Cerium Biomagnification in a Terrestrial Food Chain: Influence of Particle Size and Growth Stage

Mass-flow modeling of engineered nanomaterials (ENMs) indicates that a major fraction of released particles partition into soils and sediments. This has aggravated the risk of contaminating agricultural fields, potentially threatening associated food webs. To assess possible ENM trophic transfer, cerium accumulation from cerium oxide nanoparticles (nano-CeO₂) and their bulk equivalent (bulk-CeO₂) was investigated in producers and consumers from a terrestrial food chain. Kidney bean plants (Phaseolus vulgaris var. red hawk) grown in soil contaminated with 1000–2000 mg/kg nano-CeO₂ or 1000 mg/kg bulk-CeO₂ were presented to Mexican bean beetles (Epilachna varivestis), which were then consumed by spined soldier bugs (Podisus maculiventris). Cerium accumulation in plant and insects was independent of particle size. After 36 days of exposure to 1000 mg/kg nano- and bulk-CeO₂, roots accumulated 26 and 19 μg/g Ce, respectively, and translocated 1.02 and 1.3 μg/g Ce, respectively, to shoots. The beetle larvae feeding on nano-CeO₂ exposed leaves accumulated low levels of Ce since ∼98% of Ce was excreted in contrast to bulk<i>-</i>CeO₂. However, in nano-CeO₂ exposed adults, Ce in tissues was higher than Ce excreted. Additionally, Ce content in tissues was biomagnified by a factor of 5.3 from the plants to adult beetles and further to bugs

Physiological and Biochemical Changes Imposed by CeO₂ Nanoparticles on Wheat: A Life Cycle Field Study

Interactions of <i>n</i>CeO₂ with plants have been mostly evaluated at seedling stage and under controlled conditions. In this study, the effects of <i>n</i>CeO₂ at 0 (control), 100 (low), and 400 (high) mg/kg were monitored for the entire life cycle (about 7 months) of wheat plants grown in a field lysimeter. Results showed that at high concentration <i>n</i>CeO₂ decreased the chlorophyll content and increased catalase and superoxide dismutase activities, compared with control. Both concentrations changed root and leaf cell microstructures by agglomerating chromatin in nuclei, delaying flowering by 1 week, and reduced the size of starch grains in endosperm. Exposed to low concentration produced embryos with larger vacuoles, while exposure to high concentration reduced number of vacuoles, compared with control. There were no effects on the final biomass and yield, Ce concentration in shoots, as well as sugar and starch contents in grains, but grain protein increased by 24.8% and 32.6% at 100 and 400 mg/kg, respectively. Results suggest that more field life cycle studies are needed in order to better understand the effects of <i>n</i>CeO₂ in crop plants

Cerium Oxide Nanoparticles Impact Yield and Modify Nutritional Parameters in Wheat (Triticum aestivum L.)

The implications of engineered nanomaterials on crop productivity and food quality are not yet well understood. The impact of cerium oxide nanoparticles (<i>n</i>CeO₂) on growth and yield attributes and nutritional composition in wheat (Triticum aestivum L.) was examined. Wheat was cultivated to grain production in soil amended with 0, 125, 250, and 500 mg of <i>n</i>CeO₂/kg (control, <i>n</i>CeO₂-L, <i>n</i>CeO₂-M, and <i>n</i>CeO₂-H, respectively). At harvest, grains and tissues were analyzed for mineral, fatty acid, and amino acid content. Results showed that, relative to the control, <i>n</i>CeO₂-H improved plant growth, shoot biomass, and grain yield by 9.0%, 12.7%, and 36.6%, respectively. Ce accumulation in roots increased at increased <i>n</i>CeO₂ concentration but did not change across treatments in leaves, hull, and grains, indicating a lack of Ce transport to the above-ground tissues. <i>n</i>CeO₂ modified S and Mn storage in grains. <i>n</i>CeO₂-L modified the amino acid composition and increased linolenic acid by up to 6.17% but decreased linoleic acid by up to 1.63%, compared to the other treatments. The findings suggest the potential of nanoceria to modify crop physiology and food quality with unknown consequences for living organisms

Foliar Exposure of Cu(OH)₂ Nanopesticide to Basil (<i>Ocimum basilicum</i>): Variety-Dependent Copper Translocation and Biochemical Responses

In this study, low and high anthocyanin basil (<i>Ocimum basilicum</i>) varieties (LAV and HAV) were sprayed with 4.8 mg Cu/per pot from Cu­(OH)₂ nanowires, Cu­(OH)₂ bulk (CuPro), or CuSO₄ and cultivated for 45 days. In both varieties, significantly higher Cu was determined in leaves of CuSO₄ exposed plants (691 and 672.6 mg/kg for LAV and HAV, respectively); however, only in roots of HAV, Cu was higher, compared to control (<i>p</i> ≤ 0.05). Nanowires increased <i>n</i>-decanoic, dodecanoic, octanoic, and nonanoic acids in LAV, but reduced <i>n</i>-decanoic, dodecanoic, octanoic, and tetradecanoic acids in HAV, compared with control. In HAV, all compounds reduced eugenol (87%), 2-methylundecanal (71%), and anthocyanin (3%) (<i>p</i> ≤ 0.05). In addition, in all plant tissues, of both varieties, nanowires and CuSO₄ reduced Mn, while CuPro increased chlorophyll contents, compared with controls (<i>p</i> ≤ 0.05). Results suggest that the effects of Cu­(OH)₂ pesticides are variety- and compound-dependent

Evidence of Translocation and Physiological Impacts of Foliar Applied CeO₂ Nanoparticles on Cucumber (<i>Cucumis sativus</i>) Plants

Currently, most of the nanotoxicity studies in plants involve exposure to the nanoparticles (NPs) through the roots. However, plants interact with atmospheric NPs through the leaves, and our knowledge on their response to this contact is limited. In this study, hydroponically grown cucumber (<i>Cucumis sativus</i>) plants were aerially treated either with nano ceria powder (<i>n</i>CeO₂) at 0.98 and 2.94 g/m³ or suspensions at 20, 40, 80, 160, and 320 mg/L. Fifteen days after treatment, plants were analyzed for Ce uptake by using ICP-OES and TEM. In addition, the activity of three stress enzymes was measured. The ICP-OES results showed Ce in all tissues of the CeO₂ NP treated plants, suggesting uptake through the leaves and translocation to the other plant parts. The TEM results showed the presence of Ce in roots, which corroborates the ICP-OES results. The biochemical assays showed that catalase activity increased in roots and ascorbate peroxidase activity decreased in leaves. Our findings show that atmospheric NPs can be taken up and distributed within plant tissues, which could represent a threat for environmental and human health

Toxicity Assessment of Cerium Oxide Nanoparticles in Cilantro (<i>Coriandrum sativum</i> L.) Plants Grown in Organic Soil

Studies have shown that CeO₂ nanoparticles (NPs) can be accumulated in plants without modification, which could pose a threat for human health. In this research, cilantro (<i>Coriandrum sativum</i> L.) plants were germinated and grown for 30 days in soil amended with 0 to 500 mg kg^–1 CeO₂ NPs and analyzed by spectroscopic techniques and biochemical assays. At 125 mg kg^–1, plants produced longer roots (<i>p</i> ≤ 0.05), and at 500 mg kg^–1, there was higher Ce accumulation in tissues (<i>p</i> ≤ 0.05). At 125 mg, catalase activity significantly increased in shoots and ascorbate peroxidase in roots (<i>p</i> ≤ 0.05). The FTIR analyses revealed that at 125 mg kg^–1 the CeO₂ NPs changed the chemical environment of carbohydrates in cilantro shoots, for which changes in the area of the stretching frequencies were observed. This suggests that the CeO₂ NPs could change the nutritional properties of cilantro

Metabolomics Reveals How Cucumber (Cucumis sativus) Reprograms Metabolites To Cope with Silver Ions and Silver Nanoparticle-Induced Oxidative Stress

Due to their well-known antifungal activity, the intentional use of silver nanoparticles (AgNPs) as sustainable nanofungicides is expected to increase in agriculture. However, the impacts of AgNPs on plants must be critically evaluated to guarantee their safe use in food production. In this study, 4-week-old cucumber (Cucumis sativus) plants received a foliar application of AgNPs (4 or 40 mg/plant) or Ag⁺ (0.04 or 0.4 mg/plant) for 7 days. Gas chromatography–mass spectrometry (GC-MS)=based nontarget metabolomics enabled the identification and quantification of 268 metabolites in cucumber leaves. Multivariate analysis revealed that all the treatments significantly altered the metabolite profile. Exposure to AgNPs resulted in metabolic reprogramming, including activation of antioxidant defense systems (upregulation of phenolic compounds) and downregulation of photosynthesis (upregulation of phytol). Additionally, AgNPs enhanced respiration (upregulation of tricarboxylic acid cycle intermediates), inhibited photorespiration (downregulation of glycine/serine ratio), altered membrane properties (upregulation of pentadecanoic and arachidonic acids, downregulation of linoleic and linolenic acids), and reduced inorganic nitrogen fixation (downregulation of glutamine and asparagine). Although Ag ions induced some of the same metabolic changes, alterations in the levels of carbazole, lactulose, raffinose, citraconic acid, lactamide, acetanilide, and <i>p</i>-benzoquinone were AgNP-specific. The results of this study offer new insight into the molecular mechanisms by which cucumber responds to AgNP exposure and provide important information to support the sustainable use of AgNPs in agriculture

Effect of Cerium Oxide Nanoparticles on Rice: A Study Involving the Antioxidant Defense System and In Vivo Fluorescence Imaging

Previous studies have reported the uptake of cerium oxide nanoparticles (<i>n</i>CeO₂) by plants, but their physiological impacts are not yet well understood. This research was aimed to study the impact of <i>n</i>CeO₂ on the oxidative stress and antioxidant defense system in germinating rice seeds. The seeds were germinated for 10 days in <i>n</i>CeO₂ suspension at 62.5, 125, 250, and 500 mg L^–1 concentrations. The Ce uptake, growth performance, stress levels, membrane damage, and antioxidant responses in seedlings were analyzed. Ce in tissues increased with increased <i>n</i>CeO₂ concentrations, but the seedlings showed no visible signs of toxicity. Biochemical assays and in vivo imaging of H₂O₂ revealed that, relative to the control, the 62.5 and 125 mg <i>n</i>CeO₂ L^–1 treatments significantly reduced the H₂O₂ generation in both shoots and roots. Enhanced electrolyte leakage and lipid peroxidation were found in the shoots of seedlings grown at 500 mg <i>n</i>CeO₂ L^–1. Altered enzyme activities and levels of ascorbate and free thiols resulting in enhanced membrane damage and photosynthetic stress in the shoots were observed at 500 mg <i>n</i>CeO₂ L^–1. These findings demonstrate a <i>n</i>CeO₂ concentration-dependent modification of oxidative stress and antioxidant defense system in rice seedlings

Role of Cerium Compounds in Fusarium Wilt Suppression and Growth Enhancement in Tomato (<i>Solanum lycopersicum</i>)

The use of nanoparticles in plant protection may reduce pesticide usage and contamination and increase food security. In this study, three-week-old <i>Solanum lycopersicum</i> seedlings were exposed, by root or foliar pathways, to CeO₂ nanoparticles and cerium acetate at 50 and 250 mg/L prior to transplant into sterilized soil. One week later, the soil was inoculated with the fungal pathogen <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> (1 g/kg), and the plants were cultivated to maturity in a greenhouse. Disease severity, biomass/yield, and biochemical and physiological parameters were analyzed in harvested plants. Disease severity was significantly reduced by 250 mg/L of nano-CeO₂ and CeAc applied to the soil (53% and 35%, respectively) or foliage (57% and 41%, respectively), compared with non-treated infested controls. Overall, the findings show that nano-CeO₂ has potential to suppress Fusarium wilt and improve the chlorophyll content in tomato plants

Environmental Effects of Nanoceria on Seed Production of Common Bean (<i>Phaseolus vulgaris</i>): A Proteomic Analysis

The rapidly growing literature on the response of edible plants to nanoceria has provided evidence of its uptake and bioaccumulation, which delineates a possible route of entry into the food chain. However, little is known about how the residing organic matter in soil may affect the bioavailability and resulting impacts of nanoceria on plants. Here, we examined the effect of nanoceria exposure (62.5–500 mg/kg) on kidney bean (<i>Phaseolus vulgaris</i>) productivity and seed quality as a function of soil organic matter content. Cerium accumulation in the seeds produced from plants in organic matter enriched soil showed a dose-dependent increase, unlike in low organic matter soil treatments. Seeds obtained upon nanoceria exposure in soils with higher organic matter were more susceptible to changes in nutrient quality. A quantitative proteomic analysis of the seeds produced upon nanoceria exposure provided evidence for upregulation of stress-related proteins at 62.5 and 125 mg/kg nanoceria treatments. Although the plants did not exhibit overt toxicity, the major seed proteins primarily associated with nutrient storage (phaseolin) and carbohydrate metabolism (lectins) were significantly down-regulated in a dose dependent manner upon nanoceria exposure. This study thus suggests that nanoceria exposures may negatively affect the nutritional quality of kidney beans at the cellular and molecular level. More confirmatory studies with nanoceria along different species using alternative and orthogonal “omic” tools are currently under active investigation, which will enable the identification of biomarkers of exposure and susceptibility