What is dioxin and where does it come from?

Dioxin is not produced intentionally; it can occur when anything containing chlorine burns. Because chlorine is so pervasive in the environment, dioxin is a byproduct of natural events like forest fires, lightning and volcanoes, as well as of manmade activity, such as burning wood and backyard trash, diesel vehicle emissions and various manufacturing processes.

In the past 30 years, dioxin levels in the environment have sharply and steadily declined while production of vinyl has more than tripled.

EPA attributes the dramatic declines in dioxin emissions to regulations and voluntary industry actions. Incinerators are a good case in point. Studies consistently show that dioxin emissions from waste incinerators are primarily the result of how things are burned, not what is burned.3 Regulations have improved how incinerators operate.

EPA has stated that its "best estimates of emissions from sources that can be reasonably quantified indicate that dioxin emissions in the United States decreased about 80 percent between 1987 and 1995, primarily due to reductions in air emissions from municipal and medical incinerators, and substantial further declines continue to be documented."4 By 2004, EPA estimates dioxin emissions will be down more than 90 percent from 1987 levels.

Emissions from vinyl production are a small fraction of total emissions. Sources of greater dioxin emissions than vinyl manufacturing include open burning (the largest source), fireplaces, coal-burning utilities, vehicle emissions and metal smelting. Go to www.epa.gov for more on the dioxin inventory.

3 H. Gregor Rigo, A. John Handler, W. Steven Laurier, "The Relationship Between Chlorine In Waste Streams and Dioxin Emissions From Waste Combustor Stacks," The American Society of Mechanical Engineers, 1995.

4 "Dioxin: Summary of the Dioxin Reassessment Science," Information Sheet 1, U.S. EPA, June 12, 2000.