Artisanal and small-scale mining (ASM) has emerged as a vital economic lifeline for millions across Africa, Asia, and Latin America, driven by increasing gold prices, global demand, unemployment, and poverty. This sector accounts for approximately 28.9% of Ghana’s GDP and provides a livelihood for nearly 70% of Ghanaians, predominantly those residing in rural areas. However, this sector faces numerous environmental and health challenges, including uncontrolled mine waste disposal, contaminating water and soil with heavy metals. This review critically examines the environmental consequences of ASM waste management, focusing on informal underground tailings disposal. Using a dual-method strategy that combines systematic review and literature analysis, the study synthesizes 110 Scopus-indexed publications (2004–2024) to examine how ASM activities affect the safety, health, and ecosystems of Ghanaian ASM communities. Key findings reveal critical gaps in long-term waste management strategies, inadequate attention to health risks, and a lack of holistic socio-environmental assessments of ASM operations. The study underscores the urgent need for evidence-based interventions, including stricter regulatory enforcement, community-centered remediation, and sustainable livelihood alternatives. By addressing these gaps in Ghana, similar ASM-dependent economies can transform this sector into a force for equitable development without sacrificing environmental integrity or public health. Future research should prioritize cost-effective remediation technologies and policy frameworks that are tailored to the realities of informal mining communities.

Understanding the cycling of critical oxyanion-forming trace metals is essential, considering their growing use in green technologies and their potential environmental risks. We investigated the source, transport, and fate of vanadium (V), molybdenum (Mo), and tungsten (W) across hemiboreal and boreal landscapes in Sweden, spanning 97 hemiboreal headwater streams, one boreal headwater stream, and two unregulated boreal rivers. Spatial and temporal variability was pronounced. V occurred at the highest concentrations, with hemiboreal headwaters averaging ∼78 μg/L compared to ∼8 μg/L for Mo and ∼0.2 μg/L for W. These concentrations exceeded those in boreal headwaters and rivers by factors of up to 300, reflecting enhanced weathering under milder hemiboreal conditions. Partitioning differed strongly among elements: Mo was predominantly dissolved, W occurred in both dissolved and particulate fractions, and V shifted from dominantly dissolved in hemiboreal streams to nearly equal distribution in boreal waters. Seasonal dynamics were most pronounced during spring snowmelt, when hydrological flushing and hyporheic exchange mobilized solutes from riparian soils and porewaters. Element-carrier relationships highlighted strong associations of V and W with Fe- and Al-rich phases, and Mo with organic matter, Si, and U, particularly at river mouths. Redox transitions in wetlands and hyporheic zones further mediated mobility, promoting V release and W transport while retaining Mo under reducing conditions.Our findings demonstrate that hydrology, redox dynamics, and landscape type jointly regulate the mobility and fate of V, Mo, and W from source to sea. The distinct behaviours of these elements highlight headwater streams as critical biogeochemical control points and underscore the need to integrate colloidal, redox, and hydrological processes into monitoring and modelling frameworks. These insights have implications for evaluating ecological risks and for critical raw material (CRM) exploration in northern landscapes under a changing climate.

Water pollutants such as synthetic dyes can cause significant problems for human health and ecosystems due to their chemical properties and environmental interactions. Contamination of surface and underground water caused by the discharge of synthetic dyes is a widespread problem that arises primarily from industrial activities such as textile manufacturing, leather processing, paper production, and plastics industries. Since adsorption is one of the most efficient and reliable methods to remove pollutants from water, in this work, pine tree logging residues (LR) were used to produce boron/sulfur chemically modified biochars with superior adsorption performance and recyclability. The biochars were produced using a two-step pyrolysis procedure with potassium hydroxide as a chemical activator. The specific surface areas (B.E.T.) of the biochars were 2645 m2 g−1 for the boron-treated biochar (LR-Boron), 2524 m2 g−1 for the sulfur-treated (LR-Sulfur), and 3141 m2 g−1 for the control biochar (LR-Control, without boron or sulfur), respectively. The LR-Boron biochar showed an exceptional degree of graphitization of (ID/IG=0.45), while the LR-Sulfur biochar displayed an ID/IG= 1.02; for comparison, the LR-Control exhibited an ID/IG= 0.81, showing that the sample subjected to boron treatment created carbon-rich in graphitic structures. The three biochars were evaluated as adsorbents for removing reactive black-5 azo dye (RB-5) from water and mixtures of several dyes in synthetic aqueous effluents. The adsorption data showed that all carbons exhibited outstanding RB-5 removal performance. Kinetic measurements were well fitted by the Avrami fractional order model, and the LR-sulfur carbon displayed the fastest adsorption kinetics. Isotherm measurements were well fitted by the Liu model, with a theoretical Qmax of around 1419 mg g−1 (LR-Control), 1586 mg g−1 (LR-Boron), and 1766 mg g−1 (LR-Sulfur) at 316 K. The presence of sulfur-functional groups on the LR-Sulfur biochar surface was probably the reason for the superior adsorption performance of this biochar. Both sulfur and boron-treated biochars exhibited higher regeneration potentials, maintaining around 60–67 % removal capacity after 7 cycles compared to 35 % for the LR-Control biochar. Thermodynamic adsorption studies showed that the adsorption process was endothermic, favorable, and compatible with physical adsorption. All produced biochars were highly efficient for removal of pollutants from concentrated synthetic effluents.

Acid sulfate soils (AS-soils), common in coastal, estuarine, and mining-impacted areas, form under reducing conditions and can cause severe environmental degradation by releasing acidity and mobilizing heavy, trace, and toxic metals when sulfide minerals oxidize under changing hydrological conditions. AS-soils exhibit redox gradients that govern iron (Fe) and sulfur (S) cycling, affecting their mobility, mineral forms, and isotopic compositions. This study combines Fe/S ratios, δ56Fe and δ34S isotope systematics, sequential extractions, and groundwater monitoring to assess redox-driven processes in two AS-soil profiles from northern Sweden. In reduced zones, negative δ56Fe and δ34S values signal microbial Fe(III) and sulfate reduction, producing Fe(II) and sulfides. In oxidized zones, secondary Fe (oxy)hydroxides and sulfates form, inheriting isotopic signals from precursor sulfides. Groundwater δ56Fe enrichment reflects Fe oxidation, while high δ34S values (up to +45.2 ‰) indicate ongoing sulfate reduction. Groundwater Fe/S ratios (0.07–8.24) reveal redox interactions but are unreliable as sole redox indicators. Sequential extractions show that redox-sensitive pools—water-soluble, exchangeable, and organic-bound phases—exhibit strong isotope fractionation and drive short-term cycling, despite their small mass. Isotopic signals from different Fe phases within each profile likely offset each other when measured in bulk (∼0.06–0.11 ‰), diluting any clear redox-related patterns. Similarly, δ34S values trace a shift from oxidized to stable sulfide-bound forms across depths and redox zones. The results emphasize the value of combining isotopic and phase-specific analyses to unravel redox heterogeneity, trace element fluxes, and identify acidification-prone zones. Environmentally, maintaining saturated conditions, encouraging reducing environments, and monitoring reactive Fe and S fractions can help limit the mobilization of heavy, trace, and toxic metals in AS-soils under shifting hydrology.

Tungsten (W) is an emerging contaminant of concern whose high mobility in the environment is of scientific debate. It is also a critical raw material whose mining is expected to increase. Mine waste management aims to create an anoxic environment of neutral pH to limit sulfide oxidation and acid mine drainage. This study evaluates the stability of W-minerals under such geochemical conditions to develop recommendations for W mine waste management. Intact cores of legacy mine tailings from Morkulltjärnen, Sweden, were collected and analyzed using whole rock geochemistry and XRD. Monolayers with minutes amounts of W were generated by hydroseparation and studied using SEM-EDS, automated mineralogy, and microprobe analysis. Scheelite concentrates from the decommissioned processing plant were analyzed with XRF and 7 step sequential extractions. Groundwater was collected from eight wells in the Morkulltjärnen tailings in 2023 and 2024 and analyzed for 71 elements, anions and chemophysical parameters. This is one of the first field studies presenting mineralogical signs of scheelite weathering with tabular morphology, rod-shaped and porous structure, and loss of W from the crystal lattice, leading to very high concentrations (up to 23 mg/L) of dissolved W in anoxic and alkaline groundwater. This shows that standard mine waste management practices are unsuitable for scheelite, and action is needed to limit W mobilization into the surrounding environment from scheelite-rich tailings. Adsorption onto Fe-(hydr)oxides may be effective for controlling W mobilization from legacy mine waste, but in new mines, sulfides and tungstates should be separated in the processing plant and stored under anoxic and oxic conditions, respectively.

Acid sulfate soils (AS-soils) are sulfide-bearing sediments that remain benign in waterlogged conditions but become environmentally harmful after exposure to oxygen. Sulfide oxidation generates acidity, element mobilization, compositional changes in soils and water bodies, and adverse effects on biota. This study enhances the geochemical and mineralogical understanding of the element source in oxidized and unoxidized AS-soils samples from Luleå, northern Sweden. An adapted sequential extraction scheme was conducted to determine the element distribution in primary and secondary phases. The extraction differentiates the H2O-soluble from the exchangeable fraction, labile and stable organic fractions, differentiated reducible from oxidisable phases, and residual fractions. Mineralogical changes were monitored at each step of the extraction sequence. Compositional maps obtained through microprobe quantified trace elements within the pyrite structure, which are susceptible to mobilization after weathering. The mineralogical and compositional findings of this study support strategies to mitigate environmental impacts from AS-soils oxidation. It is shown that framboidal pyrites are highly reactive to oxidation, contributing to acidification and releasing elements such as Cu, Mn, Mo, and Ni, highlighting sulfide exposure risk. In unoxidized samples, S is present in primary Fe sulfides and as organic S, while in oxidized samples, S occurs as secondary sulfate minerals. Organic matter strongly associates with Cu, Mo, and S, and is an important source of these elements in the sediments. From the most labile phases and pore water, Cd, Mn, Mo, and S were predominantly leached, indicating their high bioavailability. These findings demonstrate the importance of maintaining AS-soils in waterlogged conditions to prevent acidification and metal mobilization.

Study region: Sweden

Study focus: Groundwater is an essential resource accounting for approximately 50 % of drinking water in Sweden. Groundwater quality is affected by natural and anthropogenic processes and can strongly impact the health of humans. Elevated metal concentrations, including Al, Cd, Cu, Fe, Mn, Pb, and Zn, have been linked to neurodegenerative disease (NDD) progression, including multiple sclerosis (MS) and Parkinson’s disease, (PD) and additional research is needed investigating groundwater as a potential pathway for heavy metal exposure in relation to NDDs. The main objectives of this study were to map elemental distribution within groundwater aquifers and correlate it with MS and PD disease prevalence on a regional scale in Sweden.

New hydrological insights for the region: Results from groundwater mapping indicate the presence of several elemental hotspots for Cu, Fe, Pb, and Zn, which are representative of anthropogenic pollution events. Results from the disease prevalence regression showed a weak positive correlation between MS and Cu plus Zn (R2 = 0.342, p = 0.023), whereas for PD a moderate positive correlation was present with Zn plus electrical conductivity (R2 =0.416, p = 0.008). While these elements were most strongly correlated to the disease prevalence, other elements including Cu, Cd, and Pb also displayed weak correlations. The potential role of these elements in these diseases should not be discounted as multi-element exposure through groundwater could be an important factor in NDD development.

The water quality in headwater streams depends on the groundwater origin and its transport pathways before it eventually discharges as surface water. In this case study, we present the Ce anomaly of over 100 hemiboreal headwater streams in Sweden and discuss the potential of the Ce anomaly to define two stream end members as proxies for the stream origin. The data show a relation between topography and the Ce anomaly, with more negative values (−0.8 to −0.4) in hilly catchments with distinct slopes, defined as an oxidized groundwater end member. The second end member is dominated by groundwater discharge from reduced, organic-rich riparian and wetland soils (reduced groundwater) having small Ce anomalies (−0.3 to zero). Element concentrations show a wide range, depending on the end member of the stream. For example, redox elements (Fe, Mn, S and N) show concentrations up to five times in streams with small negative Ce anomalies (reduced groundwater) compared to the concentrations in streams with large negative Ce anomalies. While element concentrations (of the classic redox elements Fe, Mn, S, N) show seasonal variations due to a summer drought period and the resulting reduced conditions, the Ce anomaly is constant, offering an excellent indicator of the dominant groundwater flow paths regardless of seasonal variations.

Acid sulfate soils (AS-soils) are a common feature along coastlines in many countries that can have significant environmental and economic impacts. AS-soils oxidation may cause soil and water acidification, the release and mobilization of metals and the formation of new precipitated phases. In northern Sweden, some soils are already oxidized and constitute an environmental concern. This study aimed to analyze the geochemistry and mineralogy of AS-soils profiles by identifying element depletion and accumulation zones, the parent material, minerals that contribute to acidity and their oxidation products as well as anomalous element content values that could be related to anthropogenic sources. Two soil profiles were drilled close to the Lule River in Södra Sunderbyn, Luleå. The profiles were characterized by an oxidized zone (OZ) with a declining trend in element content, a transition zone (TZ) where elements tended to accumulate and a reduced zone (RZ) where elements had their maximum content. The pH was a key determinant of the element distribution. Cadmium, Co, Ni and Zn were found to be typical elements released into the environment during AS-soils oxidation. After sample incubation, pH measurements showed a pronounced decrease in layers with higher S and total organic carbon (TOC) content. Both profiles developed a larger thickness of potential acid-risk sediments according to S, TOC and pH measurements during incubation. Iron sulfides were identified as the main acidity generators, represented by an abundance of framboidal pyrites with a Mn-rich rim formed under anoxic-euxinic conditions. Iron sulfates and iron oxyhydroxides (FeOOH, FeOH3) were identified as the most common products of oxidation processes.

Herein, a novel sulfur-doped carbon material has been synthesized via a facile and sustainable single-step pyrolysis method using lignin-sulfonate (LS), a by-product of the sulfite pulping process, as a novel carbon precursor and zinc chloride as a chemical activator. The sulfur doping process had a remarkable impact on the LS-sulfur carbon structure. Moreover, it was found that sulfur doping also had an important impact on sodium diclofenac removal from aqueous solutions due to the introduction of S-functionalities on the carbon material’s surface. The doping process effectively increased the carbon specific surface area (SSA), i.e., 1758 m2 g−1 for the sulfur-doped and 753 m2 g−1 for the non-doped carbon. The sulfur-doped carbon exhibited more sulfur states/functionalities than the non-doped, highlighting the successful chemical modification of the material. As a result, the adsorptive performance of the sulfur-doped carbon was remarkably improved. Diclofenac adsorption experiments indicated that the kinetics was better described by the Avrami fractional order model, while the equilibrium studies indicated that the Liu model gave the best fit. The kinetics was much faster for the sulfur-doped carbon, and the maximum adsorption capacity was 301.6 mg g−1 for non-doped and 473.8 mg g−1 for the sulfur-doped carbon. The overall adsorption seems to be a contribution of multiple mechanisms, such as pore filling and electrostatic interaction. When tested to treat lab-made effluents, the samples presented excellent performance.