1,4-Dioxin

Not to be confused with dioxane or digoxin.

For the chemical compounds which are environmental pollutants, see polychlorinated dibenzodioxins.

Template:Chembox new Dioxin is a heterocyclic, organic, antiaromatic compound with the chemical formula C₄H₄O₂. There are two isomers, 1,2-dioxin (or o-dioxin) and 1,4-dioxin (or p-dioxin). Their chemical structures are shown at right. The ortho isomer 1,2-dioxin is very unstable due to its peroxide-like characteristics. The known properties of 1,4-dioxin are listed in the infobox to the right.

1,4-dioxin can be prepared by cycloaddition, namely by the Diels-Alder reaction.

Dioxin is used as a blanket term for a family of chemical compounds that are formed through combustion, chlorine bleaching and manufacturing processes. The combination of heat and chlorine creates dioxin. Since chlorine is often a part of the earth's environment, natural ecological activity such as volcanic activity and forest fires can lead to the formation of dioxin. Nevertheless, dioxin, a highly carcinogenic and toxic compound, is mostly created by human activity.

Other meanings

Skeletal formulas and substituent numbering schemes of Dioxin isomers

The skeletal formula and substituent numbering scheme of dibenzo-1,4-dioxin, the parent compound of PCDDs

The word dioxin can also in a general way refer to compounds whose molecules have a dioxin core skeletal structure with substituent molecular groups attached to it. For example, dibenzo-1,4-dioxin is a compound whose structure consists of two benzo- groups fused onto a 1,4-dioxin ring as shown below (see also Dibenzodioxin).

Because of their extreme importance as environmental pollutants, current scientific literature uses the name dioxins commonly for simplification to denote the chlorinated derivatives of dibenzo-1,4-dioxin, more precisely the polychlorinated dibenzodioxins (PCDDs), among which TCDD, a tetrachlorinated derivative, is the best known. The polychlorinated dibenzodioxins, which can also be classified in the family of halogenated organic compounds, have been shown to bioaccumulate in humans and wildlife due to their lipophilic properties, and are known teratogens, mutagens, and carcinogens. References under the main article on polychlorinated dibenzodioxins.

Additionally, sometimes with dioxins a similar, but unrelated compound type the polychlorinated dibenzofurans of like importance are also implied.

Toxicity

Some dioxin derivatives are carcinogenic, and directly correllated with an increase in the likelihood of attaining cancer (see above). Scientists are working to establish their exact toxicity. The job is made difficult because we are not dealing with pure chemicals, but a mixture, and toxicity depends on the particular molecular arrangement of the compound, that of the highest toxicity is the 2,3,7,8-tetrachlorodibenzo-1,4-dioxin (pictured here as well). When people say dioxins, they often refer to these chlorinated derivatives, not the compound described in this article. These cases are discussed in detail in the article on Polychlorinated dibenzodioxin or PCDD but the toxicity of even some of these is disputed. The Vietnamese Veterans case, the Seveso case, and Viktor Yushchenko's chloracne case and more are all discussed in that article. Another group of compounds of similar toxicity to that of the PCDD's are the polychlorinated dibenzofurans, their toxicity is also discussed with Dioxin derivatives, sometimes calling them all erroneously dioxins.

Health and Safety

Preventing dioxin release into the environment

In January, 1997, The U.S. Environmental Protection Agency's New England office and the Maine Department of Environmental Protection announced a precedent-setting program to control levels of dioxin in waste water discharges from Lincoln Pulp & Paper Company of Lincoln Maine. Per EPA, "The dioxin limits in the Lincoln permit are the most stringent ever required of a paper mill by EPA anywhere in the country. Lincoln, an integrated bleached kraft paper mill making recycled products from waste sawdust, has agreed to the terms of federal and state waste water discharge permits that will require the company to achieve the following:

• A non-detect (10 parts per quadrillion [ppq]) dioxin limit at the bleach plant, the most stringent limit ever issued in the country. (The company's current permit has no dioxin limit or requirements.) This is the first permit ever issued that requires the elimination of detectable levels of dioxin at the bleach plant;
• A reopener provision which allows the permit to be modified to include any more stringent national technology-based dioxin controls which may become effective during the life of the permit;
• No increases in dioxin, even if the plant expands production;
• Compliance within one year (the law allows up to 3 years);
• An 80% Total Suspended (TSS) removal limit to assure efficient treatment plant removal of dioxin;
• An extensive biological monitoring program in collaboration with the US Fish and Wildlife Service;
• A reopener provision which allows for the permit to be modified if future dioxin concentrations in fish warrant further action."

Per EPA: "It sets a high standard for other mills and substantially advances our efforts to achieve Governor King's goal of lifting dioxin related fish consumption advisories and ultimately eliminating the discharge of dioxin."