The review combined searches of Web of Science, Scopus, MEDLINE and Google Scholar with event-specific searches and institutional information from the World Information Service on Energy, the United Nations Environment Programme, GRID-Arendal and the World Health Organization. It followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews. The researchers built an inventory of disasters and their reported characteristics, then searched separately for studies measuring exposure, health outcomes or associations involving people directly affected by each event. Fourteen eligible studies assessed health consequences in Mariana and Brumadinho.

Forty-three of the 49 inventoried events were classified as dam failures, while six were categorized as overflows; these figures describe the review’s inventory and should not be interpreted as the proportion of every tailings disaster occurring worldwide. Asia accounted for 41% of the recorded events, South America for 33%, Africa for 14% and North America for 10%. The distribution may partly reflect where mining is intensive and where large numbers of tailings storage facilities operate, although the review did not systematically test this explanation. Clusters were reported in Minas Gerais in Brazil, Kachin State in Myanmar, Potosí in Bolivia, mining regions in China, and gold- and copper-producing areas in Peru and Mexico.

Gold was the commodity most frequently represented, appearing in 12 of the 49 events, followed by copper and jade with seven each and iron with five. Information on potentially toxic elements was available for only 10 disasters. Among those events, arsenic and lead were each reported in nine, while mercury, manganese and zinc appeared in six. These frequencies describe what investigators documented, not what was necessarily absent from other tailings. The results also show why treating mining waste as a single-contaminant problem would be misleading: tailings can contain mixtures of elements, and their movement and bioavailability can change with water conditions, oxidation-reduction reactions, pH and interactions among minerals.

Contamination does not automatically mean that people have been exposed at harmful levels, and the presence of an element in tailings is not itself evidence of a clinical disease. Human exposure may occur through ingestion, inhalation or skin contact as particles and contaminants move through water, sediment, soil, air, food and biota. The environmental persistence of the released material makes long-term surveillance important, but baseline conditions matter. In the upper Rio Doce basin, for example, soils and river sediments already contained elevated concentrations of several elements before the Mariana accident because of historical mining. Conversely, measurements after the disaster found higher concentrations in the estuary, far from that legacy source, showing why background conditions must be assessed across the full affected area rather than extrapolated from one locality.

Studies following Brumadinho provide the most extensive health evidence in the review. The Brumadinho Health Project enrolled 3,080 residents aged 12 or older, with baseline data collected in 2021, approximately two years after the failure. Hypertension, high cholesterol and depression were among the most frequently reported diagnoses. In an assessment of 2,740 adults, depressive symptoms affected 29.3%, post-traumatic stress symptoms 22.9% and anxiety symptoms 18.9%. Adjusted analyses linked several psychiatric outcomes with female sex and residence in mining areas, but the observational design does not establish that the disaster caused the conditions.

Other Brumadinho findings included multimorbidity in 53.8% of 2,777 adults. After adjustment, residents of directly affected areas had higher odds of multimorbidity than the reference group, with an adjusted odds ratio of 1.6 and a 95% confidence interval of 1.3–2.0. Respiratory assessments of 2,772 adults found asthma in 7.2% and chronic obstructive pulmonary disease in 3.5%; dry cough was reported by 23.6% and nasal irritation by 31.8%. In biomonitoring, concentrations above reference values were found for manganese in 38.08% of participants, arsenic in 33.37%, lead in 5.04%, mercury in 0.76% and cadmium in 0.17%. Such measurements document internal exposure, but the review stresses that they do not by themselves demonstrate toxic effects or disease.

Evidence from Mariana was similarly mixed in both type and strength. In an exploratory cross-sectional study of 507 residents, 37% reported worse health than before the disaster. Among spontaneously reported problems, respiratory conditions represented 40%, skin conditions 15.8% and behavioral disorders 11%. Blood testing of 300 participants from Regência, Povoação and Campo Grande identified elevated levels of aluminum, arsenic, mercury and nickel, while a subsequent study of 279 residents found urinary arsenic, cadmium and nickel positively associated with 8-OHdG, a biomarker of oxidative stress and DNA damage. No association was found for mercury or lead. The authors classified the latter result as evidence of an exposure-related biomarker association, not a clinical outcome or causal effect.

The review divided the literature into three descriptive levels: biomonitoring showing internal exposure; documented health outcomes and health-system indicators; and statistical analyses relating exposure variables to outcomes or biomarkers. The distinction was not a quality scale, and none of the included studies supplied evidence sufficient for causal inference. Cross-sectional designs, self-reported symptoms, geographic proxies and a lack of pre-disaster population baselines were recurring limitations. Toxicological literature provides context for potential effects of arsenic, cadmium, lead, mercury, manganese, aluminum and crystalline silica, but those general hazards cannot be treated as outcomes directly observed after these disasters. The review therefore calls for integrated, longitudinal surveillance combining environmental measurements, periodic biomonitoring and epidemiological follow-up, alongside safer tailings management, stronger monitoring and robust regulatory oversight.

Subject of Research: Global evidence on human exposure and health after mining tailings dam failures

Article Title: Mining tailings dam failures and human health: a scoping review of environmental exposure, potentially toxic elements, and epidemiological evidence, 2015–2025

Article References: Souza, T. P., Ferreira, A. D., Viana, D. G., de Sousa, J. E. S., & Ferreira, T. O. (2026). Mining tailings dam failures and human health: a scoping review of environmental exposure, potentially toxic elements, and epidemiological evidence, 2015–2025. Environmental Geochemistry and Health, 48(16), Article 651. https://doi.org/10.1007/s10653-026-03542-9

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03542-9

Keywords: mining tailings, dam failures, public health, potentially toxic elements, epidemiology, biomonitoring, environmental contamination, Brumadinho, Mariana, risk assessment, Mining, tailings

The scientific significance of the work lies in its ability to separate two overlapping chemical fingerprints in the same waters. The team identified a technogenic association of elements, one whose composition is dictated by mining activity, and a regional association that develops under purely natural conditions. The technogenic signature is dominated by elevated concentrations of cobalt, copper, zinc, and cadmium, while the regional background is characterized by the accumulation of rare earth elements alongside comparatively low heavy metal levels. Distinguishing these two associations matters because it allows regulators and scientists to determine how much of the contamination in any given water sample is attributable to human industry rather than to the geology of the region itself.

Chemically, the waters at both sites are far from the acidic nightmares often associated with abandoned mines. The authors report that the waters are predominantly sodium-calcium bicarbonate and sulfate-bicarbonate types, with total dissolved solids below 200 milligrams per liter and a neutral pH. Trace element concentrations generally range from single-digit values to hundreds of micrograms per liter. That combination of low salinity and near-neutral acidity might sound benign, but the study demonstrates that even modestly mineralized, pH-neutral waters can carry a dangerous cargo of heavy metals when the surrounding rock has been fractured, exposed, and dewatered by decades of mining.

The mechanism behind this quiet contamination is sulfide weathering. Tin and tungsten ores typically occur with accessory sulfide minerals such as pyrite, sphalerite, and galena. When mine workings and waste rock dumps expose these minerals to oxygen and water, they oxidize, releasing sulfate and metals into solution. Previous work cited by the authors, including cross-scale investigations of galena and sphalerite weathering in mine waste rock, has shown that molecular-scale oxidation reactions ultimately control field-scale mobilization of lead, zinc, and cadmium. In Eastern Transbaikalia, the neutral pH suggests that carbonate minerals in the host rock are buffering the acidity that sulfide oxidation generates, but buffering does not remove the dissolved metals; it simply keeps them in a form that travels through groundwater and surface water systems without the dramatic visual cue of orange, acidified runoff.

The sampling design captured the full gradient of mining influence. Water was collected directly from mine workings, including adit drainage that flows out of underground tunnels, from the flooded open pit, and from tailings storage facilities where finely ground ore waste has been deposited. These are the three hotspots where the environmental assessment revealed significant pollution. Because adit drainage represents groundwater that has circulated through fractured ore zones, it integrates the geochemistry of the entire disturbed system. Tailings facilities, meanwhile, present an enormous reactive surface area of crushed sulfide-bearing material, making them persistent sources of metals that can continue releasing contaminants for decades or even centuries after closure.

To translate concentrations into environmental meaning, the researchers compared measured values against Russian regulatory benchmarks, including water quality standards for aquatic objects of fishery importance established by the Ministry of Agriculture and hygienic norms under SanPiN 1.2.3685-21. They then applied the official Criteria for Assessing the Environmental Situation of Territories, approved in 1992 by the Ministry of Environmental Protection and Natural Resources of the Russian Federation, which defines thresholds for classifying territories as zones of ecological emergency or ecological disaster. By these standards, the waters draining from the adits, the open pit, and the tailings facilities crossed the thresholds that place them in the most severe categories of environmental degradation, a formal designation with real implications for land use and remediation priorities.

The rare earth element signal adds an intriguing geochemical dimension to the story. In the regional association, meaning waters shaped by natural processes rather than mining, rare earth elements accumulate while heavy metals remain depleted. This pattern is consistent with long-established observations in groundwater geochemistry, notably the classic work on rare elements in groundwater by S. R. Krainov, which showed that natural waters in certain geological provinces develop characteristic rare earth enrichments. The contrast between the two associations gives the authors a diagnostic tool: a water sample enriched in cobalt, copper, zinc, and cadmium points to mining influence, while one enriched in rare earths with low heavy metals reflects the natural regional background. This kind of fingerprinting is increasingly valuable as agencies worldwide grapple with attributing contamination at legacy mine sites.

Eastern Transbaikalia is no stranger to this problem. The region hosts a long history of rare-metal mining, including tungsten, molybdenum, tin, and tantalum operations, and Chechel’s earlier publications have documented ecological and hydrogeochemical consequences at tungsten and molybdenum deposits and the distribution of rare alkaline elements in mining waters across the area. Earlier studies of the Orlovskoe tantalum deposit and of the Modonkul River, which receives drainage from mining territories in southeastern Transbaikalia, have documented similar patterns of technogenic alteration of water chemistry. The new study extends this body of work by systematically comparing the two association types and by formally classifying the environmental status of the affected waters, connecting site-scale chemistry to the regulatory framework used to declare ecological emergencies.

The findings resonate far beyond Siberia. Abandoned and legacy mines are a global challenge, from the contaminated groundwater documented at historical mine sites in Japan to heavy metal pollution in water and soil around tin mining regions in Hunan Province, China, and arsenic-laden gold mining wastes in Ghana. Acid mine drainage remains one of the most studied and most stubborn environmental problems in the world, and the Transbaikalian case adds an important nuance: significant metal pollution can occur in waters that remain neutral and dilute, meaning that visual inspection or simple pH measurements are not sufficient to assess risk. Monitoring programs that focus only on acidity may dramatically underestimate the metal load reaching rivers, fishery waters, and drinking water supplies downstream of abandoned deposits.

For remediation planners, the study’s identification of the three most polluted water types, adit drainage, open-pit water, and tailings facility water, offers a practical roadmap. These are the points where intervention, whether through passive treatment systems, covering and isolation of tailings, or controlled drainage collection, would yield the greatest environmental return. The work was completed under a Russian state assignment focused on geoecological assessment of geosystem transformation in Transbaikalia under modern climate and technogenesis, reflecting a growing recognition that legacy mining landscapes must be understood quantitatively before they can be restored. As demand for tin and tungsten, both critical metals for modern electronics and technology, continues to drive new mining worldwide, the waters of Eastern Transbaikalia stand as a sobering reminder of what unmanaged mine closure leaves behind.

Subject of Research: Hydrogeochemical assessment of water pollution from abandoned tin-tungsten mines in Eastern Transbaikalia, Russia

Article Title: Environmental impact of tin-tungsten deposits mining (Eastern Transbaikalia, Russia)

Article References: Chechel, L. P., & Zamana, L. V. (2026). Environmental impact of tin-tungsten deposits mining (Eastern Transbaikalia, Russia). Environmental Monitoring and Assessment, 198(9), Article 1029. https://doi.org/10.1007/s10661-026-15764-6

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15764-6

Keywords: abandoned mines, tin mining, tungsten mining, Eastern Transbaikalia, heavy metals, rare earth elements, acid mine drainage, tailings, water quality, hydrogeochemistry, ecological emergency, sulfide weathering

The study, published in Frontiers in Geochemistry, examined mine wastes from two strikingly different legacy mining regions: the town of Cobalt in Ontario, Canada, and three historic mine sites in Cornwall, England. Despite vast differences in geology, ore type, and processing methods spanning a millennium of mining history, the researchers found that cobalt in both locations showed consistently high potential for mobilization — meaning it could readily dissolve and travel into aquatic environments where it might enter the food chain.

“The concentrations we found at Cobalt, Canada were extraordinary,” the research indicates, with high-grade Nipissing tailings containing up to 5,630 milligrams of cobalt per kilogram of material — roughly 900 times higher than the Cornwall sites. Even the low-grade tailings at Cobalt reached 1,230 milligrams per kilogram, dwarfing the averages of 40, 76, and 59 milligrams per kilogram found at Poldice, Wheal Unity, and Dolcoath mines in Cornwall respectively. These concentrations far exceed residential soil quality guidelines set by regulatory bodies in Ontario, Canada, the United States, and the European Union.

The research team, led by Gabriel Ziwa of the Camborne School of Mines at the University of Exeter, employed a sophisticated battery of analytical techniques to understand not just how much cobalt was present, but in what chemical forms. Using X-ray diffraction, scanning electron microscopy, and electron microprobe analysis, they identified the specific minerals hosting the cobalt — a crucial step because a metal locked inside a stable crystal is far less dangerous than one sitting on a mineral surface ready to dissolve at the first change in water chemistry.

At Cobalt, Canada, the picture was dominated by a striking pink mineral called erythrite — a cobalt arsenate that formed as needle-like crystals growing on silicate and carbonate grains throughout the tailings. This secondary mineral, containing roughly 20.8 percent cobalt by weight, proved to be the most widespread cobalt-bearing phase at the site. The researchers also identified primary cobalt minerals including cobaltite, safflorite, and skutterudite, alongside cobalt incorporated into arsenopyrite, loellingite, pyrite, and chalcopyrite. Secondary phases such as arseniosiderite, scorodite, and iron oxyhydroxides also harboured significant cobalt concentrations.

In Cornwall, by contrast, no dedicated cobalt minerals were found at all. Instead, cobalt existed only as a trace component — typically less than one percent by weight — hidden inside common sulfide minerals like pyrite, chalcopyrite, and arsenopyrite, and in secondary phases such as scorodite and iron-manganese oxyhydroxides. Yet this difference in mineralogical hosting made almost no difference to the metal’s behaviour when subjected to sequential extraction testing.

The most alarming result came from the BCR sequential extraction analysis, a standardized European protocol that subjects mine waste to progressively stronger chemical leaches to simulate what might happen under different environmental conditions. In both the Canadian and British samples, an average of 46 percent of the total cobalt was extracted in the very first, mildest step — the “exchangeable” fraction that represents metal most easily dissolved by slight changes in acidity. This means nearly half the cobalt in these wastes is sitting in a form that could be released into water with only minor pH shifts.

Applying the Risk Assessment Code framework developed by Perin and colleagues, the researchers classified cobalt in the Cornwall samples as ranging from high risk to very high risk, with individual samples reaching exchangeable fractions of up to 62 percent. At Cobalt, Canada, values ranged from 28 to 58 percent, placing the metal in medium to very high risk categories. According to the RAC guidelines, metals exceeding 50 percent in the exchangeable fraction are considered to easily enter the food chain — a classification that directly implicates these mine wastes as potential vectors for human cobalt exposure through crops, livestock, and water supplies.

The chemistry behind this mobilization is well understood. At Cornwall’s acidic sites, where paste pH values ranged from 3.72 to 5.77, sulfide minerals like pyrite generate acid through oxidation, and any cobalt-bearing phases dissolve readily, releasing cobalt ions and arsenic oxyanions into solution. At Cobalt, Canada, the near-neutral pH of 7.50 to 7.84 currently stabilizes erythrite within its thermodynamic stability field — but the researchers warn this equilibrium is fragile. A shift toward acidity, whether from changing oxidation conditions or altered hydrology, could dissolve the erythrite and release its cobalt payload. The iron and manganese oxyhydroxides that scavenge cobalt in both locations are themselves thermodynamically unstable under reducing conditions, meaning buried or waterlogged wastes could also release their stored metal.

What makes this research particularly significant is its implication for the future. Cobalt demand is projected to surge as electric vehicle adoption accelerates globally, and governments worldwide have designated it a strategic resource. Yet the environmental behaviour of cobalt in mine waste has been remarkably understudied compared to metals like arsenic or lead. The Exeter team’s finding that cobalt behaves similarly across such geologically different settings — a five-element silver-cobalt-nickel vein deposit in Precambrian rocks versus polymetallic tin-copper-arsenic veins in Devonian-Carboniferous host rocks — suggests that the metal’s mobility in mine waste may follow predictable patterns worldwide. If confirmed by further research, this would mean that every new cobalt mine opening today is generating waste with the same latent capacity to contaminate water and food chains that century-old sites in Canada and England are only now revealing.

Subject of Research: Geochemistry and mineralogy of cobalt mobility in legacy mine wastes from Cobalt, Canada and Cornwall, England

Article Title: Geochemistry and mineralogy of Cobalt in mine wastes: examples from Cobalt, Canada and Cornwall, England

Article References: Ziwa, G., Crane, R., & Hudson-Edwards, K. A. (2025). Geochemistry and mineralogy of Cobalt in mine wastes: examples from Cobalt, Canada and Cornwall, England. Frontiers in Geochemistry, 3, Article 1543695. https://doi.org/10.3389/fgeoc.2025.1543695

Image Credits: AI Generated

DOI: 10.3389/fgeoc.2025.1543695

Keywords: cobalt, mine waste, tailings, geochemistry, mineralogy, erythrite, sequential extraction, mobility, critical raw materials, contamination, Cornwall, Ontario

The research, published in Frontiers in Geochemistry, analyzed 71 samples spanning nearly every environmental compartment of the Guanajuato River Basin: bedrock, mine tailings, soils, stream sediments, ancient overbank sediments, surface water, and groundwater. The goal was ambitious. Rather than simply measuring how much arsenic or lead was present, the team wanted to determine where those elements came from, whether from the hydrothermal mineralization that formed the district’s famous silver veins, or from the centuries of mining that exploited them. This distinction matters enormously, because elevated concentrations of toxic elements alone cannot discriminate between natural geological enrichment and human contamination, particularly in terrain where both share a common origin.

The study area is geochemically extraordinary. The Guanajuato Mining District hosts low-sulfidation epithermal silver-gold vein systems controlled by the Veta Madre fault zone, a structure that geologists have described as a fossil geothermal system. Hydrothermal activity generated mineral assemblages enriched in silver, gold, lead, zinc, copper, arsenic, antimony, and mercury. In other words, the basin’s rocks were naturally loaded with potentially toxic elements long before the first shovel struck ore. Historical records indicate that Guanajuato was a premier silver-producing region during the eighteenth century, generating substantial volumes of mining waste and profoundly altering the basin’s fluvial architecture. The legacy tailings were derived directly from the same hydrothermal mineralization that naturally enriches the bedrock, creating substantial overlap between natural and mining-related geochemical signatures.

To disentangle these overlapping signals, the researchers deployed a two-pronged analytical strategy. First, they applied multivariate statistics, including Spearman rank correlation, principal component analysis, and hierarchical cluster analysis, to identify elemental associations across the solid and aqueous matrices. Second, they trained an exploratory Random Forest classifier, a machine learning algorithm that builds hundreds of decision trees, using bedrock samples as a geogenic reference class and mine tailings samples as a mining-related reference class. The model achieved an out-of-bag error of 0.12, meaning it correctly classified about 88 percent of training samples it had not seen during model fitting. The researchers then applied the trained model to soils, stream sediments, and overbank sediments to estimate their relative geochemical affinity to each reference class.

The multivariate statistics revealed two principal geochemical associations in the solid samples. The first, comprising aluminum, iron, chromium, vanadium, and nickel, showed strong positive correlations and was interpreted as geogenic, reflecting the natural composition of the basin’s mafic-ultramafic and volcano-sedimentary lithologies. The second association, involving sulfur, arsenic, cadmium, lead, copper, and zinc, was interpreted as mineralized and mining-related. The Random Forest analysis identified sulfur, cadmium, and arsenic as the leading predictors for discriminating between the two reference classes. At the matrix level, median affinity scores for overbank sediments and soils shifted toward the geogenic reference class at 61 and 63 percent respectively, while stream sediments occupied an intermediate position with nearly equal median scores of 49 percent geogenic and 51 percent mining-related affinity.

This intermediate position of stream sediments is geochemically telling. It suggests that modern stream sediments integrate both natural and mining-derived materials, reflecting the long-term influence of weathering, erosion, and sediment transport processes operating throughout the basin. Historical records indicate that large volumes of finely ground wastes were deposited in tailings piles or discharged directly into drainage channels during ore processing. Because these materials are more susceptible to weathering and erosion than the original bedrock, they serve as an efficient mechanism for the downstream redistribution of metal(loid)s and contribute to the persistence of mining-related signatures in modern sediments. Spatially, stream sediment samples located near the historical mining district generally showed lower median geogenic affinity scores and coincided with higher values of a standardized sulfur-plus-cadmium-plus-arsenic index, while elevated index values also occurred at some downstream locations, indicating that this geochemical signature was not restricted to the immediate vicinity of historical tailings deposits.

Perhaps the most striking finding concerns what the preindustrial overbank sediments reveal. These samples were obtained from a roughly two-meter-high floodplain terrace previously dated to pre-industrial depositional periods ranging from 2450 to 9410 years before present. Their concentrations of arsenic, cadmium, copper, and zinc demonstrate that weathering of naturally mineralized lithologies supplied trace elements to the fluvial system long before the onset of intensive mining. The authors conclude that historical mining has amplified and redistributed preexisting hydrothermal geochemical signatures rather than introducing entirely new elemental assemblages. This is a crucial insight for environmental management in naturally mineralized basins worldwide, where elevated elemental concentrations may be misclassified as contamination when they actually reflect geological inheritance.

The water chemistry told a different story. Bicarbonate-type waters dominate the basin, but groundwater is enriched in sodium, silicon, fluoride, arsenic, and zinc, whereas surface waters exhibit higher overall mineralization with calcium-magnesium-sulfate signatures. Most dissolved metal(loid) concentrations remained below the analytical limit of quantification in both surface and groundwater, a contrast the researchers attribute to the carbonate-rich composition of Guanajuato mine tailings, which buffers acidity and limits acid mine drainage generation, favoring metal(loid) retention through interactions with iron-manganese oxyhydroxides and carbonate phases. Arsenic represents an important exception because its mobility may increase under circumneutral to alkaline conditions through desorption from mineral surfaces, making it one of the few elements occurring at measurable dissolved concentrations while also showing enrichment in solid matrices.

The risk assessment revealed spatially heterogeneous environmental concerns. Ecological risk was highest in mine tailings, driven primarily by elevated arsenic, cadmium, and copper, with two specific tailings deposits classified as moderate ecological risk while the remaining deposits were classified as low risk. Water quality and human health risks were restricted to localized groundwater and downstream surface water sites. Among surface waters, particularly high pollution index values coincided with elevated manganese concentrations, whereas high index values in groundwater coincided with arsenic concentrations exceeding drinking-water guideline values. For groundwater samples with quantified arsenic, carcinogenic risk estimates exceeded the upper acceptable level of 1.0E-04, with the highest values observed in two specific production wells. The authors emphasize that these estimates indicate potential carcinogenic concern under the evaluated long-term exposure scenario but require careful interpretation given the high proportion of arsenic measurements below the quantification limit.

The researchers are transparent about the limitations of their approach. The Random Forest model was trained on a limited dataset of only 12 lithological and 13 mine tailings samples, making the findings exploratory rather than definitive. Variable importance measures based on mean decrease in impurity may be biased when predictors are highly correlated, and the Random Forest is primarily a predictive classification algorithm rather than a mechanistic source-apportionment model. Water sampling was restricted to the dry season, so the hydrochemical patterns represent low-flow conditions and may not capture seasonal variations in metal(loid) mobility. Nevertheless, the integrated evaluation of multiple environmental matrices provides a screening framework for interpreting mining-related impacts in naturally mineralized basins, identifying priority areas for continued monitoring, particularly specific groundwater sites and tailings deposits with elevated ecological risk. For a basin shaped by five centuries of mining, the message is clear: the past is not buried, it is flowing downstream, one sediment particle at a time.

Subject of Research: Geochemical connectivity among mine tailings, soils, sediments, and waters in a historical mining basin integrating multivariate statistics and exploratory random forest modeling

Article Title: Geochemical connectivity among mine tailings, soils, sediments, and waters in a historical mining basin integrating multivariate statistics and exploratory random forest modeling

Article References: Rueda-Garzon, L. F., Carrillo-Chávez, A., Miranda-Avilés, R., Calvo-Ramos, D., Morales-Martínez, J. L., Muñoz-Torres, C., & García-Martínez, R. (2026). Geochemical connectivity among mine tailings, soils, sediments, and waters in a historical mining basin integrating multivariate statistics and exploratory random forest modeling. Frontiers in Geochemistry, 4, Article 1919883. https://doi.org/10.3389/fgeoc.2026.1919883

Image Credits: AI Generated

DOI: 10.3389/fgeoc.2026.1919883

Keywords: geochemistry, mining, machine learning, arsenic, Guanajuato, random forest, environmental risk, source apportionment, Geochemical, connectivity, mine, tailings

The mines at Crocette and Pestarena tell a story that stretches back to the end of the thirteenth century, when the first official documents recorded underground gold mining in the valley. Operations continued into the mid-twentieth century, ending at Pestarena in 1961 as ore grades declined and costs rose. The gold was locked in quartz-carbonate veins hosted in paragneisses and micaschists at Pestarena and in orthogneisses at Crocette, where it occurred alongside sulfide minerals, chiefly pyrite and arsenopyrite, with lesser galena, sphalerite, pyrrhotite and chalcopyrite. Extraction relied on mercury amalgamation and, from the late 1880s, cyanidation, both of which generated enormous quantities of waste rock and fine-grained tailings that were dumped around the processing plants with little regard for the consequences.

That carelessness left a lasting mark. Sulfide minerals in the exposed waste oxidize when they meet air and water, generating acid or neutral mine drainage that mobilizes potentially toxic elements into soils, groundwater and streams. Previous investigations had already documented alarming conditions: soils near Crocette with arsenic concentrations ranging from 145 to more than 40,000 milligrams per kilogram, a natural background value for the area calculated at 477 milligrams per kilogram against an Italian regulatory threshold of just 20 to 50, and surface waters in the most contaminated samples reaching 279 micrograms of arsenic per liter, far above the Italian limit of 10. A 2025 study by members of the same team found that three quarters of groundwater and surface water samples at the two sites were contaminated with arsenic, with other elements exceeding thresholds in groundwater downstream of the tailings.

To build a complete picture, the researchers merged decades of earlier geochemical and mineralogical data with a new sampling campaign conducted in May and July 2024, collecting 28 fresh samples of waste rock, tailings, soil and sediment from depths of up to 30 centimeters. The new material was analyzed at an accredited laboratory using a four-acid digestion followed by inductively coupled plasma emission spectroscopy and mass spectrometry, covering more than fifty elements, while mineralogy was resolved with X-ray powder diffraction and scanning electron microscopy. Because decades of erosion and dispersion have blurred the boundary between waste and native soil, the team classified every sample under two scenarios: a conservative one counting only material clearly located on waste dumps, and a broader one that also included adjacent, vegetation-free or chemically distinctive material, mirroring the distinction between indicated and inferred resources in resource estimation.

The mineralogical work revealed the fingerprints of intense chemical weathering. Alongside the dominant quartz, feldspars and micas inherited from the host rocks, the waste contains secondary minerals that record the breakdown of the original sulfides: scorodite, formed from the alteration of arsenopyrite; jarosite, precipitated as pyrite and pyrrhotite oxidize; and alunite, produced during the alteration of aluminosilicates. Electron microscopy also identified grains of monazite-(Ce), a phosphate mineral that can carry up to seventy percent rare earth oxides, dominated by cerium with significant lanthanum, praseodymium and neodymium, along with traces of residual arsenopyrite, ilmenite, zircon and barite. Scheelite, a calcium tungstate and one of the world’s principal tungsten ores, appeared among the minor minerals, a hint of the critical metals hiding in plain sight.

When the researchers normalized their measured concentrations against the composition of the upper continental crust, the scale of the enrichment became striking. At Pestarena, arsenic in the waste is a median of roughly 1,700 to 2,000 times more abundant than in average crustal rock, while bismuth, tungsten and antimony show median enrichments of about 100, 35 and 15 respectively, with slight enrichment of beryllium and of the light rare earth elements lanthanum, cerium, praseodymium and neodymium. At Crocette the picture is even more dramatic: arsenic reaches a median enrichment of around 4,000 times crustal values, followed by tungsten at 50, antimony at 40 and bismuth at 26. These figures matter because arsenic, bismuth, antimony and tungsten all appear on the European Union’s list of critical raw materials, the strategic elements underpinning semiconductors, photovoltaics, clean energy technologies and defense applications.

The same waste that concentrates these valuable elements also drives the environmental damage, and the team quantified that damage using standard contamination indices. River sediments collected away from the mine workings proved uncontaminated, but sediments from the drainage channels of the mine tunnels and the tailings outflows showed heavy to extreme arsenic contamination, moderate to heavy lead contamination and high ecological risk, driven overwhelmingly by arsenic. In the surrounding soils, the geo-accumulation index placed Pestarena in the heavily to extremely contaminated category for arsenic, with a mean value of 3.5 and individual samples exceeding 5.0, alongside moderate lead contamination, while Crocette soils fell in the moderately to heavily contaminated range. The potential ecological risk index, which weights each element by its toxicity, averaged 296.4 at Pestarena and 251.1 at Crocette, both within the moderate risk category, with arsenic contributing the dominant share, followed by lead and cobalt.

What elevates the study beyond a conventional contamination survey is its economic framing. By estimating the volumes of waste rock and tailings at each site from field observations and stratigraphic data, and applying bulk densities of 1.5 grams per cubic centimeter for waste rock and 1.8 for tailings, the researchers calculated the residual quantities of arsenic, bismuth, antimony and tungsten still locked in the dumps. They then multiplied these quantities by plausible recovery rates of 60 to 80 percent, consistent with efficiencies of 77 to 99 percent reported for tungsten, 81 to 99 percent for arsenic, up to 98 percent for antimony and 76 to 99 percent for bismuth in comparable secondary resources, and by average market prices from 2000 to 2021. Arsenic emerges as the most abundant target, with bismuth, antimony and tungsten present in significant quantities, although the authors stress that these preliminary estimates cannot by themselves establish economic feasibility, since remediation, processing and residue disposal costs must all be weighed against revenues.

The technical pathways for such recovery already exist. Published case studies describe arsenic and antimony extraction from antimony flotation waste by acid leaching, the recovery of antimony and bismuth from copper smelter flue dusts through acid chloride leaching and selective precipitation, the stabilization of arsenic as crystalline scorodite during copper electrorefining, and the recovery of tungsten and arsenic from tungsten-bearing residues using alkaline leaching with pressure oxidation, deep eutectic solvents paired with electrodialysis, or acid leaching followed by solvent extraction. Arsenic occupies a paradoxical position in this landscape: it is both a valuable resource, essential for gallium arsenide semiconductors and electronic technologies, and one of the world’s most notorious poisons, capable of causing severe chronic health effects through contaminated water and food. Any recovery scheme must therefore be paired with safe long-term management of the arsenic left behind, for example by precipitation as scorodite or vitrification, to prevent the problem simply migrating from one waste heap to another.

The broader message is one of reframing. Within the European Union, mining and quarrying generated nearly 500 million tonnes of waste in 2022, the second largest share of any economic activity, and the Circular Economy Action Plan together with the Critical Raw Materials Act now explicitly encourages treating old waste heaps as anthropogenic deposits rather than burdens. The Anzasca Valley study suggests that remediation and resource recovery need not be opposing goals: excavating and processing contaminated waste can simultaneously reduce ecological risk, clean up soils and water, and supply strategic materials that Europe currently imports at geopolitical peril. The authors caution that further work is needed to characterize the materials more precisely, optimize treatment processes and evaluate the full economic and environmental sustainability of recovery strategies. But their central conclusion is clear: the mountains of waste left behind by a thousand years of Alpine gold mining may yet prove to be among the most valuable things those mines ever produced.

Subject of Research: Environmental impact assessment and critical raw material recovery from abandoned gold mining waste in the Western Alps

Article Title: From environmental burden to resource potential: environmental impact evaluation and Critical Raw Materials recovery from abandoned gold mining waste in the Western Alps (NW Italy)

Article References: Zaniboni, L., Cavallo, A., De Luca, D. A., Lasagna, M., Padoan, E., Martin, M., & Dino, G. A. (2026). From environmental burden to resource potential: environmental impact evaluation and Critical Raw Materials recovery from abandoned gold mining waste in the Western Alps (NW Italy). Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38241-6

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38241-6

Keywords: critical raw materials, arsenic, gold mining, mine waste, tailings, circular economy, environmental contamination, ecological risk, Western Alps, Italy, tungsten, antimony

The research team, led by Yanan Chen and Rui Liu of Yunnan University together with colleagues from the Yunnan Institute of Geo-Environment Monitoring and the University of Hong Kong, collected sixty composite soil samples from the watershed. The sampling design deliberately spanned the human geography of the landscape: tailings land, farmland, bare land, grassland, and natural forest. At each location, soils were drawn from four distinct layers, from the top ten centimeters down to ninety centimeters. This depth-resolved approach matters because many contamination surveys stop at the surface, potentially underestimating the total inventory of pollutants that could migrate downward toward groundwater or upward through plant roots. The seven elements measured were cadmium, chromium, copper, nickel, lead, zinc, and mercury, a roster that covers the most ecologically consequential heavy metals associated with phosphate extraction.

Phosphate ore is naturally laced with metals. When rock is mined, crushed, and processed, those impurities are liberated and concentrated in waste tailings, which can then be dispersed by wind and water. Cadmium is a particular concern in phosphate deposits worldwide, because it substitutes chemically for calcium in the mineral lattice and survives processing. The Jinning area, upstream of Dianchi Lake in Yunnan Province, has been shaped by phosphate extraction for years, and the lake itself has long suffered from nutrient pollution and algal blooms. What the new study adds is a quantitative picture of how the toxic metal burden is distributed not just across the landscape horizontally, but vertically through the soil profile, and how that distribution differs depending on what people have done with the land.

The headline finding is unambiguous. Tailings land emerged as the principal contamination hotspot of the entire watershed. In the surface layer of tailings-affected soils, cadmium reached an average concentration of 0.70 milligrams per kilogram, with a standard deviation of 0.35, while lead averaged 176.8 milligrams per kilogram, with a striking standard deviation of 130.0 that reflects the patchiness of deposition. The Nemerow comprehensive pollution index, a composite measure that emphasizes the worst pollutant at a site, registered 2.085 for tailings land, a value that signals substantial multi-element contamination. No other land-use type approached this level. Farmland, grassland, bare land, and natural forest carried comparatively lower burdens, though the study found that soil properties and metal concentrations varied meaningfully among all five categories.

Depth turned out to be as important as location. Across the watershed, soil organic matter, total nitrogen, available phosphorus, and available potassium generally declined with depth, while pH increased, a pattern consistent with the biological enrichment of topsoil by vegetation and agricultural management. The toxic metal risk followed a parallel vertical gradient in the most contaminated zone. The potential ecological risk index, a widely used metric developed by Lars Hakanson that weights each metal by its toxicity, fell from 184.52 in the top ten centimeters of tailings land to 110.34 in the sixty-to-ninety-centimeter layer. Notably, mean risk index values exceeded the threshold of 150, the boundary of moderate ecological risk, only in the upper thirty centimeters of soil. Below that, the risk declined, suggesting that the contamination is still largely a surface phenomenon rather than a fully penetrated profile.

Within the overall metal burden, two elements dominated the risk calculation. Cadmium and mercury contributed the largest shares of the potential ecological risk index, a reflection of their outsized toxicity coefficients relative to their measured concentrations. This is a critical nuance for remediation planning. An element like zinc might be present at elevated concentrations by mass, yet contribute comparatively little to ecological risk because it is far less toxic per unit. Cadmium, by contrast, is a cumulative poison that damages kidneys and bones in humans and disrupts soil organisms at low concentrations, and it is readily taken up by crops. Mercury, meanwhile, can be transformed by microbes into methylmercury, the form that bioaccumulates in aquatic food webs. A watershed that drains toward a major lake, as this one does toward Dianchi, makes that aquatic pathway particularly relevant.

The study deployed a battery of complementary assessment tools, each answering a slightly different question. The single-factor pollution index evaluates each element against a background or regulatory threshold, isolating which specific metals exceed safe levels. The Nemerow index then folds those individual scores into a single comprehensive value that is dominated by the worst offender. The geo-accumulation index compares measured concentrations to pre-industrial background values, providing a historical perspective on how much of the burden is anthropogenic. The enrichment ratio normalizes metal concentrations against a reference element to correct for natural variations in soil texture. Finally, the potential ecological risk index translates concentrations into a measure of harm potential. By triangulating across these methods, the researchers reduced the uncertainty that any single index can carry, and the convergence of their results on tailings land as the priority zone strengthens the case for targeted intervention.

The practical implications extend beyond the watershed itself. The authors identify tailings-affected soils as the priority management unit for the Jinning area, meaning that remediation resources should be concentrated where the risk index is highest rather than spread uniformly across the landscape. This finding aligns with a growing international consensus that mine tailings disposal sites are among the most consequential and undermanaged sources of metal contamination, and that approaches such as phytostabilization, the use of plants to immobilize metals in place, can be effective first steps in arid and semi-arid settings. The depth-resolved data also carry a warning for agriculture: because the moderate risk is confined to the upper thirty centimeters, the layer where most crop roots feed, the contamination is precisely where it can most easily enter the food chain. Cadmium accumulation in vegetables grown near phosphate operations has been documented in other Chinese mining regions, and the Yunnan-Guizhou phosphate belt is known for elevated cadmium in both ore and agricultural products.

For Dianchi Lake, the study adds a new dimension to an old problem. The lake’s celebrated struggles with eutrophication have focused attention on nitrogen and phosphorus runoff from farms and cities, but the metal dimension of upstream land use has received less systematic attention. The finding that available phosphorus declines with depth while surface soils in tailings areas carry elevated cadmium and lead suggests that the same erosion processes that move nutrients downslope can also mobilize metals toward the water. Sediments in receiving lakes are the ultimate sink for such particles, and metal-laden sediment can remobilize under changing chemical conditions. The research was supported by the National Natural Science Foundation of China and Yunnan Provincial programs, reflecting regional investment in understanding the environmental legacy of phosphate extraction.

What makes the study broadly significant is its methodological lesson: depth matters, and land use matters, and they matter together. A survey that sampled only surface soils across all five land-use types would have correctly flagged tailings land but might have overstated the uniformity of the risk. A survey that sampled only one land-use type at multiple depths would have missed the spatial contrast entirely. By crossing the two dimensions, the researchers produced a risk map that is actionable in three dimensions, identifying not just where to intervene but how deep remediation needs to reach. As phosphate demand continues globally, driven by fertilizer production and battery chemistry, watersheds like Jinning will multiply. The soils above Dianchi Lake now offer a measured, layered baseline for managing them, and a reminder that the most important environmental data sometimes lies well below the surface.

Subject of Research: Distribution of potentially toxic elements and ecological risk across land-use types and soil depths in a phosphate-mining watershed upstream of Dianchi Lake, China

Article Title: Land-use and depth-dependent distribution of potentially toxic elements and ecological risk in soils of a phosphate-mining watershed upstream of Dianchi Lake, China

Article References: Chen, Y., Liu, R., Shih, K., Zhang, H., Ma, H., & Gao, Y. (2026). Land-use and depth-dependent distribution of potentially toxic elements and ecological risk in soils of a phosphate-mining watershed upstream of Dianchi Lake, China. Environmental Geochemistry and Health, 48(15), Article 613. https://doi.org/10.1007/s10653-026-03514-z

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03514-z

Keywords: phosphate mining, potentially toxic elements, soil contamination, cadmium, mercury, ecological risk index, tailings, soil depth, land use, Dianchi Lake, Yunnan, geochemistry

Tailings storage facilities, known in the industry as TSFs, are the embankments and impoundments built to contain the fine-grained residue that remains after gold ore is crushed and processed. On the Witwatersrand, the gold-bearing basin that underlies much of Gauteng Province, these facilities rise as pale, treeless hills that dominate the horizon of townships and informal settlements. Under dry Highveld conditions, particularly during the windy winter months, fine dust can be lifted from tailings surfaces and carried into nearby communities. Residents may inhale respirable dust containing crystalline silica and, in some cases, low concentrations of uranium and other metals associated with gold-bearing ore. Assessing the health risks of such exposure requires not only measurements of dust concentration but also a clear picture of how long, and in what settings, people are actually exposed to whatever the wind carries off the dumps.

That second ingredient is precisely what time-activity data provide, and it is precisely what has been missing for the communities of the West Rand. Exposure assessment in environmental epidemiology depends fundamentally on the product of concentration and duration: a person who spends twelve hours a day outdoors near a dust source faces a very different exposure profile from someone who works in an office across town and sleeps behind closed windows. Yet regulatory models and risk assessments in South Africa, as in many countries, have often relied on generic assumptions imported from international guidelines, typically European or North American time budgets that assume substantial time indoors, in sealed buildings, with mechanical ventilation. Such assumptions map poorly onto communities where many homes are informal structures, where cooking and socializing happen outdoors, where unemployment keeps large numbers of people at home all day, and where children play on unpaved ground close to the tailings themselves.

The research team set out to replace those assumptions with locally observed data. Their study focused on residential communities situated in proximity to tailings storage facilities along the West Rand, the western arm of the Witwatersrand gold field that runs through municipalities such as Merafong and the areas around Randfontein and Westonaria. Participants across a range of age groups were asked to document and recall how they spent their time across a representative day, capturing the categories of activity that exposure scientists use to partition daily life: time indoors at home, time indoors elsewhere such as school or work, time outdoors near the residence, time spent further afield, and time in transit. By collecting this information separately for children of different ages, working-age adults, and older residents, the study was able to construct age-stratified time budgets rather than a single community average.

The age-stratified approach matters because exposure risk is not distributed evenly across a lifetime. Infants and young children breathe more air per unit of body weight than adults, their respiratory tracts are still developing, and their behaviors, crawling on floors, playing in dust, hand-to-mouth contact, can amplify contact with contaminated soil and particulates. School-age children spend large portions of the day in classrooms that may or may not offer protection from outdoor dust, and many walk routes to and from school that pass close to tailings footprints. Adults of working age may be away from the residential exposure zone for much of the day, or, where unemployment is high, may remain in it continuously. Elderly residents, particularly those with pre-existing respiratory or cardiovascular conditions, are among the most vulnerable to particulate pollution yet may spend nearly all of their time within a few hundred meters of home. Without age-specific data, a risk model that averages across these very different patterns will underestimate exposure for some groups and overestimate it for others.

While the detailed numerical results reside in the full publication, the study’s contribution can be understood at two levels. At the level of raw evidence, it provides measured, locally grounded estimates of the hours per day that West Rand residents of different ages spend in locations and microenvironments relevant to tailings-derived dust exposure. At the level of method, it demonstrates a practical protocol for gathering such data in resource-constrained, high-exposure settings, where survey-based recall and structured questionnaires are often the only feasible instruments. Studies of this kind commonly reveal that total time outdoors near the home is substantially higher than default values assumed in international exposure models, particularly for children and for adults who are not formally employed, and that time in enclosed, mechanically ventilated environments is correspondingly lower. The West Rand findings are significant precisely because they anchor risk calculations in the actual rhythms of life in mining-adjacent communities rather than in borrowed assumptions.

The broader context makes the work urgent. The Witwatersrand has produced gold since 1886, and the region’s legacy tailings footprint extends across hundreds of square kilometers, much of it now surrounded or penetrated by residential development that expanded during and after apartheid-era planning, when Black communities were frequently located on marginal land close to mine dumps. Re-mining operations, in which companies reprocess old tailings to extract residual gold, add a contemporary layer of activity: trucks, conveyors, and processing plants that can re-suspend dust from deposits that had partially stabilized. Community organizations and environmental justice groups on the West Rand have for years raised concerns about respiratory illness, silicosis-like symptoms, and the long shadow of mining waste, while regulatory attention to residential proximity has grown through frameworks such as South Africa’s National Environmental Management Act and guidelines addressing buffer distances around tailings facilities. Sound policy in this contested space depends on defensible exposure estimates, and defensible exposure estimates depend on exactly the kind of time-activity data this study supplies.

The findings also speak to an international audience of exposure scientists, because time-activity patterns are among the most context-dependent variables in all of environmental health research. A time budget measured in a North American suburb, with its sealed houses, air conditioning, and car commutes, is simply a different object from one measured in a settlement of informal dwellings where daily life unfolds outdoors. Researchers in the exposure sciences have increasingly recognized that microenvironment models, which calculate total exposure as the sum of concentrations multiplied by time spent in each distinct setting, are only as good as the time-location inputs they receive. Studies from low- and middle-income countries remain underrepresented in this literature relative to the size of the populations potentially affected, which makes locally generated datasets from places like the West Rand valuable well beyond their immediate geography. They offer reference points for other mining-affected regions of southern Africa, and for the wider Global South, where tailings facilities and residential communities frequently coexist.

For residents themselves, the practical significance lies in what follows from measurement. Age-specific time budgets can inform where and when dust-control interventions will deliver the greatest benefit: rehabilitating tailings surfaces with vegetation or covers, adjusting re-mining activities during high-wind seasons, considering buffer zones in land-use planning, and targeting school and household-level measures, such as improved ventilation practices and dust-suppression around play areas, toward the groups whose daily routines place them most directly in the exposure pathway. Public health authorities can use the same data to refine health risk assessments and to prioritize environmental monitoring locations. Community advocates gain a documented, quantified account of how mining infrastructure shapes the daily lives of those living in its shadow, evidence that can carry weight in consultations, licensing processes, and debates over land use.

The study also underscores a deceptively simple point that recurs throughout exposure science: people are not passive receptors of pollution, and the dose they receive reflects the texture of their days. Understanding that texture, hour by hour and age group by age group, is an unglamorous but essential foundation for protecting public health in landscapes shaped by extraction. For the communities of the West Rand, where gold mine waste has been a neighbor for generations, having their actual patterns of movement and activity captured in the peer-reviewed literature represents a step toward risk assessments that see them as they are. It is a reminder that the path from a mine dump to a person’s lungs runs not only through the air, but through the ordinary details of where people live, work, learn, and play, and that measuring those details is where credible environmental health protection begins.

As gold mining continues its long retreat across the Witwatersrand, the waste it leaves behind will outlast the industry itself, and the populations living alongside that waste will continue to grow. Research that documents, with precision, how those populations inhabit their environment converts a legacy of neglect into an evidence base for action. The age-specific time-spent patterns reported for the West Rand provide a template for how such evidence can be gathered and a foundation on which dust management, urban planning, and public health interventions can now be built, in South Africa and in every other region where communities and mine tailings share the same ground.

Subject of Research: Age-specific time-spent patterns among residents living near gold mine tailings storage facilities in the West Rand, South Africa

Article Title: Age-specific time-spent patterns among residents living near gold mine tailings storage facilities in the West Rand, South Africa

Article References: Kalumbi, L. R., Masekameni, M. D., Utembe, W., & Brouwer, D. (2026). Age-specific time-spent patterns among residents living near gold mine tailings storage facilities in the West Rand, South Africa. Journal of Exposure Science & Environmental Epidemiology. https://doi.org/10.1038/s41370-026-00972-6

Image Credits: AI Generated

DOI: 10.1038/s41370-026-00972-6

Keywords: Age-specific, time-spent, patterns, residents, living, near, gold, mine, tailings, storage, facilities, West