3 Natural Attenuation of Pharmaceuticals in the Aquatic …
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biodegradation in winter contributes to the increased concentration of pharmaceuticals in winter (Camacho-Munoz et al. 2010). The lack of significant seasonal differences in concentration of pharmaceuticals found in River Ouse was attributed to its
lower annual variability in flow rate compared to that in River Foss (i.e., two orders of
magnitude vs. three orders of magnitude flow variation). Gago-Ferrero et al. (2017)
reported a persistent occurrence of antidepressants and benzodiazepines over the year
due to their continuous consumption throughout the year. In contrast, antihypertensive and β-blockers experienced the highest occurrence in the summer compared to
the winter season.
3.2.2 Sorption
Of the various phenomena taking place simultaneously in a water-sediment system,
sorption/desorption processes significantly affect the fate and transport of hydrophobic pharmaceuticals. Generally, the sorption behavior of any compound is estimated
with the help of the sorption coefficient (K D ), also defined as the solid–water distribution coefficient. It is affected by several factors, such as, fraction of organic
carbon, type of sediment, surface sorption on mineral constituents, percentage distribution of clay, sand and silt, ion exchange capacity, pH of the system, and ability to
form complexes with metal ions, such as, Ca, Mg, Fe or Al, and H–bonding. Neither
the organic fraction nor any of the other parameters are homogeneously distributed
across a river segment, thus sorption capacity may vary widely. Differences in fraction organic carbon in sediments and the nature of organic matter give rise to differences in sorption capacity. The soft amorphous rubbery organic matter shows lower
sorption of hydrophobic pharmaceuticals than the hard condensed glassy organic
matter. The rubbery organic matter mainly consists of partially degraded or reconstituted biopolymers (e.g., polysaccharides, lignin, lipoproteins, amino acids, lipids,
and humic substances), while condensed organic matter is present in kerogen, black
carbon, and coal. Pharmaceuticals with high octanol/water partition coefficient (log
K ow ) show higher sorption on sediments rich in organic matter. Such compounds can
strongly adsorb via hydrophobic interactions onto fats and lipids of bacterial origin
present in sediments (e.g., aliphatic and aromatic groups). Additionally, they can also
undergo electrostatic sorption onto negatively charged extracellular polysaccharide
moieties. Finally, chemical interactions with several bacterial proteins and nucleic
acids have also been reported. Since K D shows large variability due to difference
in organic matter fraction (f OC ), an organic carbon normalized partition coefficient
(K OC ) is commonly used (Eq. 3.1) (Radovi´ c et al. 2016).
K D = f OC × K OC
(3.1)
This organic carbon normalized sorption coefficient, K OC , for any compound
shows lower variability compared to K D . Equation (3.1) can be used when the fraction of organic carbon in soil/sediment is predetermined. Often the K OC values are
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biodegradation in winter contributes to the increased concentration of pharmaceuticals in winter (Camacho-Munoz et al. 2010). The lack of significant seasonal differences in concentration of pharmaceuticals found in River Ouse was attributed to its
lower annual variability in flow rate compared to that in River Foss (i.e., two orders of
magnitude vs. three orders of magnitude flow variation). Gago-Ferrero et al. (2017)
reported a persistent occurrence of antidepressants and benzodiazepines over the year
due to their continuous consumption throughout the year. In contrast, antihypertensive and β-blockers experienced the highest occurrence in the summer compared to
the winter season.
3.2.2 Sorption
Of the various phenomena taking place simultaneously in a water-sediment system,
sorption/desorption processes significantly affect the fate and transport of hydrophobic pharmaceuticals. Generally, the sorption behavior of any compound is estimated
with the help of the sorption coefficient (K D ), also defined as the solid–water distribution coefficient. It is affected by several factors, such as, fraction of organic
carbon, type of sediment, surface sorption on mineral constituents, percentage distribution of clay, sand and silt, ion exchange capacity, pH of the system, and ability to
form complexes with metal ions, such as, Ca, Mg, Fe or Al, and H–bonding. Neither
the organic fraction nor any of the other parameters are homogeneously distributed
across a river segment, thus sorption capacity may vary widely. Differences in fraction organic carbon in sediments and the nature of organic matter give rise to differences in sorption capacity. The soft amorphous rubbery organic matter shows lower
sorption of hydrophobic pharmaceuticals than the hard condensed glassy organic
matter. The rubbery organic matter mainly consists of partially degraded or reconstituted biopolymers (e.g., polysaccharides, lignin, lipoproteins, amino acids, lipids,
and humic substances), while condensed organic matter is present in kerogen, black
carbon, and coal. Pharmaceuticals with high octanol/water partition coefficient (log
K ow ) show higher sorption on sediments rich in organic matter. Such compounds can
strongly adsorb via hydrophobic interactions onto fats and lipids of bacterial origin
present in sediments (e.g., aliphatic and aromatic groups). Additionally, they can also
undergo electrostatic sorption onto negatively charged extracellular polysaccharide
moieties. Finally, chemical interactions with several bacterial proteins and nucleic
acids have also been reported. Since K D shows large variability due to difference
in organic matter fraction (f OC ), an organic carbon normalized partition coefficient
(K OC ) is commonly used (Eq. 3.1) (Radovi´ c et al. 2016).
K D = f OC × K OC
(3.1)
This organic carbon normalized sorption coefficient, K OC , for any compound
shows lower variability compared to K D . Equation (3.1) can be used when the fraction of organic carbon in soil/sediment is predetermined. Often the K OC values are