Polystyrene Microplastic Exposure Adversely Affects Oocyte Quality and Ovary Health Status in Mytilus galloprovincialis

Microplastics pose a growing threat to marine ecosystems as they can accumulate in aquatic organisms, interfering with essential physiological processes including reproduc- tion. This study analyzed the effects of short-term exposure (48 h) to two concentrations (0.5 and 1 μg/mL) of 5 μm diameter polystyrene microplastic bead particles in female Mytilus galloprovincialis mussels, a bioindicator species of the Mediterranean Sea. Histo- logical analyses revealed progressive oocyte degeneration and the development of hyper- trophic PAS-positive mucous cells, indicative of a stress response, in a dose-dependent manner. Changes in hemocyte classes, which are major effectors of bivalve immunity, were evidenced by the May–Grünwald Giemsa reaction. Biochemical data showed that microplastics increased levels of stress proteins, such as HSP70 and p53, and altered the composition of ovarian glycoproteins. Metabolomic analysis based on 1H NMR spectrome- try revealed significant alterations in metabolites involved in energy (glucose, glycogen, and malonate) and amino acid (branched-chain amino acids arginine, glycine, glutamate, histidine, betaine, and choline) metabolism, suggesting impairment to bioenergetic and antioxidant pathways. Overall, these results suggest that even short-term exposure to polystyrene microplastic beads can alter the ovarian function and metabolism of female M. galloprovincialis, highlighting their vulnerability.