Bioaccumulation And Phytotoxicity Of Cerium Dioxide Nanoparticle To Arabidopsis Thaliana

The use of nanotechnology in industries,medicine,energy,agriculture and cosmetics has increased rapidly.Metal oxide nanoparticles have a variety of applications and huge market potential due to their unique catalytic,magnetic,electrical and optic properties.For example,Cerium dioxide nanoparticles?CeO₂ NPs?are widely applied in different applications including fuel cells,catalysts,microelectronics,glass and ceramic applications and as diesel additives to improve fuel oxidation.Nanoparticles?NPs?can enter into the atmosphere,aquatic and terrestrial environment with unknown consequences.The potential risk of NPs exposure to the environment and their ecotoxicity get more attention.However,better knowledge about their effects to plants are very urgent.On the one hand,Plant is closely linked with environmental factors,such as soil,water and atmosphere;On the other hand,Plant is a significant base component of the ecosystem,and the starting point of the accumulation of toxic substances.NPs can accumulate step by step through food chain,may cause toxicity to senior biological.So it is significant for risk assessment to research the phytotoxicity,uptake and accumulation of NPs to plants.In this research,Different concentrations of CeO₂ NPs and CeO₂ Bulk?100 mg/L,200 mg/L,500 mg/L,1000 mg/L,2000 mg/L,3000 mg/L?and the Ce ions released by CeO₂ NPs were added into agar culture-medium to study the difference of toxicity between CeO₂ NPs and CeO₂ Bulk to Arabidopsis thaliana.TEM and ICP-MS were used to study the difference of uptake and accumulation between CeO₂ NPs and CeO₂ Bulk by Arabidopsis thaliana.The content of MDA,H₂O₂ and total chlorophyll were measured to find a preliminary analysis of toxic mechanisms.CeO₂ NPs could agglutinate at 2000 mg/L concentration in deionized water under TEM,and the average particle size was 0.447?m,while the CeO₂ Bulk was 75.89 ?m.The sedimentation ability of CeO₂ NPs in 1/2 MS medium was much better than in deionized water.The Ce ions released by CeO₂ NPs and CeO₂ Bulk was detected by supercentrifugation and ultrafiltrationtubes?Ultra-4 Millipore,USA?.According to results,the second way could be more precise.In addition,CeO₂ NPs could release more cerium ions than CeO₂ Bulk.According to the result of growing expression,biomass and root length,at 200-500 mg/L,CeO₂ NPs could promote root length and biomass.while 2000-3000 mg/L CeO₂ NPs would inhibit the growth of plant.CeO₂ Bulk could increase biomass at 200-500 mg/L,and No obvious effects could be found under 1000-3000 mg/L CeO₂ Bulk treatments.Plants also growed well under Ce ions treatments,which could confirm the reason of toxic effects was CeO₂ NPs itself,not Ce ions.It was proved that CeO₂ NPs and CeO₂ Bulk can be absorbed and accumulated by Arabidopsis thaliana from the roots to the shoots by using TEM and ICP-MS technology.The uptake of CeO₂ NPs was much more than CeO₂ Bulk.The uptake of Ce under Ce ions treatment was little.CeO₂ NPs could be observed in the cell of Arabidopsis thaliana leaves through TEM,and most of them accumulated in the intercellular space and near the cell walls.CeO₂ NPs could enter into the cell through cell walls,surrounded and damaged the chloroplasts,caused cellular damage,while a small amount of CeO₂ Bulk accumulated in leaf cells with no obvious toxic effects.Membrane lipid peroxidation level in Arabidopsis thaliana was serious under 2000 mg/L and 3000 mg/L CeO₂ NPs treatment,as content of MDA and H₂O₂ increased significantly,and chlorophyll content decreased sharply,and PS ? actual photosynthetic efficiency is reduced,which affected plant photosynthesis efficiency.while CeO₂ Bulk have no toxic effects to plants.