Heavy Metal-contaminated Soils Research Articles

Stabilization of Arsenic and Heavy Metal Contaminated Soil Using Fishery By-Products and Evaluation of Heavy Metal Uptake in Crops

Objectives : Heavy metals eluted from mine waste pollute surrounding soil and water systems, which can spread to crops and have a harmful effect on the human body. The purpose of this study was to evaluate the feasibility of recycling discarded mussel shells(MS) and manila clam shells (MC) as stabilizers for the immobilization of arsenic(As) and heavy metals(Pb, Zn) in soil.Methods : MS and MC were processed with -#10 mesh natural material, -#20 mesh natural material, and -#10 mesh calcined material and treated at 0-10 wt%. After 1 week or 4 weeks of wet curing, it was eluted with 0.1 N HCl and the concentrations of As, Pb, and Zn in the soil were analyzed through inductively coupled plasma optical emission spectroscopy(ICP-OES) analysis. In addition, red lettuce was cultivated in the stabilized soil and the concentration of heavy metals that were transferred to crops was evaluated. The stabilization mechanism was investigated by scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX) analysis.Results and Discussion : The stabilization efficiency for arsenic and heavy metals was in the order of natural -#10 mesh < natural -#20 mesh < calcined -#10 mesh. The calcined stabilizer showed a high stabilization efficiency of 98% at a 2 wt% treatment level. Pb was not detected in the red lettuce grown in the stabiliz ed soil, and the standard for leafy vegetables (Pb-0.3 mg/kg or less) was satisfied according to the Ministry of Food and Drug Safety. The SEM-EDX analysis revealed that As was stabilized through Ca-As precipitation and heavy metals(Pb, Zn) were stabilized through pozzolanic reactions.Conclusion : Stabilizers developed from MS and MC can be effectively applied to the stabilization of As and heavy metal-contaminated soil, and are expected to be used as economical and environmentally friendly stabilizers.

Heavy metal tolerance in crop plants: an in silico comprehensive analysis of Metal- tolerance gene family in barley

Heavy metal contamination in soil is a global concern due to its harmful effect to all living organisms. Phytoremediation is an emerging cost- effective technology, which utilizes different types of hyperaccumulator plants for the removal of heavy metal pollutants. Crop plants have been suggested as a good candidate for recultivation of agricultural soil in phytoremediation process, however the molecular mechanisms responsible for the crop tolerance to heavy metals is still unknown. Metal-tolerance proteins (MTPs) are divalent cation transporters that play critical roles in metal tolerance and ion homeostasis in plants. The current study identified 12 HvMTPs in the barley (Hordeum vulgare, Hv) genome; the majority of MTPs were hydrophobic proteins found in the vacuolar membrane. Gene expression profiling suggests that HvMTPs play an active role in maintaining barley nutrient homeostasis throughout its life cycle. The expression of barley HvMTP genes in the presence of heavy metals revealed that these MTPs were induced by at least one metal ion, implying their involvement in metal tolerance.

Impact of petroleum contamination on soil properties in Absheron Peninsula, Azerbaijan

This study aims to assess the extent of hydrocarbon and heavy metal contamination in soils from specific areas on Azerbaijan's Absheron Peninsula, including Absheron, Suraxanı, and Baku, and to evaluate the impact of this contamination on soil properties. Soil samples were analyzed for Total Petroleum Hydrocarbons (TPH) and heavy metals, including aluminum, arsenic, cadmium, lead, and iron, alongside assessments of soil physical, chemical and biological properties. The results revealed significant contamination across all studied areas, particularly in Suraxanı, where TPH levels reached 190 ± 20 mg/kg, exceeding the environmental standard of 100 mg/kg. Similarly, Suraxanı soils exhibited alarmingly high concentrations of heavy metals, with aluminum at 30,128 ± 1,500 mg/kg, arsenic at 50.94 ± 2.5 mg/kg, and cadmium at 0.153 ± 0.01 mg/kg, all surpassing acceptable limits. These contaminants severely degraded soil health, evidenced by increased bulk density (1.7 g/cm³ in Suraxanı) and reduced soil porosity. Microbial activity, a key indicator of soil fertility, was also markedly lower in contaminated regions, with the total bacterial count in Suraxanı being less than half that of the uncontaminated area. The findings underscore the urgent need for comprehensive soil management practices and stricter environmental regulations to mitigate contamination's adverse effects and protect both ecosystems and public health in Azerbaijan’s petroleum contaminated areas.

Research Progress in the Joint Remediation of Plants–Microbes–Soil for Heavy Metal-Contaminated Soil in Mining Areas: A Review

Plants growing in heavy metal (HM)-contaminated soil have evolved a special detoxification mechanism. The rhizosphere gathers many living substances and their secretions at the center of plant roots, which has a unique ecological remediation effect. It is of great significance to thoroughly understand the ecological process of rhizosphere pollution under heavy metals (HMs) stress and develop biotechnology for joint remediation using plants and their coexisting microbial systems according to the mechanism of rhizosphere stress. Microbes can weaken the toxicity of HM pollutants by transforming the existing forms or reducing the bioavailability in the rhizosphere. Microbes survive in the HM-polluted soils through the production of stress-resistant substances, the participation of proteins, and the expression of heavy metal resistance genes, which strengthens the resistance of plants. Moreover, microbes can improve the nutritional status of plants to improve plant resistance to HMs. Plants, in turn, provide a habitat for microbes to survive and reproduce, which greatly accelerates the process of bioremediation. Briefly, the combined remediation of soil HMs pollution by plants and microbes is a promising, green, and sustainable strategy. Here, we mainly elucidate the joint remediation mechanism of plant–microbe symbiosis and introduce the coping characteristics of plants, microbes, and their symbiotic system, hoping to provide a scientific basis for the remediation of HM-contaminated soil in mining areas and the sustainable development of the ecological environment.

Endogenous silicon-activated rice husk biochar prepared for the remediation of cadmium-contaminated soils: Performance and mechanism

Biochar is widely used for the remediation of heavy metal-contaminated soils. However, pristine biochar generally has limited active functional groups and adsorption sites, thereby exhibiting low immobilization performance for heavy metals. In addition to carbon (C), silicon (Si) is another common macro-element present in rice husk biochar, but it often exists in the form of amorphous oxide and therefore contributes little to the adsorption performance for heavy metals. The transformation of amorphous Si oxide to dissolved silicate through a precipitation effect can significantly improve its heavy metal immobilization capability. Herein, the amorphous Si oxide in rice husk biochar was activated by sodium hydroxide and then the dissolved silicate was immobilized by calcium salt. The as-synthetized Si-activated biochar was used to remediate cadmium (Cd)-contaminated soils. The results indicated that Si-activated rice husk biochar could reduce Cd migration and environmental risks by the transformation from exchangeable Cd into carbonate-bound and residual Cd. With increasing Ca: Si molar ratio, the content of CaCl2 and H2O-extractable Cd exhibited a decreasing trend. Moreover, a higher addition amount of Si-activated biochar improved the Cd immobilization efficiency. The application of 1.0% Ca/Si molar ratio of 2: 2 Si-activated rice husk biochar decreased the CaCl2-Cd and H2O-Cd concentration by a maximum of 83.7% and 90.5% compared with pristine rice husk biochar, respectively. The present work proposes an approach for highly efficient remediation of Cd-polluted soils by biochar.

Source-specific ecological and human health risk analysis of topsoil heavy metals in urban greenspace: a case study from Tianshui City, northwest China.

Soil contamination of heavy metals in urban greenspaces can exert detrimental impacts on ecological biodiversity and the health of inhabitants through cross-media migration-induced risks. Here, a total of 72 topsoil samples were collected from greenspaces in the popular tourist city of Tianshui, ranging from areas with parks, residential, road, industrial and educational soils. The study aimed to evaluate an integrated source-specific ecological and human health risk assessment of heavy metals. Among the analyzed heavy metals, except Cr (mean), all exceeded the local background values by 1.30-5.67-fold, and Hg, Cd, Pb and As were the metals with large CV values. The Igeo and CF results showed Hg, Cd, As and Pb exhibited significantly high pollution levels and were the primary pollution factors. The mean PLI values indicated moderate pollution in educational (2.21), industrial (2.07), and road (2.02) soils but slight pollution in park (1.84) and residential (1.39) greenspaces. The Igeo, CF, and PLI results also revealing that these heavy metals are more likely to be affected by human activity. Four primary source factors were identified based on PMF model: coal combustion (25.57%), agricultural sources (14.49%), atmospheric deposition (20.44%) and mixed sources (39.50%). In terms of ecological risk, the mean IRI values showed considerable risks in educational soils (287.52) and moderate risks in road (215.09), park (151.27) and residential (136.71) soils. And the contribution ratio of atmospheric deposition for park, residential, road, industrial and educational greenspaces were 57.72%, 65.41%, 67.69%, 59.60% and 75.76%, respectively. In terms of human health risk, the HI (below 1) and CR (below 1.00E-04) for adults from soils of all land use types was negligible. However, children have more significant non-carcinogenic and carcinogenic hazards especially in residential soils, the HI (above 1) and CR (above 1.00E-04) revealed the significance of regarding legacy As contamination from coal combustion when formulating risk mitigation strategies in this area. The proposed method for source and risk identification makes the multifaceted concerns of pollution and the different relevant risks into a concrete decision-making process, providing robust support for soil contamination control.

Accumulation of Cd and Pb in soils irrigated with sewage and non-sewage water in Prayagraj, India

Unmanaged agricultural fields and the extended usage of sewage irrigation water can raise the concentration of heavy metals (Cd and Pb) in the soil, turning it into barren soil. The study was conducted during 2022-23 at four sewage and non-sewage irrigated sites in Prayagraj namely Naini, Baxibandh, Rasulabad and Draupadi Ghat. The representative soil samples were taken at depths of 0-15, 15-30, 30-45 and 45-60 cm. Di-acid mixture method was used for the estimation of heavy metals (Cd and Pb) in the soil sample by AAS (Atomic Absorption Spectrophotometer) (AAnalyst600, Perkin Elmer Inc., MA, USA). Contamination factor (CF) and enrichment factor % (EF) of different sites showed various results which fulfill the basic criteria of present and future prospective of research. The highest concentration of Cd and Pb was found in the surface layer (0-15 cm) of sewage and non-sewage irrigated sites at Naini i.e., Cd (4.46±0.42 and 1.05±0.08 mg/kg) and Pb (6.53±0.62 and 1.18±0.12 mg/kg) respectively. The lowest concentration of Cd and Pb was found in the sub-surface layer (45-60 cm) of sewage and non-sewage irrigated sites at Draupadi Ghat i.e., Cd (1.02±0.09 and 0.16±0.01 mg/kg) and Pb (1.68±0.12 and 0.18±0.01 mg/kg) respectively. The concentration of heavy metals cadmium (Cd) and lead (Pb) declined with soil profile depth in both sewage and non-sewage irrigated soils. The long-term persistence of heavy metal contamination in soil can lead to severe issues; therefore, regular monitoring of sewage-irrigated soils is necessary to minimize heavy metal pollution.

Harnessing Lignocellulosic Crops for Phytomanagement of Contaminated Soils: A Multi-Country Study

The dwindling availability of agricultural land, caused by factors such as rapid population growth, urban expansion, and soil contamination, has significantly increased the pressure on food production. To address this challenge, cultivating non-food crops on contaminated land has emerged as a promising solution. This approach not only frees up fertile soil for food production but also mitigates human exposure to contaminants. This work aimed to examine the impact of soil contamination with Cd, Pb, Ni, and Zn on the growth, productivity, metal accumulation, and the tolerance of five lignocellulosic non-food crops: switchgrass (Panicum virgatum L.), biomass sorghum (Sorghum bicolor L. Moench), giant reed (Arundo donax L.), African fodder cane (Saccharum spontaneum L. spp. aegyptiacum Willd. Hackel), and miscanthus (Miscanthus × giganteus Greef et Deu.). A two-year pot experiment was conducted in Greece, Italy, and Portugal, following the same protocols and applying various levels of metals: Cd (0, 4, 8 mg kg−1), Pb and Zn (0, 450, 900 mg kg−1), and Ni (0, 110, 220 mg kg−1). The experimental design was completely randomized, with three replicates for each treatment. The results showed that switchgrass and sorghum generally maintained their height and productivity under Cd and Pb stress but were adversely affected by high Zn and Ni concentrations. Giant reed and African fodder cane showed reduced height and productivity at higher Ni and Zn levels. Miscanthus exhibited resilience in height but experienced productivity reductions only at the highest Zn concentration. Heavy metal uptake varied among crops, with switchgrass and sorghum showing high Cd and Pb uptake, while giant reed accumulated the most Cd and Zn. Miscanthus had the highest Ni accumulation. The tolerance indices indicated that switchgrass and sorghum were more tolerant to Cd and Zn at lower concentrations, whereas miscanthus had lower tolerance to Cd but a higher tolerance to Zn at higher concentrations. Giant reed and African fodder cane demonstrated stable tolerance across most heavy metals. Accumulation indices highlighted the effectiveness of switchgrass and sorghum in Cd and Pb uptake, while miscanthus excelled in Ni and Zn accumulation. The cluster analysis revealed similar responses to heavy metal stress between African fodder cane and giant reed, as well as between sorghum and miscanthus, with switchgrass displaying distinct behavior. Overall, the study highlights the differential tolerance and accumulation capacities of these crops, indicating the potential for phytoremediation applications and biomass production in heavy metal-contaminated soils.

Biosurfactant-assisted bio-electrokinetic enhanced remediation of heavy metal-contaminated soil.

Environmental soil contamination is a serious problem for humans worldwide, as it causes many diseases. The present study focuses on utilizing biosurfactants produced by Pseudomonas stutzeri (P. stutzeri) NA3 and Bacillus cereus (B. cereus) EN6, as an electrolyte for removing chromium (Cr) from contaminated soil using the electrokinetic (EK) process. As a result, biosurfactants produced by P. stutzeri NA3 and B. cereus EN6, being lipopeptides, increase heavy metal mobility in the EK process. The Cr removal efficiency of a novel electrolyte (biosurfactants) in the EK process was compared with that of NA3 and EN6 biosurfactants. The EK results revealed a maximum Cr removal of 75 and 70% by NA3 and EN6, respectively, at the end of 7 days. The biosurfactant aids in the breaking down of the heavy metals that are present deeper into the soil matrix. From the metagenomics analysis, it was identified that biosurfactant changes the microbial community with an enhanced ability to remove heavy metals. The phytotoxicity assay confirms that NA3 biosurfactant solution showed 95% seed germination and can lower hazardous pollutants in the soil. The application of biosurfactants as a potent electrolyte for the remediation of hazardous pollutants is an integrated process. Overall, the results of this study suggest that biosurfactants can serve as an economic and efficient electrolyte in the EK process to remove Cr from polluted soil.

Determination of Heavy Metal Concentrations at Ewu-Elepe, Ikorodu Dumpsite, Lagos, Nigeria

Heavy metal contamination of soil at dumpsites poses risks and hazards to humans and the ecosystems through inhalation of dust particles or dermal contact with the contaminated soil. Dumpsites are usually located at the outskirts of residential areas, but due to population increase in the urban centers as result of rural-urban movement which has become living habitats without considering the health implications. Thus, Ewu-Elepe dumpsite, located on the outskirts of Ikorodu, Lagos may pose a serious threat to residents of this area due to the improper disposal and ineffective management of waste at the dumpsite also, due to the metalic health issue recorded in this area. Therefore, this study was designed to determine the Heavy Metal Concentrations (HMC) and identify the type of Key Environmental Indicators (KEIs) responsible for the heavy metal contamination at the dumpsite. The Principal Component Analysis (PCA), Nemerow Integrated Pollution Index (NIPI), and Pollution Index (PI) procedures were adopted. The Akaike Information Criteria (AIC) was employed to determine the best KEI responsible for the presence of a particular heavy metal on the dumpsite. The Heavy Metals (HMs) found on the dumpsite were Zinc, Copper, Lead, Cadmium, Calcium, Manganese, and Iron. The identified KEIs on the dumpsite were: potential Hydrogen (pH), Electrical Conductivity (EC), Total Organic Carbon (TOC), Total Nitrogen (TN), Phosphorous (P), and Carbon Exchange Capacity (CEC). The AIC at 5% showed that the most significant KEI responsible for Zn was EC with the least value (16.21), pH for Pb (26.70), P for Ca (20.71), TOC for Cu (24.61) and Mn (81.09), TN for Cd (44.97), and CEC for Fe (41.04). The PCA and NIPI estimates for the heavy metals across the 20 sample points were (1760.57, 3.00); (1825.85, 2.30); (1330.80, 2.60); (1644.68, 2.40); (1602.57, 9.70); (1469.93, 2.40); (1379.85, 3.20); (1872.82, 2.40); (1859.30, 8.40); (1397.56, 2.30); (1995.32, 4.70); (1518.62, 3.10); (1565.33, 1.80); (1332.29, 5.10); (1748.59, 2.50); (1664.70, 3.90); (1792.24, 4.10); (1801.79, 2.30); (1801.18, 2.30); (1743.27, 2.00), respectively, implying that the dumpsite was highly concentrated in HMs. Copper, lead, cadmium, calcium, manganese, and iron highly polluted Ewu-Elepe dumpsite with potential hydrogen, electrical conductivity, total organic carbon, total nitrogen, phosphorous, and carbon exchange capacity as the key environmental indicators for the heavy metals.

Model test of in-situ remediation for heavy metal-contaminated clayey soil by artificial freezing and shaft washing

The low permeability of clayey soil and the pressure of liquid extraction and injection tend to form preferential flow paths in the soil, diminishing the remediation efficiency of shaft washing. Therefore, a new in-situ repair method combining artificial freezing and shaft washing is proposed. Using Pb and Cd contaminated clayey soil as the research object, in-situ model tests of different eluent types, concentrations, and suction modes were conducted to investigate the removal rate of heavy metals and the distribution of temperature and water field. The results demonstrated that the artificial freezing method can effectively induce the water (eluent) migration from the unfrozen zone to the freezing front. Besides, it effectively resolved the issue of poor washing efficiency caused by preferential flow between the extraction and injection wells during the extraction process. After five freeze-thaw cycles, the removal rate of Pb and Cd reached 46.16 % and 59.04 %, respectively. The combination of artificial freezing and plastic drainage plate technology merges artificial freezing and shaft washing methods to achieve the remediation of heavy metal-contaminated soil, providing a reference for the in-situ remediation of heavy metal-contaminated clayey soil.

Mode of application of sulfonated graphene modulated bioavailable heavy metal contents and microbial community composition in long-term heavy metal contaminated soil

Nanomaterials are increasingly recognized for their potential in soil remediation. However, their impact on soil microbial communities in contaminated soil remains poorly understood. In this study, we investigated the dynamic effects of sulfonated graphene (SG) following one-time or repeated applications on heavy metal availability and soil microbial communities in long-term heavy metal-contaminated soil over 180 days. Our findings revealed that one-time SG application at 30 mg kg−1 significantly increased the bioavailable cadmium (Cd) and copper (Cu) contents by approximately 30 %–40 % after 2 and 180 days. Repeated SG applications, however, displayed no significant influence on heavy metal availability. One-time SG application, coupled with the increased available Cd, induced significant enrichment of some specific functional bacterial genera involved in glycan biosynthesis metabolism and biosynthesis of other secondary metabolites, thereby decreasing the available contents of heavy metals after 90 days. However, the shifts in bacterial community structure and function were subsequently partially recovered after 180 days. Conversely, repeated SG treatments led to minimal alterations after 90 days while leading to similar shifts in the bacterial community at 60 mg kg−1 after 180 days. The fungal community structure remained largely unaltered across all SG treatments. Intriguingly, SG treatments substantially stimulated fungal biomass, with the stimulation degree dependent on SG dosage. These results provide valuable insights for developing phytoremediation strategies, suggesting tailored SG applications during specific growth phases to optimize remediation efficiency.

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

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

Heavy Metal Contamination and Risk of Sunflower Germination and Heavy Metal Translocation

Background: Heavy metal contamination in soils adversely affects plant growth, particularly in crops used for phytoremediation, such as sunflower (Helianthus annuus L.). Understanding the response of different sunflower varieties to heavy metal stress is crucial for developing effective phytoremediation strategies.Objective: This study aimed to evaluate the impact of nickel (Ni), cadmium (Cd), and lead (Pb) on the germination, growth attributes, and metal translocation of two sunflower varieties, Hysun-33 and FH-533.Methods: Sunflower seeds of Hysun-33 and FH-533 were sown in sand-filled pots treated with 0, 50, 100, 150, and 200 mM of Ni, Cd, and Pb. Germination rates, shoot and root lengths, and dry biomass were measured after 20 days. Metal concentrations in roots and shoots were analyzed using atomic absorption spectroscopy, and statistical analyses, including ANOVA and regression, were performed to assess the effects of metal concentrations.Results: Germination rates for Hysun-33 decreased from 79% at 0 mM to 0% at 200 mM, while FH-533 dropped from 75% to 5%. Shoot lengths decreased by 47% at 150 mM Ni, and root biomass was reduced by 62% under 200 mM Cd for both varieties.Conclusion: Cadmium posed the greatest threat to sunflower growth, emphasizing the need for enhanced metal tolerance in phytoremediation applications. Reducing heavy metal contamination in crops is vital for improving food safety and public health.

Effective soil remediation with fungal Co-inoculation and king grass for robust cadmium and chromium phytoextraction

Bioremediation, an economical and environmentally friendly approach, provides a sustainable solution for mitigating heavy metal contamination in soils. This study identifies four fungal strains—Trichoderma harzianum DAA8, Trichoderma reesei DAA9, Rhizomucor variabilis DFB3, and Trichoderma asperellum LDA4—that exhibit tolerance to cadmium (Cd) and chromium (Cr). These strains were isolated from soils impacted by heavy metal contamination in mining regions. Rigorous examinations of these strains led us to determine their Minimum Inhibitory Concentrations (MICs) and optimal absorption-reduction conditions. Our microscopic data and GC-MS analysis indicate that these strains can accumulate Cd and Cr by generating compounds, such as ketones and imines, in heavy metal environments. We evaluated the remediation efficacy of both single and co-cultures of Rhizomucor variabilis DFB3 and Trichoderma asperellum LDA4 in conjunction with king grass, a plant known for its heavy metal accumulation capabilities. Our findings indicated an impressive 41.9% increase in plant biomass and 47.2% and 64.4% increase in Cd and Cr accumulation respectively. The removal rates of Cd and Cr were 16.5% and 19.0%, respectively, following the co-inoculation of Rhizomucor variabilis DFB3 and Trichoderma asperellum LDA4. These rates represent increases of 37.1% and 33.7% compared to the removal rates achieved with king grass alone. This study not only advances strategies to manage Cd-Cr contamination but also sets a pathway for efficient heavy metal soil remediation using a microbial-plant combined technique.

Evaluation of the remediation effect of solid waste synergistic materials on heavy metal-contaminated soil

In this study, we investigated the effect of various solid waste materials such as fly ash (CFA), steel slag, and kaolinite on the simultaneous stabilization of As, Cd, Cu, Pb, and Zn in the soil of abandoned lead-smelting slag plant. Synchronous stabilization of HMs in highly contaminated soils was achieved using the application of 29 % formulated material Fe/Ca-Si based co-remediation material (FCS) with a ratio of FeSO4 + CFA + kaolinite of 14 %: 12 %: 3 %, the bioavailable content of HMs As, Cd, Cu, Pb, and Zn was reduced by 71.55 %, 49.62 %, 91.35 %, 61.37 %, and 41.45 %, respectively, and had little effect on the pH of the soil. Leaching toxicity analyses guaranteed the safety of restorative materials. The results of the field validation experiments showed that the FCS was able to effectively reduce the content of HMs in plant rhizomes and stabilized with maintenance time. European Community Bureau of Reference (BCR) and Wenzel sequential extraction procedures showed that FCS promoted the transformation of HMs in soil from unstable to stable phases. The analysis of soil microbial community diversity by FCS showed that it created a favorable soil living environment for microorganisms and was conducive to the stabilization of HMs. SEM, Surface scanning analysis, XRD, and FTIR results showed that FCS reacts with HMs to form a stable phase. Cost analysis showed that it has certain economic benefits. In conclusion, FCS is feasible for soil remediation in lead-smelting slag-polluted areas and also provides a way for high value-added utilization of solid waste.

Invasive Amaranthus spp. for heavy metal phytoremediation: Investigations of cadmium and lead accumulation and soil microbial community in three zinc mining areas

Amaranthus spp. are a group of strongly invasive and vigorous plants, and heavy metal phytoremediation using alien invasive Amaranthus spp. has been a popular research topic. In this study, the bioconcentration factor (BCF) and translocation factor (TF) of Amaranthus spp. were evaluated, focusing on the accumulation potential of cadmium (Cd) and lead (Pb) by plants from three different zinc mining areas, namely Huayuan (HYX), Yueyang (LYX), and Liuyang (LYX). The HYX area has the most severe Cd contamination, while the LYX area has the most apparent Pb contamination. The results showed that Amaranthus spp. had a strong Cd and Pb enrichment capacity in low-polluted areas. To elucidate the underlying mechanisms, we used high-throughput sequencing of 16S rRNA and internal transcribed spacer (ITS) regions to analyze rhizosphere bacterial and fungal communities in three areas. The results showed significant differences in the structure, function, and composition of microbial communities and complex interactions between plants and their microbes. The correlation analysis revealed that some key microorganisms (e.g., Amycolatopsis, Bryobacterium, Sphingomonas, Flavobacterium, Agaricus, Nigrospora, Humicola) could regulate several soil factors such as soil pH, organic matter (OM), available nitrogen (AN), and available phosphorus (AP) to affect the heavy metal enrichment capacity of plants. Notably, some enzymes (e.g., P-type ATPases, Cysteine synthase, Catalase, Acid phosphatase) and genes (e.g., ZIP gene family, and ArsR, MerR, Fur, NikR transcription regulators) have been found to be involved in promoting Cd and Pb accumulation in Amaranthus spp. This study can provide new ideas for managing heavy metal-contaminated soils and new ways for the ecological resource utilization of invasive plants in phytoremediation.

Hybrid machine learning approach integrating GMDH and SVR for heavy metal concentration prediction in dust samples.

In agricultural regions prone to dust storms, heavy metal contamination of soil and crops from airborne particulates poses significant risks to food safety and public health. This study has assessed the potential of machine learning models for predicting concentrations of toxic heavy metals like arsenic, chromium, and lead in dust from the agricultural Sistan region of southeastern Iran. This region experiences frequent dust storms mobilizing particulates from local dried lakes onto agricultural lands. The metals including nickel, copper, magnesium, cobalt, zinc, chromium, arsenic, and lead were measured in summer dust samples during 2012-2018 across 15 stations. Two hybrid models were developed combining group method of data handling (GMDH) and support vector regression (SVR) machine learning with harmony search optimization (H) so as to predict toxic metals arsenic, chromium, and lead using nickel, copper, magnesium, cobalt, and zinc inputs. Standard error maps were uncertainty higher in southern and western areas, and they are most impacted by dust storms. Results demonstrated that the hybrid GMDH + H and SVR + H models improved the accuracy of individual GMDH and SVR models in predicting heavy metals. The GMDH + H model performed the best for the lead with an agreement index (d-index) of 0.98, root mean square error (RMSE) of 2.87ppm, normalized RMSE (NRMSE) of 0.12, and coefficient of determination (RR) of 0.96. The SVR + H model showed the highest accuracy for arsenic and chromium, obtaining d-index 0.96, RMSE 0.47ppm, NRMSE 0.09, and RR 0.92 for arsenic, and d-index 0.96, RMSE 11.24ppm, NRMSE 0.16, and RR 0.93 for chromium. Taylor's diagram and heatmap analysis confirmed the superiority of the hybrid techniques. This work demonstrates the utility of state-of-the-art computing for addressing complex environmental health challenges.

Preparation of Polymeric Aluminum Chloride-Loaded Porous Carbon and Evaluation of Its Pb2+ Immobilization Mechanisms in Soil

In recent years, the remediation of heavy metal-contaminated soils has attracted great attention worldwide. Previous research on the removal of toxic heavy metals from wastewater effluents through adsorption by typical solid wastes (e.g., fly ash and coal gangue) has mainly focused on the control of wastewater pollutants. In this study, a coal gangue (CG) by-product from Hancheng City was used as a raw material to prepare polymeric aluminum chloride-loaded coal gangue-based porous carbon (PAC-CGPC) by hydrothermal synthesis. This material was subsequently employed to assess its performance in mitigating Pb2+ in soils. In addition, the effects of the pore structure of the prepared material on the adsorption rates, adsorption mechanisms, and plant root uptakes of soil Pb2+ were investigated in this study. The raw CG and prepared PAC-CGPC materials exhibited specific surface areas of 1.8997 and 152.7892 m2/g, respectively. The results of adsorption kinetics and isotherms indicate that the adsorption of Pb2+ based on PAC-CGPC mainly follows a pseudo-second-order kinetic model, suggesting that chemisorption may be the dominant process. In addition, the adsorption isotherm results showed that the Freundlich model explained better the adsorption process of Pb2+, suggests that the adsorption sites of lead ions on APC-CGPC are not uniformly distributed and tend to be enriched in APC, and also shows the ion exchange between aluminum and lead ions. The thermodynamic model fitting results demonstrated the occurrence of spontaneous and exothermic PAC-CGPC-based adsorption of Pb2+, involving ion exchange and surface complexation. The effects of the PAC-CGPC addition on soybean plants were further explored through pot experiments. The results revealed substantial decreases in the Pb2+ contents in the soybean organs (roots, stems, and leaves) following the addition of the PAC-CGPC material at a dose of 3% compared with the control and raw CG groups. Furthermore, the addition of the PAC-CGPC material at a dose of 3% effectively reduced the bioavailable Pb2+ content in the soil by 82.11 and enhanced soybean growth by 15.3%. These findings demonstrated the inhibition effect of the PAC-CGPC material on the translocation of Pb2+ in the soybean seedlings. The modified CG adsorbent has highly pore structure and good hydrophilicity, making it prone to migration in unsaturated soils and, consequently, enhancing Pb2+ immobilization. This research provides theoretical support for the development of CG-based materials capable of immobilizing soil pollutants.

Impact of Plant Growth-Promoting Rhizobacteria on Spinach Growth Concerned with Industrial Effluents Contaminated with Chromium

Heavy metal pollution in soil poses a significant threat to the environment and human health as it accumulates throughout the food chain. Remediation of soil contamination involves biological, chemical, and physical methods. Plant growth-promoting rhizobacteria inoculation helps some plants stabilize heavy metals in polluted soil by forming chelates with the metals. An experiment was conducted to examine the impact of Plant growth-promoting rhizobacteria on spinach growth and heavy metal stability in polluted soil with industrial effluents. The study found that Plant growth-promoting rhizobacteria (S1 and S2) enhanced growth and yield parameters, with fresh weights reaching 18% and 14%, highest dry weights at 10% and 40%, and longest roots at 11%. The treatment with Plant growth-promoting rhizobacteria S1 recorded the highest SPAD values (27%). Chemical parameters revealed that Cr levels in roots peaked in treatments without PGPR. The results concluded that PGPR can effectively remediate heavy metal-contaminated soils and industrial effluent-irrigated soils used for food crop growth.