The Fundão dam was one of the megastructures of the Germano mining complex, located in the municipality of Mariana, Minas Gerais, southeastern Brazil. The mining complex had an installed capacity of 23milliontons/year of iron ore concentrate. In addition to Fundão, the complex contained two more dams: Santarém and Germano, the latter being the highest dam in Brazil, with a height of 175m and a projected volume of up to 160millionm3 of tailings (Samarco, 2013). Open pit mines, piles of sterile material deposits, industrial plants and pipelines are also part of the Germano Complex.

The Fundão dam began operating in 2008 and was designed to contain a total of 79.6millionm3 of fine tailings (mud) and 32millionm3 of sandy tailings during its 25-year lifespan (SUPRAM, 2008). In November 2015, Fundão contained 56.4millionm3 of iron ore tailings deposited in merely seven years of operation, a result of the never-before attained records of Brazilian production in the years 2013 to 2015 (IBRAM, 2015). In order to accommodate this volume, it was necessary to construct dikes, using the sandy reject itself as a construction material from the upstream embankment method (Ávila, 2012).

Among the most common methods of tailings disposal, the one with the greatest economic advantage is the upstream embankment. However, it poses a significant challenge to the geotechnical engineer, due to the fact that water is the primary instability agent. Indeed, dams using the upstream embankment method are considered “unforgiving structures” and represent up to 66% of the worldwide reported mine tailings dams failures (Rico et al., 2008; Ávila, 2012; Kossoff et al., 2014).

According to Prieto (2014), the main disadvantages and restrictions of this technology are: foundation of later lifts is on unstable tailing slime, unused in earthquake zones; high level of monitoring using instrumentation required during operation; and recommendation that the rate of raised tailings dams be, preferably, no more than 5m/year.

Since the beginning of the operation, in 2008, the Fundão dam had presented several anomalies related to drainage construction defects, upwellings, mud and water management errors and saturation of sandy material. In some situations, emergency measures were implemented (Samarco, 2016b), one of them known as retreat of the dam axis was begun in 2013. According to Samarco (2016b), the retreat represented: “… a temporary solution, it was decided to realign the dam on the left shoulder by moving it behind the section of the gallery to be filled with concrete, in order to allow the continuation of the landfill embankment. (…) The retreat would move the crest closer to the water of the reservoir and the mud contained within, but it was anticipated that the dam would quickly return to its original alignment once the buffering operations were done.”

However, the retreat was maintained until the collapse of the dam. According to Samarco (2016b): “As the dam embankment continued, surface upwellings began to appear at the retreat of the left shoulder at various elevations and on various occasions during 2013. The saturated mass with sandy tailings was growing, and in August 2014, the drainage carpet controlling this saturation reached its maximum capacity. Meanwhile, the mud under the landfill was responding to the increase in the load that was being deposited by the embankment. The way in which it responded, and the consequent effect on the sands, was what finally made the sands liquefy.”

Technical reports on the Fundão disaster (Samarco, 2016b) concluded that the collapse was due to liquefaction of the material, a phenomenon that occurs when solid materials (sandy tailings) lose their mechanical resistance and present fluid characteristics. Basically, the disaster occurred because of some key factors such as: structural damage to the starter dike, resulting in increased saturation; the attempt to solve structural problems with a concrete gallery that caused the axis of the dam to retract (Fig. 1), later being raised on mud; and the unforeseen deposition of sludge in critical regions. In upstream embankment dams, it is essential for the stability of the structure that the deposition of unsaturated sandy tailing create a beach, at least 200m wide, immediately upstream of the dam crest.

Fig. 1.

Fundão dam. (A) Formation of sandy tailings beach 300m wide and upstream mud deposition, highlighting the critical limit of contact between sandy tailings and sludge (orange line), image of 2011. (B) Retreated axis for emergency works in a concrete gallery brings the crest closer to the critical limit of contact between sandy tailings and sludge (red dashed arrow), image of 2013. (C) Embankment of the dam displaced axis in the critical limit of contact between sandy tailings and sludge (orange line), 2015 image. Adapted from Google Earth Pro.

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The total collapse of the Fundão tailings dam took place on 05 November 2015, between 3:00 pm and 4:00 pm. About 43millionm3 of tailings (80% of the total contained volume) were unleashed, generating mud waves 10m high, killing 19 people and causing irreversible environmental damage to hundreds of watercourses in the basin of the Doce River and associated ecosystems (Samarco, 2016b).

Most of the tailings (>90%) remained along the 120km stretch between the Fundão dam and the hydroelectric power plant reservoir Risoleta Neves (UHE-RN), located in the municipalities of Rio Doce and Santa Cruz do Escalvado (Samarco, 2016a). The tailings remained in the Doce River channel, downstream of the UHE-RN along 548km, reaching the Atlantic Ocean. Forty downstream municipalities were affect and hundreds of thousands of people (included indigenous) were left without access to clean water (Neves et al., 2016; IBAMA, 2015b). Therefore, in this study, the environmental damage was grouped into two sections: one upstream and the other downstream of the UHE-RN.

High resolution orthorectified satellite images (spatial resolution of 50cm) were used to identify the environmental damage caused by the mass displacement along the 120km upstream stretch of the UHE-RN. Two moments were compared: (1) a mosaic of images obtained prior to the dam burst (World View-2, World View-3 and GeoEye); (2) images obtained after the dam burst (World View-2, Pléiades and World View-3). The images were imported into the Geographic Information System and the elements were converted into vectors overlapping the area stained by the tailings. Information for the 548km downstream stretch of the UHE-RN, was obtained from technical reports produced by regulatory and inspection agencies and available literature.

Over a span of only 12h, along the 120km stretch between the Fundão dam and the UHE-RN, the mass displacement created a patch of 2020ha and the tailings accumulated in channels, in floodplains and in the UHE-RN reservoir. This UHE-RN has not yet resumed electric power production due to the huge volume of tailings deposited in the reservoir, around 10millionm3.

The tailings directly hit 135 identified semideciduous seasonal forest fragments, in a 298ha of vegetation suppression, located on the banks of Gualaxo do Norte and Carmo Rivers and its tributaries. The tailings also directly hit 863.7ha of Permanent Preservation Areas associated to watercourses, which were in protected areas, as defined by the federal forest code. Santarém Stream (11.9km impacted), Gualaxo do Norte River (68.4km) and Carmo River (24.7km) were the main rivers and streams completely silted by the tailings. In addition, 294 small creeks were affected by the tailings (Fig. 2 and Fig. S1). Little attention has been given to the pollution potential of the tons of chemical compounds (flocculants and coagulants), specifically sodium hydroxide, which spilled out along with the tailings.

Fig. 2.

Elements of natural and cultural heritage damaged by the Fundão tailings dam.

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Out of the 806 buildings directly hit by the tailings, at least 218 were completely destroyed. These were residences, public buildings, commercial real estate, centennial churches and ancient farms distributed among 10 districts of five municipalities: Mariana, Barra Longa, Ponte Nova, Santa Cruz do Escalvado and Rio Doce. Bento Rodrigues, just 6km from the Fundão dam, was the most damaged district with 84% of the affected buildings totally destroyed, followed by Paracatu de Baixo (40% of the buildings hit were destroyed). A total of 21.1km of rural roads, 12 bridges/passages and the small hydroelectric plant of Bicas were also damaged.

Areas of cultural heritage also suffered greatly. Damages include, at least two archeological sites, six places of historical and cultural interest, more than 2000 sacred pieces/material heritage, five caves, a 2.2km stretch of the Estrada Real and preserved areas of the landscape complex in the junction of the Carmo and Piranga Rivers and the urban complex of Bento Rodrigues. One of the main cultural heritage assets irreversibly affected was the São Bento chapel, an 18th-century building surrounded by stone walls (Fig. 3 and Fig. S2).

Fig. 3.

Buildings affected by the Fundão tailings dam: (A) District of Bento Rodrigues, Mariana and (B) Urban area of the municipality of Barra Longa.

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Parts of three tourist routes (Estrada Real, Estrada Parque Caminhos da Mineração and Caminho de São José) were also severely impacted causing losses to the local economy. The mud affected, irreversibly, areas of important archeological and speleological potential had not yet been studied, made it impossible to evaluate the exact impact on the loss of scientific knowledge.

The flood plains favored a larger accumulation of tailings (Fig. S3), on average more than 50cm high, and in some places estimated at more than 3m thick (Samarco, 2016a; IBAMA, 2016b). The mass displacement was so intense that it excavated the soil and altered original river beds. The tailings stain damaged four protected areas: APA Barra Longa, APE Ouro Preto/Mariana and the Biosphere Reserves of the Espinhaço Mountains and Atlantic Forest (UNESCO, 2011). There was also damage to Priority Areas for Biodiversity Conservation (MMA, 2007; Drummond et al., 2005) – named Quadrilátero Ferrífero and Florestas da Borda Leste do Quadrilátero – and in key areas for the conservation of six rare Brazilian plants (sensuGiulietti et al., 2009), named SE204 – Ouro Preto.

Considering that the disaster occurred in one of the most important regions for biodiversity conservation, it is estimated that the loss was significant (Fernandes et al., 2016). Tons of fish from 21 different species died in large numbers (IBAMA, 2015a). Isolated reports have identified the death of large mammals, such as the South American tapir (Tapirus terrestris L.), as well as turtles, birds, amphibians and invertebrates. However, no study has been published by the scientific community to account for long-term effects in main ecological components and populations of endemic species of flora and fauna.

Along the Doce River, downstream of the UHE-RN, about 5.5millionm3 of tailings were deposited in the first days after the disaster (Samarco, 2016a; IBAMA, 2016a). Very fine tailing particles caused severe changes to the physico-chemical characteristics of the Doce River and estuarine region, increasing the turbidity levels in Minas Gerais up to 6000 times (600,000 NTU) higher than the upper limit established by law for this parameter (SEMAD, 2015). However, the impact monitoring conducted by Samarco presented very low volume of data and several physical and chemical parameters were not reported. This situation was a consequence of using inadequate methods for monitoring impacts (IBAMA, 2016c,d,e).

Three different types of sediment layers from the tailings (IBAMA, 2015a, 2016c,d,e) were detected at the mouth of the Doce River: a thick sediment deposited along the mouth; a plume deposited on the bottom; and another thinner widespread plume on the surface (floating plume). Some early projections predicted the plume would have little impact and the pollutant material would dissipate in a few months (Puff, 2015). A year after the dispersion started, 170km of beaches were contaminated by mud, 110km to the north of the Doce River mouth and 60km to the south. The plumes have already spread over more than 770km2, having a huge effect on protected coastal zones such as the Comboios Biological Reserve, an important place for spawning of sea turtles, Santa Cruz Wildlife Refuge and APA Costa das Algas. In the long-term, the pollution plumes could reach regions near the city of Rio de Janeiro (IBAMA, 2015a, 2016c,e; Marta-Almeida et al., 2016).

After carrying out measures for minimizing post-disaster risks, a stage involving emergency engineering work, tailings/sediments removal is considered essential and the most frequent action adopted in events of disasters with mass displacement, including collapses of mining tailings dams (UNESCO, 2010; Kossoff et al., 2014; Bowker and Chambers, 2015).

Two examples of cases of the post-disaster management to remove tailings released by the collapse of the dam occurred in Spain and in Hungary. The collapse of the dam in Andalusia, Spain, in 1998 (UNEP, 2001) released more than 2millionm3 of zinc tailings containing sulphide-related trace elements (As, Cu, Pb, Zn and Ca) and more than 4millionm3 of acidic water, which were deposited over 45km of channels and floodplains on the Guadiamar and Agrio Rivers. A plan for cleaning was presented to authorities three days after the disaster with the adoption of a cleaning protocol of the affected areas (Ginige, 2014). In 12 months, about 7millionm3 of tailings and contaminated materials that had accumulated in the river channels, floodplains and on infrastructure works were removed. The material removed was then deposited in the exhausted mining pit of the company responsible for the dam (WWF, 2002). Another case occurred in 2010 in Ajka, Hungary. Damage control action was taken after the release of over 600,000m3 of tailings in the environment over 14km. The red mud was collected along the affected areas and disposed of inside a dam, which had already been reconstructed, seven days after the collapse (Kátai-Urbán, 2010). In the medium and long term, an extensive cleaning of debris and materials dragged by the flow of tailings was conducted (Jávor and Hargitai, 2011).

Compared with cases presented, one year after the Fundão tragedy, Samarco has conducted only 0.17millionm3 clean-up actions in urban area of Barra Longa (Samarco, 2016c), and not yet removed, monitored or properly disposed of tailings deposited in rivers, streams and flood areas. This goes against the premise of total removal of tailings in rivers affected supported by federal government. According to this premise, the company Samarco should evaluate each area regarding the possibility of total removal and proper disposal of tailings, employing alternative treatment techniques. Tailing management should only be considered as a second alternative when technical infeasibility to remove it is proven (IBAMA, 2016b).

As a wide-ranging strategy of landscape recovery (UNEP, 2001; Hudson-Edwards et al., 2003), the tailings removal should be a priority action for the regions affected by the Fundão collapse. The tailing is a source of fine inhalable particulate material, composed of minerals such as hematite, martite, magnetite and goethite. Studies show that prolonged inhalation of particulate material originated from iron mining is associated with the increase in cases of respiratory and cardiovascular diseases (Braga et al., 2007; Gomes et al., 2011). Leaching tests and toxicological bioassays performed in the region of Bento Rodrigues suggest that the tailings and contaminated soils represent a potential risk of cytotoxicity and cellular DNA damage, due to the indication of a high potential of mobilization of elements such as iron, aluminum, manganese and arsenic from the tailings into the water (Segura et al., 2016). Veronez et al. (2016) also indicate genotoxic and biochemical effects induced by iron ore, from the experimental studies which indicated the Fe and Mn accumulation can induce oxidative stress during the metamorphosis of Lithobates catesbeianus (L.) tadpoles.