Dioxinas y furanos

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UNEP Regional Awareness Raising Workshop on POPs

Puerto Iguazu, Argentina, April 1-3, 1998

Polychlorinated Dioxins and Furans: Sources, Emissions, Formation, and Control
National Risk Management Research Laboratory Office of Research and Development U.S. Environmental Protection Agency Research Triangle Park, NC 27711
In collaboration with the staff ofU.S. EPA National Center for Environmental Assessment
NRMRL

Dr. Paul M. Lemieux

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Polychlorinated Dioxins and Furans: Sources, Emissions, Formation, and Control
Presentation to UNEP Regional Awareness Raising Workshops on POPs: Iguazu, Argentina, April 1-3, 1998 Dr. Paul M. Lemieux Thank you for allowing me the opportunity to present an outline of work performed by the United StatesEnvironmental Protection Agency (EPA) on sources, emissions, formation, and control of polychlorinated dioxins and furans. I trust that this presentation will serve as an introduction to the scientific information and terminology used in the risk assessment and risk management of dioxins and dioxin-like chemicals. The text of the presentation is formatted to be read in conjunction with the accompanyingslides, which are indicated by sequence number and title. The presentation covers the chemical structure of these chemicals; a brief note on how they affect humans; the concept of toxicity equivalence; emission sources in the United States; measurement techniques; formation mechanisms; exposure routes; and control schemes. Should additional information be desired on any of these topics, the EPAInternet site (http://www.epa.gov/) offers a valuable resource where work products from the dioxin reassessment and other United States regulatory activities are posted for public dissemination. Note that my main area of expertise lies in the combustion research area dealing with pollutant formation and control. I wish to acknowledge my colleagues at the EPA National Center for EnvironmentalAssessment for their input on the exposure and health related aspects of this presentation.

Slide 4:

Dioxins, furans, and PCBs: structural similarities

Dioxins, Furans, and PCBs: Structural Similarities
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2,3,7,8-Tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzofuran

Polychlorinated dibenzopara-dioxins 75 congeners / 7 consideredtoxic
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Polychlorinated dibenzofurans 135 congeners / 10 considered toxic
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3,3',4,4',5,5'-Hexachlorobiphenyl

PCBs 209 congeners / 13 considered Òdioxin-likeÓ
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NRMRL

The structure of dioxins, furans, and PCBs warrants special consideration, as it is the specific shape of the molecules and attached chlorine atoms that governs their toxicity. Dioxin is theabbreviated, common, name for the 75 chemicals comprising the family of polychlorinated dibenzopara-dioxins (PCDDs). The most toxic of the dioxin molecules, 2,3,7,8-tetrachlorodibenzo-p-dioxin, is depicted in the upper left of slide 4. All dioxin molecules have in common two benzene rings joined by two oxygen molecules (dioxin). Varying numbers of chlorine atoms (up to eight) can be located at differentpositions around this structure, resulting in 75 different structural configurations known as congeners. Note the flat, planar structure of this molecule and the symmetrical location of the chlorine atoms at the far ends. Seven of the PCDD congeners are considered to exhibit “dioxin-like” toxicity, resulting from the structural configuration of the chlorine atoms. Furans are depicted in the upperright corner of slide 4, the specific example being 2,3,7,8tetrachlorodibenzofuran. Polychlorinated dibenzofurans (PCDFs) differ structurally from PCDDs only by a carbon-carbon bond substituting for one of the oxygen bonds. Differing possible arrangements of chlorine atoms around the dibenzofuran molecule give rise to 135 congeners, of which 10 are considered to exhibit toxic, “dioxin-like,”...