DDT

DDT, a synthetic insecticide in the family of organic halogen compounds that acts as a contact poison, disrupting the nervous systems of a wide variety of insects, while also posing harmful effects to many other animal species through environmental persistence and bioaccumulation.

Chemical characteristics and actions

Pure DDT is a colorless crystalline solid with a melting point of 108–109 °C (226.4–228.0 °F), though the commercial form is typically an amorphous powder containing 65–80 percent active compound mixed with related chemicals. This form is highly stable and does not dissolve easily in water, properties that contribute to its long-lasting effectiveness in the environment. DDT readily dissolves, however, in fats and oils, leading to its accumulation in the tissues of living organisms over time.

DDT kills insects by interfering with the normal function of nerve cells. The chemical prevents sodium channels in neurons from closing properly after activation, causing repeated and uncontrolled nerve signals. This overstimulation produces tremors, convulsions, paralysis, and ultimately death.

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Discovery and later development

DDT was first synthesized in 1874 by Austrian chemist Othmar Zeidler, who formed the compound by reacting chloral with chlorobenzene in the presence of sulfuric acid. While working for the J.R. Geigy chemical company in Basel, Switzerland, chemist Paul Hermann Müller set out to find a powerful synthetic insecticide that could be produced cheaply and remain effective on contact. He envisioned a chemical deadly to insects but safe for crops and relatively harmless to warm-blooded animals. In 1939, having spent several years systematically testing compounds in search of the ideal formula, he discovered DDT’s insecticidal properties.

During and after World War II, DDT was found to be effective against lice, fleas, and mosquitoes (the carriers of typhus, of plague, and of malaria and yellow fever, respectively) as well as the Colorado potato beetle, the spongy moth, and other insects that attack valuable crops. Owing to this broad effectiveness, DDT quickly became one of the most widely used insecticides in the world, being heavily applied in agriculture, homes, and mosquito-control programs throughout the late 1940s and 1950s. Its use in the United States reached its highest levels in 1959, and global production peaked in 1963, before growing concerns about insect resistance and environmental and health effects eventually led to restrictions.

Environmental harm and bioaccumulation

DDT’s effectiveness came with a hidden cost: the chemical lingered in soils for years and steadily accumulated in the environment. As insects contaminated with DDT were eaten by birds and other animals, the pesticide moved up the food chain, becoming increasingly concentrated in the tissues of predators. One of DDT’s most damaging effects was eggshell thinning in birds. Songbirds and birds of prey—including eagles, hawks, and falcons—were especially vulnerable, with dramatic declines in their populations linked to DDT exposure. Public concern over these ecological impacts grew in the 1960s, fueled in part by Rachel Carson’s influential book Silent Spring (1962). By the 1970s, many countries had banned the pesticide, though it is still used in some regions to control mosquitoes that spread malaria.