Dioxins: What are they?
Dioxins are a group of more than 200 chemicals with a similar structure but varying levels of toxicity, including polychlorinated biphenyls (PCBs), polychlorinated dibenzo dioxins (PCDDs), and polychlorinated dibenzo furans (PCDFs).Dioxins are found just about everywhere - they are present in the atmosphere, soil, rivers and the food chain. They occur naturally as a result of incomplete burning of organic materials during natural events such as volcanoes and forest fires.
But they are also produced during many man-made events which involve combustion such as waste incineration and in chemical and fertiliser manufacturing plants. They may, for example, be produced during chlorine-based bleaching processes in paper mills, or during the manufacture of herbicides. They are also found in low levels in cigarette smoke and vehicle exhaust fumes.
The introduction of a new chlorine production technique in 1900 meant that they became more widespread. However, in recent years manufacturing and environmental controls have reduced the production of dioxins, and the main source now is the burning of fossil fuels and incineration processes. But because of their potential toxicity, exposure even at low levels, remains a concern.
In living organisms, toxic chemicals are often taken up and stored by fat. This means they can persist in the food chain through a process called bioaccumulation.
They are mainly found in meat and dairy produce, but are also found in poultry, fish and on unwashed fruit and vegetables:
- Fish accumulate dioxins through exposure to water - dioxins are repelled by the water and attach themselves to the fatty fish.
- Unless - as was the case in Belgium - feed becomes contaminated, animals are usually exposed to dioxins in the air settling on their food. They accumulate in the fatty tissue of animals, and the longer that animal lives, the greater the build up.
- Dioxins in the air also land on fruit and vegetables, but washing can get rid of these - they are not absorbed into the plant itself.
What are the risks?
Environmental campaign groups describe dioxins as among the most dangerous toxins known. Scientists are working to establish their exact toxicity, but a draft report from the US Environmental Protection Agency indicates dioxins are considered a serious threat to public health.The health risks depend on several factors, including the level of exposure and the particular form of dioxin. For most people, levels in the general environment are not high enough to cause an immediate reaction but over a longer period, potential risks to health include:
- Damage to the immune and reproductive system (with lowering of the sperm count).
- An increased incidence of diabetes.
- A significant increase in the risk of cancer.
- Discolouration of the skin.
- Rashes and redness.
- Vomiting.
- Diarrhoea.
- Lung infections.
- Damage to the nervous systems.
In 1997, a World Health Organisation group declared the most toxic dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD) a class 1 carcinogen, meaning it causes cancer in humans.
Also of concern is the effect dioxins can have on unborn children and infants, as they can be passed through the placenta or carried in breast milk although the World Health Organisation emphasise that the benefits of breast feeding far outweigh any risks to the baby and child.
While governments and environmental bodies strive to minimise the risk, it’s important to keep in mind that it’s very unlikely that most people in the general population will be exposed to a level of dioxins high enough to cause significant toxic effects.
