Tailings Site Research Articles

Prediction of soil heavy metal content around mine tailings using multiple methods combined with transformed hyperspectral reflectance data

The extensive accumulation of tailings can potentially cause heavy metal contamination in the surrounding farmland soil. Accurately predicting the spatial distribution of heavy metals in farmland soil is crucial for assessing the potential environmental hazards of tailings.This study focuses on the spatial distribution and the quantitative prediction of heavy metals (chromium (Cr), vanadium (V), and copper (Cu)) in soils surrounding mine tailings using advanced spectral data analysis and multiple prediction models. The original hyperspectral reflectance data were processed using first-order differential (FD), second-order differential (SD), reciprocal logarithmic (LR), and continuum removal (CR) transformations to highlight the positions of characteristic bands. Multiple linear regression (MLR), stepwise linear regression (SLR), partial least squares regression (PLSR), random forest (RF), and back propagation artificial neural network (BP-ANN) models were used to establish inversion models for Cr, V, and Cu based on bands with high correlation coefficients. The performance of the inversion models was evaluated using the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), and residual predictive deviation (RPD). The results indicate that the raw hyperspectral data from the measured soil exhibit a weak response to heavy metal content in the study area. However, applying FD, SD, and CR transformations significantly enhances the sensitivity of soil spectral data to heavy metal concentrations, facilitating subsequent modeling. Among these, the SD transformation is particularly beneficial for modeling the Cr and Cu elements in the soil. For the V element, the FD transformation yields data that are more suitable for modeling. Regarding the inversion models based on the measured spectral data, the BP-ANN model exhibited the best predictive performance. Specifically, when combined with SD spectral data, the BP-ANN achieved the highest predictive accuracy for Cu content (R² = 0.85, RPD = 2.12). The RF model demonstrated the next best performance, with its optimal inversion model also utilizing SD spectral data for predicting Cu content (R² = 0.76, RPD = 1.90). On the other hand, the MLR model exhibited the poorest performance and is unsuitable for predicting heavy metal content in the region using the measured spectral data. This study highlights the potential of spectral data in environmental monitoring and provides a technical reference for the inversion assessment and regulation of heavy metals in farmlands surrounding tailing sites.

The Long-Term Performance of a High-Density Polyethylene Geomembrane with Non-Parametric Statistic Analysis and Its Contribution to the Sustainable Development Goals

The tailings from gold beneficiation can cause various negative impacts, necessitating measures to prevent their transport and environmental contamination. Geomembranes serve as hydraulic barriers in mining tailings reservoirs, thereby supporting the Sustainable Development Goals (SDGs). To ensure that the geomembrane effectively mitigates environmental impact, it is essential to study its durability when applied in the field. This article examines the long-term performance of an HDPE geomembrane exposed for 7 and 11 years at a gold mining tailing site in Brazil. Samples were exhumed from different locations at the dam, and their properties were evaluated. Non-parametric statistics were employed using the Kernel Density Estimator (KDE). For the 11-year-old geomembranes, the probability of the geomembrane reaching nominal failure in terms of tensile strength was 0.4%. The peel separation values exceeded the maximum allowable by the GRI GM13 standard. Although the geomembranes showed significant antioxidant depletion, suggesting they were close to or had already reached their residual stages, they approached nominal failure based on their stress crack resistance but did not rupture. The environmental analysis indicated no significant contamination in the area, corroborating that the geomembrane is fulfilling its function. The non-parametric methodology proved promising for durability analysis and could be applied to other engineering projects with geosynthetics, thereby adding reliability to decision-making in alignment with sustainable development.

High-carbon wood ash biochar enhances native tree survival and growth on sand-capped mine tailings.

Use of waste wood biomass for bioenergy produces wood ash as a by-product; this ash is typically landfilled, but can potentially play an important role in soil improvement and forest restoration. In particular, high-carbon wood ash biochar (HCWAB) could supply nutrients, improve substrate water-holding capacity and pH, and emulate the ecosystem benefits of wildfire residues. Thickened tailings sites at metal mines across Canada are subject to stringent restoration regulations that entail planting of native trees to promote rapid reforestation. While HCWAB may prove beneficial in this context, field trials have been very limited to date. We conducted a large-scale, replicated field trial on sand-capped tailings at an operational gold mine in the Canadian boreal forest to assess the impact of HCWAB (at dosages of 0, 6.4, 12.8, and 19.1 t/ha) on survival and growth of four native tree species, as well as substrate chemical properties and element uptake in tree tissues. After 2years, the survival of planted, native trees was highest at low to moderate application rates; HCWAB dosages above 13 t/ha presented reduced tree survival to levels comparable to unamended substrates. Tree growth was higher across all HCWAB doses relative to growth in samples planted on untreated substrates; tree species and initial size also had large impacts on final tree survival and aboveground growth. The survival of Betula papyrifera was significantly higher than other species, while smaller transplanted trees in general survived in greater numbers compared to larger size classes. Volunteer herbaceous vegetation significantly increased at the higher HCWAB application dosages and tree performance was negatively correlated with vegetation cover, consistent with a resource competition effect. HCWAB additions to sand-capped mine tailings did not significantly alter tree tissue concentrations or substrate availability of potentially toxic metals (Cd, Cu, Al). We conclude that low to moderate dosages of HCWAB on sand-capped tailings, particularly between 6.4 and 12.8 t/ha, may offer benefits to early tree survival, growth, and substrate nutrient status without causing significant risks of phytotoxicity and recommend future field trials focus on strategies to reduce tree competition with competing vegetation.

Release of Radioactive Particles to the Environment.

When environmental impact and risks associated with radioactive contamination of ecosystems are assessed, the source term and deposition must be linked to ecosystem transfer, biological uptake and effects in exposed organisms. Thus, a well-defined source term is the starting point for transport, dose, impact and risk models. After the Chornobyl accident, 3-4 tons of spent nuclear fuel were released and radioactive particles were important ingrediencies of the actual source term. As Chornobyl particles were observed in many European countries, some scientists suggested that radioactive particles were "a peculiarity of the Chornobyl accident." In contrast, research over the years has shown that a major fraction of refractory elements such as uranium (U) and plutonium (Pu) released to the environment has been released as particles following a series of past events such as nuclear weapons tests, non-criticality accidents involving nuclear weapons, military use of depleted uranium ammunition, and nuclear reactor accidents. Radioactive particles and colloids have also been observed in discharges from nuclear installations to rivers or to regional seas and are associated with nuclear waste dumped at sea. Furthermore, radioactive particles have been identified at uranium mining and tailing sites as well as at other NORM sites such as phosphate or oil and gas industrial facilities. Research has also demonstrated that particle characteristics such as elemental composition depend on the emitting source, while characteristics such as size distribution, structure, and oxidation state influencing ecosystem transfer will also depend on the release scenarios. Thus, access to advanced particle characteristic techniques is essential within radioecology. After deposition, localized heterogeneities such as particles will be unevenly distributed in the environment. Thus, inventories can be underestimated, and impact and risk assessments of particle contaminated areas may suffer from unacceptable large uncertainties if radioactive particles are ignored. The present paper will focus on key sources contributing to the release of radioactive particles to the environments, as well as linking particle characteristics to ecosystem behavior and potential biological effects.

Assessment of Mercury Contamination in Water and Soil from Informal Artisanal Gold Mining: Implications for Environmental and Human Health in Darmali Area, Sudan

Mercury contamination stemming from artisanal and small-scale gold mining (ASGM) operations poses significant environmental and health concerns. This study focuses on the Darmali area in River Nile State, Sudan, where the reprocessing of amalgamation tailings has led to mercury contamination. This study assessed the mercury content in soil and tailings samples, as well as in tap and groundwater, to evaluate the human health risks from ASGM activities and assess contamination levels within the study area. Soil and water samples were collected from various locations, including agricultural, residential, and tailings sites, as well as groundwater and tap water from the Nile. Mercury analysis was conducted using MA-3000 (NIC), and geo-accumulation index analysis revealed extreme pollution levels in areas with tailings and moderate pollution levels in agricultural and residential areas. Hazard quotients were applied to assess health risks, with inhalation of mercury vapor identified as the primary exposure route. The results indicated that tailings pose significant health risks, particularly for children, while water samples and soil from agricultural and residential areas did not pose significant risks. These findings underscore the urgent need for authorities and local communities to address mercury contamination by removing and treating tailings from affected areas to mitigate health risks.

Potential of Pinus radiata, Eucalyptus globulus and Acacia dealbata for the long-term phytostabilization of copper mine tailings

Many contaminated tailings throughout the world cause environmental and human-health related problems due to air and water drift. Tailing phytostabilization is a promising solution, but only certain plant species may tolerate and grow in these contaminated areas. We analyzed the chemical properties of a vegetated and unvegetated area in a tailing site in Central Chile. In addition, in the vegetated area we analyzed the metals content of roots, stems, and foliage in 41-years old plantations of Pinus radiata, Acacia dealbata, and Eucalyptus globulus (the only three species that survived from a total of 34 species planted), and determined height (H), and diameter at breast height (DBH). The results indicated that, except for pH, Se, Pb, and organic matter, all components (nutrients and metals) were two- to three- fold lower in the vegetated tailing compared to that of the unvegetated tailing. The analysis of plant tissues indicated that Cu was higher in the roots of P. radiata (2,073 mg kg−1) and lower in the stems of the same species (4.1 mg kg−1). However, the ability to take up and transport Cu to the shoots was higher in A. dealbata and lower in P. radiata (bioaccumulation factor of 0.19 and 0.06, respectively).

Assessing the radiological hazards due to radionuclides in sediments and tailings around Kilembe copper mines, Western Uganda

ABSTRACT Copper mining in Kilembe Valley, Western Uganda, between 1956 and 1982 resulted in multiple tailing sites, raising concerns about potential increases in the natural background radiation. In this study, the radioactivity concentrations of 226Ra, 232Th, and 40K in 31 sediments and tailing samples from the Kilembe copper mines area were determined using HPGe-based gamma spectrometry. The mean activity concentrations of 226Ra, 232Th, and 40K in sediment samples were 38.6 ± 8.9, 37.4 ± 7.8, and 708.0 ± 147.3 Bq kg−1, respectively. While in tailing samples, the mean values were 171.3 ± 31.7, 34.8 ± 14.9, and 792.4 ± 208.2 Bq kg−1, respectively. These values exceeded global averages of 35, 30, and 400 Bq kg−1 for 226Ra, 232Th, and 40K, respectively. To assess the radiological hazards due to radionuclides in sediments and tailings, several parameters such as the radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), gamma representative index (Iγ), absorbed dose rate (D), total annual effective dose (Etot), and total excess lifetime cancer risk (ELCRtot) were determined. In sediments, most of these hazard parameters were above the world’s average values, except Raeq, Iγ, Hex, and Hin. While in tailings, all the hazard parameters surpassed the global average values except Raeq and Hex. Pearson correlation coefficient and hierarchical cluster analysis showed that 226Ra was the main contributor to the assessed radiological hazards. The study suggests potential radiological risks linked to natural radioactivity from sediments and mine tailings, especially when used as building materials.

Numerical Simulation of Geophysical Models to Detect Mining Tailings’ Leachates within Tailing Storage Facilities

The effective detection and monitoring of mining tailings’ leachates (MTLs) plays a pivotal role in environmental protection and remediation efforts. Electrical resistivity tomography (ERT) is a non-invasive technique widely employed for mapping subsurface contaminant plumes. However, the efficacy of ERT depends on selecting the optimal electrode array for each specific case. This study addresses this challenge by conducting a comprehensive review of published case studies utilizing ERT to characterize mining tailings. Through numerical simulations, we compare the imaging capabilities of commonly used electrode configurations, six ERT arrays, aiming to identify the optimal array for MTLs’ detection and monitoring. In addition, field surveys employing ERT were conducted at the El Mochito mine tailings site to detect zones saturated with leachates within the tailing storage facilities (TSFs). The findings indicate that the “Wenner-Schlumberger” array exhibits superior data resolution for MTL detection. However, the choice of the optimal electrode array is contingent on factors such as survey location, geological considerations, research objectives, data processing time and cost, and logistical constraints. This study serves as a practical guide for selecting the most effective electrode array in the context of pollutant penetration from mining tailings, employing the ERT technique. Furthermore, it contributes valuable insights into characterizing zones saturated with mining tailing leachates within the TSFs, providing a solid foundation for informed environmental management and remediation strategies.

Pb-resistant Pantoea rwandensis promotes maize's growth by altering Pb accumulation in biomass and soil Pb immobilization.

In lead (Pb)-contaminated soil, inoculating phosphate-solubilizing bacteria (PSB) to reduce the phytoavailability of Pb and to change the soil nutrients is an important way to inhibit the Pb uptake by plants. In this study, we isolated the native Pb-resistant Pantoea rwandensis from a tailings site. We employed broth culture and pot experiments to investigate the effect of the inoculation of P. rwandensis on Pb immobilization in the soil, the soil nutrients, the microbial community, and Pb accumulation in the biomass of maize (Zea mays L.). The results showed that P. rwandensis not only tolerated Pb2+ but also dissolved Ca3(PO4)2 by secreting oxalic acid, tartaric acid, lactic acid, and acetic acid, which significantly increased the amount of dissolved P, up to 567.50 mg.L-1. In the pot experiment, the application of culture filtrate, an inoculation with P. rwandensis, or a mixture of culture filtrate and P. rwandensis increased the soil residual Pb by 49.57%, 89.81%, and 41.69%, respectively, compared to the control. Consequently, the increase in the residual Pb in the soil inhibited its uptake by maize, and an inoculation of P. rwandensis or a mixture of culture filtrate and P. rwandensis decreased the accumulation of Pb in the shoot biomass of maize by 61.65% and 72.48% and in the roots of maize by 26.00% and 39.59%, respectively. Meanwhile, P. rwandensis and the mixture of culture filtrate and P. rwandensis increased the shoot biomass of maize by 54.39% and 17.86% and the root biomass of maize by 108.77% and 17.86%, respectively. A P. rwandensis inoculation increased the biodiversity of the fungal community and the abundance of Proteobacteria, Mortierella, and Sphingomonas. Our results demonstrate that an inoculation with P. rwandensis could promote the transformation of Pb fractions and a functional change in the soil bacterial community, ultimately decreasing Pb accumulation in the biomass and promoting the development of maize.

Assembly processes and ecological dynamics of root-associated bacterial communities during phytoremediation of vanadium-titanium mine tailings using Millettia pinnata

The vanadium-titanium magnetite (V–Ti) mine tailings are a reservoir of heavy metals, posing a grave peril to the adjacent soil environment. Millettia pinnata has emerged as a proficient pioneer tree species for the purpose of phytoremediation of V–Ti tailings. In the course of phytoremediation, the soil microbiota play an indispensable role within the rhizosphere ecosystem. The aim of this study was to dissect the underlying mechanisms governing the assembly processes of the bacterial community. The βNTI and RCbray analyses revealed that while the overall community assembly manifested deterministic attributes, rare taxa were chiefly impacted by stochastic processes (73.7%), inclusive of dispersal limitation and undominated mechanisms. In contrast, the abundant subcommunity was primarily subject to deterministic forces (84.3%), notably heterogeneous selection. Mantel test, regression analysis and ecological niche analysis showed that soil nitrogen availability emerged as a pivotal driver of the microbial assembly processes, exerting substantial influence on both rare (Mantel's r = 0.6817, p = 0.0001) and abundant taxa (Mantel's r = 0.5103, p = 0.0001) by amplifying their diversity and community turnover, constricting habitat niche breadth and overlap, and fostering the proliferation of ecological specialists. However, the heavy metal content was not found to wield significant influence in shaping the structure and assembly of the rhizosphere community (p > 0.05). The present results affirm the proposition that rare taxa are important in upholding ecological stability and providing essential microbial ecosystem services, while abundant taxa serve to fortify the entirety of the community. These insights advance our understanding of the community dynamics pertaining to the rhizosphere community associated with M. pinnata, holding paramount theoretical implications for the endeavour of plant-assisted ecological restoration in polluted tailings sites.

Further development and application of a method for assessing radionuclide surface activity distribution and source location based on measurements of ambient dose equivalent rate. Examples for Andreeva Bay, Chernobyl NPP and Istiklol

A method for reconstructing surface activity density (SAD) maps based on the solution of the Fredholm equation has been developed and applied. The construction of SAD maps was carried out for the site of the temporary storage (STS) of spent fuel and radioactive waste (RW) in Andreeva Bay using the results of measuring campaign in 2001–2002 and for the sheltering construction of the solid RW using the results of measurements in 2021. The Fredholm equation was solved in two versions: under conditions of a barrier-free environment and taking into account buildings and structures located on the industrial site of the STS Andreeva Bay. Lorenz curves were generated to assess the compactness of the distributions of SAD and ambient dose equivalent rate (ADER) for the industrial site and the sheltering construction at STS Andreeva Bay, the area of the IV stage uranium tailing site near the city of Istiklol in the Republic of Tajikistan, and for roofs of the Chernobyl nuclear power plant. The nature of impact of the resolution (fragmentation) of the raster, the value of the radius of mutual influence of points (contamination sites), the height of the radiation detector above the scanned surface and the angular aperture of the radiation detector on the accuracy of the SAD reconstruction is shown. The method developed allows more accurate planning of decontamination work when only ADER measurements data is available. The proposed method can be applied to support the process of decontamination of radioactively contaminated territories, in particular during the remediation of the STS Andreeva Bay.

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.

Determination of Natural Radioactivity Levels and Resultants Radiological Hazard from Soil Samples around Gold Mining Area in Ijesa-land South-Western Nigeria

Activity concentration levels and some radiological parameters owing to natural radioactivity in the soil samples randomly obtained in gold tailing sites in Ijesa­-land Southwestern Nigeria were analyzed. Analyzed results from 30 soil samples using multi-channeled NaI gamma detector show that the activity concentration of 233U; ranged from 17.42 0.54 to 49.892.42 BqKg-1; 232Th ranged from 22.10 4.70 to 76.557.44BqKg-1 and 40K; ranged from 307.0023.90 to 693.5851.50 BqKg-1 in the samples were measured. The mean absorbed dose rate calculated was marginally higher than the world average of 59nGyh-1. The average annual effective dose rate (outdoor) for all samples ranged from 0.08 + 01. 11mSv.y-1 with a mean of 0.07 which stays far below the permitted worldwide limit of 1mSv.y-1hy by International Commission on Radiation Protection (ICRP 2010). The calculated hazard indices for external and internal remained to be lower than unity signifying that mineworkers and individuals active in such area are not exposed radiation hazard.

Heavy metal pollution characteristics and systemic risk assessment of the environment around the tailings site

Heavy metal pollution characteristics and systemic risk assessment of the environment around the tailings site

Unlocking the potential of microbes: biocementation technology for mine tailings restoration - a comprehensive review.

Mine tailings contain finer particles, crushed rocks, dugout-soil, water, and organic and inorganic metals or metalloids, including heavy metals and radionuclides, which are dumped as waste or non-economic by-products generated during mining and mineral processing. These abundant and untreated materials seriously threaten the environment, human health, and biodiversity because of the presence of heavy metals, radionuclides, and associated primary and secondary toxic components, including the risk of tailings dam failures. Biocementation technology, which involves the use of mining microbes to secrete cement-like materials that bind soil particles together, is a promising approach to restore mine tailing sites and reduce their mobility and toxicity. However, there is a lack of literature on the combined interactions among mining microbes, tailings residues, biocementation, and low-carbon cement (LCC) prospects. This comprehensive review article explores the prospects of mining microbes for mine tailings restoration using biocementation technology, the key influencing factors and their impact, mechanisms and metabolic pathways, and the effectiveness of biocementation technology in restoring mine tailings sites. In addition, it reviews the utilization of mine tailings materials as an alternative source of cement or construction materials for LCC technology. Furthermore, this review highlights the important issues, challenges, limitations, and applications of biocementation technology for mine tailings rehabilitation. Finally, it provides insights for future research and implementation of biocementation for mine tailings restoration and utilization of tailing materials in the industrial sector to reduce carbon emissions/footprints and achieve net-zero goals.

Trace Elements Contamination of Kilembe Copper Mine Catchment Soils in Kasese District, Western Uganda

ABSTRACT The mining and processing of copper in the Kilembe area, Western Uganda from 1956 to 1982 left behind several tailing sites containing cupriferous and coralliferous pyrites. A study was conducted to establish the concentrations of trace elements in point sources (tailings) within Kilembe mine and the distribution of trace elements within catchment soils. Mine tailings and catchment soils were sampled, acid digested and tested for elemental concentrations using ICP-MS. Tailings appeared to be the main sources of trace element contamination of soils with very high concentrations (mg kg−1) of Cu (240–11500), Co (101–180) and Ni (140–248) compared with average world crust concentration of Cu (20–75), Co (1–15) and Ni (20) mg kg−1. The concentration (mg kg−1) of Cu (3.5–975), Co (4.9–110) and Ni (5.3–180) in soils along the mine zone and downstream were significantly higher than upstream trace element concentrations and in many samples exceeding recommended agricultural thresholds. Positive and significant correlations were observed between Fe and Mn with all trace elements in soil, suggesting adsorption and co-precipitation processes. The major factors influencing trace element distributions in the soils were distances and locations relative to point sources of contaminants, with soils close to and downhill of tailing sites more contaminated with trace elements. Remediation of soils to reduce trace elements is recommended in addition to containment of tailing erosion.

Effects of high‐carbon wood ash biochar on volunteer vegetation establishment and community composition on metal mine tailings

Pyrolyzed organic waste, also known as biochar, is commonly used as a soil amendment and has recently been promoted to remediate metal mine tailings by increasing substrate pH, enhancing water and nutrient retention, and reducing bioavailability of toxic metals. Bottom ash from bioenergy facilities can contain high levels of charcoal residue, and thus qualify as a type of biochar according to international standards; the availability of this material at low costs makes it of particular interest in the context of tailings remediation. Naturally recruiting vegetation is critical in areas of primary succession such as mine tailings, and thus understanding vegetation responses on these substrates is essential. We examined responses of naturally regenerated “volunteer” vegetation to additions of high‐carbon wood ash biochar at a range of application rates (from 0 to 30 metric tons [t]/ha) at two gold mine tailings sites in northern Ontario, Canada over a 2‐year period. Volunteer vegetation cover increased with biochar dosage, peaking at 10–20 t/ha. Wood ash biochar amendments altered substrate physical properties (pH, electrical conductivity [EC], bulk density, total carbon [TC], and nitrogen [TN]), but effects varied by site and with dosage. Substrate TC and EC increased significantly with dosage at both sites with highest measures detected in the 10–20 t/ha amendment range. Species composition showed site‐ and dosage‐specific responses to biochar additions; however, species accumulation curves consistently showed peak species richness at intermediate dosages in both sites and both years of growth. Observed changes in volunteer vegetation suggest that low to moderate dosage applications of high‐carbon wood ash biochar can be highly beneficial for revegetation of mine tailings, but that wood ash impurities can result in deleterious effects at high dosages. Results from these field experiments demonstrate the potential of wood ash in tailings restoration and incentivizes additional in situ experiments to further discern site‐specific mechanisms.

Levels of Metals and Microbial Biomass in Cobalt Coleman Mine Tailings (Canada) Three Decades after Land Reclamation

Investigations of restored metal contaminated tailings in Canada with regard to their long-term ability to sustain plant and associated microbiological populations are limited. The specific objectives of the present study were to assess (1) The current levels of total and bioavailable metals and (2) Microbial biomass in Cobalt Coleman mine tailings reclaimed in 1990. The level of microbial biomass was determined using Phospholipid Fatty Acid analysis (PLFA). Metal analysis revealed that the concentration of total Arsenic (As) was >100 and 20 ´ higher in the Nipissing tailing compared to the non-tailing site and the Cart Lake tailing. The same trend was observed to a lesser degree for total Cobalt (Co) and Copper (Cu) concentrations. Overall, the total metal levels remain high >30 years after phytoremediation, but the bioavailable metal amount was low. This suggests that soil metal impacts on biota are minimal. The reclaimed tailing exhibited significantly lower levels (p≤0.05) of organic matter compared to non-tailing reference areas. More importantly, the analyses revealed significantly high (p≤0.05) total microbial biomass in non-tailing soil samples (with higher organic matter content) compared to tailing soils. A strong positive correlation (r = 0.87) was observed between organic matter and total microbial biomass. In contrast to other studies, the pH of the two tailing sites was neutral (7.1 and 7.5) and negatively correlated (r = -95) with bacterial and fungal abundance. Bacteria dominated the microbial communities in all the sites including the non-tailing area, indicating that the targeted region is still under severe environmental stress. Overall, the metal levels in the targeted tailings remain high and the phytoremediation did not improve significantly the soil quality (organic matter, microbial biomass) over the last three decades.

Direct observation of Mn distribution/speciation within and surrounding a basidiomycete fungus in the production of Mn-oxides important in toxic element containment

Biogenic manganese (Mn) oxides occur ubiquitously in the environment including the uranium (U) mill tailings at the Ningyo-toge U mine in Okayama, Japan, being important in the sequestration of radioactive radium. To understand the nanoscale processes in Mn oxides formation at the U mill tailings site, Mn2+ absorption by a basidiomycete fungus, Coprinopsis urticicola, isolated from Ningyo-toge mine water samples, was investigated in the laboratory under controlled conditions utilizing electron microscopy, synchrotron-based X-ray analysis, and fluorescence microscopy with a molecular pH probe. The fungus’ growth was first investigated in an agar-solidified medium supplemented with 1.0 mmol/L Mn2+, and Cu2+ (0–200 μM), Zn2+ (0–200 μM), or diphenyleneiodonium (DPI) chloride (0–100 μM) at 25 °C. The results revealed that Zn2+ has no significant effects on Mn oxide formation, whereas Cu2+ and DPI significantly inhibit both fungal growth and Mn oxidation, indicating superoxide-mediated Mn oxidation. Indeed, nitroblue tetrazolium and diaminobenzidine assays on the growing fungus revealed the production of superoxide and peroxide. During the interaction of Mn2+ with the fungus in solution medium at the initial pH of 5.67, a small fraction of Mn2+ infiltrated the fungal hyphae within 8 h, forming a few tens of nm-sized concentrates of soluble Mn2+ in the intracellular pH of ∼6.5. After 1 day of incubation, Mn oxides began to precipitate on the hyphae, which were characterized as fibrous nanocrystals with a hexagonal birnessite-structure, these forming spherical aggregates with a diameter of ∼1.5 μm. These nanoscale processes associated with the fungal species derived from the Ningyo-toge mine area provide additional insights into the existing mechanisms of Mn oxidation by filamentous fungi at other U mill tailings sites under circumneutral pH conditions. Such processes add to the class of reactions important to the sequestration of toxic elements.

Characterization of diazotrophic root endophytes in Chinese silvergrass (Miscanthus sinensis)

BackgroundPhytoremediation is a potentially cost-effective way to remediate highly contaminated mine tailing sites. However, nutrient limitations, especially the deficiency of nitrogen (N), can hinder the growth of plants and impair the phytoremediation of mine tailings. Nevertheless, pioneer plants can successfully colonize mine tailings and exhibit potential for tailing phytoremediation. Diazotrophs, especially diazotrophic endophytes, can promote the growth of their host plants. This was tested in a mine-tailing habitat by a combination of field sampling, DNA-stable isotope probing (SIP) analysis, and pot experiments.ResultsBacteria belonging to the genera Herbaspirillum, Rhizobium, Devosia, Pseudomonas, Microbacterium, and Delftia are crucial endophytes for Chinese silvergrass (Miscanthus sinensis) grown in the tailing, the model pioneer plant selected in this study. Further, DNA-SIP using 15N2 identified Pseudomonas, Rhizobium, and Exiguobacterium as putative diazotrophic endophytes of M. sinensis. Metagenomic-binning suggested that these bacteria contained essential genes for nitrogen fixation and plant growth promotion. Finally, two diazotrophic endophytes Rhizobium sp. G-14 and Pseudomonas sp. Y-5 were isolated from M. sinensis. Inoculation of another pioneer plant in mine tailings, Bidens pilosa, with diazotrophic endophytes resulted in successful plant colonization, significantly increased nitrogen fixation activity, and promotion of plant growth.ConclusionsThis study indicated that diazotrophic endophytes have the potential to promote the growth of pioneer plant B. pilosa in mine tailings.EAsdjSo3ZCTEVznKh83dpJVideo