To duckweeds (Landoltia punctata), nanoparticulate copper oxide is more inhibitory than the soluble copper in the bulk solution

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

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

Role of particle size-dependent copper bioaccumulation-mediated oxidative stress on Glycine max (L.) yield parameters with soil-applied copper oxide nanoparticles

Increased impetus on the application of nano-fertilizers to improve sustainable food production warrants understanding of nanophytotoxicity and its underlying mechanisms before its application could be fully realized. In this study, we evaluated the potential particle size-dependent effects of soil-applied copper oxide nanoparticles (nCuO) on crop yield and quality attributes (photosynthetic pigments, seed yield and nutrient quality, seed protein, and seed oil), including root and seed Cu bioaccumulation and a suite of oxidative stress biomarkers, in soybean (Glycine max L.) grown in field environment. We synthesized three distinct sized (25 nm = S [small], 50 nm = M [medium], and 250 nm = L [large]) nCuO with same surface charge and compared with soluble Cu2+ ions (CuCl2) and water-only controls. Results showed particle size-dependent effects of nCuO on the photosynthetic pigments (Chla and Chlb), seed yield, potassium and phosphorus accumulation in seed, and protein and oil yields, with nCuO-S showing higher inhibitory effects. Further, increased root and seed Cu bioaccumulation led to concomitant increase in oxidative stress (H2O2, MDA), and as a response, several antioxidants (SOD, CAT, POX, and APX) increased proportionally, with nCuO treatments including Cu2+ ion treatment. These results are corroborated with TEM ultrastructure analysis showing altered seed oil bodies and protein storage vacuoles with nCuO-S treatment compared to control. Taken together, we propose particle size-dependent Cu bioaccumulation-mediated oxidative stress as a mechanism of nCuO toxicity. Future research investigating the potential fate of varied size nCuO, with a focus on speciation at the soil-root interface, within the root, and edible parts such as seed, will guide health risk assessment of nCuO.

Exploring the nano-wonders: unveiling the role of Nanoparticles in enhancing salinity and drought tolerance in plants

Plants experience diverse abiotic stresses, encompassing low or high temperature, drought, water logging and salinity. The challenge of maintaining worldwide crop cultivation and food sustenance becomes particularly serious due to drought and salinity stress. Sustainable agriculture has significant promise with the use of nano-biotechnology. Nanoparticles (NPs) have evolved into remarkable assets to improve agricultural productivity under the robust climate alteration and increasing drought and salinity stress severity. Drought and salinity stress adversely impact plant development, and physiological and metabolic pathways, leading to disturbances in cell membranes, antioxidant activities, photosynthetic system, and nutrient uptake. NPs protect the membrane and photosynthetic apparatus, enhance photosynthetic efficiency, optimize hormone and phenolic levels, boost nutrient intake and antioxidant activities, and regulate gene expression, thereby strengthening plant's resilience to drought and salinity stress. In this paper, we explored the classification of NPs and their biological effects, nanoparticle absorption, plant toxicity, the relationship between NPs and genetic engineering, their molecular pathways, impact of NPs in salinity and drought stress tolerance because the effects of NPs vary with size, shape, structure, and concentration. We emphasized several areas of research that need to be addressed in future investigations. This comprehensive review will be a valuable resource for upcoming researchers who wish to embrace nanotechnology as an environmentally friendly approach for enhancing drought and salinity tolerance.

Biotic and Abiotic Interactions in Freshwater Mesocosms Determine Fate and Toxicity of CuO Nanoparticles

Transformation, dissolution, and sorption of copper oxide nanoparticles (CuO-NP) play an important role in freshwater ecosystems. We present the first mesocosm experiment on the fate of CuO-NP and the dynamics of the zooplankton community over a period of 12 months. Increasingly low (0.08-0.28 mg Cu L-1) and high (0.99-2.99 mg Cu L-1) concentrations of CuO-NP and CuSO4 (0.10-0.34 mg Cu L-1) were tested in a multiple dosing scenario. At the high applied concentration (CuO-NP_H) CuO-NP aggregated and sank onto the sediment layer, where we recovered 63% of Cu applied. For the low concentration (CuO-NP_L) only 41% of applied copper could be recovered in the sediment. In the water column, the percentage of initially applied Cu recovered was on average 3-fold higher for CuO-NP_L than for CuO-NP_H. Zooplankton abundance was substantially compromised in the treatments CuSO4 (p < 0.001) and CuO-NP_L (p < 0.001). Community analysis indicated that Cladocera were most affected (bk = -0.49), followed by Nematocera (bk = -0.32). The abundance of Cladocera over time and of Dixidae in summer was significantly reduced in the treatment CuO-NP_L (p < 0.001; p < 0.05) compared to the Control. Our results indicate a higher potential for negative impacts on the freshwater community when lower concentrations of CuO-NP (<0.1 mg Cu L-1) enter the ecosystem.

Deep Learning-Based Automatic Duckweed Counting Using StarDist and Its Application on Measuring Growth Inhibition Potential of Rare Earth Elements as Contaminants of Emerging Concerns

In recent years, there have been efforts to utilize surface water as a power source, material, and food. However, these efforts are impeded due to the vast amounts of contaminants and emerging contaminants introduced by anthropogenic activities. Herbicides such as Glyphosate and Glufosinate are commonly known to contaminate surface water through agricultural industries. In contrast, some emerging contaminants, such as rare earth elements, have started to enter the surface water from the production and waste of electronic products. Duckweeds are angiosperms from the Lemnaceae family and have been used for toxicity tests in aquatic environments, mainly those from the genus Lemna, and have been approved by OECD. In this study, we used duckweed from the genus Wolffia, which is smaller and considered a good indicator of metal pollutants in the aquatic environment. The growth rate of duckweed is the most common endpoint in observing pollutant toxicity. In order to observe and mark the fronds automatically, we used StarDist, a machine learning-based tool. StarDist is available as a plugin in ImageJ, simplifying and assisting the counting process. Python also helps arrange, manage, and calculate the inhibition percentage after duckweeds are exposed to contaminants. The toxicity test results showed Dysprosium to be the most toxic, with an IC50 value of 14.6 ppm, and Samarium as the least toxic, with an IC50 value of 279.4 ppm. In summary, we can provide a workflow for automatic frond counting using StarDist integrated with ImageJ and Python to simplify the detection, counting, data management, and calculation process.

Uptake, accumulation, toxicity, and interaction of metallic-based nanoparticles with plants: current challenges and future perspectives

The rapid development of industrialization is causing several fundamental problems in plants due to the interaction between plants and soil contaminated with metallic nanoparticles (NPs). Numerous investigations have been conducted to address the severe toxic effects caused by nanoparticles in the past few decades. Based on the composition, size, concentration, physical and chemical characteristics of metallic NPs, and plant types, it enhances or lessens the plant growth at various developmental stages. Metallic NPs are uptaken by plant roots and translocated toward shoots via vascular system based on composition, size, shape as well as plant anatomy and cause austere phytotoxicity. Herein, we tried to summarize the toxicity induced by the uptake and accumulation of NPs in plants and also we explored the detoxification mechanism of metallic NPs adopted by plants via using different phytohormones, signaling molecules, and phytochelatins. This study was intended to be an unambiguous assessment including current knowledge on NPs uptake, accumulation, and translocation in higher plants. Furthermore, it will also provide sufficient knowledge to the scientific community to understand the metallic NPs-induced inhibitory effects and mechanisms involved within plants.

Alleviation of chromium stress in plants using metal and metal oxide nanoparticles

Chromium (Cr), one of the hazardous pollutants, exists predominantly as Cr(VI) and Cr(III) in the environment. Cr(VI) is more toxic than Cr(III) due to its high mobility and solubility. Elevated levels of Cr in agricultural soil due to various anthropogenic activities cause Cr accumulation in plants, resulting in a significant reduction in plant yield and quality due to Cr-induced physiological, biochemical and molecular alterations. It can infiltrate the food chain through crop plants and cause harmful effects in humans via biomagnification. Cr(VI) is linked to cancer in humans. Therefore, mitigation strategies are required to remediate Cr-polluted soils and limit its accumulation in plants for safe food production. Recent research on metal and metal oxide nanoparticles (NPs) has shown that they can effectively reduce Cr accumulation and phytotoxicity. The effects of these NPs are influenced by their type and dose, exposure method, plant species and experimental settings. In this review, we present an up-to-date compilation and comprehensive analysis of the existing literature regarding the process of uptake and distribution of Cr and impact and potential mechanisms of metal and metal oxide nanoparticles led mitigation of Cr-induced stress in plants. We have also discussed recent developments, existing research gaps and future research directions in the field of Cr stress mitigation by NPs in plants. Overall, this review can provide valuable insights in reducing Cr accumulation and toxicity using metal and metal oxide nanoparticles, thereby promoting safe and sustainable cultivation of food and phytostabilization of Cr-polluted soil.

Ethylene accelerates copper oxide nanoparticle-induced toxicity at physiological, biochemical, and ultrastructural levels in rice seedlings

The enormous use of metal-based nanoparticles (NPs) in different sectors may result in enhanced accumulation in agricultural soil, which could impose negative effects on crop productivity. Hence, strategies are needed to explore the mechanisms of copper oxide nanoparticle (CuO NP)-induced toxicity in crops. The present study aimed to investigate the involvement of ethylene in CuO NP-induced toxicity in rice seedlings. Here, our results indicate that 450 mg L^-1 of CuO NPs induced toxic effects in rice seedlings. Thus, it was evidenced by the reduced plant biomass accumulation, enhanced oxidative stress indicators, and cellular ultrastructural damages. More importantly, the exogenous supply of ethylene biosynthesis and signaling antagonists cobalt (Co) and silver (Ag) respectively provided tolerance and improved the defense system of rice seedlings against CuO NP toxicity. The ethylene antagonists could significantly reduce the extent of ultrastructural and stomatal damage by controlling the ROS accumulation in rice seedlings under CuO NP stress. Furthermore, Co and Ag augmented the antioxidant defense system against CuO NP-induced toxicity. Contrary to that, all oxidative damage attributes were further enhanced exogenous application of ethylene biosynthesis precursor [1-aminocyclopropane-1-carboxylic acid (ACC)] in the presence of CuO NPs. In addition, ACC could increase the CuO NP-induced stomatal and ultrastructural damages by reducing the ROS-scavenging ability in rice seedlings. Taken together, these results indicate the involvement of ethylene in CuO NP-induced toxicity in rice seedlings.

Comparative bioaccumulation, translocation, and phytotoxicity of metal oxide nanoparticles and metal ions in soil-crop system

Exposure of the soil environment to metal nanoparticles (MNPs) has been extensive because of their indiscriminate use and the disposal of MNP products in various applications. In MNP-amended soil, various crops can absorb the nanoparticles, and accumulation of the MNPs in farm products has potential risks for bioconcentration in humans and livestock. Here, we evaluated the comparative bioaccumulation, translocation, and phytotoxicity of MNPs (ZnO and CuO NPs) and metal ions (Zn(NO3)2 and Cu(NO3)2) in four different crops, namely lettuce, radish, bok choy, and tomato. We carried out pot experiments to evaluate the phytotoxicity in the crops from the presence of MNPs and metal ions. Phytotoxicity from different treatments differed depending on the plant species, and metal types. In addition, exposure to Zn and Cu showed positive dose-dependent effects on their bioaccumulation in each crop. However, there were no significant differences in metal bioaccumulation depending on whether the crops were exposed to MNPs or metal ions. By calculating the bioconcentration factor (BCF) and translocation factor (TF), we were able to estimate the biological uptake and translocation abilities of MNPs and metal ions for each crop. It was found that lettuce and radish had greater BCFs than bok choy and tomato, while bok choy and tomato had higher TFs. Also, the uptake and translocation of Zn were better than those of Cu. However, the values for BCF and TF for each crop showed no significant differences between MNP and metal ion exposure. A micro X-ray fluorescence (μ-XRF) spectrometer analysis demonstrated that only Zn elements appeared in the primary veins and edges of all leaves and the storage root of radish. Our study aims to estimate bioaccumulation, translocation, and the implied potential risks from MNPs accumulated in different plant species.

The Role of Nanoparticles in Response of Plants to Abiotic Stress at Physiological, Biochemical, and Molecular Levels

In recent years, the global agricultural system has been unfavorably impacted by adverse environmental changes. These changes in the climate, in turn, have altered the abiotic conditions of plants, affecting plant growth, physiology and production. Abiotic stress in plants is one of the main obstacles to global agricultural production and food security. Therefore, there is a need for the development of novel approaches to overcome these problems and achieve sustainability. Nanotechnology has emerged as one such novel approach to improve crop production, through the utilization of nanoscale products, such as nanofertilizer, nanofungicides, nanoherbicides and nanopesticides. Their ability to cross cellular barriers makes nanoparticles suitable for their application in agriculture. Since they are easily soluble, smaller, and effective for uptake by plants, nanoparticles are widely used as a modern agricultural tool. The implementation of nanoparticles has been found to be effective in improving the qualitative and quantitative aspects of crop production under various biotic and abiotic stress conditions. This review discusses various abiotic stresses to which plants are susceptible and highlights the importance of the application of nanoparticles in combating abiotic stress, in addition to the major physiological, biochemical and molecular-induced changes that can help plants tolerate stress conditions. It also addresses the potential environmental and health impacts as a result of the extensive use of nanoparticles.

Duckweed: a potential phytosensor for heavy metals

Globally, heavy metal (HM) contamination is one of the primary causes of environmental pollution leading to decreased quality of life for those affected. In particular, HM contamination in groundwater poses a serious risk to human health and the potential for destabilization of aquatic ecosystems. At present, strategies to remove HM contamination from wastewater are inefficient, costly, laborious, and often the removal poses as much risk to the environment as the initial contamination. Phytoremediation, plant-based removal of contaminants from soil or water, has long been viewed as an economical and sustainable solution to remove toxic metals from the environment. However, to date, phytoremediation has demonstrated limited successes despite a large volume of literature supporting its potential. A key aspect for achieving robust and meaningful phytoremediation is the selection of a plant species that is well suited to the task. For the removal of pollutants from wastewater, hydrophytes, like duckweed, exhibit significant potential due to their rapid growth on nutrient-rich water, ease of collection, and ability to survive in various ecosystems. As a model for ecotoxicity studies, duckweed is an ideal candidate, as it is easy to cultivate under controlled and even sterile conditions, and the rapid growth enables multi-generational studies. Similarly, recent advances in the genetic engineering and genome-editing of duckweed will enable the transition from fundamental ecotoxicity studies to engineered solutions for phytoremediation of HMs. This review will provide insight into the suitability of duckweeds for phytoremediation of HMs and strategies for engineering next-generation duckweed to provide real-world environmental solutions.

Copper uptake kinetics and toxicological effects of ionic Cu and CuO nanoparticles on the seaweed Ulva rigida

Copper ion (Cu²⁺) and copper oxide (CuO) nanoparticle (NP) ecotoxicity are of increasing concern as they are considered to be a potential risk to marine systems. This study represents the first attempt to evaluate CuO NP impacts on the seaweeds and Cu²⁺ on the chlorophyte Ulva rigida. Effects on oxidative stress, antioxidant defence markers, photosystem II function, thalli growth, and cell viability in U. rigida exposed for 4 up 72 h to1 and 5 mg L^-1 Cu²⁺ and CuO NPs were examined. Hydrogen peroxide (H₂O₂) generation, superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, and growth inhibition seemed to be reliable and early warning markers of toxicity. The most important variables of the principal component analysis (PCA): H₂O₂ generation, antioxidant stress markers, and growth-based toxicity index, were higher at 1 mg L^-1 CuO NPs compared to CuSO₄ and at 5 mg L^-1 CuSO₄ compared to CuO NPs. Intracellular uptake kinetics fit well to the Michaelis-Menten equation. The higher toxicity at 5 mg L^-1 CuSO₄ compared to 1 mg L^-1 was due to the higher Cu uptake with increasing concentration, suggesting and higher accumulation ability. On the contrary, 1 mg L^-1 CuO NPs induced more strongly toxicity effects than 5 mg L^-1. The relatively stronger effect of CuO NPs at 1 mg L^-1 than the respective CuSO₄ concentration could be attributed to the higher rate of initial uptake (V_c) and the mean rate of Cu uptake [C_max/(2 × K_m)] at CuO NP treatment. The intracellular seaweed experimental threshold of Cu, which coincided with the onset of oxidative stress, was within the Cu concentration range recorded in Mediterranean Ulva spp., indicating that it may pose a substantial risk to marine environments.

Behavior and toxicity assessment of copper nanoparticles in aquatic environment: A case study on red swamp crayfish

With the wide use of copper nanoparticles (CuNPs) in various industrial and commercial applications, they inevitably enter the aquatic environment. However, their behavior in the aquatic environment and potential toxicity to aquatic organisms remain little known. In this study, we investigated the behavior of CuNPs in freshwater, as well as the toxicity and bioaccumulation of CuNPs and copper sulfate (CuSO₄), used as a positive control for copper ions toxicity, in red swamp crayfish (Procambarus clarkii). The results showed that CuNPs released copper ions into freshwater and aggregated rapidly in freshwater, and their release of copper ions and aggregation slowed down at a higher concentration of CuNPs. The calculated 72-h LC₅₀ values for crayfish were 1.18 and 0.54 mg/L for CuNPs and CuSO₄, respectively. Cu accumulation in the gill and hepatopancreas from CuSO₄ treatments was significantly higher than that from CuNPs, and the highest Cu bioaccumulation level in crayfish was found in the gill, followed by hepatopancreas and muscle with the exposure of copper. The activities of the antioxidative enzymes in the crayfish significantly decreased after exposure to CuNPs for 48 h, compared to the control (without CuNPs or CuSO₄). Histological examination revealed that there was no significant alteration of hepatopancreas in the crayfish exposed to CuNPs. Meanwhile, the growth of crayfish was not significantly inhibited by CuNPs. These results suggested that CuNPs exposure can induce oxidative stress in the crayfish, gill is the main tissue for their accumulation, and their toxicity is mainly caused by the released copper ions.

Helping plants to deal with heavy metal stress: the role of nanotechnology and plant growth promoting rhizobacteria in the process of phytoremediation

Heavy metals (HMs) are not destroyable or degradable and persist in the environment for a long duration. Thus, eliminating and counteracting the HMs pollution of the soil environment is an urgent task to develop a safe and sustainable environment. Plants are in close contact with the soil and can play an important role in soil clean-up, and the process is known as phytoremediation. However, under HM contaminated conditions, plants suffer from several complications, like nutrient and mineral deficiencies, alteration of various physiological and biological processes, which reduces the plant's growth rate. On the other hand, the bioavailability of HMs is another factor for reduced phytoremediation, as most of the HMs are not bioavailable to plants for efficient phytoremediation. The altered plant growth and reduced bioavailability of HMs could be overcome and enhance the phytoremediation efficiency by incorporating either nanotechnology, i.e., nanoparticles (NPs) or plant growth promoting rhizobacteria (PGPR) along with phytoremediation. Single incorporation of NPs and PGPR might improve the growth rate in plants by enhancing nutrient availability and uptake and also by regulating plant growth regulators under HM contaminated conditions. However, there are certain limitations, like a high dose of NPs that might have toxic effects on plants. Thus, the combination of two techniques such as PGPR and NPs-based remediation can conquer the limitations of individual techniques and consequently enhance phytoremediation efficiency. Considering the negative impacts of HMs on the environment and living organisms, this review is aimed at highlighting the concept of phytoremediation, the single or combined integration of NPs and PGPR to help plants deal with HMs and their basic mechanisms involved in the process of phytoremediation. Additionally, the complications of using NPs and PGPR in the phytoremediation process are discussed to determine future research questions and this will assist to stimulate further research in this field and increase its effectiveness in practical application.

Estimation of health risks due to copper-based nanoagrochemicals

This study estimated health risks due to two types of copper-based nanoagrochemicals (Cu (OH)₂ and CuO nanoparticles (NPs)), during inadvertent ingestion of soil and consumption of leafy vegetables for a hypothetical exposure scenario. The dissolution of copper-based nanoagrochemicals in human digestive system was considered for estimating realistic doses. No risk was found during soil ingestion (hazard quotient (HQ) <1). HQ (no dissolution of Cu (OH) ₂ nanopesticides) (HQ= 0.015) comes out to be 2 times higher than that of HQ (100% dissolution of Cu (OH)₂ nanopesticides into copper ions) (HQ= 0.007). In case of risk from consumption of leafy vegetables, the following order of risk was found (high to low HQ value): Cu (OH)₂ (HQ= 1925) >CuO NPs (1402). Combined exposure of Cu (OH)₂ nanopesticide through soil ingestion as well as consumption of contaminated edible leafy vegetables resulted in health risks. The calculated maximum allowable applicable concentration values of Cu (OH)₂ and CuO NPs without posing risk to human and plant toxicity were found to be 1.14 and 0.45 mg/L, respectively. These findings can be used now for deciding safe use of copper-based nanoagrochemicals.

Cross-examination of engineered nanomaterials in crop production: Application and related implications

The review presents the current knowledge on the development and implementation of nanotechnology in crop production, giving particular attention to potential opportunities and challenges of the use of nano-sensors, nano-pesticides, and nano-fertilizers. Due to the size-dependent properties, e.g. high reactivity, targeted and controlled delivery of active ingredients, engineered nanomaterials (ENMs) are expected to be more efficient agrochemicals than conventional agents. Growing production and usage of ENMs result in the spread of ENMs in the environment. Because plants constitute an important component of the agri-ecosystem, they are subjected to the ENMs activity. A number of studies have confirmed the uptake and translocation of ENMs by plants as well as their positive/negative effects on plants. Here, these endpoints are briefly summarized to show the diversity of plant responses to ENMs. The review includes a detailed molecular analysis of ENMs-plant interactions. The transcriptomics, proteomics and metabolomics tools have been very recently employed to explore ENMs-induced effects in planta. The omics approach allows a comprehensive understanding of the specific machinery of ENMs occurring at the molecular level. The summary of data will be valuable in defining future studies on the ENMs-plant system, which is crucial for developing a suitable strategy for the ENMs usage.

Cutting-edge spectroscopy techniques highlight toxicity mechanisms of copper oxide nanoparticles in the aquatic plant Myriophyllum spicatum

Copper oxide nanoparticles (CuO-NPs) have been increasingly released in aquatic ecosystems over the past decades as they are used in many applications. Cu toxicity to different organisms has already been highlighted in the literature, however toxicity mechanisms of the nanoparticulate form remain unclear. Here, we investigated the effect, transfer and localization of CuO-NPs compared to Cu salt on the aquatic plant Myriophyllum spicatum, an ecotoxicological model species with a pivotal role in freshwater ecosystems, to establish a clear mode of action. Plants were exposed to 0.5 mg/L Cu salt, 5 and 70 mg/L CuO-NPs during 96 h and 10 days. Several morphological and physiological endpoints were measured. Cu salt was found more toxic than CuO-NPs to plants based on all the measured endpoints despite a similar internal Cu concentration demonstrated via Cu mapping by micro particle-induced X-ray emission (μPIXE) coupled to Rutherford backscattering spectroscopy (RBS). Biomacromolecule composition investigated by FTIR converged between 70 mg/L CuO-NPs and Cu salt treatments after 10 days. This demonstrates that the difference of toxicity comes from a sudden massive Cu²⁺ addition from Cu salt similar to an acute exposure, versus a progressive leaching of Cu²⁺ from CuO-NPs representing a chronic exposure. Understanding NP toxicity mechanisms can help in the future conception of safer by design NPs and thus diminishing their impact on both the environment and humans.

Impact of CuO nanoparticles on maize: Comparison with CuO bulk particles with special reference to oxidative stress damages and antioxidant defense status

The present study aimed to systematically investigate the particle size effects of copper (II) oxide [CuO nanoparticles (<50 nm) and CuO bulk particles (<10 μm)] on maize (Zea mays L.). Bioaccumulation of Cu, in vivo ROS generation, membrane damage, transcriptional modulation of antioxidant genes, cellular redox status of glutathione and ascorbate pool, expression patterns of COPPER TRANSPORTER 4 and stress responsive miRNAs (miR398a, miR171b, miR159f-3p) with their targets were investigated for better understanding of the underlying mechanisms and the extent of CuO nanoparticles and CuO bulk particles induced oxidative stress damages. More restricted seedling growth, comparatively higher membrane injury, marked decline in the levels of chlorophylls and carotenoids and severe oxidative burst were evident in CuO bulk particles challenged leaves. Dihydroethidium and CM-H2DCFDA staining further supported elevated reactive oxygen species generation in CuO bulk particles stressed roots. CuO bulk particles exposed seedlings accumulated much higher amount of Cu in roots as compared to CuO nanoparticles stressed plants with low root-to-shoot Cu translocation. Moderately high GR expression with maintenance of a steady GSH-GSSG ratio in CuO nanoparticles challenged leaves might be accountable for their rather improved performance under stressed condition. miR171b-mediated enhanced expression of SCARECROW 6 might participate in the marked decline of chlorophyll content in CuO bulk particles exposed leaves. Ineffective recycling of AsA pool is another decisive feature of inadequate performance of CuO bulk particles stressed seedlings in combating oxidative stress damages. Taken together, our findings revealed that toxicity of CuO bulk particles was higher than CuO nanoparticles and the adverse effects of CuO bulk particles on maize seedlings might be due to higher Cu ions dissolution.

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

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

Ecotoxicity to Freshwater Organisms and Cytotoxicity of Nanomaterials: Are We Generating Sufficient Data for Their Risk Assessment?

The aim of the present study was to investigate the eco-cytotoxicity of several forms of nanomaterials (NM), such as nano-CuO, nano-TiO₂, nano-SiO₂ and nano-ZnO, on different aquatic species (Raphidocelis subcapitata, Daphnia magna and Lemna minor) following standard protocols and on human cell lines (Caco-2, SV-80, HepG2 and HaCaT). Predicted no-effect concentrations (PNEC) or hazard concentrations for 5% of the species (HC₅) were also estimated based on the compilation of data available in the literature. Most of the NM agglomerated strongly in the selected culture media. For the ecotoxicity assays, nano-CuO and nano-ZnO even in particle agglomeration state were the most toxic NM to the freshwater organisms compared to nano-TiO₂ and nano-SiO₂. Nano-ZnO was the most toxic NM to R. subcapitata and D. magna, while nano-CuO was found to be very toxic to L. minor. Nano-CuO was very toxic to Caco-2 and HepG2 cells, particularly at the highest tested concentrations, while the other NM showed no toxicity to the different cell lines. The HC₅ and PNEC values are still highly protective, due to data limitations. However, the present study provides consistent evidence of the potential risks of both nano-CuO and nano-ZnO against aquatic organisms and also their effects on public health.

Bok choy (Brassica rapa) grown in copper oxide nanoparticles-amended soils exhibits toxicity in a phenotype-dependent manner: Translocation, biodistribution and nutritional disturbance

The comparative toxicity of nano/bulk cupric oxide (CuO) and ionic copper (Cu) in Rosie and Green bok choy (Brassica rapa) varieties, with higher and lower anthocyanin contents, respectively, was investigated. Both phenotypes were cultivated for 70 days in natural soil amended with nano CuO (nCuO), bulk CuO (bCuO), and Cu chloride (CuCl₂) at 75, 150, 300, and 600 mg Cu/kg soil. Essential elements in tissues, agronomical parameters, chlorophyll content, and Cu distribution in leaf were determined. In both varieties, nCuO treatments significantly increased Cu uptake in roots, compared with bCuO and CuCl₂ (p ≤ 0.05). At all treatment concentrations, Rosie variety had more Cu than Green. More physiological impairments such as chlorophyll and leaf biomass reduction were observed in treated-Rosie varieties, compared to Green plants. The adverse effects were higher in nCuO-treated plants than their bCuO- or ionic Cu-exposed counterparts. Different distribution patterns of the translocated Cu in leaf midrib and parenchyma depended on particle size and plant phenotype, as demonstrated by two-photon microscopy. The different effects of CuO-based compounds in Rosie and Green varieties may be related to the anthocyanin content. These findings help to understand the factors involved in nanoparticles uptake and translocation to plant edible parts.

In vitro copper oxide nanoparticle toxicity on intestinal barrier

The use of CuO nanoparticles (NPs) has increased greatly and their potential effects on human health need to be investigated. Differentiated Caco-2 cells were treated from the apical (Ap) and the basolateral (Bl) compartment with different concentrations (0, 10, 50 and 100 μg/mL) of commercial or sonochemically synthesized (sono) CuO NPs. Sono NPs were prepared in ethanol (CuOe) or in water (CuOw), obtaining CuO NPs differing in size and shape. The effects on the Caco-2 cell barrier were assessed via transepithelial electrical resistance (TEER) evaluation just before and after 1, 2 and 24 hours of exposure and through the analysis of cytokine release and biomarkers of oxidative damage to proteins after 24 hours. Sono CuOe and CuOw NPs induced a TEER decrease with a dose-dependent pattern after Bl exposure. Conversely, TEER values were not affected by the Ap exposure to commercial CuO NPs and, concerning the Bl exposure, only the lowest concentration tested (10 μg/mL) caused a TEER decrease after 24 hours of exposure. An increased release of interleukin-8 was induced by sono CuO NPs after the Ap exposure to 100 μg/mL and by sono and commercial CuO after the Bl exposure to all the concentrations. No effects of commercial and sono CuO NPs on interleukin-6 (with the only exception of 100 μg/mL Bl commercial CuO) and tumor necrosis factor-α release were observed. Ap treatment with commercial and CuOw NPs was able to induce significant alterations on specific biomarkers of protein oxidative damage (protein sulfhydryl group oxidation and protein carbonylation).

Root System Architecture, Copper Uptake and Tissue Distribution in Soybean (Glycine max (L.) Merr.) Grown in Copper Oxide Nanoparticle (CuONP)-Amended Soil and Implications for Human Nutrition

Understanding the potential uptake and biodistribution of engineered nanoparticles (ENPs) in soil-grown plants is imperative for realistic toxicity and risk assessment considering the oral intake of edibles by humans. Herein, growing N-fixing symbiont (Bradyrhizobium japonicum) inoculated soybean (Glycine max (L.) Merr.) for a full lifecycle of 120 days, we assessed the potential influence of particle size (25, 50, and 250 nm) and concentration (0, 50, 100, 200, and 500 mg/kg soil) of Copper oxide nanoparticles (CuONPs) on: (1) root system architecture, (2) soil physicochemical attributes at the soil-root interface, and (3) Cu transport and accumulation in root, stem, leaf, and seed in soybean, and compared them with the soluble Cu2+ ions and water-only controls. Finally, we performed a comparative assessment of total seed Cu levels in soybean with other valuable food sources for Cu intake and discussed potential human health implications. Results showed particle size- and concentration-dependent influence of CuONPs on Cu uptake and distribution in root, stem, leaf, and seed. Alterations in root architecture (root biomass, length, volume, and area) were dependent on the Cu compound types, Cu concentrations, and their interactions. Concentration-response relationships for all three sizes of CuONPs and Cu2+ ions were found to be linear. Furthermore, CuONPs and Cu2+ ions had inhibitory effects on root growth and development. Overall, soybean responses to the smallest size of CuONPs-25 nm-were greater for all parameters tested compared to the two larger-sized CuONPs (50 nm, 250 nm) or Cu2+ ions. Results suggest that minor changes in soil-root physicochemical attributes may not be a major driver for Cu uptake in soybean. Cu bioaccumulation followed the order: root > leaf > stem > seed. Despite reduction in root architecture and seed yield, the smallest size CuONPs-25 nm led to increased total seed Cu uptake compared to the larger-sized CuONPs or Cu2+ ions. Our findings also suggest that soil amendment with CuONPs, and more so with the smallest size of CuONPs-25 nm-could significantly improve seed nutritional Cu value in soybean as reflected by the % Daily Values (DV) and are rated "Good" to "Very Good" according to the "World's Healthiest Foods" rating. However, until the potential toxicity and risk from CuONP-fortified soybean seed ingestion is characterized in humans, we caution recommending such seeds for daily human consumption when addressing food Cu-deficiency and associated diseases, globally.

Chronic exposure to copper oxide nanoparticles causes muscle toxicity in adult zebrafish

Repeated deposition of copper oxide nanoparticles (CuO-NPs) into aquatic systems makes them a global threat since the NPs accumulate in various organs of the fish particularly skeletal muscle. In the present study, adult zebrafish were exposed to different concentrations of CuO-NPs (1 and 3 mg/L) for a period of 30 days. The status of functional markers (acetylcholinesterase, creatine kinase-MB, and lactate dehydrogenase) and oxidative stress markers (oxidants and antioxidants) were analyzed. The histological changes in muscle were studied followed by the immunohistochemistry expression for catalase. Further, the expression of myoD, myogenin, pax7, β-actin, and desmin was examined by semi-quantitative reverse transcriptase polymerase chain reaction. The results indicated that chronic exposure to CuO-NPs causes muscular damage as evidenced by elevated levels of functional markers. There was a significant increase in the oxidants with reduction in the antioxidant levels, implying that the antioxidant enzymes were unable to scavenge the free radicals induced by the CuO-NPs. The histopathological analysis showed degeneration and atrophy in the treated groups confirming muscle damage. The immunohistochemical catalase expression in the muscle was reduced in the treated groups further supporting the evidence that the antioxidant has suffered a decline. The altered gene expression indicates skeletal muscle damage due to the CuO-NPs exposure. Overall, the data suggest that chronic exposure to CuO-NPs caused muscular toxicity which may lead to muscle degeneration in adult zebrafish.

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

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

Surface modification induced cuprous oxide nanoparticle toxicity to duckweed at sub-toxic metal concentrations

Nanoparticle capping agents are critical for controlling the growth, oxidation state, and final particle size during aqueous synthesis. However, despite the known phytotoxicity of cetyltrimethylammonium bromide (CTAB) to plants, it is used to synthesize metal oxide nanoparticles of uniform size and with mesoporous structure. Among the few studies that have investigated how CTAB influences nanoparticle toxicity, CTAB has never been identified as the primary cause of nanoparticle toxicity in environmental systems; rather nanoparticle surface charge or morphology was identified as the driver of toxicity in environmentally relevant systems. In the current study, CTAB release from CTAB surface modified Cu₂O nanoparticles (SM-Cu₂O NPs) inhibited duckweed (Landoltia punctata) growth, even when administered at subtoxic Cu concentrations. Organic ligands, such as humic acid (HA) and ethylenediaminetetraacetic acid (EDTA), lessened growth inhibition associated with exposure to SM-Cu₂O NPs, likely through electrostatic and hydrophobic interactions with CTAB. Such results highlight the need for a more holistic approach to nanoparticle surface modification and improved communication between toxicologists and synthetic chemists to develop green alternatives for nanoparticle synthesis.

Understanding the Phenomenon of Copper Ions Release from Copper-Modified TFC Membranes: A Mathematical and Experimental Methodology Using Shrinking Core Model

Type of metal and metal-oxide NPs added to modify Thin-Film Composites Reverse Osmosis Membranes (TFC-RO) can alter their anti-biofouling properties by changing the dissolution process. The development of a mathematical model can facilitate the selection of these NPs. This work consists of a mathematical and experimental methodology to understand copper-based NPs dissolution of three copper species incorporated into TFC-RO membranes: Cu-NPs, CuO-NPs and Cu-Oligomer complexes formed in situ during the polymerization process. Biocidal capacity of copper species into the membrane was evaluated using colony forming unit method (CFU) over E. coli. In addition, copper ion release kinetics for both NPs and modified membranes were determined. A model based on the shrinking core model (SCM) was validated and applied to determine the limiting rate step in the dissolution process and simulate the ion release kinetics. Fitted curves reached a good adjustment with the experimental data, demonstrating the SCM can be applied to predict ion release process for copper-based NPs in suspension and the modified membranes. All membranes reached similar inhibition rate >50%, however, differences in the dissolution level of copper-based NPs in membrane were noted, suggesting a dual-type effect that defined the copper toxicity into the membrane, associated to the dissolution capacity and ROS production.

Current status of plant metabolite-based fabrication of copper/copper oxide nanoparticles and their applications: a review

Since green mode of nanoparticles (NPs) synthesis is simple, advantageous and environment friendly relative to chemical and physical procedures, various plant species have been used to fabricate copper and copper oxide nanoparticles (Cu/CuO-NPs) owing to the presence of phytochemicals which often act as capping as well as stabilizing agent. These Cu/CuO-NPs are highly stable and used in the degradation of organic dyes like methylene blue and reduction of organic compounds such as phenols. They are also used as antibacterial, antioxidant and antifungal agent due to their cytotoxicity. They are also examined for agricultural crops growth and productivity. Cu-NPs increased the root and shoot growth of mung bean. In wheat plants, these particles reduced shoot growth; and enhanced the grain yield and stress tolerance through starch degradation. Similarly, CuO-NPs treated seedlings have shown reduced chlorophyll, carotenoid and sugar content, whereas proline and anthocyanins were increased in Brassica rapa seedlings. Overall, this review presents the recent understanding of plant-mediated Cu and CuO-NPs fabrication and their application in biomedicine, environmental remediation and agricultural practices. A comparison of the traditional/conventional method of fabrication of NPs with those of green protocols has also been made. Some misconception of copper chemistry has also been critically discussed in terms of oxidation and reduction reactions.

Comparative effects of Cu (60-80 nm) and CuO (40 nm) nanoparticles in Artemia salina: Accumulation, elimination and oxidative stress

In this study, nanotoxicity tests were made by exposure of Artemia salina to copper (Cu 60-80 nm) and copper oxide (CuO 40 nm) nanoparticles (NPs) at different concentrations (0.2, 1, 5, 10, 25, and 50 mg/l) during some exposure duration. Characterization of Cu and CuO NPs were performed using Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS), Zeta Potential, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transformation Infrared (FT-IR) analyzes. In organisms, the accumulation and elimination rates of NPs was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis and the oxidative stress effects on A. salina were determined by Glutathione (GSH) and Thiobarbituric acid reactive substances (TBARS) analysis methods. Both NPs were found to differ in accumulation and elimination rates at each application time and in parallel with the increase in concentration. In each group, it was determined that ion release increased with application time. The results showed that the accumulation rates in Cu NPs had a tendency to increase at 48 h and to decrease at 72 h in concentrations of 0, 2 and 1 mg/l, respectively. And in the all other concentrations have been seen an increasing trend within the time. In the CuO NPs (40 nm), accumulation rates were a decrease trend at 48th hour and an increase trend at 72nd hour except 10 mg/l concentration. In the 10 mg/l group was an increase trend with the application period. Cu NP, TBARS value increased with increasing concentrations and the highest increase was observed at 24 h of 5 ppm group. The groups showed a tendency to increase-decrease-increase-decrease in TBARS levels in terms of elapsed time (24th, 48th, 72nd hour and elimination) (5 ppm and 10 ppm groups tended to decrease in TBARS level at 72nd hour). TBARS increased with increasing concentration ratios in CuO NPs (40 nm).

Effect of Chlamydomonas reinhardtii on the fate of CuO nanoparticles in aquatic environment

In this study, the effect of Chlamydomonas reinhardtii on the fate of CuO nanoparticles (CuO-NPs) in aquatic environment were investigated in terms of the colloidal stability, the free Cu²⁺ releasing, extracellular adsorption Cu (Cu_ex) and intracellular assimilation Cu (Cu_in). The results showed that, with the increasing microalgal density, the absolute value of zeta potential of CuO-NPs decreased and the mean hydrodynamic diameter (MHD) became larger, leading to a better aggregation and settling behavior of CuO-NPs. The microalgae also promoted the free Cu²⁺ releasing, however, inhibited adsorption and assimilation of metal nanoparticles (MNPs) into microalgal cells, resulting in the reduction of the Cu_ex and Cu_in per microalgal cell. The phenomenon was probably due to the reduced chance of contact between microalgae and MNPs. The internalization of CuO-NPs was also observed in microalgal cells by high resolution transmission electron microscope (HRTEM). Furthermore, the results of fast fourier transform (FFT)/inversed FFT (IFFT) analysis indicated that the CuO-NPs was reduced to Cu₂O-NPs in the microalgae cells. The above results suggested that the microalgae can significantly affect the fate of MNPs, and subsequently, influencing the bioavailability and toxicity of MNPs in the aquatic environment.

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.

Transport and retention of copper oxide nanoparticles under unfavorable deposition conditions caused by repulsive van der Waals force in saturated porous media

Currently, copper oxide nanoparticles (CuO NPs) have been widely used in industry, manufacturing and agriculture. The transport and retention of CuO NPs are vital to understanding the fate as well as the life cycle of CuO NPs in the environment. This study systematically investigates the transport and retention of CuO NPs in saturated porous media, and the experimental results were explained by the CFT and DLVO theory. The van der Waals force between CuO NPs and collector was repulsive, resulting in the unfavorable deposition condition. Column experiments were conducted with saturated quartz sand under environmentally relevant pH (6, 8, 9), ionic strength (IS, 1, 10, 50 mM), and humic acid (HA, 0.1-10 mg-C/mL). Experimental results show that the breakthrough curves (BCTs) were affected by different pH and IS. Under pH 6 and 9, the mobility of CuO NPs was enhanced by high IS while the mobility was inhibited by high IS under pH 8. The mobility of CuO NPs was enhanced by humic acid and the effect was best at 0.5 mg-C/mL HA. The experimental results were successfully explained by CFT and DLVO theory, the main mechanisms were aggregation of CuO NPs, interaction energy and collision between CuO NPs and collector. In general, these findings can improve our understanding of the transport and retention of CuO NPs in subsurface environments, and suggest pH, IS, HA may be key factors governing mobility and stability of CuO NPs in natural environment.

Fe0 nanoparticles improve physiological and antioxidative attributes of sunflower (Helianthus annuus) plants grown in soil spiked with hexavalent chromium

Contamination of agricultural land by chromium (Cr) can inhibit physiological and biochemical processes in plants, leading to reduced crop productivity and food/feed safety. Owing to their fine size, large surface area, and high adsorption affinity for metals, nanomaterials have shown a potential for phytoremediation of heavy metal-contaminated soils. Nanomaterials enhance fitness of plants under metal stress through their modifying effects on plant physiology and biochemistry. The aim of this study was to assess the performance of sunflower (Helianthus annuus) plants grown in soil spiked with hexavalent chromium (Cr IV; 0, 75 and 150 ppm) and the potential role of nano-zerovalent iron (Fe0 nanoparticles; 0, 1 and 2%) to ameliorate Cr toxicity. Results revealed that the Cr uptake decreased by increasing the concentration of Fe0 nanoparticles, causing a significant enhancement in plant morphological and physiological attributes. Treatment with Fe0 nanoparticles reduced bioaccumulation factor (BAF) (in both root and shoot tissues) and translocation factor (TF); however, the magnitude of BAF and TF decreased significantly by increasing the level of Cr(VI). Chromium stress increased the activities of antioxidant enzymes, which further increased by Fe0 nanoparticle application, resulting in improved growth traits. A significant positive correlation was found between growth, BAF and TF of seedlings treated with Fe0 nanoparticles (both 1 and 2%) upon Cr exposure (75 and 150 ppm). The results demonstrated the potential of Fe0 nanoparticles to improve performance of sunflower plants under Cr toxicity through reducing their Cr uptake, which was accompanied by enhanced activity of detoxification enzymes (SOD, CAT, POX, and APX) in cells.

Impacts of Aerosol Copper on Marine Phytoplankton: A Review

Atmospheric deposition brings both nutrients and toxic components to the surface ocean, resulting in important impacts on phytoplankton. Field and lab studies have been done on the iron (Fe) fertilization on marine phytoplankton. However, studies on other trace metals are limited. Both bioassay experiments and field observations have suggested that aerosols with high copper (Cu) concentrations can negatively affect the primary productivity and change phytoplankton community structure. Note that with increasing human activities and global environmental changes (e.g., ocean acidification, warming, deoxygenation, etc.), the input of aerosol Cu could exceed toxicity thresholds at certain times or in some sensitive oceanic regions. Here, we provide a comprehensive review on aerosol Cu and marine phytoplankton studies by summarizing (1) physiological effects and toxicity thresholds of Cu to various phytoplankton taxa, (2) interactions between Cu and other metals and major nutrients, and (3) global distribution of surface seawater Cu and atmospheric Cu. We suggest that studies on aerosols, seawater chemistry, and phytoplankton should be integrated for understanding the impacts of aerosol Cu on marine phytoplankton, and thereafter the air–sea interaction via biogeochemical processes.

Effect of copper nanoparticles and ions on spermatozoa motility of sea trout (Salmo trutta m. Trutta L.)

Nanoproducts are being increasingly used in various industrial products, leading to a greater risk of water pollution through their discharge into environment as production byproducts. Increased levels of environmental pollution with nanoproducts pose a threat to all living organisms. Nanopollutants may have toxic effects on gametes and fertilization process in species with external fertilization, thereby reducing effectiveness of reproduction or greatly impairing it. The objective of the present study was to determine the effect of copper nanoparticles (Cu and CuO) and copper ions (CuSO₄·5H₂O) on the spermatozoa motility of sea trout and compare their harmful effects. Copper nanoparticles (NPs) of primary particle size <100 nm and CuO NPs of particle size <50 nm as well as a solution of CuSO₄·5H₂O were used for the study. Concentration of the products tested (CuNPs, CuONPs, and CuSO₄·5H₂O) was expressed as mg Cu L^-1 in the media regardless of dissolution and aggregation. A suspension with concentration up to 500 mg L^-1 in an aquatic environment was tested. Spermatozoa motility under direct contact with copper at 10 s post activation was evaluated using an automated system (CASA). Copper products in an aqueous environment primarily cause a reduction of spermatozoa velocity (VCL). A significant reduction of velocity in CuSO₄·5H₂O salt solution occurred at concentration starting from 8 mg L^-1, whereas in solutions containing CuNPs and CuONPs this process is observed from 50 mg L^-1. Reduction of percentage of motile spermatozoa occurred in CuNPs from a concentration of 125 mg L^-1, while in CuONPs and CuSO₄·5H₂O, the effect began at concentration from 250 mg L^-1. In a solution of CuSO₄·5H₂O at a concentration of 500 mg L^-1, strong agglutination of sperm cells occurred and movement ceased (immobilization IC100). Exposure to CuONPs decreased the motility rate to below IC50, while for CuNPs, the motility rate reached 80%. Changes in linearity (LIN) and amplitude of head displacement (ALH) differed according to Cu products. Cu as CuSO₄·5H₂O and CuONPs impaired the LIN, while CuNPs lowered ALH. Duration of motility increased at low CuSO₄·5H₂O concentration. The effect of Cu ion on sea trout spermatozoa motility was more harmful than that of copper nanoparticles. The various copper products used affected motility parameters differently. Contamination of aqueous environment with copper primarily caused reduction in male gamete velocity, which may impair reproduction. Various copper products had different effects on LIN, ALH, and motility duration, which can also affect fertilization.

Comparative contributions of copper nanoparticles and ions to copper bioaccumulation and toxicity in barnacle larvae

Cu nanoparticles (CuNPs) have been widely used in numerous products, and may become a potential threat to marine organisms, but their behavior in the marine environments and potential toxicity to marine organisms remain little known. In the present study, we investigated the behavior of CuNPs in seawater, as well as the toxicity and bioaccumulation of CuNPs and copper sulfate (CuSO₄) in barnacle larvae (Balanus amphitrite), a dominant fouling invertebrate in marine environment. CuNPs tended to aggregate in natural seawater and released Cu ion rapidly into seawater. The aggregation and release were especially higher at a lower concentration of CuNPs, e.g., 94-96% of CuNPs were released as Cu ions at 20 μg/L after 24 h. The larger size of CuNPs (40 nm) tended to display a higher solubility than the 20 nm CuNPs did. Humic acids enhanced the aggregation and inhibited the dissolution of CuNPs, and had a protective effect on the survival of nauplii II at higher Cu concentrations (100-200 μg/L). Comparison of the lethal concentrations showed that CuNPs were generally less toxic to the two stages of barnacle larvae (nauplii II and VI) than the Cu ions. The calculated 48-h LC₅₀ values for nauplii II were 189.5 μg/L, 123.2 μg/L, and 89.8 μg/L for 20 nm CuNPs, 40 nm CuNPs, and CuSO₄, respectively. However, the lethal concentrations of Cu bioaccumulation in the barnacle larvae were comparable between CuNPs and Cu ions when expressed by the actual tissue Cu bioaccumulation. Barnacle larval settlement decreased with an increase of Cu concentrations of both CuNPs and CuSO₄, and was significantly inhibited at 100 μg/L CuSO₄ and 150 μg/L CuNPs. Our results indicated that the toxicity of CuNPs could not be solely explained by the released Cu ions, and both CuNPs and the released Cu ion contributed to their toxicity and bioaccumulation in barnacle larvae.

Addition-omission of zinc, copper, and boron nano and bulk oxide particles demonstrate element and size -specific response of soybean to micronutrients exposure

Plant response to microelements exposure can be modulated based on particle size. However, studies are lacking on the roles of particle size and specific microelements in mixed exposure systems designed for plant nutrition, rather than toxicology. Here, an addition-omission strategy was used to address particle-size and element-specific effects in soybean exposed to a mixture of nano and bulk scale oxide particles of Zn (2 mg Zn/kg), Cu (1 mg Cu/kg) and B (1 mg B/kg) in soil. Compared to the control, mixtures of oxide particles of both sizes significantly (p < 0.05) promoted grain yield and overall (shoot and grain) Zn accumulation, but suppressed overall P accumulation. However, the mixed nano-oxides, but not the mixed bulk-oxides, specifically stimulated shoot growth (47%), flower formation (63%), shoot biomass (34%), and shoot N (53%) and K (42%) accumulation. Compared by particle size, omission of individual elements from the mixtures evoked significant responses that were nano or bulk-specific, including shoot growth promotion (29%) by bulk-B; inhibition (51%) of flower formation by nano-Cu; stimulation (57%) of flower formation by bulk-B; grain yield suppression (40%) by nano-Zn; B uptake enhancement (34%) by bulk-Cu; P uptake stimulation by nano-Zn (14%) or bulk-B (21%); residual soil N (80%) and Zn (42%) enhancement by nano-Cu; and residual soil Cu enhancement by nano-Zn (72%) and nano-B (62%). Zn was responsible for driving the agronomic (biomass and grain yield) responses in this soil, with concurrent ramifications for environmental management (N and P) and human health (Zn nutrition). Overall, compared to bulk microelements, nanoscale microelements played a greater role in evoking plant responses.

Biochemical and physiological effects of copper compounds/nanoparticles on sugarcane (Saccharum officinarum)

The widespread use of copper based nanomaterials has been accompanied by an increasing interest in understanding their potential risks. It is essential to understand the effects of these nanoparticles on edible crops by performing long-term experiments at relevant exposure concentrations. Sugarcane is the source of 70% of the world's sugar supply and the widespread use of refined sugar and the consumption of raw sugarcane can provide a route for nanoparticles to enter the food supply. In order to evaluate the biochemical and physiological effects of copper nanoparticle exposure, sugarcane was grown for one year in soil amended with 20, 40, and 60 mg/kg of Kocide 3000 (a copper based fungicide), copper metal nanoparticles, micro-sized CuO, and CuCl₂. The results show that stress indicators such as catalase and ascorbic peroxidase enzymatic activity in the sugarcane plant were activated by all the copper based materials at different concentrations. Sugarcane plants exposed to nearly all copper treatments showed dosage dependent increases in copper concentrations in root tissues. Translocation of copper to aerial tissues was minimal, with copper concentrations not being significantly different from controls. In addition, Chlorophyll A content was higher in plants treated with Kocide 3000 at 20 and 60 mg/kg, μCuO at 20 mg/kg, and CuCl₂ at 20 and 60 mg/kg. To our knowledge, this is the first report on the effects of nano-copper compounds in sugarcane crop.

Interaction of CuO nanoparticles with duckweed (Lemna minor. L): Uptake, distribution and ROS production sites

CuO engineered nanoparticles (NPs) are of increasing concern due to their extensive use in daily life and adverse effect on aquatic organisms. The investigations on the toxicity of CuO NPs to aquatic plants through uptake from roots versus fronds are limited. This paper discusses the interactions of CuO NPs with Lemna minor, a floating plant. After CuO NPs (150 μg L^-1) exposure for 7 days, the frond number, frond surface area and dry weights of whole plants significantly decreased by 32%, 47% and 33%; the responses were dose-dependent. Microscopy imaging showed that the epidermis was severely damaged in fronds, edges were severely sloughed off and cell integrity was damaged in roots. Shrinkage of both chloroplast and starch grains were observed in the frond cells. Internalization of CuO NPs in root and frond cells during CuO NPs (1 mg L^-1) exposure was confirmed with the root Cu levels of Lemna minor being three times higher than the fronds by using transmission electron microscopy and flame atomic absorption spectrophotometry. Reactive oxygen species, mainly H₂O₂ (increased by 56%) and ·OH (increased by 57%), accumulated in Lemna minor tissues in response to CuO NPs exposure. Moreover, chloroplasts were confirmed as a site of ROS production. These findings are helpful for better understanding the biological responses of aquatic plants upon NPs exposure.

Toxicity of copper oxide nanoparticles to Neotropical species Ceriodaphnia silvestrii and Hyphessobrycon eques

The increase of production and consumption of copper oxide nanostructures in several areas contributes to their release into aquatic ecosystems. Toxic effects of copper oxide nanoparticles (CuO NPs), in particular, on tropical aquatic organisms are still unknown, representing a risk for biota. In this study, the effects of rod-shaped CuO NPs on the Neotropical species Ceriodaphnia silvestrii and Hyphessobrycon eques were investigated. We also compared the toxicity of CuO NPs and CuCl₂ on these species to investigate the contribution of particles and cupper ions to the CuO NPs toxicity. Considering the low copper ions release from CuO NPs (<1%), our results revealed that the toxicity of CuO NPs to C. silvestrii and H. eques was mainly induced by the NPs. The 48 h EC₅₀ for C. silvestrii was 12.6 ± 0.7 μg Cu L^-1 and for H. eques the 96 h LC₅₀ was 211.4 ± 57.5 μg Cu L^-1 of CuO NPs. There was significant decrease in reproduction, feeding inhibition and increase in reactive oxidative species (ROS) generation in C. silvestrii exposed to CuO NPs. In fish H. eques, sublethal exposure to CuO NPs caused an increase in ROS generation in gill cells and an increase in cells number that were in early apoptotic and necrotic stages. Our results showed that CuO NPs caused toxic effects to C. silvestrii and H. eques and ROS play an important role in the toxicity pathway observed. Data also indicated that C. silvestrii was among the most sensitive species for CuO NPs. Based on predicted environmental concentration in water bodies, CuO NPs pose potential ecological risks for C. silvestrii and H. eques and other tropical freshwater organisms.

Rhizosphere interactions between copper oxide nanoparticles and wheat root exudates in a sand matrix: Influences on copper bioavailability and uptake

The impact of copper oxide nanoparticles (CuONPs) on crop production is dependent on the biogeochemistry of Cu in the rooting zone of the plant. The present study addressed the metabolites in wheat root exudates that increased dissolution of CuONPs and whether solubility correlated with Cu uptake into the plant. Bread wheat (Triticum aestivum cv. Dolores) was grown for 10 d with 0 to 300 mg Cu/kg as CuONPs in sand, a matrix deficient in Fe, Zn, Mn, and Cu for optimum plant growth. Increased NP doses enhanced root exudation, including the Cu-complexing phytosiderophore, 2'-deoxymugineic acid (DMA), and corresponded to greater dissolution of the CuONPs. Toxicity, observed as reduced root elongation, was attributable to a combination of CuONPs and dissolved Cu complexes. Geochemical modeling predicted that the majority of the solution phase Cu was complexed with citrate at low dosing or DMA at higher dosing. Altered biogeochemistry within the rhizosphere correlated with bio-responses via exudate type, quantity, and metal uptake. Exposure of wheat to CuONPs led to dose-dependent decreases in Fe, Ca, Mg, Mn, and K in roots and shoots. The present study is relevant to growth of a commercially important crop, wheat, in the presence of CuONPs as a fertilizer, fungicide, or pollutant. Environ Toxicol Chem 2018;37:2619-2632. © 2018 SETAC.

Temporal Evolution of Copper Distribution and Speciation in Roots of Triticum aestivum Exposed to CuO, Cu(OH)2, and CuS Nanoparticles

Utilization of nanoparticles (NP) in agriculture as fertilizers or pesticides requires an understanding of the NP properties influencing their interactions with plant roots. To evaluate the influence of the solubility of Cu-based NP on Cu uptake and NP association with plant roots, wheat seedlings were hydroponically exposed to 1 mg/L of Cu NPs with different solubilities [CuO, CuS, and Cu(OH)₂] for 1 h then transferred to a Cu-free medium for 48 h. Fresh, hydrated roots were analyzed using micro X-ray fluorescence (μ-XRF) and imaging fluorescence X-ray absorption near edge spectroscopy (XANES imaging) to provide laterally resolved distribution and speciation of Cu in roots. Higher solubility Cu(OH)₂ NPs provided more uptake of Cu after 1 h of exposure, but the lower solubility materials (CuO and CuS) were more persistent on the roots and continued to deliver Cu to plant leaves over the 48 h depuration period. These results demonstrate that NPs, by associating to the roots, have the potential to play a role in slowly providing micronutrients to plants. Thus, tuning the solubility of NPs may provide a long-term slow delivery of micronutrients to plants and provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs.

Assessment of the effects of metal oxide nanoparticles on the growth, physiology and metabolic responses in in vitro grown eggplant (Solanum melongena)

Nanoparticles (NPs) are widely used in various domestic products and their usage is constantly increasing which in turn can raise several environmental health issues. Like other abiotic stresses, nanomaterials also affect the growth of crop plants. Solanum melongena is a common vegetable crop grown in the tropics and subtropics regions with medicinal properties. In this study, S. melongena was analyzed for its response to three commercially important metallic nanoparticles, namely NiO, CuO, and ZnO, at four different concentrations (100, 250, 500 and 1000 mg/L). The growth of the eggplant seedlings was suppressed by all the NPs in a concentration-dependent manner and among them, NiO was shown to be more toxic as it suppressed the root and shoot growth effectively. Total chlorophyll contents were decreased in the NP-treated plants compared to control plants. Significant changes were found in the secondary metabolites such as anthocyanins, total phenolic and total flavonoid contents in the NP-treated plants. A dose-dependent increase in the reactive oxygen species (ROS) generation was noticed in the NP-treated plants which are evidenced by the 4-nitro blue tetrazolium chloride (NBT) and 3,3'-diamiobenzidine (DAB) histochemical staining. The DNA damage imposed by the NP in the seedlings of eggplants may be due to the elevated ROS and MDA (malondialdehyde) production. NiO NP was found to be more toxic comparable to CuO and ZnO NPs in the present study. Apart from the toxic effects, nanoparticles also showed profound effects on the production of important secondary metabolites such as phenolics and flavonoid compounds.

Assessing the release of copper from nanocopper-treated and conventional copper-treated lumber into marine waters II: Forms and bioavailability

One application of nanocopper is as a wood-preserving pesticide in pressure-treated lumber. Recent research has shown that pressure-treated lumber amended with micronized copper azole (MCA), which contains nanosized copper, releases copper under estuarine and marine conditions. The form of copper released (i.e., ionic, nanocopper [1-100 nm in size]) is not fully understood but will affect the bioavailability and toxicity of the metal. In the present study, multiple lines of evidence, including size fractionation, ion-selective electrode electrochemistry, comparative toxicity, and copper speciation were used to determine the form of copper released from lumber blocks and sawdust. The results of all lines of evidence supported the hypothesis that ionic copper was released from MCA lumber and sawdust, with little evidence that nanocopper was released. For example, copper concentrations in size fractionations of lumber block aqueous leachates including unfiltered, 0.1 μm, and 3 kDa were not significantly different, suggesting that the form of copper released was in the size range operationally defined as dissolved. These results correlated with the ion-selective electrode data which detects only ionic copper. In addition, comparative toxicity testing resulted in a narrow range of median lethal concentrations (221-257 μg/L) for MCA lumber blocks and CuSO4 . We conclude that ionic copper was released from the nanocopper pressure-treated lumber under estuarine and marine conditions. Environ Toxicol Chem 2018;37:1969-1979. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Green Synthesis of Metal and Metal Oxide Nanoparticles and Their Effect on the Unicellular Alga Chlamydomonas reinhardtii

Recently, the green synthesis of metal nanoparticles has attracted wide attention due to its feasibility and very low environmental impact. This approach was applied in this study to synthesise nanoscale gold (Au), platinum (Pt), palladium (Pd), silver (Ag) and copper oxide (CuO) materials in simple aqueous media using the natural polymer gum karaya as a reducing and stabilising agent. The nanoparticles' (NPs) zeta-potential, stability and size were characterised by Zetasizer Nano, UV-Vis spectroscopy and by electron microscopy. Moreover, the biological effect of the NPs (concentration range 1.0-20.0 mg/L) on a unicellular green alga (Chlamydomonas reinhardtii) was investigated by assessing algal growth, membrane integrity, oxidative stress, chlorophyll (Chl) fluorescence and photosystem II photosynthetic efficiency. The resulting NPs had a mean size of 42 (Au), 12 (Pt), 1.5 (Pd), 5 (Ag) and 180 (CuO) nm and showed high stability over 6 months. At concentrations of 5 mg/L, Au and Pt NPs only slightly reduced algal growth, while Pd, Ag and CuO NPs completely inhibited growth. Ag, Pd and CuO NPs showed strong biocidal properties and can be used for algae prevention in swimming pools (CuO) or in other antimicrobial applications (Pd, Ag), whereas Au and Pt lack these properties and can be ranked as harmless to green alga.