EPA/600/6-88/005Cc

DO NOT QUOTE OR CITE

June 1994External Review Draft

 

ESTIMATING EXPOSURE TO DIOXIN-LIKE COMPOUNDS

 

VOLUME III: Site-Specific Assessment Procedures

 

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

1.0. INTRODUCTION 1-1 return
  • 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
go to chapter 2.0. ESTIMATING EXPOSURES AND RISKS 2-1 return
  • 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
go to chapter 3.0. EVALUATING ATMOSPHERIC RELEASES OF DIOXIN-LIKE COMPOUNDS FROM COMBUSTION SOURCES 3-1 return
  • 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
go to chapter 4.0. ESTIMATING EXPOSURE MEDIA CONCENTRATIONS 4-1 return
  • 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
  • 4.4. 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
go to chapter 5.0. DEMONSTRATION OF METHODOLOGY 9-1 return
  • 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
go to chapter 6.0. USER CONSIDERATIONS 6-1 return
  • 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
go to chapter 7.0. UNCERTAINTY 7-1 return
  • 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
      • 7.2.3.10. 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
go to TABLES return
go to TABLES 1  
go to table Table 1-1 Toxicity equivalency factors (TEF) for CDDs and CDFs 1-3
go to table Table 1-2 Dioxin-Like PCBs 1-4
go to table Table 1-3 Nomenclature for dioxin-like compounds 1-5
go to TABLES 2  
go to table Table 2-1 Summary of exposure pathway parameters selected for the demonstration scenarios of Chapter 5 2-15
go to table Table 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
go to TABLES 3  
go to table Table 3-1 The number of dioxin-like and total congeners within dioxin, furan, and coplanar PCB homologue groups 3-8
go to table Table 3-2 Emission factors and average emissions used for the hypothetical incinerator 3-22
go to table Table 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
go to table Table 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
go to table Table 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
go to table Table 3-6 Factors that influence the dry deposition removal rate in the atmosphere 3-50
go to table Table 3-7 A summary of dry deposition velocities for particles 3-52
go to table Table 3-8 Typical particle size distribution in particulate emissions from incineration 3-53
go to table Table 3-9 Wet deposition scavenging coefficients per particle diameter category (micrometers), expressed per second of time 3-57
go to table Table 3-10 Emissions of PCDD/Fs (g/sec) from the hypothetical incinerator 3-59
go to table Table 3-11 Modeling parameters used in the COMPDEP modeling of PCDD/F emissions from the hypothetical incinerator 3-61
go to table Table 3-12 Predicted annual average vapor-phase concentrations of PCDD/Fs (g/m3) 3-63
go to table Table 3-13 Predicted annual average particle-phase air concentrations of PCDD/Fs (g/m3) 3-64
go to table Table 3-14 Predicted total (vapor + particle) ambient air concentrations of PCDD/Fs (g/m3) 3-65
go to table Table 3-15 Predicted annual dry deposition fluxes of particle-bound PCDD/Fs (g/m2-yr) 3-66
go to table Table 3-16 Prediced annual wet deposition fluxes of particle-bound PCDD/Fs (g/m2-yr) 3-67
go to table Table 3-17 Predicted total (dry + wet) deposition fluxes of particle-bound PCDD/Fs (g/m2-yr) 3-68
go to TABLES 4  
go to table Table 4-1 Available Biota to Sediment Accumulation Factors, BSAF, for dioxin-like compounds 4-41
go to table Table 4-2 Available Biota to Sediment Accumulation Factors, BSAF, for PCBs 4-46
go to table Table 4-3 Ratios of dioxins and furans in milk fat (MF) and body fat (BF) to concentrations in diets of farm animals 4-67
go to table Table 4-4 Ratios of PCBs in milk fat (MF) and body fat (BF) to concentrations in diets of lactating cows 4-69
go to table Table 4-5 Ranges of concentrations of PCDDs, PCDFs, and PCBs in municipal waste combustor ash (results in ng/g or ppb) 4-91
go to TABLES 5  
go to table Table 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
go to table Table 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
go to table Table 5-3 Summary of key source terms for the six exposure scenarios and the example compounds 5-16
go to table Table 5-4 Exposure media concentrations estimated for all scenarios and pathways 5-21
go to table Table 5-5 Lifetime average daily dose (LADD) estimates for all scenarios and exposure pathways (all results in mg/kg-day) 5-24
go to table Table 5-6 Percent contribution of the different exposure pathways within each exposure scenario 5-35
go to table Table 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
go to table Table 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
go to TABLES 6  
go to table Table 6-1 Parameters used to estimate exposure media concentrations for this assessment 6-2
go to table Table 6-2 Contribution of above ground vegetation concentrations of 2,3,7,8-TCDD from air-to-leaf transfers and particulate depositions 6-52
go to table Table 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
go to TABLES 7  
go to table Table 7-1 Summary of off-site soil contamination from Tier and 2 sites of the National Dioxin Study 7-15
go to table Table 7-2 Description of soil, sediment, and fish sampling program of dioxin-like compounds undertaken by the Connecticut Department of Environmental Protection 7-19
go to table Table 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
go to table Table 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
go to table Table 7-5 Model parameters and results for effluent discharge model validation testing 7-40
go to table Table 7-6 Summary of plant concentration versus soil concentration data for 2,3,7,8-TCDD 7-52
go to table Table 7-7 Observed air and beef concentrations, and fate parameters for individual dioxin and furan congeners 7-66
go to table Table 7-8 Model parameters used for all dioxin-like congeners 7-68
go to table Table 7-9 Results of validation exercise showing observed and predicted concentrations of dioxin-like compounds in whole beef 7-71
go to table Table 7-10 Comparison of concentrations of dioxin-like compounds found in hay in a rural setting with model predictions of grass concentrations 7-73
go to table Table 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
go to table Table 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
go to table Table 7-13 Uncertainties associated with the lifetime, body weight, and exposure duration parameters 7-111
go to table Table 7-14 Uncertainties associated with the soil ingestion pathway 7-115
go to table Table 7-15 Uncertainties associated with the dermal exposure pathway 7-118
go to table Table 7-16 Uncertainties associated with the water ingestion pathway 7-120
go to table Table 7-17 Uncertainties associated with the fish ingestion pathway 7-124
go to table Table 7-18 Uncertainties and sensitivities associated with estimating vapor and particle-phase air concentrations from contaminated soils 7-130
go to table Table 7-19 Uncertainties associated with vegetable and fruit ingestion exposure algorithms 7-134
go to table Table 7-20 Uncertainties associated with beef and milk ingestion exposure algorithms 7-140
go to table Table 7-21 Distributions for a Monte Carlo exercise which developed soil cleanup levels at residential and industrial sites 7-142
go to table Table 7-22 Summary of Monte Carlo distributions used in a fish consumption assessment 7-143
go to table Table 7-23 Summary of Monte Carlo distributions used in a food chain study 7-145
go to FIGURES return
go to FIGURES 2  
go to table Figure 2-1 Roadmap for assessing exposure and risk to dioxin and dioxin-like compounds 2-8
go to FIGURES 3  
go to table Figure 3-1 Homologue profile emission factors for source categories of dioxin-like compound release 3-9
go to FIGURES 4  
go to table Figure 4-1 Diagram of the fate, transport, and transfer relationships for the on-site source category 4-8
go to table Figure 4-2 Diagram of the fate, transport, and transfer relationships for the off-site source category 4-9
go to table Figure 4-3 Diagram of the fate, transport, and transfer relationships for the stack emission source category 4-10
go to table Figure 4-4 Diagram of the fate, transport, and transfer relationships for the effluent discharge source category 4-11
go to table Figure 4-5 Watershed delivery ratio, SDw, as a function of watershed size 4-24
go to FIGURES 6  
go to table Figure 6-1 Results of sensitivity analysis of algorithms estimating exposure site vapor phase air concentrations resulting from off-site soil contamination 6-35
go to table Figure 6-2 Results of sensitivity analysis of algorithms estimating exposure site particle phase air concentrations resulting from off-site soil contamination 6-36
go to table Figure 6-3 Results of sensitivity analysis of algorithms estimating exposure site soil concentrations resulting from erosion from off-site soil contamination 6-38
go to table Figure 6-4 Results of sensitivity analysis of algorithms estimating surface water and bottom sediment concentrations resulting from a site of soil contamination 6-42
go to table Figure 6-5 Results of sensitivity analysis of algorithms estimating fish tissue concentrations given bottom sediment concentrations 6-45
go to table Figure 6-6 Results of sensitivity analysis of algorithms estimating on-site vapor phase air concentrations from on-site soil contamination 6-46
go to table Figure 6-7 Results of sensitivity analysis of algorithms estimating on-site particle phase air concentrations from on-site soil contamination 6-47
go to table Figure 6-8 Results of sensitivity analysis of algorithms estimating above ground vegetations concentrations due to vapor phase transfers 6-49
go to table Figure 6-9 Results of sensitivity analysis of algorithms estimating above ground vegetation concentrations resulting from particle phase depositions 6-50
go to table Figure 6-10 Results of sensitivity analysis of algorithms estimating below ground vegetation concentrations resulting from soil to root transfers 6-59
go to table Figure 6-11 Results of sensitivity analysis of algorithms estimating beef fat concentrations resulting from soil contamination 6-60
go to table Figure 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
go to table Figure 6-13 Results of sensitivity analysis of algorithms estimating surface water and fish concentrations resulting from effluent discharge 6-66
go to table Figure 6-14 Results of sensitivity analysis of algorithms estimating surface water and fish concentrations resulting from stack emissions 6-68
go to FIGURES 7  
go to table Figure 7-1 Schematic of effluent discharge model showing all parameter inputs and observed fish concentrations 7-38
go to table Figure 7-2 Comparison of predicted and observed fish tissue concentrations for validation of the effluent discharge model 7-46
go to table Figure 7-3 Overview of model to predict beef concentrations from air concentrations 7-62
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.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

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.

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

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

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:

  • 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:

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