COVER PAGE

DO NOT QUOTE OR CITE

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.

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.

• I: VOLUME I
• II: VOLUME II.
• III: VOLUME III.
• IV: RECOMMENDATIONS
• V: TABLES
• VI: FIGURES
• VII: FOREWORD
• VIII: PREFACE
• IX: AUTHORS, CONTRIBUTORS, AND REVIEWERS

• 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

• 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

• 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

• 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

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

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.