Heavy Metal Remediation Research Articles

Modern-Day Green Strategies for the Removal of Chromium from Wastewater

Chromium is an essential element in various industrial processes, including stainless steel production, electroplating, metal finishing, leather tanning, photography, and textile manufacturing. However, it is also a well-documented contaminant of aquatic systems and agricultural land, posing significant economic and health challenges. The hexavalent form of chromium [Cr(VI)] is particularly toxic and carcinogenic, linked to severe health issues such as cancer, kidney disorders, liver failure, and environmental biomagnification. Due to the high risks associated with chromium contamination in potable water, researchers have focused on developing effective removal strategies. Among these strategies, biosorption has emerged as a promising, cost-effective, and energy-efficient method for eliminating toxic metals, especially chromium. This process utilizes agricultural waste, plants, algae, bacteria, fungi, and other biomass as adsorbents, demonstrating substantial potential for the remediation of heavy metals from contaminated environments at minimal cost. This review paper provides a comprehensive analysis of various strategies, materials, and mechanisms involved in the bioremediation of chromium, along with their commercial viability. It also highlights the advantages of biosorption over traditional chemical and physical methods, offering a thorough understanding of its applications and effectiveness.

Application of waste eggshells elevates phytoremediation efficiency of Pb-Zn mine-contaminated farmland and mitigates soil greenhouse gas emissions: A field study

Remediating heavy metal (HM)-contaminated farmlands and sequestering soil carbon for emission reduction have been prominent topics in environmental research in recent years. However, few studies have looked into the soil greenhouse gas (GHG) impacts of growing hyperaccumulators in composite HM-contaminated farmland, as well as agronomic measures to remediate soil HMs while mitigating GHG emissions. To investigate fertilization measures to improve phytoremediation efficiency and mitigate GHG emissions, S. photeinocarpum was planted with three different fertilization measures on farmland contaminated by lead-zinc (Pb-Zn) mines (1200 kg ha−1 eggshell, 125 kg ha−1 28-homobrassinolide, and 16.7 kg ha−1 mineral potassium fulvic acid) during its growth period. The findings are as follows: Eggshell application significantly enhanced the translocation factor (TF) of Pb, Zn, and cadmium (Cd) from the roots to the shoots of Solanum photeinocarpum. Moreover, eggshells notably increased the bioaccumulation factor (BCF) of Cd and Pb in plant shoots by 120.75% and 159.09%, respectively. Regarding GHG emissions, the combined application of eggshells and 28-homobrassinolide substantially lowered the global warming potential (GWP) of the soil. Correlation analyses revealed that eggshell application increased the relative abundance of the Gemmatimonadota bacterial phylum in the soil, facilitating Pb and Cd migration from the roots to shoot tissues in S. photeinocarpum. Eggshell use inhibited nitrate nitrogen (NO3−-N) transformation into nitrous oxide (N2O) by the Myxococcota bacterial phylum and reduced N2O release from the soil. The application of low-cost eggshells can achieve a win-win situation of soil HM remediation and GHG emission reduction, as well as provide simple and scalable management measures for HM-contaminated farmland.

The Impact of Beneficial Microorganisms on Soil Vitality: A Review

The paper summarizes the literature on the critical impact of beneficial microorganisms on soil vitality. Common soil microorganisms, including bacteria, fungi, algae, protozoa, and viruses contribute significantly to enhancing soil fertility through processes such as nitrogen fixation, phosphorus solubilization and mobilization, sulfur cycle, composting, and heavy metal remediation. Their abundance and biomass vary significantly across taxa within the uppermost 15 cm of soil, with bacteria dominating numerically and fungi contributing substantially to biomass. These microorganisms mediate essential biogeochemical cycles in soil, including carbon, nitrogen, and phosphorus cycles, by facilitating the decomposition of organic matter and recycling soil nutrients. Nitrogen-fixing bacteria like Rhizobium are prevalent symbionts capable of biologically fixing nitrogen. Additionally, bacteria such as Micrococcus spp., Enterobacter aerogens, Pseudomonas capacia, fungi including Aspergillus niger, A. flavus, A. japonicas, Penicillum spp., and actinomycetes like Streptomyces play crucial roles in phosphorus solubilization, making phosphorus available for plant uptake. This synthesis underscores the critical role of beneficial microorganisms in maintaining soil vitality. These organisms interact with plants through beneficial relationships, influencing soil fertility dynamics by enhancing nutrient availability, promoting plant growth, and controlling pathogens. The use of biofertilizers has emerged as a sustainable strategy to improve crop yields and restore soil fertility, reducing environmental impacts linked to chemical fertilizers. Understanding the intricate dynamics of soil-beneficial microorganism and their interactions with Plants are pivotal for optimizing agricultural practices, ensuring long-term soil health, and enhancing productivity in sustainable farming systems.

Effect of Electrode Positioning on Electrokinetic Remediation of Contaminated Soft Clay with Surface Electrolyte.

Soft clay contamination is an increasingly global issue with significant implications for land development and human health. Electrokinetic remediation (EKR) has demonstrated significant potential for cleaning contaminated soils. It is crucial to develop efficient processes that minimize environmental impact and reduce costs. A series of citric acid (CA)-enhanced EKR tests were conducted using a novel experimental setup, with the electrolyte positioned above the soil surface, to examine the impact of four different electrode arrangements on the effectiveness of EKR. The position of the electrode end had a significant impact on the migration of ions in the anolyte and catholyte, which in turn affected the volume reduction in the anolyte, the magnitude of the current, and the migration of heavy metals. The electrode arrangement mode c (electrodes suspended in the electrolytes) can enhance the migration of the anolyte and reduce the drainage of the soil, making it an effective measure for improving the removal rate of heavy metals. After the heavy metal remediation is complete, the bearing capacity of the soil should be increased. Changing the electrode arrangement to mode d (anode suspended in the anolyte, a very small part of the cathode inserted into the soil) is an effective measure for reducing the soil water content and improving soil strength.

Metal and metal oxide nanomaterials for heavy metal remediation: novel approaches for selective, regenerative, and scalable water treatment

Heavy metal contamination in water sources poses a significant threat to environmental and public health, necessitating effective remediation strategies. Nanomaterial-based approaches have emerged as promising solutions for heavy metal removal, offering enhanced selectivity, efficiency, and sustainability compared to traditional methods. This comprehensive review explores novel nanomaterial-based approaches for heavy metal remediation, focusing on factors such as selectivity, regeneration, scalability, and practical considerations. A systematic literature search was conducted using multiple academic databases, including PubMed, Web of Science, and Scopus, to identify relevant articles published between 2013 and 2024. The review identifies several promising nanomaterials, such as graphene oxide, carbon nanotubes, and metal-organic frameworks, which exhibit high surface areas, tunable surface chemistries, and excellent adsorption capacities. Surface functionalization with specific functional groups (e.g., carboxyl, amino, thiol) significantly enhances the selectivity for target heavy metal ions. Advances in regeneration strategies, including chemical desorption, electrochemical regeneration, and photocatalytic regeneration, have improved the reusability and cost-effectiveness of these materials. Scalability remains a critical challenge, but recent developments in synthesis methods, such as green synthesis and continuous-flow synthesis, offer promising solutions for large-scale production. The stability and longevity of nanomaterials have been improved through surface modification and the development of hybrid nanocomposites. Integrating nanomaterials with existing water treatment infrastructure and combining them with other remediation techniques, such as membrane filtration and electrochemical methods, can enhance overall treatment efficiency and feasibility. In conclusion, nanomaterial-based approaches hold immense promise for revolutionizing heavy metal remediation and advancing sustainable water management practices. As future research is geared towards retrofitting existing treatment plants, it is equally critical to mitigate unintended environmental and public health consequences associated with the widespread production and use of nanomaterials, such as their leachability into water systems and environmental persistence.

Binary Biosorption of Cu(II) and Cr(VI) by Naturally Formed Biofilm Matrices

Water pollution poses a significant ecological threat, contributing to the widespread degradation of aquatic ecosystems. Among the pollutants, heavy metals pose severe risks to both organisms and human health, emphasizing the urgent need for effective pollution control technologies. Biosorption presents a promising, cost-effective, and environmentally friendly solution to mitigate heavy metal contamination. Biofilms, consisting of microbial communities, have emerged as potential biosorbents for heavy metals. Since heavy metals can exist as cations and anions concurrently in aquatic environments, understanding their behavior in binary systems is essential for biosorption strategies. This study focuses on the binary biosorption of Cu(II) and Cr(VI), representing cationic and anionic heavy metals. Specific adsorption sites are identified by analyzing adsorption kinetics, isotherms, and IR spectra of biofilms. The results indicate that biofilms, in a binary scenario, demonstrate nearly identical adsorption capacities for Cu(II) and Cr(VI). Moreover, the adsorption process follows the Langmuir adsorption model, emphasizing the potential of biofilms as effective biosorbents for the simultaneous removal of cationic and anionic heavy metals. This study advocates for a sustainable approach to heavy metal remediation through the utilization of biofilms.

Bhargavaea beijingensis a promising tool for bio-cementation, soil improvement, and mercury removal

Microbially Induced Calcite Precipitation (MICP) has emerged as a promising technique for bio-cementation, soil improvement, and heavy metal remediation. This study explores the potential of Bhargavaea beijingensis, a urease-producing bacterium, for these applications. Six ureolytic bacteria were isolated from calcareous bricks mine soil and screened for urease and calcite production. B. beijingensis exhibited the highest urease activity and calcite precipitation. Urease activity, calcite precipitation, sand solidification, heavy metal removal efficiency, and compressive strength were evaluated. It showed significant heavy metal removal efficiency, particularly highest for HgCl2. Mortar blocks treated with B. beijingensis or its crude enzyme exhibited improved compressive strength, suggesting its potential for bio-cementation. Crack remediation tests demonstrated successful crack healing in mortar blocks using the bacterium or its enzyme. This study identifies B. beijingensis as a novel and promising MICP agent with potential applications in bio-cementation, soil improvement, and heavy metal remediation. Hence, B. beijingensis diversified abilities prove superior performance compared to commonly used strains like Bacillus subtilis and Shewanella putrefaciens in bio-cementation applications. Its high urease activity, calcite precipitation, and heavy metal removal abilities make it a valuable candidate for sustainable and eco-friendly solutions in various fields.

Effects of Acid Modified Mineral Materials on Soil Cadmium Pollution and Plant Remediation

In response to the problem of soil heavy metal pollution, acid modified mineral materials were used to study the changes in adsorption performance, surface charge, and other indicators of four clay mineral materials, vermiculite, arsenic sandstone, shale, and zeolite, under acid modified conditions. The changes in soil physicochemical properties, heavy metal content, and plant growth before and after remediation were analyzed. The study showed that the introduction of acid modified adsorption materials increased the specific surface area and cation exchange capacity, enhanced adsorption performance, and provided theoretical reference for the mechanism and effect of remediation of cadmium contaminated soil. To optimize the application amount of remediation materials and develop cheap, effective, and scalable heavy metal remediation materials, it has important practical significance. Bangladesh J. Bot. 53(3): 803-809, 2024 (September) Special

Sustainable Stabilizer Derived from Calcium- and Phosphorus-Rich Biowaste for Remediation of Heavy Metal-Contaminated Soil: A Critical Review

Soil pollution by heavy metals (HMs) is a major environmental problem around the world. The addition of biowaste-based stabilizers for HM remediation has recently gained attention due to its relatively low cost and eco-risk, abundance, ease of operation, and quick remediation results. Among these stabilizers, shell (crustacean shell, bivalve shell, and eggshell), starfish, and bone-based stabilizers are particularly attractive because of their high Ca and P contents, allowing for highly efficient HM immobilization and simultaneous supplement of nutrients to the soil. However, a comprehensive review focusing on these stabilizers is currently missing. Therefore, this review attempts to summarize the HM immobilization efficiency of these stabilizers and the mechanisms associated with HM stabilization, and perform an operation cost estimation and cost comparison. Cost comparisons among different stabilizers are widely ignored in reviews due to the lack of reliable cost estimation tools or methods. However, for practical application in soil remediation, cost is one of the most important factors to consider. Thus, a simple but reasonable cost estimation method is developed and discussed in this review. Bivalve shell-based stabilizers demonstrated the most promising results for the immobilization of soil HMs in terms of higher performance and lower cost. Current research limitations, challenges, and recommendations regarding possible future research directions are also provided.

Investigating the Interactive Effect of Arbuscular Mycorrhizal Fungi and Different Chelating Agents (EDTA and DTPA) with Different Plant Species on Phytoremediation of Contaminated Soil

Heavy metal (HM) contamination in soil poses a severe environmental threat, jeopardizing ecosystem health and potentially entering the food chain through plant uptake. Phytoremediation, a bioremediation technique utilizing plants to remove or immobilize contaminants, offers a sustainable and eco-friendly solution for HM remediation. This study investigated the interactive effects of arbuscular mycorrhizal fungi (AMF) and chelating agents (EDTA and DTPA) on the growth of maize (Zea mays L.) and alfalfa (Medicago sativa L.) cultivated in metal-contaminated soil and their impact on HM uptake by these plants. The findings revealed that AMF and chelating agents have complex interactive effects on plant growth and metal accumulation. Maize (Zea mays L.) shoot dry matter increased with AMF and chelating agents at lower concentrations. Both plants generally showed a significant (p ≤ 0.05) increase in shoot dry matter with amendments, with AMF × EDTA (10 mmol/kg) being the most effective for alfalfa. DTPA and EDTA generally reduced the DTPA-extractable metals in soil, suggesting potential for metal removal. However, the effects of AMF on metal availability were variable. Metal concentrations in maize (Zea mays L.) shoots increased with increasing DTPA and EDTA concentrations, while the effects of AMF were more complex. The alfalfa shoot metal content showed varied responses, with EDTA (5 mmol/kg) effectively reducing the metal uptake. In general, treatments involving chelating agents (DTPA and EDTA) tend to result in higher bioaccumulation factor (BF) values compared to the non-treated controls for most HMs in both plant species. Mycorrhizal fungi (AMF) treatment alone or in combination with chelating agents also showed that varied effects on HM uptake in both the alfalfa and maize treatments with chelating agents, especially at higher concentrations, generally promoted the greater translocation of HMs in both plant species. Both alfalfa and maize responded differently to treatments, with some treatments showing higher translocation factor (TF) values for certain HMs in one species compared to the other. Mycorrhizal fungi (AMF) treatment alone or in combination with chelating agents also showed varied effects on HM uptake and translocation in both alfalfa and maize. Further research is required to optimize remediation strategies that balance plant health and metal mobilization.

Editorial: Remediation and health risks of heavy metal contaminated soils

Editorial: Remediation and health risks of heavy metal contaminated soils

Vermicomposting Bio Earth: A Sustainable Approach for Enhanced Nutrient Content and Heavy Metal Remediation in Soil Management

<p style="text-align:justify; margin-bottom:11px"><span style="font-size:11pt"><span style="line-height:150%"><span style="font-family:Calibri,"sans-serif""><span lang="EN-US" style="font-size:12.0pt"><span style="line-height:150%"><span style="font-family:"Times New Roman","serif"">The present study obtained the Bio Earth sample from six locations, represented as LS-(1-6). The collected bio earth sample was blended with an adult earthworm (<i>Eisenia fetida</i>). The experimental investigation was conducted for 108 days, and earthworms showed maximum biomass and population ephemerality in Bio Earth samples (Bio Earth + cow dung). However, the pre-treated and post-treated samples were monitored through physicochemical analysis like pH, electrical conductivity (EC), bulk density (<i>ρ</i>), total organic content (TOC), total nitrogen (TN), total phosphorous (TP), total potassium (TK), C:N ratio, and heavy metals. Among the six Bio Earth samples, the most significant LS-3 reveals the reduction of operating parameters and finds the below detection limit of heavy metals. At the initial level of LS-3, samples were found to be pH-7.2, EC-1.4 ms/cm, <i>ρ</i>-0.8 g/cm<sup>3</sup>, TOC-8.6%, TN-0.6%, TP- 0.3%, TK-0.4%, C:N ratio-16.3%, heavy metals (Zn-448.8 mg/kg; Cu-132.5 mg/kg; Ni-61.4 mg/kg; Pb-91.2 mg/kg; Cr-116.3 mg/kg), whereas the post-treated vermicomposting sample results were exhibited at pH-6.8, EC-2.167 ms/cm, <i>ρ</i>-0.85 g/cm<sup>3</sup>, TOC-9.54%, TN-0.67%, TP-0.48%, TK-0.13%, C:N ratio-14.23%, heavy metals (Zn-64.13 mg/kg; Cu-5.5 mg/kg; Ni-7.26 mg/kg; Pb-101 mg/kg; Cr-51 mg/kg). The data displays that vermicomposting (using <em>E. fetida</em>) is an applicable technology for decomposing organic matter into prosperous nutrient soil enlargement.</span></span></span></span></span></span></p>

Harnessing Moringa oleifera root powder (MORP) for the sustainable remediation of heavy metal contaminated water.

Heavy metal environmental pollution is rapidly increasing due to the increase in industrialization and urbanization. Industrial processes, such as paint production, mining, and raw materials producing industries release effluents rich in heavy metals, like Pb2+, Cd2+, Cu2+, and Cr3+. These heavy metals are dangerous because they persist in nature, are non-biodegradable and they have high tendency to accumulate in the environment and in living organisms who are exposed to them. This work studied the removal of heavy metals (Cu, Pb, Cr, and Cd) from aqueous solution using Moringa oleifera root powder (MORP) as the adsorbent. The MORP was characterized by SEM, FTIR, BET, and XRD. Batch adsorption experiments carried out investigated the effects of adsorbate concentration, adsorbent dosage, agitation time, pH and temperature on adsorption. The optimum parameters are: contact time (90 min); pH (9); adsorbent dose (0.6); metal ion concentration (30 mg L-1) for Cr and 40 mg L-1 for the rest; and temperature (50 °C) for Cu and Pb, and 70 °C for Cr and Cd. These experimental data were analyzed with 5 isotherm models (Temkin, Flory-Huggins, Langmuir, D-R and Freundlich). The result obtained fitted best to Temkin isotherm in comparison to others. Kinetic studies revealed that the pseudo-second order kinetic model best described the adsorption (with high R2 values ranging from 0.9810-0.9976) compared to pseudo-first order and intra-particle diffusion kinetics model. Results of the thermodynamic study showed that the sorption process was endothermic for Cu and Pb, but exothermic for Cd and Cr. The adsorbent showed good adsorptive tendencies toward the ions studied, and could be applied on an industrial scale for the remediation of metal contaminated water.

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.