Distribuzione e concentrazione della contaminazione da microplastiche in specie ittiche destinate al consumo umano (Mar Ligure 2018 - 2021)

The purpose of this work was to analyze the relationships between microplastics and the fish stock of some of the most common fish species in the Ligurian Sea, to assess the presence, concentration and distribution of fibers, fragments and any microspheres, analyzing the stomach contents of samples collected during the monitoring period, between November 2018 and November 2021. In this study, 588 samples were considered, for a total of 10 fish species from different environments, in a coastal area from Albisola to Cogoleto. At the same time, a parallel project was carried out. The #PlasticLess Project, in conjunction with Lifegate which saw the management and data analysis of a SeaBin device located within the Marina of Varazze (SV). The analysis of the contents of the stomachs allowed to verify the alarming presence of foreign elements (especially fibers and fragments) in about a quarter of the samples. In 588 samples, from 10 different species, 7% would be affected by the ingestion of fibers while 18% by the ingestion of fragments alone. It was not possible to clarify if this phenomenon could be the root cause for the death of the individuals, however, the absence of large fragments in the stomach contents, would suggest a reduction in the number and size of the fragments, which could be linked to the muscular action of the stomach, capable of reducing ingested microplastics into easily evacuated fractions. To identify chemical composition of the fragments it has been used IR absorption spectral technique, that highlights two main low-density polymers: polyethylene (PE) and polypropylene (PP). Polyethylene (PE) is the most common plastic polymer, followed by polypropylene (PP). Both these materials, as they have low density, would remain in the upper layer, close to the sea surface, at the disposal of small pelagic predators for a longer period. The previous study conducted during the master's degree thesis about the individuals of Engraulis encrasicolus confirmed the results obtained: they voluntarily prey fragments, selecting those transparent and white, probably confusing them with their natural preys. This species is one of the most important prey of Trachurus mediterraneus, Scomber colias, and Auxis rochei, which could be affected by this form of pollution following the ingestion of small clupeids; this behavior would also justify the prevalence of these two colors of fragments compared to others. Only for Mugil cephalus it would be possible to guess a voluntary and direct predation of the floating microplastics on the surface layer of water in harbour area. Textile fibers are more frequent than plastic fragments, a situation that could probably be generated by a more intense passive filtration through the gills. Dark fibers, especially blue and black, represent the most widespread presence of these colors in the marine environment. SeaBin device was observed from the third week of September 2018, until the end of August 2019, for a duration of 46 weeks. The autumnal accumulation of debris is caused for the most part by fluvial transport, accentuated by frequent rains, while during spring and summer season this accumulation would be related to other forms of direct pollution. Microplastics found in some stomach of Mugil cephalus, sampled near the SeaBin, showed the same types of plastic pollution found in the device, confirming that they are expose to this kind of plastic particles. The results shows an huge presence of plastic fibers and fragments. The future approach to the problem should consist in researching the sources of origin of these materials, in order to plan preventive actions aimed at limiting, if possible, the production and dispersion of such materials. They also highlight that colors such as green, yellow and red are less common than other in the fishes’ stomach contents of the analyzed species.