Chlorinated hydrocarbon insecticides, such as chlordane, DDT, toxaphene, 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 (Carson 1962). DDT is a manufactured 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 (Carson 1962). 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.

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. Some predatory birds, most notably the bald eagle, peregrine falcon, and brown pelican were so heavily impacted by the pesticide that they required federal listing as an endangered or threatened species under the Endangered Species Act. This was because the principal metabolite (breakdown product) of DDT, DDE, prevents normal calcium deposition during eggshell formation, causing females to lay thin-shelled eggs that often break before hatching. 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.

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. 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 in sidebar). 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 emergency (e.g., outbreak of malaria). DDT is still used in other (primarily tropical) countries. 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 and DDE persist in the environment for a very long time. DDT 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 is another chlorinated hydrocarbon permitted for use in the United States. However, the EPA has suspended the sole manufacturer's permit to produce and sell this pesticide until the manufacturer submits results from studies required to support reregistration of the chemical.

Carson, Rachel. 1962. Silent Spring. Houghton Mifflin Company, Boston, Massachusetts

United States Department of Agriculture. 1952. Insects: The Yearbook of Agriculture. United States Government Printing Office.