Search Results (329)

South Dongting Lake is an essential aquatic ecosystem that receives substantial water inflows from the Xiangjiang and Zishui Rivers. However, it is significantly impacted by human activities, including mining, smelting, and farming. These activities have led to serious contamination of the lake’s sediments with heavy metals (HMs). This study investigated the distribution, mobility, and influencing factors of HMs at the sediment–water interface. To this end, sediment samples were analyzed from three key regions (Xiangjiang River estuary, Zishui River estuary, and northeastern South Dongting Lake) using traditional sampling methods and Diffusive Gradients in Thin Films (DGT) technology. Analysis of fifteen HMs (Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, V, Cr, Cu, Tl, Co, and Fe) revealed significant spatial heterogeneity. The results showed that Cr, Cu, Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, and Fe exhibited high variability (CV > 0.20), whereas V, Tl, and Co demonstrated stable concentrations (CV < 0.20). Concentrations were found to exceed background values of the upper continental crust of eastern China (UCC), Yangtze River sediments (YZ), and Dongting Lake sediments (DT), particularly at the Xiangjiang estuary (XE) and in the northeastern regions. Speciation analysis revealed that V, Cr, Cu, Ni, and As were predominantly found in the residual fraction (F4), while Pb and Co were concentrated in the oxidizable fraction (F3), Mn and Zn appeared primarily in the exchangeable fractions (F1 and F2), and Cd was notably dominant in the exchangeable fraction (F1), suggesting a high potential for mobility. Additionally, DGT results confirmed a significant potential for the release of Pb, Zn, and Cd. Contamination assessment using the Pollution Load Index (PLI) and Geoaccumulation Index (Igeo) identified Pb, Bi, Ni, As, Se, Cd, and Sb as major pollutants. Among these, Bi and Cd were found to pose the highest risks. Furthermore, the Risk Assessment Code (RAC) and the Potential Ecological Risk Index (PERI) highlighted Cd as the primary ecological risk contributor, especially in the XE. The study identified sediment grain size, pH, electrical conductivity, and nutrient levels as the primary influencing factors. The PMF modeling revealed HM sources as mixed smelting/natural inputs, agricultural activities, natural weathering, and mining/smelting operations, suggesting that remediation should prioritize Cd control in the XE with emphasis on external inputs. Full article

This work investigated the ion exchange technique for selective separation of rare earth elements (REE) from acid mine drainage (AMD), using different column systems, pH values, and eluent concentrations. Systematic analysis of pH and eluent concentration showed that an initial pH of 6.0 and 0.02 mol L⁻¹ NH₄EDTA are the optimal conditions, achieving 98.4% heavy REE purity in the initial stage (0 to 10 bed volumes). This represents a 32-fold increase compared to the original AMD (6.7% heavy REE). The speciation of REE and impurities was determined by Visual Minteq 4.0 software using pH 2.0, which corresponds to the pH at the inlet of the fractionation column. Under this condition, La and Nd and the impurities (Ca, Mg, and Mn) remained in the fractionation column, while Al was partially retained. In addition, the heavy REE (Y and Dy) were mainly in the form of REE-EDTA complexes and not as free cations, which made fractionation more feasible. The fractionation column minimized impurities, retaining 100% of Ca and 67% of Al, generating a liquor concentrated in heavy REE. This sustainable approach adopted herein meets the critical needs for scalable recovery of REE from diluted effluents, representing a circular economy strategy for critical metals. Full article

Abandoned smelting sites in karst terrain pose a serious environmental problem due to the complex relationship between specific hydrogeological elements and heavy metal contamination. This review combines work from across the globe to consider how karst-specific features (i.e., rapid underground drainage, high permeability, and carbonate mineralogy) influence the mobility, speciation, and bioavailability of “metallic” pollutants, such as Pb, Cd, Zn, and As. In some areas, such as Guizhou (China), the Cd content in the surface soil is as high as 23.36 mg/kg, indicating a regional risk. Molecular-scale analysis, such as synchrotron-based XAS, can elucidate the speciation forms that underlie toxicity and remediation potential. Additionally, we emphasize discrepancies between karst in Asia, Europe, and North America and synthesize cross-regional contamination events. The risk evaluation is complicated, particularly when dynamic flow systems and spatial heterogeneity are permanent, and deep models like DI-NCPI are required as a matter of course. The remediation is still dependent on the site; however, some technologies, such as phytoremediation, biosorption, and bioremediation, are promising if suitable geochemical and microbial conditions are present. This review presents a framework for integrating molecular data and hydrogeological concepts to inform the management of risk and sustainable remediation of legacy metal pollution in karst. Full article

This study investigates the emission characteristics and environmental impacts of pollutants from bagasse-fired biomass boilers through the integrated field monitoring of two sugarcane processing plants in Guangxi, China. Comprehensive analyses of flue gas components, including PM_2.5, NOx, CO, heavy metals, VOCs, HCl, and HF, revealed distinct physicochemical and emission profiles. Bagasse exhibited lower C, H, and S content but higher moisture (47~53%) and O (24~30%) levels compared to coal, reducing the calorific values (8.93~11.89 MJ/kg). Particulate matter removal efficiency exceeded 98% (water film dust collector) and 95% (bag filter), while NOx removal varied (10~56%) due to water solubility differences. Heavy metals (Cu, Cr, Ni, Pb) in fuel migrated to fly ash and flue gas, with Hg and Mn showing notable volatility. VOC speciation identified oxygenated compounds (OVOCs, 87%) as dominant in small boilers, while aromatics (60%) and alkenes (34%) prevailed in larger systems. Ozone formation potential (OFP: 3.34~4.39 mg/m³) and secondary organic aerosol formation potential (SOAFP: 0.33~1.9 mg/m³) highlighted aromatic hydrocarbons (e.g., benzene, xylene) as critical contributors to secondary pollution. Despite compliance with current emission standards (e.g., PM < 20 mg/m³), elevated CO (>1000 mg/m³) in large boilers indicated incomplete combustion. This work underscores the necessity of tailored control strategies for OVOCs, aromatics, and heavy metals, advocating for stricter fuel quality and clear emission standards to align biomass energy utilization with environmental sustainability goals. Full article

Revegetation is considered a sustainable option for mine area remediation. However, the sustainability and risk evolution of revegetation for large antimony mine slag remain incompletely understood. In this study, we focused on the revegetation project of the waste slag heap of XKS, the world’s largest antimony mine. Systematically analyzed the physicochemical properties, total metal(loid) content, and BCR sequential extraction and applied the modified comprehensive pollution risk assessment (MCR) method to evaluate ecological risk evolution. The results showed that revegetation can effectively increase the nutrient content, and the total content of nitrogen and phosphorus maximally increased by 5.15 and 1.89 times, respectively, after 10 years of remediation. Long-term revegetation could mitigate the metal(loid) contamination, and the average contents of As and Sb decreased by 88.72–93.18% and 93.47–89.87%, respectively. BCR analysis showed that the percentage of residual As and residual Sb increased from 64.75% and 85.88% to 78.38% and 91.58%, respectively. The MCR assessment method showed that revegetation could effectively reduce the ecological risk level. This study provides important multidimensional evidence for the ecological restoration of antimony mining areas, which can provide practical guidance for subsequent slag management and risk control. Full article

This study investigates the weathering crust composite of serpentine, pyroxenite and granite in the Niangniangmiao area, the weathering crusts inside and outside the mining area were compared respectively, systematically revealing the distribution patterns, migration pathways, and ecological element activity characteristics of high-background elements (e.g., chromium (Cr) and nickel (Ni)) through precise sampling, the Tessier five-step sequential extraction method, and a migration coefficient model. Key findings include: (1) Element distribution and controlling mechanisms: The average Cr and Ni contents in the serpentinite profile are significantly higher than those in pyroxenite. However, the semi-weathered pyroxenite layer exhibits an inverted Cr enrichment ratio in relation to serpentinite, 1.8× and 1.2×, respectively, indicating that mineral metasomatic sequences driven by hydrothermal alteration dominate element differentiation; the phenomenon of inverted enrichment of high-background elements occurs in the weathering crust profiles of the two basic rocks. (2) Dual impacts of mining activities on heavy metal enrichment: Direct mining increases topsoil Cr content in serpentinite by 40% by disrupting parent material homology, while indirect activities introduce exogenous Zn and Cd (Spearman correlation coefficients with Cr/Ni are from ρ = 0.58 to ρ = 0.72). Consequently, the bioavailable fraction ratio value of Ni outside the mining area (21.14%) is significantly higher than that within the area (14.30%). (3) Element speciation and ecological element activity: Over 98% of Cr in serpentine exists in residual fractions, whereas the Fe-Mn oxide-bound fraction (F3) of Cr in extra-mining pyroxenite increases to 5.15%. The element activity in ecological systems ranking of Ni in soil active fractions (F1 + F2 = 15%) follows the order: granite > pyroxenite > serpentine. Based on these insights, a scientific foundation for targeted remediation in high-background areas (e.g., prioritizing the treatment of semi-weathered pyroxenite layers) can be provided. Full article

Active and abandoned mining sites are significant sources of heavy metals and metalloid pollution, leading to serious environmental issues. This study assessed the environmental risks posed by potentially toxic elements (PTEs), specifically arsenic (As) and antimony (Sb), in the Technosols (mining residues) of the former Pejão coal mine complex in Northern Portugal, a site impacted by forest wildfires in October 2017 that triggered underground combustion within the waste heaps. Our methodology involved determining the “pseudo-total” concentrations of As and Sb in the collected heap samples using microwave digestion with aqua regia (ISO 12914), followed by analysis using hydride generation-atomic absorption spectroscopy (HG-AAS). The concentrations of As an Sb ranging from 31.0 to 68.6 mg kg⁻¹ and 4.8 to 8.3 mg kg⁻¹, respectively, were found to be above the European background values reported in project FOREGS (11.6 mg kg⁻¹ for As and 1.04 mg kg⁻¹ for Sb) and Portuguese Environment Agency (APA) reference values for agricultural soils (11 mg kg⁻¹ for As and 7.5 mg kg⁻¹ for Sb), indicating significant enrichment of these PTEs. Based on average I_geo values, As contamination overall was classified as “unpolluted to moderately polluted” while Sb contamination was classified as “moderately polluted” in the waste pile samples and “unpolluted to moderately polluted” in the downhill soil samples. However, total PTE content alone is insufficient for a comprehensive environmental risk assessment. Therefore, further studies on As and Sb fractionation and speciation were conducted using the Shiowatana sequential extraction procedure (SEP). The results showed that As and Sb levels in the more mobile fractions were not significant. This suggests that the enrichment in the burned (BCW) and unburned (UCW) coal waste areas of the mine is likely due to the stockpiling of lithic fragments, primarily coals hosting arsenian pyrites and stibnite which largely traps these elements within its crystalline structure. The observed enrichment in downhill soils (DS) is attributed to mechanical weathering, rock fragment erosion, and transport processes. Given the strong association of these elements with solid phases, the risk of leaching into surface waters and aquifers is considered low. This work underscores the importance of a holistic approach to environmental risk assessment at former mining sites, contributing to the development of sustainable remediation strategies for long-term environmental protection. Full article

The influence of petroleum hydrocarbons (PHCs) on the transport and transformation of heavy metals may limit bioremediation efficiency. The mechanisms by which PHC degradation intermediates control heavy metal distribution in calcareous soils from karst areas require further exploration. This study systematically investigated how compositional changes in diesel fuel during aging regulated the fate of Cd and Pb in calcareous soils. The results demonstrated that the low-molecular-weight fractions of diesel fuel (C₁₀−C₁₆) were preferentially degraded. This degradation process altered zeta potential, cation exchange capacity (CEC), and pH, thereby promoting Cd stabilization through electrostatic attraction and speciation transformation. Particularly, reducible Cd content showed a strong positive correlation with C₁₆ content (r = 0.88, p < 0.05). Furthermore, the degradation of C₁₀−C₁₆ fractions caused Pb transformation from residual to bioavailable fractions by stimulating microbial activity. Residual Pb content was positively correlated with C₁₀−C₁₆ fractions (r = 0.55, p < 0.05). Notably, dissolved organic matter (DOM) and CaCO₃ content in calcareous soils enhanced Cd and Pb adsorption, thereby weakening the interactions between these metals and C₁₀−C₁₆ fractions. Consequently, multiple linear regression (MLR) models relying exclusively on C₁₀−C₁₆ degradation parameters showed poor fitting coefficients for Cd/Pb mobility. The present work provides scientific guidance for heavy metal bioremediation in calcareous soils. Full article

Yuexi County, a key tea-producing area in eastern Dabie Mountain, may face potential heavy metal(oid) (HM) contamination risks due to nearby mining and intensive agricultural activities. This study investigated seven HMs (As, Cd, Cr, Hg, Ni, Pb, and Zn) in paired soil–tea samples using multiple analytical approaches, including the geoaccumulation index (I_geo), the potential ecological risk index (RI), bioconcentration factor (BCF), and positive matrix factorization (PMF) with Monte Carlo simulation for health risk assessment. Results showed that Zn (82.65 mg/kg) and Cd (0.15 mg/kg) were the most enriched HMs in soils with higher I_geo values than other HMs. PMF analysis identified four major HM sources: mining and transportation (27.75%), agricultural activities (26.90%), natural soil parent material (26.17%), and industrial emissions (19.18%). Tea plants exhibited selective HM absorption, with Hg showing the highest bioaccumulation (BCF = 0.45), while As, Cr, and Pb had minimal uptake (BCF < 0.05). Although health risk assessments confirmed that both non-carcinogenic and carcinogenic risks from soil and tea consumption were within safe limits for adults and children, Cr and Ni required special attention due to their risk contributions. Overall, ecological and health risks in the region were found to be low. These findings provide important scientific support for pollution monitoring, risk management, and overcoming trade barriers in tea-growing regions with acidic soils. Future research should integrate HM speciation analysis with seasonal monitoring to further optimize tea plantation management strategies. Full article

The widespread implementation of anaerobic digestion (AD) systems for organic waste treatment is increasingly challenged by emerging contaminants, including microplastics (MPs), antibiotics, and heavy metals (HMs), which exhibit environmental persistence and pose risks to ecological and human health. This review critically examines the sources, transformation pathways, and advanced mitigation strategies for these contaminants within AD systems. MPs, primarily derived from fragmented plastics and personal care products, accumulate in digestates and act as vectors for adsorbing toxic additives and pathogens. Antibiotics, introduced via livestock manure and wastewater, exert selective pressures that propagate antibiotic resistance genes (ARGs) while disrupting methanogenic consortia. HMs, originating from industrial and agricultural activities, impair microbial activity through bioaccumulation and enzymatic interference, with their bioavailability modulated by speciation shifts during digestion. To combat these challenges, promising mitigation approaches include the following: (1) bioaugmentation with specialized microbial consortia to enhance contaminant degradation and stabilize HMs; (2) thermal hydrolysis pretreatment to break down MPs and antibiotic residues; (3) chemical passivation using biochar or sulfides to immobilize HMs. Co-digestion practices inadvertently concentrate these contaminants, with MPs and HMs predominantly partitioning into solid phases, while antibiotics persist in both liquid and solid fractions. These findings highlight the urgency of optimizing mitigation strategies to minimize contaminant mobility and toxicity. However, critical knowledge gaps persist regarding the long-term impacts of biodegradable MPs, antibiotic transformation byproducts, and standardized regulatory thresholds for contaminant residues in digestate. This synthesis underscores the necessity for integrated engineering solutions and policy frameworks to ensure the safe resource recovery from AD systems, balancing energy production with environmental sustainability. Full article

Heavy metals in peatland pose significant ecological risks due to their persistence, bioaccumulation, and dynamic mobilization under fluctuating environmental conditions. Understanding heavy metal dynamics in subtropical peatlands is critical for addressing global gaps in wetland metal cycling, as these ecosystems face intensified organic decomposition and climatic fluctuations that amplify mobilization risks—contrasting starkly with stable northern counterparts. This study investigates the geochemistry of heavy metals (Cr, Cu, Cd, and Pb) of Dajiuhu peatland in central China, using sequential extraction, gradient diffusion (DGT), and random forest modeling. The mean concentrations of Cr, Cu, Cd, and Pb in peat samples were 24.6 ± 13.7 mg/kg, 14.9 ± 2.51 mg/kg, 1.15 ± 0.62 mg/kg, and 54.9 ± 16.16 mg/kg. Principal component analysis identified three sources: plant-derived litter, bedrock weathering, and atmospheric deposition. Metal speciation revealed the predominance of residual fractions (Cr: 64%, Cu: 61%, Pb: 65%, Cd: 35%), with Cd exhibiting higher mobility (exchangeable: 20%, reducible: 25%). DGT measurements further confirmed distinct migration behaviors, as Cd stored in peat actively diffuses into the surrounding environment, while Pb present in the environment becomes immobilized within the peat matrix. Environmental factors regulate heavy metal speciation through distinct mechanisms. The exchangeable fractions of Cu and Cr are primarily controlled by the C/N ratio, whereas their oxidizable forms are significantly associated with Al content and pH levels. The exchangeable fractions of Pb and Cd are largely influenced by oxidation-reduction potential (ORP) and Ca concentrations, and their reduced forms are closely linked to total sulfur (TS) content. Furthermore, the reducible fractions of Cr and Cd are not only regulated by ORP but also modulated by TS. Our study highlights that the mobility of heavy metals in subtropical peatlands is likely to increase substantially as a result of environmental changes. Full article

Agricultural monitoring reveals cadmium (Cd) as the most prevalent heavy metal pollutant in Chinese agricultural soils, with 7.0% of sampled sites exceeding the national soil environmental quality standard (GB 15618-2018), creating substantial risks for crop safety. In situ remediation is a cost-effective method that can modify the speciation and migration properties of Cd in soil. The previous stage of research studies conducted basic characterization of materials and predicted their adsorption capacity in solution environments. This study focuses on the application effects in soil environment. We cross-linked modified biochar and calcium alginate hydrogels to fabricate a composite material (MB-CA) and determined its excellent adsorption performance for cadmium. This study is a continuation of our previous work, focusing on determining the thermodynamic model of adsorption materials, the applicable environment of composite materials, the influence on soil microorganisms, and its effect on the reduction in Cd content in agricultural products. The research found that the adsorption of Cd²⁺ by MB-CA conforms to the Freundlich isotherm model. MB-CA has the ability to regulate pH, achieving outstanding adsorption capacity at pH 4–6. The effect of MB-CA on lettuce is verified through pot experiment and field experiment. The Cd²⁺ content in plants decreased by 63.11% and 76.92%, respectively. Additionally, MB-CA did not negatively impact microbial abundance. This study further discussed the performance and application effect of MB-CA, providing new solutions for soil remediation. Full article

Potentially toxic elements (PTE), such as cadmium (Cd), lead (Pb), and arsenic (As), threaten rice (Oryza sativa L.) crop productivity and pose significant risks to human health when they are present in soil. This review summarizes the current understanding of soil and rice contamination with As, Cd, and Pb to provide an in-depth understanding of the dynamics of these contaminants and the mechanisms regulating their flow from soil to plants. It focuses on the following aspects: (1) these metals’ geochemical distribution and speciation in soil–rice systems; (2) factors influencing the transformation, bioavailability, and uptake of these metals in paddy soils; (3) metal uptake, transport, translocation, and accumulation mechanisms in rice grains; and (4) the roles of transporters involved in metal uptake, transport, and accumulation in rice plants. Moreover, this review contributes to a clearer understanding of the environmental risks associated with these toxic metals in soil–rice ecosystems. Furthermore, it highlights the challenges in simultaneously managing the risks of As, Cd, and Pb contamination in rice. The study findings may help inspire innovative methods, biotechnological applications, and sustainable management strategies to mitigate the accumulation of As, Cd, and Pb in rice grains while effectively addressing multi-metal contamination in paddy soils. Full article

Cobalt–zeolite composite catalysts (Co–zeolite) and their heterogeneous catalytic systems have garnered significant research attention owing to their superior catalytic activity and cost-effectiveness. The speciation of cobalt within these catalysts—either through impregnation onto the zeolite framework or structural incorporation within the aluminosilicate matrix—is critically governed by the employed synthesis methodology, which subsequently dictates their distinct catalytic advantages in targeted reaction systems. Compared to homogeneous catalytic systems, heterogeneous Co–zeolite configurations demonstrate enhanced structural integrity that effectively mitigates cobalt leaching, thereby improving catalyst recyclability while minimizing environmental contamination. This review systematically examines recent advancements in Co–zeolite fabrication techniques and their catalytic performance across diverse applications, including Fischer–Tropsch synthesis, nitrogen oxide abatement, hydrogenation processes, and oxidative transformations. Particular emphasis is placed on elucidating the metal-framework interactions, with analysis of synergistic effects arising from multi-valent cobalt speciation and bimetallic cooperativity between cobalt and secondary transition metals. This work critically evaluates current challenges in Co–zeolite catalyst design. Finally, we propose future research directions focusing on a precise identification of active species and mechanistic elucidation, innovative synthesis strategies for cobalt speciation control, machine learning-guided catalyst optimization, and the advancement of eco-friendly catalysts. Full article

An experimental and computational methodology was developed for ionic speciation of Pb²⁺ and Cd²⁺ with dissolved organic matter (DOM) in surface seawater (SSW) from the Bay of Bengal (BoB) in eastern Bangladesh. Differential pulse anodic stripping voltammetry (DPASV) with a thin mercury film glassy carbon electrode (TMFGC) was used to measure free and DOM-bound Pb²⁺ and Cd²⁺. A continuous binding model was used to calculate the binding constants for metal ions with experimentally found complex ligands like DOM in the BoB. The ionic speciation and distribution of all major naturally occurring ions and toxic Pb²⁺, Cd²⁺, and DOM were calculated using a computational chemical equilibrium model, MINTEQA. We found that the change in pH with increasing dissolved carbon dioxide due to global warming will cause drastic changes in the bioavailability of Pb²⁺ by the year 2050. Full article