Influence of nitrogen limitation on the bioaccumulation kinetics of hematite nanoparticles in the freshwater alga Euglena intermedia

Abstract

Although the toxic effects of nanoparticles on aquatic organisms have been intensively investigated, less is known about the bioaccumulation kinetics of the particles as an indicator of toxicity. In the present study, we used a radiotracer-based method to examine the bioaccumulation kinetics of well-dispersible hematite nanoparticles (HemNPs) in the freshwater mixotrophic alga Euglena intermedia. Because nitrogen limitation of phytoplankton growth is common in aquatic ecosystems, we also compared the difference in nanoparticle accumulation by nutrient-enriched and nitrogen-depleted cells. HemNP accumulation in E. intermedia increased linearly with exposure time. More interestingly, nitrogen limitation induced the cell-surface adsorption and subsequent internalization of HemNPs. Both processes increased with increasing starvation time and with decreasing ambient nitrogen concentrations in the experimental medium. These inductive effects could be attributed to the increased irregularity/roughness of the E. intermedia cell surface and to an increase in cell-surface-attached polysaccharides of the nitrogen-depleted algal cells. Considering the ubiquity of phytoplankton nutrient limitation in many aquatic ecosystems, its impacts on the environmental behavior, effects, and fates of nanoparticles must be taken into account in ecosystem studies of nanoparticles.