"Brazil's Fukushima" — that is what the tragedy that struck Brazil on 5 November last has been dubbed, following the collapse of two dams in the south-east of the country. The name conveys the gravity of a social and environmental disaster whose true scale is not yet clear.

The collapse of the dams owned by mining company Samarco, built to contain wastewater, has caused eleven deaths and twelve missing persons, and is the worst environmental disaster in Brazil's history and among the most serious ever to have occurred anywhere in the world.

The wall of mud that engulfed the village of Bento Rodrigues contained highly toxic substances such as mercury, arsenic, lead and other heavy metals. As biologists feared, the poisonous tide — made up of 62 million cubic metres of toxic sludge — first devastated the basin of the Rio Doce and its tributaries in Minas Gerais, and is now poised to poison the sea off Espírito Santo.

According to Marcos Freitas, executive coordinator of the Instituto virtual internacional de mudanças globais (Ivig), the tragedy was caused by Samarco's negligence, the company being guilty of serious failures in maintenance and safety, and it is the most serious disaster ever caused by a mining company. The quantity of toxic sludge released is reportedly two and a half times greater than the second worst incident of its kind, which occurred on 4 August 2014 at the Mount Polley mine in British Columbia, Canada.

Despite the immediate alarm, nothing was done to prevent the toxic wave from reaching the Brazilian coastline of the Atlantic Ocean, in one of Brazil's most biodiverse regions. "The arrival of the toxic mud in the ocean could have an environmental impact equivalent to the contamination of a tropical forest the size of the Brazilian Pantanal," declared biologist André Ruschi, director of the Estação Biologia Marinha Augusto Ruschi di Aracruz, Santa Cruz, in Espírito Santo.

Ruschi believes that the environmental damage caused by this tsunami of mud could take at least one hundred years to be completely reabsorbed. "A disaster of global proportions with consequences that are difficult to imagine, for which we could pay an enormous price."

Among the principal victims of the disaster are the Krenak people, an indigenous people who live on the banks of the contaminated river and must now rely on supplies of drinking water and food. "The river was everything to us — it did not just provide us with water and fish, it was a source of culture for us," said tribal chief Leomir Cecilio de Souza. "The river has sustained our people since the time of our ancestors; it was sacred. But now it is dead."

Racing swiftly towards the sea, the toxic tide left behind a ghostly landscape of dead animals, uprooted trees and a thick layer of solidified mud. So far the Brazilian government has imposed two fines on Samarco, owned by industry giants Vale and Bhp Billiton: one of approximately 60 million dollars and another of 250 million. Experts estimate, however, that the damage to the ecosystem and biodiversity will carry a cost of several billion dollars.

Furthermore, the company — which initially denied on several occasions that the mud was toxic — has still not provided a complete list of the substances contained in the sludge that poured out of the dams. Concern is now focused on the other 200 similar dams scattered across the country, which could pose a risk.

Humanitarian and environmental organisations are calling for tighter regulations and are denouncing the close relationship between politicians and mining companies, which last year spent more than seven million dollars on political and advertising campaigns.