Trace elements can be toxic when they cannot be easily removed after entering an ecosystem, so a long-term assessment is fundamental to guide ecosystem restoration after catastrophic pollution. In 1998, a pyrite mining accident in Aznalcóllar (south-western Spain) spilled toxic waste over a large area of the Guadiamar river basin, where, after restoration tasks, the Guadiamar Green Corridor was established. Eight years after the mine accident (2005–2006), the ground-dwelling insectivorous lizard Psammodromus algirus registered high trace-element levels within the study area compared to specimens from a nearby unpolluted control site. In 2017, 20 years after the accident, we repeated the sampling for this lizard species and also quantified trace elements in vegetation as well as in arthropod samples in order to identify remnant trace-element accumulation with the aim of assessing the transfer of these elements through the trophic web. We found remnant trace-element contamination in organisms of the polluted site compared to those from the unpolluted site. All trace-element concentrations were higher in arthropods than in plants, suggesting these compounds bioaccumulate through the trophic web. Lizards from the polluted areas had higher As, Cd, and Hg concentrations than did individuals from the unpolluted area. Lizard abundance between sampling periods (2005–06 and 2017) did not vary in unpolluted transects but strongly declined at polluted ones. By contrast, the Normalized Difference Vegetation Index indicated that in the study period, the vegetation was similar at the two sampling sites. These results suggest that, 20 years after the accident, the trace-element pollution could be the cause of a severe demographic decline of the lizard in the polluted area.

Thallium (Tl) is a trace metal of severe toxicity. Its health concerns via consumption of contaminated vegetables have often been overlooked or underestimated. This study was designed to gain insight into the actual level and distribution characteristics of Tl and metal (loid)s (Pb, Cd, Cr, Sb, Mn, Cu, Zn, Ni, and Co) in agricultural soils and common vegetables cultivated in different zones (upstream, midstream, and downstream) of a densely populated residential area in a typical mine city, which has been open-pit exploiting Tl-bearing pyrite minerals since 1960s. The results show that most of the agricultural soils exhibit contaminated levels of Tl, with Tl contents (upstream: 1.35–4.31 mg/kg, midstream: 2.43–5.19 mg/kg, and downstream: 0.65–2.33 mg/kg) mostly exceeding the maximum permissible level (MPL) for agricultural land use (1 mg/kg). Sequential extraction procedure indicates that even Tl is predominantly retained in the residual fraction, significant levels of Tl are still present in the geochemically mobile fractions. Besides, metals like Cu, Cd, Mn, and Co are mostly distributed in the labile fractions. Almost all metal (loid)s in edible parts of the vegetables exceed their corresponding MPL for consumption. The chronic daily intake (CDI) and hazard quotient (HQ) values calculated for inhabitants at different ages indicate non-negligible Tl risks via consumption of local vegetables, especially for children. Therefore, it is critical to establish effective measures for hazardous waste management and enforceable regulations in Tl-polluted area to mitigate potential severe impacts of Tl on human health through food chain.

The Wiśniówka rock strip mining area (south-central Poland) with quartzite quarries, acid water bodies and tailings piles is one of the most unique acid mine drainage (AMD) sites throughout the world. This is due to the occurrence of enormous amounts of pyrite unknown in sedimentary formations worldwide. Of the two mineralization zones, one that is the most abundant in arsenical pyrite occurs in the lowermost Upper Cambrian formation of the Podwiśniówka quarry. The As-rich pyritiferous clastic rocks are exposed as a result of deep quartzite extraction during 2013–2014. In addition, the clayey-silty shale interbeds are enriched in rare earth element (REE) minerals. The mining operation left an acidic lake with a pH of about 2.4–2.6 and increased contents of sulfates, metal(loid)s and REE. The Podwiśniówka pyrite-rich waste material was stacked up in many places of the mining area giving rise to strongly acidic spills that jeopardized the neighboring environment. One of these unexplored tailings piles was a source of extremely sulfate- and metal(loid)-rich pools with unusual enrichments in As (up to 1548 mg L⁻¹) and REE (up to 24.84 mg L⁻¹). These distinctly exceeded those previously reported in the Wiśniówka area. A broad scope of geochemical, mineralogical and petrographic methods was used to document these specific textural and mineralogical properties of pyrite facilitating its rapid oxidation. The pyrite oxidation products reacted with REE-bearing minerals releasing these elements into acid water bodies. Statistical methods were employed to connect the obtained tailings pool hydrogeochemical data with those derived from this and the previous studies of the Podwiśniówka and Wiśniówka Duża acid pit lakes. In contrast to metal(loid) profiles, the characteristic shale-normalized REE concentration patterns turned out to be more suitable for solving different AMD issues including provenance of mine waste material in the tailings pile examined.

Thallium (Tl) is a well-recognized hazardous heavy metal with very high toxicity. It is usually concentrated in sulfide minerals, such as pyrite (FeS₂), sphalerite (ZnS), chalcopyrite (CuS) and galena (PbS). Here, this study was carried out to investigate the indigenous microbial communities via 16S rRNA gene sequence analysis in typical surface sediments with various levels of Tl pollution (1.8–16.1 mg/kg) due to acid mine drainage from an active Tl-containing pyrite mining site in South China. It was found with more than 50 phyla from the domain Bacteria and 1 phyla from the domain Archaea. Sequences assigned to the genera Ferroplasma, Leptospirillum, Ferrovum, Metallibacterium, Acidithiobacillus, and Sulfuriferula manifested high relative abundances in all sequencing libraries from the relatively high Tl contamination. Canonical correspondence analysis further uncovered that the overall microbial community in this area was dominantly structured by the geochemical fractionation of Tl and geochemical parameters such as pH and Eh. Spearman's rank correlation analysis indicated a strong positive correlation between acidophilic Fe-metabolizing species and Tlₜₒₜₐₗ, Tlₒₓᵢ, and Tlᵣₑₛ. The findings clarify potential roles of such phylotypes in the biogeochemical cycling of Tl, which may facilitate the development of in-situ bioremediation technology for Tl-contaminated sediments.

In this study, reactive pyrite (FeS2) particles were prepared through a modified hydrothermal method and tested for immobilization of Cr(VI) in contaminated soil and synthetic groundwater. The addition of a NaAc buffer in the synthetic process resulted in pyrite particles of greater specific surface area, more uniform size, and more crystalline structure. The particles can effectively immobilize Cr(VI) in both water and a model Chinese loess soil. Over 99.9% of Cr(VI) was rapidly removed from water at pH 6.0 (Initial Cr(VI) = 25 mg/L, FeS2 dosage = 0.48 g/L), and the removal remained high (>82%) even at pH 9.5. Both adsorption and reductive precipitation were found operative in the Cr(VI) immobilization, with ∼66% of Cr immobilized due to reduction. Fe(II) ions associated on the FeS2 surface played a key role in the reduction of Cr(VI) to Cr(III), and S22− also facilitated the reductive removal of Cr(VI). The presence of humic acid enhanced Cr(VI) removal at pH 4.0, but the effect was negligible at pH 6.0. Batch kinetic tests showed that treating a Cr(VI)-laden soil with 0.48 g/L (as Fe) of FeS2 decreased the equilibrium water-leachable Cr(VI) by >99.0% at pH 6.0 and by >70.0% at pH 9.0. The distribution coefficient (Kd) value of the pyrite-amended soil was 1477.8 at pH 6.0, which is 306 times higher than for the untreated soil. Column elution tests showed that installation of a 3-cm reactive layer of FeS2 in a soil column was able to capture the leachable Cr(VI) from the soil, and the retardation factor (Rd) for the 3-cm FeS2 layer sample was 381 times higher than that for the plain soil. The synthetic pyrite particles may serve as an reactive material for effective removal or immobilization of Cr(VI) in contaminated water or soil.

Sulfidized nanoscale zero-valent iron (S-nZVI) is a promising material for in situ soil remediation. However, its transformation (i.e., aging) and effects on the microbial community in soil ecosystems are largely unknown. In this study, S-nZVI having low (S-nZVI (L)) and high sulfur-doping (S-nZVI (H)) were incubated in soil microcosms and bare nZVI was used as a control. Their aged products were characterized using microspectroscopic analyses and the changes in the corresponding soil microbial community were determined using high-throughput sequencing analyses. The results indicate that severe corrosion of both bare and S-nZVI occurred over 56 days of aging with significant morphological and mineral changes. Magnetite, lepidocrocite, and goethite were detected as the main aged products. In addition, sulfate ions, pyrite, and iron polysulfide were formed in the aged products of S-nZVI. Cr(VI) removal test results indicated that S-nZVI(L) achieved the best results after aging, likely because of the optimal FeS arrangement on its nanoparticle surfaces. The presence of nZVI and S-nZVI increased the abundance of some magnetotactic microorganisms and altered bacterial and fungal community structures and compositions. Moreover, the addition of S-nZVI enriched some bacterial and fungal genera related to sulfur cycling because of the presence of sulfide-bearing material. The findings reveal the transformation of S-nZVI during aging and its effects on microbial communities in soil ecosystems, thereby helping to the evaluation of S-nZVI application in soil remediation.

Exposure to toxic metals from nonferrous metal(loid) smelter soils can pose serious threats to the surrounding ecosystems, crop production, and human health. Bioremediation using microorganisms is a promising strategy for treating metal(loid)-contaminated soils. Here, a native microbial consortium with sulfate-reducing function (SRB1) enriched from smelter soils can tolerate exposures to mixtures of heavy metal(loid)s (e.g., As and Pb) or various organic flotation reagents (e.g., ethylthionocarbamate). The addition of Fe²⁺ greatly increased As³⁺ immobilization compared to treatment without Fe²⁺, with the immobilization efficiencies of 81.0% and 58.9%, respectively. Scanning electronic microscopy-energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed that the As³⁺ immobilizing activity was related to the formation of arsenic sulfides (AsS, As₄S₄, and As₂S₃) and sorption/co-precipitation of pyrite (FeS₂). High-throughput 16S rRNA gene sequencing of SRB1 suggests that members of Clostridium, Desulfosporosinus, and Desulfovibrio genera play an important role in maintaining and stabilizing As³⁺ immobilization activity. Metal(loid)s immobilizing activity of SRB1 was not observed at high and toxic total exposure concentrations (220–1181 mg As/kg or 63–222 mg Pb/kg). However, at lower concentrations, SRB1 treatment decreased bioavailable fractions of As (9.0%) and Pb (28.6%) compared to without treatment. Results indicate that enriched native SRB1 consortia exhibited metal(loid) transformation capacities under non-toxic concentrations of metal(loid)s for future bioremediation strategies to decrease mixed metal(loid)s exposure from smelter polluted soils.

Mine waste classification preceding mining constitutes a proactive solution to classify and segregate mine waste into geo-environmental domains based upon the magnitude of their environmental risks. However, upstream classification requires multi-disciplinary and integrated approaches. This study integrates geological modeling and kinetic modeling to inform upstream mine waste classification based on the pH generated from the main acid-generating and acid-neutralizing reactions once the mine solid waste is stored in oxidizing conditions. Geological models were used to depict the ante-mining spatial distribution of the main reactive minerals: pyrite, albite and calcite. Subsequently, the corresponding block models were created. The dimension of the elementary voxels for each block model was set at 40х40х40 m for this study. The kinetic modeling approach was performed using PHREEQC and VS2DRTI to consider unsaturated conditions. The kinetic modeling simulated a 1D column for each voxel. The column simulates the excavated state of the hosting rock involving kinetic reactions and unsaturated flow under highly oxidizing conditions. Subsequently, the resulting pH for different intervals of time was assigned to its respective voxel. The outcome consists of a spatio-temporal visualization of the pH defining ante-mining geo-environmental domains, thereby providing the opportunity for formulating proactive management measures regarding the hazardous geo-environmental domains.

Acid mine drainage (AMD) due to the mining of sulfide deposits is one of the most important causes of water pollution worldwide. Remediation measures, especially in historical abandoned mines, require a deep knowledge of the geochemical characteristics of AMD effluents and metal fluxes, considering their high spatial and temporal evolution, and the existence of point and diffuse sources with a different response to rainfall events. This study investigates the temporal variations and hydrogeochemical processes affecting the composition of main AMD sources from the Tharsis mines (SW Spain), one of most important historical metal mining districts in the world. To address this, a fortnightly-monthly sampling was performed during two years in the main AMD sources and streams within the mine site covering different hydrological conditions. A seasonal pattern was observed linked to hydrological variations; higher pollutant concentrations were observed during the dry season (maximum values of 4,6 g/L of Al, 11,8 g/L of Fe, and 67 g/L of sulfate) and lower ones were observed during the rainy periods. Stream samples exhibited a negative correlation between electrical conductivity (EC) and flow, while positive values were observed in AMD sources, where groundwater fluxes were predominant. High flow also seems to be the main driver of Pb fluxes from AMD sources, as the concentration of Pb in waters increased notably during these events. The precipitation of secondary Fe minerals may limit the mobility of As and V, being retained in the proximity of mine sites. The concentration of Zn in waters seems to be controlled by the original grade in the metal deposit from which the waste is generated, together with the age of these wastes. The pollutant load delivered by the Tharsis mines to the surrounding water courses is very high; e.g., mean of 733 ton/yr of Al or 2757 ton/yr of Fe, deteriorating the streams and reservoirs downstream.

The N, S, and Fe-tridoped carbon catalysts (NSFe-Cs), Fe/ACNS1 and Fe/ACNS2, were synthesized by wet impregnation with different concentration of ammonium ferrous sulfate solution. The prepared catalysts have a similar textural structure. The N species, S species, Feᴵᴵ and Feᴵᴵᴵ were simultaneously introduced onto the surface of catalysts. Comparison with the only Fe doped catalyst, NSFe-Cs showed greater stability and higher phenol removal in catalytic wet peroxide oxidation at different reaction condition. The main intermediates including p-hydroxybenzoic acid, formic acid, and maleic acid were determined in the treated wastewater. The high catalytic activity for NSFe-C was related to the ability of H₂O₂ decomposition. NSFe-Cs have more amount of Feᴵᴵ partially due to the formation of FeS₂, which promoted the decomposition of H₂O₂ on Fe/ACNS1 and Fe/ACNS2 surface. The generation of ·OH and ·HO₂/·O₂⁻ radicals in the bulk solution was crucial to phenol degradation, and the decomposition of H₂O₂ complied with the pseudo-first-order kinetics. The highly linear relationship between decomposition kinetic constant for H₂O₂ and the amount of surface groups suggested, including Feᴵᴵ species, pyridinic N/Fe-bonded N, pyrrolic N as well as graphitic N were responsible to the high activity of NSFe-Cs.