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TABLE OF CONTENTS

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.2 PURPOSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1.3 INTENDED AUDIENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

1.4 SELECTION OF STUDIES FOR THE HANDBOOK . . . . . . . . . . . . . . . . . . . 1-5

1.5 APPROACH USED TO DEVELOP RECOMMENDATIONS FOR EXPOSURE

FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

1.6 CHARACTERIZING VARIABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

1.7 USING THE HANDBOOK IN AN EXPOSURE ASSESSMENT . . . . . . . . . 1-12

1.8 THE USE OF AGE GROUPINGS WHEN ASSESSING EXPOSURE . . . . . 1-14

1.9 CONSIDERING LIFESTAGE WHEN CALCULATING EXPOSURE AND RISK

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16

1.10 GENERAL EQUATIONS FOR CALCULATING DOSE . . . . . . . . . . . . . . . 1-17

1.11 CUMULATIVE RISK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21

1.12 RESEARCH NEEDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22

1.13 ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-23

1.14 REFERENCES FOR CHAPTER 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-25
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LIST OF TABLES

Table 1-1. Considerations Used to Rate Confidence in Recommended Values . . . . . . . . . . . 1-28

Table 1-2. Summary of Exposure Factor References and Confidence Ratings . . . . . . . . . . . 1-30

Table 1-3. Characterization of Variability in Exposure Factors . . . . . . . . . . . . . . . . . . . . . . . 1-31

Table 1-4. Integrating EPA’s Guidance on Selecting Age Groups for Monitoring and Assessing

Childhood Exposures to Environmental Contaminants with EPA’s Supplemental Guidance for

Assessing Susceptibility from Early-Life Exposure to Carcinogens For Those Contaminants

Which Act Via a Mutagenic Mode of Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-32

LIST OF FIGURES 

Figure 1-1. Schematic of Dose and Exposure: Oral Route . . . . . . . . . . . . . . . . . . . . . . . . . . 1-33
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1. INTRODUCTION

1.1 BACKGROUND 

In 1993, the National Academy of Sciences (NAS) released Pesticides in the Diets of 

Infants and Children (NAS, 1993), which highlighted that important differences can exist 

between children and adults with respect to risks posed by pesticides. Because of physiological 

and behavioral differences, exposures among children are expected to be significantly different 

than exposures among adults. Children may be more exposed to some environmental toxicants 

because they consume more food and water per unit of body weight and have a higher ratio of 

surface area to volume than adults. Equally important, rapid changes in behavior and physiology 

during childhood may lead to differences in exposure during childhood as a child grows up. In 

1995, EPA established a policy “to consider the risks to infants and children consistently and 

explicitly as a part of risk assessments generated during its decision making process, including 

the setting of standards to protect public health and the environment”(U.S. EPA 1995) . 

Recognizing that exposures among infants, toddlers, adolescents, and teenagers can vary 

significantly, the U.S. Environmental Protection Agency (EPA) recently published its “Guidance 

on Selecting Age Groups for Monitoring and Assessing Childhood Exposures to Environmental 

Contaminants (U.S. EPA. 2005a).” This update and revision of the 2002 interim final 

Child-specific Exposure Factors Handbook (U.S. EPA, 2002) is designed specifically to 

complement EPA’s recommended set of childhood age groups: 

< Less than 12 months old: birth to <1 month, 1 to <3 months, 3 to <6 months, and 6 to <12 

months. 

< Greater than 12 months old: 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. 

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) 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). Dust and tracked-in soil 

accumulates most effectively in carpets, where young children spend significant amount of time 

(Lewis et al., 1999). Children living in agricultural areas may experience higher exposures to 

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pesticides than do other children. Pesticides may be tracked into their homes by family members. 

In addition, children living in agricultural areas may also play in nearby fields or be exposed via 

consumption of contaminated breast milk from their farmworker mother (Eskenazi et al., 1999). 

In terms of risk, children may also differ from adults in their vulnerability to 

environmental pollutants because of toxicodynamic differences (for example, when exposures 

occur during periods of enhanced periods of susceptibility) and/or toxicokinetic differences (i.e., 

differences in absorption, excretion, and metabolism) (U.S. EPA, 2000c). Toxic contaminants in 

the environment can cause neurodevelopmental disabilities. The developing brain and nervous 

system can be particularly sensitive to environmental contaminants. For example, elevated blood 

lead levels and prenatal exposures to even relatively low levels of lead result in behavior 

disorders and reductions of intellectual function. Exposure to high levels of methylmercury can 

result in developmental disabilities (Myers and Davidson, 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). With respect to contaminants which are 

carcinogenic via a mutagenic mode of action, 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 help implement the Order, EPA 

established the Office of Children’s Health Protection (OCHP) [renamed the Office of Children’s 

Health Protection and Environmental Education (OCHPEE) in 2005], whose job it is to work 

with Program and Regional offices within 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, have made coverage 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, ORD developed a Strategy for Research on Environmental Risks to Children 

(EPA, 2000c). The goal of this research strategy was to improve the quality of risk assessments 

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for children. This Child-specific Exposure Factors Handbook is further intended to support 

EPA’s efforts to improve exposure and risk assessments for children (U.S. EPA 2002). 

In 1997, 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. OCHP’s 

child-related risk assessment policy and methodology guidance document survey (U.S. EPA, 

1999a) highlighted the Exposure Factors Handbook as a source of information on exposure 

factors for children. EPA’s Children’s Environmental Health Yearbook (U.S. EPA, 1998) also 

lists the Exposure Factors Handbook as a source of exposure information for children. However, 

the EPA Program Offices identified the need to consolidate all children’s exposure data into a 

single document. The goal of this Child-specific Exposure Factors Handbook is to fulfill this 

need. This Handbook provides non-chemical-specific data on exposure factors that can be used to 

assess doses from dietary and non-dietary ingestion exposure, dermal exposure, and inhalation 

exposure among children. 

This handbook provides generic exposure factors data for the EPA recommended set of 

childhood age groups in the following areas: 

C breast milk ingestion; 

C food ingestion, including homegrown foods and other dietary-related data; 

C drinking water ingestion; 

C soil ingestion; 

C hand-to-mouth and object-to-mouth activity; 

C dermal exposure factors such as surface areas and soil adherence; 

C inhalation rates; 

C activity duration and frequency in different locations and various 

microenvironments; 

C duration and frequency of consumer product use; 

C body weight data; and 

C duration of lifetime. 

It is a compilation of available data from a variety of sources. Most of these data have 

been described in detail in EPA’s Exposure Factors Handbook (1997a), but data published after 

the release of the Exposure Factors Handbook are also included here. This latest handbook 

updates the 2002 interim final Child-Specific Exposure Factors Handbook (U.S. EPA, 2002). 

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With very few exceptions, the data presented here derive from the analyses of the individual 

study authors. Because the studies included here 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. EPA made every attempt to 

clearly label the statistics presented. Authors have sometimes used different age ranges to 

describe data for children; in most cases, the original data are unavailable and the study results 

cannot be reallocated into the age groups used in this handbook. Every effort has been made to 

reallocate source data into the age groups recommended by the EPA in the report entitled 

Guidance on Selecting Age Groups for Monitoring and Assessing Childhood Exposures to 

Environmental Contaminants (U.S. EPA, 2005a), when sufficiently detailed data are available. 

Within the constraint of presenting the original material as accurately as possible, EPA has made 

an effort to present discussions and results in a consistent manner. The strengths and limitations 

of each study are discussed to provide the reader with a better understanding of the uncertainties 

associated with the values derived from the study. 

Because of the large number of tables in this handbook, tables are presented at the end of 

each chapter, before the appendices, if any. In conjunction with the Guidance on Selecting Age 

Groups for Monitoring and Assessing Childhood Exposures to Environmental Contaminants, 

this handbook is adopting 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). 

1.2 PURPOSE 

The purpose of this update and revision of the Child-specific Exposure Factors 

Handbook is to (1) most importantly, complement EPA's new set of recommended childhood age 

groups, as noted above, including a standardized way to define specific age groups (X to < Y); 

(2) to highlight changes in risk assessment practice first presented in the EPA’s Cancer 

Guidelines regarding the need to consider children as lifestages rather than as subpopulations 

(U.S. EPA, 2005b); (3) emphasize a major recommendation in EPA’s Supplemental Guidance 

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

exposures and risks across lifestages rather than relying on the use of a lifetime average adult 

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exposure to calculate risk; and lastly, (4) to incorporate any new exposure factors data/research 

that have become available since the early 2000's. 

As with the earlier version of the handbook, this new version will summarize key data on 

human behaviors and characteristics which affect children’s exposure to environmental 

contaminants, and provide recommended values to use for these factors. These 

recommendations are not legally binding on any EPA program and should be interpreted as 

suggestions that Program Offices or individual exposure assessors can consider and modify as 

needed. The decision as to whether to use site-specific or national values for an assessment may 

depend on the quality of the competing data sets as well as on the purpose of the specific 

assessment. The handbook has strived to include discussions of the issues which assessors 

should consider in assessing exposure among children of different ages, and may be used in 

conjunction with the EPA document entitled Socio-demographic Data Used for Identifying 

Potentially Highly Exposed Populations (U.S. EPA, 1999b). 

This handbook is intended to be a continuously evolving document. Updates will be 

posted in the NCEA home page as new data become available. 

1.3 INTENDED AUDIENCE 

The Child-Specific Exposure Factors Handbook may be used by exposure and risk 

assessors, economists, and other interested parties as a source for data and/or EPA 

recommendations on numeric estimates for behavioral and physiological characteristics needed 

to estimate childhood exposure to toxic contaminants. 

1.4 SELECTION OF STUDIES FOR THE HANDBOOK 

The data presented in this handbook have been compiled from various sources, which 

include EPA’s Exposure Factors Handbook (U.S. EPA, 1997a), government reports, and 

information presented in the peer-reviewed scientific literature. Studies were chosen that were 

seen as useful and appropriate for estimating exposure factors. The handbook contains 

summaries of selected studies published through June 2006. 

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General Considerations 

Many scientific studies were reviewed for possible inclusion in this handbook. Generally, 

studies identified in the Exposure Factors Handbook (U.S. EPA, 1997a) as key studies were also 

included, as are new studies that became available after publication of the 2002 Child-Specific 

Exposure Factors Handbook (U.S. EPA, 2002). Key studies from the Exposure Factors 

Handbook were generally defined as the most useful for deriving exposure factors. The 

recommended values for most exposure factors are based on the results of these studies. As in 

the Exposure Factors Handbook, the key studies were selected based on the following 

considerations: 

C Level of peer review: Studies were selected predominantly from the peerreviewed literature and final government reports. Internal or interim reports were 

therefore avoided. 

C Accessibility: Studies were preferred that the user could access in their entirety if 

needed. 

C Reproducibility: Studies were sought that contained sufficient information so that 

methods could be reproduced, or at least so the details of the author’s work could 

be accessed and evaluated. 

C Focus on exposure factor of interest: Studies were chosen that directly address 

the exposure factor of interest or address related factors that have significance for 

the factor under consideration. As an example of the latter case, one selected 

study contains useful ancillary information concerning fat content in fish, 

although it does not directly address fish consumption. 

C Pertinence of data to the U.S.: Studies were selected that addressed the U.S. 

population. Data from populations outside the U.S. were sometimes included if 

U.S. data were limited for a specific exposure factor. Studies similar in 

methodology are also used to support or enhance the U.S. data. 

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C Primary data: Studies were deemed preferable if based on primary data, but 

studies based on secondary sources were also included when they offered an 

original analysis. For example, the handbook cites studies of food consumption 

based on original data collected by the U. S. Department of Agriculture (USDA) 

National Food Consumption Survey. 

C Currency of information: Studies were chosen only if they were sufficiently 

recent to represent current exposure conditions. This is an important 

consideration for those factors that change with time. In some instances, recent 

data were very limited. Therefore, the data provided in these instances were the 

only available data. Limitations as to the age of the data were noted. 

C Adequacy of data collection period: Because most users of the handbook are 

primarily addressing chronic exposures, studies were sought that utilized the most 

appropriate data collection techniques for the characterization of long-term 

behavior. 

C Validity of approach: Studies that used experimental procedures or approaches 

that more likely or closely capture the desired measurement were selected. In 

general, 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 rely on validated indirect measurement methods such as surrogate 

measures (e.g., heart rate for inhalation rate) and questionnaires. If questionnaires 

or surveys were used, proper design and procedures include an adequate sample 

size for the population under consideration, a response rate large enough to avoid 

biases, and avoidance of bias in the design of the instrument and interpretation of 

the results. 

C Representativeness of the population: Studies seeking to characterize the national 

population, a particular region, or sub-population were selected if they were 

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appropriately representative of that population. Studies with limitations in areas 

where little data exist were included and are noted as such. 

C Variability in the population: Studies were sought that characterized any 

variability within populations (e.g., variability due to age, gender, ethnicity). 

C Minimal (or defined) bias in study design: Studies were sought that were 

designed with minimal bias, or if biases were suspected to be present, the 

direction of the bias (i.e., an overestimate or underestimate of the parameter) is 

either stated or apparent from the study design. 

C Minimal (or defined) uncertainty in the data: Studies were sought that have 

minimal uncertainty in the data, which was judged by evaluating all the 

considerations listed above. Studies that identify uncertainties, such as those due 

to inherent variability in environmental and exposure-related parameters or 

possible measurement error, were preferred. Studies that document quality 

assurance/quality control measures were also preferred. 

1.5 APPROACH USED TO DEVELOP RECOMMENDATIONS FOR 

EXPOSURE FACTORS 

As discussed above, EPA first reviewed all literature pertaining to a factor and 

determined key studies. These key studies were used to derive recommendations for the values 

of each factor for each of the childhood age groups discussed earlier. The recommended values 

were derived solely from 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. EPA’s procedure for developing recommendations was as follows: 

1. Key studies were evaluated in terms of both quality and relevance to specific populations 

(general U. S. population, age groups, gender, etc.). The criteria for assessing the quality 

of studies are described in Section 1.4. 

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2. If only one study was classified as key for a particular factor, the mean value from that 

study was selected as the recommended central tendency 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 is presented and the user of this handbook must employ judgment in selecting 

the most appropriate value for the lifestage or local population of interest. 

3. The variability of the factor across the lifestage was discussed. This document attempts 

to characterize the variability of each of the factors. Variability refers to true 

heterogeneity or diversity in a population. Differences among individuals in a population 

are referred to as inter-individual variability, differences for one individual over time is 

referred to as intra-individual variability. Since most of the studies used to derive 

exposure factors data are short term in nature, they present the variability in short term 

exposures across a population sample and often do not allow analysis of either intertemporal variability within individuals nor inter-individual variability of long term 

average exposures. Inter-individual variability in this handbook is characterized in one 

or more of the following 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. 

4. Uncertainties were discussed in terms of data limitations, 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 or scenario uncertainties if models or scenarios were used to derive the 

recommended value. 

5. Finally, 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 

EPA’s judgment on the quality of the underlying data used to derive the recommendation. 

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This judgment was made using the guidelines shown in Table 1-1. Table 1-1 is an 

adaptation of the General Considerations discussed in Section 1.4. Clearly this is a 

continuum from low to high, and judgment was used to determine these ratings. 

Recommendations given in this handbook are accompanied by a discussion of the 

rationale for their qualitative rating. 

Table 1-2 summarizes the principal exposure factors addressed in this Handbook and identifies 

the key tables that the reader may refer to when searching for a specific exposure factor. 

It is important to note that the study elements listed in Table 1-1 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 depend on the exposure factor of interest. Also, the 

relative weights given to the elements for the various factors were subjective and based on the 

professional judgement of the authors of this handbook. In general, most studies would rank 

high with regard to "level of peer review," "accessibility," "focus on the factor of interest," and 

"data pertinent to the U.S." 

These elements are important considerations for inclusion of a study in this handbook. 

However, a high score of these elements does not necessarily translate into a high overall score. 

Other elements in Table 1-1 were also examined to determine the overall score. For example, the 

adequacy of the data collection period may be more important when determining usual intake of 

foods in a population; on the other hand, it is not as important for factors where long-term 

variability may be small, such as tapwater intake. In the case of tapwater intake, the currency of 

the data was a critical element in determining the final rating. In addition, some exposure factors 

are more easily measured than others. For example, soil ingestion by children is 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 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. 

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1.6 CHARACTERIZING VARIABILITY AND UNCERTAINTY 

It is critical to note the distinction between uncertainty and variability. Uncertainty 

reflects our inability to be sure about the true value of a factor. Variability refers to the fact that 

children are not exactly alike - thus, for any given age, they may be different in terms of their 

weight, their behavior, what they like to eat and how much they eat, etc. These differences are 

important for exposure and risk assessors, as well as risk managers, to take into account if the 

range of exposures and risks faced by children are to be understood. For example, if one were to 

consider acute risks to US children under the age of 18 (about 73 million in 2005 - U.S. Census 

Bureau, the upper 99th percentile, while at the upper reaches of the range of variability, still 

accounts for 730,000 children on any given day - this may be important information for an 

exposure assessor to share with a risk manager. This document characterizes variability of each 

of the factors. Variability is characterized in one or more of the following 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) to the exposure data have not been performed by the 

authors of this handbook, but have been reproduced as they were found in the literature. 

Recommendations on the use of these distributions are made where appropriate based on the 

adequacy of the supporting data. The list of exposure factors and the way in which variability 

has been characterized throughout this handbook (i.e., average, median, upper percentiles, 

multiple percentiles, fitted distribution) are presented in Table 1-3. The term “upper percentile” 

is used throughout this handbook, and it is intended to represent values in the upper tail (i.e., 

between 90th and 99.9th percentile) of the distribution of values for a particular exposure factor. 

A detailed presentation on variability and uncertainty for exposure factors and algorithms used in 

estimating exposure is presented in EPA’s Exposure Factors Handbook (U.S. EPA, 1997a). 

In the recommendations, an attempt was made to present percentile values that are 

consistent with the exposure estimators defined in Guidelines for Exposure Assessment (U.S. 

EPA, 1992a) (i.e., mean, 50th, 90th, 95th, 98th, and 99.9th percentile). However, this was not 

always possible, because the data available were limited for some factors, or the authors of the 

study 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 

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estimate of exposure by using maximum or near maximum values for one or more sensitive 

exposure factors, leaving others at their mean value. 

The use of probabilistic analysis such as Monte Carlo requires a selection of distributions 

or histograms for the input parameters. This handbook is not intended to provide complete 

guidance on the use of probabilistic analyses. There are efforts in the Agency and elsewhere 

aimed at providing guidance on the use of these techniques. 

1.7 USING THE HANDBOOK IN AN EXPOSURE ASSESSMENT 

Some of the steps for performing an exposure assessment are (1) determining the 

pathways of exposure; (2) identifying the environmental media which transports the 

contaminant; (3) determining the contaminant concentration; (4) determining the exposure time, 

frequency, and duration; and (5) identifying the exposed populations and lifestages. Many of the 

issues related to characterizing exposure from selected exposure pathways have been addressed 

in a number of existing EPA guidance documents. These include, but are not limited to the 

following: 

C Guidelines for Exposure Assessment (U.S. EPA, 1992a); 

C Dermal Exposure Assessment: Principles and Applications (U.S. EPA, 1992b); 

C Methodology for Assessing Health Risks Associated with Indirect Exposure to 

Combustor Emissions (U.S. EPA, 1990); 

C Risk Assessment Guidance for Superfund, Part A (U.S. EPA, 1989); 

C Risk Assessment Guidance for Superfund, Part E (U.S. EPA, 2004); 

C Estimating Exposures to Dioxin-Like Compounds (U.S. EPA, 1994a); 

C Selection Criteria for Mathematical Models Used in Exposure Assessments: 

Groundwater Models (U.S. EPA, 1988a); 

C Selection Criteria for Mathematical Models Used in Exposure Assessments: 

Surface Water Models (U.S. EPA, 1987); 

C Standard Scenarios for Estimating Exposure to Chemical Substances During Use 

of Consumer Products (U.S. EPA, 1986a); 

C Pesticide Assessment Guidelines, Subdivisions K (U.S. EPA, 1984) and U, (U.S. 

EPA, 1986b); 

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C Methods for Assessing Exposure to Chemical Substances, Volumes 1-13 (U.S. 

EPA, 1983-1989); 

• Guiding Principles for Monte Carlo Analysis (U.S. EPA, 1997b); 

• Policy for Use of Probabilistic Analysis in Risk Assessment at the U.S. 

Environmental Protection Agency, May 15, 1997 ; 

• Guiding Principles for Monte Carlo Assessments (EPA/600/R-97/001) 

(http://www.epa.gov/ncea/monteabs.htm) 

• Options for Developing Parametric Probability Distributions for Exposure 

Factors (EPA/600/R-00/058) July 2000 (U.S. EPA, 2000a) 

• Sociodemographic Data for Identifying Potentially Highly Exposed Populations 

(U.S. EPA, 1999) 

• Framework for Cumulative Risk Assessment (U.S. EPA, 2003a) 

• Example Exposure Scenarios (U.S. EPA 2003b) 

• Guidance on Selecting Age Groups for Monitoring and Assessing Childhood 

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

• Cancer Guidelines for Carcinogen Risk Assessment (U.S. EPA, 2005b) and 

Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to 

Carcinogens (U.S. EPA, 2005c) 

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. 

Most of the data presented in this handbook are derived from studies that target (1) the 

general population (e.g., USDA food consumption surveys) or (2) a sample population from a 

specific area or group (e.g., Calabrese’s et al. (1989) soil ingestion study using children from the 

Amherst, MA area). It is necessary for risk or exposure assessors characterizing a diverse 

population to identify and enumerate certain groups within the general population who are at risk 

for greater contaminant exposures or who exhibit a heightened sensitivity to particular 

contaminants. For further guidance on addressing susceptible populations, the reader is referred 

to Socio-demographic Data Used for Identifying Potentially Highly Exposed Subpopulations 

(U.S. EPA, 2001) 

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1.8 THE USE OF AGE GROUPINGS WHEN ASSESSING EXPOSURE 

When this handbook was first published in 2002, no specific guidance existed with regard 

to which age groupings should be used when assessing children’s exposure. Age groupings 

varied from case to case and among Program and Regional offices within the EPA. They 

depended on availability of data and were often based on professional judgement or historical 

use. 

The development of standardized age bins was the subject of discussion in a 2000 EPA 

workshop titled “Issues Associated with Considering Developmental Changes in Behavior and 

Anatomy When Assessing Exposure to Children” (U.S. EPA, 2000b). The purpose of this 

workshop was to gain insight and input into factors that need to be considered when developing 

standardized age bins and to identify future research necessary to accomplish these goals. 

Panelists were divided into two groups. One group focused their discussions on defining and 

characterizing the important facets of behavioral development during childhood while the other 

group focused on defining and characterizing the physiological development during childhood. 

During the workshop, it was recognized that the ultimate goal of exposure assessment is to 

develop a day-to-day model of human life that can predict the contaminant exposures an 

individual is likely to face at any point in life. However, this is not likely to be accomplished in 

the near future and assessors often need to classify individuals into age bins in order to simplify 

the exposure model. The recommendations listed below are those of the panel members and 

were considered by EPA in the development of age groupings: 

• Panelists agreed that child development is a series of discrete events, but these 

events occur along a contiuum. 

• Age grouping/bins are a useful guide to fulfill the Agency’s immediate need, but 

are only a crude approximation of an underlying distribution. Ultimately, 

sufficient data should be gathered to develop a continuous multivariate model that 

can replace bins. 

• Adequacy of existing exposure data is highly variable. 

• A considerable amount of additional information already exists, but it is dispersed 

in the literature. It was recommended that EPA consults with experts in 

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developmental biology, physiology, pharmacology, and toxicology and conducts 

an in-depth review of the literature. 

• Long term research should include the development of integrated data sets that 

combines information about the exposure factors with biomarkers of exposure 

and effects. 

• The definition of age groups/bins for childhood exposure assessment are 

inextricably linked to toxicokinetic and toxicodynamic issues. 

• The two break out groups (i.e., behavioral and physiological) offered the 

following preliminary ideas for age groupings: 

Age grouping based on behavioral characteristics 

0-2 months 

2 - 6 months 

6-12 months 

1-2 years 

2-6 years 

6-11 years 

11-16 years 

16-21 years 

Age grouping based on physiological characteristics 

0-1 month 

1-6 months 

6-12 months 

1- 3 years 

3-9 years 

9-21 years 

One can observe that there was fairly good agreement among the two groups with regard 

to the age groupings that are important for infants and toddlers. However, there was some 

disagreement with regard to the older children. Appropriate consideration of age groupings 

depend not only on behavioral and physiological characteristics, but also on the specific scenario 

being studied and contaminant of concern. 

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Based upon consideration of the findings of the technical workshop, as well as analysis of 

available data, EPA developed guidance which established a set of recommended age groups for 

development of exposure factors for children entitled “Guidance on Selecting Age Groups for 

Monitoring and Assessing Childhood Exposures to Environmental Contaminants” (U.S. EPA, 

2005a). This revision of the Handbook was developed specifically to present exposure factors 

data in a manner consistent with EPA’s recommended set of childhood age groupings. 

The recommenced age groups are as follows: 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 (U.S. EPA, 2005a). 

1.9 CONSIDERING LIFESTAGE WHEN CALCULATING EXPOSURE AND RISK

 A key component of 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, 

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 should calculate chronic 

exposures by summing time-weighted exposures that occur at each lifestage; this handbook 

provides data arrayed by childhood age in order to support this new guidance. This approach is 

expected to increase the accuracy of risk assessments because it will take into account lifestage 

differences in exposure. Depending on whether body-weight-adjusted childhood exposures are 

either smaller or larger as compared with those for adults, calculated risks could either decrease 

or increase as 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 recommended that in those cases where age-related differences in toxicity were 

also found to occur, differences in both toxicity and exposure would need to be integrated across 

all relevant age intervals. This guidance describes such a case for carcinogens that act via a 

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mutagenic mode of action, where age dependent potency adjustments factors (ADAFs) of 10x 

and 3x are recommended for children ages birth < 2 years, and 2 < 16 years, respectively when 

there is exposure during those years. 

Table 1-4, along with Chapter 6 of the “Supplemental Guidance” have 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 lifestage specific changes in exposure and potency. 

Thus, Lifetime Cancer Risk (for a population with average life expectancy of 70 years) = 

Σ (Exposure x Duration x Potency x ADAF) summed across all the age groups presented in 

Table 1-4. This is a departure from the way cancer risks have historically been calculated based 

upon the premise that risk is proportional to the daily average of long term adult dose. 

1.10 GENERAL EQUATIONS FOR CALCULATING DOSE 

The definition of exposure as used in the Exposure Guidelines (U.S. EPA, 1992a) is the 

“contact of a chemical, physical, or biological agent with the outer boundary of an organism.” 

This means contact with the visible exterior of a person such as the skin, and openings such as 

the mouth, nostrils, and lesions. The process of a contaminant entering the body can be 

described in two steps: contact (exposure) followed by entry (crossing the boundary). The dose 

is the amount of agent available at human exchange boundaries (skin, lungs, gut) where 

absorption takes place during some specified time. An example of exposure and dose for the oral 

route as presented in the EPA Exposure Guidelines is shown in Figure 1-1. Starting with a 

general integral equation for exposure (U.S. EPA, 1992a), several dose equations can be derived 

depending upon boundary assumptions. 

Average Daily Dose (ADD) has been used when assessing risks for many noncancer effects -

this metric averages doses over the period of time over which exposure occurred. The ADD can be 

calculated by averaging the potential dose (Dpot) over body weight and an averaging time. 

ADDpot = [C x IR x ED] / [BW x AT] (1-1) 

Where:

C = Contaminant Concentration

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IR = Intake Rate

ED = Exposure Duration

BW = Body Weight

AT = Averaging Time

Note that the advent of childhood age groupings means that separate ADD’s should be calculated 

for each age group considered. Chronic exposures can then be calculated by summing across 

each lifestage specific ADD. 

Cancer risks have traditionally been calculated in those cases where a linear nonthreshold model is assumed, in terms of lifetime probabilities by utilizing dose values presented 

in terms of lifetime ADDs (LADDs). The LADD takes the form of the Equation 1-1, with 

lifetime replacing averaging time. While the use of LADD may be appropriate when developing 

screening level estimates of cancer risk, as discussed in Section 1.9 above, EPA is now 

recommending that risks should be calculated by integrating exposures or risks throughout all 

lifestages. 

Contaminant concentration is the concentration of the contaminant in the medium (air, 

food, soil, etc.) 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 this 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 that 

affect dermal exposure are the amount of material that comes into contact with the skin and the 

rate at which the contaminant is absorbed. 

The exposure duration is the period of time over which exposure occurs. 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 9, Activity Factors, gives some examples of population 

behavior/activity patterns that may be useful for estimating exposure durations. 

When the above parameter values intake rate (IR) and exposure duration (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 

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duration is the length of time exposure occurs at the concentration and the intake rate specified 

by the other parameters in the equation. 

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 

contaminant per kg of body weight per day (mg/kg-day)). The dose is usually expressed in terms 

of mg/kg-day or other mass/mass-time units. 

In most cases (inhalation and ingestion exposure), the dose-response parameters for 

carcinogen 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 which can be 

combined with the dose-response relationship to calculate risk. 

The body weight to be used in the exposure Equation 1-1 depends on the units of the 

exposure data presented in this handbook. For the food ingestion and water intake data presented 

in chapters 3 and 4 respectively, 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/d/kg body weight. In this case, the body weight has already been included in the 

“intake rate” term in Equation 1-2 and the exposure assessor does not need to explicitly include 

body weight. Body weight data presented in chapter 11 may be used in other instances when the 

intake rate has not been normalized by body weight. 

The units of intake in this handbook for some of the exposure factors (e.g., breast milk 

intake) are not normalized to body weight. In this case, the exposure assessor needs to use 

(in Equation 1-1) the average weight of the exposed population during the time when the 

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exposure actually occurs. If the body weight of the individuals in the population whose risk is 

being evaluated is non-standard in some way (e.g., children may be smaller than the national 

population) and if reasonable values are not available in the literature, then a model of intake as a 

function of body weight must be used. One such model is discussed in Appendix 1A of the 

Exposure Factors Handbook (U.S. EPA, 1997a). Some of the parameters (primarily 

concentrations) used in estimating exposure are exclusively site specific, and therefore default 

recommendations could 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: 

C

C

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 exposure concentrations 

(HEC) on which inhalation unit risks, and reference concentrations, are based (U.S. EPA, 

1994b). EPA has traditionally approximated children’s respiratory exposure by using adult 

values, although a recent review (Ginsberg, et al., 2005) concluded that there may be some cases 

where young children's greater ventilation 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 recently discussed at a 

peer involvement workshop hosted by EPA in 2006 (workshop results and references to be 

published in 2007).

 Consideration of lifestage-particular physiological characteristics in the dosimetry 

analysis may result in a refinement to the human equivalent concentration (HEC) to insure 

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relevance in risk assessment across lifestages, or might conceivably conclude with multiple 

HECs, and corresponding inhalation unit risk values (e.g., separate for childhood and adulthood) 

(U.S. EPA, 2005b, c). 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/lifestage-specific assumptions in to the models. 

There are no specific exposure factor assumptions in the derivation of 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 contaminant. 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. However, the Food Quality Protection Act (FQPA) of 

1996 states that for threshold effects, 

“an additional tenfold margin of safety for the chemical residue and other sources of 

exposure shall be applied for infants and children to take into account potential pre- and postnatal toxicity and completeness of data with respect to exposure and toxicity to infants and 

children. Notwithstanding such requirement for an additional margin of safety, the 

Administrator may use a different margin of safety for the pesticide chemical residue only if, on 

the basis of reliable data, such margin of safety will be safe for infants and children.” 

In addition, FQPA lists several factors that must be considered when assessing risks to 

children, such as available information concerning the special susceptibility of children to 

pesticide chemical residues, neurological differences between children and adults, and effects of 

in utero exposure. 

1.11 CUMULATIVE RISK 

EPA recognizes that children may be exposed to mixtures of contaminants both indoors 

and outdoors. Exposure may also occur through more than one pathway. New directions in risk 

assessments in EPA put more emphasis on total exposures via multiple pathways (U.S. EPA, 

2003a). Over the last several years, EPA has developed a methodology for assessing risk from 

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multiple contaminants. For more information, the reader is referred to EPA’s Framework for 

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

1.12 RESEARCH NEEDS 

The data for several exposure factors for children are limited. The following list is a 

compilation of areas for future research related to childhood exposure factors: 

C More recent information is needed on breastmilk consumption and the incidence 

and duration of breastfeeding. 

C Information on children’s food handling practices that might exacerbate exposure 

is needed to better characterize exposures among children. 

C Further research on fish intake among children, particularly recreational and 

subsistence populations, is needed. 

C Further research is needed on consumption of ethnic foods by children. 

C Research is needed to better estimate soil intake rates, particularly on how to 

extrapolate short-term data to chronic exposures. Research is also needed to 

refine the methods to calculate soil intake rates (i.e., inconsistencies among tracers 

and input/output misalignment errors indicate a fundamental problem with the 

methods). In addition, there are no data for children <1 year or >7 years of age. 

Additional information on soil ingestion among children that provides better 

estimates of upper percentile rates is needed, in particular. Research is also 

needed to better understand the relative contribution of soil vs. dust ingestion. 

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C Further research is needed on dermal and non-dietary ingestion exposure factors, 

including the microenvironments in which children spend time and the types of 

materials that they contact, as well as information on the rate at which they 
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contact contaminated surfaces, the fraction of the contaminants that are transferred 

to skin and object surfaces, and the amount of the object/skin entering the mouth. 

C Further research is needed to obtain better soil adherence rates for additional 

activities involving children. 

C Further data is needed on the frequency and duration of use and kinds of consumer 

products used by children. 

C Additional data on inhalation dosimetry and modeling, including inhalation rates 

that are specific to children’s activities. 

C Research is needed to derive a methodology to extrapolate from short-term data to 

long-term or chronic exposures. 

1.13 ORGANIZATION 

The handbook is organized as follows: 

Chapter 1 Provides the overall introduction to the handbook. 

Chapter 2 Provides factors for estimating exposure through ingestion of 

breast milk. 

Chapter 3 Provides factors for estimating human exposure through ingestion 

foods, including fish. 

Chapter 4 Provides factors for estimating exposure through ingestion of 

drinking water. 

Chapter 5 Provides factors for estimating exposure as a result of ingestion of 

soil. 

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Chapter 6 Presents factors for estimating exposure to environmental 

contaminants from other non-dietary ingestion such as hand-to

mouth and object-to-mouth activity. 

-

Chapter 7 Provides factors for estimating exposure as a result of inhalation of 

vapors and particulates. 

Chapter 8 Provides factors for estimating dermal exposure to environmental 

contaminants that come in contact with the skin. 

Chapter 9 Presents data on activity factors (activity patterns, population 

mobility, and occupational mobility). 

Chapter 10 Presents data on consumer product use. 

Chapter 11 Presents data on body weight. 

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1.14 REFERENCES FOR CHAPTER 1 

Calabrese, E.J.; Pastides, H.; Barnes, R.; Edwards, C.; Kostecki, P.T.; et al. (1989) How much soil do young 

children ingest: an epidemiologic study. In: Petroleum Contaminated Soils, Lewis Publishers, Chelsea, MI. 

pp. 363-397. 

EO (1997). Executive Order 13045. Protection of Children for Environmental Health Risks and Safety Risks. 

Available on line at http://yosemite.epa.gov/ochp/ochpweb.nsf/content/whatwe_executiv.htm. 

Eskenazi, B.; Bradman, A.; Castriona, R. (1999) Exposure of children to organophosphate pesticides and their 

potential adverse health effects. Environmental Health Perspectives, 107(S3): 409-19. 

Gilbert, R.O. (1987) Statistical methods for environmental pollution monitoring. New York: Van Nostrand 

Reinhold. 

Ginsberg G.; Foos B.; Firestone M. (2005) Review and analysis of inhalation dosimetry methods for application to 

children's risk assessment. J Toxicol. Environ. Health A. 68(8):573-615. 

Gurunathan, S.; Robson, M.; Freeman N.; Buckley, B.; Roy, A.; Meyer, R.; Bukowski, J.; Lioy, P.J. (1998) 

Accumulation of chloropyrifos on residential surfaces and toys accessible to children. Environmental Health 

Perspectives, 106(1):9-16. 

Lewis, R. G.; Fortune C.; Willis, R. D.; Camann, D. E.; Antley, J. T. (1999) Distribution of pesticides and 

polycyclic aromatic hydrocarbons in house dust as a function of particle size. Environmental Health 

Perspectives, 107(9). 

Myers, G.J.; Davidson, P.W. (2000) Does methylmercury have a role in causing developmental disabilities in 

children? Environmental Health Perspectives, 108(S3):413-420. 

Nishioka, M.G.; Burkholder, H.M.; and Brinkman, 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 healthmonograph based on papers developed from the Workshop: Identifying Critical Windows of Exposure for 

Children's Health held September 14-15, 1999 in Richmond, VA. Environmental Health Perspectives, 

108(S3):451-5. 

U.S. Census ((2006). State Population Estimates - Characteristics. Table 1: Estimates of the population by selected 

age groups in the United States, States, and Puerto Rico. Available on line at: 

http://www.census.gov/popest/states/asrh/tables/SC-EST2005-01Res.xls. 

U.S. EPA. (1983-1989) Methods for assessing exposure to chemical substances. Volumes 1 13. Washington, DC: 

Office of Toxic Substances, Exposure Evaluation Division. 

U.S. EPA. (1984) Pesticide assessment guidelines subdivision K, exposure: reentry protection. Office of Pesticide 

Programs, Washington, DC. EPA/540/9-48/001. Available from NTIS, Springfield, VA; PB-85-120962. 

U.S. EPA. (1986a) Standard scenarios for estimating exposure to chemical substances during use of consumer 

products. Volumes I and II. Washington, DC: Office of Toxic Substance, Exposure Evaluation Division. 

U.S. EPA. (1986b) Pesticide assessment guidelines subdivision U, applicator exposure monitoring. Office of 

Pesticide Programs, Washington, DC. EPA/540/9-87/127. Available from NTIS, Springfield, VA; PB 85 

133286. 

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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. WPA/600/8 

87/042. Available from NTIS, Springfield, VA; PB-88-139928/AS. 

U.S. EPA. (1988a) Selection criteria for mathematical models used in exposure assessments: groundwater models. 

Exposure Assessment Group, Office of Health and Environmental Assessment, Washington, DC. EPA/600/8 

88/075. Available from NTIS, Springfield, VA; PB-88-248752/AS. 

U.S. EPA. (1989) Risk assessment guidance for Superfund. Human health evaluation manual: part A. Office of 

Solid Waste and Emergency Response, Washington, DC. Available from NTIS, Springfield, VA; PB 

90-155581.http://www.epa.gov/oswer/riskassessment/ragsa/index.htm 

U.S. EPA. (1990) Methodology for assessing health risks associated with indirect exposure to combustor emissions. 

EPA 600/6-90/003. Available from NTIS, Springfield, VA; PB-90-187055/AS. 

U.S. EPA. (1992a) Guidelines for exposure assessment. Washington, DC: Office of Research and Development, 

Office of Health and Environmental Assessment. EPA/600/Z-92/001. 

U.S. EPA. (1992b) Dermal exposure assessment: principles and applications. Washington, DC: Office of Health and 

Environmental Assessments. EPA/600/8-9/011F. 

U.S. EPA. (1994a) Estimating exposures to dioxin-like 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. EPA/600/8-90/066F. October, 1994. 

U.S. EPA. (1995). Policy on evaluating health risks to children. Science Policy Council. October 20, 1995. 

Available on line at http://www.epa.gov/OSA/spc/2poleval.htm. 

U.S. EPA. (1997a) Exposure factors handbook. Washington, DC: National Center for Environmental Assessment, 

Office of Research and Development. EPA/600/P-95/002Fa,b,c. 

U.S. EPA. (1997b) Guiding principles for Monte Carlo analysis. Washington, DC: Office of Research and 

Development, Risk Assessment Forum. EPA/600/R-97/001. 

U.S. EPA. (1998) The EPA children's environmental health yearbook. Washington, DC: U.S. Environmental 

Protection Agency. 

U.S. EPA. (1999a) Child-related risk assessment policy and methodology guidance document survey, draft report. 

Washington, DC: Office of Children's Health Protection. 

U.S. EPA. (1999b) Sociodemographic Data Used for Identifying Potentially Highly Exposed Populations. U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-99/060. Available on line at: 

(http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=22562. 

U.S. EPA. (2000a) Options for developing parametric probability distributions for exposure factors. Washington, 

DC: National Center for Environmental Assessment, Office of Research and Development. 

EPA/600/R-00/058). (http://www.epa.gov/ncea/paramprob4ef.htm). 

U.S. EPA. (2000b) Summary Report of the Technical Workshop on Issues Associated with Considering 

Developmental Changes in Behavior and Anatomy When Assessing Exposure to Children. Draft report.

Washington, DC: Office of Research and Development, Risk Assessment Forum, September, 2000. 

U.S. EPA. (2000c) Office of Research and Development. Strategy for research on environmental risks to children. 

Washington, DC: Office of Research and Development. EPA/600/R-00/068. 
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3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

1-27

U.S. EPA. (2001) Identifying Potentially Highly Exposed Children's Populations. Draft Report. Washington, DC: 

National Center for Environmental Assessment, Office of Research and Development. 

U.S. EPA. (2002) Child-Specific Exposure Factors Handbook (Interim Final). Washington, D.C., National Center 

for Environmental Assessment, Office of Research and Development. EPA-600-P-00-002B. 

U. S. EPA. (2003a) Framework for Cumulative Risk Assessment. Washington, DC: U.S. Environmental Protection 

Agency, Risk Assessment Forum. EPA/630/P-02/001F. Available on line at: 

http://cfpub.epa.gov/ncea/raf/recordisplay.cfm?deid=54944. 

U.S. EPA. (2003b) Example Exposure Scenarios. National Center for Environmental Assessment, Washington, DC; 

EPA/600/R03/036. Available on line at: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=85843. 

U.S. EPA. (2004) Risk assessment guidance for Superfund. Human health evaluation manual: part E. Supplemental 

Guidance for Dermal Risk Assessment. Office of Solid Waste and Emergency Response, Washington, DC. 

EPA/540/R/99/005. 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 (2005). U.S. Environmental Protection Agency, Washington, D.C., EPA/630/P03/003F. Available on line at: http://oaspub.epa.gov/eims/xmlreport.display?deid=146583&z_chk=33084. 

U.S. EPA. (2005b) Guidelines for Carcinogen Risk Assessment. Risk Assessment Forum, Washington, DC. 

EPA/630/P-03/001F. 

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

Risk Assessment Forum, Washington, DC. EPA/630/R-03/003F. Available on line at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=116283. 
Table 1-1. Considerations Used to Rate Confidence in Recommended Values 

CONSIDERATIONS HIGH CONFIDENCE LOW CONFIDENCE 

Study Elements 

Level of peer review The studies received high The studies received limited 

level of peer review (e.g., they peer review. 

appear in peer review 

journals). 

Accessibility The studies are widely The studies are difficult to 

available to the public. obtain (e.g., draft reports, 

unpublished data). 

Reproducibility The results can be reproduced The results cannot be 

or methodology can be reproduced, the methodology is 

followed and evaluated. hard to follow, and the 

author(s) cannot be located. 

Focus on factor of The studies focused on the The purpose of the studies was 

interest exposure factor of interest. to characterize a related factor. 

Data pertinent to U.S. The studies focused on the The studies focused on 

U.S. population. populations outside the U.S. 

Primary data The studies analyzed primary The studies are based on 

data. secondary sources. 

Currency The data were published after The data were published before 

1990. 1990. 

Adequacy of data The study design captures the The study design does not very 

collection period measurement of interest (e.g., accurately capture the 

usual consumption patterns of measurement of interest. 

a population). 

Validity of approach The studies used the best There are serious limitations 

methodology available to 

capture the measurement of 

interest. 

with the approach used. 

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Study sizes The sample size is greater 

than 

100 samples. 

The sample size depends on 

how the target population is 

defined. As the size of a 

sample relative to the total 

size of the target population 

increases, estimates are made 

with greater statistical 

assurance that the sample 

results reflect actual 

characteristics of the target 

population.

 The sample size is less than 

20 samples. 

Representativeness of 

the population 

The study population is the 

same as population of interest. 

The study population is very 

different from the population 

of interest.a 

Variability in the 

population 

The studies characterized 

variability in the population 

studied. 

The characterization of 

variability is limited. 

Lack of bias in study 

design(a high 

rating is 

desirable) 

Potential bias in the studies 

are stated or can be 

determined from the study 

design. 

The study design introduces 

biases in the results. 

Response rates

 In-person interviews

 Telephone interviews

 Mail surveys 

The response rate is greater 

than 80%. 

The response rate is greater 

than 80%. 

The response rate is greater 

than 70%. 

The response rate is less than 

40%. 

The response rate is less than 

40%. 

The response rate is less than 

40%. 

Measurement error The study design minimizes 

measurement errors. 

Uncertainties with the data 

exist due to measurement error. 

Other Elements 

Number of studies The number of studies is 

greater than 3. 

The number of studies is 1. 

Agreement between 

researchers 

The results of studies from 

different researchers are in 

agreement. 

The results of studies from 

different researchers are in 

disagreement. 

a

 Differences include age, sex, race, income, or other demographic parameters. 

1-29
Table 1-2. Summary of Exposure Factor References and Confidence Ratings

 EXPOSURE 

FACTOR 

REFERENCE CONFIDENCE 

RATING 

(mean/upper

percentile) 

Breast milk intake rate Table 2-11 Medium/Medium 

Drinking water intake rate Table 4-7 High/High 

Food Intake- General 

Population

(fruit, vegetables, meats,

dairy

products, grains, fats,

fish) 

Table 3-50 High/Low 

Fish intake - Recreational Table 3-50 Low/Low 

Fish Intake - Native 

 American 

Subsistence 

Population 

Table 3-50 Low/Low 

Home produced food

intake 

Table 3-50 Low/Low 

Soil ingestion rate Table 5-21 Medium/Low 

Mouthing behavior Table 6-21 (mouthing time)

Table 6-22 (mouthing frequency) 

Low/Low 

Inhalation rate Table 7-21 Medium/Medium 

Dermal Factors Surface Area 

Whole Body: Tables 8-6, 8-7, 8-8

Body Parts: Table 8-3

Solid Adherence 

Tables 8-9, 8-10, 8-16 

Medium/Medium 

Body Weight Age 0 to <2 months: Table 11-1

Older Infants and Children: Tables 11

9, 11-10, 11-11 - High/High 

Activities 

(Showering, Swimming, 

 Time 

Indoors/Outdoors, etc.) 

Tables 9-75 and 9-76 Medium/Medium 

1-30
Table 1-3. Characterization of Variability in Exposure Factors 

Exposure Factors

 Average Median Upper 

percentile

 Multiple 

Percentiles

 Fitted 

Distributions 

Breast milk intake rate T T

Total intake rate for major 

food groups 

T T T

Qualitative 

discussion for 

long-term 

T

Individual food intake rate T

Drinking water intake rate T T T T

Fish intake rate for general 

population, recreational 

marine, recreational 

freshwater, and Native 

American 

T T T T

Serving size for foods T T

Home produced food intake 

rates 

T T T T

Soil intake rate T T T Qualitative 

discussion for 

long-term 

Mouthing Behavior T

Inhalation rate T T T

Surface area 

Soil adherence 

T

T

T T

Body weight T T T T

Time indoors 

Time outdoors 

Showering time 

T

T

T T T T

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Table 1-4. Integrating EPA’s Guidance on Selecting Age Groups for Monitoring and Assessing 

Childhood Exposures to Environmental Contaminants with EPA’s Supplemental Guidance for 

Assessing Susceptibility from Early-Life Exposure to Carcinogens For Those Contaminants 

Which Act Via a Mutagenic Mode of Action 

Exposure Age Group Exposure Duration (yr) ADAF (Age-Dependent 

Potency Adjustment 

Factor) 

birth to < 1 month 0.083 10x 

1 < 3 months 0.167 10x 

3 < 6 months 0.25 10x 

6 < 12 months 0.5 10x 

1 to < 2 years 1 10x 

2 to < 3 years 1 3x 

3 to < 6 years 3 3x 

6 to < 11 years 5 3x 

11 to < 16 years 5 3x 

16 to < 21 years 5 1x 

> 21 years (21 to < 70 yr) 49 1x 

Note: Age groups for cancer potency adjustment (birth to < 2 years; 2 to < 16 years; and 16 

years and above) are represented by the three colored bands of exposure age groups. 

1-32
1-33

Chem ical O rgan Effect

Exposure

Internal

Dose

Biologically

Effective 

Dose

M etabolism

A pplied

Dose

Potential

Dose

G .I. Tract

U ptake

M outh

Intake

Figure 1-1. Schematic of Dose and Exposure: Oral Route

Source: U.S. EPA, 1992a