The Absorption Translocation, Transformation And Phytotoxicity Of Different Surface Charge CeO₂ NPs With Cucumber

With the rapid development of nanotechnology,nanomaterials have brought convenience to industrial production and daily life.Meanwhile,the impact of nanomaterials on environment has also attracted people's attention.Nano-CeO₂ is one of the widely used nanomaterials.It will enter to the environment in various forms,migrate and transform in atmosphere,soil and water,and absorbed by plants.The study of the effect of nano-CeO₂ on plants is of great significance.But there is still a lot of uncertainty about how nano-CeO₂ is absorbed and transformed by plants.So we use Cs and PAA to modify nano-CeO₂,respectively,and used to treat cucumber seedlings.The mechanism of transfer and transformation of Ce in cucumber plants was explored by synchrotron radiation XANES and?–XRF.The results showed that:?1?TEM results showed that the shape of Cs-CeO₂ and PAA-CeO₂ NPs is similar to that of Raw-CeO₂ NPs,with a uniform particle size of about 7 nm.FT-IR and TGA results showed that the success of surface modification.?2?ICP-MS results show that Cs-CeO₂ NPs with positively charge adsorbed on the root surface strongly due to the negative charge on the root surface,which led to a high Ce content in the roots of the Cs-CeO₂ group.However,in the leaves,the content of Ce in the PAA-CeO₂ group was higher than that in the PAA-CeO₂ group.?3?The XANES results showed that the proportion of Ce???was 11.0%and21.6%in the plant roots of group Cs-CeO₂ and PAA-CeO₂,while the ratio of Ce???in leaves was 35.5%and 32.0%,respectively.The results of?-XRF showed that the Ce elements were mainly accumulated on the veins and leaf edges.So,combined with the previous research,we speculate that the mechanism of plant uptake and transport of Ce in cucumber is that Ce enter root via lateral root or root tip and then transport from root to leaf by two ways of transportation:A part of CeO₂ releases Ce³⁺under the effect of root exudates,they combine with organic acids to form a complex,which is transported upwards along the vascular bundles in the form of Ce?III?,and eventually accumulates in the veins.The other part of CeO₂ NPs is transported upwards from the root tip or lateral root through the casparian strip gap into the root,and finally accumulates at the edge of the leaf.