Uptake patterns for nitrogen and sulfur source by aquatic plants and various nitrogen acquisition strategies: Affected by mining activities

Understanding the nitrogen and sulfur uptake strategies of mine plants, including sources and preferences for nitrogen forms (ammonium nitrogen (NH4+) vs nitrate nitrogen (NO3-)), is critical to improving understanding of the role of plants in participating in the biogeochemical cycles of nitrogen and sulfur in mining areas. In this study, the stable N and S isotopic compositions of two species of aquatic plants (calamus and reed) in Linhuan mining area were analyzed to determine their absorption strategies for different nitrogen and sulfur sources. The results showed that river water was the largest source of nitrogen and sulfur, contributing 54.6% and 53.9% respectively. NO3- is the main form of nitrogen uptake by reed and calamus, followed by NH4+. In order to adapt to the change of nitrogen form in the environment, reed and calamus tend to absorb and utilize NO3- to maintain their absorption of nitrogen. Mine effluents from mining activities provide at least 12.9% and 16.8% sulfate to reed and calamus respectively, and the effect of mine effluents on reed and calamus sulfur has been underestimated. This study reveals the key factors controlling plant isotope composition, and the use of nitrogen and sulfur isotope composition of aquatic plants can help quantify the level of influence of mining activities, and understand the biogeochemical cycle of nitrogen and sulfur in mining areas.

Identification of sources and analysis of spatial distribution of soil heavy metals in northern China coal mining areas

The mining and utilization of coal resources has not only promoted rapid economic development but also poses a potential threat to the ecological environment. The purpose of this study is to clarify the effects both of mining and land use types on the spatial distribution and particular sources of heavy metals in soil, using inverse distance weighted (IDW) and the Positive Matrix Factorization (PMF) model. A total of 99 topsoil and profile soil samples across different land use types and mining conditions were collected. The contamination of soil with Cd, Pb, and Hg in the research area was most severe, with the coefficient of variation (CV) of Hg being the largest, while also being heavily influenced by human activities. Severely polluted regions were mainly distributed in the center of the coal mining area, as well as near the highway. The contents of heavy metals for various land use patterns were ranked as follows: forestland > farmland > bare land > grassland > building land. Hg, Cd, Pb, Cr, and Zn had showed migration in the 0-60 cm depth range, and the enrichment factors (EFs) of Cd, Pb, Hg, and As in the soil profile were the most significant. The PMF demonstrated that the contributions of industrial activities and atmospheric deposition, transportation and mining activities, agricultural activities, and natural sources accounted for 31.25%, 28.13%, 22.24%, and 18.38%, respectively. The migration and deposition of atmospheric particulate matter from coal mining, transportation, and coal combustion under winds triggered heavy metal contamination in semi-arid areas of northern China. This phenomenon has important implications for the prevention and reduction of heavy metal pollution through various effective measures in coal-mining cities in northern China.

Contamination and health risks brought by arsenic, lead and cadmium in a water-soil-plant system nearby a non-ferrous metal mining area

Heavy metal(loid)s contamination prevails in the water-soil-plant system around non-ferrous metal mining areas. The present study aimed to evaluate the heavy metal(loid)s contamination in Nandan Pb-Zn mining area (Guangxi, China). A total of 36 river water samples, 75 paired paddy soil and rice samples, and 128 paired upland soil and plant samples were collected from this area. The concentrations of arsenic (As), lead (Pb), and cadmium (Cd) in these samples were measured. Results showed that the average water quality indexes (WQIs) at the 12 sampling sites along the main river ranged from 41 to 5008, indicating the water qualities decreasing from "Excellent" to "Undrinkable". The WQIs nearby tailings or industrial park were significantly higher than those at the other sites. 34.0% and 64.5% of soil samples exceeded the risk screening values for As and Cd. The Pb and Cd concentrations in all rice samples exceeded the Chinese food safety limits by 18.7% and 82.7%, respectively. Leafy vegetables had a higher concentration of As, Pb, and Cd than other vegetables, exceeding the maximum permissible limits by 14.1%, 61.2%, and 40.0%, respectively. The biological accumulation coefficient (BAC) of Cd was the highest in rice and lettuce leaves. The hazard quotients (HQs) of As and Cd, indicating non-carcinogenic risks, were 4.15 and 1.76 in adult males, and 3.40 and 1.45 in adult females, all higher than the permitted level (1.0). The carcinogenic probabilities of As and Cd from rice and leafy vegetables consumption were all higher than 1 × 10-4. We conclude that metal(loid)s contamination of the water-soil-plant system has posed great non-carcinogenic and carcinogenic risks to the local population.

Tracing sulfate sources and transformations of surface water using multiple isotopes in a mining-rural-urban agglomeration area

Rapid urbanization and mining activities are exacerbating sulfate (SO42-) pollution in surface water, and the information on its sources and transformations is crucial for understanding the sulphur cycle in mining areas. In this study, the SO42- in the surface water of Huaibei mining area were monitored and the main sources of pollution and biogeochemical processes were identified using stable isotopes (δD, δ18O-H2O, δ34S-SO42- and δ18O-SO42-) and water chemistry. The results demonstrated the SO42- content in the Huihe River and Linhuan subsidence water area (SWA) is higher than that in other rivers and SWAs, which exceeded the environmental quality standard of surface water. The SO42- content of different rivers and SWAs showed seasonal differences, and the dry season was higher than the wet season. In addition, the SO42- in Tuohe River and Suihe River is primarily caused by urban sewage and agriculture activities, while in Zhonghu and Shuoxihu SWA is mainly contributed by natural evaporate dissolution. Notably, the input of SO42- in the Huihe River and Linhuan SWA caused by mining activities cannot be disregarded. The aerobic environment and isotopic fractionation of surface water indicate that sulfide oxidation is not the major cause of SO42- formation. This work has revealed the multiple sources and transformation mechanisms of SO42-, and provided a reference for the development of comprehensive management and effective remediation strategies of SO42- contamination in surface water around mining areas.

Radon exhalation characteristics after pyrolysis of long flame coal

Coal pyrolysis is a important method for classifying and utilizing coal resources and contributes to enhanced comprehensive resource utilization. However, In high-temperature areas such as coal pyrolysis, there is an abnormal phenomenon release of radioactive gas radon, understanding the relationship between temperature and radon exhalation characteristics, as well as the underlying mechanisms, holds great importance for assessing radon pollution in mining areas. After coal undergoes pyrolysis under high temperature conditions, its material composition, pore structure, water content, and other properties have changed. The pyrolysis products in different atmosphere environments have differences, and the characteristics of radon emission are also different. To address this, the present study conducted coal pyrolysis experiments in both aerobic and anaerobic environments, using long flame coal sourced from Yulin, China. The radon release concentration of the pyrolysis products was measured. The research findings indicate that during pyrolysis at elevated temperatures, the ratio of coal mass loss is constantly increasing. High temperatures promote the development of pores and fissures, and significant changes in coal properties at temperature thresholds (300 °C and 500 °C). The specific surface area, pore volume, and fracture ratio all display substantial increases, and the amplitude of change is greater under aerobic conditions. The fractal dimension of total pores and macropores shows continuous growth, while the specific surface area, pore volume, and fracture ratio exhibit a strong negative correlation with the radon emission rate of pyrolysis products. The expansion and penetration of pores and cracks, along with the release of a substantial amount of pyrolysis gas, accelerate the transformation, migration, and exhalation of radon, resulting in a negative correlation between the heat treatment temperature and the radon release rate of pyrolysis products. Under aerobic conditions, the radon release rate of pyrolysis products decreases more significantly.

Distribution and transformation of potentially toxic elements in crack under coal mining disturbance

In China, coal provides about 56.8% of the energy. Most of China's coal mines are shaft mines, which cause the surface to collapse and crack during the mining process. The soil near the cracks changes its physicochemical properties due to the altered stress conditions. This will affect the distribution of PTEs in the soil. We collected 18 samples from a selected crack in the abandoned land. The pH, Eh, and PTE and their fractions of the samples were determined. With the test results, we understand the distribution characteristics of pH, Eh, PTEs, and their fractions at the cracks. Meanwhile, we explored the key factors that contribute to this distribution. It was determined that crack decreases surface soil pH while increasing Eh. The total amount of 7 PTEs is higher in the bottom soil of the main crack and 2 m away from the main crack. The content of reducible fractions of PTEs increases with the increase of soil Eh. The oxidizable and residual fractions of PTEs adsorbed to the clay particles migrate to and enrich the deeper layers of the main crack. This study emphasizes the effect of crack generation on the distribution of PTEs in soil. It provides insights to describe the distribution of PTE throughout the full life cycle of crack.

Phytoremediation strategies for heavy metal-contaminated soil by selecting native plants near mining areas in Inner Mongolia

Phytoremediation technology, as an eco-friendly and cost-effective approach, is widely used to restore soil contaminated by heavy metal(loid)s. However, the adaptability and absorption capacity of plants to multiple elements are the crucial factors affecting the application of phytoremediation in mining areas. In this study, dominant native plant species and their paired soils were collected near a lead-zinc mine in Inner Mongolia, to assess the ecological risk of heavy metal(loid)s and phytoremediation potential. The results showed that Cd and As were the dominant soil pollutants, with levels of 90.91% and 100%, respectively, exceeding the risk intervention values for soil contamination of agricultural land. The rates of Pb, Cu, and Zn exceeding the risk screening values were 69.70%, 60.61%, and 96.97%, respectively. Extremely high ecological risk of heavy metal(loid)s was observed in this area. The ability of native plants accumulating heavy metals varied among species. The bioconcentration factor (BCF) varied from 0.14 to 2.59 for Cd, 0.02 to 0.45 for As, 0.06 to 0.76 for Pb, 0.05 to 2.69 for Cr, 0.15 to 1.00 for Cu, and 0.22 to 4.10 for Zn. Chinese Cinquefoil Herb (Potentilla chinensis Ser.) showed the potential to accumulate multiple toxic elements based on the biomass, shoot content, translocation factor (TF), BCF, and metal extraction rate (MER), while, other species showed the potential to accumulate single toxic element: goosefoot (Chenopodium album L.), Lespedeza daurica (Laxm.) Schindl. and peashrubs (Caragana korshinskii Kom.), Herba Artemisiae Scopariae (Artemisia capillaris Thunb.), alfalfa (Medicago sativa L.), and Moldavian Dragonhead (Dracocephalum moldavica L.) for Cd, As, Cr, Cu, and Zn, respectively. Furthermore, wild leek (Allium ramosum L.), cogongrass (Imperata cylindrica (L.) Beauv.), fringed sagebrush (Artemisia frigida Willd.), and field bindweed (Convolvulus arvensis L.) were selected for phytostabilization of specific elements, considering the heavy metal contents in the roots and low TF values. This study provides a reference for selecting appropriate species for the remediation of heavy metal-contaminated soils in certain mining areas.

Immobilization of Cd in the soil of mining areas by FeMn oxidizing bacteria

Microorganisms are widely used in large-scale pollution remediation due to their rapid reproduction and low cost. In this study, bioremediation batch experiments and characterization methods were adopted to investigate the mechanism of FeMn oxidizing bacteria on the immobilization of Cd in mining soil. The results showed that the FeMn oxidizing bacteria successfully reduced 36.84 % of the extractable Cd in the soil. The exchangeable forms, carbonate-bound forms, and organic-bound forms of Cd in the soil decreased by 11.4 %, 8 %, and 7.4 %, respectively, due to the addition of FeMn oxidizing bacteria, while FeMn oxides-bound and residual forms of Cd increased by 19.3 % and 7.5 %, as compared to the control treatments. The bacteria promotes the formation of amorphous FeMn precipitates such as lepidocrocite and goethite, which have high adsorption capacity on soil Cd. The oxidation rates of Fe and Mn in the soil treated with the oxidizing bacteria reached 70.32 % and 63.15 %, respectively. Meanwhile, the FeMn oxidizing bacteria increased soil pH and decreased soil organic matter content, further decreasing the extractable Cd in the soil. The FeMn oxidizing bacteria have the potential to be used in large mining areas to assist in the immobilization of heavy metals.

Soil acidification in a tailing area of ionic rare earth in Southeast China

Ionic rare earth ores are now commonly mined using the ammonium sulfate in situ leaching method, causing soil acidification in tailings. To evaluate the degree of soil acidification in tailings and the influence of mining activities on acidification, we selected an ionic rare earth tailing and a nearby unmined area in Southeast China. This tailing had been closed for 12 years. We sampled the soil from the surface to the bedrock in layers and determined soil properties related to soil acidification. The results showed that the average soil pH was 5.0 in the unmined area and 4.5 in the mined area (tailing area). Rare earth mining led to a decrease in soil pH of 0.47 units per 10 years, which was 2-5 times higher than that of other land uses. The shallow soil acidification in the mined area is not affected by mining. Deep soils were significantly acidified and the H⁺ concentration in the soil solution was approximately nine times that of the unmined area soil. Deep soil acidification is influenced very little by natural factors. The average soil ammonium‑nitrogen (NH₄⁺-N) and nitrate‑nitrogen contents in the mined area were 58.34 mg kg^-1 and 8.19 mg kg^-1, respectively, 84 times and 21 times that of the unmined area. There were large amounts of NH₄⁺, NO₃^-, and H⁺ in the soil of the mined area, indicating that soil acidification is closely related to exogenous NH₄⁺-N input and nitrogen transformation. Nitrification is the most important driver of soil acidification in mining areas. Continued nitrification of excess NH₄⁺-N will continue to produce H⁺ and migrate with water, which will cause long-term harm to the soil and surrounding environment in the mining area. Therefore, it is necessary to remove the enriched NH₄⁺-N in tailings soil to avoid further soil acidification.

Exploring relationship of soil PTE geochemical and "VIS-NIR spectroscopy" patterns near Cu-Mo mine (Armenia)

PTE contamination of soils remains one of the global environmental concerns. The ways of detecting and monitoring PTE concentrations in soils varies including traditional field sampling accompanied by sample preparation and chemical analysis and state of the art visible and near-infrared (Vis-NIR) spectroscopic approaches. Among the different Machine Learning (ML) to extract soil information from spectra and to explore the relationship between spectral reflectance data and soil PTE content PLSR method is a well-established one to construct a soil PTE estimation model. This study aimed to explore the relationship of soil PTE geochemical and VIS-NIR spectroscopy characteristics in agricultural soils near Cu-Mo mine area in Armenia. PLSR method is applied to identify the links between the spectra and agricultural soil Ti, V, Cr, Mn, Fe, Co, Ba, Pb, Zn, Cu, Sr, Zr and Mo contents to reveal the potential of VIS-NIR spectroscopy in ex-situ monitoring of Kajaran soils. The results show that different portions of VIS-NIR spectra are responsible for Ti (1100-1200 nm, 2350-2500 nm), V (350-500 nm, 700-750 nm, 1000-1100 nm, 1400-2500 nm), Cr (1300-1400 nm, 1900-2100 nm) and Ba (450-500 nm, 600-800 nm, 1050-1700 nm, 2000-2100 nm, 2350-2400 nm) estimations through PLSR correspondingly. However, among the studied PTEs Ti and V, which shows significant negative correlations in VIS-NIR spectra registered at around 400-600 nm and 850-1150 nm regions, are remarkable and promising with the PLSR estimation results using VIS-NIR spectra Ti (R²_Test = 0.74), V (R²_Test = 0.71). This study shows that VIS-NIR spectroscopy has a high potential for the estimation of at least several PTE in soils and PLSR modelis reliable for deriving information from there.

A comprehensive assessment of heavy metal(loid) contamination in leafy vegetables grown in two mining areas in Yunnan, China-a focus on bioaccumulation of cadmium in Malabar spinach

Contamination of leafy vegetables grown in heavy metal(loid)-polluted mining areas pose serious health risks. This study aimed to explore the heavy metal(loid) contamination of leafy vegetables near two mining areas, by collecting samples from 14 different leafy vegetable species in Yunnan Province, China. The lead (Pb), cadmium (Cd), arsenic (As), and copper (Cu) contents of the samples were determined, and risks to human health were calculated using the hazard quotient and hazard index (HI). Moreover, Malabar spinach was identified as a leafy vegetable that exhibits low accumulation of heavy metal(loid)s. The accumulation capacity of different Malabar spinach varieties was verified, and a Cd soil safety threshold was determined using a pot experiment. Overall, Pb and Cd were the main soil and vegetable contaminants found in both study sites. The HI values for all leafy vegetables, apart from Malabar spinach, were greater than 1, indicating the presence of risks to human health; moreover, the health risks were greater for children than adults. The Malabar spinach pot experiment results showed that only some Cd forms exceeded China's maximum permissible standards. Furthermore, Malabar spinach varieties A (instant Malabar spinach), C (extra-large leaf green vine Malabar spinach), and F (large leaf Malabar spinach) displayed the lowest Cd accumulation. We calculated Cd total and bioavailable soil safety thresholds of 4.75 and 0.77 mg kg-1, respectively. However, further research is required to validate soil heavy metal safety thresholds for different vegetables. Ultimately, the heavy metal(loid) contamination of leafy vegetables described here was more serious than anticipated. Finally, the results of this study can inform residents living near these mining areas of a low-risk leafy vegetable, which will reduce the harm caused by heavy metal(loid) contamination in the area.

Migration, accumulation, and risk assessment of potentially toxic elements in soil-plant (shrub and herbage) systems at typical polymetallic mines in Northwest China

In grassland systems of the semi-arid mining area, the migration, accumulation, and bioavailability of potentially toxic elements (PTEs) are important ecological and health risk issues. Thirty-eight pairs of topsoil (0-20 cm) and plant samples were collected around Baiyin City and in Dongdagou stream valley to investigate the migration of PTEs in soils, transfer of PTEs in soil-plant (shrub and herbage) systems, and assess the risk in soils and plants. The total concentrations of PTE (Hg, As, Cu, Zn, Cd, and Pb) were analyzed following digestion in mixture acid solution, and bioavailable PTE was extracted with a strong chelating agent (DTPA-TEA-CaCl₂). The transfer factor (TF) and bioaccumulation factor (BCF) were calculated to examine the migration of PTEs in soil-plant. Hazard quotient (HQ) and total hazard index (THI) were calculated to assess the risk and migration of PTEs in soils. The results showed that PTEs in soils and plants of study area exceeded the soil background value and Hygienic Standard for Feeds. Correlation among the total Hg, As, Cu, Zn, Cd, and Pb in soils of Dongdagou stream valley was significant at p < 0.01. A good correlation was exhibited between PTEs in root/aboveground parts of plants and DTPA-soil extractable. Difference of TF and BCF was existed between Dongdagou stream valley and around Baiyin City. Hg, Cu, Zn, Cd, and Pb were mainly accumulated in soils near the mining area. The calculated THI exceeded 1, and As and Pb were the major risk factors. The ability to absorb and transfer Hg, As, Cu, and Pb of plants was lower in more serious polluted area. As had a stronger migration capacity in study area. PTEs in soils had an adverse health effect for residents, and PTEs in plants may cause toxicity to cattle and sheep.

Changes in arsenic accumulation and metabolic capacity after environmental management measures in mining area

Due to the public health concern of arsenic, environmental management measures in mining areas had been implemented. To assess the effect of environmental management measures in the mining area comprehensively, arsenic accumulation in the urine, hair, nails, and urinary metabolites of residents in a realgar mining area in Hunan province, China were investigated in 2019, and the changes in arsenic levels in the biomarkers during 2012-2019 were tracked. The importance of confounding factors (age, sex, occupation, residence, clinical history, vegetable source, cooking fuel, smoking, alcohol consumption, BMI) was analyzed using the Boruta algorithm. After the implementation of environmental management measures (including ceasing mining and smelting activities, building landfills, adjusting the planting structure, and soil restoration), urine, hair, and nail arsenic concentration decreased drastically but were still excessive. Arsenic accumulation was highest in older male miners who were long settled in the mining area and consumed homegrown vegetables. The only factor for changes in urinary arsenic levels was the cooking fuel type; residents using wood as cooking fuel experienced sustained arsenic exposure. Occupation and sex were important for determining arsenic changes in the hair and nails. Short-term arsenic accumulation in urine was affected by arsenic exposure, while long-term accumulation in hair and nails by arsenic metabolic capacity. The percentage of urinary arsenic metabolism and arsenic methylation indices of the participants in the mining area were within the normal range (%iAs: 10-30 %, %MMA: 10-20 %, % DMA: 60-80 %); samples indicated worse metabolic capacity than the reference population. The arsenic metabolic capacity of male miners was relatively weak, probably aggravated by alcohol drinking and smoking. Without soil remediation, arsenic exposure will continue. Homegrown vegetables and biomass fuels should be abandoned; reduced cigarette and alcohol consumption is recommended. Urinary arsenic would be more proper for assessing environmental remediation in mining areas.

Morphological characterization, hazardous metal contamination, source identification, and health risk assessment of the fine road dust from Dachang mining area, China

Dachang mining area in China is known as "paradise for mineralogists" due to its most reserves of Sn, Sb, Pb, and Zn non-ferrous metal resources; thus, its evaluation for heavy metal assessment and consequent health risk is unavoidable. Sixty road dust samples were collected from study area to explore pollution level, ecological, and health risks from heavy metals and were analyzed by an inductively coupled plasma optical emission spectrometer and atomic fluorescence spectrometer. The results showed that average concentration of all the heavy metals in road dust in both mining and residential areas were remarkable higher than its corresponding background values, the former being more severe, except for Cr and Co. The morphological investigation showed that most of the particles were much less than 100 μm illustrating fine part of the road dust samples. Based on integrated pollution indices, Cd, Sb, As, Zn, and Pb were extremely contaminated and exceeded hundred times of the maximum risk value. The health risk assessment revealed substantially higher carcinogenic and non-carcinogenic risks to children and adult. Highest non-carcinogenic risk resulted from arsenic in mining and residential area with HQ_ing of 644.56 and 267.94 respectively (standard HQ ≥ 1) while carcinogenic risk to children (1.94E + 00) which greatly exceeded from the threshold value of (1.0E-4). Sb, Cd, and Pb also posed carcinogenic and non-carcinogenic risk in road dust which is caused by excessive mining activities and heavy vehicle movement in the study area.

Geochemical fingerprint and spatial pattern of mine water quality in the Shaanxi-Inner Mongolia Coal Mine Base, Northwest China

The spatial distribution of mine water quality and geochemical controls must be investigated for water safety and ecosystem protection in Shaanxi-Inner Mongolian Coal Mine Base (SICMB). Based on 122 mine water samples collected from 14 mining areas, self-organizing maps (SOM) combining with principal component analysis (PCA) derived that the mine water samples were classified into seven clusters. Clusters 1 and 3 (C1 and C3) samples were dominant by HCO3-Ca and mixed types, which were distributed in the recharge area of the middle SICMB. In this area, the active groundwater circulation contributed to the good water quality. Cluster 2 (C2) samples were characterized by HCO3-Na type, mainly distributed in the discharge area of the middle SICMB. These samples were threatened by heavy fluorine contamination and high residual sodium carbonate (RSC) because of slow groundwater flow in this area. Clusters 4 and 5 (C4 and C5) samples, distributed in the northeast and middle SICMB, were characterized by high Cl- concentration and light fluorine contamination. They were influenced by anthropogenic input through faults or underground mining. In contrast, Clusters 6 and 7 (C6 and C7) samples with high salinity and sulfate were distributed in the southwest SICMB. The deep groundwater circulation enhanced water-rock interaction and contributed to poor water quality. These findings are beneficial to the management of mine water resources in the SICMB and provide an insight to investigate the mine water quality in large spatial scale.

Unmixing the coupling influence from driving factors on vegetation changes considering spatio-temporal heterogeneity in mining areas: a case study in Xilinhot, Inner Mongolia, China

Considering the spatio-temporal heterogeneity, this study resolved the coupling influence of a variety of driving factors on vegetation changes in mining areas and discovered the influencing characteristics of the respective driving factors, especially mining activities. First, the spatio-temporal characteristics of FVC (fractional vegetation cover) variation were analyzed in the Sheng-Li mining area. Second, the quantitative relationships among the natural factors (temperature, precipitation, and elevation), artificial factors (mining activities, urban activities), and FVC were constructed by GTWR (geographically and temporally weighted regression) to quantify the contribution of each factor to the change in FVC. Third, the influencing characteristics of the respective driving factors, especially mining activities, were analyzed and summarized. The results show that (1) the FVC change was mainly influenced by natural factors in the areas far from mines and towns and artificial factors in the areas close to mines and towns. (2) The contribution of mining activities to vegetation change (C-Mine) was spatially characterized by two features: (a) distance attenuation characteristics: C-Mine showed logarithmic decrement with distance; (b) directional heterogeneity: C-Mine varied significantly in different directions. In particular, there was a high C-Mine area located near multiple mining areas, and the range of this area shifted to include the mine with more production over time. Overall, unmixing the coupling influence from driving factors with spatio-temporal heterogeneity and achieving a quantitative description of the influencing characteristics in mining areas were the main contributions of this study. The quantification methods and results in this paper provide important support for decision-making on ecological protection and restoration in mining areas.

Physiological adaptability of three gramineae plants under various vegetation restoration models in mining area of Qinghai-Tibet Plateau

Large-scale coal mining activities on the QTP have affected the natural grassland ecosystem which will take decades to recover. Therefore, looking for an effective vegetation restoration method is the most effective way to restore the ecosystem. In this study, we explored the effects of three vegetation restoration modes (coal mine spoils planting (CK), organic fertilizer planting (OF), and cover soil planting (CS)) on the five cold-resistance related physiological indices of three native Gramineae plants (Elymus nutans, Poa crymophila and Festuca sinensis) growing in three different habitats (shady slope, sunny slope, and flat slope). The higher contents of soluble sugar (SS) in the Elymus nutans (213.46 mg/g) and Festuca sinensis (202.84 mg/g) were recorded under the CS treatment in the sunny slope habitat. The FP contents of Elymus nutans (421.31 μg/g), Poa crymophila (310.06 μg/g), and Festuca sinens (288.45 μg/g) were higher under the CK treatment in the flat ground habitat. The higher (P < 0.05) content of chlorophyll (Chl) was recorded in the Elymus nutans (2.13 mg/g) under the CS treatment in the sunny slope habitat compared to the other two plants. We observed lower MDA contents in the Elymus nutans (3.19 nmol/g) and Festuca sinensis (3.56 nmol/g) under the CK treatment growing in the shady slope habitat. In the shady slope habitat, the H₂O₂ contents of Elymus nutans (15.86 μmol/g), Poa crymophila (6.78 μmol/g), and Festuca sinensis (8.76 μmol/g) under the CS treatment were significantly lower compared to other treatments. Based on membership function method, the low-temperature adaptability order of the three restoration plants from strong to weak was Elymus nutans > Festuca sinensis > Poa crymophila. While the effectiveness order of the three vegetation restoration models in alpine mining areas from good to bad was CS > OF > CK. This study will provide a theoretical and guiding significance to evaluate the effectiveness of different restoration methods, formulate optimal restoration strategies and guide the sustainable restoration of the damaged ecosystems of the alpine mining areas.

Probabilistic health risk assessment for residents exposed to potentially toxic elements near typical mining areas in China

Public health problems caused by toxic elements in mining areas have always been an important topic worldwide. However, existing studies have focused on single exposure routes and common toxic elements, which might underestimate the risks faced by residents. In this study, three typical mining areas in central China were selected to assess the health risks of 14 potentially toxic elements through five exposure routes using Monte Carlo simulations. The results indicated that the 95th percentile non-carcinogenic risk values to humans via rice and vegetable ingestion ranged from 9.8 to 26.0 and 6.2 to 19.0. The corresponding carcinogenic risks ranged from 1.4E-2 to 6.3E-2 and from 2.9E-3 to 2.3E-2, respectively. Therefore, residents face serious health risks. Multi-element analysis showed that cadmium (Cd), boron (B), and arsenic (As) were the main contributors to rice non-carcinogenicity, whereas Cd and nickel (Ni) were the main elements of rice carcinogenicity. B and lead (Pb) played an essential role in the non-carcinogenesis of vegetables, and B, Ni, and Cd played an essential role in carcinogenesis. Accidental ingestion is the main route of soil exposure. In these three areas, the probability of non-carcinogenic risk faced by adults was 40%, 0%, and 1%, respectively, while the probabilities for children were 100%, 62%, and 83%, respectively. Regarding carcinogenicity, the risk for both adults and children was up to 100%. This study emphasizes the overall health risks in polluted areas via multi-route and multi-element analysis. This conclusion is helpful to comprehensively assess the potential health risks faced by residents in mining areas and provide baseline data support and a scientific basis for formulating reasonable risk control measures.

The temporal response of dissolved heavy metals to landscape indices in the Le'an river, China

Heavy metals in watersheds are a serious concern due to their toxicity, abundance, and persistence in the environment, especially in mining areas. Source analyses and exploration of other related factors are one of the most important methods to help with effective prevention and control of heavy metal pollution in watersheds. In this study, the concentrations of Cr, Co, Ni, Cu, Zn, As, Cd, Sb, Ba and Pb were measured in the Le'an River, and PCA (principal component analysis) and APCS-MLR (absolute principal component scores - multivariate linear regression) methods were used to identify the sources of the dissolved heavy metals. Additionally, a CA (correlation analysis) method was used to explore the correlations between landscape indices and concentrations of heavy metals. Results show that the main sources for these dissolved heavy metals are mining activities, fertilizers, pesticides, and natural sources. Specific results of PCA and APCS-MLR suggest that Cu, Zn, Cd, Ba are mainly related to mining activities, Cr and Pb are due to fertilizers and pesticides, and Co and Ni are mainly due to natural sources. Correlations between landscapes and heavy metals revealed significant temporal variations, with the strongest responses of dissolved heavy metals to landscape indices appearing in December and March. The propensity of positive or negative responses of the heavy metals to landscape indices are determined by the sources, and their temporal variations may be related to the seasonal changes of rainfall and plant metabolism.

Heavy metals speciation and distribution of microbial communities in sediments from the abandoned Mo-Ni polymetallic mines, southwest of China

Chemical fractions of heavy metals (Mo, Ni, Cu, Zn, Fe, Mn, Pb, Cd, and Cr) and compositions of bacteria and fungi in surface sediments from the Mo-Ni polymetallic mine area were analyzed. The results indicated that the mean concentrations of Mo, Ni, Cu, Zn, and Cd were higher than their background values. The mean percentage of Cr in residual fraction was much higher than that of other heavy metals. Mo, Cu, Zn, Fe, and Pb were mainly associated with oxidizable fraction. The dominant proportions of Mn and Cd were found in exchangeable fraction with mean percentages of 93.46% and 54.50%, respectively. According to RAC classification and potential ecological risk index (PERI), the Cd with high bioavailability had a very high environmental risk. The MisSeq sequencing results of bacteria and fungi revealed that microbial communities discrepantly respond to different sampling sites. The most abundant phylum of bacteria and fungi were Proteobacteria and Ascomycota, respectively. The bioavailable heavy metals including Mo-B, Pb-B, and Cd-B were recognized to have important influences on both dominant bacterial and fungal communities. The present study manifested that the bioavailability of heavy metal is very important to assess the potential environmental risk and plays a key role in shaping microbial structure.

Soil contamination and health risk assessment from heavy metals exposure near mining area in Bac Kan province, Vietnam

Mining activities in Vietnam have resulted in potential heavy metals contamination, which unfavorably influences soil quality and represents a risk to human health. This study was designed to investigate the heavy metals contamination in the vicinity of the Pb-Zn and Au mines. Soil samples were collected along the stream, and then, solutions were prepared by a modified Aqua Regia method. They were analyzed by ICP-MS for trace elements, and the analytical result data of 7 elements (As, Cd, Co, Cu, Ni, Pb, and Zn) were used to define pollution indices with statistical results and to interpret the health risk assessment. For the preliminary identification of the pollution sources near the Pb-Zn mine of the elements, statistical analysis (including principal component analysis and Spearman correlation coefficient) and information about mineral composition ore and surrounding rocks were applied. The analytical results of heavy metals showed that the average concentrations of As and Pb were higher than the Vietnam standard for residential soil by about eight and three times, respectively. Pollution indices also indicated that Pb and As were the highest contamination factors in the soil near Pb-Zn mine and Au mine, respectively. Statistical analysis results revealed that the pollution sources of these elements in the soil near the Pb-Zn mine were a combination of anthropogenic and geogenic sources. Health risk assessment pointed out that children were at higher risk than adults in both non-carcinogenic and carcinogenic risk.

Nitrate sources and transformations in surface water of a mining area due to intensive mining activities: Emphasis on effects on distinct subsidence waters

The increase in NO₃^- content in surface water caused by intensive mining activities in Huainan City, China, has attracted considerable attention owing to the deterioration of water quality and the degradation of ecosystems in recent years. The Huainan mining area, which is highly disturbed by anthropogenic activities, was selected as a typical observation area, and the surface water was classified as open subsidence water (OSW), closed subsidence water (CSW), and river water (RW). Moreover, the hydrochemical parameters and the δ¹⁵N and δ¹⁸O values of nitrate were employed to quantitatively trace the sources and biochemical transformation of NO₃^-, and the contribution ratios of different NO₃^- sources were estimated using the stable isotope analysis in R based on the Bayesian model. There was evident nitrification in the study area, but no significant denitrification has occurred. A substantial portion of δ¹⁵N-NO₃^- demonstrated complex sources of NO₃^-. Compared with those of CSW, the NO₃^- compositions of the OSW approached to those of the RW due to river recharge and discharge, and were greatly affected by anthropogenic activities. The proportional contribution of manure and sewage in the OSW was found to be the highest with a mean value of 39.5 % ± 12.3 %, which was followed by that of mine drainage (mean: 22.1 % ± 13.1 %), chemical fertilizer (mean: 17.5 % ± 10.6 %), and soil organic nitrogen (mean: 17.5 % ± 11.6 %). In the RW, the highest mean contribution of manure sewage was 35.2 % ± 9.7 %, which was followed by that of chemical fertilizer (mean: 29.3 % ± 7.2 %), mine drainage (mean: 23.4 % ± 13.0 %), and soil organic nitrogen (mean: 10.9 % ± 8.3 %). In contrast, the contribution of chemical fertilizer to the CSW was the highest with a mean value of 33.9 % ± 13.6 %, which was followed by that of soil organic nitrogen (mean: 26.5 % ± 13.8 %), mine drainage (mean: 18.1 % ± 11.6 %). Therefore, NO₃^- in the surface water of the mining area primarily originates from chemical fertilizers and manure sewage. In addition, the contribution of mine drainage to nitrate in the study area indicates the potential impact of mining activities on surface water. These findings highlight the value of classifying different types of surface water in tracing NO₃^- contamination sources, and provide relevant theoretical basis for tracing nitrate sources in other areas.

Assessment of the environmental changes in arid and semiarid mining areas using long time-series Landsat images

Coal mining provides energy to support the development of society. However, mining affects the environment. Thus, substantial attention has been placed on environmental change in mining areas. Research assessing the environmental change in arid and semiarid mining areas has mainly been conducted by analyzing the variation in a single factor. However, the impact of coal mining on the environment is manifold, and there is no comprehensive assessment method. In this paper, we used a remote sensing index referred to as the comprehensive evaluation index (CEI) to comprehensively assess the environmental changes in arid and semiarid mining areas. The CEI in this study was calculated by integrating the changes in vegetation coverage (VC), land surface temperature (LST), and soil moisture (SM) using long time-series Landsat images. The Shendong mining area located in Northwest China was the study area. The results indicate that the environment of the Shendong mining area improved overall from 2000 to 2018. Environmentally degraded areas accounted for approximately 7.59% of the mining area and were concentrated in areas damaged by coal mining.

Evaluating the genesis and dominant processes of groundwater salinization by using hydrochemistry and multiple isotopes in a mining city

The increasing salinization of groundwater renders it challenging to maintain the water quality. Moreover, knowledge regarding the characteristics and mechanism of groundwater salinization in mining areas remains limited. This study represents the first attempt of combining the hydrochemical, isotope (δD, δ¹⁸O, δ³⁷Cl, and ⁸⁷Sr/⁸⁶Sr) and multivariate statistical analysis methods to explore the origin, control, and influence of fluoride enrichment in mining cities. The TDS content of groundwater ranged from 275.9 mg/L to 2452.0 mg/L, and 54% of the groundwater samples were classified as class IV water according to China's groundwater quality standards (GB/T 14848-2017), indicating a decline in the water quality of the study area. The results of the groundwater ion ratio and isotope discrimination analysis showed that dissolution and evaporation involving water-rock interactions and halite were the main driving processes for groundwater salinization in the study area. In addition to the hydrogeological and climatic conditions, mine drainage inputs exacerbated the increasing salinity of the groundwater in local areas. The mineral dissolution, cation exchange, and evaporation promoted the F^- enrichment, while excessive evaporation and salinity inhibited the F^- enrichment. Gangue accumulation and infiltration likely led to considerable F^- enrichment in individual groundwater regions. Extensive changes in the groundwater salinity indicated differences in the geochemical processes that controlled the groundwater salinization. Given the particularity of the study area, the enrichment of salinization and fluoride triggered by mining activities cannot be ignored.

Spatial patterns of Zn, Cd, and Pb isotopic compositions of ground and surface water in mine areas of South Korea reflecting isotopic fractionation during metal attenuation

As application of multiple metal isotopes can effectively constrain geochemical behavior of contaminants and assess contamination sources and pathways, field-scale studies on the geochemically interlinked fractionation of Zn and Cd isotopes in groundwater are needed. In this study, we collected groundwater samples from multi-level samplers downstream of tailings dumps as well as surface water, ore mineral, precipitate, and tailings samples at the Sambo and Buddeun metallic ore mines in South Korea, and analyzed their Zn, Cd, Pb, and sulfur isotopic compositions. Furthermore, isotopic ratios of ore mineral samples from additional four mines in South Korea (Dangdu, Dongbo, Gomyeong, Samgwang) were compared. A dual isotopic approach using Zn and Cd isotopes was used to assess fractionation processes, and Pb isotopic signatures reflecting their sources were assessed. Increasing trends of δ⁶⁶Zn and δ¹¹⁴Cd with decreasing Zn and Cd concentrations were observed in groundwater, which was saturated with respect to ZnS (amorphous and sphalerite) and CdS (greenockite). Moreover, for some groundwater samples, δ⁶⁶Zn showed a positive relationship with δ³⁴S_SO4. These results suggest that Zn and Cd are precipitated as sulfide following sulfate reduction. In the plot of δ⁶⁶Zn against δ¹¹⁴Cd, relatively high and/or increasing δ⁶⁶Zn in groundwater suggested the effect of fractionation due to sulfide precipitation, while variable and high δ¹¹⁴Cd values suggested the fractionation by adsorption and/or sulfide precipitation, which were based on positive fractionation factors for δ⁶⁶Zn and δ¹¹⁴Cd during sulfide precipitation and mostly negative and positive fractionation factors for δ⁶⁶Zn and δ¹¹⁴Cd, respectively, during adsorption. This study shows that the combined use of Zn and Cd isotopes in groundwater can effectively differentiate between adsorption and sulfide precipitation following sulfate reduction in groundwater. Additionally, the ²⁰⁸Pb/²⁰⁶Pb ratios of most water samples reflected those of ore and tailings samples, which verified usefulness of Pb isotopes in water in investigating Pb contamination sources.

Identification of nitrate sources and transformations in basin using dual isotopes and hydrochemistry combined with a Bayesian mixing model: Application in a typical mining city

The external nitrogen load input caused by human activities exacerbates the eutrophication process of aquatic ecosystems in mining areas, causing water quality problems. However, knowledge of the sources and environmental behavior of nitrate in the surface water of mining areas is still very limited. This study investigated the nitrate content and spatiotemporal variation characteristics of surface water in the Linhuan mining area, identified the sources and transformation processes of nitrate using isotopes and hydrochemistry, and evaluated the contribution rates of different potential nitrate sources based on a Bayesian mixing model. The nitrogen pollution in the surface water in the mining area seriously exceeded class Ⅴ of the Environmental Quality Standard of Surface Water of China (GB3838-2002). The NO₃^- content ranged from 0.87 to 3.41 mg/L, showing obvious seasonal and spatial differences. Isotope and NO₃^-/Cl^- analysis indicated that nitrate in the subsidence area water (SAW) was mainly derived from chemical fertilizer (NF) and soil organic nitrogen (NS), while nitrate in the mainstream of the Huihe River water (HRW) was mainly derived from manure/sewage (MS). The nitrate in the tributary of the Baohe River water (BRW) was mainly derived from soil NS, and nitrification was a nitrogen conversion pathway in the soil. The results of the Bayesian mixing model showed that the main sources of nitrate in the BRW, HRW and SAW were NF (34.5%), MS (68.8%) and NF (40.8%) in the wet season, and NS (33.4%), MS (70.9%) and NF (58.1%) in the dry season, respectively. The results of this study provide a new integrated method for the identification of nitrate pollution sources in mining areas, and this method can be used to improve the biogeochemical information of nitrogen in the aquatic ecosystems of mining areas and help formulate relevant measures to reduce water nitrogen pollution.

Naturally selected dominant weeds as heavy metal accumulators and excluders assisted by rhizosphere bacteria in a mining area

Managers need more practical and promising plants for use in heavy metal phytoremediation. Although previous studies have identified the potential of some weeds and microbial strains in phytoremediation, the potential of dominant weeds and the relationship between weeds and their rhizosphere bacterial strains are still unknown. In our study, we examined dominant weeds in the Dabaoshan mine located in Guangdong province, China to test their abilities as heavy metal accumulators and excluders. Results suggest that Ludwigia prostrata exhibited the highest potential for accumulating Cu, Pb and Zn compared with the other plants. Specifically, L. prostrata accumulated 71.58, 130.76 and 454.72 mg kg^-1 of Cu, Pb and Zn, respectively; the species' translocation factor of Zn was 2.04, indicating a high accumulation of Zn. In contrast, the Cd translocation factor (TF) of Digitaria sanguinalis was 0.18, significantly lower than that of other plant species examined. Our results suggest that Ludwigia prostrata hyperaccumulates Zn and may also serve as a potential candidate remediation plant for Cu and Pb due to its high absolute accumulation amount of Cu and Pb, while Digitaria sanguinalis may be a potential candidate as a Cd excluder. We also found that rhizosphere bacterial communities were shaped by individual dominant plant species. Chloroflexi was the most dominant phylum in accumulator plant such as Fimbristylis miliacea, while Cyanobacteria was the most dominant phylum in excluder plant such as Digitaria sanguinalis. Our study provides insights for selecting new weedy forbs and grasses, rhizosphere bacterial species and developing approaches for phytoremediation and phytostabilization.

Source apportionment of heavy metal and their health risks in soil-dustfall-plant system nearby a typical non-ferrous metal mining area of Tongling, Eastern China

The agricultural land-atmospheric dustfall-plant system around the mining area is at high risks of heavy metal pollution caused by mining-smelting activities. In this study, 118 samples (including rhizospheric soils, background soils, soil-forming parent rocks, crops, vegetables, medicinal plants and atmospheric dustfall) were collected nearby Tongling Cu-Fe-Au mining area, Eastern China. We studied the concentrations, migration, sources, and health risks through consumption of two main crops (corn and rice), six kinds of vegetables, and medicinal plants (Fengdan, Paeonia ostii) for six metal elements (Cu, Zn, Cr, Cd, Pb and Hg). Results revealed Cr and Cd in soils, and Cd, Cr, Pb, Cu and Zn in dustfall showed a relatively high contamination degree. The mean contents of Cr and Pb in corn kernels, as well as Cd, Cr and Pb in rice grains and all vegetables, and Cr in Fengdan cortex moutan exceeded the corresponding food safety limits in China. The transfer capability of Cr in corn kernels and rice grains, Pb in edible vegetables, and Cd in cortex moutan were the strongest, respectively. Health risk assessment results showed Cr had the greatest non-carcinogenic risk, followed by Pb and Cd. The results of pearson's correlation analysis (CA), hierarchical cluster analysis (HCA), and principal component analysis (PCA) indicated Zn-Cr, Pb and Cd-Cu-Hg in the plants might derive from different geochemical end-members. Source apportionment based on lead isotope showed that mining-smelting activities were the major source of Pb in atmospheric dustfall and agricultural soils, with the average contribution rates of 66% and 50%, respectively. Vehicle emissions from diesel fuels (50%-68%) and mining-smelting activities (16%-25%) contributed mainly to Pb accumulation in plants. Hence, our study suggested the accumulations of Pb in plants might be mainly from the direct foliar uptake of atmospheric Pb related to vehicle emissions and mining-smelting activities.

Potentially toxic metal contamination and microbial community analysis in an abandoned Pb and Zn mining waste deposit

Bioindicators have been widely used to assess the contamination of lead/zinc (Pb/Zn) in smelter areas, mining waste disposal areas and in areas containing slags from Pb ore smelting. In this context, the analysis involving microorganisms has gained prominence as a complementary tool in studies aimed at assessing contaminated sites. Therefore, the objective of this study was to assess the contamination of Pb, Zn and cadmium (Cd) in an area where a PbZn smelter operated, using the integration of geochemical and microbial data. The experimental analysis was conducted to characterize the soil collected at three different sites (samples NS, EW and EP). The analysis conducted was physicochemical, metal concentration, metal speciation and analysis of the microbial community through high-throughput sequencing technique. Through the results it was observed that the high concentrations of metals altered the bacterial community present in the soil. Differences were noted between the microbial communities according to the sampling site, especially in sample EP, collected at the margin of the dirt road, which presented higher metal concentrations and microbial diversity. The main phyla detected in the samples were: Proteobacteria, Bacteroidetes and Acidobacteria. Bacteria tolerant to the presence of potentially toxic metals (PTM), such as Rhodoplanes, Kaistobacter, Sphingomonas and Flavisolibacter were identified in the analyzed samples. The phylogenetic groups identified in the study area are similar to those obtained in other studies in metal contaminated areas. The differences between the bacterial communities in each sample indicate that the concentration of PTM may have influenced the microbial community in the soil. Thus, it is noted the importance of the integration of geochemical and microbial data to evaluate the impact of the improper disposal of high PTM concentrated slags in natural soils.

Manganese tolerance and accumulation characteristics of a woody accumulator Camellia oleifera

This study intended to help illustrate the Mn accumulation ability of Camellia oleifera and provide it as a novel species for possible use in Mn-contaminated sites. Field surveys have been carried out on Mn accumulation in C. oleifera growing near Mn mining area in Hezhou. Pot growth experiments in soil and sand culture were conducted to investigate Mn tolerance, accumulation, and translocation patterns in C. oleifera. C. oleifera grew well and showed no symptoms of Mn toxicity at a Mn treatment level below 1026 mg kg^-1 in soil culture and 15.0 mmol L^-1 in sand culture. Mn concentrations in leaves and stems reached a maximum of 9612.8 ± 83.5 and 6134.8 ± 94.0 mg kg^-1, respectively, in soil culture and 28,465.8 ± 1276.7 and 15,398.4 ± 1148.6 mg kg^-1, respectively, in sand culture. Meanwhile, most of the Mn taken from the substrates was transported to the aboveground tissues in soil and sand culture, e.g., over 92.07% of the total Mn taken up by C. oleifera was translocated to shoots in the 10.0 mmol L^-1 treatment. Our findings confirmed that C. oleifera exhibited extraordinary Mn accumulation and toleration abilities, and C. oleifera was a suitable species for phytoremediation of Mn-contaminated sites in Guangxi Province.

Multistage remediation of heavy metal contaminated river sediments in a mining region based on particle size

Sediment pollution is an important environmental problem, and the remediation of heavy metal contaminated sediments is crucial to river ecosystem protection, especially in mining regions. In this work, characteristics of heavy metals (Cu, Zn, Cd, As and Hg) were investigated, including contents and fractions based on particle size (PS) in river sediments. Chemical leaching and stabilization for sediment remediation were performed, and the technology feasibility was assessed. The results indicated that the heavy metals were primarily reserved within fine sediments (PS < 75 μm), comprising 79.8% of the total. For the sequentially extracted fractions, residual fraction dominated the total content in large PS sections (PS > 150 μm), while the oxidizable fraction, reducible fraction and weak acid extractable fraction dominated the total content in fine sediments, except for that of Hg. Chemical leaching can transform most metals in sediments from large-sized particles to fine particles because the metals are absorbed by fine particles in solution rather than complexation. The stabilization suggested that cement could be an effective agent for ecological risk control for heavy metals. In field engineering, a total of 145,000 m³ sediment was divided into various sections by PS and synchronously washed by eluting agents. Finally, clean sediments (PS > 150 μm) were used as building material and clean backfilling; meanwhile, heavily polluted sediments (PS < 150 μm) were buried as general industrial solid waste after stabilization treatment. Over 90% of the contaminated sediments were reused throughout multistep remediation. Furthermore, a reduction in waste and harm, along with resources, was obtained. This study provided a feasible technology for heavy metal contaminated sediment remediation.

Verbal Memory and Learning in Schoolchildren Exposed to Manganese in Mexico

Manganese (Mn) is an essential nutrient for cellular function, but in high concentrations, it is neurotoxic. Environmental exposure to Mn has been associated with cognitive effects in children. This study aimed to assess the effect of environmental exposure to Mn on verbal memory and learning in schoolchildren residents from two municipalities in the state of Hidalgo, Mexico. Cross-sectional studies were conducted in 2006 and 2013 with a total of 265 schoolchildren of 7 to 11 years old. Children's Auditory Verbal Learning Test-2 (CAVLT-2) was used to assess verbal memory and learning. Mn exposure tertiles were defined according to hair manganese (MnH) levels determined by atomic absorption spectrophotometry. Linear regression models were used to estimate the association between MnH levels and CAVLT-2 scores. The models were adjusted by potential confounders. The lowest and highest exposure tertiles were defined below and above MnH levels of ≤ 0.72 and ≥ 3.96 μg/g, respectively. Mn exposure was significantly associated with an average of 5- to 9-point decrease in learning curves and summary CAVLT-2 scores in the highest tertile. This study adds to the evidence of decreased verbal memory and learning in schoolchildren environmentally exposed to manganese.

Changes of solute transport characteristics in soil profile after mining at an opencast coal mine site on the Loess Plateau, China

Dramatic changes in soil during opencast coal mine activities inevitably change soil water and solute movement. The objectives of this study were to assess the effects of mining on solute transport in different soil profiles and to find the relationships between solute transport parameters and soil physicochemical characteristics. After taking undisturbed soil columns from the different soil profiles of natural land (NLs) and reclaimed mine land (RLs), ammonium nitrate displacement studies were conducted, and the breakthrough curves (BTCs) of NO₃^- and NH₄⁺ were obtained. Due to mining and reconstruction, soil texture became coarser, bulk density increased 2.77-15.15%, cation exchange capacity (CEC), soil organic matter (SOM), and total nitrogen (TN) content decreased 19.54-37.25%, 53.66-72.05%, and 42.58-58.55%, respectively. Additionally, the distributions of the physicochemical properties changed. The BTCs of NO₃^- for all soil columns can be well explained by both the convection-dispersion equation (CDE) and the two-region model (T-R). The transport parameters average pore water velocity (v), dispersion coefficient (D), and dispersivity (λ) were lower in RLs, which indicates that solutes became difficult to penetrate after mining. A significantly correlated relationship of bulk density and soil texture with the v, D, and λ parameters only occurred in the RLs samples. This result indicates that transport processes in NLs columns became more complicated and that soil texture and bulk density played an important role in the transport process of RLs columns. The two-site model could well describe NH₄⁺ transport for both NLs and RLs and provided a slightly better fit in RLs. This finding also gave evidence that RLs became homogeneous after mining and reconstruction. The parameter retardation factor (R) was significantly correlated to CEC, bulk density and soil texture in RLs. These results suggest that soil becomes homogeneous after mining and reconstruction and that high bulk density and fine soil texture could decrease the risk of leaching of solutes.

Different exposure profile of heavy metal and health risk between residents near a Pb-Zn mine and a Mn mine in Huayuan county, South China

Heavy metal contamination of environmental media in mining area is a global major concern because of its potential threat for human health through food chain. However, the comparison of exposure level and health risk is scarce among people living in the vicinity of mining area with different pollution source. In this study, the concentrations of Mn, Cd, As, Pb, Cu, Zn, Cr and Ni in soil, air, water, rice, vegetable, fish, poultry meat and pork from a Pb-Zn mining area and a Mn mining area in Huayuan county, China were determined by inductively coupled plasma mass spectrometry. Results showed that the environmental media and foodstuffs in the two areas were contaminated by Cd, Pb, Zn, Cu, Cr and Ni. However, the pollution was more serious in Pb-Zn mining area than Mn mining area. The total hazard index (HI) was 6.59 and 4.55 in Pb-Zn mining area and Mn mining area, respectively, indicating a moderate non-carcinogenic risk of local people. As intake via rice ingestion was the predominant contributor to the total HI in the two mining areas, accounting for 25% and 35%, respectively. For Pb-Zn mining area, Cd intake through vegetable consumption and Mn intake via air inhalation appeared to be another two important components contributing to HI. This study highlights the multi-element and multi-pathway exposure assessment to evaluate the potential health risk and emphasizes concerns to reduce As and Cd in agricultural products as well as Mn in air to decrease the detrimental health effects of local resident.

Effective phytoremediation of low-level heavy metals by native macrophytes in a vanadium mining area, China

Heavy metal contamination, particularly vanadium contamination in mining and smelting areas, is a worldwide serious problem threatening the ecological system and human health. The contamination level of vanadium, arsenic, cadmium, chromium, mercury, and lead in sediments and waters in a vanadium mining area in China was investigated in the present study. The behavior of heavy metal uptake by 12 native aquatic macrophytes was evaluated, including 5 species of emergent aquatic plants (Acorus calamus, Scirpus tabernaemontani, Typha orientalis, Phragmites australis, and Bermuda grass), 3 species of floating plants (Marsilea quadrifolia, Nymphaea tetragona, and Eleocharis plantagineiformis), and 4 species of submerged plants (Hydrilla verticillata, Ceratophyllum demersum, Myriophyllum verticillatum, and Potamogetom crispus). Different heavy metal accumulation abilities were found across these macrophytes. Generally, they tended to accumulate higher contents of chromium, and C. demersum showed a particularly higher accumulation capacity for vanadium. The heavy metals were preferentially distributed in roots, instead of translocation into leaves and stems, indicating an internal detoxification mechanism for heavy metal tolerance in macrophytes. In 24-day laboratory hydroponic experiments, the macrophytes had a satisfied phytoremediation performance for heavy metals, when their concentrations were at the microgram per liter level. Particularly, vanadium was effectively removed by P. australis and C. demersum, the removal efficiencies of which were approximately 50%. In addition, a combination of terrestrial plant (Bermuda grass) and aquatic macrophytes (P. australis, M. quadrifolia, and C. demersum) exhibited high uptake capacity of all the six heavy metals and their residual concentrations were 95 (vanadium), 39.5 (arsenic), 4.54 (cadmium), 17.2 (chromium), 0.028 (mercury), and 7.9 (lead) μg/L, respectively. This work is of significant importance for introducing native macrophytes to remove low-level heavy metal contamination, particularly vanadium, and suggests phytoremediation as a promising and cost-effective method for in situ remediation at mining sites.

Continuous impact of mining activities on soil heavy metals levels and human health

Soils samples collected during different geochemical surveys of the city of Kajaran located near the biggest Cu-Mo mining area in Armenia were subjected to the multivariate geostatistical analysis and geochemical mapping in order to reveal soil heavy metals spatial distribution pattern and assess human health risk level under continuous impact of mining activities. In addition, human health risk assessment was done for the contents of Pb, Cu, Zn, Co, Mo, Mn, Ti, and Fe. The results of Principal Component Analysis and Cluster Analysis verify each other and were also complemented by the spatial distribution features of studied heavy metals indicating that two groups of elements have been generated. The first anthropogenically predominated group includes the main industrial elements Mo and Cu, and their accessories Pb and Zn while Ti, Mn, Fe and Co with the naturally predominant contents were observed in the second group. Moreover, the study reveals that the superposition of geogenic and anthropogenic components lead to the alteration of the shapes of areas with the high natural contents of heavy metals and formation of polluted areas with the intensive anomalies of elements. Health risk assessment showed that Mo was the only studied element which poses a non-carcinogenic risk to adult and children's health in some sampling sites during the whole period of investigations. Moreover, in all studied locations multi-elemental non-carcinogenic risk to children health from all studied heavy metals were detected. Special attention was given to the soils of kindergarten territories, and the results indicated that Hazard Index in kindergartens was >1 indicating an adverse health effect to children. The results obtained can serve as a basis for the development and implementation of risks reduction measures and systematic monitoring program planning.

Heavy metal content of edible plants collected close to an area of intense mining activity (southern Portugal)

The Neves-Corvo mining complex (MC) situated in southern Portugal exploits one of the most world's important copper deposits. Agricultural soils surrounding the MC, used by the inhabitants for crop production, contain excessive amounts of As, Cu, Pb, and Zn. Thus, a potential risk to human consumption exists if edible plants grow on these substrata. Arsenic and Pb were not detected in edible samples collected near the MC and 5 km away, but in the leaves-structural or adsorbed onto the surface. In general, Zn was the most mobile element in both contaminated and reference areas as seen by the bioaccumulation factors (BAF). The tolerable upper intake (TUI) values for Cu are a reason of concern, since in 57.1% of the cases, the TUI values are above the recommended upper limit of 5 mg/day, in the case of Ficus carica, Cucurbita pepo, and Phaseolus vulgaris, whereas in 28.6% of the cases, the TUI values are near this limit (C. pepo and Citrus x sinensis). The consumption of such vegetables from these areas must be banned or strongly reduced, since long-term accumulation of Cu can cause a chronic toxicity in humans.

Improvement of cadmium phytoremediation by Centella asiatica L. after soil inoculation with cadmium-resistant Enterobacter sp. FM-1

This study examined the potential of a cadmium-resistant Enterobacter sp. FM-1 to promote plant growth and assist in cadmium accumulation in both mine-type C. asiatica L. and non-mine type C. asiatica L. tissues in highly cadmium-polluted soils. The results indicated that Enterobacter sp. FM-1 significantly promoted growth and alleviated metal toxicity in both types of C. asiatica L. Meanwhile, inoculation with Enterobacter sp. FM-1 in contaminated soil can increased cadmium bioavailability in soil. Furthermore, it will increase plant uptake and the accumulation of cadmium in C. asiatica L. leaves, stems and roots compared to that in an uninoculated plant. However, mine-type C. asiatica L. had better cadmium tolerance than the non mine-type C. asiatica L. Because of its native metal-tolerant ability, which could easily grow and proliferate, and had a better performance under cadmium-contamination conditions. Additionally, inoculation with Enterobacter sp. FM-1 significantly enhanced the bioaccumulation factor (BAF) and the translocation factor (TF) values in both types of C. asiatica L. even under high cadmium concentration soil condition. Hence, based on higher BAF and TF values and strong cadmium accumulation in the leaves and stems, we concluded that inoculation with Enterobacter sp. FM-1 is potentially useful for the phytoremediation of cadmium-contaminated sites by Centella asiatica L.

Comparison of the common spatial interpolation methods used to analyze potentially toxic elements surrounding mining regions

The appropriate spatial interpolation methods must be selected to analyze the spatial distributions of Potentially Toxic Elements (PTEs), which is a precondition for evaluating PTE pollution. The accuracy and effect of different spatial interpolation methods, which include inverse distance weighting interpolation (IDW) (power = 1, 2, 3), radial basis function interpolation (RBF) (basis function: thin-plate spline (TPS), spline with tension (ST), completely regularized spline (CRS), multiquadric (MQ) and inverse multiquadric (IMQ)) and ordinary kriging interpolation (OK) (semivariogram model: spherical, exponential, gaussian and linear), were compared using 166 unevenly distributed soil PTE samples (As, Pb, Cu and Zn) in the Suxian District, Chenzhou City, Hunan Province as the study subject. The reasons for the accuracy differences of the interpolation methods and the uncertainties of the interpolation results are discussed, then several suggestions for improving the interpolation accuracy are proposed, and the direction of pollution control is determined. The results of this study are as follows: (i) RBF-ST and OK (exponential) are the optimal interpolation methods for As and Cu, and the optimal interpolation method for Pb and Zn is RBF-IMQ. (ii) The interpolation uncertainty is positively correlated with the PTE concentration, and higher uncertainties are primarily distributed around mines, which is related to the strong spatial variability of PTE concentrations caused by human interference. (iii) The interpolation accuracy can be improved by increasing the sample size around the mines, introducing auxiliary variables in the case of incomplete sampling and adopting the partition prediction method. (iv) It is necessary to strengthen the prevention and control of As and Pb pollution, particularly in the central and northern areas. The results of this study can provide an effective reference for the optimization of interpolation methods and parameters for unevenly distributed soil PTE data in mining areas.

Hydrological and pollution processes in mining area of Fenhe River Basin in China

The hydrological and pollution processes are an important science problem for aquatic ecosystem. In this study, the samples of river water, reservoir water, shallow groundwater, deep groundwater, and precipitation in mining area are collected and analyzed. δD and δ¹⁸O are used to identify hydrological process. δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- are used to identify the sources and pollution process of NO₃^-. The results show that the various water bodies in Fenhe River Basin are slightly alkaline water. The ions in the water mainly come from rock weathering. The concentration of SO₄^2- is high due to the impact of coal mining activity. Deep groundwater is significantly less affected by evaporation and human activity, which is recharged by archaic groundwater. There are recharge and discharge between reservoir water, river water, soil water, and shallow groundwater. NO₃^- is the main N species in the study area, and forty-six percent of NO₃^--N concentrations exceed the drinking water standard of China (NO₃^--N ≤ 10 mg/L content). Nitrification is the main forming process of NO₃^-. Denitrification is also found in river water of some river branches. The sources of NO₃^- are mainly controlled by land use type along the riverbank. NO₃^- of river water in the upper reaches are come from nitrogen in precipitation and soil organic N. River water in the lower reaches is polluted by a mixture of soil organic N and fertilizers.

A heavy metal module coupled with the SWAT model and its preliminary application in a mine-impacted watershed in China

Heavy metal behavior in soil and water requires modeling for a better understanding of the potential adverse impacts on the ecosystem as well as on humans. A heavy metal transport and transformation module is combined with the well-established SWAT (Soil and Water Assessment Tool) model for the purpose of simulating the fate and transport of metals at the watershed scale. The heavy metal module accounts for sorption, complexation and slow reactions among metal species; the heavy metals in the upland are allowed to transport vertically through percolation and evaporation-induced water rising as well as horizontally through soil erosion and surface/subsurface runoff; the heavy metals in the water body, in contrast, are modeled to undergo settling, resuspension, diffusion and burial processes. As a demonstration, the SWAT-laden heavy metal module (SWAT-HM) was calibrated to simulate zinc (Zn) and cadmium (Cd) dynamics in an upstream watershed of the Liuyang River in China, which has been impacted by mining activities for decades. The model simulations were found to agree reasonably well with the monitored results. In particular, the elevation of metal loads in channels with precipitation events was well represented, demonstrating that a considerable amount of Zn and Cd in the waste rock dumps and contaminated soil was released into rivers through rainfall. After a simulation of 6years (2009-2014), the simulated Zn and Cd concentrations were used as a surrogate for the Predicted Environmental Concentration (PEC), whereby an ecological risk assessment was conducted for the demonstrative mining area. This initiative toward developing a heavy metal module combined with SWAT has high potential for application in environmental risk analysis and pollution control.

Phytoremediation of Cadmium by Native Plants Grown on Mining Soil

The Gümüsköy mining area is located about 25 km west of Kutahya and is the largest silver deposit in Turkey. The present study investigated translocation and accumulation of cadmium (Cd) from the soil into 11 native plants. Plant and soil samples were collected from the field, and Cd concentrations were analyzed by inductively coupled plasma mass spectroscopy. Mean Cd values in the soil, root, and shoot of native plants in the study area were 82.8 ± 5, 55.4 ± 6, and 43.5 ± 4 mg kg^- 1, respectively. Plants were separated into several groups according to the enrichment coefficients for shoot and root values of plants. These groups showed Carduus nutans and Phlomis could be potentially bioaccumulator plants useful for phytoremediation of mining soils contaminated by Cd.

The spatial distribution and accumulation characteristics of heavy metals in steppe soils around three mining areas in Xilinhot in Inner Mongolia, China

Metal deposition has become a major environmental problem in China due to its adverse effects on human and ecosystem health, particularly in Inner Mongolia, where frequent dust storms (due to steppe degradation and desertification) and soil pollution (associated with the increasing mining activities) have occurred in recent decades. To assess spatial distribution of heavy metals and the influences of mining activities on geochemical behavior of heavy metals in soils, soil samples with depth of 0-10, 10-20, and 20-30 cm at each site were collected from different directions in the vicinity of three mines (coal mine, gold mine, and fluorite mine) in a typical steppe zone of Inner Mongolia, China. Six elements (Cd, Pb, Zn, Cr, Cu, and Ni) in the soils were analyzed using inductively coupled plasma emission spectrometer (ICP-OES). The results indicated that the average concentrations of Cd, Pb, Zn, Cr, Cu, and Ni in the soil of the study area around three mines were lower than the second class level of the National Soil Environment Safety Standard, but mostly were higher than the background value of soil in the Inner Mongolia. Northwest, southwest, and northeast wind directions have a great influence on the distribution of metals in coal, gold, and fluorite mine area, respectively. The concentration of heavy metals in coal, gold, and fluorite increased with the distance from the center of the mine, then reached a peak, then decreased gradually. The vertical mobility of metals in soil profiles was slightly significant for Cd > Cr > Zn > Ni in coal mine area and was not significant in gold and fluorite mines. Multivariate statistical methods such as principal component analysis and cluster analysis, coupled with correlation coefficient analysis, showed that Cd, Cu, Cr, and Ni in the mining area came from the same source, while Zn and Pb came from the other source. That the sources of heavy metals in the mining area were discussed would not only enhance our knowledge regarding the soil pollution status in the study area but would also provide us information to manage the sources of these elements in the study area.

Influence of a Former Mining Area in the Heavy Metals Concentrations in Blood of Free-Living Mediterranean Pond Turtles (Mauremys leprosa)

The objective of this study was to assess metal exposure in the Mediterranean Pond Turtle (Mauremys leprosa) inhabiting a watercourse in an ancient mining district polluted by different metals ("Rambla de Las Moreras", southeastern Spain) and included in the Ramsar Convention. For this purpose, mercury (Hg), lead (Pb), copper (Cu), zinc (Zn) and cadmium (Cd) were analysed in blood samples from 42 M. leprosa healthy adults (27 males and 13 females). The highest median concentrations were found for Zn, followed by Cu, Pb, Hg and Cd (366, 33, 9, 0.83 and 0.14 µg/dL, respectively). Although the literature regarding toxic metals in freshwater turtles is relatively scarce, Pb may cause deleterious effects in our population. In general, males presented higher levels than females, which could be due to maternal transfer during egg formation. The significant correlations between Cu-Cd and Cu-Hg suggest the implication of an efficient mechanism of detoxification involving metallothioneins.

Soil contamination assessment for Pb, Zn and Cd in a slag disposal area using the integration of geochemical and microbiological data

Improper disposal of mining waste is still considered a global problem, and further details on the contamination by potentially toxic metals are required for a proper assessment. In this context, it is important to have a combined view of the chemical and biological changes in the mining dump area. Thus, the objective of this study was to evaluate the Pb, Zn and Cd contamination in a slag disposal area using the integration of geochemical and microbiological data. Analyses of soil organic matter (SOM), pH, Eh, pseudo-total concentration of metals, sequential extraction and microbial community by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were conducted. Metal availability was evaluated based on the geoaccumulation index (I _geo), ecological risk ([Formula: see text]), Risk Assessment Code (RAC) and experimental data, and different reference values were tested to assist in the interpretation of the indices. The soil pH was slightly acidic to neutral, the Eh values indicated oxidized conditions and the average SOM content varied from 12.10 to 53.60 g kg^-1. The average pseudo-total concentrations of metals were in the order of Zn > Pb > Cd. Pb and Zn were mainly bound to the residual fraction and Fe-Mn oxides, and a significant proportion of Cd was bound to the exchangeable and carbonate fractions. The topsoil (0-20 cm) is highly contaminated (I _geo) with Cd and has a very high potential ecological risk ([Formula: see text]). Higher bacterial diversity was mainly associated with higher metal concentrations. It is concluded that the integration of geochemical and microbiological data can provide an appropriate evaluation of mining waste-contaminated areas.

Sulfate migration in a river affected by acid mine drainage from the Dabaoshan mining area, South China

Sulfate, a major component of acid mine drainage (AMD), its migration in an AMD-affected river which located at the Dabaoshan mine area of South China was investigated to pursue the remediation strategy. The existing factors of relatively low pH values of 2.8-3.9, high concentrations of SO4(2-) (∼1940 mg L(-1)) and Fe(3+) (∼112 mg L(-1)) facilitated the precipitation of schwertmannite (Fe8O8(OH)6SO4·nH2O) in the upstream river. Geochemical model calculations implied the river waters were supersaturated, creating the potential for precipitation of iron oxyhydroxides. These minerals evolved from schwertmannite to goethite with the increasing pH from 2.8 to 5.8 along the river. The concentration of heavy metals in river waters was great reduced as a result of precipitation effects. The large size of the exchangeable sulfate pool suggested that the sediments had a strong capacity to bind SO4(2-). The XRD results indicated that schwertmannite was the predominant form of sulfate-bearing mineral phases, which was likely to act as a major sulfate sink by incorporating water-borne sulfate into its internal structure and adsorbing it onto its surface. The small size of reduced sulfur pools and strong oxidative status in the surface sediments further showed that SO4(2-) shifting from water to sediment in form of sulfate reduction was not activated. In short, precipitation of sulfate-rich iron oxyhydroxides and subsequent SO4(2-) adsorption on these minerals as well as water dilution contributed to the attenuation of SO4(2-) along the river waters.

Variations and constancy of mercury and methylmercury accumulation in rice grown at contaminated paddy field sites in three Provinces of China

Many paddy fields have been contaminated by mercury (Hg) in mining areas of China. In this study, twenty-six rice cultivars and three Hg contaminated paddy fields in different geographic regions were selected for field trials and aimed to investigate the variations and similarities in total Hg (THg) and methylmercury (MeHg) accumulations in brown rice (seeds) across sites. Our results revealed widescale cultivar variation in THg (13-52 ng g(-1) at Wanshan) and MeHg (3.5-23 ng g(-1)) accumulation and %MeHg (17.7-89%) in seeds. The ability to translocate is an important factor in the levels of THg and MeHg in seed. Cultivar tended to stability in THg accumulation across sites. Some cultivars accumulated lower concentrations of both THg and MeHg in seeds at fields seriously contaminated by Hg. Present results suggest that appropriate cultivar selection is a possible way to reduce THg and MeHg accumulation in seeds of rice grown in Hg-contaminated regions.