DDT

DDT (dichloro-diphenyl-trichloroethane) is perhaps the most recognized of all insecticides because it's use helped reveal the many hazards associated with synthetic (man-made) pesticides. This colorless, odorless, insoluble toxic pesticide contains up to fourteen chemical compounds. It is known for its ability to eradicate (destroy) pesky insects such as flies, lice, and mosquitoes, as well as agricultural pests. Although first synthesized in 1874 by German chemist Othmar Zeidler, DDT was not used as an insecticide until 1939. It was then that Swiss scientist Paul Hermann Muller (1899-1965) discovered its insect-killing properties.

DDT is very durable. In some applications it is effective for 12 years. Water cannot wash it away and it resists breakdown by light and air. Its strength and persistence have resulted in DDT's transfer to "non-target" living organisms. Once in an ecosystem (an inter-related community of animals, plants, and bacteria), it can pass on from crops to birds and from water to fish, eventually affecting the whole food chain.

DDT Exposure

When ingested by humans, DDT is stored in body fats and can be passed on to nursing babies. Low levels of DDT in humans are harmless but large concentrations can cause severe health problems such as liver cancer. When applied to an insect, DDT is easily absorbed through the body surface. After attacking the nervous system, DDT causes paralysis. Some insects have a resistance to DDT, thereby making the insecticide ineffective. These resistant insects are able to reproduce and pass this trait on to their offspring.

Many problems arise when larger animals are exposed to DDT or eat smaller animals that have ingested (eaten) the toxin (poison). For example, while DDT is more toxic to fish than birds, it still causes widespread bird deaths. With high levels of exposure, DDT causes convulsions and paralyzes the birds' nerve centers. In smaller concentrations, it can weaken their egg shells and can cause sharp declines in the species' reproductive rate. DDT ingestion by peregrine falcons is thought to have caused their almost complete extinction in most regions of the United States.

The Benefits of DDT

The benefits of DDT were demonstrated in the 1940s when it was used in World War I (1939-1945) to clear out mosquito-infested areas prior to invasion. Even after the war, the use of DDT in the United States almost completely wiped out malaria (an infectious disease characterized by severe chills and fever) and yellow fever. In tropical areas, the use of DDT has helped save millions of lives that would otherwise have been lost to disease. DDT was also routinely applied as a crop dust or water spray on orchards, gardens, fields, and forests. At one point it was registered for use on 334 agricultural crops.

As part of a 1945 experiment, two researchers drain an artificial pond to see if fish were harmed by exposure to a DDT.

In 1962 Rachel Carson's (1907-1964) landmark book, Silent Spring, exposed the dangers of unregulated pesticide use. Spurred by public pressure, state and federal governments turned their attention to the regulation of pesticides. In 1972, the United States Environmental Protection Agency (EPA) banned the use of DDT. Today, DDT is restricted in the United States, Europe, and Japan. However, many other countries still use DDT widely for malaria control, delousing, and the eradication of other disease-spreading insects.