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The chemical name for dioxin is: 2,3,7,8- tetrachlorodibenzo para dioxin (TCDD).

The name “dioxins” is often used for the family of structurally and chemically related polychlorinated dibenzo para dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs).

Certain dioxin-like polychlorinated biphenyls (PCBs) with similar toxic properties are also included under the term “dioxins”.

Some 419 types of dioxin-related compounds have been identified but only about 30 of these are considered to have significant toxicity, with TCDD being the most toxic.

Dioxins are classed as a persistant organic pollutants, (POPs), also known as PBTs (Persistent, Bioaccumulative and Toxic) or TOMPs (Toxic Organic Micro Pollutants.)

POPs are a small set of toxic chemicals that remain intact in the environment for long periods and accumulate in the fatty tissues of animals. You can find out more about POPS here

burning plastic & cow

Dioxins occur as by-products in  the incineration of chlorine-containing substances such as PVC (polyvinyl chloride), in the chlorine bleaching of paper, and from natural sources such as volcanoes and forest fires, waste incineration, and backyard trash burning, and herbicide manufacturing. More on burning plastic here

The most toxic chemical in the class is 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD). The highest environmental concentrations of dioxin are usually found in soil and sediment, with much lower levels found in air and water.

The word “dioxins” may also refer to other similarly acting chlorinated compounds (see Dioxins and dioxin-like compounds).

Dioxins are of concern because of their highly toxic potential. Experiments have shown they affect a number of organs and systems. Once dioxins have entered the body, they endure a long time because of their chemical stability and their ability to be absorbed by fat tissue, where they are then stored in the body. Their half-life in the body is estimated to be seven to eleven years.

In the environment, dioxins tend to accumulate in the food chain. The higher in the animal food chain one goes, the higher the concentration of dioxins.

“Humans are primarily exposed to dioxins by eating food contaminated by these chemicals. Dioxin accumulates in the fatty tissues, where they may persist for months or years. People who have been exposed to high levels of dioxin have developed chloracne, a skin disease marked by severe acne-like pimples. Studies have also shown that chemical workers who are exposed to high levels of dioxins have an increased risk of cancer. Other studies of highly exposed populations show that dioxins can cause reproductive and developmental problems, and an increased risk of heart disease and diabetes. More research is needed to determine the long-term effects of low-level dioxin exposures on cancer risk, immune function, and reproduction and development.”

Doixin is a known human carcinogen and the most potent synthetic carcinogen ever tested in laboratory animals. A characterization by the National Institute of Standards and Technology of cancer causing potential evaluated dioxin as over 10,000 times more potent than the next highest chemical (diethanol amine), half a million times more than arsenic and a million or more times greater than all others.” From the World Health Organisation

“Dioxins, which are highly toxic even at low doses, are produced when plastics are manufactured and incinerated. While dioxin levels in the U.S. environment have been declining for the last 30 years, they break down so slowly that some of the dioxins from past releases will still be in the environment many years hence.

In its 2000 final draft reassessment of the health effects of dioxins, the EPA concluded that dioxins have the potential to produce an array of adverse health effects in humans. The agency’s report estimated that the average American’s risk of contracting cancer from dioxin exposure may be as high as one in 1,000–1,000 times higher than the government’s current “acceptable” standard of one in a million.

Dioxins are also endocrine disruptors, substances that can interfere with the body’s natural hormone signals. Dioxin exposure, moreover, can damage the immune system and may affect reproduction and childhood development.” The green guide

Dioxins are unintentionally, but unavoidably produced during the manufacture of plastics containing chlorine, including PVC and other chlorinated plastic feedstocks.

Halogenated plastics include:
Chlorine based plastics:
Chlorinated polyethylene (CPE)
Chlorinated polyvinyl chloride (CPVC)
Chlorosulfonated polyethylene (CSPE)
Polychloroprene (CR or chloroprene rubber, marketed under the brand name of Neoprene)
PVC
Fluorine based plastics:
Fluorinated ethylene propylene (FEP)

Burning these plastics can release dioxins. 

More on PVC here

More on burning plastic here

Other Sources

U.S. Department of Health and Human Services

Wikkipedia

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