Nanocellulose enhances the dispersion and toxicity of ZnO NPs to green algae Eremosphaera viridis

The presence of nanocellulose reduces the aggregation of ZnO NPs and enhances the bio-uptake of Zn ions to algal cells. The widespread cellulose nanomaterials from industrial production and natural plant degradation inevitably lead to the accumulation of nanocellulose in the aquatic environment. However, the effect of nanocellulose on the fate, transport and biotoxicity of zinc oxide nanoparticles (ZnO NPs) remains largely unexplored. The present study investigated the interactions between nanocellulose and ZnO NPs. The addition of naturally-derived cellulose nanocrystals (CNCs) significantly reduced the aggregation of ZnO NPs, resulting in enhanced bioavailability and toxicity to the algae Eremosphaera viridis. The ZnO–CNC association enhanced the envelopment of the algal cells and exerted strong oxidative stress as compared to bare ZnO NPs. The excessive reactive oxygen species generation could result in the breakdown of membrane lipid and disruption of antioxidant enzyme activity, where lipid synthesis was inhibited and protein folding might occur. The presence of CNCs also improved the concentration of Zn ions inside the algal cell through intracellular transportation. This can affect the flow of substances between algae cells and the environment, and further influence the metabolism of microalgae. This work is crucial for improving our insight into the mechanism for combined effects from multiple nanomaterials, such that the composite risks of such combined effects to aquatic organisms can be identified.