Historical Background

    DDT was the first of the chlorinated organic insecticides.  It was fist prepared in 1873.   In 1948, a Swiss scientist, Paul Muller was awarded the Nobel Prize in Physiology and Medicine for discovering the use of DDT as an insecticide.  The use of DDT increased enormously after World War II.  The main reasons being its effectiveness against mosquitoes, that could spread malaria, and lice that carried typhus.  In one decade DDT reduced the cases of malaria from 75 million to 5 million in India.  During this period the World Heath Organization estimated that approximately 25 million people were saved by DDT.  With a low price and minimal toxicity to mammals DDT seemed like the the ideal insecticide, and the percent yield in some crop fields doubled.  In the 1940's problems started to emerge that were related to extended use of DDT.  Many insects became immune to the substance and also in the 1960's the harmful effects on the reproductive systems of fish and birds were apparent.  Rachel Carson, an American marine biologist, wrote Silent Spring, an article that questioned the safety of DDT.  It takes much work to degrade DDT into a nonpoisonous compound and can also remain in the food chain for prolonged periods.  The reason that DDT is harmful over an extended period of time is because it is stored in fatty tissue and has a half live of eight years.  There will be a build up of DDT and it will not be metabolized for eight years.  The United States banned the use of DDT in 1973 and the wildlife population returned.  The bald eagle and the osprey were the two animals that showed the biggest increase in population after the banning of the substance.  There was a 90% reduction of DDT in Lake Michigan by 1978.  DDT is still used in other countries around the world, particularly in tropical regions.

   DDT kills insects by affecting the nervous system.  It differs form most other insecticides because it lasts a  for a long period time.  DDT decays slowly and appears in plants and in animals that eat plants.  It also appears in human beings because it is absorbed into the body tissues from the animals and plants that people eat.