Concern and interest related to the effects of nanomaterials on living organisms are growing in both the scientific and public communities. Reports have described the toxicity of nanoparticles (NPs) on micro and macro organisms, including some plant species. Nevertheless, to the authors' knowledge there are no reports on the biotransformation of NPs by edible terrestrial plants. Here, shown for the first time, is evidence pertaining to the biotransformation of ZnO and CeO 2 NPs in plant seedlings. Although the NPs did not affect soybean germination, they produced a differential effect on plant growth and element uptake. By using synchrotron X-ray absorption spectroscopy we obtained clear evidence of the presence of CeO 2 NPs in roots, whereas ZnO NPs were not present. Random amplified polymorphic DNA assay was applied to detect DNA damage and mutations caused by NPs. Results obtained from the exposure of soybean plants to CeO 2 NPs show the appearance of four new bands at 2000 mg L −1 and three new bands at 4000 mg L −1 treatment. In this study we demonstrated genotoxic effects from the exposure of soybean plants to CeO 2 NPs.

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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 . Cerium uptake and oxidation state within tissues were determined using ICP-OES and XAS, respectively. 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 germination of tomato and cucumber was reduced by 30% and 20%, respectively (p < 0.05). Root growth was significantly promoted (p < 0.05) by nanoceria in cucumber and corn but reduced (p < 0.05) in alfalfa and tomato. Almost at 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.

Recent investigations show that carbon-based and metal-based engineered nanomaterials (ENMs), components of consumer goods and agricultural products, have the potential to build up in sediments and biosolid-amended agricultural soils. In addition, reports indicate that both carbon-based and metal-based ENMs affect plants differently at the physiological, biochemical, nutritional, and genetic levels. The toxicity threshold is species-dependent and responses to ENMs are driven by a series of factors including the nanomaterial characteristics and environmental conditions. Effects on the growth, physiological and biochemical traits, production and food quality, among others, have been reported. However, a complete understanding of the dynamics of interactions between plants and ENMs is not clear enough yet. This review presents recent publications on the physiological and biochemical effects that commercial carbon-based and metal-based ENMs have in terrestrial plants. This document focuses on crop plants because of their relevance in human nutrition and health. We have summarized the mechanisms of interaction between plants and ENMs as well as identified gaps in knowledge for future investigations.