Study On Toxicity And Mechanism Of Nano CeO₂ With Different Morphology To Lettuce

With the continuous development of nanotechnology,nanomaterials are widely used in the fields of medicine,environmental protection and chemical industry.In the process of use,nanomaterials will inevitably enter the environment through various channels,and the environmental effects caused by nanomaterials have attracted widespread attention.Because of excellent physical and chemical properties,nano cerium dioxide（nano CeO₂）has been one of the most widely used nanomaterials,and has great application prospects.During the production,use and treatment,nano CeO₂enters the environment through various channels and interacts with plants.In turn,it may affect human health through the food chain.Therefore,more attention needs to be paid to the plant effect of nano CeO₂.In this paper,four kinds of nano CeO₂ with different morphologies were selected as research objects.Lactuca sativa were used as a model plant.Combined with conventional ecotoxicological methods and synchrotron radiation technology,the absorption,translocation and transformation of nano CeO₂ with different morphologies in plants and the differences in toxicity mechanisms were discussed.The work mainly includes the following:1.Nano CeO₂ with different morphologies were synthesized and deeply characterized.（1）Rod CeO₂:average particle size 106±18.3 nm（long diameter）/10.8±0.7 nm（short diameter）;（2）Cubic CeO₂:average size 33.3±7.8 nm（3）3 nm CeO₂:average particle size 3.8±0.7 nm,morphology similar to a sphere（4）Bulk CeO₂:irregular shape and size.Zeta potential results shown that Rod CeO₂ and 3 nm CeO₂were positive charge after being dispersed in water,while Cubic CeO₂ and Bulk CeO₂were negative.2.The effect of Nano CeO₂ with different morphologies to plant was studied.Firstly,it was found through exposure experiments that Rod CeO₂ and 3 nm CeO₂caused significant inhibitory effects on the growth of Lactuca sativa,but Cubic CeO₂and Bulk CeO₂ did not cause this effect.Secondly,ICP-MS was used to determine the content of Ce in the roots and stems of plants.The results showed that the Ce content in the roots and stems of the plants were Rod CeO₂>3 nm CeO₂>Cubic CeO₂>Bulk CeO₂,which may be electrostatically charged.Rod CeO₂ and 3 nm CeO₂ were more easily adsorbed on the negatively charged root surface.The TEM results also showed that a large amount of CeO₂ were adsorbed on the root surface in the Rod CeO₂ and 3nm CeO₂ treatment groups,a small amount of Cubic CeO₂ were adsorbed on the root surface,and there was no Bulk CeO₂.Furthermore,needle-like substance was found in the Rod CeO₂ and 3 nm CeO₂ groups intercellular space,which may be cerium phosphate,the product of CeO₂ transformation.The antioxidant enzyme activities in plant roots also showed that the plants treated with Rod CeO₂ and 3nm CeO₂ have sufferced serious oxidative stress.3.XANES results showed that some Ce（IV）in the roots of Lactuca sativa exposed to Rod CeO₂,Cubic CeO₂ and 3 nm CeO₂ were transformed to Ce（III）,and the transformation ratios were 16.9%,7.2%and 13.5%,respectively.Bulk CeO₂ was not transformed in the roots of Lactuca sativa.Previous research has shown that lettuce plants are very sensitive to Ce（III）,and even at a concentration of 0.5 mg/L,root growth was significantly inhibited.In this work,we used different morphologies of nano CeO₂to treat Lactuca sativa.,and found that plant toxicity was different,and that the degree of transformation of nano CeO₂ with different morphologies in roots were different.Therefore,we speculated that the phytotoxicity of nano CeO₂ with different morphologies were closely related to its biotransformation.The physical and chemical properties of nano CeO₂ determined by the morphology,and then affect the biological effect of nano CeO₂.