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Analysis of microplastics and Potentially Toxic Elements contamination in an estuarine system (Ría de Betanzos, Galicia)
Summary
This thesis investigates microplastic and potentially toxic element contamination in the sediments of a Spanish estuary, finding both pollutants distributed throughout the system with concentrations influenced by proximity to human activities. The findings highlight the vulnerability of estuarine ecosystems to combined plastic and chemical pollution.
Estuaries are natural environments of fundamental importance, scene of flourishing biodiversity, both marine and terrestrial. They are also a focal point for global trade and a place for many human activities. This thesis focuses on the distribution of microplastics and potentially toxic elements in the sediments of the estuarine area of Ría de Betanzos - located in Galicia, Spain - and aims to understand the processes responsible. 25 samples were collected from different locations over three sampling campaigns. On all of them was performed a digestion in Aqua Regia that allowed the dissolution of the samples and the subsequent analysis by ICP-OES. The calculated concentrations were then analysed to understand influencing factors and temporal differences. On eight samples, density separations in ZnCl2 were performed and the resulting filters were analysed to determine the number of microplastics within each sample. The results were then represented on maps to obtain geographic distribution infomation. Lastly, a Raman spectroscopy was performed on two previously analysed samples to try to determine the polymeric nature of the contained microplastics, by confronting the spectra with the ones from a polymers database. PTEs showed to be strongly influenced by the fine-grained content in sediments. Concentrations were only in a few cases above the considered backgrounds but anyhow non-threatening and below the Spanish law limit for dredged materials. Values also showed variations linked to seasonality and climatic events. For Microplastics, whose presence was influenced by grain size and TOC content, no regulation was available for comparison, that was then performed using a previous study’s results. The findings were substantially in line with a few discrepancies, attributable to the differences in the applied methodology. As for the Raman spectroscopy, despite some encouraging results, no clear information over the polymers of the analysed microplastic could be gained.