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2. How are humans exposed to dioxins?

  • 2.1 What are the principal source of exposure to dioxins?
  • 2.2 What are the other possible sources of dioxin contamination?
  • 2.3 How do dioxins act on living organisms?

Three ways of exposure to dioxins exist: background exposure (mainly through diet), industrial accidents and workplace contamination.

2.1 What are the principal source of exposure to dioxins?

2.1.1 Over 90 percent of human background exposure to dioxins occurs through the diet, essentially with fats from animal origin. Dioxins emitted by various sources deposit on farmland and water bodies and bioaccumulate in the food chains. Other sources of food contamination include contaminated animal feed, sewage sludge contaminated with dioxins, flooding of pastures, waste effluents and inappropriate food processing. More...

2.1.2 In industrialized countries, the daily intake of dioxins (PCDDs and PCDFs) is in the order of 1-3 pg I-TEQ per kg body weight per day, which is close to the Tolerable Intake value set by the World Health Organization (WHO) (see question 6.3). If PCBs are included, the daily intake can be 2 or 3 times higher. Diets low in animal fat result in lower intakes, while consumption of highly contaminated foodstuffs may lead to higher intakes. The body burden of dioxins increases during childhood and reaches an equilibrium around the age of 20. More...

2.1.3 During growth, the intake per kilogram of body weight decreases partly as a result of an increasing average body weight. Recent studies from the Netherlands, United Kingdom and Germany show decreasing dioxin levels in food and consequently a dietary intake lower by almost 2 since the early 90's. More...

2.1.4 For breast fed babies, the daily intake of dioxins per kg of body weight may be ten to hundred times greater than for adults. Breast milk is more contaminated in industrialized areas (10-35 pg I-TEQ/g milk fat) than in developing countries (< 10 pg I-TEQ/g milk fat). However, the levels are decreasing, especially in industrialized countries. Individual contamination can vary by a factor of 5 to 10, depending on age of the mother, number of breastfed babies, length of nursing period and food habits. More...

2.2 What are the other possible sources of dioxin contamination?

2.2.1 Local populations can be accidentally exposed to high dioxin levels, like in Seveso (Italy) in 1976, after an explosion at a chemical factory, or from fires in electrical equipment containing PCBs. Accidental contamination of rice oil in Japan and Taiwan resulted in intakes of dioxin-like compounds many thousand times higher than normal. More...

2.2.2 Industrial activities in which dioxins are unintentionally produced (such as waste incineration or production of certain pesticides or chemicals) may result in exposures of certain workers. In the past, some workers accidentally exposed to high concentrations of dioxins had TCDD blood levels up to thousands of times higher than usual, but today, many industrial sources of dioxins have been identified and the workers' overall exposure has been reduced or eliminated. More...

2.3 How do dioxins act on living organisms?

2.3.1 The toxic dioxins can alter key biochemical and cellular functions by interacting with a cellular receptor called Ah, affecting the hormonal system and the way cells grow and develop. The mechanism of action of dioxins appears to be the same in both humans and animals. More...

2.3.2 Being highly lipophilic, dioxins dissolve in fat. They need to be transformed in the liver to become water soluble before they can be excreted. However, dioxins are metabolized slowly and therefore tend to bioaccumulate, especially in fat and in the liver.

The speed of elimination of dioxins can vary with dose, quantity of body fat, age and sex. The process of elimination of dioxins and PCBs is similar in animals and man, but it is faster in most other mammals. Rodents only reach the same body burdens, or tissue concentration, at much higher exposure compared to humans. This is why body burden must be used as a reference when comparing risks for humans and animals.

The biological half-life, which technically characterizes the speed of elimination, varies largely for the various dioxins and dioxin-like compounds. However the average half-life of 2,3,7,8-TCDD is being used for practical purposes. More...

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