Chlorine is found in nature and is on the periodic chart of elements. But the chlorine produced by the chemical industry is not in its natural form and its use results in products and wastes which are toxic to wildlife, humans or the ecosystem.
Through a process called electrolysis, the chlor-alkali industry uses large amounts of electricity to break the bond between the sodium and chlorine atoms, splitting the salt compound. The sodium reacts with water to form sodium hydroxide, sold commercially as caustic soda. The chlorine atoms join together in pairs to form chlorine gas, Cl2, also called "elemental chlorine."
Chlorine gas is extremely unstable and reactive: the gas used to kill and maim soldiers in World War I was chlorine gas. When it comes into contact with organic (carbon-containing) molecules, the chlorine binds tightly to the carbon atoms, creating new substances called organochlorines.
Many organochlorines are toxic, persistent and/or bioaccumulative and are rarely found naturally. Nature generally produces only small quantities of such chemicals which are either tightly channeled into subsequent chemical reactions or manufactured for defensive or biocidal uses. For instance grasshoppers can synthesize a type of organochlorine to repel ants. Either way, these natural toxins are not freely available to contaminate the environment. In addition, some volatile organochlorines are generated by phytoplankton during normal metabolism and released to the atmosphere in fairly large quantities; these naturally occurring organochlorines are thought to play a role in the natural regulation of the ozone layer.
Over 11,000 organochlorines are now in commerce. Organochlorines are useful to industry because they tend to be very stable and they resist natural breakdown processes. But this also means that they may persist in the environment for decades, moving up the foodchain and contaminating wildlife and humans.
PVC plastic is now the single largest use for chlorine today using about one third of all global production.
Other organochlorines are found as unwanted by-products in manufacturing processes that use chlorine.
Organochlorines are formed in the wastewater from pulp and paper plants when chlorine is used to bleach paper. Water disinfection using chlorine gas for drinking water and sewage discharges has been found to create toxic, persistent chemicals.
Many more organochlorines, such as dioxins, are produced by accident and these are often even more toxic or persistent than the original chemical.
Source document for this section:
The chlor-alkali industry starts with ordinary salt -- an abundant, natural compound. The chemical name for ordinary salt is sodium chloride. Each crystal contains sodium and chlorine atoms in equal proportions.
Salt, or sodium chloride, is the raw material for chlorine production.
Some organochlorines are sold as products such as:
ACHIEVING ZERO DIOXIN: An emergency strategy for dioxin
elimination (9/94).