What is Dioxin? - Definition, Chemical Structure & Examples

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Dioxins are a toxic chemical that is often found in food. There are hundreds of different forms of dioxins, but we will look at the general structure and some specific examples.

Dioxins Overview

We need to eat to survive, but often there are compounds in the foods we eat on a daily basis that could cause us harm. One group of these compounds are dioxins.

Dioxins are a group of chemicals with a similar chemical structure. They are created through some natural processes like volcanoes, but are also emitted into the air by burning trash. Dioxins are heavily present in our food supply, as such, whenever you eat something (particularly meat and dairy products) it probably contains dioxins.

Dioxins are highly toxic, but at the typical levels found in food they probably won't cause any immediate issues. Yet food producers still need to be wary of high levels of dioxins, and thus these levels are strictly monitored. Regulations have helped to bring down emissions from industrial sources by 90% since 1987.

Dioxins are very stable compounds, so once they are in the body they stay there and accumulate over time, usually in the lipids (fatty tissue). Thus, one way to reduce exposure to dioxins is by consuming less fat. This can be done by cutting the fat off of meat or eating low fat dairy and meat products.

There are over 400 different dioxins, although only 30 of them are considered toxic. The chemical formula of dioxin is: C4 H4 O2. It is a cyclic compound and non-aromatic. The most common way this forms is in the para formation:

The para dioxin
Para dioxin

The ortho formation (the oxygen atoms right next to each other) is also possible, but it is not as stable so it does not occur as frequently.

Ortho dioxin


Most of the toxic chemicals have the form of polychlorinated dibenzodioxins (PCDDs). This family of dioxin derivatives has the dioxin between two benzene rings:

Polychlorinated dibenzodioxins (PCDD) puts a benzene ring on either side of the dioxin ring

When PCDD is drawn in this way it may be difficult to identify the dioxin ring, because dioxin is supposed to have two double bonds, and there is only one shown here. There are two ways we can look at this in order to understand why this is still dioxin. First, these benzene rings are fully conjugated, which means that the double bond (at any given moment) could be in the position shown or in another position:

Benzene double bonds continually resonate into other positions
PCDD resonance

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