Biotransformation of Ceria Nanoparticles in Cucumber Plants
Peng Zhang,†,# Yuhui Ma,†,# Zhiyong Zhang,†,* Xiao He,† Jing Zhang,‡ Zhi Guo,§ Renzhong Tai,§ Yuliang Zhao,† and Zhifang Chai† Key Laboratory for Biological Eﬀects of Nanomaterials and Nanosafety, Key Laboratory of Nuclear Analytical Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China, ‡Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China, and §Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China. #These authors contributed equally to this work. ABSTRACT Biotransformation is a critical factor that may modify the toxicity, behav†
ior, and fate of engineered nanoparticles in the environment. CeO2 nanoparticles (NPs) are generally recognized as stable under environmental and biological conditions. The present study aims to investigate the biotransformation of CeO2 NPs in plant systems. Transmission electron microscopy (TEM) images show needlelike clusters on the epidermis and in the intercellular spaces of cucumber roots after a treatment with 2000 mg/L CeO2 NPs for 21 days. By using a soft X-ray scanning transmission microscopy (STXM) technique, the needlelike clusters were veriﬁed to be CePO4. Near edge X-ray absorption ﬁne structure (XANES) spectra show that Ce presented in the roots as CeO2 and CePO4 while in the shoots as CeO2 and cerium carboxylates. Simulated studies indicate that reducing substances (e.g., ascorbic acids) played a key role in the transformation process and organic acids (e.g., citric acids) can promote particle dissolution. We speculate that CeO2 NPs were ﬁrst absorbed on the root surfaces and partially dissolved with the assistance of the organic acids and reducing substances excreted by the roots. The released Ce(III) ions were precipitated on the root surfaces and in intercellular spaces with phosphate, or form complexes with carboxyl compounds during translocation to the shoots. To the best of our knowledge, this is the ﬁrst report conﬁrming the biotransformation and in-depth exploring the translocation process of CeO2 NPs in plants. KEYWORDS: CeO2 . CePO4 . nanoparticles . plant . biotransformation
ncreasing production and use of nanomaterials have raised concerns about their potential hazardous eﬀects to the environment and human health.1,2 Deﬁning the behavior of nanomaterials in the environmental and biological systems is a critical research focus before aiming to understand their environmental risks.3,4 As an essential component of the environment, plants play a crucial role in preserving the ecological equilibrium as well as providing the food sources of animals and human beings. The ongoing production and use of engineered nanoparticles (ENPs) have greatly increased the possibility of plant exposure to them, via an aerial or root pathway. Once adsorbed to the plant surfaces, the ENPs may be taken up, translocated, and stored in diﬀerent tissues of plants, followed by being transferred to the food webs, accumulating in higher-level organisms, and causing possible biomagniﬁcations.5,6 Investigations on the behavior and fate of ENPs within plants are of great importance for exploring the ZHANG ET AL.
mechanism of phytotoxicity and the full-life cycle risk assessment of ENPs. Biotransformation, which is deﬁned as biochemical modiﬁcation by living organisms, has been studied for a long time on the common pollutants. In the process of biotransformation, either enhanced toxicity or detoxiﬁcation is possible.7 In terms of ENPs, they may also be modiﬁed by the ambient environmental media and biological systems and their ﬁnal fate and toxicity to organisms may be altered.8 Typical transformations of nanomaterials most studied recently include redox reaction, sulﬁdation, phosphorylation, and macromolecular/ molecular...