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Office of Air Quality Planning And Standards Office of Air And Radiation U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711

May 1997

Disclaimer This report has been reviewed by the Office Of Air Quality Planning And Standards, U.S. Environmental Protection Agency,and has been approved for publication. Any mention of trade names or commercial products is not intended to constitute endorsement or recommendation for use.




The 1990 Clean Air Act Amendments contain a list of 189 hazardous air pollutants (HAPs) which the U.S. Environmental Protection Agency (EPA) must study, identify sources of, and determine ifregulations are warranted.a Two of these HAPs, chlorinated dibenzo-p-dioxins (CDD) and chlorinated dibenzofurans (CDF), are the subject of this document. This document describes the properties of dioxins and furans as air pollutants, defines their origin, identifies source categories of air emissions, and provides dioxin and furan emissions data in terms of emission factors and national emissionsestimates. This document is a part of an ongoing EPA series designed to assist the general public at large, but primarily to assist State/local air regulatory agencies in identifying sources of HAPs and determining emission estimates.

A dioxin is any compound that contains the dibenzo-p-dioxin nucleus, and a furan is any compound that contains the dibenzofuran nucleus. The term isomers refersto compounds with the same empirical formulas. The term homologues refers to compounds within the same series (e.g., CDD or CDF), but with a different number of chlorine atoms (tetra-CDD, penta-CDF, etc.). The 2,3,7,8-TCDD and 2,3,7,8-TCDF compounds represent the most toxic compounds of their respective families. The nationwide emissions estimate of dioxins and furans presented in this document arebased on the two 2,3,7,8 compounds and, to the extent practicable, the base year 1990. In a limited number of cases where more recent data were available (e.g., on-road mobile sources), a different base year was used (1991 or 1992) for estimating nationwide emissions.

CDD and CDF have no known technical use and are not intentionally produced. They are formed as unwanted byproducts of certainchemical processes during the manufacture of chlorinated intermediates and in the combustion of chlorinated materials. Dioxins and furans are emitted into the atmosphere from a wide variety of processes such as waste incineration,

Caprolactam was delisted from the list of HAPs (Federal Register Volume 61, page 30816, June 18, 1996). iii

combustion of solid and liquid fuels in stationarysources for heat and power generation, crematories, iron and steel foundries/scrap metal melting, combustion-aided metal recovery, kraft pulp and paper production/black liquor combustion, internal combustion engines, carbon regeneration, forest fires, organic chemical manufacture and use, and Portland cement manufacture.

The toxicity equivalency factor (TEF) method is an interim procedure forassessing the risks associated with exposures to complex mixtures of CDD/CDF. This method relates the toxicity of the 210 structurally related pollutants (135 CDF and 75 CDD), and the toxicity of the most highly studied dibenzo-p-dioxin, 2,3,7,8-TCDD. The TEF method is used as a reference in relating the toxicity of the other 209 compounds (i.e., in terms of equivalent amounts of 2,3,7,8-TCDD). Thisapproach simplifies risk assessments, including assessments of exposure to mixtures of CDD and CDF such as incinerator flyash, hazardous wastes, contaminated soils, and biological media. In 1989, as a result of the active involvement of EPA in an international effort aimed at adopting a common set of TEFs, a set of TEFs were agreed upon and implemented and were called International TEFs/89...
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