Sanders Beach Community Association

Education - Chemicals of ACW - Part 1 - Dioxin

Mar 15, 2005

First in a Series

What is dioxin?
Dioxin is the common name used to refer to the chemical 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD. In addition to dioxin itself there are other compounds, such as the polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and some polychlorinated biphenyls (PCBs), that have similar structures and activity as dioxin. These are often commonly referred to as dioxin-like compounds or "dioxins".

How are dioxins formed?
Dioxins are chemical contaminants that have no commercial usefulness by themselves. They are formed during combustion processes, such as waste incineration, forest fires and backyard trash burning, and during manufacturing processes such as herbicide manufacture and paper manufacture. e.g. dioxin was a contaminant of the herbicide Agent Orange used as a defoliant by U.S. forces in Vietnam.

Why are dioxins of concern?
People are constantly exposed to dioxins through ingestion of dioxins that are present at low levels as environmental contaminants in food. Although they are at low levels in food , some dioxins are very slowly removed from the body and therefore they accumulate in our fat tissue. In laboratory animals, dioxins are highly toxic, cause cancer, and alter reproductive, developmental and immune function.

What are the health effects of dioxin on humans?
Studies have shown that dioxin exposure at high levels in exposed chemical workers leads to an increase in cancer. Other studies in highly exposed people show that dioxin exposure can lead to reproductive and developmental problems, increased heart disease and increased diabetes. Dioxins ability to cause birth defects (teratogenicity) has not been established in humans but studies in mice have shown that dioxin and similar chemicals can produce congenital defects.

In general the effects of dioxin on humans were only observed in populations that were highly exposed. The effect of the long term low level exposure that is normally experienced by the general population is not known. The long-term effects of dioxin exposure on human immunity, reproduction and development, and other organs and systems remain focal points for ongoing research, as are the molecular and cellular mechanisms by which dioxin causes these health effects.

What are the biological mechanisms of dioxin's toxicity?
The way in which dioxin affects cells is similar in some way to the way in which hormones such as estrogen work. Dioxin enters a cell and binds to a protein present in cells known as the Ah receptor. The receptor when bound to dioxin can then bind to DNA and alter the expression of some genes. This can lead to alterations in the level of specific proteins and enzymes in the cell. It is not known exactly how changes in the levels of these different proteins cause the toxicity of dioxin.

Continued next newsletter. Source: http://www.niehs.nih.gov/oc/factsheets/dioxin.htm
Reproduced with permission