Environmental behavior, potential phytotoxicity, and accumulation of copper oxide nanoparticles and arsenic in rice plants

Nanotechnology in sustainable agriculture: A double-edged sword

Nanotechnology is a rapidly developing discipline that has the potential to transform the way we approach problems in a variety of fields, including agriculture. The use of nanotechnology in sustainable agriculture has gained popularity in recent years. It has various applications in agriculture, such as the development of nanoscale materials and devices to boost agricultural productivity, enhance food quality and safety, improve the efficiency of water and nutrient usage, and reduce environmental pollution. Nanotechnology has proven to be very beneficial in this field, particularly in the development of nanoscale delivery systems for agrochemicals such as pesticides, fertilizers, and growth regulators. These nanoscale delivery technologies offer various benefits over conventional delivery systems, including better penetration and distribution, enhanced efficacy, and lower environmental impact. Encapsulating agrochemicals in nanoscale particles enables direct delivery to the targeted site in the plant, thereby reducing waste and minimizing off-target effects. Plants are fundamental building blocks of all ecosystems and evaluating the interaction between nanoparticles (NPs) and plants is a crucial aspect of risk assessment. This critical review therefore aims to provide an overview of the latest advances regarding the positive and negative effects of nanotechnology in agriculture. It also explores potential future research directions focused on ensuring the safe utilization of NPs in this field, which could lead to sustainable development. © 2024 Society of Chemical Industry.

Zinc oxide application alleviates arsenic-mediated oxidative stress via physio-biochemical mechanism in rice

Arsenic (As) pollution in cultivated soils poses a significant risk to the sustainable growth of agriculture and jeopardizes food security. However, the mechanisms underlying how zinc (Zn) regulates the toxic effects induced by As in plants remain poorly understood. Hence, this study aimed to explore the potential of ZnO as an effective and environmentally friendly amendment to alleviate As toxicity in rice, thereby addressing the significant risk posed by As pollution in cultivated soils. Through a hydroponic experiment, the study assessed the mitigating effects of different ZnO dosages (Zn5, 5 mg L-1; Zn15, 15 mg L-1; Zn30, 30 mg L-1) on rice seedlings exposed to varying levels of As stress (As0, 0 µM L-1; As25, 25 µM L-1). The findings of the study demonstrate significant improvements in plant height and biomass (shoot and root), with a notable increase of 16-40% observed in the Zn15 treatment, and an even more substantial enhancement of 29-53% observed in the Zn30 treatment under As stress, compared to respective control treatment. Furthermore, in the Zn30 treatment, the shoot and root As contents substantially reduced by 47% and 63%, respectively, relative to the control treatment. The elevated Zn contents in shoots and roots enhanced antioxidant enzyme activities (POD, SOD, and CAT), and decreased MDA contents (13-25%) and H2O2 contents (11-27%), indicating the mitigation of oxidative stress. Moreover, the expression of antioxidant-related genes, OsSOD-Cu/Zn, OsCATA, OsCATB, and OsAPX1 was reduced when rice seedlings were exposed to As stress and significantly enhanced after Zn addition. Overall, the research suggests that ZnO application could effectively mitigate As uptake and toxicity in rice plants cultivated in As-contaminated soils, offering potential solutions for sustainable agriculture and food security.

Impact of nCuO containing treated wastewater on soil microbes and dissolved organic matter in paddy field leachate

Using treated wastewater (TWW) resources in agriculture is a major pathway for disseminating nanoparticles. Copper-oxide nanoparticles (nCuO) offer potential benefits, but their presence in the environment poses risks to agricultural and environmental sustainability. This study examined soil microbial transformations and the composition of leachate dissolved organic matter (DOM) of paddy soils irrigated with nCuO-contaminated TWW at different concentrations (T2: 0.02 mgL-1, T3: 0.2 mgL-1, T4: 2.0 mgL-1) and examined the differences in Cu source (T5: 0.2 mgL-1 CuSO4). Results showed negative impacts on the absolute microbial abundance with up to 46 % reduction relative to the control treatment (T1). Changes in relative abundance of specific microbes at the genus level deviated from the corresponding phyla. Acidobacteria, Actinobacteria, Chloroflexi, and Verrucomicrobia phyla increased in the surface (0-3 cm) and subsurface (3-15 cm) layers responding differently to nCuO. In the 0-3 cm layer, Nitrospirae, Euryarchaeota, and Crenarchaeota increased, but only Dechloromonas genus from Proteobacteria increased with increasing nCuO. No significant variations were observed in the DOM composition, except in T4, which had a significantly low content of dissolved organic carbon (DOC), total dissolved nitrogen, and terrestrial humic-like and protein-like components. Ninety-eight distinct genera were identified, of which 44%, including 15 bacteria and two archaea, varied between the surface and subsurface, among treatments, and significantly correlated with more DOM parameters in the subsurface. T4 had the highest microbial diversity in the 0-3 layer, and Cu treatments slightly increased the diversity index in the subsurface. Moreover, the effects differed by Cu source, with T3 showing 10 % more reduction in the subsurface and 17 % less reduction in the surface than T5. The variable microbial responses to nCuO and their strong correlations with DOM highlight the need to consider the potential consequences of low nCuO concentrations on biogeochemical cycles.

Effects of CuO nanoparticles in composted sewage sludge on rice-soil systems and their potential human health risks

The release of metal-based nanoparticles (MNPs) into sewage systems is worrisome due to their potential impact on crop-soil systems that are amended with sewage sludge. This study aimed to investigate the effects of copper oxide nanoparticles (CuO NPs) in composted sewage sludge (CSS) on rice-soil systems and to assess the health risks associated with consuming CuO NP-contaminated rice produced by CSS amendment. CSS was treated with three doses of CuO NPs, resulting in Cu levels below the sludge limits (1500 mg Cu kg-1) for reuse as a soil amendment. Results showed that CuO NPs in CSS at environmentally acceptable levels had no negative effect on rice growth and yield. In fact, they enhanced biomass production, tillering capacity, and soil fertility by increasing N and K levels in the soil. In addition, CuO NPs in CSS (450-1450 mg Cu kg-1) promoted the accumulation of macro- and micro-minerals in rice grains, thereby improving the nutritional value of rice. However, Cu contamination in CSS led to elevated levels of toxic metals, especially As, in rice grains, posing potential health risks to both adults and children. In the presence of higher CuO NPs contamination in CSS, the hazard quotient of As exceeded one, indicating an increased risks of toxic metal exposure via rice consumption. This study raises concerns about potential long-term threats to human health posed by MNPs contamination in CSS and highlights the need to reevaluate the permissible limits of hazardous elements in sludge to ensure its safe reuse in agriculture.

Application of surface-enhanced Raman scattering to qualitative and quantitative analysis of arsenic species

Given the toxicity of arsenic, there is an urgent need for the development of efficient and reliable detection systems. Raman spectroscopy, a powerful tool for material characterization and analysis, can be used to explore the properties of a wide range of different materials. Surface-enhanced Raman spectroscopy (SERS) can detect low concentrations of chemicals. This review focuses on the progress of qualitative and quantitative studies of the adsorption processes of inorganic arsenic and organic arsenic in aqueous media using Raman spectroscopy in recent years and discusses the application of Raman spectroscopy theory simulations to arsenic adsorption processes. Sliver nanoparticles are generally used as the SERS substrate to detect arsenic. Inorganic arsenic is chemisorbed onto the silver surface by forming As-O-Ag bonds, and the Raman shift difference in the As-O stretching (∼60 cm-1) between As(V) and As(III) allows SERS to detect and distinguish between As(V) and As(III) in groundwater samples. For organic arsenicals, specific compounds can be identified based on spectral differences in the vibration modes of the chemical bonds. Under the same laser excitation, the intensity of the Raman spectra for different arsenic concentrations is linearly related to the concentration, thus allowing quantitative analysis of arsenic. Molecular modeling of adsorbed analytes via density functional theory calculation (DFT) can predict the Raman shifts of analytes in different laser wavelengths.

Human health risks associated with metals in paddy plant (Oryza sativa) based on target hazard quotient and target cancer risk

Paddy plants (Oryza sativa) contaminated with metals could be detrimental to human health if the concentrations of metals exceed the permissible limit. Thus, this study aims to assess the risk of the concentrations of As, Se, Cu, Cr, Co, and Ni and their distributions in various parts (roots, stems, leaves, and grains) of paddy plants collected from Sekinchan, Malaysia. Both soil and plant samples were digested according to the United States Environmental Protection Agency (USEPA) Method 3050B and the metal concentrations were determined by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The highest mean translocation factor (TF) was from soil to roots (TF roots/soil ranged from 0.12 to 6.15) and the lowest was from leaves to grain (TF grain/leaves ranged from 0.06 to 0.87). Meanwhile, the bioaccumulation factor (BAF) for all metals was less than 1.0 indicating that paddy plants only absorb metals from the soil but do not accumulate in the grains. The average daily intake for As (1.15 ± 0.25 µg/kg/day) has exceeded the limit proposed by ATSDR and IRIS USEPA (0.30 µg/kg/day). Target cancer risk (TR) of 1.10 × 10^-3 for As through rice consumption indicates that the potential cancer risk exists in one out of 1000 exposed individuals. The results from this study could serve as a reference for researchers and policymakers to monitor and formulate strategies in managing As and other metals in paddy plants, especially in Southeast Asian countries.

Phytotoxic effects of chemically synthesized copper oxide nanoparticles induce physiological, biochemical, and ultrastructural changes in Cucumis melo

Nanotechnology has achieved great attention due to its impressive performance especially engineered nanoparticles (ENPs). Copper-based nanoparticles offer favorable development in the fabrication of agrochemicals including fertilizers and pesticides in the field of agriculture. However, their toxic impact on melon plants (Cucumis melo) still needs to be investigated. Therefore, the aim of the current work was performed to focus on the toxic impact of Cu oxide nanoparticles (CuONPs) in hydroponically grown Cucumis melo. Our results demonstrated that CuONPs with 75, 150, and 225 mg/L significantly (P<0.005) suppressed the growth rate and badly affect physiological and biochemical activities in melon seedlings. Also, results revealed remarkable phenotypical changes besides significantly reduced fresh biomass and decreased levels of total chlorophyll contents in a dose-dependent manner. Atomic absorption spectroscopy (ASS) analysis exhibited that C. melo treated with CuONPs accumulates NPs in the shoot. Moreover, exposure to higher CuONPs (75-225mg/L) significantly increased the reactive oxygen species (ROS) accumulation, malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) level in the shoot and induced toxicity in melon root with an increase in electrolyte leakage. Furthermore, antioxidant enzyme peroxidase (POD) and superoxide dismutase (SOD) activity in the shoot significantly increased under exposure to higher CuONPs. Exposure to higher concentrations of CuONPs (225 mg/L) significantly deformed the stomatal aperture. Furthermore, reducing the number and abnormal size of palisade mesophyll and spongy mesophyll cells were investigated especially at high doses of CuONPs. Overall, our current work demonstrates that CuONPs of 10-40 nm size provide direct evidence for a toxic effect in C. melo seedlings. Our findings were expected to inspire the safe production of NPs and agrifood security. Thus, CuONPs prepared from toxic route and its bioaccumulation into our food chain through crop plants possess a serious threat to the ecological system.

Synthesis and characterization of copper oxide nanoparticles: its influence on corn (Z. mays) and wheat (Triticum aestivum) plants by inoculation of Bacillus subtilis

Nanotechnology is now playing an emerging role in green synthesis in agriculture as nanoparticles (NPs) are used for various applications in plant growth and development. Copper is a plant micronutrient; the amount of copper oxide nanoparticles (CuONPs) in the soil determines whether it has positive or adverse effects. CuONPs can be used to grow corn and wheat plants by combining Bacillus subtilis. In this research, CuONPs were synthesized by precipitation method using different precursors such as sodium hydroxide (0.1 M) and copper nitrate (Cu(NO₃)₂) having 0.1 M concentration with a post-annealing method. The NPs were characterized through X-ray diffraction (XRD), scanning electron microscope (SEM), and ultraviolet (UV) visible spectroscopy. Bacillus subtilis is used as a potential growth promoter for microbial inoculation due to its prototrophic nature. The JAR experiment was conducted, and the growth parameter of corn (Z. mays) and wheat (Triticum aestivum) was recorded after 5 days. The lab assay evaluated the germination in JARs with and without microbial inoculation under CuONP stress at different concentrations (25 and 50 mg). The present study aimed to synthesize CuONPs and systematically investigate the particle size effects of copper (II) oxide (CuONPs) (< 50 nm) on Triticum aestivum and Z. mays. In our results, the XRD pattern of CuONPs at 500 °C calcination temperature with monoclinic phase is observed, with XRD peak intensity slightly increasing. The XRD patterns showed that the prepared CuONPs were extremely natural, crystal-like, and nano-shaped. We used Scherrer's formula to calculate the average size of the particle, indicated as 23 nm. The X-ray diffraction spectrum of synthesized materials and SEM analysis show that the particles of CuONPs were spherical in nature. The results revealed that the synthesized CuONPs combined with Bacillus subtilis used in a field study provided an excellent result, where growth parameters of Z. Mays and Triticum aestivum such as root length, shoot length, and plant biomass was improved as compared to the control group.

Recent Advances in Nano-Enabled Seed Treatment Strategies for Sustainable Agriculture: Challenges, Risk Assessment, and Future Perspectives

Agro seeds are vulnerable to environmental stressors, adversely affecting seed vigor, crop growth, and crop productivity. Different agrochemical-based seed treatments enhance seed germination, but they can also cause damage to the environment; therefore, sustainable technologies such as nano-based agrochemicals are urgently needed. Nanoagrochemicals can reduce the dose-dependent toxicity of seed treatment, thereby improving seed viability and ensuring the controlled release of nanoagrochemical active ingredients However, the applications of nanoagrochemicals to plants in the field raise concerns about nanomaterial safety, exposure levels, and toxicological implications to the environment and human health. In the present comprehensive review, the development, scope, challenges, and risk assessments of nanoagrochemicals on seed treatment are discussed. Moreover, the implementation obstacles for nanoagrochemicals use in seed treatments, their commercialization potential, and the need for policy regulations to assess possible risks are also discussed. Based on our knowledge, this is the first time that we have presented legendary literature to readers in order to help them gain a deeper understanding of upcoming nanotechnologies that may enable the development of future generation seed treatment agrochemical formulations, their scope, and potential risks associated with seed treatment.

Melatonin-mediated resistance to copper oxide nanoparticles-induced toxicity by regulating the photosynthetic apparatus, cellular damages and antioxidant defense system in maize seedlings

The pollution of nanoparticles (NPs) has linked with severe negative effects on crop productivity. Thus, effective strategies are needed to mitigate the phytotoxicity of NPs. The aim of present study was to evaluate the efficacy of exogenously applied melatonin (MT) in mitigating the toxic effects of copper oxide nanoparticles (CuO NPs) from maize seedlings. Therefore, we comprehensively investigated the inhibitory effects of MT against CuO NPs-induced toxicity on morpho-physiological, biochemical and ultrastructural levels in maize. Our results show that CuO NPs (300 mg L^-1) exposure displayed significantly reduction in all plant growth traits and induced toxicity in maize. Furthermore, 50 μM MT provided maximum plant tolerance against CuO NPs-induced phytotoxicity. It was noticed that MT improved plant growth, biomass, photochemical efficiency (Fv/Fm), chlorophyll contents (Chl a and Chl b), SPAD values and gas exchange attributes (stomatal conductance, net photosynthetic rate, intercellular CO₂ concentration and transpiration rate) under CuO NPs stress. In addition, MT enhanced the antioxidant defense system and conferred protection to ultrastructural (mainly chloroplast, thylakoids membrane and plastoglobuli) damages and stomatal closure in maize plants subjected to CuO NPs stress. Together, it can be stated that the exogenous supply of MT improves the resilience of maize plants against the CuO NPs-induced phytotoxicity. Our current findings can be useful for the enhancement of plant growth and yield attributes in CuO NPs-contaminated soils. The reported information can provide insight into the MT pathways that can be used to improve crop stress tolerance in a challenging environment.

Trophic transfer of Cu nanoparticles in a simulated aquatic food chain

The goal of the current study was to quantify the trophic transfer of copper nanoparticles (CuNPs) in a food chain consisting of the microalga Pseudokirchneriella subcapitata as the representative of primary producer, the grazer Daphnia magna, and the omnivorous mysid Limnomysis benedeni. To quantify the size and number concentration of CuNPs in the biota, tissue extraction with tetramethylammonium hydroxide (TMAH) was performed and quantification was done by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The bioconcentration factor (BCF) of the test species for CuNPs varied between 10² - 10³ L/kg dry weight when expressing the internal concentration on a mass basis, which was lower than BCF values reported for Cu²⁺ (10³ - 10⁴ L/kg dry weight). The particle size of CuNPs determined by sp-ICP-MS ranged from 22 to 40 nm in the species. No significant changes in the particle size were measured throughout the food chain. Moreover, the measured number of CuNPs in each trophic level was in the order of 10¹³ particles/kg wet weight. The calculated trophic transfer factor (mass concentration basis) was > 1. This indicates biomagnification of particulate Cu from P. subcapitata to L. benedeni. It was also found that the uptake of particulate Cu (based on the particle number concentration) was mainly from the dietary route rather than from direct aqueous exposure. Furthermore, dietary exposure to CuNPs had a significant effect on the feeding rate of mysid during their transfer from daphnia to mysid and from alga through daphnia to mysid. This work emphasizes the importance of tracing the particulate fraction of metal-based engineered nanoparticles when studying their uptake and trophic transfer.

Nanoscale zerovalent copper (nZVC) catalyzed environmental remediation of organic and inorganic contaminants: A review

Over the past decade, the nano zerovalent copper has emerged as an effective nano-catalyst for the environment remediation processes due to its ease of synthesis, low cost, controllable particle size and high reactivity despite its release during the remediation process and related concentration dependent toxicities. However, the improvised techniques involving the use of supports or immobilizer for the synthesis of Cu⁰ has significantly increased its stability and motivated the researchers to explore the applicability of Cu⁰ for the environment remediation processes, which is evident from access to numerous reports on nano zerovalent copper mediated remediation of contaminants. Initially, this review allows the understanding of the various resources used to synthesize zerovalent copper nanomaterial and the structure of Cu⁰ nanoparticles, followed by focus on the reaction mechanism and the species involved in the contaminant remediation process. The studies comprehensively presented the application of nano zerovalent copper for remediation of organic/inorganic contaminants in combination with various oxidizing and reducing agents under oxic and anoxic conditions. Further, it was evaluated that the immobilizers or support combined with various irradiation sources originates a synergistic effect and have a significant effect on the stability and the redox properties of nZVC in the remediation process. Therefore, the review proposed that the future scope of research should include rigorous focus on deriving an exact mechanism for synergistic effect for the removal of contaminants by supported nZVC.

Effects and Mechanisms of Copper Oxide Nanoparticles with Regard to Arsenic Availability in Soil-Rice Systems: Adsorption Behavior and Microbial Response

Copper oxide nanoparticles (CuO NPs) are widely used as fungicides in agriculture. Arsenic (As) is a ubiquitous contaminant in paddy soil. The present study was focused on the adsorption behavior of CuO NPs with regard to As as well as the characteristics of the microbial community changes in As-contaminated soil-rice systems in response to CuO NPs. The study found that CuO NPs could be a temporary sink of As in soil; a high dose of CuO NPs promoted the release of As from crystalline iron oxide, which increased the As content in the liquid phase. The study also found that the As bioavailability changed significantly when the dose of CuO NPs was higher than 50 mg kg^-1 in the soil-rice system. The addition of 100 mg kg^-1 CuO NPs increased the microbial diversity and the abundance of genes involved in As cycling, decreased the abundance of Fe(III)-reducing bacteria and sulfate-reducing genes, and decreased As accumulation in grains. Treatment with 500 mg kg^-1 CuO NPs increased the abundance of Fe(III)-reducing bacteria and sulfate-reducing genes, decreased Fe plaques, and increased As accumulation in rice. The adverse effects of CuO NPs on crops and associated risks need to be considered carefully.

Impacts of typical engineering nanomaterials on the response of rhizobacteria communities and rice (Oryza sativa L.) growths in waterlogged antimony-contaminated soils

The combined eco-risks of Sb (widely presented in soils, especially nearing mining areas) and the engineering nanomaterials (ENMs) (applied in agriculture and soil remediation) still remain uncovered. The current study investigated the impacts of single and combined exposure of CuO, CeO₂ nanoparticles (NPs) and multi-walled carbon nanotube (MWCNTs) with Sb on rice growths and rhizosphere bacterial communities. The results showed that co-exposure of CuO NPs (0.075 wt%) with Sb (III) posed the most adverse impacts on root biomass and branches (up to 66.59% and 70.00% compared to other treatments, respectively). Treatments containing MWCNTs showed insignificant dose-dependent effects, while CeO₂ NPs combined with Sb (III) showed significant synergistic stimulating effects on the fresh weights of root and shoot, by 68.30% and 73.48% (p < 0.05) compared to single Sb exposure, respectively. The rice planting increased the percentage of non-specifically sorbed Sb in soils by 1.50-14.49 than the no-planting stage. Analysis on microbial communities revealed that co-exposure of CuO NPs with Sb (III) induced the greatest adverse impacts on rhizobacteria abundances and community structures at both phylum and genus levels. Therein, significant decrease of Bacteroidetes, Acidobacteria and increase of Firmicutes abundance at the phylum level were observed. This study provided information about the risks of different ENMs released to Sb-contaminated soils under flooded condition on both crops and bacterial communities.

Transformation of copper oxide nanoparticles as affected by ionic strength and its effects on the toxicity and bioaccumulation of copper in zebrafish embryo

This study aimed to investigate the transformation of copper oxide nanoparticles (CuO NPs) in aquatic environments under different ionic strength and further examine its effects on copper toxicity and bioaccumulation by monitoring the responses and uptake behaviours of zebrafish embryo. Ionic strength (IS) was simulated according to surface water (1.5 mM), groundwater (15 mM), and wastewater (54 mM), representing low-, mid-, and high-IS water, respectively. At the highest exposure of 10 mg CuO/L, zebrafish larvae mortality was increased from 21.3% to 33.3%, when IS decreased from 54 to 1.5 mM. Low-IS solution also caused the highest numbers of delayed hatching embryo (81.3%) and opaque yolk deformation (36.3%). Copper bioaccumulation markedly increased when larvae were exposed to low-IS water (35%) relative to high-IS water (15%). Exposing to low-IS particularly enhanced copper uptake (~15 ng Cu/g inside embryo), facilitating the copper accumulation in the heart of larvae, whereas aggregated CuO NPs (>500 nm) in mid- and high-IS water were blocked from the embryo and found abundantly in the body axis and tail. Results indicate that CuO NPs in low-IS solutions rapidly form the relatively small CuO NP aggregates with a high copper dissolution, which would pose great concern for aquatic organisms.

Green magnesium oxide nanoparticles-based modulation of cellular oxidative repair mechanisms to reduce arsenic uptake and translocation in rice (Oryza sativa L.) plants

Arsenic (As) accumulation catastrophically disturbs the stability of agricultural systems and human health. Rice easily accumulates a high amount of As from agriculture fields as compare with other cereal crops. Hence, innovative soil remediation methods are needed to deal with the detrimental effects of As on human health causing food security challenges. Here, we report the green synthesis and characterization of magnesium oxide nanoparticles (MgO-NPs) from a native Enterobacter sp. strain RTN2, which was genetically identified through 16S rRNA gene sequence analysis. The biosynthesis of MgO-NPs in reaction mixture was confirmed by UV-vis spectral analysis. X-ray diffraction (XRD) and fourier transform-infrared spectroscopy (FTIR) analysis showed the crystalline nature and surface properties of MgO-NPs, respectively. Moreover, electron microscopy (SEM-EDS, and TEM) imaging confirmed the synthesis of spherical shape of MgO-NPs with variable NPs sizes ranging from 38 to 57 nm. The results revealed that application of MgO-NPs (200 mg kg^-1) in As contaminated soil significantly increased the plant biomass, antioxidant enzymatic contents, and decreased reactive oxygen species and acropetal As translocation as compared with control treatment. The study concluded that biogenic MgO-NPs could be used to formulate a potent nanofertilizer for sustainable rice production in metal contaminated soils.

Mobility of arsenic in the growth media of rice plants (Oryza sativa subsp. japonica. 'Koshihikari') with exposure to copper oxide nanoparticles in a life-cycle greenhouse study

The increasing arsenic (As) concentration in agriculture media poses increasing risks to both environment and human health. Arsenic mobility determines its bioavailability and entry into the food chain. Nanoparticle application may help to control As mobility in crop cultivation media, and thus decreasing As bioavailability for plants. This research studied the adsorption kinetics of As(V) on copper oxide nanoparticles (nCuO) and nCuO dissolution in a hydroponic solution, and the effects of nCuO on As mobility in a greenhouse system exposed to As(V) addition of 10 mg/kg and nCuO at 0.1-100 mg/L for a life-cycle growth of rice. Arsenic adsorption was dependent on both the total mass and the concentration of nCuO as well as the initial concentration of As(V), while nCuO dissolution was mainly dependent on nCuO concentration regardless of As(V). Arsenic in the simulated paddy was quickly mobilized from soil to aqueous phase during week 1, and further interacted with components in water phase, sediment-water interfacial transition and rice plants. Copper (Cu) and As speciation in the soil were observed by X-Ray Absorption Near Edge Spectrometry. Dissolved Cu was complexed with organic ligands. As(V) was adsorbed to kaolinite, or reduced to As(III) and adsorbed to ferrihydrite. Percent As removal from water phase in the growth container was determined by both nCuO application and As(V) initial concentration. Based on our previous finding that As accumulation in rice grains was significantly decreased by nCuO at 50 mg/L and the results of this study on As adsorption capacity of nCuO and As removal from water due to nCuO application, nCuO at 50 mg/L was proposed to be an appropriate application in rice paddy to immobilize As. Further research is needed in actual agriculture to verify the appropriate nCuO application and get an integrated beneficial effect for rice plants and humans.

Phytohormonal Roles in Plant Responses to Heavy Metal Stress: Implications for Using Macrophytes in Phytoremediation of Aquatic Ecosystems

Heavy metals can represent a threat to the health of aquatic ecosystems. Unlike organic chemicals, heavy metals cannot be eliminated by natural processes such as their degradation into less toxic compounds, and this creates unique challenges for their remediation from soil, water, and air. Phytoremediation, defined as the use of plants for the removal of environmental contaminants, has many benefits compared to other pollution-reducing methods. Phytoremediation is simple, efficient, cost-effective, and environmentally friendly because it can be carried out at the polluted site, which simplifies logistics and minimizes exposure to humans and wildlife. Macrophytes represent a unique tool to remediate diverse environmental media because they can accumulate heavy metals from contaminated sediment via roots, from water via submerged leaves, and from air via emergent shoots. In this review, a synopsis is presented about how plants, especially macrophytes, respond to heavy metal stress; and we propose potential roles that phytohormones can play in the alleviation of metal toxicity in the aquatic environment. We focus on the uptake, translocation, and accumulation mechanisms of heavy metals in organs of macrophytes and give examples of how phytohormones interact with plant defense systems under heavy metal exposure. We advocate for a more in-depth understanding of these processes to inform more effective metal remediation techniques from metal-polluted water bodies. Environ Toxicol Chem 2021;40:7-22. © 2020 SETAC.

Impact of copper oxide nanoparticles on the germination, seedling growth, and physiological responses in Brassica pekinensis L

Wide application of nanoparticles causes considerable environmental, health, and safety problems. However, their potential impact and mechanisms on plant growth are not completely clear. In the present study, the effects of different concentration of copper oxide nanoparticles (nCuO) on seed germination and seedling growth, as well as physiological parameters of Brassica pekinensis L., were investigated. The seeds were exposed to 10-, 100-, and 1000-mg L-1 nCuO suspensions and 0.8-mg L-1 Cu2+ released from 1000-mg L-1 nCuO for 7 day. The results showed that nCuO did not affect the germination rate, germination potential, and germination index of B. pekinensis but significantly affected the vitality index. The growth of roots and shoots of B. pekinensis was promoted at 10-mg L-1 nCuO, while they were inhibited under 1000-mg L-1 nCuO and Cu2+ ion treatments, and roots suffered more damage than shoots. Cu content in shoots and roots of B. pekinensis increased with increasing concentrations of nCuO, which is significantly higher in roots as compared with shoots. Roots and shoots accumulated more Cu under nCuO treatments compared with Cu2+ ion treatment. nCuO treatments led to significant lignification in roots of B. pekinensis. Furthermore, nCuO increased in the contents of soluble sugar and protein in shoots, while nCuO at 1000 mg L-1 significantly inhibited the content of soluble protein in roots. In addition, concentration-dependent augmentation of lipid peroxidation, hydrogen peroxide and superoxide generation, and antioxidant enzyme activity were noticed in shoots and roots of B. pekinensis seedlings under nCuO and Cu2+ ion treatments. Altogether, the results strongly suggested that the phytotoxicity of nCuO in B. pekinensis was caused by both the nanoparticles itself and the released Cu2+ ions.

Effects of Copper Oxide Nanoparticles on the Growth of Rice (Oryza Sativa L.) Seedlings and the Relevant Physiological Responses

Rice (Oryza sativa L.), a major staple food for billions of people, was assessed for its phytotoxicity of copper oxide nanoparticle (CuO NPs, size < 50 nm). Under hydroponic condition, seven days of exposure to 62.5, 125, and 250 mg/L CuO NPs significantly suppressed the growth rate of rice seedlings compared to both the control and the treatment of supernatant from 250 mg/L CuO NP suspensions. In addition, physiological indexes associated with antioxidants, including membrane damage and antioxidant enzyme activity, were also detected. Treatment with 250 mg/L CuO NPs significantly increased malondialdehyde (MDA) content and electrical conductivity of rice shoots by 83.4% and 67.0%, respectively. The activity of both catalase and superoxide dismutase decreased in rice leaves treated with CuO NPs at the concentration of 250 mg/L, while the activity of the superoxide dismutase significantly increased by 1.66 times in rice roots exposed to 125 mg/L CuO NPs. The chlorophyll, including chlorophyll a and chlorophyll b, and carotenoid content in rice leaves decreased with CuO NP exposure. Finally, to explain potential molecular mechanisms of chlorophyll variations, the expression of four related genes, namely, Magnesium chelatase D subunit, Chlorophyll synthase, Magnesium-protoporphyrin IX methyltransferase, and Chlorophyllide a oxygenase, were quantified by qRT-PCR. Overall, CuO NPs, especially at 250 mg/L concentration, could affect the growth and development of rice seedlings, probably through oxidative damage and disturbance of chlorophyll and carotenoid synthesis.

Differential impacts of copper oxide nanoparticles and Copper(II) ions on the uptake and accumulation of arsenic in rice (Oryza sativa)

Arsenic (As) in rice grains is a serious food safety concern. Some coexisting engineered nanoparticles (ENPs) were shown to alter the accumulation and speciation of As in rice grains. However, investigation on the effects of copper oxide nanoparticles (CuO NPs), a popular ingredient in pesticides, on the uptake and accumulation of As is rare. We explored the potentially different impact of CuO NPs and corresponding Cu(II) ions on the accumulation of two As species in rice seedlings in a hydroponic system. Rice seedlings were treated with a combinations of 1 mg/L of arsenite (As(III)) or arsenate (As(V)) and 100 mg/L of CuO NPs or Cu(II) for 6 days. Both forms of Cu significantly reduced the accumulation of total As in rice tissues, with Cu(II) exhibiting significantly greater effect than CuO NPs. As speciation in rice roots was markedly affected by both forms of Cu, and the impacts were Cu-form dependent. For example, the co-existence of As(V) with CuO NPs led to a 45% decrease of As(V) in rice roots, while the co-existence of As(V) with Cu(II) caused a 47% increase in As(V) in rice roots. As speciation in rice shoots was less affected by co-present Cu than in rice roots. Co-occurring As(III) or As(V) lowered Cu concentration in rice roots by 40% and 50% in treatments with CuO NPs, but did not affect Cu content in rice roots co-exposed to Cu(II). The study confirmed the reciprocal effect of co-occurring CuO NPs or Cu(II) and As in rice paddies and highlighted the unique "nano-effect" of CuO NPs. The results alsos showed that the initial oxidation state of As plays an important role in the interactions between As and Cu. The results shed light on the current debate on the safe applications of nano-enabled agrichemicals vs. conventional metal salts in agriculture.

Exposure to Copper Oxide Nanoparticles and Arsenic Causes Intergenerational Effects on Rice (Oryza sativa japonica Koshihikari) Seed Germination and Seedling Growth

Offspring generation (F1) rice (Oryza sativa japonica Koshihikari) seed germination and seedling growth tests were conducted for 18 d to investigate intergenerational effects of arsenic (As) and copper oxide nanoparticles (nCuO), with seeds harvested from a life cycle study exposed to As (0 and 10 mg/kg) and nCuO (0, 0.1, 1.0, 10, 50, and 100 mg/L). Seed germination and seedling growth of F1 plants were influenced by treatments experienced by parent generation (F0) plants (p < 0.05). Seeds produced from plants in F0 treatment with nCuO 50 mg/L had the lowest germination percentage and shortest seedling shoot length and root length in F1 control (F1C) and As at 10 mg/kg (F1As) alone treatments (p < 0.05). The shoot length and root length were decreased, whereas the number of root branches was increased in F1As treatment compared with F1C (p < 0.001). Interaction of As and nCuO also caused differential seed germination and seedling growth at various nCuO concentrations in quasi-F0 treatment (seeds receiving the same exposure as F0 plants; p < 0.05). Copper and As uptake in F1C seedlings were not affected by seeds' F0 exposure; this indicated that the transgenerational effects on rice seedling growth were not dependent on total Cu or As uptake in seedlings. The enhanced effects on seedlings from quasi-F0 treatment were influenced by additional exposure to nCuO and As that also interacted to affect Cu and As uptake in seedlings. Environ Toxicol Chem 2019;38:1978-1987. © 2019 SETAC.

Liquid assisted pulsed laser ablation synthesized copper oxide nanoparticles (CuO-NPs) and their differential impact on rice seedlings

Hydroponic experiments were conducted to investigate impact of laser ablated copper oxide nanoparticles (CuO-NPs) on rice seedlings. The present work demonstrates that exposure of lower concentrations (5, 10, 20, and 50 µM) of CuO-NPs enhance growth (in terms of fresh and dry weight and length), of rice seedlings. However, at higher concentrations (100, 200, and 500 µM) of CuO-NPs, growth (in terms of length, fresh weight and dry weight) decreased significantly (P < 0.05). Further, photosynthetic pigments (total chlorophyll and carotenoids) and protein contents were also found to be in accordance with the results of growth. This had occurred due to enhanced level of CuO-NPs accumulation at higher doses which also enhanced the level of oxidative stress markers such as hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). Chlorophyll a fluorescence parameters (F_v/F_m and qP and except NPQ) and amount of some minerals (Ca, Mg, Na, and K) increased at lower concentrations of CuO-NPs. In contrast, the levels of F_v/F_m and qP were significantly (P < 0.05) reduced at higher concentration of CuO-NPs, which might be due to enhanced accumulation of Cu and oxidative stresses markers. Our results showed that lower dosages of pulsed laser ablated CuO-NPs (5, 10, 20, and 50 µM) might be beneficial for growth and development of rice seedlings.

Aggregation, Sedimentation, and Dissolution of Copper Oxide Nanoparticles: Influence of Low-Molecular-Weight Organic Acids from Root Exudates

The rhizosphere is an essential pathway for the uptake of metal-based nanoparticles (MNPs) by plant roots. However, the interaction between root exudates and MNPs is still unclear. In this study, we initially identified the major low-molecular-weight organic acids (LMWOAs) in the rice root exudates using hydroponics. Then, the individual LMWOAs were added to CuO nanoparticle suspensions to investigate their effects on the environmental behavior of the MNPs. The results showed that both the variety and the concentration of LMWOAs impacted the aggregation, sedimentation, and dissolution of CuO nanoparticles (NPs). Almost all LMWOAs except succinic acid inhibited the aggregation of CuO NPs by enhancing the electrostatic repulsive force between NPs. The presence of citric and oxalic acids rather than lactic acid greatly improved the stability of CuO NP suspensions, but other acids showed a low promoting and high inhibiting effect on NP sedimentation. Moreover, all the LMWOAs from root exudates facilitated the dissolution of CuO NPs with a positive dose-dependent correlation, especially formic acid. Notably, citric acid, as the most abundant LMWOAs in rice root exudates, largely determined the aggregation, sedimentation, and dissolution of CuO NPs. This study provides a better understanding on NP-plant interactions in the rhizosphere.

Distribution and Speciation of Copper and Arsenic in Rice Plants ( Oryza sativa japonica 'Koshihikari') Treated with Copper Oxide Nanoparticles and Arsenic during a Life Cycle

A 6 × 2 factorial study was conducted to investigate the effects of copper oxide nanoparticles (nCuO, 0-100 mg/L), arsenic (As, 0-10 mg/kg), and their interaction on uptake, distribution, and speciation of Cu and As in rice plants ( Oryza sativa japonica 'Koshihikari'). Arsenic (in As-addition treatments) and Cu in seedling roots (SRs) were 1.45 and 1.58 times those in soil, respectively. Arsenic and Cu concentrations further increased in mature plant roots (MRs), which were 2.06 and 2.35 times those in soil, respectively. Arsenic and Cu concentrations in seedling shoots (SSs) were 79% and 54% lower than those in SRs, respectively. The mature stems, however, contained only 3% and 44% of As and Cu in SSs. Copper in flag leaves did not vary much compared to that in stems, whereas As was 14.5 times that in stems. Species transformations of Cu and As were observed in rice including reductions of Cu(II) to Cu(I) and As(V) to As(III). Arsenic in dehusked grains was negatively correlated with Cu and was lowered by nCuO below the WHO (World Health Organization) maximum safe concentration for white rice (200 ng/g). This may alleviate As adverse effects on humans from rice consumption.

The Role of Nanotechnology in the Fortification of Plant Nutrients and Improvement of Crop Production

Nutrient deficiency in food crops is seriously affecting human health, especially those in the rural areas, and nanotechnology may become the most sustainable approach to alleviating this challenge. There are several ways of fortifying the nutrients in food such as dietary diversification, use of drugs and industrial fortification. However, the affordability and sustainability of these methods have not been completely achieved. Plants absorb nutrients from fertilizers, but most conventional fertilizers have low nutrient use and uptake efficiency. Nanofertilizers are, therefore, engineered to be target oriented and not easily lost. This review surveys the effects of the addition of macro- and nanonutrients to soil, the interaction, and the absorption capability of the plants, the environmental effect and food content of the nutrients. Most reports were obtained from recent works, and they show that plants nutrients could be enriched by applying nanoparticulate nutrients, which are easily absorbed by the plant. Although there are some toxicity issues associated with the use of nanoparticles in crop, biologically synthesized nanoparticles may be preferred for agricultural purposes. This would circumvent the concerns associated with toxicity, in addition to being pollution free. This report, therefore, offers more understanding on the application of nanotechnology in biofortification of plant nutrients and the future possibilities offered by this practice. It also highlights some of the ills associated with the introduction of nanomaterials into the soil for crop’s improvement.

Physiological Effects of Copper Oxide Nanoparticles and Arsenic on the Growth and Life Cycle of Rice ( Oryza sativa japonica 'Koshihikari')

A factorial study was conducted to evaluate the phytotoxicity of copper oxide nanoparticles (nCuO, 0.1-100 mg/L), arsenic (As, 0 and 10 mg/kg), and their interaction to rice plants ( Oryza sativa japonica 'Koshihikari') during the life cycle. No significant effect was observed on seed germination. The main effects of nCuO and As were observed on lengths and biomasses of seedling shoots and roots and on root branching. The interaction between nCuO and As also significantly influenced these parameters. nCuO addition increased Cu uptake in seedlings and generally improved seedling growth. With As addition, As was highly concentrated in roots and increased in shoots, and seedling growth was also inhibited. Additionally, nCuO and As had significant main and interaction effects on mature plant dry biomass, panicle number, total grain weight, average grain weight, and several other panicle parameters. Moreover, nCuO and As interacted to affect panicle emergence. nCuO also decreased As accumulation in dehusked grains. The accelerated heading stage by nCuO may help shorten the life cycle of rice plants, thereby reducing As accumulation in grains. This study is the first to examine the influence of nCuO in combination with As on the life cycle of rice plants.

Metallic nanoparticles influence the structure and function of the photosynthetic apparatus in plants

The applications of nanoparticles continue to expand into areas as diverse as medicine, bioremediation, cosmetics, pharmacology and various industries, including agri-food production. The widespread use of nanoparticles has generated concerns given the impact these nanoparticles - mostly metal-based such as CuO, Ag, Au, CeO₂, TiO₂, ZnO, Co, and Pt - could be having on plants. Some of the most studied variables are plant growth, development, production of biomass, and ultimately oxidative stress and photosynthesis. A systematic appraisal of information about the impact of nanoparticles on these processes is needed to enhance our understanding of the effects of metallic nanoparticles and oxides on the structure and function on the plant photosynthetic apparatus. Most nanoparticles studied, especially CuO and Ag, had a detrimental impact on the structure and function of the photosynthetic apparatus. Nanoparticles led to a decrease in concentration of photosynthetic pigments, especially chlorophyll, and disruption of grana and other malformations in chloroplasts. Regarding the functions of the photosynthetic apparatus, nanoparticles were associated with a decrease in the photosynthetic efficiency of photosystem II and decreased net photosynthesis. However, CeO₂ and TiO₂ nanoparticles may have a positive effect on photosynthetic efficiency, mainly due to an increase in electron flow between the photosystems II and I in the Hill reaction, as well as an increase in Rubisco activity in the Calvin and Benson cycle. Nevertheless, the underlying mechanisms are poorly understood. The future mechanistic work needs to be aimed at characterizing the enhancing effect of nanoparticles on the active generation of ATP and NADPH, carbon fixation and its incorporation into primary molecules such as photo-assimilates.

Copper oxide nanoparticles and arsenic interact to alter seedling growth of rice (Oryza sativa japonica)

Arsenic (As) causes phytotoxicity to rice plants, decreases rice production and causes serious human health concerns due to rice consumption. Additional stresses may be posed to rice plants due to the increasing release into the environment by the expanding production and application of copper oxide nanoparticles (nCuO). The influence of nCuO on As uptake in and effects on rice (Oryza sativa japonica) are explored here for the first time. An 18-d factorial experiment was conducted to determine main effects of nCuO (0, 0.1, 1.0, 10, 50, and 100 mg/L) and As (0 and 10 mg/kg), and the interaction between nCuO and As on rice seed germination and seedling growth. Arsenic alone decreased the germination percentage. Both As and nCuO reduced seedling shoot and root length, and exhibited interactive effects. nCuO and As also produced an interaction effect on the number of root branches (NRB) of rice seedlings. Notably, high nCuO concentrations (50 and 100 mg/L) mitigated the negative effect of As on the NRB. Copper uptake in shoots and roots was linearly correlated with Cu concentration in the sand without As addition (R² > 0.756). Whereas, As addition to the sand produced non-monotonic changes in Cu concentrations in shoots and roots versus Cu concentration in the sand (R² > 0.890). Arsenic concentration in shoots had a slightly negative linear correlation with Cu concentration in the sand (R² = 0.275).