ii

Notice

The information in this document has been funded by the United States 

Environmental Protection Agency. It has been subjected to the Agency’s 

peer and administrative review and has been approved for publication as 

an EPA document.

Abstract

The Conceptual Framework for the U.S. EPA’s National Exposure Research 

Laboratory (NERL) provides a foundation for addressing NERL’s research 

mission and its scientific leadership goals. The document defines the domain 

of exposure science; describes the uses for exposure science within the EPA; 

and provides the principles for developing and implementing NERL research. 

NERL’s mission is to conduct human health and ecological exposure research 

that provides the pertinent databases, predictive models, and analytical tools 

necessary for the EPA to carry out its mission. Fulfilling the EPA’s mission to 

protect human health and the environment carries with it the challenge of 

understanding exposures for tens of thousands of chemical contaminants, 

a wide range of biological stressors, and many physical stressors. Exposure 

science provides the Agency with the fundamental knowledge and tools 

necessary to assess potential exposures for emerging environmental threats 

and to mitigate exposures to known contaminants and stressors. 

The Conceptual Framework articulates the importance of exposure science 

in both assessing and managing risks. Internally, the document creates 

our identity as the National Exposure Research Laboratory and provides 

a common understanding and a common language for exposure research 

and its applications. The document also communicates NERL’s mission; 

organizational goals; and processes for strategic planning, communication 

and organizational development. Externally, the document is intended to 

define and advance the field of exposure science for both the EPA and the 

broader scientific community.
iii

Letter from the Director

I am pleased to present this framework document. The goals for the 

document are to provide a clear and concise conceptual framework for 

exposure science and an outline for the role of exposure science at the 

EPA. It also describes the principles for how we move forward as a national 

laboratory committed to providing scientific understanding, knowledge, 

and assessment tools that inform Agency policy decisions and aid in 

implementing Agency regulatory programs. 

As such, the concepts presented in this framework are the foundation for 

NERL’s future. This document is a product of considerable discussion and 

input from across the laboratory. I would like to particularly acknowledge 

Linda Sheldon and Rochelle Araujo — the primary authors of the document 

— as well as NERL’s division directors, who took a leadership role in 

developing the framework. Additionally, I would like to thank the NERL 

BOSC Subcommittee for their constructive comments, which have been 

incorporated into the document. 

NERL is uniquely positioned to address the Nation’s most challenging 

environmental exposure questions. I am confident that this framework will 

serve us well as we move exposure science into the 21st century.

Lawrence W. Reiter, Ph.D.

Director, National Exposure Research Laboratory

Office of Research and Development

Research Triangle Park, North Carolina 
iv

Foreword

The exposure framework document was written with the goal of defining 

the domain of exposure science, the uses for exposure science within the 

EPA, and the principles for developing and implementing NERL research. 

In creating this framework, the laboratory’s Associate Directors and Division 

Directors gathered to reflect, discuss, and define exposure science and their 

vision for developing and maintaining a strategy-focused organization that 

provides exposure science leadership at national and international levels. 

We wish to thank the following individuals for their time spent crafting this 

framework: Rochelle Araujo, Robert Dyer, Roy Fortmann, Florence Fulk, Fred 

Hauchman, Daniel Heggem, S.T. Rao, Mark Rodgers, Linda Sheldon, and 

Eric Weber.
Table of Contents

1.0 Introduction ..................................................................................................................... 1

2.0 Exposure Science ............................................................................................................. 5

3.0 Exposure Science at U.S. EPA ......................................................................................... 15

 3.1 Role of Exposure Science in the Risk Assessment/Risk Management Context ................. 15

 3.2 Role of Exposure in EPA Regulations ......................................................................... 19

4.0 Exposure Research at NERL ............................................................................................. 25

 4.1 Research Products: To have an impact, what must we deliver? ..................................... 26

 4.1.1 Developing a Research Portfolio ....................................................................... 27

 4.1.2 Designing a Research Program ........................................................................ 28

 4.1.3 Communicating NERL’s Research .................................................................... 29

 4.2 Internal Business Processes: To succeed, how do we carry out our work? ....................... 30

 4.2.1 Management Principles .................................................................................. 30

 4.2.2 Management Processes .................................................................................. 31

 4.3 Employee/Organization Capacity: To achieve our vision, what competencies 

 are needed? ........................................................................................................... 32

 4.3.1 Strategic Workforce Planning .......................................................................... 32

 4.3.2 Leadership Development within the Workforce .................................................. 34

 4.4 Financial Resources Management: To achieve our goals, how do we 

 efficiently allocate resources? .................................................................................. 36

 4.4.1 Financial Resilience ....................................................................................... 36

 4.4.2 Optimization and Integration ........................................................................... 36

References ............................................................................................................................ 39

Appendix A ........................................................................................................................... 41

Acronyms .............................................................................................................................. 42

List of Figures

Figure 2-1 Conceptual diagram of exposure ............................................................................... 5

Figure 2-2 The highest concentrations and the most susceptible populations 

 create the greatest potential risk ............................................................................. 6

Figure 2-3 Source-to-outcome framework for human health exposure research .............................. 8

Figure 2-4 Source-to-outcome framework for ecological exposure research ................................... 9

Figure 3-1 Framework for protecting human health and the environment .................................... 16

Figure 4-1 Aligning NERL’s business as a Strategy-Focused Organization ................................... 25

Figure 4-2 Evaluation filters and criteria for assessing potential research areas ........................... 27

Figure 4-3 Scientific expertise for exposure research ................................................................ 33

Figure A-1 Research planning in EPA ..................................................................................... 41

v

1.0 Introduction

The challenges of environmental protection range from 

understanding the potential 

risk associated with exposure 

of humans and ecosystems to a 

newly manufactured chemical, to 

minimizing human exposure to 

pathogens at public beaches, to 

linking human activities on the 

landscape with physical alterations 

of ecosystems. 

In the United States, there are 

more than 75,000 industrial 

chemicals currently tracked 

by the U.S. Environmental 

Protection Agency (EPA), with an 

estimated 2,200 new chemicals 

manufactured or imported each 

year. Since 2001, the list of 

environmental chemicals reported 

in the Centers for Disease Control 

and Prevention’s First, Second, 

and Third National Report on 

Human Exposure to Environmental 

Chemicals has grown from 27 to 

148 (NRC, 2006) — evidence 

of both the need and ability to 

monitor the public for exposure 

to contaminants of concern. The 

popular media routinely reports 

concerns about contaminants in 

drinking water supplies, at public 

beaches, and in the Nation’s 

surface waters. A June 2007 

Newsweek article (Underwood, 

2007) highlighted a growing 

public awareness of potential 

risks associated with “emerging 

contaminants,” including 

pharmaceuticals, cosmetics, 

and antibacterial soaps. Cited 

in the article was a 2002 survey 

by the U.S. Geological Survey 

which detected a number of 

these compounds in 80 percent 

of the 139 streams it examined 

(Koplin, 2002). While each of the 

compounds was generally present 

in small quantities, findings like 

these raise an overarching question: 

“What happens when a person is 

exposed to a whole cocktail of them 

(Underwood, 2007)?”

Other contaminants are not 

chemicals manufactured for 

product use; rather they are 

byproducts of modern society. 

As an example, particulates in 

air come from power plants, 

automobile emissions, and 

emissions from natural sources. In 

addition, many other contaminants 

can be formed when emissions 

from biogenic and anthropogenic 

sources interact in the 

environment. 

For ecosystems, environmental 

protection goes beyond 

minimizing exposures to chemical 

contaminants and includes the 

restoration and maintenance of the 

physical and biological integrity 

of ecosystems. Understanding the 

relationships between land use, 

such as urban development and 

Exposure science provides the Agency with the fundamental 

knowledge and tools necessary to assess potential exposures 

and risks to emerging environmental threats and to 

mitigate exposures to known contaminants and stressors.

1

1.0
agricultural activities, and how 

these activities can physically alter 

ecosystems is a critical component 

of environmental protection. In the 

EPA’s 2006 report on the condition 

of wadeable streams in the United 

States, stream bed sediments 

and river bank disturbance were 

identified as two of the most 

widespread stressors degrading 

stream condition for fish and other 

aquatic life. Both of these stressors 

represent physical alteration of 

stream systems and are typically 

associated with human activity 

alongside streams.

Fulfilling the EPA mission 

to protect human health 

and the environment carries 

with it the challenge of 

understanding exposures for 

tens of thousands of chemical 

contaminants, a wide range of 

biological stressors, and many 

physical stressors. The EPA’s 

National Exposure Research 

Laboratory (NERL) is uniquely 

positioned to address the 

Nation’s most challenging 

environmental exposure 

questions. Exposure science 

provides the Agency with 

the fundamental knowledge 

and tools necessary to assess 

potential exposures and risks to 

emerging environmental threats 

and to mitigate exposures 

to known contaminants and 

stressors. NERL’s combined 

expertise in modeling, chemistry, 

physics, meteorology, statistics, 

computational science, 

microbiology, ecology, molecular 

biology, geographic information 

systems, and remote sensing 

enables the Laboratory to bring 

cutting-edge research and 

technology to the field of exposure 

science.

NERL’s mission is to conduct 

human health and ecological 

exposure research that provides the 

pertinent databases and predictive 

modeling and analytical tools 

necessary for the EPA to carry 

out its mission. NERL produces 

research to reduce critical exposure 

uncertainties associated with the 

Agency’s policy decisions and 

provides international leadership in 

exposure science. This document 

is a conceptual framework for 

addressing NERL’s research 

mission and achieving its goal 

of scientific leadership. In the 

following sections, the document 

will:

 define the domain of exposure 

science (Section 2.0);

 describe the uses for exposure 

science within the EPA (Section 

3.0); and

 provide the principles for 

developing and implementing 

NERL research within the context 

of the conceptual framework 

(Section 4.0).

The primary audience for this 

document is the NERL research 

community. Internally, the 

document creates our identity 

as the National Exposure 

Research Laboratory. It provides 

a common understanding and a 

common language for exposure 

research and its applications. 

As an internal resource, it also 

communicates our mission, 

our organizational goals, and 

the processes for strategic 

planning, communication, and 

organizational development. 

Externally, the document is 

intended to define and advance 

the field of exposure science 

for both EPA and the broader 

scientific community. Very 

importantly, it articulates the 

importance of exposure science 

in both assessing and managing 

risks. Finally, the document 

communicates our mission and 

our goals to our partners and 

collaborators both within and 

outside of EPA. 

2

NERL’s mission is 

to conduct human 

health and ecological 

exposure research for 

the EPA to carry out 

its mission. NERL 

produces research to 

reduce critical exposure 

uncertainties associated 

with the Agency’s policy 

decisions and provides 

international leadership 

in exposure science.
Fulfilling the EPA mission to protect 

human health and the environment 

carries with it the challenge of 

understanding exposures for 

tens of thousands of chemical 

contaminants, a wide range of 

biological stressors, and many 

physical stressors.

2.0

Figure 2-1. Conceptual diagram of 

exposure

Distribution of

Stressors in Space

and Time

Exposure

Distribution of

Receptors in Space

and Time

For exposure to occur, the stressor 

and the receptor must intersect 

in both space and time . . . . 

Exposure science characterizes and 

predicts this intersection.

2.0 Exposure Science

Exposure is the contact of a stressor with a receptor for a 

specific duration of time (Zartarian, 

et.al, 2005). A stressor is any 

biological, physical, or chemical 

agent that can potentially lead to 

an adverse impact. This is a very 

general concept and includes those 

stressors that lead to exposure 

through direct contact as well as 

those stressors that act indirectly 

through a series of environmental 

processes. A receptor is a living 

organism or group of organisms. 

In human health research, 

the individual or population of 

individuals is the receptor. In 

ecological research, the receptor 

can be individual plants or animals, 

communities of plants or animals, 

or groups of communities organized 

into an ecosystem. 

For exposure to occur the stressor 

and the receptor must intersect in 

both space and time, as illustrated 

in Figure 2-1 (below). Exposure 

science characterizes and predicts 

this intersection. This fundamental 

definition is consistent with EPA’s 

Guidelines for Risk Assessment 

(USEPA, 1992) and its Guidelines 

for Ecological Risk Assessment 

(USEPA, 1998).

Exposure is described in terms 

of the magnitude, frequency, 

and duration of contact. For 

most stressors, the magnitude of 

exposure to a receptor is a critical 

characteristic in determining 

adverse effects. Likewise, both 

the frequency and the timing of 

exposures can have an important 

impact. Exposure can be either 

continuous or intermittent 

depending upon the source of 

the stressor, its persistence in 

the environment, and receptor 

activities that lead to contact with 

the stressor. Exposure durations 

can range from short-term or acute 

(i.e., minutes to hours) to longterm or persistent (i.e., years). For 

example, exposure to an accidental 

chemical release would be shortterm and intermittent. While at 

the other end of the spectrum, 

chemicals such as lead, dioxins, 

polychlorinated biphenyls (PCBs), 

and organochlorine pesticides are 

persistent in the environment and 

can be found in environmental 

media where humans and wildlife 

have frequent contact. Because of 

this, exposures to these chemicals 

5
Figure 2-2. The highest concentrations and the most susceptible 

populations create the greatest potential risk.

Distribution of 

Stressors in Environmental Media

Highest

Intensities

Greatest

Potential

Risk

Susceptible

Subpopulations

Individual Activities and

Locations

Vulnerability Factors

(Exposure/Activity)

 Age or life stage

 Culture and lifestyle

 Activities and occupation

 Geographic locations/

 distributions

 Socioeconomic status

Susceptibility Factors

(Biological)

 Age or life stage

 Gender

 Genetic differences

 Health status

 Previous exposures

are generally continuous and 

persistent. Additionally, for some 

stressors, there are very specific 

receptor life stages (such as fetal 

development) where specific and 

characteristic exposure routes may 

predominate and where exposure 

will lead to an enhanced adverse 

outcome.

Exposure assessment is the process 

for identifying potentially exposed 

populations and pathways of 

exposure, as well as quantifying the 

magnitude, frequency, duration, 

and time-pattern of exposure. 

The adverse impact of exposure 

depends upon the characteristics 

of the exposure, the potency of the 

stressor, and the susceptibility of 

the receptor. The greatest adverse 

impact of any given stressor will be 

to those individuals, populations, 

communities, or ecosystems that 

are most exposed and/or most 

susceptible to the exposure. This 

concept is illustrated in Figure 2-2 

(right), which expands upon the 

simplified illustration in Figure 2-1.

Within the exposure research 

framework, vulnerability refers 

to characteristics of a receptor 

(e.g., an individual, population or 

ecosystem) that places them at 

increased risk of an adverse effect 

(USEPA, 2005). The text box above 

shows some of the ways that a 

receptor may be more vulnerable. 

Included are factors that can 

lead to increased susceptibility 

or higher exposure. Susceptibility 

refers to characteristics that lead 

to a greater response for the 

same exposure. The concepts 

of differential exposure and 

susceptibility are crucial given the 

EPA’s mandate to protect not only 

the general population, but also 

those populations at greatest risk. 

Exposure assessments, therefore, 

should identify and understand 

those conditions that lead to 

the highest stressor intensities 

and resulting exposures, as well 

as those situations that lead to 

exposure for the most susceptible 

receptors.

Figure 2-2 suggests that both 

stressors and receptors vary in 

time and space; however, there is 

an important distinction between 

human and ecological exposure 

research in this regard. The human 

receptor is essentially the same 

in all locations; only stressor 

intensity, population characteristics 

(e.g., density), and susceptibility 

will vary in space. For ecological 

exposures, location determines 

not only the stressors present and 

their intensities, but also which 

receptors might be present, and the 

circumstances under which they 

encounter the stressor. That is, the 

organisms that are present vary as 

a function of location, as well.

6
Differences Between Human Health and Ecological Research Disciplines

Human Health Research Ecological Research

• Agency is responsible for human health outcomes 

solely related to environmental stressors

• Agency is responsible for health of the entire 

ecosystem

• Chemical and biological agents are primary stressors 

of concern

• Physical condition along with chemical and 

biological agents are primary stressors of concern

• Single Receptor - human at individual or population 

level 

• Multiple Receptors – individual plant or animal 

species, communities of plants and animals, or 

entire ecosystems

• Receptors (humans) are the same at all locations – 

population density, vulnerability, and susceptibility may 

change across locations

• Receptors will vary across locations – location 

will determine what receptors are present and the 

circumstances for contact with the stressor

• Traditionally, risks have been evaluated for a single 

stressor at a time

• Risks are evaluated for multiple stressors, using 

a systems approach 

• Exposures and outcomes stop with consideration of 

the human receptor

• Exposures and outcomes can cascade when the 

outcome in one receptor serves as the stressor for 

another

• Exposure and outcomes are of interest at 

additional levels of biological organization

There are many commonalities 

between human and ecological 

exposure science and these 

commonalities serve as the basis 

for this framework document. 

There are also differences that 

must be recognized in order to 

have a complete understanding 

of the science. For example, our 

understanding of the concepts of 

human and ecological exposure 

science is influenced by the EPA’s 

responsibilities in the two areas. 

The EPA is responsible for human 

health outcomes solely related to 

environmental stressors (primarily 

chemical or biological agents). In 

contrast, the Agency is responsible 

for protecting the condition or state 

of entire ecosystems from multiple 

stressors, including physical, 

chemical, and biological agents. 

Important differences between 

the human health and ecological 

disciplines are shown in the table 

below.

The goal of exposure science is to 

characterize, forecast, hindcast, 

and manage exposures. In addition 

to identifying and characterizing 

stressors and receptors, exposure 

research also characterizes and 

links the processes that impact 

the movement and interactions 

of stressors from their sources 

through the environment, and 

their intersection with receptors. 

This includes understanding and 

describing the interactions of 

multiple stressors, with diverse 

environments, and multiple 

receptors. In very simple terms, the 

elements of exposure science can 

be illustrated within a “source-tooutcome” framework (Figures 2-3 

and 2-4 on following pages), in 

both forward and reverse directions, 

providing the critical link between 

sources of environmental stressors 

and associated impacts. 

7
 Figure 2-3 (below) is an adaptation 

of the source-to-outcome framework 

developed by the National Research 

Council (NRC, 1983, 1998). 

The processes that are important 

for exposure science start with a 

stressor entering the environment 

and end with dose characterization. 

Starting in the upper left-hand 

corner, stressors (primarily 

chemical or biological) are released 

into the environment from a source. 

Many stressors can be transformed 

through a number of processes, 

including chemical reactions and 

biological degradation. Stressors 

or their transformation products 

move through the environment and 

can be found in environmental 

media including air, water, soil, 

dust, and food. The intensity of 

exposure depends upon the stressor 

concentration in the media, as well 

as the duration of contact with the 

receptor. Exposure becomes “dose” 

when the stressor moves across the 

receptor’s body barrier. The text 

under each box in Figure 2-3 shows 

the information that is used to 

characterize the various processes 

represented in the boxes. The 

arrows between the boxes represent 

models that are used to link the 

processes. 

Figure 2-3. Source-to-outcome framework for human health exposure research

Source/Stressor

Characterization

Environmental

Characterization

Transport and

Transformation

Environmental

Concentration

Exposure

Dose

Effects

Receptors:

• Individual

• Population

• Sensitive 

Sub-population

Chemical

Biological

Exposure Effects

Atmosphere

Vegetation

Habitat Conditions

Hydrosphere

Lithosphere

Flow Dynamics

Dispersion

Kinetics

Thermodynamics

Spatial Variability

Distribution

Temporal Variability

Meteorology

Air

Water

Soil/Dust

Food

Pathway

Duration

Intensity

Frequency

Absorbed Target

Acute

Chronic

8
Figure 2-4 (below) shows that with 

several modifications, the same 

framework can be used to describe 

the interaction of environmental 

factors that contribute to ecological 

exposures. For example, “source” 

may also refer to activities that 

give rise to non-chemical stressors, 

such as changes to habitat from 

expanding human populations. 

“Environmental characterization” 

includes the full suite of ecological 

conditions, as well as those 

that affect pollutant/stressor 

concentrations. For ecological 

research, “dose” is replaced by 

an equivalent measure of the 

stressor’s impact on the receptor, 

that is, stressor intensity within 

the domain of the receptor. An 

example of a quantity equivalent 

to dose, where the receptor is a 

stream’s fish community, might be 

the turbidity in a stream, caused by 

excessive sediments, that prevents 

a fish from finding its food. The 

figure below illustrates the concept 

that the receptor is determined 

by the location and environmental 

characteristics. Finally, the multiple 

arrows from the effects box 

illustrate a sequence of feedbacks 

that can lead to cascading impacts. 

For example, the response of an 

ecosystem to a stressor might 

include shifts in vegetation, which 

would feed back to the exposure 

pathway via environmental 

characterization. Similarly, an 

ecosystem response that includes 

a change in microbial communities 

could alter the biogeochemical 

processes that affect transport and 

transformation. In the ultimate case 

of cascading exposures, an affected 

organism may become the prey/

food for another organism, thus 

entering the exposure continuum 

directly as the immediate source 

of exposure (environmental 

concentration). Although there are 

some circumstances (secondary 

infection spread) in human 

exposure research where exposures 

and outcomes can loop back to 

serve as stressors, this is not as 

common and, thus, has not been 

illustrated in Figure 2-3.

Figure 2-4. Source-to-outcome framework for ecological exposure research

Source/Stressor

Characterization

Environmental

Characterization

Transport and

Transformation

Environmental

Concentration

Exposure

Dose

Effects

Receptors:

• Individual

• Community

• Population

• Ecosystem

Chemical

Biological

Physical

Exposure Effects

Atmosphere

Vegetation

Habitat Conditions

Hydrosphere

Lithosphere

Flow Dynamics

Dispersion

Kinetics

Thermodynamics

Spatial Variability

Distribution

Temporal Variability

Meteorology

Air

Water

Soil

Food

Pathway

Duration

Intensity

Frequency

Internal Mass

Count

Length

Area

Acute

Chronic

9

Cascading Impacts
Although 

the sourceto-outcome 

framework 

for human 

health and 

the framework 

for ecological 

research have 

been diagramed 

separately in 

this document, 

it is important 

to recognize 

that the two 

are closely 

intertwined 

and should be considered together. 

Healthy ecosystems are required 

for human well-being; they provide 

clean air, water, and protection 

from disease. In turn, humans are 

part of these ecosystems and can 

positively or negatively impact the 

state of ecosystems through their 

actions and management practices.

Exposure to environmental stressors 

is considerably more complex 

than illustrated in Figure 

2-4. Multiple 

stressors enter 

the environment 

at the same 

time from 

many different 

sources. 

Stressors 

can remain 

unchanged or 

they can be 

transformed 

by physical, 

chemical, 

or biological 

processes 

to become 

different 

agents. These stressors or their 

transformation products can 

partition and move through many 

different environmental media 

(i.e., air, water, soil, sediment, 

and the plant and animal life of 

a particular region). Stressors or 

their transformation products can 

take many different 

pathways to 

reach the receptor. In the 

simplest case, exposure to a given 

stressor would be in a single 

media through a single pathway, 

although multimedia, multipathway 

exposures are the more common 

case. Definitions for concepts 

associated with multimedia, 

multipathway exposure are given 

in the text box below. Aggregate 

exposure is the sum of exposures 

to a single stressor from all sources 

and pathway(s) over a given time 

period. Cumulative risks are 

those that result from aggregate 

exposures to a single stressor over 

multiple time periods, or from 

concurrent and/or synergistic 

exposures to multiple stressors. 

Exposure science must describe 

the complexity of stressors, the 

environment, and the receptors 

as they interact. As examples, 

when stressors from multiple 

sources reach the receptor 

by the same pathway, 

it may be necessary 

to determine 

relative source 

Exposure media:

environment or media in 

which stressor exists as it 

interacts with the receptor.

Exposure pathway:

the course that the 

chemical takes from its 

source to the receptor.

Aggregate exposure:

sum of exposure to a single 

stressor from all sources 

and pathways.

10
contributions. 

Likewise, when 

a stressor comes 

in contact with 

a receptor by 

multiple pathways, 

dosimetry must be 

used to integrate 

the exposures 

as they would 

lead to a health 

outcome. Although 

the concepts 

of aggregate 

exposures and 

cumulative risk are relatively new 

for human health exposure science, 

understanding impacts of multiple 

stressors from many different 

sources has been a fundamental 

aspect of ecological exposure 

science that should be extended to 

both disciplines.

Models are the underpinnings of 

understanding and controlling 

environmental health risks within 

this basic framework for exposure 

science. Exposure science 

characterizes the movement, 

chemical transformations, removal, 

distribution, and interaction of 

stressors and receptors in time and 

space, at different locations and 

on multiple scales. With such a 

broad scope, 

it is necessary to go beyond the 

simple measurement of conditions 

for each component of the 

source-to-outcome framework 

and focus on the processes that 

control movement along the 

framework. Models provide the 

ability to summarize and link our 

knowledge of exposure processes 

and to mathematically quantify 

and predict concentrations of 

chemicals, biological and physical 

conditions, exposures, and dose. 

Process models enable us to be 

both prospective and retrospective 

in describing exposures and 

outcomes. Moreover, 

the assessment 

of cumulative and 

aggregate exposures 

requires the use of 

integrated multimedia 

models. The use of 

models is central to 

Agency decision-making 

processes (NRC, 

2007). The EPA uses 

models to inform the 

exposure assessment 

process (distributions, 

uncertainty, and 

variability), assess 

compliance, and 

evaluate alternate regulations. 

As shown in the text box below, 

there are many uses for exposure 

models. Both conceptual and 

computational models also allow us 

to systematically evaluate our state 

of knowledge as well as identify 

data gaps and research needs. The 

importance of models in exposure 

science will continue to 

increase as computational 

methods advance. 

Uses of Exposure Models

Research Uses:

 Provide exposure hypotheses

 Synthesize data collected on

 the state of a system

 Provide explanations of factors

 impacting exposure

Management Uses:

 Assess exposure/dose to stressors

 Project future conditions or

 trends

 Extrapolate to situations where

 observations are not available

 Assess the contribution of

 individual sources

 Evaluate the impacts of different

 policies or future scenarios

 Evaluate post-implementation

11 impact of regulations
Throughout this framework, it is 

important to distinguish between 

exposure science and exposure 

research. 

Exposure science is applied 

in the practice of assessing 

and managing environmental 

health risk; whereas exposure 

research is conducted to address 

critical gaps that will limit the 

application of exposure science 

and in this manner serves to 

improve the quality of exposure 

science. Specifically, exposure 

research provides the scientific 

understanding of the processes 

involved in exposure science, 

develops the tools (methods 

and models) for conducting 

the science, provides the data 

that are used to understand 

environmental and exposure 

conditions, and provides inputs to 

the models. 

A complete exposure research 

program in NERL must include 

model development, observational 

measurement research and 

methods development. As already 

discussed, modeling research 

provides the underpinning for 

exposure science. Observational 

measurement studies provide 

a fundamental understanding 

of model processes, along with 

inputs for models, and data 

for model evaluation. Methods 

research provides the tools that 

allow observational measurements 

to be made and interpreted. 

These measurement tools also 

have direct application for 

compliance monitoring. 

This document describes NERL’s 

exposure research program. NERL 

recognizes that full understanding of 

an environmental issue from source 

to outcome can only be achieved 

by conducting integrated, crossdisciplinary, and focused research 

and by applying the outputs of this 

research to inform policy. 

This can be achieved by NERL 

exposure researchers working in 

full coordination with toxicologists, 

epidemiologists, engineers, risk 

assessors, and decision makers both 

within and outside of EPA. Research 

responsibilities within ORD (EPA’s 

Office of Research and Development) 

are organized around the source-tooutcome framework. The engineering 

laboratory (NRMRL) is responsible 

for research that characterizes 

sources; NERL is responsible 

for research associated with fate 

and transport, environmental 

concentrations, exposure and dose; 

and the health laboratory (NHEERL) 

is responsible for characterizing 

health outcomes associated with 

exposures. The engineering laboratory 

is also responsible for developing 

and evaluating methods for source 

reduction. Conducting integrated 

multidisciplinary research with 

scientists in these sister laboratories 

is crucial to addressing the nation’s 

most important environmental 

health issues, however developing 

relationships with scientists in 

academia, other governmental 

organizations and nongovernmental 

organizations is also needed to fully 

develop integrated multidisciplinary 

research programs.

12
Exposure science is applied in the practice 

of assessing and managing environmental 

health risk; whereas exposure research is 

conducted to address critical gaps that will 

limit the application of exposure science 

and in this manner serves to improve the 

quality of exposure science.

3.1 Role of Exposure 

Science in the Risk 

Assessment/Risk 

Management Context

The mission of the EPA is to safeguard public health 

and the environment from 

environmental stressors. The 

mechanism for environmental 

protection is to minimize human 

and ecosystem exposures to 

stressors of concern as part of riskbased assessments. The EPA sets 

its priorities, targets its actions, 

and measures its outcomes based 

on assessing and managing risk. 

Regardless of the Agency program 

or regional office that raises 

the issue, there are three broad 

questions related to environmental 

decisions (see text box below).

3.0 Exposure 

Science 

at U.S. EPA

Broad Questions Related 

to Agency Problems:

 Is mitigation necessary?

 (impact on the receptor)

 How best to mitigate?

 (impact on the stressor)

 Was mitigation successful?

 (accountability)

The mission of the EPA is 

to safeguard public health 

and the environment from 

environmental stressors.

15

3.0
Figure 3.1 (below) overlays 

the concepts of stressor and 

receptor on the source-tooutcome framework. The figure 

then incorporates the processes 

associated with environmental 

management practices, including 

risk assessment, development 

of environmental policies 

and regulations, compliance 

monitoring, and risk management. 

Finally, the three questions that 

face the EPA are overlaid in the 

figure. As highlighted in the figure 

and discussed below, exposure 

is uniquely positioned at the 

Figure 3-1. Framework for protecting human health and the environment

Was mitigation successful?

Source

Environmental

Concentration/

Condition

Exposure Dose Outcome

EPA Policy/

Regulation

Risk Assessment

(Receptor Impact)

Risk Management

(Stressor/Exposure 

Reduction)

Compliance

Monitoring

Is mitigation necessary?

How best to mitigate?

intersection of the stressor and the 

receptor, and plays a pivotal role 

in addressing each of the broad 

Agency questions. 

Is mitigation necessary?

Risk assessments are used to 

determine whether mitigation 

is necessary and they focus on 

impacts to the receptor. All risk 

assessments are based on the 

concept that:

 

Exposure must be used implicitly 

or explicitly to determine risk. 

Very simply, risk assessment 

is a four-step process (see text 

box, right; NRC,1983). Hazard 

identification determines 

qualitatively, whether a stressor will 

cause an adverse outcome. Doseresponse assessments establish the 

quantitative relationship between 

dose and the incidence of effects. 

This information is used, in turn, 

to develop a “safe” exposure level, 

often referred to as a reference 

dose (RfD). Exposure assessment 

determines the route, magnitude, 

Risk = Exposure  Hazard

16
Steps in Risk Assessment 

Process

 Hazard Identification

 Dose-Response Assessment

 Exposure Assessment

 Risk Characterization

frequency, and distribution of 

exposure. Risk characterization 

is conducted by comparing the 

“safe” exposure level to the 

distributions of exposure thereby 

determining the risk of an adverse 

outcome. Mitigation is required for 

exposures at or above the “safe” 

level. Although other information 

along the continuum (i.e., sources, 

environmental concentrations, etc.) 

may provide inputs to the exposure 

assessment, exposure is the metric 

that is used to evaluate risk.

Risk assessments can be 

conducted either by determining 

dose-response using toxicity 

studies coupled with an 

independent exposure assessment 

or by conducting environmental 

epidemiology studies where 

exposure estimates and health 

outcomes are determined for a 

specific cohort. Environmental 

epidemiology is crucially dependent 

on high-quality exposure estimates. 

Although epidemiology may 

not provide evidence of causal 

associations, it does provide critical 

information on measurable adverse 

health effects in real populations 

associated with exposure to real 

environmental stressors. 

How best to mitigate?

Risk to a receptor is most often 

lowered by reducing exposure. 

The “safe” exposure level is 

determined by the dose response 

assessment described in the 

previous section. Activities 

designed to bring exposures 

down to that level are developed 

using information on the 

sources, pathways, and routes 

that lead to the exposures. 

These activities can be directed 

toward various processes 

along the source-to-outcome 

continuum. Standards most 

often target source controls or 

environmental concentrations, 

while some actions, such as 

fish advisories or ozone alerts, 

target individual actions in order 

to reduce exposure. For those 

standards that target environmental 

concentrations, environmental 

monitoring is used to assess 

compliance. When monitoring 

results exceed the standard, risk 

mitigation activities are then 

directed at the sources of the 

environmental stressors. 

Exposure must be used implicitly 

or explicitly to determine risk.

Mitigation activities can be 

developed without the use of 

exposure tools and information, 

however, ensuring the development 

of activities that are the most 

protective, with the least burden, 

requires an understanding of 

exposure. Exposure science 

provides information on the levels 

and processes that control fate and 

transport, environmental conditions 

and concentrations, and exposure 

pathways. Techniques, such as 

source apportionment and exposure 

reconstruction, are used to relate 

exposures or environmental 

concentrations back to sources. 

Monitoring methods are developed 

to evaluate exposures and to assess 

compliance to standards. Models 

across the continuum are used to 

summarize available knowledge 

needed for regulatory decisions 

and provide the ability to evaluate 

alternative regulations, while also 

offering a framework in which to 

assess compliance (NRC, 2007). 

17
Was mitigation successful?

Over the last several years, there 

has been an increased interest 

in assessing the effectiveness of 

EPA’s regulatory and non-regulatory 

decisions. Research and data 

across the entirety of Figure 3-1 

can be used to address this area. 

This is a new area of research 

for the Agency, with the initial 

emphasis placed on developing 

and validating indicators along 

the source-to-outcome continuum 

(USEPA, 2007). Exposure science 

is expected to play a very important 

role in this research area, because 

it is crucial to linking stressorbased metrics to receptor-based 

metrics. 

18
3.2 Role of Exposure in 

EPA Regulations

The EPA’s regulations and policies 

have been formulated to use 

exposure information according to 

the general principles outlined on 

pages 16-18. However, depending 

on the nature of the contaminant, 

the environmental medium, and 

the appropriate treatment of risk, 

regulations may outline different 

activities and address exposure 

in either an explicit or implicit 

manner. There are four primary 

areas where the EPA can increase 

the effectiveness of environmental 

protection programs by enhancing 

its emphasis on exposure 

assessment, and investing in 

exposure research:

1. Developing current 

standards/policies

(e.g., developing and evaluating 

exposure metrics and models 

that can be used in the risk 

assessment process, understanding 

the mitigation or enhancement 

of exposure by human activity 

or natural processes, developing 

and applying reliable exposure 

indicators for environmental 

epidemiology);

2. Achieving current standards/

policies

(e.g., developing analytical 

methods to determine compliance, 

developing and applying models 

to predict the impact of mitigation 

strategies, providing information to 

implement mitigation and simulate 

alternative scenarios and policies);

3. Evaluating the impact of 

standards/policies

(e.g., reconstructing exposures 

to determine environmental 

concentrations of contaminants 

relative to exposed populations, 

developing and applying public 

health indicators along the source–

to-outcome framework, evaluating 

environmental concentrations 

against model predictions); and

4. Developing the science

for the next generation of

standards/policies

(e.g., developing science for 

assessing cumulative risks, 

identifying sources of pollution 

with the greatest risk, determining 

the potential extent of exposure to 

emerging contaminants).

19

The EPA 

is facing a 

number of 

new challenges 

for which a 

one-pollutant, 

one-medium, 

one-exposure 

approach for 

assessing and 

managing risk 

is no longer 

adequate.
The text box on page 21 identifies 

the major exposure elements of 

the EPA’s enabling legislation. 

Identifying and understanding 

those elements are critical to 

strengthening and expanding the 

Agency’s use of exposure science. 

Exposure has not often played a 

large role in the risk assessment 

and risk mitigation processes. 

Environmental regulations were 

often developed to address 

contamination that was so severe 

and immediate to its source that 

ambient monitoring data or source 

emissions were adequate surrogates 

for exposure. The National Ambient 

Air Quality Standards, developed 

under the Clean Air Act, and the 

EPA’s drinking water standards, 

developed under the Safe Drinking 

Water Act, are but a few examples 

of this approach. 

This process worked well for the 

EPA in the past and will continue 

to work well for situations, as long 

as certain conditions are met:

 The standard is not a riskbased standard (e.g., best available 

technology); therefore, the risk 

assessment process is not used.

 The surrogate exposure estimate 

is either much greater or lower than 

the risk level, thus better, more 

realistic exposure information will 

not change the action.

 There is only one source and 

pathway of exposure, and the 

relationship between source, 

environmental concentration, and 

exposure is well defined.

 There is only one pathway 

for exposure, and the pollutant 

concentration is relatively 

homogenous, so that a single 

measure of environmental 

concentration can be used to 

estimate exposure.

20

Understanding 

exposures and 

approaches for 

reducing exposures 

will be critical in 

making informed 

decisions that protect 

public health and the 

environment while 

preserving human 

well-being and 

sustainability.
Environmental Regulations and Statutes with Exposure Components

Clean Water Act – Establishes the structure for regulating the discharge of pollutants into U.S. waters. 

Exposure information is used to set standards to achieve uses, determine achievability of uses via technology 

and total maximum daily load (TMDL) controls (point, nonpoint sources), and establish watershed planning 

and best management practices.

Safe Drinking Water Act – Establishes safe standards of purity and requires all public water systems to meet 

primary standards. Exposure research is used to develop methods to improve exposure assessments, improve 

microbial detection techniques, detect and classify unregulated contaminants.

Clean Air Act – Established National Ambient Air Quality Standards for the protection of public health and 

the environment; sets limits on how much of a pollutant can be released in the air. Exposure research is 

used to develop exposure metrics for epidemiological research that evaluates health impacts of criteria 

pollutants, develop exposure assessments for air toxics, determine impact of atmospheric processes on air 

quality, and provide models for air quality and exposure analysis and prediction.

Toxic Substances Control Act – Requires reporting and/or testing of industrial chemicals produced or 

imported into the U.S. that may pose an environmental or human-health hazard. Exposure information is 

used to develop methods to measure exposures to industrial chemicals, analyze and report exposure levels 

based on real-world data, and to conduct exposure assessments on a wide array of chemicals.

Federal Insecticide, Fungicide & Rodenticide Act – Establishes federal control of pesticide distribution, sale 

and use. Exposure research is used to develop methods and models to characterize exposures to pesticides, 

model the fate and transport of pesticides through ground water.

Endangered Species Act – Prohibits any action that results in a “taking” of a listed species, or adversely 

affects habitat of a listed species. Exposure information is used to determine (cumulative) risks to 

individuals of endangered species (including habitat), and register pesticides based on exposure risk to 

endangered species.

Food Quality Protection Act – Requires EPA to set limits on the amount of pesticides that may remain in or 

on foods based on risks to infants and children from exposure from all sources. Exposure research is used to 

develop important exposure scenarios, identify and quantify factors for children’s exposure, develop highquantity, high-quality exposure data, develop models for estimating exposure and dose to pesticides.

Federal Food, Drug & Cosmetic Act – Requires EPA to address risks to infants and children from exposure 

to pesticides in diets; requires the development and implementation of a screening program for endocrine 

effects, including estrogenicity. Exposure information is used to study exposures to susceptible populations, 

analyze exposures to endocrine disrupting compounds, develop generic techniques to model consumer 

exposure.

Comprehensive Environmental Response, Compensation, and Liability Act – Provides EPA authority to 

clean up and/or prevent releases of hazardous substances. Exposure science is used to specify testing and 

monitoring requirements, determine appropriate groundwater remediation, determine the exposit to which 

contaminated soils and debris must be excavated.

Resource Conservation and Recovery Act – Requires EPA to control the generation, transportation, 

treatment, storage, and disposal of hazardous waste to protect human health and the environment. Exposure 

science is used to measure chemicals at hazardous waste sites, assess risks for leaking underground storage 

tanks, establish operation standards and promulgate monitoring and control regulations, and specify criteria 

for acceptable location of treatment, storage and disposal of facilities.

21
The need for good exposure 

information is highlighted when 

we consider the potential risks and 

adverse outcomes associated with 

underestimating exposures, along 

with the potential costs to 

society of overestimating 

exposures. This is especially 

true for situations where a 

simple approach to exposure 

assessment is not adequate 

(see text box, right). In these 

situations, the overall quality 

of the risk assessment will be 

limited, to a great extent, by 

the quality of the exposure 

assessment. As an example, 

in risk assessments of 

waterborne pathogens which 

have a very large temporal 

and spatial variability, the 

uncertainty surrounding 

the various components of 

the exposure assessment 

can easily be up to several 

orders of magnitude. This 

level of uncertainty can 

have a profound impact on 

the regulatory action that 

is taken, as well as the 

confidence in that action. 

The EPA is facing a number of 

new challenges for which a onepollutant, one-medium, oneexposure approach for assessing 

and managing risk is no longer 

adequate. There is growing 

awareness of potential exposures 

to new types of contaminants 

(e.g., nanomaterials), pressures 

of population growth on 

natural ecosystems, complex 

systems that involve multiple 

stressors, and pollutants 

with significant spatial and 

temporal variability (leading to 

different exposure scenarios 

for different populations). 

Additionally, there is a 

need to consider how the 

consequences of a particular 

risk management action 

may lead to unintended 

consequences. For example, 

a regulation established 

to reduce exposure to one 

contaminant may increase 

exposure to another 

contaminant (e.g., decreases 

in nitrogen loading in 

streams may increase the 

bioavailability of mercury). 

Understanding exposures and 

approaches for reducing exposures 

will be critical in meeting these 

challenges and in making informed 

decisions that protect public 

health and the environment while 

preserving human well-being and 

sustainability.

Assessments Requiring Refined 

Exposure Estimates

 Aggregate exposures from multiple 

pathways and routes

 Cumulative risks from exposures to 

multiple stressors

 Exposures to stressors with significant 

spatial and temporal variability (e.g., fine 

particulate sulfate vs. coarse particulate 

matter in air, chemical contaminants vs. 

microbes in drinking water, etc.)

 Exposures and risks from sources rather 

than to single pollutants from a source

 Total risk associated with regulatory 

options

22
The need for good exposure information 

is highlighted when we consider the 

potential risks and adverse outcomes 

associated with underestimating exposures, 

along with the potential costs to society of 

overestimating exposures.

4.04.0 Exposure Research 

at NERL

As a research organization, NERL has two interrelated 

goals: to provide leadership in 

exposure science and to conduct 

high-quality research to support 

the EPA’s mission. Achieving 

these goals requires a strategic 

approach that will inform not only 

the research we do, but also the 

processes we use to implement 

this research. This conceptual 

framework document is the 

first crucial step in developing 

and communicating such an 

approach by providing a common 

understanding of exposure science, 

its role in supporting the EPA’s 

environmental protection agenda, 

and subsequent implications for 

the way NERL conducts business. 

The consistent delivery of highquality, high-impact products 

depends upon developing an 

organization whose components 

function to achieve its mission. 

The first three chapters of this 

framework describe a vision of 

exposure science and the role of 

NERL in achieving the Agency’s 

mission to protect the environment 

and human health. Figure 4-1 

illustrates how the business 

of NERL — the employees, 

resources, and practices — must 

be aligned and in balance with 

the development, production 

and communication of research 

products in order to fulfill that 

vision. Thus, this final section 

will discuss how the concepts of 

exposure science, presented in 

Sections 2.0 and 3.0 and Figure 

3-1, provide the foundation for 

NERL’s research and management 

practices. 

Figure 4-1. Aligning NERL’s business as a Strategy-Focused 

Organization (Adapted from Kaplan and Norton, 2001)

25
The four elements of a strategyfocused organization, outlined 

below, address the direction NERL 

is taking to achieve its mission.

1. Research Products:

We construct and deliver a portfolio 

of relevant exposure research 

programs that are responsive to the 

Agency needs. (To have an impact, 

what must we deliver?)

2. Internal Business Processes:

We use collaborative, creative, and 

efficient processes to implement 

our research. (To succeed, how do 

we carry out our work?)

3. Employee/Organizational 

Capacity: We recruit, retain, 

and develop a work force with 

the competencies needed to lead 

our organization and conduct our 

research. (To achieve our vision, 

what competencies are needed?)

4. Financial Resources 

Management: We allocate our 

resources efficiently and effectively. 

(To achieve our goals, how do we 

efficiently allocate our resources?) 

Developing and maintaining a 

strategy-focused organization at the 

laboratory level will enable NERL 

to achieve its science mission, 

create better solutions though 

linkages, integration, and synergy, 

ensure efficiency of research and 

resources, leverage resources and 

expertise, and provide a stable 

environment for conducting and 

completing research.

4.1 Research Products: To 

have an impact, what must 

we deliver?

For NERL to advance exposure 

research in service to the Agency’s 

mission, the research products 

must be well conceived, well 

executed, and well communicated. 

In this section, we address the 

processes by which we identify 

those strategic research directions 

that will:

 enhance environmental 

protection through a better 

understanding of exposure; 

 construct and execute a critical 

path for research implementation, 

and; 

 translate research into tools and 

communication forms that best 

serve our clients and partners. 

Developing and maintaining a 

strategy-focused organization at the 

laboratory level will enable NERL to 

achieve its science mission.

NERL’s research 

products 

must be well 

conceived, 

well executed, 

and well 

communicated.

26
4.1.1 Developing a Research 

Portfolio

For NERL’s science leadership and 

high-quality responsive research to 

have an impact on environmental 

protection, NERL’s portfolio must 

contain a set of programs that 

address critical exposure science 

needs directly related to the Agency 

goals for air, water, and land 

protection, as well as the health of 

humans and ecosystems. To that 

end, NERL’s research portfolio 

should be developed in alignment 

with ORD’s planning process, 

including the Multi-year Plans 

(MYPs). Developing NERL’s range 

of research programs is a dynamic 

process that entails periodically 

assessing the current programs and 

identifying future areas of research. 

Figure 4-2 (below) outlines the 

factors that are used to evaluate 

potential programs for inclusion in 

our research portfolio. 

Evaluation factors range from 

questions about Agency priorities 

to NERL’s ability to advance the 

state of the science. First and 

foremost, the area of research must 

be essential to EPA’s and ORD’s 

environmental protection mission. 

Also, and of great importance 

to NERL, it must be exposure 

research as articulated within this 

document. Areas that pass though 

these two initial filters are then 

considered in light of several other 

criteria. 

For the many issues that meet 

those broad considerations, any 

decision by NERL to undertake 

a research effort must take into 

consideration the nature and 

scope of the problem, the extent 

to which it is being addressed 

by others, and the likelihood of 

having a significant impact. Does 

NERL bring a unique capability 

Does the research support 

the Agency’s Mission?

Is it exposure research?

The proposed research should meet one or more of the following criteria:

Does it require 

NERL’s expertise or 

unique facilities?

Does it require 

an integrated 

approach that only 

NERL can provide?

Is exposure and 

exposure data an 

integral part of the 

overall research 

question?

Does the scope 

and scale of 

the research 

require NERL’s 

involvement?

Is it a priority research 

area for the Agency?

Is it the right time for 

NERL’s involvement?

Figure 4-2. Evaluation filters and criteria for assessing potential research areas

27
to the issue, either through 

the Laboratory’s expertise or 

through unique facilities that 

are unavailable elsewhere? 

Does it require an integrated 

multidisciplinary program? Some 

research areas are well engaged 

by other organizations and NERL’s 

incremental contribution would 

add marginal value. Alternatively, 

the problems within the area may 

be so broad in scope or generally 

intractable that NERL’s efforts 

would make insufficient headway to 

justify the effort.

Ultimately, a research commitment 

by NERL must be implemented by 

its workforce, requiring that NERL 

have the appropriate workforce 

size, skill mix, and other resources 

to address the issue. 

4.1.2 Designing a Research 

Program

Integrated, multidisciplinary, 

exposure research programs are 

developed for each program area 

in NERL’s portfolio based on the 

principles of exposure science and 

designed to be results-oriented 

and customer-focused. Programs 

should have clear priorities, 

critical paths for meeting each 

priority, and a set of products 

and outcomes that demonstrate 

the research effectiveness. 

Appendix A on page 41 provides 

an overview of how ORD identifies 

the research outcomes required 

by a given Multi-year Plan (MYP). 

This section presents information 

specifically related to developing 

and implementing NERL’s exposure 

research programs to address the 

goals developed in the MYP.

Because EPA is a mission-driven 

Agency, all of ORD research is 

applied. The types of research 

required for environmental 

protection and conducted by 

NERL can be thought of as falling 

into one of two complementary 

categories: core and problemdriven. Core research seeks to 

understand the key biological, 

chemical, and physical processes 

that underlie environmental 

systems, and leads to products 

that may address issues common 

to many EPA programs. Examples 

of core research in NERL include 

efforts to understand exposure and 

factors responsible for exposure, 

as well as research to develop 

predictive models and tools for 

describing exposure pathways of 

stressors in human and ecological 

systems. Problem-driven research 

is directed at specific Agency 

needs that arise due to regulatory 

requirements or court-ordered 

deadlines. In problem-driven 

research, NERL brings existing 

knowledge, tools, models, and 

data to bear on high-priority 

Agency problems, augmented by 

limited, focused research efforts to 

address gaps and deficiencies in 

existing knowledge. An important 

characteristic of problem-driven 

research is that it be packaged 

in forms that are most readily 

communicated to and used by 

the clients, especially program 

offices. As an example of problemdriven research, NERL develops 

analytical methods for identifying 

and defining unregulated drinking 

water contaminants, which informs 

EPA’s Office of Water in setting 

regulatory requirements of the Safe 

Drinking Water Act. By maintaining 

a portfolio that balances core and 

problem-driven research, NERL is 

best able to address the exposure 

science research needs of the 

Agency. 

In all circumstances, research 

programs are initiated by 

first considering the Agency’s 

environmental protection goals 

28
and developing an understanding 

of exposure issues related to 

achieving these goals. As described 

in Chapter 2, the Agency may 

employ exposure science in 

deciding whether mitigation is 

necessary; in determining how best 

to mitigate; and in establishing the 

effectiveness of mitigation actions 

or policies. Below are examples of 

environmental protection questions 

faced by the Agency that illustrate 

each of these perspectives.

 Does exposure to particulate 

matter 2.5 micrometers or smaller 

in ambient air cause death and 

hospitalizations? 

 How should the introduction 

of invasive species through ballast 

water discharge be regulated?

 Have the efforts to control 

mercury in combustion sources 

resulted in a measurable decrease 

in the levels of mercury in the 

environment, leading to reduced 

exposures to humans and 

ecosystems? 

Articulating such questions 

and translating them into 

scientific objectives are the first 

steps in outlining a research 

implementation plan. Overlaying 

these questions onto the source-tooutcome conceptual model helps 

develop the context for the role of 

exposure, assists in constructing 

the critical path for the research, 

and aids in identifying key partners 

and points in integration. Once a 

critical path for achieving those 

scientific objectives is outlined, 

the current limitations of exposure 

science and the critical needs 

for exposure data, methods, and 

models are determined. Should 

the science needs exceed NERL’s 

ability to address them, NERL 

directs its research efforts towards 

those questions that either have the 

greatest uncertainty or provide the 

greatest opportunity for advancing 

science to support exposure and 

risk assessment.

4.1.3 Communicating NERL’s 

Research

Conducting cutting-edge research 

is not enough. To have an impact, 

the results of our research 

programs must be communicated 

to our customers, stakeholders, 

partners, and to the scientific 

community. NERL’s communication 

strategy for research will focus on 

having a high impact in advancing 

environmental protection and the 

state of exposure science. 

To be recognized as leaders 

in the research community, 

NERL scientists must publish 

in high-impact, peer-reviewed 

journals. Other activities such 

as membership in professional 

societies, participation on editorial 

review boards and science advisory 

committees, and development 

of workshops, workgroups and 

committees are also required. 

Communication within the 

scientific community maximizes the 

exchange of ideas and approaches 

to support the Agency’s mission. 

Measures of success in this area 

include peer-reviewed publications, 

reports rated as highly-cited and 

publications rated as 

having high-impact. 

NERL 

must also 

ensure 

that our 

research 

is used by the Agency by delivering 

high-quality, high-impact 

products to our clients. Working 

cooperatively, NERL scientists, 

Division Directors, Associate 

Directors, and Assistant 

Laboratory Directors must 

make certain that NERL 

research products, which 

include peer-reviewed 

software, methods, reports, and 

journal articles, are strategically 

provided to its customers for use 

in their decision-making. NERL 

should promote implementation 

of its tools within the Agency by 

providing workshops, Internet 

downloads, and user manuals that 

advance these tools and models. 

NERL will also demonstrate the 

intended use of its high-quality 

methodology through case studies 

and pilot programs with its 

partners. Finally, NERL should 

track its results against metrics for 

success, including bibliographic 

analysis, citation indices, and 

customer use or satisfaction 

surveys.

29
4.2 Internal Business 

Processes: To succeed, how 

do we carry out our work?

NERL believes that sound science 

can only come out of a sound 

organization — that ultimately 

what we do depends on how 

we do it. Forging an effective, 

responsive research 

organization out of many 

talented individuals and 

geographically-separated 

divisions requires 

a shared, cohesive 

vision of ourselves, 

commitment to a set 

of working principles, 

and the development of 

business practices that 

integrate and leverage our 

capabilities.

4.2.1 Management 

Principles

NERL, as a laboratory, is 

committed to conducting 

high-quality, relevant 

exposure research 

in an integrated, 

multidisciplinary, 

collaborative, and 

effective manner. Our 

management processes 

are crucial to achieving 

this goal and should 

promote our core 

organizational principles. 

The core principles 

that underpin NERL’s 

structures and management 

processes are articulated in the 

following paragraphs.

 We are the National Exposure 

Research Laboratory.

The title NERL embraces several 

important principles. We think 

and act as a single laboratory. We 

provide leadership at national and 

international levels in exposure 

science. Finally, the EPA is the 

client base, thus NERL must 

plan and conduct its research 

based on direct consultation and 

communication with our clients 

within the Agency.

 Science comes first. 

We need to understand where 

we are going with our science, 

and then manage ourselves and 

our resources to get there. As a 

corollary, NERL will develop and 

use only those processes that are 

required to manage its science. 

NERL will not use processes that 

are more complex than needed to 

achieve its science goals.

 Apply multidisciplinary 

approaches where applicable.

The EPA is faced with many 

large, complex problems that 

are often best addressed with 

multidisciplinary research programs 

that use cutting-edge research 

tools. Developing an environment 

that fosters such collaborative, 

multidisciplinary research will 

set us above other organizations. 

This concept applies to research 

we conduct within NERL as well 

as research that is 

conducted across ORD. 

Collaborative research 

allows scientific 

processes to be used 

in understanding 

and managing the 

impact of stressors 

as they move from 

sources to humans and 

ecosystems. This brings 

multiple perspectives 

to a problem for better 

solutions, and provides 

opportunities to leverage 

NERL’s state-of-thescience knowledge and 

skills in multiple areas. 

 Seek functional 

solutions first.

Organizations often 

use structural fixes to 

deal with functional 

problems and this 

usually does not work. 

NERL should be able to 

work within the current 

structure and optimize 

its implementation 

processes to achieve the 

established goals.

 Optimize use of existing 

resources.

NERL has an impressive array 

of resources to accomplish its 

mission. Additionally, the Agency 

has many different high-priority 

problems to address. NERL will 

strive to optimally align its existing 

resources, including staffing, 

with the highest-priority Agency 

problems that require exposure 

science.

30
Basis for Prioritizing Research

 Agency needs

 Ability to demonstrate an impact

 Ability to make a unique

 contribution

 Appropriate balance between

 core and problem-driven

 research

4.2.2 Management Processes

Several processes must be in 

place for NERL to implement 

an optimized cross-laboratory 

research program. These processes 

should allow NERL to fully 

integrate planning across the 

laboratory; optimize use of staff, 

research dollars, and facilities; 

and efficiently manage resources. 

If successfully executed, they 

should serve as a starting point 

for changing the laboratory 

culture and moving forward. 

Importantly, they will allow NERL 

to work together as a laboratory 

to produce relevant, high-quality 

research results. 

Implementation Plans and 

Divisional Business Plans are the 

documents that fully articulate 

what we do and translate into 

how we do it. For those plans to 

be effective, they must be shaped 

and informed by the strategic 

directions as developed above 

and fully integrated across 

the laboratory. Currently, 

Implementation Plans serve 

as the basis for planning and 

should provide the mechanism 

for integration. Each plan is 

intended to develop a focused, 

integrated research program 

that is conducted to solve 

a complex environmental 

problem of national 

significance. The process 

is designed to consider the 

Agency’s highest priority 

needs and NERL’s resources in 

addressing key Agency needs. 

Developing and conducting 

a set of well-integrated 

research programs at 

the laboratory level is an 

optimization challenge. 

Each Implementation Plan 

must direct NERL resources 

to address the high-priority 

exposure associated with an 

environmental problem. The full 

set of plans must optimally deploy 

those resources to move exposure 

science forward. Thus, prior to 

developing individual plans, 

NERL must look across plans to 

prioritize the research and identify 

leveraging opportunities (see text 

box below). It is understood that 

the highest-priority research should 

be resourced first. However, as 

a part of this process, resources 

(staff and FTEs) must also be 

balanced across both divisions 

and plans. The overall goal is to 

ensure that sufficient resources 

are available for successfully 

conducting the most relevant 

and responsive research in those 

areas where NERL plans to make 

a commitment. Understanding 

the priorities and the distribution 

of resources will also allow NERL 

to make informed decisions 

about redirecting resources, 

when needing to respond to new 

initiatives or when faced with 

reduced resources. Finally, NERL 

should use the information on 

science priorities and proposed 

research to direct workforce 

planning (as described in section 

4.3).

A number of non-traditional 

approaches will be needed 

to staff and implement 

multidisciplinary research across 

NERL. The primary goal is to 

ensure that critical expertise is 

provided to all programs across 

the laboratory. Other goals 

include greater efficiency, 

increased collaboration, 

development of new skills and 

capabilities, advancement 

of new technologies, and 

increased scientific leadership. 

Centers of Excellence 

(COE) are envisioned as one 

approach for efficiently using 

critical technical expertise 

in integrated laboratory 

research programs. The 

general concept for a COE is 

based on identifying research 

areas or capabilities of 

common need that present 

opportunities for leveraging 

facilities and experienced 

staff to optimize technical 

performance. Potential areas 

for establishing COEs include 

the development of analytical 

methods and technologies, and 

the application of statistical 

methods and informatics. 

31
In addition to the challenges 

presented by planning and carrying 

out research in a number of highpriority areas, NERL faces the 

challenge of creating integrated, 

multidisciplinary research programs 

across six divisions in four 

locations. NERL has traditionally 

managed much of its research 

at the level of the individual 

researcher or branch; however, 

creating an integrated exposure 

program will require nontraditional 

approaches to management. 

Creating and embracing this 

exposure framework is a 

prerequisite for NERL to function 

as a single national exposure 

laboratory. With a common vision, 

NERL can be unified in purpose 

and in action. The development 

of implementation plans by 

researchers from across NERL, who 

have been challenged to plan from 

a NERL-wide perspective, is also 

essential for creating an integrated 

exposure program. 

Finally, the research, once 

planned, needs to be executed 

in an integrated fashion; across 

disciplines, across the sourceto-exposure pathway, and across 

locations. To that end, NERL is 

exploring organizational practices 

and new technologies that promote 

collaboration and integration, 

such as virtual teams and Webbased communications. As NERL 

moves forward, it is important to 

identify and implement proven 

and time-tested best management 

and organizational practices; to 

seek the counsel of organizational 

leaders and consultants to guide 

the process; and to commit to 

adopting management systems that 

simplify rather than complicate 

laboratory operations. 

4.3 Employee/

Organization Capacity: To 

achieve our vision, what 

competencies are needed?

Achieving NERL’s goals to provide 

leadership in exposure science 

and conduct high-quality science 

to support EPA’s mission requires, 

first and foremost, that we have 

scientists with the necessary 

skills to conduct cutting-edge 

exposure research. We must also 

have a workforce that embraces 

the concept of integrated, 

multidisciplinary research programs 

and that has the flexibility to adapt 

to changing technical demands 

and changing organizational needs. 

Finally, we must develop leadership 

throughout the organization 

to successfully meet today’s 

challenges and the challenges 

of the future. This section will 

discuss the concepts for strategic 

workforce planning and approaches 

for developing our leaders within 

NERL.

4.3.1 Strategic Workforce 

Planning

NERL has a number of challenges 

when developing a strategic 

workforce plan. As with all Federal 

organizations, we have a very stable 

workforce with little staff turnover; 

NERL faces 

the challenge 

of creating 

integrated, 

multidisciplinary 

research programs 

across six divisions 

in four locations.

32
yet we are a scientific organization 

that must keep pace with the 

newest science and changing 

science needs. Thus our planning 

must identify those critical areas 

where we need expertise and the 

number of staff/researchers needed 

in each area. We must also develop 

strategies for providing more 

flexibility within the workforce. 

Finally, we want to identify, 

develop, and reward staff who work 

across organizational boundaries, 

who participate in integrated, 

multidisciplinary research and who 

can adapt to new technologies and 

new problems. 

NERL is a large research 

organization with six divisions in 

four geographical locations. Each 

division has a unique history that 

has led to strengths within various 

scientific disciplines. Nonetheless, 

the workforce within these divisions 

and across NERL as a whole should 

possess a diverse set of skills 

and expertise that can be used to 

address complex exposure research 

questions.

Figure 4-3 (below) depicts the 

varied expertise that will be 

required to address the full 

range of exposure issues for both 

human health and environmental 

protection. The box on the lefthand side of the figure shows 

the scientific expertise needed 

to assess stressors and their 

movement throughout the 

environment. The box on the 

right-hand side shows the 

needed expertise to describe 

the distribution, behaviors, and 

characteristics of the receptor that 

will lead to exposure and dose. 

The box at the bottom of the figure 

shows the technical expertise that 

cuts across disciplines and is used 

to address important exposure 

issues. 

A work force consisting of only 

principal investigators, even if 

all of the required disciplines are 

represented, is not sufficient to 

carry out a program of exposure 

research. In order to provide a 

stable environment for conducting 

and completing our research, NERL 

must develop a self-sustaining 

workforce that can operate 

independently of ORD’s changing 

Figure 4-3. Scientific expertise for exposure research

33
budget. Our staff must include 

both principal investigators and 

staff who can provide technical 

support for these investigators. 

With this approach, all of our 

scientists can still maintain critical 

science programs regardless 

of funding levels. As funding 

increases, additional work can be 

accomplished using extramural 

mechanisms.

A strategic workforce plan should 

evaluate the core science that we 

conduct and the critical expertise 

and numbers of staff (both PIs and 

technical support staff) needed to 

conduct this science. To effectively 

leverage our resources and to 

provide the greatest flexibility, this 

analysis should be done not only 

at the divisional level but also at 

the laboratory level. Structures 

such as the NERL-wide Centers of 

Excellence can be used to maintain 

the intellectual base for the 

expertise that provides technical 

input to all exposure research 

across the laboratory (see lower box 

in figure 4-3). Since the workforce 

in NERL is very stable, we must 

be able to anticipate scientific 

workforce needs five to ten years in 

advance. It is very important that 

our planning also include education 

and training for our current staff 

to insure that everyone has stateof–the-art skills and understands 

how these skills can be applied 

to important exposure issues. 

We must also devise strategies 

for obtaining scientific expertise 

rapidly in new areas as they 

emerge. 

Finally, as we hire new staff, 

we must ensure that our hiring 

strategies identify not only the 

scientific expertise that is required 

but also the core set of traits 

and competencies that our staff 

must possess to be effective 

contributors in NERL. As examples, 

traits and competencies that 

would be consistent with the 

goals set forth in the framework 

would include: commitment 

to NERL’s mission, innovative, 

communicative, professional, 

flexible, forward-thinking, and 

collaborative. Individuals with 

these attributes will enable NERL 

to advance exposure science and 

address the Agency’s most pressing 

environmental protection issues 

through cutting-edge, integrated 

multidisciplinary research.

4.3.2 Leadership Development 

within the Workforce

NERL is its people and every 

individual in the laboratory must 

feel responsible and 

work towards 

its success. 

It is important that NERL’s planning 

include education and training for 

staff to insure that everyone has stateof-the-art skills and understands 

how these skills can be applied to 

important exposure issues.

34
Thus, it is important that we 

develop individual leadership at all 

levels throughout the organization. 

For continued success, we must 

also promote organizational 

leadership by developing our next 

generation of leaders. 

Consistent with the principles of 

a strategy-focused organization, 

leadership development will be 

derived based on the concepts set 

out in the exposure framework, 

which defines who we are, 

what we want to excel 

in, and what we 

want to be 

known for. 

From this starting point, both 

the individual and organizational 

traits and competencies required 

for leadership throughout the 

organization can be identified. 

Individual competencies would 

address scientific, programmatic, 

and organizational leadership. 

Organizational competencies 

would address the direction of the 

organization — what we excel in 

and what we are known for. 

Understanding our direction and 

developing a list of traits and 

competencies for leadership in the 

organization is a critical first step 

toward leadership development 

in NERL. Our leadership vision 

and competencies must then be 

communicated throughout the 

organization, so every individual 

knows what they should be striving 

for in their development efforts. 

Leadership programs specifically 

targeted toward essential traits and 

competencies need to be developed 

and implemented throughout the 

organization. 

Finally, we must mentor, encourage, 

and reward our staff as they develop 

and use the requisite leadership 

skills. To be successful, leadership 

development must be a continual 

process and truly reflect NERL — 

based on who we want to be.

35
4.4 Financial Resources 

Management: To achieve 

our goals, how do we 

efficiently allocate 

resources?

For NERL’s researchers and staff 

to achieve the objectives outlined 

in this framework, they must be 

supported by capital and financial 

resources — buildings and 

equipment, administrative and 

technical support, and an adequate 

budget. This requires the effective 

and efficient allocation of financial 

resources. The need to leverage 

those resources and to promote 

science integration lead us to 

perform that allocation with both 

NERL-wide and division-specific 

perspectives in mind. The business 

plans prepared by each division 

must be developed in concert and 

with complementary 

elements, in 

order 

to achieve the NERL objectives 

of resilience, optimization, and 

integration.

4.4.1 Financial Resilience

Historically, NERL has used its 

financial resources to enhance its 

scientific capabilities, employing a 

number of mechanisms to provide 

research support to its principal 

investigators. As uncertainty 

in budgets has increased and 

effective funding levels decreased, 

NERL has been moving to a model 

of supporting research with inhouse staff. During the transition, 

extramural funds will continue to 

support in-house research as well 

as address high-priority acquisition 

needs. Funds that support in-house 

research are provided to divisions 

in a manner that reflects the 

size, productivity, and disciplinespecific demands of its investigator 

workforce, whereas the priorities 

for extramural acquisitions 

are determined as part 

of the ORD planning 

process.

4.4.2 Optimization and 

Integration

The optimal distribution of 

financial resources across NERL 

should both sustain the critical 

scientific capabilities to advance 

exposure research and promote 

the integration of organizations 

and scientific disciplines to 

that end. Research planning 

— at both the strategic and 

implementation levels — lays the 

critical path for NERL research. 

Planning collectively promotes 

the transparent and effective 

deployment of budgetary resources 

at each stage of that critical 

path. Similarly, the acquisition 

and maintenance of cutting-edge 

facilities and instrumentation are 

essential to a high-performing 

workforce. Planning for large 

capital investments, then, must 

align with the highest priority 

research as well as the potential for 

collaborative use of the facilities 

and instruments.

36
Any decision by NERL to undertake a research 

effort must take into consideration the nature 

and scope of the problem, the extent to which it 

is being addressed by others, and the likelihood of 

having a significant impact.

37
Integrated, multidisciplinary, exposure 

research programs are developed for each 

program area in NERL’s portfolio based on 

the principles of exposure science and designed 

to be results-oriented and customer-focused.
References

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Buxton, H.T., 2002. Pharmaceuticals, Hormones, and Other Organic Wastewater 

Contaminants in U.S. Streams, 1999-2000: A National Reconnaissance. 

Environmental Science and Technology, vol. 36, no. 6, p. 1202-1211. 

NRC, 1983. Risk Assessment in the Federal Government: Managing the Process. The 

National Academies Press, Washington, DC.

NRC, 1998. Research Priorities for Airborne Particulate Matter: I. Immediate Priorities 

and a Long-Range Research Portfolio. The National Academies Press, Washington, 

DC.

NRC, 2004. Air Quality Management in the United States. The National Academies Press, 

Washington, DC.

NRC, 2006. Human Biomonitoring for Environmental Chemicals. The National Academies 

Press, Washington, DC.

NRC, 2007. Models in Environmental Regulatory Decision Making. The National 

Academies Press, Washington, DC.

Underwood, A., 2007. Rivers of Doubt. Newsweek, 149(23):58, 60.

USEPA, 1992. Guidelines for Exposure Assessment. U.S. Environmental Protection 

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

USEPA, 1998. Guidelines for Ecological Risk Assessment. U.S. Environmental Protection 

Agency, Washington, DC, EPA/630/R-95/002F.

USEPA, 2003. Framework for Cumulative Risk Assessment. U.S. Environmental Protection 

Agency, Washington, DC, EPA/600/P-02/001F.

USEPA, 2004. Air Quality Criteria for Particulate Matter. U.S. Environmental Protection 

Agency, Washington, DC, EPA 600/P-99/002aF-bF.

Zartarian, V., Bahadori, T., McKone, T., 2005. Adoption of an Official ISEA Glossary. 

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39
Creating and embracing this 

exposure framework is a prerequisite 

for NERL to function as a single 

national exposure laboratory. With 

a common vision, NERL can be 

unified in purpose and in action.
The EPA’s research agenda is 

determined by means of a research 

planning process involving every 

organizational level within the 

Agency. Figure A-1 is a simplified 

diagram for this process. ORD’s 

research is driven by the five 

Agency goals described in the U.S. 

EPA’s Strategic Plan (www.epa.gov/

ocfo/plan/plan.htm). Within each 

goal, ORD works in partnership with 

numerous stakeholders to identify 

the highest priority research 

topics. The objective is to focus 

on environmental problems that 

pose the greatest risk to people 

and the environment; to reduce 

uncertainties which will improve 

our ability to identify risks; and to 

clearly help the Agency fulfill its 

regulatory mandate. For each goal, 

ORD commits to reaching certain 

milestones and delivering specific 

products within a given time 

period. 

ORD’s Multi-Year Plans (MYP) 

provide the long-term (5 to 10 year) 

focus for a given area of research, 

integrating efforts across all of 

ORD’s Labs and Centers. For each 

MYP, an ORD team conceptualizes 

a framework for the research 

with long-term goals that will be 

addressed across ORD. NERL plays 

a vital role in the development of 

the MYPs. All of NERL’s research 

is included in these plans, and the 

Laboratory is held accountable for 

meeting commitments contained in 

MYPs. 

NERL develops research 

Implementation Plans, using 

ORD’s MYPs as roadmaps. The 

Implementation Plans bring the 

planning process to the operational 

level within the Laboratory. 

Separate plans are developed 

for each of ORD’s MYPs and are 

intended to develop focused and 

integrated programs. For each 

Implementation Plan, steering 

committees made up of scientists, 

Associate Laboratory Directors, 

and Managers within NERL and 

across the Agency are charged 

with identifying the important 

programmatic research questions. 

Scientists across the Laboratory 

are then tasked with developing 

specific research programs to 

address these questions.

In summary, while the problems 

NERL is tasked to solve are defined 

by the Agency’s planning process, 

the research agenda for solving 

those problems is determined by 

NERL and its staff. Although the 

relative emphasis in topic areas 

may change as ORD priorities 

and budgets shift, substantial 

efforts are made by NERL to build 

and maintain research programs 

that are relevant to the scientific 

problems and responsive to the 

Agency needs. 

Appendix A

NERL’s Research Within the Context of ORD

Sets

national

environmental

goals

Establishes research

priorities; formulates

critical scientific questions,

long-term goals, and

major milestones

Maps out research agenda in context

of ORD priorities; identifies critical paths

Devises approaches for

addressing scientific uncertainties

Conducts research; postulates hypotheses and 

develops/uses methodologies to test hypotheses

EPA

ORD

NERL

Division

Scientist

Congress

Promulgates Environmental Statutes

Strategic Plan

Multi-Year

 Plan

Research

 Implementation Plan

Research Plan

Projects

Figure A-1. Research planning in EPA

41
BOSC ...................................................... Board of Scientific Counselors

COE .....................................................................Centers of Excellence

EPA..................................................... Environmental Protection Agency

FTE........................................................................ Full Time Employee

MYP..............................................................................Multi-year Plan

NERL ......................................... National Exposure Research Laboratory

NHEERL.. National Health and Environmental Effects Research Laboratory

NRC .............................................................National Research Council

NRMRL ..........................National Risk Management Research Laboratory

ORD............................................... Office of Research and Development

PI ........................................................................ Principal Investigator

RfD.............................................................................. Reference Dose

TMDL............................................................Total Maximum Daily Load

USEPA ............................United States Environmental Protection Agency

Acronyms

42