Dioxins and Furans


Dioxins And Furans: Where They Come From

by Todd Paddock, Academy of Natural Sciences July, 1989


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.

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 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.

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.


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