Cytotoxicity of polystyrene nanoplastics involves mitochondrial dysfunction and DNA damage in hemocytes of the Pacific oyster

Nanoplastics represent an increasing ecological threat to marine ecosystems, with the potential to disrupt immune responses, oxidative stress pathways, and bioenergetics. We employed an in vitro cellular bioassay to investigate the distribution, metabolic disruption, and genotoxicity resulting from 24 h of exposure to polystyrene nanoplastics (NanoPS, approximately 90 nm) in the hemocytes of the Pacific oyster (Crassostrea gigas). Transmission electron microscopy suggested the internalization and distribution of NanoPS within vesicles, the cytosol, and the nuclei of exposed hemocytes. Cytotoxicity assays revealed that metabolic activity (resazurin assay, LC50 = 91.6 mg/L) was more sensitive than lysosomal integrity (neutral red assay, LC50 = 252.3 mg/L). Exposure to NanoPS also increased the levels of reactive oxygen species and DNA damage as low as 1.2 mg/L. Metabolic assays revealed that enhancing mitochondrial metabolism through galactose supplementation increased the cytotoxicity and DNA damage caused by NanoPS. Conversely, promoting anaerobic metabolism with glucose supplementation reduced these effects. Co-exposures with the mitochondrial uncoupler FCCP did not decrease cellular viability but elevated DNA damage. We suggest that mitochondria are a sensitive target of nanoplastics in bivalve hemocytes, highlighting the importance of considering aerobic metabolism in assessing nanoplastic toxicity. The strong correlation with the published in vivo effects of this same NanoPS highlights the biological relevance of this cellular toxicity assessment. This research supports the use of hemocyte-based cellular assays to complement in vivo studies for characterizing nanoplastic toxicity mechanisms in marine organisms.