A week after a dam storing mining waste collapsed in southeast Brazil, the human cost is clear, with 110 killed and 238 missing, presumed dead, but the environmental impact is still being evaluated.
Authorities fear the mineral-laced slurry released by the collapse could eventually pollute the Sao Francisco River, the second-longest in Brazil, which hosts various species of fish and has many towns on its banks.
Daily tests carried out by Brazil's national water agency ANA in the Paraopeba tributary, muddied along 200 kilometres by the dam burst, show the presence of metals in the water have spiked to unhealthy levels.
Residents along the riverbanks have already said fish they relied on for food were floating to the surface, dead.
"Most of us here are very rural, riverside people, so we use the Paraopeba River to feed ourselves. It gives us fish, we use it to water our plants, and now we can't do this anymore, so many people have been affected by the dam breaking," one local, Leda de Oliveira, 31, told AFP.
The latest ANA results showed iron, magnesium and aluminum at worrying levels. It added that, while trace levels of lead and mercury had initially spiked, they had since fallen to normal counts. Arsenic -- another impurity often found in iron ore waste -- was not a problem, according to the tests.
But those measured just water quality, and not the way the elements were being absorbed in sediment, food chains and the general ecosystem. Experts say the real long-term effects of the dam break at the mine, located near the town of Brumadinho and owned by Brazilian mining giant Vale, may not be evident for years.
"Right now there are many unknowns -- how toxic is the waste? How mobile are the toxins? Will the waste move again? It is only when these things are known that we will really know how bad this will be," an expert in landslides, Professor David Petley at Britain's University of Sheffield, told AFP.
Immediate action, "very expensive if done properly," was needed to contain the pollution, he said, adding: "There is a lot of waste in the river. There is a risk that this now moves downstream in floods, or that toxins that it releases might move."
Petley said it was to be hoped that measures to contain pollution were better now, but added that both disasters were "scandalous failures."