Inrush of acidic mine water from abandoned coal mines poses serious threat to groundwater environment by mobilizing heavy metals and lowering pH, thereby endangering ecosystems and human health. In this study, inrush water samples from nine abandoned coal mines in Wangcang, Sichuan, China, were analyzed for eight heavy metals (Cr(VI), Fe, Mn, Hg, As, Zn, Pb, and Cd) using inductively coupled plasma-mass spectrometry (ICP-MS). The ecological risk was assessed through species sensitivity distribution (SSD) based on native aquatic species data, while health risks were evaluated using USEPA exposure models. Results showed that the mine water was acidic (pH 1.6-7.1) with high metal concentrations, particularly Fe, Zn, Mn, and Cd, with mean values of 1048, 11.5, 4.6, and 0.49 mg/L, respectively, exceeding the Chinese Class III groundwater quality standards. The SSD-derived hazardous concentration for 5% of species (HC5) values ranged from 7.08 & times; 103 mu g/L (Hg) to 3.09 & times; 10(5) mu g/L (Pb), indicating that aquatic species were more sensitive to Hg than Pb. Risk quotients (RQs) revealed Fe as the dominant ecological risk factor across all sites. Although non-carcinogenic hazard indices (HIs) remained below 1, carcinogenic risk from Cr(VI), Cd, and As exceeded the 1 & times; 10(-4) threshold, with oral ingestion identified as the primary exposure pathway. The findings indicate substantial ecological and health risks from abandoned mine inflows, warranting targeted remediation of Fe and carcinogenic metals.

Dissolved black carbon (DBC) plays a critical but poorly understood role in the photochemical transformation of organic pollutants. Its structural heterogeneity, determined by biomass source and pyrolysis temperature, strongly influences its photosensitization efficiency. This study systematically investigated the molecular characteristics of DBC derived from rice, wheat and corn straw and examined their effects on the photodegradation kinetics and pathways of alpha-nitroso-beta-naphthol (alpha N beta N). Fourier transform ion cyclotron resonance mass spectrometry analysis revealed that DBC primarily comprises CHO compounds with lignin-derived and fused-ring aromatic structures. With increasing pyrolysis temperature, lignin transforms into highly condensed polycyclic aromatic frameworks characterized by enhanced unsaturation and aromaticity. This molecular transformation directly governs the photochemical activity of DBC, as evidenced by linear correlations between the molecular features of DBC (i.e., unsaturation and aromaticity) and its optical properties, steady-state concentrations of reactive intermediates (RIs) and alpha N beta N photolysis rates. Mechanistic studies identified the triplet-excited state of DBC ((DBC)-D-3*) as the dominant RI responsible for alpha N beta N degradation via dehydrogenation, condensation and redox reactions. While most photoproducts exhibit lower ecotoxicity than alpha N beta N, exceptions such as 2-nitro-1-naphthol and coumarin underscore source-dependent risk variations. These findings advance the molecular-level understanding of the environmental implications of DBC, emphasizing its dual function as both a photochemical promoter and a modulator of pollutant behavior.

The coexistence of heavy metals and organic pollutants in wastewater presents a significant environmental challenge in terms of toxicity and complexity, hindering effective treatment and remediation. In this study, a novel coupled system termed "Light-Shewanella-Hematite" (LSH) was developed by integrating photocatalysis with microbial metabolism. The system leverages the photoexcitation properties of iron oxide minerals under sunlight to generate electron-hole pairs. The electrons are subsequently utilized by electroactive bacteria for efficient electron transfer and heavy metal reduction, while the holes oxidize organic contaminants. Batch experiments and photoelectrochemical analyses were conducted to evaluate the effects of hematite on Cr(VI) removal by Shewanella oneidensis MR-1 (S. oneidensis) under illuminated and dark conditions. In addition, the influence of phenol on Cr(VI) removal by LSH was examined. Under dark conditions, S. oneidensis mediated the removal of Cr(VI) through bioelectronic pathways. Under illuminated conditions, hematite generated photoelectrons and holes from the electrons harnessed by S. oneidensis to facilitate Cr(VI) reduction. The system demonstrated excellent light-responsive performance, reducing 98 % Cr(VI) within 9 h. Notably, the addition of phenol significantly accelerated the Cr(VI) reduction rate, achieving 98 % removal in just 1.5 h. This process is primarily driven by the regulation of hematite-derived photoelectrons in S. oneidensis extracellular electron transfer and the oxidation of phenol by photoholes. Overall, this study advances understanding of microbe-mineral interactions and their synergistic roles in the simultaneous removal of Cr(VI) and phenol in aqueous systems.

Pyrite oxidation by Acidithiobacillus ferrooxidans (A. ferrooxidans) is the leading cause of acid mine drainage (AMD), and controlling this type of microorganism using advanced materials is key to addressing this environmental issue. This study demonstrates that pH is the predominant factor governing pyrite oxidation, with lower pH enhancing A. ferrooxidans activity and consequently increasing AMD generation. A pH-responsive controlled-release antimicrobial (PAR/NH2-MSN@SA) system has been developed to address the limitations of conventional biocides (environmental sensitivity, short-term efficacy). Under the optimized conditions (200 mu L 3-aminopropyltriethoxysilane (APTS), initial SA concentration of 5 g/L, feed ratio of 2:1, solution pH of 5.0, and adsorption time of 48 h), the optimized NH2-MSN carrier exhibited exceptional sorbic acid (SA) adsorption capacity (268.37 mg/g, 16.76% loading content), with a minimum inhibitory concentration of 10 mg/L against A. ferrooxidans. The release mechanism involves amino protonation-triggered molecular chain cleavage under acidic conditions, enabling pH-responsive SA release. The release behavior of PAR/NH2-MSN@SA was analyzed using four kinetic models; the fitting results showed that the release curve best fit the first-order release kinetics model. In simulated AMD systems, the treatment group showed significantly stabilized pH and oxidationreduction potential (Delta pH = 0.7, Delta oxidation-reduction potential = 246.6 mV) compared to biotic controls, while achieving 67.35% and 59.92% reductions in total Fe and SO42-leaching, respectively. This work establishes a practical approach to regulating sustained microbial activity, providing new insights for developing in situ AMD control technologies targeting the microbial promotion mechanism.

Elevated sulfate concentrations in groundwater pose risks to drinking water safety and subsurface stability; however, accurate source apportionment remains challenging in systems influenced by mixed natural and anthropogenic inputs. This study examines a landfill-impacted aquifer in the red-bed region of southwestern Sichuan, China, with particular emphasis on the coupling between dissolved organic matter (DOM) and sulfate biogeochemical processes. A multi-tracer approach integrating hydrochemical analysis, sulphur (δ³⁴S) and oxygen (δ¹⁸O) isotopes, and three-dimensional excitation-emission matrix spectroscopy (3D-EEM) was employed. Groundwater evolution is primarily characterized by Ca²⁺ and SO₄²⁻, with hydrochemical facies transitioning from HCO₃-Ca to SO₄-Ca under landfill influence. sulfate sources display pronounced seasonal variability, with atmospheric deposition dominating in the wet season (46%) and landfill leachate in the dry season (36%). Distinct differences in DOM composition are observed among sources: landfill-affected groundwater is enriched in humic- and fulvic-like substances, where the humification index (HIX) is positively correlated with SO₄²⁻ concentrations and δ³ ⁴S values, whereas the biological index (BIX) shows a negative correlation. In contrast, groundwater influenced by gypsum dissolution is characterized by protein-like DOM, accounting for 76-88% of total DOM. By incorporating DOM fluorescence indices (HIX and BIX) as continuous covariates into a dual-isotope Bayesian mixing model (MixSIAR), dynamic source apportionment is achieved. This integration enhances source discrimination by explicitly accounting for DOM-mediated biogeochemical processes, providing a robust framework for tracing sulfate contamination in landfill-impacted groundwater systems.

Groundwater contamination in chemical industrial parks (CIPs) is a significant threat to global water security due to spills, leaks, and discharges, as well as the complexity of concealing a diverse range of industrial pollutants. In this article, we collected 30 groundwater samples from zones of presumed influence across a CIP, including upstream background, within-park, periphery, and downstream, located in Luxian County, Sichuan, China. We employed excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) coupled with comprehensive hydrochemical analysis to deconvolve the dissolved organic matter (DOM) signature and statistically link its fluorescent components to specific hydrogeochemical processes and anthropogenic sources. Results revealed that industrial activities have transformed the groundwater to Ca-HCO3Cl and CaNa-HCO3Cl types from the hydrochemical facies comprising Ca-HCO3 and CaMg-HCO3 types. Hydrogeology and groundwater chemistry depend primarily on weathering and atmospheric precipitation, but industrial effluents and evaporation concentration also significantly affect them. EEM-PARAFAC identified three dominant fluorescent components: fulvic-like (C1), humic-like (C2), and tryptophan-like (C3), with the latter serving as a sensitive indicator of recent anthropogenic inputs. The spatial distribution of these components, particularly the enrichment of C3, is primarily governed by anthropogenic inputs (e.g., sewage leakage), modulated by local hydrological conditions. This work demonstrates the integration of optical spectroscopy with conventional hydrochemistry for source apportionment in complex industrial settings. It provides a mechanistic understanding of pollution propagation and a practical, rapid diagnostic tool for targeted groundwater protection in CIPs.

The liver plays a central role in xenobiotic metabolism and is consequently highly vulnerable to chemical-induced injury. Nevertheless, the mechanisms underlying diuron-induced hepatotoxicity remain poorly understood. Zebrafish (Danio rerio) were exposed to diuron at concentrations of 50 and 500 μg/L for 21 days, with subsequent analysis of the induced hepatotoxicity employing a combination of physiological, biochemical, and metabolomic techniques. Results showed that diuron significantly bioaccumulated in zebrafish, with bioconcentration factor (BCF) values ranging from 14.0 to 40.49 L/kg. Tissue distribution analysis indicated that the liver was the primary site of accumulation (491.48 ± 19.48 ng/g), while the brain also showed substantial accumulation (334.84 ± 10.90 ng/g) at an exposure concentration of 500 μg/L. Further examination of diuron metabolism in the liver identified 13 metabolites produced through demethylation, hydrolysis, oxidation, and C-N bond cleavage. These metabolic alterations correlated with histopathological damage, oxidative stress, and lipid peroxidation. Untargeted metabolomics further revealed a significant disruption in key metabolic pathways, particularly in arginine metabolism and the TCA cycle. Mechamistically, diuron-induced hepatotoxicity in zebrafish is characterized by the downregulation of key metabolites, namely gamma-Glutamyltyrosine, Leucylproline, and Malate, collectively contributing to the disruption of the tricarboxylic acid cycle alongside arachidonic acid, glutathione, and arginine metabolic pathways. These disturbances may represent the core mechanisms underlying hepatotoxicity. These findings will improve understanding of metabolic disorders in the liver and provide valuable insights into ecological risk assessments related to chemicals, and provide novel mechanistic insights into diuron induced hepatotoxicity.

Coal mining has resulted in pollution of groundwater in mining areas, which poses a risk to human health. However, understanding of groundwater evolution in mining areas and the associated implications remains insufficient. This study collected 13 groundwater samples from an abandoned coal mine in southwestern China. Ionic ratio analysis, hydrochemical simulation, health risk assessment, and entropy-weighted water quality index (EWQI) were applied to characterize the groundwater quality and the associated risks to human health. Monte Carlo analysis was used to quantify the uncertainty in the health risk assessment. The results indicated that the groundwater samples are of the HCO3-Ca and SO4-Ca water chemistry types. Water-rock interaction and mining activities were the main processes regulating groundwater hydrochemistry. Acid mine drainage was mainly responsible for elevated groundwater sulfate in the study area. EWQI ranged from 13 to 515 (mean of 111), and 75% of the samples fell within classes 1 and 2, meeting the World Health Organization (WHO) drinking water standards. Health risk assessment indicated adults to be more at risk from groundwater ingestion than children, with this result confirmed by uncertainty analysis. This study comprehensively examined groundwater evolution and its potential impacts through the example of a typical mining area. The results provides valuable insights into the identification of factors affecting groundwater, the evolution of hydrochemical processes, and the sustainable development of groundwater resources in mining areas globally.

Microbially induced carbonate precipitation (MICP) is an emerging bioremediation technology commonly used for the removal of metal elements from water. The feasibility of using this technological process to remove rare earth elements (REEs) from acid mine drainage (AMD) is investigated in this study. The indigenous ureolytic bacterial consortium UBC (95.29 % of Lysinibacillus, 2.7 % of Citrobacter, and 1.7 % of Pseudomonas) was successfully obtained from AMD sludge by targeted acclimation (four acclimation transfers) and a ureolytic bacterium strain U1 (Lysinibacillus fusiformis) was isolated from UBC. U1 can tolerate pH of 4, whereas UBC can tolerate pH as low as 3 by altering the community structure. The interaction between ureolytic bacteria and REEs was then studied using strain U1. U1 can tolerate up to 100 mg L-1 of REEs. Light REEs La, Ce, and Nd showed significant hormesis effect on bacterial growth. REEs precipitation experiments showed that REEs were removed by bacterial adsorption and accumulation, as well as by co-precipitation with calcite. The presence of Ca2+ significantly enhanced the removal of REEs. Finally, the performance of UBC in synthetic AMD solution was explored. The results showed that UBC can tolerate the AMD environment and maintain its functionality. It entered the logarithmic growth phase after 16 h and removed >99.9 % of REEs within 32 h. Other metal ions were also removed to varying extents. This study demonstrates that MICP is capable of effectively removing REEs from AMD, thereby expanding its application, and providing a promising approach for the resource recovery of AMD.

The diversity of hydrochemical types in surface water and groundwater in the Dexing mining area in Jiangxi Province reflects the complexity of the hydrogeochemical environment there. The average pH and total dissolved solids (TDS) of the groundwater were greater during the dry sampling season than during the wet sampling season. In contrast, the average TDS and SO42− concentrations in surface water are greater during the wet season than during the dry season. The concentrations of Fe and Mn in surface water and groundwater exceeded the World Health Organization standard by 1702 and 233 times, respectively. Ion correlation analysis indicated that the hydrochemical evolution of surface water and groundwater were influenced mainly by the weathering and dissolution of carbonatite and silicate, with the carbonates mainly derived from dolomite dissolution. The hydrochemical changes during the dry season were more susceptible to the weathering and dissolution of carbonatite and silicate. The correlations between surface water and groundwater were greater during the wet season than during the dry season, and the level of reverse cation exchange was greater during the dry season. Furthermore, the groundwater is more susceptible to the effects of mining. Based on the regional hydrogeological conditions, a conceptual model of groundwater circulation was established, indicating that metal mining has altered the original groundwater flow pattern and exacerbated groundwater pollution in the Dexing mining area.

In this study, Scenedesmus obliquus (S. obliquus) has been employed as a model organism to investigate the bioaccumulation, metabolism, and toxicity mechanisms of tricresyl phosphate (TCP). The results indicated that S. obliquus enhanced TCP degradation in water by 97 % after 14 days. The bioaccumulation factor of tricresyl phosphate in S. obliquus were calculated to be 8. When exposed to a high concentration of TCP (160 μmol/L), the algal growth rate was initially negative at 24 h, but gradually recovered over time. By 96 h, the inhibition rate was 64.74 % and the EC50 values was determined to be 86.41 μmol/L. Prolonged exposure to TCP substantially inhibited photosynthesis in S. obliquus, as indicated by a significant reduction in chlorophyll content. The addition of humic acid (HA), a representative substance of dissolved organic matter, exacerbated TCP toxicity by increasing ROS production, indicating a synergistic effect between HA and TCP. Conversely, a mixed nitrogen source reduced TCP toxicity. Four TCP metabolites were identified, resulting from hydroxylation, ketonization, hydrolysis, and ester bond cleavage. ECOSAR analysis revealed that these metabolites exhibit lower toxicity compared to TCP. These findings indicate that metabolic transformations within the algae may mitigate TCP toxicity, whereas HA significantly exacerbates TCP-induced oxidative stress. This study offers novel insights into the ecological risks of TCP in aquatic environments, especially in the presence of natural organic matter.

The acidic environment and lack of carbon sources in acid mine drainage (AMD) limit the effectiveness of sulfate-reducing bacteria (SRB) in its treatment. The use of urease-producing bacteria (UPB) to hydrolyze urea and drive SRB to treat AMD addresses these two key limitations. Based on the pollution characteristics of AMD from an abandoned sulfur iron mine in Southwest China, this study investigates the feasibility of the combined UPB-SRB treatment for simulated AMD, explores the synergistic mechanism, and evaluates the practical application of this synergy in the treatment of real AMD. The UPB-SRB combination outperforms the individual use of UPB or SRB. When UPB neutralized the pH of simulated AMD from 2 to 5, the highest cost-effectiveness was observed: the solution's pH increased to 7.2, with removal efficiencies for SO42-, Fe, Fe2+, and Mn2+ reaching 89.18 %, 95.59 %, 95.81 %, and 88.2 %, respectively. The reaction products of the UPB-SRB synergy included FeOOH, Fe2O3, FeS, Fe, and MnS. UPB utilized ammonia generated from urea hydrolysis to improve the acidic environment, while its metabolic by-products, including amino acids, organic acids, alcohols, and vitamin B, provided carbon and nitrogen sources for SRB. In the treatment of real AMD, the synergistic effect of UPB-SRB achieved removal efficiencies of 96.89 % for SO42-, 100 % for Fe, and 99.89 % for Mn2+, and raised the pH from 2 to 8. The treated AMD showed no bio-toxicity or potential risks and demonstrated agricultural reuse potential. By replacing traditional carbon/nitrogen sources with urea-containing wastewater, the combined use of UPB and SRB provides an efficient, safe, and cost-effective solution for AMD disposal, offering a novel approach to optimizing SRB-based AMD treatment and urea wastewater resource utilization.

Constructed wetlands (CWs) are widely recognized as the potential hotspots for producing highly toxic methylmercury (MeHg). This presents an obstacle to the widespread application of CWs. A comprehensive discussion on strategies to control mercury methylation in CWs is currently lacking. This review highlighted the potential impacts of differences in oxygen supply and consumption in various CWs, the characteristics of influent quality, the interactions between different substrates and mercury (including mercury adsorption, reduction), and plants on microbial mercury methylation in CWs. We also proposed the potential strategies for human intervention in regulating or controlling microbial mercury methylation in CWs, including oxygenation, nitrate inhibition, selection of substrates with high adsorption capacity, weak reducibility and low organic matter release, and plant management. Knowledge summarized in this review would help achieve a comprehensive understanding of various research gaps in previous studies and point out future research directions by focusing on CWs types, influent quality, substrates selection and plants management, to reduce the mercury methylation in CWs.

Black phosphorus nanosheets (BPNS), a novel two-dimensional nanomaterial, have garnered significant attention in biomedical and technological applications due to their exceptional physicochemical properties. However, their widespread use raises concerns about potential environmental risks. In this study, we elucidate the toxicological mechanisms of BPNS on Daphnia magna (D. magna), a model aquatic organism. The results reveal that BPNS is efficiently absorbed and accumulates in the intestinal tract of D. magna. Exposure to low concentrations of BPNS significantly alters developmental and reproductive performance, as evidenced by a 2-day acceleration in the time to first brood and an increase in body length from 3.1 to 3.3 mm. Furthermore, BPNS exposure induces oxidative stress in D. magna, characterized by elevated reactive oxygen species (ROS) levels, enhanced activities of superoxide dismutase (SOD) and catalase (CAT), and increased malondialdehyde (MDA) concentrations. RNA sequencing analysis indicates that dysregulation of iron homeostasis plays a pivotal role in mediating oxidative stress in D. magna. Concurrently, detoxification mechanisms are activated, as evidenced by upregulation of genes associated with chitin and carbohydrate metabolism, as well as cuticle structure components. Additionally, BPNS exposure modulates key signaling pathways, including the lysosomal pathway, starch and sucrose metabolism, and steroid biosynthesis, which collectively enhance the stress tolerance of D. magna. These findings provide critical insights into the ecological implications of BPNS release into aquatic ecosystems, highlighting the need for comprehensive risk assessments of emerging nanomaterials.

Understanding the hydrological-geochemical impacts on rare earth elements (REEs) in riparian zones is critical for sustainable pollution management under intensifying climate extremes. This study decoded seasonal regulatory mechanisms governing REE dynamics in a semi-arid riparian zone overlying the Maoniuping deposit, revealing that natural processes can be leveraged for low-energy remediation. The findings indicated that seasonal thermal-hydrologic fluctuations resulted in distinct geochemical microenvironments that governed REE mobility and fate. In surface water (SW), REE enrichment was dominated by runoff and precipitation inputs during wet season, whereas shallow groundwater (SGW) exhibited intensified REE accumulation in the dry season due to prolonged water-rock interactions under elevated temperatures and reduced water levels. Multivariate analyses revealed that REE concentrations in SW were strongly associated with adsorption onto Al-Fe-Mn colloids. In contrast, REE dynamics in SGW during the wet season were significantly influenced by temperature, water level, Al, Fe, Mn, HCO3- , SO42- , and NO3- , while dry-season dynamics were primarily governed by temperature and Al alone. Water level indirectly suppressed REE release by enhancing HCO3- and non-polar organic compounds (NPOC) levels while reducing the level of oxidation-reduction potential (ORP). Temperature exerted control through its effects on NPOC and ORP. Notably, seasonal partitioning patterns also shifted markedly in groundwater: particulate and colloidal phases prevailed under dry conditions, whereas dissolved REE fractions increased significantly during the wet season. These findings established a mechanistic framework linking climate variability to REE mobilization through cascading biogeochemical processes, offering scientific support for adaptive, low-energy strategies to mitigate REE contamination in mining-impacted riparian systems.

Mining has resulted in changes to groundwater, with associated deleterious effects on quality of water and hazards to human health. However, there remain insufficient comprehensive examinations of the groundwater evolution in areas of mining and the associated potential impacts. This study aimed to investigate sources of groundwater, its hydro-chemical evolution, quality of water, and possible hazards to human health. The study applied self-organizing map (SOM), hydro-chemical methods, tracing of isotopes, models for the evaluation of health risk, and the entropy-weighted water quality index (EWQI), and health risk evaluation models to data obtained by collecting 20 samples of groundwater from the Dashu mining area, Southwest China. The results indicated HCO3-Ca center dot Mg to be the predominant groundwater category in the area of study, which is transformed into SO4 center dot Cl-Ca center dot Mg and SO4 center dot Cl-Na types by anthropogenic activities. The dominant factors regulating groundwater hydrochemistry in the area of study were interactions between groundwater and the geology, mining activities, and atmospheric precipitation. Major chemical processes regulating groundwater quality were dissolution of calcite, dolomite, and rock salt, and the dominant sources of SO42-were gypsum dissolution and mine water input. Groundwater was predominantly of good quality, with points of poor quality concentrated in residential areas and cultivated land, suggesting the impacts of anthropogenic activities. The study area showed a low risk of non-carcinogenic health risks from groundwater heavy metals, with aluminum, iron, and manganese identified as the main risk factors. The results of this study can guide groundwater conservation and management in the study area and other mining areas within the Yangtze River basin by improving the identification of influencing factors and enhancing the understanding of processes regulating hydrochemical evolution.

Heterotrophic nitrification-aerobic denitrification bacteria (HN-AD) have been demonstrated to possess denitrification potential. The limited effectiveness of HN-AD in remediating nitrogen-polluted surface waters is attributed to its low C/N ratio. In this study, a magnetite photogenerated electrons coupled HN-AD bacteria system was constructed and its nitrogen removal mechanisms were revealed. The results demonstrated the electrons photo-generated by magnetite can effectively stimulate the growth of the HN-AD (Delftia sp., Y19).The coupled system of the ammonium and nitrate reached removal rates of 80.1 % and 71.3 %, which were 4 times higher than the strain Y19 alone (20.3 %, 15.2 %). Compared with dark conditions, the activity of enzymes (AMO, HAO, NAR and NIR) related to nitrogen removal in Y19 was increased by 4.81, 4.75, 6.45 and 4.78 times under sunlight irradiation, respectively. This suggests that the electrons photo-generated from magnetite can enhance the metabolic activities of the Y19 strain. Furthermore, the concentration of ferric ions dissolved from magnetite has been detected as equaling 0.13 mg/L, which plays a crucial role in the reduction of nitrate. The denitrification mechanisms of the coupled system can be incorporated: heterotrophic nitrification and aerobic denitrification by strain Y19, photogenerated electrons reduction of magnetite, the reduction of ferric ions, and the adsorption of magnetite. After 9 days of running the simulator, the magnetite-Y19 coupled system achieved removal rates of 100 % for nitrate and chemical oxygen demand, and 36 % for ammonium. This study offers novel insights into the utilization of photogenerated electrons by microorganisms for remediating the low C/N ratio wastewater.

Mining activities cause elevated sulfate (SO42-) levels in groundwater, negatively impacting the groundwater quality in karst areas. Determining the sources and contamination pathways of SO42- in groundwater from karst mining areas is challenging due to the unique permeability, susceptibility to contamination and chemical reactivity of karst aquifers. The sources and geochemical processes of SO42- in the aquifer of the karst mining areas in Southwest China were investigated using a combination of hydrodynamics, geochemistry, multiple isotopes (δ2H, δ18O, δ34S and 87Sr/86Sr) and microbiology. The results showed along the direction of groundwater movement, the concentration of SO42- gradually increases. Atmospheric precipitation is the main groundwater source in the study area and the hydrogeochemical processes are controlled by carbonate and evaporite dissolution as well as human activities. SO42- in the groundwater mainly originates from the oxidation of sulfide minerals, evaporite dissolution, and sulfur-containing fertilizers. The hydrodynamic conditions and mining activities control the sources, contributions of SO42-, microbial community and the bacterial sulfate reduction in groundwater. The results of this study can deepen the understanding of the influence of hydrodynamic conditions of aquifers in karst mining areas on SO42- hydrogeochemical behavior and provide a scientific basis for water resource management in karst mining areas.

This study determined the hydro-chemical properties of groundwater in a typical mining area and its associated human health risks, focusing on the Guangwang mining area. Groundwater samples were analyzed for toxic metals, after which analysis of principal components, the entropy-weighted water quality index, and Spearman analysis of correlation were applied to the collected data. The Environmental Protection Agency of the United States’s health hazard appraisal was utilized to assess the hazards of toxic metals in the local water supply to the health of both grownups and juveniles. HCO3-Na and SO4⋅Cl-Ca⋅Mg were found to be the predominant groundwater hydro-chemical types. The eastern section of the area of study showed the greatest average total dissolved solids (16,347.00 mg/L) and SO42− (8980.00 mg/L) levels. It was determined that the groundwater hydro-chemical type was Ca-HCO3 and that limestone leeching and the evaporative level in the coal seam aquifer were the predominant factors regulating groundwater hydrochemistry. Six of the ten assessed metals exceeded the World Health Organization’s safe water for drinking standards, with particularly high Al (66.97 mg/L) and Cd (194.53 μg/L). Spearman correlation analysis showed significant correlations between Mn, Al, Cu, and Zn, which could be attributed to bauxite minerals associated with the coal mine. Release of metal ions was attributed to the oxidation of metal sulfide minerals, which is driven by mining-induced water–rock interaction. The intake of water for drinking was shown to be the predominant route of hazard to human health. The hazard index decreased from east to west due to the level of abandoned coal mines in the eastern region, along with well-developed fissures. The total carcinogenic hazard for grownups exceeded that of juveniles due to the greater quantity of water for drinking consumed and higher surface area of skin amongst grownups. The results can guide groundwater pollution regulation activities in mining areas to minimize potential hazards of groundwater quality to the health of humans.

Calcium sulfate coprecipitation is a widely adopted method for removing heavy metal ions in engineering. However, the commonly used dihydrate calcium sulfate (CaSO4·2H2O, DH) phase shows limited efficiency in removing Zn2+ ions. To enhance this process, we regulated the crystal phase of calcium sulfate and explored how its composition affects the mechanism of Zn2+ immobilization. Coprecipitation experiments indicate that as the molar fraction of hemihydrate calcium sulfate (CaSO4·0.5H2O, HH) increases in the mixture, the efficiency of Zn2+ immobilization by calcium sulfate improves. When the HH molar fraction surpasses 15.6%, the immobilization capacity levels off. Mechanistic studies show that Zn2+ is mainly immobilized through structural doping within the crystal's water channels rather than by surface adsorption. In both DH and HH, zinc ions occupy these water channels instead of replacing Ca2+ ions. The larger water channels in HH contribute to its greater capacity for zinc ion immobilization. However, high-concentration Na+ ions interfere with HH formation, preventing further increases in zinc ion immobilization capacity and causing it to reach equilibrium. This research offers theoretical insights for optimizing calcium sulfate coprecipitation in managing heavy metal pollution in water bodies.