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Dioxins are a group of organic polyhalogenated compounds that are significant because they act as environmental pollutants. They are commonly referred to as dioxins for simplicity in scientific publications because every PCDD molecule contains a dioxin skeletal structure. Typically, the p-dioxin skeleton is at the core of a PCDD molecule, giving the molecule a dibenzo-p-dioxin ring system. Members of the PCDD family have been shown to bioaccumulate in humans and wildlife due to their lipophilic properties, and are known teratogens, mutagens, and confirmed (avered) human carcinogens. They are organic compounds.
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.
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.
Exposure to high concentrations of especially toxic dioxins can cause an acne-like condition known as chloracne which mainly affects the face and upper body, which may last several years after exposure. Chloracne is difficult to cure and can be disfiguring. Other problems include:
•Discolouration of the skin.
•Rashes and redness.
•Damage to the nervous systems.
Most concerns now lie with the potential of dioxins to cause cancer. A peer-reviewed study of the population of Seveso (where an explosion in a chemical manufacturing plant in 1976 liberated large quantities of dioxins into the environment) found that, in the ten years following the accident both men and women more likely to have cancer, especially of the blood and lymph tissue, as well as breast cancer.
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.
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- First report on bioaccumulation and processing of antibacterial ingredient TCC in fish (eurekalert.org)
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