After the Fundão iron ore mining dam rupture in November 2015, yellow/ocher emulsions never before reported on the continental shelf adjacent to the Doce River began to be seen, both in coalesced and foam forms. XRD analyses pointed to a prevailing composition of iron and kaolinite with a substantial contribution of an organic-metallic compound, measured in multiple periods over 2 years of sampling. Optical microscopy images allowed the identification of micelles composed of nanoparticles of iron oxyhydroxide making up this emulsion. The generation of dendritic snowflake-shaped microcrystals on fiber filters after water sample filtration and heating confirmed the presence of micelles composed of iron oxyhydroxide nanoparticles enveloped by organic polymers. After losing water, the micelles may act as a self-assembly template seed, where the polymer acts in the oriented adsorption of nanoparticles according to their crystallographic structure. The study brought to light the distinct behavior of a portion of the tailings material, which has already been reported to not have the same flocculation process as the clay minerals previously found in the suspended particulate material (SPM) before the dam rupture.

Since November of 2015, when ore tailings from a dam rupture reached the Atlantic Ocean, researchers are trying to assess the degree of impact across the Doce River and adjacent coastal area. This study aims to use the zooplankton dynamics as a tool to evaluate the environmental impact in the coastal region, five years after the rupture, during periods of low and high river flow. Doce River flow varied from 49 to 5179 m ³/s and structured the zooplankton community between periods of low and high river flow, but salinity and chlorophyll-a had stronger correlation with depth (r = 0.40 and − 0.40 respectively) than with the Doce River discharge variation along the sampling period (r < 0.2). On the other hand, inorganic particles in the water and total metal concentration (dissolved + particulate), used as tracers of the iron enriched tailing (Al, Cd, Cr, Cu, Fe, V), were correlated with fluvial discharge and showed to be the main factor driving the zooplankton community dynamics. For assessing the degree of environmental impact, we tested the ecological indexes for the zooplankton community. Margalef Richness, Pielou Evenness and Shannon-Wiener Diversity varied from 2.52, 0.40 and 1.39 (all registered during high river flow period) to 9.02, 0.85 and 3.44 (all registered during low river flow period), respectively. Along with those community indicators, we evaluated the response of representative taxonomical genera such as Paracalanus, Oikopleura and Temora, regarding the Doce River flow, and found population patterns that established a baseline for future monitoring in the region. Our results showed that the zooplankton community is more fragile when the river discharge is stronger, and this pattern is confirmed by all indicators tested.

In the past several decades, anthropogenic changes throughout drainage basins have threatened physical, hydrological and ecological river-to-ocean continuum balances. Dams are one of these anthropogenic influences that can seriously affect sediment fluxes to the ocean. Here, we investigate the formation and dispersion of a high-concentration mud suspension (HCMS) at a river mouth due to a tailing dam failure. In November 2015, the Fundão dam (Mariana-MG, Southeast Brazil) failure released approximately 39.2 million m ³ of tailings into the Doce River system. The slurry travelled 660 km down to the river mouth, reaching the Atlantic Ocean. Pre- and Post-dam failure surveys were used to investigate temporal and spatial changes in Suspended Particulate Matter (SPM) concentration, seabed sediment grain size and seabed sediment bulk density along the inner shelf. Results indicate that the combination of the tailing dam failure with an extremely dry seasonal condition led to the formation of a HCMS, altering, at least in a short term, the sedimentary processes along the inner shelf, leading to high sedimentation rates and low seabed sediment bulk density. Changes in particle size defined by an increase in clay content, a significant increase in SPM concentration in the inner shelf and a decrease in seabed sediment bulk density were observed as a result of the dam failure. SPM concentrations were higher near the seabed than at the surface, reaching up to 9000 mg/l. The highest SPM concentration measured during a major flood in January 2014 reached around 100 mg/l, The combination of a HCMS with tailings high clay content resulted in low values of seabed sediment bulk density and the formation of fluid mud along the inner shelf. In the first week after the tailings arrival, a 5 cm thick tailing fluid mud was observed. In this stage of bed formation, bed strength is lower, easing particle reentrainment by waves or currents. Thus, tailings could be advected, spreading the impact along the coast.

Zooplankton were sampled five days after the tailings from the Samarco dam rupture reached the ocean in the coastal region at the mouth of the Doce River. This was one of the largest environmental disasters in Brazilian history, and the impacts on the marine biota are not yet fully understood. This study aimed to evaluate the zooplankton community short term responses to the metal enrichment after the tailings reached the coastal region in different scenarios. Our results showed an acute impact on the zooplankton community, which peaked in abundance (222,958.60 ind/m ³) and decreased in diversity (H′ = 1.23) near the river mouth. Two copepod species, Parvocalanus sp. and Oithona nana, composed up to 61% of the total abundance and they were correlated with concentrations of Fe, Pb, Cu and Zn in particulate fraction. These species feed opportunistically on nanophytoplankton, which dominated the autotroph community, possibly in response to the iron enrichment caused by the mud flow. A shift on zooplankton species composition was also observed. During the first three days, we found the presence of oceanic species in the 20 and 30 m isobaths during an incomplete upwelling event, which directly correlated with the presence of Calanoides carinatus. However, only three days later, following a cold front passage and consequent increase of water turbidity, those species were already absent, and the zooplankton community was significantly altered (PERMANOVA, df = 1, pseudo-F = 9.2247, p = .001). Zooplankton responded quickly to the environmental changes detected during our sampling period and proved to be key factors in costal monitoring, especially in dynamic oceanographic areas such as the Doce River coastal region.

This work aims to characterize, in mineral and chemical terms, the ore tailings related to the Mariana disaster (MG, Brazil), occurred on 5 November 2015, and assess its correlation with sediments found in the continental shelf adjacent to the Doce River mouth (ES, Brazil). This study uses samples of tailings and seabed sediments collected at the mouth of the Doce River from 2012 to 2019. Elemental compositions of all samples were determined by X-ray fluorescence measurements; however, Synchrotron Resonant X-Ray Diffraction proved to be a remarkable technique to characterize the crystallographic phases of iron present in sediments. Studies and analyzes of the sediment samples showed that the tailings have a notable feature of the iron-crystallographic phases, mainly observed in the period after the Fundão dam failure, as compared with sediments collected in the period before. This set of iron-containing mineral phases, here called the Iron Mineralogical Set (IMS), consists of the main phases of hematite and magnetite and the minority phases of goethite and greenalite and it is used as a marker of tailings. Mass ac magnetic susceptibility measures supported the concept of the IMS as a marker. It is suggested a relationship between the content of the IMS in the sediment samples as a function of the measures of mass magnetic susceptibility. The IMS had shown the influence of tailings on the sea bed sediment indicating that there is no possibility, at the current stage, of predicting how many years this material will still be at the seabed.

In November 2015, a mining dam failure dumped approximately 32 million m3 of very fine iron-rich tailing material into the Doce River watershed and the adjacent continental shelf, Southeast Brazil. Previous settling column experiments demonstrated different properties and behavior of flocs between natural sediment samples and those contaminated by the iron ore tailing, in which the presence of smaller and more porous flocs in the last was explained by a very fine fraction of clay and or a metallic coating (Grilo et al., 2018). As nanoparticles possess unique physical and chemical properties due to their high specific area and nanoscale size, their transport, persistence and bioavailability in the environment are essential aspects to be considered in risk assessment and management (Wiesner et al., 2009). Nanoparticles such as iron oxyhydroxide hold high reactivity with different ions (Antelo et al., 2005), where adsorption may increase or decrease the charge on the surface of nanoparticles and affect their stability (Breeuwsma and Lyklema, 1973).