Search Results (134)

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

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

Soil heavy metal contamination poses critical challenges to ecological sustainability in mining regions, particularly in acidic soils from copper sulfide mines. This study developed a sustainable remediation strategy using a carbonyl iron powder–biochar composite (CIP@BC) derived from agricultural waste (rice husk) and industrial byproducts. The composite was synthesized through an energy-efficient mechanical grinding method at a 10:1 mass ratio of biochar to carbonyl iron powder, aligning with circular economy principles. Material characterization revealed CIP particles uniformly embedded within biochar’s porous structure, synergistically enhancing surface functionality and redox activity. CIP@BC demonstrated exceptional Cu²⁺ immobilization capacity (910.5 mg·g⁻¹), achieved through chemisorption and monolayer adsorption mechanisms. Notably, the remediation process concurrently improved key soil health parameters. Soil incubation trials demonstrated that 6% CIP@BC application elevated soil pH from 4.27 to 6.19, reduced total Cu content by 29.43%, and decreased DTPA-extractable Cu by 67.26%. This treatment effectively transformed Cu speciation from bioavailable to residual fractions. Concurrent improvements in electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (OM), and soil water content (SWC) collectively highlighted the composite’s multifunctional remediation potential. This study bridges environmental remediation with sustainable land management through an innovative waste-to-resource approach that remediates acidic mine soils. The dual functionality of CIP@BC in contaminant immobilization and soil quality restoration provides a scalable solution. Full article

The pyrolysis of sewage sludge into biochar, enhanced by incorporating agriculture waste rich in inorganic minerals and lignocellulosic compounds, provides an effective approach for achieving sludge-harmless treatment and resourceful utilization. In this study, sewage sludge and maize straw-based biochar (SMB) was prepared using the co-pyrolysis method, and the effects of different application ratios (0%, 1%, 3%, and 5%, w/w) of SMB on soil properties, ryegrass growth, microbial community structure, and Pb content and speciation in the contaminated soil of constructed wetlands were investigated. The results showed that SMB had a high carbon content (28.58%) and was rich in functional groups (e.g., -C-O, -C-N). The results indicated that increasing SMB dosage (0–5% w/w) in Pb-contaminated soil elevated soil pH from 6.40 to 7.93, cation-exchange capacity (CEC) from 30.59 to 79.03 cmol/kg (+158%), and organic carbon content by 65% (from 176.79 mg/kg to 107.3 mg/kg), while reducing available phosphorus and potassium by 20% and 30%, respectively, resulting in a 6% decline in ryegrass leaf length. SMB application enriched Pb-resistant bacteria (e.g., Sphingomonas abundance increased from 10.3% to 11.2%) and enhanced Pb immobilization. After 55 days, the total soil Pb increased by 33%, and the residual fraction Pb significantly increased by 7.3% to 21.7%, driven by functional group complexation, ion exchange, pH, and CEC improvements. Full article

Wood ash, a byproduct of woody biomass power generation, has potential as an alternative K fertilizer due to its high K content and pH-raising properties. However, concerns remain about heavy metal contaminants like Cr and the limited understanding of element dynamics in soil–solution–crop systems after wood ash’s application. This study examined the effects of 1% (w/w) wood ash on element dynamics and komatsuna (Brassica rapa var. perviridis) uptake in low-K soil through a pot experiment. XRD was used to analyze mineral composition, SEM-EDS to observe surface and elemental properties, and XANES to examine Cr speciation in wood ash. Soil solution analysis covered macro- and micronutrients, heavy metals, anions, pH, and DOC, while crop element concentrations and aboveground dry weight were also quantified. The chemical speciation of Cu and Cr in a soil solution was modeled using Visual MINTEQ. Wood ash significantly increased K concentrations (from 17 mg/L to 650 mg/L) in the soil solution, along with Ca, Mg, P, and Mo, while reducing Ni, Mn, Zn, and Cd levels. Komatsuna K uptake surged from 123 mg/kg to 559 mg/kg, leading to a 3.31-fold biomass increase. Notably, the Cd concentration in the crops dropped significantly from 0.709 to 0.057 mg/kg, well below the Codex standard of 0.2 mg/kg. Although Cu and Cr concentrations rose in the soil solution, crop uptake remained low due to >99% complexation with fulvic acid, as confirmed by Visual MINTEQ modeling. This study confirms that wood ash is an effective K fertilizer, but emphasizes the need for risk mitigation strategies to ensure safe and sustainable agricultural application. Full article

Ensuring food security is essential for achieving sustainable global development, requiring a balance between sufficient food production and maintaining its safety and nutritional value. However, this objective faces considerable challenges due to the infiltration of toxic metal species into the food supply. Heavy metals and metalloids, depending on their molecular form and daily dose, exhibit varying degrees of toxicity, making the precise identification of their species essential for assessing their impact on human health and the environment. This study focuses on identifying the primary anthropogenic sources and dissemination pathways of heavy metal pollutants, with an emphasis on their speciation and bioavailability. It examines how toxic metal species, such as Pb²⁺, Cd²⁺, Hg²⁺, and various arsenic species (AsIII and AsV), infiltrate ecosystems, bioaccumulate within the food chain, and ultimately compromise food safety and nutritional value. Furthermore, the research explores the physiological and biochemical disruptions caused by these toxic metal species, including the displacement of essential ions from enzymatic active sites and transport proteins due to competitive binding by pollutants, oxidative stress induced by reactive oxygen species generation, and cellular dysfunction affecting metabolic pathways and signaling cascades, all of which contribute to both chronic and acute health conditions. By providing a detailed analysis of exposure routes and toxicological processes, this paper highlights the far-reaching consequences of heavy metal contamination on public health and agricultural sustainability. Special attention is given to the need for precise terminology, as the toxicity of metals is inherently linked to their daily dose and chemical species rather than their elemental form. Finally, this study advocates for integrated, multidisciplinary strategies aimed at mitigating these risks, enhancing ecosystem stability, and ensuring long-term food security in the face of environmental challenges. Full article