Metabolomics analysis of TiO2 nanoparticles induced toxicological effects on rice (Oryza sativa L.)

Downregulation of the photosynthetic machinery and carbon storage signaling pathways mediate La2O3 nanoparticle toxicity on radish taproot formation

The molecular and physiological mechanisms of how rare earth oxide nanoparticles (NPs) alter radish (Raphanus sativus L.) taproot formation and cracking were investigated in the present study. We compared plants that received suspensions of 10, 50, 100, 300 mg L^-1 of La₂O₃ NPs, 300 m L^-1 La₂O₃ bulk-particles (BPs), 0.8 m L^-1 La³⁺, or only water for six days during their tuber formation period. 100 and 300 mg L^-1 La₂O₃ NPs exposure decreased storage root biomass by 38% and 60%, respectively, and they both induced visible root cracking. Physiological analyses showed that La₂O₃ NPs exposure (>100 mg L^-1) significantly inhibited leaf net photosynthetic rate, cell wall pectin synthesis of both storage root epidermis and xylem parenchyma tissues, but increased the contents of cellulose and hemicellulose 1 in root epidermis cell walls. Moreover, transcriptome analysis further found that La₂O₃ NPs changed root cell wall structure by down-regulating core genes involved in cell wall pectin and IAA biosynthesis, which coincided with the observed La₂O₃ NPs-induced root cracking. Our results revealed the molecular mechanisms related to cell wall carbohydrate metabolism in response to NPs stress, providing a step forward for understanding the causes of NPs phytotoxicity on edible plant taproot formation and cracking.

Metabolomics reveals the inhibition on phosphorus assimilation in Chlorella vulgaris F1068 exposed to AgNPs

Phosphorus removal by algae-based biotechnology can be achieved through algal assimilation, surface adsorption, or abiotic precipitation. However, there are still unavailable how these phosphorus removal processes were affected by nanoparticles in wastewater. Here, we employed a non-targeted metabolomic approach to reveal the impact of silver nanoparticles (AgNPs) on the phosphorus assimilation by a unicellular green alga Chlorella vulgaris F1068 (C. vulgaris F1068). Results showed that AgNPs mostly inhibited total phosphorus (TP) removal by the algal assimilation, with TP removal efficiency being reduced by 66.2% (with 0.20 mg/L AgNPs) of the control (without AgNPs). Metabolomics analysis also indicated that AgNPs disturbed metabolic responses related to phosphorus assimilation. AgNPs inhibited phospholipid metabolism which included inositol phosphate metabolism and phosphatidylinositol signaling system (downregulation of glycerol-3-phosphate and myo-inositol, as well as upregulation of serine). Metabolites related to phosphorus assimilation products were impacted through downregulation of guanine, glutamine, alanine, and aspartic acid, as well as upregulation of succinic acid, thereby impeding the algal assimilation of phosphorus. Moreover, perturbation of glutathione metabolism induced by oxidative stress stimulated the alteration of membrane state (upregulation of glycine). These findings contribute to a molecular-scale perspective of nanoparticles on algae-based biotechnology in phosphorus removal.

Effects of TiO2 Nanoparticles Incorporation into Cells of Tomato Roots

In this study, tomato plants were grown in vitro with and without incorporation of TiO₂ nanoparticles in Murashige and Skoog (MS) growth medium. The aim of this study was to describe the morphological (area and roundness cell) and mechanical (Young’s Modulus) change in the different tissue of tomato root, epidermis (Ep), parenchyma (Pa), and vascular bundles (Vb), when the whole plant was exposed to TiO₂ nanoparticles (TiO₂ NPs). light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), wavelength dispersive X-ray fluorescence (WDXRF) techniques were used to identify changes into the root cells when TiO₂ NPs were incorporated. TiO₂ NPs incorporation produces changes in the area, roundness, and Young’s Modulus of the tomato root. When tomato root is exposed to TiO₂ NPs, the Ep and Vb area size decreases from 260.92 µm² to 160.71 µm² and, 103.08 µm² to 52.13 µm², respectively, compared with the control area, while in Pa tissue the area size was increased considerably from 337.72 mm² to 892.96 mm². Cellular roundness was evident in tomato root that was exposed to TiO₂ NPs in the Ep (0.49 to 0.67), Pa (0.63 to 0.79), and Vb (0.76 to 0.71) area zones. Young’s Modulus in Pa zone showed a rigid mechanical behavior when tomato root is exposed to TiO₂ NPs (0.48 to 4.98 MPa control and TiO₂ NPs, respectively). Meanwhile, Ep and Vb were softer than the control sample (13.9 to 1.06 MPa and 6.37 to 4.41 MPa respectively). This means that the Pa zone was stiffer than Ep and Vb when the root is exposed to TiO₂ NPs. Furthermore, TiO₂ NPs were internalized in the root tissue of tomato, accumulating mainly in the cell wall and intercellular spaces, with a wide distribution throughout the tissue, as seen in TEM.

Application of TiO2 nanoparticles to reduce bioaccumulation of arsenic in rice seedlings (Oryza sativa L.): A mechanistic study

The possible application of TiO₂ nanoparticles (nano-TiO₂) to alleviate arsenic bioaccumulation in rice seedlings and such a functioning with their crystalline structure were investigated. Specifically, nano-TiO₂ with anatase and rutile structures and the bulk TiO₂ at 0, 10, 100, and 1000 mg/L were amended to the hydroponic exposure systems with arsenic concentration at 1 mg/L, and the plant was exposed for 7 days. Our findings indicated that nano-TiO₂ significantly reduced arsenic bioaccumulation in rice seedlings by 40-90% via strong sorption process, but their growth was not affected. Nano-TiO₂ amendment notably alleviated oxidative stress resulting from arsenic exposure. Without nano-TiO₂ amendment, the iron plaque on root surfaces served as a strong barrier to inhibit arsenic uptake by rice seedlings. Interestingly, nano-TiO₂ amendment significantly decreased the iron plaque amount by 50-63% and weakened the arsenic retention in this barrier by 47-99%, further verifying the overwhelming superiority of nano-TiO₂ in inhibiting arsenic uptake by rice seedlings. Rutile nano-TiO₂ (NRT) at 1000 mg/L presented to be a promising candidate for controlling arsenic uptake by the exposed rice seedlings, with no significant oxidative stress by the amended nano-TiO₂, thereby mitigating health risk of arsenic to humans via food chain.

Uterine metabolic disorder induced by silica nanoparticles: biodistribution and bioactivity revealed by labeling with FITC

Extensive application of nanomaterials has dramatically increased the risk of silica nanoparticle (SiNP, SiO₂) exposure, yet their biological effect on reproduction has not been fully elucidated. By tracking the uterine biodistribution of SiNP in pregnant mice, this study was conducted to evaluate the biological effect of SiNP on reproduction. First, SiNP was conjugated with FITC, and then the FITC-SiNP was administrated to trophoblast (100 µg/mL, 24 h) in vitro and pregnant mice (0.25 mg/mouse, 2-24 h) in vivo. It was found that the FITC-SiNP was internalized by trophoblast and deposited in the uterus. The internalization of SiNP caused trophoblast dysfunction and apoptosis, while SiNP accumulation in the uterus induced diffuse inflammatory infiltration. The genome-wide alteration of gene expression was studied by high throughput sequencing analysis, where 75 genes were found to be dysregulated after SiNP exposure, among which ACOT2, SCD1, and CPT1A were demonstrated to regulate the biosynthesis of unsaturated fatty acids. Moreover, the suppression of unsaturated fatty acids caused mitochondrial overload of long-chain fatty acyl-CoA (LACoA), which further induced both trophoblast apoptosis and endometrial inflammation. In conclusion, the successful conjugation of FITC onto SiNP facilitated the tracking of SiNP in vitro and in vivo, while exposure to FITC-SiNP induced uterine metabolic disorder, which was regulated by the ACOT/CPT1A/SCD1 axis through the biosynthesis of unsaturated fatty acids signaling pathway.

Pentachlorophenol and ciprofloxacin present dissimilar joint toxicities with carbon nanotubes to Bacillus subtilis

Discharged carbon nanotubes (CNTs) likely interact with co-existing organic contaminants (OCs) and pose joint toxicity to environmental microbes. Herein, hydrophobic pentachlorophenol (PCP) and hydrophilic ciprofloxacin (CIP) were used as representative OCs and their joint toxicities with CNTs to Bacillus subtilis were systematically investigated at cellular, biochemical, and omics levels. The 3-h bacterial growth half inhibitory concentrations of CNTs, PCP, and CIP were 12.5 ± 2.6, 3.5 ± 0.5, and 0.46 ± 0.03 mg/L, respectively, and they all could damage cell membrane, increase intracellular oxidative stress, and alter bacterial metabolomics and transcriptomics; while CNTs-PCP and CNTs-CIP binary exposures exhibited distinct additive and synergistic toxicities, respectively. CNTs increased bacterial bioaccumulation of PCP and CIP via destabilizing and damaging cell membrane. PCP reduced the bioaccumulation of CNTs, while CIP had no significant effect; this difference could be owing to the different effects of the two OCs on cell-surface hydrophobicity and CNTs electronegativity. The additive toxicity outcome upon CNTs-PCP co-exposure could be a result of the balance between the increased toxicity from increased PCP bioaccumulation and the decreased toxicity from decreased CNTs bioaccumulation. The increased bioaccumulation of CIP contributed to the synergistic toxicity upon CNTs-CIP co-exposure, as confirmed by the increased inhibition of topoisomerase Ⅳ activity and interference in gene expressions regulating ABC transporters and lysine biosynthesis. The findings provide novel insights into environmental risks of CNTs.

Effects of different surface-coated nTiO2 on full-grown carrot plants: Impacts on root splitting, essential elements, and Ti uptake

The production and environmental release of surface-modified titanium dioxide nanoparticles (nTiO₂) have increased. Hence, crops may be directly exposed to the nTiO₂ in soil. In this study, we grew carrots in soils amended with pristine, hydrophilic and hydrophobic surface-coated nTiO₂ at 100, 200, and 400 mg kg^-1 until full-plant maturity. The content of Ti in plant secondary roots treated with different nTiO₂ at 400 mg kg^-1 was in the order of hydrophobic > hydrophilic > pristine treatments, with values of 140.1, 100.5, and 64.3 mg kg^-1, respectively. The fresh biomass of the taproot was significantly decreased by all nTiO₂ forms at 400 mg kg^-1 by up to 56 %, compared to control. Pristine nTiO₂ at 100 mg kg^-1 enhanced the fresh weight of leaves by 51 % with respect to control. Remarkably, an abnormal increase of taproot splitting was found in plants treated with all nTiO₂ forms. In carrots treated with the surface-coated nTiO₂, the accumulation of Ca, Mg, Fe, and Zn increased in leaves; but Mg, Mn, and Zn decreased in taproots. These results suggest that future regulation of nTiO₂ release into soils should consider its surface coating properties since the phytotoxicity effects depend on nTiO₂ outer structure.

R, P. R, Kalia A, Bhardwaj K, Bhardwaj P, Abd-Elsalam KA, Valis M, Kuca K. Nanohybrid Antifungals for Control of Plant Diseases: Current Status and Future Perspectives

The changing climatic conditions have led to the concurrent emergence of virulent microbial pathogens that attack crop plants and exhibit yield and quality deterring impacts on the affected crop. To counteract, the widespread infections of fungal pathogens and post-harvest diseases it is highly warranted to develop sustainable techniques and tools bypassing traditional agriculture practices. Nanotechnology offers a solution to the problems in disease management in a simple lucid way. These technologies are revolutionizing the scientific/industrial sectors. Likewise, in agriculture, the nano-based tools are of great promise particularly for the development of potent formulations ensuring proper delivery of agrochemicals, nutrients, pesticides/insecticides, and even growth regulators for enhanced use efficiency. The development of novel nanocomposites for improved management of fungal diseases can mitigate the emergence of resilient and persistent fungal pathogens and the loss of crop produce due to diseases they cause. Therefore, in this review, we collectively manifest the role of nanocomposites for the management of fungal diseases.

Biostimulation and toxicity: The magnitude of the impact of nanomaterials in microorganisms and plants

Background

Biostimulation and toxicity constitute the continuous response spectrum of a biological organism against physicochemical or biological factors. Among the environmental agents capable of inducing biostimulation or toxicity are nanomaterials. On the < 100 nm scale, nanomaterials impose both physical effects resulting from the core’s and corona’s surface properties, and chemical effects related to the core’s composition and the corona’s functional groups.

Aim of Review

The purpose of this review is to describe the impact of nanomaterials on microorganisms and plants, considering two of the most studied physical and chemical properties: size and concentration.

Key Scientific Concepts of Review

Using a graphical analysis, the presence of a continuous biostimulation-toxicity spectrum is shown considering different biological responses. In microorganisms, the results showed high susceptibility to nanomaterials. Simultaneously, in plants, a hormetic response was found related to nanomaterials concentration and, in a few cases, a positive response in the smaller nanomaterials when these were applied at a higher level. With the above, it is concluded that: (1) microorganisms are more susceptible to nanomaterials than plants, (2) practically all nanomaterials seem to induce responses from biostimulation to toxicity in plants, and (3) the kind of response observed will depend in a complex way on the nanomateriaĺs physical and chemical characteristics, of the biological species with which they interact, and of the form and route of application and on the nature of the medium -soil, soil pore water, and biological surfaces- where the interaction occurs.

A comprehensive integrated transcriptome and metabolome analyses to reveal key genes and essential metabolic pathways involved in CMS in kenaf

Numbers of critical genes and pathways were found from the levels of transcriptome and metabolome, which were useful information for understanding of kenaf CMS mechanism. Cytoplasmic male sterility (CMS) is a maternally inherited trait in higher plants that leads to the inability to produce or release functional pollen. However, there is lack of comprehensive studies to reveal the molecular basis of CMS occurrence in kenaf. Herein, we performed transcriptome and UPLC-MS-based metabolome analyses in the anthers of a CMS (UG93A) and its maintainer (UG93B) to sort out essential genes and metabolites responding to CMS in kenaf. Transcriptome characterized 7769 differentially expressed genes (DEGs) between these two materials, and pathway enrichment analysis indicated that these DEGs were involved mainly in pentose and glucuronate interconversions, starch and sucrose metabolism, taurine and hypotaurine metabolism. In the metabolome assay, a total of 116 significantly different metabolites (SDMs) were identified between the CMS and its maintainer line, and these SDMs were involved in eight KEGG pathways, including flavone and flavonol biosynthesis, glycerophospholipid metabolism, flavonoid biosynthesis, glycosylphosphatidylinositol-anchor biosynthesi. Integrated analyses of transcriptome and metabolome showed that 50 genes had strong correlation coefficient values (R² > 0.9) with ten metabolites enriched in six pathways; notably, most genes and metabolites of flavonoid biosynthesis pathways and flavone and flavonol biosynthesis pathways involved in flavonoids biosynthetic pathways were downregulated in CMS compared to those in maintainer. Taken together, the decreased accumulation of flavonoids resulted from the compromised biosynthesis pathways coupled with energy deficiency in the anthers may contribute largely to CMS in UG93A of kenaf.

Ecological Drawbacks of Nanomaterials Produced on an Industrial Scale: Collateral Effect on Human and Environmental Health

Currently, hundreds of different nanomaterials with a broad application in products that make daily lives a little bit easier, in every aspect, are being produced on an industrial scale at thousands of tons per year. However, several scientists, researchers, politics, and ordinary citizens have stated their concern regarding the life cycle, collateral effects, and final disposal of these cutting-edge materials. This review summarizes, describes, and discusses all manuscripts published in the Journal Citation Reports during the last 10 years, which studied the toxicity or the effects of nanomaterials on human and environmental health. It was observed that 23.62% of the manuscripts analyzed found no ecological or human risks; 54.39% showed that several nanomaterials have toxicological effects on the ecosystems, human, or environmental health. In comparison, only 21.97% stated the nanomaterials had a beneficial impact on those. Although only 54.39% of the manuscripts reported unfavorable effects of nanomaterials on ecosystems, human, or environmental health, it is relevant because the potential damage is invaluable. Therefore, it is imperative to make toxicological studies of nanomaterials with holistic focus under strictly controlled real conditions before their commercialization, to deliver to the market only innocuous and environmentally friendly products.

Recent Developments in the Application of Nanomaterials in Agroecosystems

Nanotechnology implies the scientific research, development, and manufacture, along with processing, of materials and structures on a nano scale. Presently, the contamination of metalloids and metals in the soil has gained substantial attention. The consolidation of nanomaterials and plants in ecological management has received considerable research attention because certain nanomaterials could enhance plant seed germination and entire plant growth. Conversely, when the nanomaterial concentration is not properly controlled, toxicity will definitely develop. This paper discusses the role of nanomaterials as: (1) nano-pesticides (for improving the plant resistance against the biotic stress); and (2) nano-fertilizers (for promoting the plant growth by providing vital nutrients). This review analyzes the potential usages of nanomaterials in agroecosystem. In addition, the adverse effects of nanomaterials on soil organisms are discussed. We mostly examine the beneficial effects of nanomaterials such as nano-zerovalent iron, iron oxide, titanium dioxide, nano-hydroxyapatite, carbon nanotubes, and silver- and copper-based nanomaterials. Some nanomaterials can affect the growth, survival, and reproduction of soil organisms. A change from testing/using nanomaterials in plants for developing nanomaterials depending on agricultural requirements would be an important phase in the utilization of nanomaterials in sustainable agriculture. Conversely, the transport as well as ecological toxicity of nanomaterials should be seriously examined for guaranteeing its benign usage in agriculture.

TiO2 nanoparticles induced sugar impairments and metabolic pathway shift towards amino acid metabolism in wheat

TiO₂-nanoparticles (TiO₂-NP) have the potential to impair plant development. Nevertheless, the metabolic processes behind the physiological responses to TiO₂-NP are still far from being fully understood. In this study, Triticum aestivum plants were exposed for 21 days to different concentrations (0; 5; 50; 150 mg L^-1) of TiO₂-NP (P25). After treatment, the metabolite profiles of roots and leaves were analysed. The content of >70 % of the identified metabolites changed in response to P25 and the impact on metabolic pathways increased with TiO₂-NP dose, with leaves showing higher alterations. Roots up-regulated monosaccharides, azelaic acid, and γ-aminobutanoic acid and triggered the tyrosine metabolism, whereas leaves up-regulated the metabolisms of reserve sugars and tocopherol, and the phenylalanine and tryptophan pathways. Both organs (mainly leaves) up-regulated the aspartate family pathway together with serine, alanine and valine metabolisms and the glycerolipids' biosynthesis. In addition, the citrate and glyoxylate metabolisms were down-regulated in both organs (highest dose). Sugar biosynthesis breakdown, due to photosynthetic disturbances, shifted the cell metabolism to use amino acids as an alternative energy source, and both ROS and sugars worked as signalling molecules activating organ dependent antioxidant responses. Concluding, these NP-pollutants severely impact multiple crop metabolic pathways and may ultimately compromise plant performance.

Metabolomics revealing the response of rice (Oryza sativa L.) exposed to polystyrene microplastics

Large amounts of microplastics accumulate in the agricultural soil. Microplastics would stress the crops but the underlying mechanism remains unclear. Herein, a laboratory exposure and field trials were carried out to investigate the response of rice (Oryza sativa L. II You. 900) to stress induced by polystyrene microplastics (PS-MPs) using a metabolomic approach. After laboratory exposure for 21 days, the decreases in shoot biomass of rice exposed to low, medium and high doses of PS-MPs were 13.1% (CV = 4.1%), 18.8% (CV = 3.7%), and 40.3% (CV = 9.2%), respectively, while the antioxidant enzymes showed an inverted upper-U shape when exposed to PS-MPs. A total of 24 samples from three exposure dose levels were included in the metabolic analysis. The metabolites of 12 amino acids, 16 saccharides, 26 organic acids and 17 others (lipids and polyols) in leaves decreased after the exposure to both 50 mg L^-1 and 250 mg L^-1 PS-MPs doses with hydroponically-cultured. The inhibition of perturbed biological pathway causes the biosynthesis of amino acids, nucleic acids, fatty acids and some secondary metabolites decreased which indicate that the energy expenditure exceeded the substance accumulation. In order to further validate the effects of PS-MPs on rice leaves obtained from the laboratory-scale experiments, a field-trial experiment was conducted. After 142 days of cultivation in farmland, the results with a maximum of 25.9% lower biomass in the crops exposed with PS-MPs. As such, the presence of PS-MPs may affect rice production by altering the metabolic systems of rice. Long-term exposure of PS-MPs to rice might be a potential risk to rice safety and quality.

Concentration- and nutrient-dependent cellular responses of microalgae Chlorella pyrenoidosa to perfluorooctanoic acid

Perfluorooctanoic acid (PFOA), an emerging and persistent pollutant, could cause toxicity effects on aquatic organisms. However, this was generally assessed under high exposure concentrations of PFOA and nutrient-enriched conditions, which was not accordant with the actual environments. Therefore, to comprehensively understand the toxicity effects of PFOA on aquatic organisms, the cellular responses of microalgae, Chlorella pyrenoidosa, to PFOA under different concentrations (≤ 1.0 mg/L) and nutrient conditions were investigated in this study. Results show that PFOA at concentrations less than 1.0 mg/L had no significant effects on algal growth and chlorophyll contents, and no oxidative damages were generated to destroy membrane integrity and morphology. However, N,P-limited and -starved conditions significantly decreased algal growth and chlorophyll contents, and induced oxidative stresses to ruin the structure and function of cell membrane. Moreover, the deficiency of P had more severe negative effect on algae than that of N, and they both influenced the toxicity responses of microalgae to 1.0 mg/L PFOA. The adsorption and uptake percentages of PFOA by algal cells were both less than 10%, and increased adsorption but decreased uptake of PFOA amounts occurred under N,P-limited and -starved conditions. These findings will be useful to understand the toxicity effects of PFOA on microalgae in aquatic environments.

Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends

Nanotechnology is a tool that in the last decade has demonstrated multiple applications in several sectors, including agroindustry. There has been an advance in the development of nanoparticulated systems to be used as fertilizers, pesticides, herbicides, sensors, and quality stimulants, among other applications. The nanoencapsulation process not only protects the active ingredient but also can affect the diffusion, interaction, and activity. It is important to evaluate the negative aspects of the use of nanoparticles (NPs) in agriculture. Given the high impact of the nanoparticulated systems in the agro-industrial field, this review aims to address the effects of various nanomaterials on the morphology, metabolomics, and genetic modification of several crops.

Effects of ketoprofen on rice seedlings: Insights from photosynthesis, antioxidative stress, gene expression patterns, and integrated biomarker response analysis

Pharmacologically active compounds found in reclaimed wastewater irrigation or animal manure fertilizers pose potential risks for agriculture. The mechanism underlying the effects of ketoprofen on rice (Oryza sativa L.) seedlings was investigated. The results showed that low concentrations (0.5 mg L^-1) of ketoprofen slightly stimulate growth of rice seedlings, while high concentrations can significantly inhibit growth by reducing biomass and causing damage to roots. Ketoprofen affects photosynthetic pigment content (Chla, Chlb, and carotenoids) and chlorophyll synthesis gene (HEMA, HEMG, CHLD, CHLG, CHLM, and CAO) expression. Fluorescence parameters such as minimum fluorescence (F₀), maximum fluorescence (F_m), variable fluorescence (F_v), potential photosynthetic capacity (F_v/F₀), maximum quantum efficiency of PSII photochemistry (F_v/F_m), electron transfer rate (ETR), and Y(II), Y(NPQ), Y(NO) values were affected, showing photosynthetic electron transfer was blocked. Active oxygen radical (O₂^•-and H₂O₂), malondialdehyde and proline content increased. Superoxide dismutase, catalase and ascorbate peroxidase activities, glutathione content and antioxidant-related gene (FSD1, MSD1, CSD1, CSD2, CAT1, CAT2, CAT3, APX1, APX2) expression were induced. Higher integrated biomarker response values of eight oxidative stress response indexes were obtained at higher ketoprofen concentrations. Ultrastructure observation showed that ketoprofen causes cell structure damage, chloroplast swelling, increase in starch granules, and reduction in organelles. This study provides some suggested toxicological mechanisms and biological response indicators in rice due to stress from pharmacologically active compounds.

Multi-omics analyses reveal molecular mechanisms for the antagonistic toxicity of carbon nanotubes and ciprofloxacin to Escherichia coli

With the increasing production and application, engineered nanomaterials (ENMs) are being discharged into the environment, where they can interact with co-existing contaminants, causing complicated joint toxicity to organisms that needs to be studied. The case study of ENMs-contaminant joint toxicity and the understanding of relative mechanisms are very insufficient, particularly the mechanisms of molecular interactions and governing processes. Herein, a typical ENMs, carbon nanotubes (CNTs, 0-60 mg/L), and a common antibiotic, ciprofloxacin (CIP, 0-900 mg/L), were selected as the analytes. Their joint toxicity to a model microbe Escherichia coli was specifically investigated via biochemical, transcriptomics, and metabolomics approaches. The result revealed an antagonistic effect on growth inhibition between CNTs and CIP. Mitigations in cell membrane disruption and oxidative stress were involved in the antagonistic action. CIP (48.8-244 mg/L) decreased the bioaccumulation of CNTs (7.2 mg/L) via reducing cell-surface hydrophobicity and hindering the bio-nano interaction, which could attenuate the toxicity of CNTs to bacteria. CNTs (7.2 and 14.4 mg/L) alleviated the disturbance of CIP (122 and 244 mg/L) to gene expressions especially related to nitrogen compound metabolism, oxidoreductase activity, and iron-sulfur protein maturation, probably through relieving the CIP-induced inhibition of DNA gyrase activity. Further, CNTs (7.2 and 14.4 mg/L) offset the impact of CIP (122 and 244 mg/L) on bacterial metabolome via the regulation of biosynthesis of unsaturated fatty acids and metabolisms of some amino acids and glutathione. The findings shed new light on the molecular mechanisms by which ENMs present joint effect on contaminant toxicity, and provide important information for risk assessments of CNTs and fluoroquinolones in the environment.

Metabolomics Reveals Antioxidant Stress Responses of Wheat (Triticum aestivum L.) Exposed to Chlorinated Organophosphate Esters

In this study, wheat (Triticum aestivum L.) was exposed to three of the most typical chlorinated organophosphate esters (OPEs), which are widely present in farmland soil, at environmental concentrations to assess their accumulation, disruption on metabolism, and oxidative stress in wheat. The three OPEs accumulated distinctly in the root and then translocated to the shoot. After exposure for 7 days, the content of chlorophyll b decreased, while the levels of carotenoid and activities of antioxidases, malonaldehyde, and reactive oxygen species increased significantly in both the root and shoot, indicating that the target OPEs caused significant oxidative stresses and affected photosynthesis in wheat. Untargeted metabolomics revealed concentration- and species-dependent metabolic responses of the three OPEs. Saccharides were downregulated, which might be due to the reduced photosynthesis activities. On the other hand, the chlorinated OPEs induced increases in respiration and antioxidative metabolites, revealing that the antioxidant system of wheat was active in scavenging ROS. The disturbance of tris(1,3-dichloro-2-propyl)phosphate on the metabolisms in wheat tissues was the strongest. These results contribute to the food safety and crop quality assessment of chlorinated OPEs and clarify the underlying mechanisms of their phytotoxicities.

Integration of transcriptomics and metabolomics reveals the responses of earthworms to the long-term exposure of TiO2 nanoparticles in soil

Titanium dioxide nanoparticles (nTiO₂) are widely used and their environmental occurrence has raised concerns about the potential toxicity to biota. However, few studies have investigated the effect of long-term exposure to nTiO₂ on soil invertebrates. This study therefore for the first time investigated the long-term (120 days) effect of nTiO₂ (0, 5, 50, and 500 mg/kg) on the phenotypes, transcriptomic, and metabolomic profiles of earthworm (Eisenia fetida) in soil. The results showed that the long-term exposure to nTiO₂ did not significantly affect the growth, reproduction, and Ti content of earthworms. However, the antioxidant system and the transcriptomic and metabolomic profiles of earthworms were significantly affected. The superoxide dismutase (SOD) activity and the reduced glutathione/oxidized glutathione (GSH/GSSG) ratio significantly decreased under the 500 mg/kg nTiO₂ treatment. The metabolomics analysis showed that glycine and pyroglutamic acid contents involved in the GSH metabolism were significantly altered under the 500 mg/kg treatment. Moreover, transcriptomics and metabolomics data revealed that the long-term exposure to nTiO₂ affected the synthesis of carbohydrates, proteins, and lipids. However, the transcriptomics results indicated that the genes involved in ribosome biogenesis in eukaryotes pathway and TGF-beta signaling pathway were upregulated, which could explain why the growth and reproduction of earthworms were apparently not affected by the nTiO₂ exposure. The combination of transcriptomics and metabolomics reveals the global responses that cannot be observed by conventional toxicity endpoints, facilitating the assessment of long-term ecological effect of engineered nanoparticles in the environment.

Silver nanoparticles affect phenolic and phytoalexin composition of Arabidopsis thaliana

Silver nanoparticles are widely used in industry, medicine, biotechnology and agriculture. As a consequence, these nanoparticles are reaching the environment as waste products, which might have a negative impact on the environment, especially on plants. This includes the elicitation of various biochemical processes in plants. In this article, we report on the changes in secondary metabolic profile of Arabidopsis thaliana seedlings subjected to silver nanoparticle treatment in vitro. Briefly, various sizes (10 nm, 40 nm and 100 nm in diameter) and concentrations (0.5-5.0 ppm) of silver nanoparticles were tested. Ultraperformance liquid chromatography coupled with ultraviolet and fluorescence detectors as well as hyphenated to a high-resolution mass spectrometer (UPLC-PDA-FLR, UPLC-HESI-HRMS) and HPLC - ion trap mass spectrometer (HPLC-ESI-MS/MS), were applied to identify and quantify secondary metabolites. To understand whether silver ions could induce changes in the secondary metabolite profile, seedlings treated with silver nitrate in concentrations equivalent to these of nanoparticles were also analysed. The results showed significant differences in the accumulation of phenolic and indole compounds between treatments. Silver nanoparticles and silver ions induced the biosynthesis of camalexin, hydroxycamalexin O-hexoside and hydroxycamalexin malonyl-hexoside. These compounds are important phytoalexins for Brassicaceae family (especially for Camelinae clad) and are also synthetized in response to biotic and abiotic stresses. Statistically significant changes have been also observed for five phenolic compounds and 5'Glucosyl-dihydroneoascorbigen in different treatment conditions.

Metabolic disturbance in hippocampus and liver of mice: A primary response to imidacloprid exposure

Imidacloprid (IMI) is one of the most frequently used neonicotinoid insecticides, but recent studies have shown adverse effects on mammals. IMI was found to be neurotoxic and hepatotoxic. In the present study, the effects of repeated oral administration of two doses of IMI (5 and 20 mg/kg/day) for 28 days on hippocampus and liver of female KM mice were studied. The histopathological and biochemical experiments indicated obvious damages to the hippocampus and liver of mice in the high-dose group (20 mg/kg/day). Using a high-throughput metabolomics platform based on ultrahigh performance liquid chromatography/hybrid quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS), we studied effects of IMI on metabolic profiles in the hippocampus and liver of mice. Significant differences among the control group, the low-dose group and the high-dose group were clearly presented using multivariate analysis. The changed metabolic profile in the low-dose group (5 mg/kg/day) revealed that the metabolic disturbance in the hippocampus and liver of mice had been induced by low-dose of IMI, although no significant histopathological changes were observed in the low-dose group. Six differential metabolites in the hippocampus and 10 differential metabolites in the liver were identified as the possible biomarkers to distinguish IMI exposure from the control group using the variable importance in projection (VIP) value and receiver operating characteristic (ROC) analysis. The metabolism disturbances of important biochemical pathways in the hippocampus and liver of mice in the exposed groups were elucidated, mostly concentrated in lipid metabolism, amino acid metabolism, nucleotide metabolism, carbohydrate metabolism, and energy metabolism (p < 0.05). Such investigations give out a global view of IMI-induced damages in the hippocampus and liver of mice and imply a health risk associated with early metabolic damage in mice.

Untargeted Metabolic Pathway Analysis as an Effective Strategy to Connect Various Nanoparticle Properties to Nanoparticle-Induced Ecotoxicity

Elucidation of the relationships between nanoparticle properties and ecotoxicity is a fundamental issue for environmental applications and risk assessment of nanoparticles. However, effective strategies to connect the various properties of nanoparticles with their ecotoxicity remain largely unavailable. Herein, an untargeted metabolic pathway analysis was employed to investigate the environmental risk posed by 10 typical nanoparticles (AgNPs, CuNPs, FeNPs, ZnONPs, SiO₂NPs, TiO₂NPs, GO, GOQDs, SWCNTs, and C₆₀) to rice (a staple food for half of the world's population). Downregulation of carbohydrate metabolism and upregulation of amino acid metabolism were the two dominant metabolic effects induced by all tested nanoparticles. Partial least-squares regression analysis indicated that a zerovalent metal and high specific surface area positively contributed to the downregulation of carbohydrate metabolism, indicating strong abiotic stress. In contrast, the carbon type, the presence of a spherical or sheet shape, and the absence of oxygen functional groups in the nanoparticles positively contributed to the upregulation of amino acid metabolism, indicating adaptation to abiotic stress. Moreover, network relationships among five properties of nanoparticles were established for these metabolic pathways. The results of the present study will aid in the understanding and prediction of environmental risks and in the design of environmentally friendly nanoparticles.

Impact of polystyrene nanoplastics (PSNPs) on seed germination and seedling growth of wheat (Triticum aestivum L.)

Microplastics and nanoplastics are emerging pollutants of global concern. However, the understanding of their ecological effects on terrestrial plants is still limited. We conducted the systematic research to reveal the impact of polystyrene nanoplastics (PSNPs) (0.01-10 mg/L) on seed germination and seedling growth of wheat (Triticum aestivum L.). The results showed that PSNPs had no discernible effect on seed germination rate whereas significantly (p < 0.01) increased root elongation by 88.6 %-122.6 % when compared with the control. Similarly, remarkable increases in carbon, nitrogen contents, and plant biomass were also observed after exposure to PSNPs. Moreover, PSNPs could reduce the shoot to root biomass ratio (S:R ratio) of wheat seedlings. Furthermore, the imagings of a 3D laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM) indicated that PSNPs were taken up and subsequently down-top transported to shoot. The absorption and accumulation of four micronutrients (Fe, Mn, Cu and Zn) in wheat were generally reduced in varying degrees. Notably, metabolomics analysis revealed that all PSNPs treatments altered the leaf metabolic profiles mainly by regulating energy metabolisms and amino acid metabolisms. These findings are expected to provide new insights into the effects of PSNPs on crop plants.

Foliar spray of TiO2 nanoparticles prevails over root application in reducing Cd accumulation and mitigating Cd-induced phytotoxicity in maize (Zea mays L.)

Cadmium (Cd) pollution is considered one of the global environmental issues due to its adverse effects on plant and human health. With the rapid development of nanotechnology and the practical application of engineered nanoparticles (ENPs) in agriculture, the mechanisms underlying the interactions between NPs and heavy metal on their uptake, accumulation, and phytotoxicity in crops are still not fully understood. Therefore, the impact of TiO₂ NPs (0, 100, 250 mg/L) and Cd (0, 50 μM) co-exposure on hydroponic maize (Zea mays L.) was determined under two exposure modes. Results showed that root co-exposure to TiO₂ NPs and 100 mg/L Cd significantly enhanced Cd uptake and produced greater phytotoxicity in maize than foliar exposure to TiO₂ NPs. Meanwhile, plant dry weight and chlorophyll content showed a reduction of 45.3% and 50.5%, respectively, when compared with single Cd treatment. In addition, the accumulation of Ti in shoots and roots increased by 1.61 and 4.29 times, respectively when root exposure to 250 mg/L TiO₂ NPs. By contrast, foliar exposure of TiO₂ NPs could markedly decrease shoot Cd contents from 15.2% to 17.8% and had a stronger influence on alleviating Cd-induced toxicity via increasing superoxide dismutase (SOD) and glutathione S-transferase (GST) activities and upregulating several metabolic pathways, including galactose metabolism and citrate cycle, alanine, aspartate and glutamate metabolism, as well as glycine, serine and threonine metabolism. This study provides a new strategy for the application of TiO₂ NPs in crop safety production in Cd contaminated soils.

Antioxidant mechanisms to counteract TiO2-nanoparticles toxicity in wheat leaves and roots are organ dependent

Nanoparticles (NP) bioactivity is under deep scrutiny. In this work, the antioxidant response to TiO₂-NP in wheat (Triticum aestivum) was determined. For that, enzymatic and the non-enzymatic antioxidants were evaluated in plants exposed to the P25 anatase:rutile material composed of TiO₂-NP and under environmentally realistic doses (0; 5; 50; 150 mg/L for 20 days). Shoot but not root growth was reduced. In leaves, thiol metabolism and ascorbate accumulation were the preferred route whereas in roots the pre-existing antioxidant capacity was preferentially utilized. Both leaves and roots showed increased glutathione reductase and dehydroascorbate reductase activities and decreased ascorbate peroxidase activity. Roots, nevertheless, presented higher enzymatic basal levels than leaves. On the other hand, when examining non-enzymatic antioxidants, the ratio of reduced-to-oxidized glutathione (GSH/GSSG) increased in leaves and decreased in roots. Exposed leaves also presented higher total ascorbate accumulation compared to roots. TiO₂-NP exposure down regulated, with more prominence in roots, antioxidant enzyme genes encoding catalase, ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase. In leaves, superoxide dismutase gene expression was increased. All data pinpoint to TiO₂-NP toxicity above 5 mg/L, with aerial parts being more susceptible, which draws concerns on the safety doses for the use of these NPs in agricultural practices.

Nanoholes Regulate the Phytotoxicity of Single-Layer Molybdenum Disulfide

Single-layer molybdenum disulfide (SLMoS₂) are applied as a hot 2D nanosheet in various fields involving water treatments. Both intentional design and environmental or biological processes induce many nanoholes in SLMoS₂. However, the effects of nanoholes on the environmental stability and ecotoxicity of SLMoS₂ remain largely unknown. The present work discovered that visible-light irradiation induced nanoholes (diameters, approximately 20 nm) in the plane of SLMoS₂, with irregular edges and increased interplanar crystal spacing. The ratios of Mo to S in pristine and transformed SLMoS₂ were 0.53 and 0.33, respectively. After 96 h exposure at concentrations from 0.1 to 1 mg/L, the above nanoholes promoted algal division, induced a stress-response hormesis, decreased the generation of •OH, and mitigated the cell shrinkage and wall rupture of Chlorella vulgaris induced by SLMoS₂. In terms of stress response, the nanohole-bearing SLMoS₂ induced fewer vacuoles and polyphosphate bodies of Chlorella vulgaris than the pristine form. Metabolomic analysis revealed that nanoholes perturbed the metabolisms of energy, carbohydrates, and fatty acids. This work proposes that nanoholes cause obvious effects on the environmental fate and ecotoxicity of SLMoS₂ and that the environmental risks of engineered nanomaterials should be reevaluated using nanohole-bearing rather than pristine forms for testing.

Metabolic responses of the green microalga Dunaliella salina to silver nanoparticles-induced oxidative stress in the presence of salicylic acid treatment

In the present study, the biochemical responses and antioxidant enzymes activity of the Dunaliella salina, a green microalga, to the interaction of silver nanoparticles (AgNPs) and salicylic acid (SA) were investigated. Algal suspensions in the phase of logarithmic growth were subjected to the concentrations of 0, 5, 15, and 25 pM AgNPs with or without 1 mM SA. AgNPs level of 25 pM declined cell division but highly accumulated levels of chlorophyll, β-carotene, proteins, free amino acid, carbohydrates, and hydrogen peroxide, which was associated with enhanced the activity of proteolysis, lipid peroxidation, and antioxidant enzymes. SA-treated cells at 25 pM AgNPs improved cell growth but declined the activities of antioxidant enzymes and proteolytic along with a lower accumulation of metabolites except β-carotene relative to untreated controls. These results suggest that AgNPs treatment induce oxidative stress in D. salina cells, which tolerated by alga through the metabolic modifications and accumulating β-carotene, while SA induces AgNPs tolerance by the mechanisms that direct carbon flux to growth and β-carotene biosynthesis rather than the antioxidant enzymes or osmoprotectant metabolites.

Metabolomics and transcriptomics reveal defense mechanism of rice (Oryza sativa) grains under stress of 2,2',4,4'-tetrabromodiphenyl ether

2,2',4,4'-Tetrabromodiphenyl ether (BDE-47), a predominant polybrominated diphenyl ether (PBDE), has received extensive attention for its potential environmental impact. An integrated study of metabolomics and transcriptomics was conducted on two rice (Oryza sativa) cultivars, Lianjing-7 (LJ-7) and Yongyou-9 (YY-9), which have been identified as tolerant and sensitive cultivars to BDE-47, respectively. The objective was to investigate the molecular mechanisms of their different ability to tolerate BDE-47. Both rice plants were cultivated to maturity in soils containing three concentrations of BDE-47 (10, 20, and 50 mg/kg). Metabolomic analyses of rice grains identified 65 metabolites in LJ-7 and 45 metabolites in YY-9, including amino acids, saccharides, organic acids, fatty acids, and secondary metabolites. In the tolerant cultivar LJ-7 exposed to 50 mg/kg BDE-47, concentrations of most of the metabolites increased significantly, with α-ketoglutaric acid increased by 20-fold and stigmastanol increased by 12-fold. In the sensitive cultivar YY-9, the concentrations of most metabolites increased after the plant was exposed to 1 and 10 mg/kg BDE-47 but decreased after the plant was exposed to 50 mg/kg BDE-47. Transcriptomic data demonstrated that regulation of gene expressions was affected most in LJ-7 exposed to 50 mg/kg BDE-47 (966 genes up-regulated and 620 genes down-regulated) and in YY-9 exposed to 10 mg/kg BDE-47 (85 genes up-regulated and 291 genes down-regulated), in good accordance with the observed metabolic alternation in the two cultivars. Analyses of metabolic pathways and KEGG enrichment revealed that many biological processes, including energy consumption and biosynthesis, were perturbed in the two rice cultivars by BDE-47. A majority of metabolites and genes involved in dominating pathways of energy consumption (e.g., tricarboxylic acid cycle) and the biosynthesis (e.g., metabolism of saccharides and amino acids) were enhanced in LJ-7 by BDE-47. In contrast, energy consumption was increased while biosynthetic processes were inhibited in YY-9 by BDE-47, which could lead to the sensitivity of YY-9 to BDE-47. The combined results suggest that the different defensive abilities of these two rice cultivars in response to BDE-47 could be attributed to their differences in energy-consumption strategy and biosynthesis of nutritional components in grains. This study provides a useful reference for rice cultivation in PBDE-polluted areas.

Phytotoxicity induced by engineered nanomaterials as explored by metabolomics: Perspectives and challenges

Given the wide applications of engineered nanomaterials (ENMs) in various fields, the ecotoxicology of ENMs has attracted much attention. The traditional plant physiological activity (e.g., reactive oxygen species and antioxidant enzymes) are limited in that they probe one specific process of nanotoxicity, which may result in the loss of understanding of other important biological reactions. Metabolites, which are downstream of gene and protein expression, are directly related to biological phenomena. Metabolomics is an easily performed and efficient tool for solving the aforementioned problems because it involves the comprehensive exploration of metabolic profiles. To understand the roles of metabolomics in phytotoxicity, the analytical methods for metabolomics should be organized and discussed. Moreover, the dominant metabolites and metabolic pathways are similar in different plants, which determines the universal applicability of metabolomics analysis. The analysis of regulated metabolism will globally and scientifically help determine the ecotoxicology that is induced by ENMs. In the past several years, great developments in nanotoxicology have been achieved using metabolomics. However, many knowledge gaps remain, such as the relationships between biological responses that are induced by ENMs and the regulation of metabolism (e.g., carbohydrate, energy, amino acid, lipid and secondary metabolism). The phytotoxicity that is induced by ENMs has been explored by metabolomics, which is still in its infancy. The detrimental and defence mechanisms of plants in their response to ENMs at the level of metabolomics also deserve much attention. In addition, owing to the regulation of metabolism in plants by ENMs affected by multiple factors, it is meaningful to uniformly identify the key influencing factor.

Comparative molecular and metabolic responses of wheat seedlings (Triticum aestivum L.) to the imazethapyr enantiomers S-IM and R-IM

The enantioselective effects of imazethapyr (IM) enantiomers on wheat seedlings in a hydroponic medium were studied. R-IM at 0.05mg/L exerted a stronger inhibitory effect on shoot weight and root weight than 0.05mg/L S-IM, suggesting that R-IM more severely inhibited growth. Oxidative damage, based on the anthocyanin content, malondialdehyde (MDA) content, antioxidant enzyme activities and transcript levels of antioxidant enzyme genes, were studied together with the cellular ultrastructure of wheat leaves. The anthocyanin and MDA contents in the R-IM treatment group were significantly increased compared with those in the control group, but no significant changes were observed in the S-IM treatment group. The antioxidant enzyme activities of CAT and SOD were inhibited by 0.32- and 0.73-fold, respectively, in the 14day R-IM treatment group compared to those in the control. However, the transcript levels of antioxidant enzyme genes, including CuZnSOD, POD and CAT, were downregulated in the 14day R-IM exposure group, but those of DHAR were not. The number and size of starch granules increased and chloroplast swelling was observed in wheat leaf cells after R-IM exposure, which showed that photosynthetic functions were potentially disturbed. These results directly or indirectly imply that R-IM exposure causes more oxidative stress and exerts a stronger negative effect on wheat than S-IM. A metabolomics approach revealed that the tricarboxylic acid cycle was heavily suppressed by R-IM treatment. Some amino acids (proline, threonine, lysine, valine) were increased by only the R-IM treatment, indicating the activation of antioxidant pathways. The decrease in a series of fatty acids implied that the cell membrane composition changed in response to R-IM. These results provide a deeper understanding of the enantioselective effects of IM enantiomers on the molecular and metabolic responses in wheat seedlings.

Transcriptome Reveals the Rice Response to Elevated Free Air CO2 Concentration and TiO2 Nanoparticles

Increasing CO₂ levels are speculated to change the effects of engineered nanomaterials in soil and on plant growth. How plants will respond to a combination of elevated CO₂ and nanomaterials stress has rarely been investigated, and the underlying mechanism remains largely unknown. Here, we conducted a field experiment to investigate the rice (Oryza sativa L. cv. IIyou) response to TiO₂ nanoparticles (nano-TiO₂, 0 and 200 mg kg^-1) using a free-air CO₂ enrichment system with different CO₂ levels (ambient ∼370 μmol mol^-1 and elevated ∼570 μmol mol^-1). The results showed that elevated CO₂ or nano-TiO₂ alone did not significantly affect rice chlorophyll content and antioxidant enzyme activities. However, in the presence of nano-TiO₂, elevated CO₂ significantly enhanced the rice height, shoot biomass, and panicle biomass (by 9.4%, 12.8%, and 15.8%, respectively). Furthermore, the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that genes involved in photosynthesis were up-regulated while most genes associated with secondary metabolite biosynthesis were down-regulated in combination-treated rice. This indicated that elevated CO₂ and nano-TiO₂ might stimulate rice growth by adjusting resource allocation between photosynthesis and metabolism. This study provides novel insights into rice responses to increasing contamination under climate change.

Applications of metabolomics in assessing ecological effects of emerging contaminants and pollutants on plants

Metabolomics, the global profiling of metabolite composition, is a powerful technique that can be applied to answer a diverse set of research questions concerning effects of toxicants on organisms. It has recently emerged as a tool to understand complex environmental perturbations in biological systems, especially at sub-lethal concentrations. Organisms can be affected by different stressors such as xenobiotics or increase in concentration of natural compounds such as nitrogen, phosphorous, and sulfur. Metabolomics has facilitated a better understanding of the effects of these perturbations on organisms such as plants, animals, and humans providing phenotypic and biological information in a high throughput manner. In this review, we will discuss recent applications of metabolomics to study the ecological effects of different environmental perturbations, including nanoparticles, pharmaceuticals and personal care products, pesticides, as well as the changes in natural compounds found in the environment with a focus on plant systems.

Nanoparticle TiO2 size and rutile content impact bioconcentration and biomagnification from algae to daphnia

Little information is available about effect of particle size and crystal structure of nTiO₂ on their trophic transfer. In this study, 5 nm anatase, 10 nm anatase, 100 nm anatase, 20 nm P25 (80% anatase and 20% rutile), and 25 nm rutile nTiO₂ were selected to investigate the effects of size and crystal structure on the toxicity, bioconcentration, and trophic transfer of nTiO₂ to algae and daphnia. In the exposed daphnids, metabolic pathways affected by nTiO₂ and nTiO₂-exposed algae (nTiO₂-algae) were also explored. The 96 h IC₅₀ values of algae and the 48 h LC₅₀ values of daphnia were 10.3, 18.9, 43.9, 33.6, 65.4 mg/L and 10.5, 13.2, 37.0, 28.4, 60.7 mg/L, respectively, after exposed to nTiO₂-5A, nTiO₂-10A, nTiO₂-100A, nTiO₂-P25, and nTiO₂-25R, respectively. The bioconcentration factors (BCFs) for 0.1, 1, and 10 mg/L nTiO₂ in daphnia ranged from 21,220 L/kg to 145,350 L/kg. The nTiO₂ biomagnification factors (BMFs) of daphnia fed with 1 and 10 mg/L nTiO₂-exposed algae were consistently greater than 1.0 (5.7-122). The results show that the acute toxicity, BCF, and BMF all decreased with increasing size or rutile content of nTiO₂. All types of nTiO₂ were largely accumulated in the daphnia gut and were not completely depurated within 24 h. At the molecular level, 22 Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways of daphnia were impacted by the nTiO₂ and nTiO₂-algae treatments, including glutathione metabolism, aminoacyl-tRNA biosynthesis, among others. Six and four KEGG metabolic pathways were significantly disturbed in daphnids exposed to nTiO₂ and nTiO₂-algae, respectively, indicating the presence of algae partially alleviated the negative impact of nTiO₂ on metabolism. These findings increase understanding of the impacts of physicochemical properties of nTiO₂ on the food chain from molecular scale to that of the whole organism, and provide new insight into the ecological effect of nanomaterials.

Toxic Effects of TiO₂ NPs on Zebrafish

Titanium dioxide nanoparticles (TiO₂ NPs) have become a widely used nanomaterial due to the photocatalytic activity and absorption of ultraviolet light of specific wavelengths. This study investigated the toxic effects of rutile TiO₂ NPs on zebrafish by examining its embryos and adults. In the embryo acute toxicity test, exposure to 100 mg/L TiO₂ NPs didn’t affect the hatching rate of zebrafish embryos, and there was no sign of deformity. In the adult toxicity test, the effects of TiO₂ NPs on oxidative damage in liver, intestine and gill tissue were studied. Enzyme linked immunosorbent assay (ELISA) and fluorescence-based quantitative real-time reverse transcription PCR (qRT-PCR) were used to detect the three antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT) and glutathione S transferase (GSTs) in the above mentioned zebrafish organs at protein and gene levels. The results showed that long-term exposure to TiO₂ NPs can cause oxidative damage to organisms; and compared with the control group, the activity of the three kinds of enzyme declined somewhat at the protein level. In addition, long-term exposure to TiO₂ NPs could cause high expression of CAT, SOD and GSTs in three organs of adult zebrafish in order to counter the adverse reaction. The effects of long-term exposure to TiO₂ NPs to adult zebrafish were more obvious in the liver and gill.

Phytotoxic effects of silver nanoparticles and silver ions to Arabidopsis thaliana as revealed by analysis of molecular responses and of metabolic pathways

The acute (3 days) and chronic (whole life history) responses of Arabidopsis thaliana following exposure to silver nanoparticles (AgNPs) and Ag⁺ ions (AgNO₃) in respectively a hydroponic medium and in soil were studied. After 3 days of hydroponic exposure, AgNPs (1.0 and 2.5 mg/L) exerted more severe inhibitory effects on plant (shoot and root) growth and photosynthesis than the same concentrations of Ag⁺ ions. In soil cultivation, the photoperiod, the autonomous, and the vernalization pathways were down-regulated to 0.15- to 0.5-fold of the control after 12.5 mg/kg AgNPs treatment. This exposure caused a decrease of approximately 25%-40% as compared to the control of the transcription of flowering key genes including AP1, LFY, FT and SOC1, and finally resulted in a delayed flowering time of 5 days. Only autonomous and vernalization pathways were inhibited by Ag⁺ ion treatment and ultimately the time of flowering in treated plants was delayed by 3 days. The energy production related metabolic pathways in the tricarboxylic acid cycle and in sugar metabolism were stimulated stronger by AgNPs than by Ag⁺ ion treatment, thus releasing more energy and accelerating the physiological metabolic responses against stress in the AgNPs treatment while subsequently reducing the plant growth and yield at the maturation stage. Importantly, shikimate-phenylpropanoid biosynthesis, and tryptophan and galactose metabolisms were regulated only by the AgNPs treatment, which was a specific effect of nanoparticles. This work provides a systematic understanding at the molecular, physiological as well as metabolic level of the effects of AgNPs and Ag⁺ ions in A. thaliana.

Can nano-SiO2 reduce the phytotoxicity of acetaminophen? - A physiological, biochemical and molecular approach

This study aimed at evaluating the interactive effects of acetaminophen (AC; 400 mg kg^-1) and silicon dioxide nanomaterial (nano-SiO₂;3 mg kg^-1) on soil-grown barley. After 14 days of growth, plant growth, evaluated in terms of fresh and dry weight, was greatly inhibited by AC, independently of being or not co-treated with nano-SiO₂. Plants growing under high levels of AC did not show any increase in malondialdehyde (MDA) nor thiols contents, though levels of superoxide anion (O₂^.-) and hydrogen peroxide (H₂O₂) were increased in leaves and roots, respectively. When plants were co-treated with nano-SiO₂, reactive oxygen species (ROS) content remained unchanged, but lipid peroxidation (LP) was diminished and the thiol redox network was up-regulated in roots. The evaluation of the response of the antioxidant system showed that AC affected both non-enzymatic and enzymatic components in an organ-specific manner: proline levels and superoxide dismutase (SOD) activity were enhanced, whilst catalase (CAT) activity decreased in leaves; ascorbate content and CAT activity were diminished in roots. In response to the nano-SiO₂ co-treatment, this pattern was not vastly altered, despite for ascorbate peroxidase (APX), whose activity was greatly enhanced in both organs. Overall, combining biometric, biochemical and molecular approaches, this study revealed that, although AC impaired plant growth and development, it did not trigger a harsh oxidative stress condition. Maybe by this reason, the ameliorating potential of nano-SiO₂ was not so evident; yet, nano-SiO₂ was able to reduce LP and to stimulate thiol content and APX activity, possibly as a defense mechanism against AC-induced stress.

Effects of the exposure of TiO2 nanoparticles on basil (Ocimum basilicum) for two generations

There is a lack of information about the transgenerational effects of titanium dioxide nanoparticles (nano-TiO₂) in plants. This study aimed to evaluate the impacts of successive exposure of nano-TiO₂ with different surface properties to basil (Ocimum basilicum). Seeds from plants exposed or re-exposed to pristine, hydrophobic, or hydrophilic nano-TiO₂ were cultivated for 65 days in soil unamended or amended with 750 mg·kg^-1 of the respective particles. Plant growth, concentration of titanium and essential elements, as well as content of carbohydrates and chlorophyll were evaluated. There were no differences on Ti concentration in roots of plants sequentially exposed to pristine or hydrophobic nano-TiO₂, or in roots of plants exposed to the corresponding particle, only in the second cycle. However, sequential exposure to hydrophilic particles resulted in 65.2% less Ti in roots, compared to roots of plants exposed the same particles, only in the second cycle. The Ti concentrations in shoots were similar in all treatments. On the other hand, pristine and hydrophilic particles reduced Mg in root by 115% and 81%, respectively, while pristine and hydrophobic particles reduced Ni in shoot by 84% and 75%, respectively, compared to unexposed plants in both cycles. Sequential exposure to pristine nano-TiO₂ increased stomatal conductance (214%, p ≤ 0.10), compared to plants that were never exposed. Hydrophobic and hydrophilic nano-TiO₂ reduced chlorophyll b (52%) and total chlorophyll (30%) but increased total sugar (186%) and reducing sugar (145%), compared to unexposed plants in both cycles. Sequential exposure to hydrophobic or hydrophilic nano-TiO₂ resulted in more adverse effects on photosynthesis but in positive effects on plant growth, compared to pristine nano-TiO₂.

Enhanced organic contaminants accumulation in crops: Mechanisms, interactions with engineered nanomaterials in soil

The mechanism of enhanced accumulation of organic contaminants in crops with engineered nanomaterials (ENMs) were investigated by co-exposure of crops (Ipomoea aquatica Forsk (Swamp morning-glory), Cucumis sativus L. (cucumber), Zea mays L. (corn), Spinacia oleracea L. (spinach) and Cucurbita moschata (pumpkin))to a range of chemicals (polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polybrominated diphenyl ether (PBDE)) and ENMs (TiO₂, Ag, Al₂O₃, graphene, carbon nanotubes (CNTs)) in soil. Induced by 50 mg kg^-1 graphene co-exposure, the increase range of BDE-209, BaP, p,p'-DDE, HCB, PYR, FLU, ANT, and PHEN in the plants were increased in the range of 7.51-36.42, 5.69-32.77, 7.09-59.43, 11.61-66.73, 4.58-57.71, 5.79-109.07, 12.85-109.76, and15.57-127.75 ng g^-1, respectively. The contaminants in ENMs-spiked and control soils were separated into bioavailable, bound and residual fractions using a sequential ultrasonic extraction procedure (SUEP) to investigate the mechanism of the enhanced accumulation. The bioavailable fraction in spiked soils showed no significant difference (p > 0.05) from that in the control, while the bound fraction increased in equal proportion (p > 0.05) to the reduction in the residual fraction. These results implied that ENMs can competitively adsorbed the bound of organic contaminants from soil and co-transferred into crops, followed by a portion of the residual fraction transferred to the bound fraction to maintain the balance of different fractions in soils. The mass balance was all higher than 98.5%, indicating the portion of degraded contaminants was less than 1.5%. These findings could expand our knowledge about the organic contaminants accumulation enhancement in crops with ENMs.

Metabolomic analysis of two rice (Oryza sativa) varieties exposed to 2, 2', 4, 4'-tetrabromodiphenyl ether

Polybrominated diphenyl ethers (PBDEs) are toxic chemicals widely distributed in the environment, but few studies are available on their potential toxicity to rice at metabolic level. Therefore we exposed ten rice (Oryza sativa) varieties to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a predominant congener of PBDEs, in hydroponic solutions with different concentrations. Two varieties that showed different biological effects to BDE-47, YY-9 and LJ-7, were screened as sensitive and tolerant varieties according to changes of morphological and physiological indicators. Metabolic research was then conducted using gas chromatography-mass spectrometry combined with diverse analyses. Results showed that LJ-7 was more active in metabolite profiles and adopted more effective antioxidant defense machinery to protect itself against oxidative damages induced by BDE-47 than YY-9. For LJ-7, the contents of 13 amino acids and 24 organic acids, especially l-glutamic acid, beta-alanine, glycolic acid and glyceric acid were up-regulated significantly which contributed to scavenging reactive oxygen species. In the treatment of 500 μg/L BDE-47, the contents of these four metabolites increased by 33.6-, 19.3-, 10.6- and 10.2-fold, respectively. The levels of most saccharides (such as d-glucose, lactulose, maltose, sucrose and d-cellobiose) also increased by 1.7-12.4 fold which promoted saccharide-related biosynthesis metabolism. Elevation of tricarboxylic acid cycle and glyoxylate and dicarboxylate metabolism enhanced energy-producing processes. Besides, the contents of secondary metabolites, chiefly polyols and glycosides increased significantly to act on defending oxidative stress induced by BDE-47. In contrast, the levels of most metabolites decreased significantly for YY-9, especially those of 13 amino acids (by 0.9%-67.1%) and 19 organic acids (by 7.8%-70.0%). The positive metabolic responses implied LJ-7 was tolerant to BDE-47, while the down-regulation of most metabolites indicated the susceptible nature of YY-9. Since metabolic change might affect the yield and quality of rice, this study can provide useful reference for rice cultivation in PBDEs-polluted areas.

The phytotoxicities of decabromodiphenyl ether (BDE-209) to different rice cultivars (Oryza sativa L.)

Decabromodiphenyl ether (BDE-209), as a major component of brominated flame retardants, has been detected in the agricultural soil in considerable amount. Given that BDE-209 is toxic, ubiquitous and persistent, BDE-209 might induce toxic effects on rice cultivars planted in contaminated soil. A comparative study was conducted on phytotoxicities and GC-MS based antioxidant-related metabolite levels to investigate the differences of phytotoxicities of BDE-209 to rice cultivars in Yangtze River Delta of China. Rice seedlings were treated with BDE-209 at 0, 10, 50, 100 and 500 μg/L in a hydroponic setup. Results showed that BDE-209-induced phytotoxicites were cultivar-dependent and that the antioxidant defense systems in the cultivars were disturbed differently. Among the three selected cultivars (Jiayou 5, Lianjing 7 and Yongyou 9), Jiayou 5 and Lianjing 7 displayed lower toxic effects than Yongyou 9 in terms of the growth inhibition, lipid peroxidation and DNA damage. The increases of antioxidant enzymes were significantly higher in Jiayou 5 and Lianjing 7 than those in Yongyou 9. Multivariate analysis of antioxidant-related metabolites in the three cultivars indicated that l-tryptophan and l-valine were the most important ones among 10 metabolites responsible for the separation of cultivars. The up-regulation of l-tryptophan and l-valine were likely plant strategies to increase their tolerance. The current results provided an insight into the development of rice cultivars with higher BDE-209 tolerance.

Plant Response to Metal-Containing Engineered Nanomaterials: An Omics-Based Perspective

The increasing use of engineered nanomaterials (ENMs) raises questions regarding their environmental impact. Improving the level of understanding of the genetic and molecular basis of the response to ENM exposure in biota is necessary to accurately assess the true risk to sensitive receptors. The aim of this Review is to compare the plant response to several metal-based ENMs widely used, such as quantum dots, metal oxides, and silver nanoparticles (NPs), integrating available "omics" data (transcriptomics, miRNAs, and proteomics). Although there is evidence that ENMs can release their metal components into the environment, the mechanistic basis of both ENM toxicity and tolerance is often distinct from that of metal ions and bulk materials. We show that the mechanisms of plant defense against ENM stress include the modification of root architecture, involvement of specific phytohormone signaling pathways, and activation of antioxidant mechanisms. A critical meta-analysis allowed us to identify relevant genes, miRNAs, and proteins involved in the response to ENMs and will further allow a mechanistic understanding of plant-ENM interactions.