Phytotoxicity, uptake and transformation of nano-CeO2 in sand cultured romaine lettuce

Abstract

Toxicity and uptake of nano-CeO₂ (nCeO₂) in edible vegetables are not yet fully understood. In the present study, we grew romaine lettuce in sand amended with nCeO₂. At high concentrations (1000 and 2000 mg/kg), nCeO₂ diminished the chlorophyll content by 16.5% and 25.8%, respectively, and significantly inhibited the biomass production. nCeO₂ (≥100 mg/kg) altered antioxidant enzymatic activities and malondialdehyde levels in the plants. nCeO₂ (≥500 mg/kg) triggered a remarkable increase of nitrate-N level in the shoots, which can be converted to toxic nitrite in humans thereby posed risk to human health. Concentration dependent accumulation of Ce in the plant tissues was observed. X ray absorption near edge spectroscopy (XANES) results indicate that Ce presented as nCeO₂ and CePO₄ in the roots while as nCeO₂ and Ce carboxylates in the shoots. Chelation of Ce³⁺ by citric acid or precipitation of Ce³⁺ by PO₄^3- reduced the translocation and toxicity of nCeO₂, indicating that release of Ce³⁺ played a critical role in the toxicity nCeO₂.

Keywords: CeO(2); Lettuce; Nanomaterials; Toxicity; Transformation.