Abandoned PbZn mining wastes and their mobility as proxy to toxicity: A review

Serum metabolic changes link metal mixture exposures to vascular endothelial inflammation in residents living surrounding rivers near abandoned lead-zinc mines

Metal exposure is associated with vascular endothelial inflammation, an early pathological phenotype of atherosclerotic cardiovascular events. However, the underlying mechanism linking exposure, metabolic changes, and outcomes remains unclear. We aimed to investigate the metabolic changes underlying the associations of chronic exposure to metal mixtures with vascular endothelial inflammation. We recruited 960 adults aged 20-75 years from residential areas surrounding rivers near abandoned lead-zinc mine and classified them into river area and non-river area exposure groups. Urine levels of 25 metals, Framingham risk score (FRS), and serum concentrations of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), as biomarkers of vascular endothelial inflammation, were assessed. A "meet-in-the-middle" approach was applied to identify causal intermediate metabolites and metabolic pathways linking metal exposure to vascular endothelial inflammation in representative metabolic samples from 64 participants. Compared to the non-river area exposure group, the river area exposure group had significantly greater urine concentrations of chromium, copper, cadmium, and lead; lower urine concentrations of selenium; elevated FRS; and increased concentrations of ICAM-1 and VCAM-1. In total, 38 differentially abundant metabolites were identified between the river area and non-river area exposure groups. Among them, 25 metabolites were significantly associated with FRS, 8 metabolites with ICAM-1 expression, and 10 metabolites with VCAM-1 expression. Furthermore, fructose, ornithine, alpha-ketoglutaric acid, urea, and cytidine monophosphate, are potential mediators of the relationship between metal exposure and vascular endothelial inflammation. Additionally, the metabolic changes underlying these effects included changes in arginine and proline metabolism, pyrimidine metabolism, starch and sucrose metabolism, galactose metabolism, arginine biosynthesis, and alanine, aspartate, and glutamate metabolism, suggesting the disturbance of amino acid metabolism, the tricarboxylic acid cycle, nucleotide metabolism, and glycolysis. Overall, our results reveal biomechanisms that may link chronic exposure to multiple metals with vascular endothelial inflammation and elevated cardiovascular risk.

Study on the variation mechanism of Zn isotope in polluted farmland soil

Zn isotope can help to clarify the migration, transformation and source contribution of Zn in farmland soil. However, the research on Zn isotope value of different end members in farmland soil is incomprehensive, and the variation of Zn isotope in farmland soil caused by different factors in different polluted areas is unclear, which hinders the usage of Zn isotope tracing method in farmland soil. Thus, a Pb-Zn mine polluted farmland in southwest China was selected as the research object and the end elements and farmland soil samples with different Zn contamination were systematically collected to analyse Zn content, fraction and isotopic composition. The effects of different end members and processes of eluviation, organic adsorption and inorganic adsorption on Zn isotopic composition in soil were analysed, and the relationship between these three processes and environmental variables was analysed to clarify the change mechanism. The results can enrich the fractionation mechanism of Zn isotopes, expand the application of Zn isotope in tracing the sources, and provide geochemical evidence for remediation of Zn pollution in farmland soil.

Dynamic Inhibition of Calcite Dissolution in Flowing Acidic Pb2+ Solutions

Reactions of mineral surfaces with dissolved metal ions at far-from-equilibrium conditions can deviate significantly from those in near-equilibrium systems due to steep concentration gradients, ion-surface interactions, and reactant transport effects that can lead to emergent behavior. We explored the effect of dissolved Pb2+ on the dissolution rate and topographic evolution of calcite (104) surfaces under far-from-equilibrium acidic conditions (pH 3.7) in a confined single-pass laminar-flow geometry. Operando measurements by digital holographic microscopy were conducted over a range of Pb2+ concentrations ([Pb2+] = 0 to 5 × 10-2 M) and flow velocities (v = 1.67-53.3 mm s-1). Calcite (104) surface dissolution rates decreased with increasing [Pb2+]. The inhibition of dissolution and the emergence of unique topographic features, including micropyramids, variable etch pit shapes, and larger scale topographic patterns, became increasingly apparent at [Pb2+] ≥ 5 × 10-3 M. A better understanding of such dynamic reactivity could be crucial for constructing accurate models of geochemical transport in aqueous carbonate systems.

Evaluation of heavy metal speciation distribution in soil and the accumulation characteristics in wild plants: A study on naturally aged abandoned farmland adjacent to tailings

Heavy metal composite pollution is widespread in the surrounding environment of tailings ponds in arid and semi-arid regions, leading to the abandonment of substantial agricultural land. This study investigates the speciation distribution and plant accumulation characteristics of heavy metals in abandoned farmland with different durations of natural aging. The aim is to comprehend the local heavy metal behavior pattern in the soil-plant system and offer insights for environmental remediation. Our findings reveal that Cd stands out as the primary heavy metal pollutant in this area. The mobility ranking of heavy metals is Cd > Pb > Zn > Cu, with Cd and Pb mobility decreasing along the basin. Notably, active Pb exhibits a higher affinity for soil binding compared to other metals. The predominant plant species in the region are primarily small shrubs, herbaceous plants, and semi-shrubs that demonstrate tolerance to drought and salt. Most plant samples showed elevated levels of Cd, Pb, and Zn, surpassing the maximum tolerance levels for dietary minerals in livestock. This elevated metal content poses potential threats to the health of local livestock and wildlife, yet it is also considered a potential for phytoremediation. Selected dominant plant species from the current study include Kalidium foliatum & gracile which shows potential as a Cd accumulator and indicator. Neotrinia splendens and Reaumuria songarica demonstrate potential as Cd excluders, with the latter exhibiting higher tolerance to Cd (62.9 mg/kg). Additionally, our observations indicate that different plant parts exhibit distinct responses to heavy metals, and Zn synergistically influences the aerial part accumulation of Cd. This study holds significant importance in understanding the complex behavior patterns of multi-metal pollutants in the natural environment. The identification of native plants with remediation potential is valuable for phytoremediation of environment pollution in mining area.

Organic amendment application affects the release behaviour, bioavailability, and speciation of heavy metals in zinc smelting slag: Insight into dissolved organic matter

Organic amendments are commonly used in assisted phytostabilization of mine wastes by improving their physicochemical and biological properties. These amendments are susceptible to leaching and degradation, resulting in the generation of dissolved organic matter (DOM), which significantly influences the geochemical behaviour of heavy metals (HMs). However, the geochemical behaviour of HMs in metal smelting slag driven by organic amendment-derived DOM remains unclear. In this study, we investigated the impact of cow manure-derived DOM on the release behaviour, bioavailability, and speciation of HMs (Cu, Pb, Zn, and Cd) in zinc smelting slag using a multidisciplinary approach. The results showed that DOM enhanced the weathering of the slag, with a minimal impact on the slag's mineral phases, except for causing gypsum dissolution. The DOM addition resulted in a slight increase in HM release from the slag during the initial inoculation period, followed by a reduction in HM release during the later period. Furthermore, the DOM addition increased the diversity and relative abundance of the bacterial community. This, in turn, led to a decrease in the dissolved organic carbon (DOC) content and enhanced the transformation of labile DOM compounds into recalcitrant compounds. The variation in HM release during various inoculation periods can be attributed to the bacterial decomposition and transformation of DOM, which further enhanced the transformation of HM fractions. Specifically, during the later period, DOM promoted the conversion of a portion of the reducible and oxidizable fractions of Cu, Pb, and Zn into the acid-soluble and residual fractions. Moreover, it partially transformed the reducible, oxidizable, and residual fractions of Cd into the acid-soluble fraction. Overall, this study provides new insights into the geochemical behaviour of HMs in slag governed by the coupling effect of DOM and the bacterial community. These findings have implications for the use of organic amendments in assisted phytostabilization of metal smelting slag. ENVIRONMENTAL IMPLICATION: Metal smelting slag is hazardous due to its high levels of HMs, and its improper disposal has serious consequences for the ecosystem. Organic amendments are employed in assisted phytostabilization of the slag site by improving its microecological properties. However, the impact of organic amendment-derived DOM on HM migration and transformation in slag remains unclear. This study indicated that the coupling effects of DOM and microbes governed the geochemical behaviour of HMs in slag. These findings provide new insights into how organic amendments impact the geochemical behaviour of HMs in slag, contributing to the development of phytostabilization technology.

Application of biological soil crusts for efficient cadmium removal from acidic mine wastewater

Utilizing an acid-resistant biological soil crust (BSC) species that we discovered, we developed a device capable of efficiently removing cadmium (Cd) from mine wastewater with varying levels of acidity. Our research has demonstrated that this particular BSC species adapts to acidic environments by regulating the balance of fatty acids and acid-resistant enzymes. At a Cd concentration of 5 mg/L, the BSC grew well. When the initial Cd concentration was 2 mg/L, and the flow rate was set at 1 mL/min (at pH levels of 3, 4, and 5), BSC had a high removal rate of Cd, and the removal rate increased with the increase of pH (from 90% to 97%). Chemisorption is the primary removal mechanism in the initial stage, where the functional groups and minerals on the surface of the BSC play a significant role. In addition, BSC also adapts to Cd stress by changing bacterial community structure. It was discovered through infrared spectroscopy and two-dimensional correlation analysis that hydrophilic groups, specifically phosphate and carboxyl groups, exhibited the highest reactivity during the Cd binding process. Protein secondary structure analysis confirmed that as the pH increased, the adsorption capacity of the BSC increased; making biofilm formation easier. This study presents a novel approach for the treatment of acidic wastewater.

Alleviating the adverse effects of Cd-Pb contamination through the application of silicon fertilizer: Enhancing soil microbial diversity and mitigating heavy metal contamination

The use of silicon fertilizer (SF) as a means of remediating cadmium (Cd) and lead (Pb) pollution has proven to be beneficial. However, the mechanism via which SF enhances soil quality and crop productivity under Cd- and Pb-contaminated soil (S) remains unclear. This study investigated the impacts of chemical fertilizer, mineral SF (MSF), and organic SF (OSF) on microbial community structure, activity of nutrient acquisition enzymes, and growth of tobacco in the presence of S condition. SF significantly reduced the contents of Cd and Pb in soil under S condition by 6.92-42.43% and increased plant height and leaf area by 15.27-81.77%. Moreover, the use of SF was observed to increase the efficiency of soil carbon and phosphorus cycling under S condition by 6.88-23.08%. Concurrently, SF was found to play a crucial role in facilitating the establishment of a complex, efficient, and interdependent molecular ecological network among soil microorganisms. In this context, Actinobacteriota, Bacteroidota, Ascomycota, and Basidiomycota were observed to be integral components of this network. SF was found to have a substantial positive impact on the metabolic functions and organismal systems of soil microorganisms. Moreover, the combined utilization of the Mantel test and partial least squares path model provided empirical evidence supporting the assertion that the administration of SF had a positive impact on both soil nutrient acquisition enzyme activity and tobacco growth, which was attributed to the enhancement of soil microbial diversity resulting from the application of SF. Furthermore, compared with MSF, OSF has advantages in reducing soil Pb and Cd content, promoting tobacco agronomic traits, increasing the number of key microbial communities, and maintaining the structural stability of microbial networks. The aforementioned findings, therefore, suggest that the OSF played a pivotal role in alleviating the adverse impacts of S, thereby demonstrating its efficacy in this particular process.

Geochemical properties, heavy metals and soil microbial community during revegetation process in a production Pb-Zn tailings

Lead-zinc (Pb-Zn) tailings pose a significant environmental threat from heavy metals (HMs) contamination. Revegetation is considered as a green path for HM remediation. However, the interplay between HM transport processes and soil microbial community in Pb-Zn tailings (especially those in production) remain unclear. This study investigated the spatial distribution of HMs as well as the crucial roles of the soil microbial community (i.e., structure, richness, and diversity) during a three-year revegetation of production Pb-Zn tailings in northern Guangdong province, China. Prolonged tailings stockpiling exacerbated Pb contamination, elevating concentrations (from 10.11 to 11.53 g/kg) in long-term weathering. However, revegetation effectively alleviated Pb, reducing its concentrations of 9.81 g/kg. Through 16 S rRNA gene amplicon sequencing, the dominant genera shifted from Weissella (44%) to Thiobacillus (17%) and then to Pseudomonas (comprising 44% of the sequences) during the revegetation process. The structural equation model suggested that Pseudomonas, with its potential to transform bioavailable Pb into a more stable form, emerged as a potential Pb remediator. This study provides essential evidence of HMs contamination and microbial community dynamics during Pb-Zn tailings revegetation, contributing to the development of sustainable microbial technologies for tailings management.

Enhancing soil ecological security through phytomanagement of tailings in erosion-prone areas

Revegetation is effective in improving soil quality in ecologically fragile areas. However, little is known about the impact of diverse phytomanagement strategies of tailings on soil quality and ecological security in erosion-prone areas. We investigated the water stability, soil aggregate nutrients, and the risk of heavy metal contamination of abandoned tailings under phytomanagement and in adjacent bare land on the Loess Plateau. The results showed that phytomanagement significantly enhanced soil aggregate stability, as demonstrated by higher contents of soil organic carbon (SOC), glomalin-related soil protein (GRSP), aromatic-C, and alkene-C in macro-aggregates. The pollution load index (PLI) and ecological risk index (RI) of soil heavy metals were lower in shrub/herbaceous mixed forests than in natural grasslands and planted forests. The risk of heavy metal contamination was higher in macro-aggregates (>0.25 mm) than in micro-aggregates (<0.25 mm) and was significantly and positively correlated with the SOC and GRSP contents of the aggregates. Our study demonstrates that soil aggregate quality is closely related to the fate of heavy metals. Diversified tailing revegetation measures can improve soil quality and ensure ecological security.

A critical review on the migration and transformation processes of heavy metal contamination in lead-zinc tailings of China

The health risks of lead-zinc (Pb-Zn) tailings from heavy metal (HMs) contamination have been gaining increasing public concern. The dispersal of HMs from tailings poses a substantial threat to ecosystems. Therefore, studying the mechanisms of migration and transformation of HMs in Pb-Zn tailings has significant ecological and environmental significance. Initially, this study encapsulated the distribution and contamination status of Pb-Zn tailings in China. Subsequently, we comprehensively scrutinized the mechanisms governing the migration and transformation of HMs in the Pb-Zn tailings from a geochemical perspective. This examination reveals the intricate interplay between various biotic and abiotic constituents, including environmental factors (EFs), characteristic minerals, organic flotation reagents (OFRs), and microorganisms within Pb-Zn tailings interact through a series of physical, chemical, and biological processes, leading to the formation of complexes, chelates, and aggregates involving HMs and OFRs. These interactions ultimately influence the migration and transformation of HMs. Finally, we provide an overview of contaminant migration prediction and ecological remediation in Pb-Zn tailings. In this systematic review, we identify several forthcoming research imperatives and methodologies. Specifically, understanding the dynamic mechanisms underlying the migration and transformation of HMs is challenging. These challenges encompass an exploration of the weathering processes of characteristic minerals and their interactions with HMs, the complex interplay between HMs and OFRs in Pb-Zn tailings, the effects of microbial community succession during the storage and remediation of Pb-Zn tailings, and the importance of utilizing process-based models in predicting the fate of HMs, and the potential for microbial remediation of tailings.

A circular economy approach to drinking water treatment residue management in a catchment impacted by historic metal mines

Drinking water treatment residues (DWTR) from mining areas which remove and contain potentially toxic elements (PTE) could still potentially be used as a soil amendment to restore contaminated sites in the same catchment, thus eliminating waste and reducing the chemical and physical mobility of the pollutants. To assess this restorative and regenerative approach to DWTR management, field and pot trials were established with soils from a historic Pb-Zn mine site in the North East of England, amended with either local DWTR or the nearest available municipal green waste compost (GWC). Soils from the mine site were found to have very low levels of nutrients and very high levels of PTE (Pb and Zn > 13, 000 mg/kg). The perennial grass species Phalaris arundinacea, known for many ecosystem service benefits including soil stabilization, was used throughout this study. The application of the BCR sequential extraction to soils amended with the DWTR in the pot trials found a significant decrease in the bioavailability of Pb and Cu (p < 0.05) after plant growth when compared with an unamended control. The field trial involved 648 pre-grown grass plants planted-out into mine soils amended with either DWTR, GWC or a mixture (MIX) of the two, all at rates of 25-30% w/w. Both amendments and the MIX had significant positive effects on biomass production compared to the unamended control in the following order GWC > MIX > DWTR (p < 0.05). Results of the elemental analysis of biomass from the field trial were generally ambiguous and did not reflect the decreased bioavailability noted in the pot trials using the BCR procedure. Pot trials, however, showed increases in plant growth and decreases in concentrations of Cr, Cu, Pb and Zn in above ground biomass following the application of both amendments. Further work should involve the testing of a mixture of DWTR and other soil amendments to enhance plant growth. The success of these trials should provide confidence for those working in drinking water treatment and catchment management to reuse the waste residues in a circular economy and a sustainable way that could improve water quality over time.

Mining-related multi-resistance genes in sulfate-reducing bacteria treatment of typical karst nonferrous metal(loid) mine tailings in China

Management of tailings at metal mine smelter sites can reduce the potential hazards associated with exposure to toxic metal(loid)s and residual organic flotation reagents. In addition, microbes in the tailings harboring multi-resistance genes (e.g., tolerance to multiple antimicrobial agents) can cause high rates of morbidity and global economic problems. The potential co-selection mechanisms of antibiotic resistance genes (ARGs) and metal(loid) resistance genes (MRGs) during tailings sulfate-reducing bacteria (SRB) treatment have been poorly investigated. Samples were collected from a nonferrous metal mine tailing site treated with an established SRB protocol and were analyzed for selected geochemical properties and high throughput sequencing of 16S rRNA gene barcoding. Based on the shotgun metagenomic analysis, the bacterial domain was dominant in nonferrous metal(loid)-rich tailings treated with SRB for 12 months. KEGGs related to ARGs and MRGs were detected. Thiobacillus and Sphingomonas were the main genera carrying the bacA and mexEF resistance operons, along with Sulfuricella which were also found as the main genera carrying MRGs. The SRB treatment may mediate the distribution of numerous resistance genes. KOs based on the metagenomic database indicated that ARGs (mexNW, merD, sul, and bla) and MRGs (czcABCR and copRS genes) were found on the same contig. The SRB strains (Desulfosporosinus and Desulfotomaculum), and the acidophilic strain Acidiphilium significantly contributed to the distribution of sul genes. The functional metabolic pathways related to siderophores metabolism were largely from anaerobic genera of Streptomyces and Microbacterium. The presence of arsenate reductase, metal efflux pump, and Fe transport genes indicated that SRB treatment plays a key role in the metal(loid)s transformation. Overall, our findings show that bio-treatment is an effective tool for managing ARGs/MRGs and metals in tailings that contain numerous metal(loid) contaminants.

Impact of past mining activities on water quality in a karst area in the Cévennes region, Southern France

Sampling and analysis of groundwater and surface water were conducted to assess the potential impacts of abandoned mines on water quality in a karst area in Southern France. The results of multivariate statistical analysis and geochemical mapping revealed that water quality is affected by contaminated drainage from abandoned mine sites. Acid mine drainage with very high concentrations of Fe, Mn, Al, Pb and Zn was identified in a few samples collected from mine openings and near waste dumps. In general, neutral drainage with elevated concentrations of Fe, Mn, Zn, As, Ni and Cd was observed due to buffering by carbonate dissolution. The contamination is spatially limited around abandoned mine sites, suggesting that metal(oid)s are sequestered in secondary phases that form under near-neutral and oxidizing conditions. However, the analysis of seasonal variations in trace metal concentrations showed that the transport of metal contaminants in water is highly variable according to hydrological conditions. During low flow conditions, trace metals are likely to be rapidly sequestered in Fe-oxyhydroxides and carbonate minerals in the karst aquifer and the river sediments, while low or no surface runoff in intermittent rivers limits the transport of contaminants in the environment. On the other hand, significant amounts of metal(loid)s can be transported under high flow conditions, primarily in dissolved form. Dissolved metal(loid) concentrations in groundwater remained elevated despite dilution by uncontaminated water, likely as a result of the increased leaching of mine wastes and the flushing of contaminated waters from mine workings. This work shows that groundwater is the main source of contamination to the environment and highlights the need to better understand the fate of trace metals in karst water systems.

Effect of past century mining activities on sediment properties and toxicity to freshwater organisms in northern Sweden

The release of toxic metals from local mining activities often represents a severe environmental hazard for nearby lake ecosystems. Previous studies on the impact of mining have primarily focused on single lakes, with less emphasis on spatial and temporal recovery patterns of multiple lakes within the same catchment, but with different hydrological connection and distance to the pollutant source. This knowledge gap prevents us from assessing the real environmental risk of abandoned mines and understanding ecosystem recovery. This study explores the intensity and spatial patterns of sediment contamination and the potential for ecosystem recovery in three lakes in close vicinity of a lead (Pb) and zinc (Zn) mine in Sweden that has been inoperative for >20 years. Dated (²¹⁰Pb and ¹³⁷Cs) sediment cores from each lake were used to reconstruct temporal patterns in trace element deposition and relate those with past mining activities. Results show that all lakes were affected by mining, indicated by increasing Pb and Zn concentrations and decreasing organic matter content, at the onset of mining. However, the extent and timing of mining impact differed between lakes, which was partly ascribed to differences in the historical use of tailings and settling ponds. Assessment of toxicity levels in sediments, based on normalized Probable Effect Concentration Quotient (PEC-Q) to organic matter content, provided more consistent results with the historical mining than conventional methods, showing a decreasing impact in lakes once the operations ceased. Still, sediment Pb concentrations were > 10 times higher than pre-mining values, evidencing the urgent need for remediation actions in the study lakes. This study highlights the importance of considering spatial heterogeneity in metal deposition, sediment organic matter content, and hydrological connectivity with tailings when risk assessments are performed in mining-impacted lakes. The use of normalized PEC-Q in toxic assessments is also recommended.

Performance and mechanisms of PropS-SH/Ce(dbp)3 coatings in the inhibition of pyrite oxidationtion for acid mine drainage control

Inhibition of tailings oxidation could availably control the generation of acid mine wastewater from its source. Organosilanes serving as a high-efficiency inhibitor of the oxidation of pyrite, bring some problems including safety hazards caused by large amounts of organic solvents, difficult high-temperature curing, poor long-term properties, and so on. In our work, the PropS-SH/Ce (dbp)₃ (PS/Ce (dbp)₃) passivator with excellent passivation performance and self-healing properties was prepared by choosing 3-mercaptopropyltrimethoxysilane (PropS-SH) and dibutyl phosphate (Ce (dbp)₃) as the main passivating agent and the repair agent, respectively. We reduced the ratio of ethanol to water by adjusting the pH of the organosilane condensation and also achieved room-temperature curing by extending the curing time. Electrochemical and chemical leaching experiments results showed that the most appropriate addition of Ce (dbp)₃ was 0.2 wt% for enhancing the passivation performance of the passivated coating. In a 6-month chemical leaching experiment, the PS/Ce (dbp)₃-0.2 passivation coating cured at room temperature showed a better passivation effect and maintained 90.55% and 78.54% of total Fe and SO₄^2- passivation efficiencies. The passivation and self-healing mechanisms were investigated by FT-IR, XPS, ²⁹Si NMR, and other characterization methods, which were as follows: silane formed a cross-linked mesh structure by Si-O-Si bonding, in which Ce (dbp)₃ was physically filled. And the Si-OH on the surface of the passivation film formed Fe-O-Si bonds with the hydroxyl groups on the surface of the pyrite, thus attaching to the surface of the pyrite and isolating the oxidation medium. When the passivation coating was locally damaged, the oxidation reaction caused a change in pH, which accelerated the dissolution of Ce (dbp)₃ in the passivation layer. Ce³⁺ underwent a valence change and formed a CeO₂ precipitate, while dbp^- could form a complex with Fe²⁺ on the pyrite surface, both of which worked together to repair the broken passivation coating and prevent the oxidation reaction.

Potentially toxic elements in smoke particles and residual ashes by biomass combustion from Huangshi National Mine Park, China

This paper investigates the fractional and spatial distribution characteristics of potentially toxic elements (PTEs) in smoke particles and residual ashes from mine-park-biomass combustion. It then evaluates the consequential potential environment risk by using a Geo-accumulation index and Nemerow pollution index methods. Biomass combustibles are comprised of Camphor leaves (CL), Camphor dead-branch (CB), Ramie (RA), Miscanthus sinensis (MS), and Dryopteris (DR). The results show that the products of combustion contain PTEs, As, Cr, Cu, and Zn, etc. Among them, the content of As, Cr, Cu, Pb elements in smoke particles of CB was higher than other combustibles. Moreover, Cr, Mn, Ni, and Pb in residual ashes of CL were higher than others. The proportion of acid-soluble and reducible fraction of As in residual ash was higher, while Cr existed mainly in the oxidizable and residual fraction. Besides, the available state of As gradually decreased from 74% (400 °C) to 41% (800 °C), indicating that the increase of temperature significantly reduced the bioavailability of As. Meanwhile, with the increase of temperature, the concentration of PTEs in smoke particles decreased and PTEs in residual ashes increased in different degrees. The risk evaluation results indicate that PTEs may cause moderate or higher levels of contamination. The overall contamination level of PTEs in the residual ashes of CB was higher than that of other plant. The results show in this study would contribute to understanding the environmental risks of wildfire and prescribed burning in PTEs-contaminated areas.

Soil microbial communities and their co-occurrence networks in response to long-term Pb-Zn contaminated soil in southern China

Mining causes extreme heavy metal (HM) contamination to surrounding environments and poses threats to soil microbial community. The effects of HMs on soil microbial communities are not only related to their total amounts but also associated with the distribution of chemical fractions. However, the effects of chemical fractions on soil microbes and their interactions remain largely unclear. Here we investigated soil physicochemical properties and bacterial and fungal communities of soil samples from the control area and lightly (L), moderately (M), and heavily (H) contaminated areas, respectively, which were collected from long-term Pb-Zn slag contamination area in the southern China. The results showed that bacterial and fungal community composition and structure were significantly affected by HMs, while community diversity was not significantly affected by HMs. The critical environmental factor affecting bacterial and fungal communities was pH, and the impacts of chemical fractions on their changes were more significant than the total amounts of HMs. Variance partitioning analysis (VPA) revealed fungal community changes were mostly driven by HM total amounts, but bacterial community changes were mostly driven by soil chemical properties. Co-occurrence network indicated that interactions among species of fungal network were sparser than that of bacterial network, but fungal network was more stable, due to a more significant number of keystone taxa and a lower percentage of positive associations. These illustrated that the fungal community might serve as indicator taxa for HM-contaminated status, and specific HM-responsive fungal species such as Triangularia mangenotii, Saitozyma podzolica, and Cladosporium endophytica, and genus Rhizophagus can be considered relevant bioindicators due to their less relative abundance in contaminated areas. Additionally, HM-responsive bacterial OTUs representing five genera within Sulfurifustis, Thiobacillus, Sphingomonas, Qipengyuania, and Sulfurirhabdus were found to be tolerant to HM stress due to their high relative abundance in contaminated levels.

Coriander (Coriandrum sativum) Cultivation Combined with Arbuscular Mycorrhizal Fungi Inoculation and Steel Slag Application Influences Trace Elements-Polluted Soil Bacterial Functioning

The cultivation of aromatic plants for the extraction of essential oils has been presented as an innovative and economically viable alternative for the remediation of areas polluted with trace elements (TE). Therefore, this study focuses on the contribution of the cultivation of coriander and the use of arbuscular mycorrhizal fungi (AMF) in combination with mineral amendments (steel slag) on the bacterial function of the rhizosphere, an aspect that is currently poorly understood and studied. The introduction of soil amendments, such as steel slag or mycorrhizal inoculum, had no significant effect on coriander growth. However, steel slag changed the structure of the bacterial community in the rhizosphere without affecting microbial function. In fact, Actinobacteria were significantly less abundant under slag-amended conditions, while the relative proportion of Gemmatimonadota increased. On the other hand, the planting of coriander affects the bacterial community structure and significantly increased the bacterial functional richness of the amended soil. Overall, these results show that planting coriander most affected the structure and functioning of bacterial communities in the TE-polluted soils and reversed the effects of mineral amendments on rhizosphere bacterial communities and their activities. This study highlights the potential of coriander, especially in combination with steel slag, for phytomanagement of TE-polluted soils, by improving soil quality and health.

Arsenic and Heavy Metals in Sediments Affected by Typical Gold Mining Areas in Southwest China: Accumulation, Sources and Ecological Risks

Gold mining is associated with serious heavy metal pollution problems. However, the studies on such pollution caused by gold mining in specific geological environments and extraction processes remain insufficient. This study investigated the accumulation, fractions, sources and influencing factors of arsenic and heavy metals in the sediments from a gold mine area in Southwest China and also assessed their pollution and ecological risks. During gold mining, As, Sb, Zn, and Cd in the sediments were affected, and their accumulation and chemical activity were relatively high. Gold mining is the main source of As, Sb, Zn and Cd accumulation in sediments (over 40.6%). Some influential factors cannot be ignored, i.e., water transport, local lithology, proportion of mild acido-soluble fraction (F1) and pH value. In addition, arsenic and most tested heavy metals have different pollution and ecological risks, especially As and Sb. Compared with the other gold mining areas, the arsenic and the heavy metal sediments in the area of this study have higher pollution and ecological risks. The results of this study show that the local government must monitor potential environmental hazards from As and Sb pollution to prevent their adverse effects on human beings. This study also provides suggestions on water protection in the same type of gold-mining areas.

Pyrite bio-leachate, mine wastewater can sterilize the rice (Oryza sativa L.) seeds and promote the germination

We developed the way to use pyrite bio-leachate (PBL), the wastewater of bioleaching of refractory gold ore in agriculture. PBL contains high amount of iron and at certain concentration, iron has toxicity on microorganisms. Therefore PBL can be used for rice seed sterilization. Method 1 is soaking rice seeds in 100%, 10%, and 2% PBL for 1, 2, 3, and 4 days (25℃) and drying them. Method 2 is soaking rice seeds in 100%, 10%, and 2% PBL for 30 min, 60 min, and 120 min (25℃), wetting for 2 days under the shade and drying for 5 days. Method 1 with 100%, 10%, and 2% PBL did not sterilize rice seeds completely. Method 2 with 100% and 10% PBL showed the complete sterilization effect and enhanced the germination of rice seeds in any soaking time. Similar results were achieved in seedbed experiments. PBL which has serious potential to pollute the environment can be used for rice seed sterilization. Soaking rice seeds in 100% and 10% PBL for 30 min, 60 min, and 120 min (25℃), wetting for 2 days under the shade and drying them for 5 days, can sterilize the rice seeds completely and enhance the germination.

Chronic toxicity, bioavailability and bioaccumulation of Zn, Cu and Pb in Lactuca sativa exposed to waste from an abandoned gold mine

Abandoned mines with untreated waste cause environmental pollution. The complex mixture of mining waste includes high metal content, anthropogenic chemicals and sterile rocks. Adverse effects of contaminated soils have been widely assessed by the use of plants. The aim of this study was to assess the chronic toxicity of a contaminated soil by waste from an abandoned gold mine on Lactuca sativa and its relationship with the bioavailability and bioaccumulation of Zn, Cu and Pb. Soil samples were taken from the site of mining waste stacking and a reference site in La Planta (Argentina). Contamination indices were calculated and acute and chronic exposures on L. sativa were carried out. Phytotoxicity indices, morphological and biochemical parameters, and concentrations of Zn, Cu and Pb in pseudo total and bioavailable soil fractions and in plant tissue were determined. Concentration- and time-dependent toxicity effects were observed, especially on plant width, fresh aerial biomass, leaf area and percentage of plants with completely necrotic aerial biomass. High levels of Zn (1453.3 ± 220.3 μg g-1) were found in plant tissue compared to Pb (277.2 ± 18.0 μg g-1) and Cu (255.3 ± 25.6 μg g-1). Toxicological endpoints correlated with metal uptake and mining waste concentration. In addition, bioaccumulation factors correlated with mobilisable and water soluble fractions. The concentration of Pb in aerial biomass surpassed the permissible concentrations in leaf vegetables, even at the reference site, indicating that lettuce crop consumption could be risky for the local population's health. This study demonstrated a strong relationship between metal bioavailability, toxicity endpoints and bioaccumulation, contributing with novel information to future ecotoxicological risk assessments and remediation plans.

Selected technology-critical elements as indicators of anthropogenic contamination of surface water and suspended solids on the example of the Biała Przemsza River (Poland)

Pollution of surface waters from anthropogenic activities is a global problem, affecting natural ecosystems, having a large impact on the life and health of living organisms. The development of mining and metallurgic industries of Pb and Zn ores in the Biała Przemsza cachment area has had a strong influence on the surface waters and suspended solids. This paper proposes the use of selected critical elements such as Tl, Te, Ga, Ge and In as indicators of anthropogenic pollution of surface waters and suspended solids on the example of the Biała Przemsza River. The impact of strongly anthropogenic urban-industrial catchment on the temporal and spatial distribution of the selected TCEs content in the water and suspension of the Biała Przemsza River depending on the oxygen, pH and Eh conditions is presented. Research has shown that selected critical elements such as Te, Ge, and In can be indicators of anthropogenic pollution of surface waters. In the case of the Biała Przemsza River, elements such as Ga and Tl cannot be indicators of anthropogenic pollution due to their presence in the zinc and lead ore deposits occurring in the river basin. Correlation matrices showed significant relationships between the selected TCEs and other water parameters. The calculated water pollution indices confirmed that the Biała Przemsza River is the most polluted in the last three sampling points.

Insights into mechanisms governing the passive removal of inorganic contaminants from acid mine drainage using permeable reactive barrier

The permeable reactive barrier has been deemed as the most prudent and pragmatic way to passively manage and remediate acid mine drainage (AMD). Herein, insights into mechanisms governing the removal of inorganic contaminants from AMD using a permeable reactive barrier (PRB), i.e. pervious concrete, were reported. In particular, the effects of varying dosages, i.e., 6, 10, 30, and 60 g, of cementitious materials comprising CEM I 52.5R with or without fly ash, hydrated lime, and gypsum were evaluated whilst the fate of chemical species was underpinned using the state-of-the-art analytical techniques, along with PHREEQC geochemical modelling. The role of gypsum, a product formed from the interaction of PRB with AMD in heavy metals attenuation was also elucidated. Findings revealed cementitious materials to play an indispensable role in the removal of inorganic contaminants from AMD. Furthermore, alkalinity from used materials increases the pH (i.e. pH ≥ 12.5) of AMD leading to the precipitation of chemical species. Specifically, the efficacy registered the following sequence: Lime ≥ CEM I ≥ 30%FA ≥ Gypsum with ≥99 for Al and Fe except for Gypsum which attained ≥98 while the performance for Zn removal registered the following sequence, 97 ≥ 98 ≥ 88.8 ≥ 45% for CEM I ≥ Lime ≥30%FA ≥ Gypsum, respectively. Chemical species exist as divalent, trivalent, oxyanions, and other complexes in solution as predicted by PHREEQC. Moreover, they were removed as metal hydroxides, oxyhydrosulphates, and gypsum hence corroborating findings from XRD, SEM-EDS, and FTIR results. Mechanisms which were responsible for the removal of chemical species were precipitation, adsorption, co-adsorption, co-precipitation, ion exchange, and complexation. Henceforth, this study explicitly demonstrated mechanisms that underpin the removal of inorganic contaminants from AMD using PRB and findings from this study will be used to develop effective PRB for the management of acid mine drainage and the receiving environment.

Spontaneous vegetation colonizing abandoned metal(loid) mine tailings consistently modulates climatic, chemical and biological soil conditions throughout seasons

This study aimed to evaluate whether the improvement in soil conditions induced by the vegetation spontaneously colonizing abandoned metal(loid) mine tailings from semiarid areas is consistent throughout seasons and to identify if the temporal variability of that conditions is of similar magnitude of that of the surrounding forests. Soil climatic (temperature and moisture), chemical (pH, electrical conductivity and water-soluble salts and metal(loid)s) and biological (water-soluble organic carbon and ammonium, microbial biomass carbon, dehydrogenase and β-glucosidase activity, organic matter decomposition and feeding activity of soil dwelling organisms) parameters were seasonally evaluated for one year in bare soils and different vegetated patches within metalliferous mine tailings and surrounding forests in southeast Spain. The results indicated that the improvement in soil conditions (as shown by softening of climatic conditions and lower scores for salinity and water-soluble metals and higher for biological parameters) induced by vegetation colonization was consistent throughout seasons. This amelioration was more evident in the more complex vegetation patches (trees with herbs and shrubs under the canopy), compared to bare soils and simpler soil-plant systems (only trees), and closer to forest soils outside the tailings. Bare soils and, to a lesser extent, vegetation patches solely composed by trees, showed stronger seasonal variability in temperature, moisture content, salinity, and water-soluble metals. In contrast, changes in biological and biological-related parameters were more pronounced in the more complex vegetation patches within mine tailings and surrounding forests due to its greater biological activity. In summary, the results demonstrated that vegetation patches formed by spontaneous colonization act as microsites that modulate seasonal variability in soil conditions and stimulate biological activity. This suggests that tailings vegetation patches might have higher resilience against climate change effects than bare soils. Therefore, they should be preserved as valuable spots in the phytomanagement of metal(loid)s mine tailings from semiarid areas.

An Experimental Investigation of the Environmental Risk of a Metallurgical Waste Deposit

The aim of this study is to investigate the environmental risk of long-term metallurgical waste disposal. The investigated site was used for the open storage of lead and zinc waste materials originating from a lead smelter and refinery. Even after remediation was performed, the soil in the close vicinity of the metallurgical waste deposit was heavily loaded with heavy metals and arsenic. The pollutants were bound in various compounds in the form of sulfides, oxides, and chlorides, as well as complex minerals, impacting the pH values of the investigated soil, such that they varied between 2.8 for sample 6 and 7.34 for sample 8. In order to assess the environmental risk, some eight soil samples were analyzed by determining the total metal concentration by acid digestion and chemical fractionation of heavy metals using the BCR sequential extraction method. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine six elements (As, Cd, Cu, Pb, Zn, and Ni). Total concentrations of the elements in the tested soil samples were in the range of 3870.4–52,306.18 mg/kg for As, 2.19–49.84 mg/kg for Cd, 268.03–986.66 mg/kg for Cu, 7.34–114.67 mg/kg for Ni, 1223.13–30,339.74 mg/kg for Pb, and 58.21–8212.99 mg/kg for Zn. The ratio between the mean concentrations of the tested metals was determined in this order: As > Pb > Zn > Cu > Ni > Cd. The BCR results showed that Pb (50.7%), Zn (49.2%), and Cd (34.7%) had the highest concentrations in mobile fractions in the soil compared to the other metals. The contamination factor was very high for Pb (0.09–33.54), As (0.004–195.8), and Zn (0.14–16.06). According to the calculated index of potential environmental risk, it was confirmed that the mobility of Pb and As have a great impact on the environment.

Soil contamination with cadmium and potential risk around various mines in China during 2000-2020

Cadmium (Cd) pollution in mining areas is the most important challenge for soil environment management in China. Assessing the actual Cd pollution risk in various mining areas and identifying the core areas requiring supervision can provide a basis for government departments and industries to carry out detailed further investigations in key areas. In this study, we collated published data on metal mine circumjacent soil contaminated by Cd in China from 2002 to 2020 to conduct a comprehensive study on soil cadmium pollution and ecological and health risks in mining areas. The temporal and spatial variations of Cd concentrations and the pollution source were investigated. Results indicated that the Cd concentration in soil was strongly associated with the types of mining area. The Cd pollution in the circumjacent soil of lead-zinc and tungsten mines with high heavy metal pollution discharging coefficient was more serious than the soil around other mines. Identification of temporal and spatial variations for soil Cd in China indicated that the high Cd concentrations were found in the central, southern, and southwestern regions of China, and the distribution of mining activities in these regions are relatively concentrated. Meanwhile, a temporal turning point in the mean soil Cd concentration occurred in these regions in 2012, which indicated that the heavy metal control management policy implemented by the government was effective. The ecological risk of soil Cd pollution around mining areas was moderate to high. Health risk assessment showed that some regions adjacent mining areas had a high non-carcinogenic risk, notably, lead-zinc and tungsten mining areas were more serious. Supervision should focus on reducing ecological risks and protecting the safety of agricultural products rather than concentrating on health risks. The research results provide a reference for the priority management of contaminated soil in mining areas.

Pb-Bearing Ferrihydrite Bioreduction and Secondary-Mineral Precipitation during Fe Redox Cycling

The significant accumulation of Pb from anthropogenic activities threatens environmental ecosystems. In the environment, iron oxides are one of the main carriers of Pb. Thus, the redox cycling of iron oxides, which is due to biotic and abiotic pathways, and which leads to their dissolution or transformation, controls the fate of Pb. However, a knowledge gap exists on the bioreduction in Pb-bearing ferrihydrites, secondary-mineral precipitation, and Pb partitioning during the bioreduction/oxidation/bioreduction cycle. In this study, Pb-bearing ferrihydrite (Fh_Pb) with various Pb/(Fe+Pb) molar ratios (i.e., 0, 2, and 5%) were incubated with the iron-reducing bacterium Shewanella oneidensis MR-1 for 7 days, oxidized for 7 days (atmospheric O2), and bioreduced a second time for 7 days. Pb doping led to a drop in the rate and the extent of the reduction. Lepidocrocite (23–56%) and goethite (44–77%) formed during the first reduction period. Magnetite (72–84%) formed during the second reduction. The extremely-low-dissolved and bioavailable Pb concentrations were measured during the redox cycles, which indicates that the Pb significantly sorbed onto the minerals that were formed. Overall, this study highlights the influence of Pb and redox cycling on the bioreduction of Pb-bearing iron oxides, as well as on the nature of the secondary minerals that are formed.

Soils of the Ribeira Valley (Brazil) as Environmental Protection Barriers: Characterization and Adsorption of Lead and Cadmium

In waste disposal areas, soils can be used as environmental protection barriers to retain potentially toxic metals. Although most studies focus on lateritic soils, it is still of interest to evaluate other soil types, aiming to select the best materials among those available near the contamination area, reducing costs and construction efforts. This paper characterizes and evaluates the behavior of 13 soil materials collected in a region (Ribeira Valley, Brazil) with a history of improper mining waste disposal for the retention of lead (Pb) and cadmium (Cd) and their possible use as environmental protection barriers. All soils were acidic, kaolinitic, with negatively charged particles. Soils were grouped into three classes according to soil properties, such as particle size distribution, cation exchange capacity (CEC), and specific surface area (SSA), using cluster and principal component analysis. The Pb and Cd adsorption capacities ranged from 288 to 479 µg g−1 and 207 to 326 µg g−1, respectively, obtained from batch equilibrium tests. In general, all soils presented suitable characteristics for the retention of Pb and Cd, but four of them (1 to 4) showed the highest adsorption capacities, probably due to their larger SSA, CEC and percentage of fines (clay + silt).

A new diformyl phenol based chemosensor selectively detects Zn2+ and Co2+ in the nanomolar range in 100% aqueous medium and HCT live cells

A new diformyl phenol based chemosensor that can sense Zn2+ and Co2+ in the nanomolar range in 100% aqueous solution and in HCT cells was explored.

Vegetation and Environmental Changes on Contaminated Soil Formed on Waste from an Historic Zn-Pb Ore-Washing Plant

Simple Summary

Remnants of former Zn-Pb mining in southern Poland are an important element of geographical space. Some of the post-mining areas have found new economic and residential functions. Many of them are undergoing ecological succession and constitute valuable natural habitats enriching biodiversity of the surrounding landscapes. There are places where we can observe and document various ecological and geochemical transformations in its historical and contemporary aspects. These changes provide a basis for observing and functioning of ecosystems developing in an area transformed under the influence of Zn-Pb mining.

Abstract

Post-mining waste from Zn-Pb ore exploitation undergoes processes of spontaneous succession and changes in soil chemical composition. The Zakawie area was industrially transformed by historical mining activity, ore enrichment, and the metallurgical processing of Zn-Pb ore. The subject of the study was to analyse the rate of vegetation succession (from 1999 to 2019), soil chemistry, and the relationships between them in an anthropogenic habitat with high concentrations of potentially toxic metals. Ecological and geochemical studies were carried out in an area contaminated with waste from a disused Zn-Pb ore-washing plant. Between 1999 and 2019, the transformation of grassland and meadow vegetation into scrub and forest–grassland communities was observed. This transformation led to a decrease in the area of Molinietum caeruleae meadow (from 25.8% in 1999 to 10.7% in 2019), whose place was taken by Prunus spinosa and Rhamnus cathartica. The community of xerothermic limestone grasslands completely disappeared, being replaced in favour of the Diantho-Armerietum and Prunus spinosa community. In this period, the share of lifeforms of plants and species composition (46 and 60, respectively) also changed. The Shannon and Simpson biodiversity index reached high values in the second investigation period, and it was 0.893 and 0.86, respectively. The anthrosols had a high content of Zn—85,360 mg kg⁻¹, Pb—28,300 mg kg⁻¹, Cd—340 mg kg⁻¹, and As—1200 mg kg⁻¹. Carbonates, clay minerals, and fe-oxides are predominant in the mineral composition of the rhizosphere; the metal-bearing phases are stable; and hardly soluble minerals include smithsonite, cerussite, monheimite, hemimorphite, and oxides of Fe and Fe-Mn. Mineralisation/crust processes formed on the epidermis, and their influences on root development were found. Scanning electron microscopy and energy-dispersive X-ray spectroscopy studies on rhizosphere soil components provide information on the type of minerals and their susceptibility to heavy metals release. The identification of some biotic and mineral structures in rhizospheres can be an interesting source of information on pedogenic processes identified in back-scattered electron images.

Treatment of Soil Contaminated by Mining Activities to Prevent Contamination by Encapsulation in Ceramic Construction Materials

Mining is an essential activity for obtaining materials necessary for the well-being and development of society. However, this activity produces important environmental impacts that must be controlled. More specifically, there are different soils near new or abandoned mining productions that have been contaminated with potentially toxic elements, and currently represent an important environmental problem. In this research, a contaminated soil from the mining district of Linares was studied for its use as a raw material for the conforming of ceramic materials, bricks, dedicated to construction. Firstly, the contaminated soil was chemically and physically characterized in order to evaluate its suitability. Subsequently, different families of samples were conformed with different percentages of clay and contaminated soil. Finally, the conformed ceramics were physically and mechanically characterized to examine the variation produced in the ceramic material by the incorporation of the contaminated soil. In addition, in this research, leachate tests were performed according to the TCLP method determining whether encapsulation of potentially toxic elements in the soil occurs. The results showed that all families of ceramic materials have acceptable physical properties, with a soil percentage of less than 80% being acceptable to obtain adequate mechanical properties and a maximum of 70% of contaminated soil to obtain acceptable leachate according to EPA regulations. Therefore, the maximum percentage of contaminated soil that can be incorporated into the ceramic material is 70% in order to comply with all standards. Consequently, this research not only avoids the contamination that contaminated soil can produce, but also valorizes this element as a raw material for new materials, avoiding the extraction of clay and reducing the environmental impact.

Bioleaching for environmental remediation of toxic metals and metalloids: A review on soils, sediments, and mine tailings

Owing to industrial evolution, a huge mass of toxic metals, including Co, Cu, Cr, Mn, Ni, Pb, and Zn, and metalloids, such as As and Sb, has inevitably been released into the natural environment and accumulated in soils or sediments. Along with modern industrialization, many mineral mines have been explored and exploited to provide materials for industries. Mining industries also generate a vast amount of waste, such as mine tailings, which contain a high concentration of toxic metals and metalloids. Due to the low economic status, a majority of mine tailings are simply disposed into the surrounding environments, without any treatment. The mobilization and migration of toxic metals and metalloids from soils, sediments, and mining wastes to water systems via natural weathering processes put both the ecological system and human health at high risk. Considering both economic and environmental aspects, bioleaching is a preferable option for removing the toxic metals and metalloids because of its low cost and environmental safety. This chapter reviews the recent approaches of bioleaching for removing toxic metals and metalloids from soils, sediments, and mining wastes. The comparison between bioleaching and chemical leaching of various waste sources is also discussed in terms of efficiency and environmental safety. Additionally, the advanced perspectives of bioleaching for environmental remediation with consideration of other influencing factors are reviewed for future studies and applications.

Distribution of Pb, Zn and Cd in stream and alluvial sediments in the area with past Zn smelting operations

The sources of Zn, Pb and Cd in alluvial and stream sediments have been studied in the area of historical Zn smelting tradition. 30 samples of stream sediments and samples from 4 alluvial sediment profiles were collected. Fractions 0.125–0.063 and < 0.063 mm were analysed by the means of ICP-MS prior 4-acid digestion. The highest levels of Zn, Cd and Pb were detected in the alluvial sediments in the closest vicinity to the abandoned slag and ore roasting residue waste dumps, reaching 96 and 4520 mg/kg, 522 and 26,800 mg/kg and 3.7 and 31 mg/kg for Pb, Zn and Cd in stream and alluvial sediments, respectively. The Voglajna River then transports contamination particles into the Savinja River, which afterwards flows into the Sava River. Consequently, the anomaly can even be detected in the Sava River, more than 30 km downstream. Higher levels of Pb, Zn and Cd have been found in fraction < 0.063 mm compared to 0.125–0.063 mm fraction. Impacts of historically contaminated soil erosion and in particular the wash-out of Zn-smelting waste from the improperly managed waste dump were recognised as the dominant sources of Zn, Cd and Pb in the stream and alluvial sediments.

A novel biofilm bioreactor derived from a consortium of acidophilic arsenite-oxidizing bacteria for the cleaning up of arsenite from acid mine drainage

Arsenite (As(III)) was considered to be of great concern in acid mine drainage (AMD). A promising approach for cleaning up of arsenite from AMD is microbial oxidation of As(III) followed by adsorptions. However, there is virtually no research about the acidophilic bioreactor for As(III) oxidation so far. In this study, we formed a new biofilm bioreactor with a consortium of acidophilic As(III) oxidation bacteria. It is totally chemoautotrophic, with no need to add any carbon or other materials during the operations. It works well under pH 3.0-4.0, capable of oxidizing 1.0-20.0 mg/L As(III) in 3.0-4.5 h, respectively. A continuous operation of the bioreactor suggests that it is very stable and sustainable. Functional gene detection indicated that the biofilms possessed a unique diversity of As(III) oxidase genes. Taken together, this acidophilic bioreactor has great potential for industrial applications in the cleaning up of As(III) from AMD solution.

Spatial distribution, ecological risk and sources of heavy metals in soils from a typical economic development area, Southeastern China

Identification and quantification of the distribution, ecological risk, and sources of heavy metals in soils are essential for regional pollution control and management. In this study, spatial analysis (SA), GeogDetector model (GDM), and positive matrix factorization (PMF) model were combined to evaluate the status, ecological risk, and sources of heavy metals in soils from a typical coastal economic development area in Southeastern China. The mean contents of Cd, Pb, Cr, Cu, and Zn in the surface soils (0-20 cm) were 0.45, 41.72, 90.50, 47.86, and 145.33 mg/kg, respectively. In accordance, the mean contents of Cd exceeded the risk screening value for contamination of agricultural soil in China. Our results revealed that industrial and residential soils had higher enrichment of heavy metals than agricultural and fallow soils. Industrial production was the major driving factors influencing the spatial distribution of heavy metals. Soil OM and pH were found to be the most important factors affecting the potential ecological risk of heavy metals, followed by distance from the industrial enterprises and roads. Heavy metals in the study area were mainly originated from industrial emissions/atmospheric deposition, agricultural sources, and followed by natural sources. Therefore, regular monitoring and source control for heavy metals, especially for Cd, along with the integrated soil environmental management in the study area are crucial to ensure soil health and ecosystem security.

Sources and migration of heavy metals in a karst water system under the threats of an abandoned Pb-Zn mine, Southwest China

Water quality is of great concern under the threats of an abandoned Pb-Zn mine within a vulnerable karst area. This study focuses on tracing the sources, migration and relevant geochemical controls of heavy metals along with surface- and groundwater flow, and assessing their hazards posed to the environment by indexes of heavy metal pollution (HPI) and ecological risks (ERI). We analyzed the concentrations of lead (Pb), zinc (Zn), cadmium (Cd) and copper (Cu) in filtered and digested surface water (SW) and groundwater (GW) samples. Whilst sulfate concentrations, δ³⁴S_SO4 isotope, and other physical-chemical parameters were measured in filtered SW and GW. Clearly elevated concentrations of Zn and Cd have been observed in the upstream of the Sidi River (max. 1540.3/1676.7, and 19.9/19.4 μg/L, for filtered/digested contents, respectively), and that of digested Pb and Cu (max. 17.8 and 114.6 μg/L, respectively) in the downstream karst groundwater. Zn and Cd are likely introduced by the Sidi River which is found mostly in the dissolved phase. While Pb and Cu are sourced from the remobilization of upper lying polluted soil which mostly existed in the particulate phase. Zn and Cd concentrations in the karst groundwater peak at the losing section while Pb and Cu in the river peaks at the gaining section as a result of metals transport with SW-GW exchange. Dilution significantly decreases total metals concentration in the non-karst area. Due to the buffer effect caused by carbonates dissolution and bacterial sulfate reduction, a steady neutral pH can reduce the concentrations of the dissolved metals in the karst area. The ERI and HPI assessments show an acceptable level for surface- and groundwater. A long-term observation on the contents of undissolved metals needs to be conducted in karst areas which are threatened by metal(s) mines.

Effect of mineral supplementation on lead bioavailability and toxicity biomarkers in sheep exposed to mining pollution

The chronic exposure of livestock to lead (Pb) pollution in historical mining areas may represent significant and unnecessary costs for farmers and primary producers, in addition to important food safety risks. Here, we evaluate the effect of mineral supplements, in the form of a commercial mineral block (MB), to reduce Pb bioavailability and toxicity in sheep through an experimental approach under real farming conditions in an abandoned mining area. Blood, fecal Pb levels, and soil ingestion, along with different blood and plasma biomarkers were studied. Experiment 1 was carried out with 3-months-old female lambs, n = 54, fenced in two contiguous MB and non-MB-supplemented plots. After 20 days of treatment, blood Pb level was lower in MB-supplemented sheep than in those that were non-MB-supplemented. Experiment 2 was carried out with 2-months-old female lambs, n = 34, fenced in a single plot and MB-supplemented during the first 20 days of experiment. After MB supplementation, blood Pb level in sheep was also reduced by almost half, falling below the threshold of subclinical intoxication, and then increased again after 20 days without MB. Experiment 3 was carried out with adult rams, n = 10, fenced in a single MB-supplemented plot during the first 20 days of experiment. In this case, blood Pb level decreased by day 40. Soil ingestion was not reduced by MB supplementation in any of the experiments. MB supplementation favored antioxidant status by increasing SOD activity and reducing GPX activity and MDA levels. In conclusion, the MB supplementation seemed to reduce Pb bioavailability by increasing its fecal excretion, but renal excretion and bone deposition may also have favored the reduction of blood Pb concentration. Mineral supplements may be a new easy-to-apply and cost-effective way to reduce livestock exposure in Pb polluted sites.

Natural Seed Limitation and Effectiveness of Forest Plantations to Restore Semiarid Abandoned Metal Mining Areas in SE Spain

The natural regeneration of forests in mining areas is typically hampered by edaphic stress. Semiarid conditions add a climatic stress that challenges the restoration of these harsh ecosystems. This is the case of Tetraclinisarticulata (Vahl) Masters mixed forests in the Western Mediterranean region colonizing mining structures abandoned three decades ago. We studied the factors controlling the natural establishment of nine shrub and tree species key in these forests in eight metal mine tailings in SE Spain. In addition, we assessed the success of reintroducing 1480 individuals of the nine species 15 months after planting in one of the tailings. Specifically, we analyzed the effect of (i) species identity in terms of sapling survival, growth, nutritional status and metal bioaccumulation, and (ii) adding organic amendments into the planting holes on the same parameters. Our results indicated that natural colonization is a recent process, with seedling cohorts that vary up to two orders of magnitude among species and a practical absence of adult plants in most species excepting T. articulata. We identified seed limitation as a key factor controlling seedling density, which was significantly explained by the distance from the border of the tailing to the closest adult out of the tailing. Soil metal concentration did not have any explanatory power on the density of naturally-established seedlings, whereas soil fertility was relevant only for Rhamnus lycioides L. Overall survival of planted individuals was over 80%, survival and growth remarkably differing among species. Organic amendments had neutral or negative effects on plant survival, but significantly increased the growth of survivors despite their modest effects on leaf nutrient contents. Most species showed high metal bioaccumulation, which was exacerbated by organic amendments. We discuss how biodiversity conservation programs can benefit from the affordable and successful plantation of stress-tolerant local species, but come at the expense of potential metal transfer through trophic webs.

Metalliferous Mining Pollution and Its Impact on Terrestrial and Semi-terrestrial Vertebrates: A Review

Metalliferous mining, a major source of metals and metalloids, has severe potential environmental impacts. However, the number of papers published in international peer-reviewed journals seems to be low regarding its effects in terrestrial wildlife. To the best of our knowledge, our review is the first on this topic. We used 186 studies published in scientific journals concerning metalliferous mining or mining spill pollution and their effects on terrestrial and semi-terrestrial vertebrates. We identified the working status of the mine complexes studied, the different biomarkers of exposure and effect used, and the studied taxa. Most studies (128) were developed in former mine sites and 46 in active mining areas. Additionally, although several mining accidents have occurred throughout the world, all papers about effects on terrestrial vertebrates from mining spillages were from Aznalcóllar (Spain). We also observed a lack of studies in some countries with a prominent mining industry. Despite >50% of the studies used some biomarker of effect, 42% of them only assessed exposure by measuring metal content in internal tissues or by non-invasive sampling, without considering the effect in their populations. Most studied species were birds and small mammals, with a negligible representation of reptiles and amphibians. The information gathered in this review could be helpful for future studies and protocols on the topic and it facilitates a database with valuable information on risk assessment of metalliferous mining pollution.

Factors influencing heavy metal availability and risk assessment of soils at typical metal mines in Eastern China

China exemplifies the serious and widespread soil heavy metal pollution generated by mining activities. A total of 420 soil samples from 58 metal mines was collected across Eastern China. Total and available heavy metal concentrations, soil physico-chemical properties and geological indices were determined and collected. Risk assessments were applied, and a successive multivariate statistical analysis was carried out to provide insights into the heavy metal contamination characteristics and environmental drivers of heavy metal availability. The results suggested that although the degrees of pollution varied between different mine types, in general they had similar contamination characteristics in different regions. The major pollutants for total concentrations were found to be Cd and As in south and northeast China. The availability of Zn and Cd is relatively higher in south China. Soil physico-chemical properties had major effect on metal availability where soil pH was the most important factor. On a continental scale, soil pH and EC were influenced by the local climate patterns which could further impact on heavy metal availability. Enlightened by this study, future remediation strategies should be focused on steadily increasing soil pH, and building adaptable and sustainable ecological system to maintain low metal availabilities in mine site soils.

Interactions of cadmium and zinc in high zinc tolerant native species Andropogon gayanus cultivated in hydroponics: growth endpoints, metal bioaccumulation, and ultrastructural analysis

Cadmium (Cd) and zinc (Zn) toxicity causes physiological disorders and harms plants, interfering with the rehabilitation of areas affected by mining activities. This study evaluated how the exposure to Zn and/or Cd affects the growth of native andropogon grass (Andropogon gayanus Kunth) plants originally found in areas contaminated with Cd and/or Zn due to zinc mining activities. Plants were cultivated for 7 weeks in a nutrient solution treated with Zn (142.3-854.0 μM) or Cd (0.9-13.3 μM) separately or combined with a molar ratio of 64:1 (Zn:Cd). A control treatment was grown in a complete Hoagland and Arnon solution (without Cd). Plant height, stem diameter, internode length, dry weight, Cd and Zn concentration, and accumulation in shoots/roots, as well as ultrastructure of roots and leaves were analyzed at the end of the experiment. The root dry weight was not significantly affected by the addition of the metals. Moreover, Zn provided higher shoot dry weight (up to 160%) relative to control. Andropogon grass tolerated both metals better separately than when applied together. Transmission electron microscopy analyses showed modifications such as vesiculation and vacuolation in the ultrastructure of andropogon tissues by Cd and/or Zn. The andropogon grass was tolerant to the doses tested, evidencing that it has potential for recovering areas contaminated with Zn and/or Cd.

Characterization of Mining-Related Aromatic Contaminants in Active and Abandoned Metal(loid) Tailings Ponds

This study reports on the compositional diversity of organic compounds in metal(loid)-bearing tailings samples from both active and abandoned tailings ponds. Tailings samples were qualitatively analyzed by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS). In addition, the priority PAHs (16), PAEs (6), and phenols (2) were quantitatively analyzed using gas chromatography-mass spectrometry (GC-MS). We attribute the presence of some of aromatic organics in studied tailings ponds to particular sources. Mineral floatation reagents are likely the major sources of small-ring aromatics in tailings ponds, and products from metallurgical processing and burning of fossil fuels in the mining area or further afield are also possible contributors and might be the main source of large-ring aromatics. We found that tailings ponds abandoned for decades can still have organics concentrations at levels of concern. Large-ring aromatics are generally more toxic than other contaminants, and these were more abundant in abandoned tailings ponds. This suggests that these large-ring organics do not readily decompose or biodegrade into less toxic byproducts, as do volatiles and many other organic compounds. Our aromatic contaminants database provides an important starting point for researchers to investigate and compare similar contaminants that might be also present in other tailings ponds and emphasizes the necessity of considering their transformations over time.

The Use of Mining Waste Materials for the Treatment of Acid and Alkaline Mine Wastewater

The mining of metal ores generates both liquid and solid wastes, which are increasingly important to manage. In this paper, an attempt was made to use waste rocks produced in the mining of zinc and lead to neutralizing acid mine drainage and alkaline flotation wastewater. Waste rock is a quartz-feldspar rock of hydrothermal origin. It is composed of, besides quartz and potassium feldspar (orthoclase), phyllosilicates (chlorite and mica), and sulfides (chiefly pyrite). To determine its physicochemical parameters and their variability, acid mine water and flotation wastewater were monitored for 12 months. Acid mine drainage (AMD) is characterized by a low pH (~3), high zinc concentration (~750 mg·L−1), and high sulfate content (~6800 mg·L−1). On the other hand, the determinations made for flotation wastewater showed, among others, a pH of approximately 12 and ca. 780 mg·L−1 of sulfates. AMD and flotation wastewater neutralization by the waste rock was shown to be possible and efficient. However, in both cases, the final solution contained elevated concentrations of metals and sulfates. Premixing AMD with alkaline flotation wastewater in the first step and then neutralizing the obtained mixture with the waste rock was considered the best solution. The produced solution had a circumneutral pH. However, the obtained solution does not meet the legislative requirements but could be further treated by, for example, passive treatment systems. It is noteworthy that the proposed approach is low cost and does not require any chemical reagents.

Contamination of stream waters, sediments, and agricultural soil in the surroundings of an abandoned copper mine by potentially toxic elements and associated environmental and potential human health-derived risks: a case study from Agrokipia, Cyprus

Abandoned mining areas have left a legacy of environmental damage with potential public health implications. The present study aimed at (1) assessing the level of contamination of the sites surrounding the Agrokipia abandoned copper mine in Cyprus through the mobilization of potentially toxic elements (PTEs), (2) correlating results with the mineralogy of the area, (3) discussing potential ecological and human health risks, and (4) proposing regeneration strategies. To this effect, the levels of 22 PTEs and other major elements were assessed in the acidic water of pit lakes, the tailings, the waters, and sediments of several streams originating from the mining site and flowing through the village of Agrokipia, and from agricultural soil from an impacted adjacent olive orchard. The pH values of water (pH < 2.7) in the pit lakes uncovered the acidic and oxidizing conditions that prevailed in the area. The acidity and the examined PTE concentrations in stream waters followed a decreasing trend with increasing distance from the tailing, reaching background values in a distance of 1500 m. The tailing spoil-heap was significantly enriched with Cu, Zn, Pb, Cd, Cr, and Ag (e.g., enrichment factor values up to 29 for Cu and 120 for Ag). Stream sediments and agricultural soil were contaminated with PTEs (mainly Cu, Zn, Pb, Cd, Cr, Ag, and Li), as evident by several contamination indices (i.e., enrichment and contamination factor). The level of contamination was correlated with the reported mineralogy of the site. The values of the degree of contamination (Cdeg = 62) and pollution load index (PLI = 2.4) indicated contamination of the sediments of the Voulgarides stream flowing through the village, suggesting potential public health implications to the local community. In addition, the values of the ecological risk factor suggested that the studied streams pose moderate ecological risks, mainly mediated by Cd and Cu. Overall, the results highlighted the need for undertaking regeneration measures for safeguarding environmental sustainability and public health.

Bioimmobilization of toxic metals by precipitation of carbonates using Sporosarcina luteola: An in vitro study and application to sulfide-bearing tailings

Metal release from mining wastes is a major environmental problem affecting ecosystems that requires effective, low-cost strategies for prevention and reclamation. The capacity of two strains (UB3 and UB5) of Sporosarcina luteola was investigated to induce the sequestration of metals by precipitation of carbonates in vitro and under microcosm conditions. These strains carry the ureC gene and have high urease activity. Also, they are highly resistant to metals and have the capacity for producing metallophores and arsenophores. SEM, EDX and XRD reveal that the two strains induced precipitation of calcite, vaterite and magnesian calcite as well as several (M²⁺)CO₃ such as hydromagnesite (Mg²⁺), rhodochrosite (Mn²⁺), cerussite (Pb²⁺), otavite (Cd²⁺), strontianite (Sr²⁺), witherite (Ba²⁺) and hydrozincite (Zn²⁺) in vitro. Inoculation of the mixed culture of UB3+UB5 in tailings increased the pH and induced the precipitation of vaterite, calcite and smithsonite enhancing biocementation and reducing pore size and permeability slowing down the oxidation of residual sulfides. Results further demonstrated that the strains of S. luteola immobilize bioavailable toxic elements through the precipitation and coprecipitation of thermodynamically stable (M²⁺)CO₃, Fe-Mn oxyhydroxides and organic chelates.

In vitro assessment of mineral blocks as a cost-effective measure to reduce oral bioavailability of lead (Pb) in livestock

Soil contamination in former mining districts is a persistent problem resulting from the historic lack of legal requirements as regards land restoration after mine closures. Much of this polluted land is currently being used worldwide for livestock and big game production, with the consequent health risks for the animals exposed and the subsequent threats to food safety. Soil remediation and restoration may be unfeasible or difficult to accomplish in the short term when pollution affects large territories and other alternatives must, therefore, be explored in order to reduce the probability of grazing animals being exposed to this contamination. In this paper, we study the use of mineral blocks (MBs) as a potential alternative by which to reduce the oral bioavailability of lead (Pb) in polluted soils by means of a simplified in vitro assay simulating gastrointestinal pH conditions. Experiments were carried out with twelve commercial MBs of different compositions in order to identify the most useful to be tested in further in vivo bioavailability studies. The results showed that one of them reduced the bioaccessibility of Pb from polluted soil by 88.2% and 75.9% under gastric and intestinal conditions, respectively, when compared with assays containing only polluted soil without MBs. The MB in question had the highest phosphorus content (7%) and one of the highest calcium contents (10%) of all those tested. Furthermore, negative correlations were detected between the content of calcium and phosphorus in the MBs and the percentage of bioaccessible Pb under gastric conditions, and between phosphorus and bioaccessible Pb under intestinal conditions. The use of MBs with a high phosphorus and calcium content should consequently be tested in vivo as a cost-effective (€ 0.6-1.5/sheep/month) tool by which to reduce the bioavailability of Pb for extensive grazing livestock reared in contaminated areas.

NTA-enhanced Pb remediation efficiency by the phytostabilizer Athyrium wardii (Hook.) and associated Pb leaching risk

Nitrilotriacetic acid (NTA), a biodegradable chelant, has been promoted to effectively assist Pb phytoextraction, while a few researches available on the phytostabilizer of Athyrium wardii (Hook.). In this study, two incubation experiments and a subsequent column experiment were conducted to investigate the effects of application of NTA on Pb availability in soils and Pb accumulation in A. wardii and associated leaching risk. The application of NTA significantly increased the exchangeable Pb and Pb bound to carbonates along with a decreased pH, leading to enhanced Pb availability in soils. It was more effective in enhancing Pb availability in soils by adding 2 mmol kg^-1 NTA into soils at once for 7 d, thus demonstrating potential for enhancing Pb uptake by A. wardii. After the addition of 2 mmol kg^-1 NTA for 7 d, Pb concentrations in roots of A. wardii was enhanced by 23.8%, along with 10.6% of increase for Pb accumulation in roots. No significant changes were observed for the biomass of A. wardii. Meanwhile, the available Pb and TCLP-extractable Pb in 0-20 cm soils increased by 11.1-23.4% and 7.1-31.2%, thus promoting Pb leaching in 0-20 cm soils. However, there were no changes for Pb leaching risk levels of 20-40 cm soils. No Pb was detected in the leachates from all columns. The application of 2 mmol kg^-1 NTA at once for 7 d is therefore proved to show greater potential in enhancing Pb remediation efficiency by the phytostabilizer of A. wardii without increasing Pb leaching risk into groundwater.

Metal Content of Stream Sediments as a Tool to Assess Remediation in an Area Recovering from Historic Mining Contamination

Lead and zinc mining was booming in the early 1900s in and near Joplin, Missouri; a town within the Tri-State Mining District, USA. After the ore became depleted, mining companies moved out, leaving a profoundly disturbed land. Presently, over 90% of the land has been remediated. We collected sediment samples along two creeks flowing through the historically contaminated area that have been identified as major contributors of metals to downstream reservoirs, Center Creek (14 samples) and Turkey Creek (30 samples). Sediment metal content was determined by aqua regia extraction, the potentially bioavailable fraction by 0.11 M acetic acid extraction, and toxicity by ΣPEC-QCd,Pb,Zn. Zinc and lead content in sediments were high in both creeks notwithstanding remediation actions; e.g., median concentrations of 521 mg/kg Pb and 5425 mg/kg Zn in Center Creek, corresponding to 19 and 52 times the background concentration. The metals’ distribution followed no discernible pattern downstream. The potentially bioavailable fraction varied between 0.36% (Pb, Center Creek) and 4.96% (Zn, Turkey Creek). High toxicity was found in 40% of the samples in Turkey Creek and 78.5% of the samples in Center Creek. While this level of toxicity would likely affect aquatic organisms, its limited mobility under alkaline conditions suggests a lesser threat to humans. On the other hand, this high toxicity will likely persist in sediments for at least a few decades, based on their high metal content and low mobility.