Titanium dioxide nanoparticles (100-1000 mg/l) can affect vitamin E response in Arabidopsis thaliana

Metal and metal oxide nanoparticles-induced reactive oxygen species: Phytotoxicity and detoxification mechanisms in plant cell

Nanotechnology is advancing rapidly in this century and the industrial use of nanoparticles for new applications in the modernization of different industries such as agriculture, electronic, food, energy, environment, healthcare and medicine is growing exponentially. Despite applications of several nanoparticles in different industries, they show harmful effects on biological systems, especially in plants. Various mechanisms for the toxic effects of nanoparticles have already been proposed; however, elevated levels of reactive oxygen species (ROS) molecules including radicals [(e.g., superoxide (O2•‒), peroxyl (HOO•), and hydroxyl (HO•) and non-radicals [(e.g., hydrogen peroxide (H2O2) and singlet oxygen (1O2) is more important. Excessive production/and accumulation of ROS in cells and subsequent induction of oxidative stress disrupts the normal functioning of physiological processes and cellular redox reactions. Some of the consequences of ROS overproduction include peroxidation of lipids, changes in protein structure, DNA strand breaks, mitochondrial damage, and cell death. Key enzymatic antioxidants with ROS scavenging ability comprised of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and glutathione reductase (GR), and non-enzymatic antioxidant systems including alpha-tocopherol, flavonoids, phenolic compounds, carotenoids, ascorbate, and glutathione play vital role in detoxification and maintaining plant health by balancing redox reactions and reducing the level of ROS. This review provides compelling evidence that phytotoxicity of nanoparticles, is mainly caused by overproduction of ROS after exposure. In addition, the present review also summarizes the intrinsic detoxification mechanisms in plants in response to nanoparticles accumulation within plant cells.

Less is more: The hormetic effect of titanium dioxide nanoparticles on plants

Titanium dioxide nanoparticles have attracted considerable attention due to their extensive applications; however, their multifaceted influence on plant physiology and the broader environment remains a complex subject. This review systematically synthesizes recent studies on the hormetic effects of TiO2 nanoparticles on plants - a phenomenon characterized by dual dose-response behavior that impacts various plant functions. It provides crucial insights into the molecular mechanisms underlying these hormetic effects, encompassing their effects on photosynthesis, oxidative stress response and gene regulation. The significance of this article consists in its emphasis on the necessity to establish clear regulatory frameworks and promote international collaboration to standardize the responsible adoption of nano-TiO2 technology within the agricultural sector. The findings are presented with the intention of stimulating interdisciplinary research and serving as an inspiration for further exploration and investigation within this vital and continually evolving field.

Environmental behaviors and toxic mechanisms of engineered nanomaterials in soil

Engineered nanomaterials (ENMs) are inevitably released into the environment with the exponential application of nanotechnology. Parts of ENMs eventually accumulate in the soil environment leading to potential adverse effects on soil ecology, crop production, and human health. Therefore, the safety application of ENMs on soil has been widely discussed in recent years. More detailed safety information and potential soil environmental risks are urgently needed. However, most of the studies on the environmental effects of metal-based ENMs have been limited to single-species experiments, ecosystem processes, or abiotic processes. The present review formulated the source and the behaviors of the ENMs in soil, and the potential effects of single and co-exposure ENMs on soil microorganisms, soil fauna, and plants were introduced. The toxicity mechanism of ENMs to soil organisms was also reviewed including oxidative stress, the release of toxic metal ions, and physical contact. Soil properties affect the transport, transformation, and toxicity of ENMs. Toxic mechanisms of ENMs include oxidative stress, ion release, and physical contact. Joint toxic effects occur through adsorption, photodegradation, and loading. Besides, future research should focus on the toxic effects of ENMs at the food chain levels, the effects of ENMs on plant whole-lifecycle, and the co-exposure and long-term toxicity effects. A fast and accurate toxicity evaluation system and model method are urgently needed to solve the current difficulties. It is of great significance for the sustainable development of ENMs to provide the theoretical basis for the ecological risk assessment and environmental management of ENMs.

The interaction between titanium dioxide nanoparticles and light can have dualistic effects on the physiological responses of plants

The model plant Arabidopsis thaliana was exposed to combined stress factors, i.e., titanium dioxide nanoparticles (TiNPs) and high light. The concentrations of TiNPs used for irrigation were 250, 500, and 1000 μg/mL. This study shows that TiNPs alter the morphology and nanomechanical properties of chloroplasts in A. thaliana, which leads to a decrease in membrane elasticity. We found that TiNPs contributed to a delay in the thermal response of A. thaliana under dynamic light conditions, as revealed by non-invasive thermal imaging. The thermal time constants of TiNP-treated plants under excessive light are determined, showing a shortening in comparison to control plants. The results indicate that TiNPs may contribute to an alleviation of temperature stress experienced by plants under exposure to high light. In this research, we observed a decline in photosystem II photochemical efficiency accompanied by an increase in energy dissipation upon exposure to TiNPs. Interestingly, concentrations exceeding 250 µg/mL TiNPs appeared to mitigate the effects of high light, as shown by reduced differences in the values of specific OJIP parameters (FV/FM, ABS/RC, DI0/RC, and Pi_Abs) before and after light exposure.

Physiological and molecular effects of TiO2 nanoparticle application on UV-A radiation stress responses in Solanum lycopersicum L

Nanoparticles (NPs) of titanium dioxide (TiO2) alter photosynthetic and biochemical parameters in Solanum lycopersicum L., possibly due to their photocatalytic properties given by energy absorption in the UV-A range; however, the joint effects TiO2 NPs and UV-A radiation are not well understood. This work evaluates the combined responses of TiO2 NPs and UV-A radiation at the physiological and molecular levels in S. lycopersicum. In a split growth chamber, the presence (UV-A +) and absence (UV-A -) of UV-A were combined with 0 (water as a control), and 1000 and 2000 mg L-1 of TiO2 NPs applied at sowing. At the end of exposure (day 30 after sowing), the photosynthetic performance was determined, and biochemical and molecular parameters were evaluated in leaf tissues. Better photochemical performance in UV-A + than UV-A - in control plants was observed, but these effects decreased in 1000 and 2000 mg TiO2 L-1, similar to net CO2 assimilation. A clear increase in photosynthetic pigment levels was recorded under UV-A + compared to UV-A - that was positively correlated with photosynthetic parameters. A concomitant increase in total phenols was observed on adding TiO2 in UV-A - conditions, while a decreasing trend in lipid peroxidation was observed for the same treatments. There was an increase in psbB gene expression under TiO2/UV-A + treatments, and a reduced expression of rbcS and rbcL under UV-A - . These results suggest that the reduction in photosynthetic performance on applying high doses of TiO2 NPs is probably due to biochemical limitation, while UV-A achieves the same result via the photochemical component.

Combined analysis of transcriptomics and metabolomics on the cumulative effect of nano-titanium dioxide on mulberry seedlings

Introduction

Titanium dioxide nanoparticles (TiO₂ NPs) are among the most widely used inorganic nanomaterials in industry, medicine and food additives. There are increasing concerns regarding their potential risks to plants and the environment. Mulberry trees are widely grown in China due to their high survival rate and ability to aid ecological recovery.

Methods

Herein, the effects of TiO₂ NPs with different concentrations (100, 200, 400 and 800 mg/L) on the growth and physiology of the mulberry tree were systematically evaluated in aspects of physiology, transcriptomics and metabolomics.

Results

Results showed that TiO₂ NPs could be absorbed by the mulberry sapling root system and be transferred to the plant shoot. This results in the destruction of mulberry sapling root and leaf tissue. Furthermore, the number of chloroplasts and their pigment contents were reduced and the homeostasis of metal ions was disrupted. The toxic effects of TiO₂ NPs attenuated the mulberry sapling's stress resistance, the contents of malondialdehyde in 100 mg/L, 200 mg/L 400 mg/L and 800 mg/L treatment groups increased by 87.70%, 91.36%, 96.57% and 192.19% respectively compared with the control group. The transcriptomic data showed that TiO₂ NPs treatment mainly affected the expression of genes related to energy synthesis and transport, protein metabolism, and response to stress. Meanwhile, the results of metabolomics showed that 42 metabolites produced significant differences in mulberry, of which 26 differential metabolites were up-regulated in expression and 16 differential metabolites were down-regulated, mainly including metabolic pathways such as secondary metabolite biosynthesis, citric acid cycle, and tricarboxylic acid cycle, and was not conducive to the seed germination and or growth of the mulberry sapling.

Discussion

This study enriches the understanding of the effects of TiO₂ NPs on plants and provides a reference for the comprehensive scientific assessment of the potential risks of nanomaterials on plants.

Advances in transport and toxicity of nanoparticles in plants

In recent years, the rapid development of nanotechnology has made significant impacts on the industry. With the wide application of nanotechnology, nanoparticles (NPs) are inevitably released into the environment, and their fate, behavior and toxicity are indeterminate. Studies have indicated that NPs can be absorbed, transported and accumulated by terrestrial plants. The presence of NPs in certain edible plants may decrease harvests and threaten human health. Understanding the transport and toxicity of NPs in plants is the basis for risk assessment. In this review, we summarize the transportation of four types of NPs in terrestrial plants, and the phytotoxicity induced by NPs, including their impacts on plant growth and cell structure, and the underlying mechanisms such as inducing oxidative stress response, and causing genotoxic damage. We expect to provide reference for future research on the effects of NPs on plants.

Phytochemical and physiological reactions of feverfew (Tanacetum parthenium (L.) Schultz Bip) to TiO2 nanoparticles

Nanomaterials can be used as elicitors for improving the biosynthesis of secondary metabolites in medicinal plants. The present study was conducted to assay the titanium dioxide-nanoparticles (TiO₂-NPs) effects on feverfew (Tanacetum parthenium) as an anti-cancer plant. The study showed that TiO₂-NPs application increased the amounts of the main compounds and oxygenated monoterpene in essential oils, thereby causing an improvement in the quantity and quality of the essential oils compared to control. The highest effect was related to 1500 ppm TiO₂-NPs concentration. Regarding parthenolide, TiO₂-NPs had no positive effect on parthenolide content and the highest content was observed in control. Increasing the concentrations over 1500 ppm resulted in a decrease in chlorophyll content, capitule diameter, flower yield, and harvest index compared to other concentrations and control. Additionally, the results indicated that TiO₂-NPs foliar spray reduced flower number, biological yield, fresh weight, and dry weights compared with untreated plants. The increase in quality and content of essential oil and lack of increase in parthenolide content, and reproductive and vegetative characteristics showed that TiO₂-NPs mainly affected the content and composition of essential oil. Totally, the application of TiO2-NPs in terms of positive effect on the yield and metabolites (without damaging biological effects) can be recommended and followed up to the concentration of 1000 ppm. Overall, the results indicated that improving the synthesis of valuable medicinal metabolites using TiO₂-NPs has promising results depending on the type of species, concentration used and target metabolites.

Potential of green synthesized titanium dioxide nanoparticles for enhancing seedling emergence, vigor and tolerance indices and DPPH free radical scavenging in two varieties of soybean under salinity stress

BACKGROUND

Considering titanium dioxide nanoparticles (TiO₂ NPs) role in plant growth and especially in plant tolerance against abiotic stress, in the present work, TiO₂ NPs were green synthesized using an aqueous solution of Aloe vera leaf extract as a capping agent and titanium tetrachloride as a precursor. These green synthesized TiO₂ NPs were characterized using different techniques: UV spectrophotometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Results revealed that synthesized TiO₂ NPs possess a tetragonal morphology with a size ranging from 10 to 25 nm. Additionally, the present work evaluated the effects of three concentrations of TiO₂ NPs (0, 30 and 50 ppm) and six NaCl concentrations (0, 25, 50, 100, 150 and 200 mM) and their interactions with respect to germination parameters, vigor indices, oxidative stress and DPPH free radical scavenging of two varieties of soybean (Glycine max L. var. 22 and 35).

RESULTS

Results demonstrated that all germination traits and vigor indices were negatively affected under all salinity levels. Also, the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) were significantly increased by increasing the NaCl concentrations in two soybean varieties. Most interestingly, TiO2 NPs (30 ppm) mediated positive effects on germination parameters, reducing H2O2 and MDA contents by enhancing antioxidant (decreasing IC50) whereas 50 ppm showed an intermediate response under both control and saline soil conditions.

CONCLUSION

Our findings demonstrate the growth enhancement effects of TiO₂ NPs application as well as its ameliorative potential in dealing with salinity.

TiO2 nanoparticle synthesis, characterization and application to shoot regeneration of water hyssop (Bacopa monnieri L. Pennel) in vitro

Water hyssop (Bacopa monnieri L. Pennel) is a medicinal aquatic herb used to treat diseases in South Asia. Various regeneration protocols have been developed or modified in vitro to ensure the availability of biomass and secondary metabolites of Bacopa. We applied hydrothermally treated titanium dioxide (TiO₂) nanoparticles (NPs) (TiO₂-NPs) at different concentrations. Three explants, distal portion of half leaf (DPHL), proximal portion of half leaf (PPHL) and full leaf (FL), were used to evaluate response to TiO₂. Regeneration from the three explants in vitro was similar except for shoot length. Application of TiO₂-NPs exerted significant, but variable, effects on all parameters except percentage of shoot formation, which was 100%. Interactive effects of explant and TiO₂-NPs exhibited significant, but variable, effects on fresh weight and percentage of callus formation. All explants produced more shoots using TiO₂-NPs compared to control treatments. DPHL explants with application of 8 mg/l TiO₂ produced more shoots than controls. Similarly, FL explant treated with 2 mg/l TiO₂-NPs produced more shoots/explant than controls. All concentrations of TiO₂-NPs produced significantly longer shoots compared to controls. Increased elongation of shoots justifies use of TiO₂-NPs for propagation of plants in vitro during acclimatization. Use of TiO₂-NPs for rapid elongation of shoots ultimately fosters survival of plants.

Deciphering the iPBS retrotransposons based genetic diversity of nanoparticles induced in Vitro seedlings of industrial hemp (Cannabis sativa L.)

BACKGROUND

The phytochemicals contained in hemp are highly significant and can be modified or altered by employing in vitro elicitors like nanoparticles (NPs). Application of NPs type, concentration, and treatment time regulate the germination, growth, and phytohemicals.

METHODS AND RESULTS

In vitro sterilized seeds of cannabis were augmented on Murashige and Skoog (MS) medium supplemented with silver (Ag) and titanium dioxide (TiO₂) nanoparticles at different concentrations (0, 200, 400, 800, 1200 and 1600 mg/L) for one month. Results revealed that supplementation of NPs resulted in reduced germination (%), root length and longer shoots and seedling fresh wt compared to control.

CONCLUSIONS

Maximum germination was recorded on MS medium supplemented with 1600 mg/L TiO₂NPs (92.50%) followed by 1600 mg/L AgNPs (80.00%). Supplementation of 800 mg/L AgNPs yielded longer shoots, roots, seedlings fresh weight, and chlorophyll-b contents compared to all other treatments. Whereas, maximum chlorophyll-a, carotenoids, and MDA contents were attributed to 1200 mg/L TiO₂NPs. PCR results using eight iPBS-retrotransposons primers yielded a total of 101 bands with 98 polymorphic bands. Whereas, minimum (0.28) and maximum (0.42) gene diversity was associated with 2095 and 2228 primers.

Titanium and Zinc Based Nanomaterials in Agriculture: A Promising Approach to Deal with (A)biotic Stresses?

Abiotic stresses, such as those induced by climatic factors or contaminants, and biotic stresses prompted by phytopathogens and pests inflict tremendous losses in agriculture and are major threats to worldwide food security. In addition, climate changes will exacerbate these factors as well as their negative impact on crops. Drought, salinity, heavy metals, pesticides, and drugs are major environmental problems that need deep attention, and effective and sustainable strategies to mitigate their effects on the environment need to be developed. Besides, sustainable solutions for agrocontrol must be developed as alternatives to conventional agrochemicals. In this sense, nanotechnology offers promising solutions to mitigate environmental stress effects on plants, increasing plant tolerance to the stressor, for the remediation of environmental contaminants, and to protect plants against pathogens. In this review, nano-sized TiO₂ (nTiO₂) and ZnO (nZnO) are scrutinized, and their potential to ameliorate drought, salinity, and xenobiotics effects in plants are emphasized, in addition to their antimicrobial potential for plant disease management. Understanding the level of stress alleviation in plants by these nanomaterials (NM) and relating them with the application conditions/methods is imperative to define the most sustainable and effective approaches to be adopted. Although broad-spectrum reviews exist, this article provides focused information on nTiO₂ and nZnO for improving our understanding of the ameliorative potential that these NM show, addressing the gaps in the literature.

Titanium dioxide nanoparticles mitigate cadmium toxicity in Coriandrum sativum L. through modulating antioxidant system, stress markers and reducing cadmium uptake

Anthropogenic activities are the foremost reason of metal pollution in soils of the cultivated areas, resulting abnormal physiochemical processes in plants. Among metals contaminants, cadmium (Cd) is one of the most injurious contaminants that deleteriously affect physiological activities, growth and yield of the crop plants. Keeping in view the stress mitigation potential of titanium dioxide (TiO₂), the existing research work was premeditated to inspect the beneficial role of seed priming with titanium dioxide nanoparticles (TiO₂-NPs) on biochemical, morphological and physiological characteristics of Coriandrum sativum L. (coriander) plants under Cd stress. For this purpose, C. sativum seeds were primed with 0, 40, 80 and 160 mg L^-1 TiO₂-NPs. Cadmium stress triggered a significant decrease in chlorophyll a content (49%), chlorophyll b content (44%), photosynthetic rate (62%) and plant growth (51%) as compared with control. Tanium dioxide nanoparticles treated seedlings exhibited reduced Cd contents besides improved agronomic traits (seedlings biomass, number of seeds and yield). The TiO₂-NPs treatment declined the magnitude of EL and MDA by 1.5 fold and 1.71 fold, respectively. Furthermore, TiO₂-NPs diminished oxidative injuries in plants exposed to Cd stress. Additionally, TiO₂-NPs enhanced the biosynthesis of osmatic regulators (proline) by 47% which helped in the mitigation of Cd persuaded toxicity in plants. Briefly, treatment of 80 mg L^-1 TiO₂-NPs perhaps ameliorates the deleterious influence of Cd stress and enhance the yield of coriander.

Genetic factors controlling nTiO2 nanoparticles stress tolerance in barley (Hordeum vulgare) during seed germination and seedling development

Titanium dioxide nanoparticle (nTiO2) is one of the most produced nanoparticles worldwide. Its mechanism on crop development and performance is unclear as it is hard to predict their toxicity or benefit. Therefore, understanding the genetics of crop development under nTiO2 is a prerequisite for their applications in agriculture and crop improvement. Here, we aimed to examine the influnce of 300ppm nTiO2 on seed germination, seedling morphology, root-related traits in 121 worldwide spring barley (Hordeum vulgare L.) accessions. Results show that nTiO2 significantley affected all traits scored in this study. Response to nTiO2 treatment, clear wide natural variation among accesions was detected. Remarkably, 10 genotypes showed increased root length under nTiO2 at the seedling stage indicating that nTiO2 enhanced the root elongation. Genome-wide association scan (GWAS) was applied using 9K single nucleotide polymorphism (SNPs) in a mixed-linear model that revealed 86 significant marker-trait associations with all traits scored in this study. Many significant SNPs were physically located near candidate genes, of which 191 genes were detected within the linkage disequilibrium and distributed over all barley chromosomes. Mostly, the genes harboured by chromosome 2H, specially calcium-binding genes family, regulate the variation of seedling length-related traits. Candidate genes on 7H encode zinc finger protein that controls the rate of germination. Therefore, these genomic regions at 2H and 7H can be targeted to select for improved seedling development and seed germination under nTiO2 stress in soils. These results improve understanding the genetic control of seed germination and seedling development under high levels of nTiO2 that can support plant breeding and crop improvement programmes.

Aquatic Environment Exposure and Toxicity of Engineered Nanomaterials Released from Nano-Enabled Products: Current Status and Data Needs

Rapid commercialisation of nano-enabled products (NEPs) elevates the potential environmental release of engineered nanomaterials (ENMs) along the product life cycle. The current review examined the state of the art literature on aquatic environment exposure and ecotoxicity of product released (PR) engineered nanomaterials (PR-ENMs). Additionally, the data obtained were applied to estimate the risk posed by PR-ENMs to various trophic levels of aquatic biota as a means of identifying priority NEPs cases that may require attention with regards to examining environmental implications. Overall, the PR-ENMs are predominantly associated with the matrix of the respective NEPs, a factor that often hinders proper isolation of nano-driven toxicity effects. Nevertheless, some studies have attributed the toxicity basis of observed adverse effects to a combination of the released ions, ENMs and other components of NEPs. Notwithstanding the limitation of current ecotoxicology data limitations, the risk estimated herein points to an elevated risk towards fish arising from fabrics' PR-nAg, and the considerable potential effects from sunscreens' PR-nZnO and PR-nTiO2 to algae, echinoderms, and crustaceans (PR-nZnO), whereas PR-nTiO2 poses no significant risk to echinoderms. Considering that the current data limitations will not be overcome immediately, we recommend the careful application of similar risk estimation to isolate/prioritise cases of NEPs for detailed characterisation of ENMs' release and effects in aquatic environments.

Dose-Dependent Effect of ZnO Quantum Dots for Lettuce Growth

As the cadmium-free semiconductor quantum dots, ZnO quantum dots (ZnO QDs) have wide potential applications in agriculture. However, the effects of ZnO quantum dots on crop growth and nutritional quality have not been fully studied. In this work, the lettuce was sprayed with different concentrations of ZnO QDs from 50 to 500 mg·L^-1 to evaluate their influence on lettuce antioxidant, biomass, and nutritional quality. The results showed that ZnO QDs existed in the lettuce in the form of Zn²⁺. Lettuce treated with 500 mg·L^-1 ZnO QDs would produce a large amount of reactive oxygen species (ROS), which adversely affected the absorption of nutrients, soluble protein content, and chlorophyll content, thus reducing plant biomass. When the concentrations range from 50 to 200 mg·L^-1, the antioxidant enzyme systems of lettuce were triggered to counteract the damage caused by excessive ROS. Moreover, ZnO QDs at this level promoted Ca, Mg, Fe, Mn, Zn, and B absorption and accumulation; increased soluble sugar content; and improved the lettuce biomass and nutritional quality.

Toxicity assessment of synthesized titanium dioxide nanoparticles in fresh water algae Chlorella pyrenoidosa and a zebrafish liver cell line

This study aims to assess the toxicity of the commonly-spread titanium dioxide nanoparticles (TiO₂ NPs) by evaluating the exposure impact of the particles on both freshwater algae Chlorella pyrenoidosa and zebrafish liver cell line (ZFL), the two common in vitro models in toxicological studies. To compare the toxic effects of TiO₂ NPs with different physiochemical properties, three types of manufactured TiO₂ were used: bulk TiO₂, Degussa P25 TiO₂, and ultrafine TiO₂ NPs. Both short and long-term biological responses of green algae, such as the effect on the cell growth rate, pigment autofluorescence, and esterase activity were investigated. The dosage, physical property of TiO₂ particles, and their interactions with algal cells affect cellular growth, especially after short-term exposure. The hydrodynamic size plays a critical role in determining the acute toxicity to C. pyrenoidosa in terms of autofluorescence and esterase activity, while all types of TiO₂ NPs show toxic effects after exposure for 14 days. However, this observation is not seen when studying the effect of introduced particles in ZFL, for the precipitated Degussa P25 TiO₂ showed the highest cellular inhibition. Interestingly, despite the obvious overall toxicity toward C. pyrenoidosa, the photocatalytical properties of TiO₂ NPs may contribute to the enhanced photosynthesis in the low concentration range (<40 µg mL^-1). Overall, we found that the physical interactions between TiO₂ particles and the cells, particles' size and dispersibility play critical role in the cytotoxic effect for both algal and ZFL cells, while the photocatalytical properties of TiO₂ particles may produce mixed effects on the cytotoxicity of green algae.

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

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

Exposure Route of TiO2 NPs from Industrial Applications to Wastewater Treatment and Their Impacts on the Agro-Environment

The tremendous increase in the production and consumption of titanium dioxide (TiO2) nanoparticles (NPs) in numerous industrial products and applications has augmented the need to understand their role in wastewater treatment technologies. Likewise, the deleterious effects of wastewater on the environment and natural resources have compelled researchers to find out most suitable, economical and environment friendly approaches for its treatment. In this context, the use of TiO2 NPs as the representative of photocatalytic technology for industrial wastewater treatment is coming to the horizon. For centuries, the use of industrial wastewater to feed agriculture land has been a common practice across the globe and the sewage sludge generated from wastewater treatment plants is also used as fertilizer in agricultural soils. Therefore, it is necessary to be aware of possible exposure pathways of these NPs, especially in the perspective of wastewater treatment and their impacts on the agro-environment. This review highlights the potential exposure route of TiO2 NPs from industrial applications to wastewater treatment and its impacts on the agro-environment. Key elements of the review present the recent developments of TiO2 NPs in two main sectors including wastewater treatment and the agro-environment along with their potential exposure pathways. Furthermore, the direct exposure routes of these NPs from production to end-user consumption until their end phase needs to be studied in detail and optimization of their suitable applications and controlled use to ensure environmental safety.

Effects of titanium dioxide nanoparticles on the myocardium of the adult albino rats and the protective role of β-carotene (histological, immunohistochemical and ultrastructural study)

Titanium dioxide nanoparticles (TiO₂ NPs) are the most produced nanomaterials. TiO₂ NPs are used as a drug carrier and molecular imaging vehicle in the cardiovascular system. We aimed to study TiO₂ NPs effects on the ventricular myocardium and evaluate the ameliorative effects of β-carotene (βC). Forty adult albino rats were divided into four groups: negative control group (Ι) received a distilled water. Treated group (II): received 20 mg/kg/day TiO₂NPs intraperitoneally. Protected group (III): received 10 mg/kg/day βC orally together with TiO₂ NPs in a dose of 20 mg/kg/day intraperitoneally. Positive control group (IV) was given βC orally in a dose of 10 mg/kg/day for 14 days. Sections were stained with hematoxylin & eosin, bromphenol blue (BPB), and periodic acid Schiff (PAS). Anti-desmin & anti-CD45 immunohistochemical staining and electron microscopic examination were performed. Group (II) revealed fragmented myofibrils and inflammatory infiltrations. In group (III), normal cardiomyocytes with less inflammatory infiltrations. The optical density of PAS and BPB staining and anti-desmin showed a very highly significant decrease in the group (II) versus the control groups (P < 0.001). A highly significant increase in the optical density of group (III) versus group (II) (P < 0.01). Also, the area percentage mean values of collagen fibers and anti-CD45 in the group (II) showed a very highly significant increase versus the control groups (P < 0.001). Group (III) revealed a very highly significant decrease in the area percentage versus group (II) (P < 0.001). In conclusion: TiO₂ NPs adversely affected the histological structure of the adult rat ventricular myocardium in acute exposure (14 days) and the damage was less with βC.

Physiological and biochemical response of wheat (Triticum aestivum) to TiO2 nanoparticles in phosphorous amended soil: A full life cycle study

Nanoparticles (NPs) application in soil as nano-fertilizers to increase crop yield is getting attention due to their higher efficiency and less environmental risks. This study investigated the interactive effects of variable titanium dioxide nanoparticles (TiO₂-NPs) levels (0, 30, 50 and 100 mg kg^-1) superimposed to phosphorus (P) fertilizer application in soil at the rates of 0, 25 and 50 mg kg^-1 on wheat crop. Physiological parameters of plants, their antioxidant enzymes activities (SOD, POD), and contents of crude protein, H₂O₂, MDA and metals/nutrients (Al, Ca, Mg, Fe, Zn and Cu) were measured. Data on physiological traits revealed that application of 50 mg kg^-1 of TiO₂-NPs without P fertilizer significantly enhanced the root and shoot length by 63 and 26%, respectively. Increased contents of nutrients in the shoots, viz., Ca (316%), Cu (296%), Al (171%) and Mg (187%) with 50 mg kg^-1 TiO₂-NPs treatment reflected improvement in crop growth and grain quality. Furthermore, P contents in plant tissues were raised up to 56% with 50 mg kg^-1 of TiO₂-NPs even in the absence of P fertilizer. In the soil, concentration of phytoavailable P was significantly increased up to 63.3% in the presence of 50 mg kg^-1 TiO₂-NPs as compared to control. Contents of crude protein in grain were also enhanced by 22.8% (at P₅₀) and 17.4% (at P₂₅) with 50 mg kg^-1 TiO₂-NPs application. Along with P application, TiO₂-NPs triggered the activities of SOD (2.06-33.97%) and POD (up to 13.19%), and H₂O₂ production (50.6-138.8%). However, MDA contents were not elevated significantly at any level of TiO₂-NPs, and remained at par with control. It was noteworthy that highest level of TiO₂-NPs, viz., 100 mg kg^-1 exhibited plant and nutrients response lower than that with 50 mg kg^-1. Further, TiO₂-NPs triggered the bioavailability of micronutrient heavy metals (Zn, Cu and Fe) and Al, which could have toxicity at higher concentrations. These results suggested that TiO₂-NPs might have some affinities with phosphate compounds and metal ions in the soil to bring them in soluble form, which enhanced their bioavailability. Although it improved the crop yield and quality, but toxic or negative impact of TiO₂-NPs was also apparent at higher dose. Therefore, investigations on the potential interactions of NPs with other nutrients and toxic metals are needed to enhance our understanding for the safer application of nano-fertilizer.

Common mechanisms activated in the tissues of aquatic and terrestrial animal models after TiO2 nanoparticles exposure

Titanium dioxide nanoparticles (TiO₂-NPs) are among the most popular manufactured and widely used nanoparticles. They are released into the environment, affecting terrestrial and aquatic ecosystems, with unexpected consequences to organisms and human health. The present study investigates the mediated toxicity imposed to the freshwater fish species, zebrafish (Danio rerio) and the prussian carp (Carassius gibelio), and to the terrestrial land snail Cornu aspersum, after their exposure to sublethal concentrations of TiO₂-NPs. Oxidative, proteolytic, genotoxic and apoptotic parameters in fish liver and gills, as well as on snail hemocytes were studied and the swimming performance was estimated in order to (a) estimate and suggest the most susceptible animal, and (b) propose a common battery of biomarkers as the most suitable indicator for biomonitoring studies against TiO₂-NPs. Our in vivo experiments demonstrated that NPs induced detrimental effects on animal physiology and swimming behavior, while no general pattern was observed in species and tissues responsiveness. Generally, TiO₂-NPs seemed to activate a group of molecules that are common for aquatic as well as terrestrial animals, implying the existence of a conserved mechanism. It seems that after exposure to TiO₂-NPs, a common mechanism is activated that involves the stimulation of immune system with the production of ROS, damage of lysosomal membrane, protein carbonylation, lipid peroxidation, DNA damage, following proteolysis by ubiquitin and finally apoptosis. Thus, the simultaneous use of the latter biomarkers could be suggested as a reliable multi parameter approach for biomonitoring of aquatic and terrestrial ecosystems against TiO₂-NPs.

Facilitated transport of nTiO2-kaolin aggregates by bacteria and phosphate in water-saturated quartz sand

The soil major component of clay plays an important role in governing the fate and transport of engineered nanomaterials (e.g., the most commonly used titanium dioxide nanoparticles; nTiO₂) in the subsurface environments via forming nTiO₂-clay aggregates. This research is designed to unravel the interplay of naturally-occurring bacteria (Escherichia coli) and phosphate on the transport and retention of nTiO₂-kaolin aggregates in water-saturated porous media. Our results showed that nTiO₂-nTiO₂ homoaggregates and nTiO₂-kaolin heteroaggregates dominated in the nTiO₂-kaolin nanoaggregate suspension. Transport of nTiO₂-kaolin aggregates was enhanced with the copresence of E. coli and phosphate, particularly at the low pH of 6.0. This effect is due to the greater adsorption of phosphate and thus the greater enhancement in repulsive interaction energies between aggregates and sand grains at pH 6.0 (vs. pH 9.0). The charged "soft layer" of E. coli cell surfaces changed the aggregation state and the heterogeneous distribution of nTiO₂-kaolin aggregates, and subsequently stabilized the nTiO₂-nTiO₂ homoaggregates and nTiO₂-kaolin heteroaggregates via TEM-EDX measurements and promoted the physical segregation between the aggregates (separation distance = 0.486 vs. 0.614 μm without vs. with the presence of E. coli) via 2D/3D AFM identifications, both of which caused greater mobility of nTiO₂-kaolin aggregates with the presence of E. coli. Nonetheless, transport of nTiO₂-kaolin aggregates was lower with the copresence of E. coli and phosphate vs. the singular presence of phosphate due to the competitive adsorption of less negatively charged E. coli (vs. phosphate) onto the aggregates. Taken altogether, our findings furnish new insights into better understanding the fate, transport, and potential risks of nTiO₂ in real environmental settings (soil and sediment aquifer) where clay, bacteria, and phosphate ubiquitously cooccur.

Impact of synthesized metal oxide nanomaterials on seedlings production of three Solanaceae crops

Prospective involvement of metal oxide nanomaterials as a prominent agriculture practice for improving existing crop production directed the present investigation for synthesizing of ZnO and TiO₂ nanomaterials as an attempt to enhance the transplants production of some Solanaceae crops. The morphological characterizations of the prepared nanomaterials indicated that the hydrothermal synthesized ZnO was produced in nanorod structure with an average aspect ratio of 7. However, SEM and TEM micrographs of microwave prepared TiO₂ evident that it has a nanoparticle structure with an average diameter of 43 nm. The BET results confirmed the high specific areas of the two prepared metal oxide nanomaterials. The two synthesized metal oxide nanomaterials were coated in gel and mixed with the seeds of eggplant, pepper and tomato crops at four concentrations 0, 50, 100 and 150 mg/L, whilst the control seeds were germinated in distilled water without gel-coating. The results pointed to the outstanding effect of TiO₂ and ZnO nanoparticles on germination characters and seedlings growth. The maximum transplants lengths, fresh and dry weight were recorded at the level 100 mg/L whatever the crop plant used. Hastening germination operation of nanomaterials-gel coated seedlings compared to control plants may be ascribed to the reduction of mean germination time and coefficient variation of the germination process besides increasing the mean germination rate and the synchrony of germination traits. Overall, better performance of growing transplants has been accredited for nanoparticles-gel coated seedlings more than the control treatments which could be efficient for the safer production of transplants in an innovative way.

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

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

Changes in morphology, chlorophyll fluorescence performance and Rubisco activity of soybean in response to foliar application of ionic titanium under normal light and shade environment

Titanium (Ti) is considered an essential element for plant growth; however, its role in crop performance through stimulating the activities of certain enzymes, enhancing chlorophyll content and photosynthesis, and improving crop morphology and growth requires more study. We therefore conducted a laboratory experiments to study the effects of ionic Ti application on morphology, growth, biomass distribution, chlorophyll fluorescence performance and Rubisco activity of soybean (Glycine max L.) under normal light (NL) and shade conditions (SC). In this study, we sprayed soybean plants with five different levels of ionic Ti (T1 = 0, T2 = 1.25, T3 = 2.5, T4 = 5 and T5 = 10 mg Ti Plant-1) through foliar application method. Our results show that with increasing moderate (2.5 mg Ti Plant-1) Ti concentration, the chlorophyll pigments (chlorophyll [Chl] a, b, carotenoid [Car]), plant biomass, photochemical efficiency of photosystem II (Fv/Fm), and electron transport rate (ETR) of soybean increased, but higher levels (5-10 mg Ti Plant-1), resulted in leaf anatomical and chloroplast structural disruptions under both NL and SC. Soybean plants showed maximum biomass, leaf area, leaf thickness, Chl a, b, Car, Rubisco activity, Fv/Fm and ETR for T3 at 2.5 mg Ti Plant-1; however, declined significantly for T5 at high concentration of 10 mg Plant-1. In NL, the application of 2.5 mg Ti Plant-1 (T3) increased the Chl a, b, and total Chl contents 40, 20, and 27% as compared to control treatment (T1). In SC, the application of 1.25 mg Ti mg Plant-1 (T2) increased the Chl a, b, and total Chl contents 38, 19, and 14% as compared to control treatment. In NL, the Fv/Fm, qP, PSII, and ETR were higher in the T3 treatment over the T1 (control) by 7, 0.3, 16, and 16%, respectively. In SC, the Fv/Fm, qP, PSII, and ETR were higher in the T3 treatment over the T1 (control) by 5, 5, 19, and 19%, respectively. Moreover, Rubisco activity was at peak (55 and 6% increase under NL and SC) at 2.5 mg Ti Plant-1and decreased with increasing Ti concentration, reaching the lowest at 10 mg Ti Plant-1, which indicates that leaf cells were damaged as observed in the leaf anatomy. We concluded that ionic Ti expresses a hormesis effect: at lower concentrations, promoting soybean growth, however, at higher concentrations, suppressing soybean growth both under NL and SC. We therefore suggest that under different light stress conditions, Ti application could serve to mitigate abiotic stresses, especially in intercropping systems.

Toxicity and mechanisms of action of titanium dioxide nanoparticles in living organisms

Titanium dioxide nanoparticles (TiO₂ NPs) are one of the most widely used nanomaterials in the consumer products, agriculture, and energy sectors. Their large demand and widespread applications will inevitably cause damage to organisms and ecosystems. A better understanding of TiO₂ NP toxicity in living organisms may promote risk assessment and safe use practices of these nanomaterials. This review summarizes the toxic effects of TiO₂ NPs on multiple taxa of microorganisms, algae, plants, invertebrates, and vertebrates. The mechanism of TiO₂ NP toxicity to organisms can be outlined in three aspects: The Reactive Oxygen Species (ROS) produced by TiO₂ NPs following the induction of electron-hole pairs; cell wall damage and lipid peroxidation of the cell membrane caused by NP-cell attachment by electrostatic force owing to the large surface area of TiO₂ NPs; and TiO₂ NP attachment to intracellular organelles and biological macromolecules following damage to the cell membranes.

Carbon nanomaterials alter plant physiology and soil bacterial community composition in a rice-soil-bacterial ecosystem

The aim of this study was to compare the toxicity effects of carbon nanomaterials (CNMs), namely fullerene (C₆₀), reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs), on a mini-ecosystem of rice grown in a loamy potted soil. We measured plant physiological and biochemical parameters and examined bacterial community composition in the CNMs-treated plant-soil system. After 30 days of exposure, all the three CNMs negatively affected the shoot height and root length of rice, significantly decreased root cortical cells diameter and resulted in shrinkage and deformation of cells, regardless of exposure doses (50 or 500 mg/kg). Additionally, at the high exposure dose of CNM, the concentrations of four phytohormones, including auxin, indoleacetic acid, brassinosteroid and gibberellin acid 4 in rice roots significantly increased as compared to the control. At the high exposure dose of MWCNTs and C₆₀, activities of the antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD) in roots increased significantly. High-throughput sequencing showed that three typical CNMs had little effect on shifting the predominant soil bacterial species, but the presence of CNMs significantly altered the composition of the bacterial community. Our results indicate that different CNMs indeed resulted in environmental toxicity to rice and soil bacterial community in the rhizosphere and suggest that CNMs themselves and their incorporated products should be reasonably used to control their release/discharge into the environment to prevent their toxic effects on living organisms and the potential risks to food safety.

Uptake and transformations of engineered nanomaterials: Critical responses observed in terrestrial plants and the model plant Arabidopsis thaliana

With the applications of engineered nanomaterials (ENMs) continually expanding and production quickly growing, residues of ENMs will end up in the environment at levels that may be harmful to non-target organisms. Many of the tunable properties that have made them desirable, such as type, size, charge, or coating, also contribute to the current difficulties in understanding the fate of ENMs in the environment. This review article focuses on studies that investigate plant-ENM interactions, including techniques used to study these interactions and documented plant responses due to the phytotoxic effects of ENMs. The many variables which can be altered for an experiment, such as type, size, and concentration of ENMs, make it difficult to formulate generalizations about the uptake mechanism involved, or to make an inference on the subcellular localization and distribution of the internalized ENMs in plant tissue. In order to avoid these challenges, studies can utilize a model organism such as Arabidopsis thaliana, and a combination of analytical techniques that can reveal complementary information in order to assess how the different experimental conditions influence the uptake and phytotoxicity of ENMs. This review presents recent studies regarding plant-ENM interactions employing Arabidopsis to demonstrate how the use of this model plant can advance our understanding of plant-ENM interactions and guide additional studies using other plant species. Overarching results suggest that more sensitive tests and consistency in experimental designs are needed to fully assess and understand the phytotoxic effects of ENMs in the environment.

Wheat chronic exposure to TiO2-nanoparticles: Cyto- and genotoxic approach

This study investigates the phytotoxicity of chronic exposure (up to 20 d) of different TiO₂ nanoparticles (TiO₂-NP) concentrations (5, 50, 150 mg L^-1) in Triticum aestivum. Germination was not affected by TiO₂-NP exposure and seedling shoot length (3 d) was enhanced. Contrarily, plants' shoot growth (20 d) was impaired. Effects on membrane permeability and total antioxidant capacity in TiO₂-NP chronic exposure were organ dependent: increased in leaves and decreased in roots. Roots also showed lower levels of lipid peroxidation. Flow cytometry revealed no changes in ploidy levels as well as in the cell cycle dynamics for both organs. However, TiO₂-NP induced clastogenic effects in roots with increases in micronucleated cells in root tips in a dose dependent manner. Also, increases of DNA single/double strand breaks were found in leaves, and effects were similar to all doses. Ti uptake and translocation to leaves were confirmed by ICP-MS, which was dependent on NP concentration. Overall, these data indicate that TiO₂-NP phytotoxicity is more severe after longer exposure periods, higher doses and more severe for shoots than roots. The observed effects are a result of both direct and indirect (oxidative stress and/or water imbalances) action of TiO₂-NP. Additionally, results highlight the negative impact that TiO₂-NP may have on crop growth and production and to the risk of trophic transfer.

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

The wide occurrence and high environmental concentration of titanium dioxide nanoparticles (nano-TiO₂) have raised concerns about their potential toxic effects on crops. In this study, we employed a GC-MS-based metabolomic approach to investigate the potential toxicity of nano-TiO₂ on hydroponically-cultured rice (Oryza sativa L.) after exposed to 0, 100, 250 or 500 mg/L of nano-TiO₂ for fourteen days. Results showed that the biomass of rice was significantly decreased and the antioxidant defense system was significantly disturbed after exposure to nano-TiO₂. One hundred and five identified metabolites showed significant difference compared to the control, among which the concentrations of glucose-6-phosphate, glucose-1-phosphate, succinic and isocitric acid were increased most, while the concentrations of sucrose, isomaltulose, and glyoxylic acid were decreased most. Basic energy-generating ways including tricarboxylic acid cycle and the pentose phosphate pathway, were elevated significantly while the carbohydrate synthesis metabolism including starch and sucrose metabolism, and glyoxylate and dicarboxylate metabolism were inhibited. However, the biosynthetic formation of most of the identified fatty acids, amino acids and secondary metabolites which correlated to crop quality, were increased. The results suggest that the metabolism of rice plants is distinctly disturbed after exposure to nano-TiO₂, and nano-TiO₂ would have a mixed effect on the yield and quality of rice.

Titanium as a Beneficial Element for Crop Production

Titanium (Ti) is considered a beneficial element for plant growth. Ti applied via roots or leaves at low concentrations has been documented to improve crop performance through stimulating the activity of certain enzymes, enhancing chlorophyll content and photosynthesis, promoting nutrient uptake, strengthening stress tolerance, and improving crop yield and quality. Commercial fertilizers containing Ti, such as Tytanit and Mg-Titanit, have been used as biostimulants for improving crop production; however, mechanisms underlying the beneficial effects still remain unclear. In this article, we propose that the beneficial roles Ti plays in plants lie in its interaction with other nutrient elements primarily iron (Fe). Fe and Ti have synergistic and antagonistic relationships. When plants experience Fe deficiency, Ti helps induce the expression of genes related to Fe acquisition, thereby enhancing Fe uptake and utilization and subsequently improving plant growth. Plants may have proteins that either specifically or nonspecifically bind with Ti. When Ti concentration is high in plants, Ti competes with Fe for ligands or proteins. The competition could be severe, resulting in Ti phytotoxicity. As a result, the beneficial effects of Ti become more pronounced during the time when plants experience low or deficient Fe supply.