Exploring the Impact of Polystyrene Microplastic Beads on Male Gonads of the Marine Mussel, <scp> <i>Mytilus galloprovincialis</i> </scp>

Plastic, with its remarkable versatility and numerous applications, has greatly benefited humanity. However, its extreme resistance to natural degradation means it persists in the environment for long periods, causing global environmental problems. Furthermore, the fragmentation of plastic waste leads to the formation of microplastics (MP), which are minuscule particles that can accumulate in aquatic ecosystems. This poses a threat to marine fauna and, indirectly, to humans, as it also endangers the reproductive health of individuals. This study aimed to investigate the effects of microplastics on the structure and function of the testis of Mytilus galloprovincialis, chosen as a model species for its ecological and commercial relevance. Mussels were exposed for 48 h to 5 μm polystyrene MPs at two concentrations (0.5 and 1 μg/mL), then the testes were subjected to morphological and molecular analyses. Morphological analyses revealed that MPs alter the structure of the sperm cyst in a dose-dependent manner, disrupting cellular interactions between germ cells. These structural deviations may be linked to contact damage and the onset of oxidative stress. Alongside specific histological staining, this condition is primarily demonstrated through biochemical, molecular, and metabolic investigations. Metabolomics, based on proton nuclear magnetic resonance (¹H NMR), combined with chemometrics, made it possible to comprehensively explore the time-dependent metabolic disturbances triggered by MPs in the gonads of mussels during the short-term study. Ultimately, the dose-dependent stress condition caused by MPs also disrupts the proper chromatin folding of spermatozoa. This suggests that these particles, in addition to hindering gametogenesis, may also impact the fertilizing capacity of these cells.