Dichlorodiphenyltrichloroethane (DDT) is an insecticide used in agriculture. The United States banned the use of DDT in 1972, but some countries still use the chemical. DDT has also been used in the past for the treatment of lice. It is still in use outside the United States for the control of mosquitoes that spread malaria. DDT and its related chemicals persist for a long time in the environment and in animal tissues.