Remediation Of Metal-contaminated Soils Research Articles

Microplastics in heavy metal-contaminated soil drives bacterial community and metabolic changes

Microplastic (MP) and heavy metal pollution in soil are global issues. When MPs invade the soil, they combine with heavy metals and adversely affect soil organisms. Six common MPs—polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and polytetrafluoroethylene—were selected for this study to examine the effects of various concentrations and MP types on the physicochemical properties, bacterial community, and soil metabolism of heavy metal-contaminated soil. MP enhanced predation and competition among heavy metal-contaminated soil bacteria. Heavy metal-MPs alter metabolites in lipid metabolism, other pathways, and the bacterial community. MP treatment promotes energy production and oxidative stress of soil bacteria to resist the toxicity of heavy metals and degrade MP pollution. In conclusion, MP treatment changed the metabolism of the microbiome in heavy metal-contaminated soil and increased the abundance of Proteobacteria that responded to MPs and heavy metal pollution by 11.54 % on average. This study explored bacteria for the ecological regeneration and provided ideas for MPs and heavy metal-contaminated soil remediation.

Influence of Carbons on Metal Stabilization and the Reduction in Soil Phytotoxicity with the Assessment of Health Risks

Despite notable achievements in the development and application of the remediation of metal-contaminated soils, the search for and study of promising immobilizing agents continues. This article presents a new approach to using brown coal and activated carbon and their application for metal stabilization. An experiment was conducted to test Medicago falcata L. on soils from industrial areas contaminated with varying levels of lead (Pb), cadmium (Cd), chromium (Cr), zinc (Zn), copper (Cu), and nickel (Ni) with the addition of carbons. This plant is a stress-tolerant leguminous species. In this study, the total content of metals in soil and the available forms to plants (single extractions with 0.02 M ethylenediaminetetraacetic acid, EDTA) were determined, along with metal contents in the plant. The use of carbons lowered the phytoavailable forms of metals for plants and thus, resulted in a reduction in the phytotoxicity of the soils. The contents of the tested metals in the roots and shoots were lower than in the combinations of soils with no carbon added. The activated carbon had a stronger effect on limiting the availability of metals than brown coal in relation to plants growing on soils without added carbon; the percentage of reduction for the shoots was Cr (18.2%) > Zn (11.5%) > Ni (10.7%) > Cu (10.3%) > Cd (8.9%) > Pb (2.4%) and Cu (13.3%) > Cr (12.5%) > Zn (10.5%) > Pb (9.0%) > Ni (5.7%) > Cd (4.6%) for roots. Metals reduced the growth of Medicago falcata L. roots from 44 to 21%, while the growth of shoots was reduced from 25 to 2%. Adding carbons to soils in all combinations resulted in a decrease in the following pollution indices: pollution index (PI), pollution load index (PLI), and non-carcinogenic (HQ) and carcinogenic risk factors (ILCR).

The Hotspots and Trends of Patented Technologies for Heavy Metal-Contaminated Soil Remediation: A Systematic Review

Heavy metal soil pollution severely threatens human health and food safety. This study used PRISMA to systematically review heavy metal-contaminated soil remediation patents in the Derwent Patent Database from 2003 to 2023. A total of 1744 patents were selected. The results of the analysis show that related patent applications are growing around the world. Among them, China has the most significant number of patents, but the layout of transnational patents needs to be revised. Countries have different preferences in transnational patent technology. Technological development is generally balanced, and there is no apparent monopoly. However, the need for continuous in-depth research on inventors is an obstacle to technological development. In addition, the technology in this field is concentrated in chemistry and engineering. Currently, the mainstream technology is soil remediation agents, and thermal desorption technology has also attracted much attention. Future technologies will use new polymer materials and advanced machinery to improve efficiency and control repair costs. In addition, remediation has shifted from the total amount of heavy metals to the control of practical parts. This study summarizes the current status of heavy metal-contaminated soil remediation technology and analyzes future development trends, providing a reference for technology development.

Recovery of biochar particles laden with lead in saturated porous media by DC electric field

The co-transport behavior of environmental pollutants with biochar particles has aroused great interests from researchers due to the concerns about pollutant diffusion and environmental exposure after biochar is applied to soil. In this work, the recovery and co-transport behavior of biochar micron-/nano-particles (BCMP and BCNP) and lead (Pb2+) in saturated porous media were investigated under different ionic strength conditions (IS = 1, 5 and 10 mM) under a direct current electric field. The results showed that the electric field could significantly enhance the mobility of Pb adsorbed biochar particles, particularly BCNP. The recovery of Pb laden biochar particles was improved by 1.8 folds, reaching 78.8% at maximum under favorable condition at +0.5 V cm−1. According to the CDE (Convection-Dispersion-Equation) model and DLVO (Derjaguin-Landau-Verwey-Overbeek) theory analysis, the electric field facilitated the transport of Pb carried biochar mainly by increasing the negative charges on biochar surface and improving the repulsive force between biochar and porous media. High IS was favorable for biochar transport under the electric field, but inhibited desorbing Pb2+ from biochar (18% by maximum at IS = 10 mM). By switching the electric field power, a two-stage strategy was established to maximize the recovery of both biochar particles and Pb, where BCNP and Pb recovery were higher than electric field free case by 90% and 35%, respectively. The findings of this study can help build a biochar recovery approach to prevent potential risks from biochar application in heavy metal contaminated soil remediation.

Deciphering the corrosion puzzle: Nano-iron-biochar composite – Not a quick fix for metal immobilization in peat soils

The use of zero-valent iron nanoparticles in the remediation of metal-contaminated soils has received considerable attention. Upon introduction into the soil, zero-valent iron particles corrode into iron oxides, known for their high adsorption capacity for potentially toxic metals. While limited research has directly compared zero-valent iron micro- and nanoparticles, it is important to investigate whether particle size contributes to effective soil remediation. This study focuses on elucidating the comparative kinetics of iron corrosion using iron powder and a nano-iron-biochar composite. In a model experiment, these materials were exposed to a cellulose/biochar mixture and peat for five months. Mössbauer spectroscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and transmission electron microscopy with electron diffraction were used to analyze the corrosion products. The results show a slow corrosion rate in the nano-iron-biochar composite in cellulose due to the protective effect of biochar on the embedded iron nanoparticles. In addition, iron corrosion in peat was inhibited, likely due to the presence of humic substances. Transmission electron microscopy after five months of corrosion revealed round metal particles encased in a graphite capsule with visible channels. Large dissolved organic matter molecules in the peat likely block these channels, inhibiting metallic iron corrosion. Consequently, the nano-iron-biochar composite emerges as a slow-reacting option for immobilizing soil metals in peat. This study highlights the need for further research involving long-term field experiments.

Electrokinetic remediation: Past experiences and future roadmap for sustainable remediation of metal-contaminated soils

Soil pollution due to heavy metals has become a serious environmental concern in the past decade, adversely affecting soil conditions and global food security. Due to this, considerable attention has been given to developing suitable remediation technologies, particularly for heavy metals. Among them, Electrokinetic Remediation (EKR) is a promising developing technique due to its great efficiency for fine-grained soils. The use of an electric field to remove contaminants from soil is effective on a wide range of matrices irrespective of the heterogeneity. In this context, the present study provides a detailed discussion on the design and operational considerations of EKR, mainly, power, electrode, and electrolyte characteristics. The major limitations of EKR, innovative modifications of EKR operations to overcome the limitations, and EKR-integrated technologies have been addressed. The optimization of regulating parameters ensures maximum efficiency towards removal of contaminants at minimum cost of treatment, thus, highlighting the engineering aspect of electrokinetics at field scale. The sustainability concerns arising from EKR and its possible alternative solutions have been discussed, to provide useful information and prospects to researchers in the field.

The potential of ferrihydrite-synthetic humic-like acid composite as a soil amendment for metal-contaminated agricultural soil: Immobilization mechanisms by combining abiotic and biotic perspectives

In-situ passivation technique has attracted increasing attention for metal-contaminated agricultural soil remediation. However, metal immobilization mechanisms are mostly illustrated based on metal speciation changes and alterations in soil physicochemical properties from a macroscopic and abiotic perspective. In this study, a ferrihydrite-synthetic humic-like acid composite (FH-SHLA) was fabricated and applied as a passivator for a 90-day soil incubation. The heavy metals immobilization mechanisms of FH-SHLA were investigated by combining both abiotic and biotic perspectives. Effects of FH-SHLA application on soil micro-ecology were also evaluated. The results showed that the 5%FH-SHLA treatment significantly decreased the DTPA-extractable Pb, Cd and Zn by 80.75%, 46.82% and 63.63% after 90 days of incubation (P < 0.05), respectively. Besides, 5% FH-SHLA addition significantly increased soil pH, soil organic matter content and cation exchange capacity (P < 0.05). The SEM, FTIR, and XPS characterizations revealed that the abiotic metal immobilization mechanisms by FH-SHLA included surface complexation, precipitation, electrostatic attraction, and cation-π interactions. For biotic perspective, in-situ microorganisms synergistically participated in the immobilization process via sulfide precipitation and Fe mineral production. FH-SHLA significantly altered the diversity and composition of the soil microbial community, and enhanced the intensity and complexity of the microbial co-occurrence network. Both metal bioavailability and soil physiochemical parameters played a vital role in shaping microbial communities, while the former contributed more. Overall, this study provides new insight into the heavy metal passivation mechanism and demonstrates that FH-SHLA is a promising and environmentally friendly amendment for metal-contaminated soil remediation.

Integrated approaches for heavy metal-contaminated soil remediation: harnessing the potential of Paulownia elongata S. Y. Hu, Oscillatoria sp., arbuscular mycorrhizal fungi (Glomus mosseae and Glomus intraradices), and iron nanoparticles.

In recent years, researchers have extensively investigated the remediation of heavy metal-contaminated soil using plants, microorganisms, and iron nanoparticles. The objective of this study was to investigate and compare the individual and simultaneous effects of Paulownia elongata S. Y. Hu, cyanobacteria (Oscillatoria sp.), arbuscular mycorrhizal fungi (AMF) including Glomus mosseae and Glomus intraradices, and zero-valent iron nanoparticles (nZVI) on the remediation of heavy metal-contaminated soil containing chromium (Cr VI and Cr III) and nickel (Ni). The study found significant variations in parameters such as pH (acidity), electrical conductivity (EC), nitrogen (N), phosphorus (P), potassium (K), and organic carbon (OC) among different treatments. The addition of cyanobacteria, AMF, and nZVI influenced these properties, resulting in both increases and decreases compared to the control treatment. The treatment involving a combination of cyanobacteria, AMF, and nZVI (CCAN25) exhibited the highest increase in growth parameters, such as total dry mass, root length, stem diameter, and leaf area, while other treatments showed varied effects on plant growth. Moreover, the CCAN25 treatment demonstrated the highest increase in chlorophyll a, chlorophyll b, and carotenoid levels, whereas other treatments displayed reductions in these pigments compared to the control. Moderate phytoaccumulation of Cr and Ni in P. elongata samples across all treatments was observed, as indicated by the bioconcentration factor and bioaccumulation coefficient values being less than 1.0 for both metals. The findings provide insights into the potential application of these treatments for soil remediation and plant growth enhancement in contaminated environments.

Pseudomonas sp. Bacteria: potentially toxic metal-contaminated soil remediation potentials - minimum inhibitory concentration investigation and application

Agricultural inputs used for correction or nutrition in agriculture have a composition that, in addition to containing desirable elements, often includes potentially toxic metals that contaminate the soil. Faced with this scenario, one can observe the appearance of various remediation techniques, amongst them, bio-remediation. This technique has been shown to be highly promising, as there is a wide variety of genera and species of microorganisms. In this study, the application of Pseudomonas sp. bacteria in soil from bean cultivation was investigated, with the aim of removing Zn2+ and Ni2+ ions. Analyzes were carried out of soil parameters, pH in water and KCl, Zero Charge Point, exchangeable acidity, quantity of organic matter in soil and initial concentrations of ions. To evaluate the tolerance of bacteria to metal concentrations in the soil, studies of Minimum Inhibitory Concentration were conducted. A bioremediation experiment was then carried out, applying the bacteria to the soil and monitoring the process over 21 days. The results showed that Pseudomonas sp. bacteria showed good resistance to high metal concentrations, as well as remarkable capacity and efficiency in the absorption of metals, reaching 0,063 mg kg-1 and 90.5% efficiency in the removal of Ni2+ ions, and 0,012 mg kg-1 capacity and 47.9% efficiency in the removal of Zn2+ ions. These results suggest that the Pseudomonas sp. bacteria are promising for the bioremediation of soils contaminated with potentially toxic metals.

Biomineralization mechanism and remediation of Cu, Pb and Zn by indigenous ureolytic bacteria B. intermedia TSBOI

Microbially induced carbonate precipitation (MICP) is an effective and eco-friendly technology for remediating heavy metal-contaminated sites. In this study, we investigated the response discrepancies and proposed the dominant removal mechanism of the ureolytic bacteria Brucella intermedia TSBOI for different heavy metal species (Cu, Pb and Zn) under concentration gradients (0.1, 0.2, 0.4, 0.8, and 1.6 mmol/L), and explored the remediation of soil heavy metal pollution by B. intermedia TSBOI under laboratory conditions. The results showed that the heavy metal concentration significantly affected the bacterial cell concentration, urease activity, cell morphology, surface functional groups, and removal efficiency of B. intermedia TSBOI. The presence of Ca2+ negatively affected the biomass and urease activity to some extent but had a non-negligible positive effect of removing heavy metals and was more conducive to the formation and precipitation of biomineralization products. The ability of B. intermedia TSBOI to produce urease intracellularly and secrete it in large quantities to act extracellularly is key to the sustained immobilization of heavy metals and the outstanding performance of B. intermedia TSBOI bacterial solution. The results of heavy metal-contaminated soil remediation showed that B. intermedia TSBOI effectively increased the proportion of carbonate-bound states of Cu, Pb and Zn in the soil and reduced the bioavailability of heavy metals within 30 days. B. intermedia TSBOI could adapt fully to the soil environment and became a dominant genus.

Benefit evaluation of in-situ Cd immobilization with naturally occurring minerals using an analytical hierarchy process

Immobilization has a wide range of applications in heavy metal-contaminated soil remediation, and immobilization agents serve as the key to the successful application of this technology. In this study, we designed a comprehensive and efficient scoring system based on an analytic hierarchy process (AHP) to evaluate the feasibility and effectiveness of three immobilization agents (wollastonite, dolomite, and calcite) in remediating Cd-polluted soil. The scoring system comprised four criteria and 11 indicators, and the results showed that all three immobilization agents significantly reduced the accumulation of Cd in rice. The Cd reduction rates of early rice with a single application of wollastonite, dolomite, and calcite were 67.6%, 46.9%, and 83.8%, respectively. Single or combined application of dolomite and calcite decreased the available Cd concentration in early rice soil, and the application of calcite resulted in an excellent rating of both early and late rice, demonstrating its highest immobilization and stability performance. Therefore, the immobilization efficiency of the three materials in descending order followed calcite > dolomite + thioglycols > wollastonite. In summary, this comprehensive evaluation system offers new insight into assessing the efficiency of soil remediation, serving as a valuable reference for selecting immobilization agents and making decisions regarding remediation plans for heavy metal-contaminated soil.

Micro/nanoscale bone char alleviates cadmium toxicity and boosts rice growth via positively altering the rhizosphere and endophytic microbial community

This present study investigated pork bone-derived biochar as a promising amendment to reduce Cd accumulation and alleviate Cd-induced oxidative stress in rice. Micro/nanoscale bone char (MNBC) pyrolyzed at 400 °C and 600 °C was synthesized and characterized before use. The application rates for MNBCs were set at 5 and 25 g·kg−1 and the Cd exposure concentration was 15 mg·kg−1. MNBCs increased rice biomass by 15.3–26.0% as compared to the Cd-alone treatment. Both types of MNBCs decreased the bioavailable Cd content by 27.4–54.8%; additionally, the acid-soluble Cd fraction decreased by 10.0–12.3% relative to the Cd alone treatment. MNBC significantly reduced the cell wall Cd content by 50.4–80.2% relative to the Cd-alone treatment. TEM images confirm the toxicity of Cd to rice cells and that MNBCs alleviated Cd-induced damage to the chloroplast ultrastructure. Importantly, the addition of MNBCs decreased the abundance of heavy metal tolerant bacteria, Acidobacteria and Chloroflexi, by 29.6–41.1% in the rhizosphere but had less impact on the endophytic microbial community. Overall, our findings demonstrate the significant potential of MNBC as both a soil amendment for heavy metal-contaminated soil remediation and for crop nutrition in sustainable agriculture.

“Soil for Soil Remediation” Strategy Driven on Converting Natural Soils into Fe2O3-CAN-Type Zeolite Composites for Dual Ionic Heavy Metal-Contaminated Soil Remediation: Universality, Synergistic Effects, and Mechanism

Herein, we developed a universal “soil for soil remediation” strategy to utilize soil resources for cation-/anion-type heavy-metal-contaminated soil remediation. The representative natural soils fetched from 12 different areas in China have been universally converted into Fe2O3-CAN (hydroxycancrinite) zeolite composite materials. Furthermore, we discover that due to the presence of exchangeable Na+ and OH– in CAN channels together with the intrinsic surface adsorption function of Fe2O3-CAN, Fe2O3-CAN holds distinctive cation/anion dual ion-exchange functions and strong adsorption capacity, which could synergistically remediate cation-/anion-type HM-contaminated soil. When 25 g/kg Fe2O3-CAN is added into Cd/As polluted soil (100–200 ppm), Cd2+ and AsO2– in soil could be immobilized simultaneously and the Cd/As bioaccumulation in the harvested vegetables is dramatically suppressed with reduction ratios of 48.1–67.0%, effectively reducing the HM enrichment in the phytosphere. Overall, this work confirms the high universality of Fe2O3-CAN synthesis using different types of natural soils and demonstrates that the as-synthesized Fe2O3-CAN composite material can be further effectively used for soil remediation. The “soil for soil remediation” strategy developed here could improve the flexibility and economy of soil remediation, which can be extended to a broad range of locations worldwide.

Fe-biochar for simultaneous stabilization of chromium and arsenic in soil: Rational design and long-term performance

Excess chromium (Cr) and arsenic (As) coexist in soil such as chromated copper arsenate (CCA) contaminated sites, leading to high risks of pollution. Fe-biochar with adjustable redox activity offers the possibility of simultaneous stabilization of Cr and As. Here, a series of Fe-biochar with distinct Fe/C structure were rationally produced for the remediation of Cr and As contaminated soil (BCX-Fe, X represented the biomass/Fe ratio). Adsorption tests showed that maximal adsorption of BC5-Fe for Cr(VI) and As(III) reached 73.7 and 81.3 mg/g. A 90-day soil remediation experiment indicated that the introduction of 3% (w/w) Fe-biochar reduced the leaching state of Cr(VI) by 93.8–99.7% and As by 75.2–95.6%. Under simulated groundwater erosion for 10 years and acid rain leaching for 7.5 years, the release levels of Cr(VI) and As in the BC5-Fe remediated soil could meet the groundwater class IV standard in China (Cr(VI)<0.1 mg/L, As<0.05 mg/L). Accelerated aging tests demonstrated that BC5-Fe had long-term Cr and As stabilization ability. The quenching experiment, EPR, and XPS suggested that the corrosion products of Fe dominated the adsorption and redox reactions, while the O groups acted as electron transfer stations and constituted redox microcirculation in the synchronous uptake of Cr/As. Based on these insights, we believe that our study will provide meaningful information about the application potential of Fe-biochar for the heavy metal contaminated soil remediation.

An AHP-based evaluation system applied for phytoremediation method selection in heavy metal contaminated farmland

Phytoremediation assisted by chemicals is widely applied in heavy metal contaminated farmland remediation. In this study, an effective and comprehensive scoring system was established based on analytic hierarchy process (AHP) assisted by principal component analysis (PCA) and ecological hazard index (EHI). Taking the remediating effect-related characteristics of soil, plant, and microbe into account, the system was designed to encompass 3 criteria containing 9 features and 14 indexes to evaluate the remediating methods. Data of all indexes were then normalized to guarantee their comparability. Afterward, the system was applied in a farmland-remediating case study. Two widely-used methods of phytoremediation, i.e., phytoextraction and phytostabilization, together with 8 chemicals were conducted in the case study to verify the accuracy and feasibility of the evaluation system. Amaranthus hypochondriacus and Jatropha curcas L. were selected as the remediating plants for phytoextraction and phytostabilization, respectively. Urea, potassium sulfate (K2SO4), lime and dolomite were selected to assist phytoremediation. As for the results, applying potassium sulfate (K2SO4) once (EP1) and no amendments applied (SCK) are the best choice for phytoextraction and phytostabilization, respectively. SCK performed better, but with the plants growing, the scores of phytostabilization lessened while phytoextraction elevated. Thus, in the long term, EP1 should be the main remediation method with SCK being the auxiliary one in this farmland. A further endeavor was made to simplify the established system at 3 levels based on 3 principles, i.e., importance, difference, and complexity, to meet the need of different assessments. In conclusion, this comprehensive scoring evaluation system characterized as systematic, accurate, and reasonable could serve as a reference for decision-making of heavy metal contaminated soil remediation.

The combined application of γ-PGA-producing bacteria and biochar reduced the content of heavy metals and improved the quality of tomato (Solanum lycopersicum L.).

Plant growth-promoting bacteria and biochar have been widely used as immobilizers to remediate heavy metal contaminated soil. However, few studies have unraveled the effect and synergistic mechanism of combined application of plant growth-promoting bacteria and biochar on in situ heavy metal contaminated soil remediation and plant yield and quality improvement under heavy metal pollution stress. In this study, the effects of biochar, γ-PGA-producing bacteria (Bacillus amyloliquefaciens strain W25) and their combined application on Cd and Pb immobilization, γ-PGA production in soil filtrate, the bacterial community in rhizosphere soil, physicochemical properties of soil, heavy metal uptake, and quality and yield of tomato in heavy metal-contaminated soil were investigated. The application of W25, biochar, and their combinations significantly reduced Cd content in mature tomato fruits by 22-60%, increased the single fruit weight and lycopene content by 7-21% and 23-48%, respectively, and the combination of biochar and W25 had the best effect. All the treatments significantly reduced DTPA-Cd and DTPA-Pb contents in rhizosphere soil (42-53% and 6.5-35%), increased the pH value and the activities of urease-alkaline phosphatase of soil, but did not affect the expression of heavy metal transporter gene LeNRAMP1 in tomato roots. Biochar + W25 increased the relative abundance of plant growth-promoting bacteria such as Bacillus and Streptomyces. Biochar-enhanced plant growth-promoting bacteria to settle and colonize in soil significantly improved the ability of strain W25 to produce γ-PGA, and immobilized Cd in soil filtrate. The combination of biochar and plant growth-promoting bacteria ensures safe crop production in heavy metal-contaminated soil.

Chemical Speciation and Potential Mobility of Heavy Metals in Organic Matter Amended Soil

Organic matter (OM) degradation from amendments used in the remediation of metal-contaminated soils leads to modifications in soil chemical properties immediately after addition, which can also affect the soil metal distribution. Therefore, the speciation and potential mobility of heavy metals e.g., lead (Pb) and cadmium (Cd) were evaluated in three soils amended with OM. Soils, both spiked (with lead nitrate and cadmium nitrate solution) and unspiked, were treated with OM at a rate of 5 tons/ha in a moist condition. The samples were in incubation for 30 days in 30% moist condition. A chemical fractionation procedure was applied to determine the distribution of Pb and Cd in soils. The potential mobility of metals was also determined. Metals transformed from mobile to immobile fractions in both spiked and unspiked soils (not treated with organic matter), but OM increased the mobile fraction of Pb in unspiked soil and decreased it in spiked soil. In contrast, the mobile fraction of Cd decreased in soils (not treated with OM), but the OM increased the mobile fractions in spiked and unspiked soils. The mobile fraction (as a percentage of total) of Cd was higher than the mobile fraction of Pb indicating the greater mobility of Cd compared to Pb. However, the three soils showed a more or less similar pattern in transforming Pb and Cd in soils since their characteristics were almost the same.

Research Progress of Heavy Metal Contaminated Soil Remediation Methods in China

In order to effectively remediate heavy metal pollution in soil, a variety of physical, chemical and biological remediation method of materials have been proposed in the past decades. In practical application, these restoration methods have their own advantages and disadvantages in terms of scope of application, efficiency and cost. Therefore, this newspaper summarizes several common soil remediation technologies in combination with the relevant literatures in the field of heavy metal contaminated soil collected by CNKI. It is found that most physical remediation technologies have the advantages of simple equipment, easy popularization and sustainability, but they are limited to small areas and highly polluted soils; Compared with logistics repair technology, chemical repair technology with low cost, high efficiency and wide application range is used by more people; In recent years, bioremediation technology, which has the advantages of small environmental disturbance, no secondary pollution, stable and harmless products, has solved the ecological damage caused by physical and chemical remediation. The research on the remediation of heavy metal contaminated soil will help to have a comprehensive understanding of this field, which is of great significance to attract more scholars to participate in it, and provide solutions for the current ecological civilization construction of the government and other departments from the aspect of remediation of heavy metal contaminated soil ecological environment.

Choose your amendment wisely: Zero-valent iron nanoparticles offered no advantage over microparticles in a laboratory study on metal immobilization in a contaminated soil

The potential use of zero-valent iron (ZVI) nanoparticles (i.e., <100 nm in size) for the remediation of metal-contaminated soils has sparked a flurry of research in recent years. However, even reading a large number of these papers cannot completely dispel doubts that ZVI nanoparticles are indeed superior to ZVI microparticles (e.g., iron powder or grit) in immobilizing metals and metalloids in soils. Our primary objective was to compare the adsorption properties of iron-based amendments (ZVI micro- and nanoparticles, natural iron oxides) supplied in a biochar matrix in soils contaminated by a copper-nickel (Cu/Ni) smelter on the Kola Peninsula in Russia. The following iron-containing amendments were added to the studied soil: a composite of ZVI nanoparticles and biochar (synthesized by pyrolysis of iron-impregnated biochar), a mixture of iron powder (i.e., ZVI microparticles) with biochar, and a mixture of iron oxides (from natural ferromanganese nodules) with biochar. Perennial ryegrass (Lolium perenne L.) was grown in pots on untreated and amended soils for 21 days under laboratory conditions. In our time-limited study, ZVI nanoparticles did not prove superior to ZVI microparticles or natural iron oxides at immobilizing metals in copper- and nickel-contaminated soil. In other words, ZVI particles size was irrelevant under the experimental setup of this study in its effects on exchangeable metal concentrations, foliar elemental concentrations, and plant growth.

Influences of Biochar on Bioremediation/Phytoremediation Potential of Metal-Contaminated Soils.

A number of anthropogenic and weathering activities accumulate heavy metals in soils, causing adverse effects on soil characteristics, microbial activity (diversity), agricultural practices, and underground aquifers. Controlling soil heavy metal pollution is difficult due to its persistence in soils, resulting in the deposition and transmission into the food web via agricultural food products, ultimately affecting human health. This review critically explores the potential for remediation of metal-contaminated soils using a biochar-based responsible approach. Plant-based biochar is an auspicious bio-based residue substance that can be used for metal-polluted soil remediation and soil improvement as a sustainable approach. Plants with rapid growth and increased biomass can meet the requirements for phytoremediation in large quantities. Recent research indicates significant progress in understanding the mechanisms of metal accumulation and contaminant movement in plants used for phytoremediation of metal-contaminated soil. Excessive contamination reduces plant biomass and growth, which has substantial hyperaccumulating possibilities and is detrimental to the phytoremediation process. Biochar derived from various plant sources can promote the growth and phytoremediation competence of native or wild plants grown in metal-polluted soil. Carbon-enriched biochar encourages native microbial growth by neutralizing pH and providing nutritional support. Thus, this review critically discusses the influence of plant and agricultural waste-based biochar on plant phytoremediation potential in metal-contaminated soils.