Nanoplastics and ocean warming: Combined impact on physiology and surface properties of the marine microalga Dunaliella tertiolecta

Ocean warming due to climate change, in combination with emerging pollutants such as nanoplastics, poses a growing threat to marine ecosystems. This study investigates how ocean warming affects the toxicity of amine-modified polystyrene nanoplastics in the marine microalga Dunaliella tertiolecta. We investigated the combined impact of nanoplastics and temperature on algal physiology and cell surface properties by analyzing growth dynamics, reactive oxygen species (ROS) production, oxidative stress biomarkers, photosynthetic efficiency, and nanostructural and nanomechanical cell properties. Short-term exposure (5 days) to nanoplastics suppressed algal growth more at 30 °C than at 18 °C, with lower EC₅₀ values under warming conditions. Exposure to nanoplastics triggered excessive ROS production at both temperatures, leading to lipid peroxidation and increased activity of antioxidant enzymes, although these responses were attenuated at higher temperature. Photosynthetic performance also decreased significantly at both temperatures, however the impairment was less pronounced at 30 °C. Atomic force microscopy revealed that the nanoparticles adhered to the algal surfaces under both conditions, but a significant reduction in cell stiffness and adhesion was only observed at 30 °C. Overall, our results suggest that ocean warming exacerbates several negative effects of nanoplastics on marine microalgae, particularly growth inhibition and cell surface damage. As microalgae are important primary producers, the combined exposure to warming and nanoplastics poses a significant ecological risk that could disrupt the stability and productivity of marine ecosystems. These results highlight the importance of assessing the impact of nanoplastics and other pollutants under climate-relevant scenarios to improve ecological risk assessment.