Dioxins and furans belong to a chemical family with similar structures. These chemicals include polychlorinated biphenyls (PCBs), polychlorinated dibenzo dioxins (PCDDs), and polychlorinated dibenzo furans (PCDFs). Though both dioxins and furans are unintended byproducts of manufacturing for pesticides and in the bleaching of paper, they are a highly toxic family of chemicals. Dioxins are considered the most toxic chemicals ever produced by man, and furans are about one-tenth as dangerous. Environmentally, they are persistent chemicals that build up in the fatty tissue of animals, and vectors for human exposure include the food supply and air and water contamination.
These contaminates are routinely produced through the processes that solid waste incinerators use, such as copper smelters and coal-fired power plants. Other common sources of the chemicals include the incineration of medical waste, cement kilns, and wood burning, among others. Two industrial processes that are responsible for much of the production of dioxins and furans include using chlorine chemicals to bleach paper and wood pulp, and the burning of materials that contain polyvinyl chloride (PVC) plastic.
Around 95% of the air pollution level for dioxins and furans comes from the burning of chlorinated products. The largest source of these is municipal waste incineration. Widescale use of PCBs in the past, and burning of materials that contain them in waste, can increase the levels of dioxins and furans present at temperatures between 492° to 842° Fahrenheit (250° to 450° Celsius).
While the use of PCB chemicals that contained these compounds was halted in 1977, they still remain present in the environment. The concentrations worldwide are high enough as of 2011 that 10% of the normal background level of exposure to the chemicals has been shown to cause adverse health effects in humans and animals. Of particular concern is their presence in the food supply, which is the primary exposure method. They are found in most meat products, dairy, and eggs. Tests have shown that the consumption of one beef hamburger from a US fast food chain contains 250 times what is considered an acceptable daily exposure to the chemicals.
Areas where dioxins and furans have had widespread detrimental health effects include in Vietnam due to their presence in the Agent Orange defoliant used in the Vietnam War, and at environmental cleanup sites such as Times Beach, Missouri, and Love Canal, New York, in the US. Rice oil used in Taiwan and Japan as a high-temperature method of cooking fish also increases furan levels where PCBs are present. Fish are a major exposure route for the chemicals, and a 2001 study ranking levels of dioxins and furans present in breast milk listed Vietnam with the highest concentrations, and Japan second on the list.
Exposure to dioxins and furans in the environment is a cause for concern worldwide. A study into their environmental presence was conducted by drilling cores into the lake beds in the US and Switzerland. The deeper the core, the farther back in time the sediment can be traced, and it was found that dioxins were almost undetectable in the environment as of the 1940s. The conclusion was that the burning of chlorinated aromatic materials as a result of industrial processes since that time has been the major source for these contaminates.