Effects of rare earth oxide nanoparticles on root elongation of plants

The phytotoxicity of four rare earth oxide nanoparticles, nano-CeO2, nano-La2O3, nano-Gd2O3 and nano-Yb2O3 on seven higher plant species (radish, rape, tomato, lettuce, wheat, cabbage, and cucumber) were investigated in the present study by means of root elongation experiments. Their effects on root growth varied greatly between different nanoparticles and plant species. A suspension of 2000 mg L−1 nano-CeO2 had no effect on the root elongation of six plants, except lettuce. On the contrary, 2000 mg L−1 suspensions of nano-La2O3, nano-Gd2O3 and nano-Yb2O3 severely inhibited the root elongation of all the seven species. Inhibitory effects of nano-La2O3, nano-Gd2O3, and nano-Yb2O3 also differed in the different growth process of plants. For wheat, the inhibition mainly took place during the seed incubation process, while lettuce and rape were inhibited on both seed soaking and incubation process. The fifty percent inhibitory concentrations (IC50) for rape were about 40 mg L−1 of nano-La2O3, 20 mg L−1 of nano-Gd2O3, and 70 mg L−1 of nano-Yb2O3, respectively. In the concentration ranges used in this study, the RE3+ ion released from the nanoparticles had negligible effects on the root elongation. These results are helpful in understanding phytotoxicity of rare earth oxide nanoparticles.