Rather depends upon what minerals the tailings are from:
Mud from a dam that burst at an iron ore mine in Brazil earlier this month, killing 12 people and polluting an important river, is toxic, the United Nations’ human rights agency has said.
The statement contradicts claims by Samarco, the mine operator at the site of the rupture, that the water and mineral waste contained by the dam are not toxic.
Citing “new evidence”, the UN’s office of the high commissioner for human rights said in a statement the residue “contained high levels of toxic heavy metals and other toxic chemicals”.
Sure it contains toxic heavy metals. There will indeed be uranium, arsenic and all sorts in there. But then there’s those and others in the soil in your garden too. In your veg patch even. They’re known components of what we call “dirt”.
Now, if a gold mine tailings damn had broken, then I’d be worried about residual cyanide. And if a uranium tailings dam burst, there’d be more thorium around than I’d be comfortable with. A bauxite plant’s damn, well, that happened in Hungary and red mud is not nice stuff. Very alkaline indeed and damaging just for that reason.
Iron ore tailings? It’s dirt. And it will cause the same problems as dirt: kill the fish in the river, yes, make the water difficult to treat as the plume moves downstream. But once the bolus has passed through the river that’s pretty much it. The composition of the tailings won’t be greatly different from the mud that’s already on the bottom of the river.
That UN “toxic metals” is just the usual Greenpeace stuff of As at 50 ppm is toxic heavy metals. Which As is, but it really is the dose that makes the poison.
Samarco said in a statement that both pre- and post-disaster tests show the mud released in the dam burst, a mixture of water, iron oxides and silica or quartz known as tailings, presented no danger to human health and did not contain water contaminants.
While iron and manganese levels in the mud are above normal, Samarco said, they were below dangerous levels.
BHP Billiton said on Thursday that the waste was chemically stable and would not change its composition in water.
Sounds about right to me.