There are 210 different dioxins and furans. All dioxins have the same basic chemical “skeleton,” and they all have chlorine atoms as part of their make-up. Furans are similar, but have a different “skeleton”. These substances vary widely in toxicity. The one considered most toxic is referred to as 2,3,7,8-tetrachlorodibenzo-p-dioxin, or simply TCDD.

The biggest source of dioxins and furans in Canada is the large-scale burning of municipal and medical waste. Other major sources include:

• the production of iron and steel
• backyard burning of household waste, especially plastics
• fuel burning, including diesel fuel and fuel for agricultural purposes and home heating
• wood burning, especially if the wood has been chemically treated
• electrical power generation
• tobacco smoke

Dioxins can also be produced from natural processes, such as forest fires and volcanic eruptions. Most dioxins are introduced to the environment through the air. The airborne chemical can attach to small particles that can travel long distances in the atmosphere, which means that Canadians may also be exposed to dioxins and furans created in other countries.

These substances work their way up the food chain by moving into and remaining stored in body fat. Because of this, people actually take more dioxins and furans into their bodies through food than through air, water or soil. Ninety per cent of people’s overall exposure to dioxins is estimated to be from the diet. Meat, milk products and fish have higher levels of dioxins and furans than fruit, vegetables and grains.