Toxicity of nickel to soil microbial community with and without the presence of its mineral collectors-a calorimetric approach

Insight into the mechanisms of combined toxicity of cadmium and flotation agents in luminescent bacteria: Role of micro/nano particles

Currently, risk assessment and pollution management in mines primarily focus on toxic metals, with the flotation agents being overlooked. However, the combined effects of metals and flotation agents in mines remain largely unknown. Therefore, this study aimed to evaluate the combined effects of Cd and two organic flotation agents (ethyl xanthate (EX) and diethyldithiocarbamate (DDTC)), and the associated mechanisms. The results showed that Cd + EX and Cd + DDTC exhibited synergistic toxicity. The EC50 values for luminescent bacteria were 1.6 mg/L and 1.0 mg/L at toxicity unit ratios of 0.3 and 1, respectively. The synergistic effects were closely related with the formation of Cd(EX)2 and Cd(DDTC)2 micro/nano particles, with nano-particles exhibiting higher toxicity. We observed severe cell membrane damage and cell shrinkage of the luminescent bacteria, which were probably caused by secondary harm to cells through the released CS2 during their decomposition inside cells. In addition, these particles induced toxicity by altering cellular levels of biochemical markers and the transcriptional levels of transport proteins and lipoproteins, leading to cell membrane impairment and DNA damage. This study has demonstrated that particulates formed by Cd and flotation agents contribute to the majority of the toxicity of the binary mixture. This study helps to better understand the complex ecological risk of inorganic metals and organic flotation agents in realistic mining environments.

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

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

Stabilization of Ni by rhamnolipid modified nano zero-valent iron in soil: Effect of simulated acid rain and microbial response

Nickel (Ni), as one of the essential micronutrients, exists widely in nature, but high concentration of Ni in soil can pose certain biological toxicity. Nano zero-valent iron (nZVI) and rhamnolipid modified nZVI (RL@nZVI) can effectively stabilize Ni in soil. In this study, the stabilization effect of nZVI and RL@nZVI on the Ni-polluted soil under simulated acid rain and the microbial community response during the soil remediation under different Ni levels (200, 600, and 1800 mg/kg) were investigated. The results show that the addition of nZVI and RL@nZVI increased the pH of leachate to neutral and decreased the amount of Ni in leachate (23.33%-47.06% by nZVI and 50.01%-70.47% by RL@nZVI), indicating that nZVI and RL@nZVI could reduce the potential radial migration risk of Ni in soil under simulated acid rain. The addition of RL@nZVI was beneficial to recover the soil bacterial community diversity, which was inhibited by Ni pollution, and rhamnolipid coating could reduce the toxicity of nZVI. The dominant bacteria in RL@nZVI-treated soil with low, medium, and high Ni pollution were Firmicutes, Proteobacteria and Actinobacteria, respectively. Soil potential, total organic carbon, and pH were the main driving factors affecting the bacterial community structure, while Ni stress only caused changes in the relative abundance of some tolerant bacteria.

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.

Assessment of Metal Accumulation by Arthrospira platensis and Its Adaptation to Iterative Action of Nickel Mono- and Polymetallic Synthetic Effluents

Cyanobacteria-mediated wastewater remediation is an economical, efficient, and eco-friendly technology. The present work deals with the bioaccumulation performance of Arthrospira platensis (Spirulina) grown for four cycles in a medium containing nickel mono- and polymetallic synthetic effluents. The metal uptake by spirulina biomass was evaluated using neutron activation analysis. The effects of effluents on biomass production, protein, and phycobiliprotein content were assessed. Metal accumulation in the biomass depended on the effluent composition and metal ion concentrations. Nickel accumulation in the biomass was directly proportional to its concentration in effluents, and maximum uptake (1310 mg/kg) was attained in the Ni/Cr/Fe system. In the same system, biomass accumulated 110 times more chromium and 4.7 times more iron than control. The highest accumulation of copper (2870 mg/kg) was achieved in the Ni/Cu/Zn/Mo system and zinc (1860 mg/kg)—in the Ni/Cu/Zn/Sr system. In biomass grown in the media loaded with nickel and also chromium, iron, copper, strontium, zinc, and molybdenum, a decrease in productivity (on average by 10%) during the first cycle of cultivation and moderate reduction of protein content (by 15–27%) was observed. The presence of metals in the cultivation media inhibited phycobiliprotein synthesis, especially of phycocyanin, and promoted the synthesis of allophycocyanin. The maximum reduction of phycocyanin content was 77%, and the increase of allophycocyanin content—by 45%. Arthrospira platensis may be deemed as bioremediation of nickel-polluted wastewaters of complex composition.

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.

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.

Effects of typical flotation reagent on microbial toxicity and nickel bioavailability in soil

The combined toxicological effects of nickel (Ni) and butyl xanthate (BX), that is commonly used in flotation reagents for non-ferrous metals ore processing such as Ni, copper and lead ores, on soil microbial communities were studied by determining soil microbial activity, soil enzyme activities and Ni bioavailability. The results revealed that the exchangeable (EXC) and reducible (RED) fractions of Ni were higher in Ni/BX mixture than Ni alone, probably because BX reacts with Ni to form complexes that lead an increase in bioavailability of Ni. The presence of BX and Ni inhibited microbial activity and enzyme activities during the first 30-days. Then, from 30 days to 180 days, different trends were observed according to the condition: microbial activity was stimulated with BX alone while it was inhibited with Ni/BX mixture. This observation was supported by the fact that the inhibitory ratio (I) was higher for Ni/BX mixture than BX alone. Results showed that the sensitivity to one or both contaminants followed the order: urease (UA) > invertase (INV). EXC fraction of Ni/BX mixture were significantly correlated with UA, INV, I, peak power (P_peak) and peak time (T_peak), respectively (p < 0.01), suggesting that Ni bioavailability might explain the Ni toxicity against microbial communities under combined pollution conditions. Such observations allow us to better understand toxic effects of Ni pollution when accompanied with BX, facilitating precisely evaluation of potential risks in mining areas.

Molecular Biology-Based Analysis of the Interactive Effect of Nickel and Xanthates on Soil Bacterial Community Diversity and Structure

Metals and mineral flotation collector’s toxicity to the soil living system greatly compromise the sustainability of mining and ore processing. Their effects on the soil microbial community, the most active soil component, remain less understood and addressed particularly with regards to xanthates and their combination with metals. This study analyzed the interactive effects of Ni and xanthates, potassium ethyl xanthate and sodium isopropyl xanthate, on the soil bacterial community through an efficient molecular biology-based technique, the Miseq (Illumina). Both soil microbial community diversity and structure were more affected by xanthates than by Ni. The five most dominant phyla, representing 96.31% of the whole bacterial community, comprised Proteobacteria (54.16%), Firmicutes (17.51%), Actinobacteria (15.59%), Acidobacteria (4.87%), and Chloroflexi (4.16%). Different soil treatments exhibited greater difference in the species abundance/dominance than in the species numbers. Proteobacteria was the most dominant in the presence of xanthates, individually or in mixtures with nickel, while Firmicutes exhibited its highest proportion in the Ni/xanthate-treated samples. The most abundant and proportionally different bacterial species between different treatments were presented. The most abundant bacterial strains identified should be explored more for their potential application in biomining and for the prediction and biologically-based treatment and remediation of Ni and xanthate-contaminated systems.

Characterization of microbial communities of soils from gold mine tailings and identification of mercury-resistant strain

To enrich the understanding of the complex environmental system of soil and microorganisms in gold tailings, we studied the effects of environmental factors on the microbial community diversity in gold mine tailing soil in Beijing, and the strains screened from the soil with serious mercury (Hg) pollution. The results showed that microbial diversity and community composition varied among sites, and at varying depths, soil microbes were significantly affected by soil environmental factors such as lead (Pb), Hg, pH, and total organic carbon (TOC). Pb and Hg negatively affected soil microbial diversity, and less-polluted soil showed increased microbial diversities and complex community structure. Community composition analysis showed that Firmicutes, Proteobacteria and Actinobacteria were the dominant microorganisms. Moreover, Hg-resistant bacterial species isolated from soil samples were identified as Pseudomonas plecoglossicida with a high Hg tolerance efficiency. This study is important in understanding the microbial diversity and function in gold mine tailing soils and can widen the application for bioremediation process.

Microcalorimetry and enzyme activity to determine the effect of nickel and sodium butyl xanthate on soil microbial community

In non-ferrous metal tailings, combined pollution in the surrounding soil is caused by heavy metals and flotation chemicals. The combined effects of nickel (Ni) and its primary ore processing collector, sodium butyl xanthate (SBX), on soil microbial activity were investigated following the fluorescein diacetate hydrolase (FDA) and sucrase (SA) activities, and isothermal microcalorimetry during 60 days. FDA and SA activities as well as overall soil microbial activity were significantly affected by Ni, SBX and Ni/SBX mixture. The inhibition rate (I) of the growth rate constant (k) being higher with the Ni/SBX mixture than with SBX alone during the experiment. The growth rate constant (k) was positively correlated (p < 0.05 or p < 0.01) with enzyme activities (FDA and SA) indicating that k represented a valuable proxy to evaluate the toxic effect of metals and flotation reagents on soil microorganisms. Thus, microcalorimetry was a useful method to characterize soil microbial communities.