Chlorine compounds are synthesized by many species of plants and animals for very specific metabolic purposes. They are essential for the normal growth and reproduction of those organisms. The ability of organisms to synthesize these compounds has evolved over time under the stress of natural selection. Chlorine, in other words, is part of our natural ecosystem. Hydrogen chloride is produced in massive amounts in volcanoes, and many chloride salts are present in the earth's crust.
Combustion is also a major source of organochlorines.
Natural combustion sources include lightning-induced forest and brush fires as well as volcanoes. Whenever organic material is burned in the presence of chloride, organochlorines are produced. These include dioxins, chloromethane and other chlorine-containing compounds. Nearly 1.3 million American jobs are linked to chlorine chemistry. Chlorine is used to purify drinking water and to disinfect swimming pools, both of which might otherwise be contaminated with fecal microorganisms that could cause diseases such as cholera, typhoid fever and dysentery.