A 43-million-cubic-meter wave
At 4:20 PM on November 5, 2015, the Fundão tailings dam, operated by the mining company Samarco, experienced a catastrophic failure. A torrent of approximately 43 million cubic meters of iron ore tailings—a viscous, toxic mud—was unleashed. The wave of waste obliterated the village of Bento Rodrigues, located just 2.5 kilometers downstream, before engulfing other communities like Paracatu de Baixo. The disaster resulted in 19 deaths and left hundreds homeless.
The initial flow traveled down the Gualaxo do Norte and Carmo rivers, eventually reaching the major waterway of the region, the Rio Doce (Doce River). This event is considered the largest tailings dam collapse ever recorded in terms of the distance the pollutants traveled, stretching over 668 kilometers. The sheer volume of the mud, a byproduct of iron ore processing, scoured riverbanks, uprooted forests, and changed the river's geography. In some areas, turbidity levels, a measure of water cloudiness, spiked to over 600,000 Nephelometric Turbidity Units (NTU), where normal levels are below 100.
A river's toxic burden
The tailings were inert mud; they carried a cargo of heavy metals from the mining process. Studies of the water and newly deposited riverbed sediment revealed high levels of iron, manganese, arsenic, lead, and other contaminants. This toxic slurry flowed down the Rio Doce for 17 days, eventually reaching the Atlantic Ocean.
The ecological impact was immediate and devastating. The high concentration of suspended solids choked aquatic life, leading to mass die-offs of fish and other organisms. An estimated 80% of the native vegetation near the river's main channel was destroyed. The disaster affected 98 different species of fish, 11 of which were already at risk of extinction. The sediment settled on the river bottom, creating a constant source of contamination. Even today, rainfall events can re-suspend these fine, metal-laden particles, causing secondary pollution. The full recovery of the river's ecosystem is expected to take decades, if it recovers at all. The toxic plume also spread into the Atlantic, reaching the Abrolhos Marine National Park, a coral reef system and a reproduction area for humpback whales.