September 29, 2004
BY HUGH McDIARMID JR.
FREE PRESS STAFF WRITER
What are dioxins?
First identified by scientists more than 40 years ago, dioxins largely are the by-products of industrial processes including incineration and chemical manufacturing. Natural combustion, such as forest fires and volcanoes, also produce small amounts. Until their discovery and the subsequent environmental laws of the 1970s, industries released them unchecked into the air and water. After release, they settle into soil and sediment at the bottom of rivers and lakes, gradually working their way up the food chain. The term dioxin is used for a family of chlorinated chemical compounds. Can we see them?
No. Dioxins are so potent they are measured in parts per trillion. One part per trillion is roughly equivalent to one square foot of land in the state of Indiana.
Why are they bad?
Studies on animals link dioxins to hormone changes, damaged fetal development, suppressed immune systems, diabetes and cancers, among other problems. Levels in the general human population are close to those in which effects have been observed in animals, according to the U.S. Environmental Protection Agency.
The most toxic member of the dioxin family is a known cancer-causing chemical, 2,3,7,8-TCDD. More than a dozen other forms are classified by the EPA as probable carcinogens. The dioxin 2,3,7,8-TCDD was an unwanted contaminant in the defoliant Agent Orange -- manufactured at Dow Chemical Co. in Midland and dropped from airplanes on jungles during the Vietnam War -- that is believed to have sickened thousand of U.S. servicemen and Vietnamese who breathed it. "There are reams and reams and reams of information on the adverse effects on wildlife and domestic animals," said EPA researcher Linda Birnbaum, director of the EPA's experimental toxicology division and an internationally recognized dioxin expert. She calls dioxin "the most toxic manmade chemical" ever produced and says dioxin poisoning has stopped natural reproduction of Lake Ontario lake trout and of minks living near Lake Michigan.
Some scientists suggest that the effects of dioxins on human health are not as pronounced as they are in animals.
A 1999 report from the Agency for Toxic Substances and Disease Registry stated: "Although dioxin is extremely toxic in some animals, humans appear to be more resistant to its toxicologic effects than most animals in which it has been tested."
It is unclear how long-term, low-level exposures affect health.
But Birnbaum said growing evidence suggests that the levels of dioxin found in some people -- who are at the high end of the normal range -- may alter metabolism and contribute to increased incidences of diabetes, cognitive development problems and cancer.
Can't we eliminate them?
No. Some dioxins are created naturally -- by forest fires, for example. But industrial dioxin emissions have been cut by more than 90 percent since 1987 and continue to decline. The problem is that they degrade so slowly that existing dioxins will be around for many decades.
In soil, it can take between 10 and 100 years for dioxin levels to degrade by half. In humans, that half-life is between five and 12 years.
How and where do people get dioxins?
Organisms at the bottom of the food chain can take up dioxins from the soil on land and bottom sediment in lakes and rivers. Larger animals can get dioxins from the meat of prey and incidental ingestion of soil or dust that settles on plants they eat.
People typically get 95 percent of their dioxins from food. Because the chemicals are stored in body fat, foods with high fat content, such as meat, fish, dairy products and eggs, are prime dioxin sources. Plants generally do not take up dioxins from the soil.
Are dioxins in the soil a risk to humans?
Dioxins can be absorbed through inhalation of contaminated dust or incidental ingestion of soil -- especially among children.
The key questions of how readily dioxins in soil are transferred to human beings and what long-term effects they are having on the ecosystem are being studied in Midland and Saginaw counties.
Contact HUGH McDIARMID JR. at 248-351-3295 or mcdiarmid@freepress.com.
For additional articles like this one, go to the Tittabawasse River Watch web site www.trwnews.net for complete coverage of the Tittabawassee River Dow Chemical dioxin contamination saga. . The Newspaper / Media page of our site contains an extensive archive of media articles dating back to January 2002. The source organization's web site link is listed to the right of the article, visit often for other news in our area. The Newspaper / Media page may be accessed by scrolling down to the bottom of the CONTENTS section and clicking on the Newspaper/Media link.