Effects of graphene oxide on cadmium uptake and photosynthesis performance in wheat seedlings

Seed priming with graphene oxide improves salinity tolerance and increases productivity of peanut through modulating multiple physiological processes

Graphene oxide (GO), beyond its specialized industrial applications, is rapidly gaining prominence as a nanomaterial for modern agriculture. However, its specific effects on seed priming for salinity tolerance and yield formation in crops remain elusive. Under both pot-grown and field-grown conditions, this study combined physiological indices with transcriptomics and metabolomics to investigate how GO affects seed germination, seedling salinity tolerance, and peanut pod yield. Peanut seeds were firstly treated with 400 mg L⁻¹ GO (termed GO priming). At seed germination stage, GO-primed seeds exhibited higher germination rate and percentage of seeds with radicals breaking through the testa. Meanwhile, omics analyses revealed significant enrichment in pathways associated with carbon and nitrogen metabolisms in GO-primed seeds. At seedling stage, GO priming contributed to strengthening plant growth, enhancing photosynthesis, maintaining the integrity of plasma membrane, and promoting the nutrient accumulation in peanut seedlings under 200 mM NaCl stress. Moreover, GO priming increased the activities of antioxidant enzymes, along with reduced the accumulation of reactive oxygen species (ROS) in response to salinity stress. Furthermore, the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) of peanut seedlings under GO priming were mainly related to photosynthesis, phytohormones, antioxidant system, and carbon and nitrogen metabolisms in response to soil salinity. At maturity, GO priming showed an average increase in peanut pod yield by 12.91% compared with non-primed control. Collectively, our findings demonstrated that GO plays distinguish roles in enhancing seed germination, mitigating salinity stress, and boosting pod yield in peanut plants via modulating multiple physiological processes.

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Biomonitoring of heavy metals and their phytoremediation by duckweeds: Advances and prospects

Heavy metals (HMs) contamination of water bodies severely threatens human and ecosystem health. There is growing interest in the use of duckweeds for HMs biomonitoring and phytoremediation due to their fast growth, low cultivation costs, and excellent HM uptake efficiency. In this review, we summarize the current state of knowledge on duckweeds and their suitability for HM biomonitoring and phytoremediation. Duckweeds have been used for phytotoxicity assays since the 1930s. Some toxicity tests based on duckweeds have been listed in international guidelines. Duckweeds have also been recognized for their ability to facilitate HM phytoremediation in aquatic environments. Large-scale screening of duckweed germplasm optimized for HM biomonitoring and phytoremediation is still essential. We further discuss the morphological, physiological, and molecular effects of HMs on duckweeds. However, the existing data are clearly insufficient, especially in regard to dissection of the transcriptome, metabolome, proteome responses and molecular mechanisms of duckweeds under HM stresses. We also evaluate the influence of environmental factors, exogenous substances, duckweed community composition, and HM interactions on their HM sensitivity and HM accumulation, which need to be considered in practical application scenarios. Finally, we identify challenges and propose approaches for improving the effectiveness of duckweeds for bioremediation from the aspects of selection of duckweed strain, cultivation optimization, engineered duckweeds. We foresee great promise for duckweeds as phytoremediation agents, providing environmentally safe and economically efficient means for HM removal. However, the primary limiting issue is that so few researchers have recognized the outstanding advantages of duckweeds. We hope that this review can pique the interest and attention of more researchers.

Environmental and Health Impacts of Graphene and Other Two-Dimensional Materials: A Graphene Flagship Perspective

Two-dimensional (2D) materials have attracted tremendous interest ever since the isolation of atomically thin sheets of graphene in 2004 due to the specific and versatile properties of these materials. However, the increasing production and use of 2D materials necessitate a thorough evaluation of the potential impact on human health and the environment. Furthermore, harmonized test protocols are needed with which to assess the safety of 2D materials. The Graphene Flagship project (2013-2023), funded by the European Commission, addressed the identification of the possible hazard of graphene-based materials as well as emerging 2D materials including transition metal dichalcogenides, hexagonal boron nitride, and others. Additionally, so-called green chemistry approaches were explored to achieve the goal of a safe and sustainable production and use of this fascinating family of nanomaterials. The present review provides a compact survey of the findings and the lessons learned in the Graphene Flagship.

Regulatory effect of graphene on growth and carbon/nitrogen metabolism of maize (Zea mays L.)

BACKGROUND

Leakage of graphene into the environment has resulted from its increasing use. Although the impact of graphene on ecosystems is already in full swing, information regarding its impact on plants is lacking. In particular, the effects of graphene on plant growth and development vary, and basic information on the regulation of carbon and nitrogen metabolism is missing. In the current study, the way in which graphene (0, 25, 50, 100, and 200 g kg-1 ) affects maize seedlings was studied in terms of morphological and biochemical indicators. The purpose of this study was to understand better how graphene regulates plant carbon and nitrogen metabolism and to understand its interactions with leaf structure and plant growth.

RESULTS

The results showed that 50 g kg-1 graphene increased plant height, stem diameter, leaf area, and dry weight; however, this was inhibited by the high level of graphene (200 g kg-1 ). Further studies indicated that different concentrations of graphene could increase leaf thickness and vascular bundle area as well as the net photosynthetic rate (Pn) of leaves; 25 and 50 g kg-1 graphene enhanced the leaves stomatal conductance (Cond), transpiration rate (Tr), intercellular carbon dioxide (Ci), and chlorophyll content. Higher concentrations decreased the above indicators. At 50 g kg-1 , graphene increased the activity of carbon/nitrogen metabolism enzymes by increasing carbon metabolites (fructose, sucrose, and soluble sugars) and soluble proteins (nitrogen metabolites). These enzymes included sucrose synthase (SS), sucrose phosphate synthase (SPS), nitrate reductase (NR), glutamine synthase (GS), and glutamate synthase (GOGAT).

CONCLUSION

These results indicate that graphene can regulate the activities of key enzymes involved in carbon and nitrogen metabolism effectively and supplement nitrogen metabolism through substances produced by carbon metabolism by improving photosynthetic efficiency, thus maintaining the balance between carbon and nitrogen and promoting plant growth and development. The relationship between these indexes explained the mechanism by which graphene supported the growth of maize seedlings by enhancing photosynthetic carbon metabolism and maintaining metabolic balance. For maize seedling growth, graphene treatment with 50 g kg-1 soil is recommended. © 2023 Society of Chemical Industry.

Ameliorating Effects of Graphene Oxide on Cadmium Accumulation and Eco-Physiological Characteristics in a Greening Hyperaccumulator (Lonicera japonica Thunb.)

Graphene oxide (GO), as a novel carbon-based nanomaterial (CBN), has been widely applied to every respect of social life due to its unique composite properties. The widespread use of GO inevitably promotes its interaction with heavy metal cadmium (Cd), and influences its functional behavior. However, little information is available on the effects of GO on greening hyperaccumulators under co-occurring Cd. In this study, we chose a typical greening hyperaccumulator (Lonicera japonica Thunb.) to show the effect of GO on Cd accumulation, growth, net photosynthesis rate (Pn), carbon sequestration and oxygen release functions of the plant under Cd stress. The different GO-Cd treatments were set up by (0, 10, 50 and 100 mg L-1) GO and (0, 5 and 25 mg L-1) Cd in solution culture. The maximum rate of Cd accumulation in the roots and shoots of the plant were increased by 10 mg L-1 GO (exposed to 5 mg L-1 Cd), indicating that low-concentration GO (10 mg L-1) combined with low-concentration Cd (5 mg L-1) might stimulate the absorption of Cd by L. japonica. Under GO treatments without Cd, the dry weight of root and shoot biomass, Pn value, carbon sequestration per unit leaf area and oxygen release per unit leaf area all increased in various degrees, especially under 10 mg L-1 GO, were 20.67%, 12.04%, 35% and 28.73% higher than the control. Under GO-Cd treatments, it is observed that the cooperation of low-concentration GO (10 mg L-1) and low-concentration Cd (5 mg L-1) could significantly stimulate Cd accumulation, growth, photosynthesis, carbon sequestration and oxygen release functions of the plant. These results indicated that suitable concentrations of GO could significantly alleviate the effects of Cd on L. japonica, which is helpful for expanding the phytoremediation application of greening hyperaccumulators faced with coexistence with environment of nanomaterials and heavy metals.

Toxicity mechanisms of graphene oxide and cadmium in Microcystis aeruginosa: evaluation of photosynthetic and oxidative responses

The potential ecotoxicological hazard of gaphene oxide (GO) is not fully clarified for photoautotrophic organisms, especially when the interactions of GO with other environmental toxicants are considered. The objective of the current study was to better understand the mechanisms of toxicity of GO in the cyanobacteria Microcystis aeruginosa, and to identify its interactions with cadmium (Cd). The individual and combined contribution of both pollutants in cyanobacteria were evaluated after 96 hours of exposure to GO and/or Cd, using photosynthetic pigments, photosynthetic parameters, cellular indicators of peroxidative damage, viability, and intracellular ROS formation as indicators of toxicity. Interactions between GO and Cd were evaluated using Toxic Units based on the EC50 of each parameter evaluated. The results of this study indicate that single concentrations ≥ 5 µg mL-1 of GO and ≥ 0.1 µg mL-1 of Cd induced a decrease in cell biomass and a change in the photosynthetic parameters associated with primary productivity in M. aeruginosa. In the combined experiments, higher GO ratios (≥ 9.1 µg mL-1) in terms of Toxic Units decreased photochemical processes and cellular metabolism, increased oxidative stress, and ultimately affected the size of M. aeruginosa. Finally, the relationship between GO concentration, Cd concentration, and the adsorption capacity of GO with respect to the co-pollutant must be taken into account when assessing the environmental risk of GO in aquatic environments.

Toxic effects of cadmium on the physiological and biochemical attributes of plants, and phytoremediation strategies: A review

Anthropogenic activities pose a more significant threat to the environment than natural phenomena by contaminating the environment with heavy metals. Cadmium (Cd), a highly poisonous heavy metal, has a protracted biological half-life and threatens food safety. Plant roots absorb Cd due to its high bioavailability through apoplastic and symplastic pathways and translocate it to shoots through the xylem with the help of transporters and then to the edible parts via the phloem. The uptake and accumulation of Cd in plants pose deleterious effects on plant physiological and biochemical processes, which alter the morphology of vegetative and reproductive parts. In vegetative parts, Cd stunts root and shoot growth, photosynthetic activities, stomatal conductance, and overall plant biomass. Plants' male reproductive parts are more prone to Cd toxicity than female reproductive parts, ultimately affecting their grain/fruit production and survival. To alleviate/avoid/tolerate Cd toxicity, plants activate several defense mechanisms, including enzymatic and non-enzymatic antioxidants, Cd-tolerant gene up-regulations, and phytohormonal secretion. Additionally, plants tolerate Cd through chelating and sequestering as part of the intracellular defensive mechanism with the help of phytochelatins and metallothionein proteins, which help mitigate the harmful effects of Cd. The knowledge on the impact of Cd on plant vegetative and reproductive parts and the plants' physiological and biochemical responses can help selection of the most effective Cd-mitigating/avoiding/tolerating strategy to manage Cd toxicity in plants.

Toxicological effects resulting from co-exposure to nanomaterials and to a β-blocker pharmaceutical drug in the non-target macrophyte species Lemna minor

The wide use of carbon-based materials for various purposes leads to their discharge in the aquatic systems, and simultaneous occurrence with other environmental contaminants, such as pharmaceutical drugs. This co-occurrence can adversely affect exposed aquatic organisms. Up to now, few studies have considered the simultaneous toxicity of nanomaterials, and organic contaminants, including pharmaceutical drugs, towards aquatic plants. Thus, this study aimed to assess the toxic effects of the co-exposure of propranolol (PRO), and nanomaterials based on cellulose nanocrystal, and graphene oxide in the aquatic macrophyte Lemna minor. The observed effects included reduction of growth rate in 13% in co-exposure 1 (nanomaterials + PRO 5 μg L^-1), and 52-64% in co-exposure 2 (nanomaterials + PRO 51.3 mg L^-1), fresh weight reduction of 94-97% in co-exposure 2 compared to control group, and increased pigment production caused by co-exposure treatments. The analysis of PCA showed that co-exposure 1 (nanomaterials + PRO 5 μg L^-1) positively affected growth, and fresh weight, and co-exposure 2 positively affected pigments content. The results suggested that the presence of nanomaterials enhanced the overall toxicity of PRO, exerting deleterious effects in the freshwater plant L. minor, suggesting that this higher toxicity resulting from co-exposure was a consequence of the interaction between nanomaterials and PRO.

Ca alleviated Cd-induced toxicity in Salix matsudana by affecting Cd absorption, translocation, subcellular distribution, and chemical forms

Cadmium (Cd), a ubiquitous and highly toxic heavy metal pollutant, is toxic to animals and plants. Calcium (Ca) is an essential component for plant growth and reduces plant Cd absorption by competing with Cd. To gain deeper insight into the effects of Ca on Cd absorption, translocation, subcellular distribution, and chemical forms in S. matsudana seedlings under Cd stress, an investigation was conducted on these properties. Adding Ca alleviated Cd physiological toxicity in S. matsudana, reduced Cd absorption, increased the translocation from roots to shoots, lead to subcellular redistribution of Cd by increasing the proportion of Cd in soluble fractions but decreasing Cd in the cell wall and changed the chemical forms of Cd from 0.6 mol/L HCl- and 2% HAc-extracted Cd to 1 mol/L NaCl-extracted Cd. The energy dispersive X-ray analyses (EDXA) results revealed that after adding Ca, Cd was transferred through the root epidermis, cortex, endodermis, and vascular cylinder, transported to the shoots, and was highly accumulated in leaf epidermal and mesophyll cells, but less in leaf vein and guard cells. The genes involved in Cd uptake and xylem loading included NRAMP1, ZIP8, HMA2, and HMA4, which were up-regulated significantly (P < 0.05) in the Cd and Cd + Ca treatments compared to the control. The findings of this study provide new insight into the mechanism that Ca alleviates Cd toxicity in woody tree species, as well as propose an important prospect of Ca addition for improving the phytoremediation of Cd contamination.

Effect of graphene oxide on the uptake, translocation and toxicity of metal mixture to Lepidium sativum L. plants: Mitigation of metal phytotoxicity due to nanosorption

Due to its unique structure and exceptional properties, graphene oxide (GO) is increasingly used in various fields of industry and therefore is inevitably released into the environment, where it interacts with different contaminants. However, the information relating to the ability of GO to affect the toxicity of contaminants is still limited. Therefore, the aim of our study was to synthesize GO, to examine the phytotoxicity of different concentrations of GO and its co-exposure with the metal mixture using garden cress (Lepidium sativum L.) as a test organism and to evaluate the potential of GO to affect toxicity of metals and their uptake by plants. The metal mixture (MIX) containing Ni (II), Zn (II), Cr (III) and Cu (II) was prepared in accordance with the maximum-permissible-concentrations (MPC) accepted for the inland waters in the EU. Additionally, the capacity of GO to adsorb metals was studied in specific conditions of the phytotoxicity test and assessed using adsorption isotherms. Our data indicate that in most cases the tested concentrations of MIX, GO and MIX + GO did not affect seed germination, root growth and biomass of roots and seedlings, however, they were found to alter photosynthesis processes, enhance production of carotenoids and H₂O₂ as well as to activate lipid peroxidation. Additionally, our study revealed that GO affects the accumulation of tested metals in roots and shoots of the MIX-exposed L. sativum. This is due to the capacity of GO to adsorb metals from the growth medium. Therefore, low concentrations of GO can be used for water decontamination.

Combined effect of single-walled carbon nanotubes and cadmium on human lung cancer cells

Co-exposure of widely used single-walled carbon nanotubes (SWCNTs) and ubiquitous cadmium (Cd) to humans through ambient air is unavoidable. Studies on joint toxicity of SWCNTs and Cd in human cells are scarce. We aimed to investigate the joint effects of SWCNTs and Cd in human lung epithelial (A549) cells. Results showed that SWCNTs were safe while Cd induce significant toxicity to A549 cells. Remarkably, Cd-induced cell viability reduction, lactate dehydrogenase leakage, cell cycle arrest, dysregulation of apoptotic gene (p53, bax, bcl-2, casp3, and casp9), and mitochondrial membrane potential depletion were significantly mitigated following SWCNTs co-exposure. Cd-induced intracellular level of reactive oxygen species, hydrogen peroxide, and lipid peroxidation were significantly attenuated by SWCNT co-exposure. Moreover, glutathione depletion and lower activity of antioxidant enzymes after Cd exposure were also effectively abrogated by co-exposure of SWCNTs. Inductively coupled plasma-mass spectrometry study indicated that higher adsorption of Cd on SCWNTs might decreased cellular uptake and the toxic potential of Cd in A549 cells. Our work warranted further research to explore the potential mechanism of joint effects of SWCNTs and Cd at in vivo levels.

Phytotoxicity of Chemical Compounds from Cinnamomum camphora Pruning Waste in Germination and Plant Cultivation

Much previous research has indicated most composts of pruning waste are characterized by potential phytotoxicity, it is highly correlated with the chemical compounds of raw materials. Cinnamomum camphora, a common kind of pruning waste in Southeast Asia and East Asia, is characterized by intense bioactivities due to complex chemical components. This study investigated the potential phytotoxicity of C. camphora pruning waste in light of germination and higher plant growth. C. camphora extracted from leaves completely inhibited seed germination and still showed suppression of root elongation at an extremely low dosage. C. camphora extract also displayed significant inhibition of nutrient absorption in tomato seedlings, including moisture, available nutrients (N, P and K) and key microelements (Fe, Mn, Zn and S). The gene expression of aquaporins and transporters of nitrate and phosphate was significantly up-regulated in roots. This could be regarded as a positive response to C. camphora extract for enhancing nutrient absorption. Moreover, the severe damage to the plasma membrane in roots caused by C. camphora extract might seriously affect nutrient absorption. Camphor is the main component of the C. camphora extract that may induce the phytotoxicity of plasma membrane damage, resulting in the inhibition of nutrient absorption and low biomass accumulation. This study provided a new understanding of the ecotoxicological effects of C. camphora pruning waste, indicating that the harmless disposal of pruning waste requires much attention and exploration in the future.

Toxic effects of the combined cadmium and Cry1Ab protein exposure on the protective and transcriptomic responses of Pirata subpiraticus

Cadmium (Cd) pollution poses a serious threat to agricultural production and paddy field fauna. Crystalline proteins (e.g., Cry1Ab and Cry1Ac) are secreted by Bacillus thuringiensis, which can manage pests via a complicated toxic mechanism and have been widely used for pest control due to the commercialization of transgenic crops (e.g., cotton and rice) that expresses Bt insecticidal proteins. Nonetheless, studies on the effects of combined stress of Cd and Cry1Ab protein on field indicator species are limited. In the present study, we showed that spiders, Pirata subpiraticus, fed with Cd-containing flies+Cry1Ab had dramatically higher Cd accumulation than that in the spiders fed with Cd-containing flies (p < 0.05). In addition, the enrichment of Cd led to the activation of the protective mechanism by elevating the concentrations of glutathione peroxidase, glutathione S-transferase, and metallothionein in the spiders (p < 0.05). An in-depth transcriptome analysis revealed that the activities of ion metal binding proteins, transporters, and channels might play essential roles in the Cd accumulation process. More importantly, the higher Cd concentration in the combined Cd+Cry1Ab exposure prolonged developmental duration of P. subpiraticus, due to the down-regulated cuticle proteins (CPs) encoding genes involved in the molting process, which was regulated by a series of putative transcriptional factors such as ZBTB and zf-C2H2. Collectively, this integrated analysis illustrates that the combined Cd+Cry1Ab exposure increases the adverse effects of Cd stress on the growth, antioxidase, and CPs encoding genes of P. subpiraticus, thus providing a research basis and prospect for the rationality of transgenic Cry1Ab crops in the cultivation of heavy metal contaminated soil.

Effects of Graphene Oxide on Atrazine Phytotoxicity Effects of Graphene Oxide on Photosynthetic Response of Iris Pseudacorus to Atrazine Stress and Accumulation of Atrazine in the Plant

To evaluate combined effects of co-existed pesticides and nanomaterials on aquatic plants, the toxicity of herbicide atrazine (ATZ) on Iris pseudacorus in the presence and absence of Graphene oxide (GO) was investigated using chlorophyll a fluorescence transients. Results showed that GO reduced ATZ accumulation in plant. ATZ or ATZ combined with GO mainly blocked electron transport beyond Q_A at PSII as indicated by the sharp rise of the J-step level of fluorescence rise kinetics. The pronounced increase in Fm and the loss of I-step were observed when ATZ was at 2.0 mg·L^- 1 implying the damage on the oxygen evolution complex and PSI. GO at environmentally relevant concentration did not exhibit significant photosynthetic inhibitory effects on I. pseudacorus. GO at 1.0 mg·L^- 1 promoted photosynthesis of I. pseudacorus under ATZ stress at 2.0 mg·L^- 1. These result indicated that the presence of GO alleviated the photosynthesis inhibition by ATZ at high levels.

Effects of three graphene-based materials on the growth and photosynthesis of Brassica napus L

The environmental safety and threats of graphene-based materials (GBMs) to the agroecosystem have attracted increasing attention in recent years. However, the mechanisms underlying the effects of GBMs on plants remain unclear. Here, we investigated the phytotoxicity of reduced graphene oxide (RGO), graphene oxide (GO) and amine-functionalized graphene (G-NH2) on Brassica napus L. The results revealed that RGO impaired photosynthesis mainly by decreasing the chlorophyll content and Rubisco activity. A further gene-level analysis suggested that this effect of RGO might be due to its toxicity on sulfate transmembrane transporter and nitrogen metabolism, which ultimately led to nutrient imbalance. However, GO directly damaged the photosystem by disrupting the chloroplast structure, and a decrease in Rubisco activity indicated that GO also inhibits carbon fixation. Further gene-level analysis demonstrated that GO has toxicity on the chloroplast membrane, photosystem, photosynthethic electron transport and F-type ATPase. In addition, G-NH2 at 10-1000 mg L-1 showed no significant toxicity. These findings shed light on the potential mechanism for the toxicity of GBMs on plants for risk assessment.

Nanomaterial sulfonated graphene oxide advances the tolerance against nitrate and ammonium toxicity by regulating chloroplastic redox balance, photochemistry of photosystems and antioxidant capacity in Triticum aestivum

The current study was designed to assess nanomaterial sulfonated graphene oxide (SGO) potential in improving tolerance of wheat chloroplasts against nitrate (NS) and ammonium (AS) toxicity. Triticum aestivum cv. Ekiz was grown under SGOs (50-250-500 mg L^-1) with/without 140 mM NS and 5 mM AS stress. SGOs were eliminated the adverse effects produced by stress on chlorophyll fluorescence, potential photochemical efficiency and physiological state of the photosynthetic apparatus. SGO reversed the negative effects on these parameters. Upon SGOs exposure, the induced expression levels of photosystems-related reaction center proteins were observed. SGOs reverted radical accumulation triggered by NS by enabling the increased superoxide dismutase (SOD) activity and ascorbate (AsA) regeneration. Under AS, the turnover of both AsA and glutathione (GSH) was maintained by 50-250 mg L^-1 SGO by increasing the enzymes and non-enzymes related to AsA-GSH cycle. 500 mg L^-1 SGO prevented the radical over-accumulation produced by AS via the regeneration of AsA and peroxidase (POX) activity rather than GSH regeneration. 50-250 mg L^-1 SGO protected from the NS+AS-induced disruptions through the defense pathways connected with AsA-GSH cycle represented the high rates of AsA/DHA and, GSH/GSSG and GSH redox state. Our findings specified that SGO to NS and AS-stressed wheat provides a new potential tool to advance the tolerance mechanism.

Mutual impacts and interactions of antibiotic resistance genes, microcystin synthetase genes, graphene oxide, and Microcystis aeruginosa in synthetic wastewater

The physiological impacts and interactions of antibiotic resistance gene (ARG) abundance, microcystin synthetase gene expression, graphene oxide (GO), and Microcystis aeruginosa in synthetic wastewater were investigated. The results demonstrated that the absolute abundance of sul1, sul2, tetW, and tetM in synthetic wastewater dramatically increased to 365.2%, 427.1%, 375.2%, and 231.7%, respectively, when the GO concentration was 0.01 mg/L. Even more interesting is that the sum gene copy numbers of mcyA-J also increased to 243.2%. The appearance of GO made the significant correlation exist between ARGs abundance and mcyA-J expression. Furthermore, M. aeruginosa displayed better photosynthetic performance and more MCs production at 0.01 mg/L GO. There were 65 pairs of positive correlations between the intracellular differential metabolites of M. aeruginosa and the abundance of sul1, sul2, tetM, and tetW with various GO concentrations. The GO will impact the metabolites and metabolic pathway in M. aeruginosa. The metabolic changes impacted the ARGs, microcystin synthetase genes, and physiological characters in algal cells. Furthermore, there were complex correlations among sul1, sul2, tetM, tetW, mcyA-J, MCs, photosynthetic performance parameters, and ROS. The different concentration of GO will aggravate the hazards of M. aeruginosa by promoting the expression of mcyA-J, producing more MCs; simultaneously, it may cause the spread of ARGs.

Graphene oxide promoted chromium uptake by zebrafish embryos with multiple effects: Adsorption, bioenergetic flux and metabolism

The increasing production and application of graphene oxide (GO, a popular carbon nanomaterial), makes their release into aqueous environment inevitably. The capability of GO to enhance the toxicity of background contaminants has been widely concerned. However, the effect of GO on heavy metal accumulation in fish embryos remains unclear. Here, we show that GO-promoted chromium (Cr) uptake by zebrafish embryos with multiple effects. The adsorption accelerated the aggregation and settlement of Cr⁶⁺-adsorbed GO and decreased the Cr⁶⁺ concentration in the upper water, which enhanced the interaction of chorions and contaminants (Cr⁶⁺, GO and Cr⁶⁺-adsorbed GO). In the presence of GO, the Cr content in chorions and intra-chorion embryos was increased by four times and 57% respectively, compared to that of the single Cr⁶⁺ exposure. Furthermore, GO+Cr⁶⁺ increased the oxygen consumption rates, embryonic acid extrusion rates and ATP production, induced more serious oxidative stress, and disturbed amino acid metabolism, fatty acid metabolism and TCA cycle. These findings provide new insights into the effect of GO on heavy metal bioaccumulation and toxicity during embryogenesis.

Graphene oxide decreases Cd concentration in rice seedlings but intensifies growth restriction

The extensive use of graphene oxide (GO) results in its inevitable entry into the environment, raising risks to the environment, especially the ecological risks when coexisting with other contaminants. Nevertheless, how GO affects the biological behavior of Cd in plants remains poorly understood. Here, we report that the transcript levels of Cd transporters, including OsIRT1, OsIRT2, OsNramp1, OsNramp5, and OsHMA2, were decreased by 56-96% in Cd-stressed rice seedlings with exposure to 400 mg L^-1 GO compared with those without GO exposure. The in situ non-invasive microelectrodes test revealed that GO clearly reduced the net Cd influx of rice roots. Thus, GO exposure decreased the level of Cd in rice seedlings by approximately 60%, compared with the GO-free condition. However, the analyses of biomass, chlorophyll fluorescence parameters and Evans blue staining, indicated that GO had adverse effects on the robustness of plants under the Cd co-contaminated condition. Taken together, although GO reduced the accumulation of Cd in rice seedlings, it still negatively affected plant growth. Therefore, the positive and negative impacts of GO on crop production are of concern. Our findings provide new information for establishing a wider phytotoxicity evaluation system for the safe manufacture and use of GO.

Integrating transcriptome and physiological analyses to elucidate the essential biological mechanisms of graphene phytotoxicity of alfalfa (Medicago sativa L.)

The phytotoxicity of nanoparticles has attracted considerable interest, given the broad applications of nanomaterials in different fields. Alfalfa (Medicago sativa L.) is a major forage crop grown worldwide with a high protein content. The molecular regulation mechanisms involved in nanomaterial-treated alfalfa were examined in this research. In our lab, 18 cDNA libraries of Golden Empress (GE) and Bara 310SC (SC) under control (CK), middle (10 g kg^-1)- and high (20 g kg^-1)-graphene stress treatments were constructed in 2019. All clean reads were matched to the reference Medicago_truncatula genome, the mapping ratio was higher than 50%, and a total of 3946 differentially expressed genes (DEGs) were obtained. The number of DEGs that reflect transcriptional activity is proportional to the degree of stress. For example, 1241/610 and 1794/1422 DEGs were identified as significant in the leaves of GE/SC under mid- and high-graphene treatment, respectively. Furthermore, GO analysis of the DEGs annotated in some significant biochemical process terms included 'response to abiotic stimulus', 'oxidation-reduction process', 'protein kinase activity', and 'oxidoreductase activity'. KEGG pathway analysis of the DEGs revealed strongly mediated graphene-responsive genes in alfalfa mainly linked to the 'biosynthesis of amino acids', 'isoflavonoid biosynthesis', 'linoleic acid metabolism', and 'phenylpropanoid biosynthesis' pathways. In addition, hundreds of DEGs, including photosynthetic, antioxidant enzyme, nitrogen metabolism, and metabolic sucrose and starch genes, have been identified as potentially involved in the response to graphene. Physiological findings revealed that enzymes related to the metabolism of nitrogen play a crucial role in the adaptation of graphene stress to alfalfa. Ultimately, in response to graphene stress, a preliminary regulatory mechanism was proposed for the self-protective mechanism of alfalfa, which helps to explain the phytotoxicity of the molecular mechanism of nanoparticle-treated crops.

Phototransformation of Graphene Oxide on the Removal of Sulfamethazine in a Water Environment

Graphene oxide (GO) is widely used in various fields and has raised concerns regarding its potential environmental fate and effect. However, there are few studies on its influence on coexisting pollutants. In this study, the phototransformation of GO and coexisting sulfamethazine (SMZ) under UV irradiation was investigated, with a focus on the role of reactive oxygen species. The results demonstrated that GO promoted the degradation of SMZ under UV irradiation. The higher the concentration of GO, the higher the degradation rate of SMZ, and the faster the first-order reaction rate. Two main radicals, ∙OH and ¹O₂, both contributed greatly in terms of regulating the removal of SMZ. Cl⁻, SO₄²⁻, and pH mainly promoted SMZ degradation by increasing the generation of ∙OH, while humic acid inhibited SMZ degradation due to the reduction of ∙OH. Moreover, after UV illumination, the GO suspension changed from light yellow to dark brown with increasing absorbance at a wavelength of 225 nm. Raman spectra revealed that the I_D/I_G ratio slightly decreased, indicating that some of the functional groups on the surface of GO were removed under low-intensity UV illumination. This study revealed that GO plays important roles in the photochemical transformation of environmental pollutants, which is helpful for understanding the environmental behaviors and risks of nanoparticles in aquatic environments.

Combined effects of carbon nanotubes and cadmium on the photosynthetic capacity and antioxidant response of wheat seedlings

A detailed study of nanomaterials has revealed their broad application prospects. However, the presence of carbon nanotubes (CNTs) in the environment has been increasing and has aroused concerns regarding their toxicity to crops when combined with heavy metals. In the present study, the effects of Cd on the photosynthetic capacity and antioxidant activity of wheat seedlings in the presence of single-walled CNTs (SW) and multi-walled CNTs (MW) were investigated. Our results indicated that SW (5-40 mg L-1) and MW (10-40 mg L-1) significantly increased the oxidative stress response of wheat seedlings to Cd. Compared with Cd alone, CNTs combined with Cd decreased net photosynthetic rate, stomatal conductance, transpiration rate, primary maximum photochemical efficiency of photosystem II, actual quantum yield, photosynthetic electron transport rate, root canal protein, and ribulose-1,5-bisphosphate carboxylase/oxygenase content. Moreover, combined treatments increased the content of superoxide anion, superoxide dismutase, guaiacol peroxidase, cytochrome, and malondialdehyde in wheat seedlings. Moreover, membrane lipid peroxidation was aggravated, causing serious damage to the wheat membrane system. In addition, the toxicity of the SW treatment and the combined treatment with SW and Cd was higher than that of the MW treatment.

New insight into the mechanism of graphene oxide-enhanced phytotoxicity of arsenic species

Graphene oxide (GO) has exhibited significant potential to improve crop cultivation and yield. The application of GO in agriculture will inevitably result in interactions with conventional contaminants, causing potential changes to environmental behavior and toxicity of conventional contaminants. This study explored the joint phytotoxicity of GO and arsenic species (arsenite [As (III)], arsenate [As (V)]) to monocot (Triticum aestivum L.) and dicot (Solamun lycopersicum) plant species. Under the environmentally relevant concentrations, GO (1 mg/L) significantly increased the phytotoxicity of As (III) and As (V) (1 mg/L), with effects being both As- and plant species-specific. One mechanism of enhanced arsenic phytotoxicity could be GO-induced up-regulation of the aquaporin and phosphate transporter related genes expression, which would lead to the increased accumulation of As (III) and As (V) in plants. In addition, co-exposure with GO resulted in more severe oxidative stress than single As exposure, which could subsequently induce damage in root plasma membranes and compromise key arsenic detoxification pathways such as complexation with glutathione and efflux. Co-exposure to GO and As also led to more significant reduction in macro- and micronutrient content. The provided data highlight the high-impact of nanomaterials on the environmental risk of As in agricultural systems.

Health Beneficial Properties of Grapevine Seed Extract and Its Influence on Selected Biochemical Markers in the Blood, Liver and Kidneys of Rattus norvegicus

Cadmium (Cd) is a heavy metal that occurs in all areas of the environment, including the food chain. In the body, it causes oxidative stress by producing free radicals that are harmful to the cells. Grape seed extract (GSE) contains a wide range of biologically active components that help to neutralize the adverse effects of free radicals. In this study, the effects of GSE prepared form semi-resistant grapevine cultivar Cerason, which is rich in phenolics, on biochemical markers of brown rats exposed to the effects of cadmium were monitored. GSE increased the plasma antioxidant activity and, in the kidneys and the liver, Cd content was significantly lowered by GSE co-administration. Accordingly, the increase in creatinine content and alanine aminotransferase activity and the decrease of catalase and superoxide dismutase activities caused by cadmium were slowed down by GSE co-administration. The results of this work reveal that grape seed extract offers a protective effect against the intake of heavy metals into the organism.

Graphene oxide exhibited positive effects on the growth of Aloe vera L

There is increasing evidence for graphene associated plant growth promotion, however, the chronic effects of soil-applied graphene remain largely unexplored. The present study investigated the morphological, physiological and biochemical responses of graphene oxide (GO) on Aloe vera L. over the concentration range of 0-100 mg/L for four months. Our results demonstrated that GO, with the best efficiency at 50 mg/L, could enhance the photosynthetic capacity of leaves, increase the yield and morphological characters of root and leaf, improve the nutrient (protein and amino acid) contents of leaf, without reducing the content of the main bioactive compound aloin. Compared with leaves, the effect of GO on root growth was more obvious. Although the electrolyte leakage and MDA content were raised at high concentrations, GO treatment did not increase the root antioxidant enzymes activity or decrease the root vigor, which excluding typical stress response. Furthermore, injection experiments showed that the GO in vivo did not change the plant growth state obviously. Taken together, our study revealed the role of GO in promoting Aloe vera growth by stimulating root growth and photosynthesis, which would provide theory basis for GO application in agriculture and forestry.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00979-3.

Enhanced Cytotoxicity of Cadmium by a Sulfated Polysaccharide from Abalone

Consumption of seafood is a common route of cadmium ion (Cd²⁺) exposure to consumers. The seafood matrices may alter the toxicity profile of Cd²⁺ due to the interaction between Cd²⁺ and biomacromolecules in seafood. In this study, enhanced cytotoxicity of Cd²⁺ was found in the presence of an abalone gonad sulfated polysaccharide (AGSP) and the mechanism was investigated at a metabolic level. The formation of the AGSP-Cd²⁺ complex was demonstrated by isothermal titration calorimetry. The level of reactive oxygen species (ROS) increased and mitochondrial membrane potential reduced upon exposure to the AGSP-Cd²⁺ complex as compared with those of Cd²⁺ exposure. The decreased cell viability after incubation with the AGSP-Cd²⁺ complex also suggested enhanced Cd²⁺ toxicity induced by AGSP. The metabolomics and lipidomics analysis revealed that, compared with the Cd²⁺ group, the AGSP-Cd²⁺ downregulated the phospholipid metabolism and resulted in more serious damage in the cellular membrane. The lipid metabolism disorder, in turn, amplified the generation of ROS, leading to a decrease in cell viability. These results provided new evidence of the enhanced Cd²⁺ toxicity upon interaction with seafood polysaccharides, and much attention should be paid to the effect of food ingredients on heavy metal ion toxicity.

Enhanced Cd accumulation by Graphene oxide (GO) under Cd stress in duckweed

Effective phytoremediation by aquatic plant such as duckweed could be applied to solve Cd pollution. In the present study, the impact of Graphene oxide (GO) on the accumulation of Cd in duckweed has been studied. The response of duckweed was also investigated, concluding growth, Cd²⁺ flux, and gene expression response. Results showed that GO promoted the accumulation of Cd in duckweed. After 6 h of Cd enrichment in duckweed, Cd content was about 1.4 times that of the control group at fronds and 1.25 times that of the control group at roots, meanwhile, Cd content in the water system was 0.67 times that of the control group. The Cd²⁺ influx increased significantly. 4471 genes were up-regulated and 3230 genes were down-regulated significantly as duckweed treated with GO under Cd treatment. Moreover, phagosome pathway was downregulated, some key proteins: Stx7, Rab7 and Tubastatin B (TUBB) were significantly downregulated with GO addition under Cd stress. Scanning electron microscope (SEM) observation showed that GO and Cd were attached on the cell surface of duckweed as white crystal. GO could be applied in phytoremediation by duckweed of Cd in aquatic system.

Effects of foliar application of graphene oxide on cadmium uptake by lettuce

Although graphene oxide (GO) has been widely used to enhance soil quality and crop yield, there is currently little information regarding the effects of foliar application of GO on cadmium (Cd) toxicity to plants. In this study, we investigated the response to GO in lettuce cultivated under Cd stress in hydroponic conditions. Lettuce was grown from seeds in a nutrient solution supplemented with 2 mg/L Cd and the leaves were sprayed with 0, 30, and 60 mg/L GO. The results indicated that application of 30 mg/L GO significantly increased the total length, surface area, average diameter, and hair number of lettuce roots, and effectively alleviated the negative effects of Cd on root growth. Furthermore, foliar application of 30 mg/L GO, but not 60 mg/L GO, significantly improved the quality of lettuce, including reduction in Cd accumulation in leaves and roots and increase in soluble sugar, protein, and vitamin C content. Transmission electron microscopy revealed that GO nanoparticles, which entered the leaves and were subsequently transported to the roots via the vascular system (phloem), reduced the damaging effect of Cd on cellular organelles, including the cell wall and membrane, chloroplasts, and starch granules. The effect may be attributed to the absorption of GO by lettuce cells, where it fixed Cd2+, thus reducing Cd2+ bioavailability, or to the improvement of Cd tolerance through regulation of lettuce metabolic pathways. Gaussian simulation analysis revealed that Cd caused significant changes in the GO molecule, resulting in detachment of an epoxy group from the GO carbon ring and breakage of OH bonds in hydroxyl groups, whereupon the oxygen freed from the OH bond formed a new bond with Cd. Collectively, these results indicate that foliar application of 30 mg/L GO can enhance the tolerance of lettuce to Cd, promote plant growth, and improve nutritional quality.

Differential impact of some metal(loid)s on oxidative stress, antioxidant system, sulfur compounds, and protein profile of Indian mustard (Brassica juncea L.)

Levels of arsenic (As), chromium (Cr), and copper (Cu) are increasing in the soils worldwide. Such contaminants cause toxicity in the plant systems which adversely affects growth and productivity. The objective of the present investigation was to elucidate individual and combined effects of As, Cr, and Cu (100 μM each) stress in metal hyper-accumulator plant Indian mustard (Brassica juncea L.), exposed for a week. The highest accumulation was in the roots and in decreasing order viz. Cu > As > Cr. The magnitude of oxidative stress was maximal in combined stress, followed by As, Cr, and then Cu stress. Glutathione in conjunction with glutathione reductase, glutathione peroxidase, and glutathione S-transferase increased in all set of stress treatments, notably when exposed to Cr alone. In addition, the level of sulfur-rich compounds like cysteine, phytochelatins, and non-protein thiols increased under each stress indicating efficient coupling of the enzyme system and sulfur-containing compounds during stress conditions. The highest tolerance or growth index of plants was recorded for Cu. Protein profiling of leaf tissues showed modulation of protein patterns in each stress. Mediator of RNA polymerase II transcription subunit 1 isoform X1, RuBisCO (large subunit), and ribosomal protein S3 proteins were more abundant under Cr and Cu stress. Zinc finger A20/AN1 domain-containing stress-associated protein 5-like protein was more abundant under Cu stress. HSP (15.7 kDa) and autophagy protein 5-like were in higher abundance under As and combined stress. Our results suggest that Indian mustard has a differential mode of defense against a particular stressor at the level of protein expression profile.

Foliar graphene oxide treatment increases photosynthetic capacity and reduces oxidative stress in cadmium-stressed lettuce

The application of graphene oxide (GO) in the environment can have a positive or negative effect on the toxicity of pollutants, but the effect of GO on cadmium (Cd2+)-stressed lettuce has not yet been thoroughly studied. Therefore, we assessed the potential effects of foliar GO sprays on photosynthesis and antioxidant systems in Cd-stressed lettuce. We found that the foliar application of 30 mg L-1 of GO could significantly reduce signs of Cd2+ toxicity in lettuce. We observed increased net photosynthetic rates, stomatal conductance, transpiration rates, chlorophyll content, primary maximum photochemical efficiency of photosystem II, actual quantum yield, photosynthetic electron transport rates, ribulose-1,5-bisphosphate carboxylase and oxygenase concentrations, and biomass in Cd2+-stressed lettuce treated with GO. In addition, the foliar application of 30 mg L-1 of GO reduced the accumulation of the reactive oxygen species O·̄2 and H2O2, malondialdehyde content, and the activity of antioxidant enzymes. The decreased antioxidant enzyme activity could have been due to the decrease in reactive oxygen species. Cd2+ pollution is highly destructive to agricultural products, and the foliar application of GO provides a new potential tactic to improve the tolerance of plants to heavy metals.

Reduced graphene oxide mitigates cadmium-induced cytotoxicity and oxidative stress in HepG2 cells

Numerous applications of reduced graphene oxide (RGO) and pervasive cadmium (Cd) have led concern about their co-exposure to the environment and human. We studied the combined effects of RGO and Cd in human liver (HepG2) cells. Initially, we found that RGO (up to 50 μg/ml) did not harm to HepG2 cells while Cd induced dose-dependent (1-10 μg/ml) cytotoxicity. Exciting observations were that a non-cytotoxic concentration of RGO (25 μg/ml) effectively mitigates the toxic effects of Cd (2 μg/ml) such as cell viability reduction, lactate dehydrogenase release, and irregular cell morphology. Cd-induced cell cycle arrest, induction of caspases (3 and 9) enzymes activity, and loss of mitochondrial membrane potential were also significantly alleviated by RGO co-exposure. Moreover, generation of pro-oxidants (reactive oxygen species and hydrogen peroxide levels) and depletion of antioxidants (glutathione level and superoxide dismutase activity) due to Cd exposure was effectively attenuated by RGO co-exposure. Mitigating effect of RGO could be due to strong adsorption of Cd on the large surface area of RGO sheets, which decrease the cellular uptake and bioavailability of Cd for HepG2 cells. This study warrants future research on potential mechanisms of mitigating effects of RGO against Cd-induced toxicity in animal models.

Graphene oxide exposure suppresses nitrate uptake by roots of wheat seedlings

Despite the large number of studies reporting the phytotoxicity of graphene-based materials, the effects of these materials on nutrient uptake in plants remain unclear. The present study showed that nitrate concentrations were significantly decreased in the roots of wheat plants treated with graphene oxide (GO) at 200-800 mg L^-1. Non-invasive microelectrode measurement demonstrated that GO could significantly inhibit the net NO₃^- influx in the meristematic, elongation, and mature zones of wheat roots. Further analysis indicated that GO could be trapped in the root vacuoles, and that the maximal root length and the number of lateral roots were significantly reduced. Additionally, root tip whitening, creases, oxidative stress, and weakened respiration were observed. These observations indicate that GO is highly unfavorable for vigorous root growth and inhibits increase in root uptake area. At the molecular level, GO exposure caused DNA damage and inhibited the expression of most nitrate transporters (NRTs) in wheat roots, with the most significantly downregulated genes being NRT1.3, NRT1.5, NRT2.1, NRT2.3, and NRT2.4. We concluded that GO exposure decreased the root uptake area and root activity, and decreased the expression of NRTs, which may have consequently suppressed the NO₃^- uptake rate, leading to adverse nitrate accumulation in stressed plants.

Effects of nanomaterials on metal toxicity: Case study of graphene family on Cd

The risk of heavy metal cadmium (Cd) on aquatic organisms has drawn widespread attentions, but the effects of nanomaterials (e.g. graphene (G)) on Cd toxicity are rarely clarified. It was known that mixture of contaminants may exhibit more severe impact than the individual metal. Here, we conducted a study systematically on the effects of nanomaterials on the toxicity of Cd to Scenedesmus Obliquus (S. obliquus) with or without the presence of graphene family materials (GFMs) derived from G, such as graphene oxide (GO) and amine-modified graphene (GNH). Our results showed that the influence of GFMs on the acute toxicity of Cd to S. obliquus is in the order of GO > G > GNH based on their EC₅₀ of Cd-GFMs. The effects of GFMs on the cytotoxicity and oxidative damage of Cd to S. obliquus are varied with the concentrations of GFMs. The differences between the effects of GFMs on Cd toxicity may attribute to their different surface oxygen-containing functional groups contained in the nanomaterials. The adsorption capacity of nanomaterials on metal ions, their dispersibility in water and their interaction mode with organisms, may dominate main contributions to their effects on Cd toxicity. Our study aids to clarify the interference of nanoparticles on the ecotoxicity of metals, to avoid the misunderstanding of the potential risk of metals in the complicate water environments.

Effects of carbon nanotubes on growth of wheat seedlings and Cd uptake

Carbon nanotubes (CNTs) have been widely used in many scientific fields including plant sciences due to their unique physical and chemical properties. However, little is known about the toxic effects of CNTs combined with cadmium (Cd) on wheat. The aim of this study was to investigate the effects of single-walled carbon nanotubes (SW) and multi-walled carbon nanotubes (MW) on the phytotoxicity of Cd in wheat. A hydroponic culture was carried out to study wheat seedling growth in six treatments, namely Cd only (Cd); MW only (MW); SW only (SW); SW combined with Cd (SWCd); MW combined with Cd (MWCd); and a control (neither Cd nor carbon nanotubes). Compared with the Cd, SW/MW alone, CNTsCd treatments induced a reduction in total root length, root surface area, average root diameter, number of root hairs, and the dry weight of shoots and roots, which indicated that wheat growth and development was significantly inhibited. In addition, an obvious decrease in tubulins in the roots was observed. However, SW/MWCd induced a significant increase in glutathione S-transferase and cyochrome P450 in the shoots and roots, which indicated that the defense ability of wheat seedlings had improved, thus alleviating Cd stress. Moreover, Cd content increased significantly in shoot and root tissues with an increase in SW/MW content, compared to the Cd treatment. According to the transmission electron microscopy, CNTs alone destroyed the cell structure, and this devastating phenomenon was deepened after combining Cd and CNTs due to CNTs carrying Cd to attack cells. Compared with MW, SW had a greater effect on wheat seedlings. To conclude, CNTs increase the toxicity of Cd to wheat seedlings. These results are significant as they evaluate indirect phytotoxicity of CNTs for adsorbing heavy metals and plant growth regulators. In view of the widespread exposure of agricultural crops to Cd, the nanotoxicity of CNTs should be seriously considered in relation to food security in the future.

Carboxylated graphene oxide-chitosan spheres immobilize Cu2+ in soil and reduce its bioaccumulation in wheat plants

Due to the strong interaction with pollutants and the huge adsorption capacity, graphene adsorbents are widely applied in water decontamination. However, graphene adsorbents are seldom used in soil remediation, because the adsorptive sites on graphene would be occupied by soil components. In this study, we prepared carboxylated graphene oxide-chitosan (GO-COOH/CS) spheres for the immobilization of Cu²⁺ from water and soil. The pores in GO-COOH/CS allowed the internal diffusion of Cu²⁺ solution, while they blocked the direct contact between the solid soil and the adsorptive sites on graphene sheets. Therefore, the high adsorption capacity of GO-COOH/CS spheres (78 mg/g) was largely retained for the soil Cu²⁺ fixation. The partition coefficient (PC) for Cu²⁺ adsorption onto GO-COOH/CS spheres was 4.2 mg/g/μM at C_e of 0.48 mg/L and q_e of 31 mg/g, while the PC value decreased to 0.096 mg/g/μM at C_e of 91.4 mg/L and q_e of 78 mg/g. At initial Cu²⁺ concentrations of 120 mg/L and lower, the fixation efficiencies were all higher than 99% and the corresponding free Cu²⁺ concentrations in leachates were lower than 1.0 mg/L. The Cu²⁺ fixation on GO-COOH/CS spheres largely reduced its bioaccumulation in wheat roots from 127.8 μg/g to 51.2 μg/g. The toxicity evaluations suggested that GO-COOH/CS spheres were of low toxicity to wheat seedlings and did not amplify the toxicity of Cu²⁺. The implications to the design of graphene adsorbents for soil remediation are discussed. Overall, our results collectively indicated that porous GO-COOH/CS spheres were high-performance adsorbents for the immobilization of Cu²⁺ to reduce Cu²⁺ bioaccumulation in plants.