Silver nanoparticle toxicity effect on growth and cellular viability of the aquatic plant Lemna gibba

Nanomaterials in plant physiology: Main effects in normal and under temperature stress

Global climate change and high population growth rates lead to problems of food security and environmental pollution, which require new effective methods to increase yields and stress tolerance of important crops. Nowadays the question of using artificial chemicals is very relevant in theoretical and practical terms. It is important that such substances in low concentrations protect plants under stress conditions, but at the same time inflict minimal damage on the environment and human health. Nanotechnology, which allows the production of a wide range of nanomaterials (NM), provides novel techniques in this direction. NM include structures less than 100 nm. The review presents data on the methods of NM production, their properties, pathways for arrival in plants and their use in human life. It is shown that NM, due to their unique physical and chemical properties, can cross biological barriers and accumulate in cells of live organisms. The influence of NM on plant organism can be both positive and negative, depending on the NM chemical nature, their size and dose, the object of study, and the environmental conditions. This review provides a comparative analysis of the effect of artificial metal nanoparticles (NPm), the commonly employed NMs in plant physiology, on two important aspects of plant life: photosynthetic apparatus activity and antioxidant system function. According to studies, NM affect not only the functional activity of photosynthetic apparatus, but also structural organization of chloroplats. In addition, the literature analysis reflects the dual action of NM on oxidative processes, and antioxidant status of plants. These facts considerably complicate the ideas about possible mechanisms and further use of NPm in biology. In this regard, data on the effects of NM on plants under abiotic stressors are of great interest. Separate section is devoted to the use of NM as adaptogens that increase plant stress tolerance to unfavorable temperatures. Possible mechanisms of NM effects on plants are discussed, as well as the strategies for their further use in basic science and sustainable agriculture.

Ecotoxicity and trophic transfer of metallic nanomaterials in aquatic ecosystems

Metallic nanomaterials (MNMs) possess unique properties that have led to their widespread application in fields such as electronics and medicine. However, concerns about their interactions with environmental factors and potential toxicity to aquatic life have emerged. There is growing evidence suggesting MNMs can have detrimental effects on aquatic ecosystems, and are potential for bioaccumulation and biomagnification in the food chain, posing risks to higher trophic levels and potentially humans. While many studies have focused on the general ecotoxicity of MNMs, fewer have delved into their trophic transfer within aquatic food chains. This review highlights the ecotoxicological effects of MNMs on aquatic systems via waterborne exposure or dietary exposure, emphasizing their accumulation and transformation across the food web. Biomagnification factor (BMF), the ratio of the contaminant concentration in predator to that in prey, was used to evaluate the biomagnification due to the complex nature of aquatic food chains. However, most current studies have BMF values of less than 1 indicating no biomagnification. Factors influencing MNM toxicity in aquatic environments include nanomaterial properties, ion variations, light, dissolved oxygen, and pH. The multifaceted interactions of these variables with MNM toxicity remain to be fully elucidated. We conclude with recommendations for future research directions to mitigate the adverse effects of MNMs in aquatic ecosystems and advocate for a cautious approach to the production and application of MNMs.

Metallic nanoparticles and photosynthesis organisms: Comprehensive review from the ecological perspective

This review presents a comprehensive analysis of the ecological implications of metallic nanoparticles (MNPs) on photosynthetic organisms, particularly plants and algae. We delve into the toxicological impacts of various MNPs, including gold, silver, copper-based, zinc oxide, and titanium dioxide nanoparticles, elucidating their effects on the growth and health of these organisms. The article also summarizes the toxicity mechanisms of these nanoparticles in plants and algae from previous research, providing insight into the cellular and molecular interactions that underpin these effects. Furthermore, it discusses the reciprocal interactions between different types of MNPs, their combined effects with other metal contaminants, and compares the toxicity between MNPs with their counterpart. This review highlights the urgent need for a deeper understanding of the environmental impact, considering their escalating use and the potential risks they pose to ecological systems, especially in the context of photosynthetic organisms that are vital to ecosystem health and stability.

Toxicological effects of nanoparticles in plants: Mechanisms involved at morphological, physiological, biochemical and molecular levels

The rapid advancement of nanotechnology has led to unprecedented innovations across diverse industries, including pharmaceuticals, agriculture, cosmetics, electronics, textiles, and food, owing to the unique properties of nanoparticles. The extensive production and unregulated release of synthetic nanoparticles may contribute to nanopollution within the ecosystem. In the agricultural sector, nanotechnology is increasingly utilized to improve plant productivity, enhance resistance to stressors, and reduce the usage of chemicals. However, the uncontrolled discharge of nanoparticles into the natural environment raises concerns regarding possible plant toxicological impacts. The review focuses on the translocation of these particles within the plants, emphasizing their phytotoxicological effects at morphological, physiological, biochemical, and molecular levels. Eventhough the beneficial aspects of these nanoparticles are evident, excessive usage of nanoparticles at higher concentrations may lead to potential adverse effects. The phytotoxicity resulting from excessive amounts of nanoparticles affects seed germination and biomass production, disrupts the photosynthesis system, induces oxidative stress, impacts cell membrane integrity, alters gene expression, causes DNA damage, and leads to epigenetic variations in plants. Nanoparticles are found to directly associate with the cell membrane and cell organelles, leading to the dissolution and release of toxic ions, generation of reactive oxygen species (ROS) and subsequent oxidative stress. The present study signifies and accumulates knowledge regarding the application of nanoparticles in agriculture and illustrates a clear picture of their possible impacts on plants and soil microbes, thereby paving the way for future developments in nano-agrotechnology. The review concludes by addressing current challenges and proposing future directions to comprehend and mitigate the possible biological risks associated with nanoparticles in agriculture.

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.

The biochemical and growth-associated traits of basil (Ocimum basilicum L.) affected by silver nanoparticles and silver

BACKGROUND

The biochemical and growth changes resulting from exposure of basil (Ocimum basilicum L.) seedlings to silver nanoparticles and silver were investigated. Over a two-week period, seedlings were exposed to different concentrations (0, 40, and 80 ppm) of silver nanoparticles and silver.

RESULTS

Our findings revealed that at concentrations of 40 and 80 ppm, both silver nanoparticles and silver nitrate led to decreased weight, root and shoot length, as well as chlorophyll a and b content. Conversely, these treatments triggered an increase in key biochemical properties, such as total phenols, carotenoids and anthocyanins, with silver nanoparticles showing a more pronounced effect compared to silver nitrate. Moreover, the levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) rose proportionally with treatment concentration, with the nanoparticle treatment exhibiting a more substantial increase. Silver content showed a significant upswing in both roots and leaves as treatment concentrations increased.

CONCLUSIONS

Application of varying concentrations of silver nanoparticles and silver nitrate on basil plants resulted in reduced growth and lower chlorophyll content, while simultaneously boosting the production of antioxidant compounds. Notably, anthocyanin, carotenoid, and total phenol increased significantly. However, despite this increase in antioxidant activity, the plant remained unable to fully mitigate the oxidative stress induced by silver and silver nanoparticles.

Silver nanoparticle ecotoxicity and phytoremediation: a critical review of current research and future prospects

Silver nanoparticles (AgNPs) are widely used in various industries, including textiles, electronics, and biomedical fields, due to their unique optical, electronic, and antimicrobial properties. However, the extensive use of AgNPs has raised concerns about their potential ecotoxicity and adverse effects on the environment. AgNPs can enter the environment through different pathways, such as wastewater, surface runoff, and soil application and can interact with living organisms through adsorption, ingestion, and accumulation, causing toxicity and harm. The small size, high surface area-to-volume ratio, and ability to generate reactive oxygen species (ROS) make AgNPs particularly toxic. Various bioremediation strategies, such as phytoremediation, have been proposed to mitigate the toxic effects of AgNPs and minimize their impact on the environment. Further research is needed to improve these strategies and ensure their safety and efficacy in different environmental settings.

Insight interactions of engineered nanoparticles with aquatic higher plants for phytoaccumulation, phytotoxicity, and phytoremediation applications: A review

With the growing age of human civilization, industrialization has paced up equally which is followed by the innovation of newer concepts of science and technology. One such example is the invention of engineered nanoparticles and their flagrant use in widespread applications. While ENPs serve their intended purposes, they also disrupt the ecological balance by contaminating pristine aquatic ecosystems. This review encompasses a comprehensive discussion about the potent toxicity of ENPs on aquatic ecosystems, with a particular focus on their impact on aquatic higher plants. The discussion extends to elucidating the fate of ENPs upon release into aquatic environments, covering aspects ranging from morphological and physiological effects to molecular-level phytotoxicity. Furthermore, this level of toxicity has been correlated with the determination of competent plants for the phytoremediation process towards the mitigation of this ecological stress. However, this review further illustrates the path of future research which is yet to be explored. Determination of the genotoxicity level of aquatic higher plants could explain the entire process comprehensively. Moreover, to make it suitable to be used in natural ecosystems phytoremediation potential of co-existing plant species along with the presence of different ENPs need to be evaluated. This literature will undoubtedly offer readers a comprehensive understanding of the stress induced by the irresponsible release of engineered nanoparticles (ENP) into aquatic environments, along with insights into the resilience characteristics of these pristine ecosystems.

Adverse effects of silver nanoparticles on aquatic plants and zooplankton: A review

With the rapid development of nanotechnology in the past decades, AgNPs are widely used in various fields and have become one of the most widely used nanomaterials, which leads to the inevitable release of AgNPs to the aquatic environment through various pathways. It is important to understand the effects of AgNPs on aquatic plants and zooplankton, which are widely distributed and diverse, and are important components of the aquatic biota. This paper reviews the effects of AgNPs on aquatic plants and zooplankton at the individual, cellular and molecular levels. In addition, the internal and external factors affecting the toxicity of AgNPs to aquatic plants and zooplankton are discussed. In general, AgNPs can inhibit growth and development, cause tissue damage, induce oxidative stress, and produce genotoxicity and reproductive toxicity. Moreover, the toxicity of AgNPs is influenced by the size, concentration, and surface coating of AgNPs, environmental factors including pH, salinity, temperature, light and co-contaminants such as NaOCl, glyphosate, As(V), Cu and Cd, sensitivity of test organisms, experimental conditions and so on. In order to investigate the toxicity of AgNPs in the natural environment, it is recommended to conduct toxicity evaluation studies of AgNPs under the coexistence of multiple environmental factors and pollutants, especially at natural environmental concentrations.

How Can Biological and Chemical Silver Nanoparticles Positively Impact Physio-Chemical and Chloroplast Ultrastructural Characteristics of Vicia faba Seedlings?

Through interactions with plant cells, silver nanoparticles (AgNPs) with both biological and chemical origins can stimulate physiological and metabolic processes in plants. To ensure their safe application in the food chain, it is necessary to investigate their effects on plant systems. Therefore, the effects of chemical AgNPs (chem-AgNPs) and biologically synthesized AgNPs (bio-AgNPs) at different levels (i.e., 0, 10, and 50 ppm) on physiological and biochemical traits {i.e., root and shoot growth traits, photosynthetic pigments (Chl a, Chl b, carotenoids, and total pigments), soluble sugars, total carbohydrates, starch, H₂O₂, and antioxidant enzyme activities} of Vicia faba L. seedlings were investigated. AgNPs were biosynthesized from silver nitrate (AgNO₃) by a green synthesis approach using Jatropha curcas seed extract. The synthesized AgNPs were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), zeta potential, Fourier-transform infrared spectra (FT-IR), and X-ray diffraction (XRD). The results showed that bio-AgNPs at 10 ppm resulted in the highest growth, physiological, and biological traits of faba bean seedlings in comparison with those obtained from both AgNO₃ and chem-AgNPs treatments. On the other hand, all AgNPs treatments adversely affected the chloroplast ultrastructure, however, fewer negative effects were obtained with the application of 10 ppm bio-AgNPs. In addition, the roots and shoots of seedlings contained the lowest Ag content under different treatments at 10 ppm AgNPs in comparison to the highest level of AgNPs (50 ppm), which indicates that additional studies should be incorporated to ensure safe use of lower concentrations of bio-AgNPs in seed priming. In conclusion, the application of biogenic nanoparticles at 10 ppm can be recommended to enhance plant growth and the productivity of strategic crops.

Productivity and Phytochemicals of Asclepias curassavica in Response to Compost and Silver Nanoparticles Application: HPLC Analysis and Antibacterial Activity of Extracts

The application of compost and metallic nanoparticles has a significant impact on the productivity and chemical composition of horticulture plants. In two subsequent growing seasons, 2020 and 2021, the productivity of Asclepias curassavica L. plants treated with various concentrations of silver nanoparticles (AgNPs) and compost was assessed. In the pot experiments, the soil was amended with 25% or 50% compost, and the plants were sprayed with 10, 20, and 30 mg/L of AgNPs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and dynamic light scattering (DLS) were used to characterize AgNPs. The TEM measurements of AgNPs showed that the particles had spherical forms and ranged in size from roughly 5 to 16 nm. Leaf methanol extracts (LMEs) were prepared from the treated plants and assayed against the growth of two soft rot bacteria, Dickeya solani and Pectobacterium atrosepticum. The maximum plant height, diameter, number of branches/plant, total fresh weight (g), total dry weight (g), and leaf area (cm²) was recorded when levels of 25% compost + AgNPs 20 mg/L, 25% compost, or 50% + AgNPs 20 mg/L, 25% compost + AgNPs 30 mg/L or 50% compost + AgNPs 20 mg/L, 50% compost + AgNPs 20 mg/L, 50% compost + AgNPs 30 or 20 mg/L, and 25% compost + AgNPs 30 mg/L, respectively, were applied. The plants treated with 25% or 50% compost + 30 mg/L AgNPs showed a high chlorophyll content, while the plants treated with 50% compost + AgNPs 30 mg/L or 20 mg/L showed the highest extract percentages. The highest inhibition zones (IZs), 2.43 and 2.2 cm, against the growth of D. solani were observed in the LMEs (4000 mg/L) extracted from the plants treated with compost (v/v) + AgNPs (mg/L) at the levels of 50% + 30 and 25% + 30, respectively. The highest IZs, 2.76 and 2.73 cm, against the growth of P. atrosepticum were observed in the LMEs (4000 mg/L) extracted from the plants treated at the levels of 50% + 30 and 25% + 30, respectively. Several phenolic compounds such as syringic acid, p-coumaric acid, chlorogenic acid, cinnamic acid, ellagic acid, caffeic acid, benzoic acid, gallic acid, ferulic acid, salicylic acid, pyrogallol, and catechol, as well as flavonoid compounds such as 7-hydroxyflavone, naringin, rutin, apigenin, quercetin, kaempferol, luteolin, hesperidin, catechin, and chrysoeriol, were identified in the LMEs as analyzed by HPLC with different concentrations according to the treatment of compost + AgNPs used for the plants. In conclusion, the specific criteria that were utilized to measure the growth of A. curassavica revealed the novelty of compost and AgNPs combination treatments, particularly at a concentration of 50% compost + AgNPs 30 mg/L or 20 mg/L, which is better for the growth and phytochemical production of A. curassavica in the field.

Silver contamination and its toxicity and risk management in terrestrial and aquatic ecosystems

Silver (Ag), a naturally occurring, rare and precious metal, is found in major minerals such as cerargyrite (AgCl), pyrargyrite (Ag₃SbS₃), proustite (Ag₃AsS₃), and stephanite (Ag₅SbS₄). From these minerals, Ag is released into soil and water through the weathering of rocks and mining activities. Silver also enters the environment by manufacturing and using Ag compounds in electroplating and photography, catalysts, medical devices, and batteries. With >400 t of Ag NPs produced yearly, Ag NPs have become a rapidly growing source of anthropogenic Ag input in the environment. In soils and natural waters, most Ag is sorbed to soil particles and sediments and precipitated as oxides, carbonates, sulphides, chlorides and hydroxides. Silver and its compounds are toxic, and humans and other animals are exposed to Ag through inhalation of air and the consumption of Ag-contaminated food and drinking water. Remediation of Ag-contaminated soil and water sources can be achieved through immobilization and mobilization processes. Immobilization of Ag in soil and groundwater reduces the bioavailability and mobility of Ag, while mobilization of Ag in the soil can facilitate its removal. This review provides an overview of the current understanding of the sources, geochemistry, health hazards, remediation practices and regulatory mandates of Ag contamination in complex environmental settings, including soil and aquatic ecosystems. Knowledge gaps and future research priorities in the sustainable management of Ag contamination in these settings are also discussed.

Silver Inhibits Lemna minor Growth at High Initial Frond Densities

Silver nanoparticles (AgNPs) are the most popular engineered nanomaterials in consumer products due to their antimicrobial properties. They enter aquatic ecosystems via insufficient purified wastewaters from manufacturers or consumers. AgNPs inhibit growth of aquatic plants, including duckweeds. Growth media nutrient concentration and initial duckweed frond density can affect growth. However, it is not well understood how frond density affects nanoparticle toxicity. We investigated the toxicity of 500 µg/L AgNPs and AgNO₃ on Lemna minor at different initial frond densities (20, 40, and 80 fronds per 28.5 cm²) over 14 days. Plants were more sensitive to silver at high initial frond densities. Growth rates based on frond number and area were lower for plants at 40 and 80 initial frond density in both silver treatments. AgNPs had no effect on frond number, biomass, and frond area at 20 initial frond density. However, AgNO₃ plants had lower biomass than control and AgNP plants at 20 initial frond density. Competition and crowding at high frond densities resulted in reduced growth when silver was present, therefore plant density and crowding effects should be considered in toxicity studies.

Phyto-Synthesis, Characterization, and In Vitro Antibacterial Activity of Silver Nanoparticles Using Various Plant Extracts

Aloe vera, Mentha arvensis (mint), Coriandrum sativum (coriander), and Cymbopogon citratus (lemongrass) leaf extracts were used to synthesize stable silver nanoparticles (Ag-NPs) by green chemistry. UV-vis spectrophotometry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy techniques were used to characterize these biosynthesized nanoparticles. The data indicated that the silver nanoparticles were successfully synthesized, and the narrower particle size distribution was at 10-22 nm by maintaining a specific pH. As a short-term post-sowing treatment, Ag-NP solutions of different sizes (10 and 50 ppm) were introduced to mung bean seedlings, and the overall increase in plant growth was found to be more pronounced at 50 ppm concentration. The antibacterial activity of Ag-NPs was also investigated by disc diffusion test, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) test. The zones of inhibition (ZOI) were shown by Escherichia coli (E. coli) (1.9, 2.1, 1.7, and 2 mm), followed by Staphylococcus aureus (S. aureus) (1.8, 1.7, 1.6, and 1.9 mm), against coriander, mint, Aloe vera, and lemongrass, respectively. MIC and MBC values of E. coli, and S. aureus ranged from 7 to 8 µg/mL. Overall, this study demonstrates that Ag-NPs exhibit a strong antimicrobial activity and thus might be developed as a new type of antimicrobial agent for the treatment of bacterial infection.

Lemna trisulca L.: a novel phytoremediator for the removal of zinc oxide nanoparticles (ZnO NP) from aqueous media

Several aquatic plant species have been proposed for phytoremediation of waters polluted with heavy metals and pesticides According to the limited information available, aquatic macrophytes also have a promising potential to remove NPs from aqueous media. Although there is considerable information on the remediation potential of Lemna spp., the capacity of Lemna trisulca seems to be neglected, particularly for nanoparticle removal. Therefore, in the current study, we aimed to investigate the removal efficiency of L. trisulca exposed to 3 different ZnO NP concentrations (2.5, 5, and 10 ppm) for 1, 4, and 7 days in Hoagland solutions and the removal percentage were measured on each duration and compared among groups. The accumulated zinc levels were measured in whole plant material and bioconcentration factors were calculated for each group. In addition, the effect of ZnO NPs on the photosynthetic activity of the plant was evaluated via analyzing the photosynthetic pigment (chlorophyll a and b) concentration. The removal percentage ranged between 9.3 and 72.9% and showed a gradual increase in all experimental groups based both on dose and test duration. The statistical comparisons of the removal percentage among the groups with or without the plant indicate that L. trisulca had a significant effect on removal rates particularly between 1st and 4th days of exposure, however, did not show any progress at 7th days. The only significant difference for chl-a and chl-b levels was observed in 10 ppm ZnO NP-exposed plants at 7th days.

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.

Fate, bioaccumulation and toxicity of engineered nanomaterials in plants: Current challenges and future prospects

The main focus of this review is to discuss the current advancement in nano-metallic caused phytotoxicity on living organisms and current challenges in crops. Nanostructured materials provide new tools in agriculture to boost sustainable food production, but the main concern is that large-scale production and release of nanomaterials (NMs) into the ecosystem is a rising threat to the surrounding environment that is an urgent challenge to be addressed. The usage of NMs directly influences the transport pathways within plants, which directly relates to their stimulatory/ inhibitory effects. Because of the unregulated nanoparticles (NMs) exposure to soil, they are adsorbed at the root surface, followed by uptake and inter/intracellular mobility within the plant tissue, while the aerial exposure is taken up by foliage, mostly through cuticles, hydathodes, stigma, stomata, and trichomes, but the actual mode of NMs absorption into plants is still unclear. NMs-plant interactions may have stimulatory or inhibitory effects throughout their life cycle depending on their composition, size, concentration, and plant species. Although many publications on NMs interactions with plants have been reported, the knowledge on their uptake, translocation, and bioaccumulation is still a question to be addressed by the scientific community. One of the critical aspects that must be discovered and understood is detecting NMs in soil and the uptake mechanism in plants. Therefore, the nanopollution in plants has yet to be completely understood regarding its impact on plant health, making it yet another artificial environmental influence of unknown long-term consequences. The present review summarizes the uptake, translocation, and bioaccumulation of NMs in plants, focusing on their inhibitory effects and mechanisms involved within plants.

Comparative evaluation on the toxic effect of silver (Ag) and zinc oxide (ZnO) nanoparticles on different trophic levels in aquatic ecosystems-A review

Silver (Ag) and zinc oxide (ZnO) are considered to be harmful nanoparticles (NPs) to the aquatic organisms as their intake causes toxic impacts to wildlife, through direct ingestion or by the transference along trophic levels. Over usage and ultimate disposal of metallic particles from the industries subsequently lead to pollution of the aquatic environment. Exposure of NPs in aquatic ecosystem alters biological and physicochemical parameters of the water and aquatic organisms and determine their potential ecotoxicological impacts. Prolonged exposure of aquatic organisms to these NPs results in differential bioaccumulation and distribution into internal organs like liver, kidney, gills, brain and muscle tissue. The contact of NPs to aquatic organisms induces various types of toxic traits including cytotoxicity, genotoxicity and epigeneticity. Taking this in consideration this present review focus on the comparative impact of ZnO and Ag nanoparticles towards both vertebrates and invertebrates in aquatic ecosystems.

Ethylene participates in zinc oxide nanoparticles induced biochemical, molecular and ultrastructural changes in rice seedlings

Nowadays, the applications of engineered nanoparticles (ENPs) have been significantly increased, thereby negatively affecting crop production and ultimately contaminating the food chain worldwide. Zinc oxide nanoparticles (ZnO NPs) induced oxidative stress has been clarified in previous studies. But until now, it has not been investigated that how ethylene mediates or participates in ZnO NPs-induced toxicity and related cellular ultrastructural changes in rice seedlings. Here, we reported that 500 mg/L of ZnO NPs reduced the fresh weight (54.75% and 55.64%) and dry weight (40.33% and 47.83%) in shoot and root respectively as compared to control. Furthermore, ZnO NPs (500 mg/L) reduced chlorophyll content (72% Chla, 70% Chlb), induced the stomatal closure and ultrastructural damages by causing oxidative stress in rice seedlings. These cellular damages were significantly increased by exogenous applications of ethylene biosynthesis precursor (ACC) in the presence of ZnO NPs. In contrary, ZnO NPs induced damages on the above-mentioned attributes were reversed through the exogenous supply of ethylene signaling and biosynthesis antagonists such as silver (Ag) and cobalt (Co) respectively. Interestingly, ZnO NPs accelerate ethylene biosynthesis by up-regulating the transcriptome of ethylene biosynthesis responsive genes. The antioxidant enzymes activities and related gene expressions were further increased in ethylene signaling and biosynthesis associated antagonists (Ag and Co) treated seedlings as compared to sole ZnO NPs treatments. In contrary, the above-reported attributes were further decreased by ACC together with ZnO NPs. In a nutshell, ethylene effectively contributes in ZnO NPs induced toxicity and causing ultrastructural and stomatal damage in rice seedlings. Such findings could have potential implications in producing genetic engineered crops, which will be able to tolerate nanoparticles toxicity in the environment.

Toxicological effects of leachate extracts from asphalt mixtures nanomodified under Daphnia magna and Landoltia punctata test organisms

The incorporation of nanomaterials in binders in the paving area has been studied to improve the mechanical behavior of asphalt mixtures. However, asphalt mixture compounds are susceptible to leaching and deposition in the environment. In this context, this research aimed to investigate the toxic effect of two leachate extracts from asphalt mixtures nanomodified with 2% carbon nanotube and 3% organophilic nanoclay, compared to conventional mixture, using Daphnia magna and Landoltia punctata as test organisms. The nanomaterials were characterized to confirm morphology, stability and effective diameter. Extracts were chemically characterized using the Fourier-Transform Infrared Spectroscopy (FTIR) technique, which indicated presence of functional groups of the asphalt binder in greater intensity in the leachate from conventional mixture. Acute toxicity with D. magna indicated EC_50,48h of 83.5 ± 6.2 mL/L for leachate extract from conventional mixture, 306.0 ± 87.6 mL/L for leachate extract from mixture with nanoclay and 464.8 ± 32.1 mL/L for leachate extract from mixture with carbon nanotube. No leachate caused significant chronic toxicity. As for L.punctata, concentrations that caused 50% growth inhibition were 127.5 mL/L for the leachate extract from mixture with carbon nanotube, 196.9 mL/L for the leachate extract from mixture with nanoclay and 205 mL/L for the leachate extract from conventional mixture. For these test organisms, there is no evidence of negative impacts directly associated with the use of the present nanomaterials in asphalt mixtures. The incorporation of these nanos may also reduce the acute toxicity of the mixtures.

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.

Biosynthesized silver nanoparticles induce phytotoxicity in Vigna radiata L

With the recent developments in the field of nanotechnology, the biosynthesis of nanoparticles has increased tremendously. Silver nanoparticles (SNPs) are among the most synthesized nanoparticles and this extensive synthesis can elevate the amounts of SNPs in the environment, which, consequently, pose a serious threat to the ecosystem and can bring unwanted environmental effects. As plants are an important part of ecosystem, investigation of toxic effects of SNPs on plants is particularly interesting. This study evaluates the potential risk of SNPs interaction with plants. For this, seeds of Vigna radiata L. were screened in presence of SNPs (20 mgL^-1) using the germination, growth, and biochemical parameters as a phototoxicity criterion. The 19.57 nm average-sized SNPs were synthesized via the biosynthesis method. These biosynthesized SNPs were then applied on two varieties of V. radiata (Azri and High cross 404) and found to have variety dependent toxic effects on seed germination, growth, and biochemical parameters. Seed germination, root length, shoot length, fresh weight, chlorophyll, carotenoid, sugar content, and total proteins were reduced by 20, 46, 50, 18, 55, 62, 82, and 67%, respectively, in High cross 404, when compared with control (distilled water). The variety Azri was less sensitive than the variety High cross 404. In conclusion, the results demonstrated that SNPs affect seed germination and seedling growth when internalized and accumulated in plants, revealing that SNPs were responsible for the side effects. More in-depth research is required, in the form of different concentrations of SNPs or different plant species, to draw a logical conclusion and develop legislation about the safe use of biosynthesized SNPs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01073-4.

Silver Nanoparticle's Toxicological Effects and Phytoremediation

The advancement in nanotechnology has brought numerous benefits for humans in diverse areas including industry, medicine, and agriculture. The demand in the application of nanomaterials can result in the release of these anthropogenic materials into soil and water that can potentially harm the environment by affecting water and soil properties (e.g., soil texture, pH, organic matter, and water content), plants, animals, and subsequently human health. The properties of nanoparticles including their size, surface area, and reactivity affect their fate in the environment and can potentially result in their toxicological effects in the ecosystem and on living organisms. There is extensive research on the application of nano-based materials and the consequences of their release into the environment. However, there is little information about environmentally friendly approaches for removing nanomaterials from the environment. This article provides insight into the application of silver nanoparticles (AgNPs), as one of the most commonly used nanomaterials, their toxicological effects, their impacts on plants and microorganisms, and briefly reviews the possibility of remediation of these metabolites using phytotechnology approaches. This article provides invaluable information to better understand the fate of nanomaterials in the environment and strategies in removing them from the environment.

Influence of GdVO4:Eu3+ Nanocrystals on Growth, Germination, Root Cell Viability and Oxidative Stress of Wheat (Triticum aestivum L.) Seedlings

The increasing application of lanthanide-doped nanocrystals (LDNCs) entails the risk of a harmful impact on the natural environment. Therefore, in the presented study the influence of gadolinium orthovanadates doped with Eu³⁺ (GdVO₄:Eu³) nanocrystals on wheat (Triticum aestivum L.), chosen as a model plant species, was investigated. The seeds were grown in Petri dishes filled with colloids of LDNCs at the concentrations of 0, 10, 50 and 100 µg/mL. The plants’ growth endpoints (number of roots, roots length, roots mass, hypocotyl length and hypocotyl mass) and germination rate were not significantly changed after the exposure to GdVO₄:Eu³⁺ nanocrystals at all used concentrations. The presence of LDNCs also had no effect on oxidative stress intensity, which was determined on the basis of the amount of lipid peroxidation product (thiobarbituric acid reactive substances; TBARS) in the roots. Similarly, TTC (tetrazolium chloride) assay did not show any differences in cells’ viability. However, root cells of the treated seedlings contained less Evans Blue (EB) when compared to the control. The obtained results, on the one hand, suggest that GdVO₄:Eu³⁺ nanocrystals are safe for plants in the tested concentrations, while on the other hand they indicate that LDNCs may interfere with the functioning of the root cell membrane.

Exposure Media and Nanoparticle Size Influence on the Fate, Bioaccumulation, and Toxicity of Silver Nanoparticles to Higher Plant Salvinia minima

Silver nanoparticles (AgNPs) are favoured antibacterial agents in nano-enabled products and can be released into water resources where they potentially elicit adverse effects. Herein, interactions of 10 and 40 nm AgNPs (10-AgNPs and 40-AgNPs) with aquatic higher plant Salvinia minima at 600 µg/L in moderately hard water (MHW), MHW of raised calcium (Ca²⁺), and MHW containing natural organic matter (NOM) were examined. The exposure media variants altered the AgNPs’ surface properties, causing size-dependent agglomeration. The bio-accessibility in the ascending order was: NOM < MHW < Ca²⁺, was higher in plants exposed to 10-AgNPs, and across all exposures, accumulation was higher in roots compared to fronds. The AgNPs reduced plant growth and the production of chlorophyll pigments a and b; the toxic effects were influenced by exposure media chemistry, and the smaller 10-AgNPs were commonly the most toxic relative to 40-AgNPs. The toxicity pattern was linked to the averagely higher dissolution of 10-AgNPs compared to the larger counterparts. The scanning electron microscopy and X-ray fluorescence analytical techniques were found limited in examining the interaction of the plants with AgNPs at the low exposure concentration used in this study, thus challenging their applicability considering the even lower predicted environmental concentrations AgNPs.

Effects of metal nanoparticle-mediated treatment on seed quality parameters of different crops

The increasing population of the world requires novel techniques to feed everyone, which can replace or work along with traditional methods to increase production of agricultural crops. In recent times, nanotechnology is considered as a promising and emerging approach to be incorporated in agriculture to improve productivity of different crops by the administration of nanoparticles through seed treatment, foliar spray on plants, nano-fertilizers for balanced crop nutrition, nano-herbicides for effective weed control, nanoinsecticides for plant protection, early detection of plant diseases and nutrient deficiencies using diagnostics kits, and nano-pheromones for effective monitoring of pests. Further, distinct nanoparticles with unique physicochemical and biological properties are used in agriculture to increase the percentage of seed germination, which is the initial step to increase the crop yield. In the context of agricultural crops, nanoparticles have both positive effects on seed quality parameters, such as germination percentage, seedling length, seedling dry weight and vigor indices, as well as negative impacts of causing toxicity toward the environment. Thus, the aim of this review article is to provide a comprehensive overview on the effects of super-dispersive metal powders, such as zinc, silver, and titanium nanoparticles on the seed quality parameters of different crops. In addition, the drawback of conventional seed growth enhancers, impact of metal nanoparticles toward seeds, and mechanism of nanoparticles to increase seed germination were also discussed.

A review on in vivo and in vitro nanotoxicological studies in plants: A headlight for future targets

Owing to the unique properties and useful applications in numerous fields, nanomaterials (NMs) received a great attention. The mass production of NMs has raised major concern for the environment. Recently, some altered growth patterns in plants have been reported due to the plant-NMs interactions. However, for NMs safe applications in agriculture and medicine, a comprehensive understanding of bio-nano interactions is crucial. The main goal of this review article is to summarize the results of the toxicological studies that have shown the in vitro and in vivo interactions of NMs with plants. The toxicity mechanisms are briefly discussed in plants as the defense mechanism works to overcome the stress caused by NMs implications. Indeed, the impact of NMs on plants varies significantly with many factors including physicochemical properties of NMs, culture media, and plant species. To investigate the impacts, dose metrics is an important analysis for assaying toxicity and is discussed in the present article to broadly open up different aspects of nanotoxicological investigations. To access reliable quantification and measurement in laboratories, standardized methodologies are crucial for precise dose delivery of NMs to plants during exposure. Altogether, the information is significant to researchers to describe restrictions and future perspectives.

Effect of AuNPs and AgNPs on the Antioxidant System and Antioxidant Activity of Lavender (Lavandula angustifolia Mill.) from In Vitro Cultures

The aim of this study was to determine the effect of gold and silver nanoparticles on the activity of antioxidant enzymes (ascorbate peroxidase (APX), superoxide dismutase (SOD), guaiacol peroxidase (POX), and catalase (CAT)), the free radical scavenging capacity, and the total polyphenol capacity of lavender (Lavandula angustifolia Mill.) cultivar “Munstead” propagated in vitro. In the experiment, fragments of lavender plants were cultivated in vitro on medium with the addition of 1, 2, 5, 10, 20, and 50 mg∙dm⁻³ of AgNPs or AuNPs (particle sizes 24.2 ± 2.4 and 27.5 ± 4.8 nm, respectively). It was found that the nanoparticles increase the activity of the antioxidant enzymes APX and SOD; however, the reaction depends on the NP concentration. The highest APX activity is found in plants propagated on media with 2 and 5 mg∙dm⁻³ of AgNPs. AuNPs significantly increase the APX activity when added to media with a concentration of 10 mg∙dm⁻³. The highest SOD activity is recorded at 2 and 5 mg∙dm⁻³ AgNP and AuNP concentrations. The addition of higher concentrations of nanoparticles to culture media results in a decrease in the APX and SOD activity. The addition of AuNPs to culture media at concentrations from 2 to 50 mg∙dm⁻³ increases the POX activity in comparison to its activity when AgNPs are added to the culture media. No significant influence of NPs on the increase in CAT activity was demonstrated. AgNPs and AuNPs increased the free radical scavenging capacity (ABTS^•+). The addition of NPs at concentrations of 2 and 5 mg∙dm⁻³ increased the production of polyphenols; however, in lower concentrations it decreased their content in lavender tissues.

Silver Nanoparticle-Infused Cotton Fiber: Durability and Aqueous Release of Silver in Laundry Water

Although the application of silver nanoparticles to commercial antibacterial items is well-established, there have been increasing concerns that such particles might leach out, particularly into laundry water from textile products. A recently developed process wherein silver nanoparticles are synthesized in situ within the cotton fiber itself promises, however, to achieve the desired washing durability. In this study, the silver release behavior of the silver nanoparticle-infused cotton fabric during consecutive launderings in water and a detergent solution was analyzed. Silver nanoparticles (12 ± 3 nm in diameter) were uniformly produced throughout the entire volume of cotton fiber with a concentration of 3017 ± 56 mg/kg. A combination of colorimetric, spectroscopic, and elemental analyses showed (1) nonlinear silver release behavior, with a rapid release from externally formed nanoparticles during the initial washing and a plateau-like release from internally formed nanoparticles during extended washing, and (2) superior nanoparticle-leach resistance compared to those in commercial and laboratory-prepared textiles analyzed in the literature. The internal nanoparticles immobilized within cotton fiber exhibited persistent antibacterial activity after 50 home laundering cycles.

Nanoparticles Affect the Expression Stability of Housekeeping Genes in Plant Cells

Purpose

We report on the expression stability of several housekeeping/reference genes that can be used in the normalization of target gene expression in quantitative real-time PCR (qRT-PCR) analysis of plant cells challenged with metal nanoparticles (NPs).

Materials and Methods

Uniform cell suspension cultures of Hypericum perforatum were treated with 25 mg/l silver and gold NPs (14-15 nm in diameter). Cells were collected after 0.5, 4.0, and 12 h. The total RNA isolated from the cells was analyzed for the stability of ACT2, ACT3, ACT7, EF1-α, GAPDH, H2A, TUB-α, TUB-β, and 18S rRNA genes using qRT-PCR. The cycle threshold (Ct) values of the genes were analyzed using the geNorm, NormFinder, BestKeeper, and RefFinder statistical algorithms to rank gene stability. The stability of the top-ranked genes was validated by normalizing the expression of HYP1.

Results

The expression of the tested housekeeping genes varied with treatment duration and NP types. EF1-α in gold NP treatment and TUB-α and EF1-α in silver NP treatment ranked among the top three positions. However, none of the genes retained their top ranking with time and across NP types.

Conclusion

EF1-α can be used as a reference for treatment involving both silver and gold NPs in H. perforatum cells. TUB-α can be used only for silver NP-treated cells. The expression instability of most of the housekeeping genes highlights the importance of systematic standardization of reference genes for NP treatment conditions to draw proper conclusions on the target gene expression.

Toxicity, Bioaccumulation and Biotransformation of Glucose-Capped Silver Nanoparticles in Green Microalgae Chlorella vulgaris

Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials in consumer products. When discharged into the aquatic environment AgNPs can cause toxicity to aquatic biota, through mechanisms that are still under debate, thus rendering the nanoparticles (NPs) effects evaluation a necessary step. Different aquatic organism models, i.e., microalgae, mussels, Daphnia magna, sea urchins and Danio rerio, etc. have been largely exploited for NPs toxicity assessment. On the other hand, alternative biological microorganisms abundantly present in nature, i.e., microalgae, are nowadays exploited as a potential sink for removal of toxic substances from the environment. Indeed, the green microalgae Chlorella vulgaris is one of the most used microorganisms for waste treatment. With the aim to verify the possible involvement of C. vulgaris not only as a model microorganism of NPs toxicity but also for the protection toward NPs pollution, we used these microalgae to measure the AgNPs biotoxicity and bioaccumulation. In particular, to exclude any toxicity derived by Ag⁺ ions release, green chemistry-synthesised and glucose-coated AgNPs (AgNPs-G) were used. C. vulgaris actively internalised AgNPs-G whose amount increases in a time- and dose-dependent manner. The internalised NPs, found inside large vacuoles, were not released back into the medium, even after 1 week, and did not undergo biotransformation since AgNPs-G maintained their crystalline nature. Biotoxicity of AgNPs-G causes an exposure time and AgNPs-G dose-dependent growth reduction and a decrease in chlorophyll-a amount. These results confirm C. vulgaris as a bioaccumulating microalgae for possible use in environmental protection.

Phytoremediation of engineered nanoparticles using aquatic plants: Mechanisms and practical feasibility

Certain plants have demonstrated the capability to take up and accumulate metals, thus offering the potential to remediate metal-contaminated water and sediment. Several aquatic species have further been identified which can take up metal and metal oxide engineered nanoparticles (ENPs). It is important to evaluate if aquatic plants exhibiting potential for metal phytoremediation can be applied to remediation of metallic ENPs. Understanding the interactions between ENPs and aquatic plants, and evaluating possible influences on metal uptake and phytoremediation processes is therefore essential. This review article will address the feasibility of green plants for treatment of ENP-affected aquatic ecosystems. Discussion will include common types of ENPs in current use; transformations of ENPs in aquatic systems; the importance of microorganisms in supporting plant growth; ENP entry into the plant; the influence of microorganisms in promoting plant uptake; and recent findings in phytoremediation of ENP-affected water, including applications to constructed wetlands.

Physiological, structural and ultrastructural impacts of silver nanoparticles on the seagrass Cymodocea nodosa

Silver nanoparticles (AgNPs) are an emerging contaminant, currently considered to be a significant potential risk to the coastal environment. To further test potential risk, and to determine effect concentrations and sensitive response parameters, toxic effects of environmentally relevant AgNP concentrations on the seagrass Cymodocea nodosa were evaluated. Alterations of the cytoskeleton, endoplasmic reticulum, ultrastructure, photosystem II function, oxidative stress markers, cell viability, and leaf, rhizome and root elongation in C. nodosa exposed to AgNP concentrations (0.0002-0.2 mg L^-1) under laboratory conditions for 8 days were examined. An increase in H₂O₂ level, indicating oxidative stress, occurred after the 4th day even at 0.0002 mg L^-1. Increased antioxidant enzyme activity, potentially contributing to H₂O₂ level decline at the end of the experiment, and reduced protein content were also observed. Actin filaments started to diminish on the 6th day at 0.02 mg L^-1; microtubule, endoplasmic reticulum, chloroplast and mitochondrion disturbance appeared after 8 days at 0.02 mg L^-1, while toxic effects were generally more acute at 0.2 mg L^-1. A dose-dependent leaf elongation inhibition was also observed; as for juvenile leaves, toxicity index increased from 2.8 to 40.7% with concentration. Hydrogen peroxide (H₂O₂) overproduction and actin filament disruption appeared to be the most sensitive response parameters, and thus could be utilized as early warning indicators of risk to seagrass meadows. A risk quotient of 1.33 was calculated, confirming previous findings, that AgNPs may pose a significant risk to the coastal environment.

Effects of titanium dioxide nanoparticles on leaf cell structure and viability, and leaf elongation in the seagrass Halophila stipulacea

The ecotoxicity of titanium dioxide nanoparticles (TiO₂ NPs) is of increasing concern due to their extensive use in a variety of applications. This study aims to achieve a better understanding of TiO₂ NP ecotoxicity by assessing for the first time their effects on seagrasses. Changes in leaf cell structure and viability, and leaf elongation in Halophila stipulacea exposed under laboratory conditions to environmentally relevant TiO₂ NP concentrations (0.0015-1.5 mg L^-1) for 8 days were assessed. Actin filament (AF) disturbance firstly occurred in differentiating cells at 0.0015 mg L^-1 on the 8th day, while in meristematic cells at 0.15 mg L^-1 on the 6th day, both deteriorating concentration- and time-dependently. Endoplasmic reticulum (ER) appeared aggregated firstly at 0.015 mg L^-1 on the 8th day and earlier at the highest concentrations, while microtubules and cell ultrastructure appeared unaffected. Dead cells mainly occurred in older leaves; dead tooth, margin and intercostal epidermal cells exceeded 5% at 0.15-1.5 mg L^-1. A significant leaf elongation inhibition occurred at 0.015-1.5 mg L^-1 in older leaves and at 1.5 mg L^-1 in young apical leaves. AF, ER and leaf elongation impairment in H. stipulacea, being susceptible response parameters, could be used as early warning markers. A risk quotient >1 was calculated, indicating that TiO₂ NPs may pose a significant risk to the environment. The data presented underline the need for additional TiO₂ NP-seagrasses toxicity information, and could be utilized for the protection of the coastal environment.

Toxicological effects of AgNPs on duckweed (Landoltia punctata)

Silver nanoparticles (AgNPs) are widely applied in several types of products since they act as a biocide. However, their high level of release into the environment can bring risks to ecosystems. Thus, the toxicity of AgNPs toward duckweed (Landoltia punctata) was investigated by monitoring the growth rate inhibition and the effect on the photosynthetic metabolism through morphological and ultrastructural analysis. The AgNPs were characterized by transmission electron microscopy and the effective diameter (dynamic light scattering) and zeta potential were determined. Plants were grown according to the environmental conditions recommended in ISO/DIS 20079 and then exposed to different concentrations of AgNPs. Inhibition of the growth rate was measured based on the EC₅₀ and changes in the morphology, cellular structures and photosynthetic pigments were evaluated along with the silver accumulation. Although the results showed low growth inhibition when compared to other studies, significant damage to the ultrastructure, decreases in the photosynthetic pigments and starch grains, an increase in the phenolic compounds and physiological changes, such as a loss of color, were observed. Moreover, the accumulation of silver ions was noted and this could lead to bioamplification in consumer organisms, since duckweed belongs to the first level of the food chain.

Silver nanoparticles regulate Arabidopsis root growth by concentration-dependent modification of reactive oxygen species accumulation and cell division

Silver nanoparticles (AgNPs) are widely used in industry, increasing their potential level in the environment. Plant root, the key organ absorbing water and nutrients, are directly exposed to the soil. Little is known about AgNP-mediated effects on plant root growth. Here, we show that AgNPs are absorbed by root and mostly localized in cell wall and intercellular spaces, which affect root growth in a dose-dependent manner. Increased root elongation was observed when Arabidopsis was exposed to an AgNP concentration of 50 mg L^-1, while decreased elongation was observed at concentrations of equal to or more than 100 mg L^-1. Similarly, there was an increase in the number of cells in the root apical meristem and also in cell-cycle related gene expression (CYCB1;1) at 50 mg L^-1 AgNP, while both cell number and gene expression declined at concentrations equal to or more than 100 mg L^-1. This indicates that AgNPs regulate root growth by affecting cell division. Reactive oxygen species (ROS) related genes were deferentially expressed after 50 mg L^-1 AgNP treatment. Further studies showed that AgNPs induce ROS accumulation in root tips in a dose-dependent manner. KI treatment, which scavenges H₂O₂, partially rescued AgNP-inhibited root growth. The application 50 mg L^-1 AgNPs also rescued the root length phenotype of upb1-1, a mutant with slightly higher ROS levels and longer root length. Our results revealed that ROS mediate the dose-dependent effects of AgNPs on root growth. These findings provide new insights into mechanisms underlying how AgNPs regulate root growth in Arabidopsis.

Silver nanoparticle toxicity effect on the seagrass Halophila stipulacea

Information on silver nanoparticle (AgNP) phytotoxicity on seagrasses is provided for the first time. Toxic effects of environmentally relevant AgNP concentrations on Halophila stipulacea were assessed to identify sensitive biomarkers, to determine threshold effect concentrations and to evaluate potential risks. Potential alterations in the cytoskeleton, endoplasmic reticulum, cell ultrastructure and viability, oxidative stress parameters and elongation in H. stipulacea leaves exposed to AgNP concentrations ranging from 0.0002 to 0.2 mg L^-1 for 8 days were examined. The first signs of actin filament (AF) response in differentiating cells, exhibiting disorientation and slight bundling, were observed on the 4th day at 0.0002 mg L^-1, while at the end of the experiment and at the higher concentrations, AFs were extremely bundled. Endoplasmic reticulum was affected in meristematic and differentiating cells; massive aggregations and loss of the "grainy" structure were observed, initially on the 6th day at 0.002 mg L^-1. Effects on microtubules were detected on the last day at 0.2 mg L^-1. An increase in H₂O₂ levels on the 4th and/or 6th day even at 0.0002 mg L^-1 was followed by a decrease on, or up to the last day. On the 6th day at the lowest concentration, elevated malondialdehyde content, and superoxide dismutase and peroxidase activity were detected, indicating oxidative damage and antioxidant defense mechanism activation. Dead epidermal cells mainly occurred at 0.02 and 0.2 mg L^-1, while no dead vein cells were detected. A significant inhibition in leaf elongation was observed only at 0.2 mg L^-1. Therefore, AF disturbance in differentiating leaf cells, being a susceptible response parameter, could be regarded as an early warning indicator of risk posed by AgNPs to H. stipulacea meadows, while most of the remaining parameters examined also constitute useful biomarkers. The lowest observed effect concentration (0.0002 mg L^-1), being within the range of environmentally relevant AgNPs concentrations, suggests the possibility of negative impacts of AgNPs on seagrass health. A risk quotient of 1.33 was calculated, indicating that AgNPs may pose a significant potential risk to the coastal environment. The data presented highlight the importance of future research to further investigate the seagrass-AgNP interactions, stress the need for a refinement of the environmental risk assessment of AgNPs and could be utilized for the design of biomonitoring programs for rational management of the coastal environment.

Phytotoxicity of silver nanoparticles on Vicia faba: Evaluation of particle size effects on photosynthetic performance and leaf gas exchange

Nanotechnology is an emerging field in science and engineering, which presents significant impacts on the economy, society and the environment. The nanomaterials' (NMs) production, use, and disposal is inevitably leading to their release into the environment where there are uncertainties about its fate, behaviour, and toxicity. Recent works have demonstrated that NMs can penetrate, translocate, and accumulate in plants. However, studies about the effects of the NMs on plants are still limited because most investigations are carried out in the initial stage of plant development. The present study aimed to evaluate and characterize the photochemical efficiency of photosystem II (PSII) of broad bean (Vicia faba) leaves when subjected to silver nanoparticles (AgNPs) with diameters of 20, 51, and 73 nm as well as to micrometer-size Ag particles (AgBulk). The AgNPs were characterized by transmission electron microscopy and dynamic light scattering. The analyses were performed by injecting the leaves with 100 mg L^-1 aqueous solution of Ag and measuring the chlorophyll fluorescence imaging, gas exchange, thermal imaging, and reactive oxygen species (ROS) production. In addition, silver ion (Ag⁺) release from Ag particles was determined by dialysis. The results revealed that AgNPs induce a decrease in the photochemical efficiency of photosystem II (PSII) and an increase in the non-photochemical quenching. The data also revealed that AgNPs affected the stomatal conductance (g_s) and CO₂ assimilation. Further, AgNPs induced an overproduction of ROS in Vicia faba leaves. Finally, all observed effects were particle diameter-dependent, increasing with the reduction of AgNPs diameter and revealing that AgBulk caused only a small or no changes on plants. In summary, the results point out that AgNPs may negatively affect the photosynthesis process when accumulated in the leaves, and that the NPs themselves were mainly responsible since negligible Ag⁺ release was detected.

Chemically synthesized silver nanoparticles induced physio-chemical and chloroplast ultrastructural changes in broad bean seedlings

This study was conducted to explore the effects of priming of seven-year-old aged seeds with different concentrations of silver nanoparticles (AgNPs) on growth of broad bean (Vicia faba L.). Seeds were primed with different concentrations of AgNPs for 6 h before growing in the plastic trays. Different growth parameters like growth attributes, photosynthetic pigments, carbohydrates, antioxidant enzymes and chloroplast ultrastructure were estimated after 14 days of germination. Priming with AgNPs affected the root and shoot growth attributes as compared with control depending upon concentrations of AgNPs. In all treatments, photosynthetic pigments increased significantly above control levels, but total soluble sugars decreased in 10 and 50 ppm AgNPs and slightly increased in 100 ppm AgNPs as compared with control. Starch accumulation was apparent in all treated seedlings above that of control levels. Mesophyll cells of all treated seedlings were altered with electron dense particles than control. Priming with AgNPs affected the chloroplast structure which appeared in the form of less stacking of Greene, formation of protrusions and extensions, irregular shape of chloroplasts as compared with spindle shaped regular chloroplasts of control. In all treatments, total phenols were slightly affected as compared with control. The antioxidant enzyme activities in seedlings varied with the dose and type of antioxidants. Overall, AgNPs adversely affected the chloroplast ultrastructure, but increased growth of seedlings and starch accumulation. Further studies are required to explore the effects of AgNPs on the long-term on crop productivity of aged seeds.

Combination analysis of the physiology and transcriptome provides insights into the mechanism of silver nanoparticles phytotoxicity

Silver nanoparticles (AgNPs) have adverse impacts on plants when released into environments, but their toxic mechanism is still a matter of debate. Here we present a combined analysis of physiology and transcriptome of Arabidopsis thaliana leaves exposure to 30 mg L^-1 AgNPs and Ag⁺ for six days to explore the toxicity mechanism of AgNPs on Arabidopsis. Both transcriptomic and physiological results showed that AgNPs induced reactive oxygen species (ROS) accumulation and damaged photosynthesis. The toxicity of AgNPs is not merely attributable to Ag⁺ release and much higher photosynthetic toxicity and ROS accumulation were observed in 30 mg L^-1 AgNPs than that in 0.12 mg L^-1 Ag⁺. About 60% genes were similarly up- or down-regulated at the same concentration of AgNPs and Ag⁺ and these genes were enriched in photosynthesis and response to the stimulus. However, 302 genes, including those involved in glucosinolates synthesis, were specifically regulated under AgNPs treatments. In conclusion, more than the released Ag⁺, nanoparticle-specific effects are responsible for the toxicity of AgNPs in Arabidopsis thaliana.

Graphene oxide mediated reduction of silver ions to silver nanoparticles under environmentally relevant conditions: Kinetics and mechanisms

We systematically investigated the reduction mechanisms and reduction kinetics of silver ions (Ag ions) by graphene oxide (GO) under ambient condition. UV-vis spectroscopy, transmission electron microscopy, and electron diffraction results revealed that silver nanoparticles (Ag NPs) could be formed from aqueous Ag ions in the presence of GO at pH 8 under light. Formation of Ag NPs increased with increasing pH (7.4, 8, and 9) and temperature (from 30 to 90); however, the increasing ionic strength and dissolved oxygen reduced the Ag NPs yield. The Ag ions reduction by GO followed pseudo-first-order kinetics under both dark and light, and light irradiation significantly accelerated the Ag NPs formation induced by GO. The phenolic-OH on GO was the dominating electron donator for Ag ion reduction in dark. Exposure to light increased the concentration of phenolic-OH on the GO surface, thereby stimulating the reduction rate of Ag ions by GO. In addition, the light induced electron-hole pairs on GO surface and light activated oxygen-centered radicals on GO surface promoted the reduction of adsorbed Ag ions by GO. Our findings provide important information for the role of GO in reducing Ag ions to Ag NPs in aquatic environments, and shed light on understanding the environmental fate and risk of both Ag ions and GO materials.

Toxicity of nanosilver and fumonisin B1 and their interactions on duckweed (Lemna minor L.)

In the environment co-contamination of several toxicants commonly occurs. However, toxicological studies usually are focused on only one toxicant. The aim of this study was to investigate toxicity of silver nanoparticles (AgNP) and mycotoxin fumonisin B₁ (FB₁) and their possible interactions as well as to explore tentative mechanism of their toxic effect. Duckweed (Lemna minor L.) was treated with AgNP or FB₁ (at concentrations 0.5 and 1.0 mg L^-1) or with their combination at same concentrations for 3 days. Both AgNP and FB₁, applied individually significantly affected levels of certain nutrients, reduced growth rate and the levels of photosynthetic pigments though AgNP at a much greater extent compared to FB₁. Furthermore, AgNP induced ROS generation, lipid peroxidation and increase of antioxidative enzymes activities, while FB₁ induced changes only in the activities of antioxidative enzymes. Those results implicate that phytotoxicity of both AgNP and FB1 can be associated with imbalance of mineral and cell redox status. However, toxic actions of AgNp singly applied were more pronounced. Combined treatment with AgNP and FB₁ produced higher degree of changes in all parameters than corresponding concentrations of AgNP or FB₁ alone implying their additive effects. Additionally, higher level of FB1 found in medium, and higher level of intracellular Ag following combined treatment indicates interaction of two toxicants at the transport level/uptake in the cell which resulted in higher accumulation of Ag in duckweed cells. The latter in turn exerted higher toxicity to duckweed compared to single treatment of AgNP.

Toxicity assessment of anatase (TiO2) nanoparticles: A pilot study on stress response alterations and DNA damage studies in Lens culinaris Medik

The research was targeted to investigate the effect of nano-TiO₂ (anatase) on germination, vigour index, stress enzymes and mitotic cell cycle profile in lentils (Lens culinaris Medik.). Seed germination results indicated that TiO₂ NP (Nanoparticle) at lowest concentration promotes seed germination, vigour index and biomass; however, at higher concentrations, they showed significant reduction in growth parameters and photosynthetic pigments in concentration-dependent manner. NP treatments triggered an excessive formation of reactive oxygen species (ROS) which was evident from increased production of stress enzymes, lipid peroxidation, augmented DNA damage and aberrant mitotic cell division. The results exhibit a dose-dependent modification of NP- mediated oxidative stress and genotoxicity in lentil.

Physiological and Biochemical Responses of Pearl Millet (Pennisetum glaucum L.) Seedlings Exposed to Silver Nitrate (AgNO3) and Silver Nanoparticles (AgNPs)

A rapid and continuous growth of silver nanoparticles (AgNPs) via their precursor “silver nitrate” (AgNO₃) has increased their environmental risk because of their unsafe discharge into the surrounding environment. Both have damaging effects on plants and induce oxidative stress. In the present study, differential responses in the morpho-physiological and biochemical profiles of P. glaucum (L.) seedlings exposed to various doses of AgNPs and AgNO₃ were studied. Both have forms of Ag accelerated the reactive oxygen species (ROS) production, which adversely affected the membrane stability as a result of their enhanced accumulation, and resulted in a significant reduction in growth, that is, root length, shoot length, fresh and dry biomass, and relative water content. AgNO₃ possessed a higher degree of toxicity owing to its higher accumulation than AgNPs, and induced changes in the antioxidants’ enzyme activity: superoxide dismutase (SOD), peroxidase (POD), catalases (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and glutathione reductase (GR) activity, as well as proline content, total phenolic, and total flavonoids contents (TFCs) under all tested treatments (mM). A decline in photosynthetic pigments such as total chlorophyll content and carotenoid content and alterations in quantum yield (Fv/Fm), photochemical (qP), and non-photochemical quenching (NPQ) indicated the blockage of the electron transport chain (ETC), which led to a significant inhibition of photosynthesis. Interestingly, seedlings exposed to AgNPs showed less damaging effects on P. glaucum (L.) seedlings, resulting in relatively lower oxidative stress in contrast to AgNO₃. Our results revealed that AgNO₃ and AgNPs possessed differential phytotoxic effects on P. glaucum (L.) seedlings, including their mechanism of uptake, translocation, and action. The present findings may be useful in phytotoxic research to design strategies that minimize the adverse effects of AgNPs and AgNO₃ on crops, especially in the agriculture sector.

Effects of a chronic exposure to different water temperatures and/or to an environmental cadmium concentration on the reproduction of the threespine stickleback (Gasterosteus aculeatus)

Knowledge about combined effects of chemicals and temperature on reproductive capacity of fish are rare in literature, especially when it comes to the effects of chronic low-dose chemical exposure combined to the thermal stress. The aim of the study was to evaluate the single and combined effects of temperature (16, 18, 21 °C) and an environmentally relevant concentration of waterborne cadmium (1 µg L^-1, nominal concentration) on the reproductive outputs of threespine stickleback (Gasterosteus aculeatus), and their consequences on offspring survival parameters. The high temperature (21 °C) was the only factor that affected parental parameters (gonadosomatic index "GSI", and vitellogenin "VTG" particularly). On females, 21 °C had a stimulating effect on gonadal development evaluated by an early increase, followed by a sharp decrease of GSI, probably indicating gonadal atresia. Promoting effect of temperature was corroborated by an early production of VTG. In vitro fertilization assays showed interesting results, particularly cadmium effects. As it was supposed, high temperature had a negative impact on offspring parameters (significant decrease in survival and an increase of unhatched embryos). Parental exposure to the very low concentration of cadmium had also negative consequences on mortality rate (significant increase) and hatching rate (significant decrease). Our results indicate that in a global warming context, high temperature and its combination with contaminant may impact reproductive capacity of G. aculeatus, by decreasing parental investment (low eggs and/or sperm quality).

Discerning the Sources of Silver Nanoparticle in a Terrestrial Food Chain by Stable Isotope Tracer Technique

The increasing use of silver-containing nanoparticles (NPs) in commercial products has led to NP accumulation in the environment and potentially in food webs. Identifying the uptake pathways of different chemical species of NPs, such as Ag2S-NP and metallic AgNPs, into plants is important to understanding their entry into food chains. In this study, soybean Glycine max L. was hydroponically exposed to Ag2S-NPs via their roots (10-50 mg L-1) and stable-isotope-enriched 109AgNPs via their leaves [7.9 μg (g fresh weight)-1]. Less than 29% of Ag in treated leaves (in direct contact with 109AgNP) was accumulated from root uptake of Ag2S-NPs, whereas almost all of the Ag in soybean roots and untreated leaves sourced from Ag2S-NPs. Therefore, Ag2S-NPs are phytoavailable and translocate upward. During trophic transfer the Ag isotope signature was preserved, indicating that accumulated Ag in snails most likely originated from Ag2S-NPs. On average, 78% of the Ag in the untreated leaves was assimilated by snails, reinforcing the considerable trophic availability of Ag2S-NPs via root uptake. By highlighting the importance of root uptake of Ag2S-NPs in plant uptake and trophic transfer to herbivores, our study advances current understanding of the biogeochemical fate of Ag-containing NPs in the terrestrial environment.

Impacts of Silver Nanoparticles on Plants: A Focus on the Phytotoxicity and Underlying Mechanism

Nanotechnology was well developed during past decades and implemented in a broad range of industrial applications, which led to an inevitable release of nanomaterials into the environment and ecosystem. Silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in various fields, especially in the agricultural sector. Plants are the basic component of the ecosystem and the most important source of food for mankind; therefore, understanding the impacts of AgNPs on plant growth and development is crucial for the evaluation of potential environmental risks on food safety and human health imposed by AgNPs. The present review summarizes uptake, translocation, and accumulation of AgNPs in plants, and exemplifies the phytotoxicity of AgNPs on plants at morphological, physiological, cellular, and molecular levels. It also focuses on the current understanding of phytotoxicity mechanisms via which AgNPs exert their toxicity on plants. In addition, the tolerance mechanisms underlying survival strategy that plants adopt to cope with adverse effects of AgNPs are discussed.

Physiological and biochemical effect of silver on the aquatic plant Lemna gibba L.: Evaluation of commercially available product containing colloidal silver

This paper aims to evaluate the effects of a product containing colloidal silver in the aquatic environment, using duckweed Lemna gibba as a model plant. Therefore, growth parameters, photosynthetic pigments content and protein content as physiological indices were evaluated. Changes in the content of non-enzymatic antioxidants and activity of several antioxidant enzymes, alongside with the accumulation of hydrogen peroxide and lipid peroxidation end-products were assessed to explore the potential of colloidal silver to induce oxidative stress. The commercially available colloidal silver product contained a primary soluble form of silver. The treatment with colloidal silver resulted in significant physiological and biochemical changes in L. gibba plants and a consequent reduction of growth. Accumulation of silver caused altered nutrient balance in the plants as well as a significant decrease in photosynthetic pigments content and protein concentration. The antioxidative response of L. gibba plants to treatment with colloidal silver was inadequate to protect the plants from oxidative stress caused by metal accumulation. Silver caused concentration-dependent and time-dependent hydrogen peroxide accumulation as well as the elevation of lipid peroxidation levels in L. gibba plants. The use of commercially available products containing colloidal silver, and consequent accumulation of silver, both ionic and nanoparticle form in the environment, represents a potential source of toxicity to primary producers in the aquatic ecosystem.

Dominant Role of Silver Ions in Silver Nanoparticle Toxicity to a Unicellular Alga: Evidence from Luminogen Imaging

Despite the extensive studies on silver nanoparticle (AgNP) toxicity, the contribution of released silver ions to the toxicity still remains debatable. This study investigated the toxicity of AgNPs with different sizes (20 and 60 nm) toward a phytoplankton Euglena gracilis, with a focus on evaluating the contributions of dissolved Ag to the toxicity by combining a newly developed aggregation-induced emission luminogen (AIEgen)-based imaging technique and a traditional inductively coupled plasma mass spectrometry (ICP-MS) method. Smaller AgNPs, which dissolved much faster, exhibited greater toxicity, as evidenced by lower 50% growth inhibition concentration (EC₅₀). However, the average Ag⁺ concentration at each EC₅₀ was comparable to the EC₅₀ of AgNO₃, and similar subcellular Ag distribution patterns were observed in both AgNPs and AgNO₃ exposed algae. More silver ions were internalized in algae treated with smaller AgNPs. With the application of luminogen imaging technology, we for the first time demonstrated that few Ag(I) were presented intracellularly in algae exposed to AgNPs when any released Ag in the medium was complexed by cysteine. Ag(I) was mainly distributed in cellular debris, organelles, and metal-rich granules fractions. No conclusive evidence for AgNP internalization was documented. Our results strongly suggested that Ag⁺ released from AgNPs extracellularly dominated the AgNP toxicity. The findings of this work provide new and useful insight into the toxicity of AgNPs in aquatic environments.