(noun) The synthetic chlorinated hydrocarbon pesticide dichlorodiphenyltrichloroethane. DDT was extensively used worldwide as an insecticide in the 1940s and 1950s, both for crop protection and to eliminate insects carrying diseases such as malaria and typhus, until studies proved its high toxicity to both animals and humans. DDT was banned in the United States in 1972, and many other nations banned the use of DDT in the 1970s and 1980s. Today, very few nations permit the insecticide's use, though it is still regularly used in India and North Korea.
DDT is highly toxic to birds, particularly birds of prey, because of its magnification properties. Rather than breaking down, the insecticide accumulates in the food chain and is absorbed by fish, rodents and other small animals, which are then hunted by birds of prey. The birds accumulate high concentrations of the toxin in their body fat, and it inhibits the proper formation of eggshells. Eggshell thinning due to DDT use was a major cause of raptor population declines in the 1960s and 1970s, and top tier predators such as the bald eagle and peregrine falcon declined critically because of thin eggshells that would be crushed by nesting parents. Certain seabirds, most notably the brown pelican, were also impacted by the widespread use of DDT and suffered catastrophic population decline.
Once the insecticide was banned and conservation initiatives were undertaken to protect declining species, the birds' numbers recovered, though they still face additional threats unrelated to DDT use.