114: Insecticides: Organic Chlorines, Pyrethrins/Pyrethroids, and Insect Repellents

ORGANIC CHLORINE PESTICIDES

History and Epidemiology

Until the 1940s, commonly available pesticides included highly toxic arsenicals, mercurials, lead, sulfur, and nicotine. When Nobel Prize-winning chemist Paul Müller demonstrated the insecticidal properties of dichlorodiphenyltrichloroethane (DDT) in the early 1940s, a whole new class of pesticides was introduced. The organic chlorine insecticides were inexpensive to produce, nonvolatile, environmentally stable, and had relatively low acute toxicity when compared to previous 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).¹⁶⁴ 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 (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.³⁴ By 1953, DDT alone was credited for saving an estimated 50 million lives and with averting one billion cases of human disease. It has also been credited with eliminating malaria from the United States and Europe. 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 1970.⁴⁶