It started as a torrent of mud that flattened a village and frightened neighbourhoods. Now the mineral sludge that killed at least 12 people and polluted more than 600 kilometres of river system has arrived at the Atlantic Ocean, extending its trail of destruction to a delicate marine environment.

The mudflow stems from the failure of the Fundao dam at the BHP Billiton-Vale joint venture Samarco Mineracoes in Minas Gerais, Brazil. The dam burst on November 5, taking with it millions of cubic metres of tailings from Samarco's iron ore operation. At least 12 people are still missing.

The mud buried a number of towns in the south-eastern state, including the worst affected, Bento Rodrigues, 40 kilometres downstream, on its way to the state of Espirito Santo, north of Rio de Janeiro on Brazil's coast.