Dioxin, as shown on the right, is an organic chemical that consists of a pair of benzene rings, 2 oxygen atoms and 4 chlorine atoms. Interestingly, DDT also has 2 benzene rings and contains chlorine atoms, so DDT and dioxin share several characteristics:
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.
- Both DDT and Dioxin are toxic in small quantities.
- Neither of them degrades in the environment - they both exist indefinitely once released into the envionment.
- Both dissolve and accumulate in fat.
Dioxin enters the environment in several different ways:
The toxicity of dioxin is something that does not seem to be agreed upon. Dioxin became notorious in the 1980s because of Agent Orange and several dioxin dumps (like Love Canal) discovered in the U.S. You will see many, many pages on the web (for example 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:
- The manufacture of certain herbicides
- The manufacture of bleached paper
- The burning of PVC plastics (see Question 217).
"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.