Heavy Metal Chelator Research Articles

Therapeutic potential of traditional herbal plants and their polyphenols in alleviation of mercury toxicity.

Mercury (Hg) is a major environmental contaminant significantly impacting human health. As a naturally occurring element, mercury has been extensively mobilized into aquatic and terrestrial ecosystems over thousands of years, largely due to anthropogenic activities such as mining and metal extraction. Acute mercury toxicity causes extensive physiological damage, affecting vital organs including the kidneys, heart, liver, brain, and skin. Phytochemicals, known for their diverse pharmacological properties, have shown promise in mitigating metal-induced toxicities, including mercury. These compounds exhibit protective effects against mercury-induced multi-organ damage through mechanisms such as reactive oxygen species (ROS) scavenging, cyclooxygenase (COX) inhibition, and anti-inflammatory activity. This review explores the therapeutic potential of traditional herbal plants and their phytoconstituents in alleviating mercury-induced toxicity. Key findings highlight several plants with hepatoprotective effects, mitigating necrosis and anatomical distortion in liver cells. Phytochemicals such as quercetin, rutin, salicylic acid, ferulic acid, 6-gingerol, and 6-shogaol play pivotal roles in downregulating molecular pathways activated by mercury exposure. Other bioactive compounds, including acetogenin and gallic acid, exhibit potent antioxidant properties, with mechanisms such as ROS scavenging and inhibition of lipid peroxidation. This review also highlights certain compounds, such as aloe-emodin and gentisic acid, which exhibit potential for mitigating mercury toxicity through mechanisms like inhibiting oxidative stress and enhancing cellular defense pathways. However, these compounds remain underexplored, with no significant studies conducted to evaluate their efficacy against mercury-induced toxicity, presenting a critical area for future research. These findings underscore the potential of phytochemicals as effective agents in combating mercury toxicity through antioxidant mechanisms, cellular signalling regulation, and heavy metal chelation.

Enzyme-Instructed Interfacial Jamming of Pillar[5]arenes for Macroscopic Signal Amplification.

Enzyme-instructed signal generation at liquid-liquid interfaces presents a novel strategy for controlling and detecting biochemical processes on macroscopic scales. Here, we explore the self-assembly and jamming of pillar[5]arene (P[5]A) derivatives at the oil-water interface via a copper-mediated "click" reaction, providing a versatile platform for generating observable signals. The formation of a pillar[5]arenes network at the droplet interface reduces interfacial tension, allowing droplets to adopt various nonequilibrium shapes based on the interfacial jamming process. By varying concentrations of P[5]A derivatives and ascorbic acid (AA), we fine-tune the surface coverage of droplets, offering control over the jamming dynamics. Additionally, we introduce a signal amplification mechanism where the dephosphorylation of a dormant reductant by alkaline phosphatase (ALP) triggers the "click" reaction at the interface. This system enables the quantification of ALP activity through macroscopic surface changes with inhibition of ALP by heavy metals and metal chelators reducing surface coverage. This approach represents a promising method for amplifying molecular signals into detectable macroscopic outputs with potential applications in biochemical sensing and materials science.

Suppression of mycotoxins production and efficient chelation of heavy metals using natural melanin originated from Aspergillus flavus and Aspergillus carbonarius

BackgroundThis study employed melanin synthesized by Aspergillus flavus and Aspergillus carbonarius to inhibit the production of mycotoxins and bioremediation of heavy metals (HMs).MethodsFirst, twenty fungal isolates were obtained from soil samples, and were evaluated to produce melanin. The melanin of the most potent producers has undergone several confirmatory experiments, including, Dihydroxyphenylalanine (DOPA)-inhibitor-kojic acid pathway detection, High-performance liquid chromatography (HPLC), Fourier-transform infrared (FTIR) and Nuclear magnetic resonance (NMR). Additionally, the melanin production culture conditions were optimized. The antioxidant activity of melanin was detected with 1,1-Diphenyl-2-picrylhydrazyl (DPPH). HPLC was used to measure the mycotoxins produced in culture media supplemented with melanin. Molecular docking study investigated molecular interactions between melanin and mycotoxins through in silico approaches. FTIR and Energy-dispersive X-ray spectroscopy (EDX) were utilized to determine the percentage of melanin-chelated HMs, and an atomic absorption spectrophotometer (AAS) was used to detect HMs removal efficiency.ResultsThe melanin-enriched medium (0.3% and 0.4%) exhibited complete inhibition of aflatoxin B1 (AF-B1) by A. flavus and ochratoxin A (OTA) by A. carbonarius, respectively. Furthermore, melanin showed effective HM removal efficiency, increasing with melanin concentration. The removal efficiency of Cd+2 and Cr+6 by 1 mg/mL melanin was 49% and 63%, respectively. When the concentration of melanin was increased to 15 mg/mL, the removal efficiency of Cd+2 and Cr+2 increased to 60% and 77%, respectively.ConclusionThe study exhibited a natural approach for melanin production, using melanin as a heavy metal-chelating agent and capability to inhibit the production of aflatoxin B1 and ochratoxin A. Further, the study provides significant evidence regarding the bioremediation pipeline, for melanin production through biotechnological processes by filamentous fungi.

Synergy of biochar and biofertilizers to improve bell pepper fruit biochemical quality with increased soil carbon, Azospirillum population and mycorrhization

Sustainable crop production depends more on maintaining good soil health. Biochar significantly improves the soil's physical, chemical, biological and nutritional properties while aiding in carbon sequestration. Biofertilizers, which promote nutrient cycling, heavy metal chelation and the production of plant growth substances are crucial to sustainable agriculture. While the individual benefits of biochar and biofertilizers are well-documented, their combined effect in vegetable farming is less studied. The synergistic application of biochar and biofertilizers can improve soil health and nutrient dynamics, enhancing crops' biochemical properties. In a pot culture experiment, California Wonder bell peppers were treated with biochar and biofertilizers, including Azospirillum, Vesicular Arbuscular Mycorrhiza (VAM), and Serendipita indica. These were applied directly to the soil during transplanting. Results showed that plants treated with biochar + Azospirillum had higher flavonoid, total soluble protein and ascorbic acid content. Biochar + VAM treatment resulted in higher polyphenol content, total dry matter and root volume. S. indica reduced the vegetative period and induced earlier flowering. Biochar also increased soil organic carbon (2.89 %), improved the rhizosphere Azospirillum population and enhanced fungal endophytes' root colonization. Combining biochar and biofertilizer improves bell pepper plant performance, enhances biochemical parameters and improves soil health.

Preparation, characterization of pearl powder and its in vivo detoxification potential for heavy metals in mice

Rapid industrialization has heightened concerns over heavy metal pollution, its persistence in the environment, and the potential health risks posed to humans and ecosystems. Traditional Chinese Medicine (TCM) has utilized natural compounds for their medicinal properties, including detoxification, for centuries. This study aims to evaluate the detoxifying efficacy of pearl powder, derived from Hong Kong pearl oyster shells, a product with a long history of use in TCM, in chelating heavy metals like mercury, lead, and aluminium, and assess its protective effects against organ damage. Through a combination of in vitro and in vivo methodologies, In vitro experiments assessed pearl powder's chelation capabilities in controlled conditions, while in vivo studies in animal models investigated its impact on kidney and liver health and its overall safety profile. The results demonstrate that pearl powder, at doses up to 500 mg/kg body weight (b.w), effectively chelates heavy metals, facilitating their removal and offering protective effects against renal and liver damage. Safety assessments, including cytotoxicity and acute toxicity tests, confirmed the non-toxic nature of pearl powder, with a median lethal dose (lethal dose 50 %, LD50) of 5000 mg/kg body weight. Pearl powder from Hong Kong pearl oyster shells demonstrates significant potential as a natural detoxifying agent against heavy metal accumulation. These findings validate the traditional use of pearl powder in TCM, showcasing its potential as a natural remedy to mitigate heavy metal accumulation and its associated health risks. Integrating traditional knowledge with modern scientific methods, this research highlights the relevance of natural detoxifying agents in combating heavy metal pollution.

Exopolysaccharide-Producing Bacteria Regulate Soil Aggregates and Bacterial Communities to Inhibit the Uptake of Cadmium and Lead by Lettuce.

The accumulation of heavy metals in the soil not only causes serious damage to the soil ecosystem, but also threatens human health through the food chain. Exopolysaccharides have the functions of adsorbing and chelating heavy metals and reducing their bioavailability in the soil. In our study, exopolysaccharide-producing bacteria with a high efficiency in adsorbing cadmium (Cd) and lead (Pb) were screened from heavy metal-contaminated farmland. Through pot experiments, the influence of functional strains on the size distribution, heavy metal content, and bacterial community structure of soil aggregates in lettuce was studied using high-throughput sequencing technology. The results show that 11 strains secreting exopolysaccharides were initially screened from heavy metal-contaminated soil. Among them, strain Z23 had a removal rate of 88.6% for Cd and 93.2% for Pb. The rate at which Cd was removed by strain Z39 was 92.3%, and the rate at which Pb was removed was 94.4%. Both strains belong to Bacillus sp. Strains Z23 and Z39 induced the formation of Fe2Pb(PO4)2, Cd2(PO4)2, and Pb2O3 in the solution. The pot experiments showed that strains Z23 and Z39 increased (19.1~23.9%) the dry weight and antioxidant enzyme activity of lettuce roots and leaves, while reducing (40.1~61.7%) the content of Cd and Pb. Strains Z23 and Z39 increased the proportion of microaggregates (<0.25 mm) and the content of exopolysaccharides in rhizosphere soil and reduced (38.4-59.7%) the contents of available Cd and Pb in microaggregates, thus inhibiting the absorption of heavy metals by lettuce. In addition, the exopolysaccharide content and the bacterial community associated with heavy metal resistance and nitrogen (N) cycling (Patescibacteria, Saccharimonadales, Microvirga, and Pseudomonas) in microaggregates were key factors affecting the available heavy metal content in soil. These results show that the exopolysaccharide-producing bacteria Z23 and Z39 reduced the absorption of Cd and Pb by lettuce tissues, thus providing strain resources for the safe utilization of soils that exceed heavy metal standards for farmland and for reducing the heavy metal content in vegetables.

Transcriptomics combined with physiological analysis provided new insights into the enhancing Dendrobium nobile resilience to Cu stress through Ce modulation

In the face of escalating environmental challenges, understanding the mechanisms through which plants can resist heavy metal stress is paramount. This study delves into the efficacy of cerium (Ce), a rare earth element, in mitigating copper (Cu) toxicity in Dendrobium nobile Lindl., an orchid plant with significant medicinal and ornamental value. Through a comprehensive experimental approach that encompasses physiological, biochemical, and molecular analyses, we demonstrate that Ce application notably enhances D. nobile's tolerance to Cu stress. The investigation revealed that Ce supplementation significantly ameliorated the adverse effects of Cu on plant growth, evidenced by a notable decrease in Cu accumulation within the plant tissues. At the molecular level, transcriptome sequencing uncovered the upregulation of genes involved in antioxidant defense mechanisms, heavy metal chelation, and stress response signaling pathways. Key findings include the enhanced activities of antioxidant enzymes such as superoxide dismutase, peroxidase, and catalase, alongside an increase in the levels of antioxidants and phytochelatins, which collectively contribute to the detoxification of Cu. Furthermore, Ce was found to influence the subcellular distribution of Cu, promoting its sequestration in less harmful cellular compartments. Our study provides novel insights into the role of Ce in modulating plant responses to heavy metal stress, highlighting its potential as a mitigative agent against Cu toxicity. The elucidation of specific gene regulations and pathway activations offers a foundation for future research aimed at enhancing plant resilience to environmental stresses through biotechnological interventions.

The mitigating effects and mechanisms of Bacillus cereus on chronic cadmium poisoning in Litopenaeus vannamei based on histopathological, transcriptomic, and metabolomic analyses

Shrimp are non-negligible victims of cadmium (Cd) contamination, and there is still a lack of strategies for mitigating Cd toxicity in shrimp. Bacillus cereus, with its significant heavy metal (HM) tolerance and chelating effects, is a representative beneficial bacterium to be investigated for mitigating the toxicity of Cd exposure. This study revealed the effects and potential mechanisms of B. cereus in mitigating chronic Cd toxicity in shrimp by analyzing growth performance, hepatopancreatic Cd accumulation, pathology, as well as comprehensive hepatopancreatic transcriptomics and metabolomics in Litopenaeus vannamei. The results showed that shrimp's growth inhibition, hepatopancreatic Cd accumulation and physiological structure damage in B. cereus+chronic Cd group were effectively alleviated compared with the chronic Cd treatment group. The pathways related to amino acid metabolism, glycolipid metabolism, immune response, and antioxidant stress were significantly activated in the B. cereus+chronic Cd group, including glycolysis, pentose phosphate pathway, oxidative phosphorylation, biosynthesis of amino acids, and biosynthesis of unsaturated fatty acids pathways. The key differentially expressed genes (e.g., macrophage migration inhibitory factor, glycine cleavage system H protein, glycine dehydrogenase, phosphoglucomutase-2, asparaginase, ATP synthase subunit, cytochrome c, and 4-hydroxyphenylpyruvate dioxygenase) and metabolites (e.g., L-leucine, D-ribose, gluconic acid, 6-Phosphogluconic acid, sedoheptulose 7-phosphate, 1-Kestose, glyceric acid, arachidic acid, prostaglandins, 12-Keto-tetrahydro-leukotriene B4, and gamma-glutamylcysteine) associated with the above pathways were significantly altered. This study demonstrated that B. cereus is an effective mitigator for the treatment of chronic Cd poisoning in shrimp. B. cereus may play a role in alleviating the toxicity of Cd by enhancing the antioxidant performance, immune defense ability, metabolic stability, and energy demand regulation of shrimp. The study provides reference materials for the study of B. cereus in alleviating Cd toxicity of shrimp and broadens the application of probiotics in treating HM toxicity.

Fungal Peptidomelanin: A Novel Biopolymer for the Chelation of Heavy Metals.

Melanin is an amorphous, highly heterogeneous polymer found across all kingdoms of life. Although the properties of melanin can greatly vary, most forms are insoluble and strongly absorb light, appearing dark brown to black. Here, we describe a water-soluble form of melanin (peptidomelanin) secreted by the spores of Aspergillus niger (strain: melanoliber) during germination. Peptidomelanin is composed of an insoluble L-DOPA core polymer that is solubilized via short, copolymerized heterogeneous peptide chains forming a "corona" with a mean amino acid length of 2.6 ± 2.3. Based on in vitro experiments, we propose a biochemical copolymerization mechanism involving the hydroxylation of tyrosynylated peptides. Peptidomelanin is capable of chelating heavy metals such as lead, mercury, and uranium (as uranyl) in large quantities. Preliminary data indicates that peptidomelanin may have applications for the remediation of heavy metals in situ, including in agricultural settings.

Enhancing high-efficient cadmium biosorption of Escherichia coli via cell surface displaying metallothionien CUP1

ABSTRACT Cadmium (Cd) is one of the common heavy metal pollutants in soil, which can induce various diseases and pose a serious threat to human health. Metallothioneins (MTs) are well-known for their excellent metal binding ability due to a high content of cysteine, which has great potential for heavy metal chelation. In this study, we used the Escherichia coli (E. coli) surface display system LPP-OmpA to construct a recombinant plasmid pBSD-LCF encoding LPP-OmpA-CUP1-Flag fusion protein. Then we displayed the metallothionein CUP1 from Saccharomyces cerevisiae on E. coli DH5α surface for Cd removing. The feasibility of surface display of metallothionein CUP1 in recombinant E. coli DH5α (pBSD-LCF) by Lpp-OmpA system was proved by flow cytometry and western blot analysis, and the specificity of the fusion protein in the recombinant strain was also verified. The results showed that the Cd2+ resistance capacity of DH5α (pBSD-LCF) was highly enhanced by about 200%. Fourier-transform infrared spectroscopy showed that sulfhydryl and sulfonyl groups were involved in Cd2+ binding to cell surface of DH5α (pBSD-LCF). Meanwhile, Cd removal rate by DH5α (pBSD-LCF) was promoted to 95.2%. Thus, the recombinant strain E. coli DH5α (pBSD-LCF) can effectively chelate environmental metals, and the cell surface expression of metallothionein on E. coli can provide new ideas and directions for heavy metals remediation.

Preparation of a New Heavy Metal Chelating Agent and Its Removal of Copper Ions in Wastewater

In this study, a new type of dithiocarbamate (DTCs) heavy metal chelating agent MF-DTC was prepared by carbon disulfide modified melamine formaldehyde resin prepolymer, and the structure of the chelating agent and chelating products was characterized by infrared, ultraviolet, elemental analysis, thermogravimetry, scanning electron microscopy and other means: the process of chelating agent Cu was studied, and the results showed that MF-DTC chelating agent had a higher adsorption capacity, and compared with the traditional chelating agent SDD and Na2S, it had higher chelating capacity under acidic conditions, it can be directly used to treat heavy metals in acidic wastewater. Moreover, the environmental stability of heavy metals after chelation is high. Heavy metals are not easy to be leached again after treatment.

The Effect of Two Siderophore-Producing Bacillus Strains on the Growth Promotion of Perennial Ryegrass under Cadmium Stress.

Cadmium (Cd) is a highly toxic and cumulative environmental pollutant. Siderophores are heavy metal chelators with high affinity to heavy metals, such as Cd. Ryegrass (Lolium perenne L.) has a potential remediation capacity for soils contaminated by heavy metals. Consequently, using ryegrass alongside beneficial soil microorganisms that produce siderophores may be an effective means to remediate soils contaminated with Cd. In this study, the Bacillus strains WL1210 and CD303, which were previously isolated from the rhizospheres of Nitraria tangutorum in Wulan and Peganum harmala L. in Dachaidan, Qinghai, China, respectively, both arid and sandy environments, were evaluated for heavy metal pollution mitigation. Our quantitative analyses have discerned that the two bacterial strains possess commendable attributes of phosphorus (P) solubilization and potassium (K) dissolution, coupled with the capacity to produce phytohormones. To assess the heavy metal stress resilience of these strains, they were subjected to a cadmium concentration gradient, revealing their incremental growth despite cadmium presence, indicative of a pronounced tolerance threshold. The subsequent phylogenetic analysis, bolstered by robust genomic data from conserved housekeeping genes, including 16S rDNA, gyr B gene sequencing, as well as dnaK and recA, delineated a species-level phylogenetic tree, thereby confirming the strains as Bacillus atrophaeus. Additionally, we identified the types of iron-carrier-producing strains as catechol (WL1210) and carboxylic acid ferrophilin (CD303). A genomic analysis uncovered functional genes in strain CD303 associated with plant growth and iron carrier biosynthesis, such as fnr and iscA. Ryegrass seed germination assays, alongside morphological and physiological evaluations under diverse heavy metal stress, underscored the strains' potential to enhance ryegrass growth under high cadmium stress when treated with bacterial suspensions. This insight probes the strains' utility in leveraging alpine microbial resources and promoting ryegrass proliferation.

Effects of cadmium and zinc interactions on the physiological biochemistry and enrichment characteristics of Iris pseudacorus

Compound pollution with cadmium (Cd) and zinc (Zn) is common in nature. The effects of compounded Cd and Zn on the growth and development of Iris pseudacorus in the environment and the plant’s potential to remediate heavy metals in the environment remain unclear. In this study, the effects of single and combined Cd and Zn stress on I. pseudacorus growth and the enrichment of heavy metals in I. pseudacorus seedlings were investigated. The results showed that under Cd (160 μM) and Zn (800 μM) stress, plant growth was significantly inhibited and photosynthetic performance was affected. Cd+Zn200 (160 μM + 200 μM) reduced the levels of malondialdehyde, hydrogen peroxide, and non-protein thiols by 31.29%, 53.20%, and 13.29%, respectively, in the aboveground tissues compared with levels in the single Cd treatment. However, Cd+Zn800 (160 μM + 800 μM) had no effect. Cd and Zn800 inhibited the absorption of mineral elements, while Zn200 had little effect on plants. Compared with that for Cd treatment alone, Cd + Zn200 and Cd+Zn800 reduced the Cd content in aboveground tissues by 54.15% and 49.92%, respectively, but had no significant effect on Cd in the root system. Zn significantly reduced the Cd content in subcellular components and limited the content and proportion of Cd extracted using water and ethanol. These results suggest that a low supply of Zn reduces Cd accumulation in aboveground tissues by promoting antioxidant substances and heavy metal chelating agents, thus protecting the photosynthetic systems. The addition of Zn also reduced the mobility and bioavailability of Cd to alleviate its toxicity in I. pseudacorus.

Glycine-Rich RNA-Binding Protein AtGRP7 Functions in Nickel and Lead Tolerance in Arabidopsis.

Plant glycine-rich RNA-binding proteins (GRPs) play crucial roles in the response to environmental stresses. However, the functions of AtGRP7 in plants under heavy metal stress remain unclear. In the present study, in Arabidopsis, the transcript level of AtGRP7 was markedly increased by Ni but was decreased by Pb. AtGRP7-overexpressing plants improved Ni tolerance, whereas the knockout mutant (grp7) was more susceptible than the wild type to Ni. In addition, grp7 showed greatly enhanced Pb tolerance, whereas overexpression lines showed high Pb sensitivity. Ni accumulation was reduced in overexpression lines but increased in grp7, whereas Pb accumulation in grp7 was lower than that in overexpression lines. Ni induced glutathione synthase genes GS1 and GS2 in overexpression lines, whereas Pb increased metallothionein genes MT4a and MT4b and phytochelatin synthase genes PCS1 and PCS2 in grp7. Furthermore, Ni increased CuSOD1 and GR1 in grp7, whereas Pb significantly induced FeSOD1 and FeSOD2 in overexpression lines. The mRNA stability of GS2 and PCS1 was directly regulated by AtGRP7 under Ni and Pb, respectively. Collectively, these results indicate that AtGRP7 plays a crucial role in Ni and Pb tolerance by reducing Ni and Pb accumulation and the direct or indirect post-transcriptional regulation of genes related to heavy metal chelators and antioxidant enzymes.

Optimization of Siderophore Production in Three Marine Bacterial Isolates along with Their Heavy-Metal Chelation and Seed Germination Potential Determination.

Siderophores are low-molecular-weight and high-affinity molecules produced by bacteria under iron-limited conditions. Due to the low iron (III) (Fe+3) levels in surface waters in the marine environment, microbes produce a variety of siderophores. In the current study, halophilic bacteria Bacillus taeanensis SMI_1, Enterobacter sp., AABM_9, and Pseudomonas mendocina AMPPS_5 were isolated from marine surface water of Kalinga beach, Bay of Bengal (Visakhapatnam, Andhra Pradesh, India) and were investigated for siderophore production using the Chrome Azurol S (CAS) assay. The effect of various production parameters was also studied. The optimum production of siderophores for SMI_1 was 93.57% siderophore units (SU) (after 48 h of incubation at 30 °C, pH 8, sucrose as carbon source, sodium nitrate as nitrogen source, 0.4% succinic acid), and for AABM_9, it was 87.18 %SU (after 36 h of incubation period at 30 °C, pH 8, in the presence of sucrose, ammonium sulfate, 0.4% succinic acid). The maximum production of siderophores for AMPPS_5 was 91.17 %SU (after 36 h of incubation at 35 °C, pH 8.5, glucose, ammonium sulfate, 0.4% citric acid). The bacterial isolates SMI_1, AABM_9, and AMPPS_5 showed siderophore production at low Fe+3 concentrations of 0.10 µM, 0.01 µM, and 0.01 µM, respectively. The SMI_1 (73.09 %SU) and AMPPS_5 (68.26 %SU) isolates showed siderophore production in the presence of Zn+2 (10 µM), whereas AABM_9 (50.4 %SU) exhibited siderophore production in the presence of Cu+2 (10 µM). Additionally, these bacterial isolates showed better heavy-metal chelation ability and rapid development in seed germination experiments. Based on these results, the isolates of marine-derived bacteria effectively produced the maximum amount of siderophores, which could be employed in a variety of industrial and environmental applications.

Sodium dimethyl dithiocarbamate, as a capable heavy metal chelating agent: Production and applications

Sodium dimethyl dithiocarbamate (SDDC) is a universal heavy metal precipitant/chelating agent, which is widely used in the treatment of heavy metals in industrial wastewater and fly ash from waste incineration. It can be utilized as a heavy metal precipitant, fungicide, agricultural insecticide, rubber vulcanization accelerator, styrene-butadiene rubber polymerization terminator, polymerization inhibitor, mineral processing reagent, etc. This review article focuses on the research of the production and application of SDDC in heavy metal chelation. The following three benefits of using SDDC as a heavy metal chelating agent are: (1) it can chelate with various heavy metal ions at room temperature to generate insoluble chelate salts and precipitates, which can be easily removed; (2) SDDC can perform chelation reaction with varies heavy metal ions at the same time; (3) as a heavy metal chelating agent, SDDC is simple to use and low costs, which is significantly better than other heavy metal chelating agents and precipitants. This review paper presents novel ideas for the performance enhancement based on SDDC in removing heavy metals and is a prospect for the research, development, production, and applications of SDDC.

Stabilization effect of chelating agents on heavy metals in two types of municipal solid waste incineration fly ash

Municipal solid waste incineration (MSWI) fly ash is complex in composition and contains large amounts of heavy metals. To investigate the effects of different passivating agents on Cd, Pb, Cr, Ni and Zn in different types of fly ash, 7 reagents were selected as passivating agents, including 3 inorganic reagents (Na2S, Na3PO4, NaH2PO4) and 4 organic reagents (SDD, DDTC, TMT, thiourea). The results showed that at low addition levels, sulfur-containing organic chemicals and phosphates were more effective in chelating these metals in both grate furnace incineration fly ash (GF FA) and circulating fluidised bed incineration fly ash (CFB FA), while Na2S was more effective in chelating heavy metals in CFB FA. In addition, agents containing -N-CS groups showed better chelation of heavy metals in GF FA, while heavy metals in CFB FA were more affinity to agents containing -SH groups. The ternary compound TMT-NaH2PO4-SDD (m1:m2:m3 = 2:3:1) was an excellent chelating agent for Pb, Cd in the GF FA, and TMT-Na2S-thiourea (m1:m2:m3 = 2:1:3) was a suitable chelating agent for these metals in CFB FA. The chelation rate of Cd and Pb after the treatments mixed ternary reagents was above 99%, and the leaching amount was much lower than the limit value of pollution control standards for domestic landfills. Moreover, under different pH leaching conditions, the leaching concentrations of Cd and Pb in the fly ashes treated with the ternary mixture were lower than the standard limits. In general, the ternary compound can effectively chelate heavy metals in fly ash, which provides a reference for selecting a suitable stabilizer combination for heavy metal in fly ash.

Bioremediation of heavy metal-contaminated environment: developed strategies and potential use of biosurfactants as chelators

Abstract Heavy metal pollution damages the ecosystems and presents a major problem for public health. Thus, an urgent need was developed to decrease the high levels of heavy metals in the soil and aquatic environments. With this aim, numerous physicochemical strategies were developed. However, they are money-consuming, require the use of energy and chemical additives and can release secondary compounds that can pollute and cause great damage to the environment. Then, biological methods based on the investigation of bacteria, fungi and plants along with their derived secondary active metabolites became the best alternatives. Using plant capacities, different phytoremediation strategies were developed such as phytoextraction, phytovolatilization, rhizofiltration and phytostabilization. Regarding bioremediation, bacterial biosorption of heavy metals, biolixiviation and lagooning offer great potential for their environmental cleaning. Additionally, the use of secondary active metabolites, such as biosurfactants, is well-studied. Generally, they are a class of structurally very varied molecules commonly synthesized by many microorganisms with amphiphilic character. Owing to their anionic charge, they have the capacity to sequestrate heavy metals permitting their elimination. Glycolipids and lipopeptides are among the most recognized biosurfactants with interesting heavy metal chelating properties.

Thermochemical heat storage utilization of MSWI fly ash after carbonation enhancement with ammonia water regulation: Carbon sequestration efficiency, heavy metal immobilization, and heat storage characteristics analysis

Accelerated carbonation is an effective method of treating municipal solid waste incineration fly ash (FA). However, the efficiency of CO2 sequestration is limited and the usage of products is uncertain. This study proposed a method for enhancing carbonation by ammonia water (NH4OH) regulation and thermochemical heat storage of its products. The influences of NH4OH on CO2 sequestration and heavy metals immobilization were investigated. The results demonstrated that the carbon sequestration efficiency improved from 65.2% to 98.3%, with the NH4OH addition increasing (0–20%). NH4OH promoted the conversion of calcium chloride (CaCl2) and calcium sulfate (CaSO4), which were not originally involved in the carbonation reaction, to calcium carbonate (CaCO3). Excess NH4OH increased the release of heavy metals into the liquid phase due to the chelation of heavy metals by ammonia ions (NH4+) and the effect of high pH. The appropriate amount of NH4OH (8%) offered a high-efficient immobilization of heavy metals. The energy density of FA samples increased from 226.6 kJ/kg to 1207.8 kJ/kg with the NH4OH addition increasing, positively correlating with the content of CaCO3. After the thermal cycle treatment, the non-ammonia carbonated FA had a serious sintering phenomenon with chlorellestadite (Ca5(P,Si,S)3O12(Cl,OH,F)), which was produced from the reaction between CaSO4 and other compounds; while the carbonated FA with NH4OH addition (8%) showed good thermal cycle stability with fine particles and single component (calcium oxide). Therefore, the carbonation treatment in this study is a novel and highly-efficient method, with the final products providing an alternative material for thermochemical heat storage.

Microbial Melanin: Renewable Feedstock and Emerging Applications in Food-Related Systems

Melanin is among the most important natural pigments produced by various organisms, from microbes to plants and mammals. Melanins possess great properties such as radioprotective and antioxidant activity, heavy metal chelation and absorption of organic compounds. The biosynthesis of melanin through the DOPA metabolic pathway and/or the DHN pathway mainly involves the tyrosinase and laccase enzymes that catalyze the oxidation of phenolic and indolic substrates to form melanin classes, namely eumelanin, pheomelanin, allomelanins and pyomelanin. The cost-efficient production of melanin at a large scale, with a chemically specified composition, constitutes a major technical challenge. Alternative production routes including highly efficient microbial stains cultivated on renewable resources could sustain and up-scale melanin production capacity. The strategy of valorizing low-cost and abundant agro-industrial waste and byproduct streams complies with concepts of sustainable development and circular economy, thus eliminating the environmental footprint. Genetic engineering tools could substantially contribute to enhancing melanogenesis in natural producers via target gene overexpression and the recombination of novel strains. The production of biobased films for food packaging applications reinforced with melanin nanoparticles constitutes a market segment of high interest due to environmental and societal concerns around the end-of-life management of conventional plastics, gradual depletion of fossil resources, sustainability issues and high performance.