Ddt - or 2,2-bis(p-chlorophenyl)-1,1,1,-trichloroethane, chlorinated hydrocarbon compound used as an insecticide. First introduced during the 1940s, it killed insects that spread disease and feed on crops. Swiss scientist Paul Müller was awarded the 1948 Nobel Prize in Physiology or Medicine for discovering (1939) DDT's insecticidal properties. DDT, however, is toxic to many animals, including humans, and it is not easily degraded into nonpoisonous substances and can remain in the environment and the food chain for prolonged periods. By the 1960s its harmful effects on the reproductive systems of fish and birds were apparent in the United States, where the insecticide had been heavily used for agricultural purposes. After the United States banned its use in 1972, the wildlife population returned, particularly the bald eagle and the osprey. Nevertheless, DDT use continues in parts of the world, particularly in tropical regions, to control the mosquitoes that spread malaria. In 2001 the Stockholm Convention on Persistent Organic Pollutants called for the phasing out of DDT once a cost-effective alternative becomes available.

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