Remediation techniques for removal of heavy metals from the soil contaminated through different sources: a review

Novel insights into the effect of arbuscular mycorrhizal fungi inoculation in soils under long-term biosolids application: Emphasis on antibiotic and metal resistance genes, and mobile genetic elements

The application of biosolids can improve soil fertility and crop productivity but also accompanies risks of heavy metals and antibiotics introduction. In the presence of heavy metals contamination, using arbuscular mycorrhizal fungi (AMF) is a promising strategy to enhance soil microbial community stability and plant tolerance resistance to heavy metals, and to reduce the spread of antibiotic resistance genes (ARGs). The present study investigated the impacts of AMF inoculation on soil and plant heavy metal contents, and soil microbial communities by pot experiments. The results showed that AMF inoculation significantly enhanced plant biomass, and reduced soil and plant heavy metals contents. While AMF inoculation did not alter bacterial and fungal community compositions, it increased bacterial diversity at higher biosolids concentrations. Notably, AMF inoculation enhanced microbial network complexity and increased keystone taxa abundance. Furthermore, several beneficial microorganisms with high resistance to heavy metals were enriched in AMF-inoculated soils. Metagenomic analysis revealed a reduction in the mobile genetic element (MGE) gene IS91 in AMF-inoculated soils and an increase in heavy metal resistance genes compared to soils without AMF. The possibility of reduction in MGE-mediated spread of ARGs is one of the key findings of this study. As a caution, this study also detected enrichment of few ARGs in high biosolids-amended soils with AMF inoculation. Overall, AMF inoculation could be a valuable strategy in agriculture for mitigating the environmental risks associated with biosolids, heavy metals and antibiotic resistance, thereby promoting sustainable soil management and health.

Complete genome sequence of Pseudarthrobacter sp. NIBRBAC000502770 from coal mine of Hongcheon on Republic of Korea

OBJECTIVES

The data were collected to obtain the complete genome sequence of Pseudarthrobacter sp. NIBRBAC000502770, isolated from the rhizosphere of Sasamorpha in a heavy metal-contaminated coal mine in Hongcheon, Republic of Korea. The objective was to explore the strain's genetic potential for plant growth promotion and heavy metal resistance, particularly arsenate and copper. The aim focused on identifying microbes that enhance plant growth in metal-tolerant environments and evaluating the strain's bioremediation and agricultural uses. This study sought key genes for bioremediation and agricultural applications in contaminated soils, aiding sustainable management and biotechnology.

DATA DESCRIPTION

We report the complete genome sequence of Pseudarthrobacter sp. NIBRBAC000502770, isolated from a coal mine in Hongcheon, Republic of Korea. The genome contains a chromosome (4,403,796 bp) and a plasmid (74,326 bp, named pMK-1) with 286-fold coverage. Genome annotation identified 4,209 genes, including 3,926 protein-coding genes, 51 tRNA genes, and 15 rRNA genes, with a G + C content of 66.1%. Functional analysis revealed genes related to plant growth promotion and heavy metal resistance, such as arsenate (arsR, arsC) and copper (copC, copD) resistance genes. Genes involved in auxin biosynthesis suggest potential agricultural applications. The genome and plasmid are available in GenBank (CP041198.1, CP014497.1), offering insights into bioremediation and plant growth in metal-contaminated environments.

Application risk and value of Cd-enriched poplar wood: Wood properties, leaching characteristics and brown rot resistance

This study investigated the application risk and value of Cd-enriched poplar wood, focusing on its wood properties, leaching characteristics, and brown rot resistance. The results indicated that Cd deposition in cell walls significantly inhibited brown rot fungi, thereby enhancing decay resistance. Furthermore, the extent of improvement in brown rot resistance was linked to wood density: the higher the density of Cd-enriched poplar wood, the stronger its resistance to brown rot. As the Cd concentration increased, the Cd distribution abundance and the wood crystallinity gradually increased. Structural changes were observed, including fluctuating microfibril angle and double wall thickness of fibers and vessels. Cd concentrations exceeding 50 mg/kg altered the chemical composition of the cell walls. The binding form of Cd in wood cell wall showed a trend of bound Cd ＞ free Cd ＞ residual Cd. Cd leaching occurred under cyclic soaking in water, which may lead to secondary contamination. However, under the condition of 75 % relative humidity, Cd leaching was negligible, suggesting potential for safer use in controlled environments. These findings provide valuable insights into the management and application of Cd-enriched wood, especially in contexts where decay resistance is critical or in water-exposed environments.

Conservative mechanism through various rapeseed (Brassica napus L.) varieties respond to heavy metal (Cadmium, Lead, Arsenic) stress

Introduction

Heavy metal soil pollution is a global issue that can be efficiently tackled through the process of phytoremediation. The use of rapeseed in the phytoremediation of heavy metal-contaminated agricultural land shows great potential. Nevertheless, its ability to tolerate heavy metal stress at the molecular level remains unclear.

Methods

Here, with 7-day seedlings as raw materials, we investigated physiological and biochemical indexes, analyzed the transcriptome sequencing for different treated materials (control, 50×, and 100×), combined with the results of transcriptome and proteome sequencing of the near-isogenic lines (F338 and F335) to reveal the response mechanism to heavy metal stress. Due to oxidative stress response caused by heavy metal stress, there are heavy effects on the emergence of rapeseeds and the growth of seedlings. Although rapeseed can alleviate oxidative stress by enhancing the enzyme activity, especially peroxidase in the oxidation system, this process has its limits. Rapeseed plants activate antioxidase, transport enzymes, and biological regulation to cope with heavy metal stress. Among these responses, peroxidase, ABC transporters, and abscisic acid are particularly significant in this process.

Results and discussion

Based on this study, we identified a breeding material with high adsorption capacity for heavy metals, which contributed to the research on resistance breeding in rapeseed. The results of this study may be useful to alleviate heavy metal soil pollution and tackle edible oil shortages in China.

A phytoremediation approach for the restoration of coal fly ash polluted sites: A review

Coal fly ash (CFA) is a predominant waste by-product of coal combustion which is disposed of in open ash dams that utilize large pieces of land. This waste material is classified as a hazardous substance in South Africa as well as in other countries due to its fine particles that are easily blown to the atmosphere and the unacceptable levels of heavy metals and persistent organic pollutants. Contaminants in CFA can pollute surface and ground water, agricultural sites, soil and therefore pose risks to the health of humans and the environment. More than 500 million tons of CFA is produced yearly and over 200 million tons remain unused globally. The production will continue due to high consumer energy demands, especially in countries with heavy reliance on coal for power generation. Despite a significant progress made on the application of phytoremediation approach for decontamination of polluted sites, there is very limited evidence for its potential in the rehabilitation of CFA dumps. Low organic carbon, microbial activities and availability of nutrients including nitrogen contribute to restricted plant growth in CFA, and therefore converting ash dumps to barren lands devoid of vegetation. Leguminous plant species can fix atmospheric nitrogen through symbiotic association with bacteria. Therefore, their intercropping mixture development can improve the chemistry of the substrate and facilitate nutrients availability to the companion plants. This approach can enhance the performance of phytoremediation and promote sustainable practices. The paper provides an overview of the ongoing burden of CFA disposal and discusses the ecological and economic benefits of using legumes, aromatic and bioenergy plants. We identify knowledge gaps to establishing vegetation in ash dumping sites, and provide insights to encourage continued research that will enhance the applicability of phytoremediation in restoration programs.

Precise application of water and fertilizer to crops: challenges and opportunities

Precision water and fertilizer application technologies have emerged as crucial innovations in sustainable agriculture, addressing the pressing need to enhance crop yield and quality while optimizing resource use and minimizing environmental impacts. This review systematically explores the latest advancements in precision water and fertilizer application technologies. It examines the integration of advanced sensors, remote sensing, and machine learning algorithms in precision agriculture, assessing their roles in optimizing irrigation and nutrient management. The study evaluates various precision techniques, including micro-irrigation systems, variable rate technology (VRT), and predictive modeling, along with their implementation in diverse agricultural settings. Furthermore, the review addresses the challenges posed by soil environmental heterogeneity and emphasizes the necessity for a scientific index system to guide precise applications. Advanced irrigation methods, such as subsurface drip irrigation and micro-sprinkling, improve water-use efficiency and reduce salinity levels, while precision fertilization techniques optimize nutrient uptake and minimize leaching. The integration of machine learning and remote sensing facilitates real-time monitoring and adaptive management, resulting in increased resource use efficiency and reduced environmental pollution. However, the effectiveness of these technologies is contingent upon addressing soil heterogeneity and developing standardized application indices. This review highlights the novel combination of advanced sensing technologies and data analytics in precision agriculture, enabling targeted interventions tailored to specific field conditions. It underscores the importance of integrating soil microbial community dynamics and biochemical indicators with precision management practices to enhance soil fertility and crop performance. Furthermore, the development of predictive models and time series analysis tools represents a significant advancement in anticipating and responding to changing environmental conditions. Precision water and fertilizer application technologies offer substantial benefits for sustainable agricultural practices by improving crop yields, enhancing resource efficiency, and mitigating environmental impacts. The strategic integration of these technologies with tailored agricultural practices and robust monitoring systems is essential for optimizing nutrient cycling and maintaining soil health. Addressing existing challenges through interdisciplinary research and collaborative efforts will further advance the implementation of precision agriculture, contributing to long-term soil sustainability and global food security.

Review on the relationship between microplastics and heavy metals in freshwater near mining areas

Microplastics (MPs), degraded from plastic wastes, have drawn significant attention worldwide due to its prevalence and rapid transition. Contamination of freshwater with MPs has become an emerging global issue. Heavy metals (HMs), a prominent global pollutant, also garnered much attention due to their potential interaction with MPs, presenting a multifaceted environmental threat. The primary source of HM contamination in freshwater has been identified as mining sites. Additionally, the increasing use of plastic materials within mining areas raises concerns about MP release into the surrounding freshwater environments. Recent studies only provide information on the contamination of HMs status with MPs. However, studies on the mechanism responsible for MPs contamination from both external and internal sources of freshwater MPs and HMs are limited. The knowledge gaps in the deposition and fate of MPs in various mining situations and the possibility of combined impacts of heavy metals and MPs in the ecosystem raise ecological concerns. Here, we review the origins of MPs and HM pollution within mining sites and explore the potential combined detrimental impacts on plants and animal life. We found out that polystyrene (PS) and polyethylene (PE) have higher adsorption affinity to heavy metals, and the mingle toxic consequence of the MPs and HM can depend on the MP surface properties, pH, and salinity of the neighboring water solution. The Langmuir and Freundlich isotherm models enable the efficient design of adsorption systems. The Langmuir model describes single-layer adsorption at homogeneous sites, while the Freundlich model addresses multilayer adsorption on heterogeneous surfaces. The crucial mechanism of adsorption and desorption that underlies the occurrence of both MPs and heavy metals is a decisive matter in this issue.

Multifaceted roles of zinc nanoparticles in alleviating heavy metal toxicity in plants: a comprehensive review and future perspectives

Heavy metal (HM) toxicity is a serious concern across the globe owing to their harmful impacts on plants, animals, and humans. Zinc oxide nanoparticles (ZnO-NPs) have gained appreciable attention in mitigating the adverse effects of abiotic stresses. The exogenous application of ZnO-NPs induces tolerance against HMs by improving plant physiological, metabolic, and molecular responses. They also interact with potential osmolytes and phyto-hormones to regulate the plant performance under HM stress. Moreover, ZnO-NPs also work synergistically with microbes and gene expression which helps to withstand HM toxicity. Additionally, ZnO-NPs also restrict the uptake and accumulation of HMs in plants which improves the plant performance. This review highlights the promising role of ZnO-NPs in mitigating the adverse impacts of HMs in plants. In this review, we explained the different mechanisms mediated by ZnO-NPs to counter the toxic effects of HMs. We also discussed the interactions of ZnO-NPs with osmolytes, phytohormones, and microbes in mitigating the toxic effects of HMs in plants. This review will help to learn more about the role of ZnO-NPs to mitigate HM toxicity in plants. Therefore, it will provide new insights to ensure sustainable and safer production with ZnO-NPs in HM-polluted soils.

Optimization of extracellular polysaccharides (EPS) production by Stenotrophomonas rhizophila JC1 and its protective effect on alfalfa under Pb2+ stress

Stenotrophomonas rhizophila JC1 and its extracellular polysaccharides (EPS) have been shown to effectively adsorb heavy metals in previous studies. The fermentation conditions of EPS by S. rhizophila JC1 were optimized using the Box-Behnken design (BBD). The composition, structural characteristics, and heavy metal adsorption capacity of EPS were systematically evaluated. The alleviation mechanism of Pb2+ stress on alfalfa was investigated through EPS inoculation. The maximum EPS yield reached 0.313 %. EPS consisted of glucose, glucosamine, galactose, and mannose in a molar ratio of 12.20:1:22.29:1.68. EPS also contained four distinct polymers with molecular weights of 623,683.71 Da, 144,072.27 Da, 105,892.21 Da, and 51,094.79 Da. The adsorption processes conformed to the pseudo-second-order model and Langmuir isotherm model. High Pb2+ concentrations significantly reduced germination percentage, germinative force, root length, fresh weight, and soluble protein, inhibited photosynthesis, exacerbated oxidative stress, and caused damage to the antioxidant system, thereby inhibiting seedling growth. EPS at low concentrations can promote alfalfa seed germination and mitigate Pb2+ stress by reducing the aforementioned damage. This study highlights the potential of EPS in soil remediation and enhancing plant resistance to heavy metal stress.

Isolation of biocrust cyanobacteria and evaluation of Cu, Pb, and Zn immobilisation potential for soil restoration and sustainable agriculture

Soil contamination by heavy metals represents an important environmental and public health problem of global concern. Biocrust-forming cyanobacteria offer promise for heavy metal immobilisation in contaminated soils due to their unique characteristics, including their ability to grow in contaminated soils and produce exopolysaccharides (EPS). However, limited research has analysed the representativeness of cyanobacteria in metal-contaminated soils. Additionally, there is a lack of studies examining how cyanobacteria adaptation to specific environments can impact their metal-binding capacity. To address this research gap, we conducted a study analysing the bacterial communities of cyanobacteria-dominated biocrusts in a contaminated area from South Sardinia (Italy). Additionally, by using two distinct approaches, we isolated three Nostoc commune strains from cyanobacteria-dominated biocrust and we also evaluated their potential to immobilise heavy metals. The first isolation method involved acclimatizing biocrust samples in liquid medium while, in the second method, biocrust samples were directly seeded onto agar plates. The microbial community analysis revealed Cyanobacteria, Bacteroidota, Proteobacteria, and Actinobacteria as the predominant groups, with cyanobacteria representing between 13.3 % and 26.0 % of the total community. Despite belonging to the same species, these strains exhibited different growth rates (1.1-2.2 g L-1 of biomass) and capacities for EPS production (400-1786 mg L-1). The three strains demonstrated a notable ability for metal immobilisation, removing up to 88.9 % of Cu, 86.2 % of Pb, and 45.3 % of Zn from liquid medium. Cyanobacteria EPS production showed a strong correlation with the removal of Cu, indicating its role in facilitating metal immobilisation. Furthermore, differences in Pb immobilisation (40-86.2 %) suggest possible environmental adaptation mechanisms of the strains. This study highlights the promising application of N. commune strains for metal immobilisation in soils, offering a potential bioremediation tool to combat the adverse effects of soil contamination and promote environmental sustainability.

Ecological risk assessment of heavy metals contaminated mining sites of eastern india using soil and moss

The blooming industrialization and urbanization is leading to increased mining operations. These intensified mining activities emit heavy metals into the environment, posing serious threats to ecosystems. Hence, this study focused on assessing heavy metal pollution in mining soil, utilizing mosses as bioindicators. The ecological risk, geo-accumulation factor, and contamination factor have been calculated to know the harmful effect of heavy metals on ecosystem. The study covered three distinct mining sites of eastern India within Odisha: Jajpur's Sukinda Valley (SP1, Cr), Keonjhar's Joda-Barbil (SP2, Fe and Mn), and Sundargarh's Koira-Joda (SP3, Fe). The collection of 48 soil samples through random sampling revealed significant variations in heavy metal concentrations. SP1 recorded Cr concentration of 6572 ± 445 mg/kg and Ni of 8042.47 ± 501.38 mg/kg, surpassing eco-toxicological levels. The storage site in SP2 exhibited the highest Fe concentration at 9872 ± 502 mg/kg, and Mn levels in SP3 were at 7884 ± 432 mg/kg. Storage areas in all three regions held the highest concentrations of heavy metals. Mosses in studied area demonstrated as potential bioindicators for monitoring heavy metal pollution. EF and Igeo assessments showed Cd, Pb, Hg, and other heavy metal contamination compared to earlier investigations. This study indicated higher ecological risks for Pb, As, Cu, Ni, and Zn. The Hyophila involuta accumulates Mn, Cr, Cd, Pb, Fe, and Hg, while Barbula arcuata accumulates Mn, As, and Cu in SP1. Hyophila involuta and Trematodon longicollis accumulate Mn, Cr, Cd, Pb, Fe, Hg, and Zn in SP2. Trematodon ambiguous accumulates Cd, Fe, and Ni, while Fissidens diversifolius accumulates Mn, Cr, Hg, As, Cu, and Zn in SP3. These findings emphasize the necessity of monitoring heavy metal pollution in contaminated zones using moss as a potential bioindicator.

Comparative assessment of Brassica cultivars for genotypic variability in phytoremediation of soil exposed to lead (Pb) contamination

The soil pollution caused with accretion of pollutant elements like lead (Pb) is the major environmental concern nowadays. Phytoremediation of contaminated soils using Brassica cultivars that act as hyperaccumulator plants for Pb emerges as an important technique for decontamination of Pb spiked soils. Therefore, pot study was carried out to compare the efficiency of three Brassica cultivars and select the most efficient cultivar for phytoremediation of Pb spiked soils. The experimental soil was contaminated with Pb applied @ 0, 125, 250, 500, 750, and 1,000 mg kg-1 soil. Our outcomes reflected that increased rates of Pb pollution in soil from 125 to 1,000 mg kg-1 soil resulted in decline of yield but enhanced the Pb acquisition of all Brassica cultivars. Comparison of cultivars indicated the highest biomass production (16.7 g pot-1), Pb acquisition (4,011.7 μg pot-1), contamination indices i.e., tolerance index (70.6), and bioaccumulation coefficient (17.03) by Brassica juncea produced thereby proving it as the most efficient cultivar for phytoremediation of Pb spiked soil.

Remediation of cadmium contaminated soil using electrokinetic-phytoremediation system with rotary switching electrodes

Considering both electrokinetic remediation and phytoremediation have limitations, an electrokinetic phytoremediation (EP) system was constructed to obtain efficient and environmentally friendly remediation results. This study indicates that the electric field can promote the absorption of Cd by ryegrass with little impact on soil physicochemical properties under the condition of rotary switching electrodes, and the accumulation of Cd in the aboveground and underground parts of ryegrass increased by 145.2% and 93.7%, respectively. The DC electric field combined with ryegrass under rotary switching electrode mode proved to be the optimal condition for the remediation of Cd contaminated soil with a remediation efficiency of 66.7%. Moreover, the rotary switching of the electrodes alleviated the suppression of the growth of ryegrass by the DC electric field. During the EP remediation process, the electric field promoted the transformation of the residue state of Cd to the other forms, which accelerated the desorption rate of Cd from the soil and facilitated the migration of Cd into plants. In conclusion, EP is a green and efficient remediation technology for heavy metal contaminated soil with good application prospects.

The Concentration of Potentially Toxic Elements in Common Carp (Cyprinus carpio) Fish: Systematic Review and Meta-Analysis and Dietary Health Risk Assessment

Common carp (Cyprinus carpio) is one of the most consumed fish in the world and can be exposed to various forms of pollution, such as potential toxic elements (PTEs). Several studies have been conducted on the concentration of PTEs in common carp fish. The aims of the current study were to meta-analyze the concentration of PTEs in common carp fish and estimate human health risks in consumers. A search was conducted in international databases, including Scopus, PubMed, Science Direct, Web of Science, and Embase to retrieve papers up to January 20, 2024. The non-carcinogenic risk due to PTEs in fish fillets was calculated via the target hazard quotient (THQ), and the carcinogenic risk due to iAs in fish fillets was calculated via cancer risk (CR). The highest concentrations of Cu, methyl-Hg, and Ni were observed in the fillets of common carp fish. The non-carcinogenic risk was lower than 1 in all countries; hence, consuming common carp fish does not pose a non-carcinogenic risk. Adult consumers in Iraq were exposed to an unacceptable carcinogenic due to iAs in common carp fish. Hence, it is recommended that plans be conducted to reduce the concentration of PTEs in common carp fish in Iraq.

Assessment of growth, reproduction, and vermi-remediation potentials of Eisenia fetida on heavy metal exposure

Heavy metal pollution is a significant environmental concern with detrimental effects on ecosystems and human health, and traditional remediation methods may be costly, energy-intensive, or have limited effectiveness. The current study aims were to investigate the impact of heavy metal toxicity in Eisenia fetida, the growth, reproductive outcomes, and their role in soil remediation. Various concentrations (ranging from 0 to 640 mg per kg of soil) of each heavy metal were incorporated into artificially prepared soil, and vermi-remediation was conducted over a period of 60 days. The study examined the effects of heavy metals on the growth and reproductive capabilities of E. fetida, as well as their impact on the organism through techniques such as FTIR, histology, and comet assay. Atomic absorption spectrometry demonstrated a significant (P < 0.000) reduction in heavy metal concentrations in the soil as a result of E. fetida activity. The order of heavy metal accumulation by E. fetida was found to be Cr > Cd > Pb. Histological analysis revealed a consistent decline in the organism's body condition with increasing concentrations of heavy metals. However, comet assay results indicated that the tested levels of heavy metals did not induce DNA damage in E. fetida. FTIR analysis revealed various functional group peaks, including N-H and O-H groups, CH2 asymmetric stretching, amide I and amide II, C-H bend, carboxylate group, C-H stretch, C-O stretching of sulfoxides, carbohydrates/polysaccharides, disulfide groups, and nitro compounds, with minor shifts indicating the binding or accumulation of heavy metals within E. fetida. Despite heavy metal exposure, no significant detrimental effects were observed, highlighting the potential of E. fetida for sustainable soil remediation. Vermi-remediation with E. fetida represents a novel, sustainable, and cutting-edge technology in environmental cleanup. This study found that E. fetida can serve as a natural and sustainable method for remediating heavy metal-contaminated soils, promising a healthier future for soil.

Application Prospect of Ion-Imprinted Polymers in Harmless Treatment of Heavy Metal Wastewater

With the rapid development of industry, the discharge of heavy metal-containing wastewater poses a significant threat to aquatic and terrestrial environments as well as human health. This paper provides a brief introduction to the basic principles of ion-imprinted polymer preparation and focuses on the interaction between template ions and functional monomers. We summarized the current research status on typical heavy metal ions, such as Cu(II), Ni(II), Cd(II), Hg(II), Pb(II), and Cr(VI), as well as metalloid metal ions of the As and Sb classes. Furthermore, it discusses recent advances in multi-ion-imprinted polymers. Finally, the paper addresses the challenges faced by ion-imprinted technology and explores its prospects for application.

Biomonitoring and Biomathematical Modeling of Health Risks Associated with Dumpsite Grown Vegetables in Lagos State

Conversion of dumpsites to farm lands in several communities is a usual practice in Nigeria. Wastes accumulate heavy metals in a variety of forms. This study assessed the concentration, degrees of contamination, and attendant health risk of heavy metals (HMs), using two major indigenous vegetables (Amaranthus viridis and Talinum triangulare) grown on five major dumpsites in Lagos state. After wet digestion, the mean concentrations of the HMs in the vegetable samples were evaluated using atomic absorption spectrophotometer (AAS). Daily intake of metals (DIM), target hazard quotient (THQ), and hazard index (HI) biomathematics were employed in the assessment of non-carcinogenic health risk. Incremental lifetime cancer risk (ILCR) assessment was used to assess carcinogenicity. The obtained result shows that the concentrations of HMs fell within the following ranges: (0.37 to 0.59), (0.07 to 1.36), (0.30 to 1.92), (0.00 to 0.03), and (0.00 to 0.04) mg/kg; for zinc (Zn), lead (Pb), Iron (Fe), cadmium (Cd), and chromium (Cr), respectively, with low to moderate variability. At Ikorodu dumping site, the Pb concentration was above the World Health Organization (WHO) permissible range and has the highest contamination factor. DIM for Pb was also above threshold values (> 1) in both adults and children, while the THQ values for Fe, Pb, and Cd were above 1 (> 1) in both adults and children. HI values for the vegetables exceeded WHO normal range (> 1), except Abule-Egba dumps' samples (70% HI greater than 1 in adults and 90% HI greater than 1 in children). Additionally, the ILCR values of above 50% of the samples were above the WHO (10-6) limits, with the highest value in children (Cd, 1.064 × 10-3) indicating high risk of carcinogenicity over a life time of exposure. Thus, the results revealed great health risk from consumption of vegetables from the four major dumping sites, with children being at greater risk.

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Effect of various phosphorus levels on the extraction of Cd, the transformation of P, and phosphorus-related gene during the phytoremediation of Cd contaminated soil

Phytoremediation has emerged as a common technique for remediating Cd pollution in farmland soil. Moreover, phosphorus, an essential element for plants, can alter the pectin content of plant cell walls and facilitate the accumulation of Cd in plant tissues, thereby enhancing phytoremediation efficiency. Therefore, pot experiments were conducted in order to investigate the effect of phosphorus levels on Cd extraction, phosphorus transformation and phosphorus-related genes during phytoremediation. The results revealed that an optimal application of suitable phosphate fertilizers elevated the soil's pH and electrical conductivity (EC), facilitated the conversion of soil from insoluble phosphorus into available forms, augmented the release of pertinent enzyme activity, and induced the expression of phosphorus cycling-related genes. These enhancements in soil conditions significantly promoted the growth of ryegrass. When applying phosphorus at a rate of 600 mg/kg, ryegrass exhibited plant height, dry weight, and chlorophyll relative content that were 1.27, 1.26, and 1.18 times higher than those in the control group (P0), while the Cd content was 1.12 times greater than that of P0. The potentially toxic elements decline ratio and bioconcentration factor were 42.86% and 1.17 times higher than those of P0, respectively. Consequently, ryegrass demonstrated the highest Cd removal efficiency under these conditions. Results from redundancy analysis (RDA) revealed a significant correlation among pH, total phosphorus, heavy metal content, phosphorus forms, soil enzyme activity, and phosphorus-related genes. In conclusion, this study suggests applying an optimal amount of suitable phosphate fertilizers can enhance restoration efficiency, leading to a reduction in soil Cd content and ultimately improving the safety of crop production in farmlands.

Calcium polypeptide mitigates Cd toxicity in rice via reducing oxidative stress and regulating pectin modification

KEY MESSAGE

Calcium polypeptide plays a key role during cadmium stress responses in rice, which is involved in increasing peroxidase activity, modulating pectin methylesterase activity, and regulating cell wall by reducing malondialdehyde content. Cadmium (Cd) contamination threatens agriculture and human health globally, emphasizing the need for sustainable methods to reduce cadmium toxicity in crops. Calcium polypeptide (CaP) is a highly water-soluble small molecular peptide acknowledged for its potential as an organic fertilizer in promoting plant growth. However, it is still unknown whether CaP has effects on mitigating Cd toxicity. Here, we investigated the effect of CaP application on the ability to tolerate toxic Cd in rice. We evaluated the impact of CaP on rice seedlings under varying Cd stress conditions and investigated the effect mechanism of CaP mitigating Cd toxicity by Fourier transform infrared spectroscopy (FTIR), fluorescent probe dye, immunofluorescent labeling, and biochemical analysis. We found a notable alleviation of Cd toxicity by reduced malondialdehyde content and increased peroxidase activity. In addition, our findings reveal that CaP induces structural alterations in the root cell wall by modulating pectin methylesterase activity. Altogether, our results confirm that CaP not only promoted biomass accumulation but also reduced Cd concentration in rice. This study contributes valuable insights to sustainable strategies for addressing Cd contamination in agricultural ecosystems.

Dual Z-scheme heterojunction Ce2Sn2O7/Ag3PO4/V@g-C3N4 for increased photocatalytic degradation of the food additive tartrazine, in the presence of persulfate: Kinetics, toxicity, and density functional theory studies

This study involved the synthesis of a Ce2Sn2O7/Ag3PO4/V@g-C3N4 composite through hydrothermal methods, followed by mechanical grinding. The resulting heterojunction exhibited improved catalytic activity under visible light by effectively separating electrons and holes (e-/h+). The degradation of Tartrazine (TTZ) reached 93.20% within 50 min by employing a ternary composite at a concentration of 10 mg L-1, along with 6 mg L-1 of PS. The highest pseudo-first-order kinetic constant (0.1273 min-1 and R2 = 0.951) was observed in this system. The dual Z-scheme heterojunction is developed by Ce2Sn2O7, Ag3PO4, and V@g-C3N4, and it may increase the visible light absorption range while also accelerating charge carrier transfer and separation between catalysts. The analysis of the vulnerability positions and degradation pathways of TTZ involved the utilization of density functional theory (DFT) and gas chromatography-mass spectrometry (GC-MS) to examine the intermediate products. Therefore, Ce2Sn2O7/Ag3PO4/V@g-C3N4 is an excellent ternary nanocomposite for the remediation of pollutants.

Increased risk of heavy metal accumulation in mangrove seedlings in coastal wetland environments due to microplastic inflow

The recovery phase of mangrove seedlings in coastal wetland ecosystems can be negatively affected by exposure to external pollutants. This study aimed to investigate the impact of microplastics (MPs) influx, specifically polystyrene (PS) and polymethyl methacrylate (PMMA), on the growth of Aegiceras corniculatum seedlings and their accumulation of heavy metals (HMs). PS and PMMA significantly increased HMs accumulation (up to 21.0-548%), particularly in the roots of seedlings, compared to the control treatment (CK). Additionally, elevated activities of malondialdehyde and catalase enzymes were observed in the leaves of seedlings, while peroxidase enzyme activity decreased. Topological analysis of the root sediment microbiota coexistence network revealed that the modularization data increased from 0.69 (CK treatment) to 1.07 (PS treatment) and 5.11 (PMMA treatment) under the combined stress of MPs and HMs. This suggests that the introduction of MPs intensifies microbial modularization. The primary cause of increased HMs accumulation in plants is the MPs input, which influences the secretion of organic acids by plants and facilitates the shift of HMs in sediment to bioavailable states. Furthermore, changes in microbial clustering may also contribute to the elevated HMs accumulation in plants. This study provides valuable insights into the effects of external pollutants on mangrove seedlings and offers new perspectives for the preservation and restoration of mangrove coastal wetlands.

Cadmium biosorption and mechanism investigation using two cadmium-tolerant microorganisms isolated from rhizosphere soil of rice

Microbial remediation of cadmium-contaminated soil offers advantages like environmental friendliness, cost-effectiveness, and simple operation. However, the efficacy of this remediation process relies on obtaining dominant strains and a comprehensive understanding of their Cd adsorption mechanisms. This study identified two Cd-resistant bacteria, Burkholderia sp. 1-22 and Bacillus sp. 6-6, with significant growth-promoting effects from rice rhizosphere soil. The strains showed remarkable Cd resistance up to ∼200 mg/L and alleviated Cd toxicity by regulating pH and facilitating bacterial adsorption of Cd. FTIR analysis showed crucial surface functional groups, like carboxyl and amino groups, on bacteria played significant roles in Cd adsorption. The strains could induce CdCO3 formation via a microbially induced calcium precipitation (MICP) mechanism, confirmed by SEM-EDS, X-ray analysis, and elemental mapping. Pot experiments showed these strains significantly increased organic matter and enzyme activity (e.g., urease, sucrase, peroxidase) in the rhizosphere soil versus the control group. These changes are crucial for restricting Cd mobility. Furthermore, strains 6-6 and 1-22 significantly enhance plant root detoxification of Cd, alleviating toxicity. Notably, increased pH likely plays a vital role in enhancing Cd precipitation and adsorption by strains, converting free Cd into non-bioavailable forms.

Endophytic bacteria for Cd remediation in rice: Unraveling the Cd tolerance mechanisms of Cupriavidus metallidurans CML2

The utility of endophytic bacteria in Cadmium (Cd) remediation has gained significant attention due to their ability to alleviate metal-induced stress and enhance plant growth. Here, we investigate C. metallidurans CML2, an endophytic bacterial strain prevalent in rice, showing resilience against 2400 mg/L of Cd(II). We conducted an in-depth integrated morphological and transcriptomic analysis illustrating the multifarious mechanisms CML2 employs to combat Cd, including the formation of biofilm and CdO nanoparticles, upregulation of genes involved in periplasmic immobilization, and the utilization of RND efflux pumps to extract excess Cd ions. Beyond Cd, CML2 exhibited robust tolerance to an array of heavy metals, including Mn2+, Se4+, Ni2+, Cu2+, and Hg2+, demonstrating effective Cd(II) removal capacity. Furthermore, CML2 has exhibited plant growth-promoting properties through the production of indole-3-acetic acid (IAA) at 0.93 mg/L, soluble phosphorus compounds at 1.11 mg/L, and siderophores at 22.67%. Supportively, pot experiments indicated an increase in root lengths and a decrease in Cd bioaccumulation in rice seedlings inoculated with CML2, consequently reducing Cd translocation rates from 43% to 31%. These findings not only contribute to the understanding of Cd resistance mechanisms in C. metallidurans, but also underscore CML2's promising application in Cd remediation within rice farming ecosystems.

Revitalizing contaminated lands: A state-of-the-art review on the remediation of mine-tailings using phytoremediation and genomic approaches

The mining industry has historically served as a critical reservoir of essential raw materials driving global economic progress. Nevertheless, the consequential by-product known as mine tailings has consistently produced a substantial footprint of environmental contamination. With annual discharges of mine tailings surpassing 10 billion tons globally, the need for effective remediation strategies is more pressing than ever as traditional physical and chemical remediation techniques are hindered by their high costs and limited efficacy. Phytoremediation utilizing plants for remediation of polluted soil has developed as a promising and eco-friendly approach to addressing mine tailings contamination. Furthermore, sequencing of genomic DNA and transcribed RNA extracted from mine tailings presents a pivotal opportunity to provide critical supporting insights for activities directed towards the reconstruction of ecosystem functions on contaminated lands. This review explores the growing prominence of phytoremediation and metagenomics as an ecologically sustainable techniques for rehabilitating mine-tailings. The present study envisages that plant species such as Solidago chilensis, Festuca arundinacea, Lolium perenne, Polygonum capitatum, Pennisetum purpureum, Maireana brevifolia, Prosopis tamarugo etc. could be utilized for the remediation of mine-tailings. Furthermore, a critical evaluation of the organic and inorganic ammendments that optimize conditions for the remediation of mine tailings is also provided. The focus of this review extends to the exploration of environmental genomics to characterize microbial communities in mining sites. By delving into the multifaceted dimensions of phytoremediation and genomics for mine tailings, this study contributes to the ongoing efforts to revitalize contaminated lands for a sustainable and environmentally friendly future.

A Holistic Approach to Circular Bioeconomy Through the Sustainable Utilization of Microalgal Biomass for Biofuel and Other Value-Added Products

Emissions from transportation and industry primarily cause global warming, leading to floods, glacier melt, and rising seas. Widespread greenhouse gas emissions and resulting global warming pose significant risks to the environment, economy, and society. The need for alternative fuels drives the development of third-generation feedstocks: microalgae, seaweed, and cyanobacteria. These microalgae offer traits like rapid growth, high lipid content, non-competition with human food, and growth on non-arable land using brackish or waste water, making them promising for biofuel. These unique phototrophic organisms use sunlight, water, and carbon dioxide (CO2) to produce biofuels, biochemicals, and more. This review delves into the realm of microalgal biofuels, exploring contemporary methodologies employed for lipid extraction, significant value-added products, and the challenges inherent in their commercial-scale production. While the cost of microalgae bioproducts remains high, utilizing wastewater nutrients for cultivation could substantially cut production costs. Furthermore, this review summarizes the significance of biocircular economy approaches, which encompass the utilization of microalgal biomass as a feed supplement and biofertilizer, and biosorption of heavy metals and dyes. Besides, the discussion extends to the in-depth analysis and future prospects on the commercial potential of biofuel within the context of sustainable development. An economically efficient microalgae biorefinery should prioritize affordable nutrient inputs, efficient harvesting techniques, and the generation of valuable by-products.

Remediation of toxic metal and metalloid pollution with plant symbiotic fungi

Anthropogenic activities have dramatically accelerated the release of toxic metal(loid)s into soil and water, which can be subsequently accumulated in plants and animals, threatening biodiversity, human health, and food security. Compared to physical and chemical remediation, bioremediation of metal(loid)-polluted soil using plants and/or plant symbiotic fungi is usually low-cost and environmentally friendly. Mycorrhizal fungi and endophytic fungi are two major plant fungal symbionts. Mycorrhizal fungi can immobilize metal(loid)s via constitutive mechanisms, including intracellular sequestration with vacuoles and vesicles and extracellular immobilization by cell wall components and extracellular polymeric substances such as glomalin. Mycorrhizal fungi can improve the efficacy of phytoremediation by promoting plant symplast and apoplast pathways. Endophytic fungi also use constitutive cellular components to immobilize metal(loid)s and to reduce the accumulation of metal(loid)s in plants by modifying plant physiological status. However, a specific mechanism for the removal of methylmercury pollution was recently discovered in the endophytic fungi Metarhizium, which could be acquired from bacteria via horizontal gene transfer. In contrast to mycorrhizal fungi that are obligate biotrophs, some endophytic fungi, such as Metarhizium and Trichoderma, can be massively and cost-effectively produced, so they seem to be well-placed for remediation of metal(loid)-polluted soil on a large scale.

Influence of soil amendments on phytostabilization, localization and distribution of zinc and cadmium by marigold varieties

Marigolds (Tagetes erecta L.) were evaluated for phytoremediation potential of cadmium (Cd) and zinc (Zn) as a function of amendment application to soil. Vermicompost (V), biodigestate (Bi), and combined V + Bi (VBi) were used as soil amendments in Zn and Cd co-contaminated soils. Application of soil amendments can alter physicochemical properties of soils, particularly pH, EC, CEC and nutrient concentrations. The VBi treatment resulted in highest percentage growth rate in biomass (52 %) for the Twenty yellow variety of marigold. Also, in the VBi treatment, leaves of Dragon yellow variety exhibited maximal accumulation of Zn and Cd. Flower extracts of Twenty yellow in the V treatment had substantial carotenoid content (71.7 mg L-1) and lowest IC50 value (43.7 mg L-1), thus indicating it had highest DPPH free radical scavenging activity. Dragon yellow exhibited highest values of ferric reducing antioxidant power (FRAP; 2066 mg L-1), total flavonoids content (TFC; 64.1 mg L-1), and total phenolics content (TPC; 50.9 mg L-1). Using X-ray fluorescence (XRF) spectroscopy, the atomic percentages of Zn and Cd in all marigold varieties and treatments showed similar patterns over flower surfaces, seeds, and flower petals in descending order. Prime yellow in the V treatment resulted in higher Zn accumulation in roots (bioconcentration factor of root value) > 1 and translocation factor value < 1, indicating an enhanced ability of the plant for phytostabilization. Application of V altered antioxidant activities and production of bioactive compounds as well as enhanced the excluder potential of Cd and Zn, particularly in the Prime yellow variety. Application of Bi contributed to increased flower numbers, suggesting that floriculturists cultivating marigolds for ornamental purposes may be able to generate revenue in terms of productivity and quality of flowers when marigolds are grown on contaminated land.

The efficient applications of native flora for phytorestoration of mine tailings: a pan-global survey

Mine tailings are the discarded materials resulting from mining processes after minerals have been extracted. They consist of leftover mineral fragments, excavated land masses, and disrupted ecosystems. The uncontrolled handling or discharge of tailings from abandoned mine lands (AMLs) poses a threat to the surrounding environment. Numerous untreated mine tailings have been abandoned globally, necessitating immediate reclamation and restoration efforts. The limited feasibility of conventional reclamation methods, such as cost and acceptability, presents challenges in reclaiming tailings around AMLs. This study focuses on phytorestoration as a sustainable method for treating mine tailings. Phytorestoration utilizes existing native plants on the mine sites while applying advanced principles of environmental biotechnology. These approaches can remediate toxic elements and simultaneously improve soil quality. The current study provides a global overview of phytorestoration methods, emphasizing the specifics of mine tailings and the research on native plant species to enhance restoration ecosystem services.

Microwave promoted graft copolymerization of poly(ethylacrylate) onto k-carrageenan for removal of Cd and Ni from aqueous solution

Microwave promoted graft copolymerization of poly (ethyl acrylate) onto kappa-carrageenan in presence of a redox pair (ascorbic acid and potassium persulfate) led to the formation of a novel copolymer hydrogel, kappa-carrageenan-graft-poly (ethylacrylate). By varying the reaction conditions such as the microwave power, reaction time, concentration of kappa-carrageenan, ascorbic acid and persulfate, copolymers of highest percentage grafting was obtained and characterized by FT-IR, SEM, TGA and XRD. The copolymer was evaluated as an adsorbent for the adsorption of Ni(II) and Cd(II). Various adsorption parameters such as contact time, pH, initial metal ion concentration, temperature, electrolyte strength and adsorbent dosage were varied to obtain the optimum conditions for the adsorption. The adsorption data for Cd(II), fitted better for Langmuir and Ni(II), fitted much better for Freundlich adsorption isotherm model. Maximum adsorption obtained for cadmium ions and nickel ions was 308.6 mg/g-1 and 305.8 mg/g-1 respectively. The adsorption of both metal ions followed pseudo second order kinetic model. The positive ΔH values endorsed the adsorption process to be endothermic in nature. The negative values of ΔG indicate the spontaneity of the adsorption process while the positive ΔS values showed that the adsorption of metal ions proceeded with increased randomness at the surface of the copolymer. High recovery percentage of the metal ions from the adsorbent indicates that the copolymer can be used for more adsorption cycles.

What do we know about dermal bioaccessibility of metals coated on antibacterial films?

Antibacterial films have gained attention since the outbreak of the COVID-19 pandemic; however, the impact of metals contained in antibacterial films on human safety have not been sufficiently investigated. This study reports on the important features that must be considered when assessing the bioaccessibility of Ag, Cu, and Zn in antibacterial films. Specifically, the effects of the artificial sweat component (i.e., amino acid and pH), surface weathering of antibacterial films, wipe sampling, and sebum were carefully examined. Our findings suggest that amino acids greatly affect bioaccessibility as amino acids act as ligands to facilitate metal ion leaching. In addition, constant exposure to ultraviolet C causes the film surface to oxidize, which significantly increases metal bioaccessibility due to the electrostatic repulsion between metal oxides and organic substrates. The presence of sebum in artificial sweat and physical damage to the film surface had no significant effects. Furthermore, the wipe sampling used to mimic the realistic dermal contact suggests the feasibility of applying this method for the assessment of bioaccessibility of metals in antibacterial films. The method offers significant advantages for evaluating the human safety aspects of skin contact with consumer products in future research.

Heavy metals pollution from smelting activities: A threat to soil and groundwater

Throughout the literature, the word "heavy metal" (HM) has been utilized to describe soil contamination; in this context, we characterize it as those elements with a density greater than 5 g per cubic centimeter. Contamination is one of the major global health concerns, especially in China. China's rapid urbanization over the past decades has caused widespread urban water, air, and soil degradation. This study provides a complete assessment of the soil contamination caused by heavy metals in China's mining and smelting regions. The study of heavy metals (HMs) includes an examination of their potential adverse impacts, their origins, and strategies for the remediation of soil contaminated by heavy metals. The presence of heavy metals in soil can be linked to both natural and anthropogenic processes. Studies have demonstrated that soils contaminated with heavy metals present potential health risks to individuals. Children are more vulnerable to the effects of heavy metal pollution than adults. The results highlight the significance of heavy metal pollution caused by mining and smelting operations in China. Soil contaminated with heavy metals poses significant health concerns, both carcinogenic and non-carcinogenic, particularly to children and individuals living in heavily polluted mining and smelting areas. Implementing physical, chemical, and biological remediation techniques is the most productive approach for addressing heavy metal-contaminated soil. Among these methods, phytoremediation has emerged as a particularly advantageous option due to its cost-effectiveness and environmentally favorable characteristics. Monitoring heavy metals in soils is of utmost importance to facilitate the implementation of improved management and remediation techniques for contaminated soils.

Heavy metal tolerance, and metal biosorption by exopolysaccharides produced by bacterial strains isolated from marine hydrothermal vents

The present study highlights heavy metal tolerance, EPS production, and biosorption capacity of four hydrothermal vent bacterial strains, namely Exiguobacterium aquaticum, Mammaliicoccus sciuri, Micrococcus luteus, and Jeotgalicoccus huakuii against As, Cd, Cr, Cu, Co, Pb and Ni. The biosorption assay showed high removal efficiency of As (83%) by E. aquaticum, Cd (95%) by M. sciuri, Cu (94%) by M. luteus, and Ni (89%) by J. huakuii and their produced EPS with these metals in aqueous solution were 84%, 85%, 98%, and 91%, respectively. The maximum EPS yield was attained by optimized medium composition consisting of 1% Xylose, and 1% NaCl at pH 7. In metal-amended conditions, the four bacterial strains showed induced EPS production in the initial concentrations. SEM with EDX and CLSM images showed that the growth and EPS production of bacterial strains were affected by metal ion concentrations. A phenol sulphuric acid method and BCA assay were used to identify both the carbohydrate and total protein content of four extracted EPS. A DPPH assay revealed that EPS influences free radical scavenging and has a highly enhanced synergistic effect with its antioxidant activity. FT-IR analysis of four extracted EPS showed the shifting of peaks in the functional groups of EPS before and after adsorption of metal ions. At pH 5 and after 60 min contact time metal removal efficiency and adsorption capacity increased as calculated for As, Cd, Cu, and Ni by four extracted EPS: (86%, 20 mg/g), (74%, 19 mg/g), (94%, 60 mg/g) and (89%, 32 mg/g) and (89%, 16 mg/g), (85%, 16 mg/g), (96%, 22 mg/g) and (91%, 16 mg/g), respectively. The Langmuir compared to the Freundlich model was found to better represent the adsorption by EPS providing maximum adsorption capacities for As (34.65 mg/g), Cd (52.88 mg/g), Cu (24.91 mg/g), and Ni (58.38 mg/g).

Bioaccumulation and health risk of metal contamination from different tiers of food chain in Ennore estuary, Southeast coast of India

The concentration and bioaccumulation of heavy metals were investigated in four distinct components (water, sediment, benthic organisms, and fish) in the Ennore estuary. The average concentration of studied metals in water is 2-5 times higher in the sediment. The geoaccumulation index in the sediment, particularly for Cd, 55 folds greater than WHO and USEPS standards. The indices like MI, Cdeg, PLI, and PERI demonstrated low contamination levels, whereas Igeo and Cf revealed elevated levels of cadmium (Cd), signifying a moderate degree of contamination. Human health indices like Target Hazard Quotation (THQ) values generally fell within permissible limits (<1), except for lead (Pb) and iron (Fe). However, HI values exceeded 1, indicating a non-carcinogenic health risk for consumers. The Target Risk for lead (TRPb) value for Oreochromis urolepis was 1.0 × 10-5, suggesting a significant cancer risk and may leads to other fish species in future if carcinogenic metals bioaccumulation.

Effects of elevation and geomorphology on cadmium, lead and chromium enrichment in paddy soil and rice: A case study in the Xiangtan basin of China

The distributions of heavy metals in paddy fields and rice along river valleys were studied to explore the key factors affecting the accumulation of heavy metals in the upstream terraces and downstream plains. Results from 975 sampling sites showed that elevation, growing season and soil organic matter (OM) had significant effects on the content of Cd and Pb in topsoil and rice. The content of Cd (0.47-0.66 mg kg-1) and Pb (49.9-68.6 mg kg-1) in paddy fields with low elevation (30-60 m) in the downstream plains was significantly higher than the content of Cd (0.29-0.38 mg kg-1) and Pb (43.9-56.3 mg kg-1) in the upstream terraces with high altitude (60-90 m). In the double-rice production area, late rice generally produced grains with higher Cd and Pb content than early rice. Soil Cd was positively increased with the content of OM, especially in the downstream plains. When elevation was used for principal component analysis, plains with low elevation were grouped together with high content of total and soluble Cd, OM and Pb in soil, as well as high content of Cd and Pb in late rice. Altitude is one of the key factors affecting Cd content in rice. Although content of Cr (93.7-138.0 mg kg-1) was significantly higher than that of Cd and Pb in soil, content of Cr was lower than that of Cd in rice. These results indicate that paddy fields with elevation of 30-60 m in the downstream plains had high risk to produce late rice with Cd and Pb content exceeding the food safety standard 0.2 mg kg-1, which may be resulted from the driving force of runoff on soil soluble Cd and Pb from terraces to alluvial plains in river valleys.

'Remediability Score' as a tool for selecting the most suitable remediation technology for contaminated sites

Land gets contaminated due to different human activities like illegal industrial discharges, mining activities, and spillage of chemicals. The pollutants released through these activities can have prolonged effects on the environment and human health. Therefore, there is a need for immediate remediation of the contaminated site. Different remediation technologies are available for remediating a land contaminated with a particular contaminant. Selection of the most appropriate remediation technology among all those available would help in quick and efficient remediation of the land. There are multiple factors deciding the appropriateness of a technology for a given case. 'Remediability' is a term introduced in the scientific literature recently to describe the ease with which a contaminated land can be remediated and 'Remediability Score (RS)' quantifies remediability in a 0-100 scale. The higher the value of RS, the greater is the difficulty for remediation. The factors influencing remediability were presented before a group of experts in a Delphi process for assigning comparative importance. From the importance score obtained in a Saaty scale of 1 to 9, the weights of factors were calculated using Fuzzy AHP. The overall RS was calculated by taking the weighted impact of the factors after their magnitudes were normalized. RS for the various remediation technologies feasible for a contaminated site, Kuzhikandam, near Kochi, Kerala was calculated. The site was revealed to be contaminated with heavy metals and organic compounds in a field investigation. The most suitable technology for remediating the selected site was found to be vitrification with an RS of 22. The next best technology, stabilization/solidification, had an RS of 25. The study showed that RS can be a reliable matric for selecting the most suitable remediation technology for a contaminated site.

Combining microbiome and pseudotargeted metabolomics revealed the alleviative mechanism of Cupriavidus sp. WS2 on the cadmium toxicity in Vicia unijuga A.Br

Cadmium (Cd) pollution is one of the most severe toxic metals pollution in grassland. Vicia unijuga (V. unijuga) A.Br. planted nearby the grassland farming are facing the risk of high Cd contamination. Here, we investigated the beneficial effects of a highly Cd tolerant rhizosphere bacterium, Cupriavidus sp. WS2, on Cd contaminated V. unijuga. Through plot experiments, we set up four groups of treatments: the control group (without WS2 or Cd), the Cd group (with only Cd addition), the WS2 group (with only WS2 addition), and the WS2/Cd group (with WS2 and Cd addition), and analyzed the changes in physiological indicators, rhizosphere microorganisms, and stem and leaf metabolites of V. unijuga. Results of physiological indicators indicated that Cupriavidus sp. WS2 had strong absorption and accumulation capacity of Cd, exogenous addition of strain WS2 remarkably decreased the Cd concentrations, and increased the plant heights, the biomass, the total protein concentrations, the chlorophyll contents and the photosynthetic rate in stems and leaves of V. unijuga under Cd stress. Cd treatment increased the abundance of Cd tolerant bacterial genera in rhizosphere microbiome, but these genera were down-regulated in the WS2/Cd group. Pseudotargeted metabolomic results showed that six common differential metabolites associated with antioxidant stress were increased after co-culture with WS2. In addition, WS2 activated the antioxidant system including glutathione (GSH) and catalase (CAT), reduced the contents of oxidative stress markers including malondialdehyde (MDA) and hydrogen peroxide (H2O2) in V. unijuga under Cd stress. Taken together, this study revealed that Cupriavidus sp.WS2 alleviated the toxicity of V. unijuga under Cd exposure by activating the antioxidant system, increasing the antioxidant metabolites, and reducing the oxidative stress markers.

Technological and economic analysis of electrokinetic remediation of contaminated soil: A global perspective and its application in Indian scenario

Globally million hectares of land annually is getting contaminated by heavy metalloids like As, Cd, Cr, Hg, Pb, Co, Cu, Ni, Zn, and Se, with current concentrations in soil above geo-baseline or regulatory standards. The heavy metals are highly toxic, mobile, and persistent and hence require immediate and effective mitigation. There are many available remediation techniques like surface capping, encapsulation, landfilling, soil flushing, soil washing, electrokinetic extraction, stabilization, solidification, vitrification, phytoremediation, and bioremediation which have been evolved to clean up heavy metal-contaminated sites. Nevertheless, all of the technologies have some applicability and limitations making the soil remediation initiative unsustainable. Among the available technologies, electrokinetic remediation (EKR) has been comparatively recognized to mitigate contaminated sites via both in-situ and ex-situ approaches due to its efficiency, suitability for use in low permeability soil, and requirement of low potential gradient. The work critically analyzes the EKR concerning techno, economic, and sustainability aspect for evaluating its application on various substrates and environmental conditions. The current soil contamination status in India is presented and the application of EKR for the heavy metal remediation from soil has been evaluated. The present work summaries a comprehensive and exhaustive review on EKR technology proving its effectiveness for a country like India where the huge amount of waste generated could not be treated due to lack of infrastructure, technology, and economic constraints.

Enhancement of heavy metals desorption from the soil by eddy deep leaching in hydrocyclone

An eddy deep leaching technology was developed in this paper to address the challenge of treating heavy metal contaminants in industrial mining areas. The desorption effect of As, Cd, Sb and Pb was investigated utilizing chemical leaching and physical eddy techniques. It was found that the heavy metals concentration increased with decreasing particle size. The highest proportion of Cd in the form distribution of soil was in the bound to iron and manganese oxides, while the maximum proportion of As, Sb and Pb were in the residual. The optimal solid-liquid ratio of the hydrocyclone was 1:20, and the corresponding separation efficiency and flow rate were 84.7% and 1.76 m3/hr, respectively. The grade efficiency of soil particle separation increases with particle size and exceeds 99% for particles above 1,000 µm. Leaching experiments have revealed that oxalic acid (OA) and a combination of oxalic acid and EDTA (OAPE) were more efficient than citric acid (CA) and a combination of citric acid and EDTA (CAPE) for the desorption of heavy metals, respectively. The comparison of OAPE and eddy leaching found that the latter improved the desorption efficiency by 9.4%, 7.5%, 7.2% and 7.8% for As, Cd, Sb and Pb compared to the former, respectively. The results demonstrated that the eddy leaching technique could further enhance the desorption efficiency of heavy metals. It is expected to provide technical support for soil remediation with reduced usage of leaching agents.

Characteristics of soil contamination by potentially toxic elements in mine areas of Mongolia

Soil contamination by potentially toxic elements (PTEs), such as metal(loid)s, in mining areas was characterized on a nationwide scale in Mongolia to understand the contamination status throughout the country, according to mine types. Positive matrix factorization (PMF) analysis exhibited better classification and explanation of soil contamination according to ore types compared to conventional statistical analysis methods such as principal component analysis (PCA) and hierarchical cluster analysis (HCA). The results of PMF analysis for metal(loid) contents in 1425 topsoil samples collected from 272 mines illuminated four Factors, which primarily contributed to As (Factor 1), Pb, Zn, and Cd (Factor 2), Ni (Factor 3), and Cu and Cd (Factor 4) contaminations, respectively. In hard-rock gold mines, As was enriched and the contribution of Factor 1 was high (31.2%) due to the affinity between As and Au. In placer gold mines, the contribution of Factor 3 (41.8%) was high due to the affinity between Ni and weathering-resistant heavy minerals. For base metal, fluorite, and coal mines, contributions of Factors 2 (32.1-50.9%) and 4 (17.7-33.6%) were high owing to sulfides containing Pb-Zn-d and Cu. These impacts of mine types were altered by local geology (e.g., skarn). Meanwhile, Hg amalgamation contributed to Hg contamination in a few hard-rock gold mines. These results suggest that soil contaminants in mining areas are mainly affected by the type of deposits with geochemical affinities, region-specific ore characteristics, and artificial processing. Understanding these effects will help establish national strategies for countermeasures, such as soil rehabilitation in mining areas.

Foliar spraying of indoleacetic acid (IAA) enhances the phytostabilization of Pb in naturally tolerant ryegrass by limiting the root-to-shoot transfer of Pb and improving plant growth

Exogenous addition of IAA has the potential to improve the metal tolerance and phytostabilization of plants, but these effects have not been systematically investigated in naturally tolerant plants. Ryegrass (Lolium perenne L.) is a typical indigenous plant in the Lanping Pb/Zn mining area with high adaptability. This study investigated the phytostabilization ability and Pb tolerance mechanism of ryegrass in response to Pb, with or without foliar spraying of 0.1 mmol L-1 IAA. The results indicated that appropriate IAA treatment could be used to enhance the phytostabilization efficiency of naturally tolerant plants. Foliar spraying of IAA increased the aboveground and belowground biomass of ryegrass and improved root Pb phytostabilization. Compared to Pb-treated plants without exogenous IAA addition, Pb concentration in the shoots of ryegrass significantly decreased, then increased in the roots after the foliar spraying of IAA. In the 1,000 mg kg-1 Pb-treated plants, Pb concentration in the shoots decreased by 69.9% and increased by 79.1% in the roots after IAA treatment. IAA improved plant growth, especially in soils with higher Pb concentration. Foliar spraying of IAA increased shoot biomass by 35.9% and root biomass by 109.4% in 1,000 mg kg-1 Pb-treated plants, and increased shoot biomass by 196.5% and root biomass by 71.5% in 2,000 mg kg-1 Pb-treated plants. In addition, Pb stress significantly decreased the content of photosynthetic pigments and anti-oxidase activities in ryegrass, while foliar spraying of IAA remedied these negative impacts. In summary, foliar spraying of IAA could increase the biomass and improve the Pb tolerance of ryegrass.

Research progress and hotspots on microbial remediation of heavy metal-contaminated soil: a systematic review and future perspectives

Microbial remediation technology has received much attention as a green, ecological, and inexpensive technology, and there is great potential for the application of microbial remediation technology for heavy metals (HMs) contaminated soil alone and in conjunction with other technologies in environmental remediation. To gain an in-depth understanding of the latest research progress, research hotspots, and development trends on microbial remediation of HMs-contaminated soil, and to objectively reflect the scientific contributions and impacts of relevant countries/regions, institutions, and individuals of this field, in this manuscript, ISI Web of Knowledge's Web of Science™ core collection database, data visualization, and analysis software Bibliometrix, VOSviewer, and HistCite Pro were used to collect and analyze the relevant literature from 2000 to 2022, and 1409 publications were subjected to scientometric analyses. It involved 327 journals, 5150 authors, 75 countries/regions, and 2740 keywords. The current progress and hotspots on microbial remediation of HMs-contaminated soil since the twenty-first century were analyzed in terms of the top 10 most productive countries (regions), high-yielding authors, source journals, important research institutions, and hotspots of research directions. Over the past 22 years, China, India, and the USA have been the countries with the most articles. The institution and author with the most publications are the Chinese Acad Sci and Zhu YG, respectively. Journal of Hazardous Materials is the most productive journal. The keywords showed 6 co-occurrence clusters. These findings revealed the research hotspots, knowledge gaps, and future exploration trends related to microbial remediation of HMs-contaminated soil.

Synthesis of Tungsten Oxide, Iron Oxide, and Copper-Doped Iron Oxide Nanocomposites and Evaluation of Their Mixing Effects with Cyromazine against Spodoptera littoralis (Boisduval)

Nanotechnology research is emerging as a cutting-edge technology, and nanocomposites have played a significant role in pest control. Therefore, the present study focuses on the synthesis of tungsten oxide (WO3), iron oxide (magnetic nanoparticle, MNP), and copper-doped iron oxide (MNP-Cu) nanocomposites and explores the different effects of their binary combinations with the insecticide cyromazine against Spodoptera littoralis. The synthesized nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy. None of the tested nanomaterials showed any toxicity against the different stages of S. littoralis. Larval and pupal durations increased with increasing cyromazine and nanomaterial concentrations. The longest larval and pupal durations were recorded under treatment with the mixture of cyromazine (100 mg/L) + MNP-Cu (500 mg/L); the survival periods were 23.5 and 15.6 days, compared with 10.8 and 7.7 days in the control, respectively. The percentages of pupation and adult emergence were negatively affected by all treatments. Among the 500 mg/L nanomaterial combinations, only cyromazine (25 mg/L) and WO3 (500 mg/L) resulted in adult emergence (at a rate of 27.3%). Some abnormalities in the S. littoralis stages were observed following treatment with the tested materials. The glutathione S-transferase and alpha-esterase enzyme activities in S. littoralis were significantly increased after treatment with cyromazine, followed by cyromazine/MNP-Cu combinations. The quantitative polymerase chain reaction (Q-PCR) data showed that all treated insects had a higher immune response than the control. Finally, mixes of nanocomposites and cyromazine may be suggested as viable alternatives for S. littoralis management.

Microbial Biosurfactant: Candida bombicola as a Potential Remediator of Environments Contaminated by Heavy Metals

Industrial interest in surfactants of microbial origin has intensified recently due to the characteristics of these compounds, such as biodegradability and reduced toxicity, and their efficiency in removing heavy metals and hydrophobic organic compounds from soils and waters. The aim of this study was to produce a biosurfactant using Candida bombicola URM 3712 in a low-cost medium containing 5.0% molasses, 3.0% corn steep liquor and 2.5% residual frying oil for 144 h at 200 rmp. Measurements of engine oil tension and emulsification were made under extreme conditions of temperature (0 °C, 5 °C, 70 °C, 100 °C and 120 °C), pH (2-12) and NaCl concentrations (2-12), demonstrating the stability of the biosurfactant. The isolated biosurfactant was characterized as an anionic molecule with the ability to reduce the surface tension of water from 72 to 29 mN/m, with a critical micellar concentration of 0.5%. The biosurfactant had no toxic effect on vegetable seeds or on Eisenia fetida as a bioindicator. Applications in the removal of heavy metals from contaminated soils under dynamic conditions demonstrated the potential of the crude and isolated biosurfactant in the removal of Fe, Zn and Pb with percentages between 70 and 88%, with the highest removal of Pb being 48%. The highest percentage of removal was obtained using the cell-free metabolic liquid, which was able to remove 48, 71 and 88% of lead, zinc and iron from the soil, respectively. Tests in packed columns also confirmed the biosurfactant's ability to remove Fe, Zn and Pb between 40 and 65%. The removal kinetics demonstrated an increasing percentage, reaching removal of 50, 70 and 85% for Pb, Zn and Fe, respectively, reaching a greater removal efficiency at the end of 24 h. The biosurfactant was also able to significantly reduce the electrical conductivity of solutions containing heavy metals. The biosurfactant produced by Candida bombicola has potential as an adjuvant in industrial processes for remediating soils and effluents polluted by inorganic contaminants.

Sources, distribution, associated health risks and remedial technologies for inorganic contamination in groundwater: A review in specific context of the state of Haryana, India

Haryana is one of the leading states in India in the agricultural and industrial production. With the expansion of these sectors, a continuous increase in water demand is leading to water crises arising from overexploitation and quality deterioration of the available water. Contamination of aquifer resources is a significant concern, because majority of population depends on the groundwater for various agricultural, industrial, and domestic needs. This review article provides an overview of groundwater contamination, associated health risks with different contaminants with regions severely affected by poor water quality, and delves in identifying the sources, by observing and recognising the types of industries dominant in the state with types of effluents discharge. It further suggests the possible mitigation measures such as advanced remedial technologies and proper management practices from the consequent contamination sources. It has been observed during the perusal of various studies and data that the degree of contamination was considerably higher in districts with heavy agro-industrial activities. The groundwater resources in three highly industrialized districts were found to be gravely contaminated with toxic heavy metals. Alongwith heavy metals, the salinity, hardness, nitrate, and fluoride are also posing significant problems in the aquifer resources of Haryana state. The article also discusses various technologies for remediation of different pollutants from groundwater so it can be made potable after treatment.

Quantitative proteomic analysis of the mechanism of Cd toxicity in Enterobacter sp. FM-1: Comparison of different growth stages

Enterobacter sp. are widely used in bioremediation, but the mechanism of Cadmium (Cd) toxicity in Enterobacter sp. has been poorly studied. In the present study, we determined the tolerance of Enterobacter sp. FM-1 to Cd by analyzing the physiological and biochemical responses of FM-1 induced under Cd stress. Differentially expressed proteins (DEPs) under exposure to different Cd environments were analyzed by 4D-label-free proteomics to provide a comprehensive understanding of Cd toxicity in FM-1. The greatest total number of DEPs, 1148, was found in the High concentration vs. Control comparison group at 10 h. When protein expression was compared after different incubation times, FM-1 showed the highest Cd tolerance at 48 h. Additionally, with an increasing incubation time, different comparison groups gradually began to show similar growth patterns, which was reflected in the GO enrichment analysis. Notably, only 815 proteins were identified in the High concentration vs. Control group, and KEGG enrichment analysis revealed that these proteins were significantly enriched in the pyruvate metabolism, oxidative phosphorylation, peroxisome, glyoxylate and dicarboxylate metabolism, and citrate cycle pathways. These results suggested that an increased incubation time allows FM-1 adapt and survive in an environment with Cd toxicity, and protein expression significantly increased in response to oxidative stress in a Cd-contaminated environment during the pre-growth period. This study provides new perspectives on bacterial participation in bioremediation and expands our understanding of the mechanism of bacterial resistance under Cd exposure.

Effects of resource availability on the growth, Cd accumulation, and photosynthetic efficiency of three hyperaccumulator plant species

Plants that hyperaccumulate heavy metals such as cadmium (Cd) are important agents of phytoremediation. Availability of resources such as light, nutrients, and water can affect heavy metal accumulation by plants, but the responses of hyperaccumulators to different levels of resource availability remain little studied. To test such responses, three Cd hyperaccumulators, Solanum nigrum, Bidens pilosa, and Taraxacum mongolicum, were grown in Cd-contaminated soil; subjected to three levels of light, nutrient, or water availability; and measured for growth, Cd accumulation, and photosynthetic efficiency. All three species accumulated more total biomass and grew taller if given high than low water or light (each P < 0.001). Species accumulated four to eight times more Cd (190-309 versus 24-68 μg Cd g-1 mass) under high than low light. High water availability increased Cd accumulation by 89% in B. pilosa but decreased it by 31% and 40% in S. nigrum and B. pilosa, respectively. Effects of nutrients on both growth and accumulation varied between species; Cd accumulation by S. nigrum and T. mongolicum was respectively 14% and 54% lower at high than low nutrients, while it was 130% higher in B. pilosa. Light but not water or nutrient availability affected effective and maximum quantum yields and electron transport rate. Findings from this study suggest that low levels of light may constrain phytoremediation of Cd in soil and that testing species of Cd hyperaccumulators individually for responses to levels of water and nutrients will inform selection of species for phytoremediation.

Exploring the adsorption efficacy of Cassia fistula seed carbon for Cd (II) ion removal: Comparative study of isotherm models

The current study demonstrates the potential of Cassia fistula seed carbon (CFSC), a waste lignocellulosic biomass, to eliminate Cd (II) ion-from saturated liquid samples. The efficient removal of about 93.2% (w/v) of Cd (II) ions from 10 mg/L concentration was achieved within 80 min of treatment. The CFSC dosage of 100 mg/50 mL accounted as optimal for enhanced Cd (II) removal. Cd (II) adsorption onto CFSC was observed to be maximum at pH 6. The investigational trials were assessed with three isotherm models such Dubinin-Radushkevich, Freundlich, and Langmuir. The specifications obtained from this experimental study align well with the Langmuir isotherm model, which describes the maximal adsorption capacity of 68.02 mg/g. Cd (II) adsorption data from this study exhibited the R2 of 0.9 under pseudo-second-order. Maximum desorption (76.3% w/v) was obtained with 0.3 M HCL. This study revealed that thermally activated C. fistula seed carbon (CFSC) can be tuned to be lucrative adsorbent for Cd (II) elimination from water and waste-water.

In-situ physical and chemical remediation of Cd and Pb contaminated mine soils cultivated with Chinese cabbage: A three-year field study

Soils pollution with heavy metals (HMs) is a serious concern due to their toxic effects on crop yield, crop quality, soil environment, and human health. In the current study, four stabilizers of calcium carbonate (CC), dolomite (DL), zeolite (ZL), and steel slag (SS) were applied to cadmium (Cd) and lead (Pb)-contaminated soils as in-situ chemical remediation techniques along with in-situ physical remediation techniques i.e. soil covering (SC) and soil dilution (SD) under real field conditions. For three years, Chinese cabbage (Brassica rapa L.) was grown on the amended fields to examine how the amendments impacted Cd and Pb uptake in plants. The stabilization efficiency of SS, CC, and SC were 75.7 %, 66.0 %, and 71.1 %, respectively, for Cd, and 55.6 %, 55.6 %, and 70.0 %, respectively, for Pb. Results indicated that stabilizer soil amendments significantly decreased the exchangeable (F1) and carbonates bound (F2) fractions of both Cd and Pb. For instance, F1 fraction of Cd decreased from 10.2 (control) to 1.8-2.9 % (with stabilizers). The stabilizers increased Chinese cabbage dry weight by 11.4-22.5 % and decreased Cd and Pb uptake by 67.4 % and 24 %, respectively. The results demonstrated that in-situ chemical remediation technique showed promising results and maintained its efficiency for more than 130 weeks. Current study indicated that chemical remediation of Cd and Pb contaminated soil is more effective and last longer than physical remediation.

Assessment of heavy metal contamination in street dust: concentrations, bioaccessibility, and human health risks in coal mine and thermal power plant complex

Coal mining has also been associated with adverse environmental and health impacts including cancer and respiratory disorders, with the presence of thermal power plants exacerbating the problem of heavy metal pollution. Minimal studies have been conducted on the environmental impacts, health risks, and bioaccessibility of heavy metals in coal mine areas. Consequently, samples of street dust were collected from different locations in the Singrauli mine complex and analysed. Heavy metals (Cu, Ni, Zn, Cr, Co, As, and Mo) were found to be higher than the background concentration, with the maximum concentration was found in areas close to the Thermal Power Plants, like Near Vindyachal TPP, Near Shakti Nagar TPP, and Anpara. The highest geo-accumulation index value was found for Co, Mo, Zn, and As, indicating moderate to strong pollution levels. Health risk assessment (for both adults and children) revealed that Cr and Fe posed significantly higher Hazard Quotient and Hazard Index (HI) values, indicating significant non-carcinogenic threats. Moreover, Carcinogenic Risk (CR) values for Cd, Cr, and Ni indicated a risk of carcinogenicity to the public exposed to road dust. The study also examined the bioaccessibility of the metals, which showed that the gastric phase accumulated a higher percentage of Ni (42.52%), Pb (34.79%), Co (22.22%), As (20%) and Cu (15%) than the intestinal phase. Strong positive correlation was observed between metal concentration (Cu, Pb, Cr, Fe, Zn, and Mn), HI, and CR of adult and child, while bioaccessibility of intestinal phase was positively correlated with gastric phase of metals (Cu, Ni, Co, As, and Mn).