Environmental Engineering Reference
In-Depth Information
What are Dioxins?
Dioxins and furans are some of the most toxic chemicals known.
Dioxin is a general term that describes a group of hundreds of
chemicals that are highly persistent in the environment. The
most toxic compound is 2,3,7,8-tetrachlorodibenzo-p-dioxin or
TCDD (Figure 6.3). Polychlorinated dibenzofurans are similar
to dibenzodioxins, but with a single oxygen connecting the
two benzene rings instead of two oxygens.
The toxicity of other dioxins and dioxin-like PCBs are mea-
sured in relation to TCDD. Dioxins and furans are not made
on purpose, but are formed as unintentional byproducts of
industrial processes that use chlorine, such as chemical and
pesticide manufacturing, pulp and paper mills that use chlo-
rine bleach, the production of polyvinyl chloride (PVC) plas-
tics, the production of chlorinated chemicals, and incineration
of wastes containing plastic. Dioxin, a contaminant in the
herbicide Agent Orange, was found at Love Canal in Niagara
Falls, New York, and was the basis for evacuations at Times
Beach, Missouri and Seveso, Italy. The industrial accident in
Seveso led to many cases of Acquired Dioxin-Induced Skin
Haematoma, in which the skin acquires disfiguring red lumps.
Dioxins, like PCBs, are organic molecules with varying
numbers and arrangements of chlorine atoms. They are partic-
ularly toxic to the immune system and to developing embryos,
in which effects may occur immediately or may be delayed for
a long period of time, perhaps impairing reproduction once
10
1
9
O
2
8
3
7
O
4
6
5
Figure 6.3 Dioxin molecule, showing the various positions where Cl atoms may be attached.
2,3,7,8 TCDD is the most toxic
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