Comparative multi-biomarker hazard assessment of weathered environmental microplastics and their DMSO-extractable leachates in Mytilus galloprovincialis

Environmental microplastics (EMPs) are recognized contaminants of marine ecosystems, yet the contribution of chemicals released during their environmental weathering remains insufficiently characterized. As an a priori hazard assessment rather than an environmentally realistic exposure scenario, weathered EMPs collected from the Moroccan Atlantic coast (polyethylene, PE; polypropylene, PP; and polystyrene, PS) and their corresponding DMSO-extractable leachates (LPE, LPP, and LPS) were evaluated in the mussel Mytilus galloprovincialis following a 72 h exposure. Raman microspectroscopy and SEM/EDX analyses detected particles smaller than 1.22 μm within hemolymph cells, with PP showing the highest degree of internalization among particulate treatments. Lysosomal membrane stability decreased across all treatments, whereas genotoxic responses varied according to polymer type and exposure form. DNA fragmentation was highest in mussels exposed to LPE (≈47%), while LPS produced the greatest increase in micronucleus frequency. Gene-expression analyses revealed increased transcription of p53 and Bax together with reduced expression of DNA-ligase in several treatments, particularly those involving leachates. Overall, leachate exposures elicited stronger genotoxic responses than the corresponding particulate fractions. These findings highlight the importance of considering not only microplastic particles but also the chemicals released during environmental weathering when evaluating the biological impacts of plastic pollution in marine organisms.