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EPA/600/R-06/044F | September 2008 An Exploratory Study: Assessment of Modeled Dioxin Ex
EPA/600/R-06/044F

September 2008

An Exploratory Study: Assessment of Modeled Dioxin 

Exposure in Ceramic Art Studios

National Center for Environmental Assessment

Office of Research and Development

U.S. Environmental Protection Agency

Washington, DC 20460
ii

DISCLAIMER

This document has been reviewed in accordance with U.S. Environmental Protection 

Agency policy and approved for publication. Mention of trade names or commercial products 

does not constitute endorsement or recommendation for use.

ABSTRACT

The purpose of this report is to describe an exploratory investigation of potential dioxin 

exposures to artists/hobbyists who use ball clay to make pottery and related products. Dermal, 

inhalation and ingestion exposures to clay were measured at the ceramics art department of Ohio 

State University in Columbus, OH. The measurements were made in two separate studies: one 

in April 2003 and one in July 2004. This assessment combines the results of these two studies. 

Estimates of exposure were made based on measured levels of clay in the studio air, deposited on 

media representing food and on the skin of artists. Dioxin levels in the clay were based on levels 

reported in the literature for commercial ball clays commonly used by ceramic artists. 

Hypothetical dioxin dose estimates were calculated for each subject assuming that all 

used a 20% ball clay blend with 162 pg TEQ/g. The single-day total doses across the 10 subjects 

ranged from 0.32 to 7.1 pg TEQ/d, with an average of 1.44 pg TEQ/d (SD = 2.0). The dermal 

pathway was the major contributor to total dose, exceeding 67% for all subjects. A Monte Carlo 

simulation was conducted to explore how doses could vary in a broad population of artists. This 

simulation suggested a mean total dose of 6.4 pg TEQ/d (SD = 8.4), median of 3.5 pg TEQ/d, 

and 90th percentile of 14.8 pg TEQ/d. 

Preferred Citation:

U.S. Environmental Protection Agency (EPA). (2008) An exploratory study: Assessment of modeled dioxin 

exposure in ceramic art studios. National Center for Environmental Assessment, Washington, DC;

EPA/600/R-06/044F. Available from the National Technical Information Service, Springfield, VA, and online at 

http://www.epa.gov/ncea.
iii

CONTENTS

LIST OF TABLES.......................................................................................................................... v

LIST OF FIGURES ....................................................................................................................... vi

LIST OF ABBREVIATIONS AND ACRONYMS ..................................................................... vii

PREFACE...................................................................................................................................... ix

AUTHORS, CONTRIBUTORS, AND REVIEWERS .................................................................. x

ACKNOWLEDGMENTS ............................................................................................................. xi

1. INTRODUCTION AND BACKGROUND .............................................................................. 1

2. APPROACH OVERVIEW........................................................................................................ 5

2.1. GENERAL STRATEGY.................................................................................................. 5

2.2. CHARACTERIZATION PROCEDURES ....................................................................... 6

2.2.1. Dermal Contact...................................................................................................... 6

2.2.2. Inhalation............................................................................................................... 6

2.2.3. Ingestion ................................................................................................................ 7

3. SAMPLING METHODS........................................................................................................... 8

3.1. SAMPLE COLLECTION................................................................................................. 8

3.1.1. Personal Air Sampling........................................................................................... 8

3.1.2. Area Air Sampling................................................................................................. 9

3.1.3. Skin Sampling ..................................................................................................... 10

3.1.3.1. April 2003............................................................................................... 10

3.1.3.2. July 2004 ................................................................................................ 11

3.1.4. Surface Wipe Sampling....................................................................................... 11

3.1.5. Surrogate Food and Beverage ............................................................................. 12

3.2. SAMPLE PREPARATION AND ANALYSIS.............................................................. 12

3.2.1. Filtration and Drying........................................................................................... 12

3.2.2. Gravimetric Analysis........................................................................................... 13

3.2.3. Quality Control Samples..................................................................................... 13

4. DIOXIN CONTENT OF CLAY AND STUDIO RESIDUES ................................................ 15

5. DOSE ESTIMATION PROCEDURES................................................................................... 21

5.1. DERMAL CONTACT.................................................................................................... 21

5.1.1. Estimating Particle Loading on Skin................................................................... 21

5.1.2. Estimating Monolayer Load................................................................................ 21

5.1.3. Estimating Fraction Absorbed............................................................................. 23

5.1.4. Calculating Dermal Dose .................................................................................... 25

5.2. INHALATION................................................................................................................ 26

5.3. INGESTION ................................................................................................................... 27

5.4. TOTAL DOSE................................................................................................................ 27

6. QUESTIONNAIRE RESULTS............................................................................................... 28

7. COMPARING EXPOSURES ACROSS SUBJECTS............................................................. 30
iv

7.1. DERMAL CONTACT.................................................................................................... 31

7.1.1. Clay Loads on Surfaces....................................................................................... 36

7.1.2. Dermatologist Report .......................................................................................... 37

7.2. INHALATION................................................................................................................ 37

7.2.1. Particle Levels in Air........................................................................................... 37

7.2.2. Inhalation Dose.................................................................................................... 41

7.2.3. Classroom Exposure............................................................................................ 42

7.3. INGESTION ................................................................................................................... 42

7.4. TOTAL DOSE................................................................................................................ 42

8. MONTE CARLO SIMULATION OF THE EXPOSURE DATA .......................................... 47

9. UNCERTAINTY ..................................................................................................................... 57

9.1 GENERAL UNCERTAINTY ISSUES ........................................................................... 57

9.2. DERMAL EXPOSURE UNCERTAINTIES ................................................................. 57

9.2.1. Absorption Fraction............................................................................................. 57

9.2.2. Monolayer ........................................................................................................... 60

9.2.3. Exposure Under Clothing.................................................................................... 60

9.3. INHALATION UNCERTAINTIES ............................................................................... 61

9.4. INGESTION UNCERTAINTIES................................................................................... 63

10. CONCLUSIONS.................................................................................................................... 65

REFERENCES ............................................................................................................................. 67

APPENDIX A: SUBJECT QUESTIONNAIRE RESULTS ..................................................... A-1

APPENDIX B: EVALUATION OF CLAY DUST MODELING .............................................B-1

APPENDIX C: SEM AND EDS DATA BY SUBJECT............................................................C-1

APPENDIX D: ALTERNATIVE METHOD FOR ESTIMATING DERMAL 

ABSORPTION.................................................................................................. D-1

APPENDIX E: SKIN RINSING DATA ....................................................................................E-1

APPENDIX F: PICTURES OF ARTISANS PRIOR TO SKIN RINSE

PROCEDURE...................................................................................................F-1

APPENDIX G: REAL-TIME PARTICLE CONCENTRATION DATA................................. G-1

APPENDIX H: RESPICON

TM

, CASCADE IMPACTOR, PDR-1000, CLIMET®

DATA FOR EACH INDIVIDUAL SUBJECT............................................... H-1

APPENDIX I: MONTE CARLO CALCULATION OUTLINE.................................................I-1

APPENDIX J: MONTE CARLO SIMULATION RESULT GRAPHICS..................................J-1
v 

LIST OF TABLES

Table 1. Raw ball clay dioxin concentrations.............................................................................. 16

Table 2. Processed ball clay dioxin concentrations (pg/g) .......................................................... 17

Table 3. Percentage ball clay in the clay mixtures used during this study .................................. 18

Table 4. Particle size distribution of Tennessee ball clay............................................................ 22

Table 5. Percent absorbed over time............................................................................................ 23

Table 6. Questionnaire questions on duration and frequency of subject’s clay work ................. 28

Table 7. Questionnaire questions about clay work ...................................................................... 29

Table 8. Artisan activities of each subject ................................................................................... 32

Table 9. Hypothetical estimates of dermal dose .......................................................................... 33

Table 10. Percent contribution to dermal dose by body part ....................................................... 35

Table 11. Comparing clay loads on surfaces to clay loads on hands........................................... 36

Table 12. Particle concentrations in air and mass median aerodynamic diameter

(MMAD) based on cascade impactor ...........................................................................38

Table 13. Hypothetical estimates of inhalation dose ................................................................... 41

Table 14. Clay deposition and hypothetical estimates of ingestion dose .................................... 43

Table 15. Hypothetical estimates of total dioxin dose (pg TEQ/d) ............................................. 44

Table 16. Percent contribution to total dioxin dose ..................................................................... 45

Table 17. Dose estimates by activity ........................................................................................... 46

Table 18. Monte Carlo simulation input parameters and sampling distributions........................ 48

Table 19. Clothing scenarios based on questionnaire responses ................................................. 50

Table 20. Descriptive statistics of dioxin doses from ball clay use, based on a Monte Carlo 

simulation ..................................................................................................................... 51

Table 21. Physical properties of dioxin congeners and concentration in processed clay ............ 59

Table 22. Exposure under clothing .............................................................................................. 62
vi 

LIST OF FIGURES

Figure 1. Conceptual diagram.........................................................................................................3

Figure 2. Scanning electron microscopy (SEM) and energy dispersive spectroscopy 

(EDS) data......................................................................................................................20

Figure 3. Scatter plot of adjusted absorption data versus time with trend line.............................25

Figure 4. Real-time particle concentration for Subject 3 using the CI-500 particle

counter. ..........................................................................................................................39

Figure 5. Sculpture Session 1 with dog present............................................................................40

Figure 6. Sculpture Session 2 with dog present............................................................................40

Figure 7. Frequency distribution of total dose (pg TEQ/d) based on Monte Carlo 

simulation.......................................................................................................................51

Figure 8. Cumulative probability distribution of total dose (pg TEQ/d) based on Monte 

Carlo simulation.............................................................................................................52

Figure 9. Sensitivity analysis based on percent contribution to variance for total dose...............53

Figure 10. Sensitivity analysis based on percent contribution to variance for dermal dose.........54

Figure 11. Sensitivity analysis based on percent contribution to variance for ingestion

dose..............................................................................................................................55

Figure 12. Sensitivity analysis based on percent contribution to variance for inhalation 

dose..............................................................................................................................56
vii 

LIST OF ABBREVIATIONS AND ACRONYMS 

ACGIH American Conference of Governmental Industrial Hygienists 

 ̊C degrees Centigrade 

CDD chlorinated dibenzo-p-dioxin 

CDD/F chlorinated dibenzo-p-dioxin and chlorinated dibenzofurans 

CDF chlorinated dibenzofuran 

cm centimeter 

DI deionized 

EDS energy dispersive spectroscopy 

ET extrathoracic 

g gram 

GFF glass fiber filters 

HpCDD heptachlorodibenzo-p-dioxin 

Hz hertz 

HxCDD hexachlorodibenzo-p-dioxin 

ICRP International Commission on Radiological Protection 

IRB Institutional Review Board 

kg kilogram 

Kow octanol-water partition coefficient 

L liter 

LRB laboratory record book 

m meter 

mg milligram 

mL milliliter 

mm millimeter 

MMAD mass median aerodynamic diameter 

MPPD Multiple Path Particle Dosimetry 

MSS model sum of squares 

NA not available 

NIST National Institute of Standards and Technology 
viii 

LIST OF ABBREVIATIONS AND ACRONYMS (continued)

NM not measured 

OCDD octachlorodibenzo-p-dioxin 

OSHA Occupational Safety and Health Administration 

OSU Ohio State University 

PCB polychlorobiphenyls 

PCDD polychlorinated dibenzo-p-dioxin 

PeCDD pentachlorodibenzo-p-dioxin 

pg pictogram 

ppt parts per thousand 

PU pulmonary 

2

r regression coefficient squared 

RIVM National Institute of Public Health and the Environment 

RSS residual sum of squares 

SD standard deviation 

SEM scanning electron microscopy 

TB tracheobronchial 

TCDD tetrachlorodibenzo-p-dioxin 

TEF toxic equivalency factor 

TEQ toxic equivalent 

TSS total corrected sum of squares 

TWA time-weighted average 

UMDES University of Michigan Dioxin Exposure Study 

U.S. EPA United States Environmental Protection Agency 

WHO World Health Organization 

μg microgram 

μm micrometer 
ix

PREFACE

Dioxins were discovered in ball clay in 1996 as a result of an investigation to 

determine the sources of elevated dioxin levels in two chicken samples from a national survey of 

poultry. The investigation indicated that the contamination source was ball clay added to 

chicken meal as an anti-caking agent. The purpose of this study is to evaluate another potential 

exposure scenario associated with ball clay, namely its use in ceramic art studios. This 

exploratory investigation makes preliminary exposure estimates that can be used to evaluate 

whether more detailed follow-up analyses are needed. Hypothetical dioxin exposure estimates 

were calculated using an assumption of dioxin levels in the ball clay based on measurements 

from other studies. The study was conducted during 2003 and 2004 by the National Center for 

Environmental Assessment with contract support provided by Battelle in Columbus, Ohio. 
x

AUTHORS, CONTRIBUTORS, AND REVIEWERS

PRINCIPAL AUTHOR

John Schaum, National Center for Environmental Assessment, U.S. Environmental Protection 

Agency, Washington, DC (U.S. EPA Project Manager)

AUTHORS

Ryan James, Battelle (Battelle Project Manager)

James Brown, National Center for Environmental Assessment, U.S. Environmental Protection 

Agency, Research Triangle Park, NC

Dwain Winters, Office of Pollution Prevention and Toxic Substances, U.S. Environmental 

Protection Agency, Washington, DC

CONTRIBUTORS

Ian MacGregor and Christine Mattingly of Battelle served as the technicians for the project. 

INTERNAL REVIEWERS

Mark F. Boeniger, National Institute for Occupational Safety and Health, Cincinnati, OH

David Crawford, Office of Solid Waste and Emergency Response, U.S. Environmental 

Protection Agency, Washington, DC

Mike Dellarco, Office of Research and Development, U.S. Environmental Protection Agency, 

Washington, DC 

Kim Hoang, Region 9, U.S. Environmental Protection Agency, San Francisco, CA

Chong Kim, Office of Research and Development, U.S. Environmental Protection Agency, 

Research Triangle Park, NC

Sid Soderholm, National Institute for Occupational Safety and Health, Washington, DC

Dan Stralka, Region 9, U.S. Environmental Protection Agency, San Francisco, CA

EXTERNAL REVIEWERS

Peter deFur, Environmental Stewardship Concepts, Richmond, VA

Alesia Ferguson, University of Arkansas Medical Sciences, Little Rock, AR
xi

AUTHORS, CONTRIBUTORS, AND REVIEWERS (continued)

Bruce Hope, Oregon’s Department of Environmental Quality, Portland, OR

Clint Skinner, Skinner Associates, Creston, CA

Woodhall Stopford, Duke University, Durham, NC

ACKNOWLEDGMENTS

The authors thank the Ohio State University (OSU) Ceramics Area and the OSU Division 

of Dermatology for their cooperation during this study. In addition, the authors thank Joe 

Ferrario at the U.S. Environmental Protection Agency/Environmental Chemistry Laboratory 

(Stennis Space Center, Mississippi) for his assistance in evaluating dioxin levels in ball clay.
1

1. INTRODUCTION AND BACKGROUND

Ball clay is a natural clay mined commercially in the United States, primarily in 

Kentucky, Tennessee, and Mississippi. A total of 1.21 million metric tons was mined in the 

United States in 2005. Its plasticity makes ball clay an important commercial resource for a 

variety of commercial uses. In 2005, it was used as follows: floor and wall tile—40%, sanitary 

ware (sinks, toilets, etc.)—25%, exports—17%, ceramics—11%, fillers, extenders and 

binders—4%, pottery—1.5%, and miscellaneous purposes—1.9% (USGS, 2007). 

Dioxins were discovered in ball clay in 1996 as a result of an investigation to determine 

the sources of elevated dioxin levels in two chicken samples from a national survey of poultry 

(Ferrario et al., 1997). The investigation indicated that soybean meal added to chicken feed was 

the source of the dioxin contamination. Further investigation showed that the dioxin 

contamination occurred when ball clay was mixed with the soybean meal as an anti-caking agent 

(Ferrario et al., 2000b; U.S. FDA, 2000). In 1997, the U.S. Food and Drug Administration 

(FDA) asked producers or users of clay products in animal feeds to cease using ball clay in all 

animal feeds and feed ingredients (U.S. FDA, 1997).

During the same time period that the present study was conducted, a completely 

independent study called the University of Michigan Dioxin Exposure Study (UMDES) was 

being conducted (Franzblau et al., 2008). UMDES measured chlorinated dibenzo-p-dioxins

(CDDs), chlorinated dibenzofurans (CDFs), and polychlorinated biphenyls (PCBs) in serum of 

946 subjects who were a representative sample of the general population in five Michigan 

counties. The individual with the highest blood level (211 ppt TEQ) among all 946 subjects had 

practiced ceramics art in her home for over 30 years. A follow-up analysis was performed to 

explore the source of this subject’s exposure. Based on the similarity of the congener profile of 

the subject’s blood and the clay she used, Franzblau et al. concluded that exposure from the 

ceramics work was the most likely reason for the elevated blood levels. The clay used by the 

subject was a liquid formulation with unknown geologic origin. Sample analysis showed that it 

contained 223 ppt TEQ with a profile that matched ball clay. Franzblau et al. concluded that 

ceramic clay may be a significant nonfood and nonindustrial source of human exposure to 

dioxins and recommended further research to more precisely characterize the routes of exposure.

The purpose of this study is to explore the possible dioxin exposures of artists using ball 

clay in ceramic art studios. The study was conducted at a single facility with 10 artists and 

therefore cannot be considered to be representative of all possible types of studios and practices. 

Ceramic art is conducted in a wide variety of studios ranging from small residential operations to 

large commercial facilities. Cleanliness, ventilation, and safety practices also vary widely within 

these types of studios. This study was conducted at the Ohio State University (OSU) Ceramics 
2

Art Department. The OSU studio is a modern facility with excellent ventilation and

maintenance. During the peer review of this study, an industrial hygienist commented that the 

OSU studio was an unusually clean and newly renovated facility (Eastern Research Group, 

2008). Accordingly, the exposures measured in this study are most representative of similar 

university studios. Many different kinds of activities can occur in these studios including mixing 

clay, sculpting, operating a wheel, tending kilns, etc. Although many of these practices occurred 

at the OSU facility, this study is not representative of all possible ceramic art activities. 

This exploratory investigation makes preliminary exposure estimates that can be used to 

evaluate whether more detailed follow-up analyses are needed. The limited resources available 

for this study required a strategy to base the analysis on existing data to the fullest extent 

possible. 

Dioxin exposure is primarily a function of the dioxin concentration in the clay and an 

individual’s level of exposure to the clay. Although studies in the literature provided 

information about dioxin levels in clay, no information could be found on clay exposure levels in 

ceramic art studios. Therefore, this study was designed to measure total clay exposures in a 

ceramic art studio. No dioxin measurements were made in this study, rather the dioxin levels in 

ball clay were assumed based on measurements from other studies. Three exposure pathways 

were evaluated: inhalation, dermal contact, and incidental ingestion. The evaluations involved 

measuring levels of clay particulates in air, clay residues on skin, and clay deposition on media 

representing food and beverages. These data provided a basis for estimating potential dioxin 

exposures and resulting doses, conducting an initial analysis of which exposure pathways 

contribute most to total dose, and evaluating how individual behaviors affect exposure/dose. 

Ultimately, the data helped develop distributions for input parameters for conducting a Monte 

Carlo analysis to estimate how dioxin exposure/dose may vary across a wide population of 

artists. Figure 1 provides a conceptual diagram of the key components of this study.

An alternative way to evaluate dioxin exposures is by blood testing. While this provides 

a direct measure of dioxin exposure, it represents exposures from all sources, not just work in an 

art studio. Also, a blood study would not have provided any insights about how dioxin 

exposures may occur in an art studio. Normal background exposures vary widely and factors 

such as diet and age are known to have large impacts on dioxin body burden. Accordingly, a 

blood study would require a large number of subjects with controls to reduce the effects of these
3 

Figure 1. Conceptual diagram. 

Exposure Data from 

Study:

-Clay measurements: 

air level, skin load, and

deposition to food 

-Questionnaire: 

exposure duration, ball 

clay in blend 

External Data:

-Dioxin concentration in 

clay 

-Absorption fractions 

Deterministic Analysis:

Used point estimates for 

all exposure parameters 

Outputs:

Hypothetical 

dermal, 

ingestion, and 

inhalation doses 

for 10 subjects 

Monte Carlo Analysis:

Used distributions for all 

exposure parameters 

Outputs:

Distribution of 

dermal, ingestion, 

and inhalation 

doses in broad 

population of artists 

in well maintained 

studios

factors. Also blood tests have very high analytical costs. On the basis of costs alone, blood 

testing was beyond the scope of this effort. The clay exposure testing done here provided a low 

cost way to explore the problem and gives future researchers an informed basis for deciding if 

blood testing or other types of follow-up work are needed. 

 Dioxin concentrations and exposures are presented in terms of toxic equivalents (TEQs). 

TEQs allow concentrations of dioxin mixtures to be expressed as a single value computed by 

multiplying each congener concentration by a toxicity weight (toxic equivalency factor or TEF) 

and summing across congeners. TEFs are expressed as a fraction equal to or less than 1 with 1 

corresponding to the most toxic dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin 

(2,3,7,8-TCDD). The TEQ data presented here are based on TEFs from the 1998 World Health 

Organization (WHO) recommendations (Van den Berg et al., 1998). In 2005, WHO updated the 

TEFs (Van den Berg et al., 2006). As discussed in Chapter 4, these updates had little impact on 

the literature values used here, so no adjustments were made. 

The term ―dioxins‖ is used in this study to refer collectively to the tetra- through 

octa-chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans (CDD/Fs) with chlorine 

substitutions in all of the 2,3,7,8 positions. This term is commonly defined to include the 

12 co-planar pentachlorobiphenyls (PCBs) which also demonstrate dioxin-like toxicity. 

However, PCBs are not addressed in this study. PCBs have been shown to make up a small 

Inhalation parameters

-Clay measurements: 

air level, skin load, and

deposition to food

-Questionnaire: 

exposure duration, ball 

clay in blend

External Data:

-Dioxin concentration in 

clay

-Absorption fractions

-Inhalation parameters
4

fraction of the total TEQs in a wide variety of background soils (U.S. EPA, 2007) and, therefore,

are probably not important contributors to TEQs in ball clay. 
5

2. APPROACH OVERVIEW

While working in a ceramics studio, artists may be exposed to dioxin-contaminated clay 

via three pathways: dermal contact, particle inhalation, and incidental ingestion. Exposure could 

also occur via open cuts or eyes and this possibility is discussed in Chapter 9 on uncertainty.

The general strategy and procedures used to characterize each pathway are described below.

2.1. GENERAL STRATEGY 

The site selected for this study was the Ceramics Area in Hopkins Hall at OSU in 

Columbus, OH. The Ceramics Area, housed in the basement of Hopkins Hall, has eight rooms, 

including classrooms, studios, a storage area, a glaze-mixing area, a clay recycling area, and a 

furnace room. This facility was selected because it offered a convenient location for assessing 

exposures during a variety of typical ceramic art activities. 

An extensive ventilation system is used through out the studio with hoods located in 

several areas such as where clay mixing is conducted. The kilns are located in two rooms which 

are isolated from classrooms and other areas frequented by the students. These rooms are 

dedicated to kiln operations and no art work is performed in them. The studio has six kilns fired 

with natural gas (sizes in cubic feet: 28 [2 units], 40, 70, 7, and 25) and nine electric kilns (sizes 

in cubic feet: 60 [2 units], 27, 5 [4 units], 28, and 0.3). The small electric unit is unvented and 

used to test the temperature program on small pieces. All other kilns are equipped with 

ventilation hoods (vented outside the building). The kilns are generally heated slowly to a 

maximum temperature of about 1,200°C (2,200°F) and pieces are baked for about 9 to 15 hours. 

They are generally operated 2–3 times/week and daily during busy periods at the end of 

semesters. 

The exposure measurements were carried out in two separate studies. The first study was 

conducted in April 2003 and the second in July 2004. The results of both studies have been 

combined in this report. Seven artisans and one nonartisan staff member in the OSU Ceramics 

Department were recruited to serve as subjects for the first study, and two additional artisans 

were recruited for the second study. An open solicitation was presented to the students and 

departmental staff, and the first volunteers were selected. The subjects included three males and 

seven females ranging in age from about 20–40 years. Approval for human subjects was 

obtained via the Battelle Institutional Review Board (IRB) and the U.S. Environmental 

Protection Agency (EPA). Upon approval by the Battelle IRB and EPA, OSU determined that 

review by their IRB was not necessary. The testing was conducted while the subjects conducted 
6

a variety of unscripted tasks, including clay mixing/preparation, sculpting, pottery wheel work, 

and molding. 

To assess dioxin exposure levels, it is necessary to estimate dioxin levels in the various 

exposure media (i.e., clay used by the artists, dust particles suspended in the studio air, and dust 

settled onto surfaces). No actual dioxin measurements were made in this study. Rather, dioxin 

levels were estimated using literature-reported concentrations of dioxins in ball clay and 

information about the amount of ball clay in the clay mixtures used by the artists. Chapter 4 

discusses the details about this procedure.

A questionnaire was administered to subjects during the first study to gather information 

on their routines involving clay artwork. Chapter 6 summarizes the questionnaire data as 

presented in Appendix A.

2.2. CHARACTERIZATION PROCEDURES

The following procedures were used to characterize each exposure pathway.

2.2.1. Dermal Contact 

Dermal contact with clay can occur via direct handling of the clay, deposition from the 

air onto exposed skin, transfer from surfaces, and splashing during wheel operations. The 

amount of clay on skin was measured using rinsing procedures. Additionally, surface wipes 

were collected in work areas to evaluate dermal exposures via transfers from surfaces. To 

further evaluate dermal exposure, a dermatologist examined the condition of the stratum 

corneum, the outermost layer of skin, before and after Subjects 1–8 worked with clay. The 

primary focus of this examination was to determine if any damage to skin may have occurred 

that would affect dermal absorption.

2.2.2. Inhalation

Both personal and area air-monitoring techniques were used to assess inhalation 

exposures. Personal air samplers provide data most representative of an individual’s exposure 

because they sample the air in a person’s breathing zone and reflect changes in concentration due 

to their movement. An area sampler provides a general indication of exposure for people in its 

vicinity and also can achieve lower detection levels. Both the personal and area-monitoring 

techniques provided particle size-selective data, so that the deposition site of the particles in the 

respiratory tract (nose/mouth, tracheobronchial airways, and alveolar region) could be 

determined.

Two types of personal air samplers were used: real-time and time-integrating. Similarly, 

two types of area air samplers were used: real-time and time-integrating. The real-time air 
7

samplers provided data on particle levels on a nearly continuous basis (every minute). The 

integrating samplers collected particles over the entire time period of a work activity, yielding a 

time-weighted average (TWA) concentration. In this sampling design, the real-time exposure 

monitoring was used to assess frequency, magnitude, and duration of peak exposures as well as 

TWA across the entire sampling time, while the integrating samplers provided information on 

average exposures. 

2.2.3. Ingestion 

Inadvertent ingestion of clay or dust can occur in several ways. Clay particles in the air 

can deposit on food or in beverages. Deposition onto surrogate food samples (a quartz filter was 

used to represent food and a beaker of water was used to represent a beverage, see Section 3.1.5.

for further details) was measured to evaluate this pathway. Ingestion can also occur via transfers 

from hands to food or cigarettes (though no smoking was allowed in the OSU studio) and via 

transfers to the mouth resulting from wiping the hands or licking the lips. These possibilities 

were evaluated qualitatively through observations about individual behaviors. Finally, ingestion 

can also occur via particle deposition in the nose, mouth, and tracheobronchial airways; 

clearance to the throat; and swallowing. This process was evaluated using inhalation modeling 

(see Appendix B). 
8

3. SAMPLING METHODS

Methods used for collecting, preparing, and analyzing samples are described below.

3.1. SAMPLE COLLECTION

Samples were collected from personal air, area air, skin rinses, surface wipes, and 

surrogate food and beverages.

3.1.1. Personal Air Sampling

The RespiconTM Model 8522 particle sampler (TSI Incorporated, Shoreview, MN) is a 

two-stage virtual impactor with a three-stage gravimetric filter sampler. The sampler sorts 

airborne particulate matter into three size ranges. Each size range is collected on a 37-mm glass 

fiber filter (GFF). The particle size collection ranges are as follows: stage 1, aerodynamic 

particle diameter (Dae) < 4 μm; stage 2, 4 < Dae < 10 μm; and stage 3, 10 < Dae < 100 μm. 

Before the start of sampling, three preweighed GFFs were removed from their protective 

polystyrene containers (47-mm Millipore petri slides) and loaded into the RespiconTM using 

nonmetallic filter forceps. A unique laboratory record book (LRB) identification number was 

assigned to each GFF during tare weighing, and this weight was recorded onto the sampling data 

sheet at that time. The RespiconTM was then assembled, and the total flow checker head was 

installed. A personal sampling pump (SKC model no. 224-PCXR4, Eighty Four, PA) was 

attached to the total flow head, and the flow rate through the RespiconTM was adjusted to 3.11 L

per minute (L/min) + 2%, according to the manufacturer’s specifications. All flows were 

verified by employing a calibrated National Institute of Standards and Technology 

(NIST)-traceable Buck calibrator (Model M5, A.P. Buck, Orlando, FL). After confirmation of 

the manufacturer’s suggested flow rates at each stage of the sampler, the total flow checker was 

replaced with the standard (100 μm) inlet head. A nylon chest harness (TSI Incorporated, 

Shoreview, MN) was used to place the RespiconTM in each subject’s breathing zone, 

approximately 15–20 cm below the chin. The personal sampling pump was attached to the 

subject’s belt and connected to the RespiconTM. Sampling was initiated by starting flow through 

the RespiconTM and continued throughout a subject’s entire work shift, typically 2–2.5 hours. 

The average sampling volume was 387 L. Following sampling, the pump was turned off, the 

RespiconTM was disassembled, and the filters were returned to their polystyrene petri dish 

containers for transportation back to the laboratory for gravimetric analysis. Quality control 

samples, such as field blank samples and matrix spike samples, were collected and analyzed for 

each sampling technique (see Section 3.2.3). 
9

The personal DataRAM-1000 (pDR-1000, Thermo Electron Corporation, Franklin, MA) 

sampler was also used to measure personal particle exposure passively. No pump is required for 

this instrument; instead, the air surrounding the sampler circulates freely through the open 

sensing chamber by natural convection, diffusion, and background air motion. Particle 

concentrations are measured using a light-scattering (nephelometry) technique. This instrument 

responds optimally to particles with diameters in the range of 0.1–10 μm but will also respond to 

a lesser extent to larger diameter particles. Via internal calibration, the sampler converted 

particles/m3to mg/m3as final data units.

Before the start of sampling, the instrument sensor was zeroed by placing it in a 

resealable bag into which particle-free (filtered) air was pumped. All zero operations were 

performed successfully. To begin sampling, the instrument was clipped to the subject’s waistline 

(on the belt or strap holding the SKC pump) and the unit was activated. The pDR-1000 collected 

data at 1 Hz and was programmed to record these data as 1-minute averages over the duration of 

the sampling period. At the conclusion of sampling (typically 2–2.5 hours), data logging was 

stopped and the instrument was turned off. The data were then uploaded to a personal computer 

using software provided by the manufacturer and an RS-232 serial port connection. 

3.1.2. Area Air Sampling 

To assess the particle size and concentration in the ceramic studio’s air, a 6-stage Delron®

cascade impactor (Delron Research Products, Powell, OH) was employed. Each stage filters out 

successively smaller particles so that the following particle sizes are collected in successive 

stages: >32 μm, 16–32 μm, 8–16 μm, 4–8 μm, 2–4 μm, and 0.5–2 μm; the final GFF collects all 

particles smaller than 0.5 μm in diameter. Particles accumulate on glass slides underneath each 

impactor orifice. To prevent particle loss due to bouncing, a small amount of vacuum grease was 

applied to each glass slide. The area coverage of the grease on the slide was determined by the 

approximate size of the impactor nozzle below which the slide was to be placed. Correct airflow 

rate through the impactor ensures that the correct particle sizes are collected on each stage. A 

carbon-vane pump (Gast Co., Benton Harbor, MI), with a critical orifice that provides a pressure 

drop of at least 430 mm of mercury, was used to ensure the flow rate of 24 L/min. 

Before the start of sampling, preweighed glass slides were removed from their protective 

polystyrene petri slide containers and loaded into the impactor using clean forceps or tweezers. 

Unique LRB numbers, assigned to each slide during tare weighing, were recorded on sample 

data forms. The impactor tower was then assembled and flow was initiated to verify the required 

pressure drop. For each sample, the pressure drop was between 480 and 510 mm of mercury. 

Flows were also verified using the Buck calibrator. Sampling times were approximately 

2–2.5 hours, giving an average sample volume of approximately 2,900 L. Following sampling, 
10

the impactor was disassembled and all slides were returned to their respective petri dish 

containers for transportation back to the laboratory for gravimetric analysis.

The Climet® CI-500 innovation laser particle counter (Redlands, CA) was a second 

sampling device used to measure area particle concentrations. In a manner similar to the 

pDR-1000, the Climet® CI-500 measures particle number concentration using nephelometry. A 

self-contained pump sampled air at a constant flow rate of approximately 3 L/min. In the count 

mode, the Climet® CI-500 measures particles in six particle size ranges: 0.3–0.5 μm, 0.5–1 μm, 

1–2.5 μm, 2.5–5 μm, 5–10 μm, and >10 μm. The sampling frequency for the instrument is 1 Hz, 

and the data were logged as 1-minute averages. The particle counts were converted from 

particles/m3 to mg/m3as final data units. The particle counts did not exceed the manufacturer’s 

recommended maximum (200–250 counts/cm3 at 3 L/min) at any time except for a few minutes 

during two of the sampling periods. No instrument zero or span checks were necessary. 

Following sampling, the data were uploaded to a computer using an RS-232 serial cable and 

software provided by the manufacturer. The Climet® CI-500 was located in close proximity to 

the cascade impactor and generally very near the subject. For example, when the subject was 

working with clay at a wheel, the two air samplers were placed on the side of the wheel opposite 

the subject at a height and distance from the wheel similar to the subject’s mouth and nose. The 

inlet to the Climet® was oriented in a vertical direction.

3.1.3. Skin Sampling 

The total skin area of hands, arms, face, feet, and legs was estimated using a combination 

of direct measurements and regression models based on body weight and height (U.S. EPA, 

1997). The subject’s exposed body parts were rinsed with a dilute soap solution (~2% soap in 

deionized [DI] water, by weight). Approximately 100–150 mL of the soap solution was used to 

rinse each exposed body part. After each body part was rinsed, the washbasin contents were 

transferred to a polypropylene bottle with small amounts of DI water rinses. The bottle was 

labeled and sealed with a screw-top cap. The washbasin was then rinsed again, wiped out, and 

reused. Between the first and second studies, the procedures differed as described below.

3.1.3.1. April 2003

All subjects wore short-sleeved shirts, long pants, socks, and shoes. Therefore, the only 

exposed skin areas were the hands and forearms, and the rinsing was limited to these body parts. 

At three times during each subject’s work session, the subject’s exposed skin was examined for 

clay residue. When clay was observed visually, the affected areas of the subject’s body were 

rinsed. Rinses were performed at approximately equally spaced intervals, and the last rinse 
11 

usually coincided with the conclusion of the sampling period. The average of the three 

measurements was used to represent the session. 

3.1.3.2. July 2004 

Both subjects wore short-sleeved shirts, short pants, and sandals. Therefore, the exposed 

skin areas included the hands, arms, legs, and feet, and the rinsing was expanded from the first 

tests to include all of these body parts. The subjects’ faces were also rinsed during these tests. 

Although no visible residues were apparent on the faces, this area was included for the sake of 

completeness. 

 The rinse samples were collected in a washbasin using a squirt bottle of soap solution 

while the subjects used their hands to gently wipe off the affected area. Rinses were conducted 

in the following manner: 

 Hands. Moving downward from the wrist, the technician rinsed the residual clay off 

both sides of the artisans’ hand; the residual clay from each hand was rinsed into separate 

containers and analyzed separately. 

 Arms. Moving downward from the elbow, the artisans rinsed the residual clay from their 

arms. 

 Feet. Moving downward from the ankle, the artisans rinsed the residual clay from their 

feet. 

 Legs. Moving downward from the top of the exposed area of the legs, the artisans rinsed 

the residual clay from their legs. 

 Face. The artisans rinsed the residual clay from their faces. 

 Skin rinse samples were collected at the close of each work session. In addition, if at any 

point during the work session the subject indicated the need to wash an exposed body part, it was 

rinsed into a sample container reserved for that body part. 

3.1.4. Surface Wipe Sampling 

 A 20 × 20 cm horizontal surface near the subject’s workspace was selected and cleaned 

with dilute soap solution before the subject began working with any clay. These surfaces were 

porous concrete tabletops. Wipe samples of this area were taken immediately after cleaning (to 

confirm that low levels were present before starting the work session) and at the end of the work 

session. The wipe sampling procedure consisted of the following steps. The selected area was 

wiped with 10 × 10 cm rayon gauze wipes wetted with ~5 mL isopropanol using the following 
12

procedure. The wipe was secured between the thumb and forefinger of one hand, and the surface 

was wiped five times in one direction using evenly applied pressure. The soiled side of the wipe 

was folded to the inside and, in an orthogonal direction, the surface was wiped five more times. 

This soiled side of the wipe was again folded to the inside and the wipe was placed into its 

prelabeled, resealable bag for transportation back to the laboratory for gravimetric analysis. The 

entire wiping process above was then repeated using one additional wipe. 

3.1.5. Surrogate Food and Beverage 

An 85-mm diameter quartz fiber filter and a 125-mL polypropylene jar filled with 

100 mL DI water served as surrogates for food and beverage samples, respectively. Before clay 

work began, both were placed in a location where the artisan indicated he or she might normally 

place food or drink. In most cases, this location was away from the direct work area but still in 

the same room. However, occasionally clay workers placed food and beverage directly adjacent 

to their work. To begin sampling, the lid of the polycarbonate petri dish containing the food 

surrogate and the screw-cap lid on the beverage surrogate were removed. Following the 

conclusion of sampling, the lid to the petri dish was replaced and sealed with Teflon®tape, and 

the polypropylene jar was secured for transportation back to the laboratory for gravimetric 

analysis.

3.2. SAMPLE PREPARATION AND ANALYSIS

Procedures used for sample preparation, analysis, and quality control are described 

below.

3.2.1. Filtration and Drying 

To collect the clay rinsed from the subject’s skin during the skin rinse sampling 

procedure and the clay deposited into the surrogate beverage sample, the clay-liquid suspensions 

were filtered through a preweighed 85-mm diameter quartz fiber filter in a Buchner funnel using 

vacuum filtration. Any remaining clay in the sample container was rinsed with several small 

aliquots of DI water to ensure complete transfer of the clay to the filter. All filters from the 

vacuum filtration procedure were subsequently placed on clean 10-cm watch glasses and dried 

overnight at 100°C (212°F). The gauze wipes for surface residues were dried in this fashion as 

well. No drying was required for the 37-mm RespiconTM filters or glass slides.
13

3.2.2. Gravimetric Analysis 

The accuracy of the analytical balance (AT-20, Mettler-Toledo) used for all gravimetric 

analyses was confirmed daily with weights approved by NIST. The calibration weights ranged 

from 0.001 mg to 100 g. All 37-mm GFFs, 85-mm quartz fiber filter paper, 37-mm glass slides, 

and gauze wipes were conditioned in a temperature- and humidity-controlled balance room 

(temperature 22–23°C (72–73°F), relative humidity 46–56%) for a minimum of 24 hours before 

tare and final weights were recorded. For conditioning, the lid of the container holding the filter 

or slide was left slightly ajar, and the resealable bags containing the gauze wipes were left open. 

For both kinds of filters and glass slides, three separate weights were recorded to the nearest μg. 

The weight was acceptable if the range of the three independent measurements was less than 10 

μg. For gauze wipes, the three separate weights were recorded to the nearest tenth of a mg and 

the acceptability criterion was that the range of the measurements be less than 1 mg.

3.2.3. Quality Control Samples 

At least one field blank sample was collected for each type of gravimetric sample, 

including the RespiconTM, cascade impactor, food and beverage, and surface wipe samples. 

Such samples were collected by transporting the sampling media to the field location and placing 

them into their respective sampling device or position for sampling. As soon as the medium was 

ready for sampling, it was collected as if the sampling time had come to a close and transported 

back to the laboratory for gravimetric analysis. The detection limits for the gravimetric 

measurements were determined by multiplying the standard deviation of the field blank net 

weights by 3. The detection limits for each type of gravimetric measurement were as follows:

0.0025–0.015 mg/m3for each stage of the cascade impactor, 0.878 mg/m3for each stage of the 

RespiconTM, 10.6 mg for the surface wipes, 0.6–1 mg for the food/beverage deposition samples, 

and 0.6–1.6 mg for the dermal rinse samples.

As a quality control check, the skin rinse, surface wipe, and food and beverage sampling 

and analysis methods were tested in a controlled laboratory setting (Battelle Laboratory in 

Columbus, OH). For the skin rinse method evaluation, approximately 3 g of clay (obtained from 

one of the artisan subjects) was handled carefully without dropping any until the entire sample 

was spread over the hands and forearms of a Battelle researcher. The skin rinse and analysis 

method described above was performed, and recoveries of 87 + 3% of the clay applied were 

obtained. This compares favorably with Kissel et al. (1996), who obtained 93% recovery when 

rinsing wet soil from the skin of human subjects using a similar sampling method. Similarly, for 

the surface wipe method, approximately 1 g of clay was deposited onto a precleaned laboratory 

bench, the wipe method described above was performed, and recoveries of 94 + 5% were 

obtained. For the food and beverage samples, approximately 50 mg of clay was added to those 
14

sampling matrices and recoveries of 90 and 95%, respectively, were obtained using the 

gravimetric analysis procedures described above.
15 

4. DIOXIN CONTENT OF CLAY AND STUDIO RESIDUES 

 As discussed earlier, this study made no dioxin measurements in clays, dust residues, or 

other materials from the Ohio State University ceramics studio. Instead, the possible levels were 

estimated on the basis of other studies. A number of studies have measured dioxin levels in raw 

and processed ball clay. Raw clay is the clay as it comes out of the ground. Processed clays are 

the result of the initial processing, which is usually conducted at or near the mining site before 

shipping. This processing typically involves drying with hot air at 120 ̊C and pulverizing in a 

series of milling stages (Ferrario and Byrne, 2002). The following studies describe dioxin levels 

in raw and processed clay: 

 Ferrario and Byrne (2002, 2000). Both papers present data for processed ball clay used 

at one ceramics manufacturer. The mean of seven samples of processed ball clay was 

3,172 pg/g TEQ. Additional data are presented on dioxin levels in clay mixtures and 

fired products. The authors noted that dioxin levels in the dust samples collected at the 

facility were the same as those in the unfired clay mixtures. 

 Ferrario et al. (2000a). This study compared the mean levels in eight raw clay samples 

from Mississippi (see Table 1) to the mean levels in four processed ball clay samples. 

This comparison showed that the processed clays had much lower levels of 

2,3,7,8- TCDD and higher levels of 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (HxCDD), 

1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD), and octachlorodibenzo-p-dioxin 

(OCDD) than the raw clay. The mean total TEQ of the processed clay (977 pg/g TEQ) 

was 37% lower than the raw clay (1,513 pg/g TEQ). 

 Ferrario et al. (2000b). This study also presents the data for raw and processed clay 

described in Ferrario et al. (2000a). In addition, it presents dioxin levels in a variety of 

other types of clays and discusses the evidence of a natural origin for their presence. 

 Ferrario et al. (2007, 2004). These studies collected processed ball clay directly from 

four art-supply retailers. All ball clay types sold by these retailers were purchased in 

22.7-kg (50-pound) bags. One type of ball clay was sold by all four retailers, five types 

were sold by two of the retailers, and seven types were sold by only one retailer. Thus, a 

total of 21 bags, representing 13 different types of ball clays, were purchased and 

sampled. A ceramics expert confirmed that the most commonly used ball clays for 

making artware and pottery were represented in these samples. Table 2 summarizes these 

data. 
16 

Table 1. Raw ball clay dioxin concentrations 

Congener

PCDD concentration (pg/g dry weight)

Range Median Mean Mean TEQ

2,3,7,8-TCDD 253–1,259 617 711 711

1,2,3,7,8-PeCDD 254–924 492 508 508

1,2,3,4,7,8-HxCDD 62–193 134 131 13

1,2,3,6,7,8-HxCDD 254–752 421 456 46

1,2,3,7,8,9-HxCDD 1,252–3,683 1,880 2,093 209

1,2,3,4,6,7,8-HpCDD 1,493–3,346 2,073 2,383 24

OCDD 8,076–58,766 4,099 20,640 2

Total 1,513

HpCDD = heptachlorodibenzo-p-dioxin; HxCDD = hexachlorodibenzo-p-dioxin; OCDD = 

octachlorodibenzo-p-dioxin; PCDD = polychlorinated dibenzo-p-dioxin; PeCDD = pentachlorodibenzo-p-dioxin; 

TCDD = tetrachlorodibenzo-p-dioxin; TEQ = toxic equivalent. 

Source: Ferrario et al. (2000a). 

Because the data from Ferrario et al. (2007, 2004) represented the types of clays most 

likely used in ceramic art studios, these data were selected as the most representative ones to be 

used in this study. Accordingly, it was assumed here that the dioxin TEQ levels in clay could 

range from 289 to 1,470 pg/g with an average of 808 pg/g. Table 2 shows the TEQs from this 

study were calculated on the basis of the WHO-98 TEFs (Van den Berg et al., 1998). In 2005, 

WHO updated the TEFs (Van den Berg et al., 2006). These updates increased the TEF for 

OCDD from 0.0001 to 0.0003. None of the TEFs for the other six congeners used to estimate 

the ball clay TEQs were changed by the WHO update. The increase in the OCDD TEF would 

cause the overall average to increase by 6%. It was decided to use the TEQ estimates for ball

clay as originally reported instead of updating it on the basis of the 2005 WHO TEFs. This was 

based on two reasons, first the change would have been relatively minor and second it would 

have complicated comparisons to exposure estimates which have not yet been updated on the 

basis of the new TEFs.
17 

Table 2. Processed ball clay dioxin concentrations (pg/g) 

Average

Standard 

deviation Median Minimum Maximum

WHOTEFaAvg

TEQ

PCDDs

2,3,7,8-TCDD 76 60 63.5 21.8 291 1 76.0

1,2,3,7,8-PeCDD 374 144 387 125 588 1 374

1,2,3,4,7,8-HxCDD 335 141 313 142 636 0.1 33.5

1,2,3,6,7,8-HxCDD 526 204 523 167 944 0.1 52.6

1,2,3,7,8,9-HxCDD 1,480 608 1,570 394 2,550 0.1 148

1,2,3,4,6,7,8-HpCDD 9,780 4,480 8,600 3,940 19,500 0.01 97.8

OCDD 254,000 88,200 233,000 118,000 471,000 0.0001 25.4

Total

TCDD 1,450 606 1,600 412 2,370

PeCDD 4,600 1,890 4,880 1,560 7,140

HxCDD 13,500 5,710 12,800 4,800 21,900

HpCDD 25,000 11,700 24,400 9,320 44,900

b Total TEQs 808 318 771 289 1,470 808

 

a World Health Organization Toxic Equivalency Factors (WHO-TEFs) based on Van den Berg (1998) 

b The overall average presented by Ferrario et al. (2007) is based on averaging the mean congener levels across 

samples. An alternative approach is to compute the average on the basis of the TEQ for each sample. This 

approach yields an average of 819 pg/g (SD = 303 pg/g). Similarly, the median TEQ is 810 pg/g based on the 

individual samples. The minimum and maximum TEQ values are reported on the basis of the individual samples. 

HpCDD = heptachlorodibenzo-p-dioxin; HxCDD = hexachlorodibenzo-p-dioxin; OCDD = 

octachlorodibenzo-p-dioxin; PCDD = polychlorinated dibenzo-p-dioxin; PeCDD = pentachlorodibenzo-p-dioxin; 

TCDD = tetrachlorodibenzo-p-dioxin; TEQ = toxic equivalent. 

Source: Ferrario et al. (2007, 2004). 

 All of these studies indicate that ball clay has relatively high levels of CDDs and very 

low levels of CDFs. Based on Ferrario et al. (2007, 2004), about 95% of the TEQs in processed 

clay are contributed by four congener groups: TCDDs (9%), pentachlorodibenzo-p-dioxin 

(PeCDDs) (46%), HxCDDs (28%), and HpCDDs (12%). 
18 

 Artists commonly use a mixture of clays to achieve various physical properties and visual 

effects. The percentage of ball clay in the mixture can vary widely. The amount of ball clay in 

the mixtures used on days when the testing occurred ranged from 0 to 100% with an average of 

21.5% (see Table 3). Although 4 of the 10 subjects used mixtures containing no ball clay on the 

test days, on other days these subjects would likely use mixtures that do contain ball clay. This 

is because students are required to conduct a variety of projects, and some of these are better 

suited to using ball clay and others are not. Accordingly, it was assumed here that the ball clay 

portion of clay mixtures used by artists can range from 0 to 100% with an average of 20%. 

Furthermore, it was assumed that the dioxin levels in the nonball clays were negligible. This is 

supported by Ferrario et al. (2000b), who analyzed 15 different mined clays and concluded their 

dioxin levels were significantly lower than levels in ball clay. 

Table 3. Percentage ball clay in the clay mixtures used during this study

Subject Percentage ball clay

1 0

2 27

3 48

4 0

5 20

6 0

7 0

8 15

9 100

10 5

 Finally, it was assumed that the dusts suspended in the air and settled onto food or skin 

would have the same dioxin levels as the clay. Material other than clay may contribute to these 

dusts, further diluting dioxin concentrations. This possibility was evaluated using scanning 

electron microscopy (SEM) with energy dispersive spectroscopy (EDS). These techniques were 

applied to four types of samples: 
19 

 Blank GFF 

 Dust on a GFF collected from a storeroom at the Battelle Laboratory (not impacted by 

clay) 

 TM Air particles on a Respicon GFF collected in the studio 

 Clay used by subjects 

 Figure 2 shows SEM photographs and elemental spectra of samples associated with 

Subject 6. A visual comparison of the SEM photographs suggests that the particles on the 

RespiconTM filter appear to differ from those in the storeroom dust. Also, the spectra of the 

particles on the RespiconTM filters resemble clay more than those of storeroom dust. The clay 

samples and RespiconTM filter samples had high abundances of titanium, iron, and aluminum, 

which were not seen in the GFF blank or in the storeroom dust sample. Similar results were 

found for all eight subjects in the April 2003 tests, as shown in Appendix C. The analysis was 

not repeated in the July 2004 tests. These observations suggest that clay dominates the air 

particles collected in the studio. On this basis, it was assumed that the studio dust was 

dominated by clay and no further dilution factor was needed to adjust dioxin concentrations.
20

Figure 2. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) data.

Blank glass fiber filter (GFF) Dust particles on GFF in Battelle storeroom

Sample of clay used by Subject 6 Clay particles on Respicon filter used by Subject 6

Blank glass fiber filter (GFF) Dust particles on GFF in Battelle storeroom

Sample of clay used by Subject 6 Clay particles on Respicon filter used by Subject 6
21

5. DOSE ESTIMATION PROCEDURES

This chapter presents the procedures used to estimate the dioxin dose to artisans from all 

three routes of exposure: dermal contact, inhalation, and ingestion. Because the dermal dose is 

expressed on an absorbed basis, the dose by other pathways must also be expressed on an 

absorbed dose basis. This provides an equivalent basis for comparison and addition across 

pathways. All doses are presented as daily estimates. No adjustments are made for the 

frequency with which artists work with clay. Therefore, these dose estimates should be 

interpreted as the dose that could occur on a day that clay work is conducted, rather than as a 

long-term average. 

5.1. DERMAL CONTACT

A fraction absorbed approach is used to estimate dermal absorption. This method has 

been widely used to assess dermal exposures to solid residues and is endorsed in current Agency 

guidance (U.S. EPA, 2004, 1992). Kissel et al. (2007) have proposed a more mechanistic model. 

This model has not yet been incorporated into Agency guidance and therefore, was not chosen as 

the primary basis for this assessment. However, the model is presented in Appendix D with a 

discussion of how it could be applied to this situation.

5.1.1. Estimating Particle Loading on Skin 

As described earlier, rinsing procedures were used to determine the total amount of clay 

on exposed skin. This mass was divided by the exposed skin area to derive a loading in units of 

mg/cm2. 

5.1.2. Estimating Monolayer Load 

The monolayer is the layer of particles immediately adjacent to the skin. According to 

the monolayer theory, the only significant dermal absorption comes from chemicals contained in 

this first layer (U.S. EPA, 2004, 1992). This theory would not apply in all situations such as 

those involving rapid absorption and long exposure times. In such situations the monolayer 

could be depleted, and the contaminant in higher layers could diffuse downward and ultimately 

be absorbed into the skin. Experimental evidence supporting the monolayer theory has been 

published by Duff and Kissel (1996), Roy and Singh (2001), and Touraille et al. (2005). These 

studies used exposure times of 24 hours or longer and were conducted with 2,4-D, BaP, and 

4-cyanophenol. The similarity of these chemicals to dioxins and the use of exposure times 

similar to the ones of concern here, suggest that the monolayer theory should be applicable to 

exposure scenarios considered in this study. 
22

To properly apply the dermal absorption fractions, it was necessary to determine whether 

residue loads on skin exceeded monolayer loads. The monolayer load for a specific soil can be 

estimated on the basis of the median particle size. Assuming spherical particles and 

face-centered packing, the monolayer loads can be calculated as follows (U.S. EPA, 2004): 

Lmono = π ρ dp / 6 (1) 

where 

Lmono = monolayer load (mg/cm2) 

ρ = particle density (mg/cm3) 

dp = physical particle diameter (cm) 

 The average particle density of the processed clays analyzed by Ferrario et al. (2004) was 

2.64 g/cm3. Clays typically have very small particles relative to other components of soil. The 

U.S. Department of Agriculture (USDA) defines clays as having less than 2 μm diameter 

particles (Brady, 1984). Table 4 shows the particle size specifications for a Tennessee ball clay 

(Ceramics Materials Info, 2003). Reviewing the specifications for a variety of commercial ball 

clays, median particle sizes ranged from about 0.5 to 1.0 μm (Ceramics Materials Info, 2003). 

Table 4. Particle size distribution of Tennessee ball clay 

Particle diameter (μm) 20 10 5 2 1 0.5 0.2

% finer than 99 97 93 81 72 56 35

Source: Ceramics Materials Info (2003). 

 The particle sizes found in the studio air had median physical diameters ranging across 

subjects from 8 to 27 μm (this is derived from the mass median aerodynamic diameter [MMAD] 

range of 13 to 44 μm described in Appendix B and converted to physical diameters using the 

procedure in Appendix B, Footnote 1). These airborne particles appear larger than what would 

be expected from the original clay product. This may be explained by the bonding of particles 

caused by the addition of water to the clay or the firing process, which fuses particles. Particles 

that accumulate on the skin primarily from air deposition are likely to resemble the air particles 

more than the original clay particles. Particles that transfer to skin primarily from direct 

handling of the clay should more closely resemble the original clay product than the airborne 

particles. Accordingly, the particle sizes of the clay residues on skin could vary widely, with 
23

medians ranging from 0.5 to 27 μm. For purposes of the central exposure estimates, the 

geometric mean of this range is assumed, i.e., 3.7 μm. This implies a monolayer load of 

0.5 mg/cm2. Chapter 9 further discusses the uncertainty resulting from this assumption. 

5.1.3. Estimating Fraction Absorbed 

 Three studies have examined dermal absorption of TCDD from soil (Roy et al., 2008; 

Shu et al., 1988; Poiger and Schlatter, 1980). The Roy et al. (2008) data were selected as the 

best basis for estimating dermal absorption fractions applicable to the ceramics studio. This was 

because the test soil was most fully described allowing comparisons to the clay, and multiple 

exposure times were used allowing evaluation of how dose varies with time. 

 Roy et al. (2008) conducted a variety of experiments in which TCDD was applied to soil 

on human skin in vitro, rat skin in vitro, and rat skin in vivo. The experiments were conducted 

with both a low organic carbon soil and a high organic carbon soil. Ferrario et al. (2007, 2004) 

studied 21 samples of processed ball clay used in ceramics studios. They found that the organic 

carbon content of these samples ranged from 0.06 to 1.1% with a median and geometric mean of 

approximately 0.4%. This level is very similar to the level in the low organic carbon soil used by 

Roy et al. (0.45%). Accordingly, this discussion focuses on the Roy et al. results for the low 

organic carbon soil applied to human skin in vitro. For purposes of evaluating human exposure 

to TCDD contaminated soil, Roy et al. (2008) made three adjustments to their 24-hour 

absorption percentage from the human skin in vitro tests: 

 The amount of TCDD found in the skin at the end of the experiment (0.20%) was added 

to the amount in the receptor fluid to get total absorption 

 The absorption percentage was multiplied by two to reflect the ratio observed between 

the rat in vivo tests with low carbon soil and rat in vitro tests with low carbon soil 

 The absorption percentage was multiplied by another factor of two to make it applicable 

to soil loads less than or equal to the monolayer 

Table 5 shows that in the present study, these adjustments were made for each data point. 

Finally these adjusted data were fit to a polynomial function relating absorption percentage and 

time (see Figure 3). The equation for this function is as follows (converting percent to fraction): 

AFdermal = (0.0005t

2

 + 0.05t + 0.7692)/100 (2) 

where 

AFdermal = dermal absorption fraction 

t = time (hour) 
24

Table 5. Percent absorbed over time 

a c d Time Receptor Fluid Receptor Fluid Adjusted Best Fit

b (hr) (%) + Skin (%) (%) (%)

1 0.02 0.22 0.88 0.82

2 0.08 0.28 1.12 0.87

4 0.07 0.27 1.08 0.98

8 0.02 0.22 0.88 1.20

24 0.28 0.48 1.92 2.26

48 0.91 1.11 4.44 4.32

72 1.54 1.74 6.96 6.96

96 2.25 2.45 9.8 10.18

a

 Percent absorbed into receptor fluid from human skin in vitro testing by Roy et al. (2008). b

 Addition of 0.2% absorbed into skin at end of experiment. 

c

 Multiplied by a factor of 2 for the in vitro:in vivo ratio and by another factor of 2 for application to soil loads equal 

to or less than monolayer. 

d

 Based on Eq. 2. 

hr = hour. 
25

Figure 3. Scatter plot of adjusted absorption data versus time with trend line.

Source: Adapted from Roy et al. (2008).

5.1.4. Calculating Dermal Dose 

The rinsing experiments indicated that clay loading exceeded the monolayer load in 

some, but not all, cases. The dermal absorption fractions presented above were applied to the 

measured loads where these were less than or equal to monolayer loads. At soil loadings greater 

than monolayer, the dermal absorption fraction was applied to only the monolayer load. 

Accordingly, the dose of dioxins absorbed through the skin of the artisan subjects during this 

study was estimated using the following equation for each body part and then summed:

Ddermal = SA L C AFdermal (3)

where

Ddermal = dermally absorbed dose (pg TEQ/d)

SA = skin area exposed (cm2)

L = daily clay loading on skin (measured or monolayer, whichever is less) 

(mg/cm2-day)

C = dioxin concentration in clay (pg TEQ/g)

AFdermal = dermal absorption fraction

Percent Absorbed vs Time

y = 0.0005x2 + 0.05x + 0.7692

R

2

 = 0.9956

0

2

4

6

8

10

12

0 20 40 60 80 100 120

Time (hr)

Percent
26

The approach used in this study assumes that dermal exposure is limited to the 

skin area which is not covered by clothing. As discussed in Chapter 9, a number of 

studies have shown that dusts can penetrate clothing and deposit on skin. Since none of 

these studies were specific to ceramic art studios it is uncertain how they apply in this 

situation (see Chapter 9 for a full discussion of the uncertainties associated with this 

issue). 

5.2. INHALATION 

The portion of particles that enter the respiratory tract through the nose or mouth 

(inhalability) depends mainly on particle size, route of breathing (through the nose or mouth), 

wind speed, and a person’s orientation with respect to wind direction. Inhaled particles may be 

either exhaled or deposited in the extrathoracic (ET), tracheobronchial (TB), or pulmonary (PU) 

airway. The deposition of particles in the respiratory tract depends primarily on inhaled particle 

size, route of breathing, tidal volume, and breathing frequency (American Conference of 

Governmental Industrial Hygienists, 2004; International Commission on Radiological Protection, 

1994). Appendix B presents a detailed discussion of how to consider these factors and estimate 

the amount of particulate that deposits in various regions of the respiratory tract.

The absorbed inhalation dose is estimated as follows:

Dinhalation = Dr C AFr (1g/1,000 mg) (4)

where

Dinhalation = inhalation dose (pg TEQ/d)

Dr = dose of particles to region r of the respiratory tract (mg/d)

C = dioxin concentration on particles (pg/g)

AFr = absorption fraction for region r of the respiratory tract

This equation is used to estimate the absorbed dose to the three regions of the respiratory 

tract (ET, TB, and PU) and then summed to derive total inhalation dose. In general, particles 

deposited in the ET and TB regions clear rapidly (within 1–2 days) to the throat and are 

swallowed. Accordingly, the absorption of dioxin from particles deposited in these regions is 

treated as if the particles had been ingested with an absorption fraction of 0.3 (U.S. EPA, 2003). 

The particles depositing in the PU region remain there a long time, and most of them are 

ultimately absorbed directly into the body (assumed absorption fraction of 0.8 based on U.S. 

EPA, 2003). Chapter 9 discusses inhalation uncertainties.
27

5.3. INGESTION 

The ingestion dose is estimated by assuming that all particles deposited on the surrogate

food and beverage samples are ingested. For both types of samples, the dose was calculated 

using the equation below: 

Dingestion = (F + B) C AFingestion (5)

where

Dingestion = ingestion dose (pg TEQ/d)

F = deposited clay on food (g/d)

B = deposited clay on beverage (g/d)

C = dioxin concentration in clay (pg TEQ/g)

AFingestion = absorption fraction for ingestion

AFingestion was assumed to equal 0.3 based on recommendations in U.S. EPA (2003) for 

ingestion of dioxin in soil. The ingestion of dioxin from inhaled particles is included in the 

inhalation dose as discussed above. Chapter 9 discusses ingestion uncertainties.

5.4. TOTAL DOSE 

The total absorbed dose was estimated to be the sum of the dermal absorption, inhalation, 

and ingestion doses as shown below:

Dtotal = Ddermal + Dinhalation + Dingestion (6)

where

Dtotal = total dose (pg TEQ/d)

Ddermal = dermally absorbed dose (pg TEQ/d)

Dinhalation = inhalation dose (pg TEQ/d)

Dingestion = ingestion dose (pg TEQ/d)
28

6. QUESTIONNAIRE RESULTS 

 The complete questionnaire and all responses are presented in Appendix A. The 

questionnaire focused on characterizing each subject’s work with clay in terms of 

frequency/duration, type of activity, clothing worn, and impact on skin. Table 6 summarizes the 

questionnaire results for the amount of time that the subjects spent working directly with clay. 

The subjects worked with clay, on average, for 30 hours per week and 38 weeks per year over a 

6-year period. The times varied widely, however, reflecting the types of students involved. A 

student obtaining an advanced degree in ceramics is likely to work with clay daily over many 

years. In contrast, a student who takes a pottery class to fulfill a general education requirement 

is likely to experience similar exposures, but only for 1–3 hours per day over the duration of the 

class (9 months or less). 

Table 6. Questionnaire questions on duration and frequency of subject’s 

clay work 

Question (n = 8) Mean (SD) Median Max Min

Approximately how many hours 

per week do you work with clay? 30 (21) 23 70 10

Approximately how many weeks 

per year do you work with clay? 38 (10) 38 52 20

How long (years) have you been 

doing clay work with this level of 

intensity?

6 (8) 3 24 1

SD = standard deviation. 

Table 7 summarizes the participants’ answers to several questions about their clay work. 

Some of the questions address the types of clothing worn, how often the subjects wash their 

hands, and whether the subjects could correlate any skin health effects with working with clay. 

All eight subjects answered that they have dry skin because of the clay work. In general, the 

subjects wash their hands soon after working with clay: their faces and arms within a few hours 

and the rest of their bodies within 24 hours. The responses indicate that one subject gets a rash 

when using the wheel for throwing, another subject has nasal congestion due to clay work, and 

another subject’s fingernails do not grow well. 
29

Table 7. Questionnaire questions about clay work 

Question (n = 8)

Summary of answers 

(number of subjects with similar answers)

What type of clay artwork do you 

do?

Hand building/sculptural work (7), throwing on wheel 

(3), mixing clay, and maintenance work (1).

What types of clothing do you wear 

while you work?

In general, long sleeves and pants in cool weather and 

short sleeves and pants or shorts in warm weather; both 

closed-toe shoes and sandals are worn at times.

What areas of skin typically are 

exposed to the clay while you work?

Always face and hands; 

exposed.

arms, legs, and feet when 

In relation to the time you complete 

working with clay, when do you 

wash parts of your body that have 

been exposed to clay?

Soon after: hands (8), arms (1), face (1).

Within a few hours: arms (2), face (6).

Within 24 hours: face (1), rest of body (4).

How do you wash your skin after you 

work with clay?

Soap and water or just water (8).

Do you correlate any skin health 

issues with how much you work with 

clay? If yes, what?

Dryness (8), rash on hands when using wheel (1), nasal 

congestion (1), fingernails do not grow well (1).
30

7. COMPARING EXPOSURES ACROSS SUBJECTS 

 In this chapter, a hypothetical dioxin dose is estimated for each subject and used to 

evaluate which pathways and activities contribute most to total dose. This is done by assuming 

that each subject uses clay with the same level of dioxin. More specifically, it is assumed that 

each subject uses a clay mixture with 20% ball clay and that the ball clay contains 808 pg TEQ/g 

(these are typical values as discussed in Chapter 4). Accordingly, the dioxin levels in the clay 

were assumed to be 20% of 808 pg TEQ/g or 162 pg TEQ/g. This concentration was also 

assumed to apply to inhaled dust and dust settled onto food. A variety of other factors were also 

held constant across subjects to facilitate this analysis:

 Exposure duration. Chapter 6 presents the questionnaire results, which indicate a 

median weekly time for clay work of 23 hours. Assuming a 5-day work week, this would 

correspond to about 4 hours/day. This value was applied to all subjects. 

 Monolayer load. The monolayer load varies depending on particle size but is assumed 

2 here to be 0.5 mg/cm for all subjects. This is based on the geometric mean of the range 

of possible median particle sizes, i.e., 0.5 to 27 μm (see Section 5.1 for further discussion 

of this issue). 

 Dermal absorption fraction. This will depend on exposure time, as discussed in 

Section 5.1. The time that the skin is exposed to clay will vary with individual behaviors 

and body parts. Some body parts (such as hands and faces) are likely to be washed more 

frequently than others (such as feet, legs, and arms), resulting in longer exposure times. 

The questionnaire data collected during this study (see Chapter 6) suggest that the artists 

generally wash their hands soon after working with clay, wash their faces and arms 

within a few hours, and wash the rest of their body within 24 hours. Accordingly, the 

exposure time for feet and legs was assumed to be 24 hours, and the absorption fraction 

corresponding to 24 hours was applied (2.3%). The exposure time for hands, arms, and 

face was assumed to be 4 hours with a corresponding 1.0% absorption. 

 Ingestion absorption fraction. This was set to 0.3 based on recommendations by EPA 

for ingestion of dioxin in soil (U.S. EPA, 2003). 

 Inhalation absorption fraction. This was set to 0.3 for ET and TB regions based on the 

assumption that the area is rapidly cleared to the gastrointestinal tract. It was set to 0.8 

for the PU region based on recommendations by EPA for inhalation of dioxin in air (U.S. 

EPA, 2003). 

 The hypothetical dioxin dose for each subject is calculated using the constant values 

described above and their individual exposure conditions (e.g., dust level in air, clay load on 

skin, clay load on food). The dose estimates are considered to be hypothetical because they are 
31

based on assumed dioxin levels in the various exposure media rather than on studio-specific 

measurements. Chapter 8 uses Monte Carlo simulations to analyze the possible variability in 

dose resulting from a range of dioxin levels in clay, ball clay mixtures, and exposure factors.

 This chapter first addresses each pathway separately (dermal contact, inhalation, and 

ingestion) and then addresses total dose. Individual exposures vary widely, and it is important to 

consider the subject’s activity and clothing in evaluating the results. Table 8 is provided as a 

reference for this purpose with summaries of each participant’s activities and clothing. 

7.1. DERMAL CONTACT 

 As described in Section 5.1, the mass of clay rinsed from the skin was used to estimate 

clay loadings on the skin for each exposed body part. The rinsing data are presented in 

Appendix E. Section 5.1 also explains that the skin loading is compared to the monolayer load, 

and the absorption fraction is applied to the lower amount. Table 9 shows the dermal absorption 

estimate for each subject. Subjects 1 through 8 wore clothing that limited their exposures to only 

hands and arms (although arm exposure was detected on only Subjects 1 and 6). The estimates 

for Subjects 9 and 10 include hands, arms, legs, and feet because they wore clothing allowing 

exposure to these areas. All subjects could have had exposure to the face, but this was evaluated 

only for Subjects 9 and 10. Pictures of the clay residues on skin are shown in Appendix F. 

Table 9 shows that 6 of the 10 subjects had skin loadings exceeding the monolayer. The 

absorbed dose ranged from 0.23 to 7.09 pg TEQ/d with a mean of 1.35 pg TEQ/d (SD = 2.05).

 The relationships between the activities of the subjects and their dermal exposure are

discussed below: 

 Wheel work (Subjects 6 and 9). This activity led to the highest dermal exposures. The 

high exposures were caused by the close proximity of the subjects to the wheel, the 

splashing of wet clay onto their bodies, and the use of both hands to mold the clay. The 

total dermal dose for Subject 9 was about 4 times greater than that for Subject 6, resulting 

primarily from their clothing difference. Both had similar hand and arm exposure, but 

Subject 9 had high exposure to legs and feet and Subject 6 had no exposure in these 

areas. 
32

Table 8. Artisan activities of each subject 

Artisan/staff

(minutes sampled) Description of activity Clothing

Test 1, April 2003

Subject 1/male

(153 min)

Wedged clay on a wedging board to remove air from the 

clay before kneading and shaping clay by hand. Used a 

wooden press to press the clay into flat, approximately 

2.5-cm thick sheets. Also, pounded semi-dry clay into 

balls, placed in ball mill for smoothing rough edges.

Short-sleeved shirt, long 

pants, socks, shoes

Subject 2/male,

nonartisan staff

(84 min)

Poured powdered components into large mixer for clay 

manufacture while wearing dust mask and while the dust 

removal system was operational. Weighed out portions of 

clay, and bagged and stored them. Subject moved to gas 

kiln room, where he cut blocks, built the kiln up a bit, and 

vacuumed. Finally, subject used compressed air to clean 

the dust off himself.

Short-sleeved shirt, long 

pants, socks, shoes

Subject 3/female

(124 min)

Subject wedged clay and covered a prefabricated mold 

with clay using her hands to mold and shape the clay. 

Short-sleeved shirt, long 

pants, socks, shoes

Subject 4/female

(121 min)

Subject cut pre-wedged and formed blocks of clay into 

5-cm thick pieces, loaded the blocks into a pneumatic 

press, pressed a pattern into each, cut blocks to the proper 

shape, and then stacked the finished pieces to be fired.

Long-sleeved shirt (rolled 

up), long pants, socks, 

shoes

Subject 5/male

(136 min)

Subject hand rolled clay into 60-cm long ―snake-like‖ 

cylinders, which he then hand-formed into conical pots.

Short-sleeved shirt, long 

pants, socks, shoes

Subject 6/female

(123 min)

Subject threw a variety of clay items, including a pitcher, 

a vase, pots, and bowls on the pottery wheel.

Short-sleeved shirt, long 

pants, socks, shoes

Subject 7/female

(124 min)

Subject 

items.

wedged, rolled, cut, and hand-built a variety of Short-sleeved shirt, long 

pants, socks, shoes

Subject 8/female

(138 min)

Subject 

pieces o

wedged, 

f clay an

rolled, shaped, cut, and hand-built large 

d placed them on a mold.

Short-sleeved shirt, long 

pants, socks, shoes

Test 2, July 2004

Subject 9/female,

five sessions

(295–476 min)

Subject threw a variety of clay items, including 

bowls, vases, and cups, on the pottery wheel.

plates, Short-sleeved shirt, short 

pants, sandals

Subject 10/female, 

three sessions

(406–438 min)

Subject sculpted detailed designs into clay tiles and 

plaques; also chipped small bits of excess clay off pieces 

of art that had already been fired.

Short-sleeved shirt, 

3/4-length pants, sandals

min = minute. 
33

Table 9. Hypothetical estimates of dermal dose 

Body part

Clay load on skin 2 (mg/cm ) aSkin area 2 b (cm )Fraction 

uncovered

Absorbed dioxin 

dose

c,d,e (pg TEQ/d)

Subject 1

Hands 0.38 970 1.0 0.58

Arms 0.15 2,406 0.5 0.29

Total 0.87

Subject 2

Hands [2.01] 970 1.0 0.77

Subject 3

Hands [0.51] 865 1.0 0.69

Subject 4

Hands 0.17 855 1.0 0.23

Subject 5

Hands [2.61] 1,005 1.0 0.80

Subject 6

Hands [9.25] 790 1.0 0.63

Arms [2.99] 2,005 0.6 0.95

Total 1.58

Subject 7

Hands 0.26 785 1.0 0.33

Subject 8

Hands [1.90] 715 1.0 0.57
34

Table 9. continued. 

Body part

Clay load on skin 2 (mg/cm ) aSkin area 2 b (cm )Fraction 

uncovered

Absorbed dioxin 

dose

c,d,e (pg TEQ/d)

Subject 9

Hands [10.12] 857 1.0 0.68

Arms [1.50] 2,265 0.75 1.35

Lower legs [0.72] 2,161 1.0 3.96

Feet 0.26 1,151 1.0 1.09

Face 0.03 374 1.0 0.02

Total 7.09

Subject 10

Hands 0.20 783 1.0 0.24

Arms 0.04 2,271 0.9 0.13

Lower legs 0.11 2,095 0.1 0.08

Feet 0.03 1,109 1.0 0.11

Face 0.04 368 1.0 0.02

Total 0.59

a 2 All bracketed loads exceed monolayer of 0.5 mg/cm and were reduced to this value in absorption calculation. 

b Skin area is for total body parts; for two-sided parts, it is the sum of right and left sides. 

c 2 2 Absorption = skin load (mg/cm -day) × skin area (cm ) × fraction uncovered × dioxin concentration in clay 

(pg TEQ/g) × 10-3 mg/g × absorption fraction. 

d All calculations assume dioxin concentration in clay = 162 pg TEQ/g and absorption fraction is 2.3% for feet and 

legs, and 1.0% for hands, arms, and face. 

e Results from Subjects 1 through 8 are based on one work session, from Subject 9 are based on average of five 

sessions, and from Subject 10 are based on average of three sessions. 

TEQ = toxic equivalent. 
35

 Mixing (Subject 2). Subject 2 was involved in the mixing and handling of dry clays and 

furnace/kiln maintenance during the work session. This activity produced relatively large 

hand loadings. 

 Wedging and molding (Subjects 1, 3, 4, 5, 7, and 8). Wedging clay involves kneading 

and hitting clay against a tabletop to purge air pockets from the clay. During the wedging 

process, the clay is firm and dry as compared with clay used on the wheel. This activity 

2 produced a wide range of hand loadings (from 0.17 to 2.61 mg/cm ). 

 Sculpting (Subject 10). This involved sculpting activities on dry clay. At times, fine 

detailing tools were used that involved very little contact with the clay, resulting in low 

hand loading. 

 Table 10 shows the percent contribution to the dermal dose by body part for Subjects 9 

and 10. Subjects 9 and 10 were tested in July 2004 and wore summer clothing, which allowed 

exposure to their legs and feet. Leg and foot exposure accounted for 71% of the total dose for 

Subject 9 and 33% of the total dose for Subject 10. This reflects the relatively large surface 

areas and higher absorption fraction (due to longer exposure time) for these parts. The 

uncovered portion of Subject 10’s lower legs was only 10%, so the leg contribution to total dose 

was much less than that of Subject 9. Facial exposures were low, accounting for only 0.2–4% of 

total dose. 

Table 10. Percent contribution to dermal dose by body part 

Body part

Percentage of dose

Subject 9 (wheel) Subject 10 (sculpture)

Hands 10 41

Arms 19 22

Legs 56 14

Feet 15 19

Face 0.2 4
36

7.1.1. Clay Loads on Surfaces 

The horizontal surfaces in ceramic art studios can have high dust loads resulting from air 

deposition. Most clay on the hands of artisans probably results from direct contact with clay, but 

some could also result from contact with surfaces. In the interest of exploring this issue, wipe 

samples were collected from the work surface of each subject. The sampled surfaces were 

porous concrete tabletops. The artisans involved in wedging used a nonporous plastic composite 

surface. Table 11 shows the surface sampling results. The surface dust loads ranged from 0.2 to 

7 mg/cm2, which are high compared with dust loads on floors in residences (i.e., 0.005 to 0.7 

mg/cm2) (Lioy et al., 2002). The efficiency of transfers from surfaces to hands will vary 

depending on the type of surface, type of residue, hand condition, force of contact, etc. Rodes et 

al. (2001) conducted hand press experiments on particle transfer to dry skin and measured 

transfers with central values of about 50% from hard surfaces. Table 11 shows that several of 

the ratios of hand loads to surface loads exceed 50% by a wide margin. Subject 6 was working 

on a wheel and clearly had hand loads resulting from direct contact with clay. Similarly, 

Subjects 5 and 8 had very high hand loads that must have resulted from direct clay contact. The 

other subjects had ratios ranging from 0.05 to 0.30, which are in the range that could result from 

surface transfers. Observation of the subjects indicated that almost all contact with the work 

surface also involved some contact with the clay. Therefore, the hand residues are most likely 

derived from a combination of direct clay contact and transfers from surfaces. 

Table 11. Comparing clay loads on surfaces to clay loads on hands 

Subject

Clay loading on surface

2 (mg/cm )

Clay load on hand

2 (mg/cm )

Ratio of hand load to 

surface load

1 7.002 0.38 0.05

2 NA 2.01 NA

3 2.966 0.51 0.17

4 0.572 0.17 0.30

5 0.774 2.61 3.4

6 0.238 9.25 38.9

7 1.206 0.26 0.22

8 0.419 1.90 4.5

NA = Nonartisan subject was not working at a surface during sampling, so this type of sample was not collected. 
37

7.1.2. Dermatologist Report 

The dermatologist did not diagnose any serious skin health problems among the subjects. 

Small abrasions and common skin conditions such as dryness and cracking, as the subjects 

reported on the questionnaires, were noted, but changes in these conditions could not be detected 

based on before and after observations. 

7.2. INHALATION

Estimating the inhalation dose involved measuring particle concentrations in air and 

modeling deposition to various regions of the respiratory system. Classroom exposures were not 

estimated.

7.2.1. Particle Levels in Air 

As described in Chapter 3, four different sampling techniques were used during the April 

2003 tests to measure clay particle concentrations in air: two personal monitors and two area 

monitors. The data from all four devices are shown in Appendices G and H. The RespiconTM

personal air sampler normally would have been the best indicator of individual exposures, but 

the blanks were high, resulting in a high detection limit and a high frequency of nondetects in the 

data. Instead, the cascade impactor was chosen as the best indicator of daily exposure. Although 

this is an area sampler, it was located near the subjects and the subjects were generally stationary 

during the test. Thus, it should have been a reasonable indicator of individual exposures. Also, 

the cascade impactor uses deposition collectors and gravimetric techniques to estimate air 

concentrations; consequently, it is a more direct measurement technique than the other two 

instruments (pDR-1000 and Climet

®

), which use light scattering to estimate particle 

concentration. These optical devices provide a nearly continuous readout of concentration 

levels, making them better suited to evaluating short-term fluctuations in particle levels rather 

than long-term concentrations.

Only the cascade and Climet® monitors were used in the July 2004 tests. The instruments 

were located even closer to the individuals, i.e., within 30 cm of their breathing zones. The data 

were used in a fashion consistent with the April 2003 tests, i.e., daily exposures were based on 

the cascade data and the Climet® was used to evaluate short-term fluctuations.

Table 12 presents the air data for each subject on the basis of the cascade measurements. 

The MMADs were estimated by fitting the data to log-normal distributions (see the discussion in 

Appendix B). Table 12 indicates that the range for total particulate matter is 0.084 to 

0.99 mg/m3. Note that the upper end of this range is less than the Occupational Safety and 

Health Administration (OSHA) standard for total particulates of 15 mg/m3(OSHA, 2004). 
38

Table 12. Particle concentrations in air and mass median aerodynamic diameter 

(MMAD) based on cascade impactor 

Subject MMAD (μm) Total concentration 3 (mg/m )

1 26.9 0.35

2 44.6 0.47

3 18.5 0.99

4 25.0a 0.37

5 25.0a 0.13

6 20.2 0.61

7 13.0 0.51

8 26.7 0.64

9 32.6 0.084

10 16.0 0.24

a Nondetects prevented calculation 

the remaining first eight subjects. 

of the MMAD for these subjects; they were assumed equal to the average over 

Subject 3’s concentration was the highest because students were cleaning the floor near the area 

samplers (see the discussion below). Subject 9’s concentration was the lowest, resulting from a 

relatively low activity level during the testing time period. Subject 5’s concentration was also 

low, likely because a steady breeze entered through an open window in the room in which 

sampling was occurring. All of the other subjects had fairly similar concentrations. Subject 2 

was the only one who changed room locations during the sampling period and the sampling 

equipment was moved with him. 

 The two subjects using wheels (Subjects 6 and 9) had very different air exposures. 

Because a great deal of water is used to moisten clay during wheel molding (the clay was 

saturated with water and a pan of water was placed directly next to the artisans for their use), this 

setting would not be expected to produce much clay dust, which was observed for Subject 9. 

Subject 6, however, had fairly high air levels. Subject 6 was located near a classroom that, as 

discussed below, had high activity levels. Therefore, this subject’s high air levels may have been 

associated more with the classroom activities than the wheel activities. 
39

Figure 4 shows the plot of concentration versus time (based on the Climet® CI-500 area 

particle counter) for Subject 3, who worked in an area designated for graduate student work 

adjacent to a large classroom. Approximately 50 minutes into the sampling session, about 

20 students from the adjacent classroom began sweeping and wiping down the surfaces. This 

activity continued for approximately 15 minutes and generated a significant cloud of dust. 

Figure 4 shows particle levels began rising at about 50 minutes, peaked sharply at 

60–70 minutes, and declined to low levels at about 80 minutes. 

Figure 4. Real-time particle concentration for Subject 3 using the CI-500 particle 

counter.

During two of Subject 10’s sculpture work sessions, a small dog was present. The dog’s 

movement disturbed dust on the floor of the ceramics studio and, in turn, increased the particle 

concentration. Figures 5 and 6 are the real-time traces for the Climet® monitor for the sculpting 

work sessions during which the dog was present. The dog was present for the entire first 

sculpting work session. This was reflected in the relatively constant variation in the particle 

concentration throughout the work session. During the second sculpting work session, the dog 

did not arrive until 138 minutes into sampling. Note the increase in overall particle 

concentration and increase in variability of particle concentration after arrival of the dog. The 

presence of a dog in the studios and classrooms is not likely to be a common occurrence, 

Area Particle Concentration 

using the CI-500 Particle Counter

0

10

20

30

40

0 25 50 75 100 125

Time (min)

particle conc. (mg/m

3

)
40

Figure 5. Sculpture Session 1 with dog present.

Figure 6. Sculpture Session 2 with dog present.

Sculpture Session 1

0

5

10

15

20

25

30

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)

Sculpture Session 2

0

2

4

6

8

10

12

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3

)
41

especially during the regular school year. Therefore, the particle concentrations during the work 

sessions when the dog was present (1 and 2) were not used to estimate the exposures for this 

subject. It should be noted, however, that pets, which may be present in many ceramic art 

studios, can increase the suspended dust levels and spread dust to other areas. 

7.2.2. Inhalation Dose 

 Table 13 shows the absorbed dose in various regions of the respiratory system for all 

10 subjects. The total inhalation doses ranged from 0.006 to 0.09 pg TEQ/d with an average of 

0.04 pg TEQ/d. Most particle deposition was found to occur in the ET region. Appendix B 

presents the modeling to support these estimates. 

Table 13. Hypothetical estimates of inhalation dose 

Subject

Absorbed dose (pg TEQ)a

b ET b TB PUc Total

1 0.032 0.001 0.003 0.035

2 0.033 0.001 0.003 0.036

3 0.082 0.002 0.010 0.094

4 0.028 0.001 0.002 0.031

5 0.012 0.000 0.001 0.014

6 0.054 0.001 0.004 0.059

7 0.049 0.001 0.006 0.057

8 0.048 0.001 0.003 0.052

9 0.005 0.000 0.001 0.006

10 0.022 0.001 0.002 0.025

a Dose calculated using procedures in Appendix B for nasal breathing; subject exposure concentrations from 

Appendix H; 4-hour exposure duration and dioxin concentration of 162 pg TEQ/g clay. 

b Absorption fraction of 0.3 assumed, since these regions rapidly clear into the gastrointestinal tract. 

c Absorption fraction of 0.8 assumed, in part, due to slow particle clearance from this region. 

ET = extrathoracic; PU = pulmonary; TB = tracheobronchial; TEQ = toxic equivalent. 
42

The inhalation exposure estimates assume that no respiratory protection was used. 

Generally, this was true, however, Subject 2 used a dust mask while pouring powdered clay into 

a mixer for clay preparation. This reduced his inhalation exposures relative to levels reported 

here. 

7.2.3. Classroom Exposure 

Estimating student exposures in a classroom setting was not an objective of this study. 

However, some insight on this issue can be gained from the data for Subjects 1, 3, and 6. These 

subjects performed their clay activities adjacent to the undergraduate classroom during times 

when undergraduate classes of 20–25 students were participating in clay-related activities. The 

area particle samples collected for these subjects are generally representative of the inhalation 

exposure of students in those classes. As discussed above, students in this class swept the floor 

during Subject 3’s testing period, producing elevated particle concentrations for about 

30 minutes. 

7.3. INGESTION

The ingestion dose was calculated by assuming that all deposited material on the 

surrogate food and beverage samples was ingested. As Table 14 shows, clay deposition onto the 

food and beverage samples reached detectable levels in only 5 out of 16 total samples. The 

deposition amounts for the nondetects were assumed to equal half the detection limit. The 

resulting ingestion doses ranged from 0.03 to 0.1 pg TEQ/d. The field technicians did not 

observe hand-to-mouth activities for any of the subjects. Also, none of the subjects ate food or 

smoked without first washing the clay from their hands. No deposition samples were collected 

for Subjects 9 and 10.

7.4. TOTAL DOSE

Table 15 lists the hypothetical estimates of total dioxin dose derived by summing across 

exposure pathways for each subject. The total doses ranged from 0.32 to 7.10 pg TEQ/d with an 

average of 1.44 pg TEQ/d. Table 16 shows the percentage contribution of each exposure 

pathway to the total dose of each subject. Dermal absorption is the major contributor to total 

dose for all subjects, exceeding 67% for all subjects. Ingestion and inhalation contribute similar 

amounts, generally in the range of 1–20%. Table 17 shows the dose estimates by activity. The 

highest total doses were associated with wheel activities. 
43

Table 14. Clay deposition and hypothetical estimates of ingestion dose

Subject

Clay deposited onto 

food (mg)

Clay deposited into 

beverage (mg)

Ingestion dose 

a, b (pg TEQ/d)

1 0.71 0.66 0.07

2 <DL <DL 0.03

3 <DL <DL 0.03

4 <DL 0.72 0.05

5 <DL <DL 0.03

6 <DL <DL 0.03

7 1.66 <DL 0.1

8 1.50 <DL 0.09

a Ingestion dose (pg TEQ) = (deposited clay on food [mg] + deposited clay on beverage [mg]) × dioxin 

concentration in clay (pg TEQ/g) × absorption fraction × (1 g/1,000 mg). 

b All calculations assume dioxin concentration in clay = 162 pg TEQ/g, absorption fraction = 0.3, all deposited clay 

is ingested, and nondetects were set equal to half the detection limit. 

DL = detection limit (0.60 mg); TEQ = toxic equivalent. 
44

Table 15. Hypothetical estimates of total dioxin dose (pg TEQ/d)

Subject

Estimated dioxin dose (pg TEQ/d)

Inhalation Ingestion Dermal absorption Total

1 0.035 0.07 0.87 0.97

2 0.036 0.03 0.77 0.84

3 0.094 0.03 0.69 0.81

4 0.031 0.05 0.23 0.32

5 0.014 0.03 0.80 0.84

6 0.059 0.03 1.58 1.67

7 0.057 0.1 0.33 0.49

8 0.052 0.09 0.57 0.71

9 0.006 NM 7.09 7.10

10 0.025 NM 0.59 0.62

Mean (SD) 0.041 (0.025) 0.05 (0.03) 1.35 (2.05) 1.44 (2.02)

Median 0.036 0.04 0.73 0.82

Minimum 0.006 0.03 0.23 0.32

Maximum 0.094 0.10 7.09 7.10

NM = not measured; SD = standard deviation; TEQ = toxic equivalent. 
45

Table 16. Percent contribution to total dioxin dose

Subject

Percentage of dose

Inhalation Ingestion Dermal absorption

1 3.6 7.2 89.2

2 4.3 3.6 92.1

3 11.5 3.7 84.7

4 9.9 15.8 74.3

5 1.6 3.6 94.8

6 3.5 1.8 94.7

7 11.7 20.6 67.7

8 7.4 12.7 79.9

9 0.1 NM 99.9

10 4.1 NM 95.9

NM = not measured. 
46

Table 17. Dose estimates by activity

Activity Subject

Inhalation 

dose 

(pg TEQ/d)

Ingestion

dose

(pg TEQ/d)

Dermal

dose (pg 

TEQ/d)

Total dose 

(pg TEQ/d)

Wedging and 

molding

1 0.035 0.07 0.87 0.97

3 0.094 0.03 0.69 0.81

4 0.031 0.05 0.23 0.32

5 0.014 0.03 0.80 0.84

7 0.057 0.1 0.33 0.49

8 0.052 0.09 0.57 0.71

Mixing 2 0.036 0.03 0.77 0.84

Wheel 6 0.059 0.03 1.58 1.67

9 0.006 NM 7.09 7.10

Sculpting 10 0.025 NM 0.59 0.62

NM = not measured; TEQ = toxic equivalent. 
47

8. MONTE CARLO SIMULATION OF THE EXPOSURE DATA

Chapter 7 presented hypothetical dose estimates for each subject, assuming that all were 

using typical amounts of ball clay with average dioxin levels. In this chapter, Monte Carlo 

simulations are used to explore the doses that could occur in a broad population of artists with a 

wide range of behaviors using ball clay with differing levels of dioxin. The simulations are 

based largely on the range of activities observed during this study. As noted in the Introduction, 

the OSU studio has a modern ventilation system and is well maintained. Therefore, these 

simulations are most representative of how doses may vary in similar facilities. A wider range of 

results would be expected across all types of ceramic art facilities. Appendix I provides a 

detailed outline of the Monte Carlo procedure.

The general strategy for selecting input value distributions was as follows. The 

distribution of skin surface areas across adults in the general population was assumed to be 

log-normal with mean and standard deviation from the Exposure Factors Handbook (U.S. EPA, 

1997). Similarly, the dioxin concentration in clay was assumed to have a log-normal distribution 

with mean and standard deviation from Ferrario et al. (2007, 2004). The rationale for choosing 

log-normal distributions was that physiological parameters and environmental media 

concentrations are commonly found to have these types of distributions. The remaining 

exposure factor parameters were based on observations from this study. These were generally 

assumed to have triangular distributions with ranges based on minimum and maximum values 

and peaks based on means. The rationale for choosing a triangular distribution was that (1) the 

small sample sizes associated with the study observations prevented fitting the data to standard 

distributions and (2) it reflected the likelihood that a central value would occur most often. In 

some cases (e.g., clay load on face), only two data points were available and a uniform 

distribution was assumed. Table 18 lists the distributions assumed for all input variables.

Crystal Ball 7 software was used to conduct 1,000 trial simulations. For each simulation 

trial, a set of parameter values was obtained by randomly sampling the parameter distributions 

shown in Table 18 and then computing the dioxin dose. Chapter 5 presents the equations used to 

calculate the dose. All simulation trials first select a set of values for the dioxin concentration in 

ball clay, the fraction of ball clay in the blend used by the artist, gender, and the exposure 

duration. Table 18 shows the general parameters. The simulation then calculates the dose from 

the dermal, inhalation, and ingestion pathways, as discussed below:

 Dermal. The simulation was designed to first select a total body surface area from 

log-normal distributions for females and males. Subsequently, skin surface areas for 
48

Table 18. Monte Carlo simulation input parameters and sampling distributions

Parameter Distribution Basis

General parameters

Dioxin concentration in ball clay 

(pg TEQ/g)

Log-normal (mean = 808, 

SD = 318)

Ferrario et al. (2007, 2004) (n = 21)

Fraction of ball clay in blend Triangular (0, 0.2, 1.0) Data in this study (n = 10)

Exposure duration (hr/d) Triangular (1, 4, 10) Judgment and data from this study (n = 8) 

Gender selector Uniform (0, 1.0) Used to select male 50% of time, and female 

50% of time

Dermal absorption parameters

Total body surface area for 2 males (cm )Log-normal (mean = 19,700, 

SD = 1,900)

Exposure Factors Handbook

1997) (n = 32)

(U.S. EPA, 

Total body surface area for 2 females (cm )Log-normal (mean = 17,300, 

SD = 1,680)

Exposure Factors Handbook

1997) (n = 57)

(U.S. EPA, 

Clothing selector Uniform (0, 1.0) This is applied using Table 19. Judgment and 

data from this study (n = 8) 

Clay load 2 on hand (mg/cm ) Triangular (0.1, 3.0, 10) Range and mean based on observations from 

this study (n = 10)

Clay load 2 on arm (mg/cm ) Triangular (0.04, 0.35, 3.0) Data in this study (n = 4)

Clay load 2 on leg (mg/cm ) Uniform (0.1, 0.70) Data in this study (n = 2)

Clay load 2 on feet (mg/cm ) Uniform (0.03, 0.3) Data in this study (n = 2)

Clay load 2 on face (mg/cm ) Uniform (0.03, 0.04) Data in this study (n = 2)

Ingestion parameters

Clay load on food (mg) Triangular (0.3, 0.7, 1.66) Range and mean

this study (n = 8)

based on observations from 

Clay load on beverage (mg) Triangular (0.3, 0.5, 0.72) Range and mean based on observations from 

this study (n = 8)

Inhalation parameters

Particle concentration in air 3 (mg/m )Triangular (0.08, 0.44, 0.99) Range and mean based on observations from 

this study (n = 10)

Median particle size (μm) Triangular (13, 25, 45) Judgment and data from this study (n = 10)

Lung parameters Male—50%; female—50% Based on general population

Fraction of time engaged in light

vs. moderate exertion.

Uniform (0, 1.0) Judgment

Breathing type Oronasal—13%; nasal—87% Brown (2005)

hr = hour; d = day; SD = standard deviation; TEQ = toxic equivalent. 
49

individual body parts were calculated by multiplying the total surface area by the average 

percentage of total surface area. These percentages were obtained from U.S. EPA, 1997: 

hands—5.2%; arms—14%; legs—31.8%; feet—6.8%; and face—2.5% (assumes face 

area equals one-third of head area). This approach ensures that simulation trials have 

realistically matched body part areas. Since the body part area calculations give total 

areas, a fraction unclothed was used to reduce this to the exposed area. These fractions 

were based on four clothing scenarios as shown in Table 19. These clothing scenarios 

were based on questionnaire responses and judgment about typical apparel for a moderate 

climate. A clothing scenario was selected randomly for each simulation trial according to 

the time fractions shown in Table 19. Distributions were also assumed for the clay loads 

on skin. These were assumed to be spread uniformly over the entire unclothed area. As 

discussed in Section 5.1, dermal absorption was assumed to be limited to the monolayer 

that was held constant at the median value of 0.5 mg/cm2 (the impact of changing this 

value is discussed as an uncertainty issue in Chapter 9). Finally, the absorption fractions 

(as presented in Section 5.1) were applied to derive the absorbed dose from exposed body 

parts and then summed to derive total dermal dose. 

 Inhalation. Section 5.2 summarizes and Appendix B presents the procedures used to 

calculate the inhalation dose. Distributions were used to represent the variability in total 

particulate concentration in air and median particle size (see Table 18). Breathing was 

assumed to be either oronasal (13%) or nasal (87%), based on Brown (2005). Inhalation 

parameters (see Appendix B) were based on gender. The rate of breathing was 

determined by the fraction of time engaged in light versus moderate exertion. These 

fractions were varied randomly from 0 to 1.0 using a uniform distribution. Depositions to 

various parts of the respiratory system were modeled as described in Appendix B, 

multiplied by the absorption fraction, and summed to derive the total inhalation dose. 

 Ingestion. The variability in ingested dose was simulated using distributions for the 

levels of clay in the food and beverages as shown in Table 18. As discussed in 

Section 5.3, all deposited material was assumed to be ingested. 

Two Monte Carlo stimulations were conducted. The first simulation was designed to 

evaluate the influence of clay use only. Accordingly, it was conducted using the distributions for 

dioxin concentration in the clay and the fraction of ball clay in the blend used by the artists. All 

other inputs were held constant at their central values. The summer clothing scenario was used 

(i.e., short-sleeved shirt, short pants, sandals). This simulation produced a mean total dose of 

14 pg/d, median of 12 pg/d, and 90th percentile of 28 pg/d. These results are best compared to 

the hypothetical dose estimate for Subjects 9 and 10 (see Chapter 7) because they wore summer 

clothing matching the simulation assumption. Subject 9 had a dose estimate of 7.1 pg/d, 

corresponding to about the 25th percentile of the simulation. Subject 10 had a dose of 0.62 pg/d, 

corresponding to about the 2nd percentile of the simulation. This simulation suggests that clay 
50

 

Table 19. Clothing scenarios based on questionnaire responses 

Clothing scenario Time fraction

Fraction unclothed

Arms Legs Feet

Long-sleeved shirt, long pants, shoes 0.2 0 0 0

Short-sleeved shirt, long pants, shoes 0.6 0.67 0 0

Short-sleeved shirt, short pants, shoes 0.1 0.67 0.67 0

Short-sleeved shirt, short pants, sandals 0.1 0.67 0.67 1.0

choice alone can account for a wide range of exposures with the potential to elevate exposures 

above the hypothetical estimates for the 10 subjects. 

 The second simulation used the distributions for all parameters as shown in Table 18. 

This simulation produced a mean total dose of 6.4 pg/d, median of 3.5 pg/d, and 90th percentile 

of 14.8 pg/d. The standard deviation (8.43) exceeds the mean indicating that the results have a 

wide spread. The hypothetical dose estimates of most subjects would have corresponded to low 

percentiles of this simulation except Subject 9 (75th percentile). Table 20 shows the simulation 

results for each pathway. The simulation means for each pathway exceeded by 3 to 4 times the 

pathway means of the hypothetical dose estimates for the 10 subjects. As observed during the 

field study, the ingestion and inhalation doses are much smaller than the dermal dose. The total 

dose is plotted as a frequency diagram in Figure 7 and as a cumulative probability diagram in 

Figure 8. Figure 7 shows a highly skewed distribution with a peak around 2 pg TEQ/d and a 

long tail to the right extending to about 28 pg TEQ/d. A detailed report showing all inputs and 

outputs for this simulation is presented in Appendix J. 

 A sensitivity analysis was performed using the Crystal Ball 7 software. Each input 

parameter was evaluated using contribution to variance. Figure 9 shows the results of this 

analysis applied to the total dose; it shows that the fraction of ball clay in the blend contributed 

most to variance (45.2%), followed by clothing selected (36.2%) and dioxin concentration 

(13.8%). Figures 10, 11, and 12 show similar sensitivity analyses were also conducted for each 

exposure pathway separately. 

 Overall, the simulation suggests that higher exposures than those reflected in the 

hypothetical dose estimates of the 10 subjects may occur. This results from the skewed input 

distributions, which generally have long right-hand tails. Also 6 of the 10 subjects had hand 
51

Figure 7. Frequency distribution of total dose (pg TEQ/d) based on Monte 

Carlo simulation.

Table 20. Descriptive statistics of 

Monte Carlo simulation 

dioxin doses from ball clay use, based on a 

Pathway Mean 

Standard 

deviation Median th 90 percentile

Dermal dose 

(pg TEQ/d)

6.2 8.3 3.2 14.4

Ingestion dose 

(pg TEQ/d)

0.14 0.10 0.11 0.26

Inhalation dose 

(pg TEQ/d)

0.11 0.13 0.07 0.26

Total dose 

(pg TEQ/d)

6.4 8.4 3.5 14.8

pg = picogram; TEQ = toxic equivalent. 
52

Figure 8. Cumulative probability distribution of total dose (pg TEQ/d) based 

on Monte Carlo simulation.
53

Figure 9. Sensitivity analysis based on percent contribution to variance for 

total dose. 
54

Figure 10. Sensitivity analysis based on percent contribution to variance for 

dermal dose.
55

Figure 11. Sensitivity analysis based on percent contribution to variance for 

ingestion dose. 
56

Figure 12. Sensitivity analysis based on percent contribution to variance for 

inhalation dose. 

exposure only, and the simulation uses a range of clothing that will result in more skin exposure 

in most trials. 

 Many of the input distributions used in this simulation were based on very limited data or 

judgment. A number of the distributions were based on data from this study, and the degree to 

which the study subjects represented a broader population of artists is unknown. Similarly, the 

degree to which the studio conditions observed in this study represent a broader set of studios is 

unknown. The simulation should be interpreted as a preliminary indication of how to extrapolate 

the study results to a broader population of artists working in well maintained academic 

facilities.
57

9. UNCERTAINTY

This chapter discusses general uncertainty issues and uncertainties related to the three 

exposure pathways: dermal, inhalation, and ingestion.

9.1. GENERAL UNCERTAINTY ISSUES

The sensitivity analyses showed that the dioxin concentrations in clay and the fraction of 

ball clay used account for a large part of the overall variance in the exposure estimates. Thus, it 

is important to consider the uncertainty in the assumptions regarding these two parameters.

The dioxin levels in ball clay were assumed on the basis of the study by Ferrario et al. 

(2007, 2004). An important uncertainty issue is whether the ball clay sampled by Ferrario is 

representative of the ball clay used in the studio and by the broader community of ceramic 

artists. Ferrario et al. (2007, 2004) explained that the major mining companies market a total of 

32 ball clay products of which 13 were sampled. Although marketing data were not available to 

do true statistical sampling, a ceramics expert confirmed that the most commonly used ball clays 

were included in this study. The samples were collected from 22.7-kg (50-pound) bags in the 

same form as delivered to ceramic studios. Four of the 21 samples analyzed by Ferrario et al.

(2007, 2004) matched exactly the primary type of ball clay used in the OSU ceramics studio.

As explained earlier, ceramic artists use a wide range of clay blends with ball clay 

contents ranging from 0 to 100%. The hypothetical dose estimates were based on the assumption 

of 20% ball clay in the blend, which is the average fraction used by the 10 subjects in this study. 

It is unknown how representative this is of the wider population of ceramic artists. The ball clay 

fraction assumption may also affect other exposure factors. For example, it could affect how 

much clay adheres to skin. Soil adherence to skin has been shown to be influenced by moisture 

content and particle size. Ball clay is similar to other clays in terms of these properties. The 

primary way that ball clay is unique from other clays is its high plasticity. It is not known how 

this property would affect skin adherence.

9.2. DERMAL EXPOSURE UNCERTAINTIES 

9.2.1. Absorption Fraction

A fraction absorbed approach is used to estimate dermal absorption based on current 

Agency guidance. Appendix D presents an alternative approach using a more mechanistic 

model. This model predicts an absorbed dose that is about three times higher than the fraction 

absorbed approach. The mechanistic model appears very promising but it has had limited 

testing, and it is not yet clear whether it provides more realistic estimates. 
58

The exposures in the studio are caused by clay, but the dermal absorption fraction is 

derived from soil experiments. An important uncertainty issue is whether clay has properties 

that differ significantly from soil and consequently make the soil-derived absorption estimates 

invalid for clay. The soil used by Roy et al. (1990) was 16.7% clay. This fraction of the soil 

should have properties similar to those of the studio clay. The organic carbon content of the clay 

is approximately the same as that of the low organic soil used by Roy et al. In terms of particle 

size, clays typically have lower particle sizes than soil and would be expected to more strongly 

sorb organic contaminants (e.g., dioxins) as compared with normal soils, all other factors being 

equal. As discussed in Chapter 5, commercial ball clay specifications report a median particle 

size of about 0.75 μm, which is smaller than that of the Roy et al. (1990) soil (median diameter 

of about 10 μm). The particle sizes measured in the studio air had median diameters ranging 

from 8 to 27 μm, which are larger than those of the soils used by Roy et al. (1990). This may be 

explained by the bonding of particles caused by the addition of water to the clay or the firing 

process, which fuses particles. Thus, it appears that the particle size of the soil used by Roy et al. 

falls within the range present in the studio.

The residues found on the skin are likely to vary with body location and activity. For 

example, a wheel operator will have hand residues similar to the raw clay but the residue on the 

face may more resemble room dust. The dermal absorption from these different types of 

residues may vary. No information is currently available to account for these types of 

differences. 

The studies on dermal absorption of dioxin from soil by Roy et al. and other investigators 

have exclusively used TCDD. It is important to consider whether results for TCDD can be 

extrapolated to the other dioxin congeners found in clay. As mentioned previously, Table 21 

lists the compounds of concern in the clay are the tetra- through octa-CDD congener groups. 

This table indicates that molecular weight and the octanol-water partition coefficient (Kow) 

increase with chlorine substitution. Molecular weight and Kow have been identified as key 

chemical properties affecting dermal absorption (U.S. EPA, 1992). These properties also relate 

to how tightly bound chemicals are to soils and their release kinetics. The higher chlorinated 

congeners would be released from soils more slowly and permeate skin more slowly than TCDD. 

Thus, use of TCDD experiments to represent the penta–octa dioxin congeners found in clay 

probably leads to some overestimates of dermal absorption, but it is uncertain to what degree. 

A related question is whether TCDD-derived dermal absorption values can be applied to 

TEQs. Table 21 shows only about 9% of the TEQ in processed clay is derived from TCDD. The 

TEFs used to determine TEQs discount the hepta- and octa- congeners much more 
59

Table 21. Physical properties of dioxin congeners and concentration in 

processed clay 

Congener

Molecular 

weight a Log Kow

Concentration 

in processed 

b clay

(pg/g)

Concentration in

b processed clay

(pg TEQ/g)

% of total 

TEQ

TCDD 322 6.1 to 7.1 76 76 9

PeCDD 356.4 6.2 to 7.4 374 374 46

HxCDD 390.9 6.85 to 7.8 2,341 234 28

HpCDD 425.3 8.0 9,780 97.8 12

OCDD 459.8 8.2 254,000 25.4 3

Total 808

a U.S. EPA (2000). 

b Average values from Ferrario et al. (2007, 2004). 

HpCDD = heptachlorodibenzo-p-dioxin; HxCDD = hexachlorodibenzo-p-dioxin; Kow = octanol-water partition 

coefficient; OCDD = octachlorodibenzo-p-dioxin; PeCDD = pentachlorodibenzo-p-dioxin; pg = pictogram; 

TCDD = tetrachlorodibenzo-p-dioxin; TEQ = toxic equivalent. 

than the tetra- and penta- groups. The overestimates of dermal absorption for the higher 

chlorinated congeners due to their higher molecular weights and Kow values will be compensated 

to some extent by the large discounts during the TEQ calculation and thus make extrapolation of 

dermal absorption data from TCDD to TEQs more reasonable. 

 The amount of chemical that is dermally absorbed has been shown to be related to skin 

thickness and whether the skin is dead or alive (U.S. EPA, 1992). Skin thickness varies across 

body parts and across individuals. No information was found that could be used to account for 

these factors in this analysis. 

 Another source of uncertainty in the dermal absorption estimates concerns the condition 

of the skin. Some of the artists reported dryness and cracking of skin due to clay activities. 

These conditions were observed by the dermatologist, but correlation with clay activities could 

not be confirmed. Wheel operations involve work with wet clay which would hydrate the skin. 

The abrasive nature of this work could also reduce the thickness of the stratum corneum which is 

considered the primary barrier to permeation (U.S. EPA, 1992). It is possible that these 

conditions would allow more dermal permeation than normal intact skin. However, any 
60

increased permeation would be limited to the surface areas associated with the damaged skin. 

Exposure could also occur through the eyes where absorption would likely be greater than intact 

skin. This would be limited to particles that contact the eye surface which is probably minimal.

9.2.2. Monolayer

As discussed in Section 5.1, the monolayer calculation is also an important source of 

uncertainty for the dermal absorption estimates. The monolayer load is estimated on the basis of 

the median particle size and assumption of ideal packing. Actual monolayers will be composed 

of a mix of sizes with complex packing that could result in loadings higher or lower than this

theoretical estimate. It is also uncertain how to best characterize the size distribution of particles 

on the skin. The particles in the original clay product have a median particle size of about 0.5 to 

1.0 μm, and the airborne particles have medians ranging from 8 to 27 μm. The particles on the 

skin could more closely resemble either the airborne particles or the clay particles, depending on 

the deposition mechanism. Accordingly, particle sizes of the clay residues on skin could vary 

widely, with medians ranging from 0.5 to 27 μm. For purposes of the central exposure 

estimates, the geometric mean of this range was assumed, i.e., 3.7 μm. This implies a monolayer 

load of 0.5 mg/cm2. The monolayer loads corresponding to the upper and lower ends of the 

particle size range are 0.07 to 3.7 mg/cm2. This uncertainty is dampened in the dose estimate as 

a result of the assumption that absorption occurs from only the monolayer. This dampening is 

especially strong for low-exposure subjects. For example, the dose estimates for Subject 4 (who 

had the lowest dermal exposure) corresponding to the low and high ends of the monolayer load 

range would be 0.1 and 0.23 pg TEQ/d. Thus, a 37-fold variation in monolayer load resulted in 

only a 2.3-fold variation in dose. The dampening is less (but still significant) for Subject 9 (who 

had the highest dermal exposures). For this subject, the doses corresponding to the low and high 

ends of the monolayer load range would be 1.1 and 15.8 pg TEQ/d, respectively. While the 

monolayer load assumption has a reduced impact on absorbed dose, it remains an important 

uncertainty.

9.2.3. Exposure Under Clothing

The peer reviewers of this study highlighted the possibility of under clothing exposure as 

an important uncertainty issue (Eastern Research Group, 2008). Kissel et al. (1998) 

demonstrated that clothing can reduce dermal exposure to soil during activities such as planting, 

pipe laying and play. However, Kissel’s study and others (Fenske, 1988; Fenske et al., 1990; 

Raheel, 1991; Kawar et al., 1978) have shown that the clothing is not 100% effective in 

preventing dermal exposure. Under clothing exposure can result from both particle penetration 

through fabric and direct deposition of particles from air that circulates under loose fitting 
61

clothing. The amount of under clothing exposure depends on the particle characteristics, 

clothing type, body location, and individual behavior. Driver et al. (2007) derived clothing 

penetration factors from a large exposure database for pesticide handlers. This analysis 

suggested a median penetration factor of 10%. No studies were found which were specific to 

ceramic artists or clay penetration through clothing. Given the lack of data specific to ceramic 

artists, the present study has assumed that any exposure occurring under clothing would be 

negligible compared to the amount occurring on unclothed areas. The uncertainty associated 

with this assumption is evaluated here using the data collected for Subjects 9 and 10. 

Subjects 9 and 10 wore short-sleeved shirts and short pants. The skin surface areas 

covered by these articles of clothing were estimated using surface area data presented in U.S. 

EPA, 1997. For both subjects, the surface area covered by their shirts is estimated to be half of 

the trunk (0.5 × 35% = 17.5% of total body surface area) and 25% of the arms (0.25 × 14%

= 3.5% of the total body area) for a total of 21% (17.5% + 3.5%) of the total body surface area. 

Subject 9 wore shorts covering about half of her legs, so the surface area covered by her shorts is 

estimated as half of the trunk (0.5 × 35% = 17.5% of total body surface area) plus one-half of the 

legs (0.5 × 32% = 16% of total body area) for a total of 33.5% (17.5% + 16%) of the total body 

surface area. Subject 10 wore short pants covering about 75% of the legs, so the surface area 

covered by her pants is estimated as half of the trunk (0.5 × 35% = 17.5% of total body surface 

area) plus 75% of the legs (0.75 × 32% = 24% of total body area) for a total of 41.5% (17.5% + 

24%) of the total body surface area.. Both Subjects are assumed to have a total surface area of 

17,000 cm

2 which is the mean for adult females.

The clay load on the pants is assumed to match the load measured on the lower legs and 

the load on the shirt is assumed to match the load measured on the arms. It is assumed that 10% 

of the clothing load penetrates to the skin, based on Driver et al. (2007). Based on these 

assumptions, the doses occurring from 24-hour exposures under clothing are estimated as 3.5 pg 

TEQ/d for Subject 9 and 0.53 pg TEQ/d for Subject 10 (see Table 22). These doses equal 50% 

of the dose from the unclothed area for Subject 9 and 58% of the dose from the unclothed area 

for Subject 10. These estimates are uncertain, but suggest that exposure under clothing can be 

important to consider and should be explored further in future research. 

9.3. INHALATION UNCERTAINTIES 

Data from the cascade sampler were used to estimate inhalation exposures. These data 

were considered to be the most reliable because no samples were below detection limits and the 

sampler uses a direct measurement method. The cascade, an area sampler, was located as near 

the subject as possible but normally would not represent an individual’s exposure as accurately 
62

Table 22. Exposure under clothing

Clothing

Surface area 

covered 

2 (cm )

Clothing 

load 

2 (mg/cm )

Skin load 

under 

clothing 

2 (mg/cm )

Absorbed 

dose (pg 

TEQ/d)

Subject 9 Shirt 3,570 1.50 0.15 2.0

Pants 5,700 0.72 0.072 1.5

Subject 10 Shirt 3,570 0.04 0.004 0.05

Pants 7,050 0.11 0.011 0.3

TEQ = toxic equivalent.

as a personal air monitor. Unfortunately, the data from the RespiconTM personal monitor were 

dominated by nondetects and could not be used. The limited RespiconTM data that were above 

detection limits generally indicated higher levels than the cascade, suggesting that personal 

exposures may have been higher than those detected by the area monitor. Accordingly, use of 

the cascade data may have resulted in underestimates of inhalation exposures. 

 As discussed in Chapter 7, increases in suspended dust levels were associated with 

sweeping and the presence of a dog. It is likely that similar effects could be caused by other 

activities such as children playing or vacuuming. A small study, such as this one, cannot capture 

the broad range of activities and associated dust levels that may occur in a ceramic art studio. 

 This study estimated dioxin inhalation on the basis of particulate levels. Additional 

inhalation exposure is likely to occur via vapors. Franzblau et al. (2008) conducted a follow-up 

study to a large survey of dioxin levels in blood. The highest levels found in the survey were for 

an individual who conducted ceramic art activities in her home over thirty years. The study 

presents the hypothesis that inhalation of dioxins volatilized from an unvented kiln in her home 

was the dominant route of exposure. No measurements could be made to confirm the relative 

importance of the possible exposure pathways since the ceramic work was no longer being 

conducted and the authors recommended further investigation to confirm their hypothesis. The 

kilns at the OSU studio are well vented and therefore likely to be a less important source of 

exposure. Further thoughts on the potential for vapor inhalation at the OSU studio are presented 

below: 
63

 Under equilibrium conditions at room temperature, about half of the TCDD is partitioned 

to particulate and rest is in vapor phase. As chlorination increases, the fraction 

partitioned to particulates increases, with PeCDD (dominant contributor to TEQs in ball 

clay) over 80% and OCDD almost 100% in particulate phase (U.S. EPA, 2004). So 

under equilibrium conditions at room temperature, exposure to dioxin TEQs in vapor 

phase would be less than half of dioxin particulate exposure. 

 The dioxins in the clay will be vaporized during kiln operations. The OSU studio has 

6 kilns fired with natural gas and 9 electric kilns. The kilns are generally heated slowly 

to a maximum temperature of about 1,200°C (2,200°F) which is comparable to 

commercial incinerators and sufficient to destroy dioxins. Therefore, vapor releases are 

of most concern during the initial warm-up phase. The OSU kilns are located in 2 rooms 

which are isolated from classrooms and other areas frequented by the students. An 

extensive ventilation system is used with hoods located over all kilns except one small 

electric unit. Any vapors which escape the kilns would be expected to return to room 

temperature equilibrium with particles after transport away from the kiln. 

9.4. INGESTION UNCERTAINTIES 

 The only ingestion pathway quantitatively evaluated in this study was direct ingestion of 

clay deposited from the air onto food items. This was estimated by measuring deposition on to 

surrogate food/beverage samplers over the testing period (1–2 hours). Two uncertainties 

associated with this approach are discussed below: 

 2 Deposition area—An 85 mm diameter (area = 57 cm ) quartz fiber filter was used to 

simulate a small sandwich, cookie, bagel or other small snack item. A medium-sized 

2 hamburger bun has a surface area of approximately 62 cm and a standard piece of bread 

2 has an area of approximately 100 cm . So larger snack items could have an area twice 

2 the sampler size. A 125-mL jar (diameter of about 6 cm, area = 28 cm ) filled with 

deionized water was used to simulate a beverage such as coffee or soda. The diameter of 

the 125-mL jar closely matches that of a typical soda can. Coffee cups have diameters of 

70 to 80 mm and a surface area which is about twice that of the 125-mL jar. Thus, 

food/beverage items with higher deposition areas could increase ingestion amounts by 

over twice the measured values. 

 Surface load—Wipe samples were collected from surfaces near the work area of each 

2 subject. These loads ranged from 0.2 to 7 mg/cm . The maximum clay loading on the 

2 food was 1.66 mg or 0.03 mg/cm . Thus, the surface loads were much higher than the 

food loads. This is likely due to the location of the food samplers which were placed 

outside of the immediate work area at a location that the subjects indicated they would 

normally place foods or beverages. If food was placed near the work areas, deposition 

could increase by 10 times or more than the measured levels. 
64

Clay ingestion may also occur via hand-to-food transfers. Snack foods such as potato 

chips, cookies, sandwiches, etc are typically eaten by hand. If hands are not washed prior to 

eating, clay on hands can be transferred to the food items and subsequently ingested. While this 

behavior may be common, it was not observed during this study. Accordingly, it is not included 

in the primary exposure assessment of this study. However, some idea of the possible 

importance of this pathway can be evaluated as follows. Hand contact with food is primarily 

limited to the fingertips which are assumed to equal 25 cm2(calculated as 5% of an average adult 

male hand—500 cm2—U.S. EPA, 1997). Clay loads on hands measured 0.17 to 10.12 mg/cm2. 

If 50% of the clay on fingertips are transferred to the food, then 2 to 125 mg could be ingested. 

Additional ingestion could result from multiple contacts with food items after the fingertips are 

replenished with clay. The maximum ingestion levels based on deposition was estimated as 

about 2 mg of clay. This suggests that hand-to-food transfers could increase ingestion by over

50-fold.

Other possible mechanisms for clay ingestion include hand-to-mouth transfers or 

deposition/splattering of clay on to lips and removal by licking. These behaviors were not 

observed during this study but could be a common occurrence. Smoking was not allowed in the 

study facility, but where this occurs, the potential for hand-to-mouth transfer is increased. 

The average-soil-ingestion rate for adults in residential settings is estimated to be

50 mg/day (U.S. EPA, 1997, 1989). This is much higher than the maximum clay ingestion levels 

estimated in this study based on deposition (about 2 mg). It is difficult to evaluate how 

applicable this soil ingestion rate may be to clay ingestion in a ceramic art studio. However, the 

scenarios presented above imply that it may be possible. This was evaluated using a 

modification to the Monte Carlo simulation presented in Chapter 8. In this simulation, the 

ingestion rate was inputted as a flat distribution from 1 to 50 mg and all other inputs were kept 

the same as those described in Table 18. The mean ingestion dose increased by a factor of 

17 (from 0.14 to 2.4 pg TEQ) and total dose increased by a factor of 1.3 (from 6.4 to 8.64 pg 

TEQ). 

The above discussion suggests that a number of plausible scenarios could occur which 

would result in greater clay ingestion than observed in this study. The peer reviewers of this 

study emphasized their concern that this pathway may have been underestimated (Eastern 

Research Group, 2008). This is a high priority issue for future research and demonstrates the 

importance of good hygiene practices regarding food placement and hand washing to prevent 

these types of exposures. 
65

10. CONCLUSIONS 

 Hypothetical dioxin dose estimates were calculated for each subject assuming that all 

used a 20% ball clay blend with 162 pg TEQ/g. The single-day total doses across the 10 subjects 

ranged from 0.32 to 7.1 pg TEQ/d, with an average of 1.44 pg TEQ/d (SD = 2.0). The dermal 

dose was the major contributor to total dose, exceeding 67% for all subjects. Ingestion and 

inhalation contributed similar amounts, generally in the range of 1 to 20% of total dose. Hand 

and arm exposure accounted for much of the dermal dose for all subjects. The two subjects who 

wore summer clothing had foot and leg exposures accounting for about 33 to 71% of the dermal 

dose. Facial exposures were low accounting for less than 4% of total dermal dose. 

 Clay exposure was found to be highly dependent on the type of work being performed. 

Throwing clay on the wheel resulted in much higher clay exposures than did any other clay 

activities. This is due to the increased contact with clay while working on the wheel and the wet, 

sticky consistency of the clay needed for that work. Emptying bags and mixing dried clays also 

led to high exposures. 

 A Monte Carlo simulation was performed to model how doses could vary in a broad 

population of artists with exposures outside the hypothetical scenario evaluated in this study. 

This simulation produced a mean total dose of 6.4 pg TEQ/d (SD = 8.4), median of 3.5 pg 

TEQ/d, and 90th percentile of 14.8 pg TEQ/d. This mean is over times 4 times greater than the 

mean of the hypothetical dose estimates for the 10 subjects. All of the 10 subject doses 

corresponded to low percentiles of the Monte Carlo simulation except Subject 9 (75th percentile). 

Also, it indicated that the fraction of ball clay in the blend, clothing, and dioxin concentration 

contributed most to variance in total dose. Many of the input distributions used in this 

simulation were based on very limited data or judgment. Therefore, the simulation results are 

best interpreted as preliminary indications of how to extrapolate the observations of this study to 

a broader population of artists in similar types of studios, i.e., well maintained academic 

facilities. It is likely that the range of exposures across all types of ceramic art facilities 

(individual, commercial, etc.) is wider than observed here and further study is recommended to 

explore this possibility. 

This study included a comprehensive uncertainty analysis. The two most important 

uncertainties are highlighted below: 

 Studies have shown that in a variety of occupational situations, particulates can penetrate 

clothing and deposit on skin. It is unclear if and to what extent this may occur in ceramic 

art studios. Accordingly, this study assumed that dermal exposure under clothing was 

negligible. An evaluation of this issue suggests that if exposure under clothing occurs, 

dermal doses may increase by 50% or more. 
66

 The only ingestion pathway evaluated in this study was deposition on to food. Although 

not observed during this study, other pathways could occur such as hand-to-food transfers 

and hand-to-mouth transfers. Where these occur, ingestion doses could increase 

substantially, perhaps by over an order of magnitude relative to the ingestion estimates 

presented here. 

 

 In the general population, daily intakes of CDD/CDFs are estimated to average 0.65 pg 

TEQ/kg-day or 45 pg TEQ/d for a 70-kg adult (Lorber, 2002). More than 90% of this intake is 

derived from food ingestion. These intake values are based on the ―administered‖ dose or the 

amount taken into the body before absorption. The hypothetical doses presented in this report 

are on an absorbed dose basis. Thus, the general population dose must be converted to an 

absorbed basis to compare it to the values presented here. Lorber (2002) reports that about 80% 

of dioxins in foods are absorbed into the body. Applying this factor, the general population adult 

dose on an absorbed basis is 36 pg TEQ/d. Comparing these values to the average of the 

hypothetical doses for the 10 subjects estimated here (1.44 pg TEQ/d) indicates that the ball clay 

dose is 4% of the general population adult dose (on a TEQ basis). Similarly, the Monte Carlo 

simulation suggested a mean dose of 6.4 pg TEQ/d which is 18% of the general population adult 

dose (on a TEQ basis). Note that the general population dioxin dose is a long-term average and 

the ball clay dioxin doses are estimates for a single day when exposure occurs. Accordingly, this 

comparison implies that ball clay use is a frequent event, so that the long-term daily average ball 

clay dose is similar to the single-day dose. If ball clay use is infrequent, then the long-term 

average dose from ball clay will be reduced and adjustments would be needed to make a valid 

comparison to the general population dioxin dose. 
67

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A-1

APPENDIX A

SUBJECT QUESTIONNAIRE RESULTS

Table A-1. Subject 1

Question Answer

Approximately how many hours per week do 

you work with clay?

50 hours.

Approximately how many weeks per year? 40 weeks.

How long have you been doing clay work with 

this level of intensity?

1 year.

What type of clay artwork do you do? Hand building, sculptural work. Largely 

consists of rolling out slabs and assembling 

clay parts.

What types of clothing do you wear while you 

work?

Short sleeve t-shirt and jeans and closed toe 

shoes.

What areas of skin typically are exposed to the 

clay while you work?

Hands and forearms.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Yes. Dryness. No cracking/bleeding. I use 

lotion 3–4 times through the day.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: 

when rolling slabs—once per hour.

when assembling clay—3 or more times per 

hour.

Face: 1–2 times per day.

How do you wash your skin after you work 

with clay?

Water only.

Do you treat your skin with anything in 

particular after working with clay?

Yes, Aveeno® brand lotion.
A-2

Table A-2. Subject 2

Question Answer

Approximately how many hours per week do 

you work with clay?

10–15 hours.

Approximately how many weeks per year? 15–25 weeks.

How long have you been doing clay work with 

this level of intensity?

24 years.

What type of clay artwork do you do? Mixing clay and maintenance activities 

associated with the OSU Ceramics area.

What types of clothing do you wear while you 

work?

Long and short sleeves, long pants, work 

shoes.

What areas of skin typically are exposed to the 

clay while you work?

Hands, arms, and face.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Dryness and cracking.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: 2 minutes.

Face: 5 hours.

How do you wash your skin after you work 

with clay?

Soap and water.

Do you treat your skin with anything in 

particular after working with clay?

Lotion during winter, but when my hands are 

very dry a product called Satin Hands® is 

used.
A-3

Table A-3. Subject 3

Question Answer

Approximately how many hours per week do 

you work with clay?

25 hours.

Approximately how many weeks per year? 30 weeks.

How long have you been doing clay work with 

this level of intensity?

14 months.

What type of clay artwork do you do? Functional—thrown on wheel.

Structural—hand built.

What types of clothing do you wear while you 

work?

Jeans with t-shirt and sandals (summer) or 

long sleeves and closed toe shoes (winter).

What areas of skin typically are exposed to the 

clay while you work?

Hands, arms, face, neck, and feet.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Dry cracking skin and cuticles on hands, red 

small-bump rash on backs of hands and 

inner forearms when using wheel, nasal 

congestion.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Arms and hands: 3 to 5 minutes.

Feet, face, and neck: 1–10 hours.

How do you wash your skin after you work 

with clay?

Water only if returning to work, soap, and 

water when finished.

Do you treat your skin with anything in 

particular after working with clay?

Aveda® hand cream, Neutrogena® Swiss 

therapy lotion.
A-4

Table A-4. Subject 4

Question Answer

Approximately how many hours per week do 

you work with clay?

More than 70 hours.

Approximately how many weeks per year? 50 weeks.

How long have you been doing clay work with 

this level of intensity?

2 years.

What type of clay artwork do you do? Functional pots, cups, bowls, etc.

What types of clothing do you wear while you 

work?

Overalls, long/short sleeve shirts and 

sneakers.

What areas of skin typically are exposed to the 

clay while you work?

Face, hands, sometimes arms and legs.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Extremely dry with cracking on fingertips.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: 10 minutes.

Face and body: 10–24 hours.

How do you wash your skin after you work 

with clay?

Water only if returning to work, soap, and 

water when finished.

Do you treat your skin with anything in 

particular after working with clay?

Heavy cream lotion or bag balm at the end 

of the day and at intervals throughout the 

day.
A-5

Table A-5. Subject 5

Question Answer

Approximately how many hours per week do 

you work with clay?

More than 14 hours.

Approximately how many weeks per year? 35 weeks.

How long have you been doing clay work with 

this level of intensity?

6 years.

What type of clay artwork do you do? Hand building objects about 1.5 feet tall.

What types of clothing do you wear while you 

work?

Short sleeves/pants and shoes.

What areas of skin typically are exposed to the 

clay while you work?

Hands, lower arms, face.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Yes, dryness, sometimes cracking.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: <5 minutes.

Arms: 8 hours.

Face: 0.5–8 hours.

How do you wash your skin after you work 

with clay?

Soap and water.

Do you treat your skin with anything in 

particular after working with clay?

Lotion.
A-6

Table A-6. Subject 6

Question Answer

Approximately how many hours per week do 

you work with clay?

30–40 hours.

Approximately how many weeks per year? 30–40 weeks.

How long have you been doing clay work with 

this level of intensity?

25 weeks.

What type of clay artwork do you do? Throwing objects using wheel, hand 

building, and sculptural work.

What types of clothing do you wear while you 

work?

Short sleeves, pants, shorts, and flip flops 

shoes.

What areas of skin typically are exposed to the 

clay while you work?

Arms, hands, feet, face.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Yes, dry skin on feet and hands and nails 

being unable to grow healthily.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: 30 minutes.

Legs, feet, and face: 3–5 hours.

How do you wash your skin after you work 

with clay?

Soap and water.

Do you treat your skin with anything in 

particular after working with clay?

Lotion.
A-7

Table A-7. Subject 7

Question Answer

Approximately how many hours per week do

you work with clay?

10 hours.

Approximately how many weeks per year? 40 weeks.

How long have you been doing clay work with 

this level of intensity?

4 years.

What type of clay artwork do you do? Clay sculpture. Rolling out slabs, pressing 

them into molds. Limited work throwing 

objects using wheel.

What types of clothing do you wear while you 

work?

Short sleeves and pants (winter/spring/fall) 

and shorts (summer).

What areas of skin typically are exposed to the 

clay while you work?

Arms, hands, and face.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Dryness and cracking.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: 1–2 minutes.

Face and legs 1–2 minutes (powdered clay) 

or end of day (wet clay).

How do you wash your skin after you work 

with clay?

Soap and water.

Do you treat your skin with anything in 

particular after working with clay?

Lotion.
A-8

Table A-8. Subject 8

Question Answer

Approximately how many hours per week do 

you work with clay?

20 hours.

Approximately how many weeks per year? 52 weeks.

How long have you been doing clay work with 

this level of intensity?

6 years.

What type of clay artwork do you do? Large clay sculpture. Rolling out slabs, cut 

and bend them and then press them together.

What types of clothing do you wear while you 

work?

Pants or shorts, short sleeves or tank tops, 

sneakers or sandals.

What areas of skin typically are exposed to the 

clay while you work?

Arms, neck, hands, calves, and shins.

Do you correlate any skin health issues with 

how much you work with clay? If yes, what?

Dryness and cracking.

In relation to the time you complete working 

with clay, when do you wash parts of your 

body that have been exposed to clay?

Hands: 5 minutes.

Face and legs: 4–24 hours.

How do you wash your skin after you work 

with clay?

Soap and water or just water.

Do you treat your skin with anything in 

particular after working with clay?

Lotion.
 

APPENDIX B 

EVALUATION OF CLAY DUST INHALATION 

The methodology used to evaluate the dose of clay dust and associated dioxin received 

via inhalation is discussed in this appendix. The appendix is divided into four sections: clay 

dust size distribution, particle inhalability, respiratory deposition of clay dust, and delivered dose 

estimates. 

B.1. CLAY DUST SIZE DISTRIBUTION 

As discussed in the main body of this report, the size distribution of clay dust was 

measured using a Delron® cascade impactor and a Climet® during regular daily activities in the 

art studio. The Climet® optically determines particle concentration for six size bins with the 

associated physical particle diameter (dp) of 0.3–0.5, 0.5–1, 1–2.5, 2.5–5, 5–10, and >10 μm. 

Aerodynamic particle diameter (Dae) can be estimated for the Climet®’s size bins by assuming 

that the airborne clay dust has a density of 2.6 g/cm3

, similar to that of bulk clay.1 Using this 

approach, a clay particle with a dp of 10 μm has a Dae of 16 μm. The Delron® cascade impactor 

fractionates particles directly, based on their Dae, into the seven ranges of <0.5, 0.5–2, 2–4, 4–8, 

8–16, 16–32, and >32 μm. 

During normal artisan activities (Subjects 1–8), 64 + 9% (mean + SD) of the aerosol is 

associated with particles having a Dae > 16 μm based on average Climet® data. Based on 

average impactor data, 63 + 13% of the aerosol is associated with a Dae > 16 μm (Subjects 1–8). 

The particle size distributions to which the artisans were exposed was assumed to be lognormally distributed.2

 The cascade impactor data were selected for estimating particle size 

distributions for the following reasons: (1) the impactor measures particle size based on the 

aerodynamic behavior of particles, whereas the Climet® uses light scattering to estimate a 

physical particle size; (2) the impactor affords a better characterization of the large particles than 

does the Climet® because it contains an additional size bin of 16–32 μm; and (3) particle 

deposition in the respiratory tract is a function of Dae. Thus, uncertainty in estimates of 

respiratory deposition is reduced by the direct measurement of Dae by the impactor. The clay 

1

 Dae = dp {(clay density * Cc(dp) )/(H2O density * Cc(Dae) )}0.5, where: Cc(dp) and Cc(Dae) are the 

Cunningham slip correction factor for the physical and aerodynamic particle size, respectively. For more 

information, the reader is referred to ICRP (1994), page 239. 

2

For more information about particle sizing and the log-normal distribution, the reader is referred to Hinds 

(1999). 

B-1 
dust size distribution was not estimated for runs where two or more of the impactor stages were 

below the nondetect level. 

When engaged in normal artisan activities, the mass median aerodynamic diameter 

(MMAD) of clay dust to which artisans were exposed ranged from 13 to 45 μm. Table B-1 

provides a characterization of clay dust exposures for each subject. Figure B-1 illustrates a 

log-probability plot of a typical (i.e., near the average MMAD) clay dust particle size 

distribution and a background sample from the studio. The prevalence of fewer large particles in 

the background aerosol can be explained easily, based on particle-settling velocities. The 

settling velocities for the Dae of 1-, 10-, and 20-μm particles are 3.5 × 10-3, 0.3, and 1.2 cm/s, 

respectively. Due to their rapidly settling velocities, large particles (Dae > 10 μm) are 

maintained in the air only by active generation or resuspension from surfaces. The substantive 

presence of large particles (52% of mass associated with a Dae > 10 μm) in the background 

sample is suggestive of particle resuspension due to movement (e.g., walking and setting up 

sampling equipment in the studio). 

Table B-1. Clay dust size distribution and concentration during normal 

activities 

Subject 

Size distributiona 

Total concentration 

(mg/m3 MMAD (μm) σg )

1 26.9 3.9 0.35 

2 44.6 4.8 0.47 

3 18.5 4.3 0.99 

4 NA NA 0.37 

5 NA NA 0.13 

6 20.2 3.0 0.61 

7 13.0 3.6 0.51 

8 26.7 3.3 0.64 

Mean + SD 25.0 + 11 3.8 + 0.7 0.51 + 0.25 

B-2 
Figure B-1. Clay dust particle size distribution during normal artisan 

activities from analysis of cascade impactor data. Illustrated are the data for 

Subject 8 (☐ ) and a background sample when work was not being done in 

the studio (○). The dashed and solid lines illustrate the log-normal 

distribution for these respective data. The mass median aerodynamic 

diameter (MMAD) of clay dust was 27 μm (σg = 3.3) for Subject 8, whereas 

the background sample had an MMAD of 11 μm (σg = 4.6). 

a

 The aerosol size distribution is described in terms of the mass median aerodynamic diameter (MMAD) and 

geometric standard deviation (σg). 

NA = not available. 

Data were also available for two subjects during specific activities (i.e., when sculpting 

and using a pottery wheel) (see Table B-2). During pottery wheel operations, an average 

MMAD of 33 μm with a geometric standard deviation (σg) of 5.4 was observed. A dog was 

present during two of the sculpting runs. The MMAD with the dog present was 21 μm versus 

only 16 μm without the dog. The shift toward larger particles when the dog was present appears 

to be consistent with particle resuspension due to the dog’s movement around the studio. 

B-3 
Table B-2. Clay dust size distribution and concentration during specific 

activities 

Subject 

Size distributiona Total 

concentration 

(mg/m3 MMAD (μm) σg )

Subject 9 

(Pottery wheel) 

Run 1 

Run 2 

Run 3 

Run 4 

Run 5 

33.7 

NA 

24.8 

NA 

39.3 

6.2 

NA 

4.3 

NA 

5.6 

0.049 

0.046 

0.102 

0.073 

0.152 

Mean + SD 32.6 + 7.3 5.4 + 0.9 0.085 + 0.044 

Subject 10b 

(Sculpting work) 

Run 1 

Run 2 

Run 3 

21.2 

20.4 

16.0 

3.9 

3.2 

3.5 

0.48 

0.24 

0.24 

a

 The aerosol size distribution is described in terms of the mass median aerodynamic diameter (MMAD) and 

geometric standard deviation (σg).

b

 A dog was present during Runs 1 and 2 but not during Run 3. Therefore, these three runs were not averaged as 

was done in the case of the pottery wheel work. 

NA = not available 

B.2. PARTICLE INHALABILITY 

For a given particle size, inhalability is the ratio of the particle concentration that enters 

the respiratory tract through the nose or mouth to the concentration of these particles in the 

ambient air. Inhalability depends mainly on particle size (i.e., Dae), route of breathing, wind 

speed, and a person’s orientation with respect to wind direction. Wind speeds in the art studio 

were assumed to be 0.3 m/s or less (Baldwin and Maynard, 1998). The artisans were presumed 

to move about the studio such that their orientation was random with respect to wind direction. 

The clay dust aerosol present under normal activities in the art studio was observed to 

have an average MMAD of 25 μm and σg of 3.8. Hence, 50% (on average, by mass) of the 

airborne clay dust is composed of particles having a Dae of >25 μm, a size that is generally 

considered to be unable to penetrate the thorax (ACGIH, 2004). These large particles 

(Dae >25 μm), if inhaled, will deposit almost completely and exclusively in the extrathoracic 

(ET) airways. Thus, determining inhalability is key to estimating the delivered dose of these 

B-4 
 

large particles. For smaller particles, inhalability still describes the fraction of airborne particles 

that may enter the respiratory tract and thereby the availability of these particles for deposition in 

the lung. 

Only limited data are available on the inhalability of particles from calm air (wind speeds 

of 0.3 m/s and less). Inhalability from calm air depends on the route of breathing. Logistic 

functions describing particle inhalability during nasal [P(IN)] and oral [P(IO)] breathing are given 

by Ménache et al. (1995) and Brown (2005): 

1 P(I N ) = 1− (B-1) 1+ exp(10.32 − 3.114 ln(Dae )) 

1.44 P(I O ) = (B-2) 1+ 0.44exp(0.0195 Dae ) 

Note that these equations depend only on aerodynamic particle diameter, Dae. Given by Eq. B-1, 

P(IN) begins a rapid decline from 0.95 at Dae = 11 μm, to 0.5 at Dae = 27.5 μm, and 0.1 at 

Dae = 56 μm. Eq. B-2 predicts a slow decline in P(IO) from 0.95 at Dae = 8 μm, to 0.5 at 

Dae = 74 μm, and 0.1 at Dae = 175 μm. 

Figure B-2 illustrates particle inhalability predicted by Eqs. B-1 and B-2 (shown by solid 

lines) along with relevant experimental data. Based on high wind speeds (1–8 m/s), the 

American Conference of Governmental Industrial Hygienists (ACGIH) inhalability criterion is 

also illustrated (shown by dashed lines) for comparative purposes. Eq. B-1 for P(IN) describes 

the experimental nasal inhalability data well with an r

2

 of 0.86 (model sum of squares divided by 

the total corrected sum of squares). A negative r

2

 is obtained for the fit of the ACGIH (2004) 

criterion to these data.3

 Equation B-2 describes the experimental oral inhalability data with an r

2 

of 0.69, whereas the ACGIH criterion fit with an r

2

 of 0.32. 

B.3. RESPIRATORY DEPOSITION OF CLAY DUST 

Inhaled particles may be either exhaled or deposited in the ET, tracheobronchial (TB), or 

pulmonary (PU) airways. The deposition of particles in the respiratory tract depends primarily 

3

An r

2

 is calculated as the model sum of squares (MSS) divided by the total corrected sum of squares 

(TSS). The MSS equals the TSS minus the residual sum of squares (RSS). In typical linear regressions, 

when a model is fitted to a data set, the resulting r

2

 must be non-negative because the least square fitting 

procedure assures RSS < TSS. When r

2

 is computed on excluded data, i.e., data not used to fit the model, 

the RSS can exceed the TSS. In this case, r

2

 (which is not the square of r) can be negative, indicating that 

the mean of the data is a better predictor than the model. 

B-5 
 Dae (μm) Dae (μm)

Figure B-2. Particle inhalability from calm air for nasal [P(IN)] and oral 

[P(IO)] breathing as a function of aerodynamic particle diameter (Dae). Left 

panel [── Eq. B-1, ● Breysse and Swift (1990), + Hinds et al. (1998), ○ Hsu 

and Swift (1999), - - - ACGIH (2004)]. Right panel [── Eq. B-2, ○ Aitken et 

al. (1999), ● Kennedy and Hinds (2002), - - - ACGIH (2004)]. 

 

Table B-3. Breathing patterns used in particle deposition calculationsa 

Activity Males Females 

Sitting VT (mL) 

f (min-1) 

750 

12 

464 

14 

Light exercise VT (mL) 

f (min-1) 

1,250 

20 

992 

21 

a

 Source: ICRP (1994), Table 8. 

on inhaled particle size (i.e., Dae), route of breathing (through the nose or mouth), tidal volume 

(VT), and breathing frequency (f ). Reference respiratory values for males and females were 

adopted from the International Commission on Radiological Protection (ICRP, 1994). In 

addition to breathing patterns (see Table B-3) necessary for deposition calculations, males and 

females were assumed to have a functional residual capacity of 3,300 mL and 2,680 mL, 

respectively. The majority (70%) of the subjects were female; only Subjects 1, 2, and 5 were 

male. 

Particle deposition in the respiratory tract was predicted using the publicly available 

Multiple Path Particle Dosimetry (MPPD) model.4

 The MPPD model was developed by the 

4

 The MPPD program is available on request from the CIIT Centers for Health Research 

(<asgharian@ciit.org>). 

B-6 
CIIT Centers for Health Research (CIIT), United States, in collaboration with the National 

Institute of Public Health and the Environment (RIVM), the Netherlands, and the Ministry of 

Housing, Spatial Planning and the Environment, the Netherlands. The MPPD model may be 

used to predict the deposition in the human respiratory tract for particles between 0.01 and 

20 μm in diameter. In the lung, the model considers deposition by the mechanisms of impaction, 

sedimentation, and diffusion. Additional model details are available elsewhere 

(de Winter-Sorkina and Cassee, 2002). For the size of the clay dust, only impaction and 

sedimentation are of concern. 

Using the MPPD model, deposition was predicted for the ET, TB, and PU regions of the 

respiratory tract. Particle deposition was estimated individually for oral and nasal breathing. 

During oral breathing, deposition in the TB airways did not always reach zero by a Dae of 20 μm 

(the upper limit for the MPPD model). For Dae > 20 μm, deposition in the TB airways was 

estimated by a best fit polynomial (3rd or 4th degree) determined using CurveExpert 1.3 

(112B Crossgate St., Starkville, MS 39759). This polynomial function was fitted to TB 

deposition fractions for Dae from 10 to 20 μm. The predicted ET deposition during oral 

breathing for a Dae > 20 μm was taken as one minus the TB deposition fraction for oral 

breathing. For nasal breathing, these additional steps were unnecessary because TB deposition 

was well under 1% at a Dae of 20 μm. 

External to the MPPD model, all of the predicted deposition fractions were corrected for 

particle inhalability using Eqs. B-1 and B-2. The current version of MPPD model offers an 

inhalability correction for nasal breathing only. For a given Dae, an inhalability corrected 

deposition fraction is the product of the uncorrected deposition fraction and the predicted 

inhalability for that Dae. Unless otherwise specified, all mention of particle deposition fractions 

in the main body of this report and subsequently in this appendix refer explicitly to inhalability 

corrected deposition fractions. 

The deposition fraction (DFr) of an aerosol in a region of the respiratory tract is the 

integral of the deposition fractions across all particle sizes in the aerosol: 

∞

DFr (MMAD,σ g ) = ∫ DFr (di ) ρ(di ) δdi (B-3) 

0 

B-7 
 

 

where 

DFr(di) = the deposition fraction in region, r, of particles having an aerodynamic 

diameter of di 

ρ(di) = the mass fraction associated with the interval δdi 

The total deposition fraction for the respiratory tract is the sum of DFr for the ET, TB, and 

PU regions. Eq. B-3 can be approximated by summing the particle deposition fractions at known 

intervals or percentiles of the particle size distribution. Here, the interval of 1% was used and 

the approximation is 

0.99 

∑

P =0.01

1 DFr (
 MMAD,σ ) ≈ DFr (
 d ) (B-4) g i 100
 

where 

DFr(di) = the deposition fraction in region, r, of particles having an aerodynamic 

diameter di (the particle size associated with a given percentile, P, of the size 

distribution). 

For a log-normal distribution, di is given by 

(P) d = MMADσ (B-5) z 

i g 

where 

z(P) = the normal standard deviate for a given probability 

Table B-4 provides the predicted regional deposition fractions for the clay dust in the 

respiratory tract of each subject for oral and nasal breathing at two activity levels. These 

deposition fraction estimates were based on each subject’s measured aerosol exposure size 

distribution (see Tables B-1 and B-2). Subjects 4 and 5 lacked aerosol size distribution data and 

were assumed exposed to an aerosol with an MMAD of 25 μm and σg of 3.8, this being the 

average for artisans during normal activities (see Table B-1). The deposition fraction estimates 

for Subject 10 were based on Run 3, when the dog was not present in the studio. 

B-8 
 

 

 

 

 

B.4. DELIVERED DOSE ESTIMATES 

The rate of particle deposition in a region of the respiratory tract may be expressed as: 

•

Dr (t) =
 C(t) ƒ(t)VT (t) DFr(t) (B-6) 

where 

D ̇ r = the rate of deposition per unit time in region r 

C = the exposure concentration 

f = breathing frequency 

VT = tidal volume 

DFr = the deposition fraction in region r
 

Note that all of the variables in Eq. B-6 may vary with time. The dose to a respiratory region is 

determined by integrating Eq. B-6 over the exposure duration. 

Table B-4. Regional deposition fractions (corrected for inhalability) for clay 

dust in the respiratory tract 

Subject 

Sitting Light exercise 

Nasal breathing Oral breathing Nasal breathing Oral breathing 

ET TB PU ET TB PU ET TB PU ET TB PU 

1 0.441 0.015 0.022 0.473 0.082 0.058 0.473 0.006 0.011 0.516 0.060 0.052 

2 0.336 0.011 0.016 0.412 0.059 0.042 0.360 0.004 0.008 0.442 0.044 0.037 

3 0.472 0.028 0.033 0.431 0.104 0.067 0.531 0.010 0.020 0.486 0.074 0.075 

4 0.447 0.021 0.022 0.471 0.091 0.050 0.487 0.007 0.013 0.521 0.064 0.056 

5 0.458 0.016 0.023 0.479 0.086 0.061 0.492 0.006 0.011 0.523 0.063 0.054 

6 0.526 0.023 0.022 0.521 0.108 0.053 0.566 0.007 0.012 0.581 0.075 0.059 

7 0.549 0.035 0.041 0.432 0.128 0.085 0.622 0.013 0.025 0.498 0.090 0.095 

8 0.451 0.018 0.017 0.507 0.087 0.041 0.483 0.005 0.010 0.557 0.061 0.046 

9 0.368 0.020 0.023 0.396 0.077 0.047 0.410 0.007 0.014 0.437 0.054 0.053 

10 0.533 0.030 0.033 0.462 0.118 0.072 0.593 0.010 0.020 0.525 0.083 0.081 

ET = extrathoracic; PU = pulmonary; TB = tracheobronchial. 

B-9 
 

 

 

 

 

By assuming that aerosol characteristics and an individual’s activity levels are fairly 

constant over discrete periods of time, the dose to a respiratory region may be approximated by: 

n 

Dr = 0.06∑(VT ƒ) j (CT ) j [Fm DFm,r + FN DFN ,r ] j (B-7) 

j=1 

where 

Dr = the dose (μg) to region r of the respiratory tract 

VT and f = tidal volume (mL) and breathing frequency (min-1) for a specified 

activity j 

C and T = exposure concentration (mg/m3

) and duration (hr) during activity j 

Fm and FN = the fraction of a breath entering the respiratory tract through the mouth 

and nose, respectively, during activity j 

DFm,r and DFN,r = the deposition fraction for oral and nasal breathing, respectively, in 

region r of the respiratory tract while performing activity j 

Constant 0.06 = a unit conversion parameter 

As expressed, an “activity” in Eq. B-7 could be associated with changes in exposure 

concentration, the particle size distribution, and/or an individual’s exertion level. For simplicity, 

only two exertion levels (sitting and light exercise) and a single particle size distribution (see 

Tables B-1 and B-2) were considered for each subject. 

The fraction of flow through the mouth (Fm in Eq. B-7) increases with activity level and 

varies between individuals. For the two activity levels considered here, most people (87%) will 

breathe through their nose (Niinimaa et al., 1981). Hence, for these people, Fm = 0 and FN = 1 in 

Eq. B-7. However, 13% of people will be oronasal breathers even at rest, i.e., they will breathe 

simultaneously through the nose and mouth (Niinimaa et al., 1981). This latter group is 

commonly referred to in the literature as “mouth breathers” (e.g., ICRP, 1994). Derived from 

Niinimaa et al. (1981), the fraction of air respired through the mouth (Fm) is well described by a 

modified exponential function in the form of 

⎛ ⎞ γ ⎜ ⎟ Fm =α exp • (B-8) ⎜ ⎟ ⎝V e ⎠

B-10 
 

 

 

where 

V ̇ e = minute ventilation 

α = 0.748 

γ = −7.09 (r

2

 = 0.997) in mouth breathers for 10 < V ̇ e< 80 L/min 

γ = −18.3 (r

2

 = 0.998) in normal augmenters for 35.3 < V ̇ e < 80 L/min 

For V ̇ e < 35.3 L/min, normal augmenters breathe entirely through the nose, i.e., Fm = 0. 

FN is one minus Fm regardless of the activity. 

Table B-5 gives the estimated clay dust doses to regions of the respiratory tract for each 

subject during nasal and oronasal breathing. Estimates are for a 4-hour exposure assuming that 

the exposed individual spent 50% of his or her time sitting and 50% engaged in light exercise. 

For oronasal breathing in Table B-5, there is a small positive bias in ET doses and a 

corresponding negative bias in TB doses calculated by Eq. B-7. In other words, this method of 

calculating ET and TB doses shifts the pattern of deposition toward the head relative to the 

real-life pattern of deposition. This shift occurs due to deposition being calculated at a higher 

airflow rate through the nose and mouth than actually occurs during oronasal breathing. The 

deposition calculations presumed that all inhaled airflow was through the nose or mouth. In 

reality, inhaled air is partitioned between the nose and the mouth, and the actual flows (for sitting 

and light exercise) are roughly half of that used in the deposition calculations. For breathing by 

a single route (nasal or oral), changing activity from sitting to light exercise approximately 

triples flow rates but only slightly increases ET deposition and modestly decreases TB 

deposition (see Table B-4). The effect of using Eq. B-7 for calculating doses during oronasal 

breathing should similarly affect the pattern of deposition. Ultimately, particles deposited in the 

ET and TB regions will typically be cleared to the throat and swallowed within 24 to 48 hours 

postdeposition (ICRP, 1994). Hence, the exact site of deposition (i.e., ET versus TB) is of little 

significance because both regions effectively contribute to ingested doses. 

B-11 
Table B-5. Regional doses (μg) of clay dust in the respiratory tracta 

Subject 

Nasal breathing Oronasal breathing 

ET TB PU ET TB PU 

1 664 12 20 693 53 48 

2 678 11 19 757 52 47 

3 1,677 47 75 1,612 143 154 

4 580 13 19 598 45 41 

5 256 4.6 7.7 264 21 19 

6 1,114 22 29 1,126 85 70 

7 1,011 30 49 917 90 100 

8 997 18 24 1,067 72 57 

9 110 2.9 4.5 114 8.8 9.2 

10 455 12 18 431 39 39 

Mean 754 17 27 758 61 58 

SD 460 13 21 445 39 42 

a Doses calculated by Eq. B-7 as described in the text. 

ET = extrathoracic; PU = pulmonary; TB = tracheobronchial. 

Table B-6 provides estimates of the dioxin absorption in each subject for nasal and 

oronasal breathing. Particles deposited in the ET and TB regions clear rapidly (within 1–2 days) 

to the throat and are swallowed. The absorption of dioxin from particles deposited within the ET 

and TB regions was treated as if the particles had been ingested. Dose estimates for oronasal 

breathing are slightly more conservative from a safety or risk perspective than presuming nasal 

breathing. However, nasal breathing may be considered as representative of the majority of the 

population (87%). Oronasal breathing is thought to represent 13% of healthy individuals 

(Niinimaa et al., 1981). In contrast to healthy subjects, Chadha et al. (1987) found that the 

majority (11 of 12) of patients with asthma or allergic rhinitis breathe oronasally even at rest. 

On average across all the subjects, dioxin doses are about 1.2 times greater for oronasal than for 

nasal breathing. 

B-12 
Table B-6. Estimates of dioxin absorptiona

 (pg TEQ) 

Subject 

Nasal breathing Oronasal breathing 

ET and 

TBb

 PUc Total 

ET and 

TBb PUc Total 

1 0.033 0.003 0.035 0.036 0.006 0.043 

2 0.034 0.003 0.036 0.039 0.006 0.045 

3 0.084 0.010 0.094 0.085 0.020 0.105 

4 0.029 0.002 0.031 0.031 0.005 0.037 

5 0.013 0.001 0.014 0.014 0.002 0.016 

6 0.055 0.004 0.059 0.059 0.009 0.068 

7 0.051 0.006 0.057 0.049 0.013 0.062 

8 0.049 0.003 0.052 0.055 0.007 0.063 

9 0.005 0.001 0.006 0.006 0.001 0.007 

10 0.023 0.002 0.025 0.023 0.005 0.028 

Mean 

SD 

0.038 

0.023 

0.004 

0.003 

0.041 

0.026 

0.040 

0.023 

0.007 

0.006 

0.047 

0.029 

a Dioxin concentration was assumed to be 162 pg toxic equivalent (TEQ) per gram clay. 

b Absorption fraction of 0.3 assumed, extrathoracic (ET) and tracheobronchial (TB) rapidly clear into the 

gastrointestinal tract. 

c Absorption fraction of 0.8 assumed, due to slow clearance from pulmonary (PU) region. 

B-13 
REFERENCES FOR APPENDIX B 

ACGIH (American Conference of Governmental Industrial Hygienists). (2004) TLVs and BEIs: based on the 

documentation of the threshold limit values for chemical substances and physical agents and biological exposure 

indices. Cincinnati, OH: ACGIH Worldwide. 

Aitken, RJ; Baldwin, PEJ; Beaumont, GC; et al. (1999) Aerosol inhalability in low air movement environments. 

J Aerosol Sci 30:613–626. 

Baldwin, PEJ; Maynard, AD. (1998) A survey of wind speeds in indoor workplaces. Ann Occup Hyg 42:303–313. 

Breysse, PN; Swift, DL. (1990) Inhalability of large particles into the human nasal passage: in vivo studies in still 

air. Aerosol Sci Technol 13:459–464. 

Brown, JS. (2005) Particle inhalability at low wind speeds. Inhal Toxicol 17:831–837. 

Chadha, TS; Birch, S; Sacker, MA. (1987) Oronasal distribution of ventilation during exercise in normal subjects 

and patients with asthma and rhinitis. Chest 92(6):1,037–1,041. 

de Winter-Sorkina, R; Cassee, FR. (2002) From concentration to dose: factors influencing airborne particulate 

matter deposition in humans and rats. Bilthoven, The Netherlands: National Institute of Public Health and the 

Environment (RIVM); report no. 650010031/2002. Available online at 

http://www.rivm.nl/bibliotheek/rapporten/650010031.html 

Hinds, WC. (1999) Aerosol technology: properties, behavior, and measurement of airborne particles (2nd ed.). 

New York, NY: Wiley-Interscience. 

Hinds, WC, Kennedy, NJ, and Tatyan, K. (1998) Inhalability of large particles from mouth and nose breathing. 

J Aerosol Sci 29(1):277–278. 

Hsu, DJ; Swift, DL. (1999) The measurement of human inhalability of ultralarge aerosols in calm air using 

manikins. J Aerosol Sci 30:1,331–1,343. 

ICRP (International Commission on Radiological Protection). (1994) Human respiratory tract model for 

radiological protection: a report of a task group of the International Commission on Radiological Protection. 

Oxford, United Kingdom: Elsevier Science Ltd. ICRP publication 66; Annals of the ICRP. Vol. 24, pp. 1–482. 

Kennedy, NJ; Hinds, WC. 2002. Inhalability of large solid particles. J Aerosol Sci 33:237–255. 

Ménache, MG; Miller, FJ; Raabe, OG. (1995) Particle inhalability curves for humans and small laboratory animals. 

Ann Occup Hyg 39:317–328. 

Niinimaa, V; Cole, P; Mintz, S; et al. (1981) Oronasal distribution of respiratory airflow. Respir Physiol 43:69–75. 

B-14 
C-1

Figure C-1b. Clay particles on Subject Filter. Figure C-2b. Clay particles on Subject Filter. 

APPENDIX C 

SEM AND EDS DATA BY SUBJECT 

Figure C-1a. Sample of clay used by Subject 1. Figure C-2a. Sample of clay used by Subject 2. 
Figure C-3b. Clay particles on Subject 

Filter. Figure C-4b. Clay particles on Subject Filter. 

C-2
 

Figure C-3a. Sample of clay used by Subject 3. Figure C-4a. Sample of clay used by Subject 4. 
Figure C-6b. Clay particles on Subject 

Filter. Figure C-5b. Clay particles on Subject Filter. 

C-3
 

Figure C-5a. Sample of clay used by Subject 5. Figure C-6a. Sample of clay used by Subject 6. 
Figure C-8b. Clay particles on Subject 

Filter. 

Figure C-7b. Clay particles on SubjecFilter. 

C-4
 

Figure C-7a. Sample of clay used by Subject 7. Figure C-8a. Sample of clay used by Subject 8. 
D-1 

APPENDIX D 

ALTERNATIVE METHOD FOR ESTIMATING DERMAL ABSORPTION 

 This document uses the fraction absorbed approach to estimate dermal absorption, which 

is the method recommended in current U.S. Environmental Protection Agency guidance (U.S. 

EPA, 2004, 1992). The discussion below presents an alternative approach using a more 

mechanistic model. 

 Kissel et al. (2007) present a flux based model for estimating an upper limit of dermal 

absorption from soil: 

(D-1)

where 

AbsDose = absorbed dose (pg) 

Csoil,0 = concentration of dioxin in soil at t = 0 (pg mg

-1) 

L = soil load on exposed skin (mg cm

-2) 

A = area of skin exposed (cm2) 

t = exposure time (hr) 

Jmulti = flux rate of chemical through skin from multi layer experiment (ng cm-2 hr) 

Cmulti = concentration of chemical in soil used in multi layer experiment (ng mg-1) 

Cmulti,sat = saturation concentration of chemical in soil used in multi layer experiment 

(ng mg

-1) 

Csoil,sat = saturation concentration of chemical in soil used in exposure scenario 

(ng mg

-1) 

This equation was derived from a mass balance of the chemical on the soil and assumes that the 

flux is proportional to the concentration. The model uses the exponential term to represent the 

decline in absorption rate that occurs over time as the contaminant is depleted from the soil. 

 Kissel et al. (2007) suggest estimating the ratio of the saturated soil concentrations on the 

basis of the ratio of organic carbon concentration in the soil used in the experiment to the organic 

carbon concentration in the soil used in the exposure scenario. As discussed in Section 5, this 

report derives the dermal absorption properties of dioxin from Roy et al. (2008), who measured 

dermal absorption of tetrachlorodibenzo-p-dioxin (TCDD) in soil with an organic carbon content 

of 0.45% and applied at supermonolayer coverage (monolayer estimated as 3 mg/cm2 and 

amount applied was 6 mg/cm2). Since the carbon content of the soil used in the Roy et al. tests 

was essentially identical to that of the clay, this ratio is one and it drops out of the equation. 

 If the amount of dioxin absorbed is less than about 10% of the original amount on the 

skin, then Eq. D-1 can be approximated as 

AbsDose Csoil ,0L A1 exp t (J multi /C ) multi (Cmulti ,sat /Csoil ,sat ) / L
D-2 ( / )

soil ,0 multi Cmulti AbsDose  C A t J

 (D-2) 

 For purposes of comparing this approach to the absorption fraction method, Eq. D-2 was 

applied to exposure scenario for Subject 2. The exposure conditions for Subject 2 were as 

follows: 

Csoil,0 = 162 pg g-1 = 0.162 pg mg

-1

A = 970 cm2

T = 4 hr 

 

The 4-hour average flux rate from Roy et al. (2008) was calculated as follows: 

J AF C L t multi soil  /

(D-3) 

where 

AF = Absorption Fraction = 0.0027 (for 4 hr, includes amount in skin) 

Csoil = 1 ng mg-1

L = 6 mg cm

-2

t = 4 hr

This yields a flux estimate of 0.004 ng cm-2hr-1. The experiment was conducted at 1 ppm or 

1 ng mg-1. Thus, the term (Jmulti/Cmulti) in Eq. D-2 is equal to 0.004 mg cm-2hr-1. Substituting 

into Eq. D-2, the absorbed dose is calculated as 2.5 pg which is higher than the value reported in 

Table 9 (0.77 pg) based on the fraction absorbed approach. Note that the amount of dioxin in the 

monolayer can be estimated as 79 pg (0.162 pg mg-1× 0.5 mg cm-2× 970 cm2). This means that 

the absorbed dose is less than 10% of the applied dose and Eq. D-2 is approximately equivalent 

to Eq. D-1. 

 The Kissel et al. model is conceptually different from the absorption fraction method in 

that it assumes that the fluxes measured in the supporting experiment (and normalized by 

concentration) can be applied to the exposure scenario of concern. Whereas, the absorption 

fraction method assumes that the absorption fraction measured in the supporting experiment can 

be applied to the exposure scenario of concern. In the present document, the absorption fraction 

method is refined by adjusting the experimentally derived absorption fraction on the assumption 

that the absorption occurs exclusively from the monolayer and applying this to the monolayer (or 

actual soil load on skin if less than monolayer) in the exposure scenario of concern. The flux 

based approach has a stronger scientific basis and has the advantage that it is less dependent on 
D-3

uncertain monolayer calculations. Additionally, in the form presented by Kissel et al., it can 

account for reductions in flux rate as the chemical is depleted from the soil. Accordingly, this 

approach has significant advantages over the absorption fraction method and is likely to become 

the preferred approach in the future. Further research is recommended for the continued 

development and validation of this promising approach.
D-4

REFERENCES FOR APPENDIX D

Kissel JC, Spalt EW, Shirai JH, Bunge AL. (2007) Dermal absorption of chemical contaminants from soil (book 

chapter) in Dermal Absorption and Toxicity Assessment, 2nd ed. (Roberts, MS and KA Walters, eds). Marcel 

Dekker Inc, New York, 

Roy, TA; Hammerstrom, K; Schaum, J. (2008) Percutaneous absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin 

(TCDD) from soil. J Toxicol Environ Health, Part A (Accepted).

U.S. EPA (Environmental Protection Agency). (1992) Dermal exposure assessment: principles and applications. 

Office of Science Policy, Office of Research and Development, Washington, DC; EPA/600/8-91/011B. Available 

online at http://www.epa.gov/osa/spc.

U.S. EPA (Environmental Protection Agency). (2004) Risk assessment guidance for Superfund. Vol. I: human 

health evaluation manual (part E, supplemental guidance for dermal risk assessment). Office of Superfund 

Remediation and Technology Innovation, Washington, DC; EPA/540/R/99/005. Available online at 

http://www.epa.gov/superfund/programs/risk/ragse/index.htm.
E-1

APPENDIX E

SKIN RINSING DATA

Table E-1. Weight of clay rinsed from skin of each subject during each 

individual skin rinse (g)

Subject Rinse 1 Rinse 2 Rinse 3

1 0.321 NAa0.773

2 2.957 2.804 0.083

3 0.558 0.427 0.333

4 0.139 0.126 0.18

5 2.908 1.919 3.042

6 9.893 12.522 10.319

7 0.158 0.149 0.313

8 0.443 1.018 2.618

a

Sample lost during analysis.

NA = not available. 
E-2

Table E-2. Residual clay (mg)

Subject Right Hand Left Hand Arms Legs Feet Face

Subject 9

Wheel

9,750 11,243 398.55 509.80 214.40 16.70

1,874 2,352 790.25 596.25 144.00 0.00

4,059 4,270 388.60 1,276.70 267.20 4.35

1,536 2,845 5,005.35 958.50 220.65 9.60

1,367 3,426 8,630.60 273.95 2,991.50 524.60

Subject 10

Sculpture

70 14 33.50 8.40 17.40 0.00

83 65 58.50 42.85 42.65 9.80

74 98 131.80 9.20 14.10 25.70
F-1

APPENDIX F 

PICTURES OF ARTISANS PRIOR TO SKIN RINSE PROCEDURE 

Figure F-1. Subjects 1–4.
F-2

Figure F-2. Subjects 5–8.
F-3

Figure F-3. Subject 9. 
F-4

Figure F-4. Subject 10. 
G-1

APPENDIX G

REAL-TIME PARTICLE CONCENTRATION DATA

Figure G-1. Subject 1.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

10

0 20 40 60 80 100 120 140 160

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

1

2

3

4

5

0 20 40 60 80 100 120 140 160

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

10

0 20 40 60 80 100 120 140 160

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

1

2

3

4

5

0 20 40 60 80 100 120 140 160

Time (min)

particle conc., mg/m

3
G-2

Figure G-2. Subject 2.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

10

0 20 40 60 80 100

Time (min)

particle conc., mg/m

3

Mixing and bagging 

of powdered clay

Subject cleaned off 

using compressed air

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100

Time (min) 

particle conc., mg/m

3

Subject cleaned off 

using compressed air

Mixing and bagging 

of powdered clay

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

10

0 20 40 60 80 100

Time (min)

particle conc., mg/m

3

Mixing and bagging 

of powdered clay

Subject cleaned off 

using compressed air

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

10

0 20 40 60 80 100

Time (min)

particle conc., mg/m

3

Mixing and bagging 

of powdered clay

Subject cleaned off 

using compressed air

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100

Time (min) 

particle conc., mg/m

3

Subject cleaned off 

using compressed air

Mixing and bagging 

of powdered clay

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100

Time (min) 

particle conc., mg/m

3

Subject cleaned off 

using compressed air

Mixing and bagging 

of powdered clay
G-3

Figure G-3. Subject 3.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.2

0.4

0.6

0.8

1

0 25 50 75 100 125

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

5

10

15

20

25

30

35

40

0 25 50 75 100 125

Time (min)

particle conc., mg/m

3

Classroom cleaning

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.2

0.4

0.6

0.8

1

0 25 50 75 100 125

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

5

10

15

20

25

30

35

40

0 25 50 75 100 125

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.2

0.4

0.6

0.8

1

0 25 50 75 100 125

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

5

10

15

20

25

30

35

40

0 25 50 75 100 125

Time (min)

particle conc., mg/m

3

Classroom cleaning
G-4

Figure G-4. Subject 4.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 2 0 4 0 6 0 8 0 100 120

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 2 0 4 0 6 0 8 0 100 120

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120

Time (min)

particle conc., mg/m

3
G-5

Figure G-5. Subject 5.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.05

0.1

0.15

0.2

0.25

0.3

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

0.05

0.1

0.15

0.2

0.25

0.3

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3
G-6

Figure G-6. Subject 6.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

1 0

0 3 0 6 0 9 0 120

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

2

4

6

8

1 0

0 3 0 6 0 9 0 120

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120

Time (min)

particle conc., mg/m

3
G-7

Figure G-7. Subject 7.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

1

2

3

4

5

0 10 20 30 40

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

1

2

3

4

5

0 20 40 60 80 100 120

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

1

2

3

4

5

0 10 20 30 40

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

1

2

3

4

5

0 20 40 60 80 100 120

Time (min)

particle conc., mg/m

3
G-8

Figure G-8. Subject 8.

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

1

2

3

4

5

6

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3

Personal Particle Concentration 

using the pDR-1000 Particle Counter

0

1

2

3

4

5

6

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3

Area Particle Concentration 

using the CI-500 Particle Counter

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 140

Time (min)

particle conc., mg/m

3
G-9

Figure G-9. Subject 9.

Wheel Session 2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 60 120 180 240 300

Time (min)

Particle conc. (mg m-3)

Wheel Session 2

Time (min)

Particle conc. (mg m-3)

Wheel Session 1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)

Wheel Session 1

Time (min)

Particle conc. (mg m-3)

Wheel Session 2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 60 120 180 240 300

Time (min)

Particle conc. (mg m-3)

Wheel Session 2

Time (min)

Particle conc. (mg m-3)

Wheel Session 2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 60 120 180 240 300

Time (min)

Particle conc. (mg m-3)

Wheel Session 1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)

Wheel Session 1

Time (min)

Particle conc. (mg m-3)

Wheel Session 1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)
G-10

Figure G-9. continued.

Wheel Session 4

0

0.5

1

1.5

2

2.5

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)

Wheel Session 4

Time (min)

Particle conc. (mg m-3)

Wheel Session 3

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 60 120 180 240 300 360 420 480

Time (min)

Particle conc. (mg m-3)

Wheel Session 3

Time (min)

Particle conc. (mg m-3)

Wheel Session 4

0

0.5

1

1.5

2

2.5

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)

Wheel Session 4

Time (min)

Particle conc. (mg m-3)

Wheel Session 4

0

0.5

1

1.5

2

2.5

0 60 120 180 240 300 360 420

Time (min)

Particle conc. (mg m-3)

Wheel Session 3

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 60 120 180 240 300 360 420 480

Time (min)

Particle conc. (mg m-3)

Wheel Session 3

Time (min)

Particle conc. (mg m-3)

Wheel Session 3

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 60 120 180 240 300 360 420 480

Time (min)

Particle conc. (mg m-3)
G-11

Figure G-9. continued.

Wheel Session 5

Time (min)

Particle conc. (mg m-3)
G-12

Figure G-10. Subject 10.

Time (min)

Sculpture Session 2

Time (min)

Particle conc. (mg m-3)

Sculpture Session 1

Particle conc. (mg m-3)

Time (min)

Sculpture Session 2

Time (min)

Particle conc. (mg m-3)

Sculpture Session 2

Time (min)

Particle conc. (mg m-3)

Sculpture Session 1

Particle conc. (mg m-3)
G-13

Figure G-10. continued.

Sculpture Session 3

Time (min)

Particle conc. (mg m-3)

Background Particle Concentration

Particle conc. (mg m-3)

Time (min)

Sculpture Session 3

Time (min)

Particle conc. (mg m-3)

Background Particle Concentration

Particle conc. (mg m-3)

Time (min)
H-1

APPENDIX H

RESPICONTM, CASCADE IMPACTOR, PDR-1000, AND CLIMET® CI-500,

DATA FOR EACH INDIVIDUAL SUBJECT

Table H-1. Concentration by particle diameter (μm) as measured by the 

RespiconTM Air Sampler (mg/m3)

a, b

Aerodynamic 

diameter <4 4–10 10–100 Total

Subject 1 <DL <DL 1.03 1.90

Subject 2 <DL <DL 1.54 2.42

Subject 3 <DL <DL <DL 1.32

Subject 4 <DL <DL 1.75 2.63

Subject 5 <DL <DL <DL 1.32

Subject 6 1.06 1.25 1.69 4.00

Subject 7 <DL <DL <DL 1.32

Subject 8 <DL <DL 1.23 2.11

Backgroundc<DL <DL <DL 1.32

a DL (Detection Limit) = 0.878 mg/m3

.

b 1⁄2 DL was used in place of the <DL results for the purpose of calculating the total concentration.

cBased on measurements taken late at night when no students were present in building.
H-2

Table H-2. Concentration by particle diameter (μm) as measured by the Cascade 

Impactor Air Sampler (mg/m3)

a, b

Aerodynamic 

diameter 0.5–2 2.0–4.0 4.0–8.0 8.0–16 16–32 >32 μm Total

Subject 1 <DL 0.02 0.06 0.02 0.06 0.18 0.35

Subject 2 <DL 0.04 0.03 0.05 0.02 0.31 0.47

Subject 3 0.06 0.08 0.19 0.15 0.13 0.39 0.99

Subject 4 <DL <DL 0.03 0.05 0.05 0.22 0.37

Subject 5 <DL <DL <DL <DL <DL 0.10 0.13

Subject 6 <DL 0.04 0.08 0.14 0.10 0.23 0.61

Subject 7 0.04 0.05 0.11 0.12 0.06 0.15 0.51

Subject 8 <DL 0.03 0.07 0.11 0.10 0.31 0.64

Backgroundc<DL <DL <DL <DL 0.017 0.085 0.13

a DL (Detection Limit) = 0.015 mg/m3

.

b 1⁄2 DL was used in place of the <DL results for the purpose of calculating the total concentration.

cBased on measurements taken late at night when no students were present in building.
H-3

Table H-3. Particle concentration as measured by the pDR-1000 Air 

Sampler (mg/m3)

Mean Maximum Minimum

Subject 1 0.75 8.42 0.047

Subject 2 0.57 8.33 0.016

Subject 3 0.30 0.84 0.093

Subject 4 0.14 0.81 0.027

Subject 5 0.049 0.27 0.019

Subject 6 1.22 7.70 0.078

Subject 7 0.32 3.51 0.080

Subject 8 0.34 5.14 0.015

Table H-4. Concentration by particle diameter (μm) as measured by the 

Climet CI-500 Air Sampler (mg/m3)

a

Physical 

diameter 0.3–0.5 0.5–1.0 1.0–2.5 2.5–5.0 5.0–10 >10.0 Total

Subject 1 0.001 0.005 0.026 0.222 0.560 1.499 2.313

Subject 2 0.001 0.002 0.016 0.166 0.535 1.747 2.467

Subject 3 0.002 0.009 0.058 0.411 1.214 3.756 5.450

Subject 4 0.002 0.003 0.013 0.124 0.323 0.964 1.429

Subject 5 0.008 0.002 0.003 0.025 0.055 0.167 0.260

Subject 6 0.011 0.006 0.029 0.260 0.679 1.746 2.731

Subject 7 0.005 0.010 0.054 0.377 0.631 0.817 1.895

Subject 8 0.006 0.004 0.021 0.186 0.578 1.878 2.672

Backgroundb0.009 0.005 0.002 0.010 0.010 0.019 0.055

aConcentration calculations assume particle density of 2.6 g/cm3

.

bBased on measurements taken late at night when no students were present in building.
H-4

Table H-5. Average concentrations by particle diameter ranges (μm) 

measured by the Cascade Impactor Air Sampler (mg/m3)

a, b

Aerodynamic 

diameter 0.5–2 2.0–4.0 4.0–8.0 8.0–16 16–32 >32 Total

Subject 9 

Session 1

0.004 <DL 0.004 0.008 0.007 0.024 0.049

Subject 9 

Session 2

<DL <DL 0.005 0.007 0.008 0.024 0.046

Subject 9 

Session 3

0.004 0.008 0.012 0.013 0.020 0.044 0.102

Subject 9 

Session 4

<DL <DL 0.004 0.005 0.009 0.053 0.073

Subject 9 

Session 5

0.007 0.008 0.004 0.026 0.026 0.081 0.152

Subject 10 

Session 1c

0.019 0.034 0.075 0.079 0.075 0.198 0.480

Subject 10 

Session 2c

0.005 0.015 0.034 0.052 0.040 0.092 0.237

Subject 10 

Session 3

0.011 0.018 0.047 0.054 0.032 0.079 0.241

Backgroundd0.004 <DL 0.003 0.006 0.004 0.005 0.023

a DL (Detection Limit) = 0.0025 mg/m3

.

b 1⁄2 DL was used in place of the <DL results for the purpose of calculating the total concentration.

cConcentration not adjusted for presence of dog.

dBased on measurements taken late at night when no students were present in building.
H-5

Table H-6. Concentration by particle diameter ranges (μm) measured by the 

Climet® CI-500 Air Sampler (mg/m3)

a

Physical 

diameter 0.3–0.5 0.5–1.0 1.0–2.5 2.5–5.0 5.0–10 >10.0 Total

Subject 9 

Session 1

0.008 0.003 0.005 0.026 0.042 0.070 0.155

Subject 9 

Session 2

0.010 0.005 0.003 0.014 0.027 0.058 0.117

Subject 9 

Session 3

0.006 0.004 0.005 0.026 0.054 0.124 0.220

Subject 9 

Session 4

0.012 0.007 0.011 0.055 0.113 0.240 0.439

Subject 9 

Session 5

0.011 0.008 0.004 0.018 0.026 0.048 0.115

Subject 10 

Session 1b

0.018 0.015 0.067 0.353 0.746 1.430 2.629

Subject 10 

Session 2b

0.003 0.005 0.031 0.172 0.367 0.700 1.278

Subject 10 

Session 3

0.006 0.008 0.039 0.181 0.341 0.656 1.231

Backgroundc0.012 0.009 0.003 0.011 0.012 0.016 0.064

aConcentration calculations assume particle density of 2.6 g/cm3

.

bConcentration not adjusted for presence of dog.

cBased on measurements taken late at night when no students were present in building.
I-1

APPENDIX I

MONTE CARLO CALCULATION OUTLINE

I.1. SELECT GENERAL EXPOSURE PARAMETERS

Dioxin concentration in clay (C) from distribution

Fraction ball clay in blend (Fblend) from distribution

Exposure duration (ED) from distribution

Select value for gender selector (0 to 0.5 means male, >0.5 to 1.0 means female)

Total body surface area males (SA) from distribution

Total body surface area females (SA) from distribution

I.2. COMPUTE DERMAL DOSE

Table I-1. Select value for clothing selector and determine fraction of body 

unclothed

Clothing Selector

Fraction Unclothed (FU)

FUarm FUleg FUfeet

0 to 0.2 0 0 0

0.2 to 0.8 0.67 0 0

0.8 to 0.9 0.67 0.67 0

0.9 to 1.0 0.67 0.67 1.0

Monolayer load (ML) = 0.5 mg/cm2

Dermal absorption fraction for feet (DAFfeet) = 0.0226 (assumes 24-hour exposure)

Dermal absorption fraction for legs (DAFlegs) = 0.0226 (assumes 24-hour exposure)

Dermal absorption fraction for hands (DAFhand) = (0.0005 ED2+ 0.05 ED + 0.7692)/100

Dermal absorption fraction for arms (DAFarms) = (0.0005 ED2+ 0.05 ED + 0.7692)/100

Dermal absorption fraction for face (DAFface) = (0.0005 ED2+ 0.05 ED + 0.7692)/100

Select clay load on hand (Lhand) from distribution

Adjust Lhand: if Lhand > ML, then Lhand = ML, if Lhand < ML, then Lhand = Lhand.
I-2

Total hand surface area (SAhand) = 0.052 SA

Dose to hand (Dhand) = (C Fblend DAFhand Lhand SAhand) 0.001

Select clay load on arm (Larm) from distribution

Adjust Larm: if Larm > ML, then Larm = ML, if Larm < ML, then Larm = Larm.

Total arm surface area (SAarm) = 0.014 SA

Dose to arm (Darm) = (C Fblend DAFarm Larm SAarm FUarm) 0.001

Select clay load on leg (Lleg) from distribution

Adjust Lleg: if Lleg > ML, then Lleg = ML, if Lleg < ML, then Lleg = Lleg.

Total hand surface area (SAleg) = 0.318 SA

Dose to hand (Dleg) = (C Fblend DAFleg Lleg SAleg FUleg) 0.001

Select clay load on feet (Lfeet) from distribution

Adjust Lfeet: if Lfeet > ML, then Lfeet = ML, if Lfeet < ML, then Lfeet = Lfeet.

Total feet surface area (SAfeet) = 0.068 SA

Dose to feet (Dfeet) = (C Fblend DAFfeet Lfeet SAfeet FUfeet) 0.001

Select clay load on face (Lface) from distribution

Adjust Lface: if Lface > ML, then Lface = ML, if Lface < ML, then Lface = Lface.

Total face surface area (SAface) = 0.025 SA

Dose to face (Dface) = (C Fblend DAFface Lface SAface) 0.001

Total dermal dose (Dder) = Dhand + Darm + Dleg + Dfeet + Dface

I.3. COMPUTE INGESTION DOSE

Ingestion absorption fraction (Fing) = 0.3

Clay load on food (Lfood) from distribution

Clay load on beverage (Lbev) from distribution

Total ingestion dose (Ding) = C Fblend Fing (Lfood + Lbev) 0.001

I.4. COMPUTE INHALATION DOSE

Particulate concentration in air (Cair) from distribution

Mass mean aerodynamic particle size (MMAD) from distribution

Geometric SD for particle distribution = 4
I-3

Select value for activity selector (AS) from distribution

Walk time = AS ED

Light exertion time (LET) = ED (1 – AS)

Table I-2. Set respiration parameters

Slow walk Light exertion

Female Male Female Male

Tidal volume (TV) (mL) 464 750 992 1,250

Breathing frequency F

(times/min) 14 12 21 20

Ventilation rate Ve

(l pm) TV*F/1,000 = 6.5 TV*F/1,000 = 9

TV*F/1,000 = 21 TV*F/1,000 = 

25

Residual lung capacity 

(mL)

2,680 3,300 2,680 3,300

Select value for Breath Selector

0 to 0.13 means oralnasal breather, >0.13 to 1.0 means nasal breather

Compute regional doses using MPPD Subroutine (see below where Dn = dose to nose, Dm = dose 

to mouth, Dtb = dose to tracheal bronchial and Dpu = Dose to pulmonary)

Absorption fraction for nose, mouth, and TB = 0.3

Absorption fraction for PU = 0.8

Compute total inhalation dose (Dinh) = 0.3(Dn + Dm + Dtb) + 0.8Dpu

I.5. COMPUTE TOTAL DOSE (DTOTAL) = DDER + DING + DINH

MPPD Subroutine

MPPD (plus extrapolation curves for particles over 20 μm, see Appendix B) used to generate 

deposition fractions over a range particle sizes for each respiratory region and scenario based on 

breathing pattern, tidal volume, breathing frequency and residual lung capacity. The deposition 

fractions for each particle size (based on aerodynamic diameter or Dae) are multiplied by the 

inhalation fraction: 
I-4

Inhalation Fraction oral breather, Io = 1.44 / (1 + 0.44exp (0.0195Dae))

Inhalation Fraction nasal breather, In = 1- (1.0 / (1 + exp (10.32-3.114 lnDae))

This results in eight sets of MPPD outputs for deposition fractions in ET, TB, and PU (corrected 

for inhalation) which are stored in the spreadsheet:

Table I-3. Output categories for deposition fractions

Slow Walk Light Exertion

Nasal Oral Nasal Oral

Male 1 2 3 4

Female 5 6 7 8

The particle size distribution is divided into 100 intervals and DF to each region is computed by 

summing the deposition fraction over each interval

Deposition to each region are calculated for slow walk and light exertion and then summed. For 

example, deposition to the nose, Dn is calculated as follows:

Dn = Cair [Vt F ED DFn]light + Cair [Vt F ED DFn]slow
 

Crystal Ball Report - Full 

Simulation started on 7/23/2008 at 10:07:17
 

Simulation stopped on 7/23/2008 at 10:15:22
 

Run preferences: 

Number of trials run 1,000 

Monte Carlo 

Random seed 

Precision control on

 Confidence level 95.00% 

Run statistics: 

Total running time (sec) 485.46 

Trials/second (average) 2 

Random numbers per sec 37 

Crystal Ball data: 

Assumptions 18 

 Correlations Correlations 0

Correlated groups 0 

Decision variables 0 

Forecasts 4 

APPENDIX J

 MONTE CARLO SIMULATION RESULT GRAPHICS
 

J-1
 
Forecasts 

Worksheet: [VarDp-Dep monte6.xls]Monte 

Forecast: Ingestion Dose (pg/d) 

Summary: 

Entire range is from 0.005 to 1.001 

Base case is 0.058 

After 1,000 trials, the std. error of the mean is 0.003 

Statistics: Forecast values 

Trials 

Mean 

1,000 

0.135 

Median 0.110 

Mode ---

Standard Deviation 0.102 

Variance 0.010 

Skewness 2.08 

Kurtosis 11.29 

Coeff. of Variability 

Minimum 

0.76 

0.005 

Maximum 1.001 

Range Width 

Mean Std. Error 

0.997 

0.003 

J-2
 
Forecast: Ingestion Dose (pg/d) (cont'd) 

Percentiles: Forecast values 

0% 0.005 

10% 0.035 

20% 0.053 

30% 0.073 

40% 0.092 

50% 0.110 

60% 0.133 

70% 0.161 

80% 0.202 

90% 0.258 

100% 1.001 

J-3
Forecast: Inhalation Dose 

Summary: 

Entire range is from 0.00 to 1.12 

Base case is 0.03 

After 1,000 trials, the std. error of the mean is 0.00 

Statistics: Statistics: Forecast values Forecast values 

Trials 1,000 

Mean 0.11 

Median 0.07 

Mode ---

Standard Deviation 0.13 

Variance 0.02 

Skewness 2.78 

Kurtosis 14.10 

Coeff. of Variability 1.10 

Minimum 0.00 

Maximum 1.12 

Range Width 1.11 

Mean Std. Error 0.00 

J-4
 
Forecast: Inhalation Dose (cont'd) 

Percentiles: Forecast values 

0% 0.00 

10% 0.02 

20% 0.03 

30% 0.04 

40% 0.06 

50% 0.07 

60% 0.09 

70% 0.12 

80% 0.17 

90% 0.26 

100% 1.12 

J-5
Statistics: Statistics: Forecast values Forecast values 

Trials 

Mean 

1,000 

6.18 

Median 3.23 

Mode ---

Standard Deviation 8.32 

Variance 69.30 

Skewness 3.71 

Kurtosis 23.60 

Coeff. of Variability 

Minimum 

1.35 

0.14 

Maximum 91.63 

Range Width 

Mean Std. Error 

91.48 

0.26 

Forecast: Total Dermal Dose 

Summary: 

Entire range is from 0.14 to 91.63 

Base case is 3.32 

After 1,000 trials, the std. error of the mean is 0.26 

J-6
 
Forecast: Total Dermal Dose (cont'd) 

Percentiles: Forecast values 

0% 0.14 

10% 0.96 

20% 1.42 

30% 1.90 

40% 2.45 

50% 3.23 

60% 4.46 

70% 6.07 

80% 8.90 

90% 14.42 

100% 91.63 

J-7
Statistics: Statistics: Forecast values Forecast values 

Trials 

Mean 

1,000 

6.43 

Median 3.50 

Mode ---

Standard Deviation 8.43 

Variance 71.03 

Skewness 3.67 

Kurtosis 23.22 

Coeff. of Variability 

Minimum 

1.31 

0.17 

Maximum 92.39 

Range Width 

Mean Std. Error 

92.22 

0.27 

Forecast: Total Dose (pg/d) 

Summary: 

Entire range is from 0.17 to 92.39 

Base case is 3.41 

After 1,000 trials, the std. error of the mean is 0.27 

J-8
 
Forecast: Total Dose (pg/d) (cont'd) 

Percentiles: Forecast values 

0% 0.17 

10% 1.07 

20% 1.55 

30% 2.08 

40% 2.73 

50% 3.50 

60% 4.69 

70% 6.36 

80% 9.15 

90% 14.80 

100% 92.39 

End of Forecasts 

J-9
Assumption: Activity selector 

Uniform distribution with parameters:
 

Minimum
 0.00 

Maximum
 1.00 

Assumption: Breath Selector 

Uniform distribution with parameters: 

Minimum 0.00 

Maximum 1.00 

Assumption: Clay load Assumption: Clayload onarm(mg/cm2) (mg/cm2) 

Triangular distribution with parameters: 

Minimum 0.04 

Likeliest 0.35 

Maximum 3.00 

Assumption: Clay load on beverage (mg) 

Triangular distribution with parameters: 

Minimum 0.30 

Likeliest 0.50 

Maximum 0.72 

Worksheet: [VarDp-Dep monte6.xls]Monte 

Assumptions 

J-10
 
Assumption: Clay load on face (mg/cm2) 

Uniform distribution with parameters: 

Minimum 

Maximum 

0.030 

0.040 

Assumption: Clay load on feet (mg/cm2) 

Uniform distribution with parameters: 

Minimum 

Maximum 

0.03 

0.30 

Assumption: Clay load on food (mg) 

Triangular distribution with parameters: 

Minimum 

Likeliest Likeliest 

Maximum 

0.30 

0 70 . 

1.66 

Assumption: Clay load on hand (mg/cm2) 

Triangular distribution with parameters: 

Minimum 

Likeliest 

Maximum 

0.10 

3.00 

10.00 

J-11
 
Assumption: Clay load on leg (mg/cm2) 

Uniform distribution with parameters: 

Minimum 

Maximum 

0.10 

0.70 

Assumption: clothing selector 

Uniform distribution with parameters: 

Minimum 0.00 

Maximum 1.00 

Assumption: Dioxin conc in ball clay (pg/g) 

Lognormal distribution with parameters: 

Mean 808.00 

Std Dev Std. Dev. 318 00 . 

Assumption: Exposure Duration (hr/d) 

Triangular distribution with parameters: 

Minimum 1.00 

Likeliest 4.00 

Maximum 10.00 

J-12
 
Assumption: Fraction of ball clay in blend 

Triangular distribution with parameters: 

Minimum 

Likeliest 

Maximum 

0.00 

0.20 

1.00 

Assumption: Gender Selector 

Uniform distribution with parameters: 

Minimum 0.00 

Maximum 1.00 

Assumption: MMAD (um) 

Triangular distribution with parameters: 

Minimum 13.00 

Likeliest Likeliest 25 00 . 

Maximum 45.00 

Assumption: Particle Concentration in Air(mg/m3) 

Triangular distribution with parameters: 

Minimum 0.08 

Likeliest 0.44 

Maximum 0.99 

J-13
 
Assumption: Total Body Surface Area Females (cm2) 

Lognormal distribution with parameters: 

Mean 17,300.00 

Std. Dev. 2,100.00 

Assumption: Total Body surface Area Males (cm2) 

Lognormal distribution with parameters: 

Mean 19,700.00 

Std. Dev. 1,900.00 

End of Assumptions 

J-14
 
National Center for Environmental AssessmentOffice of Research and De

elopment

PRESORTED STANDARD

POSTAGE & FEES PAID

EPA

PERMIT NO. G-35

EPA/600/R-06/044F | September 2008 An Exploratory Study: Assessment of Modeled Dioxin Expo