Dioxins, Dioxins

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Today, concentrations of dioxins are found in all humans, with higher levels commonly found in persons living in more industrialized countries. The most toxic dioxin, 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD), became well known as a contaminant of Agent Orange, an herbicide used in the Vietnam War.

Australia, New Zealand and the United Kingdom all have substantial research into body burdens and sources. Tolerable daily, monthly or annual intakes have been set by the World Health Organization and a number of governments. Dioxins enter the general population almost exclusively from ingestion of food, specifically through the consumption of fish, meat, and dairy products since dioxins are fat-soluble and readily climb the food chain.

Affected compounds include the wood preservative pentachlorophenol, and also herbicides such as 2,4-dichlorophenoxyacetic acid (or 2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Higher levels of chlorination require higher reaction temperatures and greater dioxin production. See Agent Orange for more on contamination problems in the 1960s. Dioxins may also be formed during the photochemical breakdown of the common antimicrobial compound triclosan.

Such materials include tampons, and a wide variety of food packaging substances. The use of these materials means that all Western humans receive at least a very small daily dose of dioxinhowever, it is disputed whether such exceptionally tiny exposures have any clinical relevance. It is even controversially discussed whether dioxins might have a non-linear dose-response curve with beneficial health effects in a certain lower dose range, a phenomenon called hormesis.

In humans, the highly chlorinated dioxins are stored in fatty tissues and are neither readily metabolized nor excreted. The estimated elimination half-life for highly chlorinated dioxins (4-8 chlorine atoms) in humans ranges from 7.8 to 132 years.

It is believed that dioxins with few chlorines, which thus contain hydrogen atoms on adjacent pairs of carbons, can more readily be oxidized by cytochromes P450. The oxidized dioxins can then be more readily excreted rather than stored for a long time.

The TEQ approach and current TEFs have been adopted internationally as the most appropriate way to estimate the potential health risks of mixture of dioxins. Recent data suggest that this type of linear scaling factor may not be the most appropriate treatment for complex mixtures of dioxins; further research into non-linear toxicity models is required to substantiate this hypothesis.

In 1994, the US EPA reported that dioxins are a probable carcinogen, but noted that non-cancer effects (reproduction and sexual development, immune system) may pose an even greater threat to human health. TCDD, the most toxic of the dibenzodioxins, is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). TCDD has a half-life of approximately 8 years in humans, although at high concentrations, the elimination rate is enhanced by metabolism.

Several buildings of the Spolana chemical plant were heavily contaminated by dioxins. Miroslav uta: Spolana asovan bomba na behu Labe , Sedm generace, 10/2002 Unclear amount of dioxins were flushed into the Elbe and Mulde rivers during the 2002 European flood, contaminating the soils.

Source: Wikipedia > Polychlorinated Dibenzodioxins