Occurrence and effects of pharmaceuticals in freshwater ecosystems

Over the last 10-15 years pharmaceuticals have been identified as a widespread pollutant in freshwater systems having entered the environment predominantly via the domestic sewage system where removal by treatment systems is often poor. This thesis provides detailed reviews and meta-analyses of existing data regarding pharmaceutical pollutants, examines the occurrence of five pharmaceuticals in semi-rural and urban catchments of West Yorkshire and their effects on freshwater ecosystems using both laboratory and field experiments. A critical review and meta-analysis of 155 published pharmaceutical papers found 204 pharmaceuticals were present in rivers across large parts of Europe, North America and Asia. However, spatial and methodological gaps were identified in the research body with almost no research evident in Africa, South America, the Middle East and large parts of Asia. Furthermore, research effort was focused around a small number of commonly studied compounds often employing poorly representative grab sampling techniques. Treated and untreated effluent of sewage treatment plants, combined sewer overflows and their receiving freshwaters were monitored for five pharmaceuticals (diclofenac, erythromycin, ibuprofen, mefenamic acid and propranolol). All compounds were detected at very high frequencies across all samples confirming them as a ubiquitous and widespread pollutant in freshwaters. Data showed pronounced seasonal (winter maxima) and diurnal (late morning and late evening) peaks in concentrations. Periods of high flow were characterised by reduced concentrations, possibly due to dilution within receiving waters. No appreciable attenuation of pharmaceuticals was observed across an intensively sampled 5 km study reach of the River Aire in Leeds suggesting the pollution burden placed on rivers by pharmaceuticals extends well downstream of individual waste water point sources. Laboratory experiments revealed significant increases in mortality of the freshwater shrimp Gammarus pulex were observed during extended exposures to environmental levels of erythromycin and when combined in mixture with propranolol. A first application of 1H NMR environmental metabolomics to the study of pharmaceutical effects on freshwater biota was coupled with this experiment highlighting its potential use in ecotoxicological research. Sublethal, metabolic changes associated with energy storage and metabolism were observed with potential future applications for biomarker development centred on the osmolyte TMAO. The pharmaceuticals studied here were found to pose no detectable risk to leaf litter decomposition in streams although a further experiment demonstrated a reduction in organic matter processing of freshwater sediments, coupled with some complex stimulatory and inhibitory effects on respiration and nutrient cycling at environmentally relevant concentrations. Taken as a whole this work has added substantial knowledge to this growing research area and has allowed the construction of a conceptual framework that links measured environmental concentrations with effects at the sublethal and individual organism level mediated to the ecosystem and functional level via complex interactions between macroinvertebrates and microbial communities. Overall, this body of research has demonstrated that pharmaceuticals should be treated as a widespread pollutant of on-going major concern capable of eliciting significant effects on freshwater ecosystems. Therefore, they require substantial further research and scrutiny from regulators and policy makers if the negative consequences of their presence in rivers are to be avoided or mitigated.