Identifying sources of acid mine drainage and major hydrogeochemical processes in abandoned mine adits (Southeast Shaanxi, China)

Acid mine drainage (AMD) has resulted in significant risks to both human health and the environment of the Han River watershed. In this study, water and sediment samples from typical mine adits were selected to investigate the hydrogeochemical characteristics and assess the environmental impacts of AMD. The interactions between coexisting chemical factors, geochemical processes in the mine adit, and the causes of AMD formation are discussed based on statistical analysis, mineralogical analysis, and geochemical modeling. The results showed that the hydrochemical types of AMD consisted of SO4-Ca-Mg, SO4-Ca, and SO4-Mg, with low pH and extremely high concentrations of Fe and SO42-. The release behaviors of most heavy metals are controlled by the oxidation of sulfide minerals (mainly pyrite) and the dissolution/precipitation of secondary minerals. Along the AMD pathway in the adit, the species of Fe-hydroxy secondary minerals tend to initially increase and later decrease. The inverse model results indicated that (1) oxidative dissolution of sulfide minerals, (2) interconversion of Fe-hydroxy secondary minerals, (3) precipitation of gypsum, and (4) neutralization by calcite are the main geochemical reactions in the adit, and chlorite might be the major neutralizing mineral of AMD with calcite. Furthermore, there were two sources of AMD in abandoned mine adits: oxidation of pyrite within the adits and infiltration of AMD from the overlying waste rock dumps. The findings can provide deeper insight into hydrogeochemical processes and the formation of AMD contamination produced in abandoned mine adits under similar mining and hydrogeological conditions.

Health risk assessment of potentially toxic elements (PTEs) concentrations in soil and fruits of selected perennial economic trees growing naturally in the vicinity of the abandoned mining ponds in Kuba, Bokkos Local Government Area (LGA) Plateau State, Nigeria

This study was designed to determine the level of potentially toxic elements (PTEs) contamination in soil and selected fruits and assesses the health risk of inhabitants in the abandoned tin mining community in Kuba, Bokkos LGA. Samples of the abandoned mine soil and selected fruits mango (Magnifera indica), guava (Psidium guajava), avocado pear (Persea americana), and banana (Musa spp)) from the vicinity of the abandoned mine were analyzed for the presence of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) using inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the levels of all the PTEs analysed in the abandoned mine soil samples were significantly (p < 0.05) higher than their corresponding values in the control soil from the non-mining area. Except for Cd, the mean concentrations of As, Cr, Cu, Mn, Ni, and Pb were significantly higher than the FAO/WHO maximum permissible limit. Except for Zn in guava fruits and Cd in avocado fruits, the mean concentration of PTEs in fruits from abandoned mines was significantly (p < 0.05) higher than their corresponding control values. In contrast, the mean levels of As, Cr, Cu, Mn, Ni, and Pb in the investigated fruits were significantly (p < 0.05) higher than FAO/WHO maximum permissible limits established for fruits. The studied fruits remarkably took up and bioaccumulated PTEs from the abandoned mine soil. Mango fruit significantly bioaccumulated As (5.40), Cd (3.40), and Zn (2.81). Guava fruit bioaccumulated As (1.50) and Cd (4.60), while avocado bioaccumulated As (3.53), Cd (3.80), and Zn (6.48). Banana bioaccumulated As (0.96), Cd (0.80), and Zn (6.78). The hazard quotient values for PTEs investigated in fruits for adults, and children were several folds greater than 1. The hazard index (HI) for the PTEs through consuming fruits for children and adults was greater than 1, indicating that possible health risks exist for both local children and adults. However, the HI values for the children were higher than those for adults, implying that children were exposed to more potential noncarcinogenic health risks from PTEs than adults. The total cancer risk (TCR) values for Cr and Ni for all the fruits studied were within 10-3-10-1, which is several-fold higher than the permissible limits (10-6 and < 10-4), indicating high carcinogenic risk. TCR values for Cd and Pb in all the fruits, except for Cd in guava and avocado fruits for children, were within the range of 10-5-10-4, indicating that they are associated with moderate risk. The CR values for all the PTEs in all the fruits for adults and children except for mango fruit adults were within 10-2-10-1, indicating high carcinogenic risk. In conclusion, the results and risk assessment provided by this study indicate that human exposure to fruits from abandoned mines suggests a high vulnerability of the local community to PTE toxicity. Long-term preventive measures to safeguard the health of the residents need to be put in place.

Spatial variability of arsenic fractionation in an abandoned arsenic-containing mine: Insights into soil particle sizes and quantitative mineralogical analysis

Soil particle sizes and mineral phases play a major role in the migration of arsenic (As) in mine. In this study, soil As fractionation and mineralogical composition in different particle sizes soil at naturally mineralized and anthropogenically disturbed zones from an abandoned mine were comprehensively studied. The results showed that soil As contents in anthropogenically disturbed mining zone (MZ), processing zone (PZ), and smelting zone (SZ) were increased with decreasing of soil particle sizes. The contents of As in the fine soil particles (0.45-2 μm) reached to 850-4800 mg·kg^-1, which mainly existed at readily soluble, specifically sorbed, and Al-oxide fractions, and contributed to 25.9-62.6 % of the total As contents in soil. Conversely, soil As contents in naturally mineralized zone (NZ) were decreased with decreasing of soil particle sizes and As was mainly accumulated in the coarse fraction of soil (0.075-2 mm). Despite the speciation of As in 0.075-2 mm soil mainly existed as residual fraction, the content of non-residual As fraction reached up to 1636 mg·kg^-1, indicating a high potential risk of As in naturally mineralized soil. The utilization of scanning electron microscopy, fourier transform infrared spectroscopy combined with mineral liberation analyzer revealed that soil As in NZ and PZ was mainly retained by iron (hydrogen)oxide, while whereas the dominant host minerals for soil As in MZ and SZ were the surrounding rocks of calcite and the iron-rich silicate mineral biotite. Notably, both of the calcite and biotite exhibited high mineral liberation, which was partly contributed to a significant portion of mobile As fraction in MZ and SZ soil. The results suggested that the potential risks of soil As from SZ and MZ at abandoned mine, particularly in the fine soil particles, should be a prior concern.

Ecological and health risks from heavy metal sources surrounding an abandoned mercury mine in the island paradise of Palawan, Philippines

A recent survey that determined heavy metal concentrations in an abandoned Hg mine in Palawan, Philippines, found the occurrence of Hg with As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Tl, V, and Zn. While the Hg originated from the mine waste calcines, the critical knowledge about the origin of the other heavy metals remains unknown. This study assessed the ecological and health risks from heavy metal pollution surrounding the abandoned Hg mine. Principal component analysis (PCA) showed that the abandoned mine and natural sources (i.e., local geology) are the two main contributors of heavy metal pollution. Historically, the mine waste calcines (retorted ore) were used as construction material for the wharf and as land filler for the adjacent communities. There is highly strong ecological risk associated with the heavy metals: Ni, Hg, Cr, and Mn contribute 44.3%, 29.5%, 10.7%, and 8.9% to the potential ecological risk index (RI), respectively. Hazard index (HI) exceeded 1 for both adults and children in all the sampling locations, implying non-carcinogenic adverse effects. The total cancer risk over a lifetime (LCR) also exceeded the threshold limit of 10^-4 for both adults and children, contributed mainly by Cr (91.8%) and As (8.1%). By combining the results of the PCA and risk assessments, a clear link between heavy metal source apportionment to ecological and health risks was established. It was estimated that the abandoned mine contributed to most of the ecological and health risks for people living near the wharf that was built using the calcine, as well as the nearby Honda Bay. The findings of this study are expected to help policy makers develop regulations that will safeguard the ecosystem and the general public from the damaging impacts of heavy metals from the abandoned mine.

The positive effects of mineral-solubilizing microbial inoculants on asymbiotic nitrogen fixation of abandoned mine soils are driven by keystone phylotype

Toward the restoration of the increasing numbers of abandoned mines across China, external-soil spray seeding technologies have become more extensively utilized. However, considerable challenges remain that seriously hamper the effectiveness of these technologies, such as inadequate nutrient availability for plants. Previous studies have shown that mineral-solubilizing microbial inoculants can increase the nodules of legumes. However, their effects on symbiotic nitrogen fixation (SNF), asymbiotic nitrogen fixation (ANF), and diazotrophic communities remain unknown. Further, research into the application of functional microorganisms for the restoration of abandoned mines has been conducted either in greenhouses, or their application in the field has been too brief. Thus, we established a four-year field experiment in an abandoned mine and quantified the SNF, ANF, and diazotrophic communities. To the best of our knowledge, this study is the first to describe the long-term application of specific functional microorganisms for the remediation of abandoned mine sites in the field. We revealed that mineral-solubilizing microbial inoculants significantly increased the soil ANF rate and SNF content. There was no significant correlation between the diazotrophic alpha diversity and soil ANF rate; however, there were strong positive associations between the relative abundance and biodiversity of keystone phylotype (module #5) within ecological clusters and the ANF rate. Molecular ecological networks indicated that microbial inoculants increased network complexity and stability. Moreover, the inoculants significantly enhanced the deterministic ratio of diazotrophic communities. Furthermore, homogeneous selection predominantly mediated the assembly of soil diazotrophic communities. It was concluded that mineral-solubilizing microorganisms played a critical role in maintaining and enhancing nitrogen, which offers a new solution with great potential for the restoration of ecosystems at abandoned mine sites.

Source and evolution of sulfate in the multi-layer groundwater system in an abandoned mine-Insight from stable isotopes and Bayesian isotope mixing model

The source and evolution of sulfate (SO₄^2-) in groundwater from abandoned mines are widely concerned environmental issues. Herein, major dissolved ions, multi-isotopes (δ³⁴S, δ¹⁸O_sulfate, δ²H and δ¹⁸O_water), machine learning (Self-organizing maps) and Bayesian isotope mixing model were used to identify the source and evolution of SO₄^2- in an abandoned mine (Fengfeng mine, northern China) with a multi-layer groundwater system. Groundwater in the study area was mainly divided into three clusters (Cluster I, Cluster II and Cluster III), dominated by Na-SO₄, Ca-SO₄ and Ca-HCO₃ types, respectively. According to δ²H and δ¹⁸O_water, groundwater in the study area mainly originated from atmospheric precipitation. δ³⁴S, δ¹⁸O_sulfate and SO₄^2- suggested that bacterial sulfate reduction did not affect the SO₄^2- isotopic composition. Dual SO₄^2- isotopes, and MixSIAR model revealed that the main source of SO₄^2- in the study area was pyrite oxidation/gypsum dissolution, accounting for an average of 57.4 % (gypsum), 71.24 % (pyrite oxidation) and 52.93 % (pyrite oxidation) of SO₄^2- in the samples of Clusters I-III, respectively. Combined with the hydrochemical diagrams, the evolution of SO₄^2- in different clusters of samples was derived. Cluster I was mainly gypsum dissolution; In contrast, Clusters II and III were mainly pyrite oxidation accompanied by carbonate dissolution, and Cluster II was also influenced by cation exchange. These findings will help in developing management strategies for protecting groundwater quality, which will provide a reference for the study of solute sources and S cycling in abandoned mines.

Phytoextraction of Cu, Cd, Zn and As in four shrubs and trees growing on soil contaminated with mining waste

Mining activity has degraded large extensions of soil and its waste is composed of metals, anthropogenic chemicals, and sterile rocks. The use of native species in the recovery of polluted soils improves the conditions for the emergence of other species, tending to a process of ecosystem restoration. The objective of this study was to evaluate the bioaccumulation of metal(loid)s in four species of native plants and the effect of their distribution and bioavailability in soil with waste from an abandoned gold mine. Soil samples were taken from two sites in La Planta, San Juan, Argentina: Site 1 and Site 2 (mining waste and reference soil, respectively). In Site 1, vegetative organ samples were taken from Larrea cuneifolia, Bulnesia retama, Plectrocarpa tetracantha, and Prosopis flexuosa. The concentration of metal(loid)s in soil from Site 1 were Zn > As > Cu > Cd, reaching values of 7123, 6516, 240 and 76 mg kg^-1, respectively. The contamination indices were among the highest categories of contamination for all four metal(loid)s. The spatial interpolation analysis showed the effect of the vegetation as the lowest concentration of metal(loid)s were found in rhizospheric soil. The maximum concentrations of As, Cu, Cd and Zn found in vegetative organs were 371, 461, 28, and 1331 mg kg^-1, respectively. L. cuneifolia and B. retama presented high concentrations of Cu and Zn. The most concentrated metal(loid)s in P. tetracantha and P. flexuosa were Zn, As and Cu. Cd was the least concentrated metal in all four species. The values of BAF and TF were greater than one for all four species. In conclusion, the different phytoextraction capacities and the adaptations to arid environments of these four species are an advantage for future phytoremediation strategies. Their application contributes to the ecological restoration and risk reduction, allowing the recovery of ecosystem services.

Pollution characteristics and environmental availability of toxic elements in soil from an abandoned arsenic-containing mine

Understanding the pollution characteristics and assessing the ecological risk of toxic metals in mine soil are crucial to controlling and managing risks in abandoned mine areas. In this study, the profile soil pollution characteristics and modified ecological risk of As, Cd, Hg, Pb, Sb, and Tl for both the different mining functional areas and the downstream impacted areas at a large-scale abandoned arsenic-containing mine were studied. Results showed that both the profile soils at the mining functional areas and the surface layer in downstream sites are heavily polluted by As, Cd, Hg, Sb, and Tl. As, Hg, Sb, and Tl mainly accumulated on soils with a depth of 0-1.5 m. In contrast, these metals in the mining site were gradually increased with soil depth above the bedrock strata. Cd and Pb were mainly concentrated at depth of 2.5-3.5 m in the smelting with by-product processing site. The speciation of metals in the profile soils mainly occurred in residual fraction. However, high levels of potential mobile As and Sb were found in mining soils and smelting surface soils, as well as Tl in deep soils at mining functional sites and top soils at downstream sites, with their mean contents in these areas arrived to 2950 mg kg^-1, 9.64 mg kg^-1, and 0.98 mg kg^-1, respectively. In addition, the modified ecological risk assessment (NIRI_m) values revealed a substantial ecological risk of As, Cd, Hg, and Sb in both the entire profile soils at the mining, smelting sites and topsoil (0-1.5 m) at the adjacent downstream site. In summary, the pollution characteristics and potential ecological risk of toxic metals in profile soils from the different functional sites at arsenic-containing mine were significantly different and suitable control strategies for available toxic elements should be adopted in the different functional sites of mine.

Impact assessment of ephemeral discharge of contamination downstream of two legacy base metal mines using environmental DNA

Mining and processing metalliferous ores can degrade the environment well beyond the footprint of the mine, particularly where on-site containment and post-mining remediation has been insufficient to prevent releases of solid and aqueous mine wastes. In this study, we investigated the potential of sediment and water chemistry coupled with environmental (e)DNA metabarcoding to evaluate discrete and cumulative ecological impacts of two legacy base metal (copper (Cu), zinc (Zn), lead (Pb)) mines (Peelwood and Cordillera) which discharge metals via ephemeral tributaries into perennial Peelwood Creek. Although the two mine streams exceeded Australian guidelines for sediment and freshwater quality for Cu, Zn and Pb, Peelwood Creek had relatively low sediment and water metal concentrations, suggesting a low potential for environmental toxicity. Although sediment and water chemistry defined the extent of biological impacts, metabarcoding showed that Peelwood and Cordillera mines had discrete impacts and Peelwood mine was the main source of contamination of Peelwood Creek. Metabarcoding showed that prokaryotes can be good indicators of metal contamination whereas eukaryotes did not reflect contamination impacts in Peelwood Creek. Metabarcoding results showed that benthic communities downstream of Cordillera mine were less impacted than those below Peelwood mine, suggesting that Peelwood mine should be considered for further remediation.

Prospect of abandoned metal mining sites from a hydrogeochemical perspective

Land exploitation for mining sector may leave a series of environmental impacts on our ecosystem if not appropriately managed. Therefore, the present study attempts to evaluate the various environmental aspects due to abandoned metal mining including former iron ore, bauxite, and tin mining lands in view of its hydrogeochemical behavior. Mine-impacted waters and sediments were ascertained from former mining ponds, mine tailings, and impacted streams for interpretation of aqueous and sediment geochemistry, major and trace elements, hydrochemical facies, chemical weathering rate and CO₂ consumption, and water quality classification. Results indicated that the environmental impact of the long-abandoned iron ore mine was still evident with some high concentration of metals and acidic pH. Higher concentrations of Fe and Mn in water were noticeable in some areas while other trace elements (Pb, Zn, As, Cd, Cr, and Cu) were found below the recommended guideline values. Sediment quality reflected the trend of water quality variables mainly associated with metal(loid) elements, resulting in potential ecological risk, classified as having low to moderate risk. There were variations in terms of hydrochemical facies of the waters suggesting the influence of minerals in water. The chemical weathering rate suggests that contribution of carbonate mineral weathering was more important (up to 60%) than silicate weathering. The resulting CO₂ consumption by mineral weathering was estimated to be in the range of 1.7-9.8 × 10⁷ mol/year (former bauxite and tin mining areas can act as temporary sinks for CO₂). Water quality classifications according to several chemical indices (Kelly's ratio, sodium absorption ratio, soluble sodium percentage, residual sodium carbonate, magnesium absorption ratio, and permeability index) were also discussed in regards to mine water reuse for irrigation purpose. The findings suggest that a holistic approach that integrates all important hydrogeochemical aspects is essential for a thorough evaluation of the implication of medium- to long-term mining exploitation on its surrounding ecosystems. This would be beneficial in light of restoration potential of degraded mining land so as for future mitigation strategies in the mining sector.

Geogenic and anthropogenic interactions at a former Sb mine: environmental impacts of As and Sb

Mining activities are acknowledged to introduce contaminants into localised environments and cause wider spread diffuse pollution. The concentration, distribution and fate of arsenic (As) and antimony (Sb) were studied at the former metalliferous Louisa Mine at Glendinning, Scotland. Soils and surface water were sampled and subsequently analysed to map the distribution of contamination and identify pollution sources. The maximum concentrations of As and Sb of 15,490 and 1504.2 mg kg^-1, respectively, were determined in soils associated with the ore processing area and spoil heaps. The fractions of dissolved As and Sb in soils were < 1 and < 5% of total soil content, respectively, confirming findings of previous studies that As and Sb are relatively immobile. Yet, the concentrations of As and Sb released by soils exceeded regulatory limits. Concentrations of As and Sb in surface water in the immediate vicinity of the mine were impacted by a gully discharge, but rapidly diluted. While the concentrations affected by the run-off waters did not exceed EU environmental standards for freshwater, the concentrations of both, As and Sb, sharply increased above the said environmental standards approximately 100 m downstream of the mine site. The unaltered As-to-Sb ratio in water samples suggests a geogenic source. While there is a justifiable concern about the soil pollution caused by the historic mining in the area, the Glenshanna Burn is affected more by indigenous geochemical processes than the derelict mine.

Effect of drying treatment on the leachability of metallic elements from weathered solid mine wastes

Leaching of toxic metallic elements (Cu, Zn, As, Cd, and Pb) from two solid mine wastes was characterized under different drying treatments. During 14 batch decant-refill leaching steps, samples were intermittently dried four times in 40 °C oven or -20 °C freezer. For all leachates, the pH, pE, Fe²⁺/Fe³⁺, and SO₄^2- were analyzed. The parameters of the two-site model (k_fast, k_slow, and f_fast) and labile fractions (F1 + F2) were determined. High levels of toxic metallic elements were determined in waste samples; however, their leaching was limited, as evidenced by the magnitudes of F1 + F2, f_fast, and k_slow. Leachate solutions were acidic, at pH 3-4, and oxic, at 150 mV < Eh 300 < mV, thus having negligible Fe²⁺. Leachate concentrations of toxic metallic elements increased (4-58%) after drying at 40 °C and were strongly correlated (r² = 0.780) with those of sulfate in liquid phase. The mass of element elution was in the order of 40 °C drying > -20 °C drying ≥ continuous wetting. Results indicate that the element leachability is increased through drying events and the leachate concentration is associated with the dissolution reaction of sulfur-bearing minerals. Frequent occurrence of prolonged droughts along with high temperatures over the mine waste disposal site, can enhance the leaching potential of toxic metallic elements.

Baseline study on the levels of heavy metals in seawater and macroalgae near an abandoned mine in Manicani, Guiuan, Eastern Samar, Philippines

Lateritic nickel ore stockpiles are still present in Manicani Island after mining activities were suspended in 2001. This study aimed to assess the water quality in the island by measuring the levels of Pb, Ni and Cu in seawater and Sargassum polycystum samples collected quarterly in 2018. The levels of the three heavy metals in seawater samples were 0.388 ± 0.058-1.508 ± 0.120 mg/L Pb, 0.457 ± 0.003-0.531 ± 0.005 mg/L Cu, and 0.122 ± 0.008-0.628 ± 0.281 mg/L Ni. All values are above the permissible limits recommended by DENR and USEPA. Ni (13.630 ± 7.341-160.120 ± 3.375 mg/kg) had the highest concentration in S. polycystum, significantly higher than Pb ( Collapse

Key Words

• Abandoned mine
• Heavy metals
• Macroalgae
• Manicani Island
• Seawater

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MESH Headings

• Environmental Monitoring/methods
• Metals, Heavy/analysis
• Mining
• Nickel/analysis
• Philippines
• Sargassum/chemistry
• Seawater/analysis
• Seaweed/chemistry
• Water Pollutants, Chemical/analysis

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Affiliation(s)

Olga G Corales-Ultra Division of Natural Sciences and Mathematics, University of the Philippines Visayas Tacloban College, Magsaysay Boulevard, Tacloban City, Leyte 6500, Philippines.
Reynaldo P Peja Division of Natural Sciences and Mathematics, University of the Philippines Visayas Tacloban College, Magsaysay Boulevard, Tacloban City, Leyte 6500, Philippines; Environmental Management Department, Visayas State University - Alangalang, Alangalang, Leyte 6517, Philippines
Eulito V Casas Division of Natural Sciences and Mathematics, University of the Philippines Visayas Tacloban College, Magsaysay Boulevard, Tacloban City, Leyte 6500, Philippines

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Efficacy of biocementation of lead mine waste from the Kabwe Mine site evaluated using Pararhodobacter sp

Biocementation of hazardous waste is used in reducing the mobility of contaminants, but studies on evaluating its efficacy have not been well documented. Therefore, to evaluate the efficacy of this method, physicochemical factors affecting stabilized hazardous products of in situ microbially induced calcium carbonate precipitation (MICP) were determined. The strength and leach resistance were investigated using the bacterium Pararhodobacter sp. Pb-contaminated kiln slag (KS) and leach plant residue (LPR) collected from Kabwe, Zambia, were investigated. Biocemented KS and KS/LPR had leachate Pb concentrations below the detection limit of < 0.001 mg/L, resisted slaking, and had maximum unconfined compressive strengths of 8 MPa for KS and 4 MPa for KS/LPR. Furthermore, biocemented KS and KS/LPR exhibited lower water absorption coefficient values, which could potentially reduce the water transportation of Pb²⁺. The results of this study show that MICP can reduce Pb²⁺ mobility in mine wastes. The improved physicochemical properties of the biocemented materials, therefore, indicates that this technique is an effective tool in stabilizing hazardous mine wastes and, consequently, preventing water and soil contamination.

Assessment of the environmental impact of an abandoned mine using an integrative approach: A case-study of the "Las Musas" mine (Extremadura, Spain)

The mine abandonment is generally associated with the release of potentially toxic metals into the environment, which may depend on metals speciation, soil properties and climate conditions. The goal of the present work was to assess the environmental impact of the abandoned Pb-Zn mine "Las Musas" (Spain) using an integrative approach. The impact on soils and surface waters was performed using: chemical parameters, quantification of potentially toxic metals (Cd, Cu, Pb and Zn), and ecotoxicological responses using lethal and sub-lethal bioassays with organisms' representative of different trophic level ((soil: Eisenia fetida (mortality and reproduction test); Latuca sativa and Lollium perenne (seedling emergence); and water: Vibrio fischeri (luminescence inhibition), Daphnia magna (immobility and reproduction test), Thamnocephalus platyurus (mortality), Pseudokirchneriella subcapitata (growth inhibition)). The results showed soils with neutral to slight alkaline pH (7.64-8.18), low electric conductivity (125-953 μS/cm) and low organic matter levels (0.20-1.85%). For most of the soil samples, Pb was the only metal which surpassed the limit proposed by the Canadian soil quality guidelines, with values ranging from 42.2 to 181.4 mg/kg. The ecotoxicological results showed that the soils with the highest levels of Pb induced a decrease on E. fetida reproduction and on L. sativa germination, indicating negative impacts on the habitat function. The analysis of the surface waters showed levels of Zn surpassing the legal limit adopted from the Water Framework Directive (37.0 to 69.0 μg/L). The ecotoxicological results highlight the importance of bioassays that evaluate the behavior of species, when assessing the risk of mining areas with non-acid soils and waters with high nutrients/organic matter concentrations and low concentrations of potentially toxic metals. The results indicated a moderate environmental risk from potentially toxic metals, at the areas analyzed around the Azuaga mine.

Parametric assessment of hydrochemical changes associated to underground pumped hydropower storage

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porous medium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandoned mines for constructing UPHS plants. This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.

Comparisons of human risk assessment models for heavy metal contamination within abandoned metal mine areas in Korea

This study was initiated to develop a model specialized to conduct human risk assessments (HRAs) of abandoned metal mine areas in Korea. The Korean guideline (KG) model used in study was formulated via modification of the original Korean guidelines on HRAs of soil contamination. In addition, the newly developed model was applied to the HRAs of two abandoned metal mines contaminated with arsenic (As) and heavy metals (Cd, Cu, Pb, and Zn). The results of the KG model were compared with those of two internationally renowned models [Contaminated land exposure assessment (CLEA) and CSOIL models]. The HRA results of the three models indicated that the areas of concern were unsafe when it came to both carcinogenic and non-carcinogenic hazards. Furthermore, the hazards in both areas were mostly attributed to As and the predominant exposure pathways were identified as crop intake in the KG model and surface soil dermal contact in CLEA and CSOIL models. Accordingly, measures to protect against As exposure should be established immediately to prevent adverse health effects on inhabitants in these areas. A comparison of HRA results revealed significant differences between KG, CLEA, and CSOIL models due to the various types of exposure pathways, contaminants, and input data, such as exposure factors and receptor parameters. This study suggests that set-up of an exposure scenario is crucial for the successful performance of HRAs, and the most relevant HRA model should be deliberately selected to attain risk assessment goals.

Soil attenuation of the leaching potential of mine-related metallic elements (Zn, As, and Cd) under different leachate solute compositions

Leachate from abandoned mine is frequently enriched with toxic elements but their off-site movement is not well addressed. In this study, the attenuation potential of mine-related metallic elements (Zn, As, and Cd) through downward soil was investigated using batch equilibrium sorption and seepage column studies under simulated leachate composition (single, binary, and ternary solutes in 5-mM CaSO₄). In the batch result, the retention of Cd was suppressed by 40-45% in the presence of Zn while the Zn was less affected by Cd. The retention of As increased by 14-25% in the presence of both cations, with a greater effect from Zn. The phenomena were explained by the combined effects of sorption selectivity, the relative element abundance, and the operating sorption mechanism (nonspecific vs. specific). These effects also influenced the effluent element concentrations in the seepage study, as numerically indicated by a two-site model fit and moment analysis (e.g., the peak arrival time and peak concentration). For 500 PV seepage, element retention by the column (M_retention) was strongly correlated (r² = 0.907) with the sorption constant (K_d^∗) during the sorption-dominant stage, but the same correlation was poor (r² = 0.346) during the depletion-dominant stage, due to the desorption resistance of As compared to Zn and Cd. Therefore, the attenuation of the leaching potential by surrounding soils and the effect of cosolutes dissolved in the leachate phase must be concurrently understood when assessing the off-site leaching of metallic elements from abandoned mine sites.

Factors influencing As(V) stabilization in the mine soils amended with iron-rich materials

Chemical stability of As(V) in amended mine-impacted soils was assessed according to functions of incubation period (0, 1, 2, 4, and 6 months), amendment dose (2.5 and 5%), and application timing (0 and 3rd month). Six soils contaminated with 26-209 mg kg^-1 of As(V) were collected from two abandoned mine sites and were treated with two alkaline iron-rich materials (mine discharge sludge (MS) and steel-making slag (SS)). Seventeen to 23% of As(V) in soils was labile. After each designated time, As(V) stability was assessed by the labile fractions determined with sequential extraction procedures (F1-F5). Over 6 months, a reduction (26.9-70.4%) of the two labile fractions (F1 and F2) and a quantitative increase (7.4-29.9%) of As(V) in F3 were observed (r ² = 0.956). Two recalcitrant fractions (F4 and F5) remained unchanged. Temporal change of As(V) stability in a sample was well described by the two-domain model (k _fast, k _slow, and F_fast). The stabilization (%) correlated well with the fast-stabilizing domain (F_fast), clay content (%), and Fe oxide content (mg kg^-1), but correlated poorly with kinetic rate constants (k _fast and k _slow). Until the 3rd month, the 2.5%-MS amended sample resulted in lower As(V) stabilization (25-40%) compared to the 5% sample (50-60%). However, the second 2.5% MS addition on the 2.5% sample upon the lapse of the 3rd month led to a substantial reduction (up to 38%) of labile As(V) fraction in the following 4th and 6th months. As a result, an additional 15-25% of As(V) stability was obtained when splitting the amendment dose into 3-month intervals. In conclusion, the As(V) stabilization by Fe-rich amendment is time-dependent and its efficacy can be improved by optimizing the amendment dose and its timing.

Extractive waste management: A risk analysis approach

Abandoned mine sites continue to present serious environmental hazards because the heavy metals associated with extractive waste are continuously released into the environment, where they threaten human life and the environment. Remediating and securing extractive waste are complex, lengthy and costly processes. Thus, in most European countries, a site is considered for intervention when it poses a risk to human health and the surrounding environment. As a consequence, risk analysis presents a viable decisional approach towards the management of extractive waste. To evaluate the effects posed by extractive waste to human health and groundwater, a risk analysis approach was used for an abandoned nickel extraction site in Campello Monti in North Italy. This site is located in the Southern Italian Alps. The area consists of large and voluminous mafic rocks intruded by mantle peridotite. The mining activities in this area have generated extractive waste. A risk analysis of the site was performed using Risk Based Corrective Action (RBCA) guidelines, considering the properties of extractive waste and water for the properties of environmental matrices. The results showed the presence of carcinogenic risk due to arsenic and risks to groundwater due to nickel. The results of the risk analysis form a basic understanding of the current situation at the site, which is affected by extractive waste.

Soil attenuation of the seepage potential of metallic elements (Cu, Zn, As(V), Cd, and Pb) at abandoned mine sites: A batch equilibrium sorption and seepage column study

Soil attenuation of off-site leaching potential of metallic elements at the two abandoned mine sites was investigated using batch sorption and layered column studies. In batch study, the leachate concentration-specific sorption (K_d^*) by downgradient clean soils was in the order of Pb>Cu>Cd>Zn>As for DY site and Pb>As>Cu>Cd>Zn for BS site. In the layered (mine+clean) soil column, element elution was significantly reduced (e.g., no initial flush, retarded peak arrival, and lower peak concentration) while sulfate elution can be an indicator of the dissolution of sulfur-bearing minerals in mine soils. The greatest reduction was observed for Pb and Cu while the lowest was for Cd (2-19%) and Zn (6-51%), consistent with the batch data. Both the reduced elution at slow seepage and concentration drop after flow interruption support the time-limited propensity. In column segments, the sorptive elements (Cu, Pb, and As) were dominantly found in the inlet while less sorptive ones (Zn and Cd) in the outlet. Both batch and column data suggest that the element leaching with mine leachate movement can be greatly attenuated by the interactions with the surrounding downgradient soil during the seepage process.

Association of cadmium with diabetes in middle-aged residents of abandoned metal mines: the first health effect surveillance for residents in abandoned metal mines

OBJECTIVE

The aim of this study was to determine the association between urinary cadmium (U-cd) concentration and diabetes in middle-aged Korean residents of abandoned mines using the first Health Effect Surveillance for Residents in Abandoned Metal mines (HESRAM).

METHODS

This study was cross-sectional study conducted on 719 residents between 40-70 years in 38 abandoned metal mines in Korea. Data was collected by HESRAM from 2008 to 2011. The correlation coefficient of U-cd and fasting blood glucose, odds ratio in urinary cadmium tertiles and diabetes prevalence was analyzed according to the sex category.

RESULTS

The correlation coefficient U-cd concentration and fasting blood glucose was 0.182 in male. Logistic regression analysis in male revealed a third tertile odds ratio of U-cd (2 μg/g creatinine < U-cd) while diabetes prevalence was 1.81 (95 % CI 1.05-3.12) with adjusted age, BMI, smoking and alcohol consumption, region, family income. On the other hand, the odds ratio for third tertile of U-cd (3 μg/g creatinine < U-cd) between diabetes prevalence in female was 1.39 (95 % CI 0.52-3.72) in addition to adjusted menopausal status.

CONCLUSIONS

Environmental exposure to cadmium in abandoned mine residents was associated with diabetes in male. Closed monitoring and periodic evaluation of the health effects of chronic environmental exposure on abandoned mines residents will be needed.

Antimony in the soil-water-plant system at the Su Suergiu abandoned mine (Sardinia, Italy): strategies to mitigate contamination

This study was aimed to implement the understanding of the Sb behavior in near-surface environments, as a contribution to address appropriate mitigation actions at contaminated sites. For this purpose, geochemical data of soil (8 sites), water (29 sites), and plant (12 sites) samples were collected. The study area is located at Su Suergiu and surroundings in Sardinia (Italy), an abandoned mine area heavily contaminated with Sb, with relevant impact on water bodies that supply water for agriculture and domestic uses. Antimony in the soil horizons ranged from 19 to 4400 mg kg(-1), with highest concentrations in soils located close to the mining-related wastes, and concentrations in the topsoil much higher than in the bedrock. The Sb readily available fraction was about 2% of the total Sb in the soil. Antimony in the pore water ranged from 23 to 1700 μg L(-1), with highest values in the Sb-rich soils. The waters showed neutral to slightly alkaline pH, redox potential values indicating oxidizing conditions, electrical conductivity in the range of 0.2 to 3.7 mS cm(-1), and dissolved organic carbon ≤2 mg L(-1). The waters collected upstream of the mine have Ca-bicarbonate dominant composition, and median concentration of Sb(tot) of 1.7 μg L(-1) (that is total antimony determined in waters filtered through 0.45 μm), a value relatively high as compared with the background value (≤0.5 μg L(-1) Sb) estimated for Sardinian waters, but below the limits established by the European Union and the World Health Organization for drinking water (5 μg L(-1) Sb and 20 μg L(-1) Sb, respectively). The waters flowing in the mine area are characterized by Ca-sulfate dominant composition, and median concentrations of 7000 μg L(-1) Sb(tot). Extreme concentrations, up to 30,000 μg L(-1) Sb(tot), were observed in waters flowing out of the slag materials derived from the processing of Sb-ore. The Sb(III) was in the range of 0.8 to 760 μg L(-1) and represented up to 6% of Sb(tot). In the waters collected downstream of the mine, median Sb(tot) concentrations decreased as distance from the mine area increases: 1300 μg L(-1) Sb(tot) in the stream Rio Ciurixeda at 3 km distance, and 25 μg L(-1) Sb(tot) in the main River Flumendosa 15 km further downstream. Attenuation of Sb contamination was mainly due to dilution. Results of modeling, carried out by both EQ3 and Visual MINTEQ computer programs, suggest that sorption of dissolved Sb onto solid phases, and/or precipitation of Sb-bearing minerals, likely give a minor contribution to attenuation of Sb contamination. The slightly alkaline pH and oxidizing conditions might favor the persistence of inorganic Sb(V)-bearing species at long distance in the studied waters. Concentrations of Sb in the plants Pistacia lentiscus and Asparagus ranged from 0.1 to 22 mg kg(-1), with maximum values in plants growing very close to the mining-related wastes. The P. lentiscus grows well on the soils highly contaminated with Sb at Su Suergiu and might be used for revegetation of the Sb-rich heaps, thus contributing to reduce the dispersion of contaminated materials. Major effects of contamination were observed on the water bodies located downstream of the Su Suergiu abandoned mine. The maximum load (16.6 kg Sb per day) to the Flumendosa, the main aquatic recipient, was observed after heavy rain events. Therefore, priorities of mitigation actions should be focused on minimizing the contact of rain and runoff waters on the heaps of mining wastes.

Antimony in the soil-water-plant system at the Su Suergiu abandoned mine (Sardinia, Italy): strategies to mitigate contamination

This study was aimed to implement the understanding of the Sb behavior in near-surface environments, as a contribution to address appropriate mitigation actions at contaminated sites. For this purpose, geochemical data of soil (8 sites), water (29 sites), and plant (12 sites) samples were collected. The study area is located at Su Suergiu and surroundings in Sardinia (Italy), an abandoned mine area heavily contaminated with Sb, with relevant impact on water bodies that supply water for agriculture and domestic uses. Antimony in the soil horizons ranged from 19 to 4400 mg kg(-1), with highest concentrations in soils located close to the mining-related wastes, and concentrations in the topsoil much higher than in the bedrock. The Sb readily available fraction was about 2% of the total Sb in the soil. Antimony in the pore water ranged from 23 to 1700 μg L(-1), with highest values in the Sb-rich soils. The waters showed neutral to slightly alkaline pH, redox potential values indicating oxidizing conditions, electrical conductivity in the range of 0.2 to 3.7 mS cm(-1), and dissolved organic carbon ≤2 mg L(-1). The waters collected upstream of the mine have Ca-bicarbonate dominant composition, and median concentration of Sb(tot) of 1.7 μg L(-1) (that is total antimony determined in waters filtered through 0.45 μm), a value relatively high as compared with the background value (≤0.5 μg L(-1) Sb) estimated for Sardinian waters, but below the limits established by the European Union and the World Health Organization for drinking water (5 μg L(-1) Sb and 20 μg L(-1) Sb, respectively). The waters flowing in the mine area are characterized by Ca-sulfate dominant composition, and median concentrations of 7000 μg L(-1) Sb(tot). Extreme concentrations, up to 30,000 μg L(-1) Sb(tot), were observed in waters flowing out of the slag materials derived from the processing of Sb-ore. The Sb(III) was in the range of 0.8 to 760 μg L(-1) and represented up to 6% of Sb(tot). In the waters collected downstream of the mine, median Sb(tot) concentrations decreased as distance from the mine area increases: 1300 μg L(-1) Sb(tot) in the stream Rio Ciurixeda at 3 km distance, and 25 μg L(-1) Sb(tot) in the main River Flumendosa 15 km further downstream. Attenuation of Sb contamination was mainly due to dilution. Results of modeling, carried out by both EQ3 and Visual MINTEQ computer programs, suggest that sorption of dissolved Sb onto solid phases, and/or precipitation of Sb-bearing minerals, likely give a minor contribution to attenuation of Sb contamination. The slightly alkaline pH and oxidizing conditions might favor the persistence of inorganic Sb(V)-bearing species at long distance in the studied waters. Concentrations of Sb in the plants Pistacia lentiscus and Asparagus ranged from 0.1 to 22 mg kg(-1), with maximum values in plants growing very close to the mining-related wastes. The P. lentiscus grows well on the soils highly contaminated with Sb at Su Suergiu and might be used for revegetation of the Sb-rich heaps, thus contributing to reduce the dispersion of contaminated materials. Major effects of contamination were observed on the water bodies located downstream of the Su Suergiu abandoned mine. The maximum load (16.6 kg Sb per day) to the Flumendosa, the main aquatic recipient, was observed after heavy rain events. Therefore, priorities of mitigation actions should be focused on minimizing the contact of rain and runoff waters on the heaps of mining wastes.