Dioxin

What are dioxins?

Pure dioxins are colorless solids or crystals. They are an unused byproduct of various combustion and manufacturing processes, and they can occur naturally as the result of forest fires or volcanic eruptions. Scientists have found dioxins in sediments in lakes and rivers, plant leaves, and other organic substances.

The peak period for dioxin production in the U.S. was during the 1960s and 1970s, when they were released by the pesticide, manufacturing, and municipal waste incineration industries. Since then, regulations have dramatically reduced dioxin levels. Sediment samples from around the world indicate an 80% decline in dioxin concentrations since 1970.

The majority of dioxin released into the environment results from:

• waste incineration;
• fossil fuel (coal, oil, natural gas, wood) combustion;
• chemical and paper manufacturing;
• automobile exhaust;
• cigarette smoke; and
• soot from home fireplaces.

Opinions are divided about the human health risk related to dioxin. However, studies of possible dioxin health effects are ongoing.

How much dioxin is released by electric utilities?

According to the U.S. Environmental Protection Agency (EPA), the electric utility industry accounts for roughly 1% of national manmade dioxin releases. The combustion conditions in utility boilers produce dioxin in concentrations much lower than those produced in residential, commercial, and industrial boilers, furnaces, or fireplaces. Collectively, U.S. coal-fired power plants emit 0.2 pounds per year and oil-fired plants release 0.01 pounds annually.

How could I be exposed to dioxin?

Dioxin is common and is found in the soil, water, and air. Therefore, humans are continuously exposed to low background levels. For the average person, more than 90% of dioxin exposure can be attributed to the consumption of meat, dairy products, and fish.

Airborne concentrations of dioxins are highest near urban industrial sites. Rural areas usually have extremely low levels. In urban and suburban settings, dioxin concentrations tend to rise during colder months when home furnaces and wood stoves are used for heating. Dioxin particulates found in municipal incineration fly ash are 100 times greater than those found in fly ash from oil-fired power plants.

What does EPA say?

EPA recently released a draft dioxin risk assessment updating earlier studies that had classified dioxin as a probable human carcinogen. The new risk assessment demonstrates continued uncertainty about the human health effects of dioxin exposure. It raises three specific questions about dioxins:

• Is there a low level of exposure that is harmless?
• Are current exposure levels harmful to adults or children?
• What are the most important sources of dioxins?

EPA and others are working to resolve these questions and reach consensus on what level of dioxin exposure is "acceptable."

Where can I get more information?

• Chemical Industry Institute of Toxicology
  6 Davis Drive
  P.O. Box 12137
  Research Triangle Park, N. Carolina 27709-2137
  phone (919)558-1310
  
  
• Electric Power Research Institute
  3412 Hillview Ave.
  P.O. Box 10412
  Palo Alto, California 94303
  phone (650)855-2000
  
  
• Statistical Abstract of the United States, 1997, The National Data Book, U.S. Department of Commerce, Economics, and Statistics Administration, Bureau of the Census, 1997.
  
  
• Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units' Final Report to Congress, Volume 1 and 2, U.S. Environmental Protection Agency, 1998.
• Toxicological Profile for Chlorinated Dibenzo-p-Dioxins, U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substance and Disease Registry, 1997.