Soil Remediation Strategies Research Articles

Physiological response of <i>Vigna unguiculata</i> to heavy metal contamination in mechanic workshop soils: A controlled pot experiment

Soil contamination as a result of heavy metals has become a critical environmental challenge due to its far-reaching consequences for food security, human health, and ecosystem integrity. Anthropogenic activities are contributes to the release of heavy metals such as cadmium (Cd), lead (Pb), zinc (Zn), and chromium (Cr) which are of particular concern due to their high toxicity, persistence, bioaccumulation and non-biodegradability. Automobile servicing centers, commonly referred to as mechanic workshops, significantly contribute to soil contamination in urban areas because they handle various repair activities that release heavy metals into the environment. In this study physicochemical properties and heavy metals were assessed in soils from automobile workshops using pot experiments. The result showed that the soils are predominantly sandy loam, exhibiting elevated electrical conductivity (EC), signaling the presence of ionic contaminants. The study also revealed a metal concentration trend of Zn > Cr > Pb > Cd in the soils, which was mirrored in the plants growing in the contaminated sites. Notably, the metal transfer factor (MTF) exceeded unity in many locations, indicating hyperaccumulation of heavy metals in the Vigna unguiculata and highlighting the associated environmental and health risks. The trend in MTF values was Cd > Pb > Zn > Cr, suggest that cadmium poses the greatest risk of bioaccumulation. These findings emphasize the urgent need for continuous monitoring of soils in automobile workshop areas to mitigate pollution risks. Implementing effective soil management practices and remediation strategies is imperative to safeguard human health, ensure food security, and protect ecosystems.

Machine learning combined with geodetector to predict the spatial distribution of soil heavy metals in mining areas.

An accurate understanding of the spatial distribution of soil heavy metals (HMs) is crucial for the effective prevention of soil pollution and remediation strategies. Traditional machine learning models often overlook the spatially stratified heterogeneity inherent to environmental data, which can impair predictive accuracy. Therefore, we combined the Geodetector model (GDM) with machine learning models. The factor detection results were used to screen covariates to consider the local spatial heterogeneity of model features. The interaction detection results were used to construct spatially stratified covariates to consider the spatially stratified heterogeneity of model features. The results showed that covariate screening largely avoided the introduction of redundant features. The constructed spatially stratified covariates improved the predictive performance of the model (both the R-squared (R2) and root mean square error (RMSE) of different models were optimized). Among these, the XGB model exhibited the best performance. Analysis of the factors influencing Pb and Cr revealed that the interaction between pH and NDVI was the main determinant of Pb spatial distribution (q=0.3516, XGB Importance Score=93). In contrast, the interaction between DEM and pH (q=0.7156, XGB Importance Score=121) as well as the distance to waste piles (q=0.6390, XGB Importance Score=66), were the main driving factors for the spatial distribution of Cr. The current work provides an improved approach for interrogating the factors that influence HM distribution in soil. This study offers valuable insights into the spatial distribution of soil HMs. The proposed methodology can be applied in future soil pollution assessments and environmental management strategies, thus contributing to more precise pollution prevention and remediation efforts.

Adsorption Characteristics of Cadmium onto Calcite and Its Agricultural Environmental Relevance

Calcite (CaCO3), a common component of calcium-based fertilizers, has been recognized for its effectiveness as a cadmium (Cd) immobilization agent in the solidification/stabilization (S/S) method. This strategy is a widely used chemical remediation technique aimed at reducing the bioavailability and toxicity of Cd in contaminated soils. This study comprehensively evaluated the potential of calcite for Cd remediation through geochemical analyses, including adsorption isotherms, saturation index, ion concentration changes, and X-ray diffraction (XRD) analysis. Adsorption isotherm experiments indicated that Cd adsorption onto calcite aligns more closely with the Freundlich isotherm model, suggesting a heterogeneous surface with a maximum adsorption capacity of 1.56 mg g−1. Based on chemical states result, optimal conditions for CdCO3 precipitation with low Cd concentrations were identified at pH above 7.9. XRD analysis confirmed the formation of Ca0.67Cd0.33CO3 at higher Cd concentrations, indicating that chemisorption is the dominant immobilization mechanism. Additionally, variations in Ca2+ and CO32− concentrations supported the substitution of Cd for Ca on the calcite surface. These findings highlight calcite’s potential as an effective material for Cd immobilization, providing valuable insights for the developing more sustainable soil remediation strategies.

Arsenic modifies the microbial community assembly of soil-root habitats in Pteris vittata.

Pteris vittata, renowned for its ability to hyperaccumulate arsenic, presents a promising solution to the escalating issue of global soil arsenic contamination. This fern cultivates a unique underground microbial community to enhance its environmental adaptability. However, our understanding of the assembly process and the long-term ecological impacts of this community remains limited, hindering the development of effective soil remediation strategies. This study addresses this gap by investigating soil-root habitats from three geographically diverse fields comprising a gradient of arsenic contamination, complemented by a time-scale greenhouse experiment. Field investigations reveal that arsenic stress influences community assembly dynamics in the rhizosphere by enhancing processes of homogeneous selection. Greenhouse experiments further reveal that arsenic exposure alters the assembly trajectory of rhizosphere communities by promoting key microbial modules. Specifically, arsenic exposure increases the enrichment of a core taxon (i.e. Rhizobiaceae) in the rhizosphere, both in field and greenhouse settings, boosting their abundance from undetectable levels to 0.02% in the soil after phytoremediation. Notably, arsenic exposure also promotes a pathogenic group (i.e. Spirochaetaceae) in the rhizosphere, increasing their abundance from undetectable levels to 0.1% in the greenhouse. This raise concerns that warrant further investigation in future phytoremediation studies. Overall, this study elucidates the assembly dynamics of the soil microbiome following the introduction of a remediation plant and emphasizes the often-overlooked impacts on soil microbial community following phytoremediation. By probing the ecological impacts of remediation plants, this work advances a more nuanced understanding of the complex ecological implications inherent in phytoremediation processes.

Improving Lettuce Tolerance to Cadmium Stress: Insights from Raw vs. Cystamine-Modified Biochar

Understanding the interactions among biochar, plants, soils, and microbial communities is essential for developing effective and eco-friendly soil remediation strategies. This study investigates the role of cystamine-modified biochar (Cys-BC) in alleviating cadmium (Cd) toxicity in lettuce, comparing its effects to those of raw biochar. Lettuce plants were exposed to Cd stress (1–5 mg kg−1), and the effects of Cys-BC were assessed by measuring plant biomass, photosynthetic efficiency, antioxidant activity, Cd bioavailability, and soil microbial diversity. Cys-BC significantly enhanced plant biomass, with increases in above-ground growth (40.54–44.95%) and root biomass (37.54–47.44%) compared to Cd-stressed controls. Photosynthetic parameters improved by up to 91.02% for chlorophyll-a content and 37.93% for the net photosynthetic rate. Cys-BC mitigated oxidative stress, increasing antioxidant activities by 73.83% to 99.39%. Additionally, Cys-BC reduced available Cd levels in the soil, primarily through enhanced cation exchange rather than changes in pH. Plant responses to Cd stress included increased glutathione reductase activity and elevated cysteine levels, which further contributed to Cd passivation. Microbial diversity in the soil increased, particularly among sulfur- and nitrogen-cycling bacteria such as Deltaproteobacteria and Nitrospira, suggesting their role in mitigating Cd stress. These findings highlight the potential of Cys-BC as an effective agent for the remediation of Cd-contaminated soils.

Effect of coexisting nutrient divalent cations on cadmium transport in soil-herbal crop systems

Cadmium (Cd) pollution in Chinese herbal medicines poses a serious risk to medication safety. Regulating Cd uptake, transport, and accumulation in plants through ion-ion interactions offers a novel, environmentally sustainable, and practical approach to address this issue. However, the effects and underlying mechanisms of coexisting divalent cations zinc (Zn), magnesium (Mg), and manganese (Mn) on Cd uptake by Ligusticum sinense cv. Chuanxiong (L. chuanxiong) have not been comprehensively studied or well understood. In this study, the application of coexisting these cations (Zn, Mg, Mn) could significantly promote the growth of L. chuanxiong (21.11%–36.04%) and change the mobility of Cd in the soil-crop system. Specifically, adding Zn decreased Cd content in soil and plants by 18.23% and 20.62%, respectively, while Mg increased it by 10.99% and 62.27%. Mn addition, however, had no significant effect. Similar trends in soil enzyme activity were also observed with Zn, Mg, and Mn treatments. Simultaneously, the findings explore how coexisting divalent cations influence plant physiological responses, including photosynthesis and antioxidant capacities, enabling L. chuanxiong to better manage Cd stress. This study underscores the potential of ion-to-ion interactions as an effective approach to mitigate Cd accumulation, offering a practical and sustainable solution for enhancing the safety of Chinese herbal medicines. Additionally, the effects of mixed cation applications on Cd dynamics are complex, shaped by interactions between ion types, dosages, and their specific properties. These insights provide a foundation for developing more effective remediation strategies for Cd-contaminated soils, particularly in the cultivation of medicinal plants.

Impact of gradient zero-valent iron pollution from steel works on soil microaggregate geochemical processes and dissipative structures

Abstract: Zero-valent iron (ZVI) contamination from steel works poses significant threats to soil quality and ecosystem health, particularly affecting soil microaggregates, which are fundamental to soil structure and function. In this study, we systematically investigated the impact of gradient ZVI pollution on the organic geochemical environment of soil microaggregates around steel works located in the core water source area of the Middle Route of the South-to-North Water Diversion Project in China. Advanced analytical techniques, including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), were employed to comprehensively characterize the geochemical processes, mineralogy, and organic matter environment of soil microaggregates. The findings revealed that soils near the steel works were acidified and strongly oxidized, with heavy metal contents, particularly Fe, significantly decreasing with increasing distance from the steel works (Fe content decreased from 27,516.2 mg/kg to 23,492.6 mg/kg). The pH of soils near the steel works was lower, while oxidation-reduction potential (ORP) and electrical conductivity were higher. XPS analysis indicated a higher content of reactive oxygen species (ROS) near the steel works and significantly lower soil organic matter content. The iron valence distribution showed spatial differences, with higher Fe2⁺ content on the surface of soil microaggregates near the steel works and Fe³⁺ dominating in areas farther away. These results suggest an evolutionary sequence of ZVI from Fe (0) oxidation to Fe(II) and then to Fe(III). The formation of dissipative structures in soil microaggregates due to ZVI contamination significantly affects soil physicochemical properties and the organic environment. This study provides valuable insights into the multifaceted impacts of industrial activities on soil ecosystems and offers a scientific basis for soil conservation and remediation strategies.

A comprehensive evaluation of bioremediation effects of oil-contaminated soils using various dosages of exogenous nitrogen supplementation: TPH removal, ecological toxicity, and microecological response

Biostimulation with exogenous nitrogen addition is a common strategy for remediation of petroleum-contaminated soils. However, the comprehensive effects of various dosages of exogenous nitrogen application on hydrocarbon removal, soil ecotoxicity, and microecological response are not clear. In this study, a petroleum-contaminated soil with total petroleum hydrocarbon (TPH) content of 8553 mg/kg was remediated by adding NH4Cl to adjust C/N ratio of 100/1(N1), 100/2(N2), 100/5(N3), and 100/10(N4), respectively. After 210 days of remediation, the TPH removal efficiency was the highest in the N2(32.55 %) when compared with that in the N1(28.43 %), N3(27.87 %) and N4 (22.60 %) treatments. PICRUSt2 analysis revealed that the abundances of oorA and oorB genes encoding EC 1.2.7.11 were significantly enhanced in the N1 and N2 but decreased in the N3 and N4 treatments, indicating that conversion of pyruvate to acetyl-CoA for participation in TCA cycle was enhanced due to low dosage of NH4Cl addition. The gene abundances of NxrA and NxrB encoding nitrification, nirK and nirS encoding denitrification in the N1 and N2 treatments were lower than those in the N3 and N4 treatments, suggesting low dose of NH4Cl addition reduces soil nitrogen loss and stabilizes taxonomic diversities. Acute toxicity test found that the earthworm weight inhibition rates in the N1, N2, N3, and N4 treatments were −2.48 %, 9.57 %, and 5.83 % and 60.21 %, respectively. This result revealed that NH4Cl application with C/N ratio of 100/2 contribute to TPH degradation and stabilization of soil ecological function, which were facilitated to remediation of petroleum-contaminated soil.

The Effects of Straw-Returning Processes on the Formation of Fe-Mn (Hydr)oxide Colloids and Arsenic Bioavailability

The objective of this study was to investigate the effect of straw return on the formation of Fe-Mn colloids in arsenic-contaminated soils and its subsequent influence on arsenic behavior. It was observed that organic matter (SD) resulting from straw decomposition interacted with iron/manganese (hydr)oxides (Fe/Mn (hydr)oxides) present in the soil, leading to the formation of colloidal particles. These particles significantly influenced the fixation and release of arsenic. The experimental results indicated that an increase in SD content facilitated the formation of colloidal particles. The highest concentration of colloidal particles was observed at a C/Fe-Mn ratio of 2.2, which significantly reduced the bioavailability and mobility of arsenic in the soil. The increase in SD content also diminished the depositional attachment efficiency of SD/Fe-Mn, thereby enhancing its migration through the soil. The actual field soil-filled column experiments further demonstrated that the content of SD significantly influenced arsenic bioavailability and mobility. Specifically, at a C/Fe-Mn ratio of 2.2, the inhibition of arsenic migration and bioavailability was found to be 1.46 times more effective compared to a C/Fe-Mn ratio of 0.4. Therefore, the return of straw to the field represents an effective soil remediation strategy for mitigating the bioavailability of arsenic by modulating the C/Fe-Mn ratio. This approach offers a novel perspective on strategies for heavy metal remediation.

Assessment of trace metal elements in selected Plants around the vicinity of Ebedei Gas Flaring Station located at Ebedei Village, Ukwani Local Government Area, Delta State, Nigeria

This study evaluated the trace metal elements in selected plants around the Ebedei Gas Flaring Station, Ukwani Local Government Area, Delta State, Nigeria. The plants analyzed include Azadirachta indica, Cymbopogon citratus, Moringa oleifera, Carica papaya) and Alstonia boonei. The analysis revealed that Alstonia boonei had the highest concentration of Copper at 6.87 mg/kg, while the lowest concentration of Lead (0.06 mg/kg) was found in Carica papaya. The trace metal levels in the plants ranged from 0.06 mg/kg for Lead to 6.87 mg/kg for Copper, with Azadirachta indica showing moderate levels across all measured metals. These concentrations were within the permissible limits set by WHO for vegetables, indicating no immediate threat to consumers. However, the study highlights the potential for bioaccumulation over time, which could elevate these levels and pose health risks. The study thus recommends conducting regular monitoring of trace metal levels in plants around gas flaring sites to prevent potential health hazards. In addition, soil remediation strategies should be implemented to reduce metal uptake by plants and public awareness campaigns should be carried out to educate the local population on the risks of consuming plants from contaminated areas.

Breakthrough in soil remediation advancement: Nonthermal plasma powers polyvalent Ce-Mn (Hydro)oxide-enhanced nanographene to securely stabilize thallium-laden soils

The urgent need for remediation of thallium (Tl)-contaminated soils arises from its widespread presence as a poisonous heavy metal (HM), coupled with numerous challenges such as high costs, long durations, secondary pollution risks, and technological limitations. In the study, a novel approach has been introduced to the remediation of Tl-contaminated soils using calcium sulphoaluminate cement. This innovation involves the employment of nonthermal plasma-irradiated polyvalent Ce-Mn (hydro)oxide-modified nanographene (NTP-P-Ce-Mn-NGs) to intensify the cementation and immobilization of Tl species. The chemical speciation of Tl contaminants influenced by the dosage of NTP-P-Ce-Mn-NGs in the cementation was measured to explore the potential enhancement mechanisms brought by NTP-P-Ce-Mn-NGs in the sulphoaluminate cementation. Comprehensive strategies were adopted to explore the reaction pathways. In orthogonal (OD) experiments, compressive strengths ranging from 22.14 to 56.78 MPa in sulphoaluminate-cemented cubes were achieved. Remarkably, when NTP-P-Ce-Mn-NGs were introduced, the leached Tl concentration was reduced to 0.21–21.46 µg/L. This significant reduction was attributed to the NTP-P-Ce-Mn-NGs-induced more uniform hydration reactions and a more holistic microstructure. The presence of diverse valent Ce and Mn species within the matrix was confirmed, revealing a reliable interaction between NTP-irradiated high-valent Mn and Ce with monovalent Tl ions. This interaction induced multiple redox reactions, immobilizing Tl contaminants within the matrix and the cementation encapsulation. This study represents a significant milestone in Tl pollution control, paving the way for more efficient and cost-effective soil remediation strategies.

Effects of simulated low-temperature thermal remediation on the microbial community of a tropical creosote contaminated soil.

In the search for more sustainable remediation strategies for PAH-contaminated soils, an integrated application of thermal remediation and bioremediation (TEB) may allow the use of less impacting temperatures by associating heating to biological degradation. However, the influence of heating on soil microbiota remains poorly understood, especially in soils from tropical regions. This work investigated the effects of low-temperature heating on creosote-contaminated soil bacteria. We used culture-dependent and 16S rRNA sequencing methods to compare the microbial community of soil samples heated to 60 and 100 oC for 1h in microcosms. Heating to 60°C reduced the density of cultivable heterotrophic bacteria compared to control soil (p < 0.05), and exposure to 100°C inactivated the viable heterotrophic community. Burkholderia-Caballeronia-Paraburkholderia (BCP) group and Sphingobium were the predominant genera. Temperature and incubation time affected the Bray-Curtis dissimilarity index (p < 0.05). At 60°C and 30 days incubation, the relative abundance of Sphingobium decreased and BCP increased dominance. The network of heated soil after 30 days of incubation showed fewer nodes and edges but maintained its density and complexity. Both main genera are associated with PAH degradation, suggesting functional redundancy and a likely potential of soil microbiota to maintain biodegradation ability after exposure to higher temperatures. We concluded that TEB can be considered as a potential strategy to bioremediate creosote-contaminated soils, allowing biodegradation in temperature ranges where thermal remediation does not completely remove contaminants. However, we recommend further research to determine degradation rates with this technology.

Fe(III) reduction mediates vanadium release and reduction in vanadium contaminated paddy soil under different organic amendments

Vanadium(V) contaminated soil is abundant in iron(Fe) oxides due to co-occurrence of V and Fe bearing minerals. However, biogeochemical transformation of redox-active V and Fe in soil, and the bacteria involved, has remained less investigated. This study explored the extent to which microbial mediated organic decomposition coupled to Fe(III) reduction contributed to V(V) release/reduction in V-contaminated paddy soil under different organic amendments. Soil flooding decreased toxic reducible V while increased less toxic oxidizable V. Glucose and straw promoted V(V) release with temporarily increasing V(V) concentration by 73.59–106.34 mg/kg compared to the control treatment and subsequently promoted V(V) reduction with decreasing V(V) to concentrations eventually similar to the control treatment. Biochar incorporation under glucose and straw amendments moderately alleviated V(V) release. The significantly positive correlation between Fe(II) and V(V) concentrations during the V solubilization process indicated a temporal coupling of Fe(III) reduction and V(V) release. Clostridium and Massilia mediated Fe(III) reductive dissolution and V(V) release, while Anaeromyxobacter, Sphingomonas, Bryobacter, Acidobacteriaceae and Anaerolineaceae contributed to V(V) reduction. This study provides a deeper understanding of V biotransformation coupled to Fe and C cycling and suggests a remediation strategy for V-contaminated soils via regulating Fe(III) reduction to weaken V(V) release or to promote V(V) reduction.

Synergistic contributions of plant growth-promoting rhizobacteria and exogenous fulvic acid to enhance phytoremediation efficiency of perfluorooctanoic acid (PFOA)-contaminated soils: Boosting PFOA bioavailability and elevating pak choi tolerance

Perfluorooctanoic acid (PFOA), a synthetic perfluoroalkyl compound, has caused extensive soil contamination over several decades, posing serious health risks to humans through bioaccumulation in plants and subsequent transfer via the food chain. Due to the durability of PFOA in soil and its propensity to migrate and accumulate in plants, phytoremediation has been recognized as an effective remediation method. However, the phytotoxicity of PFOA and the adsorption of PFOA by soil hindered the efficiency of traditional phytoremediation. Therefore, this research employed plant growth-promoting rhizobacteria (PGPR)-assisted phytoremediation, augmented with the bio-stimulant fulvic acid (FA), to devise an effective soil remediation strategy tailored for PFOA contamination removal. The results indicated that Rhizobium sp. strain ZY2, endowed with PGP traits, significantly increased the root weight and shoot weight of pak choi by 194.67 % and 37.38 %, respectively, versus the non-inoculation treatment. Furthermore, inoculation with strain ZY2 enhanced soil alkaline phosphatase, protease, and cellulase activities, bolstering soil nutrient cycling and resource availability. On the other hand, compared to treatment with strain ZY2 alone, additional exogenous FA drastically reduced the residual fraction of PFOA in soil from 34.1 % to 1.9 %, likely mediated by complex electrostatic and hydrophobic interactions between FA and soil components. Ultimately, FA addition increased PFOA concentration in pak choi by 8.1-fold. Furthermore, FA could increase the relative abundance of beneficial rhizosphere bacteria (Actinobacterota and Methylotener, etc.), thereby creating a more favorable microenvironment for plant growth. In conclusion, the combined use of strain ZY2 and FA in phytoremediation notably strengthened plant resilience to PFOA, minimized soil sorption, and achieved high remediation efficacy, offering an effective system to mitigate PFOA-soil pollution's environmental and health risks.

Evaluating heavy metals-related risk in staple crops and making financing strategy for corresponding soil remediation across China

China's staple crops face heavy metal (HMs) contamination, a widespread issue lacking a national assessment. We used machine learning (ML) to assess risks of 8 HMs in rice, wheat, and maize, and estimated a financing strategy for soil remediation via linear optimization and computable general equilibrium (CGE). The accumulation of HMs in crops depends on Soil-HMs, climate, soil properties, and crop types. Cd and Hg pose major soil pollution risks, while Cr, Pb, and Cd are the most threatening in crops. High-risk zones are located at the warm temperature and subtropical zones, with wheat most vulnerable. Over a quarter (26.77 %) of the nation's croplands are classified as high-risk, with a significant 60.89 % falling into the medium-risk category, leaving merely 12.34 % of the agricultural land in a safe condition. The estimated remediation cost is 58596.73 billion RMB and the crop loss is 808.03 billion RMB in a ten-year remediation period at the context of secure crop supply. The reallocation of social investment rather than raising new taxation for the remediation is beneficial to the GDP increase and social welfare despite some loss in the household income and enterprise income. This study provides a comprehensive evaluation for Crop-HMs risk and remediation policy, crucial for national crop security.

Response of soil heavy metal forms and bioavailability to the application of microplastics across five years in different soil types

Microplastics (MPs) potentially alter physicochemical and transformation of heavy metals (HMs) in soils, which may depend on the specific characteristics of soil types. However, the dynamical and long-term mechanisms remain to be elucidated. A five-year incubation experiment was conducted to evaluate the influence of MPs on the chemical speciation of Pb, Ni, Cu, Cr, Cd, and As in the meadow, tidal, cinnamon, saline-alkali, and brown soils. From the first year to the fifth year, the clay value of the meadow, tidal, cinnamon, and saline-alkali soils was increased by 31.35 %, 9.63 %, 30.12 %, and 33.12 %, respectively; the pH values of the cinnamon and saline-alkali soils were increased by 15.02 % and 15.86 %, respectively. Besides, speciation distribution results suggested that the application of MPs reduced the liable available (LB) form (F2–dissolved and F3–ion exchangeable) of HMs and increased the potentially available (PB) form (F5–minerals and F6–organic-bound fraction) of HMs in all soils. Compared with other forms, F2 HMs fraction was the most responsive to MPs. Furthermore, the average bioconcentration factor (BCF) of Cr and Pb decreased by 73.75 % and 70.41 % in soils, respectively. Interestingly, soil type showed more impact on the form of HMs, which was associated with the different physicochemical parameters of soils, while application time displayed more impact on the bioavailability of HMs. Moreover, our results suggested that soils with higher clay content and pH values (such as cinnamon and saline-alkali soils) may mitigate the bioavailability of HMs more effectively in the presence of MPs, while soils with lower clay content may be more vulnerable to HMs contamination over time. This work highlights the importance of long-term monitoring of the impact of MPs on HMs dynamics for effective mitigation of soil contamination risks. Our study provides valuable guidance for soil remediation strategies and environmental quality management across different soil types.

Asynchronous Synergetic Remediation Strategy for Cd-Contaminated Soil via Passivation and Phytoremediation Technology

Cadmium (Cd) contamination in soil has emerged as a significant challenge for agricultural production. Phytoremediation and passivation are key techniques for remediating Cd-contaminated soil. However, few studies have focused on the synergistic effects of these two techniques. In this work, the effectiveness of synergetic remediation strategies, both synchronous and asynchronous, utilizing passivation and phytoremediation techniques, was explored. The results of pot experiments and field experiments indicated that optimal remediation effects were obtained by asynchronous synergetic remediation, removing over 80% of bioavailable Cd within 14 days. Mechanistic studies conducted using XPS analysis, soil property analysis, and microbial diversity analysis confirmed that the chelation effect of SDD and soil pH value are the primary factors contributing to the effectiveness of both remediation strategies. In contrast, the variations in microbial populations are identified as the crucial factors influencing the varying outcomes of the two sequential remediation approaches. This research demonstrates that asynchronous synergistic remediation is a promising strategy for mitigating Cd contamination in soil.

Selective lead capture using amide-containing COFs: A novel strategy for efficient soil remediation

A critical consideration in the application of phytoremediation to remediate sludge soil contaminated with heavy metals is the potential for leaching risks that prevail prior to the efficient uptake of these metals by plants. The most cost-effective method is to use heavy metal stabilizers with selective adsorption. A novel amide-based COF material (COF-TH) has been synthesized as a heavy metal stabilizer for Pb. COF-TH exhibits significant selectivity for Pb in five-metal-mixed solutions, with a distribution coefficient KD as high as 3279 mL·g–1, which was more than 7.3 times that of other heavy metals. The maximum adsorption capacity of COF-TH for Pb was 189 mg·g–1. The adsorption fitted Langmuir model and intra-particle diffusion model, and satisfied pseudo-second-order kinetic model. The excellent selectivity and adsorption performance originate from the complexation between abundant amide groups and Pb ions. Pot experiments and leaching assays confirm that COF-TH decreased Pb leachate concentrations by 77.8 % without significantly decreasing total phytoextracted amounts of other heavy metals, due to the high selectivity of COF-TH to Pb. Additionally, its positive impact on plant growth and microbial diversity makes it a promising soil remediation agent. This investigation offers a novel approach to mitigate the leaching risk of a specific heavy metal Pb during sludge land application by integrating soil phytoremediation with stabilization techniques.

Impact of arsenic and PAHs compound contamination on microorganisms in coking sites: From a community to individual perspective

Arsenic (As) and polycyclic aromatic hydrocarbons (PAHs) are highly toxic, carcinogenic and teratogenic, and are commonly found in soils of industrial sites such as coking plants. They exert environmental stresses on soil microorganisms, but their compounding effects have not been systematically studied. Exploring the effects of compound contamination on microbial communities, species and genes is important for revealing the ecological damage caused by compound contamination and offering scientific insights into soil remediation strategies. In this study, we selected soil samples from 0 to 100 cm depth of a coking site with As, PAHs and compound contamination. We investigated the compound effects of As and PAHs on microbial communities by combining high-throughput sequencing, metagenomic sequencing and genome assembly. Compared with single contamination, compound contamination reduced the microbial community diversity by 10.68%–12.07% and reduced the community richness by 8.39%–18.61%. The compound contamination decreased 32.41%–46.02% of microbial PAHs metabolic gene abundance, 11.36%–19.25% of cell membrane transport gene abundance and 12.62%–57.77% of cell motility gene abundance. Xanthobacteraceae, the biomarker for compound contaminated soils, harbors arsenic reduction genes and PAHs degradation pathways of naphthalene, benzo [a]pyrene, fluorene, anthracene, and phenanthrene. Its broad metabolic capabilities, encompassing sulfur metabolism and quorum sensing, facilitate the acquisition of energy and nutrients, thereby conferring ecological niche advantages in compound contaminated environments. This study underscores the significant impacts of As and PAHs on the composition and function of microbial communities, thereby enriching our understanding of their combined effects and providing insights for the remediation of compound contaminated sites.

Quantitative Soil Characterization for Biochar-Cd Adsorption: Machine Learning Prediction Models for Cd Transformation and Immobilization.

Soil pollution with cadmium (Cd) poses serious health and environmental consequences. The study investigated the incubation of several soil samples and conducted quantitative soil characterization to assess the influence of biochar (BC) on Cd adsorption. The aim was to develop predictive models for Cd concentrations using statistical and modeling approaches dependent on soil characteristics. The potential risk linked to the transformation and immobilization of Cd adsorption by BC in the soil could be conservatively assessed by pH, clay, cation exchange capacity, organic carbon, and electrical conductivity. In this study, Long Short-Term Memory (LSTM), Bidirectional Gated Recurrent Unit (BiGRU), and 5-layer CNN Convolutional Neural Networks (CNNs) were applied for risk assessments to establish a framework for evaluating Cd risk in BC amended soils to predict Cd transformation. In the case of control soils (CK), the BiGRU model showed commendable performance, with an R2 value of 0.85, indicating an approximate 85.37% variance in the actual Cd. The LSTM model, which incorporates sequence data, produced less accurate results (R2=0.84), while the 5-layer CNN model had an R2 value of 0.91, indicating that the CNN model could account for over 91% of the variation in actual Cd levels. In the case of BC-applied soils, the BiGRU model demonstrated a strong correlation between predicted and actual values with R2 (0.93), indicating that the model explained 93.21% of the variance in Cd concentrations. Similarly, the LSTM model showed a notable increase in performance with BC-treated soil data. The R2 value for this model stands at a robust R2 (0.94), reflecting its enhanced ability to predict Cd levels with BC incorporation. Outperforming both recurrent models, the 5-layer CNN model attained the highest precision with an R2 value of 0.95, suggesting that 95.58% of the variance in the actual Cd data can be explained by the CNN model's predictions in BC-amended soils. Consequently, this study suggests developing ecological soil remediation strategies that can effectively manage heavy metal pollution in soils for environmental sustainability.