A7.1 Dioxins and Polychlorinated and Polychlorinated Biphenyls (PCBs)
Dioxin is the molecule shown here:
Figure 7.1 Dioxin
However, many related molecules are collectively referred to as dioxins which are toxic, do not decompose in the environment, and are passed on in food chains.

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Dioxins are considered highly toxic and cause disruption to hormones as well as cellular and genetic damage.
Dioxins are known to cause cancer.
Dioxins contain unsaturated six-member heterocyclic rings with two oxygen atoms, usually in positions 1 and 4. For example the following structures, where a chlorine atom or atoms can be in a number of different positions on the benzene rings:
Figure 7.2 PCB structure
Figure 7.3 Polychlorinated dibenzo-p-dioxins (PCDDs). 7 of these are toxic.
Figure 7.4 Polychlorinated benzofurans (PCBFs). 10 of these are toxic.
PCBs are not strictly speaking dioxins.
PCBs are molecules with this structure shown below and 12 of them have “dioxin-like” toxicity.
Figure 7.5 PCB structure
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