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Dioxins are chemicals produced as by-products of incomplete combustion and through certain chemical processes. Major sources of dioxins in the environment include burning of municipal, toxic, hospital, and domestic wastes; specific industrial processes including metal smelting and refining; and paper and pulp bleaching. Dioxins can also be found as contaminants in some insecticides, herbicides, and wood preservatives, and in cigarette smoke. There are at least 100 different kinds of dioxins, including tetrachlorodibenzo-p-dioxin (TCDD), which is the most toxic and is considered a known human carcinogen. There are also numerous dioxin-like compounds, so-called because they have similar chemical, physical, and toxicological properties to the dioxins. These include the chlorinated dibenzo-p-dioxins (CDDs), chlorinated dibenzofurans (CDFs), and certain coplanar polychlorinated biphenyls (PCBs). Environmental release estimates are often presented in terms of toxic equivalents (TEQs). TEQs are derived from a toxicity weighting system that converts all mixture components to a single value normalized to the toxicity of TCDD.The most common routes of exposure for dioxins occur through the diet, particularly from ingestion of animal fats including meats, full-fat dairy products, and fatty fish. Exposure can also occur through breathing incineration gases released from medical, municipal, and hazardous waste incinerators and industrial sources such as paper mills, cement kilns, and metal smelters.
Measurement of TCDD in human blood adjusting for lipids (Table P2) and EPA estimates of dioxin releases in the environment (Figure PDI1).
Dioxin levels in the general population of the United States are very low (Table P2). Dioxin levels in the environment have been declining for the last 30 years due to stricter regulations on emissions and reductions in man-made sources. Releases from industrial sources have decreased approximately 80–90% since the 1980s (U.S. EPA, 2006). However, dioxins break down so slowly that past releases will remain in the environment for many years (Figure PDI1).
Table P2. 50th and 95th percentiles for tetrachlorodibenzo-p-dioxin (TCDD) in blood samples from the U.S. population (picograms/gram, lipid adjusted), 1999–2004.
Source: Fourth National Report on Human Exposure to Environmental Chemicals,
* For certain chemicals like TCDD, each individual sample has its own limit of detection (LOD), which is the level at which a measurement has a 95% probability of being greater than zero. In 1999–2000 and 2001–2002, 12.1 pg/g and 5.8 pg/g, respectively, represented the maximum LOD among the samples analyzed and the geometric mean or average concentration of TCDD in all the samples was less than the maximum LOD so the estimate was reported as < LOD. In 2003-2004 the LOD was 3.8 pg/g.
95th percentile of TCDD concentration in the U.S. population: 5.2 pg/g (see Table P2)
Reduce air toxic emissions to decrease the risk of adverse health effects caused by airborne toxics. A specific numerical level for environmental concentration has not yet been set for dioxin.
Reduce exposure of the population to pesticides, heavy metals, and other toxic chemicals, as measured by blood and urine concentrations of the substances or their metabolites. A specific numerical level for metabolite concentration has not yet been set for dioxin.
Workers exposed to dioxin-contaminated air are at high risk of exposure. The general population is at risk of inhaling and ingesting dioxins.
A national goal has been set to reduce and measure dioxins in the environment and in the human body. People can help prevent exposure to dioxins by following existing Federal Dietary Guidelines, particularly by increasing consumption of fruits, vegetables, and grain products. Certain occupations are at high risk of dioxin exposure.