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, CeO(2) nanoparticles (NPs) might be released into the aquatic environment. In this paper, the interaction of CeO(2) NPs and Ce(3+) ions (0~10 mg/L) with duckweed (Lemna minor L.) was investigated. CeO(2) NPs significantly inhibited the root elongation of duckweed at concentrations higher than 0.1 mg/L, while the inhibition threshold of Ce(3+) 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 Ce(3+) ions was greater than that of CeO(2) NPs at the same concentration. According to the in situ distribution of Ce in plant tissues by μ-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 CeO(2) NPs. We speculated that the toxicity of CeO(2) NPs to duckweed was mainly due to its high sensitivity to the released Ce(3+) ions. To our knowledge, this is the first study on the toxicity of CeO(2) NPs to an aquatic higher plant.