Microbiological and spectroscopic analysis of microplastics in commercial fishes

The aim of this thesis is the evaluation of the plastic impact on ecosystems and especially on human health. First, the attention will be focused on the identification of plastic pollutants, extracted by aquatic organisms, and their physico-chemical characterization. Microplastics characterization has been carried out by using some spectroscopic techniques (IR optical absorption, micro-Raman and X-ray photoelectron spectroscopies) and scanning electron microscopy (SEM/EDX and STEM). A screening for susceptibility to antibiotics ofbacteria isolated from plastics extracted by gills and gastrointestinal tract will be presented and discussed. Plastics washing processes of synthetic clothings have been lately identified as responsible for about 35% of primary microplastic release in aquatic environment. The released fibres and debris behave as potential vectors for spread of pathogenic bacteria through aquatic organisms, contributing to the diffusion of multiple antibiotic resistance in marine environments. Ultimately, microplastics play a potential and crucial role in conveying antibiotic resistance by humans food ingestion. In Chapter 1, an overview of microplastics pollution in aquatic environments and their classification are reported. In Chapter 2, results about the effect of water temperature, salinity and pH on the immune response of mussels from Faro Lake and Tyrrehenian sea by flow cytometry and Raman spectroscopy are presented and discussed. In Chapter 3, the methodologies generally adopted for sampling, identification and characterization of plastics extracted by fishes are described, focusing the attention on the mechanisms underlying the techniques used to investigate the microplastics composition and their morphological properties. In Chapter 4, the occurrence of microplastics in Zeus faber and Lepidopus caudatus from the Tyrrhenian Sea, juveniles of Engraulis encrasicolus and Sardina pilchardus from Southern Tyrrhenian Sea, Boops boops from the northern coasts of Sicily (Central Mediterranean) was evaluated in order to quantify the amount and the typology of plastics within the gastrointestinal tract of the samples and, in turn, to evidence that Mediterranean sea is affected by plastic pollution. In Chapter 5, the potential effects of plastics on humans’ health are remarked. To this purpose, an in-depth study of the plastics extracted by the Pagellus erithrynus, going from the northernmost portion of the Strait of Messina, was carried out. Particularly, microbiological assays showed the presence of Enterobacteriaceae, Aeromonadaceae, Vibrionaceae, and Pseudomonaceae families both in gills and gastrointestinal tract. Bacterial isolates were screened for susceptibility to antibiotics using the Kirby-Bauer test, choosing the molecules most used in human therapy. Finally, the main contents of the thesis are summarized in the last chapter, remarking challenges and future perspectives. Still, there are significant disconnects in the integration of knowledge derived from laboratory and field studies. It is well known and also emerged by the results reported in this thesis that microplastic transport over a range of spatial scales and with different residence times will be influenced by particle characteristics, external forces (e.g. flow regimes), physical site characteristics (e.g. bottom topography), the degree of biofouling, and anthropogenic activity (e.g. dam release), however there is a lack of data on this. Nevertheless, it is predicted that impacts on biota will mirror that of the marine environment. Thus, some efforts in this direction will be still made to safeguard the health of the system and of the future generations.