and ketoprofen was enhanced by a factor of two in the
absence of oxygen, whereas diclofenac was the most stable pharmaceuticals.
The biotransformation fate of anti-influenza drugs in real surface water samples
was studied by Azuma et al. (2017). Among the drugs studied, the biodegradability
of laninamivir octanoate and oseltamivir was high followed by laninamivir, amantadine, favipiravir, octanoate, peramivir, and zanamivir. Oseltamivir exhibited slower
biotransformation than that of laninamivir with a half-life of 112–139 days, which further reduced to about 80% after one month. Phototransformation for such compounds
may be neglected in the water-sediment system.
3.2.4 Phototransformation
In the photolytic process, as the name suggests, one of the most important factors is
light. In an engineered system, light is often used artificially. However, for natural
attenuation in surface waters, solar radiation serves as the light source. The process
of photolysis is catalyzed by light of a specific wavelength or energy, which acts as