aldrin (C12H8Cl6), one of the several isomers (compounds with the same composition but different structures) of hexachlorohexahydrodimethanonaphthalene, a chlorinated hydrocarbon formerly used as an insecticide. Aldrin was first prepared in the late 1940s and is manufactured by the reaction of hexachlorocyclopentadiene with bicycloheptadiene (both derived from hydrocarbons obtained from petroleum). Aldrin stimulates the central nervous system and is toxic to warm-blooded animals; poisoning can result from ingestion, inhalation, or absorption through the skin.
The insecticide dieldrin is made from aldrin by treatment with peroxyacetic acid. Isodrin, a stereoisomer (see isomerism) of aldrin, is made from cyclopentadiene and hexachlorobicycloheptadiene; it has insecticidal properties similar to those of aldrin and can be treated with peroxyacetic acid to form another insecticide, endrin, a stereoisomer of dieldrin.
In 1974 the U.S. Environmental Protection Agency withdrew approval for the use of aldrin and its derivatives in all applications except termite control. In 1987 all uses of these insecticides were banned.