Toxicity assessment of cerium oxide nanoparticles in cilantro (Coriandrum sativum L.) plants grown in organic soil

Engineered nickel oxide nanoparticles affect genome stability in Allium cepa (L.)

Indiscriminate uses of engineered nickel oxide nanoparticles (NiO-NPs) in heavy industries have ushered their introduction into the natural environment, ensuing novel interactions with biotic components of the ecosystem. Though much is known about the toxicity of NiO-NPs on animals, their phytotoxic potential is not well elucidated. NiO-NP hinders intra-cellular homeostasis by producing ROS in excess, having profound effect on the antioxidant profile of exposed animal and plant tissues. In the present study, bulbs of the model plant Allium cepa were treated with varying concentrations of NiO-NP (10 mg L^-1 - 500 mg L^-1) to study changes in ROS production and potential genotoxic effect. The data generated proved a concomitant upsurge in intracellular ROS accumulation with NiO-NP dosage that could be correlated with increased genotoxicity in A. cepa. Augmented in situ ROS production was revealed through DCFH-DA assay, with highest increase in fluorescence (70% over control) in bulbs exposed to 125 mg L^-1 NiO-NP. Effect of NiO-NP on genomic DNA was studied through detailed analyses of RAPD profiles which allows detection of even slightest changes in DNA sequence of treated plants. Significant differences in band intensity, loss and appearance of bands as well as genomic template stability and band sharing indices of treated plants revealed increased vulnerability of genomic DNA to NiO-NP, at even lowest concentration (10 mg L^-1). This is the first report of NiO-NP induced genotoxicity on A. cepa, which confirms the nanoparticle as a potent environmental hazard.

Plant Response to Engineered Metal Oxide Nanoparticles

All metal oxide nanoparticles influence the growth and development of plants. They generally enhance or reduce seed germination, shoot/root growth, biomass production and physiological and biochemical activities. Some plant species have not shown any physiological change, although significant variations in antioxidant enzyme activity and upregulation of heat shock protein have been observed. Plants have evolved antioxidant defence mechanism which involves enzymatic as well as non-enzymatic components to prevent oxidative damage and enhance plant resistance to metal oxide toxicity. The exact mechanism of plant defence against the toxicity of nanomaterials has not been fully explored. The absorption and translocation of metal oxide nanoparticles in different parts of the plant depend on their bioavailability, concentration, solubility and exposure time. Further, these nanoparticles may reach other organisms, animals and humans through food chain which may alter the entire biodiversity. This review attempts to summarize the plant response to a number of metal oxide nanoparticles and their translocation/distribution in root/shoot. The toxicity of metal oxide nanoparticles has also been considered to see if they affect the production of seeds, fruits and the plant biomass as a whole.

X-ray Spectroscopy Uncovering the Effects of Cu Based Nanoparticle Concentration and Structure on Phaseolus vulgaris Germination and Seedling Development

Nanoparticles properties such as solubility, tunable surface charges, and singular reactivity might be explored to improve the performance of fertilizers. Nevertheless, these unique properties may also bring risks to the environment since the fate of nanoparticles is poorly understood. This study investigated the impact of a range of CuO nanoparticles sizes and concentrations on the germination and seedling development of Phaseolus vulgaris L. Nanoparticles did not affect seed germination, but seedling weight gain was promoted by 100 mg Cu L^-1 and inhibited by 1 000 mg Cu L^-1 of 25 nm CuO and CuSO₄. Most of the Cu taken up remained in the seed coat with Cu hotspots in the hilum. X-ray absorption spectroscopy unraveled that most of the Cu remained in its pristine form. The higher surface reactivity of the 25 nm CuO nanoparticles might be responsible for its deleterious effects. The present study therefore highlights the importance of the nanoparticle structure for its physiological impacts.

Nanotechnology: The new perspective in precision agriculture

Nanotechnology is an interdisciplinary research field. In recent past efforts have been made to improve agricultural yield through exhaustive research in nanotechnology. The green revolution resulted in blind usage of pesticides and chemical fertilizers which caused loss of soil biodiversity and developed resistance against pathogens and pests as well. Nanoparticle-mediated material delivery to plants and advanced biosensors for precision farming are possible only by nanoparticles or nanochips. Nanoencapsulated conventional fertilizers, pesticides and herbicides helps in slow and sustained release of nutrients and agrochemicals resulting in precise dosage to the plants. Nanotechnology based plant viral disease detection kits are also becoming popular and are useful in speedy and early detection of viral diseases. In this article, the potential uses and benefits of nanotechnology in precision agriculture are discussed. The modern nanotechnology based tools and techniques have the potential to address the various problems of conventional agriculture and can revolutionize this sector.

Health risk assessment of rare earth elements in cereals from mining area in Shandong, China

To investigate the concentrations of rare earth elements in cereals and assess human health risk through cereal consumption, a total of 327 cereal samples were collected from rare earth mining area and control area in Shandong, China. The contents of 14 rare earth elements were determined by Inductively Coupled Plasma—Mass Spectrometry (ICP—MS). The medians of total rare earth elements in cereals from mining and control areas were 74.22 μg/kg and 47.83 μg/kg, respectively, and the difference was statistically significant (P < 0.05). The wheat had the highest rare earth elements concentrations (109.39 μg/kg and 77.96 μg/kg for mining and control areas, respectively) and maize had the lowest rare earth elements concentrations (42.88 μg/kg and 30.25 μg/kg for mining and control areas, respectively). The rare earth elements distribution patterns for both areas were characterized by enrichment of light rare earth elements. The health risk assessment demonstrated that the estimated daily intakes of rare earth elements through cereal consumption were considerably lower than the acceptable daily intake (70 μg/kg bw). The damage to adults can be neglected, but more attention should be paid to the effects of continuous exposure to rare earth elements on children.

Toxicity of combined mixtures of nanoparticles to plants

An increasing production and using of nanoproducts results in releasing and dispersing nanoparticles (NPs) in the environment. Being released into various environment components, NPs may interact with numerous pollutants, including other NPs. This research aimed at assessing toxicity of combined binary mixtures of NPs. The study focused on assessing mixtures of NPs believed to be toxic (nano-ZnO+nano-CuO) and nano-ZnO/nano-CuO with the ones that are insignificantly toxic or non-toxic NPs (nano-TiO₂/nano-Cr₂O₃/nano-Fe₂O₃). Toxicity of combined mixtures proved comparable to toxicity of individual mixtures of NPs (the sum of effects triggered by individual types of NPs comprising respective mixtures). Toxicity evaluation was based on two parameters: seed germination and inhibition of root growth with respect to four plant species: Lepidium sativum, Linum utisassimmum, Cucumis sativus and Triticum aestivum. The findings showed combined mixtures of NPs to be significantly less toxic in comparison to individual mixtures, irrespective of their components. Within the scope of concentrations used, greatest differences between the toxicity of mixtures were reported at the 100mgL^-1 concentration. Toxicity levels of combined and individual mixtures might have been determined by a lower total concentration of Zn and Cu metals and a greater aggregation of particles in combined mixtures than in individual mixtures.

Surface coating changes the physiological and biochemical impacts of nano-TiO2 in basil (Ocimum basilicum) plants

Little is known about the effects of surface coating on the interaction of engineered nanoparticles (ENPs) with plants. In this study, basil (Ocimum basilicum) was cultivated for 65 days in soil amended with unmodified, hydrophobic (coated with aluminum oxide and dimethicone), and hydrophilic (coated with aluminum oxide and glycerol) titanium dioxide nanoparticles (nano-TiO₂) at 125, 250, 500, and 750 mg nano-TiO₂ kg^-1 soil. ICP-OES/MS, SPAD meter, and UV/Vis spectrometry were used to determine Ti and essential elements in tissues, relative chlorophyll content, carbohydrates, and antioxidant response, respectively. Compared with control, hydrophobic and hydrophilic nano-TiO₂ significantly reduced seed germination by 41% and 59%, respectively, while unmodified and hydrophobic nano-TiO₂ significantly decreased shoot biomass by 31% and 37%, respectively (p ≤ 0.05). Roots exposed to hydrophobic particles at 750 mg kg^-1 had 87% and 40% more Ti than the pristine and hydrophilic nano-TiO₂; however, no differences were found in shoots. The three types of particles affected the homeostasis of essential elements: at 500 mg kg^-1, unmodified particles increased Cu (104%) and Fe (90%); hydrophilic increased Fe (90%); while hydrophobic increased Mn (339%) but reduced Ca (71%), Cu (58%), and P (40%). However, only hydrophobic particles significantly reduced root elongation by 53%. Unmodified, hydrophobic, and hydrophilic particles significantly reduced total sugar by 39%, 38%, and 66%, respectively, compared with control. Moreover, unmodified particles significantly decreased reducing sugar (34%), while hydrophobic particles significantly reduced starch (35%). Although the three particles affected basil plants, coated particles impacted the most its nutritional quality, since they altered more essential elements, starch, and reducing sugars.

Tissue deposition and toxicological effects of commercially significant rare earth oxide nanomaterials: Material and physical properties

Rare earth oxide (REO) materials are found naturally in earth's crust and at the nanoscale these REO nanoparticles exhibit unique thermal, electrical, and physicochemical properties. REO nanoparticles are widely used in different industrial sectors for ceramics, glass polishing, metallurgy, lasers, and magnets. Recently, some of these REO nanoparticles have been identified for their potential application in medicine, including therapy, imaging, and diagnostics. Concurrent research into the REO nanomaterials' toxicities has also raised concern for their environmental impacts. The correlation of REO nanoparticles mediated toxicity with their physiochemical properties can help to design nanoparticles with minimal effect on the environment and living organisms. In vitro assay revealed toxicity toward Human squamous epithelial cell line (CCL30) and Human umbilical vascular endothelial cells (HUVEC) at a concentration of 100 µM and higher. In vivo results showed, with the exception of CeO₂ and Gd₂ O₃ , most of the naoparticles did not clear or had minimum clearance (10-20%) from the system. Elevated levels of alanine transferase were seen for animals given each different nanoparticle, however the increases were not significant for CeO₂ and Dy₂ O₃ . Nephrotoxicity was only seen in case of Dy₂ O₃ and Gd₂ O₃ . Lastly, histological examination revealed presence of swollen hepatocytes which further confirms toxicity of the commercial REO nanomaterials. The in vivo toxicity is mainly due to excessive tissue deposition (70-90%) due to the commercial REO nanoparticles' poor physical properties (shape, stability, and extent of agglomeration). Therefore, optimization of nanoparticles physical properties is very important. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 904-917, 2017.

Concentrations and health risk assessment of rare earth elements in vegetables from mining area in Shandong, China

To investigate the concentrations of rare earth elements in vegetables and assess human health risk through vegetable consumption, a total of 301 vegetable samples were collected from mining area and control area in Shandong, China. The contents of 14 rare earth elements were determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The total rare earth elements in vegetables from mining and control areas were 94.08 μg kg^-1 and 38.67 μg kg^-1, respectively, and the difference was statistically significant (p < 0.05). The leaf vegetable had the highest rare earth elements concentration (984.24 μg kg^-1 and 81.24 μg kg^-1 for mining and control areas, respectively) and gourd vegetable had the lowest rare earth elements concentration (37.34 μg kg^-1 and 24.63 μg kg^-1 for mining and control areas, respectively). For both areas, the rare earth elements concentration in vegetables declined in the order of leaf vegetable > taproot vegetable > alliaceous vegetable > gourd vegetable. The rare earth elements distribution patterns for both areas were characterized by enrichment of light rare earth elements. The health risk assessment demonstrated that the estimated daily intakes (0.69 μg kg^-1 d^-1 and 0.28 μg kg^-1 d^-1 for mining and control areas, respectively) of rare earth elements through vegetable consumption were significantly lower than the acceptable daily intake (70 μg kg^-1 d^-1). The damage to adults can be neglected, but more attention should be paid to the effects of continuous exposure to low levels of rare earth elements on children.

Effect of metal and metal oxide nanoparticles on growth and physiology of globally important food crops: A critical review

The concentrations of engineered metal and metal oxide nanoparticles (NPs) have increased in the environment due to increasing demand of NPs based products. This is causing a major concern for sustainable agriculture. This review presents the effects of NPs on agricultural crops at biochemical, physiological and molecular levels. Numerous studies showed that metal and metal oxide NPs affected the growth, yield and quality of important agricultural crops. The NPs altered mineral nutrition, photosynthesis and caused oxidative stress and induced genotoxicity in crops. The activities of antioxidant enzymes increased at low NPs toxicity while decreased at higher NPs toxicity in crops. Due to exposure of crop plants to NPs, the concentration of NPs increased in different plant parts including fruits and grains which could transfer to the food chain and pose a threat to human health. In conclusion, most of the NPs have both positive and negative effects on crops at physiological, morphological, biochemical and molecular levels. The effects of NPs on crop plants vary greatly with plant species, growth stages, growth conditions, method, dose, and duration of NPs exposure along with other factors. Further research orientation is also discussed in this review article.

Physiological and biochemical response of plants to engineered NMs: Implications on future design

Engineered nanomaterials (ENMs) form the basis of a great number of commodities that are used in several areas including energy, coatings, electronics, medicine, chemicals and catalysts, among others. In addition, these materials are being explored for agricultural purposes. For this reason, the amount of ENMs present as nanowaste has significantly increased in the last few years, and it is expected that ENMs levels in the environment will increase even more in the future. Because plants form the basis of the food chain, they may also function as a point-of-entry of ENMs for other living systems. Understanding the interactions of ENMs with the plant system and their role in their potential accumulation in the food chain will provide knowledge that may serve as a decision-making framework for the future design of ENMs. The purpose of this paper was to provide an overview of the current knowledge on the transport and uptake of selected ENMs, including Carbon Based Nanomaterials (CBNMs) in plants, and the implication on plant exposure in terms of the effects at the macro, micro, and molecular level. We also discuss the interaction of ENMs with soil microorganisms. With this information, we suggest some directions on future design and areas where research needs to be strengthened. We also discuss the need for finding models that can predict the behavior of ENMs based on their chemical and thermodynamic nature, in that few efforts have been made within this context.

Exposure of engineered nanomaterials to plants: Insights into the physiological and biochemical responses-A review

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.

Exposure of agricultural crops to nanoparticle CeO2 in biochar-amended soil

Biochar is seeing increased usage as an amendment in agricultural soils but the significance of nanoscale interactions between this additive and engineered nanoparticles (ENP) remains unknown. Corn, lettuce, soybean and zucchini were grown for 28 d in two different soils (agricultural, residential) amended with 0-2000 mg engineered nanoparticle (ENP) CeO2 kg-1 and biochar (350 °C or 600 °C) at application rates of 0-5% (w/w). At harvest, plants were analyzed for biomass, Ce content, chlorophyll and lipid peroxidation. Biomass from the four species grown in residential soil varied with species and biochar type. However, biomass in the agricultural soil amended with biochar 600 °C was largely unaffected. Biochar co-exposure had minimal impact on Ce accumulation, with reduced or increased Ce content occurring at the highest (5%) biochar level. Soil-specific and biochar-specific effects on Ce accumulation were observed in the four species. For example, zucchini grown in agricultural soil with 2000 mg CeO2 kg-1 and 350 °C biochar (0.5-5%) accumulated greater Ce than the control. However, for the 600 °C biochar, the opposite effect was evident, with decreased Ce content as biochar increased. A principal component analysis showed that biochar type accounted for 56-99% of the variance in chlorophyll and lipid peroxidation across the plants. SEM and μ-XRF showed Ce association with specific biochar and soil components, while μ-XANES analysis confirmed that after 28 d in soil, the Ce remained largely as CeO2. The current study demonstrates that biochar synthesis conditions significantly impact interactions with ENP, with subsequent effects on particle fate and effects.

Interaction of metal oxide nanoparticles with higher terrestrial plants: Physiological and biochemical aspects

Multiple applications of metal oxide nanoparticles (MONPs) could result in their accumulation in soil, threatening higher terrestrial plants. Several reports have shown the effects of MONPs on plants. In this review, we analyze the most recent reports about the physiological and biochemical responses of plants to stress imposed by MONPs. Findings demonstrate that MONPs may be taken up and accumulated in plant tissues causing adverse or beneficial effects on seed germination, seedling elongation, photosynthesis, antioxidative stress response, agronomic, and yield characteristics. Given the importance of determining the potential risks of MONPs on crops and other terrestrial higher plants, research questions about field long-term conditions, transgenernational phytotoxicity, genotype specific sensitivity, and combined pollution problems should be considered.

Molecular and physiological responses to titanium dioxide and cerium oxide nanoparticles in Arabidopsis

Changes in tissue transcriptomes and productivity of Arabidopsis thaliana were investigated during exposure of plants to 2 widely used engineered metal oxide nanoparticles, titanium dioxide (nano-titania) and cerium dioxide (nano-ceria). Microarray analyses confirmed that exposure to either nanoparticle altered the transcriptomes of rosette leaves and roots, with comparatively larger numbers of differentially expressed genes found under nano-titania exposure. Nano-titania induced more differentially expressed genes in rosette leaves, whereas roots had more differentially expressed genes under nano-ceria exposure. MapMan analyses indicated that although nano-titania up-regulated overall metabolism in both tissues, metabolic processes under nano-ceria remained mostly unchanged. Gene enrichment analysis indicated that both nanoparticles mainly enriched ontology groups such as responses to stress (abiotic and biotic), and defense responses (pathogens), and responses to endogenous stimuli (hormones). Nano-titania specifically induced genes associated with photosynthesis, whereas nano-ceria induced expression of genes related to activating transcription factors, most notably those belonging to the ethylene responsive element binding protein family. Interestingly, there were also increased numbers of rosette leaves and plant biomass under nano-ceria exposure, but not under nano-titania. Other transcriptomic responses did not clearly relate to responses observed at the organism level, possibly because of functional and genomic redundancy in Arabidopsis, which may mask expression of morphological changes, despite discernable responses at the transcriptome level. In addition, transcriptomic changes often relate to transgenerational phenotypic development, and hence it may be productive to direct further experimental work to integrate high-throughput genomic results with longer term changes in subsequent generations. Environ Toxicol Chem 2017;36:71-82. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Green-synthesised cerium oxide nanostructures (CeO2-NS) show excellent biocompatibility for phyto-cultures as compared to silver nanostructures (Ag-NS)

The use of nanostructures (NS) in plant tissue culture can be beneficial only if we have their complete bio-safety and biocompatibility profile.

Physiological and biochemical responses of sunflower (Helianthus annuus L.) exposed to nano-CeO2 and excess boron: Modulation of boron phytotoxicity

Little is known about the interaction of nanoparticles (NPs) with soil constituents and their effects in plants. Boron (B), an essential micronutrient that reduces crop production at both deficiency and excess, has not been investigated with respect to its interaction with cerium oxide NPs (nano-CeO₂). Considering conflicting results on the nano-CeO₂ toxicity and protective role as antioxidant, their possible modulation on B toxicity in sunflower (Helianthus annuus L.) was investigated. Sunflower was cultivated for 30 days in garden pots containing original or B-spiked soil amended with nano-CeO₂ at 0-800 mg kg^-1. At harvest, Ce and B concentrations in tissues, biomass, and activities of stress enzymes in leaves were determined. Results showed that in the original soil, Ce accumulated mainly in roots, with little translocation to stems and leaves, while reduced root Ce was observed in plants from B-spiked soil. In the original soil, higher levels of nano-CeO₂ reduced plant B concentration. Although morphological effects were not visible, changes in biomass and oxidative stress response were observed. Sunflower leaves from B-spiked soil showed visible symptoms of B toxicity, such as necrosis and chlorosis in old leaves, as well as an increase of superoxide dismutase (SOD) activity. However, at high nano-CeO₂ level, SOD activity decreased reaching values similar to that of the control. This study has shown that nano-CeO₂ reduced both the B nutritional status of sunflower in original soil and the B phytotoxicity in B-spiked soil.

Engineered nanomaterial-mediated changes in the metabolism of terrestrial plants

Engineered nanomaterials (ENMs) possess remarkable physicochemical characteristics suitable for different applications in medicine, pharmaceuticals, biotechnology, energy, cosmetics and electronics. Because of their ultrafine size and high surface reactivity, ENMs can enter plant cells and interact with intracellular structures and metabolic pathways which may produce toxicity or promote plant growth and development by diverse mechanisms. Depending on their type and concentration, ENMs can have positive or negative effects on photosynthesis, photochemical fluorescence and quantum yield as well as photosynthetic pigments status of the plants. Some studies have shown that ENMs can improve photosynthetic efficiency via increasing chlorophyll content and light absorption and also broadening the spectrum of captured light, suggesting that photosynthesis can be nano-engineered for harnessing more solar energy. Both up- and down-regulation of primary metabolites such as proteins and carbohydrates have been observed following exposure of plants to various ENMs. The potential capacity of ENMs for changing the rate of primary metabolites lies in their close relationship with activation and biosynthesis of the key enzymes. Several classes of secondary metabolites such as phenolics, flavonoids, and alkaloids have been shown to be induced (mostly accompanied by stress-related factors) in plants exposed to different ENMs, highlighting their great potential as elicitors to enhance both quantity and quality of biologically active secondary metabolites. Considering reports on both positive and negative effects of ENMs on plant metabolism, in-depth studies are warranted to figure out the most appropriate ENMs (type, size and optimal concentration) in order to achieve the desirable effect on specific metabolites in a given plant species. In this review, we summarize the studies performed on the impacts of ENMs on biosynthesis of plant primary and secondary metabolites and mention the research gaps that currently exist in this field.

Lessons learned: Are engineered nanomaterials toxic to terrestrial plants?

The expansion of nanotechnology and its ubiquitous applications has fostered unavoidable interaction between engineered nanomaterials (ENMs) and plants. Recent research has shown ambiguous results with regard to the impact of ENMs in plants. On one hand, there are reports that show hazardous effects, while on the other hand, some reports highlight positive effects. This uncertainty whether the ENMs are primarily hazardous or whether they have a potential for propitious impact on plants, has raised questions in the scientific community. In this review, we tried to demystify this ambiguity by citing various exposure studies of different ENMs (nano-Ag, nano-Au, nano-Si, nano-CeO2, nano-TiO2, nano-CuO, nano-ZnO, and CNTs, among others) and their effects on various groups of plant families. After scrutinizing the most recent literature, it seems that the divergence in the research results may be possibly attributed to multiple factors such as ENM properties, plant species, soil dynamics, and soil microbial community. The analysis of the literature also suggests that there is a knowledge gap on the effects of ENMs towards changes in color, texture, shape, and nutritional aspects on ENM exposed plants.

Effects of uncoated and citric acid coated cerium oxide nanoparticles, bulk cerium oxide, cerium acetate, and citric acid on tomato plants

Little is known about the physiological and biochemical responses of plants exposed to surface modified nanomaterials. In this study, tomato (Solanum lycopersicum L.) plants were cultivated for 210days in potting soil amended with uncoated and citric acid coated cerium oxide nanoparticles (nCeO2, CA+nCeO2) bulk cerium oxide (bCeO2), and cerium acetate (CeAc). Millipore water (MPW), and citric acid (CA) were used as controls. Physiological and biochemical parameters were measured. At 500mg/kg, both the uncoated and CA+nCeO2 increased shoot length by ~9 and ~13%, respectively, while bCeO2 and CeAc decreased shoot length by ~48 and ~26%, respectively, compared with MPW (p≤0.05). Total chlorophyll, chlo-a, and chlo-b were significantly increased by CA+nCeO2 at 250mg/kg, but reduced by bCeO2 at 62.5mg/kg, compared with MPW. At 250 and 500mg/kg, nCeO2 increased Ce in roots by 10 and 7 times, compared to CA+nCeO2, but none of the treatments affected the Ce concentration in above ground tissues. Neither nCeO2 nor CA+nCeO2 affected the homeostasis of nutrient elements in roots, stems, and leaves or catalase and ascorbate peroxidase in leaves. CeAc at 62.5 and 125mg/kg increased B (81%) and Fe (174%) in roots, while at 250 and 500mg/kg, increased Ca in stems (84% and 86%, respectively). On the other hand, bCeO2 at 62.5 increased Zn (152%) but reduced P (80%) in stems. Only nCeO2 at 62.5mg/kg produced higher total number of tomatoes, compared with control and the rest of the treatments. The surface coating reduced Ce uptake by roots but did not affect its translocation to the aboveground organs. In addition, there was no clear effect of surface coating on fruit production. To our knowledge, this is the first study comparing the effects of coated and uncoated nCeO2 on tomato plants.

Uptake, translocation and physiological effects of magnetic iron oxide (γ-Fe2O3) nanoparticles in corn (Zea mays L.)

Iron oxide nanoparticles (γ-Fe2O3 NPs) have emerged as an innovative and promising method of iron application in agricultural systems. However, the possible toxicity of γ-Fe2O3 NPs and its uptake and translocation require further study prior to large-scale field application. In this study, we investigated uptake and distribution of γ-Fe2O3 NPs in corn (Zea mays L.) and its impacts on seed germination, antioxidant enzyme activity, malondialdehyde (MDA) content, and chlorophyll content were determined. 20 mg/L of γ-Fe2O3 NPs significantly promoted root elongation by 11.5%, and increased germination index and vigor index by 27.2% and 39.6%, respectively. However, 50 and 100 mg/L γ-Fe2O3 NPs remarkably decreased root length by 13.5% and 12.5%, respectively. Additionally, evidence for γ-Fe2O3 NPs induced oxidative stress was exclusively found in the root. Exposures of different concentrations of NPs induced notably high levels of MDA in corn roots, and the MDA levels of corn roots treated by γ-Fe2O3 NPs (20-100 mg/L) were 5-7-fold higher than that observed in the control plants. Meanwhile, the chlorophyll contents were decreased by 11.6%, 39.9% and 19.6%, respectively, upon NPs treatment relative to the control group. Images from fluorescence and transmission electron microscopy (TEM) indicated that γ-Fe2O3 NPs could enter plant roots and migrate apoplastically from the epidermis to the endodermis and accumulate the vacuole. Furthermore, we found that NPs mostly existed around the epidermis of root and no translocation of NPs from roots to shoots was observed. Our results will be highly meaningful on understanding the fate and physiological effects of γ-Fe2O3 NPs in plants.

Phytotoxicity, Uptake, and Translocation of Fluorescent Carbon Dots in Mung Bean Plants

Fluorescent carbon dots (CDs) have been widely studied in bioscience and bioimaging, but the effect of CDs on plants has been rarely studied. Herein, mung bean was adopted as a model plant to study the phytotoxicity, uptake, and translocation of red emissive CDs in plants. The incubation with CDs at a concentration range from 0.1 to 1.0 mg/mL induced physiological response of mung bean plant and imposed no phytotoxicity on mung bean growth. The lengths of the root and stem presented an increasing trend up to the treatment of 0.4 mg/mL. Confocal imaging showed that CDs were transferred from the roots to the stems and leaves by the vascular system through the apoplastic pathway. The uptake kinetics study was performed and demonstrated that the CDs were abundantly incubated by mung beans during both germination and growth periods. Furthermore, in vivo visualization of CDs provides potential for their successful application as delivery vehicles in plants based on the unique optical properties.

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-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.

Facet Energy and Reactivity versus Cytotoxicity: The Surprising Behavior of CdS Nanorods

Responsible development of nanotechnology calls for improved understanding of how nanomaterial surface energy and reactivity affect potential toxicity. Here, we challenge the paradigm that cytotoxicity increases with nanoparticle reactivity. Higher-surface-energy {001}-faceted CdS nanorods (CdS-H) were less toxic to Saccharomyces cerevisiae than lower-energy ({101}-faceted) nanorods (CdS-L) of similar morphology, aggregate size, and charge. CdS-H adsorbed to the yeast's cell wall to a greater extent than CdS-L, which decreased endocytosis and cytotoxicity. Higher uptake of CdS-L decreased cell viability and increased endoplasmatic reticulum stress despite lower release of toxic Cd(2+) ions. Higher toxicity of CdS-L was confirmed with five different unicellular microorganisms. Overall, higher-energy nanocrystals may exhibit greater propensity to adsorb to or react with biological protective barriers and/or background constituents, which passivates their reactivity and reduces their bioavailability and cytotoxicity.

Effects of Silver Nanoparticles on Radish Sprouts: Root Growth Reduction and Modifications in the Nutritional Value

Reports indicate that silver nanoparticles (nAg) are toxic to vegetation, but little is known about their effects in crop plants. This study examines the impacts of nAg on the physiology and nutritional quality of radish (Raphanus sativus) sprouts. Seeds were germinated and grown for 5 days in nAg suspensions at 0, 125, 250, and 500 mg/L. Seed germination and seedling growth were evaluated with traditional methodologies; the uptake of Ag and nutrients was quantified by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and changes in macromolecules were analyzed by infrared (IR) spectroscopy. None of the nAg concentrations reduced seed germination. However, the water content (% of the total weight) was reduced by 1.62, 1.65, and 2.54% with exposure to 125, 250, and 500 mg/L, respectively, compared with the control. At 500 mg/L, the root and shoot lengths were reduced by 47.7 and 40%, with respect to the control. The seedlings exposed to 500 mg/L had 901 ± 150 mg Ag/kg dry wt and significantly less Ca, Mg, B, Cu, Mn, and Zn, compared with the control. The infrared spectroscopy analysis showed changes in the bands corresponding to lipids (3000-2800 cm(-1)), proteins (1550-1530 cm(-1)), and structural components of plant cells such as lignin, pectin, and cellulose. These results suggest that nAg could significantly affect the growth, nutrient content and macromolecule conformation in radish sprouts, with unknown consequences for human health.

Environmental Stresses Increase Photosynthetic Disruption by Metal Oxide Nanomaterials in a Soil-Grown Plant

Despite an increasing number of studies over the past decade examining the interactions between plants and engineered nanomaterials (ENMs), very few have investigated the influence of environmental conditions on ENM uptake and toxicity, particularly throughout the entire plant life cycle. In this study, soil-grown herbaceous annual plants (Clarkia unguiculata) were exposed to TiO2, CeO2, or Cu(OH)2 ENMs at different concentrations under distinct light and nutrient levels for 8 weeks. Biweekly fluorescence and gas exchange measurements were recorded, and tissue samples from mature plants were analyzed for metal content. During peak growth, exposure to TiO2 and CeO2 decreased photosynthetic rate and CO2 assimilation efficiency of plants grown under high light and nutrient conditions, possibly by disrupting energy transfer from photosystem II (PSII) to the Calvin cycle. Exposure Cu(OH)2 particles also disrupted photosynthesis but only in plants grown under the most stressful conditions (high light, limited nutrient) likely by preventing the oxidation of a primary PSII reaction center. TiO2 and CeO2 followed similar uptake and distribution patterns with concentrations being highest in roots followed by leaves then stems, while Cu(OH)2 was present at highest concentrations in leaves, likely as ionic Cu. ENM accumulation was highly dependent on both light and nutrient levels and a predictive regression model was developed from these data. These results show that abiotic conditions play an important role in mediating the uptake and physiological impacts of ENMs in terrestrial plants.

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

Interactions of nCeO2 with plants have been mostly evaluated at seedling stage and under controlled conditions. In this study, the effects of nCeO2 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 nCeO2 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 nCeO2 in crop plants.

Copper nanoparticles/compounds impact agronomic and physiological parameters in cilantro (Coriandrum sativum)

The environmental impacts of Cu-based nanoparticles (NPs) are not well understood. In this study, cilantro (Coriandrum sativum) was germinated and grown in commercial potting mix soil amended with Cu(OH)2 (Kocide and CuPRO), nano-copper (nCu), micro-copper (μCu), nano-copper oxide (nCuO), micro-copper oxide (μCuO) and ionic Cu (CuCl2) at either 20 or 80 mg Cu per kg. In addition to seed germination and plant elongation, relative chlorophyll content and micro and macroelement concentrations were determined. At both concentrations, only nCuO, μCuO, and ionic Cu, showed statistically significant reductions in germination. Although compared with control, the relative germination was reduced by ∼50% with nCuO at both concentrations, and by ∼40% with μCuO, also at both concentrations, the difference among compounds was not statistically significant. Exposure to μCuO at both concentrations and nCu at 80 mg kg(-1) significantly reduced (p≤ 0.05) shoot elongation by 11% and 12.4%, respectively, compared with control. Only μCuO at 20 mg kg(-1) significantly reduced (26%) the relative chlorophyll content, compared with control. None of the treatments increased root Cu, but all of them, except μCuO at 20 mg kg(-1), significantly increased shoot Cu (p≤ 0.05). Micro and macro elements B, Zn, Mn, Ca, Mg, P, and S were significantly reduced in shoots (p≤ 0.05). Similar results were observed in roots. These results showed that Cu-based NPs/compounds depress nutrient element accumulation in cilantro, which could impact human nutrition.

Fate and Phytotoxicity of CeO2 Nanoparticles on Lettuce Cultured in the Potting Soil Environment

Cerium oxide nanoparticles (CeO2 NPs) have been shown to have significant interactions in plants. Previous study reported the specific-species phytotoxicity of CeO2 NPs by lettuce (Lactuca sativa), but their physiological impacts and vivo biotransformation are not yet well understood, especially in relative realistic environment. Butterhead lettuce were germinated and grown in potting soil for 30 days cultivation with treatments of 0, 50, 100, 1000 mg CeO2 NPs per kg soil. Results showed that lettuce in 100 mg·kg-1 treated groups grew significantly faster than others, but significantly increased nitrate content. The lower concentrations treatment had no impact on plant growth, compared with the control. However, the higher concentration treatment significantly deterred plant growth and biomass production. The stress response of lettuce plants, such as Superoxide dismutase (SOD), Peroxidase (POD), Malondialdehyde(MDA) activity was disrupted by 1000 mg·kg-1 CeO2 NPs treatment. In addition, the presence of Ce (III) in the roots of butterhead lettuce explained the reason of CeO2 NPs phytotoxicity. These findings demonstrate CeO2 NPs modification of nutritional quality, antioxidant defense system, the possible transfer into the food chain and biotransformation in vivo.

Metallic Nanoparticle (TiO2 and Fe3O4) Application Modifies Rhizosphere Phosphorus Availability and Uptake by Lactuca sativa

Application of engineered nanoparticles (NPs) with respect to nutrient uptake in plants is not yet well understood. The impacts of TiO2 and Fe3O4 NPs on the availability of naturally soil-bound inorganic phosphorus (Pi) to plants were studied along with relevant parameters. For this purpose, Lactuca sativa (lettuce) was cultivated on the soil amended with TiO2 and Fe3O4 (0, 50, 100, 150, 200, and 250 mg kg(-1)) over a period of 90 days. Different techniques, such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman, and Fourier transform infrared spectroscopy (FTIR) were used to monitor translocation and understand the possible mechanisms for phosphorus (P) uptake. The trends for P accumulation were different for roots (TiO2 > Fe3O4 > control) and shoots (Fe3O4 > TiO2 > control). Cystine and methionine were detected in the rhizosphere in Raman spectra. Affinities of NPs to adsorb phosphate ions, modifications in P speciation, and NP stress in the rhizosphere had possibly contributed to enhanced root exudation and acidification. All of these changes led to improved P availability and uptake by the plants. These promising results can help to develop an innovative strategy for using NPs for improved nutrient management to ensure food security.

Dissolved cerium contributes to uptake of Ce in the presence of differently sized CeO2-nanoparticles by three crop plants

Cerium uptake into plants in the presence of CeO₂ nanoparticles occurs not only in nanoparticulate form, but also as dissolved ions.

Particle-size dependent accumulation and trophic transfer of cerium oxide through a terrestrial food chain

The accumulation and trophic transfer of nanoparticle (NP) or bulk CeO2 through a terrestrial food chain was evaluated. Zucchini (Cucurbita pepo L.) was planted in soil with 0 or 1228 μg/g bulk or NP CeO2. After 28 d, zucchini tissue Ce content was determined by ICP-MS. Leaf tissue from each treatment was used to feed crickets (Acheta domesticus). After 14 d, crickets were analyzed for Ce content or were fed to wolf spiders (family Lycosidae). NP CeO2 significantly suppressed flower mass relative to control and bulk treatments. The Ce content of zucchini was significantly greater when exposure was in the NP form. The flowers, leaves, stems, and roots of zucchini exposed to bulk CeO2 contained 93.3, 707, 331, and 119,000 ng/g, respectively; NP-exposed plants contained 153, 1510, 479, and 567 000 ng/g, respectively. Crickets fed NP CeO2-exposed zucchini leaves contained significantly more Ce (33.6 ng/g) than did control or bulk-exposed insects (15.0-15.2 ng/g). Feces from control, bulk, and NP-exposed crickets contained Ce at 248, 393, and 1010 ng/g, respectively. Spiders that consumed crickets from control or bulk treatments contained nonquantifiable Ce; NP-exposed spiders contained Ce at 5.49 ng/g. These findings show that NP CeO2 accumulates in zucchini at greater levels than equivalent bulk materials and that this greater NP intake results in trophic transfer and possible food chain contamination.

Cerium oxide nanoparticles alter the antioxidant capacity but do not impact tuber ionome in Raphanus sativus (L)

The effects of nCeO2 on food quality are not well known yet. This research was performed to determine the impact of nCeO2 on radish (Raphanus sativus L.). Plants were cultivated to full maturity in potting soil treated with nCeO2 at concentrations of 0, 62.5, 125, 250, and 500 mg/kg. Germination, growth, photosynthesis, ionome, and antioxidants were evaluated at different growth stages. Results showed that at 500 mg/kg, nCeO2 significantly retarded seed germination but did not reduce the number of germinated seeds. None of the treatments affected gas exchange, photosynthesis, growth, phenols, flavonoids, and nutrients' accumulation in tubers and leaves of adult plants. However, tubers' antioxidant capacity, expressed as FRAP, ABTS(•-) and DPPH, increased by 30%, 32%, and 85%, respectively, in plants treated with 250 mg nCeO2kg(-1) soil. In addition, cerium accumulation in tubers of plants treated with 250 and 500 mg/kg reached 72 and 142 mg/kg d wt, respectively. This suggests that nCeO2 could improve the radical scavenging potency of radish but it might introduce nCeO2 into the food chain with unknown consequences.

Phytosynthesis of nanoparticles: concept, controversy and application

Nanotechnology is an exciting and powerful discipline of science; the altered properties of which have offered many new and profitable products and applications. Agriculture, food and medicine sector industries have been investing more in nanotechnology research. Plants or their extracts provide a biological synthesis route of several metallic nanoparticles which is more eco-friendly and allows a controlled synthesis with well-defined size and shape. The rapid drug delivery in the presence of a carrier is a recent development to treat patients with nanoparticles of certain metals. The engineered nanoparticles are more useful in increasing the crop production, although this issue is still in infancy. This is simply due to the unprecedented and unforeseen health hazard and environmental concern. The well-known metal ions such as zinc, iron and copper are essential constituents of several enzymes found in the human system even though the indiscriminate use of similar other metal nanoparticle in food and medicine without clinical trial is not advisable. This review is intended to describe the novel phytosynthesis of metal and metal oxide nanoparticles with regard to their shape, size, structure and diverse application in almost all fields of medicine, agriculture and technology. We have also emphasized the concept and controversial mechanism of green synthesis of nanoparticles.

Evidence of translocation and physiological impacts of foliar applied CeO2 nanoparticles on cucumber (Cucumis sativus) 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 (Cucumis sativus) plants were aerially treated either with nano ceria powder (nCeO2) at 0.98 and 2.94 g/m(3) 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.

Trophic transfer, transformation, and impact of engineered nanomaterials in terrestrial environments

Engineered nanomaterials (ENMs) are released into the environment with unknown implications in the food chain. Recent findings demonstrate that ENMs may accumulate and/or increase concentrations of the component metal or carbon nanomaterials in the fruits/grains of agricultural crops, have detrimental or beneficial effects on the agronomic traits, yield, and productivity of plants, induce modifications in the nutritional value of food crops, and transfer within trophic levels. Given this information, important questions needed to be resolved include a determination of actual or predicted concentrations of ENMs through the development of new and perhaps hybridized analytical tools, assessment of the nutritional content modifications and/or accumulation of ENMs, component metal, and cocontaminants in edible plants and their implications on human diet, nutrition, and health, assessment of the consequences of ENM-induced changes in soil health, physiological process, and yield on agricultural production and food security, and transfer of ENMs in trophic levels. Given the significant implications of ENMs exposure and the rather large knowledge gaps that exist, it will be prudent to observe judicious and targeted use of ENMs so as to minimize environmental release until a comprehensive environmental fate and effects assessment can be undertaken.

Influence of CeO2 and ZnO nanoparticles on cucumber physiological markers and bioaccumulation of Ce and Zn: a life cycle study

With the dramatic increase in nanotechnologies, it has become increasingly likely that food crops will be exposed to excess engineered nanoparticles (NPs). In this study, cucumber plants were grown to full maturity in soil amended with either CeO2 or ZnO NPs at concentrations of 0, 400, and 800 mg/kg. Chlorophyll and gas exchange were monitored, and physiological markers were recorded. Results showed that, at the concentrations tested, neither CeO2 nor ZnO NPs impacted cucumber plant growth, gas exchange, and chlorophyll content. However, at 800 mg/kg treatment, CeO2 NPs reduced the yield by 31.6% compared to the control (p ≤ 0.07). ICP-MS results showed that the high concentration treatments resulted in the bioaccumulation of Ce and Zn in the fruit (1.27 mg of Ce and 110 mg Zn per kg dry weight). μ-XRF images exhibited Ce in the leaf vein vasculature, suggesting that Ce moves between tissues with water flow during transpiration. To the authors' knowledge, this is the first holistic study focusing on the impacts of CeO2 and ZnO NPs in the life cycle of cucumber plants.

Synchrotron verification of TiO2 accumulation in cucumber fruit: a possible pathway of TiO2 nanoparticle transfer from soil into the food chain

The transfer of nanoparticles (NPs) into the food chain through edible plants is of great concern. Cucumis sativus L. is a freshly consumed garden vegetable that could be in contact with NPs through biosolids and direct agrichemical application. In this research, cucumber plants were cultivated for 150 days in sandy loam soil treated with 0 to 750 mg TiO2 NPs kg(-1). Fruits were analyzed using synchrotron μ-XRF and μ-XANES, ICP-OES, and biochemical assays. Results showed that catalase in leaves increased (U mg(-1) protein) from 58.8 in control to 78.8 in 750 mg kg(-1) treatment; while ascorbate peroxidase decreased from 21.9 to 14.1 in 500 mg kg(-1) treatment. Moreover, total chlorophyll content in leaves increased in the 750 mg kg(-1) treatment. Compared to control, FTIR spectra of fruit from TiO2 NP treated plants showed significant differences (p ≤ 0.05) in band areas of amide, lignin, and carbohydrates, suggesting macromolecule modification of cucumber fruit. In addition, compared with control, plants treated with 500 mg kg(-1) had 35% more potassium and 34% more phosphorus. For the first time, μ-XRF and μ-XANES showed root-to-fruit translocation of TiO2 in cucumber without biotransformation. This suggests TiO2 could be introduced into the food chain with unknown consequences.