In inorganic cyanides, the CN group is present as the negatively charged cyanide ion. These compounds are highly toxic. Cyanide poisoning refers to harmful effects of inhaling hydrogen cyanide or of ingesting cyanides.
Hydrogen cyanide is highly toxic because it inhibits the oxidative processes of the cells.
Acute poisoning from hydrogen cyanide or cyanides is manifested by dizziness, nausea, staggering, and loss of consciousness. Death may occur rapidly after ingesting as little as 300 milligrams of the salts or inhaling as little as 100 milligrams of hydrogen cyanide. Exposure to concentrations of 200-500 parts of hydrogen cyanide per 1,000,000 parts of air for 30 minutes is also usually fatal.