DDT

Dichlorodiphenyltrichloroethane (DDT) is one of the best-known synthetic pesticides. It was first synthesized by German chemist Othmar Zeidler in 1874. However, it remained a laboratory curiosity until Swiss chemist Paul Hermann Müller discovered its insecticidal properties in 1939. DDT was adopted for widespread use in public health programs. It was the most effective agent known at eradicating diseases that are transmitted by insects and was the first synthetic organic substance used in large quantities for insect control. As a consequence, the undesirable side effects of chlorinated hydrocarbons were first discovered along with it. During World War II, DDT was used by the military and civilians to control the spread of malaria and typhus by mosquitoes and lice, respectively. As a result of his discovery of DDT's insecticidal properties, Müller, of Geigy Pharmaceutical, was awarded the 1948 Nobel Prize in Physiology and Medicine.

[Page 120]After the war, DDT was used as an agricultural insecticide. The first reports of ecological problems related to the use of DDT were published in 1950. These reports were followed by the publication in 1962 of Rachel Carson's Silent Spring, which documented the chemical's devastating effect on the ecosystem and launched the modern environmental movement. The American biologist highlighted the environmental impacts of the indiscriminate spraying of DDT in the United States and questioned the release of the chemical into the environment without analyzing its effects on ecology and human health. The book suggested that DDT and other pesticides could cause cancer, explaining that their agricultural use was a threat to wildlife. Silent Spring resulted in an extensive public outcry that led to the ban of DDT in the United States. DDT was first banned in Hungary in 1968, Norway and Sweden in 1970, and the United States in 1972, but it was not banned in the United Kingdom until 1984. It was subsequently banned for agricultural use worldwide under the Stockholm Convention, though it is still being used in some underdeveloped countries for disease vector control. The Stockholm Convention was signed by 98 countries and is endorsed by most environmental groups.

Available epidemiological and experimental data indicate that the presence and persistence of DDT and its metabolites worldwide are still problems of great relevance to public health. The use of DDT in vector control has been largely replaced by less persistent insecticides. The large-scale manufacture and distribution of organochlorines took place after the accidental discovery of DDT. It is an organochlorine insecticide commonly used for the control of disease-bearing insects and on a variety of food crops. Although DDT has been banned in most nations because of its potential for human toxicity and severe ecological effects, it is still found worldwide as a contaminant because of its extreme persistence and high mobility in the environment.

DDT has the molecular formula C14H9Cl5 and molar mass of 354.49 g/mol. Its density is 0.99 g/cm3, and its boiling point is 109 degrees C. Its structure is similar to the pesticides dicofol and methoxychlor. It is a highly hydrophobic, colorless, crystalline solid with a weak odor. It is soluble in most organic solvents, fats, and oils and is produced by the reaction of chloral (CCl3CHO) with chlorobenzene (C6H5Cl) in the presence of sulfuric acid, which acts as a catalyst. Trade names that DDT has been marketed under include Anofex, Cezarex, Chlorophenothane, Clofenotane, Dicophane, Dinocide, Gesarol, Guesapon, Guesarol, Gyron, Ixodex, Neocid, Neocidol, and Zerdane. Commercial DDT is a mixture of some related compounds. The components include p, p-DDT isomer (77 percent), o, p’-DDT (15 percent), dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyldichloroethane (DDD). DDE and DDD are also the major metabolites and breakdown products of DDT in the environment and in the body. Total DDT in a sample, therefore, refers to the sum of all DDT congeners (p, p-DDT, o, p-DDT, DDE, and DDD).

...