Toxic effect of cadmium adsorbed by different sizes of nano-hydroxyapatite on the growth of rice seedlings

A review of the influence of nanoparticles on the physiological and biochemical attributes of plants with a focus on the absorption and translocation of toxic trace elements

Trace elements (TEs) from various natural and anthropogenic activities contaminate the agricultural water and soil environments. The use of nanoparticles (NPs) as nano-fertilizers or nano-pesticides is gaining popularity worldwide. The NPs-mediated fertilizers encourage the balanced availability of essential nutrients to plants compared to traditional fertilizers, especially in the presence of excessive amounts of TEs. Moreover, NPs could reduce and/or restrict the bioavailability of TEs to plants due to their high sorption ability. In this review, we summarize the potential influence of NPs on plant physiological attributes, mineral absorption, and TEs sorption, accumulation, and translocation. It also unveils the NPs-mediated TE scavenging-mechanisms at plant and soil interface. NPs immobilized TEs in soil solution effectively by altering the speciation of TEs and modifying the physiological, biochemical, and biological properties of soil. In plants, NPs inhibit the transfer of TEs from roots to shoots by inducing structural modifications, altering gene transcription, and strengthening antioxidant defense mechanisms. On the other hand, the mechanisms underpinning NPs-mediated TEs absorption and cytotoxicity mitigation differ depending on the NPs type, distribution strategy, duration of NP exposure, and plants (e.g., types, varieties, and growth rate). The review highlights that NPs may bring new possibilities for resolving the issue of TE cytotoxicity in crops, which may also assist in reducing the threats to the human dietary system. Although the potential ability of NPs in decontaminating soils is just beginning to be understood, further research is needed to uncover the sub-cellular-based mechanisms of NPs-induced TE scavenging in soils and absorption in plants.

Effects of nanoparticles on trace element uptake and toxicity in plants: A review

Agricultural soils are receiving higher inputs of trace elements (TEs) from anthropogenic activities. Application of nanoparticles (NPs) in agriculture as nano-pesticides and nano-fertilizers has gained rapid momentum worldwide. The NPs-based fertilizers can facilitate controlled-release of nutrients which may be absorbed by plants more efficiently than conventional fertilizers. Due to their large surface area with high sorption capacity, NPs can be used to reduce excess TEs uptake by plants. The present review summarizes the effects of NPs on plant growth, photosynthesis, mineral nutrients uptake and TEs concentrations. It also highlights the possible mechanisms underlying NPs-mediated reduction of TEs toxicity at the soil and plant interphase. Nanoparticles are effective in immobilization of TEs in soil through alteration of their speciation and improving soil physical, chemical, and biological properties. At the plant level, NPs reduce TEs translocation from roots to shoots by promoting structural alterations, modifying gene expression, and improving antioxidant defense systems. However, the mechanisms underlying NPs-mediated TEs uptake and toxicity reduction vary with NPs type, mode of application, time of NPs exposure, and plant conditions (e.g., species, cultivars, and growth rate). The review emphasizes that NPs may provide new perspectives to resolve the problem of TEs toxicity in crop plants which may also reduce the food security risks. However, the potential of NPs in metal-contaminated soils is only just starting to be realized, and additional studies are required to explore the mechanisms of NPs-mediated TEs immobilization in soil and uptake by plants. Such future knowledge gap has been highlighted and discussed.

Remediation of fluoride contaminated soil with nano-hydroxyapatite amendment: Response of soil fluoride bioavailability and microbial communities

Nano-hydroxyapatite (NHAP), possessing high defluoridation capacity, has been widely used to remove fluoride (F) from polluted water, but little is known about how it affects the bioavailability and toxicity of soil F towards plants. Here, the impact of NHAP (2% w/w) amendment on immobilization, speciation and accumulation of F was studied in a soil-plant system. The results revealed that the NHAP amendment worked effectively to reduce levels of water-soluble F (37.3%-87.8%) and increase available P (76.6%-147%). X-ray photoelectron spectroscopy analysis indicated that the formation of insoluble CaF₂ and the ion exchange of F^- with OH^- into NHAP might be involved in the mechanism of F immobilization and soil pH elevation. Exposure to NHAP significantly decreased the abundance of Cyanobacteria in tested soils, and Gemmatimonadetes abundance in bulk soil was significantly higher than that in rhizosphere soil at 1,000 mg kg^-1 F spiked level. Additionally, NHAP amendment decreased F accumulation in wheat shoots (9.10%-18.7%) and roots (3.88%-22.4%), which could mainly be attributed to the reduction of soil bioavailable F and the supplement of Ca from NHAP. These results suggest that NHAP could be a promising amendment to be applied to acidic soil contaminated with F.

Microplastic particles increase arsenic toxicity to rice seedlings

Hydroponic experiments were conducted to study the effects of microplastic particles of polystyrene (PS) and polytetrafluoroethylene (PTFE) on arsenic (As) content in leaves and roots of rice seedlings, and the changes in root vigor and physiological and biochemical indicators under single or combined PS and PTFE with As(III) treatment. Rice biomass decreased with increasing concentrations of PS, PTFE, and As(III) in the growth medium. The highest root (leaf) biomass decreases were 21.4% (10.2%), 25.4% (11.8%), and 26.2% (16.2%) with the addition of 0.2 g L^-1 PS, 0.2 g L^-1 PTFE, and 4 mg L^-1 As(III), respectively. Microplastic particles and As(III) inhibited biomass accumulation by inhibiting root activity and RuBisCO activity, respectively. The addition of As(III) and microplastic particles (PS or PTFE) inhibited photosynthesis through non-stomatal and stomatal factors, respectively; furthermore, net photosynthetic rate, chlorophyll fluorescence, and the Chl a content of rice were reduced with the addition of As(III) and microplastic particles (PS or PTFE). Microplastic particles and As(III) induced an oxidative burst in rice tissues through mechanical damage and destruction of the tertiary structure of antioxidant enzymes, respectively, thereby increasing O₂^- and H₂O₂ in roots and leaves, inducing lipid peroxidation, and destroying cell membranes. When PS and PTFE were added at 0.04 and 0.1 g L^-1, respectively, the negative effects of As(III) on rice were reduced. Treatment with 0.2 g L^-1 PS or PTFE, combined with As(III), had a higher impact on rice than the application of As(III) alone. PS and PTFE reduced As(III) uptake, and absorbed As decreased with the increasing concentration of microparticles. The underlying mechanisms for these effects may involve direct adsorption of As, competition between As and microplastic particles for adsorption sites on the root surface, and inhibition of root activity by microplastic particles.

Cadmium-resistant rhizobacterium Bacillus cereus M4 promotes the growth and reduces cadmium accumulation in rice (Oryza sativa L.)

Rice farmland cadmium pollution is an increasing problem for food safety. Cd-resistant bacterial strain was isolated from rice rhizosphere soil and identified as Bacillus cereus M4. Treatment with M4 fermentation broth increased rice seedlings growth in vermiculite, while reduced Cd accumulation in grains of rice grown in Cd-contaminated potted soil from 0.309 to 0.186 mg/kg. Indoleacetic acid (IAA) was detected in M4 metabolites and in potted soil solutions supplemented with M4 broth. M4 broth increased the abundance of Bacillus from 0.54% to 0.95% and changed the soil bacterial community composition. These findings indicate that M4 promotes rice growth by secreting IAA and altering the rhizospheric soil microenvironment, via soil solution composition and microbial community, which may affect Cd translocation from soil to rice roots, thereby decreasing grain Cd accumulation. Therefore, B. cereus M4 is potentially suitable for the bioremediation of Cd-contaminated paddy soils.

Effect of a dentifrice containing different particle sizes of hydroxyapatite on dentin tubule occlusion and aqueous Cr (VI) sorption

Background

Dentin hypersensitivity is a common negative oral condition that can be treated with dentifrice containing hydroxyapatite (HA). The study evaluated the effect of nano-HA dentifrice on plugging the dentinal tubules for an anti-sensitivity reaction compared to a dentifrice containing common-sized particles. Also, the adsorption capacity of different particle sizes of HA mixed in a dentifrice and which is the optimal particle size was considered.

Methods

Fourty premolar dentine discs and fourty molar dentine discs were randomly divided into 4 groups: distilled water group, ordinary dentifrice group and 80, 300 nm HA dentifrice group. Each dentin disc was brushed with a dentifrice twice daily at 7600 rpm under 100 g force for 2 mins for 7 consecutive days and divided into two parts, half of the dentin disc was detected by the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the other half was brushed with distilled water and observed by SEM. One milliliter dentifrice solution (80 nm HA dentifrice, 300 nm HA dentifrice, ordinary dentifrice) was added to 50 ml potassium dichromate solution for 1, 14, and 28 d. The residual Chromium (Cr⁶⁺) concentration in the supernatant was measured by the diphenylcarbon phthalocyanine hydrazine method. The elemental constitution in the precipitate was detected by EDS. The Kruskal-Wallis test was used to analyze surface mineralization and different plugging rates of dentinal tubules. The absorption capacity of dentifrices were also evaluated by the Kruskal-Wallis test.

Results

The plugging rate in the HA dentifrice group was higher than that in the ordinary dentifrice group, and the 80 nm HA dentifrice group showed the best result. The atomic percentages of Ca and P of 80 nm dentifrice group on the surface of dentinal tubules were the highest. The 80 nm HA dentifrice group showed the best adsorption and stable effect of Cr⁶⁺, followed by the 300 nm HA dentifrice group. The 300 nm HA dentifrice and the ordinary dentifrice showed desorption phenomenon.

Conclusions

The dentifrice containing HA, especially the 80 nm HA dentifrice, exerts good dentinal tubule occlusion and surface mineralization effect. This dentifrice was also a good adsorbent of Cr⁶⁺.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

Reduction of arsenic toxicity in two rice cultivar seedlings by different nanoparticles

In this study, we investigated arsenic uptake and enzymatic activities in rice seedlings after the addition of nanoparticles. Hydroponic experiments were conducted to investigate the effects of different nanomaterials (high-quality graphene oxide, multilayer graphene oxide, 20 nm hydroxyapatite (HA₂₀), 40 nm hydroxyapatite (HA₄₀), nano-Fe₃O₄ (nFe₃O₄) and nano-zerovalent iron [nFe]) on the biomass, arsenic uptake, and enzyme activities in seedlings of the rice cultivars T705 and X24. Compared with the control, the addition of different nanomaterials increased seedling growth, with X24 rice growing better than T705 rice. Nanomaterials effectively reduced arsenic uptake in T705 rice seedlings under low and high arsenic concentrations; however, they were only effective at lower arsenic concentrations in X24 seedlings. nFe₃O₄ and nFe performed better than other nanomaterials in preventing arsenic from being transported to the aboveground parts of the rice seedlings. Different nanomaterials obviously influenced enzyme activities in the T705 seedlings at low arsenic concentrations (≤ 0.8 mg L^-1). High-quality and multilayer graphene oxide decreased enzyme activities in the aboveground parts of the T705 seedlings, whereas, HA₂₀ and HA₄₀ increased the enzyme activities. nFe₃O₄ and nFe also reduced the effect of antioxidants in the aboveground parts of the T705 seedlings. Nanomaterials effectively reduced the arsenic uptake of T705 and X24 rice seedlings at low arsenic concentrations.

Direct Observation of Simultaneous Immobilization of Cadmium and Arsenate at the Brushite-Fluid Interface

Cadmium (Cd²⁺) and Arsenate (As⁵⁺) are the main toxic elements in soil environments and are easily taken up by plants. Unraveling the kinetics of the adsorption and subsequent precipitation/immobilization on mineral surfaces is of considerable importance for predicting the fate of these dissolved species in soils. Here we used in situ atomic force microscopy (AFM) to image the dissolution on the (010) face of brushite (dicalcium phosphate dihydrate, CaHPO₄·2H₂O) in CdCl₂- or Na₂HAsO₄-bearing solutions over a broad pH and concentration range. During the initial dissolution processes, we observed that Cd or As adsorbed on step edges to modify the morphology of etch pits from the normal triangular shape to a four-sided trapezium. Following extended reaction times, the respective precipitates were formed on brushite through a coupled dissolution-precipitation mechanism. In the presence of both CdCl₂ and Na₂HAsO₄ in reaction solutions at pH 8.0, high-resolution transmission electron microscopy (HRTEM) showed a coexistence of both amorphous and crystalline phases, i.e., a mixed precipitate of amorphous and crystalline Cd_{(5- x)}Ca _x(AsO₄)_{(3- y)}(PO₄) _yOH phases was detected. These direct dynamic observations of the transformation of adsorbed species to surface precipitates may improve the mechanistic understanding of the calcium phosphate mineral interface-induced simultaneous immobilization of both Cd and As and subsequent sequestration in diverse soils.

Adsorption Behavior of Selective Recognition Functionalized Biochar to Cd(II) in Wastewater

Biochar is an excellent absorbent for most heavy metal ions and organic pollutants with high specific surface area, strong aperture structure, high stability, higher cation exchange capacity and rich surface functional groups. To improve the selective adsorption capacity of biochar to designated heavy metal ions, biochar prepared by agricultural waste is modified via Ionic-Imprinted Technique. Fourier transform infrared (FT-IR) spectra analysis and X-ray photoelectron spectroscopy (XPS) analysis of imprinted biochar (IB) indicate that 3-Mercaptopropyltrimethoxysilane is grafted on biochar surface through Si-O-Si bonds. The results of adsorption experiments indicate that the suitable pH range is about 3.0-8.0, the dosage is 2.0 g·L^-1, and the adsorption equilibrium is reached within 960 min. In addition, the data match pseudo-second-order kinetic model and Langmuir model well. The computation results of adsorption thermodynamics and stoichiometric displacement theory of adsorption (SDT-A) prove that the adsorption process is spontaneous and endothermic. Finally, IB possesses a higher selectivity adsorption to Cd(II) and a better reuse capacity. The functionalized biochar could solidify designated ions stably.