Page 542 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

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VetBooks.ir Chapter 38

Organochlorines

Steve M. Ensley

INTRODUCTION BACKGROUND
The organochlorines (OCs) are still causing adverse Even though DDT was first synthesized by Othmar
health effects in humans and animals in 2017. Most OCs Zeidler in 1874, it was another 40 years before this com-
were banned in the United States in the 1980s. Despite pound was used as an insecticide. Paul Mueller, a Swiss
the ban these chemicals are still causing adverse health in chemist, rediscovered DDT in 1939 while investigating
animals in the United States and worldwide. insecticides for use against clothes moths and carpet bee-
Historically many methods have been used and devel- tles. Mueller won the Nobel Prize in 1948 for this work.
oped to control or eliminate insects and other plant and ani- “This pleasant smelling, greasy white powder (DDT) has
mal pests that have threatened man and his food supply. had an influence on human ecology perhaps unmatched
Chemicals used in the past to control insects include sulfur by any other chemical discovery including gunpowder,
(used before 1000 BC and is still used today), vinegar, sulfanilamide, penicillin, and plutonium” (Metcalf, 1973).
whale oil and arsenic (used in the 1500s), nicotine (used in The insecticidal properties of technical HCH (t-hexa-
the 1600s), rotenone from the plant Derris eliptica,pyre- chlorocyclohexane; commonly known as benzene hex-
thrum from Chrysanthemum cinerariaefolium,copperarse- achloride) and the first cyclodiene insecticides (e.g.,
nate (used in the 1800s) and calcium and lead arsenate aldrin, dieldrin, chlordane) were discovered as a result of
(used in the early 1900s). There were major changes in the the commercial interest in new uses for chlorine and
development of insecticides in the 1930s when the synthetic hydrocarbons such as cyclopentadiene and benzene. The
organic chemical industry began developing compounds to first use of the chlorinated hydrocarbons was for dielec-
control insects. Chlorinated compounds such as aldrin and trics and as fire retardants. The use of these compounds
dieldrin, used as insecticides, became available for use in as insecticides occurred when benzene was added to liq-
the 1940s. Dichlorodiphenyltrichloroethane (DDT) became uid chlorine in the field and it was noted that the product
available during World War II and was used extensively as killed insects.
an insecticide worldwide. OCs were effective because they As with many insecticides there are many unintended
persist in the environment (Leonard et al., 1999; Hites secondary targets for every insecticide (Uzoukwu and
et al., 2004; Hoekstra et al., 2005). Because of that persis- Sleight, 1972; Furie and Trubowitz, 1976; Hathway,
tence, most have been eliminated from use today. Lindane 1977). Hexachlorocyclopentadiene, a raw material used in
(gamma-hexachlorocyclohexane) and endosulfan are the manufacturing chemicals, was known to be stable and
most biodegradable OCs and are still used today. was found to react easily with cyclopentadiene in a Diels-
The diphenyl aliphatic OCs, such as DDT, affect the Alder reaction, which leads to the production of chlor-
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peripheral nerves and brain by slowing sodium (Na ) dane. It was discovered later to react with norbornadiene
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influx and inhibiting potassium (K ) outflow. This results (a bicyclic hydrocarbon) to produce aldrin. Allylic chlori-
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in excess intracellular K in the neuron, which partially nation of chlordane produces heptachlor. The intermediate
depolarizes the cell. hexachloronorbornadiene reacts with cyclopentadiene to
In the 1980s, the mechanism of toxicity for the cyclo- produce isodrin and after epoxidation, dieldrin, and endrin
diene OC insecticides was determined. These compounds are produced. Technical hexachlorocyclohexane (t-HCH)
were found to be noncompetitive antagonists acting on can be used to produce the gamma isomer lindane. One of
the chloride ion channel of the gamma-aminobutyric acid the problems with the production of lindane is the ineffi-
A (GABA) receptor. ciency of the process; for every ton of lindane produced,

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