DDT
2,2-bis(p-chlorophenyl)-1,1,1,-trichloroethane is a chlorinated hydrocarbon used as an insecticide. DDT was first introduced during the 1940s. It killed insects that feed on crops and spread disease. Swiss scientist Paul Müller was awarded the 1948 Nobel Prize in Physiology and Medicine for discovering DDT's insecticidal properties.
DDT is toxic to many animals, including humans. DDT is not easily degraded into nonpoisonous substances and can remain in the food chain for prolonged periods. The United States banned its use in 1972. However, DDT use continues in much of the world, particularly in tropical regions.
PCBs
PCB's are a class of compounds where two phenyl rings are substituted with multiple chlorine atoms at ten possible positions.There is sufficient evidence for the carcogenicity [local] of several mixtures of polychlorinated biphenyls.
Since 1974, all uses of polychlorinated biphenyls in the United States have been confined to closed systems such as electrical capacitors and transformers, vacuum pumps, and gas-transmission turbines. Before 1972, polychlorinated biphenyls were used in transformer cooling liquids, heat-transfer and hydraulic fluids, vacuum pump fluids, lubricants, plasticizers, fillers in investment casting waxes, surface coatings and sealants, pesticide extenders, and copy paper.
PCB's are no longer produced in the United States, except for limited research and development applications.
The release of PCB's from prior industrial uses and the persistence of the compounds in the environment have resulted in widespread contamination of water and soil, with subsequent potential exposure of the general population. For contrasting view of the current state of environmental enhancement, see hudsonwatch and clearwater.
Dioxin
See jmol: Dioxin
Dioxin is formed by burning chlorine-based chemical compounds with hydrocarbons. Incinerators burning chlorinated wastes are the major source of dioxin in the environment (95%). Dioxin is one of the most toxic substances known.
For an Australian perspective of the issue, read The Dioxin Controversy: Spilling Over into Schools [local]
