Impact of environmental microplastics alone and mixed with benzo[a]pyrene on cellular and molecular responses of Mytilus galloprovincialis

The hazard of microplastic (MP) pollution in marine environments is a current concern. However, the effects of environmental microplastics combined with other pollutants are still poorly investigated. Herein, impact of ecologically relevant concentrations of environmental MP alone (50 µg/L) or combined with B[a]P (1 µg/L) was assessed in mussel Mytilus galloprovincialis after a short-term exposure (1 and 3 days) to environmental MP collected from a north-Mediterranean beach. Raman Microspectroscopy (RMS) revealed bioaccumulation in mussel hemolymph of MP, characterized by polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyethylene vinyl acetate (PEVA) and high-density polyethylene (HDPE), with abundance of MP sized 1.22–0.45 µm. An increase of B[a]P was detected in mussels after 3-day exposure, particularly when mixed with MP. Both contaminants induced cytotoxic and genotoxic effects on hemocytes as determined by lysosomal membrane stability (LMS), micronuclei frequency (FMN), and DNA fragmentation rate by terminal dUTP nick-end labeling (TUNEL). About apoptosis/DNA repair processes, P53 and DNA-ligase increased at 1-day exposure in all conditions, whereas after 3 days increase of bax, Cas-3 and P53 and decrease of Bcl-2 and DNA-ligase were revealed, suggesting a shift towards a cell apoptotic event in exposed mussels. Overall, this study provides new insights on the risk of MP for the marine ecosystem, their ability to accumulate xenobiotics and transfer them to marine biota, with potential adverse repercussion on their health status.