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LIFTING THE VEIL ON MARINE LITTER - Towards a better understanding of Marine Litter in the North Atlantic: Method Development, Occurrence and Impacts
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This PhD thesis addressed several gaps in understanding marine litter and microplastics in the North-East Atlantic, developing standardized monitoring methods and conducting toxicity experiments on marine species. The study found no significant trend in seafloor litter around the UK over 25 years but confirmed that even environmental-level microplastic concentrations cause chronic harm to marine organisms.
The central aim of this thesis was to gain a better understanding of marine litter, including microplastics, in the North-East Atlantic ecosystem. We addressed several knowledge gaps in relation to the standardisation of marine litter and MP monitoring methods, analytical method development, field exposure of MP in both abiotic and biotic matrices, and laboratory exposure and chronic toxicity of MP to marine species. No significant temporal trend was observed in seafloor litter around the UK for the past 25 years (Chapter 3) We demonstrated that existing fisheries surveys using trawls can be used to monitor seafloor litter. Macro litter on the seafloor is widespread but patchy within the seas surrounding the UK, ranging from 0 to 1835 pieces km-2 of seafloor and dominated by plastics. Over the entire 25-year period (1992–2017), 63% of the 2461 trawls contained at least one plastic litter item. Microplastics accumulate in North Sea sediments with a high organic carbon content (Chapter 4) Microplastics are present in sediments of the Southern North Sea (0 - 3,146 particles/kg dry weight) and at the sea surface of North West Europe (0 - 1.5 microplastic particles/m3). The highest concentrations of microplastics were found in estuaries and in sediments areas with a high organic carbon content. Sediments act as sinks for microplastics (mainly fibers and spheres), they are less heterogenous and contain higher concentrations of microplastics compared to surface waters (mainly fragments). North East Atlantic Porbeagle sharks digest microplastics but the health impact is unclear (Chapter 5) Microplastics are present in high concentrations in top predators living in the North East Atlantic, up to 10.4 particles per g wet weight (w.w.) content and 9.5 particles per g w.w. tissue. This equates to individual microplastics loads as high as 3850 particles per spiral valve. These high concentrations might deliver a first indication of bioaccumulatution. We developed a method for quantifying microplastics in spiral valves of porbeagle sharks. No possible health effects of microplastic contamination were found. Long-term microplastic exposure has adverse health effects on juvenile oysters (Chapter 6) Juvenile oysters, Crassostrea gigas, exposed for a period of 80 days to 106 particles L-1, represented by 6 µm polystyrene (PS) microbeads, showed an increased death rate compared to a control treatment receiving no microplastics. Weight and shell length remained comparable, but the Condition Index of the oysters in the highest concentration reduced significantly towards the end. The oysters in the highest MP exposure showed the lowest mean Lysosomal Stability score throughout the experiment. Microplastics in sediments detected using forensic science methods (Chapter 7) The selective fluorescent staining using Nile Red (NR), followed by density-based extraction and filtration allows for rapid analysis of microplastics in sediments using simple photography through an orange filter at low cost. Image-analysis allows fluorescent particles down to a few micrometres to be identified and counted. Europe underfunds marine litter research on marine litter risks (Chapter 8) The past decade, the best represented topics within European marine litter projects were ‘Policy, Governance and Management’ and ‘Monitoring’. The underrepresented topics were ‘Risk Assessment’, ‘Fragmentation’ and ‘Assessment Tools’. From the evidence we gathered, it remains difficult to create a complete understanding of the marine litter issue in the North East Atlantic, much more work is required. What is clear, is that we found marine litter, including microplastic across all investigated sites and samples. The collected evidence suggests that current properties and quantities of marine litter in the North East Atlantic are expected to cause a significant impact on the ecosystem.
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