Contribution to the characterization of the toxicity of plastic microparticles/nanoparticles (MP/NP) and benzo[a]pyrene in the seaworm Hediste diversicolor

The widespread presence of microplastics (MPs) in marine ecosystems poses significant threats to marine organisms due to their potential for ingestion, accumulation, and acting as vectors for harmful pollutants like Benzo[a]pyrene (B[a]P). This thesis explores the toxicological effects of environmentally relevant concentrations of MPs (10 and 50 mg/kg sediment) and B[a]P (1 µg/kg sediment), both individually and in combination, on the marine polychaete Hediste diversicolor over exposure periods of 3 and 7 days. The first objective was to evaluate the widespread biochemical and metabolomic disruptions induced by these contaminants across the entire seaworm body, through the analysis of bioaccumulation and alterations in histological, biochemical, and metabolomic parameters. The results confirmed bioaccumulation of both pollutants, with MPs shown to enhance B[a]P uptake. The study further revealed significant physiological disturbances, including increased acidic mucus production as a defense response, activation of oxidative stress pathways to prevent lipid peroxidation, and imbalances in amino acid metabolism, osmoregulatory function, and energy production, all indicative of compromised metabolic health. These findings demonstrate that even low concentrations of MPs and B[a]P can have synergistic toxic effects, threatening the health of marine organisms. The second objective of the study focused on investigating the cytotoxic and genotoxic impacts of these contaminants on the coelomic fluid, a vital component of the circulatory and immune systems in marine invertebrates. The analysis revealed that exposure to MPs and B[a]P led to a marked reduction in lysosomal membrane stability, along with increased micronuclei formation and DNA fragmentation, suggesting severe genetic damage. Additionally, apoptosis-related markers, such as P53, Bax, and Caspase-3, were upregulated, while Bcl-2 expression decreased, pointing to an enhanced apoptotic response in coelomocytes, especially in groups exposed to both contaminants. These findings highlight the dual threat posed by MPs, not only through direct toxicity but also by facilitating the transport and accumulation of xenobiotics like B[a]P, which can synergistically impair cellular integrity, metabolic function, and overall organismal health. This study provides new insights into the mechanisms of MP toxicity and their potential long-term impacts on marine ecosystems