Microplastics, such as polyethylene (PE) and polystyrene (PS), can adsorb pollutants like pyrene, which can then be transferred to marine mussels (Mytilus galloprovincialis). This study shows that pyrene accumulates in mussel tissues, particularly in the digestive system, and causes various cellular and molecular responses, including immunological changes, lysosomal instability, peroxisomal proliferation, antioxidant stress, and genotoxic effects. Transcriptomic analysis using a DNA microarray revealed significant gene expression changes, indicating potential molecular mechanisms of microplastic toxicity. The study also demonstrated that microplastics can act as vectors for chemical pollutants, increasing their bioavailability and toxicity in mussels. The results suggest that microplastics pose a significant risk to marine organisms, with potential long-term ecological impacts. The study used a Weight of Evidence (WOE) approach to assess the risk, integrating data on bioavailability, biomarker responses, and toxicological effects. The findings highlight the need for further research on the effects of microplastics and their associated pollutants on marine ecosystems. The study was supported by the Italian Ministry for University and Research and the Centro Assistenza Ecologica ECOCAE.Microplastics, such as polyethylene (PE) and polystyrene (PS), can adsorb pollutants like pyrene, which can then be transferred to marine mussels (Mytilus galloprovincialis). This study shows that pyrene accumulates in mussel tissues, particularly in the digestive system, and causes various cellular and molecular responses, including immunological changes, lysosomal instability, peroxisomal proliferation, antioxidant stress, and genotoxic effects. Transcriptomic analysis using a DNA microarray revealed significant gene expression changes, indicating potential molecular mechanisms of microplastic toxicity. The study also demonstrated that microplastics can act as vectors for chemical pollutants, increasing their bioavailability and toxicity in mussels. The results suggest that microplastics pose a significant risk to marine organisms, with potential long-term ecological impacts. The study used a Weight of Evidence (WOE) approach to assess the risk, integrating data on bioavailability, biomarker responses, and toxicological effects. The findings highlight the need for further research on the effects of microplastics and their associated pollutants on marine ecosystems. The study was supported by the Italian Ministry for University and Research and the Centro Assistenza Ecologica ECOCAE.