Heavy Metal Remediation Research Articles

Effects of phosphate-solubilizing bacteria Aspergillus flavus AF-LRH1 on promoting phosphorus solubilization, wheat growth and soil heavy metal remediation

Increasing nutrient supply level and eliminating pollution risk are essential to promote farmland soil use. In the soil-plant nutrition cycle, phosphorus is a limiting nutrient, toxic metals such as Cd and Pb are stress threats. Utilizing microorganisms as a bio-amendment could be a viable approach to enhance the cycling of soil phosphorus nutrients and immobilize Cd and Pb in the soil. This study involved the isolation of Aspergillus flavus AF-LRH1, a phosphate solubilizing fungal strain from soil. The strain exhibited the capacity to solubilize calcium phosphate, attaining a phosphorus concentration of 220.73 mg L−1 in the medium. High performance liquid chromatography analysis showed that AF-LRH1 produced a combination of organic acids (tartaric acid 260.7 mg L−1, fumaric acid 0.8 mg L−1, citric acid 911.9 mg L−1) to dissolve Ca3(PO4)2 by providing H+ ions. AF-LRH1 also utilizes NH4+ for the biosynthesis of amino acids and releases protons, which facilitate the dissolution of insoluble Ca3(PO4)2 and calcium phytate. Through these processes, calcium phosphate is partly converted into hydroxyapatite because of biological solubilization. AF-LRH1 strain showed the capability to recover phosphorus from various types of sludge-based solid residue by increasing the solubility of insoluble phosphate compounds for plant nutrient supply. In addition, the combining addition of AF-LRH1 strain and phosphate-containing amendments (calcium phosphate, sludge ash and biochar) benefited the decontamination of Pb and Cd contaminated soil. This finding confirmed the AF-LRH1 could be a promising environmental-friendly biofertilizer suitable for agricultural applications and bioremediation of heavy metal contaminated soil.

Facile preparation of NiFe2O4 decorated chitosan-graphene oxide for efficient remediation of Co(II) and adsorption mechanism

In the background of severe water pollution, adsorption is a charming technique for heavy metal remediation. In this work, NiFe2O4 decorated chitosan-graphene oxide (NFCG) was prepared by simple hydrothermal method for Co(II) remediation application. Adsorption mechanism was elaborately elucidated based on multiple evidences extracted from adsorption fitting (isotherms, thermodynamics and kinetics), spectroscopic test (XPS, UV–Vis absorption, fluorescent emission and Raman spectra) and the hard-soft acid-base (HSAB) theory inspection. Result shows, for Co(II) with initial concentration 200 mg·L−1, NFCG with dosage 500 mg·L−1 reaches adsorption equilibrium in 24 min, rendering removal percentage and adsorption amount 96.87 % and 387.48 mg·g−1, respectively. Owing to the efficient recovery enabled by paramagnetism, NFCG keeps adsorption amount 311.01 mg·g−1 for Co(II) after six consecutive cycles. Moreover, NFCG exhibits selectivity towards Co(II) under the coexistence of common interfering substances. Adsorption fitting suggests chemical adsorption based on heterogeneous affinity. Spectroscopic analysis discloses, CO, CO, -C(=O)NH-, OH and aromatic part contribute to Co(II) adsorption via electron donation, forming CoO bond. This atomic scale adsorption mechanism was substantiated by HSAB theory calculation. In brief, this work provides basic knowledge and technical support for fabricating high efficiency magnetic bio adsorbent.

Remediation of heavy metal contaminated soil in mining areas with vaterite-type biological calcium carbonate

In recent years, research on the remediation of heavy metal contaminated soil by microbially induced carbonate precipitation (MICP) technology has yielded significant findings. However, when utilizing MICP for remediation in situ, urea and calcium chloride may produce high concentrations of NH4+ and Cl-, which subsequently cause secondary pollution. If the biological calcium carbonate (Bio-CaCO3) produced by MICP is employed as a highly efficacious adsorbent, secondary pollution can be avoided while remediating heavy metal pollution. In this study, vaterite-type Bio-CaCO3 was prepared under the regulation of sophorolipids, and the remediation effect and mechanisms for heavy metal contaminated soil were investigated. The results demonstrated that sophorolipids facilitate the formation and stabilization of vaterite-type Bio-CaCO3. The addition of vaterite-type Bio-CaCO3 could notably increase the content of soil organic matter, enhance soil urease activity, and reduce soil catalase activity. On the 30th day of remediation with vaterite-type Bio-CaCO3, the active state content of Pb and Cd in the soil exhibited a decrease of 41.23% and 35.00%, respectively. Additionally, the exchangeable state content demonstrated a reduction of 6.61% and 8.48%, while the carbonate-bound state exhibited an increase of 12.05% and 13.89%, respectively. The principal mechanisms for the remediation of heavy metal contaminated soil by vaterite-type Bio-CaCO3 may be attributed to ion exchange, chemical precipitation, physical adsorption, and complexation reactions. The analysis of the microbial community structure demonstrated that vaterite-type Bio-CaCO3 could enhance the abundance of multiple genera with urease-producing genes, including Pseudomonas, Staphylococcus, and Bacillus while maintaining the soil biodiversity. This study provides a new idea for the remediation of heavy metal contaminated soil around the mining area and offers technical support for the construction of green mines.

Three-dimensional bioprinted materials in alginate-hyaluronic acid complex based hydrogel based bio-ink as absorbents for heavy metal ions removal

Major environmental and health effects arise from the presence of heavy metals in water, including lead (Pb²⁺), mercury (Hg²⁺), chromium (Cr⁶⁺), cadmium (Cd²⁺), and arsenic (As³⁺), which contribute significantly to water pollution and pose severe risks to ecosystems and human health. This study demonstrates the fabrication of 3D printed self-regenerative functional living materials, a fungi, by using mixture of sodium alginate and hyaluronic acid hydrogel as absorbents to remove the heavy metals from the environment. Bioprinting has emerged as a transformative technology for fabricating complex biological constructs. The bioprinting experiments, conducted with optimized parameters, revealed the viscoelastic behavior of the hydrogel, suitable for 3D bioprinting applications. MicroCT analysis indicated that the hydrogel's porosity and structural properties support fungal growth in a controlled three-dimensional setting. Microscopic analyses, including phase contrast microscopy, FESEM, and HRTEM, provided insights into the cellular morphology of the bioprinted constructs. Cell viability was assessed using flow cytometry with FDA and PI staining, showing a significant population of live cells, affirming the biocompatibility of the hydrogel. Additionally, the study explored the hydrogel's potential for heavy metal removal from water samples. Multi-element standard solutions containing Copper(Cu²⁺), Cadmium(Cd²⁺), Nickel(Ni²⁺), Cobalt(Co²⁺), and Ferrous(Fe³⁺) ions at different concentrations were incubated with hydrogel patches embedded with Aspergillus flavus. Atomic absorption spectrophotometry analysis showed rapid initial removal rates of metal ions, with maximum removal efficiency achieved around the 12th hour. Comparisons with a control hydrogel without the fungal strain demonstrated significantly enhanced removal efficiency due to the presence of Aspergillus flavus. This study highlights the dual functionality of sodium alginate with hyaluronic acid -based hydrogels for bioprinting fungi and for environmental remediation of heavy metals, offering promising applications in environmental cleanup.

The Marine-Origin Exopolysaccharide-Producing Bacteria Micrococcus Antarcticus HZ Inhibits Pb Uptake in Pakchoi (Brassica chinensis L.) and Affects Rhizosphere Microbial Communities.

Exopolysaccharides (EPSs) produced by microorganisms play an important role in biotolerance and reducing heavy metal (HM) contamination by limiting the migration of HMs into plants. However, research on the application of EPS-producing marine bacteria for soil heavy metal remediation remains limited, particularly regarding their mechanisms of HM immobilization in soil and impact on plant growth. In this study, the EPS-producing marine bacterium Micrococcus antarcticus HZ was investigated for its ability to immobilize Pb and produce EPSs in soil filtrate. The effects on the growth quality and biomass of pakchoi (Brassica chinensis L.), as well as bacterial communities in inter-root soil contaminated with Pb, were also investigated. The results indicated that HZ could reduce the Pb concentration in the soil filtrate, achieving a removal rate of 43.25-63.5%. The EPS content and pH levels increased in the presence of Pb. Pot experiments showed that adding HZ significantly increased the biomass of pakchoi (9.45-14.69%), vitamin C (Vc) (9.69-12.92%), and soluble protein content (22.58-49.7%). HZ reduced the Pb content in the roots (17.52-47.48%) and leaves (edible tissues) (43.82-52.83%) of pakchoi. HZ increased soil enzyme activities (alkaline phosphatase, dehydrogenase, and urease), and the contents of ammonium nitrogen and nitrate nitrogen. Additionally, HZ also increased the relative abundance of beneficial bacteria (e.g., Proteobacteria, Cyanobacteria, and Chlorobacteria) in the inter-root soil, which have prophylactic and heavy-metal fixation functions. In summary, HZ reduces effective Pb content in edible tissues, roots, and inter-root soil by regulating inter-root soil microbial community structure, increasing soil pH, nitrogen content, and soil enzyme activity, and altering dominant phylum abundance.

Enrichment characteristics of Cd and Hg and regulation of heavy metal transporter signaling in Pleurotus ostreatus

Currently, heavy metal pollution has emerged as a global issue. Compared with green plants, edible fungi, significant crops cultivated worldwide, present a greater capacity to accumulate heavy metals (HMs). However, the enrichment characteristics and functions of heavy metal transporters (HMATs) in the accumulation of HMs in edible fungi are still unclear. Cadmium (Cd) and mercury (Hg) are the primary HMs enriched in edible fungi. This study focused on Pleurotus ostreatus, the second largest edible mushroom worldwide, to examine the enrichment process. In this study, a series of different concentrations of CdCl2 and HgCl2 (0, 0.01, 0.05, 0.5, 2, 5, 10, and 20 mg/L) were used to mimic HMs pollution. HMs in the experimental concentration range did not affect the mycelial growth rate or fruiting body yield of P. ostreatus. However, in the 20 mg/L treatment group, the HMs were mainly concentrated in the cap, with about 4.4 mg/kg Cd and 2.7 mg/kg Hg, and were predominantly present in the most toxic ion exchange state. Thirteen HMATs were identified in the genome database of P. ostreatus. Using RT-qPCR, seven HMATs (24093, 1066001, 1106787, 1066344, 1079972, 1095088, and 1104877) whose expression levels were more than twice that of the control under most concentrations of HMs were selected for further investigation of their transport functions and their involvement in signal regulation. Among them, gene 24093 was involved in the absorption of Cd and Hg. These transporters are regulated by ROS, Ca2+, and NO signals under HM stress. This study provides target genes for reducing the risk of HM accumulation through molecular means, and serves as a reference for HM remediation using edible fungi.

Hydroxyapatite self-doped biochar with MgO modification immobilizes heavy metal and alters soil microbial community

Functionalized biochars are highly effective in the remediation of heavy metals and the improvement of soil properties. In this study, we prepared a hydroxyapatite self-doped biochar (FB) using fish scales as raw material, and impreged FB with MgCl2 following by pyrolysis to obtain MgO-loaded FB (MFB). A soil incubation experiment was conducted to explore the influence of MFB on the immobilization of Cu, Cd, and Pb, alongside the impact on the soil properties and bacterial community. The results demonstrated that the nano-hydroxyapatite components and MgO micro-nanoparticles on MFB promoted the immobilization of heavy metals in soils through dissolution-precipitation and ion-exchange. The availability of Cu, Cd, and Pb in soils amended with MFB was significantly decreased by 69.1 %, 63.5 %, and 53.7 %, respectively, compared to CK. Furthermore, the MFB amendment significantly increased soil organic carbon and available P, as well as enhanced enzyme activities related to the C-, N-, and P-cycles. Notably, the MgO loaded on biochar played a crucial role in altering the diversity and composition of soil bacterial communities. The complexity and stability of the co-occurrence networks of bacterial communities increased following MgO-loaded biochar addition, and there were more frequent positive interactions among bacterial taxa within the network. The effects of MFB on immobilizing heavy metals and shaping bacterial communities were conducive to the restoration of soil ecological functions. These findings provide a promising strategy for the remediation of heavy metal contaminated soils.

Role of white rot fungi in sustainable remediation of heavy metals from the contaminated environment

ABSTRACT Heavy metal contamination has severe impacts on the natural environment. The currently existing physico-chemical methods have certain limitations, restricting their wide-scale application. The use of biological agents like bacteria, algae, and fungi can help eliminate heavy metals without adversely affecting flora and fauna. Due to their inherent ability to withstand adverse environmental conditions, nowadays, mycoremediation approaches are receiving considerable attention for heavy metal removal from contaminated sites. In this review, we emphasised the role of white rot fungi in remediation of heavy metal along with different factors influencing biosorption, effects on exposed fungi, and the mechanisms involved. Bibliometric analysis tools have been applied to literature search and trend analysis of the research on white rot fungi-mediated heavy metal removal. Annual growth rates and average citations per document are 5.08% and 35.48, respectively. Phanerochaete chrysosporium, Pleurotus ostreatus, and Trametes versicolor have been widely explored for the remediation of heavy metals. In addition to providing some prospects, the review also highlighted a few limitations, including inconsistent removal and effects of environmental factors influencing the functioning of white rot fungi. Overall, white rot fungi have been found to have immense potential to be widely utilised for sustainable remediation of heavy metal-contaminated environments.

Microbial Contributions to Heavy Metal Phytoremediation in Agricultural Soils: A Review.

Phytoremediation is a sustainable technique that employs plants to reinforce polluted environments such as agroecosystems. In recent years, new strategies involving the plant microbiome as an adjuvant in remediation processes have been reported. By leveraging this microbial assistance to remediate soils contaminated with heavy metals such As, Pb, Cd, Hg, and Cr, plants can sequester, degrade, or stabilize contaminants more efficiently. Remarkably, some plant species are known for their hyper-accumulative traits in synergy with their microbial partners and can successfully mitigate heavy metal pollutants. This sustainable biotechnology based on plant-microbe associations not only aids in environmental cleanup but also enhances biodiversity, improves soil structure, and promotes plant growth and health, making it a promising solution for addressing agro-pollution challenges worldwide. The current review article emphasizes the potential of synergistic plant-microbe interactions in developing practical and sustainable solutions for heavy metal remediation in agricultural systems, which are essential for food security.

Biochar-based adsorption for heavy metal removal in water: a sustainable and cost-effective approach.

The increasing contamination of aquatic bodies by heavy metals poses a significant threat to environment and human health, necessitates innovative, sustainable and cost-effective remediation strategies. Due to their persistence and toxicity, heavy metals like copper (Cu), lead (Pb), mercury (Hg), and cadmium (Cd) pose severe threats, even in trace amounts. Traditional removal methods of these heavy metals, like chemical precipitation, oxidation/reduction, filtration, ion exchange, membrane separation, and adsorption, are costly, inefficient, and have drawbacks. As an efficient and low-cost adsorbent, biochar has the potential for heavy metal remediation from water. Biochar is a versatile carbonaceous material produced through pyrolysis of organic wastes, emerged as a powerful adsorbent for heavy metal removal from contaminated water. The unique property of biochar makes it an effective medium immobilizing and capturing of heavy metals like Pb, Cd, As and Hg. Various factors affect its adsorption potential and capacity. Feedstocks type, composition, activation methods, and production processes including the pyrolysis temperature, temperature rate and residence time significantly impact the efficacy of biochar. Therefore, this review has assessed, compared, and contrasted different forms of biochar along with their production methods, modification techniques and mechanisms for their potential use as an adsorbent for heavy metal removal from the contaminated water. Modified biochar offers an environmentally friendly and cost-effective solution for water purification and remediation of toxic heavy metals from water. This review highlights the biochar potential as a crucial component for future research projects focusing on water treatment technologies, providing avenues for safer and cleaner water resources.

Ecological characteristics of tall fescue and spatially organized communities: Their contribution to mitigating cadmium damage

The threat of cadmium (Cd) stress to agricultural soil environments, as well as their productivity attracting growing global interest. Tall fescue (Festuca arundinacea Schreb.) is a strong candidate for the remediation of heavy metals in soil. However, the joint analysis of Cd tolerance, physiological responses, and multifaceted plant microbiomes in tall fescue fields has not been extensively researched. Therefore, this study employed microbial sequencing (i.e., 16S and ITS sequencing) to investigate the differences in microbial community structure among various plant compartments of Cd-resistant tall fescue (cv. ‘Arid3′) and Cd-sensitive tall fescue (cv. ‘Barrington’). Furthermore, we examined the mechanism of resistance to Cd by introducing three different bacteria and a fungus that were isolated from the ‘Arid3′ rhizosheath soil. It highlighted the potential application of enriched taxa such as Delftia, Novosphingobium, Cupriavidus and Torula in enhancing the activity of antioxidant defense systems, increasing the production of osmotic regulatory substances, and stimulating the expression of Cd-resistance genes. This ultimately promoted plant growth and enhanced phytoremediation efficiency. This study shed light on the response mechanism of the tall fescue microbiome to Cd stress and underscored the potential of tall fescue-microbe co-culture in the remediation of heavy metal-contaminated areas.

Evidence that beneficial microbial inoculation enhances heavy metal-contaminated soil remediation: Variations in plant endophyte communities

Microbial remediation of heavy metal (HM)-contaminated soil is a sustainable approach; however, the impact of microbial inoculation on the internal environment of plants remains understudied. Thus, Enterobacter sp. FM-1 (Enterobacter sp.) and the hyperaccumulator Bidens pilosa L. (B. pilosa L.) were used to study these effects. Through analyses of plant physiological and biochemical characteristics, the endophytic microbial community composition, microbial co-occurrence networks and functional predictions, the potential mechanisms by which Enterobacter sp. benefits the phytoremediation of HM-contaminated soil by B. pilosa L. were elucidated. Inoculation with Enterobacter sp. promoted the growth of B. pilosa L. and influenced the endophytic microbial community diversity in B. pilosa L. Interactions among endophytes facilitated the formation of microbial networks, with endophytic fungi playing a more prominent role than endophytic bacteria as the level of HM contamination increased. Functional predictions via PICRUSt2 revealed that endophytic bacteria are involved primarily in processes related to carbohydrate metabolism, ABC transporters, and amino acid metabolism. In conclusion, this study provides evidence for the beneficial role of microbes in improving the plant endosphere environment.

Immobilizing lead in aqueous solution and loess soil using microbially induced carbonate/phosphate precipitation (MICP/MIPP) under harsh pH environments

The bioaccumulation of heavy metals due to metallurgical and smelting activities threatens human health. Although microbial-induced carbonate/phosphate precipitation (MICP/MIPP) technology has been applied to heavy metal remediation, the relative merits of MICP and MIPP, especially under extreme pH environments, have not yet been documented. In this study, Sporosarcina pasteurii (SP)-based MICP and Bacillus megaterium (BM)-based MIPP were applied to immobilize lead (Pb) in aqueous solution and loess soil. The results showed that the BM retained a strong phosphorolysis ability when under strongly acidic conditions, while the ureolysis ability of SP approached zero. Furthermore, the bioprecipitates obtained under BM-based MIPP had a denser appearance, presumably due to the enrichment of calcite and apatite crystals. The results also showed that Pb immobilization was achieved through bacterial adsorption, the chelate function of sodium glycerophosphate (SGP), large organic matter complexation, and biomineralization through the MICP/MIPP mechanism. Under SP-based MICP, SP and large organic matter immobilized Pb2+ at rates of 17.6 % and 31.7 %, respectively, while under BM-based MIPP, BM, organic matter, and SGP immobilized Pb2+ at rates of 21.5 %, 23.4 %, and 48.5 % respectively. The MICP and MIPP mechanisms dominated Pb immobilization at rates of 78.6 % and 99.6 %, respectively.

Growth Behaviours of Two Rhizospheric Bacterial Strains in the Presence of Different Cadmium Concentrations and Temperatures

Understanding the interaction of Cd with plants, as well as the search for alternatives to minimize its effects, has caught the interest of the scientific community, due to the accelerated growth of contamination with this metal and its high toxicity. The aim of the present study was to evaluate the ability of two rhizospheric bacterial strains LC7504001.1 Burkholderia cepacia (C65RLIM) and FJ972527.1 Pseudomonas aeruginosa (C85RLIM) to three concentrations of cadmium (100, 300 and 500 mg/L) and to compare the growth behaviour with increasing temperature from 32 to 45°C. The results show different growth patterns for each strain tested against exposure to the three cadmium concentrations and the four temperatures tested. The Pseudomonas aeruginosa strain (C85RLIM) had the best adaptive behaviour to the three cadmium concentrations tested, and also showed stability when subjected to 500 mg/L CdCl2 and temperatures between 40 and 45°C. The results predict the possible behaviour of rhizospheric bacteria in the face of global warming and heavy metal remediation processes.

Mechanistic insights into cadmium removal from environmental waters using silicon-enhanced lignin-derived hydrochar and pyrochar

This study explores the improved cadmium (Cd2+) removal from environmental waters using silicon-modified hydrochar and silicon-modified pyrochar derived from industrial lignin. Despite the widespread use of lignin-based chars in environmental remediation, the specific role of silicon in enhancing these materials’ properties and their mechanisms for Cd2+ removal remain inadequately studied. Physicochemical analyses indicate that the introduction of silicon promotes the consumption of C–O bonds in hydrochar, facilitating the formation of Si–O bonds. In pyrochar, silicon introduction enhances the synthesis of silicate minerals. Results showed that silicon-modified pyrochar, in particular, exhibited a markedly higher Cd2+ adsorption capacity in environmental water, being 14.71, 16.83, and 1.87 times that of hydrochar, pyrochar, and silicon-modified hydrochar, respectively. Silicon-modified pyrochar also demonstrated excellent selective adsorption and reusability for Cd2+, showing optimal performance in actual water bodies. Notably, silicon-modified pyrochar maintained a high Cd2+ removal rate of up to 99 % after multiple cycles. Adsorption experiments revealed that the main mechanisms in lignin–based carbons are ion exchange and complexation precipitation, contributing about 70 % of the adsorption capacity. Specifically, silicon-modified hydrochar removes Cd2+ mainly through complexation precipitation with oxygen–containing groups (CO and SiO), while silicon-modified pyrochar relies mainly on mineral precipitation (Na2SiO3 and Na2CO3) and the ion exchange process. These findings underscore the transformative impact of silicon modification on lignin-derived chars, offering valuable insights for developing more effective and sustainable solutions for heavy metal remediation in aquatic environments.

Bioinspired, Carbohydrate-Containing Polymers Efficiently and Reversibly Sequester Heavy Metals.

Water scarcity and heavy metal pollution are significant challenges in today's industrialized world. Conventional heavy metal remediation methods are often inefficient and energy-intensive, and produce chemical sludge. To address these issues, we developed a bioinspired, carbohydrate-containing polymer system for efficient and selective heavy metal removal. Using ring opening metathesis polymerization, we synthesized polymers bearing amphiphilic glucuronate side chains capable of selectively binding heavy metal cations in mixed media. In samples containing high concentrations of heavy metals (>550 ppb), these polymers rapidly form a filterable precipitate upon metal capture, reducing the concentration of cation to <1.5 ppb within 3 min, as measured by inductively coupled plasma mass spectrometry. This system effectively removes cadmium ions from highly contaminated solutions to levels below the Agency for Toxic Substances and Disease Registry limit for Cd2+ in drinking water and selectively removes both Cd2+ and Pb2+ from lake water spiked with trace amounts of metal. Acidification triggers protonation of the glucuronate groups, releasing the heavy metals and resolubilizing the polymer. This capture-and-release process can be repeated over multiple cycles without loss of binding capacity. As such, this study introduces a novel class of recyclable materials with pH-responsive properties, offering potential for applications in water remediation and beyond.

Emerging Catalytic Strategies Driven by External Field for Heavy Metal Remediation

Heavy metal pollution presents significant environmental and public health risks due to its widespread occurrence and resistance to degradation. There is a pressing need for innovative solutions to address the challenge of heavy metal ion removal from water resources. In this review, we highlight recent advancements in emerging catalytic strategies for efficient heavy metal remediation, leveraging various external fields such as electric, mechanical, magnetic, and thermoelectric fields, as well as their synergetic coupling with photocatalysis technology. These novel approaches offer promising avenues for enhancing heavy metal removal efficacy and environmental sustainability. In particular, this review focuses on recent breakthroughs in new materials systems capable of functioning under diverse external fields, heralding future advancements in heavy metal remediation. Finally, we discuss the current challenges and future perspectives in this emerging research area.

Genome-Wide Analysis of the Nramp Gene Family in Kenaf (Hibiscus cannabinus): Identification, Expression Analysis, and Response to Cadmium Stress.

Kenaf (Hibiscus cannabinu) is a grass bast fiber crop that has the ability to tolerate and accumulate heavy metals, and it has been considered as a potential heavy metal accumulator and remediation plant. Nramp is a natural resistance-related macrophage, which plays an important role in the transport of divalent metal ions, plant growth and development, and abiotic stress. In this study, the Nramp gene family of kenaf was analyzed at the whole genome level. A total of 15 HcNramp genes were identified. They are distributed unevenly on chromosomes. Phylogenetic analysis classified 15 HcNramp proteins into 3 different subfamilies. All proteins share specific motif 4 and motif 6, and the genes belonging to the same subfamily are similar in structure and motif. The promoters are rich in hormone response, meristem expression, and environmental stress response elements. Under different treatments, the expression levels of HcNramp genes vary in different tissues, and most of them are expressed in roots first. These findings can provide a basis for understanding the potential role of the Nramp gene family in kenaf in response to cadmium (Cd) stress, and are of great significance for screening related Cd tolerance genes in kenaf.

Nano-Hydroxyapatite Modified Tobacco Stalk-Based Biochar for Immobilizing Cd(II): Interfacial Adsorption Behavior and Mechanisms

Biochar, an eco-friendly, porous carbon-rich material, is widely studied for immobilizing heavy metals in contaminated environments. This study prepared tobacco stalks, a typical agricultural waste, into biochar (TSB) modified by hydroxyapatite (HAP) at co-pyrolysis temperatures of 350 °C and 550 °C to explore its Cd(II) adsorption behavior and relevant mechanisms. XRD, SEM–EDS, FTIR, and BET analyses revealed that HAP successfully incorporated onto TSB, enriching the surface oxygen-containing functional groups (P–O and carboxyl), and contributing to the enhancement of the specific surface area from 2.52 (TSB350) and 3.63 m2/g (TSB550) to 14.07 (HAP–TSB350) and 18.36 m2/g (HAP–TSB550). The kinetics of Cd(II) adsorption onto TSB and HAP–TSB is well described by the pseudo-second-order model. Isotherm results revealed that the maximum adsorption capacities of Cd(II) on HAP–TSB350 and HAP–TSB550 were approximately 13.17 and 14.50 mg/g, 2.67 and 9.24 times those of TSB350 and TSB550, respectively. The Cd(II) adsorption amounts on TSBs and HAP–TSBs increased significantly with increasing pH, especially in HAP–TSB550. Ionic strength effects and XPS analysis showed that Cd(II) adsorption onto HAP–TSBs occurred mainly via electrostatic interaction, cation exchange with Ca2+, complexation with P–O and –COOH, and surface precipitation. These findings will provide a modification strategy for the reutilization of tobacco agricultural waste in the remediation of heavy metal contaminated areas.

Interfacial dynamics mediate surface binding events on supramolecular nanostructures

The dynamic behavior of biological materials is central to their functionality, suggesting that interfacial dynamics could also mediate the activity of chemical events at the surfaces of synthetic materials. Here, we investigate the influence of surface flexibility and hydration on heavy metal remediation by nanostructures self-assembled from small molecules that are decorated with surface-bound chelators in water. We find that incorporating short oligo(ethylene glycol) spacers between the surface and interior domain of self-assembled nanostructures can drastically increase the conformational mobility of surface-bound lead-chelating moieties and promote interaction with surrounding water. In turn, we find the binding affinities of chelators tethered to the most flexible surfaces are more than ten times greater than the least flexible surfaces. Accordingly, nanostructures composed of amphiphiles that give rise to the most dynamic surfaces are capable of remediating thousands of liters of 50 ppb Pb2+-contaminated water with single grams of material. These findings establish interfacial dynamics as a critical design parameter for functional self-assembled nanostructures.