United States
               Environmental Protection
              Office of Research and
              Washington DC 20460
June 1994
External Review Draft
Exposure to

Volume I:
Executive Summary
  (Do  Not
  Cite or
                This document is a preliminary draft. It has not been formally
               released by EPA 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.
                       U.S. Environmental Protection Agency
                       Region 5, Library (PL-12J)
                       77 West Jackson Boulevard, 12th Floor
                       Chicago, tl 60604-3590

DO NOT QUOTE OR CITE                                              June 1994
                                                           External Review Draft

                         VOLUME I:  Executive Summary
                        U.S. Environmental Protection Agency
                        Region 5, Library (PU12J)
                        77 West Jackson Boulevatd. 12th
                        Chicago, It 60604*3590

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.
                                                         Printed on Recycled Paper


      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  	       v
Figures	,	      vi
Foreword  	      vii
Preface	      viii
Authors, Contributors, and Reviewers  	      xi

 I.   INTRODUCTION    	     1
     1.1.    BACKGROUND	     1
           DOCUMENT	     6

           AND BACKGROUND EXPOSURES  	     9
     II.2.    SOURCES   	     12
           11.2.1.      Theories of Formation During Combustion	     12
           II.2.2.      Estimates of Annual Releases of
                     Dioxin-Like Compounds	     14
           11.3.1.      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

     111.1.    EXPOSURE EQUATION  	     48
           III.3.1.     Overview of Fate, Transport, and Transfer
                    Algorithms of the Methodology  	     52
           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

                          CONTENTS (cont'd)
    IV.4.   EXPOSURE  	    107
    IV.6.   COPLANAR PCBS	    109
    IV.8.   GLOBAL IMPACTS 	    111


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

I-2.     Dioxin-Like PCBs	     4

I-3.     Nomenclature for dioxin-like compounds	     5

11-1.     Possible number of positional CDD (or BDD) and
        CDF (or BDF) congeners	     10

II-2.     CDD and CDF air emission estimates for West Germany, Austria,
        United Kingdom, Netherlands, Switzerland, and the
        United States  	     17

II-3.     Current CDD and CDF multi-media emission estimates for the
        United States  	     19

II-4.     Summary of CDD/F levels in United States food (pg/g fresh weight)  .     27

II-5.     Summary of CDD/F levels in environmental media and
        food (whole weight basis)	     28

II-6.     Estimated TEQ background exposures in the United States	     35
111-1.    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  	     59

III-2.    Exposure media concentrations estimated for the demonstration of
        the stack emission source category	     67

III-3.    Lifetime Average Daily Doses,  LADD, for the high end stack emission
        demonstrations scenario (LADD in units of ng/kg-day) 	     68

III-4.    Percent contribution of the different exposure pathways within each
        exposure scenario   	     70

III-5.    Summary of key tests of the fate, transport, and transfer models ...     82

IV-1.    Analysis of air emission sources  	     99


11-1      Structure of Dioxins and Furans	     9

II-2     Structure of dioxin-like PCBs	     11

II-3     Estimated TEQ emissions to air from combustion sources in the
        United States  	     22

ll-4     Background environmental levels in TEQ	     29

II-5     Background TEQ exposures for North America by pathway	     37

II-6     Comparison of background TEQ exposures for North America,
        Germany, and the Netherlands	     38

111-1     Roadmap for assessing exposure and risk to dioxin-like
        compounds	     50

III-2     Diagram of the fate, transport, and transfer relationships
        for the on-site source category  	     53

III-3     Diagram of the fate, transport, and transfer relationships
        for the off-site source category	     53

III-4     Diagram of the fate, transport, and transfer relationships
        for the stack emission source category	     54

III-5     Diagram of the fate, transport, and transfer relationships
        for the effluent discharge source category 	     54

III-6     Results of sensitivity analysis of algorithms estimating
        above and below ground vegetation, and  beef fat
        concentrations resulting from stack emissions	     74


      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
                                      Michael A. Callahan
                                      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
      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-DO-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 for Volume I include all authors listed below.

Primary authors of each chapter are listed below in alphabetical order.
Jerry Blancato                                     Chapter  6
U.S. Environmental Protection Agency
Las Vegas, NV

Elizabeth Brown                                    Chapter  4
Versar, Inc.

David Cleverly                                     Chapter  3
U.S. Environmental Protection Agency
Washington, DC

Jeff Dawson                                       Chapter  3
Versar, Inc.

Keith Drewes                                      Chapter  4
Versar, Inc.

Carl D'Ruiz                                        Chapter  3
Versar, Inc.

Robert J. Fares                                    Chapter  4
Versar, Inc.

Geoffrey Huse                                     Chapters 2, 4, 5
Versar, Inc.

Tim Leighton                                       Chapters 3, 5
Versar, Inc.

Matthew Lorber                                    Chapters 3, 4
U.S. Environmental Protection Agency
Washington, DC

Nica Mostaghim                                    Chapter 4
Versar, Inc.

Linda Phillips                                       Chapter 3, 4, 5
Versar, Inc.

John L. Schaum                                    Chapter 1-5
U.S. Environmental Protection Agency
Washington, DC

Greg Schweer                                      Chapter 2 - 5
Versar, Inc.

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
                                       I-xi i


      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, Ml

In addition,  the following experts outside of EPA  have reviewed and/or contributed to this

            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
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 0. 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 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
Thomas Lahre
Phil Lorang
Dennis Pagano
Dallas Safriet
Joseph Wood
George Streit
Anne Pope
Walter Stevenson
Jim Crowder
Joe Somers
  Office of Pollution, Pesticides and Toxic
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

                          DRAFT-DO NOT QUOTE OR CITE

                                I.  INTRODUCTION

      In May of 1991, the Environmental Protection Agency (EPA) announced a scientific
reassessment of the human  health and exposure issues concerning dioxin and dioxin-like
compounds (56 FR 50903).  This reassessment has resulted in two reports: a health
reassessment document (EPA, 1994), and Estimating Exposure to Dioxin-Like Compounds
[this three-volume report], which expands upon a 1988 draft exposure report titled,
Estimating Exposure to 2,3,7,8-TCDD (EPA, 1988). The health and exposure
reassessment documents can be used together to assess potential health risks from
exposure to dioxin-like compounds.  In a related area, EPA has also discussed the data and
methods for evaluating risks to aquatic life from 2,3,7,8-tetrachlorodibenzo-p-dioxin
(2,3,7,8-TCDD) (EPA, 1993).
      The purpose of the exposure  portion of the dioxin reassessment is to describe the
causes and magnitude of background exposures, and provide site-specific procedures for
evaluating the incremental exposures due to specific sources of dioxin-like compounds.
      In September of  1992, EPA convened workshops to review the first public drafts of
the health (EPA, 1992a) and the exposure documents (EPA, 1992b).  The current draft  of
the exposure document incorporates changes as a result of that workshop as well as other
review comments.
      The exposure document is presented in three volumes.  Following  is a summary of
the material contained in each of the three volumes:

Volume I - Executive Summary
      This volume includes  summaries of findings from Volumes II  and III.  It also includes
      a unique section on research needs and recommendations  for dioxin-like
Volume II - Properties, Sources, Environmental Levels, and Background Exposures
      This volume presents and evaluates information on the physical-chemical
      properties, environmental  fate,  sources, environmental  levels, and  background
      human exposures to dioxin-like compounds.  It summarizes and evaluates relevant
      information obtained from published literature searches, EPA program offices and

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      other Federal agencies, and published literature provided by peer reviewers of
      previous versions of this document.  The data contained in this volume is current
      through 1993 with some new information published in early 1994.
Volume III - Site-Specific Assessment Procedures
      This volume presents procedures for evaluating the incremental impact from
      sources of dioxin released into the environment.  The sources covered include
      contaminated soils, stack emissions, and point discharges into surface water. This
      volume includes sections on:  exposure parameters and exposure scenario
      development; stack emissions and atmospheric transport modeling; aquatic and
      terrestrial  soil, sediment, and food chain modeling; demonstration of methodologies;
      and uncertainty evaluations including exercises on sensitivity analysis and model
      validation, review of Monte Carlo assessments conducted for dioxin-like
      compounds, and other discussions.  The data contained in this volume  is current
      through 1993 with some new information published in early 1994.

      Dioxin-like compounds are defined to include those compounds with nonzero
Toxicity Equivalency Factor  (TEF) values as defined in a 1989 international scheme, I-
TEFs/89.  This procedure was developed under the auspices of the North Atlantic Treaty
Organization's Committee on Challenges of Modern Society (NATO-CCMS, 1988a;  1988b)
to promote international consistency in addressing contamination involving CDDs and
CDFs.  EPA has adopted the l-TEFs/89  as an interim procedure for assessing the risks
associated with exposures to complex  mixtures of CDDs and CDFs (EPA, 1989). As
shown in Table 1-1, this TEF scheme assigns nonzero values to all chlorinated  dibenzo-p-
dioxins (CDDs) and chlorinated dibenzofurans (CDFs)  with chlorine substituted in the
2,3,7,8  positions. Additionally, the analogous brominated compounds (BDDs  and BDFs)
and certain polychlorinated biphenyls (PCBs, see Table I-2) have recently been identified as
having dioxin-like toxicity (EPA, 1994)  and  thus are also included in the definition of
dioxin-like compounds. However, EPA has not assigned TEF values for BDDs, BDFs, and
PCBs.  In the case of PCBs, research on the applicability of the TEF approach  is ongoing
but there is not yet any formal  EPA policy.  The nomenclature adopted here for purposes
of describing these compounds is summarized in Table I-3.

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Table 1-1. Toxicity Equivalency Factors (TEF) for CDDs and CDFs.
            Compound                    TEF
            Mono-, Di-, and Tri-CDDs        0
            2,3,7,8-TCDD                 1
            Other TCDDs                  0
            2,3,7,8-PeCDD                0.5
            Other PeCDDs                 0
            2,3,7,8-HxCDD                0.1
            Other HxCDDs                 0
            2,3,7,8-HpCDD                0.01
            Other HpCDDs                 0
            OCDD                       0.001

            Mono-, Di-, and Tri-CDFs        0
            2,3,7,8-TCDF                 0.1
            Other TCDFs                  0
            1,2,3,7,8-PeCDF               0.05
            2,3,4,7,8-PeCDF               0.5
            Other PeCDFs                 0
            2,3,7,8-HxCDF                0.1
            Other HxCDFs                 0
            2,3,7,8-HpCDF                0.01
            Other HpCDFs                 0
            OCDF                        0.001
Source: EPA, 1989.

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Table 1-2.  Dioxin-Like PCBs.
             IUPAC No.
3,3',4,4'-tetra PCB
3,4,4',5-tetra PCB
2,3,3',4,4'-penta PCB
2,3,4,4',5-penta PCB
2,3',4,4',5-penta PCB
3,3',4,4',5-penta PCB
2,3,3',4,4',5-hexa PCB
2,3,3',4,4',5'-hexa PCB
2,3',4,4',5,5'-hexa PCB
3,3',4,4',5,5'-hexa PCB
2,3,3',4,4',5,5'-hepta PCB
Source:   EPA, 1992a.

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Table 1-3.  Nomenclature for dioxin-like compounds.

















Any one particular member of the same chemical family; e.g., there are 75
congeners of chlorinated dibenzo-p-dioxins.

Group of structurally related chemicals that have the same degree of chlorination.
For example, there are eight homologues of CDDs, monochlorinated through

Substances that belong to the same homologous class.  For example,  there are 22
isomers that constitute the homologues of TCDDs.

Denoted by unique chemical notation.  For example, 2,4,8,9-
tetrachlorodibenzofuran is referred to as 2,4,8,9-TCDF.

Symbol for homologous class: dibenzo-p-dioxin

Symbol for homologous class: dibenzofuran

Symbol for mono, i.e., one halogen substitution

Symbol for di, i.e., two halogen substitution

Symbol for tri, i.e., three halogen substitution

Symbol for tetra, i.e., four halogen substitution

Symbol for penta, i.e., five halogen substitution

Symbol for hexa, i.e., six halogen substitution

Symbol for hepta, i.e., seven halogen substitution

Symbol for octa,  i.e., eight halogen substitution

Chlorinated dibenzo-p-dioxins,  halogens substituted in any position

Chlorinated dibenzofurans, halogens substituted  in any position

Polychlorinated biphenyls

Halogen substitutions in the 2,3,7,8 positions
Source:  EPA, 1989.

                          DRAFT-DO NOT QUOTE OR CITE

      The procedure relates the toxicity of 210 structurally related individual CDD and
CDF congeners and is based on a limited data base of in vivo and jn vitro toxicity testing.
By relating the toxicity of the 209 CDDs and CDFs to the highly-studied 2,3,7,8-TCDD,
the approach simplifies the assessment of risks involving exposures to mixtures of CDDs
and CDFs (EPA, 1989).
      In general, the assessment of the human health risk to a mixture of CDDs and
CDFs, using the TEF procedure, involves the following steps (EPA, 1989):

      1.     Analytical determination of the CDDs and CDFs in the sample.
      2.     Multiplication  of congener concentrations in the sample by the TEFs in Table
             1-1 to express the concentration in terms of 2,3,7,8-TCDD equivalents
      3.     Summation of the products in Step 2 to obtain the  total TEQs in the sample.
      4.     Determination of human exposure to the mixture in question, expressed in
             terms of TEQs.
      5.     Combination of exposure from step 4 with toxicity  information on 2,3,7,8-
             TCDD to estimate risks associated with the mixture.

      Samples of this calculation for several environmental mixtures are provided in EPA
(1989).  Also, this procedure is demonstrated in Volume III of this assessment in the
context of the demonstration of the stack emission source category. The seventeen
dioxin-like congeners are individually modeled from stack to exposure site.  TEQ
concentrations are estimated given predictions of individual congener concentrations using
Steps 2 and 3 above.

      Users of the dioxin exposure  document should recognize the following:
1.  This document does not  present  detailed procedures for evaluating multiple sources of
release.  However, it can be used  in two ways to address this issue. Incremental impacts
estimated with procedures in Volume III can be compared to background exposure
estimates which are presented in Volume II.  This would be a way of comparing the
incremental impact of a  specific source to an individual's total exposure. If the releases

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from multiple sources behave independently, it is possible it model them individually and
then add the impacts. For example, if several stack emission sources are identified and
their emissions quantified, and it is desired to evaluate the impact of all sources
simultaneously, then it may be possible to model each stack emission source individually
and then sum the concentrations and depositions at points of interest in the surrounding
2. The procedures and estimates presented in this three-volume exposure document best
serve as an information source for evaluating exposures to dioxin-like compounds. This
document was not generated for purposes of supporting any specific regulation.  Rather, it
is intended to be a general information source which Agency programs can adopt or
modify as needed for their individual purposes.  For example, the demonstration scenarios
of Volume III were not crafted as Agency policy on "high end" or "central tendency"
scenarios for evaluating land contamination, stack emissions, or effluent discharges.
Rather, they were designed to illustrate the site-specific methodologies in Volume III.
3. The understanding of the exposure to dioxin-like compounds continues to expand.
Despite being one of the most studied groups of organic environmental contaminants, new
information is generated almost daily about dioxin-like compounds.  This document is
considered to be current through 1993, with some information  published early in 1994
included as well. Section IV of Volume I, Executive Summary, discusses research needs
for dioxin exposure evaluation.

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                         REFERENCES FOR INTRODUCTION
NATO/CCMS (North Atlantic Treaty Organization, Committee on the Challenges of Modern
      Society). (1988a) International toxicity equivalency factor (I-TEF) method of risk
      assessment for complex mixtures of dioxins and related compounds.  Report No.

NATO/CCMS (North Atlantic Treaty Organization, Committee on the Challenges of Modern
      Society). (1988b) Scientific basis for the development of international toxicity
      equivalency (I-TEF) factor method of risk assessment for complex mixtures of
      dioxins and related compounds.  Report No. 178.

U.S. Environmental Protection Agency. (1988) Estimating exposure to 2,3,7,8-TCDD.
      U.S. Environmental Protection Agency, Office of Health and Environmental
      Assessment, Washington, DC; EPA/600/6-88/005A.

U.S. Environmental Protection Agency. (1989) Interim procedures for estimating risks
      associated with exposures to mixtures of chlorinated dibenzo-p-dioxins and
      -dibenzofurans (CDDs and CDFs) and 1989 update. U.S. Environmental Protection
      Agency, Risk Assessment Forum, Washington, DC; EPA/625/3-89/016.

U.S. Environmental Protection Agency. (1992a)  Health reassessment of dioxin-like
      compounds. Chapters 1-8.  U.S. Environmental Protection Agency, Office of Health
      and Environmental Assessment, Washington,  DC.  EPA/600/AP-92/001a through
      EPA/600/AP-92/001h. August 1992 Workshop Review Draft.

U.S. Environmental Protection Agency. (1992b)  Estimating Exposure to Dioxin-Like
      Compounds. U.S. Environmental Protection Agency, Office of Health and
      Environmental Assessment, Washington, DC.  EPA/600/6-88/005B. August 1992
      Workshop Review Draft.

U.S. Environmental Protection Agency. (1993) Interim Report on Data and Methods for
      Assessment of 2,3,7,8-Tetrachlorodibenzo-p-dioxin Risks to Aquatic Life and
      Associated Wildlife.  Environmental  Research  Laboratory, Duluth, MN, Office of
      Research and Development, U.S. Environmental Protection Agency.  EPA/600/R-
      93/055.  March,  1993.

U.S. Environmental Protection Agency. (1994) Health Assessment for 2,3,7,8-TCDD and
      Related Compounds.  Public Review Draft. EPA/600/EP-92/001.

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                          AND BACKGROUND EXPOSURES

       Polychlorinated dibenzodioxins (CDDs), polychlorinated dibenzofurans (CDFs), and
polychlorinated biphenyls (PCBs) are chemically classified as halogenated aromatic
hydrocarbons. The chlorinated and brominated dibenzodioxins and dibenzofurans are
tricyclic aromatic compounds with similar physical and chemical properties, and both
classes are quite similar structurally. There are 75 possible different positional  congeners
of CDDs and  135 different CDF congeners. Only 7 of the 75 possible CDD congeners, and
10 of the 135 possible CDF congeners, those with chlorine substitution in the 2,3,7,8
positions, are thought to have dioxin-like toxicity.  Likewise, there are 75 possible different
positional congeners of BDDs and 135 different congeners of BDFs (see Table 11-1). The
basic structure and numbering of each chemical class is shown in Figure 11-1.
       There are 209 possible PCB congeners, only 11  of which are thought to have
dioxin-like toxicity.  These dioxin-like congeners have four or more chlorine atoms with

                     Figure II-1.  Structure of Dioxins and Furans.
                        X  = 1 to 4, Y = 1 to 4, X + Y

                          DRAFT-DO NOT QUOTE OR CITE
Table 11-1.  Possible number of positional CDD (or BDD) and CDF (or BDF) congeners
Halogen substitution
CDDs (or BDDs)
Number of Congeners
CDFs (or BDFs)
no more than one substitution in the ortho positions (positions designated 2, 2', 6 or 6' in
Figure II-2).  Dioxin-like PCBs are listed in Table I-2. These compounds are sometimes
referred to as coplanar PCBs, since the rings can rotate into the same plane if not
blocked from rotation by ortho-substituted chlorine atoms.  The physical/chemical
properties of each congener vary according to the  degree and position of chlorine
substitution.  The basic structure and numbering of each chemical class is shown in Figure
       In general, these compounds have very low water solubility, high octanol-water
partition coefficients, low vapor pressure and tend to bioaccumulate.  Volume II presents
congener-specific values for water solubility, vapor pressure,  partition coefficients and
photo quantum yields.
       Despite a growing body of literature from laboratory, field, and monitoring studies

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                       Figure 11-2. Structure of dioxin-like PCBs.
                         X = 1 to 5, Y =  1 to 5, X + Y >  1
examining the environmental fate and environmental distribution of CDDs and CDFs, the
fate of these environmentally ubiquitous compounds is not yet well understood.  In soil,
sediment, and the water column,  CDDs/CDFs are primarily associated with paniculate and
organic matter because of their high lipophilicity and low water solubility. In a detailed
evaluation of ambient air monitoring studies in which researchers evaluated the partitioning
of dioxin-like compounds between the vapor and particle phases, a principal conclusion
was that the higher chlorinated congeners, the hexa through hepta congeners, were
principally sorbed to airborne particulates, whereas the tetra and penta congeners
significantly, if not predominantly, partition to the vapor phase.  This finding is consistent
with vapor/particle partitioning as theoretically modeled in Bidleman (1988). Dioxin-like
compounds  exhibit little potential  for  significant  leaching or volatilization  once sorbed to
particulate matter. The available evidence indicates that CDDs and CDFs, particularly the
tetra- and higher chlorinated congeners, are extremely stable compounds under most
environmental conditions.  The only environmentally significant transformation process  for
these congeners is believed to be  photodegradation of nonsorbed species in the gaseous
phase, at the soil-air or water-air interface, or in  association with organic cosolvents.
CDDs/CDFs  entering the atmosphere  are removed either by photodegradation or by
deposition.   Burial in-place, resuspension back into the air, or erosion of soil to water
bodies appears to be the predominant fate of CDDs/CDFs sorbed to soil.  CDDs/CDFs

                         DRAFT-DO NOT QUOTE OR CITE

entering the water column primarily undergo sedimentation and burial.  The ultimate
environmental sink of CDDs/CDFs is believed to be aquatic sediments.
      Little specific information exists on the environmental transport  and fate of the 11
coplanar PCBs.  However, the available information on the physical/chemical properties of
coplanar PCBs coupled with the body of information  available on the widespread
occurrence and  persistence of PCBs in the environment indicates that these coplanar PCBs
are likely to be associated primarily with soils and sediments, and to be thermally and
chemically stable. PCBs volatilize from the surfaces  of soils and water bodies and are
dispersed via air movement.  Subsequently they can  be deposited back into soil or water.
In water bodies, they can be spread via sediment transport.  Though not rapid  processes,
these mechanisms account for the widespread  environmental occurrence of PCBs.
Photodegradation to less chlorinated congeners followed by slow anaerobic and/or aerobic
biodegradation is believed to  be the principal path for destruction of PCBs.

11.2.  SOURCES
      Ancient human tissue  sampling shows much lower CDD/F levels than found today
(Ligon et al., 1989). Studies of  sediment cores in lakes near  industrial centers  of the
United States have shown that  dioxins and furans were quite low until about 1920
(Czuczwa, et al., 1984; Czuczwa and Hites, 1985; Smith, et al., 1992). These studies
show increases in CDD/F concentrations beginning in the 1920s and continuing until about
1970. Declining concentrations have been measured since this time.   These trends
cannot be explained by  changes in natural processes and have been shown to correspond
to chlorophenol production trends (Czuczwa and Hites, 1984).  On this basis,  it appears
that the presence of dioxin-like  compounds in the environment occurs  primarily as a result
of anthropogenic practices. This section will review the theories of formation and emission
of these compounds, and then  discuss the possible sources which can release them to the

11.2.1. Theories of Formation During Combustion
      The emission of  CDDs and CDFs into the environment from combustion processes
can be explained by three principal theories, which should not be regarded as being
mutually exclusive: (1) contaminated feedstock, (2) formation from precursors, and (3)

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                          DRAFT-DO NOT QUOTE OR CITE

 formation de novo.  In general, the primary theories can be summarized as follows:
       (1)  The feed material to the combustor contains CDDs and CDFs and some portion
 survives the thermal stress imposed by the heat of the incineration or combustion process,
 and is subsequently emitted from the stack.  While this explanation is not thought to be
 the principal explanation for dioxin  and furan emissions from combustor sources
 (explanations 2 and 3 below are thought to  be the predominant cause of these emissions),
 in fact it is the single theory best thought to explain the release of the dioxin-like, coplanar
       (2) CDDs/CDFs are ultimately formed from the thermal breakdown and molecular
 rearrangement of precursor compounds. Precursor compounds are chlorinated aromatic
 hydrocarbons having a structural resemblance to the CDD/CDF molecule.  Among the
 precursors that have been identified are polychlorinated biphenyls (PCBs), chlorinated
 phenols (CPs), and chlorinated benzenes (CBs).   The formation of CDDs/CDFs is believed
 to occur after the precursor has condensed and adsorbed onto the binding sites on the
 surface of fly ash particles. The active sites of the surface of fly ash particles promote the
 chemical reactions forming CDDs/CDFs. These reactions have been  observed to be
 catalyzed by the presence of inorganic chlorides  sorbed to the particulate.  Temperature in
 a range of 250-450°C has been identified as a necessary condition for these reactions to
 occur, with either lower or higher temperatures inhibiting the process.  Therefore, the
 precursor theory focuses on the region of the combustor that is downstream and away
 from the high temperature zone of the furnace or combustion chamber.  This is a location
 where the gases and smoke derived from combustion  of the organic  materials have cooled
 during conduction through flue ducts, heat exchanger  and boiler tubes, air pollution control
 equipment or the stack.
       (3) CDDs/CDFs are synthesized de novo in the same region  of the combustion
 process as described in (2), e.g. the so-called cool zone. In this theory,  CDDs/CDFs are
formed from moieties bearing little resemblance to the molecular structure of CDDs and
CDFs.  In broad terms, these are non-precursors  and include such diverse substances as
petroleum products, chlorinated plastics (PVC), non-chlorinated plastics (polystyrene),
cellulose, lignin, coke, coal, particulate carbon, and hydrogen chloride gas.  Formation of
CDDs/CDFs requires the presence of a chlorine donor (a molecule that provides a chlorine
atom to the pre-dioxin molecule) and the formation and chlorination of a chemical

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intermediate that is a precursor. The primary distinction between theories (2) and (3) is
that theory (2) requires the presence of precursor compounds in the feed material whereas
theory (3) begins with the combustion of diverse substances that are not defined as
precursors, which eventually react to form precursors and eventually, dioxin-like

11.2.2. Estimates of Annual Releases of Dioxin-Like Compounds
       PCBs were produced in relatively large quantities for use in such commercial
products as dielectrics, hydraulic fluids, plastics and paints.  They are no longer produced,
but continue to be released to the environment through the use and disposal of products
manufactured years ago. The chlorinated and brominated dioxins and furans, on the other
hand, have never  been intentionally produced other than on a laboratory scale basis for use
in chemical analyses.  They are, however, generated as byproducts from various
combustion and chemical processes.  Dioxin-like compounds are released  to the
environment in  a variety of ways and in varying quantities depending upon the source.
The dioxin like compounds have been found in all media and all parts of the world.  This
ubiquitous nature  of these compounds suggests that multiple sources exist  and that long
range transport can occur. An unresolved issue is how the relative impacts from local
versus distant sources compare at a particular location.  Presumably in industrial areas
local sources will  dominate and in rural areas distant sources will dominate.  However, site
specific considerations such as stack height, wind patterns, magnitude  of local sources,
etc. could influence these comparisons.

       The major  identified sources of environmental release have been grouped into four
major types for the purposes  of this report:

• Industrial/Municipal Processes:  Dioxin-like compounds can be formed through the
chlorination of naturally occurring phenolic compounds such as those present in wood
pulp.  The formation of CDDs and CDFs resulting from  the use of chlorine bleaching
processes in the manufacture of bleached pulp and paper has in the past resulted in the
presence  of CDDs and CDFs in paper products as well as in liquid and solid wastes from
this industry, although more recently this industry has made process changes to minimize

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                          DRAFT-DO NOT QUOTE OR CITE

CDD/CDF formation. Occasionally, municipal sewage sludge has been found to contain
CDDs and CDFs.

•  Chemical Manufacturing/Processing Sources:  Dioxin-like compounds can be formed as
by-products from the manufacture of chlorine and such chlorinated compounds as
chlorinated phenols, PCBs, phenoxy herbicides, chlorinated benzenes, chlorinated aliphatic
compounds, chlorinated catalysts, and halogenated diphenyl ethers.  Although the
manufacture of many chlorinated phenolic intermediates and products, as well as PCBs,
was terminated in the late 1970s in the United States, the  continued limited use and
disposal of these compounds can result in releases of CDDs, CDFs, and PCBs to the

•  Combustion and Incineration Sources: Dioxin-like compounds can be generated and
released to the environment from various combustion processes when chlorine donor
compounds are present. These processes can include incineration of wastes such as
municipal solid waste, sewage sludge, hospital and hazardous wastes; metallurgical
processes such as high temperature steel production, smelting operations,  and scrap metal
recovery furnaces; and  the burning of coal, wood, petroleum products, and used tires for
power/energy generation.

•  Reservoir Sources:  The persistent and hydrophobic nature of these compounds cause
them to accumulate in soils, sediments and organic matter  and to persist in waste disposal
sites.  The dioxin-like compounds in these "reservoirs" can  be redistributed by dust or
sediment resuspension  and transport. Such releases are not original sources in a global
sense, but can be on a  local scale. For example,  releases may occur  naturally from
sediments via volatilization or via operations which disturb them such as dredging. Aerial
deposition and accumulation on leaves may lead to releases during forest fires or leaf
composting  operations.

      As awareness of these possible sources has grown in recent years,  a number of
changes have occurred  which should reduce the release rates (Rappe, 1992).  For
example, releases of dioxin-like compounds have  been reduced due to the switch to

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                          DRAFT-DO NOT QUOTE OR CITE

unleaded automobile fuels (and associated use of catalytic converters and reduction in
halogenated scavenger fuel additives), process changes at pulp and paper mills, new
emission standards and upgraded emission controls for incinerators, and reductions in the
manufacture of chlorinated phenolic intermediates and products.
      Table 11-2 presents CDD and CDF air emission estimates for Germany, Austria, the
United Kingdom, the Netherlands, Switzerland and the U.S. All the countries except
Austria estimate that municipal waste incinerators are an important source (new emission
standards in Germany indicate that the emissions from this source are now nearer the
lower end of the range listed in Table 11-2). Medical waste incinerators, wood burning and
metal smelters/refiners also appear  to be generally important sources.  Rappe (1992) and
Lexen et al. (1992) have identified emissions from ferrous and non-ferrous metals smelting
and refining facilities as potentially the largest current source in Sweden.  Rappe (1992)
reported that changes in various industrial practices have lead to  reductions in dioxin
emissions in Sweden from 400 - 600 g of TEQ/yr in 1985 to 100 - 200 g TEQ/yr in 1991.
      Nationwide emission estimates for  the United States have not  previously been
compiled. This task was attempted as part of this project and the air emissions are
summarized in Table II-2 and a detailed estimate of emissions to all media are presented in
Table II-3. For each source, emissions to  air, water, land, and  product are estimated
where appropriate and where  data are adequate to enable an estimate to be made. The
term "product"  is defined to include substances or articles (e.g., paper pulp or sewage
sludge that is distributed/marketed commercially) that are known to contain dioxin-like
compounds and whose subsequent use may result in releases to the environment. In order
to make each source emission estimate, information was required concerning both the
"emission factor" term for the source (e.g., grams TEQ per kg of  material processed) and
the "production" term for the  source (e.g., kg of material processed annually in the U.S.).
Because the quantity and quality of the available information for both terms for each
emission source varies considerably, a confidence rating of "high", "medium", or "low"
was assigned to both terms.  In addition, the uncertainty  in these national release
estimates is reflected by presenting  (where possible) for each source category both a
central or "best guess" value and a possible range from a lower to an upper estimate.  In
general, the emission estimates are quite uncertain since the nationwide approximations
were derived by extrapolating only a few facility tests. Insufficient data were available to

                                        16                                     4/94

Table 11-2.     CDD and CDF air emission estimates for West Germany, Austria, United Kingdom, Netherlands,
             Switzerland, and the United States.
Emission Source
Industrial/Municioal Processes
Pulp and paper mills
Sewage sludge incineration
Chemical Manuf ./Processing Sources
Organic chemical manufacture
Combustion and Incineration Sources
Incineration/Energy Recovery
Municipal waste incineration
Hazardous waste incineration
Hospital waste incineration
Cement kilns
Metallurgical Processes
Tire combustion
Ferrous metal smelting/refining
Nonferrous metal smelting/refining
Scrap electric wire recovery
Drum and barrel reclamation
Power/Energy Generation
Vehicle fuel combustion - leaded
- unleaded
- diesel
West Germany"
(9 TEQ/yri

0.01 - 1.1

5.4 - 432
0.5 - 72

1.3- 18.9
38 - 380

*g TEQ/yr)



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                       Table 11-2.     COD and CDF air emission estimates for West Germany, Austria, United Kingdom, Netherlands,
                                      Switzerland, and the United States.
Emission Source
Wood burning
Coal combustion - residential
- industrial
- utility
Oil combustion - residential
Charcoal briquette combustion (residential)
West Germany*
(g TEQ/yr}


67 - 926


Table 11-3. Current CDD and CDF multi-media emission estimates for the United States.
Emieeion Source
MuetriaJ/Municipal Praceaea*
Bleached chemical pulp and paper mill*
Publicly Owned Treatment Work.
Chemical Manuf ./Procaaaing/
Aliphatic Chlorine Compound*
Dioxazina Dyee/Pigmenta
Cornbintion and Incineration Source*
Incineration/ Energy Recovery
Municipal waste incineration
Hazardous waata incineration
Medical waata incineration
Kraft Mack liquor boiler.
Sewage aludge incineration
Carbon reactivation furnace.
Cement kiln*
Metallurgical Procaeaea
Ferroue metal amelting/refining
Secondary copper emetting/refming
Secondary lead .melting/refining
Scrap electric wire recovery













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                                  Table 11-3.  Current CDD and CDF multi-media emission estimates for the United States.
Emission Source
Drum and barrel reclamation
Power/Enarpv Generation
Tire combustion
Vehicle fuel combustion - leadad
- unleaded
Wood burning - residential
- industrial
Coal combuation - reaidential
- industrial
- utility
Oil combuation - residential
Charcoal briquette combuation
Reservoir Sources
Pentachlorophenol treated surfaces
Forest ftraa
Emieeione la TEQ/vr) to Media.




































•   CR = Confidence rating.  First letter is,rating assigned to "production" estimate; second letter is rating assigned to "emission factor" : H =  High Confidence,   M  =
    Medium, Confidence,         L = Low Confidence.
6   See Kraft black liquor boilers below.          c   See Sewage sludge incineration below.
*   Leaded fuel production in the United States and the manufacture of motor vehicle engines requiring leaded fuel have been prohibited in the United States.
•   TOTAL reflects only the total of the estimates made in this report.  There are many unknowns as reflected by the number of blank cells.
'   It is not known what fraction, if any, of the estimated emissions from forest fires represents a "reservoir" source.  The estimated emissions  may be solely the result of
NA = Not applicable             NEG  =  Expected to be negligible or non-existent.         BLANK = Insufficient data available upon which to base an estimate.

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statistically derive estimates of the range of uncertainty surrounding the central emission
estimates. Instead, a judgement-based approach was used that assigned a factor of 10
from the low to high end of the range for the low confidence class, a factor of 5 for the
medium confidence class and a factor of 2 for the high confidence class. It is emphasized
that these ranges should be interpreted as judgements which are symbolic of the relative
uncertainty among sources, and not statistical derivations of  uncertainty. The emission
factors and production values used to generate air emission estimates are illustrated in
Figure II-3.  Key source categories are discussed below:

•  Hospital Waste Incinerators:    Collectively, this may be the  largest source in the United
States.  This is due to the facts that most of these incinerators  do not rely  on highly
sophisticated control technologies, are high in number (over 6000 facilities) and burn high
chlorine content waste. Although the dioxin emissions from these facilities are collectively
large, individually they are relatively small.  Therefore, local impacts may also be relatively
small.  However, the area of impact is an uncertain issue in general for combustors.
Germany recognized the importance of these facilities several years ago  and instituted
emission limits which required facilities to upgrade their technology or ship  waste to
hazardous waste incinerators.

•  Municipal Waste Incinerators:   The current emissions from this category appear
relatively high, but upgrading is occurring that should substantially reduce these emissions
in the near future.  Dioxin is also present in the  ash generated from these facilities.  The
amount estimated to be in municipal incinerator waste ash nationally is the  largest among
the few source categories where estimates could be made concerning  solid  residues.

• Cement Kilns: EPA is currently evaluating dioxin levels in the clinker dust and stack
emissions from these facilities.  The preliminary information suggests that collectively
these facilities could be a moderate to large source.  About 1 6% of the facilities burn
hazardous waste as an auxiliary fuel; limited data suggests that the CDD/F  levels in  clinker
dust and stack emissions of these kilns may be  significantly higher than the kilns which do
not burn hazardous waste.
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                               DRAFT-DO NOT QUOTE OR CITE
Sources (tested/total units)

Medical Waste Incineration (6/6700)

Municipal Waste Incineration (30/171)

Cement Kilns (17/212)

Wood Burning (Industrial) (2/7?)

Secondary Copper Smelting (1/24)

Forest Fires

Diesel Fuel Combustion

Wood Burning (Residential)

Hazardous Waste Incineration (6/1

Sewage Sludge Incineration (3/199)

Kraft Black Liquor Boilers (3/104)

Drum Reclamation (1/77)

Secondary Lead Smelting (3/23)

Unleaded Fuel combustion

Tire Combustion (1/77)
                           Emission Factor

                                (ug / kg)
Annual "Production"

(thousand metric tons / yr)
Annual TEQ Emission Range





Derivation of emission factors and annual "production" (e.g., kg of waste incinerated)

are presented in Chapter 3, Volume II. The emission factor for diesel fuel and

unleaded fuel combustion are based on //g of TEQ per km driven.  The difference

in  bar shading indicates  the degree of confidence in the estimate.  The set of

numbers following the source categories indicates the number of facilities for

which stack test data are available versus the number of  facilities in the category.

                    Figure II-3.  Estimated TEQ emissions to air  from combustion sources in the United States.

                          DRAFT-DO NOT QUOTE OR CITE

•  Wood Burning:  A large quantity of wood is burned at industrial operations, but the
practice has not been well characterized. The emission estimates presented here are
based on stack tests at two facilities.  A number of studies have found dioxins in the
emissions and ash/soot from wood fires in nonindustrial situations. The emission
estimates for residential wood burners were made on the basis of two recent European
studies.  CDD/Fs may also be emitted during forest fires, but very little direct emission
data are available for evaluating this issue. The estimates shown here were derived from
tests on wood stoves under conditions  of uncontrolled draft.  Considering the many
differences between  combustion in wood stoves and forest fires, these estimates must  be
considered highly uncertain.  Only one test has been conducted that directly measured
CDD/F in smoke of forest fires (Clement and Tashiro, 1991).  Low levels were detected,
but the authors caution that some portion of these emissions could represent resuspended
material from aerial deposits  rather than originally formed material. The theory that much
of today's body burden could be due to natural sources (such as forest fires) has been
largely discounted by testing of ancient tissues which show levels much lower than those
found today (Ligon et al. 1989).

•  Metals Industry:   Secondary smelters which recover metal from waste products such
as scrap  automobiles have the potential for dioxin formation due to chlorine in the plastic
in  the feed material.  Processes in the primary metals industry, such as sintering of iron
ore, have also been identified as potential sources.  Germany (see Table II-2) has identified
the metals industry as potentially one of the most important. Table II-3 estimates
moderate emissions for secondary copper smelting (based on testing at only one facility)
and relatively low emissions for secondary lead smelting (based on testing at three
facilities). No data are available to estimate emissions from other secondary smelters or
primary smelters. Accordingly, these facilities are a high priority for future emissions

•  Diesel Vehicles:  The literature on dioxin emissions from diesel vehicles is quite  limited
and somewhat contradictory. The tunnel study by Oehme et al.  (1991) suggests a
relatively high level of emissions.  This study is based on Norwegian fuels which may differ
in  composition from U.S. fuels and, although aggregate samples  were collected

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representing hundreds of vehicles, the indirect method of analysis introduces uncertainty.
Much lower emissions were measured by Marklund et al. (1990) on the basis of direct
tailpipe tests involving diesel fuel in a heavy-duty Swedish vehicle (Marklund et al., 1990).
This study reported no emissions at a detection limit of 100 pg/l or approximately 0.05
ng/km.  This is a factor of 100 lower than the emission rate reported by Oehme et al.
(1991).  Because this study's results are based on only one vehicle using Swedish fuel,
this emission factor is also quite uncertain.  These two studies yield a very wide range of
emission estimates and clearly suggests that further testing is needed.

•  Coal-Fired Utilities:  The importance of these facilities remains unknown.  Only one
U.S. facility has been tested and no detectable levels of dioxin were found. If dioxin were
present  at the  detection limit, an emission factor can  be calculated which suggests that,
due to their number, these plants could collectively represent a  moderately sized source.
The potential importance of this source is enhanced by several factors. In addition to
being numerous, they are large in size  and their high stacks indicate that they could impact
very large areas. Testing is currently underway to better characterize these emissions.

•  Pulp  and Paper Mills:  These facilities can  have dioxin releases to  water, land  and
paper products.  The paper industry has recently made process changes which they
estimate have  reduced  dioxin emissions by 90% from 1988 to  1992 (NCASI,  1993).
Extensive surveys  encompassing virtually all mills have been conducted, making this
industry one of the best characterized  in terms of dioxin emissions.

      The other combustors evaluated in this report  appear to  be relatively minor sources
on a national scale (although their local impacts could be important to evaluate).  These
include  sewage sludge  incinerators, hazardous waste incinerators, Kraft liquor boilers,
drum and barrel reclaimers, tire combustors, carbon reactivation furnaces and  scrap
electric  wire recovery facilities. The releases associated with chemical manufacturing
could not be quantified due to the lack of test data. Potentially such releases  could occur
via the product itself or as emissions to the air, land or water.  Such releases have lead to
the termination of  production of PCBs and some phenoxy herbicides.  Recently, some
claims have been made that significant dioxin  emissions may occur during the production

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of vinyl chloride monomer and associated products.  These claims have been strongly
disputed by the industry.  Insufficient emission data are currently available to make an
independent evaluation.
       Several investigators have attempted to conduct "mass balance" checks on the
estimates of national dioxin releases to the environment. Basically, this procedure involves
comparing estimates of the emissions to estimates of aerial deposition. Such studies in
Sweden (Rappe, 1991) and Great Britain (Harrad and Jones, 1992) have suggested that
the estimated deposition exceeds the estimated emissions by about 10 fold. These
studies are acknowledged to be quite speculative due to the strong potential for
inaccuracies in emission and deposition estimates.  In addition, the apparent discrepancies
could be explained by long range transport from outside the country, resuspension and
deposition of reservoir sources, atmospheric transformations or unidentified sources.
Bearing these limitations in mind, this procedure has been used here to compare the
estimated emissions and deposition in the United States.
       Deposition measurements have been made at a number of locations in Europe (see
Volume II) and two places in the United States (Koester and Hites, 1992).  These limited
data suggest that a deposition rate of 1 ng TEQ/m2-yr is typical of remote areas and that
2-6 ng TEQ/m2-yr is more typical of populated areas.  Applying the values of 1  ng TEQ/m2-
yr to Alaska and 2-6 ng TEQ/m2-yr to the continental United States, the total U.S.
deposition can be estimated as 20,000 to 50,000 g TEQ/yr. This range can be compared
to the range of emissions for the United States, 3,300 to 26,000 g TEQ/yr, as presented
in Table II-3. It is not clear whether this type of mass balance can ever be refined to the
point where definitive conclusions can be drawn. However, it remains one of the few
methods of evaluating the existence  of unknown sources.

       Polychlorinated dibenzo-p-dioxins (CDDs), polychlorinated dibenzofurans (CDFs),
and polychlorinated biphenyls (PCBs) have been found throughout the world in  practically
all media including air, soil, water, sediment, fish and shellfish, and other food products
such as meat and dairy products. The highest levels of these compounds are found in
soils, sediments, and biota; very low levels are found in water and air. The widespread
occurrence observed is not unexpected considering the numerous sources that emit these

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compounds into the atmosphere, and the overall resistance of these compounds to biotic
and abiotic transformation.

11.3.1.  United States Food Data
      All available data on background levels in United States food are summarized in
Table II-4. "Background"  concentrations are defined here as those for which no source of
dioxin-like compound contamination was identified to have  impacted the concentrations
reported. The background TEQ estimates are presented first assuming that nondetects
equal half the detection limits and second assuming that nondetects equal zero. For food
groups such as eggs, a wide range of TEQ estimates are seen indicating a high percent of
nondetects among individual congeners.  The higher of the  two TEQ estimates, that
calculated using half the detection limit for nondetects, are generally comparable to the
TEQ estimates derived from studies conducted in Germany (Furst et al. 1991) and Canada
(Gilman and  Newhook, 1991).  The German and Canadian studies did not,  however, report
how nondetects were treated in deriving  their TEQs, but did report many nondetects in
some food groups.  In summary, the limited number of United States food samples and the
high incidence of nondetects make an uncertain basis for estimating national background
levels, although they are reasonably consistent with food level estimates reported for
Canada and  Germany. It  is clear that more data are needed to adequately characterize the
levels of dioxin-like compounds in the United States food supply.  Although a large scale
survey could confirm residue levels of CDD/F, some attention also needs to be  paid to
sampling/analytical methodology. Since many of the  detected values are only a few
multiples above reported detection limits, significant uncertainty  results in reported mean
values when there are many nondetects in a food category.

11.3.2.  Summary of Media Levels
      The estimated levels of CDD/CDFs in  environmental media and  food  are summarized
in Table 11-5  and shown graphically in Figure  11-4. Except for the TEQ levels in European
food which are based on  data reported for German  food by Furst et al. (1990), all other
TEQ levels presented in Figure II-4 are based on the data analyzed in this study. The
background  TEQ levels of CDD/CDFs in water and air were found to be lower than in  any
of the other environmental media evaluated and were not included in Figure II-4. For  most

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     Table 11-4.  Summary of CDD/F levels in United States food (pg/g fresh weight)




Mean TEQ
ND = 0.5 DL




Mean TEQ
ND = zero




Number of





Stanley & Bauer (1989),
LaFleur et al. (1990),
Schecter et al. (1993)
Stanley & Bauer (1989),
LaFleur et al. (1990),
Schecter et al. (1993)
Stanley & Bauer (1989),
Schecter et al. (1993)
Stanley & Bauer (1989),
Schecter et al. (1993)

EPA, 1991b
EPA, 1992
ND = Nondetect; DL - Detection Limit

                               DRAFT-DO NOT QUOTE OR CITE
        Table 11-5.     Summary of CDD/F levels in environmental media and food (whole
                       weight basis).
Soil, ppt:
Sediment, ppt:
Fish, ppt:
Air, pg/m3:
Water, ppq:
Milk, ppt:
Dairy, ppt:
Eggs, ppt:
Beef ppt:
Pork, ppt:
Chicken, ppt:
North America*
7.96 ± 5.70 (n = 95)
3.91b (n = 7)
1.16 ± 1.21 (n = 60)
0.0949 ± 0.24 (n = 84)
0.0056 ± 0.0079
(n = 214)
0.07°'d (n = 2)
0.36 ± 0.29 (n = 5)
0.135 ± 0.119 (n = 8)
0.48 ± 0.99 (n = 14)
0.26 ± 0.13 (n = 12)
0.19 ± 0.29 (n = 9)
8.69 (n=133)
34.89" (n = 20)
0.93f (n = 18)
0.108° (n=454)
0.05h (n = 168)
0.08' (n = 10)
0.152d (n = 1)
0.321; 0.61k (n = 7)
                DRAFT-DO NOT QUOTE OR CITE
                                                            7 98 ± 5.70; n
            iiiiiiiiiii tii/iiiiiii/iiii/iiiiiiiiiiiii
            1111111111111111111111111111111 n
                                      0.36 ± 0.2 I; n=5
         028 ± 0.13; n
0.1               1                10
Media Concentration (ppt of TEQ)
                     North America [b]  Un Europe [c]
                      Figure II-4. Background environmental levels in TEQ.

[a] based on an examination of raw data reported by EPA (1991 b);  [b]  based on N. American studies;
[c] environmental media levels based on various European studies, food levels based on FCirst, et al. (1990), egg levels
   based on Beck, et al. (1989)

                          DRAFT-DO NOT QUOTE OR CITE

media, the average levels appear to be similar between North America and Europe.
However, differences were noted in three areas:

•  Sediment:  The background levels in Europe were estimated to be higher than North
America. It should be noted, however, that only the 2,3,7,8-TCDD/F and OCDD/F
congeners were analyzed for background sediment sites in the United States and Europe.
The sediment data are quite variable and can be very high in impacted areas (i.e., 2,3,7,8-
TCDD levels over 1000 ppt have been measured in industrial areas). Also, it was difficult
to interpret whether some of the European  data truly represent unimpacted areas.  Thus,
these differences may be due more to the weakness of the data base and interpretation
difficulties, rather than real differences.

•  Dairy Products: The data on dairy products suggest that North America levels are
higher than European. Dairy products include a wide variety of food items with varying
amounts of fat.  Thus, the CDD/F levels would vary correspondingly.  Differences in the
mix of dairy products used for the North America and  European estimates could  explain
these differences.

•  Pork:   The pork data suggests that North America levels are higher than European
levels. The low number of samples collected in both Europe and North America  may mean
this estimate is not representative.

       In general, the differences noted above probably reflect the sparseness or
inequalities in the data rather than real differences. The small number of samples available
for analysis, particularly for food, should be considered when evaluating data from the
United States and elsewhere. The human tissue data  (see discussion below) suggest
similar body burden levels in the North America, Europe and other  industrial countries.
Thus, it seems likely the media levels would also be similar. Large scale "market basket"
type food surveys would be needed to confirm these levels.

II.3.3. Conclusions for Mechanisms of Impact to Food Chain
       CDD/F can enter aquatic systems by either direct effluent discharges or

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atmospheric deposition.  CDD/Fs in the atmosphere can deposit directly onto water bodies
or onto watersheds and run off into the water system.  The mechanism of impact which
dominates in aquatic systems will depend on site specific conditions.
      This assessment proposes the hypothesis that the primary mechanism by which
dioxin-like compounds enter the terrestrial food chain is via atmospheric deposition.
Deposition can occur directly onto plant surfaces or onto soil. Soil deposits can enter the
food chain via direct ingestion (i.e. earth worms, fur preening by burrowing animals,
incidental ingestion by grazing animals, etc).  CDD/F in soil can become available to plants
by volatilization and vapor absorption or particle resuspension and adherence to plant
surfaces.  In addition, CDD/F in soil can adsorb directly to underground portions of plants,
but uptake from soil via the roots into above ground portions of plants is thought to be
insignificant (McCrady, et al. 1990).
      Support for this air-to-food hypothesis is provided by Hites (1991) who concluded
that "background  environmental levels  of PCD/F are caused by PCD/F entering the
environment through the atmospheric pathway." His conclusion was based on
demonstrations that the congener profiles in lake sediments could be linked to congener
profiles of combustion sources.  Further argument supporting this hypothesis is offered

• Numerous studies have shown that CDD/Fs are emitted into the air from a wide variety
of sources (see Chapter 3 of Volume II).

• Studies have shown that CDD/Fs can be measured in wet and dry deposition in most
locations including remote areas (Koester and Hites, 1993; Rappe, 1991).

• Numerous studies have shown that CDD/Fs are commonly found in  soils throughout the
world (see Chapter 4 of Volume II). Atmospheric transport and deposition is the only
plausible  mechanism that could lead to this widespread distribution.

• Models of the air-to-plant-to-animal food chain have been constructed.  Exercises with
these models show that measured deposition rates and air concentrations can be used to
predict measured food levels (Travis and Hattemer-Frey,  1991; also see Chapter 7  of

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Volume III).

Alternative mechanisms to the air-to-food hypothesis seem less likely:

      - Uptake from water into food crops and livestock is minimal due to the
      hydrophobic nature of these compounds. Travis and Hattemer-Frey (1987,
       1991) estimate water intake accounts for less than 0.01 % of the total daily
      intake of 2,3,7,8-TCDD in cattle. Experiments by McCrady,  et al. (1990)
      show very little uptake in plants from aqueous solutions.

      - Relatively little uptake is expected in food from soil residues that originate
      from sources other than atmospheric dispersion, i.e. pesticides, sewage
      sludge, and waste disposal  operations.  Pesticides are discussed below.
      Sewage sludge application onto agricultural fields is not a widespread
      practice and the amount of CDD/F in this material is quite low compared to
      the amount emitted to the atmosphere (See Chapter 3 of Volume II).  Waste
      disposal operations can be the dominant source of CDD/F in soils at isolated
      locations such as Times Beach,  but are not sufficiently widespread to explain
      the ubiquitous nature of these compounds.

      - The  contribution of CDD/Fs to  the environment via pesticides has been
      reduced in recent years but remains  somewhat uncertain. In the  past,
      CDD/Fs have been associated with certain phenoxy herbicides. Many of
      these compounds are no longer  produced and EPA has sponsored data call-
      ins requiring certain pesticide manufacturers to test their products for dioxin
      content.  The responses, so far, indicate that levels in these products are
      below or near the limit of quantitation (see Chapter 3 of Volume II).

      - Uptake into food from paper products also appears to be minimal. In the
      early  1980s, testing showed that CDD/Fs could migrate from paper
      containers into food. Current levels  in paper products are now much lower,
      and food testing in products such as milk and beef have shown detectable

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      levels prior to packaging, suggesting packaging is not the major source (see
      Chapter 4 of Volume II).

      A related issue is whether the CDD/F in food results more from current or past
emissions.  Sediment core sampling indicates that CDD/F levels in the environment began
increasing around the beginning of the twentieth century and have been declining since
about 1980 (Smith et al, 1992). Thus, CDD/Fs have  been accumulating for many years
and may have created a reservoir that continues to impact the food chain.  As discussed in
Chapter 3 of Volume II, researchers in several countries have attempted to compare
known emissions with deposition rates.  These studies may suggest that annual deposits
exceed annual emissions.  One explanation may  be that the reservoir sources cause
deposition through volatilization/atmospheric scavenging or particlo resuspension. These
mass balance studies are highly uncertain and it  remains unknown how much of the food
chain impact is due to current versus past emissions.

      Small amounts of dioxin-like compounds may be formed during natural fires
suggesting that these compounds may have always been present in  the environment.
However,  it is generally believed that much more of these compounds have been produced
and released into the environment in association with man's industrial and combustion
practices,  and as a result, environmental levels are likely to be higher in modern times than
they were in prior times. However, the trend may now be reversing (i.e., releases and
environmental levels may be gradually decreasing) due to changes in industrial practices
(Rappe, 1992).  As discussed earlier, the potential for environmental releases of dioxin-like
compounds have been reduced due to the switch to unleaded automobile fuels (and
associated use of catalytic converters and reduction in halogenated scavenger fuel
additives), process changes at pulp and paper mills, improved emission controls for
incinerators, and  reductions in the manufacture and use of chlorinated phenolic
intermediates and products.
      Studies that may be used to assess temporal trends in human exposure to dioxins
and furans are extremely limited.  Analysis of sediment core layers has shown increases in
CDD/CDF  concentrations beginning in the 1920's and continuing until the late 1970's

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                          DRAFT-DO NOT QUOTE OR CITE

(Smith et al, 1992). Another useful study for evaluating changes in human exposure over
time is EPA's National Human Adipose Tissue Survey or NHATS.  The purpose of NHATS
is to monitor the human body burden of selected chemicals in the general U.S. population
(EPA, 1991 a). The results of this study indicate that exposure to certain dioxins and furan
congeners may have decreased over this 5-year time period.  However, further studies are
needed to verify that these changes are not a result of protocol changes, but actual
reductions in exposures. A recent study by Patterson et al. (1994) found decreases in
PCB body burdens from 1982 to 1988/89 based on human tissue and blood testing.

       Table II-6 illustrates the derivation of a background exposure  level to CDD/F for the
United States on the  basis of diet. This estimate was derived using the upper-range
background concentrations  (i.e., those calculated using one-half the detection limit for the
non-detects) and central estimates of  ingestion rates.  This approach yields a total
background exposure estimate for CDD/Fs of 119 pg TEQ/d.  The exposures by pathway
are diagrammed in Figure II-5.
      The background exposure estimates are intended to be representative of the general
population. They do  not account for individuals with higher consumption rates of a
specific food group (e.g., subsistence fishermen, nursing infants, and subsistence farmers--
these are discussed Section II-6).  The fish concentration used to estimate background
exposures, represents the average value found in fish from fresh and estuarine waters (see
Section 4.5 of Volume II).  Correspondingly, the ingestion rate used here reflects the per
capita average ingestion rate of fresh/estuarine fish (EPA, 1989).  Many individuals are
likely to have higher ingestion rates of marine fish.  However, the limited data on marine
species indicates that the dioxin levels may be one to two orders of magnitude lower than
fresh/estuarine water fish (also see Section 4.5 of V. II).
       The contact rates for ingestion of fish, soil,  and water, and inhalation were  derived
from the Exposure Factors Handbook  (EPA, 1989).  For food  products such as milk, dairy,
eggs, beef, pork, and  poultry, a different approach was taken because there is evidence
that consumption rates have changed since the data for the Exposure Factors Handbook
were collected. Contact rates for these food groups were derived from commodity
disappearance data from the United States Department of Agricultures's (USDA) report on

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                      DRAFT-DO NOT QUOTE OR CITE
                    Table 11-6.   Estimated TEQ background exposures in the United States.
Soil ingestion
Fish ingestion
Water ingestion
Milk ingestion
Dairy ingestion
Eggs ingestion
Beef and veal
Pork ingestion
Chicken ingestion

North America
8.0 ppt
0.095 pg/m3
0.0056 ppq
0.07d ppt
0.36 ppt
0.14 ppt
0.48 ppt
0.26 ppt
0.19 ppt
100 mg/day
6.5 g/day
23 rn3/day
1 .4 L/day
251 g/day
67 g/day
29 g/day
77 g/day
47 g/day
68 g/day
8.0 x 1Q-10
7.8 x 10'9
2.2x 10"9
7.8 x 10'12
1.8 x 10'8
2.4 x 10'8
4.1 x 10'9
3.7 x 10'8
1.2x TO'8
1.3x TO'8
1.08 x 10"7
Footnotes: NA = Not applicable, NDA = No Data Available.
"  Values from Table 4-10, Chapter 4, Volume II of this assessment.
b  Values from Exposure Factors Handbook (EPA, 1989), and EPA (1984)
c  Daily intake = Contact rate x Cone. TEQ x Unit Conversion (soil unit conversion = 10"12, all other media unit conversion = 10'9)
d  Value was calculated from data in EPA (1991b).

                         DRAFT-DO NOT QUOTE OR CITE

Food Consumption, Prices, and Expenditures between 1970 and 1992 (USDA, 1993), and
intake data from USDA's Nationwide Food Consumption Survey (NFCS) (USDA, 1992).
USDA (1993) estimated per capita consumption rates using disappearance data (i.e., the
quantity of marketabie food commodities utilized in the  United States over a specified time
period) divided by the total population.  The average of USDA disappearance and NFCS
intake rates were used in this study to represent the most current estimates of typical
ingestion rates in the United States.
      These background exposure estimates for the United States are comparable to
analogous estimates for European countries, as displayed in Figure II-6. These include
estimates for Germany, which range from 79 pg TEQ/day  based on Fiirst, et al. (1990) to
158 pg TEQ/day based on Furst, et al. (1991), 118-126 pg TEQ/day exposure via
numerous routes in the Netherlands (Theelen, 1991), and  140-290 pg TEQ/day for the
typical Canadian exposed mainly through food ingestion (Oilman and Newhook, 1991).  It
is generally concluded by these researchers that dietary intake is the primary pathway of
human exposure to CDDs and CDFs.  Over 90 percent of human exposure is estimated to
occur through the diet, with foods from animal origins being the predominant sources.
      Background exposures can also be estimated on  the basis of body  burdens through
the use of pharmacokinetic models.  Pharmacokinetic compartmental models are presented
in Chapter 6 of Volume II which can be used to estimate daily dose intake of 2,3,7,8-
TCDD from adipose tissue or  blood lipid concentrations. Using this approach,  exposure
levels to  2,3,7,8-TCDD are estimated to be about 10 to 30 pg/day which is consistent
with the estimates derived using diet-based approaches. The model can also be applied to
other dioxin congeners with knowledge of their biophysical properties.
       The most extensive United States study of CDD/F body burdens is the National
Human Adipose Tissue Survey (NHATS) (EPA, 1991 a).  This survey analyzed for CDD/Fs
in 48 human tissue samples which were composited from 865 samples.  These samples
were collected during  1987 from autopsied cadavers and surgical patients. The sample
compositing prevents  use of this data to examine the distribution of CDD/F levels in tissue
among individuals.  However, it did allow conclusions in the following areas:

      •      National Averages:  The national averages  for all TEQ congeners were
             estimated and totaled to 28 pg of TEQ/g.

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                DRAFT-DO NOT QUOTE OR CITE
    Beef Ingestion
   Dairy Ingestion
    Milk Ingestion
Chicken Ingestion
    Pork Ingestion
    Fish Ingestion
    Egg Ingestion
    Soil Ingestion
  Water Ingestion
                           Total Exposure = 119 pg/day
                 0.0        10.0       20.0       30.0        40.0
                       North America Daily Intake (pg/day) of TEQ
               Figure II-5. Background TEQ exposures for North America by pathway.

                      DRAFT-DO NOT QUOTE OR CITE
       NORTH AMERICA [a]
            119 pg/day

        GERMANY [b]
          79 pg/day
           NETHERLANDS  [c]
               117 pg/day
[a] based on current assessment
[b] based on Fiirst, et al. (1990, 1991)
[cl based on Theelen (1991)
        Figure II-6. Comparison of background TEQ exposures for North America, Germany, and the Netherlands.

                         DRAFT-DO NOT QUOTE OR CITE

      •     Age Effects:  Tissue concentrations of CDD/Fs  were found to increase with
      •     Geographic Effects:  In general, the average CDD/F tissue concentrations
            appeared fairly uniform geographically.
      •     Race Effects:  No significant difference in CDD/F tissue concentrations were
            found on the basis of race.
      •     Sex Effects:  No significant difference in CDD/F tissue concentrations were
            found between males and females.
      •     Temporal Trends:  The 1987 survey showed decreases in tissue
            concentrations relative to the 1982 survey for all congeners.  However, it is
            not known whether these declines were due to  improvements in the
            analytical methods or actual reductions in body  burden levels. The percent
            reductions among individual congeners varied from 9 percent to 96 percent.

      New information on levels of dioxin-like compounds in  human tissue/blood has
recently been published (Patterson et al., 1994).  The adipose tissue samples (collected
from 28 individuals) were analyzed for PCBs 77, 81, 126 and 169. The TEQ levels for
these coplanar  PCBs summed to 17 ppt (using the toxic equivalency factors proposed by
Safe, 1990).  The PCB levels generally exceeded the mean 2,3,7,8-TCDD level (10.4 ppt)
and PCB-126 exceeded the 2,3,7,8-TCDD level by over an order of magnitude.  The
authors found that the PCBs contributed  24% of the total TEQs.  Patterson et al. (1994)
also studied serum collected by the CDC blood bank in Atlanta during 1982, 1988 and
1989. These samples were pooled from over 200 donors.  The serum data appears to
indicate a decrease in exposure to PCBs from 1982 to 1988/1989. In general, the
Patterson et  al. (1994) data suggests that the coplanar PCBs can contribute significantly
to body burdens of dioxin-like compounds.  The data suggest  that the coplanar PCBs can
increase the total background body burden to over 40 ppt of  TEQ. This conclusion is
uncertain because the people studied by Patterson et al. (1994) may not be representative
of the overall U.S. population,  and the toxic equivalency factors proposed by Safe (1990)
have been acknowledged to be conservative.
      Levels of these compounds found in human tissue/blood appear similar in Europe
and North America. Schecter (1991) compared levels of dioxin-like compounds found in

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blood among people from U.S. (100 subjects) and Germany (85 subjects). Although mean
levels of individual congeners  differed by as much as a factor of two between the two
populations, the total TEQ averaged 42 ppt in the German subjects and was 41 ppt in the
pooled U.S. samples.

       Certain groups of people may have higher exposures to the dioxin-like compounds
than the general population. This section discusses such exposures which result from
dietary habits.  Other population segments can be highly exposed due to occupational
conditions or industrial accidents and are discussed in the Epidemiology Chapter if the
Dioxin Health Reassessment Document (EPA, 1994) and should be consulted if further
details are desired.
       Although the subpopulations discussed below have the potential for high exposure
to dioxin-like compounds, a careful evaluation is needed to confirm this possibility. It
would generally be inappropriate to compute the total background exposure for a certain
group by simply adding the dioxin intake  from the highly consumed food to the  background
exposure levels. The background exposure estimate assumes a typical pattern of food
ingestion, whereas persons  in  a subpopulation who have a high consumption rate of one
particular food type are likely to eat less of other food types. Ideally, the assessor should
base this evaluation on the entire diet of the subpopulation and use case-specific values
for food ingestion rates and concentrations of dioxin-like compounds.
       One group of potentially highly exposed individuals is nursing infants. Schecter et
al. (1992)  reports that a study of 42 U.S. women found  an  average of 16 ppt of TEQ (3.3
ppt of 2,3,7,8-TCDD) in the lipid portion  of breast milk.  A much larger study in Germany
(n = 526) found an average of 29 ppt of TEQ in  lipid portion of breast milk.  The level in
human breast milk can be predicted on the basis of the estimated dioxin intake by the
mother. Such procedures have been developed by Smith (1987) and Sullivan et al. (1991)
and are presented in Chapters 5 and 6 of Volume  II.
       Using these procedures and assuming that an infant breast feeds for one year, has
an average weight during  this  period of 10 kg, ingests 0.8 kg/d of breast milk and that the
dioxin concentration in milk fat is 20 ppt of TEQ, the average daily dose to the infant over
this period  is predicted to be  about 60 pg of TEQ/kg-d.  This value is much higher than

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the estimated range for background exposure to adults (i.e., 1-3 pg of TEQ/kg-d).
However, if a 70 yr averaging time is used, then the lifetime average daily dose is
estimated to be 0.8 pg of TEQ/kg-d which is near the lower end of the adult background
exposure range.  On a mass basis, the cumulative dose to the infant under this scenario is
about 210 ng compared to a lifetime background dose of about 1700 to 5100 ng
(suggesting that 4 to 12 percent of the lifetime dose may occur as a result of breast
feeding).  Traditionally, EPA has used the  lifetime average daily dose as the basis for
evaluating cancer risk and the average daily dose (i.e., the daily exposure per unit body
weight occurring during an exposure event) as the more appropriate indicator of risk for
noncancer endpoints.  This issue is discussed further in the  companion document on dioxin
health effects.
      The possibility of high exposure to  dioxin as a result  of fish consumption is most
likely to occur in situations where individuals consume a large quantity of fish from  one
location where the dioxin level in the fish are elevated above background levels.  Most
people eat fish from multiple sources and  even  if large quantities are consumed are  not
likely to have unusually high exposures. However, individuals who fish regularly for
purposes of basic subsistence are likely to obtain their fish from one source and have the
potential for elevated exposures. Such individuals may consume quite large quantities of
fish. EPA (1989)  presents studies that indicate that recreational anglers near large water
bodies consume 30 g/d (as a mean) and 140 g/d (as an upper estimate). Wolfe and
Walker (1987) found subsistence fish ingestion rates up to 300 g/d in  a study conducted
in Alaska.
      Several studies have identified potentially highly exposed populations as a result of
fish consumption:

      • Svensson et al. (1991) found elevated blood levels of CDDs and CDFs in high
fish consumers living near the Baltic Sea in Sweden.
      • Dewailly et al. (1994)  observed  elevated levels of coplanar PCBs  in the blood of
fishermen on the north shore of  the Gulf of the  St. Lawrence River who consume large
amounts of seafood. Coplanar PCB levels were 20 times higher among the 10 highly
exposed fishermen than among the controls.  Dewailly et al. (1994) also observed elevated
levels of coplanar  PCBs in the breast milk  of Inuit women of Arctic Quebec. The principal

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                          DRAFT-DO NOT QUOTE OR CITE

source of protein for the Inuit people is fish and sea mammal consumption.
       • Studies are underway to evaluate whether native Americans living on the
Columbia River in Washington have high dioxin exposures as a result of fish consumption.
These tribes consume large quantities of salmon from the river. A recent study (Columbia
River Intertribal Fish Commission, 1993) suggests that these individuals have an average
fish consumption rate of 30 g/day.  Currently studies are underway to measure dioxin
levels in fish from this region.

       The  possibility of high exposure to dioxin  as a result of consuming meat and dairy
products is most likely to occur in situations where individuals  consume a large quantity of
these foods from one location where the dioxin level is elevated above background levels.
Most people eat meat and diary products from multiple sources and  even if large quantities
are consumed are not likely to have unusually high exposures.  Individuals who raise their
own livestock for purposes of basic subsistence, however, have the potential for elevated
exposures.  No epidemiological studies were found in the literature evaluating this issue.
Volume III of this document, however, presents methods for evaluating this type of
exposure on a site-specific basis.
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                               REFERENCES FOR VOLUME II
Bidleman, T.F. (1988)   Atmospheric processes. Wet and dry deposition of organic
      compounds are controlled by their vapor-particle partitioning.  Environ. Sci. Techol.,
      22:4, pp 361-367.

Beck, H.; Eckart, K.; Mathar, W.; Wittkowski, R.  (1989) PCDD and PCDF body burden
      from food intake in the Federal Republic of Germany.  Chemosphere  18 (1-6):

Clayton, P.; Davis, B.;  Duarte-Davidson, R.; Halsall, C.; Jones, K.C.;  Jones, P. (1993)
      PCDDs and PCDFs in ambient UK urban air.  Presented at: Dioxin '93,  13th
      Symposium on Dioxins and Related  Compounds; Vienna, Austria; September 1993.

Clement, R.E.; Tashiro, C. (1991) Forest fires as a source of PCDD and PCDF. Presented
      at: Dioxin '91, 11th International Symposium on Chlorinated Dioxins and Related
      Compounds; RTP, NC. September 23 - 27, 1991.

Columbia River Intertribal Fish Commission (1993) A fish consumption survey of the
      Umtilla, Nez Perce, Yakima, and  Warm Springs tribes of the Columbia River basin.
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Czuczwa, J.M.; Hites,  R.A. (1984)  Environmental fate of combustion-generated
      polychlorinated  dioxins and furans. Environ. Sci. Techol.,  18:6, pp 444-450.

Czuczwa, J.M.; Hites,  R.A. (1985)  Historical record of polychlorinated dioxins and furans
      in Lake Huron sediments. In: Keith, L.H.;  Rappe, C.; Choudhary, G., eds.
      Chlorinated Dioxins and Dibenzofurans in the Total Environment.  Butterworth
      Publishers, Boston, MA.  pp. 59-63.

Czuczwa, J.M.; McVeety, B.D.; Hites, R.A. (1984) Polychlorinated  dibenzo-p-dioxins  and
      dibenzofurans in sediments from Siskiwit Lake, Isle Royale. Science 226.

Dewailly, E.; Ryan, J.J.; Laliberte, C.; Bruneau, S.; Weber, J.P.; Gingras, S.; Carrier, G.
      (1994)  Exposure of remote maritime populations to coplanar  PCBs.  Environmental
      Health Perspectives. Vol. 102, Suppl.  1:205-209.

ECETOC  (1992) European Centre for Ecotoxicology and Toxicology of Chemicals.
      Exposure of man to dioxins:  a perspective on industrial waste incineration.
      Technical Report No. 49.  Brussels,  Belgium.

Fiedler, H.; Hutzinger, 0. (1992) Sources and sinks of dioxins: Germany. Chemosphere,

Fiirst, P.; Furst, C.; Groebel, W.  (1990) Levels of PCDDs and PCDFs in food-stuffs from
      the Federal Republic of Germany. Chemosphere 20 (7-9):   787-792.
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Fiirst, P.; Furst, L; Widmers, K. (1991)  Body burden with PCDD and PCDF from food.
       In: Biological Basis for Risk Assessment of Dioxins and Related Compounds.
       Banbury Report #35.  Edited by M. Gallo, R. Scheuplein and K. Van der Heijden.
       Cold Springs Harbor Laboratory Press.  Plainview, NY.

Oilman, A; Newhook, R. (1991) An updated assessment of the exposure  of Canadians to
       dioxins and furans.  Chemosphere 23:1661-1667.

Harrad, S.J.; Jones, K.C. (1992) A source inventory  and budget for chlorinated dioxins
       and furans in the United Kingdom environment. The Science of the Total
       Environment 126:89-107.

Hites, R.A.  (1991) Atmospheric transport and deposition of polychlorinated dibenzo-p-
       dioxins and dibenzofurans.  Prepared for the U.S. Environmental Protection Agency,
       Methods Research Branch, Atmospheric Research and Exposure Assessment
       Laboratory, Office of Research and Development, Research Triangle Park, NC.

Koester, C.J.;  Hites, R.A. (1992) Wet and dry deposition of chlorinated dioxins and furans.
       Environ. Sci. Technol. 26:1375-1382.

Konig,  J.; Balfanz, E.; Gunther, W.J.;  Liebl, K.H.; Buchen,  M. (1993b) Ambient air levels of
       polychlorinated  biphenyls at different sites in Hessen, Germany.  Presented at:
       Dioxin '93, 13th Internacional Symposium on Chlorinated Dioxins and Related
       Compounds; Vienna, Austria; September 1993.

Koning, J.; Sein, A.A.; Troost, L.M.; Bremmer, H.J. (1993)  Sources of dioxin emissions
       in the Netherlands.  Presented at:  Dioxin '93,  13th International Symposium on
       Chlorinated Dioxins  and Related Compounds; Vienna, Austria; September 1993.

LaFleur, L.; Bousquet, T.; Ranage, K.;  Brunck, B.; Davis, T.; Luksemburg, W.; Peterson, B.
       (1990)  Analysis of  TCDD and TCDF on the ppq-level in milk and food sources.
      Chemosphere 20(10-12):1657-1662.

Lexen,  K.; De Wit, C; Jansson,  B.;  Kjeller, L.O.; Kulp,  S.E.; Ljung, K.; Soderstrom, G.;
      Rappe,  C. (1992) Polychlorinated dibenzo-p-dioxin and dibenzofuran levels and
      patterns in samples  from different  Swedish industries analyzed within the Swedish
      dioxin survey.  Presented at: Dioxin '92, 12th  International Symposium on Dioxins
      and Related Compounds; Tampere, Finland; August 1992.

Liebl, K.; Buchen, M.; Ott,  W.; Fricke, W. (1993) Polychlorinated dibenzo(p)dioxins and
      dibenzofurans in ambient air; concentration and deposition measurements in
      Hessen, Germany. Presented at Dioxin '93,  13th International Symposium on
      Chlorinated Dioxins  and Related Compounds; Vienna, Austria; September 1993.

Ligon, W.V.; Dorn, S.B.; May, R.J.; Allison, M.J. (1989) Chlorodibenzofuran and
      chlorodibenzo-p-dioxin levels in Chilean mummies dated  to about 2800 years before
      the present.  Environ. Sci. Technol. 23:1286-1290.

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 Marklund, S.; Andersson, R.; Tysklind, M.; Rappe, C.; Egeback, K.E.; Bjorkman, E.;
       Grigoriadis, V. (1990)  Emissions of PCDDs and PCDFs in gasoline and diesel fueled
       cars. Chemosphere 20(5):553-561

 McCrady, J.K.; McFarlane, C.; Gander, L.K. (1990) The transport and fate of 2,3,7,8-
       TCDD in soybean and corn.  Chemosphere 21:359-376.

 NCASI  (1993) National Council of the Paper Industry for Air and Stream Improvement.
       Summary of data reflective of pulp and paper industry progress in reducing the
       TCDD/TCDF content of effluents,  pulps and  wastewater treatment sludges.  New
       York, NY.  NCASI, June,  1993.

 Oehme, M.; Larssen,S.; Brevik, E.M. (1991) Emission factors of PCDD/F for road vehicles
       obtained by a tunnel experiment. Chemosphere, 23:1699-1708.

 Patterson, D.G.; Todd, G.D.; Turner, W.E.;  Maggio, V.; Alexander, L.R.; Needham, L.L.
       (1994)  Levels of nonortho-substituted  polychlorinated biphenyls, dibenzo-p-dioxins,
       and dibenzofurans in human serum and adipose tissue. Environmental  Health
       Perspectives. Vol.  101, Suppl. 1:195-204.

 Rappe, C. (1991)  Sources of human exposure to PCDDs and PCDFs. In:  Gallo, M.;
       Scheuplein, R.; Van der Heijden, K.,  eds.   Biological basis for risk assessment of
       dioxins  and related compounds. Banbury  Report #35. Plainview, NY: Cold Spring
       Harbor Laboratory  Press.

 Rappe, C. (1992)  Sources of PCDDs and  PCDFs. Introduction. Reactions, levels, patterns,
       profiles and trends. Chemosphere 25(1-21:41-44.

 Riss, A.; Aichinger, H.  (1993) Reduction of dioxin  emissions and regulatory  measures in
       Austria.  Presented at:  Dioxin '93, 13th International Symposium on Chlorinated
       Dioxins and Related Compounds; Vienna, Austria; September 1993.

 Safe, S.  (1990) Polychlorinated biphenyl, dibenzo-p-dioxins, dibenzofurans,  and related
       compounds: environmental and mechanistic considerations which support the
       development of toxic equivalency factors. CRC Crit.  Rev. Toxicol. 21:51-88.

 Schatowitz, B.; Brandt, G.; Gafner,  F.; Schlumpf, E.; Biihier,  R.; Hasler, P.;  Nussbaumer, T.
       (1993)  Dioxin emissions from wood combustion.  Presented at:  Dioxin  '93, 13th
       International Symposium on Chlorinated Dioxins and Related Compounds; Vienna,
      Austria; September 1993.

Schecter, A. (1991) Dioxins and related compounds in humans and in the environment.
      In: Biological Basis for Risk Assessment of Dioxins and Related Compounds.
      Banbury Report #35. Edited by M.  Gallo, R. Scheuplein and K. Van der Heijden.
      Cold Spring Harbor Laboratory Press. Plainview, NY.

Schecter, A.; Papke, 0.; Ball, M.; Startin,  J.R.; Wright, C.; Kelly, M. (1993)  Dioxin levels
      in food from the U.S. with estimated daily intake.  Submitted to Dioxin '93.

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Schecter, A.; Papke, 0.; Ball, M.; Startin, J.R.; Wright, C.; Kelly, M.  (1992) Dioxin and
      dibenzofuran levels in food from the United States as compared to levels in food
      from other industrial countries.  12th International Symposium on Dioxins and
      Related Compounds.  Tampere, Finland August 1992. Finnish Institute of
      Occupational Health, Helsinki, Finland, pp. 243-246.

Smith, A.H.  (1987)  Infant exposure assessment for breast milk dioxins and furans
      derived from waste incineration emissions. Risk Analysis 7(3): 347-353.

Smith, R.M.; O'Keefe,  P.W.; Aldous, K.M.; Briggs, R.; Hilker, D.R.; Connor, S.  (1992)
      Measurement of PCDFs and PCDDs in air samples and lake sediments at  several
      locations in upstate New York.  Chemosphere 25(1-2): 95-98.

Stanley, J.S.; Bauer, K.M. (1989)  Chlorinated dibenzo-p-dioxin and dibenzofuran  residue
      levels in food.  Sacramento, CA: State of California Air Resources Board. ARB
      Contract No. A6-197-32.

Sullivan, M.J.; Custance, S.R.; Miller, C.J. (1991)   Infant exposure to dioxin in  mother's
      milk resulting from maternal ingestion of contaminated fish. Chemosphere  23(8-

Svensson, E.G.; Nelsson, A.;  Hansson, M.; Rappe, C.; Akesson, B.; Skerfving, S. (1991)
      Exposure to dioxins and dibenzofurans through the consumption of  fish. New
      England Journal of Medicine. 324(1):8-12.

Theelan, RMC. (1991)   Modeling of human exposure to  TCDD  and I-TEQ in the
      Netherlands: background and occupational.  In: Gallo M, Scheuplein r;, Van der
      Heijden, K, eds. Biological Basis for Risk Assessment of  Dioxins and Related
      Compounds. Banbury Report #35. Plainview, NY.

Travis, C.C.; Hattemer-Frey, H.A. (1987) Human exposure to  2,3,7,8-TCDD.
      Chemosphere 1 6,:2331-2342.

Travis, C.C.; Hattemer-Frey, H.A. (1991) Human exposure to  dioxin. Sci. Total Environ.
      104: 97-127.

U.S. Department of Agriculture  (1992)  Food and nutrient intakes by  individuals in the
      United States, 1  day, 1987-88:  Nationwide Food  Consumption Survey 1987-88.
      Washington, DC:  USDA Human Nutrition Information Service.  NFCS Rpt. No. 87-I-
      1 in preparation.

U.S. Department of Agriculture  (1993)  Food consumption, prices, and expenditures,
      1970-1992. Washington, DC:  USDA Economic Research Service.  Statistical
      Bulletin 867.

U.S. Environmental Protection Agency. (1984)   An  estimation  of the daily food  intake
      based on data from the 1977-1978 USDA Nationwide Food Consumption Survey.
      Washington, DC., Office of Radiation Programs, EPA 520/1-84-015.

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U.S. Environmental Protection Agency. (1989) Exposure Factors Handbook.  Exposure
      Assessment Group, Office of Health and Environmental Assessment, Office of
      Research and Development, U.S. Environmental Protection Agency. EPA/600/8-
      89/043.  July, 1989.

U.S. Environmental Protection Agency. (1991 a) Chlorinated dioxins and furans in the
      general U.S. population:  NHATS FY87 results. Washington, D.C. Office of Toxic
      Substances, EPA-560/5-91-003.

U.S. Environmental Protection Agency. (1991b) Feasibility of environmental monitoring
      and exposure assessment for a municipal waste combustor: Rutland Vermont Pilot
      Study. Washington, DC:  Office of Research and Development, EPA-600/8-91/007.

U.S. Environmental Protection Agency. (1992)  National study of chemical residues in
      fish. Washington, DC: Office of Science and Technology. EPA/823-R-02-008.

U.S. Environmental Protection Agency. (1994)  Health Assessment for 2,3,7,8-TCDD and
      Related Compounds.  External Review Draft.  EPA/600/BP-92/001a-c.

Wevers, M.; De Fr<§, R; Rymen,  T.  (1992)  Dioxins and dibenzofurans in tunnel air. Vol 9
      (Sources of Exposure)  of Extended Abstracts.  Presented at:  Dioxin '92,  12th
      International Symposium  on  Chlorinated Dioxins and Related Compounds; Tampere,
      Finland; August 1992.

Wevers, M.; De Fre", R.; Van Cleuvenbergen, R.; Rymen, T. (1993) Concentrations of
      PCDDs and PCDFs in ambient air at selected locations in Flanders. Presented at
      Dioxin  '93, 13th International Symposium on Chlorinated Dioxins  and Related
      Compounds; Vienna, Austria; September 1993.

Wolfe, R.J.; Walker, R.J. (1987) Subsistence Economics in Alaska: Productivity,
      Geography and Developmental Impacts. Arctic Anthropology  24(2):56-81.
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      Volume III describes  procedures for conducting site specific exposure assessments
to estimate potential dose.  A potential dose is defined as a daily amount of contaminant
inhaled, ingested, or otherwise coming in contact with outer surfaces of the body,
averaged over an individual's body weight and lifetime. The general equation used to
estimate potential dose normalized over body weight and lifetime is as follows:
        Lifetime Average Daily Dose (LADD) = (exposure media concentration x
                 contact rate x contact fraction x exposure duration ) /
                               (body  weight x lifetime)
This procedure is used to estimate dose in the form needed to assess cancer risks.  Each
of the terms in this exposure equation is discussed briefly below:
       • Exposure media concentrations:   These include the average concentrations in
the media to which individuals are exposed. Media considered in this assessment include
soil, air, water, vegetables/fruits, fish, beef, and milk.
       • Contact rate:  These include the  ingestion rates, inhalation rates, and soil
contact rates for the exposure pathways.
       • Contact fraction:  This term describes the distribution of total contact between
contaminated and uncontaminated media.   For example, a contact fraction of 0.8 for
inhalation means that 80% of the air inhaled over the exposure period contains dioxin-like
compounds in vapor form or sorbed to air-borne particulates.
       • Exposure duration:  This is the overall time period of exposure, mostly pertinent
to adult exposures. Another exposure duration considered in this methodology is one
associated with a childhood pattern of soil ingestion.  The exposure duration in this case is
5 years.
       • Body weight:  For all the pathways, the  human adult body weight of 70 kg is
assumed. This value represents the  United States population average.  The body weight
for child soil ingestion is 17 kg (EPA, 1989).

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       • Lifetime:   Following convention, and because cancer risk slope factors are
derived based on a 70-year human lifetime, the average adult lifetime assumed throughout
this document is 70 years.

       Before making exposure estimates, the assessor needs to gain a more complete
understanding of the exposure setting and the contamination source. The approach used
for this assessment is termed the exposure scenario approach. A  "road map" of that
procedure including identification of chapters in Volumes  II and III  where key information
can be found,  is shown in Figure 111-1. Brief descriptions of 7 steps in this approach are:
       Step 1.  Identify Source:  Three principal sources are addressed in this document:
contaminated soils, stack emissions, and effluent discharges.
       Step 2.  Estimate Release Rates:  Estimating the release of contaminants from the
initial source is the first step towards  estimating the concentration in the exposure media.
Releases from soil contamination include volatilization, and wind and soil erosion.  Stack
emissions and effluent discharges  are point source releases into the  environment.
       Step 3.  Estimate Exposure Point Concentrations:  Contaminants released from
soils, emitted from stacks, or discharged into surface waters move through the
environment to points where human exposure  may occur, and/or to impact environmental
media to which humans are exposed.   Various fate, transport, and transfer models are
used to predict exposure media concentrations given source releases.
       Step 4.  Characterize Exposed  Individuals and Exposure Patterns:  Exposed
individuals in the scenarios of this  assessment are individuals who are exposed in their
home environments.  They are residents who breathe air at their residence, fish
recreationally,  have a home garden, farm, and  are children ages 2-6 for the soil ingestion
pathway.  Exposures which are occur at the workplace or other locations are not
discussed in this assessment, although the procedures could be adapted for other
exposure sites. Each of these pathways  are evaluated separately. Since it is unlikely  that
single individuals would experience all  of these pathways, the exposures across pathways
are not added.  Each pathway has  a set of exposure parameters including contact rates,
contact fractions, body weights, exposure durations,  and  a lifetime.
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                            DRAFT-DO NOT QUOTE OR CITE

   Step 1.   Identify Sources

            A.   Soil, on and off-site
            B.   Stack emissions

            C.   Effluent Discharges

   Step 2.   Estimate Release Rates

            A.   Volatilization, erosion, etc.
            B.   Stack emissions

            C.   Effluent discharges

   Step 3.   Estimate Exposure Point Concentrations

            A.   Transport, bioaccumulation, etc.
            B.   Atmospheric dispersion, deposition, etc.

   Step 4.   Characterize Exposed Individuals and
            Exposure Patterns

            A.   Contact rates, exposure durations

   Step 5.   Put It Together in Terms of Exposure

            A.   Scenario concept expanded
            B.   Demonstration with scenarios

   Step 6.   Estimate Exposure and Risk

            A.   Equations and background
            B.   Results for example scenarios

   Step 7.   Assess Uncertainty

            A.   Parameter uncertainty/variability,
                 validity of media concentrations,
                 other models
            B.   Sensitivity analysis, parameter
Chapter 4, Volume II
Chapter 3, Volume III
Chapter 3, Volume II
Chapter 3, Volume II
Chapter 4,
Chapter 3,
Chapter 3,
Chapter 4,
Chapter 3,
Chapter 4, Volume
Chapter 3, Volume
This Chapter
This Chapter
Chapter 5, Volume
This Chapter
Chapter 5, Volume
Chapter 7, Volume

Chapter 6, Volume
Figure 111-1.  Road map for assessing exposure and risk to dioxin-like compounds.

                          DRAFT-DO NOT QUOTE OR CITE
       Step 5.  Put It Together in Terms of Exposure Scenarios:  A common framework
for assessing exposure is with the use of "settings" and "scenarios." Settings are the
physical aspects of an exposure area and the scenario characterizes the behavior of the
population in the setting and determines the severity of the exposure.  A wide range of
exposures are possible depending on behavior pattern assumptions.  An exposure scenario
framework offers the opportunity to vary any number of assumptions and parameters to
demonstrate the impact of changes to exposure and risk estimates.
       Step 6.  Estimate Exposure:   The end result of having followed the above 5 steps
are estimates of individual exposures to a characterized source of contamination.
       Step 7.  Assess Uncertainty:   Uncertainties should be considered when applying
procedures in this document to a particular site. Pertinent issues explored in this
assessment include:  1) model predictions of exposure media concentrations compared to
field  measurements, 2) similarities and differences for alternate models for estimating
exposure media concentrations, 3) sensitivity of model results to a range  of values for
methodology parameters,  4) mass balance checks, and 5) qualitative and quantitative
discussions on the uncertainties with the model parameters and exposure estimates
generated for the demonstration scenarios.

       Literally hundreds of fate and transport models have been published which differ
widely in their technical sophistication, level of spatial or temporal resolution, need for site
specific parameterization, and so on.  This makes selection of the most appropriate one for
any particular situation very difficult.  For this assessment, relatively simple,  screening
level models are used to model fate, transport,  and transfer of dioxin-like compounds from
the source to the exposure media. Simple assumptions are often made in order to arrive at
the desired result, which is long-term average exposure media concentrations.  Perhaps the
most critical of the assumptions made is that the source strength remains constant
throughout the period  of exposure.
       It is important to understand that EPA is not endorsing the algorithms of this
assessment as the best ones for use in all dioxin assessments. They are suggested as
reasonable starting points for site-specific or general assessments.  All assumptions for the
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models and selection of parameter values are carefully described. If these assumptions do
not apply to a particular situation, or where assessors require more spatial or temporal
resolution, more complex models should be selected.  Finally, it cannot be overemphasized
that measured concentrations are generally more reliable than modeled ones. Assessors
should use measured concentrations if available and if such measurements can be
considered spatially and temporally representative for the exposed populations.

III.3.1.  Overview of Fate, Transport, and Transfer Algorithms of the Methodology
      Figures III.2 through III.5 provide an overview of algorithms used to evaluate the
fate, transport, and transfer of dioxin-like compounds from contaminated soil,  stack
emissions, and effluent discharge (called "source categories" in this document).
Algorithms are presented which link each of these sources to estimated concentrations in
a number of media which may be contaminated as a result, and are therefore potential
"exposure media":  1) surface soils, 2) surface-water associated media: suspended and
bottom sediment and dissolved phase concentrations, 3) air including  the vapor phase and
in paniculate form, and 4) biota including beef, milk, fruit and vegetables, and fish.  The
remainder of this section describes how each potential exposure medium can be affected
by each source, and the algorithms used to make this link.
       • Surface soils:   Exposure to contaminated soil may be a result of direct contact
with soil on the site of the "source" contamination, or indirectly  after  the contaminated
soil has been transported off-site. These cases are known as the "on-site" scenario and
the "off-site" scenario, respectively. In either case, soil concentrations are specified for
the contaminated source.  For the on-site scenario, the soil at the residence  or farm (where
exposures occur) is contaminated. In the off-site scenario, soil contamination  is assumed
to be adjacent to an accessible area known as the "exposure site".  Examples  here would
include a landfill or a Superfund site. Residues which reach the exposure site  mix with soil
already there; the mixing is assumed to take place to either a "tilled" depth or a "non-tilled
depth". The tilled depth is assumed to be 20 cm (approximately 8 inches), typical of soil
mixing for growing below-ground vegetables. The concentrations derived from using a 20
cm mixing depth are also used to estimate concentrations for dermal contact for
individuals in farming families (i.e., dermal contact is assumed to occur as a result of
                                         52                                    4/94

   Wind erosion
   Near-field dispwion
                                                           Vegetables and
               Vapor and Paniculate
                                        Wet* dry parade OeposXion
                                        Air-to-leaf vapor phase
                                                  Pasture Grass
                                                   Cattle Feed
                                            Vegetables and
     Soi lo root transfers

Steady state between 3 compartment*
      Organic carton normalized
       ov>cen*»ftona an tqual
Figure 111-2.   Diagram of the fate, transport,  and transfer
        relationships for the on-site source  category.
                                                          Vegetables and
                Vapor and Paniculate
     Far-field dispersion
                                                       Wtt + dry pvtfefe dfOto/Oon
                                                       Alr-io4ftf vapor proof
                                     Pasture G
                                      Cattle Feed
                    Boat* dairy aolt dht
                                      Vegetables and
                                 Scil-to-root transttn
               Study statt between 3 compartments
          Organic carbon normaSzad
          concentrations m equal
Figure 111-3.   Diagram of the  fate, transport, and transfer
       relationships for the off-site  source category.

                  Dry plus Wat Deposition
                                                    Vegetable* and

    Emlttlon factor*
                                               Parade washof
                                               Mr-to-M vapor phatefantler*
                                                     Pasture Grass
                                                       Cattle Feed
                                     Betrt dairy catttodM
So« mixing
                              Site Soils
Vegetables and
                                     Sol-to-root trantfort
                       Mast balance mOHttlnta
                       Stiady st*» bttmttn 3 ccmfmrtnwM
Sediment d»»v»ry
            Equt/Mum   Organic ctrbon
             partitioning   conotntrttiora an tqual
 Figure 111-4.  Diagram of the fate, transport, and transfer
   relationships for the stack emission source category.
                                               Blot* Suspended Sotd*
                                               Accumulation Factor
 Figure 111-5.  Diagram of the fate, transport, and transfer
 relationships for the effluent discharge source category.

                           DRAFT-DO NOT QUOTE OR CITE
farming activities).  The non-tilled mixing depth is assumed to be 5 cm (approximately 2
inches) when erosion transports residues to a site of exposure where deep tilling or
plowing does not routinely occur.  The concentrations derived using this mixing depth are
used for dermal contact exposures in residential settings, for childhood soil ingestion in
residential and farm settings, and for cattle soil ingestion (used in estimation of beef and
milk concentrations).
       Exposure site soils can also be impacted from stack emissions due to  air transport
of either vapor or particulate residues from the stack to the exposure site. Deposition
modeling for particles allows for estimation of tilled and  non-tilled soil concentrations.
When stack emissions are the source, however, the nontilled depth of mixing is assumed
to 1 cm (about 0.4 inch) instead of 5 cm, on the assumption that particle deposition is a
less turbulent process than soil  erosion. A key  assumption for evaluating the exposure site
as a result of both off-site erosion and stack emissions is that contaminants impact a thin
layer of soil  and  do, in fact, dissipate.  For the on-site soil scenario, on the other hand, the
contamination is assumed to extend into the soil and surface concentrations  are not
dissipated over time.  Dissipation processes could include volatilization, photolysis, or
other processes.  A soil  dissipation half-life of ten years  is assumed for all dioxin-like
       • Surface Water:  The  principal assumption driving the solutions for  the soil and
stack emission source categories is that the suspended and bottom sediments of water
bodies  originate as watershed soils, which are subsequently eroded. For the stack
emission source  category, a portion of the sediments also originates from directly-
depositing particulates.  The process of erosion transports soils within the watershed to
the water body.  Unit rates of erosion along with watershed size  determine the total
potential amount of soil  which could be delivered to the  water body.  Sediment delivery
ratios reduce that potential amount.  A mass balance assures that soil eroding on an
annual  basis becomes either suspended or bottom sediment within an annualized volume
of surface water. "Enrichment" of eroded soil is assumed, which means that eroded soil
from a  contaminated source is assumed to  be higher in concentration of dioxin-like
compounds than in situ, off-site soils. Once in the water body, a standard partitioning
model based on the organic carbon partition coefficient,  Koc, determines the concentration
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                          DRAFT-DO NOT QUOTE OR CITE
of contaminant in the water in truly dissolved form and the concentration on suspended
sediments. The organic carbon normalized concentrations of suspended and bottom
sediment are assumed to be equal. Watershed soil concentrations are model input
parameters for determining the effect on surface water from contaminated soils.  For stack
emissions, a total (dry + wet) deposition rate of contaminant which represents average
depositions onto the  watershed is specified as an input parameter, as well as a mixing
depth representing the watershed.  In this way, average watershed soil concentrations are
calculated for the stack emission source category.
      For effluent discharges as sources, watershed soils are not considered.  An amount
of contaminant is discharged into an annual flow volume to obtain a simple  dilution
concentration.  This total concentration is partitioned into a truly dissolved phase and a
phase sorbed to suspended sediments using the organic carbon partition coefficient, the
Koc. Bottom sediments are not considered for effluent discharges.
      • Soil to Air:   From contaminated soils, residues become airborne via the
processes of volatilization and wind erosion.  For on-site soil contamination, these vapor
and particle  phase fluxes are translated to ambient air concentrations using  a near-field
dispersion model.  For the off-site scenario, the same approach  is used to estimate
ambient air exposure site concentrations, except that a far-field dispersion model is used.
These airborne reservoirs are the basis for inhalation  exposures, and are also used to
estimate plant concentrations for vegetable ingestion and in grass and feed  for estimating
beef and milk concentrations.
      • Stack Emissions, Atmospheric Transport Modeling:  Air dispersion/deposition
models consider the basic physical processes of advection, turbulent diffusion, and
removal via wet and  dry deposition to estimate the atmospheric transport, resulting
ambient air concentration, and settling of particles.  Volume III uses the COMPDEP model
for air dispersion and deposition modeling.  Besides discussions in Volume III, further
discussions  on the COMPDEP model can be found in EPA (1990d).
      COMPDEP contains modifications of the Industrial Source Complex model (Short-
Term version), and COMPLEX I to incorporate algorithms to estimate dispersion, and
resulting ambient air  concentrations, and wet and dry deposition flux.  COMPLEX  I is a
second level screening model applicable to stationary combustion sources located in


                          DRAFT-DO NOT QUOTE OR CITE
complex and rolling topography (EPA, 1986). The model was developed specifically to
evaluate the effects of complex terrain that exceeds the stack height of the source as
developed by Turner (1986). To account for pollutant deposition, the concentration
algorithms in COMPLEX  1 were replaced with those from the  Multiple Point Source
Algorithm with Terrain Adjustments Including Deposition and Sedimentation (MPTER-DS)
model (Rao and Sutterfield, 1982). The MPTER-DS algorithms incorporate the gradient
transfer theory described by Rao (1981), and are extensions of the traditional Gaussian
plume algorithms. The dispersion  algorithms contained in the  Industrial Source Complex,
Short-term version (ISCST), have been incorporated in COMPDEP to analyze ground-level
receptors located below  the height of the emission plume. COMPDEP uses the generalized
Briggs (1975, 1979) equation to estimate  plume-rise and downwind dispersion as a
function of wind speed and atmospheric stability. A wind-profile exponent law is used to
adjust the observed mean wind speed from the measurement  height to the emission height
for the plume rise and pollutant concentration calculations.  The Pasquill-Gifford curves are
used to calculate lateral  and vertical plume spread (EPA, 1986). These curves are based
on Pasquill's definitions  of atmospheric stability classes, e.g.,  extremely unstable,
moderately unstable, slightly unstable, neutral, slightly stable, and moderately stable, that
correspond to various intensities of solar radiation and wind speeds (Seinfeld,  1986).  The
incorporation of these two basic models into COMPDEP permits analysis of a source
located  in all types of terrain.  Further details on the use of the COMPDEP model are:
       1. Emission factors:  The  first step in the use of the COMPDEP model is to
determine "emission factors" for dioxin-like congeners.  These factors are defined as the
//g (or other mass unit) congener emitted per kg (or other mass unit) feed material
combusted.  Once assuming a rate of feed material combusted in appropriate units,
kg/day,  these emission factors can be translated to the units appropriate for atmospheric
transport modeling, //g/sec. This assessment promotes the generation of specific congener
emission factors, rather  than TEQ  or homologue group emission factors. A TEQ
concentration can be generated for exposure media concentrations once congener-specific
concentrations are estimated using the Toxicity Equivalency Factor (TEF) scheme. This
recommendation is made because fate, transport, and transfer parameters, and TEFs,  are
different for specific congeners, leading to a TEQ exposure media concentration which
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would be different but more accurate than, say, assuming only a TEQ emission factor and
one set of parameters for further modeling.  Emission factors for the demonstration were
generated from actual test data from an incinerator burning  organic wastes (source
otherwise unspecified).  Emission estimates for this example incinerator are similar to
emissions that are known to be emitted from combustors employing sophisticated air
pollution control devices (e.g.,  scrubbers combined with fabric filters).  In order to place
the demonstration scenario in context, the emissions from the hypothetical incinerator
were ranked with other types of waste incinerators that are well controlled with some
combination of a scrubber device and/or a fabric filter, as follows:
             1. Medical waste incineration:  25  - 200 ng TEQ/kg waste combusted.
             2. Hazardous waste incineration:  0.18 - 119  ng TEQ/kg waste combusted.
             3. Hypothetical waste incinerator:  4.5 ng TEQ/kg waste combusted.
             4. Municipal solid waste incineration:  0.05 - 3 ng TEQ/kg  waste combusted.
             5. Sewage sludge incineration: 0.002 - 0.03  ng TEQ/kg sludge combusted.
      2.  Vapor/Particle Partitioning:  The second step in atmospheric transport modeling
is to determine the percent of totally emitted dioxin-like  congener which  is in a vapor
phase, and the percent which is in the particle phase.  The partitioning of stack emissions
into these two  phases was examined by reviewing stack testing data, ambient  air sampling
data, and  a theoretical approach developed in Bidleman  (1988). A summary of the
vapor/particle (VI?) partitioning surmised from these three sources is given in Table 111-1.
From this  review, it is generally concluded that:
      a.  Stack gas sampling:   The  stack gas sampling methods in use today to monitor
and measure the concentration of CDDs/CDFs emitted to the air from combustion sources
do not provide  a credible basis for assuming the  vapor phase and  particle bound
partitioning at the point of release. There is no consistent pattern to the interpretation of
V/P based on where the CDD/CDF segregates in the instrument, e.g., the glass fiber filter
or the XAD resin. Factors that may contribute to this are: the relatively long residence
time spent traversing the stack interior; the  probe to the instrument  is inserted  into a
relatively hostile environment of the hot combustion gas; the static temperature of the
particulate filter caused by heating the particulate filter housing; the fact that located
between the particulate trap and the vapor trap is a condensing section consisting of glass
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Table 111-1.  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.
                          4CDD  5CDD  6CDD  7CDD 8CDD 4CDF 5CDF  6CDF 7CDF  8CDF
Ambient air

1 Average of 18 data points from 9 separate references; "not reported" and "not detected" from these
references not included in averages.
2 Average of 15 data points from 6 references; "not reported" and "not detected" from these references not
included in averages.
3 calculated from procedures in Bidleman (1988); congener group listing above are rather the V/P for specific
congeners with non-zero toxicity for single congeners within congener group (e.g., result for 4CDD is that of
2,3,7,8-TCDD), or average when more than one congener is within congener group (e.g.,  result for 5CDF is
average of P of 0.58 for 12378-PCDF and 0.70 for 23478-PCDF).

tubing surrounded by an ice bath.
       b.  Ambient air sampling: On the other hand, the ambient air sampling  methods do
give an approximate indication of the V/P ratio that seems to be responsive to changes in
temperature, and degree  of chlorination of the CDDs/CDFs.  This is in accordance with
what would be expected  from their individual vapor pressures.  There is no artificial
heating or cooling of any component  of the sampler.  The sampler is exposed to actual
temperature, pressure, and humidity of the ambient air.  This reduces the  possibility that
the vapor phase-particle bound partitioning operationally defined as the compound
segregating to the particulate trap and vapor trap is actually  an artifact induced by artificial
heating and cooling  within the system.  Therefore, the methods present a realistic picture
of partitioning under variable ambient conditions. However,  the method has certain
limitations that currently  prevent deriving a true measurement of V/P partitioning in the
ambient air:

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       •  The glass fiber filter is designed to capture and retain particulate matter greater
       than or equal to 0.1 //m diameter. Particles less than this diameter may pass
       through the filter and be retained in the polyurethane foam vapor trap downstream.
       If this is the case, the amount of CDDs/CDFs observed to be particle bound would
       be underestimated, and the amount observed to be in vapor phase would  be
       •  The relatively high sampled volume of air passed through the system (200 to
       400 m3 of air per 24 hours) may redistribute the more volatile congeners from the
       filter to the adsorbent trap  by a process known as 'blow-off.
       c.  Theoretical partitioning: Until sampling methods are improved and modified
such that they give  results  that indicate the true V/P ratio of CDDs/CDFs in ambient air,
the theoretical construct described by Bidleman  (1988) is used to calculate the V/P ratio
for purposes of air dispersion and  deposition modeling  of emissions from the hypothetical
case demonstrated in Chapter 5 of Volume III.  Key advantages to the theoretical approach
are that the theoretical construct relies on current  adsorption theory, considers the
molecular weight and the degree of halogenation of the congeners, uses the boiling points
and vapor pressures  of the  congeners, and uses the availability of surface area for
adsorption of atmospheric particles that correspond to a  variety of ambient air shed
classifications having variable particulate matter densities.  Four  air shed classifications are
described in Bidleman (1988): "clean continental", "background", "background plus local
sources", and "urban". The classification used for the example scenarios in Chapter  5 of
Volume III, and shown in Table 111-1, is "background plus  local sources".
       3. Two runs of the COMPDEP model:  In order  to provide estimates of vapor and
particle phase concentrations of dioxin-like compounds, as well as estimates of wet/dry
particle deposition flux, it is necessary that to run the COMPDEP model twice.  Both model
runs should assume a "unit emissions release rate", e.g.,  1  g/s.  Results from these unit
runs can easily be transformed to final outputs given assumptions on emissions in vapor
and particle forms. A vapor phase run involves turning wet/dry deposition switches to the
"off" position. This inactivates a plume depletion equation that subtracts out  losses in
ambient air concentration due to particle deposition.  What is left are the Gaussian
dispersion algorithms. The  vapor phase concentrations are used for inhalation  exposures
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and also for vapor transfers onto vegetation for food chain modeling. A second run of
COMPDEP with wet/dry deposition switches turned to the "on" position is considered a
simulation of particle-bound contaminant.  Outputs from this run include wet and dry
deposition rates, and air concentrations of contaminants in the paniculate phase.  The
depositions are used in soil and food chain modeling, and the concentrations are added to
the vapor phase concentrations from the first COMPDEP run to arrive at the total air-borne
reservoir for inhalation exposures.
       4.  Assumed particle size distributions  of emitted particles:  In order to estimate
deposition flux, certain inferences must be made concerning the distribution of particulates
according to particle diameter (fjm).  The distribution of particulate matter by particle
diameter will differ from one combustion process to another, and is greatly dependent on
the type of feed material, conditions of combustion, and the efficiency of  various air
pollution control devices.  For purposes of demonstration, three particle size categories
were generalized from available data on particle fractionation: Category 1:  < 2 fjm,
Category  2:  2to10//m,  Category 3:  >  10 pm.  By using data on the proportion of
total particles emitted per size category, and conducting a surface area  to volume
calculation, it was estimated that 87.5% of the emission rate of particle-bound dioxin-like
congener  is associated with particles less than 2//m in  diameter, 9.5%  is  associated with
the particle size of 2 to 10//m,  and only 3% is associated with particles greater than 10
//m.  Finally, the particle size distribution is further simplified by assuming  a median particle
diameter to represent each broad  particle size category, as follows:
             • Particulate category 1=1 //m particle diameter
             • Particulate category 2 = 6.78 /vm particle diameter
             • Particulate category 3 = 20 fjm particle diameter
       5.  Dry deposition:   The COMPDEP estimates dry deposition flux based on  the
model  developed by Dumbauld, et al. (1976).  This model assumes that a fraction  of the
particulate comes into contact with the ground surface  by the combined processes of
gravitational settling, atmospheric turbulence, and Brownian diffusion.  The COMPDEP
model  contains enhancements to calculate dry deposition flux using a computerized routine
developed by the State of California Air Resources  Board  (CARB, 1986). The routine is
based on a summary of dry deposition velocity curves developed by  Sehmel (1980) for a
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broad range of particle diameters. For the example application of the COMPDEP model in
Chapter 5 of Volume III, particles less than 2 jjm, represented by a 1 //m size, were
assumed to deposit at a velocity of 0.00711 cm/sec. Particles between 2 and  10/ym,
represented by a 6.78 //m size, were assumed to deposit at 0.287 cm/sec.  Finally,
particles greater than 10//m,  represented by a 20//m size, were assumed to deposit at a
velocity of 2.47 cm/sec.
       6.  Wet deposition:  Wet deposition flux depends primarily on the fraction of the
time precipitation occurs and  the fraction of material removed by precipitation per unit of
time by particle size. Based on these relationships, scavenging  coefficients were
developed by Cramer (EPA, 1986) for varying types and intensities of precipitation relative
to different particle diameters by incorporating the observations of Radke, et al. (1980) in
a study of scavenging of aerosol particles by precipitation.  The principal assumptions
made in computing wet deposition flux are:  (1) The intensity of  precipitation is constant
over the entire path between  the source and the receptor;  (2) The precipitation originates
at a level above the top of the emission plume so that the precipitation passes vertically
through the entire  plume;  (3) The flux is  computed on the  bases  of fraction of  the hour
precipitation occurs as determined by hourly precipitation measurements compiled by the
National Weather Service. The remaining fraction (1-f) is subject only to dry deposition
processes.  Thus no dry deposition occurs during hours of steady precipitation, and dry
deposition occurs between the periods  of precipitation.
       • Biota:  Simple bioconcentration/biotransfer approaches are used to estimate
biota concentrations in this assessment.  Specifics for each biota considered are:
1.  Fish  -  The soil contamination and stack emission source categories estimate the
concentration of contaminant on bottom  sediments of water bodies. A fish lipid
concentration is estimated based the organic carbon normalized bottom sediment
concentration and  a BSAF, or Biota Sediment Accumulation Factor.  Whole fish
concentrations for exposure estimation then equal this lipid concentrations times a whole
fish lipid content (or a fillet lipid content).  For the effluent  discharge source category, fish
lipid concentrations are estimated as a  function  of organic  carbon normalized
concentrations and the closely related BSSAF, or Biota Suspended Solids Accumulation
Factor. This recently  introduced bioaccumulation factor (EPA, 1993) is analogous to the
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BSAF, and it is suggested in EPA (1993) that, as a first estimate, it take on the same
chemical-specific numerical value as the BSAF.
2. Vegetation  -  Concentrations in three types of vegetation are considered in this
assessment: below ground vegetables (carrots, potatoes, e.g.), above ground
vegetables/fruits (tomatoes, apples), and above ground grass and cattle feed which are
required for estimation of beef and milk concentrations.  Assumptions critical to all three
include: above ground vegetation is impacted by vapor phase transfers and particle
deposition -  there is no root to shoot translocation, outer portions of the vegetation are
only impacted with minimal within plant translocation, a steady state is reached between
vapor phase contaminants in air and vegetation, particle bound contaminants deposit onto
and mix in a vegetative reservoir and are subject to a fourteen-day dissipation half-life
which represents particle washoff, and vegetables/fruits which have an outer protective
layer (peas,  citrus e.g.) are unimpacted by dioxin-like compounds.  Below ground vegetable
concentrations are estimated from  soil  water concentrations and a Root  Concentration
Factor, or RCF.  Above ground concentrations due  to vapor phase transfers are a function
of the vapor phase air-borne reservoir, an air-to-leaf transfer factor, Bvpa,  and a surface area
to volume reduction factor, VG, which  is equal to  1.00 for grasses and other leafy
vegetation and less than  1.00 for  bulky vegetation.
3. Beef and Milk - Weighted average  concentrations  of dioxin-like compounds in the
diets of cattle raised for beef or lactating cattle are multiplied by a congener-specific
bioconcentration factor, BCF, which yields the concentrations in the fat of beef or milk.
The same congener-specific BCF is used for  beef and milk.  This presumes that dioxin-like
compounds  bioaccumulate equally in body fat and  milk fat of beef and dairy cattle.  While
there is expected to be some difference in bioaccumulation tendencies, the literature was
not clear on  this issue.  Fries and Paustenbach (1990) discuss the importance of the
dietary habits of cattle raised for beef versus those raised for dairy products; beef cattle
tend to be grazed substantially more, while dairy cattle tend  to be barn-fed for a greater
proportion of their dietary intake.  Like  this assessment. Fries and Paustenbach (1990)
model beef and milk concentrations using a single BCF for 2,3,7,8-TCDD.  They used a
BCF of 5.0 for 2,3,7,8-TCDD.  A set of BCFs for all dioxin-like congeners for this
assessment  were based on a set of data on a lactating cow (i.e., dietary intakes of dioxin
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congeners, concentrations in milk, and other pertinent quantities; McLachlan, et al., 1990).
The BCF for 2,3,7,8-TCDD from this data set was 4.32.  Beef and dairy cattle diets are
described in terms of proportions in  pasture grass, cattle feed (silage, grains), and soil.
Models described above estimate concentrations in these cattle intakes.

      EPA (1992a) states, "In exposure scenario evaluation, the assessor attempts to
determine the concentrations of chemicals in a medium or location and link this information
with the  time that individuals or populations contact the chemical. The set of assumptions
about how this contact takes place is an exposure scenario."  These assumptions can be
made many different ways producing a wide variety of scenarios  and associated exposure
levels. The number of people exposed at different levels form a distribution  of exposures.
Ideally assessors would develop this entire distribution to fully describe the exposed
population. Since the necessary information for developing a population distribution is
rarely available, EPA (1992a) recommends developing  a central and high end scenario to
provide some idea of the possible range of exposure levels.
      The basic setting for which the methodologies are demonstrated is a  rural setting
which contains both farms and non-farm residences.  The three principal sources of
contamination, the soil (both on-site and off-site), stack emission, and effluent discharge,
categories, are assumed to exist in such a setting.  "Central" scenarios are based on
typical behavior at a residence and "high end" scenarios are comprised of a  farm family
that raises a portion of its  own food. Key distinguishing features between the high end
and central scenarios include: 1) individuals in high  end scenarios are assumed to be at
their home a greater proportion of the day than the central scenarios (which impacts
assignment of contact fraction), 2) individuals in high end scenarios are exposed to
impacted beef and milk which they raise on their farm while these exposures are not
considered for the central scenarios, 3) the exposure duration  for individuals in the high
end scenario is 20 years compared to 9 years for the central scenario, and 4) certain
exposure parameters, such as water ingestion rate  which is  1.4 L/day for the central
scenarios and 2 L/day for the high end scenario, are different.
      The example scenarios were carefully crafted to be plausible and meaningful,
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considering key factors such as source strength, fate and transport parameterization,
exposure parameters, and selection of exposure pathways.   However, it should be clearly
understood that the purpose of the demonstration scenarios is to provide users of this
methodologies with a comprehensive example of their application. The demonstration
exposure scenarios were:
      Exposure Scenarios 1 and 2:  On-site Soil Contamination, Residence and Farm
      Surface soils on a 4,000 m2 (1-acre roughly) rural residence (Scenario 1) and on a
40,000  m2 (10-acres) small rural  farm (Scenario 2) contained residues of the three
example contaminants. The concentrations of the contaminants are uniformly set at 1
part per trillion, which was evaluated as reasonable background levels.
      Exposure Scenario 3: Off-site Soil Contamination, Farm
      A 40,000 m2 rural farm is located 150 m (500 ft) from a 40,000 m2 area of bare
soil contamination; an area that might be typical of contaminated industrial property. The
surface  soil at this property is contaminated with the three example compounds to the
same  concentration of 1 part per billion.  This is evaluated as reasonable  for industrial sites
of contamination of dioxin-like compounds, and three orders of magnitude higher than
concentrations for Scenarios 1  and 2.
      Exposure Scenarios 4 and 5:  Stack Emissions, Residence and Farm
      A 4,000 m2 rural residence (Scenario 4) is located 5000 meters downwind from a
stack  emission source, and  a 40,000 m2 rural farm (Scenario 5) is located 500 meters
from the same stack emission source. The emissions of dioxin-like compounds were
evaluated as within the range observed for various stack emission sources which have
sophisticated air pollution control devices (e.g., scrubbers combined with fabric filters).
      Exposure Scenario 6: Effluent discharge into a river
      As has been discussed, this source category is different from others in that the air,
soil, and vegetation at a site are not  impacted. Rather, only surface water impacts,  and
exposures to  ingestion of drinking water and fish, are considered.  The source strength
was developed from data on pulp and paper mill discharges of 2,3,7,8-TCDD.  Discharge
rates were based on data from EPA's 104-mill study (EPA, 1990c), and then reduced
considering recent improvements in the bleaching process which have reduced discharges.
      Three compounds were demonstrated for the two soil source categories, on-  and
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off-site soil contamination, and for the effluent discharge source category.  For purposes
of illustration, one compound was arbitrarily selected from each of the major classes of
dioxin-like compounds.  They are: 2,3,7,8-tetrachlorodibenzo-p-dioxin (abbreviated
2,3,7,8-TCDD), 2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PCDF), and
2,3,3',4,4',5,5'-heptachloro-PCB (HPCB).
      For the stack emission demonstration. Scenarios 4 and 5, a different approach was
taken.  Exposures to 2,3,7,8-TCDD alone are determined, as in the other demonstrations.
Emission rates for all dioxins and furans with non-zero toxicity equivalency factors
(abbreviated TEFs) were available for the demonstration  of the stack emission  source
category.  Use of the full suite of emissions allowed for the opportunity to demonstrate an
appropriate methodology for estimating TEQ exposures.  The framework takes the
individual deposition rates and concentrations for the individual congeners and models the
exposure media concentrations individually with unique fate and bioaccumulation
parameters, and then determines a final TEQ exposure media concentration  using TEFs.

III.4.1.  Results from the Demonstration of the Stack Emission Source Category
      For brevity, only the  results from the stack emission source category will be
summarized. Table III-2 gives the exposure media concentrations estimating for 2,3,7,8-
TCDD and for TEQs for Example Scenario  #5, the high end scenario for the stack emission
source category. Table III-3 gives the estimated Lifetime Average Daily Doses, LADDs, for
the exposure pathways modeled in this assessment.
      Much of the differences between exposure pathways and scenarios is due to
differences in exposure media estimation.  Therefore, the discussion below on trends for
LADD follows directly from  how the methodologies estimate exposure media
concentrations. It is important to understand that exposure estimates generated for  the
demonstration  scenarios are specific to the site conditions assumed for the examples and
are not generalizable to other sites. Following are some key observations:
      1)  The highest  exposures were associated with the off-site  soil contamination
scenario. Scenario #3.  This scenario had the highest exposure media concentrations for all
exposure media.  The source of contamination was a 40,000  m2 land area with soil
concentrations initialized at  1 ppb for the three example compounds.  The lowest LADDs
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Table 111-2. Exposure media concentrations estimated for the demonstration of the stack
emission source category1.
    Exposure media
    concentration                                  2378-TCDD        TEQ
Concentration of contaminants in soil
for soil ingestion and dermal contact
pathways, ng/kg 1 * 1 0'3
Concentration of contaminants in air
for inhalation pathway, pg/m3 1 *10~5
Concentration of contaminants in water
for water ingestion pathway, pg/L 4*10~6
Concentration of contaminants in
fish for fish ingestion pathway, ng/kg 6*10"5
Concentration of contaminants in below
ground vegetables, ng/kg fresh weight 8*10'8
Concentration of contaminants in above

      ground fruit and vegetables, ng/kg
      fresh weight                                 3*10'e             1*10'4

7.    Concentration of contaminants in
      beef for beef  ingestion pathway,
      ng/kg whole beef (22% fat)                   5 * 10'4             1 * 10'2

8.    Concentration of contaminants in
      milk for milk ingestion pathway,
      ng/kg whole milk (3.5% fat)                   6*10'5             1 MO'3
1 The exposure site was located 500 meters from the stack; emission rates of 2,3,7,8-
TCDD and TEQs were 9.2*10-" g/sec and 1.6*10'9 g/sec, respectively.
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Table 111-3.  Lifetime Average Daily Doses, LADD, for the high end stack emission
demonstrations scenario (LADD in units of ng/kg-day).
Soil ingestion
Soil dermal contact
Water ingestion
Fish ingestion
Fruit ingestion
Vegetable ingestion
Beef ingestion
Milk ingestion
1 * 1 0'9
9 * 1 O'8
8 * 1 0'8
1 * 1 0'9
were estimated for the demonstration of the stack emission source category.  Although
the intensity of the source strength between a stack emission source and a soil source
cannot be directly related, it is noted that the releases of 2,3,7,8-TCDD and TEQs used to
demonstrate the stack emission source were comparable to other stack emission sources
with sophisticated air pollution control devices.  Exposures to 2,3,7,8-TCDD were about
5% of exposures to TEQs. This mirrors the comparison of the 2,3,7,8-TCDD  release rate
and total TEQ release rate from the stack. Only a fish and a water ingestion pathway
were considered for the effluent discharge source category. The exposures estimated for
these two pathways were similar in magnitude to the fish and water ingestion exposures
estimated for demonstration of the on-site soil source category, demonstrations #1 and
#2. For those demonstrations, watershed soils were initialized at 1  ppt, a concentration
that researchers have found for 2,3,7,8-TCDD in background settings.
      2)  Differences between analogous "central" and "high end" exposures for the on-
site soil  source demonstration scenarios were near or less than an order of  magnitude.
"Analogous" exposures are those estimated for both scenarios. They include  inhalation,
soil ingestion and dermal contact, water,  vegetable/fruit, and fish ingestion  exposures.
Only beef and  milk are not analogous since they were only estimated for the high end
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scenario.  Analogous exposures were within an order of magnitude of each other because
the exposure parameters used to distinguish typical and high end exposures, the contact
rates, contact fractions, and exposure durations, themselves did not differ significantly,
and these were the only distinguishing features for the  central and high end
demonstrations of the on-site soil source category. In the stack emission scenario, placing
exposed individuals either 500 or 5000 meters away from the incinerator did significantly
impact the results. In this case, the difference was closer to 2 orders of magnitude for all
analogous exposures except water and fish exposures,  which were not a function of
distance from the stack. The order of magnitude difference in distance added about an
order of magnitude difference in exposure media concentrations and  hence LADD
       3)  It is inappropriate to compare and rank exposure pathways across all  scenarios
because the source terms are different.  However,  relationships between different
pathways within each scenario can be discussed.  Table 111-4 was constructed by summing
the LADDs for all pathways, and then determining the percent contribution by each
pathway.  Before the summation, LADDs were corrected to account  for absorption - all
ingestion LADDs assumed 50%  absorption and inhalation LADDs assumed 75% (data on
bioavailability from animal feeding studies, suggests that the absorption of 2,3,7,8-TCDD
is around 50%; 75% for inhalation reflects a general assumption of greater absorption for
this pathways; both simple assumptions made only for the purpose of this comparative
exercise).  The dermal contact LADD was the only one where absorption was already
considered in its estimation: absorbed dose was estimated as 3% of  dose contacting the
body.  Also, this exercise assumes all pathways occur simultaneously. Table 111-4  was
generated only for the 2,3,7,8-TCDD example compound, and the rows are listed generally
from the highest to lowest percentage contribution. The following observations are made:
       •  In  high end scenarios which assumed exposure to home grown beef, milk, and
fish. Scenarios 2, 3, and 5, exposures to these three foods dominated the results.  In
Scenarios where beef and milk were not considered, but fish was considered. Scenarios 1,
4, and  6, fish exposures dominated.  The general dominance of beef, fish,  and milk
exposures underscores the importance of food chain exposures.
       •   Milk exposures were lower than beef exposures because of less milk  fat
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Table 111-4.  Percent contribution of the different exposure pathways within each exposure
Exposure Pathway
Meat Ingestion
Fish Ingestion
Soil Ingestion
Milk Ingestion
Soil Dermal
Vegetable Ingestion
Fruit Ingestion
Water Ingestion
Vapor Inhalation
Particle Inhalation
Scenario #
3 4
* Assumes exposed individual experiences all relevant pathways and exposures are
ingestion (10.5 g/day milk fat versus 22 g/day beef fat) and lower concentrations in milk
as compared to beef.
       • Fish  was the principal impacted media for the effluent discharge source
category, with fish ingestion 19 times higher than water ingestion, the only two  pathways
considered for the effluent discharge category.  However, fish is much less  important than
beef or milk for the high end stack emission scenario which had a beef and  a milk
pathway, and when a small site of contamination is near a farm raising a  portion  of the
farming families beef and milk ingestion.
       • Soil ingestion exposures were also noteworthy, particularly in scenarios that did
not consider beef and milk, the central on-site scenario, #1, and the central  stack emission
scenario, #4. Soil ingestion was also the second highest pathway in the scenario
evaluating the  impact of nearby soil  contamination, #3, ranking higher than  milk or fish
ingestion.  Dermal exposures were non-trivial, but ranked behind  the four  ingestion
pathways  previously discussed: beef, milk, fish,  and soil.

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       •   Inhalation was the highest impact for the stack emission scenario when farm
animal products were not considered, in Scenario #4.  Fruit and vegetable exposures were
noteworthy only in this same scenario. These trends imply that, where farm animal
products are not being produced near a stack emission source, fish and vegetative food
products still may dominate the overall exposure,  but inhalation exposure can become
       •   Water ingestion exposures were very low in comparison to the other exposures
in these scenarios.
       These demonstration scenarios represent only one approach to scenario
development; other approaches might consider the quality of exposure media not
associated with the home environment. For example, if the bulk of an individual's
ingestion of produce comes from local  farms, and local farms may be impacted  by an
stack emission source, then perhaps 90-100% of an individual's fruit and vegetable
ingestion, rather than the 20-40% assumed in this assessment, should be considered

       This section discusses three issues pertinent to use of the methodologies. The first
subsection below discusses the use of the parameter values selected for the
demonstration scenarios for other applications.  The next subsection is a sensitivity
analysis exercise on the parameters required for algorithms estimating exposure media
concentrations.  The last subsection addresses the issue of mass balance with regard to
the source strength terms of the four source categories.

III.5.1. Categorization of Methodology Parameters.
       Table 6.1 in Chapter 6 of Volume III lists all the parameters, including names,
definitions, and units, that are required for the methodologies of this assessment except
the exposure parameters.  Exposure parameters are given in Table 2.1  in Chapter 2  of
Volume III. Table 6.1 also gives four additional pieces of information for each parameter
listed.  Three are numerical values which were used in the sensitivity analysis exercises
that are described below.  One  of those parameters is labeled  "selected", which were the
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ones used in the demonstration exposure scenarios. High and low values of parameters
selected for sensitivity analysis were carefully developed  and might be considered a
reasonable range of values for other uses of the methodology (with obvious exceptions
such as areas of contamination, distances from contaminated to exposure site, and so on).
The chemical specific parameters are those only for 2,3,7,8-TCDD.  The fourth piece of
information is a qualitative judgement on the part of the authors of this document as to the
appropriateness of using the "selected" parameter values for other assessments. This
judgement is categorized in three  ways:
1) First Order Defaults: As defaults, these parameters are independent of site specific
characteristics. As first order defaults, it is felt that the values selected for  the
demonstration scenarios carry a sufficient weight of evidence from current literature such
that these values are recommended for other assessments.  Several  of the chemical
specific parameters, such as the Henry's Constant, H, and the organic carbon partition
coefficient, Koc, fall into this category.  The qualifier above, "current literature", indicates
that new information could lead to changes in these values.
2} Second Order Defaults:  Like the above category, these parameters are judged to be
independent of site specific characteristics.  However, unlike the above category, the
current scientific weight of evidence is judged insufficient to describe values selected for
demonstration purposes as first order defaults. Parameters of principal note in this
category are the bioconcentration parameters specific to the  chemicals, such as the Biota
Sediment Accumulation Factor, or BSAF.  This parameter translates  a bottom sediment
concentration to a fish tissue concentration.  Users should carefully  review the justification
for the SOD values selected  for the demonstration scenarios  before using the same values.
3) Site Specific:  These parameters should or can be assigned values based  on site-
specific information.  The information provided on their assignment for the demonstration
scenarios, and for  selection of high and low values for sensitivity analysis testing, is useful
for determining alternate values for a specific site.  A key class of SS parameters which
are the source strength terms - the soil concentrations, effluent discharge rates, and stack
emission rates. If  users are unable to obtain site-specific information, or their use of the
methodologies is for general purposes, they should review the justification for selection of
values for methodology demonstration, as well as information provided giving ranges of
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likely values for model parameters.
      The exposure parameters can be categorized as have the contaminant fate and
transport/transfer parameters.  Assignment of these values are critical as LADD estimates
are linearly related to parameter assignments - doubling exposure duration assumptions
double LADDs, and so on. Some of the exposure parameters  are appropriately described
as first order defaults. These include:  lifetime, body weights, water ingestion rates,
inhalation rates, and an exposure duration for a childhood pattern of soil ingestion. All of
the other exposure parameters are better described as either second order defaults or site-
specific.  All exposure parameters were developed based on information and
recommendations in EPA's Exposure Factors Handbook (EPA,  1989) and Dermal Exposure
Assessment: Principals and Applications (EPA, 1992c).   Attaining site-specific information
is recommended  for exposure parameters.

III.5.2.  Sensitivity Analysis
      Sensitivity analysis was undertaken in order to evaluate the impact to exposure
media concentration estimations with changes in fate and transport/transfer model
parameters. Figure III-5 shows an example of sensitivity analysis conducted. This figure
describes the impact of key factors for the stack emission source category for determining
biota impacts. The x-axis contains the names of the parameters evaluated.  The key
below the figure  gives the definition of the parameters and the values selected for the
demonstration scenarios.  The y-axis shows the numerical change to the key model result,
in this case, vegetable and beef concentrations, to the changes made in the parameter.
These changes are noted  above and below the bars.  For example, vegetable
concentration is about 3 times  higher at 200 ft from the stack emission source than it is at
500 meters from the source, the distance used in the demonstration scenario.  Some of
the observations  made for this  test, typical for the type of observations which were made
for sensitivity testing, include:
      1)  Mixing depth, described by the parameter dnot, has very little impact on final
beef concentrations.
      2)  Nearer to and further from the stack had different impacts for above and below
vegetable concentrations  as compared  to beef concentrations. The farm was assumed to
                                        73                                    4/94

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Table 111-5. (cont'd)
                                DRAFT-DO  NOT QUOTE OR CITE
Description of Test
                               Summary of Results
Predicted vs. observed
fish tissue concentrations
With background soil concentrations of 2,3,7,8-TCDD of 1 ppt, estimated
fish concentrations were 0.6 ppt.  With a bounded site of 1  ppb soil
concentrations, fish concentrations were 3.0 ppt.  These were compared
with analagous results from the National Study of Chemical  Residues in  Fish
(NSCRF; EPA, 1992b).   For NSCRF sites that were evaluated as comparable
to background settings,  fish concentrations ranged from 0.56 ppt to  1.02
ppt.  Average fish tissue concentrations from National Priority List (NPL) and
similar industrial contaminated  sites ranged from 1.4 to 30.0 ppt, with the
30 ppt average from National Priority List (NPL) sites and all other site
averages under 4.4  ppt.  The comparison indicates that the  magnitude of
concentrations appears to have been captured, and the magnitude of
difference between background and higher source strength categories of the
NSCRF also appears to have been duplicated.
Predicted vs. observed
fish concentrations
for the 104-mill pulp
paper mill study
The "sources" of 2,3,7,8-TCDD loadings into surface water were pulp and
paper mills of the 104-mill study (EPA, 1990c).  A complete set of
"observed" data (fish concentrations from the NCSRF described above,
2,3,7,8-TCDD discharges other than non-detects, water body
characteristics, etc.) were available for only 47 mills and  95 fish samples (in
some cases, more than one fish was identified downstream of a mill). A
dichotomy  in model performance was observed for 9 mills (and 21
associated  fish samples), which differed from the other 38  in that the
receiving water body flow volumes were significantly larger.  The average
for these 9 mills was 3*1010 L/hr, while the average for the other 38 was
5*108 L/hr. The average predicted whole fish tissue concentration of
2,3,7,8-TCDD for the 38 mills was 7 ppt, and the average  observed
concentration in 74 fish was 15 ppt.  For the 8 mills and  21 fish, the
average predicted fish concentration was 0.7 ppt compared to an observed
5.3 ppt.  The correlation over all mills and samples was low, at r2 =  0.41.
However, the merit of generating this descriptor should be considered: it
assumes that the single  observed discharge of 2,3,7,8-TCDD represents
long term discharges for a given mill, that the single  or the  few fish samples
represent observed impacts from the mill, and so on.  One pertinent result
was that the maximium  "observed" fish tissue concentration of 143 ppt was
matched by the maximum predicted concentration of 89 ppt.  The key
assumption was that the pulp and paper mills were the only sources
impacting fish tissue concentrations; it is suggested that other sources
impacting the large water bodies explain why observed fish concentrations
were about an order of magnitude higher than model predictions for these
water bodies.

                                                  (cont'd on next page)

Table MI-5. (cont'd)
                                DRAFT-DO NOT QUOTE OR CITE
Description of Test
                                Summary of Results
Predicted vs. observed
water concentrations
Predicted vs. observed
beef concentrations
Predicted vs. observed
beef fatrsoil and
milk fatrsoil  concentration
Data in the literature suggests concentrations of dioxin-like compounds
mostly below 1 pg/L.  Models predicted concentrations of 1Q2 pg/L and
lower in demonstration of all  source categories.

A profile of "observed" air concentrations of dioxin-like compounds was
crafted  from available air concentration data.  An urban air profile of TEQs
developed in Volume II was 0.095 pg/m3, and  based on evidence that rural
air concentrations (which  are the ones most appropriate for beef
concentrations) are  4-6 times lower than urban air concentrations, a rural air
profile was crafted,  totalling 0.019 pg TEQ/m3. These concentrations were
routed through the food chain model to arrive at beef TEQ concentrations
which were compared with a TEQ beef concentration profile generated from
measurements in Volume  II.  A predicted TEQ concentration of 0.36 ng/kg
whole beef concentration  (19% fat) was compared to the observed  0.48 ng
TEQ/kg  in whole beef.  Also evaluated were the capabilities of the model to
evaluate air to leafy vegetation transfers (vapor and  particle) by looking at
model predictions and comparing them  a single set of observations taken in
a rural location in Minnesota (Reed,  et al.,  1990). Model  predictions and
observations also compared favorably, except for octa congeners, where
predictions were much lower  than observations.  However, the model  for
vapor/particle partitioning  indicated that the octa congeners would reside
fully on particles, i.e., 0 (particle fraction)  = 1.00.   In fact, the  for both
octa congeners equalled 0.998. Allowing calibration for 0, values equalled
0.9998 for OCDD and 0.998  for OCDF, and leafy vegetation predictions, as
well as octa beef measurements, now closely matched observations.  An air-
to-soil evaluation was also done, comparing model predictions of dioxin
congener soil concentrations with measurements taken in the United States
in rural settings.  It was found that the model generally underpredicted soil
concentrations by about an order of magnitude, although  a more close
match would  not have greatly affected  the predictions in beef since soil is
only a small part of the cattle diet.   Speculations for why the model was
underpredicting soil  concentrations included: 1) vapor transfers to soils were
not considered, 2) detritus contributions to soil concentrations  were not
considered, and 3) the assumed half-life of 10  years for this exercise might
not be long enough.

Fries (1985) had developed fatrsoil ratios for a  farm  known to be
contaminated with PBBs, compounds similar in fate and persistence, and
bioaccumulation tendencies, as the dioxin-like compounds.  Field data
showed ratios of 0.10-0.39 for beef and dairy  cow body fatrsoil, and 0.02-
0.06 for milk fat:soil.  Modeled ratios in the both soil contamination  (on and
off-site) example scenarios for 2,3,7,8-TCDD were 0.12 for beef fat:soil and
0.06 for milk fat:soil.

                          DRAFT-DO NOT QUOTE OR CITE
       A summary of key discussions from the uncertainty evaluation is now presented.
First is a summary of three exposure parameters common to all pathways:

       1.  Lifetime, Body Weights, and Exposure Durations:   Of these three parameters,
the exposure duration is the most uncertain.  The estimates of 9 and 20 years were made
in this assessment for non-farming residents  in rural settings, and farming residents in rural
settings. These values were based on assumptions of time living at one residence.  A
critical assumption of a constant soil concentration for contaminated soil sites should be
carefully considered for site-specific assessments. Data on degradation indicates very
slow rates of degradation, and only photolysis as a possible degradation mechanism,
which would not impact residues below the surface.  A mass balance exercise on the
demonstration of the off-site source category (where  a 40,000 m2 area had soil
concentrations  averaging 1 ppb 2,3,7,8-TCDD) indicates that it would take 90 years to
dissipate a reservoir of 2,3,7,8-TCDD extending 6 inches into the soil.  An adult body
weight of 70 kilograms and a lifetime of 70 years are standard assumptions for exposure
and risk and, although variability is recognized for these parameters, these variations are
not expected to add significant uncertainty in exposure estimates. The same is true for
the 17 kg child  body weight in the childhood  exposure pattern of soil ingestion.

       2.  Soil Ingestion  and Soil Dermal Contact:   Soil ingestion for older children and
adults were  not considered, which may have underestimated lifetime soil ingestion
exposures.  Pica soil ingestion patterns were  not evaluated in this assessment. The
ingestion rates  (200 mg/day for central  scenarios and 800 mg/day for high  end scenarios,
during ages  2-6) considering this appear reasonable.   For the soil dermal contact pathway,
key uncertain parameters include the soil adherence (0.2 mg/cm2-event for the central
residential scenario and 1.0 mg/cm2-event for the high end farming scenario) and the
absorption fraction (0.03 for dioxin-like  compounds).
       A major  area of uncertainty for both pathways is the estimation of soil
concentrations  where the source of contamination is located distant from the site of
exposure. For this assessment, this includes the off-site soil source category and the
stack emission  source category.  Results from sensitivity analysis exercises for the  erosion
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algorithm suggests that the 0.28 ppb soil concentration (within a 5-cm layer) used for soil
ingestion and dermal contact, and which resulted from the 1 ppb nearby (150 m) soil
contaminated site, may be high.  Specifically, when all parameters for the erosion
algorithm remained constant except the dissipation half-life, which initially was 0.0693
yr1 (half-life of 10 years)  and then was reduced by a factor of ten to 0.00693 yr'1 (half-life
of 100 years), the soil concentration 150 meters away at the site of exposure increased to
slightly above 1.00 ppb.  While dissipation of surface residues which have arrived at an
exposure site from a distant source is an appropriate assumption, the outcome of  a higher
soil concentration 150  meters from a site of  soil contamination when no dissipation is
assumed (albiet assuming infinite time such that a steady state is reached) is questionable.
Key uncertain parameters identified include the dissipation rate  (0.0693 yr1), the mixing
depth (5 cm), and the use of an enrichment ratio (equal to 3.0) which increases the
concentration of dioxin-like  compound on eroded soil relative to in-situ soil.  This latter
parameter was speculated to the one most likely to be inaccurate for evaluation of off-site
soil impacts.  Its assignment was not based on data specific to dioxin-like compounds, but
rather to general literature data on enrichment ratios for soil nutrients and pesticides
showing a range of between 1  and 5.  On the other hand, support for an  enrichment ratio
of 3.00 came in a data  set including background soil and concurrent bottom sediment data
in receiving water bodies  in Connecticut (see Table III.5 for a summary of this data set).
There, the ratio of sediment concentrations of 2,3,7,8-TCDD to soil concentrations was
2.8, suggesting that  bottom sediments are enriched in comparison to surface soils.  The
model for bottom sediment  impact from watershed soils includes the enrichment ratio,
which was set at 3.00, and the demonstration  scenarios did show a sediment:soil ratio of
2.8, like the observed data.
      An uncertain outcome was also identified for the particle deposition algorithm used
for the stack emission source category.  An analysis suggests that the soil concentration in
a 1-cm layer resulting from  depositing  particles may be underestimated by about an order
of magnitude.  The pertinent analysis for this observation came from the air-to-beef food
chain  model validation exercise conducted for dioxin-like compounds (further details of this
exercise are found in Table  III-5). There, a rural air profile of dioxin-like compounds were
deposited onto soils, and  the resulting concentrations of dioxin-like compounds were
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compared against observations from four United States reports on soil concentrations in
rural areas.  Generally, the model underpredicted soil concentrations by about an order of
magnitude.  Suggested causes for this underprediction include: 1) the model does not
consider vapor phase transfers to soils, 2) the model does not consider detritus
contributions to soil, and 3)  the half-life of 10 years may not be long enough for dioxin-like
       In summary, principally identified uncertain parameters for the algorithms
transporting eroding soil and depositing particles include: the mixing zone depth for unfilled
situation of  1 and 5 cm, the dissipation half-life of 10 years, the lack of consideration of
vapor phase depositions and detritus additions to soils, and the use of  an enrichment ratio
for eroded soil of 3.0.

       3.  Ingestion of Water:     A comparison of alternate modeling approaches for
estimating water concentrations showed  similar results to the models adopted for this
assessment.  There also does not appear to be a wide range of possible values for water
ingestion rate (1.4 L/day for central scenarios and 2.0 L/day for high end scenarios) and
contact fraction (0.75 for central scenarios and 0.90 for high end scenarios), and these are
not expected to introduce significant uncertainty into water ingestion exposure estimates.

       4.  Inhalation:   The inhalation rate assumed  for both central and high end
scenarios was 20 m3/day. The distinction in the scenarios was in the contact fractions:
central scenarios assumed a contact fraction of 0.75 and high end scenarios had a 0.90
contact fraction.  These fractions correspond to time at the home environment.  These
fractions and the inhalation rate are not expected to add significant uncertainty in
inhalation exposure estimates.
       Sensitivity analysis showed air concentrations resulting from soil emissions to be
sensitive to Koc and H, and  also to key source strength and delivery terms such as areas
of contamination and wind speed. Assuming these non-chemical specific parameters can
be known with reasonable certainty for site-specific  applications, the most uncertainty lies
with chemical specific data.
       Alternate approaches for volatilization and air dispersion tested included the
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volatilization approach developed by Jury, et al. (1983) and the box model for dispersion
calculations.  The Jury model predicted about  1/3 as much volatilization flux (given the
selection of parameters, made equal to or most analogous to the models of this
assessment) as the Hwang, et al. (1986) model of this assessment. The box model
predicted about 6 times  higher air concentrations than the near-field dispersion approach of
this assessment.  This reasonable comparison  lends some credibility to the models
      Approaches to estimate particulate phase concentrations are empirical and based on
field data. They are based on highly erodible soils  but are specific to inhalable size
particles, those less than 10yt/m. As such, they may overestimate inhalation exposures,
but may underestimate the total reservoir  of particulates, which becomes critical for the
particle deposition to vegetation algorithms. Another area of uncertainty is the assumption
that volatilized contaminants do not become sorbed to airbone particles - this is also
critical because vapor phase transfers dominate plant concentration estimation.  A final
key area of uncertainty is that transported contaminants from a contaminated to an
exposure site via erosion are assumed  not to volatilize or resuspend at the exposure site or
from soils between the contaminated and  the exposure site - air borne exposure site
concentrations may be underestimated as a result.

      5.  Fruit and Vegetable Ingestion:   All  ingestion parameters assumed are evaluated
as reasonable for general exposure  to broad categories of fruits and vegetables.  However,
great variability is expected if using these procedures on a specific site where home
gardening practices can  be more precisely ascertained. Concepts of below and  above
ground vegetations were developed to accomodate soil to root algorithms and soil to air to
vegetation algorithms.  Protected vegetations - those with outer inedible protections such
as citrus or corn - were assumed not to be impacted by dioxin-like  compounds.
      A key assumption in the vegetation algorithm, that dioxin-like compounds do not
translocate from root to shoot, was verified by two experiments.  Vapor-phase
contributions to vegetation dominated  the contaminated soil and stack emission source
categories, with one exception.  Particle depositions were more important for above
ground fruit/vegetable concentrations for the stack emission source.
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       A critical empirical parameter was the above and below ground correction factors,
     and VG^, both set at 0.01 for fruits and vegetables. These factors were justified for
dioxins based on the fact that the experiments for derivation of the below ground empirical
transfer factor and the above ground empirical transfer factor were conducted with thin
barley roots and azalea leafs, respectively. Whole plant concentrations for these
vegetations are likely to be much higher than whole plant concentrations of bulky fruits
and vegetables; hence the introduction of the VG parameters.  VG for grass was set at
1.00, which assumes that grass leaves and azalea leaves are analagous with regard to
vegetative  bulk. VG for cattle feed was set at 0.50, which assumes that some cattle feed
is leafy (hay), while some is bulky (corn silage).  A different assumption for VG of fruits
and vegetables, such as 0.10, would increase estimated concentrations and perhaps make
plant:soil concentration ratios more in line with literature values (see Table III-5).
       Experimental evidence that a VG^ for  vapor transfers of  dioxin-like compounds is
justified came in a recent study  by McCrady (1994). McCrady experimentally determined
uptake rate constants, termed kv for vapor phase  2,3,7,8-TCDD uptake into several
vegetations including kale, grass, pepper, spruce needles, apple, tomato, and azalea
leaves.  The uptake rate for an apple divided  by the uptake rate for the grass leaf was
0.02 (where uptake rates were from air to whole vegetation on a dry weight basis).  For
the tomato and pepper, the same ratios were 0.03 and 0.08. The VGag was 0.01 for fruits
and vegetables in this assessment. McCrady (1994) then went on to normalize his uptake
rates on a surface area basis instead of a mass basis; i.e., air to vegetative surface  area
instead of air to vegetative mass.  Then, the uptake rates were substantially more similar,
with the ratio of the apple uptake rate to the  grass being 1.6 instead  of 0.02;  i.e., the
apple  uptake rate was 1.6 times higher than that of grass, instead of 1/50 as much when
estimated on an air to dry weight mass basis. The ratios for tomato and pepper were 1.2
and 2.2, respectively.  In his article, McCrady (1994) concludes, "The results of our
experiments have demonstrated that the exposed surface area of plant  tissue is an
important consideration when estimating the  uptake of 2,3,7,8-TCDD from airborne
sources of vapor-phase 2,3,7,8-TCDD. The surface area to volume ratio (or surface area
to fresh weight ratio) of different plant species can be used to normalize uptake rate
constants for different plant species."  McCrady does caution, however, that uptake rates
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are only part of the bioconcentration factor estimation, and is unsure of the impact of
surface area and volume differences on the elimination phase constant, k2 (personnel
communication, J. McCrady, US EPA, ERL-Corvallis, Corvallis, OR 97333). Still, his recent
experiments do appear to justify the use of a VG parameter since the air-to-leaf transfer
parameter was developed on an air-to-whole-plant-mass basis, and his results are
consistent with the assignment of 0.01 for fruits and vegetables.
      An uncertain experimentally derived empirical factor described the transfer of
compounds from soil to below ground vegetables, the Root Concentration Factor, RCF.
An analagous uncertain parameter describes the transfer of vapor-phase dioxin-like
compounds from air to above ground vegetations, the air-to-leaf transfer factor, Bvpa.
Both of these parameters are estimated as functions of the contaminant properties; both
used contaminant octanol water partition coefficient, Kow, and the Bvpa also used
contaminant-specific Henry's Constant, H.  The Bvpa was developed in a series of
experiments by Bacci, et al. (1990,  1992) using 14 different organic contaminants  and
azalea leaves.  Adjustments to the Bvpa as formulated by Bacci were suggested by the
experiments on the transfer of 2,3,7,8-TCDD to grass leaves by McCrady and Maggard
(1993).  The adjustments dealt with the impact of photodegradation, which was not
considered in the experimental design of Bacci, and in the different plant  species used by
McCrady and Maggard.  Those adjustments were made for the dioxin-like compounds  in
this assessment. The range of log Kow for 2,3,7,8-TCDD found in the literature was 6.15
to 8.5. An alternate value of log Kow for  2,3,7,8-TCDD would more likely be higher than
lower, given the  selected value of 6.64. Increasing log  Kow tends to decrease below
ground vegetation, by as much as an order of magnitude, while increasing above ground
vegetation by as much as an order of magnitude.

      5.  Ingestion of Fish:  The key exposure parameter for this pathway was the fish
ingestion rate. The rates assumed in the demonstration scenarios were low in comparison
to estimates given for subsistence fisherman or others who live near large water bodies
where fish are commercially caught. The justification for the lower ingestion  rate for
demonstration purposes was that the setting demonstrated was described as rural,
containing farms and non-farm  residences, where the emphasis is on agriculture. A
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relatively small watershed with a small impacted water body was assumed.  Daily
ingestion rates of 1.2 (central) and 4.1 (high end) g/day were assumed, based on an
assumption of 3 fish meals per year (150 g/fish meal) obtained from the water body for
the central scenario and 10 fish meals per year for the high end scenario. Other fish
ingestion rates that can be considered for exposure assessments include: 6.5 g/day
characterized as a national average ingestion rate for freshwater and estuarine fish and
shellfish (EPA, 1984), and 30 and 140 g/day, which are  described as 50th and 90th
percentile rates for recreational fisherman in areas where large water bodies are present
(EPA, 1989).
       Other models for estimating fish concentration based on water column
concentrations, rather than suspended sediment  concentrations, were described in EPA
(1993) and demonstrated in this assessment. Results indicated that the water column
approaches would predict similar whole fish concentrations compared with the sediment
concentration approaches of  this assessment.  However, the various models would
respond differently to changes in model parameters. For example, a bioaccumulation
parameter based on whole water concentration (total contaminant, the sum of sorbed and
dissolved amounts,  divided by water volume) will be mostly insensitive to changes in
organic carbon content  of sediments.  In contrast, this is a critical parameter for
bioaccumulation parameters which are based on  sediment concentrations (as in this
assessment) or dissolved-phase water column concentrations.
       A key uncertain  parameter for estimating fish tissue concentrations is the Biota
Sediment Accumulation Factor, or BSAF, and the Biota Suspended Sediment Accumulation
Factor, or BSSAF.  A range of 0.03 to 0.30 for 2,3,7,8-TCDD is hypothesized for column
feeding fish, while the Connecticut data (CDEP, 1992) and some other data on bottom
feeding fish indicate higher BSAFs ranging up to  0.86 for 2,3,7,8-TCDD.  A value of 0.09
for 2,3,7,8-TCDD for BSAF and  BSSAF is used in this assessments. Data is scarce for
BSAF and BSSAF for other dioxin-like  compounds, although  available data does suggest
that these parameter values decrease  as the degree of chlorination increases.  A key
parameter is the  fish lipid content, which can vary from below 0.05 to above 0.20. The
model estimates a fish lipid concentration.   Multiplying fish  lipid concentration by fish lipid
content arrives at a  whole fish concentration or an edible fish concentration, depending  on
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the user's assignment and characterization of the fish lipid content variable. For this
assignment, the fish lipid  content was assigned a value of 0.07 for the demonstration
scenarios, based on lipid content of fish in EPA's Lake Ontario study (EPA, 1990a).

      7.  Beef and Milk (ngestion:  The rates of beef and milk fat ingestion are 22 and
10.5 g/day, respectively.  The median whole beef and whole milk ingestion rates are given
as 100 and 300 g/day, respectively (EPA, 1989), and these were assumed for the
demonstration scenarios.  Beef fat and milk fat contents are assumed to be 22% and
3.5%, respectively.  Only the high end demonstration scenarios included beef and  milk
ingestion pathways.  These scenarios were farm settings, and the assumption was that
farming  families would obtain a portion of their ingestion of these foods would come from
home produced  beef and  milk.  The assumptions for contact fractions for beef and milk
(fractions of their total consumption that comes from home supplies) was 0.44 and 0.40,
respectively. These were average consumption fractions for farming families,  whether or
not the farm families home consumed, and were developed from  a USDA (1966) survey of
farming  families. Since exposure estimates from these pathways are linearly related to
ingestion rate and contact fraction, these are critical exposure  parameters for site specific
      Comparison with earlier modeling approaches showed that the current approach to
estimating beef and milk concentrations is the same as earlier approaches, although
mathematically formulated differently.  Earlier approaches also estimated cattle dose of
2,3,7,8-TCDD from  contaminated  air (directly) and contaminated ground water - these
earlier estimations showed these contributions to be minimal, and they were not
considered in this assessment. Early efforts in the literature did not consider vapor
transfers to vegetations; one later assessment did include vapor transfers, and a key result
in that assessment,  as well as this one, is that vapor transfers are critical for beef  impacts.
Finally, earlier assessments considered the practice of fattening beef cattle prior to
slaughter by feeding them residue-free grains.  These efforts estimated over a 50%
reduction in beef concentration due to residue degradation or elimination and/or dilution
with increases in body fat.  The demonstrations scenarios in  this assessment did not
consider this practice.  However, this practice was considered in the air-to-beef food chain
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validation exercise.  There, a 50% reduction  in beef concentrations due to feedlot
fattening was assumed.
       Key uncertain and variable parameters for beef/milk concentrations include:  1) the
assumptions concerning vapor/particle partitioning for the stack emission source category,
2) the air-to-leaf transfer parameter, Bvpa, for  vapor phase contaminants, 3) beef cattle
exposure assumptions, 4) the weathering factor for particles depositing on vegetations
which cattle consume, and 5) uncertainties as discussed above for air to soil algorithms
and soil to air algorithms.
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                               REFERENCES FOR VOLUME III
Bacci, E.; Calamari, D.; Gaggi, C.; Vighi, M.  (1990) Bioconcentration of Organic Chemical
      Vapors in Plant Leaves: Experimental Measurements and Correlation.  Environ. Sci.
      Technol. 24: 885-889.

Bacci, E.; M.J. Cerejeira; C. Gaggi; G. Chemello; D. Calamari; M. Vighi  (1992)
      Chlorinated Dioxins: Volatilization from Soils and Bioconcentration in Plant Leaves.
      Bull, of Env. Cont.  and Tox. 48(3):401-408.

Bidleman, T.F. (1988)  Atmospheric processes. Wet and dry depostion of  organic
      compounds are controlled by their vapor-particle partitioning.  Environ. Sci. Techol.,
      22:4, pp 361-367.

Briggs, G.A. (1975). Plume rise predictions. In: Lectures on air pollution and environmental
      impact analyses, American Meteorology Society.

Briggs, G.A. (1979). Plume rise. USAEC Critical Review Series.  NTIS publication no. TID-

CARB (1986)  Subroutines for calculating dry depostion velocities using Sehmel's curves.
      Prepared by Bart Croes, California Air Resources Board.

CDEP (1992)   Data on the Connecticut Department of Environmental Protection (CDEP)
      program  to monitor soil, sediment, and fish in the vicinity of Resource Recovery
      Facilities. Data supplied by C. Fredette, CDEP,  165 Capitol Ave, Hartford, CT,

Dumbauld, R.K.; Rafferty, J.E.; Cramer, H.E. (1976)  Dispersion deposition from aerial
      spray releases. Preprint volume for the Third Symposium on Atmospheric Diffusion
      and Air Quality. American Meteorological Society.

Fries, G.F.  1985. Bioavailability of soil-borne polybrominated biphenyls  ingested by farm
      animals.  Journal of Toxicology and Environmental  Health 16: 565-579.

Fries, G.F.;  Paustenbach,  D.J. (1990)  Evaluation of Potential Transmission of 2,3,7,8-
      Tetrachlorodibenzo-p-dioxin-Contaminated Incinerator Emissions to Humans Via
      Foods. J. Toxicol.  Environ. Health 29: 1-43.

Hwang,  S.T.; Falco, J.W.; Nauman, C.H.  (1986)  Development of Advisory Levels for
      Polychlorinated Biphenyls (PCBs) Cleanup.  Exposure Assessment Group, Office of
      Research and Development, U.S. Environmental Protection Agency. EPA/600/6-
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Jury, W.A.; Spencer, W.F.; Farmer, W.J. (1983) Behavior assessment model for trace
      organics in soil I. Model description. Journal of Environmental Quality 4:558-564.

McCrady, J.K.; Maggard, S.P. (1993)  Uptake and photodegradation of 2,3,7,8-
      tetrachlorodibenzo-p-dioxin sorbed to grass foliage. Env. Sci. Technol. 27:343-350.

McCrady, J.K. (1994)  Vapor-phase 2,3,7,8-TCDD sorption to plant foliage - a species
      comparison.  Chemosphere 28(1):207-216.

McLachlan, M.S.; Thoma, H.; Reissinger, M.; Hutzinger, 0.  (1990) PCDD/F in an
      agricultural food  chain. Part  I: PCDD/F mass balance of a lactating cow.
      Chemosphere 20:1013-1020.

Paustenbach, D.; Wenning, R.; Lau, V.; Harrington, N.; Rennix, D.; Parsons, A. (1992)
      Recent developments on hazards posed by 2378-TCDD in soil: Implications for
      setting risk-based cleanup goals at residential and industrial sites. J. Tox. Env.
      Health, 36:103-149.

Radke, L.F.; Hobbs,  P.V.; Eltgroth,  M.W. (1980)  Scavenging of aerosol particles by
      precipitation.  Journal of Applied Meteorology 19:715-722.

Rao, K.S.  (1981) Analytical solutions of a gradient-trasnfer model for plume deposition
      and sedimentation. NOAA Technical memorandum.  ERL ARL-109.

Rao, K.S.; Sutterfield, L. (1982) MPTER-DS.  The MPTER model including deposition and
      sedimentation. U.S. EPA, Research Triangle Part, NC.  EPA 600/8-82/024.

Reed, L.W.; Hunt, G.T.; Maisel, B.E.; Hoyt, M.; Keefe, D.; Hackney, P. (1990)  Baseine
      assessment of PCDDs/PCDFs in the vicinity of the Elk River, Minnesota generating
      station. Chemosphere 21:159-171.

Sehmel, G.A.  (1980) Particle and gas dry depostion: A review. Atmospheric Environ. 14,
      pp 983-1011.

Seinfeld, J.H. (1986) Atmospheric chemistry and physics of  air pollution. New York,
      NY., John Wiley  and Sons.

Turner, D.B. (1986)  Fortran computer code/user's guide for COMPLEX I Version 86064:
      An air  quality dispersion model in section 4. Additional models for regulatory use.
      Source file 31 contained in UNAMAP (VERSION  6). National Techical Information
      Service, Sprinfield, VA. NTIS PB86-222361/AS.

U.S. Department of Agriculture.  (1966) Household food consumption survey 1965-1966.
      Report 12. Food Consumption of households in  the U.S., Seasons and years 1965-
      1966.  United States Department of Agriculture, Washington, D.C.  U.S.
      Government Printing Office.

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U.S. Environmental Protection Agency.  (1984) Ambient water quality criteria document
      for 2,3,7,8-tetrachlorodibenzo-p-dioxin. Office of Water Regulations and Standards,
      Washington, D.C. EPA-440/5-84-007.

U.S. Environmental Protection Agency. (1986). Industrial source complex (ISC) dispersion
      model user's guide-second edition.  Office  of Air Quality Planning and Standards,
      Research Triangle Park, NC,  EPA-450/4-86-005a.

U.S. Environmental Protection Agency.  (1989) Exposure Factors Handbook.  Office of
      Health and  Environmental Assessment. EPA/600/8-89/043.  July, 1989.

U.S. Environmental Protection Agency.  (1990a)  Lake Ontario TCDD Bioaccumulation
      Study Final Report.  Cooperative study including US EPA, New York State
      Department of Environmental Conservation,  New York State Department of Health,
      and Occidental Chemical Corporation.  May, 1990.

U.S. Environmental Protection Agency.  (1990b)  Assessment of Risks from Exposure of
      Humans, Terrestrial and Avian Wildlife, and Aquatic Life to Dioxins and Furans from
      Disposal and Use of Sludge from Bleached Kraft and Sulfite Pulp and Paper Mills.
      Office of Toxic Substances and Office of Solid Waste, EPA 560/5-90-013.  July,

U.S. Environmental Protection Agency.  (1990c)  USEPA/Paper Industry Cooperative
      Dioxin Study  "The 104 Mill Study" Summary Report and USEPA/Paper Industry
      Cooperative Dioxin Study "The 104 Mill Study" Statistical Findings and Analyses
      Office of Water Regulations  and Standards, July 13, 1990.

U.S. Environmental Protection Agency.  (1990d)  Methodology for Assessing Health Risks
      Associated  with Indirect Exposure to Combustor Emissions.  Interim Final Office of
      Health and  Environmental Assessment. EPA/600/6-90/003.  January, 1990.

U.S. Environmental Protection Agency.  (1991) A Methodology  for Estimating Population
      Exposures from the Consumption of Chemically Contaminated Fish. Prepared by
      Tetra Tech, Inc., Fairfax VA. for Office of Policy, Planning, and Evaluation and
      Office of Research and Development, US EPA.  EPA/600/9-91/017.

U.S. Environmental Protection Agency.  (1992a)  Guidelines for exposure  assessment.
      Office of Health and Environmental Assessment, Washington, DC.  EPA/600-Z-
      92/001.  published in Federal Register, May 29, 1992, p. 22888-22938.

U.S. Environmental Protection Agency.  (1992b)  National Study of Chemical Residues in
      Fish. Volumes I and II.  Office of Science and Technology EPA 823-R-92-008a &
      008b.  September, 1992.
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U.S. Environmental Protection Agency.  (1992c)  Dermal Exposure Assessment:  Principals
      and Applications.  Office of Health and Environmental Assessment. EPA/600/8-

U.S. Environmental Protection Agency.  (1993)  Interim  Report on Data and Methods for
      Assessment of 2,3,7,8-Tetrachlorodibenzo-p-dioxin Risks to Aquatic Life and
      Associated Wildlife.  Office of Research and Development, Environmental Research
      Laboratory at Duluth, MN.  EPA/600/R-93/055. March, 1993.
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      Although the dioxin-like compounds have probably been studied more than any
other set of organic compounds in the environmental field, numerous data gaps remain.
Basic questions such as what sources contribute most to human body burdens are still
unanswered.  This section summarizes the research needs  for exposure to dioxin-like

      Research on how CDD/F is formed  provides a seminal basis for understanding
CDD/F sources. Three basic theories on the formation and emission of CDD/Fs during the
combustion of chlorine-bearing wastes and fuels have been advanced by research in the
international  scientific community and are summarized in Volume II, Chapter 3, Section
3.5.  Scientific knowledge on the mechanisms  of formation of  CDD/F within combustion
processes can help to provide answers in a number of important areas, including:

      -  identification  of unknown combustion sources that have yet to be tested
      for emissions.
      -  identification  of process  changes and operating practices that will prevent
      the formation of CDD/Fs in various combustion sources.
      -  help with development of engineering controls to reduce CDD/F emissions
      at known combustion sources.

      Further research recommendations  relating to sources are outlined  below.

• Combustion Source Testing:   For purposes of setting priorities on research to  better
characterize combustion sources, consideration must be given to the estimated size of the
source on an individual and collective basis and level of confidence in current estimates.
This analysis, given in Table IV-1, suggests that the following source categories are high
priority for further testing:  1) medical waste incinerators, 2) cement kilns, 3) industrial

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Table IV-1.  Analysis of air emission sources.
Facility Type
Medical Waste
Municipal Waste
Cement Kilns
Industrial Wood Burners
Secondary Metal
Primary Metals
Forest Fires
Diesel Vehicles
Residential Wood
Hazardous Waste
Sewage Sludge
Coal Fired Power Plants
Magnitude of Release
(collectively and per
Collectively high,
individually small
Collectively high,
individually variable
Collectively high,
individually high for
facilities burning
hazardous waste
Collectively high,
individually variable
Lead and Copper appear
low to moderate.
Aluminum, Magnesium,
ferrous unknown
Unknown, some
European testing
indicates could be high
Moderate to High
Collectively moderate,
individually small
Collectively moderate,
individually small
Collectively moderate,
individually small
Uncertainty in
Emission Estimate
High, 6 of 6,700
facilities tested
Medium, 30 of
171 facilities
High, 17 of 212
kilns tested
High, 2 facilities
tested of an
unknown total
Medium, 1 of 24
copper smelters
tested, 3 of 23
lead smelters
High, no U.S. tests
High, no direct
High, 2 widely
divergent studies,
no U.S. tests
Medium, 2 recent
High, 6 of 190
facilities tested,
variable feed
Medium, 3 of 199
facilities tested
High, no recent
tests completed
Overall Priority For Further
Medium, many facilities
tested and new tests already
Medium for Pb and Cu, high
for ferrous, Al, and Mg
High for Al, Mg, Cu, Fe
Depends on results of tests
now underway

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wood burners, 4) primary metals industry (aluminum, magnesium, iron, copper) and
secondary metals industry (aluminum, magnesium, steel) and 5) diesel engine exhaust. For
each of these source categories, a field survey is needed involving emissions testing at
selected facilities.  In planning such a survey, consideration must be given to statistical
issues, cost issues, sample collection/analysis, and similar issues.
• Unknown Sources: As discussed earlier in this document, several investigators have
speculated that the identification of CDD/F sources may be incomplete on the  basis of
mass balance analyses comparing emissions to deposition.  It is not clear whether this
type of mass  balance can ever be refined to  the point where definitive conclusions can be
drawn. However, it remains one of the few  methods of evaluating the possibility that
unknown sources exist.  Thus, research is needed to refine both emission and  deposition
estimates.  Research to better characterize known sources is discussed  above.
Deposition estimates can be  improved via a combination of further field  measurements and
modeling.   Industrial sectors which are likely candidates for dioxin emissions can be
identified from knowledge about industrial processes, feed materials and theories on
• Emissions Monitoring:  Currently the monitoring of CDD/Fs  in stack gas emissions from
combustion sources cannot be conducted  continuously or on a real-time basis. The test
method (EPA  Method 23) requires sampling in the stack for 5  or more hours, and several
weeks or months lead time in developing laboratory results of the sample. This situation
raises concerns about the representativeness of the sample and about the inability to
detect variability in emissions.   From a public health perspective, a method  of continually
and instantaneously measuring emissions would be desirable.  This  situation suggests two
areas of research. The first area  would be  to develop CDD/F stack measurement/laboratory
techniques which provide quicker results. The second area would be to  identify an easily
monitored combustion parameter that strongly correlates with the magnitude of dioxin
emissions. Such parameters  may be measured inside or outside the furnace, and may
include: temperature, carbon dioxide, carbon monoxide,  oxygen,  total hydrocarbons, and
• Emission Controls:  Engineering research is needed to develop process changes or
emission controls which reduce  dioxin emissions.  For example, pollution prevention
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research is needed to determine if dioxin releases can be reduced via reductions in chlorine
content of feed material, changes in operating temperatures or other techniques.
• Combustor Ash and Scrubber Residues:  Municipal waste combustor ash and cement
kiln dust/clinker have been tested for CDD/F content. Ash from other combustor types
such as coal utilities and medical waste combustors have not  been tested.  No data was
found on CDD/F levels in effluent from scrubbers.  Research is needed on the levels of
CDD/F in these materials and the potential for their release to  the environment.
• Source-Receptor Relations:   Studies are also needed to evaluate whether CDD/F sources
contribute to human exposure in proportion to their overall contribution to environmental
loading, or  whether some sources contribute disproportionally to general population
exposure.   For example, it has been speculated that diesel exhaust emissions which occur
as extensive line sources at ground level may cause higher exposure (per unit emission)
than stack emissions from stationary sources (Jones, 1993).  One way to  link sources to
receptors is on the basis of congener profiles.  Each combustion source technology may
routinely emit a distinctive  pattern of CDD/F congeners.  This  has  been referred to as a
congener profile, and could provide a means whereby emissions from a variety of
combustion sources can be distinguished from one another.  Thus research is needed to
determine whether distinctive congener profiles can be developed  for various sources.
•  Non-Combustion Sources:  The above discussion has focused on combustion sources.
It is important, however, to study non-combustion sources. Relatively little effort has
been spent characterizing non-combustion sources (one notable exception is the pulp and
paper industry). Similarly, little information has been collected on  CDD/F levels in  most
products other than paper.  In general this research should parallel the areas identified
above for combustors, i.e. formation, source testing, identification of unknown sources,
monitoring, controls, process residues/wastes and source-receptor relationships.   This
research should focus on the following non-combustion sources:
      - Chlorophenol production:  The two compounds in this class historically of
      concern are pentachlorophenol (PCP) and trichlorophenol. Although, production and
      use of these compounds are now limited, new testing is needed of products and
      waste  streams to confirm  CDD/F levels.
      - Chlorobenzene production:  Studies in Germany have measured the
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      presence of CDD/Fs in these compounds. No United States data could be
      - Aliphatic chlorine production:  CDD/Fs can be released during the
      production of vinyl chloride, however the size of these emissions have not
      been independently confirmed.  As discussed earlier in this document,
      Greenpeace has suggested that such releases could be large and the vinyl
      chloride industry have strongly disputed  these claims. The Greenpeace
      estimates are based on information about European plants.  No data from
      the United States could be found.
      - Pesticide production:   EPA has sponsored data call-ins which has provided some
      assurance that many pesticides have low CDD/F levels.  Not all requested data has
      been received, however, and  independent testing of products  and waste streams
      may be needed to confirm levels.
      - Sewage treatment: Effluent and sludge from sewage treatment plants
      have been shown to contain CDD/F residues. More research is needed
      characterizing these levels and studying  formation mechanisms/controls.
• Reservoir Sources:  Rerelease of CDD/F from  reservoir sources could occur by dust
resuspension, erosion, volatilization, etc. The impact of these reservoir emissions
compared to current emissions on the human food chain is unknown.  Research is needed
to evaluate the magnitude of these releases and their impact on the food chain.

      Understanding the environmental fate of CDD/Fs is central to  evaluating  human
exposure.  Empirical measurements of inter-media transfers, environmental
degradation/clearance rates, and bioaccumulation are fundamental to designing
mathematical models that simulate these events.  Environmental fate models are a
valuable tool for evaluating impacts from specific sources and evaluating the
proportionality between magnitude of emissions and subsequent exposures. Although
much is known  about environmental fate and transport of CDD/Fs, a number of issues
remain that require  further research.  Key areas include:

                          DRAFT-DO NOT QUOTE OR CITE
 • Environmental Monitoring:  Knowledge of environmental levels is fundamental to
understanding how CDD/Fs behave in the environment.  More data is needed on CDD/F
levels in air, wet/dry deposition, sediments, soils, plants  and animals. As discussed below,
this information can be used to improve model formulation, parameter assignments and
model validation.
• Vapor/Particulate Partitioning:  The modeling analysis  of Volume III concluded that the
transfer of dioxin-like compounds to vegetation which  animals consume was the principal
cause for terrestrial animal food chain impact.  Thus, a better understanding of the extent
to which these compounds partition between vapor and  particle phases in ambient air in
rural and urban environments is important.  A second issue is whether this  partitioning  is
different for stack  emissions versus volatilized residues from soil.  While the volatiles are
initially in the vapor form, do they remain as such or do they sorb to  airborne particles?
• Vapor Transfers to Vegetation:  As noted above, vapor transfers to vegetation largely
explain terrestrial food chain impact.  Further research is  needed to refine the algorithms
presented in this document, with particular attention paid to: differences in transfer rates
among different  congeners, the potential for photodegradation when sorbed onto
vegetative surfaces, and the impacts of shifting wind patterns, variable  crop densities,
sunlight conditions, and other real world conditions.
• Photodegradation/Transformations  of Vapor-Phase Dioxins:  Some studies have
suggested that photodegradation of dioxin-like compounds  may occur under natural
conditions. This process is not expected to occur for sorbed dioxins, and there is very
limited data on photodegradation of dioxins while airborne in the vapor-phase.  Laboratory
studies have demonstrated that CDD/Fs undergo photolysis, typically following first order
kinetics, in the presence of a suitable hydrogen donor such as oil or an organic solvent.
Study results, when extrapolated to environmental conditions, indicate half-lives ranging
from hours to  days.  There is some evidence of reductive dechlorination, or the
transformation of dioxins of higher chlorine content to dioxins of lower chlorine content.
This suggests  the possibility that photodegradation can be both a destruction and a
formation  mechanism.  In general, it was decided that these processes are  not sufficiently
well understood  to explicitly incorporate into the procedures of this document.  The
procedures in Volume III assume no degradation of vapor-phase dioxins  during transport
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from stacks.  Photodegradation is partially accounted for in the transfer of vapor-phase
dioxins to vegetations in the air-to-leaf transfer factor, Bvpa.  The assignment of values for
this parameter is based on the air-to-leaf experiments of Bacci,  et al. (1990; 1992), with
an empirical adjustment developed from the experiments of McCrady and Maggard (1993),
who measured the impact of photodegradation in the transfer of vapor phase 2,3,7,8-
TCDD to grass leaves.  In summary, research is needed which  provides 1)
photodegradation rate constants for these compounds in the air and on plant surfaces, 2)
information on the formation products of  photodegradation of dioxins in air and on plant
surfaces, and 3) procedures to incorporate this knowledge into  fate models.  It is important
that this research be conducted in ways that convincingly simulate real world conditions
and hence provide practical results for incoroprating  into fate models.
• Soil Volatilization and Dispersion:   The models for soil volatilization and subsequent
dispersion to estimate air concentrations for food chain modeling and inhalation exposures
have not been verified. Some empirical evidence described in Volume III suggest that
these algorithms may be underestimating  air concentrations  of dioxin-like compounds (see
also the entry titled, "Predicted vs. observed  air concentrations" in Table III-5 of this
• Soil Dissipation Rates:  A soil dissipation rate of 0.0693 yr"1, corresponding to a 10-
year half-life, is assumed for all dioxin-like compounds delivered to an exposure site as
deposited particles from a stack emission source, or  as delivered via erosion from a site of
soil contamination.  Some empirical evidence described in Volume III suggests that
delivered contaminants may be more persistent and that this is  a low half-life (see also the
entry titled, "Predicted  vs. observed beef concentrations" in Table III-5 of this Volume).
Further evaluation of this dissipation assumption is recommended.
• Overland Transport Mechanisms:  The  process of  soil erosion was assumed to transport
soil-bound residues from a site of contamination to a site of exposure.  Soil erosion was
also assumed to transport residues bound to  watershed soils to surface water bodies.
Other mechanisms of soil-bound transport were not modeled, such as wind erosion
followed  by deposition. Two factors that were modeled but are uncertain is the sediment
delivery ratio, which reduced potential erosion based on the  deposition of eroded particles
prior to their destination, and the enrichment ratio, which increased the concentration of
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dioxins on eroded soil based on the assumption that eroded materials are finer and higher
in organic matter as compared to in-situ soil.
• Water Body Processes:  Because of their affinity for  organic carbon, the fate and
transport of dioxin-like compounds in water bodies is likely to be more a function of
sediment-related processes rather than water-related processes.  Key sediment processes
in water bodies include:  sorption/desorption, importance and prevalence of dissolved
organic materials in the water column, deposition/suspension/resuspension, and
downstream sediment transport.  Although procedures  for sediment modeling in surface
water bodies  is presented in the exposure document, the models are fairly  simplistic and
more development is recommended, especially for evaluating point source discharges.
• Ground Water:   The occurrence of these compounds in ground water is  expected  to be
minimal,  based  on  strong sorption to soils. Ground water impacts were not assessed in
this document.  Dioxin-like compounds, particularly PCBs, have been found, however, in
ground water below and near sites of industrial contamination.  Co-occurrence with  other
organic compounds, co-occurrence with solvents, and transport associated with oils have
been cited as causes of enhanced mobility in these settings.  The possibility that dioxins
may impact ground water in certain circumstances should be evaluated further.
• Beef Food Chain Modeling:  This document proposes the hypothesis that the air-to-food
pathway  is the  principal mechanism by which dioxin-like compounds enter  the food chain.
The air-to-beef model developed in this assessment is examined in Chapter 7 of  Volume III
with a validation exercise which provides  preliminary evidence that it will predict beef
concentrations that are consistent with observations (see also the entry titled, "Predicted
vs. observed  beef concentrations" in Table 111-5 of this  Volume).  Given the importance of
this pathway, however, further validation  work is recommended.  More information is
needed on several  of the components of the model to estimate beef and milk
concentrations. Such information includes: cattle soil ingestion rates, pasture grass
concentrations and mechanisms of transfer from the air/soil to pasture grass (and other
feeds such as corn, hay, etc), the impact of cattle production practices to cattle food
product concentrations, models and data to further develop the bioconcentration factor
(termed BCF in  exposure document) and assessment of differences in bioavailability
between  soil and vegetative intakes.
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• Bioaccumulation in Fish:  Several approaches have been suggested for estimating
uptake in fish. The approach in this assessment is based on the organic carbon normalized
concentration in water body sediments. One parameter used is termed the Biota to
Sediment Accumulation Factor, or BSAF. This is defined as the ratio of the concentration
in fish lipids to the organic carbon normalized concentration in bottom sediments. The
BSAF represents uptake by all mechanisms.  Another sediment-based parameter used in
this assessment is the BSSAF, or the Biota Suspended Sediment Accumulation Factor.
This is defined similarly to the BSAF, except it is based on the organic carbon normalized
concentration in suspended sediments.  Other parameters that have been used include the
Bioconcentration Factor, or BCF, which is based on ratios between levels in fish to levels
in water and represents only uptake from water, and the Bioaccumulation  Factor, or BAF,
which is based on ratios between levels in fish and water and representing uptake by all
mechanisms.  Further research is needed to develop congener specific values for these
factors, develop procedures explaining  how to apply these factors and to validate these
procedures with field data. A key issue that has been identified is whether BSAFs that
have been developed for one species and water body are generalizable to another species
and another water body.  This question will be difficult to answer because of the several
uncertainties associated with BSAF development:  fish migratory patterns,  variability in fish
lipid content and other differences within and between species, study design with regard
to fish and sediment  sampling, ecosystem differences, and so on.  However, after careful
examination of existing data sets and considering  key differences between species
(invertebrates vs.  vertebrates, fresh water vs. salt water, bottom feeders vs. water column
feeders, etc.), it may be possible to develop  a workable system for BSAF assignment
based on key considerations.
• Other Food Products: This document did not present site-specific assessment
procedures to evaluate all terrestrial exposure pathways.  For example, models are not
presented to estimate concentrations in such products as eggs, chicken, and pork. Further
research is needed to develop these procedures.

       Chemical specific inputs are needed for all  fate models and can contribute as much
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uncertainty to impact estimates as the conceptual formulation of the model itself.
Throughout the exposure document, the lack of congener-specific data is cited as a major
source of uncertainty.  For example, congener-specific data is lacking for basic chemical
properties such as octanol-water partition coefficients, degradation rates, and vapor
pressures.  Also, data is lacking for estimation of congener-specific incinerator emission
factors, metabolic rate constants, and bioavailability and biotransfer factors. Thus,
gathering more data on congener-specific properties is a high priority for further research.

       Key areas for exposure research are  outlined below.

• Levels in Food Products: This report estimates that about 90% of human exposure to
CDD/Fs occurs via food ingestion.  Research is needed to determine associations between
levels in food to sources and agricultural practices. Data are severely lacking on
concentrations in foods identified as critical - beef, milk, other dairy products, eggs, pork,
poultry and marine fish.  Thus, future exposure research should emphasize issues related
to levels in animal  product foods.  Key questions for further research include:

1)  What are representative concentrations of dioxin-like compounds in these food
2)  Are there regional differences in the level of food contamination? Can these be
correlated to local sources or animal raising practices?
3)  Are there differences in  body burden between: range-fed and feedlot cattle, free
ranging or caged chickens, or other alternate practices for other animals?
4)  What is the immediate source of animal contamination?
       - CDD/F incorporated within grains or other feeds
       - surface contamination on grasses and other feeds
       - contaminated dirt on grasses and other feeds
       - dirt eaten by animals while  grazing
       - food additives
       - other chemicals associated with animals or crops
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5)  Are there any significant opportunities to reduce exposure to animals by changing
feeding practices?

• Other Products:  This document presents data showing that, in some circumstances,
dioxin can migrate  into food from paper products such as milk containers.  The paper
industry has presented data indicating that recent reductions in dioxin levels in bleached
pulp suggest that such migration is minimal.  Independent testing of paper products used
in food packaging is needed to confirm these claims.
       Researchers in  Germany (Horstmann and  McLachlan, 1994) have found that some
textiles contain high levels of CDD/Fs and that they can be  transferred from the textiles to
human skin.  The researchers  speculated  that the source of these dioxins was
pentachlorophenol  preservatives used on cotton  during sea  transport.  More research is
needed on the levels of CDD/Fs in textiles, the sources of contamination and their potential
for human exposure.
• Highly Exposed Populations:  This document reports that  CDD/Fs have been measured in
human breast milk  and could contribute a  significant portion of a person's body burden.
Key questions to address in future research in this area include:

1) What is the relative rates of exposure for nursing infants from breast feeding versus
formula feeding?
2) Is there much variation in CDD/F levels for mother's milk and if so, do these variations
correlate with  any  observable factors?
3) Is there anything nursing mothers or women  of child-bearing age can do to reduce
exposure to their children?

       Other subpopulations, such as subsistence fishers and farmers, have been identified
as potentially highly exposed.  More research is needed to identify these groups and
determine their level of exposure.  Finally, studies should also be conducted examine
whether socio-economic factors can influence dioxin exposure.
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      The use of pharmacokinetics in body burden analysis has shown great potential for
estimating exposure levels.  In order to reduce the uncertainty in these procedures,
increased collection of biological samples and improvements in PK model structure and
input parameters are recommended.  In addition, further research should be conducted on
the application of these procedures to estimating target organ dose, absorbed dose,
lactational/placental transfers, and effects on offspring.

      This document does  present some information on the chemical/physical properties
of some coplanar PCBs, brief qualitative information on possible sources, some information
on environmental occurrence levels, and nothing on background exposures.  The fate and
transport models presented  in the document would be generally applicable to these
compounds, but  the chemical specific inputs need further development.
      The available information does suggest that total  PCB levels are commonly much
higher in soils and sediments than the other dioxin-like compounds. Most environmental
data are reported as total PCBs or as an Aroclor mixture.  Since congener specific data are
largely unavailable, it is not  clear what portion of these PCBs are coplanar.  Congener
specific  sampling and analysis protocols need to be evaluated.  Also, there is not yet a
concurrence on Toxicity Equivalency Factors (TEF) schemes, so even if estimates of
concentrations of coplanar PCB were made, it is not yet clear how to convert these to a
2,3,7,8-TCDD comparable basis. Thus the first goal of this research would be to derive
preliminary estimates of what portion  of the total PCBs present in the environment are the
coplanar congeners. This would involve reviewing the limited congener specific data that
is currently available and evaluating how representative it may be of PCBs in other
locations.  The various TEF schemes that have been proposed  could be used to further
assess the potential importance of these compounds.  The next logical  step would be to
conduct a large sampling and analysis program to confirm the levels of  these compounds
in the environment.  As TEF schemes  are refined they should be incorporated into this
      Other research questions  specific to PCBs include:
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1)  Are there any current sources releasing coplanar PCBs to the environment?  Under
what conditions are coplanar PCBs formed in industrial and combustion processes? What
are the emission factors are what are the locations for major sources?
2)  What are the background exposure levels to these compounds? Evaluation could be
done using both a forward analysis, starting with diet information, and in a reconstructive
manner, starting with body burdens.
3)  How persistent are the coplanar PCBs relative to the other PCBs?
4)  Is most of the body burden derived from "old PCBs" recirculating around in the
environment or is current  and future body burden significantly effected by more recently
released materials?
5)  What is the relative contribution of controlled large sources (HD electrical equipment)
versus the more uncontrolled dispersed small sources such as small capacitors and
fluorescent light ballasts?
6)  Are the pathways  of exposure for dioxin-like PCBs different than for CDD/Fs?
7)  Do PCB sources contribute to human exposure proportional to the overall contribution
to environmental loading,  or do some sources contribute disproportionally to general
population exposure?

       Considerable uncertainty remains concerning the health effects of these compounds
as well as basic exposure issues such as environmental occurrence, background exposure
levels, chemical/physical properties, and sources.  Other than some discussion on
chemical/physical properties, these compounds are not addressed in the current document.
The fate and transport models presented in the document would be generally applicable to
these compounds, but the chemical specific inputs would need further development.  No
TEF schemes have been published or adopted for these compounds. As with the coplanar
PCBs, the first goal of the research in this area would be to estimate the levels of these
compounds in the environment and human body burdens.  This estimate should initially be
attempted on basis of  existing data, but very likely a sampling and  analysis  program will be
needed to collect sufficient data for even initial estimates.  Congener specific sampling and
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analysis protocols need to be evaluated.  The next steps would be to identify/evaluate
sources and pathways of exposure and to estimate background exposure levels.

      This document presents environmental and human body burden data showing that
the dioxin-like compounds are found all around the world.  Atmospheric deposition has
been measured in remote locations such as the Arctic indicating that long range transport
of these compounds occur. It is important to better understand the geographic extent of
exposure to these compounds and how far impacts from particular sources may spread.
Thus, further research is needed to compare local, regional and global impacts.
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 Bacci, E.; Calamari, D.; Gaggi, C.; Vighi, M. (1990)  Bioconcentration of Organic Chemical
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 Bacci, E.; M.J. Cerejeira; C. Gaggi; G. Chemello; D. Calamari; M. Vighi  (1992)
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 Horstmann, M.;  McLachlan, M.S.  (1994) Textiles as a source of polychlorinated dibenzo-
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 Jones, K.  (1993)  Diesel truck emissions, an unrecognized source of CDD/CDF exposure
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 McCrady, J.K.; Maggard, S.P. (1993)  Uptake and photodegradation of 2,3,7,8-
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*U.S. GOVERNMENT PRINTING OFFICE: 1994-550-001/00153     112                                   4/94