Each temperature degree counts: warming enhances polystyrene nanoplastic toxicity via metabolic disruption in a marine cellular model

Climate change is significantly altering the thermal environment of marine species, causing shifts in animal metabolism through increased temperatures and more frequent marine heatwaves. These changes can impose additional physiological stress on coastal organisms, potentially worsening their sensitivity to environmental pollutants and metabolic disruptors such as plastics. Indeed, nanoplastics are concerning contaminants in marine ecosystems, with the potential to disrupt cellular metabolism and redox balance in aquatic organisms. This study examined if rising temperatures can influence the cellular toxicity of two model polystyrene nanoplastics (non-functionalized Plain-NanoPS and amino-functionalized NH₂-NanoPS) in primary cultures of Pacific oyster Crassostrea gigas (Magallana gigas) hemocytes. We exposed hemocytes to a range of nanoplastic concentrations (0.1 to 10 mg/L) at controlled temperatures from 16 °C to 28 °C and evaluated cellular responses using metabolic, oxidative, and viability biomarkers. This range of concentrations and temperatures reflects the NPs content in tissues and fluids, as well as temperature fluctuations in aquaculture sites and intertidal environments. Plain-NanoPS had minimal effects, while NH₂-NanoPS caused temperature-dependent toxicity, impairing ATP production, reducing metabolic activity, and increasing reactive oxygen species levels. Integrated cellular biomarker analysis showed a shift from an adaptive to a stress-dominated metabolic phenotype under combined NH₂-NanoPS exposure and warming conditions. Since both particle types exhibited similar surface charges in cell culture medium, factors other than surface charge might influence cellular toxicity. This research demonstrates that warming increases the metabolic toxicity of nanoplastics and can reduce the thermal resilience of oyster cells in vitro.