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June 1994External Review Draft

 

ESTIMATING EXPOSURE TO DIOXIN-LIKE COMPOUNDS

 

VOLUME I: Executive Summary

NOTICE

THIS DOCUMENT IS A PRELIMINARY DRAFT. It has not been formally released by the U.S. Environmental Protection Agency and should not at this stage be construed to represent Agency policy. It is being circulated for comment on its technical accuracy and policy implications. Exposure Assessment GroupOffice of Health and Environmental AssessmentU.S. Environmental Protection Agency

Washington, D.C.

DISCLAIMER

This document is an external draft for review purposes only and does not constitute U.S. Environmental Protection Agency policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

CONTENTS OVERVIEW Part I
CONTENTS Part I
go to I: INTRODUCTION 1
  • I.1. BACKGROUND 1
  • I.2. TOXICITY EQUIVALENCY FACTORS 2
  • I.3. OVERALL COMMENTS ON THE USE OF THE DIOXIN EXPOSURE DOCUMENT 6
  • REFERENCES FOR INTRODUCTION 8
go to II: PROPERTIES, SOURCES, ENVIRONMENTAL LEVELS, AND BACKGROUND EXPOSURES 9
  • II.1. CHEMICAL STRUCTURES AND PROPERTIES 9
  • II.2. SOURCES 12
    • II.2.1. Theories of Formation During Combustion 12
    • II.2.2. Estimates of Annual Releases of Dioxin-Like Compounds 14
  • II.3. OCCURRENCE AND BACKGROUND EXPOSURES 25
    • II.3.1. United States Food Data 26
    • II.3.2. Summary of Media Levels 26
    • II.3.3. Conclusions for Mechanisms of Impact to Food Chain 30
  • II.4. TEMPORAL TRENDS 33
  • II.5. BACKGROUND EXPOSURE LEVELS 34
  • II.6. HIGHLY EXPOSED POPULATIONS 40
  • REFERENCES FOR VOLUME II 43
go to III: SITE-SPECIFIC ASSESSMENT PROCEDURES 48
  • III.1. EXPOSURE EQUATION 48
  • III.2. PROCEDURE FOR ESTIMATING EXPOSURE 49
  • III.3. ESTIMATING EXPOSURE MEDIA CONCENTRATIONS 51
      III.3.1. Overview of Fate, Transport, and Transfer Algorithms of the Methodology 52
  • III.4. DEMONSTRATION OF METHODOLOGY 64
      III.4.1. Results from the Demonstration of the Stack Emission Source Category 66
  • III.5. USER CONSIDERATIONS 71
    • III.5.1. Categorization of Methodology Parameters 71
    • III.5.2. Sensitivity Analysis 73
    • III.5.3. Mass Balance Considerations for Soil Contamination 79
  • III.6. UNCERTAINTY 79
  • REFERENCES FOR VOLUME III 94
go to IV: RECOMMENDATIONS FOR FUTURE RESEARCH 98
  • IV.1. SOURCES, FORMATION, CONTROLS AND MONITORING 98
  • IV.2. ENVIRONMENTAL FATE, TRANSPORT AND BIOACCUMULATION 102
  • IV.3. CHEMICAL/PHYSICAL PROPERTIES 106
  • IV.4. EXPOSURE 107
  • IV.5 PHARMACOKINETICS 109
  • IV.6. COPLANAR PCBS 109
  • IV.7. NON-CHLORINE HALOGENATED FORMS OF DIBENZODIOXINS/FURANS AND COPLANAR
    BIPHENYLS 110
  • IV.8. GLOBAL IMPACTS 111
  • REFERENCES FOR RECOMMENDATIONS SECTION 112
V go to TABLES return
go to TABLES I  
go to table Table I-1 Toxicity equivalency factors (TEF) for CDDs and CDFs  
go to table Table I-2 Dioxin-Like PCBs  
go to table Table I-3 Nomenclature for dioxin-like compounds  
go to TABLES II  
go to table Table II-1. Possible number of positional CDD (or BDD) and CDF (or BDF) congeners  
go to table Table II-2 CDD and CDF air emission estimates for West Germany, Austria, United Kingdom, Netherlands, Switzerland, and the United States  
go to table Table II-3 Current CDD and CDF multi-media emission estimates for the United States  
go to table Table II-4 Summary of CDD/F levels in United States food (pg/g fresh weight)  
go to table Table II-5 Summary of CDD/F levels in environmental media and food (whole weight basis)  
go to table Table II-6 Estimated TEQ background exposures in the United States  
go to TABLES III  
go to table Table III-1 Percent distribution of CDDs and CDFs between vapor-phase (V) and particulate-phase (P) as interpreted by various stack sampling methods, ambient air monitoring, and ambient air theoretical partitioning  
go to table Table III-2 Exposure media concentrations estimated for the demonstration of the stack emission source category  
go to table Table III-3 Lifetime Average Daily Doses, LADD, for the high end stack emission demonstrations scenario (LADD in units of ng/kg-day)  
go to table Table III-4 Percent contribution of the different exposure pathways within each exposure scenario  
go to table Table III-5 Summary of key tests of the fate, transport, and transfer models  
go to TABLES IV  
go to table Table IV-1 Analysis of air emission sources  
VI go to FIGURES return
go to FIGURES II  
go to table Figure II-1 Structure of Dioxins and Furans  
go to table Figure II-2 Structure of dioxin-like PCBs  
go to table Figure II-3 Estimated TEQ emissions to air from combustion sources in the United States  
go to table Figure II-4 Background environmental levels in TEQ  
go to table Figure II-5 Background TEQ exposures for North America by pathway  
go to table Figure II-6 Comparison of background TEQ exposures for North America, Germany, and the Netherlands  
go to FIGURES III  
go to table Figure III-1 Roadmap for assessing exposure and risk to dioxin-like compounds  
go to table Figure III-2 Diagram of the fate, transport, and transfer relationships for the on-site source category  
go to table Figure III-3 Diagram of the fate, transport, and transfer relationships for the off-site source category  
go to table Figure III-4 Diagram of the fate, transport, and transfer relationships for the stack emission source category  
go to table Figure III-5 Diagram of the fate, transport, and transfer relationships for the effluent discharge source category  
go to table Figure III-6 Results of sensitivity analysis of algorithms estimating above and below ground vegetation, and beef fat concentrations resulting from stack emissions  
VII: FOREWORD return

The Exposure Assessment Group (EAG) within the Office of Health and Environmental Assessment of EPA's Office of Research and Development has three main functions:

(1) to conduct exposure assessments,
(2) to review assessments and related documents, and
(3) to develop guidelines for exposure assessments.

The activities under each of these functions are supported by and respond to the needs of the various EPA program offices. In relation to the third function, EAG sponsors projects aimed at developing or refining techniques used in exposure assessments.This document is the first of a three-volume set addressing exposure to dioxin related compounds. The purpose of this document is to provide an Executive Summary of Volumes II and III. Volume II describes the properties, sources, environmental levels and background exposures to dioxin-like Compounds. Volume III presents methods for assessing site-specific assessments of exposure to these compounds.

The document is intended to be used as a companion to the health reassessment of dioxin-like compounds that the Agency is publishing concurrently. It is hoped that these documents will improve the accuracy and validity of risk assessments involving this important family of compounds. Michael A. CallahanDirector

Exposure Assessment Group

VIII: PREFACE return

In April 1991, the U.S. Environmental Protection Agency (EPA) announced that it would conduct a scientific reassessment of the health risks of exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and chemically similar compounds collectively known as dioxin.

The EPA has undertaken this task in response to emerging scientific knowledge of the biological, human health, and environmental effects of dioxin. Significant advances have occurred in the scientific understanding of mechanisms of dioxin toxicity, of the carcinogenic and other adverse health effects of dioxin in people, of the pathways to human exposure, and of the toxic effects of dioxin to the environment.

In 1985 and 1988, the Agency prepared assessments of the human health risks from environmental exposures to dioxin. Also, in 1988, a draft exposure document was prepared that presented procedures for conducting site-specific exposure assessments to dioxin-like compounds. These assessments were reviewed by the Agency's Science Advisory Board (SAB).

At the time of the 1988 assessments, there was general agreement within the scientific community that there could be a substantial improvement over the existing approach to analyzing dose response, but there was no consensus as to a more biologically defensible methodology. The Agency was asked to explore the development of such a method. The current reassessment activities are in response to this request.The scientific reassessment of dioxin consists of five activities:

1. Update and revision of the health assessment document for dioxin.
2. Laboratory research in support of the dose-response model.
3. Development of a biologically based dose-response model for dioxin.
4. Update and revision of the dioxin exposure assessment document.

5. Research to characterize ecological risks in aquatic ecosystems.

The first four activities have resulted in two draft documents (the health assessment document and exposure document) for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. These companion documents, which form the basis for the Agency's reassessment of dioxin, have been used in the development of the risk characterization chapter that follows the health assessment. The process for developing these documents consisted of three phases which are outlined in later paragraphs.

The fifth activity, which is in progress at EPA's Environmental Research Laboratory in Duluth, Minnesota, involves characterizing ecological risks in aquatic ecosystems from exposure to dioxins. Research efforts are focused on the study of organisms in aquatic food webs to identify the effects of dioxin exposure that are likely to result in significant population impacts.

A report titled, Interim Report on Data and Methods for the Assessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) Risks to Aquatic Organisms and Associated Wildlife (EPA/600/R-93/055), was published in April 1993. This report will serve as a background document for assessing dioxin-related ecological risks. Ultimately, these data will support the development of aquatic life criteria which will aid in the implementation of the Clean Water Act.

The EPA had endeavored to make each phase of the current reassessment of dioxin an open and participatory effort. On November 15, 1991, and April 28, 1992, public meetings were held to inform the public of the Agency's plans and activities for the reassessment, to hear and receive public comments and reviews of the proposed plans, and to receive any current, scientifically relevant information.In the Fall of 1992, the Agency convened two peer-review workshops to review draft documents related to EPA's scientific reassessment of the health effects of dioxin.

The first workshop was held September 10 and 11, 1992, to review a draft exposure assessment titled, Estimating Exposures to Dioxin-Like Compounds. The second workshop was held September 22-25, 1992, to review eight chapters of a future draft Health Assessment Document for 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Related Compounds.

Peer-reviewers were also asked to identify issues to be incorporated into the risk characterization, which was under development.In the Fall of 1993, a third peer-review workshop was held on September 7 and 8, 1993, to review a draft of the revised and expanded Epidemiology and Human Data Chapter, which also would be part of the future health assessment document.

The revised chapter provided an evaluation of the scientific quality and strength of the epidemiology data in the evaluation of toxic health effects, both cancer and noncancer, from exposure to dioxin, with an emphasis on the specific congener, 2,3,7,8-TCDD.As mentioned previously, completion of the health assessment and exposure documents involves three phases:

Phase 1 involved drafting state-of-the-science chapters and a dose-response model for the health assessment document, expanding the exposure document to address dioxin related compounds, and conducting peer review workshops by panels of experts. This phase has been completed.

Phase 2, preparation of the risk characterization, began during the September 1992 workshops with discussions by the peer-review panels and formulation of points to be carried forward into the risk characterization. Following the September 1993 workshop, this work was completed and was incorporated as Chapter 9 of the draft health assessment document. This phase has been completed.

Phase 3 is currently underway. It includes making External Review Drafts of both the health assessment document and the exposure document available for public review and comment.

Following the public comment period, the Agency's Science Advisory Board (SAB) will review the draft documents in public session. Assuming that public and SAB comments are positive, the draft documents will be revised, and final documents will be issued.

Estimating Exposures to Dioxin-Like Compounds has been prepared by the Exposure Assessment Group of the Office of Health and Environmental Assessment, Office of Research and Development, which is responsible for the report's scientific accuracy and conclusions. A comprehensive search of the scientific literature for this document varies somewhat by chapter but is, in general, complete through January 1994.

 
IX: AUTHORS, CONTRIBUTORS, AND REVIEWERS return
The Exposure Assessment Group (EAG) within EPA's Office of Health and Environmental Assessment was responsible for the preparation of this document. General support was provided by Versar Inc. under EPA Contract Number 68-D0-0101.

Dr. William Farland, as overall Director of the Dioxin Reassessment, provided policy guidance and technical comments. Matthew Lorber of EAG served as EPA task manager (as well as contributing author) providing overall direction and coordination of the production effort.
 
AUTHORS FOR VOLUME I
Primary authors for Volume I include all authors listed below.
Primary authors of each chapter are listed below in alphabetical order.
 
AUTHORS FOR VOLUME II
Name
Chapters
Company
Carl D'Ruiz
03
Versar, Inc.
David Cleverly
03
U.S. Environmental Protection Agency Washington, DC
Elizabeth Brown
04
Versar, Inc.
Geoffrey Huse
05
Versar, Inc.
Geoffrey Huse
02
Versar, Inc.
Geoffrey Huse
04
Versar, Inc.
Greg Schweer
05
Versar, Inc.
Greg Schweer
02
Versar, Inc.
Jeff Dawson
03
Versar, Inc.
Jerry Blancato
06
U.S. Environmental Protection Agency Las Vegas, NV
John L. Schaum
05
U.S. Environmental Protection Agency Washington, DC
John L. Schaum
01
U.S. Environmental Protection Agency Washington, DC
Keith Drewes
04
Versar, Inc.
Linda Phillips
03
Versar, Inc.
Linda Phillips
05
Versar, Inc.
Linda Phillips
04
Versar, Inc.
Matthew Lorber
04
U.S. Environmental Protection Agency Washington, DC
Matthew Lorber
03
U.S. Environmental Protection Agency Washington, DC
Nica Mostaghim
04
Versar, Inc.
Robert J. Fares
04
Versar, Inc.
Tim Leighton
03
Versar, Inc.
Tim Leighton
05
Versar, Inc.
 
AUTHORS FOR VOLUME III
Primary authors of each chapter are listed below in alphabetical order.
Name
Chapters
Company
David H. Cleverly
03
U.S. Environmental Protection Agency Washington, DC
David H. Cleverly
07
U.S. Environmental Protection Agency Washington, DC
John L. Schaum
02
U.S. Environmental Protection Agency Washington, DC
John L. Schaum
01
U.S. Environmental Protection Agency Washington, DC
Matthew Lorber
07
U.S. Environmental Protection Agency Washington, DC
Matthew Lorber
01
U.S. Environmental Protection Agency Washington, DC
Paul White
07
U.S. Environmental Protection Agency Washington, DC
CONTRIBUTORS AND REVIEWERS
An earlier draft of this exposure document was reviewed by the Science Advisory Board in 1988. A revised draft was issued in August 1992 and was reviewed by a panel of experts at a peer-review workshop held September 10 and 11, 1992. Members of the Peer Review Panel for this workshop were as follows:
Name
Qualifications
Company
M. Judith Charles
Ph.D
University of North Carolina Chapel Hill, NC
Dennis Paustenbach
Ph.D
ChemRisk - A McLaren/Hart Group Alameda, CA
Ray Clement
Ph.D
Ontario Ministry of the Environment Quebec, Canada
Richard Dennison
Ph.D
Environmental Defense Fund Washington, DC
Richard Reitz
Ph.D
Dow Chemical Midland, MI
In addition, the following experts outside of EPA have reviewed and/or contributed to this document:
Name
Qualifications
Company
Michael Bolger
US Food and Drug Administration Washington, DC
James Falco
Ph.D
Battelle Northwest Richland, WA
Heidelore Fiedler
Ph.D
University of Bayreuth Federal Republic of Germany
Charles Fredette
Connecticut Department of Environmental Protection Hartford, CT
George Fries
Ph.D
United States Department of Agriculture Beltsville Agricultural Research Center Beltsville, MD
Laura Green
Ph.D, D.A.B.T
Cambridge Environmental, Inc. Cambridge, MA
Dale Hattis
Ph.D
Clark University Worcester, MA
Steven Hinton
Ph.D., P.E.
National Council of the Paper Industry for Air and Stream Improvement Tufts University Medford, MA
Kay Jones
Zephyr Consulting Seattle, WA
George Lew
California Air Resources Board Sacremento, CA
Thomas E. McKone
Ph.D
Lawrence Livermore National Laboratory Livermore, CA
Derek Muir
Ph.D
Freshwater Institute Department of Fisheries and Oceans Winnipeg, MB, Canada
Marvin Norcross
Ph.D
Food Safety Inspection Service, USDA Washington, DC
Vlado Ozvacic
Ph.D
Ministry of the Environment Toronto, ON, Canada
Thomas Parkerton
Ph.D
Manhattan College Riverdale, NY
Christopher Rappe
Ph.D
University of Umea Institute of Environmental Chemistry Umea, Sweden
Curtis C. Travis
Ph.D
Oak Ridge National Laboratory Oak Ridge, TN
Thomas O. Tiernan
Ph.D
Wright State University Dayton, OH
Thomas Umbreit
Ph.D
Agency for Toxic Substances and Disease Registry Atlanta, GA
G.R. Barrie Webster
Ph.D
University of Manitoba Winnipeg, Canada
The following individuals within EPA have reviewed and/or contributed to this document:

OFFICE

REVIEWERS/CONTRIBUTORS

Office of Research and Development
  • Frank Black
  • Brian Gullett
  • Joel McCrady
  • Philip Cook
  • Donna Schwede
  • Bill Petersen
  • James Kilgroe
Office of Air and Radiation
  • Pam Brodowicz
  • George Streit
  • Thomas Lahre
  • Anne Pope
  • Phil Lorang
  • Walter Stevenson
  • Dennis Pagano
  • Jim Crowder
  • Dallas Safriet
  • Joe Somers
  • Joseph Wood
Office of Pollution, Pesticides and Toxic Substances
  • Joe Cotruvo
  • Steven Funk
  • Pat Jennings
  • Leonard Keifer
  • Robert Lipnick
  • Tom Murray
Office of Water
  • Ryan Childs
  • Mark Morris
  • Edward Ohanian
  • Al Rubin
  • Maria Gomez Taylor
Office of General Counsel Chuck Elkins
Office of Policy, Planning and Evaluation Dwain Winters