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Organic chlorine pesticides are complex, cyclic, polychlorinated hydrocarbons having molecular weights generally in the range of 300 to 550 daltons. They are nonvolatile solids at room temperature. Most act as central nervous system (CNS) stimulants. In contrast, chlorinated hydrocarbon solvents and fumigants are low-molecular-weight, alkyl compounds that are volatile liquids or gases, and generally have CNS-depressant effects (Chap. 106). The pyrethrins, which are extracted from chrysanthemum flowers, are highly effective contact poisons. When properly used they have almost no mammalian systemic toxicity. These molecules are rapidly hydrolyzed and broken down by light with no environmental persistence or bioaccumulation.

History and Epidemiology

Until the 1940s, commonly available pesticides included highly toxic arsenicals, mercurials, lead, sulfur, and nicotine. When Nobel Prize–winning chemist Paul Möller demonstrated the insecticidal properties of dichlorodiphenyltrichloroethane (DDT) in the early 1940s, a whole new class of pesticides was introduced.51 The organic chlorine insecticides were inexpensive to produce, nonvolatile, environmentally stable, and had relatively low acute toxicity when compared to previously available insecticides. Most organic chlorines have a negative temperature coefficient, making them more insecticidal at lower temperatures, and less toxic to warm-blooded organisms (Table 114–1).172 Widespread use of these xenobiotics occurred from the 1940s until the mid-1970s. They were highly effective and revolutionized modern agriculture, allowing unprecedented crop output from each acre of arable land. Because of their stability, organic chlorines were used extensively in structural protection (from termites, carpenter ants) and soil treatments. Medical and public health applications of DDT and its analogues were also found in the control of typhus and eradication of malaria by eliminating the mosquito vector.41 By 1953, DDT alone was credited for saving an estimated 50 million lives, and for averting one billion cases of human disease. It is suggested that because of this consequential impact on human health, DDT is the single most important factor in the population explosion that occurred between 1950 and 1970.52

Table 114–1. Classification of Organic Chlorine Insecticides

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