Marine Pollution: Mytilus Galloprovincialis as a Model Organism to Assess Micro- and Nanoplastic Impact

The rapid increase in plastic production and its mismanagement have led to the accumulation of plastic debris across marine ecosystems, where fragmentation processes continuously generate microplastics (MP) (<5 mm) and nanoplastics (NP)(<100 nm). These particles form a new class of contaminants able to interact with biological systems on multiple levels because of their small size, high surface-area-to-volume ratio, and ability to adsorb and transport toxic chemicals. Their presence in the water column and sediments raises particular concern for filter-feeding organisms, which are especially prone to passive ingestion and consequently accumulate xenobiotic tissue. Among marine invertebrates, the bivalve Mytilus galloprovincialis is widely recognised as a bioindicator species for environmental monitoring. Its sessile lifestyle and efficient filtering apparatus make it an ideal model to assess the biological impacts of micro- and nanoplastics (MNP) exposure. In this context, our research concentrated on the tissue-specific effects of polystyrene-based MNPs in M. galloprovincialis. Specifically, the study aimed to compare the impact of micro- (5 µm) and nano-plastics (0.1 µm) exposure on respiratory and reproductive tissues. Exposure durations (1, 3, and 11 days) and concentrations were selected based on realistic environmental conditions. Morphofunctional alterations were investigated through the integration of histological, biochemical, and molecular endpoints. Results showed severe time-dependent toxic effects in all examined organs. In the gills, the respiratory epithelium was notably affected, and oxidative stress, glycoprotein localisation, and their expression were significantly altered. In the female, the ovaries showed widespread structural disorganisation and a clear increase in atresia. The observed oxidative damage was associated with altered expression of cytoskeletal proteins and changes in protein glycosylation. The imbalance in redox signalling and the resulting inflammatory responses were demonstrated by significant haemocyte infiltration. Despite these effects, proliferative activity and collagen distribution remained largely unaffected.