In vivo bioaccumulation and responses of hemocytes of mussels Perna viridis to microplastics and nanoplastics exposure

Growing micro- and nano-plastic (MNPs) pollution in the environment poses a threat to marine animals. Due to their excellent filtration capacity, bivalves can easily ingest MNPs, which could be translocated to open circulation system with potential risks. In the present study, the accumulation and elimination of MNPs (200 nm and 1 µm) in the mussel hemolymph serum and hemocytes were firstly quantified, and the differential sensitiveresponses of two subpopulations of hemocytes were then explored by in vivo exposure under environmentally relevant concentration of MNPs (200 µg/L). We demonstrated that MNPs were readily translocated into hemolymph serum, but were immediately followed by efficient internalization by hemocytes. Remarkably, concentrations of MNPs in hemolymph were only 0.63 and 0.39 times lower than the ambient exposure concentration. Granulocytes displayed a much higher potential of accumulating MNPs than the agranulocytes. MPs were more readily internalized by granulocytes, with their estimated maximum bioaccumulation factor (BCF) of 0.29 L/g. Due to the primary function of phagocytic encapsulation of MNPs by granulocytes, lysosome features especially the decline of subsequent lysosome membrane potential could be a potential sensitive biomarker in response to MNPs exposure. Our results provided insights on the bioaccumulation of MNPs at the cellular levels in marine bivalves.