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

Michael G. Holland

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

TABLE 114–1.Classification of Organic Chlorine Pesticides
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TABLE 114–1. Classification of Organic Chlorine Pesticides
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Classes of Organic Chlorines Specific Organic Chlorine; CASa Registry# Brand Name(s) Current EPA Registration (US) Acute Oral Toxicity (Man) Dermal Absorption Lipid Storage Specific Characteristics
Hexachloro-­cyclohexanes Lindane (γ isomer) 58–89–9

Kwell;

Gustafson Flowable; Sorghum Guard

 Topical scabicide; Agricultural use cancelled 2006 Moderate High Low Topical scabicide: Seizures, CNS excitation; musty odor
DDT and analogues DDT-Dichlorodiphenyltrichloroethane 50–29–3 Neocid, Ixodex, Anofex, others Cancelled 1972 Low to moderate Low Highest Tremors, CNS excitation; odorless
Methoxychlor 72–43–5 Marlate Cancelled 2003 Low Low Moderate Less toxic DDT substitute
Dicofol 115–32–2 Kelthane Residential Use Banned 1998; Cotton, Citrus, Apple Low Low Low
Chlorobenzilate 510–15–6 Benzilan, BenzoChlor Cancelled 1983 Low Low Low Much less environmental persistence than DDT
Cyclodienes and related compounds Aldrin 309–00–2 Aldrex, Octalene, Toxadrin Cancelled 1974 High High High Rapidly metabolized to Dieldrin; mild “chemical” odor
Dieldrin 60–57–1 Dieldrite, Octalox, Quintox Cancelled 1974 High High High Stereoisomer of Endrin; early and late seizures; odorless
Endrin 72–20–8 Hexadrin Cancelled 1974 Highest High None Most toxic organic chlorine; rapid onset seizures, status epilepticus
Chlordane 57–74–9 Octachlor, Toxichlor, others Cancelled 1988 Moderate High High Early and late seizures occur
Endosulfan 115–29–7 Thiodan, Cyclodan, others REDb 2002 High High Low Strong sulfur odor
Heptachlor 76–44–8 Drinox Restricted: fire ant control, soil treatment Moderate High High Toxic metabolite heptachlor epoxide; odor of camphor
Isobenzan 297–78–9 Telodrin Never Registered High Moderate High

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