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What is Dioxin?
Dioxin is the name given to a group of 200+ chemicals that are formed as unwanted by-products of industrial manufacturing and burning activities. The major sources of dioxins include chemical and pesticide manufacture, burning household trash, forest fires, and burning of industrial and medical waste products. In the case of the Tittabawassee River flood plain, the source is known: Dow Chemical
Click here to listen to more of the Dr. Linda Birnbaum (EPA) presentation: "Dioxin, are we at risk?". You are hearing a clip from the video when this page is opened.
Chemical Structure of a few of the most toxic dioxins: TCDD & TCDF
Dioxin belongs to a family of chemicals with related properties and toxicity. There are 75 different dioxins, or polychlorinated dibenzodioxins (PCDDs), 135 different furans, or polychlorinated dibenzofurans (PCDFs), and 209 different polychlorinated biphenyls (PCBs). Each different form is called a "congener."
Not all of the "dioxin-like" chemicals have dioxin-like toxicity, and the toxic ones are not equally toxic. Only 7 of the 75 dioxins, 10 of the 135 furans, and 12 of the 209 PCBs have dioxin-like toxicity. These 29 different dioxins, furans, and PCBs all exhibit similar toxic effects caused by a common mechanism: binding to a particular molecule known as the aryl hydrocarbon or "Ah" receptor (see Chapter 5 of the CHEJ TSD).
It is believed that the tighter the binding to the Ah receptor, the more toxic the chemical. The most potent member of this family is 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD, which also has the greatest affinity for the Ah receptor.
The word "dioxin" is often used imprecisely. Some people restrict its use only to 2,3,7,8-TCDD, the most toxic and most studied dioxin. Others extend its use to the whole class of chemicals with similar toxicity and whose effects are controlled or triggered by the Ah receptor. In this report, the terms "dioxin" and "dioxins" are used to refer to any of the dioxin family members that bind to the Ah receptor and elicit dioxin like effects.
Although all dioxin-like compounds are thought to act in the same way, they are not all equally toxic. Their different toxicities may be due to their unique properties of absorption, distribution, metabolism, and elimination in a body and/or strengths of binding to the Ah receptor. Therefore, the health risk of each congener is assessed by rating their toxicities relative to TCDD, the most potent of the dioxins. TCDD is assigned a value of "1" and each of the 17 toxic dioxins/furans and 12 PCBs is assigned a "toxicity factor" that estimates its toxicity relative to TCDD. The resulting estimates are called toxic equivalency factors (TEFs), which have been recently updated by the World Health Organization.1 The toxic equivalency (TEQ) is determined by multiplying the concentration of a dioxin congener by its toxicity factor. The total TEQ in a sample is then derived by adding all of the TEQ values for each congener. While TCDD is the most toxic form of dioxin, 90% of the total TEQ value results from dioxin-like compounds other than TCDD.
The TEQ system is not perfect, but it is a reasonable way of estimating the toxicity of a mixture of dioxin-like compounds. There is good experimental support for the assumptions that underlie the TEQ system.1,2 TEQs make it possible to take toxicity data on TCDD, a compound about which our knowledge is vast, and estimate toxicity for other compounds about which much less is known.
The links below offer quite a bit of information on what it is, how it can harm you, and what to do to avoid it.