Dieldrin

Dieldrin is a chlorinated hydrocarbon originally produced by Bayer AG as an insecticide. The molecule has a ring structure based on naphthalene.

Dieldrin is closely related to aldrin which itself breaks down to form dieldrin. Aldrin is not toxic to insects, it is oxidised in the insect to form dieldrin which is the active compound. Both dieldrin and aldrin are named after the Diels-Alder reaction which is used to form aldrin from a mixture of norbornadiene and hexachlorocyclopentadiene.

Originally developed in the 1940s as an alternative to DDT, dieldrin proved to be a highly effective insecticide and was very widely used during the 1950s to early 1970s. Endrin is a stereoisomer of dieldrin.

However, it is an extremely persistent organic pollutant, it does not easily break down. Furthermore it tends to accumulate as it is passed along the food chain. Long-term exposure has proven toxic to a very wide range of animals including humans, far greater than to the original insect targets. For this reason it is now banned in most of the world.