Early evidences of niche shifts in estuarine fishes following one of the world's largest mining dam disasters

Long-term trends in the functional structure of estuarine fish assemblages in a subtropical estuary and its relationships with local environmental variability, man-made changes, and climatic drivers

Climate and anthropogenic impacts are prevalent in marine and estuarine ecosystems. Rapid environmental changes have altered biological diversity and the ecological services associated with ecosystems around the world. The consequences of these impacts on estuarine ecosystems are worrying, given that estuaries are essential habitats for maintaining the diversity of species functions, as they act as sources for larger ecosystems through the recruitment and replacement of species. Through long-term standardized monitoring (1996-2019), we evaluated the temporal variability of the functional structure of fish species in a subtropical estuary using Principal Component Analysis (PCA), and their relationship with environmental, climatic, and anthropogenic variables using Generalized Additive Models (GAM). We investigate the hypothesis that natural disturbances associated with El Niño events and anthropogenic ones related with changes in the estuary morphology will lead to a decrease in the diversity of functions of the fish assemblage in the Patos Lagoon Estuary in south Brazil (32°S). Our findings suggest an overall downward trend in the fish functional structure, especially in the second half (2006-2019) of the time series, which seems to be associated with a combination of abiotic effects (salinity and temperature), global climate phenomena (ENSO phases) and anthropogenic impacts (changes in the morphology of the estuarine mouth and its connection with the sea). These findings rise concern considering the current climate change scenario, where phenomena such as El Niño may become more frequent and intense. Therefore, the evidence from this study suggests that extreme natural climatic events in synergy with anthropogenic disturbances may imply biodiversity losses over time and, consequently, loss of ecosystem processes in a subtropical estuary.

Gobionellus stomatus Starks 1913 (Oxudercidae: Gobionellinae): range extension for the coastal zone of the Brazilian Amazon region

Gobionellus stomatus, a fish species endemic to Brazil, was previously known to occur from the State of Piauí to the State of Rio Grande do Sul. Here we present the first record of this species for the State of Maranhão, specifically for the Upaon-Açu island, extending its distribution further west, to the coastal zone of the Amazon region. This species inhabits estuarine ecosystems susceptible to environmental pressures, such as pollution and the introduction of non-native species. Despite G. stomatus being classified as of least concern for conservation, it is crucial to highlight potential risks associated with human activities in these environments, emphasizing the importance of preservation measures to mitigate future impacts on the populations of this species, as well as of other estuarine gobies.

Assessing the reclamation of a contaminated site affected by the Fundão dam tailings trough phytoremediation and bioremediation

The rupture of the Fundão dam (Brazil) spread tailings contaminated with sodium and ether-amine into the Doce River Basin. Aiming at rehabilitating a contaminated riparian site, phytoremediation with native species of the Atlantic Forest was performed under four treatments: ES-1: physical remediation (sediment scraping) + chemical remediation (organic matter) + bioremediation (double inoculation with the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis and the plant growth-promoting bacteria Bacillus subtilis); ES-2: chemical remediation + bioremediation; ES-3: physical remediation + chemical remediation; ES-4: chemical remediation. Ether-amine and sodium contents, plant growth and, soil quality parameters were compared among treatments and relative to preserved and degraded sites. Two years after planting, the outstanding plant growth was attributed to the phytoremediation of ether-amine and ammonium, followed by a significant increase in soil microbial biomass (Phospholipid fatty acids-PLFAs), particularly the Gram+ bacteria and total fungi but not AMF, whose response was independent of the inoculation. While sodium and ether-amine declined, soil K, P, NO3- contents, dehydrogenase and acid phosphatase activities, cation exchange capacity (CEC) and soil aggregation increased, especially in ES-1. Thus, such remediation procedures are recommended for the restoration of riparian areas affected by the Fundão tailings, ultimately improving sediment fertility, aggregation and stabilization.

Food web structure of fish communities of Doce River, 5 years after the Fundão dam failure

The rupture of the Fundão dam is considered the largest mining failure in history, which had a particularly detrimental impact on fish populations, as the mud from the ore tailings significantly altered the water quality and habitat of Doce River basin. This study aimed to assess the trophic structure of fish communities in areas impacted and not impacted by the dam rupture in the Doce River basin. To evaluate the food web structure, community-wide trophic niche, and trophic positions of fish, stable isotopes of carbon (δ13C) and nitrogen (δ15N) were utilized across ten sites (seven impacted and three control). In general, fish appeared to assimilate resources such as invertebrates, algae, and periphyton, although the importance of each resource varied among sites. The site closest to the dam rupture exhibited a more simplified trophic structure compared to the control sites and those nearer the river mouth. In this site, most fish species occupied a similar trophic position. Trophic niches also exhibited the greatest dissimilarity between the site closest to the dam failure and those farther away from it, with an expansion of trophic niche breadth observed with an increase in the distance from the dam rupture. Our study provided valuable insights into the trophic structure of fish communities within the Doce River basin, shedding light on the trophic ecology of the 59 fish species investigated. We also emphasize the importance of our study for future assessments of ore tailings dam failure disasters and evaluating the effectiveness of mitigation measures for Doce River basin recovery.

Long-term impacts on estuarine benthic assemblages (2015-2020) after a mine tailing spill in SE Brazil

The Rio Doce estuary was critically impacted in 2015 by the world's largest mining tailing spill, with still unclear long-term effects on the aquatic biota. Here we present a long-term (2015 to 2020) assessment of estuarine benthic assemblages, where we demonstrate that despite a decline in the absolute concentrations of potentially toxic elements; sediment contamination is still above pre-impact conditions. The presence of these contaminants is likely responsible for a continued low habitat quality for the benthic fauna, characterized by a reduction of 96 % of the macroinvertebrate density and persistent change in the benthic assemblage composition. Our study supports previous work indicating the long-term nature of pollution impacts in estuaries, and demonstrate that although water quality levels were quickly adequate under regulatory terms, they largely lack significance to the overall ecosystem health assessment, as they are not related to the recovery of bottom- dwelling assemblages in estuarine ecosystems.

Doce river mining tailings can be an influencing factor in loggerhead turtles reproductive success in Brazil

In November 2015, a tailings dam ruptured and affected the second largest nesting site of loggerhead sea turtles in Brazil. This study aimed to evaluate the reproductive success, and trace elements in female's plasma, freshly laid eggs, unhatched eggs, and dead hatchlings of loggerhead turtles that nest in the coastal area exposed to the mining waste (Povoação, Espírito Santo state) and compare them with animals from an area that was not affected by the tailings (Praia do Forte, Bahia state). Plasma concentrations of As, Cd, Cr, Fe, and Zn were significantly higher in samples from Povoação in comparison to turtles from Praia do Forte. In Povoação, unhatched eggs and dead hatchlings had higher As, Cu, Hg, Mn, and Zn concentrations than freshly laid eggs, and trace elements correlated with the hatching and emergence success. Our findings suggest that the higher concentrations of some metals may influence the incubation period and reproductive success of loggerheads in the affected area.

Impacts of mining pollution on coastal ecosystems: is fish body condition a reliable indicator?

Identifying reliable biological indicators is fundamental to efficiently assess human impacts on biodiversity and to monitor the outcomes of management actions. This study investigates whether body condition is an appropriate indicator of putative effects from iron ore mining tailings on marine fishes, focusing on the world's largest mining disaster - known as the Mariana disaster, in Brazil. Eight species were used to test the hypothesis that individuals inhabiting an area severely impacted by tailings have reduced body condition in comparison to those in control areas near (<60 km) and distant (>120 km) from the impact site. Contrary to our prediction, no significant difference in condition was detected between the impacted area and both near and distant controls in seven of the eight species. The results indicate that body condition, as measured by the scaled mass index, has limited applicability as indicator of impact from mining pollution on the fishes analysed. Hypotheses that could explain our findings are proposed, including nutrient provisioning from continental drainage that could indirectly influence fish condition and compensate for the deleterious effects of mining pollution.

Possible niche compression and individual specialization in Pacific Arctic beluga (Delphinapterus leucas) from the 19th to 20th century

Cetaceans have shown a potential to be used as sentinel species for tracking environmental change in marine ecosystems, yet our assessment of change is typically limited to recent decades and lacks ecological baselines. Using historical museum specimens, we compared community niche metrics and degree of individual dietary specialization in groups of Pacific Arctic beluga (Delphinapterus leucas) from the 1800s (n = 5) to 1900s (n = 10) using stable carbon and nitrogen isotopes drilled from teeth. Beluga occupied a broader trophic niche and demonstrated a higher degree of individual specialization in the 1800s than in the 1900s. The cause of this shift is difficult to confirm given long timescales and constraints of specimen-based research but could indicate changes in the prey base or competition. The scale and nature of this detected shift provide perspective for continued research on these climate-vulnerable species.

Remote sensing monitoring of mining tailings in the fluvial-estuarine-coastal ocean continuum of the Lower Doce River Valley (Brazil)

Water clarity is a key parameter of aquatic ecosystems impacted by mining tailings. Tracking down tailings dispersion along the river basin requires a regional monitoring approach. The longitudinal fluvial connectivity, river-estuary-coastal ocean, and the lateral connectivity, river-floodplain-alluvial lakes are interconnected by hydrological flows, particularly during high fluvial discharge. The present study aims to track the dispersal of iron ore tailing spill, from the collapse of the Fundão dam (Mariana, MG, Brazil), on November 5, 2015, in the Lower Doce River Valley. A semi-empirical model of turbidity data, as a water clarity proxy, and multispectral remote sensing data (MSI Sentinel-2), based on different hydrological conditions and well-differentiated water types, yielded an accuracy of 92%. Five floods (> 3187m³ s^-1) and five droughts (< 231m³ s^-1) events occurred from 2013 to 2020. The flood of January 2016 occurred one month after the mining slurries reached the coast, intruding tailings on some alluvial and coastal plain lakes with highly turbid waters (> 400 NTU). A fluvial plume is formed in the inner shelf adjoining the river mouth on high flow. The dispersion of river plume was categorized as plume core (turbidity > 200 NTU), plume core and inner shelf waters (100-199 NTU), other shelf water (50-99 NTU), and offshore waters (< 50 NTU). Fluvial discharge and local winds are the main drivers for river plume dispersion and transport of terrigenous material along the coast. This work provides elements for evaluating the impact of mining tailings and an approach for remote sensing regional monitoring of surface water quality.

Ecotoxicological impacts of the Fundão dam failure in freshwater fish community: Metal bioaccumulation, biochemical, genetic and histopathological effects

This study investigates the ecotoxicological impacts of the Fundão dam rupture, one of the major environmental disaster that occurred in Brazil and in the world mining industry history, through multi-biomarkers responses and metals bioaccumulation in the fish community of different trophic levels. Specimens of the fishes (omnivorous/herbivorous and carnivorous) were collected along the Doce River channel and its affluent Guandú River, and in different lakes and coastal lagoons adjacent to the river channel, in the Espirito Santo State, Southeast of Brazil. Four sampling collections were carried out over two years (2018 to 2020, during dry and rainy seasons). For both trophic groups the biomarkers responses indicated physiological alterations related to metals exposure and showed strong seasonal variations. The principal component analysis and integrated biomarker response index showed that DNA damage and lipid peroxidation were more associated with dry season 2 (Sep/Oct 2019) and the oxidative damage in proteins, metallothioneins concentration and the activity of superoxide dismutase in the gills showed a greater association with rainy season 2 (Jan/Feb 2020). On the other hand, the enzymes of energy metabolism, catalase and histological damage in the liver and the gills, were more associated with the dry and rainy campaigns of the first year of monitoring. The multivariate approach also suggested a temporal intensification in the bioaccumulation of metals and biological effects in the lacustrine environments. Thus, these results demonstrate that the release of mineral residues from the rupture of the Fundão mine dam affects the health status of the fish from the Doce River basin, provoking metals bioaccumulation, hepatic and branchial damage in the fish besides inducing of enzyme activity related to metal contamination, even four years after the rupture.

Franciscana dolphins, Pontoporia blainvillei, as environmental sentinels of the world's largest mining disaster: Temporal trends for organohalogen compounds and their consequences for an endangered population

On November 5th, 2015, the Fundão dam collapsed in Minas Gerais, southeastern Brazil, releasing millions of cubic meters of mud containing mining residue into the Doce River. Two weeks later, the mud arrived to the marine environment, triggering changes in franciscana dolphin habitat, Pontoporia blainvillei, from Franciscana Management Area Ia. This is an isolated population of the most endangered cetacean species in the South Atlantic Ocean. Organohalogen compounds (OHCs) may pose a threat to this endangered population because of their endocrine disrupting properties. Hence, this study sought to determine if there were differences in the bioaccumulation profile of OHC (PCBs, DDTs, Mirex, HCB, HCHs, PBDEs, PBEB, HBBZ and MeO-BDEs) in franciscana dolphins before and after dam collapse and to build a temporal trend. Blubber of 33 stranded individuals was collected in Espírito Santo state for organohalogen assessment between 2003 and 2019. Differences were found between franciscana dolphins collected prior to and after the disaster. Additionally, significant temporal trends for organochlorine pesticides and natural and anthropogenic organobromine were detected. The increase in pesticide concentrations after 2015 is suggestive of their reavailability in the environment. The decline in organobromine over time could be due to their debromination in the marine environment and alterations in the composition of their natural producers. PCBs remained stable during the period of the study. Our findings show an increase in endocrine disruptor concentrations, which is of great concern for this endangered population.

Marine shrimps as biomonitors of the Fundão (Brazil) mine dam disaster: A multi-biomarker approach

The disruption of the Fundão dam released 43 million m³ of mine tailings into the Doce River until it flowed into the ocean through the estuary. The mine tailing changed the composition of metals in water and sediment, creating a challenging scenario for the local biota. We used multivariate analyzes and the integrated biomarker response index (IBR) to assess the impact of mine tailings on the bioaccumulation profile (As, Cd, Cr, Cu, Fe, Mn, Pb and Zn) as well as the biomarkers response in gills, hepatopancreas and muscle of shrimps sampled from different sectors during two dry seasons (dry1 and dry2) (Sep/Oct 2018; 2019) and two wet seasons (wet1 and wet2) (Jan/feb 2019; 2020). There was seasonal and local effect under bioaccumulation and biomarker response revealing that the pattern responses seen in each sector sampled changed according to the season. The greater IBR added to the strong association among the most metals tissue content (Cd, Cr, Cu and Mn) and sectors sampled during dry 1 suggests greater bioavailability of these metals to the environment in this period. Estuarine sectors stand out for high Fe bioavailability, especially during wet1, which seems to be associated with greater metallothionein content in hepatopancreas of shrimps. Native species of marine shrimps proved to be successful indicators of sediment quality besides being sensitive to water contamination by metals. The multi-biomarkers approach added to multivariate analysis supports the temporal and seasonal effects, signalizing the importance of continuous monitoring of the estuarine region to better know about the bioavailability of these metals, mainly Fe, and their long-term effects on the local biota.

Impacts of tailings of Fundão dam (Brazil) rupture on marine fish: Metals bioaccumulation and physiological responses

This study evaluated the impacts of the mining tailings after the rupture of the Fundão dam on fish communities on the Atlantic Ocean southeast coast. Four sample collections were carried out over two years (2018-2020), in seasonal periods. Omnivorous/herbivorous and carnivorous fish were collected for analysis of metal bioaccumulation, multibiomarkers of environmental contamination and histopathology. Metal bioaccumulation was stronger correlated in carnivorous fish in the dry-2018 collection, besides higher activity of antioxidant enzymes, energy metabolism and higher morphological damage; however, there was less oxidative damage and less metallothioneins induction, and these variables were strongly associated with the wet-2020 collection. In a temporal view, it was possible to observe a reduction in metal levels in fish, except in the mouth of the Doce River. These events can be explained by seasonal natural events, which tend the resuspension and boost metal levels, mainly in the mouth region during the rainy season.

Variability in nearshore fish biodiversity indicators after a mining disaster in eastern Brazil

The rupture of the Fundão mining dam (Doce river basin, Brazil) caused a wide range of negative impacts. Yet, assemblage-level implications to estuarine and coastal fishes remain unclear, partly due to the lack of pre-disaster information. Based on monthly otter trawl surveys, we analyzed spatial and seasonal variability in univariate (total biomass, biomass of species vulnerable to exploitation, rarefied richness and evenness) and multivariate (species composition and trophic composition) indicators of fish biodiversity in the Doce river delta, eastern Brazil. We determined the independent and interactive effects of environmental, seasonal and spatial variables on species composition to test whether environmental alterations provoked by mine tailings could affect assemblage's organization. Most indicators present idiosyncratic spatiotemporal patterns, suggesting they have complementary roles in revealing changes in fish biodiversity. Environmental variables, including those affected by the Fundão dam collapse such as turbidity, dissolved oxygen and pH, were much more important than seasonal and spatial predictors in explaining the variation in fish species composition. These findings highlight the potential from mine tailings to disrupt local ichthyofauna and indicate a preponderant role of environmental conditions in assemblage structuring. Given the lack of data prior to rupture, our results may be used as a baseline against which to assess temporal trends in fish biodiversity relative to changes detected in less disturbed estuarine and coastal assemblages.

Fish otolith microchemistry as a biomarker of the world's largest mining disaster

The Fundão dam collapse occurred in late 2015, resulting in the largest disaster in the world involving mine tailings, releasing at least 50 million m³ of iron ore tailings into the Doce river basin (Brazil). Studies realized along the Doce river after the disaster showed high concentrations of some elements above recommended Brazilian standards in different environmental matrices such as Al, Ba, Co, Fe, Hg, Mn, and Ni. This study aims to test the hypothesis that otolith microchemistry can be used as a pollution biomarker over time, that is, the otoliths sampled in the directly impacted area (Doce estuary) will present higher concentrations of the chemical elements in relation to the two other indirectly impacted estuaries (Ipiranga and São Mateus). The marine catfish Genidens genidens was chosen as a sentinel species, as this species presents several features that characterize it as a key species of the estuarine environment. The hypothesis was tested from a comparison between estuaries of the element/Ca ratios (Ba, Fe, and Mn) from the otolith edge (representing more recent deposition) and through the elemental composition profile, from core to edge of otolith. For the otolith edge analyses, it was possible to determine significant differences between estuaries in all three element:Ca ratios (Ba, Fe, and Mn). For the profile analysis (from core to edge), the Doce river showed consistent concentrations of Fe:Ca and Ba:Ca ratios higher than those of the Ipiranga and São Mateus estuaries throughout the life of the fish. In otoliths sampled in the Doce estuary, the possible identified peak of the Ba:Ca and Mn:Ca ratios, was probably associated with the Fundão Dam disaster. The present study showed that otolith microchemistry can be used as a sclerochronological biomarker of metallic aquatic pollution.

Marine fish assemblages of Eastern Brazil: An update after the world's largest mining disaster and suggestions of functional groups for biomonitoring long-lasting effects

When the Fundão dam collapsed in Brazil, 50 million m³ of iron ore tailings were released into the Doce river, resulting in the world's largest mining disaster. The contaminated mud was transported 668 km downstream of the Doce river and reached the Atlantic Ocean 17 days after the collapse. Seven months later, there was evidence that the tailings had reached the largest and richest coral reef formation in the South Atlantic Ocean. This study provides the first description of species composition, abundance, and diversity patterns of fish assemblages in estuaries, coastal areas, and coral reefs affected by the rupture of the mining dam in the Doce river. A linear mixed model (GLMM) was used to evaluate the influence of salinity on fish abundance across estuarine and coastal ecosystems. In addition, based on functional traits related to habitat use and feeding habits, this study identified fish species suitable as bioindicators of the long-lasting effects of this major mining disaster. Bottom trawls were used to sample five estuaries and their respective coastal areas, and a visual census was employed to sample five reef areas, representing an impact gradient. A total of 269 species were recorded in all three habitats, but only seven were shared among them. The results showed lower similarity in assemblages among estuarine areas compared to the coastal and reef areas. Species composition among estuaries and reef ecosystems was more heterogeneous. In contrast, coastal habitats exhibited high homogeneity. Salinity had no statistically significant effect on fish abundance either in estuaries (p = 0.22) and along the coast (p = 0.14). Twelve fish species were identified as suitable bioindicators for evaluating the long-lasting effects of resuspension of contaminated sediments. These species are commonly found in the ecosystems under the influence of the disaster inhabiting potentially contaminated substrates and substrate-associated benthic preys.

Biochemical response and metals bioaccumulation in planktonic communities from marine areas impacted by the Fundão mine dam rupture (southeast Brazil)

The rupture of the Fundão dam (Mariana, MG, southeast Brazil) released a huge flood of mine tailings to Doce river basin and its adjacent coastal area, in November 2015. This catastrophic event exposed aquatic communities to metal contamination related to mine tailings, but its biological effects are still poorly understood. This study investigates how biochemical response related to metal exposure vary between locations and seasons during the years of 2018-2020, in planktonic communities (micro and mesoplankton). Marine microplankton collected in sectors in front and south of the Doce river mouth presented the highest lipid peroxidation (LPO) and induction of metallothioneins (MT). Mesoplankton collected in sectors in front and north of the Doce river mouth presented highest LPO, while MT in this size class did not respond to a clear spatial pattern. Our results showed that metals affected biomarkers in a non-linear pattern and highlighted the complex relationship between metals, biochemical parameters, and seasonality. The variation in biochemical biomarkers indicates physiological stress related to metals, once sectors contaminated by metals, especially Fe, Mn and Cd, presented stronger biochemical responses. Comparison of metal levels with bioaccumulation data collected before the impact indicates Fe, Cd, Cr and Cu more than 2-fold higher after disaster in sectors closer to the river. Literature showed that these sectors present zooplanktonic assemblages with lower biomass and biodiversity, suggesting that the opportunistic species that thrives in the area are also under biochemical stress, but possibly relies on repair or defense mechanisms. The physiological stress detected by this study is possibly related to the mine tailings, considering the metals that stood out and the proximity with the Doce river mouth. This suggests that the impacts related to the failure of Fundão dam are still affecting the marine planktonic community even three to four years after the environmental disaster.

Temporal trends of trace elements bioaccumulation by a vulnerable cetacean (Pontoporia blainvillei) before and after one of the largest mining disasters worldwide

One of the largest environmental disasters worldwide occurred on November 5th^, 2015, when the Fundão dam collapsed in Mariana (Minas Gerais State, Southeast Brazil). The tailing mud flooded the Doce River basin and reached the sea in the coast of Espírito Santo State (ES), Southeast Brazil. This coastal region is the habitat of the most isolated population of franciscana dolphins (Pontoporia blainvillei), with the lowest populational census and lowest genetic diversity in Franciscana Management Area Ia (FMA Ia) - 18° 25'S and 21° 17'S. This study aimed to assess the bioaccumulation of trace-elements (As, Cd, Cu, Fe, Hg, Mn, and Zn) in muscle, liver and kidney of franciscana dolphins collected near the Doce River's mouth before (n = 32) and after (n = 19) the tailing mud reached the sea. The Generalized Additive Model (GAM) showed increasing temporal trends of Hg and Zn in muscle and liver after the dam failure, probably related to higher concentrations and bioavailability in the water column and sediments from the Doce River. Declining trends were found for As and Cu muscular and hepatic concentrations and Fe concentrations in kidney due to their lower bioavailability after the disaster, caused by association with tailings mud trapped in the riverbanks and suspended particulate material. Additionally, higher As and Hg concentrations found in the first period of sampling may be due to historical contamination by mining activities. The full extent of the impacts caused by the Fundão dam failure is still unknown. However, due to their rapid increase and remobilization process, toxic effects can be induced in the biota by these elements. Elements' bioaccumulation in this study contributes to the knowledge of franciscana dolphins from FMA Ia. Considering the conservation concern regarding this franciscana population and its scarce knowledge, the impact of this disaster can be alarming for species conservation.

Fish biodiversity of a tropical estuary under severe anthropic pressure (Doce River, Brazil)

Abstract The Doce River has undergone severe changes over the last centuries (e.g., flow regulation, pollution, habitat and species loss). Here, we present the first comprehensive fish biodiversity assessment of the Doce River estuary and a summary of the main impacts and their drivers for the whole river since the early 18th century. Carangiformes, Siluriformes and Eupercaria incertae sedis were the most representative orders for the 115 species recorded. Most species are native (87.8%), euryhaline/peripheral (80%) and zoobenthivorous (33.9%). Threatened (Paragenidens grandoculis, Genidens barbus, and Lutjanus cyanopterus) and near threatened (Cynoscion acoupa, Dormitator maculatus, Lutjanus jocu, Lutjanus synagris, and Mugil liza) species are peripheral. Thirteen species are exotic at the country (Butis koilomatodon, Coptodon rendalli, and Oreochromis niloticus) or the basin level (e.g., Pygocentrus nattereri and Salminus brasiliensis). The catfish Cathorops cf. arenatus is reported for the first time on the eastern coast of Brazil and Paragenidens grandoculis, considered extinct in the Doce River, was discovered in the estuary.

Effects of seasonal contaminant remobilization on the community trophic dynamics in a Brazilian tropical estuary

In tropical estuaries, wet seasons are responsible for the downstream transport of allochthonous material from the upper basin and flooded plains. Although allochthonous matter is commonly associated to nutrient and detritus input, pollutants are also transported throughout the basin or suspended from the river bottom via strong streamflow remobilization and rainfall dynamics. We assessed community and population trophic niche-based patterns using organisms' stable isotopes signatures in the wet and the dry seasons to test if estuarine trophic diversity is affected by remobilization of metal-contaminated material from a mining dam collapse that occurred in the Doce river basin, Brazil. Trophic depletion was detected community-wide and in a key consumer group (bottom-dwelling fishes) at the end of the wet season in the impacted Doce river estuary (DRE). Conversely, higher trophic diversity values were recorded in a well-preserved estuary used as control site. Stable isotopes mixing models indicated in the DRE that G. genidens, a predator fish species, presented poor-quality diet based on pollutant-tolerant tiny organisms, a finding that strongly contrasts from diet described in other, little-impacted Brazilian estuaries. Although wet seasons are expected to increase trophic, functional and taxonomic diversity in tropical estuaries, in the DRE the rainfall-driven dynamics poses a threat to the community due to the presence of ore tailings.

Benthic bioturbation: A canary in the mine for the retention and release of metals from estuarine sediments

After the largest mining tailings spill in Brazil, the Rio Doce estuarine ecosystem was severely impacted by metal contamination. In a 28-day laboratory experiment, we examined the effects of the polychaeta Laeonereis sp. on fluxes of oxygen and metal across the sediment-water interface. The density-dependent effect of Laeonereis sp. in the oxygen and metal fluxes was tested at low and high (74 and 222 ind m^-2, respectively) densities, and compared with defaunated controls. The higher worm density had an amplified effect on the oxygen flux, sediment uptake of Al and Mn, and Fe oxidation compared with the control, but no significant effects on other metals (Ba, Cd, Co, Cr, Cu, Ni, and Zn). Higher worm density increased the oxidation of Fe phases, but no effect in the solid phase of other metals. Consequently, Laeonereis sp. bioturbation prevents the reduction of Fe phases and the release of metal-bound-contaminants to estuarine systems.

Iron ore tailings as a source of nutrients to the coastal zone

The Fundão dam rupture was one of the largest environmental disasters worldwide and released millions of m³ of iron ore tailings into the Doce River basin in southeastern Brazil. Here we assessed the supply of dissolved nutrients associated to tailings in the Doce River estuary and its adjacent coastal zone. First, we observed an acute increase in dissolved silicates (From 16.26 μM to 175.47 μM) and nitrate (From 5.56 μM to 50.69 μM) in the estuary when compared to days prior to the event. Coastal marine ecosystems showed significant concentrations of nitrite (From 0.72 μM to 2.99 μM) and phosphate (From 0.09 μM to 2.30 μM) one year after the disaster, which we attribute mainly to nutrient recycling. The chronic effects include an increase in nutrient load to the coastal zone with a predominance of nitrogenous species, which may increase the limitation of phosphorus and silica to marine primary production.

Time-sequence development of metal(loid)s following the 2015 dam failure in the Doce river estuary, Brazil

In the context of the Doce river (Southeast Brazil) Fundão dam disaster in 2015, we monitored the changes in concentrations of metal(loid)s in water and sediment and their particulate and dissolved partitioning over time. Samples were collected before, during, and after the mine tailings arrival to the Doce river estuary (pre-impact: 12, 10, 3 and 1 day; acute stage: tailing day - TD and 1 day after - DA; chronic stage: 3 months and 1 year post-disaster). Our results show that metal(loid) concentrations significantly increased with time after the disaster and changed their chemical partitioning in the water. 35.2 mg Fe L^-1 and 14.4 mg Al L^-1 were observed in the total (unfiltered) water during the acute stage, while aqueous Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se and Zn concentrations all exceeded both Brazilian and international safe levels for water quality. The Al, Fe and Pb partitioning coefficient log (K_d) decrease in the acute stage could be related to the high colloid content in the tailings. We continued to observe high concentrations for Al, Ba, Cd, Cr, Cu, Fe, V and Zn mainly in the particulate fraction during the chronic stage. Furthermore, the Doce river estuary had been previously contaminated by As, Ba, Cr, Cu, Mn, Ni and Pb, with a further increase in sediment through the tailing release (e.g. 9-fold increase for Cr, from 3.61 ± 2.19 μg g^-1 in the pre-impact to 32.16 ± 20.94 μg·g^-1 in the chronic stage). Doce river sediments and original tailing samples were similar in metal(loid) composition for Al, As, Cd, Cr, Cu, Fe, V and Zn. As a result, these elements could be used as geochemical markers of the Fundão tailings and considering other key parameters to define a baseline for monitoring the impacts of this environmental disaster.

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.

Contamination and oxidative stress biomarkers in estuarine fish following a mine tailing disaster

BACKGROUND

The Rio Doce estuary, in Brazil, was impacted by the deposition of iron mine tailings, caused by the collapse of a dam in 2015. Based on published baseline datasets, the estuary has been experiencing chronic trace metal contamination effects since 2017, with potential bioaccumulation in fishes and human health risks. As metal and metalloid concentrations in aquatic ecosystems pose severe threats to the aquatic biota, we hypothesized that the trace metals in estuarine sediments nearly two years after the disaster would lead to bioaccumulation in demersal fishes and result in the biosynthesis of metal-responsive proteins.

METHODS

We measured As, Cd, Cr, Cu, Fe, Mn, Pb, Se and Zn concentrations in sediment samples in August 2017 and compared to published baseline levels. Also, trace metals (As, Cd, Cr, Cu, Fe, Hg, Mn, Pb, Se and Zn) and protein (metallothionein and reduced glutathione) concentrations were quantified in the liver and muscle tissues of five fish species (Cathorops spixii, Genidens genidens, Eugerres brasilianus, Diapterus rhombeus and Mugil sp.) from the estuary, commonly used as food sources by local populations.

RESULTS

Our results revealed high trace metal concentrations in estuarine sediments, when compared to published baseline values for the same estuary. The demersal fish species C. spixii and G. genidens had the highest concentrations of As, Cr, Mn, Hg, and Se in both, hepatic and muscle, tissues. Trace metal bioaccumulation in fish was correlated with the biosynthesis of metallothionein and reduced glutathione in both, liver and muscle, tissues, suggesting active physiological responses to contamination sources. The trace metal concentrations determined in fish tissues were also present in the estuarine sediments at the time of this study. Some elements had concentrations above the maximum permissible limits for human consumption in fish muscles (e.g., As, Cr, Mn, Se and Zn), suggesting potential human health risks that require further studies. Our study supports the high biogeochemical mobility of toxic elements between sediments and the bottom-dwelling biota in estuarine ecosystems.