EPA/600/6-88/005Cc

DO NOT QUOTE OR CITE June 1994

External Review Draft

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 Group

Office of Health and Environmental Assessment

U.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.

Tables viii

Figures xiii

Foreword xv

Preface xvi

Authors, Contributors, and Reviewers xix

1. INTRODUCTION 1-1

1.1. BACKGROUND 1-1

1.2. TOXICITY EQUIVALENCY FACTORS 1-2

1.3. OVERALL COMMENTS ON THE USE OF THE DIOXIN EXPOSURE

DOCUMENT 1-6

1.4. NOTES ON THE USE OF PROCEDURES IN VOLUME III 1-7

REFERENCES FOR CHAPTER 1 1-11

2. ESTIMATING EXPOSURES AND RISKS 2-1

2.1. INTRODUCTION 2-1

2.2. EXPOSURE EQUATION 2-2

2.3. RISK EQUATION 2-4

2.4. PROCEDURE FOR ESTIMATING EXPOSURE 2-7

2.5. STRATEGY FOR DEVISING EXPOSURE SCENARIOS 2-10

2.6. EXPOSURE PATHWAYS AND PARAMETERS 2-13

2.6.1. Soil Ingestion 2-14

2.6.2. Soil Dermal Contact 2-18

2.6.3. Vapor and Dust Inhalation 2-19

2.6.4. Water Ingestion 2-20

2.6.5. Beef and Dairy Product Ingestion 2-20

2.6.6. Fish Ingestion 2-22

2.6.7. Fruits and Vegetables 2-25

REFERENCES FOR CHAPTER 2 2-27

3. EVALUATING ATMOSPHERIC RELEASES OF DIOXIN-LIKE

COMPOUNDS FROM COMBUSTION SOURCES 3-1

3.1. INTRODUCTION 3-1

3.2. ESTIMATING THE EMISSIONS OF DIOXIN-LIKE COMPOUNDS FROM

ANTHROPOGENIC COMBUSTION SOURCES 3-3

3.2.1. A Stragey for Generating Emission Factors 3-4

3.2.2. Use of Homologue Profiles for Estimating

Congener Specific Emission Factors 3-6

3.2.3. Estimation of Emissions of Dioxin-Like

Compounds from the Hypothetical Incinerator 3-20

3.2.4. Estimation of the Vapor Phase/Particle Phase

Partitioning of Emissions of Dioxin-Like

Compounds 3-21

3.2.4.1. Vapor phase/particulate phase

inferences from stack measurements 3-23

3.2.4.2. Discussion of vapor/particle ratios

derived from stack test methods 3-27

3.2.4.3. Vapor/particle partitioning of PCDD/Fs

from ambient air sampling 3-29

3.2.4.4. Discussion of the vapor/particle

partitioning in ambient air sampling

studies 3-37

3.2.4.5. Theoretical prediction of vapor/particle

partitioning of PCDD/Fs under ambient

conditions 3-38

3.2.4.6. Discussion of vapor/particle

partitioning 3-42

3.2.5. Estimation of the Concentration of Dioxin-Like

Compounds in Incineration Ash 3-44

3.3. AIR DISPERSION/DEPOSITION MODELING OF THE STACK GAS

EMISSIONS OF DIOXIN-LIKE COMPOUNDS 3-45

3.3.1. Basic Principles Used to Estimate Atmospheric

Dispersion/Deposition of Stack Emissions 3-46

3.3.2. Estimation of Dry Surface Deposition Flux 3-47

3.3.3. Estimation of the Particle Size Distribution

in the Stack Emissions 3-51

3.3.4. Estimation of Wet Deposition Flux 3-54

3.3.5. The Requirement to Run the COMPDEP Model Twice 3-55

3.4. RESULTS OF AIR DISPERSION MODELING OF CONGENER-SPECIFIC

EMISSIONS FROM THE HYPOTHETICAL ORGANIC WASTE

INCINERATOR 3-58

3.5. REVIEW OF PROCEDURES FOR ESTIMATING SITE-SPECIFIC

IMPACTS FROM A STACK EMISSION SOURCE 3-62

REFERENCES FOR CHAPTER 3 3-70

4. ESTIMATING EXPOSURE MEDIA CONCENTRATIONS 4-1

4.1. INTRODUCTION 4-1

4.2. BACKGROUND FOR SOLUTION ALGORITHMS 4-2

4.3. ALGORITHMS FOR THE "ON-SITE SOIL"

SOURCE CATEGORY 4-7

4.3.1. Surface Water and Sediment Contamination 4-7

4.3.2. Vapor-Phase Air Concentrations 4-27

4.3.3. Particulate-Phase Air Concentrations 4-32

4.3.4. Biota Concentrations 4-35

4.3.4.1. Fish concentrations 4-35

4.3.4.2. Vegetation concentrations 4-48

4.3.4.3. Beef and milk concentrations 4-65

4.4. ALGORITHMS FOR THE "OFF-SITE" SOURCE CATEGORY 4-76

4.4.1. Exposure Site Soil Concentrations 4-78

4.4.2. Off-site Transport of Air-borne Contaminants 4-85

4.4.3. Specific Cases of Off-Site Soil Contamination 4-87

4.4.3.1. Landfills receiving ash from

municipal waste incinerators 4-87

4.4.3.2. Land application of sludge from

pulp and paper mills 4-97

4.4.3.3. Sites studied in the National

Dioxin Study 4-100

4.5. ALGORITHMS FOR THE STACK EMISSION

SOURCE CATEGORY 4-102

4.5.1. Steady-State Soil Concentrations 4-104

4.5.2. Surface Water Impacts 4-106

4.6. ALGORITHMS FOR THE EFFLUENT DISCHARGE

SOURCE CATEGORY 4-112

4.6.1 The Simple Dilution Model 4-114

REFERENCES FOR CHAPTER 4 4-122

5. DEMONSTRATION OF METHODOLOGY 9-1

5.1. INTRODUCTION 5-1

5.2. STRATEGY FOR DEVISING EXPOSURE SCENARIOS

FOR DEMONSTRATION PURPOSES 5-2

5.3. EXAMPLE EXPOSURE SCENARIOS 5-9

5.4. EXAMPLE COMPOUNDS 5-12

5.5. SOURCE TERMS 5-13

5.6. RESULTS 5-20

5.6.1. Observations Concerning Exposure Media

Concentrations 5-23

5.6.2. Observations Concerning LADD Exposure Estimates 5-32

REFERENCES FOR CHAPTER 5 5-45

6. USER CONSIDERATIONS 6-1

6.1. INTRODUCTION 6-1

6.2. CATEGORIZATION OF METHODOLOGY PARAMETERS 6-1

6.3. SENSITIVITY ANALYSIS 6-14

6.3.1. Limitations of the Sensitivity

Analysis Exercises 6-14

6.3.2. Methodology Description and

Parameter Assignments 6-18

6.3.3. Results 6-33

6.3.3.1. Estimation of off-site air

concentrations in the vapor phase 6-34

6.3.3.2. Estimation of off-site air

concentrations in the particulate phase 6-34

6.3.3.3. Estimation of soil erosion impacts

to nearby sites of exposure 6-37

6.3.3.4. Estimation of soil erosion impacts

to nearby surface water bodies 6-41

6.3.3.5. Estimation of fish tissue concentrations 6-43

6.3.3.6. Estimations of on-site air concentrations

in the vapor phase 6-44

6.3.3.7. Estimation of on-site air concentrations

in the particulate phase 6-45

6.3.3.8. Vapor-phase transfers and particle phase

depositions to above ground vegetations 6-47

6.3.3.9. Estimation of below ground vegetation

concentrations 6-54

6.3.3.10. Beef fat concentration estimation 6-58

6.3.3.11. Vegetable/fruit and beef/milk concentrations

resulting from stack emissions 6-62

6.3.3.12. Water and fish concentrations resulting

from effluent discharges 6-65

6.3.3.13. Water and fish concentrations resulting

from stack emission 6-67

6.3.4. Key Trends from the Sensitivity Analysis Testing 6-70

6.4. MASS BALANCE CONSIDERATIONS 6-72

REFERENCES FOR CHAPTER 6 6-78

7. UNCERTAINTY 7-1

7.1. INTRODUCTION 7-1

7.2. AN EVALUATION OF THE ALGORITHMS USED TO

ESTIMATE EXPOSURE MEDIA CONCENTRATIONS 7-3

7.2.1. Uncertainaties and Variabilities with Chemical-Specific

Parameters and Assumptions 7-4

7.2.2. A Discussion of Uncertainty Issues Associated With Use

of COMPDEP for Transport and Dispersion of Stack

Emitted Contaminants 7-8

7.2.3. Comparing Model Estimations of Exposure and Environmental

Media With Those Found in the Literature 7-11

7.2.3.1. The impact to soils of point source releases

of dioxin-like compounds 7-12

7.2.3.2. Soil concentrations and concurrent

concentrations in bottom sediment and fish 7-16

7.2.3.3. Other bottom sediment concentration data 7-29

7.2.3.4. Data on water concentrations of dioxin-like

compounds 7-31

7.2.3.5 Data on fish concentrations in the literature 7-32

7.2.3.6. Impact of pulp and paper mill effluent discharges

on fish tissue concentrations 7-36

7.2.3.7. Examination of observed air concentrations 7-48

7.2.3.8. Impacts of contaminated soils to vegetations 7-51

7.2.3.9. A validation exercise for the beef

bioconcentration algorithm 7-61

7.2.3.9.1. Air and beef concentrations 7-62

7.2.3.9.2. Summary of algorithms, key

assumptions, and parameter

values 7-67

7.2.3.9.3. Results and discussion 7-70

7.2.3.9.4. Conclusions 7-78

7.2.3.10. Comparison of modeled beef and milk

concentrations with concentrations found 7-81

7.2.4. Alternate Modeling Approaches for Estimating Environmental

and Exposure Media Concentrations 7-84

7.2.4.1. An alternate approach for estimating bottom

sediment concentrations from watershed soil

concentrations 7-84

7.2.4.2. An alternate modeling approach for estimating

water concentrations given a steady input load

from overland sources 7-85

7.2.4.3. Estimating fish tissue concentrations based on

water column concentrations rather than bottom

sediment concentrations 7-88

7.2.4.4. Other modeling approaches and considerations for

air concentrations resulting from soil

volatilization 7-94

7.2.4.5. Alternate models for estimating plant

concentrations from soil concentrations 7-98

7.2.4.6. Alternate modeling approaches for estimating

beef and milk concentrations 7-101

7.3. UNCERTAINTIES ASSOCIATED WITH EXPOSURE PATHWAYS 7-108

7.3.1. Lifetime, Body Weights, and Exposure Durations 7-109

7.3.2. Soil Ingestion Exposure 7-110

7.3.3. Soil Dermal Contact Pathway 7-114

7.3.4. Water Ingestion 7-117

7.3.5. Fish Ingestion Exposure 7-119

7.3.6. Vapor and Particle Phase Inhalation Exposure 7-124

7.3.7. Fruit and Vegetable Ingestion 7-129

7.3.8. Beef and Milk Ingestion 7-133 7.4. USE OF MONTE CARLO TECHNIQUES FOR ASSESSING EXPOSURE

TO DIOXIN-LIKE COMPOUNDS 7-139

REFERENCES FOR CHAPTER 7 7-146

1-1 Toxicity equivalency factors (TEF) for CDDs and CDFs 1-3

1-2 Dioxin-Like PCBs 1-4

1-3 Nomenclature for dioxin-like compounds 1-5

2-1 Summary of exposure pathway parameters selected for the

demonstration scenarios of Chapter 5 2-15

2-2 Fish consumption estimates from the USDA 1977-78 National Food

Consumption Survey (consumptions were recorded for three day

periods; N = 36249; units are grams/day/person; SF = shellfish) 2-23

3-1 The number of dioxin-like and total congeners within

dioxin, furan, and coplanar PCB homologue groups 3-8

3-2 Emission factors and average emissions used for the

hypothetical incinerator 3-22

3-3 Percent distribution of dioxins and furans between vapor

phase (V) and particulate phase (P) as interpreted by various

stack sampling methods 3-24

3-4 Percent distribution of dioxins and furans between vapor

phase (V) and particulate phase (P) in ambient air as observed

in ambient air sampling studies 3-31

3-5 Fractions of dioxins and furans calculated to partition

to particles in various classifications of ambient air using

the method of Bidleman (1988), Junge (1977), and Whitby (1978) 3-42

3-6 Factors that influence the dry deposition removal

rate in the atmosphere 3-50

3-7 A summary of dry deposition velocities for particles 3-52

3-8 Typical particle size distribution in particulate

emissions from incineration 3-53

3-9 Wet deposition scavenging coefficients per particle

diameter category (micrometers), expressed per second

of time 3-57

3-10 Emissions of PCDD/Fs (g/sec) from the hypothetical incinerator 3-59

3-11 Modeling parameters used in the COMPDEP modeling of

PCDD/F emissions from the hypothetical incinerator 3-61

3-12 Predicted annual average vapor-phase concentrations of

PCDD/Fs (g/m³) 3-63

3-13 Predicted annual average particle-phase air concentrations

of PCDD/Fs (g/m³) 3-64

3-14 Predicted total (vapor + particle) ambient air concentrations

of PCDD/Fs (g/m³) 3-65

3-15 Predicted annual dry deposition fluxes of particle-bound

PCDD/Fs (g/m²-yr) 3-66

3-16 Prediced annual wet deposition fluxes of particle-bound

PCDD/Fs (g/m²-yr) 3-67

3-17 Predicted total (dry + wet) deposition fluxes of

particle-bound PCDD/Fs (g/m²-yr) 3-68

4-1 Available Biota to Sediment Accumulation Factors, BSAF,

for dioxin-like compounds 4-41

4-2 Available Biota to Sediment Accumulation Factors, BSAF,

for PCBs 4-46

4-3 Ratios of dioxins and furans in milk fat (MF) and body fat (BF)

to concentrations in diets of farm animals 4-67

4-4 Ratios of PCBs in milk fat (MF) and body fat (BF) to concentrations

in diets of lactating cows 4-69

4-5 Ranges of concentrations of PCDDs, PCDFs, and PCBs in municipal

waste combustor ash (results in ng/g or ppb) 4-91

5-1 Environmental fate parameters for the three example compounds

demonstrated for the soil contamination source categories and

the effluent discharge source category 5-14

5-2 Key source terms and fate parameters for 2,3,7,8-TCDD and for

individual dioxin and furan congeners with non-zero TEFs

for the demonstration of the stack emission source category 5-15

5-3 Summary of key source terms for the six exposure scenarios

and the example compounds 5-16

5-4 Exposure media concentrations estimated for all scenarios

and pathways 5-21

5-5 Lifetime average daily dose (LADD) estimates for all scenarios

and exposure pathways (all results in mg/kg-day) 5-24

5-6 Percent contribution of the different exposure pathways

within each exposure scenario 5-35

5-7 Exposures to low soil concentrations of 2,3,7,8-TCDD assuming

lifetime exposure durations and unlimited contact with impacted

media, compared with exposures assuming limited durations and

limited contact 5-38

5-8 Comparison of exposure pathway contributions to total daily

exposure as estimated in example Scenario #2 and in Travis and

Hattemer-Frey (1991) 5-41

6-1 Parameters used to estimate exposure media concentrations

for this assessment 6-2

6-2 Contribution of above ground vegetation concentrations of

2,3,7,8-TCDD from air-to-leaf transfers and particulate

depositions 6-52

6-3 Results of sensitivity test of modeling vapor/particle partitioning

for volatilized residues (note:soil concentration equals 1 ppt

in tests below) 6-55

7-1 Summary of off-site soil contamination from Tier and 2 sites of

the National Dioxin Study 7-15

7-2 Description of soil, sediment, and fish sampling program of

dioxin-like compounds undertaken by the Connecticut Department

of Environmental Protection 7-19

7-3 Frequency of nondetects and detection limits for soil,

and fish, for three congeners in the Connecticut Department

of Environmental Protection data set 7-23

7-4 Results for Connecticut Department of Environmental Protection

sampling, including soil, sediment and fish concentrations, and

key concentration ratios of sediment to soil and the Biota

Sediment Accumulation Factor (BSAF) ratio 7-24

7-5 Model parameters and results for effluent discharge model

validation testing 7-40

7-6 Summary of plant concentration versus soil concentration data for

2,3,7,8-TCDD 7-52

7-7 Observed air and beef concentrations, and fate parameters

for individual dioxin and furan congeners 7-66

7-8 Model parameters used for all dioxin-like congeners 7-68

7-9 Results of validation exercise showing observed and

predicted concentrations of dioxin-like compounds in whole

beef 7-71

7-10 Comparison of concentrations of dioxin-like compounds found

in hay in a rural setting with model predictions of grass

concentrations 7-73

7-11 Calibration exercise showing improvements in grass and beef

concentrations when the fraction sorbed parameter, f , drops

minutely below 1.00 for OCDD and OCDF 7-74

7-12 Comparison of concentrations of dioxin-like compounds found in

soils described as "rural" or "background" with model predictions

of soil concentrations 7-76

7-13 Uncertainties associated with the lifetime, body weight,

and exposure duration parameters 7-111

7-14 Uncertainties associated with the soil ingestion pathway 7-115

7-15 Uncertainties associated with the dermal exposure pathway 7-118

7-16 Uncertainties associated with the water ingestion pathway 7-120

7-17 Uncertainties associated with the fish ingestion pathway 7-124

7-18 Uncertainties and sensitivities associated with estimating

vapor and particle-phase air concentrations from

contaminated soils 7-130

7-19 Uncertainties associated with vegetable and fruit ingestion

exposure algorithms 7-134

7-20 Uncertainties associated with beef and milk ingestion

exposure algorithms 7-140

7-21 Distributions for a Monte Carlo exercise which developed

soil cleanup levels at residential and industrial sites 7-142

7-22 Summary of Monte Carlo distributions used in a fish

consumption assessment 7-143

7-23 Summary of Monte Carlo distributions used in a food

chain study 7-145

2-1 Roadmap for assessing exposure and risk to dioxin

and dioxin-like compounds 2-8

3-1 Homologue profile emission factors for source categories

of dioxin-like compound release 3-9

4-1 Diagram of the fate, transport, and transfer relationships

for the on-site source category 4-8

4-2 Diagram of the fate, transport, and transfer relationships

for the off-site source category 4-9

4-3 Diagram of the fate, transport, and transfer relationships

for the stack emission source category 4-10

4-4 Diagram of the fate, transport, and transfer relationships

for the effluent discharge source category 4-11

4-5 Watershed delivery ratio, SD_w, as a function of

watershed size 4-24

6-1 Results of sensitivity analysis of algorithms estimating exposure

site vapor phase air concentrations resulting from off-site

soil contamination 6-35

6-2 Results of sensitivity analysis of algorithms estimating exposure

site particle phase air concentrations resulting from off-site

soil contamination 6-36

6-3 Results of sensitivity analysis of algorithms estimating exposure

site soil concentrations resulting from erosion from off-site

soil contamination 6-38

6-4 Results of sensitivity analysis of algorithms estimating surface

water and bottom sediment concentrations resulting from a site of

soil contamination 6-42

6-5 Results of sensitivity analysis of algorithms estimating fish

tissue concentrations given bottom sediment concentrations 6-45

6-6 Results of sensitivity analysis of algorithms estimating on-site

vapor phase air concentrations from on-site soil contamination 6-46

6-7 Results of sensitivity analysis of algorithms estimating on-site

particle phase air concentrations from on-site soil contamination 6-47

6-8 Results of sensitivity analysis of algorithms estimating above ground

vegetations concentrations due to vapor phase transfers 6-49

6-9 Results of sensitivity analysis of algorithms estimating above ground

vegetation concentrations resulting from particle phase depositions 6-50

6-10 Results of sensitivity analysis of algorithms estimating below

ground vegetation concentrations resulting from soil to root

transfers 6-59

6-11 Results of sensitivity analysis of algorithms estimating beef

fat concentrations resulting from soil contamination 6-60

6-12 Results of sensitivity analysis of algorithms estimating

above and below ground vegetation, and beef and milk fat

concentrations resulting from stack emissions 6-63

6-13 Results of sensitivity analysis of algorithms estimating

surface water and fish concentrations resulting from effluent

discharge 6-66

6-14 Results of sensitivity analysis of algorithms estimating

surface water and fish concentrations resulting from stack

emissions 6-68

7-1 Schematic of effluent discharge model showing all parameter

inputs and observed fish concentrations 7-38

7-2 Comparison of predicted and observed fish tissue concentrations

for validation of the effluent discharge model 7-46

7-3 Overview of model to predict beef concentrations from air

concentrations 7-62

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.

The purpose of this document is to present and evaluate methods for conducting site-specific assessments of exposure to dioxin-like compounds. It is the third in a three volume set addressing these compounds. The first volume provides an overall executive summary and the second volume describes the properties, sources, environmental levels, and background exposures to dioxin-like 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. Callahan

Director

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.

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.

Primary authors of each chapter are listed below in alphabetical order.

David H. Cleverly Chapters 3, 7

U.S. Environmental Protection Agency

Washington, DC

Matthew Lorber Chapter 1-7

U.S. Environmental Protection Agency

Washington, DC

John L. Schaum Chapters 1, 2

U.S. Environmental Protection Agency

Washington, DC

Paul White Chapter 7

U.S. Environmental Protection Agency

Washington, DC

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:

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:

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: