Gold Mine in Laos Accused of Toxic Pollution

The current pollution, he said, stems from the spillover of cyanide, a chemical often used in mining to dissolve gold so that it flows out of the rock in a process called leaching.

The cyanide can be leaked into the soil and then into the water supply. Mineral residues from mining operations also release toxic components if left in the open.

“The company has taken safety measures. During the dry season there is not much of a problem," he said.

"But during rainy season, there is an issue if the amount of water [in the treatment plant] is too much," resulting in the spillover of cyanide, he said
http://www.rfa.org/english/news/laos/mine-06062013112052.html