NNational Center for Environmental Assessment CEA

U.S. Environmental Protection Agency 

Office of Research and Development 

EPA/600/F-08/010 | www.epa.gov 
 

EPA’s National Center for Environmental Assessment (NCEA) is a leader in the science of human health and ecological risk assessment, a process used to determine how pollutants or other stressors may impact human health and the environment. 

NCEA occupies a critical position in EPA’s Office of Research and Development (ORD) between researchers in other parts of 

ORD and outside of EPA who are generating new findings and data and the regulators in EPA’s Program Offices and Regions 

who must make regulatory, enforcement, and remedial action decisions. NCEA prepares technical reports and assessments that 

integrate and evaluate the most up-to-date research and serve as major elements of the science foundation supporting EPA policies. NCEA also conducts cutting-edge research to develop innovative quantitative risk assessment methods and tools that help 

extrapolate between experimental data and real-world scenarios, improve our understanding of uncertainties, and facilitate careful weighing of evidence. 

NCEA’s workforce is our strength—its scientists are recognized internationally for their expertise in toxicology, epidemiology, 

biology, chemistry, and statistics. NCEA scientists serve on many federal government workgroups that are addressing critical 

environmental challenges and questions. 

Examples of NCEA’s major efforts include: 

•	 Conducting human health risk assessments and managing EPA’s Integrated Risk Information System (IRIS) 

(http://www.epa.gov/iris) 

•	 Producing Integrated Science Assessments for reviews of the National Ambient Air Quality Standards 

(NAAQS) (http://www.epa.gov/ncea/isa) 

•	 Providing human health and ecological risk assessment research, methods, guidelines, training materials, and 

technical support to EPA’s Program Offices and Regions and the public (http://www.epa.gov/ncea/risk) 

•	 Developing methods for integrating, deriving, and synthesizing cause and effect relationships for use in 

impairment investigations and risk assessments (http://www.epa.gov/caddis) 

•	 Providing scientific information and decision tools to resource managers, policy makers, and other stakeholders in order to support them as they decide whether and how to respond to global climate change

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

•	 Preparing EPA’s Report on the Environment ( http://www.epa.gov/ncea/roe) 

For more information, see NCEA’s Web site at http://www.epa.gov/ncea 

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www.epa.gov/ncea 

National Center for Environmental Assessment 

Who We Are & What We Do 
www.epa.gov/ncea 

NCEA Ensures National Air Quality Standards 

Consider Best and Most Recent Science 

Integrated Science Assessments 

Clean air is an important goal in implementing EPA’s 

mission of protecting public health and the environment. NCEA supports this mission by creating the 

scientific assessments that underlie development 

of the National Ambient Air Quality Standards 

(NAAQS). These ambient or outdoor air pollution 

standards protect public health and the environment 

from adverse effects caused by six principal air 

pollutants, including ozone and particulate matter, 

known as the “criteria” air pollutants (see box). It 

is essential for the standards to be based on the best 

and most current scientific information. Scientists 

worldwide are conducting research and publishing 

their findings about the health and environmental 

effects of air pollutants, with about 100 new articles 

in the published literature each month. As findings 

emerge, NCEA evaluates this new science and often 

re-interprets the existing information base to prepare 

the Integrated Science Assessments (ISAs), to provide 

the scientific basis for EPA’s decisions on retaining or 

revising the air quality standards. This is an essential 

part of executing the Clean Air Act (CAA) mandate 

to “accurately reflect the latest scientific knowledge 

useful in indicating the kind and extent of identifiable effects on public health and the environment which may be expected 

from the presence of [a] pollutant in ambient air.” 

How Do Integrated Science Assessments Use the Latest Science? 

NCEA scientists identify, evaluate, integrate, and assess the most up-to-date and policy-relevant science for the criteria air 

pollutants, documenting their analyses in the ISAs, previously called Air Quality Criteria Documents. Through review of scientific findings from atmospheric chemistry, physics, epidemiology, toxicology, ecology, and exposure research for the six criteria 

pollutants, NCEA ensures that the basis for decisions on air quality standards reflect the best science available from all of these 

disciplines. After conducting a literature review, which includes consideration of thousands of multidisciplinary publications, 

NCEA identifies key information, performs new, focused analyses as needed, and integrates this scientific evidence to address 

the most policy-relevant questions at EPA. NCEA’s goal is to meet the Clean Air Act requirement for a 5-year review cycle 

for each of the criteria pollutants. All ISAs are subjected to a rigorous and extensive peer review by the Clean Air Scientific 

Advisory Committee, which consists of noted experts appointed by the EPA Administrator to comment on the technical quality 

of the NAAQS reviews. 

Using the Latest Exposure Science for ISAs 

Because humans breathe a variable mixture of clean air and pollutants from many outdoor and indoor sources all day, it can 

sometimes be difficult to separate pollutant sources and isolate specific effects. NCEA’s research and state-of-the-science 

assessments on ambient-level pollutant identification techniques and exposure processes have helped exposure scientists make 

NCEA’s Integrated Science Assessments 

for the Six “Criteria” Air Pollutants 

•	 Ground-level Ozone—AQCD final in 2006 

•	 Lead—AQCD final in 2006 

•	 Particulate Matter—ISA-Criteria draft is currently 

under review in 2009 

•	 Carbon Monoxide—AQCD final in 2000, 

Workshops for next review cycle started in 2008 

•	 Nitrogen Dioxide—ISA-Health Criteria final in 

July 2008 and ISA for Oxides of Nitrogen and 

Sulfur - Environmental Criteria final in 2008 

•	 Sulfur Dioxide—ISA-Health Criteria final in 

September 2008 and ISA for Oxides of Nitrogen 

and Sulfur - Environmental Criteria final in 

2008 

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better and more accurate estimates of what groups and individuals actually breathe. NCEA scientists then use these exposure 

estimates to help epidemiologists interpret data on effects measured in studies conducted throughout the U.S. and the world. 

These data are then used in analyses and assessments NCEA makes using the measurements of the actual concentrations of 

outdoor pollutants along with an understanding of the uncertainties in these measurements to assess the strength of causality or 

association between exposures and effects. 

Using the Most Up-to-Date Epidemiology in ISAs 

Human epidemiological studies provide the most compelling evidence for 

the regulation of air pollutants because direct effects on human health can 

be quantified. Careful integration and interpretation of results from a large 

number of human studies, while considering the complexity of the information they provide, is needed to assess public health risks. Epidemiological 

studies can provide direct evidence for or against the need to revise or retain 

a standard for a criteria air pollutant. During the NAAQS review process, 

NCEA scientists consider the strengths and limitations, consistency, and 

robustness of the available evidence to describe the health effects of criteria 

pollutants, assess the concentrations at which health effects are observed, and

identify susceptible populations. 

Interpretation of Clinical Studies in ISAs 

The criteria air pollutants (see box above) for which the NAAQS are written 

benefit from a long series of controlled human exposure studies where ozone, particulate matter, or sulfur dioxide, for example, 

are given to human subjects in controlled doses. This puts the criteria pollutants at a real advantage over some other environmental pollutants because the interpretation and assessment of human health effects from real ambient exposures can be easier 

with these controlled exposures, lessening the need for extrapolation from complex animal experiments, or control of possible 

confounding elements. NCEA scientists evaluate these controlled human studies where they are available and have published 

results of their reanalyses to better inform the scientific basis for decision-making on the standards. 

Improved Understanding through Research and Information Management 

In recognition of the tremendous importance of air quality to public health and the environment, EPA has implemented a 

substantial research program related to air quality. This and other research programs produce research findings that are essential 

to understand and integrate in the ISAs. To support effective assessments, NCEA has designed and is now implementing a 

state-of-the-science information management system, the Health and Environmental Research Online (HERO) data base 

system. 

Scientific Integration to Inform Decisions 

The great extent and diversity of information available on the criteria air pollutants presents a challenge to risk assessors. Of 

key importance is to integrate information from clinical, human exposure, epidemiological and animal toxicology studies to 

provide a coherent and comprehensive understanding of the nature and magnitude of human health effects posed by these 

pollutants. NCEA has developed and applied a coherent framework to draw conclusions on causality (i.e., the nature and 

likelihood of adverse effects to be caused by exposure) and to characterize the levels at which such effects may occur. This 

comprehensive integration provides the internationally recognized fundamental scientific basis for establishing the national 

ambient air quality standards. 

For More Information 

EPA’s Air Quality Criteria Documents / Integrated Science Assessments Web site: http://www.epa.gov/ncea/isa 

EPA’s NAAQS Web site: http://www.epa.gov/ttn/naaqs/ 

Recent science assessments in 

which the NCEA review and integra -

tion of the evidence from epidemio -

logical studies was critical include: 

•	 Air Quality Criteria for Ozone

and Related Photochemical 

Oxidants (Final 2006) 

•	 Air Quality Criteria for

Particulate Matter (Final 2004) 

•	 Air Quality Criteria for Lead

(2006) 

Clean Air Research Program: http://www.epa.gov/ord/npd/cleanair-research-intro.htm 

U.S. Environmental Protection Agency 6/09 

Office of Research and Development 

Integrated Science Assessments 
www.epa.gov/ncea 

Report on the Environment 

EPA’s Report on the Environment: 

Answering Key Questions about U.S. Health 

and Environment 

EPA’s 2008 Report on the Environment (2008 ROE) compiles 

the most reliable indicators currently available to answer 23 

questions of critical importance to EPA’s mission and the 

nation’s environment. The questions are divided into five 

topics: air, water, land, human health, and ecological condition. The report presents 85 indicators— numerical values 

derived from actual measurements of a stressor, state or 

ambient condition, exposure, or human health or ecological 

condition over a specified geographic domain, whose trends 

over time represent or draw attention to underlying trends in 

the condition of the environment. 

With help and data from NOAA, USDA, Department of the 

Interior, and other agencies and private sector collaborators, 

NCEA scientists led a team from across EPA’s Program and 

Regional offices that developed the report, reviewed and 

updated indicators from the 2003 Draft ROE, developed new 

indicators, and screened them against the new 2008 ROE 

indicator definition and criteria. Each indicator underwent 

extensive external peer review and public comment before 

being incorporated into the 2008 ROE. The report itself was 

subjected to internal EPA and interagency review, followed 

by independent peer review by EPA’s Science Advisory 

Board as well as public comment. Following final revisions, 

EPA’s 2008 ROE was released to the public on May 20, 2008. 

NCEA also has been working across the Agency to improve 

the utility of the ROE for Agency planning and decisionmaking, and with colleagues from European and North 

American environmental offices to improve environmental 

reporting and to advance indicator science. 

What Are the Findings in the Report on the 

Environment? 

The 2008 ROE compiles the most reliable indicators 

incorporating the latest available data to help track critical 

trends in the environment and human health. The report also 

identifies key limitations of these indicators and gaps where 

reliable indicators do not yet exist. These gaps and limitations 

highlight the disparity between the current state of knowledge 

and the goal of full, reliable, and insightful representation 

of environmental conditions and trends, and they provide 

direction for future research and monitoring efforts. 

Examples of Key Questions Addressed in 

EPA’s 2008 Report on the Environment 

What are the trends in outdoor air quality 

and their effects on human health and 

the environment? 

What are the trends in extent and condition 

of fresh waters and their effects on human 

health and the environment? 

What are the trends in land cover and 

their effects on human health and the 

environment? 

What are the trends in health status in the 

United States? 

What are the trends in the extent and distribution of the nation’s ecological systems? 

U.S. Environmental Protection Agency 

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Percent reduction in native fish species diversity in the contiguous U.S. 

from historical levels to 1997-2003a

Percent of area 


in each category 

15% 7% 

55% 

2% 

21% 

Percent reduction


in species:
 

0%


>0 to <10% a

Data are displayed by 6-digit hydrologic unit code (HUC) watershed. Percent reduction is based on the 10 to <25% number of native species present during the period 1997-2003, compared with historical numbers 25 to <50% documented prior to 1970. A speciesis considered “present” if there is at least one record of its presence

50% in any 8-digit HUC within the 6-digit HUC. 

Fishless Data source: NatureServe, 2006 

Report on the Environment 

Examples of Indicators Presented in EPA’s Report on the Environment 

Air: emissions and ambient concentrations of carbon monoxide, lead, particulate matter, nitrogen 


oxides, ozone, volatile organic compounds, green house gases, and acid deposition
 

Water: stream flows, nitrogen and phosphorus, pesticides in streams, wetland extent, hypoxia in the 


Gulf of Mexico, fish tissue contaminants, and sediment quality 


Land: land cover, forest extent and type, quantity of municipal and hazardous solid waste generated, 


and fertilizer used for agriculture
 

Human Health: mortality, life expectancy at birth, infant mortality, cancer incidence, asthma prevalence, 

birth defects, preterm delivery, blood levels for lead, mercury, cadmium, persistent organic pollutants, 

and cotinine, and urinary levels of pesticides and phthalates 

Ecological Condition: land cover, forest extent and type, urbanization and population change, coastal 


benthic communities, birds, harmful algal bloom outbreaks, U.S. and global mean temperature, sea 


surface temperature, and sea level
 

Examples of the findings in the 2008 ROE 

include: 

• Blood lead levels show a steady decline 

since the 1980s. 

• Continuing annual declines have been 

seen in indicators of hazardous waste 

generation and all air emissions indicators 

with the exception of greenhouse gases. 

• Moderate or high disturbances of bottom 

invertebrate communities have been found 

in approximately 1/3 of benthic coastal 

communities and 2/3 of wadeable streams. 

• Between 2002 and 2007, there has been a 

45% decline in the number of high priority 

clean-up sites with spreading goundwater 

contamination. The map of the U.S., from the 2008 Report on the Environment shows the percent reduction in 

native fish species diversity from 1970 to 1997-2003. These data are part of the Fish Faunal 

Intactness Indicator in the Report on the Environment. Watershed covering about one-fifth 

(21 percent) of the area of the contiguous U.S. appear to have fish faunas that are fully intact, 

retaining the entire complement of fish species that were present before 1970. Watersheds 

covering nearly a quarter (24 percent) of the area have lost 10 percent or more of their native 

fish species. 

What Are Future Plans for 

the Report on the Environment? 

It is NCEA’s goal to utilize the internet in 

order to provide timely updates for indicators 

and produce new editions of the ROE every 4 years and to time updates with the Agency’s strategic planning process. New 

editions will reflect revisions or additions to the key questions, updates and revisions of the indicators, and addition of new 

indicators. An electronic version of the report, the e-ROE, has provided users with the ability to navigate and query the report 

and additional content. It will be updated on an ongoing basis to keep the ROE content as current as possible. 

For More Information 

EPA Report on the Environment 2008 Home Page: http://www.epa.gov/ncea/roe 

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www.epa.gov/ncea 

IRIS: An Influential and High Quality Source 

of Health Effects Information for Chemical 

Risk Assessment 

IRIS 

When conducting human health risk assessments that 

support decisions on air emissions, water discharges, 

or contaminated site clean-ups, risk assessors need 

high quality, peer reviewed information about human 

health effects that may result from exposure to 

chemical pollutants. More often than not, they use 

the EPA’s Integrated Risk Information System (IRIS), 

a Web-based database of chemical assessments and 

quantitative toxicity values that have been developed 

by EPA and undergone rigorous peer reviews. 

NCEA is responsible for preparing the IRIS 

assessments, managing the peer review process, and 

maintaining the online database. The main purpose of 

IRIS is to meet EPA statutory, regulatory, or program 

implementation needs, with special emphasis on 

chemicals of high interest to the public or other 

levels of government. Because of the high quality 

of its assessments, IRIS is used widely beyond EPA, 

including internationally. 

What is IRIS’ Role in Protecting 


Human Health? 


IRIS values are used in combination with site-specific 

exposure information and, as such, play an essential 

role in protecting human health. By incorporating 

available scientific research findings into a comprehensive assessment, IRIS provides information that 

risk assessors and managers can use to assess risk 

and make decisions. Information in IRIS is a key part 

of evaluating the potential for adverse health effects 

from exposure to chemicals in the environment, and 

IRIS assessments can have broad impact in the form 

of regulatory—and other—decisions made by risk 

managers. IRIS provides data for the human health 

hazard identification and dose-response assessment 

phases of chemical risk assessments and includes 

information about cancer or non-cancer endpoints 

depending on the availability and quality of toxicological and epidemiological data. This information 

can be used in combination with exposure information 

to characterize the public health risks of a particular 

substance in a given situation. Many environmental 

stakeholders—EPA programs and regions, state and 

local governments, federal and international agencies, 

U.S. Environmental Protection Agency 

Office of Research and Development 

“The documents [produced for IRIS] are the gold 

standard in risk assessments performed by program 

offices, other federal agencies, states, and even 

international organizations.” 

EPA Board of Scientific Counselors 

ORD Human Health Risk Assessment Research Program Review

April 2008 

Health Effects Information Available on IRIS 

Carcinogenicity information: 

A cancer slope factor is a plausible upper bound, 

approximating a 95% confidence limit, on the increased 

cancer risk from lifetime exposure to an agent by 

ingestion. This estimate, usually expressed in units of 

proportion (of a population) affected per mg of substance/ 

kg body weight-day, is generally reserved for use in the 

low-dose region of the dose-response relationship 

An inhalation unit risk is a plausible upper-bound, 

approximating a 95% confidence limit, on the increased 

lifetime cancer risk estimated to result from continuous 

exposure to an agent at a concentration of 1 μg/m3 in air. 

Cancer assessments also include a qualitative weight-ofevidence characterization which describes the likelihood 

that a chemical may cause cancer in humans and the 

conditions where carcinogenic effects might be expressed. 

Non-cancer information: 

A reference dose (RfD) is an estimate of a daily oral 

exposure to the human population (including sensitive 

subgroups) that is likely to be without an appreciable risk 

of harmful effects over a lifetime. 

A reference concentration (RfC) is an estimate of a 

continuous inhalation exposure to the human population 

(including sensitive subgroups) that is likely to be without 

an appreciable risk of harmful effects during a lifetime. 

EPA Board of Scientific Counselors 

ORD Human Health Risk Assessment Research Program Review

April 2008 

EPA’s IRIS Web site receives over 20,000 hits a day 

from readers in over 150 countries. 

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What Are Future Plans for IRIS? 

EPA’s NCEA will continue to update IRIS and add new assessments to ensure it continues as a trusted key resource for 

chemical risk assessors. In addition, NCEA plans to update IRIS assessments that are more than 10 years old, when new studies 

are available to support a revised toxicity value. NCEA will incorporate new assessment and modeling tools into IRIS as they 

are adequately developed and peer reviewed. 

For more information 

Integrated Risk Information System (IRIS) Web site: http://www.epa.gov/iris 

IRIS Hot line: http://www.epa.gov/iris/comments.htm 

EPA’s Risk Website: http://www.epa.gov/risk/ 

U.S. Environmental Protection Agency 6/09 

Office of Research and Development 

Examples of IRIS Assessments 

Benzene—widely used as an 

industrial solvent, an intermediate in 

chemical synthesis, and a component 

of gasoline 

The assessment supported U.S. EPA’s Office of Air and Radiation, Office 

of Mobile Sources’ Final Rule: Control of Hazardous Air Pollutants from 

Mobile Sources (2007) which set new standards that establish controls on 

gasoline, passenger vehicles, and gas cans to reduce emissions of benzene 

and other mobile source air toxics. 

Diesel engine exhaust—mix of gas 

and particle pollutants emitted from 

diesel engines 

NCEA’s Health Assessment Document for Diesel Engine Exhaust has 

informed EPA efforts to reduce pollution from diesel engines. A March 

2008 rule set standards to reduce emissions from locomotive and marine 

diesel engines by up to 90 percent. EPA also requires reductions in 

pollution from new heavy-duty trucks and buses. Starting in 2006, diesel 

fuel contains 97 percent less sulfur. 

Boron and compounds—boric acid 

and sodium salts of boron are used 

for a variety of industrial purposes 

and as fire retardants, laundry 

additives, fertilizers, herbicides, and 

insecticides 

First IRIS assessment to use data-derived adjustment factors rather 

than using default uncertainty factors. Uncertainty factors are used in 

the derivation of non-cancer toxicity values that account for variation in 

susceptibility among the human population, uncertainty in extrapolating 

animal data to humans, and other uncertainties. Data-derived adjustment 

factors provide better estimates of uncertainty compared to traditional 

default uncertainty factors. 

IRIS 

industry, and non-governmental organizations—use risk assessment to inform decisions to protect public health, such as 

determining allowable levels of contaminants in drinking water. 

The process for developing IRIS assessments is scientifically rigorous and collaborative, involving several rounds of scientific 

review. Toxicologists, biologists, health scientists, epidemiologists, and statisticians develop the assessments using available 

scientific findings from the peer-reviewed literature. Biologically based mathematical models and data on mode of action 

by which chemicals exert their toxic effects are used to answer questions about the human relevance of animal studies, to 

extrapolate between animals and humans, to identify and assess sensitive subpopulations, and to select appropriate methods 

to extrapolate from experimental doses to the generally low doses that people may encounter in their environments. Because 

the assessments must reflect EPA’s opinion, they undergo in-depth reviews by scientists throughout the Agency. The draft 

assessments also receive review by scientists in other federal agencies and by highly-qualified independent external experts 

whose scientific disciplines are appropriate for the chemical under review. On occasion, an assessment may be reviewed by 

independent expert panels formed by the National Research Council of the National Academy of Sciences. The public also has 

opportunities to comment on draft assessments and contribute data. 

IRIS contains information on more than 540 chemicals. Each year, EPA publishes in the Federal Register a list of ongoing and 

new assessments. NCEA solicits nominations for new and updated assessments from the public and within EPA. Assessments 

are updated as new scientific information or methods evolve that could significantly change IRIS information. 

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NCEA’s Global Change Research Program provides critical information to improve society’s ability to effectively respond to 

the risks and opportunities presented by global change. The program addresses the potential consequences of global climate 

change on air and water quality, aquatic ecosystems, human health, and socioeconomic systems in the United States. It also 

generates decision-support tools for resource managers coping with a changing climate. These products are used by EPA, 

communities, states, and others in adapting to climate variability and change. 

The impacts of global change effects are often unique to a location such as a watershed or municipality. EPA’s Global Change 

Research Program emphasizes a place-based approach to respond to global change issues particular to a given area. As a 

result, partnerships are established with locally-based decision makers to ensure that the program is responsive to their unique 

scientific information needs and the socioeconomic realities at their locales. At the same time, NCEA scientists are working 

to advance assessment science and develop more general approaches to adaptation that can be applied at multiple scales 

and locations. 

What Are NCEA’s Major Contributions 

to Global Change Research? 

The Global Change Research Act of 1990, directs 

agencies to “produce information readily usable 

by policymakers attempting to formulate effective 

strategies for preventing, mitigating, and adapting 

to the effects of global change” and to undertake 

periodic scientific assessments. The 13 Federal 

agencies that make up the U.S. Climate Change 

Science Program are developing a series of 21 

synthesis and assessment products (SAPs) in 

response to the mandate of the U.S. Climate Change 

Science Program’s Strategic Plan (2003). NCEA 

scientists are lead authors for two of the SAPs. 

The Global Change Research Program has three 

major areas of emphasis: air quality, water quality/ 

aquatic ecosystems, and human health impacts from 

global change. NCEA scientists are involved in 

a multi-lab collaboration that assesses the consequences of global change for U.S. air quality. NCEA 

also evaluates the sensitivity to climate change of 

water quality goals and the opportunities available 

within the provisions of the Clean Water Act and 

the Safe Drinking Water Act to address anticipated 

impacts. For example, NCEA scientists are engaged 

in assessments covering a range of aquatic ecosystems and issues including coral reefs, watersheds, 

estuaries, biocriteria and aquatic invasive species. 

These efforts are done in collaboration with the 

Office of Air and Radiation and the Office of Water. 

NCEA Scientists Are Lead Authors on Synthesis

and Assessment Products (SAPs)

SAP 4.4: Preliminary Review of Adaptation Options 

for Climate-sensitive Ecosystems and Resources

The report explains seven “adaptation approaches” 

for six resource areas: national parks, national 

forests, national wildlife refuges, wild and scenic 

rivers, estuaries, and marine protected areas, which

can be used to maintain or increase the resilience

of ecological systems to climate change. 

SAP 4.6: Analyses of the Effects of Global Change 

on Human Health and Welfare and Human 

Systems

The report focuses on impacts of global climate 

change on three broad dimensions of the human 

condition: human health, human settlements, and 

human welfare. The report examines potential

impacts of climate change on human society, 

opportunities for adaptation, and associated

recommendations for addressing data gaps and 

near- and long-term research goals. 

Health impacts that stem from climate change and associated changes in air and water quality also are evaluated by NCEA. For 

example, NCEA participated in the Health Sector Assessment of the Global Change Research Program’s Climate Change 

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 www.epa.gov/ncea 

NCEA’s Global Change Research Program: 

Assessing the Impacts of Climate Change 

Global Change 
Global Change 

Impacts on the United States. As a result, NCEA scientists evaluated direct 

heat effects with respect to mortality, morbidity, violence, and hospital 

visits and climate impacts on aeroallergens. 

In addition to assessments, NCEA develops interactive decision-support 

tools that support informed discussion of climate variability and change. 

For example, the Climate Assessment Tool provides users of EPA’s 

BASINS 4.0—a multi-purpose environmental analysis system that integrates a geographical information system (GIS), national watershed data, 

and modeling tools—the capability to examine climate sensitivities and 

impacts. NCEA also is developing a set of GIS-based population and land 

use projections. This project, Integrated Climate and Land Use Scenarios 

(ICLUS) provides scientists and decision makers a national data base of 

county-level population and land use changes through 2100 which are 

designed to be consistent with the Intergovernmental Panel on Climate 

Change’s Special Report on Emission Scenarios. Combined with information on changing climate and environmental conditions, these projections 

allow users to assess future impacts of climate change. 

What Are Future Plans for the Global Change 

Research Program? 

NCEA will continue to be actively involved in the Interagency Climate 

Change Science Program. NCEA will also continue to advance assessment science by developing innovative interactive tools for understanding 

local scale systems and their sensitivities. The long-term goal of NCEA’s 

efforts is to provide the approaches, methods, and models to quantitatively 

evaluate the effects of global change on air and water quality, associated 

impacts on aquatic ecosystems and human health and adaptive responses to 

ameliorate adverse consequences of these changes. 

For More Information 

NCEA’s Global Change Program: 

http://www.epa.gov/ncea/global.htm 

EPA’s Climate Change Program: http://www.epa.gov/climatechange/ 

EPA Global Change Research Program: 

http://www.epa.gov/ord/npd/globalresearch-intro.htm 

U.S. Climate Change Science Program: 

http://www.usgcrp.gov/usgcrp/ 

NCEA’s Global Change-Related 

Water Quality and Aquatic 

Ecosystems Reports 

•	 A Screening Assessment of the

Potential Impacts of Climate 

Change on Combined Sewer 

Overflow (CSO) Mitigation in the 

Great Lakes and New England 

Regions 

•	 Climate and Land Use Change 

Effects on Ecological Resources 

in Three Watersheds: A 

Synthesis Report 

•	 Climate Change Effects on

Stream and River Biological 

Indicators: A Preliminary 

Analysis 

•	 Climate Change and Interacting

Stressors: Implications for Coral 

Reef Management in American 

Samoa 

•	 Effects of Climate Change on

Aquatic Invasive Species and 

Implications for Management 

and Research 

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www.epa.gov/ncea 

Risk Assessment Tools 

NCEA Methods, Models, and Databases Provide 

the Scientific Basis for Improved Health 

and Ecological Risk Assessments 

What types of human health problems are caused by 

substances in the environment? How likely is it that 

ecological resources, such as watersheds, will experience degradation when exposed to different amounts 

of a pollutant? How severe is the potential harm likely

to be? These are examples of key questions addressed 

in risk assessments conducted by scientists at the U.S. 

EPA. Risk assessments provide decision makers with 

the scientific information they need to make informed 

decisions about actions that may be taken to protect 

human health and the environment. 

Scientists at NCEA conduct cutting edge research 

to develop innovative and quantitative risk assessment tools that combine knowledge about biology, 

physiology, toxicology, ecology and statistics. They 

are continually working to create and enhance 

methods, models, and databases that inform EPA risk 

assessments. State-of-the-art tools and data help risk 

assessors extrapolate between experimental data and 

real-world scenarios, characterize uncertainties, and 

facilitate careful weighing of evidence. 

NCEA’s dose-response assessment tools help characterize the risk of an adverse effect in humans at a 

specified dose. Exposure assessment tools help determine the potential sources of a chemical, pathways 

(e.g., inhalation vs. ingestion) leading to exposure, 

and the magnitude and duration of contact with the 

substance. Ecological risk assessment tools support 

decision making to address ecological concerns such 

as degradation of surface waters due to pollution. The guidance and tools highlighted here represent only a few of the entire 

library that are available on NCEA’s Web site, www.epa.gov/ncea. 

Risk Assessment Methods 

NCEA scientists are world leaders in developing and applying novel, state-of-the-art risk assessment methods. They are EPA 

leaders in methods development, chairing and participating in many cross-agency workgroups. For example they have contributed significantly to framework documents that identify key issues to consider for different types of risk assessments (e.g., 

for metals, for children) and ways to address those issues. They have also contributed to the development of risk assessment 

guidelines that offer more specific procedural information (e.g., Guidelines for Carcinogen Risk Assessement, Guidelines for 

Ecological Risk Assessment). While the guidances do not mandate exactly how assessments should be developed, they provide 

EPA and other risk assessors with rigorously-vetted approaches that help improve the quality, consistency and use in decision 

making of their assessments. 

Dose-Response Modeling Highlights 

Benchmark Dose (BMD) Modeling Software provides data-management tools and a user-friendly interface to support application of different mathematical models to fit a dose-response dataset. This software is extremely important since it is used in all 

of EPA’s Integrated Risk Information System (IRIS) assessments, which provide the scientific basis for many regulatory and 

public health decisions. The BMD approach can be used for both non-cancer and cancer dose-response assessments. 

Figure 1—Dose response with N = 10 Figure 2—Dose response with N = 50 

Fraction AffectedFraction Affected 

Gamma Multi-Hit Model Gamma Multi-Hit Model 

0 

0.2 

0.4 

0.6 

0.8 

1 

0 50 100 150 200 

dose 

Gamma Multi-Hit 

0 

0.2 

0.4 

0.6 

0.8 

1 

0 50 100 150 200 

dose 

Gamma Multi-Hit 

NOAEL 

NOAEL 

BMDL BMD BMDL BMD 

This graphic illustrates how the NOAEL is highly dependent 

on sample size, and how the BMD approach addresses 

this limitation. In this example, identical dose-response 

data points from toxicology studies with different sample 

sizes are shown. Figure 1 shows observed response and 

statistical confidence limits for response levels in a study 

that tested 10 animals at each dose level, and Figure 2 

shows the same observations for 50 animals tested at each 

dose level. The NOAEL derived from the study using fewer 

animals is higher compared to the NOAEL from the study 

with greater statistical confidence. The BMD approach 

fits a curve to the data and estimates a response rate that 

more appropriately reflects the uncertainty due to smaller 

sample size. 

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Risk Assessment Tools 

It is more informative than the traditional approach of using a no observed adverse effect level (NOAEL) or lowest observed 

adverse effect level (LOAEL) as the basis for dose-response assessment. In the BMD approach, the risk assessor fits a flexible 

curve to the dose-response data and uses the results to select a dose level that is associated with a predetermined benchmark 

response, such as a 10% increase in the incidence of a particular toxic effect. The BMD approach uses more information 

provided in reports of toxicological studies, and provides more information to risk assessors, than the NOAEL/LOAEL 

approach, and is preferred when suitable data sets are available. The NCEA BMD web-based modeling tools provide a significant benefit to the international risk assessment community. 

Physiologically based pharmacokinetic (PBPK) models use available measured physiological data to more accurately 

characterize how the body absorbs, metabolizes, distributes, stores, and excretes a chemical and predict the internal dose of 

the chemical at specific target organs. NCEA scientists published guidance for applying PBPK models in human health risk 

assessments and quantifying the impact of age-related and other inter-individual differences that may affect health risk. This is 

an innovative and cutting-edge approach that reduces uncertainty in risk assessments and is now used routinely in IRIS assessments when suitable data are available. 

Methods and Guidance for Assessing Chemical Mixtures 

In real world scenarios, people are not exposed to one chemical at a time—rather, they experience myriad exposures on a daily 

basis. To address this fact, NCEA has developed methods and guidance to evaluate exposure to mixtures from environmental 

media such as drinking water, air and soil. NCEA scientists have conducted research and published methods that address these 

real world exposure scenarios by quantifying chemical mixture exposures and estimating potential health risks resulting from 

these exposures. 

Exposure Assessment Tools 

The Exposure Factors Handbook is an important resource developed by NCEA that provides key information for nearly 

all exposure assessments conducted by EPA. It contains statistical data on factors such as drinking water consumption, soil 

ingestion, inhalation rates, dermal factors including skin area and soil adherence factors, consumption of fruits and vegetables, 

fish, meats, dairy products, homegrown foods, breast milk intake, human activity factors, consumer product use, and residential 

characteristics. This information is used in risk assessments to calculate human exposure to contaminants. Values are recommended for the general population and for various segments of the population who may have characteristics different from 

the general population. The Child-Specific Exposure Factors Handbook consolidates child specific data into one resource, and 

the Example Exposure Scenarios Tool provides outlines of scenarios to demonstrate how to best use the data in the Exposure 

Factors Handbook. NCEA released a revised and expanded version of the Child-Specific Exposure Factors Handbook in 

September 2008 and a revised and expanded version of the Exposure Factors Handbook will be available in draft form in 2009. 

Ecological Risk Assessment Tools 

Two cutting-edge ecological tools include the Causal Analysis/Diagnosis Decision Information System (CADDIS) and the 

Integrated Climate and Land Use Scenarios (ICLUS). CADDIS allows watershed managers to determine what has caused 

impairment in a water body with a web-based suite of resources. ICLUS provides scientists with a means to assess future 

impacts of climate change on different land use scenarios. For more information on CADDIS and ICLUS please see the fact 

sheets entitled CADDIS and NCEA’s Global Change Research Program. 

For More Information 

EPA NCEA Human Health Guidelines Web Page: http://www.epa.gov/ncea/healthrisk.htm 

EPA NCEA Ecological Guidelines Web Page: http://www.epa.gov/ncea/ecorisk.htm 

EPA’s Benchmark Dose Software (BMDS) Web Page: http://www.epa.gov/ncea/bmds 

EPA NCEA Human Health Risk Tools Web Page: http://www.epa.gov/ncea/risktools.htm 

EPA NCEA Chemical Mixtures Risk Assessment Guidance Web Page: 

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

EPA NCEA Physiologically Based Pharmacokinetic (PBPK) Web Page: http://www.epa.gov/ncea/pbpk 

EPA Exposure Factors Handbook Web Page: http://www.epa.gov/ncea/efh 

EPA Child-Specific Exposure Factors Handbook Web Page: http://www.epa.gov/ncea/child 

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CADDIS: A Tool to Help Scientists Identify 

Causes of Degradation of Streams and Rivers 

Causal Analysis/Diagnosis Decision Information System 

Watershed management scientists turn into environmental detectives when streams, rivers, or wetlands become so impacted 

by human activities that there are observable effects on plant and animal life. The scientists need to determine what stressor 

or stressors are causing harmful effects so that effective solutions can be developed and implemented. To unravel these environmental mysteries, NCEA, working with colleagues from the Agency’s Office of Water (OW), Regional offices, and other 

ORD laboratories created the Causal Analysis/Diagnosis Decision Information System (CADDIS), an online resource that 

helps scientists find, access, organize, use, and share information to determine what has negatively affected the ecology of the 

water body. 

CADDIS is built upon EPA’s Stressor Identification process, which is a formal method for identifying causes of impairments 

to aquatic ecosystems. The system includes a step-by-step guide to conducting a causal analysis, example worksheets, and 

informative material on several commonly encountered candidate causes. CADDIS also has a conceptual model library 

for common stressors, including phosphorus, a nutrient that can lead to harmful algal blooms and other effects when high 

levels are discharged into aquatic systems. The system features advice on how to use specific data analysis methods and 

manage data for a causal assessment, downloadable data analysis tools, and other information sources, such as databases of 

stressor-response information. 

In What Situations Would CADDIS Be 

Helpful and How? 

Observations that might prompt the use of 

CADDIS include: 

• kills of fish, invertebrates, plants, or other 

wildlife or domestic animals 

• anomalies in any life form, such as tumors, 

lesions, parasites, or disease
 

• altered community structure, such as the absence, 

reduction, or dominance of a particular species 

or group 

• loss of species or shifts in abundance 

• response of indicators designed to monitor or 

detect biological, community, or ecological 

condition (e.g., Index of Biotic Integrity or 

Invertebrate Community Index) 

• changes in the reproductive cycle, population 

structure, or genetic similarity 

• alteration of ecosystem function, such as nutrient 

cycles, respiration, and photosynthetic rates
 

• alteration of the aerial extent and pattern of 

different ecosystems (e.g., shrinking wetlands 

or change in the mosaic of open water, wet 

meadows, sandbars, and riparian shrubs 

and trees) 

The name CADDIS 

recognizes the caddis 

fly’s role as a frequently 

used bioindicator for 

detecting impacts of 

aquatic pollutants. 

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Regarding the benefit of using CADDIS: 

“...the Stressor Identification procedure provided a 

clear, easily understandable format for us to explain 

and support our conclusions. Our ability to present 

the results of our analysis in a form that was understandable to both scientists and non-scientists. 

I believe was critical to the ultimate adoption 

and approval of the TMDL [Total Maximum Daily 

Load—the maximum amount of a pollutant that a 

water body can receive and still meet water quality 

standards and an allocation of that amount to the 

pollutants sources].” 

Lee Dunbar, 

Connecticut TMDL/WQS program 
EPA’s Stressor Identification Framework Used in 

Management Action: 

Eliminate or Control Sources, Monitor Results 

Biological Condition Restored or Protected 

CADDIS 

Detect or Suspect Biological Impairment 

Stressor Identification 

Evaluate Data from the Case 

Identify Probable Cause 

Evaluate Data from Elsewhere 

List Candidate Causes 

Define the Case 

Identify and Apportion Sources 

Decision-maker 

and 

Stakeholder 

Involvement 

As Necessary: 

Acquire Data, 

and 

Iterate Process 

Causal Analysis/Diagnosis Decision Information System 

• CADDIS provides the following basic information on 8 common candidate 

causes of biological impairment:
	

»	 what to consider (e.g., sources and site evidence) when deciding whether 

to include stressors as candidate causes 

»	 ways to measure stressors 

»	 relevant literature reviews 

»	 conceptual model diagrams showing linkages among stressors and their 

potential sources and effects 

CADDIS brings together significant amounts of information in an efficient and 

effective way. It helps state and local water quality managers develop TMDLs 

designed to address pollutants contributing to biological impairment in streams. 

It assists watershed managers with planning and coordination of data collection, 

best management practices, and technology solutions to address the causes and 

sources of impairment. 

Common Candidate Causes 

of Biological Impairment 

in Aquatic Ecosystems 

Excess metals 

Increased sedimentation 

Excess nutrients 

Low dissolved oxygen 

High temperature 

Altered ionic strength 

Flow alteration 

Unspecified toxic chemicals 

What Are Future Plans for 

CADDIS? 

NCEA scientists plan to develop improved 

versions of CADDIS based on user input 

and feedback. These plans include adding 

modules for deriving empirical stressorresponse relationships, stressor-specific 

tolerance values and databases, syntheses of 

relevant literature and statistical methods, 

candidate cause summaries, and conceptual 

models. NCEA also plans to add more case 

studies, including those relevant to terrestrial 

systems, with links to relevant CADDIS 

pages and capabilities for user input. 

For More Information 

EPA’s Causal Analysis/Diagnosis Decision 

Information System (CADDIS) Web Page: 

http://www.epa.gov/caddis 

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www.epa.gov/ncea 

National Emergencies 

NCEA Responds: Technical Assistance 

for Emergency Response and Recovery 

Environmental emergencies involve sudden increased threats to public health and the environment from the release or potential 

release of hazardous materials due to accidents or natural or man-made disaster events. They happen without warning, and 

the need for environmental assessment is acute. The environmental questions add to the anxiety and loss of the more obvious 

physical damage. As soon as the dust begins to settle, many scientific questions need to be addressed quickly. How should 

sampling be conducted to measure exposure levels quickly and accurately? How significant are the risks to public health (e.g. 

first responders, clean-up personnel, residents) and the environment? Are proposed clean-up and recovery methods effective 

and when is it safe for re-entry by the public? 

Scientists in NCEA help respond to these questions by providing on-call technical support to emergency response and recovery 

personnel in the EPA’s Office of Solid Waste and Emergency Response and EPA regions who are primarily responsible for 

coordinating EPA’s emergency response programs. 

Hurricanes Katrina and Rita 

NCEA scientists and managers contributed to EPA’s 

environmental and human health impact assessment 

of the aftermath of Hurricanes Katrina and Rita in the 

Gulf Coast region in 2005. NCEA scientists partici

pated in an interagency workgroup on guidance 

and standards for local officials, and they provided 

critical internal peer reviews of water and sediment 

sampling and analysis plans and public communica

tion materials. The ability of NCEA scientists to 

respond quickly to internal EPA requests for scientific 

expertise helped EPA and other Federal Agencies 

make better decisions in these crisis situations. 

Elevated Lead in Washington, DC 

Drinking Water 

In 2004 and 2005, the District of Columbia Water 

and Sewer Authority detected high levels of lead 

in numerous samples of residential drinking water. 

NCEA scientists evaluated the potential impacts on 

children’s blood lead levels and analyzed risks for 

a “highly exposed” subpopulation of infants who 

consumed reconstituted formula prepared with tap 

water. Results from the health assessment helped 

inform response actions by local officials, such as 

issuance of public health advisories, replacement of 

many lead water pipes throughout the city, and corrosion control measures. The assessment results were 

used by EPA’s Office of Water and EPA Region 3 in 

communicating risk to Washington, DC residents. 

Due to control treatments that have been 

House with Asbestos Cement Shingles Water Contamination and Debris 

er at Empire landfill in 

uemine parish 

Massive Debris Pile for Grinding and 

Incinerations 

Debris Grind

Plaq

Clean up of debris from Hurricane Katrina generated 

health concerns because debris from older buildings 

may contain asbestos and lead. ORD scientists 

developed a methodology to assess risks from the 

release of these hazardous substances in trial testing 

of grinding and burning (incineration) technologies 

that potentially will be used to manage the debris. 

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National Emergencies 

implemented, DC is now in compliance with safe drinking water act requirements, and risks to children from lead in drinking 

water have been reduced. 

Collapse of the World Trade Center 

In the days following the attack on the World Trade Center towers on September 

11, 2001, EPA initiated numerous air monitoring activities to better understand 

the impact of emissions from that disaster. Using these data, NCEA scientists 

conducted a screening of the potential for risk to the general population associ

ated with off-site inhalation exposure of emissions in the aftermath of the attack. 

This assessment did not address exposures and potential impacts that could have 

occurred to rescue workers, firemen, and other site workers nor did it consider 

indoor exposures. NCEA’s work resulted in important analyses that could 

improve EPA’s responses to future national emergencies. 

Asbestos Contamination in Libby, Montana 

In 1999, an EPA Emergency Response Team went to Libby to investigate local 

concerns about asbestos-contaminated vermiculite that is mined in the town. 

Vermiculite is a mineral that, when heated, pops creating pockets of air that make 

it suitable for use as insulation or as a soil amendment. The asbestos contamina

tion in Libby is a distinct form of asbestos. Since 1999, EPA has been working 

closely with the community to clean up contamination and reduce risks to human 

health. EPA conducted a screening level risk assessment in 2001, and NCEA 

scientists are currently working on a toxicity assessment specific to the unique 

asbestos in Libby, Montana. This assessment will ensure EPA’s site clean-up in 

Libby, MT, is protective of human health. This work has broad scale implications 

because 80 percent of the world’s vermiculite was produced from the Libby mine 

and the materials were processed in over 200 locations across the United States. 

What Are Future Plans for Incidence Response? 

NCEA scientists will continue to provide advice and scientific support to EPA 

Program Offices, Regions, and the Emergency Response Program when envi

ronmental crises arise. By building experience with real-world situations, NCEA 

scientists are developing innovative approaches for exposure assessments and risk 

assessments that will be applicable to natural and man-made disasters. 

For More Information 

EPA Response to 2005 Hurricanes Web Page: http://www.epa.gov/katrina/ 

EPA NCEA World Trade Center Response Web Page: 

http://www.epa.gov/ncea/wtc.htm 

EPA Region 3 Lead in Drinking Water Web Page: http://www.epa.gov/dclead/ 

EPA Region 8 Libby Asbestos Web page: 

http://www.epa.gov/region8//superfund/libby/index.html 

Superfund Health Risk Technical Support Center (STSC) Hot Line: 513-569-7300 

NCEA’s Superfund Health Risk 

Technical Support Center 

This hotline resource is used 

by EPA regional and program 

office hazardous waste site 

managers to obtain the latest 

information on health risks 

from toxic substances. There 

are over 1,500 sites on 

Superfund’s National Priorities 

List that require site assess -

ment and clean-up. When 

toxicity values are not avail -

able in EPA’s Integrated Risk 

Information System (IRIS) 

database, NCEA can provide 

Superfund risk assessors with 

provisional peer-reviewed 

toxicity values for specific 

chemicals as requested. The 

hotline responds to about 250 

calls a year. All assistance 

is provided on a rapid turnaround basis. 

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SCIENCE

Office of Research and Development 

National Center for Environmental Assessment 

Washington, DC 20460 

June 2009 

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