What is dioxin?

A close up of a plant being sprayed with pesticides. — Dioxin is an organic chemical that was previously used in pesticides. Lucas Ninno / Getty Images

Dioxin, shown on the right, is an organic chemical that consists of a pair of benzene rings, two oxygen atoms and four chlorine atoms. The chemical DDT also has two benzene rings and contains chlorine atoms, so DDT and dioxin share several characteristics:

Both DDT and dioxin are toxic in small quantities.
Neither of them degrades in the environment -- they both exist indefinitely once released.
Both dissolve and accumulate in fat.

You may recall that DDT, which was sprayed liberally starting in the 1940s to control agricultural insects and mosquitoes, was banned in the 1960s because it accumulated in the fat of animals and destroyed their ability to reproduce. Dioxin suffers from the same problem.

Dioxin enters the environment in several different ways:

The manufacture of certain herbicides
The manufacture of bleached paper
The burning of PVC plastics

The toxicity of dioxin is something that the scientific community does not seem to agree upon. Dioxin became notorious in the 1980s because of Agent Orange and several dioxin dumps (like Love Canal) discovered in the United States. You will see many, many pages on the Web (such as this one) that describe dioxin as the most toxic substance on the planet. Then you will see other references like this one from Encyclopedia Britannica:

"Toxicologists mistakenly concluded from studies on laboratory animals that TCDD (dioxin) was one of the most toxic of all man-made substances… Subsequent research, however, discounted most of these inferences, which were based on the effects of very high doses of TCDD on guinea pigs and other peculiarly susceptible animals. Among humans, the only disease definitely found related to TCDD is chloracne, which develops shortly after exposure to the chemical."

Nonetheless, it is certain that dioxin is not good, does persist in the environment and accumulates in fat like DDT. For certain animals, dioxin is an acutely toxic substance.

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