Multiple Heavy Metals Research Articles

Mixed heavy metal stress induces global iron starvation response

Multiple heavy metal contamination is an increasingly common global problem. Heavy metals have the potential to disrupt microbially mediated biogeochemical cycling. However, systems-level studies on the effects of combinations of heavy metals on bacteria are lacking. For this study, we focused on the Oak Ridge Reservation (ORR; Oak Ridge, TN, USA) subsurface which is contaminated with several heavy metals and high concentrations of nitrate. Using a native Bacillus cereus isolate that represents a dominant species at this site, we assessed the combined impact of eight metal contaminants, all at site-relevant concentrations, on cell processes through an integrated multi-omics approach that included discovery proteomics, targeted metabolomics, and targeted gene-expression profiling. The combination of eight metals impacted cell physiology in a manner that could not have been predicted from summing phenotypic responses to the individual metals. Exposure to the metal mixture elicited a global iron starvation response not observed during individual metal exposures. This disruption of iron homeostasis resulted in decreased activity of the iron-cofactor-containing nitrate and nitrite reductases, both of which are important in biological nitrate removal at the site. We propose that the combinatorial effects of simultaneous exposure to multiple heavy metals is an underappreciated yet significant form of cell stress in the environment with the potential to disrupt global nutrient cycles and to impede bioremediation efforts at mixed waste sites. Our work underscores the need to shift from single- to multi-metal studies for assessing and predicting the impacts of complex contaminants on microbial systems.

AN INTEGRATED APPROACH FOR SAFE REMOVAL OF CHROMIUM (VI) BY BREVIBACTERIUM SP.

Chromium (VI) tolerant Brevibacterium sp. AKR2 was isolated from the tannery effluent polluted site and consequently screened for chromate removal potential and exopolymer production. This strain showed stable growth with white-gray colonies on LB-agar plates supplemented with chromate (1500mg/L). Strain AKR2 was taxonomically identified by 16S rRNA sequencing as Brevibacterium sp. (MN932133). Presumptive biochemical tests were also performed. This strain was found to have multiple heavy metals and antibiotic tolerance patterns. Additionally, the tolerance profile of Brevibacterium sp. against Cr(VI) (2-30mg/mL) was investigated. Cr(VI) reduction ability at 1000 and 1500mg/L of K2CrO4 highlighted that the strain AKR2 reduced 91 and 86% of chromate oxyanions, respectively, after 24h of incubation. Enhanced exopolymer i.e. 1.275mg/mL dry weight was observed by growing in LB-broth medium under chromate stress conditions 1500mg/L as compared to EPS yield under non-stress 0.15mg/mL. Hence, the current investigation suggests the possible use of chromate resistant Brevibacterium sp. as an emerging tool for remediating the sites polluted with elevated levels of Cr(VI).

Nanovesicle and extracellular polymeric substance synthesis from the remediation of heavy metal ions from soil

Heavy metal toxicity affects aquatic plants and animals, disturbing biodiversity and ecological balance causing bioaccumulation of heavy metals. Industrialization and urbanization are inevitable in modern-day life, and control and detoxification methods need to be accorded to meet the hazardous environment. Microorganisms and plants have been widely used in the bioremediation of heavy metals. Sporosarcina pasteurii, a gram-positive bacterium that is widely known for its calcite precipitation property in bio-cementing applications has been explored in the study for its metal tolerance ability for the first time. S. pasteurii SRMNP1 (KF214757) can tolerate silver stress to form nanoparticles and can remediate multiple heavy metals to promote the growth of various plants. This astounding property of the isolate warranted extensive examinations to comprehend the physiological changes during an external heavy metal stress condition. The present study aimed to understand various physiological responses occurring in S. pasteuriiSRMNP1 during the metal tolerance phenomenon using electron microscopy. The isolate was subjected to heavy metal stress, and a transmission electron microscope examination was used to analyze the physiological changes in bacteria to evade the metal stress. S. pasteurii SRMNP1 was tolerant against a wide range of heavy metal ions and can withstand a broad pH range (5–9). Transmission Electron Microscopy (TEM) examination of S. pasteurii SRMNP1 followed by 5 mM nickel sulfate treatment revealed the presence of nanovesicles encapsulating nanosized particles in intra and extracellular spaces. This suggests that the bacteria evade the metal stress by converting the metal ions into nanosized particles and encapsulating them within nanovesicles to efflux them through the vesicle budding mechanism. Moreover, the TEM images revealed an excessive secretion of extracellular polymeric substances by the strain to discharge the metal particles outside the bacterial system. S. pasteurii can be foreseen as an effective bioremediation agent with the potential to produce nanosized particles, nanovesicles, and extracellular polymeric substances. This study provides physiological evidence that, besides calcium precipitation applications, S. pasteurii can further be explored for its multidimensional roles in the fields of drug delivery and environmental engineering.

Clean hydrometallurgical route for highly efficient decontamination and recycling of multiple heavy metals from hazardous Pb smelting residues: Multi-objective leaching optimization, adsorption, and risk assessment

Huge amounts of Pb smelting residues were generally stored in landfills or unprocessed worldwide, and thus demand novel strategies to implement clean production. In this paper, we proposed a clean, efficient and economical hydrometallurgical route to recycle the toxic heavy metals including Zn, Pb and Cd from the Pb residue by the biodegradable low-molecular-weight organic acids (LMWOAs) and the cation exchange resin (CER, 001 × 7). The multi-objective leaching process of the three metals was optimized by combining saturated D-optimal design with desirability function simultaneously. The recovery rates of Zn, Pb and Cd were 88.72–96.36, 65.40–85.31 and 92.63–97.10% at the optimal conditions of 0.73–1.00 mol L−1 agent concentrations, 2.0–3.3 solution pH values and 71–120 min durations, respectively. Adsorption with CER from the resulting leachates recycled over 91.48% of the metal ions. The treated residues were almost completely decontaminated. Therefore, this research filled the gap of clean production route of hydrometallurgical recycling for metal resources from the low-grade slag.

Fluorescent sensor array based on Janus silica nanoflakes to realize pattern recognition of multiple aminoglycoside antibiotics and heavy metal ions

The development of highly sensitive and selective chemical sensor arrays that can be used for the recognition of multiple organic and inorganic compounds has been a pressing demand and persistent challenge. We combined the Pickering emulsion and quantum dots (QDs) doping technology to fabricate Janus silica nanoflakes–based fluorescence sensor arrays for the pattern recognition of multiple heavy metal ions and aminoglycoside antibiotics. Janus silica nanoflakes were embedded with green and red light–emitting CdTe QDs as signal sensing units. The aptamer and sulfhydryl-specific recognition elements were modified and attached to the sides for the simultaneous recognition of heavy metal ions and aminoglycosides. The thiol groups chelated the target metal ions, resulting in the fluorescence quenching of the QDs. The aptamers provided specific recognition sites for aminoglycosides, and the fluorescence intensities of the QDs were enhanced in the presence of aminoglycosides. The parameters characterizing the fluorescence sensor array were optimized, and by analyzing the fluorescence response patterns following the linear discriminant analysis method, we observed that the sensor array could discriminate between the target compounds successfully. Finally, Cu2+ and Co2+ were detected in crayfish samples, and the results were confirmed following the inductively coupled plasma atomic emission spectroscopy technique.

Silicon-Rich Biochar Detoxify Multiple Heavy Metals in Wheat by Regulating Oxidative Stress and Subcellular Distribution of Heavy Metal

Silicon is a quasi-essential trace nutrient for plant growth and is frequently employed to remediate soils of heavy metal pollution in agriculture. However, silicon’s role and mechanism in reducing heavy metal toxicity have not been well understood, especially for multi-heavy metals such as cadmium, zinc, lead, and arsenic (usually treated as a heavy metal). In this study, the effects of different silicon-rich materials (silicate, rice husk biochar (RHB), and RHB + bentonite) on growth trait, antioxidant response, heavy metal accumulation, and distribution of wheat grown in two soils polluted by multiple heavy metals (Cd, Zn, Pb, and As) were investigated. The results revealed that the addition of silicon-rich materials enhanced plant growth, improved the photosynthetic attributes in leaf tissues, and decreased the contents of Cd, Zn, Pb, and As in wheat shoots and grains. The examination of the subcellular distribution of heavy metals in plants implied that silicon-rich materials transferred heavy metals as intracellular soluble fractions to the cell walls, indicating the reduction of mobility and toxicity of heavy metals in the plants. In addition, the application of the silicon-rich materials reduced oxidative damage in plants by downregulating plant antioxidant response systems and decreasing the production of malondialdehyde (MDA), ascorbic acid (AsA), and glutathione (GSH). Moreover, fractionation analysis of soil heavy metals showed that silicon-rich amendments could convert bioavailable heavy metals into immobilized forms. With the comparation of different silicon-rich materials, combined RHB and bentonite could better remediate multi-heavy metal-polluted soils and promote wheat production. The effect of the silicate component was stressed in this paper but some of the potential benefits might have arisen from other components of the biochar.

Exploration and removal of multiple metal ions using mixed-linker-architected Zn-MOF in aqueous media

A Zn-based 3D MOF, [Zn2(H3L1)(L2)].H2O named PUC-5 was synthesized using trimesic acid (H3L1) and 1-(3-aminopropyl)Imidazole (L2) by solvothermal method. PUC-5 has been characterized using SCXRD, PXRD, FT-IR, SEM, XPS, TGA, BET and Zeta potential techniques. The PUC-5 exhibited extremely high water and pH stability. We explored the utility of PUC-5 as a sensitive probe for the detection and removal of multiple heavy metal ions (Fe2+, Pb2+ and V5+) from water. The detection limits calculated in the case of Fe2+, Pb2+ and V5+ were 0.129 µM, 0.113 µM and 0.246 µM which were found to be lower than the limits established by the world health organisation (WHO) for drinking water. The detection ability of PUC-5 towards targeted metal ions was further confirmed by Zeta potential, FTIR and XPS techniques. Moreover, the adsorption potential of PUC-5 towards Fe2+, Pb2+ and V5+ was studied by the ICP-MS method. Different kinetic and isotherm models were used to assess the effects of time, temperature, adsorbent content and initial metal ions concentration on PUC-5′s ability to adsorbFe2+, Pb2+, and V5+. The adsorption process of metal ions could be well depicted by Pseudo-second-order kinetics and Langmuir isotherm models suggesting monolayer chemisorption with maximum adsorption capacities of 208.7, 192.6 and 203.6 mg g−1 for Fe2+, Pb2+ and V5+ respectively. Furthermore, the thermodynamic parameters support the spontaneous behaviour and exothermic nature of the adsorption process. Interestingly, PUC-5 is a recyclable material and can be reused with high adsorption efficiency suggesting a high potential of adsorbent towards Fe2+, Pb2+ and V5+.

A Logic Fluorescent Chemosensor Based on Eu3+ Functionalized Cd‐MOFs for Sensing Fe3+ and Cu2+ Synchronously

AbstractOne of the most critical and yet unsolved issues is the effective monitoring of multiple heavy metal ions in complex systems through their specific function in fluorescence detection. In this work, luminescence‐active cadmium base metal‐organic frameworks (Cd‐MOFs) based on the planar and rigid π‐conjugated structure ligand benzo‐(1,2;3,4;5,6)‐tris (thiophene‐2’‐carboxylic acid) (H3BTTC) was chosen. A series of sensing experiments demonstrated that the Cd‐MOFs exhibits selective and sensitive response for Fe3+ and Eu3+ through fluorescence “turn off” and “antenna effect” respectively. In addition, the encapsulation of Eu3+ inside the Cd‐MOFs (Eu3+@Cd‐MOFs) led to an excellent probe with dual emission. To this end, a programmable fluorescence platform was developed to detect Fe3+ and Cu2+, in which the emission peaks of both the ligand and Eu3+ are completely quenched by Fe3+. The ratiometric detection of Cu2+ leads to a decrease in Eu3+ emission, while the ligand emission remains stable. To demonstrate the strategy, the fluorescence (Output) of Cd‐MOFs, Eu3+@Cd‐MOFs, and the analytes (Eu3+, Fe3+, and Cu2+, input) achieved elementary Boolean logic operations (OR, NOR, AND) and they constitute a logic fluorescent chemosensor to analyze Fe3+ and Cu2+ synchronously.

Preparation of iron/calcium-modified biochar for phosphate removal from industrial wastewater

Phosphorous pollution is one of the main factors causing water eutrophication. For the treatment of wastewater, metal-modified biochar has emerged as a promising adsorbent with enhanced affinity for anions such as phosphate. Biochar modified with Fe or Ca are suitable for the treatment of low-concentration phosphorous wastewater (<100mg/L). However, the use of modified biochar to remove high concentrations of phosphate from industrial wastewater is challenging. In this study, biochar from poplar wood, wheat bran, bagasse, and bamboo were prepared and loaded with Fe and Ca, and its adsorption performance and degradation mechanism in the presence of high phosphate concentrations were investigated. The phosphate adsorption capacity of the Fe/Ca-modified biochar was 12–70 times higher than that before the modification. The best type of biochar for phosphate removal was iron/calcium oxide-modified bamboo biochar (ZFCO-BC) through batch experiments. X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) analyses showed that ZFCO-BC reacted with wastewater to produce stable vivianite (Fe3(PO4)2·(H2O)8), which did not cause secondary release. ZFCO-BC exhibited a synergistic effect on the removal of 21 metals, including Cr, Cu, Co, Cd, As, Pb, and Y, from complex polluted water. Meanwhile, after 48 h of reaction, the concentration of phosphate decreased from 1660 to 0.061 mg/L, and the final value in the wastewater was lower than the phosphate discharge index indicated by the GB T31962-2015 Sewage Discharge into Urban sewer Water Quality Standard. This study shows that a single remediation system based on ZFCO-BC can remove phosphate and multiple heavy metals from contaminated water, providing a cost-effective treatment solution for complex polluted water bodies, such as industrial wastewater and groundwater.

Prevalence of Antibiotics and Cr, Cd, Cu Metals Co-resistant Coliforms in Refuse Dumpsites and Air of Surrounding Buildings in a Nigerian Urban Setting

Prevalence of co-resistance to antibiotics and Cr6+, Cd2+, and Cu2+ among coliforms from dumpsites and surrounding buildings’ indoor and outdoor air was investigated in Warri town, in the Niger Delta region of Nigeria. A total of 1,465 coliforms were isolated with McConkey and Eosin Methylene Blue Agar, and 38.8% had multiple antibiotics resistance (MAR) index ≥ 0.3 based on nine antibiotics. The prevalence of coliform bacteria with a MAR index of ≥ 0.3 varied (20.0 - 69.2%) and was lower in indoor and outdoor air farther away from the dumpsites. All dumpsite isolates were resistant to Cr and Cd but not to Cu, while resistance varied (48.5 - 100%) among indoor and outdoor air isolates. Plasmid-encoded resistance was indicated when the mean MAR (0.48 ± 0.04 - 0.5 ± 0.04) and multiple heavy metal resistance (MHMR) indexes (0.66 ± 0.00) declined to 0.11 ± 0.01 - 0.36 ± 0.03 and 0.33 ± 0.00, respectively, after curing. The differences in MAR indexes of isolates from the four dumpsite locations and between indoor and outdoor air isolates were only significant (P &lt; 0.05) after curing, unlike the MHMR index, where there was no significant difference before and after curing. The prevalence of metals and antibiotics co-resistance, which was based on the concomitant reduction in MAR and MHMR indexes after curing, was higher in isolates from dumpsites than in indoor and outdoor air (32.1 - 38.1 vs 0.0 - 16.8%). The role of plasmid-encoded genes in the co-resistance phenomenon was therefore indicated. Dumpsites as selective pressure spots for the emergence of resistance genes in bacteria should be of public health concern in countries characterised by indiscriminate dumping of wastes, as this can result in potential spread to houses via bioaerosols.

Highly permeable positively charged nanofiltration membranes with multilayer structures for multiple heavy metal removals

Positively charged nanofiltration (NF) membranes have been vitally employed to treat heavy metal ions contained in wastewater. Nevertheless, positively charged NF membranes possessing both high permeance and rejections continue to be a bottleneck in engineering applications owing to the trade-off between rejection and permeance. Herein, a highly permeable and positively charged NF membrane with multilayer structures was prepared using a chitosan interlayer-assisted low-temperature interfacial polymerization and surface grafting polyethyleneimine (CIL-IP-P) strategy. The chemical components, surface morphologies, and separation characteristics of the prepared NF membranes were investigated systematically. The construction of a chitosan interlayer increased hydrophilicity and influenced the IP reaction by modulating the monomer diffusion. Grafting polyethyleneimine (PEI) further resulted in NF membranes with higher electro-positivity, larger specific surface area, and narrower average pore diameter. Hence, the trade-off between rejection and permeance in conventional positively charged NF membranes was surmounted. An excellent water permeance of 10.9 ± 0.6 L m−2 h−1 bar−1 and a satisfactory rejection for heavy metals (93.3, 92.8, 91.0, 90.4, and 89.2 % for Ni2+, Mn2+, Cu2+, Cd2+, and Pb2+) were observed. The CIL-IP-P strategy provided in this study is promising to tailor a high-performance positively charged NF membrane for fast heavy metal removals.

Simultaneous electrochemical detection of multiple heavy metal ions in milk based on silica-modified magnetic nanoparticles

A sensitive and simple analytical method integrated with Fe3O4@SiO2-based extraction with direct electrochemical detection was applied to individually and simultaneously analyze heavy metal ions, including Cd2+, Pb2+, Cu2+, and Hg2+. The Fe3O4@SiO2-based electrochemical sensor was developed through the mixture of heavy metal ions with Fe3O4@SiO2 after alkali treatment, which was modified onto the working electrode surface. The Fe3O4@SiO2 with negative charges after alkali treatment could easily interact with heavy metal ions with positive charges by electrostatic force. Under the optimized conditions, the developed analytical method could be applied to individually and simultaneously detect heavy metal ions with good sensitivity. The detection limits were all in the nanomolar range, and the recoveries ranged from 96.0 to 104.3% for heavy metal ions in milk. Therefore, the proposed analytical method exhibited great potential for quantitatively analyzing multiple heavy metal ions in milk.

Novel Plasmid Carrying Mobile Colistin Resistance Gene mcr-4.3 and Mercury Resistance Genes in Shewanella baltica: Insights into Mobilization of mcr-4.3 in Shewanella Species.

Shewanella species have been identified as progenitors of several clinically important antibiotic resistance genes. The aim of our study was to analyze Shewanella baltica strains isolated from the gut contents of wild Atlantic mackerel (Scomber scombrus) for the presence of both known and novel variants of antibiotic resistance genes (ARGs), using Illumina-based whole-genome sequencing (WGS). Thirty-three S. baltica strains were isolated from Atlantic mackerel collected in the northern North Sea. WGS revealed the presence of several new variants of class C and class D beta-lactamases. Nearly 42% (14/33) of the strains carried the mobile colistin resistance gene mcr-4.3. To understand the genetic context of mcr-4.3, we determined the complete genome sequence of strain 11FHM2, using a combination of Oxford Nanopore- and Illumina-based sequencing. The complete genome sequence is 5,406,724 bp long, with one contig representing a chromosome of 5,068,880 bp and three contigs representing novel plasmids (pSBP1, 194,145 bp; pSBP2_mcr4, 86,727 bp; and pSBP3, 56,972 bp). Plasmid pSBP2_mcr4 contains the mobile colistin resistance gene mcr-4.3, as well as the mercury resistance operon merRPAT. Plasmid pSBP1 carries genes encoding resistance against copper, zinc, chromium, and arsenic. Plasmid pSBP3 does not carry any antibiotic or heavy metal resistance genes. Analysis of the flanking region of mcr-4.3 suggests that a phage integrase may be involved in the mobilization of mcr-4.3 in Shewanella spp. Our results provide insights into the mobile mcr-4.3 present in Shewanella spp. and highlight the importance of the marine environment in the emergence and dissemination of clinically important resistance genes. IMPORTANCE We identified two new plasmids in Shewanella baltica isolated from wild Atlantic mackerel (Scomber scombrus) collected from the northern North Sea, one plasmid carrying the mcr-4.3 gene for colistin resistance and the operon merRPAT for mercury resistance and the other carrying multiple heavy metal resistance genes. The marine environment has been recognized as a source of new resistance genes that are found in human pathogens. Selection pressure from heavy metals is seen in the marine environment, especially associated with human activities, such as waste discharge, mining, and in aquaculture settings. This would help maintain and disseminate these plasmids in the environment. Our study provides insights into the mobilization of colistin resistance genes in Shewanella spp. and highlights the importance of the marine environment in the emergence and dissemination of clinically important antibiotic resistance genes.

A spatial distribution – Principal component analysis (SD-PCA) model to assess pollution of heavy metals in soil

With the rapid development of urbanization, heavy metal pollution of soil has received great attention. Over-enrichment of heavy metals in soil may endanger human health. Assessing soil pollution and identifying potential sources of heavy metals are crucial for prevention and control of soil heavy metal pollution. This study introduced a spatial distribution - principal component analysis (SD-PCA) model that couples the spatial attributes of soil pollution with linear data transformation by the eigenvector-based principal component analysis. By evaluating soil pollution in the spatial dimension it identifies the potential sources of heavy metals more easily. In this study, soil contamination by eight heavy metals was investigated in the Lintong District, a typical multi-source urban area in Northwest China. In general, the soils in the study area were lightly contaminated by Cr and Pb. Pearson correlation analysis showed that Cr was negatively correlated with other heavy metals, whereas the spatial autocorrelation analysis revealed that there was strong association in the spatial distribution of eight heavy metals. The aggregation forms were more varied and the correlation between Cr contamination and other heavy metals was lower. The aggregation forms of Mn and Cu, Zn and Pb, on the other hand, were remarkably comparable. Agriculture was the largest pollution source, contributing 65.5 % to soil pollution, which was caused by the superposition of multiple heavy metals. Additionally, traffic and natural pollution sources contributed 17.9 % and 11.1 %, respectively. The ability of this model to track pollution of heavy metals has important practical significance for the assessment and control of multi-source soil pollution.

A Fully Integrated, Ready-to-Use Distance-Based Chemosensor for Visual Quantification of Multiple Heavy Metal Ions.

Point-of-care devices offering quantitative results with simple steps would allow great useability for untrained end-users. Here, we report a ready-to-use chemosensor integrating automatic sample metering, on-chip reaction, gravitational-magnetic separation, and a distance-based readout for visual quantification of multiple heavy metal ions. Deoxyribozymes (DNAzymes), probe-modified magnetic microparticles (MMPs), and polystyrene microparticles (PMPs) are preloaded into a microfluidic chip and freeze-dried. After the water sample is collected with automatic volume metering, the particles are resuspended, and the MMPs and PMPs hybridize with DNAzyme at its two termini, forming the "MMPs-DNAzyme-PMPs" structure. When target metal ions are present, the DNAzymes are cleaved, yielding an increased number of free PMPs. All on-chip reactions are controlled by stopping the liquid flow at capillary valves and bursting it with hand-controlled tilting. Using the chip with a gravitational-magnetic separator, the free PMPs are separated from "MMPs-DNAzyme-PMPs" and accumulate into the trapping channel with a nozzle, forming a visual bar with growing distances proportional to the concentration of target metal ions. The achieved limit of detection (LOD) values for Cu2+ (103.1 nM), Pb2+ (69.5 nM), and Ag+ (793.6 nM) are below the maximum contamination levels. High selectivity of 100-fold, 200-fold, and 20-fold against interference is obtained. Moreover, by integrating three identical channels in parallel, simultaneous detection of the above-mentioned heavy metal ions in fresh and tap water samples is also achieved with high accuracy. Together, this fully integrated and easily operated platform embodies excellent potential for rapid, on-site sensing by unskilled users.

Bioremediation of Multiple Heavy Metals Mediated by Antarctic Marine Isolated Dietzia psychralcaliphila JI1D

Extreme environments host numerous microorganisms perfectly adapted to survive in such harsh conditions. In recent years, many bacteria isolated from these inhospitable environments have shown interesting biotechnological applications, including the bioremediation of polluted sites by hydrocarbons and heavy metals. In this work, we present Dietzia psychralcaliphila JI1D, a psychrophilic bacterium, isolated from Deception Island, Antarctica, which is able to resist high concentrations (up to 1000 ppm) of heavy metals and to favor their removal from polluted water systems. In detail, D. psychralcaliphila JI1D can actively promote the sequestration of arsenic, copper, and zinc from the medium up to a maximum of 31.6%, 49.4%, and 38.9%, respectively. Moreover, genome analysis allowed for the identification of heavy metal tolerance genes, thus shedding light on the mechanisms underlying the detoxification ability of the bacterium. Other than the demonstrated ability of D. psychralcaliphila JI1D to degrade polycyclic aromatic hydrocarbons, this study indicates the possibility of using this bacterium in the bioremediation of contaminated matrices, for example, those containing inorganic pollutants.

Self-regulated immobilization behavior of multiple heavy metals via zeolitization towards a novel hydrothermal technology for soil remediation

More efficient soil remediation technologies are highly anticipated to treat large quantities of heavy metal-polluted urban sites nowadays. Herein, a novel hydrothermal technology of converting heavy metal-polluted soils into zeolites for in-situ immobilizing heavy metals was proposed. The zeolites (analcime and cancrinite) could be synthesized hydrothermally with certain Na/Si and Al/Si ratios. The formed zeolites could manage to change their species and structure during zeolitization to accommodate different heavy metals in soil according to their size and charge. Since smaller-size Cu2+ was introduced, analcime and some cancrinite possessing small cages could be formed adaptively to immobilize the Cu2+ by replacing Na+ and forming Cu2+-OH and Cu2+-O. Whereas, cancrinite with large channels managed to form to immobilize the larger-size Cd2+ by forming Cd2+-O. Interplanar spacing variation of zeolites also corresponded to their structural change for accommodating different heavy metals. Leaching results showed the amounts of Cu and Cd leached from the synthesized zeolites were reduced to 0.005% and 0.05% respectively, reflecting a more stable immobilization of smaller heavy metals by small cages, in agreement with the results of distribution coefficient (Kd). Negligible effect of pH environment on the leaching rates further confirmed the stable structural immobilization of heavy metals by zeolites.

Using recoverable sulfurized magnetic biochar for active capping to remediate multiple heavy metal contaminated sediment

Due to anthropogenic activities, heavy metals are discharged into the hydrosphere and deposit onto the sediment. Heavy metals remobilize through physical disturbance and change in environmental conditions, posing a risk to environments and human health. Among several remediation methods, active layer capping is considered to be more feasible due to its financial and technical advantages; however, its long-term effects remain unknown. To overcome this problem, this work applied a novel, recoverable amendment, sulfurized magnetic biochar (SMBC), to remediate multiple heavy metal (Cu, Ni, Zn, Cr, Hg, and MeHg) contaminated sediment. Physiochemical characterization shows magnetite (Fe3O4) crystalline in both magnetic biochar (MBC) and SMBC, with such characteristics resulting in a greater surface area (324.9 and 346.3 m2/g) than BC (39.6 m2/g) and SBC (65.0 m2/g). FeS crystalline was also observed in SMBC, which plays an important role in controlling heavy metal release from sediment. Microcosm experiments indicated the effectiveness of SMBC in lowering aquatic Cu, Ni, Zn, Hg, and MeHg releases was significantly greater than the other three biochar materials. Notably, the recovery of SMBC by magnetism was 87%, demonstrating the exceptional recoverability of SMBC from seawater and sediment. Based on its robust capability in lowering Cu, Ni, Zn, Hg, and MeHg release and excellent recoverability from seawater and sediment, this technique represents a practical alternative to conventional approaches for heavy metal immobilization from sediment.

Assessing the ecological risk and ecotoxicity of the microbially mediated restoration of heavy metal-contaminated river sediment

Anthropogenic activities such as mining, smelting industries, and the application of pesticides in agriculture might result in contamination of multiple heavy metals in the environment. Heavy metal contamination of sediment is a serious environmental problem, and thus the remediation of contaminated sediment is a worldwide challenge. Several strategies have been developed for the remediation of contaminated sediment, however the ecological risk and ecotoxicity of the restored sediment have rarely been evaluated. We assessed whether river sediment highly contaminated with heavy metals could be restored using microbial bioleaching followed by evaluating the residual toxicity and ecological risk of the microbially remediated sediment. Sequential extraction revealed that the bioavailable levels of Cu, Ni, and Zn in the contaminated sediment exceeded sediment quality guideline (SQG) thresholds. It was consequently found that acidophilic sulfur-oxidizing Acidicaldus sp. SV5 effectively bioleached Cu, Ni, and Zn from the contaminated sediment, reducing the bioavailable fraction of these elements below SQG thresholds. The ecological risk assessment indicated that SV5-driven remediation significantly reduced the potential ecological risk of the contaminated sediment. The residual ecotoxicity of the microbially remediated sediment was also tested with the soil nematode Caenorhabditis elegans. There was a significant decrease in the body burden of Cu, Ni, and Zn in C. elegans and a reduction in the toxicological effect on survival, growth, and reproduction in the microbially remediated sediment. Our study suggests that a combination of chemical analysis, chemical-based ecological risk assessment, and ecotoxicity tests would be helpful for the development of efficient and eco-friendly strategies for the restoration of contaminated sediment, which could be incorporated into sediment quality management practices.

Investigation of the Distribution of Heavy Metals in the Soil of the Dahuangshan Mining Area of the Southern Junggar Coalfield, Xinjiang, China

Coal mining activities have a series of impacts on the local eco-environment, such as air pollution due to the release of toxic gases, contamination of soil with heavy metals, disturbance and contamination of surface and subsurface water, and damage to land resources with surface subsidence and accumulation of solid waste materials. This study investigated the distribution of heavy metals in mining sites by analyzing the heavy metal content in soil samples from different sites in the Dahuangshan mining area of the southern Junggar coalfield (Xinjiang, China). The results show that area C has the highest Cu content; and area B has the highest Mn content, the highest Zn content, the highest As content, and the highest Cd content, which indicate that area B underwent potential multiple heavy metal contamination. It also shows that the Cd is the major heavy metal for all three areas. The different eco-environmental indices, including the Nemerow comprehensive pollution index, the geo-accumulation index, and the potential ecological risk index, all show the same results, i.e., that Cd is the major potential contaminant in all three types of soil.