The toxicity to plants of the sewage sludges containing multiwalled carbon nanotubes

Emerging concern of nano-pollution in agro-ecosystem: Flip side of nanotechnology

Nanomaterials (NMs) have proven to be a game-changer in agriculture, showcasing their potential to boost plant growth and safeguarding crops. The agricultural sector has widely adopted NMs, benefiting from their small size, high surface area, and optical properties to augment crop productivity and provide protection against various stressors. This is attributed to their unique characteristics, contributing to their widespread use in agriculture. Human exposure from various components of agro-environmental sectors (soil, crops) NMs residues are likely to upsurge with exposure paths may stimulates bioaccumulation in food chain. With the aim to achieve sustainability, nanotechnology (NTs) do exhibit its potentials in various domains of agriculture also have its flip side too. In this review article we have opted a fusion approach using bibliometric based analysis of global research trend followed by a holistic assessment of pros and cons i.e. toxicological aspect too. Moreover, we have also tried to analyse the current scenario of policy associated with the application of NMs in agro-environment.

Carbon nanotubes in plant dynamics: Unravelling multifaceted roles and phytotoxic implications

Carbon nanotubes (CNTs) have emerged as a promising frontier in plant science owing to their unique physicochemical properties and versatile applications. CNTs enhance stress tolerance by improving water dynamics and nutrient uptake and activating defence mechanisms against abiotic and biotic stresses. They can be taken up by roots and translocated within the plant, impacting water retention, nutrient assimilation, and photosynthesis. CNTs have shown promise in modulating plant-microbe interactions, influencing symbiotic relationships and mitigating the detrimental effects of phytopathogens. CNTs have demonstrated the ability to modulate gene expression in plants, offering a powerful tool for targeted genetic modifications. The integration of CNTs as sensing elements in plants has opened new avenues for real-time monitoring of environmental conditions and early detection of stress-induced changes. In the realm of agrochemicals, CNTs have been explored for their potential as carriers for targeted delivery of nutrients, pesticides, and other bioactive compounds. CNTs have the potential to demonstrate phytotoxic effects, detrimentally influencing both the growth and developmental processes of plants. Phytotoxicity is characterized by induction of oxidative stress, impairment of cellular integrity, disruption of photosynthetic processes, perturbation of nutrient homeostasis, and alterations in gene expression. This review aims to provide a comprehensive overview of the current state of knowledge regarding the multifaceted roles of CNTs in plant physiology, emphasizing their potential applications and addressing the existing challenges in translating this knowledge into sustainable agricultural practices.

Structural characteristics of dissolved black carbon and its interactions with organic and inorganic contaminants: A critical review

Biochar (BC) is a sustainable and renewable carbonaceous material, and its soluble component, dissolved black carbon (DBC), is the key to understanding BC's geological and environmental processes. Although the relationship between the changes in DBC structure and its properties, functions, and associated environmental risks has been explored, a gap remains in our understanding of DBC's fate and behavior in the natural environment. Thus, in this review, we have highlighted the molecular and chemical compositions and the structural evolution of DBC during pyrolysis, the influence of DBC's physicochemical properties on its fate and transport, DBC's interaction with soil and its contaminants, and DBC stability in soil and water environments along with potential risks. Based on our in-depth assessment of DBC and its biogeochemical roles, we believe that future studies should focus on the following: (1) using advanced techniques to understand the chemical and molecular structure of DBC deeply and concisely and, thus, determine its fundamental role in the natural environment; (2) investigating the multi-functional properties of DBC and its interaction mechanisms; and (3) evaluating the environmental behaviors of and risks associated with DBC after BC application. In future, it is necessary to gain a deeper insight into the fate and transport of DBC with contaminants and study its associated risks under BC application in the environment.

Toxicity of biochar influenced by aging time and environmental factors

The extensive application of biochar has drawn more attentions on its potential risk to aquatic organisms. However, the influence of environmental factors (i.e. pH, HA, SDBS and aging time) after they discharged into environment on their toxicity have not been clarified. Here, we synthesized biochar with local pine needles via pyrolysis, and then aged in different media. Followed, the toxicity of pristine and aged biochar was checked with Scenedesmus obliquus (S. obliquus). Our investigation showed that the toxicity of biochar was mitigated when aged in different pH levels or SDBS, while it was opposite in the presence of HA. The increment of pH decreased the toxicity of both the pristine and the aged biochar, while the presence of HA did same impact on the pristine biochar. The presence of SDBS decreased the toxicity of pristine biochar but increased that of aged biochar. Meanwhile, we showed these environmental factors (pH, HA, SDBS and aging time) influenced the biochar toxicity may be due to the adjustment of the aggregation and adhesion of biochar on cell surfaces or the intracellular oxidative stress. Further, the PFRs contained in biochar did influence the toxicity, along with the physicochemical properties of biochar (i.e. carbon structure, functional group or surface charge). Our results aimed to reflect the toxicity profile of biochar in the natural aquatic environment, without misunderstanding of potential ecological risk of biochar in the future application.

Interactive effects of metals and carbon nanotubes in a microcosm agrosystem

Agricultural soils are exposed to multiple contaminants through the use of agrochemicals or sewage sludge, introducing metals, nanomaterials and others. Among nanomaterials, carbon nanotubes (CNTs) are known for their large surface area and adsorption capabilities, possibly modifying other element behavior. However, to date, very little is known about the impacts of such interactions in agrosystems. In this study, we aimed at understanding the transfer and toxicity of contaminants (Cd, Pb, Zn and CNTs) in microcosms including native soil bacteria, earthworms and lettuce. After a 6 week exposure, no effect of the addition of CNTs to metal contaminated soils was detected on bacterial concentration or earthworm growth. However, in lettuce, an interactive effect between CNTs and metals was highlighted: in the soil containing the highest metal concentrations the addition of 0.1 mg kg^-1 CNTs led to a biomass loss (-22%) and a flavonoid concentration increase (+27%). In parallel, the addition of CNTs led to differential impacts on elemental uptake in lettuce leaves possibly related to the soil organic matter content. For earthworms, the addition of 10 mg kg^-1 CNTs resulted in an increased body elemental transfer in the soil with the higher organic matter content (Pb: + 34% and Zn: + 25%).

Metal/Metalloid-Based Nanomaterials for Plant Abiotic Stress Tolerance: An Overview of the Mechanisms

In agriculture, abiotic stress is one of the critical issues impacting the crop productivity and yield. Such stress factors lead to the generation of reactive oxygen species, membrane damage, and other plant metabolic activities. To neutralize the harmful effects of abiotic stress, several strategies have been employed that include the utilization of nanomaterials. Nanomaterials are now gaining attention worldwide to protect plant growth against abiotic stresses such as drought, salinity, heavy metals, extreme temperatures, flooding, etc. However, their behavior is significantly impacted by the dose in which they are being used in agriculture. Furthermore, the action of nanomaterials in plants under various stresses still require understanding. Hence, with this background, the present review envisages to highlight beneficial role of nanomaterials in plants, their mode of action, and their mechanism in overcoming various abiotic stresses. It also emphasizes upon antioxidant activities of different nanomaterials and their dose-dependent variability in plants' growth under stress. Nevertheless, limitations of using nanomaterials in agriculture are also presented in this review.

Implication of Wood-Derived Hierarchical Carbon Nanotubes for Micronutrient Delivery and Crop Biofortification

A similarity of metal alloy encapsulation with the micronutrient loading in carbon nanoarchitecture can be fueled by exploring carbon nanocarriers to load micronutrient and controlled delivery for crop biofortification. A wood-derived nanoarchitecture model contains a few-graphene-layer that holds infiltrated alloy nanoparticles. Such wood-driven carbonized framework materials with legions of open porous architectures and minimized-tortuosity units further decorated carbon nanotubes (CNTs), which originate from heat treatment to carbonized wood samples. These wood-derived samples can alleviate micronutrient nanoparticle permeation and delivery to the soil. A rapid heat shock treatment can help in distributing N-C-NiFe metal alloy encapsulation in carbon frameworks uniformly in that case; higher heating and rapid extinction of heat shock have led to formation of good dispersion of nanoparticles. The wood-carbon framework decorated with metal alloys displays promising electrocatalytic features and cyclic stability for hydrogen evolution. Envisaged from this strategy, we obtain enough evidence to form an opinion that a singular heat shock process can even lead to a strategy of faster growth of a wood-carbon network with well-dispersed micronutrient metal salts in porous matrices for high-efficiency delivery to the soil. Having envisaged the formation of ultrafine nanoparticles with a good dispersion profile in the case of transition metals and alloy encapsulation in the carbon network due to the rapid heating and quenching rates, we anticipate that the loading of micronutrients in the wood-derived nanoarchitecture of carbonized wood derived carbon nanotube (CW-CNT), which can offer an application in seed germination and enhance growth rates of crops. The experience of controlled experiments on germination of tomato seeds on a medium containing CW-CNT that can diffuse the seed coat with the promotion of water uptake inside seeds for enhanced germination and growth of tomato seedlings can be further extended to cereal crops.

Multi-Wall Carbon Nanotubes Promote the Growth of Maize (Zea mays) by Regulating Carbon and Nitrogen Metabolism in Leaves

Previous studies have suggested that multiwalled carbon nanotubes (MWCNTs) promote plant growth; however, the mechanism is yet to be fully understood. In this study, the effects of MWCNTs (20, 100, and 500 mg/L) on the carbon (C) and nitrogen (N) metabolism in maize were studied to explore the molecular mechanism of the action of MWCNTs on plants. The results showed that 100 mg/L MWCNTs increased the shoot fresh and dry weight, root fresh weight, and seedling length while other doses showed no significant effects. Further studies showed that 100 mg/L MWCNTs increased the chlorophyll content, transpiration rate, stomatal conductance, and intercellular CO₂ concentration, by 50.6%, 60.8%, 47.2%, and 32.1%, respectively. Activities of key enzymes including sucrose synthase (SS), sucrose phosphate synthase (SPS) and phosphoenolpyruvate carboxylase (PEPC) that are involved in the carbon metabolism, and nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthetase (GOGAT) that are involved in N metabolism, were all upregulated by 100 mg/L MWCNTs, which contributed to the increase of the accumulation of carbohydrates (sugar and starch), soluble protein, and N in plants. These findings suggest that MWCNTs can improve plant growth by regulating the key enzymes involved in C and N metabolism thereby enhancing the carbohydrate production and the use of N and improving plant growth. This study provides significant insights into the molecular mechanism of the positive effects of MWCNTs on plants and provide a basis for the agricultural application of MWCNTs.

A Novel Mechanism Underlying Multi-walled Carbon Nanotube-Triggered Tomato Lateral Root Formation: the Involvement of Nitric Oxide

Abundant studies revealed that multi-walled carbon nanotubes (MWCNTs) are toxic to plants. However, whether or how MWCNTs influence lateral root (LR) formation, which is an important component of the adaptability of the root system to various environmental cues, remains controversial. In this report, we found that MWCNTs could enter into tomato seedling roots. The administration with MWCNTs promoted tomato LR formation in an approximately dose-dependent fashion. Endogenous nitric oxide (NO) production was triggered by MWCNTs, confirmed by Greiss reagent method, electron paramagnetic resonance (EPR), and laser scanning confocal microscopy (LSCM), together with the scavenger of NO. A cause-effect relationship exists between MWCNTs and NO in the induction of LR development, since MWCNT-triggered NO synthesis and LR formation were obviously blocked by the removal of endogenous NO with its scavenger. The activity of NO generating enzyme nitrate reductase (NR) was increased in response to MWCNTs. Tungstate inhibition of NR not only impaired NO production, but also abolished LR formation triggered by MWCNTs. The addition of NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of mammalian nitric oxide synthase (NOS)-like enzyme, failed to influence LR formation. Collectively, we proposed that NO might act as a downstream signaling molecule in MWCNT control of LR development, at least partially via NR.

Nanoparticles Used for Extraction of Polycyclic Aromatic Hydrocarbons

This article offers a review on the application of nanoparticles (NPs) that have been used as sorbents in the analysis of polycyclic aromatic hydrocarbons (PAHs). The novel advances in the application of carbon NPs, mesoporous silica NPs, metal, metal oxides, and magnetic and magnetised NPs in the extraction of PAHs from matrix solutions were discussed. The extraction techniques used to isolate PAHs have been highlighted including their advantages and limitations. Methods for preparing NPs and optimized conditions of NPs extraction efficiency have been overviewed since proper extraction procedures were necessary to achieve optimum analytical results. The aim was to provide an overview of current knowledge and information in order to assess the need for further exploration that can lead to an efficient and optimum analysis of PAHs.

Toxicity of carbon nanotubes to white rot fungus Phanerochaete chrysosporium

Carbon nanotubes (CNTs) are widely used in diverse areas with increasing annual production, thus the environmental impact of CNTs needs thorough investigation. In this study, we evaluated the effect of pristine multi-walled CNTs (p-MWCNTs) and oxidized multi-walled CNTs (o-MWCNTs) on white rot fungus Phanerochaete chrysosporium, which is the decomposer in carbon cycle and also has many applications in environmental remediation. Both p-MWCNTs and o-MWCNTs had no influence on the dry weight increase of P. chrysosporium and the pH value of culture system. The fibrous structure of P. chrysosporium was disturbed by p-MWCNTs seriously, while o-MWCNTs had litter influence. The ultrastructural changes were more evident for P. chrysosporium exposed to p-MWCNTs and only p-MWCNTs could penetrate into the cell plasma. The chemical composition of P. chrysosporium was nearly unchanged according to the infrared spectra. The laccase activity was suppressed by p-MWCNTs, while o-MWCNTs showed stimulating effect. The decoloration of reactive brilliant red X-3B was not affected by both CNT samples. However, serious inhibition of wood degradation was observed in the p-MWCNTs exposed groups, suggesting the potential threat of CNTs to the decomposition of carbon cycle. The implication to the environmental risks and safe applications of carbon nanomaterials is discussed.

Nontoxic fluorescent carbon nanodot serving as a light conversion material in plant for UV light utilization

In this study, water-soluble fluorescent carbon nanodots (CNDs) were directly injected into the leaf of nicotiana tabacum. With the help of UV-to-blue light conversion nanomaterial, the photosynthetic rate of the leaf was improved 18% upon additional 6 W UV irradiation. The photostability and toxicity of different kinds of CNDs were discussed. The results showed that CNDs functionalized with NH2-groups on their surfaces could maintain good fluorescence in plant leaf, and CNDs with complex surface groups tended to have high toxicity to the plant. The NH2-functionalized CNDs with non-toxicity and good photostability were used as in vivo light conversion material for direct utilization of UV light in the solar energy.

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.

Fate and transformation of nanoparticles (NPs) in municipal wastewater treatment systems and effects of NPs on the biological treatment of wastewater: a review

Fate, transformation of NPs in WWTP & effects on wastewater treatment.

Illumina MiSeq sequencing reveals long-term impacts of single-walled carbon nanotubes on microbial communities of wastewater treatment systems

In this study, phenol wastewater treatment systems treated with different concentrations of single-walled carbon nanotubes (SWCNTs) (0-3.5g/L) were exposed to phenol and carbon nanotubes (CNTs) shock loadings to investigate the long-term impacts of SWCNTs on microbial communities. Phenol removal remained high efficiency (>98%) in SWCNTs-treated groups but decreased in non-treated group (85.1±1.9%) when exposed to high concentration of phenol (500mg/L). However, secondary dosing of SWCNTs in SWCNTs-treated groups would decrease the phenol removal efficiency. Illumina MiSeq sequencing revealed that the diversity, richness and structure of microbial communities were shifted under phenol shock loading, especially under high phenol concentration, but not under CNTs shock loading. In response to phenol and CNTs shock loadings, Rudaea, Burkholderia, Sphingomonas, Acinetobacter, Methylocystis and Thauera became dominant genera, which should be involved in phenol removal. These results suggested that a proper amount of SWCNTs might have positive effects on phenol wastewater treatment systems.

Interactions of carbon nanotubes with aqueous/aquatic media containing organic/inorganic contaminants and selected organisms of aquatic ecosystems--A review

Due to their unique molecular architecture translating into numerous every-day applications, carbon nanotubes (CNTs) will be ultimately an increasingly significant environmental contaminant. This work reviews qualitative/quantitative analyses of interactions of various types of CNTs and their chemically modified analogues with aqueous/aquatic media containing organic and inorganic contaminants and selected organisms of aquatic ecosystems. A special emphasis was placed on physicochemical interactions between CNTs as adsorbents of heavy metal cations and aromatic compounds (dyes) with its environmental consequences. The studies revealed CNTs as more powerful adsorbents of aromatic compounds (an order of magnitude higher adsorption capacity) than metal cations. Depending on the presence of natural organic matter (NOM) and/or co-contaminants, CNTs may act as Trojan horse while passing through biological membranes (in the absence of NOM coordinating metal ions). Nanotubes, depending on flow conditions and their morphology/surface chemistry, may travel with natural waters or sediment with immobilized PAHs or metals and/or increase cyto- and ecotoxicity of PAHs/metal ions by their release via competitive complexation, or cause synergic ecotoxicity while adsorbing nutrients. Additionally, toxicity of CNTs against exemplary aquatic microorganisms was reviewed. It was found for Daphnia magna that longer exposures to CNTs led to higher ecotoxicity with a prolonged CNTs excretion. SWCNTs were more toxic than MWCNTs, while hydrophilization of CNTs via oxidation or anchoring thereto polar/positively charged polymer chains enhanced stability of nanotubes dispersion in aqueous media. On the other hand, bioavailability of functionalized CNTs was improved leading to more complex both mechanisms of uptake and cytotoxic effects.

The influence of multiwalled carbon nanotubes on polycyclic aromatic hydrocarbon (PAH) bioavailability and toxicity to soil microbial communities in alfalfa rhizosphere

Carbon nanotubes (CNTs) may affect bioavailability and toxicity of organic contaminants due to their adsorption properties. Recent studies have observed the influence of multiwalled carbon nanotubes (MWNTs) on the fate of polycyclic aromatic hydrocarbons (PAHs) and other organic contaminants. Greenhouse studies (49 d) were conducted with alfalfa plants in two different soil types. Four treatment conditions (0, 25, 50, or 100 mg/kg MWNTs+100 mg/kg PAHs mixture-pyrene and phenanthrene) were tested in order to determine their effects on soil microbial community composition and PAH residues. Microbial community structure in the two highest treatments (50 mg/kg and 100 mg/kg MWNTs) showed a dramatic shift in the presence of MWNTs in sandy loam soil (1% organic matter) in comparison to the control (0 mg/kg MWNTs). Many microbial fatty acid methyl ester (FAMEs) markers (i15:0, 16:1ω5c, 10Me17:0, 10Me16:0) were missing in the control soil. However, there was a lower abundance of these FAMEs in the 25 mg/kg MWNT treatment (except 10Me17:0) and a higher presence of these FAMEs in the 50 mg/kg and 100 mg/kg MWNT treatments compared to control. In contrast, microbial community composition was not influenced by the MWNT treatments in sandy clay loam soil (5.9% organic matter). However, pyrene degradation in sandy clay loam soil significantly increased by 21% in the highest MWNT treatment group (100 mg/kg) and 9.34% in 50 mg/kg MWNT treatment. Under the conditions tested in this study, MWNTs significantly impacted the soil microbial community distribution and PAH degradation and effects were dependent on soil types, specifically organic matter content.

Study on the correlation between copper oxide nanoparticles induced growth suppression and enhanced lignification in Indian mustard (Brassica juncea L.)

In this study, the morphological, physiological and molecular level effects of copper oxide nanoparticles (CuONPs) were studied in an economically important oil seed crop Brassica juncea L. The possible involvement of lignification on shoot-root growth retardation was also studied. The seedlings were exposed to 0, 20, 50, 100, 200, 400 and 500mg/L of CuONPs in semi-solid half strength Murashige and Skoog medium under controlled growth chamber conditions for 14 days. Exposure to CuONPs resulted in suppression of shoot-growth, reduction in total chlorophyll and carotenoids contents as well modification of root system architecture such as shortening of primary and lateral roots. Significant increases in hydrogen peroxide formation, peroxidase enzyme activity and lignification of shoots and roots were observed. The lipid peroxidation levels increased significantly in shoots and roots of B. juncea seedlings. Phloroglucinol-HCl staining revealed enhanced lignification of shoot and roots. Gene expression studies revealed significant activation of CuZn superoxide dismutase (CuZnSOD) in roots at all concentrations of CuONPs exposure. In shoots significant up-regulation of CuZnSOD gene was observed upon exposure to 100, 200 and 400 mg/L of CuONPs exposure. However no change in the expression levels of MnSOD gene was observed in both stem and roots. The expression of catalase (CAT) and ascorbate peroxidase (APX) genes were also not changed in shoots. However, significant inhibition of CAT and APX genes were observed in roots of B. juncea plants under exposure to 100, 200, 400 and 500 mg/L of CuONPs exposure. The SOD enzyme activity significantly increased in roots under exposure to 50-500 mg/L of CuONPs and in shoots as a result of exposure to 100-500 mg/L of CuONPs. The APX activity significantly decreased in roots upon exposure to 50-500 mg/L of CuONPs. In shoots, the APX activity significantly decreased upon exposure to 200-500 mg/L of CuONPs.

A mechanistic study on the toxic effect of copper oxide nanoparticles in soybean (Glycine max L.) root development and lignification of root cells

Copper oxide nanoparticles (CuONPs) are widely used in several products and their release into the environment can cause toxicity to major food crops. In this study, toxic responses as a result of CuONPs exposure were studied in soybean (Glycine max L.) seedlings. The plants were grown in 1/2 strength Murashige and Skoog medium containing 0, 50, 100, 200, 400, and 500 mg/L of CuONPs in a growth chamber at 26 ± 2 °C with 16/8 h light/dark photoperiod for 14 days. The toxic effects of CuONPs were tested on the shoot and root development, total chlorophyll content, hydrogen peroxide generation, peroxidase (POD) enzyme activity, and lignification of root cells. The mRNA expression of different genes involved in lignin biosynthesis viz. phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD), peroxidase 2 (POD2), peroxidase 4 (POD4), and peroxidase 7 (POD7) was studied using real-time polymerase chain reaction. Exposure to 500 mg/L of CuONPs significantly reduced the shoot growth, weight, and total chlorophyll content. However, the root length and fresh weights were significantly reduced at all concentrations of CuONPs exposure. Exposure to 100, 200, 400, and 500 mg/L of CuONPs significantly increased the hydrogen peroxide level, POD activity, and lignin contents of roots. Treatment with 2,7-dichlorofluorescein diacetate indicated a concentration-dependent increase in reactive oxygen species generation in roots. Staining with phloroglucinol-HCl revealed a concentration dependant increase in lignification of root cells. The expression levels of PAL, C4H, and CAD genes were significantly up-regulated upon exposure to 100, 200, and 400 mg/L of CuONPs. Significant up-regulation in the expression levels of POD2 and POD4 genes was observed upon exposure to 100, 200, 400, and 500 mg/L of CuONPs. Exposure to 200, 400, and 500 mg/L of CuONPs resulted in significant up-regulation of POD7 gene. These results for the first time show that exposure to CuONPs causes enhanced lignification of root cells and thereby affect root development in soybean seedlings.

Physiological and molecular level effects of silver nanoparticles exposure in rice (Oryza sativa L.) seedlings

The physiological and molecular level changes of silver nanoparticles (AgNPs) exposure were investigated in rice (Oryza sativa L.) seedlings. The seedlings were exposed to different concentrations of (0, 0.2, 0.5 and 1 mg L(-1)) AgNPs for one week. Significant reduction in root elongation, shoot and root fresh weights, total chlorophyll and carotenoids contents were observed. Exposure to 0.5 and 1 mg L(-1) of AgNPs caused significant increase in hydrogen peroxide formation and lipid peroxidation in shoots and roots, increased foliar proline accumulation and decreased sugar contents. AgNPs exposure resulted in a dose dependant increase in reactive oxygen species generation and also caused cytotoxicity as evidenced by increased dihydroethidium, 3'-(p-hydroxyphenyl) fluorescein and propidium iodide fluorescence. Tetramethylrhodamine methyl ester assay showed decreased mitochondrial membrane potential with increasing concentrations of AgNPs exposure in roots. Real Time PCR analysis showed differential transcription of genes related to oxidative stress tolerance viz. FSD1, MSD1, CSD1, CSD2, CATa, CATb, CATc, APXa and APXb in shoots and roots of rice seedlings. The overall results suggest that exposure to AgNPs caused significant physiological and molecular level changes, oxidative stress and also resulted in the induction oxidative stress tolerance mechanisms in rice seedlings.

Carbon and fullerene nanomaterials in plant system

Both the functionalized and non functionalized carbon nanomaterials influence fruit and crop production in edible plants and vegetables. The fullerene, C60 and carbon nanotubes have been shown to increase the water retaining capacity, biomass and fruit yield in plants up to ~118% which is a remarkable achievement of nanotechnology in recent years. The fullerene treated bitter melon seeds also increase the phytomedicine contents such as cucurbitacin-B (74%), lycopene (82%), charantin (20%) and insulin (91%). Since as little as 50 μg mL-1 of carbon nanotubes increase the tomato production by about 200%, they may be exploited to enhance the agriculture production in future. It has been observed that, in certain cases, non functionalized multi-wall carbon nanotubes are toxic to both plants and animals but the toxicity can be drastically reduced if they are functionalized.

Fabricated nanoparticles: current status and potential phytotoxic threats

Nanotechnology offers unique attributes to various industrial and consumer sectors, and has become a topic of high interest to scientific communities across the world. Our society has greatly benefitted from nanotechnology already, in that many products with novel properties and wide applicability have been developed and commercialized. However, the increased production and use of nanomaterials have raised concerns about the environmental fate and toxicological implications of nanoparticles and nanomaterials. Research has revealed that various nanomaterials may be hazardous to living organisms. Among biota, plants are widely exposed to released nanomaterials and are sensitive to their effects. The accumulation of nannmaterials in the environment is a potential threat, not only because of potential damage to plants hut also because nanoparticles may enter the food chain. Although the literature that addresses the safety of nanoproducts is growing, little is known about the mechanisms by which these materials produce toxicity on natural species, including humans. In this paper, we have reviewed the literature relevant to what phytotoxic impact fabricated nanoparticles (e.g., carbon nanotubes, metallic and metal oxide nanoparticles, and certain other nanomaterials) have on plants. Nanoparticles produce several effects on plant physiology and morphology. Nanoparticles are known to affect root structure, seed germination, and cellular metabolism. Nanoparticles inhibit growth, induce oxidative stress, morphogenetic abnormalities and produce clastogenic disturbances in several plant species. The size, shape and surface coating of NPs play an important role in determining their level of toxicity. Of course, the dose, route of administration, type of dispersion media, and environmental exposure also contribute to how toxic nanoparticles are to plants. Currently, nanotoxicity studies are only in their initial phases of development and more research will be required to identify the actual threat nanoproducts pose to the plant system. To date, data show that there is a large variation in the phytotoxicity caused by different NPs. Moreover, the studies conducted thus far have mostly relied on microscopy to detect effects. Studies that incorporate measures and analyses undertaken with more modern tools are needed. Among new data that are most urgently needed on NPs is how fabricated NPs behave once released into the environment, and how exposure to them may affect plant resistance, metabolic pathways, and plant genetic responses. In this review, we have attempted to collect, present and summarize recent findings from the literature on nanoparticle toxicity in plants. To strengthen the analysis, we propose a scheme for accessing NP toxicity. We also recommend how the potential challenges presented by increased production and release of NPs should be addressed. It is our belief and recommendation that every nanomaterial-based product be subjected to appropriate toxicity and associated assessment before being commercialized.

Assessment of silver nanoparticle-induced physiological and molecular changes in Arabidopsis thaliana

In this study, the effect of silver nanoparticles and silver ions on Arabidopsis thaliana was investigated at physiological and molecular levels. The seedlings were grown in sublethal concentrations of silver nanoparticles and silver ions (0.2, 0.5, and 1 mg/L) in 1/4 Hoagland's medium for 14 days under submerged hydroponic conditions. Significantly higher reduction in the total chlorophyll and increase in anthocyanin content were observed after exposure to 0.5 and 1 mg/L silver nanoparticles as compared to similar concentrations of silver ions. Lipid peroxidation increased significantly after exposure to 0.2, 0.5, and 1 mg/L of silver nanoparticles and 0.5 and 1 mg/L of silver ions. Qualitative analysis with dichloro-dihydro-fluorescein diacetate and rhodamine 123 fluorescence showed a dose-dependent increase in reactive oxygen species production and changes in mitochondrial membrane potential in the roots of seedlings exposed to different concentrations of silver nanoparticles. Real-time PCR analysis showed significant upregulation in the expression of sulfur assimilation, glutathione biosynthesis, glutathione S-transferase, and glutathione reductase genes upon exposure to silver nanoparticles as compared with silver ions. Overall, based on the physiological and molecular level responses, it was observed that exposure to silver nanoparticles exerted more toxic response than silver ions in A. thaliana.

Effects of nano-TiO₂ on photosynthetic characteristics of Ulmus elongata seedlings

The physiological and ecological responses of Ulmus elongata to different concentrations of nano-anatase TiO2 solutions were investigated in this study and we found that with foliar application of 0.1% (T1), 0.2% (T2) and 0.4% (T3) nano-anatase TiO2 solution the net photosynthetic rate of U. elongata seedlings were lower, comparing with the control (CK) (no spraying). TiO2 solution had no effect on the carbon isotope values (δ(13)C), indicating the lower photosynthetic capacity was not caused by stomatal limitation. The nitrogen isotope values (δ(15)N) decreased, but the foliar metal elements, such as Mg, K and Mn contents were not affected by nano-anatase TiO2 which promoted the Cu uptake. Fourier transform infrared spectroscopy showed that the nano-anatase TiO2 enhanced the absorbance of U. elongata leaves, especially for 1064, 1638, 2926 and 3386 cm(-1) bands, indicating the synthesis of carbohydrate and lipid compounds was a kind of mechanism under the toxic effects of nanonanoparticles.

The influence of ZnO and TiO2 nanoparticles on the toxicity of sewage sludges

More and more often sewage sludges become the place of deposition of nanoparticles (NPs), the use of which in consumer products is increasing. In turn, the increasing amount of sewage sludges enforces the need for their utilization (e.g. through the application of sludges to the soil). Therefore, the presence of NPs in sewage sludges may create a new threat to the environment. Thus it becomes important to perform evaluation of the toxicity of sewage sludges in the context of their content of NPs. The objective of the study was to estimate the effect of nanoparticles of ZnO (nano-ZnO) and TiO2 (nano-TiO2) and their bulk counterparts (bZnO and bTiO2) on the toxicity of sewage sludges in relation to selected organisms (plants – Lepidium sativum and Sinapis alba, and microorganisms – Vibrio fischeri and 11 different strains from Microbial Assay for Risk Assessment – MARA). The study also involved the estimation of other factors that may have an effect on the phytotoxicity of NPs in sewage sludge: the size of the particles, the dose of the sewage sludge, the time of NP–sewage sludge contact and light conditions. The effect of both nano-ZnO and nano-TiO2 on the toxicity of the sludges is dependent on the kind of NPs and their concentration. Sludges containing NPs displayed a different level of toxicity from their bulk counterparts. All of the factors estimated (size of particles, dose of sludge, contact time and light conditions) had a significant effect on the phytotoxicity of NPs which was dependent both on the kind of the NPs and on that of the sewage sludge. Estimation of the leachate toxicity indicated a greater sensitivity of plants to the presence of NPs as compared to the sensitivity of microorganisms. Leachates caused a greater reduction of bioluminescence of V. fischeri in the presence of nano-TiO2 than nano-ZnO. Nano-ZnO caused a reduction of the toxicity of the sewage sludge leachates.

Effect of magnetic nanoparticles on tobacco BY-2 cell suspension culture

Nanomaterials are structures whose exceptionality is based on their large surface, which is closely connected with reactivity and modification possibilities. Due to these properties nanomaterials are used in textile industry (antibacterial textiles with silver nanoparticles), electronics (high-resolution imaging, logical circuits on the molecular level) and medicine. Medicine represents one of the most important fields of application of nanomaterials. They are investigated in connection with targeted therapy (infectious diseases, malignant diseases) or imaging (contrast agents). Nanomaterials including nanoparticles have a great application potential in the targeted transport of pharmaceuticals. However, there are some negative properties of nanoparticles, which must be carefully solved, as hydrophobic properties leading to instability in aqueous environment, and especially their possible toxicity. Data about toxicity of nanomaterials are still scarce. Due to this fact, in this work we focused on studying of the effect of magnetic nanoparticles (NPs) and modified magnetic nanoparticles (MNPs) on tobacco BY-2 plant cell suspension culture. We aimed at examining the effect of NPs and MNPs on growth, proteosynthesis - total protein content, thiols - reduced (GSH) and oxidized (GSSG) glutathione, phytochelatins PC2-5, glutathione S-transferase (GST) activity and antioxidant activity of BY-2 cells. Whereas the effect of NPs and MNPs on growth of cell suspension culture was only moderate, significant changes were detected in all other biochemical parameters. Significant changes in protein content, phytochelatins levels and GST activity were observed in BY-2 cells treated with MNPs nanoparticles treatment. Changes were also clearly evident in the case of application of NPs. Our results demonstrate the ability of MNPs to negatively affect metabolism and induce biosynthesis of protective compounds in a plant cell model represented by BY-2 cell suspension culture. The obtained results are discussed, especially in connection with already published data. Possible mechanisms of NPs' and MNPs' toxicity are introduced.

Utilization of municipal sewage sludge as additives for the production of eco-cement

The effects of using dried sewage sludge as additive on cement property in the process of clinker burning were investigated in this paper. The eco-cement samples were prepared by adding 0.50-15.0% of dried sewage sludge to unit raw meal, and then the mixtures were burned at 1450 °C for 2 h. The results indicated that the major components in the eco-cement clinkers were similar to those in ordinary Portland cement. Although the C(2)S phase formation increased with the increase of sewage sludge content, it was also found that the microstructure of the mixture containing 15.0% sewage sludge in raw meal was significantly different and that a larger amount of pores were distributed in the clinker. Moreover, all the eco-cement pastes had a longer initial setting time and final setting time than those of plain cement paste, which increased as the sewage sludge content in the raw meal increased. All the eco-cement pastes had lower early flexural strengths, which increased as the sewage sludge content increased, while the compressive strengths decreased slightly. However, this had no significant effect on all the strengths at later stages. Furthermore, the leaching concentrations of all the types of eco-cement clinkers met the standard of Chinese current regulatory thresholds.