Dioxin, formed by burning chlorine-based chemical compounds with hydrocarbons, is one of the most toxic chemicals known. Dioxin is a general term that describes a group of hundreds of chemicals that are highly persistent in the environment. It was the highly toxic impurity of Agent Orange, a defoliant used during the Vietnam War, and was the basis for evacuations in Times Beach, Missouri, and Seveso, Italy.

Dioxin has become the synonym for polychlorinated dibenzo[1,4]dioxins (PCDD) in general or the most toxic congener 2,3,7,8-tetrachloro dibenzo[1,4]dioxin (TCDD) in particular. PCDD comprise a group of seventy-five structurally similar compounds, so-called congeners. The individual congeners differ in the number and positions of the chlorine atoms in the molecule. Structurally related are the polychlorinated dibenzofurans (PCDF) (135 congeners). PCDD and PCDF are stable and fat-soluble molecules classified as persistent organic pollutants (POPs). The central element of the PCDD is the dioxin 6-ring...