EPA/600/R-08/135 

August 2009 

www.epa.gov/ncea 

Highlights of the Child-Specific

Exposure Factors Handbook

National Center for Environmental Assessment

Office of Research and Development

U.S. Environmental Protection Agency

Washington, DC 20460
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NOTICE 

The U.S. Environmental Protection Agency through its Office of Research and Development, National Center for 

Environmental Assessment, funded the research described here under contract no. EP-W-04-035 with Versar, Inc. 

This document contains a brief overview of the contents of the 2008 version of the Child-Specific Exposure Factors 

Handbook, which was published earlier, i.e., 2002 and revised in 2005. This highlights document has been 

subjected to the Agency’s administrative review and has been approved for publication as an EPA document. 

Preferred Citation: 

U.S. Environmental Protection Agency (EPA). (2009) Highlights of the child-specific exposure factors handbook. 

National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/135. Available from the National 

Technical Information Service, Springfield, VA and online at http://www.epa.gov/ncea. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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FOREWORD 

In 2008, the U.S. Environmental Protection Agency (EPA), Office of Research and Development, National Center 

for Environmental Assessment (NCEA) published a revised version of its original 2002 Child-Specific Exposure 

Factors Handbook. Its purpose is to provide exposure/risk assessors with information on behavioral and 

physiological factors that can be used in assessing exposures among children. The Handbook presents information 

on children’s exposure factors, based on selected studies published through July 2008. It uses a standard set of age 

categories for children, ages 0 to <21 years old, to permit comparison of data among multiple sources and to provide 

consistency among different types of exposure factors. The Handbook provides recommended values for the 

various exposure factors based on these standard age groups. These revisions assist exposure assessors with the 

implementation of the recommendations presented in the EPA’s 2005 Guidelines for Carcinogen Risk Assessment 

and the Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens. 

Specifically, the 2005 Guidelines emphasized the need to consider childhood as a series of life stages rather than 

children as subpopulations and to sum exposures and risks across life stages rather than relying on the use of a 

lifetime average adult exposure to calculate risk. 

The goals for revising the Handbook were to 

(1) most importantly, reanalyze data and present the information using the standardized set of childhood age 

groups as recommended in EPA's 2005 Guidance on Selecting Age Groups for Monitoring and Assessing 

Childhood Exposures to Environmental Contaminants; and 

(2) incorporate new exposure factors data/research that had become available since the early 2000s. 

This Highlights document was developed to provide a brief overview of the contents of the Child-Specific Exposure 

Factors Handbook and to facilitate access to its exposure factors recommendations. As such, it contains a subset of 

the information provided in the complete Handbook. This Highlights document is a product of the EPA’s Exposure 

Factors Program. NCEA established the Exposure Factors Program to develop tools and databases that improve the 

scientific basis of exposure and risk assessment by (1) identifying exposure factors needs in consultation with 

clients, and exploring ways for filling data gaps; (2) compiling existing data on exposure factors needed for 

assessing exposures/risks; and (3) assisting clients in the use of exposure factors data. These activities are supported 

by and respond to the needs of the various EPA program offices. 

EPA invites you to visit http://epa.gov/risk/guidance.htm where you can view and download chapters from the 

Child-Specific Exposure Factors Handbook as well as the Exposure Factors Handbook. Each chapter in these 

handbooks presents recommended values for exposure factors as well as a discussion of the underlying data used to 

develop the recommendations. NCEA intends to update its Web site periodically so that the information provided 

by the Exposure Factors Program is current and relevant. 

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CONTENTS 

ACRONYMS AND ABBREVIATIONS ..........................................................................................................................vi

ABOUT THE HANDBOOK ............................................................................................................................................vii

INTENDED AUDIENCE ...................................................................................................................................................1

BACKGROUND ................................................................................................................................................................1

SELECTION OF STUDIES FOR THE HANDBOOK ......................................................................................................3

General Assessment Factors..........................................................................................................................................3

Selection Criteria ...........................................................................................................................................................3

APPROACH USED TO DEVELOP RECOMMENDATIONS FOR EXPOSURE FACTORS ........................................5

SUGGESTED REFERENCES FOR USE IN CONJUNCTION WITH THE HANDBOOK ............................................6

CONSIDERING LIFESTAGE WHEN CALCULATING EXPOSURE AND RISK ........................................................8

FUNDAMENTAL PRINCIPLES OF EXPOSURE ASSESSMENT.................................................................................8

Dose Equations..............................................................................................................................................................9

Use of Exposure Factors Data in Probabilistic Analyses.............................................................................................11

CUMULATIVE EXPOSURES ........................................................................................................................................12

REFERENCES .................................................................................................................................................................13

LIST OF TABLES 

Table 1. Summary of Recommended Exposure Factors for Children...........................................................17

Table 2. Characterization of Variability in Exposure Factors.......................................................................25

Table 3. Considerations Used to Rate Confidence in Recommended Values...............................................26

Table 4. Summary of Confidence Ratings for Exposure Factor Recommendations.....................................27

Table 5. Age-Dependent Potency Adjustment Factor (ADAF) by Exposure Age Group ............................28

LIST OF FIGURES 

Figure 1. The Exposure-Dose Effect Continuum ...........................................................................................29

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ACRONYMS AND ABBREVIATIONS 

ADAF = Age Dependent Adjustment Factors 

ADD = Average Daily Dose 

BMD = Benchmark Dose 

C = Contaminant Concentration 

cm 2 = Square Centimeter 

ED = Exposure Duration 

g = Gram 

GAF = General Assessment Factor 

Hc = Human Equivalent Concentration 

IR = Intake Rate 

kg = Kilogram 

LADD = Lifetime Average Daily Dose 

m 2 = Square Meter 

m 3 = Cubic Meter 

mg = Milligram 

mL = Milliliter 

NCEA = National Center for Environmental Assessment 

OCHP = Office of Children’s Health Protection 

OCHPEE = Office of Children’s Health Protection and Environmental Education 

ORD = Office of Research and Development 

PBPK = Physiologically-Based Pharmacokinetic 

RfD = Reference Dose 

RfC = Reference Concentration 

SPC = Science Policy Council 

USDA = United States Department of Agriculture 

U.S. EPA = U.S. Environmental Protection Agency 

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ABOUT THE HANDBOOK 

This Highlights document presents an overview 

of the information provided in the U.S. EPA’s ChildSpecific Exposure Factors Handbook (U.S. EPA 

2008a). The Handbook reviews and summarizes data 

on the various factors used in the exposure 

assessment of children (i.e., individuals <21 years 

old) and provides recommendations for the exposure 

assessment community. The Handbook contains 17 

chapters: an introduction (Chapter 1), a discussion 

about the variability and uncertainty in assessing 

exposure factors (Chapter 2), and 

nonchemical-specific data on exposure factors for the 

U.S. EPA recommended set of childhood age groups 

in the following areas: 

• ingestion of water and other select liquids 

(Chapter 3); 

• non-dietary ingestion factors (Chapter 4); 

• ingestion of soil and dust (Chapter 5); 

• inhalation rates (Chapter 6); 

• dermal exposure factors (Chapter 7); 

• body weight (Chapter 8); 

• intake of fruits and vegetables (Chapter 9); 

• intake of fish and shellfish (Chapter 10); 

• intake of meat, dairy products, and fats (Chapter 

11); 

• intake of grain products (Chapter 12); 

• intake of home-produced foods (Chapter 13); 

• total food intake (Chapter 14); 

• human milk intake (Chapter 15); 

• activity factors (Chapter 16); and 

• consumer products (Chapter 17). 

The Child-Specific Exposure Factors Handbook 

was first published in 2002 (U.S. EPA, 2002a). 

Subsequently, the U.S. EPA published its Guidance 

on Selecting Age Groups for Monitoring and 

Assessing Childhood Exposures to Environmental 

Contaminants (U.S. EPA, 2005a). To the extent 

possible, source data for the independent studies cited 

in the earlier version of the Handbook were obtained 

and reanalyzed to conform to the standard age 

categories: birth to <1 month, 1 to <3 months, 3 to <6 

months, 6 to <12 months, 1 to <2 years, 2 to <3 

years, 3 to <6 years, 6 to <11 years, 11 to <16 years, 

and 16 to <21 years. 

The data presented in the Child-Specific Exposure 

Factors Handbook were compiled from various 

sources including the U.S. EPA’s Exposure Factors 

Handbook (U.S. EPA, 1997a), government reports, 

and information presented in the scientific literature, 

published through July 2008. The data presented are 

generally the result of analyses by the individual 

study authors. However, in some cases, the U.S. EPA 

conducted analysis of published primary data to 

present results for the recommended age groups. 

Studies presented in the Handbook were chosen 

because they were seen as useful and appropriate for 

estimating exposure factors based on the following 

evaluation elements: (1) soundness; (2) applicability 

and utility; (3) clarity and completeness; (4) 

variability and uncertainty; and (5) evaluation and 

review. 

Generally, studies were designated as ―key‖ or 

―relevant‖ studies. Key studies were considered the 

most useful for deriving recommendations, while 

relevant studies provided applicable or pertinent data, 

but not necessarily the most important for a variety of 

reasons (e.g., data were outdated, limitations in study 

design). The Handbook provides recommended 

values for exposure factors based on its interpretation 

of the key studies. Key recommendations from the 

Handbook are summarized in Table 1 (see pages 17­

24) of this Highlights document. Additional 

recommendations and detailed supporting 

information can be found in the individual chapters 

of the Handbook. These recommendations are not 

legally binding and should be interpreted as 

suggestions that U.S. EPA Program Offices or 

individual exposure/risk assessors can consider and 

modify as needed based on their own evaluation of a 

given risk-assessment situation. In certain cases, 

different values may be appropriate in consideration 

of policy, precedent, strategy, or other factors (e.g., 

more up-to-date data of better quality or more 

representative of the population of concern). The 

U.S. EPA also assigned confidence ratings of low, 

medium, or high to each recommended value based 

on the evaluation elements described above. These 

ratings are not intended to represent uncertainty 

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analyses; rather, they represent the U.S. EPA’s 

judgment on the quality of the underlying data used 

to derive the recommendations. 

All tables and figures have been placed at the end 

of the Handbook. 

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INTENDED AUDIENCE 

The Child-Specific Exposure Factors Handbook 

(U.S. EPA 2008a) is intended for use by exposure 

and risk assessors both within and outside the U.S. 

EPA as a reference tool and primary source of 

exposure factor information. It may be used by 

exposure and risk assessors, economists, and other 

interested parties as a source for data and/or U.S. 

EPA recommendations on numeric estimates for 

behavioral and physiological characteristics needed 

to estimate childhood exposure to toxic contaminants 

and other environmental stressors. 

BACKGROUND 

Because of physiological and behavioral 

differences, environmental exposures among children 

differ from exposures among adults. Children may be 

more exposed to some environmental contaminants 

because (1) they consume more of certain foods and 

water per unit of body weight than adults; (2) they 

have a higher ratio of body surface area to volume 

than adults; and (3) they experience important, rapid 

changes in behavior and physiology that may lead to 

differences in exposure. Many studies have shown 

that young children can be exposed to various 

contaminants, including pesticides, during normal 

oral exploration of their environment (i.e., 

hand-to-mouth behavior) and by touching floors, 

surfaces, and objects such as toys (Eskenazi et al., 

1999; Gurunathan et al., 1998; Lewis et al., 1999; 

Nishioka et al., 1999; Garry, 2004). Dust and 

tracked-in soil accumulate in carpets, where young 

children spend a significant amount of time (Lewis et 

al., 1999). Children living in agricultural areas may 

experience higher exposures to pesticides than do 

other children (Curwin et al., 2007). They may play 

in nearby fields or be exposed via consumption of 

contaminated human milk from their farmworker 

mothers (Eskenazi et al., 1999). 

In terms of risk, children may also differ from 

adults in their vulnerability to environmental 

pollutants because of toxicodynamic differences 

(e.g., when exposures occur during periods of 

enhanced susceptibility) and/or toxicokinetic 

differences (i.e., differences in absorption, 

metabolism, and excretion) (U.S. EPA, 2000a). The 

immaturity of metabolic enzyme systems and 

clearance mechanisms in young children can result in 

longer half-lives of environmental contaminants 

(Ginsberg et al., 2002; Clewell et al., 2004). The 

cellular immaturity of children and the ongoing 

growth processes account for elevated risk (AAP, 

1997). Toxic chemicals in the environment can cause 

neurodevelopmental disabilities, and the developing 

brain can be particularly sensitive to environmental 

contaminants. For example, elevated blood lead 

levels and prenatal exposures to even relatively low 

levels of lead can result in behavior disorders and 

reductions of intellectual function in children 

(Landrigan et al., 2005). Exposure to high levels of 

methylmercury can result in developmental 

disabilities (e.g., intellectual deficiency, speech 

disorders, and sensory disturbances) among children 

(Myers et al., 2000). Other authors have described the 

importance of exposure timing (i.e., preconceptional, 

prenatal, and postnatal) and how it affects the 

outcomes observed (Selevan et al., 2000). It has also 

been suggested that higher levels of exposure to 

indoor air pollution and allergens among inner-city 

children compared to non-inner-city children may 

explain the difference in asthma levels between these 

two groups (Breysee et al., 2005). With respect to 

contaminants that are carcinogenic via a mutagenic 

mode of action, the U.S. EPA has found that 

childhood is a particularly sensitive period of 

development in which cancer potencies per year of 

exposure can be an order of magnitude higher than 

during adulthood (U.S. EPA, 2005c). 

Executive Order 13045: Protection of Children 

from Environmental Health Risks and Safety Risks, 

signed in 1997, requires all federal agencies to 

address health and safety risks to children, to 

coordinate research priorities on children’s health, 

and to ensure that their standards take into account 

special risks to children (EO, 1997). To implement 

the Order, the U.S. EPA established the Office of 

Children’s Health Protection (OCHP) (renamed the 

Office of Children’s Health Protection and 

Environmental Education [OCHPEE] in 2005), who 

works with Program and regional offices within the 

U.S. EPA to promote a safe and healthy environment 

for children by ensuring that all regulations, 

standards, policies, and risk assessments take into 

account risks to children. Legislation, such as the 

Food Quality Protection Act and the Safe Drinking 

Water Act amendments of 1996, has made coverage 

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of children’s health issues more explicit, and research 

on children’s health issues is continually expanding. 

As a result of the emphasis on children’s risk, the 

U.S. EPA’s ORD developed a Strategy for Research 

on Environmental Risks to Children (U.S. EPA, 

2000a). The goal of the Strategy is to improve the 

quality of risk assessments for children. The ChildSpecific Exposure Factors Handbook (U.S. EPA, 

2008a) is intended to support the U.S. EPA/ORD’s 

efforts to improve exposure and risk assessments for 

children. 

In 1997, the U.S. EPA/ORD/NCEA published 

the Exposure Factors Handbook (U.S. EPA, 1997a). 

The Handbook includes exposure factors and related 

data on both adults and children. Subsequently, the 

U.S. EPA Program Offices identified the need to 

consolidate all children’s exposure data into a single 

document, and the interim final Child-Specific 

Exposure Factors Handbook was published in 2002 

to fulfill this need (U.S. EPA, 2002a). The 2008 

Handbook (U.S. EPA, 2008a) updates the 2002 

edition of the Child-Specific Exposure Factors 

Handbook. It provides nonchemical-specific data on 

exposure factors that can be used to assess 

contributions from dietary and non-dietary ingestion 

exposure, dermal exposure, and inhalation exposure 

among children. Although the preconceptional and 

prenatal (fetal) life stages are important to consider, 

they are not covered in the Handbook. 

Preconceptional exposures are included in the 

Exposure Factors Handbook (U.S. EPA, 1997a) 

since they relate to maternal and paternal exposures, 

and exposure factors for pregnant and lactating 

women are being developed as part of a separate 

effort. The Handbook also highlights the changes in 

risk-assessment practices that were first presented in 

the U.S. EPA’s Cancer Guidelines (U.S. EPA, 

2005b), regarding the need to consider children as 

life stages rather than as subpopulations. It also 

emphasizes a major recommendation in U.S. EPA’s 

Supplemental Guidance for Assessing Susceptibility 

from Early-Life Exposure to Carcinogens (U.S. EPA, 

2005c) to sum exposures and risks across life stages 

rather than relying on the use of a lifetime average 

adult exposure to calculate risk. 

The Child-Specific Exposure Factors Handbook 

(U.S. EPA, 2008a) does not include 

chemical-specific data or information on 

physiological parameters that may be needed for 

exposure assessments involving 

physiologically-based pharmacokinetic (PBPK) 

modeling. The U.S. EPA has developed guidance on 

how to use and applications of PBPK information in 

risk assessment in the report titled Use of 

Physiologically Based Pharmacokinetic (PBPK) 

Models to Quantify the Impact of Human Age and 

Interindividual Differences in Physiology and 

Biochemistry Pertinent to Risk (U.S. EPA, 2006a). 

With very few exceptions, the data presented in 

the Handbook were derived from the analyses of the 

individual study authors. Because the studies 

included in the Handbook vary in terms of their 

objectives, design, scope, presentation of results, etc., 

the level of detail, statistics, and terminology may 

vary from study to study and from factor to factor. 

For example, some authors used geometric means to 

present their results, while others used arithmetic 

means or distributions. Authors sometimes used 

different age ranges to describe data for children. In 

most cases, the original data were unavailable, and 

the study results could not be reallocated into the 

standard age groups used in the Handbook. When 

adequate detailed data were available, efforts were 

made to reallocate source data into the standard age 

groups recommended by the U.S. EPA in the report 

titled Guidance on Selecting Age Groups for 

Monitoring and Assessing Childhood Exposures to 

Environmental Contaminants (U.S. EPA, 2005a). 

Within the constraint of presenting the original 

material as accurately as possible, the U.S. EPA 

made an effort to present discussions and results in a 

consistent manner. The strengths and limitations of 

each study were discussed to provide the reader with 

a better understanding of the uncertainties associated 

with the values derived from the study. 

Most of the data presented in the Handbook were 

derived from studies that targeted (1) the general 

national population (e.g., USDA food consumption 

surveys) or (2) a sample population from a specific 

area or group (e.g., soil ingestion in children from a 

three-city area in southeastern Washington State). If 

it is necessary to characterize a population that is not 

directly covered by the data in the Handbook, the risk 

or exposure assessor should evaluate whether these 

data may be used as suitable substitutes for the 

population of interest or whether there is a need to 

seek additional population-specific data. The 

decision as to whether to use site-specific or national 

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values for an assessment depends both on the quality 

of the competing data sets as well as on the purpose 

of the specific assessment. If information is needed 

for identifying and enumerating populations who 

may be at risk for greater contaminant exposures or 

who exhibit a heightened sensitivity to particular 

chemicals, the reader is referred to 

Socio-demographic Data Used for Identifying 

Potentially Highly Exposed Populations (U.S. EPA, 

1999). 

In conjunction with the Guidance on Selecting 

Age Groups for Monitoring and Assessing Childhood 

Exposures to Environmental Contaminants (U.S. 

EPA, 2005a), the Handbook adopted the age group 

notation ―X to < Y‖ (e.g., the age group 3 to <6 years 

is meant to span a 3-year time interval from a child’s 

3rd birthday up until the day before his or her 6th 

birthday). 

SELECTION OF STUDIES FOR THE 

HANDBOOK 

Information in the Handbook was summarized 

from studies documented in the scientific literature 

and other available sources. Studies were chosen that 

were seen as useful and appropriate for estimating 

exposure factors for children. The Handbook contains 

summaries of selected studies published through July 

2008. 

Certain studies described in the Handbook are 

designated as ―key,‖ that is, the most useful for 

deriving exposure factors. The recommended values 

for most exposure factors are based on the results of 

the key studies. Other studies are designated 

"relevant," meaning applicable or pertinent, but not 

necessarily the most important. This distinction was 

made on the strength of the attributes listed in the 

―General Assessment Factors‖ listed below. 

General Assessment Factors 

The U.S. EPA recognizes the need to evaluate 

the quality and relevance of scientific and technical 

information used in support of Agency actions (U.S. 

EPA, 2002b, 2003a, 2006b). When evaluating 

scientific and technical information, the U.S. EPA’s 

Science Policy Council (SPC) recommends using 

five General Assessment Factors (GAFs): (1) 

soundness, (2) applicability and utility, (3) clarity and 

completeness, (4) uncertainty and variability, and (5) 

evaluation and review (U.S. EPA, 2003a). These 

GAFs were adapted and expanded to include specific 

considerations deemed to be important during 

evaluation of exposure factors data, and were used to 

judge the quality of the underlying data used to 

derive recommendations. 

Selection Criteria 

The selection of key studies that form the basis 

for the exposure factor recommendations provided in 

the Child-Specific Exposure Factors Handbook (U.S. 

EPA, 2008a) as well as the confidence ratings for 

these recommendations, were based on specific 

criteria within each of the five GAFs, as follows: 

(1) Soundness: Scientific and technical 

procedures, measures, methods, or models 

employed to generate the information are 

reasonable for, and consistent with, the intended 

application. 

Adequacy of the Study Approach: In 

general, more confidence was placed on 

experimental procedures or approaches that 

more likely or closely captured the desired 

measurement. Direct exposure data collection 

techniques, such as direct observation, 

personal monitoring devices, or other known 

methods were preferred where available. If 

studies utilizing direct measurement were not 

available, studies were selected that relied on 

validated indirect measurement methods. 

Studies were also deemed preferable if based 

on primary data, but studies based on 

secondary sources were also included where 

they offered an original analysis. In general, 

higher confidence was placed on exposure 

factors based on primary data. 

Minimal (or Defined) Bias in Study Design: 

More confidence was placed on exposure 

factors based on studies that minimized bias. 

Studies were sought that were designed with 

minimal bias, or at least if biases were 

suspected to be present, the direction of the 

bias (i.e., an over or underestimate of the 

parameter) was either stated or apparent from 

the study design. 

(2) Applicability and Utility: The information is 

relevant for the Agency’s intended use. 

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Focus on Exposure Factor of Interest: 

Studies were preferred that directly addressed 

the exposure factor of interest, or addressed 

related factors that have significance for the 

factor under consideration. 

Representativeness of the Population: More 

confidence was placed in studies that 

specifically addressed the United States 

population. Data from populations outside the 

United States were sometimes included if 

behavioral patterns or other characteristics of 

exposure were similar. Additionally, studies 

seeking to characterize a particular region or 

population were selected, if appropriately 

representative of that population. 

Currency of Information: More confidence 

was placed in studies that were sufficiently 

recent to represent current exposure 

conditions. This is an important consideration 

for those factors that change with time. Older 

data were evaluated and considered in 

instances where the variability of the exposure 

factor over time was determined to be 

insignificant or unimportant. In some cases, 

recent data were very limited. Therefore, the 

data provided in these instances were the only 

available data. Limitations on the age of the 

data were noted. Recent studies are more 

likely to use state-of-the-science 

methodologies that reflect advances in the 

exposure assessment field. Consequently, 

exposure factor recommendations based on 

current data were given higher confidence 

ratings than those based on older data—except 

in cases where the age of the data would not 

affect the recommended values. 

Adequacy of Data Collection Period: 

Because most users of the Handbook are 

primarily addressing chronic exposures, 

studies were sought that utilized the most 

appropriate techniques for collecting data to 

characterize long-term behavior. Higher 

confidence ratings were given to exposure 

factor recommendations that were based on an 

adequate data collection period. 

(3) Clarity and Completeness: The degree of 

clarity and completeness with which the data, 

assumptions, methods, quality assurance, 

sponsoring organizations, and analyses employed 

to generate the information are documented. 

Accessibility: Studies that the user could 

access in their entirety, if needed, were 

preferred. 

Reproducibility: Studies that contained 

sufficient information so that methods could 

be reproduced, or could be evaluated, based 

on the details of the author’s work, were 

preferred. 

Quality Assurance: Studies with documented 

quality-assurance/quality-control measures 

were preferred. Higher confidence ratings 

were given to exposure factors that were 

based on studies where appropriate quality 

assurance/quality control measures were used. 

(4) Variability and Uncertainty: The variability 

and uncertainty (quantitative and qualitative) in 

the information or the procedures, measures, 

methods, or models are evaluated and 

characterized. 

Variability in the Population: Variability 

arises from true heterogeneity across people, 

places, or time and can affect the precision of 

exposure estimates and the degree to which 

they can be generalized. The types of 

variability include spatial, temporal, and 

interindividual. Studies were sought that 

characterized any variability within 

populations. Higher confidence ratings were 

given to exposure factors that were based on 

studies where variability was well 

characterized. 

Uncertainty: Uncertainty represents a lack of 

knowledge about factors affecting exposure or 

risk and can lead to inaccurate or biased 

estimates of exposure. The types of 

uncertainty include scenario, parameter, and 

model. Studies were sought with minimal 

uncertainty in the data, which was judged by 

evaluating all the considerations listed above. 

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Studies were preferred that identified 

uncertainties, such as those due to inherent 

variability in environmental and 

exposure-related parameters or possible 

measurement error. Higher confidence ratings 

were given to exposure factors based on 

studies where uncertainty had been 

minimized. 

(5) Evaluation and Review: The information or 

the procedures, measures, methods, or models are 

independently verified, validated, and peer 

reviewed. 

Peer Review: Studies selected were those 

from the peer-reviewed literature and final 

government reports. Unpublished and internal 

or interim reports were avoided. 

Number and Agreement of Studies: Higher 

confidence was placed on recommendations 

where data were available from more than one 

key study and there was good agreement 

between studies. 

APPROACH USED TO DEVELOP 

RECOMMENDATIONS FOR EXPOSURE 

FACTORS 

As a first step to develop recommendations, the 

U.S. EPA reviewed the literature pertaining to a 

factor and determined key studies. These key studies 

were used to derive recommendations for the values 

of each factor. The recommended values were 

derived solely from the U.S. EPA’s interpretation of 

the available data. Different values may be 

appropriate for the user in consideration of policy, 

precedent, strategy, or other factors such as 

site-specific information. 

In providing recommendations for the various 

exposure factors, an attempt was made to present 

percentile values that are consistent with the exposure 

estimators defined in Guidelines for Exposure 

Assessment (i.e., mean, 50th, 90th, 95th, 98th, and 

99.9th percentiles) (U.S. EPA. 1992a). However, this 

was not always possible because the data available 

were limited for some factors, or the study authors 

did not provide such information. It is important to 

note, however, that these percentiles were discussed 

in the Guidelines within the context of risk 

descriptors and not individual exposure factors. For 

example, the guidelines state that the assessor may 

derive a high-end estimate of exposure by using 

maximum or near maximum values for one or more 

sensitive exposure factors, leaving others at their 

mean value. The term ―upper percentile‖ is used 

throughout the Handbook, and it is intended to 

represent values in the upper tail (i.e., between 90th 

and 99.9th percentiles) of the distribution of values 

for a particular exposure factor. 

The U.S. EPA’s procedure for developing 

recommendations was as follows: 

(1) Study Review and Evaluation: Key studies 

were evaluated in terms of both quality and 

relevance to specific populations (general U.S. 

population, age groups, gender, etc.). The GAFs 

described earlier were used as criteria for 

assessing the quality of studies. 

(2) Single Versus Multiple Key Studies: If only 

one study was classified as key for a particular 

factor, the mean value from that study was 

selected as the recommended central value for 

that population. If multiple key studies with 

reasonably equal quality, relevance, and study 

design information were available, a weighted 

mean (if appropriate, considering sample size and 

other statistical factors) of the studies was chosen 

as the recommended mean value. If the key 

studies were judged to be unequal in quality, 

relevance, or study design, the range of means 

was presented, and the user of the Handbook must 

employ judgment in selecting the most 

appropriate value for the population of interest. 

Recommendations for upper percentiles, when 

multiple studies were available, were calculated 

as the midpoint of the range of upper percentile 

values of the studies for each age group where 

data were available. 

(3) Variability: The variability of the factor 

across the population was described. For 

recommended values, as well as for each of the 

studies on which the recommendations are based, 

variability was characterized in one or more of 

three ways: (1) as a table with various percentiles 

or ranges of values; (2) as analytical distributions 

with specified parameters; and/or (3) as a 

qualitative discussion. Analyses to fit standard or 

parametric distributions (e.g., normal, lognormal) 

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to the exposure data were not performed by the 

authors of the Handbook, but they have been 

reproduced as they were found in the literature. 

Recommendations on the use of these 

distributions were made where appropriate based 

on the adequacy of the supporting data. The list of 

exposure factors and the way in which variability 

was characterized throughout the Handbook (i.e., 

average, median, upper percentiles, multiple 

percentiles, and fitted distribution) are presented 

in Table 2. 

(4) Uncertainty: Uncertainties were discussed in 

terms of data limitations. Such limitations 

include the range of circumstances over which the 

estimates were (or were not) applicable, possible 

biases in the values themselves, a statement about 

parameter uncertainties (measurement error, 

sampling error) and model/scenario uncertainties, 

if models/scenarios were used to derive the 

recommended value. Chapter 2 of the Handbook 

presents a discussion of variability and 

uncertainty for exposure factors. 

(5) Confidence Ratings: Finally, the U.S. EPA 

assigned a confidence rating of low, medium, or 

high to each recommended value. This rating is 

not intended to represent an uncertainty analysis; 

rather, it represents the U.S. EPA’s judgment on 

the quality of the underlying data used to derive 

the recommendation. This judgment was made 

using the GAFs described earlier. Table 3 

provides an adaptation of the GAFs as they 

pertain to the confidence ratings for the exposure 

factor recommendations. Clearly, there is a 

continuum from low to high. Therefore, the 

assignment of a rating to a particular factor 

involves professional judgment. 

Recommendations given in the Handbook are 

accompanied by a discussion of the rationale for 

their rating. 

It is important to note that the study elements 

listed in Table 3 do not have the same weight 

when arriving at the overall confidence rating for 

the various exposure factors. The relative weight 

of each of these elements for the various factors is 

subjective and based on the professional 

judgment of the authors of the Handbook. Also, 

the relative weights depend on the exposure factor 

of interest. For example, the adequacy of the data 

collection period may be more important when 

determining usual intake of foods in a population, 

but it is not as important for factors where 

long-term variability may be small, such as tap 

water intake. In the case of tap water intake, the 

currency of the data was a critical element in 

determining the final rating. In general, most 

studies ranked high with regard to "level of peer 

review," "accessibility," "focus on the factor of 

interest," and "data pertinent to the United States" 

because the U.S. EPA specifically sought studies 

for the Handbook that met these criteria. 

The elements in Table 3 were important 

considerations for inclusion of a study in the 

Handbook. However, a high score for these 

elements does not necessarily translate into a high 

overall rating. Other considerations also informed 

the assigned confidence ratings. One such 

consideration was the ease at which the exposure 

factor of interest could be measured. For example, 

soil ingestion by children can be estimated by 

measuring, in the feces of children, the levels of 

certain elements found in soil. Body weight, 

however, can be measured directly, and it is 

therefore a more reliable measurement. The fact 

that soil ingestion is more difficult to measure 

than body weight is reflected in the overall 

confidence rating given to both of these factors. 

In general, the better the methodology used to 

measure the exposure factor, the higher the 

confidence in the value. 

(6) Recommendation Tables: The U.S. EPA 

developed a table at the beginning of each chapter 

of the Child-Specific Exposure Factors Handbook 

(U.S. EPA, 2008a) that summarizes the 

recommended values for the relevant factor. 

Table 1 summarizes the principal exposure factors 

addressed in the Handbook. Table 4 summarizes 

the confidence ratings assigned to the various 

factors. 

SUGGESTED REFERENCES FOR USE IN 

CONJUNCTION WITH THE HANDBOOK 

The main steps for performing an exposure 

assessment are (1) identifying the source of the 

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environmental contamination and the media that 

transports the contaminant; (2) determining the 

contaminant concentration; (3) determining the 

exposure scenarios—including pathways and routes 

of exposure; (4) determining the exposure time, 

frequency, and duration; and (5) identifying the 

exposed population. Many of the issues related to 

characterizing exposure from selected exposure 

pathways have been addressed in a number of 

existing U.S. EPA documents. Some of these provide 

guidance while others demonstrate various aspects of 

the exposure process. These documents include, but 

are not limited, to the following, which are listed in 

chronological order: 

• Methods for Assessing Exposure to Chemical 

Substances, Volumes 1−13 (U.S. EPA, 

1983−1989) 

• Standard Scenarios for Estimating Exposure 

to Chemical Substances During Use of 

Consumer Products (U.S. EPA, 1986) 

• Selection Criteria for Mathematical Models 

Used in Exposure Assessments: Surface 

Water Models (U.S. EPA, 1987) 

• Selection Criteria for Mathematical Models 

Used in Exposure Assessments: Groundwater 

Models (U.S. EPA,1988) 

• Risk Assessment Guidance for Superfund, 

Volume I, Part A, Human Health Evaluation 

Manual (U.S. EPA, 1989) 

• Methodology for Assessing Health Risks 

Associated with Indirect Exposure to 

Combustor Emissions (U.S. EPA, 1990) 

• Risk Assessment Guidance for Superfund, 

Volume I, Part B, Development of 

Preliminary Remediation Goals (U.S. EPA, 

1991a) 

• Risk Assessment Guidance for Superfund, 

Volume I, Part C, Risk Evaluation of 

Remedial Alternatives (U.S. EPA, 1991b) 

• Guidelines for Exposure Assessment (U.S. 

EPA, 1992a) 

• Dermal Exposure Assessment: Principles and 

Applications (U.S. EPA, 1992b) 

• Estimating Exposures to Dioxin-Like 

Compounds (U.S. EPA, 1994a) 

• Soil Screening Guidance (U.S. EPA, 1996a) 

• Series 875 Occupational and Residential 

Exposure Test Guidelines - Final Guidelines 

- Group A - Application Exposure 

Monitoring Test Guidelines (U.S. EPA, 

1996b) 

• Series 875 Occupational and Residential 

Exposure Test Guidelines - Group B - Post 

Application Exposure Monitoring Test 

Guidelines (U.S. EPA, 1996c) 

• Policy for Use of Probabilistic Analysis in 

Risk Assessment at the U.S. Environmental 

Protection Agency (U.S. EPA, 1997b) 

• Guiding Principles for Monte Carlo 

Analysis (U.S. EPA, 1997c) 

• Sociodemographic Data for Identifying 

Potentially Highly Exposed Populations 

(U.S. EPA, 1999) 

• Options for Developing Parametric 

Probability Distributions for Exposure 

Factors (U.S. EPA, 2000b) 

• Risk Assessment Guidance for Superfund, 

Volume I, Part D, Standardized Planning, 

Reporting, and Review of Superfund Risk 

Assessments (U.S. EPA, 2001a) 

• Risk Assessment Guidance for Superfund 

Volume III, Part A, Process for Conducting 

Probabilistic Risk Assessments (U.S. EPA, 

2001b) 

• Framework for Cumulative Risk Assessment 

(U.S. EPA, 2003b) 

• Example Exposure Scenarios (U.S. EPA, 

2003c); 

• Risk Assessment Guidance for Superfund, 

Volume I, Part E, Supplemental Guidance for 

Dermal Risk Assessment (U.S. EPA, 2004) 

• Guidance on Selecting Age Groups for 

Monitoring and Assessing Childhood 

Exposures to Environmental Contaminants 

(U.S. EPA, 2005a) 

• Cancer Guidelines for Carcinogen Risk 

Assessment, Supplemental Guidance for 

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Assessing Susceptibility from Early-Life 

Exposure to Carcinogens (U.S. EPA, 2005b) 

• Supplemental Guidance for Assessing 

Susceptibility from Early-Life Exposure to 

Carcinogens (U.S. EPA, 2005c) 

• Protocol for Human Health Risk Assessment, 

Protocol for Hazardous Waste Combustion 

Facilities (U.S. EPA, 2005d) 

• A Framework for Assessing Health Risk of 

Environmental Exposures to Children (Final) 

(U.S. EPA, 2006c) 

• Concepts, Methods, and Data Sources for 

Cumulative Health Risk assessment of 

Multiple Chemicals, Exposures and Effects: 

A Resource Document (Final) (U.S. EPA, 

2008b) 

These documents may serve as valuable information 

resources to assist in the assessment of exposure. The 

reader is encouraged to refer to them for more 

detailed discussion. 

CONSIDERING LIFESTAGE WHEN 

CALCULATING EXPOSURE AND RISK 

A key component of U.S. EPA’s Guidance on 

Selecting Age Groups for Monitoring and Assessing 

Childhood Exposures to Environmental 

Contaminants (U.S. EPA, 2005a) involves the need 

to sum age-specific differences in exposure across 

time when assessing long-term exposure, as well as 

integrating these age-specific exposures with 

age-specific differences in toxic potency in those 

cases where information exists to describe such 

differences: an example is carcinogens that act via a 

mutagenic mode of action (Supplemental Guidance 

for Assessing Susceptibility from Early-Life Exposure 

to Carcinogens [U.S. EPA, 2005c]). When assessing 

chronic risks (i.e., exposures greater than 10% of 

human lifespan), rather than assuming a constant 

level of exposure for 70 years (usually consistent 

with an adult level of exposure), the Agency is now 

recommending that assessors calculate chronic 

exposures by summing time-weighted exposures that 

occur at each life stage; the Handbook provides data 

arrayed by childhood age in order to follow this new 

guidance. This approach is expected to increase the 

accuracy of risk assessments because it will account 

for life-stage differences in exposure. Depending on 

whether body-weight-adjusted childhood exposures 

are either smaller or larger compared to those for 

adults, calculated risks could either decrease or 

increase when compared with the historical approach 

of assuming a lifetime of a constant adult level of 

exposure. 

The Supplemental Guidance for Assessing 

Susceptibility from Early-Life Exposure to 

Carcinogens also recommends that in those cases 

where age-related differences in toxicity also occur, 

differences in both toxicity and exposure should be 

integrated across all relevant age intervals. This 

guidance describes such a case for carcinogens that 

act via a mutagenic mode of action, where age 

dependent potency adjustments factors (ADAFs) of 

10 and 3 are recommended for children ages birth 

to <2 years and 2 to <16 years, respectively, when 

there is exposure during those years and available 

data are insufficient to derive chemical-specific 

adjustment factors. 

Table 5, along with Chapter 6 of the 

Supplemental Guidance, has been developed to help 

the reader understand how to use the new sets of 

exposure and potency age groupings when 

calculating risk through the integration of life-stagespecific changes in exposure and potency. 

Thus, Lifetime Cancer Risk (for a population with 

average life expectancy of 70 years) =  (Exposure 

Duration/70 yrs  Potency  ADAF) summed across 

all the age groups presented in Table 5. This is a 

departure from the way cancer risks have historically 

been calculated which was based upon the premise 

that risk is proportional to the daily average of the 

long-term adult dose. 

FUNDAMENTAL PRINCIPLES OF

EXPOSURE ASSESSMENT

The definition of exposure as used by the 

International Programme on Chemical Safety is the 

―contact of an organism with a chemical or physical 

agent, quantified as the amount of chemical available 

at the exchange boundaries of the organism and 

available for absorption.‖ This means contact with 

the visible exterior of a person such as the skin, and 

openings such as orifices and lesions. The process of 

a chemical entering the body can be described in two 

steps: contact (exposure) followed by entry 

(crossing the boundary). In the context of 

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environmental risk assessment, risk to an individual 

or population can be represented as a continuum from 

the source through exposure to dose to effect as 

shown in Figure 1 (U.S. EPA, 2003d; IPCS, 2006). 

The process begins with a chemical or agent released 

from a source into the environment. Once in the 

environment, the chemical or agent can be 

transformed and transported through the environment 

via air, water, soil, dust, and diet. Individuals come in 

contact with the chemical through inhalation, 

ingestion, or skin/eye contact. The individual’s 

activity patterns as well as the concentration of the 

chemical will determine the magnitude, frequency, 

and duration of the exposure. The exposure becomes 

an absorbed dose when the chemical crosses an 

absorption barrier. When the chemical or its 

metabolites interact with a target tissue, it becomes a 

target tissue dose, which may lead to an adverse 

health outcome. The text under the boxes in Figure 1 

indicates the specific information that may be needed 

to characterize each box. 

Dose Equations 

Starting with a general integral equation for 

exposure (U.S. EPA, 1992a), several dose equations 

can be derived depending upon boundary 

assumptions. One of the more useful of these derived 

equations is the Average Daily Dose (ADD). The 

ADD, which is used for many noncancer effects, 

averages an external dose over the period of time 

exposure occurred, and it is normalized by body 

weight (ADDpot)(see equation 1). 

External Dose ADDpot



(1) 

Body Weight  Averaging Time

assumed, in terms of lifetime probabilities, 

utilizing dose values presented in terms of lifetime 

The exposure can be expressed in as follows: 

External Dose = C × IR × ED (2) 

Where 

C = Contaminant Concentration 

IR = Intake Rate 

ED = Exposure Duration 

Contaminant concentration is the concentration 

of the contaminant in the medium (e.g., air, food, and 

soil) contacting the body and has units of 

mass/volume or mass/mass. 

The intake rate refers to the rates of inhalation, 

ingestion, and dermal contact, depending on the route 

of exposure. For ingestion, the intake rate is simply 

the amount of food containing the contaminant of 

interest that an individual ingests during some 

specific time period (units of mass/time). Much of the 

Handbook is devoted to rates of ingestion for some 

broad classes of food. For inhalation, the intake rate 

is the rate at which contaminated air is inhaled. 

Factors presented in the Handbook that affect dermal 

exposure are skin surface area and estimates of the 

amount of soil that adheres to the skin. 

The exposure duration is the length of time of 

contaminant contact. The length of time a person 

lives in an area, frequency of bathing, time spent 

indoors versus outdoors, etc., all affect the exposure 

duration. Chapter 16, Activity Factors, describes 

examples of population behavior/activity patterns that 

may be useful for estimating exposure durations. 

When the parameter values IR and ED remain 

constant over time, they are substituted directly into 

the exposure equation. When they change with time, 

a summation approach is needed to calculate 

exposure. In either case, the exposure duration is the 

length of time exposure occurs at the concentration 

and the intake rate specified by the other parameters 

in the equation. 

Note that the advent of childhood age groupings 

means that separate ADDs should be calculated for 

each age group considered. Chronic exposures can 

then be calculated by summing across each 

life-stage-specific ADD. 

Cancer risks have traditionally been calculated in 

those cases where a linear nonthreshold model is 

by 

ADDs (LADDs). The LADD takes the form of 

Equation 1, with lifetime replacing averaging time. 

While the use of LADD may be appropriate when 

developing screening level estimates of cancer risk, 

as discussed above, the U.S. EPA is now 

recommending that risks should be calculated by 

integrating exposures or risks throughout all life 

stages (U.S. EPA, 1992a). 

For some types of analyses, dose can be 

expressed as a total amount (with units of mass, e.g., 

mg) or as a dose rate in terms of mass/time (e.g., 

mg/day), or as a rate normalized to body mass (e.g., 

with units of mg of chemical per kg of body weight 

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per day [mg/kg-day]). The LADD is usually 

expressed in terms of mg/kg-day or other 

mass/mass-time units. 

In most cases (inhalation and ingestion 

exposures), the dose-response parameters for 

carcinogenic risks have been adjusted for the 

difference in absorption across body barriers between 

humans and the experimental animals used to derive 

such parameters. Therefore, the exposure assessment 

in these cases is based on the potential dose, with no 

explicit correction for the fraction absorbed. 

However, the exposure assessor needs to make such 

an adjustment when calculating dermal exposure and 

in other specific cases when current information 

indicates that the human absorption factor used in the 

derivation of the dose-response factor is 

inappropriate. 

For carcinogens, the duration of a lifetime has 

traditionally been assigned the nominal value of 70 

years as a reasonable approximation. For exposure 

estimates to be used for assessments other than 

carcinogenic risk, various averaging periods have 

been used. For acute exposures, the doses are usually 

averaged over a day or a single event. For nonchronic 

noncancer effects, the time period used is the actual 

period of exposure (exposure duration). The objective 

in selecting the exposure averaging time is to express 

the exposure in a way that can be combined with the 

dose-response relationship to calculate risk. 

The body weight to be used in the exposure 

equation (see Equation 1) depends on the units of the 

exposure data presented in the Handbook. For 

example, for food ingestion, the body weights of the 

surveyed populations were known in the USDA 

surveys, and they were explicitly factored into the 

food intake data in order to calculate the intake as 

g/kg body weight-day. In this case, the body weight 

has already been included in the ―intake rate‖ term in 

Equations 1–2, and the exposure assessor does not 

need to explicitly include body weight. 

The units of intake in the Handbook for the 

incidental ingestion of soil and dust are not 

normalized to body weight. In this case, the exposure 

assessor will need to use the average weight of the 

exposed population during the time when the 

exposure actually occurs (shown in Equation 1). 

When making body weight assumptions, care must 

be taken that the values used for the population 

parameters in the dose-response analysis are 

consistent with the population parameters used in the 

exposure analysis. Intraspecies adjustments based on 

3⁄4 lifestage can be made using a scaling factor of BW

(U.S. EPA, 2006c; 2006d). Some of the parameters 

(primarily concentrations) used in estimating 

exposure are exclusively site specific, and, therefore, 

default recommendations should not be used. It 

should be noted that body weight is correlated with 

food consumption rates and inhalation rates. 

The link between the intake rate value and the 

exposure duration value is a common source of 

confusion in defining exposure scenarios. It is 

important to define the duration estimate so that it is 

consistent with the intake rate: 

• The intake rate can be based on an individual 

event (e.g., serving size per event). The 

duration should be based on the number of 

events or, in this case, meals. 

• The intake rate also can be based on a 

long-term average, such as 10 g/day. In this 

case, the duration should be based on the total 

time interval over which the exposure occurs. 

The objective is to define the terms so that, when 

multiplied, they give the appropriate estimate of mass 

of contaminant contacted. This can be accomplished 

by basing the intake rate on either a long-term 

average (chronic exposure) or an event (acute 

exposure) basis, as long as the duration value is 

selected appropriately. 

Inhalation dosimetry is employed to derive the 

human equivalent concentration (Hc) on which 

inhalation unit risks, and reference concentrations, 

are based (U.S. EPA, 1994b). U.S. EPA has 

traditionally approximated children’s respiratory 

exposure by using adult values, although a recent 

review (Ginsberg et al., 2002) concluded that there 

may be some cases where young children’s greater 

inhalation rate per body weight or pulmonary surface 

area as compared to adults can result in greater 

exposures than adults. The implications of this 

difference for inhalation dosimetry and children’s 

risk assessment were discussed at a peer involvement 

workshop hosted by the U.S. EPA in 2006 (Foos et 

al., 2008). 

Consideration of life-stage-particular 

physiological characteristics in the dosimetry analysis 

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may result in a refinement to the human equivalent 

concentration (Hc) to insure relevance in risk 

assessment across life stages, or might conceivably 

conclude with multiple Hcs, and corresponding 

inhalation unit risk values (e.g., separate for 

childhood and adulthood). The RfC methodology, 

which is described in Methods for Derivation of 

Inhalation Reference Concentrations and 

Applications of Inhalation Dosimetry (U.S. EPA, 

1994b), allows the user to incorporate 

population-specific assumptions into the models. The 

reader is referred to U.S. EPA guidance (U.S. EPA, 

1994b) on how to make these adjustments. 

There are no specific exposure factor 

assumptions in the derivation of Reference Doses 

(RfDs). The assessment of the potential for adverse 

health effects in infants and children is part of the 

overall hazard and dose-response assessment for a 

chemical. Available data pertinent to children’s 

health risks are evaluated along with data on adults 

and the no-observed-adverse-effect-level (NOAEL) 

or benchmark dose (BMD) for the most sensitive 

critical effect(s), based on consideration of all health 

effects. By doing this, protection of the health of 

children will be considered along with that of other 

sensitive populations. In some cases, it is appropriate 

to evaluate the potential hazard to children separately 

from the assessment for the general population or 

other population subgroups. 

Use of Exposure Factors Data in Probabilistic 

Analyses 

Although the Handbook is not intended to 

provide complete guidance on the use of Monte Carlo 

and other probabilistic analyses, some of the data in 

the Handbook may be appropriate for use in 

probabilistic assessments. The use of Monte Carlo or 

other probabilistic analysis requires characterization 

of the variability of exposure factors and requires the 

selection of distributions or histograms for the input 

parameters of the dose equations presented earlier. 

The following suggestions are provided for 

consideration when using such techniques: 

• The exposure assessor should only consider 

using probabilistic analysis when there are 

credible distribution data (or ranges) for the 

factor under consideration. Even if these 

distributions are known, it may not be 

necessary to apply this technique. For 

example, if only average exposure values are 

needed, these can often be computed 

accurately by using average values for each of 

the input parameters unless a nonlinear model 

is used. Probabilistic analysis is also not 

necessary when conducting assessments for 

screening purposes, i.e., to determine if 

unimportant pathways can be eliminated. In 

this case, bounding estimates can be calculated 

using maximum or near maximum values for 

each of the input parameters. Alternatively, the 

assessor may use the maximum values for 

those parameters that have the greatest 

variance. 

• It is important to note that the selection of 

distributions can be highly site specific and 

dependent on the purpose of the assessment. In 

some cases, the selection of distributions is 

driven by specific legislation. It will always 

involve some degree of judgment. 

Distributions derived from national data may 

not represent local conditions. The assessor 

needs to evaluate the site-specific data, when 

available, to assess their quality and 

applicability. The assessor may decide to use 

distributional data drawn from the national or 

other surrogate population. In this case, it is 

important that the assessor address the extent 

to which local conditions may differ from the 

surrogate data. 

• It is also important to consider the 

independence/dependence of variables and 

data used in a simulation. For example, it may 

be reasonable to assume that ingestion rate and 

contaminant concentration in foods are 

independent variables, but ingestion rate and 

body weight may or may not be independent. 

In addition to a qualitative statement of 

uncertainty, the representativeness assumption should 

be appropriately addressed as part of a sensitivity 

analysis. 

• Distribution functions to be used in 

probabilistic analysis may be derived by fitting 

an appropriate function to empirical data. In 

doing this, it should be recognized that in the 

lower and upper tails of the distribution the 

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data are scarce, so that several functions, with 

radically different shapes in the extreme tails, 

may be consistent with the data. To avoid 

introducing errors into the analysis by the 

arbitrary choice of an inappropriate function, 

several techniques can be used. One technique 

is using the empirical data itself rather than an 

analytic function. Another is to do separate 

analyses with several functions that have 

adequate fit but form upper and lower bounds 

to the empirical data. A third way is to use 

truncated analytical distributions. Judgment 

must be used in choosing the appropriate 

goodness-of-fit test. Information on the 

theoretical basis for fitting distributions can be 

found in a standard statistics text. Off-the-shelf 

computer software can be used to statistically 

determine the distributions that fit the data. 

Other software tools are available to identify 

outliers and for conducting Monte Carlo 

simulations. 

• If only a range of values is known for an 

exposure factor, the exposure assessor has 

several options: 

- keep that variable constant at its central 

value; 

- assume several values within the range of 

values for the exposure factor.; calculate 

a point estimate(s) instead of using 

probabilistic analysis; or 

- assume a distribution. (The rationale for 

the selection of a distribution should be 

discussed at length.) 

There are, however, cases where assuming 

a distribution is not recommended. These 

include the following: 

-- data are missing or very limited for a 

key parameter; 

-- data were collected over a short time 

period and may not represent 

long-term trends (the respondent’s 

usual behavior) - examples include 

food consumption surveys; activity 

pattern data; 

-- data are not representative of the 

population of interest because sample 

size was small or the population 

studied was selected from a local area 

and was therefore not representative 

of the area of interest; for example, 

soil ingestion by children; and 

-- ranges for a key variable are 

uncertain due to experimental error or 

other limitations in the study design 

or methodology; for example, soil 

ingestion by children. 

CUMULATIVE EXPOSURES 

The U.S. EPA recognizes that children may be 

exposed to mixtures of chemicals both indoors and 

outdoors through more than one pathway. New 

directions in risk assessments in the U.S. EPA put 

more emphasis on total exposures of multiple 

chemicals through multiple pathways (U.S. EPA, 

1986a; 2000c). Over the last several years, the U.S. 

EPA has developed a methodology for assessing risk 

from multiple chemicals. For more information, the 

reader is referred to the U.S. EPA’s Framework for 

Cumulative Risk Assessment (U.S. EPA, 2003b). 

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REFERENCES 

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Breysee, P.N.; Buckley, T.J.; Williams, D.; Beck, 

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Curlin-Brosnan, J.; Durkin, N.B.; Eggleston, P.A. 

(2005) Indoor exposures to air pollutants and 

allergens in the homes of asthmatic children in innercity Baltimore. Environ Res 98:167-176. 

Clewell, H.J.; Gentry, P.R.; Covington, T.R.; 

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EO (1997) Executive Order 13045. Protection of 

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risks. Available online at 

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(2002) Evaluation of child/adult pharmacokinetic 

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(1998) Accumulation of chloropyrifos on residential 

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origins of neurodegenerative disease in later life. 

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polycyclic aromatic hydrocarbons in house dust as a 

function of particle size. Environ Health Perspect 

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methylmercury have a role in causing developmental 

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M.C.; Lewis, R.G. (1999) Distribution of 2,4­

dihlorophenoxyacetic acid in floor dust throughout 

homes following homeowner and commercial lawn 

application: quantitative effects of children, pets, and 

shoes. Environ Sci Technol 33:1359-1365. 

Selevan, S.G.; Kimmel, C.A.; Mendola, P. (2000) 

Identifying critical windows of exposure for 

children's health. Monograph based on papers 

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Windows of Exposure for Children's Health held 

September 14-15, 1999 in Richmond, VA. Environ 

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U.S. EPA. (1983-1989) Methods for assessing 

exposure to chemical substances. Volumes 1-13. 

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exposure to chemical substances during use of 

consumer products. Volumes I and II. Office of 

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Washington, DC. 

U.S. EPA. (1987) Selection criteria for mathematical 

models used in exposure assessments: surface water 

models. Exposure Assessment Group, Office of 

Health and Environmental Assessment, Washington, 

DC; EPA/600/8-87/042. Available from NTIS, 

Springfield, VA; PB-88-139928/AS. 

U.S. EPA. (1988) Selection criteria for mathematical 

models used in exposure assessments: groundwater 

models. Exposure Assessment Group, Office of 

Health and Environmental Assessment, Washington, 

DC; EPA/600/88/075. Available from NTIS, 

Springfield, VA; PB-88-248752/AS. 

U.S. EPA. (1989) Risk assessment guidance for 

Superfund. Volume I. Human health evaluation 

manual: Part A. Interim final. Office of Solid Waste 

and Emergency Response, Washington, DC; 

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/index.htm. 

U.S. EPA. (1990) Methodology for assessing health 

risks associated with indirect exposure to combustor 

emissions. Office of Health and Environmental 

Assessment, Washington, DC; EPA 600/6-90/003. 

Available from NTIS, Springfield, VA; PB-90­

187055/AS. 

U.S. EPA. (1991a) Risk assessment guidance for 

Superfund. Volume I. Human health evaluation 

manual: Part B, Development of preliminary 

remediation goals. Office of Solid Waste and 

Emergency Response, Washington, DC; EPA/540/R92/003. Available online at 

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/index.htm. 

U.S. EPA. (1991b) Risk assessment guidance for 

Superfund. Volume I. Human health evaluation 

manual: Part C, Risk evaluation of remedial 

alternatives. Office of Solid Waste and Emergency 

Response, Washington, DC. Publication 9285.7-01C. 

Available online at 

http://www.epa.gov/oswer/riskassessment/ragsc 

/index.htm. 

U.S. EPA (1992a) Guidelines for exposure 

assessment. Office of Research and Development, 

Office of Health and Environmental Assessment, 

Washington, DC; EPA/600/Z-92/001. 

U.S. EPA. (1992b) Dermal exposure assessment: 

principles and applications. Office of Health and 

Environmental Assessment, Washington, DC; 

EPA/600/8-9/011F. Available online at 

http://www.epa.gov/ncea/pdfs/efh/references 

/derexp.pdf. 

U.S. EPA. (1994a) Estimating exposures to dioxinlike compounds. Draft Report. Office of Research 

and Development, Washington, DC; EPA/600/6­

88/005Cb. 

U.S. EPA. (1994b) Methods for derivation of 

inhalation reference concentrations and applications 

of inhalation dosimetry. Office of Health and 

Environmental Assessment, Washington, DC; 

EPA/600/8-90/066F. 

U.S.EPA (1996a) Soil screening guidance. Office of 

Solid Waste and Emergency Response, Washington, 

DC; EPA/540/F-95/041. Available online at 

http://www.epa.gov/superfund/health/conmedia/soil 

/index.htm. 

U.S.EPA. (1996b) Series 875 occupational and 

residential exposure test guidelines – final guidelines 

- Group A – application exposure monitoring test 

guidelines. Office of Pesticides and Toxic 

Substances, Washington, DC; EPA/712/C96/261. 

Available online at 

http://www.epa.gov/opptsfrs/publications/OPPTS_ 

Harmonized/875_Occupational_and_Residential_ 

Exposure_Test_Guidelines/Series/875_000.pdf. 

U.S. EPA. (1996c) Series 875 occupational and 

residential exposure test guidelines - group B - post 

application exposure monitoring test guidelines. 

Office of Pesticides and Toxic Substances, 

Washington, DC; EPA/712/C96/266. Available 

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Highlights of the Child-Specific Exposure Factors Handbook 

CSEFH 

online at 

http://www.epa.gov/opptsfrs/publications/OPPTS_ 

Harmonized/875_Occupational_and_Residential_ 

Exposure_Test_Guidelines/Series/875-2000.pdf. 

U.S. EPA (1997a) Exposure factors handbook. 

National Center for Environmental Assessment, 

Office of Research and Development, Washington, 

DC; EPA/600/P-95/002Fa,b,c. 

U.S. EPA. (1997b) Policy for use of probabilistic 

analysis in risk assessment at the U.S. Environmental 

Protection Agency. Science Policy Council. 

Available online at 

http://www.epa.gov/OSA/spc/pdfs/probpol.pdf. 

U.S. EPA. (1997c) Guiding principles for Monte 

Carlo analysis. Office of Research and Development, 

Risk Assessment Forum, Washington, DC; 

EPA/600/R-97/001. Available online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=29596. 

U.S. EPA. (1999) Sociodemographic data used for 

identifying potentially highly exposed populations. 

National Center for Environmental Assessment, 

Washington, DC; EPA/600/R-99/060. Available 

online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=22562. 

U.S. EPA. (2000a) Strategy for research on risks to 

children. Office of Research and Development, 

Washington, DC; EPA/600/R-00/068. 

U.S. EPA. (2000b) Options for developing 

parametric probability distributions for exposure 

factors. National Center for Environmental 

Assessment, Office of Research and Development, 

Washington, DC; EPA/600/R-00/058. Available on 

line at http://www.epa.gov/ncea/paramprob4ef.htm. 

U.S. EPA. (2000c) Supplementary guidance for 

conducting health risk assessment of chemical 

mixtures. Risk Assessment Forum, Washington, DC; 

EPA/630/R-00/002F. Available online at 

http://www.epa.gov/NCEA/raf/pdfs/chem_mix/chem 

_mix_08_2001.pdf. 

U.S. EPA. (2001a) Risk assessment guidance for 

Superfund. Volume I. Human health evaluation 

manual: Part D. Standardized planning, reporting and 

review of Superfund risk assessments. Office of Solid 

Waste and Emergency Response, Washington, DC. 

Publication 9285.7-47. Available online at 

http://www.epa.gov/oswer/riskassessment 

/ragsd/tara.htm. 

U.S. EPA. (2001b) Risk assessment guidance for 

Superfund. Volume III. Part A. Process for 

conducting probabilistic risk assessment. Office of 

Solid Waste and Emergency Response, Washington, 

DC; EPA/540/R-02/002. Available online at 

http://www.epa.gov/oswer/riskassessment/rags3adt/. 

U.S. EPA. (2002a) Child-specific exposure factors 

handbook. Interim Final. National Center for 

Environmental Assessment, Washington, DC; 

EPA/600/P-00/002B. 

U.S. EPA (2002b). Overview of the EPA quality 

system for environmental data and technology. Office 

of Environmental Information, Washington DC; 

EPA/240/R-02/003. Available online at 

http://www.epa.gov/quality/qs-docs/overviewfinal.pdf. 

U.S. EPA (2003a). A summary of general assessment 

factors for evaluating the quality of scientific and 

technical information. Science Policy Council, 

Washington DC; EPA/100/B-03/001. Available 

online at 

http://www.epa.gov/osa/spc/pdfs/assess2.pdf. 

U. S. EPA. (2003b) Framework for cumulative risk 

assessment. Risk Assessment Forum, Washington, 

DC; EPA/630/P-02/001F. Available online at 

http://cfpub.epa.gov/ncea/raf/recordisplay.cfm?deid= 

54944. 

U.S. EPA. (2003c) Example exposure scenarios. 

National Center for Environmental Assessment, 

Washington, DC. EPA/600/R-03/036. Available 

online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=85843. 

Highlights of the Child-Specific Exposure Factors Handbook Page 

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Highlights of the Child-Specific Exposure Factors Handbook 

CSEFH 

U.S. EPA. (2003d) Human health research strategy. 

Office of Research and Development, Washington, 

DC; EPA/600/R-02/050. Available online at 

http://www.epa.gov/ORD/htm/researchstrategies.htm 

#rs01. 

U.S. EPA. (2004) Risk assessment guidance for 

Superfund. Volume I. Human health evaluation 

manual: Part E. Supplemental guidance for dermal 

risk assessment. Interim. Office of Solid Waste and 

Emergency Response, Washington, DC; EPA/540/R99/005. Available online at 

http://www.epa.gov/oswer/riskassessment/ragse 

/index.htm. 

U.S. EPA (2005a) Guidance on selecting age groups 

for monitoring and assessing childhood exposures to 

environmental contaminants Office of Research and 

Development, Washington, DC; EPA/630/P-03/003F. 

U.S. EPA. (2005b) Guidelines for carcinogen risk 

assessment. Risk Assessment Forum, Washington, 

DC; EPA/630/P-03/001F. Available online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=116283. 

U.S. EPA. (2005c) Supplemental guidance for 

assessing susceptibility from early-life exposure to 

carcinogens. Risk Assessment Forum, Washington, 

DC; EPA/630/R03/003F. Available online at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=116283. 

U.S. EPA. (2005d) Protocol for human health risk 

assessment protocol for hazardous waste combustion 

facilities. U.S. EPA, Washington, DC; EPA/530/R05/006. Available online at 

http://www.epa.gov/combustion/risk.htm. 

U.S. EPA. (2006a) Use of physiologically-based 

pharmacokinetic (PBPK) models to quantify the 

impact of human age and interindividual differences 

in physiology and biochemistry pertinent to risk 

(Final Report). Office of Research and Development, 

Washington, DC; EPA/600/R-06/014A. Available 

online at 

http://cfpub.epa.gov/ncea/CFM/recordisplay.cfm 

?deid=151384 

U.S. EPA (2006b) Guidance on systematic planning 

using the data quality objectives process. Office of 

Environmental Information, Washington DC; 

EPA/240B/06/001. Available online at 

http://www.epa.gov/QUALITY/qs-docs/g4-final.pdf. 

U.S. EPA. (2006c) A framework for assessing health 

risk of environmental exposures to children (Final). 

Office of Research and Development, Washington, 

DC; EPA/600/R-05/093F. Available online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=158363. 

U.S. EPA (2006d) Harmonization in interspecies 

extrapolation: use of BW3/4 as default method in 

derivation of the oral RfD (External Review Draft). 

Risk Assessment Forum, Washington, DC; 

EPA/630/R-06/001. Available online at 

http://cfpub.epa.gov/ncea/raf/recordisplay.cfm?deid= 

148525. 

U.S. EPA (2008a) Child-specific exposure factors 

handbook. National Center for Environmental 

Assessment, Washington, DC; EPA/600/R-06/096F. 

Available online at www.epa.gov/ncea. 

U.S. EPA (2008b) Concepts, methods, and data 

sources for cumulative health risk assessment of 

multiple chemicals, exposures and effects: a resource 

document (final). Office of Research and 

Development, Washington, DC; EPA/600/R06/013F. Available online at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid 

=190187. 

Page Highlights of the Child-Specific Exposure Factors Handbook 

16 August 2009 
Highlights of the Child-Specific Exposure Factors Handbook Page 

August 2009 17 Table 1. Summary of Recommended Exposure Factors for Children Age Group 0 to <1 mo 1 to <3 mos 3 to <6 mos 6 to <12 mos 1 to <2 yrs 2 to <3 yrs 3 to <6 yrs 6 to <11 yrs 11 to <16 yrs 16 to <18 yrs 

Ingestion of Drinking Water (mL/day)— see Chapter 3 Mean per capita 95th percentile per capita Mean consumer only 95th percentile consumer only 184 839 470 858 227 896 552 1,053 362 1,056 556 1,171 360 1,055 467 1,147 271 837 308 893 317 877 356 912 380 1,078 417 1,099 447 1,235 480 1,251 606 1,727 652 1,744 731 1,983 792 2,002 

Ingestion of Drinking Water (mL/kg-day) — see Chapter 3 Mean per capita 95th percentile per capita Mean consumer only 95th percentile consumer only 52 232 137 238 48 205 119 285 52 159 80 173 41 126 53 129 23 71 27 75 23 60 26 62 22 61 24 65 16 43 17 45 12 34 13 34 11 31 12 32 

Ingestion of Water while Swimming (mL/hour) — see Chapter 3 Mean Upper percentile - - 50 100 - - 

Hand-to-Mouth Frequency (contacts/hour) — see Chapter 4 Indoor Outdoor Mean 95th percentile Mean 95th percentile - - - - 28 65 - - 19 52 15 47 20 63 14 42 13 37 5 20 15 54 9 36 7 21 3 12 - - - - Object-to-Mouth Frequency (contacts/hour) — see Chapter 4 Mean 95th percentile - - 20 - 10 - 1 - - - Object-to-Mouth Duration (minutes/hour) — see Chapter 4 Mean 95th percentile - - 11 26 8 22 13 16 - - 
Page Highlights of the Child-Specific Exposure Factors Handbook 

18 August 2009

Table 1. Summary of Recommended Exposure Factors for Children (Continued)

Age Group 0 to <1 

mo 

1 to <3 

mos 

3 to <6 

mos 

6 to <12 

mos 

1 to <2 

yrs 

2 to <3 

yrs 

3 to <6 

yrs 

6 to <11 

yrs 

11 to <16 

yrs 

16 to <18 

yrs 

Soil/Dust Ingestion (mg/day) — see Chapter 5

Soil Dust Soil + Dust Soil pica Geophagy

Central 

Central 

Central 

Upper percentile 

 Upper percentile 

- - - - - 

30 30 60 

- - 

50 60 

100 

1,000 

50,000 

Inhalation Rate - Long-term (m3/day) — see Chapter 6

Mean 95th percentile 

3.6 7.1 

- - 

4.1 6.1 

5.4 8.1 

8.0 

12.8 

9.5 

15.9 

10.9 16.2 

12.4 18.7 

15.1 23.5 

Inhalation Rate - Short-term (m3/minute) — see Chapter 6

Sleep/nap 

SedentaryLight ModerateHeavy

Mean 

 95th percentile 

 Mean 

 95th percentile 

Mean 

 95th percentile 

 Mean 

 95th percentile 

 Mean 

 95th percentile 

3.0E-03 4.6E-03 3.1E-03 4.7E-03 7.6E-03 1.1E-02 1.4E-02 2.3E-02 2.6E-02 4.1E-02 

4.5E-03 6.4E-03 4.7E-03 6.5E-03 1.2E-02 1.6E-02 2.1E-02 2.9E-02 3.8E-02 5.2E-02 

4.6E-03 6.4E-03 4.8E-03 6.5E-03 1.2E-02 1.6E-02 2.1E-02 2.9E-02 3.9E-02 5.3E-02 

4.3E-03 5.8E-03 4.5E-03 5.8E-03 1.1E-02 1.4E-02 2.1E-02 2.7E-02 3.7E-02 4.8E-02 

4.5E-03 6.3E-03 4.8E-03 6.4E-03 1.1E-02 1.5E-02 2.2E-02 2.9E-02 4.2E-02 5.9E-02 

5.0E-03 7.4E-03 5.4E-03 7.5E-03 1.3E-02 1.7E-02 2.5E-02 3.4E-02 4.9E-02 7.0E-02 

4.7.5.7.1.1.2.3.4.7.

Skin Surface Area - Total (m2) — see Chapter 7

Total Body Mean  95th

0.29 0.34 

0.33 0.38 

0.38 0.44 

0.45 0.51 

0.53 0.61 

0.61 0.70 

0.76 0.95 

1.08 1.48 

1.59 2.06 
Table 1. Summary of Recommended Exposure Factors for Children (Continued)

Age Group 0 to <1 

mo 

1 to <3 

mos 

3 to <6 

mos 

6 to <12 

mos 

1 to <2 

yrs 

2 to <3 

yrs 

3 to <6 

yrs 

6 to <11 

yrs 

11 to <16 

yrs 

16 to <18 

yrs 

Skin Surface Area - Body Parts (m2) — see Chapter 7

Head Mean 0.053 0.060 0.069 0.082 0.087 0.087 0.104 0.136 0.149 0

 95th percentile 0.062 0.069 0.080 0.093 0.101 0.099 0.130 0.186 0.194 0

Trunk Mean 0.104 0.118 0.136 0.161 0.188 0.235 0.241 0.375 0.536 0

 95th percentile 0.121 0.136 0.157 0.182 0.217 0.270 0.301 0.514 0.694 0

Arms Mean 0.040 0.045 0.052 0.062 0.069 0.072 0.108 0.137 0.205 0

 95th percentile 0.047 0.052 0.060 0.070 0.079 0.083 0.135 0.188 0.266 0

Hands Mean 0.015 0.017 0.020 0.024 0.030 0.032 0.045 0.054 0.084 0 95th percentile 0.018 0.020 0.023 0.027 0.035 0.037 0.056 0.074 0.109 0Legs Mean 0.060 0.068 0.078 0.093 0.122 0.142 0.207 0.301 0.498 0

 95th percentile 0.070 0.078 0.091 0.105 0.141 0.162 0.259 0.413 0.645 0

Feet Mean 0.019 0.021 0.025 0.029 0.033 0.043 0.055 0.078 0.119 0

 95th percentile 0.022 0.025 0.029 0.033 0.038 0.050 0.069 0.107 0.155 0

Adherence of Solids to Skin (means; mg/cm2) — see Chapter 7 for specific activities and age groups represented by these va

Residential indoor Daycare (in & outdoors) Outdoor sports Indoor sports Activities with soil Playing in mud Playing in sediment 

0.0041 (arms); 0.011 (hands); 0.0035 (legs); 0.010 (feet) 

0.024 (arms); 0.099 (hands); 0.020 (legs); 0.071 (feet) 

0.012 (face); 0.011 (arms); 0.11 (hands); 0.031 (legs) 

0.0019 (arms); 0.0063 (hands); 0.0020 (legs); 0.0022 (feet) 

0.054 (face); 0.046 (arms); 0.17 (hands); 0.051 (legs); 0.20 (feet) 

11 (arms); 47 (hands); 23 (legs); 15 (feet) 

0.040 (face); 0.17 (arms); 0.49 (hands); 0.70 (legs); 21 (feet) 

Body Weight (kg) — see Chapter 8

Mean 4.8 5.9 7.4 9.2 11.4 13.8 18.6 31.8 56.8 

Total Fruit Intake (g/kg-day)a — see Chapter 9

Mean per capita 5.7 6.2 4.6 2.4 0.8 

95th percentile per capita 21 19 14 8.8 3.5 

Mean consumer only 10 6.9 5.1 2.7 1.1 

95th percentile consumer 26 19 15 9.3 3.8 

Highlights of the Child-Specific Exposure Factors Handbook Page 

August 2009 19
Page Highlights of the Child-Specific Exposure Factors Handbook 

20 August 2009

Table 1. Summary of Recommended Exposure Factors for Children (Continued)

Age Group 0 to <1 

mo 

1 to <3 

mos 

3 to <6 

mos 

6 to <12 

mos 

1 to <2 

yrs 

2 to <3 

yrs 

3 to <6 

yrs 

6 to <11 

yrs 

11 to <16 

yrs 

16 to <18 

yrs 

Total Vegetable Intake (g/kg-day)a — see Chapter 9

Mean per capita 95th percentile per capita 

Mean consumer only 95th percentile consumer 

4.5 

15 

6.2 

16 

6.9 

17 

6.9 

17 

5.9 

15 

5.9 

15 

4.1 9.9 4.1 9.9 

2.9 6.9 2.9 6.9 

Fish and Shellfish Intake (g/kg-day)a — see Chapter 10

General Population 

Total Fish  Mean per capita  95th percentile per capita 

 Mean consumer only  95th consumer 

- - - - 

0.43 

3.0 4.2 

10 

0.28 

1.9 3.2 8.7 

0.23 

1.5 2.2 6.2 

0.16 

1.3 2.1 6.6 

Marine  Mean per capita  95th percentile per capita 

 Mean consumer only  95th percentile consumer 

- - - - 

0.31 

2.3 3.7 9.3 

0.20 

1.5 2.8 8.0 

0.15 

1.3 2.0 5.2 

0.10 0.46 

2.0 6.5 

Freshwater  Mean per capita  95th percentile per capita 

 Mean consumer only  95th percentile consumer 

- - - - 

0.12 0.71 

2.3 7.2 

0.08 0.35 

1.8 6.2 

0.08 0.48 

1.3 4.4 

0.07 0.29 

1.4 3.3 

Recreational Marine - No age-specific recommendations; see Chapter 10 

Recreational Freshwater - No age-specific recommendations; see Chapter 10 

Native American - No age-specific recommendations; see Chapter 10 
Highlights of the Child-Specific Exposure Factors Handbook Page 

August 2009 21 Table 1. Summary of Recommended Exposure Factors for Children (Continued) Age Group 0 to <1 mo 1 to <3 mos 3 to <6 mos 6 to <12 mos 1 to <2 yrs 2 to <3 yrs 3 to <6 yrs 6 to <11 yrs 11 to <16 yrs 16 to <18 yrs 

Total Meat Intake (g/kg-day)a — see Chapter 11 Mean per capita 95th percentile per capita Mean consumer only 95th percentile consumer 1.2 6.7 3.0 9.2 4.1 9.8 4.2 9.8 4.1 9.4 4.2 9.4 2.9 6.5 2.9 6.5 2.1 4.8 2.1 4.8 Total Dairy Intake (g/kg-day)a — see Chapter 11 Mean per capita 95th percentile per capita Mean consumer only 95th percentile consumer 13 49 16 58 37 88 37 88 23 49 23 49 14 32 14 32 5.6 16 5.6 16 Total Fat Intake (g/kg-day)a — see Chapter 11 Mean per capita 95th percentile per capita Mean consumer only 95th percentile consumer 5.2 16 7.8 16 4.5 11 6.0 12 4.1 8.2 4.4 8.3 3.7 7.0 3.7 7.0 4.0 7.1 4.0 7.1 3.6 6.4 3.6 6.4 3.4 5.8 3.4 5.8 2.6 4.2 2.6 4.2 1.6 3.0 1.6 3.0 

Total Grain Intake (g/kg-day)a — see Chapter 12 Mean per capita 95th percentile per capita Mean consumer only 95th percentile consumer 2.5 8.6 3.6 9.2 6.4 12 6.4 12 6.3 12 6.3 12 4.3 8.2 4.3 8.2 2.5 5.1 2.5 5.1 
Page Highlights of the Child-Specific Exposure Factors Handbook 

22 August 2009

Table 1. Summary of Recommended Exposure Factors for Children (Continued)

Age Group 0 to <1 

mo 

1 to <3 

mos 

3 to <6 

mos 

6 to <12 

mos 

1 to <2 

yrs 

2 to <3 

yrs 

3 to <6 

yrs 

6 to <11 

yrs 

11 to <16 

yrs 

16 to <18 

yrs 

Home-produced Food Intake (g/kg-day)b — see Chapter 13

Fruits Mean  95th percentile 

- - 

8.7 

60.6 

4.1 8.9 

3.6 

15.8 

1.9 8.3 

Vegetables Mean  95th percentile 

- - 

5.2 

19.6 

2.5 7.7 

2.0 6.2 

1.5 6.0 

Meats Mean  95th percentile 

- - 

3.7 

10.0 

3.6 9.1 

3.7 

14.0 

1.7 4.3 

Fish Mean  95th percentile 

- - 

2.8 7.1 

1.5 4.7 

Total Food Intake (g/kg-day) — see Chapter 14

Mean per capita 95th percentile per capita 

20 61 

16 40 

28 65 

56 

134 

90 

161 

74 

126 

61 

102 

40 70 

24 45 

Human Milk Intake (mL/day) — see Chapter 15

Mean Upper percentile 

510 950 

690 980 

770 

1,000 

620 

1,000 

NA NA 

Human Milk Intake (mL/kg-day) — see Chapter 15

Mean Upper percentile 

150 220 

140 190 

110 150 

83 

130 

NA NA 

Lipid Intake from Human Milk (mL/day) — see Chapter 15

Mean Upper percentile 

20 38 

27 40 

30 42 

25 42 

NA NA 
Highlights of the Child-Specific Exposure Factors Handbook Page 

August 2009 23 Table 1. Summary of Recommended Exposure Factors for Children (Continued) Age Group 0 to <1 mo 1 to <3 mos 3 to <6 mos 6 to <12 mos 1 to <2 yrs 2 to <3 yrs 3 to <6 yrs 6 to <11 yrs 11 to <16 yrs 16 to <18 yrs 

Lipid Intake from Human Milk (mL/kg-day) — see Chapter 15 Mean Upper percentile 6.0 8.7 5.5 8.0 4.2 6.0 3.3 5.2 NA NA Activity Factors — see Chapter 16 Mean (minutes/day) Indoors, total Outdoors, total Mean Mean 1,440 0 1,432 8 1,414 26 1,301 139 1,353 36 1,316 76 1,278 107 1,244 132 1,260 100 

Indoors, at residence Showering Bathing Playing on sand/gravel Playing on grass Playing on dirt Mean 95th Mean 95th Mean 95th Mean 95th Mean 95th Mean 95th 1,108 1,440 15 - 19 30 18 - 52 - 33 - 1,065 1,440 20 - 23 32 43 121 68 121 56 121 979 1,296 22 44 23 45 53 121 62 121 47 121 957 1,355 17 34 24 60 60 121 79 121 63 121 893 1,275 18 41 24 46 67 121 73 121 63 121 889 1,315 18 40 25 43 67 121 75 121 49 120 

Mean (minutes/month) Swimming Mean 95th 96 - 105 - 116 181 137 181 151 181 139 181 
Page Highlights of the Child-Specific Exposure Factors Handbook 

24 August 2009

Table 1. Summary of Recommended Exposure Factors for Children (Continued)

Age Group 0 to <1 1 to <3 3 to <6 6 to <12 1 to <2 2 to <3 3 to <6 6 to <11 11 to <16 16 to <18 

mo mos mos mos yrs yrs yrs yrs yrs yrs 

Consumer Products — see Chapter 17

No age-specific recommendations; see Chapter 17. 

ab

- NA 

Analysis was conducted using slightly different age groups than those recommended in Guidance on Selecting Age Groups for Monitoring and Assessing Exposures to Environmental Contaminants (U.S. EPA, 2005a). Data were placed in the recommended age categories closest to those used in the analysisAnalysis was conducted prior to Agency’s issuance of Guidance on Selecting Age Groups for Monitoring and Assessing Childhood Exposures to Environ

Contaminants (U.S. EPA, 2005a). Thus, age groups in the original study are slightly different than those presented here. See chapters of the Child-SpecifFactors Handbook (U.S. EPA, 2008a) for details. 

= No data available and/or no recommendation made. 

= Not applicable. 
 

 

 

 

 

 

 

 

 

 

 

Highlights of the Child-Specific Exposure Factors Handbook 

CSEFH 

Table 2. Characterization of Variability in Exposure Factors 

Exposure Factors Average Median Upper percentile Multiple 

Percentiles 

Ingestion of water and other select 

liquids 

√ √ √ √

Non-dietary ingestion √ √ √

Soil and dust ingestion √ √ √

a 

Inhalation rate √ √ √ √

Surface area 

Soil adherence 

√

√

√ √ √

Body weight √ √ √ √

Intake of fruits and vegetables √ √ √ √

Intake of fish and shellfish √ √ √ √

Intake of meats, dairy products, and fats √ √ √ √

Intake of grain products √ √ √ √

Intake of home produced foods √ √ √ √

Total food intake √ √ √ √

Human milk intake √ √

Time indoors 

Time outdoors 

Time showering 

Time bathing 

Time swimming 

Time playing on sand/gravel 

Time playing on grass 

Time playing on dirt 

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

a Soil pica and geophagy. 

√ = Data available. 

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August 2009 25 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Highlights of the Child-Specific Exposure Factors Handbook 

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Table 3. Considerations Used to Rate Confidence in Recommended Values 

General Assessment Factors Increasing Confidence Decreasing Confidence 

Soundness 

Adequacy of Approach 

Minimal (or defined) Bias 

The studies used the best available 

methodology and capture the measurement of 

interest. 

As the sample size relative to that of the 

target population increases, there is greater 

assurance that the results are reflective of the 

target population. 

The response rate is greater than 80% for inperson interviews and telephone surveys, or 

greater than 70 % for mail surveys. 

The studies analyzed primary data. 

The study design minimizes measurement 

errors. 

There are serious limitations with the approach used; 

study design does not accurately capture the 

measurement of interest. 

Sample size is too small to represent the population 

of interest. 

The response rate is less than 40 %. 

The studies are based on secondary sources. 

Uncertainties with the data exist due to measurement 

error. 

Applicability and Utility 

Exposure Factor of Interest 

Representativeness 

Currency 

Data Collection Period 

The studies focused on the exposure factor of 

interest. 

The studies focused on the U.S. population. 

The studies represent current exposure 

conditions. 

The data collection period is sufficient to 

estimate long-term behaviors. 

The purpose of the studies was to characterize a 

related factor. 

Studies are not representative of the U.S. population. 

Studies may not be representative of current 

exposure conditions. 

Shorter data collection periods may not represent 

long-term exposures. 

Clarity and Completeness 

Accessibility 

Reproducibility 

Quality Assurance 

The study data could be accessed. 

The results can be reproduced, or 

methodology can be followed and evaluated. 

The studies applied and documented quality 

assurance/quality control measures. 

Access to the primary data set was limited. 

The results cannot be reproduced, the methodology 

is hard to follow, and the author(s) cannot be located. 

Information on quality assurance/control was limited 

or absent. 

Variability and Uncertainty 

Variability in Population 

Uncertainty 

The studies characterize variability in the 

population studied. 

The uncertainties are minimal and can be 

identified. Potential biases in the studies are 

stated or can be determined from the study 

design. 

The characterization of variability is limited. 

Estimates are highly uncertain and cannot be 

characterized. The study design introduces biases in 

the results. 

Evaluation and Review 

Peer Review 

Number and Agreement of Studies 

The studies received high level of peer 

review (e.g., they are published in peerreviewed journals). 

The number of studies is greater than three. 

The results of studies from different 

researchers are in agreement. 

The studies received limited peer review. 

The number of studies is one. The results of studies 

from different researchers are in disagreement. 

Page Highlights of the Child-Specific Exposure Factors Handbook 

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Highlights of the Child-Specific Exposure Factors Handbook 

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Table 4. Summary of Confidence Ratings For Exposure Factor Recommendations 

Exposure Factor Overall Confidence Rating 

Ingestion of drinking water— see Chapter 3 Medium to High 

Ingestion of water while swimming — see Chapter 3 Low 

Mouthing frequency and duration — see Chapter 4 Low 

Soil and dust ingestion — see Chapter 5 Low 

Inhalation rates— see Chapter 6 Medium 

Skin surface area — see Chapter 7 Medium for Total Surface Area 

Low for Surface Area of Individual Body Parts 

Soil adherence — see Chapter 7 Low 

Body Weight — see Chapter 8 High 

Intake of Fruits and Vegetables — see Chapter 9 High for means 

Low for long-term upper percentiles 

Intake of Fish and Shellfish — see Chapter 10 High for mean 

Medium for upper percentile 

Intake of Meats, Dairy, and Fats — see Chapter 11 High for means 

Low for long-term upper percentiles 

Intake of Grains — see Chapter 12 High for means 

Low for long-term upper percentiles 

Intake of Home-produced Foods — see Chapter 13 Low to Medium for means and short-term distributions 

Low for long-term distributions 

Total Food Intake — see Chapter 14 Medium 

Human Milk Intake — see Chapter 15 Medium 

Activity Factors — see Chapter 16 Medium for means 

Low for upper percentiles 

Highlights of the Child-Specific Exposure Factors Handbook Page 

August 2009 27 
 

 

 

 

 

 

 

 

 

 

 

 

 

Highlights of the Child-Specific Exposure Factors Handbook 

CSEFH 

Table 5. Age-Dependent Potency Adjustment Factor (ADAF) by Exposure Age Group a 

Exposure Age Groupa Exposure Duration (years) ADAF (Age-Dependent Potency 

Adjustment Factor) 

Birth to < 1 mo 0.083 10

1 to <3 mos 0.167 10

3 to <6 mos 0.25 10

6 to <12 mos 0.5 10

1 to <2 yrs 1 10

2 to <3 yrs 1 3

3 to <6 yrs 3 3

6 to <11 yrs 5 3

11 to <16 yrs 5 3

16 to <21 yrs 5 1

>21 yrs (21 to <70 yr) 49 1

a Integrating U.S. EPA’s Guidance on Selecting Age Groups for Monitoring and Assessing Childhood 

Exposures to Environmental Contaminants (U.S. EPA, 2005a) with U.S. EPA’s Supplemental Guidance for 

Assessing Susceptibility from Early-Life Exposure to Carcinogens (U.S. EPA, 2005c) for those 

contaminants which act via a mutagenic mode of action. 

Page Highlights of the Child-Specific Exposure Factors Handbook 

28 August 2009 
l

g

y

Dust

e

Population

Individual 

Populations 

Distributions

Effective

m

etc.

etc.

SOURCE/STRESSOR 

FORMATION

SOURCE/STRESSOR 

FORMATION

TRANSPORT/ 

TRANSFORMATION

TRANSPORT/ 

TRANSFORMATION

Activity 

Pattern

Activity 

Pattern

EXPOSURE EXPOSURE

• Individual 

• Community 

• Population

• Individual 

• Community 

• Population

DOSE DOSE

EARLY BIOLOGICAL 

EFFECT

EARLY BIOLOGICAL 

EFFECT

ALTERED STRUCTURE/ 

FUNCTION

ALTERED STRUCTURE/ 

FUNCTION

DISEASE DISEASE

ENVIRONMENTAL 

CHARACTERIZATION

ENVIRONMENTAL 

CHARACTERIZATION

 

 

 

 

 

 

 

 

 

 

 

 

SOURCE/STRESSOR 

FORMATION

TRANSPORT/ 

TRANSFORMATION

Activity 

Pattern

EXPOSURE

• Individual 

• Community 

• Population 

DOSE

EARLY BIOLOGICAL 

EFFECT

ALTERED STRUCTURE/ 

FUNCTION

DISEASE

ENVIRONMENTAL 

CHARACTERIZATION

Chemical 

Physical 

Microbia 

Magnitude 

Duration 

Timin 

Dispersion

Kinetics 

Thermodynamics

Distributions 

Meteorolog

Air 

Water 

Diet 

Soil and 

Pathway 

Route 

Duration 

Frequency 

Magnitud 

Activity 

Pattern 

Figure 1. The Exposure-Dose-Effect Continuum 

ALTERED STRUCTURE/ 

FUNCTION 

DISEASE 

Statistical Profile 

Reference 

Susceptible 

Susceptible 

Population 

SOURCE/STRESSOR 

FORMATION 

TRANSPORT/ 

TRANSFORMATION 

EXPOSURE 

• Individual 

• Community 

• Population 

DOSE 

EARLY BIOLOGICAL 

EFFECT 

ENVIRONMENTAL 

CHARACTERIZATION 

Cancer 

Asthma 

Infertility 

Edema 

Arrhythmia 

Enzymuria 

Necrosis 

Molecular 

Biochemical 

Cellular 

Organ 

Organis 

Absorbed 

Target 

Internal 

Biologically 

Highlights of the Child-Specific Exposure Factors Handbook 

CSEFH 

The exposure-dose-effect continuum depicts the trajectory of a chemical or agent from its 

source to an effect. The chemical or agent can be transformed and transported through the 

environment via air, water, soil, dust, and diet. Children can become in contact with the 

chemical through inhalation, ingestion, or skin/eye contact. The child’s physiology, behavior, 

and activity patterns as well as the concentration of the chemical will determine the magnitude, 

frequency, and duration of the exposure. The exposure becomes an absorbed dose once the 

chemical crosses the absorption barrier (i.e., skin, lungs, eyes, gastrointestinal tract, placenta). 

Interactions of the chemical or its metabolites with a target tissue may lead to an adverse health 

outcome. The text under the boxes indicates the specific information that may be needed to 

characterize each box in the exposure-dose-effect continuum. 

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