Uptake, translocation and ligand of silver in Lactuca sativa exposed to silver nanoparticles of different size, coatings and concentration

Silver nanoparticles in plant health: Physiological response to phytotoxicity and oxidative stress

Silver nanoparticles (AgNPs) have gained significant attention in various fields due to their unique properties, but their release into the environment has raised concerns about their environmental and biological impacts. Silver nanoparticles can enter plants following their exposure to roots or via stomata following foliar exposure. Upon penetrating the plant cells, AgNPs interact with cellular components and alter physiological and biochemical processes. One of the key concerns associated with plant exposure to AgNPs is the potential of these materials to induce oxidative stress. Silver nanoparticles can also suppress plant growth and development by disrupting essential plant physiological processes, such as photosynthesis, nutrient uptake, water transport, and hormonal regulation. In crop plants, these disruptions may, in turn, affect the productivity and quality of the harvested components and therefore represent a potential threat to agricultural productivity and ecosystem stability. Understanding the phytotoxic effects of AgNPs is crucial for assessing their environmental implications and guiding the development of safe nanomaterials. By delving into the phytotoxic effects of AgNPs, this review contributes to the existing knowledge regarding their environmental risks and promotes the advancement of sustainable nanotechnological practices.

Bioavailability and translocation of platinum nanoparticles and platinum ions in rice (Oryza sativa L.): Nanoparticles biosynthesis and size-dependent transformation

Metal nanoparticles accumulation and bioavailability in plants raised much attention, specifically transformation and transportation of nanoparticles and their corresponding ions in plants are still unknown. In this work, rice seedlings were exposed to platinum nanoparticles (PtNPs) (with three sizes of 25, 50, and 70 nm) and Pt ions (with doses of 1, 2, and 5 mg/L) to investigate the influences of particle size and Pt form on bioavailability and translocation mechanism of metal nanoparticles. Results based on single particle ICP-MS (SP-ICP-MS) demonstrated the biosynthesis of PtNPs in Pt ions treated rice seedlings. The particle size ranges at 75-79.3 nm were detected in Pt ions exposed rice roots, and further migrated up to rice shoots at 21.7-44.3 nm. After exposed to PtNP-25, the particles could transfer to shoots with the original size distribution detected in roots, even with the PtNPs dose change. PtNP-50 and PtNP-70 translocated to shoots with the particle size increase. For the rice exposure with three dose levels, PtNP-70 had the highest number-based bioconcentration factors (NBCFs) in all Pt species, while Pt ions had the highest bioconcentration factors (BCFs), a range of 1.43-2.04. All PtNPs and Pt ions could be accumulated in rice plants and further transferred to shoots, and particle biosynthesis was proved through SP-ICP-MS. The finding could help us better understand the influence of particle size and form on the transformations of PtNPs in environment.

Phytotoxic impact of bifunctionalized silver nanoparticles (AgNPs-Cit-L-Cys) and silver nitrate (AgNO3) on chronically exposed callus cultures of Populus nigra L

Owing to the unique physicochemical properties and the low manufacturing costs, silver nanoparticles (AgNPs) have gained growing interest and their application has expanded considerably in industrial and agricultural sectors. The large-scale production of these nanoparticles inevitably entails their direct or indirect release into the environment, raising some concerns about their hazardous aspects. Callus culture represents an important tool in toxicological studies to evaluate the impact of nanomaterials on plants and their potential environmental risk. In this study, we investigated the chronic phytotoxic effects of different concentrations of novel bifunctionalized silver nanoparticles (AgNPs-Cit-L-Cys) and silver nitrate (AgNO3) on callus culture of Populus nigra L., a pioneer tree species in the riparian ecosystem. Our results showed that AgNPs-Cit-L-Cys were more toxic on poplar calli compared to AgNO3, especially at low concentration (2.5 mg/L), leading to a significant reduction in biomass production, accompanied by a decrease in protein content, a significant increase in both lipid peroxidation level, ascorbate peroxidase (APX), and catalase (CAT) enzymatic activities. In addition, these findings suggested that the harmful activity of AgNPs-Cit-L-Cys might be correlated with their physicochemical properties and not solely attributed to the released Ag+ ions and confirmed that AgNPs-Cit-L-Cys phytoxicity is associated to oxidative stress.

Uptake of Silver-Containing Nanoparticles in an Estuarine Plant: Speciation and Bioaccumulation

Understanding the bioaccumulation of silver-containing nanoparticles (Ag-NPs) with different species, concentrations, and sizes in estuarine plants is critical to their related environmental risk. Herein, the distribution of Ag-NPs in tidewater, sediments, and plants (Scirpus triqueter) of field-constructed mesocosm was investigated, where tidewater was exposed to Ag0-NPs and Ag+ at environmentally relevant concentrations. Particle number concentrations (PNCs) and sizes of Ag-NPs with various species were analyzed using a multistep selective dissolution method followed by the single-particle- inductively coupled plasma mass spectrometry technique. After 30 days of exposure, more than half of Ag0-NPs were dissolved to Ag+ and about 1/4 of Ag+ were transformed into Ag0-/AgCl-NPs in tidewater. Ag-NPs in stems exposed to Ag0-NPs were found to be dominated by metallic Ag, while Ag+ exposure led to more Ag2S-NPs in stems. In roots, 71% and 51% of Ag-NPs were found as Ag2S-NPs for Ag0-NPs and Ag+ treatment groups, respectively. Plant stems had a significantly higher enrichment of Ag-NPs than roots. Based on both random forests and structure equation models, it is suggested that salinity of tidewater can regulate Ag0-NPs in tidewater indirectly by influencing AgCl-NPs in tidewater and further affect the total PNCs of Ag-NPs in plant stems. Moreover, elevated sulfate-reducing bacteria (SRB) result in more Ag2S-NPs in rhizosphere sediments, thereby enhancing the bioaccumulation of Ag-NPs by roots.

The Occurrence of Oxidative Stress Induced by Silver Nanoparticles in Chlorella vulgaris Depends on the Surface-Stabilizing Agent

Silver nanoparticles (AgNPs) are of great interest due to their antimicrobial properties, but their reactivity and toxicity pose a significant risk to aquatic ecosystems. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by agents that affect their physicochemical properties. In this study, microalga Chlorella vulgaris was used as a model organism to evaluate the effects of AgNPs in aquatic habitats. Algae were exposed to AgNPs stabilized with citrate and cetyltrimethylammonium bromide (CTAB) agents and to AgNO₃ at concentrations that allowed 75% cell survival after 72 h. To investigate algal response, silver accumulation, ROS content, damage to biomolecules (lipids, proteins, and DNA), activity of antioxidant enzymes (APX, PPX, CAT, SOD), content of non-enzymatic antioxidants (proline and GSH), and changes in ultrastructure were analyzed. The results showed that all treatments induced oxidative stress and adversely affected algal cells. AgNO₃ resulted in the fastest death of algae compared to both AgNPs, but the extent of oxidative damage and antioxidant enzymatic defense was similar to AgNP-citrate. Furthermore, AgNP-CTAB showed the least toxic effect and caused the least oxidative damage. These results highlight the importance of surface-stabilizing agents in determining the phytotoxicity of AgNPs and the underlying mechanisms affecting aquatic organisms.

Silver nanoparticles affect wheat (Triticum aestivum L.) germination, seedling blight and yield

The aim of the study was to evaluate the effect of two types of negatively charged quasi-spherical silver nanoparticles (AgNPs) at concentrations of 10, 20 and 30mgL-1 and silver ions at a concentration of 30mgL-1 on the growth, selected physiological aspects and yielding of wheat (Triticum aestivum L.) cv. Tybalt, and on plant resistance to seedling blight. Seed germination, α-amylase activity in seeds, morphology and infestation of seedlings by pathogens were assessed in a hydroponic treatment. Growth rate, PSII efficiency, heading and yield of the same plants were then analysed in pot culture. Results showed that the AgNPs and silver ions had a negative effect on roots, but reduced seedling blight and improved leaf area compared to the control. In addition, the AgNPs reduced with sodium borohydride in the presence of trisodium citrate at concentrations of 10 and 20mgL-1 stimulated germination, α-amylase activity and shoot length, which was not observed in the case of silver ions and the AgNPs reduced with sodium hypophosphite in the presence of sodium hexametaphosphate. In a pot experiment, the AgNPs improved plant growth, PSII efficiency, accelerated heading and increased yield-related parameters compared with the control. Results revealed the interaction strength in the following order: TCSB-AgNPs>SHSH-AgNPs>silver ions. TCSB-AgNPs in the lowest concentration had the most favourable effect, indicating their great potential for use in improving wheat cultivation.

Effects of Platinum Nanoparticles on Rice Seedlings (Oryza sativa L.): Size-dependent Accumulation, Transformation, and Ionomic Influence

Platinum nanoparticles (PtNPs) are increasing in the environment largely due to their wide use and application in automobile and medical industries. The mechanism of uptake behavior of different-sized PtNPs and their association with PtNPs-induced phytotoxicity to plants remains unclear. The present study investigated PtNP uptake mechanisms and phytotoxicity simultaneously to further understand the accumulation and transformation dynamics. The uptake mechanisms were investigated by comparing the uptake and toxicological effects of three different-sized PtNPs (25, 50, and 70 nm) on rice seedlings across an experimental concentration gradient (0.25, 0.5, and 1 mg/L) during germination. The quantitative and qualitative results indicated that 70 nm-sized PtNPs were more efficiently transferred in rice roots. The increase in the PtNP concentration restricted the particle uptake. Particle aggregation was common in plant cells and tended to dissolve on root surfaces. Notably, the dissolution of small particles was simultaneous with the growth of larger particles after PtNPs entered the rice tissues. Ionomic results revealed that PtNP accumulation induced element homeostasis in the shoot ionome. We observed a significant positive correlation between the PtNP concentration and Fe and B accumulation in rice shoots. Compared to particle size, the exposure concentration of PtNPs had a stronger effect on the shoot ionomic response. Our study provides better understanding of the correlation of ionomic change and NP quantitative accumulation induced by PtNPs in rice seedlings.

Micro- and nano-plastics pollution and its potential remediation pathway by phytoremediation

This review proposed that phytoremediation could be applied for the decontamination of MPs/NPs. Micro- and nano-plastics (MPs < 5 mm; NPs < 100 nm) are emerging contaminants. Much of the recent concerns have focused on the investigation of their pollution and their potential eco-toxicity. Yet little review was available on the decontamination of MPs/NPs. Recently, the uptake of MPs/NPs by plants has been confirmed. Here, in view of the current knowledge, this review introduces MPs/NPs pollution and highlights the updated information about the interaction between MPs/NPs and plants. This review proposed that phytoremediation could be a potential possible way for the in situ remediation of MPs/NPs-contaminated environment. The possible mechanisms, influencing factors, and existing problems are summarized, and further research needs are proposed. This review herein provides new insights into the development of plant-based process for emerging pollutants decontamination, as well as the alleviation of MPs/NPs-induced toxicity to the ecosystem.

Nanoparticle-based toxicity in perishable vegetable crops: Molecular insights, impact on human health and mitigation strategies for sustainable cultivation

With the advancement of nanotechnology, the use of nanoparticles (NPs) and nanomaterials (NMs) in agriculture including perishable vegetable crops cultivation has been increased significantly. NPs/NMs positively affect plant growth and development, seed germination, plant stress management, and postharvest handling of fruits and vegetables. However, these NPs sometimes cause toxicity in plants by oxidative stress and excess reactive oxygen species production that affect cellular biomolecules resulting in imbalanced biological and metabolic processes in plants. Therefore, information about the mechanism underlying interactions of NPs with plants is important for the understanding of various physiological and biochemical responses of plants, evaluating phytotoxicity, and developing mitigation strategies for vegetable crops cultivation. To address this, recent morpho-physiological, biochemical and molecular insights of nanotoxicity in the vegetable crops have been discussed in this review. Further, factors affecting the nanotoxicity in vegetables and mitigation strategies for sustainable cultivation have been reviewed. Moreover, the bioaccumulation and biomagnification of NPs and associated phytotoxicity can cause serious effects on human health which has also been summarized. The review also highlights the use of advanced omics approaches and interdisciplinary tools for understanding the nanotoxicity and their possible use for mitigating phytotoxicity.

Mitigation of lead toxicity in Vigna radiata genotypes by silver nanoparticles

Heavy metal (HM) contamination of the soil through anthropogenic activities influences the living systems and drastically impacts food chain. This study examined the application of silver nanoparticles (AgNPs) in two genotypes (G1 and G2) of Mung bean (Vigna radiata) for ameliorating the Pb toxicity. Different doses of Pb (0, 25, 50 μM) were differentially tackled by AgNPs with the aim of ameliorating the plant attributes. Both genotypes displayed statistically significant quantitative and qualitative modulations for Pb tolerance. In G2, the most prominent increase in plant height (43.79%), fresh biomass (49.56%) and total chlorophyll (20%) was observed at L2 (AgNPs 10 mg/L) in comparison with the control. Overall, photosynthetic rate was increased by 26% in G2 at L6 (AgNPs 25 mg/L + Pb 25 μM). In addition, the results presented 78.5% increase in water use efficiency of G2 while G1 experienced a maximum internal CO₂ concentration (209.8%) at L8 (Pb 50 μM). AgNPs triggered balanced uptake of minerals and improved growth of Vigna genotypes. 50 μM Pb was most hazardous and caused maximum reduction in growth of Vigna plants along with a significant suppression in photosynthetic activity, increase in MDA (199.7%) in G1 and H₂O₂ (292.8%) in G2. In comparison to control, maximum superoxide dismutase (376%), peroxidase (659.8%) and catalase (9.3%) activity was observed in G2 at L11. The application of AgNPs substantially enhanced plant growth and helped them in surviving well in absence as well as presence of Pb. G2 genotype exhibited substantial tolerance capability and revealed less impairment in the studied attributes than G1 and treatment of AgNPs i.e. 25 mg/L was the best level that yielded best results in both genotypes. The results demonstrate that AgNPs mediate response(s) of plants under Pb stress and particularly contributed to HM tolerance of plants and thus showing great promise for use in phytoremediation.

Effects of sulfidation of silver nanoparticles on the Ag uptake kinetics in Brassica rapa plants

Land application of sewage sludge containing increasing levels of silver nanoparticles (AgNPs) raises concerns about the risk for plant exposure. This study compared the uptake kinetics and distribution of Ag in Brassica rapa seedlings grown in Lufa 2.2 natural soil spiked with 20 nm Ag₂S NPs, with those from 3 to 8 nm AgNPs, 50 nm AgNPs and AgNO₃ exposures (10 mg Ag/kg dry soil). A two-compartment model was used to describe the uptake kinetics of Ag in plants, distinguishing two stages: stage I with increasing Ag uptake followed by stage II with decreasing Ag uptake. The concentration of Ag in roots from Ag₂S NPs was about 14 and 10 times lower than for the other AgNPs and AgNO₃ exposures, respectively, at the end of stage I, with root translocation rate constants being higher for Ag₂S NPs. In stage II, Ag uptake occurred only for the 50 nm AgNPs. The distribution of Ag in B. rapa exposed to pristine, ionic and sulfidized AgNPs differed at the end of exposure. This study shows that Ag uptake and distribution in plants depends on the Ag form in soil, highlighting the importance of studying the environmentally relevant chemical species in NPs risk assessment.

Silicon nanoparticles decrease arsenic translocation and mitigate phytotoxicity in tomato plants

In this study, we simulate the irrigation of tomato plants with arsenic (As)-contaminated water (from 0 to 3.2 mg L^-1) and investigate the effect of the application of silicon nanoparticle (Si NPs) in the form of silicon dioxide (0, 250, and 1000 mg L^-1) on As uptake and stress. Arsenic concentrations were determined in substrate and plant tissue at three different stratums. Phytotoxicity, As accumulation and translocation, photosynthetic pigments, and antioxidant activity of enzymatic and non-enzymatic compounds were also determined. Our results show that irrigation of tomato plants with As-contaminated water caused As substrate enrichment and As bioaccumulation (roots > leaves > steam), showing that the higher the concentration in irrigation water, the farther As translocated through the different tomato stratums. Additionally, phytotoxicity was observed at low concentrations of As, while tomato yield increased at high concentrations of As. We found that application of Si NPs decreased As translocation, tomato yield, and root biomass. Increased production of photosynthetic pigments and improved enzymatic activity (CAT and APX) suggested tomato plant adaptation at high As concentrations in the presence of Si NPs. Our results reveal likely impacts of As and nanoparticles on tomato production in places where As in groundwater is common and might represent a risk.

Determination of metallic nanoparticles in biological samples by single particle ICP-MS: a systematic review from sample collection to analysis

A systematic review of the use of single particle ICP-MS to analyse engineered nanomaterials (ENMs) in biological samples (plants, animals, body fluids) has highlighted that efforts have focused on a select few types of ENMs (e.g., Ag and TiO₂) and there is a lack of information for some important tissues (e.g., reproductive organs, skin and fatty endocrine organs). The importance of sample storage is often overlooked but plays a critical role. Careful consideration of the ENM and matrix composition is required to select an appropriate protocol to liberate ENMs from a tissue whilst not promoting the transformation of them, or genesis of new particulates. A 'one size fits all' protocol, applicable to all possible types of ENM and biological matrices, does not seem practical. However, alkaline-based extractions would appear to show greater promise for wide applicability to animal tissues, although enzymatic approaches have a role, especially for plant tissues. There is a lack of consistency in metrics reported and how they are determined (e.g. size limit of detection, and proportions of recovery), making comparison between some studies more difficult. In order to establish standardised protocols for regulatory use, effort is needed to: develop certified reference materials, achieve international agree on nomenclature and the use of control samples, and to create a decision tree to help select the best sample preparation for the type of tissue matrix.

Zein and lignin-based nanoparticles as soybean seed treatment: translocation and impact on seed and plant health

Zein nanoparticles (ZNPs) were synthesized with a cationic surfactant, didodecyldimethylammonium bromide (122.9 ± 0.8 nm, + 59.7 ± 4.4 mV) and a non-ionic surfactant, Tween 80 (118.7 ± 1.7 nm, + 26.4 ± 1.1 mV). Lignin-graft-poly(lactic-co-glycolic) acid nanoparticles (LNPs) were made without surfactants (52.9 ± 0.2 nm, − 54.9 ± 0.5 mV). Both samples were applied as antifungal seed treatments on soybeans, and their impact on germination and plant health was assessed. Treated seeds showed high germination rates (> 90% for all treatment groups), similar to the control group (100%). Root and stem lengths and the dry biomass of treated seeds were not statistically distinguishable from the control. Foliage from seed-treated plants was fed to larvae of Chrysodeixis includens with no differences in mortality between treatments. No translocation of fluorescently tagged particles was observed with fluorescence microscopy following seed treatment and germination. Nano-delivered azoxystrobin provided ~ 100% protection when LNPs were used. Results suggest ZNPs and LNPs are safe and effective delivery systems of active compounds for seed treatments.

Uptake, translocation, and transformation of silver nanoparticles in plants

This article reviews the plant uptake of silver nanoparticles (AgNPs) that occurred in soil systems and the in planta fate of Ag.

Surface Coating-Modulated Phytotoxic Responses of Silver Nanoparticles in Plants and Freshwater Green Algae

Silver nanoparticles (AgNPs) have been implemented in a wide range of commercial products, resulting in their unregulated release into aquatic as well as terrestrial systems. This raises concerns over their impending environmental effects. Once released into the environment, they are prone to various transformation processes that modify their reactivity. In order to increase AgNP stability, different stabilizing coatings are applied during their synthesis. However, coating agents determine particle size and shape and influence their solubility, reactivity, and overall stability as well as their behavior and transformations in the biological medium. In this review, we attempt to give an overview on how the employment of different stabilizing coatings can modulate AgNP-induced phytotoxicity with respect to growth, physiology, and gene and protein expression in terrestrial and aquatic plants and freshwater algae.

Trophic Transfer and Toxicity of (Mixtures of) Ag and TiO2 Nanoparticles in the Lettuce-Terrestrial Snail Food Chain

The increasing application of biosolids and agrochemicals containing silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2NPs) results in their inevitable accumulation in soil, with unknown implications along terrestrial food chains. Here, the trophic transfer of single NPs and a mixture of AgNPs and TiO2NPs from lettuce to snails and their associated impacts on snails were investigated. Both AgNPs and TiO2NPs were transferred from lettuce to snails with trophic transfer factors (defined as the ratio of the Ag/Ti concentration in snail tissues to the Ag/Ti concentration in lettuce leaves) of 0.2-1.1 for Ag and 3.8-47 for Ti. Moreover, the majority of Ag captured by snails in the AgNP-containing treatments was excreted via feces, whereas more than 70% of Ti was distributed in the digestive gland of snails in the TiO2NP-containing treatments. Additionally, AgNP-containing treatments significantly inhibited the activity of snails, while TiO2NP-containing treatments significantly reduced feces excretion of snails. Furthermore, the concurrent application of AgNPs and TiO2NPs did not affect the biomagnification and distribution patterns of Ag and Ti in snails, whereas their co-existence exhibited more severe inhibition of the growth and activity of snails than in the case of applying AgNPs or TiO2NPs alone. This highlights the possibility of nanoparticle transfer to organisms of higher trophic levels via food chains and the associated risks to ecosystem health.

Silver nanoparticles in aquatic sediments: Occurrence, chemical transformations, toxicity, and analytical methods

Sediments represent the major sink for released silver nanoparticles (AgNPs) in aquatic environments. It is well known that the environmental behavior and toxicity of AgNPs in sediments are governed by their specific chemical species instead of their total concentration. This review focuses on various chemical transformations of AgNPs in sediments, which have not been well outlined before. We first outline the concentrations of AgNPs in sediments. The predicted concentrations are 1-5 µg kg^-1 in most model studies. Once enter sediments, AgNPs are transformed to different species (e.g., Ag₂S, Ag-humic substance complexes, AgCl, and Ag⁺) during multiple chemical transformations, such as oxidative dissolution, sulfidation, chlorination, and complexation. Those chemical behaviors mitigate the toxicity of AgNPs by reducing their availability and decreasing Ag⁺ release. Benthic invertebrates and microbes are prone to be affected by AgNPs. AgNPs are found to be accumulated in sediment-dwelling organisms and transferred to higher trophic levels along the food web. Besides X-ray absorption spectroscopy, reliable separation procedures coupled with detection techniques, are powerful tools that characterize the speciation of AgNPs in sediments. More research is needed to investigate diverse chemical transformations in various sediments through development of novel techniques and mathematical models.

Plant response to silver nanoparticles: a critical review

Although several metal ions/metal nanoparticles (NPs) are toxic to both plants and animals, some of them are used as nutrients and growth promoters. Plants exposed to silver nanoparticles (Ag-NPs) have shown both beneficial and harmful effects. All concentrations of Ag-NPs are not effective for a given plant because any excess can block the passage of essential nutrients. Regulated treatment of plants by Ag-NPs may enhance their overall growth and development. It has been noticed that Ag-NPs decrease the mass of edible plants (Cucurbita pepo, Allium cepa, cabbage, and lettuce) and vegetables, but they also induce the germination of seeds in many cases. NPs interact with proteins, enzymes, and carbohydrates influencing the total biomass, root, and shoot growth of plants. Also, Ag-NPs act as an ethylene inhibitor and activate the antioxidants in onions. Their substantial quantity becomes deposited in onion leaves and bulbs. Size and concentration are the two major factors responsible for the increase/decrease of plant growth and biomass. Plants make adaptations to reduce the toxicity caused by Ag-NPs. In some cases, Ag-NPs induce root elongation and increase chlorophyll, carbohydrate, proteins, rate of photosynthesis and inhibit the biosynthesis of ethylene. This review article provides a comprehensive overview of both the beneficial and adverse effects of Ag-NPs on germination, growth, development, physiological, and biochemical characteristics of a wide range of edible and crop plants. We have also critically discussed: the chemistry, toxicity, uptake, translocation, and accumulation of Ag-NPs in plant systems.

Blocking effect of fullerene nanoparticles (nC60) on the plant cell structure and its phytotoxicity

Blockage of nanoparticles on plant pore structures might produce phytotoxicity and affect plant uptake indirectly. This study examined the blocking and phytotoxic effects of fullerene nanoparticles (nC₆₀) on plants at the cellular level. The malondialdehyde content in plant was normal during nC₆₀ exposure, implying that nC₆₀ caused no acute phytotoxicity, while the normalized relative transpiration significantly decreased, showing that the pore structure of roots was seriously blocked by nC₆₀. High power optical microscopy and transmission electron microscope showed that root endothelial cells were squeezed, and inner wall structures were damaged by the extrusion of nanoparticles. Low nC₆₀ concentrations inhibited root uptake of lindane, whereas high nC₆₀ concentrations promoted root uptake of lindane, indicating that serious pore blocking by nC₆₀ damaged root cell structure and hence ready transport of lindane from roots to shoots. Significant alterations of fatty acid (FA) saturation degree of root cell membrane indicated that nC₆₀ led to phytotoxicity in the root cell membrane after long-term exposure and nC₆₀ produced phytotoxicity in the process of blocking root pore structures and interfering with cell membrane fluidity. Moreover, the plant cell structures under phytotoxicity were more likely to be damaged mechanically by the extrusion of nanoparticles. These findings may be helpful to better understand the transport pathways of nanoparticles in plants, the phytotoxicity of nanoparticles and the potential risks of nanomaterials used in agriculture.

The fate and long-term toxic effects of NiO nanoparticles at environmental concentration in constructed wetland: Enzyme activity, microbial property, metabolic pathway and functional genes

Although the potential threats of metallic oxide nanoparticles (MNPs) to constructed wetland (CW) have been broadly reported, limited information is available regarding the long-term impact of nickel oxide nanoparticles (NiO NPs) on CWs at the environmentally relevant concentrations. Here, we comprehensively elucidated the responses in the treatment performance, enzyme activities, microbial properties, metabolic pathways and functional genes of CWs to chronic exposure of NiO NPs (0.1 and 1 mg/L) for 120 days, with a quantitative analysis on the fate and migration of NiO NPs within CWs. Nitrogen removal evidently declined under the long-term exposure to NiO NPs. Besides, NiO NPs induced a deterioration in phosphorus removal, but gradually restored over time. The activities of dehydrogenase (DHA), phosphatase (PST), urease (URE), ammonia oxygenase (AMO) and nitrate reductase (NAR) were inhibited to some extent under NiO NPs stress. Furthermore, NiO NPs exposure reduced bacterial diversity, shifted microbial composition and obviously inhibited the transcription of the ammonia oxidizing and denitrifying functional genes. The results of nickel mass balance indicated that the major removal mechanism of NiO NPs in CWs was through substrate adsorption and plants uptake. Thus, the ecological impacts of prolonged NiO NPs exposure at environmental concentrations should not be neglected.

Type-specific impacts of silver on the protein profile of tomato (Lycopersicon esculentum L.)

Silver nanoparticles (AgNPs) are particularly among the widely used nanomaterials in medicine, industry, and agriculture. The small size and large surface area of AgNPs and other nanomaterials result in their high reactivity in biological systems. To better understand the effects of AgNPs on plants at the molecular level, tomato (Lycopersicon esculentum L.) seedlings were exposed to 30 mg/L silver in the form of nanoparticle (AgNPs), ionic (AgNO₃), or bulk (Ag⁰) in 50% Hoagland media for 7 days. The effects of silver on the expression of plant membrane transporters H⁺-ATPase, vacuolar type H⁺-ATPase (V-ATPase), and enzymes isocitrate dehydrogenase (IDH), and catalase in roots was assessed using RT-qPCR and immunofluorescence-confocal microscopy. We observed significantly higher expression of catalase in plants exposed to AgNPs (Fold of expression 1.1) and AgNO₃ (Fold of expression 1.2) than the control group. The immunofluorescence imaging of the proteins confirmed the gene expression data; the expression of the enzyme catalase was upregulated 41, 216, and 770% higher than the control group in plants exposed to AgNPs, Ag⁰, and AgNO₃, respectively. Exposure to AgnO₃ resulted in the upregulation (fold of expression 1.2) of H⁺-ATPase and downregulation (fold of expression 0.7) of V-ATPase. A significant reduction in the expression of the redox-sensitive tricarboxylic cycle (TCA) enzyme mitochondrial IDH was observed in plants exposed to AgNPs (38%), AgNO₃ (48%), or Ag⁰ (77%) compared to the control. This study shows that exposure to silver affects the expression of genes and protein involved in membrane transportation and oxidative response. The ionic form of silver had the most significant effect on the expression of genes and proteins compared to other forms of silver. The results from this study improve our understanding about the molecular effects of different forms of silver on important crop species. Novelty statementSilver nanoparticles released into the environment can be oxidized and be transformed into ionic form. Both the particulate and ionic forms of silver can be taken by plants and affect plants physiological and molecular responses. Despite the extensive research in this area, there is a scarce of information about the effects of silver nanoparticles on the expression of membrane transporters especially H⁺-ATPase involved in regulating cells' electrochemical charge, and the activity of enzymes involved in oxidative stress responses. This is a unique study that evaluates the expression of cellular proton transporters and enzymes of redox balance and energy metabolisms such as membrane transporters, H⁺-ATPase, and V-ATPases, and enzymes catalase and IDH. The results provide us valuable information about the impact of silver on plants at the molecular level by evaluating the expression of genes and proteins. Key MessageThe exposure of plants to silver as an environmental stressor affects the expression of genes and proteins involved in maintaining cell's electrochemical gradient (H⁺-ATPase, V-ATPase) and redox potential (IDH, catalase).

Monitoring chemically and green-synthesized silver nanoparticles in maize seedlings via surface-enhanced Raman spectroscopy (SERS) and their phytotoxicity evaluation

The emergence of nanomaterials in consumer products has increased concern for their potential hazards in the environment and biological systems. Therefore, the monitoring of nanoparticles in biological systems is of great importance. Despite the numerous attempts, the methods to evaluate the uptake, translocation, and accumulation of nanomaterials inside the plant tissue are still limited. In this study, for the first time, we proposed the monitoring of the silver nanoparticles (AgNPs) in different tissues of the plant through surface-enhanced Raman spectroscopy (SERS) approach. For this, chemically (Che-AgNPs) and green-synthesized AgNPs (Gr-AgNPs) were prepared properly and their surfaces were functionalized with Raman-active molecule. With the contribution of electromagnetic enhancement, our NP systems provided high signal-to-noise SERS spectra. After exposure to NPs to maize seedlings as a model plant, we detected that AgNPs were accumulated mainly in the epidermis and cortex of the root and phloem parts of the shoot. Highly distinctive SERS spectra were collected from the root and shoot cross-section of each NP system. Also, the accumulation of the AgNPs was furtherly confirmed through inductively-coupled mass spectrometry and scanning electron microscopy analysis. Moreover, the exposure of AgNPs to maize seedlings led to remarkable alterations in both phytotoxic and biomolecular indicators including chlorophyll, protein and, antioxidant enzymes.

Quantifying the relative contribution of particulate versus dissolved silver to toxicity and uptake kinetics of silver nanowires in lettuce: impact of size and coating

Functionalized high-aspect-ratio silver nanowires (AgNWs) have been recognized as one of the most promising alternatives for fabricating products, with their use ranging from electronic devices to biomedical fields. Given concerns on the safety of AgNWs, there is an urgent need to investigate the relation between intrinsic properties of AgNWs and their toxicity. In this study, lettuce was exposed for either 6 or 18 d to different AgNWs to determine how the size/aspect ratio and coating of AgNWs affect the contributions of the dissolved and particulate Ag to the overall phytotoxicity and uptake kinetics. We found that the uncoated AgNW (39 nm diameter × 8.4 µm length) dissolved fastest of all AgNWs investigated. The phytotoxicity, uptake rate constants, and bioaccumulation factors of the PVP-coated AgNW (43 nm diameter × 1.8 µm length) and the uncoated AgNW (39 nm diameter × 8.4 µm length) were similar, and both were higher than that of the PVP-coated AgNW with the larger diameter(65 nm diameter × 4.4 µm length). These results showed that the diameter of the AgNWs predominantly affected toxicity and Ag accumulation in plants. Particulate Ag was found to be the predominant driver/descriptor of overall toxicity and Ag accumulation in the plants rather than dissolved Ag for all AgNWs tested. The relative contribution of dissolved versus particulate Ag to the overall effects was influenced by the exposure concentration and the extent of dissolution of AgNWs. This work highlights inherent particulate-dependent effects of AgNWs in plants and suggests that toxicokinetics should explicitly be considered for more nanomaterials and organisms, consequently providing more realistic input information for their environmental risk assessment.

Green Synthesis, Characterization, Antimicrobial, Anti-Cancer, and Optimization of Colorimetric Sensing of Hydrogen Peroxide of Algae Extract Capped Silver Nanoparticles

A green and cost-effective technique for the preparation of silver nanoparticles (Algae-AgNPs) as a colorimetric sensor for hydrogen peroxide (H2O2) is described. Silver nanoparticles were capped using the green algae (Noctiluca scintillans) extract at an optimum time of 3 h at 80 °C. The pH of the plant extract (pH = 7.0) yields nanoparticles with a mean size of 4.13 nm and a zeta potential of 0.200 ± 0.02 mV and negative polarity, using dynamic light scattering (DLS). High-resolution transmission electron microscopy (HRTEM) analysis showed regular spherical particles with the average size of 4.5 nm. Selected area electron diffraction (SAED) results revealed the polycrystalline nature of the silver nanoparticles. The obtained patterns were indexed as (111), (200), (220), and (311) reflections of the fcc (face centered cubic) silver crystal based on their d-spacing of 2.47, 2.13, 1.49, and 1.27 Å, respectively. The apparent color change from brown to colorless was observed when nanoparticles reacted with H2O2. Linear responses were obtained in three different ranges (nM, µM, and mM). Limits of detection (LOD) of 1.33 ± 0.02 and 1.77 ± 0.02 nM and quantitation limits (LOQ) of 7.31 ± 0.03 and 9.67 ± 0.03 nM were obtained for Abs and ΔAbs calibration curves, respectively. 10% v/v Algae-AgNPs solution inhibited Staphylococcus aureus over Escherichia coli, while a 50% reduction of tumor cell growth of MDA-MB-231 human breast adenocarcinoma was obtained.

To-Do and Not-To-Do in Model Studies of the Uptake, Fate and Metabolism of Metal-Containing Nanoparticles in Plants

Due to the increasing release of metal-containing nanoparticles into the environment, the investigation of their interactions with plants has become a hot topic for many research fields. However, the obtention of reliable data requires a careful design of experimental model studies. The behavior of nanoparticles has to be comprehensively investigated; their stability in growth media, bioaccumulation and characterization of their physicochemical forms taken-up by plants, identification of the species created following their dissolution/oxidation, and finally, their localization within plant tissues. On the basis of their strong expertise, the authors present guidelines for studies of interactions between metal-containing nanoparticles and plants.

Impact of foliar application of some metal nanoparticles on antioxidant system in oakleaf lettuce seedlings

BACKGROUND

Nanoparticles (NPs) serve various industrial and household purposes, and their increasing use creates an environmental hazard because of their uncontrolled release into ecosystems. An important aspect of the risk assessment of NPs is to understand their interactions with plants. The aim of this study was to examine the effect of Au (10 and 20 ppm), Ag, and Pt (20 and 40 ppm) NPs on oakleaf lettuce, with particular emphasis on plant antioxidative mechanisms. Nanoparticles were applied once on the leaves of 2-week-old lettuce seedlings, after next week laboratory analyses were performed.

RESULTS

The antioxidant potential of oakleaf lettuce seedlings sprayed with metal NPs at different concentrations was investigated. Chlorophylls, fresh and dry weight were also determined. Foliar exposure of the seedlings to metal NPs did not affect ascorbate peroxidase activity, total peroxidase activity increased after Au-NPs treatment, but decreased after applying Ag-NPs and Pt-NPs. Both concentrations of Au-NPs and Pt-NPs tested caused an increase in glutathione (GSH) content, while no NPs affected L-ascorbic acid content in the plants. Ag-NPs and Pt-NPs applied as 40 ppm solution increased total phenolics content by 17 and 15%, respectively, compared to the control. Carotenoids content increased when Ag-NPs and Au-NPs (20 and 40 ppm) and Pt-NPs (20 ppm) were applied. Plants treated with 40 ppm of Ag-NPs and Pt-NPs showed significantly higher total antioxidant capacity and higher concentration of chlorophyll a (only for Ag-NPs) than control. Pt-NPs applied as 40 ppm increased fresh weight and total dry weight of lettuce shoot.

CONCLUSIONS

Results showed that the concentrations of NPs applied and various types of metal NPs had varying impact on the antioxidant status of oakleaf lettuce. Alteration of POX activity and in biosynthesis of glutathione, total phenolics, and carotenoids due to metal NPs showed that tested nanoparticles can act as stress stimuli. However, judging by the slight changes in chlorophyll concentrations and in the fresh and dry weight of the plants, and even based on the some increases in these traits after M-NPs treatment, the stress intensity was relatively low, and the plants were able to cope with its negative effects.

Tackling Complex Analytical Tasks: An ISO/TS-Based Validation Approach for Hydrodynamic Chromatography Single Particle Inductively Coupled Plasma Mass Spectrometry

Nano-carrier systems such as liposomes have promising biomedical applications. Nevertheless, characterization of these complex samples is a challenging analytical task. In this study a coupled hydrodynamic chromatography-single particle-inductively coupled plasma mass spectrometry (HDC-spICP-MS) approach was validated based on the technical specification (TS) 19590:2017 of the international organization for standardization (ISO). The TS has been adapted to the hyphenated setup. The quality criteria (QC), e.g., linearity of the calibration, transport efficiency, were investigated. Furthermore, a cross calibration of the particle size was performed with values from dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to an additional Y-piece, an online-calibration routine was implemented. This approach allows the calibration of the ICP-MS during the dead time of the chromatography run, to reduce the required time and enhance the robustness of the results. The optimized method was tested with different gold nanoparticle (Au-NP) mixtures to investigate the characterization properties of HDC separations for samples with increasing complexity. Additionally, the technique was successfully applied to simultaneously determine both the hydrodynamic radius and the Au-NP content in liposomes. With the established hyphenated setup, it was possible to distinguish between different subpopulations with various NP loads and different hydrodynamic diameters inside the liposome carriers.