2,3,4,7,8-Pentachlorodibenzofuran

Polychlorinated dibenzofurans (PCDFs; known colloquially as furans) are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air. Incineration is controlled to minimise their production, and the flue gas is treated post-combustion. The resulting toxic fly ash must be handled as hazardous waste.

The structure of furans comprises two benzene rings (six carbon atoms) joined directly and by one oxygen atom. Chlorine atoms may be attached to this structure at any of positions 1–4 and 6–9 in the above picture, which gives 135 flavours. Hydrogen atoms are attached to the remaining positions.

Of the 135 furan flavours, the ten below exhibit dioxin-like properties and are given toxicity ratings by the World Health Organization (WHO). Furans are commonly regarded as highly toxic compounds that are environmental pollutants and persistent organic pollutants.The reference molecule for rating toxicity is 2,3,7,8-Tetrachlorodibenzo-p-dioxin.

For more information, see the Wikipedia article about dioxins and dioxin-like compounds.