Effects of pharmaceutical stressors on freshwater ecosystems processes

  • Haysem Alhassen

    Student thesis: Doctoral Thesis


    Pharmaceutically active compounds (PhACs) are important substances commonly used to improve health systems and quality of life. They enter freshwater ecosystems through several pathways, including effluent from municipal wastewater treatment plants. In recent decades, the detection of PhAC residues in different aquatic ecosystems, including freshwater ecosystems, has attracted the attention of researchers. As they are biologically active compounds, the main concern has been the possible environmental risks PhACs may pose. Despite the efforts made in relation to the effects of PhACs on freshwater ecosystems, findings have not been exhaustive, and there is a remarkable lack of understanding of the ecological effects of PhACs on vital freshwater ecosystem processes. Decomposition of leaf litter is one of the essential freshwater ecosystems processes, but there is a knowledge gap in how PhACs affect this process. This thesis provides an investigation of the possible effects of four common PhACs separately, in mixture, and in combination with environmental stressors on leaf litter decomposition rates (LLDRs). The investigation in this thesis also contributes to the answer to the question posed at the Society of Environmental Toxicology and Chemistry (SETAC) workshop in 2012, which focused on the importance of pharmaceuticals and personal care products in terms of their biological impacts on the environment, in comparison to other stressors. The study undertook a thorough, up-to-date literature review of the effects of pharmaceuticals on the species and functions of freshwater ecosystems. The study methods were based on sampling from the field and laboratory bioassays analyses to reach its conclusions. This thesis was divided into several studies in order to gain a better understanding of the interactions and effects of four selected PhACs (amoxicillin, caffeine, paracetamol, and sertraline) on leaf litter decomposition in freshwater ecosystems. Because half-life values in river water have not been reported in the literature, the first study in this research aimed to determine the half-lives of caffeine and paracetamol in water from the Cotter River by studying their photolytic breakdown. Laboratory assays were used to measure photo-degradation rates of the two compounds in milli-Q water, river water, and river water with leaf litter. The findings suggested that caffeine and paracetamol degradation by hydrolysis alone is very slow in river water, and that photolysis is a substantial contributor and accelerator of their degradation. Obtaining the data on caffeine and paracetamol half-life in river water allowed the investigation of the effect of a single PhAC on LLDRs in freshwater ecosystems. This investigation enabled the determination of a cause and effect relationship between each of the four selected PhACs and the LLDRs. It was hypothesised that each PhAC alone would adversely affect both the LLDRs and the activities of the extracellular enzymes (ECEs) released during the decomposition process. The findings suggested that there is likelihood that PhACs have adverse and wide-reaching effects on LLDRs and ECEs in freshwater ecosystems. The determination of the effect of a single PhAC from the four selected PhACs led to the investigation of the effects of various PhACs mixtures on LLDRs. The hypothesis was that additive, synergistic, and antagonistic effects would be seen in all PhACs mixture scenarios. From the results, it was found that in mixture, an antagonism effect was dominant. The final investigation in this study was the examination of the combined effects of a mixture made up of the four selected PhACs and temperature on LLDRs. It has been hypothesised that (1) the increase in temperature would increase the PhACs mixture effects on LLDRs, (2) the change in temperature level would alter the activity of the ECEs, and (3) the changes in LLDRs and ECEs would be noticed in the presence or absence of invertebrate shredders. The findings suggested that the combination of PhAC stressors and temperature affected the LLDRs, particularly at high PhAC concentrations and temperature levels, indicating a potential for unforeseen ecosystem-wide effects. The results also showed that multiple stressors (PhAC combination and temperature) have different effects on LLDRs and ECEs from that of an individual PhAC. These results highlight the importance of including climate change as a key factor when studying the effects of PhACs on freshwater ecosystems structures and functions. Finally, the thesis outlines the contribution that this research has made to filling gaps in understanding the ecological effects of freshwater ecosystems processes when they are under multiple pharmaceutical stressors, or when under combined pharmaceutical and climate (temperature) stressors. In response to the 2012 SETAC workshop question, it is evident from this study that pharmaceuticals and personal care products have biological impacts on freshwater ecosystems. With the increasing global consumption of pharmaceuticals, the continuous detection of PhACs residues in rivers and streams, and the requirement for more data to effectively manage this problem, this study provides evidence that more research is needed to fully comprehend the effects of multiple pharmaceutical-environmental stressors on freshwater ecosystems. It also provides essential information for water resources regulators, and policy makers that will assist them in making better decisions in relation to water resources management. This thesis is a foundation that paves the way for future research in the area of PhACs in freshwaters, and highlights the importance of properly investing in understanding the problems facing one of the world's most vital resources, water.
    Date of Award2021
    Original languageEnglish
    SupervisorFiona Dyer (Supervisor), Ross Thompson (Supervisor), Ashraf Ghanem (Supervisor) & Reena Ghildyal (Supervisor)

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