There has been a global increase in the use of active pharmaceutical ingredients (APIs) in recent decades due to population growth and population ageing, increasing affluence, changes in disease burdens and the increasing availability of medicines across the world. Numerous studies have been performed into the fate and occurrence of pharmaceuticals in surface waters. However, only a few studies have explored the sediment compartment. Knowledge of the fate of these compounds in sediments is needed in order to determine the risks of pharmaceuticals in the environment. Therefore, this thesis describes the development of new analytical methods and laboratory and field-based studies to understand the fate and distribution of pharmaceuticals in freshwater sediments.
Approaches for prioritising pharmaceuticals in the environment, based on their risk, were initially used to identify candidates for experimental study. Antibiotics, antidepressants and analgesics were identified as the pharmaceutical classes of most concern in surface water, sediment and the terrestrial environment.
New analytical methods were then developed for the extraction and determination of six pharmaceuticals in a range of sediments obtained from the UK and Iraq. Using ultrasonic-assisted extraction (UAE) and high performance liquid chromatography coupled with diode array detector (HPLC–DAD) or liquid chromatography tandem mass spectrometry (LC- MS/MS) for detection. Detection limits ranging from 15 to 58.5 ng g-1 and 0.03 to 3.5 ng g-1 for water and sediment were achieved, respectively. Best recoveries were obtained for atenolol, amitriptyline, mefenamic acid and diltiazem.
The analytical methods were then utilized to study the sorption, persistence and occurrence of the pharmaceuticals in water-sediment systems. Laboratory-based sorption studies showed that sorption increased in the order: mefenamic acid < cimetidine < atenolol < amitriptyline < diltiazem. Multiple linear regression analysis indicated that the sorption was driven by factors such as the pH-corrected hydrophobicity octanol/water partitioning coefficient (Log Dow) of the study compound and the cation exchange capacity, clay, organic carbon content and exchangeable Ca2+ content of the sediment. Dissipation of each pharmaceutical was found to follow first-order exponential decay. Half-lives in the sediments ranged from 9.5 d (atenolol) to 78.8 d (amitriptyline).
Finally, the occurrence and seasonal distribution of pharmaceuticals in water and sediments from River Ouse and River Foss, York, were investigated. All ten pharmaceuticals were detected at concentrations up to 59.7 ng L-1 (atenolol) and 18.4 ng g-1 (trimethoprim) in water and sediment samples, respectively. Spatial and seasonal distribution profiles revealed different inputs of WWTPs, rivers flow and usage as the main factors responsible for the pharmaceuticals distribution.
Overall, the results show that the fate and occurrence of pharmaceuticals in sediment compartment is driven by chemical use patterns, chemical properties (such as Log Dow) and environmental parameters (such as flow and sediment properties). While this study provides a step forward in understanding some of the key drivers of exposure, further work is needed before we can fully assess the fate and occurrence of pharmaceuticals in sediments at the landscape scale.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)