Microplastics in the marine environment: new frontiers of investigation of their presence and related associated effects

The overall aim of this PhD thesis is to improve the investigation of the microplastics (MPs) presence in marine ecosystems and pursue understanding their impacts on marine species. To achieve these aims the main themes discussed in this PhD thesis were divided according to two main lines of research and a Citizen Science project. The first line of research is focused on the monitoring and assessment of the level of microplastic pollution in the marine environment (Mediterranean Sea) focusing on surface water, subsurface water, and sediments. This topic was pursued evaluating the limits of the standard methodologies used in the monitoring framework, designing upgrades in traditional sampling strategies and testing innovative sampling tools to collect more and more ecologically relevant data. Particular attention was paid to the study of the subsurface layers of the water column (approx. 10 m). With the aim to produce innovative knowledges and more data to better understand MPs dynamics and behavior, sampling strategy to collect samples from depth water was improved. In addition, the results obtained has allowed to compare depth with the surface to better describe the accumulation pattern of the MPs in the marine environment. Not only the sampling strategies were improved, but the laboratory procedurals analysis was implemented too. Even nowadays the laboratorial protocols employed in samples proceeding are globally widespread. The presence of globally shared standardized protocol is still missing. In fact, the personalized protocol that exists nowadays for the MPs detection analysis, producing an extremely variability in data from all over the world, makes it difficult to compare to each other. In the current thesis the procedural strategy adopted, was focused on enhancing the MPs extraction from the samples either from surface water, subsurface layer of the water column and sediments, with the aim to achieve the better strategy to propose a universal protocol of extraction. The achievement of the presented aims regarding sampling strategy and procedural analysis were pursued thanks to three sampling campaigns performed in the Mediterranean Sea, described in the first chapter that offers the possibility to test the designed upgrades. In addition, results obtained from the three sampling campaigns were used as point of comparison to confirm the actual efficiency of the adopted upgrades. Data obtained highlight that MPs and microfiber (MFs) distribution in the marine environment was not uniform, conversely it is subjected to a patchy distribution pattern. An accumulation of plastic is observed in sediments too, especially for those plastic particles composed in high density polymers (i.e. PET and PVC) and fibers. The second line of research is aimed to test the ecotoxicological effect of natural weathered plastic leachates on a battery of marine model organisms. To achieve this goal, a battery of traditional and innovative marine model organisms was adopted, and innovative endpoints were investigated. Leachates are a long-lasting threat of our era, caused by the long-term permanence of plastic in the environment and their consequently degradation. However, the investigation in the effects caused by plastic leachates is still poorly understood. Most of the studies in this context were focused on MPs leachates obtained by artificial aged plastic, avoiding the effect of exposure to the natural environment. Conversely, in the ecotoxicological study proposed in this thesis the toxicity of environmental aged plastics collected in different areas of the European marine compartment was investigated. Plastic collected in the field were secondly micronized in order to propose a more realistic scenario. Then MPs obtained have been leached and tested at different concentration. The ecotoxicological investigations pursued in this context were aimed to better define the ecological risk to which marine organisms are exposed and to define the possible response that organisms can produce as effect of the interaction with MPs. In addition, a Weight of Evidence (WOE) model was performed in collaboration with the Polytechnical University of Marche (UNIVPM), with the aim of better define the environmental hazard of the tested leachates. Our findings pointed out that plastic weathered in natural conditions are able to release leachates solutions that affect the behavioural end-point of different marine organisms with a degree of environmental hazard between absent and slight. Finally, the third chapter of this thesis is dedicated to a Citizen Science project aimed to test an innovative sampling strategy to monitor MPs accumulation in nearshore. While many studies have investigated beached and floating microplastics (size < 5 mm) in surface waters offshore, there is almost no information on floating microplastics in surface waters at less than a few hundred meters from the coastline, where the largest plastic mass flux is suspected to occur. Due to the extreme proximity to coastal sources of pollution: tourism activities, riverine mouth systems, wastewater treatment plants and high populated cities centers coupled with the high morphological variability of the coast, the near coast environment is interested in predicted accumulation of marine debris. At the same time the coastal line is not approachable with the boats usually used by the researchers for the monitoring of MPs in open sea, caused by legislative restrictions and practical difficulties. With this purpose the citizen science project here shown was aimed to test an innovative sampling strategy to monitor MPs pollution in nearshore by using a less impactful sampling method. This project in fact, proposes to the citizens involved to participate in the collection of nearshore surface water samples by using the innovative Minimanta net, a smaller and lightweight version inspired to the traditional one. This reduced device allows to tow it from floating gears like kayaks, that are less impacting and more agile to manage in nearshore environment. Coupled with this aim the second objective of the project was to increase the awareness and the responsibility of the participants in plastic pollution theme, to promote a sustainable way of life.