A critical review on bioremediation technologies of metal(loid) tailings: Practice and policy.

Globally, most high-grade ores have already been exploited. Contemporary mining tends to focus on the extraction of lower-grade ores thereby leaving large stored tailings open to the environment. As a result, current mines have emerged as hotspots for the migration of metal(loid)s and resistance genes, thereby potentially contributing to a looming public health crisis. Therefore, the management and remediation of tailings are the most challenging issues in environmental ecology. Bioremediation, a cost-effective solution for the treatment of multi-element mixed pollution (co-contamination), shows promise for the restoration of mine tailings. This review focuses on the bioremediation technologies developed to untangle the issues of non-ferrous metal mine tailings. These technologies address the environmental risks of multi-element exposure to the ecosystem and human health risks. It provides a review and comparison of current bioremediation technologies used to mineralize metal(loid)s. The role of plant-microorganisms and their mechanisms in the remediation of tailings are also discussed. The importance of "treating waste with wastes" is crucial for advancing bioremediation technologies. This approach underscores the potential for waste materials to contribute to environmental cleanup processes. The concept of a circular economy is pertinent in this context, emphasizing recycling and reuse. There's an immediate need for international collaboration. Collaboration is needed in policy-making, funding, and data accessibility. Sharing data is essential for the growth of bioremediation globally.

Bioindicator responses to extreme conditions: Insights into pH and bioavailable metals under acidic metal environments.

Acid mine drainage (AMD) caused environmental risks from heavy metal pollution, requiring treatment methods such as chemical precipitation and biological treatment. Monitoring and adapting treatment processes was crucial for success, but cost-effective pollution monitoring methods were lacking. Using bioindicators measured through 16S rRNA was a promising method to assess environmental pollution. This study evaluated the effects of AMD on ecological health using the ecological risk index (RI) and the Risk Assessment Code (RAC) indices. Additionally, we also examined how acidic metal stress affected the diversity of bacteria and fungi, as well as their networks. Bioindicators were identified using linear discriminant analysis effect size (LEfSe), Partial least squares regression (PLS-R), and Spearman analyses. The study found that Cd, Cu, Pb, and As pose potential ecological risks in that order. Fungal diversity decreased by 44.88% in AMD-affected areas, more than the 33.61% decrease in bacterial diversity. Microbial diversity was positively correlated with pH (r = 0.88, p = 0.04) and negatively correlated with bioavailable metal concentrations (r = -0.59, p = 0.05). Similarly, microbial diversity was negatively correlated with bioavailable metal concentrations (bio_Cu, bio_Pb, bio_Cd) (r = 0.79, p = 0.03). Acidiferrobacter and Thermoplasmataceae were prevalent in acidic metal environments, while Puia and Chitinophagaceae were identified as biomarker species in the control area (LDA>4). Acidiferrobacter and Thermoplasmataceae were found to be pH-tolerant bioindicators with high reliability (r = 1, P < 0.05, BW > 0.1) through PLS-R and Spearman analysis. Conversely, Puia and Chitinophagaceae were pH-sensitive bioindicators, while Teratosphaeriaceae was a potential bioindicator for Cu-Zn-Cd metal pollution. This study identified bioindicator species for acid and metal pollution in AMD habitats. This study outlined the focus of biological monitoring in AMD acidic stress environments, including extreme pH, heavy metal pollutants, and indicator species. It also provided essential information for heavy metal bioremediation, such as the role of omics and the effects of organic matter on metal bioavailability.

Effects of three plant growth-promoting bacterial symbiosis with ryegrass for remediation of Cd, Pb, and Zn soil in a mining area.

The quality of soil containing heavy metals (HMs) around nonferrous metal mining areas is often not favorable for plant growth. Three types of plant growth promoting rhizobacteria (PGPR)-assisted ryegrass were examined here to treat Cd, Pb, and Zn contaminated soil collected from a nonferrous metal smelting facility. The effects of PGPR-assisted plants on soil quality, plant growth, and the migration and transformation of HMs were evaluated. Results showed that inter-root inoculation of PGPR to ryegrass increased soil redox potential, urease, sucrase and acid phosphatase activities, microbial calorimetry, and bioavailable P, Si, and K content. Inoculation with PGPR also increased aboveground parts and root length, P, Si, and K contents, and antioxidant enzyme activities. The most significant effect was that the simultaneous inoculation of all three PGPRs increased the ryegrass extraction (%) of Cd (59.04-79.02), Pb (105.56-157.13), and Zn (27.71-40.79), compared to CK control (without fungi). Correspondingly, the inter-root soil contents (%) of total Cd (39.94-57.52), Pb (37.59-42.17), and Zn (34.05-37.28) were decreased compared to the CK1 control (without fungi and plants), whereas their bioavailability was increased. Results suggest that PGPR can improve soil quality in mining areas, promote plant growth, transform the fraction of HMs in soil, and increase the extraction of Cd, Pb, and Zn by ryegrass. PGPR is a promising microbe-assisted phytoremediation strategy that can promote the re-greening of vegetation in the mining area while remediating HMs pollution.

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.

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.

Evidence that nano-TiO2 induces acute cytotoxicity to the agronomically beneficial nitrogen-fixing bacteria Sinorhizobium meliloti.

When nano-sized titanium dioxide (nano-TiO2) absorbs ultra-violet (UV-A) radiation, it produces reactive oxygen species that can be toxic to bacteria. We used the agronomically beneficial nitrogen-fixing bacterium Sinorhizobium meliloti strain 1021 as a model microorganism to detect nano-TiO2 toxicity. Sinorhizobium meliloti was exposed to aqueous dispersions of micrometer-sized TiO2 (micron-TiO2, 44 µm) or nanometer-sized TiO2 (nano-TiO2, 21 nm) at nominal concentrations of 0, 100, 300, 600, 900, and 1800 mg TiO2/L. There were fewer viable S. meliloti cells after exposure to nano-TiO2 under dark and UV-A light conditions. Nano-TiO2 was more toxic to S. meliloti with UV-A irradiation (100% mortality at 100 mg TiO2/L) than under dark conditions (100% mortality at 900 mg TiO2/L). Micron-TiO2 concentrations less than 300 mg TiO2/L had no effect on S. meliloti viability under dark or UV-A light conditions. Exposure to 600 mg/L or more of micron-TiO2 under UV-A light could also photo-kill S. meliloti cells (100% mortality). Further studies are needed to ascertain whether nano-TiO2 interferes with the growth of N2-fixing microorganisms in realistic agricultural environments.

Phytoextraction of cadmium-contaminated soils: comparison of plant species and low molecular weight organic acids.

To select suitable plants for phytoextraction of Cd-contaminated soils, we evaluated the phytoextraction potential of five local Cd-accumulators: Amaranthus hypochondriacus L., Solanum nigrum L., Phytolacca acinosa Roxb., Celosia argentea L., and Sedum spectabile Boreau. The plants were grown in three naturally contaminated soils with different total Cd levels (1.57, 3.89, and 22.4 mg kg-1). Throughout the experimental period, no plants showed any visible symptoms of metal toxicity. The Cd uptake of C. argentea was the greatest in the S-YS soil (105 µg plant-1) and among the greatest in the S-HC soil and S-TJ soil. Besides, C. argentea exhibited the highest bioconcentration factor (12.3) in three soils. To improve the phytoextraction efficiency of C. argentea, we applied four low molecular weight organic acids (LMWOAs): tartaric acid, malic acid, oxalic acid, and citric acid. Malic acid was more effective in enhancing Cd uptake by C. argentea than the other LMWOAs. Therefore, C. argentea may be a potential choice in actual remediation projects. Moreover, application of malic acid is an effective way to increase the phytoextraction efficiency of C. argentea.

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.

Sb(III)-resistance mechanisms of a novel bacterium from non-ferrous metal tailings.

Understanding the mechanism(s) of microbial resistance to antimony (Sb) is critical in the bioremediation of Sb polluted environments. Here a novel bacterium (Acinetobacter sp. JH7) isolated from mine tailings decreased the Microtox toxicity of a Sb(III)-containing medium. DNA sequencing and physiological testing were employed for the identification and characterization of strain JH7. Following a batch experiment, Fourier transform infrared spectroscopy (FTIR) and antimony speciation analyses determined the adsorption and oxidation of antimony. Analyses of Sb(III) distribution revealed that extracellular polymeric substances and cell walls inhibited Sb(III) entry into JH7 cells. FTIR studies indicated that key functional groups including -OH, C-N, and C-O likely participated in Sb(III) biosorption. Isothermal and kinetic studies revealed that Sb(III) sorption to viable JH7 cells fitted the Langmuir model (R2 = 0.99) and could be described by pseudo-second order kinetics (R2 = 0.99). Furthermore, the increase of anti-oxidative enzymatic activity of JH7 enhanced the intracellular detoxification of Sb(III), which would indirectly contribute to the Sb(III) resistance ability of strain JH7. Our results indicate that biosorption and ROS oxidation of Sb(III) were likely responsible for the decreased toxicity of Sb. The greater understanding how Acinetobacter sp. JH7 lowers the environmental Sb(III) toxicity could provide a basis for future research and subsequent development of technologies for the remediation of Sb contaminated sites.

Energetic contaminants inhibit plant litter decomposition in soil.

Individual effects of nitrogen-based energetic materials (EMs) 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), 4-amino-2,6-dinitrotoluene (4-ADNT), nitroglycerin (NG), and 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) on litter decomposition, an essential biologically-mediated soil process, were assessed using Orchard grass (Dactylis glomerata) straw in Sassafras sandy loam (SSL) soil, which has physicochemical characteristics that support "very high" qualitative relative bioavailability for organic chemicals. Batches of SSL soil were separately amended with individual EMs or acetone carrier control. To quantify the decomposition rates, one straw cluster was harvested from a set of randomly selected replicate containers from within each treatment, after 1, 2, 3, 4, 6, and 8 months of exposure. Results showed that soil amended with 2,4-DNT or NG inhibited litter decomposition rates based on the median effective concentration (EC50) values of 1122 mg/kg and 860 mg/kg, respectively. Exposure to 2-ADNT, 4-ADNT or CL-20 amended soil did not significantly affect litter decomposition in SSL soil at ≥ 10,000 mg/kg. These ecotoxicological data will be helpful in identifying concentrations of EMs in soil that present an acceptable ecological risk for biologically-mediated soil processes.

Potentially toxic trace element contamination, sources, and pollution assessment in farmlands, Bijie City, southwestern China.

Artisanal zinc smelting activities, which had been widely applied in Bijie City, Guizhou Province, southwestern of China, can pollute surrounding farmlands. In the present study, 177 farmland topsoil samples of Bijie City were collected and 11 potentially toxic trace elements (PTEs), namely Pb, Zn, Cu, Ni, Co, Mn, Cr, V, Hg, As, and Cd were tested to characterize the concentrations, sources, and ecological risks. Mean concentrations of these PTEs in soils were (mg/kg) as follows: Pb (127), Zn (379), Cu (93.1), Ni (54.6), Co (26.2), Mn (1095), Cr (133), V (206), Hg (0.15), As (16.2), and Cd (3.08). Pb, Zn, and Cd had coefficients of variation greater than 100% and showed a high uneven distribution and spatial variability in the study area. Correlation coefficient analysis and principal component analysis (PCA) were used to quantify potential pollution sources. Results showed that Cu, Ni, Co, Mn, and V came from natural sources, whereas Pb, Zn, Hg, As, and Cd came from anthropogenic pollution sources. Geoaccumulation index and potential ecological risk indices were employed to study the pollution degree of PTEs, which revealed that Pb and Cd shared the greatest contamination and would pose serious ecological risks to the surrounding environment. The results of this study could help the local government managers to establish pollution control strategies and to secure food safety.

Differences in soil solution chemistry between soils amended with nanosized CuO or Cu reference materials: implications for nanotoxicity tests.

Soil toxicity tests for metal oxide nanoparticles often include micrometer-sized oxide and metal salt treatments to distinguish between toxicity from nanometer-sized particles, non-nanometer-sized particles, and dissolved ions. Test result will be confounded if each chemical form has different effects on soil solution chemistry. We report on changes in soil solution chemistry over 56 days-the duration of some standard soil toxicity tests-in three soils amended with 500 mg/kg Cu as nanometer-sized CuO (nano), micrometer-sized CuO (micrometer), or Cu(NO3)2 (salt). In the CuO-amended soils, the log Cu2+ activity was initially low (minimum -9.48) and increased with time (maximum -5.20), whereas in the salt-amended soils it was initially high (maximum -4.80) and decreased with time (minimum -6.10). The Cu2+ activity in the nano-amended soils was higher than in the micrometer-amended soils for at least the first 11 days, and lower than in the salt-amended soils for at least 28 d. The pH, and dissolved Ca and Mg concentrations in the CuO-amended soils were similar, but the salt-amended soils had lower pH for at least 14 d, and higher Ca and Mg concentrations throughout the test. Soil pretreatments such as leaching and aging prior to toxicity tests are suggested.

Considering the bioavailability and bioaccessibility of metal(loid)s for risk assessment of soils affected by different non-ferrous metal activities in Southwest China.

Toxic metal(loid)s released into the soil by non-ferrous metal mining and smelting activities pose a serious threat to residents and the surrounding ecosystem. Considering only total metal(loid) concentrations likely overestimates routine (eco)toxicological risk assessment of soil. We hypothesize that considering metal(loid) bioavailability/accessibility will improve the accuracy of risk assessment. To test this hypothesis, four mining areas in Southwest China, including mining and surrounding sites, were studied. Bioavailability was determined considering metal(loid)s leached by a simulated strong acid rain (SSAR) treatment. In the four areas, the mining site showed higher cumulative releases of metal(loid)s under SSAR treatment than the agricultural field located in the surrounding sites. Thus, the bioavailable metal(loid)s contents were continuously being released during SSAR treatment and likely increased the environmental risk. Ecological and health risk assessment of soil, calculated using total metal(loid)s content, was corrected considering bioavailable/accessible metal(loid)s, which was determined by the heavy metal(loid)s forms and in vitro simulated intestinal stages. Although the corrected indices indicated that the risk of metal(loid)s-contaminated soil was reduced, unfavorable ecological and health risks remained in the four areas. Our study provides new perspectives to better predict the risk of bioavailable/accessible metal(loid)s in non-ferrous metal contaminated and surrounding soils.

Unraveling assemblage of microbial community dwelling in Dabaoshan As/Pb/Zn mine-impacted area: A typical mountain mining area of South China.

Microbial community assemblage includes microorganisms from the three domains including Bacteria, Archaea, and Eukarya (Fungi), which play a crucial role in geochemical cycles of metal(loid)s in mine tailings. Mine tailings harbor vast proportions of metal(loid)s, representing a unique source of co-contamination of metal(loid)s that threaten the environment. The elucidation of the assembly patterns of microbial communities in mining-impacted ecospheres has received little attention. To decipher the microbial community assembly processes, the microbial communities from the five sites of the Dabaoshan mine-impacted area were profiled by the MiSeq sequencing of 16S rRNA (Bacteria and Archaea) genes and internal transcribed spacers (Fungi). Results indicated that the coexistence of 31 bacterial, 10 fungal, and 3 archaeal phyla, were mainly dominated by Mucilaginibacter, Cladophialophora, and Candidatus Nitrosotalea, respectively. The distribution of microorganisms was controlled by deterministic processes. The combination of Cu, Pb, and Sb was the main factor explaining the structure of microbial communities. Functional predicting analysis of bacteria and archaea based on the phylogenetic investigation of communities by reconstruction of unobserved states analyses revealed that the metabolic pathways related to arsenite transporter, arsenate reductase, and FeS cluster were important for metal detoxification. Furthermore, the ecological guilds (pathogens, symbiotrophs, and saprotrophs) of fungal communities explained 44.5 % of functional prediction. In addition, metal-induced oxidative stress may be alleviated by antioxidant enzymes of fungi communities, such as catalase. Such information provides new insights into the microbial assembly rules in co-contaminated sites.

Physiological and biochemical responses of Leersia hexandra Swartz to nickel stress: Insights into antioxidant defense mechanisms and metal detoxification strategies.

Phytoremediation is widely considered as a cost-effective method for managing heavy metal soil pollution. Leersia hexandra Swartz shows a promising potential for the remediation of heavy metals pollution, including chromium (Cr), copper (Cu), and nickel (Ni). It is vital to understand the physiological and biochemical responses of L. hexandra to Ni stress to elucidate the mechanisms underlying Ni tolerance and accumulation. Here, we examined the metabolic and transcriptomic responses of L. hexandra exposed to 40 mg/L Ni for 24 h and 14 d. After 24-h Ni stress, gene expression of glutathione metabolic cycle (GSTF1, GSTU1 and MDAR4) and superoxide dismutase (SODCC2) was significantly increased in plant leaves. Furthermore, after 14-d Ni stress, the ascorbate peroxidase (APX7), superoxide dismutase (SODCP and SOD1), and catalase (CAT) gene expression was significantly upregulated, but that of glutathione metabolic cycle (EMB2360, GSTU1, GSTU6, GSH2, GPX6, and MDAR2) was downregulated. After 24-h Ni stress, the differentially expressed metabolites (DEMs) were mainly flavonoids (45%) and flavones (20%). However, after 14-d Ni stress, the DEMs were mainly carbohydrates and their derivatives (34%), amino acids and derivatives (15%), and organic acids and derivatives (8%). Results suggest that L. hexandra adopt distinct time-dependent antioxidant and metal detoxification strategies likely associated with intracellular reduction-oxidation balance. Novel insights into the molecular mechanisms responsible for Ni tolerance in plants are presented.

Contrasting response strategies of sulfate-reducing bacteria in a microbial consortium to As3+ stress under anaerobic and aerobic environments.

The sulfate-reducing efficiency of sulfate-reducing bacteria (SRB) is strongly influenced by the presence of oxygen, but little is known about the oxygen tolerance mechanism of SRB and the effect of oxygen on the metalliferous immobilization by SRB. The performance evaluation, identification of bioprecipitates, and microbial and metabolic process analyses were used here to investigate the As3+ immobilization mechanisms and survival strategies of the SRB1 consortium under different oxygen-containing environments. Results indicated that the sulfate reduction efficiency was significantly decreased under aerobic (47.37%) compared with anaerobic conditions (66.72%). SEM analysis showed that under anaerobic and aerobic conditions, the morphologies of mineral particles were different, whereas XRD and XPS analyses showed that the most of As3+ bioprecipitates under both conditions were arsenic minerals such as AsS and As4S4. The abundances of Clostridium_sensu_stricto_1, Desulfovibrio, and Thiomonas anaerobic bacteria were significantly higher under anaerobic than aerobic conditions, whereas the aerobic Pseudomonas showed an opposite trend. Network analysis revealed that Desulfovibrio was positively correlated with Pseudomonas. Metabolic process analysis confirmed that under aerobic conditions the SRB1 consortium generated additional extracellular polymeric substances (rich in functionalities such as Fe-O, SO, CO, and -OH) and the anti-oxidative enzyme superoxide dismutase to resist As3+ stress and oxygen toxicity. New insights are provided here into the oxygen tolerance and detoxification mechanism of SRB and provide a basis for the future remediation of heavy metal(loid)-contaminated environments.

Sulfate-reducing consortium HQ23 stabilizes metal(loid)s and activates biological N-fixation in mixed heavy metal-contaminated soil.

Sulfate-reducing bacteria (SRB) are used in the remediation of mine pollution; however, the mechanism of stabilizing multiple heavy metal(loid)s by the SRB consortium under low oxygen conditions needs further study. Indigenous microflora were extracted from non-ferrous metal-contaminated soil co-inoculated with enriched SRB consortium and assembled as the HQ23 consortium. The presence of Desulfovibrio (SRB) in HQ23 was confirmed by 16S rRNA sequencing and qPCR. The effects of culture media, dissolved oxygen (DO), SO42¯, and pH on the HQ23 growth rate, and the SO42¯-reducing activity were examined. Data indicates that the HQ23 sustained SRB function under low DO conditions (3.67 ± 0.1 mg/L), but the SRB activity was inhibited at high DO content (5.75 ± 0.39 mg/L). The HQ23 can grow from pH 5 to pH 9 and can decrease mobile or bioavailable Cr, Cu, and Zn concentrations in contaminated soil samples. FTIR revealed that Cu and Cr adsorbed to similar binding sites on bacteria, likely decreasing bacterial Cu toxicity. Increased abundances of DSV (marker for Desulfovibrio) and nifH (N-fixation) genes were observed, as well as an accumulation of nitrate-N content in soils suggesting that HQ23 stimulates the biological N-fixation in soils. This study strongly supports the future application of SRB for the bioremediation of heavy metal-polluted sites.

Impact of steel slag, gypsum, and coal gangue on microbial immobilization of metal(loid)s in non-ferrous mine waste dumps.

Non-ferrous mine waste dumps globally generate soil pollution characterized by low pH and high metal(loid)s content. In this study, the steel slag (SS), gypsum (G), and coal gangue (CG) combined with functional bacteria consortium (FB23) were used for immobilizing metal(loid)s in the soil. The result shown that FB23 can effectively decrease As, Pb, and Zn concentrations within 10 d in an aqueous medium experiment. In a 310-day field column experiment, solid waste including SS, G, and CG combined with FB23 decreased As, Cd, Cu, and Pb concentrations in the aqueous phase. Optimized treatment was obtained by combining FB23 with 1% SS, 1% G, and 1.5% CG. Furthermore, the application of solid waste (SS, G, and CG) increased the top 20 functional bacterial consortium (FB23) abundance at the genus level from 1% to 21% over 50 days in the soil waste dump. Moreover, dissolved organic carbon (DOC) and pH were identified as the main factors influencing the reduction in bioavailable As, Cd, Cu, and Pb in the combination remediation. Additionally, the reduction of Fe and sulfur S was crucial for decreasing the mobilization of the metal(loid)s. This study provides valuable insights into the remediation of metal contamination on a larger scale.

Quantifying ecological and human health risks of metal(loid)s pollution from non-ferrous metal mining and smelting activities in Southwest China.

The environmental release and transfer of heavy metal(loids) from natural and anthropogenic sources to neighboring habitats can pose an ecological threat to the exposed biota and habitat, as well as a human health risk to the residents. However, analytical tools to identify the potential contamination source(s) and assess the impact of this transfer have not been well described. Soil samples were collected from affected areas proximal to non-ferrous metal(loid)s mining and smelting facilities. Two integrated assessment methods, based on soil total metal(loid) content, included: (1) the potential ecological risk index combined with positive matrix factorization (PMF) and (2) human health risk assessment combined with PMF. Results indicated that there were four generic sources of pollution (based on PMF analyses of 115 replicated samples collected from four study areas): agricultural and industrial activities, traffic emissions, and natural sources. For ecological risk, the contribution of these metal(loid)s pollution sources were industrial activities (20.34-70.76 %), traffic emissions (18.73-56.93 %), natural sources (3.69-27.02 %), and agricultural activities (3.79-21.43 %). Health risks were higher for children than for adults. Industrial activity was a major source of non-carcinogenic risk to children (32.10-74.62 %) and adults (31.33-73.78 %), and carcinogenic risk to children (22.53-67.27 %) and adults (20.69-64.76 %). Total metal analysis indicated that As and Cd were highly enriched in the soil, but chemical fractionation revealed low As mobility. Total Cd and possibly As were the main pollutants causing the ecological risks at these contaminated sites. This study demonstrates that ecological and human health risks could be quantified to prioritize the pollution sources for reasonable contaminated site risk management.

New insights on the effect of non-ferrous metal mining and smelting activities on microbial activity characteristics and bacterial community structure.

Mining and smelting activities have brought potentially serious heavy metal(loid)s pollution to their surrounding locale. However, studies on microbial metabolic activities, community structure, and adaptation in soils proximal to non-ferrous metal mining and smelting areas are still lacking. Here the effects of biotic and abiotic characteristics of soil taken from sites surrounding inactive and active non-ferrous metal mine smelting facilities on microbial enzyme activity, microcalorimetry, and high-throughput sequencing of 16S rRNA gene barcoding were studied. Data indicated that the soils were heavily polluted by toxic metal(loid)s, of which As and Cd were the main contaminants. Microbial acid phosphatase activity and microcalorimetric total heat value were sensitive metabolic indicators in the studied areas. Actinobacteriota had the highest relative abundance, followed by Proteobacteria, Chloroflexi, and Acidobacteria. Microbial metabolic activity, bacterial community structure and phenotype varied between inactive and active sites (p < 0.05). Such analyses indicated that electrical conductivity, total As, Cu, and Mn contents, and bioavailable As, Cu, Cd, and Mn concentrations were key factors determining microbial activities, bacterial community structure, and phenotypes. Knowledge of microbial adaptation to heavy metal stressors is important for better understanding the aerial transfer of fugitive heavy metal(loid)s (and possibly microbes) and for designing future strategies for improved soil bioremediation.