Polychlorinated dioxins and furans: Overview
Description
Dioxins and furans are not manufactured intentionally other than for research. Their relevance to public and environmental health in Australia stems from their generation in small concentrations as by-products of chemical manufacture and incomplete combustion.
Substance details
Substance name: Polychlorinated dioxins and furans
CASR number: Not applicable
Molecular formula: Not applicable. This is a class of substances, the most toxic and widely studied is C12H4Cl4O2 or 2,3,7,8-tetrachlorodibenzo-p-dioxin (CASR# 1746-01-6)
Synonyms: 2,3,7,8-tetrachlorodibenzodioxin; Dioxin; TCDD; 2,3,7,8-tcdd; 2,3,7,8-T4CDD; 2,3,7,8-Tetrachlorodibenzo[b,e][1,4]dioxin; TCDBD; dibenzo-dioxin, 2,3,7,8-tetrachlorinated; 2,3,7,8-Tetrachlorodibenzo-1,4-dioxin; tetrachlorodibenzodioxin; tetradioxin; Tetrachlorodibenzo-1,4-dioxin polychlorinated dibenzo-p-dioxins (PCDDs) polychlorinated dibenzofurans (PCDFs) chlorinated dibenzo-p-dioxins (CDDs)
Physical properties
In the pure form dioxins are crystals or colourless solids. Generally present as mixtures containing a number of individual components. 2,3,7,8-TCDD is odourless, the odours of the other dioxins are not known. There are 75 compounds in the dioxin family and 135 compounds in the furan family. All have varying degrees of toxicity in comparison to the most toxic 2,3,7,8-TCDD.
Melting point: 305 - 306°C
Thermal decomposition: 700°C
Other compounds in these families will have differing properties, depending on the number and position of chlorine atoms in the molecule.
Chemical properties
Dioxins and furans are chemically classified as halogenated aromatic hydrocarbons. The most widely studied compound is 2,3,7,8-tetrachloro-p-dibenzodioxin which is often referred to simply as dioxin and is the reference for a number of compounds which are similar structurally and have dioxin-like toxicity. In general the compounds have low water solubility, low vapour pressure many are very stable and tend to bioaccumulate. There are also a number of dioxin-like PCBs, polybrominated biphenyls and mixed chlorinated and brominated congeners with dioxin-like properties.
Compounds in these families will have differing properties, depending on the number and position of halogen atoms in the molecule.
Further information
The National Pollutant Inventory (NPI) holds data for all sources of Polychlorinated dioxins and furans in Australia.
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