http://informahealthcare.com/nan ISSN: 1743-5390 (print), 1743-5404 (electronic) Nanotoxicology, 2015; 9(2): 262–270 ! 2014 Informa UK Ltd. DOI: 10.3109/17435390.2014.921344 ORIGINAL ARTICLE Origin of the different phytotoxicity and biotransformation of cerium and lanthanum oxide nanoparticles in cucumber Yuhui Ma 1 *, Peng Zhang 1 *, Zhiyong Zhang 1 , Xiao He 1 , Yuanyuan Li 1 , Jing Zhang 2 , Lirong Zheng 2 , Shengqi Chu 2 , Ke Yang 3 , Yuliang Zhao 1 , and Zhifang Chai 1 1 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, China, 2 Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Shanghai, China, and 3 Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China Abstract To investigate how the physicochemical properties of nanoparticles (NPs) affect their biological and toxicological effects, we evaluated the phytotoxicity of CeO 2 and La 2 O 3 NPs to cucumber (Cucumis sativus) plants and tried to clarify the relation between physicochemical properties of NPs and their behaviors. CeO 2 NPs had no phytotoxicity to cucumber at all tested concentrations, while La 2 O 3 NPs showed significant inhibition on root elongation (  2 mg/L), shoot elongation (at 2000 mg/L), root biomass (  2 mg/L), and shoot biomass (  20 mg/L), as well as induced more reactive oxygen species and cell death in roots (2000 mg/L). The different distribution and speciation of Ce and La in plants were determined by synchrotron-based micro X-ray fluorescence microscopy and X-ray absorption spectroscopy. In the aerial parts, all of La was combined with phosphate or carboxylic group, while a fraction of Ce was changed to Ce(III)–carboxyl complexes, implying that La 2 O 3 acted as its ionic form, while CeO 2 displayed the behavior of particles or particle–ion mixtures. The higher dissolution of La 2 O 3 than CeO 2 NPs might be the reason for their significant difference in phytotoxicity and transporting behaviors in cucumbers. To our knowledge, this is the first detailed study of the relation between the level of dissolution of NPs and their behaviors in plant systems. Keywords Biotransformation, CeO 2 and La 2 O 3 NPs, dissolution, phytotoxicity, plants History Received 23 August 2013 Revised 7 March 2014 Accepted 09 April 2014 Published online 29 May 2014 Introduction Rare earth elements (REEs) comprise a homogenous group of elements with very similar chemical and physical properties. All the REEs exhibit + 3 oxidation state. In addition, Ce 3+ can lose its single f electron to form Ce 4+ with the stable electronic configuration of xenon. Rare earth oxide (REO) nanoparticles (NPs) is one class of the most important nanomaterials, which are widely used in paint coating, polishing powder, catalysts, luminescent materials and so on (Kaneko et al., 2007). As a result, the deliberate and accidental release of REO NPs into the environment is inevitable and concerns over the potential impacts that their release may have on human health and the environment are increasing (Khodakovskaya et al., 2011). Plants represent the largest interface between the environment and the biosphere. As part of the first trophic level in the food chain, plants may serve as the primary target and a potential pathway for the transporting of REO NPs. So, it is necessary to determine the response and possible role of plants in the fate and transport of REO NPs. Among REO NPs, CeO 2 is considered to be a representative member of the industrially important class of metal oxide NPs (Johnson & Park, 2012) and insoluble under environmental conditions, so it is suited to study the mobility of NPs in biological system. Birbaum et al. (2010) found that CeO 2 NPs could be adsorbed on and incorporated in leaves but were not able to translocate within maize plants. Zhang et al. (2011) studied the uptake and distribution of two different sizes of CeO 2 NPs in cucumber plants by means of the radiotracer technique. They found that only a limited quantity of CeO 2 NPs could be transported from the roots to shoots. The uptake of bare and coated CeO 2 NPs by corn plants grown in soil was also investigated (Zhao et al., 2012). Results showed that surface coating and soil organic matter played important roles in the mobility and bioavailability of CeO 2 NPs. We previously investigated the phytotoxicity of four kinds of REO NPs (CeO 2 , La 2 O 3 , Gd 2 O 3 and Yb 2 O 3 ) to seven higher plant species (radish, rape, tomato, lettuce, wheat, cabbage and cucumber) and proved that CeO 2 NPs had significantly different effects from the other ones (Ma et al., 2010). Wang et al. (2012a) studied the chronic effect of CeO 2 NPs on tomato plants at relatively low concen- trations (0.1–10 mg/L). They documented that the applied CeO 2 NPs had a slightly positive effect on plant growth and tomato production, and CeO 2 NPs could be taken up by roots and translocated to shoots and edible tissues of tomatoes. *These authors contributed equally to this work. Correspondence: Zhiyong Zhang, 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. Tel: +86-10-88233215. Fax: +86-10-88235294. E-mail: zhangzhy@ihep.ac.cn Nanotoxicology Downloaded from informahealthcare.com by Mcgill University on 06/08/15 For personal use only.