X-ray absorption spectroscopy (XAS) corroboration of the uptake and storage of CeO(2) nanoparticles and assessment of their differential toxicity in four edible plant species

Abstract

Fate, transport, and possible toxicity of cerium oxide nanoparticles (nanoceria, CeO(2)) are still unknown. In this study, seeds of alfalfa (Medicago sativa), corn (Zea mays), cucumber (Cucumis sativus), and tomato (Lycopersicon esculentum) were treated with nanoceria at 0-4000 mg L(-1). The cerium uptake and oxidation state within tissues were determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray absorption spectroscopy (XAS), respectively. The germination rate and root elongation were also determined. Results showed that nanoceria significantly reduced corn germination (about 30% at 2000 mg L(-1); p < 0.05), and at 2000 mg L(-1), the germination of tomato and cucumber was reduced by 30 and 20%, respectively (p < 0.05). The root growth was significantly promoted (p < 0.05) by nanoceria in cucumber and corn but reduced (p < 0.05) in alfalfa and tomato. At almost all concentrations, nanoceria promoted shoot elongation in the four plant species. XAS data clearly showed the nanoceria within tissues of the four plant species. To the authors' knowledge, this is the first report on the presence nanoceria within plants.

Figure 1

Percent germination of alfalfa, □ tomato, corn, and ■ cucumber seeds treated with CeO₂ NPs solutions at 0–4000 mg/L. Data represent mean ± SE of three replicates. One-way ANOVA and Tukey’s test were used to determine statistical significance of the differences between treatment means. *Statistically significant at p ≤ 0.05.

Figure 2

Percent root (a) and stem (b) growth reduction of ■ cucumber, alfalfa, □ tomato, and corn seedlings exposed to 0–4000 mg/L CeO₂ NP suspensions. Data represent mean ± SE of three replicates. One-way ANOVA and Tukey’s test were used to determine statistical differences between treatment means. *Statistically significant at p ≤ 0.05.

Figure 3

Cerium concentration in ■ cucumber, alfalfa, □ tomato, and corn seedlings treated with CeO₂ NP suspensions at 0–4000 mg/L. Data are mean ± SE of three replicates. One-way ANOVA and Tukey’s test were used to determine statistical differences between treatment means. *Statistically significant at p ≤ 0.05.

Figure 4

XANES Ce L_III-edge normalized spectra(5723eV) of CeO₂ NPs (model compound) and spectra from cucumber, alfalfa, tomato, and corn roots exposed to 4000 mg/Lof CeO₂ NPs.