Biochar-assisted transformation of engineered-cerium oxide nanoparticles: Effect on wheat growth, photosynthetic traits and cerium accumulation

Root-Applied Cerium Oxide Nanoparticles and Their Specific Effects on Plants: A Review

With the pronounced increase in nanotechnology, it is likely that biological systems will be exposed to excess nanoparticles (NPs). Cerium oxide nanoparticles (CeO2 NPs) are among the most abundantly produced nanomaterials in the world. Their widespread use raises fundamental questions related to the accumulation in the environment and further interactions with living organisms, especially plants. NPs present in either soil or soilless environments are absorbed by the plant root systems and further transported to the aboveground parts. After entering the cytoplasm, NPs interact with chloroplast, nucleus, and other structures responsible for metabolic processes at the cellular level. In recent years, several studies have shown the impact of nanoceria on plant growth and metabolic processes. Research performed on different plants has shown a dual role for CeO2 NPs. The observed effects can be positive or negative and strongly depend on the plant species, characterization, and concentrations of NPs. This review describes the impact of root-applied CeO2 NPs on plant growth, photosynthesis, metal homeostasis, and parameters of induced oxidative stress.

Molecular mechanism for combined toxicity of micro(nano)plastics and carbon nanofibers to freshwater microalgae Chlorella pyrenoidosa

The understanding of the environmental consequences resulting from the presence of micro(nano)plastics and carbon nanofibers (CNFs) in aquatic ecosystems is currently limited. This research endeavor sought to investigate the underlying molecular mechanisms by which engineered polystyrene-based microplastics (MPs)/nanoplastics (NPs) and CNFs, both individually and in combination, elicit toxic effects on an algal species Chlorella pyrenoidosa. The findings revealed that the combined toxicity of MPs/NPs and CNFs depended on the concentration of the mixture. As the concentration increased, the combined toxicity of MPs/NPs and CNFs was significantly greater than the toxicity of each component on its own. Furthermore, the combined toxicity of NPs and CNFs was higher than that of MPs and CNFs. The study integrated data on cell membrane integrity, oxidative stress, and antioxidant modulation to create an Integrated Biomarker Response index, which demonstrated that the co-exposure of algae to NPs and CNFs resulted in more severe cellular stress compared to exposure to NPs alone. Similarly, the combination of NPs and CNFs caused greater cellular stress than the combination of MPs and CNFs. Additionally, significant changes in the expression of stress-related genes caused by MPs/NPs alone and in combination with CNFs indicated that oxidative stress response, glucose metabolism, and energy metabolism played critical roles in particle-induced toxicity. Overall, this study provides the first insight into the toxicological mechanism of MPs/NPs and CNFs mixtures at the molecular level in freshwater microalgae.

Boosting plant resilience: The promise of rare earth nanomaterials in growth, physiology, and stress mitigation

Rare earth elements (REE) have been extensively used in a variety of applications such as cell phones, electric vehicles, and lasers. REEs are also used as nanomaterials (NMs), which have distinctive features that make them suitable candidates for biomedical applications. In this review, we have highlighted the role of rare earth element nanomaterials (REE-NMs) in the growth of plants and physiology, including seed sprouting rate, shoot biomass, root biomass, and photosynthetic parameters. In addition, we discuss the role of REE-NMs in the biochemical and molecular responses of plants. Crucially, REE-NMs influence the primary metabolites of plants, namely sugars, amino acids, lipids, vitamins, enzymes, polyols, sorbitol, and mannitol, and secondary metabolites, like terpenoids, alkaloids, phenolics, and sulfur-containing compounds. Despite their protective effects, elevated concentrations of NMs are reported to induce toxicity and affect plant growth when compared with lower concentrations, and they not only induce toxicity in plants but also affect soil microbes, aquatic organisms, and humans via the food chain. Overall, we are still at an early stage of understanding the role of REE in plant physiology and growth, and it is essential to examine the interaction of nanoparticles with plant metabolites and their impact on the expression of plant genes and signaling networks.

Cerium oxide nanoparticles alleviates stress in wheat grown on Cd contaminated alkaline soil

The cadmium contamination of soil is an alarming issue worldwide and among various mitigation strategies, nanotechnology mediated management of Cd contamination has become a well-accepted approach. The Cerium Oxide Nanoparticles (CeO2-NPs) are widely being explored for their novel works in Agro-Industry and Environment, including stress mitigation in crops. Very little work is reported regarding role of CeO2-NPs in management of Cd contamination in cereal crops like wheat. Present work was planned to check efficacy of CeO2-NPs in Cd stress mitigation of wheat under alkaline calcareous soil conditions. In this experiment, 4 sets of Cd contamination (Uncontaminated control-UCC, 10, 20, and 30 mg Cd per kg soil) and 5 sets of CeO2-NPs NPs (0, 200, 400, 600, and 1000 mg NP per kg soil) were applied in pots following completely randomized design (CRD) and wheat crop was grown. The growth, physiology, yield and Cd and Ce accumulation by wheat root, shoot and grain was monitored. The maximum Cd spiking level (30 mg kg-1) was found to be most toxic for plant growth. The results showed that the nanoparticles were overall beneficial for wheat growth and maximum level (1000 mg kg-1) being the most significant one under all Cd spiking sets. In Cd-30 sets, 1000 mg kg-1 NPs application resulted in decreased soil bioavailable Cd concentration (49.63% decrease compared to 30 mg kg-1 Cd spiked sets termed as Cd-30 Control), decreased Cd accumulation in all three tissues: root (58.36% decrease), shoot (52.30% decrease) and grain (55.56% decrease) while increased root dry weight (62.14%), shoot dry weight (89.32%), total grain yield (80.08%) and improved plant physiology with respect to Cd-30 control. Nanoparticles application substantially increased wheat root, shoot and grain Ce concentrations as well. The further prospects of these nanoparticles in relation to various biotic and abiotic stresses are advised to be explored.

Improving the uptake of PAHs by the ornamental plant Sedum spectabile using nano-SiO2 and nano-CeO2

Polycyclic aromatic hydrocarbons (PAHs) pollution is a global ecological soil problem. Screening and establishing an efficient phytoremediation system would be beneficial for alleviating this problem. The ornamental plant Sedum spectabile was selected as the remediation plant to study the removal efficiencies of PAHs after adding different concentrations of nano-SiO₂, nano-CeO₂, and traditional Na-montmorillonite (Na-MMT). The results demonstrated that shoot biomass was increased and photosynthesis was enhanced by the nanomaterial amendments. The uptake of 16 PAHs by S. spectabile was remarkably increased. Moreover, the two highest shoot concentrations were 7.61 (Phe) and 12.03 (Flo) times that of the control, and the two highest translocation factors were 31 (BbF) and 28 (BaP) times that of the control. Furthermore, 16S rRNA gene sequencing showed that the addition of nano-SiO₂ increased the abundance of Acidobacteria, and the genera related to PAH degradation was higher under nanomaterial treatments. The very high Si concentration in the shoots of S. spectabile had a significant linear correlation with the concentration of PAHs. In conclusion, the S. spectabile remediation system assisted by two nanomaterials was effective for the removal of PAHs from soil, and the transfer of PAHs to easily harvested aboveground plant parts was especially worthy of attention.

Evaluation of Apical and Molecular Effects of Algae Pseudokirchneriella subcapitata to Cerium Oxide Nanoparticles

Cerium oxide engineered nanoparticles (nCeO₂) are widely used in various applications and are, also, increasingly being detected in different environmental matrixes. However, their impacts on the aquatic environment remain poorly quantified. Hence, there is a need to investigate their effects on non-target aquatic organisms. Here, we evaluated the cytotoxic and genotoxic effects of <25 nm uncoated-nCeO₂ on algae Pseudokirchneriella subcapitata. Apical (growth and chlorophyll a (Chl a) content) and genotoxic effects were investigated at 62.5-1000 µg/L after 72 and 168 h. Results demonstrated that nCeO₂ induced significant growth inhibition after 72 h and promotion post 96-168 h. Conversely, nCeO₂ induced enhanced Chl a content post 72 h, but no significant changes were observed between nCeO₂-exposed and control samples after 168 h. Hence, the results indicate P. subcapitata photosynthetic system recovery ability to nCeO₂ effects under chronic-exposure conditions. RAPD-PCR profiles showed the appearance and/or disappearance of normal bands relative to controls; indicative of DNA damage and/or DNA mutation. Unlike cell recovery observed post 96 h, DNA damage persisted over 168 h. Thus, sub-lethal nCeO₂-induced toxicological effects may pose a more serious threat to algae than at present anticipated.

Transcriptome reveals the exposure effects of CeO2 nanoparticles on pakchoi (Brassica chinensis L.) photosynthesis

In this study, soil-grown pakchoi after 2 weeks seedling cultivation were exposed to CeO₂ nanoparticles (CeO₂ NPs) at 0.7, 7, 70, and 350 mg kg^-1 for 30 days. Results showed that chlorophyll content and photosynthetic assimilation rate were decreased significantly under all treatments with the largest decrease of 34.16% (0.7 mg kg^-1 CeO₂ NPs), however, sub-stomatal CO₂ was increased dramatically under low dose of CeO₂ NPs (0.7 mg kg^-1). There were 4576, 3548, 2787, and 2514 genes up/down regulated significantly by 0.7, 7, 70, and 350 mg kg^-1 CeO₂ NPs, respectively, and 767 genes affected under all treatments. In addition, 0.7 mg kg^-1 CeO₂ NPs up-regulated 10 chlorophyll synthesis genes, 20 photosynthesis genes, and 10 carbon fixation enzyme genes; while 350 mg kg^-1 CeO₂ NPs down-regulated 5 photosynthesis genes and 28 auxin-activated genes. Among the key genes of photosynthesis, Ferredoxin-NADP reductase (PetH) was upregulated in 0.7, 7 and 70 mg kg^-1 treatments, while Photosystem II lipoprotein (Psb27) was downregulated under 7, 70 and 350 mg kg^-1 treatments. Top 20 metabolic pathways affected by CeO₂ NPs including plant hormone, amino acids, and glutathione, and carbon metabolism These results provide information about utilizing CeO₂ NPs more safely and effectively in the future.

Understanding and mitigating the distinctive stresses induced by diverse microplastics on anaerobic hydrogen-producing granular sludge

This work comparatively studied the different stress responses of anaerobic hydrogen-producing granular sludge (HPG) to several typical MPs in wastewater, i.e., polyethylene (PE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) MPs. A new approach to mitigating the inhibition caused by MPs based on biochar was then proposed. The results displayed that microbe in HPG had diverse tolerances to PE-MPs, PET-MPs and PVC-MPs, with the hydrogen production downgraded to 82.0 ± 3.2 %, 72.3 ± 2.5 % and 66.6 ± 2.3 % (p < 0.05) of control respectively, due to the distinct leachates toxicities and oxidative stress level induced by different MPs. The discrepant mitigation reflected in the hydrogen yields of biochar-based HPGs raised back to 88.7 ± 1.4 %, 85.3 ± 3.8 % and 88.5 ± 3.5 % of control. The MPs induced disintegrated granule morphology, fragile microbial viability and impaired defensive function of extracellular polymeric substances were restored by biochar. The effective mitigation was revealed to be due to the strong adsorption of MPs by biochar, reducing direct contact between microbes and MPs. Biochar addition also enhanced protection for HPG by increasing EPS secretion and weakened the oxidative damage to anaerobes induced by MPs. Biochar manifested the disparate adsorption properties of three MPs. The most superior mitigation in HPG contaminated by PVC-MPs was attributed to the strongest affinity of biochar to PVC-MPs and effective alleviation of PVC leachates toxicity.

Recent insights into the impact, fate and transport of cerium oxide nanoparticles in the plant-soil continuum

The advent of the nanotechnology era offers a unique opportunity for sustainable agriculture provided that the exposure and toxicity are adequately assessed and properly controlled. The global production and application of cerium oxide nanoparticles (CeO₂-NPs) in various industrial sectors have tremendously increased. Most of the nanoparticles end up in water and soil where they interact with soil microorganisms and plants. Investigating the uptake, translocation and accumulation of CeO₂-NPs is critical for its safe application in agriculture. Plant uptake of CeO₂-NPs may lead to their accumulation in different plant tissues and interference with key metabolic processes of plants. Soil microbes can also be affected by increasing CeO₂-NPs in soil, leading to changes in the physiology and enzymatic activity of soil microorganisms. The interactions between CeO₂-NPs, microbes and plants in the agricultural system need systemic research in ecologically relevant conditions. In the present review, The uptake pathways and in-planta translocation of CeO₂-NPs,and their impact on plant morphology, nutritional values, antioxidant enzymes and molecular determinants are presented. The role of CeO₂-NPs in modifying soil microbial community in plant rhizosphere is also discussed. Overall, the review aims to provide a comprehensive account on the behaviour of CeO₂-NPs in soil-plant systems and their potential impacts on the soil microbial community and plant health.

Ingestion and effects of cerium oxide nanoparticles on Spodoptera frugiperda (Lepidoptera: Noctuidae)

The objective of this study was to evaluate the biological and nutritional characteristics of Spodoptera frugiperda (Lepidoptera: Noctuidae), an arthropod pest widely distributed in agricultural regions, after exposure to nano-CeO₂ via an artificial diet and to investigate the presence of cerium in the body of this insect through X-ray fluorescence mapping. Nano-CeO₂, micro-CeO₂, and Ce(NO₃)₃ were incorporated into the diet (0.1, 1, 10, and 100 mg of Ce L^-1). Cerium was detected in caterpillars fed with diets containing nano-CeO₂ (1, 10 and 100 mg of Ce L^-1), micro-CeO₂ and Ce(NO₃)₃, and in feces of caterpillars from the first generation fed diets with nano-CeO₂ at 100 mg of Ce L^-1 as well. The results indicate that nano-CeO₂ caused negative effects on S. frugiperda. After it was consumed by the caterpillars, the nano-CeO₂ reduced up to 4.8% of the pupal weight and 60% of egg viability. Unlike what occurred with micro-CeO₂ and Ce(NO₃)₃, nano-CeO₂ negatively affected nutritional parameters of this insect, as consumption rate two times higher, increase of up to 80.8% of relative metabolic rate, reduction of up to 42.3% efficiency of conversion of ingested and 47.2% of digested food, and increase of up to 1.7% of metabolic cost and 8.7% of apparent digestibility. Cerium caused 6.8-16.9% pupal weight reduction in second generation specimens, even without the caterpillars having contact with the cerium via artificial diet. The results show the importance of new ecotoxicological studies with nano-CeO₂ for S. frugiperda in semi-field and field conditions to confirm the toxicity.

Nanoparticles potentially mediate salt stress tolerance in plants

In the era of climate change, salt stress is a promising threat to agriculture, limiting crop production via imposing primary effects such as osmotic and ionic, as well as secondary effects such as oxidative stress, perturbance in hormonal homeostasis, and nutrient imbalance. On the other hand, production areas are expanding into the salt affected regions due to excessive pressure for fulfilling food security targets to meet the needs of continuously increasing human population. Accumulating evidences demonstrate that supplementation of nanoparticles to plants can significantly alleviate the injurious effects caused by various harsh conditions including salt stress, and hence, regulate adaptive mechanisms in plants. Various types of NPs and nanofertilizers have shown a promising evidence so far regarding salt stress management. In this review, we recapitulate recent pioneering progress made towards acquiring salt stress tolerance in crop plants utilizing NPs. Finally, future research directions in this domain to explicate the comprehensive roles of nanoparticles in improving salt tolerance in plants are underscored. To ensure social acceptance and safe use of NPs, some conclusive directions have been elaborated in order to achieve sustainable progress in crop production under saline environments.

Metal Homeostasis and Gas Exchange Dynamics in Pisum sativum L. Exposed to Cerium Oxide Nanoparticles

Cerium dioxide nanoparticles are pollutants of emerging concern. They are rarely immobilized in the environment. This study extends our work on Pisum sativum L. as a model plant, cultivated worldwide, and is well suited for investigating additive interactions induced by nanoceria. Hydroponic cultivation, which prompts accurate plant growth control and three levels of CeO2 supplementation, were applied, namely, 100, 200, and 500 mg (Ce)/L. Phytotoxicity was estimated by fresh weights and photosynthesis parameters. Additionally, Ce, Cu, Zn, Mn, Fe, Ca, and Mg contents were analyzed by high-resolution continuum source atomic absorption and inductively coupled plasma optical emission techniques. Analysis of variance has proved that CeO2 nanoparticles affected metals uptake. In the roots, it decreased for Cu, Zn, Mn, Fe, and Mg, while a reversed process was observed for Ca. The latter is absorbed more intensively, but translocation to above-ground parts is hampered. At the same time, nanoparticulate CeO2 reduced Cu, Zn, Mn, Fe, and Ca accumulation in pea shoots. The lowest Ce concentration boosted the photosynthesis rate, while the remaining treatments did not induce significant changes. Plant growth stimulation was observed only for the 100 mg/L. To our knowledge, this is the first study that demonstrates the effect of nanoceria on photosynthesis-related parameters in peas.

Biochar-induced immobilization and transformation of silver-nanoparticles affect growth, intracellular-radicles generation and nutrients assimilation by reducing oxidative stress in maize

Silver nanoparticles (AgNPs) are used in a wide range of consumer products inevitably releases in massive quantities in the natural environment, posing a potential thread to ecosystem-safety and plant health. Here, the impact of AgNPs (100-1000 mg L^-1) without and with biochar (@2 % w/v) amendment on maize plants was assessed in hydroponics exposure medium. AgNPs exposure to plants induced dose-dependent phytotoxicity by suppressing plant growth, disturbing photosynthesis and gas exchange traits and alteration in macro- and micronutrients assimilation. At the same time, AgNPs with addition of biochar alleviated the phyto-toxic effects of AgNPs through approximately 4-8 times reduction in uptake and tissue accumulation of Ag. Moreover, activities of antioxidant enzymes in AgNPs + biochar treated plants indicated the lower oxidative stress. Electron paramagnetic resonance (EPR) spectroscopy confirmed that superoxide (O₂^-) radical was the dominant reactive oxygen species. Fourier-transform infrared spectroscopic (FTIR) and X-ray photoelectron spectroscopic (XPS) results revealed that biochar surface carboxyl and sulfur functional groups were involved in complexation process with NPs, which inhibited the oxidative dissolution and release of Ag⁺ ions besides of biochar space shield effect. Thus, the interaction of biochar with AgNPs immobilizes these NPs and can effectively reduce their bioavailability in the environmental matrix.

Transformation pathways and fate of engineered nanoparticles (ENPs) in distinct interactive environmental compartments: A review

The ever increasing production and use of nano-enabled commercial products release the massive amount of engineered nanoparticles (ENPs) in the environment. An increasing number of recent studies have shown the toxic effects of ENPs on different organisms, raising concerns over the nano-pollutants behavior and fate in the various environmental compartments. After the release of ENPs in the environment, ENPs interact with various components of the environment and undergoes dynamic transformation processes. This review focus on ENPs transformations in the various environmental compartments. The transformation processes of ENPs are interrelated to multiple environmental aspects. Physical, chemical and biological processes such as the homo- or hetero-agglomeration, dissolution/sedimentation, adsorption, oxidation, reduction, sulfidation, photochemically and biologically mediated reactions mainly occur in the environment consequently changes the mobility and bioavailability of ENPs. Physico-chemical characteristics of ENPs (particle size, surface area, zeta potential/surface charge, colloidal stability, and core-shell composition) and environmental conditions (pH, ionic strength, organic and inorganic colloids, temperature, etc.) are the most important parameters which regulated the ENPs environmental transformations. Meanwhile, in the environment, organisms encountered multiple transformed ENPs rather than the pristine nanomaterials due to their interactions with various environmental materials and other pollutants. Thus it is the utmost importance to study the behavior of transformed ENPs to understand their environmental fate, bioavailability, and mode of toxicity.

A review on control factors of pyrolysis technology for plants containing heavy metals

The treatment of plants with heavy metals, whether they grow naturally in heavy metal contaminated soil or are used for remediation of heavy metal contaminated soil has attracted increasing attention. Pyrolysis is often used for the disposal of plants with heavy metals because it stabilizes heavy metals effectively and produces biochar. The resulting products of pyrolysis are in the form of solid components (char and ash), liquid components (bio-oil and tar), together with gas components (condensable and non-condensable vapor gas). The metal amount in the char or liquid and gaseous phases can be maximized or minimized via treating a plant feedstock containing heavy metals under different conditions. In addition, the potential risk of biochar produced from plants after pyrolysis becomes a research hotspot in the field of pyrolysis technology of plants containing heavy metals. Herein, we review current literatures that emphasize the influencing factors on the metal content in the biochar, liquid and gaseous phases, as well as the potential risk of biochar.