Microbial activity and biodiversity responding to contamination of metal(loid) in heterogeneous nonferrous mining and smelting areas

Effects of soil metal(loid)s pollution on microbial activities and environmental risks in an abandoned chemical smelting site

Abandoned chemical smelting sites containing toxic substances can seriously threaten and pose a risk to the surrounding ecological environment. Soil samples were collected from different depths (0 to 13 m) and analyzed for metal(loid)s content and fractionation, as well as microbial activities. The potential ecological risk indices for the different soil depths (ordered from high to low) were: 1 m (D-1) > surface (S-0) > 5 m (D-5) > 13 m (D-13) > 9 m (D-9), ranging between 1840.65-13,089.62, and representing extremely high environmental risks, of which Cd (and probably not arsenic) contributed to the highest environmental risk. A modified combined pollution risk index (MCR) combining total content and mobile proportion of metal(loid)s, and relative toxicities, was used to evaluate the degree of contamination and potential environmental risks. For the near-surface samples (S-0 and D-1 layers), the MCR considered that As, Cd, Pb, Sb, and Zn achieved high and alarming degrees of contamination, whereas Fe, Mn, and Ti were negligible or low to moderate pollution degrees. Combined microcalorimetry and enzymatic activity measurements of contaminated soil samples were used to assess the microbial metabolic activity characteristics. Correlation analysis elucidated the relationship between metal(loid)s exchangeable fraction or content and microbial activity characteristics (p < 0.05). The microbial metabolic activity in the D-1 layer was low presumably due to heavy metal stress. Enzyme activity indicators and microcalorimetric growth rate (k) measurements were considered sensitive indicators to reflect the soil microbial activities in abandoned chemical smelting sites.

Staged SWAT calibration with bias-corrected precipitation product for enhancing flow data continuity in tributaries of the Mekong River

Accurate and continuous flow data are crucial for effective water management in large river basins worldwide. However, these catchments often face challenges regarding data continuity in the mainstream and their tributaries. This study proposes a methodological framework for enhancing flow data continuity that uses a staged calibration scheme of Soil and Water Assessment Tool (SWAT) modeling with an appropriate satellite precipitation product (SPP) for each watershed. This framework is successfully applied in the Mun-Chi River Basin, the largest tributary of the Lower Mekong River, over a 20-year period at 34 stations. The staged calibration involves partitioning the catchment into smaller sub-catchments, guided by the flow monitoring stations and flow discontinuity structures such as dams. The sequential calibration from upstream to downstream partitions the overall model calibration challenge into smaller problems and contributes to a more efficient and accurate calibration and validation. Alternative SPPs were considered to overcome monitoring gaps. Their bias was corrected using quantile mapping, and their performance was evaluated with flow simulations using the SWAT model. The assessment indicates that the CMORPH-CRT product, with a spatial resolution of 0.25°, demonstrates good suitability for hydrological modeling of the Mun-Chi River Basin. The proposed methodological framework provides a continuous time series of flow discharge at multiple stations within the watershed, offering valuable insights for sustainable water resource management strategies in river systems under changing climate and land use conditions, and supporting future studies on environmental issues.

Innovative Hyper-thermophilic Aerobic Submerged Membrane Distillation Bioreactor for Wastewater Reclamation

For the first time, a hyper-thermophilic aerobic (>60 °C) bioreactor has been integrated with direct submerged membrane distillation (MD), highlighting its potential as an advanced wastewater treatment solution. The hyper-thermophilic aerobic bioreactor, operating up to 65 °C, is tailored for high organic removal, while MD efficiently produces clean water. Throughout the study, high removal rates of 99.5% for organic matter, 96.4% for ammonia, and 100% for phosphorus underscored the impressive adaptability of microorganisms to challenging hyper-thermophilic conditions and a successful combination with the MD process. Despite the extreme temperatures and substantial salinity accumulation reaching up to 12,532 μS/cm, the biomass of microorganisms increased by 1.6 times over a 92-day period, representing their remarkable resilience. The distillation flux ranged from 6.15 LMH to 8.25 LMH, benefiting from the temperature gradient in the hyper-thermophilic setting and the design of the tubular submerged MD membrane module. The system also excels in pH control, utilizing fewer alkali and nutritional resources than conventional systems. Meiothermus, Firmicutes, and Bacteroidetes, the three dominant species, played a crucial role, showcasing their significance in adapting to high salinity and decomposing organic matter.

Microbial metabolic activity in metal(loid)s contaminated sites impacted by different non-ferrous metal activities

Many non-ferrous metal mining and smelting activities have caused severe metal(loid) contamination in the local soil environment. The metabolic activity of soil microorganisms in four areas affected by different metallurgical activities (production vs. waste disposal) was characterized using a contamination gradient from the contaminated site to the surrounding soils. Results indicated that the soil microcalorimetric and enzyme activities were correlated with the fractionated metal(loid) properties (p < 0.05). All four areas had high total As, Cd, Pb, Sb, and Zn concentrations, of which mobile As, Cu, Ni, Pb, Sb, and Zn were higher in the contaminated sites than the surrounding sites, reflecting an elevated environmental risk. Three contaminated site areas had lower microbial activities than their surrounding sites suggesting that high metal(loid) concentrations inhibited soil microbial communities. Interestingly, the fourth area (tailing pond) showed an opposite trend (i.e., increased microbial activity in contaminated vs. surrounding areas). The microbial thermodynamic parameters of this contaminated site were higher than its surrounding sites, suggesting that the selected microbial communities can develop a functional resistance to metal(loid)s stress. This study provides a theoretical basis for ecological prevention and control of metal-polluted areas.

Response of soil microbial activities and ammonia oxidation potential to environmental factors in a typical antimony mining area

Mining, smelting and tailing deposition activities can cause metal(loid) contamination in surrounding soils, threatening ecosystems and human health. Microbial indicators are sensitive to environmental factors and have a crucial role in soil ecological risk assessment. Xikuangshan, the largest active antimony (Sb) mine in the world, was taken as the research area. The soil properties, metal(loid) contents and microbial characteristics were investigated and their internal response relationships were explored by multivariate statistical analysis. The assessment of the single pollution index and Nemerow synthetic pollution index (P_N) showed that the soils were mainly polluted by Sb, followed by Cd and As, in which sampling site S1 had a slight metal(loid) pollution and the other sampling sites suffered from severe synthetic metal(loid) pollution. The microbial characteristics were dissimilar among sampling points at different locations from the mining area according to hierarchical cluster analysis. The correlation analysis indicated that fluorescein diacetate hydrolase, acid phosphatase, soil basal respiration and microbial biomass carbon were negatively correlated with P_N, indicating their sensitivity to combined metal(loid) contamination; that dehydrogenase was positively correlated with pH; and that urease, potential ammonia oxidation and abundance of ammonia-oxidizing bacteria and archaea were correlated with N (nitrogen) contents. However, β-glucosidase activity had no significant correlations with physicochemical properties and metal(loid) contents. Principal components analysis suggested bioavailable Sb and pH were the dominant factors of soil environment in Xikuangshan Sb mining area. Our results can provide a theoretical basis for ecological risk assessment of contaminated soil.

Remedial effect and operating status of a decommissioned uranium mill tailings (UMT) repository: A micro-ecological perspective based on bacterial community

From a radioecological perspective, increasing attention has been paid to the long-term stabilisation of decommissioned uranium mill tailings (UMT) repositories. However, little is known about the evaluation of decommissioning and remedial effects of UMT repositories from a microecological perspective based on bacterial communities. Here, we analysed the distribution and structure of soil community assemblies along different vertical soil profiles in a decommissioned UMT repository and explored the impact of soil properties, including physicochemical parameters, metal(loid)s, and radionuclides, on the bacterial assemblage. We found that the α diversity of the bacterial community was unaffected by variations in different soil profiles and taxa were classified at the phylum level with small significant differences. In contrast, the bacterial community structure in and around the UMT repository showed significant differences; however, this difference was significantly affected by soil metal(loid)s and physicochemical properties rather than soil radionuclides. In addition, seven bacterial genera with significant differences between the inner and surrounding regions of the repository could be used as potential indicators to further investigate the remedial effects on soil environmental quality. These findings provide novel insights into the construction of an assessment system and in situ biomonitoring of UMT repositories from a microecological perspective based on bacterial communities.

Preparation of a novel photocatalytic catalyst PW9@ZnO/Ag and the photocatalytic degradation of butyl xanthate under visible light

Photocatalytic technology is attracting considerable attention for the advantages of low cost and environmentally friendly properties. In this study, a novel photocatalyst PW₉@ZnO/Ag (PZA) was synthesized hydrothermally and characterized by a variety of means. The results indicated that ZnO and Ag NPs were successfully decorated and uniformly dispersed on PW₉ to form the composites. The prepared PZA was applied in the degradation of simulated butyl xanthate (BX) beneficiation wastewater both under the UV light and the xenon lamp, and a maximum degradation of 99.83% was obtained under the visible light with 10% ZnO loading, 1 g/L PZA, initial BX concentration of 20 mg/L, and pH 5.5. The PZA was recovered and reused for 5 times, and the degradation rates remained above 70%. Superoxide radical (·O₂^-) was the main active species for the photocatalytic degradation of BX. The experimental results demonstrate that PZA is a promising photocatalyst, making it a prospective strategy to overcome current challengers in the use of xanthate degradation and beneficiation wastewater treatment under visible light.

Contrasted speciation distribution of toxic metal(loid)s and microbial community structure in vanadium-titanium magnetite tailings under dry and wet disposal methods

Tailing disposal technologies such as dry and wet disposal methods have a profound effect on the ecosystem of mining areas. However, the chemical speciation of metal(loid)s and microbial community structure in tailings under different disposal methods are still poorly understood. Here we compared the bioavailable fraction of metal(loid)s and the microbial community in vanadium-titanium (V-Ti) magnetite tailing profiles derived from dry and wet stockpiled methods. In wet tailings, the bioavailability of Cr, Cu, Mn, Ni, V, and Zn was higher than that in dry tailings as identified by BCR sequential extraction. Especially for Cu and Ni, the oxidizable fraction was the predominant fraction except the residual fraction, accounting for 37.2-59.0% and 23.2-36.6% of the total concentration in wet tailings, respectively. Based on 16 S rRNA high-throughput sequencing, totally 12 indicator bacterial taxa were detected in dry tailings against 68 in wet tailings. As the biomarkers in wet tailings, genera Sulfuricurvum, Geobacter, and Pseudomonas were expected to be applied to the transformation of metal(loid)s in the tailings. Our results emphasize the importance of dehydration treatment of tailings before stockpiling to minimize the environmental risks caused by toxic metal(loid)s, and provide insights into the engineering application of microbial technologies in V-Ti magnetite tailing area.

Advances in the use of recycled non-ferrous slag as a resource for non-ferrous metal mine site remediation

The growing global demand for non-ferrous metals has led to serious environmental issues involving uncovered mine site slag dumps that threaten the surrounding soils, surface waters, groundwater, and the atmosphere. Remediation of these slags using substitute cement materials for ordinary Portland cement (OPC) and precursors for alkali-activated materials (AAMs) can convert hazardous solid wastes into valuable construction materials, as well as to attain the desired solidification and stabilization (S/S) of heavy metal(loid)s (HM). This review discusses the current research on the effect of non-ferrous slags on the reaction mechanisms of the OPC and AAM. The S/S of HM from the non-ferrous slags in AAM and OPC is also reviewed. HM can be stabilized in these materials based on the complex salt effect and isomorphic effects. The major challenges faced in AAMs and OPC for HM stabilization include the long-term durability of the matrix (e.g., sulfate attack, stability of volume). The existing knowledge gaps and future trends for the sustainable application of non-ferrous slags are also discussed.

Advance in remediated of heavy metals by soil microbial fuel cells: Mechanism and application

In the past decade, studies on the remediation of heavy metals contaminated soil by microbial fuel cells (MFCs) have attracted broad attention because of the self-generated power and their multifield principles such as the extracellular electron transfer (EET) reduction, electromigration for heavy metals removal. However, given the bio electro-motive power from soil MFCs is weak and fluctuated during the remediation, we need to comprehensively understand the origination of driving force in MFC based on the analysis of the fundamental rationale of ion moving in cells and improve the performance via the appropriate configurations and operations. In this review, we first described the structures of soil MFCs for heavy metals remediation and compared the advantages of different types of configurations. Then, based on the theoretical models of heavy metal migration, enrichment, and reduction in soil MFCs, the optimization of soil MFCs including the length of the remediation area, soil conductivity, control of electrode reaction, and modification of electrodes were proposed. Accordingly, this review contributes to the application of bioelectrochemistry to efficiently remove heavy metals from soils.

Migration and Transformation of Multiple Heavy Metals in the Soil–Plant System of E-Waste Dismantling Site

E-waste generation has become a major environmental issue worldwide. Heavy metals (HMs) in e-waste can be released during inappropriate recycling processes. While their pollution characteristics have been studied, the migration and transformation of different multi-metal fractions in soil–plant system of e-waste dismantling sites is still unclear. In this study, pot experiments were conducted to investigate the migration and transformation of different multi-metal fractions (Cu, Pb, Zn and Al) in the soil–plant system using two Chinese cabbage cultivars (heavy metals low-accumulated variety of Z1 and non-low-accumulated Z2) treated with or without biochar. The result showed that the acid-soluble fraction of Cu, Pb, Zn and Al in soil decreased by 5.5%, 55.7%, 7.8% and 21.3%, but the residual fraction (ResF) of them increased by 48.5%, 1.8%, 30.9% and 43.1%, respectively, when treated with biochar and plants, compared to that of the blank soil (CK). In addition, Pb mainly existed as a reducible fraction, whereas Cu existed as an oxidisable fraction. Biochar combined with plants significantly increased the ResF of multi-metals, which reduced the migration ability of Pb among all other metals. The relative amount of labelled ¹³C in the soil of Z1 was higher than that of Z2 (25.4 fold); among them, the Gram-negative bacteria (18-1ω9c, 18-1ω7c) and fungi (18-2ω6c) were significantly labelled in the Z1-treated soil, and have high correlation with HM migration and transformation. In addition, Gemmatimonadete were significantly positive in the acid-soluble fraction of HMs, whereas Ascomycota mostly contributed to the immobilisation of HMs. Therefore, the distribution of fractions rather than the heavy metal type plays an important role in the HM migration in the soil–plant system of e-waste dismantling sites.

Relationships between microbial activity, enzyme activities and metal(loid) form in NiCu tailings area

Here we combined microcalorimetry, enzyme activity measurements, and characterization of metal form in order to evaluate the effect of metal(loid)s on the activity of microbial community inhabiting tailings area with high toxic metal(loid)s concentration. Chromium (Cr), nickel (Ni), copper (Cu) and manganese (Mn) were the main pollutants. The exchangeable fractions (bioavailability) of Cu, Ni and Mn were higher in the tailings sample (Site Z), indicating a higher environmental risk. The total heat Q_total (17,726.87 J/g), peak power P_peak (541.42 μW/g) and growth rate constant k (0.11 h^-1) of Site Z were higher than that of the polluted soil around tailings (Site Y). Such observation may be explained by physiological changes within the microbial community in response to high levels of heavy metal stress, thereby increasing respiration and improving microbial activity. In contrast, enzyme activities and enzyme activities index (GmeA) of Site Z were lower than the Site Y, which is strongly influenced by changes on physical-chemical properties (TN and TOC) and the presence of Cr, Mn, and Ni. Correlation coefficient and principal component analysis (PCA) indicate that GmeA is significantly correlated (p < 0.05 or p < 0.01) with environmental factors (EC, TOC and TN), Mn and Ni concentration, Ni bioavailability, and peak time (T_peak). Therefore, GmeA represents a potential biological indicator for reporting the pollution degree in tailings area. Our results provide a theoretical basis for the prevention and control of pollution in non-ferrous metal(loid) tailings area.

Biogeography, assembly processes and species coexistence patterns of microbial communities in metalloids-laden soils around mining and smelting sites

Microbes are important component in terrestrial ecosystem, which are believed to play vital roles in biogeochemical cycles of metalloids in mining and smelting surroundings. Many studies on microbial diversity and structures have been investigated around mining and smelting sites, whereas the ecological processes and co-occurrence patterns that influence the biogeographic distributions of microbial communities is yet poorly understood. Herein, microbial biogeography, assembly mechanism and co-occurrence pattern around mining and smelting zone were systematically unraveled using 16S rRNA gene sequencing. The 66 microbial phyla co-occurring across all the samples were dominated by Proteobacteria, Chloroflexi, Acidobacteria and Crenarchaeota. Obvious distance-decay (r = 0.3448, p < 0.001) of microbial community was observed across geographic distances. Differences in microbial communities were driven by the joint impacts of soil factors, spatial and metalloids levels. Dispersal limitation dominated the microbial assemblies in whole, SC and GX sites while homogeneous selection governed that in YN site. The changes in pH and Sb level significantly influenced the deterministic and stochastic processes of microbial communities. Network analysis suggested a typical module distribution, which had apparent ecological links among taxa in modules. This study provides first insight of the mechanism to maintain microbial diversity in metalloids-laden biospheres.

Multiple factors influence bacterial community diversity and composition in soils with rare earth element and heavy metal co-contamination

The effects of long-term rare earth element (REE) and heavy metal (HM) contamination on soil bacterial communities remains poorly understood. In this study, soil samples co-contaminated with REEs and HMs were collected from a rare-earth tailing dam. The bacterial community composition and diversity were analyzed through Illumina high-throughput sequencing with 16S rRNA gene amplicons. Bacterial community richness and diversity were lower in the co-contaminated soils than in the uncontaminated soils, with clearly different bacterial community compositions. The results showed that total organic carbon and available potassium were the most important factors affecting bacterial community richness and diversity, followed by the REE and HM contents. Although the canonical correspondence analysis results showed that an REE alone had no obvious effects on bacterial community structures, we found that the combined effects of soil physicochemical properties and REE and HM contents regulated bacterial community structure and composition. The effects of REEs and HMs on bacterial communities were similar, whereas their combined contributions were greater than the individual effects of REEs or HMs. Some bacterial taxa were worth noting. These specifically included the plant growth-promoting bacteria Exiguobacterium (sensitive to REEs and HMs) and oligotrophic microorganisms with metal tolerance (prevalent in contaminated soil); moreover, relative abundance of JTB255-Marine Benthic Group, Rhodobacteraceae, Erythrobacter, and Truepera may be correlated with REEs. This study was the first to investigate the responses of bacterial communities to REE and HM co-contamination. The current results have major implications for the ecological risk assessment of environments co-contaminated with REEs and HMs.

Microbial community profiles in soils adjacent to mining and smelting areas: Contrasting potentially toxic metals and co-occurrence patterns

Mining and smelting activities have introduced severe potentially toxic metals (PTMs) contamination into surrounding soil settings. Influences of PTMs on microbial diversity have been widely studied. However, variations of microbial communities, network structures and community functions in different levels of PTMs contaminated soils adjacent to mining and smelting aera are still poorly investigated. In this study, microbial communities of soils around different levels of PTMs contamination were comprehensively studied by 16S rRNA gene amplicons high-throughput sequencing. Microbial interactions and module functions were also exploited to ascertain the discrepancies of PTMs concentration levels on microbial ecological functions. Results indicated that the microbial community composition was significantly distinct attributed to the phylum Protebacteria (p = 0.002) dominating in soil with high level PTMs contents but Actinobacteria (p = 0.002) in low level of PTMs-contaminated soil. Microbial α diversity was not significantly influenced by different levels of PTMs contaminations. Microorganisms proactively responded to PTMs content levels by means of strengthening network complexities and modularities among microbe-microbe interactions. The functions of main network modules were predicted associating membrane transport, amino acid metabolism, energy metabolism and carbohydrate metabolism. The PTMs detoxification and anti-oxidation were significantly strengthened at the high level of PTMs contamination. The present study demonstrated that modification of microbial community by the adaptive adjustment of microbial compositions and strengthening their network complexity and modularity.

Toxic response of the freshwater green algae Chlorella pyrenoidosa to combined effect of flotation reagent butyl xanthate and nickel

Butyl Xanthate (BX) is a typical flotation reagent used to extract non-ferrous nickel ores, discharged into the surrounding environment of mining areas in large quantities. However, few studies have focused on the toxicity of combined pollution of BX and nickel (Ni) on aquatic plants, especially phytoplankton, the main producer of aquatic ecosystems. The toxicity and potential mechanism of single and combined pollution of BX and Ni at different concentrations (0-20 mg L^-1) on typical freshwater algae (Chlorella pyrenoidosa) were studied. BX slightly stimulated the growth of C. pyrenoidosa on the first day, but Ni and Ni/BX mixture significantly inhibited it during incubation. Results showed that the inhibition rate (I) of the pollutants on the growth of C. pyrenoidosa followed the order: Ni/BX mixture > Ni > BX. The 96-h 20% effective inhibitory concentrations (96h-EC₂₀) of Ni and BX on C. pyrenoidosa growth were 3.86 mg L^-1 and 19.25 mg L^-1, respectively, indicating C. pyrenoidosa was sensitive to pollutants. The content of total soluble protein (TSP) and chlorophyll a (Chl-a) changed significantly, which may be caused by the damage of pollutants to cell structures (cell membranes and chloroplasts). In addition, the I of pollutants on C. pyrenoidosa growth was related to dose, superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA). The increasement of reactive oxygen species (ROS), antioxidant enzymes (SOD and CAT), and MDA content, suggested C. pyrenoidosa suffered from oxidative stress, leading to lipid oxidation. These results will help to understand the toxicity mechanism of pollutants in typical mining areas and assess the environmental risks of pollutants to primary producers in aquatic ecosystems.

Analysis of microbial community structure and diversity in surrounding rock soil of different waste dump sites in fushun western opencast mine

It is importance to understand the correlation between the physicochemical properties of different surrounding rock soil and microbial communities in Fushun western opencast mining for the ecological restoration of land after mine closure. In this study, two layers of soil samples were collected from four different areas in Fushun western opencast mining: coal gangue area (CGA), green mudstone area (GMA), oil shale area (OSA) and mixed area (MA). Then, the effects of different surrounding rock soil physicochemical properties on the microbial communities were explored using the High-throughput sequencing technique. A wide diversity of taxonomical groups were present in four soil cores, and many were correlated with soil physicochemical properties. The obvious differences in microbial communities between different areas showed the influence of different surrounding rock soil on the microbial communities were significant. Redundancy analysis and the network diagram confirmed that soil physicochemical properties pH (Pondus Hydrogenii)-AN (Available Nitrogen)-EC (Electronic Conductivity)-WC (Water Content)-TK (Total Nitrogen), Cd (Cadmium)-Ni (Nickel) had great influence on the microbial communities. Therefore, this study can provide scientific judgments for the different surrounding rock soil physicochemical properties in coal mining, microbial-mediated rock mineralization and biogeochemical cycles.

Deciphering the toxic effects of metals in gold mining area: Microbial community tolerance mechanism and change of antibiotic resistance genes

Mine tailing dumps represent significant threats to ecological environments due to the presence of toxic substances. The present work investigated the relationship among microbial activity, the community, antibiotic resistance genes (ARGs) and trace metals in soil surrounding gold mine tailings. Using microbial metabolic activity and high-throughput sequencing analysis, we found the trace metals Cd and Hg could be main factors influencing the microbial community. According to bacterial co-occurrence pattern analysis, the effects of total cadmium and total mercury on bacterial diversity are potentially mediated by influencing bacteria community in the keystone module II. Additionally, most of metal-resistant bacteria belong to Actinobacteria and Proteobacteria, and the metal tolerance suggested to be linked with various functions including replication, recombination and repair, as well as inorganic ion transport and metabolism based on PICRUSt2 analysis. We also found that metals generated by mining activity may trigger the co-selection of antibiotic resistance in the phyla Actinobacteria and Proteobacteria due to co-resistance or cross resistance. Additionally, PLS-PM analysis revealed that metals could indirectly affect ARGs by influencing bacterial diversity in gold mining areas.

Taking insights into phenomics of microbe-mineral interaction in bioleaching and acid mine drainage: Concepts and methodology

Phenomics is originally a biological concept. In the most recent years, the studies of plant and human phenomics have started, and show a strong momentum and trend of development. In this paper, based on the related research on bioleaching/acid mine drainage (AMD), we put forward the relevant concepts and methodology of phenomics of microbe-mineral interaction (MMI) in bioleaching/AMD environments. It refers to the systematic study on phenotypes of MMI on both levels of microbiome and mineralome under various environmental conditions, by which it gives the relationship between microbial/mineral genome and phenome of MMI responding to the varying environmental conditions. The pertinent methodology is of mainly (meta)-omics, synchrotron radiation-based techniques and supercomputing-based density function theory (DFT) calculation.

Alteration of mixture toxicity in nonferrous metal mine tailings treated by biochar

Nonferrous metal mining activities produce enormous amounts of tailings that contain high concentrations of toxic chemicals threatening human health and the environment. This risk could be alleviated using remediation agents such as biochar, as proposed by others. However, contradictory evidence indicates that biochar can increase or sometimes decrease bioavailable concentrations depending on the selection of metal(loid)s in mine tailings. Here three biochars derived from different raw stocks were used to treat mine tailings samples. Chemical analyses indicated that all biochars favored the stabilization of Cd, Cr, Cu, Pb, and Zn, as well as the mobilization of As and Sb. The barley root elongation bioassay showed that the tailings toxicity was only partially diminished (up to 55.8%) or even elevated (up to 20.7%) by biochar treatment. Similar results were also observed from microbial enzyme assays (increased up to 28.3% or decreased up to 24.0%). Further analyses showed that these toxic effects correlated well with the relative toxicity index (R² = 0.66 to 0.88). Toxicity testing coupled with the use of a toxicity prediction model presented here suggested that the release of As and Sb from tailings compromised the favorable effects of biochar treatment on toxic cationic metals. Such information is of paramount importance when taking countermeasures for improving bioremediation technologies.

Integrating high-throughput sequencing and metagenome analysis to reveal the characteristic and resistance mechanism of microbial community in metal contaminated sediments

Some metallic tailings from closed mines were scattered in upstream of the Miyun Reservoir, Beijing, threatening the ecological environment of rivers due to trace metals. The Liuli River, one of the main rivers affected, was investigated as a typical model in this work. In this study, we selected eight sites to assess interactions among the various geochemical factors especially between trace metals and sediment microbiota. Random forest predicted that low concentrations of Cu, Cd, Cr and Ni (lower than 61.8 mg/kg, 3.2 mg/kg, 173.2 mg/kg and 34.1 mg/kg, respectively) were able to enhance community diversity but generally, trace metals contamination impaired microbial diversity. Environmental factor correlation analysis showed that As, pH and available P were the major factors that shifted the distribution of the microbial communities. Metagenome sequencing revealed that Proteobacteria harbored the vast majority of heavy metal resistance genes followed by Actinobacteria and Bacteroidetes. Metal tolerance of Proteobacteria were achieved by exportation of metals by the corresponding transporters, by pumps and ion channels, or by their reduction via redox reactions. In addition, Proteobacteria harbored a greater ability to repair DNA damage via DNA recombination.

Natural sphalerite nanoparticles can accelerate horizontal transfer of plasmid-mediated antibiotic-resistance genes

Minerals and microorganisms are integral parts of natural environments, and they inevitably interact. Antibiotic-resistance genes (ARGs) significantly threaten modern healthcare. However, the effects of natural minerals on ARG propagation in aquatic systems are not fully understood. The present work studied the effects of natural sphalerite (NS) nanoparticles on the horizontal transfer of ARGs from Escherichia coli DH5α (CTX) (donor) to E. coli C600 (Sm) (recipient), and from E. coli DH5α (MCR) (donor) to E. coli C600 (Sm), and their underlying mechanisms. NS particles (0.5-50 mg L^-1) induced an NS-concentration-dependent increase in conjugative transfer frequency. The underlying mechanisms associated with the facilitated ARG transfer included the production of intracellular reactive oxygen species, the SOS response, changes in bacterial cell morphology, and alteration of mRNA levels of bacterial cell membrane protein-related genes and genes associated with conjugative ARG transfer. The information herein offers new mechanistic understanding of risks of bacterial resistance resulting from NS.