WikiJournal of Medicine/Dioxins and dioxin-like compounds: toxicity in humans and animals, sources, and behaviour in the environment/XML

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     <title>Dioxins and dioxin-like compounds: toxicity in humans and animals, sources, and behaviour in the environment</title>
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Dioxins and dioxin-like compounds comprise a group of chemicals including polychlorinated dibenzo''-p-''dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), as well as certain dioxin-like polychlorinated biphenyls (dl-PCB), and potentially others. They act via a common mechanism, stimulation of aryl hydrocarbon receptor (AH receptor, AHR), a vital transcription factor in cells. There are very high differences in potency among these compounds, i.e. in the ability to stimulate the receptor. This leads to ten thousand fold or higher differences in doses causing similar toxic effects. Most of these compounds are eliminated very slowly in the environment, animals, or humans, which makes them persistent. They are much more soluble in fat than in water, and therefore they tend to accumulate in lipid or fatty tissues, and concentrate along the food web (bioaccumulation and biomagnification).PCDD/PCDFs are formed mostly as side products in burning processes, but PCBs were oils manufactured for many purposes. Because of toxicity and persistence, dioxin-like compounds have been regulated strictly since 1980s, and their levels in the environment and animals have decreased by an order of magnitude or more. Therefore the effects on wildlife have clearly decreased, and even populations at the top of the food web such as fish-eating birds or seals have recovered after serious effects on their reproductive capacity and developmental effects in their young especially in 1970s and 1980s. This does not exclude the possibility of some remaining effects.In humans the intake is mostly from food of animal sources, but because our diet is much more diverse than that of such hallmark animals as white-tailed eagles or seals, the concentrations never increased to similar levels. However, during 1970s and 1980s effects were probably also seen in humans, including developmental effects in teeth, sexual organs, and the development of immune systems.Both scientists and administrative bodies debate at the moment about the importance of remaining risks. This is very important, because the AH receptors seem to be physiologically important regulators of growth and development of organs, immunological development, food intake and hunger, and in addition regulate enzymes protecting us from many chemicals. Thus a certain level of activation is needed, although inappropriate stimulation of the receptor is harmful. This dualism emphasizes the importance of benefit versus risk analysis. As a whole, regulating the emissions to the environment is still highly important, but one should be very cautious in limiting consumption of important and otherwise healthy food items and e.g. breast feeding.Distinct toxic effects of high doses of dioxins in humans have been clearly demonstrated by frank poisonings and the highest occupational exposures. Hallmark effects have been skin lesions called chloracne, various developmental effects of children, and a slightly increased risk of total cancer rate. The highest dioxin levels have been ten thousand fold higher than those seen in the general population today.

Note: This review is based on original studies and scientific reviews, independently of existing Wikipedia articles, and as interpreted by author's 35 year experience in dioxin research. However, pieces of similar information can be found in Wikipedia articles Dioxins and dioxin-like compounds, 2,3,7,8-tetrachlorodibenzodioxin, Polychlorinated dibenzodioxins, Polychlorinated dibenzofurans, Polychlorinated biphenyl, and Persistent organic pollutant.