Histological effects of and cellular responses to microplastics in the gills of Mytilus galloprovincialis

Microplastic (MP) pollution is now one of the main threats to marine ecosystems, due to MP's ubiquity, persistence, and ability to interact with aquatic organisms at different biological levels. Microplastic beads and/or fibers, resulting from the fragmentation of larger plastics or released as primary particles, can be easily ingested, or accumulated by numerous marine species, with potential toxic effects including oxidative stress, inflammation, and histopathological alterations. In this context, filter feeders such as Mytilus galloprovincialis mussels are ideal experimental models and sensitive bioindicators for monitoring the impact of marine pollutants, thanks to their ability to rapidly accumulate substances present in the water column.
The research presented in this paper is part of a project aimed at characterising the damage caused by marine contaminants on adult individuals of M. galloprovincialis. Specifically, the objective of this study was to evaluate the toxic effects of polystyrene MPs, administered at different concentrations, on the respiratory system of the chosen model. Through qualitative histological analyses including Mallory's trichrome, PAS, and Picrosirius Red staining, it has been possible to highlight significant morphological and structural alterations in the gills by comparing control and MP-exposed animals. Subsequently, the investigation was extended to the study of the cellular response to stress, using immunocytochemistry aimed at the tissue localisation of Proliferating Cell Nuclear Antigen (PCNA), a known marker of proliferation and cellular damage. Preliminary validation of the antibody by Western blot confirmed the results obtained, allowing us to accurately describe the changes in PCNA distribution following MP exposure.
The results show a more accurate picture of how microplastics compromise gill integrity, providing useful information for assessing the ecotoxicological impact of these contaminants.