“We are accustomed to look for the gross and immediate effects and to ignore all else. Unless this appears promptly and in such obvious form that it cannot be ignored, we deny the existence of hazard. Even research men suffer from the handicap of inadequate methods of detecting the beginnings of injury. The lack of sufficiently delicate methods to detect injury before symptoms appear is one of the great unsolved problems in medicine.”

Rachel Carson, Silent Spring


DDT is a strong insecticide especially potent for killing mosquitos. It is also environmentally hazardous, especially to birds. DDT dramatically reduced malaria and typhus during WWII but was also responsible for the near-extinction of several birds, most notably the bald eagle. Furthermore, a book about the harmful effect of DDT is responsible for kickstarting the modern environmental movement.

Dichloro-diphenyl-trichloroethane (DDT) is the first modern insecticide, widely used in the 1940s. The National Pesticide Information Center describes it as “effective, relatively inexpensive to manufacture, and lasts a long time in the environment.” DDT killed pests, especially mosquitos. Rats and mice fed DDT become sterile. During WWII, DDT controlled malaria, typhus, body lice, and bubonic plague.

Scientists at the time believe DDT to be harmless to humans and non-pest wildlife. People sprayed DDT both indoors and out.

DDT spray on beach

With its magic ability to kill disease-carrying pests, and nothing else, the chemical was ubiquitous. The soil half-life of DDT is 2 to 15 years and the aquatic half-life is about 150 years.

However, it eventually became clear that DDT caused birds to lay thin eggshells that oftentimes cracked. Eventually, scientists realized that the widespread use of DDT did have detrimental effects. Among other things, bald eagles nearly went extinct due to thin eggshells caused by DDT.

Silent Spring

In 1962, author Rachel Carson was already famous for her books on environmentalism. Various people alerted her that there were fewer birds each spring. They tied this to cracked shells, tracing that to the widespread aerial spraying of DDT to control mosquitos.

Carson released the book Silent Spring detailed problems with DDT. “How could intelligent beings seek to control a few unwanted species by a method that contaminated the entire environment and brought the threat of disease and death even to their own kind?” Carson acknowledged the problems of pest-borne disease and urged to use chemicals sparingly.

In 1972, the newly created US Environmental Protection Agency banned DDT except in the case of malaria outbreaks. Other countries followed suit. Today, the widespread use of DDT is banned virtually everywhere. However, the chemical is still used on an emergency basis to control malaria. Since the ban, bald eagle populations have largely recovered.