Mud tsunami wreaks ecological havoc in Brazil

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Science  04 Dec 2015:
Vol. 350, Issue 6265, pp. 1138-1139
DOI: 10.1126/science.350.6265.1138

A Brazilian Navy ship on 22 November skirts a plume of killer mud spilling from the Doce River into the Atlantic Ocean.


When Dante Pavan first heard the news of last month's mining dam collapse in southeastern Brazil, he never imagined that the wave of sludge would travel all the way to his family's old farmstead, hundreds of kilometers downstream. But as the scale of the disaster became clearer, the zoologist threw sampling gear in his truck and sped north from São Paulo for a rendezvous with the killer mud. When he saw the Doce River stained a dark orange by the iron-laced mine tailings, his first reaction was that the river “is going to turn into a fossil bed.”

Now, he and other researchers are trying to forecast the river's prospects for recovery from the disaster, unleashed on 5 November when a dam holding approximately 50 million cubic meters of waste from iron mines burst without warning near the city of Mariana in Minas Gerais state. Pavan is part of a network of scientists, backed by crowdfunding, that is analyzing river samples to assess the environmental impacts independently of the government and the mining companies that managed the dam. One controversy they hope to settle is whether the sludge was laced with two dozen heavy metals, including arsenic, copper, and mercury, and whether such toxic contamination will persist and spread through the food chain, delaying recovery.

The immediate impacts of the tsunami were tragic. It buried villages downstream, killing at least 13 people, mostly in Bento Rodrigues, the district nearest the dam. Within a day, the wave reached the Doce, one of Brazil's largest rivers outside the Amazon basin, and traversed 600 kilo meters before spilling into the Atlantic Ocean on 21 November. Before the mud reached the sea on the north coast of Espírito Santo state, environmentalists raced to dig up hundreds of nests of endangered loggerhead and leatherback sea turtles and move them to a safe haven. Brazil dispatched its new oceanographic research vessel, the Vital de Oliveira, to monitor the mud plume's effects on marine life. Speaking at the climate summit in Paris earlier this week, Brazil President Dilma Rousseff called the dam collapse “the worst environmental disaster in the history of Brazil.”

Trail of destructionCREDIT: A. CUADRA/SCIENCE

In the Doce and two small rivers near the dam, the sludge destroyed the base of the food chain—plankton, algae, freshwater shrimp, and other life forms—says Pavan, an independent consultant who specializes in environmental impact assessments for infrastructure projects in the Amazon. “From what we can see on the surface, the impacts are tremendous,” adds Alexandre Martensen, a Brazilian ecologist at the University of Toronto in Canada who helped organize the network of researchers responding to the disaster.

Pavan was one of the first scientists to sample the spill, and his quick response could shed light on how long those impacts might last. Downstream from where he first encountered the mud, he collected water and sediment samples before and after its passage. Dozens of scientists in several labs will study these and other samples still being collected; the University of Brasília will take the lead on the heavy metal analyses. They hope to sort out conflicting claims about the nature of the pollution.

The mine's owner, Samarco—jointly held by two of the world's largest mining companies, Vale and BHP Billiton—insists that the tailings deposited behind the dam were simply clay and silt. Analyses carried out by the federal government corroborate that claim; state and municipal agencies, however, say they have found elevated levels of heavy metals at downstream sites. Vale and BHP Billiton argue that the river's sediments were polluted before the mud arrived. The federal and state governments have sued the companies for 20 billion reais (about $5 billion) in damages.

Long stretches of the Doce are still stained orange, and authorities have declared the water unfit for swimming, drinking, or fishing. River conditions should be back to normal in a few months, after summer rains flush out most of the sediments, predicts Paulo Rosman, a coastal and oceanographic engineer at the Federal University of Rio de Janeiro. “The worst has passed,” he says. But regardless of whether the sludge carried toxic metals, aquatic life will be slow to recover, in no small measure because the river was in a fragile state at the outset. Its ecosystems were already under assault from pollution and excessive runoff. And because of an extreme, ongoing drought, the Doce had little water to dilute the sludge and few sanctuaries where aquatic life could escape the orange tide.

In the river's lower reaches, researchers teamed up with local fishers to rescue native fish, mollusks, and crustaceans before the onslaught and transfer them to breeding tanks. The goal was to create a “genetic reservoir” of biodiversity, so that species could be re introduced if necessary. In the meantime, scientists will have a rare opportunity to observe a major river reboot its ecosystems. Most of the Doce River's fish biomass was resilient exotic species like tilapia and dorado, which are likely to have an upper hand over native species during recolonization, says Adriano Paglia, an ecologist at the Federal University of Minas Gerais in Belo Horizonte.

“It's possible some local species will disappear,” Paglia says. “Whatever comes back will be just a sample of the diversity that existed before.”

Correction (7 December 2015): The name of the district closest to the dam is Bento Rodrigues. A previous version of this story identified it as Bento Gonçalves.

  • * * in Espírito Santo, Brazil. Herton Escobar writes for O Estado de S. Paulo newspaper.

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