Paul Müller was an industrial chemist who discovered that dichlorodiphenyltrichloroethane (DDT) could be used as an insecticide. This was the first insecticide that could actually target insects; in small doses it was not toxic to humans and yet it was stable enough to remain effective over a period of months. When DDT was introduced in 1942, the effects it would have on the environment were not well understood. It was widely hailed, in particular for its ability to reduce the incidence of tropical diseases by reducing insect populations. For his work with DDT and the role his discovery played in the fight against diseases such as typhus and malaria, Müller was awarded the 1948 Nobel Prize in medicine or physiology.
Paul Hermann Müller was born in Olten, Switzerland, on January 12, 1899, to Gottlieb and Fanny Leypoldt Müller. His father was an official on the Swiss Federal Railway, and the family moved to Lenzburg and then to Basel, where Müller was educated until the age of seventeen. After finishing his secondary education, Müller worked for several years in a succession of jobs with local chemical companies. In 1919, he entered the University of Basel to study chemistry. He did his doctoral work under F. Fichter and H. Rupe, and his dissertation examined the chemical and electrochemical reactions of m-xylidine and some related compounds. Xylidines are used in the manufacture of dyes, and when Müller received his Ph.D. in 1925 he went to work in the dye division of the J. R. Geigy Corporation, a very large Swiss chemical company. Müller married Friedel Rügsegger in 1927; they had two sons and a daughter. Müller initially conducted research on the natural products that could be derived from green plants, and the compounds he synthesized were used as pigments and tanning agents for leather. In 1935, he was assigned to develop an insecticide. At that time the only available insecticides were either expensive natural products or synthetics ineffective against insects; the only compounds that were both effective and inexpensive were the arsenic compounds , which were just as poisonous to human beings and other mammals. Müller noticed that insects absorbed and processed chemicals much differently than the higher animals, and he postulated that for this reason there must be some material that was toxic to insects alone. After testing the biological effects of hundreds of different chemicals, in 1939 he discovered that the compound DDT met most of his design criteria. First synthesized in 1873 by German chemist Othmar Zeidler , who had not known of its insecticide potential, DDT could be sprayed as an emulsion with water or could be mixed with talcum or chalk powder and dusted on target areas. It was first used against the Colorado potato beetle in Switzerland in 1939; it was patented in 1940 and went on the market in 1942.
Müller had set out to find a specific compound that would be cheap, odorless, long-lasting, fast in killing insects, and safe for plants and animals. He almost managed it. DDT in short term application is so non-toxic to human beings that it can be applied directly on the skin without ill effect. It is cheap and easy to make, and it usually needs to be applied only once during a growing season, unlike biodegradable pesticides which must often be applied several times, in larger amounts and at much higher cost. Typhus and malaria are very severe, often fatal illnesses, which are carried by body lice and mosquitoes respectively; in the 1940s several potentially severe epidemics of these diseases were averted by dusting the area and the human population with DDT. The insecticide saved many lives during World War II and increased the effectiveness of Allied forces. Soldiers fighting in both the Mediterranean and the tropics were dusted with DDT to kill lice, and entire islands were sprayed by air before invasions.
Despite these successes, environmentalists were concerned from the time DDT was introduced about the dangers of its indiscriminate use. DDT was so effective that all the insects in a dusted area were killed, even beneficial ones, eradicating the food source from many birds and other small creatures. Müller and other scientists were actually aware of these concerns, and as early as 1945 they had attempted to find some way to reduce DDT's toxicity to beneficial insects, but they were unsuccessful. Müller also believed that insecticides must be biodegradable.
Hailed as a miracle compound, DDT came into wide use, and the impact on beneficial insects was not the only problem. Because it was such a stable compound, DDT built up in the environment; this was a particular problem once it began to be used for agricultural purposes and applied over wide areas year after year. Higher animals, unharmed by individual small doses, began to accumulate large amounts of DDT in their tissues (called bio-accumulation ). This had serious effects and several bird species, most notably the bald eagle, were almost wiped out because frequent exposure to the chemical caused the shells of their eggs to be thin and fragile. Many insects also developed resistances to DDT, and so larger and larger amounts of the compound needed to be applied yearly, increasing the rate of bio-accumulation. The substance was eventually banned in many countries; in 1972 it was banned in the United States.
In addition to the 1948 Nobel Prize in physiology or medicine, Müller received an honorary doctorate from the University of Thessalonica in Greece in recognition of DDT's impact on the Mediterranean region. He retired from Geigy in 1961, continuing his research in a home laboratory. He died on October 13, 1965.
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