Uptake and translocation of manufactured nanoparticles (NPs) in plants have drawn much attention due to their potential toxicity to the environment, including food webs. In this paper, the xylem and phloem based transport of CeO NPs in hydroponic cucumber plants was investigated using a split-root system. One half of the root system was treated with 200 or 2000 mg/L of CeO NPs for 3 days, whereas the other half remained untreated, with both halves sharing the same aerial part. The quantitative distribution and speciation of Ce in different plant tissues and xylem sap were analyzed by inductively coupled plasma-mass spectrometry, transmission electron microscope, X-ray absorption near edge structure, and X-ray fluorescence. Results show that about 15% of Ce was reduced from Ce(IV) to Ce(III) in the roots of the treated-side (TS), while almost all of Ce remained Ce(IV) in the blank-side (BS). The detection of CeO or its transformation products in the xylem sap, shoots, and BS roots indicates that Ce was transported as a mixture of Ce(IV) and Ce(III) from roots to shoots through xylem, while it was transported almost only in the form of CeO from shoots back to roots through phloem. To our knowledge, this is the first report of root-to-shoot-to-root redistribution after transformation of CeO NPs in plants, which has significant implications for food safety and human health.

Different plant species respond differently to nCeO2 under different culturing conditions: for some, deficiency of P enhances the accumulation of Ce (mainly Ce3+) and phytotoxicity.

The trophic transfer and transformation of CeO nanoparticles (NPs) through a simulated terrestrial food chain were investigated using a radiotracer technique and X-ray absorption near edge structure (XANES). Radioactive CeO NPs were applied to head lettuce ( Lactuca sativa), treated via root exposure in its potting soil (5.5 or 11 mg/plant) for 30 days or foliar exposure (7.2 mg/plant, with half of the leaves treated and the other half not) for 7 days. Subsequently, two groups of land snails ( Achatina fulica) were exposed to Ce via either a direct (i.e., feeding on the lettuce leaves withCe-contaminated surfaces) or an indirect/trophic (i.e., feeding on the lettuce leaves with systemically distributed Ce) route. To evaluate the influence of exposure routes, the Ce contents of the lettuce, snail tissues, and feces were determined by radioactivity measurements. The results show that both assimilation efficiencies (AEs) and food ingestion rates of Ce are greater for the trophic (indirect) exposure. The low AEs indicate that the CeO NPs ingested by snails were mostly excreted subsequently, and those that remained in the body were mainly concentrated in the digestive gland. XANES analysis shows that >85% of Ce was reduced to Ce(III) in the digestive gland under direct exposure, whereas Ce in the rest of the food chain (including feces) was largely in its original oxidized (IV) state. This study suggests that CeO NPs present in the environment may be taken up by producers and transferred to consumers along food chains and trophic transfer may affect food safety.

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Nanoparticles (NPs) are an increasingly common contaminant in agro-environments, and their potential effect on genetically modified (GM) crops has been largely unexplored. GM crop exposure to NPs is likely to increase as both technologies develop. To better understand the implications of nanoparticles on GM plants in agriculture, we performed a glasshouse study to quantify the uptake of Fe2O3 NPs on transgenic and non-transgenic rice plants. We measured nutrient concentrations, biomass, enzyme activity, and the concentration of two phytohormones, abscisic acid (ABA) and indole-3-acetic acid (IAA), and malondialdehyde (MDA). Root phytohormone inhibition was positively correlated with Fe2O3 NP concentrations, indicating that Fe2O3 had a significant influence on the production of these hormones. The activities of antioxidant enzymes were significantly higher as a factor of low Fe2O3 NP treatment concentration and significantly lower at high NP concentrations, but only among transgenic plants. There was also a positive correlation between the treatment concentration of Fe2O3 and iron accumulation, and the magnitude of this effect was greatest among non-transgenic plants. The differences in root phytohormone production and antioxidant enzyme activity between transgenic and non-transgenic rice plants in vivo suggests that GM crops may react to NP exposure differently than conventional crops. It is the first study of NPs that may have an impact on GM crops, and a realistic significance for food security and food safety.

The release of metal ions may play an important role in toxicity of metal‐based nanoparticles. In this report, a life cycle study is carried out in a greenhouse, to compare the effects of ceria nanoparticles (NPs) and Ce3+ ions at 0, 50, 100, and 200 mg Ce kg−1 on plant growth, biological and physiological parameters, and nutritional value of soil‐grown common bean plants. Ceria NPs have a tendency to negatively affect photosynthesis, but the effect is not statistically significant. Ce3+ ionic treatments at 50, 100, and 200 mg Ce kg−1 result in increases of 1.25‐, 0.66‐, and 1.20‐fold in stomatal conductance, respectively, relative to control plants. Both ceria NPs and Ce3+ ions disturb the homeostasis of antioxidant defense system in the plants, but only 200 mg Ce kg−1 ceria NPs significantly induce lipid peroxidation in the roots. Ceria NP treatments tend to reduced fresh weight and to increase mineral contents of the green pods, but have no effect on the organic nutrient contents. On the contrary, Ce3+ ion treatments modify the organic compositions and thus alter the nutritional quality and flavor of the green pods. These results suggest that the two Ce forms may have different mechanisms on common bean plants.

The physiochemical properties of nanoparticles (NPs), including surface charge, will affect their uptake, transformation, translocation, and final fate in the environment. In this study, we compared the phytoxoxicity and transport behaviors of nano CeO2 (nCeO2) functionalized with positively charged (Cs-nCeO2) and negatively charged (PAA-nCeO2) coatings. Cucumber seedlings were hydroponically exposed to 0–1000 mg/L of Cs-nCeO2 and PAA-nCeO2 for 14 days and the contents, distribution, translocation, and transformation of Ce in plants were analyzed using inductively coupled plasma mass spectrometry, micro X-ray fluorescence (μ-XRF), and X-ray absorption near-edge spectroscopy (XANES), respectively. Results showed that the seedling growth and Ce contents in plant tissues were functions of exposure concentrations and surface charge. Cs-nCeO2 was adsorbed strongly on a 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 showed that Ce elements were mainly accumulated at the root tips and lateral roots, as well as in the veins and at the edge of leaves. XANES results revealed that the proportion of Ce­(III) was comparable in the plant tissues of the two groups. We 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 in the form of 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 through the gap of a Casparian strip at root tips/lateral roots and was transported upward as intact NPs and finally accumulated at the edge of the blade. This study will greatly advance our information on how the properties of NPs influence their phytotoxicity, uptake, and subsequent trophic transfer in terrestrial food webs.

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