Compounds . . Dichloro- methane (Methylene chloride) . .
Triiodo- methane (Iodoform) . . Tetrachlo- romethane (Carbon tetrachloride) . .
Trichloro- methane (Chloroform) ozone layer is believed to increase human exposure to ultraviolet rays, leading to increased skin cancer, eye diseases and disorders, and possible disruption of the immune system. The chlorofluorocarbon compounds of methane and ethane are collectively known as freons. They are extremely stable, unreactive, non-toxic, non- corrosive and easily liquefiable gases. Freon (CCl F ) is one of the most common freons in industrial use.
It is manufactured from tetrachloromethane by Swarts reaction. These are usually produced for aerosol propellants, refrigeration and air conditioning purposes. By , total freon production in the world was about billion pounds annually. Most freon, even that used in refrigeration, eventually makes its way into the atmosphere where it diffuses unchanged into the stratosphere.
In stratosphere, freon is able to initiate radical chain reactions that can upset the natural ozone balance. DDT, the first chlorinated organic insecticides, was originally prepared in , but it was not until that Paul Muller of Geigy Pharmaceuticals in Switzerland discovered the effectiveness of DDT as an insecticide. Paul Muller was awarded the Nobel Prize in Medicine and Physiology in for this discovery. The use of DDT increased enormously on a worldwide basis after World War II, primarily because of its effectiveness against the mosquito that spreads malaria and lice that carry typhus.
However, problems related to extensive use of DDT began to appear in the late 1940s. Many species of insects developed resistance to DDT, and it was also discovered to have a high toxicity towards fish. The chemical stability of DDT and its fat solubility compounded the problem. DDT is not metabolised very rapidly by animals; instead, it is deposited and stored in the fatty tissues.
If ingestion continues at a steady rate, DDT builds up within the animal over time. The use of DDT was banned in the United States in , although it is still in use in some other parts of the world. . .
Freons . . p,p’ -Dichlo- rodiphenyl- trichloro- ethane(DDT)