DDT (dichlorodiphenyltrichloroethane), a nonbiodegradable water-insoluble chlorinated hydrocarbon once used worldwide as a major insecticide, especially in agriculture. In recent years knowledge of its adverse impact on the environment has led to restrictions in its use. In addition, because tolerance in formerly susceptible organisms develops rapidly, DDT has been largely replaced by organophosphate insecticides in the United States and Canada, where DDT was banned in the 1970s. It is still used as a pediculicide where epidemic-scale delousing is justified, as in barracks and refugee camps. Its value as a scabicide is marginal, because scabies and crab lice quickly become resistant to it. See also scabicide.
