CeO₂ nanoparticles are widely used in various applications. Their toxicity and environmental effects have attracted more and more attention in recent years. As an important component of the ecosystem, plant is a potential way for their bioaccumulation and entry into the food chain. However, there are few reports on the absorption and transport of nCeO₂ in plants. Prof. Zhang Zhiyong’s team from CAS Key Laboratory of Biological Effects of Nanomaterials and Nanosafety, Institute of high energy physics, studied the effects of surface charge on the transport, transformation and toxicity of nCeO₂ in plants. Their research has been published on 8th, May, 2019 in ACS Appl Mater Interfaces.

The physiochemical properties of nanoparticles, including size, morphology, surface charge, chemical composition, etc. are key factors that affecting the biological effects and environmental behavior of NPs. In this study, the authors treated cucumber seedlings with positively charged (Cs) and negatively charged (PAA) CeO₂ NPs. Then, contents, distribution, translocation, and transformation of Ce in plants were analyzed using ICP-MS, μ-XRF, and XANES, respectively. Results show that the seedling growth and Ce contents in plant tissues were functions of exposure concentrations and surface charge. Cs-nCeO₂ was adsorbed strongly on the negatively charged root surface, which led to significantly higher Ce contents in the roots and lower translocation factors of Ce from the roots to shoots in Cs-nCeO₂ group than in PAA-nCeO₂ group. The results of μ-XRF show that Ce was mainly accumulated at the root tips and lateral roots, as well as in the veins and at the edge of leaves. XANES results reveal that the proportion of Ce(III) was comparable in the plant tissues of the two groups. It was speculated that Cs-nCeO₂ and PAA-nCeO₂ were partially dissolved under the effect of root exudates, releasing Ce³⁺ ions as a result. Then, the Ce³⁺ ions were transported upward as Ce(III) complexes along the vascular bundles and eventually accumulated in the veins. The other portion of Cs-nCeO₂ and PAA-nCeO₂ entered the roots at root tips/lateral roots and was transported upward as intact NPs and finally accumulated at the edge of the blade.

This study suggests that surface charge plays a key role in the absorption and transport of nanoparticles in plants. This provides a scientific basis for the research and development of targeted nano-pesticides and nano-agricultural fertilizers, and deepens the understanding of the interaction mechanisms between NPs and plants.

Two-dimensional distributions of Ce in plant tissues after treatments of nCeO₂ with different surface charges were obtained using m-XRF at Beijing Synchrotron Radiation Facility (BSRF). Ce signals were detected mainly in the root tips and the main roots under the two treatments. Moreover, the intensity of Ce in Cs-nCeO₂ group was significantly higher than that in PAA-nCeO₂ group, which was consistent with the result of ICP-MS.

Article:

Mengyao Liu, Sheng Feng, Yuhui Ma,* Changjian Xie, Xiao He, Yayun Ding, Junzhe Zhang, Wenhe Luo, Lirong Zheng, Dongliang Chen, Fang Yang,* Zhifang Chai, Yuliang Zhao, and Zhiyong Zhang*. Influence of Surface Charge on the Phytotoxicity, Transformation, and Translocation of CeO₂ Nanoparticles in Cucumber Plants. ACS Appl. Mater. Interfaces, 2019, 11, 16905-16913.