2,3,4,7,8-Pentachlorodibenzofuran

Furan

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.

Emissions of dioxins and furans from an incinerator typical of those currently operating in the UK (230,000 tonnes per year) are approximately equivalent to emissions from accidental fires in a town the size of Milton Keynes (population 230,000). That is, emissions from the Exeter Incinerator will be equivalent to half the emissions from accidental fires in Exeter.

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.

Flavour (DF stands for
dibenzo furan)

Formula

WHO Toxicity
Equivalency Factor

2,3,7,8-Cl4DF

C12H4Cl4O

0.1

1,2,3,7,8-Cl5DF

C12H3Cl5O

0.03

2,3,4,7,8-Cl5DF

C12H3Cl5O

0.3

1,2,3,4,7,8-Cl6DF

C12H2Cl6O

0.1

1,2,3,7,8,9-Cl6DF

C12H2Cl6O

0.1

1,2,3,6,7,8-Cl6DF

C12H2Cl6O

0.1

2,3,4,6,7,8-Cl6DF

C12H2Cl6O

0.1

1,2,3,4,6,7,8-Cl7DF

C12HCl7O

0.01

1,2,3,4,7,8,9-Cl7DF

C12HCl7O

0.01

Cl8DF

C12Cl8O

0.0003

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

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