Evaluation methods for assessing effectiveness of in situ remediation of soil and sediment contaminated with organic pollutants and heavy metals

Transcriptome and metabolome analysis reveal key genes and metabolic pathway responses in Leersia hexandra Swartz under Cr and Ni co-stress

Phytoremediation, an eco-friendly approach for mitigating heavy metal contamination, is reliant on hyperaccumulators. This study focused on Leersia hexandra Swart, a known chromium (Cr) hyperaccumulator with demonstrated tolerance to multiple heavy metals. Our objective was to investigate its response to simultaneous Cr and nickel (Ni) stress over 12 days. Results from physiological experiments demonstrated a significant increase in the activities of antioxidant enzymes (APX, SOD, CAT) and glutathione (GSH) content under Cr and Ni stress, indicating enhanced antioxidant mechanisms. Transcriptome analysis revealed that stress resulted in the differential expression of 27 genes associated with antioxidant activity and metal binding, including APX, SOD, CAT, GSH, metallothionein (MT), and nicotinamide (NA). Among them, twenty differentially expressed genes (DEGs) related to GSH metabolic cycle were identified. Notably, GSTU6, GND1, and PGD were the top three related genes, showing upregulation with fold changes of 4.57, 6.07, and 3.76, respectively, indicating their crucial role in metal tolerance. The expression of selected DEGs was validated by quantitative real-time PCR, confirming the reliability of RNA-Seq data. Metabolomic analysis revealed changes in 1121 metabolites, with amino acids, flavonoids, and carbohydrates being the most affected. Furthermore, glucosinolate biosynthesis and amino acid biosynthesis pathways were represented in the KEGG pathway of differentially expressed metabolites (DEMs). This study provides insights into the tolerance mechanisms of L. hexandra under the co-stress of Cr and Ni, offering a new perspective for enhancing its remediation performance.

Temporal and spatial evolution of different heavy metal fractions and correlation with environmental factors after prolonged acid mine drainage irrigation: A column experiment

Acid mine drainage (AMD) has global significance due to its low pH and elevated heavy metal content, which have received widespread attention. After AMD irrigation in mining areas, heavy metals are distributed among soil layers, but the influencing factors and mechanisms remain unclear. AMD contamination of surrounding soil is primarily attributed to surface runoff and irrigation and causes significant environmental degradation. A laboratory soil column experiment was conducted to investigate the temporal and spatial distribution of the heavy metals Cd and Cu, as well as the impact of key environmental factors on the migration and transformation of these heavy metals following long-term soil pollution by AMD. After AMD addition, the soil exhibited a significant increase in acidity, accompanied by notable alterations in various environmental parameters, including soil pH, Eh, Fe(II) content, and iron oxide content. Over time, Cd and Cu in the soil mainly existed in the exchangeable and carbonate-bound fractions. In spatial terms, exchangeable Cu increased with increasing depth. Pearson correlation analysis indicated significant negative correlations between pH and Cu, Cd, and Eh in pore water, as well as negative correlations between pH and the exchangeable fraction of Cd (F1), carbonate-bound fraction of Cd (F2), and exchangeable fraction of Cu (F1) in the solid phase. Additionally, a positive correlation was observed between pH and the residual fraction of Cu (F5). Furthermore, the soil total Cd content exhibited a positive correlation with pyrophosphate-Fe (Fep) and dithionite-Fe (Fed), while CdF1, CdF2, total Cu, and CuF1 displayed positive correlations with Fep. Our findings indicate that the presence of AMD in soil leads to alterations in the chemical fractions of Cd and Cu, resulting in enhanced bioavailability. These results offer valuable insights for developing effective remediation strategies for soils near mining sites.

Iron slag/activated carbon-electrokinetic system with anolyte recycling for single and mixture heavy metals remediation

The electrokinetic process has been proposed for in-situ soil remediation to minimize excavation work and exposure to hazardous materials. The precipitation of heavy metals in alkaline pH near the cathode is still challenging. Reactive filter media and enhancement agents have been used in electrokinetics to enhance the removal of heavy metals. This study investigated coupling industrial iron slag waste and iron slag-activated carbon reactive filter media with electrokinetic for a single and mixture of heavy metals treatment. Instead of using acid enhancement agents, the anolyte solution was recycled to neutralize the alkaline front at the cathode, reducing the operation cost and chemical use. Experiments were conducted for 2 and 3 weeks at 20 mA electric current. Copper removal increased from 3.11 % to 23 % when iron slag reactive filter media was coupled with electrokinetic. Copper removal increased to 70.14 % in the electrokinetic experiment with iron slag-activated carbon reactive filter media. The copper removal increased to 89.21 % when the anolyte solution was recycled to the cathode compartment. Copper removal reached 93.45 % when the reactive filter media-electrokinetic process with anolyte recirculation was extended to 3 weeks. The reactive filter media- an electrokinetic process with anolyte recycling was evaluated for removing copper, nickel, and zinc mixture, and results revealed 81.1 % copper removal, 89.04 % nickel removal, and 92.31 % zinc removal in a 3-week experiment. The greater nickel and zinc removal is attributed to their higher solubility than copper. The results demonstrated the cost-effectiveness and efficiency of the electrokinetic with iron slag-activated carbon reactive filter media with anolyte recirculation for soil remediation from heavy metals.

Changes in the extractability and fractionation of cadmium and copper in a contaminated soil amended with various sugarcane bagasse-based materials

Heavy-metal contamination in soil has long been a persistent challenge and the utilization of agricultural waste for in-situ stabilization remediation presents a promising approach to tackle this problem. Agricultural wastes exhibit promising potential in the remediation of contaminated land and modification could improve the adsorption performance markedly. Citric acid and Fe3O4 treated sugarcane bagasse adsorbed more heavy metals than raw materials in the aqueous system, employing these materials for heavy metal remediation in soil holds significant implications for broadening the raw material source of passivators and enhancing waste utilization efficiency. In this paper, a 120-day soil incubation study was conducted to compare the effects of pristine sugarcane bagasse (SB), citric-acid modified (SSB1, SSB2 and SSB3 with increasing proportion of citric acid) and citric-acid/Fe3O4 modified (MSB1, MSB4 and MSB7 with increasing proportion of Fe3O4) sugarcane bagasse at 1 % addition rate on cadmium (Cd) and copper (Cu) passivation. The SB, SSB1 and MSB1 did not always decrease the content of CaCl2-extractable Cd while all the seven amendments decreased the CaCl2-extractable Cu during the experiment period. Among all materials, SSB3 and MSB7 exhibited the highest efficiency in reducing the concentrations of CaCl2-extractable Cd and Cu. At Day 120, SB, SSB3 and MSB7 reduced the content of CaCl2-extractable Cd by 8 %, 18 % and 24 %, and of CaCl2-extractable Cu by 25 %, 50 % and 61 %, respectively. The efficiency of Cd and Cu immobilization was associated positively with the pH, functional groups and H-bonds of the amendments. The results suggest that the efficiency of sugarcane bagasse in heavy-metal passivation can be largely enhanced through chemical modifications using high proportions of citric acid and Fe3O4.

Arsenic uptake by Agrostis capillaris, as related to its genotypic diversity in the area of historical ore mining and processing

Common bentgrass Agrostis capillaris L. is known as tolerant to toxic elements. A hypothesis was examined that its ecotypes growing in historically polluted sites show a limited arsenic uptake and have genetic features that distinguish them from commercially available cultivars. The study was conducted in Złoty Stok, a historical area of arsenic mining. Additionally, two commercial cultivars were grown in pots with arsenic-rich soils. Based on arsenic concentrations in plant roots and shoots, bioconcentration and translocation factors BCF and TF were calculated. Commercial cultivars indicated many times higher BCF shoots and TF values compared to field plants. DNA analysis of leaf blades showed a clear distinction between the plants growing in some sites and patches in the field, and also a gene overlap between the plants in the field and commercial forms. The research did not allow for identification of ecotypes with exceptionally limited arsenic uptake. Moreover, there were no significant differences between the genotypic characteristics of plants growing in polluted sites and those poorly tolerant grown from commercially available seeds. Apparently, other factors, and not genetically determined features, are responsible for A. capillaris tolerance to arsenic in Złoty Stok.

Safe utilization and remediation potential of the mulberry-silkworm system in heavy metal-contaminated lands: A review

Mulberry cultivation and silkworm rearing hold a prominent position in the agricultural industries of many Asian countries, contributing to economic growth, sustainable development, and cultural heritage preservation. Applying the soil-mulberry-silkworm system (SMSS) to heavy metal (HM)-contaminated areas is significant economically, environmentally, and socially. The ultimate goal of this paper is to review the main research progress of SMSS under HM stress, examining factors affecting its safe utilization and remediation potential for HM-contaminated soils. HM tolerance of mulberry and silkworms relates to their growth stages. Based on the standards for HM contaminants in various mulberry and silkworm products and the bioconcentration factor of HMs at different parts of SMSS, we calculated maximum safe Cd and Pb levels for SMSS application on contaminated lands. Several remediation practices demonstrated mulberry's ability to grow on barren lands, absorb various HMs, while silkworm excreta can adsorb HMs and improve soil fertility. Considering multiple factors influencing HM tolerance and accumulation, we propose a decision model to guide SMSS application in polluted areas. Finally, we discussed the potential of using molecular breeding techniques to screen or develop varieties better suited for HM-contaminated regions. However, actual pollution scenarios are often complex, requiring consideration of multiple factors. More large-scale applications are crucial to enhance the theoretical foundation for applying SMSS in HM pollution risk areas.

Restoration of degraded estuarine and marine ecosystems: A systematic review of rehabilitation methods in Europe

This article provides a comprehensive study of ecosystem rehabilitation methods widely used in the 21st century, focusing on Europe. The review covers the evolution and trends in scientific article publication, identification of European countries demonstrating high publication outputs, collaboration patterns, leading journals, and thematic areas. Additionally, it examines primary stressors in European aquatic ecosystems, and different methods and treatments commonly employed for remediation purposes. The analysis of selected articles revealed a significant increase in studies over time, driven by public awareness and financial incentives from national, European and global organizations. Italy, Portugal and Spain were the leading countries in degraded ecosystem rehabilitation studies, mainly focusing on remediating contaminated areas where metals were identified as the primary stressor (chemical pollution). Chemical remediation method emerged as the most used, closely followed by biological remediation method, which have gained prominence in recent years due to their ecological, economic, and social combined benefits. Furthermore, recent studies demonstrate a growing trend towards the combined use of more than one treatment/method to rehabilitate ecosystems, particularly with biological treatments. This combined approach has the potential for synergistic effects in achieving more effective rehabilitation and their sustainability in the long term, thus, a focus for future research.

Effects of tire-road wear particles on the adsorption of tetracycline by aquatic sediments

Tire-road wear particles (TRWPs) are formed by friction between the tire and the road. TRWPs are ubiquitous across the globe, especially in sediments. However, the possible effects of TRWPs on tetracycline (TC) in aquatic sediments are unknown. To investigate the potential role of TRWPs as carriers of co-pollutants, this study investigated the pore surface properties and TC adsorption behavior of TRWP-contaminated sediments and explored the TC behavior in water sediments, as well as the role of aging processes and TRWPs abundance. The results showed that the surface morphology of TRWP-contaminated sediments changed and the adsorption capacity of sediments to TC increased. The TC adsorption capacity of sediments contaminated by 2% TRWPs increased from 3.15 to 3.48 mg/g. Moreover, the surface physical and chemical properties of TRWPs after UV aging changed, which further increased the TC adsorption capacity. The TC adsorption capacity of the sediments contaminated by aged TRWPs increased from 3.48 to 3.65 mg/g. Changing the proportion of aged TRWPs, we found that the adsorption capacity of sediments contaminated by different proportions of TRWPs for TC was 2% > 1% > 0.5% > 4% > blank sediment. These results may contribute to predicting the potential environmental risks of TRWPs in aquatic sediments.

Potential application of 2D nano-layered MXene in analysing and remediating endocrine disruptor compounds and heavy metals in water

With the advancement of technologies and growth of the economy, it is inevitable that more complex processes are deployed, producing more heterogeneous wastewater that comes from biomedical, biochemical and various biotechnological industries. While the conventional way of wastewater treatment could effectively reduce the chemical oxygen demand, pH and turbidity of wastewater, trace pollutants, specifically the endocrine disruptor compounds (EDCs) that exist in µg L-1 or ng L-1 have further hardened the detection and removal of these biochemical pollutants. Even in small amounts, EDC could interfere human's hormone, causing severe implications on human body. Hence, this review elucidates the recent insights regarding the effectiveness of an advanced 2D material based on titanium carbide (Ti3C2Tx), also known as MXene, in detecting and removing EDCs. MXene's highly tunable feature also allows its surface chemistry to be adjusted by adding chemicals with different functional groups to adsorb different kinds of EDCs for biochemical pollution mitigation. At the same time, the incorporation of MXene into sample matrices also further eases the analysis of trace pollutants down to ng L-1 levels, thereby making way for a more cleaner and comprehensive wastewater treatment. In that sense, this review also highlights the progress in synthesizing MXene from the conventional method to the more modern approaches, together with their respective key parameters. To further understand and attest to the efficacy of MXene, the limitations and current gaps of this potential agent are also accentuated, targeting to seek resolutions for a more sustainable application.

Preparation of landscape gardening soil using undersized fraction from aged MSW by EDTA or citric acid coupled with humic acid: Effect assessment, properties, and optimization

Undersized fraction from aged municipal solid waste (UFAMSW), as a kind of soil-like material, has been proved effective in providing a large amount of organic matter and nutrients for soil and plants. The characteristics and effectiveness of heavy metal pollution removal in UFAMSW attracted tremendous research interest from scientists recently. In this study, the heavy metal removal efficiencies and bioavailability of washing on contaminated UFAMSW were evaluated with three washing reagents including ethylene diamine tetra acetic acid (EDTA), citric acid (CA), and humic acid (HA). The effects of chelating agent concentration, pH, and washing time on metal removal were investigated and response surface methodology (RSM) was employed to optimize the washing conditions. The results indicated that the removal efficiencies of Cu, Zn, and Mn could be 53.68%, 52.12%, and 30.63% by EDTA/HA washing and 42.36%, 39.67% and 28.49% by CA/HA washing, respectively. The European Community Bureau of Reference (BCR) sequential extraction was applied to analyze the fraction change of heavy metals in UFAMSW before and after washing, and it was found that chelating agent combined with HA could contribute to the removal of the exchangeable fraction. Physical and chemical properties of UFAMSW were improved to some extent after washing with mixed HA and chelating agent and could achieve the quality standard of landscape gardening soil. Accordingly, the mixture of HA and other chelating agents could be a promising washing process for preparation of landscape gardening soil using UFAMSW.Implications: Our manuscript studies the removal of heavy metals from the contaminated undersized fraction from aged municipal solid waste (UFAMSW). UFAMSW, as a kind of soil-like material, has been proved effective in providing a large amount of organic matter and nutrients for soil and plants however often limited by heavy metal pollution. The UFAMSW used in this experiment was collected after the excavation and screening-sorting of aged refuse from Changshankou Domestic Waste Sanitary Landfill in Wuhan City, Hubei Province, Southern China. This study investigated the effects of EDTA, CA, HA, mixed EDTA/HA, and mixed CA/HA washing on heavy metal removal (Cu, Zn, and Mn), bioavailability of residual heavy metal and properties. The effects of chelating agent concentration, pH, and washing time on metal removal were investigated and then response surface methodology was employed to optimize the washing conditions. The results showed that washing by CA/HA and EDTA/HA, had a higher removal efficiency of heavy metals (Cu, Zn, and Mn) in UFAMSW compared to single HA. Meanwhile, HA has a higher removal for exchangeable fraction of heavy metals, the exchangeable concentration of Cu, Zn, and Mn in CA/HA and EDTA/HA washed UFAMSW were lower compared with UFAMSW washed by single CA and EDTA. Thus, mixing HA with EDTA or CA makes a less risk to environmental and the removal efficiency is acceptable. Additionally, CA/HA and EDTA/HA washing tend to improve soil physicochemical properties and soil fertility. Thus, mixing HA with different washing agent are potential methods for preparation of landscape gardening soil using UFAMSW.

Combined passivators regulate physiological, antioxidant potential and metals accumulation in potato grown in metals contaminated soil

To solve the problem of excessive heavy metals in farmland soil, there is a dire need for research effort to screen for the soil passivator materials. This study aimed to develop a practical novel approach for improving the potato growth and remedial effectiveness of the metals by optimal combination and dosage of various passivators. Experimental treatments were comprised of various levels of passivating agents (sepiolite, quicklime and calcium magnesium phosphate) in individual and combined form. Results showed that application of passivating agents significantly enhanced growth by optimizing photosynthetic attributes, enzymatic antioxidants, and soil health. Balanced application of passivators effectively reduce the bioavailability of metals, curbing their uptake by potato plants. Sole application of all the agents results statistically similar outcomes as compared with combined form. Additionally, passivators indirectly enhance the activity of essential antioxidant enzymes. Synergistic effect of all the agents significantly improved the tuber quality by decreasing the accumulation of proline, malondialdehyde content, and bioaccumulation of Cu, Pb, Cd, and As in potato parts. In crux, combined usage of passivating agents proved to be of better growth, improvement in antioxidative defense system, and better quality of potato. By mitigating heavy metal contamination, passivators not only enhance crop quality and yield but also ensure heavy metal-free potatoes that meet stringent food safety standards.

Silver nanoparticle ecotoxicity and phytoremediation: a critical review of current research and future prospects

Silver nanoparticles (AgNPs) are widely used in various industries, including textiles, electronics, and biomedical fields, due to their unique optical, electronic, and antimicrobial properties. However, the extensive use of AgNPs has raised concerns about their potential ecotoxicity and adverse effects on the environment. AgNPs can enter the environment through different pathways, such as wastewater, surface runoff, and soil application and can interact with living organisms through adsorption, ingestion, and accumulation, causing toxicity and harm. The small size, high surface area-to-volume ratio, and ability to generate reactive oxygen species (ROS) make AgNPs particularly toxic. Various bioremediation strategies, such as phytoremediation, have been proposed to mitigate the toxic effects of AgNPs and minimize their impact on the environment. Further research is needed to improve these strategies and ensure their safety and efficacy in different environmental settings.

Multitask Deep Learning Enabling a Synergy for Cadmium and Methane Mitigation with Biochar Amendments in Paddy Soils

Biochar has demonstrated significant promise in addressing heavy metal contamination and methane (CH4) emissions in paddy soils; however, achieving a synergy between these two goals is challenging due to various variables, including the characteristics of biochar and soil properties that influence biochar's performance. Here, we successfully developed an interpretable multitask deep learning (MTDL) model by employing a tensor tracking paradigm to facilitate parameter sharing between two separate data sets, enabling a synergy between Cd and CH4 mitigation with biochar amendments. The characteristics of biochar contribute similar weightings of 67.9% and 62.5% to Cd and CH4 mitigation, respectively, but their relative importance in determining biochar's performance varies significantly. Notably, this MTDL model excels in custom-tailoring biochar to synergistically mitigate Cd and CH4 in paddy soils across a wide geographic range, surpassing traditional machine learning models. Our findings deepen our understanding of the interactive effects of Cd and CH4 mitigation with biochar amendments in paddy soils, and they also potentially extend the application of artificial intelligence in sustainable environmental remediation, especially when dealing with multiple objectives.

Advanced biotechnology strategies for detoxification of persistent organic pollutants and toxic elements in soil

This paper aims to comprehensively examine and present the current state of persistent organic pollutants (POPs) and toxic elements (TEs) in soil. Additionally, it seeks to assess the viability of employing advanced biotechnology, specifically phytoremediation with potent microbial formulations, as a means of detoxifying POPs and TEs. In the context of the "global treaty," which is known as the Stockholm Convention, we analyzed the 3D chemical structures of POPs and its prospects for living organisms which have not been reviewed up to date. The obstacles associated with the phytoremediation strategy in biotechnology, including issues like slow plant growth and limited efficiency in contaminant uptake, have also been discussed and demonstrated. While biotechnology is recognized as a promising method for detoxifying persistent organic pollutants (POPs) and facilitating the restoration of contaminated and degraded lands, its full potential in the field is constrained by various factors. Recent advances in biotechnology, such as microbial enzymes, designer plants, composting, and nanobiotechnology techniques, have opened up new avenues for mitigating persistent organic pollutants (POPs) and toxic elements (TEs). The insights gained from this review can contribute to the development of innovative, practical, and economically viable approaches for remediating and restoring soils contaminated with persistent organic pollutants (POPs) and toxic elements (TEs). The ultimate aim is to reduce the risks to both human and environmental health.

Mechanism and application of modified bioelectrochemical system anodes made of carbon nanomaterial for the removal of heavy metals from soil

Bioelectrochemical techniques are quick, efficient, and sustainable alternatives for treating heavy metal soils. The use of carbon nanomaterials in combination with electroactive microorganisms can create a conductive network that mediates long-distance electron transfer in an electrode system, thereby resolving the issue of low electron transfer efficiency in soil remediation. As a multifunctional soil heavy metal remediation technology, its application in organic remediation has matured, and numerous studies have demonstrated its potential for soil heavy metal remediation. This is a ground-breaking method for remediating soils polluted with high concentrations of heavy metals using soil microbial electrochemistry. This review summarizes the use of bioelectrochemical systems with modified anode materials for the remediation of soils with high heavy metal concentrations by discussing the mass-transfer mechanism of electrochemically active microorganisms in bioelectrochemical systems, focusing on the suitability of carbon nanomaterials and acidophilic bacteria. Finally, we discuss the emerging limitations of bioelectrochemical systems, and future research efforts to improve their performance and facilitate practical applications. The mass-transfer mechanism of electrochemically active microorganisms in bioelectrochemical systems emphasizes the suitability of carbon nanomaterials and acidophilic bacteria for remediating soils polluted with high concentrations of heavy metals. We conclude by discussing present and future research initiatives for bioelectrochemical systems to enhance their performance and facilitate practical applications. As a result, this study can close any gaps in the development of bioelectrochemical systems and guide their practical application in remediating heavy-metal-contaminated soils.

Evaluation of newly designed flushing techniques for on-site remediation of arsenic-contaminated excavated debris

Excavated debris (soil and rock) contaminated with geogenic arsenic (As) is an increasing concern for regulatory organizations and construction stakeholders. Chelator-assisted soil flushing is a promising method for practical on-site remediation of As-contaminated soil, offering technical, economic, and environmental benefits. Ethylenediaminetetraacetic acid (EDTA) is the most prevalent chelator used for remediating As-contaminated soil. However, the extensive environmental persistence and potential toxicity of EDTA necessitate the exploration of eco-compliant alternatives. In this study, the feasibility of the conventional flushing method pump-and-treat and two newly designed immersion and sprinkling techniques were evaluated at the laboratory scale (small-scale laboratory experiments) for the on-site treatment of As-contaminated excavated debris. Two biodegradable chelators, L-glutamic acid-N,N'-diacetic acid (GLDA) and 3-hydroxy-2,2'-iminodisuccinic acid (HIDS), were examined as eco-friendly substitutes for EDTA. Additionally, this study highlights a useful post-treatment measure to ensure minimal mobility of residual As in the chelator-treated debris residues. The pump-and-treat method displayed rapid As-remediation (t, 3 h), but it required a substantial volume of washing solution (100 mL g-1). Conversely, the immersion technique demonstrated an excellent As-extraction rate using a relatively smaller washing solution (0.33 mL g-1) and shorter immersion time (t, 3 h). In contrast, the sprinkling technique showed an increased As-extraction rate over an extended period (t, 48 h). Among the chelators employed, the biodegradable chelator HIDS (10 mmol L-1; pH, 3) exhibited the highest As-extraction efficiency. Furthermore, the post-treatment of chelator-treated debris with FeCl3 and CaO successfully reduced the leachable As content below the permissible limit.

A comprehensive assessment to offer optimized remediation method for mercury contamination in Musa Bay by using hybrid Fuzzy AHP-VIKOR approach

Musa Bay, the largest wetland in Iran and one of the most important Hg-polluted media, plays a significant role in the ecosystem of the area and supports many forms of life. Mercury pollution has detrimental effects on the human body and at high levels leads to the loss of microorganisms in marine ecosystems. Hence, a comprehensive assessment for selecting an effective and sustainable remediation method is crucial to restoring the ecosystem promptly. The determination of a proper and practical treatment method not only is a case-based approach, but could be challenging due to its multi-criteria decision-making nature. Considering preferred crucial factors involved in the effectiveness of remedial actions, in this study a questionnaire is designed to assess the opinion of environmental experts, stakeholders, and some occupants of the area on remedial actions based on the importance weights of criteria. Subsequently, practical remediation and management strategies ranked by hybrid FVIKOR as a multi-criteria decision making (MCDM) method. Ranking results show that dredging and stabilization could offer a promising solution for the remediation of the case study. The results of the study demonstrate that the development of MCDM methods along with effective criteria and considering the analysis of the questionnaires, could offer the best remediation strategy for a specific contaminated site.

Bioremediation of PBDEs and heavy metals co-contaminated soil in e-waste dismantling sites by Pseudomonas plecoglossicida assisted with biochar

Biochar-assisted microbial remediation has been proposed as a promising strategy to eliminate environmental pollutants. However, studies on this strategy used in the remediation of persistent organic pollutants and heavy metals co-contaminated soil are lacking, and the effect of the combined incorporation of biochar and inoculant on the assembly, functions, and microbial interactions of soil microbiomes are unclear. Here, we studied 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) degradation and heavy metal immobilization by and biochar-based bacterial inoculant (BC/PP) in an e-waste contaminated soil, and corresponding microbial regulation mechanisms. Results showed that BC/PP addition was more effective in reducing Cu and Pb availability and degrading BDE-47 than inoculant alone. Notably, BC/PP facilitated bound-residue formation of BDE-47, reducing the ecological risk of residual BDE-47. Meanwhile, microbial carbon metabolism and enzyme activities (related to C-, N-, and P- cycles) were enhanced in soil amended with BC/PP. Importantly, biochar played a crucial role in inoculant colonization, community assembly processes, and microbiome multifunction. In the presence of biochar, positive interactions in co-occurrence networks of the bacterial community were more frequent, and higher network stability and more keystone taxa were observed (including potential degraders). These findings provide a promising strategy for decontaminating complex-polluted environments and recovering soil ecological functions.

Chinese sapindaceous tree species (Sapindus mukorosii) exhibits lead tolerance and long-term phytoremediation potential for moderately contaminated soils

Heavy metal pollution in metropolitan soils poses significant risks to human health and the entire ecosystem. Effective mitigation strategies and technologies are crucial for addressing these environmental issues. Fast-growing trees are an essential part of phytoremediation projects all over the world and provide long-term ecological benefits to mankind. This study assessed the lead tolerance and phytoremediation potential of a fast-growing soapberry tree species (Sapindus mukorossi) in moderately contaminated soil. Two independent experiments were conducted to assess its tolerance at (i) germination level and (ii) prolonged growth stage. In the germination experiments, seeds were exposed to lead (II) nitrate Pb (NO₃)₂ at various concentrations (0, 5, 10, 20, 50, 100, 200, 300, 400 and 500 μM) for 120 days. Results showed significant differences in germination time, germination index, seedling vigor index, energy of germination, final germination, germination inhibition, seedling height and root/shoot weight compared to the control experiments. In the prolonged growth experiments, seedlings were grown for six months in soils amended/spiked with different Pb concentrations (T0 = 0, T1 = 20, T2 = 50, T3 = 100, T4 = 150 and T5 = 200 mg kg-1 soil) and their biomass was determined. The highest biomass achieved in six months (T0: 12.62 g plant-1), followed by (T1: 12.33 g plant-1), (T2: 12.42 g plant-1), (T3: 11.86 g plant-1), (T4: 10.86 g plant-1) and (T5: 10.06 g plant-1) respectively. S. mukorossi showed no visible signs of Pb toxicity over a six-month period. During six months of exposure, the total Pb content in S. mucrossi tissues were classified as roots > leaves > stems. The highest cumulative absorption of Pb occurred between the fourth and fifth months of exposure. Maximum transfer factor (TF) was detected during the fourth month ranging from 0.888 to 1.012 for the different Pb concentrations. Furthermore, the growth behavior, lead accumulation, bioconcentration factors (BCF) and tolerance index (TI) indicated that S. mucrossi may tolerate moderate Pb concentrations for longer periods. These findings suggest that S. mukorossi may be deployed for long-term phytoremediation coupled with urban forest applications in the future.

Integrated application of green zero-valent iron and electrokinetic remediation of metal-polluted sediment

In recent years, more focus has been placed on integrated metal removal processes. Electrokinetic (EK) treatment is superior to other technologies because it can be applied to a variety of mediums. Green nanoparticles, on the other hand, have the potential to significantly reduce pollutant concentrations in a short period of time. In this study, we investigated the possibility of combining green zero-valent iron (nZVI) with EK on Cd and Zn-contaminated sediment. For green synthesis, extracts of dry leaves of mulberry (ML-nZVI) and oak (OL-nZVI) were used, both abundantly present in the Republic of Serbia. The results show that, despite the fact that their availability was greatly reduced, the metals were concentrated and stabilized to a significant extent in the middle of the EK cell (z/L 0.5) after all treatments. When the results were compared, OL-nZVI proved to be a more effective nanomaterial even with smaller doses of OL-nZVI, which is important in terms of achieving better economic benefits. This study identified green nano zero-valent iron as a powerful tool for metal removal when combined with electrokinetic (EK) treatment, which improves green nZVI longevity and migration. This study of the combined green nZVI-EK remediation treatment, in particular, will have an impact on future research in this field, given the achieved efficiency.

Cooperative effect of slow-release ferrous and phosphate for simultaneous stabilization of As, Cd and Pb in soil

The different chemical behavior of anionic As and cationic Cd and Pb makes the simultaneous stabilization of soils contaminated with arsenic (As), cadmium (Cd), and lead (Pb) challenging. The use of soluble, insoluble phosphate materials and iron compounds cannot simultaneously stabilize As, Cd, and Pb in soil effectively due to the easy re-activation of heavy metals and poor migration. Herein, we propose a new strategy of "cooperatively stabilizing Cd, Pb, and As with slow-release ferrous and phosphate". To very this theory, we developed ferrous and phosphate slow-release materials to simultaneously stabilize As, Cd, and Pb in soil. The stabilization efficiency of water-soluble As, Cd and Pb reached 99% within 7d, and the stabilization efficiencies of NaHCO₃-extractable As, DTPA-extractable Cd and Pb reached 92.60%, 57.79% and 62.81%, respectively. The chemical speciation analysis revealed that soil As, Cd and Pb were transformed into more stable states with the reaction time. The proportion of residual fraction of As, Cd, and Pb increased from 58.01% to 93.82%, 25.69 to 47.86%, 5.58 to 48.54% after 56 d, respectively. Using ferrihydrite as a representative soil component, the beneficial interactions of phosphate and slow-release ferrous material in stabilizing Pb, Cd, and As were demonstrated. The slow-release ferrous and phosphate material reacted with As and Cd/Pb to form stable ferrous arsenic and Cd/Pb phosphate. Furthermore, the slow-release phosphate converted the adsorbed As into dissolved As, then the dissolved As reacted with released ferrous to form a more stable form. Concurrently, As, Cd and Pb were structurally incorporated into the crystalline iron oxides during the ferrous ions-catalyzed transformation of amorphous iron (hydrogen) oxides. The results demonstrates that the use of slow-release ferrous and phosphate materials can aid in the simultaneous stabilization of As, Cd, and Pb in soil.

Degradation of hexavalent chromium and naphthalene by electron beam irradiation: Degradation efficiency, mechanisms, and degradation pathway

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in industrial wastewater have attracted much attention due to their damage to the environment and the human body. Studies have shown that there may be interactions between PAHs and HMs, leading to enhanced toxicity of both pollutants. It has been shown that traditional methods are difficult to treat a combination of PAHs and HMs simultaneously. This paper presented an innovative method for treating PAHs and HMs compound pollutants by electron beam irradiation and achieved the removal of the compound pollutants using a single means. Experiments showed that the absorbed dose at 15 kGy could achieve 100% degradation of NAP and 90% reduction of Cr (Ⅵ). This article investigated the effects of electron beam removal of PAHs and HMs complex contaminants in various water environmental matrices. The experimental results showed that the degradation of NAP followed the pseudo-first-order dynamics, and the degradation of NAP was more favorable under neutral conditions. Inorganic ions and water quality had little effect on NAP degradation. For electron beam reduction of Cr (Ⅵ), alkaline conditions were more conducive to reducing Cr (Ⅵ). Especially, adding K₂S₂O₈ or HCOOH achieved 99% reduction of Cr (Ⅵ). Experiments showed that •OH achieve the degradation of NAP, and e_aq^- achieve the reduction of Cr (Ⅵ). The results showed that the degradation of NAP was mainly achieved by benzene ring opening, carboxylation and aldehyde, which proved that the degradation of NAP was mainly caused by •OH attack. The toxicity analysis results showed that the electron beam could significantly reduce the toxicity of NAP, and the toxicity of the final product was much lower than NAP, realizing the harmless treatment of NAP. The experimental results showed that electron beam irradiation has faster degradation rates and higher degradation efficiency for NAP and Cr (Ⅵ) compared to other reported treatment methods.

Advances in the management of radioactive wastes and radionuclide contamination in environmental compartments: a review

Several anthropogenic activities produce radioactive materials into the environment. According to reports, exposure to high concentrations of radioactive elements such as potassium (⁴⁰K), uranium (²³⁸U and ²³⁵U), and thorium (²³²Th) poses serious health concerns. The scarcity of reviews addressing the occurrence/sources, distribution, and remedial solutions of radioactive contamination in the ecosystems has fueled data collection for this bibliometric survey. In rivers and potable water, reports show that several parts of Europe and Asia have recorded radionuclide concentrations much higher than the permissible level of 1 Bq/L. According to various investigations, activity concentrations of gamma-emitting radioactive elements discovered in soils are higher than the global average crustal values, especially around mining activities. Adsorption technique is the most prevalent remedial method for decontaminating radiochemically polluted sites. However, there is a need to investigate integrated approaches/combination techniques. Although complete radionuclide decontamination utilizing the various technologies is feasible, future research should focus on cost-effectiveness, waste minimization, sustainability, and rapid radionuclide decontamination. Radioactive materials can be harnessed as fuel for nuclear power generation to meet worldwide energy demand. However, proper infrastructure must be put in place to prevent catastrophic disasters.

Organic amendments for in situ immobilization of heavy metals in soil: A review

There is a growing need for soil remediation due to the increase in heavy metals (HMs) migrating into the soil environment, especially those from man-made sources dominated by industry and agriculture. In situ immobilization technology, because of its lower life cycle environmental footprint, can achieve "green and sustainable remediation" of soil heavy-metal pollution. Among the various in situ immobilization remediation agents, organic amendments (OAs) stand out as they can act as soil conditioners while acting as HMs immobilization agents, and therefore have excellent application prospects. In this paper, the types and remediation effects of OAs for HMs in situ immobilization in soil are summarized. OAs have an important effect on the soil environment and other active substances in soil while interacting with HMs in soil. Based on these factors, the principle and mechanism of HMs in situ immobilization in soil using OAs are summarized. Given the complex differential characteristics of soil itself, it is impossible to determine whether it can remain stable after heavy-metal remediation; therefore, there is still a gap in knowledge regarding the compatibility and long-term effectiveness of OAs with soil. In the future, it is necessary to develop a reasonable HMs contamination remediation program for in situ immobilization and long-term monitoring through interdisciplinary integration techniques. These findings are expected to provide a reference for the development of advanced OAs and their applications in engineering.

Methane emission reduction oriented extracellular electron transfer and bioremediation of sediment microbial fuel cell: A review

Sediment is the internal and external source of water environment pollution, so sediment remediation is the premise of water body purification. Sediment microbial fuel cell (SMFC) can remove the organic pollutants in sediment by electroactive microorganisms, compete with methanogens for electrons, and realize resource recycling, methane emission inhibiting and energy recovering. Due to these characteristics, SMFC have attracted wide attention for sediment remediation. In this paper, we comprehensively summarized the recent advances of SMFC in the following areas: (1) The advantages and disadvantages of current applied sediment remediation technologies; (2) The basic principles and influencing factors of SMFC; (3) The application of SMFC for pollutant removal, phosphorus transformation and remote monitoring and power supply; (4) Enhancement strategies for SMFC in sediments remediation such as SMFC coupled with constructed wetland, aquatic plant and iron-based reaction. Finally, we have summarized the drawback of SMFC and discuss the future development directions of applying SMFC for sediment bioremediation.

Inhibition of sediment erosion and phosphorus release by remediation strategy of contaminated sediment backfilling

The management of sediment-water interfaces, especially bed stability, is essential for controlling accumulated contaminants in the sediment. In this study, the relationship between sediment erosion and phosphorus (P) release under the remediation strategy of contaminated sediment backfilling (CSBT) was explored through a flume experiment, i.e. the dredged sediment was calcined into ceramsite after dewatering and detoxification and then backfilled to the dredged area for sediment capping, thus avoiding the introduction of foreign materials via in-situ remediation and the large-scale land occupation associated with ex-situ remediation. Acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) were used to measure the vertical distributions of flow velocity and sediment concentration in the overlying water, respectively, and diffusive gradients in thin films (DGT) was used to measure the P distribution in the sediment. The results revealed that improving bed stability from CSBT can considerably improve the robustness of sediment-water interface and reduce sediment erosion by more than 70%. The corresponding P release from the contaminated sediment could be inhibited with an inhibition efficiency as high as 80%. CSBT is a potent strategy for managing contaminated sediment. This study provides a theoretical reference for controlling sediment pollution, further supporting river and lake ecological management and environmental restoration.

Multidecadal heavy metals and microplastic deposition records in an urban lake: the ecological risk assessments and influencing factors

With the development of urbanization and economic growth, the urban lake ecosystem faces many challenges derived from external factors. As pollutants in the aquatic environment, heavy metals and microplastics negatively influence the urban lake ecosystem due to their intrinsic properties. To understand the distribution patterns and multidecadal deposition characteristics of heavy metals and microplastics, six sediment cores were collected in March 2021 from a Chinese urban lake, Xinghu Lake, and the isotopic composition of cesium-137 and lead-210 was analyzed for the chronology of the sediment core. Here, the classifications of comprehensive ecological risk evaluation methods for heavy metals and microplastics were adjusted further. Meanwhile, the correlations among heavy metals, microplastics, sediment grains, and natural and social factors were further analyzed. The results showed that the sediments of Xinghu Lake were mainly fine silt (39%), and the average surface area of sediment was 1.82 ± 0.60 m²/g. The average concentrations of cadmium, chromium, copper, nickel, lead, vanadium, and zinc were 0.268 ± 0.077, 59.91 ± 16.98, 23.29 ± 6.48, 52.16 ± 13.11, 36.83 ± 11.78, 119.57 ± 26.91, and 88.44 ± 29.68 mg/kg, respectively. The average comprehensive potential ecological risk indexes of heavy metals and microplastics in sediment cores were 46.59 ± 9.98 and 105.78 ± 23.32 in Xinghu Lake, and their risks were projected to reach high and very high levels by 2030 and 2050. The annual average temperature was the key natural factor for the abundances of heavy metals and microplastics, and the small sediment grain had a significant correlation with these. Agricultural activities were major pollution sources of heavy metals and microplastics, while the chemical fibers and plastic products were closely related to the abundance of microplastics.

A review on the clean-up technologies for heavy metal ions contaminated soil samples

The soil contamination with heavy metal ions is one of the grave intricacies faced worldwide over the last few decades by the virtue of rapid industrialization, human negligence and greed. Heavy metal ions are quite toxic even at low concentration a swell as non-biodegradable in nature. Their bioaccumulation in the human body leads to several chronic and persistent diseases such as lung cancer, nervous system break down, respiratory problems and renal damage etc. In addition to this, the increased concentration of these metal ions in soil, beyond the permissible limits, makes the soil unfit for further agricultural use. Hence it is our necessity, to monitor the concentration of these metal ions in the soil and water bodies and adopt some better technologies to eradicate them fully. From the literature survey, it was observed that three main types of techniques viz. physical, chemical, and biological were employed to harness the heavy metal ions from metal-polluted soil samples. The main goal of these techniques was the complete removal of the metal ions or the transformation of them into less hazardous and toxic forms. Further the selection of the remediation technology depends upon different factors such as process feasibility/mechanism of the process applied, nature and type of contaminants, type and content of the soil, etc. In this review article, we have studied in detail all the three technologies viz. physical, chemical and biological with their sub-parts, mechanism, pictures, advantages and disadvantages.

In vivo cadmium-assisted dilute acid pretreatment of the phytoremediation sweet sorghum for enzymatic hydrolysis and cadmium enrichment

Phytoremediation with energy crops is considered an integrated technology that provides both environment and energy benefits. Herein, the sweet sorghum cultivated on Cd-contaminated farmland (1.21 mg/kg of Cd in the soil) showed promising phytoremediation potential, and the approach for utilizing sorghum stalks was explored. Sweet sorghum bagasse with Cd contamination was pretreated with dilute acid in order to improve enzymatic saccharification and achieve Cd recovery, resulting in harmless and value-added utilization. After pretreatment, hemicelluloses were dramatically degraded, and the lignocellulosic structures were partially deconstructed with xylan removal up to 98.1%. Under the optimal condition (0.75% H₂SO₄), the highest total sugar yield was 0.48 g/g of raw bagasse; and nearly 98% of Cd was enriched in the liquid phase. Compared with normal biomass, Cd reduced the biomass recalcitrance and further facilitated the deconstruction of biomass under super dilute acid conditions. This work provided an example for the subsequent valorization of Cd-containing biomass and Cd recovery, which will greatly facilitate the development of phytoremediation of heavy metal contaminated soil.

Safe Rice Production in Cd-Contaminated Paddy Soil: Strategy and Environmental Implications

This field study explored safe rice production in Cd-contaminated red paddy soil by application of the combined Si-/Se- containing foliar inhibitors (Si or Se) and the mixture amendments of quicklime (Q), polyacrylamide (A), or/and sepiolite (S) at low (1) and high (2) application rates. The results showed that all treatments increased soil pH and decreased total P and soil organic matter (excluding QSe2). With the increasing application rates, QAS significantly decreased the available Cd because of the enhanced stabilization, while QSi and QSe significantly increased the available Cd because of the inhibited plant uptake. After remediation, QA1, QSi2, and QSe2 most effectively decreased the uptake Cd by rice to meet the threshold of National Food Safety Standard of China. The treatments excluding Q1, QA1, QSi1, and QSi2 did not dramatically change the bacterial community structure in soil. Collectively, QSe2 was recommended for remediating Cd-contaminated red paddy soil.

Overview of structure, function and integrated utilization of marine shell

Marine shell resources have received great attention from researchers owing to their unique merits such as high hardness, good toughness, corrosion resistance, high adsorption, and bioactivity. Restricted by the level of comprehensive utilization technology, the utilization rate of shells is extremely low, resulting in serious waste and pollution. The research shows that the unique brick-mud structure of shells makes them have diverse and good functional characteristics, which guides them to have great utilization potential in different fields. Hence, this review highlights the constitutive relationship between microstructure-function-application of shells (e.g., gastropods, cephalopods, and amniotes), and the comprehensive applications and development ideas in the fields of biomedicine, adsorption enrichment, pHotocatalysis, marine carbon sink, and environmental deicer. It is worth mentioning that marine shells are currently well developed in three areas: bone repair, health care and medicinal value, and drug carrier, which together promote the progress of biomedical field. In addition, an in-depth summary of the application of marine shells in the adsorption and purification of various impurities such as crude oil, heavy metal ions and dyes at low-cost and high efficiency is presented. Finally, by integrating thoughts and approaches from different applications, we are committed to providing new pathways for the excavation and future high-value of shell resources, clarifying the existing development stages and bottlenecks, promoting the development of related technology industries, and achieving the synergistic win-win situation of economic and environmental benefits.

Synchronous stabilization of As, Cd, and Pb in soil by sustained-release of iron-phosphate

Anionic arsenic (As) exhibits geochemical behavior opposite to those of cationic cadmium (Cd), and lead (Pb), which makes the synchronous remediation of As, Cd, and Pb challenging. The synchronous stabilization of As, Cd, and Pb to form Cd/Pb-phosphate and iron‑arsenic precipitates is a promising strategy. However, the effectiveness of soluble phosphate or iron-based materials is limited by the activation of Cd, Pb, or As, while low mobility hinders insoluble particles. In this study, we developed an amorphous structure that releases iron and phosphate at a sustained rate. Thus, the stabilization efficiencies of NaHCO₃-extractable As, DTPA-extractable Cd and Pb reached 44.6 %, 40.8 %, and 48.1 %, respectively. The proportion of residual fraction of As, Cd, and Pb increased by 12.1 %, 14.5 %, and 36.4 %, respectively, after 28 d. Ferrihydrite was chosen as the soil component to monitor the chemical behavior and speciation transformation of As, Cd, and Pb in the reaction. During the process, the released iron directly reacted with dissolved As to form iron‑arsenic precipitation and phosphate directly reacted with Cd/Pb to form Cd/Pb-phosphate precipitation. Simultaneously, phosphate replaced the adsorbed As and transformed into a dissolved state, which could be re-precipitated with the released iron ions. Thus, this study provides a reliable strategy for the remediation of As, Cd, and Pb combined pollution in soil.

Degradation of PAHs in soil by activated persulfate system with activated carbon supported iron-based bimetal

We developed a material of activated carbon (AC)-supported highly active iron-based bimetal (iron-copper bimetal/AC, Fe-Cu/AC) with high efficiency for polycyclic aromatic hydrocarbons (PAHs) degradation in soil by activating persulfate, benefiting from the synergistic effect that the characteristics of AC with porous carbon backbone, multiple active functional groups, high loading capacity and the characteristics of FeCu bimetal with high activity. The addition of Cu to the Fe-based/AC activator not only improved the dispersibility of Fe particles but also maintained the stability of the metal in the Fe-Cu/AC. The thermal activation (50 °C) promoted the degradation of PAHs by the Fe-Cu/AC-activated S₂O₈^2- system. Of the various systems tested, the Fe-Cu/AC-activated S₂O₈^2- system had the best degradation efficiency for 19 PAHs, with the overall efficiency following the order of Fe-Cu/AC + S₂O₈^2- > Fe-Cu + S₂O₈^2- > Fe-Cu/AC > S₂O₈^2-. The degradation mechanism of the Fe-Cu/AC-activated S₂O₈^2- system on soil PAHs showed that OH, OOH, and SO₄^- were the main active groups involved in the degradation of target PAHs. The target pollutants and their degradation products in the Fe-Cu/AC-activated S₂O₈^2- system indicated specific exposure pathways, providing a theoretical basis for the remediation of PAH-contaminated soil.

Organic ligands activate the dark formation of hydroxyl radicals (HO•) in surface soil/sediment: Yields, mechanisms, and applications

Soil is an important sink for various pollutants. Recent findings suggest that soil and sediment would spontaneously form HO^• through Fenton or Fenton-like reactions under natural conditions. In this study, the effects and mechanisms of organic ligands (OLs) on the occurrence of HO^• in surface soil/sediment were experimentally and computationally examined. Results confirmed that HO^• generation was ND-12.92 nmol/g in surface soil/sediment, and the addition of EDTA-2Na would significantly enhance the yields of HO^• by 1.4-352 times. Moisture was the decisive factor of soil HO^• generation. The release of Fe(II) from solid into the aqueous phase was essential for the stimulation of HO^• in EDTA-2Na suspensions. Furthermore, complexation reactions between Fe(II) and OLs would enhance single electron transfer (SET) reactions and the formation of O₂^•-. Interestingly, for specific OLs, their stimulations on SET and formation of O₂^•- would depress HO^• generation. Provoking HO^• generation by OLs could be efficiently used to degrade sulfamethoxazole in rice field sediment. The study provided new knowledge on how commonly synthetic OLs affect the HO^• generation in surface soil/sediment, and it additionally shed light on the engineered stimulation of in-situ Fenton reactions in natural soil/sediment.

Investigating the prospect of cleaner production in informal enterprises: A scientific assessment of environmental burdens and economic efficiency

The present study aims to assess the prospects for cleaner production (CP) and sustainable development (SD) of informally operated small manufacturing enterprises, which are frequently blamed for uncontrolled waste disposal and causing pollution to the environment. The economic efficiency level of these firms has been explored to this end, and the metallic pollution loads in the surrounding environment have been scientifically analyzed to investigate the nexus between these two. DEA (Data Envelopment Analysis)-Tobit analysis has been employed, and a pollution load index (PLI) of heavy metal pollution comprising two environmental compartments (soil and water) has been constructed based on the concentration level of metalloid pollutants in the samples collected from the surrounding areas of the studied informal firms in Bangladesh. The study disproves CP practice in majority of the informal firms in Bangladesh by observing a positive relationship between firm-level efficiency and pollution load sourced from their production activities. Afterwards, this study estimates the eco-efficiency level of firms by considering pollution load as an undesirable output and minimizing its impact in an input-oriented DEA model. Applying the eco-efficiency scores in censored Tobit regression analysis, the outcome endorses the prospect of CP for informally operated enterprises in Bangladesh. However, the CP prospect can only materialize if and only if firms are provided with adequate technical, financial, and strategic support for achieving eco-efficiency in their production. The informal and marginal nature of the studied firms restricts them from getting access to the facilities and support services needed for implementing CP and moving towards sustainable manufacturing. Therefore, this study recommends green practices in informal manufacturing and limiting the informal firms by bringing them gradually under the coverage of formalization, which is in line with the achievement of the targets mentioned in Sustainable Development Goal 8.

Simultaneous voltammetric sensing of Zn2+, Cd2+, and Pb2+ using an electrodeposited Bi-Sb nanocomposite modified carbon paste electrode

A sensor for detecting Zn²⁺, Cd²⁺, and Pb²⁺ ions simultaneously based on the square wave anodic stripping response at a bismuth antimony (Bi-Sb) nanocomposite electrode was developed. The electrode was prepared in situ by electrodepositing bismuth and antimony on the surface of a carbon-paste electrode (CPE) while also reducing the analyte metal ions. The structure and performance of the Bi-Sb/CPE electrode were studied using scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and cyclic voltammetry. Operational conditions including the concentration of Sb and Bi, the type of electrolyte, pH, and preconcentration conditions were optimized. The linear ranges were determined to be 5-200 μg L^-1 for Zn²⁺, 1-200 μg L^-1 for Cd²⁺, and 1-150 μg L^-1 for Pb²⁺ with the optimized parameters. The limits of detection were 1.46 μg L^-1, 0.27 μg L^-1, and 0.29 μg L^-1 for Zn²⁺, Cd²⁺, and Pb²⁺, respectively. Furthermore, the Bi-Sb/CPE sensor is capable of selective determination of the target metals in the presence of the common cationic and anionic interfering species (Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Co²⁺, Cl^-, SO₄ ^2- and HCO₃ ^-). Finally, the sensor was successfully applied to the simultaneous determination of Zn²⁺, Cd²⁺, and Pb²⁺ in a variety of real-world water samples.

Metal-mining-induced sediment pollution presents a potential ecological risk and threat to human health across China: A meta-analysis

Aquatic sediment polluted by potentially toxic elements (PTEs) from mining activities represents a potential health "time bomb" for humans and the local ecology, but the integrated analysis of pollution and hazards of PTEs in sediment around typical metal mines in China is limited. Presently, the associated pollution status, spatial distribution, and ecological and health hazards of Cd, Cu, Zn, Pb, Cr, and As were investigated through index evaluation, spatial analysis, health risk assessment models, and Monte Carlo simulation. Overall, the sediment exhibited varying degrees of PTE contamination; notably, the level of Cd was 104.85 times higher than its background value, and it became the most enriched element in the surveyed sediment, followed in descending order by Cu, As, Zn, Pb, and Cr. Nationally, over 64.5% of metal-mining-affected sediment presented a very high ecological risk, contributed mostly by Cd (43.2%-98.7%) followed by As, Pb, and Cu; the risk contributed by both Cr and Zn was found to be negligible. The adverse health risk posed to children by most sediment was 1.72 and 6.46 times higher than that posed to adults for cancerous and noncancerous risks, respectively. The potential noncarcinogenic risks were mainly caused by As, which contributed over 78.9% of the Hazard Index values, then followed by Pb (>9.3%). For both children and adults, the carcinogenic risk of PTEs decreased in the following order: As > Cd > Cr > Pb. The investigated sediment was found seriously affected by nearby metal mines, especially those in regions with long-term and large-scale nonferrous-metal-mining activities. This study could provide a reference for policymakers to develop control strategies for PTE pollution in sediment around mining areas.

Remediation performance and mechanisms of Cu and Cd contaminated water and soil using Mn/Al-layered double oxide-loaded biochar

The combined pollution of heavy metals is ubiquitous worldwide. Mn/Al-layered double oxide-loaded crab shells biochar (LDO/BC) was prepared, so as to remediate the combined pollution of Cd and Cu in soil and water. The pristine and used LDO/BC were characterized and the results revealed that the layered double oxide was successfully loaded on crab shells biochar (BC) and metal element Ca in crab shells was beneficial to the formation of more regular layered and flake structure. The maximal adsorption capacity (Q_m) of LDO/BC for aqueous Cu²⁺ and Cd²⁺ was 66.23 and 73.47 mg/g, respectively. LDO/BC and BC were used to remediate e-waste-contaminated soil for the first time and exhibited highly efficient performance. The extraction amount of Cu and Cd in the contaminated soil by diethylene triamine penta-acetic acid (DTPA) after treating with 5% LDO/BC was significantly reduced from 819.84 to 205.95 mg/kg (with passivation rate 74.8%) and 8.46 to 4.16 mg/kg (with passivation rate 50.8%), respectively, inferring that the bioavailability of heavy metals declined remarkably. The experimental result also suggested that after remediation by LDO/BC the exchangeable and weak acid soluble Cu and Cd in soil translated to reducible, residual and oxidizable fraction which are more stable state. Precipitation, complexation and ion exchange were proposed as the possible mechanisms for Cd and Cu removal. In general, these experiment results indicate that LDO/BC can be a potentially effective reagent for remediation of heavy metal contaminated water and soil.

Batch-mode stimulation of hydrocarbons biodegradation in freshwater sediments from historically contaminated Alūksne lake

Historical contamination of freshwater lakes with hydrocarbons (HC) due to anthropogenic activities represents a serious problem worldwide. This study was focused on hydrocarbons-contaminated sediments sampled in Lake Alūksne of glacial origin in Northeast Latvia. The batch experiments were aimed at evaluating the effect of bio-stimulation and bioaugmentation on the biodegradation of hydrocarbons in lake sediments (LS), as well as changes in microbial community structure and metabolic activity. The sediments were sampled from two points of the lake, 4-5 m and 8 m depth, respectively. These samples slightly differed by colour, count of diatoms, microbial respiration intensity and colour intensity of 2,6- dichlorophenolindophenol. Nevertheless, the trend in biodegradation activity was similar for both LS samples. The concentration of HC in LS during the 32-day incubation decreased in average from 465 mg/kg to 165 mg/kg and 117.5 mg/kg in the LS amended with nutrients and nutrients+microbial community, respectively. Different treatment types of LS resulted in differences in microbial respiration and HC-degrading activity. The Shotgun sequencing has revealed the main phyla present in the intact LS being Proteobacteria (48.8%), Actinobacteria (24.4%), Firmicutes (10.4%) and Bacteroidetes (5.0%). Incubation of LS for 32 days resulted in increasing abundance of Proteobacteria from 48.8% in the raw LS to 58-62%, mainly due to the increase of Betaproteobacteria. The functional annotation of gene families revealed that the most abundant gene families were associated with ATP binding, metal ion, magnesium ion, sulfur cluster, zinc ion binding, DNA binding and other essential components for cell functioning. The Shannon biodiversity index of culturable microorganisms in EcoPlates™ ranged from 2.28 to 2.85. The data obtained in this study indicated that the suggested approach is a potent remediation technology for further ex situ scaling up.

Sustainability prioritization of technologies for cleaning up soils polluted with oil and petroleum products: A decision support system under complex spherical fuzzy environment

The transition towards a sustainable land management (SLM) needs for utilizing appropriate technologies for controlling soil pollution, and ensures the development of environmental, economic, technical, and social dimensions in region. Using these technologies for cleaning up soils polluted with oil and petroleum products in Behbahan city (in the southwest of Iran) is considered. The soil pollution control technologies (SPCTs) can assist local authorities, governments, investors, and developers to reduce climate change, mitigate soil, water, and air pollution and construct the sustainable communities. With the aim of balance between the issues in the context of sustainability policy, criteria (principles) including environmental, economic, technical, and social aspects are considered. The research takes into consideration the applicability of a novel multi-criteria decision-making approach namely complex spherical fuzzy set-based CODAS (Combinative distance-based assessment). The approach can be used to choose the suitable technology in a sustainable mode, considering the principles related to sustainability pillars. It comprises various technologies for soil pollution control and prioritizes technologies from the most to least as: Biorestoration technology, Excavation technology, Soil venting technology, Soil flushing, and Hydraulic barriers technology.

Immobilization of exopolymeric substances from bacteria for metal removal: A study on characterization, optimization, reusability and toxicity

This study investigated the immobilization of exopolymeric substances (EPS) from Bacillus cereus using sodium alginate to form EPS beads for metal removal. The EPS beads were characterized and their optimum biosorption conditions established (biosorbent dosage, initial metal concentration and pH of metal solutions). The EPS beads were also tested for reusability by using them continuously for five metal removal cycles with desorption process in between cycles. The toxicity of the treated metal solutions was tested by phytotoxicity tests. Results revealed that EPS beads demonstrated significantly higher metal removal efficiency (Pb: 99.26%, Cr: 50.73%, Cu: 48.94%, Zn: 29.81%, Cd: 20.29%) compared to plain alginate beads (without EPS) (Pb: 84.45%, Cu: 31%, Cr: 28.37%, Zn: 11.91%, Cd: 9.37%). SEM-EDX analysis detected Cu, Pb, Zn, Cd and Cr on the surface of EPS beads. Optimum conditions for Pb removal by EPS beads were from the use of 0.1 g of biosorbent at 100 mg/L initial metal concentration and pH 5. By contrast, Cu, Zn, Cd and Cr were optimally removed by 0.3 g of biosorbent at 25 mg/L initial metal concentration and pH 5. EPS beads can be reused up to five times while maintaining a high rate of metal removal efficiency (Pb- 99.52%, Cr- 89.23%, Cu- 89.17%, Zn-52.52%, Cd-39.12%). This was achieved through desorption with nitric acid that consistently recovered 76-93% of the metal adsorbed. FTIR analysis reveals that nitric acid is capable of restoring the functional groups present within EPS beads, allowing it to bind with metal ions in repeated cycles. Metal solutions treated with EPS beads were less toxic as seedling shoots (pre-treated: 0-10 cm, post-treated: 1.2-18.1 cm) and roots (pre-treated: 0-7.8 cm, post-treated: 0.8-15.1 cm) grew well, which suggested that reduced levels of metals led to reduced phytotoxicity. This study provides an insight into the use of EPS beads for metal removal, highlighting the benefits and reusability of the beads for future wastewater treatment.

Risk control and assessment of sulfide-rich sediment remediation by controlled-release calcium nitrate

Nitrate stimulation is widely used in sediment remediation to eliminate sulfides, degrade organic pollutants and immobilize phosphorus. However, the environmental risks of nitrate escape and the subsequent release of pollutants (e.g. nitrite, ammonium and trace metals) to water bodies during its application has received less attention. In this study, controlled-release nitrate pellets (SedCaN pellets) were manufactured and applied at different sediment depths to examine their effectiveness in controlling the risk of nitrate escape and subsequent pollutant release. The germination of submerged plant was also analyzed to assess the ecological risks associated with the remediated sediment. The results showed that the SedCaN pellets slowly released calcium nitrate, which led to denitrifying sulfide oxidation, organic matter degradation and the immobilization of phosphorus as a calcium-bound species. Gas production by denitrification increased the sediment porosity (0.3-2.2%) and led to the concomitant release of nitrite, ammonium, and heavy metals, creating secondary risks. Application of the SedCaN pellets at depth decreased the nitrate escape and the secondary risks, presumably by means of a capping effect of the upper sediment. The release of nitrate, ammonium, Ni and Cu were partially limited by 91.6%, 19.0%, 61.6% and 57.4% when SedCaN pellets were incorporated into deeper sediments (7-9 cm). Moreover, the range of sulfide oxidation extended to the upper and lower sediments in the profile (column), while the sulfide oxidation efficiency reached 85.9-95.0%. Finally, increased germination of Bacopa monnieri (20.0-26%) demonstrated that in comparison to reference materials the ecological risks of the treated sediments was reduced and the habitat function of sediment was restored after nitrate-stimulating remediation. The results of this study provide valuable guidelines for nitrate-stimulating remediation of sulfide-rich (black-odor) sediments.

Resource utilization of rice husk biomass: Preparation of MgO flake-modified biochar for simultaneous removal of heavy metals from aqueous solution and polluted soil

In general, the remediation performance of heavy metals can be further improved by metal-oxide modified biochar. This work used MgO-modified rice husk biochar (MgO-5%@RHB-450 and MgO-5%@RHB-600) with high surface activity for simultaneous remediation and removal of heavy metals in soil and wastewater. The adsorption of MgO-5%@RHB-450/MgO-5%@RHB-600 for Cd(II), Cu(II), Zn(II) and Cr(VI) followed the pseudo-second order, with the adsorption capacities reaching 91.13/104.68, 166.68/173.22, 80.12/104.38 and 38.88/47.02 mg g^-1, respectively. The addition of 1.0% MgO-5%@RHB-450 and MgO-5%@RHB-600 could effectively decrease the CaCl₂-extractable Cd concentration (CaCl₂-Cd) by 66.2% and 70.0%, respectively. Moreover, MgO-5%@RHB-450 and MgO-5%@RHB-600 facilitated the transformation of exchangeable fractions to carbonate-bound and residual fractions, and reduced the exchangeable fractions by 8.1% and 9.6%, respectively. The mechanisms for the removal of heavy metals from wastewater by MgO-5%@RHB-450 and MgO-5%@RHB-600 mainly included complexation, ion exchange and precipitation, and the immobilization mechanisms in soil may be precipitation, complexation and pore filling. In general, this study provides high-efficiency functional materials for the remediation of heavy metal pollution.

Catalyzing urea hydrolysis using two-step microbial-induced carbonate precipitation for copper immobilization: Perspective of pH regulation

Microbial induced carbonate precipitation (MICP) has recently applied to immobilize heavy metals toward preventing their threats to public health and sustainable development of surrounding environments. However, for copper metallurgy activities higher copper ion concentrations cause the ureolytic bacteria to lose their activity, leading to some difficulty in forming carbonate precipitation for copper immobilization (referred to also as “biomineralization”). A series test tube experiments were conducted in the present work to investigate the effects of bacterial inoculation and pH conditions on the copper immobilization efficiency. The numerical simulations mainly aimed to compare with the experimental results to verify its applicability. The copper immobilization efficiency was attained through azurite precipitation under pH in a 4–6 range, while due to Cu²⁺ migration and diffusion, it reduced to zero under pH below 4. In case pH fell within a 7–9 range, the immobilization efficiency was attained via malachite precipitation. The copper-ammonia complexes formation reduced the immobilization efficiency to zero. The reductions were attributed either to the low degree of urea hydrolysis or to inappropriate pH conditions. The findings shed light on the necessity of securing the urease activity and modifying pH conditions using the two-step biomineralization approach while applying the MICP technology to remedy copper-rich water bodies.

Roles of humic substances redox activity on environmental remediation

Humic substances (HS) as representative natural organic matters and the most common organic compounds existing in the environment, has been applied to the treatment and remediation of environmental pollution. This review systematically introduces and summarizes the redox activity of HS for the remediation of environmental pollutants. For inorganic pollutants (such as silver, chromium, mercury, and arsenic), the redox reaction of HS can reduce their toxicity and mobilization, thereby reducing the harm of these pollutants to the environment. The concentration and chemical composition of HS, environmental pH, ionic strength, and competing components affect the degree and rate of redox reactions between inorganic pollutants and HS significantly. With regards to organic pollutants, HS has photocatalytic activity and produces a large number of reactive oxygen species (ROS) under the light which reacts with organic pollutants to accelerate the degradation of organic pollutants. Under the affection of HS, the redox of Fe(III) and Fe(II) can enhance the efficiency of Fenton-like reaction to degrade organic pollutants. Finally, the research direction of HS redox remediation of environmental pollution is prospected.

Effect of application mode (capping and amendment) on the control of cadmium release from sediment by apatite/calcite mixture and its phosphorus release risk

In this research, the influence of application mode (capping and amendment) on the control of cadmium (Cd) liberation from sediment by apatite/calcite mixture and its phosphorus release risk were investigated. The results showed that calcite addition had a limited effect on the speciation of Cd in sediment, but apatite addition had a significant impact on the fractionation of Cd in sediment. Apatite amendment could effectively immobilize the most readily mobilized Cd by transferring the acid-soluble fraction to the reducible and residual fractions. Apatite addition also could effectively reduce the concentration of toxicity characteristic leaching procedure (TCLP)-leachable Cd in sediment, and apatite had a much higher reduction efficiency of TCLP-leachable Cd than calcite. Apatite/calcite mixture capping could reduce the risk of Cd liberation from sediment into the overlying water, and the controlling efficiency of apatite/calcite mixture capping was higher than that of apatite/calcite mixture amendment. The effect of apatite/calcite mixture addition on the concentration of reactive soluble phosphorus (SRP) in the overlying water was limited. The introduction of calcite into the apatite capping layer could lower the risk of phosphorus release from apatite to the overlying water as compared to single apatite capping. However, the apatite/calcite mixture capping layer still had a relatively high risk of phosphorus liberation into the overlying water. Results of this work suggest that apatite/calcite mixture has a high potential to be used as a capping material to control Cd release from sediment from the perspective of controlling efficiency and application convenience.

Co-high-efficiency washing agents for simultaneous removal of Cd, Pb and As from smelting soil with risk assessment

Soil washing is considered a highly efficient technology due to its higher removal rate of multiple heavy metals from contaminated soil. However, previous studies on Cd, Pb and As washing agents for soils with complex contaminations did not consider the differences in As and Cd/Pb properties, resulting in the lack of effective washing compounds and washing conditions for soils with complex contaminations. Moreover, most traditional washing agents can cause secondary pollution. In this study, HEDTA and lactic acid (LA) treatments resulted in a higher Cd and Pb removal, while 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) was more effective in As removal. Most importantly, a new washing strategy was proposed with a new combined high-efficiency washing agents consisting of HEDP + LA + FeCl₃ with a ratio of 6:3:1. Considering washing efficiency and consumption under optimal washing conditions, i.e. the soil/liquid (S/L) ratio of 1:20 and washing time of 48 h, the rates of Cd, Pb and As removal were 79.93%, 69.84% and 61.55%, respectively. In addition, washing process could influence the speciation of heavy metals, especially oxidizable and residual Cd and Pb fractions, as well as reducible As fraction. The washing process using the new washing agent can significantly reduce the pollution level and health risk of Cd, Pb and As contamination. The results of this study can provide an efficient washing agent for the remediation of heavy metal-contaminated soils at smelting sites, which will help protect human health.

Effect of heavy metals on in vitro growth and development of the Momordica cymbalaria Fenzl

Heavy metals have played a great role in the genesis of the present-day civilization. Human beings are affected when these metals are added to the food chain. Although these are the most important plant nutrients, they are phytotoxic at high concentrations. Heavy metals at super optimal concentrations affect different metabolic pathways in plants and result in their ceased growth and development. They may enter plants either by their root system or through foliar uptake; stunted growth, chlorosis, necrosis, and reddish-brown discoloration are visible symptoms of severe metallic phytotoxicity. The study of heavy metal stress tolerance on Momordica cymbalaria shows the effect on the plant growth and metabolism. All heavy metals treated with high concentrations affect the overall plant growth. The Murashige and Skoog (MS) basal medium with ZnSO4 at 100 µM concentration resulted in healthy shoot development (9) with a maximum shoot length of 7.2 cm. MS basal medium with low concentration of CuSO4 (50 µM) achieved a maximum shoot number (7) with healthy leaves and shoots. MS basal medium with higher concentration of CdCl2 (150 µM) affects plant growth and reduced the regeneration capability completely.