Paul Hermann Müller’s discovery that the chlorinated organic compound dichloro-diphenyl-trichloroethane is an effective insecticide led to its widespread use for controlling vectors of disease and causes of devegetation.
It has been known for centuries that numerous species of insects are vectors of human diseases and causative agents of agricultural devegetation. The scientific community recognized this problem, and numerous researchers attempted to discover insecticides that were potent to insects yet relatively innocuous to humans, animals, and vegetation. Prior to the discovery of the insecticidal property of DDT in 1939 by Paul Hermann Müller, inorganic, arsenic-based insecticides were most commonly developed because of their effectiveness in controlling insects. These insecticides, which were initially used during the latter half of the 1800’s, however, were found to be very toxic to humans and other mammals. Other common insecticides utilized prior to the 1940’s were the inorganic fluorinated compounds plus organic-based nicotine, pyrethrum, and derris compounds. These substances, however, had limited application and insufficient permanent effect because of their instability in the environment.
Müller, a Swiss chemist, worked on developing an alternative to the most widely used inorganic arsenic-based insecticides while he was employed by the Swiss firm J. R. Geigy during the mid-1930’s. He thus did not concentrate on modifying the noncarbonaceous “inorganic” compounds consisting of the metal arsenic and other elements, which, when combined, produce arsenic salts, oxides, or hydrides depending on the elemental composition. Instead, he focused on carbon-containing “organic” compounds, which, when combined with the element chlorine, produce organochlorine compounds.
Müller’s task was to synthesize an original compound or to discover an existing one that would be not only an effective and safe insecticide but also economical and in-offensive in odor. Müller had determined from a review of the published scientific literature regarding patented insecticides that the most effective mode of inducing insecticidal activity was through direct contact of the compound with the insect. This meant that it was not necessary for the insects to consume the insecticides in order for a toxic effect (that is, death) to occur. He also concluded that for an insecticide to be effective, especially for agricultural use, it needed to be chemically stable and, accordingly, relatively resistant to decay or inactivation in the environment.
As a result of his conclusions drawn from the literature, Müller decided to study organochlorine compounds. Many compounds in this class were already known to be relatively chemically stable under ambient conditions. In addition, an organochlorine compound called chloroform was already known to exhibit insecticidal properties. Accordingly, Müller focused on studying organochlorine compounds that contained a chemical group similar to the chloroform molecule. He eventually discovered an organochlorine molecule that exhibited potent insecticidal activity.
In 1939, Müller and his research group at J. R. Geigy developed an insecticide product that they named Gesarol. Müller had discovered that the active ingredient in Gesarol was insecticidal when tested against beetles and moths. The active ingredient was the organochlorine compound dichloro-diphenyl-trichloroethane (DDT), which was originally synthesized in the laboratory of Othmar Zeidler, a German chemist, in 1874. Zeidler’s intention was not to develop an insecticide but to determine the substitution reactions involving chlorine atoms and aromatic organic compounds. Zeidler discovered the compound DDT as one of many products of such reactions, but its insecticidal property was unknown to anyone until years later.
Although Müller discovered the insecticidal properties of DDT in 1939 and the Swiss government put the compound to use almost immediately to control the devastating Colorado beetle, U.S. government approval of DDT for use as an insecticide was not initiated to any degree until 1944. The American government, through several federal health agencies, conducted tests during 1942 and 1943 to determine the effectiveness of DDT. In addition, tests were conducted also to determine potential long-term (chronic) and immediate (acute) health effects to humans. Based on the results of the governmental tests, it was concluded that DDT was indeed effective for terminating insect pests, yet relatively innocuous to human health. The product Gesarol with its active ingredient, DDT, was suggested by the J. R. Geigy company for possible use to combat the insect vectors confronted by the American troops engaged in World War II and stationed in Europe, Africa, and the South Pacific, where they were exposed to typhus-carrying lice and mosquitoes that transmitted malaria. The idea was derived from historical documentation of the use of the insecticide pyrethrum during 1900 in Cuba and 1904 in Panama to destroy the species of mosquitoes that transmitted yellow fever (Aëdes) and malaria (Anopheles) to humans. Although pyrethrum did not exhibit permanent activities, its use and the resulting benefits to soldiers in Cuba and workers in Panama demonstrated an effective application of an insecticide in order to decrease the outbreak of human diseases resulting from insect vectors. As a consequence of this historical account, the effectiveness of DDT, and the perceived innocuous impact to humans, the insecticide was selected by the U.S. government in 1944 as the optimal insecticide for use to protect American troops from the insect vectors that transmitted typhus and malaria. Later, the insecticide was released for agricultural and general commercial purposes following the war.
The impact of using DDT as an insecticide can be viewed both positively and negatively. From a positive perspective, the insecticide proved to be instrumental in controlling insect pests and, in turn, preventing outbreaks of disease and destruction of vegetation. On the negative side, DDT was eventually shown to exhibit greater toxicity and potential for adverse environmental impact than originally reported.
It was documented that the use of DDT in Italy and Japan during World War II resulted in the cessation of outbreaks of typhus
Outbreaks of malaria,
Following the U.S. government’s approval of the use of DDT for agricultural and commercial purposes, the insecticide was used extensively on American farms and in residential areas. Although it was effective and appreciated for protecting crops and combating insect infestations, concerns began to arise regarding the compound’s toxicity. Evidently, the initial toxicity testing conducted by the U.S. government during the early 1940’s and the lack of reported cases of illness among exposed troops during World War II were not accurate indicators of potential long-term or chronic health effects in humans.
Indiscriminate use of DDT during the postwar years resulted in reported contamination of food, water, and soil. In turn, the insecticide passed through the food chain, and DDT residues were detected in humans and other animals. It was discovered later that DDT has the propensity to absorb into and through biological tissue and accumulate in body fat. In addition, excessive exposure to DDT was determined to increase the risk of damaging the nervous system in humans and other mammals. These findings resulted in the eventual ban of DDT for use in the United States approximately thirty years following the discovery of its insecticidal property. It should be noted that although the insecticide is stable in the environment, tends to accumulate in fat tissue, and has the potential to induce adverse environmental impact, DDT did not cause any reported fatalities to humans. Indeed, in comparison with the alternatives available at the time, DDT was relatively safe. Unfortunately, the misuse and overuse of DDT led to excessive environmental contamination and, subsequently, to an end of its legal use.
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citation-type="booksimple" xlink:type="simple">Asimov, Isaac. Asimov’s Biographical Encyclopedia of Science and Technology. 2d rev. ed. Garden City, N.Y.: Doubleday, 1982. Presents biographical sketches of more than one thousand great scientists, including Müller. Müller’s biography presents an overview of his discovery of the insecticidal property of DDT. -
citation-type="booksimple" xlink:type="simple">Berenbaum, May R. Bugs in the System: Insects and Their Impact on Human Affairs. Boston: Addison-Wesley, 1995. Survey of the life and evolution of insects around the world, with emphasis on how insects have affected and continue to affect human beings and their societies. Chapter 9 is devoted to humans’ development of ways to eradicate insects. Includes index. -
citation-type="booksimple" xlink:type="simple">Dunlap, Thomas R. DDT: Scientists, Citizens, and Public Policy. Princeton, N.J.: Princeton University Press, 1981. Provides a historical perspective on DDT, with detailed descriptions of its uses and impacts. Includes bibliography and index. -
citation-type="booksimple" xlink:type="simple">Jukes, Thomas H., et al. Effects of DDT on Man and Other Mammals. New York: Irvington, 1973. Collection of scientific papers provides detailed information regarding the effectiveness and toxicity of DDT. -
citation-type="booksimple" xlink:type="simple">Steinberg, Ted. Down to Earth: Nature’s Role in American History. New York: Oxford University Press, 2002. An examination by an environmental historian of how geography, plants, animals, and natural resources have shaped the economic, political, and cultural institutions of the United States. Includes brief discussion of the impact of agricultural use of pesticides. -
citation-type="booksimple" xlink:type="simple">Taton, René. Science in the Twentieth Century. Translated by A. J. Pomerans. New York: Basic Books, 1966. Provides an overview of the historical sequences of events that influenced the development of various scientific disciplines and applications. -
citation-type="booksimple" xlink:type="simple">Whorton, James. Before “Silent Spring”: Pesticides and Public Health in Pre-DDT America. Princeton, N.J.: Princeton University Press, 1974. Focuses on the history and evolution of the development of insecticides in response to the need to control insects that affect agriculture and public health. Includes index.
American Farmers Increase Insecticide Use
Dutch Elm Disease Arrives in the United States
Darling Founds the National Wildlife Federation
Federal Food, Drug, and Cosmetic Act