Soil and foliar exposure of soybean (Glycine max) to Cu: Nanoparticle coating-dependent plant responses.

In this study, we investigated the effects of citric acid (CA) coated copper oxide nanoparticles (CuO NPs) and their application method (foliar or soil exposure) on the growth and physiology of soybean (Glycine max). After nanomaterials exposure via foliar or soil application, Cu concentration was elevated in the roots, leaves, stem, pod, and seeds; distribution varied by plant organ and surface coating. Foliar application of CuO NPs at 300 mg/L and CuO-CA NPs at 75 mg/L increased soybean yield by 169.5% and 170.1%, respectively. In contrast, foliar and soil exposure to ionic Cu with all treatments (75 and 300 mg/L) had no impact on yield. Additionally, CuO-CA NPs at 300 mg/L significantly decreased Cu concentration in seeds by 46.7%, compared to control, and by 44.7%, compared to equivalent concentration of CuO NPs. Based on the total Cu concentration, CuO NPs appeared to be more accessible for plant uptake, compared to CuO-CA NPs, inducing a decrease in protein content by 56.3% and inhibiting plant height by 27.9% at 300 mg/kg under soil exposure. The translocation of Cu from leaf to root and from the root to leaf through the xylem was imaged by two-photon microscopy. The findings indicate that citric acid coating reduced CuO NPs toxicity in soybean, demonstrating that surface modification may change the toxic properties of NPs. This research provides direct evidence for the positive effects of CuO-CA NPs on soybean, including accumulation and in planta transfer of the particles, and provides important information when assessing the risk and the benefits of NP use in food safety and security.

Copper oxide (CuO) nanoparticles affect yield, nutritional quality, and auxin associated gene expression in weedy and cultivated rice (Oryza sativa L.) grains.

Weedy rice grows competitively with cultivated rice and significantly diminishes rice grain production worldwide. The different effects of Cu-based nanomaterials on the production of weedy and cultivated rice, especially the grain qualities are not known. Grains were collected from weedy and cultivated rice grown for four months in field soil amended with nanoscale CuO (nCuO), bulk CuO (bCuO), and copper sulfate (CuSO4) at 0, 75, 150, 300, and 600 mg Cu/kg soil. Cu translocation, essential element accumulation, yield, sugar, starch, protein content, and the expression of auxin associated genes in grains were determined. The grains of weedy and cultivated rice were differentially impacted by CuO-based compounds. At ≥300 mg/kg, nCuO and bCuO treated rice had no grain production. Treatment at 75 mg/kg significantly decreased grain yield as compared to control with the order: bCuO (by 88.7%) > CuSO4 (by 47.2%) ~ nCuO (by 38.3% only in cultivated rice); at the same dose, the Cu grain content was: nCuO ~ CuSO4 > bCuO > control. In weedy grains, K, Mg, Zn, and Ca contents were decreased by 75 and 150 mg/kg nCuO by up to 47.4%, 34.3%, 37.6%, and 60.0%, but no such decreases were noted in cultivated rice, and Fe content was increased by up to 88.6%, and 53.2%. In rice spikes, nCuO increased Mg, Ca, Fe, and Zn levels by up to 118.1%, 202.6%, 133.8%, and 103.9%, respectively. Nanoscale CuO at 75 and 150 mg/kg upregulated the transcription of an auxin associated gene by 5.22- and 1.38-fold, respectively, in grains of weedy and cultivated rice. The biodistribution of Cu-based compounds in harvested grain was determined by two-photon microscopy. These findings demonstrate a cultivar-specific and concentration-dependent response of rice to nCuO. A potential use of nCuO at 75 and 150 mg/kg in cultivar-dependent delivery system was suggested based on enhanced grain nutritional quality, although the yield was compromised. This knowledge, at the physiological and molecular level, provides valuable information for the future use of Cu-based nanomaterials in sustainable agriculture.

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.

Sustainable synthesis and remarkable adsorption capacity of MOF/graphene oxide and MOF/CNT based hybrid nanocomposites for the removal of Bisphenol A from water.

A series of novel absorbents based on Cu-BDC MOFs decorated over graphene oxide (GrO) and carbon nanotubes (CNTs) hybrid nanocomposites, namely Cu-BDC@GrO and Cu-BDC@CNT, are synthesized via a facile and one-pot green solvothermal method for water remediation. The nanocomposites were characterized by XRD, TEM, SEM, EDS, Raman, FTIR, TGA, XPS, Zetasizer and ICP-OES instruments. XRD results confirmed the high crystalline structure of the synthesized hybrid nanocomposites. Morphological analysis by SEM and TEM verified the successful decoration of nano-sized Cu-BDC MOFs over GrO and CNT platforms; whereas, EDS and XPS analysis confirmed the presence of all components in the hybrid nanocomposites. Bisphenol A was used in this study as a model organic pollutant that is sometimes present in the industrial wastewater to test the adsorption capacity of the prepared hybrid nanomaterials toward their removal from water. The hybrid nanomaterials showed remarkable adsorption capacity of 182.2 and 164.1 mg/g toward the removal of BPA, which was several times higher than that of 60.2 mg/g for Cu-BDC MOF itself. The Langmuir, Freundlich, Temkin and D-R isotherm models were applied to analyze the experimental data and the results revealed that the Freundlich model describes the experimental data best. A kinetic study was carried out and it showed that the prepared nanomaterials could remove maximum amount of BPA from water in 30 min. The pseudo-first order, pseudo-second order and intra-particle diffusion models were applied to evaluate the kinetic data and the results suggested that the kinetics data could be well fitted to the pseudo-second order kinetic model. Additionally, the BAP adsorption process onto the hybrid nanocomposites was spontaneous and exothermic. The π-π interactions between the BPA and hybrid nanomaterials played a vital role during the BPA adsorption process. The higher adsorption capacity and water stability makes them a good candidate for water remediation applications.

Exposure of cerium oxide nanoparticles to kidney bean shows disturbance in the plant defense mechanisms.

Overwhelming use of engineered nanoparticles demands rapid assessment of their environmental impacts. The transport of cerium oxide nanoparticles (nCeO2) in plants and their impact on cellular homeostasis as a function of exposure duration is not well understood. In this study, kidney bean plants were exposed to suspensions of ∼ 8 ± 1 nm nCeO2 (62.5 to 500 mg/L) for 15 days in hydroponic conditions. Plant parts were analyzed for cerium accumulation after one, seven, and 15 days of nCeO2 exposure. The primary indicators of stress like lipid peroxidation, antioxidant enzyme activities, total soluble protein and chlorophyll contents were studied. Cerium in tissues was localized using scanning electron microscopy and synchrotron µ-XRF mapping, and the chemical forms were identified using µ-XANES. In the root epidermis, cerium was primarily shown to exist as nCeO2, although a small fraction (12%) was biotransformed to Ce(III) compound. Cerium was found to reach the root vascular tissues and translocate to aerial parts with time. Upon prolonged exposure to 500 mg nCeO2/L, the root antioxidant enzyme activities were significantly reduced, simultaneously increasing the root soluble protein by 204%. In addition, leaf's guaiacol peroxidase activity was enhanced with nCeO2 exposure in order to maintain cellular homeostasis.

Synchrotron verification of TiO2 accumulation in cucumber fruit: a possible pathway of TiO2 nanoparticle transfer from soil into the food chain.

The transfer of nanoparticles (NPs) into the food chain through edible plants is of great concern. Cucumis sativus L. is a freshly consumed garden vegetable that could be in contact with NPs through biosolids and direct agrichemical application. In this research, cucumber plants were cultivated for 150 days in sandy loam soil treated with 0 to 750 mg TiO2 NPs kg(-1). Fruits were analyzed using synchrotron µ-XRF and µ-XANES, ICP-OES, and biochemical assays. Results showed that catalase in leaves increased (U mg(-1) protein) from 58.8 in control to 78.8 in 750 mg kg(-1) treatment; while ascorbate peroxidase decreased from 21.9 to 14.1 in 500 mg kg(-1) treatment. Moreover, total chlorophyll content in leaves increased in the 750 mg kg(-1) treatment. Compared to control, FTIR spectra of fruit from TiO2 NP treated plants showed significant differences (p ≤ 0.05) in band areas of amide, lignin, and carbohydrates, suggesting macromolecule modification of cucumber fruit. In addition, compared with control, plants treated with 500 mg kg(-1) had 35% more potassium and 34% more phosphorus. For the first time, µ-XRF and µ-XANES showed root-to-fruit translocation of TiO2 in cucumber without biotransformation. This suggests TiO2 could be introduced into the food chain with unknown consequences.

Toxicity assessment of cerium oxide nanoparticles in cilantro (Coriandrum sativum L.) plants grown in organic soil.

Studies have shown that CeO2 nanoparticles (NPs) can be accumulated in plants without modification, which could pose a threat for human health. In this research, cilantro (Coriandrum sativum L.) plants were germinated and grown for 30 days in soil amended with 0 to 500 mg kg⁻¹ CeO2 NPs and analyzed by spectroscopic techniques and biochemical assays. At 125 mg kg⁻¹, plants produced longer roots (p ≤ 0.05), and at 500 mg kg⁻¹, there was higher Ce accumulation in tissues (p ≤ 0.05). At 125 mg, catalase activity significantly increased in shoots and ascorbate peroxidase in roots (p ≤ 0.05). The FTIR analyses revealed that at 125 mg kg⁻¹ the CeO2 NPs changed the chemical environment of carbohydrates in cilantro shoots, for which changes in the area of the stretching frequencies were observed. This suggests that the CeO2 NPs could change the nutritional properties of cilantro.

ZnO nanoparticle fate in soil and zinc bioaccumulation in corn plants (Zea mays) influenced by alginate.

Nanoparticles (NPs) can interact with naturally occurring inorganic and organic substances in soils, which may change their transport behavior in soil and plants. This study was performed in two steps. In the first step, corn (Zea mays) plants were cultivated for one month in soil amended with 10 nm commercial spheroid ZnO NPs at 0­800 mg kg−1 and sodium alginate at 10 mg kg−1. In the second step, the plants were grown with ZnO NPs at 400 mg kg−1 and alginate at 0, 10, 50, and 100 mg kg−1. The dynamics of Zn concentrations in soil solution and Zn accumulation in plant tissues were determined by ICP-OES. Biomass accumulation, chlorophyll concentration, and the activity of antioxidant enzymes in leaves were also quantified. Results indicate that ZnO NPs coexisting with Zn dissolved species were continuously released to the soil solution to replenish the Zn ions or ZnO NPs scavenged by roots. At 400 and 800 mg kg−1, without alginate, ZnO NPs significantly reduced the root and shoot biomass production; however, plants treated with these NP concentrations, plus alginate, had significantly more Zn in tissues with no reduction in biomass production. Alginate significantly reduced the activity of stress enzymes catalase and peroxidase, which could indicate damage in the defense system. The effects of ZnO NPs in a food crop grown in alginate enriched soil, showing an excess of Zn in the aerial parts, are yet to be reported.