Arsenic, selenium, boron, lead, cadmium, copper, and zinc in naturally contaminated rocks: A review of their sources, modes of enrichment, mechanisms of release, and mitigation strategies

Marine food web trophic interaction of trace elements and stable isotopes of carbon and nitrogen in Rabigh lagoon, Red Sea, Saudi Arabia

The increase in heavy metal pollution in mangrove ecosystems due to anthropogenic activities has been on the increase and has been studied previously. However, there is a need for a better understanding of the use of stable isotopes of carbon (δ13C) and nitrogen (δ15N) to establish trophic levels (TL) and their contamination in the food web. In this study, samples of sediment, mangrove, algae, seagrasses, crustacean, poriferans, echinoderms, molluscs, cnidarian and fishes were collected for determination of trace elements (Fe, Mn, Cu, Zn, Cd, Cr, Pb, Ni and Co) and stable isotopes. Varian 720-ES inductively coupled plasma-optical emission spectrometer (ICP-OES) and Thermo elementary analyser-ConFlo IV-Delta V Advantage mass spectrometer were used for the analysis of metals and stable isotopes respectively. The food web structure of Rabigh lagoon mangrove comprises a group of organisms such as crustacean (crab), porifera (sponges), echinoderm (starfish), mollusc (aquatic snails) and cnidarian (coral) in the second trophic level (TL = 1.0-2.0). For the third trophic level (TL = 2-3), Platycephalus bassensis (TL = 2.96) and Scomber sp. (TL = 2.30) belonging to the taxonomic group fishes are the two organisms in this trophic level. However, from the 9 trace elements determined, only Cd and Pb recorded excessive bioconcentration in the species. In terms of Total Magnification Factor (TMF) and metal concentrations, there was significant biodilution of all trace elements determined in this study except for Pb (TMF = 0.72; p > 0.05) and Co across the extracted food web consisting of molluscs, crustacean and fishes. Biodilution of Pb was not significant across the trophic levels of the food web. This study provides baseline information on the food web structure and transfer of trace elements across the food web of Rabigh mangrove, Red Sea, Saudi Arabia.

Changes in chemical speciation and mobility of arsenic during the mixing of arsenic-bearing "snow-melting" system effluent and river water in the Ishikari Plain, Japan

An effective and ingenious method called "snow-melting" system was widely implemented for snow management in the Ishikari Plain, Japan. In this system, groundwater is pumped up, mixed with snow, and discharged into a nearby river. Since the groundwater in the Ishikari Plain is contaminated with arsenic (As), the impacts of directly discharging As-bearing groundwater into the river were assessed and monitored. In-situ monitoring data collected between 2013 and 2015 showed that As concentrations were higher in the groundwater (23-95 μg/L) than in the river water (2-71 μg/L). The major As speciation in the groundwater and river water were dissolved arsenite (As(III)) and As in suspended iron (Fe)-bearing solids, respectively. Precipitation of dissolved Fe when "snow-melting" system effluent mixes with the river water could be attributed to more oxic and oxidizing conditions of the resulting fluid mixture. Dissolved iron (Fe), mainly as ferrous ion (Fe2+), coexisted with dissolved As(III) in groundwater, so after mixing with the river water, Fe2+ was oxidized to ferric ion (Fe3+) and then precipitated as amorphous Fe oxyhydroxide phases that also sequestered dissolved arsenate (As(V)) via adsorption and coprecipitation. A strong correlation between As and Fe contents in river sediments was also observed, suggesting that Fe-bearing phases play an essential role in As immobilization. The results also showed a strong interaction between groundwater and river water that affected the chemical speciation and mobility of As and Fe. In addition, it was found that discharging As-bearing groundwater did not have profound impact on river water quality. Based on the results, dissolved Fe, Fe-bearing solid phases, and geochemical conditions strongly influenced how As speciates and migrates in a system where two fluids are mixed. This study could provide significant insights concerning the impacts of As on surrounding environments where As-bearing groundwaters are used and discharged without treatment.

A nitrogen and phosphorus enriched inorganic-organic hybrid material for electrochemical detection of selenium(iv) ions

A heteroatom (nitrogen and phosphorus) enriched pyridinic bridged inorganic-organic hybrid material (HPHM) was synthesized by polycondensing phosphonitrilic chloride trimer (PNC) and 2,6-diaminopyridine in DMSO at 140 °C. The synthesized material was used as an efficient electrode material for the electrochemical detection of selenium(iv) ions [Se(iv)] in aqueous solution. The HPHM electrode (active mass loading of 4.1 mg cm-2) achieves a detection range of 5-50 ppb at a deposition potential of -1.2 V and a deposition time of 170 s with a lower limit of detection (LOD) of 2.18 ppb. This LOD is significantly below the World Health Organization's (WHO) recommended maximum level for selenium in drinking water. Moreover, the electrode material maintains high selectivity for Se(iv) ions in the presence of various interfering ions and high sensitivity over 200 cycles with only a minimal (∼6.83%) decline in current density response. The higher Se(iv) ion detection capability is attributed to the strategic incorporation of nitrogen and phosphorus heteroatoms, enhancing the material's electrochemical properties.

The interaction between metals and catecholamines: oxidative stress, DNA damage, and implications for human health

The interaction between metals and catecholamines plays a pivotal role in the generation of reactive oxygen species (ROS), leading to oxidative stress and DNA damage. ROS are linked to several diseases, including neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. This review examines how essential metals (iron, copper, zinc, manganese) and a few non-essential metal(loid)s (mercury, chromium, arsenic, aluminum, cadmium, and nickel) contribute to oxidative stress in the presence of catecholamines. In the presence of metals, catecholamines can cause oxidative DNA modification, possibly resulting in cell apoptosis, by taking part in redox reactions and oxidizing to the corresponding aminochrome with simultaneous ROS production. Essential metals are vital for physiological functions, but imbalances in their homeostasis can be harmful. Furthermore, non-essential metals, commonly encountered through environmental or occupational exposure, can exhibit significant toxicity. Previous studies on catecholamine-induced oxidative stress focused on copper and iron, but this review emphasizes the need to investigate other neurotoxic metals and expand existing knowledge on the interactions between metals, catecholamines, and DNA damage. Results from such research could help prioritizing the development of new assessment methods associated with adverse outcome pathways, to reliably predict harmful effects on human health, aiding in the development of therapeutical strategies. The present work will help to shed light on the interplay of metals, catecholamines, and DNA damage in different diseases hopefully fostering new research in this still understudied topic. Future research should investigate the molecular mechanisms through which these metals affect neuronal health and contribute to disease pathogenesis.

Mineral-dependent release, migration and enrichment of toxic elements during black shale weathering: An integrated study from profile scale to mineral scale

Chemical weathering of lithologies with high geochemical backgrounds such as black shale has been proposed to be a critical source for toxic elements in soil and water systems. However, mechanisms controlling the release, migration and enrichment of toxic elements during black shale weathering are poorly understood. This study utilized a suite of micro analytical techniques such as TESCAN integrated mineral analyzer (TIMA), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and electron micro-probe analysis (EMPA) to elucidate the intimate relationship between mineralogical transformations and elemental behaviors from profile scale to mineral scale. Mineralogical and elemental compositions for a black shale weathering profile (and surface strongly weathered materials) suggest a dominant sequence of mineral reactions as oxidation of sulfides, dissolution of carbonates, alteration of aluminosilicates, and transformation of clay minerals. Most of the toxic elements were largely released from the weathering profile and significantly enriched in the strongly weathered materials. Black shale weathering was initiated by oxidation of pyrite, sphalerite and molybdenite, and these chemical reactions dominated the release of toxic elements (e.g., As, Cd, Mo, Mn, Ni and Zn). During oxidation of pyrite, Fe (hydr)oxides pseudomorphically replaced pyrite grains, along with the release of As and Mn and their subsequent retention in Fe (hydr)oxides. Sulfuric acid generated by oxidation of sulfides firstly dissolved surrounding calcite and dolomite to significantly improve the pore-fracture networks in the weathered shale, allowing more water fluxes and transportation of Fe (hydr)oxides and concomitant migration of associated toxic elements. Then, albite and minor orthoclase were altered to illite that was responsible for the secondary enrichment of Tl throughout the weathering profile. In intense weathering stage, Fe/Mn (hydr)oxides were substantially delivered to re-precipitate in fractures and contributed to considerable enrichment of As, Ni, Co, Zn and Cd. Meanwhile, transformation of illite to kaolinite may also influence the enrichment of toxic elements. This work highlights the importance of understanding the control of mineralogical transformation on release, migration and enrichment of toxic elements during black shale weathering, such that this mineral-dependent mechanism can be implemented to risk prediction and assessment of toxic elements in black shale regions.

Migration and transformation of Pb and Cd in the unsaturated zone induced by water table fluctuations

Heavy metal migration poses serious threats to soil and groundwater environments, especially under fluctuating water table conditions, where the transport and transformation behaviors of heavy metals are more complex and difficult to predict. However, there are still limited studies on the effects of groundwater level fluctuations on the migration and transformation behavior of Pb and Cd in an unsaturated zone. This study conducted column experiments to investigate the migration, transformation, and interaction of Pb and Cd in an unsaturated zone. The results showed that Pb and Cd generally migrate to the upper sand with increasing water levels owing to their higher activity under low pH conditions. After many water table fluctuations, Pb and Cd accumulated in the sand and the Cd content in the lower layer was reduced compared to that in the upper layer. This may be due to the coexistence with Pb, leading to the conversion of some of the Cd in the sand solids to unstable (Cd(OH)2), which is susceptible to migration. The mechanism of the migration and transformation of Pb and Cd may be based on the synergistic effect of single or multiple processes, such as surface adsorption, surface precipitation, homocrystalline substitution, and interlayer cation exchange. The results show that hydrodynamic conditions affect the migration and transformation of Pb and Cd by changing the soil-groundwater hydrochemical environment, and this finding not only deepens the understanding of the heavy metal migration mechanism, but also provides an important scientific basis and technical support for the remediation of contaminated sites in areas of frequent fluctuations of the groundwater table.

Geochemical dynamics of coastal environments with shrimp farming activities in southern Bahia, Brazil

The accelerated growth of shrimp farming has led to an increased influx of organic and inorganic pollutants into water bodies, posing a threat to water quality, biodiversity, and human health. This study aimed to assess the impact of shrimp farming activities by analyzing the physical and geochemical variables of water and sediment associated with shrimp farming in Valença, Bahia. Samples were collected in triplicate, including controls, for a total of 10 samples analyzed. Results showed high levels of BOD and trace elements such as Al, Fe, and Mn, as well as low oxygen levels in the water compared to CONAMA Resolution 357/05. Principal Component Analysis and Pearson correlation revealed 38.2 % of significant correlations, mainly in water parameters like BOD and DO, influenced by seasonal variations and anthropogenic activities. Elements such as Al, Fe, and Mn were associated with Fe and Mn oxyhydroxides and aluminosilicates. No sediment concentrations exceeded CONAMA Resolution 454/12 limits; however, 48.6 % of the elements were linked to Fe and Mn oxyhydroxides and aluminosilicates. Although Co, Cu, Ni, and V correlated with Al, Fe, and Mn, they may also reflect anthropogenic inputs from shrimp farming via feed and fertilizers. Water bodies in Valença show a tendency to accumulate higher concentrations of elements in certain areas, which may not only be attributed to natural events but also to human activities like shrimp farming. This study represents a baseline for further analyses within similar enterprises and for conducting methodological studies related to aquatic life.

Investigation of spatially varying relationships between cadmium accumulation and potential controlling factors in the topsoil of island of Ireland based on spatial machine learning approaches

BACKGROUND

Cadmium (Cd) contamination in soils is a pressing environmental issue due to its toxicity and persistence. Given the diverse geological formations and intensive agricultural activities in Ireland, understanding the distribution and sources of soil Cd is particularly important.

METHODS

This study used multiple GIS-based and spatial machine learning (SML) techniques to investigate the spatial distribution and controlling factors of Cd in 16,783 topsoil samples across the island of Ireland. Three analytical methods were applied: hot spot analysis to detect clusters of high and low Cd concentrations, Geographically Weighted Pearson Correlation Coefficients (GWPCC) to explore how Cd relationships with other soil properties vary across space, and Random Forest (RF) to rank the contributing factors in Cd accumulation.

RESULTS

Hot spot analysis revealed strong spatial overlap between Cd concentrations and key geochemical variables including CIA, Fe, P, pH, SOC, and Zn. GWPCC further highlighted their spatially varying relationships, with significantly strong positive correlations between Cd and pH, Zn, and P in the central midlands. The local correlation coefficients obtained from the GWPCC ranged from negative to the highest values of 0.80, 0.92 and 0.86, respectively, which were significantly higher than the results of traditional Pearson correlation coefficients. These patterns were associated with impure limestones, Zn mineralization, and phosphate fertilizer inputs. Furthermore, the RF model ranked Zn (39.4 %) and P (17.6 %) as the most influential factors, with their importance increasing in limestone-dominated areas (50.9 % and 27.4 %), which emphasized the external contributions from local Zn mineralization and phosphate fertilizers in addition to natural accumulation.

CONCLUSION

This study demonstrated the effectiveness of integrating SML techniques with geochemical analysis for identifying Cd sources in the topsoil of Ireland, highlighting the roles of lithology and agricultural activities in Cd accumulation. The results provided valuable insights for contamination management and environmental policy development in Ireland and elsewhere.

Influence of sewage sludge compost on heavy metals in abandoned mine land reclamation: A large-scale field study for three years

Using sewage sludge compost (SSC) for abandoned mine land reclamation supports ecological sustainability, but the environmental behavior of heavy metals in this process lacks systematic field validation. Here we analyzed the dynamic changes in heavy metal composition in topsoil, surface runoff, and subsurface infiltration after large-scale reclamation. Results show that SSC application promoted plant growth by 2-4 times, enhanced the physicochemical structure of the topsoil, and increased the levels of organic matter and inorganic nutrients. Most heavy metals exhibited higher retention in SSC-treated areas compared to non-SSC areas; nonetheless, they remained within low toxicity risk levels overall. Surface runoff from areas with high SSC content exhibited elevated concentrations of heavy metals. In the 2020-M225 sample, Cd, Cu, Pb, and Zn concentrations were at least 1.5 times that of M0. Mixing application of SSC further mitigated the subsurface migration of Cr, Cu, Pb, and Zn compared to S120, with concentrations of As, Cr, Pb, and Zn in 2020-M225 being less than 1/10 of those in M0. Correlation analysis demonstrates that SSC regulated topsoil pH and the contents of organic matter, phosphorus, and Fe and Al (hydr)oxides, which synergistically enhanced the adsorption and complexation of most toxic heavy metals, thereby reducing their migratory pollution over time. This study suggests that practical SSC application (up to 225 t/ha) results in long-term effects on heavy metals characterized by in-situ multi-effect stabilization, rather than increasing overall environmental risks, and provides a technological foundation for ensuring the safe use of SSC in mine reclamation.

Early-warning ecological risk assessments of multi-element pollution in the surface soil of karst basins in southwest China based on the delayed geochemical hazard model

Soil potentially toxic element (PTE) pollution, especially in karst regions, poses significant ecological risks due to the unique geological features and environmental conditions. This study focuses on the delayed geochemical hazard (DGH) model to assess the progressive risks of cadmium (Cd) and lead (Pb) contamination in the surface soils of karst regions in southwestern China. The study found that Pb and Cd pollution in karst areas presents ecological risks, with the region's high porosity and alkaline soils facilitating the transformation of pollutants from stable to mobile forms. The analysis revealed that Pb underwent multidirectional transformations, with 28.3 % of the soil showing a transition from carbonate-bound Pb (PbC) to exchangeable Pb (PbE). However, Cd primarily transformed into carbonate-bound (CdC) and oxide-bound (CdO) forms, with 3.77 % of samples exhibiting the highest outbreak probability for the pathway from sum Cd (CdE+C+F+O+R) to CdC+O. In Pb-Cd co-contamination, Cd predominates, altering risk pathways by triggering transformations at iron-manganese oxide and organic matter binding sites, thereby increasing pollutant mobility. The most prominent combined risk pathway in Pb-Cd contamination was the shift from ME+O to MC (outbreak probability: 5.66 %), indicating enhanced mobility of both PTEs. New pathways also emerged, such as the transition from ME+C+F+O to ME+C, suggesting that Pb and Cd interactions accelerate the risk evolution, favoring highly mobile forms. These findings highlight the importance of not only considering total PTE concentrations but also their speciation and potential transformations in risk assessments. The DGH model effectively predicts evolutionary risks in co-contaminated karst areas, providing insights for early warning of multi-element pollution, particularly in vulnerable karst landscapes.

Internal and external spatial analysis of trace elements in local crayfish

Pollution in urban environments is a major health concern for humans as well as the local wildlife and aquatic species. Anthropogenic waste and discharge from storm drainage accumulate nutrients and environmental contaminants in local water systems. Locating contaminated sites using water samples over the vast landscape is a daunting task. Crayfish thrive in urban environments and have been used for biomonitoring pollutants. This study aimed to use crayfish as sentinels to monitor for elements in local environments. In this study, crayfish were used to measure metals and metalloids in lotic environments using ICP-OES analysis of abdominal and exoskeletal tissue. Using cluster analysis, geographical zones of trace element accumulation were determined. Eighteen total elements were analysed providing baseline data on local genera, biometric data, and element concentrations averaging 267.3 mg/kg Mn in the exoskeleton and with Zn averaging 6.88 mg/kg being significantly higher in the abdomen. Correlations of elements with biometric data allowed for internal analyses of elements. The elements As, Cr, Hg, Ni, and Tl demonstrated equivalent concentrations in both tissues. The crayfish locations with high abundance of elements allowed for the determination of contaminated areas with higher accumulations being areas of active urban development. These analyses gave measurable results of metal and metalloid to pinpoint potential sources of pollutants. Since crayfish are consumed globally as a food source, these methods can be used to determine the risk of toxic metals being passed through the food chain to the public.

Surface water quality evaluation of the historic Esinmirin River of antiquity, Ile-Ife, Nigeria

Esinmirin River is an important historic ancient river in Ile-Ife, the source of the Yoruba Kingdom that was associated with mystical power in stabilizing the ancient city during the period of war that would have destroyed it. The water resource needs investigation because of the recent anthropogenic and industrial activities that could affect the river. The study examines the river's physicochemical, heavy metals, and bacteriological parameters in the upstream, midstream, and downstream sections to comprehend the pollution levels of the Esinmirin River. Nine samples were collected in May 2023 by composite method at various sections using a systematic sampling technique. Twenty-one parameters including the physical, chemical, heavy metals, and bacteriological were examined. A significant departure from WHO, and SON permissible water standard limits in temperature, iron, and the various bacteria found in the research, brings to light the alarming pollution levels of the river. Though temperature (29.9 °C-30.9 °C) and iron (0.7 mg/L-1.3 mg/L) in the 3 sections were above the standard guidelines while lead, copper, and cadmium were absent, all other physicochemical parameters were within the limits. The pH values were highest in the upstream, EC and TDS in the midstream, and temperature in the downstream. At the same time, the chemical parameters and iron increase progressively from upstream to downstream. However, TBC, Escherichia Coliform, Klebsiella species, Staphylococcus Aureus species, and Enterobacter species in all the sections indicated a high level of contamination. The physical, chemical, heavy metal and bacteriological parameters were significantly related mostly at p > 0.01 and on a few occasions at p > 0.05. The study recommends awareness campaigns, routine monitoring, and water treatment before use, to protect public health.

Unveiling the potential mobility and geochemical speciation of geogenic arsenic in the deep subsurface soil of the Tokyo metropolitan area

Extensive excavations for urban and subterranean construction often lead to soil and groundwater contamination with geogenic arsenic (As), emphasizing the urgent need for effective management strategies, particularly considering the global excavation of millions of tons of soil annually. This study investigated the chemical speciation and solubility of geogenic As in soil samples collected at 25-cm intervals from boreholes extending up to 16 m deep within the alluvial Yurakucho Formation and the terrestrial Kanto Loam Formation in the Tokyo metropolitan area. Soils from the Yurakucho Formation exhibited significantly higher total As concentrations (10.5 ± 3.26 mg kg-1) compared to those from the Kanto Loam Formation (5.58 ± 1.88 mg kg-1), with notably elevated levels of water-soluble As throughout the profile. The XANES analysis revealed that As-bearing sulfide species, including As2S3 and FeAsS types, were the predominant forms in the Yurakucho Formation, while As(V) species were more prevalent in the Kanto Loam Formation. Micro-XAFS combined with micro-XRF analysis identified framboidal pyrite, characterized by micron-sized grains (∼10 µm), as the primary sink for As sequestration in the Yurakucho Formation, where As occurs mainly in sulfide-associated forms. These findings highlight the importance of characterizing geogenic As speciation to assess its leaching potential and associated environmental risks posed by As in excavated soils.

Lead-induced changes in plant cell ultrastructure: an overview

Lead (Pb) is one of the most harmful toxic metals and causes severe damage to plants even at low concentrations. Pb inhibits plant development, reduces photosynthesis rates, and causes metabolic disfunctions. Plant cells display these alterations in the form of abnormal morphological modifications resulting from ultrastructural changes in the cell wall, plasma membrane, chloroplast, endoplasmic reticulum, mitochondria, and nuclei. Depending on plant tolerance capacity, the ultrastructural changes could be either a sign of toxicity that limits plant development or an adaptive strategy to cope with Pb stress. This paper gathers data on Pb-induced changes in cell ultrastructure observed in many tolerant and hyperaccumulator plants and describes the ultrastructural changes that appear to be mechanisms to alleviate Pb toxicity. The different modifications caused by Pb in cell organelles are summarized and reinforced with hypotheses that provide an overview of plant responses to Pb stress and explain the physiological and morphological changes that occur in tolerant plants. These ultrastructural modifications could help assess the potential of plants for use in phytoremediation.

Enhanced Pb immobilization by CaO/MgO-modified soybean residue (okara) in phosphate mining wasteland soil: Mechanism and microbial community structure

Lead (Pb) contamination is an inevitable consequence of phosphate mining, necessitating the development of effective remediation strategies. This study investigated the use of CaO/MgO-modified okara (CMS) as an eco-friendly approach to remediate Pb-contaminated soils from phosphate mining wastelands. In the present study, following 30 d of CMS application, the exchangeable Pb content was significantly decreased to 10.46%, with the majority of Pb transforming into more stable forms: carbonate-bound Pb (56.44%), Fe/Mn oxide-bound Pb (11.03%), and organic-bound Pb (19.58%). Additionally, the treatment led to a substantial enhancement in total phosphorus, available phosphorus, ammonium, and soil organic matter, thereby improving soil fertility. The microbial community structure was also significantly influenced by CMS, with a notable increase in Firmicutes to 45%. Key genera within the microbial community included Azospirillum, Pseudoxanthomonas, Sphingomonas, and Microvirga, with Pseudoxanthomonas and Massilia being the main differential species. These genera were significantly positively correlated, contributing to the maintenance of microbial community homeostasis and promoting the production of CO32- and PO43-, which further accelerated Pb immobilization. The results indicate that CMS is an effective amendment for Pb immobilization in contaminated soils, enhancing soil fertility and modulating the microbial community to promote Pb stabilization. This provides valuable insights into the ecological remediation of Pb-contaminated soils and water bodies, highlighting the potential of waste reuse in environmental management.

A meta-analysis of influencing factors on soil pollution around copper smelting sites

Non-ferrous smelting activities have caused serious heavy metal(loid) pollution in soil which seriously threatens human health globally. A number of studies have been conducted to assess the characteristics and risks of soil heavy metal(loid) pollution around copper (Cu) smelting sites. However, the current research mainly focuses on soil pollution around a single smelter, and the global impact of Cu smelting on soil and its quantitative relationship with related factors need to be further studied. Meta-analysis can integrate a large amount of data and quantitatively analyze the relationship between multiple factors. To investigate the extent to which Cu smelting sites have contributed to heavy metal(loid) pollution in soils, a meta-analysis was conducted on 189 research publications from 1993 to 2023. Furthermore, a single meta regression was used to analyze the relationship between the soil heavy metal(loid)s (HMs) and influencing factors on a global scale. The results of meta-regression analysis showed that compared with the soil background value, Cu smelting significantly increased the concentration of HMs in soil (315%), with the concentration increase for each heavy metal(loid) being: Cu (1012%) > Cd (622%) > As (315%) > Pb (277%) > Zn (188%) > Cr (96%) > Ni (95%) > Mn (45%). Among these, Cu, Cd, and As were the major pollutants in soils around Cu smelting sites. Land use type was a key factor affecting HMs concentrations in surrounding soils, and the influence of non-agricultural land (381%) was greater than that of agricultural land (203%). In addition, the influence of Cu smelting on HMs were negatively correlated with distance (QM=9.86) and positively correlated with latitude (QM=10.7). There was no significant correlation between heavy metal(loid) pollution and soil chemical properties, average annual rainfall and temperature, longitude, or other factors. Our work may be meaningful to the risk control and remediation for Cu smelting sites.

DFT Study on the Mechanism of As(III) Oxidation in the Presence of Fe(II) and O2

In natural aquatic environments, the fate of arsenic (As) is significantly influenced by redox processes involving iron (Fe) species. Understanding the mechanisms governing As transformation in the presence of Fe species is crucial for comprehending its environmental impact and advancing remediation strategies. In this work, the oxidation of As(III) in oxygenated Fe(II) solutions was investigated. Density functional theory (DFT) methods were employed to explore the reaction of Fe(II) with 3O2 and subsequent As(III) oxidation by reactive species generated from Fe(II) oxidation. Electron paramagnetic resonance analysis was utilized to confirm the formation of reactive species in the solution. Based on these results, it is concluded that 1O2, ·O2H, and Fe(IV) are the critical oxidants responsible for As(III) oxidation in oxygenated Fe(II) solutions under circumneutral conditions. 1O2 readily oxidizes As(III) by forming an arsenic superoxide AsO5H3. Interaction of As(III) with ·O2H or Fe(IV) leads to As(IV), which is further oxidized to As(V) by 3O2, Fe(III), and Fe(IV).

Enhanced fluoride extraction from contaminated soil combining chelator and surfactant: Insights into adsorptive controlment of soil surface charge

Biodegradable chelators and surfactants are promising alternatives to conventional washing agents for remediating soil contaminated with toxic elements, owing to their excellent extractability and environmental compatibility. Most previous studies have primarily aimed at maximizing removal efficiency. However, understanding their underlying extraction mechanism is essential to expand the application potential of chelator- or surfactant-assisted washing systems. This study evaluated the effectiveness of chelators and surfactants in remediating fluoride (F)-contaminated soil and explored their associated extraction mechanisms. Our findings highlight a biodegradable chelator, HIDS (3-hydroxy-2,2'-imino disuccinic acid) as uniquely effective in F extraction with minimal F-bearing minerals dissolution (Ca, Fe, and Al). Chelator recovery rates and zeta potential measurements in post-washed solutions suggests that HIDS adsorbs onto soil surfaces, displacing the originally adsorbed F and enhancing the negative surface charge to inhibit F re-adsorption. Additionally, applying an anionic surfactant to enhance F extraction from soil showed promising results. Notably, a binary blend of HIDS and in-lab designed anionic surfactant, SDT (sodium N-dodecanoyl-taurinate), achieved the highest F removal rate (132 mg kg-1) under optimized washing conditions (HIDS: 10 mmol L-1, SDT: 10 mmol L-1, solution pH: 3, and washing time: 1 h), enhancing F extraction by 22% compared to HIDS-only washing (108 mg kg-1; washing time: 3 h). The FT-IR and zeta potential measurements suggested that SDT adsorbed onto the soil surface. The action of the HIDS-SDT blend towards F extraction involves the complexation and acid dissolution of F-bearing soil minerals, followed by F replacement through chelator and surfactant adsorption. This process mitigated F back-adsorption and enhanced F extraction by generating a negatively charged soil surface.

A novelty strategy for AMD prevention by biogas slurry: Acetate acid inhibition effect on chalcopyrite biooxidation and leachate

With the widespread application of anaerobic digestion technology, biogas slurry become the main source of organic amendments in practice. Comprehensive studies into the inhibitory effects of low molecular weight (LMW) organic acids, essential components in biogas slurry, on the sulfide minerals biooxidation and its bioleaching (AMD) have been lacking. In this study, acetic acid (AA) served as a representative of LMW organic acids in biogas slurry to investigate its impact on the inhibition of chalcopyrite biooxidation by Acidithiobacillus ferrooxidans (A. ferrooxidans). It was shown that AA could slow down the chalcopyrite biooxidation and inhibit the jarosite formation on the mineral surface. Compared with the control group (0 ppm AA), the sulfate increment in the leachate of the 50 ppm, 100 ppm, and 200 ppm AA-treated groups decreased by 36.4%, 66.8%, and 69.0%, respectively. AA treatment (≥50 ppm) could reduce the oxidation of ferrous ions in the leachate by one order of magnitude. At the same time, the bacterial concentration of the leachate in the 50 ppm, 100 ppm, and 200 ppm AA-treated groups decreased by 70%, 93%, and 94%, respectively. These findings provide a scientific basis for new strategies to utilize biogas slurry for mine remediation and contribute to an enhanced comprehension of organic amendments to prevent AMD in situ in mining soil remediation.

Risk assessment and impact prediction of associated heavy metal pollution in selenium-rich farmland

Selenium (Se)-rich farmland is a valuable and nonrenewable resource for addressing the global challenge of Se deficiency. However, frequent warnings of heavy metal pollution have threatened the safety and legitimacy of Se-rich functional agriculture, eventually damaged public health security. Definitive and judgmental quantitative studies on this hazardous phenomenon are still missing. Relevant reviews published in the past have summarized textual descriptions of the problem, lacking the support of the necessary statistical analysis of the data. Based on the collected publications, the present study evaluated and analyzed the sources, risks and impacts of heavy metal pollution in Se-rich farmland. Concentrations of cadmium (Cd), arsenic, lead and zinc in Se-rich farmland were significantly higher than those in non-Se-rich farmland, especially Cd. Pollution source analyses indicated that Se enrichment and heavy metal pollution occurred simultaneously in farmland, related to Se-heavy metal homology in rocks. According to environmental risk assessment, both serious Cd pollution and the narrow Se concentration range of safety utilization limited the availability of Se-rich farmland. Pollution impact predictions showed that the pollution in Se-rich farmland would result in serious human health risks to consumers and economic losses of 4000 yuan/hm2 on production side. Tackling Cd pollution was anticipated to recover economic losses (81 %) while lowering the carcinogenic (60 %) and non-carcinogenic (10 %) health risks. Our study also provided recommendations to address heavy metal pollution in Se-rich farmland. The two criteria should be followed by pollution control strategies applied to Se-rich functional agriculture including (i) not affecting the original Se enrichment in plant and (ii) not being interfered by Se in soil-plant systems. This will provide valuable information for Se-rich functional agriculture and public health security.

Spatial heterogeneity: Necessary and feasible for revealing soil trace elements pollution, sources, risks, and their links

The source diversity and health risk of trace elements (TEs) in soil make it necessary to reveal the relationship between pollution, source, and risk. However, neglect of spatial heterogeneity restricts the reliability of existing identification methods. In this study, spatial heterogeneity is proposed as a necessary and feasible factor for accurately dissecting the pollution-source-risk link of soil TEs. A comprehensive framework is developed by integrating positive matrix factorization, Geodetector, and risk evaluation tools, and successfully applied in a mining-intensive city in northern China. Overall, the TEs are derived from natural background (28.5 %), atmospheric deposition (25.6 %), coal mining (21.8 %), and metal industry (24.1 %). The formation mechanism of heterogeneity for high-variance TEs (Se, Hg, Cd) is first systematically deciphered by revealing the heterogeneous source-sink relationship. Specifically, Se is dominated (76.5 %) by heterogeneous coal mining (q=0.187), Hg is determined (92.6 %) by the heterogeneity of metal mining (q=0.183) and smelting (q=0.363), and Cd is caused (50.9 %) by heterogeneous atmospheric deposition (q>0.254) co-influenced by the terrains and soil properties. Highly heterogeneous sources are also noteworthy for their potential to pose extreme risks (THI=1.122) in local areas. This study highlights the necessity of integrating spatial heterogeneity in pollution and risk assessment of soil TEs.

Transforming restored heavy metal-contaminated soil into eco-friendly bricks: An insight into heavy metal stabilization and environmental safety

Materialization is currently the primary method for utilizing restored heavy metal-contaminated soil (RHMCS). However, compared to ordinary building materials, the migration and transformation mechanisms of heavy metals (HMs) while preparing these materials remain unclear. To bridge these gaps, this study investigated the migration and transformation mechanisms of As and Pb during the sintering of RHMCS into bricks. This study is the first to conduct a systematic study from the perspectives of both the inner and outer brick layers on the patterns and mechanisms of HM migration and transformation during the sintering process, along with the safety of product utilization. Approximately 90% of As and 36% of Pb migrated out of the RHMCS, with significant transformations observed after sintering. Adjusting the sintering parameters increased migration at long dwell times and high temperatures. These findings indicate different migration behaviors and transformations of HMs within the brick layers, emphasizing the need for cautious application and potential secondary pollution risks. A potential ecological risk index confirmed the safety of the bricks in accordance with construction material standards. Overall, this study provides crucial insights into safe and effective RHMCS utilization, contributing significantly to environmental remediation and sustainable construction practices.

Toxic Effects of Cadmium Exposure on Hematological and Plasma Biochemical Parameters in Fish: A Review

Cadmium (Cd) is a non-essential trace element that poses significant toxic effects on fish. This review focuses on hematological and plasma biochemical parameters as key indicators of fish health under Cd exposure. Hematological parameters, such as red blood cell (RBC) count, hemoglobin (Hb) concentration, and hematocrit (Ht), were selected for their critical role in oxygen transport and their sensitivity to Cd-induced disruptions, which often result in anemia and impaired oxygen delivery to tissues. Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) provide further insights into erythropoiesis and hemoglobin synthesis, both of which are essential for assessing Cd toxicity. Plasma biochemical parameters, including calcium, magnesium, glucose, cholesterol, total protein, and liver enzymes such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP), are crucial for understanding ionic balance, metabolic regulation, and organ function, especially in fish exposed to Cd. These biomarkers offer a comprehensive view of the physiological stress and organ damage caused by Cd toxicity. This review synthesizes literature findings on the toxic effects of Cd on these parameters. It also discusses potential mitigation strategies, including dietary supplementation with antioxidants and trace elements, to counteract the harmful effects of Cd exposure.

Long-term performance of the adsorption layer system for the recycling and repurposing of arsenic-bearing mudstone as road embankment

The adsorption layer system has shown great potential as a cost-effective and practical strategy for the recycling and management of excavated rocks containing potentially toxic elements (PTEs). Although this system has been employed in various civil engineering projects throughout Japan, its long-term performance to immobilize PTEs has rarely been investigated. This study aims to evaluate the effectiveness of the adsorption layer system applied in an actual road embankment approximately 11 years after construction. The embankment system is comprised of a layer of excavated arsenic (As)-bearing mudstone built on top of a bottom adsorption layer mixed with an iron (Fe)-based adsorbent. Collection of undisturbed sample was carried out by implementing borehole drilling surveys on the embankment. Batch leaching experiments using deionized water and hydrochloric acid were conducted to evaluate the water-soluble and acid-leachable concentrations of As, Fe, and other coexisting ions. The leaching of As from the mudstone layer was likely induced by As desorption from Fe-oxides/oxyhydroxides naturally present under alkaline conditions, including the oxidation of framboidal pyrite, which was identified as a potential source of As. This was supported by electron probe microanalyzer (EPMA) observations showing the presence of trace amounts of As in framboidal pyrite crystals. Arsenic leached from the mudstone layer was then immobilized by Fe oxyhydroxides found in the adsorption layer. Based on geochemical modeling and X-ray photoelectron spectroscopy (XPS) results, leached As predominantly existed as the negatively charged HAsO42- oxyanion, which is readily sequestered by Fe oxyhydroxides. Moreover, the effectiveness of the adsorption layer was assessed and its lifetime was estimated, and the results revealed it still possessed enough capacity to adsorb As released from mudstone in the foreseeable future. This prediction utilized the maximum potential amount of As that could leach from the excavated rock layer with time.

Aerobic Se(IV) reducing bacteria and their reducing characteristics in estuarine sediment

Microorganisms play a critical role in the biogeochemical cycling of selenium in natural ecosystems, particularly in reducing selenite (Se(IV)) to element selenium (Se(0)) which reduces its mobility and bioavailability. However, Se(IV)-reducing bacteria and their reducing characteristics in estuarine sediments remain inadequately understood. In this study, the reduction of Se(IV) was confirmed to be microbially driven through the cultivation of a mixture of estuarine sediment and Se(IV) under aerobic conditions. Community analysis indicates that Bacillus was primarily involved in the reduction of Se(IV). A strain with high salt tolerance (7.5 % NaCl) and Se(IV) resistance (up to 200 mM), Bacillus cereus SD1, was isolated from an estuarine sediment. The reduction of Se(IV) occurred concomitantly with the onset of microbial growth, and reduction capacity increased approximately 5-fold by adjusting the pH. In addition, Se(IV) reduction in Bacillus cereus SD1 was significantly inhibited by sulfite, and the key enzyme activity tests revealed the possible presence of a sulfite reductase-mediated Se(IV) reduction pathway. These research findings provide new insights into the bioreducing characteristics and the biogeochemical cycling of selenium in estuarine environments.

Spatiotemporal variations, source identification, and risk assessment of potentially toxic elements in the surface water of Felent Stream impacted by the silver mine

The silver deposits located in the upper basin of the Felent Stream are currently the largest producing mine in the Türkiye. It is also significantly impacted by industrial, agricultural, and thermal spring-related waste in Kütahya Province. The main objectives of this study were to examine the spatiotemporal variations of 12 dissolved potentially toxic elements (PTEs) in the surface water of Felent Stream, to identify their possible sources, and to assess their probable risks. As a result of this study, among investigated PTEs, the highest mean concentrations of 3592-14,388 µg/L for Mg and the lowest of 0.15-0.19 µg/L for Cd were noted in Felent Stream water. The average concentrations of PTEs were found in the order of Mg > Ca > Na > As > Mn > B > Zn > Ni > Cu > Pb > Cr > Cd. Remarkably, during the dry season, there was a conspicuous escalation in the average PTEs contents of water, with an approximately multifold amplification. PTEs in stream water were evaluated for their potential ecotoxicological risks and possible sources. Based on ecological risk assessment indices, the stream exhibited low pollution levels during the wet season but displayed elevated pollution levels during the dry season, indicating a general shift towards heightened pollution conditions. The hazard index (HI) data for As exhibited significant potential noncarcinogenic risks across all monitoring stations. Conversely, the carcinogenic risk (CR) data underscored the imperative nature of addressing the health risks associated with As in the waters of the studied region. Mining activities were identified as the primary origin of PTEs based on principal component analysis (PCA). Moreover, upstream regions, proximal to the mining site, emerged as the most heavily contaminated areas according to cluster analysis (CA).

Ecological risk from potentially toxic element legacy contamination in sediment from the Forth and Clyde Canal, Scotland, UK

Industrial activities on the banks of waterways can degrade both the waterbody and the surrounding area and continue to exert pressure on the environment even after the closure of the industries involved. An assessment was undertaken to determine concentration, distribution, mobility and ecological risk of potentially toxic elements (PTE) from legacy contamination in sediments of the Forth and Clyde Canal, UK. Concentrations of PTE, determined by ICP-MS following aqua regia digestion, were 5.54-219 mg kg-1 for As, < 0.025-11.0 mg kg-1 for Cd, 44.8-883 mg kg-1 for Cr, 39.3-618 mg kg-1 for Cu, 35.8-72.1 g kg-1 for Fe, 720-4460 mg kg-1 for Mn, 42.0-154 mg kg-1 for Ni, 93.9-2740 mg kg-1 for Pb, 5.36-122 mg kg-1 for Sn and 288-3640 mg kg-1 for Zn. With the exception of Fe and Mn, higher levels were observed at urban locations than at rural. Enhanced Cr, Pb and Sn content at suburban locations could be attributed to historical industrial activities on the canal bank, while widespread distribution of As and Pb was consistent with atmospheric deposition. In the inner-city area, sediment quality was severely deteriorated, and the potential ecological risk was very high. Fractionation patterns, determined using the modified BCR sequential extraction, indicated a particularly high risk of mobilization for Cd, Mn and Zn, and the highest exchangeable fraction risk from Zn. The research highlights the need to assess and, where necessary, manage legacy contaminated sites in line with the UN 2030 Agenda for Sustainable Development.

Cu(II) inhibited the transport of tetracycline in porous media: role of complexation

Tetracycline (TC) and Cu(II) coexist commonly in various waters, which may infiltrate into the subterranean environment through runoff and leaching, resulting in substantial ecological risks. However, the underlying mechanisms why Cu(II) affects the transport of TC in porous media remain to be further explored and supported by more evidence, especially the role of complexation. In this study, the transport of TC with coexisting Cu(II) was comprehensively explored with column experiments and density functional theory (DFT) calculation. At natural environmental concentrations, Cu(II) significantly inhibited the transport of TC in the quartz sand column. Cu(II) augmented the retention of TC in the column mainly via electrostatic force and complexation. The interaction between TC and TC-Cu complexes on the surface of SiO2 was investigated with first-principles calculations for the first time. There were strong van der Waals forces and coordination bonds on the surface of complexes and SiO2, leading to higher adsorption energy than that of TC and inhibiting its penetration. This study offers novel insights and theoretical framework for the transport of antibiotics in the presence of metal ions to better understand the fate of antibiotics in nature.

Leaching characteristics and environmental impact of heavy metals in tailings under rainfall conditions: A case study of an ion-adsorption rare earth mining area

Following ion-adsorption rare earth mining, the residual tailings experience considerable heavy metal contamination and gradually evolve into a pollution source. Therefore, the leaching characteristics and environmental impact of heavy metals in ion-adsorption rare earth tailings require immediate and thorough investigation. This study adopted batch and column experiments to investigate the leaching behaviour of heavy metals in tailings and assess the impact of tailings on paddy soil, thereby providing a scientific basis for environmental protection in mining areas. The results showed that Mn, Zn, and Pb contents were 431.67, 155.05, and 264.33 mg·kg-1, respectively, which were several times higher than their respective background values, thereby indicating significant heavy metal contamination in the tailings. The batch leaching experiment indicated that Mn and Pb were priority control heavy metals. Heavy metals were divided into fast and slow leaching stages. The Mn and Pb leaching concentrations far exceeded environmental limits. The DoseResp model perfectly fitted the leaching of all heavy metals from the tailings (R2 > 0.99). In conjunction with the findings of the column experiment and correlation analysis, the chemical form, rainfall pH, ammonia nitrogen, and mineral properties were identified as the primary factors controlling heavy metal release from tailings. Rainfall primarily caused heavy metal migration in the acid-extraction form from the tailings. The tailing leachate not only introduced heavy metals into the paddy soil but also caused the transformation of the chemical form of heavy metals in the paddy soil, further exacerbating the environmental risk posed by heavy metals. The study findings are significant for environmental conservation in mining areas and implementing environmentally friendly practices in rare earth mining.

Is Cadmium Genotoxicity Due to the Induction of Redox Stress and Inflammation? A Systematic Review

The transition metal cadmium (Cd) is toxic to humans and can induce cellular redox stress and inflammation. Cd is a recognized carcinogen, but the molecular mechanisms associated with its genotoxicity and carcinogenicity are not defined. Therefore, a systematic review was undertaken to examine the scientific literature that has covered the molecular mechanism of Cd genotoxicity and its relationship to cellular redox stress and inflammation. An electronic database search of PubMed, Scopus, and the Web of Science Core Collection was conducted to retrieve the studies that had investigated if Cd genotoxicity was directly linked to the induction of redox stress and inflammation. Studies included exposure to Cd via in vitro and in vivo routes of administration. Of 214 publications retrieved, 10 met the inclusion criteria for this review. Preclinical studies indicate that Cd exposure causes the induction of reactive oxygen species (ROS) and, via concomitant activity of the transcription factor NF-κβ, induces the production of pro-inflammatory cytokines and a cytokine profile consistent with the induction of an allergic response. There is limited information regarding the impact of Cd on cellular signal transduction pathways, and the relationship of this to genotoxicity is still inconclusive. Nevertheless, pre-incubation with the antioxidants, N-acetylcysteine or sulforaphane, or the necroptosis inhibitor, necrostatin-1, reduces Cd toxicity; indicative that these agents may be a beneficial treatment adjunct in cases of Cd poisoning. Collectively, this review highlights that Cd-induced toxicity and associated tissue pathology, and ultimately the carcinogenic potential of Cd, may be driven by redox stress and inflammatory mechanisms.

Qualitative and quantitative water investigation of Erin-Ijesha (Olumirin) Waterfall, Erin-Ijesha, Nigeria

This study focused on the assessment of water quality in Erin-Ijesha (Olumirin) Waterfall, a prominent natural attraction in southwestern Nigeria. The physiochemical parameters, heavy metal concentrations, and bacteriological characteristics were examined in the upstream, midstream, and downstream sections, to ensure the resource quality and safety from harm. The results revealed notable variations in water quality. The pH, Total Dissolved Solids, Electrical Conductivity, and Temperature were highest in the midstream while Total Hardness, Alkalinity, salinity, Chloride, sulphate, Phosphate, Nitrate, Calcium, and Magnesium were highest in the downstream section. The physicochemical parameters were within the acceptable limits of World Health Organization (WHO), United States Environmental Protection Agency (USEPA), and the Standard Organization of Nigeria (SON) standards, except the pH, temperature, and Total Hardness were higher than the acceptable limits of 6.5-8.5, <25 °C or >50 °C and 50 mg/L in all the sections. Iron was above the WHO, USEPA, and SON permissible limits of 3.0 mg/L in all the sections of the river while there was no indication of copper, lead, and cadmium. Bacterial contamination, particularly the presence of E. coli, exceeded recommended safety thresholds. The Total Bacterial Count (TBC) exceeded safety limits by 0.1 million cfu/mL in the downstream. The mean of the parameters was higher in some instances, and sometimes lower than the values in the various sections of the river. A significant relationship existed between most physical, chemical, and bacteriological parameters at p < 0.01. The appraisal of water quality in Olumirin Waterfalls emphasizes the need for proactive measures to ensure water safety, preserve ecosystems, and promote responsible water resource management.

A review of passive acid mine drainage treatment by PRB and LPB: From design, testing, to construction

An extensive volume of acid mine drainage (AMD) generated throughout the mining process has been widely regarded as one of the most catastrophic environmental problems. Surface water and groundwater impacted by pollution exhibit extreme low pH values and elevated sulfate and metal/metalloid concentrations, posing a serious threat to the production efficiency of enterprises, domestic water safety, and the ecological health of the basin. Over the recent years, a plethora of techniques has been developed to address the issue of AMD, encompassing nanofiltration membranes, lime neutralization, and carrier-microencapsulation. Nonetheless, these approaches often come with substantial financial implications and exhibit restricted long-term sustainability. Among the array of choices, the permeable reactive barrier (PRB) system emerges as a noteworthy passive remediation method for AMD. Distinguished by its modest construction expenses and enduring stability, this approach proves particularly well-suited for addressing the environmental challenges posed by abandoned mines. This study undertook a comprehensive evaluation of the PRB systems utilized in the remediation of AMD. Furthermore, it introduced the concept of low permeability barrier, derived from the realm of site-contaminated groundwater management. The strategies pertaining to the selection of materials, the physicochemical aspects influencing long-term efficacy, the intricacies of design and construction, as well as the challenges and prospects inherent in barrier technology, are elaborated upon in this discourse.

Natural peloids originating from subsea depths of 200 m in the hupo basin, South Korea: physicochemical properties for potential pelotherapy applications

The present study firstly reports surface sediment from the subsea depth of 200 m as a potential natural peloid. The fine-silt sediment exhibited a consistent clay mineral composition dominated by illite, chlorite, kaolinite, and diatomite. The most abundant clay mineral was illite/mica, with other minerals loosely packed in a face-to-face orientation. The thermal conductivity, specific heat capacity, and cation-exchange capacity of the sediment were in the range 0.855-0.885 W/m K, 2.718-2.821 J/g °C, and 23.06-32.96 cmol/kg, respectively. The concentrations of most toxic elements in the sediment were considerably lower than the limits set by domestic cosmetic regulations and other international standards. The analyzed samples exhibited similar properties to those of previously reported peloids, thus making them suitable for use in the field of pelotherapy; furthermore, the consistency in data across a wide peloid-distribution area is expected to enable economically viable mining. Future investigations should aim to to evaluate the long-term effects on the skin, the bioavailability of potentially hazardous substances, and the therapeutic efficacy for various skin conditions.

Inhibition of acid rock drainage with iron-silicate or phosphate film: in rainy and submerged environments

Iron phosphate-based coating and iron silicate-based coating were used to inhibit the oxidation of sulfide minerals in rainy and submerged environments. The inhibiting effectiveness of coating agents on the oxidation of iron sulfide minerals was investigated using pyrite and rock samples resulting from acid drainage. The film formed with both surface-coating agents was identified by pyrite surface analysis. It was also confirmed that the formation of coatings varies depending on the crystallographic orientation. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. Iron phosphate coating had a significantly better oxidation-inhibitory effect (84.86-98.70%) than iron silicate coating (56.80-92.36%), and at a concentration of 300 mM, H+ elution was inhibited by more than 90% throughout the experiment. Furthermore, methods for effective film formation were investigated in terms of producing Fe3+; (1) application of coating agents mixed with oxidant (H2O2), (2) application of coating agent after the use of the oxidant. In a rainy environment, applying iron phosphate-based coating using the sequential method showed oxidation inhibition effects for cycles 1-9, whereas applying the mixed material showed effects for cycles 9-13. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.

Fertilizer application alters cadmium and selenium bioavailability in soil-rice system with high geological background levels

The co-occurrence of cadmium (Cd) pollution and selenium (Se) deficiency commonly exists in global soils, especially in China. As a result, there is great interest in developing practical agronomic strategies to simultaneously achieve Cd remediation and Se mobilization in paddy soils, thereby enhancing food quality/safety. To this end, we conducted a field-plot trial on soils having high geological background levels of Cd (0.67 mg kg-1) and Se (0.50 mg kg-1). We explored 12 contrasting fertilizers (urea, potassium sulfate (K2SO4), calcium-magnesium-phosphate (CMP)), amendments (manure and biochar) and their combinations on Cd/Se bioavailability. Soil pH, total organic carbon (TOC), soil available Cd/Se, Cd/Se fractions and Cd/Se accumulation in different rice components were determined. No significant differences existed in mean grain yield among treatments. Results showed that application of urea and K2SO4 decreased soil pH, whereas the CMP fertilizer and biochar treatments increased soil pH. There were no significant changes in TOC concentrations. Three treatments (CMP, manure, biochar) significantly decreased soil available Cd, whereas no treatment affected soil available Se at the maturity stage. Four treatments (CMP, manure, biochar and manure＋urea＋CMP＋K2SO4) achieved our dual goal of Cd reduction and Se enrichment in rice grain. Structural equation modeling (SEM) demonstrated that soil available Cd and root Cd were negatively affected by pH and organic matter (OM), whereas soil available Se was positively affected by pH. Moreover, redundancy analysis (RDA) showed strong positive correlations between soil available Cd, exchangeable Cd and reducible Cd with grain Cd concentration, as well as between pH and soil available Se with grain Se concentration. Further, there was a strong negative correlation between residual Cd/Se (non-available fraction) and grain Cd/Se concentrations. Overall, this study identified the primary factors affecting Cd/Se bioavailability, thereby providing new guidance for achieving safe production of Se-enriched rice through fertilizer/amendment management of Cd-enriched soils.

Prediction of Cr(VI) and As(V) adsorption on goethite using hybrid surface complexation-machine learning model

This study aimed to develop surface complexation modeling-machine learning (SCM-ML) hybrid model for chromate and arsenate adsorption on goethite. The feasibility of two SCM-ML hybrid modeling approaches was investigated. Firstly, we attempted to utilize ML algorithms and establish the parameter model, to link factors influencing the adsorption amount of oxyanions with optimized surface complexation constants. However, the results revealed the optimized chromate or arsenate surface complexation constants might fall into local extrema, making it unable to establish a reasonable mapping relationship between adsorption conditions and surface complexation constants by ML algorithms. In contrast, species-informed models were successfully obtained, by incorporating the surface species information calculated from the unoptimized SCM with the adsorption condition as input features. Compared with the optimized SCM, the species-informed model could make more accurate predictions on pH edges, isotherms, and kinetic data for various input conditions (for chromate: root mean square error (RMSE) on test set = 5.90 %; for arsenate: RMSE on test set = 4.84 %). Furthermore, the utilization of the interpretable formula based on Local Interpretable Model-Agnostic Explanations (LIME) enabled the species-informed model to provide surface species information like SCM. The species-informed SCM-ML hybrid modeling method proposed in this study has great practicality and application potential, and is expected to become a new paradigm in surface adsorption model.

Enhanced efficiencies on purifying acid mine drainage in constructed wetlands based on synergistic adsorption of attapulgite-soda residue composites and microbial sulfate reduction

Constructed wetlands (CWs) are a promising approach for treating acid mine drainage (AMD). However, the extreme acidity and high loads of heavy metals in AMD can easily lead to the collapse of CWs without proper pre-treatment. Therefore, it is considered essential to maintain efficient and stable performance for AMD treatment in CWs. In this study, pre-prepared attapulgite-soda residue (ASR) composites were used to improve the substrate of CWs. Compared with CWs filled with gravel (CWs-G), the removal efficiencies of sulfate and Fe, Mn, Cu, Zn Cd and Pb in CWs filled with ASR composites (CWs-ASR) were increased by 30% and 10-70%, respectively. These metals were mainly retained in the substrate in stable forms, such as carbonate-, Fe/Mn (oxide)hydroxide-, and sulfide-bound forms. Additionally, higher levels of photosynthetic pigments and antioxidant enzyme activities in plants, along with a richer microbial community, were observed in CWs-ASR than in CWs-G. The application of ASR composites alleviated the adverse effects of AMD stresses on wetland plants and microorganisms. In return, the increased bacteria abundance, particularly SRB genera (e.g., Thermodesulfovibrionia and Desulfobacca), promoted the formation of metal sulfides, enabling the saturated ASR adsorbed with metals to regenerate and continuously capture heavy metals. The synergistic adsorption of ASR composites and microbial sulfate reduction maintained the stable and efficient operation of CWs. This study contributes to the resource utilization of industrial alkaline by-products and promotes the breakthrough of new techniques for low-cost and passive treatment systems such as CWs.

Mechanisms of arsenic oxidation in the presence of pyrite: An experimental and theoretical study

The mobility and toxicity of arsenic are significantly influenced by the natural minerals. A comprehensive understanding of the interaction between arsenic and minerals is crucial for elucidating the natural behavior of arsenic and advancing arsenic remediation strategies. In this study, the mechanism of As (III) oxidation in the presence of pyrite without light irritation was investigated by experimental and theoretical approaches. Quenching experiment and electron paramagnetic resonance analysis confirm •OH and •O2H is the predominant oxidant of As (III) under acidic and alkaline condition, respectively. Density Functional Theory (DFT) calculations indicate on the pyrite surface, the surface oxygen species is insignificant in As(III) oxidation but crucial for the generation of reactive oxygen species (ROS). In the solution, •OH, •O2H, Fe(IV), and 1O2 are the favored oxidants for As(III), while ROS, 3O2, and Fe(III) possess the capability to convert As(IV) to As(V). The major mechanism of As(III) oxidation in the presence of pyrite without light irritation primarily involves three elementary reactions: (1) •OH facilitating As(III) conversion to As(IV), (2) 3O2 oxidizing As(IV) to As(V) and •O2H, and (3) As(V) and •OH generating in •O2H reacting with As(III). As(IV) emerges as a critical intermediate capable of initiating chain reactions in arsenic oxidation. This study provides atomic-scale insight into the As(III) oxidation in pyrite suspension, which is important for understanding arsenic behavior in analogous oxidation systems.

Fluoride leaching from tuff breccia and its removal by natural and commercial adsorbents

In Japan, the concentration of fluoride (F-) leached from rocks, such as tuff breccia, excavated in tunnel construction projects often exceeds the Japanese environmental standard of 0.8 mg/L. Because of this, proper disposal methods are necessary for managing F--bearing excavated rocks. One effective solution based on circular economy is the use of an adsorption layer system. This system can simultaneously prevent the migration of F- released from excavated rocks and allow the recycling of this construction waste material. To determine the most suitable material for the disposal of excavated F--bearing tuff breccia from a tunnel construction in Hokkaido, Japan, four types of natural geological materials (S-1, S-2, S-3, and S-4) obtained near the tunnel construction site, as well as three types of commercial adsorbents (calcium (Ca), magnesium (Mg), and CaMg adsorbents) were selected for evaluation. The batch adsorption test results showed that S-1 and S-4 had high adsorption capacities for F-, and the adsorption process followed the Langmuir isotherm. The adsorption of F- to the natural adsorbents was strongly influenced by the pH and the presence of bicarbonate ions (HCO3-), but unaffected by chloride (Cl-) and sulfate (SO42-). There was also a strong positive correlation between the abundance of amorphous aluminum (Al) and iron (Fe) extracted and the adsorption of F-, indicating the importance of ion exchange reactions associated with surface OH- in immobilizing F-. Meanwhile, the Mg-bearing adsorbent exhibited the highest adsorption affinity for F- among the commercial adsorbents. This was attributed to adsorption through electrostatic interactions and coprecipitation with magnesium hydroxide (Mg(OH)2) formed during the hydration of magnesium oxide (MgO). To effectively incorporate these adsorbents into the adsorption layer system, parameters such as permeability and residence time need to be determined in order to maximize the retention of F- through adsorption, ion exchange and coprecipitation reactions.

Concentration of potentially toxic elements in fillet shrimps of Mediterranean Sea: Systematic review, meta-analysis and health risk assessment

In this study, an attempt was made to meta-analyzed the concentration of potentially toxic elements (PTEs) in shrimps tissue of Mediterranean Sea and health risk of consumers was estimated. Search was conducted in international databases includes Scopus, PubMed, Embase, Science Direct and Web of Science from 1 January 2010 to 20 July 2023. The random effects model used to meta-analysis of concentration of PTEs in shrimp in subgroups. In addition, non-carcinogenic and carcinogenic risks for adults and children were calculated using target hazard quotient (THQ) and cancer risk (CR). Meta-analysis concentration of PTEs in shrimps was conducted using random effects model based on country subgroups. The rank order of PTEs based on mean (pooled) level in fillet of shrimps was Fe (15.395 mg/kg-ww) > Zn (10.428 mg/kg-ww) > Cu (6.941 mg/kg-ww) Pb (5.7 mg/kg-ww) > Ni (1.115 mg/kg-ww) > As (0.681 mg/kg-ww) > Cd (0.412 mg/kg-ww) > Hg (0.300 mg/kg-ww). THQ level in adults and children due to Cd and Pb in Italy was higher than 1 value. THQ level in adults and children due to Cu, Ni, Fe, Zn and inorganic As was lower than 1 value. CR due to inorganic As in Greece and Türkiye for adults and children was higher than 1E-6 value. Therefore, it was recommended to continuously monitor and reduce the concentration of PTEs in shrimps in Italy, Greece and Türkiye, especially.

Inhibition of pyrite oxidation through forming biogenic K-jarosite coatings to prevent acid mine drainage production

This study proposes a novel method by forming biogenic K-jarosite coatings on pyrite surfaces driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) to reduce heavy metal release and prevent acid mine drainage (AMD) production. Different thicknesses of K-jarosite coatings (0.7 to 1.1 μm) were able to form on pyrite surfaces in the presence of A. ferrooxidans, which positively correlated with the initial addition of Fe2+ and K+ concentrations. The inhibiting effect of K-jarosite coatings on pyrite oxidation was studied by electrochemical measurements, chemical oxidation tests, and bio-oxidation tests. The experimental results showed that the best passivation performance was achieved when 20 mM Fe2+ and 6.7 mM K+ were initially introduced with a bacterial concentration of 4 × 108 cells·mL-1, reducing chemical and biological oxidation by 70 % and 98 %, respectively (based on the concentration of total iron dissolved into the solution by pyrite oxidation). Similarly, bio-oxidation tests of two mine waste samples also showed sound inhibition effects, which offers a preliminary demonstration of the potential applicability of this method to actual waste rock. This study presents a new perspective on passivating the oxidation of metal sulfide tailings or waste and preventing AMD.

Effect and potential mechanisms of sludge-derived chromium, nickel, and lead on soil nitrification: Implications for sustainable land utilization of digested sludge

Increasing occurrence of heavy metals (HMs) in sewage sludge threatens its widespread land utilization in China due to its potential impact on nutrient cycling in soil, requiring a better understanding of HM-induced impacts on nitrification. Herein, lab-scale experiments were conducted over 185-day, evaluating the effect of sludge-derived chromium (Cr3+), nickel (Ni2+), and lead (Pb2+) on soil nitrification at different concentrations. Quantitative polymerase chain reaction and linear regression results revealed an inhibitory sequence of gene abundance by HMs' labile fraction: ammonia-oxidizing bacteria (AOB)-ammonia monooxygenase (amoA)> nitrite oxidoreductase subunit alpha (nxrA)> nitrite oxidoreductase subunit beta (nxrB). The toxicity of HMs' incremental labile fraction decreased in the order of Ni2+>Cr3+>Pb2+, with respective threshold values of 5.01, 24.03 and 38.42 mg·kg-1. Furthermore, extending incubation time reduced HMs inhibition on ammonia oxidation, mainly related to their fraction bound to carbonate minerals. Random Forest analysis, variation partitioning analysis, and Mantel test indicated that soil physicochemical properties primarily affected nitrification genes, especially in the test of Cr3+ on AOB-amoA, nxrA, nxrB, Ni2+ for complete ammonia-oxidizing bacteria-amoA, and Pb2+ for nxrA and nxrB. These findings underline the importance of labile HMs fractions and soil physicochemical properties to nitrification, guiding the establishment of HM control standards for sludge utilization.

Nanomaterial-based optical colorimetric sensors for rapid monitoring of inorganic arsenic species: a review

Health concerns about the toxicity of arsenic compounds have therefore encouraged the development of new analytical tools for quick monitoring of arsenic in real samples with improved sensitivity, selectivity, and reliability. An overview of advanced optical colorimetric sensor techniques for real-time monitoring of inorganic arsenic species in the environment is given in this review paper. Herein, several advanced optical colorimetric sensor techniques for arsenite (As+3) and arsenate (As+5) based on doping chromogenic dyes/reagents, biomolecule-modified nanomaterials, and arsenic-binding ligand tethered nanomaterials are introduced and discussed. This review also highlights the benefits and limitations of the colorimetric sensor for arsenic species. Finally, prospects and future developments of an optical colorimetric sensor for arsenic species are also proposed. For future study in this sector, particularly for field application, authors recommend this review paper will be helpful for readers to understand the design principles and their corresponding sensing mechanisms of various arsenic optical colorimetric sensors.

Revealing the release and migration mechanism of heavy metals in typical carbonate tailings, East China

Refining the occurrence characteristics of tailings hazardous materials at source is of great importance for pollution management and ecological reclamation. However, the release and transport of heavy metals (HMs) from tailings under rainfall drenching in simulated real-world environments is less well portrayed, particularly highlighting the inherent neutralisation in tailings wastes under superimposed dynamic conditions. In this study, dynamic leaching columns simulating actual conditions were used to observe the release and transport of HMs from tailings under acid rainfall infiltration at spatial and temporal scales. The release rate of trace elements (e.g., As, Cr, Ni, Pb, Cd) is high. Neutralisation in the presence of carbonate rocks in the gangue reduces HMs release intensity from tailings with high heavy metal content, along with the precipitation of iron oxides and chromium-bearing minerals, etc. In addition, the vertical differentiation of HMs is more relevant to physical processes. In the absence of carbonate rocks in gangue, the lowest pH value is reached within 1.2 h after acid rain infiltrates the tailings. At the same time, Cu, Zn and Cd are released significantly from the minerals at the superficial level. The release of As(III) is mainly concentrated in the early and late stages of water-rock contact.

Alleviated lead toxicity in rice plant by co-augmented action of genome doubling and TiO2 nanoparticles on gene expression, cytological and physiological changes

Lead is a very toxic and futile heavy metal for rice plants because of its injurious effects on plant growth and metabolic processes. Polyploidy or whole genome doubling increases the ability of plants to withstand biotic and abiotic stress. Considering the beneficial effects of nanoparticles and tetraploid rice, this research was conducted to examine the effectiveness of tetraploid and titanium dioxide nanoparticles (TiO2 NPs) in mitigating the toxic effects of lead. A diploid (E22-2x) and it's tetraploid (T-42) rice line were treated with Pb (200 μM) and TiO2 NPs (15 mg L-1). Lead toxicity dramatically reduced shoot length (16 % and 4 %) and root length (17 % and 9 %), biological yield (55 % and 36 %), and photosynthetic activity, as evidenced by lower levels of chlorophyll a and b (30 % and 9 %) in E-22 and T-42 rice cultivars compared to the control rice plants, respectively. Furthermore, lead toxicity amplified the levels of reactive oxygen species (ROS), such as malondialdehyde and H2O2, while decreasing activities of all antioxidant enzymes, such as superoxidase, peroxidase, and glutathione predominately in the diploid cultivar. Transmission electron microscopy and semi-thin section observations revealed that Pb-treated cells in E22-2x had more cell abnormalities than T-42, such as irregularly shaped mitochondria, cell wall, and reduced root cell size. Polyploidy and TiO2 reduced Pb uptake in rice cultivars and expression levels of metal transporter genes such as OsHMA9 and OsNRAMP5. According to the findings, genome doubling alleviates Pb toxicity by reducing Pb accumulation, ROS, and cell damage. Tetraploid rice can withstand the toxic effect of Pb better than diploid rice, and TiO2 NPs can alleviate the toxic impact of Pb. Our study findings act as a roadmap for future research endeavours, directing the focus toward risk management and assessing long-term impacts to balance environmental sustainability and agricultural growth.

Biochar as Alternative Material for Heavy Metal Adsorption from Groundwaters: Lab-Scale (Column) Experiment Review

The purpose of this manuscript is to present a review of laboratory experiments (including methodology and results) that use biochar, a specific carbon obtained by a pyrolysis process from different feedstocks, as an alternative material for heavy metal adsorption from groundwater. In recent years, many studies have been conducted regarding the application of innovative materials to water decontamination to develop a more sustainable approach to remediation processes. The use of biochar for groundwater remediation has particularly attracted the interest of researchers because it permits the reuse of materials that would be otherwise disposed of, in accordance with circular economy, and reduces the generation of greenhouse gases if compared to the use of virgin materials. A review of the different approaches and results reported in the current literature could be useful because when applying remediation technologies at the field scale, a preliminary phase in which the suitability of the adsorbent is evaluated at the lab scale is often necessary. This paper is therefore organised with a short description of the involved metals and of the biochar production and composition. A comprehensive analysis of the current knowledge related to the use of biochar in groundwater remediation at the laboratory scale to obtain the characteristic parameters of the process that are necessary for the upscaling of the technology at the field scale is also presented. An overview of the results achieved using different experimental conditions, such as the chemical properties and dosage of biochar as well as heavy metal concentrations with their different values of pH, is reported. At the end, numerical studies useful for the interpretation of the experiment results are introduced.

Insights on hazardous metal bioaccessibility, and groundwater impacted by Zn residues from a legacy mine and risk evaluation of adjacent soils

This study explored the legacy impact of Zinc plant residues (ZPRs) in Kabwe, Zambia, on the environment and human health, particularly in light of the town's reputation for Pb pollution. ZPRs solid samples and groundwater within and around ZPRs zone were collected from the legacy mine, along with soils in a 10 km radius from the mine site. Bioaccessible fractions of Pb and Zn were elucidated by Japanese leaching test (JLT) and simple bioaccessibility extraction test (SBET). Cationic speciation of Pb and Zn from inhalable and ingestible ZPRs particles was investigated via sequential extraction. Groundwater in the ZPRs area showed higher Zn levels (1490 mg/L) compared to Pb (1.7 mg/L). Elevated Zn concentration were facilitated by the presence of soluble Zn sulfates while Pb was constrained due to its precipitation as anglesite. Groundwater sampled outside the ZPRs area was within the Zambia regulatory limits (< 0.5 mg/L for Pb and < 1 mg/L for Zn). Inhalation exposure to < 30 µm dust particles from ZPRs and soils near the mine indicated negligible risk, with < 3% of bioaccessible Pb in artificial lysosomal fluid. Meanwhile, oral intake of ZPRs particles < 250 µm revealed elevated bioaccessible fractions (36% for Pb and 70% for Zn). ZPRs cationic speciation of ingestible particles < 30 µm, 30-75 µm, 75-150 µm and 150-250 µm indicated that the bioaccessible Pb predominantly emanated from labile Pb fractions under gastric conditions with pH < 1. This was due to the dissolution of Pb associated with the exchangeable phase, carbonates and iron/manganese oxides; however, only exchangeable/carbonate Pb was bioaccessible at pH < 2. Hazard quotients indicated increased risks of Pb intoxication through the ingestion of ZPRs and soils near the legacy mine, with higher risks observed in children, emphasizing the need to remediate legacy mine wastes to reduce health risks and protect groundwater through monitoring in mining-affected regions.

Principles, applications, and limitations of diffusive gradients in thin films induced fluxed in soils and sediments

The diffusive gradients in thin films (DGT) technique serves as a passive sampling method, inducing analyte transport and concentration. Its application is widespread in assessing labile components of metals, organic matter, and nutrients across various environmental media such as water, sediments, and saturated soils. The DGT devices effectively reduce the porewater concentration through irreversible binding of solutes, consequently promoting the release of labile species from the soil/sediment solid phase. However, the precise quantification of simultaneous adsorption and desorption of labile species using DGT devices alone remains a challenge. To address this challenge, the DGT-Induced Fluxes in Soils and Sediments (DIFS) model was developed. This model simulates analyte kinetics in solid phases, solutions, and binding resins by incorporating factors such as soil properties, resupply parameters, and kinetic principles. While the DIFS model has been iteratively improved to increase its accuracy in portraying kinetic behavior in soil/sediment, researchers' incomplete comprehension of it still results in unrealistic fitting outcomes and an oversight of the profound implications posed by kinetic parameters during implementation. This review provides a comprehensive overview of the optimization and utilization of DIFS models, encompassing fundamental concepts behind DGT devices and DIFS models, the kinetic interpretation of DIFS parameters, and instances where the model has been applied to study soils and sediments. It also highlights preexisting limitations of the DIFS model and offers suggestions for more precise modeling in real-world environments.

Study of Kinetics and the Working Mechanism of Silica-Coated Amino-Functionalized CoFe2O4 Ferrite Nanoparticles to Treat Wastewater for Heavy Metals

This study used a simple coprecipitation method to produce pristine, silica-coated, and amino-functionalized CoFe2O4 nanoadsorbents. Amino-functionalization was done to increase the active surface area and metal ion removal efficiency. Both pristine and functionalized adsorbents were employed to recover Pb(II), Zn(II), and Cu(II) ions from wastewater. The adsorption tests were performed by varying the initial concentration of metal ions and contact time at a fixed pH of 6.5. Atomic adsorption spectroscopy was utilized to detect the proportion of metals removed from water. Additionally, the pseudo-first-order, pseudo-second-order, Freundlich, and Langmuir models were employed to compute the kinetic and isothermic data from metal ion adsorption onto the adsorbents. The amino-functionalized adsorbent showed adsorption capacities of 277.008, 254.453, and 258.398 mg/g for Cu(II), Pb(II), and Zn(II) ions, respectively. According to the adsorption results, the Langmuir isotherm and the pseudo-second-order model best suit the data. The best fitting of the pseudo-second-order model with the data indicates that coordinative interactions between amino groups and metal ions are responsible for chemisorption. The metal ions bind with -NH2 groups on the adsorbent surface through chelate bonds. Chelate bonds are extremely strong and stable, indicating the effectiveness of the CoFe2O4@SiO2-NH2 adsorbent in adsorbing heavy-metal ions. The tested adsorbent exhibited good performance, batter stability, and good reusable values around 77, 81, and 76% for Cu(II), Pb(II), and Zn(II) ions, respectively, after five adsorption cycles.

The purification of acid mine drainage through the formation of schwertmannite with Fe(0) reduction and alkali-regulated biomineralization prior to lime neutralization

Acid mine drainage (AMD) contains abundant Fe (II), Fe(III), and SO42-, as well as a large amount of dissolved toxic metals and metalloids, posing a serious threat to the environment. In this study, an integrated technique for the treatment of AMD was proposed. The technique started with pre-oxidation followed by Fe(0) reduction and alkali-regulated biomineralization and then ended with lime neutralization. The technique removed toxic metal oxyanions in the pre-oxidation stage and recovered pure schwertmannite during the subsequent alkali-regulated biomineralization. Fe(III), which could not be directly biomineralized, was reduced to Fe(II) by Fe(0). A small amount of alkali was added to regulate the hydrolytic mineralization reaction after Fe(II) oxidation in AMD, which in a single biomineralization could remove in the form of schwertmannite >95 % of soluble Fe in the AMD. In the subsequent lime neutralization process, the amount of lime required and the sludge produced were reduced by 75.4 % and 84.9 %, respectively, compared to the raw AMD. Additionally, the content of non-ferrous metals in the sludge increased 5.6-fold. Compared with non-alkali-regulated biomineralization, the schwertmannite obtained by the alkali-regulated biomineralization had a higher adsorption capacity for oxyanions (e.g., arsenic, chromium, and antimony). The new approach should significantly reduce the treatment cost of AMD and recover Fe and S elements in the form of valuable secondary minerals, such that it is reasonable to expect that it will be widely adopted in practical applications.