The Effect of Nanoparticles with Sorption Capacity on the Bioaccumulation of Divalent Ions by Aquatic Plants

Wide utilization of nanotechnologies results in the release of nanomaterials into the environment. Considering the sorption capacity of nanoparticles (NPs) and their growing concentration in aquatic environment, the modification of metal ion uptake by direct NP–metal ion reaction, including adsorption of ions onto the surface of the NPs, can be assumed. The aim of the study was to characterize the sorption capacity of zinc and titanium oxide nanoparticles (TiO2 NPs 25 and 100 nm; ZnO NPs 50 and 100 nm) and to examine the bioaccumulation of Zn(II) and Sr(II) ions by aquatic plants Salvinia natans and Elodea canadensis in the presence of the above-mentioned NPs. The results have shown that NPs can adsorb metal ions present in the water. It was also observed that the sorption efficiency strongly depends on the: (1) concentrations of NPs and increase in the range 0.01–5 g L−1; (2) pH—the highest sorption efficiency was observed at pH 8; (3) chemical composition of the medium (presence of humic substances at 0.01 g L−1 increased the sorption efficiency of Sr on TiO2 25 nm from 10 to 50%). Under some conducive conditions, even 90% of Zn(II) ions can be removed from a solution through sorption using ZnO nanoparticles. Bioaccumulation of Zn(II) and Sr(II) ions by S. natans and E. canadensis was modified in the presence of investigated NPs. Bioaccumulation of Sr in E. canadensis and S. natans was reduced by NPs of ZnO 100 nm at concentration 1 g L−1 of about 49 and 23%, respectively. Bioavailability of Zn was the most affected by NPs of ZnO 100 nm at 1 g L−1. Bioaccumulation of Zn in E. canadensis was reduced by 68%. An opposite effect was found for S. natans—addition of ZnO NPs caused an increase of Zn bioaccumulation by 45%.