Severe impacts of the Brumadinho dam failure (Minas Gerais, Brazil) on the water quality of the Paraopeba River

Effects of Cadmium and Nickel Mixtures on Multiple Endpoints of the Microalga Raphidocelis subcapitata

It is crucial to investigate the effects of mixtures of contaminants on aquatic organisms, because they reflect what occurs in the environment. Cadmium (Cd) and nickel (Ni) are metals that co-occur in aquatic ecosystems, and information is scarce on their joint toxicity to Chlorophyceae using multiple endpoints. We evaluated the effects of isolated and combined Cd and Ni metals on multiple endpoints of the chlorophycean Raphidocelis subcapitata. The results showed that Cd inhibited cell density, increased reactive oxygen species (ROS) production (up to 308% at 0.075 mg L-1 of Cd), chlorophyll a (Chl a) fluorescence (0.050-0.100 mg L-1 of Cd), cell size (0.025-0.100 mg L-1 of Cd), and cell complexity in all concentrations evaluated. Nickel exposure decreased ROS production by up to 25% at 0.25 mg L-1 of Ni and Chl a fluorescence in all concentrations assessed. Cell density and oxygen-evolving complex (initial fluorescence/variable fluorescence [F0/Fv]) were only affected at 0.5 mg L-1 of Ni. In terms of algal growth, mixture toxicity showed antagonism at low doses and synergism at high doses, with a dose level change greater than the median inhibitory concentration. The independent action model and dose-level-dependent deviation best fit our data. Cadmium and Ni mixtures resulted in a significant increase in cell size and cell complexity, as well as changes in ROS production and Chl a fluorescence, and they did not affect the photosynthetic parameters. Environ Toxicol Chem 2024;00:1-15. © 2024 SETAC.

Histopathology and changes in the expression of metallothioneins, heat shock proteins and inducible nitric oxide synthase in Prochilodus costatus from a neotropical river contaminated by heavy metals

The most recent dam rupture in Brazil released tons of mining tailings into the upper course of the Paraopeba River, affecting this river in an unprecedented way. The present study aimed to evaluate the influence of heavy metals on Prochilodus costatus, an important commercial species in Brazil, four years after the dam colapse. To this end, biomarkers of heavy metals, oxidative stress, and environmental stress were analyzed, and histological analyses of target organs were performed. The results demonstrated critical contamination of fish from the Paraopeba River. Increased expression of Metallothioneins - MTs, Heat Shock Protein - HSP70, and inducible nitric oxide synthase - iNOS, as well as greater rates of histological changes in the liver, spleen, and gonads, were observed in P. costatus. These findings demonstrate that, despite past contamination, the metals present in mining tailings have significantly increased the contamination of the Paraopeba River basin.

PAHs in franciscana dolphins from the Southwestern Atlantic Ocean: Concentration and maternal transfer assessments

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds ubiquitous in the environment and known for their toxic, mutagenic, and carcinogenic effects. These compounds can bioaccumulate in the biota and be transferred through trophic webs. The franciscana dolphin (Pontoporia blainvillei), as top predators, can be an environmental sentinels. Thus, this study aimed to provide data about PAHs concentration in their hepatic tissue collected on the coast of Espírito Santo (Franciscana Management Area, FMA Ia), Rio de Janeiro (FMA IIa), and São Paulo states (FMA IIb), in Southeastern Brazil. PAHs were detected in 86 % of franciscana dolphins (n = 50). The highest ∑PAHsTotal median concentration was reported in FMA Ia followed by FMA IIb and FMA IIa (1055.6; 523.9, and 72.1 ng.g-1 lipid weight, respectively). Phenanthrene was detected in one fetus and two neonates, showing maternal transfer of PAHs in these dolphins. Evaluating PAHs with potential toxic effects is of utmost importance for the conservation of a threatened species.

Estimating four-decadal variations of seagrass distribution using satellite data and deep learning methods in a marine lagoon

Seagrasses are marine flowering plants that inhabit shallow coastal and estuarine waters and serve vital ecological functions in marine ecosystems. However, seagrass ecosystems face the looming threat of degradation, necessitating effective monitoring. Remote-sensing technology offers significant advantages in terms of spatial coverage and temporal accessibility. Although some remote sensing approaches, such as water column correction, spectral index-based, and machine learning-based methods, have been proposed for seagrass detection, their performances are not always satisfactory. Deep learning models, known for their powerful learning and vast data processing capabilities, have been widely employed in automatic target detection. In this study, a typical seagrass habitat (Swan Lake) in northern China was used to propose a deep learning-based model for seagrass detection from Landsat satellite data. The performances of UNet and SegNet at different patch scales for seagrass detection were compared. The results showed that the SegNet model at a patch scale of 16 × 16 pixels worked well, with validation accuracy and loss of 96.3 % and 0.15, respectively, during training. Evaluations based on the test dataset also indicated good performance of this model, with an overall accuracy >95 %. Subsequently, the deep learning model was applied for seagrass detection in Swan Lake between 1984 and 2022. We observed a noticeable seasonal variation in germination, growth, maturation, and shrinkage from spring to winter. The seagrass area decreased over the past four decades, punctuated by intermittent fluctuations likely attributed to anthropogenic activities, such as aquaculture and construction development. Additionally, changes in landscape ecology indicators have demonstrated that seagrass experiences severe patchiness. However, these problems have weakened recently. Overall, by combining remote sensing big data with deep learning technology, our study provides a valuable approach for the highly precise monitoring of seagrass. These findings on seagrass area variation in Swan Lake offer significant information for seagrass restoration and management.

A multi-biomarker approach to verify chronic effects on Eisenia andrei earthworms exposed to tailings from one of the world's largest mining disasters

Mining is of great relevance to the global economy, but its activities are challenging due to socio-environmental impacts. In January 2019, an iron ore tailings dam collapsed in Brumadinho (Minas Gerais, Brazil) releasing 12 × 106 m3 of tailings, causing human losses and devastation around 3.13 × 106 m2 of a watershed. In this context, the present study aimed to investigate the potential toxic effects of tailings from the collapsed dam using earthworms Eisenia andrei as a model organism for terrestrial environments. An extensive set of tests was performed, including behavioral (avoidance), acute (mortality and biomass) and chronic tests, such as biomass, reproduction and cytotoxicity (viability and cell density and change in coelomocyte pattern). The physical-chemical characterization revealed a higher density of the tailings in relation to the control soil, which can result in physical changes, such as soil compaction and surface sealing. Aluminum, Ca, Fe, Hg, Mg, Mn, K, Na and P registered higher concentrations in the tailings compared to the control soil, while Total Nitrogen, Total Organic Carbon and Organic Matter were higher in the natural soil. Based on the avoidance test, an EC50 of 27.18 ± 2.83% was estimated. No lethality was observed in the acute exposure, nor variations in biomass in the acute and chronic assays. However, there was a tendency to reduce the number of juveniles in relation to cocoons in the proportions of 3125; 12.5 and 25%. Significant changes in viability, cell density and pattern of amebocytes and eleocytes were observed up to the 35th day of exposure. A multi-biomarker approach (Integrated Biological Response version 2) indicated concentration-dependent effects and attenuation of cellular changes over time. These are the first results of chronic effects on earthworms exposed to tailings from the B1 dam. Despite being conclusive, we highlight the possible heterogeneity of the tailings and the necessary care in extrapolating the results.

Integrating reverse osmosis to a conventional river water treatment plant as a strategy to produce drinking water after mining dam rupture events: a case study

Incidents of mining dam failure have compromised the water quality, threatening the water supply. Different strategies are sought to restore the impacted area and to guarantee the water supply. One example is water treatment plants that treat high-polluted waters within the required limits for their multiple usages. The current study assesses the integration of reverse osmosis (RO) to a river water treatment plant (RWTP) installed in Brumadinho (Minas Gerais, Brazil) to treat the water from the Ferro-Carvão stream impacted by the B1 dam rupture in 2019. The RWTP started eleven months after the mining dam rupture and is equipped with eight coagulation-flocculation tanks followed by eight pressurised filters. A pilot RO plant was installed to polish the water treated by the RWTP. Water samples were collected at different points of the water treatment plant and were characterised by their physical, chemical, and biological parameters (160 in total). The results were compared with the historical data (1997-2022) to reveal the alterations in the water quality after the rupture event. The compliance with both parameters was only achieved after the RO treatment, which acted as an additional barrier to 30 contaminants. The water quality indexes (WQI) suggested that the raw surface water, even eleven months after the incident, was unfit for consumption (WQI: 133.9) whereas the reverse osmosis permeate was ranked as excellent in the rating grid (WQI: 23.7).

Assessing the quality of constructed technosols enabled holistic monitoring of ecological restoration

The soil quality index (SQI) serves as a general ecological restoration indicator, however, statistics approaches that accurately assess the minimum data set (MDS) for SQI remain susceptible. The present study aims to evaluate the short-term reclamation results at the Ferro-Carvão stream and propose a system for ecological restoration monitoring, by selecting influential attributes and indexing soil quality. We hypothesized that the reclamation activities at the Ferro-Carvão stream, referred to as the "Marco zero" (MZ) area, can bring its soil quality to levels comparable to those of the native area. We collected soil samples at 0-20 and 20-40 cm depths from transects of MZ and reference sites (R1 and R2). Principal component analysis showed the MDS for each soil depth. Permutational analysis of variance, in conjunction with Nonmetric Multidimensional Scaling, exposed relationships between transects of areas. An additive non-linear factorial algorithm allowed SQI assessment. The results indicated a similar soil quality between transects of areas at 0-20 cm depth, whereas a dissimilarity at 20-40 cm. To sum up, reclamation activities allowed MZ-constructed Technosol to present a soil quality similar to native areas. The soil quality assessment at both depths offered insights into reclamation activities' immediate and long-term impacts on the Ferro-Carvão stream. This robust framework effectively monitors ecological restoration progress and guides future efforts in post-mining and post-dam collapse sites.

Assessment of environmental pollution and human health risks of mine tailings in soil: after dam failure of the Córrego do Feijão Mine (in Brumadinho, Brazil)

The dam failure of the Córrego do Feijão Mine (CFM) located in Minas Gerais State, Brazil, killed at least 278 people. In addition, large extensions of aquatic and terrestrial ecosystems were destroyed, directly compromising the environmental and socioeconomic quality of the region. This study assessed the pollution and human health risks of soils impacted by the tailing spill of the CFM dam, along a sample perimeter of approximately 200 km. Based on potential ecological risk and pollution load indices, the enrichments of Cd, As, Hg, Cu, Pb and Ni in soils indicated that the Brumadinho, Mário Campos, Betim and São Joaquim de Bicas municipalities were the most affected areas by the broken dam. Restorative and reparative actions must be urgently carried out in these areas. For all contaminated areas, the children's group indicated an exacerbated propensity to the development of carcinogenic and non-carcinogenic diseases, mainly through the ingestion pathway. Toxicological risk assessments, including acute, chronic and genotoxic effects, on people living and working in mining areas should be a priority for public management and mining companies to ensure effective environmental measures that do not harm human health and well-being over time.

Isolated and combined effects of cobalt and nickel on the microalga Raphidocelis subcapitata

Aquatic organisms are exposed to several compounds that occur in mixtures in the environment. Thus, it is important to investigate their impacts on organisms because these combined effects can be potentiated. Cobalt (Co) and nickel (Ni) are metals that occur in the environment and are used in human activities. To the best of our knowledge, there are no studies that investigated the combined effects of these metals on a freshwater Chlorophyceae. Therefore, this study analyzed the isolated and combined effects of Co and Ni in cell density, physiological and morphological parameters, reactive oxygen species (ROS), carbohydrates and photosynthetic parameters of the microalga Raphidocelis subcapitata. Data showed that Co affected the cell density from 0.25 mg Co L-1; the fluorescence of chlorophyll a (Chl a) (0.10 mg Co L-1); ROS production (0.50 mg Co L-1), total carbohydrates and efficiency of the oxygen evolving complex (OEC) at all tested concentrations; and the maximum quantum yield (ΦM) from 0.50 mg Co L-1. Ni exposure decreased ROS and cell density (0.35 mg Ni L-1); altered Chl a fluorescence and carbohydrates at all tested concentrations; and did not alter photosynthetic parameters. Regarding the Co-Ni mixtures, our data best fitted the concentration addition (CA) model and dose-ratio dependent (DR) deviation in which synergism was observed at low doses of Co and high doses of Ni and antagonism occurred at high doses of Co and low doses of Ni. The combined metals affected ROS production, carbohydrates, ΦM, OEC and morphological and physiological parameters.

Collapse of scallop Nodipecten nodosus production in the tropical Southeast Brazil as a possible consequence of global warming and water pollution

Mollusc rearing is a relevant global socioeconomic activity. However, this activity has faced severe problems in the last years in southeast Brazil. The mariculture scallop production dropped from 51,2 tons in 2016 to 10,2 tons in 2022 in the Baia da Ilha Grande (BIG; Rio de Janeiro). However, the possible causes of this collapse are unknown. This study aimed to analyze decadal trends of water quality in Nodipecten nodosus spat and adult production in BIG. We also performed physical-chemical and biological water quality analyses of three scallop farms and two nearby locations at BIG in 2022 to evaluate possible environmental stressors and risks. Scallop spat production dropped drastically in the last five years (2018-2022: mean ± stdev: 0.47 ± 0.45 million). Spat production was higher in colder waters and during peaks of Chlorophyll a in the last 13 years. Reduction of Chlorophyll a coincided with decreasing spat production in the last five years. Warmer periods (>27 °C) of the year may hamper scallop development. Counts of potentially pathogenic bacteria (Vibrios) and Escherichia coli were significantly higher in warmer periods which may further reduce scallop productivity. Shotgun metagenomics of seawater samples from the five studied corroborated these culture-based counts. Vibrios and fecal indicator bacteria metagenomic sequences were abundant across the entire study area throughout 2022. The results of this study suggest the collapse of scallop mariculture is the result of a synergistic negative effect of global warming and poor seawater quality.

Vibrio alginolyticus growth kinetics and the metabolic effects of iron

IMPORTANCE

Transmission of V. alginolyticus occurs opportunistically through direct seawater exposure and is a function of its abundance in the environment. Like other Vibrio spp., V. alginolyticus are considered conditionally rare taxa in marine waters, with populations capable of forming large, short-lived blooms under specific environmental conditions, which remain poorly defined. Prior research has established the importance of temperature and salinity as the major determinants of Vibrio geographical and temporal range. However, bloom formation can be strongly influenced by other factors that may be more episodic and localized, such as changes in iron availability. Here we confirm the broad temperature and salinity tolerance of V. alginolyticus and demonstrate the importance of iron supplementation as a key factor for growth in the absence of thermal or osmotic stress. The results of this research highlight the importance of episodic iron input as a crucial metric to consider for the assessment of V. alginolyticus risk.

Genotoxic and mutagenic evaluation in Eisenia foetida annelids exposed to iron ore tailings from the region of Brumadinho, MG, Brazil

Soils that have a disproportion of metallic elements due to anthropic activities endanger the terrestrial fauna. This study evaluated whether earthworms (Eisenia foetida) exposed to ore tailings from Brumadinho region presented a higher frequency of genotoxic and mutagenic damages than annelids from a reference area (control). The animals were exposed to substrates containing 0%, 25%, 50%, 75%, and 100% iron mining waste. The results indicated increased DNA damage (p < 0.05), detected by the comet assay at 25% and 50%. There was a three-fold increase in micronuclei in animals on the substrates with the highest concentrations (75% and 100%) [F = 3.095; p = 0.02]. The earthworms lost weight as the percentage of mining waste increased. We concluded that E. foetida presented DNA damage in the contaminated soils of Brumadinho. However, more research is fundamental, once the environmental disaster in Brumadinho was one of the biggest mining catastrophe in Brazil.

Unlocking the potential of microbes: biocementation technology for mine tailings restoration - a comprehensive review

Mine tailings contain finer particles, crushed rocks, dugout-soil, water, and organic and inorganic metals or metalloids, including heavy metals and radionuclides, which are dumped as waste or non-economic by-products generated during mining and mineral processing. These abundant and untreated materials seriously threaten the environment, human health, and biodiversity because of the presence of heavy metals, radionuclides, and associated primary and secondary toxic components, including the risk of tailings dam failures. Biocementation technology, which involves the use of mining microbes to secrete cement-like materials that bind soil particles together, is a promising approach to restore mine tailing sites and reduce their mobility and toxicity. However, there is a lack of literature on the combined interactions among mining microbes, tailings residues, biocementation, and low-carbon cement (LCC) prospects. This comprehensive review article explores the prospects of mining microbes for mine tailings restoration using biocementation technology, the key influencing factors and their impact, mechanisms and metabolic pathways, and the effectiveness of biocementation technology in restoring mine tailings sites. In addition, it reviews the utilization of mine tailings materials as an alternative source of cement or construction materials for LCC technology. Furthermore, this review highlights the important issues, challenges, limitations, and applications of biocementation technology for mine tailings rehabilitation. Finally, it provides insights for future research and implementation of biocementation for mine tailings restoration and utilization of tailing materials in the industrial sector to reduce carbon emissions/footprints and achieve net-zero goals.

Perceptions about massive environmental impacts: a Brazilian study case

The year 2019 brought three such impacts of high socio-environmental proportions in Brazil: the dam collapse in Brumadinho, oil spills on the coast, and fires in the Amazon. We investigated the Brazilian population's perceptions of the country's overall environmental situation, the degree to which Brazilians felt affected by these impacts considering personal and social factors, and the entities they held responsible for these disasters. Through Facebook's social media networks, we disseminated structured online surveys for Brazilian citizens above 18 years. Educational background explained how much the 775 respondents felt affected by the three evaluated events. Age was an explanatory factor for the degree to which the respondents felt affected by the dam collapse, and proximity to the disasters, while income levels were for the dam collapse and the fires in the Amazon. The government, criminal activity, and private companies were considered to be the main responsible for these three impacts. This perception reflects the series of changes in the country's environmental laws and protections that threaten biodiversity and the environment.

Past, present and future trends in the remediation of heavy-metal contaminated soil - Remediation techniques applied in real soil-contamination events

Most worldwide policy frameworks, including the United Nations Sustainable Development Goals, highlight soil as a key non-renewable natural resource which should be rigorously preserved to achieve long-term global sustainability. Although some soil is naturally enriched with heavy metals (HMs), a series of anthropogenic activities are known to contribute to their redistribution, which may entail potentially harmful environmental and/or human health effects if certain concentrations are exceeded. If this occurs, the implementation of rehabilitation strategies is highly recommended. Although there are many publications dealing with the elimination of HMs using different methodologies, most of those works have been done in laboratories and there are not many comprehensive reviews about the results obtained under field conditions. Throughout this review, we examine the different methodologies that have been used in real scenarios and, based on representative case studies, we present the evolution and outcomes of the remediation strategies applied in real soil-contamination events where legacies of past metal mining activities or mine spills have posed a serious threat for soil conservation. So far, the best efficiencies at field-scale have been reported when using combined strategies such as physical containment and assisted-phytoremediation. We have also introduced the emerging problem of the heavy metal contamination of agricultural soils and the different strategies implemented to tackle this problem. Although remediation techniques used in real scenarios have not changed much in the last decades, there are also encouraging facts for the advances in this field. Thus, a growing number of mining companies publicise in their webpages their soil remediation strategies and efforts; moreover, the number of scientific publications about innovative highly-efficient and environmental-friendly methods is also increasing. In any case, better cooperation between scientists and other soil-related stakeholders is still required to improve remediation performance.

Exploring a new approach for assessing the fate and behavior of the tailings released by the Brumadinho dam collapse (Minas Gerais, Brazil)

In 2019, the Brumadinho dam rupture released a massive amount of iron ore mining tailings into the Paraopeba River. Up to now, it remains a public health issue for the local and downstream populations. The present study aims to assess the behavior and fate of metal contamination following the disaster. Using new sampling strategies and up-to-date geochemistry tools, we show that the dissolved metal concentrations (< 0.22 µm cutoff filtration) remained low in the Paraopeba River. Although the tailings present high metal concentrations (Fe, Mn, Cd, and As), the high local background contents of metals and other previous anthropogenic contamination hamper tracing the sediment source based only on the geochemical signature. The Pb isotopic composition coupled with the metals enrichment factor of sediments and Suspended Particulate Matter (SPM) constitutes accurate proxies that trace the fate and dispersion of tailing particles downstream of the dam collapse. This approach shows that 1) The influence of the released tailing was restricted to the Paraopeba River and the Retiro Baixo reservoir, located upstream of the São Francisco River; 2) The tailings' contribution to particulate load ranged from 17 % to 88 % in the Paraopeba River; 3) Other regional anthropogenic activities also contribute to water and sediment contamination of the Paraopeba river.

Environmental risk of tailings pond leachate pollution: Traceable strategy for leakage channel and influence range of leachate

Identifying the leakage channel and the influencing range is essential for controlling the environmental risks of leachate from the tailings pond. The investigation of leachate pollution in tailings pond has the defect of focusing only on the scope of tailings pond in recent studies. This study innovatively built a comprehensive investigation and accurate verification system for leachate leakage of tailings pond integrated with the aeromagnetic survey, ground penetrating radar, hydrochemistry and isotope coupling methods. Geophysical exploration found that among the four fault zones, and the F1 was the channel for leachate to recharge the groundwater 2.53 km away from the tailings pond. The fissures inside the tailings pond were connected with the natural fissures outside, forming a leachate migration channel. The hydrochemistry and isotope characteristics showed that the groundwater far away from the tailings pond were polluted by arsenic containing leachate, which verified the geophysical exploration results. The significant correlation between arsenic and SO2-4 concentration indicated that arsenic in leachate originated from the oxidation release of sulfide minerals (i.e., arsenopyrite). This study sheds light on the comprehensive investigation of leachate leakage in the tailings pond. This development method also provides guidance for environmental risk identification of other contaminated sites.

Brumadinho dam collapse induces changes in the microbiome and the antibiotic resistance of the Paraopeba River (Minas Gerais, Brazil)

The rupture of the Córrego do Feijão dam in Brumadinho (January 25, 2019) caused serious damage to the Paraopeba River and compromised the quality of its waters for human consumption. However, the possible effects of the dam collapse on the river microbiome and its antibiotic resistance profiles are unknown. The present study aims to analyse the possible shifts in microbial diversity and enhancement of antibiotic resistance in the Paraopeba River. To this end, two sampling campaigns (February and May 2019) were performed to obtain water across the entire Paraopeba River (eight sampling locations: Moeda, Brumadinho, Igarapé, Juatuba, Varginha, Angueretá, Retiro Baixo and Três Marias; ~464 km). This sampling scheme enabled determining the effects of the disaster on the river microbiome. Total DNA and microbial isolation were performed with these water samples. The 16S rRNA-based microbiome analyses (n = 24; 2.05 million 16S rRNA reads) showed changes in microbial diversity immediately after the disaster with the presence of metal-indicating bacteria (Acinetobacter, Bacillus, Novosphingobium, and Sediminibacterium). Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) identification of bacterial isolates (n = 170) also disclosed possible indicators of faecal contamination across the Paraopeba (Cloacibacterium, Bacteroides, Feaecalibacterium, Bifidobacterium, Citrobacter, Enterobacter, Enterococcus and Escherichia). Antibiotic resistance increased significantly to ampicillin, ampicillin/sulbactam, amoxicillin/clavulanate, ceftriaxone, and cefalotin among isolates obtained in May after the disaster. The effects of toxic mud on microbiomes were felt at all points sampled up to Anguereta. The ore mud may have exacerbated the growth of different antibiotic-resistant, metal-resistant, and faecal-indicating bacteria in the Paraopeba River.

Monitoring river turbidity after a mine tailing dam failure using an empirical model derived from Sentinel-2 imagery

Sudden failure of a mine tailing dam occurred in the municipality of Brumadinho, Minas Gerais, Brazil, on January 25, 2019. Approximately 12 million cubic meters of mine tailings discharged into the Paraopeba River, producing strong environmental and societal impacts, mainly due to a massive increase in turbidity (occasionally exceeding 50,000 Nephelometric Turbidity Units [NTU] (CPRM 2019). Remote sensing is a well-established tool for quantifying spatial patterns of turbidity. However, a few empirical models have been developed to map turbidity in rivers impacted by mine tailings. Thus, this study aimed to develop an empirical model capable of producing turbidity estimates based on images from the Sentinel-2 satellite, using the Paraopeba River as the study area. We found that river turbidity was most strongly correlated with the sensor's near-infrared band (NIR) (band 8). Thus, we built an empirical single-band model using an exponential function with an (R2 of 0.91) to characterize the spatial-temporal variation of turbidity based on satellite observations of NIR reflectance. Although the role of discharged tailings in the seasonal variation of turbidity is not well understood, the proposed model enabled the monitoring of turbidity variations in the Paraopeba River associated with seasonal resuspension or deposition of mine tailings. Our study shows the capability of single-band models to quantify seasonal variations in turbidity in rivers impacted by mine tailing pollution.

History of tailings dam failure: Impacts on access to safe water and influence on the legislative framework

Tailings dams have been built since 3000 BCE and despite the advancement of construction methods, mainly in the second half of the 21st century, their ruptures were still recorded. The main direct impacts are related to the loss of human lives, impairment of physical structures and changes in water quality. In this review, different dam failure events were critically analyzed considering their social and environmental impacts, besides the gaps in current regulations framework to appropriately charge the companies involved. These aspects differ the current review paper from those currently available, which also present advancements in the discussion of actions taken after the ruptures, the impacts on water quality, and the challenges related to the water supply. It has been noticed a lack of studies and methodologies capable to predict the water quality under scenarios of tailings contamination. Studies covering that aspect would be an important tool for planning emergency responses by stakeholders. With that in mind, the article discloses the pathway toward an effective strategy in scenarios of tailing dam failure that would mitigate the impacts on water quality and guarantee access to safe water.

A partial least squares-path model of environmental degradation in the Paraopeba River, for rainy seasons after the rupture of B1 tailings dam, Brumadinho, Brazil

The present study aimed to investigate the rupture of B1 tailings dam of Córrego do Feijão mine, which drastically affected the region of Brumadinho (Minas Gerais, Brazil). The contamination of water resources reached 155.3 km from the dam site. In the river channel, high concentrations of Mn, Al, As and Fe were detected and correlated to the spillage of the tailings in the river. The presence of the tailings also affected the chlorophyll-a content in the water, as well as the reflectance of riparian forests. With the increase of metal(oid) concentrations above permitted levels, water management authorities suspended the use of Paraopeba River as resource in the impacted areas, namely the drinking water supply to the Metropolitan region of Belo Horizonte. This study aimed to evaluate possible links between tailings distribution, river water quality, and environmental degradation, which worked as latent variables in partial least squares regression models. The latent variables were represented by numerous physical and chemical parameters of water and sediment, measured four times in 22 locations during the rainy season of 2019, in addition to stream flow and to NDVI evaluated in satellite images processed daily. The modeling results suggested a relationship between river flow turbulence and increased arsenic release from sand fractions, as well as desorption of Mn from metal oxides, both representing causes of water quality reduction. They also revealed increasing iron concentrations affecting the forest NDVI (greening), which was interpreted as environmental degradation. The increase of chlorophyll-a concentrations (related with turbidity decreases), as well as the increase of river flows (responsible for dilution effects), seemed to work out as attenuators of degradation. Although applied to a specific site, our modeling approach can be transposed to equivalent dam failures and climate contexts, helping water resource management authorities to decide upon appropriate recovery solutions.

Potentially toxic elements in iron mine tailings: Effects of reducing soil pH on available concentrations of toxic elements

Tailings from iron mining are characterized by high concentrations of iron and manganese oxides, as well as high pH values. With these characteristics, most of the potentially toxic elements (PTE) contained in the tailings are somewhat unavailable. The aim of the present study was to evaluate how a reduction in the pH of iron mine tailings may affect PTE availabilities. The tailings were collected on the banks of the Gualaxo do Norte River (Mariana, MG, Brazil), one of the main areas impacted by the rupture of the Fundão Dam (Barragem de Fundão). A completely randomized experimental design was used, including five pH values (6.4, 5.4, 4.3, 3.7, and 3.4) and five replications. The concentrations of the PTE (Ba, Cr, Cd, Co, Cu, Fe, Mn, Pb, Ni, and Zn) were determined after extraction following different methodologies: USEPA 3051A, DTPA, Mehlich-1, Mehlich-3, and distilled water. A comparison of the available concentrations of the elements in the tailings with those in a soil not impacted by tailings shows that Cr, Cd, Cu, Fe, Mn, Ni, Ba, and Co were higher in the soil impacted by the tailings. The different methods used for evaluating the availability of PTE in the tailings at various pH exhibited the following decreasing order in relation to the quantity extracted: Mehlich-3 > Mehlich-1 > DTPA > distilled water. However, regarding sensitivity to change in pH, the order was DTPA > water > Mehlich-1 > Mehlich-3. The increases in the concentrations of PTE due to the reduction in the pH of the tailings did not lead to concentrations that exceed the limits of Brazilian regulations. The DTPA extractant exhibited higher coefficients of correlation between the PTE concentrations and the pH of the tailings, proving to be suitable for use in areas affected by the deposition of iron mine tailings.

Statistical process control in assessing water quality in the Doce river basin after the collapse of the Fundão dam (Mariana, Brazil)

The process of extracting information from data generated in environmental monitoring programs is often carried out using statistical tools, with Statistical Process Control (SPC) showing great potential for application in environmental monitoring. In November 2015, millions of cubic metres of tailings were dumped into the basin of the River Doce with the collapse of the Fundão dam. A study of the impact of this incident requires new approaches in data monitoring and processing, so it was sought to evaluate, using SPC tools, changes in water quality in the basin of the River Doce following the collapse of the dam. Using process charts and the process capability index (PCI), water quality parameters in the Doce and Carmo rivers were evaluated between 2009 and 2020. There, turbidity has improved since 2018, and Mn since 2016. Control charts showed that by December 2020 dissolved Fe was still not within normal pre-event fluctuation patterns. The PCI value showed that the situation worsened after the event for each of the parameters, with the lowest values for Mn and E. coli. By using a reference period, SPC makes it possible to infer the permanence of the impact of extreme pollution on the waterbody, which can be used in the routine monitoring of water quality in such events.

Influence of clay mineral content on mechanical properties and microfabric of tailings

Clay mineral content has an important influence on the mechanical behaviour of tailings, and this mechanical behaviour significantly affects the stability of tailings dams. X-ray fluorescence (XRF) and X-ray diffraction (XRD) tests were carried out on tailings from three different regions. The chemical and mineral composition of the tailings are analyzed. The strength and failure deformation of the tailings were studied by laboratory triaxial compression tests. The effect of clay content on the behaviour of tailings was investigated. The microfabric of tailings sample was examined with the scanning electron microscope (SEM) and nitrogen adsorption tests. The results show that the confining pressure corresponding to the samples exhibiting strain hardening increases with the increase of the content of clay minerals. The cohesion of tailings increases linearly, and the specific surface area decreases as the content of clay minerals increases. Nitrogen adsorption test results reveal from a microscopic point of view that changes in pore structure are associated with the content of clay minerals. The higher the content of clay minerals is, the higher the proportion of micropores is (aggregated interior). Macroscopically, the overall porosity decreases and the size of the pores increases with clay content, which will directly affect the mechanical properties of tailings.

Mineralogical Fingerprint of Iron Ore Tailings in Paraopeba River Bedload Sediments after the B1 Dam Failure in Brumadinho, MG (Brazil)

The study presents SEM-based automated mineralogy to distinguish between natural sediments and iron ore tailings deposits from the Paraopeba River, after the failure of B1 Dam in Brumadinho, Minas Gerais, Brazil. Samples were obtained from borehole cores drilled over channel bars and banks eight months after the failure. After preliminary facies description, sediments from 54 chosen intervals were subjected to density measurement, X-ray diffraction (XRD), SEM-based automated mineralogy (QEMSCAN) analysis and determination of geochemical major components. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) revealed six main mineral associations governed by different contents and ratios of quartz, kaolinite and hematite. Natural sediments are predominantly composed of mineral associations containing kaolinite, quartz and quartz + hematite with density values ranging from 2.5 to 3.3 g/cm3. Tailings deposits have density values higher than 3.5 g/cm3 and are mainly composed of hematite with occasional occurrences of kaolinite + hematite. Because of geological complexity and historical terrain occupation and usage, geochemical anomalies are common in the Paraopeba River sediments. Our data suggests that mineralogical oriented studies should precede detailed geochemical investigations, to enhance the understanding of the source of such anomalies and the environmental jeopardy associated to the occurrence. In this sense, SEM-based mineralogy has an enormous potential in environment studies.

Regional Distribution and Causes of Global Mine Tailings Dam Failures

Tailings ponds are one of the three major production facilities in metal mines. The volume of tailings increases year by year, but the storage capacity of existing tailings ponds is limited. Therefore, tailings dams must become more fine-grained and larger. The potential hazard they represent should not be underestimated. This paper reveals the causes and regional distribution patterns of 342 tailings dam failures globally from 1915 to 2021 through statistical analysis. It was found that tailings pond failures occur almost every year, with an average of 4.4 accidents/year (1947–2021). The frequency has been gradually increasing in recent years, and most tailings pond failures are directly related to heavy rainfall or earthquakes. The frequency of tailings pond failures was significantly higher in Asia (21.3%) and the Americas (57.9%), especially in China (n = 43) and the United States (n = 107). Causes of tailings pond failures differed among regions. Most tailings pond failures in Asia and Europe were related to hydroclimate, while those in South America were mainly triggered by earthquakes. This study will provide theoretical data for the pre-design as well as the safe and stable operation of global tailings ponds, which will help to prevent global tailings pond failures.

Application of Multispectral Remote Sensing for Mapping Flood-Affected Zones in the Brumadinho Mining District (Minas Gerais, Brasil)

The collapse of the tailing “Dam B1” of the Córrego do Feijão Mine (Brumadinho, Brasil) that occurred in January 2019 is considered a large socio-environmental flood-disaster where numerous people died and the local flora and fauna were seriously affected, including agricultural areas of the Paraopeba River. This study aims to map the land area affected by the flood by using multispectral satellite images. To pursue this aim, Level-2A multispectral images from the European Space Agency’s Sentinel-2 sensor were acquired before and after the tailing dam collapse in the period 2019–2021. The pre- and post-failure event analysis allowed us to evidence drastic changes in the vegetation rate, as well as in the nature of soils and surficial waters. The spectral signatures of the minerals composing the mining products allowed us to highlight the effective area covered by the flood and to investigate the evolution of land properties after the disaster. This technique opens the possibility for quickly classifying areas involved in floods, as well as obtaining significant information potentially useful for monitoring and planning the reclamation and restoration activities in similar cases worldwide, representing an additional tool for evaluating the environmental issues related to mining operations in large areas at high temporal resolution.

Effects of cadmium and cobalt mixtures on growth and photosynthesis of Raphidocelis subcapitata (Chlorophyceae)

Metals occur simultaneously in the environment, and therefore it is important to know their toxicity and mechanism of action when associated with another metal. Furthermore, anthropogenic actions increase their concentrations in the environment where they can interact and undergo transformations that can even increase their toxicity. This study aimed to evaluate the effects of cadmium (Cd) and cobalt (Co), isolated and combined, on the microalgae Raphidocelis subcapitata. Regarding the toxicity of isolated metals, the IC₅₀96 h was 0.08 mg L^-1 of Cd and 0.16 mg L^-1 of Co. Cell density decreased at all concentrations of the Cd tested. The parameters related to cell size, cell complexity and mean cell chlorophyll a (Chl a) fluorescence were significantly affected by both metals. According to species sensitivity curves (SSD), the microalgae R. subcapitata was the second most sensitive organism to Co exposure and the tenth concerning Cd. Metal mixture data were best fitted to the concentration addition (CA) model and dose-ratio dependence (DR) deviation, showing synergism at high concentrations of Co and low concentrations of Cd. Besides that, antagonism was observed at low concentrations of Co and high concentrations of Cd. Photosynthetic performance, assessed by maximum quantum yield (Φ_M) and oxygen evolving complex (OEC), presented antagonism effects for both analyzed parameters. Thus, the mixture of Cd and Co showed synergistic and antagonistic interactions for the parameters analyzed in R. Subcapitata, indicating the importance of understanding the mechanisms of toxicity of metal mixtures in phytoplankton.

Prognosis of metal concentrations in sediments and water of Paraopeba River following the collapse of B1 tailings dam in Brumadinho (Minas Gerais, Brazil)

In January 25, 2019, the B1 dam of Córrego do Feijão mine located in Brumadinho municipality (Minas Gerais, Brazil) collapsed and injected nearly 2.8 Mm³ of iron (Fe)- and manganese (Mn)-rich tailings in the Paraopeba River. This study assessed the contribution of tailings to the contamination of sediments and water by those metals. The dataset was built through daily to weekly samplings executed in the two years following the event, at 27 sites located along the Paraopeba plus 9 sites located at the confluence of main tributaries. The results evidenced a distinct contribution in the sectors "Anomalous" (8.6-63.3 km downstream from the dam) and "Natural" (115.8-341.6 km). The "Anomalous" sector presented large Fe/Al (12.2 ± 6.4) and Mn/Al (0.33 ± 0.19) ratios in sediments, thus being rich in tailings, while the "Natural" sector presented small ratios (2.4 ± 1.0; 0.06 ± 0.03) comparable to the natural sediments. A 500-700 m³/s stream flow discharge in the Paraopeba caused pronounced drops to the Fe/Al and Mn/Al ratios in the "Anomalous" sector, attributed to the mixture of contaminated sediments from the main water course with uncontaminated sediments injected by the tributaries during the event. Non-linear regressions showed Fe/Al and Mn/Al declines in the "Anomalous" sector, related with tailings mobilization downstream. The concentrations of Fe and Al in the sediments correlated positively with the corresponding concentrations in the Paraopeba water, conditioned by raising discharge rates and variations in the water pH. The contribution of tailings to the Fe correlation was demonstrated. No direct relation was established between the Mn concentrations in water and stream discharge, because manganese is associated with fine particles in the tailings that are mobilized to the water column even under low flows. The preliminary results of Seasonal Autoregressive Integrated Moving Average models predicted the return of Paraopeba to a pre-collapse condition in 7-11 years.

Isolation and molecular identification of native As-resistant bacteria: As(III) and As(V) removal capacity and possible mechanism of detoxification

The study of arsenic (As)-resistant microorganisms with high As removal capacity is fundamental for the development of economically sustainable technologies used for the treatment of water contaminated with metalloid. In the current study, four bacterial strains were isolated from As-contaminated water samples of the Xichu region, Mexico. Based on 16S rRNA gene sequencing and phylogenetic analysis of the isolated strains, Rhodococcus gordoniae, Microbacterium hydrocarbonoxydans, Exiguobacterium indicum, and Pseudomonas kribbensis were identified as potential As removal strains. R. gordoniae shows the highest growth capacity in both As(III) and As(V). R. gordoniae, M. hydrocarbonoxydans, and E. indicum removed approximately 81.6, 79.9, and 61.7% of As(III), as well as 77.2, 68.9, and 74.8% of As(V), respectively. P. kribbensis removed only about 80.2% of As(V). This study contributes to the possible detoxification mechanisms employed by these bacteria. Such insight could be crucial in the successful implementation of in situ bioremediation programs using these little-known bacteria.

Manganese-Induced Neurotoxicity through Impairment of Cross-Talk Pathways in Human Neuroblastoma Cell Line SH-SY5Y Differentiated with Retinoic Acid

Manganese (Mn) is an important element; yet acute and/or chronic exposure to this metal has been linked to neurotoxicity and neurodegenerative illnesses such as Parkinson’s disease and others via an unknown mechanism. To better understand it, we exposed a human neuroblastoma cell model (SH-SY5Y) to two Mn chemical species, MnCl₂ and Citrate of Mn(II) (0–2000 µM), followed by a cell viability assay, transcriptomics, and bioinformatics. Even though these cells have been chemically and genetically modified, which may limit the significance of our findings, we discovered that by using RA-differentiated cells instead of undifferentiated SH-SY5Y cell line, both chemical species induce a similar toxicity, potentially governed by disruption of protein metabolism, with some differences. The MnCl₂ altered amino acid metabolism, which affects RNA metabolism and protein synthesis. Citrate of Mn(II), however, inhibited the E3 ubiquitin ligases–target protein degradation pathway, which can lead to the buildup of damaged/unfolded proteins, consistent with histone modification. Finally, we discovered that Mn(II)-induced cytotoxicity in RA-SH-SY5Y cells shared 84 percent of the pathways involved in neurodegenerative diseases.

Mercury Concentrations in Four Marine Fishery Resources from Rio de Janeiro Coast, SW Atlantic, and Potential Human Health Risk Via Fish Consumption

Mercury (Hg) contamination has caused ecological and socioeconomic problems worldwide. One of the main Hg contamination routes by the human populations is through fish ingestion. Herein, we analyzed the total Hg concentrations (THg) in highly consumed marine fish species: Brazilian flathead Percophis brasiliensis, Atlantic bigeye Priacanthus arenatus, Stripped weakfish Cynoscion guatucupa, and Jamaica weakfish C. jamaicensis. The specimens were collected from fishing landings off the Rio de Janeiro, SW Atlantic. Additionally, we calculate the estimated weekly intakes (EWI) and the maximum amount of fish (MAF) that can be safely ingested, both based on the provisional tolerable weekly intake (PTWI). The highest THg concentrations were recorded in P. brasiliensis with a mean of 340.59 μg/kg (dry weight) and the lowest in P. arenatus (115.75 μg/kg). THg concentrations were positively related to the δ¹⁵N ratios indicating an increase in contamination with trophic level. All samples showed THg concentrations below the established limits by Brazilian and international regulation. Hg intake via human fish consumption does not exceed the PTWI. The EWI varied from 1.41% (P. arenatus size class I) to 11.52% (P. brasiliensis class II) of the PTWI, while the estimated EWI for "fish consumers" varied between 8.35 and 68.07% PTWI. The MAF estimated for an adult (70 kg) could safely consume between 1277.85 and 7075.50 g/week. This study is an important baseline for monitoring and future comparisons. Therefore, it is important to maintain monitoring of mercury levels in fish species in different marine regions, especially those species most consumed by humans.

Exploring the Potential for Utilization of Medium and Highly Sulfidic Mine Tailings in Construction Materials: A Review

Medium and highly sulfidic tailings are high-volume wastes that can lead to severe environmental damage if not properly managed. Due to the high content of sulfide minerals, these tailings can undergo weathering if put in contact with oxygen and water, generating acid mine drainage (AMD). The moderate-to-high sulfide content is also an important technical limitation for their implementation in the production of construction materials. This paper reviews the use of sulfidic tailings as raw material in construction products, with a focus on cement, concrete, and ceramics. When used as aggregates in concrete, this can lead to concrete degradation by internal sulfate attack. In building ceramics, their implementation without prior treatment is undesirable due to the formation of black reduction core, efflorescence, SOx emissions, and their associated costs. Moreover, their intrinsic low reactivity represents a barrier for their use as supplementary cementitious materials (SCMs) and as precursors for alkali-activated materials (AAMs). Nevertheless, the production of calcium sulfoaluminate (CSA) cement can be a suitable path for the valorization of medium and highly sulfidic tailings. Otherwise difficult to upcycle, sulfidic tailings could be used in the clinker raw meal as an alternative raw material. Not only the SO3 and SiO2-rich bulk material is incorporated into reactive clinker phases, but also some minor constituents in the tailings may contribute to the production of such low-CO2 cements at lower temperatures. Nevertheless, this valorization route remains poorly explored and demands further research.

The Effects of Internal Erosion on the Physical and Mechanical Properties of Tailings under Heavy Rainfall Infiltration

The stability of tailings dam will be affected by the internal erosion under unsteady seepage caused by heavy rainfall infiltration which changes the physical and mechanical properties of tailings. In this paper, the hydraulic sedimentary model was established to investigate the effects of dry beach slope on the sedimentary characteristics of tailings in upstream tailings dam, and the results indicated that the dry beach with a larger slope has a more obvious stratification of tailings. Additionally, the sand column model was built to investigate the effects of internal erosion on the physical and mechanical properties of sedimentary tailings under unsteady seepage, and the results indicated that the migration of fine-grained tailings was caused by internal erosion increases the permeability and reduces the shear strength of the tailings. After internal erosion of tailings under heavy rainfall in 50 years return period for 24 h, the average particle size of downstream tailings (sample DT), midstream tailings (sample MT), and upstream tailings (sample UT) increased by 6.4%, 12.0%, and 2.4%, respectively, the hydraulic conductivity of the samples DT, MT, and UT increased by 27.2%, 17.9%, and 15.3%, respectively, and the shear strength of each samples decreased by 20.9%, 15.1%, and 12.4%, respectively.

Failure risk of brazilian tailings dams: a data mining approach

This paper proposes the use of a hybrid method that combines Biased Random Key Genetic Algorithm (BRKGA) with a local search heuristic to separate Brazilian tailing dam data into groups. The goal was identifying dams similar to Fundão and B1 failed dams. The groups were created by solving the clustering problem by BRKGA. The clustering problem consists in separating a set of objects into groups such that members of each group are similar to each other. The data was composed by 427 dams, with the actual 425 dams of Brazilian Register of Tailing Dams and the two Brazilian failed dams from the last years. Computational experiments considering real data available are presented to demonstrate the efficacy of the proposed method producing feasible solutions. Thus, it is expected that the good results can be applied in the identification of tailings dams with risk potentials, assisting in the identification of these dams.

Application of remote sensing in environmental impact assessment: a case study of dam rupture in Brumadinho, Minas Gerais, Brazil

The collapse of mining tailing dams in Brumadinho, Minas Gerais, Brazil, that occurred in 2019 was one of the worst environmental and social disasters witnessed in the country. In this sense, monitoring any impacted areas both before and after the disaster is crucial to understand the actual scenario and problems of disaster management and environmental impact assessment. In order to find answers to that problem, the aim of this study was to identify and analyze the spatiality of the impacted area by rupture of the tailing dam of the Córrego do Feijão mine in Brumadinho, Minas Gerais, by using orbital remote sensing. Land use and land occupation, phytoplankton chlorophyll-a, water turbidity, total suspended solids on water, and carbon sequestration efficiency by vegetation (CO₂Flux) were estimated by orbital imagery from the Landsat-8/OLI and MSI/Sentinel-2 sensors in order to assess the environmental impacts generated by the disaster. Data were extracted from spectral models in which the variables that best demonstrated the land use variation over the years were sought. Mean comparison by t-test was performed to compare the time series analyzed, that is, before and after the disaster. Through the analysis of water quality, it was observed that the environmental impact was calamitous to natural resources, especially water from Córrego do Feijão.

In Silico Target Prediction of Overexpressed microRNAs from LPS-Challenged Zebrafish (Danio rerio) Treated with the Novel Anti-Inflammatory Peptide TnP

miRNAs regulate gene expression post-transcriptionally in various processes, e.g., immunity, development, and diseases. Since their experimental analysis is complex, in silico target prediction is important for directing investigations. TnP is a candidate peptide for anti-inflammatory therapy, first discovered in the venom of Thalassophryne nattereri, which led to miRNAs overexpression in LPS-inflamed zebrafish post-treatment. This work aimed to predict miR-21, miR-122, miR-731, and miR-26 targets using overlapped results of DIANA microT-CDS and TargetScanFish software. This study described 513 miRNAs targets using highly specific thresholds. Using Gene Ontology over-representation analysis, we identified their main roles in regulating gene expression, neurogenesis, DNA-binding, transcription regulation, immune system process, and inflammatory response. miRNAs act in post-transcriptional regulation, but we revealed that their targets are strongly related to expression regulation at the transcriptional level, e.g., transcription factors proteins. A few predicted genes participated concomitantly in many biological processes and molecular functions, such as foxo3a, rbpjb, rxrbb, tyrobp, hes6, zic5, smad1, e2f7, and npas4a. Others were particularly involved in innate immunity regulation: il17a/f2, pik3r3b, and nlrc6. Together, these findings not only provide new insights into the miRNAs mode of action but also raise hope for TnP therapy and may direct future experimental investigations.

Spectro-temporal analysis of the Paraopeba River water after the tailings dam burst of the Córrego do Feijão mine, in Brumadinho, Brazil

Remote sensing is an important tool for environmental assessment, especially in the event of disasters such as the tailings dam burst at the Córrego do Feijão mine, located in the Paraopeba River basin, Brazil. Thus, this study aimed to carry out a spectro-temporal analysis of the Paraopeba River water given the dam burst, using multispectral images from the MSI sensor onboard Sentinel-2 satellites. For this analysis, sections along the river were defined by the creation of buffers, with 10-km intervals each, starting from the origin of the burst. For each section, the average visible to near-infrared (NIR) reflectance values per band and the Normalized Difference Water Index (NDWI) were obtained. We found that the red edge and NIR bands (B5, B6, B7, B8, and B8A) showed higher reflectance values when compared to the visible bands in the months immediately after the disaster, especially in the first 20 km. In these months, negative NDWI values were also found for almost all sections downstream, demonstrating the large volume of mining tailings in the Paraopeba River. The seasonal variation of the observed values indicates the resuspension of the material deposited at the river bottom with the beginning of the rainy season. Finally, we highlight the usefulness of the MSI/Sentinel-2 red edge and NIR bands for further studies on the monitoring from space of water bodies subjected to contamination by large amounts of mud with iron ore tailings and contaminants, as occurred in the state of Minas Gerais, southeastern Brazil.

On the effects of iron ore tailings micro/nanoparticles in embryonic and larval zebrafish (Danio rerio)

Iron ore tailings (IOT) represent a major problem in the mining industry worldwide due to large volumes of waste disposed in mine sites. IOT are exposed to the environment and subjected to wind and water dispersion, even under non-catastrophic scenarios as dam collapses, and the effects of these particles to the biota are still mostly unknown. This work aimed to prepare and to characterize a suspension containing the finest (micro/nano range) particles of IOT and to evaluate its effects on development and behavior of zebrafish (Danio rerio), at both embryonic and larval stages. IOT suspension comprised 37 mg L^-1 of a multi-mineral material mainly composed by hematite and quartz, in a size-range of 33-1400 nm. Regarding in vivo toxicological assays, no robust alterations were recorded in functional, morphological and behavioral end-points analyzed, although a significant adhesion of IOT particles on zebrafish chorion was observed, without a prejudice of embryo hatching. Under applied conditions, iron ore particles did not present harmful effects to the initial stages of zebrafish development, and the particle size range and potential interactions with SiO₂ content might be behind such effect.

From sinks to sources: The role of Fe oxyhydroxide transformations on phosphorus dynamics in estuarine soils

The availability of phosphorus (P) in estuarine ecosystems is ultimately controlled by the nature of interactions between dissolved P and the soil components (e.g., soil minerals), especially iron (Fe) oxyhydroxides. P retention on Fe oxyhydroxides and its subsequent availability depends on mineral crystallinity and susceptibility to dissolution. However, in estuarine soils, geochemical conditions (e.g., redox oscillation and high soil organic matter content) may alter the fate of P and decrease the environmental quality of estuarine waters. The large input of Fe-rich tailings into the Rio Doce Estuary in Brazil in 2015 after a rupture of a Fe ore tailings dam (i.e., "Mariana mine disaster") offers a unique framework to evaluate the Fe oxyhydroxides role in P availability in estuarine soils, their potential effects on the cycling of P and eutrophication. We observed a significant correlation between Fe minerals and the P content in the estuary soils, suggesting that P enrichment was promoted by the deposited Fe-rich tailings. Adsorption isotherm curves indicated that mine tailings had a strong affinity for P due to presence of crystalline Fe oxyhydroxides in the tailings. Significant losses of Fe (62%) and P (56%) from the estuarine soil was observed two years after the initial impact and in response to redox conditions oscillations. Additionally, the content of high crystallinity Fe oxyhydroxides decreased significantly, whereas that of low crystallinity Fe oxyhydroxides showed an increase over time. These changes were associated with the dissimilatory Fe reduction, which led an increase in the concentrations of readily available P (2015: 2.30 ± 0.41 mg kg^-1; 2017: 3.83 ± 1.82 mg kg^-1; p < 0.001) in the studied soils. Moreover, in 2017, the dissolved P content exceeded the recommended environmental safety limits by five times. Our results indicate that Fe oxyhydroxides are a continuous source of dissolved P for the ecosystem, and Fe-rich tailings deposited in the estuarine ecosystem may be linked to a potential eutrophication.

Negative impacts of mining on Neotropical freshwater fishes

Abstract Mining activities have significantly affected the Neotropical freshwater ichthyofauna, the most diverse in the world. However, no study has systematized knowledge on the subject. In this review, we assembled information on the main impacts of mining of crude oil, gold, iron, copper, and bauxite on aquatic ecosystems, emphasizing Neotropical freshwater fishes. The information obtained shows that mining activities generate several different disturbances, mainly via input of crude oil, metals and other pollutants, erosion and siltation, deforestation, and road construction. Mining has resulted in direct and indirect losses of fish diversity in several Neotropical waterbodies. The negative impacts on the ichthyofauna may change the structure of communities, compromise entire food chains, and erode ecosystem services provided by freshwater fishes. Particularly noteworthy is that mining activities (legal and illegal) are widespread in the Neotropics, and often located within or near protected areas. Actions to prevent and mitigate impacts, such as inspection, monitoring, management, and restoration plans, have been cursory or absent. In addition, there is strong political pressure to expand mining; if – or when – this happens, it will increase the potential of the activity to further diminish the diversity of Neotropical freshwater fishes.

Mineralogical and Geochemical Characterization of Gold Mining Tailings and Their Potential to Generate Acid Mine Drainage (Minas Gerais, Brazil)

For more than 30 years, sulfide gold ores were treated in metallurgic plants located in Nova Lima, Minas Gerais, Brazil, and accumulated in the Cocoruto tailings dam. Both flotation and leaching tailings from a deactivated circuit, as well as roasted and leaching tailings from an ongoing plant, were studied for their acid mine drainage potential and elements’ mobility. Detailed characterization of both tailings types indicates the presence of fine-grain size material hosting substantial amounts of sulfides that exhibit distinct geochemical and mineralogical characteristics. The samples from the ongoing plant show high grades of Fe in the form of oxides, cyanide, and sulfates. Differently, samples from the old circuit shave higher average concentrations of Al (0.88%), Ca (2.4%), Mg (0.96%), and Mn (0.17%), present as silicates and carbonates. These samples also show relics of preserved sulfides, such as pyrite and pyrrhotite. Concentrations of Zn, Cu, Au, and As are higher in the tailings of the ongoing circuit, while Cr and Hg stand out in the tailings of the deactivated circuit. Although the obtained results show that the sulfide wastes do not tend to generate acid mine drainage, leaching tests indicate the possibility of mobilization of toxic elements, namely As and Mn in the old circuit, and Sb, As, Fe, Ni, and Se in the tailings of the plant that still works. This work highlights the need for proper management and control of tailing dams even in alkaline drainage environments such as the one of the Cocoruto dam. Furthermore, strong knowledge of the tailings’ dynamics in terms of geochemistry and mineralogy would be pivotal to support long-term decisions on wastes management and disposal.

Experimental Study of Mesostructure Deformation Characteristics of Unsaturated Tailings with Different Moisture Content

A portion of the accumulated tailings in a tailings pond exhibits an unsaturated state. The mechanical properties of unsaturated tailings affect the safety and stability of tailings dams. To investigate the effect of moisture content on the deformation characteristics of unsaturated tailings in the mesoscale, a special testing apparatus is applied to experimentally study the settlement deformation and mesostructure evolution of unsaturated tailings under continuous load. The results show that the mesostructure deformation of unsaturated tailings with different moisture contents under load is the same and can be divided into four stages: pore compression, elastic deformation, structure change, and further compaction. However, the critical pressures of the four stages are significantly different; there is an optimal moisture content corresponding to the maximum deformation resistance. Moreover, the influence of the liquid bridge regime on the mesostructure deformation of unsaturated tailings is discussed in this paper.

Occurrence and abundance of clinically relevant antimicrobial resistance genes in environmental samples after the Brumadinho dam disaster, Brazil

On January 25th 2019, the structure damming a pond containing ore mining wastes and iron burst at Brumadinho City, Brazil. About 11.7 million m³ of a tailings-mud mixture was released from the dam, causing destruction along 300 km of the Paraopeba River toward the São Francisco River. The environments with a high content of metals may provide a suitable environment for horizontal gene transfer, including antimicrobial resistance genes (ARGs). Therefore, this study aimed to detect and quantify clinically relevant ARGs in environmental samples after the Brumadinho dam disaster. Soil, sediment, and water samples were collected within 300 km of the Brumadinho dam disaster at unaffected and affected sites. Physical-chemical parameters of water samples were measured. Total DNA was extracted and 65 clinically relevant ARGs were researched by PCR. The most prevalent ARGs were selected for real-time quantitative PCR analysis. The average of the physical-chemical parameters was higher in the affected sites when compared to the unaffected sites, especially turbidity, concentration of Fe and Al. A total of 387 amplicons from 29 ARGs were detected, which confer resistance to β-lactams, quinolones, aminoglycosides, tetracyclines, sulphonamides, phenicols, macrolides, glycopeptides, and polymyxins, including extended-spectrum β-lactamases-encoding genes, and mcr-7.1. The sul1 gene had higher total concentrations than bla_TEM, tetB and qnrB in the environmental samples, and the diversity and abundance of ARGs increased at the sites affected by the Brumadinho dam disaster. Therefore, we point out that the contamination by the Brumadinho dam disaster tailings resulted in an increase in the amount and abundance of ARGs in the environment.

Metal concentrations and biological effects from one of the largest mining disasters in the world (Brumadinho, Minas Gerais, Brazil)

The rupture of the Brumadinho mining tailings dam in Brazil is considered one of the largest mining disasters in the world, resulting in 244 deaths and 26 missing people, in addition to the environmental consequences. The present study aims to evaluate the concentrations of multiple elements and the biological effects on water and sediments of the Paraopeba River after the Brumadinho Dam rupture. The tailings are formed by fine particulate material with large amounts of Fe, Al, Mn, Ti, rare earth metals and toxic metals. In the water, the levels of Fe, Al, Mn, Zn, Cu, Pb, Cd and U were higher than those allowed by Brazilian legislation. In the sediments, Cr, Ni, Cu and Cd levels were higher than the established sediment quality guidelines (TEL-NOAA). The differences in metal concentrations in the water and sediments between the upstream and downstream sides of the dam illustrate the effect of the tailings in the Paraopeba River. Toxicological tests demonstrated that the water and sediments were toxic to different trophic levels, from algae to microcrustaceans and fish. The fish exposed to water and sediments containing mine ore also accumulated metals in muscle tissue. This evaluation emphasizes the necessity of long-term monitoring in the affected area.

Revealing Tropical Technosols as an Alternative for Mine Reclamation and Waste Management

This study was based on the premise that Technosols constructed under tropical conditions are a valuable tool for inexpensive mine reclamation programs. These anthropogenic soils are still poorly studied in Brazil and are not recognized by the Brazilian Soil Classification System. Given the importance of mining to the Brazilian economy (the sector accounts for 20% of all products exported and 5% of the gross domestic product), there is an urgency to properly manage the large amount of waste produced. For this purpose, we suggest the use of Technosols as a strategy to overcome both land degradation and waste production by presenting a successful case of mine rehabilitation combining limestone wastes and tropical grasses. We show that Technosols constructed from the mine spoils can develop into soils suitable for agriculture in a few years, promoting land reclamation and producing food and energy. These soils are also valuable resources that can provide important ecosystem services, such as organic carbon storage.