| dc.description.abstract | Microplastics are ubiquitous contaminants in the global environment. River systems are key in the transport of microplastics from terrestrial sources to the marine environment. The River Thames, the UKs second largest river, is important to the Southeast of the UK, providing vital fresh drinking water to its catchment population. This thesis aimed to investigate the occurrence and distribution of microplastics in the non-tidal River Thames ecosystem. This aim was achieved through three objectives, i) To investigate the occurrence and distribution of microplastics along the trajectory of the River Thames in samples collected above and below three suspected point sources of microplastic contamination to the river. ii) To investigate the occurrence of microplastics in benthic invertebrates sampled from the sediments of the River Thames and establish how feeding mode and surrounding environment influence ingestion levels. iii) To investigate the invasive zebra mussel, Dreissena polymorpha, as an indicator species of microplastic pollution in the River Thames. The results have shown that microplastic pollution is abundant in the River Thames ecosystem. Water and sediment samples showed significant increases in microplastic abundance along the trajectory of sampling sites. Water microplastic abundances increased 17-fold and sediment microplastic abundance by 6-fold along the trajectory of sampling sites, with increases in downstream samples from each point source of contamination. However, each point source sampled cannot be fully attributed to the cause of increased microplastic abundances observed, instead it is likely a result of the numerous anthropogenic factors and sources of microplastics to the river, which have not been sampled in this study. Quantification and characterization of microplastics in invertebrate species revealed ingestion by 12 benthic species sampled. By identifying differences in contamination levels between native and invasive, epifaunal and infaunal dwelling species, and the influence of the sediment microplastic abundance on the number of microplastic particles ingested by invertebrates, dependent upon primary feeding mode. The invasive zebra mussel, Dreissena polymorpha, showed potential as an indicator species of microplastic pollution in the river, showing a positive relationship between microplastic ingestion and water microplastic abundance. The results from all environmental samples revealed high contamination in the river of microplastic fragments and fibres composed of polyethylene, polypropylene, cellulosic, and polyester polymers. This highlights the importance of cellulosic contamination in the river, with all invertebrates sampled showing high contamination levels. Findings highlight the complexity of microplastic contamination in the River Thames system which is a highly changeable environment, especially over spatial and temporal scales, and threats from anthropogenic sources are a considerable issue. This research provides first evidence of microplastics in the non-tidal Thames upon which further research can be built upon. | en_GB |
