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Cyanide and Metal Cyanide

Cyanide is a regulated inorganic contaminant in drinking and bottled water in the U.S., as enforced by the U.S. EPA and the U.S. FDA Center for Food Safety and Applied Nutrition (CFSAN). The typical source of cyanide in the U.S. is industrial contamination. In some countries, staple food products such as sorghum and cassava are also sources of cyanide.

Metal cyanide complexes are negatively charged ionic complexes consisting of one or more cyanide ions (CN) bound to a single transition metal cation. These complexes have the general formula [M(CN)b]x–, where M represents a transition metal cation (such as Ag+, Au+, Cu+, Ni2+, Fe2+, Co3+, etc.); b is the number of bound cyanide ions; and x is the total anionic charge of the complex.

Metal cyanide complexes are of environmental concern because they release cyanide upon dissociation. In environmental waters below pH 9.3, the cyanide ion converts to HCN, an extremely toxic substance. Metal cyanide complexes are also used in the mining and reclamation of precious metals, and in the metal finishing industry.