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KNOW YOUR ENVIRONMENT
A publication of the Environmental Associates
Dioxins and Furans: Where They Come From
by Todd Paddock,
Academy of Natural Sciences
Dioxins have caused a great deal of concern because they have been found in many places and are extremely toxic. Furans are similar chemicals and are often found with dioxins.
Dioxins and furans have never been manufactured deliberately, except in small amounts for research purposes. They are unintentionally created in two major ways: 1) by the processes used to manufacture some products, for example, certain pesticides, preservatives, disinfectants, and paper products; 2) when materials are burned at low temperatures, for example, certain chemical products, leaded gasoline, plastic, paper, and wood.
Dioxins and furans from manufacturing
Dioxins can be inadvertently formed during the manufacture of a group of chemicals called chlorophenols, and the products made from them. Chlorophenols have been widely used to preserve wood, hides, textiles, paints, glues, and other materials, as disinfectants, and to keep industrial cooling waters free of nuisance organisms. Some of these uses have been phased out.
A chlorophenol called 2,4,5-trichlorophenol is always contaminated with the most toxic kind of dioxin or furan, called 2,3,7,8-TCDD. After 2,4,5-trichlorophenol was identified as a source of dioxins, manufacturers that used 2,4,5-trichlorophenol found ways to remove the contaminant from their products. This often meant that the 2,3,7,8-TCDD was then concentrated in the wastes from such production.
Improper disposal of such waste resulted in the contamination of the town of Times Beach in Missouri, the Love Canal in New York, and other areas. Many highly contaminated sites remain where these wastes were handled, stored, or landfilled. 2,4,5-trichlorophenol is no longer produced in the U.S.
Other chlorophenols can contain dioxins and furans. Pentachlorophenols, which are used to preserve wood, can contain relatively high levels of dioxins and furans, including many highly toxic kinds. Wood treatment facilities and sawmills have been significant sources of contamination, and wastes from their facilities are now treated as hazardous, or are proposed to be treated as such.
Polychlorinated biphenyls (PCBs) have been widely used as cooling fluids in electrical equipment and some industrial cooling systems. Such fluids are often a mixture of PCBs and other chemicals. PCBs can contain low levels of furans, and the other chemicals can contain low levels of both dioxins and furans. Very large amounts of PCBs have been released to the environment. They are no longer manufactured in the U.S., and are being removed from most uses.
Dioxins and furans were discovered in the waste products of some pulp and paper mills in 1985, after fish downstream from the mills were found to contain low levels of 2,3,7,8-TCDD. Since then, extremely small amounts of dioxins and furans have been found in some paper products. The EPA and the paper industry have been working together to understand the problem and reduce or eliminate the amounts inadvertently formed in the manufacture of paper. Presently, it is believed that a chlorine bleaching process used at some paper mills is responsible for the creation of dioxins and furans.
Dioxins and furans from burning
Many of the products and wastes that are contaminated with dioxins and furans will produce larger amounts when burned. For example, when treated wood is eventually burned, the chlorophenols that burn with it could be a widespread source of dioxins and furans. Also, wood treatment facilities often collect waste pentachlorophenol in ponds, and in the past set fire to the ponds to reduce their volume. This practice generated significant amounts of dioxins and furans.
PCBs can produce large amounts of furans when they are burned, and the chemicals that are often mixed with PCBs for use in electrical equipment can produce dioxins. Fires involving transformers and capacitors have contaminated buildings, power stations, locomotives, and other places with dioxins and furans.
Polybrominated biphenyls (PBBs) are widely used as flame retardants in textiles, carpets, and plastics. These materials are resistant to igniting but will burn in a building fire or incinerator. When they burn, they can be a source of dioxins and furans.
Polyvinyl chloride (PVC) is a common plastic that can produce dioxins and furans when burned. PVC is often present in municipal waste in large amounts, and is believed to contribute to the dioxins and furans from incinerators.
Many sources of combustion produce dioxins and furans. Incinerators, both municipal and industrial, are significant sources. Dioxins and furans have been found both in the incinerator ash and in the gases and tiny particles escaping through stacks. Power plants, smelters, steel mills, and oil and wood stoves and furnaces all emit dioxins and furans.
Greater amounts of dioxins and furans are produced when material is burned inefficiently and at low temperatures. For example, the amounts of dioxins and furans formed during incineration can be reduced by higher temperatures and more complete burning. Modern incinerators produce smaller amounts of dioxins and furans than older ones, and new technology is expected to reduce the amounts even further.
Leaded gasolines, which contain chlorinated additives, produce very small amounts of dioxins and furans when they are burned. Thus, autos may contribute significant amounts of dioxins and furans, especially in urban areas. In the U.S. and much of Europe, the use of leaded fuel has declined dramatically in the past decade and will continue to decline, thus reducing this source considerably.
Because dioxins and furans have been found in the chimneys of wood burning stoves, it has been proposed that forest fires and other natural burning is responsible for a large amount of the dioxins and furans present in our environment.
Cores drilled from the bottom of the Great Lakes and from a lake in Switzerland were analyzed for dioxins and furans. Researchers can count the years in such cores, just as you can count the rings in a tree. In the sediment cores from all lakes, they found almost undetectable amounts of dioxins and furans before around 1940, a time they say corresponds to the large scale production and incineration of chlorinated aromatics. There are many sources of dioxins and furans. Some of them, such as the use of chlorophenols, the incineration of waste, and other sources of combustion, are widespread and numerous. Others, such as contaminated manufacturing and waste sites, are few in number and usually local problems. Reducing the creation and release of dioxins and furans will require attention to all these sources.This article is based on information contained in a Special Report: Dioxins and Furans, published by the Environmental Associates. Follow this link to learn more.
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