Managing soils of environmental significance: A critical review

A comprehensive assessment of heavy metals, VOCs and petroleum hydrocarbon in different soil layers and groundwater at an abandoned Al/Cu industrial site

Compound pollution at industrial sites impedes urban development, especially when there is a lack of understanding about the spatial variations of internal pollution in industrial areas producing light-weight materials. In this study, spatial distribution and ecological risks of potentially toxic elements (PTEs), volatile organic compounds (VOCs), and petroleum hydrocarbons (C10-40) in the soil and groundwater of an Al/Cu (aluminum/copper) industrial site have been analyzed comprehensively. Results revealed the progressive clustering of pollutants in different soil layers, which indicated varying levels of penetration and migration of pollutants from the surface downward. Furthermore, severity of pollution varied according to pollutant type, with Cu (5-10,228 mg kg-1) often exceeding the background levels significantly (>40). Cd (0.03-2.60 mg kg-1) and Hg (0.01-3.73 mg kg-1) were found at elevated concentrations in deeper soil layers, suggesting distinct variations of PTEs across different soil depths. Among the more hazardous VOCS, polychlorinated biphenyls (1.80-234 μg kg-1) were particularly prevalent in the deeper layers of soil. Petroleum hydrocarbons (C10-40) were widely detected (6-582 mg kg-1), showing significant migration potential from surface to deep soil. These findings suggest that prolonged industrial activities lead to deep-seated accumulation of pollutants, which also impacts the groundwater, contributing to long-term dispersion of contaminants. Furthermore, multivariate statistical analysis indicated certain positive correlations among the distribution of Cu, Pb and petroleum hydrocarbons, indicating possible coupling of these pollutants. Severe Cu pollution caused an ecological risk in the surface soil layer (covering >20 % area of high pollution site, contributing >40 % ecological risk). While the Hg and Cd posed significant risks in the deeper soil layers, showing higher risk coefficients and mobility. The study provides crucial insights into the transformation of urban areas with a history of industrial uses into community spaces and highlights the risks posed by the remaining pollutants.

Assembly processes and co-occurrence of bacterial communities in tree rhizosphere under Pb-Zn contamination

Rhizosphere bacteria are critical for supporting plant performance in stressful environments. Understanding the assembly and co-occurrence of rhizosphere bacterial communities contributes significantly to both plant growth and heavy metal accumulation. In this study, Ligustrum lucidum and Melia azedarach were planted in soils with simulated varying levels of Pb-Zn contamination. The Rhizosphere bacterial communities were investigated by using 16S rRNA gene sequencing. The impacts of Pb-Zn contamination on the diversity and structure of the rhizosphere bacterial community were found to be greater than those of both tree species. The variation in bacterial community structure in both trees was mainly driven by the combinations of Pb-Zn and soil properties. Deterministic processes (non-planted, 82 %; L. lucidum, 73 %; M. azedarach, 55 %) proved to be the most important assembly processes for soil bacterial communities, but both trees increased the importance of stochastic processes (18 %, 27 %, 45 %). The rhizosphere co-occurrence networks exhibited greater stability compared to the non-planted soil networks. Rare taxa played a dominant role in maintaining the stability of rhizosphere networks, as most of the keystone taxa within rhizosphere networks belonged to rare taxa. Dissimilarities in the structure and network complexity of rhizosphere bacterial communities were significantly associated with differences in tree biomass and metal accumulation. These variations in response varied between both trees, with L. lucidum exhibiting greater potential for phytoremediation in its rhizosphere compared to M. azedarach. Our results offer valuable insights for designing effective microbe-assisted phytoremediation systems.

Coupling of radon and microbial analysis for dense non-aqueous-phase liquid tracing and health risk assessment in groundwater under seasonal variations

Dense non-aqueous-phase liquids (DNAPLs) represent one of the most hazardous contaminants of groundwater, posing health risks to humans. Radon is generally used to trace DNAPLs; however, external factors, such as rainfall or stream water, can influence its efficacy. To overcome these limitations, this study pioneered the integration of radon and microbial community structures to explore DNAPL tracing and natural attenuation in the context of seasonal variations for human health risk assessments. The results showed that a radon tracer can estimate DNAPL saturation in the source zone, especially during the dry season when radon deficiency predominates. However, samples exhibited mixing effects during the wet season because of local precipitation. Moreover, bioremediation and low health risks were observed in the plume boundary zone, indicating that microbial dechlorination was a predominant factor determining these risks. The abnormal patterns of radon observed during the wet season can be elucidated by examining microbiological communities. Consequently, a combined approach employing radon and microbial analysis is advocated for the boundary zone, albeit with a less intensive management strategy, compared with that for the source zone. This novel coupling method offers a theoretical and practical foundation for managing DNAPL-contaminated groundwater.

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.

Impacts of multiple environmental factors on soil bacterial community assembly in heavy metal polluted paddy fields

Soil microorganisms play pivotal roles in driving essential biogeochemical processes in terrestrial ecosystems, and they are sensitive to heavy metal pollution. However, our understanding of multiple environmental factors interaction in heavy metal polluted paddy fields to shape microbial community assembly remain limited. In the current study, we used 16S rRNA amplicon sequencing to characterize the microbial community composition in paddy soils collected from a typical industry town in Taihu region, eastern China. The results revealed that Cd and Pb were the major pollutant, and Proteobacteria, Acidobacteria and Chloroflexi were the dominate indigenous bacterial phyla. Linear regression and random forest analysis demonstrated that soil pH was the most important predictor of bacterial diversity. Mantel analysis showed that bacterial community structure was mainly driven by pH, CEC, silt, sand, AK, total Cd and DTPA-Cd. The constructed bacterial co-occurrence network, utilizing a random matrix theory-based approach, exhibited non-random with scale-free and modularity features. The major modules within the networks also showed significant correlations with soil pH. Overall, our study indicated that soil physiochemical properties made predominant contribution to bacterial community diversity, structure and their association in Cd/Pb polluted paddy fields. These findings expand our knowledge of the key environmental drivers and co-occurrence patterns of bacterial community in polluted paddy fields.

Trends in research on characterization, treatment and valorization of hazardous red mud: A systematic review

Meta-analysis of red mud-related literature in English published from 1976 to 2022 and in Chinese from 1990 to 2022 was performed to support critical analysis and evaluation of the available literature based on the following aspects of red mud research: (a) characterization, (b) treatment for harmfulness minimization, (c) recovery of valuable metals, (d) environmental applications, and (e) uses as construction materials. It was found that (a) sinter red mud tended to contain more silica and calcium, and less iron, sodium and aluminium compared to Bayer red mud; (b) gypsum was the most frequently used agent for harmfulness reduction treatment of red mud, followed by flue gas/CO2; (c) the mean optimal pH for adsorption of major anionic pollutants was 8.42 ± 1.13 (arsenite), 3.73 ± 0.68 (arsenate), 3.50 ± 2.38 (phosphate), 4.43 ± 1.04 (fluoride) and 3.80 ± 1.54 (chromate); (d) wastewater treatment has attracted more attention compared to contaminated soils and waste gases; (e) recovery of iron and scandium has attracted more attention compared to other metals; (f) cement making has been the focus in construction uses. Most of the research findings were based on laboratory-scale experiments that focused on efficacy rather than efficiency. There was a lack of integrated approaches for research in red mud valorization.

Development of a Multifaceted Perspective for Systematic Analysis, Assessment, and Performance for Environmental Standards of Contaminated Sites

Contaminated soil and groundwater can pose significant risks to human health and ecological environments, making the remediation of contaminated sites a pressing and sustained challenge. It is significant to identify key performance indicators and advance environmental management standards of contaminated sites. The traditional study currently focuses on the inflexible collection of related files and displays configurable limitations regarding integrated assessment and in-depth analysis of published standards. In addition, there is a relative lack of research focusing on the analysis of different types of standard documents. Herein, we introduce a cross-systematic retrospective and review for the development of standards of the contaminated sites, including the comprehensive framework, multifaceted analysis, and improved suggestion of soil and groundwater standards related to the environment. The classification and structural characteristics of different types of files are systematically analyzed of over 300 national, trade, local, and group standards for the contaminated sites. It exhibits that trade standards are the main types and testing methods are the important format within numerical considerations of soil standards. The guide standard serves as a crucial component in environmental management for investigating, assessing, and remediating of contaminated sites. Future improvement plans and development directions are proposed for advancing robust technical support for effective soil contamination prevention and control. This multidimensional analysis and the accompanying suggestions can provide improved guidance for Chinese environmental management of contaminated sites and sparkle the application of standards in a wide range of countries.

Upscaling the remediation of acidic landscapes - the coastal floodplain prioritisation method

Over 24 million hectares of the world's coastal floodplains are underlain by acid sulfate soils (ASS). Drainage of these sediments has led to widespread environmental degradation, raising serious health concerns. To date, onsite rehabilitation has been complicated by differing stakeholder priorities, with resources often allocated to sites with more vocal proponents rather than those exposed to more significant environmental impacts. To address this issue, this paper introduces the Coastal Floodplain Prioritisation (CFP) Method; a novel, data driven and spatially explicit multi-criteria assessment that ranks floodplain catchment areas according to their risk of transferring acidic drainage waters to an estuary. Results can be used to prioritise where remediation actions are likely to have the greatest benefit. The method was applied across six different estuaries in south-east Australia, with major field campaigns undertaken at each site. Within each estuary, the largest acid fluxes and impacts are identified with relevant mitigation measures provided. On a catchment scale, the results reflect the broader hydrogeomorphic characteristics of each estuary, including the historic acid formation conditions and recent anthropogenic drainage activities. Low-lying backswamps were identified as the highest risk zones within each estuary. These areas are also the most vulnerable to sea level rise. Reinstatement of tidal inundation to these backswamps effectively remediates acid sulfate soil discharges and provides a nature-based solution for adaptation to sea level rise with a range of co-benefits to encourage further investment.

Shaping the concentration of petroleum hydrocarbon pollution in soil: A machine learning and resistivity-based prediction method

A new method relying on machine learning and resistivity to predict concentrations of petroleum hydrocarbon pollution in soil was proposed as a means of investigation and monitoring. Currently, determining pollutant concentrations in soil is primarily achieved through costly sampling and testing of numerous borehole samples, which carries the risk of further contamination by penetrating the aquifer. Additionally, conventional petroleum hydrocarbon geophysical surveys struggle to establish a correlation between survey results and pollutant concentration. To overcome these limitations, three machine learning models (KNN, RF, and XGBOOST) were combined with the geoelectrical method to predict petroleum hydrocarbon concentrations in the source area. The results demonstrate that the resistivity-based prediction method utilizing machine learning is effective, as validated by R-squared values of 0.91 and 0.94 for the test and validation sets, respectively, and a root mean squared error of 0.19. Furthermore, this study confirmed the feasibility of the approach using actual site data, along with a discussion of its advantages and limitations, establishing it as an inexpensive option to investigate and monitor changes in petroleum hydrocarbon concentration in soil.

Deciphering the recent trends in pesticide bioremediation using genome editing and multi-omics approaches: a review

Pesticide pollution in recent times has emerged as a grave environmental problem contaminating both aquatic and terrestrial ecosystems owing to their widespread use. Bioremediation using gene editing and system biology could be developed as an eco-friendly and proficient tool to remediate pesticide-contaminated sites due to its advantages and greater public acceptance over the physical and chemical methods. However, it is indispensable to understand the different aspects associated with microbial metabolism and their physiology for efficient pesticide remediation. Therefore, this review paper analyses the different gene editing tools and multi-omics methods in microbes to produce relevant evidence regarding genes, proteins and metabolites associated with pesticide remediation and the approaches to contend against pesticide-induced stress. We systematically discussed and analyzed the recent reports (2015-2022) on multi-omics methods for pesticide degradation to elucidate the mechanisms and the recent advances associated with the behaviour of microbes under diverse environmental conditions. This study envisages that CRISPR-Cas, ZFN and TALEN as gene editing tools utilizing Pseudomonas, Escherichia coli and Achromobacter sp. can be employed for remediation of chlorpyrifos, parathion-methyl, carbaryl, triphenyltin and triazophos by creating gRNA for expressing specific genes for the bioremediation. Similarly, systems biology accompanying multi-omics tactics revealed that microbial strains from Paenibacillus, Pseudomonas putida, Burkholderia cenocepacia, Rhodococcus sp. and Pencillium oxalicum are capable of degrading deltamethrin, p-nitrophenol, chlorimuron-ethyl and nicosulfuron. This review lends notable insights into the research gaps and provides potential solutions for pesticide remediation by using different microbe-assisted technologies. The inferences drawn from the current study will help researchers, ecologists, and decision-makers gain comprehensive knowledge of value and application of systems biology and gene editing in bioremediation assessments.

Red mud-biochar composites (co-pyrolyzed red mud-plant materials): Characteristics and improved efficacy on the treatment of acidic mine water and trace element-contaminated soils

The use of commercially sourced dopants for synthesizing biochar-based composites could be economically undesirable. The current work aimed to explore the possibility of making low-cost biochar-based composites using red mud (an industrial waste from alumina production) as dopants. Two types of red mud were used: one from a Bayer process and another from a sintering process. Different techniques (wet chemical, magnetic, SEM-EDS, FTIR, XPS and XRD analyses) were adopted to characterize the synthesized red mud-biochar composites, along with the pristine biochar. The composites were superior to the pristine biochar in terms of acid neutralizing capacity, specific surface area, and degree of magnetization. Two laboratory simulation experiments were conducted to assess the improved efficacy of the composites on the treatment of acidic mine water and mine water-contaminated soils. In general, application of the composites resulted in a significantly higher removal rate of mine water-borne trace elements compared to the pristine biochar treatment. The composites also had better effects on immobilizing the soil-borne trace elements and weakening the uptake of trace elements by the test vegetable plant species grown in the composite-treated soils, as compared to the pristine biochar-treated soil. By comparison, the sintering red mud-biochar composite had a generally better performance compared to the Bayer red mud-biochar composite.

Current and emerging trends in bioaugmentation of organic contaminated soils: A review

Organic contaminated soils constitute an important environmental problem, whereas field applicability of existing physical-chemical methods has encountered numerous obstacles, such as high chemical cost, large energy consumption, secondary pollution, and soil degradation. Bioaugmentation is an environmentally friendly and potentially economic technology that efficiently removes toxic pollutants from organic contaminated soils by microorganisms or their enzymes and bioremediation additives. This review attempted to explore the recent advances in bioaugmentation of organic contaminated soils and provided a comprehensive summary of various bioaugmentation methods, including bacterial, fungus, enzymes and bioremediation additives. The practical application of bioaugmentation is frequently limited by soil environmental conditions, microbial relationships, enzyme durability and remediation cycles. To tackle these problems, the future of bioaugmentation can be processed from sustainability of broad-spectrum bioremediation carriers, microbial/enzyme agents targeting combined contaminants, desorption of environmentally friendly additives and small molecular biological stimulants. Findings of this research are expected to provide new references for bioaugmentation methods that are practically feasible and economically potential.

Development of a new methodology for multifaceted assessment, analysis, and characterization of soil contamination

It is important to identify key performance and core progress features of soil contamination management practices. Traditional research currently focuses on numerical statistics of contaminated sites but exhibits structural limitations regarding cross-assessment and in-depth analysis of published findings. Herein, we report a multidimensional perspective to assess the environmental management performance of soil contamination via systematic and historical development of construction land risk control and remediation lists (RCRLs). The considered contaminated sites are mainly concentrated in Northern China, Yangtze River Delta, Pearl River Delta, and Sichuan-Chongqing regions. Monthly historical overviews indicate that most lists are updated 4-5 times within 32 months. Direct chemical-related industrial production results in the largest number of contaminated sites. Arsenic and lead are the most common heavy metals of concern in soil contamination. The fiscal revenue index exhibits the best positive performance in terms of the number of contaminated sites. By employing the site number, update frequency, and published contents of different calculation proportions, ten types of integrated assessment indicators (IAIs) are established to evaluate the environmental achievements in various provincial regions in regard to soil contamination protection. This multifaceted strategy can provide advanced guidance for Chinese environmental management and expand the application of soil pollution risk control and remediation in a wide range of countries.

Long-Term Sustainability of Marble Waste Sludge in Reducing Soil Acidity and Heavy Metal Release in a Contaminated Mine Technosol

A field-based experiment was set up to evaluate the effectiveness of a single application of marble waste sludge (MWS) on chemical immobilization of potentially hazardous trace elements (PHE) within the soil profile of a mine Technosol under natural assisted remediation for 12 years. Results showed that MWS amendment significantly reduced soil acidity and PHE mobility compared to unamended soil, thus improving soil health and plant growth. The amendment application had a sustained acid-neutralizing action, as soil pH remains relatively constant at between 5.8 and 6.4 throughout the entire profile (70 cm depth). In addition to diluting pollutants, the treatment triggered a redistribution of trace elements among the various operationally defined geochemical pools, shifting the PHE speciation from water-soluble forms to fractions associated with carbonates (29% Cd), metal oxides (40–48% Zn, Cd, Cu, and Ni), organic matter (22% Cu and Ni), and insoluble secondary oxidation minerals and residual phases (80–99% As, Cr, Sb, Tl, and Pb), thereby effectively limiting its potential environmental significance. MWS treatment to immobilize PHE in the contaminated mine Technosol was effective and persistent while in the untreated soil metal release is continuing over time.

Geochemical Partitioning of Heavy Metals and Metalloids in the Ecosystems of Abandoned Mine Sites: A Case Study within the Moscow Brown Coal Basin

Significant environmental impacts of mining activities connected with high-sulfur materials result from the production of acid mine drainage and potentially toxic elements, which easily migrate to adjacent ecosystems due to the typical absence of vegetation on spoil heaps and toeslope talus mantle. In this paper, we present the results of the first comprehensive study of the ecosystems affected by acidic and metal-enriched (Al, Ca, Co, Cu, Fe, Mg, Mn, Ni, and Zn) mine drainage conducted at spoil heaps and adjacent talus mantle under semihumid climate conditions within the Moscow Brown Coal Basin (Central Russian Upland, Tula Region, Russia). A total of 162 samples were collected, including 98 soil samples, 42 surface water samples, and 22 plant samples (aerial tissues of birch). Coal talus mantle materials of Regosols were characterized by the increased concentration of water-soluble Ca, K, Mg, and S, and all mobile fractions of Al, Co, S, and Zn. The chemical composition of birch samples within the zones affected by acid mine drainage differed insignificantly from those in the unpolluted ecosystems with black soils, due to the high tolerance of birch to such conditions. Differences between the affected and undisturbed sites in terms of the chemical composition decreased in the following order: waters > soils > plants. The geochemical characterization of plants and soils in coal mining areas is essential for the mitigation of negative consequences of mining activities.