DDT (dichlorodiphenyltrichloroethane) is a colorless, crystalline, tasteless and almost odorless organochloride known for its insecticidal properties and environmental impacts. First synthesized in 1874, DDT's insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939. It was used in the second half of World War II to control malaria and typhus among civilians and troops. After the war, DDT was also used as an agricultural insecticide and its production and use duly increased. The United States banned the use of DDT in 1972, but some countries still use the chemical. In December 2000, in a convention organized by the United Nations Environment Program, 122 nations agreed to a treaty banning twelve very toxic chemicals. Included among the twelve was DDT. However, the treaty allowed the use of DDT to combat malaria until other alternatives become available. Before it can take effect the treaty must be ratified by 50 of the nations that agreed to it in principle. 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 related chemicals persist for a long time in the environment and in animal tissues. People are most likely to be exposed to DDT from food, including meat, fish, and dairy products. DDT can be absorbed by eating, breathing, or touching products contaminated with DDT. In the body, DDT is converted into several metabolic products, including the metabolite dichlorodiphenyldichloroethene (DDE). DDT and DDE are stored in the body’s fatty tissues. In pregnant women DDT and DDE can be passed to the fetus. Both chemicals are found in breast milk, resulting in exposure to nursing infants. Human health effects from DDT at low environmental doses are unknown. However, following exposure to high doses human symptoms can include vomiting, tremors or shakiness, and seizures. Laboratory animal studies showed effects on both the liver and reproduction. DDT is considered a possible human carcinogen. DDE acts as a weak androgen receptor antagonist, but not as an estrogen. p,p'-DDT, DDT's main component, has little or no androgenic or estrogenic activity. The minor component o,p'-DDT has weak estrogenic activity.