Interaction of Cerium Oxide Nanoparticles and Ionic Cerium with Duckweed (Lemna minor L.): Uptake, Distribution, and Phytotoxicity

As one of the most widely used nanomaterials, CeO2nanoparticles (NPs) might be released into the aquatic environment. In this paper, the interaction of CeO2NPs and Ce3+ions (0~10 mg/L) with duckweed (Lemna minorL.) was investigated. CeO2NPs significantly inhibited the root elongation of duckweed at concentrations higher than 0.1 mg/L, while the inhibition threshold of Ce3+ions was 0.02 mg/L. At high doses, both reduced photosynthetic pigment contents led to cell death and induced stomatal deformation, but the toxicity of Ce3+ions was greater than that of CeO2NPs at the same concentration. According to the in situ distribution of Ce in plant tissues byμ-XRF, the intensity of Ce signal was in the order of root > old frond > new frond, suggesting that roots play a major role in the uptake of Ce. The result of XANES showed that 27.6% of Ce(IV) was reduced to Ce(III) in duckweed treated with CeO2NPs. We speculated that the toxicity of CeO2NPs to duckweed was mainly due to its high sensitivity to the released Ce3+ions. To our knowledge, this is the first study on the toxicity of CeO2NPs to an aquatic higher plant.