Despite being used in 90% of gold production: gold cyanidation is controversial due to the toxic nature of cyanide. Although aqueous solutions of cyanide degrade rapidly in sunlight, the less-toxic products, such as cyanates and thiocyanates, may persist for some years. The famous disasters have killed few people — humans can be warned not to drink or go near polluted water, but cyanide spills can have a devastating effect on rivers, sometimes killing everything for several miles downstream. The cyanide is soon washed out of river systems and, as long as organisms can migrate from unpolluted areas upstream, affected areas can soon be repopulated. According to Romanian authorities, in the Someș river below Baia Mare, the plankton returned to 60% of normal within 16 days of the spill; the numbers were not confirmed by Hungary or Yugoslavia.
Famous cyanide spills include:
Such spills have prompted fierce protests at new mines that involve use of cyanide, such as Roşia Montană in Romania, Lake Cowal in Australia, Pascua Lama in Chile, and Bukit Koman in Malaysia.