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12. What are Dioxins/Furans? Dioxins/furans are a group of POPs comprising three structurally closely related chemical families and having similar chemical properties: the chlorinated dibenzo-p-dioxins (CDDs), the chlorinated dibenzofurans (CDFs) and certain dioxin-like polychlorinated biphenyls (PCBs). Dioxins/furans (PCDD/PCDF) are unintentional by-products of industrial and thermal processes involving organic matters and chlorine, formed and released as a result of incomplete combustion or chemical reactions. Dioxins/furans are also produced by natural processes such as forest fires and volcanic eruptions. Dioxins are often found in the form of mixtures rather than as single chemical compounds in the environment. More than 400 types of dioxin-related compounds have been identified, of which about 30 are considered to possess significant toxicity. The toxicity of dioxins varies depending on the individual chemical structure and form. The most toxic forms of dioxins are 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 1,2,3,7,8-PeCDD. Scientists use a relative toxicity scale known as "toxicity equivalent (TEQ)" for comparison of toxicity of different types or mixtures of dioxins to that of 2,3,7,8-TCDD which is assigned a toxicity value of unity. |
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