DDT is one of the most controversial chemical compounds in recent history. It has proven effectiveness as an insecticide, but its potent toxicity isn't limited to insects. Banned by many countries including the United States, DDT is nonetheless still used -- legally or illegally -- in some places.
What Is DDT?
DDT, also known as dichloro-diphenyl-trichloroethane, belongs to a class of pesticides known as organochlorides. A synthetic chemical compound that must be made in a laboratory (it doesn't occur in nature), DDT is a colorless, crystalline solid.
DDT can't be dissolved in water; it is, however, easily dissolved in organic solvents, fats or oils. As a result of its tendency to dissolve in fats, DDT can build up in the fatty tissues of animals that are exposed to it. This accumulated build-up is known as bioaccumulation, and DDT is described by the EPA as a persistent, bioaccumulative toxin.
Because of this bioaccumulation, DDT remains in the food chain, moving from crayfish, frogs and fish into the bodies of animals that eat them. Therefore, DDT levels are often highest in the bodies of animals near the top of the food chain, notably in predatory birds like eagles, hawks, pelicans, condors and other meat-eating birds.
DDT also has serious health effects on humans. According to the EPA, DDT can cause liver damage including liver cancer, nervous system damage, birth defects and other reproductive harm.
A Brief History of DDT
DDT was first synthesized in 1874, but it wasn't until 1939 that Swiss biochemist Paul Hermann Müller discovered its potency as an all-purpose insecticide. For that discovery, Müller was awarded the Nobel Prize in 1948.
Before the introduction of DDT, insect-borne diseases like malaria, typhus, yellow fever, bubonic plague and others killed untold millions of people worldwide. During World War II, use of DDT became common among American troops who needed it to control these illnesses, especially in Italy and in tropical regions like the South Pacific.
After World War II, the use of DDT expanded as farmers discovered its effectiveness at controlling agricultural pests, and DDT became the weapon of choice in anti-malaria efforts. However, some insect populations evolved with a resistance to the insecticide.
DDT, Rachel Carson and 'Silent Spring'
As the use of DDT spread, a handful of scientists noticed that its reckless use was causing considerable harm to wildlife populations. These scattered reports culminated in the now-famous book by scientist and author Rachel Carson, Silent Spring, which describes the dangers of widespread pesticide use. (The book's title comes from the effect DDT and other chemicals were having on songbirds, which were disappearing in some regions.)
Silent Spring became a best-selling book, and its publication is often credited with the rise of the modern environmental movement. In the years that followed, scientists worldwide were reporting that birds with high levels of DDT in their bodies were laying eggs that had shells so thin they broke before hatching, causing bird populations to plunge. And the more DDT the birds had in their bodies, the thinner their eggshells.
DDT Banned Worldwide
As evidence of the harm DDT was causing began to grow, countries worldwide started to ban the chemical or restrict its use. By 1970, Hungary, Norway and Sweden had banned DDT, and despite overwhelming pressure from the U.S. chemical industry, the production and use of DDT was banned in the United States in 1972.
In 2004, the treaty known as the Stockholm Convention on Persistent Organic Pollutants (POPs), which was signed by 170 countries including the United States, restricted the use of DDT to emergency insect control, e.g., in the event of a malaria outbreak. In some countries, however, DDT is still regularly used for controlling mosquitoes and other insects, and it is still used in agriculture in a few places such as India and sub-Saharan Africa.