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Chlorinated Hydrocarbons (Organochlorines) - DDT

Chlorinated hydrocarbon insecticides, such as chlordane, DDT, toxaphene, aldrin and dieldrin were the main family of insecticides used following their introduction after World War II. Many of these chemicals originated from attempts to develop agents of chemical warfare, but were found to be lethal to insects. (3)

DDT (Dichloro-Diphenyl-Trichloroethane) is a man-made chemical widely used to control insects on agricultural crops and insects that carry diseases like malaria and typhus. The value of DDT as an insecticide was first discovered in 1939 and the discoverer won the Nobel Prize(3). In the 1952 edition of the U.S. Department of Agriculture's book "Insects: The Yearbook of Agriculture," the agency hailed it as one or our safest all-around insecticides based on its "cost, ease of handling, safety to humans, effectiveness in destroying the pest, and safety to wildlife." It was not until decades later that the true impact of DDT on wildlife was known.

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Problems associated with DDT, as well as many chlorinated hydrocarbons, involved their tendency to concentrate in the fat of humans, livestock, aquatic foodchains, and wildlife. This latter phenomena, called bioaccumulation, has had, and continues to have, severe adverse effects on many forms of wildlife.

Many predatory birds were heavily impacted by DDT. DDT was a major reason for the decline of the bald eagle in North America in the 1950s and 1960s as well as the brown pelican and the peregrine falcon. DDT and its metabolites (breakdown products), DDD and DDE, are toxic to embryos and disrupt calcium absorption,**** thereby impairing eggshell quality. Studies in the 1960s and 1970s failed to find a mechanism for the hypothesized thinning. However, more recent studies in the 1990s and 2000s have laid the blame at the feet of DDE. Some studies have shown that although DDE levels have fallen dramatically, eggshell thickness remains 10–12 percent thinner than before DDT was first used. In addition, DDT, DDE and other chlorinated hydrocarbons, can affect the parents behavior during incubation and can result in death of unhatched embryos and eagle chicks.

DDT is also highly toxic to aquatic life, including crayfish, daphnids, sea shrimp and many species of fish. DDT may be moderately toxic to some amphibian species, especially in the larval stages.

The Service was heavily involved in studying the affects of DDT on fish and wildlife, a process which began shortly after the chemical came into use as a pesticide (see US Fish and Wildlife Service Historic News Releases - DDT.) By 1945, the Service determined that DDT is "Capable of Considerable Damage to Wildlife, Beneficial Insects, and Indirectly to Crops" (see News Release of August 22, 1945 [pdf file]).

The Service continued to conduct studies on, and to voice its concern over, the effects of DDT on fish and wildlife for more than 25 years. It was not until 1972, and then because of the potential harm to human health, that the Environmental Protection Agency (EPA) banned the use of DDT in the United States barring a public health or economic emergency. Restrictions that control the use of aldrin and dieldrin were imposed in the United States in 1974.

Since implementation of these restrictions, residues of the pesticides have significantly decreased in many regions where they were formerly used. However, DDT, DDD and DDE persist in the environment for a very long time. DDT, DDD and DDE residues can still be found in most areas of the United States.

Other chlorinated hydrocarbon insecticides still being used in the US include dicofol and endosulfan. Methoxychlor was another chlorinated hydrocarbon permitted for use in the United States. However, in 2004, the EPA determined that methoxychlor was not eligible for reregistration .

US Fish and Wildlife Service Historic News Releases - DDT

Other Links:

Rachel Carson: A Conservation Legacy

Pest Management (IPM)