Impatto delle microplastiche e loro funzione di carrier per contaminanti persistenti in specie ittiche del Mar Mediterraneo con diverse strategie alimentari

The presence of microplastics in the marine environment was first observed in the 1970s and growing scientific interest has revealed that these are widespread and ubiquitous in the marine environment: over 92% of all plastic objects in the oceans are microplastics. This PhD study aims to increase the knowledge about the impact, distribution and abundance of microplastics in fish species with different feeding habits in the Mediterranean Sea. Within the scope of this study is included the assessment of the levels of persistent contaminants (PBDEs, PCBs and FRs) in fish tissues and its possible correlation with the presence of microplastics. A digestion method of organic matter was developed and validated in order to isolate and characterize the microplastics in the fish gastro-intestinal tracts. Mullus barbatus and Merluccius merluccius were tested and validated as small-scale bioindicators of plastic pollution in three different areas. Eight fish species from the same area (Ligurian Sea) were examined, all of them had ingested microplastics with different characteristics. The ingestion rates and numbers of particle per individual were significantly different between species. The species with the highest percentages of ingestion are Boops boops, with 36.8%, and Sardina pilchardus, with 34.8%. The study of stable isotopes of nitrogen and carbon (δ15N and δ13C), has allowed to define the trophic level and identify the main food resources exploited by the species, highlighting an inverse correlation between the trophic level and the number of plastics per individual as well as a change in feeding strategies related with plastics presence for some species (Scomber scombrus e Trachurus trachurus). The assessment of the levels of persistent contaminants (PBDEs, PCBs and FRs) in fish muscles has shown that, for some species and in relation to certain contaminants (total PCB and lower chlorinated PCB in Boops boops, Bde-183 in Engraulis encrasicolus), the presence of plastics is inversely correlated to the levels of pollutants measured. In all other cases, the chemicals analysed were found at same concentrations regardless of the presence/absence of microplastics. This highlighting the complexity of the issue and the necessity of target studies and standardised methodologies to clarify the role of plastics as a source of contaminants for edible fish species. Overall, this research should be considered as a starting point for a future science-policy interface based on a full awareness of the issue of marine litter and for the achievement of a better state of conservation and protection of fish resources in Mediterranean Sea.