Dioxins are not intentionally produced. They are the unintended by-products of processes involving chlorine, such as waste incineration, chemical and pesticide manufacturing, and the bleaching of paper (above). Photo: Stock Exchange

Dioxins are a group of hundreds of highly persistent organic compounds. According to the National Academy of Sciences, one prominent dioxin chemical, 2,3,7,8-TCDD, is “among the most toxic anthropogenic substance[s] ever identified.”

This remarkably blunt statement prefaces the Academy’s scientific review of EPA’s reassessment of the health risks posed by dioxins, a long-delayed process that began 15 years ago.

Three of the most important conclusions of EPA’s draft reassessment are:
1) Many dioxins are likely human carcinogens and the general population may face a greater than 1 in 1,000 increased risk of contracting cancer as a result of dioxin exposure.

2) There appears to be no “safe” level of exposure to dioxins, and the “background” dioxin levels found in average Americans closely approach the levels at which adverse effects might be expected to occur.

3) Dioxins mimic human hormones, and their non-cancer effects include adverse impacts on human reproduction and fetal and early-childhood development, and suppression of the immune system. Dioxins are closely related to furans and certain forms of polychlorinated biphenyls (PCBs). Unlike PCBs, however, dioxins are not intentionally produced. Instead, they are the unintended by-products of processes involving chlorine, such as waste incineration, chemical and pesticide manufacturing, and the bleaching of paper.

In recent years, the level of dioxins released to the environment has decreased substantially from a peak in the early 1970s.

However, dioxins persist long after they have been created and released. Currently, up to half of human exposure to dioxins results from the re-release into the environment of dioxins that were produced years ago.
For typical Americans, 95 percent of dioxin exposure comes from the food we eat. Because dioxins are fat-soluble and do not easily metabolize, they bioaccumulate (increase in concentration) as they move up the food chain to humans.

Dioxins are present at elevated levels in fish, meat, and dairy products, particularly in high-fat foods such as butter and cheese.

Unfortunately, many people are exposed to additional, concentrated sources of dioxins. American soldiers and the people of Vietnam were exposed to dioxin-contaminated Agent Orange, used as a defoliant during the war. Times Beach, Missouri, was declared a Superfund site and abandoned after dioxin-contaminated oils were used for dust control.

The town of Midland, Michigan, and the Tittabawassee and Saginaw Rivers are contaminated with high levels of dioxins from the nearby Dow Chemical plant. See related article.

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