Research Advances on Plant Toxicity Induced by Nanoparticles of Rare Earth Oxide

Rare earth oxide nanoparticles (REO NPs) have caught the attention by scientists worldwide as they can potentially harm the environment due to the toxicity associated with the particle size as well as the chemical property. With the advancement of nanotechnology, NPs inevitably enter the environment through various channels causing detrimental effects on the environment and human health. Therefore, studying the translocation and transformation of REO NPs in media and the response mechanism of plants toward the toxicity carries important theoretical and practical significance for the material applications and ecological security. This article summarizes the mechanism and affecting factors associated with the toxicity of REO NPs on the crops cultivated on soil or hydroponics and discusses the prospects of future research and utilization of the NPs. Currently, the toxic effects induced by REO NPs on plants were believed to include (1) the inhibition of root growth and development and (2) the retardation of chlorophyll synthesis reducing the photosynthetic efficiency and biomass accumulation. The toxicity mechanisms focused by various studies were mainly on (1) the functions directly caused by the dissolved REO NPs ions or their competing with other mineral ions on nutrient absorption, (2) the obstruction of selective cellular permeability, the production of oxygen free radicals, and the lipid peroxidation of cell membrane, and (3) the adherence of particles on surface of the plant tissues interfering normal water and nutrients transportation and ion exchange. Major factors that affect the toxicity might encompass the properties of REO NPs (such as, solubility, electrification, particle size, and shape), the sensitivity or tolerance of a plant to REO NPs, and the environmental conditions (such as, acidity, alkalinity, electrification, etc.).The study on toxic effects of REO NPs has fewer types of selected pollutants, mainly for plants in seedling stage, and fewer study on molecular biology, soil culture methods, and all environmental conditions. In the later stage, we can conduct in-depth research from the above aspects.