Cyanide is used in the production of organic chemicals such as nitrile, nylon, acrylic plastics, and synthetic rubber. It is also used in the electroplating, metal processing, steel hardening, and photographic industries. The wastes from such industries not only contains cyanide but also significant amounts of heavy metals such as copper, nickel, zinc, silver, and iron. Since cyanide ions are highly reactive, metal complexes of variable stability and toxicity are readily formed. Ore processing in gold and silver mining operations uses dilute solutions of sodium cyanide (100 to 500 ppm), which is inexpensive ($1.75/kg, 2003 price) and highly soluble in water, and under mildly oxidizing conditions, dissolves the gold contained in the ore. Each year 2 to 3 million tons of cyanide are industrially produced. Food processing industries that handle crops such as cassava and bitter almonds also generate considerable quantities of cyanide waste because of the presence of the cyanogenic glucosides that are present in the plant material.