Toxicity And Mechanism Of Two Rare Earth Oxide Nanoparticles On Lettuce

Rare Earth Oxides Nanoparticles?REO-NPs?were widely used in materials science,biomedicine,cosmetics,environmental analysis and other fields due to their unique physical and chemical properties.In the process of application,REO-NPs would enter the environment in the form of combustion,factory waste gas,and wastewater,then carry out migration and transformation in soil,water and atmosphere through water vapor transport,rainfall,and infiltration,at last affect the ecological environment and endangering human health.Therefore,the study on the REO-NPs transference and transformation rules in environmental media and the toxic response mechanism of plants had important theoretical value and practical significance for the application of REO-NPs and the evaluation of its ecological security effect.Toxic effects and toxic mechanism of Nd₂O₃ and La₂O₃ NPs on hydroponic cultivated lettuce were studied by analyzing biomass,moisture content,photosynthetic characteristics,fluorescence characteristics,contents of nutrient elements and distribution of La and Nd in this paper.The main research results were as follows:?1?Toxic effects of different treatments on lettuceFresh weight,moisture content,chlorophyll content,stomatal conductance,photosynthetic rate,transpiration rate and F_v/F_m under treatments of 100 mg L^-1La₂O₃NPs,100,125 mg L^-11 Nd₂O₃ NPs were significantly lower?p<0.05?than those of control,125,150 mg L^-1 La₂O₃ NPs,150 mg L^-1 Nd₂O₃ NPs.However,the characteristics value mentioned above under treatments of 150 mg L^-1 La₂O₃,Nd₂O₃BPs,20 mg L^-1 La³⁺and Nd³⁺were higher than those of control,but there was no significant difference.?2?Effects of different treatments on nutrient content of lettuceWith the increase of the concentrations of La₂O₃ and Nd₂O₃ NPs,the contents of macroelements?N,P?and microelements?Mg,Mn,Ca?in lettuce shoot was decreased,N,Mg and Ca contents of root was decreased,but the contents of P and Mn increased with the increase of the treatment concentration.The effect of 150 mg L^-1 La₂O₃,Nd₂O₃BPs?20 mg L^-1 La³⁺,Nd³⁺treatment on nutrient element content of lettuce was no significant difference from the control group.?3?Contents and distribution of La and Nd in lettuceWith the increase of the concentration of La₂O₃ and Nd₂O₃ NPs,the content of La and Nd in lettuce root and shoot increased.The content of La and Nd in lettuce shoot treated with 150 mg L^-1 La₂O₃ and Nd₂O₃ BPs were significantly lower than the same concentration of nanoparticles.The Nd and La content of lettuce root treated with 20mg L^-1 La³⁺and Nd³⁺were significantly lower than 150 mg L^-1 La₂O₃ and Nd₂O₃ NPs.TEM results showed that La and Nd mainly distributed in intercellular space and cytoplasm,which indicated that the two kinds of nanoparticles damaged the selective permeability of cell membrane,and then made a large number of nanoparticles enter plant tissues and organelles.?4?Analysis of toxic effects and toxic factors of NPs,BPs and ions150 mg L^-1 La₂O₃ and Nd₂O₃ NPs had a significant inhibitory effect on lettuce?p<0.05?,while 150 mg L^-1 BPs had a promotive effect on lettuce growth,indicated that the smaller hydrodynamic diameter and higher concentration of nanoparticles were the main factors led the toxicity.Besides,La₂O₃ and Nd₂O₃ BPs were not toxic.In addition,1.5 times higher than the maximum concentrations of La³⁺and Nd³⁺dissolved from150 mg L^-1 La₂O₃ and Nd₂O₃ NPs,20 mg L^-1 La³⁺and Nd³⁺did not inhibit lettuce growth,which indicated that the toxicity effect on lettuce was not the ions dissolved from the two nanoparticles,but the nanoparticles themselves.