Background

Dioxins are the general name for a group of 210 compounds of similar structures, which differ due to the amount of chlorine in the molecule and where the chlorine is bound. These compounds, known as polychlorinated dibenzo-dioxins and polychlorinated dibenzofurans, vary greatly in toxicity.  Most of these compounds pose no threat to health at the levels commonly found in the environment but 17 of them are of more concern. The most toxic is 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD). Dioxins are non-flammable, colourless solids or crystals at room temperature with no perceptible odour.

Dioxins may be formed during natural processes such as incomplete combustion - for example, during forest fires. Dioxins are not produced commercially, but very small amounts may be formed during the production of some solvents and when chlorinated organic matter and fossil fuels are burnt. Very small amounts may therefore be formed during industrial, domestic and municipal incineration. Small amounts are also released during metal smelting, processing and refining and during the use of chlorine for bleaching of pulp in paper mils.

Dioxins have been detected at low levels in cigarette smoke and motor vehicle emissions.

Dioxins can remain in the environment for a long time and soils and sediments, which are contaminated with dioxins, can release low levels back into the atmosphere.

However, dioxins can be broken down following exposure to UV light.

Dioxins have been found to be present in very small amounts in some food products including meat, dairy products and fish.

Dioxins are toxic by ingestion or inhalation. Most non-occupational exposure to dioxins is via ingestion through consumption of food contaminated with dioxins.

The principal adverse health effect of exposure to dioxins is a form of acne known as chloracne. This is a severe skin disease which mainly affects the face and upper body with acne-like spots that may be present many years after exposure. Exposure to high levels of dioxins may also cause rashes, redness, discolouration of the skin and excess body hair. Liver damage has been observed in individuals exposed to high levels of dioxins.

Children exposed to dioxins would be expected to display similar effects to those seen in exposed adults, although appear to be more sensitive than adults. Experiments in animals suggest that TCDD may reduce fertility and causes adverse developmental effects, particularly in the development of the male reproductive system. There is some evidence from mothers being exposed to dioxins due to the accidental release in Seveso, Italy, that the ratio of boys to girls being born was altered, and babies had thyroid problems.

The International Agency for Research on Cancer has classified TCDD as causing cancer in humans. However, it has concluded that it is not possible to classify the other forms of dioxins as to their ability to cause cancer in humans.

Key Points       Production and Uses

• Dioxins - Production and Uses
  Added/updated: 5 November 2008