Mines use toxic chemicals including cyanide, mercury, and sulphuric acid, to separate metal from ore. The chemicals used in the processing are generally recycled, however residues may remain in the tailings, which in developing countries are often dumped directly into lakes or rivers with devastating consequences. The accidental spillage of processing chemicals can also have a serious impact on the environment. For example, at the Baia Mare mine in Romania cyanide is used to extract gold from slurry. In January 2000 a dam containing tens of thousands of tonnes of slurry burst, poisoning the local river with cyanide and heavy metals. Up to 100 tonnes of cyanide were released into the river, a tributary of the Danube. The drinking water supply for more than 2 million people was affected. Within hours, dead fi sh were seen washed up along the river.