Phytotoxicity of iron-based materials in mung bean: Seed germination tests

Cu-II-directed self-assembly of fullerenols to ameliorate copper stress in maize seedlings

Widespread use of copper-based agrochemical may cause copper excessive accumulation in agricultural soil to seriously threaten crop production. Recently, fullerenols are playing important roles in helping crops build resistance to abiotic stresses by giving ingenious and successful resolutions. However, there is a lack of knowledge on their beneficial effects in crops under stresses induced by heavy metals. Herein, the visual observation of Cu2+-mediated assembly of fullerenols via electrostatic and coordination actions was carried out in vitro, showing that water-soluble nanocomplexes and water-insoluble cross-linking nanohybrids were selectively fabricated by precisely adjusting feeding ratios of fullerenols and CuSO4. Furthermore, maize simultaneous exposure of fullerenols and CuSO4 solutions was tested to investigate the comparative effects of seed germination and seedling growth relative to exposure of CuSO4 alone. Under moderate Cu2+ stresses (40 and 80 μM), fullerenols significantly mitigated the detrimental effects of seedlings, including phenotype, root and shoot elongation, biomass accumulation, antioxidant capacity, and Cu2+ uptake and copper transporter-related gene expressions in roots. Under 160 μM of Cu2+ as a stressor, fullerenols also accelerated germination of Cu2+-stressed seeds eventually up to the level of the control. Summarily, fullerenols can enhance tolerance of Cu2+-stressed maize mainly due to direct detoxification through fullerenol-Cu2+ interactions restraining the Cu2+ intake into roots and reducing free Cu2+ content in vivo, as well as fullerenol-maize interactions to enhance resistance by maintaining balance of reactive oxygen species and optimizing the excretion and transport of Cu2+. This will unveil valuable insights into the beneficial roles of fullerenols and its mechanism mode in alleviating heavy metal stress on crop plants.

Effects of foliar iron oxide nanoparticles (Fe3O4) application on photosynthetic parameters, distribution of mineral elements, magnetic behaviour, and photosynthetic genes in tomato (Solanum lycopersicum var. cerasiforme) plants

This study aims to examine the effect of foliar magnetic iron oxide (Fe3O4) nanoparticles (IONP) application on the physiology, photosynthetic parameters, magnetic character, and mineral element distribution of cherry tomatoes (Solanum lycopersicum var. cerasiforme). The IONP suspension (500 mg L-1) was sprayed once (S1), twice (S2), thrice (S3), and four times (S4) a week on seedlings. Upon 21 days of the treatments, photosynthetic parameters (chlorophyll, carotenoids, photosynthetic yield, electron transport rate) were elucidated. Inductively-coupled plasma-optical emission spectrometer (ICP-OES) and vibrating sample magnetometer (VSM) were used to determine the mineral elements and abundance of magnetic power in the seedlings. In addition, the RT-qPCR method was performed to quantify the expressions of photosystem-related (PsaC, PsbP6, and PsbQ) and ferritin-coding (Fer-1 and Fer-2) genes. Results revealed that the physiological and photosynthetic indices were improved upon S1 treatment. The optimal dosage of IONP spraying enhances chlorophyll, carotenoid, electron transport rate (ETR), and effective photochemical quantum yield of photosystem II (Y(II)) but substantially diminishes non-photochemical quenching (NPQ). However, frequent IONP applications (S2, S3, and S4) caused growth retardation and suppressed the photosynthetic parameters, suggesting a toxic effect of IONP in recurrent treatments. Fer-1 and Fer-2 expressions were strikingly increased by IONP applications, suggesting an attempt to neutralize the excess amount of Fe ions by ferritin. Nevertheless, frequent IONP treatment fluctuated the mineral distribution and caused growth inhibition. Although low-repeat foliar applications of IONP (S1 in this study) may help improve plant growth, consecutive applications (S2, S3, and S4) should be avoided.

Effects of the application of nanoscale zero-valent iron on plants: Meta analysis, mechanism, and prospects

In order to determine the ideal conditions for the application of nanoscale zero-valent iron (nZVI) in agricultural production, this review studies the effects of nZVI application on plant physiological parameters, presents its mechanism and prospective outcomes. In this research, it was observed that the application of nZVI had both favorable and unfavorable effects on plant growth, photosynthesis, oxidative stress, and nutrient absorption levels. Specifically, the application of nZVI significantly increased the biomass and length of plants, and greatly reduced the germination rate of seeds. In terms of photosynthesis, there was no significant effect for the application of nZVI on the synthesis of photosynthetic pigments (chlorophyll and carotenoids). In terms of oxidative stress, plants respond by increasing the activity of antioxidant enzyme under mild nZVI stress and trigger oxidative burst under severe stress. In addition, the application of nZVI significantly increased the absorption of nutrients (B, K, P, S, Mg, Zn, and Fe). In summary, the application of nZVI can affect the plant physiological parameters, and the degree of influence varies depending on the concentration, preparation method, application method, particle size, and action time of nZVI. These findings are important for evaluating nZVI-related risks and enhancing nZVI safety in agricultural production.

Effects of biochar and zero valent iron on the bioavailability and potential toxicity of heavy metals in contaminated soil at the field scale

Heavy metals (HMs) such as copper, nickel and chromium are toxic, so soil contaminated with these metals is of great concern. In situ HM immobilization by adding amendments can decrease the risk of contaminants being released. A five-month field-scale study was performed to assess how different doses of biochar and zero valent iron (ZVI) affect HM bioavailability, mobility, and toxicity in contaminated soil. The bioavailabilities of HMs were determined and ecotoxicological assays were performed. Adding 5 % biochar, 10 % ZVI, 2 % biochar + 1 % ZVI, and 5 % biochar + 10 % ZVI to soil decreased Cu, Ni and Cr bioavailability. Metals were most effectively immobilized by adding 5 % biochar + 10 % ZVI, and the extractable Cu, Ni, and Cr contents were 60.9 %, 66.1 % and 38.9 % lower, respectively, for soil with 5 % biochar + 10 % ZVI added than unamended soil. The extractable Cu, Ni, and Cr contents were 64.2 %, 59.7 % and 16.7 % lower, respectively, for soil with 2 % biochar + 1 % ZVI added than unamended soil. Experiments using wheat, pak choi and beet seedlings were performed to assess the remediated soil toxicity. Growth was markedly inhibited in seedlings grown in extracts of soil with 5 % biochar, 10 % ZVI, or 5 % biochar + 10 % ZVI added. More growth occurred in wheat and beet seedlings after 2 % biochar + 1 % ZVI treatment than the control, possibly because 2 % biochar + 1 % ZVI simultaneously decreased the extractable HM content and increased the soluble nutrient (carbon and Fe) content of the soil. A comprehensive risk assessment indicated that adding 2 % biochar + 1 % ZVI gave optimal remediation at the field scale. Using ecotoxicological methods and determining the bioavailabilities of HMs can allow remediation methods to be identified to efficiently and cost-effectively decrease the risks posed by multiple metals in soil at contaminated sites.

Potential toxicity of landfill leachate to zebrafish and mung beans

Landfill leachate has become a major public health concern due to its adverse health effects. However, its toxicological effects have not been thoroughly determined because of its complex composition. To address this issue, two model organisms were used in this study, including mung beans and zebrafish. Bean seedlings were exposed to different concentrations of landfill leachate (1%, 5%, 10%, 15%, and 20%, v/v, leachate/deionized water) for 7 days. Low concentrations (1%) of landfill leachate increased the growth of mung beans, whereas high concentrations (15% and 20%) of landfill leachate inhibited the growth and development of seedlings. Furthermore, landfill leachate reduced chlorophyll levels but increased malondialdehyde levels, leading to an increased rate of root-tip micronuclei. Zebrafish embryos were exposed to different concentrations of landfill leachate (0.5%, 1.0%, 1.2%, and 1.5%, v/v, leachate/E3 medium) for 120 h. The results showed that landfill leachate significantly decreased lower levels of hatching rate and heart rate but increased the mortality and malformation rates of embryos. Moreover, 1.0% landfill leachate reduced the frequency of spontaneous movement and the light stimulation reaction of embryos. Embryos exposed to leachate showed less exploratory behavior and fewer mirror attacks in the black and white areas. Our results suggest that exposure to landfill leachate could cause developmental toxicity and genotoxicity in plants and fish. The findings can improve our understanding of the environmental toxicity of landfill leachate and provide additional evidence for its risk assessment and management.

Iron nanoparticles induced the growth and physio-chemical changes in Kobresia capillifolia seedlings

Iron nanoparticles (NPs) priming is known to affect the seed germination and seedling growth in many plants. However, whether it has an important role in stimulating the growth of perennial Qinghai-Tibet Plateau plants remains unclear. In this study, the effects of seed priming with different concentrations of nFe2O3 and FeCl3 (10, 50, 100, 500, and 1000 mg L-1) on seed germination, plant growth, photosystem, antioxidant enzyme activities, root morphology, and biomass distribution of Kobresia capillifolia were evaluated under laboratory conditions. The results showed that compared with treatment materials, concentration had more significant effects on K. capillifolia development. There was no significant impact on germination rate were discovered under all treatments, but decreased the seed mildew rate at 100 mg L-1 nFe2O3. Compare with control, Fe-based priming significantly decreased root biomass. All Fe-based treatments increased rubisco activity of leaves, and significantly enhanced Pn at ranged from 10 to 100 mg L-1. Meanwhile, chlorophyll contents were decreased, the chloroplasts were swollen, and thylakoids were disorganized under all Fe treatments. Iron-based priming significantly enhanced SOD, POD, and CAT activities in Kobresia roots. In conclusion, the thick cuticle-covered seed coat of K. capillifolia postponed the penetration of FeNPs into seeds, so FeNPs priming had a weak impact on seed germination. The sustainable release of Fe ions from FeNPs and the uptake of Fe ions by roots affected the physiology, biochemistry and morphology of K. capillifolia. The findings of this study provide an in-depth understanding of how FeNPs impact the alpine meadow plant, K. capillifolia.

Heterogeneous Activation of Peroxymonosulfate by a Spinel CoAl2O4 Catalyst for the Degradation of Organic Pollutants

Bimetallic catalysts have significantly contributed to the chemical community, especially in environmental science. In this work, a CoAl2O4 spinel bimetal oxide was synthesized by a facile co-precipitation method and used for the degradation of organic pollutants through peroxymonosulfate (PMS) activation. Compared with Co3O4, the as-prepared CoAl2O4 possesses a higher specific surface area and a larger pore volume, which contributes to its becoming increasingly conducive to the degradation of organic pollutants. Under optimal conditions (calcination temperature: 500 °C, catalyst: 0.1 g/L, and PMS: 0.1 g/L), the as-prepared CoAl2O4 catalyst could degrade over 99% of rhodamine B (RhB) at a degradation rate of 0.048 min−1, which is 2.18 times faster than Co3O4 (0.022 min−1). The presence of Cl− could enhance RhB degradation in the CoAl2O4/PMS system, while HCO3− and CO32− inhibit RhB degradation. Furthermore, the considerable reusability and universality of CoAl2O4 were testified. Through quenching tests, 1O2 and SO4•− were identified as the primary reactive species in RhB degradation. The toxicity evaluation verified that the degraded solution exhibited lower biological toxicity than the initial RhB solution. This study provides new prospects in the design of cost-effective and stable cobalt-based catalysts and promotes the application of PMS-based advanced oxidation processes for refractory wastewater treatment.

Nano-Iron and Nano-Zinc Induced Growth and Metabolic Changes in Vigna radiata

The widespread industrial use and consequent release of nanosized iron (nFe3O4) and zinc oxide (nZnO) particles into the environment have raised concerns over their effects on living organisms, including plants. These nanoparticles are the source of their respective metal ions and although plants require both Fe and Zn ions for proper growth, excessive levels of these metals are toxic to them. A better understanding of the effects of these nanoparticles on plants also offers an opportunity for their useful applications in agriculture. The present work evaluates the changes in seed germination, plant growth, photosynthetic capacity, levels of biomolecules and antioxidant enzymes in Vigna radiata (L.) Wilczek when grown in the presence of nFe3O4 (size 1–4 nm) and nZnO (size 10–20 nm) and compared to the control plants. The plants were raised hydroponically for up to 14 days at two different concentrations of nanoparticles, viz. 10 and 100 mg/L. Inductively coupled plasma mass spectrometry (ICP-MS) results established that V. radiata can accumulate Fe and Zn in shoots with high efficiency. The results indicated that nFe3O4 had a favourable effect on V. radiata, whereas no apparent benefit or toxicity of nZnO was observed at the tested concentrations.

The combined toxicity and mechanism of multi-walled carbon nanotubes and nano zinc oxide toward the cabbage

The natural environment is a complex system, and there is never only one kind of nanomaterial entering the environment. However, many studies only considered the plant toxicity of one kind of nanomaterial and do not consider the influence of two or more kinds of nanomaterials on plant toxicity. Multi-walled carbon nanotubes (MWCNTs) and zinc oxide nanoparticles (ZnO NPs) are two common and widely used nanomaterials in water environment, so these two kinds of nanomaterials were chosen to explore the effects of their combined toxicity on cabbage. This study investigated the toxicity of MWCNTs combined with ZnO NPs on cabbage by measuring the length of roots and stems, chlorophyll content, oxidative stress, antioxidant enzyme activity, metal element content, and root scanning electron microscopy. The toxicity of single MWCNTs toward cabbage was attributed to direct oxidative damage, while the toxicity of single ZnO NPs toward cabbage was due to the high level of zinc concentration. Moreover, ZnO NPs (10 mg/L) ameliorated MWCNTs toxicity toward cabbage by improving the activity of antioxidant enzymes. ZnO NPs (50 and 100 mg/L) because of the high content of zinc disrupted the balance of other metals in the plant and increased the toxicity of MWCNTs. In conclusion, the combined toxicity of different concentrations and types of nanomaterials should be considered for a more accurate assessment of environmental risks.

Photocatalytic Degradation of Sugarcane Vinasse Using ZnO Photocatalyst: Operating Parameters, Kinetic Studies, Phytotoxicity Assessments, and Reusability

ABSTRACT

Photocatalytic degradation performance is highly related to optimized operating parameters such as initial concentration, pH value, and catalyst dosage. In this study, the impact of various parameters on the photocatalytic degradation of anaerobically digested vinasse (AnVE) has been determined through decolourization and chemical oxygen demand (COD) reduction efficiency using zinc oxide (ZnO) photocatalyst. In this context, the application of photocatalytic degradation in treating sugarcane vinasse using ZnO is yet to be explored. The COD reduction efficiency and decolourization achieved 83.40% and 99.29%, respectively, under the conditions of 250 mg/L initial COD concentration, pH 10, and 2.0 g/L catalyst dosage. The phytotoxicity assessment was also conducted to determine the toxicity of AnVE before and after treatment using mung bean (Vigna radiata). The reduction of root length and the weight of mung bean indicated that the sugarcane vinasse contains enormous amounts of organic substances that affect the plant's growth. The toxicity reduction in the AnVE solution can be proved by UV-Vis absorption spectra. Furthermore, the catalyst recovery achieved 93% in the reusability test. However, the COD reduction efficiency and decolourization were reduced every cycle. It was due to the depletion of the active sites in the catalyst with the adsorption of organic molecules. Thus, it can be concluded that the photocatalytic degradation in the treatment of AnVE was effective in organic degradation, decolorization, toxicity reduction and can be reused after the recovery process.

Physiological impacts of zero valent iron, Fe3O4 and Fe2O3 nanoparticles in rice plants and their potential as Fe fertilizers

Fe-based nanoparticles (Fe-based NPs) have great potential as a substitute for traditional Fe-fertilizer; however, their environmental risk and impact on plant growth are not fully understood. In this study, we compared the physiological impacts of three different Fe-based NP formulations: zero-valent iron (ZVI), Fe₃O₄ and Fe₂O₃ NPs, on hydroponic rice after root exposure for 2 weeks. Fe-normal (Fe(+)) and Fe-deficiency (Fe(-)) conditions were compared. Results showed that low dose (50 mg L^-1) of ZVI and Fe₃O₄ NPs improved the rice growth under Fe(-) condition, while Fe₂O₃ NPs did not improve plant growth and caused phytotoxicity at high concentration (500 mg L^-1). Under Fe(+) conditions, none of the Fe-based NPs exhibited positive effects on the rice plants with plant growth actually being inhibited at 500 mg L^-1 evidenced by reduced root volume and leaf biomass and enhanced oxidative stress in plant. Under Fe(-) condition, low dose (50 mg L^-1) of ZVI NPs and Fe₃O₄ NPs increased the chlorophyll content by 30.7% and 26.9%, respectively. They also alleviated plant stress demonstrated by the reduced oxidative stress and decreased concentrations of stress related phytohormones such as gibberellin and indole-3-acetic acid. Low dose of ZVI and Fe₃O₄ NPs treatments resulted in higher Fe accumulation in plants compared to Fe₂O₃ NPs treatment, by down-regulating the expression of IRT1 and YSL15. This study provides significant insights into the physiological impacts of Fe-based NPs in rice plants and their potential application in agriculture. ZVI and Fe₃O₄ NPs can be used as Fe-fertilizers to improve rice growth under Fe-deficient condition, which exist in many rice-growing regions of the world. However, dose should be carefully chosen as high dose (500 mg L^-1 in this study) of the Fe-based NPs can impair rice growth.