"Dioxin" is a term for a family of persistent chemicals (i.e., substances that do not break down chemically or break down very slowly) that are created through various natural and synthetic processes including incineration, forest fires, metal smelting and certain industrial operations involving chlorine and other organic compounds. Because chlorine can be found almost everywhere on earth (e.g. in salt), dioxin will be formed when most things burn, including wood, food, garbage and vinyl.
Studies have shown that when burning is well controlled as it is in modern incinerators, very little dioxin is made or emitted. The amount of chlorine or vinyl going into the incinerator is not a reliable indicator of the amount of dioxin coming out. Rather, incinerator design and operation have far more important impacts. However, in uncontrolled burning (e.g., volcanoes, forest fires, old incinerators, backyard burn barrels and accidental building fires), dioxin can be formed in larger amounts.
Toxicity of dioxins
Research has shown some dioxins are highly toxic to animals while others are not. The International Agency for Research on Cancer (IARC) has classified the most toxic form (called 2,3,7,8-TCDD) as a human carcinogen. The U.S. Environmental Protection Agency (EPA) typically measures levels of various dioxins by weighting them relative to the toxicity of 2,3,7,8-TCDD ("toxic equivalents" or "TEQ"). EPA estimated in 1995 that about 3,000 grams (about six pounds) of dioxin TEQ were generated annually in the United States from all known sources. The vinyl industry, using EPA protocols, measured its emissions from all U.S. manufacturing operations on the same basis and found that the industry contributed about 13 grams - less than 1 percent of the total amount generated.
Since dioxins are persistent substances, they do not degrade easily under most conditions. Once emitted, they can be absorbed by plants or settle on river bottoms, where they can be eaten by animals or fish and, eventually, humans. They are soluble in fat and can accumulate in our bodies. We all have minute quantities of dioxin in our bodies. Evidence suggests they have been present in the environment since prehistoric times. Nevertheless, EPA says that "currently there is no clear indication of increased disease in the general population attributable to dioxin-like compounds." The effect of dioxins in the types and amounts commonly seen in humans continues to be studied.
Dioxin levels in the Environment.
The good news about dioxin is that levels in the environment are declining, and levels in our bodies also appear to be declining. This has happened even as vinyl production has climbed in recent decades. Here is what EPA and other federal agencies say:
- Dioxin levels in the environment have declined significantly since the 1970s, following EPA regulatory controls and industry actions. EPA's best estimates of emissions from sources that can be reasonably quantified indicate that dioxin emissions in the United States decreased by about 80 percent between 1987 and 1995, primarily due to reductions in air emissions from municipal and medical waste incinerators, and substantial further declines continue to be documented." ("Dioxin: Summary of the Dioxin Reassessment Science," Information Sheet 1, U.S. EPA, June 12, 2000)
- "As a result of EPA's efforts, along with efforts by state government and private industry, known industrial emissions in the United States will be reduced by more than 90 percent from 1980 levels within the next year or so." ("Questions and Answers about Dioxin," Interagency Working Group on Dioxin, July 2000)
Dioxin in Building Fires
It is impossible to prevent formation of small amounts of dioxin in an accidental building fire by avoiding the use of certain building materials. This is because of the omni-presence of chlorine in materials such as wood and synthetics. Moreover, all materials - synthetic and natural - when they burn emit hundreds of different chemicals, many of which are persistent and highly toxic. In a typical accidental fire, carbon monoxide and heat are recognized as the most serious threats. The best preventive action to take against accidental fires is to install smoke alarms and (particularly in commercial buildings) sprinklers to alert occupants and extinguish fires that do occur. Early detection and suppression save lives.
Further preventative actions
The fact that dioxin can be produced naturally means that it will never be eliminated from the environment altogether. EPA and other agencies suggest that the best ways to help further reduce existing levels in the environment are to minimize uncontrolled and accidental burning (e.g., backyard burning, roadside leaf burning, landfill fires and other uncontrolled fires). As experience has shown, the combination of regulation and voluntary action by industry and individuals are key to preventing dioxin from becoming an environmental or public health problem.