U.S. Environmental Protection Agency 

Washington, DC 20460 

EPA/600/R-07/045F 

May 2008 

2008 EPA’s Report on the Environment 

Recycled/Recyclable–Printed with Vegetable Oil Based Inks on 100% Postconsumer, Process Chlorine Free Recycled Paper 
DISCLAIMER 

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. 

Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 

Preferred Citation: 

U.S. Environmental Protection Agency (EPA). (2008) EPA’s 2008 Report on the Environment. National Center for Environmental 

Assessment, Washington, DC; EPA/600/R-07/045F. Available from the National Technical Information Service, Springfield, VA, and 

online at http://www.epa.gov/roe. 

EPA will update the environmental indicators presented in this report when data become available. Please visit the electronic report at 

www. epa.gov/roe for the most up-to-date information on the Report on the Environment. 
iii

Message from the Assistant Administrator 

for Research and Development 

I am pleased to present EPA’s 2008 Report on the Environment (ROE). 

This report compiles, in one place, the most reliable indicators currently 

available to answer key questions about trends in human health and the 

condition of the nation’s environment. 

EPA’s 2008 Report on the Environment demonstrates the importance of 

scientifically sound information to help us understand the state of the 

environment, identify areas of concern, and monitor progress. We can all 

celebrate the fact that our air is cleaner, our water is purer, and our land is 

better protected than it was just a generation ago. Today, we are beginning 

to measure just how much progress we have made. Though we once 

took our environment for granted, we now understand the importance 

of environmental quality for our future. Much work remains to be done, 

however, and we must continue to build on our record of progress. 

I thank the many EPA staff members from every program and Region; our 

federal, tribal, state, and local government partners; and the independent 

scientists and research institutions who contributed to this report. The 

2008 ROE represents the culmination of an effort that began in 2001 

when EPA embarked on a bold initiative to assemble, for the first time, 

indicators of national conditions that are important to the Agency’s mission 

to protect human health and the environment. EPA first presented this 

information in its 2003 Draft Report on the Environment. We have since 

revised and refined the ROE in response to feedback from EPA’s Scientific 

Advisory Board and our stakeholders, and we have updated the indicators 

to reflect the latest available data. 

EPA’s 2008 Report on the Environment is part of an important national 

dialogue on how we can improve our ability to assess the nation’s 

environmental quality and human health, and how we can use that 

knowledge to better manage for measurable environmental results. 

I invite you to participate in this dialogue with us and our partners. 

Your comments and feedback are essential to our future efforts. 

George Gray, Ph.D. 

Science Advisor and 

Assistant Administrator for 

Research and Development 
Acknowledgements


Development of this report was a collaborative effort that could not have been 

accomplished without the substantial commitment of many people, both inside 

and outside EPA. EPA thanks the following individuals and organizations for their 

contributions to this effort. 

ROE Leads 

Denice Shaw – Project Lead (EPA)


Peter Preuss – Director, 


National Center for Environmental 


Assessment (EPA)


Core ROE Team 

Arden Calvert (EPA)


Cynthia Curtis (EPA)


Danelle Lobdell (EPA)


Guy Tomassoni (EPA)


Heather Case (EPA)


James Canavan (EPA)


Jay Messer (EPA)


Julie Damon (EPA)


Macara Lousberg (EPA)


Maricruz MaGowan (EPA)


Marjorie Jones (EPA)


Michael Hadrick (EPA)


Monica Jones (EPA)


Patricia Murphy (EPA)


Rebecca Calderon (EPA)


William Nickerson (EPA)


EPA Office/Region Leads 

Ann Williamson (EPA)


Barbara Klieforth (EPA)


Beth Walls (EPA)


Brenda Groskinsky (EPA)


Carmen Maso (EPA)


Debra Forman (EPA)


Gerard Bulanowski (EPA)


Matthew Hoagland (EPA)


Michelle Hiller-Purvis (EPA)


Nicoletta DiForte (EPA)


Nora McGee (EPA)


Randolph Perfetti (EPA)


Richard Sumpter (EPA)


Ronald McHugh (EPA)


Stuart Kerzner (EPA) 

Vance Fong (EPA) 

William Rhea (EPA) 

Winona Victery (EPA) 

Contributors 

Adam Sapp (LUMCON)


Alan Herlihy (EPA)


Andrea Cherepy (EPA)


Anne Grambsch (EPA)


Anne Keller (EPA)


Anne Marsh (Heinz Center)


Anne Pope (EPA)


Arthur Flaks (EPA)


Barry Burgan (EPA)


Belinda Hawkins (EPA)


Bill Wilber (USGS) 


Brad Schultz (EPA)


Brad Smith (USDA Forest Service)


Bruce Stein (NatureServe)


Carrie Knowlton (ASPH/EPA Fellow)


Charles Aloe (ASPH/EPA Fellow)


Charles Maurice (EPA)


Cheryl Pressley (EPA)


Chris Davis (CommEnSpace)


Chris Zervas (NOAA)


Cindy Heil (Florida Fish and Wildlife 


Research Institute)


Claudia Walters (EPA)


Coe Owen (EPA) 


Colleen Haney (EPA)


Collin Homer (USGS)


Cpan Lee (EPA)


Dan Axelrad (EPA)


Dan Petersen (EPA)


David Hrdy (EPA)


David Mintz (EPA)


David Schmeltz (EPA)


Deborah Burgin (EPA)


Dennis Beauregard (EPA)


Dennis Doll (EPA)


Devon Payne-Sturges (EPA)


Dick Reynolds (NOAA)


Donna Myers (USGS)


Doreen Vetter (EPA)


Douglas Solomon (EPA)


Elizabeth Corr (EPA)


Elizabeth Jackson (EPA)


Ellen Tarquinio (EPA)


Eric Leuliette (NOAA)


Erik Winchester (EPA)


Ethan McMahon (EPA)


Ethel Brandt (EPA)


Fred Dimmick (EPA)


Gilberto Alvarez (EPA)


Grace Smith (EPA)


Gretchen Smith 


(University of Massachusetts)


Heather Shoven (EPA)


Henry Lee (EPA)


Henry Schuver (EPA)


Hope Pillsbury (EPA)


Ingrid Sunzenauer (EPA)


James Hemby (EPA)


James Wickham (EPA)


Jan Moneysmith (EPA) 


Jane Leggett (EPA)


Jason Samenow (EPA)


Jawauna Greene (EPA)


Jay Lawrimore (NOAA)


Jeanne Allen (EPA)


Jeff Cohen (EPA)


Jennifer Margolies (EPA)


Jessica Smith-Armstrong (EPA)


Jim Afghani (EPA)


Jim Cabot (EPA)


iv 
Jim Pendergast (EPA)


John Coulston (USDA Forest Service)


John Macauley (EPA)


John Richardson (EPA)


John Stoddard (EPA)


John Van Sickle (EPA)


Jon Schweiss (EPA)


Jonathan Hall (EPA)


Joseph Greenblott (EPA)


Katherine Dowell (EPA)


Kenneth Dixon (EPA)


Kent Cavender-Bares (Heinz Center)


Kevin Summers (EPA)


Kurt Riitters (USDA Forest Service)


Lael Butler (EPA)


Lara Akinbami (CDC)


Larry Master (NatureServe)


Larry Reisman (EPA)


Larry Starfield (EPA)


Laura Nielsen (EPA)


Lawrence Martin (EPA)


Leanne Stahl (EPA)


Lee Kyle (EPA)


Linda Heath (USDA Forest Service)


Linda Young (University of Florida)


Marc Pitchford (NOAA)


Margaret Sheppard (EPA)


Mark Sather (EPA)


Mark Tedesco (EPA)


Mary Christman (University 


of Florida)


Mary White (EPA)


Melanie Hoff (EPA)


Melanie Magee (EPA) 


Michael McDonald (EPA)


Michael Rylko (EPA)


Motria Caudill (EPA)


Myra Price (EPA)


Nancy Baker (USGS)


Nancy Rabalais (LUMCON)


Nancy Wentworth (EPA)


Neil Burns (EPA)


Nicole Paquette (EPA)


Nita Sylvester (EPA)


Phil Kaufmann (EPA)


Phil Lorang (EPA)


Philip Jalbert (EPA)


Priscilla Halloran (EPA)


Ravi Rao (EPA)


Renee Dagseth (EPA)


Richard Haeuber (EPA)


Richard Norris (EPA)


Rick Durbrow (EPA)


Robin O’Malley (Heinz Center)


Rona Birnbaum (EPA)


Roseanne Lorenzana (EPA)


Roy Simon (EPA)


Ruth Knapp (EPA)


Sean Hogan (EPA)


Sherri White (EPA)


Stan Meiburg (EPA)


Steve Montzka (NOAA)


Steve Nerem (University of Colorado)


Steve Paulson (EPA)


Susan Holdsworth (EPA)


Suzanne Annand (EPA)


Tamara Saltman (EPA)


Thomas Armitage (EPA)


Thomas Forbes (EPA)


Tim Lewis (EPA)


Tim Wade (EPA)


Tom Dahl (Fish and Wildlife Service)


Tom Loveland (USGS)


Tom Smith (NOAA)


Tony Olsen (EPA)


Tracey Miller (EPA)


Tracey Woodruff (EPA)


Velu Senthil (EPA)


Veronica Blette (EPA)


Vipul Bhatt (EPA)


Virginia Engle (EPA)


Walter Schoepf (EPA)


Wen Huang (USDA)


Environmental Indicators 

Steering Committee 

Bharat Mathur (EPA)


Clifford Gabriel (EPA)


Donald Welsh (EPA)


Ed Chu (EPA)


George Gray (EPA) (Co-chair)


Hal Zenick (EPA)


Ira Leighton (EPA)


Jerry Clifford (EPA)


John Reeder (EPA)


Kathy O’Brien (EPA)


Kimberly Nelson (EPA)


Linda Travers (EPA)


Louise Wise (EPA)


Maryann Froehlich (EPA)


Mike Shapiro (EPA)


Molly O’Neill (EPA) (Co-chair)


Norm Neidergang (EPA)


Ray Spears (EPA)


Rob Brenner (EPA)


Ron Kreizenbeck (EPA)


William Sanders (EPA)


Indicator Peer Reviewers 

Anitra Pawley 

Bailus Walker 

David Fairley 

Debra Reinhart 

George Hepner 

George Hidy 

Hans Paerl 

James Carlisle 

James Listorti 

John Day 

Kevin Armbrust 

Kevin Civerolo 

Lawrence Kapustka 

Lyle Chinkin 

Lynn Goldman 

N. Scott Urquhart 

P. Barry Ryan 

Robert Pojasek 

Stanley Gregory 

Steven Bartell 

Terry Spittler 

William Creal 

2007 Science Advisory 

Board Panel 

Aaron Cohen 

Alan Steinman 

Allan Legge 

Barry Wilson 

Chi-Yeung John Suen 

David Dzombak 

Deborah Neher 

Deborah Swackhamer (Chair) 

Dennis Grossman 

Duncan Patten 

Fred Benfield 

Gary Sayler 

George Lambert 

Henry Anderson 

Judith Weis 

M. Granger Morgan 

v 
Maria Morandi 

Mark Borchardt 

Philip Hopke 

Ramesh Reddy 

Robert Twiss 

Timothy Buckley 

2003 Science Advisory 

Board Panel 

Alan Steinman 

Ann Marie Gebhart 

Arturo Keller 

Charles Kolb 

Cynthia Warrick 

George Lambert 

John McManus 

Joseph Bunnell 

Joseph Helble 

Kathryn Saterson 

Maria Morandi 

Mark Bain 

Mark Schwartz 

Norman LeBlanc 

Oswald Schmitz 

Peter Scheff 

Philip Bromberg 

Stephen Trombulak 

Timothy Buckley 

Virginia Dale (Chair) 

Interagency Reviewers 

Al Cobb (DOE)


Anthony Swift (DOT)


Benjamin Simon (DOI)


Camille Mittelholtz (DOT)


Christine McDonald (OMB)


Claudia McMurray (State of 


California)


Drue Barrett (CDC)


Edward Stern (DOL)


Edwin Foulke (DOL)


Edwin Pinero (OFEE)


Hodayah Finman (DOS)


Jack Kaye (NASA)


Janet Irwin (OMB)


Jens Svenson (DOL)


John (Jack) Brellenthin (TVA)


Kevin Neyland (OMB)


Kimberly Miller (OMB)


Marge Cavanaugh (NSF)


Mark Bashor (CDC)


Mary Glackin (NOAA)


Maureen Dunn (TVA)


Patricia Ferrebee (OSD)


Rex Geveden (NASA)


Shawn Alam (DOI)


Shelia Newton (NIH)


Ted Heintz (CEQ)


Teresa Fryberger (OSTP)


Captain Todd Stiles (NOAA)


Vijam Rai (DOI)


Willie Taylor (DOI)


Woodie Kessel (DHHS)


Communications and 

Publications 

Crystal Samuels (EPA) 

Linda Bailey-Becht (EPA) 

Linda Tuxen (EPA) 

Maureen Johnson (EPA) 

Melissa Anley-Mills (EPA) 

Robert Cassell (EPA) 

Contractor Support 

Team Leads 

Eastern Research Group, Inc. (ERG) 

Chris Lamie 

Jan Connery (Project Manager) 

Jenny Helmick 

John Wilhelmi 

Linda Cook 

Naida Gavrelis 

Ross & Associates 

Environmental Consulting, Ltd. 

Nancy Tosta 

Menzie-Cura & Associates, Inc. 

Charles Menzie 

vi 
Contents


1 Introduction ............................................................................. 1-1


2 Air 

2.1	 Introduction ............................................................. 2-3


2.2	 What Are the Trends in Outdoor Air Quality and Their Effects on 


Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6


2.3	 What Are the Trends in Greenhouse Gas Emissions and Concentrations?................... 2-62


2.4 What Are the Trends in Indoor Air Quality and Their Effects on Human Health?.............. 2-73


3 Water


3.1	 Introduction ............................................................. 3-3


3.2	 What Are the Trends in the Extent and Condition of Fresh Surface Waters 


and Their Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6


3.3	 What Are the Trends in the Extent and Condition of Ground Water 


and Their Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25


3.4	 What Are the Trends in the Extent and Condition of Wetlands 


and Their Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30


3.5	 What Are the Trends in the Extent and Condition of Coastal Waters 


and Their Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35


3.6	 What Are the Trends in the Quality of Drinking Water and Their Effects on Human Health? . . . . . 3-52


3.7	 What Are the Trends in the Condition of Recreational Waters 


and Their Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-57


3.8	 What Are the Trends in the Condition of Consumable Fish and Shellfish 


and Their Effects on Human Health? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-59


4 Land 

4.1	 Introduction ............................................................. 4-3


4.2	 What Are the Trends in Land Cover and Their Effects on Human Health and the Environment? ... 4-5


4.3	 What Are the Trends in Land Use and Their Effects on Human Health and the Environment? .... 4-13


4.4	 What Are the Trends in Wastes and Their Effects on Human Health and the Environment? ...... 4-23


4.5	 What Are the Trends in Chemicals Used on the Land and Their Effects on Human Health 


and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29


4.6	 What Are the Trends in Contaminated Land and Their Effects on 


Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42


5 Human Exposure and Health 

5.1	 Introduction ............................................................. 5-3


5.2	 What Are the Trends in Human Exposure to Environmental Contaminants, 


Including Across Population Subgroups and Geographic Regions? . . . . . . . . . . . . . . . . . . . . . . . 5-7


5.3	 What Are the Trends in Health Status in the United States? . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31


5.4	 What Are the Trends in Human Disease and Conditions for Which Environmental Contaminants 


May Be a Risk Factor, Including Across Population Subgroups and Geographic Regions? ....... 5-39


6 Ecological Condition 

6.1	 Introduction ............................................................. 6-3


6.2	 What Are the Trends in the Extent and Distribution of the Nation’s Ecological Systems?........ 6-7


6.3	 What Are the Trends in the Diversity and Biological Balance of the Nation’s Ecological Systems? . 6-18


6.4	 What Are the Trends in the Ecological Processes That Sustain the Nation’s Ecological Systems? . . 6-27


6.5	 What Are the Trends in the Critical Physical and Chemical Attributes 


of the Nation’s Ecological Systems? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31


6.6	 What Are the Trends in Biomarkers of Exposure to Common Environmental Contaminants 


in Plants and Animals? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45


7 Afterword................................................................ 7-1


Appendix A Acronyms and Glossary ............................................................. A-1


Appendix B Development of EPA’s 2008 ROE.................................................... B-1


Appendix C Comparison of Indicators Used in EPA’s 2008 ROE and the 2003 Draft ROE ............... C-1


CHAPTER 1

EPA’s 2008 Report on the Environment 1-1

T

o accomplish its mission, the U.S. Environmental Protection Agency (EPA) must pay close attention to trends in 

the condition of the nation’s air, water, and land, and to 

associated trends in human exposure and health and the condition of ecological systems. Data on environmental trends serve 

two key purposes: they provide valuable input to EPA in developing its strategic outlook and priorities, and they allow EPA 

and the public to assess whether the Agency is succeeding in its 

overall mission to protect human health and the environment. 

EPA prepared this Report on the Environment (ROE) to accomplish these purposes. 

In 2001, EPA embarked on a bold initiative to assemble, for 

the first time, an extensive set of environmental indicators that 

are important to its mission. EPA presented these indicators in 

its Draft Report on the Environment Technical Document, released 

in 2003. Since then, EPA has revised, updated, and refined the 

ROE in response to scientific developments and to feedback 

from public stakeholders and EPA’s Science Advisory Board 

(SAB). EPA’s 2008 Report on the Environment presents the 

results of this work. 

The 2008 ROE compiles, in one place, the most reliable 

indicators currently available to answer 23 questions that EPA 

believes are of critical importance to its mission and the nation’s 

environment. The indicators are supported by data gathered 

from federal and state agencies and non-governmental organizations. All of the indicators were peer-reviewed to meet exacting 

standards for accuracy, representativeness, and reliability. This 

2008 ROE presents trends wherever adequate data are currently 

available, and it establishes reliable national baselines where they 

are not. Equally important, the report identifies key limitations 

of these indicators and gaps where reliable indicators do not 

yet exist. This report does not propose actions to reduce data 

limitations or fill gaps, nor does it analyze the costs and benefits 

of doing so. 

1. Introduction

Chapter 1
CHAPTER 1

1-2 EPA’s 2008 Report on the Environment

Written for a broad range of environmental professionals, the 

ROE provides the technical foundation for two other components of EPA’s ROE project: 

•	 EPA’s 2008 Report on the Environment: Highlights of National 

Trends, which presents highlights of the ROE that EPA 

believes would be of significance to the interested public. 

•	 An electronic version of the ROE (the e-ROE, available 

at http://www.epa.gov/roe), which provides online access 

to printable versions of both reports, as well as to the data, 

methodology, references, and sources of additional information behind the indicators presented in the ROE. 

EPA is committed to periodically updating the ROE and 

its component indicators so that the latest information on 

environmental status and trends is available to EPA, external scientists, and interested members of the public on a 

long-term basis. 

Organization of This Report

Exhibit 1-1 provides a schematic framework for EPA’s 2008 

Report on the Environment:

•	 The ROE: The report is organized around five main 

chapters: “Air,” “Water,” “Land,” “Human Exposure and 

Health,” and “Ecological Condition.” These five chapters 

relate to EPA’s five strategic goals (Clean Air, Clean and 

Safe Waters, Healthy Land, Healthy Communities and Ecosystems, Stewardship and Compliance) and serve to focus 

the ROE on issues important to EPA’s mission to protect 

human health and the environment.

•	 ROE chapters: Each chapter is organized around a set of 

questions that EPA considers to be important and relevant 

to its mission. 

•	 ROE questions: For each question, the ROE:

° Describes the issues covered by the question. These 

issues include EPA’s regulatory responsibilities, as well as 

areas where the Agency conducts or sponsors research, 

exerts policy leadership, provides information to the 

public, or shares an interest in human health and the 

environment with its federal, state, and tribal partners.

° Presents indicators that are available to help answer the 

question; discusses critical indicator gaps that prevent 

the question from being fully answered; and reviews the 

challenges to filling these gaps. 

•	 ROE indicators: All indicators presented in the ROE 

were peer-reviewed against an indicator definition and 

criteria (see Box 1-1) to ensure that they are useful, objective, transparent, and scientifically reliable. Each indicator describes what the data show and any limitations that 

generate uncertainty in the trend characterized by the 

indicator.

Further detail on the ROE chapters, questions, and indicators 

is provided below. Several sections follow the five main 

ROE chapters:

•	 Chapter 7, “Afterword,” discusses the next steps for 

improving indicators and summarizes the challenges to 

answering the questions and synthesizing and integrating 

information across indicators. 

•	 Appendix A lists acronyms and provides a glossary of 

terms that have particular definitions within this document 

or whose definitions are not commonly available. 

•	 Appendix B describes the process used to develop the 

2008 ROE. 

•	 Appendix C compares indicators used in the 2003 Draft 

ROE Technical Document with those in this 2008 version. 

ROE Chapters

EPA has important mandates to protect air, water, and land 

(e.g., in the case of land, to ensure the safety of pesticides and 

chemicals used in commerce, to ensure the reduction and 

proper disposal of wastes, and to prevent and clean up contaminated lands). The Agency is therefore interested in trends in 

these media. In reality, however, most human health and ecosystem effects are influenced by many factors, including stressors acting through multiple media and non-environmental 

factors that are outside EPA’s mission. EPA believes it is vitally 

important to conduct surveillance of trends in indicators of 

human health and ecological condition, even if they cannot 

be linked with confidence to national or regional trends in 

pollutant emissions or concentrations, in order to determine 

whether they warrant the Agency’s closer attention. 

Exhibit 1-1. The ROE framework

Chapter

Chapter

Chapter

Chapter

Indicator

Indicator

Indicator

Indicator

Question

Question

Question

Chapter

WHAT THE

DATA SHOW

ROE

CHAPTERS

ROE

QUESTIONS

ROE

INDICATORS 

EPA FOCUS

ROE INDICATOR 

DEFINITION AND CRITERIA

THE 

ROE

GAPS&CHALLENGES

LIMITATIONS
CHAPTER 1

EPA’s 2008 Report on the Environment 1-3

To accommodate EPA’s interest in both media-specific and 

broader, more complex environmental trends, the Agency has 

used the following conceptual model to organize the ROE 

indicators among the chapters:

•	 Air, water, and land chapters (Chapters 2, 3, and 4):

The air, water, and land chapters focus on trends in these 

individual media, and on resulting trends in their effects on 

human health and ecological systems. An effect indicator is 

included in a media chapter only if the condition or effect 

can be demonstrably linked at the national level to trends 

in stressors associated with that particular environmental medium. 

For example, indicators of lake and stream acidity and ozone 

damage to trees are placed in the air chapter (rather than 

the ecological condition chapter) because trends in these 

effects indicators are clearly linked to trends in the emissions 

and concentration of particular air pollutants. Specifically, 

downward trends in the acidity of lakes and streams in certain geologically sensitive regions of the country are clearly 

linked to declining acid deposition; the type of damage 

to leaves in forest plants described by the indicator can be 

clearly attributed to ozone exposure. However, these indicators are exceptional: the ROE’s three media chapters include 

very few indicators of effects, because most effects indicators cannot be linked with confidence to stressors associated 

with a single environmental medium. 

•	 Human exposure and health and ecological condition chapters (Chapters 5 and 6): These two chapters 

address questions about trends in human exposure and 

health and ecological condition that are influenced by 

contaminants in more than one medium and by factors that 

are broader than EPA’s mission. For example, the human 

exposure and health chapter includes a question about 

trends in human disease and conditions for which environmental contaminants may be a risk factor; these trends also 

are influenced by other factors, such as lifestyle, genetics, 

and the quality of medical care. The ecological condition 

chapter includes a question about trends in diversity and 

biological balance of the nation’s ecological systems; these 

trends are influenced not only by trends in contaminants in 

multiple media but also by factors such as land use, invasive 

species, and natural resource management. Trends in the 

health or ecological indicators covered in Chapters 5 and 

6 cannot be attributed with any confidence to particular

contaminants or other causes covered in the ROE’s media 

chapters. This is true even though epidemiological and laboratory studies may have demonstrated a clear relationship 

between a contaminant and a health or ecological effect. 

ROE Questions

The 23 questions presented in the ROE were developed 

by EPA. These are questions the Agency believes should be 

answered with confidence if it is to be adequately informed 

about important environmental trends; however, they are not 

necessarily questions that EPA can fully answer at present based 

on the indicators that meet the ROE definition and criteria. 

Each question asks about environmental trends, indicating 

EPA’s interest in monitoring how the status of the environment and human exposure and health changes over time. 

The latest data point in the trend represents the most current 

information on the status of the environment or health when 

the data were gathered; for some indicators, only the baseline 

status is available. 

ROE Indicators

Environmental conditions can be represented in many ways. 

For reasons discussed below, the ROE relies on an indicator approach. To maintain a high level of scientific integrity 

and consistency among the indicators used in the ROE, EPA 

established an explicit definition and six criteria (see Box 1-1) 

that all ROE indicators must meet. The criteria are based in 

part on EPA’s Information Quality Guidelines (http://www.

epa.gov/quality/informationguidelines/), which cover important information that EPA provides to the public. Together, 

the six criteria are intended to ensure that all indicators in 

the ROE are useful to EPA and the public, and that they are 

objective, transparent, and based on high-quality, comparable, and representative data across space and time. The ROE 

emphasizes indicators that can be tracked over time; therefore, 

one-time studies are not included unless they serve as baselines 

for future trends. 

The ROE indicator definition intentionally excludes some 

categories of indicators. For example, ROE indicators include 

measures of pollutant emissions, but not measures of more 

Indicator definition: For EPA’s 2008 Report on the 

Environment, an indicator is a numerical value 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.

Indicator criteria:

•	 The indicator is useful. It answers (or makes an important contribution to answering) a question in the ROE.

•	 The indicator is objective. It is developed and presented 

in an accurate, clear, complete, and unbiased manner.

•	 The indicator is transparent and reproducible. The specific 

data used and the specific assumptions, analytic methods, 

and statistical procedures employed are clearly stated.

•	 The underlying data are characterized by sound collection methodologies, data management systems to protect 

their integrity, and quality assurance procedures.

•	 Data are available to describe changes or trends and the 

latest available data are timely. 

•	 The data are comparable across time and space, and representative of the target population. Trends depicted in 

this indicator accurately represent the underlying trends 

in the target population.

Box 1-1. Indicator Definition and Criteria
CHAPTER 1

1-4 EPA’s 2008 Report on the Environment

general causal factors such as energy generation or agricultural 

production. Also excluded are economic indicators such as 

the value of land or natural resources and the cost of pollution 

control, or efficiency factors such as pollutant emissions per 

vehicle mile traveled. Because ROE indicators focus on actual 

physical measurements, administrative indicators such as permits issued, regulations promulgated, and enforcement actions 

undertaken also are excluded. Indicators based on results predicted by environmental fate and transport models or risks to 

people or ecological systems are excluded as well, because they 

are not based on actual measurements. 

Indicators, whether they represent baseline conditions or 

trends, involve uncertainties. While statistical analyses could 

have been presented for some of the indicators in this report, 

such analyses require considerably more complex indicator 

development and peer review than was possible given the time 

and resource constraints for the 2008 ROE. Therefore, EPA 

determined that this report would not include presentations of 

statistical confidence in the status of and trends in the indicators. When the word “trend” is used in an indicator, it simply 

means the direction of change and does not imply statistical 

significance. EPA recognizes that uncertainty is an important 

issue and does plan to quantify uncertainty in future versions 

of the ROE and its indicators. 

EPA also recognizes that many others types of environmental 

data and information are available, in addition to indicators, 

that could potentially be used to answer the ROE questions. 

Many environmental reports, particularly those that focus on 

particular issues or locations, conduct integrated assessments 

by gathering and weighing the strengths and weaknesses of all 

the relevant information available. This integrated approach 

is not feasible for the ROE because it covers so many different 

topics across the entire nation.

EPA selected the indicators for this 2008 ROE based on indicators suggested by EPA, other federal agencies, state agencies, 

and non-governmental organizations. EPA developed a list of 

proposed indicators that it believed could play a significant role 

in answering the questions in the ROE. These included indicators from the 2003 Draft ROE that EPA judged to be relevant 

and consistent with the 2008 ROE indicator definition and 

criteria, as well as many new indicators (see Appendix C). Indicators that did not make a significant contribution to answering 

the questions were excluded from further consideration. The 

time frame for developing the ROE did not allow for development of additional indicators.

In creating this list, EPA reviewed all the indicator reports it 

could find, whether developed by EPA or others, and consulted with experts within and outside the Agency. Generally, 

EPA used existing indicators and did not invest in developing 

entirely new indicators for the 2008 ROE. 

The proposed indicators were evaluated via an independent 

public peer review process (see http://www.epa.gov/roe for 

detailed information). Of the proposed indicators, 85 were 

ultimately selected for inclusion in the ROE. Appendix B provides more information on the indicator development process. 

Each indicator consists of a graphic(s) or table(s) and explanatory text. All indicators present the most recent relevant, 

quality-assured data available when this report went to press. 

EPA intends to update these indicators in the e-ROE as new 

data become available. The baselines and reference levels for 

most indicators follow the underlying sources. Complete 

documentation of the indicator data sources can be found at 

http://www.epa.gov/roe. For ease of use in both the print and 

e-versions, each indicator was developed to stand alone, with 

sufficient information for the reader to understand its scope, 

origin, and data sources. As a result, some redundancies of text 

exist in the hardcopy version of the document. 

Some indicators are used to answer more than one ROE question. In most cases, these indicators are presented with the 

question that they are first used to answer and referenced when 

they are used to answer another question later in the ROE. For 

example, the Blood Cotinine indicator is first used to answer 

a question in the air chapter and then another question in the 

human exposure and health chapter. The indicator is presented 

in the air chapter; the human exposure and health chapter refers 

the reader to the air chapter for details. Tables listing indicators 

and their page numbers are provided as navigation aids at the 

end of this introduction (Table 1-1), in the introduction to each 

chapter, and in the introduction to each question. 

EPA released the first edition of the ROE as a draft report 

in 2003 (see http://www.epa.gov/roe). A number of changes 

have been incorporated into this 2008 edition in response 

to comments on the 2003 draft. The major changes are:

•	 Questions: The ROE questions were revised to present 

a more consistent format and comprehensive coverage of 

EPA’s interests across chapters. 

•	 Indicators: The indicator definitions and criteria were 

revised. As a result, several changes were made to the 

2003 indicators, including combining some indicators 

and deleting others. Also, new indicators have been 

added that were not available for the 2003 version of the 

report. See Appendix C for details. 

•	 Indicator placement: Indicators of health or environmental effects that are linked predominantly to a single 

medium (air, water, land) were moved from the human 

exposure and health or ecological condition chapter to 

the chapter for the relevant medium.

•	 Spatial scale: National-level indicators were the focus 

of the 2003 Draft ROE and continue to be the focus in 

this 2008 ROE. However, as discussed under “Regional 

Indicators,” the 2008 ROE demonstrates how relevant 

indicators might be identified, developed, and presented 

at finer geographic scales.

Box 1-2. Changes from the 2003 Draft ROE
CHAPTER 1

EPA’s 2008 Report on the Environment 1-5

More than half of the indicators and supporting 

data derive from sources other than EPA, including other federal agencies, state agencies, and nongovernmental organizations. These external sources 

also maintain many environmental data sets that are 

valuable for other purposes and offer potential for 

development of future ROE indicators. Many of these 

data sets, though important, were not included in 

this 2008 ROE because the data do not yet meet the 

ROE indicator criteria. For example, since 1971, the 

Centers for Disease Control and Prevention (CDC), 

EPA, and the Council of State and Territorial Epidemiologists have maintained a surveillance system for 

collecting and periodically reporting data on occurrences and causes of waterborne disease outbreaks 

(WBDOs). These surveillance activities are useful in 

characterizing the epidemiology of WBDOs, identifying changing trends in the etiologic agents that 

cause WBDOs, and determining why the outbreaks 

occurred. However, because of several limitations, 

including under-reporting and differences in how 

states investigate and report outbreaks, these data do 

not currently meet the ROE criteria for an indicator. 

EPA continues to work with CDC and other federal, 

state, and private organizations on important programs such 

as this one, so that they may meet the indicator criteria and be 

used in future editions of the ROE.

Regional Indicators

The ROE focuses on trends within the U.S., even though the 

indicators may be affected by sources outside U.S. borders. 

National-level indicators (indicators for which nationally consistent data are available) are the focus of this report. However, 

highly aggregated national data may mask important variations that take place at finer scales. Therefore, the ROE takes 

two preliminary steps to demonstrate how indicators might be 

identified, developed, and presented at finer geographic scales. 

•	 National data are broken out by major geographic region for 

32 indicators for which the data are sufficiently representative 

at that geographic scale. Rather than adopt regionalization 

schemes based on natural boundaries that would not be 

consistent among indicators, and because EPA Regions play 

an important role in the way EPA’s environmental protection efforts are implemented, EPA chose to use EPA Regions 

for the 25 indicators where this was possible. EPA Regions 

follow state borders and do not reflect natural boundaries 

based on physiography, climate, or biota. To aid readers who 

are unfamiliar with EPA Regional boundaries, the ten EPA 

Regions are delineated in Exhibit 1-2, and also depicted in 

icons on each indicator graphic that displays regional data.

•	 Eight Regional Indicators (indicators that cover an EPA 

Region or substantial parts of one or more EPA Regions) were 

selected to demonstrate how such indicators can answer part 

of an ROE question that is unique to a particular Region, or 

could eventually be expanded to answer an ROE question at 

the national level. Like the National Indicators, all Regional 

Indicators were peer-reviewed against the ROE indicator 

definition and criteria. EPA hopes that the Regional Indicators 

will serve as useful models, and that lessons learned from them 

will help the Agency identify and present a more robust set 

of indicators that answer ROE questions at multiple scales in 

the future. However, it is important to note that the Regional 

Indicators are presented as examples only: trends in these indicators are not necessarily representative of similar trends in other 

regions or in the nation as a whole; they do not represent an 

exclusive set of indicators needed to answer the ROE questions at a regional scale; and they may or may not scale up to 

National Indicators. EPA may or may not include these indicators in future versions of the ROE. 

Conclusion

The Report on the Environment represents a commitment by EPA 

to continually improve the quality and quantity of information 

available to understand the condition of human health and the 

environment and how it is changing over time. Within EPA, 

this commitment provides ongoing opportunities to use the 

ROE to inform strategic planning and related activities. The 

ROE also creates opportunities to establish and strengthen 

partnerships among federal, state, tribal, and non-governmental 

organizations for monitoring, data sharing, and data needs 

planning to support indicator development and improvement. 

As mentioned earlier, the topics of air, water, land, human 

exposure and health, and ecological condition under which the 

indicators are presented are all interconnected. Changes in one 

medium affect other media; human health is affected by environmental condition; and environmental condition is affected 

by human factors. In reality, humans and ecological systems are 

exposed to multiple pollutants from multiple sources; large spatial and temporal variations in environmental exposures exist; 

and numerous non-environmental factors also have influence. 

EPA recognizes these complexities; to improve future versions 

of the ROE, EPA will continue to seek ways to better link and 

integrate indicators across questions and chapters.

Exhibit 1-2. The EPA Regions

9

9

9

6

7

4

8

10

10

5

3

2 1

WA

AK

ID

CA

NV

AZ NM

TX

OK AR

KS MO

CO UT

WY

MT ND

SD

NE IA

MN

WI

MI

IN

KY

TN

MS AL GA

SC

NC

VA

PA

NY

ME

WV

FL

OH IL

LA

OR

NH

VT

MA

RI

CT NJ

DE

MD

DC

HI

Guam

Trust Territories

American Samoa

Northern Mariana 

Islands

2

PR

VI
CHAPTER 1

1-6 EPA’s 2008 Report on the Environment

Table 1-1. ROE Questions and Supporting Indicators1

Air Chapter Section Page

Outdoor Air Quality

What are the trends in outdoor air quality and their effects on human health 

and the environment?

2.2 2-6

Carbon Monoxide Emissions 2.2.2 2-9

Ambient Concentrations of Carbon Monoxide 2.2.2 2-11

Lead Emissions 2.2.2 2-12

Ambient Concentrations of Lead 2.2.2 2-14

Nitrogen Oxides Emissions 2.2.2 2-16

Ambient Concentrations of Nitrogen Dioxide 2.2.2 2-18

Volatile Organic Compounds Emissions 2.2.2 2-20

Ambient Concentrations of Ozone 2.2.2 2-22

Ozone Injury to Forest Plants 2.2.2 2-24

Particulate Matter Emissions 2.2.2 2-26

Ambient Concentrations of Particulate Matter 2.2.2 2-29

Regional Haze 2.2.2 2-33

Sulfur Dioxide Emissions 2.2.2 2-34

Acid Deposition 2.2.2 2-37

Lake and Stream Acidity 2.2.2 2-42

Percent of Days with Air Quality Index Values Greater Than 100 2.2.2 2-44

Mercury Emissions 2.2.2 2-46

Air Toxics Emissions 2.2.2 2-48

Ambient Concentrations of Benzene 2.2.2 2-51

Concentrations of Ozone-Depleting Substances 2.2.2 2-52

Ozone Levels over North America 2.2.2 2-54

Ozone and Particulate Matter Concentrations for U.S. Counties in the

U.S./Mexico Border Region

2.2.2 2-56

Ambient Concentrations of Manganese Compounds in EPA Region 5 2.2.2 2-58

Greenhouse Gases

What are the trends in greenhouse gas emissions and concentrations? 2.3 2-62

U.S. Greenhouse Gas Emissions 2.3.2 2-64

Atmospheric Concentrations of Greenhouse Gases 2.3.2 2-66

1 As mentioned earlier, some indicators are used to answer more than one question. In most cases, these indicators are presented where they are first used to answer 

a question and referenced under subsequent questions.
CHAPTER 1

EPA’s 2008 Report on the Environment 1-7

Table 1-1. ROE Questions and Supporting Indicators (continued)

Air Chapter (continued) Section Page

Indoor Air Quality

What are the trends in indoor air quality and their effects on human health? 2.4 2-73

U.S. Homes Above EPA’s Radon Action Level 2.4.2 2-74

Blood Cotinine Level 2.4.2 2-76

Water Chapter Section Page

Water and Watersheds

What are the trends in the extent and condition of fresh surface waters and 

their effects on human health and the environment?

3.2 3-6

High and Low Stream Flows 3.2.2 3-8

Streambed Stability in Wadeable Streams 3.2.2 3-11

Lake and Stream Acidity 2.2.2 2-42

Nitrogen and Phosphorus in Wadeable Streams 3.2.2 3-13

Nitrogen and Phosphorus in Streams in Agricultural Watersheds 3.2.2 3-15

Nitrogen and Phosphorus Loads in Large Rivers 3.2.2 3-17

Pesticides in Streams in Agricultural Watersheds 3.2.2 3-19

Benthic Macroinvertebrates in Wadeable Streams 3.2.2 3-21

Ground Water

What are the trends in the extent and condition of ground water and their 

effects on human health and the environment?

3.3 3-25

Nitrate and Pesticides in Shallow Ground Water in Agricultural Watersheds 3.3.2 3-27

Wetlands

What are the trends in the extent and condition of wetlands and their effects 

on human health and the environment?

3.4 3-30

Wetland Extent, Change, and Sources of Change 3.4.2 3-32

Coastal Waters

What are the trends in the extent and condition of coastal waters and their 

effects on human health and the environment?

3.5.2 3-35

Wetland Extent, Change, and Sources of Change 3.4.2 3-32

Trophic State of Coastal Waters 3.5.2 3-38

Coastal Sediment Quality 3.5.2 3-42

Coastal Benthic Communities 3.5.2 3-44

Coastal Fish Tissue Contaminants 3.8.2 3-61

Submerged Aquatic Vegetation in the Chesapeake Bay 3.5.2 3-46

Hypoxia in the Gulf of Mexico and Long Island Sound 3.5.2 3-48
CHAPTER 1

1-8 EPA’s 2008 Report on the Environment

Table 1-1. ROE Questions and Supporting Indicators (continued)

Water Chapter (continued) Section Page

Drinking Water

What are the trends in the quality of drinking water and their effects on 

human health?

3.6 3-52

Population Served by Community Water Systems with No Reported 

Violations of Health-Based Standards

3.6.2 3-54

Recreational Water

What are the trends in the condition of recreational waters and their effects 

on human health and the environment?

3.7 3-57

Consumable Fish and Shellfish

What are the trends in the condition of consumable fish and shellfish and 

their effects on human health?

3.8 3-59

Coastal Fish Tissue Contaminants 3.8.2 3-61

Contaminants in Lake Fish Tissue 3.8.2 3-63

Land Chapter Section Page

Land Cover

What are the trends in land cover and their effects on human health and the 

environment? 

4.2 4-5

Land Cover 4.2.2 4-7

Forest Extent and Type 6.2.2 6-8

Land Cover in the Puget Sound/Georgia Basin 4.2.2 4-10

Land Use

What are the trends in land use and their effects on human health and the 

environment?

4.3 4-13

Land Use 4.3.2 4-14

Urbanization and Population Change 4.3.2 4-19

Wastes

What are the trends in wastes and their effects on human health and the 

environment?

4.4 4-23

Quantity of Municipal Solid Waste Generated and Managed 4.4.2 4-24

Quantity of RCRA Hazardous Waste Generated and Managed 4.4.2 4-26

Chemicals Used on the Land

What are the trends in chemicals used on the land and their effects on 

human health and the environment? 

4.5 4-29

Fertilizer Applied for Agricultural Purposes 4.5.2 4-30

Toxic Chemicals in Production-Related Wastes Combusted for Energy 

Recovery, Released, Treated, or Recycled

4.5.2 4-33

Pesticide Residues in Food 4.5.2 4-37

Reported Pesticide Incidents 4.5.2 4-39
CHAPTER 1

EPA’s 2008 Report on the Environment 1-9

Table 1-1. ROE Questions and Supporting Indicators (continued)

Land Chapter (continued) Section Page

Contaminated Land

What are the trends in contaminated land and their effects on human health 

and the environment?

4.6 4-42

Current Human Exposures Under Control at High-Priority Cleanup Sites 4.6.2 4-44

Migration of Contaminated Ground Water Under Control at High-Priority 

Cleanup Sites

4.6.2 4-47

Human Exposure and Health Chapter Section Page

Exposure to Environmental Contaminants

What are the trends in human exposure to environmental contaminants, 

including across population subgroups and geographic regions?

5.2 5-7

Blood Lead Level 5.2.2 5-10

Blood Mercury Level 5.2.2 5-12

Blood Cadmium Level 5.2.2 5-13

Blood Persistent Organic Pollutants Level 5.2.2 5-15

Blood Cotinine Level 2.4.2 2-76

Urinary Pesticide Level 5.2.2 5-22

Urinary Phthalate Level 5.2.2 5-26

Health Status

What are the trends in health status in the United States? 5.3 5-31

General Mortality 5.3.2 5-33

Life Expectancy at Birth 5.3.2 5-35

Infant Mortality 5.3.2 5-36

Disease and Conditions

What are the trends in human disease and conditions for which 

environmental contaminants may be a risk factor, including across 

population subgroups and geographic regions?

5.4 5-39

Cancer Incidence 5.4.2 5-43

Childhood Cancer Incidence 5.4.2 5-46

Cardiovascular Disease Prevalence and Mortality 5.4.2 5-48

Chronic Obstructive Pulmonary Disease Prevalence and Mortality 5.4.2 5-52

Asthma Prevalence 5.4.2 5-55

Infectious Diseases Associated with Environmental 

Exposures or Conditions

5.4.2 5-59

Birth Defects Prevalence and Mortality 5.4.2 5-62

Low Birthweight 5.4.2 5-65

Preterm Delivery 5.4.2 5-67
CHAPTER 1

1-10 EPA’s 2008 Report on the Environment

Table 1-1. ROE Questions and Supporting Indicators (continued)

Ecological Condition Chapter Section Page

Extent and Distribution

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

ecological systems?

6.2 6-7

Land Cover 4.2.2 4-7

Forest Extent and Type 6.2.2 6-8

Forest Fragmentation 6.2.2 6-11

Wetland Extent, Change, and Sources of Change 3.4.2 3-32

Land Use 4.3.2 4-14

Urbanization and Population Change 4.3.2 4-19

Land Cover in the Puget Sound/Georgia Basin 4.2.2 4-10

Ecological Connectivity in EPA Region 4 6.2.2 6-13

Relative Ecological Condition of Undeveloped Land in EPA Region 5 6.2.2 6-14

Diversity and Biological Balance

What are the trends in the diversity and biological balance of the nation’s 

ecological systems?

6.3 6-18

Coastal Benthic Communities 3.5.2 3-44

Benthic Macroinvertebrates in Wadeable Streams 3.2.2 3-21

Bird Populations 6.2.2 6-20

Fish Faunal Intactness 6.2.2 6-21

Submerged Aquatic Vegetation in the Chesapeake Bay 3.5.2 3-46

Non-Indigenous Benthic Species in the Estuaries of the Pacific Northwest 6.2.2 6-23

Ecological Processes

What are the trends in the ecological processes that sustain the 

nation’s ecological systems?

6.4 6-27

Carbon Storage in Forests 6.4.2 6-28

Physical and Chemical Attributes

What are the trends in the critical physical and chemical attributes 

of the nation’s ecological systems?

6.5 6-31

U.S. and Global Mean Temperature and Precipitation 6.5.2 6-32

Sea Surface Temperature 6.5.2 6-37

Streambed Stability in Wadeable Streams 3.2.2 3-11

High and Low Stream Flows 3.2.2 3-8

Sea Level 6.5.2 6-39

Nitrogen and Phosphorus Loads in Large Rivers 3.2.2 3-17

Nitrogen and Phosphorus in Wadeable Streams 3.2.2 3-13
CHAPTER 1

EPA’s 2008 Report on the Environment 1-11

Table 1-1. ROE Questions and Supporting Indicators (continued)

Ecological Condition Chapter (continued) Section Page

Physical and Chemical Attributes (continued)

What are the trends in the critical physical and chemical attributes 

of the nation’s ecological systems? (continued)

6.5 6-31

Nitrogen and Phosphorus in Streams in Agricultural Watersheds 3.2.2 3-15

Lake and Stream Acidity 2.2.2 2-42

Hypoxia in the Gulf of Mexico and Long Island Sound 3.5.2 3-48

Ecological Exposure to Contaminants

What are the trends in biomarkers of exposure to common environmental 

contaminants in plants and animals?

6.6 6-45

Coastal Fish Tissue Contaminants 3.8.2 3-61

Contaminants in Lake Fish Tissue 3.8.2 3-63

Ozone Injury to Forest Plants 2.2.2 2-24

Air

Chapter 2
Contents

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.1.1 Overview of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

2.1.2 Organization of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

2.2 What Are the Trends in Outdoor Air Quality and Their Effects on Human 

Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2.2.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

2.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-60

2.3 What Are the Trends in Greenhouse Gas Emissions and Concentrations? . . . . . . . . . . . . 2-62

2.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-62

2.3.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-63

2.3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-72

2.4 What Are the Trends in Indoor Air Quality and Their Effects on Human Health? . . . . . . 2-73

2.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-73

2.4.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-74

2.4.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-79
AIR

EPA’s 2008 Report on the Environment 2-3

2.1 Introduction

Air provides the oxygen and carbon dioxide needed to 

sustain human, animal, and plant life on Earth, and the 

composition of trace gases in the atmosphere plays an 

important role for the climate. Air pollution can adversely affect 

these critical functions of the atmosphere in many ways. High 

levels of air pollution, whether indoors or outdoors, can harm 

human health by triggering asthma attacks, aggravating allergies, and contributing to or potentially causing various diseases. 

Certain types of outdoor air pollution can impair visibility and 

damage other valued resources, such as forests, lakes and streams, 

and building surfaces. On a global scale, air pollution released 

worldwide can eventually change the atmosphere’s composition 

with important consequences, including depletion of the Earth’s 

ozone layer and climate change. 

An important component of EPA’s mission is to protect and 

improve air quality in order to avoid or mitigate the consequences of air pollution’s harmful effects. State and tribal air 

pollution control agencies help fulfill this mission by implementing many of the air pollution control requirements that 

EPA sets at the federal level. Other federal partners, the academic community, industry and trade associations, and nongovernmental organizations all conduct important research 

that contributes to the current understanding of regional, 

national, and global air quality issues. 

Efforts to maintain good air quality are complicated by population increase, energy consumption, motor vehicle use, and other 

factors that can lessen air quality. Outdoor air is polluted by 

emissions from a broad array of industrial and mobile sources, as 

well as everyday activities like dry cleaning, painting, and refueling vehicles. Emissions from natural sources, such as wildfires, 

also contribute to outdoor air pollution. Similarly, indoor air 

quality is affected not only by these outdoor sources, but also by 

sources found within buildings, such as home heating devices, 

tobacco smoke, consumer products, and building materials. In 

this chapter, EPA assesses national trends in the condition of air, 

stressors that influence air quality, and associated exposures and 

effects among humans and ecological systems. ROE indicators 

are presented to address three fundamental questions about the 

state of the nation’s air:

•	 What are the trends in outdoor air quality and their 

effects on human health and the environment? This 

question examines a broad spectrum of outdoor air quality 

issues, including polluted air that people breathe at ground 

level, deposition of air pollutants to land and water, and 

depletion of the Earth’s ozone layer. For each issue, information is provided both on the main stressors (emissions 

sources) and potential health and environmental effects.

•	 What are the trends in greenhouse gas emissions and 

concentrations? This question focuses on releases and 

atmospheric concentrations of certain so-called “greenhouse gases,” or gases in the atmosphere that help regulate 

the Earth’s temperature and thus contribute to climate 

change—a topic introduced in this chapter and revisited in 

Chapter 6, “Ecological Condition.”

ROE Approach

This 2008 Report on the Environment:

•	 Asks questions that EPA considers 

important to its mission to protect 

human health and the environment. 

•	 Answers these questions, to the extent 

possible, with available indicators.

•	 Discusses critical indicator gaps, limitations, and challenges that prevent the 

questions from being fully answered.

ROE Questions

The air, water, and land chapters (Chapters 

2, 3, and 4) ask questions about trends in 

the condition and/or extent of the environmental medium; trends in stressors to 

the medium; and resulting trends in the 

effects of the contaminants in that medium 

on human exposure, human health, and 

the condition of ecological systems. 

The human exposure and health and 

ecological condition chapters (Chapters 

5 and 6) ask questions about trends in 

aspects of health and the environment 

that are influenced by many stressors 

acting through multiple media and by 

factors outside EPA’s mission. 

ROE Indicators

An indicator is derived from actual measurements of a pressure, state or ambient 

condition, exposure, or human health or 

ecological condition over a specified geographic domain. This excludes indicators 

such as administrative, socioeconomic, and 

efficiency indicators.

Indicators based on one-time studies are 

included only if they were designed to serve 

as baselines for future trend monitoring. 

All ROE indicators passed an independent 

peer review against six criteria to ensure 

that they are useful; objective; transparent; 

and based on data that are high-quality, 

comparable, and representative across space 

and time. 

Most ROE indicators are reported at the 

national level. Some national indicators 

also report trends by region. EPA Regions 

were used, where possible, for consistency 

and because they play an important role in 

how EPA implements its environmental 

protection efforts.

Several other ROE indicators describe 

trends in particular regions as examples of 

how regional indicators might be included 

in future versions of the ROE. They are 

not intended to be representative of trends 

in other regions or the entire nation.

EPA will periodically update and revise 

the ROE indicators and add new indicators 

as supporting data become available. In the 

future, indicators will include information 

about the statistical confidence of status 

and trends. Updates will be posted electronically at http://www.epa.gov/roe.

Additional Information

You can find additional information about 

the indicators, including the underlying 

data, metadata, references, and peer review, 

at http://www.epa.gov/roe.

EPA’s 2008 Report on the Environment (ROE): Essentials
AIR

2-4 EPA’s 2008 Report on the Environment

•	 What are the trends in indoor air quality and their 

effects on human health? This question considers air 

quality in indoor settings, such as homes, offices, and 

schools, and how poor indoor air quality can affect human 

health and welfare, whether by causing adverse health 

effects or by impairing productivity. 

These ROE questions are posed without regard to whether 

indicators are available to answer them. This chapter presents 

the indicators available to answer these questions, and also 

points out important gaps where nationally representative data 

are lacking.

While this chapter focuses on air quality, readers should not 

infer that air quality trends are completely independent of 

the other themes in ROE: water, land, human exposure and 

health, and ecological condition. High levels of air pollution 

are linked to many broader environmental concerns. Because 

air interfaces directly with water and land, air pollutants can 

enter these media through various fate and transport mechanisms, such as wet deposition into surface waters, dry deposition of gaseous pollutants, and gravitational settling onto 

soils, vegetation, and other surfaces. Conversely, chemicals in 

surface water and soil can enter outdoor air through processes 

like evaporation and resuspension of wind-blown dust. Thus, 

in a very general sense, air quality is related to selected topics 

covered in the water chapter and the land chapter. Further, 

nearly every topic addressed in this chapter is primarily motivated by some specific concern regarding human health or 

ecological effects. Therefore, air quality and climate change 

are conceptually linked to many topics addressed in the 

human exposure and health and ecological condition chapters. 

Air quality issues that are connected with other ROE themes 

are introduced and examined in this chapter, and addressed 

further in later sections of the ROE as appropriate. 

2.1.1 Overview of the Data

When developing the 27 ROE indicators in this chapter, EPA 

accessed and compiled data collected by many parties. The 

individual data sources that were evaluated can be classified 

into four general categories:

•	 National emissions inventories. Emissions data were 

queried from databases known as emissions inventories. 

These inventories are composites of measured and estimated emission rates for industrial sources, mobile sources, 

area sources, and natural sources. Industry and state, tribal, 

and local agencies provide most of the data compiled in 

these inventories.

•	 Ground-level ambient air monitoring data. Ambient 

air concentrations measured at ground level primarily come 

from measurements collected in a nationwide network of 

ambient air monitoring stations (i.e., the State and Local 

Air Monitoring Stations network, other special purposes 

monitors). State, tribal, and local agencies operate most 

of these stations and submit their validated measurement 

results to a centralized database.

•	 Deposition measurements. Data on deposition of 

outdoor air pollutants come from samples collected and 

analyzed at fixed locations throughout the country as part 

of the National Atmospheric Deposition Program and the 

Clean Air Status and Trends Network.

•	 Other data sources. The remaining ROE indicators in 

this chapter draw from various other data sources, including satellite measurements of stratospheric ozone depletion, 

an evaluation of pollution-related injury to forest plants, 

surveys on radon in homes and evidence of exposure to 

environmental tobacco smoke, an inter-agency assessment 

of regional haze, and articles in the peer-reviewed literature 

on historical concentrations of greenhouse gases estimated 

from ice core samples. 

Tracking the country’s air quality is a complicated endeavor 

and cannot be done with any single indicator. Multiple indicators are needed to characterize indoor air quality separately 

from outdoor air quality, air quality trends at ground level 

separately from changing atmospheric conditions aloft, and air 

pollution levels for the many different pollutants of potential 

concern. Regardless of the issue of interest, a particular challenge in developing this chapter’s indicators is that air quality 

can vary considerably with location and time. Consequently, 

all underlying data sources must be sufficiently representative, 

both spatially and temporally.

Spatial resolution is a critical consideration due to associated 

spatial variations in population density, industrial emissions 

sources, traffic patterns, and meteorological conditions that 

dictate relevant atmospheric fate and transport processes. Temporal resolution also must be considered because ambient air 

concentrations of certain pollutants vary considerably with time 

of day (partly due to sunlight’s contribution to photochemical 

reactions and due to variations in dilution), day of week (partly 

due to changes in commuting patterns), and season (mostly due 

to changes in meteorological conditions). Temporal resolution is 

particularly important when interpreting air quality trends: long 

enough time frames must be considered to ensure that trends 

reflect sustained changes in air quality, rather than natural fluctuations in atmospheric conditions. 

This chapter presents only data that meet the ROE indicator 

definition and criteria (see Box 1-1, p. 1-3). Note that nonscientific indicators, such as administrative and economic 

indicators, are not included in this definition. Thorough documentation of the indicator data sources and metadata can be 

found online at http://www.epa.gov/roe. All indicators were 

peer-reviewed during an independent peer review process 

(again, see http://www.epa.gov/roe for more information). 

Readers should not infer that the indicators included reflect 

the complete state of knowledge on the nation’s air. Many 

other data sources, publications, and site-specific research 

projects have contributed substantially to the current understanding of air quality trends, but are not used in this report 

because they did not meet some aspect of the ROE indicator 

criteria.
AIR

EPA’s 2008 Report on the Environment 2-5

2.1.2 Organization of 

This Chapter 

This chapter’s remaining three sections are framed around 

the three overarching questions that EPA seeks to answer 

about trends in air. Each section introduces the question and 

its importance, presents the National Indicators that help 

answer the question, and discusses what these indicators, taken 

together, say about the question. The chapter also presents two 

Regional Indicators that meet the ROE indicator definition 

and criteria and help to answer a question at a smaller geographic scale. Each section concludes by listing major challenges to answering the questions and identifying important 

data gaps. 

Table 2-1 lists the indicators used to answer the three questions in this chapter and shows the locations where the indicators are presented. 

 Table 2-1. Air—ROE Questions and Indicators

Question Indicator Name Section Page

What are the trends 

in outdoor air quality 

and their effects on 

human health and the 

environment?

Carbon Monoxide Emissions (N/R)

Ambient Concentrations of Carbon Monoxide (N/R)

Lead Emissions (N)

Ambient Concentrations of Lead (N)

Nitrogen Oxides Emissions (N/R)

Ambient Concentrations of Nitrogen Dioxide (N/R)

Volatile Organic Compounds Emissions (N/R)

Ambient Concentrations of Ozone (N/R)

Ozone Injury to Forest Plants (N/R)

Particulate Matter Emissions (N/R)

Ambient Concentrations of Particulate Matter (N/R)

Regional Haze (N)

Sulfur Dioxide Emissions (N/R)

Acid Deposition (N)

Lake and Stream Acidity (N)

Percent of Days with Air Quality Index Values Greater Than 100 (N/R)

Mercury Emissions (N)

Air Toxics Emissions (N/R)

Ambient Concentrations of Benzene (N)

Concentrations of Ozone-Depleting Substances (N)

Ozone Levels over North America (N)

Ozone and Particulate Matter Concentrations for U.S. Counties in the 

U.S./Mexico Border Region (R) 

Ambient Concentrations of Manganese Compounds in EPA Region 5 (R)

2.2.2 2-9

2.2.2 2-11

2.2.2 2-12

2.2.2 2-14

2.2.2 2-16

2.2.2 2-18

2.2.2 2-20

2.2.2 2-22

2.2.2 2-24

2.2.2 2-26

2.2.2 2-29

2.2.2 2-33

2.2.2 2-34

2.2.2 2-37

2.2.2 2-42

2.2.2 2-44

2.2.2 2-46

2.2.2 2-48

2.2.2 2-51

2.2.2 2-52

2.2.2 2-54

2.2.2 2-56

2.2.2 2-58

What are the trends in 

greenhouse gas emissions 

and concentrations?

U.S. Greenhouse Gas Emissions (N)

Atmospheric Concentrations of Greenhouse Gases (N)

2.3.2 2-64

2.3.2 2-66

What are the trends in 

indoor air quality and their 

effects on human health?

U.S. Homes Above EPA’s Radon Action Level (N)

Blood Cotinine Level (N)

2.4.2 2-74

2.4.2 2-76

N = National Indicator

R = Regional Indicator

N/R = National Indicator displayed at EPA Regional scale
AIR

2-6 EPA’s 2008 Report on the Environment

2.2 What Are the Trends 

in Outdoor Air Quality 

and Their Effects on 

Human Health and the 

Environment?

2.2.1 Introduction

Outdoor air—the air outside buildings, from ground level to 

several miles above the Earth’s surface—is a valuable resource 

for current and future generations because it provides essential gases to sustain life and it shields the Earth from harmful 

radiation. Air pollution can compromise outdoor air quality in 

many ways. Outdoor air pollution, for instance, is associated 

with various adverse health effects including asthma attacks 

and cancer; outdoor air pollution can also contribute to “acid 

rain,” damage crops and surfaces of treasured buildings and 

monuments, and diminish the protective ozone layer in the 

upper atmosphere. Maintaining clean air is a challenging task, 

especially considering the growing stressors on outdoor air 

quality such as increased population growth, increased use of 

motor vehicles, and increased energy consumption.

Outdoor air pollution contains numerous substances of both 

natural and anthropogenic origin. While natural sources 

release some potentially harmful substances into the air (e.g., 

pollen, mold spores, dust), emissions sources of anthropogenic 

origin are of particular interest because regulatory and voluntary reductions can lead to decreased emissions and associated 

air quality improvements. Accordingly, this section focuses 

on outdoor air quality issues caused at least in part by human 

activity and acknowledges and quantifies contributions from 

natural sources, as appropriate.

Most outdoor air quality issues can be traced back to emissions 

sources that release pollutants into the air. Emissions sources 

are typically classified into different categories, such as point 

sources (e.g., power plants, industrial facilities), area sources 

(e.g., air pollution sources over a diffuse area, such as gasoline 

stations and dry cleaners), mobile sources (e.g., cars, trucks, 

airplanes, off-road vehicles), and natural sources (e.g., wildfires, 

wind-blown dust, volcanoes, vegetation). Once pollutants are 

airborne, prevailing wind patterns carry and disperse them 

from their sources to other locations. Atmospheric chemical 

reactions may consume some airborne pollutants and create 

others. As pollutants mix in the atmosphere, depending on 

their chemical and physical properties, some pollutants deposit 

to the Earth’s surface near their sources, while others remain 

airborne for hours, days, or years. Deposition of air pollutants, especially those that are persistent and bioaccumulative, 

can lead to accumulation of contaminants in other media. The 

levels of air pollution at a given location and at a given time are 

influenced by emissions from nearby and distant sources as well 

as by atmospheric factors, such as meteorology.

Human exposure to outdoor air pollution is a function of the 

composition and magnitude of air pollution, combined with 

human activity patterns. Ambient concentration data, while 

useful for characterizing outdoor air quality, ultimately do not 

quantify exposures, because ambient air monitoring equipment measures air quality at fixed outdoor locations, while 

people breathe air in multiple indoor and outdoor environs 

throughout a day. Whether people are harmed by poor air 

quality depends on the mixture of pollutants found in the air, 

exposure doses and durations, individuals’ susceptibilities to 

diseases, and other factors. Similarly, air pollutants’ interactions with ecosystems determine whether air pollution causes 

harmful environmental effects. For a complete understanding 

of a given air pollution issue, information is therefore typically sought on emissions sources, ambient air concentrations, 

exposures, and effects. 

Outdoor air pollution can contain hundreds of different pollutants, which are typically grouped into various categories based 

on shared attributes. Some categories are defined by pollutants’ 

physical attributes (e.g., gases, particulate matter), while others 

by regulatory terminology (e.g., criteria pollutants, air toxics). 

The indicators used to answer the question regarding outdoor 

air quality are organized into the following three categories, 

which were selected based on the different parts of the atmosphere to which they pertain and the different types of information available to support indicator development:

•	 Criteria pollutants. The following six common pollutants 

are referred to as criteria pollutants: carbon monoxide, lead, 

nitrogen dioxide, ozone, particulate matter of different size 

fractions, and sulfur dioxide. These pollutants are known 

as “criteria pollutants” because EPA regulates them by 

developing human health-based or environmentally based 

criteria (or science-based guidelines) for setting permissible levels. Specifically, the Clean Air Act requires EPA 

to set National Ambient Air Quality Standards (NAAQS) 

for these pollutants that are commonly found in outdoor 

air and can harm human health or the environment. The 

NAAQS have been modified and, in some cases, revoked 

since they were originally established. EPA is required to 

periodically review and update the NAAQS to reflect the 

latest scientific information on how outdoor air quality 

affects human health and the environment. Extensive data 

are available on criteria pollutants’ emissions (or emissions 

of the pollutants’ precursors) and ambient concentrations.

•	 Air toxics and other air pollutants. Air toxics, also 

known as hazardous air pollutants, are known or suspected 

to cause cancer and are associated with other serious health 

effects, such as reproductive effects or birth defects, or 

adverse environmental effects. The Clean Air Act specifically identifies 188 air toxics. Numerous other air pollutants 

exhibit toxicity even though they are not classified as air 

toxics; included among these other pollutants are several 

hundred chemicals whose emissions are tracked in EPA’s 

Toxics Release Inventory.
AIR

EPA’s 2008 Report on the Environment 2-7

•	 Stratospheric ozone issues. The ozone layer occurs in 

the stratosphere between 6 and 20 miles above the Earth’s 

surface and protects the Earth’s biota from harmful effects 

of the sun’s ultraviolet radiation. Past and ongoing releases 

of a number of synthetic chemicals from throughout 

the world have depleted the ozone layer, allowing more 

ultraviolet radiation to reach the Earth’s surface. This can 

lead to increased incidence of skin cancer, cataracts, and 

other health problems.1 Further, high levels of ultraviolet 

radiation can cause detrimental ecological effects, such as 

stressing productivity of marine phytoplankton, which are 

essential components of the oceanic food web.2

Air pollution is manifest over a range of spatial and temporal 

domains—an important factor to consider when evaluating 

trends for the three categories considered in this section. The 

spatial domains of air pollution issues vary widely. Air pollution can be local in nature. For instance, ambient concentrations of benzene tend to be greatest in the proximity of major 

sources (e.g., oil refineries, chemical production facilities) and in 

high-traffic areas; long-range transport is relatively unimportant 

due to benzene’s photochemical reactivity and the dilution that 

occurs over longer distances. Air pollution can also extend over 

regional and national scales. For example, emissions sources 

hundreds of miles away can contribute to airborne fine particulate matter at a given location.3

 Finally, a few air pollution 

issues are global in nature, such as intercontinental transport 

of particles during dust storms. Stratospheric ozone depletion, 

as another example, is affected by releases of ozone-depleting 

substances from countries worldwide. The spatial domains ultimately determine the minimum spatial resolution of monitors 

needed to adequately characterize trends.

Temporal scales also vary among pollutants and typically reflect 

some combination of changes in emissions and fluctuations 

in weather. Ambient air concentrations of some air pollutants, like ground-level ozone, have considerable diurnal and 

seasonal variations.4 However, temporal variations are far less 

pronounced for pollutants that are long-lived in the atmosphere, including many ozone-depleting substances. Temporal variations largely determine the appropriate monitoring 

frequency for quantifying trends and the most meaningful 

statistic (or averaging time) used to report ambient air concentrations. When quantifying and interpreting long-term trends 

in outdoor air quality, attention also must be paid to changes 

in emissions estimation techniques and advances in ambient air 

monitoring technologies. Unless otherwise noted, the outdoor 

air quality indicators only come from data sets generated using 

consistent methodologies over the entire time frame of interest.

The nationwide air quality trends in this section are generally 

consistent with those documented in other EPA publications, 

though readers should not expect to find perfect concordance among individual data points. This is because some 

publications address different spatial domains or time frames 

and may use less rigorous selection criteria when identifying 

and compiling data sets. 

2.2.2 ROE Indicators

The 23 outdoor air quality indicators track emissions, ambient concentrations, and pollution-related effects over varying 

spatial domains and time spans, depending on the availability 

of underlying data. The indicators include 21 National Indicators (12 of which break national data down into the ten EPA 

Regions) and two Regional Indicators. The most extensive 

temporal coverage of these indicators tracks trends from 1964 

to the present.

Indicators were developed using data compiled from multiple 

sources. Emissions indicators are based on EPA’s National 

Emissions Inventory (NEI), a database of measured and estimated emissions for numerous pollutants and source categories. At the writing of this report, NEI data were available for 

1990 through 2002, but the indicators only present data for 

those inventory years that are fully updated and are developed 

using consistent methodologies. Ground-level ambient air 

concentration indicators were developed from data in EPA’s 

Air Quality System (AQS), a clearinghouse of validated ambient air monitoring results submitted largely by tribal, state, 

and local environmental agencies. The ambient concentration 

indicators present data through calendar year 2006, which is 

the most recent calendar year having a complete, validated 

set of monitoring data available from AQS when this report 

was prepared. Remaining indicators draw from different 

monitoring programs, including regional haze data from the 

Interagency Monitoring of Protected Visual Environments, 

acid deposition measurements from the multi-agency National 

Atmospheric Deposition Program and Clean Air Status and 

Trends Network, ozone injury observations from the U.S. 

Forest Service’s Forest Health Monitoring Program, and 

monitoring of stratospheric ozone levels and concentrations of 

ozone-depleting substances conducted by the National Oceanic and Atmospheric Administration.

Table 2-2 shows how indicators are classified into three general categories (criteria pollutants, air toxics and other pollutants, stratospheric ozone issues) and then further organized by 

pollutant. For each pollutant and to the extent supported by 

ROE indicators, relevant emissions indicators are presented 

first, immediately followed by ambient concentration indicators, and next by effects indicators. With this organization, 

readers can readily compare trends in emissions, ambient 

concentrations, and effects for the same pollutant.

1 World Meteorological Organization. 2007. Scientific assessment of ozone 

depletion: 2006. Geneva, Switzerland. 

2 DeMora, S., S. Demers, and M. Vernet. 2000. The effects of UV radiation in 

the marine environment. Cambridge, United Kingdom: Cambridge University Press.

3 U.S. Environmental Protection Agency. 2004. The particle pollution 

report: Current understanding of air quality and emissions through 2003. 

EPA/454/R-04/002. Research Triangle Park, NC.

4 U.S. Environmental Protection Agency. 2004. The ozone report: Measuring 

progress through 2003. EPA/454/K-04/001. Research Triangle Park, NC.
AIR

2-8 EPA’s 2008 Report on the Environment

Table 2-2. ROE Indicators of Trends in Outdoor Air Quality and Their Effects 

on Human Health and the Environment

National Indicators Section Page

Criteria Pollutants and Their Precusors

Carbon Monoxide Emissions (N/R) 2.2.2 2-9

Ambient Concentrations of Carbon Monoxide (N/R) 2.2.2 2-11

Lead Emissions 2.2.2 2-12

Ambient Concentrations of Lead 2.2.2 2-14

Nitrogen Oxides Emissions (N/R) 2.2.2 2-16

Ambient Concentrations of Nitrogen Dioxide (N/R) 2.2.2 2-18

Volatile Organic Compounds Emissions (N/R) 2.2.2 2-20

Ambient Concentrations of Ozone (N/R) 2.2.2 2-22

Ozone Injury to Forest Plants (N/R) 2.2.2 2-24

Particulate Matter Emissions (N/R) 2.2.2 2-26

Ambient Concentrations of Particulate Matter (N/R) 2.2.2 2-29

Regional Haze 2.2.2 2-33

Sulfur Dioxide Emissions (N/R) 2.2.2 2-34

Acid Deposition 2.2.2 2-37

Lake and Stream Acidity 2.2.2 2-42

Percent of Days with Air Quality Index Values Greater Than 100 (N/R) 2.2.2 2-44

Air Toxics and Other Pollutants

Mercury Emissions 2.2.2 2-46

Air Toxics Emissions (N/R) 2.2.2 2-48

Ambient Concentrations of Benzene 2.2.2 2-51

Stratospheric Ozone Issues

Concentrations of Ozone-Depleting Substances 2.2.2 2-52

Ozone Levels over North America 2.2.2 2-54

Regional Indicators Section Page

Ozone and Particulate Matter Concentrations for U.S. Counties in the U.S./

Mexico Border Region

2.2.2 2-56

Ambient Concentrations of Manganese Compounds in EPA Region 5 2.2.2 2-58

N/R = National Indicator displayed at EPA Regional scale
AIR

EPA’s 2008 Report on the Environment 2-9

INDICATOR | Carbon Monoxide Emissions

Carbon monoxide (CO) gas forms primarily when carbon fuels are not burned completely. Mobile 

sources account for the majority of CO emissions (U.S. 

EPA, 2003). These sources include both on-road vehicles 

(e.g., cars, trucks, motorcycles) and nonroad vehicles and 

engines (e.g., farm equipment, construction equipment, 

aircraft, marine vessels). Consequently, high concentrations of CO generally occur in areas with heavy traffic 

congestion. In cities, as much as 95 percent of all CO 

emissions may come from automobile exhaust (U.S. EPA, 

2003). Other sources of CO emissions include industrial 

processes, non-transportation fuel combustion, and natural 

sources, such as wildfires. Fuel-burning appliances also 

are a large source of CO releases in indoor environments. 

Undetected releases of carbon monoxide in indoor settings 

can present serious health risks to building occupants. The 

CO Concentrations indicator (p. 2-11) describes health 

hazards associated with inhaling CO.

This indicator presents CO emissions from traditionally inventoried anthropogenic source categories: (1) “Fuel 

combustion,” which includes emissions from coal-, gas-, 

and oil-fired power plants and industrial, commercial, and 

institutional sources, as well as residential heaters (e.g., 

wood-burning stoves) and boilers; (2) “Other industrial 

processes,” which includes chemical production, petroleum refining, metals production, and industrial processes 

other than fuel combustion; (3) “On-road vehicles,” 

which includes cars, trucks, buses, and motorcycles; and 

(4) “Nonroad vehicles and engines,” such as farm and 

construction equipment, lawnmowers, chainsaws, boats, 

ships, snowmobiles, aircraft, and others. The indicator 

also includes estimates of biogenic CO emissions in 2002. 

Biogenic emissions were estimated using the Biogenic 

Emissions Inventory System Model, Version 3.12, with 

data from the Biogenic Emissions Landcover Database and 

2001 annual meteorological data. 

CO emissions data are tracked by the National Emissions Inventory (NEI). The NEI is a composite of data from 

many different sources, including industry and numerous 

state, tribal, and local agencies. Different data sources use 

different data collection methods, and many of the emissions 

data are based on estimates rather than actual measurements. 

For most fuel combustion sources and industrial sources, 

emissions are estimated using emission factors. Emissions 

from on-road and nonroad sources were estimated using 

EPA-approved modeling approaches (U.S. EPA, 2007a).

NEI data have been collected since 1990 and cover all 

50 states and their counties, D.C., the U.S. territories of 

Puerto Rico and Virgin Islands, and some of the territories 

of federally recognized American Indian nations. Data are 

presented for 1990 and from 1996 to 2002; prior to 1996, 

only the 1990 data have been updated to be comparable to 

the more recent inventories. 

What the Data Show

This indicator focuses on trends in CO emissions from 

anthropogenic sources. However, CO emissions from biogenic sources were estimated for 2002 to provide a sense of 

the relative contributions of natural versus anthropogenic 

emissions (Exhibit 2-1, panel B). Nationally, biogenic 

emissions were estimated to contribute approximately 5 

percent to the CO emissions from all sources during 2002. 

Nationwide estimated anthropogenic CO emissions have 

decreased 35 percent between 1990 and 2002, the most 

recent year for which aggregate NEI emissions estimates 

are available (Exhibit 2-1, panel A). Almost the entire 

emissions reduction is attributed to decreased emissions 

from on-road mobile sources. In 2002, mobile sources 

(both on-road and nonroad sources combined) accounted 

for 90 percent of the nation’s total anthropogenic CO 

emissions. The CO emissions reductions are reflected in 

corresponding reductions in ambient concentrations (the 

CO Concentrations indicator, p. 2-11). 

Net estimated anthropogenic CO emissions declined 

in all EPA Regions between 1990 and 2002 (Exhibit 

2-2). The largest decrease (10.84 million tons) occurred 

in Region 9, and the smallest decrease (1.33 million tons) 

occurred in Region 10.

Exhibit 2-1. CO emissions in the U.S. by 

source category, 1990 and 1996-2002

Year

A. Anthropogenic CO emissions by source categorya

0

20

40

60

80

100

120

140

160

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

Emissions (million tons)

Biogenic 

5%

Anthropogenic

95%

B. Relative amounts of CO 

emissions from anthropogenic 

and biogenic sources, 2002

Fuel combustion

On-road vehicles

Nonroad vehicles and engines

Other industrial processes

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

all fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

Data source: U.S. EPA, 2007b
AIR

2-10 EPA’s 2008 Report on the Environment

INDICATOR | Carbon Monoxide Emissions (continued)

Indicator Limitations

•	 Comparable CO emissions estimates through the NEI are 

available only for 1990 and 1996-2002. Data for 1991-1995 

are not provided due to differences in emissions estimation 

methodologies from other inventory years, which could 

lead to improper trend assessments. 

•	 CO emissions from “miscellaneous sources,” including 

wildfires, are not included in the total emissions. Yearly 

fluctuations in wildfire emissions have the potential to 

mask trends in anthropogenic emissions and therefore have 

been excluded from the trends graphics. Details on emissions from miscellaneous sources can be found by downloading 2002 NEI inventory data for the “nonpoint sector” 

(http://www.epa.gov/ttn/chief/net/2002inventory.html). 

•	The emissions data for CO are largely based on estimates 

that employ emission factors generated from empirical 

and engineering studies, rather than on actual measurements of CO emissions. Although these estimates are 

generated using well-established approaches, the estimates have uncertainties inherent in the emission factors 

and emissions models used to represent sources for which 

emissions have not been directly measured.

•	The methodology for estimating emissions is continually 

reviewed and is subject to revision. Trend data prior to 

any revisions must be considered in the context of 

those changes.

•	 Not all states and local agencies provide the same data or 

level of detail for a given year.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

biogenic and anthropogenic CO emissions data in the 

NEI (U.S. EPA, 2007b) (http://www.epa.gov/ttn/chief/

net/2002inventory.html). This indicator aggregates the 

NEI data by source type (anthropogenic or biogenic), 

source category, and EPA Region. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. <ftp://ftp.

epa.gov/EmisInventory/2002finalnei/documentation/

mobile/2002_mobile_nei_version_3_report_092807.pdf>

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

Exhibit 2-2. CO emissions in the U.S. by

EPA Region, 1990 and 1996-2002a Emissions (million tons)

Year

0

5

10

15

20

25

30

Data source: U.S. EPA, 2007b

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

all fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

v
AIR

EPA’s 2008 Report on the Environment 2-11

INDICATOR | Ambient Concentrations of Carbon Monoxide

Carbon monoxide (CO) gas forms primarily when carbon fuels are not burned completely. Elevated ambient 

air concentrations of CO are hazardous because inhaled 

CO enters the bloodstream and reduces the amount of 

oxygen that the blood can deliver to the body’s organs and 

tissues. If exposure concentrations are high enough, potentially serious cardiovascular and neurological effects can 

result. Visual impairment, reduced work capacity, reduced 

manual dexterity, poor learning ability, and difficulty in 

performing complex tasks are all associated with exposure 

to elevated CO levels (U.S. EPA, 2000). 

Motor vehicle exhaust currently accounts for the 

majority of CO emissions nationwide, and as much as 95 

percent of CO emissions in cities with high traffic congestion. Other anthropogenic sources of CO emissions 

include fossil fuel combustion for heating and power 

generation, metals processing, and chemical manufacturing. The highest ambient air concentrations of CO often 

occur during nighttime inversion conditions, which trap 

pollutants near ground level. These conditions are most 

frequently observed during the cold winter months (U.S. 

EPA, 2003).

This indicator presents ambient CO concentrations 

in parts per million (ppm) from 1980 to 2006, based on 

continuous measurements averaged over 8-hour time 

frames. The 8-hour standard is indicative of exposures 

occurring over a sustained period of time, for example, 

an outdoor worker’s exposure over the course of a work 

day. This indicator displays trends in the annual second 

highest 8-hour CO concentrations for 144 sites in 102 

counties nationwide that have consistent data for the 

period of record in the State and Local Air Monitoring 

Stations network or by other special purpose monitors. 

It also shows trends in the average 8-hour measurements 

in each EPA Region. This indicator’s exhibits display the 

National Ambient Air Quality Standard (NAAQS) for 

CO as a point of reference, but the fact that the national or 

any regional second highest 8-hour values fall below the 

standard does not mean that all monitoring sites nationally or in the EPA Region also are below the standard. 

The indicator displays trends in the number of the 144 sites 

nationwide at which reported CO concentrations were 

above the level of the 8-hour standard, but this statistic is 

not displayed for each EPA Region.

What the Data Show

The 2006 annual second highest 8-hour CO concentration averaged across 144 monitoring sites nationwide was 

75 percent lower than that for 1980, and is the lowest level 

recorded during the past 27 years (Exhibit 2-3, panel A). 

The downward trend in CO concentrations in the 1990s 

parallels the downward trend observed in CO emissions, 

which has been attributed largely to decreased emissions 

from mobile sources (the CO Emissions indicator, p. 2-9). 

In addition, of the 144 sites used to determine this trend 

(out of 375 total monitoring sites that were operating in 

2006), the number reporting CO concentrations above the 

level of the CO standard declined to zero over the same 

period (Exhibit 2-3, panel B).

Also shown in Exhibit 2-3 (panel A) are the 90th and 10th

percentiles based on the distribution of annual statistics at 

the monitoring sites. This provides additional graphical 

representation of the distribution of measured concentrations across the monitoring sites for a given year. Thus, the 

graphic displays the concentration range where 80 percent 

of measured values occurred for that year. 

Consistent with the nationwide trend, CO levels in all 

ten EPA Regions have steadily decreased since 1980, with 

percent reductions over this period ranging from 68 percent (Region 7) to 85 percent (Region 1) (Exhibit 2-4).

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

Year

Year

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

0

2

4

6

8

10

12

14

16

A. Ambient concentrations

0

10

20

30

40

50

60

B. Number of trend sites above NAAQS

Annual second highest 8-hour 

 concentration (ppm)

Number of trend sites with annual second highest

8-hour concentration above the level of the 

NAAQS (9 ppm) 

10% of sites have 

concentrations below this line

NAAQS = 9 ppm

90% of sites have concentrations below this line

Average

Median

a

Coverage: 144 monitoring sites in 102 counties nationwide (out of 

a total of 375 sites measuring CO in 2006) that have sufficient 

data to assess CO trends since 1980.

Data source: U.S. EPA, 2007

Exhibit 2-3. Ambient CO concentrations in the 

U.S., 1980-2006a
AIR

2-12 EPA’s 2008 Report on the Environment

INDICATOR | Ambient Concentrations of Carbon Monoxide (continued)

Indicator Limitations

•	 Because most CO monitoring sites are located in hightraffic urban areas, the nationwide trends presented in 

this indicator might not accurately reflect conditions 

outside the immediate urban monitoring areas. 

•	 Because of the relatively small number of trend sites in 

some EPA Regions, the regional trends are subject to 

greater uncertainty than the national trends. Some EPA 

Regions with low average concentrations may include 

areas with high local concentrations, and vice versa. 

•	To ensure that long-term trends are based on a consistent 

set of monitoring sites, selection criteria were applied to 

identify the subset of CO monitoring sites with sufficient 

data to assess trends since 1980. Monitoring sites without sufficient data are not included in the trend analysis. 

Some excluded monitoring sites reported CO concentrations above the level of the CO standard over the time 

frame covered by this indicator. In 2006, for example, 

one monitoring site in the U.S. recorded CO concentrations above the level of the NAAQS, but did not have 

sufficient long-term data to be considered a trend site for 

this indicator.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

CO ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). National and regional trends in this indicator are 

based on the subset of CO monitoring stations that have 

sufficient data to assess trends since 1980. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. <http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. <http://www.epa.gov/air/

airtrends/aqtrnd03/>

U.S. EPA. 2000. Air quality criteria for carbon monoxide, 

2000. EPA/600/P-99/001F. Research Triangle Park, NC. 

<http://www.epa.gov/NCEA/pdfs/coaqcd.pdf>

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

0

2

4

6

8

10

12

16

14

Annual second highest 8-hour 

concentration (ppm)

Year

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

Exhibit 2-4. Ambient CO concentrations in the 

contiguous U.S. by EPA Region, 1980-2006a

a

Coverage: 141 monitoring sites 

in the EPA Regions (out of a total 

of 375 sites measuring CO in 

2006) that have sufficient data to 

assess CO trends since 1980.

Data source: U.S. EPA, 2007 10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

NAAQS = 9 ppm

INDICATOR | Lead Emissions

Lead is a naturally occurring metal found in small amounts in rock and soil. Lead has been used industrially in the 

production of gasoline, ceramic products, paints, metal 

alloys, batteries, and solder. In the past, automotive sources 

were the major contributors of lead emissions to the atmosphere. After leaded motor vehicle fuels were phased out 

during the 1970s and 1980s, the contribution of air emissions of lead from the transportation sector, and particularly 

the automotive sector, greatly declined. Today, industrial 

processes, primarily metals processing, account for a large 

portion of lead emissions to the atmosphere and the highest 

levels of airborne lead are usually found near industrial operations that process materials containing lead, such as smelters 

(U.S. EPA, 2003). Exposure to lead occurs mainly through 

inhalation of air and ingestion of lead in food, water, soil, or 

dust. The Lead Concentrations indicator (p. 2-14) describes 

health hazards associated with lead exposures. 

This indicator presents lead emissions from traditionally inventoried anthropogenic source categories: (1) “Fuel 

combustion,” which includes emissions from coal-, gas-, 

and oil-fired power plants and industrial, commercial, 

and institutional sources, as well as residential heaters and 

v
AIR

EPA’s 2008 Report on the Environment 2-13

boilers; (2) “Other sources,” which includes chemical 

production and petroleum refining; (3) “On-road vehicles,” which includes cars, trucks, buses, and motorcycles; 

(4) “Nonroad vehicles and engines,” such as farm and 

construction equipment, lawnmowers, chainsaws, boats, 

ships, snowmobiles, aircraft, and others; and (5) “Metals 

industrial processing.” Since metals processing is one of 

the largest sources of lead emissions, the indicator includes 

a metals source category in addition to the four categories 

presented in the other emissions indicators. 

For the years 1970 through 1985, the primary source 

for lead emissions data was the National Emissions Data 

System (NEDS) archives. Since 1990, lead emissions data 

have been tracked by the National Emissions Inventory 

(NEI). The NEI is a composite of data from many different sources, including industry and numerous state, tribal, 

and local agencies. Different data sources use different 

data collection methods, and many of the emissions data 

are based on estimates rather than actual measurements. 

For most industrial processes and fuel combustion sources, 

emissions are estimated using emission factors. Emissions 

from on-road and nonroad sources were estimated using 

EPA-approved modeling approaches (U.S. EPA, 2007a). 

Data for lead emissions cover all 50 states and their counties, D.C., the U.S. territories of Puerto Rico and Virgin 

Islands, and some of the territories of federally recognized 

American Indian nations. 

What the Data Show

Between 1970 and 2002, estimated nationwide lead emissions decreased by 99 percent (219,210 tons), mostly due 

to reductions from on-road vehicle sources after lead was 

removed from gasoline (Exhibit 2-5). Since 1990, further 

declines in lead emissions occurred, mostly due to reductions from on-road vehicles and nonroad vehicles and 

engines. Sharp declines in nationwide air concentrations 

of lead between 1980 and 1990 paralleled the emissions 

reductions (the Lead Concentrations indicator, p. 2-14). 

Indicator Limitations

•	 Although lead emissions trends have been generated using 

well-established estimation methods, the data reflect 

estimates based on empirical and engineering models and 

not actual measurement of lead emissions. These estimates have uncertainties inherent in the emission factors 

and emissions models used to represent sources for which 

emissions have not been directly measured.

•	The method for estimating lead emissions for fuel combustion and industrial sources changed in 1999 to reduce 

uncertainties inherent in the previous method (U.S. 

EPA, 2003). Despite the change in methodology, the 

long-term trend is still reliable. 

•	 Not all states and local agencies provide the same data or 

level of detail for a given year.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

lead emissions data from two sources. Emissions data 

from 1970 to 1985 are from EPA’s NEDS archives, and 

data summaries for this time frame can be found in 

various EPA publications (e.g., U.S. EPA, 2001). Emissions data for 1990-1999 and 2002 are available from the 

NEI (U.S. EPA, 2007b) (http://www.epa.gov/ttn/chief/

net/2002inventory.html). This indicator aggregates the 

emissions data by source category.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. <ftp://ftp.

epa.gov/EmisInventory/2002finalnei/documentation/

mobile/2002_mobile_nei_version_3_report_092807.pdf>

INDICATOR | Lead Emissions (continued)

Exhibit 2-5. Lead emissions in the U.S. by 

source category, 1970-1999 and 2002a

a

Emissions inventory 

data are presented 

for years that allow 

reliable estimation of 

long-term trends. 

b

Data for 1990-1999 

and 2002 are average 

annual emissions 

(thousand tons per 

year) and are therefore 

comparable to the 

annual emissions 

shown for the earlier years. 

Data source: U.S. EPA, 2001, 2007b

Year

0

1

2

3

4

5

6

’90 ’92 ’94 ’96 ’98 ’02

Year

Emissions 

(thousand tons per year)

Detail

0

50

100

150

200

250

’70 ’75 ’80 ’85 ’90-’99 and ’02b

Emissions (thousand tons per year)

Other sources

Nonroad vehicles and engines

Fuel combustion

Metals industrial processing

On-road vehicles
AIR

2-14 EPA’s 2008 Report on the Environment

INDICATOR | Lead Emissions (continued)

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

U.S. EPA. 2001. National air quality and emissions trends 

report, 1999. EPA/454/R-01/004. Research Triangle Park, 

NC. <http://www.epa.gov/air/airtrends/aqtrnd99/>

v

INDICATOR | Ambient Concentrations of Lead 

Lead is a naturally occurring metal found in small amounts 

in rock and soil. Despite steep decreases in emissions 

since 1970 (the Lead Emissions indicator, p. 2-12), lead 

remains an important environmental health issue because 

exposure to high levels has been associated with serious 

health effects, including neurological impairments such as 

seizures, mental retardation, and behavioral disorders (CDC, 

2005). Even at low doses, lead exposure can have adverse 

effects on the nervous systems of fetuses and young children 

(the Blood Lead indicator, p. 5-10) (U.S. EPA, 2006). People 

can be exposed to lead by inhaling airborne particles that 

contain lead, drinking contaminated water, eating contaminated food items, or ingesting non-food items that contain 

lead, such as dust and paint chips. 

Lead has been used industrially in the production of 

gasoline, ceramic products, paints, metal alloys, batteries, 

and solder. Some chemicals containing lead were previously added to gasoline to enhance vehicle performance, 

but that practice was phased out during the 1970s and 

1980s. As a result, air emissions of lead from the transportation sector decreased dramatically during that period 

(the Lead Emissions indicator, p. 2-12). Today, the highest levels of airborne lead are usually found near industrial 

operations that process materials containing lead, such as 

smelters (U.S. EPA, 2003).

This indicator presents ambient lead concentrations in 

micrograms per cubic meter (μg/m3

) from 1980 to 2006. 

Trends for this indicator are based on measurements made 

at 15 monitoring stations in 10 counties nationwide. These 

trend sites were selected because they are part of the State 

and Local Air Monitoring Stations network or are special 

purpose monitors and they have consistently measured 

ambient air concentrations of lead over the entire period of 

interest. Reported values are annual maximum quarterly 

averages. This indicator’s exhibit displays the lead National 

Ambient Air Quality Standard (NAAQS) as a point 

of reference, but the fact that the average national lead 

concentrations fall below the standard does not mean that 

all monitoring sites also are below the standard. 

What the Data Show

Between 1980 and 2006, average lead concentrations 

decreased 96 percent nationally (Exhibit 2-6, panel A). 

This decrease, which occurred mostly during the 1980s 

and early 1990s, is largely attributed to reduced lead 

content in gasoline (U.S. EPA, 2003). In addition, of 

the 15 sites used to determine this trend (out of 161 total 

monitoring sites that were operating in 2006), the number reporting lead concentrations above the level of the 

NAAQS declined to zero over the same period (Exhibit 

2-6, panel B).

Also shown in Exhibit 2-6 (panel A) are the 90th and 10th

percentiles based on the distribution of annual statistics at 

the monitoring sites. This provides additional graphical 

representation of the distribution of measured concentrations across the monitoring sites for a given year. Thus, the 

exhibit displays the concentration range where 80 percent 

of measured values occurred for each year. 

Indicator Limitations

•	 Because most lead monitoring sites are located in urban 

areas, the nationwide trends might not accurately reflect 

conditions outside the immediate urban monitoring areas. 

•	 To ensure that long-term trends are based on a consistent 

set of monitoring sites, selection criteria were applied to 

identify the subset of lead monitoring sites with sufficient 

data to assess trends since 1980. Monitoring sites without 

sufficient data are not included in the trend analysis. Some 

excluded monitoring sites reported lead concentrations 

above the level of the lead standard over the time frame 

covered by this indicator. In 2006, for example, two 

monitoring sites recorded lead concentrations above the 

level of the NAAQS, but did not have sufficient long-term 

data to be considered trend sites for this indicator.
AIR

EPA’s 2008 Report on the Environment 2-15

INDICATOR | Ambient Concentrations of Lead (continued)

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

lead ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). National trends in this indicator are based on the 

subset of lead monitoring stations that have sufficient data 

to assess trends since 1980.

References

CDC (Centers for Disease Control and Prevention, 

National Center for Environmental Health). 2005. Third 

national report on human exposure to environmental 

chemicals. NCEH Pub. No. 05-0570. 

<http://www.cdc.gov/exposurereport/report.htm>

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. 

<http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2006. Air quality criteria for lead. EPA/600/

R-5/144aF. Research Triangle Park, NC. <http://cfpub.

epa.gov/ncea/cfm/recordisplay.cfm?deid=158823>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

Year

Year

A. Ambient concentrations

B. Number of trend sites above NAAQS

a

Coverage: 15 monitoring in 10 counties nationwide (out of a total of 

161 sites measuring lead in 2006) that have sufficient data to assess 

lead trends since 1980.

Data source: U.S. EPA, 2007 Annual maximum quarterly average concentration (μg/m3)

Number of trend sites with annual maximum 

quarterly average concentration above the 

level of the NAAQS (1.5 μg/m3)

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

0.0

0.5

1.0

1.5

2.0

2.5

0

1

2

3

4

5

Exhibit 2-6. Ambient lead concentrations in 

the U.S., 1980-2006a

90% of sites have concentrations below this line

NAAQS = 1.5 μg/m3

10% of sites have 

concentrations below this line

Average

Median

v
AIR

2-16 EPA’s 2008 Report on the Environment

INDICATOR | Nitrogen Oxides Emissions

Nitrogen oxides” (NOx

) is the term used to describe the 

sum of nitric oxide (NO), nitrogen dioxide (NO2), and 

other oxides of nitrogen. Most airborne NOx comes from 

combustion-related emissions sources of human origin, 

primarily fossil fuel combustion in electric utilities, hightemperature operations at other industrial sources, and 

operation of motor vehicles. However, natural sources, like 

biological decay processes and lightning, also contribute to 

airborne NOx. Fuel-burning appliances, like home heaters and gas stoves, produce substantial amounts of NOx

 in 

indoor settings (U.S. EPA, 2003).

NOx plays a major role in several important environmental and human health issues. Short-term and long-term 

exposures to elevated air concentrations of NO2 are associated with various acute and chronic respiratory effects (U.S. 

EPA, 1993). NOx and volatile organic compounds react in 

the presence of sunlight to form ozone, which also is associated with human health and ecological effects (the Ozone 

Concentrations indicator, p. 2-22). NOx

 and other pollutants react in the air to form compounds that contribute to 

acid deposition, which can damage forests and cause lakes 

and streams to acidify (the Acid Deposition indicator, p. 

2-37). Deposition of NOx also affects nitrogen cycles and 

can contribute to nuisance growth of algae that can disrupt 

the chemical balance of nutrients in water bodies, especially 

in coastal estuaries (the Lake and Stream Acidity indicator, 

p. 2-42; the Trophic State of Coastal Waters indicator, 

p. 3-38). NOx also plays a role in several other environmental issues, including formation of particulate matter 

(the PM Concentrations indicator, p. 2-29), decreased visibility (the Regional Haze indicator, p. 2-33), and global 

climate change (the U.S. Greenhouse Gas Emissions indicator, p. 2-64; the Greenhouse Gas Concentrations indicator, 

p. 2-66). 

This indicator presents NOx emissions from traditionally inventoried anthropogenic source categories: (1) “Fuel 

combustion: selected power generators,” which includes 

emissions from coal-, gas-, and oil-fired power plants that are 

required to use continuous emissions monitors (CEMs) to 

report emissions as part of the Acid Rain Program (ARP); (2) 

“Fuel combustion: other sources,” which includes industrial, 

commercial, and institutional sources, as well as residential 

heaters and boilers not required to use CEMs; (3) “Other 

industrial processes,” which includes chemical production and 

petroleum refining; (4) “On-road vehicles,” which includes 

cars, trucks, buses, and motorcycles; (5) “Nonroad vehicles 

and engines,” such as farm and construction equipment, 

lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft, 

and others. Since a substantial portion of airborne NOx

 comes 

from fossil fuel combustion in electric utilities, this indicator 

includes the separate category for “selected power generators” in addition to the four categories presented in the other 

emissions indicators. The indicator also includes estimates of 

biogenic NOx emissions in 2002. Biogenic emissions were 

estimated using the Biogenic Emissions Inventory System 

Model, Version 3.12, with data from the Biogenic Landcover 

Database and 2001 annual meteorological data. 

NOx emissions data are tracked by the National Emissions Inventory (NEI). The NEI is a composite of data 

from many different sources, including industry and 

numerous state, tribal, and local agencies. Different data 

sources use different data collection methods, and many of 

the emissions data are based on estimates rather than actual 

measurements. For major electricity generating units, most 

data come from CEMs that measure actual emissions. For 

other fuel combustion sources and industrial processes, 

data are estimated using emission factors. Emissions from 

on-road and nonroad sources were estimated using EPAapproved modeling approaches (U.S. EPA, 2007a). 

NEI data have been collected since 1990 and cover all 

50 states and their counties, D.C., the U.S. territories of 

Puerto Rico and Virgin Islands, and some of the territories 

of federally recognized American Indian nations. Data are 

presented only for 1990 and the years from 1996 to 2002; 

“

Exhibit 2-7. NOx emissions in the U.S. by 

source category, 1990 and 1996-2002

Year

A. Anthropogenic NOX emissions by source categorya

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

Emissions (million tons)

Biogenic 

5%

Anthropogenic

95%

B. Relative amounts of NOX 

emissions from anthropogenic 

and biogenic sources, 2002

0

5

10

15

20

25

30

35

On-road vehicles

Nonroad vehicles and engines

Fuel combustion: 

selected power generatorsb

Fuel combustion: other sources

Other industrial processes

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

b

This category includes 

emissions from only those 

power plants required to use continuous emissions monitors under the 

Acid Rain Program.

Data source: U.S. EPA, 2007b
AIR

EPA’s 2008 Report on the Environment 2-17

INDICATOR | Nitrogen Oxides Emissions (continued)

prior to 1996, only the 1990 data have been updated to be 

comparable to the more recent inventories. 

What the Data Show

This indicator focuses on trends in NOx emissions from 

anthropogenic sources. However, NOx emissions from 

biogenic sources were estimated for 2002 to provide a sense 

of the relative contributions of natural versus anthropogenic 

emissions. Nationally, biogenic emissions were estimated to 

contribute approximately 5 percent to NOx emissions from 

all sources during 2002 (Exhibit 2-7, panel B).

According to the NEI data, estimated nationwide 

anthropogenic emissions of NOx decreased by 17 percent 

between 1990 and 2002 (from 25,160,000 to 20,917,000 

tons) (Exhibit 2-7, panel A). This downward trend results 

primarily from emissions reductions at electric utilities and 

among on-road mobile sources. Although total nationwide anthropogenic NOx

 emissions decreased during this 

period, emissions from some sources (such as nonroad 

vehicles and engines) have increased since 1990. 

Estimated anthropogenic NOx emissions in nine of 

the ten EPA Regions decreased between 1990 and 2002 

(Exhibit 2-8). The percent change in emissions over this 

time frame ranged from a 36 percent decrease (in Region 

2) to a 6 percent increase (in Region 10), and the largest 

absolute reduction (919,000 tons) occurred in Region 3.

Indicator Limitations

•	 Comparable NOx emissions estimates through the NEI 

are available only for 1990 and 1996-2002. Data for 

1991-1995 are not provided due to differences in emissions estimation methodologies from other inventory 

years, which could lead to improper trend assessments. 

•	 NOx emissions from miscellaneous sources are not 

included in the total emissions. 

•	Though NOx emissions from most electric utilities are 

measured directly using continuous monitoring devices, 

NOx emissions data for most other source types are 

estimates. These estimates are generated using wellestablished approaches, but still have uncertainties inherent in the emission factors and emissions models used 

to represent sources for which emissions have not been 

directly measured.

•	The methodology for estimating emissions is continually 

reviewed and is subject to revision. Trend data prior to 

any revisions must be considered in the context of 

those changes.

•	 Not all states and local agencies provide the same data or 

level of detail for a given year.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

anthropogenic and biogenic NOx

 emissions data in EPA’s 

NEI (U.S. EPA, 2007b) (http://www.epa.gov/ttn/chief/

net/2002inventory.html). This indicator aggregates the NEI 

data by source type (anthropogenic or biogenic), source 

category, and EPA Region. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. 

<ftp://ftp.epa.gov/EmisInventory/2002finalnei/

documentation/mobile/2002_mobile_nei_version_3_

report_092807.pdf>

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

U.S. EPA. 1993. Air quality criteria for oxides of nitrogen. 

EPA/600/8-91/049aF-cF. Research Triangle Park, NC.

Exhibit 2-8. NOx emissions in the U.S. by EPA 

Region, 1990 and 1996-2002a

Year

Emissions (million tons) a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

Data source: U.S. EPA, 2007b

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

0

1

2

3

4

5

6

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

v
AIR

2-18 EPA’s 2008 Report on the Environment

INDICATOR | Ambient Concentrations of Nitrogen Dioxide

Nitrogen dioxide (NO2

) is a reddish-brown, highly reactive gas that is formed in the ambient air through the 

oxidation of nitric oxide (NO). Nitrogen dioxide is one 

in a group of highly reactive gases generically referred to 

as “nitrogen oxides” (NOx), all of which contain nitrogen 

and oxygen in varying amounts. NOx plays a major role in 

the formation of ozone in the atmosphere through a complex series of reactions with volatile organic compounds. 

NO2 is the most widespread and commonly found nitrogen oxide (U.S. EPA, 2003). 

Short-term exposures (e.g., less than 3 hours) to low 

levels of NO2 may lead to changes in airway responsiveness 

and lung function in individuals with preexisting respiratory illnesses. These exposures may also increase respiratory illnesses in children. Long-term exposures to NO2

may lead to increased susceptibility to respiratory infection 

and may cause irreversible alterations in lung structure 

(U.S. EPA, 1995).

Atmospheric transformation of NOx

 can lead to the 

formation of ozone and nitrogen-bearing particles (e.g., 

nitrates, nitric acid). Deposition of nitrogen can lead to fertilization, eutrophication, or acidification of terrestrial, wetland, and aquatic (e.g., fresh water bodies, estuaries, coastal 

water) systems. These effects can alter competition among 

existing species, leading to changes in species abundance and 

distribution within communities. For example, eutrophic 

conditions in aquatic systems can produce explosive growth 

of algae leading to hypoxia or an increase in levels of toxins 

harmful to fish and other aquatic life (U.S. EPA, 1993). 

This indicator presents ambient NO2

 concentrations in 

parts per million (ppm) from 1980 to 2006, based on the 

annual arithmetic average. The indicator displays trends 

averaged over 87 sites in 64 counties nationwide that have 

consistent data for the period of record in the State and 

Local Air Monitoring Stations network or by special purpose monitors. It also shows trends in the annual average 

NO2 measurements in each EPA Region. This indicator’s 

exhibits display the NO2 National Ambient Air Quality 

Standard (NAAQS) as a point of reference, but the fact that 

the national or any regional average values fall below the 

standard does not mean that all monitoring sites nationally or in the EPA Region also are below the standard. 

This indicator displays trends in the number of the 87 sites 

nationwide at which NO2

 concentrations exceeded the level 

of the annual average standard over the period of record, but 

this statistic is not displayed for each EPA Region. 

What the Data Show 

The national annual average NO2 concentration in 2006 

was 41 percent lower than that recorded in 1980 (Exhibit 

2-9, panel A). Also shown on this graph are the 90th and 

10th percentiles of NO2 concentrations based on the distribution of annual statistics at the monitoring sites. This provides additional graphical representation of the distribution 

of measured concentrations across the monitoring sites for 

a given year. Thus, for each year, the graphic displays the 

concentration range where 80 percent of measured values 

occurred. The highest annual average NO2

 concentrations are typically found in urban areas. In addition, of 

the 87 sites used to determine this trend (out of 369 total 

monitoring sites that were operating in 2006), the number 

reporting NO2 concentrations above the level of the NO2

standard declined from seven sites in 1981 to zero sites 

since 1992 (Exhibit 2-9, panel B).

NO2

 levels in all ten EPA Regions have steadily 

decreased since 1980, with percent reductions over this 

time ranging from 20 percent in Region 8 to 49 percent in 

Region 1 (Exhibit 2-10). 

Year

Year

A. Ambient concentrations

B. Number of trend sites above NAAQS

Annual average concentration (ppm)

Number of trend sites with annual 

average concentration above the level of the 

NAAQS (0.053 ppm) 

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

0.00

0.01

0.02

0.03

0.04

0.05

0.06

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

0

2

4

6

8

NAAQS = 0.053 ppm

Median

10% of sites have 

concentrations below this line

90% of sites have concentrations below this line

Average

Exhibit 2-9. Ambient NO2 concentrations in the 

U.S., 1980-2006a

a

Coverage: 87 monitoring sites in 64 counties nationwide (out of a 

total of 369 sites measuring NO2 in 2006) that have sufficient data 

to assess NO2 trends since 1980.

Data source: U.S. EPA, 2007
AIR

EPA’s 2008 Report on the Environment 2-19

INDICATOR | Ambient Concentrations of Nitrogen Dioxide (continued)

The decrease in NO2

 concentrations in this indicator is 

consistent with the decreasing NOx emissions observed 

over the past decade (the Nitrogen Oxides Emissions indicator, p. 2-16). 

Indicator Limitations 

•	 Because ambient monitoring for NO2 occurs almost 

exclusively in high-traffic urban areas, the average 

concentrations presented in this indicator likely may not 

reflect NO2 levels in rural areas. Also, in rural areas, air 

mass aging could foster greater relative levels of peroxyacetyl nitrate (PAN) and nitric acid which can cause a 

positive interference in NO2 measurements. 

•	The measurement of NO2 is based on the conversion of 

NO2 to NO and the subsequent detection of NO using 

the chemiluminescence technique. Because there are 

other nitrogen-containing compounds, such as PAN and 

nitric acid, that can be converted to NO, the chemiluminescence technique may overestimate NO2

 concentrations due to these interferences. Measurement devices 

with ultraviolet photolytic converters are less prone to 

interferences than devices with heated surfaces (or catalysts) upstream of the chemiluminescence detector.

•	 Because of the relatively small number of trend sites in 

some EPA Regions, the regional trends are subject to 

greater uncertainty than the national trends. Some EPA 

Regions with low average concentrations may include 

areas with high local concentrations, and vice versa. 

•	To ensure that long-term trends are based on a consistent set of monitoring sites, selection criteria were 

applied to identify the subset of NO2 monitoring sites 

with sufficient data to assess trends since 1980. Monitoring sites without sufficient data are not included in the 

trend analysis. Some excluded monitoring sites reported 

NO2 concentrations above the level of the NO2 standard 

over the time frame covered by this indicator. In 2006, 

however, no monitoring sites in the U.S. measured NO2

concentrations above the level of the NAAQS.

Data Sources 

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

NO2 ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). National and regional trends in this indicator are 

based on the subset of NO2 monitoring stations that have 

sufficient data to assess trends since 1980.

References 

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. 

<http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

U.S. EPA. 1995. Review of the national ambient air quality standards for nitrogen oxides: Assessment of scientific 

and technical information. EPA/452/R-95/005. Research 

Triangle Park, NC.

U.S. EPA. 1993. Air quality criteria for oxides of nitrogen. 

EPA/600/8-91/049aF-cF. Research Triangle Park, NC.

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10b

Annual average concentration (ppm)

Nat’l

Year

0.00

0.01

0.02

0.03

0.04

0.05

0.06

’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

NAAQS = 0.053 ppm

Exhibit 2-10. Ambient NO2 concentrations in the 

contiguous U.S. by EPA Region, 1980-2006a,b

a

Coverage: 87 monitoring sites 

in the EPA Regions (out of a 

total of 369 sites measuring 

NO2 in 2006) that have 

sufficient data to assess NO2

trends since 1980.

b

Because NO2 in Region 10 has 

been at such low 

concentrations, none of this 

Region’s monitoring sites have a complete record dating back to 1980. 

Thus, no trend line for Region 10 is shown.

Data source: U.S. EPA, 2007

v
AIR

2-20 EPA’s 2008 Report on the Environment

INDICATOR | Volatile Organic Compounds Emissions

Volatile organic compounds (VOCs) are a large group of organic chemicals that include any compound of carbon 

(excluding carbon monoxide, carbon dioxide, carbonic acid, 

metallic carbides or carbonates, and ammonium carbonate) 

and that participate in atmospheric photochemical reactions. VOCs are of interest in part because they contribute 

to ozone formation (U.S. EPA, 2003a). Ozone (the Ozone 

Concentrations indicator, p. 2-22) is formed from chemical reactions involving airborne VOCs, airborne nitrogen 

oxides, and sunlight. VOCs are also of interest because 

many individual VOCs are known to be harmful to human 

health (the Benzene Concentrations indicator, p. 2-51; the 

Air Toxics Emissions indicator, p. 2-48). Health effects vary 

by pollutant. VOCs are emitted from a variety of sources, 

including motor vehicles, chemical manufacturing facilities, 

refineries, factories, consumer and commercial products, and 

natural (biogenic) sources (mainly trees) (U.S. EPA, 2003b).

This indicator presents VOC emissions from traditionally inventoried anthropogenic source categories: 

(1) “Fuel combustion,” which includes emissions from 

coal-, gas-, and oil-fired power plants and industrial, commercial, and institutional sources, as well as residential 

heaters and boilers; (2) “Other industrial processes,” which 

includes chemical production, petroleum refining, metals 

production, and processes other than fuel combustion; (3) 

“On-road vehicles,” which includes cars, trucks, buses, and 

motorcycles; and (4) “Nonroad vehicles and engines,” such 

as farm and construction equipment, lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft, and others. The 

indicator also includes estimates of biogenic VOC emissions in 2002. Biogenic emissions were estimated using the 

Biogenic Emissions Inventory System Model, Version 3.12, 

with data from the Biogenic Emissions Landcover Database and 2001 annual meteorological data. 

VOC emissions data are tracked by the National Emissions Inventory (NEI). The NEI is a composite of data 

from many different sources, including industry and 

numerous state, tribal, and local agencies. Different data 

sources use different data collection methods, and many of 

the emissions data are based on estimates rather than actual 

measurements. For most fuel combustion sources and 

industrial sources, emissions are estimated using emission 

factors. Emissions from on-road and nonroad sources were 

estimated using EPA-approved modeling approaches (U.S. 

EPA, 2007a). 

NEI data have been collected since 1990 and cover all 

50 states and their counties, D.C., the U.S. territories of 

Puerto Rico and Virgin Islands, and some of the territories 

of federally recognized American Indian nations. Data are 

presented only for 1990 and the years from 1996 to 2002; 

prior to 1996, only the 1990 data have been updated to be 

comparable to the more recent inventories.

What the Data Show

This indicator focuses on trends in VOC emissions from 

anthropogenic sources. However, VOC emissions from 

biogenic sources were estimated for 2002 to provide a sense 

of the relative contributions of natural versus anthropogenic 

emissions. Nationally, biogenic emissions were estimated 

to contribute approximately 72 percent to VOC emissions 

from all sources during 2002 (Exhibit 2-11, panel B). Thus, 

VOC emissions from biogenic sources are larger than the 

VOC emissions from all anthropogenic sources combined. 

According to NEI data, national total estimated VOC 

emissions from anthropogenic sources, excluding wildfires and prescribed burns, decreased by 25 percent 

between 1990 and 2002 (from 23,048,000 to 17,194,000 

tons) (Exhibit 2-11, panel A). The overwhelming majority of anthropogenic emissions reductions were observed 

among industrial processes and on-road mobile sources. 

Combined, these two source categories accounted for 84 

percent of the total nationwide estimated anthropogenic 

VOC emissions in 1990 (excluding wildfires and prescribed burns), but accounted for only 72 percent of the 

nationwide anthropogenic emissions in 2002. 

Exhibit 2-11. VOC emissions in the U.S. by 

source category, 1990 and 1996-2002

Year

A. Anthropogenic VOC emissions by source categorya

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

Emissions (million tons)

Anthropogenic

28%

Biogenic

72%

B. Relative amounts of VOC 

emissions from anthropogenic 

and biogenic sources, 2002

0

5

10

15

20

25

On-road vehicles

Fuel combustion

Other industrial processes

Nonroad vehicles and engines

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

Data source: U.S. EPA, 2007b
AIR

EPA’s 2008 Report on the Environment 2-21

INDICATOR | Volatile Organic Compounds Emissions (continued)

Trends in estimated anthropogenic VOC emissions in 

nine of the ten EPA Regions were consistent with the overall decline seen nationally from 1990 to 2002 (Exhibit 2-12). 

Changes in VOC emissions ranged from a 52 percent reduction (Region 9) to a 16 percent increase (Region 10).

Indicator Limitations

•	 Comparable VOC emissions estimates through the NEI 

are available only for 1990 and 1996-2002. Data for 

1991-1995 are not provided due to differences in emissions estimation methodologies from other inventory 

years, which could lead to improper trend assessments.

•	 VOC emissions from “miscellaneous sources” are not 

included in the total emissions. Details on emissions from 

miscellaneous sources can be found by downloading 2002 

NEI inventory data for the “nonpoint sector” (http://

www.epa.gov/ttn/chief/net/2002inventory.html).

•	VOC emissions data are largely based on estimates that 

employ emission factors generated from empirical and 

engineering studies, rather than on actual measurements 

of VOC emissions. These estimates are generated using 

well-established approaches, and quality assurance measures are implemented to ensure that the emissions data 

entered in NEI meet data quality standards (U.S. EPA, 

2006). Nonetheless, the estimates have uncertainties 

inherent in the emission factors and emissions models 

used to represent sources for which emissions have not 

been directly measured. 

•	The methodology for estimating emissions is continually 

reviewed and is subject to revision. Trend data prior to 

any revisions must be considered in the context of 

those changes.

•	 Not all states and local agencies provide the same data or 

level of detail for a given year.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

biogenic and anthropogenic VOC emissions data in the 

NEI (U.S. EPA, 2007b) (http://www.epa.gov/ttn/chief/

net/2002inventory.html). This indicator aggregates the 

NEI data by source type (anthropogenic or biogenic), 

source category, and EPA Region. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. <ftp://ftp.epa.gov/

EmisInventory/2002finalnei/documentation/mobile/2002_

mobile_nei_version_3_report_092807.pdf>

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2006. NEI quality assurance and data 

augmentation for point sources. Research Triangle Park, 

NC. <ftp://ftp.epa.gov/EmisInventory/2002finalnei/

documentation/point/augmentation_point/

2002nei_qa_augmentation_report0206.pdf>

U.S. EPA. 2003a. Requirements for preparation, adoption, 

and submittal of implementation plans: Definitions. Code 

of Federal Regulations 40CFR51.100(s).

U.S. EPA. 2003b. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

Exhibit 2-12. VOC emissions in the U.S. by 

EPA Region, 1990 and 1996-2002a

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Year

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

Data source: U.S. EPA, 2007b Emissions (million tons)

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

0

1

2

3

4

5

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

v
AIR

2-22 EPA’s 2008 Report on the Environment

INDICATOR | Ambient Concentrations of Ozone

Ozone is a gas found in different parts of the atmosphere. Ozone in the upper atmosphere, or stratosphere, 

helps protect the Earth from the sun’s harmful rays. (The 

Ozone Levels over North America indicator, on page 

2-54, describes trends in stratospheric ozone levels over the 

U.S.) In the lowest level of the atmosphere, the troposphere, ozone is harmful to both human health and the 

environment. For this reason, ozone is often described as 

being “good up high and bad nearby” (U.S. EPA, 2003a). 

Although some industrial sources release ozone directly 

into the environment, most ground-level ozone forms in 

the air from chemical reactions involving nitrogen oxides 

(NOx), volatile organic compounds (VOCs), and sunlight. 

Ozone levels are typically highest during the afternoon 

hours of the summer months, when the influence of direct 

sunlight is the greatest. These highest levels occur during what is known as the “ozone season,” which typically 

occurs from May 1 to September 30 but whose time frame 

varies by state (U.S. EPA, 2003b).

Variations in weather conditions play an important role 

in determining ozone levels. Daily temperatures, relative humidity, and wind speed can affect ozone levels. In 

general, warm dry weather is more conducive to ozone 

formation than cool wet weather. Wind can affect both 

the location and concentration of ozone pollution. NOx

and VOC emissions can travel hundreds of miles on air 

currents, forming ozone far from the original emissions 

sources. Ozone also can travel long distances, affecting 

areas far downwind. High winds tend to disperse pollutants and can dilute ozone concentrations. However, 

stagnant conditions or light winds allow pollution levels to 

build up and become more concentrated.

Inhalation exposure to ozone has been linked to numerous respiratory health effects, including acute reversible 

decrements in lung function, airway inflammation, cough, 

and pain when taking a deep breath. Ozone exposure can 

aggravate lung diseases such as asthma, leading to increased 

medication use and increased hospital admission and visits 

to emergency rooms. In addition, evidence is highly suggestive that ozone directly or indirectly contributes to 

non-accidental and cardiopulmonary-related mortality, but 

the underlying mechanisms by which such effects occur 

have not been fully established (U.S. EPA, 2006). Although 

people with lung disease are most susceptible to the effects 

of ozone, even healthy people who are active outdoors can 

suffer from ozone-related health effects. Further, evidence 

suggests that older adults (more than 65 years old) appear to 

be at excess risk of ozone-related mortality or hospitalization (U.S. EPA, 2006). Elevated concentrations of ozone 

can also affect vegetation and ecosystems, as the Ozone 

Injury to Forest Plants indicator (p. 2-24) describes further 

(U.S. EPA, 2006). 

This indicator presents ambient ground-level ozone 

concentrations in parts per million (ppm) from 1978 to 

2006. Data are shown for 8-hour averaging times, based 

on continuous ozone monitoring data and consistent with 

this pollutant’s National Ambient Air Quality Standard 

(NAAQS). The 8-hour standard is indicative of exposures 

occurring over a sustained period of time (e.g., an outdoor 

worker’s exposure over the course of a work day). Trends 

for this indicator represent 201 sites in 150 counties nationwide that have data for the period of record in the State 

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Averaging period

Averaging period

B. Number of trend sites above NAAQS

A. Ambient concentrations

’78-’80 ’82-’84 ’86-’88 ’90-’92 ’94-’96 ’98-’00 ’02-’04

’78-’80 ’82-’84 ’86-’88 ’90-’92 ’94-’96 ’98-’00 ’02-’04

NAAQS = 0.08 ppmb

Average

Median

10% of sites have concentrations below this line

90% of sites have concentrations below this line

0

40

80

120

160

Exhibit 2-13. Ambient 8-hour ozone 

concentrations in the U.S., 1978-2006a Average of fourth highest daily maximum 8-hour concentrations for three consecutive calendar years (ppm) Number of trend sites with average of fourth highest daily maximum 8-hour concentrations for three consecutive calendar years above the level of the NAAQS (0.08 ppm)

a

Coverage: 201 monitoring sites in 150 counties nationwide (out of 

a total of 1,194 sites measuring ozone in 2006) that have sufficient 

data to assess ozone trends since 1978.

b

The figure displays the 1997 NAAQS (0.08 ppm). Future versions of 

the ROE will compare ozone concentrations to the recently 

promulgated 2008 NAAQS (0.075 ppm) or to the NAAQS in effect at 

the time.

Data source: U.S. EPA, 2007
AIR

EPA’s 2008 Report on the Environment 2-23

INDICATOR | Ambient Concentrations of Ozone (continued)

and Local Air Monitoring Stations network or by other 

special purpose monitors. The indicator also displays trends 

in ozone measurements in each EPA Region. This indicator’s exhibits display the corresponding 1997 NAAQS as a 

point of reference, but the fact that the national or regional 

concentrations fall below the standard does not mean that 

all monitoring sites nationally or in any EPA Region also 

are below the standard. The indicator displays trends in 

the number of the 201 sites nationwide at which ozone 

concentrations exceeded the level of the 1997 standard, but 

this statistic is not displayed for each EPA Region. 

Trends in ozone concentrations can be difficult to discern because of the year-to-year variations in the concentrations. By presenting data for rolling 3-year time periods, 

this indicator smoothes out the “peaks” and “valleys” in 

the trend, making it easier to see the long-term trend. 

Three years is consistent with the 3-year period used to 

assess compliance with the ozone standards. For the 8-hour 

trends in this report, a 3-year average of the fourth highest 

daily maximum 8-hour concentration in each year is used 

to be consistent with the 8-hour ozone standard. 

What the Data Show

Between the 1978-1980 and 2004-2006 averaging periods, nationwide fourth highest daily maximum 8-hour 

ambient ozone concentrations decreased by 25 percent 

(Exhibit 2-13, panel A). Although the 8-hour ozone levels 

in 2004-2006 were the lowest on record and the number 

of trend sites measuring ozone concentrations above the 

level of the 1997 8-hour NAAQS decreased by 75 percent 

over the time frame covered in this indicator (Exhibit 

2-13, panel B), ambient air monitoring data collected in 

2006 and reported to EPA’s Air Quality System indicate 

that approximately 77 million people lived in counties 

where 8-hour average ozone concentrations are above 

the level of the 1997 primary ozone NAAQS. Among the 

ten EPA Regions, the most substantial declines in 8 hour 

levels were observed in EPA Regions that originally had 

the highest ozone concentrations (EPA Regions 1 and 9) 

(Exhibit 2-14). Over the entire period of record, Region 

10 consistently showed the lowest Regional ozone levels.

Also shown in Exhibit 2-13 (panel A) are the 90th and 

10th percentiles based on the distribution of statistics at 

the monitoring sites. This provides additional graphical 

representation of the variability of measured concentrations 

across the monitoring sites for a given 3-year period. Thus, 

the graphic displays the concentration range where 80 percent of measured values occurred for that 3-year period. 

In summary, despite reductions in ambient concentrations of ozone over the past quarter century and decreases in 

the emissions of ozone precursors since 1990 (the Nitrogen 

Oxides Emissions indicator, p. 2-16; the VOC Emissions 

indicator, p. 2-20.), ozone remains one of the most persistent 

and ubiquitous air pollution issues in the U.S.

 Indicator Limitations

•	 Short-term trends in ozone concentrations are often 

highly dependent on meteorological conditions. This 

complicates efforts to interpret data for any given year. 

Air quality trends over the longer term are far less likely 

to be influenced by unusual meteorological conditions.

•	 Because most of the monitoring sites are located in urban 

areas, the trends might not accurately reflect conditions 

outside the immediate urban monitoring areas. 

•	 Because of the relatively small number of trend sites in 

some EPA Regions, the regional trends are subject to 

greater uncertainty than the national trends. Some EPA 

Regions with low average concentrations may include 

areas with high local concentrations, and vice versa. 

•	 To ensure that long-term trends are based on a consistent 

set of monitoring sites, selection criteria were applied to 

identify the subset of ozone monitoring sites with sufficient 

data to assess trends since 1978. Monitoring sites without 

sufficient data are not included in the trend analysis. Some 

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

NAAQS = 0.08 ppmb

Average of fourth highest daily 

maximum 8-hour concentrations for 

three consecutive calendar years (ppm)

Exhibit 2-14. Ambient 8-hour ozone 

concentrations in the contiguous U.S. by EPA 

Region, 1978-2006a

a

Coverage: 201 monitoring 

sites in the EPA Regions (out of 

a total of 1,194 sites measuring 

ozone in 2006) that have 

sufficient data to assess ozone 

trends since 1978.

b

The figure displays the 1997 

NAAQS (0.08 ppm). Future 

versions of the ROE will 

compare ozone concentrations 

to the recently promulgated 

2008 NAAQS (0.075 ppm) or 

to the NAAQS in effect at 

the time.

Data source: U.S. EPA, 2007

Averaging period

’78-’80 ’86-’88 ’94-’96 ’02-’04
AIR

2-24 EPA’s 2008 Report on the Environment

INDICATOR | Ambient Concentrations of Ozone (continued)

excluded monitoring sites reported ozone concentrations 

above the level of the ozone standard over the time frame 

covered by this indicator. In 2006, for example, 187 monitoring sites (in addition to the trend sites shown in Exhibit 

2-13, panel B) recorded ozone concentrations above the 

level of the 1997 NAAQS, but did not have sufficient longterm data to be included in this indicator.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

ozone ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). National and regional trends in this indicator are 

based on the subset of ozone monitoring stations that have 

sufficient data to assess trends since 1978.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. <http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2006. Air quality criteria for ozone and related 

photochemical oxidants. EPA/600/R-05/004aF-cF. 

Research Triangle Park, NC. <http://cfpub.epa.gov/ncea/

cfm/recordisplay.cfm?deid=149923>

U.S. EPA. 2003a. Ozone: Good up high, bad nearby. 

EPA/451/K-03/001. Washington, DC. <http://www.epa.

gov/oar/oaqps/gooduphigh/> 

U.S. EPA. 2003b. Latest findings on national air quality—2002 status and trends. EPA/454/K-03/001. Research 

Triangle Park, NC. <http://www.epa.gov/air/airtrends/

aqtrnd02/2002_airtrends_final.pdf>

v

INDICATOR | Ozone Injury to Forest Plants

Air pollution can have noteworthy cumulative impacts on forested ecosystems by affecting regeneration, 

productivity, and species composition (U.S. EPA, 2006). In 

the U.S., ozone in the lower atmosphere is one of the pollutants of primary concern. Ozone injury to forest plants 

can be diagnosed by examination of plant leaves. Foliar 

injury is usually the first visible sign of injury to plants 

from ozone exposure and indicates impaired physiological 

processes in the leaves (Grulke, 2003).

This indicator is based on data from the U.S. Department 

of Agriculture (USDA) Forest Service Forest Inventory and 

Analysis (FIA) program. As part of its Phase 3 program, 

formerly known as Forest Health Monitoring, FIA examines 

ozone injury to ozone-sensitive plant species at ground monitoring sites in forest land across the country. For this indicator, 

forest land does not include woodlots and urban trees. Sites 

are selected using a systematic sampling grid, based on a global 

sampling design (White et al., 1992; Smith et al., 2003). At 

each site that has at least 30 individual plants of at least three 

ozone-sensitive species and enough open space to ensure that 

sensitive plants are not protected from exposure by the forest 

canopy, FIA looks for damage on the foliage of ozone-sensitive 

forest plant species. Because ozone injury is cumulative over 

the course of the growing season, examinations are conducted 

in July and August, when ozone injury is typically highest. 

Monitoring of ozone injury to plants by the USDA Forest 

Service has expanded over the last 10 years from monitoring 

sites in ten states in 1994 to nearly 1,000 monitoring sites 

in 41 states in 2002. The data underlying this indicator are 

based on averages of all observations collected in 2002, the 

latest year for which data are publicly available, and are broken down by EPA Region. Ozone damage to forest plants is 

classified using a subjective five-category biosite index based 

on expert opinion, but designed to be equivalent from site 

to site. Ranges of biosite values translate to no injury, low or 

moderate foliar injury (visible foliar injury to highly sensitive or moderately sensitive plants, respectively), and high 

or severe foliar injury, which would be expected to result in 

tree-level or ecosystem-level responses, respectively (Coulston et al., 2004; U.S. EPA, 2006).

What the Data Show

There is considerable regional variation in ozone injury to 

sensitive plants (Exhibit 2-15). The highest percentages of 

observed high and severe foliar injury, which are most likely 

to be associated with tree or ecosystem-level responses, 

are primarily found in the Mid-Atlantic and Southeast 

regions. In EPA Region 3, 12 percent of ozone-sensitive 

plants showed signs of high or severe foliar damage, and in 

Regions 2 and 4, the values were 10 percent and 7 percent, 

respectively. The sum of high and severe ozone injury 

ranged from 2 percent to 4 percent in EPA Regions 1, 7, and 

9; and no high or severe foliar damage was observed in EPA 

Regions 5, 6, 8, and 10. The percentage of sites showing no 

damage was greater than 55 percent in every EPA Region, 

and no ozone-related foliar damage was observed at any of 

the 129 biosites in EPA Regions 8 and 10.
AIR

EPA’s 2008 Report on the Environment 2-25

INDICATOR | Ozone Injury to Forest Plants (continued)

Indicator Limitations

•	 Field and laboratory studies were reviewed to identify 

the forest plant species in each region that are highly sensitive to ozone air pollution. Other forest plant species, 

or even genetic variants of the same species, may not be 

harmed at ozone levels that cause effects on the selected 

ozone-sensitive species. 

•	 Because species distributions vary regionally, different 

ozone-sensitive plant species were examined in different 

parts of the country. These target species could vary with 

respect to ozone sensitivity, which might account for 

some of the apparent differences in ozone injury among 

EPA Regions.

•	 Ozone damage to foliage is considerably reduced under 

conditions of low soil moisture, but most of the variability in the index (70 percent) was explained by ozone 

concentration (Smith et al., 2003).

•	 Ozone may have other adverse impacts on plants (e.g., 

reduced productivity) that do not show signs of visible 

foliar injury (U.S. EPA, 2006).

•	Though FIA has extensive spatial coverage based on a 

robust sample design, not all forested areas in the U.S. 

are monitored for ozone injury.

•	 Even though the biosite data have been collected over 

multiple years, most biosites were not monitored over 

the entire period, so these data cannot provide more 

than a baseline for future trends.

Data Sources

Data were provided by the USDA Forest Service’s Ozone 

Biomonitoring Program, which maintains a database of 

plant injury statistics by state (USDA Forest Service, 2006) 

(http://nrs.fs.fed.us/fia/topics/ozone/data/). This indicator 

aggregates the state data by EPA Region.

References

Coulston, J.W., K.H. Riitters, and G.C. Smith. 2004. A 

preliminary assessment of the Montréal process indicators of air pollution for the United States. Environ. Monit. 

Assess. 95:57-74.

Grulke, N.E. 2003. The physiological basis of ozone injury 

assessment attributes in Sierran conifers. In: Bytnerowicz, 

A., M.J. Arbaugh, and R. Alonso, eds. Ozone air pollution 

in the Sierra Nevada: Distribution and effects on forests. 

New York, NY: Elsevier Science, Ltd. pp. 55-81.

Smith, G., J. Coulston, E. Jepsen, and T. Prichard. 2003. A 

national ozone biomonitoring program—results from field 

surveys of ozone sensitive plants in Northeastern forests 

(1994-2000). Environ. Monit. Assess. 87:271-291.

USDA Forest Service (United States Department of Agriculture Forest Service). 2006. Ozone bioindicator data. 

Accessed 2006. <http://nrs.fs.fed.us/fia/topics/ozone/data/>

U.S. EPA (United States Environmental Protection 

Agency). 2006. Air quality criteria for ozone and related 

photochemical oxidants. EPA/600/R-05/004aF-cF. 

Research Triangle Park, NC. <http://cfpub.epa.gov/ncea/

cfm/recordisplay.cfm?deid=149923>

White, D., A.J. Kimerling, and W.S. Overton. 1992. Cartographic and geometric component of a global sampling 

design for environmental monitoring. Cartogr. Geograph. 

Info. Sys. 19:5-22. 

Exhibit 2-15. Ozone injury to forest plants in 

the U.S. by EPA Region, 2002a,b

Degree of injury:

Percent of monitoring sites in each category:

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

None Low Moderate High Severe

Region 1 

(54 sites)

Region 2 

(42 sites)

Region 3 

(111 sites)

Region 4 

(227 sites)

Region 5 

(180 sites)

Region 6 

(59 sites)

Region 7 

(63 sites)

Region 8 

(72 sites)

Region 9 

(80 sites)

Region 10 

(57 sites)

a

Coverage: 945 monitoring sites, 

located in 41 states.

b

Totals may not add to 100% due to 

rounding.

Data source: USDA Forest Service, 

2006

100.0

76.3

100.0

85.7

94.9

75.6

75.3

55.9

61.9

68.5

12.5

9.5

5.1

18.3

10.1

18.0

21.4

16.7

8.8

3.2

6.1

7.0

14.4

7.1

11.1

1.3

3.7

1.3

1.6

4.0

2.4

4.5

3.5

7.1

7.2

v
AIR

2-26 EPA’s 2008 Report on the Environment

INDICATOR | Particulate Matter Emissions

Particulate matter” (PM) is the general term used to describe solid particles and liquid droplets found in the 

air. The composition and size of these airborne particles 

and droplets vary. Some particles are large enough to be 

seen as dust or dirt, while others are so small they can only 

be seen using a powerful microscope. Two size ranges, 

known as PM10 and PM2.5, are widely monitored, both at 

major emissions sources and in ambient air. PM10 includes 

particles that have aerodynamic diameters less than or 

equal to 10 microns (μm), approximately equal to oneseventh the diameter of human hair. PM2.5 is the subset of 

PM10 particles that have aerodynamic diameters less than 

or equal to 2.5 μm. 

Particles within the two size ranges behave differently in 

the atmosphere. PM2.5, or fine particles, can remain airborne for long periods and travel hundreds of miles. Coarse 

particles, or the subset of PM10 that is larger than 2.5 μm, 

do not remain airborne as long and their spatial impact is 

typically limited because they tend to deposit on the ground 

downwind of emissions sources. Larger coarse particles are 

not readily transported across urban or broader areas because 

they are generally too large to follow air streams and they 

tend to be removed easily on contact with surfaces. In 

short, as the particle size increases, the amount of time the 

particles remain airborne decreases. The PM Concentrations 

indicator (p. 2-29) describes the various ways PM can harm 

human health and the environment (U.S. EPA, 2004). 

PM can be emitted directly or formed in the atmosphere. 

“Primary” particles are those released directly to the 

atmosphere. These include dust from roads and soot from 

combustion sources. In general, coarse PM is composed 

largely of primary particles. “Secondary” particles, on the 

other hand, are formed in the atmosphere from chemical 

reactions involving primary gaseous emissions. Thus, these 

particles can form at locations distant from the sources 

that release the precursor gases. Examples include sulfates 

formed from sulfur dioxide emissions from power plants 

and industrial facilities and nitrates formed from nitrogen 

oxides released from power plants, mobile sources, and 

other combustion sources. Unlike coarse PM, a much 

greater portion of fine PM (PM2.5) contains secondary 

particles (U.S. EPA, 2004). 

This indicator presents trends in annual average primary PM emissions data tracked by the National Emissions Inventory (NEI). The NEI tracks emission rate data, 

both measured and estimated, for primary particles only. 

Because secondary particles are not released directly from 

stacks, the NEI instead tracks the precursors that contribute to formation of secondary particles. These precursors 

include nitrogen oxides, sulfur dioxide, ammonia, and 

other gases (e.g., particle-producing organic gases), some 

of which are addressed in separate indicators (the Nitrogen 

Oxides Emissions indicator, p. 2-16; the Sulfur Dioxide 

Emissions indicator, p. 2-34). Particles formed through 

secondary processes are not included in this indicator.

Primary emissions of PM can exist as solid or liquid matter (the “filterable” portion) or as gases (the “condensable” 

portion). Data for the condensable portion exist only for 

the years 1999 to 2002. To allow for a valid comparison 

of emissions trends from 1990 to 2002, only data for the 

filterable portion of PM10 and PM2.5 are included in the 

trend graphs. Condensables are, however, included in the 

inset pie charts shown in Exhibits 2-16 and 2-18 (i.e., panel 

B in both exhibits).

All emissions data presented in this indicator are taken 

from the NEI. Primary particulate emissions data are 

presented for the traditionally inventoried anthropogenic 

source categories: (1) “Fuel combustion,” which includes 

“

Exhibit 2-16. PM10 emissions in the U.S. by 

source category, 1990 and 1996-2002

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years 

are fully up to date. Data are 

available for inventory years 

1991-1995, but these data 

have not been updated to 

allow comparison with data 

from 1990 and 1996-2002.

b

Starting in 1999, EPA began 

tracking condensable 

particulate emissions 

separately from filterable 

particulate emissions. In 

order to display data 

generated using a consistent methodology, emissions of 

condensable particulate from 1990 to 2002 are not included in 

Panel A. However, condensable particulate emissions are 

included in Panel B.

Data source: U.S. EPA, 2007b

Year

A. Anthropogenic PM10 emissions by source categorya,b

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

Emissions (million tons)

Anthropogenic

14%

Fugitive dust

60%

B. Relative amounts of PM10 

emissions from anthropogenic 

and other sources, 2002b

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Miscellaneous 

and natural 

sources 

26%

On-road vehicles

Nonroad vehicles and engines

Fuel combustion

Other industrial processes
AIR

EPA’s 2008 Report on the Environment 2-27

INDICATOR | Particulate Matter Emissions (continued)

emissions from coal-, gas-, and oil-fired power plants and 

industrial, commercial, and institutional sources, as well 

as residential heaters and boilers; (2) “Other industrial 

processes,” which includes chemical production, petroleum 

refining, metals production, and processes other than fuel 

combustion; (3) “On-road vehicles,” which includes cars, 

trucks, buses, and motorcycles; and (4) “Nonroad vehicles 

and engines,” such as farm and construction equipment, 

lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft, and others. For 2002 only, this indicator includes a 

comparison of these anthropogenic sources with emissions 

from miscellaneous and natural sources, such as agriculture 

and forestry, wildfires and managed burning, and fugitive 

dust from paved and unpaved roads. Biogenic emissions 

were estimated using the Biogenic Emissions Inventory 

System Model, Version 3.12, with data from the Biogenic 

Emissions Landcover Database and 2001 annual meteorological data. The NEI also documents estimates of primary 

emissions from fugitive dust and miscellaneous sources. 

The NEI is a composite of data from many different 

sources, including industry and numerous state, tribal, and 

local agencies. Different data sources use different data 

collection methods, and many of the emissions data are 

based on estimates rather than actual measurements. For 

most fuel combustion sources and industrial sources, emissions are estimated using emission factors. Emissions from 

on-road and nonroad sources were estimated using EPAapproved modeling approaches (U.S. EPA, 2007a). 

NEI data have been collected since 1990 and cover all 

50 states and their counties, D.C., the U.S. territories of 

Puerto Rico and Virgin Islands, and some of the territories 

of federally recognized American Indian nations. Data are 

presented for 1990 and the years from 1996 to 2002; prior 

to 1996, only the 1990 data have been updated to be comparable to the more recent inventories.

What the Data Show

Primary PM10 Emissions Trends

Estimated primary PM10 emissions from anthropogenic 

sources decreased 27 percent nationally between 1990 and 

2002 (Exhibit 2-16, panel A). Of these sources, those in 

the fuel combustion category saw the largest absolute and 

relative decrease in emissions (656,000 tons; 55 percent). 

Primary PM10 emissions from the group of sources including miscellaneous and natural sources and fugitive dust 

were estimated to account for 86 percent of total primary 

PM10 emissions (including condensables from stationary and 

mobile sources) in 2002, the majority of which was attributable to fugitive dust from roads (Exhibit 2-16, panel B). 

Changes in estimated primary anthropogenic PM10

emissions from 1990 to 2002 varied widely among EPA 

Regions, ranging from an increase of 16 percent (Region 

8) to a decrease of 75 percent (Region 2) (Exhibit 2-17).

Primary PM2.5 Emissions Trends

Estimated primary PM2.5 emissions from anthropogenic 

sources decreased 44 percent nationally between 1990 and 

2002 (Exhibit 2-18, panel A). The largest absolute and 

relative decline in PM2.5 was seen in the fuel combustion 

source category (621,000 tons; 68 percent). Primary emissions from the group of sources including miscellaneous 

and natural sources and fugitive dust were estimated to 

account for 64 percent of the total PM2.5 emissions (including condensables from stationary and mobile sources) 

nationally in 2002 (Exhibit 2-18, panel B).

Primary anthropogenic PM2.5 emissions decreased in all 

ten EPA Regions from 1990 to 2002, with percent reductions ranging from 21 percent (Region 4) to 71 percent 

(Region 2) (Exhibit 2-19).

Indicator Limitations

•	 Comparable PM emissions estimates through the 

NEI are available only for 1990 and 1996-2002. Data 

for 1991-1995 are not provided due to differences in 

0

100

200

300

400

500

600

700

800

’90 ’97’96 ’98 ’99 ’00 ’01 ’02

Exhibit 2-17. PM10 emissions in the U.S. by 

EPA Region, 1990 and 1996-2002a,b

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Year

Emissions (thousand tons)

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data 

have not been updated to allow 

comparison with data from 

1990 and 1996-2002.

b

Starting in 1999, EPA began tracking condensable particulate 

emissions separately from filterable particulate emissions. In 

order to display data generated using a consistent methodology, 

emissions of condensable particulate from 1999 to 2002 are not 

included in this figure.

Data source: U.S. EPA, 2007b
AIR

2-28 EPA’s 2008 Report on the Environment

INDICATOR | Particulate Matter Emissions (continued)

emissions estimation methodologies from other inventory 

years, which could lead to improper trend assessments. 

•	 Because the emissions indicators focus on sources of 

anthropogenic origin, PM emissions from miscellaneous sources (e.g., wildfires) are not included in the 

trend line. Details on emissions from these sources can 

be found by downloading 2002 NEI inventory data for 

the “nonpoint sector” (http://www.epa.gov/ttn/chief/

net/2002inventory.html).

•	The emissions data for PM are largely based on estimates 

that employ emission factors generated from empirical 

and engineering studies, rather than on actual measurements of PM emissions. Although these estimates are 

generated using well-established approaches, the estimates have uncertainties inherent in the emission factors 

and emissions models used to represent sources for which 

emissions have not been directly measured.

•	The methodology for estimating emissions is continually 

reviewed and is subject to revision. Trend data prior to 

these revisions must be considered in the context of those 

changes.

•	The indicator tracks primary PM emissions. Particles 

that form in the air through secondary processes are not 

included in this indicator, but are considered in the PM 

Concentrations indicator (p. 2-29). 

•	 Not all states and local agencies provide the same data or 

level of detail for a given year.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

biogenic and anthropogenic PM emissions data in the 

NEI (U.S. EPA, 2007b) (http://www.epa.gov/ttn/chief/

net/2002inventory.html). This indicator aggregates the 

Exhibit 2-18. PM2.5 emissions in the U.S. by 

source category, 1990 and 1996-2002

Year

A. Anthropogenic PM2.5 emissions by source categorya,b

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

Emissions (million tons)

B. Relative amounts of PM2.5 

emissions from anthropogenic 

and other sources, 2002b

0.0

0.5

1.0

1.5

2.0

2.5

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years 

are fully up to date. Data are 

available for inventory years 

1991-1995, but these data 

have not been updated to 

allow comparison with data 

from 1990 and 1996-2002.

b

Starting in 1999, EPA began 

tracking condensable 

particulate emissions 

separately from filterable 

particulate emissions. In 

order to display data 

generated using a consistent methodology, emissions of 

condensable particulate from 1990 to 2002 are not included in 

Panel A. However, condensable particulate emissions are included 

in Panel B.

Data source: U.S. EPA, 2007b

Anthropogenic

36%

Fugitive dust

31%

Miscellaneous 

and natural 

sources 

33%

On-road vehicles

Nonroad vehicles and engines

Fuel combustion

Other industrial processes

Exhibit 2-19. PM2.5 emissions in the U.S. by

EPA Region, 1990 and 1996-2002a,b Emissions (thousand tons)

Year

a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

b

Starting in 1999, EPA began tracking condensable particulate 

emissions separately from filterable particulate emissions. In 

order to display data generated using a consistent methodology, 

emissions of condensable particulate from 1999 to 2002 are not 

included in this figure.

Data source: U.S. EPA, 2007b

0

100

200

300

400

500

600
AIR

EPA’s 2008 Report on the Environment 2-29

INDICATOR | Particulate Matter Emissions (continued)

NEI data by source type (anthropogenic or biogenic), 

source category, and EPA Region. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. <ftp://ftp.

epa.gov/EmisInventory/2002finalnei/documentation/

mobile/2002_mobile_nei_version_3_report_092807.pdf>

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2004. Air quality criteria for particulate matter (October 2004). EPA 600/P-99/002aF-bF. Research 

Triangle Park, NC. <http://cfpub.epa.gov/ncea/cfm/

recordisplay.cfm?deid=87903>

v

INDICATOR | Ambient Concentrations of Particulate Matter

Particulate matter” (PM) is the general term used for a 

mixture of solid particles and liquid droplets found in 

the air. Airborne PM comes from many different sources. 

“Primary” particles are released directly into the atmosphere from sources such as cars, trucks, heavy equipment, 

forest fires, and burning waste. Primary particles also 

consist of crustal material from sources such as unpaved 

roads, stone crushing, construction sites, and metallurgical operations. “Secondary” particles are formed in the air 

from reactions involving precursor chemicals such as sulfates (which are formed from sulfur dioxide emissions from 

power plants and industrial facilities), nitrates (which are 

formed from nitrogen dioxide emissions from cars, trucks, 

and power plants), and carbon-containing reactive organic 

gas emissions from cars, trucks, industrial facilities, forest 

fires, and biogenic sources such as trees. 

Ambient air monitoring stations throughout the country 

measure air concentrations of two size ranges of particles: 

PM2.5 and PM10. PM2.5 consists of “fine particles” with 

aerodynamic diameters less than or equal to 2.5 microns 

(μm). PM10 includes both fine particles (PM2.5) and “coarse 

particles,” which is the subset of PM10 that is larger than 

2.5 μm and smaller than 10 μm. The chemical makeup of 

particles varies across the U.S. For example, fine particles 

in the eastern half of the U.S contain more sulfates than 

those in the West, while fine particles in southern California contain more nitrates than those in other areas of the 

U.S. Carbon is a substantial component of fine particles 

everywhere (U.S. EPA, 2004a).

Fine particles also have seasonal patterns. PM2.5 values in 

the eastern half of the U.S. are typically higher in the third 

calendar quarter (July-September), when sulfates are more 

commonly formed from sulfur dioxide emissions from power 

plants in that part of the country. Fine particle concentrations 

tend to be higher in the fourth calendar quarter (OctoberDecember) in many areas of the West, in part because fine 

“

Year

Year

A. Ambient concentrations

B. Number of trend sites above NAAQS

0

25

50

75

100

125

150

175

0

5

10

15

20

25

35

30

’90’88 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

’90’88 ’92 ’94 ’96 ’98 ’00 ’02 ’06’04

NAAQS = 150 μg/m3

90% of sites have concentrations below this line

Average

Median

10% of sites have 

concentrations below this line

Exhibit 2-20. Ambient 24-hour PM10

concentrations in the U.S., 1988-2006a Second highest 24-hour concentration (μg/m3

)

Number of trend sites with second highest 

24-hour concentration above the level of the 

NAAQS (150 μg/m3

)

a

Coverage: 301 monitoring sites in 199 counties nationwide (out of a 

total of 902 sites measuring PM10 in 2006) that have sufficient data 

to assess PM10 trends since 1988.

Data source: U.S. EPA, 2007
AIR

2-30 EPA’s 2008 Report on the Environment

INDICATOR | Ambient Concentrations of Particulate Matter (continued)

particle nitrates are more readily formed in cooler weather, 

and wood stove and fireplace use produces more carbon. 

Many recent epidemiologic studies show statistically 

significant associations of various ambient PM indicators 

(e.g., coarse or fine particulate, short-term or long-term 

concentrations) with a variety of cardiovascular and respiratory health endpoints, including mortality, hospital admissions, emergency department visits, other medical visits, 

respiratory illness and symptoms, and physiologic changes 

in pulmonary function (U.S. EPA, 2004b). Sensitive groups 

that appear to be at greatest risk to such PM effects include 

older adults, individuals with cardiopulmonary disease such 

as asthma or congestive heart disease, and children (U.S. 

EPA, 2004b). Unlike other criteria pollutants, PM is not a 

single specific chemical entity, but rather a mixture of particles from different sources with different sizes and chemical 

compositions. Toxicological studies suggest that some airborne particles are more toxic than others, due to differences 

in their chemical composition—a topic that is thoroughly 

reviewed in other publications (e.g., U.S. EPA, 2004b). 

PM also can cause adverse impacts to the environment. Fine 

particles are the major cause of reduced visibility in parts of the 

U.S., including many National Parks and Wilderness Areas 

(the Regional Haze indicator, p. 2-33). PM deposition affects 

vegetation and ecosystems by altering nutrient and chemical 

cycles in soils and surface water. For example, deposition of 

particles containing nitrogen and sulfur may change the nutrient balance and acidity of aquatic environments so that species 

composition and buffering capacity change (the Lake and 

Stream Acidity indicator, p. 2-42.). Some particles that deposit 

onto plant leaves can corrode leaf surfaces or interfere with 

plant metabolism. PM also causes soiling and erosion damage 

to materials, including monuments, statues, and other objects 

of cultural importance (U.S. EPA, 2004b).

This indicator presents trends in PM10 and PM2.5 concentrations, using averaging times consistent with the 

pollutants’ corresponding National Ambient Air Quality 

Standards (NAAQS). For PM10, trend data from 1988 to 

2006 are presented for the second highest 24-hour concentrations measured at the trend sites during each calendar 

year. For PM2.5, trend data from 1999 to 2006 are presented 

for seasonally weighted annual average concentrations and 

Second highest 24-hour 

concentration (μg/m3

)

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

Exhibit 2-21. Ambient 24-hour PM10

concentrations in the contiguous U.S. by EPA 

Region, 1988-2006a

a

Coverage: 292 monitoring sites 

in the EPA Regions (out of a total 

of 902 sites measuring PM10 in 

2006) that have sufficient data to 

assess PM10 trends since 1988.

Data source: U.S. EPA, 2007 10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

’90’88 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

0

20

40

60

80

100

120

140

180

160

Year

NAAQS = 150 μg/m3

Averaging period

A. Ambient concentrations

B. Number of trend sites above NAAQS

0

5

10

15

20

0

50

100

150

200

250

300

NAAQS = 15 μg/m3

90% of sites have concentrations below this line

10% of sites have concentrations below this line 

Average

Median

Averaging period

a

Coverage: 752 monitoring sites in 508 counties nationwide (out of a 

total of 786 sites measuring PM2.5 in 2006) that have sufficient data 

to assess PM2.5 trends since 1999.

Data source: U.S. EPA, 2007 Number of trend sites with seasonally weighted annual average concentration for three consecutive calendar years above the level of the NAAQS (15 μg/m3

)

Exhibit 2-22. Ambient annual PM2.5 concentrations 

in the U.S., 1999-2006a

’99-’01 ’00-’02 ’01-’03 ’02-’04 ’03-’05 ’04-’06

’99-’01 ’00-’02 ’01-’03 ’02-’04 ’03-’05 ’04-’06

Seasonally weighted annual average 

concentration for three consecutive 

calendar years (μg/m3

)
AIR

EPA’s 2008 Report on the Environment 2-31

INDICATOR | Ambient Concentrations of Particulate Matter (continued)

for the 98th percentiles of 24-hour average concentrations 

measured at the trend sites over three consecutive calendar years. Trend data are based on measurements from the 

State and Local Air Monitoring Stations network and from 

other special purpose monitors. This indicator presents PM10

trends for 301 monitoring sites in 199 counties nationwide 

and PM2.5 trends for 752 monitoring sites in 508 counties 

nationwide. For both PM10 and PM2.5, the indicator displays 

trends for the entire nation and for the ten EPA Regions.

The indicator’s exhibits display the pollutants’ NAAQS as 

points of reference. However, the fact that the national values or those shown for EPA Regions fall below the standards 

does not mean that all monitoring sites nationally or in any 

particular EPA Region also are below the standards. The 

indicator displays trends in the number of PM10 monitoring 

sites and PM2.5 monitoring sites nationwide that recorded 

ambient air concentrations above the level of the standards, 

but these statistics are not displayed for each EPA Region. 

What the Data Show

PM10 Concentration Trends

In 2006, the national 24-hour PM10 concentration (based on 

the second highest 24-hour concentration at each site) was 

37 percent lower than the average 1988 level (Exhibit 2-20, 

panel A). Additionally, of the 301 sites used to determine 

this trend (out of 902 total monitoring sites that were operating in 2006), the number reporting PM10 concentrations 

above the level of the 24-hour standard declined 78 percent 

between 1988 and 2006 (Exhibit 2-20, panel B). All EPA 

Regions experienced a steady decrease in 24-hour PM10 levels over this period (Exhibit 2-21). EPA Region 10 showed 

the greatest relative decrease (68 percent) since 1988.

Also shown in Exhibit 2-20 (panel A) are the 90th and 

10th percentiles based on the distribution of annual statistics 

at the monitoring sites. This provides additional graphical 

representation of the distribution of measured concentrations across the monitoring sites for a given year. Thus, the 

graphic displays the concentration range where 80 percent 

of measured values occurred for that year. (Note that this 

presentation style also applies to panel A in Exhibits 2-22 

and 2-24, discussed below.)

PM2.5 Concentration Trends

Seasonally weighted average PM2.5 concentrations over the 

2004-2006 averaging period were the lowest since nationwide 

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Seasonally weighted annual average 

concentration for three consecutive 

Nat’l

calendar years (μg/m3

)

Averaging period

NAAQS = 15 μg/m3

Exhibit 2-23. Ambient annual PM2.5 concentrations 

in the contiguous U.S. by EPA Region, 1999-2006a

a

Coverage: 736 monitoring 

sites in the EPA Regions (out 

of a total of 786 sites 

measuring PM2.5 in 2006) that 

have sufficient data to assess 

PM2.5 trends since 1999.

Data source: U.S. EPA, 2007

’99-’01 ’00-’02 ’01-’03 ’02-’04 ’03-’05 ’04-’06

0

5

10

15

20

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

A 5

Averaging period

Averaging period

A. Ambient concentrations

B. Number of trend sites above NAAQS

a

Coverage: 752 monitoring sites in 508 counties nationwide (out of a 

total of 811 sites measuring PM2.5 in 2006) that have sufficient data 

to assess PM2.5 trends since 1999.

Data source: U.S. EPA, 2007

98th percentile of 24-hour 

concentrations for three consecutive 

calendar years (μg/m3

)

Number of trend sites with 98th percentile of 24-hour 

concentrations for three consecutive calendar years 

above the level of the NAAQS (35 μg/m3

)

Exhibit 2-24. Ambient 24-hour PM2.5

concentrations in the U.S., 1999-2006a

0

15

30

45

60

’99-’01 ’00-’02 ’01-’03 ’02-’04 ’03-’05 ’04-’06

’99-’01 ’00-’02 ’01-’03 ’02-’04 ’03-’05 ’04-’06

10% of sites have 

concentrations below this line

Average

Median

90% of sites have 

concentrations below this line NAAQS = 35 μg/m3

0

100

200

300

400
AIR

2-32 EPA’s 2008 Report on the Environment

INDICATOR | Ambient Concentrations of Particulate Matter (continued)

monitoring began in 1999 (Exhibit 2-22, panel A). The trend 

is based on measurements collected at 752 monitoring stations 

that have sufficient data to assess trends over that period. The 

seasonally weighted annual average concentrations decreased 

10 percent between the 1999-2001 averaging period and the 

2004-2006 averaging period. The number of monitoring sites 

in this trend (752 out of 786 total sites that were operating in 

2006) reporting ambient air concentrations above the level of 

the annual average PM2.5 standard declined 61 percent over 

this period (Exhibit 2-22, panel B).

Regional declines were greatest in portions of the West 

(EPA Region 9), the Southeast (EPA Region 4), and the 

Midwest (EPA Region 5), where seasonally weighted average PM2.5 levels over the 2004-2006 averaging period were 

19 percent, 11 percent, and 11 percent lower than those in 

1999-2001 averaging period, respectively (Exhibit 2-23). 

In 2004-2006, the average of 98th percentiles of 24-hour 

PM2.5 concentrations at the 752 monitoring sites used 

for the trend was 10 percent lower than the 1999-2001 

level (Exhibit 2-24, panel A). The number of monitoring 

sites in this trend (752 out of a total of 811 sites that were 

operating in 2006) reporting ambient air concentrations 

above the level of the 24-hour PM2.5 standard declined 

46 percent over this period (Exhibit 2-24, panel B). All 

ten EPA Regions experienced decreasing 24-hour PM2.5

levels between the 1999-2001 averaging period and the 

2004-2006 averaging period, with Region 9 showing the 

largest decline (25 percent) (Exhibit 2-25). 

Indicator Limitations

•	 Because there are far more PM10 and PM2.5 monitors 

in urban areas than in rural areas, the trends might not 

accurately reflect conditions outside the immediate urban 

monitoring areas.

•	 Potential biases may exist for some PM2.5 ambient concentration measurements due to losses from volatilization of 

nitrates and other semi-volatile materials and retention of 

particle-bound water associated with hygroscopic species.

•	 Due to the relatively small number of monitoring sites 

in some EPA Regions, the regional trends are subject to 

greater uncertainty than the national trends. Some EPA 

Regions with low average concentrations may include 

areas with high local concentrations, and vice versa. 

•	 To ensure that long-term trends are based on a consistent 

set of monitoring sites, selection criteria were applied to 

identify the subset of PM monitoring sites with sufficient 

data to assess trends over the time frames covered by this 

indicator. Monitoring sites without sufficient data are not 

included in the trend analysis. Some excluded monitoring 

sites reported PM concentrations above the level of the PM 

standard during the years covered by this indicator. In 2006, 

for example, 41 monitoring sites (in addition to the trend 

sites shown in Exhibit 2-20, panel B) recorded PM10 concentrations above the level of the NAAQS, but did not have 

sufficient long-term data to be included in this indicator. 

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

PM ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). National and regional trends in this indicator are 

based on the subset of PM monitoring stations that have 

sufficient data to assess trends over the period of record 

(i.e., since 1988 for PM10 and since 1999 for PM2.5).

References 

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. <http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2004a. The particle pollution report: Current understanding of air quality and emissions through 

2003. EPA 454/R-04/002. Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd04/pm.html>

U.S. EPA. 2004b. Air quality criteria for particulate matter (October 2004). EPA 600/P-99/002aF-bF. Research 

Triangle Park, NC. <http://cfpub.epa.gov/ncea/CFM/

recordisplay.cfm?deid=87903>

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

0

15

30

45

60

NAAQS = 35 μg/m3

98th percentile of 24-hour concentrations for 

three consecutive calendar years (μg/m3

)

Averaging period

Exhibit 2-25. Ambient 24-hour PM2.5

concentrations in the contiguous U.S. by EPA 

Region, 1999-2006a

a

Coverage: 736 monitoring sites 

in the EPA Regions (out of a total 

of 811 sites measuring PM2.5 in 

2006) that have sufficient data to 

assess PM2.5 trends since 1999.

Data source: U.S. EPA, 2007

’99-’01 ’00-’02 ’01-’03 ’02-’04 ’03-’05 ’04-’06

v
AIR

EPA’s 2008 Report on the Environment 2-33

INDICATOR | Regional Haze

Visibility impairment occurs when air pollution, especially particles, scatter and absorb light. The resulting haze 

not only limits the distance one can see, but also degrades 

the color, clarity, and contrast of scenes. As the PM Concentrations indicator (p. 2-29) describes further, the same 

pollutants that impair visibility are linked to serious health 

effects. Visibility impairment occurs throughout the country, including both urban and rural areas. Regional haze is 

visibility impairment caused by the cumulative air pollutant 

emissions from numerous sources over a wide geographic 

area (U.S. EPA, 2004a). Regional haze has been identified as an important issue for all of the National Parks and 

Wilderness Areas, such as the Grand Canyon, Great Smoky 

Mountains, Mount Rainier, Shenandoah, Yellowstone, and 

Yosemite National Parks (U.S. EPA, 2003). 

The particles that impair visibility include both primary 

and secondary pollutants. The primary pollutants of concern are particles that are emitted directly into the atmosphere, such as dust from roads or soot (elemental carbon) 

from combustion sources (e.g., wood combustion). Secondary pollutants of concern are particles that form in the 

atmosphere from chemical reactions and physical processes, 

such as sulfates (formed from sulfur dioxide emissions from 

power plants and other industrial facilities) and nitrates 

(formed from nitrogen oxides emitted from power plants, 

automobiles, and other types of combustion sources). 

Humidity can increase the effect of pollution on visibility, causing some particles to become more efficient at scattering light and impairing visibility (U.S. EPA, 2003). In 

the eastern U.S., where annual average relative humidity 

levels are between 70 percent and 80 percent, reduced visibility mainly results from secondarily formed sulfates and 

high humidity, along with a somewhat lower contribution from organic carbon and nitrates (U.S. EPA, 2004b). 

The effect of humidity is particularly strong in summer. 

Humidity is less of a factor in the West, as average values are generally between 50 percent and 60 percent. In 

western states, primary emissions from sources like wood 

smoke and nitrates contribute a large percentage of the 

total particulate loading, though secondarily formed sulfates also contribute to visibility impairment. Without the 

effects of anthropogenic sources of pollution, the annual 

average natural visual range in the U.S. would vary with 

location, and is estimated to range from 75 to 150 km (45 

to 90 miles) in the East and from 200 to 300 km (120 to 

180 miles) in the West (U.S. EPA, 2003).

This indicator reports visibility estimates calculated from 

measurements of particulate matter (PM) constituents 

collected at 38 monitoring sites between 1992 and 2004 

at National Parks, Wilderness Areas, and other protected 

sites under the Interagency Monitoring of Protected Visual 

Environments (IMPROVE) network. Values are presented 

a

Coverage: 28 monitoring sites in the western U.S. and 10 monitoring sites in the eastern U.S. with sufficient 

data to assess visibility trends from 1992 to 2004.

b

Visual ranges are calculated from the measured levels of different components within airborne particles and 

these components’ light extinction efficiencies.

Data source: IMPROVE, 2007

Exhibit 2-26. Visibility in selected National Parks and Wilderness Areas in the U.S., 1992-2004a,b
AIR

2-34 EPA’s 2008 Report on the Environment

INDICATOR | Regional Haze (continued)

for 10 Eastern (east of 100 degrees west longitude) sites 

and 28 Western (west of 100 degrees west longitude) sites. 

Visibility, expressed as visual range, is calculated from the 

measured levels of different components within airborne 

particles and these components’ light extinction efficiencies. 

The IMPROVE algorithm (Debell et al., 2006) includes an 

adjustment for ammonium sulfate and ammonium nitrate 

to account for their adsorption of water vapor from the 

atmosphere under elevated relative humidity conditions. 

The IMPROVE particle data are generated by laboratory 

analysis of 24-hour duration filter samples collected at each 

site on a one-day-in-three schedule. This indicator tracks 

visibility in three categories: worst visibility conditions (the 

average of the 20 percent worst visibility days); best visibility conditions (the average of the 20 percent best visibility 

days); and mid-range visibility conditions (the average of the 

remaining 60 percent of days). 

What the Data Show

On average, the best visibility in selected National Parks 

and Wilderness Areas in the East, as calculated from the 

measured concentrations of components of PM, is only 

slightly better than the worst visibility in selected National 

Parks and Wilderness Areas in the West (Exhibit 2-26). 

In 2004, the average visual range for the worst days in the 

East was 31 km (19 miles), compared to 137 km (85 miles) 

for the best visibility days. In the West, the average visual 

range in 2004 extended from 109 km (68 miles) on the 

worst days to 260 km (162 miles) on the best days. In both 

regions, the average visual range in selected National Parks 

and Wilderness Areas increased since 1992 for worst, midrange, and best visibility days. The increased visual ranges 

between 1992 and 2004 for mid-range visibility days were 

46 percent in the East and 14 percent in the West. 

Indicator Limitations

•	These data represent visibility in a sampling of selected 

National Parks and Wilderness Areas and are not representative of other rural or urban areas. 

Data Sources

Summary data in this indicator were provided by the 

National Park Service Air Quality Division, based on ambient air monitoring data collected as part of the IMPROVE 

network (IMPROVE, 2007) and a computational algorithm 

last updated in August 2007 (http://vista.cira.colostate.

edu/views/Web/IMPROVE/SummaryData.aspx). Visibility trends in this indicator are derived from the subset 

of IMPROVE monitoring stations outside urban areas that 

have sufficient data to assess trends between 1992 and 2004.

References

Debell, L.J., K.A. Gebhart, W.C. Malm, M.L. Pitchford, 

B.A. Schichtel, and W.H. White. 2006. Spatial and seasonal 

patterns and temporal visibility of haze and its constituents 

in the United States: Report IV. <http://vista.cira.colostate.

edu/improve/Publications/Reports/2006/2006.htm>

IMPROVE (Interagency Monitoring of Protected Visual 

Environments). 2007. Data from the IMPROVE network 

based on the “New IMPROVE algorithm” (updated 

August, 2007). Accessed 2007. <http://vista.cira.colostate.

edu/views/Web/IMPROVE/SummaryData.aspx>

U.S. EPA (United States Environmental Protection 

Agency). 2004a. The particle pollution report: Current 

understanding of air quality and emissions through 2003. 

EPA/454/R-04/002. Research Triangle Park, NC.

<http://www.epa.gov/air/airtrends/aqtrnd04/pm.html>

U.S. EPA. 2004b. The ozone report: Measuring progress 

through 2003. EPA/454/K-04/001. Research Triangle 

Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd04/ozone.html>

U.S. EPA. 2003. Latest findings on national air quality 

—2002 status and trends. EPA/454/K-03/001. Research 

Triangle Park, NC. <http://www.epa.gov/air/airtrends/

aqtrnd02/2002_airtrends_final.pdf>

v

INDICATOR | Sulfur Dioxide Emissions

Sulfur dioxide (SO2

) belongs to the family of sulfur 

oxide (SOx) gases. These gases are formed when fuel 

containing sulfur (mainly coal and oil) is burned (e.g., 

for electricity generation) and during metal smelting and 

other industrial processes. High concentrations of SO2

 are 

associated with multiple health and environmental effects 

(U.S. EPA, 2003). The highest concentrations of SO2 have 

been recorded in the vicinity of large industrial facilities. 

Although relatively few people live in areas where SO2

concentrations exceed the National Ambient Air Quality 

Standards (NAAQS), SO2 emissions are an important 

environmental issue because they are a major precursor to 

ambient PM2.5 concentrations: many more people live in 

PM2.5 non-attainment areas, which has several documented 

human health and ecological effects (the PM Concentrations indicator, p. 2-29). 
AIR

EPA’s 2008 Report on the Environment 2-35

INDICATOR | Sulfur Dioxide Emissions (continued)

Health effects associated with SO2

 depend on the exposure concentrations and durations, and on the susceptibility 

of exposed populations. Asthmatics are much more susceptible to SO2

 exposure than people who do not have asthma 

(U.S. EPA, 1986). Effects associated with longer-term 

exposures to high concentrations of SO2, in conjunction 

with high levels of PM, include respiratory illness, alterations in the lungs’ defenses, and aggravation of existing 

heart or lung disease. The most susceptible populations 

under these conditions include individuals with cardiovascular disease or chronic lung disease, children, and older 

adults (U.S. EPA, 1982). 

Many other environmental concerns are associated with 

high concentrations of SO2. For example, airborne SO2, 

along with NOx, contributes to acidic deposition (the Acid 

Deposition indicator, p. 2-37); SO2 is a major precursor to 

PM2.5 (the PM Concentrations indicator, p. 2-29); and SO2

contributes to impaired visibility (the Regional Haze indicator, p. 2-33). SO2

 exposure also can harm vegetation by 

increasing foliar injury, decreasing plant growth and yield, 

and decreasing the number and variety of plant species in a 

given community. Finally, SO2 can accelerate the corrosion of materials (e.g., concrete, limestone) that are used 

in buildings, statues, and monuments that are part of the 

nation’s cultural heritage (U.S. EPA, 1982). 

This indicator presents SO2 emissions from traditionally inventoried anthropogenic source categories: (1) “Fuel 

combustion: selected power generators,” which includes 

emissions from coal-, gas-, and oil-fired power plants that 

are required to use continuous emissions monitors (CEMs) 

to report emissions as part of the Acid Rain Program 

(ARP); (2) “Fuel combustion: other sources,” which 

includes industrial, commercial, and institutional sources, 

as well as residential heaters and boilers not required to use 

CEMs; (3) “Other industrial processes,” which includes 

chemical production and petroleum refining; (4) “Onroad vehicles,” which includes cars, trucks, buses, and 

motorcycles; (5) “Nonroad vehicles and engines,” which 

include farm and construction equipment, lawnmowers, 

chainsaws, boats, ships, snowmobiles, aircraft, and others. 

Because a substantial portion of airborne SO2

 comes from 

fossil fuel combustion in electric utilities, this indicator 

includes the separate “Fuel combustion: selected power 

generators” category in addition to the four categories 

presented in the other emissions indicators.

SO2 emissions data are tracked by the National Emissions 

Inventory (NEI). The NEI is a composite of data from 

many different sources, including industry and numerous state, tribal, and local agencies. Different data sources 

use different data collection methods, and many of the 

emissions data are based on estimates rather than actual 

measurements. For major electricity generating units, most 

data come from CEMs that measure actual emissions. For 

other fuel combustion sources and industrial processes, 

data are estimated using emission factors. Emissions from 

on-road and nonroad sources were estimated using EPAapproved modeling approaches (U.S. EPA, 2007a). 

NEI data have been collected since 1990 and cover all 

50 states and their counties, D.C., the U.S. territories of 

Puerto Rico and Virgin Islands, and some of the territories 

of federally recognized American Indian nations. Data are 

presented only for 1990 and from 1996 to 2002; prior to 

1996, only the 1990 data have been updated to be comparable to the more recent inventories. 

What the Data Show

National estimated SO2 emissions decreased 37 percent 

between 1990 and 2002 (from 23,064,000 to 14,639,000 

tons) (Exhibit 2-27). This downward trend resulted 

primarily from emissions reductions at electric utilities. Between 1990 and 2002, air emissions from electric 

utilities have consistently accounted for roughly two-thirds 

of the nationwide SO2 emissions. 

Net SO2 emissions declined in all EPA Regions between 

1990 and 2002 (Exhibit 2-28). During this time frame, the 

largest percent reductions in SO2

 emissions were seen in 

Regions 1 (59 percent), 2 (49 percent), and 5 (48 percent), 

and the smallest reductions were observed in Regions 6 (15 

percent) and 9 (18 percent).

Exhibit 2-27. SO2 emissions in the U.S. by 

source category, 1990 and 1996-2002a

a

Data are presented for 1990 and 1996-2002, as datasets from 

these inventory years are fully up to date. Data are available for 

inventory years 1991-1995, but these data have not been updated 

to allow comparison with data from 1990 and 1996-2002.

b

This category includes emissions from only those power plants 

required to use continuous emissions monitors under the Acid 

Rain Program.

Data source: U.S. EPA, 2007b

Year

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

Emissions (million tons)

0

5

10

15

20

25

30

Fuel combustion: 

selected power generatorsb

Fuel combustion: other sources

Other industrial

processes

On-road and 

nonroad 

mobile 

sources
AIR

2-36 EPA’s 2008 Report on the Environment

INDICATOR | Sulfur Dioxide Emissions (continued)

Indicator Limitations

•	Though emissions from most electric utilities are measured directly using continuous monitoring devices, 

SO2 emissions data for other source types are based on 

estimates that employ emission factors generated from 

empirical and engineering studies. Although these estimates are generated using well-established approaches, 

the estimates have uncertainties inherent in the emission 

factors and emissions models used to represent sources 

for which emissions have not been directly measured. 

•	 Comparable SO2 emissions estimates through the NEI 

are available only for 1990 and 1996-2002. Data for 

1991-1995 are not provided due to differences in emissions estimation methodologies from other inventory 

years, which could lead to improper trend assessments.

•	 SO2 emissions from “miscellaneous sources” are not 

included in the total emissions. Details on emissions from 

miscellaneous sources can be found by downloading 2002 

NEI inventory data for the “nonpoint sector” (http://

www.epa.gov/ttn/chief/net/2002inventory.html).

•	The methodology for estimating emissions is continually 

reviewed and is subject to revision. Trend data prior to 

these revisions must be considered in the context of 

those changes. 

•	 Not all states and local agencies provide the same data or 

level of detail for a given year. 

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

SO2 emissions data in the NEI (U.S. EPA, 2007b) 

(http://www.epa.gov/ttn/chief/net/2002inventory.html). 

This indicator aggregates the NEI data by source category 

and EPA Region. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. <ftp://ftp.

epa.gov/EmisInventory/2002finalnei/documentation/

mobile/2002_mobile_nei_version_3_report_092807.pdf>

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

U.S. EPA. 1986. Second addendum to the air quality 

criteria for particulate matter and sulfur oxides (1982): 

Assessment of newly available health effects information. 

EPA/450/S-86/012. Research Triangle Park, NC.

U.S. EPA. 1982. Air quality criteria for particulate matter 

and sulfur oxides. EPA/600/P-82/020a-c. Research Triangle Park, NC.

Exhibit 2-28. SO2 emissions in the U.S. by EPA 

Region, 1990 and 1996-2002a

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Year

Emissions (million tons) a

Data are presented for 1990 

and 1996-2002, as datasets 

from these inventory years are 

fully up to date. Data are 

available for inventory years 

1991-1995, but these data have 

not been updated to allow 

comparison with data from 

1990 and 1996-2002.

Data source: U.S. EPA, 2007b

’90 ’96 ’97 ’98 ’99 ’00 ’01 ’02

0

1

2

3

4

5

6

7

8

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

v
AIR

EPA’s 2008 Report on the Environment 2-37

INDICATOR | Acid Deposition

Every year, millions of tons of sulfur dioxide and nitrogen oxides are emitted to the atmosphere as a result of 

the burning of fossil fuels and from other high temperature 

sources (the Sulfur Dioxide Emissions indicator, p. 2-34; 

the Nitrogen Oxides Emissions indicator, p. 2-16). These 

gases react with water, oxygen, and oxidants to form acidic 

compounds, which may be carried hundreds of miles by 

the wind—even across state or national borders. Acid 

deposition occurs when these compounds fall to the Earth 

in one of two forms: wet (dissolved in rain, snow, and fog) 

or dry (solid and gaseous particles deposited on surfaces 

during periods of no precipitation). While wet deposition is the more widely recognized form (more commonly 

referred to as “acid rain”), dry deposition can account for 

20 to 80 percent of total acid deposition depending on 

location and climate (MACTEC Engineering and Consulting, Inc., 2005). In the environment, acid deposition 

causes soils and water bodies to acidify, which can make 

the water unsuitable for some fish and other wildlife. Some 

types of ecosystems, those with less “buffering” capacity, 

are more sensitive to acid deposition than others.

Scientists often use acid neutralizing capacity, a measure 

of the amount of anions, protons, and non-proton cations 

in the water, as an indicator of which lakes and streams are 

most sensitive to acidification (NAPAP, 1991). Most surface 

waters in the West do not exhibit many symptoms of acidification, because relatively small amounts of acid deposition 

occur in acid-sensitive regions. In the Northeast and along 

the Appalachian Mountains, however, relatively high levels 

of acid deposition occur in acid-sensitive regions, or regions 

without enough geochemical buffering capacity to prevent 

acidification of surface waters by acid deposition (the Lake 

and Stream Acidity indicator, p. 2-42). Therefore, reductions in acid deposition have the largest impact on acidification of lakes and streams in those areas.

Acid deposition damages some trees, particularly at 

high elevations, and speeds the decay of buildings, statues, 

and sculptures that are part of our national heritage (U.S. 

EPA, 2003). The nitrogen portion of acid deposition also 

contributes to eutrophication in coastal ecosystems, the 

symptoms of which include potentially toxic algal blooms, 

fish kills, and loss of plant and animal diversity. Acidification of lakes and streams can increase the amount of 

methylmercury available in aquatic systems (Winfrey and 

Rudd, 1990). Finally, increased levels of sulfate in groundlevel air, a phenomenon related to dry deposition, can contribute to decreased visibility as well as a variety of human 

health problems (U.S. EPA, 2003).

Total acid deposition in this indicator is determined using 

wet deposition measurements and dry deposition calculated 

from ambient air concentration measurements. Wet deposition is measured through chemical analysis of rainwater 

collected at sites across the U.S. The primary source of wet 

deposition information comes from the National Atmospheric Deposition Program/National Trends Network. 

The chemical components of wet deposition include sulfate, 

nitrate, and ammonium. Dry deposition is not measured 

directly. EPA’s Clean Air Status and Trends Network determines dry deposition inferentially by measuring ambient 

air concentrations of acidic compounds and then calculating deposition rates using a multi-layer model that depends 

on meteorological data collected at the sites as well as local 

vegetative conditions (http://www.epa.gov/castnet/). 

Chemicals measured include components of particulate 

matter (sulfate [SO4

2-] and nitrate [NO3-

]), gaseous nitric 

acid (HNO3), sulfur dioxide (SO2), ammonia (NH3), and 

ammonium (NH4

+). 

Exhibit 2-29. Wet sulfate (SO4

2-

) deposition in 

the contiguous U.S., 1989-1991 and 2004-2006a

a

Coverage: 169 

monitoring sites in 

1989-1991 and 202 

monitoring sites in 

2004-2006.

Data source: NADP, 

2007

Wet SO4

2- deposition 

(kilograms per hectare): 

0 8 4 12 16 20 24 28 >32

A. Average wet SO4

2- deposition, 1989-1991

B. Average wet SO4

2- deposition, 2004-2006

Monitoring site
AIR

2-38 EPA’s 2008 Report on the Environment

INDICATOR | Acid Deposition (continued)

This indicator uses the 3-year average from 1989-1991 as 

a baseline, as this period immediately predates controls on 

sulfur and nitrogen oxide emissions mandated by the 1990 

Clean Air Act Amendments. Baseline data are compared to 

the most recent 3-year average data available (2004-2006). 

Use of 3-year average data helps ensure that trends reflect 

actual changes in acid deposition, instead of shorter-term 

fluctuations in meteorological conditions. Additionally, 

this indicator presents annual trend data for total deposition, which characterizes deposition over the entire period 

of record, not just for the baseline and most recent 3-year 

average periods.

What the Data Show

Wet Deposition Trends

Analyses of long-term monitoring data from the National 

Atmospheric Deposition Program show that wet deposition 

of both sulfur and nitrogen compounds has decreased over 

the last 17 years (Exhibits 2-29 and 2-30).

Wet sulfate deposition decreased across much of the U.S. 

during the 1990s (Exhibit 2-29). The greatest reductions 

in wet sulfate deposition occurred in the Mid-Appalachian 

region (Maryland, New York, West Virginia, Virginia, 

and most of Pennsylvania) and the Ohio River Valley. Less 

dramatic reductions were observed across much of New 

England and portions of the Southern Appalachians. Average regional decreases in wet deposition of sulfate between 

the periods 1989-1991 (panel A) and 2004-2006 (panel B) 

were approximately 35 percent in the Northeast, 33 percent 

in the Midwest, 28 percent in the Mid-Atlantic, and 20 

percent in the Southeast. 

Wet nitrate deposition decreased approximately 33 

percent across the Northeast and 27 percent in the 

Mid-Atlantic between the periods 1989-1991 (Exhibit 

2-30, panel A) and 2004-2006 (panel B). However, there 

is a high degree of variability in the measurements used to 

calculate these percentages, complicating efforts to reliably 

estimate trends for wet nitrate deposition. Wet deposition 

of inorganic nitrogen has not changed substantially in the 

rest of the country over this period. 

Total Deposition Trends

As with wet deposition, total deposition (the sum of wet 

and dry deposition) decreased between 1989-1991 and 

2004-2006, and reductions were more substantial for 

sulfur compounds than for nitrogen compounds (Exhibits 

2-31 and 2-32). In the eastern U.S., where data are most 

abundant, total sulfur deposition decreased by 36 percent 

between 1990 and 2005 (Exhibit 2-33), while total nitrogen deposition decreased by 19 percent over the same time 

frame (Exhibit 2-34). Note that total nitrogen deposition 

in this indicator does not include nitrogen components, 

such as ammonia, which can be a significant portion of the 

dry deposition.

 Indicator Limitations

•	 Geographic coverage is limited, particularly for dry deposition (and thus total deposition as well), but the concentration of sites in the Midwest and Northeast is justified by 

the fact that acid rain is much more of a problem in those 

regions than it is in the West, Great Plains, or Southeast. 

•	 Measurement techniques for dry deposition have improved 

substantially, but characterization of dry deposition still 

requires a combination of measurements and modeling, 

which has inherent uncertainties. Further, dry deposition 

presented in this indicator does not include contributions 

from deposition of gaseous ammonia. 

Exhibit 2-30. Wet nitrate (NO3

-

) deposition in 

the contiguous U.S., 1989-1991 and 2004-2006a

a

Coverage: 169 

monitoring sites in 

1989-1991 and 202 

monitoring sites in 

2004-2006.

Data source: NADP, 

2007

B. Average wet NO3

-

 deposition, 2004-2006

Wet NO3

-

 deposition 

(kilograms per hectare):

0 2 4 6 8 10 12 14 16 18 20 22 >24

A. Average wet NO3

-

 deposition, 1989-1991

Monitoring site
AIR

EPA’s 2008 Report on the Environment 2-39

INDICATOR | Acid Deposition (continued)

a

Coverage: 37 monitoring sites in 1989-1991 

and 73 monitoring sites in 2004-2006.

Data source: NADP, 2007; U.S. EPA, 2007 

Exhibit 2-31. Total sulfur deposition in the contiguous U.S., 1989-1991 and 2004-2006a

A. Average total sulfur deposition, 1989-1991

Dry sulfur deposition Wet sulfur deposition

1.3

4.9

8.2

8.3 8.3

5.6

12.5

12.9

13.2 16.6

18.8

11.9

14.9

19.9

15.9

16.2

16.2 18.0

10.6

18.9

7.5

7.3

9.6

21.3

20.9

13.1

14.7

25.4

0.5

0.7

1.3

1.3

13.1

16.4 19.8

20.2

21.8

B. Average total sulfur deposition, 2004-2006

10

20

5

Numbers indicate total sulfur deposition (kilograms per hectare), 

averaged over a 3-year period.

Sizes of circles indicate the relative magnitude of total sulfur deposition.

Colors in circles indicate the breakdown of total sulfur deposition:

0.5

0.6

0.8

1.0 1.1

0.6

1.1

1.5

1.0

6.9

1.2

1.9

0.9

0.7

0.8 0.8

1.2

1.1

0.7

0.7

1.3

1.2

4.1

4.4

5.2

5.3

2.1

3.5

6.4

6.0 6.5

7.5

8.8

8.6

7.7 16.1

5.2

4.7

5.2

5.0

8.9

9.2

8.0

8.3 8.1 7.5 7.1

9.4

11.5

12.913.2

13.4

21.3

11.2

10.2 10.0

9.2 8.9

11.8

8.9

10.9

12.6

12.8

12.1

15.9 10.5

10.2

4.6 4.7

3.9

3.4

6.3
AIR

2-40 EPA’s 2008 Report on the Environment

INDICATOR | Acid Deposition (continued)

Exhibit 2-32. Total nitrogen deposition in the contiguous U.S., 1989-1991 and 2004-2006a

B. Average total nitrogen deposition, 2004-2006

A. Average total nitrogen deposition, 1989-1991

a

Coverage: 37 monitoring sites in 1989-1991 and 73 monitoring sites in 2004-2006.

Data source: NADP, 2007; U.S. EPA, 2007

6.4

1.6

1.7 2.5

1.2

2.3

6.8 6.2

9.5 8.9

9.0 8.4

10.4

10.3

10.9

10.1 8.4

9.7

6.0

5.6

8.4

8.7

8.9

9.1

9.0 11.0

9.0

9.8

9.7

9.7

6.8 6.5

3.8

10.2

6.9

8.3

8.1

1.1

1.9

1.7

1.3

1.3

2.6

3.0

3.3

2.0 1.6

2.0

2.4

4.1

4.8

1.3

1.7

1.4

2.7 2.2

2.5

2.6

5.0

6.5

5.7 2.6 6.8

7.1

4.6

5.3

6.0 6.6

8.0

6.6 7.5 7.6

7.3 9.2

7.8 8.6

9.1

8.1

7.8 5.7

5.9

9.6

6.5

5.8 7.0

7.5

8.9

8.3

7.9

6.9 8.0

8.0

8.3 5.9

4.3 3.6

3.2

2.9

6.1 9.1

7.7

6.4

4.2

7.0

7.0

6.2

4.0

4.2

3.6

Wet NO3

- Dry HNO3 deposition deposition

Dry NH4

+ deposition

Dry NO3

- deposition

Wet NH4

+ deposition

10

15

5

Numbers indicate total nitrogen deposition (kilograms per hectare), averaged 

over a 3-year period.

Sizes of circles indicate the relative magnitude of total nitrogen deposition.

Colors in circles indicate the breakdown of total nitrogen deposition:

Numbers indicate total nitrogen deposition (kilograms per hectare), averaged 

over a 3-year period.

Sizes of circles indicate the relative magnitude of total nitrogen deposition.

Colors in circles indicate the breakdown of total nitrogen deposition:

Dry nitrogen deposition Wet nitrogen deposition

10 15

5
AIR

EPA’s 2008 Report on the Environment 2-41

INDICATOR | Acid Deposition (continued)

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Atmospheric Programs, based on deposition 

data from two sources. Wet deposition data are from the 

National Atmospheric Deposition Program/National Trends 

Network (NADP, 2007) (http://nadp.sws.uiuc.edu/), and 

dry deposition data are from the Clean Air Status and 

Trends Network (U.S. EPA, 2007) (http://www.epa.gov/

castnet). This indicator aggregates data across 3-year periods 

to avoid influences from short-term fluctuations in meteorological conditions, and wet deposition data were interpolated 

among monitoring stations to generate the maps shown in 

Exhibits 2-29 and 2-30. 

References

MACTEC Engineering and Consulting, Inc. 2006. Clean 

Air Status and Trends Network (CASTNET): 2005 annual 

report. Prepared for U.S. EPA, Office of Air and Radiation. 

<http://www.epa.gov/castnet/library.html>

MACTEC Engineering and Consulting, Inc. 2005. Clean 

Air Status and Trends Network (CASTNET): 2004 annual 

report. Prepared for U.S. EPA, Office of Air and Radiation. 

<http://www.epa.gov/castnet/library.html>

NADP (National Atmospheric Deposition Program). 2007. 

Data from the NADP/National Trends Network. 

Accessed 2007. <http://nadp.sws.uiuc.edu>

NAPAP (National Acid Precipitation Assessment Program). 

1991. 1990 integrated assessment report. Washington, DC.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Clean Air Status and Trends 

Network. Accessed 2007. <http://www.epa.gov/castnet/>

U.S. EPA. 2003. Latest findings on national air quality: 

2002 status and trends. EPA/454/K-03/001. Research 

Triangle Park, NC. <http://www.epa.gov/air/airtrends/

aqtrnd02/2002_airtrends_final.pdf>

Winfrey, M.R., and J.W.M. Rudd. 1990. Environmental 

factors affecting the formation of methyl mercury in low 

pH lakes. Environ. Toxicol. Chem. 9(7):853-869.

Year

a

Coverage: 34 monitoring sites in the eastern United States.

Data source: MACTEC Engineering and Consulting, Inc., 2006

Exhibit 2-33. Total sulfur deposition in the 

eastern United States, 1990-2005a

0

5

10

15

20

25

’90 ’91 ’92 ’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

10% of sites have annual 

sulfur deposition below this line

90% of sites have annual sulfur deposition 

below this line

Average

Median

Total annual sulfur deposition 

(kilograms per hectare, as sulfur)

Year

’90 ’91 ’92 ’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

Total annual nitrogen deposition

 (kilograms per hectare, as nitrogen)

a

Coverage: 34 monitoring sites in the eastern United States.

Data source: MACTEC Engineering and Consulting, Inc., 2006

0

2

4

6

8

10

12

10% of sites have annual nitrogen deposition

below this line

90% of sites have annual nitrogen deposition

below this line

Average

Median

Exhibit 2-34. Total nitrogen deposition in the 

eastern United States, 1990-2005a

v
AIR

2-42 EPA’s 2008 Report on the Environment

INDICATOR | Lake and Stream Acidity

Acid deposition can have serious effects on aquatic ecosystems. For example, aquatic organisms in acidified waters can develop calcium deficiencies that weaken 

bones and exoskeletons and cause eggs to be weak or brittle. 

Acidified waters can impair the ability of fish gills to extract 

oxygen from water and change the mobility of certain trace 

metals (e.g., aluminum, cadmium, manganese, iron, arsenic, 

mercury), which in turn can place fish and other species 

sensitive to these metals at risk (NAPAP, 1991). The Acid 

Deposition indicator (p. 2-37) explains the factors that contribute to acid deposition and describes how acid deposition 

patterns have changed over the last 17 years.

The susceptibility of a water body to acidification 

depends on the ability of the water and watershed soils to 

neutralize the acid deposition it receives. The best measure of this ability is acid neutralizing capacity (ANC), 

which characterizes the amount of dissolved compounds 

that will counteract acidity. Every body of water has a 

measurable ANC, which depends largely on the surrounding watershed’s physical characteristics, such as geology, 

soils, and size. The ANC of a body of water reflects the 

relative proportions of positive and negative ions entering 

the water from sources such as atmospheric inputs and the 

soil and bedrock surrounding and underlying the water 

body. The higher the ANC, the more acid a water body 

can neutralize and the less susceptible it is to acidification. 

As ANC approaches zero, the ability to neutralize acidity 

decreases. Surface water with an ANC greater than 200 

microequivalents per liter (μeq/L) is usually considered 

insensitive to acidification; surface water with an ANC less 

than 50 μeq/L is considered highly sensitive to acidification (is often seasonally acidic); and surface water with an 

ANC less than 0 μeq/L is considered chronically acidic, 

meaning the watershed no longer has the capacity to neutralize further acid deposition (U.S. EPA, 2003). ANC can 

be negative when anions exceed non-proton cations (i.e., 

when there are free protons [H+ ions] in solution). 

The National Acid Precipitation Assessment Program 

identified several regions in the U.S. as containing many of 

the surface waters sensitive to acidification (Exhibit 2-35). 

Where soil buffering capacity is poor, lakes and streams 

may be vulnerable to acidification (NAPAP, 1991). 

This indicator is derived from ANC measurements on 

probability survey samples representing 8,664 lakes and 

75,113 km of streams in the four geographic regions shown 

in Exhibit 2-36. These measurements were collected as 

part of the Temporally Integrated Monitoring of Ecosystems (TIME) project and on 78 additional acid-sensitive 

lakes and 78 acid-sensitive streams in the Long-Term 

Monitoring (LTM) project, for which data were available 

between 1992 and 2005 (U.S. EPA, 2003, 2007). The lakes 

sampled include only those in areas potentially sensitive 

to acidification with areas greater than 1 hectare. This 

indicator focuses only on the northeastern U.S.; because 

monitoring is not ongoing for western, Midwestern, and 

southeastern water bodies, trend data for those parts of the 

country are not available.

What the Data Show

Between the early 1990s and 2005, ANC in lakes in the 

Adirondack Mountains and in streams in the Northern 

Appalachians (southern New York, west-central Pennsylvania, and eastern West Virginia) increased to a degree 

where many water bodies that were considered “chronically 

acidic” in the early 1990s were no longer classified as such in 

2005 (Exhibit 2-36, panels A and C). Specifically, between 

1991-1994 and 2005, the percent of chronically acidic water 

bodies decreased in the Adirondack Mountains (from 13.0 

percent to 6.2 percent) and in the Northern Appalachian 

Plateau (from 11.8 percent to 8.0 percent). Additionally, 

acid-sensitive lakes in New England are beginning to show 

a decrease in acidity: the percent of chronically acidic lakes 

in this region decreased from 5.6 percent in 1991-1994 to 

4.3 percent in 2005 (panel B). This trend suggests that surface waters in these three regions are beginning to recover 

from acidification, though acidic surface waters are still 

found in these regions.

The trend of increasing ANC in the Adirondack Mountains, the Northern Appalachian Plateau, and New England between the early 1990s and 2005 corresponds with 

a decrease in acid deposition in each of these regions (the 

Acid Deposition indicator, p. 2-37) and reduced air emissions of the main precursors to acid deposition, which are 

sulfur dioxide (the Sulfur Dioxide Emissions indicator, p. 

2-34) and nitrogen oxides (the Nitrogen Oxides Emissions 

indicator, p. 2-16). 

ANC in the Ridge and Blue Ridge Region (east-central 

Pennsylvania, western Maryland, and western Virginia) 

Data source: NAPAP, 1991

Exhibit 2-35. Areas with acid-sensitive waters 

in the contiguous U.S.

West Upper 

Midwest

New

England

Mid-Atlantic

Coastal Plain

Adirondacks

Mid-Atlantic

Highlands

Southeastern

Highlands

Florida
AIR

EPA’s 2008 Report on the Environment 2-43

INDICATOR | Lake and Stream Acidity (continued)

has not risen from its 1987 level (Exhibit 

2-36, panel D). Therefore, the number 

of water bodies classified as “chronically 

acidic” in this region remained essentially 

unchanged between 1987 and 2005. 

Indicator Limitations

•	ANC sampling is limited to four regions, 

all in the Northeast. (There is no longterm coverage in the Southeast, West, or 

Midwest.) These four regions were chosen 

for sampling because previous research 

has shown that they are among the most 

sensitive to acid deposition due to the soils 

and other watershed characteristics. In 

addition, as the Acid Deposition indicator (p. 2-37) shows, many of these regions 

receive the highest rates of acid deposition 

in the U.S. For these reasons, the waters 

sampled are likely to be at the greatest risk 

of becoming acidified. 

•	 Interpreting trends for this indicator is 

complicated because multiple factors 

contribute to changes in ANC levels. For 

example, in areas where watershed soil 

characteristics are changing (e.g., decreases 

in concentrations of base cations in the 

soil), even dramatic reductions in acid 

deposition will not necessarily result in 

large rebounds in ANC levels.

Data Sources

Summary data in this indicator were 

provided by EPA’s Office of Atmospheric 

Programs and are taken from a publication documenting how surface waters have 

responded to reduced air emissions of acid 

rain precursors (U.S. EPA, 2003) and from 

more recent unpublished results (U.S. EPA, 

2007). Trends are based on data collected 

in two networks: the TIME project and the 

LTM project. Because both networks are 

operated by numerous collaborators in state agencies, academic institutions, and other federal agencies, the monitoring data are not available in a single publication or database. 

The trend data in this indicator are based on observations 

documented in several publications (see pages 15-17 of 

U.S. EPA, 2003).

References

NAPAP (National Acid Precipitation Assessment Program). 

1991. Acid deposition: State of science and technology, 

volume II, aquatic processes and effects. Washington, DC.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Unpublished data from the Temporally 

Integrated Monitoring of Ecosystems (TIME) network.

U.S. EPA. 2003. Stoddard, J.L., J.S. Kahl, F.A. Deviney, 

D.R. DeWalle, C.T. Driscoll, A.T. Herlihy, J.H. Kellogg, 

P.S. Murdoch, J.R. Webb, and K.E. Webster. Response of 

surface water chemistry to the Clean Air Act Amendments 

of 1990. EPA/620/R-03/001. Research Triangle Park, NC.

U.S. EPA. 1988. Chemical characteristics of streams in the 

mid-Atlantic and southeastern United States. Volume I: 

Population descriptions and physico-chemical relationships. 

EPA/600/3-88/021a. Washington, DC.

Data source: U.S. EPA, 1988, 2003, 2007

Exhibit 2-36. Lake and stream acidity in selected acid-sensitive 

regions in the U.S., 1987-2005

Year

Percent of lakes that are 

chronically acidic

A. Adirondack Mountains

0

5

10

15

6.2 8.1

13.0

1991-1994 2000 2005

Year

Percent of lakes that are 

chronically acidic

B. New England

0

5

10

15

1991-1994 2000 2005

4.3 5.6 5.5

Percent of stream miles that 

are chronically acidic

C. Northern

Appalachian Plateau

0

5

10

15

Year

1993-1994 2000 2005

8.5 8.0

11.8

Percent of stream miles that 

are chronically acidic

D. Ridge and Blue

Ridge Region

0

5

10

15

Year

1987 2000 2005

5.0 5.0 5.0

v
AIR

2-44 EPA’s 2008 Report on the Environment

The Air Quality Index (AQI) provides information on pollutant concentrations of ground-level ozone, 

particulate matter, carbon monoxide, sulfur dioxide, and 

nitrogen dioxide. Formerly known as the Pollutant Standard Index, the nationally uniform AQI is used by state 

and local agencies for reporting daily air quality and air 

quality related health advisories to the public. 

In 1999, the AQI was updated to reflect the latest science on air pollution health effects and to make it more 

appropriate for use in contemporary news media (U.S. 

EPA, 2003a). It also serves as a basis for community-based 

programs that encourage the public to take action to 

reduce air pollution on days when levels are projected to 

be of concern. The index has been adopted by many other 

countries (e.g., Mexico, Singapore, Taiwan) to provide 

the public with information on air quality.

The AQI is based on pollutant concentration data 

measured by the State and Local Air Monitoring Stations 

network and by other special purpose monitors. The AQI 

is monitored in city groupings known as metropolitan 

statistical areas (MSAs), which are defined by the Office 

of Management and Budget. For most pollutants in the 

index, the concentration is converted into index values 

between 0 and 500, “normalized” so that an index value 

of 100 represents the short-term, health-based standard 

for that pollutant as established by EPA (U.S. EPA, 1999). 

The higher the index value, the greater the level of air 

pollution and health risk. An index value of 500 reflects a 

risk of imminent and substantial endangerment of public 

health. The level of the pollutant with the highest index 

value is reported as the AQI level for that day. An AQI 

value greater than 100 means that at least one criteria 

pollutant has reached levels at which people in sensitive 

groups may experience health effects. A complete description of how AQI values are calculated and what they 

represent is documented in many publications (e.g., U.S. 

EPA, 2003b).

This indicator is based on the percent of days across 93 

large MSAs (500,000 people or more) during the year 

that recorded an AQI greater than 100 at one or more 

monitoring sites in the MSA. While the AQI indicator 

is calculated from ambient concentration data for criteria 

pollutants, this indicator’s trends should not be expected 

to mirror the trends in the other ambient concentration 

indicators, due to the differing spatial coverage of monitoring stations across the various indicators.

The percent of days with AQI greater than 100 was 

calculated in two steps. First, for each year, the total 

number of days with AQI above 100 in each of the 93 

MSAs was summed in order to get a national total. Then, 

the national total was divided by the total number of days 

in the annual sample (365 × 93, or 33,945 days) to obtain 

INDICATOR Percent of Days with Air Quality Index Values 

Greater Than 100

Year

0

1

2

3

4

5

6

7

8

’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

1990-1992: 3-year

average = 4.5%

2004-2006: 3

1999 was the first year PM2.5

was included in the AQI -year

average = 2.8%

A. AQI trend based on all criteria pollutants (1990-2006)

Year

’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

1990-1992: 3-year

average = 4.3%

2004-2006: 3-year

average = 1.9%

B. AQI trend based on ozone (1990-2006)

Year

0

1

2

3

4

5

6

7

8

’00 ’02 ’04 ’06

2004-2006: 3-year

average = 1.1%

1999-2001: 3-year

average = 2.1%

C. AQI trend based

on PM2.5 (1999-2006)d

0

1

2

3

4

5

6

7

8

Exhibit 2-37. Percent of days with Air Quality 

Index (AQI) greater than 100 in selected U.S.

metropolitan areas, 1990-2006a,b Percent of total days with AQI > 100 Percent of total days with AQI > 100 Percent of total days with AQI > 100

a

Coverage: 93 metropolitan 

areas for AQI trend based on 

all criteria pollutants, 90 

metropolitan areas for AQI 

trend based on ozone, and 89 

metropolitan areas for AQI 

trend based on PM2.5.

b

For each MSA, the percentage 

of days with AQI greater than 

100 was calculated by dividing 

the number of days per year 

with AQI greater than 100 by 

365 total days. However, 

because PM2.5 is not 

monitored daily in some areas, 

the actual percentage of days 

with AQI greater than 100 

might be higher than what is shown in Panels A and C.

c

Lead does not factor into the AQI calculation for all criteria pollutants.

d

Data for 1990-1998 are not shown because 1999 was the first year 

that PM2.5 was included in the AQI. 

Data source: U.S. EPA, 2007

c

 
AIR

EPA’s 2008 Report on the Environment 2-45

the percentage of days with AQI above 100 in a year. Note 

that this calculation will understate the actual percentage of days with AQI above 100 for pollutants that are not 

measured daily (e.g., PM2.5).

Data are presented for 1990 through 2006. However, 

because meteorology can strongly influence AQI values in 

a given year, the change in AQI over time is evaluated by 

comparing the 3-year average observation at the beginning of the period of record (i.e., 1990-1992) to the 3-year 

average at the end (i.e., 2004-2006). Comparing 3-year 

averages reduces the potential for biases introduced by 

years with unique meteorological conditions. The air quality data that go into the index consist of daily (24-hour) 

measurements for PM10 and PM2.5 and continuous (1-hour) 

measurements for CO, NO2, ozone, and SO2. Lead measurements do not factor into the AQI. Of the pollutants 

considered, only four (CO, ozone, PM, and SO2

) usually 

exhibit AQI values greater than 100. 

What the Data Show

AQI Based on All Criteria Pollutants (Except Lead)

The percent of days with AQI greater than 100 in 93 

large MSAs based on all criteria pollutants (except lead) 

decreased from 4.5 over the 1990-1992 time frame to 

2.8 over the 2004-2006 time frame (Exhibit 2-37, panel 

A). The AQI data based on all criteria pollutants are not 

directly comparable over this time frame, because PM2.5

measurements started to factor into the index in 1999. For 

this reason, the indicator also presents AQI trends based 

strictly on ozone and PM2.5 measurements.

AQI Based on Ozone Only

For a nearly identical subset of MSAs, the percent of days 

with AQI values greater than 100 due to ozone levels alone 

(based on the 1997 NAAQS) decreased from 4.3 over the 

1990-1992 time frame to 1.9 over the 2004-2006 time 

frame (Exhibit 2-37, panel B). Before PM2.5 became part of 

the index in 1999, ozone typically accounted for more than 

90 percent of the days with AQI greater than 100. 

AQI Based on PM2.5 Only

In the 1999-2001 period, PM2.5 concentrations accounted 

for 2.1 percent of days with AQI greater than 100. This 

contribution decreased in subsequent years, falling to 1.1 

percent for the 2004-2006 period.

AQI in the EPA Regions Based on All Criteria Pollutants

(Except Lead)

Trends in AQI based on all criteria pollutants (except lead) 

between 1990 and 2006 varied across the ten EPA Regions 

(Exhibit 2-38). For nine of the Regions, the percent of days 

with AQI greater than 100 in 2006 was lower than that in 

1990, though substantial year-to-year variability occurred. 

In Region 8, the percent of days with AQI greater than 100 

in 2006 was higher than that observed in 1990. However, 

as noted above, the AQI values for 1990 and 2006 are not 

directly comparable, because PM2.5 measurements did not 

factor into AQI prior to 1999. 

Indicator Limitations

•	The AQI does not address hazardous air pollutants. 

•	Air quality can vary across a single MSA. In assigning a 

single number for each pollutant in each MSA, the AQI 

does not reflect this potential variation. 

•	The data for this indicator are limited to MSAs comprising urban and suburban areas with populations greater 

than 500,000. Thus, this indicator does not reflect MSAs 

smaller than 500,000 or rural areas.

•	The AQI does not show which pollutants are causing 

the days with an AQI of more than 100, or distinguish 

between days with AQI slightly above 100 and days with 

much higher AQI.

•	 This composite AQI indicator does not show which 

specific MSAs, or how many MSAs, have problems—a 

specific number of days could reflect a few areas with persistent problems or many areas with occasional problems.

INDICATOR Percent of Days with Air Quality Index Values 

Greater Than 100 (continued)

Year

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

Exhibit 2-38. Percent of days with Air Quality 

Index (AQI) greater than 100 in selected U.S.

metropolitan areas by EPA Region, 1990-2006a,b

a

Coverage: 93 metropolitan areas.

b

Trend is based on AQI data for 

all criteria pollutants, except for 

lead. Note that 1999 was the 

first year that PM2.5 was 

included in the AQI. 

Data source: U.S. EPA, 2007

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

Percent of total days

’90 ’91 ’92 ’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’05’04 ’06

0

5

10

15
AIR

2-46 EPA’s 2008 Report on the Environment

•	 This indicator only covers the days on which ambient monitoring occurred. Because PM2.5 is not sampled 

daily in some areas, the data presented in this indicator 

may understate the actual number of days on which AQI 

values were greater than 100 due to PM2.5 concentrations. 

Although ozone is not sampled throughout the year, the 

percent of days with AQI greater than 100 is believed to 

be accurate because monitoring occurs throughout the 

summer, when ozone concentrations are highest.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

AQI values computed from ambient air monitoring data 

for criteria pollutants found in EPA’s Air Quality System 

(U.S. EPA, 2007). Spreadsheets with the processed AQI 

data for the 93 MSAs considered in this indicator are publicly available (http://www.epa.gov/air/airtrends/factbook.

html). This indicator aggregates the processed AQI data 

nationally and by EPA Region.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. Accessed 

2007. <http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2003a. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

U.S. EPA. 2003b. Air Quality Index: A guide to air quality 

and your health. EPA-454/K-03-002. <http://www.epa.

gov/airnow//aqibroch/AQI_2003_9-3.pdf>

U.S. EPA. 1999. Air quality index reporting, 40 CFR part 58. 

<http://www.epa.gov/ttn/oarpg/t1/fr_notices/airqual.pdf>

INDICATOR Percent of Days with Air Quality Index Values 

Greater Than 100 (continued)

v

INDICATOR | Mercury Emissions

Mercury is an element that occurs naturally in the environment. However, many industrial processes, such 

as coal combustion, medical and hazardous waste incineration, municipal waste combustion, gold mining, and 

certain chemical manufacturing operations, have increased 

the amount of mercury released to the air. What happens 

to mercury after it is emitted depends on several factors: 

the form of mercury emitted, the location of the emissions sources, how high above the landscape the mercury 

is released (e.g., the height of the stack), the surrounding terrain, and the weather. Depending on these factors, 

atmospheric mercury can be transported over a range of 

distances before it is deposited, potentially resulting in 

deposition on a local, regional, continental, or global scale. 

While some domestic anthropogenic mercury emissions 

are deposited within the contiguous U.S., the majority 

of such emissions combine with anthropogenic emissions 

from other countries and natural emissions worldwide to 

form a pool of mercury that circulates globally (Seigneur 

et al., 2004; U.S. EPA, 1996). 

Because it does not degrade in the environment, most 

mercury emitted to the atmosphere eventually deposits 

onto land or water bodies. Through a series of chemical 

transformations and environmental transport processes, 

airborne mercury that deposits to the Earth’s surface can 

eventually accumulate in the food web (the Lake Fish Tissue indicator, p. 3-63), most profoundly in those species 

near the top of the food web (e.g., shark, swordfish). The 

Blood Mercury indicator (p. 5-12) describes the human 

health effects associated with mercury exposure. 

This indicator presents mercury emissions from the following categories: (1) “Industrial processes: gold mining”; 

(2) “Industrial processes: hazardous waste incineration”; (3) 

“Industrial processes: electric arc furnaces”; (4) “Industrial 

processes: chlorine production”; (5) “Industrial processes: 

medical waste incinerators”; (6) “Industrial processes: 

municipal waste combustors”; (7) “Other industrial processes,” which includes chemical production and other 

miscellaneous industrial processes; (8) “Fuel combustion: 

industrial, commercial, and institutional boilers”; and (9) 

“Fuel combustion: utility coal boilers.” In order to better 

characterize mercury emissions, this indicator presents 

different source categories than other emissions indicators in the Report on the Environment, including separate 

categories for utility coal boilers and various industrial 

processes that release mercury (e.g., medical waste incineration, municipal waste combustion, hazardous waste 

incineration, gold mining).
AIR

EPA’s 2008 Report on the Environment 2-47

INDICATOR | Mercury Emissions (continued)

Mercury emissions data are tracked by the 

National Emissions Inventory (NEI). The 

NEI is a composite of data from many different sources, including industry and numerous 

state, tribal, and local agencies. Different data 

sources use different data collection methods, 

and many of the emissions data are based on 

estimates rather than actual measurements. 

For most fuel combustion sources and industrial processes, emissions are estimated using 

emission factors. 

NEI data have been collected since 1990 

and cover all 50 states and their counties, 

D.C., the U.S. territories of Puerto Rico and 

Virgin Islands, and some of the territories 

of federally recognized American Indian 

nations. Data are presented for the baseline 

period (1990-1993) and the latest year for 

which data are available (2002). The baseline 

period represents a mix of years depending 

on data availability for various source types. 

While NEI data for air toxics (including 

mercury) were also compiled for 1996 and 

1999, the methodology used in those years 

for air toxics differs considerably from the 

methodology used in 1990-1993 and 2002 

and therefore cannot be compared directly to 

those data.

What the Data Show

Between 1990-1993 and 2002, annual nationwide air 

emissions of mercury decreased from 245 tons per year to 

119 tons per year, a decrease of 52 percent (Exhibit 2-39). 

The decline in mercury emissions is attributed primarily 

to decreased emissions from medical waste incinerators and 

municipal waste combustors. In 2002, coal-burning power 

plants were the largest anthropogenic source of mercury 

emissions to the air in the U.S., accounting for 42 percent 

of all domestic anthropogenic mercury emissions.

Indicator Limitations

•	The emissions data in this indicator are primarily based 

on estimates, not direct measurements. Although these 

estimates have inherent uncertainties, the data have been 

generated using well-established estimation methods.

•	The trend shown is based on nationwide aggregate data. 

Regional and state trends may be different.

•	 Not all states and local agencies provide the same data or 

level of detail for a given year.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

mercury emissions data in the NEI (U.S. EPA, 2007) 

(http://www.epa.gov/ttn/chief/net/2002inventory.html). 

This indicator aggregates the NEI data by source category. 

References

Seigneur, C., K. Jayaraghavan, K. Lohman, P. Karamchandani, and C. Scott. 2004. Global source attribution for mercury deposition in the United States. Environ. Sci. Technol. 

38:555-569.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 1996. Mercury study report to Congress, 

volumes I to VII. EPA/452/R-96/001b. Washington, DC.

<http://www.epa.gov/mercury/report.htm>

Exhibit 2-39. Mercury emissions in the U.S. by source category, 

1990-1993 and 2002

a

1990-1993 is considered the baseline period for mercury emissions. The baseline period 

spans multiple years due to the availability of emissions data for various source 

categories. The data presented for the baseline period are annual emissions (tons per 

year) and are therefore comparable to the 2002 data.

b

Mercury emissions from mobile sources are not depicted because they have been 

estimated only for inventory year 2002 (0.8 tons) and not for the baseline period.

Data source: U.S. EPA, 2007

Year

Emissions (tons per year)

Gold mining

Electric arc furnaces

Medical waste incinerators

Hazardous waste incineration

Chlorine production

Other industrial processes

Municipal waste combustors

Industrial, commercial, and 

institutional boilers

Industrial processes

Fuel combustion

Utility coal boilers

0

50

100

150

200

250

1990-1993a 2002b

v
AIR

2-48 EPA’s 2008 Report on the Environment

INDICATOR | Air Toxics Emissions 

Toxic air pollutants, also known as air toxics or hazardous air pollutants (HAPs), are those pollutants that 

are known or suspected to cause cancer or are associated 

with other serious health (e.g., reproductive problems, 

birth defects) or ecological effects. Examples of air toxics include benzene, found in gasoline; perchloroethylene, 

emitted from some dry cleaning facilities; and methylene 

chloride, used as a solvent by a number of industries. Most 

air toxics originate from anthropogenic sources, including 

mobile sources (e.g., cars, trucks, construction equipment), 

stationary sources (e.g., factories, refineries, power plants), 

and indoor sources (e.g., building materials, cleaning 

solvents). Some air toxics are also released from natural 

sources such as volcanic eruptions and forest fires. Secondary formation of certain air toxics, such as acetaldehyde 

and formaldehyde, can also occur when precursor chemicals react in the atmosphere. The Clean Air Act identifies 

188 air toxics associated with industrial sources. Twenty 

of these air toxics also are associated with mobile sources 

(U.S. EPA, 2003). 

People who inhale certain air toxics at sufficient concentrations may experience various health effects, including 

cancer, damage to the immune system, and neurological, 

reproductive (e.g., reduced fertility), developmental, or 

respiratory health problems (CDC, 2005). Air toxics also 

can present risks through other exposure pathways. For 

example, air toxics may deposit onto soils or surface waters, 

where they can then enter the food web and may eventually be ingested by humans. Plants and animals also may be 

harmed by exposures to air toxics (U.S. EPA, 2003).

Air toxics emissions data are tracked by the National 

Emissions Inventory (NEI). The NEI is a composite of 

data from many different sources, including industry and 

numerous state, tribal, and local agencies. Different data 

sources use different data collection methods, and many of 

the emissions data are based on estimates rather than actual 

measurements. For most fuel combustion sources and 

industrial sources, emissions are estimated using emission 

factors. Emissions from on-road and nonroad sources were 

estimated using EPA-approved modeling approaches (U.S. 

EPA, 2007a). 

NEI data have been collected since 1990 and cover all 50 

states and their counties, D.C., the U.S. territories of Puerto 

Rico and the Virgin Islands, and some of the territories of 

federally recognized American Indian nations. The NEI 

includes baseline air toxics data for the 1990-1993 period 

and since then has been updated every 3 years. The baseline 

period represents a mix of years depending on data availability for various source types. While NEI data for air toxics 

were also compiled for 1996 and 1999, the methodology 

used in those years for air toxics differed considerably from 

the methodology that was used in 2002. Therefore, the 1996 

and 1999 data are not presented because comparing the two 

inventories might lead to invalid conclusions.

This indicator first presents emissions data for all air toxics 

combined, both at the national level and broken down into 

the ten EPA Regions. Consistent with the other emissions 

indicators, the national data are organized into the following 

source categories: (1) “Stationary sources,” which include 

fuel combustion sources (coal-, gas-, and oil-fired power 

plants; industrial, commercial, and institutional sources; 

as well as residential heaters and boilers) and industrial 

processes (chemical production, petroleum refining, and 

metals production) categories; (2) “Fires: prescribed burns 

and wildfires,” for insights on contributions from some 

natural sources; (3) “On-road vehicles,” which include cars, 

trucks, buses, and motorcycles; and (4) “Nonroad vehicles 

and engines,” such as farm and construction equipment, 

lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft, 

and others. 

In addition to presenting emissions data aggregated across 

all 188 air toxics, the indicator presents emissions trends for 

five individual air toxics: acrolein, benzene, 1,3-butadiene, 

ethylene dibromide, and hydrazine. These compounds 

were selected for display because EPA’s 1999 National Air 

Toxics Assessment estimates that they present the greatest 

nationwide health risks (whether for cancer or non-cancer 

endpoints) among the subset of air toxics for which available emissions and toxicity data supported an evaluation 

(U.S. EPA, 2006). This indicator breaks the emissions data 

for these five air toxics into multiple source categories, with 

Exhibit 2-40. Air toxics emissions in the U.S. by

source category, 1990-1993 and 2002

a

1990-1993 is considered the baseline period for air toxics 

emissions. The baseline period spans multiple years due to the 

availability of emissions data for various source categories. The 

data presented for the baseline period are annual emissions (tons 

per year) and are therefore comparable to the 2002 data. 

Data source: U.S. EPA, 2007b Emissions (million tons per year)

0

1

2

3

4

5

6

7

8

1990-1993a 2002

Year

On-road vehicles

Nonroad vehicles 

and engines

Stationary 

sources (not 

including fires)

Fires (prescribed 

burns and 

wildfires)
AIR

EPA’s 2008 Report on the Environment 2-49

INDICATOR | Air Toxics Emissions (continued)

the most appropriate categories for display purposes differing from one air toxic to the next.

What the Data Show

Trends Aggregated Across All 188 Air Toxics

According to NEI data, estimated annual emissions for the 

188 air toxics combined decreased 36 percent, from 7.2 

million tons per year in the baseline period (1990-1993) 

to 4.6 million tons per year in 2002 (Exhibit 2-40). This 

downward trend resulted primarily from reduced emissions from stationary sources and on-road mobile sources. 

In 2002, air toxics emissions in the ten EPA Regions 

ranged from 166,000 tons in Region 1 to 1,056,000 tons 

in Region 4 (Exhibit 2-41). Regional trends cannot be 

characterized, because a complete set of state and local air 

toxics emissions data are not available for the 1990-1993 

baseline period. 

Trends for Selected Air Toxics

Exhibit 2-42 shows emissions trends for five compounds 

believed to account for the greatest health risks that are 

attributed to air toxics, according to a recent modeling 

study (U.S. EPA, 2006). The five plots in this exhibit show 

how emissions trends vary from compound to compound. 

Estimated emissions decreased between the baseline period 

(1990-1993) and 2002 for all five selected air toxics: acrolein (51 percent decrease; see panel A), benzene (17 percent; 

panel B), 1,3-butadiene (38 percent; panel C), ethylene 

dibromide (63 percent; panel D), and hydrazine (84 percent; 

panel E).

Indicator Limitations

•	The emissions data are largely based on estimates. 

Although these estimates are generated using wellestablished approaches, the estimates have inherent 

uncertainties. The methodology for estimating emissions 

is continually reviewed and is subject to revision. Trend 

data prior to any revisions must be considered in the 

context of those changes. 

•	The indicator is an aggregate number that represents 

contributions from 188 different chemicals with widely 

varying toxicities and human exposures. Therefore, 

the nationwide trend for total air toxics and the resulting health effects likely differs from emissions trends for 

specific chemicals. Similarly, because the indicator is a 

nationwide aggregate statistic, the trend may not reflect 

emissions trends for specific locations.

•	 Not all states and local agencies provide the same data or 

level of detail for a given year. 

•	 There is uncertainty associated with identifying which 

air toxics account for the greatest health risk nationwide. 

Toxicity information is not available for every compound, 

and emissions and exposure estimates used to characterize risk have inherent uncertainties. Additional limitations 

associated with the National Air Toxics Assessment are 

well documented (U.S. EPA, 2006). 

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

air toxics emissions data in the NEI (U.S. EPA, 2007b) 

(http://www.epa.gov/ttn/chief/net/2002inventory.html). 

This indicator aggregates the NEI data by source category, 

EPA Region, and selected air toxics. 

References

CDC (Centers for Disease Control and Prevention). 

2005. Third national report on human exposure to 

environmental chemicals. NCEH Pub. No. 05-0570. 

Accessed September 9, 2005. 

<http://www.cdc.gov/exposurereport/report.htm>

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Documentation for the final 2002 mobile 

National Emissions Inventory, Version 3. <ftp://ftp.

epa.gov/EmisInventory/2002finalnei/documentation/

mobile/2002_mobile_nei_version_3_report_092807.pdf>

Exhibit 2-41. Air toxics emissions in the U.S. by

EPA Region, 2002

Data source: U.S. EPA, 2007b

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10

Emissions (million tons)

EPA Region
AIR

2-50 EPA’s 2008 Report on the Environment

INDICATOR | Air Toxics Emissions (continued)

U.S. EPA. 2007b. Data from the 2002 National Emissions 

Inventory, Version 3.0. Accessed 2007. 

<http://www.epa.gov/ttn/chief/net/2002inventory.html>

U.S. EPA. 2006. 1999 national-scale air toxics assessment. 

<http://www.epa.gov/ttn/atw/nata1999> February.

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/>

a

These five air toxics were selected for presentation because they 

are estimated to present the greatest overall health risks 

nationwide for cancer and non-cancer endpoints.

b

1990-1993 is considered the baseline period for air toxics 

emissions. The baseline period spans multiple years due to the 

availability of emissions data for various source categories. The 

data presented for the baseline period are annual emissions (tons 

per year) and are therefore comparable to the 2002 data. 

Data source: U.S. EPA, 2007b

Exhibit 2-42. Emissions of selected air toxics in the U.S. by source category, 1990-1993 and 2002a

E. Hydrazine emissions

Miscellaneous organic 

chemical manufacturing

Other sources

Industrial organic 

chemical production

Industrial inorganic 

chemical production

Organic liquid distribution

Year

Emissions (tons per year)

1990-1993b 2002

0

5

10

15

20

25

30

35

40

D. Ethylene dibromide emissions

Miscellaneous 

organic chemical 

manufacturing

Industrial organic 

chemical production

Other sources

Year

Emissions (tons per year)

1990-1993b 2002

0

10

20

30

40

50

60

70

C. 1,3-Butadiene emissions

Other sources

Nonroad vehicles

and engines

Prescribed burns

and wildfires

On-road vehicles

Year

Emissions (thousand tons per year)

1990-1993b 2002

0

10

20

30

40

50

60

70

80

90

B. Benzene emissions

Residential wood 

combustion

Oil and natural gas 

production

Other sources

Prescribed burns

and wildfires

Nonroad vehicles

and engines

On-road vehicles

Year

Emissions (thousand tons per year)

1990-1993b 2002

0

100

200

300

400

500

600

A. Acrolein emissions

Other sources

Nonroad vehicles 

and engines

On-road vehicles

Structural fires

Prescribed burns 

and wildfires

Year

Emissions (thousand tons per year)

1990-1993b 2002

0

10

20

30

40

50

60

70

v
AIR

EPA’s 2008 Report on the Environment 2-51

INDICATOR | Ambient Concentrations of Benzene

Benzene is an air toxic emitted from gasoline service stations, motor vehicle exhaust and fuel evaporation, 

the burning of coal and oil, and various other sources. In 

addition to being a common air pollutant, benzene may 

also contaminate water. Urban areas generally have higher 

ambient air concentrations of benzene than other areas.

People exposed to benzene at sufficient concentrations 

may experience various health effects, including cancer 

and damage to the immune system, as well as neurological, 

reproductive (e.g., reduced fertility), developmental, respiratory, and other health problems. Plants and animals may 

also be harmed by exposures to benzene (U.S. EPA, 2003).

Benzene is the most widely monitored air toxic. Data 

from the National Air Toxics Trends Sites network is 

expected to provide trends information for other air toxics 

in the next Report on the Environment. 

This indicator reflects ambient concentrations in micrograms per cubic meter (μg/m3

) of benzene from 1994 to 

2006, based on the annual average. This indicator displays 

trends averaged over 23 urban monitoring sites that have 

consistent data for the period of record from Photochemical Assessment Monitoring Stations, Urban Air Toxics 

Monitoring Stations, and Non-Methane Organic Compound Monitoring Stations. 

What the Data Show

Benzene concentrations declined 55 percent from 1994 to 

2006 (Exhibit 2-43). 

Also shown in Exhibit 2-43 are the 90th and 10th percentiles based on the distributions of annual average concentrations at the 23 monitoring sites. These data provide 

additional graphical representation of the distribution of 

measured concentrations across the monitoring sites for 

a given year: the shaded area in the exhibit displays the 

concentration range where 80 percent of measured values 

occurred for each year.

Indicator Limitations

•	 Benzene data represent only 23 urban sites in the U.S. 

•	 Because of the limited number of sites that are primarily located in urban areas, Exhibit 2-43 does not necessarily represent an overall national trend in benzene 

concentrations.

•	 Benzene, while an important air toxic, is only one of 

many toxics typically found in outdoor air.

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, based on 

benzene ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). National trends in this indicator are based on the 

subset of benzene monitoring stations that have sufficient 

data to assess trends since 1994.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. 

<http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2003. National air quality and emissions trends 

report—2003 special studies edition. EPA/454/R-03/005. 

Research Triangle Park, NC. 

<http://www.epa.gov/air/airtrends/aqtrnd03/> 

Year

a

Coverage: 23 monitoring sites nationwide (out of a total of 230 

sites measuring benzene in 2006) that have sufficient data to 

assess benzene trends since 1994.

Data source: U.S. EPA, 2007 Annual average concentration (μg/m3

)

Exhibit 2-43. Ambient benzene concentrations 

in the U.S., 1994-2006a

’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’06

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

10% of sites have 

concentrations below this line

Median

90% of sites have concentrations 

below this line

Average

v
AIR

2-52 EPA’s 2008 Report on the Environment

INDICATOR | Concentrations of Ozone-Depleting Substances 

Ozone, a gas present throughout the Earth’s atmosphere, is a pollutant at the Earth’s surface but forms a protective layer in the stratosphere, helping shield the Earth from 

the sun’s ultraviolet (UV) radiation. Exposure to UV rays 

is associated with skin cancer, cataracts, and other human 

health and ecological problems (U.S. EPA, 2006). 

Starting in the late 1970s, stratospheric ozone levels were 

observed to be declining due to worldwide releases of 

various human-produced chemicals referred to as ozonedepleting substances (ODSs), particularly halocarbons such 

as the long-lived chlorofluorocarbons (CFCs), brominecontaining halons, and methyl bromide. Through rapid catalytic reactions with ozone, the chlorine and bromine from 

these chemicals have depleted the protective ozone layer (the 

Ozone Levels over North America indicator, p. 2-54).

Worldwide production and consumption of ODSs is 

being progressively eliminated under the provisions of the 

1987 Montreal Protocol on Substances That Deplete the 

Ozone Layer. Over time, reducing the atmospheric loading 

of ODSs is expected to result in global increases in stratospheric ozone. However, because some ODS gases have 

long atmospheric lifetimes, and because of pre-phaseout 

ODS stockpiling for post-phaseout use, ambient concentrations of ODSs have only recently begun to stabilize and 

in some cases begun to decline. While some gases, like 

methyl chloroform, decay quickly in the atmosphere, other 

gases, like CFCs and halons, have atmospheric lifetimes on 

the order of hundreds or thousands of years. 

Measures of effective equivalent troposphere chlorine 

(EECl) and effective equivalent stratospheric chlorine 

(EESC) are commonly used to represent atmospheric concentrations of ODSs. Both represent ODS concentrations 

weighted by their potential to catalyze the destruction of 

stratospheric ozone relative to the ability of chlorine to do 

so. (EESC is typically derived by adding a 3-year time lag to 

EECl to account for the time it takes for emissions of ODSs 

at the Earth’s surface to migrate from the troposphere to the 

stratosphere and cause stratospheric ozone depletion.) 

This indicator presents trends in concentrations of 

tropospheric ODSs as EECl. The EECl trend is based on 

measurements from the National Oceanic and Atmospheric Association (NOAA) Climate Monitoring and 

Diagnostics Laboratory and estimates of halocarbon emissions from industrial and international sources from 1995 

to 2006. Concentrations of EECl are presented as weighted 

averages based on ground-based measurements of mixing 

ratios5

 since 1995 at the following remote locations: Alert, 

Northwest Territories, Canada; Barrow, Alaska; Niwot 

Ridge, Colorado; Mauna Loa, Hawaii; American Samoa; 

Cape Grim, Tasmania, Australia; and the South Pole 

(NOAA CMDL, 2003). Data on total EECl are also available for 1992 through 1994, but these years of monitoring 

5 The mixing ratio is the ratio of the partial pressure of a gas to the total 

atmospheric pressure.

are only presented in the chemical-specific graphs because 

the monitoring did not include methyl bromide, a quantitatively important ODS. Because most ODSs have long 

atmospheric half-lives, the ODS concentrations shown in 

this indicator reflect past and recent contributions from 

emissions sources within the U.S. and worldwide.

What the Data Show

Total EECl resulting from ODS emissions reached its 

peak concentration in the mid-1990s at slightly over 2,700 

parts per trillion of air by volume and has slowly declined 

by approximately 12 percent since then (Exhibit 2-44). 

Although tropospheric concentrations of CFCs and several 

other individual ODS compounds have begun to decline, 

concentrations of halons and selected hydrochlorofluorocarbons (HCFCs) have not yet stabilized. 

Declines in EECl abundances of several ODSs in the 

troposphere between 1992 and 2006 have contributed to 

the decline in total EECl (Exhibit 2-45). EECl attributed 

to methyl chloroform has decreased by nearly 90 percent 

over this period due to decreased emissions as well as its 

short atmospheric lifetime. EECl associated with CFCs has 

decreased more slowly: 2006 levels are approximately 5 

percent lower than the peak tropospheric concentration that 

occurred between 1995 and 1997. The slow decay of CFCs 

is a result of continued emissions of CFCs from stockpiles in 

developed countries, continued use in developing countries, 

and their longer atmospheric lifetimes. EECl from methyl 

bromide has decreased nearly 20 percent from its peak in 

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’06’05

a

Effective equivalent chlorine (EECl) is typically used to represent 

atmospheric concentrations of ozone-depleting substances. The 

EECl reflects contributions from multiple ozone-depleting 

substances, weighted by their potential to catalyze the destruction 

of stratospheric ozone.

Data source: NOAA, 2007 Effective equivalent chlorine concentration (parts per trillion) 

Exhibit 2-44. Global effective equivalent chlorine 

concentrations, 1995-2006a

0

2,400

2,500

2,600

2,700

2,800
AIR

EPA’s 2008 Report on the Environment 2-53

INDICATOR | Concentrations of Ozone-Depleting Substances (continued)

1998; however, continued use of methyl bromide in developing countries and in developed countries through critical 

use exemptions slows the decrease in EECl associated with 

this compound. EECl from methyl bromide exhibits seasonal variations, which likely results from the seasonal use of 

this chemical as a soil fumigant. 

Although some tropospheric ODSs have declined in concentration, others, including halons and HCFCs, continue to 

increase (Exhibit 2-45). EECl estimated from halon emissions 

has increased by more than 50 percent from 1992 to 2006, 

and EECl attributed to HCFCs in 2006 is more than 2.5 

times higher than that from 1992. These trends reflect continued emissions of these ODSs from stockpiles in developed 

countries and continued production and consumption in 

developing countries (and developed countries for HCFCs), 

as well as the longer atmospheric lifetimes of halons. 

Indicator Limitations

•	The calculation of EECl depends on the understanding 

of the interactions and atmospheric residence times of 

many different gases; incorrect knowledge about these 

factors could affect trends in the EECl. 

•	 EECl is calculated by weighting each ODS’s concentration by the substance’s ability to catalyze destruction of 

stratospheric ozone, or the ozone destruction potential. 

The ozone destruction potentials used to transform the 

data have inherent uncertainties, which can affect the 

trend analyses.

•	 Factors additional to trends in halocarbons affect trends 

in stratospheric ozone. These factors include changes in 

climate (e.g., temperature, winds), changes in emissions 

and concentrations of trace gases like nitrous oxide and 

methane, and changes in aerosol loading such as occurs 

after an explosive volcanic eruption.

Data Sources

Tropospheric concentrations of ODSs presented in this 

indicator are based on measurements made by NOAA’s 

Global Monitoring Division and summarized at an online 

data repository (NOAA, 2007) (ftp://ftp.cmdl.noaa.gov/

hats/Total_Cl_Br/). The trend in this indicator was developed from a 2007 data file available from the repository, 

which updates tropospheric ODS concentrations previously 

reported in the peer-reviewed literature (Montzka et al., 

1999, 2003). 

References

Montzka, S.A., J.H. Butler, B.D. Hall, D.J. Mondeel, and 

J.W. Elkins. 2003. A decline in tropospheric organic bromine. Geophys. Res. Lett. 30(15):1826.

Montzka, S.A., J.H. Butler, J.W. Elkins, T.M. Thompson, 

A.D. Clarke, and L.T. Lock. 1999. Present and future trends 

in the atmospheric burden of ozone-depleting halogens. 

Nature 398(6729):690-694.

NOAA (National Oceanic and Atmospheric Administration). 2007. Online repository of global tropospheric mixing 

ratios of ozone-depleting gases. Accessed 2006. 

<ftp://ftp.cmdl.noaa.gov/hats/Total_Cl_Br/>

NOAA CMDL (National Oceanic and Atmospheric 

Administration, Climate Monitoring and Diagnostics 

Laboratory). 2003. Summary report no. 27. Boulder, CO.

<http://www.cmdl.noaa.gov/publications/annrpt27/>

U.S. EPA (United States Environmental Protection 

Agency). 2006. Air quality criteria for ozone and related 

photochemical oxidants. EPA/600/R-05/004aF-cF. 

Research Triangle Park, NC. <http://cfpub.epa.gov/ncea/

cfm/recordisplay.cfm?deid=149923>

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’06

a

Effective equivalent chlorine (EECl) is typically used to represent 

atmospheric concentrations of ozone-depleting substances. The EECl 

of ozone-depleting substances is calculated from the substances’ 

atmospheric concentrations and their potential to catalyze the 

destruction of stratospheric ozone.

b

The chlorofluorocarbons (CFCs) considered in this figure are CFC-11, 

CFC-12, and CFC-113.

c

The halons considered in this figure are halon 1211 and halon 1301. 

d

The hydrochlorofluorocarbons (HCFCs) considered in this figure are 

HCFC-22, HCFC-141b, and HCFC-142b.

Data source: NOAA, 2007 Effective equivalent chlorine concentration (parts per trillion) 

Exhibit 2-45. Global effective equivalent chlorine 

concentrations of selected ozone-depleting 

substances, 1992-2006a

’92 ’93 ’94

0

200

400

600

800

1,000

1,200

1,400

CFCsb

CH3Br

CCI4

Halonsc

CH3CCI3 HCFCsd

v
AIR

2-54 EPA’s 2008 Report on the Environment

INDICATOR | Ozone Levels over North America

Ozone is a gas present throughout the Earth’s atmosphere; 90 percent resides in the stratosphere, the layer 

of the atmosphere that starts about 6 to 9 miles above the 

Earth’s surface at mid-latitudes, and the rest is located in 

the troposphere, the atmospheric layer that lies between 

the stratosphere and the Earth’s surface. The environmental and human health implications of ground-level ozone 

are very different from those of ozone higher in the atmosphere, leading to the maxim: “Good up high, bad nearby” 

(U.S. EPA, 2003). In the troposphere, ozone poses both 

health and ecological risks, but the natural layer of ozone 

in the stratosphere shields and protects the Earth’s surface from the sun’s harmful ultraviolet (UV) rays, which 

can lead to more cases of skin cancer, cataracts, and other 

health problems (U.S. EPA, 2006). 

Increases in surface UV radiation have been associated with reductions in total column ozone levels based 

on spectral measurements at a number of sites in Europe, 

North America, South America, Antarctica, and New 

Zealand (Kerr and McElroy, 1993; Booth and Madronich, 

1994; WMO et al., 2007). For example, measurements 

between 1989 and 1993 over Toronto indicated that for 

every 1 percent decrease in total column ozone, after 

accounting for seasonal and daily variables not related to 

ozone, there was a corresponding increase—between 1.1 

percent and 1.3 percent—in erythemally active UV-B 

radiation (Kerr and McElroy, 1993). 

Ozone in the stratosphere is constantly being produced 

naturally from dissociation of oxygen molecules by highly 

energetic UV solar radiation. While this ozone is being 

transported poleward and downward through the natural 

motions of air in the stratosphere, it also is being naturally 

destroyed through catalytic reactions involving primarily 

nitrogen and hydrogen oxides. 

Releases of various human-produced chemicals, such as 

the long-lived chlorofluorocarbons, bromine-containing 

halons, and methyl bromide (the Concentrations of OzoneDepleting Substances indicator, p. 2-52), have depleted the 

levels of protective stratospheric ozone starting in the late 

1970s, particularly at medium to high latitudes. The U.S. 

has been a major contributor to the global emissions of these 

halocarbons, accounting for about a quarter of total worldwide emissions before the major ozone-depleting substances 

(ODSs) were banned in the 1990s. It takes about 3 years for 

emissions of ODSs at the Earth’s surface to migrate to the 

stratosphere and cause stratospheric ozone depletion (WMO 

et al., 2007).

This indicator tracks trends in the deviation from 

pre-1980 levels in total annually averaged ozone values 

integrated over the 35 to 60 degrees north latitude belt 

(the latitudes roughly corresponding to North America) 

from 1964 to 2006. The estimates are based on data from 

several different sources including ground-based and satellite 

measurements. The data on total ozone from ground-based 

measurements are from a network of surface stations, which 

are equipped with spectrophotometers. These instruments 

measure how thick the ozone layer would be if compressed 

in the Earth’s atmosphere (at sea level and at 0°C), where 

one Dobson Unit (DU) is defined to be 0.01 mm thickness 

at standard temperature and pressure. Reliable data from 

regular measurements at these ground-based stations are 

available extending back to the 1960s, although geographical coverage is limited before the 1970s (Fioletov et al., 

2002; WMO et al., 2007).

Near-continuous global total ozone data are available 

from satellite measurements beginning in 1979. These satellite data come from four sources: (1) The Global Ozone 

Monitoring Experiment (GOME) refers to data collected 

from instruments on board the European Space Agency’s 

ERS-2 satellite, for which validated data are available 

dating back to 1996; (2) The Solar Backscatter Ultraviolet (SBUV) instruments have been collecting data since 

1979, with one instrument (SBUV) on board the Nimbus 

7 satellite and the other instruments (SBUV/2) on board 

a sequence of NOAA satellites; (3) The “merged satellite 

data” refer to total ozone data dating back to 1970 (not 

all years inclusive) constructed by merging observations 

from the SBUV/2 data and data collected by Total Ozone 

Mapping Spectrometer (TOMS) instruments on board the 

Nimbus 7 satellite; and (4) The National Institute of Water 

and Atmospheric Research (NIWA) assimilated data set 

Year

’80 ’90 ’95 ’00 ’05

a

Total ozone refers to the total ozone concentration in a column of air 

between the Earth’s surface and the top of the atmosphere.

b

Trend data are representative of latitudes ranging from 35 degrees 

north to 60 degrees north.

Data source: WMO et al., 2007 Percent deviation in total ozone levels from 1964-1980 levels

Exhibit 2-46. Total ozone levels over North 

America, 1964-2006a,b

’65 ’70 ’75

-8

-9

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

’85

Ground-based data

Merged satellite data

GOME satellite data

SBUV-SBUV/2 satellite data

NIWA assimilated satellite

data
AIR

EPA’s 2008 Report on the Environment 2-55

INDICATOR | Ozone Levels over North America (continued)

is a merged data set constructed from observations dating 

back to 1979 collected by the TOMS, GOME, and SBUV 

instruments. Other publications provide further documentation on the four satellite data sets used in this indicator 

(WMO et al., 2007). 

What the Data Show

There was little ozone change (beyond natural variations 

such as those resulting from the 11-year solar sunspot cycle) 

before the late 1970s, but decreases in stratospheric ozone 

began to occur after 1979 (Exhibit 2-46). The ground-based 

data and four satellite data sets have similar ozone variations, 

with differences typically less than 0.5 percent. The midlatitude decline of approximately 6 percent between 1979 

and 1995 is in general agreement with previous profile trend 

estimates from satellite and ground-based records. 

However, total ozone levels have begun to recover since 

1995. For the mid-latitudes of the Northern Hemisphere, 

the average of the total ozone levels for the 4-year period 

from 2002 to 2005 is about 3 percent lower than the 

pre-1980 levels in the Northern Hemisphere (WMO et 

al., 2007). While this indicator covers the entire 35 to 60 

degrees north latitude belt, ozone varies little by longitude 

and the estimated 3 percent change in total ozone levels 

can be taken to apply to North America. 

This 3 percent change over North America is very similar 

to the statistically significant globally averaged 3.5 decrease 

in total ozone between pre-1980 levels and 2002-2005 

(WMO et al., 2007). The decrease in the mid-latitudes of 

the Southern Hemisphere, by contrast, has been nearly twice 

as high as observed in the Northern Hemisphere, due largely 

to the springtime “ozone hole” over Antarctica. The trends 

in this indicator are consistent with well understood seasonal 

variations in ozone, and with natural variations such as those 

due to the 11-year solar cycle and the effects of volcanic 

eruptions, suggesting that the long-term trends are those 

resulting from the emissions of ODSs. 

Indicator Limitations

•	 Fioletov et al. (2002) used estimates of ozone changes 

from several different, independent sources to derive 

some data used for this indicator. Differences in the calibration of instruments used to obtain the ground-based 

and satellite datasets together with interruptions in the 

observational records produce datasets with measurement errors typically around a few percent (WMO et al., 

2007). The figure presented does, however, show good 

overall agreement among the different data sources for 

changes in total ozone. 

Data Sources

Summary data for this indicator were provided by the 

World Meteorological Organization. The 1964-2006 data 

in this indicator are taken from the Organization’s 2006 

Scientific Assessment of Ozone Depletion (WMO et al., 

2007), which presents ozone data based on multiple sets of 

measurements (e.g., Fioletov et al., 2002). 

References

Booth, R.C., and S. Madronich. 1994. Radiation amplification factors—improved formulation accounts for large 

increases in ultraviolet radiation associated with Antarctic 

ozone depletion. In: Weiler, C.S., and P.A. Penhale, eds. 

Ultraviolet radiation and biological research in Antarctica. 

Antarctic Research Series. Washington, DC: American 

Geophysical Union. pp. 39-42.

Fioletov, V.E., G.E. Bodeker, J.B. Kerr, A.J. Miller, R.D. 

McPeters, and R. Stolarski. 2002. The global ozone and 

zonal total ozone variations estimated from ground-based 

and satellite measurements: 1978-2000. J. Geophys. Res. 

107(D22).

Kerr, J.B., and C.T. McElroy. 1993. Evidence for large 

upward trends of ultraviolet-B radiation linked to ozone 

depletion. Science 262:1032-1034.

U.S. EPA (United States Environmental Protection 

Agency). 2006. Air quality criteria for ozone and related 

photochemical oxidants. EPA/600/R-05/004aF-cF. 

Research Triangle Park, NC. <http://cfpub.epa.gov/ncea/

cfm/recordisplay.cfm?deid=149923> 

U.S. EPA. 2003. Ozone: good up high, bad nearby. 

EPA/451/K-03/001. Washington, DC. 

<http://www.epa.gov/oar/oaqps/gooduphigh/>

WMO (World Meteorological Organization), et al. 2007. 

Scientific assessment of ozone depletion: 2006. Geneva, 

Switzerland. <http://ozone.unep.org/Assessment_Panels/

SAP/Scientific_Assessment_2006>

v
AIR

2-56 EPA’s 2008 Report on the Environment

INDICATOR Ozone and Particulate Matter Concentrations for 

U.S. Counties in the U.S./Mexico Border Region

The border between the U.S. and Mexico spans approximately 2,000 miles, from the Pacific Ocean to the 

Gulf of Mexico. The area is subjected to a unique blend 

of increased industrial development (especially on the 

Mexican side of the border), intense pressures because of 

the shifting and growing population related to this development, and an arid climate that can exacerbate many air 

quality problems. Ozone and particulate matter are air 

pollutants of particular concern. Rapid population growth 

in urban areas of the (U.S./Mexico) border has resulted 

in unplanned development, greater demand for land and 

energy, traffic congestion, increased waste generation, 

overburdened or unavailable waste treatment and disposal 

facilities, increased frequency of chemical emergencies, and 

an adverse impact on air quality (U.S. EPA, 2003).

Ground-level ozone is harmful to both human health 

and the environment (the Ozone Concentrations indicator, 

p. 2-22). Although some industrial sources release ozone 

directly into the environment, most ground-level ozone 

forms from chemical reactions involving nitrogen oxides, 

volatile organic compounds, and sunlight. Ozone levels are 

typically highest during the afternoon hours of the summer 

months, when the influence of direct sunlight is the greatest (U.S. EPA, 2006). 

Exhibit 2-47. Ambient ozone, PM10, and PM2.5 concentrations in U.S. counties in the U.S./Mexico border 

area, 1986-2006a

0

2

4

6

8

10

12

14

16

18

Average of annual average 

concentrations from three consecutive 

calendar years (μg/m3)

C. PM2.5 concentrations 

(1999-2006)

’99-’01 ’01-’03 ’03-’05

Averaging period

0

25

50

75

100

125

150

Averaging period

Average of the second highest 24-hour

concentrations from three consecutive

calendar years (μg/m3)

A. Ozone concentrations 

(1986-2006)

Counties with ambient air monitoring sites included in this indicator

’88-’90 ’92-’94 ’96-’98 ’00-’02 ’04-’06

Averaging period

Average of fourth highest daily 

maximum 8-hour concentrations from 

three consecutive calendar years (ppm)

B. PM10 concentrations 

(1988-2006)c

Region 6 

border 

counties

National 

average

Region 9 

border 

counties

NAAQS = 15 μg/m3

a

Coverage: 29 ozone monitoring sites, 

32 PM10 monitoring sites, and 14 

PM2.5 monitoring sites located in U.S. 

counties along the U.S./Mexico

border that have sufficient data to 

assess trends over the time frames in 

which these pollutants were 

monitored.

b The figure displays the 1997 NAAQS 

(0.08 ppm). Future versions of the 

ROE will compare ozone 

concentrations to the recently 

promulgated 2008 NAAQS (0.075 

ppm) or to the NAAQS in effect at 

the time.

c

National PM10 data are not depicted 

because the approach used to track 

PM10 concentrations in the U.S./Mexico border region 

differs from that used on the national scale.

Data source: U.S. EPA, 2007

NAAQS = 150 μg/m3

0.00

0.02

0.04

0.06

0.08

0.10

0.12

’86-’88 ’89-’91 ’92-’94 ’95-’97 ’98-’00 ’01-’03 ’04-’06

San

Diego

Pima

Yuma

Cochise

Imperial

Santa Cruz

Grant

Brewster

Luna

Webb

Dona

Ana

Hidalgo

El Paso

Cameron

Texas

Arizona New Mexico California

Mexico

NAAQS = 0.08 ppmb
AIR

EPA’s 2008 Report on the Environment 2-57

INDICATOR Ozone and Particulate Matter Concentrations for 

U.S. Counties in the U.S./Mexico Border Region (continued)

“Particulate matter” (PM) is the general term used for a 

mixture of solid particles and liquid droplets found in the 

air. Primary PM is released directly from emissions sources 

into the atmosphere, while secondary PM is formed in 

the air from reactions involving precursor chemicals (e.g., 

nitrogen oxides, sulfur dioxide, particle-producing organic 

gases). Ambient air monitoring stations measure air concentrations of two size ranges of particles: PM2.5 (fine particles with aerodynamic diameter less than or equal to 2.5 

micrometers [μm]) and PM10 (particles with aerodynamic 

diameters less than or equal to 10 μm, including PM2.5). 

Exposure to coarse particles (i.e., particles with aerodynamic 

diameters between 2.5 and 10 μm) can aggravate respiratory 

conditions such as asthma, and exposure to fine particles is 

associated with various additional human health effects (the 

PM Concentrations indicator, p. 2-29) (U.S. EPA, 2004). 

This indicator shows trends in ambient air concentrations of ozone and particulate matter in the U.S. counties at the U.S./Mexico border area in comparison to 

U.S. national trends, where appropriate. These trends are 

shown for the longest duration of time supported by the 

underlying monitoring data. For ozone, this indicator 

reports the average of the fourth highest daily maximum 

8-hour concentrations for three consecutive calendar 

years. For PM10, this indicator reports the 3-year average 

of the second highest 24-hour concentrations. For PM2.5, 

this indicator reports the 3-year average of the seasonally 

weighted annual average concentration. For ozone and 

PM2.5, national trend lines are also depicted because the 

statistics used to report data in this indicator are the same 

as those used in the corresponding national indicators. 

For PM10, national data are not presented, because this 

indicator tracks data over 3-year averaging periods, while 

the national indicator tracks data over single-year intervals. This indicator is based on all monitoring stations 

that operated on the U.S. side of the border during this 

time period. 

In EPA Region 6, ozone monitoring data from border 

locations were collected in Dona Ana County in New 

Mexico and El Paso, Brewster, Webb, Hidalgo, and Cameron Counties in Texas. In EPA Region 9, ozone monitoring data from border locations were collected in the counties of Cochise, Pima, and Yuma in Arizona and Imperial 

and San Diego in California. PM10 sampling data for EPA 

Region 6 are from Cameron, Hidalgo, Webb and El Paso 

Counties in Texas and Dona Ana, Luna, and Grant Counties in New Mexico. PM2.5 data were available for all of 

the above counties except for Luna County, New Mexico. 

For EPA Region 9, PM10 monitoring data were collected 

in the counties of Cochise, Pima, Santa Cruz, and Yuma 

in Arizona and Imperial and San Diego in California. For 

EPA Region 9, PM2.5 monitoring data were collected in 

the counties of Cochise, Pima, and Santa Cruz in Arizona 

and Imperial and San Diego in California.

What the Data Show

Trends for 8-Hour Ozone Concentrations

In EPA Region 6, average border ozone concentrations 

decreased by 11 percent between the 1986-1988 and 1992-

1994 time periods (a smaller decrease than the national average, which was 13 percent) and by 4 percent between the 

1993-1995 and 2004-2006 periods (again, smaller than the 

national average decrease of 11 percent) (Exhibit 2-47, panel 

A). In EPA Region 9, however, border ozone concentrations decreased by 6 percent between the 1986-1988 and 

1992-1994 time periods and then decreased by 11 percent 

between the 1993-1995 and 2004-2006 periods.

Trends for 24-Hour PM10 Concentrations

In EPA Region 6, the second highest 24-hour PM10 concentrations at border monitoring sites varied considerably 

over the period of record, most likely due to variation in 

meteorological conditions (e.g., rainfall, wind speed) and 

soil erosion (Exhibit 2-47, panel B); no clear long-term 

trend is apparent from the data. In EPA Region 9, on the 

other hand, corresponding PM10 concentrations at border monitoring sites did not exhibit such strong temporal 

variations, and the average second highest 24-hour concentration at border monitoring sites for the 2004-2006 time 

frame was 37 percent lower than that for the 1988-1990 

time frame. 

Trends for Annual Average PM2.5 Concentrations

Between 1999-2001 and 2004-2006, average annual ambient PM2.5 exhibited no clear trend in the border counties of 

EPA Region 6, but decreased by 17 percent in the border 

counties of EPA Region 9 (Exhibit 2-47, panel C). Average 

annual ambient PM2.5 concentrations decreased 10 percent 

nationwide over the same period. 

Indicator Limitations

•	 Many counties along the U.S./Mexico border do not 

have ambient air quality monitors; these counties are not 

characterized by this indicator. 

•	This indicator does not include data from the Mexican 

side of the border. When a technical review concludes 

the quality of these data is appropriate for the intended 

use, the indicator will be updated.

•	 Short-term trends in PM10 concentrations are often 

highly dependent on meteorological conditions. The 

maximum concentration for a given site can be influenced by wind-blown dust and will exhibit considerable 

variations from day to day. Trends over the longer term 

are far less likely to be influenced by unusual meteorological conditions. 
AIR

2-58 EPA’s 2008 Report on the Environment

INDICATOR Ozone and Particulate Matter Concentrations for 

U.S. Counties in the U.S./Mexico Border Region (continued)

•	The long-term ozone trends are derived from an increasing number of monitors over the course of time from 

1986 to 2006, but an analysis of the limited number of 

border sites that have full periods of record show that the 

slopes of the trends are similar to those in this indicator.

•	Average air pollutant concentrations may mask higher 

values in some areas along the border and in the nation.

•	 Because most of the monitoring sites are located in urban 

areas, the trends might not accurately reflect conditions 

outside the immediate urban monitoring areas. 

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Air Quality Planning and Standards, Region 

6, and Region 9. These summaries were based on ozone 

and PM ambient air monitoring data in EPA’s Air Quality 

System (U.S. EPA, 2007) (http://www.epa.gov/ttn/airs/

airsaqs/). Trends in this indicator are based on the subset 

of ozone and PM monitoring stations located in counties 

along the U.S./Mexico border that have sufficient data to 

assess trends over the period of record.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data from the Air Quality System. 

Accessed 2007. <http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2006. Air quality criteria for ozone and related 

photochemical oxidants. EPA/600/R-05/004aF-cF. 

Research Triangle Park, NC. <http://cfpub.epa.gov/ncea/

cfm/recordisplay.cfm?deid=149923>

U.S. EPA. 2004. Air quality criteria for particulate matter (October 2004). EPA 600/P-99/002aF-bF. Research 

Triangle Park, NC. <http://cfpub.epa.gov/ncea/CFM/

recordisplay.cfm?deid=87903>

U.S. EPA. 2003. Border 2012: U.S.-Mexico environmental 

program. EPA/160/R-03/001. Washington, DC.

v

Manganese is a naturally occurring metal that is ubiquitous in the environment. Exposure to low levels 

of manganese in the diet is considered to be nutritionally 

essential for people and animals (ATSDR, 1997). However, exposures to elevated concentrations of manganese 

are harmful to human health and have been associated with 

subtle neurological effects, such as slowed eye-hand coordination. Manganese compounds are hazardous air pollutants 

emitted by iron and steel production plants, power plants, 

coke ovens, and many smaller metal processing facilities. 

Manganese also may be contributed in border communities 

by vehicles using Canadian fuel with the additive methylcyclopentadienyl manganese tricarbonyl (MMT). 

Although manganese compounds are air pollutants of 

concern nationwide, they are of special concern in EPA 

Region 5. The 1999 National Emissions Inventory showed 

that Region 5 had the highest manganese emissions of all 

EPA Regions, contributing 36.6 percent of all manganese 

compounds emitted nationwide (U.S. EPA, 2005a). Emissions from industrial sources in Region 5 occurred from 

various facilities, such as those that manufacture steel or 

process iron ores and alloys for steelmaking. Between 1988 

and 2003, manganese emissions from point sources declined 

both nationally (26.2 percent) and in EPA Region 5 (36.7 

percent). Year-to-year variability in manganese emissions is 

high, however, and recent emissions data (1996-2003) suggest a weaker trend: emissions dropped 7.6 percent and 12.4 

percent nationwide and in EPA Region 5, respectively (U.S. 

EPA, 2005b). 

EPA’s National Air Toxics Assessment (NATA) is 

intended to provide a better understanding of the health 

risks resulting from inhalation exposure to air toxics. Based 

on 1999 emissions inventories, the most recent NATA 

results (U.S. EPA, 2006) identify manganese compounds as 

the largest contributor to neurological non-cancer health 

risk in the U.S. Modeled estimates of ambient manganese 

compounds in all 3,222 U.S. counties show that among the 

50 counties with the highest concentrations nationwide, 20 

are located in EPA Region 5. 

This indicator presents ambient concentrations of manganese compounds measured as total suspended particulates (TSP) by direct monitoring. This indicator addresses 

manganese in the TSP fraction (not PM10 or PM2.5) because 

it is the most complete dataset in EPA Region 5 in terms of 

INDICATOR Ambient Concentrations of Manganese Compounds in 

EPA Region 5
AIR

EPA’s 2008 Report on the Environment 2-59

geographic and temporal coverage. TSP metals data have 

been commonly used in human health risk assessments. EPA 

recently has begun to recommend PM10 as the most appropriate fraction for evaluating people’s exposure to toxic metals (U.S. EPA, 2002), but PM10 metals data are sparse at this 

time, both nationally and in EPA Region 5. Data from a 

limited number of sites in EPA’s Air Quality System (AQS) 

with collocated PM10 and TSP speciation monitors suggest that the proportion of manganese in PM10 versus TSP 

is about 50 percent at most sites and can be as high as 75 

percent. TSP manganese data therefore should be considered a conservative estimate of PM10 manganese exposures. 

PM2.5 metals data are plentiful since the establishment of the 

Speciation Trends Network in 2000, but this size fraction is 

believed to underestimate human exposures.

Data were considered for 58 monitoring sites in EPA 

Region 5 that had a complete year of data reported to 

the AQS national database in 2006. Average manganese 

concentrations were calculated for each monitoring site. 

A concentration trend was determined using a subset 

of 21 of the monitoring sites with six or more complete 

years of data between 2000 and 2006. As annual average 

concentrations are representative of long-term inhalation 

exposures, the ambient monitoring data are displayed in 

comparison with the manganese reference concentration 

(RfC). The RfC is an estimate of a chronic inhalation 

exposure that is likely to be without appreciable risk of 

adverse non-cancer effects during a lifetime. The RfC 

for manganese is 0.05 micrograms per cubic meter (μg/

m3

), based on impairment of neurobehavioral function in 

people. At exposures increasingly greater than the RfC, 

the potential for harmful effects increases (ATSDR, 1997; 

U.S. EPA, 1999). Monitoring sites were classified into different categories based on land use as defined in AQS. 

What the Data Show

In 2006, the median average annual ambient concentrations of manganese as TSP in EPA Region 5 were 0.024 

μg/m3

 at the 15 residential sites, 0.024 μg/m3 at the 16 sites 

in commercial or high-traffic areas, and 0.046 μg/m3 at 

the 24 industrial sites (Exhibit 2-48). The average annual 

ambient concentration of manganese at three predominantly agricultural and forest sites in EPA Region 5 was 

0.02 μg/m3

, but this is not depicted in the figure due to the 

limited number of monitoring sites to characterize a distribution. Greater concentration differences were observed in 

the 90th percentile values: below 0.1 μg/m3 at the residential, commercial, and high-traffic sites, compared to 0.39 

μg/m3

 at the predominantly industrial sites. In 2006, 18 of 

the 58 sites had average manganese concentrations higher 

than the RfC; 12 of these sites were categorized as industrial, two commercial or high-traffic, and four residential. 

The average annual manganese concentration averaged 

across 21 trend sites showed a 28 percent decline between 

2000 and 2006 (Exhibit 2-49). Additional years of data 

may be needed to confirm this trend. The trend sites had 

the following land use designations: commercial and hightraffic (six sites), industrial (nine sites), and residential (six 

sites). None of the trend sites had agricultural or forest land 

use designations. 

Indicator Limitations

•	AQS data represent several sites per state, but do not have 

full geographic or temporal coverage. Some emissions 

“hotspots” are included, while others may exist that have 

not been monitored. 

•	The land use categories are only generally indicative 

of the area represented by an ambient air monitor. For 

example, a site categorized as “industrial” may adjoin a 

densely populated community where many residents are 

exposed to ambient pollution. 

INDICATOR Ambient Concentrations of Manganese Compounds in 

EPA Region 5 (continued)

Exhibit 2-48. Ambient manganese 

concentrations in EPA Region 5 by land use 

category, 2006a,b Annual average concentration (μg/m3

)

Land use category

a

Coverage: 55 monitoring sites in 

EPA Region 5, with 16 sites in 

commercial or high-traffic land use 

areas, 24 sites in industrial areas, 

and 15 sites in residential areas.

b

Concentrations are for manganese 

in total suspended particulate 

matter.

c

The 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 

deleterious effects during a lifetime.

Data source: U.S. EPA, 2007

0.0

0.1

0.2

0.3

0.4

Commercial or 

high-traffic areas

Industrial Residential

RfCc = 0.05 μg/m3

90th percentile

75th percentile

Median

25th percentile

10th percentile

RfCc = 0.05 μg/m3
AIR

2-60 EPA’s 2008 Report on the Environment

2.2.3 Discussion

What These Indicators Say About Trends 

in Outdoor Air Quality and Their Effects on 

Human Health and the Environment

Criteria Pollutants and Their Precursors 

Because of regulatory monitoring and reporting requirements, 

criteria pollutants have some of the most extensive data available to support National Indicators for emissions and ambient 

air concentrations. Nationwide, air emissions of every criteria 

pollutant (or the corresponding precursors) have decreased 

between 1990 and 2002—the period of record covered by 

the National Emissions Inventory. During that time frame, 

substantial decreases in air emissions were observed for carbon 

monoxide, nitrogen oxides, particulate matter, sulfur dioxide, 

and volatile organic compounds. Even more pronounced 

emissions reductions occurred for lead, but this decrease 

extends back to the 1970s. With few exceptions, downward 

trends in criteria pollutant emissions were observed in the ten 

EPA Regions, similar to the corresponding national trends. 

Consistent with the emissions trends, every criteria pollutant showed decreasing ambient air concentrations based on 

aggregate measurements from the nation’s ambient air monitoring system, which measures levels of air pollution primarily in urban and suburban areas. The magnitude of air quality 

improvements, observed both nationally and in all ten EPA 

Regions, varies across pollutants. Carbon monoxide, lead, 

and nitrogen dioxide concentrations decreased considerably 

between 1980 and the present, and ambient concentrations of 

these three pollutants in most or all areas in the U.S. are now 

below the level of the corresponding air quality standards that 

protect human health and the environment. In contrast, air 

Data Sources

Summary data in this indicator were provided by EPA 

Region 5, based on ambient air monitoring data for manganese compounds reported in EPA’s AQS (U.S. EPA, 2007) 

(http://www.epa.gov/ttn/airs/airsaqs/). Trends in this indicator are based on the subset of monitoring stations located 

in EPA Region 5 that have sufficient manganese concentration data to assess trends over the period of record.

References

ASTDR (Agency for Toxic Substances and Disease Registry). 1997. Toxicological profile for manganese (update). 

Draft for public comment. Atlanta, GA: U.S. Department of 

Health and Human Services.

U.S. EPA (United States Environmental Protection Agency). 

2007. Data from the Air Quality System. Accessed 2007. 

<http://www.epa.gov/ttn/airs/airsaqs/>

U.S. EPA. 2006. 1999 national-scale air toxics assessment. 

<http://www.epa.gov/ttn/atw/nata1999> February.

U.S. EPA. 2005a. 1999 National Emissions Inventory data. 

<http://www.epa.gov/air/data> August.

U.S. EPA. 2005b. 1999 Toxics Release Inventory data. 

<http://www.epa.gov/tri> December.

U.S. EPA. 2002. Quality assurance guidance document—

model quality assurance project plan for the national air 

toxics trends stations. Washington, DC.

U.S. EPA. 1999. Integrated Risk Information System (IRIS) 

on manganese. Washington, DC. 

<http://www.epa.gov/iris/subst/0373.htm>

INDICATOR Ambient Concentrations of Manganese Compounds in 

EPA Region 5 (continued)

2000 2001 2002 2003 2004 2005 2006

Exhibit 2-49. Ambient manganese 

concentrations in EPA Region 5, 2000-2006a,b

a

Coverage: 21 monitoring sites in EPA Region 5 (out of a total of 

58 sites measuring manganese in 2006) that have sufficient data 

to assess manganese trends since 2000. 

b

Concentrations are for manganese in total suspended particulate 

matter. 

c

The 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 

deleterious effects during a lifetime.

Data source: U.S. EPA, 2007 Annual average concentration (μg/m3

)

Year

0.00

0.04

0.08

0.12

0.16

0.20

90% of sites have

concentrations below

this line

10% of sites have concentrations below this line

Median

RfCc = 0.05 μg/m3

Average

v
AIR

EPA’s 2008 Report on the Environment 2-61

quality improvements for ozone and particulate matter (particularly PM2.5) were less pronounced; and, based on monitoring data collected in 2006 and reported in EPA’s Air Quality 

System, ambient concentrations of ozone, particulate matter, 

or both pollutants in 105 metropolitan statistical areas where 

approximately 138 million people lived were greater than the 

level of their corresponding health-based standards.6 In short, 

every criteria pollutant has showed improving air quality over 

the past one or two decades, but the progress has been slowest 

for the two pollutants—ozone and PM2.5—most influenced by 

meteorology and secondary formation processes. 

The nationwide trends and those presented for the ten EPA 

Regions are based on aggregate statistics across numerous monitoring stations and may not reflect air quality trends at finer scales 

or for different subsets of monitoring stations. For example, the 

significant downward trend in ozone in EPA Region 9 is largely 

influenced by air quality improvements in Los Angeles and other 

metropolitan areas in southern California. In other urban areas in 

EPA Region 9, ozone improvements have been more modest or 

even different directionally.7 Similarly, PM2.5 concentrations have 

increased over the last 5 years at selected monitoring stations near 

the border between U.S. and Mexico (the Ozone and PM Concentrations Along U.S./Mexico Border indicator, p. 2-56), even 

though the national trend for this pollutant is downward. 

The ROE indicators on criteria pollutants’ environmental 

effects are limited to three issues. First, long-term monitoring data show that wet deposition of acidic sulfates and 

nitrates decreased between 1989 and 2006, consistent with 

the decreased emissions for sulfur dioxide and nitrogen oxides 

over roughly the same time frame. As a result of the decreased 

acid deposition, many surface waters throughout the Adirondack Mountains, the Northern Appalachian region, and New 

England have begun to recover from past acidification (the 

Lake and Stream Acidity indicator, p. 2-42). Second, data 

on ozone injury to forest plants are sufficient for establishing national and regional baseline conditions against which 

future data can be compared. These baseline conditions show 

considerable variation in ozone damage across EPA Regions 

(the Ozone Injury to Forest Plants indicator, p. 2-24). Third, 

visibility in protected areas (e.g., National Parks, Wilderness 

Areas) has increased between 1992 and 2004 (the Regional 

Haze indicator, p. 2-33), consistent with a corresponding 

decrease in fine particle concentrations. 

Overall, for criteria pollutants, the ROE indicators provide 

fairly complete information on outdoor air quality trends, 

but limited insights on associated health and environmental 

effects. As expected, emissions trends are generally consistent 

with trends observed among corresponding ambient concentrations and, where data are available, effects.

Air Toxics and Other Air Pollutants

Between 1990 and 2002, nationwide emissions aggregated 

across 188 air toxics (hazardous air pollutants) decreased (the 

Air Toxics Emissions indicator, p. 2-48). Decreased emissions 

were also observed for two air toxics of particular interest: 

benzene and mercury (the Mercury Emissions indicator, p. 

2-46). However, sufficiently complete and consistent monitoring data currently cannot support ROE indicators for ambient 

concentration of air toxics, with two exceptions. First, ambient air concentrations of benzene at 23 monitoring sites across 

the nation decreased 55 percent between 1994 and 2006—a 

decrease reasonably consistent with corresponding emissions 

reductions. Second, ambient air concentrations of manganese 

compounds measured at 21 monitoring sites in EPA Region 5 

decreased by 28 percent between 2000 and 2006, though the 

period of record evaluated may be too short to consider this 

decrease an actual air quality trend. 

Stratospheric Ozone Issues

Since 1990, the U.S. phased out most production and import 

of ozone-depleting substances. Consequently, consumption 

of ozone-depleting substances in the U.S. decreased during 

this last decade, along with globally representative ambient 

air concentrations of ozone-depleting substances in the lower 

atmosphere (the Concentrations of Ozone-Depleting Substances indicator, p. 2-52). While such decreases are expected 

to help restore the stratospheric ozone layer, stratospheric 

ozone levels over North America actually decreased slightly 

since the 1980s, though have remained largely unchanged in 

the last decade (the Ozone Levels over North America indicator, p. 2-54). This trend is due to various factors, including 

ongoing use of ozone-depleting substances worldwide and the 

fact that ozone-depleting substances are extremely long-lived 

in the atmosphere.

Limitations, Gaps, and Challenges8

The 23 ROE indicators in this section characterize trends for 

numerous important outdoor air quality issues, but also have 

notable limitations. All emissions indicators, for instance, 

are partly based on estimates. Although these estimates have 

inherent uncertainties, the emissions inventory data are 

believed to be of high quality and are periodically updated to 

remain consistent with the current scientific understanding of 

emissions from different source categories. The main limitation of the ambient concentration indicators is the monitoring 

sites’ limited spatial coverage. These indicators are composites of air quality measurements taken across the country, 

but primarily in populated areas: they may not totally reflect 

trends for rural settings. While the national trends for criteria pollutants and benzene are toward improved air quality, 

6 This statement is based on the current particulate matter standards and on the 

1997 8-hour ozone standard (0.08 ppm). Future versions of the ROE will be 

based upon the recently promulgated 2008 ozone standard (0.075 ppm) or on 

the NAAQS in effect at the time.

7 U.S. Environmental Protection Agency. 2004. The ozone report: Measuring 

progress through 2003. EPA/454/K-04/001. Research Triangle Park, NC.

8 While the ROE indicators provide valuable information about trends in 

outdoor air quality, the indicators are more limited in their ability to describe 

trends in associated effects on human health and the environment. As 

described in Chapter 1, it is difficult to establish causal relationships between 

specific stressors and outcomes. In the case of outdoor air, there are few 

“effects” indicators with clear causal linkages.
AIR

2-62 EPA’s 2008 Report on the Environment

ambient concentrations of these pollutants can vary greatly on 

a local scale. In certain areas, such as those experiencing rapid 

population growth or near newly constructed point sources, 

ambient air concentrations of selected pollutants may be 

increasing, contrary to the national trends; conversely, ambient air concentration in other parts of the country are decreasing more rapidly than the national trends depict.

Though the emissions and ambient concentration indicators 

are reasonably complete for the criteria pollutants, gaps in 

nationally representative indicators remain for most air toxics 

and other air pollutants. However, a large number of these air 

toxics and other air pollutants are released by a small number 

of sources nationwide, and these pollutants’ emissions and 

ambient concentrations are more appropriately tracked at the 

local level, rather than with National Indicators. Another gap 

in National Indicators is for air toxics and other air pollutants 

that are ubiquitous in the nation’s outdoor air (e.g., mobile 

source air toxics). Although nationwide trends in air toxics 

concentrations have been estimated with models, nationally 

representative ambient air monitoring data on air toxics would 

provide EPA with a more direct measure of important outdoor 

air quality trends. Many local-scale monitoring networks have 

tracked trends for some of these pollutants, but nationwide 

indicators could not be developed for pollutants other than 

benzene due to limited spatial coverage of monitoring sites, 

use of differing sampling and analytical methods over the 

years, inconsistent application of quality assurance and quality 

control practices, and other factors. 

ROE indicators for ambient concentrations of some common air toxics are expected to be developed in coming years, 

based on measurements currently being collected in multiple networks. The National Air Toxics Trends Stations, for 

instance, are a recently implemented network of monitoring 

sites specifically designed to characterize long-term trends in 

several air toxics believed to account for the greatest health 

risks nationwide.9

 Additionally, data being collected as part of 

a nationwide PM2.5 speciation network are expected to provide long-term trend information on concentrations of metals, 

ions, and carbon constituents of fine particulate matter.10

Finally, ongoing operation of the Mercury Deposition Network (part of the National Atmospheric Deposition Program) 

is gathering data to support trends analysis on atmospheric 

deposition of mercury—an issue of particular significance 

when evaluating contamination levels in fish and shellfish. 

National-level exposure and effects indicators can help EPA 

better characterize nationwide trends in outdoor air quality and 

their effects, but key challenges complicate efforts to develop 

these. For example, ambient concentration data do not quantify 

exposures, because ambient air monitoring equipment measures 

air quality at fixed outdoor locations, while people breathe air in 

multiple indoor and outdoor settings during a typical day. Actual 

human exposure to air pollution can be measured through use 

of personal monitoring devices, which sample the air that people 

breathe as they move through different microenvironments. 

Some researchers have used such devices to quantify exposures 

to specific pollutants in some locations.11 However, conducting such studies on a national scale over an extended time frame 

would be an extremely resource-intensive task. Consequently, no 

nationally representative studies currently support ROE indicators that characterize exposure to outdoor air pollutants. Another 

gap pertaining to effects attributed to outdoor air quality is that 

the scientific understanding of how all air pollutants, whether 

acting alone or in combination, can affect human health and the 

environment is incomplete and continues to evolve.

While the indicators document what is currently known about 

selected outdoor air quality issues, ongoing scientific research 

continues to broaden the knowledge base on many important 

topics, ranging from designing innovative emissions control 

technologies to enhancing atmospheric fate and transport modeling to developing metrics that better connect air quality to 

public health and ecological outcomes. 

2.3 What Are the 

Trends in Greenhouse 

Gas Emissions and 

Concentrations?

2.3.1 Introduction

Greenhouse gases, such as carbon dioxide, methane, nitrous 

oxide, and certain synthetic chemicals, trap some of the 

Earth’s outgoing energy, thus retaining heat in the atmosphere.12 Changes in the radiative balance of the Earth—the 

balance between energy received from the sun and emitted 

from Earth—as a result of this heat trapping alter weather 

patterns and climates at global and regional scales.13 Natural 

factors, such as variations in the sun’s output, volcanic activity, the Earth’s orbit, the carbon cycle, and others, also affect 

the radiative balance.14 However, increasing concentrations of 

greenhouse gases due to human activity are affecting various 

aspects of climate, such as surface air temperature and subsurface ocean temperature. Since 1750, the net global effect of 

human activities has been one of warming.15 Human health, 

agriculture, water resources, forests, wildlife, and coastal areas 

all are vulnerable to climate change.16 The purpose of this 

9 U.S. Environmental Protection Agency. 2004. National monitoring strategy: 

Air toxics component. Final draft. July. <http://www.epa.gov/ttnamti1/files/

ambient/airtox/atstrat804.pdf>

10 U.S. Environmental Protection Agency. 1999. Strategic plan: Development 

of the particulate matter (PM2.5) quality system for the chemical speciation 

monitoring trend sites. April 16, 1999.

11 Jantunen, M., O. Hanninen, K. Koistinen, and J.H. Hashim. 2002. PM 

measurements: Personal and indoor air monitoring. Chemosphere 49:993-1007.

12 National Research Council. 2005. Radiative forcing of climate change: 

Expanding the concept and addressing uncertainties. pp. 1, 9, vii, and others.

13 Ibid., p. 11.

14 Ibid., p. 13.

15 Intergovermental Panel on Climate Change. 2007. Climate change 2007: The 

physical science basis (fourth assessment report), 2007. p. 3.

16 National Research Council. 2005. Radiative forcing of climate change: 

Expanding the concept and addressing uncertainties. pp. 4, 19-20.
AIR

EPA’s 2008 Report on the Environment 2-63

section is to evaluate long-term trends in air emissions and 

ambient concentrations of greenhouse gases that are contributing to climate change, but not to evaluate the effects that these 

emissions and concentrations cause.17

Though the focus of this question is on greenhouse gases, 

related factors can also alter the Earth’s climate. Certain 

radiatively important substances, like black carbon (soot), are 

technically not greenhouse gases due to their physical state, 

but they nonetheless affect the flow of energy through the 

atmosphere. Some of these substances, such as sulfate aerosols, have negative radiative forcings that can lead to cooling 

effects. Another related factor is albedo (the reflectivity of the 

Earth’s surface), which affects the portions of absorbed and 

outgoing energy. Natural and human factors can affect albedo 

on a global scale (through changes in large-scale features 

like the polar ice caps) or on a local or regional scale (e.g., by 

increased amounts of dark paved surfaces that absorb energy). 

Although this question does not address radiatively important 

substances that are not greenhouse gases or non-chemical factors like albedo, these influences are also important to understanding the planet’s energy balance and the ways human 

activities may affect that balance.18 Quantitative information 

on the relative radiative forcings from greenhouse gases, other 

radiatively important substances, and selected non-chemical 

factors is available in other publications.19

Some greenhouse gases are emitted exclusively from human 

activities (e.g., synthetic halocarbons). Others occur naturally but are found at elevated levels due to human inputs 

(e.g., carbon dioxide). The anthropogenic sources result from 

energy-related activities (e.g., combustion of fossil fuels in 

the electric utility and transportation sectors), agriculture, 

land-use change, waste management and treatment activities, 

and various industrial processes. Major greenhouse gases and 

emissions sources include:

•	 Carbon dioxide, widely reported as the most important 

anthropogenic greenhouse gas.20 Carbon dioxide occurs 

naturally as part of the global carbon cycle, but human 

activities have increased atmospheric loadings through 

combustion of fossil fuels and other emissions sources.21

Natural sinks that remove carbon dioxide from the atmosphere (e.g., oceans, plants) help regulate carbon dioxide 

concentrations, but human activities can disturb these 

processes (e.g., deforestation) or enhance them. 

•	 Methane, which comes from many sources, including 

human activities such as coal mining, natural gas distribution, waste decomposition in landfills, and digestive 

processes in livestock and agriculture.22 Natural sources 

include wetlands and termite mounds. 

•	 Nitrous oxide, which is emitted during agricultural and 

industrial activities, as well as during combustion of solid 

waste and fossil fuels. 

•	 Various synthetic chemicals, such as hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and other synthetic gases, which are released as a result of commercial, 

industrial, or household uses.

•	 Many other gases that are known to trap heat in the 

atmosphere. Examples include water vapor, which occurs 

naturally as part of the global water cycle, and ozone, 

which occurs naturally in the stratosphere and is found in 

the troposphere largely due to human activities. 

Each gas has a different ability to absorb heat in the atmosphere, due to differences in its atmospheric half-life and the 

amount and type of energy that it absorbs. For example, it 

would take thousands of molecules of carbon dioxide to equal 

the warming effect of a single molecule of sulfur hexafluoride—the most potent greenhouse gas, in terms of ability to 

absorb heat, evaluated by the Intergovernmental Panel on Climate Change.23 To facilitate comparisons between gases that 

have substantially different properties, the Panel has developed 

a set of scaling factors called “global warming potentials,” as 

discussed further in the indicator write-ups.

The remainder of this section focuses on greenhouse gas 

emissions and concentrations, given that greenhouse gases 

can affect radiative forcings, thus leading to climate change. 

However, climate change can also affect atmospheric concentrations of many substances through various feedback mechanisms. Other publications provide detailed information on the 

broader issues of how climate change can affect air quality.24

2.3.2 ROE Indicators

To characterize trends in greenhouse gases, this chapter 

presents two indicators—one describing emissions from U.S. 

sources and the other describing concentrations (Table 2-3).

The U.S. Greenhouse Gas Emissions indicator covers the 

1990-2005 period, with data from EPA’s Inventory of U.S. 

Greenhouse Gas Emissions and Sinks. This inventory is a 

database that tracks both greenhouse gas emissions directly 

attributable to human activities and greenhouse gas sinks (e.g., 

sequestration of carbon in forests). The indicator stratifies 

emissions into trends for different gases and source categories. 

17 In a general sense, climate change is conceptually connected to every other 

theme in this report. The broadest discussion of potential effects associated 

with greenhouse gases in this report is in Section 6.5, which discusses critical 

physical and chemical attributes of ecosystems, including ROE indicators that 

track changes in air temperature, precipitation, sea surface temperature, and 

sea level—all of which affect ecosystems.

18 Detailed information on these related factors can be found in various scientific 

publications, such as those prepared by the Intergovernmental Panel on Climate 

Change, a panel formed by the World Meteorological Organization to compile 

and synthesize the growing body of scientific literature on climate change.

19 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

the scientific basis (fourth assessment report). Cambridge, United Kingdom: 

Cambridge University Press. p. 4.

20 Ibid., p. 2.

21 U.S. Environmental Protection Agency. 2006. Inventory of U.S. greenhouse 

gas emissions and sinks: 1990-2004. EPA/430/R-06/002. Washington, DC. 

22 National Research Council. 2001. Climate change science: An analysis of 

some key questions. Washington, DC: National Academy Press.

23 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

The scientific basis (fourth assessment report). Cambridge, UK: Cambridge 

University Press.

24 Intergovermental Panel on Climate Change. 2007. Climate change 2007: 

Impacts, adaptation, and vulnerability (fourth assessment report). Cambridge, 

UK: Cambridge University Press.
AIR

2-64 EPA’s 2008 Report on the Environment

Emissions are weighted by “global warming potentials” to 

facilitate comparison among the gases.

The Greenhouse Gas Concentrations indicator summarizes 

both direct measurements of ambient air concentrations from 

the last half-century and observations for earlier time frames 

based on chemical analyses of air bubbles found in ice core samples. The gases in these bubbles represent the outdoor air that 

was trapped in ice at the time the ice was formed. Combined, 

these two measurements provide extensive historical coverage 

for the atmospheric concentrations of greenhouse gases. 

Many greenhouse gases are extremely long-lived in the atmosphere, with some remaining airborne for tens to hundreds of 

years after being released. These long-lived greenhouse gases 

become globally mixed in the atmosphere, and their concentrations reflect past and recent contributions from emissions 

sources worldwide. This context is an important backdrop for 

the two greenhouse gas indicators in this section: increasing 

atmospheric concentrations of greenhouse gases is a global 

issue, resulting from emissions from sources in the U.S. combined with emissions from sources in other countries.

INDICATOR | U.S. Greenhouse Gas Emissions

The Earth’s climate is determined by the balance between energy received from the sun and energy 

emitted back to space from the Earth and its atmosphere. 

Certain gases in the atmosphere, such as carbon dioxide 

(CO2), methane (CH4), nitrous oxide (N2O), water vapor, 

and others, trap some of the outgoing energy, retaining 

heat in the Earth’s atmosphere. These are the so-called 

“greenhouse gases” (GHGs). The best understood GHGs 

emitted by human activities are CO2, CH4, N2O, and certain fluorinated compounds. 

Changes in GHG emissions are influenced by many longterm factors, including population and economic growth, 

land use, energy prices, technological changes, and interannual temperatures. On an annual basis, combustion of 

fossil fuels, which accounts for most GHG emissions in the 

U.S., generally fluctuates in response to changes in general 

economic conditions, energy prices, weather, and the availability of non-fossil alternatives (U.S. EPA, 2007). 

This indicator uses data and analysis from the Inventory 

of U.S. Greenhouse Gas Emissions and Sinks (U.S. EPA, 

2007), an assessment of the anthropogenic sources and 

sinks of GHG emissions for the U.S. and its territories for 

the 1990-2005 period. The inventory constitutes estimates 

derived from direct measurements, aggregated national statistics, and validated models in most source categories. An 

extensive discussion of the methods for each source type 

and gas and the uncertainties inherent in the calculations is 

available in EPA (2007) and its Annex 7. 

The indicator is expressed in terms of CO2

 equivalents, 

meaning that emissions of different gases are weighted 

by their “global warming potential” (GWP). A GWP is a 

measure of how much a given mass of GHG is estimated 

to contribute to radiative forcing that contributes to global 

warming over a selected period of time, compared to 

the same mass of CO2

, for which the GWP is 1.0. EPA is 

mandated to use the GWPs documented in the Intergovernmental Panel on Climate Change’s Second Assessment 

Report (IPCC, 1996), which characterize GWP for a 

Exhibit 2-50. Greenhouse gas emissions in the 

U.S. by gas, 1990-2005

a

Teragrams of carbon dioxide equivalents are the units 

conventionally used in greenhouse gas inventories prepared 

worldwide. For reference, one teragram equals one million metric 

tons. 

b

HFCs are hydrofluorocarbons, PFCs are perfluorocarbons, and SF6

is sulfur hexafluoride.

Data source: U.S. EPA, 2007

Year

Emissions (teragrams of carbon 

dioxide equivalents)a

’90 ’91 ’92 ’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

HFCs, PFCs, and SF6

b

Methane

Nitrous oxide

Carbon dioxide

’04 ’05

Table 2-3. ROE Indicators of Trends in Greenhouse Gas Emissions and Concentrations 

National Indicators Section Page

U.S. Greenhouse Gas Emissions 2.3.2 2-64

Atmospheric Concentrations of Greenhouse Gases 2.3.2 2-66
AIR

EPA’s 2008 Report on the Environment 2-65

INDICATOR | U.S. Greenhouse Gas Emissions (continued)

100-year time horizon—the effect of the gas on radiative 

forcing over 100 years. Annex 6 of the U.S. GHG inventory includes extensive information on GWPs and how 

they relate to emissions estimates (U.S. EPA, 2007).

This indicator focuses on the six types of compounds 

currently covered by agreements under the United Nations 

Framework Convention on Climate Change. These compounds are CO2

, CH4, N2O, hydrofluorocarbons (HFCs), 

perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). This 

indicator does not include emissions estimates for substances 

such as chlorofluorocarbons (CFCs), methyl bromide, sulfates, black carbon, and organic carbon. These substances are 

excluded primarily because either their emissions have not 

been quantified in the U.S. GHG inventory or they have 

different types of effects on climate than those of the six 

GHGs included in the U.S. inventory and, therefore, most 

cannot be compared directly to the GHG. Combined, these 

excluded substances may account for a considerable portion 

of climate change, but their omission cannot be scientifically 

quantified in comparable terms. 

This indicator presents emissions data in units of teragrams of CO2

 equivalents (Tg CO2 Eq). These units are 

conventionally used in GHG inventories prepared worldwide. For reference, one teragram (Tg) is equal to one million metric tons. 

What the Data Show

In 2005, total U.S. greenhouse gas emissions were 7,260 

Tg CO2 Eq, up 16 percent from 1990 (Exhibit 2-50). CO2

is the primary greenhouse gas emitted by human activities, representing approximately 84 percent of greenhouse 

gas emissions in 2005. From 1990 to 2005, total emissions 

of CO2 increased by 1,028 Tg CO2 Eq (20 percent). CH4

represents the second largest U.S. GHG emission, accounting for 7 percent of net emissions in 2005. CH4

 emissions declined about 11 percent from 1990 to 2005, due 

largely to reduced emissions from landfills and coal mining 

operations. The primary sources of CH4 emissions include 

decomposition of wastes in landfills, coal mine seepage, 

natural gas systems, and enteric fermentation in domestic 

livestock. N2

O constituted about 6 percent of net U.S. 

GHG emissions in 2005; these emissions declined by about 

3 percent from 1990 to 2005. The main anthropogenic 

activities producing N2

O are agricultural soil management, 

fuel combustion in motor vehicles, manure management, 

nitric acid production, human sewage, and stationary fuel 

combustion. Emissions of HFCs, PFCs, and SF6 accounted 

for the remaining GHG emissions in 2005, and the aggregate weighted emissions of this group of gases rose by 74 

Tg CO2

 Eq since 1990, nearly doubling during that time 

frame. Despite being emitted in smaller quantities than 

the other principal greenhouse gases, HFCs, PFCs, and 

SF6 are important because many of them have extremely 

high global warming potentials and, in the cases of PFCs 

and SF6

, atmospheric lifetimes of 700 to 50,000 years. The 

emissions in this indicator are a continuation of the trend 

of increasing GHG emissions observed over many decades, 

with total CO2-equivalent emissions increasing by about 

one fifth since 1970 (U.S. EPA, 2007; RIVM/TNO, 

2003). CO2 has constituted a slightly growing portion, 

while CH4 has been a declining component of the total. 

Looking at GHG emissions by source shows that 

energy-related activities (e.g., fuel combustion, gas leakage) accounted for 85 percent of total U.S. emissions in 

2005 (Exhibit 2-51). Emissions due to energy use have 

increased 19 percent between 1990 and 2005. Agriculture 

is the second largest source of GHG emissions, accounting 

for 7 percent of the total in 2005. Industrial processes and 

waste account for the remaining GHG emissions depicted 

in Exhibit 2-51. This indicator does not depict trends in 

GHG emissions from the use of solvents and other products or non-CO2

 GHG emissions from land use change 

and forestry, because GHG emissions from these source 

categories account for less than 0.5 percent of the total 

estimated emissions in EPA’s GHG inventory.

U.S. GHG emissions are partly offset by uptake of 

carbon and “sequestration” in forests, trees in urban areas, 

agricultural soils, and landfilled yard trimmings and food 

scraps. In aggregate, these removals of CO2 from the atmosphere offset about 14 percent of total U.S. CO2

 emissions 

in 2005 (Exhibit 2-51). 

Exhibit 2-51. Greenhouse gas emissions in the 

U.S. by industrial sector, 1990-2005

a

Teragrams of carbon dioxide equivalents are the units conventionally 

used in greenhouse gas inventories prepared worldwide. For 

reference, one teragram equals one million metric tons. 

Data source: U.S. EPA, 2007

Year

Emissions (teragrams of 

carbon dioxide equivalents)a

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

’90 ’91 ’92 ’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

-2,000

-1,000

Agriculture

Industrial processes

Energy

Land use, land-use change, and forestry (sink)

Waste
AIR

2-66 EPA’s 2008 Report on the Environment

INDICATOR | U.S. Greenhouse Gas Emissions (continued)

With one-twentieth of the world’s population (U.S. 

Bureau of the Census, 2006), the U.S. currently emits 

about one-fifth of global GHGs: CO2

, CH4, N2O, HFCs, 

PFCs, and SF6 (Baumert et al., 2005). 

Indicator Limitations

•	This indicator does not yet include emissions of GHGs or 

other radiatively important substances that are not explicitly covered by the United Nations Framework Convention on Climate Change and its subsidiary protocol. 

Thus, it excludes such gases as those controlled by the 

Montreal Protocol and its Amendments, including CFCs 

and hydrochlorofluorocarbons. Although the U.S. reports 

the emissions of these substances as part of the U.S. GHG 

inventory (see Annex 6.2 of the U.S. GHG inventory), 

the origin of the estimates is fundamentally different 

from those of the other GHG and therefore cannot be 

compared directly with the other emissions discussed in 

this indicator. 

•	 This indicator does not include aerosols and other emissions that do affect radiative forcing and that are not 

well-mixed in the atmosphere, such as sulfate, ammonia, 

black carbon, and organic carbon. Emissions of these compounds are highly uncertain and have qualitatively different effects than the six types of emissions in this indicator. 

•	This indicator does not include emissions of other compounds—such as CO, NOx

, nonmethane volatile organic 

compounds, and substances that deplete the stratospheric 

ozone layer—which indirectly affect the Earth’s radiative 

balance (for example, by altering GHG concentrations, 

changing the reflectivity of clouds, or changing the distribution of heat fluxes). 

•	The U.S. GHG inventory does not account for “natural” emissions of GHGs, such as from wetlands, tundra 

soils, termites, and volcanoes. These excluded sources are 

discussed in Annex 5 of the U.S. GHG inventory (U.S. 

EPA, 2007). The U.S. GHG inventory does include, in 

its “Land Use, Land-Use Change, and Forestry” category, emissions from changes in the forest inventory 

due to fires, harvesting, and other activities, and from 

agricultural soils.

Data Sources

The data used for this indicator were published in EPA’s 

inventory of greenhouse gas emissions and sinks for years 

1990-2005 (U.S. EPA, 2007). Specifically, emissions by 

GHG shown in Exhibit 2-50 are taken from Table ES-2 of 

that reference, and emissions by industrial sector are taken 

from Table ES-4. 

References 

Baumert, K., T. Herzog, and J. Pershing. 2005. Navigating 

the numbers: Greenhouse gas data and international climate policy. Washington DC: World Resources Institute.

<http://pdf.wri.org/navigating_numbers_chapter2.pdf>

IPCC (Intergovenmental Panel on Climate Change). 1996. 

Climate change 1995: The science of climate change. 

Cambridge, UK: Cambridge University Press.

RIVM/TNO. 2003. Emission database for global atmospheric research. Version 3.2. 2003. 

<http://www.mnp.nl/edgar/>

U.S. Bureau of the Census. 2006. World POPClock; 

USPOPClock. 

<http://www.census.gov/ipc/www/popclockworld.html>

U.S. EPA (United States Environmental Protection 

Agency). 2007. Inventory of U.S. greenhouse gas emissions 

and sinks: 1990-2005. <http://www.epa.gov/

climatechange/emissions/usinventoryreport.html>

v

INDICATOR | Atmospheric Concentrations of Greenhouse Gases

The Earth’s temperature depends mainly on the amount of energy received from the sun, the portion reflected back 

into space, and the extent to which the atmosphere retains 

heat. Natural forces (e.g., volcanoes, changes in the Earth’s 

orbit) and human activities (e.g., emissions of so-called 

“greenhouse gases,” land use change) affect the amount of 

energy held in the Earth-atmosphere system and therefore 

affect the Earth’s climate. Human activities in all countries 

have altered the chemical composition of the atmosphere 

by the emissions and accumulation in the atmosphere of 
AIR

EPA’s 2008 Report on the Environment 2-67

INDICATOR | Atmospheric Concentrations of Greenhouse Gases (continued)

greenhouse gases. The primary gases that retain heat in the 

atmosphere are water vapor, carbon dioxide (CO2

), methane 

(CH4), nitrous oxide (N2O), and certain manufactured gases 

such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and sulfur hexafluoride (SF6

). 

Once emitted, gases remain in the atmosphere for varying amounts of time. Very “short-lived” compounds, such 

as particulate matter (PM), remain airborne on average for 

only hours or days. CH4 also has a relatively short average 

lifetime, though much longer than PM, remaining in the 

atmosphere for roughly 12 years. The half-life of CO2 emissions is roughly 100 years (5 to 200 years: IPCC, 2001), but 

about a quarter of emissions today will still be in the atmosphere after hundreds of years and about one-tenth for hundreds of thousands of years (Archer and Ganopolski, 2005; 

Archer et al., 1998). Finally, many of the synthetic gases such 

as halocarbons are extremely long-lived, remaining in the 

atmospheric for hundreds or even tens of thousands of years. 

When emissions—from the U.S. (the U.S. Greenhouse Gas 

Emissions indicator, p. 2-64) as well as other countries—

remain in the atmosphere over long periods, they accumulate and are measured as atmospheric concentrations. U.S. 

GHG emissions from 1890 to 2000 are estimated to have 

contributed about one-fifth of the increase in global GHG 

concentrations (den Elzen et al., 2005).

This indicator shows trends in the accumulation of the 

following principal GHGs in the atmosphere: CO2

, CH4, 

N2O, and selected halocarbons. Recent data are from 

global networks that monitor the concentrations of these 

gases in the atmosphere. Geological data come from gas 

measurements made of air trapped in ice cores at the time 

the ice was formed. Because the gases shown in this indicator remain in the atmosphere for long periods, they are 

well-mixed, so that measurements at individual locations 

are globally representative. This indicator summarizes 

GHG concentration measurements reported in a collection of studies published in the peer-reviewed literature. 

In order to provide the most extensive temporal coverage, 

A. 647,426 BC to 339 BC B. 9002 BC to 1975 AD

Exhibit 2-52. Global atmospheric concentrations of carbon dioxide (CO2) over geological time and in 

recent years

C. 1958 AD to 2006 AD

CO2 concentration (ppm)

Year (negative values = BC)

Trend lines and data sources:

9002 BC to 1978 AD

Law Dome, East Antarctica 

75-year smoothed 

(Etheridge et al., 1998)

Siple Station, West 

Antarctica (Neftel et al., 

1994)

EPICA Dome C, Antarctica 

(Flückiger et al., 2002)

Mauna Loa, Hawaii 

(NOAA-ESRL, 2007a)

Lampedusa Island, Italy 

(Chamard et al., 2001)

Shetland Islands, Scotland 

(Steele et al., 2002)

Cape Grim, Australia (Steele 

et al., 2002)

1958 AD to 2006 AD

Barrow, Alaska (Thoning 

and Tans, 2000)

Cape Matatula, American 

Samoa (Thoning and 

Tans, 2000)

South Pole, Antarctica 

(Thoning and Tans, 

2000)

647,426 BC to 339 BC

EPICA Dome C, Antarctica 

(Siegenthaler et al., 2005)

Vostok Station, Antarctica 

(Barnola et al., 2003)

0

50

100

150

200

250

300

350

400

-750,000 -500,000 -250,000 0 -10,000 -8000 -6000 -4000 -2000 0 2000 1955 1965 1975 1985 1995 2005
AIR

2-68 EPA’s 2008 Report on the Environment

INDICATOR | Atmospheric Concentrations of Greenhouse Gases (continued)

this indicator aggregates comparable, high-quality data 

from individual studies that each focused on different time 

frames. None of the data in this indicator are based on 

modeled concentrations. 

What the Data Show 

Exhibits 2-52 through 2-54 show the evolution of 

concentrations of three principal GHGs in the atmosphere over three intervals: geological time (hundreds 

of thousands of years), the past 11,000 years, and recent 

decades. The exhibits represent data sets covering a wide 

range of latitudes, showing some latitudinal differences 

in concentrations but also showing a high level of consistency—indicating that the gases are well-mixed and that 

the sampling can be considered spatially representative. 

The graphs show patterns of large cycles of concentrations over geological time, and they also depict increases 

in concentrations in the industrial era (post-1780) that 

exceed concentrations over the past hundreds of thousands 

of years. 

The concentration of CO2

, the most important 

anthropogenic GHG, has varied considerably over 

geological time (Exhibit 2-52). Over the past 650,000 

years, CO2 concentrations have generally cycled over 

several-thousand-year periods from highs around 285-300 

parts per million (ppm) to lows around 180-185 ppm. From 

at least 900 A.D. to 1800 A.D., CO2 concentrations stayed 

relatively constant at about 270-290 ppm (panel B). Over 

the past 150 years, CO2 concentrations increased steadily 

from approximately 270-290 ppm in pre-industrial times 

to 382 ppm in 2006, a 36 percent increase (panels B and 

C). Almost all of this increase is due to human activities 

(IPCC, 2007), and the concentrations measured currently 

are the highest observed over the entire period of record.

B. 8945 BC to 1980 AD C. 1985 AD to 2006 AD

Year (negative values = BC)

Vostok Antarctica ice core (Petit et al., 

1999)

Greenland GRIP ice core (Blunier and 

Brook, 2001)

Greenland GISP2 ice core (Blunier and 

Brook, 2001)

Antarctica Byrd Station ice core 

(Blunier and Brook, 2001)

EPICA Dome C, Antarctica 

(Spahni et al., 2005)

Law Dome, Antarctica (Etheridge et al., 

2002)

Various Greenland locations (Etheridge 

et al., 2002)

Greenland Site J (WDCGG, 2005)

EPICA Dome C, Antarctica (Flückiger et 

al., 2002)

Cape Grim, Australia (NOAA-ESRL, 

2007b)

Shetland Islands, Scotland (Steele 

et al., 2002)

Mauna Loa, Hawaii (NOAA-ESRL, 

2007c)

Exhibit 2-53. Global atmospheric concentrations of methane (CH4) over geological time and in recent years

Trend lines and data sources:

CH4 concentration (ppb)

646,729 BC to 281 BC 8945 BC to 1980 AD 1985 AD to 2006 AD

A. 646,729 BC to 281 BC

0

500

1,000

1,500

2,000

-650,000 -500,000 -350,000 -200,000 -50,000 -10,000 -8000 -6000 -4000 -2000 0 2000 1985 1990 1995 2000 2005
AIR

EPA’s 2008 Report on the Environment 2-69

INDICATOR | Atmospheric Concentrations of Greenhouse Gases (continued)

CH4

 concentrations also cycled widely over the past 

650,000 years, but peaks remained below 800 parts per 

billion (ppb) until after 1800 A.D. (Exhibit 2-53). Concentrations slightly increased between 1000 A.D. and 1730 

A.D. (panel B). It then took approximately 175 years (c. 

1905) to add 200 ppb to atmospheric CH4

 concentrations, 

approximately 40 years (c. 1945) to add the next 200 ppb, 

approximately 20 years (c. 1965) to add the next 200 ppb, 

and approximately 10 years (c. 1975) to add the next 200 

ppb (panel B). In 2006, CH4 concentrations at the two 

stations considered were 1,727 ppb and 1,788 ppb (panel 

C), and these current levels far exceed the natural range 

surmised from the ice core samples. The rates of CH4 concentration increase began to slow by the late 1970s, with 

approximately 300 ppb added to atmospheric concentrations 

between 1978 and 2006 (panels B and C). Overall, global 

CH4

 concentrations have more than doubled in the past 150 

years. The most recent data show a significant difference 

in CH4 concentrations across latitudes—a pattern of peak 

concentrations in the most northern latitudes decreasing 

toward the southern latitudes, suggesting net sources of CH4

in northern latitudes. Yet, despite the latitudinal differences 

in concentrations, the pattern over the past two centuries 

shows a common trend in all locations.

N2

O concentrations (Exhibit 2-54) vacillated widely 

through geological time, with ice sample measurements 

ranging from as low as 180 ppb to above 280 ppb. Despite 

considerable inter-decadal variability, N2O stayed mostly 

below 280 ppb from 1756 A.D. until the 1920s (panel B), 

from which point levels began to rise rapidly to approximately 320 ppb in 2006 (panels B and C), the highest level 

recorded over the more than 100,000 years of data available. 

Concentrations of the halocarbons (or gases that contain the 

halogens chlorine, fluorine, bromine, or iodine) were essentially zero a few decades ago, but have increased rapidly as 

they were incorporated into industrial products and processes 

(Exhibit 2-55). Concentrations of hydrochlorofluorocarbons 

HCFC-141b and HCFC-142b increased through 2006, but 

A. 104,301 BC to 1871 AD B. 9000 BC to 1976 AD

Exhibit 2-54. Global atmospheric concentrations of nitrous oxide (N2O) over geological time and in 

recent years

C. 1978 AD to 2006 AD

Trend lines and data sources:

Greenland GISP2 ice core (Sowers et 

al., 2003)

Taylor Dome, Antarctica (Sowers et 

al., 2003)

EPICA Dome C, Antarctica (Flückiger 

et al., 2002)

Antarctica (Machida et al., 1995)

Antarctica (Battle et al., 1996)

Barrow, Alaska (NOAA-ESRL, 2007d)

Cape Grim, Australia (AGAGE, 2007)

Mauna Loa, Hawaii (NOAA-ESRL, 

2007d)

South Pole, USA station (NOAA-ESRL, 

2007d)

104,301 BC to 1871 AD 9000 BC to 1976 AD 1978 AD to 2006 AD

Year (negative values = BC)

N2O concentration (ppb)

-10,000 -8000 -6000 -4000 -2000 2000 0 1975 1980 1985 1990 1995 2000 2005

0

200

225

250

275

300

325

350

-125,000 -100,000 -75,000 -50,000 -25,000 0 25,000
AIR

2-70 EPA’s 2008 Report on the Environment

INDICATOR | Atmospheric Concentrations of Greenhouse Gases (continued)

are expected to gradually stabilize over this decade as they are 

phased out in industrialized countries as part of the Montreal 

Protocol on Substances That Deplete the Ozone Layer. The 

concentration of HFC-23, which is a byproduct of HCFC-22 

production, has increased more than five-fold between 1978 

and 2006. Halocarbons that are not controlled by the Montreal Protocol (because they do not contribute to stratospheric 

ozone losses) mostly continued to increase because of their 

widespread use as substitutes for the Montreal Protocol gases. 

Indicator Limitations

•	 Water vapor is not tracked in this indicator, as it is generally accepted that human activities have not increased the 

concentration of water vapor in the atmosphere. 

•	 Some radiatively important atmospheric constituents that 

are substantially affected by human activities (such as tropospheric ozone, black carbon, aerosols, and sulfates) are 

not included in this indicator because of their spatial and 

temporal variability and the inadequacy of available data 

to characterize long-term averages or trends.

•	 Concentration data are not available for all the halogenated compounds that are potentially important GHGs. 

For instance, global concentration data are not sufficient 

yet to track trends in concentrations of SF6

 and PFCs.

•	 Ice core measurements are not taken in real time, which 

introduces some error into the date of the sample. Dating 

accuracy for the ice cores ranged up to ±20 years (often 

less), depending on the method used and the time period 

of the sample. Diffusion of gases from the samples, which 

would tend to reduce the measured values, may also add 

a small amount of uncertainty. More information on the 

accuracy of measurements of ice samples and other measurement methods can be found at http://cdiac.esd.ornl.

gov/by_new/bysubjec.html#atmospheric.

Data Sources

The data in this indicator come from multiple sources. 

Summary global atmospheric concentration data for CO2

(Exhibit 2-52), CH4 (Exhibit 2-53), and N2O (Exhibit 2-54) 

were provided by EPA’s Office of Atmospheric Programs, 

based on GHG concentration measurements reported in a 

collection of studies published in the peer-reviewed literature. References for the underlying data are included in the 

corresponding exhibits, and some data sets are also available 

in electronic format at http://www.epa.gov/climatechange/

science/recentac.html.

Summary global atmospheric concentration data for 

selected halocarbons (Exhibit 2-55) are a subset of the data 

depicted in IPCC’s Fourth Assessment Report (IPCC, 2007).

References

AGAGE (Advanced Global Atmospheric Gases Experiment). 2007. Monthly mean N2

O concentrations for Cape 

Grim, Australia. Accessed 2007. <http://agage.eas.gatech.

edu/data.htm>

Archer, D., and A. Ganopolski. 2005. A movable trigger: Fossil fuel CO2

 and the onset of the next glaciation. 

Geochem. Geophys. Geosys. 6(Q05003). <http://geosci.

uchicago.edu/~archer/reprints/archer.ms.next_ice_age.pdf>

Archer, D., H. Kheshgi, and E. Maier-Reimer. 1998. 

Dynamics of fossil fuel neutralization by Marine CaCO3. 

Global Biogeochem. Cycles 12:259-276. <http://geosci.

uchicago.edu/~archer/reprints/gbc98/neutral_gbc.pdf>

Barnola, J.M., D. Raynaud, C. Lorius, and N.I. Barkov. 2003. 

Historical CO2 record from the Vostok ice core. In Trends: A 

compendium of data on global change. Oak Ridge, TN: U.S. 

Department of Energy. <http://cdiac.esd.ornl.gov/trends/

co2/vostok.htm>

Battle, M., M. Bender, T. Sowers, P. Tans, J. Butler, J. Elkins, 

J. Ellis, T. Conway, N. Zhang, P. Lang, and A. Clarke. 1996. 

Histories of atmospheric gases from firn at the South Pole. 

Nature 383:231-235.

Blunier, T., and E.J. Brook. 2001. Timing of millenial-scale 

climate change in Antarctica and Greenland during the last 

glacial period. Science 291:109-112. 

Chamard, P., L. Ciattaglia, A. di Sarra, and F. Monteleone. 

2001. Atmospheric CO2

 record from flask measurements 

at Lampedusa Island. In Trends: A compendium of data on 

global change. Oak Ridge, TN: U.S. Department of Energy. 

<http://cdiac.esd.ornl.gov/trends/co2/lampis.htm>

Exhibit 2-55. Global atmospheric concentrations 

of selected halocarbons, 1978-2006a

1975 1980 1985 1990 1995 2000 2005

Year

Concentration (parts per trillion) a

Trends are presented for hydrochlorofluorocarbons (HCFCs) and 

hydrofluorocarbons (HFCs) with sufficient data to support 

long-term trend analysis. 

Data source: IPCC, 2007

1

10

100

1,000

HCFC-22

HCFC-141b

HCFC-142b

HFC-23

HFC-125

HFC-134a

HFC-152a
AIR

EPA’s 2008 Report on the Environment 2-71

INDICATOR | Atmospheric Concentrations of Greenhouse Gases (continued)

den Elzen, M., J. Fuglestvedt, N. Höhne, C. Trudinger, J. 

Lowe, B. Matthewso, B. Romstadv, C. Pires de Campos, 

and N. Andronova. 2005. Analysing countries’ contribution to climate change: Scientific and policy-related 

choices. Env. Sci. Policy 8(6):614–636.

Etheridge, D.M., L.P. Steele, R.J. Francey, and R.L. Langenfelds. 2002. Historical CH4

 records since about 1000 

A.D. from ice core data. In Trends: A compendium of 

data on global change. Oak Ridge, TN: U.S. Department 

of Energy. <http://cdiac.esd.ornl.gov/trends/atm_meth/

lawdome_meth.html>

Etheridge, D.M., L.P. Steele, R.L. Langenfelds, R.J. 

Francey, J.M. Barnola, and V.I. Morgan. 1998. Historical CO2

 records from the Law Dome DE08, DE08-2, and 

DSS ice cores. In Trends: A compendium of data on global 

change. Oak Ridge, TN: U.S. Department of Energy. 

<http://cdiac.esd.ornl.gov/trends/co2/lawdome.html>

Flückiger, J., E. Monnin, B. Stauffer, J. Schwander, T.F. 

Stocker, J. Chappellaz, D. Raynaud, and J.M. Barnola. 

2002. High resolution Holocene N2

O ice core record and 

its relationship with CH4 and CO2. Global Biogeochem. 

Cycles 16(1):1010.

IPCC (Intergovernmental Panel on Climate Change). 2007. 

Climate change 2007: The physical science basis (fourth assessment report). Cambridge, UK: Cambridge University Press.

IPCC (Intergovernmental Panel on Climate Change). 2001. 

Climate change 2001: The scientific basis (third assessment 

report). Cambridge, UK: Cambridge University Press.

Machida, T., T. Nakazawa, Y. Fujii, S. Aoki, and O. 

Watanabe. 1995. Increase in atmospheric nitrous oxide 

concentration during the last 250 years. Geophys. Res. 

Lett. 22(21):2921-2924.

Neftel, A., H. Friedli, E. Moor, H. Lötscher, H. Oeschger, 

U. Siegenthaler, and B. Stauffer. 1994. Historical CO2 record 

from the Siple Station ice core. In Trends: A compendium of 

data on global change. Oak Ridge, TN: U.S. Department of 

Energy. <http://cdiac.esd.ornl.gov/trends/co2/siple.htm>

NOAA-ESRL (National Oceanic and Atmospheric 

Administration, Earth System Research Laboratory). 2007a. 

Monthly mean CO2

 concentrations for Mauna Loa, Hawaii. 

Accessed 2007. <ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/

co2_annmean_mlo.txt>

NOAA-ESRL (National Oceanic and Atmospheric 

Administration, Earth System Research Laboratory). 

2007b. Monthly mean CH4

 concentrations for Cape Grim, 

Australia. Accessed 2007. <ftp://ftp.cmdl.noaa.gov/ccg/

ch4/flask/month/cgo_01D0_mm.ch4>

NOAA-ESRL (National Oceanic and Atmospheric 

Administration, Earth System Research Laboratory). 

2007c. Monthly mean CH4

 concentrations for Mauna Loa, 

Hawaii. Accessed 2007. <ftp://ftp.cmdl.noaa.gov/ccg/ch4/

in-situ/mlo/mlo_01C0_mm.ch4>

NOAA-ESRL (National Oceanic and Atmospheric 

Administration, Earth System Research Laboratory). 

2007d. Monthly mean N2O concentrations for Barrow, 

Alaska, Mauna Loa, Hawaii, and the South Pole. Accessed 

2007. <http://www.esrl.noaa.gov/gmd/hats/insitu/cats/

cats_conc.html>

Petit, J.R., J. Jouzel, D. Raynaud, N.I. Barkov, J.M. 

Barnola, I. Basile, M. Bender, J. Chappellaz, J. Davis, G. 

Delaygue, M. Delmotte, V.M. Kotlyakov, M. Legrand, V. 

Lipenkov, C. Lorius, L. Pépin, C. Ritz, E. Saltzman, and 

M. Stievenard. 1999. Climate and atmospheric history of 

the past 420,000 years from the Vostok Ice Core, Antarctica. Nature 399:429-436.

Siegenthaler, U., T. F. Stocker, E. Monnin, D. Lüthi, J. 

Schwander, B. Stauffer, D. Raynaud, J.M. Barnola, H. 

Fischer, V. Masson-Delmotte, and J. Jouzel. 2005. Stable 

carbon cycle-climate relationship during the late pleistocene. Science 310:1313-1317.

Sowers, T., R.B. Alley, and J. Jubenville. 2003. Ice core 

records of atmospheric N2

O covering the last 106,000 

years. Science 301(5635):945-948.

Spahni, R., J. Chappellaz, T.F. Stocker, L. Loulergue, G. 

Hausammann, K. Kawamura, J. Flückiger, J. Schwander, 

D. Raynaud, V. Masson-Delmotte, and J. Jouzel. 2005. 

Atmospheric methane and nitrous oxide of the late Pleistocene from Antarctic ice cores. Science 310:1317-1321. 

Steele, L.P., P.B. Krummel, and R.L. Langenfelds. 2002. 

Atmospheric CO2 and CH4 concentrations from sites in 

the CSIRO Atmospheric Research GASLAB air sampling 

network (October 2002 version). In Trends: A compendium of data on global change. Oak Ridge, TN: U.S. 

Department of Energy. <http://cdiac.esd.ornl.gov/trends/

atm_meth/csiro/csiro-cgrimch4.html>

Thoning, K.W., and P.P. Tans. 2000. Atmospheric CO2

records from sites in the NOAA/CMDL continuous monitoring network. In Trends: A compendium of data on global 

change. Oak Ridge, TN: U.S. Department of Energy. 

<http://cdiac.esd.ornl.gov/trends/co2/nocm-sp.htm>

WDCGG (World Data Centre for Greenhouse Gases). 

2005. Atmospheric CH4

 concentrations for Greenland Site 

J. Accessed 2005. <http://gaw.kishou.go.jp/wdcgg.html>

v
AIR

2-72 EPA’s 2008 Report on the Environment

2.3.3 Discussion

What These Indicators Say About Trends 

in Greenhouse Gas Emissions and 

Concentrations

For several greenhouse gases, the nation’s estimated combined 

emissions that are directly attributable to human activity have 

increased 16 percent between 1990 and 2005 (the U.S. Greenhouse Gas Emissions indicator, p. 2-64). Emissions sources 

occur in several sectors of the U.S. economy, with the highest 

contribution—and the greatest recent growth—attributed to 

energy use, primarily electricity generation and transportation. As well as detailing the increase, the U.S. Greenhouse 

Gas Emissions indicator compares contributions of different 

greenhouse gases by normalizing for each gas’s ability to affect 

the Earth’s energy balance. The results show that carbon dioxide (CO2

) makes up the bulk of the nation’s anthropogenic 

greenhouse gas emissions. Both observations demonstrate that 

fossil fuel combustion is clearly the country’s major source of 

anthropogenic greenhouse gas emissions.

Data on atmospheric concentrations of greenhouse gases have 

extraordinary temporal coverage (the Greenhouse Gas Concentrations indicator, p. 2-66). For CO2

, methane (CH4), and 

nitrous oxide (N2O), concentration data span several hundred 

thousand years; and for selected halocarbons, concentration 

data span virtually the entire period during which these synthetic gases were widely used. Thus, these concentration data 

provide an excellent basis for answering the question regarding trends in greenhouse gas concentrations. The historical 

data for CO2, CH4, and N2O show considerable temporal 

variability in these gases’ concentrations; however, concentrations observed in the past 50 years are higher than those over 

the entire period of record evaluated—even when considering 

natural fluctuations. In short, the historical context provided 

by ice cores shows that present concentrations of these three 

greenhouse gases are unprecedented over the last 650,000 

years, and demonstrate that the recently increasing levels 

reflect the influence of human activity. For the various halocarbons considered, concentrations have increased between 

1980 and 2006, with some increases spanning more than two 

orders of magnitude, but the rate at which these concentrations is increasing has slowed in recent years. 

Taken together, the well-documented long-term trends in 

concentrations of greenhouse gases, along with corresponding 

increases in emissions from anthropogenic sources, show that 

human activity is causing increased concentrations of greenhouse gases in the Earth’s atmosphere—a finding echoed in 

many prominent reviews on the science of climate change.25,26

Limitations, Gaps, and Challenges

Although they provide extensive insights into greenhouse 

gas emissions and concentrations, the two greenhouse gas 

indicators have limitations and gaps that should be acknowledged. The emissions trends, for instance, are based largely on 

estimates, which have uncertainties inherent in the engineering calculations and estimation methodologies developed for 

the U.S. greenhouse gas emissions inventory. Uncertainty of 

the magnitude of the emissions varies among the gases and 

sources, though estimated emissions from some of the largest sources (e.g., CO2

 emissions from fossil fuel combustion) 

are considered highly accurate.27 One gap in the emissions 

indicator is that EPA’s greenhouse gas inventory does not track 

every greenhouse gas or every emissions source. Examples 

of greenhouse gases not included in the inventory are ozone 

and selected chlorofluorocarbons. The most notable sources 

not tracked in the inventory are natural sources, such as CH4

from wetlands, CO2 and CH4 from thawing permafrost, 

and multiple emissions from volcanoes. Though this is not 

necessarily a limitation or a gap, it is important to note that 

EPA’s greenhouse gas inventory, by design, tracks only this 

nation’s anthropogenic emissions of greenhouse gases.28 For 

perspective on how the nation’s emissions compare to those 

from other countries, recent data estimate that the U.S. emits 

approximately 20 percent of the total worldwide amounts of 

selected greenhouse gases. Having national emissions indicators on a more complete set of greenhouse gases and emissions 

sources would further improve EPA’s ability to track pressures 

that affect climate change.

The Greenhouse Gas Concentrations indicator (p. 2-66) tracks 

trends in measured airborne levels of greenhouse gases regardless of the anthropogenic or natural sources that released them, 

which helps account for some of the inherent limitations and 

uncertainties in the emissions indicator. However, the concentration data have limitations and gaps of their own. Historical 

concentrations from ice core samples are not measured in real 

time, which introduces some minor uncertainty into the data 

set; consistency among measurements made by multiple laboratories at different locations suggests this uncertainty is relatively 

low.29 While the concentration data thoroughly characterize 

trends for CO2 (the most important anthropogenic greenhouse 

gas) and other extensively studied gases, a gap in the concentration data, as with the emissions data, is that not all greenhouse 

gases have been monitored. Long-term trend data for ozone, 

for instance, are currently not available. Measuring globally 

representative trends in tropospheric ozone concentrations 

presents technical challenges, because ozone is a short-lived gas 

(which does not lend well to ice core measurements) with concentrations that exhibit tremendous spatial variations (which 

would require extensive monitoring to characterize worldwide 

25 National Research Council. 2001. Climate change science: An analysis of 

some key questions. Washington, DC: National Academy Press.

26 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

The scientific basis (fourth assessment report). Cambridge, UK: Cambridge 

University Press. 

27 U.S. Environmental Protection Agency. 2007. Inventory of U.S. greenhouse 

gas emissions and sinks: 1990-2005. EPA/430/R-07/002. Washington, DC. 

28 den Elzen, M., J. Fuglestvedt, N. Höhne, C. Trudinger, J. Lowe, B. Matthews, B. 

Romstad, C. Pires de Campos, and N. Andronova. 2005. Analysing countries’ 

contribution to climate change: Scientific and policy-related choices. Env. Sci. 

Policy 8(6):614-636.

29 Barnola, J., D. Raynaud, C. Lorius, and N.I. Barkov. 2003. Historical CO2

record from the Vostok ice core. In: Trends: A compendium of data on global 

change. Oak Ridge, TN: U.S. Department of Energy.
AIR

EPA’s 2008 Report on the Environment 2-73

trends). Another gap is the lack of ROE indicators for radiatively important substances, such as soot and aerosols. Though 

these substances technically are not greenhouse gases, tracking 

trends in these substances’ concentrations is important due to 

their ability to alter the Earth’s energy balance.

2.4 What Are the Trends 

in Indoor Air Quality 

and Their Effects on 

Human Health?

2.4.1 Introduction

“Indoor air quality” refers to the quality of the air in a home, 

school, office, or other building environment. Most pollutants 

affecting indoor air quality come from sources inside buildings, although some originate outdoors. Typical pollutants of 

concern include combustion products such as carbon monoxide, particulate matter, and environmental tobacco smoke; 

substances of natural origin such as radon; biological agents 

such as molds; pesticides; lead; asbestos; ozone (from some 

air cleaners); and various volatile organic compounds from a 

variety of products and materials. Indoor concentrations of 

some pollutants have increased in recent decades due to such 

factors as energy-efficient building construction and increased 

use of synthetic building materials, furnishings, personal care 

products, pesticides, and household cleaners.

The potential impact of indoor air quality on human health 

nationally is considerable, for several reasons. Americans, 

on average, spend approximately 90 percent of their time 

indoors,30 where the concentrations of some pollutants are 

often 2 to 5 times higher than typical outdoor concentrations.31 Moreover, people who are often most susceptible to 

the adverse effects of pollution (e.g., the very young, older 

adults, people with cardiovascular or respiratory disease) tend 

to spend even more time indoors.32 Health effects that have 

been associated with indoor air pollutants include irritation of 

the eyes, nose, and throat; headaches, dizziness, and fatigue; 

respiratory diseases; heart disease; and cancer. 

Indoor air pollutants originate from many sources. These 

sources can be classified into two general categories:

•	 Indoor sources (sources within buildings themselves).

Combustion sources in indoor settings, including tobacco, 

heating and cooking appliances, and fireplaces, can release 

harmful combustion byproducts such as carbon monoxide 

and particulate matter directly into the indoor environment. 

Cleaning supplies, paints, insecticides, and other commonly 

used products introduce many different chemicals, including volatile organic compounds, directly into the indoor 

air. Building materials are also potential sources, whether 

through degrading materials (e.g., asbestos fibers released 

from building insulation) or from new materials (e.g., 

chemical off-gassing from pressed wood products). Other 

substances in indoor air are of natural origin, such as mold 

and pet dander. 

•	 Outdoor sources. Outdoor air pollutants can enter buildings through open doors, open windows, ventilation systems, 

and cracks in structures. Some pollutants come indoors 

through building foundations. For instance, radon forms in 

the ground as naturally occurring uranium in rocks and soils 

decays. The radon can then enter buildings through cracks 

or gaps in structures. In areas with contaminated ground 

water or soils, volatile chemicals can enter buildings through 

this same process. Volatile chemicals in water supplies can 

also enter indoor air when building occupants use the water 

(e.g., during showering, cooking). Finally, when people enter 

buildings, they can inadvertently bring in soils and dusts on 

their shoes and clothing from the outdoors, along with pollutants that adhere to those particles. 

In addition to pollutant sources, the air exchange rate with the 

outdoors is an important factor in determining indoor air pollutant concentrations. The air exchange rate is affected by the 

design, construction, and operating parameters of buildings and 

is ultimately a function of infiltration (air that flows into structures through openings, joints, and cracks in walls, floors, and 

ceilings and around windows and doors), natural ventilation (air 

that flows through opened windows and doors), and mechanical ventilation (air that is forced indoors or vented outdoors by 

ventilation devices, such as fans or air handling systems). Outdoor climate and weather conditions combined with occupant 

behavior can also affect indoor air quality. Weather conditions 

influence whether building occupants keep windows open or 

closed and whether they operate air conditioners, humidifiers, 

or heaters, all of which can impact indoor air quality. Weather 

also has a large effect on infiltration. Certain climatic conditions 

can increase the potential for indoor moisture and mold growth 

if not controlled by adequate ventilation or air conditioning.

The link between some common indoor air pollutants and 

health effects is very well established. Radon is a known 

human carcinogen and is the second leading cause of lung 

cancer.33,34 Carbon monoxide is toxic, and short-term exposure to elevated carbon monoxide levels in indoor settings 

can be lethal.35 Episodes of Legionnaires’ disease, a form of 

pneumonia caused by exposure to the Legionella bacterium, 

have been associated with buildings with poorly maintained 

air conditioning or heating systems.36,37 In addition, numerous 

30 U.S. Environmental Protection Agency. 1989. Report to Congress on indoor 

air quality: Volume 2. EPA/400/1-89/001C. Washington, DC.

31 U.S. Environmental Protection Agency. 1987. The total exposure assessment 

methodology (TEAM) study: summary and analysis. EPA/600/6-87/002a. 

Washington, DC.

32 U.S. Environmental Protection Agency. 1997. Exposure factors handbook: 

volume 3—activity factors. EPA/600/P-95/002Fa. Washington, DC.

33 U.S. Environmental Protection Agency. 2003. EPA assessment of risks from 

radon in homes. EPA/402/R-03/003. Washington, DC.

34 National Research Council. 1999. Health effects of exposure to indoor radon: 

biological effects of ionizing radiation (BEIR), report VI. Washington, DC: 

National Academy Press. <http://www.epa.gov/iaq/radon/beirvi.html>

35 Raub, J.A., M. Mathieu-Nolf, N.B. Hampson, S.R. Thom. 2000. Carbon 

monoxide poisoning—a public health perspective. Toxicology 145:1-14.
AIR

2-74 EPA’s 2008 Report on the Environment

indoor air pollutants—dust mites, mold, pet dander, environmental tobacco smoke, cockroach allergens, and others—are 

“asthma triggers,” meaning that some asthmatics might experience asthma attacks following exposure.38

While these and other adverse health effects have been 

attributed to specific pollutants, the scientific understanding 

of some indoor air quality issues continues to evolve. One 

example is “sick building syndrome,” which occurs when 

building occupants experience similar symptoms after entering a particular building, with symptoms diminishing or 

disappearing after they leave the building; these symptoms are 

increasingly being attributed to a variety of building indoor 

air attributes. 

Researchers also have been investigating the relationship 

between indoor air quality and important issues not necessarily related to health, such as student performance in 

the classroom and productivity in occupational settings.39

Another evolving area is research in “green building” design, 

construction, operation, and maintenance that achieves energy 

efficiency and enhances indoor air quality.

2.4.2 ROE Indicators

Two National Indicators that fully meet the indicator criteria 

are discussed in this section. These indicators address two specific issues and do not cover the wide range of issues associated 

with indoor air quality. The two indicators focus on radon 

and environmental tobacco smoke. The indicator on radon 

levels in homes is based on EPA’s 1992 National Residential 

Radon Survey, 2000 U.S. Census data, and production and 

sales statistics for radon mitigation systems. Environmental 

tobacco smoke is addressed using biomarker data for cotinine, 

a metabolite linked exclusively to chemicals found in tobacco 

smoke. The Centers for Disease Control and Prevention have 

reported these biomarker data in multiple releases of their 

National Health and Nutrition Examination Survey.

36 Allan, T., et al. 2001. Outbreak of Legionnaires’ disease among automotive 

plant workers—Ohio, 2001. MMWR 50(18):357-359.

37 Fields, B.S., R.F. Benson, and R.E. Besser. 2002. Legionella and Legionnaires’ 

disease: 25 years of investigation. Clin. Microbiol. Rev. 15(3):506-526.

38 Institute of Medicine. 2000. Clearing the air: Asthma and indoor air exposures. Washington, DC: National Academy Press. 

39 U.S. Environmental Protection Agency. 2003. Indoor air quality and student 

performance. EPA/402/K-03/006. Washington, DC.

INDICATOR | U.S. Homes Above EPA’s Radon Action Level

Radon is a radioactive gas. It comes from the decay of uranium that is naturally occurring and commonly 

present in rock and soils. It typically moves up through the 

ground to the air above and into a home through pathways 

in ground contact floors and walls. Picocuries per liter of 

air (pCi/L) is the unit of measure for radon in air (the metric equivalent is becquerels per cubic meter of air). 

Each year, radon is associated with an estimated 21,100 

lung cancer deaths in the U.S., with smokers at an increased 

risk; radon is the second leading cause of lung cancer after 

smoking, and 14.4 percent of lung cancer deaths in the 

U.S. are believed to be radon-related (U.S. EPA, 2003). To 

reduce the risk of lung cancer, EPA has set a recommended 

“action level” of 4 pCi/L for homes. At that level, it is costeffective for occupants to reduce their exposure by implementing preventive measures in their homes.

This indicator presents (1) the number of U.S. homes 

estimated to be at or above the EPA recommended radon 

action level of 4 pCi/L and (2) the number of homes with 

an operating radon mitigation system. The gap between 

the homes in these two categories is the number of homes 

that have not yet been mitigated (generally, homes are only 

mitigated if the EPA recommended radon action level of 

4 pCi/L or more is measured). The data for this indicator 

were extracted from the National Residential Radon Survey (U.S. EPA, 1992a), which estimated radon levels in the 

U.S. housing stock. The number of homes at or above 4 

pCi/L was estimated by applying the results of the Radon 

Survey (U.S. EPA, 1992a) to 2000 U.S. Census data 

on the number of U.S. households. The 1992 National 

Residential Radon Survey was based on the housing 

stock that would be covered by EPA’s radon testing policy 

(i.e., homes that should test). This included only homes 

Table 2-4. ROE Indicators of Trends in Indoor Air Quality and Their Effects 

on Human Health

National Indicators Section Page

U.S. Homes Above EPA’s Radon Action Level 2.4.2 2-74

Blood Cotinine Level 2.4.2 2-76
AIR

EPA’s 2008 Report on the Environment 2-75

INDICATOR | U.S. Homes Above EPA’s Radon Action Level (continued)

intended for regular (year-round) use but covers singlefamily homes, mobile homes, and multi-unit and group 

quarters (U.S. EPA, 1992b). The 1992 residential survey 

estimated that about one in 15 homes in EPA’s “should 

test” category would have a radon level of 4 pCi/L or 

more. The measure of the number of homes with operating mitigation systems was developed from radon vent fan 

sales data provided voluntarily by fan manufacturers. 

What the Data Show

There was a 308 percent increase in the number of homes 

with operating mitigation systems from 1990 to 2006, 

going from 175,000 to 714,000 homes over 17 years; 

but during the same period, there has been a 22 percent 

increase in the estimated number of homes with radon 

levels at or above 4 pCi/L, from about 6.4 million to 7.8 

million homes (Exhibit 2-56, panel A). Panel B of Exhibit 

2-56 shows radon potential in homes at the county level 

based on indoor radon measurements, geology, aerial 

radioactivity, soil permeability, and foundation type. 

Zone 1 is the highest radon potential area, followed by 

Zone 2 (medium), and Zone 3 (low). 

It has been reported anecdotally that radon vent fans 

and mitigation systems are also being used to control for 

soil gases and vapor intrusion in homes in the vicinity 

of Superfund sites, underground or aboveground storage tank sites, and similar sites as an element of corrective 

action plans. While radon vent fans and mitigation systems 

used in this way may provide a radon reduction benefit, 

they could be considered a subtraction from the number 

of homes with operating mitigation systems, thus slightly 

reducing the slope of the trend line.

Indicator Limitations

•	 The indicator presumes that radon vent fans are used for 

their intended purpose; the available information supports 

this premise. Even if fans are used for managing vapor 

intrusion, a radon risk reduction benefit still occurs.

•	A home with an operating mitigation system is presumed 

to have a vent fan with an average useful life of 10 years. 

Each year the total number of homes with operating 

mitigation systems is adjusted to reflect new additions 

and subtractions (i.e., vent fans installed 11 years earlier).

•	The number of homes with radon levels at or above 4 

pCi/L is an estimate based on one year of measurement 

data extrapolated for subsequent years based on population data, rather than on continuing measurements.

•	This indicator does not track the number of homes 

designed and built with radon-resistant new construction 

features, which can help diminish radon entry in homes. 

Thus, more people are likely being protected from 

elevated indoor air exposures to radon than suggested by 

the trends in operating radon mitigation systems alone. 

Data Sources

Summary data in this indicator were provided by EPA’s 

Office of Radiation and Indoor Air, based on two types of 

information. The number of homes with estimated indoor 

air concentrations at or above EPA’s radon action level was 

originally derived from the National Residential Radon 

Survey (U.S. EPA, 1992a) and is updated with U.S. Census 

B. EPA map of radon zones

Data source: U.S. EPA, 1992a, 2007 Homes (millions)

Exhibit 2-56. Homes at or above EPA’s radon 

action level and homes with operating mitigation 

systems in the U.S., 1990-2006

’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

Year

A. Trend data

Zone 1: Counties with predicted average indoor radon 

screening levels greater than 4 pCi/L

Zone 2: Counties with predicted average indoor radon 

screening levels from 2 to 4 pCi/L

Zone 3: Counties with predicted average indoor radon 

screening levels less than 2 pCi/L

Guam – 

preliminary 

zone designation

0

1

2

3

4

5

6

7

8

Homes with estimated radon 

indoor air concentrations at or 

above 4 pCi/L

Homes with radon 

mitigation systems
AIR

2-76 EPA’s 2008 Report on the Environment

INDICATOR | U.S. Homes Above EPA’s Radon Action Level (continued)

data; and the number of homes with radon mitigation systems was developed from unpublished sales data provided 

by radon vent fan manufacturers (U.S. EPA, 2007).

References

U.S. EPA, 2007. Unpublished sales data provided by radon 

vent manufacturers. 

U.S. EPA. 2003. EPA assessment of risks from radon in 

homes. EPA/402/R-03/003. Washington, DC. 

<http://www.epa.gov/radiation/docs/assessment/

402-r-03-003.pdf>

U.S. EPA. 1992a. National residential radon survey: 

Summary report. EPA/402/R-92/011. 

Washington, DC. October.

U.S. EPA. 1992b. Technical support document. 

EPA/400/R-92/011.

v

INDICATOR | Blood Cotinine Level

Environmental tobacco smoke (ETS) contains a mixture of toxic chemicals, including known human carcinogens. Persistent exposure to ETS is associated with numerous health-related disorders or symptoms, such as coughing, 

chest discomfort, reduced lung function, acute and chronic 

coronary heart disease, and lung cancer (IARC, 2004; 

NTP, 2002; U.S. EPA, 1992; CDC, 2005). Children are at 

particular risk from exposure to ETS, which can exacerbate 

existing asthma among susceptible children and also greatly 

increase the risk for lower respiratory tract illness, such as 

bronchitis and pneumonia, among younger children (CDC, 

2005). Younger children appear to be more susceptible to 

the effects of ETS than are older children (U.S. EPA, 1992).

Household ETS exposure is an important issue because 

many people, especially young children, spend much time 

inside their homes. Based on data reported from the 1994 

National Health Interview Survey, the Department of 

Health and Human Services estimates that 27 percent of 

children age 6 years and younger are exposed to ETS in 

the home (U.S. DHHS, 2000).

Exposure to ETS leaves traces of specific chemicals in 

people’s blood, urine, saliva, and hair. Cotinine is a chemical 

that forms inside the body following exposure to nicotine, 

an ingredient in all tobacco products and a component of 

ETS. Following nicotine exposures, cotinine can usually 

be detected in blood for at least 1 or 2 days (Pirkle et al., 

1996). Active smokers almost always have blood cotinine 

levels higher than 10 nanograms per milliliter (ng/mL), 

while non-smokers exposed to low levels of ETS typically 

have blood concentrations less than 1 ng/mL (CDC, 2005). 

Following heavy exposure to ETS, non-smokers can have 

blood cotinine levels between 1 and 10 ng/mL. 

This indicator reflects blood cotinine concentrations 

in ng/mL among non-smokers for the U.S. population, 

age 3 years and older, as measured in the 1999-2000 and 

2001-2002 National Health and Nutrition Examination 

Survey (NHANES). NHANES is a series of surveys conducted by the Centers for Disease Control and Prevention’s 

(CDC’s) National Center for Health Statistics, designed 

to collect data on the health and nutritional status of the 

civilian, non-institutionalized U.S. population using a 

complex, stratified, multistage, probability-cluster design. 

Blood cotinine also was monitored in non-smokers age 4 

years and older as part of NHANES III, between 1988 and 

1991. CDC’s National Center for Environmental Health 

conducted the laboratory analyses for the biomonitoring 

samples. Beginning in 1999, NHANES became a continuous and annual national survey. 

What the Data Show

As part of NHANES III (1988-1991), CDC estimated 

that the median blood serum level (50th percentile) of 

cotinine among non-smokers in the general U.S. population 

was 0.20 ng/mL. In NHANES 1999-2000, the estimated 

median serum level among non-smokers nationwide was 

0.06 ng/mL. During the 2001-2002 survey, the estimated 

blood cotinine levels for the U.S. population were very 

similar to 1999-2000, with the median concentration actually below the limit of detection, and the geometric mean 

0.06 ng/mL (see Exhibit 2-57). This marks a 70 percent 

decrease from levels measured in the 1988-1991 NHANES 

III survey—a reduction that suggests a marked decrease in 

exposure to ETS. 

Exhibit 2-57 also shows the results of the NHANES 

1999-2000 and 2001-2002 survey, for different subpopulations. Similar decreasing trends in blood cotinine levels 

between NHANES III (1988-1991) and the most recent 

2001-2002 survey were observed in each of the population groups defined by age, sex, and race/ethnicity (CDC, 

2005). These data reveal three additional observations: 

(1) non-smoking males have higher cotinine levels than 

non-smoking females; (2) of the ethnic groups presented, 
AIR

EPA’s 2008 Report on the Environment 2-77

INDICATOR | Blood Cotinine Level (continued)

non-Hispanic blacks had the highest cotinine levels; and 

(3) on average, people below age 20 have higher levels of 

blood cotinine than people age 20 years and older.

Exhibit 2-58 shows the percentage of children between 

the ages of 4 and 17 with specified blood cotinine levels, 

for the total age group and by selected race and ethnicity 

breakdowns within the specified age group. Among the 

three subgroup populations presented, Mexican American children had the lowest percentage of blood cotinine 

levels greater than 1.0 ng/mL; this was evident for both 

1988-1994 and 1999-2002 time periods (10.7 percent 

and 5.2 percent, respectively), which changed little for 

the 2001-2004 time frame (4.8 percent, data not shown). 

Black, non-Hispanic children had the largest decline of the 

three subgroups in the percentage of blood cotinine levels 

greater than 1.0 ng/mL, but that population also started 

off with the highest percentage above 1.0 ng/mL (36.6 

percent) (Federal Interagency Forum on Child and Family 

Statistics, 2005, 2007). 

Indicator Limitations

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes 

in estimates between the two time periods do not 

Total, age 3 years

and older

Sex

Male

Female

Race and ethnicityd

Age group

3-11 years

12-19 years

20+ years

Survey years 

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

Sample size 

5,999

6,813

2,789

3,149

3,210

3,664

1,174

1,414

1,773

1,902

3,052

3,497

Geometric mean 

NC

0.06

NC

0.08

NC

0.05

NC

0.11

NC

0.09

NC

0.05

50th

0.06

<LOD

0.08

<LOD

<LOD

<LOD

0.11

0.07

0.11

0.05

<LOD

<LOD

75th

0.24

0.16

0.30

0.23

0.18

0.12

0.57

0.54

0.35

0.17

0.11

0.50

90th

1.02

0.93

1.20

1.17

0.85

0.71

1.88

2.23

1.65

1.53

0.63

0.62

95th

1.96

2.19

2.39

2.44

1.85

1.76

Black, non-Hispanic

Mexican American

1999-2000

2001-2002

1999-2000

2001-2002

1,333

1,599

2,241

1,877

NC

0.16

NC

0.06

0.13

0.13

<LOD

<LOD

0.51

0.57

0.14

0.16

1.43

1.77

0.51

0.73

2.34

3.12

1.21

2.11

3.37

3.21

2.56

3.12

1.48

1.38

Exhibit 2-57. Blood cotinine concentrations for the non-smoking U.S. population age 3 years and older by

selected demographic groups, 1999-2002

Geometric mean and selected percentiles

for blood cotinine concentrations (ng/mL)a, b, c

White, non-Hispanic 1999-2000

2001-2002

1,950

2,845

NC

0.05

0.05

<LOD

0.21

0.12

0.95

0.80

1.92

1.88

a

 NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result. 

b

 <LOD = below the limit of detection (LOD) of the analytical method. The LOD varied by year and by individual sample: 83 percent of 

measurements had a LOD of 0.015 ng/mL, and 17 percent of measurements had a LOD of 0.05 ng/mL.

c

 Refer to CDC, 2005, for confidence intervals for reported values. 

d

 Other racial and ethnic groups are included in the “total” only.

Data source: CDC, 2005
AIR

2-78 EPA’s 2008 Report on the Environment

INDICATOR | Blood Cotinine Level (continued)

necessarily reflect a trend. Earlier data 

sets are available (e.g., NHANES III), but 

the data are not directly comparable to 

NHANES 1999-2002. As CDC releases 

additional survey results (e.g., 2003-2004), 

it will become possible to more fully evaluate trends (CDC, 2002, 2004). 

Data Sources

Data used for this indicator were extracted 

from two reports that present results of 

the ongoing NHANES: the data shown in 

Exhibit 2-57 were obtained from a CDC 

report (2005), and the data shown in Exhibit 

2-58 were obtained from a report by the 

Federal Interagency Forum on Child and 

Family Statistics (2005). The underlying 

laboratory data supporting both reports are 

available online in SAS® transport file formats 

at http://www.cdc.gov/nchs/about/major/

nhanes/datalink.htm.

References

CDC (Centers for Disease Control and 

Prevention). 2005. Third national report on 

human exposure to environmental chemicals. 

NCEH Pub. No. 05-0570. July. Accessed 

September 9, 2005. <http://www.cdc.gov/

exposurereport/report.htm>

CDC. 2004. NHANES analytic guidelines. June 2004 version. Accessed October 21, 2005. <http://www.cdc.gov/

nchs/data/nhanes/nhanes_general_guidelines_june_04.

pdf>

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Last update August 30, 

2002. Accessed October 11, 2005. <http://www.cdc.gov/

nchs/data/nhanes/guidelines1.pdf>

Federal Interagency Forum on Child and Family Statistics. 

2007. America’s children: Key national indicators of wellbeing, 2007. Washington, DC: U.S. Government Printing 

Office. Accessed October 2007. <http://www.childstats.

gov/americaschildren/>

Federal Interagency Forum on Child and Family Statistics. 

2005. America’s children: Key national indicators of wellbeing, 2005. Washington, DC: U.S. Government Printing 

Office. Accessed December 20, 2005. 

<http://www.childstats.gov/pdf/ac2005/ac_05.pdf>

IARC (International Agency for Research on Cancer). 

2004. IARC working group on the evaluation of carcinogenic risks to humans. Evaluation of carcinogenic risks 

to humans, volume 83: Tobacco smoke and involuntary 

smoking. Lyon, France.

NTP (National Toxicology Program) 2002. Report on 

carcinogens, 10th edition.

Pirkle, J.L., K.M. Flegal, J.T. Bernert, D.J. Brody, R.A. 

Etzel, K.R. Maurer. 1996. Exposure of the U.S. population to environmental tobacco smoke: The third national 

health and nutrition examination survey, 1988 to 1991. J. 

Amer. Med. Assoc. 275:1233-1240.

U.S. DHHS (United States Department of Health and 

Human Services). 2000. Healthy people 2010. Second edition. Washington, DC: U.S. Government Printing Office 

<http://www.healthypeople.gov/Document/HTML/

Volume2/27Tobacco.htm#_Toc489766224>

U.S. EPA (United States Environmental Protection 

Agency). 1992. Respiratory health effects of passive smoking: Lung cancer and other disorders. Washington, DC.

Exhibit 2-58. Blood cotinine concentrations in U.S. children 

age 4 to 17 by race and ethnicity, 1988-1994 and 1999-2002a

More than 1.0 ng/mL

0.05 to 1.0 ng/mL

Concentration:b

Percent of children

0

10

20

30

40

50

60

70

80

90

100

Year

Total Black,

non-Hispanic

Mexican

American

White,

non-Hispanic

’88-’94 ’99-’02 ’88-’94 ’99-’02 ’88-’94 ’99-’02 ’88-’94 ’99-’02

a

Cotinine concentrations are reported for non-smoking 

children only. 

b

Concentrations below 0.05 ng/mL are not presented 

here because this was the detection limit for many of 

the samples. 

Data source: Federal Interagency Forum on Child and Family Statistics, 2005

63.7

41.0

57.9

59.4 72.8

5.2

62.5

35.5

23.7 16.5

36.6

22.4

10.7

41.3

24.2 19.1

v
AIR

EPA’s 2008 Report on the Environment 2-79

2.4.3 Discussion

What These Indicators Say About Trends 

in Indoor Air Quality and Their Effects on 

Human Health

The two indoor air quality indicators provide insights into 

issues of very different origin: radon is a substance in indoor 

air produced by a natural source, while environmental tobacco 

smoke (as evaluated by the presence of blood cotinine) in 

indoor environments is linked entirely to human behavior.

The Homes Above EPA’s Radon Action Level indicator (p. 

2-74) tracks two statistics: the number of homes estimated to 

be at or above EPA’s action level (4 pCi/L) for radon, and the 

number of homes with operating radon mitigation systems. 

Evaluating trends in radon mitigation systems is relevant 

because properly operated systems are expected to reduce 

radon to levels below the action level, and therefore also are 

expected to reduce radon-related health risks among building occupants. Between 1990 and 2006, the number of homes 

with radon mitigation systems increased more than four-fold, 

but these homes account for less than 10 percent of the nation’s 

homes currently believed to have radon levels at or above 

EPA’s action level. Some residents are being protected against 

radon exposures through radon-resistant new construction 

techniques used when a home is built. Estimates of radonresistant new construction practices are not included in the 

indicator, however, because while they substantially reduce 

radon levels in homes with high radon potential, they do not 

always reduce the levels below the action level.

The Blood Cotinine indicator (p. 2-76) tracks blood concentrations of cotinine, a metabolite of nicotine, and shows that 

exposure to environmental tobacco smoke among non-smokers 

decreased considerably in the last decade. This decrease was 

observed for all population groups, defined by age (including children), sex, and ethnicity. However, children’s blood 

cotinine levels, on average, are still more than twice the levels 

observed in adults. A logical explanation for the downward 

trend in blood cotinine levels is modified behavior, whether 

reduced smoking prevalence or more widespread restriction of 

areas in which individuals are allowed to smoke. 

Taken together, these indicators show that an increasing number of Americans have reduced indoor air exposures to two 

known carcinogens. Though these improvements are encouraging, both radon and environmental tobacco smoke remain 

important indoor air quality issues. In the case of radon, for 

example, the increase in the number of homes estimated to 

be at or above the EPA’s radon action level is outpacing the 

increase in the use of radon mitigation systems.

Limitations, Gaps, and Challenges

The two indicators in this section provide extensive, but not 

comprehensive, information on the corresponding indoor air 

quality issues that they characterize. An important limitation 

of the Homes Above EPA’s Radon Action Level indicator, 

for instance, is that it does not track the number of homes 

designed and built with radon-resistant new construction features, which can diminish radon entry in homes and therefore 

reduce radon exposures and the associated lung cancer risk. 

Thus, more people are likely being protected from elevated 

indoor air exposures to radon than is suggested by trends in 

radon mitigation systems alone. 

The Blood Cotinine indicator also has certain limitations. 

For example, exposure to environmental tobacco smoke 

does not occur exclusively indoors: some proportion of blood 

cotinine levels measured in non-smokers reflects exposures 

that occurred outdoors. In addition, nationally representative blood cotinine data are not available for children under 3 

years old—an age group with documented susceptibilities to 

environmental tobacco smoke.40 Nonetheless, none of these 

limitations call into question this indicator’s main finding: 

nationwide, exposures to environmental tobacco smoke 

among non-smokers are decreasing. Moreover, reliable survey 

data on smoking behavior corroborates this downward trend.41

The two indoor air quality indicators provide useful insights 

into trends for radon and environmental tobacco smoke, but 

they leave some gaps that EPA would like to fill to better 

answer the overarching question on nationwide indoor air 

quality trends and associated health effects. For example, 

ROE indicators could not be developed for indoor air quality trends for molds, some combustion products, chemicals 

found in common household cleaners and building materials, and certain persistent pollutants and endocrine disruptors 

that have been identified in household dust.42,43 There is no 

quantitative, nationally representative inventory of emissions 

sources in indoor environments, nor is there a nationwide 

monitoring network that routinely measures air quality inside 

homes, schools, and office buildings. These gaps in nationwide indicators do not mean that nothing is known about the 

broad range of indoor air quality issues and associated health 

effects. Rather, information on these issues can be gleaned 

from numerous publications by governmental agencies and 

in the scientific literature. Data from these other publications 

and information resources, though valuable in understanding 

indoor air quality, are not presented in this report as indicators 

because they are not sufficiently representative on a national 

scale or because they do not track an issue over time.

The challenges associated with filling these indicator gaps 

are well known. Although methods to monitor indoor air 

40 U.S. Environmental Protection Agency. 1992. Respiratory health effects of 

passive smoking: Lung cancer and other disorders. EPA/600/6-90/006F. 

Washington, DC.

41 U.S. Department of Health and Human Services. 2000. Healthy people 2010: 

Understanding and improving health. Second edition. Washington, DC: U.S. Government Printing Office. November. <http://www.health.gov/healthypeople/>

42 Rudel, R.A., D.E. Camann, J.D. Spengler, L.R. Korn, and J.G. Brody. 2003. 

Phthalates, alkylphenols, pesticides, polybrominated diphenyl ethers, and 

other endocrine-disrupting compounds in indoor air and dust. Env. Sci. Tech. 

37(20):4543-4553.

43 Stapleton, H.M., N.G. Dodder, J.H. Offenberg, M.M. Schantz, and S.A. Wise. 

2005. Polybrominated diphenyl ethers in house dust and clothes dryer lint. 

Env. Sci. Tech. 39(4):925-931.
AIR

2-80 EPA’s 2008 Report on the Environment

quality are available, there is considerable variability among 

building types, occupants’ behaviors, climate conditions, 

and ventilation systems for indoor environments in the U.S. 

This variability, combined with access issues and the number 

of different pollutants to address, makes a statistically based 

evaluation of our nation’s millions of residences, thousands of 

office buildings, and more than 100,000 schools a challenging 

and resource-intensive task. Further, it is difficult to directly 

measure how changes in indoor air quality translate into corresponding changes in human health effects, because many 

health outcomes attributed to poor indoor air quality (e.g., 

asthma attacks) have numerous environmental and non-environmental risk factors.
Water

Chapter 3
Contents

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.1.1 Overview of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.1.2 Organization of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.2 What Are the Trends in the Extent and Condition of Fresh Surface Waters and 

Their Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.2.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

3.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3.3 What Are the Trends in the Extent and Condition of Ground Water and Their 

Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.3.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

3.3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29

3.4 What Are the Trends in the Extent and Condition of Wetlands and Their Effects 

on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

3.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

3.4.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31

3.4.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

3.5 What Are the Trends in the Extent and Condition of Coastal Waters and Their 

Effects on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

3.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35

3.5.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37

3.5.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-51

3.6 What Are the Trends in the Quality of Drinking Water and Their Effects 

on Human Health? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-52

3.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-52

3.6.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53

3.6.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-56

3.7 What Are the Trends in the Condition of Recreational Waters and Their Effects 

on Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-57

3.7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-57

3.7.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-58

3.7.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-58

3.8 What Are the Trends in the Condition of Consumable Fish and Shellfish and 

Their Effects on Human Health? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-59

3.8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-59

3.8.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-60

3.8.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-66
WATER

EPA’s 2008 Report on the Environment 3-3

3.1 Introduction

T

he nation’s water resources have immeasurable value. These 

resources encompass lakes, streams, ground water, coastal 

waters, wetlands, and other waters; their associated ecosystems; and the human uses they support (e.g., drinking water, recreation, and fish consumption). The extent of water resources (their 

amount and distribution) and their condition (physical, chemical, 

and biological attributes) are critical to ecosystems, human uses, 

and the overall function and sustainability of the hydrologic cycle.

Because the extent and condition of water can affect human 

health, ecosystems, and critical environmental processes, 

protecting water resources is integral to EPA’s mission. EPA 

works in partnership with other government agencies that are 

also interested in the extent and condition of water resources, 

both at the federal level and at the state, local, or tribal level.

In this chapter, EPA seeks to assess national trends in the extent 

and condition of water, stressors that influence water, and 

associated exposures and effects among humans and ecological systems. The ROE indicators in this chapter address seven 

fundamental questions about the state of the nation’s waters:

•	 What are the trends in the extent and condition 

of fresh surface waters and their effects on human 

health and the environment? This question focuses on 

the nation’s rivers, streams, lakes, ponds, and reservoirs.

•	 What are the trends in the extent and condition of 

ground water and their effects on human health and 

the environment? This question addresses subsurface 

water that occurs beneath the water table in fully saturated 

soils and geological formations.

•	 What are the trends in the extent and condition 

of wetlands and their effects on human health and 

the environment? Wetlands—including swamps, bogs, 

marshes, and similar areas—are areas inundated or saturated 

by surface or ground water often and long enough to support 

a prevalence of vegetation typically adapted for life in saturated soil conditions.

•	 What are the trends in the extent and condition of 

coastal waters and their effects on human health and 

the environment? Indicators in this report present data 

for waters that are generally within 3 miles of the coastline 

(except the Hypoxia in Gulf of Mexico and Long Island 

Sound indicator). 

•	 What are the trends in the quality of drinking 

water and their effects on human health? People 

drink tap water, which comes from both public and private 

sources, and bottled water. Sources of drinking water can 

include both surface water (rivers, lakes, and reservoirs) and 

ground water.

•	 What are the trends in the condition of recreational 

waters and their effects on human health and the 

environment? This question addresses water used for a wide 

variety of purposes, such as swimming, fishing, and boating.

•	 What are the trends in the condition of consumable 

fish and shellfish and their effects on human health?

This question focuses on the suitability of fish and shellfish 

for human consumption. 

ROE Approach

This 2008 Report on the Environment:

•	 Asks questions that EPA considers 

important to its mission to protect 

human health and the environment. 

•	 Answers these questions, to the extent 

possible, with available indicators.

•	 Discusses critical indicator gaps, limitations, and challenges that prevent the 

questions from being fully answered.

ROE Questions

The air, water, and land chapters (Chapters 

2, 3, and 4) ask questions about trends in 

the condition and/or extent of the environmental medium; trends in stressors to 

the medium; and resulting trends in the 

effects of the contaminants in that medium 

on human exposure, human health, and 

the condition of ecological systems. 

The human exposure and health and 

ecological condition chapters (Chapters 

5 and 6) ask questions about trends in 

aspects of health and the environment 

that are influenced by many stressors 

acting through multiple media and by 

factors outside EPA’s mission. 

ROE Indicators

An indicator is derived from actual measurements of a pressure, state or ambient 

condition, exposure, or human health or 

ecological condition over a specified geographic domain. This excludes indicators 

such as administrative, socioeconomic, and 

efficiency indicators.

Indicators based on one-time studies are 

included only if they were designed to serve 

as baselines for future trend monitoring. 

All ROE indicators passed an independent 

peer review against six criteria to ensure 

that they are useful; objective; transparent; 

and based on data that are high-quality, 

comparable, and representative across space 

and time. 

Most ROE indicators are reported at the 

national level. Some national indicators 

also report trends by region. EPA Regions 

were used, where possible, for consistency 

and because they play an important role in 

how EPA implements its environmental 

protection efforts.

Several other ROE indicators describe 

trends in particular regions as examples of 

how regional indicators might be included 

in future versions of the ROE. They are 

not intended to be representative of trends 

in other regions or the entire nation.

EPA will periodically update and revise 

the ROE indicators and add new indicators 

as supporting data become available. In the 

future, indicators will include information 

about the statistical confidence of status 

and trends. Updates will be posted electronically at http://www.epa.gov/roe.

Additional Information

You can find additional information about 

the indicators, including the underlying 

data, metadata, references, and peer review, 

at http://www.epa.gov/roe.

EPA’s 2008 Report on the Environment (ROE): Essentials
WATER

3-4 EPA’s 2008 Report on the Environment

These ROE questions are posed without regard to whether 

indicators are available to answer them. This chapter presents 

the indicators available to answer these questions, and also 

points out important gaps where nationally representative data 

are lacking.

Each of the seven questions is addressed in a separate section 

of this chapter. However, all the questions are fundamentally connected—a fact that is highlighted throughout the 

chapter text and indicator summaries. All water is part of the 

global hydrologic cycle, and thus it is constantly in motion—

whether it is a swiftly flowing stream or a slow-moving 

aquifer thousands of years old. A stream may empty into a 

larger river that ultimately discharges into coastal waters. An 

aquifer may be recharged by surface waters, or feed surface 

waters or wetlands through springs and seeps. In each case, 

the extent and condition of one water resource can affect the 

extent and condition of another type. One example of this 

interdependence can be found in the movement of nutrients. 

Together, several of the ROE indicators track nutrient levels 

in water bodies ranging from small wadeable streams to 

coastal estuaries. Additional ROE indicators describe some 

of the effects that may be associated with excess nutrients, 

such as eutrophication and hypoxia. 

In addition to the links within the water cycle, there are 

many connections between the extent and condition of water 

and other components of the environment. Air (addressed in 

Chapter 2), land (Chapter 4), and water all are environmental 

media, and the condition of one medium can influence the 

condition of another. For example, contaminants can be transferred from air to water via deposition, or from land to water 

through runoff or leaching. 

Chapter 5, “Human Exposure and Health,” and Chapter 6, 

“Ecological Condition,” examine the relationships between 

human life, ecosystems, and some of the environmental conditions that can affect them. Humans and ecosystems depend 

on water, so stressors that affect the extent and condition of 

water—such as droughts, pathogens, and contaminants—may 

ultimately affect human health or ecological condition.

3.1.1 Overview of the Data

The indicators in this chapter reflect several different methods 

of collecting and analyzing data on the extent and condition 

of water resources; in some cases, indicators employ a combination of methods. Some of the indicators in this chapter are 

based on probabilistic surveys, with sample or monitoring locations chosen to be representative of a large area (e.g., an EPA 

Region or the nation as a whole). Examples of probabilistic 

surveys include EPA’s Wadeable Streams Survey and National 

Coastal Assessment, and the U.S. Fish and Wildlife Service’s 

Wetlands Status and Trends Survey. Other indicators reflect 

targeted sampling or monitoring—for example, collecting 

water samples in an area prone to hypoxia in order to ascertain 

the extent and duration of a particular hypoxic event. In some 

cases, data are based on regulatory reporting, which may in 

turn reflect probabilistic or targeted sampling. For example, the 

ROE indicator on drinking water is based on review of monitoring conducted by water systems, with results reported by the 

states to EPA, as required by federal law.

One of the challenges in assessing the extent and condition 

of water resources is that a single data collection method is 

rarely perfect for every combination of spatial and temporal 

domains. In general, there is an inherent tradeoff in representing trends in water resources. For example, a probabilistic survey may provide an accurate representation of national trends, 

but the resolution may be too low to definitively characterize 

the resource at a smaller scale. In some cases, results can be 

disaggregated to the scale of EPA Regions or ecoregions without losing precision. However, these indicators are generally 

not designed to inform the reader about the condition of his 

or her local water bodies, for example, or the quality of locally 

harvested fish.

Likewise, it is often convenient to compare trends in terms of 

annual averages—particularly where it is not practical to collect data every day of the year. However, averaging and periodic sampling can obscure or overlook extreme events, such as 

spikes in water contaminants after a pesticide application or a 

large storm. Thus, representative extent or condition data cannot depict the full range of variations and extremes—some of 

which may be critical to ecosystems or to humans—that occur 

in smaller areas or on smaller time scales.

This chapter presents only data that meet the ROE indicator 

definition and criteria (see Box 1-1, p. 1-3). Note that nonscientific indicators, such as administrative and economic 

indicators, are not included in this definition. Thorough 

documentation of the indicator data sources and metadata 

can be found online at http://www.epa.gov/roe. All indicators were peer-reviewed during an independent peer review 

process (again, see http://www.epa.gov/roe for more information). Readers should not infer that the indicators in this 

chapter reflect the complete state of knowledge. Many other 

data sources, publications, and site-specific research projects 

have contributed substantially to the current understanding of 

status and trends in water, but are not included in this report 

because they do not meet the ROE indicator criteria.

3.1.2 Organization of This Chapter

The remainder of this chapter is organized into seven sections 

corresponding to the seven questions that EPA seeks to answer 

about trends in water. Each section introduces a question and 

discusses its importance, presents the ROE indicators used to 

help answer the question, and discusses what the indicators, 

taken together, say about the question. The ROE indicators 

include National Indicators as well as several Regional Indicators that meet the ROE definition and criteria and help to 

answer a question at a smaller geographic scale. Each section 

concludes by highlighting the major challenges to answering 

the question and identifying important information gaps.

Table 3-1 lists the indicators used to answer the seven questions in this chapter and shows the locations where the indicators are presented.
WATER

EPA’s 2008 Report on the Environment 3-5

Table 3-1. Water—ROE Questions and Indicators

Question Indicator Name Section Page

What are the trends in the extent and 

condition of fresh surface waters and 

their effects on human health and the 

environment?

High and Low Stream Flows (N)

Streambed Stability in Wadeable Streams (N)

Lake and Stream Acidity (N)

Nitrogen and Phosphorus in Wadeable Streams (N)

Nitrogen and Phosphorus in Streams in Agricultural 

Watersheds (N)

Nitrogen and Phosphorus Loads in Large Rivers (N)

Pesticides in Streams in Agricultural Watersheds (N)

Benthic Macroinvertebrates in Wadeable Streams (N)

3.2.2 3-8

3.2.2 3-11

2.2.2 2-42

3.2.2 3-13

3.2.2 3-15

3.2.2 3-17 

3.2.2 3-19

3.2.2 3-21

What are the trends in the extent 

and condition of ground water and 

their effects on human health and the 

environment?

Nitrate and Pesticides in Shallow Ground Water in 

Agricultural Watersheds (N)

3.3.2 3-27

What are the trends in the extent 

and condition of wetlands and their 

effects on human health and the 

environment?

Wetland Extent, Change, and Sources of Change (N) 3.4.2 3-32

What are the trends in the extent 

and condition of coastal waters and 

their effects on human health and the 

environment?

Wetland Extent, Change, and Sources of Change (N)

Trophic State of Coastal Waters (N/R)

Coastal Sediment Quality (N/R)

Coastal Benthic Communities (N/R)

Coastal Fish Tissue Contaminants (N/R) 

Submerged Aquatic Vegetation in the Chesapeake Bay (R)

Hypoxia in the Gulf of Mexico and Long Island Sound (R)

3.4.2 3-32

3.5.2 3-38

3.5.2 3-42

3.5.2 3-44

3.8.2 3-61

3.5.2 3-46

3.5.2 3-48

What are the trends in the quality of 

drinking water and their effects on 

human health?

Population Served by Community Water Systems with No 

Reported Violations of Health-Based Standards (N/R)

3.6.2 3-54

What are the trends in the condition 

of recreational waters and their 

effects on human health and the 

environment?

No ROE indicators 

What are the trends in the condition 

of consumable fish and shellfish and 

their effects on human health?

Coastal Fish Tissue Contaminants (N/R)

Contaminants in Lake Fish Tissue (N) 

3.8.2 3-61

3.8.2 3-63

N = National Indicator

R = Regional Indicator

N/R = National Indicator displayed at EPA Regional scale
WATER

3-6 EPA’s 2008 Report on the Environment

3.2 What Are the 

Trends in the Extent 

and Condition of 

Fresh Surface Waters 

and Their Effects on 

Human Health and the 

Environment?

3.2.1 Introduction

Though lakes, ponds, rivers, and streams hold less than one 

thousandth of a percent of the water on the planet, they 

serve many critical functions for the environment and for 

human life. These fresh surface waters sustain ecological 

systems and provide habitat for many plant and animal species. They also support a myriad of human uses, including 

drinking water, irrigation, wastewater treatment, livestock, 

industrial uses, hydropower, and recreation. Fresh surface 

waters also influence the extent and condition of other water 

resources, including ground water, wetlands, and coastal 

systems downstream.

The extent of fresh surface waters reflects the influence and 

interaction of many stressors. It can be affected by direct withdrawal for drinking, irrigation, industrial processes, and other 

human use, as well as by the withdrawal of ground water, 

which replenishes many surface waters. Hydromodifications 

such as dam construction can create new impoundments and 

fundamentally alter stream flow. Land cover can affect drainage patterns (e.g., impervious pavement may encourage runoff 

or flooding). Weather patterns—e.g., the amount of precipitation, the timing of precipitation and snowmelt, and the conditions that determine evaporation rates—also affect the extent 

of fresh surface waters. Changing climate could also affect the 

extent of fresh surface water that is available.

The condition of fresh surface waters reflects a range of characteristics. Physical characteristics include attributes such as 

temperature and clarity. Chemical characteristics include 

attributes such as salinity, nutrients, and chemical contaminants (including contaminants in sediments, which can impact 

water quality and potentially enter the aquatic food web). 

Biological characteristics include diseases, pathogens, and—in 

a broader sense—the status of plant and animal populations 

and the condition of their habitat. In addition to their effects 

on the environment, many of these characteristics can ultimately affect human health, mainly through drinking water, 

recreational activities (e.g., health effects in swimmers due 

to pathogens and harmful algal blooms), or consumption of 

fish and shellfish. Because these three topics are complex and 

encompass many types of water bodies, each is addressed in 

greater detail in its own section of this report (see Sections 3.6, 

3.7, and 3.8, respectively). 

Like extent, the condition of fresh surface waters can be influenced by a combination of natural and anthropogenic stressors, 

such as: 

•	 Point source pollution, including contaminants discharged directly into water bodies by industrial operations, as well as nutrients and contaminants in sewage. Even 

treated sewage contains nutrients that affect the chemical 

composition of the water.

•	 Nonpoint source pollution, which largely reflects contaminants, nutrients, and excess sediment in runoff from 

urban and suburban areas (e.g., stormwater) and agricultural 

land. Other sources include recreational activities (e.g., 

boating and marinas) and acid mine drainage. Nonpoint 

source pollution can be influenced by land cover (e.g., 

impervious surfaces that encourage runoff) and land use 

(e.g., certain forestry techniques and agricultural practices 

that encourage runoff and erosion). Nonpoint sources 

tend to be more variable than point sources. For example, 

pesticide concentrations in streams reflect the location and 

timing of pesticide application.

•	 Air deposition. Acidic aerosols, heavy metals, and other 

airborne contaminants may be deposited directly on water 

or may wash into water bodies after deposition on land. 

For example, mercury emitted to the air from combustion 

at power plants can be transported and deposited in lakes 

and reservoirs. 

•	 Invasive species. Invasives are non-indigenous plant and 

animal species that can harm the environment, human 

health, or the economy.1

 Invasive species can crowd out 

native species and alter the physical and chemical condition 

of water bodies.

•	 Natural factors. Precipitation determines the timing 

and amount of runoff and erosion, while other aspects of 

weather and climate influence heating, cooling, and mixing 

in lakes—which affect the movement of contaminants and 

the cycling of nutrients. The mineral composition of bedrock and sediment helps determine whether a water body 

may be susceptible to acidification.

The condition of fresh surface waters also may be influenced 

by extent. Stream flow patterns influence contaminant and 

sediment loads, while changes in the shape of water bodies—

e.g., eliminating deep pools or creating shallow impoundments—can change water temperature. The extent of surface 

waters also represents the extent of habitat—a key aspect of 

biological condition. Some plant and animal communities 

are sensitive to water level (e.g., riparian communities), while 

1 National Invasive Species Council. 2005. Five year review of Executive Order 

13112 on invasive species. Washington, DC: U.S. Department of the Interior.
WATER

EPA’s 2008 Report on the Environment 3-7

others may be adapted to particular seasonal fluctuations in 

flow. Stressors that affect extent may ultimately affect the 

condition of freshwater habitat—for example, hydromodifications that restrict the migration of certain fish species.

3.2.2 ROE Indicators

Eight ROE indicators characterize either the extent or the condition of fresh surface waters (Table 3-2). One of these indicators presents information about stream flow patterns, an aspect 

of surface water extent. The other seven indicators characterize 

various aspects of condition, including the physical condition 

of sediments, the condition of benthic communities, and the 

chemical condition of the water itself. Several of these indicators track concentrations of nutrients, which can impact many 

different types of water bodies if present in excess (e.g., through 

eutrophication). Supporting data come from several national 

monitoring programs: EPA’s Environmental Monitoring and 

Assessment Program (EMAP), EPA’s Wadeable Streams Assessment, EPA’s Temporally Integrated Monitoring of Ecosystems 

(TIME) and Long-Term Monitoring (LTM) projects, and 

three programs administered by the U.S. Geological Survey 

(USGS) (the National Water Quality Assessment [NAWQA] 

program, the National Stream Quality Accounting Network 

[NASQAN], and the USGS stream gauge network).

Table 3-2. ROE Indicators of Trends in the Extent and Condition of 

Fresh Surface Waters and Their Effects on Human Health and the Environment

National Indicators Section Page

High and Low Stream Flows 3.2.2 3-8

Streambed Stability in Wadeable Streams 3.2.2 3-11

Lake and Stream Acidity 2.2.2 2-42

Nitrogen and Phosphorus in Wadeable Streams 3.2.2 3-13

Nitrogen and Phosphorus in Streams in Agricultural Watersheds 3.2.2 3-15

Nitrogen and Phosphorus Loads in Large Rivers 3.2.2 3-17

Pesticides in Streams in Agricultural Watersheds 3.2.2 3-19

Benthic Macroinvertebrates in Wadeable Streams 3.2.2 3-21
WATER

3-8 EPA’s 2008 Report on the Environment

INDICATOR | High and Low Stream Flows

Flow is a critical aspect of the physical structure of stream ecosystems (Poff and Allan, 

1995; Robinson et al., 2002). High flows shape 

the stream channel and clear silt and debris from 

the stream, and some fish species depend on 

high flows for spawning. Low flows define the 

smallest area available to stream biota during the 

year. In some cases, the lowest flow is no flow at 

all—particularly in arid and semi-arid regions 

where intermittent streams are common. 

Riparian vegetation and aquatic life in intermittent streams have evolved to complete their life 

histories during periods when water is available; 

however, extended periods of no flow can still 

impact their survival (Fisher, 1995). Changes in 

flow can be caused by dams, water withdrawals, 

ground water pumping (which can alter base 

flow), changes in land cover (e.g., deforestation or urbanization), and weather and climate 

(Calow and Petts, 1992). 

This indicator, developed by the Heinz Center (in press), describes trends in stream flow 

volumes based on daily flow data collected by 

the U.S. Geological Survey’s (USGS’s) nationwide network of stream flow gauging sites 

from 1961 to 2006.

The first part of this indicator describes 

trends in high flow volume, low flow volume, 

and variability of flow in streams throughout 

the contiguous 48 states, relative to a baseline 

period of 1941-1960. Data were collected at 

two sets of USGS stream gauging stations: a 

set of approximately 700 “reference” streams 

that have not been substantially affected by 

dams and diversions and have had little change 

in land use over the measurement period, and 

a separate set of approximately 1,000 “nonreference” streams that reflect a variety of 

conditions (the exact number of sites with sufficient data varies from one metric to another). 

The indicator is based on each site’s annual 

3-day high flow volume, 7-day low flow volume, and variability (computed as the difference between 

the 1st and 99th percentile 1-day flow volumes in a given 

year, divided by the median 1-day flow). Annual values 

for each metric were examined using a rolling 5-year 

window to reduce the sensitivity to anomalous events. For 

each site, the median value for the 5-year window was 

compared to the median value for the 1941-1960 baseline 

period. The indicator shows the proportion of sites where 

high flow, low flow, or variability of flow was more than 

30 percent higher or 30 percent lower than the baseline. It 

also shows differences of more than 60 percent.

This indicator also examines no-flow periods in streams 

in grassland and shrubland areas of the contiguous 48 states. 

Data represent 280 USGS “reference” and “non-reference” 

stream gauging sites in watersheds with at least 50 percent 

grass or shrub cover, as defined by the 2001 National Land 

Cover Database (NLCD) (MRLC Consortium, 2007). The 

indicator reports the percentage of these streams with at 

least one no-flow day in a given year, averaged over a rolling 5-year window. Results are displayed for all grassland/

shrubland streams, as well as for three specific ecoregion 

divisions (Bailey, 1995). This indicator also reports on the 

duration of no-flow periods. For a subset of 163 grassland/

Non-reference 

streams

Reference 

streams

Non-reference

streams

Reference 

streams

>30% increase

Data source: Heinz Center, 2007

Exhibit 3-1. Changes in high flow in rivers and streams of 

the contiguous U.S., 1961-2006, compared with 1941-1960 

baselinea,b 

A. Increased high flow volume

a

Coverage: 1,719 stream gauging sites (712 reference, 1,007 non-reference) in the 

contiguous U.S. with flow data from 1941 to 2006. Reference streams have not 

been substantially affected by dams and diversions; non-reference streams may or 

may not have been affected in this way. 

b

Based on the annual 3-day high flow. For each stream site, the median high flow 

was determined over a rolling 5-year window, then compared against the baseline. 

Results are plotted at the midpoint of each window. For example, the value for 

2002-2006 is plotted at the year 2004. 

 

1960 2010

2010

B. Decreased high flow volume

Year

Year

Percent of stream sites 

>60% increase

0

10

20

30

40

50

Percent of stream sites 

0

10

20

30

40

50

Non-reference 

streams

Reference 

streams

Non-reference

streams

Reference 

streams

>60% decrease

>30% decrease

1970 1980 1990 2000

1960 1970 1980 1990 2000
WATER

EPA’s 2008 Report on the Environment 3-9

INDICATOR | High and Low Stream Flows (continued)

shrubland streams that had at least one no-flow 

day during the study period, the duration of 

the maximum no-flow period in each year was 

averaged over a rolling 5-year window and 

compared with the average no-flow duration 

for the same site during the 1941-1960 baseline 

period. A no-flow period more than 14 days 

longer than the baseline was described as a 

“substantial increase”; a no-flow period more 

than 14 days shorter than the baseline was classified as a “substantial decrease.”

What the Data Show

In an average year during the period of 

record, roughly 20 percent of streams had 

increases in high flow volume of more than 

30 percent, relative to the 1941-1960 baseline 

(Exhibit 3-1, panel A). A similar percentage had decreases of more than 30 percent 

(Exhibit 3-1, panel B). Large fluctuations in 

high flow volume are apparent over time, 

with both sets of trends suggesting relatively 

wet periods in the early 1980s and mid-1990s 

and relatively dry periods around 1990 and 

the early 2000s. Reference and non-reference 

stream sites show similar patterns, although 

larger decreases in high flow volume were 

more common in the non-reference streams.

Since the early 1960s, more streams have 

shown increases in low flow volumes than have 

shown decreases, relative to the 1941-1960 

baseline period (Exhibit 3-2). Among the many 

streams with larger low flows are a few (2 to 

4 percent in an average year) with increases of 

more than 600 percent. Fluctuations over time 

are apparent, and while not as pronounced 

as the shifts in high flow (Exhibit 3-1), they 

generally tend to mirror the same relatively wet 

and dry periods. Reference and non-reference 

streams show similar low flow patterns over 

time, but reference sites are less likely to have 

experienced decreases in low flow.

Except for a few brief periods in the mid-1960s and again 

around 1980, decreased flow variability has been much more 

common than increased variability (Exhibit 3-3). Reference and non-reference streams have shown similar patterns 

in variability over time, although reference streams were 

slightly less likely to experience changes overall.

In areas with primarily grass or shrub cover, roughly 15 to 

20 percent of stream sites typically have experienced periods 

of no flow in a given year (Exhibit 3-4). Overall, the number 

of streams experiencing no-flow periods has declined slightly 

since the 1960s. Streams in the California/Mediterranean 

ecoregion have shown the greatest decrease in no-flow frequency, but they still experience more no-flow periods than 

streams in the other two major grassland/shrubland ecoregion 

divisions. Among grassland/shrubland streams that have experienced at least one period of no flow since 1941, more streams 

have shown a substantial decrease in the duration of no-flow 

periods (relative to the 1941-1960 baseline) than a substantial 

increase (Exhibit 3-5).

Indicator Limitations

•	The 1941-1960 baseline period was chosen to maximize 

the number of available reference sites and should 

Non-reference 

streams

Reference 

streams

Non-reference

streams

Reference 

streams

>30% increase

Non-reference

streams

Reference 

streams

Data source: Heinz Center, 2007

Exhibit 3-2. Changes in low flow in rivers and streams of 

the contiguous U.S., 1961-2006, compared with 1941-1960 

baselinea,b 

A. Increased low flow volume

a

Coverage: 1,609 stream gauging sites (673 reference, 936 non-reference) in the 

contiguous U.S. with flow data from 1941 to 2006. Reference streams have not 

been substantially affected by dams and diversions; non-reference streams may or 

may not have been affected in this way. 

b

Based on the annual 7-day low flow. For each stream site, the median low flow was 

determined over a rolling 5-year window, then compared against the baseline. 

Results are plotted at the midpoint of each window. For example, the value for 

2002-2006 is plotted at the year 2004. 

 

1960 2010

2010

B. Decreased low flow volume

Year

Year

Percent of stream sites

>60% increase

>600% increase

Percent of stream sites

Non-reference 

streams

Reference 

streams

Non-reference

streams

Reference 

streams

>60% decrease

>30% decrease

1970 1980 1990 2000

1960 1970 1980 1990 2000

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

70
WATER

3-10 EPA’s 2008 Report on the Environment

INDICATOR | High and Low Stream Flows (continued)

provide a sufficiently long window to account 

for natural variability (Heinz Center, in 

press); however, it does not necessarily reflect 

“undisturbed” conditions. Many dams and 

waterworks had already been constructed by 

1941, and other anthropogenic changes (e.g., 

urbanization) were already widespread.

•	 Although the sites analyzed here are spread 

widely throughout the contiguous U.S., 

gauge placement by USGS is not a random 

process. Gauges are generally placed on larger, 

perennial streams and rivers, and changes seen 

in these larger systems may differ from those 

seen in smaller streams and rivers.

•	This indicator does not characterize trends 

in the timing of high and low stream flows, 

which can affect species migration, reproduction, and other ecological processes. 

Data Sources

The data presented in this indicator were provided by the Heinz Center (2007), which conducted this analysis for a forthcoming update 

to its report, The State of the Nation’s Ecosystems

(Heinz Center, in press). Underlying stream 

flow measurements can be obtained from the 

USGS National Water Information System 

database (USGS, 2007) (http://waterdata.usgs.

gov/nwis).

References

Bailey, R.G. 1995. Description of the ecoregions of the United States. Second edition. 

Misc. Publ. No. 1391 (rev). Washington, DC: 

USDA Forest Service. <http://www.fs.fed.us/

land/ecosysmgmt/ecoreg1_home.html>

Calow, P., and G.E. Petts, eds. 1992. 

The rivers handbook: Hydrological and 

ecological principles. Volume 1. Oxford, UK: 

Blackwell Scientific.

Fisher, S.G. 1995. Stream ecosystems of the 

western United States. In: Cushing, C.E., K.W. Cummings, and G.W. Minshall, eds. River and stream ecosystems, ecosystems of the world 22. New York, NY: 

Elsevier.

Heinz Center (The H. John Heinz III Center for Science, 

Economics, and the Environment). 2007. Data provided to 

EPA by Anne Marsh, Heinz Center. October 15, 2007.

Heinz Center. In press. The state of the nation’s ecosystems: Measuring the lands, waters, and living resources of 

the United States. 2007 update. 

MRLC Consortium. 2007. National Land Cover Database 

2001 (NLCD 2001). Accessed 2007. 

<http://www.mrlc.gov/nlcd.php> 

Poff, N.L., and J.D. Allan. 1995. Functional organization 

of stream fish assemblages in relation to hydrologic variability. Ecology 76:606-627.

Robinson, C.T., K. Tockner, and J.V. Ward. 2002. The fauna 

of dynamic riverine landscapes. Freshwater Biol. 47:661-677.

USGS (United States Geological Survey). 2007. National 

Water Information System. Accessed 2007. 

<http://waterdata.usgs.gov/nwis>

Non-reference 

streams

Reference 

streams

Non-reference

streams

Reference 

streams

>30% increase

Data source: Heinz Center, 2007

Exhibit 3-3. Changes in flow variability in rivers and streams 

of the contiguous U.S., 1961-2006, compared with 

1941-1960 baselinea,b 

A. Increased flow variability

a

Coverage: 1,754 stream gauging sites (733 reference, 1,021 non-reference) in the 

contiguous U.S. with flow data from 1941 to 2006. Reference streams have not 

been substantially affected by dams and diversions; non-reference streams may or 

may not have been affected in this way. 

b

Based on the annual range of 1-day flows. For each stream site, the median 

variability was determined over a rolling 5-year window, then compared against the 

baseline. Results are plotted at the midpoint of each window. For example, the value 

for 2002-2006 is plotted at the year 2004.

1960 2010

2010

B. Decreased flow variability

Year

Year

Percent of stream sites 

>60% increase

0

10

20

30

40

50

Percent of stream sites 

0

10

20

30

40

50

Non-reference 

streams

Reference 

streams

Non-reference

streams

Reference 

streams

>60% decrease

>30% decrease

1970 1980 1990 2000

1960 1970 1980 1990 2000
WATER

EPA’s 2008 Report on the Environment 3-11

INDICATOR | High and Low Stream Flows (continued)

Exhibit 3-4. Percent of grassland/shrubland 

streams in the contiguous U.S. experiencing 

periods of no flow, by ecoregion, 1961-2006a,b

a

Coverage: 280 stream gauging sites in watersheds containing 50 

percent or greater grass/shrub cover, with flow data from 1941 to 

2006. Grass/shrub cover refers to classes 52 and 71 of the 2001 

National Land Cover Database (NLCD).

b

Streams were classified based on annual data, then the 

percentage of streams in each category was averaged over a 

rolling 5-year window. Results are plotted at the midpoint of each 

window. For example, the average for 2002-2006 is plotted at the 

year 2004.

c

Ecoregions based on Bailey (1995).

Data source: Heinz Center, 2007

California/

Mediterranean

Ecoregion divisions

Grassland/ 

steppe

Desert/shrub

0

20

40

60

80

100

1960 1970 1980 1990 2000 2010

Year

Percent of stream sites

California/Mediterranean

Desert/shrub

Grassland/steppe

All three of these ecoregions

Ecoregion:c

Exhibit 3-5. Changes in the maximum duration 

of no-flow periods in intermittent grassland/ 

shrubland streams of the contiguous U.S., 

1961-2006, compared with 1941-1960 baselinea,b

a

Coverage: 163 stream gauging sites in 

watersheds containing 50 percent or greater 

grass/shrub cover, with flow data from 

1941 to 2006 and at least one no-flow day 

during this period. Grass/shrub cover refers 

to classes 52 and 71 of the 2001 National 

Land Cover Database (NLCD).

b

For each stream site, the duration of the maximum no-flow period 

in each year was averaged over a rolling 5-year window. Results 

are plotted at the midpoint of each window. For example, the value 

for 2002-2006 is plotted at the year 2004. 

c

A substantial increase means the no-flow period was more than 14 

days longer than the average duration during the 1941-1960 

baseline period; a substantial decrease means the no-flow period 

was more than 14 days shorter.

Data source: Heinz Center, 2007

0

20

40

60

80

100

1960 1970 1980 1990 2000 2010

Year

Percent of stream sites

Substantial

increasec

Substantial

decreasec

v

INDICATOR | Streambed Stability in Wadeable Streams

S treams and rivers adjust their channel shapes and particle sizes in response to the supply of water and 

sediments from their drainage areas, and this in turn can 

affect streambed stability. Lower-than-expected streambed 

stability is associated with excess sedimentation, which 

may result from inputs of fine sediments from erosion—

including erosion caused by human activities such as agriculture, road building, construction, and grazing. Unstable 

streambeds may also be caused by increases in flood 

magnitude or frequency resulting from hydrologic alterations. Lower-than-expected streambed stability may cause 

stressful ecological conditions when, for example, excessive 

amounts of fine, mobile sediments fill in the habitat spaces 

between stream cobbles and boulders. When coupled with 

increased stormflows, unstable streambeds may also lead to 

channel incision and arroyo formation, and can negatively 

affect benthic invertebrate communities and fish spawning (Kaufmann et al., 1999). The opposite condition—an 

overly stable streambed—is less common, and generally 

reflects a lack of small sediment particles. Overly stable 

streambeds can result from reduced sediment supplies or 
WATER

3-12 EPA’s 2008 Report on the Environment

INDICATOR | Streambed Stability in Wadeable Streams (continued)

stream flows, or from prolonged conditions of high sediment transport without an increase in sediment supply.

This indicator is based on the Relative Bed Stability 

(RBS), which is one measure of the interplay between sediment supply and transport. RBS is the ratio of the observed 

mean streambed particle diameter to the “critical diameter,” 

the largest particle size the stream can move as bedload 

during storm flows. The critical diameter is calculated from 

field measurements of the size, slope, and other physical characteristics of the stream channel (Kaufmann et al., 

1999). A high RBS score indicates a coarser, more stable 

bed—i.e., streambed particles are generally much larger than 

the biggest particle the stream could carry during a storm 

flow. A low RBS score indicates a relatively unstable streambed, consisting of many fine particles that could be carried 

away by a storm flow. Expected values of RBS are based on 

the statistical distribution of values observed at reference sites 

that are known to be relatively undisturbed. RBS values that 

are substantially lower than the expected range are considered to be indicators of ecological stress.

This indicator is based on data collected for EPA’s Wadeable Streams Assessment (WSA). Wadeable streams are 

streams, creeks, and small rivers that are shallow enough 

to be sampled using methods that involve wading into 

the water. They typically include waters classified as 1st

through 4th order in the Strahler Stream Order classification system (Strahler, 1952). The WSA is based on a probabilistic design, so the results from representative sample 

sites can be used to make a statistically valid statement 

about streambed stability in wadeable streams nationwide. 

Crews sampled 1,392 randomized sites throughout 

the U.S. using standardized methods (U.S. EPA, 2004). 

Western sites were sampled between 2000 and 2004; 

eastern and central sites were all sampled in 2004. Sites 

were sampled between mid-April and mid-November. At 

each site, crews measured substrate particle size, streambed 

dimensions, gradient, and stream energy dissipators (e.g., 

pools and woody debris), then used these factors to calculate the RBS.

Because streambed characteristics vary geographically, 

streams were divided into nine broad ecoregions (U.S. EPA, 

2006b), which were defined by the WSA based on groupings of EPA Level III ecoregions (Omernik, 1987; U.S. EPA, 

2007). In each ecoregion, a set of relatively undisturbed sites 

was sampled in order to determine the range of RBS values 

that would be expected among “least disturbed” streams. 

Next, the RBS for every site was compared to the distribution of RBS values among the ecoregion’s reference sites. 

If the observed RBS for a sample site was below the 5th or 

the 10th percentile of the regional reference distribution 

(depending on the ecoregion), the site was classified as “most 

disturbed.” This threshold was used because it offers a high 

degree of confidence that the observed condition is statistically different from the “least disturbed” reference condition. Any stream with an RBS above the 25th percentile of 

the reference range was labeled “least disturbed,” indicating a high probability that the site is similar to the relatively undisturbed reference sites. Streams falling between 

the 5th and 25th percentiles were classified as “moderately 

disturbed.” Note that the “least disturbed” category may 

include some streams with higher-than-expected RBS 

values, which represent overly stable streambeds. Because it 

is more difficult to determine whether overly stable streambeds are “natural” or result from anthropogenic factors, this 

indicator only measures the prevalence of unstable streambeds 

(i.e., excess sedimentation). 

What the Data Show

Roughly 50 percent of wadeable stream miles are classified 

as “least disturbed” with respect to streambed condition; 

that is, their streambed stability is close to or greater than 

what would be expected (Exhibit 3-6). Conversely, 25 percent of the nation’s wadeable streambeds are significantly 

less stable than regional reference conditions for streambed 

stability (“most disturbed”), and an additional 20 percent 

are classified as “moderately disturbed.” Approximately 5 

percent of the nation’s stream length could not be assessed 

because of missing or inadequate sample data.

Indicator Limitations

•	 Samples were taken one time from each sampling 

location during the index period (April-November). 

Although the probability sampling design results in unbiased estimates for relative streambed stability in wadeable 

streams during the study period, RBS values may be 

different during other seasons and years because of variations in hydrology.

Exhibit 3-6. Streambed stability in wadeable 

streams of the contiguous U.S., 2000-2004a

50.1

19.7

24.9

5.3

0

20

40

60

80

100

Percent of stream miles

Least disturbed

Moderately disturbed

Not assessed/no data

a

Compared with minimally 

disturbed reference sites. 

See text for definitions of the 

categories shown in the figure.

Data source: U.S. EPA, 2006b

Most disturbed
WATER

EPA’s 2008 Report on the Environment 3-13

INDICATOR | Streambed Stability in Wadeable Streams (continued)

•	Trend data are unavailable because this is the first time 

that a survey on this broad scale has been conducted, and 

the survey design does not allow trends to be calculated 

within a single sampling period (2000-2004). These data 

will serve as a baseline for future surveys. 

Data Sources

Aggregate data for this indicator were provided by EPA’s 

Wadeable Streams Assessment (U.S. EPA, 2006b). Data 

from individual stream sites can be obtained from EPA’s 

STORET database (U.S. EPA, 2006a) (http://www.epa.

gov/owow/streamsurvey/web_data.html). 

References

Kaufmann, P.R., P. Levine, E.G. Robison, C. Seeliger, and 

D. Peck. 1999. Quantifying physical habitat in wadeable 

streams. EPA/620/R-99/003. Washington, DC: U.S. Environmental Protection Agency. <http://www.epa.gov/emap/

html/pubs/docs/groupdocs/surfwatr/field/phyhab.pdf>

Omernik, J.M. 1987. Ecoregions of the conterminous 

United States. Map (scale 1:7,500,000). Ann. Assoc. Am. 

Geog. 77(1):118-125.

Strahler, A.N. 1952. Dynamic basis of geomorphology. 

Geol. Soc. Am. Bull. 63:923-938.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Level III ecoregions of the conterminous 

United States. Accessed November 2007. 

<http://www.epa.gov/wed/pages/ecoregions/level_iii.htm>

U.S. EPA. 2006a. Data from the Wadeable Streams Assessment. Accessed 2006. 

<http://www.epa.gov/owow/streamsurvey/web_data.html>

U.S. EPA. 2006b. Wadeable Streams Assessment: A collaborative survey of the nation’s streams. EPA/841/B-06/002. 

<http://www.epa.gov/owow/streamsurvey/pdf/WSA_

Assessment_May2007.pdf>

U.S. EPA. 2004. Wadeable Streams Assessment: Field 

operations manual. EPA/841/B-04/004. <http://www.

epa.gov/owow/monitoring/wsa/wsa_fulldocument.pdf>

v

INDICATOR | Nitrogen and Phosphorus in Wadeable Streams

Nitrogen and phosphorus are essential elements in aquatic ecosystems. Both nutrients are used by plants 

and algae for growth (U.S. EPA, 2005). Excess nutrients, 

however, can lead to increased algal production, and excess 

nutrients in streams can also affect lakes, larger rivers, and 

coastal waters downstream. In addition to being visually 

unappealing, excess algal growth can contribute to the loss 

of oxygen needed by fish and other animals, which in turn 

can lead to altered biological assemblages. Sources of excess 

nutrients include municipal sewage and septic tank drainfields, agricultural runoff, excess fertilizer application, and 

atmospheric deposition of nitrogen (Herlihy et al., 1998). 

This indicator measures total phosphorus and total nitrogen based on data collected for EPA’s Wadeable Streams 

Assessment (WSA). Wadeable streams—streams, creeks, 

and small rivers that are shallow enough to be sampled 

using methods that involve wading into the water—represent a vital linkage between land and water. They typically include waters classified as 1st through 4th order in the 

Strahler Stream Order classification system (Strahler, 1952). 

The WSA is based on a probabilistic design, so the results 

from representative sample sites can be used to make a 

statistically valid statement about nitrogen and phosphorus 

concentrations in all of the nation’s wadeable streams.

Crews sampled 1,392 randomized sites across the United 

States using standardized methods. Western sites were 

sampled between 2000 and 2004; eastern and central sites 

were all sampled in 2004. All sites were sampled between 

mid-April and mid-November. At each site, a water sample 

was collected at mid-depth in the stream and analyzed following standard laboratory protocols (U.S. EPA, 2004a,b). 

Because naturally occurring nutrient levels vary from 

one geographic area to another, streams were divided into 

nine broad ecoregions (U.S. EPA, 2006b), which were 

defined by the WSA based on groupings of EPA Level 

III ecoregions (Omernik, 1987; U.S. EPA, 2007). In each 

ecoregion, a set of relatively undisturbed sites was sampled 

in order to determine the range of nutrient concentrations that would be considered “low.” Next, observed 

nitrogen and phosphorus concentrations from all sites were 

compared to the distribution of concentrations among the 

ecoregion’s reference sites. If the observed result was above 

the 95th percentile of the ecoregion’s reference distribution, the concentration was labeled “high.” This threshold 

was used because it offers a high degree of confidence that 

the observed condition is statistically different from the 

condition of the reference streams. Concentrations below 

the 75th percentile of the reference range were labeled 
WATER

3-14 EPA’s 2008 Report on the Environment

INDICATOR | Nitrogen and Phosphorus in Wadeable Streams (continued)

“low,” indicating a high probability that the site is similar 

to the relatively undisturbed reference sites. Concentrations 

falling between the 75th and 95th percentiles were labeled 

“moderate.”

What the Data Show

Nationwide, 43.3 percent of wadeable stream miles had 

low total nitrogen concentrations, while high nitrogen 

concentrations were found in 31.8 percent of stream miles 

(Exhibit 3-7). The results for total phosphorus are similar to those for nitrogen, with low concentrations in 48.8 

percent of stream miles and high concentrations in 30.9 

percent (Exhibit 3-7). The concentrations associated with 

the regional thresholds vary because of natural differences among the ecoregions. Approximately 4 percent of 

the nation’s wadeable stream length could not be assessed 

because of missing or inadequate sample data.

Indicator Limitations

•	 Samples were taken one time from each sampling 

location during the index period (April-November). 

Although the probability sampling design results in an 

unbiased estimate for total nitrogen and phosphorus concentrations in wadeable streams during the study period, 

concentrations may be different during other seasons.

•	Trend data are unavailable because this is the first time 

that a survey on this broad scale has been conducted, and 

the survey design does not allow trends to be calculated 

within a single sampling period (2000-2004). These data 

will serve as a baseline for future surveys.

•	 Not all forms of nitrogen and phosphorus are equally 

bioavailable, and the ratio of nitrogen to phosphorus 

can affect the biomass and type of species of algae in 

streams. The forms of nitrogen and phosphorus and the 

nitrogen:phosphorus ratios may vary somewhat between 

the regional reference sites and the WSA streams. 

Data Sources

Aggregate data for this indicator were provided by the 

WSA (U.S. EPA, 2006b). Data from individual stream 

sites can be obtained from EPA’s STORET database (U.S. 

EPA, 2006a) (http://www.epa.gov/owow/streamsurvey/

web_data.html).

References

Herlihy, A.T., J.L. Stoddard, and C.B. Johnson. 1998. The 

relationship between stream chemistry and watershed land 

use data in the Mid-Atlantic region. US Water Air Soil 

Pollut. 105:377-386.

Omernik, J.M. 1987. Ecoregions of the conterminous 

United States. Map (scale 1:7,500,000). Ann. Assoc. Am. 

Geog. 77(1):118-125.

Strahler, A.N. 1952. Dynamic basis of geomorphology. 

Geol. Soc. Am. Bull. 63:923-938.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Level III ecoregions of the conterminous 

United States. Accessed November 2007. <http://www.

epa.gov/wed/pages/ecoregions/level_iii.htm>

U.S. EPA. 2006a. Data from the Wadeable Streams 

Assessment. Accessed 2006. <http://www.epa.gov/owow/

streamsurvey/web_data.html>

U.S. EPA. 2006b. Wadeable Streams Assessment: A collaborative survey of the nation’s streams. EPA/841/B-06/002.

<http://www.epa.gov/owow/streamsurvey/pdf/WSA_

Assessment_May2007.pdf>

U.S. EPA. 2005. National estuary program—challenges 

facing our estuaries. Key management issues: Nutrient overloading. <http://www.epa.gov/owow/estuaries/

about3.htm>

U.S. EPA. 2004a. Wadeable Streams Assessment: Field 

operations manual. EPA/841/B-04/004. <http://www.

epa.gov/owow/monitoring/wsa/wsa_fulldocument.pdf>

U.S. EPA. 2004b. Wadeable Streams Assessment: Water 

chemistry laboratory manual. EPA/841/B-04/008. 

<http://www.epa.gov/owow/monitoring/wsa/WRS_lab_

manual.pdf> 

Exhibit 3-7. Nitrogen and phosphorus in 

wadeable streams of the contiguous U.S., 

2000-2004a

Low

Moderate

0

20

40

60

80

100

A. Total nitrogen B. Total phosphorus

Percent of stream miles

48.8

16.1

30.9

43.3

20.7

31.8

Concentration:

a

Compared with minimally disturbed reference sites. See text for 

definitions of the categories shown in the figure.

Data source: U.S. EPA, 2006b

High

Not assessed/

no data

4.2 4.2

v
WATER

EPA’s 2008 Report on the Environment 3-15

Nitrogen is a critical nutrient that is generally used and reused by plants within natural ecosystems, with 

minimal “leakage” into surface or ground water, where 

nitrogen concentrations remain very low (Vitousek et al., 

2002). When nitrogen is applied to the land in amounts 

greater than can be incorporated into crops or lost to the 

atmosphere through volatilization or denitrification, however, nitrogen concentrations in streams can increase. The 

major sources of excess nitrogen in predominantly agricultural watersheds are fertilizer and animal waste; other 

sources include septic systems and atmospheric deposition. 

The total nitrogen concentration in streams consists of 

nitrate, the most common bioavailable form; organic nitrogen, which is generally less available to biota; and nitrite 

and ammonium compounds, which are typically present 

at relatively low levels except in highly polluted situations. 

Excess nitrate is not toxic to aquatic life, but increased 

nitrogen may result in overgrowth of algae, which can 

decrease the dissolved oxygen content of the water, thereby 

harming or killing fish and other aquatic species (U.S. 

EPA, 2005). Excess nitrogen also can lead to problems in 

downstream coastal waters, as discussed further in the N 

and P Loads in Large Rivers indicator (p. 3-17).

Phosphorus also is an essential nutrient for all life forms, 

but at high concentrations the most biologically active form 

of phosphorus (orthophosphate) can cause water quality 

problems by overstimulating the growth of algae. In addition to being visually unappealing and causing tastes and 

odors in water supplies, excess algal growth can contribute 

to the loss of oxygen needed by fish and other animals. 

Elevated levels of phosphorus in streams can result from 

fertilizer use, animal wastes and wastewater, and the use of 

phosphate detergents. The fraction of total phosphorus not 

in the orthophosphate form consists of organic and mineral 

phosphorus fractions whose bioavailability varies widely.

This indicator reports nitrogen and phosphorus concentrations in stream water samples collected from 1992 to 

2001 by the U.S. Geological Survey’s (USGS’s) National 

Water Quality Assessment (NAWQA) program, which 

surveys the condition of streams and aquifers in study 

units throughout the contiguous U.S. Specifically, this 

indicator reflects the condition of 129 to 133 streams 

draining watersheds where agriculture is the predominant 

land use (the exact number of sites with available data 

depends on the analyte), according to criteria outlined in 

Mueller and Spahr (2005). These watersheds are located 

in 36 of the 51 NAWQA study units (i.e., major river 

basins). Sites were chosen to avoid large point sources 

of nutrients (e.g., wastewater treatment plants). At each 

stream site, samples were collected 12 to 25 times each 

year over a 1-to-3-year period; this indicator is based on 

a flow-weighted annual average of those samples. Related 

indicators report the concentrations of nitrogen and 

phosphorus in small wadeable streams, regardless of land 

use (p. 3-13), and nitrate concentrations in ground water 

in agricultural watersheds (p. 3-15).

For nitrogen, the indicator reports the percentage of 

streams with average concentrations of nitrate and total 

nitrogen in one of five ranges: less than 1 milligram per liter 

(mg/L); 1-2 mg/L; 2-6 mg/L; 6-10 mg/L; and 10 mg/L or 

more. This indicator measures nitrate as N, i.e., the fraction of the material that is actually nitrogen. Measurements 

actually include nitrate plus nitrite, but because concentrations of nitrite are typically insignificant relative to nitrate, 

this mixture is simply referred to as nitrate. Naturally 

occurring levels of nitrate and total nitrogen vary substantially across the country, and statistical analyses of water 

quality data suggest that appropriate reference levels range 

from 0.12 to 2.2 mg/L total N, such that some streams in 

the lowest category (less than 1 mg/L) may still exceed recommended water quality criteria (U.S. EPA, 2002).

Concentrations of total phosphorus and orthophosphate 

(as P) are reported in four ranges: less than 0.1 mg/L, 0.1-0.3 

mg/L, 0.3-0.5 mg/L, and 0.5 mg/L or more. There is currently no national water quality criterion for either form to 

protect surface waters because the effects of phosphorus vary 

by region and are dependent on physical factors such as the 

a

Coverage: Nitrate data from 130 stream sites; total nitrogen data 

from 133 stream sites. Stream sites are in watersheds where 

agriculture is the predominant land use. These watersheds are 

within 36 major river basins studied by the USGS NAWQA 

program.

b

Totals may not add to 100% due to rounding.

Data source: Mueller and Spahr, 2005

Exhibit 3-8. Nitrogen in streams in agricultural 

watersheds of the contiguous U.S., 1992-2001a,b

A. Nitrate (as N)

0

20

40

60

80

100

Percent of stream sites

B. Total nitrogen

6 to <10 

mg/L

2 to <6

mg/L

1 to <2

mg/L

<1 mg/L

Concentration:

 10 mg/L

13.1

10.8

36.2

17.7

22.3

9.8

21.8

46.6

16.5

5.3

INDICATOR Nitrogen and Phosphorus in Streams in Agricultural 

Watersheds
WATER

3-16 EPA’s 2008 Report on the Environment

size, hydrology, and depth of rivers and lakes. Nuisance algal 

growths are not uncommon in rivers and streams below 

the low reference level (0.1 mg/L) for phosphorus in this 

indicator, however (Dodds and Welch, 2000), and statistical analyses of water quality data suggest that more appropriate reference levels for total P range from 0.01 to 0.075 

mg/L, depending on the ecoregion (U.S. EPA, 2002). Some 

streams in the lowest category may exceed these recommended water quality criteria. 

What the Data Show

Average flow-weighted nitrate concentrations were 2 mg/L 

or above in about 60 percent of stream sites in these predominantly agricultural watersheds (Exhibit 3-8). About 

13 percent of stream sites had nitrate concentrations of at 

least 10 mg/L (the slightly smaller percentage of streams 

with total N above 10 mg/L is an artifact of the flowweighting algorithm). Nearly half of the streams sampled 

had total nitrogen concentrations in the 2-6 mg/L range, 

and 78 percent had concentrations of 2 mg/L or above. 

Nearly half of the streams in agricultural watersheds 

had average annual flow-weighted concentrations of 

orthophosphate (as P) of at least 0.1 mg/L (Exhibit 3-9). 

Approximately 85 percent of the streams had concentrations of total phosphorus of 0.1 mg/L or above, while 13 

percent had at least 0.5 mg/L total phosphorus. 

Indicator Limitations

•	These data represent streams draining agricultural watersheds in 36 of the major river basins (study units) sampled 

by the NAWQA program in the contiguous U.S. While 

they were chosen to be representative of agricultural 

watersheds across the United States, they are the result 

of a targeted sample design, and may not be an accurate 

reflection of the distribution of concentrations in all 

streams in agricultural watersheds in the U.S.

•	This indicator does not provide information about trends 

over time, as the NAWQA program has completed only 

one full sampling cycle to date. Completion of the next 

round of sampling will allow trend analysis, using the 

data presented here as a baseline. 

Data Sources

Summary data for this indicator were provided by USGS’s 

NAWQA program. These data have been published in 

Mueller and Spahr (2005), along with the individual sampling results on which the analysis is based.

References

Dodds, W.K., and E. Welch. 2000. Establishing nutrient 

criteria in streams. J. No. Am. Benthol. Soc. 19:186-196.

Mueller, D.K., and N.E. Spahr. 2005. Water-quality, 

streamflow, and ancillary data for nutrients in streams and 

rivers across the nation, 1992-2001: U.S. Geological Survey data series 152. <http://pubs.usgs.gov/ds/2005/152/>

U.S. EPA (United States Environmental Protection 

Agency). 2005. National estuary program—challenges 

facing our estuaries. Key management issues: Nutrient 

overloading. 

<http://www.epa.gov/owow/estuaries/about3.htm>

U.S. EPA. 2002. Summary table for the nutrient criteria 

documents. Accessed November 2007. <http://www.

epa.gov/waterscience/criteria/nutrient/ecoregions/files/

sumtable.pdf>

Vitousek, P., H. Mooney, L. Olander, and S. Allison. 2002. 

Nitrogen and nature. Ambio 31:97-101.

A. Orthophosphate

(as P)

Percent of stream sites

B. Total phosphorus

0

20

40

60

80

100

a

Coverage: Orthophosphate data from 132 stream sites; total 

phosphorus data from 129 stream sites. Stream sites are in 

watersheds where agriculture is the predominant land use. 

These watersheds are within 36 major river basins studied by 

the USGS NAWQA program.

b

Totals may not add to 100% due to rounding.

Data source: Mueller and Spahr, 2005

Exhibit 3-9. Phosphorus in streams in 

agricultural watersheds of the contiguous U.S., 

1992-2001a,b

40.9

54.5

1.5

3.0

13.2

24.8

46.5

15.5

 0.5 mg/L

0.3 to <0.5

mg/L

0.1 to <0.3

mg/L

<0.1 mg/L

Concentration: 

v

INDICATOR Nitrogen and Phosphorus in Streams in Agricultural 

Watersheds (continued)
WATER

EPA’s 2008 Report on the Environment 3-17

INDICATOR | Nitrogen and Phosphorus Loads in Large Rivers

Nitrogen is a critical nutrient for plants and animals, and terrestrial ecosystems and headwater streams have 

a considerable ability to capture nitrogen or to reduce it 

to N2 gas though the process of denitrification. Nitrogen 

cycling and retention is thus one of the most important 

functions of ecosystems (Vitousek et al., 2002). When 

loads of nitrogen from fertilizer, septic tanks, and atmospheric deposition exceed the capacity of terrestrial systems 

(including croplands), the excess may enter surface waters, 

where it may have “cascading” harmful effects as it moves 

downstream to coastal ecosystems (Galloway and Cowling, 2002). Other sources of excess nitrogen include direct 

discharges from storm water or treated wastewater. This 

indicator specifically focuses on nitrate, which is one of the 

most bioavailable forms of nitrogen in bodies of water.

Phosphorus is a critical nutrient for all forms of life, but 

like nitrogen, phosphorus that enters the environment from 

anthropogenic sources may exceed the needs and capacity 

of the terrestrial ecosystem. As a result, excess phosphorus 

may enter lakes and streams. Because phosphorus is often 

the limiting nutrient in these bodies of water, an excess may 

contribute to unsightly algal blooms, which cause taste and 

odor problems and deplete oxygen needed by fish and other 

aquatic species. In some cases, excess phosphorus can combine with excess nitrogen to exacerbate algal blooms (i.e., in 

situations where algal growth is co-limited by both nutrients), although excess nitrogen usually has a larger effect 

downstream in coastal waters. The most common sources of 

phosphorus in rivers are fertilizer and wastewater, including storm water and treated wastewater discharged directly 

into the river. In most watersheds, the atmosphere is not an 

important source or sink for phosphorus.

This indicator tracks trends in nitrate and phosphorus 

loads carried by four of the largest rivers in the United 

States: the Mississippi, Columbia, St. Lawrence, and Susquehanna. While not inclusive of the entire nation, these four 

rivers account for approximately 55 percent of all freshwater 

flow entering the ocean from the contiguous 48 states, and 

have a broad geographical distribution. This indicator relies 

on stream flow and water-quality data collected by the U.S. 

Geological Survey (USGS), which has monitored nutrient 

export from the Mississippi River since the mid-1950s and 

from the Susquehanna, St. Lawrence, and Columbia Rivers 

since the 1970s. Data were collected near the mouth of each 

river except the St. Lawrence, which was sampled near the 

point where it leaves the United States. 

At the sites for which data are included in this indicator, USGS recorded daily water levels and volumetric 

discharge using permanent stream gauges. Water quality 

samples were collected at least quarterly over the period 

of interest, in some cases up to 15 times per year. USGS 

calculated annual nitrogen load from these data using 

regression models relating nitrogen concentration to discharge, day-of-year (to capture seasonal effects), and time 

(to capture any trend over the period). These models were 

used to make daily estimates of concentrations, which were 

multiplied by the daily flow to calculate the daily nutrient 

load (Aulenbach, 2006; Heinz Center, 2005). Because data 

on forms of nitrogen other than nitrate and nitrite are not 

as prevalent in the historical record, this indicator only uses 

measurements of nitrate plus nitrite. As nitrite concentrations are typically very small relative to nitrate, this mixture is simply referred to as nitrate.

0

500

1,000

1,500

2,000

2,500

1950 1960 1970 1980 1990 2000 2010

Year

Year

Annual nitrate load (thousand tons N)

Annual nitrate load (thousand tons N)

0

50

100

150

1970 1980 1990 2000 2010

Columbia R.

St. Lawrence R.

Susquehanna R.

Susquehanna

St. Lawrence

Columbia

Mississippi

Mississippi R.

a

Most measurements include 

nitrate plus nitrite, but because 

concentrations of nitrite are 

typically insignificant relative to 

nitrate, this mixture is simply 

called “nitrate.”

Data source: USGS, 2007a

Exhibit 3-10. Nitrate loads in four major 

U.S. rivers, 1955-2004a

Areas drained by these 

four rivers

1980 1990 2000

Year

Detail
WATER

3-18 EPA’s 2008 Report on the Environment

INDICATOR | Nitrogen and Phosphorus Loads in Large Rivers (continued)

What the Data Show

The Mississippi River, which drains more than 40 percent 

of the area of the contiguous 48 states, carries roughly 15 

times more nitrate than any other U.S. river. Nitrate load 

in the Mississippi increased noticeably over much of the last 

half-century, rising from 200,000-500,000 tons per year in 

the 1950s and 1960s to an average of about 1,000,000 tons 

per year during the 1980s and 1990s (Exhibit 3-10). Large 

year-to-year fluctuations are also evident. The Mississippi 

drains the agricultural center of the nation and contains 

a large percentage of the growing population, so it may 

not be surprising that the watershed has not been able to 

assimilate all the nitrogen from sources such as crop and 

lawn applications, animal manure and human wastes, and 

atmospheric deposition (e.g., Rabalais and Turner, 2001).

The Columbia River’s nitrate load increased to almost 

twice its historical loads during the later half of the 1990s, but 

by the last year of record (2002), the nitrate load had returned 

to levels similar to those seen in the late 1970s (Exhibit 3-10). 

The St. Lawrence River showed an overall upward trend in 

nitrate load over the period of record, while the Susquehanna 

does not appear to have shown an appreciable trend in either 

direction. Over the period of record, the Columbia and St. 

Lawrence carried an average of 67,000 and 66,000 tons of 

nitrate per year, respectively, while the Susquehanna averaged 

46,000 tons. By comparison, the Mississippi carried an average of 772,000 tons per year over its period of record. 

The total phosphorus load decreased in the St. Lawrence 

and Susquehanna Rivers over the period of record (Exhibit 

3-11). There is no obvious trend in the Mississippi and 

Columbia Rivers, and the year-to-year variability is quite 

large. Nitrogen and phosphorus loads tend to be substantially higher during years of high precipitation, because of 

increased erosion and transport of the nutrients to stream 

channels (Smith et al., 2003). Over the full period of 

record, average annual phosphorus loads for the Mississippi, 

Columbia, St. Lawrence, and Susquehanna were 138,000; 

11,000; 6,000; and 3,000 tons, respectively.

Indicator Limitations

•	The indicator does not include data from numerous 

coastal watersheds whose human populations are rapidly 

increasing (e.g., Valigura et al., 2000). 

•	 It does not include smaller watersheds in geologically 

sensitive areas, whose ability to retain nitrogen might be 

affected by acid deposition (e.g., Evans et al., 2000).

•	 It does not include forms of nitrogen other than nitrate. 

Although nitrate is one of the most bioavailable forms of 

nitrogen, other forms may constitute a substantial portion of the nitrogen load. Historically, nitrate data are 

more extensive than data on other forms of nitrogen.

•	 Not all forms of phosphorus included in the total phosphorus loads are equally capable of causing algal blooms.

0

50

100

150

200

250

1970 1980 1990 2000 2010

Year

Annual total phosphorus load (thousand tons P) Annual total phosphorus load (thousand tons P)

0

5

10

15

20

25

1970 1980 1990 2000 2010

Data source: USGS, 2007a

Exhibit 3-11. Total phosphorus loads in four 

major U.S. rivers, 1971-2004

70 1980 1990 2000

Year

Detail

Susquehanna

St. Lawrence

Columbia

Mississippi

Areas drained by these 

four rivers Columbia R.

St. Lawrence R.

Susquehanna R.

Mississippi R.

Year
WATER

EPA’s 2008 Report on the Environment 3-19

INDICATOR | Nitrogen and Phosphorus Loads in Large Rivers (continued)

Data Sources

Data were compiled for EPA by USGS (USGS, 2007a), 

which provided a similar analysis to the Heinz Center for 

its updated report. Nutrient loads for the Columbia, St. 

Lawrence, and Susquehanna were originally reported in 

Aulenbach (2006); portions of the Mississippi analysis were 

previously published in Goolsby et al. (1999), while other 

portions have not yet been published. Underlying nutrient 

sampling and daily stream flow data can be obtained from 

USGS’s public databases (USGS, 2007b,c).

References

Aulenbach, B.T. 2006. Annual dissolved nitrite plus nitrate 

and total phosphorus loads for Susquehanna, St. Lawrence, 

Mississippi-Atchafalaya, and Columbia River Basins, 

1968-2004. USGS Open File Report 06-1087. 

<http://pubs.usgs.gov/of/2006/1087/>

Evans, C.D., A. Jenkins, and R.F. Wright. 2000. Surface 

water acidification in the South Pennines I. Current status 

and spatial variability. Environ. Pollut. 109(1):11-20.

Galloway, J., and E. Cowling. 2002. Reactive nitrogen and 

the world: 200 years of change. Ambio 31:64-71.

Goolsby, D.A., W.A. Battaglin, G.B. Lawrence, R.S. 

Artz, B.T. Aulenbach, R.P. Hooper, D.R. Keeney, and 

G.J. Stensland. 1999. Flux and sources of nutrients in 

the Mississippi-Atchafalaya River Basin—topic 3 report 

for the integrated assessment on hypoxia in the Gulf of 

Mexico. NOAA Coastal Ocean Program Decision Analysis Series No. 17.

Heinz Center (The H. John Heinz III Center for Science, Economics, and the Environment). 2005. The state 

of the nation’s ecosystems: Measuring the lands, waters, 

and living resources of the United States. New York, NY: 

Cambridge University Press. Web update 2005: 

<http://www.heinzctr.org/ecosystems/report.html>

Rabalais, N.N., and R.E. Turner, eds. 2001. Coastal 

hypoxia: Consequences for living resources and ecosystems. Coastal and estuarine studies 58. Washington, DC: 

American Geophysical Union.

Smith, S.V., D.P. Swaney, L. Talaue-McManus, J.D. 

Bartley, P.T. Sandhei, C.J. McLaughlin, V.C. Dupra, 

C.J. Crossland, R.W. Buddemeier, B.A. Maxwell, and F. 

Wulff. 2003. Humans, hydrology, and the distribution 

of inorganic nutrient loading to the ocean. BioScience 

53:235-245.

USGS (United States Geological Survey). 2007a. Data 

provided to ERG (an EPA contractor) by Nancy Baker, 

USGS. September 12, 2007.

USGS. 2007b. National Stream Quality Accounting Network (NASQAN) data. Accessed 2007. 

<http://water.usgs.gov/nasqan/data/index.html>

USGS. 2007c. National Water Information System. 

Accessed 2007. <http://waterdata.usgs.gov/nwis/>

Valigura, R., R. Alexander, M. Castro, T. Meyers, H. 

Paerl, P. Stacey, and R. Turner, eds. 2000. Nitrogen loading in coastal water bodies—an atmospheric perspective. 

Washington, DC: American Geophysical Union.

Vitousek, P., H. Mooney, L. Olander, and S. Allison. 2002. 

Nitrogen and nature. Ambio 31:97-101.

v

INDICATOR | Pesticides in Streams in Agricultural Watersheds

Pesticides are chemicals or biological agents that kill plant or animal pests and may include herbicides, 

insecticides, fungicides, and rodenticides. More than 

a billion pounds of pesticides (measured as pounds of 

active ingredient) are used in the United States each 

year to control weeds, insects, and other organisms that 

threaten or undermine human activities (Aspelin, 2003). 

About 80 percent of the total is used for agricultural purposes. Although pesticide use has resulted in increased 

crop production and other benefits, pesticide contamination of streams, rivers, lakes, reservoirs, coastal areas, and 

ground water can cause unintended adverse effects on 

aquatic life, recreation, drinking water, irrigation, and 

other uses. Water also is one of the primary pathways by 

which pesticides are transported from their application 

areas to other parts of the environment (USGS, 2000). 

This indicator is based on stream water samples collected 

between 1992 and 2001 as part of the U.S. Geological 

Survey’s (USGS’s) National Water Quality Assessment 

(NAWQA) program, which surveys the condition of 

streams and aquifers in study units throughout the contiguous United States. Of the streams sampled for pesticides, 

this indicator focuses on 83 streams in watersheds where 

agriculture represents the predominant land use, according to criteria outlined in Gilliom et al. (2007). These 83 

streams are located in 36 of the 51 NAWQA study units 

(i.e., major river basins). From each site, NAWQA collected 10 to 49 water samples per year over a 1-to-3-year 
WATER

3-20 EPA’s 2008 Report on the Environment

INDICATOR | Pesticides in Streams in Agricultural Watersheds (continued)

period to analyze for 75 different pesticides and eight 

pesticide degradation products, which together account for 

approximately 78 percent of the total agricultural pesticide 

application in the United States by weight during the study 

period (Gilliom et al., 2007). This indicator reports on two 

variables: (1) the number of stream sites in which pesticides 

or degradation products were detected and (2) the number 

of stream sites where the annual time-weighted average 

concentration of one or more of these compounds exceeds 

standards for aquatic life. A related indicator discusses 

pesticide concentrations in ground water in agricultural 

watersheds (p. 3-19).

Several types of water quality benchmarks for aquatic life 

were used. Where available, data were compared with EPA’s 

acute and chronic ambient water-quality criteria for the 

protection of aquatic life (AWQC-ALs). The acute AWQCAL is the highest concentration of a chemical to which an 

aquatic community can be exposed briefly without resulting in an unacceptable effect. The chronic AWQC-AL 

is the highest concentration to which an aquatic community can be exposed indefinitely without resulting in 

an unacceptable effect. An exceedance was identified if a 

single sample exceeded the acute AWQC-AL or if a 4-day 

moving average exceeded the chronic AWQC-AL (per 

EPA’s definition of the chronic AWQC-AL). Results were 

also compared with aquatic life benchmarks derived from 

toxicity values presented in registration and risk-assessment 

documents developed by EPA’s Office of Pesticide Programs. These benchmarks included acute and chronic 

values for fish and invertebrates, acute values for vascular 

and nonvascular plants, and a value for aquatic community 

effects. An exceedance was identified if a single sample 

exceeded any acute benchmark or if the relevant moving 

average exceeded a chronic benchmark. Altogether, aquatic 

life benchmarks were available for 62 of the pesticides and 

degradation products analyzed. More information about the 

derivation and application of aquatic life guidelines for this 

indicator can be found in Gilliom et al. (2007).

What the Data Show

Of the streams sampled, all had at least one pesticide detection and 86 percent had five or more compounds present, 

which suggests that pesticides frequently occur as mixtures 

(Exhibit 3-12). In 57 percent of the streams sampled, at 

least one pesticide was detected at a concentration that 

exceeded one or more aquatic life benchmarks (Exhibit 

3-12). Approximately 7 percent of the streams (six of the 

83 streams sampled) had five or more pesticides at concentrations above aquatic life benchmarks.

Indicator Limitations

•	These data represent streams draining agricultural watersheds in 36 of the study units (major river basins) sampled 

by the NAWQA program in the contiguous United 

States. While they were chosen to be representative of 

agricultural watersheds across the nation, they are the 

result of a targeted sampling design, and may not be an 

accurate reflection of the distribution of concentrations 

in all streams in the nation’s agricultural watersheds.

•	This indicator does not provide information about trends 

over time, as the NAWQA program has completed only 

one full sampling cycle to date. Completion of the next 

round of sampling will allow trend analysis, using the 

data presented here as a baseline.

•	Aquatic life benchmarks do not currently exist for 21 

of the 83 pesticides and pesticide degradation products analyzed. Current standards and guidelines do not 

account for mixtures of pesticide chemicals and seasonal 

pulses of high concentrations. 

•	The pesticide benchmarks used here are designed to be 

fully protective of aquatic health. Other indicators, such 

as Coastal Sediment Quality (p. 3-42), use aquatic life 

thresholds that are less protective. Thus, these indicators 

are not necessarily comparable to one another.

•	This indicator does not provide information on the magnitude of pesticide concentrations, only whether they 

exceed or fall below benchmarks.

Exhibit 3-12. Pesticides in streams in 

agricultural watersheds of the contiguous U.S., 

1992-2001a,b

a

Coverage: 83 stream sites in watersheds where agriculture is the 

predominant land use. These watersheds are within 36 major 

river basins studied by the USGS NAWQA program.

b

Totals may not add to 100% due to rounding.

c

All streams had at least one compound detected.

Data source: Gilliom et al., 2007

0

20

40

60

80

100

Percent of stream sites

5 or more

3 or 4

1 or 2

0

Number of 

compounds: 

B. Exceedances

of aquatic life

benchmarks

A. Compounds

 detectedc

37.3

43.4

12.0

7.2

10.8

3.6

85.5
WATER

EPA’s 2008 Report on the Environment 3-21

INDICATOR | Streambed Stability in Wadeable Streams

Freshwater benthic macroinvertebrate communities are composed primarily of insect larvae, mollusks, and 

worms. They are an essential link in the aquatic food 

web, providing food for fish and consuming algae and 

aquatic vegetation (U.S. EPA, 2006b). The presence and 

distribution of macroinvertebrates in streams can vary 

across geographic locations based on elevation, stream 

gradient, and substrate (Barbour et al., 1999). These 

organisms are sensitive to disturbances in stream chemistry and physical habitat, both in the stream channel and 

along the riparian zone, and alterations to the physical 

habitat or water chemistry of the stream can have direct 

and indirect impacts on their community structure. 

Because of their relatively long life cycles (approximately 

1 year) and limited migration, benthic macroinvertebrates 

are particularly susceptible to site-specific stressors (Barbour et al., 1999). 

This indicator is based on data collected for EPA’s Wadeable Streams Assessment (WSA). Wadeable streams are 

streams, creeks, and small rivers that are shallow enough 

to be sampled using methods that involve wading into the 

water. They typically include waters classified as 1st through 

4th order in the Strahler Stream Order classification system 

(Strahler, 1952). Between 2000 and 2004, crews sampled 

1,392 sites throughout the contiguous U.S. using standardized methods (U.S. EPA, 2004a,b). Sites were sampled 

between mid-April and mid-November. At each site, a 

composite bottom sample was collected from eleven equally 

spaced transects within the sample reach. The WSA is based 

on a probabilistic design, so results from the sample sites 

can be used to make statistically valid statements about the 

percentage of wadeable stream miles that fall above or below 

reference values for the indicator. 

For this analysis, the 48 contiguous states were divided 

into nine broad ecoregions (U.S. EPA, 2006b), which were 

defined by the WSA based on groupings of EPA Level III 

ecoregions (Omernik, 1987; U.S. EPA, 2007). Benthic 

community condition was determined using two different approaches, each reflecting a distinct aspect of the 

indicator: an Index of Biological Integrity (IBI) and an 

observed/expected (O/E) predictive model. 

The IBI is an index that reduces complex information 

about community structure into a simple numerical value 

based on measures of taxonomic richness (number of taxa); 

taxonomic composition (e.g., insects vs. non-insects); taxonomic diversity; feeding groups (e.g., shredders, scrapers, 

or predators); habits (e.g., burrowing, clinging, or climbing 

taxa); and tolerance to stressors. Separate metrics were used 

for each of these categories in the nine WSA ecoregions, 

based on their ability to best discriminate among streams. 

Each metric was scaled against the 5th-95th percentiles for 

the streams in each region to create an overall IBI, whose 

value ranges from 0 to 100 (Stoddard et al., 2005). 

Once the overall IBI was established, a set of relatively 

undisturbed sites was selected in order to determine the 

range of IBI scores that would be expected among “least 

disturbed” sites. A separate reference distribution was 

developed for each ecoregion. Next, the IBI score for every 

INDICATOR | Benthic Macroinvertebrates in Wadeable Streams

INDICATOR | Pesticides in Streams in Agricultural Watersheds

Data Sources

Summary data for this indicator were provided by USGS’s 

NAWQA program, based on supporting technical data 

published in conjunction with Gilliom et al. (2007). Overall pesticide occurrence was determined from individual 

site results in Appendix 6 of Gilliom et al. (2007) (http://

water.usgs.gov/nawqa/pnsp/pubs/circ1291/appendix6/), 

while exceedances were calculated from a separate supporting data file (http://water.usgs.gov/nawqa/pnsp/pubs/

circ1291/figures/descriptions/6_05_exceeddata.txt).

References

Aspelin, A.L. 2003. Pesticide usage in the United States: 

Trends during the 20th century. Raleigh, NC: Center for 

Integrated Pest Management, North Carolina State University. <http://www.pestmanagement.info/pesticide_history/

index.pdf>

Gilliom, R.J., J.E. Barbash, C.G. Crawford, P.A. Hamilton, J.D. Martin, N. Nakagaki, L.H. Nowell, J.C. Scott, 

P.E. Stackelberg, G.P. Thelin, and D.M. Wolock. 2007. 

Pesticides in the nation’s streams and ground water, 

1992-2001. U.S. Geological Survey circular 1291. Revised 

February 15, 2007. <http://water.usgs.gov/nawqa/pnsp/

pubs/circ1291/> (document); <http://water.usgs.gov/

nawqa/pnsp/pubs/circ1291/supporting_info.php> (supporting technical information) 

USGS (United States Geological Survey). 2000. Pesticides 

in stream sediment and aquatic biota. 

<http://water.usgs.gov/nawqa/pnsp/pubs/fs09200/>

v
WATER

3-22 EPA’s 2008 Report on the Environment

INDICATOR | Streambed Stability in Wadeable Streams

sampled site was compared to the distribution of IBI scores 

among the ecoregion’s reference sites. If a site’s IBI score 

was below the 5th percentile of the regional reference distribution, the site was classified as “most disturbed.” This 

threshold was used because it offers a high degree of confidence that the observed condition is statistically different 

from the “least disturbed” reference condition. Streams 

with IBI scores above the 25th percentile of the reference 

range were labeled “least disturbed,” indicating a high 

probability that they are similar to the relatively undisturbed reference sites. Streams falling between the 5th and 

25th percentiles were classified as “moderately disturbed.” 

In addition to national totals, this indicator displays IBI 

scores for three broad regions, which are composed of multiple WSA ecoregions and which share major climate and 

landform characteristics (U.S. EPA, 2006b). 

The O/E predictive model compares the actual number 

of macroinvertebrate taxa observed at each WSA site (O) 

with the number expected (E) to be found at a site that is 

in minimally disturbed condition (Armitage, 1987). First, 

reference sites were divided into several groups based on 

the observed benthic assemblages, and the probability of 

observing each taxon in each group of sites was determined. Next, a multivariate model was used to characterize each group of reference sites in terms of their shared 

physical characteristics (variables that are largely unaffected 

by human influence, such as soil type, elevation, and latitude). This predictive model then was applied to each test 

site to determine which group(s) of reference sites it should 

be compared to. For each test site, the “expected” probability of observing each taxon was calculated as a weighted 

average based on the probability of observing that taxon in 

a particular group of reference sites and the probability that 

the test site is part of that particular group of sites, based on 

physical characteristics. The total “E” for the test site was 

generated by adding the probabilities of observing each of 

the individual taxa. The actual number of taxa collected at 

the site (O) was divided by “E” to arrive at an O/E ratio 

(Hawkins et al., 2000; Hawkins and Carlisle, 2001). An 

O/E of 1.0 means the site’s taxa richness is equal to the 

average for the reference sites. Each tenth of a point below 

1 suggests a 10 percent loss of taxa.

What the Data Show

Based on the IBI, slightly more than one-quarter of wadeable stream miles nationwide (28.2 percent) were classified as 

“least disturbed” with respect to benthic macroinvertebrate 

condition, while 41.9 percent were in the “most disturbed” 

category (Exhibit 3-13). Of the three major stream regions 

in the nation (see the inset map, Exhibit 3-13), the eastern 

highlands had the lowest percentage of “least disturbed” 

stream miles (18.2 percent), while the western region had 

the highest percentage (45.1 percent).

Because there are no agreed-upon thresholds for the O/E 

model, the results are presented in 20 percent increments of 

taxa losses for the contiguous 48 states (Exhibit 3-14). Nearly 

40 percent (38.6 percent) of wadeable stream miles have lost 

more than 20 percent of their macroinvertebrate taxa, compared to comparable minimally disturbed reference sites, and 

8.3 percent of stream miles have lost more than 60 percent 

of their macroinvertebrate taxa.

Indicator Limitations

•	Although the probability sampling design results in 

unbiased estimates for the IBI and O/E in wadeable 

streams during the April-November index period, values 

may be different during other seasons. 

•	 Reference conditions for the IBI and O/E vary from one 

ecoregion to another in both number and quality, which 

limits the degree of ecoregional resolution at which this 

indicator can be calculated. 

•	 Because “E” is subject to both model error and sampling error, O/E values near 1.0 (above or below) do not 

necessarily imply a gain or loss of species relative to the 

reference conditions.

•	Trend data are unavailable because this is the first time 

that a survey on this broad scale has been conducted, and 

the survey design does not allow trends to be calculated 

INDICATOR | Benthic Macroinvertebrates in Wadeable Streams (continued)

Exhibit 3-13. Index of Biological Integrity (IBI) for 

benthic macroinvertebrates in wadeable streams 

of the contiguous U.S., by region, 2000-2004a,b

28.2

45.1

29.0

18.2

24.9

25.9

29.0

20.4

41.9

27.4

40.0

51.8

5.0

9.5

1.7

2.0

All U.S.

West

Plains and

Lowlands

Eastern

Highlands

a

Regions based on groupings of 

EPA Level III ecoregions 

(Omernik, 1987; U.S. EPA, 

2007).

b

Totals may not add to 100% 

due to rounding. 

Data source: U.S. EPA, 2006b

Regions

IBI score:

Percent of stream miles in each category:

Least

disturbed

Moderately

disturbed

Most

disturbed

Not assessed/

no data

West

Plains and Lowlands 

Eastern 

Highlands 
WATER

EPA’s 2008 Report on the Environment 3-23

INDICATOR | Streambed Stability in Wadeable Streams

within a single sampling period (2000-2004). These data 

will serve as a baseline for future surveys. 

Data Sources

The results shown in Exhibit 3-13 were previously published 

in EPA’s 2006 Wadeable Streams Assessment (WSA) report 

(U.S. EPA, 2006b). The data in Exhibit 3-14 are based on 

frequency distributions provided by the WSA program (U.S. 

EPA, 2005) (U.S. EPA [2006b] also presents results from the 

O/E analysis, but using different categories). Data from individual stream sites can be obtained from EPA’s STORET 

database (U.S. EPA, 2006a) (http://www.epa.gov/owow/

streamsurvey/web_data.html).

References

Armitage, D. 1987. The prediction of the macroinvertebrate fauna of unpolluted running-water sites in Great 

Britain using environmental data. Freshwater Biol. 

17:41-52.

Barbour, M.T., J. Gerritson, B.D. Snyder, and J.B. Stribling. 

1999. Rapid bioassessment protocols for use in streams and 

wadeable rivers: Periphyton, benthic macroinvertebrates and 

fish. Second edition. EPA/841/B-99/002. Washington, DC: 

U.S. Environmental Protection Agency.

Hawkins, C.P., and D.M. Carlisle. 2001. Use of predictive 

models for assessing the biological integrity of wetlands and 

other aquatic habitats. In: Rader, R.B., and D.P. Batzer, 

eds. Bioassessment and management of North American 

wetlands. New York, NY: John Wiley & Sons. pp. 59-83.

Hawkins, C.P., R.H. Norris, J.N. Hogue, and J.W. Feminella. 2000. Development and evaluation of predictive 

models for measuring the biological integrity of streams. 

Ecol. Appl. 10:1456-1477.

Omernik, J.M. 1987. Ecoregions of the conterminous 

United States. Map (scale 1:7,500,000). Ann. Assoc. Am. 

Geog. 77(1):118-125.

Stoddard, J., D.V. Peck, S.G. Paulsen, J. Van Sickle, C.P. 

Hawkins, A.T. Herlihy, R.M. Hughes, F. Wright, P.R. 

Kaufmann, D.P. Larsen, G. Lomnicky, A.R. Olsen, 

S.A. Peterson, P.L. Ringold, and T.R. Whittier. 2005. 

An ecological assessment of western streams and rivers. 

EPA/620/R-05/005. Washington, DC: U.S. Environmental Protection Agency. <http://www.epa.gov/nheerl/arm/

documents/EMAP.W.Assessment.final.pdf> 

Strahler, A.N. 1952. Dynamic basis of geomorphology. 

Geol. Soc. Am. Bull. 63:923-938.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Level III ecoregions of the conterminous 

United States. Accessed November 2007. <http://www.epa.

gov/wed/pages/ecoregions/level_iii.htm>

U.S. EPA. 2006a. Data from the Wadeable Streams 

Assessment. Accessed 2006. <http://www.epa.gov/owow/

streamsurvey/web_data.html>

U.S. EPA. 2006b. Wadeable Streams Assessment: A collaborative survey of the nation’s streams. EPA/841/B-06/002. 

<http://www.epa.gov/owow/streamsurvey/pdf/WSA_

Assessment_May2007.pdf>

U.S. EPA. 2005. Data provided to ERG (an EPA contractor) by Susan Holdsworth, EPA. December 2005. 

U.S. EPA. 2004a. Wadeable streams assessment: Benthic 

laboratory methods. EPA/841/B-04/007. <http://www.

epa.gov/owow/monitoring/wsa/benthic_laboratory_

manual_040712.pdf>

U.S. EPA. 2004b. Wadeable streams assessment: Field operations manual. EPA/841/B-04/004. <http://www.epa.gov/

owow/monitoring/wsa/wsa_fulldocument.pdf>

INDICATOR | Benthic Macroinvertebrates in Wadeable Streams (continued)

v

Exhibit 3-14. Percent loss of benthic 

macroinvertebrate taxa in wadeable streams of 

the contiguous U.S., relative to the number of 

expected taxa, 2000-2004a,b

0

20

40

60

80

100

Percent of stream miles

20-40% loss

40-60% loss

60-80% loss

More than 80% loss

No loss

0-20% loss

Not assessed/no data

a

Number of expected taxa based 

on minimally disturbed 

reference sites.

b

Totals may not add to 100% due 

to rounding. 

Data source: U.S. EPA, 2005

1.8 6.5

11.9

18.4

25.3

28.8

7.4
WATER

3-24 EPA’s 2008 Report on the Environment

3.2.3 Discussion

What These Indicators Say About Trends in 

the Extent and Condition of Fresh Surface 

Waters and Their Effects on Human Health 

and the Environment

Although the indicators do not characterize the extent of all 

fresh surface waters, they do provide information about flow 

patterns in streams. As the Stream Flows indicator (p. 3-8) 

shows, substantial shifts in the volume of high and low flows 

have occurred over time, with large fluctuations between relatively “wet” and “dry” periods. In general, since the 1960s, 

more streams have experienced increases in base flow volume 

than have experienced decreases, compared to the prior 20 

years. At the same time, overall flow variability appears to 

have decreased somewhat. These shifts are particularly important in intermittent streams, where life forms may be quite 

sensitive to changes in patterns of flow and no flow. Although 

intermittent streams can be found throughout the country, the 

Stream Flows indicator focuses on those that occur in grassland and shrubland areas, many of which are arid or semi-arid 

and thus especially sensitive to water stress. As this indicator 

shows, no-flow periods have generally decreased in number 

and duration since the 1960s, although a few grassland/

shrubland streams have experienced substantial increases.

Factors that influence stream flow can include weather and climate, land cover, hydromodifications such as dams, and water 

withdrawals. Decreases in flow volume were somewhat less 

prevalent within a subset of relatively unmodified “reference” 

streams. Nonetheless, trends in the “reference” streams were 

highly similar to trends in the general population of streams 

overall, suggesting that dams, diversions, and land cover 

changes are not the major causes of the observed changes in 

stream flow over the last half-century.

The physical condition of lakes and streams is in part a function of the interaction between sediment and water. As the 

Streambed Stability indicator (p. 3-11) shows, about onefourth of the nation’s wadeable streams show significant 

evidence of excess fine sediments, which can diminish habitat. 

In some cases, excess sedimentation can reflect the influence of 

human stressors like erosion. Excess sedimentation also can be 

a symptom of broader changes in physical condition, such as 

hydromodifications that alter flow and sediment transport.

The ROE indicators provide a mixed picture of the chemical condition of fresh surface waters. Acidity in lakes and 

streams has decreased in three of the four sensitive areas 

studied (Lake and Stream Acidity indicator, p. 2-42), while 

excess nutrients are present in many streams, ranging from 

small wadeable streams to the nation’s largest rivers (three 

N and P indicators, pp. 3-13, 3-15, and 3-17). In agricultural areas, more than half of monitoring sites have at least 

one pesticide at levels that exceed guidelines for aquatic 

health (Pesticides in Agricultural Streams indicator, p. 3-19). 

These indicators reflect the influence of many stressors. For 

example, the two Agricultural Streams indicators (pp. 3-15 

and 3-19) demonstrate how chemicals applied to the land can 

ultimately affect surface waters. Conversely, efforts to reduce 

human stressors can result in improved water condition. For 

example, areas with declines in acidity correspond with areas 

of decreased acid deposition (Lake and Stream Acidity indicator, p. 2-42), while declining phosphorus loads in at least 

one river may be related to detergent bans and improved 

sewage treatment (N and P Loads in Large Rivers indicator, 

p. 3-17). The indicators also are influenced by natural stressors (e.g., year-to-year variability in nutrient loads due to 

variations in precipitation). 

One ROE indicator presents direct information on the biological condition of fresh surface waters. About 40 percent of 

the nation’s wadeable stream miles exhibit a substantial loss 

(more than 20 percent) of macroinvertebrate taxa—approximately equal to the number of stream miles considered “most 

disturbed” when other metrics of benthic community condition are considered (Benthic Macroinvertebrates in Wadeable Streams indicator, p. 3-21). Benthic macroinvertebrate 

communities are particularly sensitive to physical and chemical stressors, and thus the condition of these assemblages can 

provide information about the extent to which these stressors 

may be causing measurable harm. In addition, several other 

ROE indicators provide information about stressors that are 

known to affect biological condition. For example, the ROE 

indicators show a portion of streams with excess sedimentation, pesticides above aquatic life guidelines, nutrients at levels 

that could encourage eutrophication, and substantial changes 

in high and low stream flows.

Limitations, Gaps, and Challenges

Although the ROE indicators provide valuable information 

about the extent and condition of fresh surface waters, there 

are a few general limitations to their ability to depict trends 

over space and time. For example, trends in condition may be 

tied to the location and timing of intermittent stressors (e.g., 

pesticide application), so indicators that assess national condition using samples that are spread out over time and space may 

obscure local conditions and extreme events. Some indicators 

are also restricted to specific study areas. For example, the two 

Agricultural Streams indicators (pp. 3-15 and 3-19) do not 

characterize non-agricultural watersheds, and the Lake and 

Stream Acidity indicator (p. 2-42) does not include localized 

acidification in the West.

In addition to the challenges inherent in assessing fresh surface 

waters, there are challenges in interpreting what the indicators 

say. Ecological responses to freshwater stressors are complex 

and may depend on the species that inhabit a particular area. 

In some cases—e.g., the three indicators from the Wadeable Streams Assessment—data must be adjusted to account 

for variations in regional reference conditions. It can also be 

difficult to link effects to specific stressors, as many indicators 

reflect the interplay of multiple human and natural factors. For 

example, local bedrock can contribute high levels of nutrients 

to some rivers, while precipitation variability can drive trends 

in nutrient loads, potentially obscuring trends in anthropogenic stressors.
WATER

EPA’s 2008 Report on the Environment 3-25

There are no ROE indicators for a few key aspects of the 

extent and condition of fresh surface waters. The following 

information would help to better answer this question:

•	 Information on the extent of different types of fresh surface 

waters, stressors to extent (e.g., water usage and extent of 

snowpack), and associated effects on ecological systems.

•	 Nationally consistent information to characterize stressors 

to fresh surface water condition—specifically pollutant 

loadings from point and nonpoint sources.

•	 Information on the condition of large rivers. The N and 

P Loads in Large Rivers indicator (p. 3-17) describes 

nutrient loads at the mouth, but does not address conditions upstream.

•	 Indicators on the condition of ponds, reservoirs, and lakes, 

including the Great Lakes. A nationally consistent indicator 

of lake trophic state could bring together several aspects of 

condition (e.g., physical, chemical, and biological parameters) related to eutrophication—a problem facing many of 

the nation’s lakes.

•	 Indicators of salinity, of particular importance in arid 

regions.

•	 Information on the extent and condition of riparian zones 

and lake shoreline (the land-water interface), where much 

biological activity occurs. 

•	 Information about toxic contaminants in freshwater sediments. Sediment contaminants can accumulate through the 

food web, and may ultimately impact the health of humans 

who consume fish and shellfish.

•	 Information on the condition of fish communities, which 

can be affected by many different stressors.

In addition, there are currently no ROE indicators that 

explicitly link human health effects to the extent or condition 

of fresh surface waters. As described in Chapter 1, this type of 

information gap largely reflects the difficulty of determining 

exact causation between stressors and effects.

3.3 What Are the Trends 

in the Extent and 

Condition of Ground 

Water and Their Effects 

on Human Health and 

the Environment?

3.3.1 Introduction

A large portion of the world’s fresh water resides underground, 

stored within cracks and pores in the rock that makes up the 

Earth’s crust. The U.S. Geological Survey estimates that there 

are approximately 1 million cubic miles of ground water within 

one-half mile of the Earth’s surface—30 times the volume of 

all the world’s fresh surface waters.2 Many parts of the U.S. rely 

heavily on ground water for human uses (e.g., drinking, irrigation, industry, livestock), particularly areas with limited precipitation (e.g., the Southwest), limited surface water resources, 

or high demand from agriculture and growing populations 

(e.g., Florida). Half of the U.S. population (51 percent) relies on 

ground water for domestic uses.3

Ecological systems also rely on ground water. For example, 

some wetlands and surface waters are fed by springs and seeps, 

which occur where a body of ground water—known as an 

aquifer—reaches the Earth’s surface. While the contribution 

of ground water to stream flow varies widely among streams, 

hydrologists estimate that the average contribution of ground 

water is 40 to 50 percent in small- and medium-sized streams. 

The ground water contribution to all stream flow in the U.S. 

may be as large as 40 percent.4

The extent of ground water refers to the amount available, 

typically measured in terms of volume or saturated thickness of an aquifer. The condition of ground water reflects a 

combination of physical, biological, and chemical attributes. 

Physical properties reflect patterns of flow—i.e., the volume, 

speed, and direction of ground water flow in a given location. 

Biologically, ground water can contain a variety of organisms, 

including bacteria, viruses, protozoans, and other pathogens. 

Ground water can also contain a variety of chemicals, which 

may occur naturally or as a result of human activities. Chemicals that may occur in ground water include nutrients, metals, 

radionuclides, salts, and organic compounds such as petroleum 

products, pesticides, and solvents. These chemicals may be dissolved in water or—in the case of insoluble organic contaminants—exist as undissolved plumes.

2 U.S. Geological Survey. 1999. Ground water (general interest publication). 

Reston, VA. <http://capp.water.usgs.gov/GIP/gw_gip/>

3 Ibid.

4 Alley, W.M, T.E. Reilly, and O.L. Franke. 1999. Sustainability of ground-water 

resources. Circular 1186. Denver, CO: U.S. Geological Survey.
WATER

3-26 EPA’s 2008 Report on the Environment

Many stressors can affect the extent of ground water, including patterns of precipitation and snowmelt and human activities that change or redistribute the amount of ground water 

in an aquifer. One major way humans influence ground water 

extent is by withdrawing water for drinking, irrigation, or 

other uses (e.g., ground water extracted to lower the water 

table for mining operations). Other human activities can 

increase ground water levels, such as surface irrigation runoff 

recharging a shallow aquifer, or water pumped directly into 

the ground in order to store surface waters for future use, or 

to aid in oil and gas extraction. Human activities can affect 

ground water extent indirectly, too; for example, impervious paved surfaces may prevent precipitation from recharging 

ground water. In some cases, changes in ground water extent 

may be caused by a combination of these human and natural 

factors—for example, droughts that require humans to withdraw more water from the ground (e.g., for irrigation), while 

at the same time providing less precipitation for recharge. 

Some aquifers are more susceptible than others to changes in 

extent. For example, some deep aquifers may take thousands 

of years to recharge, particularly if they lie below highly 

impermeable confining layers.

Aquifer depletion—i.e., decreased extent—can adversely affect 

the humans and ecosystems that directly or indirectly depend 

on ground water. Less ground water available for human or 

ecological use can result in lower lake levels or—in extreme 

cases—cause perennial streams to become intermittent or 

totally dry, thus harming aquatic and riparian plants and 

animals that depend on regular surface flows. An area with a 

high water table may have plant communities that tap ground 

water directly with their roots, so even a slight lowering of 

the aquifer could affect native species—which in turn could 

benefit invasive species.5

 In addition, lower water table levels 

may lead to land subsidence and sinkhole formation in areas 

of heavy withdrawal, which can damage buildings, roads, and 

other structures and can permanently reduce aquifer recharge 

capacity by compacting the aquifer medium (soil or rock). 

Finally, changes in the ground water flow regime can lead 

to consequences such as salt water intrusion, in which saline 

ground water migrates into aquifers previously occupied by 

fresh ground water.

Although aquifer depletion can have serious effects, the opposite, far less common problem—too much ground water—can 

also be detrimental. Too much ground water discharge to 

streams can cause erosion and can alter the balance of aquatic 

plant and animal species, as has been reported in association 

with some mining sites.6

Like extent, condition is influenced by both natural sources 

and human activities. Some ground water has high levels 

of naturally occurring dissolved solids (salinity), or metals such as arsenic that can be present as a result of natural 

rock formations. Land use can affect the condition of ground 

water; for example, pesticides, fertilizers, and other chemicals applied to the land can leach into ground water, while 

waste from livestock and other animals can contribute contaminants such as nutrients, organic matter, and pathogens. 

Shallow and unconfined aquifers are particularly susceptible 

to this type of contamination. In addition, landfills may 

leach metals, solvents, and other contaminants into ground 

water (particularly older landfills that do not have liners and 

leachate collection systems). Mining operations can mobilize toxic metals, acidic compounds, and other substances 

that can impact the condition of ground water. Finally, 

chemical or biological contaminants may enter aquifers as a 

result of unintentional releases, including chemical spills on 

land, leaks from storage tanks, sewers or septic systems, and 

unplugged abandoned wells that allow a direct route of entry 

for contaminants.

Stressors that affect ground water condition ultimately affect 

the condition of water available for drinking, irrigation, or 

other human needs. In some cases, treatment may be needed 

to ensure that finished drinking water does not pose risks to 

human health. Because drinking water can come from many 

different types of water bodies, and because of the many complex issues associated with treatment and regulation of drinking water, this topic is addressed in greater detail in its own 

section of this report, Section 3.6. The condition of ground 

water also can affect ecological systems. For example, many 

fish species depend on cold, clear spring-fed waters for habitat 

or spawning grounds.7,8 In some cases, aquifers themselves may 

constitute ecosystems. For example, caves and sinkholes are 

home to many types of aquatic fauna, including invertebrates 

and fish adapted to life underground.9 Ground water can 

also affect the condition of other environmental media. For 

example, volatile ground water contaminants can potentially 

migrate into indoor air via soil vapor intrusion.

In many ways, extent and condition are intertwined. For 

example, stressors that affect extent—such as withdrawal or 

injection—can also alter physical parameters of the ground 

water flow regime, such as velocity and direction of flow. 

These physical alterations can affect patterns of discharge to 

surface waters, as well as the movement of water and contaminants within the ground (e.g., salt water intrusion).

5 Grantham, C. 1996. An assessment of ecological impacts of ground 

water overdraft on wetlands and riparian areas on the United States. 

EPA/813/S-96/001. Washington, DC: U.S. Environmental Protection Agency.

6 United States Department of the Interior. 2002. Hydrologic impacts of mining. Chapter 1. In: Permitting hydrology, a technical reference document for 

determination of probable hydrologic consequence (PHC) and cumulative 

hydrologic impact assessments (CHIA). Washington, DC. Accessed November 

8, 2003. <http://www.osmre.gov/pdf/phc2.pdf>

7 Prichard, D., J. Anderson, C. Correll, J. Fogg, K. Gebhardt, R. Krapf, S. Leonard, 

B. Mitchell, and J. Stasts. 1998. Riparian area management: A user guide to 

assessing proper functioning condition and the supporting science for lotic 

areas. Technical reference 1737-15. Denver, CO: U.S. Department of the Interior, Bureau of Land Management, National Applied Resource Sciences Center.

8 Boyd, M., and D. Sturdevant. 1997. The scientific basis for Oregon’s stream 

temperature standard: Common questions and straight answers. Portland, OR: 

Oregon Department of Environmental Quality.

9 Elliott, W.R. 1998. Conservation of the North American cave and karst biota. 

In: Wilkens, H., D.C. Culver, and W.F. Humphreys, eds. Subterranean biota. 

Amsterdam, The Netherlands: Elsevier (Ecosystems of the World series). pp. 

665-689. Preprint online at <http://www.utexas.edu/depts/tnhc/.www/

biospeleology/preprint.htm>
WATER

EPA’s 2008 Report on the Environment 3-27

3.3.2 ROE Indicators

This report presents an indicator of ground water condition 

based on a nationwide survey of shallow wells in watersheds 

where agriculture is the predominant land use (Table 3-3). 

The data come from the U.S. Geological Survey’s National 

Water Quality Assessment (NAWQA) study of major river 

basins with agricultural activities, representing a large portion 

of the nation’s land area. Agricultural land use is among the 

major sources of certain ground water contaminants such as 

nutrients and pesticides.

Table 3-3. ROE Indicators of Trends in the Extent and Condition of 

Ground Water and Their Effects on Human Health and the Environment

National Indicators Section Page

Nitrate and Pesticides in Shallow Ground Water in Agricultural Watersheds 3.3.2 3-27

Nitrogen is a critical plant nutrient, and most nitrogen is used and reused by plants within an ecosystem (Vitousek 

et al., 2002), so in undisturbed ecosystems minimal “leakage” occurs into ground water, and concentrations are 

very low. When nitrogen fertilizers are applied in amounts 

greater than can be incorporated into crops or lost to the 

atmosphere, however, nitrate concentrations in ground 

water can increase. Elevated nitrogen levels in ground water 

also might result from disposal of animal waste or onsite 

septic systems. Nitrate contamination in shallow ground 

water (less than 100 feet below land surface) raises potential 

concerns for human health where untreated shallow ground 

water is used for domestic water supply. High nitrate concentrations in drinking water pose a risk for methemoglobinemia, a condition that interferes with oxygen transport in 

the blood of infants (U.S. EPA, 2004).

More than a billion pounds of pesticides (measured as 

pounds of active ingredient) are used in the U.S. each 

year to control weeds, insects, and other organisms that 

threaten or undermine human activities (Aspelin, 2003). 

About 80 percent of the total is used for agricultural 

purposes. Although pesticide use has resulted in increased 

crop production and other benefits, pesticide contamination of ground water poses potential risks to human health 

if contaminated ground water is used as a drinking water 

source—especially if untreated.

This indicator reports on the occurrence of nitrate and 

pesticides in shallow ground water in watersheds where 

agriculture is the primary land use, according to criteria 

outlined in Gilliom et al. (2007). Ground water samples 

were collected by the U.S. Geological Survey’s (USGS’s) 

National Water Quality Assessment (NAWQA) program 

from 1992 to 2003 (pesticide sampling began in 1993). 

NAWQA surveyed 51 major river basins and aquifer regions 

across the contiguous United States during this period; the 

agricultural watersheds sampled were within 34 of these 

study units. Although agriculture is more prevalent in some 

parts of the country than in others, the watersheds were 

chosen to reflect a broad range of hydrogeologic conditions and agricultural activities. Ground water samples were 

collected from existing household wells where possible and 

new observation wells otherwise, all targeted at the uppermost aquifer and avoiding locations where ground water 

condition could be biased by point sources (e.g., directly 

INDICATOR Nitrate and Pesticides in Shallow Ground Water in 

Agricultural Watersheds

Exhibit 3-15. Nitrate in shallow ground water 

in agricultural watersheds of the contiguous

U.S., 1992-2003a,b

0

20

40

60

80

100

Percent of wells

2 to <6 mg/L

<1 mg/L

1 to <2 mg/L

6 to <10 mg/L

 10 mg/L

a

Coverage: 1,423 shallow wells in

watersheds where agriculture is

the predominant land use. These 

watersheds are within 34 major river 

basins and aquifer regions studied 

by the USGS NAWQA program.

b

Totals may not add to 100% due to 

rounding.

c

EPA’s drinking water standard for 

nitrate is a Maximum Contaminant

Level (MCL) of 10 mg/L.

Data source: USGS, 2007a

Concentration:c

21.4

13.5

23.0

7.7

34.5
WATER

3-28 EPA’s 2008 Report on the Environment

INDICATOR Nitrate and Pesticides in Shallow Ground Water in 

Agricultural Watersheds (continued)

downgradient from a septic system). Most of the wells sampled ground water from less than 20 feet below the water 

table, indicating as directly as possible the influence of land 

use on shallow ground water quality. To the extent feasible, 

the wells were intended to sample recently recharged water. 

Data analyses were based on one sample per well. Related 

indicators report concentrations of nutrients and pesticides 

in streams that drain agricultural watersheds (see the N and 

P in Agricultural Streams indicator, p. 3-15, and the Pesticides in Agricultural Streams indicator, p. 3-19).

The nitrate component of this indicator represents 1,423 

wells. Results are compared with the federal drinking water 

standard of 10 mg/L, which is EPA’s Maximum Contaminant Level (MCL) to prevent methemoglobinemia (U.S. 

EPA, 2006). MCLs are enforceable standards representing 

the highest level of a contaminant that is allowed in finished 

drinking water. MCLs take into account cost and best available treatment technology, but are set as close as possible to 

the level of the contaminant below which there is no known 

or expected risk to health, allowing for a margin of safety.

Data on 75 pesticides and eight pesticide degradation 

products were collected from 1,412 of the wells in the 

NAWQA study. These 83 chemicals account for approximately 78 percent of the total agricultural pesticide application in the United States by weight during the study period 

(Gilliom et al., 2007). Three types of U.S. EPA human 

health-related standards and guidelines were used to evaluate 

pesticide data: Maximum Contaminant Levels (MCLs) (as 

described above), Cancer Risk Concentrations (CRCs), and 

Lifetime Health Advisories (HA-Ls). In all three cases, the 

standard and guideline levels are concentrations pertaining 

to lifetime exposure through drinking water. The CRC is a 

guideline for potential carcinogens associated with a specified cancer risk of 1 in 1,000,000, based on drinking water 

exposure over a 70-year lifetime. The HA-L is an advisory 

guideline for drinking water exposure over a 70-year lifetime, considering non-carcinogenic adverse health effects. 

Specific standards and guidelines used for this indicator are 

listed in Gilliom et al. (2007), and additional information 

on these types of benchmarks, their derivation, and their 

underlying assumptions is provided in Nowell and Resek 

(1994). For this indicator, if a chemical had multiple benchmarks, the MCL took precedence; if no MCL was available, 

the lower of the CRC (at 1 in 1,000,000 cancer risk) and 

HA-L values was selected. An exceedance was identified if 

the concentration of a contaminant exceeded the relevant 

standard or guideline (Gilliom et al., 2007).

What the Data Show

During the study period:

•	 Nitrate concentrations were 2 mg/L or above in 58 percent 

of wells sampled in areas where agriculture is the primary 

land use (Exhibit 3-15). By comparison, background nitrate 

levels in areas with little human influence are generally 

expected to be below 1 mg/L (Nolan and Hitt, 2002).

•	 Nitrate concentrations in about 21 percent of the wells 

exceeded the federal drinking water standard (10 mg/L). 

•	 About 60 percent of wells in agricultural watersheds had at 

least one detectable pesticide compound, and 9.5 percent 

had detectable levels of five or more pesticides (Exhibit 

3-16). Roughly 1 percent of wells had pesticides present at 

concentrations exceeding human health benchmarks.

Indicator Limitations

•	 These data only represent conditions in agricultural 

watersheds within 34 of the major river basins and aquifer 

regions sampled by the NAWQA program from 1992 

to 2003. Although sample wells were chosen randomly 

within each agricultural watershed, the watersheds and 

aquifers themselves were selected through a targeted sample design. The data also are highly aggregated and should 

only be interpreted as an indication of national patterns.

Exhibit 3-16. Pesticides in shallow ground 

water in agricultural watersheds of the 

contiguous U.S., 1993-2003a,b

0

20

40

60

80

100

Percent of wells

1 or 2

3 or 4

5 or more

Number of 

compounds:

0

A. Compounds 

detected

B. Exceedances of 

human health 

benchmarksc

9.5

19.8

31.3

39.4

a

Coverage: 1,412 shallow wells in watersheds where agriculture is the 

predominant land use. These watersheds are within 34 major river 

basins and aquifer regions studied by the USGS NAWQA program.

b

Samples were analyzed for 75 pesticides and eight pesticide 

degradation products.

c

No wells exceeded benchmarks for more than one compound.

Data source: Gilliom et al., 2007

98.9

1.1
WATER

EPA’s 2008 Report on the Environment 3-29

INDICATOR Nitrate and Pesticides in Shallow Ground Water in 

Agricultural Watersheds (continued)

•	This indicator does not provide information about trends 

over time, as the NAWQA program has completed only 

one full sampling cycle to date. Completion of the next 

round of sampling will allow trend analysis, using the 

data presented here as a baseline.

•	 Drinking water standards or guidelines do not exist for 43 

percent (36 of 83) of the pesticides and pesticide degradation products analyzed. Current standards and guidelines 

also do not account for mixtures of pesticide chemicals and seasonal pulses of high concentrations. Possible 

pesticide effects on reproductive, nervous, and immune 

systems, as well as on chemically sensitive individuals, are 

not yet well understood. 

•	This indicator does not provide information on the 

magnitude of pesticide concentrations, only whether 

they exceed or fall below benchmarks. It also does not 

describe the extent to which they exceed or fall below 

other reference points (e.g., Maximum Contaminant 

Level Goals [MCLGs] for drinking water). 

Data Sources

Summary data for this indicator were provided by USGS’s 

NAWQA program. Nitrate data have not yet been published and were provided directly by USGS (2007a); 

however, concentration data from individual sample sites 

are publicly available through NAWQA’s online data 

warehouse (USGS, 2007b). Pesticide occurrence and 

exceedances were determined from individual site results 

in Appendix 6 of Gilliom et al. (2007) (http://water.usgs.

gov/nawqa/pnsp/pubs/circ1291/appendix6/).

References

Aspelin, A.L. 2003. Pesticide usage in the United States: 

Trends during the 20th century. Raleigh, NC: Center for 

Integrated Pest Management, North Carolina State University. <http://www.pestmanagement.info/pesticide_history/

index.pdf>

Gilliom, R.J., J.E. Barbash, C.G. Crawford, P.A. Hamilton, 

J.D. Martin, N. Nakagaki, L.H. Nowell, J.C. Scott, P.E. 

Stackelberg, G.P. Thelin, and D.M. Wolock. 2007. Pesticides in the nation’s streams and ground water, 1992-2001. 

U.S. Geological Survey circular 1291. Revised February 15, 

2007. <http://water.usgs.gov/nawqa/pnsp/pubs/circ1291/

index.html> (document); <http://water.usgs.gov/nawqa/

pnsp/pubs/circ1291/supporting_info.php> (supporting 

technical information)

Nolan, B.T., and K.J. Hitt. 2002. Nutrients in shallow 

ground waters beneath relatively undeveloped areas in the 

conterminous United States. U.S. Geological Survey water 

resources investigation report 02-4289. <http://water.usgs.

gov/nawqa/nutrients/pubs/wri02-4289/wri02-4289.pdf>

Nowell, L.H., and E.A. Resek. 1994. National standards 

and guidelines for pesticides in water, sediment, and 

aquatic organisms: Application to water-quality assessments. Rev. Environ. Contam. Toxicol. 140:1-164.

U.S. EPA (United States Environmental Protection Agency). 

2006. Drinking water contaminants. <http://www.epa.gov/

safewater/mcl.html>

U.S. EPA. 2004. Consumer factsheet on nitrates/nitrites.

<http://www.epa.gov/safewater/contaminants/dw_

contamfs/nitrates.html>

USGS (United States Geological Survey). 2007a. Data 

provided to ERG (an EPA contractor) by Nancy Baker, 

USGS. September 12, 2007.

USGS. 2007b. USGS National Water Quality Assessment 

data warehouse. Accessed 2007. <http://infotrek.er.usgs.gov/

traverse/f?p=NAWQA:HOME:14620854136944137608>

Vitousek, P., H. Mooney, L. Olander, and S. Allison. 2002. 

Nitrogen and nature. Ambio 31:97-101.

v

3.3.3 Discussion

What This Indicator Says About Trends in 

the Extent and Condition of Ground Water 

and Their Effects on Human Health and the 

Environment

The Nitrate and Pesticides in Ground Water indicator (p. 3-27) 

describes the extent to which the condition of shallow ground 

water may be influenced by human stressors—in this case, 

certain chemicals applied to land in agricultural areas. Collectively, the agricultural watersheds sampled across the nation 

had average nitrate concentrations that were substantially higher 

than the background levels one might expect in an undisturbed 

watershed. Nitrate concentrations exceeded EPA’s MCL for 

nitrate in one-fifth of the wells, though this does not necessarily reflect the condition of the water people drink if it is tested 

and treated. Nitrate concentrations were often high enough that 

they could impact ecological systems upon being introduced 

into surface waters.10,11 Pesticide compounds were detected 

10 Howarth, R., D. Anderson, J. Cloern, C. Elfring, C. Hopkinson, B. Lapointe, T. 

Malone, N. Marcus, K. McGlathery, A. Sharpley, and D. Walker. 2000. Nutrient 

pollution of coastal rivers, bays, and seas. Issues in ecology, number 7. Washington, DC: Ecological Society of America.

11 Jackson, R., S. Carpenter, C. Dahm, D. McKnight, R. Naiman, S. Postel, and 

S. Running. 2001. Water in a changing world. Issues in ecology, number 9. 

Washington, DC: Ecological Society of America.
WATER

3-30 EPA’s 2008 Report on the Environment

frequently (more than half of the shallow wells sampled). However, detected pesticide concentrations rarely exceeded human 

health-based reference points in the samples collected for this 

indicator.

Limitations, Gaps, and Challenges

One challenge in answering this question is that there are currently no national indicators of ground water extent. Comprehensive national data do not exist, particularly in terms of 

real-time water level monitoring. Statistics on water use and 

withdrawal might be considered a surrogate for ground water 

extent, but because withdrawal is but one factor that affects 

extent (other factors include recharge rate and flow patterns), 

the relationship between withdrawal and extent differs from 

one location to another. Thus, the issue of extent currently 

represents an information gap.

There are also several limitations, gaps, and challenges in 

addressing the issue of ground water condition. One notable 

limitation to the Nitrate and Pesticides in Ground Water indicator (p. 3-27) is that it does not provide information about 

trends over time. The indicator is also limited in its ability 

to represent the condition of entire aquifers. Because ground 

water condition is vertically heterogeneous, results from one 

depth do not necessarily represent other depths. This indicator 

characterizes the uppermost layer of shallow aquifers, which 

are used by many private wells. It does not provide information about the condition of deeper aquifers, which are more 

likely to be used for public water supplies.

The Nitrate and Pesticides in Ground Water indicator provides 

a representative national picture of shallow ground water condition in agricultural watersheds. At present, similar indicators do 

not exist for ground water in watersheds with non-agricultural 

land uses. Non-agricultural watersheds—particularly urban 

areas—reflect a different set of stressors, and to some extent a 

different set of chemicals (i.e., VOCs and hydrocarbons like 

MTBE12). Because many ground water stressors in urban areas 

are localized events such as plumes resulting from chemical 

spills or underground storage tank (UST) leaks, they may be 

harder to characterize on a national level—a potential challenge 

to gathering more information about ground water condition. 

Salt water intrusion is another issue that tends to occur locally, 

and for which national-scale data are not available.

3.4 What Are the Trends 

in the Extent and 

Condition of Wetlands 

and Their Effects on 

Human Health and the 

Environment?

3.4.1 Introduction

The United States has many types of wetlands, which include 

marshes, swamps, bogs, and similar marine, estuarine, or 

freshwater areas that are periodically saturated or covered by 

water. Wetlands are an integral part of the landscape because 

they provide habitat for a diverse array of plants and animals, 

act as buffers to flooding and erosion, and serve as key links in 

the global water and biogeochemical cycles.

In terms of extent, wetlands currently cover 5.5 percent of 

the surface area of the contiguous 48 states, with freshwater wetlands accounting for nearly 95 percent of the current 

wetland acreage and marine and estuarine wetlands accounting 

for the remaining 5 percent.13 Condition is somewhat harder 

to measure, as it reflects a combination of physical, chemical, 

and biological attributes. To be in healthy condition, however, 

a wetland should generally demonstrate good water quality 

and support native plant and animal communities, without the 

presence of invasive non-indigenous species. A healthy wetland 

should not show signs of stress related to substantial degradation 

or cumulative effects of smaller degradations, and should be free 

of modifications that restrict water flow into, through, or out of 

the wetland, or that alter patterns of seasonality.

Wetlands can be classified by many different attributes. First, 

they can be divided by degree of salinity—freshwater, marine, 

or estuarine. Wetlands also may be classified based on dominant 

vegetation type. For example, swamps are dominated by trees and 

shrubs, while marshes are characterized by non-woody, emergent 

(vertically oriented) plants like grasses and sedges. Other characteristics used to classify wetlands include soil type, water source, 

and the length of time a given wetland is saturated. 

The structure and function of any given wetland will be governed by a combination of interrelated factors, including topography, underlying geology (e.g., mineral composition), the 

abundance and movement of water (hydrology), and weather 

and climate. These factors ultimately determine which plant and 

animal species will thrive in a given wetland. 

All wetlands share a few basic physical, chemical, and biological 

attributes. By definition, all wetlands are saturated or covered 

12 Delzer, G.C., and T. Ivahnenko. 2003. Occurrence and temporal variability 

of methyl tert-butyl ether (MTBE) and other volatile organic compounds 

in select sources of drinking water: Results of the focused survey. USGS 

series: water-resources investigations report. Report no. 2002-4084. Reston, 

VA: U.S. Geological Survey. <http://sd.water.usgs.gov/nawqa/pubs/wrir/

wrir02_4084.pdf> 

13 Dahl, T.E. 2006. Status and trends of wetlands in the conterminous United 

States 1998 to 2004. Washington, DC: U.S. Department of the Interior, Fish 

and Wildlife Service. <http://wetlandsfws.er.usgs.gov/status_trends/> 
WATER

EPA’s 2008 Report on the Environment 3-31

Table 3-4. ROE Indicators of Trends in the Extent and Condition of Wetlands 

and Their Effects on Human Health and the Environment

National Indicators Section Page

Wetland Extent, Change, and Sources of Change 3.4.2 3-32

by water at least periodically, and wetland vegetation is adapted 

to these conditions. Thus, wetlands are like sponges, with a 

natural ability to store water. Wetlands also tend to have highly 

developed root systems that anchor trees and other vegetation in 

place. This web of roots not only holds the soil in place, but also 

filters pollutants out of the water as it flows through.

Because of their physical, chemical, and biological properties, 

wetlands serve many important environmental functions. They 

play an important role in improving natural water quality by 

filtering pollutants. This function is particularly important to 

human health because it may affect the condition of waters 

used as a source of drinking water—a topic described in greater 

detail in Section 3.6. Wetlands also act as a buffer to protect 

the shoreline from erosion and storm damage. Because of their 

sponge-like capacity to absorb water, wetlands slow the water’s 

momentum and erosive potential and reduce flood heights. 

During dry periods, the “sponge” releases water, which is critical in maintaining the base flow of many surface water systems.

Wetlands are also among the most biologically productive natural ecosystems in the world. Microbial activity in wetlands 

enriches the water and soil with nutrients. As the interface 

between terrestrial and aquatic ecological systems, wetlands 

provide food and habitat for many plant and animal species, 

including rare and endangered species. Because of these functions, wetlands support a number of human activities, including commercial fishing, shellfishing, and other industries, as 

well as recreation, education, and aesthetic enjoyment.

In addition, wetlands play a role in global biogeochemical cycles, particularly those driven in part by the microbial 

processes that occur in wetlands (e.g., the mineralization of 

sulfur and nitrogen from decaying plants and the methylation 

of mercury). Plant growth in wetlands provides a “sink” for 

many chemicals including atmospheric carbon. If a wetland is 

disturbed or degraded, these cycles can be altered and some of 

the chemicals may be released.

The extent of wetlands can be affected by a variety of natural 

stressors, such as erosion, land subsidence, changes in precipitation patterns (e.g., droughts), sea level change, hurricanes, and 

other types of storms. However, the vast majority of wetland 

losses and gains over the last few centuries have occurred as a 

result of human activity.14 For years, people have drained or 

filled wetlands for agriculture or urban and suburban development, causing habitat loss or fragmentation as well as a decline 

in many of the other important functions outlined above, such 

as improving water quality. Conversely, other human activities may increase the extent of wetlands—for example, creating 

shallow ponds or re-establishing formerly drained or modified 

wetlands on farmlands.

Wetland extent may influence condition, as wetland loss may 

result in added stress to remaining wetlands. For example, if 

fewer wetlands are available to filter pollutants from surface 

waters, those pollutants could become more concentrated in 

remaining downgradient wetlands. Wetland loss and fragmentation also lead to decreases in habitat, landscape diversity, and the 

connectivity among aquatic resources (i.e., fragmented wetlands 

essentially become isolated wildlife refuges). Thus, stressors that 

affect extent may ultimately affect condition as well.

Wetland condition also reflects the influence of stressors that 

affect topography, hydrology, climate, water condition, and 

biodiversity. For example, human modifications such as pipes 

and channels can alter the topography, elevation, or hydrology of 

wetlands, while withdrawal of ground water or upstream surface 

waters can directly reduce inflow. Natural forces and human 

activities (e.g., hurricanes, sea level change, and certain agricultural and forestry practices) can also affect wetlands through 

increased erosion or sedimentation. Pollutants in ground water 

and fresh surface waters that flow into wetlands may be toxic to 

plants and animals, and may also accumulate in wetland sediments. In addition, invasive species can alter the composition of 

wetland communities. Some of the most well-known invasives in 

the U.S. are wetland species, including plants such as phragmites 

and purple loosestrife and animals such as the nutria (a South 

American rodent introduced to the Chesapeake and Gulf states).

Another key stressor to wetlands is conversion from one wetland type to another. Although conversion can occur naturally 

through plant succession (such as marshes turning into forested 

wetlands over time), human activities can cause more drastic 

changes, such as clearing trees from a forested wetland, excavating a marsh to create an open water pond, or introducing certain 

invasive species (e.g., the nutria, which converts tidal marsh to 

open water by removing vegetation). Even if wetland extent is 

not altered, conversion from one type to another has a major ecological impact by altering habitat types and community structure.

3.4.2 ROE Indicators

An ROE indicator describes trends in wetland extent, as well as 

specific activities that have contributed to recent wetland losses 

and gains (Table 3-4). Data were collected as part of the U.S. 

Fish and Wildlife Service’s Wetlands Status and Trends survey, 

a probabilistic national survey of wetland acreage conducted 

approximately every 10 years for the past half-century. There is 

no ROE indicator for wetland condition.

14 Dahl, T.E. 2000. Status and trends of wetlands in the conterminous United 

States, 1986 to 1997. Washington, DC: U.S. Department of the Interior, Fish 

and Wildlife Service. <http://wetlandsfws.er.usgs.gov/status_trends/>
WATER

3-32 EPA’s 2008 Report on the Environment

INDICATOR | Wetland Extent, Change, and Sources of Change

Wetlands support a variety of fish and wildlife species and contribute to the aesthetic and environmental 

quality of the U.S. Millions of Americans use freshwater 

wetlands annually for hunting, fishing, bird watching, and 

other outdoor activities. Coastal wetlands provide valuable 

nursery, feeding, breeding, staging, and resting areas for an 

array of fish, shellfish, mammals, and birds (Dahl, 2000). 

In addition, wetlands serve as ground water recharge areas 

and filter contaminants from surface runoff (Mitsch and 

Gosselink, 1986). Destruction or alteration of wetlands, 

therefore, can have wide-ranging biological, chemical, and 

hydrological impacts.

Various lines of evidence suggest that when European 

settlers first arrived, wetland acreage in the area that 

would become the contiguous 48 states was more than 

twice what it is today (Dahl, 1990). Since then, extensive 

losses have occurred due to draining and filling. In addition to the sheer loss of wetland acreage, major ecological 

impacts also have resulted from the conversion of one 

wetland type to another, such as clearing trees from a 

forested wetland or excavating a shallow marsh to create 

an open water pond. These types of conversions change 

habitat types and community structure in watersheds and 

impact the animal communities that depend on them 

(Dahl, 2000).

This indicator presents data from the U.S. Fish and 

Wildlife Service’s Wetlands Status and Trends survey. 

Conducted approximately every 10 years, this survey provides an estimate of the extent of all wetlands in the contiguous U.S., regardless of land ownership. The Status and 

Trends survey uses a probabilistic design, based initially on 

stratification of the 48 contiguous states by state boundaries 

and 35 physiographic subdivisions. Within these subdivisions are located 4,375 randomly selected 4-square-mile 

(2,560-acre) sample plots. These plots are examined with 

the use of aerial imagery. Although the imagery ranges in 

scale and type, most are 1:40,000 scale, color infrared from 

the National Aerial Photography Program. Field verification is conducted to address questions of image interpretation, land use coding, and attribution of wetland gains or 

losses; plot delineations are also completed. In the 1980s to 

1990s analysis, 21 percent of the sample plots were fieldverified; in the most recent analysis, 32 percent were fieldverified (Dahl, 2000, 2006). The Fish and Wildlife Service 

used the Cowardin et al. (1979) definition of wetlands, 

which is part of the draft national standard for wetland 

mapping, monitoring, and data reporting as determined by 

the Federal Geographic Data Committee.

This indicator shows trends in the total extent of wetlands, as well as the extent of several types of freshwater 

and intertidal wetlands. In this analysis, freshwater wetlands include forested, shrub, emergent, and non-vegetated 

wetlands (e.g., shallow ponds). Intertidal wetlands include 

marine areas (e.g., tidal flats and sandbars) and estuarine 

areas (vegetated or not) that are exposed and flooded by the 

tides. Data on wetland extent are described from several 

Status and Trends analyses: 1950s-1970s, 1970s-1980s, 

1980s-1990s, and 1998-2004 (Frayer et al., 1983; Dahl and 

Johnson, 1991; Dahl, 2000, 2006). For the most recent 

period, the indicator also describes sources of wetland loss 

or gain, which the survey divided into five distinct land 

use categories along with an “other” category reflecting all 

other land use types (Dahl, 2006).

What the Data Show

Total wetland acreage declined over the last 50 years, but 

the rate of loss appears to have slowed over time. From the 

1950s to the 1970s, an average of 458,000 acres was lost 

per year (Exhibit 3-17). By the 1986-1997 period, the loss 

rate had declined to 58,600 acres per year; and in the most 

recent study period, 1998-2004, wetland area increased at a 

rate of 32,000 acres per year (Exhibit 3-17).

Gains and losses have varied by wetland type. Freshwater forested wetlands, which make up more than half 

of all freshwater wetlands, lost acreage from the 1950s 

to the 1990s but have shown gains over the last decade 

(Exhibit 3-18, panel A). Freshwater emergent wetlands 

have continued to lose acreage, although the rate of loss has 

slowed recently (panel C). Among freshwater categories, 

forested wetlands have sustained the greatest absolute losses 

since the 1950s, about 9 million acres, while emergent 

wetlands have shown the largest percentage loss (about 

21 percent). Conversely, the extent of freshwater shrub 

wetlands increased until the 1990s but declined thereafter, 

-458,000

-290,000

-58,600

+32,000

Net change in wetland extent (acres per year)

Reporting period

1954-1974 1974-1983 1986-1997 1998-2004

Exhibit 3-17. Average annual change in wetland 

acreage in the contiguous U.S., 1954-2004

Data source: Dahl, 2006

-500,000

-400,000

-300,000

-200,000

-100,000

0

100,000
WATER

EPA’s 2008 Report on the Environment 3-33

INDICATOR | Wetland Extent, Change, and Sources of Change (continued)

suggesting that some of the gains and losses 

in specific categories may reflect conversion rather than outright wetland loss or 

gain (Dahl, 2006; Exhibit 3-18, panel B). 

Shallow freshwater ponds, meanwhile, 

have increased steadily throughout the last 

50 years, with current acreage more than 

twice what it was in the 1950s, although 

still much less in absolute terms than the 

other wetland types (panel D). These 

wetlands account for a large percentage of 

the recent gains illustrated in Exhibit 3-17 

(Dahl, 2006). 

Since the 1950s, intertidal wetland acreage has decreased by about 700,000 acres, 

or 12 percent (Exhibit 3-19, panel A). 

This category includes marine, estuarine 

vegetated, and estuarine non-vegetated 

wetlands. Both estuarine types lost acreage 

overall, with estuarine vegetated wetlands, 

the predominant type, losing over 400,000 

acres (panel B). Long-term trends, however, 

indicate that losses of intertidal wetlands 

have slowed over time, with estuarine nonvegetated wetlands actually gaining acreage 

over the last decade (panel C).

Between 1998 and 2004, urban development, rural development, silviculture, 

and conversion to deepwater (e.g., the 

disappearance of coastal wetlands or flooding to create reservoirs) all contributed to losses in wetland acreage (Exhibit 3-20). However, the net change in wetland 

acreage during this period was positive, due largely to 

wetland creation and restoration on agricultural lands 

(70,770 acres) and on lands classified as “other” (349,600 

acres). This “other” category includes conservation lands, 

areas in transition from one land use to another, and other 

lands that do not fall into the major land use categories as 

defined in Dahl (2006).

Indicator Limitations

•	 Different methods were used in some of the early 

schemes to classify wetland types. As methods and spatial 

resolution have improved over time, acreage data have 

been adjusted, resulting in changes in the overall wetland 

base over time, thus reducing the accuracy of the trend.

•	 Ephemeral waters and effectively drained palustrine 

wetlands observed in farm production are not recognized 

as wetland types by the Status and Trends survey and are 

therefore not included in the indicator.

•	 Forested wetlands are difficult to photointerpret and are 

generally underestimated by the survey.

•	The aerial imagery used for this survey generally does 

not allow detection of small, isolated patches of wetland 

less than about an acre. 

•	Alaska and Hawaii are not included in the Status and 

Trends survey.

•	This survey does not include Pacific coast estuarine wetlands such as those in San Francisco Bay, Puget Sound, or 

Coos Bay, Oregon. 

Data Sources

Data for this indicator were obtained from Dahl (2006). 

Historical trends are based on data originally presented in 

earlier Fish and Wildlife Service reports (Dahl, 2000; Dahl 

and Johnson, 1991; Frayer et al., 1983).

References

Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 

1979. Classification of wetlands and deepwater habitats of 

the United States. FWS/OBS-79/31. Washington, DC: 

U.S. Department of the Interior, Fish and Wildlife Service.

<http://library.fws.gov/FWS-OBS/79_31.pdf>

Dahl, T.E. 2006. Status and trends of wetlands in the conterminous United States 1998 to 2004. Washington, DC: 

U.S. Department of the Interior, Fish and Wildlife Service.

<http://wetlandsfws.er.usgs.gov/status_trends/>

a

Based on mid-decade surveys. No analysis was conducted for the 1960s.

Data source: Dahl, 2006

A. Freshwater forested wetlands

61.2

Decade

55.2 51.9 50.7 52.0

0

10

20

30

40

50

60

70

1950s 1970s 1980s 1990s 2000s

1950s 1970s 1980s 1990s 2000s

1950s 1970s 1980s 1990s 2000s

1950s 1970s 1980s 1990s 2000s

Exhibit 3-18. Extent of selected freshwater wetlands in the 

contiguous U.S., 1950s-2000sa

B. Freshwater shrub wetlands

0

10

20

30

40

50

60

70

11.0 15.5 17.2 18.4 17.6

C. Freshwater emergent wetlands

0

10

20

30

40

50

60

70 D. Freshwater ponds

0

10

20

30

40

50

60

70

33.1 28.4 26.4 26.3 26.1

2.3 4.4 4.9 5.5 6.2

Extent (million acres)
WATER

3-34 EPA’s 2008 Report on the Environment

INDICATOR | Wetland Extent, Change, and Sources of Change (continued)

Dahl, T.E. 2000. Status and trends of wetlands in the conterminous United States 1986 to 1997. Washington, DC: 

U.S. Department of the Interior, Fish and Wildlife Service.

<http://wetlandsfws.er.usgs.gov/status_trends/>

Dahl, T.E. 1990. Wetlands losses in the United States 

1780s to 1980s. Washington, DC: U.S. Department of the 

Interior, Fish and Wildlife Service. 

<http://wetlandsfws.er.usgs.gov/status_trends/>

Dahl, T.E., and C.E. Johnson. 1991. Status and trends of 

wetlands in the conterminous United States, mid-1970s 

to mid-1980s. Washington, DC: U.S. Department of the 

Interior, Fish and Wildlife Service. 

<http://wetlandsfws.er.usgs.gov/status_trends/>

Frayer, W.E., T.J. Monahan, D.C. Bowden, and F.A. Graybill. 1983. Status and trends of wetlands and deepwater 

habitats in the conterminous United States, 1950s to 1970s. 

Ft. Collins, CO: Colorado State University. 

<http://wetlandsfws.er.usgs.gov/status_trends/>

Mitsch, W.J., and J.G. Gosselink. 1986. Wetlands. New 

York, NY: Van Nostrand Reinhold Company Inc.

Exhibit 3-19. Extent of marine and estuarine 

wetlands in the contiguous U.S., 1950s-2000sa,b

A. All intertidal wetlands (marine and estuarine)c

6.00

5.53 5.40 5.33 5.30

0

1

2

3

4

5

6

7

1950s 1970s

Decade

1980s 1990s 2000s

1950s 1970s

Decade

1980s 1990s 2000s

1950s 1970s

Decade

1980s 1990s 2000s

Extent (million acres)

B. Estuarine vegetated wetlands

0

1

2

3

4

5

6

7

Extent (million acres)

C. Estuarine non-vegetated wetlands

0

1

2

3

4

5

6

7

Extent (million acres)

5.00 4.85 4.62 4.60 4.57

0.74 0.68 0.59 0.59 0.60

a

Based on mid-decade surveys. No analysis was conducted for 

the 1960s.

b

Surveys did not include Pacific coast estuarine wetlands.

c

Panel A is the sum of panel B, panel C, and marine wetland acreage.

Data source: Dahl, 2006

Exhibit 3-20. Sources of wetland gain and loss 

in the contiguous U.S., 1998-2004

a

“Other” includes lands that do not fit into any of the other five 

categories, such as conservation land and land in transition 

between different uses. 

Data source: Dahl, 2006

+70,770

+349,600

-70,100 -51,440 -18,000 -88,960

-100,000

0

100,000

200,000

300,000

400,000

Deepwater

Urban

development

Rural development

Silviculture

Agriculture

Othera

Land use category

Net change in wetland extent (acres)

v
WATER

EPA’s 2008 Report on the Environment 3-35

3.4.3 Discussion

What This Indicator Says About Trends in 

the Extent and Condition of Wetlands and 

Their Effects on Human Health and the 

Environment

Wetland extent in the contiguous 48 states is substantially lower 

than it was prior to widespread European settlement and it 

generally continued to decline over the last 50 years (Wetlands 

indicator, p. 3-32). The rate of loss of wetlands overall and for 

most types of wetlands has slowed over time, however, and 

since 1998 the overall extent of wetlands has actually increased. 

Not all types of wetlands have experienced the same rate of 

losses or overall percent losses. For example, freshwater shrub 

wetlands actually increased over the last 50 years—providing 

evidence of wetland conversion, most likely from forested 

wetlands to shrub. The nation has also seen a steady increase 

in acreage of freshwater ponds, which account for a substantial 

portion of the recent gains in overall wetland acreage. 

This indicator also confirms the role of many of the stressors 

described in Section 3.4.1. Over the last decade, development, 

forestry, and conversion to deepwater (e.g., marsh to open 

water) have led to losses in wetland extent, while agricultural areas have experienced overall gains in wetland acreage. 

The other source of new wetland acreage is from the “other” 

land use category, which reflects the growing importance of 

constructed and restored wetlands, including ponds associated 

with golf courses and residential development.

While this indicator does not directly quantify the condition 

of the nation’s wetlands, it suggests that the condition of many 

wetlands may be impacted. As discussed in Section 3.4.1, extent 

can be a partial surrogate for condition because wetland loss can 

increase the stress on those wetlands that remain, while decreasing their connectivity. Thus, the overall decline in extent over 

the last 50 years suggests the potential for substantial ecological 

impacts such as habitat loss and increased flood impacts. Changes 

in the extent of different types of wetlands also suggest changes in 

condition. Shallow ponds, which constitute a large fraction of the 

recent gains in wetland acreage, will not perform the same range 

and type of environmental functions as the vegetated wetlands 

that disappeared between the 1950s and the 1990s, some of which 

continue to be lost. Similarly, evidence of wetland conversion indicates that even if extent is no longer declining rapidly, 

changes in wetland structure and function are still occurring. In 

the past, studies have shown that wetlands that have been created 

to mitigate wetland losses have not yet provided the same functions and values of the wetlands that were lost.15,16

Limitations, Gaps, and Challenges

By relying on aerial imagery and statistical surveying techniques, the Wetlands indicator (p. 3-32) provides a national 

estimate using a logistically plausible number of samples. 

However, a limitation to this survey is that it may omit or 

undercount certain types of wetlands, including forested wetlands—which are difficult to photointerpret—and ephemeral 

or well-drained agricultural wetlands, which are not necessarily obvious to the surveyor but are particularly threatened 

by development. This indicator also does not include wetland 

parcels smaller than about 1 acre, which become more critical 

as larger wetlands are fragmented into smaller pieces.

Wetland condition poses a larger challenge for assessment. While 

the Wetlands indicator (p. 3-32) provides information that can 

be used to infer potential wetland condition, it does not explicitly measure condition—in part because condition is difficult to 

quantify. Condition is made up of many different attributes, and 

each wetland has its own unique baseline condition and function, 

with a unique hydrologic setting and combination of plant and 

animal species. Some studies have quantified regional changes 

in specific stressors; however, national indicators would have to 

bring together many regional datasets and cover many different 

aspects of condition in order to be truly comprehensive. The lack 

of such national-scale information is currently a gap in addressing 

the question of wetland condition. Potential human health effects 

associated with wetland extent and condition are also difficult to 

quantify, and there are no ROE indicators on this topic.

Another information gap concerns the spatial patterns of 

wetland change, which are not documented in the existing 

national data. Are most large wetlands being left intact? Are 

human activities threatening to fragment larger wetlands into 

smaller pieces that are less connected and more isolated, and 

therefore less able to perform the desired ecological functions? 

Data on patterns of wetland loss—e.g., fragmentation and 

edge effects—would be a useful complement to the existing 

data on overall losses and gains.

3.5 What Are the Trends 

in the Extent and 

Condition of Coastal 

Waters and Their Effects 

on Human Health and 

the Environment?

3.5.1 Introduction

Coastal waters are one of the nation’s most important natural 

resources, valued for their ecological richness as well as for the 

many human activities they support. As the interface between 

15 National Research Council. 2001. Compensating for wetland losses under the 

Clean Water Act. Washington, DC: National Academies Press. <http://www.

nap.edu/books/0309074320/html/>

16 Mack, J.J., and M. Micacchion. 2006. An ecological assessment of Ohio mitigation banks: Vegetation, amphibians, hydrology, and soils. Ohio EPA Technical Report WET/2006-1. Columbus, OH: Ohio Environmental Protection 

Agency. <http://www.epa.state.oh.us/dsw/wetlands/WetlandBankReport.

html>
WATER

3-36 EPA’s 2008 Report on the Environment

terrestrial environments and the open ocean, coastal waters 

encompass many unique habitats, such as estuaries, coastal 

wetlands, seagrass meadows, coral reefs, mangrove and kelp 

forests, and upwelling areas.17,18 Coastal waters support many 

fish species for at least part of their life cycle, offering some 

of the most productive fisheries habitats in the world. These 

waters also provide breeding habitat for 85 percent of U.S. 

waterfowl and other migratory birds (largely in coastal wetlands),19 and support many other organisms with high public 

visibility (e.g., marine mammals, corals, and sea turtles) or 

unique ecological significance (e.g., submerged aquatic vegetation). For humans, coastal waters provide opportunities for 

tourism and recreation, and they contribute to the economy 

through transportation, fisheries, and mining and utilities.20

Lands adjacent to the coast are highly desirable places for 

people to live, and represent the most densely developed areas 

in the nation.21

Extent and condition are two key variables in assessing coastal 

waters and their ability to serve ecological and human needs. 

The extent of coastal waters—i.e., the spatial area—is particularly important in terms of the extent of specific types of 

coastal waters, such as coastal wetlands or coral reefs. The condition of coastal waters reflects a group of interrelated physical, 

chemical, biological, and ecological attributes. For example, 

nutrient levels should be sufficient to support the food web but 

not so high as to cause eutrophication, while toxic chemical contaminants in water and sediment may pose a threat to 

aquatic organisms or accumulate in the food web. Of particular concern to human health are contaminants in consumable 

fish and shellfish—a topic discussed separately in Section 3.8. 

Other key aspects of condition include levels of pathogens and 

organisms that produce biotoxins—which may pose a risk to 

human health through aquatic recreation or contaminated 

fish and shellfish, and which may impact the environment by 

injuring native populations. Also important is the degree to 

which native plant and animal populations are healthy and 

their habitats intact.

Many factors can affect the extent of coastal waters. For 

example, the extent of coastal wetlands may be influenced by 

natural events such as erosion or storms, or by human activities such as draining or filling wetlands for development. 

Natural processes can change the shape of a coastline, with 

wave action eroding some areas while building up sediment 

in others, and rivers depositing sediments at their mouth. 

Human stressors can alter these patterns—for example, 

through the construction of seawalls or barriers or through 

the channeling of rivers, which can lead to subsidence in 

coastal areas that would otherwise be naturally replenished 

by sediments.

Changes in extent may in turn affect the condition of coastal 

waters. For example, beach erosion and coastal wetland loss 

can also affect contaminant and sediment levels, nutrient 

cycling, and the condition of spawning and feeding grounds 

for fish, shellfish, and other coastal species. As described in 

Section 3.4.1, the loss of some wetlands can also affect the 

condition of the wetlands that remain.

Other stressors to the condition of coastal waters include nutrients, pathogens, and chemical contaminants, which may pose 

risks to ecological systems or to human health. Nutrients and 

pathogens occur naturally, but their abundance can be increased 

by human activities along the coast or in upstream watersheds 

that ultimately discharge to coastal waters. Major sources 

include urban and suburban storm water, agricultural runoff, 

and sewage discharge or overflows. Chemical contaminants 

may come from these same sources, as well as from industrial 

activities that discharge treated wastewaters and from atmospheric deposition of airborne pollutants.

Several other stressors can affect the quality of habitat 

and the status of native plant and animal populations. For 

example, many species are sensitive to temperature and salinity, which can be influenced by changes in weather patterns 

or the condition of freshwater inputs. Salinity is particularly important in estuaries, where species may depend on 

a steady, reliable flow of fresh water. Another factor affecting the status of native communities is the presence and 

abundance of non-indigenous species—particularly invasive 

species that can kill or crowd out native populations, or otherwise alter coastal watersheds. Populations of fish, shellfish, 

marine mammals, and other species used by humans may 

also be affected by overharvesting.

In many cases, stressors that affect coastal condition are interrelated. For example, excess nutrients can cause algal blooms 

(and subsequent decay) that result in low dissolved oxygen and 

reduced water clarity—the chain of events known as eutrophication. Temperature and salinity can also influence algal 

blooms. Some algae, such as “red tide,” produce toxins that 

pose risks to humans.

17 U.S. Environmental Protection Agency. 2004. National coastal condition 

report II. EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

18 Although the Laurentian Great Lakes are included in EPA’s Coastal Condition Report because they fall under the “Great Waters” designation, in the 

ROE they are covered in the question on fresh surface waters, Section 3.2.

19 U.S. Environmental Protection Agency. 2004. National coastal condition 

report II. EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

20 National Oceanic and Atmospheric Administration. 2005. Economic statistics 

for NOAA. May 2005. Fourth edition. U.S. Department of Commerce. 

<http://www.publicaffairs.noaa.gov/pdf/economic-statistics2005.pdf>

21 National Oceanic and Atmospheric Administration. 2004. Population trends 

along the coastal United States: 1980-2008. Coastal trends report series. Silver 

Spring, MD: U.S. Department of Commerce, National Ocean Service.
WATER

EPA’s 2008 Report on the Environment 3-37

3.5.2 ROE Indicators

Five National Indicators and two Regional Indicators 

characterize the extent and condition of coastal waters 

(Table 3-5). National Indicators describe sediment quality, benthic community condition, contamination in fish 

tissue, and several aspects of coastal water quality, as well 

as trends in the extent of marine and estuarine wetlands. 

The Regional Indicators characterize trends in the extent 

of areas with low dissolved oxygen (i.e., hypoxia) and 

the extent of submerged aquatic vegetation (SAV). These 

Regional Indicators reflect conditions in three important 

and unique coastal water bodies: the Gulf of Mexico, Long 

Island Sound, and the Chesapeake Bay.

The National Indicator on wetland extent is based on data 

gathered from aerial and ground surveys conducted as part 

of the U.S. Fish and Wildlife Service’s Wetlands Status 

and Trends study, a long-term statistical sampling effort. 

The other four National Indicators are derived from EPA’s 

second National Coastal Condition Report, which involved 

probabilistic surveys designed to represent 100 percent of 

estuarine acreage in the contiguous 48 states and Puerto 

Rico. In addition to national totals, these four indicators 

present data by EPA Region. The Regional Indicator on 

trends in hypoxia reflects data from two long-term water 

sampling programs, while the indicator on SAV is based on 

aerial imagery.

Table 3-5. ROE Indicators of Trends in the Extent and Condition of 

Coastal Waters and Their Effects on Human Health and the Environment

National Indicators Section Page

Wetland Extent, Change, and Sources of Change 3.4.2 3-32

Trophic State of Coastal Waters (N/R) 3.5.2 3-38

Coastal Sediment Quality (N/R) 3.5.2 3-42

Coastal Benthic Communities (N/R) 3.5.2 3-44

Coastal Fish Tissue Contaminants (N/R) 3.8.2 3-61

Regional Indicators Section Page

Submerged Aquatic Vegetation in the Chesapeake Bay 3.5.2 3-46

Hypoxia in the Gulf of Mexico and Long Island Sound 3.5.2 3-48

N/R = National Indicator displayed at EPA Regional scale
WATER

3-38 EPA’s 2008 Report on the Environment

INDICATOR | Trophic State of Coastal Waters

While the presence of many water pollutants can lead to decreases in coastal water quality, four interlinked 

components related to trophic state are especially critical: nutrients (nitrogen and phosphorus), chlorophyll-a,

dissolved oxygen, and water clarity. “Trophic state” 

generally refers to aspects of aquatic systems associated 

with the growth of algae, decreasing water transparency, 

and low oxygen levels in the lower water column that 

can harm fish and other aquatic life. Nitrogen is usually 

the most important limiting nutrient in estuaries, driving large increases of microscopic phytoplankton called 

“algal blooms” or increases of large aquatic bottom plants, 

but phosphorus can become limiting in coastal systems 

if nitrogen is abundant in a bioavailable form (U.S. EPA, 

2003). Nitrogen and phosphorus can come from point 

sources, such as wastewater treatment plants and industrial effluents, and nonpoint sources, such as runoff from 

farms, over-fertilized lawns, leaking septic systems, and 

atmospheric deposition. Chlorophyll-a is a surrogate 

measure of phytoplankton abundance in the water column. Chlorophyll-a levels are increased by nutrients and 

decreased by filtering organisms (e.g., clams, mussels, or 

oysters). High concentrations of chlorophyll-a indicate 

overproduction of algae, which can lead to surface scums, 

fish kills, and noxious odors (U.S. EPA, 2004). Low dissolved oxygen levels and decreased clarity caused by algal 

blooms or the decay of organic matter from the watershed are stressful to estuarine organisms. Reduced water 

clarity (usually measured as the amount and type of light 

penetrating water to a depth of 1 meter) can be caused 

by algal blooms, sediment inputs from the watershed, or 

storm-related events that cause resuspension of sediments, 

and can impair the normal growth of algae and other submerged aquatic vegetation.

This indicator, developed as part of EPA’s Coastal Condition Report, is based on an index constructed from probabilistic survey data on five components: dissolved inorganic 

nitrogen, dissolved inorganic phosphorus, chlorophyll-a,

daytime dissolved oxygen in bottom or near-bottom 

waters (where benthic life is most likely to be affected), 

and water clarity (U.S. EPA, 2004). The survey, part of 

EPA’s National Coastal Assessment (NCA), was designed 

to provide a national picture of water quality by sampling 

sites in estuarine waters throughout the contiguous 48 

states and Puerto Rico. Each site was sampled once during 

the 1997-2000 period, within an index period from July to 

September. The indicator reflects average condition during 

this index period. 

Key factors like sediment load, mixing processes, and ecosystem sensitivity naturally vary across biogeographic regions 

and even among estuaries within regions. Thus, reference 

guidelines for nutrients, water clarity, and chlorophyll-a were 

established based on variable expectations for conditions in 

different biogeographic regions. For example, due to 

Pacific upwelling during the summer, higher nutrient and 

chlorophyll-a concentrations are expected in West Coast 

estuaries than in other estuaries. Water clarity reference 

guidelines are lower for estuaries that support seagrass 

than for naturally turbid estuaries. A single national 

reference range of 2-5 milligrams per liter (mg/L) was 

used for dissolved oxygen, because concentrations below 

2 mg/L are almost always harmful to many forms of 

aquatic life and concentrations above 5 mg/L seldom 

are (Diaz and Rosenberg, 1995; U.S. EPA, 2000). The 

process of classifying individual sites varies by region and 

is described in detail, along with the regional reference 

conditions, in U.S. EPA (2004).

The overall water quality index is a compilation of the 

five components. For each site, the index is rated high if 

none of the five components received a score that would 

8

High Moderate Low

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.b

Exhibit 3-21. Coastal water quality index for the 

contiguous U.S. and Puerto Rico, by EPA 

Region, 1997-2000a

Unsampled

1

71 8

48 8 35

52 36

46 46 8

38 55 7

23 62 15

29 70

40 49 11

4

Water quality:

Percent of estuarine area in each category:

20 1

9

Data source: U.S. EPA, 2004, 2005a

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto Rico. 

Does not include the hypoxic zone in 

offshore Gulf Coast waters.

b

U.S. figures reflect the total sampled 

area. Unsampled areas were not 

included in the calculation.

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2
WATER

EPA’s 2008 Report on the Environment 3-39

INDICATOR | Streambed Stability in Wadeable Streams Trophic State of Coastal Waters (continued)

be considered environmentally unfavorable (high nitrogen, phosphorus, or chlorophyll-a levels or low dissolved 

oxygen or water clarity), and no more than one component was rated moderate. Overall water quality is low if 

more than two components received the most unfavorable 

rating. All other sites receive a moderate index score. If 

two or more components are missing, and the available components do not suggest a moderate or low index 

rating, the site is classified as “unsampled.” Data from 

the individual sites were expanded from the probability 

sample to provide unbiased estimates of the water quality 

index and each of its components for each EPA Region. 

Results were also aggregated and weighted by estuarine 

area for the entire nation.

What the Data Show

According to the index, 40 percent of estuarine surface 

area nationwide exhibited high water quality over the 

1997-2000 period, 11 percent had low water quality, and 

the remaining 49 percent was rated moderate (Exhibit 

3-21). Scores vary considerably among EPA Regions, 

ranging from high water quality in 71 percent of estuarine 

area in Region 1 to less than 10 percent in Regions 2 and 

3. Only one EPA Region had low water quality in more 

than 15 percent of its estuarine area (EPA Region 3, with 

36 percent). These percentages do not include the Great 

Lakes or the hypoxic zone in offshore Gulf Coast waters 

(see the Hypoxia in Gulf of Mexico and Long Island 

Sound indicator, p. 3-48). 

Nitrogen concentration:

Percent of estuarine area in each category:

74 17

88 12

9

84 13 3

88

82 13 5

100

12

27 1523 34

63 14 16 7

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.d

Low Moderate High Unsampled

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

Exhibit 3-22. Nitrogen concentrations in coastal 

waters of the contiguous U.S. and Puerto Rico, 

by EPA Region, 1997-2000a,b,c

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto Rico.

b

This indicator measures dissolved 

inorganic nitrogen (DIN), which is 

the sum of nitrate, nitrite, and 

ammonia.

c

Totals may not add to 100% due to 

rounding. 

d

U.S. figures reflect the total sampled area. Unsampled areas 

were not included in the calculation.

Data source: U.S. EPA, 2004, 2005a

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.d

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

Phosphorus concentration:

Percent of estuarine area in each category:

58 32 10 1

16 41 9 34

58 29 6 6

66 1024

49 37 15

2 46 52

5 95

53 38 9

Exhibit 3-23. Phosphorus concentrations in 

coastal waters of the contiguous U.S. and 

Puerto Rico, by EPA Region, 1997-2000 a,b,c

Low Moderate High Unsampled

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto Rico.

b

This indicator measures dissolved 

inorganic phosphorus (DIP), which 

equals orthophosphate. 

c

Totals may not add to 100% due to 

rounding.

d

U.S. figures reflect the total 

sampled area. Unsampled areas were not included in the 

calculation.

Data source: U.S. EPA, 2004, 2005a
WATER

3-40 EPA’s 2008 Report on the Environment

INDICATOR | Streambed Stability in Wadeable Streams Trophic State of Coastal Waters (continued)

Nitrogen concentrations were low in 82 percent of 

estuarine area and high in 5 percent nationwide, and were 

low in a majority of the estuarine area in all but one EPA 

Region (Exhibit 3-22). Regions 2 and 3 had the largest 

percentage of area with high concentrations (15 percent 

and 16 percent, respectively); several other EPA Regions 

had no areas with high concentrations. 

Phosphorus concentrations were low in 53 percent of 

estuarine area and high in 9 percent nationwide (Exhibit 

3-23). Region 9 had the largest proportion of area exceeding reference conditions (52 percent), while Region 10 had 

the least (none). 

Chlorophyll-a concentrations were low in 51 percent and high in 8 percent of estuarine area nationwide 

(Exhibit 3-24). Region 3 had the largest percentage of area 

exceeding reference conditions (27 percent); all other EPA 

Regions had 10 percent or less in this category. 

Bottom-water dissolved oxygen was above 5 mg/L 

in over three-fourths of the nation’s estuarine area and 

below 2 mg/L in only 4 percent (Exhibit 3-25). While 

effects vary with temperature and salinity, as a general 

rule, concentrations of dissolved oxygen above 5 mg/L are 

considered supportive of marine life, concentrations below 

5 mg/L are potentially harmful, and concentrations below 

2 mg/L—a common threshold for hypoxia—are associated 

with a wider range of harmful effects (e.g., some juvenile 

fish and crustaceans that cannot leave the area may die). 

Region 3 had the greatest proportion of estuarine area 

with low dissolved oxygen (21 percent), while four EPA 

Regions had no area below 2 mg/L. 

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.c

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

88 6 6

24 731 37

13 54 27 6

33 57 10

53 41 6

87

51 41 8

80 20

13

Exhibit 3-24. Chlorophyll-a concentrations in

coastal waters of the contiguous U.S. and Puerto

Rico, by EPA Region, 1997-2000 a,b

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto Rico.

b

Totals may not add to 100% due to 

rounding.

c

U.S. figures reflect the total sampled 

area. Unsampled areas were not 

included in the calculation. 

Data source: U.S. EPA, 2004, 2005a

Chlorophyll-a concentration:

Percent of estuarine area in each category:

Low Moderate High Unsampled

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.c

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

87 11 2

66 21 13

75 23 2

84 16

53 21 21 4

67 31 2

98 2

76 20 4

High

(> 5 mg/L)

Moderate

(2-5 mg/L)

Low

(< 2 mg/L) Unsampled

a

Coverage: Bottom- or near 

bottom-water dissolved oxygen in 

estuarine waters of the contiguous 

48 states and Puerto Rico. Does not 

include the hypoxic zone in offshore 

Gulf Coast waters. 

b

Totals may not add to 100% due to 

rounding.

c

U.S. figures reflect the total sampled area. Unsampled areas were 

not included in the calculation.

Data source: U.S. EPA, 2004, 2005a

Exhibit 3-25. Dissolved oxygen levels in 

coastal waters of the contiguous U.S. and 

Puerto Rico, by EPA Region, 1997-2000 a,b

Dissolved oxygen concentration:

Percent of estuarine area in each category:
WATER

EPA’s 2008 Report on the Environment 3-41

INDICATOR | Trophic State of Coastal Waters (continued)

Water clarity exceeded reference conditions (i.e., higher 

clarity) in 62 percent of the nation’s estuarine area, while 

low water clarity was observed in 25 percent of estuarine 

area (Exhibit 3-26). Region 3 had the largest proportion of 

area with low clarity (43 percent), while Region 1 had the 

smallest (none). 

Indicator Limitations

•	The coastal areas of Hawaii and a portion of Alaska 

have been sampled, but the data had not yet been 

assessed at the time this indicator was compiled. Data 

are also not available for the U.S. Virgin Islands and the 

Pacific territories.

•	 Trend data are not yet available for this indicator. Because 

of differences in methodology, the data presented here 

are not comparable with data that appeared in EPA’s first 

National Coastal Condition Report. The data presented 

here will serve as a baseline for future surveys. 

•	The NCA surveys measure dissolved oxygen conditions 

only in estuarine waters and do not include observations of dissolved oxygen concentrations in offshore 

coastal shelf waters, such as the hypoxic zone in Gulf 

of Mexico shelf waters.

•	At each sample location, the components of this indicator may have a high level of temporal variability. This 

survey is intended to characterize the typical distribution 

of water quality conditions in coastal waters during an 

index period from July through September. It does not 

consistently identify the “worst-case” condition for sites 

experiencing occasional or infrequent hypoxia, nutrient 

enrichment, or decreased water clarity at other times of 

the year. 

Data Sources

This indicator is based on an analysis published in EPA’s 

second National Coastal Condition Report (U.S. EPA, 

2004). Summary data by EPA Region have not been published, but were provided by EPA’s NCA program (U.S. 

EPA, 2005a). Underlying sampling data are housed in 

EPA’s NCA database (U.S. EPA, 2005b) (http://www.epa.

gov/emap/nca/html/data/index.html).

References

Diaz, R.J., and R. Rosenberg. 1995. Marine benthic 

hypoxia: A review of its ecological effects and the behavioral responses of benthic macrofauna. Oceanogr. Mar. 

Biol. Ann. Rev. 33:245-303.

U.S. EPA (United States Environmental Protection 

Agency). 2005a. Data provided to ERG (an EPA contractor) 

by Kevin Summers, EPA. September 2005.

U.S. EPA. 2005b. EMAP national coastal database. 

Accessed 2005. <http://www.epa.gov/emap/nca/html/

data/index.html>

U.S. EPA. 2004. National coastal condition report II. 

EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

U.S. EPA. 2003. Mid-Atlantic integrated assessment, 

MAIA—estuaries 1997-98, summary report. 

EPA/620/R-02/003.

U.S. EPA. 2000. Ambient aquatic life water quality criteria 

for dissolved oxygen (saltwater): Cape Cod to Cape Hatteras. EPA/822/R-00/12.

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.c

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto Rico.

b

Totals may not add to 100% due to 

rounding.

c

U.S. figures reflect the total sampled 

area. Unsampled areas were not 

included in the calculation.

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

95 4

38 14 43 5

66 12 19 3

47 22 31

65 11 24

44 18 38

62 13 25

82 7 10

Exhibit 3-26. Water clarity in coastal waters of 

the contiguous U.S. and Puerto Rico, by EPA 

Region, 1997-2000 a,b

High Moderate Low Unsampled

Water clarity:

Percent of estuarine area in each category:

Data source: U.S. EPA, 2004, 2005a

v
WATER

3-42 EPA’s 2008 Report on the Environment

INDICATOR | Streambed Stability in Wadeable Streams Coastal Sediment Quality

Contaminated sediments can pose an immediate threat to benthic organisms and an eventual threat to entire estuarine ecosystems. Sediments can be resuspended by anthropogenic activities, storms, or other natural events; as a result, 

organisms in the water column can be exposed to contaminants, which may accumulate through the food web and 

eventually pose health risks to humans (U.S. EPA, 2004a).

There are several ways to measure sediment quality. 

Sediments can be assessed in terms of their toxicity to 

specific organisms in bioassays, or in terms of the levels of 

contaminants that are present. Sediment quality also can be 

inferred by assessing the condition of benthic communities, 

which largely reflect the quality of the sediments in which 

they live (although other stressors may be reflected as well). 

To generate a more complete picture of sediment quality, 

scientists frequently use several of these measures together. 

This indicator presents data on sediment toxicity and 

contaminant levels. The data are from probabilistic surveys 

conducted as part of EPA’s National Coastal Assessment 

(NCA) and presented in EPA’s second National Coastal 

Condition Report (U.S. EPA, 2004b). The survey was 

designed to provide a national picture of sediment quality 

by sampling sites in estuarine waters throughout the contiguous 48 states and Puerto Rico. Each site was sampled once 

during the 1997-2000 period, within an index period from 

July to September. The indicator reflects average condition in each EPA Region during this index period. Results 

were also aggregated and weighted by estuarine area for the 

entire nation. 

Sediment toxicity is typically determined using bioassays 

that expose test organisms to sediments and evaluate their 

effects on the organisms’ survival. For this indicator, toxicity was determined using a 10-day static test on the benthic 

amphipod Ampelisca abdita, which is commonly used as a 

screening tool to identify sediments that pose sufficient 

concern to warrant further study. Sediments were classified 

as “potentially toxic” if the bioassays resulted in greater 

than 20 percent mortality (a reference condition), or “not 

likely toxic” if the bioassays resulted in 20 percent mortality or less (U.S. EPA, 2004c).

Contaminant concentrations do not directly reflect 

toxicity because toxicity also depends on contaminants’ 

bioavailability, which is controlled by pH, particle size and 

type, organic content, and other factors (e.g., mercury vs. 

methylmercury). Contaminant concentrations are a useful screening tool for toxicity, however, when compared 

with concentrations known to cause particular effects on 

benthic life. For this indicator, sediment samples were 

homogenized and analyzed for nearly 100 contaminants, 

including 25 polycyclic aromatic hydrocarbons (PAHs), 

22 polychlorinated biphenyls (PCBs), 25 pesticides, and 15 

metals, using standard wet chemistry and mass spectroscopy. The observed concentrations were then compared 

with “effects range median” (ERM) values established 

through an extensive review of toxicity tests involving 

benthic organisms, mostly Ampelisca (Long et al., 1995). 

ERM values were available for 28 contaminants. For each 

contaminant, the ERM represents the concentration at 

which there is a 50 percent likelihood of adverse effects to 

an organism, based on experimental data. For this indicator, a site was rated “potentially toxic” if one or more 

contaminants exceeded an ERM value. In practice, about 

25 percent of samples that exceed one ERM also cause 

more than 20 percent mortality in the Ampelisca bioassay 

(Long, 2000). 

Benthic community condition also can be a useful indication of sediment quality, particularly in terms of chronic 

or community effects that would not be captured in an 

acute exposure bioassay. The NCA evaluated estuarine 

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.e

Not likely toxicc Potentially toxicd Unsampled

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

89.0 5.4

73.0 13.9

92.3 3.0

87.2 0.2

38.7 60.3

99.8 0.2

79.9 20.1

94.0 6.0

1.0

12.6

4.7

13.0

5.6

Exhibit 3-27. Sediment toxicity in coastal waters

of the contiguous U.S. and Puerto Rico, by EPA 

Region, 1997-2000 a,b

Sediment toxicity:

Percent of estuarine area in each category:

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto 

Rico.

b

Totals may not add to 100% due to 

rounding.

c

Not likely toxic: Mortality of test 

species = 20% or lower

d

Potentially toxic: Mortality of test 

species > 20%

e

U.S. figures reflect the total sampled area. Unsampled areas were 

not included in the calculation.

Data source: U.S. EPA, 2004b, 2005a
WATER

EPA’s 2008 Report on the Environment 3-43

INDICATOR | Streambed Stability in Wadeable Streams Coastal Sediment Quality (continued)

sites for several aspects of benthic community condition, 

and these results are presented as a separate ROE indicator 

(Coastal Benthic Communities, p. 3-44).

What the Data Show

Nationwide, 6 percent of coastal sediments were rated 

“potentially toxic” based on the Ampelisca toxicity screening assay, although there was considerable variability from 

one EPA Region to the next (Exhibit 3-27). In Region 9, 

nearly 100 percent of estuarine area exhibited low sediment toxicity, while in some other EPA Regions, as much 

as 20 percent of estuarine sediments were “potentially 

toxic.” Data for Region 6 are inconclusive because more 

than half of the Region’s estuarine area was not sampled.

Nationally, contaminants were present at “potentially 

toxic” levels in 7 percent of estuarine sediments for which 

contamination data were available (Exhibit 3-28). There was 

considerable variability in sediment contamination from one 

EPA Region to the next, with Region 4 showing the largest 

proportion of estuarine area with sediments not likely to be 

toxic (99.9 percent) and Region 2 showing the largest proportion with “potentially toxic” sediments (24.4 percent).

Although the two figures suggest that a similar percentage of the nation’s estuarine sediments are “potentially 

toxic,” the original data source reports very little correlation between sites that caused more than 20 percent mortality in the Ampelisca bioassay and sites where one or more 

contaminants exceeded the ERM (U.S. EPA, 2004b). It 

is not unusual to find a lack of correlation—particularly 

in cases where sediment contaminants are neither highly 

concentrated nor completely absent—in part because some 

toxic chemicals may not be bioavailable, some may not be 

lethal, and not all potentially toxic chemicals are analyzed (see O’Connor et al., 1998, and O’Connor and Paul, 

2000). These results underscore the utility of a combined 

approach to screen for potentially toxic sediments.

Indicator Limitations

•	 The coastal areas of Hawaii and a portion of Alaska have 

been sampled, but the data had not yet been assessed at the 

time this indicator was compiled. Data are also not available for the U.S. Virgin Islands and the Pacific territories.

•	 Trend data are not yet available for this indicator. Because 

of differences in methodology, the data presented here 

are not comparable with data that appeared in EPA’s first 

National Coastal Condition Report. The data presented 

here will serve as a baseline for future surveys.

•	 Sample collection is limited to an index period from July 

to September. It is not likely that contaminant levels vary 

from season to season, however.

•	The Ampelisca bioassay is a single-organism screening 

tool, and the ERMs are general screening guidelines 

based largely on toxicity data from Ampelisca. Thus, 

these measures do not necessarily reflect the extent to 

which sediments may be toxic to the full range of biota 

(including microbes and plants) that inhabit a particular 

sampling location.

•	The Ampelisca bioassay tests only for short-term, not 

long-term, exposure. Both screening tests characterize 

sediments in terms of their effects on benthic organism 

mortality. This indicator does not capture other effects 

of sediment contaminants on benthic organisms, such as 

disease, stress, and reproductive effects.

•	This indicator cannot be compared quantitatively with 

indicators that use other types of contaminant guidelines. For example, the Pesticides in Agricultural Streams 

indicator (p. 3-27) uses thresholds intended to be protective of aquatic life with a margin of safety, instead of 

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.d

Not likely toxicb Potentially toxicc Unsampled

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

90.0 4.6

62.0 24.4

88.2 9.4

99.9 0.1

1.9

81.7 18.3

92.8 7.2

98.1

93.0 7.0

2.4

13.6

5.4

Exhibit 3-28. Sediment contamination in 

coastal waters of the contiguous U.S. and 

Puerto Rico, by EPA Region, 1997-2000a

Sediment contamination:

Percent of estuarine area in each category:

a

Coverage: Estuarine waters of the 

contiguous 48 states and Puerto 

Rico.

b

Not likely toxic: No contaminants 

above effects range median (ERM)

c

Potentially toxic: One or more 

contaminants above effects range 

median (ERM)

d

U.S. figures reflect the total sampled area. Unsampled areas were 

not included in the calculation.

Data source: U.S. EPA, 2004b, 2005a
WATER

3-44 EPA’s 2008 Report on the Environment

INDICATOR | Streambed Stability in Wadeable Streams Coastal Sediment Quality (continued)

thresholds shown to cause biological effects (e.g., ERMs). 

The ERM approach also is not directly comparable with 

other sediment contaminant approaches, such as EPA’s 

equilibrium partitioning (EqP) benchmarks.

Data Sources

This indicator is based on an analysis published in EPA’s second National Coastal Condition Report (U.S. EPA, 2004b). 

Summary data by EPA Region have not been published, 

but were provided by EPA’s NCA program (U.S. EPA, 

2005a). Underlying sampling data are housed in EPA’s NCA 

database (U.S. EPA, 2005b) (http://www.epa.gov/emap/

nca/html/data/index.html).

References

Long, E.R. 2000. Degraded sediment quality in U.S. 

estuaries: A review of magnitude and ecological applications. Ecol. Appl. 10(2):338-349.

Long, E.R., D.D. MacDonald, L. Smith, and F.D. Calder. 

1995. Incidence of adverse biological effects within ranges of 

chemical concentrations in marine and estuarine sediments. 

Environ. Manage. 19:81-97.

O’Connor, T.P., K.D. Daskalakis, J.L. Hyland, J.F. Paul, 

and J.K. Summers. 1998. Comparisons of sediment toxicity 

with predictions based on chemical guidelines. Environ. 

Toxicol. Chem. 17(3):468-471.

O’Connor, T.P., and J.F. Paul. 2000. Misfit between 

sediment toxicity and chemistry. Mar. Pollut. Bull. 

40(1):59-64.

U.S. EPA (United States Environmental Protection Agency). 

2005a. Data provided to ERG (an EPA contractor) by Kevin 

Summers, EPA. September 2005.

U.S. EPA. 2005b. EMAP national coastal database. 

Accessed 2005. <http://www.epa.gov/emap/nca/html/

data/index.html>

U.S. EPA. 2004a. Contaminated sediment in water. 

<http://www.epa.gov/waterscience/cs/aboutcs>

U.S. EPA. 2004b. National coastal condition report II. 

EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

U.S. EPA. 2004c. The incidence and severity of sediment 

contamination in surface waters of the United States—

national sediment quality survey. Second edition. 

<http://www.epa.gov/waterscience/cs/report/2004/

 nsqs2ed-complete.pdf>

v

INDICATOR | Coastal Benthic Communities

Benthic communities are largely composed of macroinvertebrates, such as annelids, mollusks, and crustaceans. These organisms inhabit the bottom substrates of 

estuaries and play a vital role in maintaining sediment and 

water quality. They also are an important food source for 

bottom-feeding fish, invertebrates, and birds. Communities of benthic organisms are important indicators of environmental stress because they are particularly sensitive to 

pollutant exposure (Holland et al., 1987). This sensitivity 

arises from the close relationship between benthic organisms and sediments—which can accumulate environmental 

contaminants over time—and the fact that these organisms 

are relatively immobile, which means they receive prolonged exposure to any contaminants in their immediate 

habitat (Sanders et al., 1980; Nixon et al., 1986).

This indicator is based on a multi-metric benthic communities index that reflects overall species diversity in estuarine 

areas throughout the contiguous United States (adjusted for 

salinity, if necessary) and, for some regions, the presence 

of pollution-tolerant and pollution-sensitive species (e.g., 

Weisberg et al., 1997; Engle and Summers, 1999; U.S. EPA, 

2004). The benthic community condition at each sample 

site is given a high score if the index exceeds a particular 

threshold (e.g., has high diversity or populations of many 

pollution-sensitive species), a low score if it falls below the 

threshold conditions, and a moderate score if it falls within 

the threshold range. The exact structure of the index and 

the threshold values vary from one biogeographic region to 

another, but comparisons between predicted and observed 

scores based on expert judgment are used to ensure that the 

classifications of sites from one region to another are consistent (U.S. EPA, 2004). Data were collected using probability 

samples, so the results from the sampling sites provide unbiased estimates of the distribution of index scores in estuaries 

throughout each region. 

The data for this indicator are from probabilistic surveys 

conducted as part of EPA’s National Coastal Assessment 

(NCA) and presented in EPA’s second National Coastal 

Condition Report (U.S. EPA, 2004). The survey was 

designed to provide a national picture of coastal benthic 
WATER

EPA’s 2008 Report on the Environment 3-45

INDICATOR | Coastal Benthic Communities (continued)

community condition by sampling sites in estuarine waters 

throughout the contiguous 48 states and Puerto Rico. Each 

site was sampled once during the 1997-2000 period, within 

an index period from July to September. The indicator 

reflects average condition in each EPA Region during this 

index period. Results were also aggregated and weighted 

by estuarine area for the entire nation.

What the Data Show

Nationally, 70 percent of the sampled estuarine area had a 

high benthic communities index score, with 13 percent in 

the moderate range and 17 percent scoring low (Exhibit 

3-29). Condition varied somewhat by EPA Region, with 

high index scores ranging from 51 percent of the estuarine 

area in Region 6 to 91 percent in Region 10. Region 3 

had the largest proportion of estuarine area rated low (27 

percent), while Region 10 had the lowest (4 percent). In 

the figure, the portion of the estuarine area not represented 

by the sample is noted for each Region.

The National Coastal Condition Report found that 

many of the sites with low benthic community condition 

also showed impaired water quality or sediment condition—which is not surprising given the extent to which 

these stressors and effects are related. Of the 17 percent of 

national estuarine area rated low on the benthic communities index, 38 percent also exhibited degraded sediment 

quality, 9 percent exhibited degraded water quality (U.S. 

EPA, 2004), and 33 percent exhibited degraded quality of 

both sediment and water.

Indicator Limitations

•	 The coastal areas of Hawaii and a portion of Alaska have 

been sampled, but the data had not yet been assessed at the 

time this indicator was compiled. Data are also not available for the U.S. Virgin Islands and the Pacific territories.

•	 Trend data are not yet available for this indicator. Because 

of differences in methodology, the data presented here 

are not comparable with data that appeared in EPA’s first 

National Coastal Condition Report. The data presented 

here will serve as a baseline for future surveys.

•	 Benthic indices for the Northeast, West, and Puerto 

Rico do not yet include measures of pollution-tolerant or 

pollution-sensitive species. Although species diversity has 

the largest impact on index scores in the other regions, 

index values could change in the future as these components are added to the index values for these regions.

•	 Sample collection is limited to an index period from July 

to September. Further, because benthic communities can 

be strongly influenced by episodic events, trawling, or 

climate perturbations, this indicator may not reflect the 

full range of conditions that occur at each sampling location throughout these months. 

Data Sources

This indicator is based on an analysis published in EPA’s 

second National Coastal Condition Report (U.S. EPA, 

2004). Summary data by EPA Region have not been published, but were provided by EPA’s NCA program (U.S. 

EPA, 2005a). Underlying sampling data are housed in 

EPA’s NCA database (U.S. EPA, 2005b) (http://www.epa.

gov/emap/nca/html/data/index.html).

References

Engle, V.D., and J.K. Summers. 1999. Refinement, 

validation, and application of a benthic condition 

index for northern Gulf of Mexico estuaries. Estuaries 

22(3A):624-635.

Holland, A.F., A. Shaughnessy, and M.H. Heigel. 1987. 

Long-term variation in mesohaline Chesapeake Bay benthos: Spatial and temporal patterns. Estuaries 10:227-245.

Nixon, S.W., C.D. Hunt, and B.L. Nowicki. 1986. The 

retention of nutrients (C, N, P), heavy metals (Mn, Cd, 

Benthic community condition:

Percent of estuarine area in each category:

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.b

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

High Moderate Low Unsampled

Exhibit 3-29. Coastal benthic communities 

index for the contiguous U.S. and Puerto Rico, 

by EPA Region, 1997-2000 a

a

Coverage: Estuarine waters of the 

contiguous 48 states and 

Puerto Rico.

b

U.S. figures reflect the total 

sampled area. Unsampled areas 

were not included in the calculation.

Data source: U.S. EPA, 2004, 

2005a

77 18 5

59 17 24

72 27 1

63 17 17 3

51 27 11 11

78 15 7

91 5 4

70 13 17
WATER

3-46 EPA’s 2008 Report on the Environment

INDICATOR | Coastal Benthic Communities (continued)

Pb, Cu), and petroleum hydrocarbons by Narragansett 

Bay. In: Lasserre, P., and J.M. Martin, eds. Biogeochemical processes at the land-sea boundary. New York, NY: 

Elsevier. pp. 99-122.

Sanders, H.L., J.F. Grassle, G.R. Hampson, L.S. Morse, 

S. Gerner-Price, and C.C. Jones. 1980. Anatomy of an oil 

spill: Long-term effects from the grounding of the barge 

Florida off West Falmouth, Massachusetts. J. Mar. Res. 

38:265-380.

U.S. EPA (United States Environmental Protection Agency). 

2005a. Data provided to ERG (an EPA contractor) by Kevin 

Summers, EPA. September 2005.

U.S. EPA. 2005b. EMAP national coastal database. 

Accessed 2005. <http://www.epa.gov/emap/nca/html/

data/index.html>

U.S. EPA. 2004. National coastal condition report II. 

EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

Weisberg, S.B., J.A. Ranasinghe, D.D. Dauer, L.C. 

Schnaffer, R.J. Diaz, and J.B. Frithsen. 1997. An estuarine 

benthic index of biotic integrity (B-IBI) for Chesapeake 

Bay. Estuaries 20(1):149-158.

v

INDICATOR | Submerged Aquatic Vegetation in the Chesapeake Bay

Rooted aquatic plants, also called submerged aquatic vegetation (SAV), represent an important component of 

many coastal ecosystems. SAV supports the health of these 

ecosystems by generating food and habitat for waterfowl, 

fish, shellfish, and invertebrates; adding oxygen to the 

water column during photosynthesis; filtering and trapping 

sediment that otherwise would bury benthic organisms 

and cloud the water column; inhibiting wave action that 

erodes shorelines; and absorbing nutrients, such as nitrogen 

and phosphorus, that otherwise could fuel the growth of 

unwanted planktonic algae. 

One area where SAV plays an important role is the 

Chesapeake Bay, where SAV has historically contributed 

to high primary and secondary productivity (Kemp et al., 

1984). In the early 1960s, researchers began to note the loss 

of SAV from shallow waters of the Chesapeake Bay, which 

has since become a widespread, well-documented problem 

(Batiuk et al., 2000). Review of aerial photographs taken 

from a number of sites taken between the mid-1930s and 

the mid-1960s suggests that SAV acreage is currently less 

than half of what it was during the 1930s-1960s period 

(Moore et al., 2004).

Trends in the distribution and abundance of SAV over 

time are useful in understanding trends in water quality 

(Moore et al., 2004). Although other factors such as climatic events and herbicide toxicity may have contributed 

to the decline of SAV in the Bay, the primary causes are 

eutrophication and associated reductions in light availability (Batiuk et al., 2000). Like all plants, SAV needs sunlight to grow and survive. Two key stressors that impact 

the growth of SAV are suspended sediments and excess 

nutrient pollution. Suspended sediments—loose particles 

of clay and silt that are suspended in the water—make the 

water dingy and block sunlight from reaching the plants. 

Similarly, excess nutrients in the water fuel the growth of 

planktonic algae, which also block sunlight. 

This indicator presents the distribution of SAV in the 

Chesapeake Bay and its tributaries from 1978 to 2006, as 

mapped from black and white aerial photographs. The surveys follow fixed flight routes to comprehensively survey 

all shallow water areas of the Bay and its tidal tributaries. 

Non-tidal areas are omitted from the survey. SAV beds 

a

There were no Bay-wide surveys 

from 1979 to 1983, or in 1988.

b

For years with incomplete 

photographic coverage, SAV 

acreage in the non-surveyed areas 

was estimated based on prior 

years’ surveys.

Data source: Chesapeake Bay Program, 2007

0

20

40

60

80

100

’78 ’80 ’82 ’84 ’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

Extent of SAV (thousand acres)

Exhibit 3-30. Extent of submerged aquatic 

vegetation (SAV) in the Chesapeake Bay,

1978-2006a

Mapped acreage

Estimated additional acreageb

Year

Maryland

Chesapeake

Bay Virginia
WATER

EPA’s 2008 Report on the Environment 3-47

INDICATOR | Submerged Aquatic Vegetation in the Chesapeake Bay (continued)

less than 1 square meter in area are not included due to 

the limits of the photography and interpretation. Annual 

monitoring began in 1978; however, no surveys were conducted from 1979 to 1983 or in 1988. In years when the 

entire area could not be surveyed due to flight restrictions 

or weather events, acreages in the non-surveyed areas were 

estimated based on prior years’ surveys. 

What the Data Show

The extent of SAV in the Chesapeake Bay increased from 

41,000 acres in 1978 to a peak of 90,000 acres in 2002, 

before declining to 59,000 acres in 2006 (Exhibit 3-30). 

The extent of SAV reached a minimum of 38,000 acres in 

1984. Year-to-year changes reflect a variety of phenomena. For example, the notable decline in SAV distribution between 2002 and 2003 appears to be the result of 

substantial reductions in widgeongrass populations in the 

lower and mid-bay regions. In addition to the large declines 

in widgeongrass, major declines in freshwater SAV species occurred in the upper portion of the Potomac River 

and the Susquehanna region. While populations of SAV 

appeared to be present in these segments very early in the 

growing season, persistent turbidity resulting from rain 

occurring throughout the spring and summer may have 

contributed to a very early decline, well before Hurricane 

Isabel affected the Chesapeake Bay (Orth et al., 2004). The 

extent of SAV gradually increased again through 2004 and 

2005, then declined from 2005 to 2006. Factors causing 

this latest decline are thought to include above-average 

water temperatures in the fall of 2005, a dry spring in 2006, 

and an early summer rain event in 2006 (EcoCheck, 2007).

Indicator Limitations

•	 There were no surveys in the years 1979-1983 or in 1988.

•	The indicator includes some estimated data for years with 

incomplete photographic coverage. Spatial gaps in 1999 

occurred due to the inability to reliably photograph SAV 

following hurricane disturbance. Spatial gaps in 2001 

occurred due to flight restrictions near Washington D.C. 

after the September 11th terrorist attacks. Other gaps 

occurred in 2003 due to adverse weather in the spring, 

summer, and fall (Hurricane Isabel). Acreage in the 

non-surveyed areas was estimated based on prior years’ 

surveys. In all cases, the estimated area accounted for less 

than 10 percent of the total acreage of SAV.

•	 Photointerpretation methods changed over the course of 

this study. However, data have been adjusted to account 

for any methodological inconsistencies. 

•	 Extent is just one of the variables that can be used to 

measure the condition of SAV communities. Other useful attributes that have been studied include vegetation 

health, density, and species diversity. 

Data Sources

Data were obtained from the Chesapeake Bay Program, 

which has published a version of this indicator (Chesapeake 

Bay Program, 2007) along with a link to download the 

annual summary data presented in Exhibit 3-30 (http://

www.chesapeakebay.net/pubs/statustrends/88-data-2002.

xls). These acreage statistics are based on annual SAV 

distribution maps, which are available from the Virginia 

Institute of Marine Science (VIMS, 2007) (http://www.

vims.edu/bio/sav/index.html).

References

Batiuk, R., P. Bergstrom, M. Kemp, E. Koch, L. Murray, C. Stevenson, R. Bartleson, V. Carter, N. Rybicki, J. 

Landwehr, C. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K. Moore, S. Ailstock, and M. Teichberg. 2000. 

Chesapeake Bay submerged aquatic vegetation water 

quality and habitat-based requirements and restoration 

targets: A second technical synthesis. CBP/TRS 245/00. 

EPA/903/R-00/014. Annapolis, MD: U.S. Environmental 

Protection Agency, Chesapeake Bay Program. 

<http://www.chesapeakebay.net/pubs/sav/savreport.pdf>

Chesapeake Bay Program. 2007. Bay trends & indicators: 

Bay grass abundance (baywide). Accessed November 2007. 

<http://www.chesapeakebay.net/status.cfm?sid=88>

EcoCheck. 2007. Chesapeake Bay habitat health report 

card: 2006. NOAA Chesapeake Bay Program Office and 

University of Maryland Center for Environmental Sciences, Integration and Application Network. 

<http://www.eco-check.org/reportcard/chesapeake/> 

Kemp, W.M., W.R. Boynton, R.R. Twilley, J.C. Stevenson, and L.G. Ward. 1984. Influences of submersed vascular 

plants on ecological processes in upper Chesapeake Bay. In: 

V.S. Kennedy, ed. Estuaries as filters. New York: Academic 

Press, pp. 367-394.

Moore, K.A., D.J. Wilcox, B. Anderson, T.A. Parham, 

and M.D. Naylor. 2004. Historical analysis of SAV in the 

Potomac River and analysis of bay-wide historic SAV to 

establish a new acreage goal. Report to EPA Chesapeake 

Bay Program. <http://www.vims.edu/bio/sav/Final_SAV_

Historical_Report_2004.pdf>

Orth, R.J., D.J. Wilcox, L.S. Nagey, A.L. Owens, J.R. 

Whiting, and A. Serio. 2004. 2003 distribution of submerged aquatic vegetation in Chesapeake Bay and coastal 

bays. Report to EPA Chesapeake Bay Program. 

<http://www.vims.edu/bio/sav/sav03/index.html>

VIMS (Virginia Institute of Marine Science). 2007. Bay 

grasses (SAV) in Chesapeake Bay and Delmarva Peninsula 

coastal bays. <http://www.vims.edu/bio/sav/index.html>

v
WATER

3-48 EPA’s 2008 Report on the Environment

INDICATOR | Hypoxia in the Gulf of Mexico and Long Island Sound

Nutrient pollution is one of the most pervasive problems facing U.S. coastal waters, with more than half of the 

nation’s estuaries experiencing one or more symptoms of 

eutrophication (Bricker et al., 1999; NRC, 2000; U.S. 

Commission on Ocean Policy, 2004). One symptom is low 

levels of dissolved oxygen (DO), or hypoxia. Hypoxia can 

occur naturally, particularly in areas where natural physical and chemical characteristics (e.g., salinity or mixing 

parameters) limit bottom-water DO. The occurrence of 

hypoxia in shallow coastal and estuarine areas appears to 

be increasing, however, and is most likely accelerated by 

human activities (Jickells, 1998; Vitousek et al., 1997). 

This indicator tracks trends in hypoxia in the Gulf of 

Mexico and Long Island Sound, which are prime examples 

of coastal areas experiencing hypoxia. For consistency, this 

indicator focuses on occurrences of DO below 2 milligrams per liter (mg/L), but actual thresholds for “hypoxia” 

and associated effects can vary over time and space. 

Hypoxia often is defined as a concentration of DO below 

saturation, and because saturation levels vary with temperature and salinity, the concentration that defines hypoxia 

will vary seasonally and geographically. Effects of hypoxia 

on aquatic life also vary, as some organisms are more sensitive to low DO than others. As a general rule, however, 

concentrations of DO above 5 mg/L are considered supportive of marine life, while concentrations below this are 

potentially harmful. At about 3 mg/L, bottom fishes may 

start to leave the area, and the growth of sensitive species 

such as crab larvae is reduced. At 2.5 mg/L, the larvae of 

less sensitive species of crustaceans may start to die, and the 

growth of crab species is more severely limited. Below 2 

mg/L, some juvenile fish and crustaceans that cannot leave 

the area may die, and below 1 mg/L, fish totally avoid the 

area or begin to die in large numbers (Howell and Simpson, 1994; U.S. EPA, 2000). 

The Gulf of Mexico hypoxic zone on the Texas-Louisiana 

Shelf is the largest zone of coastal hypoxia in the Western 

Hemisphere (CAST, 1999). It exhibits seasonally low oxygen 

levels as a result of complicated interactions involving excess 

nutrients carried to the Gulf by the Mississippi and Atchafalaya Rivers; physical changes in the river basin, such as channeling, construction of dams and levees, and loss of natural 

wetlands and riparian vegetation; and the stratification in the 

waters of the northern Gulf caused by the interaction of fresh 

river water and the salt water of the Gulf (CENR, 2000; 

Rabalais and Turner, 2001). Increased nitrogen and phosphorus inputs from human activities throughout the basin 

support an overabundance of algae, which die and fall to the 

sea floor, depleting oxygen in the water as they decompose. 

Fresh water from the rivers entering the Gulf of Mexico 

forms a layer of fresh water above the saltier Gulf waters and 

prevents re-oxygenation of oxygen-depleted water along 

the bottom.

In Long Island Sound, seasonally low levels of oxygen 

usually occur in bottom waters from mid-July though September, and are more severe in the western portions of the 

Sound, where the nitrogen load is higher and stratification 

is stronger, reducing mixing and re-oxygenation processes 

(Welsh et al., 1991). While nitrogen fuels the growth of 

microscopic plants that leads to low levels of oxygen in the 

Sound, temperature, wind, rainfall, and salinity can affect 

the intensity and duration of hypoxia.

Data for the two water bodies are presented separately 

because they are collected through two different sampling 

programs, each with its own aims and technical approach. 

The Gulf of Mexico survey is conducted by the Louisiana Universities Marine Consortium (LUMCON) and is 

designed to measure the extent of bottom-water hypoxia 

in the summer, with samples collected during a cruise that 

generally occurs over a 5-day period in mid- to late July 

(LUMCON, 2007b). Samples are collected day and night 

along several transects designed to capture the overall extent 

of the hypoxic zone. The number of locations varies from 

60 to 90 per year, depending on the length of the sampling 

cruise, the size of the hypoxic zone, logistical constraints, 

and the density of station locations. Long Island Sound 

sampling is conducted by the Connecticut Department of 

Environmental Protection’s Long Island Sound Water Quality Monitoring Program, and is designed to determine both 

the maximum extent and the duration of hypoxia (Connecticut DEP, 2007). Sampling is performed every month from 

October to May and every 2 weeks from June to September 

at a set of fixed locations throughout the Sound. All Long 

Island Sound samples are collected during the day.

0

2,000

4,000

6,000

8,000

10,000

Year

Area (mi2) Exhibit 3-31. Extent of dissolved oxygen less 

than 2.0 mg/L in Gulf of Mexico bottom waters 

in mid-summer, 1985-2007a

’86 ’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04 ’06

a

Only 15 square miles were affected in 1988. No data were collected 

in 1989.

Data source: LUMCON, 2007a,b
WATER

EPA’s 2008 Report on the Environment 3-49

INDICATOR | Hypoxia in the Gulf of Mexico and Long Island Sound (continued)

What the Data Show

The size of the midsummer bottom-water 

hypoxia area (<2 mg/L DO) in the Northern Gulf of Mexico has varied considerably 

since 1985, ranging from 15 square miles in 

1988 (a drought year in the Mississippi Basin) 

to approximately 8,500 square miles in 2002 

(Exhibit 3-31). The unusually low areal extent 

in 2000 also was associated with very low 

discharge from the Mississippi River (see the N 

and P Loads in Large Rivers indicator, p. 3-17). 

In the latest year of sampling, 2007, the hypoxic 

zone measured 7,900 square miles, roughly the 

size of New Jersey (Exhibits 3-31 and 3-32). 

Over the full period of record (1985-2007), the 

area with DO less than 2 mg/L has averaged 

approximately 5,200 square miles.

The maximum extent and duration of hypoxic events 

(<2 mg/L DO) in Long Island Sound also has varied 

considerably since the 1980s (Exhibit 3-33). Since 1987, 

the largest area of DO less than 2 mg/L was 212 square 

miles, which occurred in 1994; the smallest area, 2 square 

miles, occurred in 1997 (panel A). The shortest hypoxic 

event was 6 days in 1990 and the longest was 71 days, in 

1989 (panel B). In 2007, the latest year for which data are 

available, the maximum area and duration of DO less than 

2 mg/L in Long Island Sound were 31 square miles and 9 

days, respectively, with the lowest DO levels occurring in 

the western end of the Sound (Exhibits 3-33 and 3-34). 

Between 1987 and 2007, the average annual maximum 

was 68 square miles and 32 days. 

Indicator Limitations

Gulf of Mexico:

•	This indicator is based on a survey conducted over a 

5-day period when hypoxia is expected to be at its maximum extent. The indicator does not capture periods of 

hypoxia or anoxia (no oxygen at all) occurring at times 

other than the mid-summer surveys.

•	 Because the extent of hypoxia is measured through a 

single mid-summer sampling cruise, duration cannot 

be estimated.

•	This indicator does not track vertical extent of hypoxia 

or anoxic volume.

•	 Surveys usually end offshore from the Louisiana-Texas state 

line; in years when hypoxia extends onto the upper Texas 

coast, the spatial extent of hypoxia is underestimated.

Long Island Sound:

•	 Hypoxic or anoxic periods that may occur between the 

2-week surveys are not captured in the indicator.

•	 Samples are taken in the daytime, approximately 1 meter 

off the bottom. This indicator does not capture oxygen 

conditions at night (which may be lower because of the 

lack of photosynthesis) or conditions near the sedimentwater interface. 

0 15 30 45 60

Miles

L. Calcasieu

Terrebonne Bay

Mississippi R. Sabine L. Atchafalaya R.

LOUISIANA

<2.0 mg/L

Dissolved oxygen:

Data source: LUMCON, 2007b 

 N

Exhibit 3-32. Dissolved oxygen less than 2.0 mg/L in Gulf of 

Mexico bottom waters, July 21-28, 2007

Sample location

Exhibit 3-33. Maximum extent and duration 

of dissolved oxygen less than 2.0 mg/L in 

Long Island Sound bottom waters, 1987-2007

Data source: U.S. EPA, 2007

0

50

100

150

200

250

’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04

’88 ’90 ’92 ’94 ’96 ’98 ’00 ’02 ’04

Year

Area (mi2

)

’06

’06

0

20

40

60

80

Year

Duration (days)

A. Extent of dissolved oxygen less than 2.0 mg/L

B. Duration of dissolved oxygen less than 2.0 mg/L
WATER

3-50 EPA’s 2008 Report on the Environment

INDICATOR | Hypoxia in the Gulf of Mexico and Long Island Sound (continued)

Data Sources 

Maps and summary data from the 2007 Gulf of Mexico 

survey are published online (LUMCON, 2007b). Data from 

prior years were provided by LUMCON (2007a).

Data on the extent and duration of hypoxia in Long Island 

Sound have not been published, but were compiled by 

EPA’s Long Island Sound Office (U.S. EPA, 2007). Concentration maps are available online (Connecticut DEP, 

2007)—including the 2007 map shown in Exhibit 3-34.

References

Bricker, S.B., C.G. Clement, D.E. Pirhalla, S.P. Orlando, 

and D.R.G. Farrow. 1999. National eutrophication assessment: Effects of nutrient enrichment in the nation’s estuaries. Silver Spring, MD: NOAA National Ocean Service. 

<http://ian.umces.edu/neea/pdfs/eutro_report.pdf>

CAST (Council for Agricultural Science and Technology). 

1999. Gulf of Mexico hypoxia: Land and sea interactions. 

Task force report no. 134.

CENR (Committee on Environment and Natural 

Resources). 2000. Integrated assessment of hypoxia in the 

northern Gulf of Mexico. Washington, DC: National Science and Technology Council Committee on Environment 

and Natural Resources. <http://oceanservice.noaa.gov/

products/pubs_hypox.html#fia>

Connecticut DEP (Department of Environmental Protection). 2007. Long Island 

Sound Water Quality Monitoring. Accessed 

2007. <http://www.ct.gov/dep/cwp/

view.asp?a=2719&q=325534&depNav_

GID=1654>

Howell, P., and D. Simpson. 1994. Abundance of marine resources in relation to 

dissolved oxygen in Long Island Sound. 

Estuaries 17:394-402.

Jickells, T.D. 1998. Nutrient biogeochemistry of the coastal zone. Science 281:217-221.

LUMCON (Louisiana Universities Marine 

Consortium). 2007a. Data provided to 

ERG (an EPA contractor) by Nancy 

Rabalais, LUMCON. August 28, 2007. 

LUMCON. 2007b. Hypoxia in the northern Gulf of Mexico. Accessed August 2007. 

<http://www.gulfhypoxia.net/>

NRC (National Research Council). 2000. 

Clean coastal waters: Understanding and 

reducing the effects of nutrient pollution. Washington, 

DC: National Academies Press.

Rabalais, N.N., and R.E. Turner, eds. 2001. Coastal 

hypoxia: Consequences for living resources and ecosystems. Coastal and estuarine studies 58. Washington, DC: 

American Geophysical Union.

U.S. Commission on Ocean Policy. 2004. An ocean blueprint for the 21st century. Final report. Washington, DC.

U.S. EPA (United States Environmental Protection 

Agency). 2007. Data provided to ERG (an EPA contractor) by Mark Tedesco, EPA Long Island Sound Office. 

September 10, 2007.

U.S. EPA. 2000. Ambient aquatic life water quality criteria 

for dissolved oxygen (saltwater): Cape Cod to Cape Hatteras. EPA/822/R-00/12.

Vitousek, P.M., J.D. Aber, R.W. Howarth, G.E. Likens, 

P.A. Matson, D.W. Schindler, W.H. Schlesinger, and D.G. 

Tilman. 1997. Human alteration of the global nitrogen cycle: 

Sources and consequences, ecological applications. Ecol. Appl. 

7(3):737-750.

Welsh, B.L., and F.C. Eller. 1991. Mechanisms controlling summertime oxygen depletion in western Long Island 

Sound. Estuaries 14:265-278.

Data source: Connecticut DEP, 2007

Exhibit 3-34. Dissolved oxygen in Long Island Sound bottom 

waters, July 30-August 1, 2007

<1.0 mg/L

1.0 to <2.0 mg/L

3.0 to <3.5 mg/L

3.5 to <4.8 mg/L

2.0 to <3.0 mg/L

4.8 mg/L

Dissolved oxygen:

N

 

New London New Haven

Bridgeport

Stamford

Norwalk

Mattituck

Oyster Bay Smithtown

Port Jefferson

New

York

City

CONNECTICUT

NEW

YORK

0 105 15 20 25

Sample location Miles

v
WATER

EPA’s 2008 Report on the Environment 3-51

3.5.3 Discussion

What These Indicators Say About Trends in 

the Extent and Condition of Coastal Waters 

and Their Effects on Human Health and the 

Environment

Extent

Although the ROE indicators do not characterize the extent 

of all coastal waters, the Wetlands indicator (p. 3-32) shows 

that at least one type of coastal system has experienced 

changes in extent over the last half-century. The number 

of acres of marine and estuarine wetlands has decreased 

overall since the 1950s, although the rate of loss has slowed 

in recent years. While the indicator does not identify the 

exact stressors responsible for the decline in marine and 

estuarine wetlands, it does list several factors that have led 

to overall wetland loss, including development and conversion to deepwater. Section 3.4 provides further detail on how 

human activities can affect wetland extent, including human 

activities that exacerbate natural processes (e.g., storm damage). Ultimately, trends in wetland extent affect ecological 

systems, as described further below.

Condition

Together, these indicators cover much of the spectrum of 

“condition,” including three of the broad themes introduced 

in Section 3.5.1: nutrients, toxic chemical contaminants, 

and the condition of native populations and their habitat. As 

described in Section 3.5.1, excess nutrients can cause algal 

blooms that result in low dissolved oxygen and reduced water 

clarity, which in turn can harm plant and animal communities. For example, the Trophic State of Coastal Waters 

indicator (p. 3-38) shows elevated levels of nutrients and 

chlorophyll-a (a surrogate for algal abundance) in a small 

but substantial portion of the nation’s estuarine areas. These 

results are consistent with indicators that show evidence of 

eutrophication, such as decreased water clarity and hypoxia. 

The SAV in Chesapeake Bay indicator (p. 3-46) in turn offers 

an example of an ecological effect linked to eutrophication. 

Nutrient stressors cannot be attributed entirely to human 

activities; for example, the Gulf of Mexico hypoxic zone 

results in part from natural mixing parameters, and trends in 

the extent of hypoxic zones show large year-to-year variations 

related to factors like climate (Hypoxia in Gulf of Mexico and 

Long Island Sound indicator, p. 3-48). However, as the spatial 

distribution of hypoxia in Long Island Sound suggests, the 

nation’s coastal waters can experience eutrophic effects that 

are very closely related to human activities (e.g., runoff from 

impervious surfaces or combined sewer overflows in an urban 

area). Further, as the SAV in Chesapeake Bay indicator (p. 

3-46) shows, present conditions may be quite different from 

historical reference conditions. 

Overall, levels of toxic chemical contaminants are low in most 

of the nation’s estuarine sediments, but as the Coastal Sediment Quality indicator (p. 3-42) shows, condition can vary 

greatly from one region to the next. In some EPA Regions, as 

much as 20 percent of estuarine area has sediments that either 

exceed contamination reference standards or fail a screening 

test for benthic toxicity. Other indicators discuss the extent 

to which toxic contaminants may be entering and affecting 

the food web. For example, benthic communities—which are 

most directly impacted by contaminants in sediment—show 

evidence of disturbance in roughly one-third of U.S. estuaries (e.g., losses of pollution-sensitive species) (Coastal Benthic 

Communities indicator, p. 3-44). Fish tissues had at least one 

contaminant above human health guidelines in 22 percent 

of estuarine sampling sites (Coastal Fish Tissue indicator, 

p. 3-61), suggesting that bioaccumulation of certain toxic 

compounds is widespread and, in some instances, could pose 

risks to human health. This indicator suggests the importance 

of atmospheric deposition of mercury as a stressor to coastal 

water condition, as well as historical activities that released 

PCBs and DDT into upstream and coastal waters.

In ecological terms (populations, communities, and habitat), 

trends in the condition of coastal waters vary. Benthic communities in most of the nation’s estuaries are intact in terms 

of species diversity (Coastal Benthic Communities indicator, p. 3-44), which is critical because these organisms are a 

fundamental link in the coastal food web. Other populations, 

however, may be substantially lower than historical levels as 

a result of human stressors—for example, the Chesapeake 

Bay’s SAV, which is vulnerable to changes in water clarity 

(SAV in Chesapeake Bay indicator, p. 3-46). SAV is ecologically important because it is not just a plant population; it 

also provides habitat and facilitates nutrient cycling, much 

like wetlands do. SAV has recently shown increases in extent, 

which may translate into increased habitat and breeding 

grounds for various species. However, coastal habitat still continues to be threatened by human stressors. As the Hypoxia 

in Gulf of Mexico and Long Island Sound indicator (p. 3-48) 

shows, large areas of some of the nation’s coastal water bodies 

are unsuitable for fish and shellfish populations for at least a 

portion of the year.

Limitations, Gaps, and Challenges

Although the seven indicators discussed here provide a good 

overview of many important aspects of coastal extent and 

condition, there are a few key limitations to their temporal 

and spatial coverage. For example, the four indicators derived 

from the National Coastal Condition Report do not provide 

information about trends over time, as there are insufficient 

data from previous surveys to compare with recent data to 

examine potential trends.22 Another temporal limitation is 

that many surveys are conducted during an index period, not 

over a full year; thus, they may not capture phenomena that 

occur outside the sampling window.23 Spatially, the National 

22 U.S. Environmental Protection Agency. 2004. National coastal condition 

report II. EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

23 Ibid.
WATER

3-52 EPA’s 2008 Report on the Environment

Indicators are limited because they do not include data from 

Alaska, Hawaii, and most U.S. territories. Alaska contains 75 

percent of the bays, sounds, and estuarine surface area in the 

United States, while Hawaii, the Caribbean, and the Pacific 

territories represent a set of unique estuarine subsystems (i.e., 

coral reefs and tropical bays) that are not common in the 

contiguous 48 states.

One challenge in assessing coastal waters is that some aspects 

of condition vary naturally from one area to another. For 

example, some rivers naturally carry a heavy load of sediments 

or nutrients into coastal waters, while benthic community 

structure may depend on climate, depth, and geology. To 

assess coastal waters with respect to natural background conditions, several of the ROE indicators use different reference 

conditions for different regions.

To assess the extent and condition of coastal waters more fully, 

it would help to have more information in several key areas, 

including: 

•	 More information about the extent of coastal waters—e.g., 

an indicator on coastal subsidence.

•	 Nationally consistent data on coastal water pollutants 

beyond those associated with trophic state—for example, 

organics, toxics, metals, and pathogens.

•	 Consistent data on the occurrence of harmful algal blooms, 

which can be caused by many different species of algae.

•	 A National Indicator of invasive species, which are often 

transported from one area to another along shipping routes 

or via aquaculture. Little information exists on a national 

level, in part because of a lack of standard invasion metrics.

•	 Comprehensive information on the condition of the 

nation’s coral reefs—a unique and fragile habitat—and the 

status of coastal fish and shellfish communities.24

3.6 What Are the Trends 

in the Quality of Drinking 

Water and Their Effects 

on Human Health?

3.6.1 Introduction

The average American consumes 1 to 2 liters of drinking 

water per day, including water used to make coffee, tea, and 

other beverages.25 Virtually all drinking water in the United 

States comes from fresh surface water and ground water. 

Large-scale water supply systems tend to rely on surface water 

resources such as lakes, rivers, and reservoirs; these include 

the systems serving many large metropolitan areas. Smaller 

systems are more likely to use ground water, particularly 

in regions with limited surface water resources. Slightly 

more than half of the nation’s population receives its drinking water from ground water, i.e., through wells drilled into 

aquifers26 (including private wells serving about 15 percent of 

U.S. households27). If drinking water contains unsafe levels 

of contaminants, this contaminated water can cause a range 

of adverse human health effects. Among the potential effects 

are gastrointestinal illnesses, nervous system or reproductive 

effects, and chronic diseases such as cancer.

Surface waters and aquifers can be contaminated by various 

agents, including microbial agents such as viruses, bacteria, 

or parasites (e.g., E. coli, Cryptosporidium, or Giardia); chemical 

contaminants such as inorganic metals, volatile organic compounds (VOCs), and other natural or manmade compounds; and 

radionuclides, which may be manmade or naturally occurring. 

Contaminants also can enter drinking water between the treatment plant and the tap (for example, lead can leach into water 

from old plumbing fixtures or household or street-side pipes).

Drinking water contaminants can come from many sources:

•	 Human activities that contaminate the source.

Aquifers and surface waters that provide drinking water 

can be contaminated by many sources, as discussed in Sections 3.2 and 3.3. For example, chemicals from disposal 

sites or underground storage facilities can migrate into 

aquifers; possible contaminants include organic solvents 

(e.g., some VOCs), petroleum products, and heavy metals. 

Contaminants can also enter ground water or surface water 

as a result of their application to the land. Pesticides and 

fertilizer compounds (e.g., nitrate) can be carried into lakes 

and streams by rainfall runoff or snowmelt, or percolate 

through the ground and enter aquifers. Industrial wastes 

can contaminate drinking water sources if injected into 

containment wells or discharged into surface waters, as can 

mine waste (e.g., heavy metals) if not properly contained.

•	 Natural sources. As ground water travels through rock 

and soil, it can pick up naturally occurring contaminants 

such as arsenic, other heavy metals, or radionuclides. 

Some aquifers are naturally unsuitable for drinking 

because the local geology happens to include high levels of 

certain contaminants.

•	 Microbial pathogens. Human wastes from sewage and 

septic systems can carry harmful microbes into drinking 

water sources, as can wastes from animal feedlots and wildlife. Major contaminants include Giardia, Cryptosporidium,

and E. coli O157:H7. Coliform bacteria from human and 

animal wastes also may be found in drinking water if the 

water is not properly finished; these bacteria may indicate 

that other harmful pathogens are present as well.

24 U.S. Environmental Protection Agency. 2004. National coastal condition 

report II. EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/downloads.html> 

25 U.S. Environmental Protection Agency. 1997. Exposure factors handbook. 

Volume I—general factors. EPA/600/P-95/002Fa. <http://rais.ornl.gov/

homepage/EFH_Final_1997_EPA600P95002Fa.pdf>

26 U.S. Geological Survey. 1999. Ground water (general interest publication). 

<http://capp.water.usgs.gov/GIP/gw_gip/>

27 U.S. Environmental Protection Agency. 2002. The clean water and drinking 

water infrastructure gap analysis. EPA/816/R-02/020. <http://www.epa.

gov/safewater/gapreport.pdf>
WATER

EPA’s 2008 Report on the Environment 3-53

•	 Treatment and distribution. While treatment can 

remove many chemical and biological contaminants from 

the water, it may also result in the presence of certain 

disinfection byproducts that may themselves be harmful, 

such as trihalomethanes. Finished water can also become 

contaminated after it enters the distribution system, either 

from a breach in the system or from corrosion of plumbing materials, particularly those containing lead or copper. 

After water leaves the treatment plant, monitoring for lead 

in drinking water is done at the tap, and monitoring for 

microbial contaminants (as well as disinfection byproducts) 

occurs within the distribution system. 

Chemical exposure through drinking water can lead to a 

variety of long- and short-term effects. Potential health effects 

of exposure to certain metals, solvents, and pesticides can 

include chronic conditions such as cancer, which can develop 

over long periods of time (up to 70 years). Higher doses over 

shorter periods of time can result in a variety of biological 

responses, including toxicity, mutagenicity, and teratogenicity (birth defects). Short-term results might include cosmetic 

effects (e.g., skin discoloration), unpleasant odors, or more 

severe problems such as nervous system or organ damage and 

developmental or reproductive effects. The effects of some 

drinking water contaminants are not yet well understood. For 

example, certain disinfection byproducts have been associated 

with cancer, developmental, and reproductive risks, but the 

extent of this association is still uncertain.

Consuming water with pathogenic microbes can cause lifethreatening diseases such as typhoid fever or cholera—rare in 

the U.S. today—as well as more common waterborne diseases 

caused by organisms such as Giardia, Cryptosporidium, E. coli,

and Campylobacter. Health consequences of the more common 

illnesses can include symptoms such as gastrointestinal distress 

(stomach pain, vomiting, diarrhea), headache, fever, and kidney 

failure, as well as various infectious diseases such as hepatitis. 

A number of factors determine whether the presence of contaminants in drinking water will lead to adverse health effects. 

These include the type of contaminant, its concentration in 

the water, individual susceptibility, the amount of contaminated water consumed, and the duration of exposure.

Disinfection of drinking water—the destruction of pathogens 

using chlorine or other chemicals—has dramatically reduced 

the incidence of waterborne diseases such as typhoid, cholera, 

and hepatitis, as well as gastrointestinal illness, in the United 

States. Other processes required depend on the physical, 

microbiological, and chemical characteristics and the types 

of contaminants present in the source water (e.g., filtration to 

remove turbidity and biological contaminants, treatment to 

remove organic chemicals and inorganic contaminants such as 

metals, and corrosion control to reduce the presence of corrosion byproducts such as lead at the point of use).

3.6.2 ROE Indicators

This section presents an indicator that tracks trends in the total 

population served by community water systems for which 

states report no violations of health-based drinking water 

standards (Table 3-6). Data for this indicator come from EPA’s 

Safe Drinking Water Information System, Federal Version. 

This system houses all data submitted by states, EPA Regions, 

and the Navajo Nation Indian Tribe on the community water 

systems they oversee.

Table 3-6. ROE Indicators of Trends in the Quality of Drinking Water 

and Their Effects on Human Health

National Indicators Section Page

Population Served by Community Water Systems with No Reported 

Violations of Health-Based Standards (N/R)

3.6.2 3-54

N/R = National Indicator displayed at EPA Regional scale
WATER

3-54 EPA’s 2008 Report on the Environment

INDICATOR Population Served by Community Water Systems with No 

Reported Violations of Health-Based Standards

Community water systems (CWS), public water systems that supply water to the 

same population year-round, served over 286 

million Americans in fiscal year (FY) 2007 

(U.S. EPA, 2007)—roughly 95 percent of 

the U.S. population (U.S. Census Bureau, 

2007). This indicator presents the percentage 

of Americans served by CWS for which states 

reported no violations of EPA health-based 

standards for over 90 contaminants (U.S. 

EPA, 2004b). 

Health-based standards include Maximum 

Contaminant Levels (MCLs) and Treatment 

Techniques (TTs). An MCL is the highest level 

of a contaminant that is allowed in drinking 

water. A TT is a required treatment process 

(such as filtration or disinfection) intended 

to prevent the occurrence of a contaminant 

in drinking water (U.S. EPA, 2004c). TTs 

are adopted where it is not economically or 

technologically feasible to ascertain the level of 

a contaminant, such as microbes, where even 

single organisms that occur unpredictably or 

episodically can cause adverse health effects. 

Compliance with TTs may require finished 

water sampling, along with quantitative or 

descriptive measurements of process performance to gauge the efficacy of the treatment 

process. MCL-regulated contaminants tend 

to have long-term rather than acute health 

effects, and concentrations vary seasonally (if at 

all; e.g., levels of naturally occurring chemical 

contaminants or radionuclides in ground water 

are relatively constant). Thus, compliance is 

based on averages of seasonal, annual, or less 

frequent sampling.

This indicator tracks the population served by CWS for 

which no violations were reported to EPA for the period 

from FY 1993 to FY 2007, the latest year for which data 

are available. Results are reported as a percentage of the 

overall population served by CWS, both nationally and 

by EPA Region. This indicator also reports the number 

of persons served by systems with reported violations of 

standards covering surface water treatment, microbial 

contaminants (microorganisms that can cause disease), and 

disinfection byproducts (chemicals that may form when 

disinfectants, such as chlorine, react with naturally occurring materials in water and may pose health risks) (U.S. 

EPA, 2004b). The indicator is based on violations reported 

quarterly by states, EPA, and the Navajo Nation Indian 

Tribe, who each review monitoring results for the CWS 

that they oversee. 

What the Data Show

Of the population served by CWS nationally, the percentage served by systems for which no health-based violations 

were reported for the entire year increased overall from 

79 percent in 1993 to 92 percent in FY 2007, with a peak 

of 94 percent in FY 2002 (Exhibit 3-35). This indicator is 

based on reported violations of the standards in effect in 

any given year. Several new standards went into effect after 

December 31, 2001. These were the first new drinking 

water standards to take effect during the period of record 

(beginning in 1993). The results after FY 2001 would have 

been somewhat higher had it not been for violations of 

standards that became effective in FY 2002 or after 

(Exhibit 3-35; see the dark segment atop the columns 

starting in FY 2002). As EPA adds to or strengthens its 

requirements for water systems over time, compliance with 

standards comes to represent a higher level of public health 

protection. 

Fiscal year

Percent of CWS customers

Exhibit 3-35. U.S. population served by community water 

systems with no reported violations of EPA health-based 

standards, fiscal years 1993-2007a

0

10

20

30

40

50

60

70

80

90

100

’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’07’06

None

New standards 

(post-12/31/01) only

Reported violations:b

a

Coverage: U.S. residents served by community 

water systems (CWS) (approximately 95% of 

the total U.S. population).

b

Several new standards went into effect after 

12/31/01, including the Interim Enhanced 

Surface Water Treatment Rule (CWS with 

surface water sources serving 10,000 or more 

people) and the Disinfection Byproducts (DBP) Rule for CWS that disinfect. In FY 

2003, the DBP rule applied to systems serving >10,000 people; as of January 2004, 

it applied to all CWS. For FY 2002-2007, each column is divided into two segments: 

the lower portion reflects all standards in place at the time, while the upper portion 

covers sytems with reported violations of new standards but not pre-12/31/01 

standards. Adding both segments together, the total height of each column indicates 

what percent of CWS customers would have been served by CWS with no reported 

violations if the new standards had not gone into effect.

Data source: U.S. EPA, 2007
WATER

EPA’s 2008 Report on the Environment 3-55

INDICATOR Population Served by Community Water Systems with No 

Reported Violations of Health-Based Standards (continued)

When results are broken down by EPA Region, some 

variability over time is evident (Exhibit 3-36). Between 

FY 1993 and FY 2007, most Regions were consistently 

above the national percentage. Three of the Regions were 

substantially below the national average over much of 

the period of record, but as of FY 2007, only one Region 

remained well below the national percentage, largely 

because of a small number of public water systems serving 

large populations.

In FY 2007, reported violations involving surface water 

treatment rules in large CWS were responsible for exceeding health-based standards for 8.9 million people (3.1 percent of the population served by CWS nationally) (Exhibit 

3-37). Reported violations of heath-based coliform 

standards affected 10.6 million people (3.7 percent of the 

CWS-served population), and reported violations of the 

health-based disinfection byproducts standards (Stage 1) 

affected 3.6 million people (1.3 percent of the CWS-served 

population). Overall, of the 8.5 percent of the population 

served by systems with reported violations in FY 2007, 

84 percent of these cases involved at least one of these 

three rules governing treatment to prevent waterborne 

diseases—the most widespread and acute threat to health 

from drinking water—or the contaminants created by such 

treatment. 

Indicator Limitations

•	 Non-community water systems (typically relatively small 

systems) that serve only transient populations such as 

restaurants or campgrounds, or serving those in a nondomestic setting for only part of their day (e.g., a school, 

religious facility, or office building), are not included in 

population served figures.

•	 Domestic (home) use of drinking water supplied by private wells—which serve approximately 15 percent of the 

U.S. population (USGS, 2004)—is not included.

•	 Bottled water, which is regulated by standards set by the 

Food and Drug Administration, is not included.

•	 National statistics based on population served can be 

volatile, because a single very large system can sway 

the results by up to 2 to 3 percent; this effect becomes 

more pronounced when statistics are broken down at the 

regional level, and still more so for a single rule. 

•	 Some factors may lead to overstating the extent of 

population receiving water that violates standards. For 

example, the entire population served by each system in 

Exhibit 3-37. U.S. population served by

community water systems with reported 

violations of EPA health-based standards, by

type of violation, fiscal year 2007a

a

Coverage: U.S. residents served by community water systems 

(CWS) (approximately 95% of the total U.S. population).

b

Some CWS violated more than one of the selected rules.

Data source: U.S. EPA, 2007

Any violation

Selected violations

Stage 1 Disinfection

Byproducts Rule

Surface Water

Treatment Rules

Total Coliform Rule

24,279,892

3,643,104

8,945,673

10,569,935

8.5

1.3

3.1

3.7

Population served

20,472,902 7.1

Percent of 

CWS customers

Any of these 

selected rulesb

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

Percent of CWS customers

Fiscal year

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

20

40

60

80

100

0

10

30

50

70

90

Exhibit 3-36. U.S. population served by

community water systems with no reported 

violations of EPA health-based standards, by

EPA Region, fiscal years 1993-2007a,b

a

Coverage: U.S. residents served 

by community water systems 

(CWS) (approximately 95% of 

the total U.S. population).

b

Based on reported violations of 

the standards in effect in any 

given year.

Data source: U.S. EPA, 2007

’93 ’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’07’06
WATER

3-56 EPA’s 2008 Report on the Environment

3.6.3 Discussion

What This Indicator Says About Trends in 

the Quality of Drinking Water and Their 

Effects on Human Health

Most Americans served by community water systems (CWS) 

are served by facilities with no reported violations (Drinking 

Water indicator, p. 3-54). Since 1993, the percentage of Americans served by CWS for which states reported no healthbased violations has increased, although there has been some 

reversal nationally since the percentage peaked in 2002. While 

there have been noticeable differences among EPA Regions 

over the period of record, most Regions have been consistently above 90 percent since 1993. Only one Region has been 

consistently below the national average, though according to 

the data source, this result is due largely to one large metropolitan water system that is under a legal settlement to upgrade 

its treatment technology. As this result suggests, while the 

nation has thousands of CWS, a substantial percentage of the 

population depends on the quality of a small number of large 

metropolitan water systems.

Limitations, Gaps, and Challenges

As noted in the indicator description, a challenge in assessing 

national drinking water quality is that there are inherent limitations in using reporting data. Some violations may be unreported, particularly if monitoring is inadequate—leading to 

undercounting. Other violations may be overlooked because 

CWS may purchase water from other CWS and not test it for 

INDICATOR Population Served by Community Water Systems with No 

Reported Violations of Health-Based Standards (continued)

violation is reported, even though only part of the total 

population served may actually receive water that is out 

of compliance. In addition, violations stated on an annual 

basis may suggest a longer duration of violation than may 

be the case, as some violations may be as brief as an hour 

or a day. 

•	 Other factors may lead to understating the population receiving water that violates standards. CWS that 

purchase water from other CWS are not always required 

to sample for all contaminants themselves, and the CWS 

that are wholesale sellers of water generally do not report 

violations for the population served by the systems that 

purchase the water.

•	 Under-reporting and late reporting of violations by 

states to EPA affect the ability to accurately report the 

national violations total. For example, EPA estimated 

that between 1999 and 2001, states were not reporting 

35 percent of all health-based violations, which reflects a 

sharp improvement in the quality of violations data compared to the previous 3-year period (U.S. EPA, 2004a).

•	 State data verification and other quality assurance analyses indicate that the most widespread data quality problem is under-reporting of monitoring and health-based 

violations and inventory characteristics. Under-reporting 

occurs most frequently in monitoring violations; even 

though these are separate from the health-based violations covered by the indicator, failures to monitor could 

mask violations of TTs and MCLs. 

Data Sources

Data for this indicator were obtained from EPA’s Safe 

Drinking Water Information System (U.S. EPA, 2007) 

(http://www.epa.gov/safewater/data/getdata.html; 

http://www.epa.gov/safewater/data/pivottables.html). This 

database contains a record of violations reported to EPA by 

the states or other entities that oversee CWS, along with 

annual summary statistics.

References

U.S. Census Bureau. 2007. Monthly Population Estimates 

for the United States: April 1, 2000 to September 1, 2007. 

NA-EST2006-01. Accessed October 2007. <http://www.

census.gov/popest/national/tables/NA-EST2006-01.xls>. 

Available from 

<http://www.census.gov/popest/estimates.php>

U.S. EPA (United States Environmental Protection 

Agency). 2007. Safe Drinking Water Information System, 

Federal Version. Accessed October 2007. 

<http://www.epa.gov/safewater/data/getdata.html> 

U.S. EPA. 2004a. Safe Drinking Water Act 30th anniversary fact sheet: Drinking water monitoring, compliance, and enforcement. <http://www.epa.gov/safewater/

sdwa/30th/factsheets/monitoring_compliance.html>

U.S. EPA. 2004b. Safe Drinking Water Act 30th anniversary fact sheet: Drinking water standards and health effects.

<http://www.epa.gov/safewater/sdwa/30th/factsheets/

standard.html>

U.S. EPA. 2004c. Safe Drinking Water Act 30th anniversary fact sheet: Glossary. <http://www.epa.gov/safewater/

sdwa/30th/factsheets/glossary.html>

USGS (United States Geological Survey). 2004. Estimated 

use of water in the United States in 2000. 2004 revision. 

<http://water.usgs.gov/pubs/circ/2004/circ1268/> 

v
WATER

EPA’s 2008 Report on the Environment 3-57

all contaminants themselves. Conversely, the data could also 

overstate the portion of the population receiving water in violation of standards, because a violation could be as short as an 

hour or a day and could be limited to water received by only a 

small portion of a system’s customers. 

Other challenges relate to the interpretation of the Drinking 

Water indicator (p. 3-54). For example, trends can be confounded by the fact that water quality standards and treatment 

requirements change over time. Thus, an apparent increase in 

violations over time may result from new or more stringent 

MCLs rather than simply a decline in the quality of drinking 

water, as these new requirements may also affect some systems’ 

compliance with existing standards.

As described in the indicator summary, the indicator does not 

address the quality of drinking water other than that obtained 

from CWS. Information that would provide a more complete 

characterization of drinking water quality includes National 

Indicators for:

•	 Trends in drinking water quality from CWS that did

have reported violations. The Drinking Water indicator 

does not explain the nature of every reported violation, nor 

does it show how many contaminants may be above standards, the identity of the contaminants, the extent to which 

standards were exceeded, or the duration of the violations 

(some of which, especially in larger systems, were only a 

very few hours in length). 

•	 The quality of drinking water from other public 

water systems. There is no ROE indicator for drinking water quality from transient and non-transient noncommunity water systems, which are required to monitor 

quality and report violations to state authorities, but are 

regulated only for certain contaminants. 

•	 The quality of drinking water from non-public 

water supplies. Private wells, cisterns, and other nonpublic water supplies are not subject to federal regulation. 

Some private supplies are treated, and some people do test 

their private water for common contaminants. However, 

no national infrastructure, and few if any systematic state 

efforts, currently exist to collect data on trends in the quality of these supplies. Bottled water is regulated by the U.S. 

Food and Drug Administration (FDA), which is required 

by law to apply standards that are no less stringent or protective of public health than EPA’s, but there is no ROE 

indicator on the quality of bottled water.

In addition to these gaps, there are no ROE indicators to 

identify trends in health effects of interest, such as waterborne 

disease occurrence. Data are very limited for endemic waterborne illness as well as for acute waterborne disease outbreaks.

3.7 What Are the Trends 

in the Condition of 

Recreational Waters 

and Their Effects on 

Human Health and the 

Environment?

3.7.1 Introduction

The nation’s rivers, lakes, and coastal waters are used for many 

different forms of recreation. Some recreational activities take 

place in or on the water, such as swimming, boating, whitewater rafting, and surfing. Other activities may not involve 

contact with the water yet may still require water—or be 

enhanced by proximity to water. Examples include a picnic at 

the beach, hiking, nature viewing (e.g., bird watching), and 

hunting (especially waterfowl). People also engage in fishing 

and shellfishing as recreational activities.

In the questions on fresh surface waters and coastal waters 

(Sections 3.2 and 3.5), condition is defined as a combination of 

physical, chemical, and biological attributes of a water body. 

For recreational waters, condition is more specific, focusing on 

those physical, chemical, and biological attributes that determine a water body’s ability to support recreational activities. 

The particular attributes necessary to support recreation vary 

widely, depending on the nature of the activity in question. In 

a more general sense, however, the components of recreational 

condition fall into two main categories:

•	 Attributes that determine whether recreational activities can be enjoyed without unacceptable risk to human 

health—primarily pathogens and chemical contaminants 

that can affect the health of humans who are exposed during contact activities such as swimming.

•	 Attributes associated with ecological systems that support 

recreation—e.g., the status of fish and bird communities, as 

well as chemical and physical characteristics that may affect 

these populations and their habitat. These attributes also 

contribute to the aesthetic qualities important for recreational activities.

Many stressors affecting the condition of recreational waters 

fall into the broad category of contaminants. This category 

includes chemical contaminants, various pathogens (viruses, 

bacteria, and other parasites or protozoans) that can cause 

infectious disease, and pollutants such as trash or debris. These 

stressors can come from a variety of point sources and nonpoint sources, and can be discharged or washed directly into 
WATER

3-58 EPA’s 2008 Report on the Environment

recreational waters or carried downstream to lakes or coastal 

areas. Among the major sources are storm water and sediment 

runoff, direct discharge (e.g., from industrial facilities and 

sewer systems), atmospheric deposition, and recreational activities themselves (e.g., outboard motor exhaust and overboard 

discharge of sanitary wastes). Some chemicals and pathogens 

occur naturally, but their abundance may be influenced by 

other human stressors such as land use and land cover (e.g., 

paved surfaces and forestry and irrigation practices, which 

can influence runoff patterns) or by natural stressors such as 

weather and climate. Land use and land cover can influence 

recreational condition in other ways as well.

In terms of human health, the stressors that pose the greatest potential risks are chemical and biological contaminants. 

People can be exposed to these contaminants if they swim in 

contaminated waters or near storm water or sewage outfall 

pipes—especially after a rainfall event. Boating also may pose 

risks of exposure, although to a lesser extent. For toxic chemical contaminants, the main routes of exposure are through 

dermal (skin) contact or accidental ingestion. For pathogens, 

the main route of exposure is by swallowing water, although 

some infections can be contracted simply by getting polluted 

water on the skin or in the eyes. In some cases, swimmers can 

develop illnesses or infections if an open wound is exposed to 

contaminated water.

Effects of exposure to chemical and biological contaminants 

range from minor illnesses to potentially fatal diseases. The most 

common illness is gastroenteritis, an inflammation of the stomach 

and the intestines that can cause symptoms such as vomiting, 

headaches, and diarrhea. Other minor illnesses include ear, eye, 

nose, and throat infections. While unpleasant, most swimmingrelated illnesses are indeed minor, with no long-term effects. 

However, in severely contaminated waters, swimmers can 

sometimes be exposed to serious and potentially fatal diseases 

such as meningitis, encephalitis, hepatitis, cholera, and typhoid 

fever.28 Children, the elderly, and people with weakened immune 

systems are most likely to develop illnesses or infections after 

coming into contact with contaminated water.

From an ecological perspective, stressors to recreational waters 

can affect habitat, species composition, and important ecological processes. For example, changes in land cover (e.g., the 

removal of shade trees) may cause water temperature to rise 

above the viable range for certain fish species. Hydromodifications such as dams may create some recreational opportunities 

(e.g., boating), but they also may impede the migration of fish 

species such as salmon. Chemical and biological contaminants 

may harm plants and animals directly, or they may disrupt the 

balance of the food web. For example, acid deposition may 

lead to acidification in lakes, while excess nutrients can lead 

to eutrophic conditions such as low levels of dissolved oxygen, 

which in turn can harm fish and shellfish populations. Beyond 

their obvious effects on activities like fishing and nature 

viewing, stressors such as these also can be detrimental to 

recreational activities in a more aesthetic sense, as the presence 

of dead fish or visibly unhealthy plants may diminish one’s 

enjoyment of recreation in or near the water.

Ultimately, ecological effects can also impact human health. 

For example, eutrophic conditions can encourage harmful 

algal blooms—some of which can produce discomfort or illness when people are exposed through ingestion or skin or eye 

contact. One well-known type of harmful algal bloom is “red 

tide,” which in humans can cause neurotoxic shellfish poisoning and respiratory irritation.29

3.7.2 ROE Indicators

At this time, no National Indicators have been identified 

to quantify the condition of recreational waters. Individual 

states monitor certain recreational waters for a set of indicator bacteria and report monitoring results to EPA. However, 

the methodology and frequency of data collection vary among 

states, so the data are not necessarily comparable.

Challenges and information gaps for developing reliable 

National Indicators of recreational water condition are 

described in more detail in Section 3.7.3 below.

3.7.3 Discussion

Limitations, Gaps, and Challenges

Several challenges exist in assessing the condition of the 

nation’s recreational waters. Foremost is the lack of a comprehensive national system for collecting data on pathogen 

levels at beaches, a key concern in assessing the suitability of 

recreational waters with respect to human health. In addition, data on the types and extent of health effects associated with swimming in contaminated water are limited. 

The number of occurrences is likely under-reported because 

individuals may not link common symptoms (e.g., gastrointestinal ailments, sore throats) to exposure to contaminated 

recreational waters. 

Another challenge to answering this question is the breadth 

of the subject. “Recreation” encompasses a wide range of 

activities, involving different types of water bodies and 

entailing varying concepts of condition. While the recreational condition of a whitewater stream with a native 

salmon population will be determined largely by flow levels 

and condition of fish habitat, for example, the recreational 

condition of a beach will be assessed more in terms of levels 

of pathogens and chemical contaminants.

Gaps in assessing the condition of the nation’s recreational 

waters include National Indicators of pathogen levels in recreational waters (rivers, lakes, and coastal beaches), the magnitude of specific stressors—particularly contaminant loadings 

(biological and chemical)—to recreational waters, harmful 

algal blooms in recreational waters, and the condition of recreational fish and shellfish populations.

28 Pond, K. 2005. Water recreation and disease—plausibility of associations, 

sequelae and mortality. Published on behalf of World Heath Organization. 

London, United Kingdom: IWA Publishers. <http://www.who.int/water_

sanitation_health/bathing/recreadis.pdf>

29 National Research Council. 2000. Clean coastal waters: Understanding and 

reducing the effects of nutrient pollution. Washington, DC: National Academies Press.
WATER

EPA’s 2008 Report on the Environment 3-59

3.8 What Are the Trends 

in the Condition of 

Consumable Fish and 

Shellfish and Their 

Effects on Human 

Health?

3.8.1 Introduction

Fish and shellfish caught through commercial, recreational, or 

subsistence fishing are an important part of a healthful diet for 

many people. Fish and shellfish contain high-quality protein and 

other essential nutrients, are low in saturated fat, and contain 

omega-3 fatty acids. Most fish consumed in the United States 

comes from commercial fisheries, and is purchased in supermarkets or fish markets. Fishing also is one of the most popular outdoor recreational activities in the country, with more than 34 

million people per year fishing recreationally30—many of whom 

eat at least some of the fish they catch. In addition, subsistence 

fishers—people who rely on fish as an affordable food source 

or for whom fish are culturally important—consume fish and 

shellfish as a major part of their diets. Commercial, recreational, 

and subsistence fisheries all have substantial economic value for 

the nation, regions, and local communities. 

Americans consume fish and shellfish caught in the nation’s 

lakes, rivers, and estuaries and in deep ocean fisheries, as well 

as farmed fish and shellfish.31 Some of these fish and shellfish 

contain elevated levels of chemical or biological contaminants. 

This question addresses the condition of consumable fish and 

shellfish caught or farmed in the United States—whether, and 

the extent to which, these organisms contain contaminants 

that could affect the health of people who consume them. 

According to recent surveys, the average American consumes close to 13 grams of fish and shellfish per day (prepared 

weight), which amounts to slightly more than one 3-ounce 

serving per week.32 However, many Americans consume 

substantially more fish and shellfish than the national average; 

some of the highest consumption rates are among tribal and 

ethnic populations who fish for subsistence. Concern about 

fish and shellfish safety is higher for these groups as well as for 

children, pregnant and nursing women (because of possible 

effects on the fetus or infant), and other population subgroups 

who may be more vulnerable to the health effects of certain 

chemical or biological contaminants (e.g., elderly or immunosuppressed individuals).

Chemical contaminants of greatest concern in consumable fish 

and shellfish tend to be those that are persistent, bioaccumulative, and toxic (called PBTs). These chemicals can persist for 

long periods in sediments and then enter the food web when 

ingested by bottom-dwelling (benthic) organisms. Benthic 

organisms are eaten by small fish, which in turn are eaten by 

larger fish, which may be consumed by humans or wildlife. 

PBTs that are common in fresh and coastal waters include:

•	 Mercury. This highly toxic metal is present in waters 

all over the globe—a result of long-range transport and 

deposition of airborne mercury as well as direct inputs to 

water.33 Mercury in water bodies can be methylated by 

certain bacteria in bottom sediments to form methylmercury, which is more toxic and bioavailable than other forms 

of mercury.34 It also is biomagnified through aquatic food 

webs, so that it becomes particularly concentrated in larger 

and longer-lived predators such as bass, tuna, swordfish, 

and some sharks. Exposure to high levels of methylmercury 

can cause reproductive and other effects in wildlife;35 in 

humans, exposure to elevated levels is primarily associated 

with developmental and neurological health effects.36

•	 Polychlorinated biphenyls (PCBs) and the pesticide 

DDT. Though PCBs and DDT are no longer manufactured or used in the U.S., they persist in historical deposits 

in watersheds and near-shore sediments, which can continue to contaminate fish and shellfish. These chemicals 

are also circulated globally as a result of use in other parts 

of the world. Levels of PCBs and DDT are a concern in 

some bottom-feeding fish and shellfish, as well as in some 

higher-level predators. These chemicals have been linked to 

adverse health effects such as cancer, nervous system damage, reproductive disorders, and disruption of the immune 

system in both humans and wildlife.

Other chemical contaminants that may be present in fish and 

shellfish include other pesticides, metals (such as arsenic), and 

dioxins and furans.37

Biological contamination also can affect the condition of fish 

and shellfish—particularly the latter. For example, shellfish 

contaminated with pathogens from human and animal fecal 

wastes can cause gastrointestinal illness and even death in 

individuals with compromised immune systems. Sources of 

30 U.S. Department of the Interior, Fish and Wildlife Service, and U.S. Department of Commerce, U.S. Census Bureau. 2002. 2001 national survey of fishing, hunting, and wildlife-associated recreation.

31 According to the National Oceanic and Atmospheric Administration’s Fisheries of the United States—2006, imports of edible seafood made up 83 percent 

of U.S. per capita consumption in 2006. See <http://www.st.nmfs.noaa.gov/

st1/fus/fus06/08_perita2006.pdf>

32 U.S. Environmental Protection Agency. 2002. Estimated per capita fish consumption in the United States. EPA/821/C-02/003. <http://www.epa.gov/

waterscience/fish/consumption_report.pdf>

33 U.S. and global sources of mercury are described in more detail in Section 

2.2, which includes an indicator of domestic mercury emissions.

34 U.S. Environmental Protection Agency. 1997. Mercury study report to 

Congress. Volume III: Fate and transport of mercury in the environment. 

EPA/452/R-97/005. <http://www.epa.gov/mercury/report.htm>

35 U.S. Environmental Protection Agency. 1997. Mercury study report to 

Congress. Volume V: Health effects of mercury and mercury compounds. 

EPA/452/R-97/007. <http://www.epa.gov/mercury/report.htm>

36 National Research Council. 2000. Toxicological effects of methylmercury. 

Washington, DC: National Academies Press.

37 U.S. Environmental Protection Agency. In progress. National study of chemical residues in lake fish tissue. <http://www.epa.gov/waterscience/fishstudy>
WATER

3-60 EPA’s 2008 Report on the Environment

Table 3-7. ROE Indicators of Trends in the Condition of Consumable Fish 

and Shellfish and Their Effects on Human Health

National Indicators Section Page

Coastal Fish Tissue Contaminants (N/R) 3.8.2 3-61

Contaminants in Lake Fish Tissue 3.8.2 3-63

N/R = National Indicator displayed at EPA Regional scale

fecal contamination in shellfish include urban runoff, wildlife, 

wastewater treatment systems and treatment plants, agricultural runoff, and boating and marinas.

Marine biotoxins produced by certain types of algae can 

contaminate fish and shellfish as well. These toxins not only 

can harm fish and fish communities—sometimes resulting 

in massive fish kills or losses to aquaculture operations—but 

they also can make their way through the food web to affect 

seabirds, marine mammals, and humans. Mollusks such as 

mussels, clams, oysters, whelks, and other shellfish can carry 

biotoxins that have common symptoms such as irritation of 

the eyes, nose, throat, and tingling of the lips and tongue. 

Consumption of contaminated seafood can cause a range of 

other health effects in humans, depending on the organism 

involved, including gastrointestinal illness, amnesia, memory 

loss, paralysis, and even death.38,39

The growth of aquaculture, or fish farming, may affect the 

levels of certain contaminants in consumable fish and shellfish. Dense colonies can increase stress and disease transmission among fish, in some cases requiring the administration of 

antibiotics.40 Studies have also found higher levels of certain 

contaminants in farmed fish than in their wild counterparts, 

possibly due to differences in diet. For example, several studies 

have found higher concentrations of PCBs, organochlorine 

pesticides, and polybrominated diphenyl ethers (PBDEs) in 

farmed salmon.41

Overharvesting also can affect the condition of fish and shellfish—not only the species being harvested, but also the species 

that prey on them—by disrupting the food web. Because of 

depleted food sources, predators can become more susceptible to disease (such as infection of rockfish by mycobacterial 

lesions). These infections are often confined to internal organs 

and may not be apparent to anglers, although in some cases 

they are associated with external sores as well. Some types of 

mycobacteria can also infect humans who handle diseased fish 

if the infection comes into contact with an open wound. The 

slow-developing infections are usually not severe in humans, 

but in some cases they can cause major health problems, especially in people with compromised immune systems.

3.8.2 ROE Indicators

Two ROE indicators characterize levels of chemical contaminants in edible fish and shellfish species (Table 3-7). One 

indicator reports levels and occurrence of contaminants in fish 

in estuarine areas; the other, in freshwater lakes and reservoirs. 

Both indicators are based on nationwide probabilistic surveys. 

The coastal fish indicator is based on an index originally presented in EPA’s second National Coastal Condition Report. 

The underlying data were collected between 1997 and 2000 

as part of EPA’s Environmental Monitoring and Assessment 

Program (EMAP). EMAP’s probabilistic coastal surveys are 

designed to be representative of 100 percent of estuarine acreage in the contiguous 48 states. This indicator presents results 

by EPA Region.

The other indicator describes contamination of fish in inland 

lakes. This indicator is derived from fish samples collected and 

analyzed for EPA’s National Study of Chemical Residues in 

Lake Fish Tissue, a probabilistic survey designed to estimate 

the national distribution of the mean levels of selected PBT 

chemical residues in fish tissue from lakes and reservoirs. 

Note that this question does not rely on information about 

fish and shellfish consumption advisories. While many states 

and tribes issue fish consumption advice and develop fish 

advisory programs, there is great variability in how monitoring is conducted, how decisions are made to place waters 

under advisory, and what specific advice is provided when 

contamination is found in fish. Further, trends in the number 

of advisories over time may reflect changes in the frequency 

and intensity of monitoring.42 Thus, fish advisories cannot 

provide a consistent national metric for trends in the condition of consumable fish and shellfish.

38 Baden D., L.E. Fleming, and J.A. Bean. 1995. Marine toxins. In: DeWolff, 

F.A., ed. Handbook of clinical neurology: Intoxications of the nervous system. 

Part II: Natural toxins and drugs. Amsterdam, The Netherlands: Elsevier. pp. 

141-175.

39 Van Dolah, F.M. 2000. Marine algal toxins: Origins, health effects, and their 

increased occurrence. Environ. Health Persp. 108(Suppl 1):133-141.

40 Barton, B.A., and G.K. Iwama. 1991. Physiological changes in fish from stress 

in aquaculture with emphasis of the response and effects of corticosteroids. 

Annu. Rev. Fish Dis. 1:3-26.

41 Easton, M.D.L., D. Luszniak, and E. Von der Geest. 2002. Preliminary examination of contaminant loadings in farmed salmon, wild salmon and commercial salmon feed. Chemosphere 46(7):1053-1074.

42 U.S. Environmental Protection Agency. 2005. Fact sheet: National listing of 

fish advisories. EPA/823/F-05/004. <http://www.epa.gov/waterscience/

fish/advisories/2004/fs2004.pdf>
WATER

EPA’s 2008 Report on the Environment 3-61

INDICATOR | Coastal Fish Tissue Contaminants

Contaminants in fish not only affect the fish’s own health and ability to reproduce, but also affect the many species that feed on them. Contaminants also may make fish 

unsuitable for human consumption (U.S. EPA, 2000).

This indicator, derived from an indicator presented in 

EPA’s second National Coastal Condition Report (U.S. 

EPA, 2004), is based on National Coastal Assessment (NCA) 

fish tissue survey data from 653 estuarine sites throughout 

the United States. The survey was designed to provide a 

national picture of coastal fish tissue contaminants by sampling sites in estuarine waters throughout the contiguous 

48 states. Each site was sampled once during the 1997-2000 

period, within an index period from July to September. The 

indicator reflects average condition in each EPA Region 

during this index period. Results were also aggregated and 

weighted by estuarine area for the entire nation. 

Fish and shellfish analyzed in the survey included Atlantic croaker, white perch, catfish, flounder, scup, blue crab, 

lobster, shrimp, whiffs, mullet, tomcod, spot, weakfish, 

halibut, sole, sculpins, sanddabs, bass, and sturgeon. At 

each site, five to 10 whole-body fish samples were tested 

for 90 contaminants. This indicator is based on data collected from 1997 to 2000. 

To assess risks to human health, contaminant concentrations in fish tissue were compared with established EPA 

guideline ranges for recreational fishers, which were available for 16 of the 90 analytes. These guideline ranges are 

based on the consumption of four 8-ounce fish meals per 

month, and generally reflect non-cancer risks (U.S. EPA, 

2000, 2004). For most contaminants, this is done using 

whole-body concentrations; for mercury, which concentrates in the edible fillet portion of the fish, a factor of 3.0 

was used to correct whole-body concentrations in order to 

approximate fillet concentrations. The 3.0 factor represents 

the median value (range 1.5-5.0) found in the available 

literature (Windom and Kendall, 1979; Mikac et al., 1985; 

Schmidt and Brumbaugh, 1990; Kannan et al., 1998; 

Canadian Council of Ministers of the Environment, 1999).

For this indicator, a site was given a high contamination score if one or more contaminants were present at a 

concentration above the guideline ranges. A site was rated 

moderate if one or more contaminants were within the 

guideline ranges but none was in exceedance. Sites with 

all contaminants below their guideline ranges were given a 

low contamination score.

What the Data Show

Nationwide, 63 percent of sites showed low fish tissue 

contamination, 15 percent had moderate contamination, 

and 22 percent exhibited high contamination (Exhibit 

3-38). Fish tissue contamination varied substantially from 

one EPA Region to the next; for example, the percentage 

of sites with low contamination ranged from 25 percent 

(Region 1) to 83 percent (Region 4). Regions 2 and 9 had 

the largest proportion of sites with high contamination (41 

percent and 40 percent, respectively).

Data from EPA’s National Coastal Database show that 

nationwide, PCBs were the contaminants most frequently 

responsible for high fish tissue contamination, with 19 

percent of sites above EPA guideline ranges (Exhibit 3-39). 

Other chemicals present above EPA guideline ranges at 

many sites were mercury in muscle tissue (18 percent of 

sites), DDT (8 percent), and PAHs (3 percent) (Exhibit 

3-39). Inorganic arsenic, selenium, chlordane, endosulfan, 

endrin, heptachlor epoxide, hexachlorobenzene, lindane, 

and mirex were below EPA guideline ranges for all fish 

sampled in the NCA.

Indicator Limitations

•	 The indicator is limited to estuarine samples, and does not 

include data from Louisiana, Florida, Puerto Rico, Alaska, 

Region 1

Region 2

Region 3

Region 4

Region 6

Region 9

Region 10

All U.S.

Low Moderate High

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

Exhibit 3-38. Coastal fish tissue contaminants 

in the contiguous U.S. by EPA Region, 

1997-2000a,b,c

52 8 40

67 11 22

63 15 22

Level of contamination:

Percent of estuarine sites in each category:

59 7 34

83 13 4

53 20 27

39 20 41

25 38 37

a

Coverage: Estuarine waters of the 

contiguous 48 states. 

b

This indicator is based on a 

whole-body analysis of the fish. See 

text for definitions of categories.

c

Totals may not add to 100% due to 

rounding. 

Data source: U.S. EPA, 2004, 2005a
WATER

3-62 EPA’s 2008 Report on the Environment

INDICATOR | Coastal Fish Tissue Contaminants (continued)

or Hawaii, which had not been assessed at the 

time this indicator was compiled. Some of 

these areas (e.g., portions of Alaska) have now 

been surveyed, and may be included in future 

indicators.

•	The data are not broken out by trophic level of 

the fish and shellfish species, which influences 

bioaccumulation of contaminants.

•	 Whole-body contaminant concentrations 

in fish overestimate the risk associated with 

consuming only the fillet portion of the fish, 

with the exception of mercury and cadmium, 

which are generally underestimated.

•	This indicator focuses on contaminants from 

a human health risk perspective. No EPA 

guidance criteria exist to assess the ecological 

risk of whole-body contaminants in fish (U.S. 

EPA, 2004). 

•	 Some fish samples used in the survey were 

non-market-size juveniles, which are known 

to have lower contaminant levels than larger, 

market-sized fish.

•	 Samples are collected during an index period 

from July to September, and the indicator is 

only representative of this time period. It is 

unlikely, however, that contaminant levels 

vary substantially from season to season.

•	There are no trend data for this indicator. 

In EPA’s second National Coastal Condition 

Report, fish tissue contaminants are characterized by whole-body concentrations and 

compared to EPA risk-based consumption 

guideline ranges. For the first National Coastal 

Condition Report, fish contaminants were 

measured as fillet concentrations and compared to U.S. Food and Drug Administration 

(FDA) criteria. The data presented here will 

serve as a baseline for future surveys, however. 

Data Sources

This indicator is based on an analysis published 

in EPA’s second National Coastal Condition 

Report (U.S. EPA, 2004). Summary data by 

EPA Region and by contaminant have not been 

published, but were provided by EPA’s NCA 

program (U.S. EPA, 2005a). Underlying sampling data are housed in EPA’s NCA database 

(U.S. EPA, 2005b) (http://www.epa.gov/emap/

nca/html/data/index.html).

Percent of estuarine sites:

Contaminant

Guideline range

(ppm)

Arsenic (inorganic)d

Cadmium

Mercury (total body)

Mercury (muscle tissue)

Selenium

Chlordane

DDT

Dieldrin

Endosulfan

Endrin

Heptachlor epoxide

Hexachlorobenzene

Lindane

Mirex

Toxaphene

PAH (Benzo[a]pyrene)

Total PCBs

Within

guideline

range

0

<1

<1

0

0

4

0

0

0

0

0

0

0

11

0

2

24

Below

guideline

range

100

99

99

100

100

88

99

100

100

100

100

100

100

70

99

95

58

Exhibit 3-39. Coastal fish tissue contaminant 

concentrations in the contiguous U.S., compared with 

health-based guidelines, 1997-2000a,b,c

Exceeding

guideline

range

<1

0

0

8

<1

0

0

0

0

0

0

19

<1

3

18

0

<1

3.5-7.0

0.35-0.70

0.12-0.23

0.12-0.23

5.9 -12

0.59-1.2

0.059-0.12

0.059-0.12

7.0-14

0.35-0.70

0.015-0.031

0.94-1.9

0.35-0.70

0.23-0.47

0.29-0.59

0.0016-0.0032

0.023-0.047

a

Coverage: Estuarine waters of the contiguous 48 states. 

b

Concentrations were measured in whole fish tissue. Mercury data were adjusted to 

reflect concentrations in edible fillets, where mercury accumulates (adjustment 

factor of 3.0, based on the available literature). All other contaminants are 

presented as whole-body concentrations. 

c

Concentrations are compared with risk guidelines for recreational fishers for four 

8-ounce meals per month (U.S. EPA, 2000, 2004). Guidelines presented here are 

for non-cancer risk, except for PAH, which is a cancer risk guideline.

d

Inorganic arsenic estimated at 2% of total arsenic.

Data source: U.S. EPA, 2005a
WATER

EPA’s 2008 Report on the Environment 3-63

INDICATOR | Coastal Fish Tissue Contaminants (continued)

References

Canadian Council of Ministers of the Environment. 1999. 

Protocol for the derivation of Canadian tissue residue guidelines for the protection of wildlife that consume aquatic biota. 

Prepared by the Task Force on Water Quality Guidelines.

Kannan, K., R.G. Smith, R.F. Lee, H.L. Windom, P.T. 

Heimuller, J.M. Macauley, and J.K. Summers. 1998. Distribution of total mercury and methyl mercury in water, 

sediment and fish from South Florida estuaries. Arch. 

Environ. Con. Tox. 34:109-118.

Mikac, N., M. Picer, P. Stegnar, and M. Tusek-Nidari. 

1985. Mercury distribution in a polluted marine area, ratio 

of total mercury, methyl mercury and selenium in sediments, mussels and fish. Water Res. 19:1387-1392.

Schmidt, C.J., and W.G. Brumbaugh. 1990. National 

contaminant biomonitoring program: Concentrations of 

arsenic, cadmium, copper, lead, mercury, selenium, and 

zinc in U.S. freshwater fish 1976-1984. Arch. Environ. 

Con. Toxicol. 19:731-747.

U.S. EPA (United States Environmental Protection Agency). 2005a. Data provided to ERG (an EPA 

contractor) by Kevin Summers, EPA. September 2005.

U.S. EPA. 2005b. EMAP national coastal database. 

Accessed 2005. 

<http://www.epa.gov/emap/nca/html/data/index.html>

U.S. EPA. 2004. National coastal condition report II. 

EPA/620/R-03/002. <http://www.epa.gov/owow/oceans/

nccr/2005/index.html>

U.S. EPA. 2000. Guidance for assessing chemical contaminant data for use in fish advisories. EPA/823/B-00/008. 

<http://www.epa.gov/waterscience/library/fish/>

Windom, H.L., and D.R. Kendall. 1979. Accumulation 

and biotransformation of mercury in coastal and marine 

biota. In: Nriagu, J.O., ed. Biogeochemistry of mercury in 

the environment. Amsterdam, The Netherlands: Elsevier. 

pp. 303-323.

INDICATOR | Contaminants in Lake Fish Tissue

Lakes and reservoirs provide important sport fisheries and other recreational opportunities, and lake ecosystems provide critical habitat for aquatic species and support wildlife 

populations that depend on aquatic species for food. Lakes 

and reservoirs occur in a variety of landscapes and can receive 

contaminants from several sources, including direct discharges into the water, atmospheric deposition, and agricultural or urban runoff. A group of contaminants of particular 

concern are the persistent, bioaccumulative, and toxic (PBT) 

chemicals. These contaminants are highly toxic, long-lasting 

chemicals that can accumulate in fish, reaching levels that can 

affect the health of people and wildlife that eat them.

PBT contaminants can originate from a variety of sources. 

A primary source of one of the most important PBTs, 

mercury, is combustion at coal-fired power plants and other 

industrial operations (see the Mercury Emissions indicator, 

p. 2-46); mercury emitted to the air can then be transported 

and deposited in lakes and reservoirs. Among other important PBTs, most uses of DDT became illegal in the U.S. 

effective in 1973; production of PCBs in the U.S. ceased 

in 1977 and most uses were phased out by 1979 (although 

they are still emitted as a byproduct of other manufacturing 

processes); chlordane was banned in 1988; and quantifiable 

emissions of dioxin-like compounds from all known sources 

have decreased in the U.S. by an estimated 89 percent 

between 1987 and 2000 (U.S. EPA, 2006a).

This indicator is based on tissue samples of predator and 

bottom-dwelling fish species collected and analyzed for 

EPA’s National Study of Chemical Residues in Lake Fish 

Tissue. The data generated from this probabilistic survey 

(Olsen et al., 1998, in press; Stevens and Olsen, 2003, 

2004) are designed to estimate the national distribution 

of the mean levels of PBT chemicals in fish tissue from 

lakes (not including the Great Lakes) and reservoirs of the 

contiguous 48 states. The indicator consists of statistical 

distributions of the concentrations of 15 PBT chemicals 

or chemical groups in predator and bottom-dwelling fish 

tissue, including mercury, arsenic (total inorganic), dioxins/furans, total PCBs, and 11 organochlorine pesticides. 

Fourteen of these chemicals or chemical groups also appear 

in the Coastal Fish Tissue indicator (p. 3-61).

Fish samples were collected from 500 lakes and reservoirs 

over a 4-year period (2000-2003). Sampling locations were 

selected from the estimated 147,000 target lakes and reservoirs in the contiguous 48 states based on an unequal probability survey design. The lakes and reservoirs were divided 

into six size categories, and varying probabilities were 

assigned to each category in order to achieve a similar number of lakes in each size category. The lakes and reservoirs 

ranged from 1 hectare (about 2.5 acres) to 365,000 hectares 

(about 900,000 acres), were at least 1 meter (3 feet) deep, and 

had permanent fish populations. 

v
WATER

3-64 EPA’s 2008 Report on the Environment

INDICATOR | Contaminants in Lake Fish Tissue (continued)

Exhibit 3-40. Lake fish tissue PBT contaminant concentration estimates for predators (fillets) in the 

contiguous U.S., 2000-2003a

Number Number Percentiles for fillet tissue concentrations (ppm)c

of of samples 50th 5th 10th 25th 75th 90th Contaminant samples above MDLb (median)

Mercury 486 486 0.059 0.089 0.177 0.285 0.432 0.562

Total PCBs 486 486 0.000351 0.000494 0.001000 0.002161 0.008129 0.018159

TEQ dioxins/furans only 486 395 6 x 10-9 46 x 10-9 109 x 10-9 * * * Total inorganic arsenic 486 2 * * * * * * Total chlordane 486 96 0.003617 * * * * * Total DDT 486 378 0.00147 0.00694 0.01966 * * * Dicofol 486 15 * * * * * * Dieldrin 486 24 * * * * * * Total endosulfan 486 18 * * * * * * Endrin 486 3 * * * * * * Heptachlor epoxide 486 6 * * * * * * Hexachlorobenzene 485 0 * * * * * * Lindane (gamma-BHC) 486 28 * * * * * * Mirex 486 10 * * * * * * Toxaphene 486 0 * * * * * *

a

Coverage: Lakes and reservoirs of the contiguous 48 states. Each sample reported here is a composite sample from one lake.

b

MDL = method detection limit; MDLs are available online at http://www.epa.gov/waterscience/fishstudy.

c

* = less than MDL

Data source: U.S. EPA, 2006b

95th

0.833

0.033161

318 x 10-9

* 0.008266

0.03057

*

0.001193

*

*

*

*

0.000994

*

*

Because no predator or bottom-dwelling species occurs 

in all 500 lakes and reservoirs, the study focused on 12 

target predator species and six target bottom-dwelling species in order to minimize the effect of sampling different 

species. These species were chosen because they are commonly consumed in the study area, have a wide geographic 

distribution, and potentially accumulate high concentrations of PBT chemicals. Sampling teams applied consistent 

materials and methods nationwide. From each lake or 

reservoir, teams collected composite samples of five adult 

fish of similar size for one predator species (e.g., bass or 

trout) and one bottom-dwelling species (e.g., carp or catfish) (U.S. EPA, 2000). Fillets were analyzed for predators, 

and whole bodies were analyzed for bottom-dwelling fish. 

Fillet data represent the edible part of the fish most relevant 

to human health, while whole-body data are more relevant 

to wildlife consumption. A single laboratory prepared fish 

tissue samples for analysis in a strictly controlled environment, and tissue samples were sent to four analytical 

laboratories. The same laboratory analyzed tissue samples 

for each chemical group (e.g., PCBs or organochlorine 

pesticides), using the same standard analytical method, 

for the duration of the study. Concentrations of dioxins 

and furans were reported on a toxic equivalency quotient 

(TEQ) basis, which adjusts for the different toxicities of the 

various dioxin and furan compounds.

What the Data Show

Mercury, PCBs, dioxins and furans, and DDT are 

widely distributed in lakes and reservoirs in the contiguous 48 states (Exhibits 3-40 and 3-41). Mercury and 

PCBs were detected in 100 percent of both predator and 

bottom-dweller composite samples. Dioxins and furans 

were detected in 81 percent of the predator composite 

samples and 99 percent of the bottom-dweller composite samples, and DDT was detected in 78 percent of 

the predator composites and 98 percent of the bottomdweller composites. One chemical analyzed in this study 

(hexachlorobenzene) was not detected in any of the fish 

tissue samples. 
WATER

EPA’s 2008 Report on the Environment 3-65

INDICATOR | Contaminants in Lake Fish Tissue (continued)

Median concentrations in predator fillets (i.e., half of 

the lakes and reservoirs had fish with higher values) were 

as follows: mercury, 0.285 ppm; total PCBs, 2.161 ppb; 

dioxins and furans, 0.006 ppt [TEQ]; and total DDT, 

1.47 ppb (Exhibit 3-40). Median concentrations in whole, 

bottom-dwelling fish were lower for mercury (0.069 

ppm), but higher for total PCBs (13.88 ppb), dioxins and 

furans (0.406 ppt [TEQ]), and total DDT (12.68 ppb) 

(Exhibit 3-41).

Indicator Limitations

•	 Survey data are not available for Alaska, Hawaii, or 

Puerto Rico.

•	The Great Lakes, the Great Salt Lake, and lakes without 

permanent fish populations are not included in the 

target population.

•	 Because the distribution of sampling sites was based on the 

frequency of occurrence of lakes and reservoirs, contaminants in lakes and reservoirs in arid states (e.g., Arizona, 

New Mexico, and Nevada) are not well-represented.

•	 Due to the inaccessibility of some target lakes (e.g., landowner denial of access), the results are representative of the 

sampled population of lakes (approximately 80,000) rather 

than the original target population of 147,000 lakes.

•	The indicator does not compare contaminant data to 

human health thresholds; EPA has not yet finalized that 

portion of the analysis.

•	Trend data are not yet available, as this is the first time 

that a national lake fish tissue survey has been conducted 

using a probabilistic sampling design. These data will 

serve as a baseline for future surveys.

Data Sources

The data for Exhibits 3-40 and 3-41 were obtained from 

EPA’s National Lake Fish Tissue Study. A report on the 

findings of this study was still in progress at the time this 

ROE went to press; however, partial results have been 

published in U.S. EPA (2006b) (http://www.epa.gov/

waterscience/fishstudy/results.htm), along with information about how to obtain more detailed results on CD.

Contaminant 

Total PCBs 

Mercury 

TEQ dioxins/furans only 

Total inorganic arsenic 

Total chlordane 

Total DDT 

Dicofol 

Dieldrin 

Total endosulfan 

Endrin

Heptachlor epoxide

Hexachlorobenzene 

Lindane (gamma-BHC) 

Mirex 

Toxaphene 

Percentiles for whole-body tissue concentrations (ppm)c

Number

of 

samples

Number

of samples

above MDLb 90th 95th

Exhibit 3-41. Lake fish tissue PBT contaminant concentration estimates for bottom-dwellers (whole fish) 

in the contiguous U.S., 2000-2003a

5th 10th 25th 50th

(median) 75th

0.00108

0.001579

0.019

*

*

*

*

*

*

*

*

*

*

*

*

*

*

0.00182

*

*

*

19 x 10-9 59 x 10-9

*

0.002308

0.020

*

*

*

*

*

*

*

0.00423

*

*

*

165 x 10-9

*

0.005146

0.039

*

*

*

*

*

*

*

0.01268

*

*

*

406 x 10-9

*

0.013876

0.069

0.001653

*

*

*

*

*

*

0.03535

*

*

*

1067 x 10-9

*

0.070050

0.124

0.009313

*

*

*

*

*

*

0.15392

0.003436

*

*

1770 x 10-9

*

0.130787

0.220

0.025964

0.000729

*

*

*

*

0.001866

0.21863

0.024613

*

*

2006 x 10-9

0.037

0.198324

0.247

0.030931

0.001541

0.000676

*

395

395

395

395

395

395

395

395

395

395

395

395

395

395

395

395

395

393

36

197

388

8

73

23

14

0

31

19

1

25

a

Coverage: Lakes and reservoirs of the contiguous 48 states. Each sample reported here is a composite sample from one lake.

b

MDL = method detection limit; MDLs are available online

c

* = less than MDL

Data source: U.S. EPA, 2006b

 at http://www.epa.gov/waterscience/fishstudy.
WATER

3-66 EPA’s 2008 Report on the Environment

3.8.3 Discussion

What These Indicators Say About Trends 

in the Condition of Consumable Fish and 

Shellfish and Their Effects on Human Health

The ROE indicators provide baseline information about 

consumable fish in inland lakes, reservoirs, and coastal areas. 

The data were collected from a variety of species, reflecting 

many parts of the food web. The results for fish in estuarine 

sites along the Atlantic, Gulf, and Pacific coasts of the contiguous 48 states (Coastal Fish Tissue indicator, p. 3-61) varied 

substantially among the seven coastal EPA Regions. Fish from 

the coastal waters of the Southeast (EPA Region 4) generally 

had low contamination scores, while several other Regions 

had a substantial proportion with high contamination. PCBs, 

mercury, DDT, and PAHs appeared to be the contaminants 

responsible for the most high contamination scores.

The results for lake fish (Lake Fish Tissue indicator, p. 3-63) 

suggest that several chemical contaminants are widely distributed in the nation’s lakes and reservoirs, including mercury, 

dioxins and furans, PCBs, and DDT. However, some of the 

other chemicals in this screening—including certain pesticides—were detected rarely or not at all. There were some 

notable differences between predators and bottom-dwellers, 

which may be a result of how each type of fish was analyzed—

fillets for predators and whole fish for bottom dwellers. 

Limitations, Gaps, and Challenges 

As explained in Section 3.8.2, both of the ROE indicators 

have important limitations. For example, like the other coastal 

indicators from EPA’s second National Coastal Condition 

Report (presented in Section 3.5), the Coastal Fish Tissue 

indicator (p. 3-61) does not display trend data. It is also limited spatially, as adequate data for Alaska, Hawaii, the Caribbean, and the Pacific territories are not available. The lack of 

data from Alaska is especially notable because more than half 

of the nation’s commercial fish and shellfish catch comes from 

Alaskan waters.43

The Lake Fish Tissue indicator (p. 3-63) is also limited temporally and spatially, with no trend data and no coverage outside 

the contiguous 48 states. Further, unlike the coastal survey, the 

lake fish survey was not designed to produce results by region, 

and it also does not compare contaminant levels to any healthbased guidelines. Thus, while both indicators present meaningful data, the results cannot easily be compared. 

The Coastal Fish Tissue and Lake Fish Tissue indicators (pp. 

3-61 and 3-63) do provide some information about contamination and safety of fish and shellfish. However, to fully assess 

the condition of the nation’s fish and shellfish, more data are 

needed—particularly on a national level, because many issues 

have been studied locally or regionally, but have not yet been 

studied in nationally representative surveys. In addition to 

the limitations of the indicators described above, information 

gaps for answering this question include nationally consistent 

indicators of pathogens in fish and shellfish (in both fresh 

water and coastal waters) and indicators of the biological and 

chemical condition of fish and shellfish commercially farmed 

in the U.S. There are also no ROE indicators to describe the 

effects of fish and shellfish condition on human health. As 

noted in Chapter 1, it is often difficult to explicitly connect an 

observed effect to a particular stressor (e.g., the condition of 

fish and shellfish that people consume), even though there may 

be scientific evidence to suggest a possible association.

INDICATOR | Contaminants in Lake Fish Tissue (continued)

References

Olsen, A.R., B.D. Snyder, L.L. Stahl, and J.L. Pitt. In press. 

Survey design for lakes and reservoirs in the United States to 

assess contaminants in fish tissue. Environ. Monit. Assess. 

Olsen, A.R., D.L. Stevens, Jr., and D. White. 1998. Application of global grids in environmental sampling. Comp. 

Sci. Stat. 30:279-284.

Stevens, D.L., Jr., and A.R. Olsen. 2004. Spatiallybalanced sampling of natural resources. J. Am. Stat. Assoc. 

99(465):262-278.

Stevens, D.L., Jr., and A.R. Olsen. 2003. Variance 

estimation for spatially balanced samples of environmental 

resources. Environmetrics 14:593-610.

U.S. EPA (United States Environmental Protection 

Agency). 2006a. Inventory of sources of environmental 

releases of dioxin-like compounds in the United States: 

The year 2000 update. EPA/600/P-03/002a. 

<http://www.epa.gov/ncea/pdfs/dioxin/2k-update/>

U.S. EPA. 2006b. National Lake Fish Tissue Study—

results. Updated February 27, 2006. 

<http://www.epa.gov/waterscience/fishstudy/results.htm>

U.S. EPA. 2000. Field sampling plan for the national study 

of chemical residues in lake fish tissue. EPA/823/R-02/004. 

<http://www.epa.gov/waterscience/fish/study/data/ 

fieldplan.pdf>

v

43 National Oceanic and Atmospheric Administration. 2007. Fisheries of 

the United States—2006. <http://www.st.nmfs.noaa.gov/st1/fus/fus06/

fus_2006.pdf>
Land

Chapter 4
Contents

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.1.1 Overview of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.1.2 Organization of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.2 What Are the Trends in Land Cover and Their Effects on Human Health 

and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.2.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.3 What Are the Trends in Land Use and Their Effects on Human Health 

and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.3.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

4.3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-22

4.4 What Are the Trends in Wastes and Their Effects on Human Health 

and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-23

4.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-23

4.4.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-24

4.4.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28

4.5 What Are the Trends in Chemicals Used on the Land and Their Effects on 

Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

4.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

4.5.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

4.5.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41

4.6 What Are the Trends in Contaminated Land and Their Effects On 

Human Health and the Environment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42

4.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42

4.6.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

4.6.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-49
LAND

EPA’s 2008 Report on the Environment 4-3

4.1 Introduction

1 Lubowski, R.N., M. Vesterby, S. Bucholtz, A. Baez, and M.J. Roberts. 2006. 

Major uses of land in the United States, 2002. Economic Information Bulletin No. (EIB-14). U.S. Department of Agriculture, Economic Research 

Service. <http://www.ers.usda.gov/publications/eib14/>

T

he land within the boundaries of the U.S., covering nearly 

2.3 billion acres, provides food, fiber, and shelter for all 

Americans, as well as terrestrial habitat for many other 

species. Land is the source of most extractable resources, such 

as minerals and petroleum. Land produces renewable resources 

and commodities such as livestock, vegetables, fruit, grain, and 

timber; it also supports other uses, such as residential, industrial, 

commercial, and transportation uses. Additionally, land and the 

ecosystems that it is part of provide services such as trapping 

chemicals as they move through soil, storing and breaking down 

chemicals and wastes, and filtering and storing water. The use 

of land, what is applied to or released on it, and its condition 

change constantly: there are changes in the types and amounts of 

resources that are extracted, the distribution and nature of cover 

types, the amounts and types of chemicals used and wastes managed, and perceptions of the land’s value.

Numerous agencies and individuals have responsibilities for 

managing and protecting land in the U.S., in terms of resources 

associated with land (e.g., timber, minerals) and land uses (e.g., 

wilderness designations, regulatory controls). Between 30 and 

40 percent of the nation is owned or managed by public agencies.1 The other 60 to 70 percent is managed by private owners, 

under a variety of federal, state, and local laws. Local governments have primary responsibilities for regulating land use, 

while state and federal agencies regulate chemicals and waste 

that are frequently used on, stored on, or released to land. EPA 

is interested in land because human activities on land such as 

food and fiber production, land development, manufacturing, 

or resource extraction can involve the creation, use, or release 

of chemicals and pollutants that can affect the environment and 

human health. 

EPA works with other federal agencies, states, and partners to 

protect land resources, ecosystems, environmental processes, 

and uses of land through regulation of chemicals, waste, and 

pollutants, and through cleanup and restoration of contaminated lands. The complexities of responsibilities underscore 

the challenges of collecting data and assessing trends on the 

state of land.

This chapter addresses critical land questions by describing 

national trends in naturally occurring and human uses of land, 

stressors that affect land, and associated exposures and effects 

among humans and ecological systems. ROE indicators are 

presented to address five fundamental questions about the state 

of the nation’s land: 

•	 What are the trends in land cover and their effects 

on human health and the environment? “Land cover” 

refers to the actual or physical presence of vegetation or 

other materials (e.g., rock, snow, buildings) on the surface 

ROE Approach

This 2008 Report on the Environment:

•	 Asks questions that EPA considers important to its mission to protect human 

health and the environment. 

•	 Answers these questions, to the extent 

possible, with available indicators.

•	 Discusses critical indicator gaps, limitations, and challenges that prevent the 

questions from being fully answered.

ROE Questions

The air, water, and land chapters (Chapters 

2, 3, and 4) ask questions about trends in 

the condition and/or extent of the environmental medium; trends in stressors to 

the medium; and resulting trends in the 

effects of the contaminants in that medium 

on human exposure, human health, and 

the condition of ecological systems. 

The human exposure and health and 

ecological condition chapters (Chapters 

5 and 6) ask questions about trends in 

aspects of health and the environment 

that are influenced by many stressors 

acting through multiple media and by 

factors outside EPA’s mission. 

ROE Indicators

An indicator is derived from actual measurements of a pressure, state or ambient 

condition, exposure, or human health or 

ecological condition over a specified geographic domain. This excludes indicators 

such as administrative, socioeconomic, and 

efficiency indicators.

Indicators based on one-time studies are 

included only if they were designed to serve 

as baselines for future trend monitoring. 

All ROE indicators passed an independent 

peer review against six criteria to ensure 

that they are useful; objective; transparent; 

and based on data that are high-quality, 

comparable, and representative across space 

and time. 

Most ROE indicators are reported at the 

national level. Some national indicators 

also report trends by region. EPA Regions 

were used, where possible, for consistency 

and because they play an important role in 

how EPA implements its environmental 

protection efforts.

Several other ROE indicators describe 

trends in particular regions as examples of 

how regional indicators might be included 

in future versions of the ROE. They are 

not intended to be representative of trends 

in other regions or the entire nation.

EPA will periodically update and revise 

the ROE indicators and add new indicators 

as supporting data become available. In the 

future, indicators will include information 

about the statistical confidence of status 

and trends. Updates will be posted electronically at http://www.epa.gov/roe.

Additional Information

You can find additional information about 

the indicators, including the underlying data, metadata, references, and peer 

review, at http://www.epa.gov/roe.

EPA’s 2008 Report on the Environment (ROE): Essentials
LAND

4-4 EPA’s 2008 Report on the Environment

of the land (it differs from land use—see the next question). 

It is important from the perspective of understanding land 

as a resource and its ability to support humans and other 

species. Changes in land cover can affect other media (e.g., 

air and water). 

•	 What are the trends in land use and their effects on 

human health and the environment? “Land use” refers 

to the economic and cultural activities practiced by humans 

on land. Land use can have effects on both human health 

and the environment, particularly as land is urbanized or 

used for agricultural purposes. 

•	 What are the trends in wastes and their effects on 

human health and the environment? Numerous types 

of waste are generated as part of most human activities. 

Trends in waste include trends in types and quantities of, 

and mechanisms for, managing wastes. Waste trends reflect 

the efficiency of use and reuse of materials and resources 

and potential for land contamination. 

•	 What are the trends in chemicals used on the land 

and their effects on human health and the environment? Various chemicals are produced or used on land for 

many purposes. The quantity and diversity of chemicals 

and the potential for interactions among them have created 

challenges in understanding the full effects of their use. 

Pesticides, fertilizers, and toxic chemicals are examples of 

chemicals applied or released on land. 

•	 What are the trends in contaminated land and their 

effects on human health and the environment? Contaminated lands are those lands that have been affected by 

human activities or natural events such as manufacturing, 

mining, waste disposal, volcanoes, or floods that pose a 

concern to human health or the environment. The worstcontaminated lands are tracked and their cleanups overseen 

by EPA. 

These ROE questions are posed without regard to whether 

indicators are available to answer them. This chapter presents 

the indicators available to answer these questions, and also 

points out important gaps where nationally representative data 

are lacking.

4.1.1 Overview of the Data

Data are collected by many agencies with varying responsibilities for managing and protecting land and its resources. Several 

different sources and types of data are used to develop the indicators that address the questions in this chapter. They include:

•	 Satellite imagery. Data used in the land cover question 

are derived from analysis of satellite data.2 A set of data on 

U.S. land cover called the National Land Cover Database 

is currently available for the period around 2001. Analyses 

are currently underway to compare these data with earlier 

land cover data, to provide a better understanding of trends. 

Multiple agencies, including EPA, have jointly funded 

satellite data processing efforts and are working together to 

derive a common classification approach for the data. 

•	 National surveys. The data used in the land use question are primarily derived from two national surveys: the 

National Resources Inventory (NRI)3 conducted by the 

U.S. Department of Agriculture (USDA) Natural Resource 

Conservation Service and the Forest Inventory and Analysis (FIA)4 conducted by the USDA Forest Service. These 

surveys are collected over specific areas for specific USDA 

purposes; the NRI data are collected only on non-federal 

lands, and FIA data address only forest and timberlands. 

These limitations contribute to the need to rely on multiple 

data sets for national estimates. 

•	 Regulatory data. The data used for most of the chemical, 

waste, and contaminated land questions are derived from 

self-reporting or government-collected measurements to 

address regulatory requirements. For example, the chemical 

release information reported under the chemical question is 

derived from the Toxics Release Inventory based on industry reporting. These data, in general, represent only a small 

sample of the total picture of waste, chemicals, and land 

contamination. State and local governments collect additional data, but the lack of consistency in approaches makes 

compilation of national data difficult.

This chapter presents only data that meet the ROE indicator definition and criteria (see Box 1-1, p. 1-3). Note that 

non-scientific indicators, such as administrative and economic 

indicators, are not included in this definition. Thorough documentation of the indicator data sources and metadata can be 

found online at http://www.epa.gov/roe. All indicators were 

peer-reviewed during an independent peer review process 

(again, see http://www.epa.gov/roe for more information). 

Readers should not infer that the ROE indicators included 

reflect the complete state of knowledge on the nation’s land. 

Many other data sources, publications, and site-specific research 

projects have contributed to the current understanding of land 

trends, but are not used in this report because they did not meet 

some aspect of the ROE indicator criteria.

4.1.2 Organization of This 

Chapter

The remainder of this chapter is organized into five sections 

corresponding to the five questions that EPA seeks to answer 

about land. Each section introduces a question and its importance, presents the ROE indicators to help answer the question, and discusses what the ROE indicators, taken together, 

2 Multi-Resolution Land Characteristics Consortium. 2007. National Land 

Cover Database 2001 (NLCD 2001). Accessed November 28, 2007. <http://

www.mrlc.gov/mrlc2k_nlcd.asp> 

3 U.S. Department of Agriculture, Natural Resources Conservation Service. 

2007. National Resources Inventory, 2003 annual NRI: Land use. 

<http://www.nrcs.usda.gov/technical/nri/2003/nri03landuse-mrb.html>

4 Smith, W.B., P.D. Miles, J.S. Vissage, and S.A. Pugh. 2004. Forest resources of 

the United States, 2002. USDA Forest Service. <http://ncrs.fs.fed.us/pubs/

gtr/gtr_nc241.pdf>
LAND

EPA’s 2008 Report on the Environment 4-5

say about the question. Several of the National Indicators 

also provide information organized by EPA Regions, and 

one Regional Indicator addresses specific issues at a sub-EPA 

Region scale. Each section concludes by highlighting the 

major challenges to answering the question and identifying 

important information gaps. 

Table 4-1 lists the indicators used to answer the five questions 

in this chapter and shows where the indicators are presented. 

4.2 What Are the Trends 

in Land Cover and Their 

Effects on Human Health 

and the Environment?

4.2.1 Introduction

Land cover—the surface components of land that are physically present and visible—provides a means to examine 

landscape patterns and characteristics. Patterns and landscape 

characteristics are important in understanding the extent, 

availability, and condition of lands; ecological system extent, 

structure, and condition; and the potential for dispersion and 

effects of chemicals and other pollutants in and on the environment. Land cover represents a starting point from which 

a variety of monitoring activities can be performed. EPA 

considers land cover information to be critically important for 

a number of reasons, including the ability to assess nonpoint 

sources of pollution, understanding landscape variables for 

ecological analyses, assessing the behavior of chemicals, and 

analyzing the effects of air pollution. 

Land cover, in its naturally occurring condition, integrates and 

reflects a given site’s climate, geology and soils, and available 

biota over a time span of decades or longer. Land cover can be 

affected on shorter time scales by naturally occurring disturbances (e.g., storms, floods, fires, volcanic eruptions, insects, 

landslides) and human activities. Land cover represents the 

results of both naturally occurring conditions and disturbances 

and human activities such as population change, industrial 

and urban development, deforestation or reforestation, water 

diversion, and road-building. Depending on one’s perspective, 

the changes wrought by natural processes and human activities 

can be perceived as improvements or degradations of the state 

of land cover. 

Table 4-1. Land—ROE Questions and Indicators

Question Indicator Name Section Page

What are the trends in land cover and their 

effects on human health and the environment? 

Land Cover (N/R)

Forest Extent and Type (N/R)

Land Cover in the Puget Sound/Georgia Basin (R)

4.2.2 4-7

6.2.2 6-8

4.2.2 4-10

What are the trends in land use and their effects 

on human health and the environment? 

Land Use (N/R)

Urbanization and Population Change (N/R)

4.3.2 4-14

4.3.2 4-19

What are the trends in wastes and their effects 

on human health and the environment? 

Quantity of Municipal Solid Waste Generated and 

Managed (N)

Quantity of RCRA Hazardous Waste Generated 

and Managed (N)

4.4.2 4-24

4.4.2 4-26

What are the trends in chemicals used on the 

land and their effects on human health and 

the environment? 

Fertilizer Applied for Agricultural Purposes (N/R)

Toxic Chemicals in Production-Related Wastes 

Combusted for Energy Recovery, Released, 

Treated, or Recycled (N)

Pesticide Residues in Food (N)

Reported Pesticide Incidents (N)

4.5.2 4-30

4.5.2 4-33

4.5.2 4-37

4.5.2 4-39

What are the trends in contaminated land and 

their effects on human health and 

the environment? 

Current Human Exposures Under Control at 

High-Priority Cleanup Sites (N)

Migration of Contaminated Ground Water Under 

Control at High-Priority Cleanup Sites (N)

4.6.2 4-44

4.6.2 4-47

N = National Indicator

R = Regional Indicator

N/R = National Indicator displayed at EPA Regional scale
LAND

4-6 EPA’s 2008 Report on the Environment

Land cover is also important because it affects other environmental variables including water quality, watershed hydrology, 

habitat and species composition, climate, and carbon storage. 

Land cover influences the mass and energy exchanges between 

the surface and the atmosphere and thus influences weather 

and climate.5 Land cover is also a primary ingredient of ecological structure and function, with changes affecting species 

habitat and distribution. Land cover changes in watersheds can 

alter hydrologic regimes, runoff patterns, and flood buffering.6

4.2.2 ROE Indicators

The question of trends in and effects of land cover is addressed 

by two National Indicators and one Regional Indicator (Table 

4-2). Nationwide land cover information is derived from two 

data collection programs: the National Land Cover Database 

(NLCD) and the Forest Inventory and Analysis (FIA). The 

NLCD is described in more detail in the Land Cover indicator summary (p. 4-7), and the FIA is described in the Forest 

Extent and Type indicator summary (p. 6-8).

The classification approach used in the Land Cover indicator is 

primarily based on the use of satellite data processing. Where 

satellite data were not available or processed, survey data have 

been included to develop the national statistics. The classification approach used in the Land Cover in Puget Sound/Georgia Basin indicator (p. 4-10), while also based on satellite data, 

is different from the Land Cover National Indicator, and is 

described in the Regional Indicator discussion. More detailed 

definitions of land cover types are included in the box within 

the text of the Land Cover indicator (p. 4-7). 

Data for the Land Cover in Puget Sound/Georgia Basin indicator are derived from the NOAA Coastal Change Analysis Program and Landsat satellite data of both the U.S. and 

Canadian portions of the Puget Sound/Georgia Basin. This 

indicator depicts two cover classes: forest and urban. 

The data presented in the Forest Extent and Type indicator are 

derived from national surveys of forest land and timberland 

in the U.S. These data reflect total extent of forest land both 

nationally and by EPA Region, as well as trends in many species types on timberland. 

5 Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, et al. 

2003. The climatic impacts of land surface change and carbon management, 

and the implications for climate-change policy. Clim. Pol. 3:149-157. 

6 de Sherbinin, A. 2002. Land-use and land-cover change: A CIESIN thematic 

guide. Palisades, NY: Center for International Earth Science Information 

Network of Columbia University. <http://sedac.ciesin.columbia.edu/tg/

guide_main.jsp>

Table 4-2. ROE Indicators of Trends in Land Cover and Their 

Effects on Human Health and the Environment

National Indicators Section Page

Land Cover (N/R) 4.2.2 4-7

Forest Extent and Type (N/R) 6.2.2 6-8

Regional Indicators Section Page

Land Cover in the Puget Sound/Georgia Basin 4.2.2 4-10

N/R = National Indicator displayed at EPA Regional scale
LAND

EPA’s 2008 Report on the Environment 4-7

INDICATOR | Land Cover

Land cover represents the actual or physical presence of vegetation (or other materials where vegetation is 

nonexistent) on the land surface. Land cover is also often 

described as what can be seen on land when viewed from 

above. Land cover is one means to categorize landscape 

patterns and characteristics, and is critical in understanding 

the condition of the environment, including the availability of habitat, changes in habitat, and dispersion and effects 

of chemicals and other pollutants in and on the environment. For the purposes of this indicator, land cover is 

described in terms of six major classes: forest, grass, shrub, 

developed, agriculture, and other (includes ice/snow, barren areas, and wetlands). A seventh category, water, is not 

discussed as a land cover type in this chapter. See Chapter 

3 for more information on trends related to water. More 

information about forest land can be found in the Forest 

Extent and Type indicator (p. 6-8), and wetland acreage 

is discussed in greater detail in the Wetlands indicator (p. 

3-32).

In 1992, several federal agencies agreed to operate as a 

consortium, known as the Multi-Resolution Land Characteristics (MRLC) Consortium, to acquire and analyze 

satellite-based remotely sensed data for environmental 

monitoring programs (MRLC Consortium, 2006). The 

initial result of the MRLC effort was development of the 

1992 National Land Cover Dataset (NLCD), which, until 

recently, was the only comprehensive recent classification 

of land cover in the contiguous U.S. (USGS, 2007). In 

2007, the MRLC Consortium published the 2001 National 

Land Cover Database, an updated and improved version of 

the 1992 NLCD (Homer et al., 2007). The database provides information about 16 land cover classes at a 30-meter 

Exhibit 4-1. Land cover of the contiguous U.S., based on 2001 NLCD a

a

See box on p. 4-9 for definitions of land cover 

categories.

Data source: U.S. EPA, 2007b

Agriculture

Cultivated crops

Pasture/hay

Developed

High-density (impervious 80%)

Medium-density (impervious 50-79%)

Low-density (impervious 20-49%)

Open space (impervious <20%)

Forest cover

Deciduous forest

Evergreen forest

Mixed forest

Grass cover

Grassland

Shrub cover

Shrubland

Water

Open water

Other

Perennial ice/snow

Barren

Woody wetland

Emergent herbaceous wetland
LAND

4-8 EPA’s 2008 Report on the Environment

INDICATOR | Land Cover (continued)

resolution, comprising approximately 27 billion cells covering the contiguous U.S., based on Landsat images from 

1999 to 2002. Due to differences in methodology, direct 

comparison of the 1992 and 2001 NLCD data sets does not 

currently provide valid trend data. Efforts are underway to 

develop an algorithm that will allow such comparisons in 

the near future.

This indicator represents data from the 2001 NLCD and 

the U.S. Department of Agriculture Forest Service’s Forest 

Inventory and Analysis (FIA), which uses a statistical survey 

design and comparable methods to assess the extent, type, 

age, and health of forests on private and public land in all 

states. The 2001 NLCD provides a synoptic classification of 

land cover, but does not include Alaska and Hawaii, thereby 

classifying only 1.92 billion acres out of approximately 2.3 

billion acres of land in the U.S. To supplement the NLCD, 

data from the 2001 FIA were used to provide forest cover 

estimates in Alaska and Hawaii (128.6 million acres). 

For this indicator, the 16 land cover classes created in the 

NLCD were aggregated into the six major land cover types 

described above, along with water (Heinz Center, 2005).

What the Data Show

The combination of the NLCD for the contiguous 48 

states and the FIA for forest cover estimates in Alaska and 

Hawaii shows approximately 641 million acres of forest, 

449 million acres of agriculture, 419 million acres of shrub, 

291 million acres of grass, and 103 million acres of developed cover types (Exhibits 4-1 and 4-2). 

NLCD and FIA data show variation in cover types by 

EPA Region, with forest dominating in Regions 1, 2, 3, 4, 

and 10; agriculture in Regions 5 and 7; grass in Region 8; 

and shrub in Region 6 and 9 (Exhibit 4-3). Two-thirds of 

the grass acreage in the nation is located in Regions 6 and 

8, nearly two-thirds of shrub acreage is in Regions 6 and 

9, and nearly half the forest acreage is in Regions 4 and 10 

(including Alaska).

Indicator Limitations

•	 Trend data are not available for this indicator. Land 

cover data for the entire nation at adequate resolution 

to support this indicator are currently available for two 

points in time (1992 and 2001). However, due to differences in methodology in creation of the data sets, they 

are not directly comparable. The MRLC Consortium 

is developing a change product intended to enable valid 

Exhibit 4-2. Land cover types in the U.S., based 

on 2001 NLCD and FIAa,b,c

a

Coverage: All surface area of the contiguous 48 states, plus forest 

land in Alaska and Hawaii.

b

See box on p. 4-9 for definitions of land cover categories.

c

Totals may not add to 100% due to rounding.

d

“Other” includes ice/snow, barren areas, and wetlands.

Data source: Smith et al., 2004; U.S. EPA, 2007b

Agriculture

448.9 million acres

(21.9%) Forest cover

641.1 million acres

(31.2%)

Shrub cover

419.2 million acres

(20.4%)

Developed

102.5 million acres

(5.0%)

Water

33.5 million 

acres

(1.6%)

Otherd

117.7 million 

acres

(5.7%)

Grass cover

290.5 million 

acres

(14.1%)

Exhibit 4-3. Land cover types in the U.S. by 

EPA Region, based on 2001 NLCD and FIAa,b

0

50

100

150

200

250

300

350

400

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10

EPA Region 

Area (million acres) a EPA Regions Coverage: All land area of the 

contiguous 48 states (excluding 

water), plus forest land in Alaska 

and Hawaii.

b

See box on p. 4-9 for definitions of 

land cover categories. 

c

“Other” includes ice/snow, barren 

areas, and wetlands.

Data source: Smith et al., 2004; U.S. EPA, 2007b

10

9

9

6

7

4

8 10

5 3

2 1

2

Developed

Forest cover

Grass cover

Shrub cover

Agriculture

Otherc
LAND

EPA’s 2008 Report on the Environment 4-9

INDICATOR | Land Cover (continued)

comparisons of the two data sets (MRLC Consortium, 

2007a,b). The product is scheduled to be available in 

2008. Until this project is completed, there are no consistent, comprehensive, nationwide data to describe trends 

in land cover at the national or EPA Regional levels. 

•	 FIA data for forest land in Alaska and Hawaii were 

used to complement the NLCD because NLCD data 

do not currently exist for these states, although they are 

planned for late 2007. Ongoing data collection under 

both the FIA and the NLCD is needed to assess land 

cover trends.

•	 National estimates of land cover vary, depending on the 

survey approach, data sources, classification, timing, etc. 

The interaction of these variables will result in different 

estimates of the extent of any given land cover category 

depending on the data set used. Techniques relying on 

satellite data to generate land cover estimates classify what 

is visible from above, meaning they may underestimate 

developed cover in heavily treed urban areas and underestimate forest cover where trees have been harvested. For 

example, National Resources Inventory (USDA NRCS, 

2007) estimates for developed land are 6 percent above 

the NLCD estimates and FIA estimates of forestland in 

2002 are nearly 17 percent above the NLCD.

•	 No standardized land cover classification system is currently used among federal agencies. As a result of this 

limitation, there is no consistency in the assessment of 

land cover trends across agencies. 

Data Sources

Land cover data for the contiguous 48 states were obtained 

from the NLCD (U.S. EPA, 2007b). These data were 

Agricultural (NLCD 2001 definition): Areas characterized by herbaceous vegetation that has been planted; 

is intensively managed for the production of food, feed, 

or fiber; or is maintained in developed settings for specific purposes. Herbaceous vegetation must account for 

75 to 100 percent of the cover. Includes the “orchards/

vineyards/other” subcategory, which covers areas 

planted or maintained for the production of fruits, nuts, 

berries, or ornamentals. Includes two subcategories: 

“pasture/hay” and “cultivated crops.”

Developed (NLCD 2001 definition): Areas characterized by a high percentage (30 percent or greater) 

of constructed materials (e.g., asphalt, concrete, buildings). Includes four subcategories: “Developed, open 

space” (less than 20 percent impervious surface), 

“Developed, low intensity” (20-49 percent impervious 

surface), “Developed, medium intensity” (50-79 percent 

impervious surface), and “Developed, high intensity” 

(80 percent or more impervious surface). 

Shrubland (NLCD 2001 definition): Areas characterized by natural or semi-natural woody vegetation 

with aerial stems, generally less than 6 meters tall, with 

individuals or clumps not touching or interlocking. 

Both evergreen and deciduous species of true shrubs, 

young trees, and trees or shrubs that are small or stunted 

because of environmental conditions are included.

Grassland (NLCD 2001 definition): Upland areas 

dominated by grammanoid or herbaceous vegetation, 

generally greater than 80 percent of the total vegetation. 

These areas are not subject to intensive management, 

such as tilling, but can be utilized for grazing.

Forest (NLCD 2001 definition): Areas characterized 

by tree cover (natural or semi-natural woody vegetation, generally greater than 6 meters tall); tree canopy 

accounts for 25 to 100 percent of the cover. 

Forest (FIA definition): Land at least 10 percent 

stocked by forest trees of any size, including land that 

formerly had such tree cover and that will be naturally 

or artificially regenerated. Forest land includes transition zones, such as areas between heavily forested and 

nonforested lands that are at least 10 percent stocked 

with forest trees and forest areas adjacent to urban and 

built-up lands. Also included are pinyon-juniper and 

chaparral areas in the West and afforested areas. The 

minimum area for classification of forest land is 1 acre. 

Roadside, streamside, and shelterbelt strips of trees must 

have a crown width of at least 120 feet to qualify as 

forest land. Unimproved roads and trails, streams, and 

clearings in forest areas are classified as forest if less than 

120 feet wide. (FIA data are used in Alaska and Hawaii, 

due to lack of NLCD availability.) 

Other: Includes NLCD 2001 snow, ice, wetlands, and 

barren. Barren areas are defined as areas of bedrock, desert pavement, scarps, talus, slides, volcanic material, glacial debris, sand dunes, strip mines, gravel pits, and other 

accumulations of earthen material. Generally, vegetation 

accounts for less than 15 percent of total cover. <http://

www.epa.gov/mrlc/definitions.html>

Sources: U.S. EPA, 2007a; Smith et al., 2004. 

Definitions of Land Cover Categories for Exhibits 4-1, 4-2, and 4-3 
LAND

4-10 EPA’s 2008 Report on the Environment

INDICATOR | Land Cover (continued)

grouped into the major land cover categories as described 

by the Heinz Center (2005) (see technical note for the 

Heinz Center’s “Ecosystem Extent” indicator). Forest cover 

estimates for 2002 in Alaska and Hawaii were obtained 

from a report published by the FIA program (Smith et al., 

2004). FIA data in this report have a nominal date of 2002 

but represent the best data available at the end of the 2001 

field season for each state. 

References

Heinz Center (The H. John Heinz III Center for Science, Economics, and the Environment). 2005. The state 

of the nation’s ecosystems: Measuring the lands, waters, 

and living resources of the United States. New York, NY: 

Cambridge University Press. Web update 2005: 

<http://www.heinzctr.org/ecosystems>

Homer, C., J. Dewitz, J. Fry, M. Coan, N. Hossain, C. 

Larson, N. Herold, A. McKerrow, J.N. VanDriel, and J. 

Wickham. 2007. Completion of the 2001 National Land 

Cover Database for the conterminous United States. 

Photogramm. Eng. Rem. S. 73(4):337-341. 

MRLC Consortium. 2007a. Comparison of NLCD 1992 

and NLCD 2001. Accessed December 2007. 

<http://www.mrlc.gov>

MRLC Consortium. 2007b. Frequently asked questions. 

Accessed December 2007. 

<http://www.mrlc.gov/faq.php#changeproduct>

MRLC Consortium. 2006. About the MRLC program. 

Accessed January 2006. 

<http://www.mrlc.gov/about.php>

Smith, W.B., P.D. Miles, J.S. Vissage, and S.A. Pugh. 

2004. Forest resources of the United States, 2002. USDA 

Forest Service. 

<http://ncrs.fs.fed.us/pubs/gtr/gtr_nc241.pdf>

USDA NRCS (United States Department of Agriculture, 

Natural Resources Conservation Service). 2007. National 

Resources Inventory, 2003 annual NRI: Land use. 

<http://www.nrcs.usda.gov/technical/nri/2003/

nri03landuse-mrb.html>

U.S. EPA (United States Environmental Protection 

Agency). 2007a. NLCD classification schemes. Accessed 

November 28, 2007. <http://www.epa.gov/mrlc/

classification.html>

U.S. EPA. 2007b. NLCD 2001 data provided to ERG (an 

EPA contractor) by James Wickham, Office of Research 

and Development. November 29, 2007. 

<http://www.mrlc.gov/nlcd.php>

USGS (United States Geological Survey). 2007. National 

Land Cover Dataset 1992 (NLCD 1992). Accessed 

November 2007. 

<http://landcover.usgs.gov/natllandcover.php> 

INDICATOR | Land Cover in the Puget Sound/Georgia Basin

Changes in land use and corresponding changes in land 

cover can alter the basic functioning and resilience 

of ecological systems. Watersheds, for example, experience a cascade of effects among critical physical, chemical, 

and biological processes when land cover changes (NWP, 

1995; Thom and Borde, 1998). For instance, removal of 

vegetation can increase erosion, leading to impacts on 

soil and water quality, and increases in developed land 

typically result in a corresponding increase in impervious surfaces with consequences for runoff, among other 

issues. While individual impacts to a landscape may appear 

as small changes, the combined impacts of particular land 

uses or land management practices on watersheds can have 

substantial effects on water quality, species composition, 

and flooding patterns (PSAT, 2002, 2004). Such combined impacts are often referred to as “cumulative effects.” 

As a result of their potential to broadly and substantially 

influence environmental condition, land cover and use are 

important factors to monitor.

This indicator compares changes in two land cover metrics for the Puget Sound and Georgia Basin in Washington 

state and part of British Columbia, Canada. The metrics 

include percent change of urban and forest land cover. Data 

cover the period from 1995 to 2000 for the U.S. portion 

of the basin and from 1992 to 1999 for the Canadian side 

of the basin. The metrics represent the change in total 

urban or forested land area divided by total land area in the 

watershed. Forest and urban land cover are two of the most 

important factors affecting the condition of watersheds 

in the Puget Sound Basin (Alberti and Marzluff, 2004; 

Alberti, 2005). In contrast to the nationwide land cover 

indicator, which is based on NLCD data, this indicator 

relies on data derived from four assembled USGS Landsat 

scenes covering the U.S. portion of the Puget Sound Basin 

v
LAND

EPA’s 2008 Report on the Environment 4-11

INDICATOR | Land Cover in the Puget Sound/Georgia Basin (continued)

and from a combined scene covering the 

Canadian land area. The land cover data for 

all USGS 6th field watersheds in the basin 

were produced from NOAA Coastal Change 

Analysis Program (C-CAP) data and from 

Canadian Baseline Thematic Mapping 

(BTM) data. The USGS Hydrologic Unit 

Codes and Canadian watershed groupings 

provide topographically delineated watersheds, which are aggregated, or “nested,” 

into larger sub-basin and basin units.

What the Data Show

Forest Cover

Little or no change in forest cover was 

observed in 2,068 watersheds (76 percent) of 

the 2,725 watersheds assessed (Exhibit 4-4, 

panel A). However, 279 watersheds (10 percent) saw at least 2.5 percent of their mature 

forest cover converted to some other land 

cover, often bare ground, immature vegetation, or industrial/urban uses. At the same 

time, another group of 205 watersheds (8 

percent), generally those at higher elevations, 

indicated a net increase in forest cover as 

young stands or cleared areas have re-grown 

into more mature forest cover classes. 

Urbanization 

During the same period, little or no change 

in urban land cover was observed in approximately 90 percent of the 2,725 assessed 

watersheds within the basin (Exhibit 4-4, 

panel B). However, urbanization increased 

across many low-elevation watersheds and 

shoreline areas, with 158 watersheds (6 

percent) expanding the urban portion of the 

watershed by between 0.7 and 1.93 percent, and another 58 watersheds (2 percent) 

showing increases of more than 1.93 percent. 

Research has shown that as a watershed’s 

drainage area becomes paved or otherwise 

impervious, there is a high potential for 

physical, chemical, and biological impairments to both water quality conditions and 

other aquatic resources (NWP, 1995; Alberti 

and Marzluff, 2004). 

Indicator Limitations

•	 While the U.S. C-CAP data and the Canadian BTM data 

have similar and overlapping time periods, as currently 

presented, the U.S. data reflect change from 1995 to 2000 

and the Canadian data reflect change from 1992 to 1999. 

•	 The size of the data pixels and the minimum mapping 

unit size affect the classification of certain features such 

as narrow riparian corridors, and can affect the percentages in the indicators. 

Exhibit 4-4. Land cover change in watersheds of the 

Puget Sound/Georgia Basin, 1992-2000a,b

A. Forest cover B. Urbanization

Washington

British 

Columbia

Washington

British 

Columbia

Percent change in forest cover:

-5.0% or more

-4.9% to -2.5%

-2.4% to -0.1%

No change

0.1% to 0.85%

More than 0.85%

Percent change in urbanization:

No change

0.05% or less

0.051% to 0.30%

0.301% to 0.70%

0.71% to 1.93%

More than 1.93%

147 132 173

2,068

96 109

0

500

1,000

1,500

2,000

2,500

Percent change

Number of watersheds

2,329

132 30 18 158 58

0

500

1,000

1,500

2,000

2,500

Percent change

Number of watersheds

a

Coverage: 2,725 watersheds within the Puget Sound/Georgia Basin, located in the 

state of Washington and the Canadian province of British Columbia. U.S. watersheds 

are 12-digit Hydrologic Unit Code (HUC12) watersheds.

b

U.S. data reflect changes from 1995 to 2000, while Canadian data reflect changes from 

1992 to 1999.

Data source: British Columbia Integrated Land Management Bureau, 2001; CommEn 

Space, 2005; NOAA, 2006

-5.0% or more

-4.9% to -2.5%

-2.4% to -0.1%

0.1% to 0.85%

More than 0.85%

No change

No change

0.05% or less

0.051% to 0.30%

0.71% to 1.93%

More than 1.93%

0.301% to 0.70%
LAND

4-12 EPA’s 2008 Report on the Environment

INDICATOR | Land Cover in the Puget Sound/Georgia Basin (continued)

Data Sources

The full analysis has not been published as a data set, 

but it is based on publicly available data sets compiled by 

CommEn Space (http://www.commenspace.org). Raw 

data for the U.S. portion of this indicator are available 

from C-CAP (NOAA, 2006), and Canadian data are 

available from the British Columbia Integrated Land 

Management Bureau (2001). Additional technical background is provided by U.S. EPA (2006).

References

Alberti, M. 2005. The effects of urban patterns on 

ecosystem function. Int. Regional Sci. Rev. 28(2):168-192.

Alberti, M., and J. Marzluff. 2004. Resilience in urban 

ecosystems: Linking urban patterns to human and ecological 

functions. Urb. Ecosyst. 7:241-265.

British Columbia Integrated Land Management Bureau. 

2001. Baseline thematic mapping. <http://ilmbwww.gov.

bc.ca/cis/initiatives/ias/btm/index.html>

CommEn Space. 2005. Cartography services provided 

to EPA. 

NOAA (National Oceanic and Atmospheric Administration). 2006. Coastal Change Analysis Program (C-CAP) 

database. Accessed 2007. <http://www.csc.noaa.gov/crs/

lca/ccap.html>

NWP (Northwest Forest Plan). 1995. Ecosystem analysis at 

the watershed scale: Federal guide for watershed analysis. 

Portland, OR: USFS Regional Ecosystem Office.

PSAT (Puget Sound Action Team). 2004. State of the Sound. 

Report to the Washington state legislature. Olympia, WA.

PSAT. 2002. Puget Sound update. Eighth report of the 

Puget Sound ambient monitoring program. Olympia, WA.

Thom, R., and A. Borde. 1998. Human intervention in 

Pacific Northwest coastal ecosystems. In: McMurray, G.R., 

and R.J. Bailey, eds. Change in Pacific Northwest coastal 

ecosystems. NOAA Coastal Ocean Program Decision 

Analysis Series No. 11.

U.S. EPA (United States Environmental Protection 

Agency). 2006. Puget Sound Georgia Basin ecosystem 

indicators: Ecosystem indicator references and technical 

background. <http://www.epa.gov/region10/psgb/

indicators/references/index.htm>

4.2.3 Discussion

What These Indicators Say About Trends 

in Land Cover and Their Effects on Human 

Health and the Environment

The most recently available 2001 data are presented for the 

Land Cover indicator (p. 4-7). As of the writing of the ROE, 

the data are available for two points in time, 1992 and 2001, 

but cannot be compared. Work is ongoing to develop a comparison database. The data show that the largest extent of a 

cover type nationwide is forest land, followed by agriculture, 

shrubland, grassland, and developed land. 

The Land Cover in Puget Sound/Georgia Basin indicator (p. 4-10) shows that land cover in the majority of the 

approximately 2,700 sub-watersheds that constitute the Puget 

Sound and Georgia Basin did not change appreciably during the time periods covered by the indicator. The data in 

this Regional Indicator allow for discrimination of patterns 

of watersheds where land cover has changed even in the 

relatively short interval of 5 years. For example, forest cover 

tended to decrease in coastal and mid-elevation watersheds, 

while showing a net increase at higher elevations. Developed 

land cover increased somewhat in approximately 8 percent 

of the sub-watersheds, mainly in watersheds at low elevations and along the shore. These and related trends may have 

consequences for human health and ecologic conditions in the 

areas where land cover is changing. For example, increases 

in developed land cover may be associated with increases in 

impervious surface area, which can cause changes in surface 

water runoff quantity and quality to the point where detrimental effects on aquatic resources may occur.7

The Forest Extent and Type indicator (p. 6-8) provides trend 

data for forest land cover, and shows that the total amount of 

forest land in the U.S. has remained relatively constant over 

recent years. On a regional basis, however, there have been 

shifts, including increases in forest cover over the last century 

in EPA Regions 1, 2, 3, and 5 and decreases in Regions 6 and 

9. The species composition of forest cover has also shifted.8

Limitations, Gaps, and Challenges

The current lack of trend data is a key limitation of the Land 

Cover indicator (p. 4-7) as well as a gap in the data. The 

changing availability of technology since the 1970s, such as 

satellites and computing capacity to process large volumes of 

data, has provided new tools in the effort to track trends in 

7 U.S. Environmental Protection Agency. 2005. Estimating and projecting 

impervious cover in the southeastern United States. EPA/600/R-05/061. 

Athens, GA. <http://www.epa.gov/athens/publications/reports/

Exum600R05061EstimatingandProjectingImpervious.pdf>

8 These changes and their effects on the environment are described in Chapter 6.

v
LAND

EPA’s 2008 Report on the Environment 4-13

land cover. The use of these tools continues to be constrained 

due to complexities in land cover and costs of processing. This 

is one reason that trend data for national land cover using 

satellite data are not currently available.

Another gap is the lack of indicators for human health effects 

related to trends in land cover. While land cover extent may 

represent a measure of ambient conditions and is a critical 

input to many other analyses (e.g., models of the water cycle, 

carbon cycle, ecological system function), it provides limited 

insight in answering the question of effects on human health.

There are several challenges related to addressing the question of trends in land cover. Two critical challenges are (1) that 

land cover characteristics can vary depending on the scale of 

mapping or measurement and (2) that the classification systems 

used to describe land cover vary by agency and by the agencies’ needs. The variability of species and structure within land 

cover types can be important in how land cover is affected by 

pollutants or the type of habitat that is provided. While mapping or measuring the details of species and structure of forest 

or shrubland is possible on a local basis, it is very difficult to do 

consistently on a national scale. There are many different types 

or categories of land cover that can be defined at very different 

levels of detail, and different classification schema often make 

comparability among data sets and across time frames difficult. 

The major sources of data used to track land cover are based 

on national surveys using unique classifications that have been 

maintained over time to allow valid comparisons of important 

characteristics to be made. At the same time, technology is 

changing what can be measured, mapped, and classified. Data 

that can be collected from ground surveys or in some cases 

inferred from aerial photos—such as understory species—are 

seen differently in automated satellite data processing. Coordinating, integrating, and using data collected at a variety of scales 

and based on diverse data sources and classifications are challenges in tracking trends in and effects of land cover. 

4.3 What Are the Trends 

in Land Use and Their 

Effects on Human Health 

and the Environment?

4.3.1 Introduction

Land use represents the economic and cultural activities 

that are practiced at a place, such as agricultural, residential, 

industrial, mining, and recreational uses. Land use changes 

occur constantly and at many scales, and can have specific and 

cumulative effects on air and water quality, watershed function, generation of waste, extent and quality of wildlife habitat, 

climate, and human health. Land use differs from land cover in 

that some uses are not always physically obvious (e.g., land used 

for producing timber but not harvested for many years or land 

used for grazing but without animals will not be visible). Public 

and private lands frequently represent very different uses. Urban 

development seldom occurs on public lands, while private lands 

are infrequently protected for wilderness uses. 

EPA is concerned about the use of land because of the potential 

effects of land use and its byproducts on the environment. For 

example, land development creates impervious surfaces through 

construction of roads, parking lots, and other structures. Impervious surfaces contribute to nonpoint source water pollution by 

limiting the capacity of soils to filter runoff. Impervious surface 

areas also affect peak flow and water volume, which heighten 

erosion potential and affect habitat and water quality. Increased 

storm water runoff from impervious surfaces can deliver more 

pollutants to water bodies that residents may rely on for drinking and recreation.9

 Storm runoff from urban and suburban 

areas contains dirt, oils from road surfaces, nutrients from fertilizers, and various toxic compounds. Point source discharges 

from industrial and municipal wastewater treatment facilities 

can contribute toxic compounds and heated water. Impervious 

surfaces also affect ground water aquifer recharge. 

Some land development patterns, in particular dispersed growth 

such as “suburbanization,” can contribute to a variety of environmental concerns. For example, increased air pollution due 

to increased vehicle use can result in increased concentrations 

of certain air pollutants in developed areas that may exacerbate 

human health problems such as asthma.10 Another potential effect 

of land development is the formation of “heat islands,” or domes 

of warmer air over urban and suburban areas, caused by the loss 

of trees and shrubs and the absorption of more heat by pavement, buildings, and other sources. Heat islands can affect local, 

regional, and global climate, as well as air quality.11

Agricultural land uses can affect the quality of water and 

watersheds. The types of crops planted, tillage practices, and 

various irrigation practices can limit the amount of water 

available for other uses. Livestock grazing in riparian zones 

can change landscape conditions by reducing stream bank 

vegetation and increasing water temperatures, sedimentation, 

and nutrient levels. Runoff from pesticides, fertilizers, and 

nutrients from animal manure can also degrade water quality. 

Additionally, agricultural land uses may result in loss of native 

habitats or increased wind erosion and dust, exposing humans 

to particulate matter and various chemicals.12

Some land uses can accelerate or exacerbate the spread of invasive species. Certain land use practices, such as overgrazing, land 

conversion, fertilization, and the use of agricultural chemicals, 

9 U.S. Environmental Protection Agency. 2005. Estimating and projecting 

impervious cover in the southeastern United States. EPA/600/R-05/061. 

Athens, GA. <http://www.epa.gov/athens/publications/reports/

Exum600R05061EstimatingandProjectingImpervious.pdf>

10 Schwartz J. 2004. Air pollution and children’s health. Pediatrics 

113:1037-1043.

11 U.S. Environmental Protection Agency. 2003. Cooling summertime temperatures: Strategies to reduce urban heat islands. EPA/430/F-03/014. Washington, 

DC. <http://www.epa.gov/heatisland/resources/pdf/HIRIbrochure.pdf>

12 Schenker, M. 2000. Exposures and health effects from inorganic agricultural 

dusts. Environ. Health Persp. 108(Suppl 4):661-664. <http://ehp.niehs.nih.

gov/members/2000/suppl-4/661-664schenker/schenker-full.html>
LAND

4-14 EPA’s 2008 Report on the Environment

can enhance the growth of invasive plants.13 These plants can 

alter fish and wildlife habitat, contribute to decreases in biodiversity, and create health risks to livestock and humans. Introduction of invasive species on agricultural lands can reduce water 

quality and water availability for native fish and wildlife species. 

Research is beginning to elucidate the connections between 

land use changes and infectious disease. For example, fragmentation of forest habitat into smaller patches separated by agricultural activities or developed land increases the “edge effect” and 

promotes the interaction among pathogens, vectors, and hosts.14

In some cases, changes in land use may have positive effects, such 

as increasing habitat as a result of deliberate habitat restoration 

measures; and reclamation of lands for urban/suburban development as a result of cleanup of previously contaminated land.

4.3.2 ROE Indicators

The question of trends in land use is addressed by two ROE 

indicators: Land Use and Urbanization and Population Change 

(Table 4-3). The primary information sources for these indicators are the National Resources Inventory prepared by the U.S. 

Department of Agriculture’s Natural Resources Conservation 

Service, the Forest Inventory and Analysis conducted by the 

Forest Service, the Census of Agriculture from the National 

Agricultural Statistics Service, and population data collected 

by the U.S. Census Bureau. The box on pages 4-16 and 4-17 

provides definitions of the categories used in the indicators.

Land use is the purpose of human activity on the land. Unlike land cover, land use may not always be visible. For example, a unit of land designated for use as 

timberland may appear identical to an adjacent unit of 

protected forestland or, if recently harvested, may appear 

not to be in forest land cover at all. Land use is generally 

designated through zoning or regulation and is one of the 

most obvious effects of human inhabitation of the planet. 

It can affect both human health and ecological systems, 

for example by changing the hydrologic characteristics of 

a watershed, the potential of land to erode, the condition 

or contiguity of plant and animal habitat, or the spread of 

vector-borne diseases. 

This indicator tracks trends in acreages of major land uses 

over the 1977-2003 period using several data sources. These 

sources do not always cover the same time period, sample the 

same resource or geography, or use the same definitions, but 

each of them provides an important piece of the land use picture over time. Definitions for the various land use categories 

in this indicator can be found on page 4-16.

The National Resources Inventory (NRI) conducted 

by the U.S. Department of Agriculture (USDA) Natural 

Resources Conservation Service was used to track trends 

in “crop and pasture” land (row crop, orchard, and pasture 

uses) and “developed” land (residential, commercial, industrial, and transportation uses). The NRI developed estimates every 5 years on non-federal lands in the contiguous 

U.S. between 1977 and 1997, and annual estimates based 

on a smaller sample size beginning in 2001. 

The Forest Inventory and Analysis (FIA) surveys conducted by the USDA Forest Service were used to track 

trends in forest and timberlands. The FIA surveys include 

both private and public land in all 50 states. The FIA previously assessed forest and timberland acreage every 10 years, 

but the data are now updated on a rolling basis using surveys 

that sample a different portion of FIA sites every year. 

The USDA National Agricultural Statistics Service 

(NASS) Census of Agriculture was used to track trends in 

the extent of cropland, cropland used only for pasture, pastureland, and rangeland. NASS data are available for 1997 

and 2002 only. Data on the extent of grass and forested 

rangeland (typically “unimproved” grazing land) are available from the USDA Economic Research Service (ERS) 

for 5-year intervals from 1982 through 2002. 

13 Westbrooks, R.G. 1998. Invasive plants: Changing the landscape of America: 

Fact book. Washington, DC: Federal Interagency Committee for the Management of Noxious and Exotic Weeds.

14 Patz, J.A., P. Daszak, G.M. Tabor, A.A. Aguirre, M. Pearl, J. Epstein, N.D. Wolfe, 

A.M. Kilpatrick, J. Foufopoulos, D. Molyneux, D.J. Bradley, and Members 

of the Working Group on Land Use Change and Disease Emergence. 2004. 

Unhealthy landscapes: Policy recommendations on land use change and infectious disease emergence. Environ. Health Persp. 112(10):1092-1098.

INDICATOR | Land Use

Table 4-3. ROE Indicators of Trends in Land Use and Their 

Effects on Human Health and the Environment

National Indicators Section Page

Land Use (N/R) 4.3.2 4-14

Urbanization and Population Change (N/R) 4.3.2 4-19

N/R = National Indicator displayed at EPA Regional scale
LAND

EPA’s 2008 Report on the Environment 4-15

INDICATOR | Land Use (continued)

What the Data Show

The acreage of lands used for growing food and forage crops 

has declined since 1982, while developed land has increased 

and timberland has remained approximately constant 

(Exhibit 4-5). As of 2002-2003, estimates from both the 

NRI (2003 data) and the NASS (2002 data) indicate that 

between 368 and 374 million acres were used for food crop 

production, approximately 16 percent of the U.S. land area. 

Estimates of pasture or land used to support forage for livestock vary, depending on the definitions. The NRI classifies 

117 million acres as pasture, while the NASS classifies about 

61 million acres as cropland used for pasture. The NASS 

classifies more than 395 million additional acres as pasture 

or rangeland for grazing. The broader ERS estimate of land 

available for grazing totals about 587 million acres, and 

includes grassland and other non-forested pasture and range. 

If forest lands used for grazing are also included, the total 

ERS estimate for these lands is 721 million acres for 2002. 

The NASS cropland shows a decrease in the extent of cropland (5 million acres), cropland pasture (6 million acres), and 

pastureland and rangeland (3 million acres) between 1997 

and 2002. The NRI data suggest that these declines are part 

of a longer trend, with NRI cropland and pasture declining 

by slightly more than 66 million acres (12 percent) between 

1982 and 2003. ERS data also show a downward trend for 

pasture and rangeland between 1982 and 2002, with the 

largest decrease being a 24-million-acre (15 percent) decline 

in forest land used for grazing. According to the NRI, 5 

percent (108.1 million acres) of U.S. land area was considered developed15 as of 2003 (Exhibit 4-5). This represents 

a gain of 48 percent (35.2 million acres) since 1982. While 

the amount of developed land is a small fraction of the total, 

its ecological impact can be disproportionately high relative 

to other land use types. Paving and the creation of other 

impervious surfaces can change local hydrology, climate, 

and carbon cycling, leading to increased surface runoff, pollution, and degradation of wetlands and riparian zones.

15 The land use classification for developed land uses NRI data and is 

considerably different from the land cover classification for developed land, 

which uses NLCD data. See Section 4.2 for more information.

Exhibit 4-5. Land use trends in the U.S., 1977-2003a

a

See box on p. 4-16 for definitions of land use categories.

Data source: Lubowski et al., 2006; Smith et al., 2004; USDA NASS, 2004; USDA NRCS, 2007

0

100

200

300

400

500

600

700

800

NRI Pasture

Cropland

NASS Cropland pasture

Cropland

NASS Pastureland and rangeland

Area (million acres)

Year

0

100

200

300

400

500

600

700

800

1977 1987 1997 1982 1992 2002

1977 1987 1997 1982 1992 2002

ERS Forested grazing land

Grassland pasture and range

FIA Timberland NRI Developed

1977 1987 1997 1982 1992 2002 1977 1987 1997 1982 1992 2003

1977 1987 1997 1982 1992 2003 1977 1987 1997 1982 1992 2002

378.9 373.6 398.2 395.3

66.4 60.6

419.9 381.3 376.4 367.9

131.1 125.2 119.5 117.0

72.9 79.5 86.5 98.3 108.1

492.4 486.3 503.7 503.5

158 155 145 141 134

591591597 580 587
LAND

4-16 EPA’s 2008 Report on the Environment

INDICATOR | Land Use (continued)

NRI (USDA NRCS, 2004) 

Developed: A combination of land cover/use categories: 

urban and built-up areas and rural transportation land.

•	 Urban and built-up areas. A land cover/use category 

consisting of residential, industrial, commercial, and 

institutional land; construction sites; public administrative sites; railroad yards; cemeteries; airports; golf 

courses; sanitary landfills; sewage treatment plants; water 

control structures and spillways; other land used for such 

purposes; small parks (less than 10 acres) within urban 

and built-up areas; and highways, railroads, and other 

transportation facilities if they are surrounded by urban 

areas. Also included are tracts of less than 10 acres that 

do not meet the above definition but are completely surrounded by urban and built-up land. Two size categories 

are recognized in the NRI: areas of 0.25 acre to 10 acres, 

and areas of at least 10 acres.

•	 Large urban and built-up areas. A land 

cover/use category composed of developed tracts of 

at least 10 acres—meeting the definition of urban 

and built-up areas.

•	 Small built-up areas. A land cover/use category 

consisting of developed land units of 0.25 to 10 

acres, which meet the definition of urban and 

built-up areas.

•	 Rural transportation land. A land cover/use category which consists of all highways, roads, railroads 

and associated right-of-ways outside urban and builtup areas; also includes private roads to farmsteads or 

ranch headquarters, logging roads, and other private 

roads (field lanes are not included).

Cropland: A land cover/use category that includes areas 

used for the production of adapted crops for harvest. Two 

subcategories of cropland are recognized: cultivated and 

noncultivated. Cultivated cropland comprises land in 

row crops or close-grown crops and also other cultivated 

cropland, for example, hay land or pastureland that is in 

a rotation with row or close-grown crops. Noncultivated 

cropland includes permanent hay land and horticultural 

cropland.

Pastureland: A land cover/use category of land managed primarily for the production of introduced forage 

plants for livestock grazing. Pastureland cover may consist of a single species in a pure stand, a grass mixture, or 

a grass-legume mixture. Management usually consists of 

cultural treatments: fertilization, weed control, reseeding or renovation, and control of grazing. For the NRI, 

pastureland includes land that has a vegetative cover of 

grasses, legumes, and/or forbs, regardless of whether or 

not it is being grazed by livestock.

FIA (Smith et al., 2004)

Forest land: Land at least 10 percent stocked by forest 

trees of any size, including land that formerly had such 

tree cover and that will be naturally or artificially regenerated. Forest land includes transition zones, such as areas 

between heavily forested and nonforested lands that are 

at least 10 percent stocked with forest trees and forest 

areas adjacent to urban and built-up lands. Also included 

are pinyon-juniper and chaparral areas in the West and 

afforested areas. The minimum area for classification of 

forest land is 1 acre. Roadside, streamside, and shelterbelt strips of trees must have a crown width of at least 

120 feet to qualify as forest land. Unimproved roads and 

trails, streams, and clearings in forest areas are classified 

as forest if less than 120 feet wide.

Timberland: Forest land that is producing or can produce crops of industrial wood and is not withdrawn from 

timber utilization by statute or administrative regulation. 

(Areas qualifying as timberland must be able to produce 

more than 20 cubic feet per acre per year of industrial 

wood in natural stands. Currently inaccessible and inoperable areas are included.)

NASS (USDA NASS, 2004)

Cropland: A category including cropland harvested, 

cropland idle or used for cover crops or soil improvement but not harvested and not pastured, cropland 

on which all crops failed, and cropland in cultivated 

summer fallow. Not included is cropland used only for 

pasture or grazing.

Cropland pasture: Cropland used only for pasture or 

grazing, which could have been used for crops without 

additional improvement. Also included are acres of crops 

hogged or grazed but not harvested prior to grazing. 

However, cropland pastured before or after crops were 

harvested counts as harvested cropland rather than cropland for pasture or grazing.

Pastureland and rangeland: All grazable land—

irrigated or dry—that does not qualify as cropland or 

woodland pasture. In some areas, this is high-quality 

pastureland but cannot be cropped without improvements. In others, it can barely be grazed and is only marginally better than waste land.

Definitions of Land Use Categories for Exhibits 4-5, 4-6, and 4-7
LAND

EPA’s 2008 Report on the Environment 4-17

INDICATOR | Land Use (continued)

Forest lands are managed by a complex array of interests 

to meet multiple purposes, including providing habitat 

for a variety of species, recreation, and timber production. While forest is a land cover classification, timberland 

is a land use classification that reflects forest land capable of 

producing at least 20 cubic feet per acre per year of industrial wood and not withdrawn from timber utilization by 

statute or regulation. Approximately 504 million acres of 

U.S. forest land, or 22 percent of the total U.S. land area, 

qualified as timberland in 2002 (Exhibit 4-5). This total 

reflects a net gain of about 11 million acres (2 percent) 

between 1977 and 2002, which the FIA attributes largely 

to reversion of abandoned lands and reclassification of some 

National Forest lands to align with classifications used on other land ownerships 

(Smith et al., 2004).

Land use varies widely by EPA Region 

(Exhibit 4-6). According to the most 

recent data for each land use type, 

Regions 6, 8, and 9 together have more 

than three-quarters of the nation’s grazing land, while Region 4 has the largest 

portion of timberland (27 percent of total 

U.S. timberland). Trends also vary widely 

among regions. About 83 percent of the 

cropland lost between 1987 and 2003 was 

in five EPA Regions (Regions 4, 5, 6, 7, 

and 8) (Exhibit 4-7, panel A). Increases in 

developed land are responsible for part of 

this decline; for example, developed land 

increased by nearly 60 percent from 1987 

to 2003 in Region 4 (Exhibit 4-7, panel 

B). Other factors include the federal Conservation Reserve Program, which has 

assisted private landowners in converting 

about 35 million acres of highly erodable cropland to vegetative cover since 

1985 (as of 2004) (USDA Farm Service 

Agency, 2004).

Indicator Limitations

•	 Estimates are derived from a variety of inventories and 

samples, conducted over different time periods and for 

different purposes. This limits the ability to integrate 

the data and track changes over time. 

•	 The NRI does not report land use data for Alaska, which 

encompasses 365 million acres of the 2.3 billion acres 

nationwide. The NRI also does not provide data on 

federal lands (representing 20 percent of the contiguous 

U.S. land and one-third of Alaska). Because federal land 

is seldom used for agriculture or urban development, and 

there is relatively little developed or agricultural land in 

Exhibit 4-6. Land use in the U.S. by EPA Region, 2002-2003a

0

50

100

150

200

250

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10

EPA Region

Area (million acres)

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

a

See box on p. 4-16 for definitions of land use categories.

Data source: Lubowski et al., 2006; Smith et al., 2004; 

USDA NASS, 2004; USDA NRCS, 2007

FIA 

Timberland 

(2002)

NASS 

Cropland 

(2002)

ERS 

Rangeland 

(2002)

NRI 

Developed 

(2003)

ERS (Lubowski et al., 2006)

Grassland pasture and range: All open land used 

primarily for pasture and grazing, including shrub and 

brush land types of pasture; grazing land with sagebrush 

and scattered mesquite; and all tame and native grasses, 

legumes, and other forage used for pasture or grazing. Because of the diversity in vegetative composition, 

grassland pasture and range are not always clearly distinguishable from other types of pasture and range. At one 

extreme, permanent grassland may merge with cropland 

pasture; grassland is also often found in transitional areas 

with forested grazing land.

Forested land grazed: Forested grazing land consists 

mainly of forest, brush-grown pasture, arid woodlands, 

and other areas within forested areas that have grass or 

other forage growth. The total acreage of forested grazing land includes woodland pasture in farms plus estimates of forested grazing land not in farms. For many 

states, the estimates include significant areas grazed only 

lightly or sporadically. The Census of Agriculture, the 

National Resources Inventory, and the Forest Inventory 

and Analysis are the principal sources of data. 
LAND

4-18 EPA’s 2008 Report on the Environment

INDICATOR | Land Use (continued)

Alaska, the NRI data likely offer a reasonable approximation of national trends in these categories.

•	 NRI data use three subcategories of types of developed 

land: large built-up areas, small built-up areas, and rural 

transportation land. Because ecological effects from 

developed land depend on the density of development 

and many other factors, the limited NRI categories are 

not discriminating enough to support detailed analyses of 

ecological effects of developed land.

•	 The FIA data are aggregated from state inventories in 

many cases, and dates of data collection for these inventories vary by state—for example, ranging from 1980 to 

2001 for reporting 2002 estimates. 

•	 Some land uses may be administratively designated but 

not physically visible (e.g., lands that are reserved for 

parks or wilderness may appear similar to lands that are 

managed for natural resources).

NRI developed FIA Timberland

(1987-2003) 

Exhibit 4-7. Changes in land use in the U.S. by EPA Region, 1977-2003a

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

a

See box on p. 4-16 for definitions of land use categories.

Data source: Smith et al., 2004; USDA NASS, 2004; USDA NRCS, 2007 Percent change in area Change in area (million acres)

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

-8

-10

-12

-6

-4

-2

0

2

4

6

8

10

(1977-1987) (1987-1997) (1997-2001)

-40

-20

0

20

40

30

60

50

10

-10

-30

A. Acreage change

B. Percent change

NRI crop 

& pasture 

(1987-2003)

NASS crop 

& pasture 

(1997-2002)

(1977-1987) (1987-1997) (1997-2001)

NRI developed 

(1987-2003) 

NRI crop 

& pasture 

(1987-2003)

NASS crop 

& pasture 

(1997-2002)

FIA Timberland 
LAND

EPA’s 2008 Report on the Environment 4-19

INDICATOR | Land Use (continued)

•	 Land use designations are most frequently managed and 

monitored by local governments, each using different 

approaches and classifications. This makes national 

summaries difficult. 

•	 The extent of lands used for energy production, resource 

extraction, or mining is not known and represents a 

data gap.

•	 Lands specifically protected for certain uses such as wilderness or parks have been periodically inventoried for 

the nation. These statistics are currently not reported in 

a form that allows comparison with other statistics. 

Data Sources 

Data were obtained from several original sources and 

compiled by EPA Region. ERS data were obtained from 

Lubowski et al. (2006). FIA data were obtained from Smith 

et al. (2004). NASS data were published by the USDA 

National Agricultural Statistics Service (2004).

References

Lubowski, R.N., M. Vesterby, S. Bucholtz, A. Baez, and 

M.J. Roberts. 2006. Major uses of land in the United States, 

2002. Economic Information Bulletin No. (EIB-14). U.S. 

Department of Agriculture, Economic Research Service. 

<http://www.ers.usda.gov/publications/eib14/> 

Smith, W.B., P.D. Miles, J.S. Vissage, and S.A. Pugh. 2004. 

Forest resources of the United States, 2002. USDA Forest 

Service. <http://ncrs.fs.fed.us/pubs/gtr/gtr_nc241.pdf>

USDA Farm Service Agency (United States Department of 

Agriculture, Farm Service Agency). 2004. The Conservation 

Reserve Program: Summary and enrollment statistics, 2004. 

<http://www.fsa.usda.gov/Internet/FSA_File/fy2004.pdf>

USDA NASS (United States Department of Agriculture, 

National Agricultural Statistics Service). 2004. 2002 census 

of agriculture, United States summary and state data. 

Report AC-02-A-51. <http://www.nass.usda.gov/census/

census02/volume1/us/us2appxc.pdf> (QA/QC); 

<http://www.nass.usda.gov/census/census02/volume1/

USVolume104.pdf>

USDA NRCS (United States Department of Agriculture, 

Natural Resources Conservation Service). 2007. National 

Resources Inventory, 2003 annual NRI: Land use. 

<http://www.nrcs.usda.gov/technical/nri/2003/

nri03landuse-mrb.html>

USDA NRCS. 2004. National resources inventory: 2002 

annual NRI. <http://www.nrcs.usda.gov/technical/

NRI/2002/glossary.html>

INDICATOR | Urbanization and Population Change

The total number of people and their distribution on the landscape can affect the condition of the environment 

in many ways. Increasing population often means increased 

urbanization, including conversion of forest, farm, and other 

lands for housing, transportation, and commercial purposes. 

In recent years, many communities in the U.S. have seen 

an increase in developed land (residential, commercial, 

industrial, and transportation uses) that outpaces population growth. This pattern is of concern for numerous health 

and environmental reasons (Frumkin et al., 2004). For 

example, studies indicate that when land consumption rates 

exceed the rate of population growth, per capita air pollutant emissions from driving tend to be higher. Urbanization 

and population growth also tend to increase the amount of 

impervious surfaces and the quantity and types of products 

that humans produce, use, and discard, thereby affecting waste generation and management, water quality, and 

chemical production and use.

The information presented in this indicator is based on 

population data collected and analyzed on a decadal basis by 

the U.S. Census Bureau—as well as annual “intercensal” population estimates—and data collected by the U.S. Department 

of Agriculture Natural Resources Conservation Service’s 

Exhibit 4-8. Population and urbanization in the 

U.S., 1790-2000a

a

Coverage: 50 states and the District of Columbia.

Data source: U.S. Census Bureau, 1993, 2004

0

50

100

150

200

250

300

1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000

Year

Population (millions)

Rural population

Urban population

v
LAND

4-20 EPA’s 2008 Report on the Environment

INDICATOR | Urbanization and Population Change (continued)

National Resources Inventory (NRI) to track “developed” 

land. Between 1977 and 1997, the NRI developed estimates 

every 5 years on non-federal lands in the contiguous U.S. 

Since 2001 the NRI has developed annual estimates, but based 

on a smaller sample size. This indicator captures trends in 

overall population growth for both rural and urban populations; the amount of developed land relative to the amount of 

population change, nationally and by EPA Region; and overall 

population density, also nationally and by EPA Region.

What the Data Show

The U.S. population grew from a little over 4 million people 

in 1790 to over 281 million in 2000; urban population is estimated to have grown a thousandfold over that period (Exhibit 

4-8). The population nearly doubled between 1950 and 2000.

 The rates of population and developed land growth over 

5-year intervals increased between 1982 and 1997, before 

declining slightly between 1997 and 2002. Over all four 

5-year increments, the amount of developed land increased 

at nearly twice the rate of the population (Exhibit 4-9). 

Between 1982 and 2003, the amount of developed land 

in the U.S. in the 48 contiguous states (not including the 

District of Columbia) grew by more than 35 million acres, 

representing a cumulative increase of more than 48 percent. 

The Census Bureau estimates that during the same period, 

the population of the 48 states grew by nearly 58 million 

people, or just over 25 percent (Exhibit 4-10). 

There are substantial variations in population and development trends in different parts of the U.S. (Exhibit 4-10). 

Between 1982 and 2003, the growth rates for developed 

land were higher than population growth rates in every 

region except Region 8. The largest rate of increase in 

population between 1982 and 2003 occurred in Region 9, 

where population increased by more than 46 percent (nearly 

14 million people). Developed land in Region 9 increased 

by 51 percent (more than 2.8 million acres). Region 4 had 

the largest rate of increase in developed land (nearly 80 percent) and the largest absolute increases in both population 

(15.4 million) and developed land (11.8 million acres). 

Although growth rates of population and developed 

land were high in most Regions, population density varies 

significantly from one Region to the next (Exhibit 4-11). 

In 2005, EPA Region 2 was the most densely populated 

Region, at 512 people per square mile; EPA Region 10 was 

the least densely populated, with an average of approximately 15 people per square mile (including Alaska). The 

national average in 2005 was 83.8 people per square mile. 

Exhibit 4-9. Percent change in population 

and developed land in the contiguous U.S. 

and Hawaii, 1982-2002a,b

1982-

1987

1987-

1992

1992-

1997

1997-

2002b

Reporting period

Percent change

0

2

4

6

8

10

12

14

Change in population

Change in acreage 

of developed land

a

Coverage: Contiguous 48 states 

(excluding the District of Columbia) 

and Hawaii.

b

Based on changes in the NRI 

inventory approach, Hawaii was not sampled in 2002. Thus, the 

percent change in developed land from 1997 to 2002 is based on 

the 48 contiguous states only.

Data source: U.S. Census Bureau, 1996, 2002b, 2006; USDA 

NRCS, 2000, 2004

Exhibit 4-10. Percent change in population and 

developed land in the contiguous U.S. by EPA 

Region, 1982-2003a

EPA Region

Percent change a

Coverage: Contiguous 48 states 

(excluding the District of Columbia).

Data source: U.S. Census Bureau, 

1996, 2002b, 2006; USDA NRCS, 

2000, 2007

0

10

20

30

40

50

60

70

80

90

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10

Change in population

Change in acreage 

of developed land

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

All

U.S.
LAND

EPA’s 2008 Report on the Environment 4-21

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

Exhibit 4-11. Population density in the U.S. by EPA Region, 1950-2005a

a

Coverage: 50 states and the District of Columbia.

Data source: U.S. Census Bureau, 2002a,c; 2006

Year

0

100

200

300

400

500

600

Region 1 Region 2 Region 3 Region 4 Region 5 Region 6

Population density (people per mi2)

’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05

’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05 ’50’60’70’80’90’00’05

0

100

200

300

400

500

600

Region 7 Region 8 Region 9 Region 10 All U.S.

Indicator Limitations

Census data:

•	 Intercensal figures are estimates based on administrative records of births, deaths, and migration, and thus differ from 

the decennial census data in methodology and accuracy. 

•	 Sampling and non-sampling errors exist for all census 

data as a result of errors that occur during the data collection and processing phases of the census. 

•	 Puerto Rico and Virgin Islands data are not available for 

all years, and thus have not been included. This affects 

the accuracy of the statistics for Region 2. 

•	 The criteria for estimating urban population have 

changed over time as defined by the Census Bureau.

NRI data:

•	 NRI sampling procedures changed in 2000 to an annual 

survey of fewer sample sites than had previously been 

sampled (starting in 1977, the NRI sampled 800,000 

points every 5 years). Fewer sample points mean increased variance and uncertainty. 

•	 The NRI collects some data across the entire nation, 

including Puerto Rico and the Virgin Islands. Land use 

statistics, however, are not reported on federal lands 

or for Alaska and the District of Columbia. In Exhibit 

4-10, Hawaii is also excluded. 

Data Sources

Urban and rural population data for Exhibit 4-8 were 

obtained from two U.S. Census Bureau publications: data 

from 1790 to 1990 are from U.S. Census Bureau (1993); 

2000 data are from U.S. Census Bureau (2004).

In Exhibit 4-9, population change was calculated from 

annual population estimates published in U.S. Census Bureau 

(1996, 2002b, 2006) (estimates for 1982/1987, 1992/1997, and 

2002, respectively). Changes in acreage of developed land 

were calculated based on acreage figures originally reported 

every 5 years by the NRI and now reported annually. NRI 

data were obtained from two publications (USDA NRCS, 

2000, 2004) (1982-1997 and 2002 data, respectively).

Exhibit 4-10 is based on annual population estimates by 

state, published in U.S. Census Bureau (1996, 2002b, 2006), 

and NRI-developed land estimates by state, published in 

USDA NRCS (2000, 2007). The figure was developed by 

grouping the published state data by EPA Region, then calculating percent change between 1982 and 2003.

Population density by EPA Region (Exhibit 4-11) was 

calculated based on three published data sets: population 

every 10 years from 1900 to 2000 by state (U.S. Census 

Bureau, 2002a); population estimates for 2005 by state 

(U.S. Census Bureau, 2006); and land area by state (U.S. 

Census Bureau, 2002c).

INDICATOR | Urbanization and Population Change (continued)
LAND

4-22 EPA’s 2008 Report on the Environment

INDICATOR | Urbanization and Population Change (continued)

References 

Frumkin, H., L. Frank, and R. Jackson. 2004. Urban sprawl 

and public health: Designing, planning, and building for 

healthy communities. Washington, DC: Island Press. 

U.S. Census Bureau. 2006. Annual estimates of the population for the United States, Regions, states, and for Puerto 

Rico: April 1, 2000 to July 1, 2006 (NST-EST2006-01) 

released December 22, 2006. Washington, DC. <http://

www.census.gov/popest/states/tables/NST-EST2006-01.

xls> Available from <http://www.census.gov/popest/

states/NST-ann-est.html>

U.S. Census Bureau. 2004. Statistical abstract of the United 

States 2004-2005: The national data book. Washington DC. 

<http://www.census.gov/prod/2004pubs/04statab/pop.pdf> 

U.S. Census Bureau. 2002a. Demographic trends in the 20th

century: Census 2000 special reports. Washington, DC. 

<http://www.census.gov/prod/2002pubs/censr-4.pdf>

U.S. Census Bureau. 2002b. Time series of intercensal state 

population estimates: April 1, 1990 to April 1, 2000. Table 

CO-EST2001-12-00. Washington, DC. <http://www.

census.gov/popest/archives/2000s/vintage_2001/CO-EST

2001-12/CO-EST2001-12-00.html>

U.S. Census Bureau. 2002c. Population, housing units, area, 

and density for states, 2000. Washington, DC. <http://www.

census.gov/population/www/censusdata/density.html>

U.S. Census Bureau. 1996. Intercensal estimates of 

the total resident population of states: 1980 to 1990. 

Washington, DC. <http://www.census.gov/popest/

archives/1980s/st8090ts.txt>

U.S. Census Bureau. 1993. 1990 census of population 

and housing: population and unit counts, United States. 

1990-CPH-2-1. Washington, DC. <http://www.census.

gov/prod/cen1990/cph2/cph-2-1-1.pdf>

USDA NRCS (United States Department of Agriculture, 

Natural Resources Conservation Service). 2007. National 

Resources Inventory, 2003 annual NRI: Land use. 

<http://www.nrcs.usda.gov/technical/nri/2003/

nri03landuse-mrb.html>

USDA NRCS. 2004. National resources inventory: 2002 

annual NRI. <http://www.nrcs.usda.gov/technical/

nri/2002/nri02lu.html> 

USDA NRCS. 2000. Summary report: 1997 national 

resources inventory (revised December 2000). Washington, 

DC and Ames, IA: USDA Natural Resource Conservation 

Service. <http://www.nrcs.usda.gov/technical/NRI/1997/

summary_report/table1.html>

4.3.3 Discussion

What These Indicators Say About Trends 

in Land Use and Their Effects on Human 

Health and the Environment

The indicators point out that the development of land for 

human residential and commercial purposes is occurring at a 

rapid pace. In the 21-year period between 1982 and 2003, the 

acreage of developed land increased by more than 48 percent 

from its 1982 level. Population in a similar time frame grew 

at only half the rate of land development (25 percent), indicating that more land is being developed per capita now than 

25 years ago. Across EPA regions, such rates of change in 

developed land and population vary both independently and 

with respect to each other. Over a similar 20-year time frame 

(1982-2002), the extent of cropland and pastureland has slowly 

declined, with larger decreases in those regions experiencing 

either increased land development or reforestation. 

Limitations, Gaps, and Challenges

There is generally a lack of comprehensive data on the types 

and rates of land use and land cover change, and even less 

systematic evidence on the causes and consequences of these 

changes. On a global scale, the National Research Council 

identified land use dynamics as one of the grand challenges for 

environmental research.16

Two examples of land uses not addressed by the indicators, 

that can have effects in different ways on condition and extent 

of land, are the formal protection or reservation of land for 

habitat or natural resources, and mining and extraction activities. Some data are collected locally and for federal lands (e.g., 

National Park acreage) or tracked for economic indicators, but 

the national picture of the extent of land reservation and mining is not generally available.

A key challenge in answering the land use question is that 

estimates of the extent of various land uses differ across data 

sources and each source uses different classifications, measurement approaches, methodologies for analysis and interpretation, 

16 National Research Council, Committee on Grand Challenges in Environmental Sciences. 2001. Grand challenges in environmental sciences. Washington, DC: National Academies Press.

v
LAND

EPA’s 2008 Report on the Environment 4-23

and sampling time frames. The data are collected by many different agencies that manage land for many different purposes. 

The data collection efforts currently in place are derived from 

specific interests, such as tracking changes in the extent of agricultural land or farmland, or understanding how much land is 

used for timber production. These data collection efforts tend 

to develop and use their own classifications and categorization, making it difficult to integrate and use the data over time, 

across inventories, or as a national picture.

Another challenge is understanding the effects that trends in land 

use have on human health. No indicators are available, as effects 

have not been shown or quantified on a national basis. Urban 

and landscape planners have conducted site-specific studies on 

individual land uses, but little is known about overall national 

trends in land use and potential impacts on human health. 

An additional challenge is that a variety of state, county, 

and municipal laws, regulations, and practices govern the 

use of land, but aside from regulations addressing protection 

of species and their habitats, there are no national land use 

regulations that apply to all non-federal lands. There are also 

relatively few state-level efforts to organize land use data; most 

activities occur over specific local, usually urbanizing, geographic areas. This means that land use records are not maintained statewide or nationally, as they are in other nations, 

which contributes to challenges in tracking and monitoring 

land use changes. It also means that strategies to plan land use 

across jurisdictions are difficult to develop. 

Finally, a challenge in developing data to determine trends 

is the difficulty of actually delineating land use. Land use is 

generally a function of laws, policies, or management designations that may not always be possible to infer from examining 

the ground via surveys. Analysis of zoning maps or property 

records at the local level may be necessary.

4.4 What Are the Trends in 

Wastes and Their Effects 

on Human Health and the 

Environment?

4.4.1 Introduction

Every resident, organization, and human activity in the U.S. 

generates some type of waste. Many different types of wastes 

are generated, including municipal solid waste, agricultural 

and animal waste, medical waste, radioactive waste, hazardous waste, industrial non-hazardous waste, construction and 

demolition debris, extraction and mining waste, oil and gas 

production waste, fossil fuel combustion waste, and sewage 

sludge (see the glossary in Appendix A for detailed descriptions of these wastes). In general, waste generation represents 

inefficient use of materials. These materials, some of which are 

hazardous, must be managed through reuse, recycling, storage, 

treatment, and disposal. Hazardous wastes are either specifically listed as hazardous by EPA or a state, or exhibit one or 

more of the following characteristics: ignitability, corrosivity, 

reactivity, or toxicity. Generation and management of hazardous wastes have the potential to contaminate land, air, and 

water and negatively affect human health and environmental 

conditions. Tracking trends in the quantity, composition, 

and effects of these materials provides insight into the efficiency with which the nation uses (and reuses) materials and 

resources and provides a means to better understand the effects 

of wastes on human health and ecological condition. 

The amount of waste produced is influenced by economic 

activity, consumption, and population growth. Affluent societies, such as the U.S., generally produce large amounts of municipal solid waste (e.g., food wastes, packaged goods, disposable 

goods, used electronics) and commercial and industrial wastes 

(e.g., demolition debris, incineration residues, refinery sludges). 

Among industrialized nations, the U.S. generates the largest 

amounts of municipal solid waste per person on a daily basis.17

Current approaches to waste management evolved primarily due to health concerns and odor control. Waste often was 

deposited outside developed areas on nearby lands, frequently 

wetlands. Excavation of land specifically for deposition of 

wastes followed, often accompanied by burning of wastes 

to reduce volume, a practice eventually determined to be a 

contributor to degraded air quality in urban areas. Burning of 

wastes occurred at multiple levels, from backyard burning to 

large, open-burning dumps of municipal solid wastes to onsite 

burning of commercial and industrial wastes. Land disposal 

created problems such as ground water contamination, methane gas formation and migration, and disease vector hazards. 

The amount of land being used to manage the many types of 

waste generated is not known. Most municipal solid wastes 

and hazardous wastes are managed in land disposal units. 

Land disposal of hazardous wastes includes landfills, surface 

impoundments, land treatment, land farming, and underground 

injection. Modern landfill facilities are engineered with containment systems and monitoring programs. Waste management 

practices prior to the Resource Conservation and Recovery 

Act (RCRA) regulations left legacies of contaminated lands in 

many cases, which are addressed in Section 4.6 of this chapter. 

Landfills represent one of the largest human-related sources 

of methane gas in the U.S. Between 1997 and 2003, landfills 

accounted for slightly more than one-fourth of the estimated 

methane emissions attributed to human activity.18 Methane 

gas is released as wastes decompose, as a function of the total 

amount and makeup of the wastes as well as management 

17 Clark, R., and E. Capponi, eds. 2005. OECD in figures 2005: Statistics on the 

member countries. Organization for Economic Cooperation and Development (OECD) Observer. Paris, France. 

18 U.S. Environmental Protection Agency. 2006. Inventory of U.S. greenhouse gas 

emissions and sinks: 1990-2004. EPA/430/R-06/002. 

<http://yosemite.epa.gov/oar/globalwarming.nsf/content/

ResourceCenterPublicationsGHGEmissionsUSEmissionsInventory2006.html>

19 More information on air emissions related to waste management practices, 

including nitrogen oxides (NOx) and carbon monoxide (CO), is included in 

Chapter 2. 
LAND

4-24 EPA’s 2008 Report on the Environment

facility location, design, and practices.19 EPA is interested 

because gas emissions can be affected by recycling and changing product use. For example, recycling aluminum or office 

paper can reduce environmental effects (e.g., by reducing the 

need to mine bauxite or harvest trees), and it will also create 

positive environmental benefits, such as reductions in energy 

consumption and greenhouse gases (e.g., emissions associated 

with the production of products from virgin materials).20

Although data do not exist to directly link trends in waste 

with effects on human health and the environment, the 

management of waste may result in waste and chemicals in 

waste entering the environment. Hazardous waste, by definition, has the potential to negatively affect human health and 

the environment, which is why it is so strictly regulated. The 

effects associated with waste vary widely and are influenced by 

the substances or chemicals found in waste and how they are 

managed. For chemicals found in waste, EPA has been tracking a list of Priority Chemicals. These Priority Chemicals are 

documented contaminants of air, land, water, plants, and animals. Between 1991 and 2001, quantities of 17 of the Priority 

Chemicals were reduced by more than 50 percent.21,22

4.4.2 ROE Indicators

The ROE indicators for this question focus on the national trends 

in the amount of municipal solid waste and hazardous waste 

generated and their management practices (Table 4-4). Municipal solid waste trends are presented for more than four decades. 

Trends in the generation and management of municipal solid 

waste are based on estimations from a materials flow or mass 

balance approach since 1960. Changes in the amount of RCRA 

hazardous waste generated and managed are based on mandated 

biennial submissions from generators and treatment, storage, and 

disposal facilities.

20 U.S. Environmental Protection Agency. 2006. Solid waste management and 

greenhouse gases: A life-cycle assessment of emissions and sinks. Third edition. Washington, DC. <http://www.epa.gov/climatechange/wycd/waste/

SWMGHGreport.html>

21 U.S. Environmental Protection Agency. 2005. National Priority Chemicals 

Trends Report (1999-2003). EPA/530/R-05/022. 

22 U.S. Environmental Protection Agency. 2007. National Priority Chemicals 

Trends Report (2000-2004). EPA/530/R-07/001. <http://www.epa.gov/

epaoswer/hazwaste/minimize/trends.htm#report>

Municipal solid waste (also called trash or garbage) is defined at the national level as wastes consisting of 

everyday items such as product packaging, grass clippings, 

furniture, clothing, bottles and cans, food scraps, newspapers, appliances, consumer electronics, and batteries. These 

wastes come from homes, institutions such as prisons and 

schools, and commercial sources such as restaurants and 

small businesses. EPA’s definition of municipal solid waste 

(MSW) does not include municipal wastewater treatment 

sludges, industrial process wastes, automobile bodies, combustion ash, or construction and demolition debris. Once 

generated, MSW must be collected and managed, including 

reuse, recovery for recycling (which includes composting), 

combustion, and landfill disposal. Many wastes that are 

disposed in landfills represent a loss of materials that could 

be reused, recycled, or converted to energy to displace the 

use of virgin materials. 

Prior to the 1970s, MSW disposal generally consisted of 

depositing wastes in open or excavated landfills, accompanied by open burning to reduce waste volumes. Often 

industrial wastes were co-disposed with municipal garbage and refuse in urban and rural landfills. Historically, 

environmental problems associated with landfills have 

included ground water contamination, emissions of toxic 

fumes and greenhouse gases, land contamination, and 

increases in vector populations (e.g., rodents, flies, mosquitoes). Wastes have the potential to cause various types of 

environmental concerns depending on the way in which 

they are disposed. When mismanaged, potentially hazardous ingredients in some products can migrate into the 

environment, possibly posing harm to human health and 

biota; stockpiled scrap tires may ignite, often burning for 

months and causing air pollution; waste piles can create 

habitats for pests and disease vectors such as rodents and 

INDICATOR Quantity of Municipal Solid Waste Generated

and Managed

Table 4-4. ROE Indicators of Trends in Wastes and Their 

Effects on Human Health and the Environment 

National Indicators Section Page

Quantity of Municipal Solid Waste Generated and Managed 4.4.2 4-24

Quantity of RCRA Hazardous Waste Generated and Managed 4.4.2 4-26
LAND

EPA’s 2008 Report on the Environment 4-25

mosquitoes; and the physical presence of a waste management area can disrupt an ecosystem. Most wastes generated 

in the U.S. are disposed in landfills, which are subject to 

federal or state requirements to minimize environmental impacts. MSW landfills are discrete areas of land or 

excavations that receive trash/garbage, as well as various 

other types of wastes that are not included in this indicator, such as non-hazardous sludges, hazardous wastes from 

small quantity generators, non-hazardous industrial wastes, 

municipal wastewater treatment sludges, and construction 

and demolition debris. 

This indicator shows trends in the national generation 

and management of MSW on an annual basis from 1960 to 

2006. The information presented on MSW consists of estimates generated annually using a materials flow methodology and mass balance approach that relies on production 

data (by weight) for materials and products that eventually enter the waste stream. These data are collected from 

industry associations, businesses, and government agencies. 

What the Data Show

The quantity of MSW generated grew steadily from 88 

million tons (MT) in 1960 to over 251 MT in 2006, an 

increase of 185 percent (Exhibit 4-12, panel A). During 

this time, the U.S. population increased by 66 percent. 

On a per capita basis, MSW generation increased from 

2.7 pounds per person per day in 1960 to 4.6 pounds per 

person per day in 2006 (panel B). 

Of the 88 MT of MSW generated in 1960, 6 percent was 

recovered through recycling and 94 percent was landfilled 

(Exhibit 4-13). MSW quantities sent to landfills or other 

disposal peaked in 1990 at 142 MT and then began to 

decline as recycling and combustion increased. The quantity 

of MSW disposed in landfills has averaged about 135 MT 

annually since 2000, a 4.9 percent decrease from 1990. In 

2006, of the 251 MT generated, 32.5 percent was recycled 

(including composting), 13 percent combusted with energy 

recovery, and 55 percent landfilled. Since 1990, the percentage of MSW generated that was sent to landfills dropped 

from 69 to 55 percent, the percentage recycled rose from 

14 to 24 percent, the percentage composted rose from 2 to 

8 percent, and the percentage combusted with energyrecovery ranged from 13 to 15 percent. 

Indicator Limitations

•	 The data in this indicator are derived from economic 

statistics on materials generation and estimates of the 

life cycle of goods, rather than on direct measurements 

of wastes disposed of. As a result of this methodology 

and especially of differences in definitions, the figures 

reported in this indicator do not match estimates of 

INDICATOR Quantity of Municipal Solid Waste Generated

and Managed (continued)

Exhibit 4-12. Municipal solid waste generation 

in the U.S., 1960-2006 Total MSW generated (million tons/year) MSW generated per capita (pounds/person/day)

Data source: U.S. EPA, 2007

B. Per capita daily MSW generation

Year

A. Total annual MSW generation

Year

0

50

100

150

200

250

300

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

0

1

2

3

4

5

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Exhibit 4-13. Municipal solid waste 

management in the U.S., 1960-2006 MSW managed (million tons)

Data source: U.S. EPA, 2007

Year

Landfill or other disposal n r s

0

50

100

150

200

250

300

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Landfill or other disposal

Recovery 

for recycling Combustion with energy recovery

Recovery for composting
LAND

4-26 EPA’s 2008 Report on the Environment

MSW reported elsewhere (e.g., BioCycle, which includes 

construction and demolition debris, industrial wastes, 

agricultural wastes, etc., in its estimates). However, the 

waste categories in this indicator are rigorously defined 

and consistent from year to year, therefore allowing for 

reliable long-term trend analyses.

•	 The data presented on landfills represent the amount 

of waste disposed in landfills, but do not indicate the 

capacity or volume of landfills or the amount of land 

used for managing MSW. Land used for recycling facilities and waste transfer stations also is not included in this 

indicator. Data to describe the amount of land used or 

total capacity of landfills are not available nationally.

•	 The data also do not indicate the status or effectiveness 

of landfill management or the extent to which contamination of nearby lands does or does not occur. 

Data Sources

Exhibits 4-12 and 4-13 are derived from data published 

in U.S. EPA (2007). The report provides tables with 

numerical values for certain key years during the period 

of record (1960, 1970, 1980, 1990, 1995, 2000, 2002, and 

2004-2006). However, the full 44-year data set is not 

publicly available.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Municipal solid waste generation, recycling, and disposal in the United States: Facts and figures for 2006. <http://www.epa.gov/epaoswer/non-hw/

muncpl/msw99.htm>

INDICATOR Quantity of Municipal Solid Waste Generated

and Managed (continued)

Hazardous waste is waste with a chemical composition or other property that 

makes it capable of causing illness, death, or 

some other harm to humans and other life 

forms when mismanaged or released into 

the environment. Uncontrolled dumping of 

wastes, including hazardous industrial wastes, 

was commonplace in history, with numerous 

entities handling and disposing of these materials. Landfills and surface impoundments 

containing these materials were unlined and 

uncovered, resulting in contaminated ground 

water, surface water, air, and soil. Even 

with tight control of hazardous wastes from 

generation to disposal, the potential exists for 

accidents that could result in the release of 

hazardous wastes and their hazardous constituents into the environment. Through the 

Resource Conservation and Recovery Act 

(RCRA) and the subsequent 1984 Hazardous and Solid Waste Amendments, Congress 

sought to better control waste management and disposal and 

to conserve valuable materials and energy resources. 

Facilities that treat, store, or dispose of hazardous wastes 

are termed RCRA treatment, storage, and disposal facilities 

(TSDFs). Some hazardous waste generators treat, store, and 

dispose of their hazardous waste onsite, while others ship 

their waste to TSDFs. Most hazardous wastes are eventually 

disposed in landfills, surface impoundments (which eventually become landfills), land application units, or by deep 

well injection. All hazardous wastes disposed of must meet 

certain treatment standards required by the Land Disposal 

Restrictions prior to disposal. 

INDICATOR Quantity of RCRA Hazardous Waste Generated 

and Managed

Exhibit 4-14. RCRA hazardous waste generation and 

management in the U.S., 1999-2005a

a

Individual management practice quantities do not add up to the total quantity 

generated. See text for details.

Data source: U.S. EPA, 2007b

0

5

10

15

20

25

30

35

40

Year

’99 ’01 ’03 ’05 ’99 ’01 ’03 ’05 ’99 ’01 ’03 ’05 ’99 ’01 ’03 ’05 ’99 ’01 ’03 ’05 ’99 ’01 ’03 ’05

Waste generated/managed 

(million tons)

Generated Stored/ 

bulked/

transferred 

Material

recovery

Energy

recovery

Treated Disposed

v
LAND

EPA’s 2008 Report on the Environment 4-27

EPA, in partnership with the states, collects extensive data 

on the RCRA hazardous waste generation and management 

practices of TSDFs and large quantity generators (businesses 

that generate more than 2,200 pounds of RCRA hazardous 

waste, 2.2 pounds of RCRA acute hazardous waste, or 220 

pounds of spill cleanup material contaminated with RCRA 

acute hazardous waste in 1 month). These data are collected every 2 years; this indicator tracks changes in RCRA 

hazardous wastes generated and managed for the years 1999, 

2001, 2003, and 2005.

What the Data Show 

Between 1999 and 2005, the quantity of RCRA hazardous 

wastes generated decreased by 22 percent from 36.1 million 

tons (MT) to 28.0 MT (Exhibit 4-14). Included in the amount 

generated are material recovery, energy recovery, treatment, 

and wastes disposed by deep well injection. Due to RCRA 

hazardous waste regulations and data collection procedures, 

the individual management categories discussed below cannot 

be added together to obtain the total quantity generated. For 

example, under RCRA, all hazardous waste must be treated 

to meet technology-based land disposal treatment standards 

before it is placed in or on the ground, unless it meets those 

standards as generated. To minimize double-counting, the 

quantities of waste stored, bulked, transferred, or disposed by 

landfill, land treatment, or land application after treatment are 

not included in the total quantity generated, but are shown 

in the “Disposed” section of Exhibit 4-14 (along with wastes 

disposed by deep well injection). 

In addition to the 36.1 MT of RCRA waste generated 

in 1999, 0.7 MT were stored/bulked/transferred for some 

time prior to final disposition (at which time they would be 

included in wastes recovered, treated, or disposed) (Exhibit 

4-14). In 2005, the number stored/bulked/transferred rose 

to 0.8 MT. 

Looking at management activities prior to disposal, in 

1999, 7 percent of RCRA hazardous waste was sent to 

material recovery activities such as metal or solvent recovery, while 8 percent fell into this category in 2005 (Exhibit 

4-14). The proportion of RCRA hazardous waste sent for 

energy recovery increased from 4 percent of RCRA wastes 

generated in 1999 to 6 percent in 2005. The proportion 

sent to treatment declined from 14 percent in 1999 to 7 

percent in 2005. 

The quantity of RCRA hazardous wastes ultimately disposed dropped between 1999 and 2005, from 29.5 MT to 

24.9 MT; however, the proportions of waste in the three 

disposal categories remained fairly stable (Exhibit 4-15). 

In the four reporting cycles shown, the percentage of disposed RCRA hazardous wastes deep-well injected ranged 

from 90 to 92 percent of all waste disposed on land. The 

proportion disposed in landfills or surface impoundments 

that became landfills ranged between 8 and 10 percent. 

The land application and land treatment categories represent a very small percentage of disposal and dropped from 

0.1 percent in 1999 to 0.01 percent of the RCRA hazardous waste disposed in 2005.

Indicator Limitations

•	 Data are not collected from small quantity generators, but some wastes coming from these sources are

included in the RCRA hazardous waste management 

data from treatment, storage, and disposal facilities that 

receive the wastes. 

•	 Data are limited to wastes referred to as “RCRA 

hazardous waste” which are either specifically listed 

as hazardous or meet specific ignitability, corrosivity, 

reactivity, or toxicity criteria found in the U.S. Code of 

Federal Regulations Title 40, Part 261. Materials that 

are not wastes, whether hazardous or not, are not regulated by RCRA, and therefore are not included in the 

data summarized here.

•	 States have the authority to designate additional wastes 

as hazardous under RCRA, beyond those designated in 

the national program. State-designated hazardous wastes 

are not tracked by EPA or reflected in the aggregated 

information presented.

•	 The comparability of year-to-year amounts of RCRA 

hazardous waste generated and managed can be influenced by factors such as delisting waste streams (i.e., 

determining that a particular listed waste stream coming 

from a particular facility is not hazardous) or removing 

the hazardous characteristic of a waste stream. 

INDICATOR Quantity of RCRA Hazardous Waste Generated 

and Managed (continued)

Exhibit 4-15. RCRA hazardous waste disposal 

to land in the U.S. by practice, 1999-2005 Waste disposed (million tons)

Data source: U.S. EPA, 2007b

26.9

2.5

21.6 19.7

0

5

10

15

20

25

30

40

1999 2001 2003 2005

Year

Land treatment/

land application

Landfill/surface 

impoundment

Underground 

injection

0.04

0.02

0.02

22.3

2.5

0.003

1.7

2.2
LAND

4-28 EPA’s 2008 Report on the Environment

•	 The data summarized and shown in Exhibits 4-14 

and 4-15 were derived from the data and information 

collected and reported in the Biennial RCRA Hazardous Waste Report Forms (U.S. EPA, 2007a). As a result 

of methodology and criteria used to derive the results 

for these two exhibits, the quantities presented in this 

indicator do not match those individual generation or 

management quantities presented in each reporting 

cycle of the National Biennial Reports. The National 

Biennial Reports are prepared for individual reporting 

cycles and may not be comparable between reporting 

cycles due to different reporting requirements or methods of aggregation in each cycle. 

•	 Most hazardous waste generated in the U.S. is in the form 

of wastewater. The majority of these wastewaters are sent 

untreated to publicly owned treatment works (POTWs), 

treated and sent to a POTW, or discharged directly to 

surface waters through a National Pollutant Discharge 

Elimination System (NPDES) permit. Hazardous wastewaters generated and subsequently sent to POTWs or 

discharged through a NPDES permit are not included in 

this indicator. Any materials generated from these processes, such as sludge, that are considered hazardous waste 

are managed under hazardous waste regulations. 

Data Sources

This indicator is based on the publicly available data sets 

compiled by EPA. The data sets compiled from individual reporting facilities for this indicator can be found 

in National Biennial RCRA Hazardous Waste Data Files 

in EPA’s RCRAInfo national database (U.S. EPA, 2007b) 

(http://www.epa.gov/epaoswer/hazwaste/data/index.

htm#rcra-info; ftp://ftp.epa.gov/rcrainfodata).

Exhibits 4-14 and 4-15 are derived from reported data 

stored in these data files of the RCRAInfo national database. The versions of data sets from each reporting cycle to 

derive the results for this indicator were downloaded from 

the FTP site between February 2007 and August 2007. 

The analyses based on the data sets downloaded were conducted in October 2007. 

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. Biennial RCRA hazardous waste report 

instructions and forms. Accessed December 2007. <http://

www.epa.gov/epaoswer/hazwaste/data/br05/forms.htm>

U.S. EPA. 2007b. RCRAInfo national database. Accessed 

December 2007. <ftp://ftp.epa.gov/rcrainfodata>

INDICATOR Quantity of RCRA Hazardous Waste Generated 

and Managed (continued)

v

4.4.3 Discussion

What These Indicators Say About Trends in 

Wastes and Their Effects on Human Health 

and the Environment

The indicators show that municipal solid waste generation 

in the U.S. continued to rise between 1960 and 2006, in 

absolute terms. On a per capita basis, rates rose from 1960 to 

1990; however, since 1990, the daily per capita generation of 

municipal solid waste has been relatively constant, showing 

that the total increase in waste may be primarily a function 

of population growth. Hazardous waste, which is generated 

primarily through industrial processes, decreased in the time 

period shown from 1999 to 2005, although there was a small 

rise between 2003 and 2005.

Materials recovery, or recycling, is an important component of 

waste management, as it takes materials that might be considered waste and removes them from the waste disposal path 

to generate reusable marketable materials. Recycling efforts 

related to municipal solid waste have increased over the last 

four decades, showing the steepest increases between 1980 and 

2000. Municipal solid waste recycling efforts have been steady 

since 2000, with nearly a third of all municipal solid waste 

being recycled or composted. 

Recycling (material recovery and energy recovery) of hazardous wastes has remained relatively constant over the time span 

represented by the indicators, although there has been a slight 

decrease in the amount of waste sent for materials recovery. 

While recycling and composting have increased over the past 

several decades, most wastes are disposed. Disposal of municipal solid wastes in landfills saw a rise in absolute amount from 

1960 to 1990, with declines since then. Landfill as a percentage of total waste generated, however, has seen a steady 

decline from 1960 to 2006. Similarly, most hazardous wastes 

are also land-disposed, although they are required to meet 

strict standards for protecting human health and the environment prior to disposal. 

Limitations, Gaps, and Challenges

While numerous waste-related data collection efforts exist at 

the local, state, and national levels, none of these efforts result 

in nationally consistent or comprehensive data to provide a 

full understanding of the amount and locations of waste generation and management.

The two types of waste addressed in the indicators represent 

only a small percentage of the total amount of waste generated in the U.S.—the national amounts and percentage of 

total waste are unknown. Quantities of “end-of-stream” 

wastes, such as municipal solid waste, provide an indication 
LAND

EPA’s 2008 Report on the Environment 4-29

of changing trends in consumption and economic activities, 

but do not provide information on the other amounts of waste 

generated by upstream activities, including resource extraction 

and manufacturing. EPA is interested in better understanding 

the comparative amounts of the various types of waste generated, but national data are dated, inconsistent, or generally not 

available in common units to develop a comprehensive picture 

of the waste generated in the U.S. 

The amount of waste generated and managed may describe 

ambient conditions in terms of wastes in the environment, but 

does not provide any indication of the effects on human health 

or environmental condition. There have been changes in the 

management of wastes over the past few decades, designed to 

reduce hazardous and potential exposures, but data that more 

concretely measure the overall exposure (and thus effects on 

human health and the environment caused by wastes and 

waste management practices) are still lacking.

4.5 What Are the Trends 

in Chemicals Used on the 

Land and Their Effects 

on Human Health and the 

Environment?

4.5.1 Introduction

Many chemicals and chemical products are considered essential 

to modern life because of the benefits they provide. Some break 

down quickly, while others persist for long periods of time in 

the environment and may bioaccumulate in the food chain 

(e.g., persistent, bioaccumulative, and toxic chemicals [PBTs]). 

Introduction of chemicals into the environment occurs 

through acts of nature (e.g., volcanoes, hurricanes), spills on 

land, emissions to air, and discharges to water. Chemicals 

can be released through large- and small-scale industrial and 

manufacturing activity, in the production and storage of food 

and consumer products, in efforts to manage or eradicate 

insect-borne diseases (e.g., West Nile virus, Lyme disease), or 

through personal actions such as the use and improper disposal 

of household products (e.g., lawn care materials, pharmaceuticals, cleaning products, batteries, paint, automotive products) 

or wastes. Deliberate application of chemicals to the land is 

widespread in agricultural production to increase crop yields 

and control fungi, weeds, insects, and other pests.

Tracking trends in the use and disposition of chemicals in the 

U.S. is important to better understand the potential for those 

chemicals to affect human health and the environment. Many 

chemicals pose little known hazard to human health or environmental condition, while others pose risk. Many chemicals are 

recognized as carcinogens.23 The effects of chemicals on human 

health and other ecological receptors through environmental 

exposure can be acute and very toxic, subtle and cumulative over 

time, or nonexistent. Chemicals can be of concern because of 

their pervasiveness, potential to accumulate, possibilities of interaction, and often long-term unknown effects on people and the 

environment (e.g., cancer, mercury in fish). Humans and wildlife 

may be affected by certain chemicals through direct exposure, 

including accidental ingestion or inhalation, accumulation and 

uptake through the food chain, or dermal contact. 

Similarly, ecosystems and environmental processes may be compromised or contaminated through the migration and accumulation of chemicals (e.g., via uptake by plants, fugitive dust and 

volatilization, and migration to water supplies). For example, 

excessive nutrient loading from over-fertilization can result 

in runoff that causes adverse effects in aquatic ecosystems.24

Widespread exposure to, or misuse of, pesticides can harm nontargeted plants and animals (including humans), as well as lead 

to development of pesticide-resistant pest species. 

It is difficult to make generalizations about the effects of 

chemicals and chemical usage, not only because there are 

thousands of chemicals, but also because individual chemicals 

have unique ways of being absorbed and handled by living 

organisms. The risks associated with chemicals are dependent 

on many factors, including exposure and toxicity—which 

can be acute or chronic, and can occur at multiple stages of 

the chemical life cycle. Different stages in the life cycle of 

chemicals, such as manufacturing, transport, application or 

use, runoff, or accumulation, pose different hazards to humans 

and the environment. 

4.5.2 ROE Indicators

The amounts and types of chemicals applied or released 

to land through agricultural fertilizers are examined as a 

National Indicator displayed at EPA Regional scale. Three 

other National Indicators are examined, including toxic 

chemicals in production-related wastes, pesticide residues in 

food, and occurrences of pesticide-related incidents reported 

to poison control centers (Table 4-5). 

Trends in the amount of fertilizer used are based on sales data 

provided by major crop-producing states through a survey 

conducted each year since 1960. Acreage estimates are from 

an agricultural census of the 48 contiguous states conducted 

every 5 years since 1954. Trends in the quantities of Toxics 

Release Inventory-reported chemical releases are based on 

annual reports required since 1998 from facilities that meet 

certain size and usage criteria. Trends in the detection of 

pesticide residues in food are derived from randomly sampled 

data collected daily since 1993 from participating states for 

over 50 different commodities. Trends in reported pesticide 

incidents are from a pesticide surveillance system that collects 

data annually from poison control centers around the nation. 

23 U.S. Department of Health and Human Services. 2005. Report on carcinogens. Eleventh edition. Washington, DC: Public Health Service, National 

Toxicology Program.

24 Boesch, D.F., D.M. Anderson, R.A. Horner, S.E. Shumway, P.A. Tester, and 

T.E. Whitledge. 1997. Harmful algal blooms in coastal waters: Options for 

prevention, control, and mitigation. NOAA Coastal Ocean Program Decision 

Analysis Series No. 10. 
LAND

4-30 EPA’s 2008 Report on the Environment

Commercial fertilizers are applied to agricultural crops to increase crop yields. Prior to the 1950s, most farming occurred on small family farms with limited use of 

chemicals. The shift since then to larger corporate farms 

has coincided with the use of chemical fertilizers in modern agricultural practices. The three major types of commercial fertilizer used in the U.S. are nitrogen, phosphate, 

and potash. 

Nitrogen (N) is found primarily in the organic form 

in soils, but can also occur as nitrate. Because nitrate is 

extremely soluble and mobile, it can lead to nuisance algal 

growth, mostly in downstream estuaries, and cause contamination of drinking water. Phosphorus (P) occurs in soil 

in several forms, both organic and inorganic. Phosphorus 

loss due to erosion is common and phosphate, while less 

soluble than nitrate, can easily be transported in runoff. 

Phosphorus/phosphate runoff can lead to nuisance algae 

and plant growth, often in freshwater streams, lakes, and 

estuaries. Potash is the oxide form of potassium (K) and its 

principal forms as fertilizer are potassium chloride, potassium sulfate, and potassium nitrate. When used at recommended application rates, there are few to no adverse effects 

from potassium, but it is a common component of mixed 

fertilizers used for high crop yields and is tracked in the 

fertilizer use surveys conducted.

This indicator shows use of the three major fertilizers in 

pounds per acre of land per year (expressed as N, P, or K) 

used for crop production from 1960 to 2005. Data are from 

an annual survey for agricultural crops conducted by the U.S. 

Department of Agriculture (USDA) National Agricultural 

Statistics Service (NASS) and from the Economic Research 

Service (ERS) Major Land Use series. Acreage used for crop 

production includes cropland harvested and crop failure 

as estimated in the ERS series. Cropland estimates as used 

in this indicator are a subset of agricultural land estimates 

discussed in the Land Cover and Land Use indicators. NASS 

also produces an annual Agricultural Chemical Usage report on 

four to five targeted field crops, based on data compiled from 

the Agricultural Resources Management Survey (ARMS). 

The ARMS surveys farmers in major agriculture-producing 

states that together account for a large percentage of crop 

acreage for corn, soybeans, cotton, and wheat. Results are 

presented for the years 2005-2006 by EPA Region.

What the Data Show 

Based on fertilizer sales data, total use of the three major 

commercial fertilizers has steadily increased, from 46.2 

nutrient pounds per acre per year (lbs/acre/yr) in 1960 to 

138 lbs/acre/yr in 2005, an increase of 199 percent (Exhibit 

4-16). During this period, cropland used for crop production generally has fluctuated between 290 and 360 million 

acres with the largest changes occurring between 1969 

(292 million acres) and 1981 (357 million acres) (Lubowski 

et al., 2006). Since 1996, cropland used for crop production 

has ranged between 321 and 328 million acres (Lubowski 

et al., 2006). Since 1996, aggregate commercial fertilizer 

use has fluctuated between 129 and 145 lbs/acre/yr with 

peak usage in 2004. Since 1960, nitrogen accounted for the 

steepest increase in use, from 17.0 lbs/acre/yr in 1960 to 

81.6 lbs/acre/yr in 2004. Nitrogen currently accounts for 

about 56 percent of total fertilizer use, up from 37 percent 

in 1960. During the same period, phosphate and potash use 

grew more slowly; they remained steady between 25 and 

36 lbs/acre/yr each since the late 1960s and now account 

for approximately 21 percent and 23 percent of total fertilizer usage, respectively.

The four major crops in the U.S.—corn, cotton, soybeans, and wheat—account for about 60 percent of the 

principal crop acreage and receive over 60 percent of the 

N, P, and K used in the U.S. Estimates from annual NASS 

INDICATOR | Fertilizer Applied for Agricultural Purposes

Table 4-5. ROE Indicators of Trends in Chemicals Used on the Land and Their 

Effects on Human Health and the Environment 

National Indicators Section Page

Fertilizer Applied for Agricultural Purposes (N/R) 4.5.2 4-30

Toxic Chemicals in Production-Related Wastes Combusted for Energy 

Recovery, Released, Treated, or Recycled

4.5.2 4-33

Pesticide Residues in Food 4.5.2 4-37

Reported Pesticide Incidents 4.5.2 4-39

N/R = National Indicator displayed at EPA Regional scale
LAND

EPA’s 2008 Report on the Environment 4-31

Acreage reports show that from 1995 to 2006, between 76 

and 80 million acres of corn were planted annually. In 

2007, nearly 93 million acres were planted (USDA NASS, 

2007a). A total of 76.5 million acres of corn were planted 

during the survey year (2005-2006). Corn acreage is concentrated in the center of the country (EPA Regions 5 and 

7), but most EPA Regions grow some corn. Corn typically 

accounts for more than 40 percent of commercial fertilizer 

used (Daberkow and Huang, 2006). 

The acreage of land planted in cotton was 12.4 million 

acres in the most recent ARMS survey year (2006) and has 

ranged between 11 and 16 million acres since 1990. Major 

cotton-producing states include 17 southern states located 

in EPA Regions 4, 6, and 9. 

Production of winter, durum, and other spring wheat 

occurred on about 57 million acres in 2006 and is distributed across EPA Regions 5, 6, 7, 8, and 10. Wheat typically 

accounts for about 10 percent of all commercial fertilizer 

used (Daberkow and Huang, 2006). 

Soybeans were the fastest-growing crop in total acreage, 

increasing from 57.8 million acres in 1990 to 75.5 million acres in 2006 (USDA NASS, 2007c). The majority of 

soybean acreage (80 percent) is concentrated in the upper 

Midwest in EPA Regions 5 and 7. Soybeans require the 

least fertilizer per acre of the four crops described here.

Overall, production of these four crops in the ARMS states 

used slightly more than 13.25 million tons per year (MT/yr) 

of fertilizer in 2005-2006 (Exhibit 4-17) of the 21.7 MT/yr 

estimated (2005-2006 average) by ERS for all crops produced 

in the entire U.S. Of this amount, slightly less than half (5.8 

MT/yr) was applied in EPA Region 5 (Exhibit 4-17), most 

of which was used for corn. An additional 3.7 MT/yr was 

applied in EPA Region 7, primarily on corn or soybeans. 

Indicator Limitations

•	 USDA national estimates of fertilizer use are based on 

sales data provided by states, not actual fertilizer usage, 

and are susceptible to differing reporting procedures or 

accuracy from state to state. 

•	 Data to identify cropland used for crop production are 

from the major land use series discussed in the Land 

Cover and Land Use indicators (pp. 4-7 and 4-14, 

respectively) and do not include Alaska and Hawaii.

•	 Within the ARMS, not all states report fertilizer data 

every year for each crop type, making it difficult to 

establish year-to-year trends (a decrease in fertilizer use 

for a specific crop might be attributed to failure of a 

state to report, rather than an actual decrease of use).

•	 ARMS sampling is limited to program states, which 

represent 82 to 99 percent of crop acreage (across all 

surveyed crops) for the years 2005 and 2006, depending 

on crop type. 

INDICATOR | Fertilizer Applied for Agricultural Purposes (continued) Fertilizer use (nutrient pounds per acre of cropland)

Exhibit 4-16. Commercial fertilizer use in the 

U.S., 1960-2005a

a

Based on sales data. Per-acre use based on the acreage of 

harvested or failed cropland, as determined by USDA’s National 

Agricultural Statistics Service.

Data source: Lubowski, 2006; Wiebe and Gollehon, 2006 

Year

0

20

40

60

80

100

120

140

160

1960 1970 1980 1990 2000 1965 1975 1985 1995 2005

Nitrogen

Phosphate

Potash

Total

Exhibit 4-17. Fertilizer use for four common 

crops (corn, cotton, soybeans, and wheat) in 

major agriculture-producing states, by EPA 

Region, 2005-2006a

EPA Region

Fertilizer use (million nutrient tons)

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

0

1

2

3

4

5

6

7

R2 R3 R4 R5 R6 R7 R8 R9 R10

Potash

Phosphate

Nitrogen

a

Coverage: States surveyed by 

USDA’s Agricultural Resource 

Management Survey (ARMS) 

Program in 2005-2006 for corn, 

cotton, soybeans, and wheat. Each 

commodity was surveyed in a 

different subset of states, which 

together account for a substantial 

portion of the nation’s production of 

that particular commodity. No states in Region 1 were surveyed 

by the ARMS Program for corn, cotton, soybeans, or wheat. 

Data source: USDA NASS, 2006b, 2007b
LAND

4-32 EPA’s 2008 Report on the Environment

•	 The NASS Acreage report has estimates of acreage in 

production for the entire nation by crop, while fertilizer 

sales data are based only on USDA program states. Even 

though USDA program states represent the majority of 

U.S. planted acreage (often over 90 percent), the ability to generalize the data to the country as a whole is 

unknown, as non-program states, while representing a 

small percentage of a crop, might have much different 

application rates due to climate, weather, etc. 

•	 Fertilizer applied to trees that are considered agricultural crops (e.g., nut-producing trees) is included in field 

crop summaries, but fertilizer applied in silviculture 

(e.g., southern pine plantations) is not covered by the 

NASS data collection system.

•	 Loading of nutrients in aquatic systems is not necessarily 

correlated directly with fertilizer use, but rather with the 

levels of fertilizer applied in excess of amounts used by 

crops, natural vegetation, and soil biota.

Data Sources

Exhibit 4-16 is based on two sets of summary data 

from ERS. Annual estimates of fertilizer use from 1960 

through 2005, by nutrient, were obtained from Wiebe 

and Gollehon (2006) (see summary tables, http://www.

ers.usda.gov/Data/FertilizerUse/). Fertilizer use per acre 

was calculated based on annual estimates of the amount 

of cultivated (harvested or failed) cropland from 1960 to 

2005 published in Lubowski et al. (2006) (see summary 

tables, http://www.ers.usda.gov/Data/MajorLandUses/

MLUsummarytables.pdf).

Exhibit 4-17 is based on fertilizer use data from USDA’s 

2005 and 2006 ARMS survey, which were obtained from 

USDA NASS (2006b, 2007b). The published data are by 

state, so additional aggregation was required to report by 

EPA Region (USDA NASS, 2001, 2004, 2005a,b, 2006a).

References

Daberkow, S., and W. Huang. 2006. Nutrient management. In: Wiebe, K., and N. Gollehon, eds. 2006. Agricultural resources and environmental indicators, 2006 edition. 

EIB-16. U.S. Department of Agriculture, Economic 

Research Service. <http://www.ers.usda.gov/publications/

arei/eib16/eib16_4-4.pdf>

Lubowski, R.N., M. Vesterby, S. Bucholtz, A. Baez, and 

M.J. Roberts. 2006. Major uses of land in the United States, 

2002. EIB-14. U.S. Department of Agriculture, Economic 

Research Service. 

<http://www.ers.usda.gov/publications/eib14/> 

USDA NASS (United States Department of Agriculture, 

National Agricultural Statistics Service). 2007a. Acreage. 

<http://usda.mannlib.cornell.edu/usda/current/Acre/

Acre-06-29-2007.pdf>

USDA NASS. 2007b. Agricultural chemical usage, 2006 

field crop summary. May. <http://usda.mannlib.cornell.

edu/usda/current/AgriChemUsFC/AgriChemUsFC

-05-16-2007_revision.pdf>

USDA NASS. 2007c. Crop Production Historical Track 

Records. <http://usda.mannlib.cornell.edu/usda/current/

htrcp/htrcp-04-27-2007.pdf>

USDA NASS. 2006a. Acreage. <http://usda.mannlib.

cornell.edu/usda/nass/Acre/2000s/2006/

Acre-06-30-2006.pdf>

USDA NASS. 2006b. Agricultural chemical usage, 

2005 field crop summary. May. <http://usda.mannlib.

cornell.edu/usda/nass/AgriChemUsFC/2000s/2006/

AgriChemUsFC-05-17-2006.pdf>

USDA NASS. 2005a. Acreage. <http://usda.mannlib.

cornell.edu/usda/nass/Acre/2000s/2005/

Acre-06-30-2005.pdf>

USDA NASS. 2005b. Crop production: 2004 summary. 

Cr Pr 2-1 (05). <http://jan.mannlib.cornell.edu/reports/

nassr/field/pcp-bban/cropan05.pdf> 

USDA NASS. 2004. Acreage. <http://usda.mannlib.cornell.

edu/usda/nass/Acre/2000s/2004/Acre-06-30-2004.pdf>

USDA NASS. 2001. Agricultural chemical usage, 2000 

field crops summary. <http://usda.mannlib.cornell.edu/

reports/nassr/other/pcu-bb/agcs0501.pdf>

Wiebe, K., and N. Gollehon, eds. 2006. Agricultural 

resources and environmental indicators, 2006 edition. 

EIB-16. U.S. Department of Agriculture, Economic 

Research Service. <http://www.ers.usda.gov/Publications/

AREI/EIB16/>

INDICATOR | Fertilizer Applied for Agricultural Purposes (continued)

v
LAND

EPA’s 2008 Report on the Environment 4-33

Toxic chemicals are contained in waste materials produced by a wide variety of industrial activities, in both public 

(e.g., sewage treatment plants) and private facilities. These 

chemical wastes are really a composite matrix of various 

chemicals, some of which may be hazardous or toxic, and 

therefore are subject to reporting under the Toxics Release 

Inventory (TRI) program. Some of these chemicals are 

released onsite or offsite to air, water, or land (including surface impoundments and underground injection wells). The 

rest are treated, recycled, or combusted for energy recovery. 

Reductions in the quantities of TRI chemicals are desirable 

from both environmental and economic perspectives. TRI 

chemicals have known toxic properties, rendering them 

potentially hazardous to workers in both production and 

waste management facilities, and more generally to ecosystems and human health. As elements of overall business 

strategies, companies target waste reduction in ways that 

reduce costs and increase profits.

This indicator tracks trends in the amounts of toxic 

chemicals in production-related wastes that contain 

reported TRI chemicals which are either released to the 

environment or treated, recycled, or combusted for energy 

recovery. Toxic chemicals in non-production-related 

waste, such as might be associated with catastrophic events 

and remedial actions (cleanup), are not included in this 

indicator because they are not directly related to routine 

production practices.

TRI contains information on more than 650 chemicals 

and chemical categories from nine industry sectors, including manufacturing operations, certain service businesses, 

and federal facilities. Facilities are required to report to 

TRI if they employ 10 or more employees, are covered by 

a North American Industry Classification System code corresponding to a TRI-covered Standard Industrial Classification code, and manufacture more than 25,000 pounds, and/

or process more than 25,000 pounds, and/or otherwise use 

more than 10,000 pounds of a TRI-listed non-persistent, 

bioaccumulative, toxic (non-PBT) chemical during a calendar year. In addition, EPA has lowered the TRI reporting 

thresholds for certain PBT chemicals (i.e., to 100 pounds or 

10 pounds, except for dioxin and dioxin-like compounds, 

which have a threshold of 0.1 gram) and added certain other 

PBT chemicals to the TRI list of toxic chemicals. These 

PBT chemicals are of particular concern not only because 

they are toxic but also because they remain in the environment for long periods of time, are not readily destroyed, and 

build up or accumulate in body tissue (U.S. EPA, 2002b). 

EPA currently requires reporting of 16 PBT chemicals 

and four PBT chemical compound categories (U.S. EPA, 

2007b). In 2005, 23,500 facilities reported to TRI (U.S. 

EPA, 2007d). 

TRI is national in coverage and includes all U.S. territories. Because the reporting requirements for TRI have 

varied somewhat between 1998 and 2005 (the most recent 

year for which annual data reports are available in TRI), 

chemicals that were reported consistently from year to year 

over this period are presented separately in this indicator. 

Facilities that manufacture, process, or otherwise use PBT 

chemicals have lower reporting thresholds as established in 

2000 and 2001; hence these data are depicted separately in 

the exhibits. Similarly, metal mining sector land releases 

are analyzed separately because a 2003 court decision 

altered the scope of TRI reporting of these quantities 

(U.S. EPA, 2007a).25

What the Data Show

In 2005 the quantities of TRI non-PBT chemicals associated with production-related wastes tracked in this indicator 

totaled 23.6 billion pounds (Exhibit 4-18, panel A). These 

quantities have decreased by more than 4 billion pounds 

(15.7 percent) since 1998. The decrease was gradual over 

time with the exception of the year 2000, which saw an 

increase of 4.3 billion pounds from the previous year. The 

2000 increase is attributed to a few facilities that reported 

large amounts of onsite treatment and onsite recycling (U.S. 

EPA, 2002a). The amount of TRI non-PBT chemicals 

reported as treated varied between 1998 to 2005, from a 

high of nearly 13 billion pounds in the year 2000 to a low of 

8 billion pounds in 2002. In 2005, the amount treated was 

8.6 billion pounds or 2.9 percent more than in 1998. The 

amount of TRI non-PBT chemicals recycled declined by 

1 billion pounds (11.6 percent) from 1998 to 2005, varying 

from a high of 9.6 billion pounds in 2000 to the low of 8.2 

billion pounds in 2005. TRI non-PBT chemicals managed through energy recovery processes showed a decline 

of 0.62 billion pounds (17.2 percent) in the 8-year period, 

fluctuating between 3.0 and 3.7 billion pounds. Some of the 

year-to-year fluctuations may reflect changes in aggregate 

production levels in the national economy.

Reported PBT chemicals totaled 1.13 billion pounds in 

2005, having declined by 0.18 billion pounds (13.9 percent) 

over recent years since 2001 (Exhibit 4-18, panel B). The 

amount of PBT chemicals recycled declined by 26.6 percent between 2001 and 2005 (0.22 billion pounds). 

Excluding metal mining and PBT chemical releases, 

approximately 3.1 billion pounds of toxic chemicals were 

INDICATOR Toxic Chemicals in Production-Related Wastes Combusted 

for Energy Recovery, Released, Treated, or Recycled

25 The metal mining sector consists of facilities that fall within Standard 

Industrial Classification Code 10 and must report to TRI in accordance 

with Section 313 of the Emergency Planning and Community Right to 

Know Act.
LAND

4-34 EPA’s 2008 Report on the Environment

released offsite or onsite to air, land, or water in 2005. 

The 3.1 billion pounds of releases in 2005 are 18.6 percent 

less than the amount reported in 1998 (Exhibit 4-19, 

panel A). The remaining 19.6 billion pounds of non-PBT 

chemicals from all TRI sectors except metal mining were 

managed (onsite or offsite) through treatment, recycling, 

and energy recovery processes and represent an 8 percent 

decline from 1998.

Excluding metal mining releases, nearly 0.082 billion (82 

million) pounds of PBTs were released offsite or onsite to air, 

land, or water in 2005 (Exhibit 4-19, panel B). The remaining approximately 0.725 billion (725 million) pounds were 

managed (onsite or offsite) through treatment, recycling, and 

energy recovery processes. The amounts of reported PBT 

releases (excluding metal mining) have fluctuated, ranging 

from approximately 110 million pounds in 2003 to 79 million 

pounds in 2004 and 83 million pounds in 2005. 

Between 1998 and 2005 there were also distinct trends 

in media-specific and offsite releases of non-PBT toxic 

chemicals (Exhibit 4-19, panel A). All of these releases 

exclude metal mining. Air releases declined by 28.1 

percent (585 million pounds) between 1998 and 2005. 

Releases to surface waters decreased by 2 percent (nearly 

6 million pounds) and land releases dropped by nearly 18 

percent (183 million pounds). Offsite releases, which cannot be apportioned by medium in TRI, rose by 72 million 

pounds or 18 percent from 1998 to 2005. 

PBT chemicals (also excluding metal mining) released 

to air increased nearly 108 percent (3 million pounds) 

(Exhibit 4-19, panel B). PBT releases to land decreased 24 

percent (14 billion pounds) and to water 22 percent (0.035 

million pounds). Offsite PBT releases increased nearly 8 

percent (2.3 million pounds). 

Excluding PBT chemicals, the metal mining sector 

accounted for 35 percent of the total production-related 

wastes released to the environment over the 8-year period 

from 1998 through 2005, releasing approximately 14 billion 

pounds of total production-related wastes (Exhibit 4-20, 

panel A) compared to 27 billion pounds reported by all 

other industry sectors (Exhibit 4-19, panel A). Nearly all of 

the production-related wastes managed by metal mining 

facilities were releases to land. There is a downward trend 

for the quantities of total releases reported by the metal 

mining sector from 2001 to 2005 (Exhibit 4-20, panel A). 

In 2001, the metal mining industry reported nearly 2 billion 

pounds in total releases, and in 2005, only 0.77 billion 

pounds were reported. Part of this trend can be attributed 

to the court decision (Barrick Goldstrike Mines, Inc., v. EPA) 

in 2003, in which the court determined that non-PBT 

chemicals present in the waste rock below concentrations 

of 1 percent (or 0.1 percent for Occupational Safety and 

Health Administration defined carcinogens) are eligible for 

INDICATOR Toxic Chemicals in Production-Related Wastes Combusted

for Energy Recovery, Released, Treated, or Recycled (continued)

Exhibit 4-18. Quantities of toxic chemicals 

combusted for energy recovery, released, 

recycled, and treated in the U.S., as reported to 

EPA’s Toxics Release Inventory, 1998-2005a,b,c

a

Coverage: Production-related waste from facilities required to 

report to TRI, including more than 650 chemicals and chemical 

categories. Persistent, bioaccumulative, and toxic (PBT) 

chemicals are presented separately because reporting thresholds 

were changed partway through the period of record.

b

Some waste quantities may be double-counted when waste has 

been transferred from one TRI facility (which has counted waste 

as offsite disposal or as other releases) to another TRI facility 

(which has counted transferred waste as onsite disposal or as 

releases to air, land, or water).

c

Percentages reported in the “What the Data Show” section are 

based on the original data, which include more significant 

figures than shown in this exhibit.

Data source: U.S. EPA, 2007e

A. Non-PBT chemicals (1998-2005)

B. PBT chemicals (2001-2005)

Chemicals (billion pounds)

Released 0.43 0.41 0.46 0.45 0.48

0.02 0.03 0.02 0.02 0.02

0.01 0.01 0.004 0.01 0.01

0.84 0.81 0.82 0.81 0.62

1.31 1.25 1.30 1.29 1.13

Recycled

Total

Treated

Combusted for 

energy recovery

0.84 0.81 0.82 0.81

0.62

0.43 0.41 0.46 0.45

0.48

0.0

0.5

1.0

1.5

2001 2002 2003 2004 2005

Chemicals (billion pounds)

Year

Released

Treated

Combusted 

for energy 

recovery

Recycled

0

5

10

15

20

25

30

35

9.2 8.6 9.6 8.9 9.0 8.3 8.5 8.2

3.6 3.4 3.7 3.5 3.7 3.3 3.2 3.0

8.3 9.1

13.0

8.6 8.0 8.2 9.0 8.6

6.8 6.9

6.3

5.2 4.4 4.0 3.8 3.8

1998 1999 2000 2001 2002 2003 2004 2005
LAND

EPA’s 2008 Report on the Environment 4-35

the de minimis exemption. For TRI reporting purposes, the 

de minimis exemption allows facilities to disregard certain 

minimal concentrations of non-PBT chemicals in mixtures or other trade name products when making threshold 

determinations and release and other waste management 

calculations (U.S. EPA, 2007a,c).

The 1.8 billion pounds of released PBT chemicals associated with metal mining make up 80 percent of all PBT 

chemicals released between 2001 and 2005 (Exhibit 4-20, 

panel B). Nearly all of these (99.9 percent) are associated 

with releases to land. Releases of PBTs by the metal mining sector were 16.6 percent higher (56.7 million pounds) 

in 2005 than in 2001. 

Indicator Limitations

•	 TRI data reflect only “reported” chemicals, and not 

all chemicals with the potential to affect human health 

and the environment. TRI does not cover all toxic 

chemicals or all industry sectors. The following are not 

included in this indicator: (1) toxic chemicals that are 

not on the list of approximately 650 toxic chemicals 

and toxic chemical categories, (2) wastes from facilities within industrial categories that are not required to 

report to TRI, and (3) releases from small facilities with 

fewer than 10 employees or that manufactured or processed less than the threshold amounts of chemicals.

INDICATOR Toxic Chemicals in Production-Related Wastes Combusted

for Energy Recovery, Released, Treated, or Recycled (continued)

Exhibit 4-19. Quantities of toxic chemicals released in the U.S., by type of release (excluding metal 

mining), as reported to EPA’s Toxics Release Inventory, 1998-2005a,b Chemicals released (million pounds)

Year

0

500

1,000

1,500

2,000

2,500 Onsite land releases Onsite air releases Onsite surface water discharges Offsite disposal and 

other releases

a

Coverage: Production-related waste from facilities required to report to TRI, including more than 650 chemicals and chemical categories. 

Persistent, bioaccumulative, and toxic (PBT) chemicals are presented separately because reporting thresholds were changed partway through 

the period of record.

b

Some waste quantities may be double-counted when waste has been transferred from one TRI facility (which has counted waste as offsite 

disposal or as other releases) to another TRI facility (which has counted transferred waste as onsite disposal or as releases to air, land, or water). 

Data source: U.S. EPA, 2007e Chemicals released (million pounds)

B. PBT chemicals (2001-2005)

A. Non-PBT chemicals (1998-2005)

’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

Year

0

20

40

60

80

100

Onsite land releases Onsite air releases Onsite surface water discharges Offsite disposal and 

other releases

’01 ’02 ’03 ’04 ’05 ’01 ’02 ’03 ’04 ’05 ’01 ’02 ’03 ’04 ’05 ’01 ’02 ’03 ’04 ’05

0.16 0.12 0.14 0.13 0.12
LAND

4-36 EPA’s 2008 Report on the Environment

•	 TRI chemicals vary widely in toxicity, meaning that 

some low-volume releases of highly toxic chemicals 

might actually pose higher risks than high-volume 

releases of less toxic chemicals. The release or disposal of 

chemicals also does not necessarily result in the exposure 

of people or ecosystems.

•	 Vanadium releases were measured beginning in 2001; 

because the overall amounts were small relative to the 

other wastes, they are included in the 2001 to 2005 data 

for non-PBTs. 

•	 National trends in toxic chemicals in wastes released to the 

environment are frequently influenced by a dozen or so 

large facilities in any particular reporting category. These 

trends may not reflect the broader trends in the more than 

23,000 smaller facilities that report to TRI each year.

•	 Some facilities report offsite transfers for release to other 

TRI-covered facilities that report these quantities as onsite 

releases. This double-counting of release quantities is taken 

into account in the case of release for all sectors in total, but 

not for releases within individual sectors. This may cause 

some discrepancy in certain release numbers for specific 

sectors when compared with release data on all sectors. 

Data Sources

This indicator is based on data and information from EPA’s 

TRI Explorer database (U.S. EPA, 2007e), an online tool that 

allows users to generate customized reports on toxic releases 

reported to TRI and other online resources (U.S. EPA, 2005).

References

U.S. EPA (United States Environmental Protection 

Agency). 2007a. EPA analysis of decision in Barrick 

Goldstrike Mines, Inc. v. Whitman. Accessed November 

28, 2007. <http://www.epa.gov/tri/lawsandregs/barrick_

lawsuit_epa_analysis.htm> (See also http://www.nma.org/

pdf/tri/barrick_decision040203.pdf.)

U.S. EPA. 2007b. Persistent, bioaccumulative, and toxic 

(PBT) chemicals rules. Accessed November 29, 2007. <http://

www.epa.gov/triinter/lawsandregs/pbt/pbtrule.htm#rule>

U.S. EPA. 2007c. Toxic Chemical Release Inventory 

reporting forms and instructions: Revised 2006 version. 

EPA/260/C-06/901. <http://www.epa.gov/tri/report/

TRI_RFI_2006.pdf>

U.S. EPA. 2007d. 2005 TRI public data release ereport. 

<http://www.epa.gov/tri/tridata/tri05/>

U.S. EPA. 2007e. TRI Explorer. Accessed November 20, 

2007. <http://www.epa.gov/triexplorer/>

U.S. EPA. 2005. 2003 TRI public data release ereport. 

EPA/260/R-05/001. <http://www.epa.gov/tri/tridata/

tri03/index.htm>

U.S. EPA. 2002a. 2000 Toxics Release Inventory (TRI) 

public data release report. EPA/260/R-02/003. 

<http://www.epa.gov/tri/tridata/tri00/index.htm>

U.S. EPA. 2002b. 2000 Toxics Release Inventory 

(TRI) public data release report, Executive Summary. 

EPA/260/S-02/001 <http://www.epa.gov/tri/tridata/

tri00/press/execsummary_final.pdf>

INDICATOR Toxic Chemicals in Production-Related Wastes Combusted

for Energy Recovery, Released, Treated, or Recycled (continued)

Exhibit 4-20. Quantities of toxic chemicals 

released in the U.S. by the metal mining sector, 

as reported to EPA’s Toxics Release Inventory, 

1998-2005a,b,c

a

Coverage: Production-related waste from facilities required to 

report to TRI, including more than 650 chemicals and chemical 

categories. Persistent, bioaccumulative, and toxic (PBT) 

chemicals are presented separately because reporting thresholds 

were changed partway through the period of record.

b

Some waste quantities may be double-counted when waste has 

been transferred from one TRI facility (which has counted waste 

as offsite disposal or as other releases) to another TRI facility 

(which has counted transferred waste as onsite disposal or as 

releases to air, land, or water).

c

Percentages reported in the “What the Data Show” section are 

based on the original data, which include more significant 

figures than shown in this exhibit.

Data source: U.S. EPA, 2007e

3.01 3.21

2.59

1.93

1.20

0.89 0.70 0.77

0

1

2

3

4

1998 1999 2000 2001 2002 2003 2004 2005

Year

Chemicals released

(billion pounds)

0.34 0.32 0.35 0.37 0.40

2001 2002 2003 2004 2005

Year

Chemicals released

(billion pounds)

0.0

0.2

0.4

0.6

0.8

1.0

A. Non-PBT chemicals (1998-2005)

B. PBT chemicals (2001-2005)

v
LAND

EPA’s 2008 Report on the Environment 4-37

Pesticides are substances or mixtures of substances intended for preventing, destroying, repelling, or 

mitigating plant or animal pests and may include herbicides, insecticides, fungicides, and rodenticides. More than 

a billion pounds of pesticides are used in the U.S. each 

year to control weeds, insects, and other organisms that 

threaten or undermine human activities (Aspelin, 2003). 

Some of these compounds can be harmful to human health 

if sufficient quantities are ingested, inhaled, or otherwise 

contacted (see the Urinary Pesticide indicator, p. 5-22). 

Potential health effects and primary exposure routes vary 

by chemical. The most common routes of exposure for the 

general population are ingestion of a treated food source 

and contact with applications in or near residential sites. 

Pesticides may also be harmful in the environment when 

non-target organisms are exposed (U.S. EPA, 2007).

This indicator represents data from the U.S. Department of Agriculture’s Pesticide Data Program (PDP), 

which measures residue levels for hundreds of pesticides 

and their metabolites in fruits, vegetables, grains, meat, 

and dairy products from across the country, sampling 

different combinations of commodities each year. The 

analysis examines pesticides currently on the market and 

also includes continued testing for some persistent and 

bioaccumulative pesticides that have been banned since 

the 1970s, such as aldrin/dieldrin, heptachlors, and DDT 

and its metabolites. PDP data collection began in 1991 and 

includes both domestic and foreign-produced commodities. Results are published in annual reports, which include 

statistics on the number of pesticide residues detected, the 

number of residues exceeding the tolerance established 

by EPA for a given pesticide-commodity pair (Code of 

Federal Regulations, Title 40, Part 180), and the number of residues detected for which no tolerance has been 

established. This indicator depicts data from 1994 to 2005; 

data from before 1994 are considered less reliable. Between 

1994 and 2005, the number of food samples analyzed per 

year ranged from 5,771 (1996) to 13,693 (2005), with a 

general increase over time.

What the Data Show

The percent of samples with no detectable pesticide residues generally increased during the period from 1994 to 

2002 (Exhibit 4-21). Samples with no detects accounted for 

38.5 percent of samples analyzed in 1994 and rose to 57.9 

percent of samples in 2002. Data for 2003 and thereafter 

cannot be compared directly to the previous years’ data due 

to a change in the way that detects are counted. Data for 

2004 and 2005 show a lower percentage of samples with no 

detects than 2003 data, going from 53.9 percent of samples 

in 2003 to 29.5 percent in 2004 and 33.7 percent in 2005. 

The largest jump in detects in the 2003-2004 time frame 

was in those samples with detection of one pesticide or 

metabolite. These trends in number of detections have 

occurred at the same time that analytical limits of detection for various compounds have been decreasing, allowing 

the instruments to pick up ever smaller concentrations. 

Exhibit 4-22 illustrates the percentage of samples in 

which at least one pesticide residue was detected at a 

concentration exceeding the tolerance established by EPA 

for a given pesticide-commodity pair. The percentage of 

samples exceeding EPA tolerance values increased from 

0.05 percent in 1994 to 0.31 percent in 2003. Compared to 

2003, the last 2 years of data show a drop in exceedances, 

with 0.17 percent in 2004 and 0.18 percent in 2005.

Indicator Limitations

•	 As Exhibit 4-21 explains, pesticide detection data from 

2002 and earlier cannot be compared directly with data 

gathered after 2002. (Before 2003, each compound 

detected was counted separately; beginning in 2003, 

measurement of a parent compound and/or any of its 

metabolites was counted as a single detect.) 

INDICATOR | Pesticide Residues in Food

Exhibit 4-21. Pesticide detections in food in the 

U.S., 1994-2005a,b Percent of samples

Year

0

1

2

3

4 or more

a

Coverage: Based on a survey of fruits, 

vegetables, grains, meat, and dairy products 

across the U.S., with different combinations 

of commodities sampled in different years. 

Samples were analyzed for more than 290 

pesticides and their metabolites.

b

Data from 2003 to 2005 are not comparable 

to prior years due to a difference in how 

detects were counted. Prior to 2003, each 

compound detected was counted as a 

separate “residue.” Beginning in 2003, parent 

compounds and their metabolites were combined to report the 

number of “pesticides.” For example, a sample with positive 

detections for endosulfan I, endosulfan II, and endosulfan sulfate 

would have been counted as three residues in 2002. In 2003, this 

sample would have been counted as one pesticide detection. 

Data source: USDA Agricultural Marketing Service, 1996-2006a,b

0

20

40

60

80

100

1994 1995 1996 1997 1998 1999 2000 2001 2002 2004 2005 2003

Number of 

residues 

detected:b
LAND

4-38 EPA’s 2008 Report on the Environment

•	 The PDP does not sample all commodities over all 

years, so some gaps in coverage exist. Differences in 

the percent of detections for any given pesticide class 

might not be due to an increase (or decrease) in the 

predominance of detectable residues. Instead, these differences might simply reflect the changing nature and 

identity of the commodities selected for inclusion in any 

given time frame.

•	 The indicator measures pesticide residue related to dietary intake, which does not directly correlate to toxicological effects in humans or effects on the environment. 

Data Sources

Data for this indicator were obtained from a series of annual 

summary reports published by the PDP (USDA Agricultural 

Marketing Service, 1996-2006). These reports are all available from http://www.ams.usda.gov/science/pdp/. The Food 

and Drug Administration also collects data (not reported 

here) on pesticide residues in cooked food that may be a 

source of chemicals in human diets. These data are available 

at http://www.cfsan.fda.gov/~dms/pesrpts.html.

References

Aspelin, A.L. 2003. Pesticide usage in the United States: 

Trends during the 20th century. Raleigh, NC: Center for 

Integrated Pest Management, North Carolina State University. <http://www.pestmanagement.info/pesticide_

history/index.pdf>

USDA Agricultural Marketing Service. 2006a. Pesticide 

Data Program: Annual summary, calendar year 2005. 

<http://www.ams.usda.gov/science/pdp/Summary2005.pdf>

USDA Agricultural Marketing Service. 2006b. Pesticide 

Data Program: Annual summary, calendar year 2004. 

<http://www.ams.usda.gov/science/pdp/Summary2004.pdf>

USDA Agricultural Marketing Service. 2005. Pesticide 

Data Program: Annual summary, calendar year 2003. 

<http://www.ams.usda.gov/science/pdp/Summary2003.pdf>

USDA Agricultural Marketing Service. 2004. Pesticide 

Data Program: Annual summary, calendar year 2002. 

<http://www.ams.usda.gov/science/pdp/Summary2002.pdf>

USDA Agricultural Marketing Service. 2003. Pesticide 

Data Program: Annual summary, calendar year 2001. 

<http://www.ams.usda.gov/science/pdp/Summary2001.pdf>

USDA Agricultural Marketing Service. 2002. Pesticide 

Data Program: Annual summary, calendar year 2000. 

<http://www.ams.usda.gov/science/pdp/Summary2000.pdf>

USDA Agricultural Marketing Service. 2001. Pesticide 

Data Program: Annual summary, calendar year 1999. 

<http://www.ams.usda.gov/science/pdp/Summary1999.pdf>

USDA Agricultural Marketing Service. 2000. Pesticide 

Data Program: Annual summary, calendar year 1998. 

<http://www.ams.usda.gov/science/pdp/Summary1998.pdf>

USDA Agricultural Marketing Service. 1999. Pesticide 

Data Program: Annual summary, calendar year 1997.

<http://www.ams.usda.gov/science/pdp/Summary1997.pdf>

USDA Agricultural Marketing Service. 1998. Pesticide 

Data Program: Annual summary, calendar year 1996.

<http://www.ams.usda.gov/science/pdp/Summary1996.pdf>

USDA Agricultural Marketing Service. 1997. Pesticide 

Data Program: Annual summary, calendar year 1995.

<http://www.ams.usda.gov/science/pdp/Summary1995.pdf>

USDA Agricultural Marketing Service. 1996. Pesticide 

Data Program: Annual summary, calendar year 1994. 

<http://www.ams.usda.gov/science/pdp/Summary1994.pdf>

U.S. EPA. 2007. Data requirements for pesticide registration. Accessed November 28, 2007. <http://www.epa.gov/

pesticides/regulating/data_requirements.htm>

INDICATOR | Pesticide Residues in Food (continued) Percent of samples exceeding one or more tolerance levels 

Exhibit 4-22. Pesticides exceeding EPA 

tolerance levels in food in the U.S., 1994-2005a

a

Coverage: Based on a survey of fruits, vegetables, grains, meat, 

and dairy products across the U.S., with different combinations of 

commodities sampled in different years. Samples were analyzed 

for more than 290 pesticides and their metabolites. 

Data source: USDA Agricultural Marketing Service, 1996-2006a,b

Year

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

’94 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

v
LAND

EPA’s 2008 Report on the Environment 4-39

Although pesticides play a role in protecting human health, food, and crops, they pose a risk of poisoning when not used and/or stored properly. The American 

Association of Poison Control Centers (AAPCC) collects 

statistics on poisonings and represents the single largest 

source of information on acute health effects of pesticides 

resulting in symptoms and requiring health care (Calvert et 

al., 2001). The data include incidents related to individual 

pesticides and to mixtures of products (about 8 percent of 

reports). The data also include intentional exposures (suicide 

attempts and malicious use), which account for less than 3 

percent of reports. The AAPCC uses the Toxic Exposure 

Surveillance System (TESS) to collect information on all 

reported incidents. 

This indicator is based on data from TESS-published 

reports for the years 1986 through 2005. During this 

period, at least 50 percent of the U.S. population was 

covered by poison control centers (PCCs) reporting to the 

national database. Annual reports of incidents were divided 

by the percent of U.S. population served to estimate the 

total incidents nationwide, and divided by the total 

U.S. population to develop the incidence rate. Only calls 

with known outcomes are reported here; this may introduce some bias, because the percent of all reported pesticide incidents with a known outcome declined from 71 

percent in 1986-1988 to just 41 percent in 2004-2005. The 

2004-2005 data are averaged over 2 years; all other data 

are grouped into 3-year periods and presented as average 

annual rates to facilitate identification of trends. 

What the Data Show 

Between the 1986-1988 and 2001-2003 periods, there 

was an overall 40 percent decline in reported pesticide 

incidents in the U.S. In 2004-2005, however, there was a 

slight rise compared to 2001-2003, primarily in the “other 

insecticides” and “all other pesticides” categories (Exhibit 

4-23). The single largest decline occurred for the category 

of organophosphate (OP) insecticides, which saw nearly a 

79 percent drop in reported incidents between 1986-1988 

and 2004-2005. Part of the decline in reported OP-related 

incidents may be due to the substitution of other, less toxic 

insecticides for some of the OPs over time. 

Indicator Limitations 

•	 Misclassification of incidents may occur when incidents 

reported over the phone are not verified by laboratory 

tests. For example, a child found holding a pesticide 

container may not have actually been exposed, but if a 

call is received by a PCC poison specialist who determines that the reported symptoms were consistent with 

the toxicology, dose, and timing of the incident, the 

call will be registered as an incident. About 13 percent 

of calls to PCCs arise from health care professionals, but 

the majority are calls made by victims or their relatives 

or caretakers. Although some misclassification can be 

expected to occur, it is assumed to be non-differential 

among the different types of pesticides.

•	 Only calls with known outcomes are reported in this 

indicator. This may introduce some bias, because the 

percent of all reported pesticide incidents with known 

outcomes declined from 71 percent in 1986-1988 to just 

41 percent in 2004-2005.

•	 The data collection process is standardized for PCCs, 

but is a passive system. Under-reporting of incidents is a 

serious shortcoming. Studies show that medical facilities 

generally report between 24 and 33 percent of incidents 

from all substances to PCCs (Chafee-Bahamon et al., 

1983; Harchelroad et al., 1990; Veltri et al., 1987). 

•	 Data are collected by multiple poison centers, with 

follow-up likely performed in different ways. 

Data Sources

This indicator is based on summary data from annual 

reports published by the TESS (Litovitz et al., 1987-2002; 

Watson et al., 2003-2005; Lai et al., 2006) (available from 

http://www.aapcc.org/poison1.htm). Annual data from 

INDICATOR | Reported Pesticide Incidents

Exhibit 4-23. Reported pesticide incidents per 

million U.S. population by type of pesticide, 

1986-2005a,b Average number of reported incidents per year (per million population served)

Reporting period

0

20

40

60

80

100

120

140

1986-

1988

1989-

1991

1992-

1994

1995-

1997

1998-

2000

2004-

2005

2001-

2003

Disinfectants

Organophosphates

Other insecticides

Herbicides

Fungicides

Rodenticides

All other pesticides

a

This indicator tracks pesticide incidents 

reported to poison control centers 

(PCCs) that report to the AAPCC 

national database. The rate of reported 

incidents is calculated based on the 

population served by these PCCs.

b

The 2004-2005 data are averaged 

over 2 years. All other data are averaged 

over 3-year intervals. 

Data source: Lai et al., 2006; Litovitz et 

al., 1987-2002; Watson et al., 2003-2005
LAND

4-40 EPA’s 2008 Report on the Environment

these reports were grouped into 3-year periods, with the 

exception of 2004-2005 where only 2 years of data were 

grouped together, and incidence rates were calculated from 

the population served by participating PCCs; population 

figures can also be found in the annual reports. Only summary data are publicly available; raw data from individual 

cases are considered confidential.

References 

Calvert, G.M., M. Barnett, J.M. Blondell, L.N. Mehler, 

and W.T. Sanderson. 2001. Surveillance of pesticide-related 

illness and injury in humans. In: Krieger, R., ed. Handbook of pesticide toxicology. Second edition. San Diego, 

CA: Academic Press. pp. 603-641.

Chafee-Bahamon, C., D.L. Caplan, and F.H. Lovejoy. 

1983. Patterns in hospital’s use of a regional poison information center. Am. J. Public Health 73:396-400. 

Harchelroad, F., R.F. Clark, B. Dean, and E.P. Krenzelok. 

1990. Treated vs. reported toxic exposures: Discrepancies 

between a poison control center and a member hospital. 

Vet. Hum. Toxicol. 32:156-159. 

Lai, M.W., W. Klein-Schwartz, G.C. Rodgers, J.Y. Abrams, 

D.A. Haber, A.C. Bronstein, and K.M. Wruk. 2006. 2005 

annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Clin. 

Toxicol. 44:803-932. <http://www.aapcc.org/2005.htm>

Litovitz, T.L., W. Klein-Schwartz, G.C. Rodgers, Jr, 

D.J. Cobaugh, J. Youniss, J.C. Omslaer, M.E. May, A.D. 

Woolf, and B.E. Benson. 2002. 2001 annual report of 

the American Association of Poison Control Centers 

Toxic Exposure Surveillance System. Am. J. Emerg. Med. 

20(5):391-452. <http://www.aapcc.org/2001.htm>

Litovitz, T.L., W. Klein-Schwartz, S. White, D.J. 

Cobaugh, J. Youniss, J.C. Omslaer, A. Drab, and B.E. 

Benson. 2001. 2000 annual report of the American 

Association of Poison Control Centers Toxic Exposure 

Surveillance System. Am. J. Emerg. Med. 19(5):337-395. 

<http://www.aapcc.org/2000.htm>

Litovitz, T.L., W. Klein-Schwartz, S. White, D.J. Cobaugh, 

J. Youniss, A. Drab, and B.E. Benson. 2000. 1999 annual 

report of the American Association of Poison Control Centers 

Toxic Exposure Surveillance System. Am. J. Emerg. Med. 

18(5):517-571. <http://www.aapcc.org/1999.htm>

Litovitz, T.L., W. Klein-Schwartz, E.M. Caravati, J. Youniss, 

B. Crouch, and S. Lee. 1999. 1998 annual report of the 

American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. Emerg. Med. 17(5):435-487. 

<http://www.aapcc.org/1998.htm>

Litovitz, T.L., W. Klein-Schwartz, K.S. Dyer, M. Shannon, S. Lee, and M. Powers. 1998. 1997 annual report 

of the American Association of Poison Control Centers 

Toxic Exposure Surveillance System. Am. J. Emerg. Med. 

16(5):443-497. <http://www.aapcc.org/19971.htm>

Litovitz, T.L., M. Smilkstein, L. Felberg, W. KleinSchwartz, R. Berlin, and J.L. Morgan. 1997. 1996 annual 

report of the American Association of Poison Control 

Centers Toxic Exposure Surveillance System. Am. J. 

Emerg. Med. 15(5):447-500. 

<http://www.aapcc.org/1996.htm>

Litovitz, T.L., L. Felberg, W. Klein-Schwartz, and S. 

White. 1996. 1995 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. Emerg. Med. 14(5):487-537. 

<http://www.aapcc.org/1995.htm>

Litovitz, T.L., L. Felberg, R.A Soloway, M. Ford, and R. 

Geller. 1995. 1994 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance 

System. Am. J. Emerg. Med. 13(5):551-597. 

<http://www.aapcc.org/1994.htm> 

Litovitz, T.L., L.R. Clark, and R.A Soloway. 1994. 1993 

annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. 

Emerg. Med. 12(5):546-584. 

<http://www.aapcc.org/1993.htm>

Litovitz, T.L., K.C. Holm, C. Clancy, B.F. Schmitz, 

L.R. Clark, and G.M. Oderda. 1993. 1992 annual report 

of the American Association of Poison Control Centers 

Toxic Exposure Surveillance System. Am. J. Emerg. Med. 

11(5):494-555. <http://www.aapcc.org/1992.htm>

Litovitz, T.L., K.C. Holm, K.M. Bailey, and B.F. Schmitz. 

1992. 1991 annual report of the American Association of 

Poison Control Centers Toxic Exposure Surveillance System. Am. J. Emerg. Med. 10(5):452-504. 

<http://www.aapcc.org/1991.htm>

Litovitz, T.L., K.M. Bailey, B.F. Schmitz, K.C. Holm, 

and W. Klein-Schwartz. 1991. 1990 annual report of the 

American Association of Poison Control Centers Toxic 

Exposure Surveillance System. Am. J. Emerg. Med. 

9(5):461-509. <http://www.aapcc.org/1990.htm>

Litovitz, T.L., B.F. Schmitz, and K.M. Bailey. 1990. 1989 

annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. 

Emerg. Med. 8(5):394-442. 

<http://www.aapcc.org/1989.htm>

INDICATOR | Reported Pesticide Incidents (continued)
LAND

EPA’s 2008 Report on the Environment 4-41

Litovitz, T.L., B.F. Schmitz, and K.C. Holm. 1989. 1988 

annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. 

Emerg. Med. 7(5):495-545. 

<http://www.aapcc.org/1988.htm>

Litovitz, T.L., B.F. Schmitz, N. Matyunas, and T.G. Martin. 1988. 1987 annual report of the American Association 

of Poison Control Centers Toxic Exposure Surveillance 

System. Am. J. Emerg. Med. 6(5):479-515. <http://www.

aapcc.org/1987.htm>

Litovitz, T.L., T.G. Martin, and B. Schmitz. 1987. 1986 

annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. 

Emerg. Med. 5(5):405-445. 

<http://www.aapcc.org/1986.htm>

Veltri, J.C., N.E. McElwee, and M.C. Schumacher. 1987. 

Interpretation and uses of data collected in poison control 

centers in the United States. Med. Toxicol. 2:389-397.

Watson, W.A., T.L. Litovitz, G.C. Rodgers, W. KleinSchwartz, N. Reid, J. Youniss, A. Flanagan, and K.M. 

Wruk. 2005. 2004 Annual Report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am. J. Emerg. Med. 23:589-666. <http://

www.aapcc.org/2004.htm>

Watson, W.A., T.L. Litovitz, W. Klein-Schwartz, G.C. 

Rodgers, Jr., J. Youniss, N. Reid, W.G. Rouse, R.S. Rembert, and D. Borys. 2004. 2003 annual report of the American Association of Poison Control Centers Toxic Exposure 

Surveillance System. Am. J. Emerg. Med. 22(5):335-404. 

<http://www.aapcc.org/2003.htm>

Watson, W.A., T.L. Litovitz, G.C. Rodgers, Jr., W. KleinSchwartz, J. Youniss, S.R. Rose, D. Borys, and M.E. May. 

2003. 2002 annual report of the American Association of 

Poison Control Centers Toxic Exposure Surveillance System. Am. J. Emerg. Med. 21(5):353-421. 

<http://www.aapcc.org/2002.htm>

INDICATOR | Reported Pesticide Incidents (continued)

v

4.5.3 Discussion

What These Indicators Say About Trends in 

Chemicals Used on the Land and Their Effects 

on Human Health and the Environment

These indicators provide information on aspects of chemical 

use and effects. Data are presented on the amounts and types 

of chemical usage for two large sectors of the U.S. economy—

agriculture and manufacturing. The disposition of pesticides 

in food and the number of reported pesticide incidents are 

examined. Two indicators describe stressors to the environment from chemical usage. 

The amount of chemicals deliberately applied to agricultural 

land as commercial fertilizer has increased over the last 40 

years (Agricultural Fertilizer indicator, p. 4-30). Per acre total 

fertilizer use has nearly tripled since 1960, with peak usage 

occurring in 2004. Total nitrogen use has more than quadrupled over the same period. While fertilizers themselves are not 

inherently harmful, when applied improperly or in quantities above the level taken up by crops, streamside vegetation, 

or soil biota, they have the potential to contaminate ground 

water and surface water in agricultural watersheds and estuaries. Fertilizer usage in recent years, for major crops, appears 

concentrated in the states surrounding the Mississippi River. 

The Toxics Release Inventory (TRI) data (Toxic Chemicals in 

Wastes indicator, p. 4-33) show a small but steady decline in the 

quantities of TRI chemicals released to all media between 1998 

and 2005, with the exception of offsite releases (persistent, bioaccumulative, and toxic or otherwise), which increased slightly. 

Residues of potentially harmful substances used in food 

production, such as some pesticides, are assessed under food 

protection programs. While national-level indicators on the 

use and application of pesticides and pesticide loads in soil are 

lacking, the Pesticide Residues in Food indicator (p. 4-37) is 

an indirect measure of ambient conditions, providing insight 

into potential exposures from the most widely used pesticide 

products on the market. The indicator shows that between 

2003 and 2005 (after a change in sampling technique), pesticide residues were detected in 46 percent of the food commodities tested in 2003 and in 66 to 71 percent of the food 

commodities tested in 2004 and 2005. Currently available 

technology used in the U.S. Department of Agriculture’s Pesticide Data Program sampling can detect pesticide residues at 

concentrations that are orders of magnitude lower than those 

determined to have potential human health effects. Therefore, 

the number of pesticide detections that exceed federally established tolerance levels is perhaps more relevant. Results over 

the years suggest less than 1 percent of commodities tested 

were above tolerance levels.

Similarly, the Pesticide Incidents indicator (p. 4-39) provides 

information on the potential for human exposure to toxic 

substances through misuse. Reported incidents of pesticide 

exposure, which represent accidental exposure to a pesticide 

that is readily available to the public, declined between 1986 

and 2003, then rose slightly in 2004-2005. The largest decline 

occurred in organophosphate compounds, a group of insecticides that are acutely toxic to humans (and other vertebrates) 

but do not accumulate in the environment, unlike other toxic 

materials (or compounds containing them) such as chromium, 

arsenic, and heavy metals.
LAND

4-42 EPA’s 2008 Report on the Environment

Limitations, Gaps, and Challenges

While chemicals in soil or on plants may be an initial pathway 

into the environment, it is the movement and concentration 

of chemicals through the food chain that are often of greatest 

concern, as well as exposures from other media such as contaminated water or air. The indicators provide information on 

a relatively small universe of toxic chemicals and only limited 

information on the potential exposures humans may experience as a consequence of chemical use. 

Fertilizer use in agriculture has been identified as one of the 

principal uses of chemicals responsible for nutrient loading 

into non-targeted water bodies and for nonpoint source loading of nutrients within agricultural watersheds.26 Actual fertilizer use data are not available nationally. The Agricultural 

Fertilizer indicator (p. 4-30) is supported by sales data that 

do not consider mitigating factors (e.g., slow-release formulations) or agricultural practices that reduce runoff. The cost of 

fertilizer accounts for a relatively high percentage of agricultural costs, so it is generally assumed that purchased products 

eventually are applied in agricultural operations. Agricultural 

sources of fertilizer, however, are only estimated to be 85 

percent of all sources, with the remaining being primarily 

professional lawn care, consumer retail, and golf courses. The 

usage patterns associated with these nonagricultural sources 

are unknown. Additionally, the urban and suburban watersheds, where these non-tracked uses occur, are also locations 

where nutrient runoff may result from other sources such as 

turf runoff, septic systems, and sewage treatment plants. 

The indicators do not provide information related to the land 

application of sludges27 that may contain toxic metals and 

other persistent bioaccumulative substances. Sludges may be 

applied as fertilizer on agricultural or forest land in accordance 

with EPA requirements, but the implications for wildlife, 

aquatic organisms, and movement through the food chain are 

unknown. Additionally, the indicators reported provide only 

limited information on the potential exposures that target 

organisms other than humans may experience as a consequence of chemical use.

TRI data include information on a range of chemical categories such as arsenic, cyanide, dioxin, lead, mercury, and 

nitrate compounds, but do not reflect a comprehensive total 

of toxic releases nationwide. They do not include all toxic 

chemicals with the potential to affect human health and the 

environment, nor do they include all sources of potential 

releases. Facilities report release and other waste management data using various techniques, which include estimations based on emission factors, mass balancing approaches, 

engineering calculations, and actual monitoring. Estimation 

techniques and factors considered may vary widely, making 

it difficult to ensure the accuracy of reporting. TRI data only 

represent a portion of the chemical life cycle (e.g., wastes as a 

result of production) and do not take into account amounts of 

chemicals incorporated into industrial and/or consumer products that also have the potential to affect the environment and 

human health when they are used, discarded, or recycled.

There is no existing reporting system that provides information on the volume, distribution, and extent of pesticide use 

in the U.S. Estimates are developed based on information 

available through a variety of reports from multiple governmental and non-governmental entities on pesticide sales, crop 

profiles, and expert surveys. The Pesticide Residues in Food 

indicator (p. 4-37) provides information on one aspect of the 

potential for human exposure from pesticides (dietary intake 

from the commercial food supply), but does not provide a 

complete picture of all the ways in which humans can be 

exposed to pesticides, which include contaminated drinking 

water, pesticide drift, and dermal contact. 

4.6 What Are the Trends 

in Contaminated Land 

and Their Effects on 

Human Health and the 

Environment?

4.6.1 Introduction

There are many settings for contaminated lands, ranging from 

abandoned buildings in inner cities to large areas contaminated with toxic materials from past industrial or mining 

activities. Contaminated lands include sites contaminated 

by improper handling or disposal of toxic and hazardous 

materials and wastes, sites where toxic materials may have 

been deposited as a result of wind or flood, and sites where 

improper handling or accidents resulted in release of toxic or 

hazardous materials that are not wastes. 

Land contamination can result from a variety of intended, 

accidental, or naturally occurring activities and events such 

as manufacturing, mineral extraction, abandonment of 

mines, national defense, waste disposal, accidental spills, 

illegal dumping, leaking underground storage tanks, hurricanes, floods, pesticide use, and fertilizer application. Sites are 

categorized in a variety of ways, often based on the level and 

type of contamination and the regulations under which they 

are monitored and cleaned up. Box 4-1 provides an overview 

of the common types of contaminated sites. With the exception of accidental spills and contamination that result from 

naturally occurring and other unanticipated events, most land 

contamination is the result of historical activities that are no 

longer practiced. Hazardous material and waste management 

and disposal are now highly regulated.

26 Howarth, R.W., D. Walker, and A. Sharpley. 2002. Sources of nitrogen pollution to coastal waters of the United States. Estuaries 25:656-676.27 Sludges are the nutrient-rich organic materials resulting from sewage and 

wastewater treatment processes. Sludges contain many of the nutrients required 

for improved plant growth (nitrogen, phosphorus, and potassium) and other 

organic matter that can improve overall soil condition and increase productivity.
LAND

EPA’s 2008 Report on the Environment 4-43

Contaminated soils can leach toxic chemicals into nearby 

ground or surface waters, where these materials can be taken 

up by plants and animals, contaminate a human drinking water 

supply, or volatilize and contaminate the indoor air in overlying buildings. In dry areas, contamination in soil can be further 

distributed through wind-borne dusts. Once soil contamination migrates to waterways, it may also accumulate in sediments, which can be very difficult to remediate and may affect 

local ecosystems and human health. Humans can be harmed 

by contact with toxic and hazardous materials on a contaminated site via exposure to contaminated land, air, surface water, 

and ground water. When contaminated lands are not properly 

managed, humans and wildlife can be exposed to contaminants 

through inhalation, ingestion, or dermal contact. The risks of 

human exposure are site-specific and difficult to generalize at 

the national level. Potential effects may be acute or chronic. 

Some contaminated sites pose little risk to human health and 

the environment, because the level of contamination is low 

and the chance of exposure to toxic or hazardous contaminants is also low. Other contaminated sites are of greater concern because of the chemicals that may be present and their 

propensity to persist in or move through the environment, 

exposing humans or the environment to hazards. These sites 

must be carefully managed through containment or cleanup 

to prevent hazardous materials from causing harm to humans, 

wildlife, or ecological systems, both on- and offsite. 

Nationally, there are thousands of contaminated sites of varying size and significance. Many sites, particularly the largest 

Superfund National Priorities List sites: These sites 

are seriously contaminated and include industrial facilities, 

waste management sites, mining and sediment sites, and 

federal facilities such as abandoned mines; nuclear, biological, chemical, and traditional weapons productions plants; 

and military base industrial sites (e.g., used for aircraft and 

naval ship maintenance). 

Resource Conservation and Recovery Act (RCRA) 

Cleanup Baseline facilities: The RCRA Cleanup Baseline is a priority subset of a broader universe of facilities 

that are subject to cleanup under RCRA due to past or 

current treatment, storage, or disposal of hazardous wastes 

and have historical releases of contamination. 

Underground storage tanks/leaking underground 

storage tanks: Businesses, industrial operations, gas stations, and various institutions store petroleum and hazardous 

substances in large underground storage tanks that may fail 

due to faulty materials, installation, operating procedures, 

or maintenance systems, causing contamination of soil and 

ground water.

Accidental spill sites: Each year, thousands of oil, gas, 

and chemical spills occur on land and in water from a 

variety of types of incidents, including transportation (e.g., 

rail, barges, tankers, pipeline) and facility releases. 

Sites contaminated by natural disasters or terrorist activities: Disasters of any sort, naturally occurring or 

caused by humans, have the potential to contaminate lands 

and cause problems at already-contaminated sites. 

Land contaminated with radioactive and other 

hazardous materials: Many sites spanning a large area 

of land in the U.S. are contaminated with radioactive and 

other hazardous materials as a result of activities associated 

with nuclear weapons production, testing, and research. 

Brownfields: Brownfields are real property where expansion, redevelopment, or reuse may be complicated by the 

presence or potential presence of a hazardous substance, 

pollutant, or contaminant. Brownfields are often found in 

and around economically depressed neighborhoods. 

Military bases and defense sites: Some of the millions 

of acres of land used by the Department of Defense are 

contaminated from releases of hazardous substances and 

pollutants; discarded munitions, munitions constituents, 

and unexploded ordnance; and building demolition and 

debris. 

Low-level area-wide contamination: Some soil 

contamination problems involve low to moderate levels 

of contamination that encompass large geographic areas 

ranging in size from several hundred acres to many square 

miles. Low-level, area-wide contamination can occur from 

emissions related to past industrial operations (e.g., smelters), widespread agricultural pesticide applications, combustion of gasoline, and deterioration of lead-based paint. 

Past waste management sites and illegal dumping 

sites: Prior to the 1970s, solid waste was typically placed 

in unlined landfills that were not adequately designed to 

prevent adverse environmental impacts to ground water 

or surface water. Separately, illegal dumping of materials 

such as construction waste, abandoned automobiles, appliances, household waste, and medical waste, has occurred 

for decades and still occurs because of convenience and the 

cost of legal disposal. 

Abandoned and inactive mine lands: Abandoned and 

inactive mines may not have been properly cleaned up, and 

may have features ranging from exploration holes to fullblown, large-scale mine openings, pits, waste dumps, and 

processing facilities.

Box 4-1. Categorizing Contaminated Lands 
LAND

4-44 EPA’s 2008 Report on the Environment

and most severely contaminated, are tracked at the national 

level, but many others are tracked only at state or local levels. 

The number and status of contaminated sites changes frequently as sites are newly contaminated (e.g., via spills or hurricanes), discovered, documented, and cleaned up. 

4.6.2 ROE Indicators

The ROE indicators for this question focus on the trends in 

reducing potential threats to human health associated with 

site contamination at some lands contaminated by a variety of 

industrial and other activities and from current and past waste 

management activities (Table 4-6). The indicators address sites 

on the Superfund National Priorities List and facilities on the 

Resource Conservation and Recovery Act Cleanup Baseline 

where human exposure to contamination and migration of 

contaminated ground water have been documented to be 

within acceptable established health-based levels. 

Trends in the spread of contaminated ground water and 

potential human exposure to contaminants in excess of 

health-based standards are assessed through site-specific 

monitoring and modeling data collected by site personnel. 

Site data and conditions are generally reviewed and confirmed 

by federal and/or state program managers annually, or more 

frequently if site conditions warrant. 

The EPA Superfund and Resource Conservation and Recovery Act (RCRA) Programs conduct a number 

of activities to address the nation’s most severely contaminated lands. The Programs investigate and collect data on 

potentially contaminated sites to determine whether they 

are contaminated and require cleanup. When a potentially 

hazardous waste site is reported to EPA, trained inspectors 

determine whether the site presents a hazard to human 

health and the environment. Sites that pose the greatest 

threat are placed on the Superfund National Priorities List 

(NPL) or RCRA Cleanup Baseline. For RCRA, “sites” 

are more commonly referred to as RCRA Corrective 

Action Facilities.

One of the priorities for both the NPL and RCRA 

Cleanup Baseline sites is safeguarding against human 

exposures to site contamination. EPA and state officials 

determine whether there is a reasonable expectation that 

humans are exposed to site contamination and if interim 

actions are needed to reduce or eliminate all current human 

exposure in excess of health-based standards. Such activities may include removing and/or isolating contaminated 

media, providing alternative water supplies, and restricting 

access or other land use controls. Exposure at levels below 

the standards is considered protective (i.e., under control). 

Although these standards may vary from state to state, EPA 

believes that they fall within an acceptable range for gauging whether human health is protected (U.S. EPA, 2005b). 

Determinations of human exposure at levels of concern are 

based on site-specific characterization information and monitoring data (usually many analytical samples) pertaining to 

relevant environmental media (e.g., soil, indoor air, outdoor 

air, ground water, and surface water), current human activity patterns, and actions taken to prevent human exposure. 

All potential exposure routes are assessed, including inhalation, dermal contact, and ingestion of the contaminated 

media or food affected by contaminated media (U.S. EPA, 

1999, 2005b). 

This indicator describes the numbers of NPL Indicator 

Baseline sites and RCRA Cleanup Baseline sites for which 

government officials have determined that (1) humans are 

not exposed to contamination in excess of health-based 

standards (i.e., exposure is under control); (2) humans are 

reasonably expected to be exposed to contamination in 

excess of health-based standards; or (3) insufficient information exists to make a finding of exposure to contamination in excess of health-based standards. The intention of 

the indicator is not to capture an “action” or “administrative determination” on the part of EPA, but to characterize 

INDICATOR Current Human Exposures Under Control at High-Priority 

Cleanup Sites

Table 4-6. ROE Indicators of Trends in Contaminated Land and Their 

Effects on Human Health and the Environment

National Indicators Section Page

Current Human Exposures Under Control at High-Priority Cleanup Sites 4.6.2 4-44

Migration of Contaminated Ground Water Under Control at High-Priority 

Cleanup Sites

4.6.2 4-47
LAND

EPA’s 2008 Report on the Environment 4-45

Exhibit 4-24. Status of current human 

exposures under control at high-priority cleanup 

sites in the U.S., fiscal years 2000-2007

Fiscal year

Number of sites

B. Superfund National Priorities List 

Indicator Baseline sites (2002-2007)b

0

500

1,000

1,500

2,000

a

The RCRA Cleanup Baseline changed in 2006 from 1,714 to 

1,968 sites.

b

The Superfund NPL Indicator Baseline changed in 2005 from 

1,494 to 1,544 sites and in 2006 from 1,544 to 1,554 sites. 

c

For RCRA Cleanup Baseline sites and Superfund NPL Indicator 

Baseline sites, “insufficient data” includes sites officially 

classified as “insufficient data” or “no status.”

Data source: U.S. EPA, 2005a, 2006, 2007a,b,c

Under control 

(no human 

exposure to 

contamination 

in excess of 

health-based 

standards)

Reasonable 

expectation 

that exposure 

is occurring 

above 

health-based 

standards

Insufficient

datac

2002

1,494

2003

1,494

2004

1,494

2005

1,544

2006

1,554

2007

1,554

Number of sites

Fiscal year

A. RCRA Cleanup Baseline sites (2000-2007)a

0

500

1,000

1,500

2,000

2000

642

(37%

of 

total)

225

847

1,714

2001

823

(48%

of 

total)

703

188

1,714

2002

1,018

(59%

of 

total)

146

550

1,714

2003

1,246

(73%

of 

total)

91

377

1,714

2004

1,440

(84%

of 

total)

62

212

1,714

2005

1,649

(96%

of 

total)

20

45

1,714

2006

1,747

(89%

of 

total)

15

206

1,968

2007

1,830

(93%

of 

total)

15

123

1,968

120

175

109

158

101

146

148

161

113

172

109

163

1,199

(80%

of 

total)

1,227

(82%

of 

total)

1,247

(83%

of 

total)

1,235

(80%

of 

total)

1,269

(82%

of 

total)

1,282

(82%

of 

total)

INDICATOR Current Human Exposures Under Control at High-Priority 

Cleanup Sites (continued)

environmental conditions relevant to the risk to human 

health from contaminants at RCRA Cleanup Baseline and 

NPL Indicator Baseline sites. 

What the Data Show

In 2007, there were 1,968 sites on the RCRA Cleanup 

Baseline (U.S. EPA, 2007a). Of these, the percentage of 

sites where human exposure to contamination was under 

control increased from 37 percent (642 sites out of 1,714) in 

fiscal year (FY) 2000 to 93 percent (1,830 sites out of 1,968) 

in FY 2007 (Exhibit 4-24, panel A). This increase represents a combination of sites where mitigation has prevented 

exposure to contaminants and sites where there are sufficient 

data to show that exposure to contaminated media was not 

a problem, regardless of mitigation. The percentage of sites 

where officials had reasonable expectations that humans 

were exposed to contamination in excess of health-based 

standards has decreased from 13 percent (225 sites out of 

1,714) in FY 2000 to less than 1 percent (15 sites out of 

1,968) in FY 2007. 

As of September 2007, there were 1,554 sites on the NPL 

that were categorized as “Final” or “Deleted” (U.S. EPA, 

2007b,c). These are referred to as the Superfund NPL Indicator Baseline. The Superfund NPL Indicator Baseline sites 

where human exposure to contamination was under control increased as a percentage of the total: 80 percent (1,199 

of 1,494 sites) in 2002 and 82 percent (1,282 of 1,554 sites) 

in 2007 (Exhibit 4-24, panel B). As of the end of FY 2007, 

officials determined that there were reasonable expectations that humans were exposed to contamination in excess 

of health-based standards at 7 percent (109 out of 1,554) 

of the NPL Indicator Baseline sites. This is a decrease 

from 2002, when the percentage was 8 percent (120 out 

of 1,494). In 2007, there was insufficient information to 

confirm whether humans were exposed to contamination 

in excess of health-based standards at 10 percent (163 out of 

1,554) of the sites. 

Indicator Limitations

•	 The NPL does not represent all of the contaminated or 

potentially contaminated sites listed in the Comprehensive 

Environmental Response, Compensation, and Liability 

Information System (CERCLIS) database, which contains 

information on thousands of hazardous waste sites, potential hazardous waste sites, and remedial activities across the 

nation. A small percentage (less than 1 percent) of the total 

number of final and deleted NPL sites are excluded from 

the Indicator Baseline for reasons of consistency.
LAND

4-46 EPA’s 2008 Report on the Environment

•	 The indicator results are presented for the 1,714 

RCRA Cleanup Baseline sites tracked from 2000 to 

2005 and the 1,968 sites tracked in 2006 and 2007, and 

not the entire group of approximately 3,476 hazardous waste management facilities currently believed to 

be subject to RCRA Corrective Action requirements 

(e.g., initial assessments and if needed more thorough 

investigations and cleanups) (see http://www.epa.gov/

epaoswer/hazwaste/ca/lists/2020scc.pdf). 

•	 The indicator does not typically make measurements 

of exposure biomarkers among potentially exposed 

individuals at the NPL Indicator Baseline or RCRA 

Cleanup Baseline sites, but relies on environmental 

measures at or near the point of exposure and activities 

that should prevent exposure to contaminants.

•	 Concentrations of toxic and hazardous contaminants 

that must not be exceeded to designate a site as having/not having human exposures to contamination in 

excess of health-based standards vary from state to state, 

although they fall within a range determined to be acceptable to EPA (U.S. EPA, 2005a,b). 

•	 The indicator is based on certification by a responsible 

official that the criteria necessary to designate a site as 

having/not having human exposures to contamination 

in excess of health-based standards have been met (U.S. 

EPA, 1999, 2005a,b). The trend in the number of sites 

may be underestimated to the extent that certification 

lags behind the potential human exposure to contamination or certification is delayed due to insufficient or 

outdated information.

•	 This approach may not take into account certain risks 

(e.g., endocrine disruptors) where specific risk levels 

(e.g., to human health) may not have been established. 

•	 Some new sites (e.g., those created with the “reportable 

quantity” spill response program) as well as other known 

sites (e.g., spills) are not included in this indicator. 

Data Sources

Data for this indicator were provided by EPA’s Office of 

Solid Waste and Emergency Response (OSWER). A list 

showing the current status of every RCRA baseline site is 

published online (U.S. EPA, 2007a). A discussion of NPL 

indicators is available (U.S. EPA, 2005a); information on 

the current status of any individual NPL site can be queried 

using EPA’s CERCLIS database (U.S. EPA, 2006) (http://

cfpub.epa.gov/supercpad/cursites/srchsites.cfm). Data for 

previous years are not publicly accessible, however, and must 

be requested from OSWER.

References

U.S. EPA (United States Environmental Protection Agency). 

2007a. Facilities on the RCRA 2008 GPRA corrective 

action baseline. Report generated 10/25/2007. <http://

www.epa.gov/epaoswer/hazwaste/ca/lists/base08st.pdf>

U.S. EPA. 2007b. Final NPL sites—by site name (as of 

October 26, 2007). Accessed November 25, 2007. 

<http://www.epa.gov/superfund/sites/query/queryhtm/

nplfin1.htm> <http://www.epa.gov/superfund/sites/npl/

newfin.htm>

U.S. EPA. 2007c. National Priorities List (NPL) advanced 

query form. NPL status: Deleted from the final NPL. 

Accessed November 25, 2007. <http://www.epa.gov/

superfund/sites/query/advquery.htm#siteident> 

U.S. EPA. 2006. CERCLIS database. Accessed September 14, 2006. <http://cfpub.epa.gov/supercpad/cursites/

srchsites.cfm>

U.S. EPA. 2005a. Draft Superfund environmental 

indicators guidance manual: Long-term human health 

revisions. <http://www.epa.gov/superfund/accomp/ei/

eiguidance.pdf> 

U.S. EPA. 2005b. Frequently asked questions—human 

exposure under control (HE) and migration of contaminated 

ground water under control (GM) environmental indicators. 

<http://www.epa.gov/superfund/accomp/ei/ei_faqs.pdf>

U.S. EPA. 1999. Interim-final guidance for RCRA corrective 

action environmental indicators. <http://www.epa.gov/

epaoswer/hazwaste/ca/eis/ei_guida.pdf>

INDICATOR Current Human Exposures Under Control at High-Priority 

Cleanup Sites (continued)

v
LAND

EPA’s 2008 Report on the Environment 4-47

The EPA Superfund and Resource Conservation and Recovery Act (RCRA) Programs conduct a number 

of activities to address the nation’s most severely contaminated lands. The Programs investigate and collect data on 

potentially contaminated sites to determine whether they 

are contaminated and require cleanup. When a potentially 

hazardous waste site is reported to EPA, trained inspectors determine whether the site presents a hazard to human 

health and the environment. Sites that pose the greatest 

threat are placed on the National Priorities List (NPL) or 

RCRA Cleanup Baseline. 

One of the priorities for both the NPL and RCRA 

Cleanup Baseline sites is preventing the continued spread 

of contaminated ground water, often referred to as 

“plumes” of contaminated ground water. Protecting the 

ground water is especially important in areas where it is 

the primary source for drinking water and irrigation, or a 

potential source for future water supplies.

EPA and state officials determine that the migration of 

contaminated ground water is under control (i.e., not continuing to spread in concentrations above levels of concern) 

when ongoing monitoring shows that the contaminant 

plume is not expanding or negatively impacting surface 

waters (U.S. EPA, 1999). Preventing further migration 

of contaminated ground water may result from an action 

taken, such as installation of a “pump and treat” or subsurface barrier system, or because of natural attenuation of the 

contaminants. A determination of whether migration has 

been prevented is based on monitoring data (usually from 

hundreds of analytical samples) collected from ground 

water wells located within and surrounding the spatial 

extent of the ground water plume (U.S. EPA, 1999, 2005c).

This indicator describes the percentage of NPL Indicator Baseline sites and RCRA Cleanup Baseline sites where 

government officials have determined that contaminated 

ground water is not continuing to spread in concentrations 

above levels of concern (e.g., that exceed the appropriate drinking water standards). This indicator covers both 

“Final” and “Deleted” NPL Indicator Baseline sites, and 

all 1,968 RCRA Cleanup Baseline sites. The percentage 

of sites where ground water contamination continues to 

spread is also noted, as well as the number of sites where 

there are insufficient data to make a finding. The intention 

of the indicator is not to capture an “action” or “administrative determination” on the part of EPA, but to convey 

the underlying pressure on the environment and potential for human health effects resulting from contaminated 

ground water.

What the Data Show

In 2007, there were 1,968 sites on the RCRA Cleanup 

Baseline. Of the high-priority RCRA Cleanup Baseline 

sites, the percentage of sites where contaminated ground 

water has been determined to be under control increased 

from 32 percent (554 out of 1,714 sites) in fiscal year (FY) 

2000 to 79 percent (1,548 out of 1,968 sites) in FY 2007 

(Exhibit 4-25, panel A). This increase represents a combination of sites where mitigation has halted the spread of 

contaminated ground water and sites where sufficient data 

have been collected to show that contaminated ground 

water migration was not continuing, regardless of mitigation activities. The percentage of sites where officials have 

determined that contaminated ground water was spreading 

above levels of concern decreased from 18 percent (306 

out of 1,714 sites) in FY 2000 to less than 5 percent (94 out 

of 1,968 sites) in FY 2007. These sites, and the remaining 

326 sites for which there are still insufficient data to make 

a determination at the end of FY 2007, tend to be very 

complex sites where the appropriate data have yet to be 

collected due to high costs or technical difficulties. 

Ground water has not been an issue at all Superfund 

NPL sites. Of those Final and Deleted NPL Indicator Baseline sites where ground water contamination is present, the 

percentage where contaminated ground water has been 

determined to be under control increased from 61 percent 

(772 of 1,275 sites) in FY 2002 to 70 percent (977 of 1,392 

sites) (Exhibit 4-25, panel B). As of the end of FY 2007, 

contaminated ground water was confirmed to be spreading 

above levels of concern at 15 percent (213) of these NPL 

sites, while the remaining 15 percent (202 sites) had insufficient data to confirm whether contaminated ground water 

is spreading above levels of concern. These percentages do 

not include NPL Indicator Baseline sites classified as “nonground water” sites. 

Indicator Limitations

•	 The NPL does not represent all of the contaminated 

or potentially contaminated sites listed in the Comprehensive Environmental Response, Compensation, 

and Liability Information System (CERCLIS) database, 

which contains information on thousands of hazardous 

waste sites, potential hazardous waste sites, and remedial 

activities across the nation. A small percentage (less than 

1 percent) of the total number of final and deleted NPL 

sites are excluded from the NPL Indicator Baseline for 

reasons of consistency. 

•	 The indicator covers the 1,714 RCRA Cleanup Baseline sites tracked from 2000 to 2005 and the 1,968 sites 

tracked in 2006 and 2007, and not the entire group 

of 3,746 hazardous waste management sites currently 

believed to be subject to RCRA Corrective Action requirements (i.e., initial assessments, and if needed more 

thorough investigations and cleanups).

INDICATOR Migration of Contaminated Ground Water Under Control at 

High-Priority Cleanup Sites
LAND

4-48 EPA’s 2008 Report on the Environment

•	 The extent to which people have been affected, or could 

be affected, by the contaminated ground water at NPL 

or RCRA Cleanup Baseline sites is not considered in 

this indicator, but is addressed in the Current Human 

Exposures Under Control at High-Priority Cleanup 

Sites indicator (p. 4-44).

•	 The indicator does not address ground water contaminated at other types of sites, such as sites with leaking 

underground storage tanks and other sites being addressed solely by state cleanup programs.

•	 Concentrations of toxic and hazardous contaminants in 

ground water that must not be exceeded to designate a 

site as under control vary somewhat from state to state, 

though they fall within a range determined to be acceptable to EPA (U.S. EPA 2005a,c). 

•	 This indicator is based on the certification by a responsible official that the criteria necessary to designate 

whether contaminated ground water is continuing to 

spread above levels of concern have been met (U.S. EPA, 

1999, 2005a,b). Trends in the number of sites where the 

spread of contaminated ground water has been shown to 

occur above levels of concern may be underestimated to 

the extent that certification lags behind the migration of 

contaminated ground water or certification is delayed due 

to insufficient or outdated information. 

Data Sources

Data for this indicator were provided by EPA’s Office 

of Solid Waste and Emergency Response (OSWER). A 

list showing the current status of every RCRA baseline 

site is published online (U.S. EPA, 2007). A summary 

of the status of Superfund NPL sites is available online 

(U.S. EPA, 2005c); information on the current status 

of any individual NPL site can be queried using EPA’s 

CERCLIS database (U.S. EPA, 2006) (http://cfpub.epa.

gov/supercpad/cursites/srchsites.cfm). Data for previous 

years are not publicly accessible, however, and must be 

requested from OSWER.

References

U.S. EPA (United States Environmental Protection 

Agency). 2007. Facilities on the RCRA 2008 GPRA 

corrective action baseline. Report generated 10/25/2007. 

<http://www.epa.gov/epaoswer/hazwaste/ca/lists/

base08st.pdf>

U.S. EPA. 2006. CERCLIS database. Accessed September 

14, 2006. <http://cfpub.epa.gov/supercpad/cursites/

srchsites.cfm>

INDICATOR Migration of Contaminated Ground Water Under Control at 

High-Priority Cleanup Sites (continued)

Exhibit 4-25. Status of migration of contaminated 

ground water under control at high-priority 

cleanup sites in the U.S., fiscal years 2000-2007 Number of sites

Fiscal year

Fiscal year

Number of sites

A. RCRA Cleanup Baseline sites (2000-2007)a

B. Superfund National Priorities List 

Indicator Baseline sites (2002-2007)b

0

500

1,000

1,500

2,000

2000 2001 2002 2003 20052004 2006 2007

0

500

1,000

1,500

2,000

2002 2003 2004 2005 2006 2007

a

The RCRA Cleanup Baseline changed in 2006 from 1,714 to 

1,968 sites.

b

The Superfund NPL Indicator Baseline changed in 2005 from 

1,494 to 1,544 sites and in 2006 from 1,544 to 1,554 sites.

c

For RCRA Cleanup Baseline sites and Superfund NPL Indicator 

Baseline sites, “insufficient data” includes sites officially 

classified as “insufficient data” or “no status.”

d

For calculating the percentage of Superfund NPL Indicator 

Baseline sites in the “under control” category, the total does not 

include “non-ground water” sites.

Data source: U.S. EPA, 2005c, 2006, 2007

Under control 

(contaminated 

ground water 

is not continuing to spread 

in concentrations above 

levels of 

concern)d

Contaminated 

ground water 

is spreading 

above levels 

of concern

Insufficient

datac

Non-ground 

water sites

1,494 1,544 1,554 1,554 1,494 1,494

306

854

271

734

231

610

191

475

157

358

115

257

100

416

94

1,714 1,714 1,714 1,714 1,714 1,714 326

1,968 1,968

1,342

(78% 

of 

total)

1,199

(70% 

of 

total)

1,548

(79% 

of 

total)

1,452

(74% 

of 

total)

1,048

(61% 

of 

total)

554

(32% 

of 

total)

709

(41% 

of 

total)

873

(51% 

of 

total)

772

(61%

 of

 total)

291

212

219

248

201

219

247

178

188

212

226

169

213

221

162

213

202

162

826

(65%

 of

 total)

881

(67%

 of

 total)

937

(68%

 of

 total)

958

(69%

 of

 total)

977

(70%

 of

 total)
LAND

EPA’s 2008 Report on the Environment 4-49

U.S. EPA. 2005a. Draft Superfund environmental indicators 

guidance manual: Long-term human health revisions. 

<http://www.epa.gov/superfund/accomp/ei/eiguidance.pdf>

U.S. EPA. 2005b. Frequently asked questions—human 

exposure under control (HE) and migration of contaminated groundwater under control (GM) environmental 

indicators. <http://www.epa.gov/superfund/accomp/ei/

ei_faqs.pdf>

U.S. EPA. 2005c. Migration of contaminated ground 

water under control. Accessed December 13, 2005.

<http://www.epa.gov/superfund/accomp/ei/gw.htm>

U.S. EPA. 1999. Interim-final guidance for RCRA 

corrective action environmental indicators. <http://www.

epa.gov/epaoswer/hazwaste/ca/eis/ei_guida.pdf>

INDICATOR Migration of Contaminated Ground Water Under Control at 

High-Priority Cleanup Sites (continued)

4.6.3 Discussion

What These Indicators Say About Trends in 

Contaminated Lands and Their Effects on 

Human Health and the Environment

The indicators provide insights into trends in protecting 

humans and ground water from the nation’s most contaminated 

lands. In 2007, 93 percent of the facilities on the Resource 

Conservation and Recovery Act (RCRA) Cleanup Baseline 

sites showed that human exposure to contamination in excess 

of health-based standards was being prevented, while ground 

water was not spreading above levels of concern at 79 percent 

of the facilities. Similarly in 2007, the Superfund National 

Priorities List (NPL) Indicator Baseline sites showed that human 

exposure to contamination in excess of health-based standards 

has been prevented at 82 percent of the sites, and ground water 

has been prevented from spreading above levels of concern at 70 

percent of the sites with ground water contamination. 

Limitations, Gaps, and Challenges

The two ROE indicators are limited in their ability to address 

the question. Currently, there is no single information source that 

tracks the extent of contaminated land nationwide. A substantial 

amount is known about thousands of the most contaminated 

sites on the Superfund NPL Indicator Baseline sites and facilities on the RCRA Cleanup Baseline, which have been the focus 

of in-depth studies and resource-intensive cleanup operations. 

Although these facilities are some of the most seriously contaminated sites in the country, they do not reflect the full universe of 

contaminated sites or even the full universe of seriously contaminated sites. EPA would like to have information on other sites 

that require extensive cleanup, including sites contaminated with 

radioactive materials from historical nuclear weapons production, 

sites with leaking underground storage tanks, smaller accidental 

spill sites, and other cleanup sites managed by a variety of local, 

state, and federal authorities. Collectively, these contaminated 

sites outnumber the combined Superfund NPL Indicator Baseline 

sites and RCRA Cleanup Baseline facilities. 

EPA would also like to have information on the actual or 

potential acreage of contaminated land and is developing data 

for sites subject to Agency cleanup programs. Additionally, 

EPA would like to better understand the types of contamination from all sources nationally. Even where national data on 

contaminated sites are available, the affected area and the types 

and severity of contamination vary widely from site to site, 

making accurate trend analysis, aggregation, and generalization difficult or impossible. There is no comprehensive data 

source to determine the extent of these lands, populations that 

may be affected, and the potential for contamination to have 

harmful human health or ecological effects. Further, EPA is 

interested in knowing how much previously contaminated 

land has been returned to productive uses. Data associated 

with the use of previously contaminated land could help 

answer the question of trends and effects of contaminated land 

and the question of trends and effects of land use. 

Current gaps in data on contaminated lands stem from a variety 

of factors and challenges, including the multi-jurisdictional 

responsibilities for identifying, managing, and cleaning up 

contaminated lands; a focus in most contaminated lands data 

sets on measures of regulatory compliance and associated activities; high costs to identify, inventory, study, and clean up large, 

complicated sites; and complexity in the effects of contaminated 

lands on human health and the environment, including unique 

site characteristics and the inability to generalize information 

over large geographic areas.

v

Chapter 5

Human Exposure 

and Health
Contents

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

5.1.1 The Environmental Public Health Paradigm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

5.1.2 Establishing Linkages Between Environmental Contaminants and Health Outcomes . . . . . . 5-5

5.1.3 Overview of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5.1.4 Organization of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

5.2 What Are the Trends in Human Exposure to Environmental Contaminants, Including 

Across Population Subgroups and Geographic Regions? . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

5.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

5.2.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

5.3 What Are the Trends in Health Status in the United States? . . . . . . . . . . . . . . . . . . . . . . . 5-31

5.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31

5.3.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

5.3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-38

5.4 What Are the Trends in Human Disease and Conditions for Which Environmental 

Contaminants May Be a Risk Factor, Including Across Population Subgroups and 

Geographic Regions? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-39

5.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-39

5.4.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-42

5.4.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-68
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-3

5.1 Introduction

T

he health of the human population can be influenced by 

many factors, one of which is exposure to environmental 

contamination. Protecting human health from the effects 

of environmental contaminants is therefore an integral part of 

EPA’s mission. Protecting, sustaining, or restoring the health of 

people and communities is central to EPA’s various research 

and regulatory programs. In fulfilling its mission, EPA examines 

the human health impacts of contamination (physical, chemical, biological, or radiological) in air, in water, and on the land. 

Thorough study of adverse health effects associated with environmental contaminants enables the Agency to evaluate harmful 

levels of exposure and issue guidelines for the safe production, 

handling, and management of hazardous substances. 

As described in Chapters 2 through 4, people can be exposed 

to environmental contaminants in a variety of ways, and many 

contaminants are known to be or suspected of causing human 

disease. Identifying (1) the extent to which human exposures 

may be occurring or may have occurred and (2) measures of 

health outcomes possibly influenced by environmental exposures is important in determining where further study or public 

health interventions may be necessary. For example, the presence or patterns of elevated levels of environmental contaminants, as measured in human tissue through biomonitoring, is 

of interest. Similarly, a high or increasing rate of a particular 

cancer for which a hazardous substance in the environment 

may be a contributing factor is of interest. In addition, tracking 

exposures and health condition across segments of the population such as gender, race or ethnicity, or geographic location 

helps to identify differences across subgroups and guide public 

health decisions and strategies.

In this chapter, EPA seeks to assess trends in human exposure and 

disease or conditions that may be associated with environmental 

factors on a national scale. Biomonitoring and health outcome 

indicators are presented to address three fundamental questions: 

•	 What are the trends in human exposure to environmental contaminants, including across population 

subgroups and geographic regions? Data on trends 

in exposure levels provide an opportunity to evaluate the 

extent to which environmental contaminants are present 

in human tissue, independent of the occurrence of specific diseases or conditions. To address this question, this 

chapter focuses on biomonitoring indicators (or biomarkers 

of exposure) for environmental contaminants such as lead, 

mercury, and pesticides. 

•	 What are the trends in health status in the United 

States? Here the report uses several general health outcome 

indicators (life expectancy, infant mortality, and general 

mortality) to provide a broad picture of health in the U.S. 

Trends in these indicators provide a general context for 

understanding trends in specific diseases and conditions that 

may in part be linked with the environment. 

•	 What are the trends in human disease and conditions for which environmental contaminants may 

be a risk factor, including across population subgroups and geographic regions? This question looks at 

the occurrence of diseases and conditions that are known 

ROE Approach

This 2008 Report on the Environment:

•	 Asks questions that EPA considers 

important to its mission to protect 

human health and the environment. 

•	 Answers these questions, to the extent 

possible, with available indicators.

•	 Discusses critical indicator gaps, limitations, and challenges that prevent the 

questions from being fully answered.

ROE Questions

The air, water, and land chapters (Chapters 

2, 3, and 4) ask questions about trends in 

the condition and/or extent of the environmental medium; trends in stressors to 

the medium; and resulting trends in the 

effects of the contaminants in that medium 

on human exposure, human health, and 

the condition of ecological systems. 

The human exposure and health and 

ecological condition chapters (Chapters 

5 and 6) ask questions about trends in 

aspects of health and the environment 

that are influenced by many stressors 

acting through multiple media and by 

factors outside EPA’s mission. 

ROE Indicators

An indicator is derived from actual measurements of a pressure, state or ambient 

condition, exposure, or human health or 

ecological condition over a specified geographic domain. This excludes indicators 

such as administrative, socioeconomic, and 

efficiency indicators.

Indicators based on one-time studies are 

included only if they were designed to serve 

as baselines for future trend monitoring. 

All ROE indicators passed an independent 

peer review against six criteria to ensure 

that they are useful; objective; transparent; 

and based on data that are high-quality, 

comparable, and representative across space 

and time. 

Most ROE indicators are reported at the 

national level. Some national indicators 

also report trends by region. EPA Regions 

were used, where possible, for consistency 

and because they play an important role in 

how EPA implements its environmental 

protection efforts.

Several other ROE indicators describe 

trends in particular regions as examples of 

how regional indicators might be included 

in future versions of the ROE. They are 

not intended to be representative of trends 

in other regions or the entire nation.

EPA will periodically update and revise 

the ROE indicators and add new indicators 

as supporting data become available. In the 

future, indicators will include information 

about the statistical confidence of status 

and trends. Updates will be posted electronically at http://www.epa.gov/roe.

Additional Information

You can find additional information about 

the indicators, including the underlying data, metadata, references, and peer 

review, at http://www.epa.gov/roe.

EPA’s 2008 Report on the Environment (ROE): Essentials
HUMAN EXPOSURE AND HEALTH

5-4 EPA’s 2008 Report on the Environment

or suspected to be caused (to some degree) or exacerbated 

by exposures to environmental contaminants. This chapter 

uses a spectrum of indicators for health outcomes—such as 

cancer, asthma, and birth outcomes—to address this question. Both morbidity and mortality statistics are considered.

These ROE questions are posed without regard to whether 

indicators are available to answer them. This chapter presents the 

indicators available to answer these questions, and also points out 

important gaps where nationally representative data are lacking.

This chapter is not intended to be exhaustive in addressing 

these questions, nor is it intended to be a risk assessment or 

epidemiological study. Rather, it provides an overview of 

selected indicators of human exposure and disease over space 

and time, based on key data sources with sufficiently robust 

design and quality assurance. 

The indicators used here are based on data sets representative of the national population; they are not based on data 

from targeted populations or tied to specific exposures or 

releases. Therefore, these data sets cannot and should not be 

used to draw conclusions about linkages or causal relationships 

between a particular health outcome and contaminant; nor is 

it possible to directly link the health outcome or biomonitoring indicators to any of the indicators of emissions or ambient 

pollutants in air, land, or water presented in earlier chapters 

of this report. Though the chapter does not assess quantitative 

relationships between the measures of environmental contaminants and diseases, it does present some qualitative discussion 

of the research that has examined some of these relationships 

to help explain why EPA has included particular indicators. 

Sections 5.1.1 and 5.1.2 detail important principles guiding the 

selection and interpretation of exposure and health indicators 

used in this report.

5.1.1 The Environmental Public 

Health Paradigm

The relationship among and between environmental contamination, exposure, and disease is complex. Development of 

disease is multi-faceted. Relationships between environmental 

exposures and various health outcomes can only be established 

through well-designed epidemiological, toxicological, and 

clinical studies. An understanding of these factors provides 

critical context for this chapter. 

The environmental public health paradigm shown in Exhibit 

5-11 illustrates the broad continuum of factors or events that 

may be involved in the potential development of human 

disease following exposure to an environmental contaminant. 

This series of events serves as the conceptual basis for understanding and evaluating environmental health. The exhibit 

illustrates that for adverse health effects (clinical disease or 

death) to occur, many things have to happen. A contaminant 

must be released from its source, reach human receptors (via 

air, water, or land), enter the human body (via inhalation, 

ingestion, or skin contact), and be present within the body at 

sufficient doses within individuals to cause biological changes 

that may ultimately result in an observed adverse health effect.

The paradigm, however, is a linear, schematic depiction of a 

process that is complex and multi-factorial. Exposure to an 

environmental contaminant is rarely the sole cause of an adverse 

1 Adapted from: Sexton, K., S.G. Selevan, D.K. Wagener, and J.A. Lybarger. 

1992. Estimating human exposures to environmental pollutants: Availability 

and utility of existing databases. Arch. Environ. Health 47(6):398-407.

Exposure in the ambient 

environment

Air, water, and land 

(Chapters 2-4)

Contaminant 

formation and release 

from source

Transport/transformation 

in the ambient 

environment

Exhibit 5-1. Environmental public health paradigm

 Source: Adapted from Sexton et al., 1992

- Individual

- Community

- Population

Entry into body 

(dose)

Altered 

structure/function

Adverse health 

outcomes

Biomonitoring 

indicators

Health outcome 

indicators
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-5

health outcome. Environmental contaminant exposure is just 

one of several factors that can contribute to disease occurrence or to the severity of a preexisting disease. Among the 

other factors are diet, exercise, alcohol consumption, individual 

genetic makeup, medications, and other pre-existing diseases. 

Asthma, for example, can be triggered by environmental insult, 

but environmental exposures are not the “cause” of all asthma 

attacks. In addition, different contaminants can be a risk factor 

for the same disease. Taking the same example, outdoor air pollution and certain indoor air pollutants, such as environmental 

tobacco smoke, can both exacerbate asthma symptoms. Further, 

susceptibility to disease is different for each person; some individuals may experience effects from certain ambient exposure 

levels while others may not. 

Each block in Exhibit 5-1 can have indicators associated with 

it. As shown, aspects of Chapters 2 through 4 may address 

contaminant formation, release, transport, and transformation in the environment. Those chapters present indicators 

for the presence of contaminants or other stressors affecting 

air, water, and land, sometimes at locations in which people 

may be exposed. Measurements of ambient exposure levels 

are different than the biomonitoring indicators (biomarkers of 

exposures) introduced in this chapter. Other types of biomarkers exist (e.g., biomarkers of susceptibility and biomarkers of 

effect); because national-scale data do not exist for these biomarkers, they are not covered in this chapter at this time. 

The presence of a contaminant in the environment or within 

human tissue alone does not mean disease will occur. Furthermore, identification of diseases for which environmental contaminants are risk factors does not mean exposure has occurred 

or contributed to that disease. However, extensive and collaborative data collection and research efforts across the scientific 

community continue to strengthen our understanding of the 

relationships between environmental exposures and disease. 

This chapter uses indicators that are tied into the environmental 

public health paradigm as one tool for discerning notable trends 

in exposure and health. First, EPA presents biomonitoring indicators to illustrate the general extent to which people are being 

exposed to environmental contaminants. Second, indicators 

of overall health status and specific diseases and conditions are 

used to identify potential morbidity/mortality patterns, again 

recognizing that environmental exposures are only one factor 

that could influence reported trends. 

5.1.2 Establishing Linkages 

Between Environmental 

Contaminants and Health 

Outcomes

EPA uses the results of scientific research to help identify linkages between exposure to environmental contaminants and 

certain diseases, conditions, or other health outcomes. EPA 

relies on the possible linkages established through these types 

of studies to identify environmental contaminants and health 

outcomes of potential Agency interest (e.g., the indicators 

used in this chapter). Examples include radon and lung cancer; 

arsenic and cancer in several organs; lead and nervous system 

disorders; disease-causing bacteria (such as E. coli O157:H7) 

and gastrointestinal illness and death; and particulate matter and aggravation of cardiovascular and respiratory diseases. 

Such relationships between exposure and disease have been 

established through well-designed epidemiological studies 

with a defined or specified population (e.g., geographic location, susceptible populations, occupational exposures) and 

known environmental exposures. 

The causes of many diseases and other health conditions are not 

well established. In some cases, environmental contaminants are 

considered important risk factors. In other cases, available data 

suggest that environmental exposures are important, but proof is 

lacking. Developing evidence that environmental contaminants 

cause or contribute to the incidence of adverse health effects can 

therefore be challenging, particularly for those effects occurring in a relatively small proportion of the population or effects 

with multiple causes. In cases where exposure to an environmental contaminant results in a relatively modest increase in 

the incidence of a disease or disorder, a large sample size for the 

study would be needed to detect a true relationship. In addition, 

there may be factors related to both the exposure and the health 

effect—confounding factors—that can make it difficult to detect 

a relationship between exposure to environmental contaminants 

and disease. In many cases, findings from studies in humans and/

or laboratory animals may provide suggestive (rather than conclusive) evidence that exposures to environmental contaminants 

contribute to the incidence of a disease or disorder.

To reiterate, however, the national-scale ROE indicators do 

not directly link exposure with outcome and cannot be used 

to demonstrate causal relationships. However, when combined 

with other information, such as environmental monitoring 

data and data from toxicological, epidemiological, or clinical studies, these indicators can be an important key to better 

understanding the relationship between environmental contamination and health outcomes.

5.1.3 Overview of the Data

EPA draws on many resources and partnerships with other 

federal, state, and local agencies for the health data and statistical reports that underlie the biomonitoring and health 

outcome indicators used in this chapter. This chapter uses 

three key types of data sources, each with its own strengths 

and limitations:

•	 Data collected from living human subjects. This 

includes both questionnaire-based information (e.g., the 

National Center for Health Statistics’ [NCHS’s] National 

Health Interview Survey, a nationwide survey to collect 

data on personal and demographic characteristics, illnesses, 

and other topics) and biological specimens (such as NCHS’s 

National Health and Nutrition Examination Survey, which 

collects and measures some chemicals in blood and urine 

samples). This chapter focuses on data collection activities that have a national focus and use a probability-based 

sampling design. 
HUMAN EXPOSURE AND HEALTH

5-6 EPA’s 2008 Report on the Environment

•	 Vital statistics data. Vital statistics of interest for health 

include births, deaths, and fetal deaths. Vital statistics 

data used in this chapter include NCHS’s National Vital 

Statistics System.

•	 Data from surveillance activities. These include data 

from active surveillance activities such as the National Cancer Institute’s Surveillance, Epidemiology, and End Results 

Program, which collects and publishes cancer incidence and 

survival data from population-based cancer registries. It also 

includes data from more passive collection systems, such as 

the Centers for Disease Control and Prevention’s (CDC’s) 

National Notifiable Disease Surveillance System, which 

provides information about diseases that health providers 

must report to state or local public health officials.

This chapter also takes advantage of several published documents that present and summarize in one place the findings 

from many data collection activities (e.g., NCHS’s Healthy 

People 2010 Database). In addition, it uses some databases 

that provide a single point of access to a variety of reports 

and numeric public health data and ways to conduct analyses 

of those data (e.g., CDC WONDER, CDC’s Wide-ranging 

OnLine Data for Epidemiologic Research). 

The data sources used provide statistics across time, geographic 

areas, and/or subpopulations such as age groups, races, and 

ethnicities. Identifying possible differences among population subgroups, as well as evidence of whether any differences 

are narrowing or widening, may reveal trends needing study 

or intervention. This type of trend analysis is consistent with 

national public health goals aimed at eliminating health 

disparities across various groups (e.g., racial and ethnic groups, 

low-income populations).2 It addresses a continuing concern 

that minority and/or economically disadvantaged communities frequently may be exposed disproportionately to environmental contaminants. Statistics for populations that may 

be particularly susceptible to environmental contaminants, 

such as children and pregnant women, are also examined. 

However, the type and level of subpopulation breakdown 

varies across data sets, sometimes making consistent presentation of this information difficult. Standards according to 

which federal agencies report race and ethnicity statistics were 

revised in 1997. The revised standards, which became effective 

in 2003, expand the race and ethnicity categories for which 

data are collected and are aimed at increasing comparability of 

data among federal data systems. As vital records used to support federal data systems continue to be revised and come into 

compliance with the 1997 requirements, future data reporting 

and comparisons will be more straightforward. 

This chapter presents health statistics, including race and 

ethnicity subgroup categorization, as reported within the 

original data source documents or databases. The presentation 

of observed changes—temporally, spatially, or across subgroups—is descriptive, not quantitative. No statistical testing 

was performed (e.g., tests of statistical significance).

This chapter presents only data that meet the ROE indicator definition and criteria (see Box 1-1, p. 1-3). Note 

that non-scientific indicators, such as administrative and 

economic indicators, are not included in this definition. 

Thorough documentation of the indicators data sources and 

metadata can be found online at http://www.epa.gov/roe. 

All indicators were peer-reviewed during an independent 

peer review process (again, see http://www.epa.gov/roe for 

more information). Readers should not infer that the indicators included reflect the complete state of the knowledge 

on trends in health and exposure related to environmental 

exposures. Many other data sources, publications, sitespecific research projects, and epidemiological studies have 

contributed greatly to the current understanding of health 

and exposure trends, but are not used because they do not 

meet some aspect of the ROE indicator criteria.

5.1.4 Organization of This 

Chapter

The rest of this chapter is organized into sections corresponding to the three questions EPA seeks to answer about trends in 

human health and exposure. Each section introduces the question and its importance, presents the ROE indicators selected 

to help answer the question, and discusses what the indicators, 

taken together, say about the question. The ROE indicators primarily include National Indicators, but in some cases National 

Indicators are broken down by EPA Region to help to answer 

the ROE question at a smaller geographic scale. Each section 

concludes by highlighting the major challenges to answering 

the question and identifying important information gaps.

Table 5-1 lists the indicators used to answer the three questions in this chapter and shows the locations where the 

indicators are presented.

2 U.S. Department of Health and Human Services. 2000. Healthy people 2010: 

Understanding and improving health. Second edition. Washington, DC: U.S. 

Government Printing Office. <http://www.health.gov/healthypeople/>
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-7

5.2 What Are the Trends 

in Human Exposure 

to Environmental 

Contaminants, Including 

Across Population 

Subgroups and 

Geographic Regions?

5.2.1 Introduction

Understanding the extent to which human populations are 

being exposed to environmental contaminants helps identify those contaminants of potential public health concern 

and populations who may be disproportionately exposed to 

contaminants or uniquely vulnerable. For example, children 

may have disproportionately heavy exposures to environmental contaminants because they drink more water, breathe 

more air, and eat more food per pound or kilogram of body 

weight than adults; further, children may be more vulnerable 

to some environmental contaminants depending on the stage 

of development during which exposure occurs.3,4 Evaluating 

exposure across certain race or ethnic groups, or other potentially susceptible subgroups, identifies possible variations in 

exposures. Tracking the levels of environmental contaminants 

in a population also enables an assessment of how exposures to 

those contaminants are changing in that population over time.

Referring back to the environmental public health paradigm 

presented in Section 5.1.1, measurements of human exposure 

to environmental contaminants can be made in the ambient 

environment (air, water, land), at the point of human contact, or after contact and contaminant entry into the human 

body has occurred. Box 5-1 further distinguishes the different types of exposure measures. In answering this question, 

the focus is on human biomonitoring, which involves the 

Table 5-1. Human Exposure and Health—ROE Questions and Indicators 

Question Indicator Name Section Page

What are the trends in human 

exposure to environmental 

contaminants, including 

across population subgroups 

and geographic regions?

Blood Lead Level (N)

Blood Mercury Level (N)

Blood Cadmium Level (N)

Blood Persistent Organic Pollutants Level (N)

Blood Cotinine Level (N)

Urinary Pesticide Level (N)

Urinary Phthalate Level (N)

5.2.2 5-10

5.2.2 5-12

5.2.2 5-13

5.2.2 5-15

2.4.2 2-76

5.2.2 5-22

5.2.2 5-26

What are the trends in health 

status in the United States?

General Mortality (N)

Life Expectancy at Birth (N)

Infant Mortality (N)

5.3.2 5-33

5.3.2 5-35

5.3.2 5-36

What are the trends in human 

disease and conditions 

for which environmental 

contaminants may be a risk 

factor, including across 

population subgroups and 

geographic regions?

Cancer Incidence (N)

Childhood Cancer Incidence (N)

Cardiovascular Disease Prevalence (N) and Mortality (N/R)

Chronic Obstructive Pulmonary Disease Prevalence (N) 

and Mortality (N/R)

Asthma Prevalence (N)

Infectious Diseases Associated with Environmental 

Exposures or Conditions (N)

Birth Defects Prevalence and Mortality (N)

Low Birthweight (N)

Preterm Delivery (N)

5.4.2 5-43

5.4.2 5-46

5.4.2 5-48

5.4.2 5-52

5.4.2 5-55

5.4.2 5-59

5.4.2 5-62

5.4.2 5-65

5.4.2 5-67

N = National Indicator

N/R = National Indicator displayed at EPA Regional scale

3 Landrigan, P.J., C.A. Kimmel, A. Correa, and B. Eskenazi. 2004. Children’s 

health and the environment: Public health issues and challenges for risk 

assessment. Environ. Health Perspect. 112(2):257-265.

4 World Health Organization. 2006. Principles for evaluating health risks 

in children associated with exposure to chemicals. Environmental Health 

Criteria 237.
HUMAN EXPOSURE AND HEALTH

5-8 EPA’s 2008 Report on the Environment

measurement of human tissues or excreta for direct or indirect 

evidence of exposure to chemical, biological, or radiological 

substances. The ambient contaminant measurements presented 

in the media chapters are not considered here, nor can they be 

directly linked with biomonitoring data presented to answer 

this question. 

Historically, human exposure has been defined as the amount 

of a chemical, physical, or biological contaminant at the outer 

boundary of the body available for exchange or intake via 

inhalation, ingestion, or skin or eye contact.5 As such, human 

exposure to environmental contaminants has been estimated 

primarily through measurements of contaminant concentrations 

in air, water, or soil, combined with estimates of the frequency 

and duration of human contact with the contaminated media. 

These resulting exposure estimates have provided a valuable 

foundation for many of the regulatory and non-regulatory 

actions that have been taken to limit exposure to ambient 

contaminants. However, developments in data collection 

techniques and analytical methods have improved the capability 

to characterize human exposure via biomonitoring, which provides measurements of contaminants within the human body.

For a few environmental contaminants, particularly lead and 

some other metals, biomonitoring has been used for exposure 

characterization for a number of years. More recently, techniques 

for biomonitoring have been expanded to include many additional environmental contaminants. These measurements provide 

a tool that complements ambient measurements in characterizing 

human exposure to environmental contaminants. However, concentrations of environmental contaminants reported at a national 

level in blood, urine, or any other type of tissue cannot be used to 

extrapolate directly to a particular source.

The use of biological markers (or biomarkers) builds on the 

more traditional exposure assessment approach, providing 

more information on the extent to which a contaminant 

enters, remains, and acts in the body. Biomarker information 

attempts to determine the extent to which a contaminant is 

present in the body after entering through portals of entry 

such as the eyes, skin, stomach, intestines, or lungs. Given 

the complex set of factors that govern contaminants that are 

absorbed and distributed in the body, a direct measurement 

of the levels of a contaminant or related “marker” in the body 

offers more information about exposure than measured ambient levels alone.

In general, a biomarker reports the level of a substance or a 

marker (i.e., the product of an interaction between an agent 

and some target molecule or cell) present in samples collected 

from the body or produced by the body. Biomarkers of exposure

measure concentrations of a contaminant, its metabolite(s), or 

reaction product(s) in the body fluids or tissue, most commonly blood or urine. Measurements can also be taken from a 

variety of other body compartments, such as feces, breast milk, 

hair, nails, exhaled air, and tissues obtained through biopsy or 

autopsy. The exposure measure used to answer this question 

focuses on biomarkers of exposure. Biomarkers of exposure do 

not predict whether biological alterations and potential health 

effect will result. Whether a particular exposure ultimately 

results in an adverse health outcome depends on a host of factors, as is described in Section 5.1. 

5 Aldrich, T., J. Griffith, C. Cooke. 1993. Environmental epidemiology and risk 

assessment. New York, NY: Van Nostrand Reinhold.

Various approaches can be used to measure or estimate the 

levels of human exposures. No approach is best suited to 

all environmental contaminants, and each approach has 

strengths and weaknesses. Available biomonitoring data are 

used to answer the question on trends in human exposure to 

environmental contaminants.

Ambient contaminant measurements: Historically, 

human exposures have been estimated using environmental 

measurements of ambient contaminant concentrations. One 

limitation of ambient measurements is that the presence of a 

contaminant in the environment may not be fully informative regarding the extent to which individuals are exposed. 

In some cases, emissions data are used to model or estimate 

ambient concentrations.

Models of exposure: This approach combines knowledge 

of environmental contaminant concentrations with information on people’s activities and locations (e.g., time spent 

working, exercising outdoors, sleeping, shopping) to account 

for the contact with contaminants. This approach requires 

knowledge of contaminant levels where people live, work, 

and play, as well as knowledge of their day-to-day activities. 

Since model output is not a direct measure of environmental conditions or exposure, it is not considered to be a true 

indicator of exposure. 

Personal monitoring data: With personal monitoring, 

the monitoring device is worn by individuals as they engage 

in their normal day-to-day activities. This approach is 

most commonly used in workplace environments. Personal 

monitoring data provide valuable insights into the source of 

contaminants to which people are actually being exposed. 

However, a challenge with personal monitoring (as with 

biomonitoring) is ensuring that sufficient sampling is conducted to be representative of the population being studied. 

No national-scale personal monitoring data are available.

Biomonitoring data: Several environmental contaminants, 

notably heavy metals and some pesticides and other persistent 

organic pollutants, can accumulate in the body. These substances or their metabolites can be measured in human tissues 

or fluids such as blood or urine. These residues reflect the 

amount of contaminant that gets into or is present in the body, 

but by themselves do not provide information on how the 

person came into contact with the contaminant.

Box 5-1. Measuring Human Exposure
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-9

5.2.2 ROE Indicators

The answer to the question on trends in human exposure relies on national-scale biomonitoring data collected 

as part of the Centers for Disease Control and Prevention’s 

(CDC’s) National Health and Nutrition Examination Survey 

(NHANES), primarily data collected from 1999 through 

2002. As part of the survey, blood and urine samples are 

routinely collected to measure certain contaminants (or their 

metabolites) of public health concern. NHANES is conducted 

annually, but the data are combined and reported for a 2-year 

time period to provide more stable population estimates and 

to obtain adequate sample sizes for many subgroup analyses. 

CDC continues to process 2003-2004 and 2005-2006 survey 

data; raw data for the 2003-2004 survey are available for some 

data sets, but CDC-synthesized data and reports were not 

available in time for inclusion in the ROE. The chemicals in 

CDC’s current suite of biomarkers were chosen based largely 

on scientific data that suggest exposure in the U.S. population, 

the seriousness of known or suspected health effects associated 

with some levels of exposure, the availability and adequacy of 

analytical methods, and logistical and cost considerations.6

Seven individual or groups of contaminants from NHANES 

are considered, including metals, persistent organic pollutants, pesticides, and phthalates (Table 5-2). The data presented 

represent data from NHANES in its entirety or a subset of the 

original data, with emphasis on those compounds for which 

CDC was able to calculate geometric means.7

 The levels of 

detection (LOD) presented in the indicators’ exhibits vary 

from chemical to chemical. A chemical’s LOD is the level at 

which the measurement has a 95 percent probability of being 

greater than zero. Percentile estimates that are less than the 

LOD for the chemical analysis are reported as “<LOD.” In 

cases where the proportion of results below the LOD was 

greater than 40 percent, geometric means were not calculated 

and the results were reported as “NC,” or not calculated. 

Blood measurements for chemicals that can concentrate in 

lipid (e.g., dioxins, furans, PCBs, organochlorine pesticides) 

are presented per gram of total lipid as well as per whole 

weight of blood. Because these compounds are lipophilic, 

they concentrate in the body’s lipid stores, including the lipid 

in blood. Blood levels reported per gram of total lipid represent the amount of these chemicals that is stored in body 

fat. (Blood levels per whole weight of blood are included to 

facilitate comparison with studies investigating exposure to 

these chemicals that report results in these units.) For chemicals measured in urine, levels are reported as volume in urine 

and per gram of creatinine. Expressing the result per gram of 

creatinine helps adjust for the effects of urinary dilution. For 

example, if one person consumed more fluids than another 

person, that individual’s urine output is likely higher and more 

dilute than that of the other person.8

6 Centers for Disease Control and Prevention. 2005. Third national report 

on human exposure to environmental chemicals. NCEH publication no. 

05-0570. <http://www.cdc.gov/exposurereport/report.htm>

7 Geometric means are calculated by taking the log of each concentration, then 

calculating the mean of those log values, and finally taking the antilog of that 

mean. A geometric mean provides a better estimate of central tendency and 

is influenced less by high values than is the arithmetic mean. This type of distribution is common when measuring environmental chemicals in blood or 

urine. See Centers for Disease Control and Prevention. 2005. Third national 

report on human exposure to environmental chemicals. NCEH publication 

no. 05-0570. <http://www.cdc.gov/exposurereport/report.htm>

8 Centers for Disease Control and Prevention. 2005. Third national report 

on human exposure to environmental chemicals. NCEH publication no. 

05-0570. <http://www.cdc.gov/exposurereport/3rd/>

Table 5-2. ROE Indicators of Trends in Human Exposure to Environmental Contaminants

National Indicators Section Page

Blood Lead Level 5.2.2 5-10

Blood Mercury Level 5.2.2 5-12

Blood Cadmium Level 5.2.2 5-13

Blood Persistent Organic Pollutants Level 5.2.2 5-15

Blood Cotinine Level 2.4.2 2-76

Urinary Pesticide Level 5.2.2 5-22

Urinary Phthalate Level 5.2.2 5-26
HUMAN EXPOSURE AND HEALTH

5-10 EPA’s 2008 Report on the Environment

Lead is a naturally occurring metal found in small amounts in rock and soil. Lead has been used industrially in the production of gasoline, ceramic products, paints, 

metal alloys, batteries, and solder. While lead arising from 

the combustion of leaded gasoline was a major source of 

exposure in past decades, today lead-based paint and leadcontaminated dust from paint are the primary sources of 

lead exposure in the home. Lead levels can be measured in 

blood or urine.

Lead is a neurotoxic metal that affects areas of the brain 

that regulate behavior and nerve cell development (NRC, 

1993). Its adverse effects range from subtle responses to 

overt toxicity, depending on how much lead is taken into 

the body and the age and health status of the person (CDC, 

1991). Lead is one of the few pollutants for which biomonitoring and health effect data are sufficient to clearly evaluate environmental management efforts to reduce lead in 

the environment.

Infants, children, and fetuses are more vulnerable to the 

effects of lead because the blood-brain barrier is not fully 

developed in them (Nadakavukaren, 2000). Thus, a smaller 

amount of lead will have a greater effect on children than 

on adults. In addition, ingested lead is more readily absorbed 

into a child’s bloodstream, while adults absorb only 10 percent. Because of lead’s adverse effects on cognitive development, the Centers for Disease Control and Prevention 

INDICATOR | Blood Lead Level

Exhibit 5-2. Blood lead concentrations for the U.S. population age 1 year and older by selected 

demographic groups, 1999-2002

Geometric mean and selected percentiles 

for blood lead concentrations (μg/dL)a

Survey years Sample size Geometric mean 50th 75th 90th 95th

Total, age 1 year and 

older

Sex 

Male

Female

Race and ethnicityb

Black, non-Hispanic

Mexican American

White, non-Hispanic

Age group

1-5 years

6-11 years

12-19 years

20+ years

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

7,970

8,945

3,913

4,339

4,057

4,606

1,842

2,219

2,742

2,268

2,716

3,806

723

898

905

1,044

2,135

2,231

4,207

4,772

1.7

1.5

2.0

1.8

1.4

1.2

1.9

1.7

1.8

1.5

1.6

1.4

2.2

1.7

1.5

1.3

1.1

0.9

1.8

1.6

3.8

3.4

4.4

3.9

3.0

2.6

4.2

4.2

4.2

3.6

3.6

3.1

4.8

4.1

3.3

2.7

2.3

1.9

3.9

3.6

2.4

2.2

2.9

2.7

1.9

1.8

2.8

2.5

2.7

2.2

2.4

2.1

3.3

2.5

2.0

1.6

1.4

1.2

2.5

2.2

1.6

1.4

1.8

1.7

1.3

1.1

1.7

1.6

1.8

1.5

1.6

1.4

2.2

1.5

1.3

1.1

1.0

0.8

1.7

1.6

4.9

4.4

6.0

5.3

4.0

3.6

5.7

5.7

5.8

5.4

5.0

4.1

7.0

5.8

4.5

3.7

2.8

2.7

5.2

4.6

 aRefer to CDC 2005 for confidence intervals for reported values.

 bOther racial and ethnic groups are included in the “total” only.

Data source: CDC, 2005
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-11

(CDC) have defined an elevated blood lead level as equal 

to or greater than 10 micrograms per deciliter (μg/dL) for 

children under 6 years of age (CDC, 2005). 

This indicator is based on data collected by the National 

Health and Nutrition Examination Survey (NHANES). 

NHANES is a series of surveys conducted by CDC’s 

National Center for Health Statistics that is designed to collect data on the health and nutritional status of the civilian, 

non-institutionalized U.S. population using a complex, 

stratified, multistage, probability-cluster design. CDC began 

monitoring blood lead in 1976 as part of NHANES II, 

which covered the period from 1976 through 1980. Blood 

lead was also monitored in NHANES III, which covered 

the period between 1988 and 1994. CDC’s National Center 

for Environmental Health conducted the laboratory analyses for the biomonitoring samples. Beginning in 1999, 

NHANES became a continuous and annual national survey, 

visiting 15 U.S. locations per year and surveying and reporting for approximately 5,000 people annually. 

What the Data Show

The overall geometric mean blood lead levels among 

all participants age 1 year and older from NHANES 

1999-2000 and 2001-2002 were 1.7 μg/dL and 1.5 μg/

dL, respectively (Exhibit 5-2). Adults 20 years and older 

had a geometric mean lead level of 1.6 μg/dL during the 

2001-2002 NHANES. For this same period, males and 

females had geometric mean lead levels of 1.8 μg/dL and 

1.2 μg/dL, respectively. For non-Hispanic blacks, Mexican 

Americans, and non-Hispanic whites during 2001-2002, 

the geometric mean lead levels were 1.7, 1.5, and 1.4 μg/

dL, respectively. The geometric mean blood levels among 

every age, race, and ethnic group, as well as for both males 

and females, declined in the most recent 2001-2002 survey. 

Of all age groups, children age 1 to 5 had the highest 

geometric mean lead level, at 1.7 μg/dL. However, this age 

group also showed the largest decline between 1999-2000 

and 2001-2002 (2.2 μg/dL to 1.7 μg/dL). Children age 6 to 

11 and 12 to 19 had reported geometric mean lead levels of 

1.3 and 0.9 μg/dL, respectively, for the 2001-2002 survey. 

Blood lead levels have declined steadily since NHANES 

surveillance of blood lead levels across the U.S. began 

in 1976. NHANES II (1976-1980) reported a geometric 

mean blood lead level of 14.9 μg/dL among children age 

1 to 5, the population at the highest risk for lead exposure 

and effects; just over 88 percent of this high-risk population had blood lead levels greater than or equal to 10 μg/

dL (CDC, 2004a). Data collected from 1991 to 1994 as 

part of NHANES III (phase 2) showed that the geometric 

mean blood lead level for children age 1 to 5 was 2.7 μg/

dL, with 4.4 percent of children age 1 to 5 having blood 

lead levels greater than or equal to 10 μg/dL (CDC, 2005). 

Children age 1 to 5 whose blood was sampled as part of the 

1999-2002 survey had a geometric mean blood lead level 

of 1.9 μg/dL, with 1.6 percent of the children having blood 

lead levels greater than or equal to 10 μg/dL (CDC, 2005). 

(Data not shown.) 

Indicator Limitations

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes in 

estimates between the two time periods do not necessarily reflect a trend. Earlier data sets are available (e.g., 

NHANES III), but the data are not directly comparable 

to NHANES 1999-2002. As CDC releases additional 

survey results (e.g., 2003-2004), it will become possible 

to more fully evaluate trends (CDC, 2002, 2004b). 

Data Source

Data used for this indicator were extracted from two CDC 

reports that present results of the ongoing NHANES 

(CDC, 2004a, 2005). The underlying laboratory data supporting CDC’s reports are available online in SAS® transport file format at http://www.cdc.gov/nchs/about/major/

nhanes/datalink.htm.

References

CDC (Centers for Disease Control and Prevention). 2005. 

Third national report on human exposure to environmental chemicals. NCEH publication no. 05-0570. 

<http://www.cdc.gov/exposurereport/report.htm>

CDC. 2004a. Children’s blood lead levels in the United 

States. Accessed October 11, 2005. 

<http://www.cdc.gov/nceh/lead/research/kidsBLL.htm>

CDC. 2004b. NHANES analytic guidelines. June 2004 

version. <http://www.cdc.gov/nchs/data/nhanes/nhanes_

general_guidelines_june_04.pdf>

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Updated August 30, 

2002.

<http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf>

CDC. 1991. Preventing lead poisoning in young children. 

Accessed November 21, 2004. <http://aepo-xdv-www.

epo.cdc.gov/wonder/prevguid/p0000029/p0000029.asp>

Nadakavukaren, A. 2000. Our global environment: A 

health perspective. Fifth edition. Prospect Heights, IL: 

Waveland Press, Inc.

NRC (National Research Council). 1993. Measuring lead 

exposure in infants, children, and other sensitive populations. Washington, DC: National Academies Press.

INDICATOR | Blood Lead Level (continued)

v
HUMAN EXPOSURE AND HEALTH

5-12 EPA’s 2008 Report on the Environment

INDICATOR | Blood Mercury Level

Mercury is a naturally occurring metal. However, through many industrial processes (e.g., chemical 

manufacturing operations, coal combustion), mercury is 

widespread and persistent in the environment. It is found 

in elemental form and in various organic compounds and 

complexes. Methylmercury (an organic form) can accumulate in the food chain in aquatic systems and lead to high 

concentrations in predatory fish. Consumption of contaminated fish is the major source of human exposure to 

methylmercury in the U.S. (NRC, 2000). 

The human health effects of mercury are diverse and 

depend on the forms of mercury encountered and the 

severity and length of exposure. Fetuses and children may 

be more susceptible to mercury than adults, with concern 

for the occurrence of developmental and neurological 

health effects (NRC, 2000). Prenatal exposures interfere 

with the growth and migration of neurons and have the 

potential to cause irreversible damage to the developing 

central nervous system. 

This indicator quantifies the blood mercury levels 

(includes organic and inorganic) among U.S. women 

age 16 to 49 and children age 1 to 5, using data from the 

1999-2002 National Health and Nutrition Examination 

Survey (NHANES). NHANES does not report blood 

mercury data for adult males. NHANES is a series of 

surveys conducted by the Centers for Disease Control and 

Prevention’s (CDC’s) National Center for Health Statistics 

that is designed to collect data on the health and nutritional 

status of the civilian, non-institutionalized U.S. population 

using a complex, stratified, multistage, probability-cluster 

design. CDC’s National Center for Environmental Health 

conducted the laboratory analyses for the biomonitoring 

Exhibit 5-3. Blood mercury concentrations for U.S. women age 16-49 years and children (male and 

female) age 1-5 years by selected demographic groups, 1999-2002

Geometric mean and selected percentiles 

for mercury concentrations (μg/L)a

Survey years Sample size Geometric mean 50th 75th 90th 95th

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2002

1999-2002

1999-2002

1,709

1,928

370

436

579

527

588

806

705

872

387

440

318

432

424

526

447

1.0

0.8

1.4

1.1

0.8

0.7

0.9

0.8

0.3

0.3

0.3

0.3

0.4

0.3

0.5

0.4

0.3

4.9

3.0

4.8

3.2

2.6

2.1

5.0

3.0

1.4

1.2

1.1

1.3

1.6

1.3

1.5

1.4

1.2

2.0

1.7

2.6

1.8

1.4

1.1

1.9

1.5

0.5

0.7

0.5

0.6

0.8

0.7

0.9

0.6

0.5

0.9

0.7

1.3

1.1

0.9

0.7

0.9

0.8

0.3

0.3

0.2

0.3

0.2

0.3

0.5

0.3

0.2

7.1

4.6

5.9

4.1

4.0

3.5

6.9

4.6

2.3

1.9

2.1

1.7

2.7

2.6

2.4

1.9

1.8

a

Refer to CDC, 2005, for confidence intervals for reported values.

Data source: CDC, 2004a, 2005

Women age 16-49 years

Total, women age

16-49 years

Race and ethnicity

Black, non-Hispanic

Mexican American

White, non-Hispanic

Children age 1-5 years

Total, children age 

1-5 years

Sex

Male

Female

Race and ethnicity

Black, non-Hispanic

Mexican American

White, non-Hispanic
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-13

INDICATOR | Blood Mercury Level (continued)

samples. Beginning in 1999, NHANES became a continuous and annual national survey. Data for 1999-2000 and 

2001-2002 are presented here as a baseline, with the intent 

of reporting trends across time as more data become available in the future.

What the Data Show

Exhibit 5-3 presents the geometric mean and four percentiles of blood mercury for selected populations 

sampled during NHANES 1999-2000 and 2001-2002. 

For women age 16-49 years there was a small decline in 

geometric mean blood mercury levels from 1999-2000 

and 2001-2002 (1.0 and 0.8 micrograms per liter [μg/L], 

respectively). Decreases occurred for each of the four percentiles, but were most pronounced at the 90th and especially 95th percentiles. Of women tested between 1999 and 

2002, 5.7 percent had mercury levels measured between 

5.8 and 58 μg/L (data not shown). For children age 1 to 5, 

the geometric mean remained the same at 0.3 μg/L.

When the geometric means are stratified across three 

racial/ethnic groups, black, non-Hispanic women age 16 

to 49 had the highest levels during both the 1999-2000 and 

2001-2002 surveys (1.4 and 1.1 μg/L, respectively), followed 

by white non-Hispanics (0.9 and 0.8 μg/L, respectively), 

and Mexican Americans (0.8 and 0.7 μg/L, respectively). 

Among children age 1 to 5, black non-Hispanics have the 

highest geometric mean between 1999 and 2002 (0.5 μg/L), 

followed by Mexican Americans (0.4 μg/L) and white nonHispanics (0.3 μg/L) (CDC, 2004a). 

Indicator Limitations 

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes in 

estimates between the two time periods do not necessarily 

reflect a trend. As CDC releases additional survey results 

(e.g., 2003-2004) it will become possible to more fully 

evaluate trends (CDC, 2002, 2004b).

•	 Generally recognized guidelines for blood levels of 

mercury have not been established. 

Data Sources

Data used for this indicator were extracted from two CDC 

reports that present results of the ongoing NHANES (CDC, 

2004a, 2005). The underlying laboratory data supporting 

CDC’s reports are available online in SAS® transport file 

format at http://www.cdc.gov/nchs/about/major/nhanes/

datalink.htm.

References

CDC (Centers for Disease Control and Prevention). 2005. 

Third national report on human exposure to environmental chemicals. NCEH publication no. 05-0570. 

<http://www.cdc.gov/exposurereport/report.htm>

CDC. 2004a. Blood mercury levels in young children and 

childbearing-aged women—United States, 1999-2002. 

MMWR 53:1018-1020. 

<http://www.cdc.gov/mmwr/PDF/wk/mm5343.pdf>

CDC. 2004b. NHANES analytic guidelines. June 2004 

version. <http://www.cdc.gov/nchs/data/nhanes/nhanes_

general_guidelines_june_04.pdf>

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Updated August 30, 2002.

<http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf>

NRC (National Research Council). 2000. Toxicological effects of methylmercury. Washington, DC: National 

Academies Press.

INDICATOR | Blood Cadmium Level

Cadmium is a metal that is usually found in nature combined with oxygen, chlorine, or sulfur. Cadmium enters 

the environment from the weathering of rocks and minerals that contain cadmium. Exposure to cadmium can occur 

in occupations such as mining or electroplating, where 

cadmium is produced or used. Cadmium exposure can also 

occur from exposure to cigarette smoke (CDC, 2005).

Cadmium and its compounds are toxic to humans and 

animals. Once absorbed into the human body, cadmium 

can accumulate in the kidneys and remain in the body 

for decades. Chronic exposure to cadmium can result in 

serious kidney damage. Osteomalacia, a bone disorder 

similar to rickets, is also associated with long-term ingestion of cadmium. Acute airborne exposure, as occurs from 

welding on cadmium-alloy metals, can result in swelling 

(edema) and scarring (fibrosis) of the lungs (CDC, 2005).

This indicator reflects blood cadmium concentrations in 

micrograms per liter (μg/L) for the U.S. population, age 

1 year and older, as measured in the 1999-2002 National 

Health and Nutrition Examination Survey (NHANES). 

NHANES is a series of surveys conducted by the Centers 

for Disease Control and Prevention’s (CDC’s) National 

Center for Health Statistics that is designed to collect data 

on the health and nutritional status of the civilian, noninstitutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. CDC’s National 

Center for Environmental Health conducted the laboratory 

analyses for the biomonitoring samples. Beginning in 1999, 

v
HUMAN EXPOSURE AND HEALTH

5-14 EPA’s 2008 Report on the Environment

NHANES became a continuous and annual national survey; 

biomonitoring for certain environmental chemicals also was 

implemented. Data for 1999-2000 and 2001-2002 are presented here as a baseline, with the intent of reporting trends 

across time as more data become available in the future.

What the Data Show

Exhibit 5-4 presents the geometric means and selected 

percentiles for blood cadmium among participants age 1 

year and older from NHANES 1999-2000 and 2001-2002. 

During the 2001-2002 survey, the overall geometric mean 

blood cadmium level was not calculated because of the 

high number of samples that were below the method’s 

limit of detection. However, the blood cadmium levels 

at the four different percentiles (50th, 75th, 90th, and 95th) 

are very similar across the two survey periods, with levels 

ranging between 0.3 and 1.4 μg/L. The blood cadmium 

measurements were similar among males and females, as 

well as among the racial or ethnic groups sampled across 

both time periods. 

During the 1999-2000 survey, the overall geometric 

mean among participants age 20 or older was slightly 

higher (0.5 μg/L) than the geometric mean among the 

12-19 age group (0.3 μg/L). Compared to participants in 

the other age groups, those older than 20 years had higher 

cadmium levels for each of the four selected percentiles 

INDICATOR | Blood Cadmium Level (continued)

Total, age 1 year 

and older 

Sex

Male

Female

Race and ethnicityd

Black, non-Hispanic

Mexican American

White, non-Hispanic

Age group

1-5 years

6-11 years

12-19 years

20+ years

d

Other racial and ethnic groups are included in the “total” only.

a

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

b

LOD = below the limit of detection (LOD) of the analytical method (cadmium LOD = 0.04 μg/L). 

c

Refer to CDC, 2005, for confidence intervals for reported values. 

Exhibit 5-4. Blood cadmium concentrations for the U.S. population age 1 year and older by selected 

demographic groups, 1999-2002

Data source: CDC, 2005

Geometric mean and selected percentiles 

for cadmium concentrations (μg/L)a, b, c

Survey years 

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

Sample size 

7,970

8,945

3,913

4,339

4,057

4,606

1,842

2,219

2,742

2,268

2,716

3,806

723

898

905

1,044

2,135

2,231

4,207

4,772

Geometric mean 

0.4

NC

0.4

NC

0.4

NC

0.4

NC

0.4

NC

0.4

NC

NC

NC

NC

NC

0.3

NC

0.5

NC

50th

0.3

0.3

0.4

0.3

0.3

0.3

0.3

<LOD

0.4

<LOD

0.4

<LOD

<LOD

<LOD

<LOD

<LOD

0.3

<LOD

0.4

0.3

75th

0.6

0.4

0.6

0.4

0.6

0.5

0.6

0.4

0.4

0.3

0.5

0.5

<LOD

0.3

<LOD

0.3

0.3

0.6

0.3

0.6

90th

1.0

0.9

1.0

0.9

1.0

1.0

1.0

1.0

0.7

0.6

1.0

0.9

0.4

<LOD

0.4

<LOD

0.8

0.4

1.0

1.1

95th

1.3

1.3

1.3

1.4

1.3

1.4

1.4

1.4

1.1

1.0

1.3

1.4

0.4

0.3

0.4

0.4

1.1

0.8

1.5

1.6
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-15

INDICATOR | Blood Cadmium Level (continued)

during both survey periods. During the 1999-2000 survey, 

approximately half of all participants under the age of 

12 had non-detectable blood cadmium concentrations. 

This proportion increased to about 90 percent during the 

2001-2002 survey.

Indicator Limitations

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes in 

estimates between the two time periods do not necessarily reflect a trend. As CDC releases additional survey 

results (e.g., 2003-2004), it will become possible to more 

fully evaluate trends (CDC, 2002, 2004).

•	 Generally recognized guidelines for blood levels of 

cadmium have not been established. 

Data Sources

Data used for this indicator were extracted from the CDC 

report that presents results of the ongoing NHANES 

(CDC, 2005). The underlying laboratory data supporting 

CDC’s report are available online in SAS® transport file 

format at http://www.cdc.gov/nchs/about/major/nhanes/

datalink.htm.

References

CDC (Centers for Disease Control and Prevention). 2005. 

Third national report on human exposure to environmental chemicals. NCEH publication no. 05-0570. 

<http://www.cdc.gov/exposurereport/report.htm>

CDC. 2004. NHANES analytic guidelines. June 2004 

version. <http://www.cdc.gov/nchs/data/nhanes/nhanes_

general_guidelines_june_04.pdf>

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Updated August 30, 2002. 

<http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf>

INDICATOR | Blood Persistent Organic Pollutants Level

Persistent organic pollutants (POPs) are manmade organic chemicals that remain in the environment for 

years or decades. POPs are of special concern because they 

often remain toxic for decades or longer after release to 

the environment. The more persistent a toxic chemical is, 

the greater the probability for human exposure over time. 

Because they circulate globally long after being released 

into the environment, POPs are often detected in locations 

far from the original source (U.S. EPA, 2004a).

One of the major sources of POPs exposure among the 

general population is food. Food contamination begins 

with contaminated soil and/or plants, but is of greatest 

concern to humans as the POPs move up the food chain 

into animals. Because POPs typically accumulate in fatty 

tissue and are slow to be metabolized, they bioconcentrate 

(i.e., increase in concentration) with each trophic level. 

Therefore, foods such as dairy products, eggs, animal fats, 

and some types of fish are more likely to contain greater 

concentrations of POPs than fruits, vegetables, and grains. 

POPs have been linked to adverse health effects such as 

cancer, nervous system damage, reproductive disorders, 

and disruption of the immune system in both humans and 

animals (U.S. EPA, 2004a). 

This indicator presents data from the Centers for Disease 

Control and Prevention’s (CDC’s) National Health and 

Nutrition Examination Survey (NHANES) 1999-2000 and 

2001-2002. NHANES is a series of surveys conducted by 

CDC’s National Center for Health Statistics that is designed 

to collect data on the health and nutritional status of the 

civilian, non-institutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. CDC’s 

National Center for Environmental Health conducted the 

laboratory analyses for the biomonitoring samples. Beginning in 1999, NHANES became a continuous and annual 

national survey; biomonitoring for certain environmental 

chemicals also was implemented. These data are presented 

here as a baseline, with the intent of reporting trends over 

larger time periods in the future. Blood levels of POPs or 

their metabolites were measured in NHANES participants 

age 12 or older. This indicator includes the following three 

broad classes of POPs: 

•	 Organochlorine pesticides

•	 Polychlorinated dibenzo-p-dioxins (dioxins) and polychlorinated dibenzo-p-furans (furans)

•	 Polychlorinated biphenyls (PCBs)

Organochlorine pesticides were first introduced in 

the 1940s. Because of their environmental persistence, EPA 

banned most uses of these chemicals during the 1970s and 

1980s. However, many other countries still produce and/or 

use organochlorines. These fat-soluble chemicals are most 

commonly absorbed through fatty foods. These pesticides 

are associated with effects to the central nervous system 

at acute exposure levels and potential carcinogenic effects 

with long-term exposure (Reigart and Roberts, 1999). 

This indicator includes eight organochlorine pesticides that 

v
HUMAN EXPOSURE AND HEALTH

5-16 EPA’s 2008 Report on the Environment

INDICATOR | Blood Persistent Organic Pollutants Level (continued)

Exhibit 5-5. Blood concentrations of selected organochlorine pesticides and metabolites for the U.S.

population age 12 years and older, lipid-adjusted and whole weight, 1999-2002 

Geometric mean and selected percentiles 

for organochlorine pesticide metabolite concentrations (ng/g)a,b,c

Survey years Sample size Geometric mean 50th 75th 90th 95th

Continued

2001-2002

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2,275

2,275

1,661

2,249

1,661

2,249

1,933

2,286

1,933

2,286

1,964

2,298

1,964

2,298

1,679

2,305

1,679

2,305

1,669

2,279

1,669

2,279

2,159

2,159

2,187

2,187

NC

NC

NC

11.4

NC

0.07

18.3

17.0

0.11

0.10

260

295

1.54

1.81

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

<LOD

<LOD

34.4

36.3

0.26

0.25

55.1

56.3

0.37

0.39

1,150

1,400

7.49

8.81

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

15.2

0.11

<LOD

<LOD

<LOD

<LOD

20.6

21.7

0.13

0.14

31.9

33.7

0.21

0.22

537

597

3.49

3.97

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

11.1

<LOD

0.07

17.8

17.9

0.11

0.11

226

250

1.31

1.57

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

44.8

49.7

0.31

0.35

79.4

78.2

0.54

0.59

1,780

2,320

11.6

15.4

28.0

26.5

0.17

0.18

<LOD

<LOD

<LOD

<LOD

20.3

0.15

5.1

0.02

See notes at end of table.

Aldrin

Lipid-adjusted

Whole weight

Chlordane

Oxychlordane

Lipid-adjusted

Whole weight

trans-Nonachlor

Lipid-adjusted

Whole weight

DDT/DDE

p,p'-DDE

Lipid-adjusted

Whole weight

p,p'-DDT

Lipid-adjusted

Whole weight

o,p'-DDT

Lipid-adjusted

Whole weight

Dieldrin

Lipid-adjusted

Whole weight

Endrin

Lipid-adjusted

Whole weight
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-17

INDICATOR | Blood Persistent Organic Pollutants Level (continued)

were measured in NHANES 1999-2000 and 2001-2002; 

data for three of these pesticides (aldrin, dieldrin, and 

endrin) first became available with the release of results 

from NHANES 2001-2002 (CDC, 2005). 

•	 Aldrin and dieldrin. These two pesticides were widely 

used from the 1950s until 1970, when EPA prohibited 

most agricultural uses. However, they continued to be 

used to control termites until that use was prohibited in 

1987. Aldrin rapidly converts to dieldrin in the environment or after being ingested or absorbed into the body. 

Dieldrin is more persistent and often accumulates in fatty 

tissues (CDC, 2005). 

•	 Chlordane and heptachlor. EPA banned these pesticides in 1988. Within the body, chlordane is metabolized 

to oxychlordane and trans-nonachlor, and heptachlor is 

metabolized to heptachlor epoxide (CDC, 2003). Chlordane was commonly used against termites and on some 

agricultural crops and heptachlor was used primarily 

against soil insects and termites (Ritter et al., n.d.).

•	 DDT. Dichlorodiphenyltrichlorethane, or DDT, was 

banned in the U.S. in 1973 but is still produced in other 

countries, where it is used primarily to control mosquitoes. In the body or the environment, DDT breaks down 

to DDE (dichlorodiphenyldichloroethane), a more persistent chemical. DDT or DDE in the human body may 

reflect either a relatively recent exposure or cumulative 

past exposures (CDC, 2005).

•	 Endrin. Endrin is a stereoisomer (i.e., a molecule that 

is a mirror image of another molecule with the same 

molecular formula) of dieldrin. Endrin production was 

discontinued in 1986, primarily because of its persistence 

in the environment. Unlike many other organochlorine 

pesticides, endrin does not readily accumulate in body 

tissues and is metabolized and eliminated from the body 

relatively quickly (CDC, 2005).

•	 Hexachlorobenzene (HCB) was commonly used as 

a pesticide until 1965. HCB was also used in the past 

as a fungicide to protect wheat seeds, and for a variety 

of industrial purposes, including rubber, aluminum, 

Exhibit 5-5 (continued). Blood concentrations of selected organochlorine pesticides and metabolites for 

the U.S. population age 12 years and older, lipid-adjusted and whole weight, 1999-2002 

Geometric mean and selected percentiles 

for organochlorine pesticide metabolite concentrations (in ng/g)a,b,c

Survey years Sample size Geometric mean 50th 75th 90th 95th

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1,589

2,259

1,589

2,259

1,702

2,277

1,702

2,277

1,853

2,257

1,853

2,257

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

NC

15.3

14.8

0.11

0.10

<LOD

<LOD

<LOD

<LOD

<LOD

15.8

<LOD

0.10

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

23.9

21.6

0.18

0.15

<LOD

<LOD

<LOD

<LOD

<LOD

57.1

<LOD

0.41

a

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

b

<LOD = below the limit of detection (LOD) of the analytical method (see CDC, 2005, for chemical-specific LODs).

c

Refer to CDC, 2005, for confidence intervals for reported values.

Data source: CDC, 2005

Heptachlor

Heptachlor epoxide

Lipid-adjusted

Whole weight

Hexachlorobenzene (HCB)

Lipid-adjusted

Whole weight

Mirex

Lipid-adjusted

Whole weight
HUMAN EXPOSURE AND HEALTH

5-18 EPA’s 2008 Report on the Environment

INDICATOR | Blood Persistent Organic Pollutants Level (continued)

Exhibit 5-6. Blood concentrations of selected polychlorinated dibenzo-p-dioxins (dioxins), 

polychlorinated dibenzofurans (furans), and dioxin-like polychlorinated biphenyls (PCBs) for the U.S.

population age 20 years and older, lipid-adjusted and whole weight, 1999-2002a,b

Geometric mean and selected percentiles 

for dioxin, furan, and PCB concentrationsc,d,e

Survey years Sample size Geometric mean 50th 75th 90th 95th

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1,254

1,171

1,254

1,171

1,237

1,220

1,237

1,220

1,237

1,234

1,237

1,234

1,109

1,219

1,109

1,219

1,238

1,226

1,238

1,226

1,240

1,223

1,240

1,223

NC

346

NC

2.23

NC

39

NC

0.25

NC

34.6

NC

0.22

NC

9.6

NC

0.06

NC

22.7

NC

0.15

NC

17.9

NC

0.12

704

939

4.57

6.46

92

115

0.61

0.78

62.8

95.2

0.40

0.66

14.2

21.3

0.09

0.13

57.1

69.3

0.38

0.48

36.4

50.0

0.24

0.34

445

571

2.80

3.86

61.9

68.7

0.39

0.44

36.1

60.7

0.23

0.41

<LOD

14.5

<LOD

0.09

30.8

40.8

0.20

0.27

<LOD

33.1

<LOD

0.22

<LOD

333

<LOD

2.17

<LOD

40.2

<LOD

0.27

<LOD

39.2

<LOD

0.25

<LOD

10.3

<LOD

0.06

<LOD

24.5

<LOD

0.16

<LOD

19

<LOD

0.13

948

1,260

6.20

9.11

119

147

0.80

1.03

75.6

127

0.52

0.87

18.4

27.1

0.11

0.18

89.5

108

0.59

0.73

47.8

60.7

0.30

0.42

See notes at end of table.

Dioxins (pg/g)

1,2,3,4,6,7,8,9-OCDD

Lipid-adjusted

Whole weight

1,2,3,4,6,7,8-HpCDD

Lipid-adjusted

Whole weight

1,2,3,6,7,8-HxCDD

Lipid-adjusted

Whole weight

Furans (pg/g)

1,2,3,4,6,7,8-HpCDF

Lipid-adjusted

Whole weight

PCBs (units vary)

PCB 126 (pg/g)

Lipid-adjusted

Whole weight

 PCB 169 (pg/g)

Lipid-adjusted

Whole weight

Continued
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-19

INDICATOR | Blood Persistent Organic Pollutants Level (continued)

and dye production and wood preservation (U.S. EPA, 

2004b). EPA canceled registered use in 1984; however, 

HCB is still formed as a byproduct during manufacturing of other chemicals and pesticides (U.S. EPA, 2004b). 

•	 Mirex has not been produced or used in the U.S. since 

1978. It was used primarily in the southern U.S. to control 

fire ants. The primary source of exposure is dietary, most 

often through consumption of fish (U.S. EPA, 2004c). 

Dioxins and furans are similar classes of chlorinated 

aromatic chemicals, usually generated as pollutants or 

byproducts. In the environment, dioxins and furans occur 

as a mixture of about 20 compounds (termed “congeners”). 

The half-lives of these congeners range from roughly 3 to 

19 years (CDC, 2005). Human exposure occurs primarily 

through food; other sources of exposure include industrial 

accidents, burning of PCBs contaminated with dioxins and 

furans, burning of many plastics such as PVC, and spraying or 

unintended releases of contaminated herbicides such as Agent 

Orange. The detection of dioxins and furans in human blood 

can reflect either recent or past exposures (CDC, 2005).

Researchers continue to study the potential adverse 

health effects associated with dioxins and furans. Studies of 

individual congeners have shown immunotoxic, developmental/reproductive, and other systemic effects. The 

effects of individual congeners in humans are difficult to 

determine, since exposures are more likely be to mixtures of several congeners. The dioxin congener TCDD 

(2,3,7,8-tetrachlorodibenzo-p-dioxin) is the most toxic 

form of dioxin and is classified as a known human carcinogen (IARC, 1997). Uncertainties remain, however, about 

the levels and mechanisms involved in producing harmful 

effects in humans.

Exhibit 5-6 (continued). Blood concentrations of selected polychlorinated dibenzo-p-dioxins (dioxins), 

polychlorinated dibenzofurans (furans), and dioxin-like polychlorinated biphenyls (PCBs) for the U.S.

population age 20 years and older, lipid-adjusted and whole weight, 1999-2002a,b

Geometric mean and selected percentiles 

for dioxin, furan, and PCB concentrationsc,d,e

Survey years Sample size Geometric mean 50th 75th 90th 95th

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1,261

1,545

1,261

1,545

1,258

1,549

1,258

1,549

1,257

1,547

1,257

1,547

NC

23.3

NC

0.15

NC

32.6

NC

0.21

NC

23

NC

0.15

54.7

73.8

0.36

0.51

83.2

99.5

0.56

0.67

65.5

74

0.44

0.49

<LOD

44.6

<LOD

0.29

<LOD

62.8

<LOD

0.41

41

46.7

0.27

0.30

<LOD

23.9

<LOD

0.15

<LOD

35

<LOD

0.22

<LOD

26.4

<LOD

0.17

72.8

99.5

0.49

0.68

122

132

0.79

0.90

83.8

90.7

0.56

0.64

a

The 1999-2000 subsample included those aged 12-19 years and aged 20 years and older. The 2001-2002 subsample does not 

include the 12-19 year-old age group. To enable comparisons, this table presents results for the 20 and older age group only.

b

This table only includes individual congeners detected with sufficient frequency to calculate a geometric mean.

c

<LOD = below the limit of detection (LOD) of the analytical method (see CDC, 2005, for chemical-specific LODs).

d

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

e

Refer to CDC, 2005, for confidence intervals for reported values.

Data source: CDC, 2005

PCBs (units vary)

PCB 138 & 158 (ng/g)

Lipid-adjusted

Whole weight

PCB 153 (ng/g)

Lipid-adjusted

Whole weight

PCB 180 (ng/g)

Lipid-adjusted

Whole weight
HUMAN EXPOSURE AND HEALTH

5-20 EPA’s 2008 Report on the Environment

INDICATOR | Blood Persistent Organic Pollutants Level (continued)

PCBs are chlorinated aromatic hydrocarbons used in 

a variety of industries as electrical insulating and heat 

exchange fluids. PCBs are composed of mixtures of up 

to 209 different chlorinated congeners. U.S. production 

of PCBs peaked in the early 1970s; PCBs were banned in 

1979. Sources of exposure for the general population include 

releases from waste sites and fires involving transformers, 

ingestion of foods contaminated by PCBs, and migration 

from packaging materials. PCBs typically accumulate in 

fatty tissues (ATSDR, 2000).

The detection of PCBs in human blood can reflect either 

recent or past exposures. PCBs with higher degrees of chlorination persist in the human body from several months to 

years after exposure. Coplanar and mono-ortho substituted 

PCBs exhibit health effects similar to dioxins. The human 

health effects of PCBs include changes in liver function, 

elevated lipids, and gastrointestinal cancers (CDC, 2005).

What the Data Show

Organochlorine Pesticides

Exhibit 5-5 presents the lipid-adjusted and whole weight 

geometric means and four percentile values for selected 

organochlorine pesticide metabolites measured in blood. 

The overall geometric mean for p,p’-DDE (a metabolite for 

DDT) during the 1999-2000 survey was 260 nanograms 

per gram (ng/g), compared to 295 ng/g in 2001-2002. 

During the most recent survey (2001-2002), the geometric mean for trans-nonachlor (a component of technicalgrade chlordane) was 17 ng/g, compared with 18.3 ng/g in 

1999-2000. Aldrin, dieldrin, endrin, heptachlor epoxide 

(the metabolite for heptachlor), HCB, and mirex were 

not measured with sufficient frequency above the limit of 

detection to calculate a geometric mean.

Geometric mean blood concentrations of p,p’-DDE were 

compared among demographic groups after adjustment 

for the covariates of race/ethnicity, age, and gender. For 

samples collected between 1999 and 2002, the 12-19 year 

age group had less than half the blood p,p’-DDE level compared to the 20 years or older age group (CDC, 2005). The 

lipid-adjusted geometric mean level in Mexican Americans 

was 652 ng/g during the most recent survey, more than 

two and one-half times higher than levels in non-Hispanic 

whites and two times higher than levels in non-Hispanic 

blacks. It is unknown whether differences in geometric 

mean blood p,p’-DDE concentrations between different 

age groups or racial/ethnic groups represent differences in 

exposure, body size relationships, or metabolism (CDC, 

2005) (data not shown).

Dioxins and Furans

In the U.S., quantifiable emissions of dioxin-like compounds from all known sources have decreased by an 

estimated 90 percent between 1987 and 2000 (U.S. EPA, 

2006). Values reported in NHANES 1999-2000 and 

2001-2002 support that estimated decline (CDC, 2005). 

For example, among the entire NHANES 1999-2000 

sample population, TCDD (generally considered the most 

toxic dioxin) was detected less than 1 percent of the time 

(CDC, 2003). During 2001-2002, only a small number 

of the dioxin and furan congeners analyzed were detected 

frequently enough for geometric means to be calculated 

(Exhibit 5-6). TCDD continued to be among the list of 

congeners analyzed in NHANES 2001-2002, though only 

the 95th percentiles for women and non-Hispanic blacks 

could be characterized: 6.4 and 7.4 picograms per gram 

(pg/g) TCDD lipid-adjusted, respectively (data not shown). 

From NHANES 1999-2000, none of the six dioxin or 

nine furan congeners measured in the blood were detected 

with sufficient frequency to calculate a geometric mean. 

In general, the more highly chlorinated dioxin and furan 

congeners were the main contributors to the human body 

burden. The higher concentrations of these congeners 

in human samples are a result of their greater persistence 

in the environment, bioaccumulation in the food chain, 

resistance to metabolic degradation, and greater solubility 

in body fat (CDC, 2005). 

PCBs

During the NHANES 1999-2000 subsample period, 

none of the three coplanar and 25 other PCB congeners 

were measured in blood with sufficient frequency above 

the limit of detection to calculate a geometric mean. The 

frequency of detection of the eight mono-ortho substituted PCBs ranged from 2 to 47 percent (CDC, 2003). 

Coplanar PCB congeners 169 and 126, which exhibit 

dioxin-like toxicity, had a detection rate above 5 percent (CDC, 2003). In the 2001-2002 survey, a total of 

12 dioxin-like PCB compounds, three coplanar PCBs 

and nine mono-ortho-substituted PCBs, were measured 

in blood. A total of 25 non-dioxin-like PCBs were also 

included in the 2001-2002 NHANES analysis. However, 

only two coplanar PCBs and three non-dioxin-like PCB 

compounds were detected with sufficient frequency to 

calculate a geometric mean (Exhibit 5-6). Although some 

PCB congeners were detected with greater frequency during the 2001-2002 survey compared to 1999-2000, this 

may, in part, be attributed to improved limits of detection 

in NHANES 2001-2002 (CDC, 2005). After adjusting for 

a number of covariates (e.g., age, gender, blood cotinine, 

and lipid level), there were some differences observed in 

the concentrations of different PCB congeners between 

different demographic subgroups. However, it is unknown 

whether these differences represent differences in exposure, 

pharmacokinetics, or the relationship of dose per body 

weight (CDC, 2005). 
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-21

INDICATOR | Blood Persistent Organic Pollutants Level (continued)

Indicator Limitations

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes in 

estimates between the two time periods do not necessarily reflect a trend. As CDC releases additional survey 

results (e.g., 2003-2004), it will become possible to more 

fully evaluate trends (CDC, 2002, 2004).

•	 Generally recognized reference levels for organochlorine pesticides and dioxin, furan, and PCB congeners in 

blood have not yet been established. 

Data Sources

Data used for this indicator were extracted from the CDC 

report that presents results of the ongoing National Health 

and Nutrition Examination Survey (CDC, 2005). The 

underlying laboratory data supporting CDC’s report are 

available online in SAS® transport file format at http://

www.cdc.gov/nchs/about/major/nhanes/datalink.htm.

References

ATSDR (Agency for Toxic Substances and Disease Registry). 2000. Toxicological profile for polychlorinated 

biphenyls (PCBs). Atlanta, GA: U.S. Department of Health 

and Human Services, Public Health Service.

CDC (Centers for Disease Control and Prevention). 2005. 

Third national report on human exposure to environmental chemicals. NCEH publication no. 05-0570.

<http://www.cdc.gov/exposurereport/report.htm>

CDC. 2004. NHANES analytic guidelines. June 2004 

version. <http://www.cdc.gov/nchs/data/nhanes/nhanes_

general_guidelines_june_04.pdf>

CDC. 2003. Second national report on human exposure to 

environmental chemicals. NCEH publication 02-0716. 

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Updated August 30, 2002.

<http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf>

IARC (International Agency for Research on Cancer). 1997. 

Polychlorinated dibenzo-para-dioxins and polychlorinated 

dibenzofurans. IARC Monographs on the Evaluation of 

Carcinogenic Risks to Humans vol. 69. Lyon, France.

Reigart, J.R., and J.R. Roberts. 1999. Recognition and 

management of pesticide poisonings. Prepared for U.S. 

EPA. Accessed April 11, 2005. <http://www.epa.gov/

oppfead1/safety/healthcare/handbook/handbook.htm>

Ritter, L., K.R. Solomon, J. Forget, M. Stemeroff, and C. 

O’Leary. n.d. Persistent organic pollutants. Prepared for 

the International Programme on Chemical Safety within 

the framework of the Inter-Organization Programme for 

the Sound Management of Chemicals. 

<http://www.chem.unep.ch/pops/ritter/en/ritteren.pdf>

U.S. EPA (United States Environmental Protection 

Agency). 2006. An inventory of sources and environmental releases of dioxin-like compounds in the United States 

for the years 1987, 1995, and 2000. EPA/600/P-03/002F. 

Washington, DC. <http://cfpub.epa.gov/ncea/cfm/

recordisplay.cfm?deid=159286#Download>

U.S. EPA. 2004a. Pesticides: Regulating pesticides—

persistent organic pollutants (POPs). Updated August 

2004. Accessed December 7, 2004. 

<http://www.epa.gov/oppfead1/international/pops.htm>

U.S. EPA. 2004b. Hexachlorobenzene. Updated December 

2004. Accessed December 7, 2004. 

<http://www.epa.gov/pbt/pubs/hexa.htm>

U.S. EPA. 2004c. Mirex. Updated December 2004. 

Accessed December 7, 2004. 

<http://www.epa.gov/pbt/pubs/mirex.htm>

v
HUMAN EXPOSURE AND HEALTH

5-22 EPA’s 2008 Report on the Environment

INDICATOR | Urinary Pesticide Level

Pesticides are chemicals or biological agents that kill plant or animal pests. They include herbicides, insecticides, fungicides, and rodenticides. More than a billion 

pounds of pesticides are used in the U.S. each year to 

control weeds, insects, and other organisms that threaten 

or undermine human activities (Aspelin, 2003). Some of 

these compounds can be harmful to humans if ingested, 

inhaled, or otherwise contacted in sufficient quantities. 

The primary routes of exposure for the general population are ingestion of a treated food source and contact with 

applications in or near residential sites. Herbicide exposure can also result from contaminated water. Those who 

manufacture, formulate, and/or apply these chemicals can 

also be occupationally exposed. 

This indicator reports the results of human biomonitoring for three classes of non-persistent insecticides and 

three classes of herbicides, which can be measured through 

metabolites that result from the chemical breakdown of the 

pesticide within the body. Measurement of non-persistent 

pesticide metabolites in urine typically reflects recent 

exposure (i.e., in the last few days) due to the short time 

these metabolites remain within the body (CDC, 2005). 

The three classes of insecticides covered by this indicator are carbamates, organophosphates, and pyrethroids. 

Carbamate insecticides have a wide variety of uses, which 

include applications on agricultural crops, residential lawns 

and gardens, and golf courses. Carbamate insecticides do 

not persist long in the environment, so they have a low 

potential for bioaccumulation. Organophosphates are used 

to control a broad spectrum of insects. Although organophosphates are still used for insect control on many food 

crops, most residential uses are being phased out in the 

U.S. Pyrethroids are synthetic analogues of pyrethrins, 

which are natural chemicals found in chrysanthemum 

flowers. All three groups are neurotoxicants that act by 

overstimulating the nervous systems of exposed organisms. 

Symptoms of exposure to pesticides in these classes include 

muscle weakness or paralysis, difficulty breathing, difficulty concentrating, impaired coordination, and memory 

loss (CDC, 2005).

The three herbicide classes discussed here are licensed for 

both commercial and restricted use. Restricted use products 

can only be applied by certified applicators or under the 

supervision of such an applicator (U.S. EPA, 2003). The 

Exhibit 5-7. Urine concentrations of selected carbamate pesticide metabolites for the U.S. population 

age 6-59 years, 1999-2002

Geometric mean and selected percentiles

for carbamate metabolite concentrationsa,b,c

Survey years Sample size Geometric mean 50th 75th 90th 95th

1-Naphthold

μg/L of urine

μg/g of creatinine

2-Isopropoxyphenol

μg/L of urine

μg/g of creatinine

Carbofuranphenol

μg/L of urine

μg/g of creatinine

1999-2000

1999-2000

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1,998

1,998

1,917

2,503

1,917

2,502

1,994

2,530

1,994

2,529

1.70

1.52

NC

NC

NC

NC

NC

NC

NC

NC

6.20

6.80

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

2.72

3.00

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

1.22

1.25

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

12.0

11.6

<LOD

<LOD

<LOD

<LOD

0.74

<LOD

0.78

<LOD

a

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

b

<LOD = below the limit of detection (LOD) of the analytical method (see CDC, 2005, for chemical-specific LODs).

c

Refer to CDC, 2005, for confidence intervals for reported values.

d

1-Naphthol was not included in CDC, 2005.

Data source: CDC, 2003, 2005
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-23

INDICATOR | Urinary Pesticide Level (continued)

Exhibit 5-8. Urine concentrations of selected organophosphate pesticide metabolites for the U.S.

population age 6-59 years, 1999-2002

Geometric mean and selected percentiles

or organophosphate pesticide metabolite concentrationsa,b,c

Survey years Sample size Geometric mean 50th 75th 90th 95th

Dimethylphosphate

μg/L of urine

μg/g of creatinine

Dimethylthiophosphate

μg/L of urine

μg/g of creatinine

Dimethyldithiophosphate

μg/L of urine

μg/g of creatinine

Diethylphosphate

μg/L of urine

μg/g of creatinine

Diethylthiophosphate

μg/L of urine

μg/g of creatinine

Diethyldithiophosphate

μg/L of urine

μg/g of creatinine

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1,949

2,519

1,949

2,518

1,948

2,518

1,948

2,517

1,949

2,518

1,949

2,517

1,949

2,520

1,949

2,519

1,949

2,519

1,949

2,518

1,949

2,516

1,949

2,515

NC

NC

NC

NC

1.82

NC

1.64

NC

NC

NC

NC

NC

1.03

NC

0.92

NC

NC

0.46

NC

0.45

NC

NC

NC

NC

7.90

8.22

8.46

7.83

38.0

16.2

32.0

13.2

12.0

2.49

10.1

2.60

7.50

6.33

7.94

5.23

1.30

2.46

1.70

2.84

0.47

0.61

0.55

0.58

2.80

3.25

2.93

3.00

10.0

4.02

9.57

3.79

2.30

0.89

1.86

0.67

3.10

2.76

2.73

2.39

0.76

1.48

0.71

1.33

0.20

<LOD

0.20

<LOD

0.74

<LOD

0.81

<LOD

2.70

0.45

2.12

0.85

<LOD

<LOD

<LOD

<LOD

1.20

<LOD

0.92

<LOD

0.49

0.57

0.25

0.52

0.08

<LOD

0.07

<LOD

13.0

13.4

16.1

12.7

46.0

32.6

51.0

27.2

19.0

4.95

21.7

5.80

13.0

11.4

12.1

8.53

2.20

3.94

2.64

4.61

0.87

0.83

0.86

1.01

a

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

b

<LOD = below the limit of detection (LOD) of the analytical method (see CDC, 2005, for chemical-specific LODs).

c

Refer to CDC, 2005, for confidence intervals for reported values.

Data source: CDC, 2005
HUMAN EXPOSURE AND HEALTH

5-24 EPA’s 2008 Report on the Environment

INDICATOR | Urinary Pesticide Level (continued)

herbicide groups are chlorphenoxy acids, triazines, and 

chloroacetanilides. Symptoms of acute high-dose exposure 

to these herbicides can include skin and mucosal irritation 

as well as burning sensations in the nasopharynx and chest 

if inhaled (Reigart and Roberts, 1999).

This indicator presents pesticide urinary metabolite data 

collected as part of the Centers for Disease Control and Prevention’s (CDC’s) National Health and Nutrition Examination Survey (NHANES). NHANES is a series of surveys 

conducted by CDC’s National Center for Health Statistics 

that is designed to collect data on the health and nutritional 

status of the civilian, non-institutionalized U.S. population 

using a complex, stratified, multistage, probability-cluster 

design. CDC’s National Center for Environmental Health 

conducted the laboratory analyses for the biomonitoring 

samples. Beginning in 1999, NHANES became a continuous and annual national survey; biomonitoring for certain 

environmental chemicals also was implemented. Data for 

1999-2000 and 2001-2002 are presented here as a baseline, 

with the intent of reporting trends over larger time periods 

in the future. Carbamates, organophosphates, and herbicides 

were measured as part of NHANES 1999-2000; urinary 

levels of pyrethroids were added during the NHANES 

2001-2002 survey. This indicator presents data for a subsample of survey participants age 6 to 59 years. NHANES 

also measured levels of a class of persistent pesticides, the 

organochlorine pesticides, which are not discussed here but 

can be found under the Blood Persistent Organic Pollutants 

Level indicator (p. 5-15).

What the Data Show

Carbamates

Exhibit 5-7 presents the geometric means and four percentile values for unadjusted and creatinine-adjusted urinary 

concentrations of the carbamate pesticide metabolites. 

Of the three metabolites presented, only 1-naphthol was 

detected with sufficient frequency to calculate a geometric 

mean, which was 1.70 micrograms per liter (μg/L) and 1.52 

micrograms per gram (μg/g) (creatinine-adjusted).

Organophosphates

NHANES 1999-2000 and 2001-2002 measured urinary 

concentrations of dialkyl phosphates, which are the primary 

Exhibit 5-9. Urine concentrations of selected pyrethroid pesticide metabolites for the U.S. population age 

6-59 years, 2001-2002

Geometric mean and selected percentiles

of pyrethroid pesticide metabolite concentrationsa,b,c

Survey years Sample size Geometric mean 50th 75th 90th 95th

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2,539

2,538

2,539

2,538

2,525

2,524

2,539

2,538

2,539

2,538

NC

NC

NC

NC

NC

NC

NC

NC

0.32

0.32

<LOD

<LOD

0.49

0.44

1.20

1.45

<LOD

<LOD

1.69

1.46

<LOD

<LOD

0.16

0.22

0.41

0.72

<LOD

<LOD

0.69

0.58

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

0.28

0.28

<LOD

<LOD

0.89

0.78

2.50

2.55

<LOD

<LOD

3.32

3.10

a

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

b

<LOD = below the limit of detection (LOD) of the analytical method (see CDC, 2005, for chemical-specific LODs).

c

Refer to CDC, 2005, for confidence intervals for reported values.

Data source: CDC, 2005

4-Fluoro-3-phenoxybenzoic acid

μg/L of urine

μg/g of creatinine

cis-3-(2,2-Dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid

μg/L of urine

μg/g of creatinine

trans-3-(2,2-Dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid

μg/L of urine

μg/g of creatinine

cis-3-(2,2-Dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid

μg/L of urine

μg/g of creatinine

3-Phenoxybenzoic acid

μg/L of urine

μg/g of creatinine
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-25

INDICATOR | Urinary Pesticide Level (continued)

metabolites of many organophosphate compounds. Exhibit 

5-8 presents the geometric means and four percentile values 

for urinary concentrations and creatinine-adjusted urinary 

concentrations of these metabolites. Only three of the six 

urinary dialkyl phosphates presented (dimethylthiophosphate, diethylphosphate, and diethylthiophosphate) were 

measured with sufficient frequency above the limit of detection to calculate a geometric mean. The geometric means 

for those metabolites were 1.82 μg/L (1.64 μg/g creatinine), 

1.03 μg/L (0.92 μg/g creatinine), and 0.46 μg/L (0.45 μg/L 

creatinine), respectively.

Pyrethroids

Pyrethroid (parent and metabolite) compounds were not 

included in the NHANES 1999-2000 list of analytes measured in urine. During the 2001-2002 NHANES, however, 

five pyrethroid urinary metabolites were measured in urine 

samples from a subgroup of participants. Only one of these 

metabolites, 3-phenoxybenzoic acid, was measured with sufficient frequency above the limit of detection to calculate a 

geometric mean. The geometric mean concentration of this 

metabolite measured in urine was 0.32 μg/L (Exhibit 5-9). 

Herbicides

During the 1999-2000 survey, none of the direct metabolites of the three primary classes of herbicide were detected 

in urine with sufficient frequency above the limit of detection to calculate a geometric mean; therefore, data are not 

displayed. The metabolites 2,4,5-trichlorophenoxyacetic 

acid and atrazine mercapturate were detected in only 1.2 

percent and 3.3 percent, respectively, of the subsample 

(CDC, 2003). The minor metabolite 2,4-dichlorophenol 

had a geometric mean of 1.1 μg/L measured in urine; 

however, this metabolite can also be a result of metabolism 

of several other chemicals or a byproduct in the manufacture of chemicals. The findings from the 2001-2002 

survey were generally consistent with earlier findings 

showing these metabolites to be frequently near or below 

the limits of detection. Unlike the 1999-2000 results, 

2,4-dichlorophenol samples collected during 2001-2002 

were not detected with sufficient frequency above the 

detection limit to calculate a geometric mean. However, 

the reported concentrations of this metabolite at the 75th, 

90th, and 95th percentile were higher during the 2001-2002 

survey than during the 1999-2000 survey (CDC, 2005). 

(Data not shown.)

Indicator Limitations

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes in 

estimates between the two time periods do not necessarily 

reflect a trend. As CDC releases additional survey results 

(e.g., 2003-2004) it will become possible to more fully 

evaluate trends (CDC, 2002, 2004).

•	 Urine creatinine concentrations were used to adjust the 

urinary concentrations of pesticides and metabolites of 

pesticides and phthalates in subsets of adults participating 

in NHANES. Traditionally, this approach has been used 

in population groups without much diversity. However, the inclusion of multiple demographic groups (e.g., 

children) in NHANES may increase the variability in the 

urinary creatinine levels when comparing across these different study populations (Barr et al., 2004).

•	 Generally recognized reference levels for carbamate, 

organophosphate, herbicide, and pyrethroid metabolites 

in urine have not yet been established.

•	 Some metabolites may result from sources other than 

pesticide exposure. For example, 1-naphthol in the urine 

may reflect multiple sources of exposure, and is therefore 

not just an indicator of carbamate pesticide exposure. 

Data Sources

Data used for this indicator were extracted from two CDC 

publications that present results of the ongoing NHANES 

(CDC, 2003, 2005). The underlying laboratory data supporting CDC’s report are available online in SAS® transport file format at http://www.cdc.gov/nchs/about/major/

nhanes/datalink.htm.

References

Aspelin, A.L. 2003. Pesticide usage in the United States: 

Trends during the 20th century. Raleigh, NC: Center for 

Integrated Pest Management, North Carolina State University. <http://www.pestmanagement.info/pesticide_history/

index.pdf>

Barr, D.B., L.C. Wilder, S.P. Caudill, A.J. Gonzalez, 

L.L. Needham, and J.L. Pirkle. 2004. Urinary creatinine 

concentrations in the U.S. population: Implications for 

urinary biological monitoring measurements. Environ. 

Health Persp. 113:192-200. <http://ehp.niehs.nih.gov/

members/2004/7337/7337.html>

CDC (Centers for Disease Control and Prevention). 2005. 

Third national report on human exposure to environmental chemicals. NCEH publication no. 05-0570. 

<http://www.cdc.gov/exposurereport/report.htm>

CDC. 2004. NHANES analytic guidelines. June 2004 

version. <http://www.cdc.gov/nchs/data/nhanes/nhanes_

general_guidelines_june_04.pdf>

CDC. 2003. Second national report on human exposure to 

environmental chemicals. NCEH publication 02-0716.

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Updated August 30, 2002.

<http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf>
HUMAN EXPOSURE AND HEALTH

5-26 EPA’s 2008 Report on the Environment

INDICATOR | Urinary Pesticide Level (continued)

Reigart, J.R., and J.R. Roberts. 1999. Recognition 

and management of pesticide poisonings. Fifth edition. 

EPA/735/R-98/003. <http://www.epa.gov/oppfead1/

safety/healthcare/handbook/handbook.htm>

U.S. EPA (United States Environmental Protection 

Agency). 2003. Restricted use products (RUP) report. 

Accessed March 10, 2005.

<http://www.epa.gov/opprd001/rup/>

INDICATOR | Urinary Phthalate Level

Phthalates are industrial chemicals added to many consumer products such as food packaging, plastics (plastic 

bags, garden hoses, recreational toys, medical tubing, plastic clothes, etc.), adhesives, detergents, personal-care products (such as soap, shampoo, nail polish, etc.), and many 

others. Exposure can occur through food that has been in 

contact with phthalate containing packaging, as well as 

direct contact with products that contain phthalates. 

Acute high-dose exposure to di-2-ethylhexyl phthalate, 

for example, may be associated with mild gastrointestinal 

disturbances, nausea, and vertigo (U.S. EPA, 2005). Chronic 

exposure to phthalate compounds has been associated with 

damage to the liver and testes, cancer, and birth defects in 

animal studies. However, the extent to which these effects 

occur in humans is the subject of ongoing research; whether 

detected levels in humans are a health concern is not yet 

known (CDC, 2005; Kavlock et al., 2002a-g). 

This indicator is based on data collected by the National 

Health and Nutrition Examination Survey (NHANES). 

NHANES is a series of surveys conducted by the Centers 

for Disease Control and Prevention’s (CDC’s) National 

Center for Health Statistics that is designed to collect data 

on the health and nutritional status of the civilian, noninstitutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. CDC’s National 

Center for Environmental Health conducted the laboratory 

analyses for the biomonitoring samples. Beginning in 1999, 

NHANES became a continuous and annual national survey; 

biomonitoring for certain environmental chemicals also was 

implemented. Metabolites of phthalates are measured in 

urine as a biomarker of phthalate exposure in the population. Data for 1999-2000 and 2001-2002 are presented here 

as a baseline, with the intent of reporting trends across time 

as more data become available in the future.

What the Data Show

Exhibit 5-10 presents the geometric means and four percentiles for urinary concentrations and creatinine-adjusted 

urinary concentrations of 12 selected metabolites of phthalates among a subsample of participants age 6 years and older 

from the most current NHANES (2001-2002). Seven of the 

12 phthalates were also measured in the 1999-2000 survey 

and are also presented in the table. Mono-ethyl phthalate (the 

metabolite for diethyl phthalate, an industrial solvent used in 

many products including those containing fragrances) was 

the phthalate detected in the highest concentration during 

both surveys (1999-2000 and 2001-2002), with creatinineadjusted geometric mean concentrations of 163 and 167 

micrograms per gram (μg/g) of creatinine, respectively. 

In addition, other phthalate compounds such as 

mono-n-butyl phthalate (a metabolite for dibutyl phthalate, an industrial solvent used in cosmetics, printing inks, 

insecticides), mono-benzyl phthalate (a metabolite for 

benzylbutyl phthalate, an industrial solvent used in adhesives, vinyl flooring, and car care products), and mono2-ethyl-hexyl phthalate (a metabolite for di-2-ethylhexyl 

phthalate, used to produce flexible plastics) were detected 

in urine samples. Mono-cyclohexyl phthalate, monon-octyl phthalate, and mono-isononyl phthalate were 

not measured with sufficient frequency above the limit of 

detection to calculate a geometric mean for those samples 

collected between 1999 and 2002.

During the 1999-2000 and 2001-2002 surveys, the geometric mean levels for mono-ethyl phthalate, mono-n-butyl 

phthalate, mono-benzyl phthalate, and mono-2-ethylhexyl 

phthalate among specified demographic subgroups were 

compared after adjustment for the covariates of race/ethnicity, age, gender, and urinary creatinine. For those age 6-11 

years compared to the older age groups (12-19 years and 20+ 

years), urinary mono-ethyl phthalate levels were found to be 

lower, but urinary mono-butyl, mono-benzyl, and mono-2-

ethylhexyl phthalates were higher (CDC, 2005). Females 

tended to have a higher level than males for mono-ethyl, 

mono-butyl, and mono-benzyl phthalates. Non-Hispanic 

blacks had higher levels of mono-ethyl phthalate than nonHispanic whites or Mexican Americans. (Data not shown.)

Indicator Limitations

•	 Because the data from NHANES 1999-2000 and 

2001-2002 represent only two survey periods, changes in 

estimates between the two time periods do not necessarily reflect a trend. As CDC releases additional survey 

results (e.g., 2003-2004), it will become possible to more 

fully evaluate trends (CDC, 2002, 2004).

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-27

INDICATOR | Urinary Phthalate Level (continued)

Exhibit 5-10. Urine concentrations of selected phthalate metabolites in the U.S. population age 6 years 

and older, 1999-2002a

Geometric mean and selected percentiles of

phthalate metabolite concentrationsb,c,d

Survey years Sample size Geometric mean 50th 75th 90th 95th

Mono-methyl phthalate

μg/L of urine

μg/g of creatinine

Mono-isobutyl phthalate

μg/L of urine

μg/g of creatinine

Mono-(2-ethyl-5-hydroxyhexyl) phthalate

μg/L of urine

μg/g of creatinine

Mono-(2-ethyl-5-oxohexyl) phthalate

μg/L of urine

μg/g of creatinine

Mono-3-carboxypropyl phthalate

μg/L of urine

μg/g of creatinine

Mono-ethyl phthalate

μg/L of urine

μg/g of creatinine

Mono-n-butyl phthalate

μg/L of urine

μg/g of creatinine

Mono-benzyl phthalate

μg/L of urine

μg/g of creatinine

Mono-cyclohexyl phthalate

μg/L of urine

μg/g of creatinine

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

2,782

2,772

2,782

2,772

2,782

2,772

2,782

2,772

2,782

2,772

2,536

2,782

2,536

2,772

2,541

2,782

2,541

2,772

2,541

2,782

2,541

2,772

2,541

2,782

2,541

2,772

1.15

1.08

2.71

2.53

20.0

18.8

13.5

12.6

2.75

2.57

179

178

163

167

24.6

18.9

22.4

17.8

15.3

15.1

14.0

14.1

NC

NC

NC

NC

6.00

5.00

11.9

8.02

91.3

70.8

59.9

45.1

10.0

7.25

1,260

1,230

898

975

98.6

73.6

68.3

52.4

67.1

80.8

50.1

55.1

<LOD

0.40

<LOD

0.59

3.30

2.62

5.70

4.50

43.6

32.3

29.6

21.3

5.70

4.07

450

465

360

388

51.6

40.4

38.9

30.4

35.3

38.0

25.1

26.6

<LOD

<LOD

<LOD

<LOD

1.50

1.33

2.60

2.44

20.1

16.6

14.0

11.2

3.00

2.45

164

169

141

147

26.0

20.4

21.9

17.4

17.0

15.7

13.3

13.5

<LOD

<LOD

<LOD

<LOD

9.80

7.97

17.9

12.0

192

147

120

87.5

14.6

11.4

2,840

2,500

1,950

1,860

149

108

97.5

81.3

103

122

77.4

90.4

1.00

0.40

3.00

0.85

See notes at end of table. Continued
HUMAN EXPOSURE AND HEALTH

5-28 EPA’s 2008 Report on the Environment

INDICATOR | Urinary Phthalate Level (continued)

•	 Urine creatinine concentrations were used to adjust the 

urinary concentrations of phthalates and metabolites of 

phthalates in subsets of adults participating in NHANES. 

Traditionally, this approach has been used in population 

groups without much diversity. However, the inclusion of multiple demographic groups (e.g., children) in 

NHANES may increase the variability in the urinary 

creatinine levels when comparing across these different 

study populations (Barr et al., 2004).

•	 Differences in the excretion of various phthalates may be 

due to differences in either exposure or toxicokinetics. 

The low detection rates for some of the long alkyl chain 

phthalates metabolites may be due to significantly less 

metabolism to the monoester metabolite.

•	 It is unknown whether differences between ages, genders, or races/ethnicities represent differences in exposure, body-size relationships, or metabolism.

•	 Generally recognized reference levels for phthalate 

metabolites in urine have not been established. 

Data Sources

Data used for this indicator were extracted from the CDC 

report that presents results of the ongoing NHANES (CDC, 

2005). The underlying laboratory data supporting CDC’s 

report are available online in SAS® transport file format at 

http://www.cdc.gov/nchs/about/major/nhanes/datalink.htm.

References

Barr, D.B., L.C. Wilder, S.P. Caudill, A.J. Gonzalez, 

L.L. Needham, and J.L. Pirkle. 2004. Urinary creatinine 

concentrations in the U.S. population: Implications for 

urinary biological monitoring measurements. Environ. 

Health Persp. 113:192-200. <http://ehp.niehs.nih.gov/

members/2004/7337/7337.html>

CDC (Centers for Disease Control and Prevention). 2005. 

Third national report on human exposure to environmental chemicals. NCEH publication no. 05-0570. 

<http://www.cdc.gov/exposurereport/report.htm>

Exhibit 5-10 (continued). Urine concentrations of selected phthalate metabolites in the U.S. population 

age 6 years and older, 1999-2002a

Geometric mean and selected percentiles of

phthalate metabolite concentrationsb,c,d

Survey years Sample size Geometric mean 50th 75th 90th 95th

Mono-2-ethylhexyl phthalate

μg/L of urine

μg/g of creatinine

Mono-n-octyl phthalate

μg/L of urine

μg/g of creatinine

Mono-isononyl phthalate

μg/L of urine

μg/g of creatinine

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

1999-2000

2001-2002

2,541

2,782

2,541

2,772

2,541

2,782

2,541

2,772

2,541

2,782

2,541

2,772

3.43

4.27

3.12

3.99

NC

NC

NC

NC

NC

NC

NC

NC

14.8

22.8

10.8

18.2

1.60

<LOD

2.40

<LOD

<LOD

<LOD

<LOD

<LOD

7.60

9.80

5.88

7.94

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

3.20

4.10

3.08

3.89

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

<LOD

23.8

38.9

18.5

32.8

2.90

<LOD

3.51

<LOD

3.50

<LOD

4.29

<LOD

a

1999-2000 data are not available for mono-methyl phthalate, mono-isobutyl phthalate, mono-(2-ethyl-5-hydroxyhexyl) phthalate, 

mono-(2-ethyl-5-oxohexyl) phthalate, and mono-3-carboxypropyl phthalate.

b

NC = not calculated; the proportion of results below the limit of detection was too high to provide a valid result.

c

<LOD = below the limit of detection (LOD) of the analytical method (see CDC, 2005, for chemical-specific LODs).

d

Refer to CDC, 2005, for confidence intervals for reported values.

Data source: CDC, 2005
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-29

5.2.3 Discussion

What These Indicators Say About Trends 

in Human Exposure to Environmental 

Contaminants

The biomonitoring indicators presented in this section provide 

an overall representation of the levels of selected contaminants, or metabolites of contaminants, in human blood and 

urine across the U.S. population. Measurable levels of many of 

these contaminants appear in at least some subset of the populations tested. Together, these indicators help us understand 

the extent to which exposure to individual substances has or 

has not occurred on a national scale. As stated previously, the 

presence of a contaminant in human tissue does not by itself 

mean that the contaminant has caused or will cause adverse 

effects in that person. 

Lead, mercury, cadmium, persistent organic pollutant metabolites, and cotinine were reported at varying levels in sampled 

blood and the metabolites of pesticides and phthalates in the 

urine of a subset of those tested. Based on the available data, 

some notable changes in blood levels were reported over time, 

primarily for the metals. Compared to historical data collected 

by the Centers for Disease Control and Prevention (CDC), 

blood lead levels have been steadily declining since the 1980s. 

The same general observation is true for blood cotinine (see 

Section 2.4).

Most blood mercury levels in children and women tested 

were reported below 5.8 micrograms per liter (μg/L)—levels 

believed not to be associated with harmful health effects. 

However, nearly 6 percent of women tested showed blood 

mercury between 5.8 and 58 μg/L. The latter level is considered a general lower bound for neurological effects in developing fetuses and children of exposed mothers.9

Current National Health and Nutrition Examination Survey 

(NHANES) data sets provide some information about variability of biomarkers across age, gender, race, or ethnicity. 

Such analysis is only possible, however, for those chemicals 

frequently measured above the level of detection. For example, 

blood lead levels are highest among children; cadmium levels 

INDICATOR | Urinary Phthalate Level (continued)

CDC. 2004. NHANES analytic guidelines. June 2004 

version. <http://www.cdc.gov/nchs/data/nhanes/nhanes_

general_guidelines_june_04.pdf>

CDC. 2002. NHANES 1999-2000 addendum to the 

NHANES III analytic guidelines. Updated August 30, 2002.

<http://www.cdc.gov/nchs/data/nhanes/guidelines1.pdf>

U.S. EPA. 2005. Consumer factsheet on: di(2-ethylhexyl)

phthalate. Accessed March 21, 2005. <http://www.epa.

gov/safewater/dwh/c-soc/phthalat.html>

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, 

E. Faustman, P. Foster, et al. 2002a. NTP Center for the 

evaluation of risks to human reproduction: Phthalates expert 

panel report on the reproductive and developmental toxicity 

of di-n-octyl phthalate. Reprod. Toxicol. 16(5):721-734.

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, 

E. Faustman, P. Foster, et al. 2002b. NTP Center for the 

evaluation of risks to human reproduction: Phthalates expert 

panel report on the reproductive and developmental toxicity 

of di-n-hexyl phthalate. Reprod. Toxicol. 16(5):709-719.

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, 

E. Faustman, P. Foster, et al. 2002c. NTP Center for the 

evaluation of risks to human reproduction: Phthalates expert 

panel report on the reproductive and developmental toxicity 

of di-isononyl phthalate. Reprod. Toxicol. 16(5):679-708.

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, 

E. Faustman, P. Foster, et al. 2002d. NTP Center for the 

evaluation of risks to human reproduction: Phthalates expert 

panel report on the reproductive and developmental toxicity 

of di-isodecyl phthalate. Reprod. Toxicol. 16(5):655-678.

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, E. Faustman, P. Foster, et al. 2002e. NTP Center for 

the evaluation of risks to human reproduction: Phthalates 

expert panel report on the reproductive and developmental toxicity of di(2-ethylhexyl)phthalate. Reprod. Toxicol. 

16(5):529-653.

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, 

E. Faustman, P. Foster, et al. 2002f. NTP Center for the 

evaluation of risks to human reproduction: Phthalates expert 

panel report on the reproductive and developmental toxicity 

of di-n-butyl phthalate. Reprod. Toxicol. 16(5):489-527.

Kavlock, R., K. Boekelheide, R. Chapin, M. Cunningham, 

E. Faustman, P. Foster, et al. 2002g. NTP Center for the 

evaluation of risks to human reproduction: Phthalates expert 

panel report on the reproductive and developmental toxicity 

of butyl benzyl phthalate. Reprod. Toxicol. 16(5):453-487.

9 Centers for Disease Control and Prevention. 2005. Third national report 

on human exposure to environmental chemicals. NCEH publication no. 

05-0570.<http://www.cdc.gov/exposurereport/report.htm>

v
HUMAN EXPOSURE AND HEALTH

5-30 EPA’s 2008 Report on the Environment

are reported highest in the most recent survey in those 20 

years and older. Blood mercury levels are reported for children 

age 1-5 years and women of child-bearing age only, with the 

highest levels reported in the latter group. In most cases where 

disparities are observed, it is unknown whether the differences 

observed represent differences in exposure, pharmacokinetics 

(absorption, distribution, metabolism, and excretion), or the 

relationship of dose per body weight.10

Limitations, Gaps, and Challenges

Available national-level data provide information on the general magnitude of exposures that are occurring for this subset 

of contaminants. Further, they serve as a firm foundation 

or baseline for future analysis. However, available indicator 

data answer only a part of the question. At this point in time, 

most of the biomonitoring indicators alone do not (1) enable 

an extensive assessment of temporal trends; (2) identify and 

explain possible differences among some subpopulations; (3) 

provide information on the geographic distribution of the 

population of concern, or any particular “hot spots” that may 

exist; (4) reveal exposure conditions; (5) provide information 

for all contaminants of potential interest; (6) consider exposure to multiple contaminants; or (7) provide perspective as to 

whether measured levels are elevated or likely to cause harmful effects. These are the most notable limitations, challenges, 

and data gaps of EPA interest in answering the question of 

trends in exposure to environmental contaminants.

Temporal Trends

The relatively short time frame of the indicator data set limits 

the analysis of temporal trends, but these indicators can serve 

as a baseline for future analysis. Most of the indicators presented to answer this question reflect data from only one or 

two NHANES sampling periods (1999-2000 and 2001-2002). 

Only as additional NHANES reports are released every 2 

years will meaningful temporal trend analysis be possible. 

However, CDC has been monitoring blood lead and cotinine 

since approximately 1976; for these contaminants, more meaningful temporal trend analysis is possible. 

Subgroup Analysis

The adequacy of data for subgroup evaluations varies by 

indicator. The NHANES data sets presented in this chapter 

contain a sufficiently large sample size to provide reliable age, 

gender, race, and ethnicity subgroup analyses. In some cases, 

however, the numbers of observations were insufficient to 

meet statistical reliability or confidentiality requirements for 

reporting estimates for all race or ethnicity categories.11 The 

benefits of such analyses have been demonstrated in earlier 

NHANES subgroup comparisons of blood lead levels 

(e.g., children age 1-5 years, children living in urban or lowincome areas), which have allowed resources to be targeted to 

higher risk or susceptible populations. However, not all ages 

are represented for all biomarkers in NHANES. Further, in 

cases where a small percentage of samples had detectable concentrations of the measured contaminant, subgroup comparisons are impossible or less meaningful.

Geographic Trends

The data currently available do not allow for reliable regional 

subgroup analyses, because the number of geographic regions 

sampled each year is relatively small. Although the NHANES 

sampling scheme is designed to obtain a cross-section of data 

from various regions across the U.S., the data set is not sufficiently representative to allow inferences about regional levels 

of the selected biomonitoring indicators. 

Exposure Conditions

Biomonitoring data alone do not provide information on 

when or how exposure to a particular contaminant occurred. 

Many different exposure scenarios (e.g., acute high exposure versus long-term low-level exposures) can lead to the 

same concentration measured in the body. The measure does 

not necessarily identify the source(s) of that contaminant or 

how a person was exposed (e.g., exposure via drinking water 

versus food versus inhalation; environmental versus nonenvironmental source). Biomarkers of exposure integrate 

exposures across multiple exposure routes. Additional information on ambient conditions would be needed to determine what exposures contribute to concentrations in people’s 

bodies. For example, lead in children’s blood may come from 

exposure to airborne sources, contaminated water or food, 

or contaminated soil or dust. In addition, some biomarkers 

are not specific to a particular contaminant, making interpretation of the data and their significance uncertain. Lastly, 

some environmental contaminants are also produced in trace 

amounts by normal metabolic processes (e.g., formaldehyde 

and acetone), so their presence cannot always be attributed to 

external exposure.12,13

Other Environmental Contaminants

There are still many contaminants for which no biomonitoring indicators exist, and others that are simply not feasible to 

analyze using current technology or data collection methods. 

For example, although it is possible to measure the amount of 

radiation that a person is exposed to using a dosimeter, biomarkers are not yet feasible for national estimates of exposure 

to radon. Similar issues of feasibility exist with other contaminants, including most criteria air pollutants (e.g., ozone, 

nitrogen dioxide, carbon monoxide, and particulate matter), 

biological agents (e.g., molds, certain infectious agents such 

10 Centers for Disease Control and Prevention. 2005. Third national report 

on human exposure to environmental chemicals. NCEH publication no. 

05-0570.<http://www.cdc.gov/exposurereport/report.htm>

11 National Center for Health Statistics. 2006. Health, United States, 2006, 

with chartbook on trends in the health of Americans. DHHS publication 

no. 2006-1232. Hyattsville, MD Watson, W.P., and A. Mutti. 2004. Role of 

biomarkers in monitoring exposures to chemicals: Present position, future 

prospects. Biomarkers 9(3):211-242.

12 Watson, W.P., and A. Mutti. 2004. Role of biomarkers in monitoring 

exposures to chemicals: Present position, future prospects. Biomarkers 

9(3):211-242.

13 Bates, M.N., J.W. Hamilton, J.S. LaKind, P. Langenberg, M. O’Malley, and W. 

Snodgrass. 2005. Workgroup report: Biomonitoring study design, interpretation, and communication—lessons learned and path forward. Environ. Health 

Perspect. 113(11):1615-1621.
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-31

as bacteria or viruses, and dust mites), byproducts from the 

disinfection of drinking water (e.g., chlorine or chlorinecontaining compounds), and several contaminants commonly 

found in air and drinking water at Superfund sites (e.g., 

trichloroethylene and tetrachloroethylene, among others). In 

many cases, biomonitoring for these contaminants is either 

cost-prohibitive or not yet technologically feasible. However, 

biomonitoring methods are constantly evolving. For example, 

CDC has added a number of environmental contaminants to 

its biomonitoring efforts, which will be included in future 

reports. These include arsenic, polybrominated compounds, 

and perfluorinated compounds (e.g., perfluorooctane sulfonate 

and perfluorooctanoic acid), among others.14

In addition, researchers continue to evaluate whether certain 

chemicals, referred to as endocrine disruptors, may contribute to 

adverse health effects in humans and may impact the health of 

future generations. Information about the magnitude and pattern 

of human exposure to endocrine disruptors is being collected for 

only a small subset of chemicals that compose this group (e.g., 

PCBs, DDT and its metabolites); wider testing will be challenging because there are still many compounds that have not yet 

been classified as endocrine disruptors, but may someday be identified as such. Moreover, understanding the specific window of 

vulnerability during different stages of development will be critical in evaluating the potential harmful effects of these chemicals.

Multiple Contaminants

Current biomonitoring indicators do not consider the effects 

of exposures to multiple contaminants. Specifically, biomarker 

measurements that are collected in NHANES do not provide 

any perspective on how different classes of contaminants interact 

with one another once they enter the body and to what extent 

associated responses are additive, antagonistic, or synergistic.

Clinical Reference or Comparison Levels

For most available biomonitoring indicators, no general scientific consensus exists as to how to interpret measured levels of 

contaminants in blood and urine. For example, are measured 

levels associated with some clinical effect or elevated above 

some “safe” or “background” level? Tracking trends in exposure over time, combined with trends in ambient measurements 

and health outcome measurements, is a key part of establishing such reference values. Establishing background or reference ranges (distributions) will help in identifying people with 

unusually high exposure or the percentage of the populations 

with contaminant exposures above established levels of concern.

5.3 What Are the Trends 

in Health Status in the 

United States?

5.3.1 Introduction

An overarching goal of public health agencies is to increase 

quality and years of healthy life and to eliminate health disparities. Tracking historical trends in general health status can 

help identify where interventions have improved the health 

of a population or where interventions may be needed (e.g., 

exploring causative factors and preventive measures). For 

example, a key concern for EPA is what possible environmental exposures could be contributing to the diseases or conditions that are the leading causes of death in the U.S.

The topics covered under this question are broad and not 

intended to represent specific diseases or conditions related 

to the environment. Environmental contaminants from air, 

water, and land can influence the overall health of a nation. 

As described in Section 5.1, however, many factors other than 

the environment influence the health of a population, such 

as socio-demographic attributes, behavioral and genetic risk 

factors, level of preventive care, and quality of and access to 

health care. Though no consensus exists on the relative contribution of environmental exposures, tracking overall health 

in the U.S. provides important context for the next section of 

this chapter, which examines specific acute and chronic diseases and conditions that may be linked more specifically with 

exposures to environmental contaminants.

As defined by the World Health Organization, health is a state 

of complete physical, mental, and social well-being, and not 

the mere absence of disease or infirmity.15 The health status of 

a population can be measured by a wide range of factors: birth 

and death rates, life expectancy, quality of life, morbidity 

from specific diseases, risk factors, use of ambulatory care and 

inpatient care, accessibility of health personnel and facilities, 

financing of health care, health insurance coverage, and many 

other factors.16

While no single set of measures can completely characterize 

the health of a large and diverse population, CDC and other 

health agencies worldwide consistently have viewed life expectancy and mortality data as indicators of overall population 

health because they represent the cumulative effects of social 

and physical environmental factors, behavioral and genetic risk 

factors, and the level and quality of health care. These data 

include the leading causes of mortality (among both infants and 

14 Department of Health and Human Services. 2003. Candidate chemicals for 

possible inclusion in future releases of the national report on human exposure to 

environmental chemicals. Federal Register 68(189):56296-56298. September 30.

15 World Health Organization. 1946. Preamble to the constitution of the World 

Health Organization as adopted by the International Health Conference, 

New York, 19-22 June, 1946; signed on 22 July 1946 by the representatives of 

61 states (Official Records of the World Health Organization, no. 2, p. 100) 

and entered into force on 7 April 1948. 

16 U.S. Department of Health and Human Services. 2000. Healthy people 2010: 

Understanding and improving health. Second edition. Washington, DC: U.S. 

Government Printing Office. <http://www.health.gov/healthypeople/>
HUMAN EXPOSURE AND HEALTH

5-32 EPA’s 2008 Report on the Environment

the general population), which provide a broad perspective on 

the diseases and conditions that are having the greatest impact 

on the nation’s health. Infant mortality is a particularly useful 

measure of health status, because it indicates both the current 

health status of the population and predicts the health of the 

next generation.17 It reflects the overall state of maternal health 

as well as the quality and accessibility of primary health care 

available to pregnant women and infants. 

Tracking health status using such indicators provides information on changing or emerging trends. At the beginning of the 

20th century, the population of the U.S. was characterized by a 

low standard of living, poor hygiene, and poor nutrition; communicable diseases and acute conditions were major causes of 

most premature deaths. Over the course of the century, public 

health measures such as improved sanitation and drinking 

water treatment led to a dramatic decrease in deaths due to 

infectious diseases and a marked increase in life expectancy. 

As the population has aged, chronic diseases such as heart 

disease and cancer have become the leading causes of death.18

These diseases may require a different approach to prevention, 

detection, and treatment compared to the infectious and acute 

illnesses more common in the past.

5.3.2 ROE Indicators 

Other agencies such as CDC routinely assess the state of the 

nation’s health. EPA has drawn on the comprehensive data 

collection efforts and assessments conducted by these agencies 

in addressing this question. Three indicators are used to assess 

the trends in health status in the U.S. (Table 5-3). Life expectancy at birth is the number of years a newborn would expect to 

live if that person experienced the mortality schedule existing 

at the time of birth. Infant mortality is the number of infants 

who die before their first birthday. General mortality represents 

the number of all deaths nationwide and provides information 

on the leading causes of death. Mortality is also tracked using 

years of potential life lost, or the number of years “lost” by 

people in a population who die prematurely of a stated cause. 

These indicators are interrelated—e.g., declines in mortality 

result in increased life expectancy, and shifts in life expectancy 

are often used to describe changes in mortality; changes in 

infant mortality are reflected in general mortality as well. 

Where possible, the indicators for this question track health 

status among subpopulations (e.g., by gender, race, ethnicity). Generally, differences in mortality and life expectancy 

between black and white Americans have been tracked for 

the past several decades, in some cases as far back as the 1930s. 

A broader spectrum of race and ethnic group breakdowns is 

available for these indicators in more recent years, including 

American Indian/Alaska Native, Asian or Pacific Islander, 

and Hispanic origin. Subpopulation data are presented to 

the extent practicable under “What the Data Show” and/or 

within indicator exhibits.

17 National Center for Health Statistics. 2001. Healthy people 2000 final review. 

Hyattsville, MD: Public Health Service. <http://www.cdc.gov/nchs/data/

hp2000/hp2k01-acc.pdf>

18 Ibid.

Table 5-3. ROE Indicators of Trends in Health Status in the United States 

National Indicators Section Page

General Mortality 5.3.2 5-33

Life Expectancy at Birth 5.3.2 5-35

Infant Mortality 5.3.2 5-36
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-33

Overall mortality is a key measure of health in a population. Three measures of mortality are “all cause” 

mortality, cause-specific mortality, and years of potential 

life lost (YPLL). “All cause” mortality counts the total 

number of deaths due to any cause within a specified year, 

whereas cause-specific mortality statistics count the number of deaths due to a particular cause in a specified year. 

YPLL is defined as the number of years between the age 

at death and a specified age; that is, the total number years 

“lost” by persons in the population who die prematurely of 

a stated cause. Ranking the causes of death can provide a 

description of the relative burden of cause-specific mortality (NCHS, 2005).

This indicator is based on mortality data recorded in the 

National Vital Statistics System, which registers virtually 

all deaths nationwide from death certificate data. YPLL is 

calculated by subtracting the age at death from a selected 

age (e.g., 65, 75, 85), then summing the individual YPLLs 

across each cause of death (CDC, 2007). Sixty-five was 

selected as the age for this indicator to focus on deaths 

more likely to be attributable to preventable causes and less 

influenced by increasing age. The temporal coverage of the 

data is from 1933 to 2004 and data are collected from all 50 

states and the District of Columbia.

What the Data Show

An increase in the number of deaths in the U.S. has been 

observed over the last few decades, reflecting the increase 

in the size and aging of the population. However, the ageadjusted all cause mortality rates have declined yearly since 

1980 (except in years of influenza outbreaks in 1983, 1985, 

1988, 1993, and 1999) with the most recent available rate 

of 800.8 deaths per 100,000 people in 2004. Exhibit 5-11 

provides some historical perspective on trends in the ageadjusted mortality rates between 1940 and 2003, showing 

that age-adjusted rates were nearly twice as high in 1940 

as they were in 2000. The largest decline in “all cause” 

mortality rates since 1990 has occurred among black males 

compared with white males and black and white females.

The rank order of the leading causes of death has 

remained generally the same since 1999. The one difference is Alzheimer’s disease, which was the eighth leading 

cause of death between 1999 and 2003 but became the 

seventh leading cause in 2004, displacing influenza and 

pneumonia. Exhibits 5-12 and 5-13 present the leading 

causes of mortality and YPLL for 2004, respectively. The 

three leading causes of death were heart disease, cancer, 

and stroke, accounting for about 60 percent of all deaths. 

The YPLL ranking is different, with unintentional injuries, 

cancer, and heart disease as the leading three causes. 

During 2004, heart disease was the leading cause of 

death across the reported racial and ethnic groups, except 

for Asians or Pacific Islanders for whom cancer (malignant 

neoplasms) was the leading cause of death. In addition, 

diabetes was ranked as the fourth leading cause of death 

among blacks and American Indians/Alaska Natives (both 

sexes), which was a higher ranking than for most of the 

other racial and ethnic groups. (Data not shown.)

Indicator Limitations

•	 Cause of death rankings denote the most frequently 

occurring causes of death among those causes eligible 

to be ranked. The rankings do not necessarily denote 

the causes of death of greatest public health importance. 

Further, rankings of cause-specific mortality could change 

depending on the defined list of causes that are considered 

and, more specifically, the types of categories and subcategories that are used for such rankings (NCHS, 2005). 

•	 Mortality rates are based on underlying cause of death as 

entered on a death certificate by a physician. Incorrect 

coding and low rates of autopsies that confirm the cause of 

death may occur. Additionally, some individuals may have 

had competing causes of death. “When more than one 

cause or condition is entered by the physician, the underlying cause is determined by the sequence of conditions on 

the certificate, provisions of the ICD [International Classification of Diseases], and associated selection rules and 

modifications” (CDC, n.d.). Consequently, some misclassification of reported mortality might occur as a result of 

these uncertainties, as well as the underreporting of some 

causes of death. 

Data Sources

Mortality rates were obtained from vital statistics reports 

published by CDC’s National Center for Health Statistics 

(NCHS, 2001, 2007). Data in the NCHS reports are based 

INDICATOR | General Mortality

Age-adjusted rate

(per 100,000)

Year

Exhibit 5-11. Age-adjusted “all cause” mortality 

rates in the U.S., 1940-2004a,b

a

Rates are age-adjusted to the 2000 U.S. 

standard population.

b

Mortality rates were not generally reported for 

black males and black females prior to 1964.

Data source: NCHS, 2001, 2007

’40 ’50 ’60 ’70 ’80 ’90 ’00

All groups

Male (white)

Female (white)

Male (black)

Female (black)

0

500

1,000

1,500

2,000

2,500
HUMAN EXPOSURE AND HEALTH

5-34 EPA’s 2008 Report on the Environment

in part on unpublished work tables, available on the NCHS Web site at http://www.

cdc.gov/nchs/deaths.htm. Leading cause 

of death and YPLL data were extracted 

from CDC’s Web-Based Injury Statistics 

Query and Reporting System (WISQARS) 

(CDC, 2007) (http://www.cdc.gov/

ncipc/wisqars/). The underlying data in 

WISQARS come from CDC/NCHS 

annual mortality data files.

References

CDC (Centers for Disease Control and Prevention). 2007. National Center for Injury 

Prevention and Control. Web-Based Injury 

Statistics Query and Reporting System 

(WISQARS) [online]. Leading causes of 

death and years of potential life lost (YPLL) 

reports, 1999-2004. Accessed October 2, 

2007. 

<http://webappa.cdc.gov/sasweb/ncipc/

leadcaus.html>

<http://webappa.cdc.gov/sasweb/ncipc/

ypll10.html> 

CDC. n.d. CDC WONDER: Help page for 

compressed mortality file. Accessed October 2007. <http://wonder.cdc.gov/wonder/

help/cmf.html>

NCHS (National Center for Health Statistics). 2007. Deaths: Final data for 2004. 

National Vital Statistics Reports 55(19).

<http://www.cdc.gov/nchs/data/nvsr/

nvsr55/nvsr55_19.pdf>

NCHS. 2005. Deaths: Leading causes for 

2002. National Vital Statistics Reports 

53(17). <http://www.cdc.gov/nchs/data/

nvsr/nvsr53/nvsr53_17.pdf>

NCHS. 2001. Age-adjusted death rates; 

trend data based on the year 2000 standard 

population. National Vital Statistics Reports 

49(9). <http://www.cdc.gov/nchs/data/

nvsr/nvsr49/nvsr49_09.pdf>

INDICATOR | General Mortality (continued)

Percent of all YPLLa

 19.1

 16.2

 12.2

 7.9

 5.9

 4.9

 4.2

 2.3

 2.1

 2.0

YPLL

486,853

231,132

565,979

261,784

245,074

922,191

1,877,690

2,219,044

687,395

2,702,330

1,413,158

Exhibit 5-13. Years of potential life lost (YPLL) before age 65 

in the U.S., 2004

a

Totals may not add to 100% due to rounding.

Data source: CDC, 2007 

Cause of death

Accidents (unintentional injuries)

Cancer (malignant neoplasms)

Heart disease

Perinatal period

Suicide

Homicide

Congenital anomalies

HIV

Stroke (cerebrovascular)

Liver disease

All other causes 23.3

Percent of all deathsa Number 

of deaths

65,965

33,373

73,138

59,664

42,480

121,987

553,888 

652,486

112,012

532,548

150,074

Exhibit 5-12. Leading causes of death in the U.S., 2004

a

Totals may not add to 100% due to rounding.

Data source: CDC, 2007

Cause of death

Heart disease

Cancer (malignant neoplasms)

Stroke (cerebrovascular)

Chronic lower respiratory diseases

Accidents (unintentional injuries)

Diabetes mellitus

Alzheimer’s disease

Influenza and pneumonia

Nephritis

Septicemia

All other causes

27.2

23.1

6.3

5.1

4.7

3.1

2.8

2.5

1.8

1.4

22.2

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-35

Life expectancy at birth is often used to appraise the overall health of a given population (NCHS, 2006a). 

Changes in life expectancy over time are commonly used 

to describe trends in mortality. Life expectancy is the average number of years at birth a person could expect to live 

if current mortality trends were to continue for the rest of 

that person’s life. 

This indicator is based on data from the National Vital 

Statistics System, which registers virtually all deaths and 

births nationwide. The temporal coverage of the data is 

from 1933 to 2004 and data are collected from all 50 states 

and the District of Columbia. 

What the Data Show

Exhibit 5-14 presents the historical trends in life expectancy at birth for the entire population as well as by gender 

and race (black and white) between 1940 and 2004, showing an upward trend in life expectancy in the U.S. over 

time. Life expectancy at birth has increased throughout the 

20th and now into the 21st century. The overall life expectancy was the highest ever reported in 2004 at 77.8 years, 

increasing from 77.4 in 2003. 

Life expectancy continues to increase for both males 

(73.9 years in 1999 to 75.2 years in 2004) and females 

(79.4 years in 1999 to 80.4 years in 2004). The gap in life 

expectancy between males and females widened from 2.0 

years to 7.8 years between 1900 and 1979. Recently, this 

gap narrowed for the year 2000 (a difference of 5.4 years 

between males and females) and remained relatively constant through 2004 (a difference of 5.2 years between males 

and females). (Data not shown.)

The increase in life expectancy among blacks reported 

for 1999 (71.4 years) continued, with a reported life expectancy of 73.1 years in 2004. The difference in life expectancy between the black and white populations was 5.2 

years in 2004. In 2004, white females continued to have 

the highest life expectancy at 80.8 years, followed by black 

females at 76.3 years, white males at 75.7 years, and black 

males at 69.5 years (Exhibit 5-14).

Indicator Limitations

•	 Life expectancy at birth is strongly influenced by infant 

and child mortality rates. It is important to consider such 

influences when making comparisons among subgroups, 

since differences in life expectancy among certain 

subgroups may be mostly attributed to differences in 

prenatal care and other important determinants of infant 

and child mortality. 

Data Sources

The annual life expectancy data used for this indicator were 

obtained from life tables published by CDC’s National 

Center for Health Statistics (NCHS, 2006b). NCHS also 

publishes life expectancy data in its annual “deaths: final 

data” reports (e.g., NCHS, 2007); however, these reports 

generally provide year-by-year breakdowns beginning in 

1975. NCHS life table reports provide annual data back to 

before 1940. Life table methodologies used to calculate life 

expectancies are presented in each of these NCHS reports.

References

NCHS (National Center for Health Statistics). 2006a. 

Health, United States, 2006, with chartbook on trends 

in the health of Americans. DHHS Publication No. 

2006-1232. Hyattsville, MD.

NCHS. 2006b. United States life tables, 2003. National 

Vital Statistics Reports 54(14). Table 12. <http://www.cdc.

gov/nchs/data/nvsr/nvsr54/nvsr54_14.pdf>

NCHS. 2007. Deaths: Final data for 2004. National Vital 

Statistics Reports 55(19). Table 8. <http://www.cdc.gov/

nchs/data/nvsr/nvsr55/nvsr55_19.pdf>

INDICATOR | Life Expectancy at Birth 

Age (years)

Year

Exhibit 5-14. Life expectancy in the U.S. by

race and sex, 1940-2004

Data source: NCHS, 2006b, 2007

’40 ’50 ’60 ’70 ’80 ’90 ’00

All groups

Male (white)

Female (white)

Male (black)

Female (black)

50

55

60

65

70

75

80

85

0

v
HUMAN EXPOSURE AND HEALTH

5-36 EPA’s 2008 Report on the Environment

I

nfant mortality is a particularly useful measure of health 

status because it both indicates current health status of the 

population and predicts the health of the next generation 

(NCHS, 2001). Infant mortality in the U.S. is defined as 

the death of an infant from time of live birth to the age of 

1 year. It does not include still births. Overall infant mortality is composed of neonatal (less than 28 days after birth) 

and postneonatal (28 days to 11 months after birth) deaths.

This indicator presents infant mortality for the U.S. 

based on mortality data from the National Vital Statistics 

System (NVSS) based on death certificate data. The NVSS 

registers virtually all deaths and births nationwide, with 

data coverage from 1933 to 2004 and from all 50 states and 

the District of Columbia. 

What the Data Show

In 2004, a total of 27,936 deaths occurred in children under 

1 year of age, 89 fewer deaths than in 2003. Exhibit 5-15 

presents the national trends in infant mortality between 

1940 and 2004 for all infant deaths as well as infant deaths 

by gender and race (black and white). A striking decline 

has occurred during this time period, with overall infant 

mortality rates dropping from nearly 50 deaths per 1,000 

live births in 1940 to just under seven deaths per 1,000 live 

births in 2004. Beginning around 1960, the infant mortality rate has decreased or remained level each successive year 

through 2004, except for 2002. From 2000 to 2004, infant 

mortality rates ranged from 6.8 (2001 and 2004) to nearly 

7.0 (2002) per 1,000 live births. Infant mortality rates were 

highest among black males and lowest among white females, 

although this gap has been decreasing over time. 

The infant mortality rate for blacks decreased from 14.6 

per 1,000 live births in 1999 to 13.8 per 1,000 live births in 

2004. However, this is still twice the rate compared to white 

infants, which ranged from approximately 5.7 to 5.8 per 

1,000 live births between 1999 and 2004. Infant mortality 

rates among Hispanic infants have changed little since 1999. 

In 2004, the infant mortality rate for Hispanic infants was 

5.6 per 1,000 live births (NCHS, 2007a). (Data not shown.) 

In the U.S. in 2004, the 10 leading causes of infant mortality accounted for nearly 69 percent of all infant deaths, 

with the subgroup consisting of congenital anomalies (i.e., 

congenital malformations, deformations, and chromosomal 

abnormalities) having the highest rate at nearly 1.4 per 1,000 

live births. This category alone accounts for approximately 

20 percent of all infant deaths in 2004 (Exhibit 5-16). 

Congenital anomalies were generally ranked highest 

among the different racial groups. However, the leading 

cause of infant mortality among blacks was short gestation and low birthweight, followed by congenital anomalies. There were few differences in the leading causes of 

infant mortality between Hispanics and non-Hispanics. 

In addition, the Centers for Disease Control and Prevention (CDC) report a substantial difference in the leading 

causes of death during the neonatal versus the postneonatal periods. Disorders related to short gestation and low 

birthweight were the leading cause of death for neonates 

and sudden infant death syndrome was the leading cause 

of death for postneonates, based on 2003 data (NCHS, 

2007b). (Data not shown.) 

Indicator Limitations

•	 Cause of death rankings denote the most frequently 

occurring causes of death among those causes eligible 

to be ranked. The rankings do not necessarily denote 

the causes of death of greatest public health importance. 

Further, rankings of cause-specific mortality could change 

depending on the defined list of causes that are considered 

and, more specifically, the types of categories and subcategories that are used for such rankings (NCHS, 2005).

•	 Mortality rates are based on underlying cause of death as 

entered on a death certificate by a physician. Incorrect 

coding and low rates of autopsies that confirm the cause 

of death may occur. Additionally, some individuals may 

have had competing causes of death. “When more than 

one cause or condition is entered by the physician, the 

underlying cause is determined by the sequence of conditions on the certificate, provisions of the ICD [International Classification of Diseases], and associated selection 

rules and modifications” (CDC, n.d.). Consequently, 

some misclassification of reported mortality might occur 

as a result of these uncertainties, as well as the underreporting of some causes of death. 

INDICATOR | Infant Mortality

Rate (per 1,000 live births)

Year

Exhibit 5-15. Infant mortality rates in the U.S.

by race and sex, 1940-2004a,b

a

Race was reported based on the race of the 

child (1940-1979) or the race of the mother 

(1980-2004).

b

Annual infant mortality rates are not available 

prior to 1975 in published sources. Trends 

presented from 1940-1974 are based on data 

published for 1940, 1950, 1960, and 1970. 

Data source: NCHS, 2007

All groups

Male (white)

Female (white)

Male (black)

Female (black)

0

20

40

60

80

’40 ’50 ’60 ’70 ’80 ’90 ’00
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-37

Data Sources

Infant mortality data were obtained from a published 

report by CDC’s National Center for Health Statistics 

(NCHS, 2007a), which provides annual natality data back 

to 1975 and decadal data for 1940, 1950, 1960, and 1970. 

Data in the NCHS report are based in part on unpublished 

work tables, available on the NCHS Web site at http://

www.cdc.gov/nchs/deaths.htm. Leading cause of infant 

death data were extracted from CDC’s Web-Based Injury 

Statistics Query and Reporting System (WISQARS) 

(CDC, 2007) (http://www.cdc.gov/ncipc/wisqars/), with 

supporting documentation from NVSS reports (NCHS, 

2007). The underlying data in WISQARS come from 

CDC/NCHS annual mortality data files.

References

CDC (Centers for Disease Control and Prevention). 

2007. National Center for Injury Prevention and Control: 

Web-Based Injury Statistics Query and Reporting System 

(WISQARS) [online]. Leading causes of death reports, 

1999-2004. Accessed October 8, 2007. 

<http://webapp.cdc.gov/sasweb/ncipc/leadcaus.html>

CDC. n.d. CDC WONDER: Help page for compressed 

mortality file. Accessed October 2007. 

<http://wonder.cdc.gov/wonder/help/cmf.html>

NCHS (National Center for Health Statistics). 2007. 

Deaths: Final data for 2004. National Vital Statistics 

Reports 55(19). <http://www.cdc.gov/nchs/data/nvsr/

nvsr55/nvsr55_19.pdf> 

NCHS. 2005. Deaths: Leading causes for 2002. National 

Vital Statistics Reports 53(17). <http://www.cdc.gov/nchs/

data/nvsr/nvsr53/nvsr53_17.pdf>

NCHS. 2001. Healthy people 2000 final review. 

Hyattsville, MD: Public Health Service. 

<http://www.cdc.gov/nchs/data/hp2000/hp2k01-acc.pdf>

INDICATOR | Infant Mortality (continued)

Percent of all infant deathsb

 20.1

 16.6

 8.0

 6.1

 3.8

 3.7

 3.1

 3.0

 2.2

 2.1

Number of deaths

875

593

1,042

827

616

1,715

4,642

5,622

1,052

8,706

2,246

Exhibit 5-16. Leading causes of infant death in the U.S., 2004a

a

“Infant deaths” are those occurring before the age of 1.

b

Totals may not add to 100% due to rounding.

Data source: CDC, 2007

Cause of death

Congenital malformations, deformations, and chromosomal abnormalities

Disorders related to short gestation and low birthweight

Sudden infant death syndrome (SIDS)

Newborn affected by maternal complications of pregnancy

Accidents (unintentional injuries)

Newborn affected by complications of placenta, cord, and membranes

Respiratory distress of newborn

Bacterial sepsis of newborn

Neonatal hemorrhage

Circulatory system disease

 All other causes 31.2

v
HUMAN EXPOSURE AND HEALTH

5-38 EPA’s 2008 Report on the Environment

5.3.3 Discussion

What These Indicators Say About Trends in 

Health Status in the United States

ROE indicators used to answer this question show that the 

overall health of the nation has continued to improve. The 

three leading causes of death across all age groups—heart 

disease, cancer, and stroke—remain unchanged since 1999. 

In contrast, a ranking by years of potential life lost, which 

weighs deaths at an earlier age more heavily, places unintentional injuries, cancer, and heart disease as the top three 

(General Mortality indicator, p. 5-33). Although men and 

women in many other countries have longer life expectancies, general mortality rates in the U.S. continue to decline, 

and life expectancy continues a long-term upward trend 

(Life Expectancy indicator, p. 5-35). See Box 5-2 for an 

overview of health status in the U.S. compared to the rest of 

the world.

The decline in the all cause mortality rate since 1940 has been 

driven largely by declines in deaths from heart disease, stroke, 

and unintentional injuries. These trends have been linked in 

part to the resources devoted to health education, public health 

programs, health research, and health care, and the impact 

of these efforts on controlling disease. For example, public 

campaigns about smoking and the use of cholesterol-lowering 

drugs have contributed to a decline in the death rate from heart 

disease. Efforts to improve motor vehicle safety as well as safety 

in homes and workplaces have helped to lower death rates from 

unintentional injuries. New medical treatments have resulted in 

a decline in the death rate from HIV.19

Infant Mortality (p. 5-36), like the other two indicators, shows a long-term decline, likely due to widespread 

application of advances in medical knowledge (such as the 

introduction of synthetic surfactant for preterm infants and 

widespread public education about infant sleep position).20

However, infant mortality in the U.S. remains among the 

highest in the industrialized world. In 2003 and 2004, the 

infant mortality rates decreased after increasing in 2002 for 

the first time since 1958. The 2002 rise in infant mortality 

was attributed to an increase in neonatal deaths (infants less 

than 28 days old), particularly deaths of infants within the 

first week of life.21

Despite a generally improving picture of the nation’s health, 

racial and ethnic disparities in health status persist. For example, 

though the nation’s infant mortality rate has decreased, the 

infant death rate for black infants is still more than double that 

of whites. In 2004, the gap in life expectancy between the black 

and white populations is 5.2 years, though this gap has been 

narrowing.22 Differences in death rates also exist between black 

and white populations. Observed differences are believed to be 

the result of a complex interaction of genetic variations, environmental factors, and specific health behaviors.23

19 National Center for Health Statistics. 2006. Health, United States, 2006, 

with chartbook on trends in the health of Americans. DHHS publication no. 

2006-1232. Hyattsville, MD. p. 3. 

20 National Center for Health Statistics. 2001. Healthy people 2000 final review. 

Hyattsville, MD: Public Health Service. p. 206. <http://www.cdc.gov/nchs/

data/hp2000/hp2k01-acc.pdf>

21 National Center for Health Statistics. 2005. Health, United States, 2005, 

with chartbook on trends in the health of Americans. DHHS publication no. 

2005-1232. Hyattsville, MD. p. 66. 

22 Ibid. pp. 11-12. 

23 U.S. Department of Health and Human Services. 2000. Healthy people 2010: 

Understanding and improving health. Second edition. Washington, DC: U.S. 

Government Printing Office. <http://www.health.gov/healthypeople/>

The following comparisons are based on the most current 

statistics for each of the three indicators used to study U.S. 

health status. The World Health Organization (WHO) 

calculates its statistics to ensure comparability across data 

sets; the statistics may not fully match those generated by 

individual countries and reported in other reports.

Life expectancy: According to the WHO, in 2004, the 

U.S. ranked 35th in terms of life expectancy for males and 

females of the 192 WHO member states.a Japan reports the 

highest life expectancy (82 years, compared to the U.S life 

expectancy of 78 years reported by WHO).

Leading causes of death: The leading causes of death 

reported in the U.S. continue to be heart disease, cancer, 

and stroke. Worldwide, as reported for 2002, cardiovascular 

diseases accounted for the largest percentage of deaths, followed by infectious and parasitic diseases and cancer.b

Infant mortality: In 2003, the United States ranked 28th

among the 37 countries, territories, cities, or geographic 

areas with at least 1 million population considered to have 

completed counts of live births and infant deaths as indicated in the United Nations Demographic Yearbook.c

 The 

U.S. infant mortality rate for the same time period (6.9 per 

1,000 live births) was approximately 2 to 3 times higher 

than the lowest rates reported worldwide (e.g., in Hong 

Kong the rate was 2.3, in Singapore 2.5, in Japan 3.0, and in 

Sweden 3.1, per 1,000 live births).

Box 5-2. Worldwide Comparisons in Health Status

a World Health Organization. 2006. World Health Report. See Statistical Annex 

Table 1. <http://www.who.int/entity/whr/2006/annex/annex1.xls>

b World Health Organization. 2005. Incidence, prevalence, mortality, YLL, 

YLD and DALYs by sex, cause and region, estimates for 2002 as reported 

in the World Health Report 2004. <http://www.who.int/healthinfo/

bodgbd2002revised/en/index.html>

c National Center for Health Statistics. 2006. Health, United States, 2006, 

with chartbook on trends in the health of Americans. Hyattsville, Maryland. DHHS Publication No. 2006-1232. Table 25. <http://www.cdc.gov/

nchs/data/hus/hus05.pdf>
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-39

Differences also exist between men and women. Based on 2004 

data, men have a life expectancy 5.2 years less than that of 

women and have higher death rates for each of the 10 leading 

causes of death. However, women have shown increased death 

rates over the past decade in areas where men have experienced 

improvements, such as lung cancer.24

Limitations, Gaps, and Challenges

The indicators are important and widely accepted measures 

of population health status. However, the selected indicators 

cannot be expected to fully answer the question on trends in 

general U.S. health status. Limitations and information gaps 

are highlighted here. 

The indicators provide a broad measure of health status and 

include many variables that are not related to the environment. No conclusions, therefore, can or should be drawn 

about the role of exposure to environmental contaminants 

using these indicators alone. While declining mortality rates 

and increasing life expectancy suggest improving health status, 

these indicators do not address other aspects of health, such as 

morbidity, perceived well-being, or quality of life. 

The use of mortality data presents some limitations, largely 

related to uncertainties associated with the use of death certificate data. First, correct coding of the underlying cause of 

death and confirmation by autopsy may not occur. Second, 

uncertainties in intercensal population estimates can affect 

conclusions about trends in data sets. In addition, improved 

data on the health status of population subgroups—particularly 

across race and ethnic groups—would allow better characterization of potential trends across different groups. Accurate 

identification of health disparities will require improved data 

collection and the use of standardized data. For example, 

problems of race and Hispanic-origin classification can affect 

Hispanic death rates and the comparison of rates across the 

Hispanic and non-Hispanic populations.25

5.4 What Are the Trends 

in Human Disease 

and Conditions for 

Which Environmental 

Contaminants May Be 

a Risk Factor, Including 

Across Population 

Subgroups and 

Geographic Regions?

5.4.1 Introduction

As discussed throughout this report, numerous human diseases 

and conditions have been linked with exposures to environmental contaminants, some more strongly than others. Identifying 

diseases that might be associated with environmental contaminants, and determining the existing data sources available 

for them, is a key part of the effort to better characterize links 

between environmental exposures and adverse health outcomes. 

Tracking overall rates of disease in the nation, independent 

of exposure, enables the evaluation of disease patterns and 

emerging trends. It may identify diseases, conditions, and 

possible risk factors that warrant further study or intervention and can help identify where policies or interventions have 

been successful. Because the U.S. has a diverse population, an 

important component of such an analysis is identifying disparities among people of differing races and ethnicities, genders, 

education and income levels, and geographic locations. 

EPA has selected those human diseases and conditions with 

well-established associations with exposures to environmental 

contaminants and for which national data are available, recognizing again that in most cases risk factors are multi-factorial 

and that the development of a particular disease or condition 

depends on the magnitude, duration, and timing of the exposure. The diseases and conditions addressed in this question 

are associated with the contaminant sources covered by the 

questions in the three media chapters (Chapters 2, 3, and 4) of 

this report. As described in Section 5.1, however, this question 

is not intended to tie human diseases and conditions to specific 

changes in the environment being measured at the national 

level. Covered health outcomes fall into the following five 

broad categories: cancer, cardiovascular disease, respiratory 

24 National Center for Health Statistics. 2006. Health, United States, 2006, 

with chartbook on trends in the health of Americans. DHHS publication no. 

2006-1232. Hyattsville, MD. pp. 11-12.

25 National Center for Health Statistics. 2006. Deaths: Final data for 2003. 

National Vital Statistics Reports 54(13). <http://www.cdc.gov/nchs/data/

nvsr/nvsr54/nvsr54_13.pdf>
HUMAN EXPOSURE AND HEALTH

5-40 EPA’s 2008 Report on the Environment

disease, infectious disease, and birth outcome. The reasons for 

the inclusion of each are highlighted below.

Cancer

The term “cancer” refers to diseases in which abnormal cells 

divide without control, losing their ability to regulate their own 

growth, control cell division, and communicate with other cells. 

Cancer is the second leading cause of death in the U.S. (General 

Mortality indicator, p. 5-33). More than one in three people 

will develop cancer and nearly one in four will die of it.26,27 In 

response, scientists continue to explore the role that the exposure to environmental contaminants may play, along with other 

possible risk factors, in the initiation and development of cancer. 

Some environmental contaminant exposures are known risk 

factors for certain types of cancers. Examples include radon and 

lung cancer and arsenic and skin cancer. Though many types of 

cancer are suspected of being related to ambient environmental 

exposures, associations are not always clear because the etiology 

of cancer is complex and influenced by a wide range of factors. 

Many factors can increase individual cancer risk, such as age, 

genetics, existence of infectious diseases, and socioeconomic factors that can affect exposure and susceptibility. 

Childhood cancers are dissimilar from cancers in adults and 

are therefore tracked separately. They affect different anatomic 

sites and may be of embryonic origin. Though overall cancer 

incidence rates are lower in children than in adults, childhood 

cancers are the third leading cause of death in children age 

1-19 years.28 Children may be particularly susceptible to exposures in utero or during early childhood because their systems 

are rapidly developing and affected by evolving hormonal 

systems.29 As with many adult cancers, the causes of childhood 

cancers are unknown for the most part; environmental influences may be a factor and have been the subject of extensive 

research. Environmental exposures are difficult to evaluate 

because cancer is rare in children and because of challenges in 

identifying past exposure levels, particularly during potentially 

important time periods such as in utero or maternal exposures 

prior to conception.30

Cardiovascular Disease

More than one-fourth of the U.S. population lives with a 

cardiovascular disease, with more than 6 million hospitalizations each year.31 Coronary heart disease and stroke, two of 

the major types of cardiovascular disease, rank as the first and 

third leading causes of death, respectively (General Mortality 

indicator, p. 5-33), and are leading causes of premature and 

permanent disabilities. Known risk factors include smoking, 

high blood pressure, high blood cholesterol, diabetes, physical inactivity, and poor nutrition. Outdoor air pollution and 

environmental tobacco smoke are also known risk factors for 

cardiovascular disease. Particulate matter, for example, has 

been demonstrated to be a likely causal factor in both cardiovascular disease morbidity and mortality. Collective evidence 

from recent studies suggests excess risk associated with shortterm exposures to particulate matter and hospital admissions 

or emergency department visits for cardiovascular effects.32,33

Environmental tobacco smoke has been shown to be a risk 

factor for coronary heart disease morbidity and mortality and 

may contribute to stroke, though evidence is more limited.34,35

Respiratory Disease

Chronic obstructive pulmonary disease (COPD) and asthma 

are two prevalent chronic respiratory diseases in the U.S. 

Epidemiological and clinical studies have shown that ambient and indoor air pollution are risk factors in several respiratory health outcomes, including reported symptoms (nose 

and throat irritation), acute onset or exacerbation of existing 

disease (e.g., asthma), and deaths.36,37 The relationship between 

environmental tobacco smoke and diseases of the respiratory 

tract has been studied extensively in humans and in animals; 

environmental tobacco smoke has been shown to produce a 

variety of upper and lower respiratory tract disorders.38

26 American Cancer Society. 2005. Cancer facts and figures 2005. Atlanta. 

<http://www.cancer.org/downloads/STT/CAFF2005f4PWSecured.pdf>

27 National Toxicology Program. 2004. Report on carcinogens. Eleventh edition. U.S. Department of Health and Human Services, Public Health Service. 

<http://ntp.niehs.nih.gov/ntp/roc/toc11.html>

28 National Center for Health Statistics. 2004. Deaths: Final data for 2002. 

National Vital Statistics Reports 53(5). <http://www.cdc.gov/nchs/data/

nvsr/nvsr53/nvsr53_05.pdf>

29 Anderson, L.M., B.A. Diwan, N.T. Fear, and E. Roman. 2000. Critical 

windows of exposure for children’s health: Cancer in human epidemiological studies and neoplasms in experimental animal models. Environ. Health. 

Perspect. 108(Suppl 3):573-594.

30 National Cancer Institute. 2005. National Cancer Institute research on 

childhood cancers. Accessed November 2007. <http://www.cancer.gov/

cancertopics/factsheet/sites-types/childhood>

31 Centers for Disease Control and Prevention. 2005. Preventing heart disease 

and stroke. Addressing the nation’s leading killers—at a glance. Revised 

August 2005. 

32 U.S. Environmental Protection Agency. 2005. Review of the National Ambient Air Quality Standards for particulate matter: Policy assessment of scientific 

and technical information. OAQPS Staff Paper.

33 U.S. Environmental Protection Agency. 2004. Air quality criteria for 

particulate matter. Volumes I (EPA/600/P-99/002aF) and II (EPA/600/

P-99/002bF). National Center for Environmental Assessment—RTP Office, 

Office of Research and Development.

34 National Cancer Institute. 1999. Smoking and tobacco control monograph 

10: Health effects of exposure to environmental tobacco smoke. <http://

cancercontrol.cancer.gov/tcrb/monographs/10/m10_complete.pdf>

35 U.S. Department of Health and Human Services. 2006. The health consequences of involuntary exposure to tobacco smoke: A report of the Surgeon 

General. Atlanta, GA. Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease 

Prevention and Health Promotion, Office on Smoking and Health. 

<http://www.surgeongeneral.gov/library/secondhandsmoke/report/>

36 U.S. Environmental Protection Agency. 2005. Review of the National Ambient Air Quality Standards for particulate matter: Policy assessment of scientific 

and technical information. OAQPS Staff Paper.

37 U.S. Environmental Protection Agency. 2007. Review of the National 

Ambient Air Quality Standards for ozone: Policy assessment of scientific and 

technical information. OAQPS Staff Paper.

38 State of California. 2005. Proposed identification of environmental tobacco 

smoke as a toxic air contaminant. Part B: Health effects assessment for 

environmental tobacco smoke. As approved by the Scientific Review Panel 

on June 24, 2005. California Environmental Protection Agency, Office of 

Environmental Health Hazard Assessment. <http://www.arb.ca.gov/regact/

ets2006/ets2006.htm>
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-41

COPD is a group of diseases characterized by airflow obstruction, resulting in breathing-related symptoms and encompasses 

chronic obstructive bronchitis and emphysema.39,40 COPD is 

the fourth leading cause of death in the U.S. and is the leading 

cause of hospitalization in U.S. adults, particularly in older 

adults. It represents a major cause of morbidity, mortality, and 

disability.41 Air pollution may be an important contributor 

to COPD, though approximately 80 to 90 percent of COPD 

deaths is generally attributed to smoking.42

Asthma continues to receive attention in both children and 

adults. Asthma prevalence increased nearly 74 percent during 

1980-1996.43 During 2001-2003, an average annual 20 million people in the U.S. had asthma.44 Environmental contaminants such as dust mites, pets, mold, and other allergens 

are considered important triggers for asthma.45 In addition, 

the relationship between environmental tobacco smoke and 

diseases of the respiratory tract has been studied extensively 

in humans and in animals; environmental tobacco smoke has 

been shown to produce a variety of upper and lower respiratory 

tract disorders.46

Infectious Disease

Infectious diseases are acute illnesses caused by bacteria, 

protozoa, fungi, and viruses. Food and water contaminated 

with pathogenic microorganisms are the major environmental 

sources of gastrointestinal illness. Though well-established 

systems for reporting food- and waterborne cases exist, data 

reported through these largely voluntary programs must be 

interpreted with caution because many factors can influence 

whether an infectious disease is recognized, investigated, and 

reported. Changes in the number of cases reported could 

reflect actual changes or simply changes in surveillance and 

reporting. In addition, many milder cases of gastrointestinal 

illnesses go unreported or are not diagnosed, making it difficult to estimate the number of people affected every year.

The discovery of bacterial contamination of drinking water 

as the cause of many cases of gastrointestinal illness represents one of the great public health success stories of the 20th

century. Waterborne diseases such as typhoid fever and cholera 

were major health threats across the U.S. at the beginning of 

the 20th century. Deaths due to diarrhea-like illnesses, including typhoid, cholera, and dysentery, represented the third 

largest cause of death in the nation at that time. These types of 

diarrheal deaths dropped dramatically once scientists identified 

the bacteria responsible, elucidated how these bacteria were 

transmitted to and among humans in contaminated water 

supplies, and developed effective water treatment methods to 

remove pathogens from water supplies.

In addition to being of food- or waterborne origin, infectious disease can be airborne, arthropod-borne (spread by 

mosquitoes, ticks, fleas, etc.), or zoonotic (spread by rodents, 

dogs, cats, and other animals). Legionellosis can be contracted 

from naturally occurring bacteria found in water and spread 

through poorly maintained artificial water systems (e.g., air 

conditioning, ventilation systems). Arthropod-borne diseases, 

including Lyme disease, Rocky Mountain spotted fever, and 

West Nile virus, can be contracted from certain ticks and 

mosquitoes that acquire bacteria or viruses by biting infected 

mammals or birds. 

Birth Outcomes

Birth defects are structural or functional anomalies that present at birth or in early childhood. Birth defects cause physical 

or mental disability and can be fatal. They affect approximately one out of 33 babies born each year in the U.S. and 

remain the leading cause of infant mortality (Infant Mortality indicator, p. 5-36). Serious, adverse effects on health, 

development, and functional ability may be experienced by 

individuals born with birth defects.47 Birth defects have been 

linked with a variety of possible risk factors that can affect 

normal growth and development—genetic or chromosomal 

aberrations, as well as environmental factors such as exposure 

to chemicals; exposure to viruses and bacteria; and use of 

cigarettes, drugs, or alcohol by the mother. The causes of most 

birth defects are unknown, but research continues to show the 

possible influence of environmental exposures (e.g., prenatal 

exposure to high levels of contaminants such as mercury or 

PCBs). The relationship between exposure to lower concentrations of environmental contaminants and birth defects, 

however, is less clear.

Low birthweight delivery and preterm birth are considered 

important risk factors for infant mortality and birth defects. 

Low birthweight infants have a significantly increased risk of 

infant death, and those who survive are more likely to experience long-term developmental disabilities.48 Multiple birth 

babies have a low birthweight rate of more than 50 percent, 

39 Mannino, D.M. 2002. COPD epidemiology, prevalence, morbidity and mortality, and disease heterogeneity. Chest 121:121S-126S.

40 Barnes, P.J. 2000. Chronic obstructive pulmonary disease. Review article. N. 

Engl. J. Med. 343(4):269-280.

41 Mannino, D.M., D.M. Homa, L.J. Akinbami, E.S. Ford, and S.C. Redd. 

2002. Chronic obstructive pulmonary disease surveillance—United States, 

1971-2000. In: Surveillance Summaries. MMWR 51(SS06):1-16.

42 American Lung Association. 2004. Chronic obstructive pulmonary disease 

(COPD) fact sheet. Accessed February 7, 2005. <http://www.lungusa.org/

site/pp.asp?c=dvLUK9O0E&b=35020>

43 Mannino, D.M., D.M. Homa, L.J. Akinbami, J.E. Moorman, C. Gwynn, S.C. 

Redd. 2002. Surveillance for asthma—United States, 1980-1999. In: Surveillance Summaries. MMWR 51(SS-1):1-13.

44 Moorman, J.G., R.A. Rudd, C.A. Johnson, M. King, P. Minor, C. Bailey, M.R. 

Scalia, L.J. Akinbami. 2007. National surveillance for asthma—United States, 

1980-2004. In: Surveillance Summaries. MMWR 56(SS08):1-14. 

45 U.S. Institute of Medicine. 2000. Clearing the air. Asthma and indoor air 

exposures. Washington, DC: National Academy Press.

46 State of California. 2005. Proposed identification of environmental tobacco 

smoke as a toxic air contaminant. Part B: health effects assessment for 

environmental tobacco smoke. As approved by the Scientific Review Panel 

on June 24, 2005. California Environmental Protection Agency, Office of 

Environmental Health Hazard Assessment. <http://www.arb.ca.gov/regact/

ets2006/ets2006.htm>

47 Centers for Disease Control and Prevention. 2006. Improved national 

prevalence estimates for 18 selected major birth defects—United States, 

1999-2001. MMWR 54(51&52):1301-1305.

48 National Center for Health Statistics. 2005. Health, United States, 2005, 

with chartbook on trends in the health of Americans. DHHS publication no. 

2005-1232. Hyattsville, MD. p. 11.
HUMAN EXPOSURE AND HEALTH

5-42 EPA’s 2008 Report on the Environment

compared to approximately 6 percent among singletons, 

among whom the low birthweight rate rose only 1 percent 

from 1989 to 1998.49 To eliminate the effect that multiple 

births may have on birth outcomes, this report presents data 

for singleton births only. 

Environmental exposures are being investigated for possible 

associations with birth outcomes such as low birthweight, 

preterm births, and infant mortality. Some of the risk factors 

for low birthweight infants born at term include maternal 

smoking, weight at conception, and nutrition and weight gain 

during pregnancy.50 Specific examples of known or suspected 

environmental contaminant influences on birth outcomes 

include environmental tobacco smoke, lead, and air pollution. 

The most robust evidence exists for environmental tobacco 

smoke and lead.51 Environmental tobacco smoke is associated 

with increased risk of low birthweight, preterm delivery, and 

sudden infant death syndrome.52 Several studies have identified 

lead exposure as a risk factor for preterm delivery.53 Associations between air pollution and fetal growth and infant mortality have been documented. Recent studies report significant 

associations between PM10 concentration averaged over a 

month or a trimester of gestation and the risk of intrauterine 

growth reduction and low birthweight.54 Growing evidence 

shows exposure-response relationships between maternal 

exposures to air pollutants (e.g., sulfur dioxide and particulates) and preterm birth.55,56 Research continues, however, in 

establishing causal relationships between air pollution and low 

birthweight and preterm birth. Researchers also continue to 

examine possible associations between other contaminants as 

birth outcome risk factors, such as pesticides, polycyclic aromatic hydrocarbons, and others. 

5.4.2 ROE Indicators

EPA has selected indicators of health outcomes for which 

environmental exposures may be a risk factor and for which 

nationally representative data are available. Nine indicators were 

selected to address the question (Table 5-4)—two for cancer 

(including the leading sites of cancer in adults and children), 

one for cardiovascular disease (including coronary heart disease, 

stroke, and hypertension), two related to respiratory disease 

(including asthma and chronic lung conditions such as bronchitis and emphysema), one for infectious diseases (composed of 

multiple diseases and conditions), and three for birth outcomes.

49 National Center for Health Statistics. 2001. Healthy people 2000 final review. 

Hyattsville, MD: Public Health Service. p. 208. <http://www.cdc.gov/nchs/

data/hp2000/hp2k01-acc.pdf>

50 U.S. Department of Health and Human Services. 2000. Healthy people 2010: 

Understanding and improving health. Second edition. Washington, DC: U.S. 

Government Printing Office. <http://www.health.gov/healthypeople/>

51 Behrman, R.E., and A. Stith Butler, eds. 2007. Preterm birth: Causes, consequences, and prevention. Committee on Understanding Premature Birth and 

Assuring Healthy Outcomes. Institute of Medicine of the National Academies. Washington, DC: National Academies Press.

52 State of California. 2005. Proposed identification of environmental tobacco smoke 

as a toxic air contaminant. Part B: Health effects assessment for environmental 

tobacco smoke. As approved by the Scientific Review Panel on June 24, 2005. 

California Environmental Protection Agency, Office of Environmental Health 

Hazard Assessment. <http://www.arb.ca.gov/regact/ets2006/ets2006.htm>

53 Agency for Toxic Substances and Disease Registry. 2005. Toxicological profile 

for lead (update). Draft for public comment. Atlanta, GA: U.S. Department of 

Health and Human Services, Public Health Service.

54 U.S. Environmental Protection Agency. 2005. Review of the National Ambient Air Quality Standards for particulate matter: Policy assessment of scientific 

and technical information. OAQPS Staff Paper.

55 Behrman, R.E., and A. Stith Butler, eds. 2007. Preterm birth: Causes, consequences, and prevention. Committee on Understanding Premature Birth and 

Assuring Healthy Outcomes. Institute of Medicine of the National Academies. Washington, DC: National Academies Press.

56 Sram, R.J., B. Binkova, J. Dejmek, and M. Bobak. 2005. Ambient air pollution 

and pregnancy outcomes: A review of the literature. Environ. Health Perspect. 

113(4):375-382. 

Table 5-4. ROE Indicators of Trends in Human Disease and Conditions for Which

Environmental Contaminants May Be a Risk Factor

National Indicators Section Page

Cancer Incidence 5.4.2 5-43

Childhood Cancer Incidence 5.4.2 5-46

Cardiovascular Disease Prevalence and Mortality (N/R) 5.4.2 5-48

Chronic Obstructive Pulmonary Disease Prevalence and Mortality (N/R) 5.4.2 5-52

Asthma Prevalence 5.4.2 5-55

Infectious Diseases Associated with Environmental Exposures or Conditions 5.4.2 5-59

Birth Defects Prevalence and Mortality 5.4.2 5-62

Low Birthweight 5.4.2 5-65

Preterm Delivery 5.4.2 5-67

N/R = National Indicator displayed at EPA Regional scale
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-43

The indicators used to answer this question are drawn from the 

Centers for Disease Control and Prevention’s vital statistics and 

surveillance data, including the CDC WONDER Mortality 

Database, the Summary of Notifiable Diseases, the National 

Center for Health Statistics’ National Vital Statistics Reports 

and VitalStats Database, and the National Health Interview 

Survey, as well as the National Cancer Institute’s Surveillance, 

Epidemiology, and End Results Database. The time frames 

covered generally range back to the 1970s for mortality and 

incidence data and to the mid-1990s for prevalence data. 

In answering this question, both disease morbidity (incidence 

or prevalence) and mortality (resulting death) statistics are 

used. Depending on the health outcome of interest, both measures can provide useful insights about trends in disease. Both 

morbidity and mortality statistics are influenced by a number 

of factors, however, such as the accuracy of reporting mechanisms and issues related to access to, quality of, and advances 

in medical care. An overall understanding of the disease 

measures and associated statistics used to answer this question 

is important (see Box 5-3). 

Where possible, the indicators provide breakouts of population 

subgroups, such as race, ethnicity, age, and gender. Subpopulation data are presented to the extent practicable under “What 

the Data Show,” within text or shown in indicator figures. 

For cardiovascular and respiratory diseases, mortality statistics 

are provided for each of the 10 EPA Regions. For cancer, data 

for the most frequently diagnosed cancer sites in adults and 

children, along with overall cancer rates, are used to answer 

the question.

INDICATOR | Cancer Incidence

The term “cancer” is used to characterize diseases in which abnormal cells divide without control. A cancerous cell loses its ability to regulate its own growth, control 

cell division, and communicate with other cells. Cancer 

cells can invade nearby tissues and can spread through the 

bloodstream and lymphatic system to other parts of the 

body (NCI, n.d.). The risk of developing cancer increases 

with age. Environmental exposures, genetic predisposition, 

certain viruses, and socioeconomic factors may all play a 

role in the development and progression of the disease. 

For the U.S. population, age-adjusted cancer incidence 

rates for all sites combined have been stable since 1992 

(Edwards et al., 2005). Nevertheless, cancer continues to be 

the second leading cause of death in the U.S., accounting for 

about 23 percent of all deaths in 2004 (General Mortality 

indicator, p. 5-33) (NCHS, 2007). Many different types of 

cancer exist. These can develop in various organs and tissues 

within the body and contributing causal factors can vary 

depending on the cancer site and type. Therefore, tracking 

rates for individual cancer sites is more meaningful when 

evaluating cancer trends. 

Many factors are known to contribute, or suspected of 

contributing, to cancer risk. Factors including individual 

food and beverage preferences, use of tobacco products, 

exposure to natural and medical radiation (including sunlight), workplace exposures, and pharmaceutical use as well 

as exposure to substances in the air, water and soil all may 

contribute individually (i.e., additively) or synergistically 

Both morbidity and mortality can be measured using 

occurrences or rates. Occurrences represent frequency 

counts, while rates enable a comparison across populations. 

Rates are ratios that calculate the frequency of cases (of disease, condition, outcome) divided by the size of the defined 

population for a specified time period. Usually some constant (generally a multiplier of the power 10) is applied to 

convert the rate to a whole number.

Morbidity data are often used to describe the incidence and 

prevalence of a disease or condition. Both incidence and 

prevalence are often expressed as a rate per 1,000 persons 

over a particular time period. “Incidence” refers to the 

number of new cases of a disease or condition in a population during a specified time period. “Prevalence” refers to 

the total number of people with a given disease or condition 

in a population at a specified point in time.

Mortality is generally expressed as a rate and is defined as 

the proportion of the population who die of a disease or 

condition during a specified time period. The rate is usually calculated for a calendar year and is often expressed per 

100,000 persons.

Incidence, prevalence, and mortality statistics can be used 

to compare the rates of disease at two or more points in 

time, across different populations (ages, gender, racial/

ethnic groups), or between different geographic areas. 

In general, disease incidence, prevalence, and mortality 

increase with age. For this reason, when comparing different populations, the data must be adjusted to account 

for the age differences between the populations. The 

adjusted data, called “age-adjusted rates,” are used where 

possible in answering this question. Age-adjusted rates are 

weighted sums of age-specific rates and calculated using 

standard population factors. (In this report, the 2000 

U.S. standard population was used.) Unadjusted rates are 

referred to as “crude” rates.

Box 5-3. Morbidity and Mortality Measures
HUMAN EXPOSURE AND HEALTH

5-44 EPA’s 2008 Report on the Environment

(i.e., producing an effect greater than the sum of each factor 

acting alone) to the development of cancer (NTP, 2004). 

Further, the cancer hazard to any individual is dependent 

on the amount and duration of exposure and the individual’s susceptibility to a particular substance. Only in a 

small number of cases is it known what specific exposures or 

conditions are responsible for the onset and development of 

cancers (NTP, 2004). 

This indicator presents cancer incidence rates for the 

U.S. population using data collected through the National 

Cancer Institute’s Surveillance, Epidemiology, and End 

Results (SEER) Program. The SEER Program collects 

and publishes cancer incidence and survival data from 14 

population-based cancer registries and three supplemental 

registries covering approximately 26 percent of the U.S. 

population. The 10 most commonly diagnosed cancer sites 

presented are based on 2004 data compiled from SEER. 

Site classifications (e.g., lung and bronchus, colon and 

rectum) were compared to the American Cancer Society’s 

“leading sites” classification to ensure consistency in how 

data are presented (ACS, 2004).

What the Data Show

Although a slow steady increase in cancer incidence 

occurred between 1973 and 1992, peaking in 1992 with 

an age-adjusted cancer incidence of 510 cases per 100,000, 

INDICATOR | Cancer Incidence (continued)

a

Excludes basal and squamous cell skin cancers and in situ carcinoma, except urinary bladder. 

b

Rates are per 100,000 and age-adjusted to the 2000 U.S. standard population. 

c

NC = not calculated 

Data source: NCI, 2007

29.9 

13.8 

10.6 

6.8 

4.6 

4.5 

3.3

2.9 

2.9 

2.5 

18.2 

Female

Breast 

Lung and bronchus

Colon and rectum 

Corpus uteri 

Non-Hodgkin’s lymphoma

Melanoma of the skin

Thyroid

Ovary 

Pancreas

Urinary bladder

All other sites

Percent of all cancers Percent of all cancers

 30.7

 12.4

 10.3

 5.9

 4.2 

4.1 

3.6 

3.1

2.4

2.2

 21.1

Exhibit 5-18. Age-adjusted cancer incidence rates in the U.S., 2004: Ten leading cancer sites by sexa

Male

Prostate

Lung and bronchus

Colon and rectum

Urinary bladder

Non-Hodgkin’s lymphoma

Melanoma of the skin

Kidney and renal pelvis

Oral cavity and pharynx

Leukemia

Pancreas

All other sites

Rateb

159.5

73.6

56.7

36.3

24.7

24.1

17.8

15.5

15.4

13.3

NCc

Rateb

124.3

50.2

41.7

23.9

17.1

16.5

14.4

12.6

9.8

9.1

NCc

Age-adjusted rate 

(per 100,000) 

Year of diagnosis

Exhibit 5-17. Age-adjusted cancer incidence 

rates in the U.S., 1973-2004: All cancer sites for 

all ages, by race and sexa

a

Rates are age-adjusted to the 2000 U.S. 

standard population.

Data source: NCI, 2007

’75 ’80 ’85 ’90 ’95 ’00

All groups

Male (white)

Female (white)

Male (black)

Female (black)

0

200

400

600

800
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-45

INDICATOR | Cancer Incidence (continued)

overall incidence rates appear to have stabilized over the 

last 10 years (Exhibit 5-17). Some differences exist in incidence rates across age, gender, and racial groups. During 

2004, those age 65 and older had the highest incidence 

rates (2,102.4 cases per 100,000) compared to all other 

age categories (data not shown). Total (all sites combined) 

cancer incidence rates are higher for males compared to 

females and for black males compared to white males 

(Exhibit 5-17). The age-adjusted cancer incidence rate in 

2004 for black males was 637.2 cases per 100,000 compared 

to 537.9 cases per 100,000 for white males; among females, 

the age-adjusted cancer incidence rate in 2004 was 417.9 

cases per 100,000 for white females compared to 396.6 

cases per 100,000 among black females. 

Exhibit 5-18 shows the differences between the top 10 

cancer sites in males and females. For both, the top three 

cancers represent over half of all newly identified cancer 

cases in 2004. Among the most notable differences is the 

rate of urinary bladder cancer among males (36.3 cases per 

100,000), which is nearly four times that of females (9.1 

cases per 100,000). Melanoma of the skin is also higher 

among males (24.1 cases per 100,000) than females (16.5 

cases per 100,000). Thyroid cancer appears as the seventh 

leading cancer in females (14.4 cancers per 100,000), but is 

not among the top 10 for males (5.1 cases per 100,000).

Among males, prostate cancer incidence rates increased 

dramatically between 1986 and the early 1990s, with a 

decline in rates between 1992 and 1995. This increase is 

likely due to the introduction of serum prostate-specific 

antigen testing for the early detection and screening of 

prostate cancer (Hankey et al., 1999). The other four leading cancers (colon and rectum, lung and bronchus, urinary 

bladder, and non-Hodgkin’s lymphoma) have either been 

relatively stable or have showed a small decline over the last 

decade (Exhibit 5-19). 

Recent trends (i.e., since 1995) among the less prevalent 

site-specific cancers in males show small increases in the 

incidence rates for melanoma of the skin (melanoma), which 

ranged from 20.2 (1995) to 24.2 (2001) cases per 100,000, 

and cancers of the kidney and renal pelvis (kidney), which 

ranged from 15.1 (1997) to 17.8 (2003, 2004) cases per 

100,000. Overall, slightly decreasing rates were observed 

for leukemia, which ranged from 17.6 (1995) to 15.4 (2004) 

cases per 100,000, and cancers of the oral cavity and pharynx (oral cavity), which ranged from 17.7 (1996) to 15.3 

(2001, 2003) cases per 100,000. (Data not shown.)

As shown in Exhibit 5-20, among females, breast cancer remains the leading cancer and rates have generally 

increased for much of the reporting period. While lung 

cancer among males has slowly declined over the past 

decade, the rate among women has generally increased 

over time and is the second leading cancer among men and 

women in 2004. The incidence rate of colon cancer among 

women increased between 1973 and 1985 and has slowly 

declined since. The incidence of uterine (corpus uteri) 

cancer in females was relatively stable since 1986, with a 

small decrease in more recent years, ranging from 25.4 

(1997) to 23.3 (2003) cases per 100,000. The incidence rate 

of non-Hodgkin’s lymphoma has exhibited a slow increase 

since 1973. 

Age-adjusted rate 

(per 100,000) 

Year of diagnosis

Exhibit 5-19. Age-adjusted cancer incidence 

rates in the U.S., 1973-2004: Top five cancers in 

males of all agesa

a

Rates are age-adjusted to the 

2000 U.S. standard population.

Data source: NCI, 2007

Colon and rectum

Lung and bronchus

Non-Hodgkin’s lymphoma

Prostate

Urinary bladder

0

50

100

150

200

250

’75 ’80 ’85 ’90 ’95 ’00

Age-adjusted rate 

(per 100,000) 

Year of diagnosis

Exhibit 5-20. Age-adjusted cancer incidence 

rates in the U.S., 1973-2004: Top five cancers in 

females of all agesa

a

Rates are age-adjusted to the 2000 

U.S. standard population.

Data source: NCI, 2007

Breast

Colon and rectum

Corpus uteri

Lung and bronchus

Non-Hodgkin’s lymphoma

0

20

40

60

80

100

120

140

’75 ’80 ’85 ’90 ’95 ’00
HUMAN EXPOSURE AND HEALTH

5-46 EPA’s 2008 Report on the Environment

Recent trends in cancer incidence rates among the less 

prevalent site-specific cancers in females showed increases 

for melanoma, which ranged from 13.7 (1995) to 16.5 (2004) 

cases per 100,000 and thyroid cancer, which ranged from 

8.9 (1995) to 14.4 (2004) cases per 100,000. Incidence rates 

decreased for cancers of the ovary, which ranged from 14.7 

(1997) to 12.6 (2004) cases per 100,000. (Data not shown.)

Indicator Limitations

•	 SEER data cover approximately 26 percent of the U.S. 

population, though it is designed to be representative of 

the entire U.S. population.

•	 Incidence data generated from SEER are updated 

annually. There may be changes in the numerator (e.g., 

revised counts of newly identified cases) or denominator (i.e., revised population counts) numbers that result 

in small changes in the overall incidence rates for the 

same year, depending on when a query is run within the 

SEER database. For example, the SEER database queried 

in 2005 generating incidence rates for the year 2000 may 

provide different incidence rates than the database queried in 2004 for the year 2000. 

Data Sources

Cancer incidence data for this indicator were obtained by 

querying the National Cancer Institute’s SEER Program 

database through the Cancer Query Systems Web-based 

interface (NCI, 2007), available at http://www.seer.cancer.

gov/canques/incidence.html.

References

ACS (American Cancer Society). 2004. Cancer facts and 

figures, 2004. <http://www.cancer.org/downloads/STT/

CAFF_finalPWSecured.pdf>

Hankey, B.F., E.J. Feuer, L.X. Clegg, R.B. Hayes, J.M. 

Legler, P.C. Prorok, et al. 1999. Cancer surveillance series: 

Interpreting trends in prostate cancer-part I: Evidence of 

the effects of screening in recent prostate cancer incidence, 

mortality, and survival rates. J. Natl. Cancer Inst. 

91(12):1017-1024. 

Edwards, K.E., M.L. Brown, P.A. Wingo, H.L. Howe, E. 

Ward, L. Reis, et al. 2005. Annual report to the nation on 

the status of cancer, 1975-2002, featuring population-based 

trends in cancer treatment. J. Natl. Cancer Inst. 

97(19):1407-1427. 

NCHS (National Center for Health Statistics). 2007. 

Deaths: Final data for 2004. National Vital Statistics 

Reports 55(19). <http://www.cdc.gov/nchs/data/nvsr/

nvsr55/nvsr55_19.pdf>

NCI (National Cancer Institute). 2007. Surveillance, Epidemiology, and End Results (SEER) Program CANQUES 

database. SEER registry limited use, Nov 2006, Sub 

(1973-2004). National Cancer Institute, DCCPS, Surveillance Research Program. Released April 2007, based on 

November 2006 submission. Accessed September 2007.

<http://www.seer.cancer.gov/canques/incidence.html>

NCI. n.d. Dictionary of cancer terms. Accessed October 7, 

2004. <http://cancer.gov/dictionary/>

NTP (National Toxicology Program). 2004. Report on 

carcinogens. Eleventh edition. U.S. Department of Health 

and Human Services, Public Health Service.

<http://ntp.niehs.nih.gov/ntp/roc/toc11.html>

INDICATOR | Cancer Incidence (continued)

The term “cancer” is used to characterize diseases in which abnormal cells divide without control. A cancerous cell loses its ability to regulate its own growth, control 

cell division, and communicate with other cells. If left 

unchecked, cancer cells can invade nearby tissues and can 

spread through the bloodstream and lymphatic system to 

other parts of the body. The cellular changes caused by cancer cells are complex and occur over a period of time. This 

may be accelerated in children. The classification of cancers 

in children differs from the classification used for adult cancers. The International Classification of Childhood Cancer 

classifies childhood cancer based on tumor morphology 

rather than, as for adults, the site of the tumor (NCI, 2004). 

The causes of childhood cancers are largely unknown. 

Only a small percentage of cases can be explained by a few 

conditions such as specific chromosomal/genetic abnormalities (e.g., Down’s syndrome) and ionizing radiation 

exposure (NCI, 2005). Environmental exposures have long 

been suspected of increasing the risk of certain childhood 

cancers. Researchers continue to examine environmental 

influences on childhood cancer (NCI, 2005). 

This indicator presents incidence rates for childhood cancers using data collected through the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) 

Program. The SEER Program collects and publishes cancer 

incidence and survival data from 14 population-based cancer 

INDICATOR | Childhood Cancer Incidence

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-47

registries and three supplemental registries covering approximately 26 percent of the U.S. population. 

What the Data Show

In general, overall childhood (ages 0-19 years) cancer 

incidence for the U.S. has increased slightly between 1973 

and 2004 (Exhibit 5-21), increasing over time from an 

age-adjusted incidence rate of 13.8 per 100,000 in 1973 

to a high of 17.2 per 100,000 in 2002. A rate of 16.0 per 

100,000) was reported in 2004. Males generally had higher 

rates than females, although for some years the reverse was 

true. Incidence among black females and males age 0-19 

years was lower than among white females and males. In 

2004, black females and males age 0-19 years had overall 

incidence rates of 13.5 and 12.3 per 100,000, respectively, 

compared to white females and males with rates of 15.5 

and 18.7 per 100,000 (Exhibit 5-21). 

Exhibit 5-22 presents the age-adjusted incidence rates 

for the top five cancers among children 0-19 years of age 

between 1973 and 2004. In general, there are no clearly 

identifiable trends among any of the top five cancers over the 

reported time period. Leukemia continues to be the most 

frequently diagnosed cancer in children age 0-19 years.

Indicator Limitations

•	 SEER data cover approximately 26 percent of the U.S. 

population, though it is designed to be representative of 

the entire U.S. population.

•	 Incidence data generated from SEER are updated 

annually. There may be changes in the numerator (e.g., 

revised counts of newly identified cases) or denominator (i.e., revised population counts) numbers that result 

in small changes in the overall incidence rates for the 

same year, depending on when a query is run within the 

SEER database. For example, the SEER database queried 

in 2005 generating incidence rates for the year 2000 may 

provide different incidence rates than the database queried in 2004 for the year 2000. 

Data Sources

Cancer incidence data for this indicator were obtained by 

querying the National Cancer Institute’s SEER Program 

database through the Cancer Query Systems Web-based 

interface (NCI, 2007), available at http://www.seer.cancer.

gov/canques/incidence.html.

References

NCI (National Cancer Institute). 2007. Surveillance, Epidemiology, and End Results (SEER) Program CANQUES 

database. SEER registry limited use, Nov 2006, Sub 

(1973-2004). National Cancer Institute, DCCPS, Surveillance Research Program. Released April 2007, based on 

November 2006 submission. Accessed September 2007.

<http://www.seer.cancer.gov/canques/incidence.html>

NCI. 2005. National Cancer Institute research on childhood cancers. Accessed November 2007. <http://www.

cancer.gov/cancertopics/factsheet/sites-types/childhood>

NCI. 2004. Dictionary of cancer terms. Accessed October 

7, 2004. <http://cancer.gov/dictionary/>

INDICATOR | Childhood Cancer Incidence (continued) Age-adjusted rate (per 100,000)

Year of diagnosis

Exhibit 5-21. Age-adjusted cancer incidence 

rates in the U.S., 1973-2004: All cancer sites for 

ages 0-19, by race and sexa

a

Rates are age-adjusted to the 2000 U.S. 

standard population, age 0-19 years.

Data source: NCI, 2007

’75 ’80 ’85 ’90 ’95 ’00

0

4

8

12

16

20

All groups

Male (white)

Female (white)

Male (black)

Female (black)

Age-adjusted rate

(per 100,000)

Year of diagnosis

Exhibit 5-22. Age-adjusted cancer incidence 

rates in the U.S., 1973-2004: Top five cancers 

for ages 0-19a

a

Rates are age-adjusted to the 

2000 U.S. standard population, 

age 0-19 years.

Data source: NCI, 2007

Brain and other nerv ous

system

Hodgkin’s lymphoma

Leukemia

Lymphoma

Non-Hodgkin’s lymphoma

0

1

2

3

4

5

’75 ’80 ’85 ’90 ’95 ’00

v
HUMAN EXPOSURE AND HEALTH

5-48 EPA’s 2008 Report on the Environment

The broad category of cardiovascular disease (CVD) includes any disease involving the heart and blood 

vessels. Coronary heart disease, cerebrovascular disease 

(commonly known as stroke), and hypertension are the 

major cardiovascular diseases (American Heart Association, 

2007). In addition to being a major risk factor for heart 

disease and stroke, hypertension is a commonly diagnosed 

disease that can also lead to kidney damage and other 

health problems. Obesity, physical inactivity, and sodium 

intake are all important risk factors for hypertension (NIH, 

2004). Since 1900, CVD has been the leading cause of 

death in the U.S. every year except 1918 (American Heart 

Association, 2007) (General Mortality indicator, p. 5-33). 

The U.S. age-adjusted mortality rate for CVD reached a 

peak in 1950 (CDC, 1999). Between 1950 and 1999, the 

age-adjusted mortality rate for CVD declined 60 percent. 

The major risk factors for CVD include tobacco use, high 

blood pressure, high blood cholesterol, diabetes, physical inactivity, and poor nutrition (CDC, 2004; American 

Heart Association, 2007). 

Environmental exposures may also play a role in CVD 

morbidity and mortality independent of other risk factors. 

However, susceptible populations such as the elderly and 

other high-risk populations may be most impacted. For 

example, studies have shown exposure to ambient airborne particulate matter to be associated with increased 

hospitalizations and mortality among older individuals, largely due to cardiopulmonary and cardiovascular 

disease (U.S. EPA, 2004). Environmental tobacco smoke 

(ETS) may also contribute to CVD. Although the smoke 

to which a nonsmoker is exposed is less concentrated 

than that inhaled by smokers, research has demonstrated 

increased cardiovascular-related health risks associated 

with ETS (State of California, 2005). 

This indicator presents U.S. adult (age 18 and older) 

prevalence rates for heart disease (all types), coronary heart 

disease, stroke, and hypertension; and mortality rates for 

CVD as a whole as well as coronary heart disease (including myocardial infarction), stroke, and hypertension. CVD 

prevalence data were compiled between 1997 and 2006 

from the National Health Interview Survey (NHIS), conducted by the Centers for Disease Control and Prevention’s 

(CDC’s) National Center for Health Statistics (NCHS). 

The NHIS is the principal source of information on the 

health of the civilian non-institutionalized population of 

the U.S. and since 1960 has been one of the major data collection programs of NCHS. CVD prevalence is based on 

the number of adults who reported that they had ever been 

told by a doctor or other health practitioner that they had 

a specified CVD. Mortality data (all ages) were compiled 

between 1979 and 2004 using the National Vital Statistics System (NVSS), maintained by NCHS. The NVSS 

registers virtually all deaths and births nationwide, with 

data coverage from 1933 to 2004 and from all 50 states and 

the District of Columbia.

INDICATOR | Cardiovascular Disease Prevalence and Mortality Rate (per 1,000)

Year

Exhibit 5-23. Cardiovascular disease 

prevalence in U.S. adults (age 18 and older), 

1997-2006a

a

Rates presented are crude rates.

Data source: NCHS, 1999-2005, 2006a,b, 

2007

’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’06

0

50

100

150

200

250

Heart disease 

(all types)

Heart disease 

(coronary)

Hypertension

Stroke

Age-adjusted rate

(per 100,000)

Year

Exhibit 5-24. Age-adjusted cardiovascular 

disease mortality rates in the U.S., 1979-2004a,b

a

Due to differences in the ICD system used for 

classifying mortality, data from 1979-1998 

should not be directly compared to data from 

1999-2004 [ICD-9 codes: 390-434, 436-448 

(1979-1998); ICD-10 codes: I00-I78 

(1999-2004)].

b

Rates are age-adjusted to the 2000 U.S. 

standard population.

Data source: CDC, 2007

Cardiovascular 

disease (all)

Coronary heart 

disease

Hypertension

Myocardial 

infarction

Stroke

’80 ’85 ’90 ’95 ’00

0

100

200

300

400

500

600
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-49

INDICATOR | Cardiovascular Disease Prevalence and Mortality (continued)

What the Data Show

CVD Prevalence

Among adults 18 years and older, the prevalence of heart 

disease and stroke between 1997 and 2006 has remained 

essentially the same (Exhibit 5-23). In contrast, the prevalence of hypertension has shown an increase from 191.6 

cases per 1,000 in 1999 to 234.1 cases per 1,000 in 2006. 

Gender, race, and age differences in CVD prevalence 

exist. The prevalence of coronary heart disease is consistently higher among males than among females (74.1 cases 

per 1,000 compared with 54.2 cases per 1,000 for women 

in 2006). In contrast, hypertension is more prevalent 

among women (238.4 cases per 1,000 for women compared 

with 229.5 for men in 2006). Among the racial groups 

reported, American Indians and Alaska Natives typically had the highest prevalence of coronary heart disease 

between 1999 and 2003. In 2006, however, whites had the 

highest prevalence of coronary heart disease (67.8 cases per 

1,000), followed by American Indians and Alaska Natives 

(55.5 cases per 1,000), blacks or African Americans (52.0 

cases per 1,000), and Asians (28.6 cases per 1,000). In 2006, 

Asians also consistently had the lowest prevalence of stroke 

(13.8 cases per 1,000) and hypertension (157.0 cases per 

1,000) among the racial groups reported. In addition, the 

Hispanic or Latino population had a consistently lower 

prevalence of the major CVD-related diseases compared with the non-Hispanic or Latino population from 

1999-2006, the period for which these data are available. 

For example, in 2006, prevalence in Hispanics or Latinos 

was lower than in non-Hispanics or Latinos for coronary 

heart disease (31.7 versus 68.6 cases per 1,000, respectively), hypertension (147.5 versus 247.0 cases per 1,000, 

respectively), and stroke (12.2 versus 27.6 cases per 1,000, 

respectively). (Data not shown.) 

CVD Mortality

In 1998, the national age-adjusted CVD mortality rate (all 

types) was 352.0 per 100,000 compared to a rate of 541.0 

per 100,000 in 1980 (Exhibit 5-24). This decline appears 

to continue after 1999, with the rate dropping from 349.3 

per 100,000 in 1999 to 286.5 per 100,000 in 2004. Both 

coronary heart disease and stroke mortality rates have been 

declining in the U.S. The age-adjusted coronary heart 

disease mortality rate ranged from 345.2 per 100,000 in 

1980 to 197.1 per 100,000 in 1998. For stroke mortality, the 

age-adjusted rate ranged from 97.1 per 100,000 in 1979 to 

59.3 per 100,000 in 1998. The age-adjusted mortality rates 

for myocardial infarction ranged from 157.9 in 1979 to 76 

per 100,000 in 1998. The age-adjusted mortality rates for 

coronary heart disease, stroke, and myocardial infarction in 

2004 were 150.2, 50.0, and 52.3 per 100,000, respectively, 

compared to 194.6, 61.6, and 73.2 per 100,000, respectively, 

in 1999. Death rates from hypertension remained essentially 

the same between 1999 and 2004.

Both coronary heart disease and stroke mortality have 

been declining over time in each of the 10 EPA Regions 

(Exhibits 5-25 and 5-26). In 1979, coronary heart disease 

and stroke age-adjusted mortality rates ranged from 285.6 

(Region 10) to 401.9 (Region 2) per 100,000 and 80.3 

(Region 2) to 111.4 (Region 4) per 100,000, respectively. 

In 1998, coronary heart disease and stroke mortality rates 

ranged from 145.6 (Region 8) to 233.2 (Region 2) per 

100,000 and 43.2 (Region 2) to 68.5 per (Region 10) 

100,000, respectively. The observed decreases in coronary 

heart disease and stroke mortality also appear to continue 

in the 1999-2004 period.

Differences exist in CVD mortality rates among gender, 

racial, and age groups. For example, in 2004, those age 65 

and older had the highest CVD (all types), coronary heart 

disease, and stroke mortality (1,898.7, 990.8, and 346.2 per 

100,000, respectively). For the same year, the age-adjusted 

CVD, coronary heart disease, and stroke mortality rates for 

’80 ’85 ’90 ’95 ’00

Age-adjusted rate

(per 100,000)

Year

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

Exhibit 5-25. Age-adjusted coronary heart 

disease mortality rates in the U.S. by EPA 

Region, 1979-2004a,b

a

Due to differences in the ICD 

system used for classifying 

mortality, data from 1979-1998 

should not be directly compared 

to data from 1999-2004 [ICD-9 

codes: 410-414, 429.2 

(1979-1998); ICD-10 codes: 

I20-I25 (I999-2004)].

b

Rates are age-adjusted to the 

2000 U.S. standard population.

Data source: CDC, 2007

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

100

150

200

250

300

350

400

450

0

50
HUMAN EXPOSURE AND HEALTH

5-50 EPA’s 2008 Report on the Environment

those 45 to 64 years of age were 172.7, 98.5, and 22.5 per 

100,000, respectively. Notable differences in CVD (all types) 

and, specifically, coronary heart disease mortality rates 

exist between males and females, but not for stroke mortality. Coronary heart disease mortality among males in 2004 

was 194.2 per 100,000, compared to 116.7 per 100,000 for 

women. In 2004, black or African American males had the 

highest CVD mortality rate at 451.1 per 100,000 compared 

to white males (333.6 per 100,000), black or African American females (331.0 per 100,000), and white females (236.7 

per 100,000). (Data not shown.)

Indicator Limitations

•	 Prevalence data reported in the NHIS are based on 

self-reported responses to specific questions pertaining 

to CVD-related illnesses, and are subject to the biases 

associated with self-reported data. Self-reported data can 

underestimate the disease prevalence being measured if, 

for whatever reason, the respondent is not fully aware of 

his/her condition. 

•	All prevalence data are based on crude rates and are not 

age-adjusted, as CDC did not report age-adjusted data 

prior to 2002 in the data sources used for this indicator. 

Therefore, the reported disease prevalence rates across 

time or within different race and gender subgroups 

may not reflect differences in the age distribution of the 

populations being compared. 

•	 For one or more years for which data are presented, 

coronary heart disease and stroke prevalence rates presented for Native Americans and Alaska Natives have 

a relative standard error of greater than 30 percent. In 

addition, stroke prevalence rates for one or more years 

for which data are presented for Asians have a relative 

standard error of greater than 30 percent. As such, these 

rates should be used with caution as they do not meet the 

standard of reliability or precision. 

•	 CVD mortality rates are based on underlying cause of 

death as entered on a death certificate by a physician. 

Some individuals may have had competing causes of 

death. “When more than one cause or condition is entered 

by the physician, the underlying cause is determined by 

the sequence of conditions on the certificate, provisions 

of the ICD [International Classification of Diseases], and 

associated selection rules and modifications” (CDC, n.d.). 

Consequently, some misclassification of reported mortality might occur in individuals with competing causes of 

death, as well as the possible underreporting of CVD as 

the cause of death.

•	The International Classification of Diseases 9th Revision 

(ICD-9) codes were used to specify underlying cause 

of death for years 1979-1998. Beginning in 1999, cause 

of death is specified with the International Classification of Diseases 10th Revision (ICD-10) codes. The two 

revisions differ substantially, and to prevent confusion 

about the significance of any specific disease code, data 

queries are separate. 

Data Sources

CVD prevalence data were obtained from annual reports 

published by NCHS (NCHS, 1999-2007), which summarize health statistics compiled from the NHIS (http://www.

cdc.gov/nchs/products/pubs/pubd/series/ser.htm). CVD 

mortality statistics were obtained from CDC’s “compressed 

mortality” database, accessed through CDC WONDER 

(CDC, 2007) (http://wonder.cdc.gov/mortSQL.html). EPA 

Regional mortality statistics were generated by combining 

and age-adjusting state-by-state totals for each EPA Region 

using data from CDC WONDER.

References

American Heart Association. 2007. Heart disease and 

stroke statistics—2007 update. A report from the American 

Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation (115):e69-e171. 

<http://circ.ahajournals.org/cgi/content/full/

CIRCULATIONAHA.106.179918>

INDICATOR | Cardiovascular Disease Prevalence and Mortality (continued)

’80 ’85 ’90 ’95 ’00

Age-adjusted rate

(per 100,000)

Year

Exhibit 5-26. Age-adjusted stroke mortality 

rates in the U.S. by EPA Region, 1979-2004a,b

a

Due to differences in the ICD 

system used for classifying 

mortality, data from 1979-1998 

should not be directly compared 

to data from 1999-2004 [ICD-9 

codes: 430-434, 436-438 

(1979-1998); ICD-10 codes: 

I60-I69 (1999-2004)].

b

Rates are age-adjusted to the 

2000 U.S. standard population.

Data source: CDC, 2007

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

40

60

80

100

120

0

20
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-51

INDICATOR | Cardiovascular Disease Prevalence and Mortality (continued)

CDC (Centers for Disease Control and Prevention). 2007. 

CDC Wide-ranging OnLine Data for Epidemiologic 

Research (WONDER). Compressed mortality file, underlying cause of death. 1999-2004 (with ICD 10 codes) and 

1979-1998 (with ICD 9 codes). Accessed September 2007.

<http://wonder.cdc.gov/mortSQL.html>

CDC. 2004. The burden of chronic diseases and their risk 

factors—national and state perspectives. <http://www.cdc.

gov/nccdphp/burdenbook2004/pdf/burden_book2004.

pdf>

CDC. 1999. Decline in deaths from heart disease and 

stroke, United States, 1990-1999. Washington, DC.

CDC. n.d. CDC WONDER: Help page for compressed 

mortality file. Accessed September 2007. 

<http://wonder.cdc.gov/wonder/help/cmf.html>

NCHS (National Center for Health Statistics). 2007. 

Summary health statistics for U.S. adults: National Health 

Interview Survey, 2006. Vital Health Stat. 10(235). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_235.

pdf>

NCHS. 2006a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2005. Vital Health Stat. 

10(232). <http://www.cdc.gov/nchs/data/series/sr_10/

sr10_232.pdf>

NCHS. 2006b. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2004. Vital Health Stat. 

10(228). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_228.pdf>

NCHS. 2005. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2003. Vital Health Stat. 

10(225). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_225.pdf>

NCHS. 2004. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2002. Vital Health Stat. 

10(222). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_222.pdf>

NCHS. 2003. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2001. Vital Health Stat. 

10(218). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_218.pdf>

NCHS. 2002. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2000. Vital Health Stat. 

10(215). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_215.pdf>

NCHS. 2001. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1999. Vital Health Stat. 

10(212). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_212.pdf>

NCHS. 2000. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1998. Vital Health Stat. 

10(209). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_209.pdf>

NCHS. 1999. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1997. Vital Health Stat. 

10(205). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_205.pdf>

NIH (National Institute of Health). 2004. NIH news: The 

increasing number of adults with high blood pressure.

<http://www.nhlbi.nih.gov/new/press/04-08-23.htm>

State of California. 2005. Proposed identification of environmental tobacco smoke as a toxic air contaminant. Part B: 

Health effects assessment for environmental tobacco smoke. 

As approved by the Scientific Review Panel on June 24, 

2005. California Environmental Protection Agency, Office 

of Environmental Health Hazard Assessment. 

<http://www.arb.ca.gov/regact/ets2006/ets2006.htm>

U.S. EPA (United States Environmental Protection Agency). 

2004. Air quality criteria for particulate matter. Volumes 

I (EPA/600/P-99/002aF) and II (EPA/600/P-99/002bF). 

National Center for Environmental Assessment—RTP 

Office, Office of Research and Development.

v
HUMAN EXPOSURE AND HEALTH

5-52 EPA’s 2008 Report on the Environment

Exhibit 5-27. Chronic bronchitis and emphysema prevalence in U.S. adults (age 18 and older) by 

race, 1999-2006a

a

Rates presented are 

crude rates.

Data source: NCHS, 

2001-2005, 2006a,b, 

2007

Rate (per 1,000)

A. Chronic bronchitis B. Emphysema

Year

’99 ’00 ’01 ’02 ’03 ’06’05’04 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’06

All groups

Black

White

0

10

20

30

40

50

60

INDICATOR Chronic Obstructive Pulmonary Disease Prevalence 

and Mortality

Chronic obstructive pulmonary disease (COPD), sometimes referred to as chronic lung disease, is a disease 

that damages lung tissue or restricts airflow through the 

bronchioles and bronchi (NHLBI, 2003). Chronic bronchitis and emphysema are the most frequently occurring 

COPDs. Smoking is the most common cause of COPD, 

including cigarette, pipe, and cigar smoking (NHLBI, 

2003). Other risk factors in the development and progression of COPD include asthma, exposure to air pollutants 

in the ambient air and workplace environment, genetic 

factors, and respiratory infections (CDC, 2003; American 

Lung Association, 2004). 

Environmental tobacco smoke (ETS) may also increase 

the risk of developing COPD. The effect of chronic ETS 

exposure alone on pulmonary function in otherwise healthy 

adults is likely to be small. However, in combination with 

other exposures (e.g., prior smoking history, exposure to 

occupational irritants or ambient air pollutants), ETS exposure could contribute to chronic respiratory impairment. 

Children are especially sensitive to the respiratory effects of 

ETS exposure (State of California, 2005).

This indicator presents U.S. adult (age 18 and older) 

prevalence rates for chronic bronchitis and emphysema 

and mortality rates for COPD as a whole and for chronic 

bronchitis and emphysema. COPD prevalence data were 

compiled from 1999 to 2006 from the National Health 

Interview Survey (NHIS), conducted by the Centers for 

Disease Control and Prevention’s (CDC’s) National Center 

for Health Statistics (NCHS). The NHIS is the principal 

source of information on the health of the civilian noninstitutionalized population of the U.S. and since 1960 has 

been one of the major data collection programs of NCHS. 

COPD prevalence is based on the number of adults who 

reported that they had ever been told by a doctor or 

other health practitioner that they had chronic bronchitis 

or emphysema. Mortality data (all ages) were compiled 

between 1979 and 2004 using the National Vital Statistics 

System (NVSS), maintained by NCHS. The NVSS registers virtually all deaths and births nationwide, with data 

coverage from 1933 to 2004 and from all 50 states and the 

District of Columbia.

What the Data Show

COPD Prevalence

Exhibit 5-27 presents the prevalence of chronic bronchitis 

(panel A) and emphysema (panel B) from 1999 to 2006. 

The reported total prevalence of chronic bronchitis in 

U.S. adults over the age of 18 years ranged from a low of 

40 (2003) to a high of 55 (2001) cases per 1,000. A small 

increase in prevalence of chronic bronchitis can be seen 

from 1999 to 2001, with a subsequent overall decline from 

2001 to 2006. The reported total prevalence of emphysema in U.S. adults during the same time period ranged 

from 14 (1999) to 18 (2006) cases per 1,000. No notable 

change in the prevalence for emphysema was evident during this time period. Exhibit 5-27 also displays chronic 

bronchitis and emphysema prevalence by race. Chronic 

bronchitis prevalence was higher among white (designated 

as “white only”) adults than black (“black or African 

American only”) adults during 1999 (46 versus 36 cases per 

1,000, respectively), 2000 (49 versus 40 cases per 1,000, 

respectively), and 2004 (44 versus 36 cases per 1,000, 

respectively). However, in 2006 rates in black and white 

adults are the same (43 cases per 1,000). Throughout the 

entire time period, emphysema prevalence is consistently 

higher among white adults than black adults. 

In addition, the Hispanic or Latino population had a 

consistently lower prevalence of chronic bronchitis and 
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-53

’80 ’85 ’90 ’95 ’00

Age-adjusted rate

(per 100,000)

Year

R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

Nat’l

Exhibit 5-28. Age-adjusted chronic obstructive 

pulmonary disease mortality rates in the U.S. by 

EPA Region, 1979-2004a,b

a

Due to differences in the ICD 

system used for classifying 

mortality, data from 1979-1998 

should not be directly compared 

to data from 1999-2004 [ICD-9 

codes: 490-494, 496 

(1979-1998); ICD-10 codes: 

J40-J47 (1999-2004)].

b

Rates are age-adjusted to the 

2000 U.S. standard population.

Data source: CDC, 2007

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

20

25

30

35

40

45

50

55

0

INDICATOR Chronic Obstructive Pulmonary Disease Prevalence 

and Mortality (continued)

emphysema diseases than the non-Hispanic or Latino population from 1999-2006, the period for which these data 

are available. For example, in 2006, prevalence in Hispanics or Latinos was lower than non-Hispanics or Latinos 

for chronic bronchitis (22 compared to 46 cases per 1,000, 

respectively) and emphysema (4 compared to 21 cases per 

1,000, respectively). (Data not shown.)

Gender differences are also seen. In 2006, females had 

about twice the reported prevalence of chronic bronchitis 

than males (57 versus 27 cases per 1,000 respectively), a 

consistently observed difference between 1997 and 2006. 

Unlike with chronic bronchitis, the prevalence rates for 

emphysema have been consistently higher in males than in 

females. (Data not shown.)

COPD Mortality

In 2004, COPD continues to be the fourth leading cause 

of mortality, accounting for 121,987 (5.1 percent) of all 

deaths (General Mortality indicator, p. 5-33). The ageadjusted mortality rate for COPD as a whole has increased 

over time, with rates ranging from 25.5 per 100,000 in 

1979 to 41.8 per 100,000 in 1998. From 1999 to 2004, 

rates held steadier, ranging from 45.4 per 100,000 in 

1999 to 41.1 per 100,000 in 2004. Mortality rates for 

emphysema (6.9 and 6.5 per 100,000 for 1979 and 1998, 

respectively, and 6.5 and 4.6 per 100,000 for 1999 and 

2004, respectively) and chronic bronchitis (1.7 and 0.9 

per 100,000 for 1979 and 1998, respectively, and 0.2 and 

0.1 per 100,000 for 1999 and 2004, respectively) have not 

changed substantially during the same time period. (Data 

not shown.)

Exhibit 5-28 presents the overall COPD mortality 

rates in the U.S. and the 10 EPA Regions for 1979-1998 

and 1999-2004. The age-adjusted COPD mortality rates 

have been increasing in each of the 10 Regions from 

1979 to 1998. The rates ranged from 22.2 (Region 2) to 

31.2 (Region 8) per 100,000 in 1979 and 33.5 (Region 

2) to 47.9 (Region 8) per 100,000 in 1998. Between 1999 

and 2004, COPD mortality rates in each of the 10 EPA 

Regions have generally declined.

COPD age-adjusted mortality rates have been declining for males over time, with a rate of 58.7 per 100,000 in 

1999 compared to 49.5 per 100,000 in 2004. For females, 

the rates are lower than males and have been relatively 

stable between 1999 and 2004 (37.7 and 36.0 per 100,000, 

respectively). The COPD age-adjusted mortality rate is 

higher among whites (43.2 per 100,000 in 2004) compared to blacks or African Americans (28.2 per 100,000 in 

2004). COPD mortality rate increases with age: the 2004 

rates were 0.3, 1.1, 21.0, and 284.3 per 100,000 for those 

age 0-14 years, 15-44 years, 45-64 years, and 65 years and 

older, respectively. (Data not shown.) 

Indicator Limitations

•	 Prevalence data presented in the NHIS are based on 

self-reported responses to specific questions pertaining 

to COPD-related illnesses, and are subject to the biases 

associated with self-reported data. Self-reported data can 

underestimate the disease prevalence being measured if, 

for whatever reason, the respondent is not fully aware of 

his/her condition. 

•	All prevalence data are based on crude rates and are not 

age-adjusted, as CDC did not report age-adjusted data 

prior to 2002 in the data sources used for this indicator. 

Therefore, the reported disease prevalence rates across 

time or within different race and gender subgroups 

may not reflect differences in the age distribution of the 

populations being compared. 

•	 COPD mortality rates are based on underlying cause 

of death as entered on a death certificate by a physician. Some individuals may have had competing causes 

of death. “When more than one cause or condition is 
HUMAN EXPOSURE AND HEALTH

5-54 EPA’s 2008 Report on the Environment

INDICATOR Chronic Obstructive Pulmonary Disease Prevalence 

and Mortality (continued)

entered by the physician, the underlying cause is determined by the sequence of conditions on the certificate, 

provisions of the ICD [International Classification of 

Diseases], and associated selection rules and modifications” (CDC, n.d.). Consequently, some misclassification of reported mortality might occur in individuals 

with competing causes of death, as well as the possible 

underreporting of COPD as the cause of death.

•	The International Classification of Diseases 9th Revision 

(ICD-9) codes were used to specify underlying cause of 

death for years 1979-1998. Beginning in 1999, cause of 

death is specified with the International Classification of 

Diseases 10th Revision (ICD-10) codes. The two revisions differ substantially, and to prevent confusion about 

the significance of any specific disease code, data queries 

are separate. 

Data Sources

COPD prevalence data were obtained from annual reports 

published by NCHS (NCHS, 2001-2005, 2006a,b, 2007), 

which summarize health statistics compiled from the NHIS 

(http://www.cdc.gov/nchs/products/pubs/pubd/series/ser.

htm). Mortality statistics were obtained from CDC’s “compressed mortality” database, accessed through CDC WONDER (CDC, 2007) (http://wonder.cdc.gov/mortSQL.

html). EPA Regional mortality statistics were generated by 

combining and age-adjusting state-by-state totals for each 

EPA Region using data from CDC WONDER.

References

American Lung Association. 2004. Chronic obstructive pulmonary disease (COPD) fact sheet. Accessed 

February 7, 2005. <http://www.lungusa.org/site/

pp.asp?c=dvLUK9O0E&b=35020>

CDC (Centers for Disease Control and Prevention). 2007. 

CDC Wide-ranging OnLine Data for Epidemiologic 

Research (WONDER). Compressed mortality file, underlying cause of death. 1999-2004 (with ICD 10 codes) and 

1979-1998 (with ICD 9 codes). Accessed October 2007.

<http://wonder.cdc.gov/mortSQL.html>

CDC. 2003. Facts about chronic obstructive pulmonary 

disease (COPD). Accessed February 7, 2005. <http://

www.cdc.gov/nceh/airpollution/copd/copdfaq.htm>

CDC. n.d. CDC WONDER: Help page for compressed 

mortality file. Accessed September 2007. 

<http://wonder.cdc.gov/wonder/help/cmf.html>

NCHS (National Center for Health Statistics). 2007. 

Summary health statistics for U.S. adults: National Health 

Interview Survey, 2006. Vital Health Stat. 10(235). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_235.pdf>

NCHS. 2006a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2005. Vital Health Stat. 

10(232). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_232.pdf>

NCHS. 2006b. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2004. Vital Health Stat. 

10(228). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_228.pdf>

NCHS. 2005. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2003. Vital Health Stat. 

10(225). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_225.pdf>

NCHS. 2004. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2002. Vital Health Stat. 

10(222). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_222.pdf>

NCHS. 2003. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2001. Vital Health Stat. 

10(218). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_218.pdf>

NCHS. 2002. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2000. Vital Health Stat. 

10(215). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_215.pdf>

NCHS. 2001. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1999. Vital Health Stat. 

10(212). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_212.pdf>

NHLBI (National Heart, Lung, and Blood Institute). 2003. 

Chronic obstructive pulmonary disease fact sheet. NIH 

publication No. 03-5229. Bethesda, MD: U.S. Department 

of Health and Human Services. <http://www.nhlbi.nih.

gov/health/public/lung/other/copd_fact.pdf>

State of California. 2005. Proposed identification of environmental tobacco smoke as a toxic air contaminant. Part B: 

Health effects assessment for environmental tobacco smoke. 

As approved by the Scientific Review Panel on June 24, 

2005. California Environmental Protection Agency, Office 

of Environmental Health Hazard Assessment. 

<http://www.arb.ca.gov/regact/ets2006/ets2006.htm>

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-55

INDICATOR | Asthma Prevalence

Asthma is a chronic respiratory disease characterized by inflammation of the airways and lungs. During an 

asthma attack, the airways that carry air to the lungs are 

constricted, and as a result, less air is able to flow in and 

out of the lungs (NHLBI, 2004). Asthma attacks can cause 

a multitude of symptoms ranging in severity from mild 

to life-threatening. These symptoms include wheezing, 

breathlessness, chest tightness, and coughing (NHLBI, 

2004). Currently, there is no cure for asthma; however, 

people who have asthma can still lead productive lives if 

they control their asthma. Taking medication and avoiding 

contact with environmental “triggers” can control asthma. 

A family history of asthma contributes to susceptibility, but mostly what causes the development of asthma is 

unknown. Environmental exposures such as environmental 

tobacco smoke, dust mites, cockroach allergen, outdoor air 

pollution (e.g., ozone, particulate matter), pets, and mold are 

considered important triggers of an asthma attack (CDC, 

2003, 2004; U.S. EPA, 2005, 2007). 

Statistics for lifetime diagnosis prevalence, current asthma 

prevalence, and asthma attack prevalence are based on national 

estimates from the National Health Interview Survey (NHIS), 

conducted by the Centers for Disease Control and Prevention’s (CDC’s) National Center for Health Statistics (NCHS). 

The NHIS is the principal source of information on the health 

of the civilian non-institutionalized population of the U.S. 

and since 1960 has been one of the major data collection programs of NCHS. For this indicator, lifetime asthma diagnosis 

is defined as the number of adults/children who reported that 

they had ever been told by a doctor or other health practitioner that they had asthma. To determine current asthma prevalence, adults/children who had been told that they had asthma 

were asked whether they still have asthma. Asthma attack 

prevalence is based on the number of adults/children who 

reported an asthma episode or attack in the past 12 months.

What the Data Show

From 2003 to 2005, approximately 7.3 percent of the 

U.S. population reported that they currently have asthma 

(NCHS, 2007c). Reported asthma rates are highest in the 

child and adolescent population.

Adult Asthma

In adults, an increase in asthma prevalence rates (i.e., lifetime diagnosis) is evident from 1997 to 2001, with some 

decrease after 2001 and subsequent increase after 2003 

(Exhibit 5-29, panel B). The prevalence rates range from 

a low of 85 cases per 1,000 in 1999 to a high of 110 cases 

per 1,000 in 2006. Asthma was consistently higher among 

adult females than males, with a range of 98 (1999) and 

126 (2005) cases per 1,000 in females and 71 (1999) and 

95 (2006) cases per 1,000 in males. The asthma prevalence 

rate also consistently decreases in older populations. In 

2006, the asthma prevalence rates were 115 (ages 18-44 

years), 105 (ages 45-64), 117 (ages 65-74 years), and 93 (ages 

75+ years) cases per 1,000 (data not shown). 

Exhibit 5-30 compares asthma rates across racial and 

ethnic groups for the 2003-2005 time period. As shown 

in panel A, the lifetime asthma diagnosis in adults was 

highest among American Indians/Alaska Natives (131 

cases per 1,000), followed by blacks or African Americans 

(112 cases per 1,000), whites (100 cases per 1,000), and 

lowest among Asians (72 cases per 1,000). This same general pattern is seen for current asthma and asthma attack 

prevalence. Panel B shows that Hispanics or Latinos had 

lower rates across all three asthma prevalence categories than non-Hispanic whites and non-Hispanic blacks. 

For lifetime asthma diagnosis, 77 cases per 1,000 were 

reported in Hispanics or Latinos, 106 cases per 1,000 in 

non-Hispanic whites, and 111 cases per 1,000 in nonHispanic blacks.

Exhibit 5-29. Estimated lifetime asthma diagnosis prevalence in children and adults in the U.S., 

1997-2006a,b

a

Lifetime asthma diagnosis is determined 

by asking survey participants if they 

were “ever” told they had asthma.

b

Rates presented are crude rates.

Data source: NCHS, 2002a-d, 2003a-f, 

2004a,b, 2005a,b, 2006a-d, 2007a,b

All groups

Female

Male

Rate (per 1,000)

A. Children (0-17 years) B. Adults (18 years and older)

Year

’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’06’05 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’06

0

20

40

60

80

100

120

140

160

180
HUMAN EXPOSURE AND HEALTH

5-56 EPA’s 2008 Report on the Environment

Childhood Asthma

In 2006, almost 10 million children within the U.S. 

(age 0-17 years) were reported as ever having a diagnosis of asthma and nearly 4 million reported experiencing an asthma episode or attack during the previous 12 

months. As shown in Exhibit 5-31, asthma prevalence rates 

increased approximately 4 percent per year between 1980 

and 1996. Rates in subsequent years (1997-2006), reported 

in three categories, show no sharp upward or downward 

change through most of the time period, although an 

increase in current and lifetime reported asthma rates 

was observed in 2005 and 2006. Lifetime asthma diagnosis rates range from a low of 108 cases per 1,000 in 1999 

to a high of 135 cases per 1,000 in 2006. Since tracking 

began in 2001, current asthma prevalence has ranged from 

approximately 83.4 cases per 1,000 (2002) to 93 cases 

per 1,000 (2006). Between 1997 and 2006, asthma attack 

prevalence rates have varied, with the lowest rate of 52.0 

per 1,000 occurring in 2005 and the highest rate of 57.7 

cases per 1,000 occurring in 2002. Male children consistently had higher rates of asthma prevalence than female 

children (Exhibit 5-29, panel A). 

The overall pattern of asthma prevalence across races 

in children during 2003-2005 is similar to that seen 

in adults (Exhibit 5-30). One notable exception is that 

asthma prevalence in black or African American children 

was higher than asthma prevalence in American Indian/

Alaska Native children, the reverse of what was observed 

in the adult population. For example, reported lifetime 

asthma diagnosis was highest among black or African 

American children (172 cases per 1,000), followed by 

American Indians/Alaska Natives (166 cases per 1,000), 

whites (114 cases per 1,000), and Asians (78 cases per 

1,000). Hispanic children had lower asthma prevalence 

rates for all three categories than non-Hispanic white and 

non-Hispanic black children. 

INDICATOR | Asthma Prevalence (continued)

Exhibit 5-30. Asthma prevalence in the U.S. by race and Hispanic origin, 2003-2005a

a

Rates presented for age 0-17 are crude rates; rates presented for age 18 and older are age-adjusted.

b

Lifetime asthma diagnosis is determined by asking survey participants if they were “ever” told that they had asthma.

c

Current asthma prevalence is determined by asking if the survey participant still has asthma.

d

Asthma attack prevalence is determined by asking if the survey participant has had an asthma attack within the past 12 months.

Data source: NCHS, 2007c

All groups

White

Black

American Indian/

Alaska Native

Asian

All groups

Hispanic

Non-Hispanic white

Non-Hispanic black

Rate (per 1,000) 

Children

(0-17 years)

Lifetime asthma diagnosisb Current asthma prevalencec Asthma attack prevalenced

Adults

(18+ years)

Children

(0-17 years)

Adults

(18+ years)

Children

(0-17 years)

Adults

(18+ years)

A. Asthma prevalence by race

0

40

80

120

160

200

Rate (per 1,000) 

Children

(0-17 years)

Lifetime asthma diagnosisb Current asthma prevalencec Asthma attack prevalenced

Adults

(18+ years)

Children

(0-17 years)

Adults

(18+ years)

Children

(0-17 years)

Adults

(18+ years)

B. Asthma prevalence by Hispanic origin

0

40

80

120

160

200
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-57

INDICATOR | Asthma Prevalence (continued)

Indicator Limitations

•	 The NHIS questionnaire underwent major changes in 1997, 

and the data presented focus on surveys conducted from 

1997 to the most currently available release (2004). The 

redesigned NHIS is different in content, format, and mode 

of data collection from earlier versions of the survey. Due to 

changes in methodology, comparisons between 1997-2004 

NHIS estimates and pre-1997 NHIS data may not be valid. 

•	 Prevalence data reported in the NHIS are based on 

self-reported responses to specific questions pertaining 

to airway-related illnesses, and are subject to the biases 

associated with self-reported data. Self-reported data may 

underestimate the disease prevalence being measured if, 

for whatever reason, the respondent is not fully aware of 

his/her condition. 

•	 Except where otherwise noted, all prevalence data are 

based on crude rates and are not age-adjusted, as CDC 

did not report age-adjusted data prior to 2002 in the data 

sources used for this indicator. Therefore, the reported 

disease prevalence rates across time or within different 

race and gender subgroups may not reflect differences in 

the age distribution of the populations being compared. 

Data Sources

Asthma prevalence data were obtained from annual reports 

published by NCHS (NCHS, 2002a-d; 2003a-f; 2004a,b; 

2005a,b; 2006a-d; 2007a,b), which summarize health 

statistics compiled from the NHIS (http://www.cdc.gov/

nchs/products/pubs/pubd/series/ser.htm#sr10). Race and 

ethnicity data were obtained from CDC’s online “Health 

Data for All Ages” (NCHS, 2007c) (http://www.cdc.gov/

nchs/health_data_for_all_ages.htm). The data used by CDC 

to create the asthma tables in “Health Data for All Ages” 

originate from the NHIS. The pre-1997 data also originate 

from the NHIS, as compiled by NCHS in Akinbami (2006). 

References

Akinbami, L.J. 2006. The state of childhood asthma, 

United States, 1980-2005. Advance data from vital and 

health statistics. Number 381. Hyattsville, MD: National 

Center for Health Statistics. 

<http://www.cdc.gov/nchs/data/ad/ad381.pdf>

CDC (Centers for Disease Control and Prevention). 2004. 

Asthma’s impact on children and adolescents. Accessed 

November 22, 2004. 

<http://www.cdc.gov/asthma/children.htm>

CDC. 2003. Basic facts about asthma. Accessed February 

3, 2005. <http://www.cdc.gov/asthma/faqs.htm>

NCHS (National Center for Health Statistics). 2007a. 

Summary health statistics for U.S. adults: National Health 

Interview Survey, 2006. Vital Health Stat. 10(235). <http://

www.cdc.gov/nchs/data/series/sr_10/sr10_235.pdf>

NCHS. 2007b. Summary health statistics for U.S. children: National Health Interview Survey, 2006. Vital 

Health Stat. 10(234). <http://www.cdc.gov/nchs/data/

series/sr_10/sr10_234.pdf>

NCHS. 2007c. Health data for all ages. Accessed September 2007. <http://www.cdc.gov/nchs/health_data_for_

all_ages.htm>

NCHS. 2006a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2005. Vital Health Stat. 

10(232). <http://www.cdc.gov/nchs/data/series/sr_10/

sr10_232.pdf>

NCHS. 2006b. Summary health statistics for U.S. children: National Health Interview Survey, 2005. Vital 

Health Stat. 10(231). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_231.pdf>

NCHS. 2006c. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2004. Vital Health Stat. 

10(228).

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_228.pdf> Rate (per 1,000)

Exhibit 5-31. Asthma prevalence in U.S.

children (0-17 years), 1980-2006a

a

Due to changes in NHIS questions in 1997, asthma prevalence data 

collected from 1980-1996 are not directly comparable to the data 

collected from 1997-2004.

b

Lifetime asthma diagnosis is determined by asking survey 

participants if they were “ever” told their child has asthma.

c

Current asthma prevalence is determined by asking if the child still 

has asthma.

d

Asthma attack prevalence is determined by asking if the child has 

had an asthma attack within the past 12 months.

Data source: Adapted from Akinbami, 2006; NCHS, 2007b

’80 ’84 ’88 ’92 ’00

Year

’82 ’86 ’90 ’94 ’96 ’98 ’02 ’04 ’06

0

20

40

60

80

100

120

140

160

Lifetime asthma

diagnosis

b

Asthma attack

prevalenced

Current asthma

prevalencec

Asthma prevalence
HUMAN EXPOSURE AND HEALTH

5-58 EPA’s 2008 Report on the Environment

NCHS. 2006d. Summary health statistics for U.S. children: National Health Interview Survey, 2004. Vital 

Health Stat. 10(227). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_227.pdf>

NCHS. 2005a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2003. Vital Health Stat. 

10(225). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_225.pdf>

NCHS. 2005b. Summary health statistics for U.S. children: 

National Health Interview Survey, 2003. Vital Health Stat. 

10(223). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_223.pdf>

NCHS. 2004a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2002. Vital Health Stat. 

10(222). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_222.pdf>

NCHS. 2004b. Summary health statistics for U.S. children: 

National Health Interview Survey, 2002. Vital Health Stat. 

10(221).

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_221.pdf>

NCHS. 2003a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2001. Vital Health Stat. 

10(218). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_218.pdf>

NCHS. 2003b. Summary health statistics for U.S. children: 

National Health Interview Survey, 2001. Vital Health Stat. 

10(216). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_216.pdf>

NCHS. 2003c. Summary health statistics for U.S. adults: 

National Health Interview Survey, 2000. Vital Health Stat. 

10(215). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_215.pdf>

NCHS. 2003d. Summary health statistics for U.S. children: National Health Interview Survey, 2000. Vital 

Health Stat. 10(213). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_213.pdf>

NCHS. 2003e. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1999. Vital Health Stat. 

10(212). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_212.pdf>

NCHS. 2003f. Summary health statistics for U.S. children: 

National Health Interview Survey, 1999. Vital Health Stat. 

10(210). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_210.pdf>

NCHS. 2002a. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1998. Vital Health Stat. 

10(209). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_209.pdf>

NCHS. 2002b. Summary health statistics for U.S. children: 

National Health Interview Survey, 1998. Vital Health Stat. 

10(208). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_208.pdf>

NCHS. 2002c. Summary health statistics for U.S. adults: 

National Health Interview Survey, 1997. Vital Health Stat. 

10(205). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_205.pdf>

NCHS. 2002d. Summary health statistics for U.S. children: National Health Interview Survey, 1997. Vital 

Health Stat. 10(203). 

<http://www.cdc.gov/nchs/data/series/sr_10/sr10_203.pdf>

NHLBI (National Heart, Lung, and Blood Institute). 2004. 

Diseases and conditions index. Accessed November 12, 

2004. <http://www.nhlbi.nih.gov/health/dci/Diseases/

Asthma/Asthma_WhatIs.html>

U.S. EPA (United States Environmental Protection 

Agency). 2007. Review of the National Ambient Air 

Quality Standards for ozone: policy assessment of scientific 

and technical information. OAQPS Staff Paper.

U.S. EPA. 2005. Review of the National Ambient Air 

Quality Standards for particulate matter: Policy assessment 

of scientific and technical information. OAQPS Staff Paper.

INDICATOR | Asthma Prevalence (continued)

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-59

INDICATOR Infectious Diseases Associated with Environmental 

Exposures or Conditions

I

nfectious diseases are human illnesses caused by viruses, 

bacteria, parasites, fungi, and other microbes. They can be 

spread by direct contact with an infected person or animal, 

through ingestion of contaminated food or water, by insects 

like mosquitoes or ticks (disease vectors), or by contact with 

contaminated surroundings like animal droppings or contaminated air. Demographic and environmental factors such 

as population growth, increased urbanization, and alteration 

of habitats of disease-carrying insects and animals (e.g., irrigation, deforestation) may promote the spread of infectious 

diseases (CDC, 1998a). The three broad infectious disease 

categories included here are those whose appearance and 

spread may be influenced to some extent by environmental 

conditions and change. They include gastrointestinal (GI) 

disease, arthropod-borne disease, and legionellosis. 

•	 Gastrointestinal diseases. Eight notifiable GI diseases 

caused by microorganisms are discussed below: cholera, cryptosporidiosis, Escherichia coli (E. coli) O157:H7, 

giardiasis, hepatitis A, salmonellosis, shigellosis, and 

typhoid fever. The major environmental source of gastrointestinal illness is water or food that is contaminated 

with pathogenic microorganisms. The primary means of 

transmission for these eight diseases is through ingestion 

of contaminated food/water or through contact with and 

accidental ingestion of fecal matter (CDC, 2005a).

•	 Arthropod-borne diseases. Three arthropod-borne 

diseases are included: Lyme disease (transmission of 

Borrelia burgdorferi by ticks), Rocky Mountain spotted 

fever (transmission of Rickettsia rickettsii by ticks), and 

West Nile virus (transmitted by mosquitoes). Certain 

ticks and mosquitoes (arthropods) can carry bacteria and 

viruses that cause disease in humans. The arthropods 

acquire the bacteria or viruses when they bite an infected 

mammal or bird. Some studies indicate that spread of 

vector-borne disease may be influenced by land use and/

or other environmental change (CDC, 2004). In recent 

years, both Lyme disease and West Nile virus have spread 

across the U.S. (CDC, 1993, 2000, 2004). Surveillance 

for Lyme disease was initiated by the Centers for Disease 

Control and Prevention (CDC) in 1982 (CDC, 1993). 

•	 Legionellosis. Legionellosis, or Legionnaires’ disease, 

is a serious and sometimes fatal form of pneumonia. It is 

caused by Legionella bacteria, which are found naturally 

in the environment and thrive in warm water and warm 

damp places. They are commonly found in lakes, rivers, creeks, hot springs, and other bodies of water. This 

bacterium has been associated with outbreaks in the U.S. 

linked to poorly maintained artificial water systems (e.g., 

air conditioning and industrial cooling systems) and air 

ventilation systems. Infection results from inhalation of 

contaminated water sprays or mists (CDC, 2003a).

This indicator reflects occurrence of these notifiable 

diseases as reported by health departments to the National 

Notifiable Diseases Surveillance System (NNDSS). A notifiable disease is one for which regular, frequent, and timely 

information regarding individual cases is considered necessary for the prevention and control of the disease (CDC, 

2005b). Data are collected by all 50 states, five territories, 

New York City, and the District of Columbia, based on a 

list of recommended nationally notifiable infectious diseases, and compiled nationally. The temporal coverage of 

the data varies by disease. The number of states reporting 

may also vary. For example, in 1995, when cryptosporidiosis was first nationally reported, only 27 states reported; 

45 states reported this disease by 1997.

What the Data Show

Gastrointestinal Diseases

Exhibits 5-32 and 5-33 present the number of reported cases 

for each of the eight notifiable GI diseases from 1995-2005. 

In comparison to the other GI diseases, the number of newly 

identified cholera cases reported each year is low. From 1995 

to 2005, just 81 laboratory-confirmed cases of cholera were 

reported to CDC, with eight cases being reported in 2005, 

the most current reporting year. Of these 81 total cases, 51 

(63 percent) were acquired outside the U.S. The number of 

newly identified cases of typhoid fever was relatively stable 

from 1995 to 2005, ranging between a low of 321 cases in 

2002 and a high of 396 cases in 1996. In 2005, 324 cases of 

typhoid fever were reported. Hepatitis A has continued to 

decline, with 31,582 cases reported in 1995 compared to 

4,488 cases in 2005. The number of reported cryptosporidiosis cases increased in 2005 (5,659 cases). Fewer shigellosis 

cases were reported in 2004 and 2005 than in preceding 

years. No notable changes in the number of cases were 

observed for E. coli O157:H7, giardiasis (only 4 years of 

reporting data available), and salmonellosis. 

Arthropod-Borne Diseases

Exhibit 5-34 presents the number of reported cases for 

three arthropod-borne diseases. Lyme disease is the most 

commonly reported arthropod-borne disease in the U.S., 

with 23,305 cases reported in 2005, just under the record 

number reported in 2002 (23,763 cases). CDC began 

surveillance of Rocky Mountain spotted fever in 1970. 

The number of new cases of Rocky Mountain spotted 

fever reported from 1995 to 2005 has fluctuated, ranging between a low of 365 cases in 1998 and a high of 

1,936 cases in 2005. Cases of West Nile virus were first 

documented in the U.S. in 1999. A total of 80 cases were 

reported in 1999 (62 cases) and 2000 (18 cases) (data not 

shown). West Nile virus became nationally reportable in 

2002, and the number of reported cases rose from 2,840 in 
HUMAN EXPOSURE AND HEALTH

5-60 EPA’s 2008 Report on the Environment

INDICATOR Infectious Diseases Associated with Environmental 

Exposures or Conditions (continued)

2002 to 2,866 in 2003. In 2004, the number of reported 

cases decreased to 1,142; the number increased to 1,309 

reported cases in 2005.

Legionellosis

Exhibit 5-35 presents the number of reported cases of 

legionellosis within the U.S. population from 1995 to 

2005. From 1995 to 2002, the number of new cases of 

legionellosis was relatively stable, ranging from a low 

of 1,108 cases in 1999 to 1,355 cases in 1998. However, 

an increased number of new cases was reported in 2003 

(2,232), 2004 (2,093), and 2005 (2,301). 

Indicator Limitations

•	 State health departments report cases of notifiable diseases to CDC; policies for reporting can vary by disease 

or reporting jurisdiction. 

•	 Disease reporting likely underestimates the actual number 

of cases for a given time period because reporting nationally notifiable diseases to CDC is voluntary. Additionally, 

the completeness of reporting likely varies by disease. The 

degree of completeness of data reporting is influenced by 

many factors such as the diagnostic facilities available, the 

control measures in effect, public awareness of a specific 

Exhibit 5-32. Number of reported cases of gastrointestinal diseases in the U.S., 1995-2005 (part 1)

Year

Number of cases

Data source: CDC, 1996, 1997, 1998b, 1999, 2001, 2002, 2003b, 2004, 2005b, 2006, 2007

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

0

1,000

2,000

3,000

4,000

5,000

6,000

Cryptosporidiosis E. coli 0157:H7

Typhoid fever

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

0

5

10

15

20

25

Cholera

Number of cases

Year

Exhibit 5-33. Number of reported cases of gastrointestinal diseases in the U.S., 1995-2005 (part 2) Number of cases

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04’05

a

Giardiasis was not on CDC’s list of nationally notifiable infectious diseases prior to 2002.

Data source: CDC, 1996, 1997, 1998b, 1999, 2001, 2002, 2003b, 2004, 2005b, 2006, 2007

’02’03’04’05 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05 ’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04’05

Giardiasisa Hepatitis A Salmonellosis Shigellosis

0

10,000

20,000

30,000

40,000

50,000

Year
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-61

INDICATOR Infectious Diseases Associated with Environmental 

Exposures or Conditions (continued)

disease, and the interests, resources, and priorities of state 

and local officials responsible for disease control and public 

health surveillance (CDC, 2007). 

•	 Factors such as changes in case definitions for public 

health surveillance, introduction of new diagnostic tests, 

or discovery of new disease entities can cause changes 

in disease reporting that are independent of the true incidence of disease (CDC, 2004).

•	 Prior to 2005, only confirmed “neuroinvasive” cases of 

West Nile virus—the most severe form of the condition—were reported (CDC, 2005c). Beginning in 2005, 

non-neuroinvasive domestic arboviral diseases for the 

six domestic arboviruses listed were added to the list of 

nationally notifiable diseases; these included West Nile 

fever, a non-neuroinvasive form of West Nile virus (CDC, 

2007). In order to maintain reporting consistency, only 

neuroinvasive cases are presented for this indicator.

Data Sources

The data for this indicator were obtained from CDC 

annual reports that summarize data on nationally notifiable 

infectious diseases reported to CDC by state health agencies across the country (CDC, 1996, 1997, 1998b, 1999, 

2001, 2002, 2003b, 2004, 2005b, 2006, 2007). Data are 

collected and compiled from reports sent by state health 

departments to the NNDSS, which is operated by CDC. 

The NNDSS is neither a single surveillance system nor a 

method of reporting. Certain NNDSS data are reported 

to CDC through separate surveillance information systems 

and through different reporting mechanisms; however, 

these data are aggregated and compiled for publication 

purposes (CDC, 2007).

References

CDC (Centers for Disease Control and Prevention). 2007. 

Summary of notifiable diseases—United States, 2005. 

MMWR 54(53). <http://www.cdc.gov/mmwr/PDF/wk/

mm5453.pdf> See Table 1.

Exhibit 5-34. Number of reported cases of arthropod-borne diseases in the U.S., 1995-2005 Number of cases

’02 ’03 ’04 ’05

a

West Nile virus was not on CDC’s list of nationally notifiable infectious diseases prior to 2002.

Data source: CDC, 1996, 1997, 1998b, 1999, 2001, 2002, 2003b, 2004, 2005b, 2006, 2007

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

Lyme disease Rocky Mountain spotted fever West Nile virusa

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

Year

0

5,000

10,000

15,000

20,000

25,000

Exhibit 5-35. Number of reported cases of 

legionellosis in the U.S., 1995-2005

Data source: CDC, 1996, 1997, 1998b, 1999, 2001, 2002, 2003b, 

2004, 2005b, 2006, 2007 Number of cases

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

0

500

1,000

1,500

2,000

2,500
HUMAN EXPOSURE AND HEALTH

5-62 EPA’s 2008 Report on the Environment

INDICATOR Infectious Diseases Associated with Environmental 

Exposures or Conditions (continued)

CDC. 2006. Summary of notifiable diseases—United 

States, 2004. MMWR 53(53). <http://www.cdc.gov/

mmwr/PDF/wk/mm5353.pdf> See Table 1.

CDC. 2005a. Foodborne illness—frequently asked 

questions. Accessed April 11, 2005. <http://www.cdc.

gov/ncidod/dbmd/diseaseinfo/foodborneinfections_g.

htm#howdiagnosed>

CDC. 2005b. Summary of notifiable diseases—United 

States, 2003. MMWR 52(54). <http://www.cdc.gov/

mmwr/PDF/wk/mm5254.pdf> See Table 1.

CDC. 2005c. West Nile virus statistics, surveillance, and 

control: 2005 West Nile virus activity in the United States. 

Accessed October 16, 2005. <http://www.cdc.gov/ncidod/

dvbid/westnile/surv&controlCaseCount05_detailed.htm>

CDC. 2004. Summary of notifiable diseases—United 

States, 2002. MMWR 51(53). <http://www.cdc.gov/

mmwr/PDF/wk/mm5153.pdf> See Table 1.

CDC. 2003a. Legionnaires’ disease fact sheet. Accessed 

October 20, 2005. 

<http://www.air-care.com.sg/legionella-factsheet.html>

CDC. 2003b. Summary of notifiable diseases—United 

States, 2001. MMWR 50(53). <http://www.cdc.gov/

mmwr/PDF/wk/mm5053.pdf> See Table 1.

CDC. 2002. Summary of notifiable diseases—United 

States, 2000. MMWR 49(53). <http://www.cdc.gov/

mmwr/PDF/wk/mm4953.pdf> See Table 1.

CDC. 2001. Summary of notifiable diseases—United 

States, 1999. MMWR 48(53). <http://www.cdc.gov/

mmwr/PDF/wk/mm4853.pdf> See Table 1.

CDC. 2000. Update: West Nile virus activity—eastern 

United States, 2000. MMWR 49(46):1044-1047. 

<http://www.cdc.gov/mmwr/preview/mmwrhtml/

mm4946a2.htm>

CDC. 1999. Summary of notifiable diseases—United 

States, 1998. MMWR 47(53). 

<http://www.cdc.gov/mmwr/PDF/wk/mm4753.pdf>

CDC. 1998a. Preventing emerging infectious diseases. A 

strategy for the 21st century. 

CDC. 1998b. Summary of notifiable diseases—United 

States, 1997. MMWR 46(54). 

<http://www.cdc.gov/mmwr/PDF/wk/mm4654.pdf>

CDC. 1997. Summary of notifiable diseases—United 

States, 1996. MMWR 45(53). 

<http://www.cdc.gov/mmwr/PDF/wk/mm4553.pdf>

CDC. 1996. Summary of notifiable diseases—United 

States, 1995. MMWR 44(53). 

<http://www.cdc.gov/mmwr/PDF/wk/mm4453.pdf>

CDC. 1993. Lyme disease—United States, 1991-1992. 

MMWR 42(18):345-348. <http://www.cdc.gov/mmwr/

preview/mmwrhtml/00020506.htm>

INDICATOR | Birth Defects Prevalence and Mortality

Birth defects are structural or functional anomalies causing physical or mental disability, some of which can be fatal. 

Although birth defects are the leading cause of infant mortality (deaths occurring to those under 1 year of age) in the 

U.S., the cause is unknown for approximately 70 percent of 

all cases (Infant Mortality indicator, p. 5-36) (CDC, 2005). 

Many different factors may be associated with the development of birth defects, such as genetic and/or chromosomal 

aberrations, in utero exposure to viruses or bacteria, uncontrolled maternal diabetes, maternal cigarette smoke, maternal use of drugs and alcohol during pregnancy, and prenatal 

exposure to chemicals. All of these factors may influence 

normal infant growth or development, resulting in different 

types of birth defects (NICHD, 2006). 

This indicator presents birth defects prevalence at birth 

and mortality rates among infants in the U.S. as recorded 

in the National Vital Statistics System, which registers 

virtually all births and deaths nationwide. Data collection 

began in 1933 and is available through 2004. Birth defects 

data are collected on death certificates from all 50 states 

and the District of Columbia and recorded on birth certificates for 49 states and the District of Columbia. Reported 

race and ethnicity data are based on the race and ethnicity 

of the mother.

What the Data Show

Exhibit 5-36 presents the prevalence of live births with 

identified specific congenital anomalies (i.e., birth defects) 

between 1999 and 2004. The most frequently occurring 

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-63

INDICATOR | Birth Defects Prevalence and Mortality (continued)

types of birth defects were various musculoskeletal/integumental anomalies, circulatory/respiratory system anomalies, 

and heart malformations. In 2004, heart malformations 

occurred at a rate of 137.7 per 100,000 live births, which was 

highest among the specific anomalies listed (i.e., categories 

that do not include “other”). The overall rate of birth defects 

(i.e., all birth defects combined) has been relatively stable 

between 1999 and 2002, with a noticeable decline in 2003 

and 2004. Blacks have a consistently higher rate of birth 

defects than whites during this time period, with a rate of 

1,337.5 (blacks) compared with 1,064.0 (whites) birth defects 

per 100,000 live births in 2004 (data not shown). 

Rates for certain types of anomalies differ widely with 

maternal age. For example, in 2004 as in past years, infants 

of the youngest mothers (under 20 years of age) have the 

highest rates for omphalocele/gastroschisis, a defect or 

abnormality of the anterior abdominal wall (87.1 per 1,000 

live births); infants of mothers age 35 years and over have 

the highest rates for Down’s syndrome (348.3 per 1,000 

live births). (Data not shown.)

1999 2000 2001 2002 2003

1,170.2

11.0

20.1

21.5

5.9

20.0

119.8

140.6

9.0

13.3

30.2

29.8

76.3

13.7

99.0

80.9

87.9

55.7

13.1

239.9

45.5

36.9

1,170.6 

9.9

20.0

22.5

5.5

22.2

129.9

131.7

8.3

10.8

30.3

36.1

86.6

15.4

101.8

78.5

82.2

59.6

12.1

228.9

46.7

31.6

1,178.8 

9.9

19.9

22.5

5.6

24.8

122.5

139.6

9.0

12.0

31.8

34.2

88.4

14.8

102.8

80.6

82.4

58.6

11.4

226.4

45.5

36.2

1,164.2 

10.7

20.7

23.7

7.2

20.7

124.9

138.1

8.4

12.1

29.7

29.9

84.2

13.8

99.3

82.1

87.2

57.2

10.8

217.0

46.9

39.7

1,103.4

11.4

18.7

22.2

5.6

21.1

128.9

126.1

7.8

10.8

32.5

33.0

79.7

14.0

90.2

75.9

76.4

57.6

11.4

208.2

46.5

30.1

2004

1,111.8

10.9

19.3

22.4

6.9

21.5

137.7

135.3

8.7

11.8

31.9

33.9

80.8

13.6

89.5

77.7

74.8

55.7

10.4

211.1

47.9

29.3

Exhibit 5-36. Prevalence of live births in the U.S. with specific birth defects (congenital anomalies), 

1999-2004a

a

Rates are per 100,000 live births.

Data source: NCHS, 2001, 2002a,b, 2003, 2005, 2006; CDC, 2007a

Overall rate

Central nervous system anomalies 

Anencephalus

Spina bifida/meningocele

Hydrocephalus

Microcephalus

Other central nervous system anomalies

Circulatory/respiratory anomalies

Heart malformations

Other circulatory/respiratory anomalies

Gastrointestinal anomalies

Rectal atresia/stenosis

Tracheo-esophageal fistula/esophageal atresia

Omphalocele/gastroschisis

Other gastrointestinal anomalies

Urogenital anomalies

Malformed genitalia

Renal agenesis

Other urogenital anomalies

Chromosomal anomalies

Cleft lip/palate

Polydactyly/syndactyly/adactyly

Clubfoot

Diaphragmatic hernia

Other musculoskeletal/integumental anomalies

Down’s syndrome

Other chromosomal anomalies
HUMAN EXPOSURE AND HEALTH

5-64 EPA’s 2008 Report on the Environment

INDICATOR | Birth Defects Prevalence and Mortality (continued)

Birth defects continue to be the leading cause of infant 

mortality, accounting for 5,622 (20.1 percent) of the 27,936 

infant deaths in 2004 (Exhibit 5-16, Infant Mortality 

indicator, p. 5-37). Between 1979 and 1998, a decline in 

the national birth defects mortality rate has been observed, 

ranging from 255.4 per 100,000 live births in 1979 to 

157.6 per 100,000 live births in 1998. From 1999 to 2004, 

the birth defects mortality rates were 144.2 (1999), 150.9 

(2000), 136.7 (2001), 139.4 (2002), 140.4 (2003), and 137.9 

(2004) per 100,000 live births. (Data not shown.)

Birth defects mortality was consistently higher among 

black infants than white infants. In 2004, for example, 

mortality attributed to birth defects among black male and 

female infants was 169.9 and 155.6 per 100,000 infants, 

respectively; among white male and female infants, it was 

134.3 and 134.7 per 100,000 infants, respectively. (Data 

not shown.)

Indicator Limitations

•	 Because some birth defects are not recognized immediately, they are often underreported on both birth and 

death certificates (Friis and Sellers, 1999). Many anomalies 

are hard to detect at birth, which limits early ascertainment and complete reporting. The most serious and/or 

apparent anomalies are more likely to be identified and 

reported prior to hospital discharge (Honein et al., 2001). 

•	The lack of uniform reporting on birth certificates introduces additional uncertainty. For example, race information may be missing or incomplete. Also, beginning in 

2003, two states began using a revised “standard certificate of live birth;” therefore, a subset of anomaly data 

was excluded because of the lack of comparability with 

other data sets (NCHS, 2005). 

•	The congenital anomalies reported on birth certificates 

are rare events. Since a small change in the number of 

anomalies reported can result in a relatively large change 

in rates, caution should also be used in comparing yearly 

rates for a specific anomaly.

•	 The birth defects anomaly groupings that include “other” 

(e.g., other musculoskeletal anomalies) include a large 

number of non-specific birth defects and should be considered separately from the specific birth defects listed. 

•	 Birth defects mortality rates are based on underlying cause of death as entered on a death certificate by a 

physician. Incorrect coding and low rates of autopsies 

that confirm the cause of death may occur. Additionally, some individuals may have had competing causes 

of death. “When more than one cause or condition is 

entered by the physician, the underlying cause is determined by the sequence of conditions on the certificate, 

provisions of the ICD [International Classification of 

Diseases], and associated selection rules and modifications” (CDC, n.d.). Consequently, some misclassification 

of reported mortality might occur in individuals with 

competing causes of death, as well as underreporting of 

some birth defects as the cause of death.

•	 The International Classification of Diseases 9th Revision 

(ICD-9) codes were used to specify underlying cause of 

death for years 1979-1998. Beginning in 1999, cause of 

death is specified with the International Classification of 

Diseases 10th Revision (ICD-10) codes. The two revisions differ substantially, and to prevent confusion about 

the significance of any specific disease code, data queries 

are separate. The relatively large difference between birth 

defects mortality rates reported from 1979 through 1998 

and those reported beginning in 1999 may be due to some 

changes in the criteria used to report birth defects mortality during the switch from ICD-9 to ICD-10. 

Data Sources

The birth defects rate data used for this indicator are from 

National Vital Statistics Reports published by the CDC’s 

National Center for Health Statistics (NCHS, 2001, 

2002a,b, 2003, 2005, 2006). CDC’s “VitalStats”—a collection of vital statistics products including tables, data files, 

and reports that allow users to access and examine vital 

statistics and population data interactively—were used to 

obtain specific anomaly data for 2004 (CDC, 2007a). The 

birth defects mortality data were obtained from a published report by the National Center for Health Statistics 

(NCHS, 2007) and from CDC’s compressed mortality files 

(underlying cause of death), accessed via CDC WONDER 

(CDC, 2007b), at http://wonder.cdc.gov. 

References

CDC (Centers for Disease Control and Prevention). 2007a. 

VitalStats. National Center for Health Statistics. Accessed 

October 17, 2007. 

<http://www.cdc.gov/nchs/vitalstats.htm> 

CDC. 2007b. CDC Wide-ranging OnLine Data for Epidemiologic Research (WONDER). Compressed mortality 

file, underlying cause of death. 1999-2004 (with ICD 10 

codes) and 1979-1998 (with ICD 9 codes). Accessed 2007.

<http://wonder.cdc.gov/mortSQL.html>

CDC. 2005. Birth defects. Accessed September 2007.

<http://www.cdc.gov/ncbddd/bd/facts.htm>

CDC. n.d. CDC WONDER: Help page for compressed 

mortality file. Accessed September 2007. 

<http://wonder.cdc.gov/wonder/help/cmf.html>

Friis, R.H., and T.A. Sellers. 1999. Epidemiology for 

public health practice. Second edition. Gaithersburg, MD: 

Aspen Publishers.
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-65

INDICATOR | Birth Defects Prevalence and Mortality (continued)

Honein, M.A., L.J. Paulozzi, and M.L. Watkins. 2001. 

Maternal smoking and birth defects: Validity of birth data 

for effect estimation. Public Health Reports 116:327-335

NCHS (National Center for Health Statistics). 2007. 

Deaths: Final data for 2004. National Vital Statistics 

Reports 55(19). <http://www.cdc.gov/nchs/data/nvsr/

nvsr55/nvsr55_19.pdf> 

NCHS. 2006. Births: Final data for 2004. National Vital 

Statistics Reports 55(1). <http://www.cdc.gov/nchs/data/

nvsr/nvsr55/nvsr55_01.pdf> See Table 25.

NCHS. 2005. Births: Final data for 2003. National Vital 

Statistics Reports 54(2). <http://www.cdc.gov/nchs/data/

nvsr/nvsr54/nvsr54_02.pdf> See Table 49.

NCHS. 2003. Births: Final data for 2002. National Vital 

Statistics Reports 52(10). <http://www.cdc.gov/nchs/data/

nvsr/nvsr52/nvsr52_10.pdf> See Table 49.

NCHS. 2002a. Births: Final data for 2001. National Vital 

Statistics Reports 51(2). <http://www.cdc.gov/nchs/data/

nvsr/nvsr51/nvsr51_02.pdf> See Table 49.

NCHS. 2002b. Births: Final data for 2000. National Vital 

Statistics Reports 50(5). <http://www.cdc.gov/nchs/data/

nvsr/nvsr50/nvsr50_05.pdf> See Table 49.

NCHS. 2001. Births: Final data for 1999. National Vital 

Statistics Reports 49(1). <http://www.cdc.gov/nchs/data/

nvsr/nvsr49/nvsr49_01.pdf> See Table 49.

NICHD (National Institute of Child Health and Human 

Development). 2006. Birth defects and developmental 

disabilities. Accessed September 2007. <http://www.nichd.

nih.gov/womenshealth/research/pregbirth/birthdefects.cfm>

INDICATOR | Low Birthweight

The term “low birthweight” (LBW) is typically used for any infant weighing less than 2,500 grams at birth. 

Weight is a critical health measure because LBW children are 

more prone to death and disability than their counterparts. 

The etiology of LBW for term-LBW (born after 37+ 

weeks of gestation) infants and preterm-LBW (born after 

less than 37 weeks of gestation) infants differs. For termLBW infants, underlying causes include factors such as 

maternal smoking, weight at conception, and gestational 

weight gain, whereas for preterm-LBW infants, the etiology largely remains unexplained (CDC, 1994). Various 

exposures have been implicated as risk factors for termLBW (e.g., maternal smoking, maternal exposure to lead, 

diethylstilbestrol, occupational exposures) (Sram et al., 

2005; Kiely et al., 1994). The potential effect of air pollution on LBW continues to be researched (e.g., particulate 

matter, carbon monoxide, ozone).

This indicator presents the percentage of LBW infants 

born in the U.S. based on natality data reported to the 

National Vital Statistics System (NVSS). The NVSS registers virtually all deaths and births nationwide, with data 

coverage from 1933 to 2004 and from all 50 states and the 

District of Columbia. 

The data presented are based on singleton births only. 

This was done to eliminate the effect of multiple births. 

The data are presented across three maternal age groups 

(under 20 years, 20-39 years, and 40 years and older). 

Additionally, the data are stratified and reported for 

preterm (less than 37 weeks) and full-term (37 weeks and 

over) births because of the strong association between 

birthweight and gestational age. 

What the Data Show

As expected, the percent of total LBW deliveries among 

preterm births is much higher than the percent of total 

LBW deliveries among full-term births across each of the 

three maternal age categories (Exhibits 5-37 and 5-38). 

In general, small differences in the percent of LBW babies 

among maternal age categories are evident for both pre- and 

full-term births. For example, in 2004, the frequency of 

LBW babies among full-term births for mothers less than 

20 years old (4.0 percent) is almost 1 percent higher than for 

mothers who are 40 years and older (3.2 percent) and about 

1.4 percent higher than for mothers who are in the 20-39 

age group (2.4 percent) (Exhibit 5-38).

Among the full-term births, black women had consistently higher frequencies of LBW babies compared to any 

of the other racial groups reported from 1995 and 2004. 

This racial pattern is evident in 2004 for all three maternal 

age groups, and the difference is most apparent in the 40 

and older age group (6.2 percent for blacks and 2.7 percent 

for whites) (Exhibit 5-38). 

The percentages of term-LBW babies among the other 

two racial groups reported in 2004, Native Americans and 

Asians/Pacific Islanders, were 4.1 percent and 3.3 percent, 

respectively, for the 40 and older age group. In 2004, some 

v
HUMAN EXPOSURE AND HEALTH

5-66 EPA’s 2008 Report on the Environment

INDICATOR | Low Birthweight (continued)

variation in the frequency of term-LBW was reported for 

Native Americans and Asian/Pacific Islanders among the 

three different age groups reported (under 20 years, 20-39 

years, and 40 years and older), with Asian/Pacific Islanders showing the highest percentage of LBW babies (4.7 

percent) among the under 20 year age group and Native 

Americans showing the highest percentage of LBW babies 

(4.1 percent) among women 40 years and older. Hispanic 

women and non-Hispanic women had similar frequencies 

of LBW babies. For example, in 2004, the percent of LBW 

babies for Hispanic women was 2.4 percent compared to 

2.7 percent for non-Hispanic women. (Data not shown.) 

Indicator Limitations

•	 Complete reporting of natality indicators such as LBW 

may vary due to differences in the reporting requirements 

established by each state. In some states, the number of 

LBW babies may be underreported. 

Exhibit 5-37. Percent of low birthweight infants (<2,500 grams) born preterm in the U.S. by mother’s 

race and age, 1995-2004a,b

a

Preterm births are births occurring at <37 weeks gestation.

b

Data represent singleton births only.

Data source: CDC, 2007

All groups

Black

White

Percent

A. Mothers <20 years

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04’03

0

10

20

30

40

50

60

B. Mothers 20-39 years

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04’03

C. Mothers 40+ years

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’03 ’04

Exhibit 5-38. Percent of low birthweight infants (<2,500 grams) born full-term in the U.S. by mother’s 

race and age, 1995-2004a,b

a

Full-term births are births occurring at > 37 weeks gestation.

 bData represent singleton births only.

Data source: CDC, 2007

All groups

Black

White

Percent

A. Mothers <20 years

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04’03

0

1

2

3

4

5

6

7

8

9

10

B. Mothers 20-39 years

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04’03

C. Mothers 40+ years

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04 ’03
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-67

INDICATOR | Preterm Delivery

Preterm delivery is defined as delivery prior to 37 weeks of gestation (a typical pregnancy lasts 40 weeks). The 

shorter the gestational age of an infant, the more likely 

(s)he is to suffer adverse effects. Preterm birth along with 

low birthweight is the second leading cause of infant death 

(Infant Mortality indicator, p. 5-36) (NCHS, 2004, 2006), 

and accounts for nearly half of all congenital neurological 

defects, such as cerebral palsy, and more than two-thirds of 

infant deaths (Goldenberg and Rouse, 1998; NCHS, 2006). 

The determinants of preterm births are not fully known 

and the causes are often multi-factorial. Maternal highrisk conditions (e.g., infertility problems, vaginal spotting, inadequate maternal weight gain), previous history, 

socioeconomic status, smoking, alcohol consumption 

before third trimester, and multiple gestation pregnancy 

are known risk factors for preterm delivery. Environmental 

contaminants (e.g., lead, environmental tobacco smoke, air 

pollution) continue to be studied to better understand the 

strength of the associations with preterm delivery. 

This indicator presents the proportion of U.S. infants 

born prior to 37 weeks of gestation, based on natality data 

reported to the National Vital Statistics System (NVSS). The 

NVSS registers virtually all deaths and births nationwide, 

with data coverage from 1933 to 2004 and from all 50 states 

and the District of Columbia. The data presented here on 

preterm delivery were based on singleton births only. This 

was done to eliminate the effect of multiple births. The data 

are presented across three maternal age groups (under 20 

years, 20-39 years, and 40 years and older). 

What the Data Show

The proportion of infants defined as preterm has risen 18 

percent since 1990 (NCHS, 2006). A small overall increase 

in preterm births has been observed from 1995 (9.8 percent) 

Exhibit 5-39. Preterm deliveries in the U.S. by 

mother’s age and race, 1995-2004a,b Percent a

Preterm deliveries are births occurring at <37 weeks gestation.

b

Data represent singleton births only.

Data source: CDC, 2007

B. Preterm deliveries by mother’s race

All groups

Black

White

Percent

A. Preterm deliveries by mother’s age

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04’03

0

2

4

6

8

10

12

14

16

18

20

All groups

<20 years

20-39 years

40+ years

Year

’95 ’96 ’97 ’98 ’99 ’00 ’01 ’02 ’04’03

0

2

4

6

8

10

12

14

16

18

20

INDICATOR | Low Birthweight (continued)

Data Source

The data used for this indicator were public-use natality 

data (1995-2002 and 2003-2004) obtained from the Centers 

for Disease Control and Prevention’s National Center for 

Health Statistics, Division of Vital Statistics, available via 

CDC WONDER (CDC, 2007), at http://wonder.cdc.gov. 

References

CDC (Centers for Disease Control and Prevention). 2007. 

CDC Wide-ranging OnLine Data for Epidemiologic 

Research (WONDER). Natality public-use data. Accessed 

October 2007. <http://wonder.cdc.gov/natality.html>

CDC. 1994. Increasing incidence of low birthweight—

United States, 1981-1991. MMWR 43:335-339. <http://

www.cdc.gov/mmwr/preview/mmwrhtml/00030918.htm>

Kiely, J.S., K.M. Brett, S. Yu, and D.L. Rowley. 1994. Low 

birthweight and intrauterine growth retardation. In: Wilcox, 

L.S., and J.S. Marks, eds. From data to action: CDC’s public 

health surveillance for women, infants, and children. CDC’s 

maternal and child health monograph 1994. Atlanta, GA: 

Centers for Disease Control and Prevention. 

Sram R.J., B. Binkova, J. Dejmek, and M. Bobak. 2005. 

Ambient air pollution and pregnancy outcomes: A review 

of the literature. Environ. Health Perspect. 113(4):375-382.v
HUMAN EXPOSURE AND HEALTH

5-68 EPA’s 2008 Report on the Environment

5.4.3 Discussion

What These Indicators Say About Trends in 

Human Disease and Conditions for Which 

Environmental Contaminants May Be a 

Risk Factor

The indicators selected to answer this question represent 

diseases and conditions that affect multiple systems of the 

human body and are associated with a number of risk factors, some of which include exposures to contaminants that 

may be found in the air, water, and land. Some indicators 

represent chronic conditions (e.g., various cancers, heart and 

lung disease), some are primarily acute in nature (e.g., infectious diseases), and others represent conditions of the developing fetus and neonate. Understandably, no striking trends 

are evident across the broad categories of diseases represented 

by the indicators. However, some changes in disease rates or 

occurrence were observed for individual indicators. These 

relate largely to disease patterns observed over time and to 

differences observed across age groups, gender, and racial and 

ethnic groups.

Generally, the occurrence of many chronic diseases in adults is 

increasing with the aging of the population (Cancer indicator, 

p. 5-43; Cardiovascular Disease indicator, p. 5-48; Chronic 

Obstructive Pulmonary Disease indicator, p. 5-52). However, while overall cancer incidence rates showed a steady 

increase from the mid-1970s to the mid-1990s, rates have held 

relatively steady between 1997 and 2004. With the exception of prostate cancer in males and breast cancer in females, 

site-specific cancer rates also have remained fairly constant. 

Similarly, prevalence rates for cardiovascular disease and 

chronic obstructive pulmonary disease have shown no striking 

changes between 1997 and 2006, with the exception of an 

overall increase in the prevalence of hypertension during this 

time period. Prevalence rates for adult asthma have fluctuated 

from 1997 to 2006, with an overall increase during that time 

period (Asthma indicator, p. 5-55).

INDICATOR | Preterm Delivery (continued)

to 2004 (10.8 percent). The largest percent increase between 

1995 and 2000 has occurred among mothers in the 40 and 

over age group, with the percent of preterm births ranging 

from 12.0 (1995) to 13.5 percent (2004). The next largest 

percent increase was observed in the 20-39 year old maternal group, ranging from 9.2 percent (1996) to 10.3 percent 

(2004), with little overall change over time among those 

under 20 years of age (Exhibit 5-39, panel A).

In 1995, the percent of preterm births was almost twice 

as high among black mothers as among white mothers (16.4 

versus 8.5 percent) (Exhibit 5-39, panel B). From 1995 to 

2004, preterm delivery among black mothers decreased 

slightly: from 16.4 percent in 1995 to 15.9 percent in 2001, 

where the percentage has remained the same through 2004. 

During the same time, preterm delivery among white 

mothers increased slightly, rising from 8.5 percent in 1995 

to 9.9 percent in 2004, resulting in a slight narrowing of 

the difference in the preterm birth rate between black and 

white mothers. Preterm delivery for Hispanic mothers 

ranged from 10.1 (1995) to 10.9 percent (2004), compared 

to 9.7 (1996) and 10.7 (2004) percent for non-Hispanic 

mothers between 1995 and 2004. (Data not shown.)

Indicator Limitations

•	The primary measure used to determine the gestational 

age of the newborn is the interval between the first day 

of the mother’s last normal menstrual period (LMP) and 

the date of birth. This measurement is subject to error 

for reasons such as imperfect maternal recall or misidentification of the LMP because of postconception bleeding, delayed ovulation, or intervening early miscarriage. 

When the LMP and date of birth are clearly inconsistent 

with the infant’s birthweight or plurality, then a “clinical 

estimate of gestation” is used. Problems with reporting 

gestational age persist and may occur more frequently 

among some subpopulations and among births with 

shorter gestations (NCHS, 2006).

Data Source

The data used for this indicator were public-use natality 

data (1995-2002 and 2003-2004) obtained from the Centers 

for Disease Control and Prevention’s National Center for 

Health Statistics, Division of Vital Statistics, available via 

CDC WONDER (CDC, 2007), at http://wonder.cdc.gov. 

References

CDC (Centers for Disease Control and Prevention). 2007. 

CDC Wide-ranging OnLine Data for Epidemiologic 

Research (WONDER). Natality data query. Accessed 

October 2007. <http://wonder.cdc.gov/natality.html>

Goldenberg, R.L. and D.J. Rouse. 1998. Prevention of 

premature birth. New Engl. J. Med. 339:313-320.

NCHS (National Center for Health Statistics). 2006. 

Births: Final data for 2004. National Vital Statistics 

Reports 55(1). <http://www.cdc.gov/nchs/data/nvsr/

nvsr55/nvsr55_01.pdf> 

NCHS. 2004. Infant mortality statistics from the 2002 

period linked birth/infant death data set. National Vital 

Statistics Reports 53(10).

v
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-69

No distinct upward or downward patterns were revealed 

between 1995 and 2005 for most of the acute infectious gastrointestinal diseases presented in this report. An exception 

is the decrease in hepatitis A cases, which has been attributed 

to childhood vaccination for this disease.57 Other observable shifts in acute infectious diseases, such as an increase of 

cryptosporidiosis in 2005, are difficult to interpret because 

of acknowledged uncertainties in the completeness of disease reporting in a given year.58 Generally increased reported 

occurrence of arthropod-borne diseases and legionellosis bears 

watching (Infectious Diseases indicator, p. 5-59).

Review of diseases in children and birth outcomes revealed 

the following overall trends. Childhood cancer incidence has 

increased slightly since 1975, with boys having a higher incidence rate than girls. Leukemia and brain and other nervous 

system cancers remain the leading cancer sites in children 

(Childhood Cancer indicator, p. 5-46). Prevalence rates for 

childhood asthma remain at historically high levels following 

increases from 1980 through the late 1990s (Asthma indicator, p. 5-55).59 A wide range of birth defects continues to be 

reported each year, but with no notable shifts in prevalence 

observed for specific types of defects from 1999 to 2004. Heart 

malformations and other circulatory/respiratory anomalies 

and musculoskeletal/integumental anomalies remain the most 

prevalent types of birth defects based on birth certificate data 

(Birth Defects indicator, p. 5-62). Among full-term singleton births, the percentage of low birthweight infants has not 

varied from 1995 to 2004. Age of mother showed the greatest 

influence, with the greatest number of low birthweight infants 

born to younger mothers (less than 20 years old) (Low Birthweight indicator, p. 5-65). The highest rate of preterm births 

is also seen in these younger mothers, though nearly comparable and rising preterm birth rates are seen among mothers over 

the age of 40 (Preterm Delivery indicator, p. 5-67).

Some differences were observed across racial and ethnic 

groups. Observations are reported for the most recently available annual data set. Overall, cancer incidence is higher among 

black males than for any other racial group. Less disparity was 

observed between cancer incidence in white and black women. 

With childhood cancers, higher rates have been consistently 

reported in whites than in blacks (Cancer indicator, p. 5-43, 

Childhood Cancer indicator, p. 5-46). For cardiovascular disease (p. 5-48), prevalence rates were generally reported highest 

among whites and American Indians/Alaska Natives, followed 

by blacks or African Americans and Asians. Asthma rates were 

generally reported highest among blacks or African Americans 

in children and American Indians/Alaska Natives in adults, followed by whites and Asians (Asthma indicator, p. 5-55).

The percentage of preterm and low birthweight infants is consistently higher among blacks than whites (1.5 to nearly 3 times 

higher). This observation is seen across all maternal age groups 

(Preterm Delivery indicator, p. 5-67; Low Birthweight indicator, p. 5-65). When available, reported disease rates were generally lower (Asthma indicator, p. 5-55; Cardiovascular Disease 

indicator, p. 5-48; Chronic Obstructive Pulmonary Disease 

indicator, p. 5-52) or comparable (Preterm Delivery indicator, 

p. 5-67; Low Birthweight indicator, p. 5-65) in Hispanic versus 

non-Hispanic populations.

Limitations, Gaps, and Challenges

In answering this question, EPA reviewed general trends in 

morbidity and mortality of several diseases that may be related, 

at least in part, to contaminants in the environment to which 

people may be exposed. The indicators presented in this section 

provide an overall picture of specific disease rates or occurrence 

across the nation, including among some population subgroups. 

ROE indicator data sets, however, do not enable extensive 

analysis of disease trends within or across geographic regions, 

nor do they allow fully consistent reporting of trends across 

racial and ethnic groups. In addition, there are other diseases or 

conditions of potential interest for which no national scale data 

are currently available, or for which the strength of associations 

with environmental contaminants are still being evaluated. Specific limitations, data gaps, and challenges related to answering 

the question on trends in disease are highlighted below.

Geographic Patterns

Mortality data sets enable some analysis at the EPA regional level, 

but underlying data for most ROE indicators selected to answer 

this question do not currently enable meaningful analysis of geographic trends across the nation. The regional analyses presented 

in this report for cardiovascular disease and chronic obstructive 

pulmonary disease mortality reveal no discernable patterns. 

Other Diseases and Conditions for Which Environmental 

Contaminants May Be Risk Factors

Additional data are needed to prompt or enable EPA to track 

other diseases and conditions with potential environmental 

risk factors (direct or indirect), particularly those for which 

unexplained increases are being noted. Examples of diseases or 

conditions with suggestive or growing evidence that environmental contaminants are a risk factor follow. The extent 

to which national-level indicators meeting ROE criteria are 

available to track these diseases and conditions varies.

Behavioral and neurodevelopmental disorders in children 

continue to receive attention. These include disabilities of the 

functioning brain that affect a child’s behavior, motor skills, 

memory, or ability to learn. Examples include attention-deficit/

hyperactivity disorder (ADHD), dyslexia and other learning 

disabilities, cerebral palsy, mental retardation, and autism. 

Considerable evidence exists that lead and methylmercury 

are associated with mental retardation and impairment of 

mental function and attention.60 While the role of other 

57 Centers for Disease Control and Prevention. 2007. Summary of notifiable 

diseases—United States, 2005. MMWR 54(53):9. <http://www.cdc.gov/

mmwr/PDF/wk/mm5453.pdf>

58 Ibid.

59 Akinbami, L.J. 2006. The state of childhood asthma, United States, 1980-2005. 

Advance data from vital and health statistics. Number 381. Hyattsville, MD: 

National Center for Health Statistics. <http://www.cdc.gov/nchs/data/ad/

ad381.pdf> 

60 Mendola, P., S.G. Selevan, S. Gutter, and D. Rice. 2002. Environmental factors 

associated with a spectrum of neurodevelopmental deficits. Ment. Retard. 

Dev. Disabil. Res. Rev. 8(3):188-197.
HUMAN EXPOSURE AND HEALTH

5-70 EPA’s 2008 Report on the Environment

environmental contaminants in contributing to some of these 

disorders is not fully known or understood (e.g., for ADHD), 

the weight of evidence suggesting relationships between 

behavioral and neurodevelopmental effects from exposure 

to polychlorinated biphenyls (PCBs), environmental tobacco 

smoke, and other contaminants continues to grow.61,62 The 

National Health Interview Survey (NHIS) tracks ADHD and 

mental retardation, though the accurate reporting of these 

types of disorders is complicated by difficulties in diagnoses 

and possible underreporting (e.g., institutionalized children 

are excluded from the NHIS survey population).

As the U.S. population continues to age, more individuals are 

afflicted with neurodegenerative disorders such as Parkinson’s 

disease and Alzheimer’s disease. For example, Alzheimer’s 

disease is the seventh leading cause of death in the nation 

(General Mortality indicator, p. 5-33). Such diseases are 

characterized by the progressive loss of neural cells, which 

lead to central nervous system dysfunction (e.g., memory loss, 

cognitive deficits, personality changes, motor control abnormalities). The etiology of these disorders is multifactorial, but 

in many cases the etiology is unknown. Ongoing research 

is exploring the role, if any, of environmental contaminant 

exposure (e.g., heavy metals, pesticides). Thus far, findings are 

largely inconclusive due to conflicting results.63

Diabetes was reported as the sixth leading cause of death in 

the U.S. in 2004 (General Mortality indicator, p. 5-33). Two 

types of diabetes exist. Diabetes mellitus (type 2), the most 

common form, is characterized by the body’s resistance to 

insulin action and a relative deficiency of insulin. Known risk 

factors for diabetes mellitus include factors such as age, obesity, family history, physical inactivity, and dietary glycemic 

load. Type 1 diabetes results from decreased insulin production by the pancreas as part of an autoimmune response. Onset 

typically occurs before adulthood and believed to be triggered 

by genetic predisposition and possible environmental factors. 

Diabetes itself is a risk factor for the development of many 

other acute and chronic conditions. Epidemiological research 

has been conducted to evaluate possible associations between 

environmental contaminant exposure and diabetes; however, 

findings are inconclusive. Occupational and environmental 

exposures to contaminants such as arsenic, PCBs, dioxins, 

and nitrates have been examined.64,65 Other endocrine and 

metabolic disorders, such as thyroid disorders, continue to be 

studied. Research continues to evaluate the extent to which 

various environmental contaminants are capable of disrupting 

endocrine function in humans (e.g., phthalates, persistent 

organic pollutants). 

Reproductive function is another condition of interest to EPA. 

Scientists are studying whether environmental contaminants 

may cause alterations in reproductive function and contribute 

to conditions such as ovarian failure, decreased sperm counts, 

infertility, sub-fecundity, and possibly early onset of puberty. 

For example, components of cigarette smoke and other 

environmental contaminants have been studied in association 

with possible effects on female reproductive function.66 Other 

contaminants under study include pesticides, dioxins, various 

metals, and solvents. 

Renal disease is of interest because of the vital function of 

the kidneys in maintaining human health and the range of 

complex factors that lead to kidney dysfunction and disease. 

The kidneys can be seriously affected by a number of primary 

diseases such as hypertension and diabetes. Nephritis and 

nephritic syndrome were reported as the ninth leading cause 

of death in 2004 (General Mortality indicator, p. 5-33). EPA 

is interested because the kidney is known to be the target of 

some environmental contaminants. For example, as evidenced through occupational exposure, poisoning, and other 

experimental studies, exposure to heavy metals such as lead, 

cadmium, and mercury has been shown to be nephrotoxic.67,68

The U.S. Renal Data System is a national data system that 

collects, analyzes, and distributes morbidity and mortality 

information about end-stage renal disease in the U.S. 

Infectious diseases represent a continuing threat in the U.S. 

and worldwide. CDC continues to monitor infectious diseases 

and implement preventive strategies for infectious diseases 

whose incidence has increased within the past two decades or 

threatens to increase in the near future.69 Infectious diseases 

of EPA interest may shift over time, making tracking of these 

diseases more of a challenge. An area of research interest for 

arthropod-borne diseases, and a potential issue for zoonotic 

diseases, is whether their incidence may change with changes 

in environmental condition such as land use, local weather 

conditions, or other environmental disturbances.

Other Data Collection Systems

To better answer the question, expanded national-level health 

data collection systems are needed, as well as integration of 

systems that collect health data. For example, the birth certificate data currently used to track birth defects on a national 

level have limitations (see Birth Defects indicator, p. 5-62). 

61 Schantz, S.L., J.J. Widholm, and D.C. Rice. 2003. Effects of PCB exposure on 

neuropsychological function in children. Review. Environ. Health Perspect. 

111(3):357-376.

62 State of California. 2005. Proposed identification of environmental tobacco 

smoke as a toxic air contaminant. Part B: Health effects assessment for 

environmental tobacco smoke. As approved by the Scientific Review Panel 

on June 24, 2005. California Environmental Protection Agency, Office of 

Environmental Health Hazard Assessment. <http://www.arb.ca.gov/regact/

ets2006/ets2006.htm>

63 Brown, R.C., A.H. Lockwood, and B.R. Sonawane. 2005. Neurodegenerative disorders: An overview of environmental risk factors. Environ. Health 

Perspect. 113(9):1250-1256.

64 Longnecker, M.P., and J.L. Daniels. 2001. Environmental contaminants as 

etiologic factors for diabetes. Environ. Health Perspect. 109(Suppl 6):871-876.

65 Remillard, R.B., and N.J. Bunce. 2002. Linking dioxins to diabetes: Epidemiology and biologic plausibility. Review. Environ. Health Perspect. 

110(9):853-858.

66 Mlynarcikova, A., M. Fickova, and S. Scsukova. 2005. Ovarian intrafollicular 

processes as a target for cigarette smoke components and selected environmental reproductive disruptors. Review. Endocr. Regul. 39(1):21-32.

67 Klaassen, C.D., ed. 2001. Casarett and Doull’s toxicology: The basic science of 

poisons. Sixth edition. New York, NY: McGraw-Hill.

68 Jarup, L. 2003. Hazards of heavy metal contamination. Review. Br. Med. Bull. 

68:167-182.

69 Centers for Disease Control and Prevention. 1998. Preventing emerging diseases. A strategy for the 21st century. Atlanta, GA: U.S. Department of Health 

and Human Services.
HUMAN EXPOSURE AND HEALTH

EPA’s 2008 Report on the Environment 5-71

CDC recognizes the need for continuing efforts to improve 

birth defects surveillance, and recently released improved 

national prevalence estimates for major birth defects looking at 

data reported through the National Birth Defects Prevention 

Network.70 Also, as noted above, systems do not exist at the 

state or national level to track many of the diseases or conditions that may be related to environmental hazards. Existing 

environmental hazard, exposure, and disease tracking systems 

are not linked together. 

Some efforts are underway to begin tracking exposure and 

health outcomes together. For example, CDC’s “environmental public health tracking network” involves the collection 

and integration of data from environmental hazard monitoring and from human exposure and health outcome surveillance; CDC’s goal is to build a national tracking network 

(http://www.cdc.gov/nceh/tracking/). In addition, CDC has 

initiated the “environmental public health indicator project,” 

which identifies indicators of environmental hazards and 

health effects that state health departments can use to develop 

comprehensive environmental public health programs 

(http://www.cdc.gov/nceh/indicators/default.htm). Such 

programs will help bridge some existing gaps in knowledge between disease trends and environmental condition. 

These efforts also will enhance data collection efforts at the 

community level (state and local) and help ensure better temporal and spatial congruence between environmental, surveillance, and biomonitoring programs.

Lastly, data collection systems that collect data at different 

scales are available that may support future trend analysis. 

For example, CDC and the National Cancer Institute (NCI) 

have been combining forces to build a database of U.S. cancer 

statistics with data from CDC’s National Program of Cancer 

Registries and NCI’s Surveillance, Epidemiology, and End 

Results Program (http://apps.nccd.cdc.gov/uscs/). Cancer 

incidence data are available for 47 states, including six metropolitan areas, and the District of Columbia, and represent 

approximately 96 percent of the U.S. population.71 Another 

example is asthma estimate data from CDC’s state-based 

Behavioral Risk Factor Surveillance System.

70 Centers for Disease Control and Prevention. 2006. Improved national 

prevalence estimates for 18 selected major birth defects—United States, 

1999-2001. MMWR 54(51&52):1301-1305.

71 Centers for Disease Control and Prevention and National Cancer Institute. 

2006. United States cancer statistics: 2003 incidence and mortality. U.S. Cancer Statistics Working Group. <http://www.cdc.gov/cancer/npcr/npcrpdfs/

US_Cancer_Statistics_2003_Incidence_and_Mortality.pdf>

Ecological 

Condition

Chapter 6
Contents

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6.1.1 The Ecological Condition Paradigm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

6.1.2 Overview of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

6.1.3 Organization of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

6.2 What Are the Trends in the Extent and Distribution of the Nation’s Ecological Systems? . 6-7

6.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

6.2.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

6.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

6.3 What Are the Trends in the Diversity and Biological Balance 

of the Nation’s Ecological Systems? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6.3.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19

6.3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-25

6.4 What Are the Trends in the Ecological Processes That Sustain 

the Nation’s Ecological Systems? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27

6.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27

6.4.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28

6.4.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-30

6.5 What Are the Trends in the Critical Physical and Chemical Attributes 

of the Nation’s Ecological Systems? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31

6.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31

6.5.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-32

6.5.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-42

6.6 What Are the Trends in Biomarkers of Exposure to Common Environmental 

Contaminants in Plants and Animals? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45

6.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45

6.6.2 ROE Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45

6.6.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-46
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-3

6.1 Introduction

1 Daily, G.C., ed. 1997. Nature’s services: Societal dependence on natural ecosystems. Washington, DC: Island Press.

2 Norton, B. 1988. Commodity, amenity, and morality: The limits of quantification in valuing biodiversity. In: Wilson, E.O., ed. Biodiversity. Washington, DC: 

National Academies Press. p. 521.

3 U.S. EPA. 2007. About EPA. <http://www.epa.gov/epahome/aboutepa.

htm#mission>

T

he term “ecological condition” refers to the state of the 

physical, chemical, and biological characteristics of the 

environment, and the processes and interactions that connect them. Understanding ecological condition is crucial, because 

humans depend on healthy ecological systems for food, fiber, 

flood control, and other benefits,1 and many Americans attribute 

deep significance and important intangible benefits to ecological 

systems and their diverse flora and fauna.2 As noted in the introduction to this report, this chapter focuses on critical ecosystem 

characteristics that are affected simultaneously by stressors in 

multiple media, rather than those whose trends can be definitively 

shown to be the results of trends in particular air, water, or land 

stressors. The ability to report on ecological condition remains 

significantly limited by the lack of indicators, but this chapter at 

least provides a framework for examining ecological condition.

EPA’s mission, broadly stated, is “to protect human health and 

to safeguard the natural environment—air, water, and land—

upon which life depends.”3

 The translation of the mission into 

programs, initiatives, and research efforts continues to evolve 

within the Agency and is reflected in program goals, regulatory 

programs, and collaborative and educational efforts. EPA, other 

federal agencies, and state agencies collectively bear responsibility for ensuring the protection of ecological systems, including 

forests, public lands, oceans and estuaries, and particular species 

or groups of species. Trends in ecological condition provide 

insight into the degree to which the natural environment is 

being protected. 

In this chapter, EPA seeks to assess trends in critical attributes 

of ecological condition on a national scale, using indicators to 

address five fundamental questions:

•	 What are the trends in the extent and distribution of 

the nation’s ecological systems? This question examines trends in the overall extent (e.g., area and location) of 

different kinds of ecological systems (e.g. forests, undeveloped lands, and watersheds) and of spatial patterns in the 

distribution of ecological systems that affect interactions of 

nutrients, energy, and organisms. 

•	 What are the trends in the diversity and biological 

balance of the nation’s ecological systems? This question explores trends in the types and numbers of species that 

live within ecological systems. The question also examines 

biological balance in terms of the proportional distributions 

of species and the influence of interactions among native 

and invasive species on the stability of ecological systems. 

•	 What are the trends in the ecological processes that 

sustain the nation’s ecological systems? This question 

ROE Approach

This 2008 Report on the Environment:

•	 Asks questions that EPA considers 

important to its mission to protect 

human health and the environment. 

•	 Answers these questions, to the extent 

possible, with available indicators.

•	 Discusses critical indicator gaps, limitations, and challenges that prevent the 

questions from being fully answered.

ROE Questions

The air, water, and land chapters (Chapters 

2, 3, and 4) ask questions about trends in 

the condition and/or extent of the environmental medium; trends in stressors to 

the medium; and resulting trends in the 

effects of the contaminants in that medium 

on human exposure, human health, and 

the condition of ecological systems. 

The human exposure and health and 

ecological condition chapters (Chapters 

5 and 6) ask questions about trends in 

aspects of health and the environment 

that are influenced by many stressors 

acting through multiple media and by 

factors outside EPA’s mission. 

ROE Indicators

An indicator is derived from actual measurements of a pressure, state or ambient 

condition, exposure, or human health or 

ecological condition over a specified geographic domain. This excludes indicators 

such as administrative, socioeconomic, and 

efficiency indicators.

Indicators based on one-time studies are 

included only if they were designed to serve 

as baselines for future trend monitoring. 

All ROE indicators passed an independent 

peer review against six criteria to ensure 

that they are useful; objective; transparent; 

and based on data that are high-quality, 

comparable, and representative across space 

and time. 

Most ROE indicators are reported at the 

national level. Some national indicators 

also report trends by region. EPA Regions 

were used, where possible, for consistency 

and because they play an important role in 

how EPA implements its environmental 

protection efforts.

Several other ROE indicators describe 

trends in particular regions as examples of 

how regional indicators might be included 

in future versions of the ROE. They are 

not intended to be representative of trends 

in other regions or the entire nation.

EPA will periodically update and revise 

the ROE indicators and add new indicators 

as supporting data become available. In the 

future, indicators will include information 

about the statistical confidence of status 

and trends. Updates will be posted electronically at http://www.epa.gov/roe.

Additional Information

You can find additional information about 

the indicators, including the underlying 

data, metadata, references, and peer review 

at http://www.epa.gov/roe.

EPA’s 2008 Report on the Environment (ROE): Essentials
ECOLOGICAL CONDITION

6-4 EPA’s 2008 Report on the Environment

focuses on trends in the critical processes that sustain ecological systems, such as primary and secondary productivity, 

nutrient cycling, decomposition, and reproduction.

•	 What are the trends in the critical physical and 

chemical attributes of the nation’s ecological systems? This question addresses trends in the physical and 

chemical attributes of ecological systems. Physical attributes 

can include climatological patterns, hydrology, and electromagnetic radiation, as well as major physical events that 

reshape ecological systems, such as fires, floods, and windstorms. This question also examines chemical attributes such 

as pH, oxidation-reduction potential, and nutrient levels. 

•	 What are the trends in biomarkers of exposure to 

common environmental contaminants in plants and 

animals? This question examines trends in biomarkers of 

exposure to contaminants that are particularly important to 

the health of plants and animals as well as to humans who 

consume such organisms.

These ROE questions are posed without regard to whether 

indicators are available to answer them. This chapter presents 

the indicators available to answer these questions, and also 

points out important gaps where nationally representative data 

are lacking.

While the indicators of ecological condition (and those in the 

previous chapter, “Human Exposure and Health”) may be 

directly influenced by pollutants, other environmental stressors, and complex interactions among these factors, the indicators are not intended to confirm direct causal relationships. 

6.1.1 The Ecological 

Condition Paradigm

Because ecological systems are dynamic assemblages of organisms that have more or less continuously adapted to a variety 

of natural stressors over shorter (e.g., fire, windstorms) and 

longer (e.g., climate variations) periods of time, measuring 

ecological condition is a complicated endeavor. It is not as 

straightforward as monitoring water or air for temperature or 

concentrations of pollutants. The complexity of interactions 

within ecological systems makes determination of the condition of a natural system difficult.4

 In addition, people have 

altered natural ecological systems to increase the productivity 

of food, timber, fish, and game and to provide the infrastructure needed to support a modern society. How should the 

ecological condition of these altered ecological systems be 

measured and against what reference points? 

Ecological systems are not necessarily naturally occurring 

entities with well-defined, mutually exclusive boundaries; 

rather, they are constructs with boundaries determined for 

human scientific or management purposes. Consequently 

there are many ways to define ecological systems, including 

by the predominant biota, spatial scales, and physical characteristics. These factors further complicate the definition and 

measurement of ecological condition. Several recent reports 

by experts in the field have provided guidance for current and 

future efforts, however.

The National Research Council (NRC) report Ecological Indicators for the Nation5

 provides an introduction to recent national 

efforts to measure ecological condition and a thoughtful discussion of the rationale for choosing indicators. EPA’s Science 

Advisory Board (SAB) also proposed a Framework for Assessing 

and Reporting on Ecological Condition.6 The framework identified six essential attributes of ecological systems: landscape 

condition, biotic condition, chemical and physical characteristics, ecological processes, hydrology and geomorphology, 

and natural disturbance regimes. The SAB report is organized 

around questions about trends in each of these attributes, consolidating the last three into a single attribute. Neither report 

identifies specific methodologies, network designs, or actual 

datasets. The SAB and NRC documents provide the foundation for the questions that are addressed within this chapter.

Exhibit 6-1 is a conceptual depiction of the events that link 

environmental changes and ecological outcomes in this paradigm. “Stressors,” indicated by thick arrows, represent factors 

such as insect outbreaks or contaminants affecting the system. 

These stressors act directly on one or more of the “essential 

ecological attributes” shown in the circles in the center of the 

diagram. Most of these attributes can, in turn, act on and be 

acted on by others. The web of arrows among the indicators 

Exhibit 6-1. Ecological condition paradigm

Extent and

distribution

Diversity

and

biological

balance

Stressors (shown as ) affect ecological attributes directly and 

also indirectly through feedback (interaction) among the 

attributes (e.g., ).

Physical/

chemical

attributes

Ecological

processes

Exposure to

contaminants

Stressors

Stressors

Stressors

Stressors

Stressors

4 Ehrenfeld, D.H. 1992. Ecosystem health and ecological theories. In: Costanza, 

R., B.G. Norton, and B.D. Haskell, eds. Ecosystem health: New goals for 

environmental management. Washington, DC: Island Press. pp. 135-143.

5 National Research Council. 2000. Ecological indicators for the nation. Washington, DC: National Academies Press. <http://www.nap.edu/openbook.

php?isbn=0309068452>

6 U.S. Environmental Protection Agency. 2002. A framework for assessing and 

reporting on ecological condition: An SAB report. EPA/SAB/EPEC-02/009. 

<http://www.epa.gov/sab/pdf/epec02009a.pdf>
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-5

illustrates some of the possible interactions. Effects on ecological attributes can be direct or indirect. The diagram illustrates 

the fact that changes in ecological structure and processes 

provide important feedback on the chemical and physical 

structure of the environment in which these changes occur. 

The overall changes in the attributes result in altered structure 

and function of ecological systems, which in turn lead to outcomes (positive or negative) about which society is concerned.

There have been other notable efforts conducted by EPA and 

other federal agencies and institutions to describe the ecological condition of the nation, either in total or by type of 

ecological systems. These efforts include both indicator-based 

and integrative approaches. The indicator-based approaches, 

such as this report, use indicators to assess ecological condition. The integrated assessments do not rely on indicators; 

rather, they comprehensively assess a wide range of data in 

order to arrive at an overall picture of the status and trends in 

ecological systems. Indicator approaches offer the advantage of 

drawing attention to important trends and do not require an 

extensive background in ecology, but are not able to capture 

the complex interactions that characterize ecological systems. 

6.1.2 Overview of the Data

This chapter, like the others in this report, is not intended to 

be an exhaustive treatment of the condition of all ecological systems in the nation. Rather, it provides a snapshot of 

status or trends using the few ecological condition indicators 

that are available at the national level and that meet the ROE 

indicator criteria. Because ecological condition depends critically on the physical and chemical characteristics of land, air, 

and water, this chapter draws on indicators from Chapters 2 

through 4 of this report. Those chapters should be consulted 

for the data sources of those indicators. Many of the indicators 

continue to be drawn from The H. John Heinz III Center for 

Science, Economics, and the Environment report The State of 

the Nation’s Ecosystems: Measuring the Lands, Waters, and Living 

Resources of the United States.

Most of the data relied upon come from surveillance and 

monitoring surveys. The key data sources for this chapter 

reflect the fact that monitoring ecological condition is a multiorganizational task. Organizations in addition to EPA that are 

responsible for collecting the data to support indicators in this 

chapter include the U.S. Department of Commerce (National 

Oceanic and Atmospheric Administration), National Aeronautics and Space Administration, U.S. Department of Agriculture (Forest Service, Agricultural Research Service, National 

Agricultural Statistics Service, and Natural Resource Conservation Service), U.S. Department of Interior (U.S. Geological 

Survey and U.S. Fish and Wildlife Service), and NatureServe 

(a private research organization).

Programs such as the U.S. Department of Agriculture Forest 

Inventory and Analysis program and the Natural Resources 

Inventory have a long history because they measure aspects 

of the environment that are critical to multi-billion-dollar 

industries (e.g., timber, crops). Programs with a strictly “ecological” focus (e.g., the U.S. Geological Survey’s National Water 

Quality Assessment Program [NAWQA], the multi-agency 

Multi-Resolution Land Characteristics [MRLC] Consortium, 

and EPA’s Environmental Monitoring and Assessment Program 

[EMAP]) are more recent, but equally informative.

The major challenges involve adequate coverage of the diverse 

aspects of ecological condition. For example, there are numerous groups of animals and plants, but there are ROE indicators 

for only some of these. Major groups known to be undergoing 

changes, such as amphibians, are not captured by the ROE 

indicators. These challenges and limitations are described in 

each of the subsections.

This chapter presents only data that meet the ROE indicator 

definition and criteria (see Box 1-1, p. 1-3). Note that nonscientific indicators, such as administrative and economic 

indicators, are not included in this definition. Thorough documentation of the indicator data sources and metadata can be 

found online at http://www.epa.gov/roe. All indicators were 

peer-reviewed during an independent peer review process 

(again, see http://www.epa.gov/roe for more information). 

Readers should not infer that the indicators included reflect 

the complete state of knowledge on current indicators of U.S. 

ecological condition. Many other data sources, publications, 

and site-specific research projects have contributed to the current understanding of status and trends in indicators of U.S. 

ecological condition, but are not used in this report because 

they do not meet some aspect of the ROE indicator criteria.

6.1.3 Organization of 

This Chapter

The remainder of this chapter is organized into five sections, 

corresponding to the five questions EPA is seeking to answer 

regarding trends in ecological condition. Each section introduces the question and its importance, presents the National 

Indicators selected to help answer the question, and discusses 

what the indicators, taken together, say about the question. 

Some of the National Indicators presented are broken down 

by EPA Regions or other appropriate regions. In addition, 

several Regional Indicators are presented that capture regional 

trends of particular interest to EPA Regions. These Regional 

Indicators serve as models that could potentially be expanded 

to other EPA Regions in the future. A map showing the EPA 

Regions (and states within each Region) is provided in Chapter 1 (Exhibit 1-1). Each section concludes by highlighting the 

major challenges to answering the question and identifying 

important information gaps. 

Table 6-1 lists the indicators used to answer the five questions 

in this chapter and shows the locations where the indicators 

are presented.
ECOLOGICAL CONDITION

6-6 EPA’s 2008 Report on the Environment

N = National Indicator

R = Regional Indicator

N/R = National Indicator displayed at EPA Regional scale

Table 6-1. Ecological Condition—ROE Questions and Indicators

Question Indicator Name Section Page

What are the trends in the extent and 

distribution of the nation’s ecological 

systems? 

Land Cover (N/R)

Forest Extent and Type (N/R)

Forest Fragmentation (N/R)

Wetland Extent, Change, and Sources of Change (N)

Land Use (N)

Urbanization and Population Change (N)

Land Cover in the Puget Sound/Georgia Basin (R) 

Ecological Connectivity in EPA Region 4 (R)

Relative Ecological Condition of Undeveloped Land in EPA 

Region 5 (R)

4.2.2 4-7

6.2.2 6-8

6.2.2 6-11

3.4.2 3-32

4.3.2 4-14

4.3.2 4-19

4.2.2 4-10

6.2.2 6-13

6.2.2 6-14

What are the trends in the diversity 

and biological balance of the nation’s 

ecological systems? 

Coastal Benthic Communities (N/R) 

Benthic Macroinvertebrates in Wadeable Streams (N)

Bird Populations (N)

Fish Faunal Intactness (N)

Submerged Aquatic Vegetation in the Chesapeake Bay (R)

Non-Indigenous Benthic Species in the Estuaries of the 

Pacific Northwest (R)

3.5.2 3-44

3.2.2 3-21

6.3.2 6-20

6.3.2 6-21

3.5.2 3-46

6.3.2 6-23

What are the trends in the ecological 

processes that sustain the nation’s 

ecological systems? 

Carbon Storage in Forests (N) 6.4.2 6-28

What are the trends in the critical 

physical and chemical attributes of 

the nation’s ecological systems? 

U.S. and Global Mean Temperature and Precipitation (N)

Sea Surface Temperature (N)

Streambed Stability in Wadeable Streams (N)

High and Low Stream Flows (N)

Sea Level (N)

Nitrogen and Phosphorus Loads in Large Rivers (N)

Nitrogen and Phosphorus in Wadeable Streams (N)

Nitrogen and Phosphorus in Streams in Agricultural 

Watersheds (N)

Lake and Stream Acidity (N) 

Hypoxia in the Gulf of Mexico and Long Island Sound (R)

6.5.2 6-32

6.5.2 6-37

3.2.2 3-11

3.2.2 3-8

6.5.2 6-39

3.2.2 3-17

3.2.2 3-13

3.2.2 3-15

2.2.2 2-42

3.5.2 3-48

What are the trends in biomarkers of 

exposure to common environmental 

contaminants in plants and animals?

Coastal Fish Tissue Contaminants (N/R)

Contaminants in Lake Fish Tissue (N)

Ozone Injury to Forest Plants (N)

3.8.2 3-61

3.8.2 3-63

2.2.2 2-24
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-7

6.2What Are the 

Trends in the Extent 

and Distribution of the 

Nation’s Ecological 

Systems?

6.2.1 Introduction

Ecological systems,7 ranging from forests and watersheds to 

wetlands and coral reefs, are the foundation of the environment. 

An ecological system can be defined as a spatially explicit unit 

of the Earth that includes all of the organisms, along with all 

components of the abiotic environment, within its boundaries. 

Ecological systems are not isolated but blend into and interact 

with other systems. The spatial coverage and arrangement of 

ecological systems influence the types of animals and plants 

that are present; the physical, chemical, and biological processes 

in the system; and the resiliency of the systems to perturbations.8

 Ecological systems influence water and nutrient cycles, 

the building of soils, the production of oxygen, sequestration of 

carbon, and many other functions important for the health of 

the planet and people who depend on them.

This section examines trends in the extent and distribution 

of ecological systems. Extent refers to the physical coverage 

of an ecological system; it can be reflected as area or percent 

compared to a baseline or total area. Distribution includes the 

pattern or arrangement of the components of an ecological 

system and is dependent on the scale of analysis. For example, 

the national distribution of forests can be estimated by a percent coverage, but within a stand of trees the distribution may 

involve patterns of gaps, species, and edge/interior ratios. As 

noted in Section 6.1.1, ecological systems can be defined by 

predominant biota, spatial scales, and physical characteristics. 

Extent indicators typically are based on physical and biological characteristics that are observable by remote sensing, with 

indistinct boundaries operationally defined according to some 

scientific or resource management construct.9

As noted in Chapter 1, safeguarding the natural environment 

is an integral part of EPA’s mission. EPA traditionally has been 

most concerned with maintaining the quality of air, water, and 

land necessary to support balanced biological communities and 

the processes that support them; however, the success of these 

efforts requires that ecological systems not be altogether lost or 

fragmented. The potential influences of pollutants on the extent 

and distribution of ecological systems are a prime concern, and, 

in turn, the extent and distribution of ecological systems have 

far-reaching influences on air and water quality. 

Apparent trends in extent and distribution of ecological systems 

depend on the temporal and spatial scale of assessment. For this 

reason, both National and Regional Indicators are particularly 

valuable. Temporal changes occur naturally over long time scales, 

such as those associated with geological and climatological 

forces (e.g., glaciation). Change can also occur more quickly as 

a result of direct shifts in land use (e.g., forest to development 

and historical filling of wetlands), alterations of nutrient and 

hydrological cycles (e.g., dam removal), introduction of invasive 

species (e.g., Asian carp), pollutant exposure (e.g., acid rain), or 

extreme weather events, which all act over comparatively short 

time periods. Thus, trends can be the result of natural forces or 

may be accelerated by human activity.

The spatial scale of alterations also represents a significant factor in tracking ecological condition. Alterations that are short 

in duration and local in nature (e.g., seasonal droughts or a 

windfall in a closed forest canopy) may not have large-scale 

or lasting effects on ecological systems. Alterations that are 

chronic in nature and occur over large areas may affect entire 

ecosystems over long periods of time, especially if they affect 

soil formation, microclimate, refugia for recolonizing species, 

etc. Particularly relevant discussions of the importance of scale 

in ecological processes, monitoring, and management can be 

found in a number of relatively recent publications.10,11,12

Different regions and different ecological systems respond to 

stressors in different ways, resulting in unique regional distributions of species and habitats. The result is that across any slice of 

landscape the extent and distribution of ecological systems may 

shift.13 In the case of habitat loss, large impacts may occur and 

the extent of coverage may be reduced or eliminated altogether. 

More subtle changes in ecological systems can occur that are 

not captured in simple metrics of extent and distribution. These 

changes are discussed in later sections of this chapter.

Fragmentation, the division of previously uninterrupted 

habitat, can have either negative or positive impacts on 

communities.14 Examples of fragmentation include building highways through a forest, damming a river in a manner 

that limits migration of fish, or developing waterfronts in a 

manner that splits apart bordering marshlands. Fragmentation 

and the increasing area of edge habitat may force migrating 

species to find new transport corridors, may allow new species 

(e.g., competitors, pathogens, weeds) to enter areas previously 

7 Likens, G. 1992. An ecosystem approach: Its use and abuse. Excellence in 

ecology, book 3. Oldendorf/Luhe, Germany: Ecology Institute.

8 Wilson, E.O. 1992. The diversity of life. Cambridge, MA: Belknap Press.

9 The H. John Heinz III Center for Science, Economics, and the Environment. 

2005. The state of the nation’s ecosystems: Measuring the lands, waters, and 

living resources of the United States. New York, NY: Cambridge University 

Press. Web update 2005. <http://www.heinzctr.org/ecosystems/forest/

frgmnt.shtml>

10 Peterson, D.L., and V.T. Parker. 1998. Ecological scale: Theory and applications. New York: Columbia University Press.

11 Niemi, G., and M. McDonald. 2004. Application of ecological indicators. 

Annu. Rev. Ecol. Evol. Syst. 35:89-111.

12 Findlay, C.S., and L. Zheng. 1997. Determining characteristic stressor scales 

for ecosystem monitoring and assessment. J. Environ. Manage. 50(3):265-281.

13 The H. John Heinz III Center for Science, Economics, and the Environment. 

2005. Forest pattern and fragmentation. In: The state of the nation’s ecosystems: Measuring the lands, waters, and living resources of the United States. 

New York, NY: Cambridge University Press. Web update 2005. <http://

www.heinzctr.org/ecosystems/forest/frgmnt.shtml>

14 Fahrig, L. 1997. Relative effects of habitat loss and fragmentation on population extinction. J. Wildl. Manage. 61(3):603-610. 
ECOLOGICAL CONDITION

6-8 EPA’s 2008 Report on the Environment

blocked from immigration, and in some cases may actually 

increase biodiversity.15 Regardless of the impact, fragmentation likely will result in shifting distributions of species.

Trends in ecological system extent and distribution are highly 

dependent on the evaluation scale. At one scale, coastal wetlands may appear to be uninterrupted and uniform. However, 

at a more refined scale, edges, patches, corridors associated 

with tidal creeks, and discontinuous distributions of species 

become evident. Defining systems in terms of local organization or predominant species facilitates discussion and analysis, 

but may also obscure the important linkages among systems 

across landscapes. Therefore, while it is helpful to discuss 

trends in the extent and distribution of systems such as wetlands or forests, each system is tied into global water, nutrient, 

carbon, and energy cycles.

The indicators discussed in this section fall into three broad 

categories: indicators of the extent and distribution of forests, 

indicators of the extent and distribution of wetlands, and indicators of land use.

6.2.2 ROE Indicators

In this question, trends in the extent and distribution of ecological systems are evaluated for a subset of systems including 

forests, wetlands, undeveloped lands, and developed lands. 

To answer the question on extent and distribution of ecological systems, this report relies primarily on six National 

Indicators and three Regional Indicators (Table 6-2). Data on 

trends in extent and distribution of ecological systems come 

from a variety of sources, including satellite remote sensing, 

geographic information systems, and independent field studies. Information for the indicators discussed in this section is 

drawn from several national assessments including the U.S. 

Department of Agriculture (USDA) Forest Service Forest 

Inventory and Analysis program, the U.S. Fish and Wildlife 

Service’s Wetlands Status and Trends Survey, the National 

Land Cover Dataset/Database (NLCD) for 1992 and 2001, 

and the USDA National Resources Inventory.

Table 6-2. ROE Indicators of Trends in Extent and Distribution 

of the Nation’s Ecological Systems

National Indicators Section Page

Land Cover (N/R) 4.2.2 4-7

Forest Extent and Type (N/R) 6.2.2 6-8

Forest Fragmentation (N/R) 6.2.2 6-11

Wetland Extent, Change, and Sources of Change 3.4.2 3-32

Land Use 4.3.2 4-14

Urbanization and Population Change 4.3.2 4-19

Regional Indicators Section Page

Land Cover in the Puget Sound/Georgia Basin 4.2.2 4-10

Ecological Connectivity in EPA Region 4 6.2.2 6-13

Relative Ecological Condition of Undeveloped Land in EPA Region 5 6.2.2 6-14

N/R = National Indicator displayed at EPA Regional scale

INDICATOR | Forest Extent and Type

The forests of the U.S. cover extensive lands in both the eastern and western thirds of the country. While the 

amount of forest land has remained nearly unchanged since 

the beginning of the 20th century, regional changes both in 

amount and types of forest cover have occurred as a result 

of changing patterns of agriculture and development. The 

distribution of various forest cover types is a critical determinant of the condition of forest ecosystems. 

This indicator is based on data from the U.S. Department of Agriculture (USDA) Forest Service Forest Inventory and Analysis (FIA) program. The FIA program, using 

a statistical survey design and comparable methods across 

the U.S., collects various data that help assess the extent, 

type, age, and health of the nation’s forest land. Because 

the surveys are repeated over time, the FIA data provide 

an indication of trends in both the extent and composition 

15 Fahrig, L. 2003. Effects of habitat fragmentation on biodiversity. Annu. Rev. 

Ecol. Syst. 34:487-515.
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-9

INDICATOR | Forest Extent and Type (continued)

Exhibit 6-3. Timberland area in the eastern U.S. by forest type, 1953-2002a

a

Coverage: States in the eastern U.S., based on USDA Forest Service reporting regions (see map at right). These data cover timberland, as

defined by the Forest Service’s Forest Inventory and Analysis (FIA) Program. Approximately 94% of the forest land in the eastern states 

is timberland.

Data source: Smith et al., 2001, 2004

Year

East West

Longleaf-slash pine Loblolly-shortleaf pine Oak-pine Oak-hickory

Area (million acres)

0

20

40

60

80

100

120

140

0

20

40

60

80

100

120

140 White-red-jack pine

Oak-gum-cypress

Spruce-fir

Elm-ash-cottonwood Maple-beech-birch Aspen-birch Non-stocked

’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02

’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02

’53 ’63’77 ’87’97’02

Exhibit 6-2. Changes in the extent of forest land in the U.S. by EPA Region, 1907-2002a

a

Coverage: All 50 states.

Data source: Smith et al., 2001, 2004

Reporting period

-15

-10

-5

0

5

10

15

-15

-10

-5

0

5

10

15

AB CD

A B C

D

A B C

D

A B C D

A

B C

D

A B C

D

AB CD ABCD

ABCD

A

B C

D

A

B

C

D

Region 3 Region 4 Region 5 Region 6

Change in area (million acres)

Region 1

Region 7

Region 2

Region 8 Region 9 Region 10 All U.S.

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

A 1907-1938

B 1938-1953

C 1953-1977

D 1977-2002

Reporting 

periods:
ECOLOGICAL CONDITION

6-10 EPA’s 2008 Report on the Environment

INDICATOR | Forest Extent and Type (continued)

of forest land. The extent data are collected for all forest 

lands across the nation, but species composition data over 

time are only available for timberland as defined by FIA data 

collection procedures (that is, forests capable of producing 

at least 20 cubic feet per acre per year of industrial wood 

and not withdrawn from timber utilization by statute or 

regulation). Timberland makes up 94 percent of the forest 

land area in the eastern U.S. and 39 percent of forest land 

in the western U.S. as of 2002 (Smith et al., 2004). Extent 

data are collected for individual states, but have been summarized by EPA Region for this indicator.

What the Data Show

After a slight increase in forest land nationwide between 

1907 and 1938, forest acreage decreased by more than 16 

million acres between 1938 and 1977, before increasing 

by 5.3 million acres over the past three decades (Exhibit 

6-2). There are variations in trends in forest cover among 

the different EPA Regions. For example, between 1907 

and 2002, forest land declined by roughly 22 million acres 

in Region 6 and more than 12 million acres in Region 9. 

Over the same period, forest land increased by 13 million 

acres in Region 3 and by 10 million acres in Region 5. 

In addition to changes in the extent of forest, there have 

been changes in the types of forests over time (Exhibits 6-3 

and 6-4). The largest changes in the eastern U.S. over the 

1953-2002 period occurred in the maple-beech-birch forest 

type and the oak-hickory forest type, which gained 27.5 

million acres and 23 million acres, respectively, since 1953. 

In the West, the fir-spruce type and Western hardwood 

type also have increased (about 11.5 million acres each) since 

1953, while the hemlock-Sitka spruce, pinyon-juniper, and 

ponderosa-Jeffrey pine forest types have decreased by about 

13.6 million, 8.8 million, and 8.7 million acres respectively. 

The Western white pine forest type has decreased by 5.3 

million acres, or about 96 percent of its 1953 acreage. 

Indicator Limitations

•	 Data on extent of forest land have an uncertainty of 3 

to 10 percent per million acres for data reported since 

1953. In 1998 Congress mandated that the FIA move 

to annual inventories. While data now are collected 

more often, fewer data are collected in any given year. 

Because area estimates now are based on a smaller 

sample size, the precision of the national estimates may 

be reduced relative to pre-1998 dates.

•	 Most of the specific data related to species and age 

classes are only collected on lands classified as timberland and not forest land in general. 

Exhibit 6-4. Timberland area in the western U.S. by forest type, 1953-2002a

a

Coverage: States in the western U.S. (including Alaska and Hawaii), based on USDA Forest Service reporting 

regions (see map at right). These data cover timberland, as defined by the Forest Service’s Forest Inventory 

and Analysis (FIA) Program. Approximately 39% of the forest land in the western states is timberland.

Data source: Smith et al., 2001, 2004

Year

East West

’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02

’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02 ’53 ’63’77 ’87’97’02

0

10

20

30

40

0

10

20

30

40

Douglas-fir

Area (million acres)

Ponderosa-Jeffrey

pine

Western white pine Fir-spruce Hemlock-Sitka 

spruce

Larch

Lodgepole pine Redwood Western hardwood

types

Other western

softwood types

Pinyon-juniper Non-stocked
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-11

INDICATOR | Forest Extent and Type (continued)

•	 In addition to extent and species class, age class also influences the use of forest land as habitat by different species. 

Younger and older stands of forest have increased over the 

past half-decade, while middle-aged stands of more merchantable timber have decreased (Smith et al., 2001, 2004).

Data Sources

This indicator is based on data from two USDA Forest 

Service reports (Smith et al., 2001, 2004), which provide 

current and historical data on forest extent and type by 

state. Most data were obtained from the 2004 report; the 

2001 report was consulted only for 1963 data, which were 

excluded from the more recent report. Data were originally 

collected by the USDA Forest Service’s FIA program; original survey data are available from the FIA database (USDA 

Forest Service, 2005) (http://www.fia.fs.fed.us/tools-data/). 

References

Smith, W.B., P.D. Miles, J.S. Vissage, and S.A. Pugh. 

2004. Forest resources of the United States, 2002. General 

Technical Report NC-241. St. Paul, MN: USDA Forest 

Service, North Central Research Station. 

<http://ncrs.fs.fed.us/pubs/gtr/gtr_nc241.pdf>

Smith, W.B., J.S. Vissage, D.R. Darr, and R.M. Sheffield. 

2001. Forest resources of the United States, 1997. General 

Technical Report NC-219. St. Paul, MN: USDA Forest 

Service, North Central Research Station. 

<http://www.ncrs.fs.fed.us/pubs/gtr/gtr_nc219.pdf>

USDA Forest Service. 2005. Forest Inventory and Analysis, national FIA data base systems. Accessed 2005. 

<http://www.fia.fs.fed.us/tools-data/>

INDICATOR | Forest Fragmentation

The amount of forest land in the U.S. monitored by the U.S. Department of Agriculture (USDA) Forest Service 

has remained nearly constant over the past century, but the 

patterns of human land use have affected its distribution 

from one region of the U.S. to another. Forest fragmentation involves both the extent of forest and its spatial 

pattern, and is the degree to which forested areas are being 

broken into smaller patches and pierced or interspersed 

with non-forest cover. 

Forest fragmentation is a critical aspect of the extent and 

distribution of ecological systems. Many forest species are 

adapted to either edge or interior habitats. Changes in the 

degree or patterns of fragmentation can affect habitat quality for the majority of mammal, reptile, bird, and amphibian species found in forest habitats (Fahrig, 2003). As forest 

fragmentation increases beyond the fragmentation caused 

by natural disturbances, edge effects become more dominant, interior-adapted species are more likely to disappear, 

and edge- and open-field species are likely to increase.

This indicator of forest fragmentation was developed by 

the USDA Forest Service. The indicator is based on the 

2001 National Land Cover Database (NLCD), which was 

constructed from satellite imagery showing the land area of 

the contiguous U.S. during different seasons (i.e., leaves-on 

and leaves-off) around the year 2001 (Homer et al., 2007). 

The USDA Forest Service’s Southern Research Station 

performed a re-analysis of the NLCD, aggregating the four 

NLCD forest cover classes (coniferous, deciduous, mixed, 

and wetland forest) into one forest class and the remaining 

land cover classes into a single non-forest class (USDA Forest Service, 2007). A model that classifies forest fragmentation based on the degree of forest land surrounding each 

forest pixel (a square approximately 30 meters on each 

edge) for various landscape sizes (known as “windows”) 

provides a synoptic assessment of forest fragmentation for 

the contiguous U.S. by assessing each pixel’s “forest neighborhood” within various distances. 

Results are based on four degrees of forest cover: “core” 

if a subject pixel is surrounded by a completely forested 

landscape (no fragmentation), “interior” if a subject pixel is 

surrounded by a landscape that is 90 to 100 percent forest, 

“connected” if a subject pixel is surrounded by a landscape 

that is 60 to 90 percent forest, and “patchy” if the subject 

pixel is surrounded by less than 60 percent forest. The 

window (landscape) size used for this analysis was 13 by 

13 pixels, 390 meters on each edge, or about 15.2 hectares 

(37.6 acres). The window is shifted one pixel at a time over 

the map, so the target population for the indicator is all 

forested pixels in the contiguous U.S. Percent forest was 

resampled from 30-meter pixel data and aggregated by 

state to develop the EPA Region-specific breakouts.

What the Data Show

Slightly more than 26 percent of the forested pixels in the 

U.S. represent “core” forest, i.e., landscapes dominated 

by forest (Exhibit 6-5). However, the data for “interior” 

and “core” forests suggest that fragmentation is extensive, 

with few large areas of complete, unperforated forest cover. 

About 19 percent of forest pixels in the U.S. occur in a 

landscape where less than 60 percent of the “neighborhood” is forest (i.e., forest cover is “patchy”). 

There is considerable regional variation in forest fragmentation (Exhibit 6-5). Regions 1, 2, and 3 have more than 

30 percent “core” forest pixels, while fewer than 20 percent 

of the forest pixels in Region 7 are “core” forest. From the 

opposite perspective, fewer than 10 percent of forest pixels in 

v
ECOLOGICAL CONDITION

6-12 EPA’s 2008 Report on the Environment

INDICATOR | Forest Fragmentation (continued)

Region 1 are surrounded by less than 60 percent forest, compared to almost 40 percent of the forest pixels in Region 7. 

Indicator Limitations

•	 Trend information is not available for this indicator. 

Although earlier land cover data are available as part of 

the 1992 NLCD, they are not directly comparable with 

the 2001 NLCD due to differences in classification 

methodology. Efforts to compare these two products 

are ongoing.

•	 The apparent degree of connectivity depends on the size 

of the window. In a similar analysis of 1992 NLCD data, 

Riitters (2003) determined that the percentages for all 

categories (especially “core” and “connected” forest pixels) decrease rapidly as the size of the window is increased 

progressively from 18 to 162, 1,459, and 13,132 acres.

•	 Because the non-forest land cover classes were aggregated, this indicator does not distinguish between 

natural and anthropogenic fragmentation (although such 

a distinction has been made for global fragmentation by 

Wade et al., 2003).

•	 The data do not include Hawaii or Alaska, which account 

for about 1 out of every 6 acres of forest land in the U.S. 

Data Sources

An earlier version of this analysis was published in Riitters 

(2003) and Heinz Center (2005). The analysis presented 

here has not yet been published; data were provided by the 

USDA Forest Service (2007), and EPA grouped the results 

by EPA Region. This indicator is based on land cover data 

from the 2001 NLCD (MRLC Consortium, 2007).

References

Fahrig, L. 2003. Effects of habitat fragmentation on biodiversity. Annu. Rev. Ecol. Evol. Syst. 34:487-515.

Homer, C., J. Dewitz, J. Fry, M. Coan, N. Hossain, C. 

Larson, N. Herold, A. McKerrow, J.N. VanDriel, and J. 

Wickham. 2007. Completion of the 2001 National Land 

Cover Database for the conterminous United States. 

Photogramm. Eng. Rem. S. 73(4):337-341. 

The H. John Heinz III Center for Science, Economics, and 

the Environment. 2005. Forest pattern and fragmentation. 

In: The state of the nation’s ecosystems: Measuring the 

lands, waters, and living resources of the United States. New 

York, NY: Cambridge University Press. Web update 2005. 

<http://www.heinzctr.org/ecosystems/forest/frgmnt.shtml>

MRLC Consortium. 2007. National Land Cover Database 

2001 (NLCD 2001). Accessed 2007. 

<http://www.mrlc.gov/mrlc2k_nlcd.asp>

Riitters, K.H. 2003. Report of the United States on the 

criteria and indicators for the sustainable management of 

temperate and boreal forests, criterion 1: Conservation of 

biological diversity, indicator 5: Fragmentation of forest 

types. Final report. FS-766A. In: Darr, D., ed. Data report: 

A supplement to the National Report on Sustainable Forests. 

Washington, DC: USDA Forest Service. 

<http://www.fs.fed.us/research/sustain/contents.htm>

USDA Forest Service. 2007. Data provided to EPA by Kurt 

Riitters, USDA Forest Service. September 18, 2007.

Wade, T.G., K.H. Riitters, J.D. Wickham, and K.B. Jones. 

2003. Distribution and causes of global forest fragmentation. 

Conserv. Ecol. 7(2):7. 

<http://www.consecol.org/vol7/iss2/art7/>

Core Interior Connected Patchy

Degree of forest cover:c

Percent of forested pixels in each category:

10

9

9

6

7

4

8 10

5 3

2 1

EPA Regions

2

a

Coverage: Areas of the contiguous 

48 states classified as “forested” by 

the 2001 National Land Cover 

Database (NLCD). 

b

Totals may not add to 100% due to 

rounding. 

c

See text for definitions of forest 

cover categories. 

Data source: USDA Forest Service, 2007

Exhibit 6-5. Forest fragmentation in the contiguous 

U.S. by EPA Region, based on 2001 NLCDa,b

Region 1

Region 2

Region 3

Region 4

Region 5

Region 6

Region 7

Region 8

Region 9

Region 10

All U.S.

38.0

33.5

33.3

22.1

21.4

23.0

15.6

27.8

29.7

29.4

26.1

26.7

23.5

23.6

23.1

22.8

21.0

15.4

22.8

22.5

26.0

22.9

27.8

28.7

30.3

35.9

33.8

32.3

31.0

29.2

29.4

31.9

32.1

7.5

14.3

12.8

19.0

22.0

23.7

38.0

20.2

18.4

12.8

18.9

v
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-13

INDICATOR | Ecological Connectivity in EPA Region 4

As part of their natural functioning, ecological systems remove particulate 

matter and carbon dioxide from the air, 

purify surface and ground water, reduce 

flooding, and maintain biological diversity. 

These functions depend on a connected 

ecological “framework” of high-quality 

land consisting of central hubs interconnected by corridors that provide for the 

movement of energy, matter, and species 

across the landscape. This framework of 

connectivity is threatened by agricultural 

and silvicultural practices, road development, and “urban sprawl” that fragment 

the landscape. Maintaining ecological connectivity protects the entire system.

The Ecological Connectivity Indicator 

(ECI) developed by EPA Region 4 (Durbrow et al., 2001) consists of a framework 

that captures the connectivity of important 

natural areas and ecological systems across 

the landscape of the Region (Alabama, 

Florida, Georgia, Kentucky, Mississippi, 

North Carolina, South Carolina, and Tennessee). Four ecological aspects contribute 

to the functionality of the ECI infrastructure (see Carr et al., 2002, for additional 

details). The most important of the four, 

hub and corridor connectivity, forms the 

basis for this indicator. Hub and corridor connectivity shows the connections 

among critical ecological systems in the 

Region. Hubs are large areas of important natural ecosystems such as the Okefenokee National 

Wildlife Refuge in Georgia and the Osceola National 

Forest in Florida. Connections, referred to as “corridors,” 

are links to support the functionality of the hubs (e.g., 

the Pinhook Swamp which connects the Okefenokee and 

Osceola hubs). The ECI framework is based on land cover 

data obtained from the 1992 National Land Cover Dataset 

(NLCD), which was constructed from satellite imagery 

(Landsat) showing the land area of the contiguous U.S. 

during different seasons (i.e., leaves-on and leaves-off) during the early 1990s. In many locations, the best available 

Landsat images were collected between 1991 and 1993, 

with data in a few locations ranging from 1986 to 1995.

What the Data Show

The hub and connection framework covers 43 percent of 

the total land and water resources in EPA Region 4—30 

percent classified as hubs and 13 percent as corridors 

(Exhibit 6-6). Currently, 22 percent of this framework 

area is protected as conservation land, 12 percent is in 

the public domain as open water, and an additional 14 

percent is classified as wetlands, for a total of 48 percent 

of hub and corridor acreage being afforded some type of 

long-term protection. 

Indicator Limitations

•	 Trend information is not available for this indicator. The 

most important data layer used in the ECI development 

is the NLCD from the early 1990s. Establishing trends 

in the indicator may be limited by the availability of 

comparable land cover/land use data in the future. 

•	 Due to both the limited availability of data (ecological data not available or not in digital or geographic 

information system [GIS] format) and the Southeastern 

Ecological Framework (SEF) parameter that sets a size 

threshold of 5,000 acres for ecological hubs, the results 

do not comprehensively include each and every ecologically important area in the Southeast. The appropriate 

geographic scale of connectivity depends on the species 

and communities that are the focus of particular protection efforts (Carr et al., 2002).

Exhibit 6-6. Ecological hubs and corridors in EPA Region 4, 

based on 1992 NLCD

Surface area of Region 4 

(land and water)

Protected status of hubs 

and corridors

Not hubs 

or corridors

57% Corridors

 13%

Hubs

30%

Unprotected

52%

Wetlands 

(outside conservation lands)

Open waters in the public domain 

(outside conservation lands) 

12%

14%

Existing 

conservation 

lands

22%

Hubs

Corridors

Data source: U.S. EPA, 2002
ECOLOGICAL CONDITION

6-14 EPA’s 2008 Report on the Environment

INDICATOR | Ecological Connectivity in EPA Region 4 (continued)

Data Sources

The hub and corridor map was provided by EPA Region 

4’s SEF project, and is available as a GIS data layer from the 

SEF Web site’s data page (U.S. EPA, 2002) (http://geoplan.

ufl.edu/epa/data.html). The summary statistics shown in the 

pie charts in Exhibit 6-6 are presented in Carr et al. (2002). 

This analysis was based on the 1992 NLCD (USGS, 2005) 

(http://landcover.usgs.gov/natllandcover.php) and several 

additional datasets described in Carr et al. (2002); input data 

layers can be obtained on CD by following instructions on 

the SEF Web site (U.S. EPA, 2002).

References

Carr, M.H., T.D. Hoctor, C. Goodison, P.D. Zwick, J. 

Green, P. Hernandez, C. McCain, J. Teisinger, and K. 

Whitney. 2002. Final report: Southeastern Ecological 

Framework. Region 4. Atlanta, GA: U.S. Environmental 

Protection Agency. 

<http://geoplan.ufl.edu/epa/download/sef_report.pdf>

Durbrow, B.R., N.B. Burns, J.R. Richardson, and C.W. 

Berish. 2001. Southeastern Ecological Framework: A planning tool for managing ecosystem integrity. In: Hatcher, 

K.J., ed. Proceedings of the 2001 Georgia Water Resources 

Conference. Athens, GA: University of Georgia.

U.S. EPA (United States Environmental Protection 

Agency). 2002. The EPA Southeastern U.S. Ecological 

Framework project. 

<http://geoplan.ufl.edu/epa/index.html>

USGS (United States Geological Survey). 2005. National 

Land Cover Dataset 1992 (NLCD 1992). Accessed 2005.

<http://landcover.usgs.gov/natllandcover.php> 

INDICATOR Relative Ecological Condition of Undeveloped Land in 

EPA Region 5

Ecological condition in the ROE is approached using questions broadly relating to landscape, biological 

diversity, ecological function, and the physical and chemical makeup of the environment, but no attempt is made 

at the national level to capture ecological condition in a 

small number of indices. In this indicator, the ecological 

condition of undeveloped land in EPA Region 5 (Illinois, 

Indiana, Michigan, Minnesota, Ohio, and Wisconsin) is 

characterized based on three indices derived from criteria 

representing diversity, self-sustainability, and the rarity of 

certain types of land cover, species, and higher taxa (White 

and Maurice, 2004). In this context, “undeveloped land” 

refers to all land use not classified as urban, industrial, residential, or agricultural. 

Geographic units referred to as cells are used to quantify 

geographic information. A spatially explicit model using 

ecological theory and geographic information system (GIS) 

technology was used to create 20 data layers of 300-meter 

by 300-meter cells. These layers originate from several 

sources, including water quality datasets, state Natural 

Heritage Program databases (for species abundance), and 

the 1992 National Land Cover Dataset (NLCD), which 

was constructed from satellite imagery (Landsat) showing the land area of the contiguous U.S. during different 

seasons (i.e., leaves-on and leaves-off) during the early 

1990s. In many locations, the best available Landsat images 

were collected between 1991 and 1993, with data in a few 

locations ranging from 1986 to 1995. For this indicator, 

data layers were combined to generate three indices, which 

represent estimates of three criteria:

•	 Ecological diversity. The relative diversities of populations (species), communities, and ecological systems 

in any given location on the landscape. Four data layers 

were used to derive this index.

•	 Ecological self-sustainability. The potential for an 

ecological system to persist for years without external 

management; it is negatively impacted by two factors: 

landscape fragmentation and the presence of chemical, physical, and biological stressors. Twelve data layers 

were used to derive this index.

•	 Rarity. The rarity of land cover, species, and higher 

taxa. Four data layers were used to derive this index.

The model produces composite layers that are statistically independent. The scores for each criterion are normalized from 1 to 100 and each layer contributes equally 

to the final index (all of the data layers are weighted 

equally). In all the data layers and the resultant criteria 

layers, scores are normalized from 0 to 100. Zero always 

indicates the lowest quality, the greatest stress, or the 

least valuable observation, and 100 indicates the highest 

quality, least stress, or most valuable observation. While 

v
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-15

INDICATOR Relative Ecological Condition of Undeveloped Land in 

EPA Region 5 (continued)

it has not been done for this indicator, the three composite scores can be summed to result in a final “ecological 

condition” score for each cell (White and Maurice, 2004). 

Cell counts (a measure of geographic coverage) are used 

to indicate the distributions of scores associated with three 

index scores of ecological condition of undeveloped land: 

diversity, sustainability, and rarity.

What the Data Show

The frequency distributions of the 1992 baseline scores are 

quantified and plotted for each criterion (Exhibit 6-7), and 

these provide a baseline against which to track future landscape trends in diversity, sustainability, and rarity. Diversity 

scores generally run from 20 to 80 across the region, signifying that most areas are in the moderate diversity range. 

More than 90 percent of the region has sustainability scores 

above 50, but rarity scores above 50 are seldom encountered. The highest index scores are found largely in the 

northern forests of Minnesota, Wisconsin, and Michigan 

and along the large rivers in Ohio, Indiana, and Illinois 

(Exhibit 6-8).

Indicator Limitations

•	 Trend information is not available for this indicator. 

Establishing trends in the indicator may be limited by the 

availability of comparable land cover/land use data in the 

future.

•	 Although this indicator is designed to be comparable 

across undeveloped land within Region 5, layers were 

ranked within ecoregions for some of the components in 

order to account for different geophysical, geochemical, 

or climatic features of each ecoregion.

•	 Aquatic systems and connectivity resulting from water 

flow paths are not adequately covered and small, but 

potentially keystone, systems are not a part of the analysis (U.S. EPA, 2005).

•	 The data layers that contribute to each index were 

weighted equally, which may not reflect the actual relative importance of each layer (U.S. EPA, 2005).

•	 The resolution and uncertainty of the results make 

comparing the ecosystem condition score for one individual cell (300 meters by 300 meters) with another 

inappropriate, but this is not the case for comparison 

Exhibit 6-7. Distribution of index scores for the 

relative ecological condition of undeveloped 

land in EPA Region 5, 1990-1992a Area (number of cells)

A. Diversity index

0

50,000

100,000

150,000

0 20 40 60 80 100

0 20 40 60 80 100

0 20 40 60 80 100

Index score

Area (number of cells)

B. Sustainability index

50,000

0

100,000

150,000

200,000

250,000

Index score

200,000

400,000

600,000

Area (number of cells)

C. Rarity index

0

Index score

a

Coverage: Undeveloped land in EPA Region 5, based on the 

1992 National Land Cover Dataset (NLCD). For this analysis, 

“undeveloped” land is any land that the NLCD classifies as bare 

rock/sand/clay, deciduous forest, evergreen forest, mixed forest, 

shrubland, grasslands/herbaceous, woody wetlands, emergent 

herbaceous wetlands, or open water.

Data source: U.S. EPA, 2006
ECOLOGICAL CONDITION

6-16 EPA’s 2008 Report on the Environment

INDICATOR Relative Ecological Condition of Undeveloped Land in 

EPA Region 5 (continued)

between larger landscapes (U.S. EPA, 

2005).

•	 The model has not yet been field-validated 

to ensure that modeled results reflect 

actual ecosystem condition.

Data Sources

Maps and frequency distributions for the 

three indices were provided by EPA Region 

5 (U.S. EPA, 2006). An EPA report available 

online contains several related maps produced 

by the Critical Ecosystem Assessment Model 

(CrEAM), along with a list of the various datasets used as inputs for the model (White and 

Maurice, 2004, appendices). Results from the 

CrEAM model are no longer available as digital 

map layers.

References

U.S. EPA (United States Environmental 

Protection Agency). 2006. Data provided to 

ERG (an EPA contractor) by Mary White, 

EPA Region 5. August 3, 2006.

U.S. EPA. 2005. SAB review of the EPA 

Region 5 Critical Ecosystem Assessment Model. EPA/SAB/05/011. Washington, DC. <http://yosemite.epa.gov/

sab%5CSABPRODUCT.NSF/A6D38FFBC

AB115E38525702A006B6A86/$File/cream_

sab-05-011.pdf>

White, M.L., and C. Maurice. 2004. 

CrEAM: A method to predict ecological significance at the landscape scale. Chicago, IL: 

U.S. Environmental Protection Agency.

Exhibit 6-8. Relative ecological condition of undeveloped land 

in EPA Region 5, 1990-1992a 

A. Diversity index B. Sustainability index

Detail

Low High

Index score:

C. Rarity index

a

Coverage: Undeveloped land in EPA Region 5, based on the 1992 National Land Cover 

Dataset (NLCD). For this analysis, “undeveloped” land is any land that the NLCD

classifies as bare rock/sand/clay, deciduous forest, evergreen forest, mixed forest, 

shrubland, grasslands/herbaceous, woody wetlands, emergent herbaceous wetlands, 

or open water.

Data source: U.S. EPA, 2006

6.2.3 Discussion

What These Indicators Say About Trends 

in Extent and Distribution of the Nation’s 

Ecological Systems

While ecological systems are interconnected and overlapping, 

it is useful to discuss trends in terms of major types of systems. As previously mentioned, there are many ways to define 

ecological systems, including by the predominant biota, spatial 

scales, and physical characteristics. Most terrestrial systems are 

defined by predominant vegetation types. The current extent 

of these types has been assessed (see the Land Cover indicator, p. 4-7). Forests form the predominant land cover in the 

eastern and northwestern U.S. while grasslands, shrublands, 

and agricultural lands are the predominant types of vegetation in the central and western parts of the country. Trends in 

forest and wetland ecological systems are considered below. 

Trends in land development also are discussed, as this influences trends in the extent of ecological systems.

Trends in Extent and Distribution of 

Forested Ecological Systems

At a national scale, the percentage of forest land has varied 

somewhat over the last century with some decreases and some 

recent increases (see the Forest Extent and Type indicator, 

p. 6-8). Over the same period, shifts in regional distribution 

and species composition have occurred. For example, forested 

ecological systems decreased in extent in EPA Regions 6 and 9 

over the last century, but increased in extent in Regions 1, 2, 

3, and 5. The complex of tree species within a forest can have 

v
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-17

a strong influence on the community structure and functioning of a forested ecological system, and these assemblages can 

change over time. On a broad geographic scale, some forest 

types have more than doubled in acreage in the last 50 years—

for example, maple-beech-birch in the eastern U.S. and 

fir-spruce in the West. At the same time, some other types of 

forest have decreased in acreage. These compositional changes 

can be as important as changes in the overall extent of forested 

ecological systems.

At a finer regional scale, forest cover in the Puget Sound and 

Georgia Basin in the Pacific Northwest also was relatively 

stable during the 1990s (see the Land Cover in Puget Sound/

Georgia Basin indicator, p. 4-10). However, some of the forested watersheds experienced a conversion of small amounts 

of forest land to some other cover type. As discussed below, 

urbanization of low-elevation forested watersheds is a change 

that is receiving particular attention (see the Land Cover in 

Puget Sound/Georgia Basin indicator, p. 4-10). 

While extent and species composition are important aspects 

of forested ecological systems, the spatial arrangement and 

contiguity of the systems also influence the functioning of the 

systems and the distribution of wildlife species that use forests 

and adjacent areas for habitat. Fragmentation of forested systems 

can reduce or redefine the interconnections within forests, 

modifying the scale of habitat and shifting distributions of wildlife species. For example, increasing fragmentation due to forest 

clearing, development, fires, or other activities creates more 

edge habitat and limits the acreage of interior habitat. Groups 

of wildlife species may prefer one habitat over another and 

move to maximize the time spent in the preferred habitat type. 

Nationwide, almost one-fifth of forests are highly fragmented 

or “patchy,” although more than 30 percent of the forests in the 

heavily forested Regions 1, 2, and 3 are virtually unfragmented 

“core” forest (see the Forest Fragmentation indicator, p. 6-11).

Ecosystem connectivity, characterized by ecosystem “hubs” 

connected to each other by “spokes” that serve as corridors for 

the interaction of biota, was shown to account for about 40 

percent of the land cover in EPA Region 4, the southeastern 

U.S. (see the Ecological Connectivity in Region 4 indicator, p. 6-13). In this indicator, connectivity includes not only 

forested land but also wetlands and open water.

Trends in Extent and Distribution of 

Wetland Ecosystems

Wetlands are ecosystems of high biological diversity and 

support a number of ecological functions from nursery and 

breeding areas to food and protection.16 Whether inland or 

coastal, freshwater or marine, wetland acreage has declined 

over the past 50 years (see the Wetlands indicator, p. 3-32). 

The extent of the losses varies by type of wetland, with 

forested wetlands losing the most acreage and coastal wetland 

loss slowing somewhat. 

Trends in Land Development 

“Land use” refers to the visible effects of human use (see the 

Land Use indicator, p. 4-14). Changes in land use from forested 

or wetland systems to urban or agricultural environments have 

a direct impact on the ecological systems within which the 

change occurs, as well as on systems that are interconnected 

with the altered areas (e.g., watersheds and coastal areas). Some 

changes can create edge environments that are favored by certain wildlife species. Therefore, trends in land development are 

important considerations with respect to overall trends in the 

extent and distribution of ecological systems. 

Changes in land use sometimes result in changes in land cover 

and conversion from one major ecosystem type to another, 

but sometimes they do not. For example, gains in agricultural 

productivity have caused significant changes in the extent and 

location of crop and pasture land uses. Some land that had 

been used for crops or pasture has reverted to forest. Timber 

production may convert cropland to forest, or it may do little 

more than substitute one forest type or age-class distribution for another. At the same time, growth in population has 

driven an increase in the extent of developed land, much of 

which has converted crop or pasture land to developed land.

At a national scale over the last three decades, crop and 

farm acreages have decreased, timberland (productive forest 

land) has remained fairly constant, and developed lands have 

increased (see the Land Use indicator, p. 4-14). Within the 

larger-scale trends, many subtle shifts occur at smaller scales. 

The increase in developed lands has received particular attention in National and Regional Indicators. 

Increases in the numbers and changes in the spatial distribution of human populations explain part of the increase in 

developed lands. However, developed land increased by almost 

two times the increase in population from 1982 to 2003, suggesting that during this period people were making a proportionally greater use of the landscape (see the Urbanization and 

Population Change indicator, p. 4-19). Geographically, the 

rate of development was four times the population growth rate 

in the Northeast, one to three times the population growth 

rate in the South and Midwest, and nearly equal to the growth 

rate in the West. The increases in developed land suggest 

there were comparable decreases in other types of lands. To 

the extent that these other lands afford habitat to animals and 

plants, shifts in land use result in shifts in the extent and distribution of ecological systems. Increases in developed land also 

impact physical and chemical factors; for example, more runoff 

from impervious surfaces leads to greater loading of nutrients 

and contaminants, more unstable hydrology, reduced ground 

water inputs, and increased stream temperatures.

The degree of change in developed lands appears to be associated with types of locations that emerge as focal points for 

increasing stress on ecological systems. For example, in the 

Puget Sound and Georgia Basin area of the Pacific Northwest, 

16 Dahl, T.E. 2000. Status and trends of wetlands in the conterminous United 

States 1986 to 1997. Washington, DC: U.S. Department of the Interior, U.S. 

Fish and Wildlife Service.
ECOLOGICAL CONDITION

6-18 EPA’s 2008 Report on the Environment

forest conversion to other types of land use is occurring along 

the coast while older growth forests are observed at higher 

elevations (see the Land Cover in Puget Sound/Georgia Basin 

indicator, p. 4-10). Further, trends indicate that impervious 

surface coverage is increasing to the point where detrimental 

impacts to aquatic resources may occur.17 In the Great Lakes 

region, most of the undeveloped lands occur in the northern 

forests or along the major rivers (see the Condition of Undeveloped Land in Region 5 indicator, p. 6-14). Proximity to 

developed areas has an obvious effect on the quality of these 

ecological systems. The highest quality systems make up about 

3 percent of the total and are located in the most remote and/

or protected areas. 

Limitations, Gaps, and Challenges 

While many of the indicators in this section provide baseline 

information, trend information is available for only a few of 

the major types of systems—forests and wetlands. There are no 

ROE indicators for other types of terrestrial or aquatic systems 

including grasslands, shrublands, and marine hard bottom 

communities such as coral reefs, or for finer-scale ecosystem 

classifications such as riparian zones or habitat for threatened 

and endangered species. Filling these gaps in information would 

help EPA to better evaluate trends in ecological condition. 

One of the challenges in capturing meaningful changes relates 

to location and scale. The importance of location-specific 

changes is evident in some of the indices. For example, small 

changes in certain areas, such as near-coastal areas of the 

Pacific Northwest, could have disproportionately large effects 

on coastal waters relative to a similar change in the middle of 

an expansive prairie. In addition, the appearance of fragmentation in ecological systems depends on the area over which 

data were extracted.18 Thus, choosing locations and assessment 

areas have obvious impacts on trend assessment. Conversely, 

the implications of trends are manifested at scales that are location- and area-specific. Important consequences of changes 

can be captured or missed depending on how the information 

is aggregated and presented. 

Another challenge relates to understanding the factors underlying changes that occur over various time scales and their 

effects on human health and ecological condition. Principal 

among these is recognizing that natural cycles and natural 

variability bring about changes that may appear as “trends” 

over one time scale but will appear as cycles or variations 

over longer time scales. Familiar examples include population variations among predators and prey or temperature 

variations associated with the advance and retreat of ice ages. 

Distinguishing these natural cycles and variations from trends 

caused by human-induced perturbations is yet another challenge. In some cases the relationships may be evident, as in 

the influence of urbanization on watersheds or the impact of 

lost sand dunes on subsequent beach erosion. In other cases 

factors influencing changes may be difficult to discern, such 

as long-term shifts in major plant communities.

6.3 What Are the Trends 

in the Diversity and 

Biological Balance of 

the Nation’s Ecological 

Systems?

6.3.1 Introduction

Trends in the biological diversity of the nation’s ecological 

systems can be viewed in terms of both the numbers of species present in an ecological system and the extent to which 

some of the species are threatened or endangered. “Biological balance” refers to the interrelationships among organisms, including the structure of food webs and the ability of 

ecological systems to maintain themselves over time. Balance 

is a dynamic characteristic rather than a fixed state. 

The biological diversity and balance within ecological systems are often used to judge the health of the system, and 

their reduction often represents a response to pollutants or 

other stressors. Restoring biodiversity and biological balance has been a focus of EPA’s attention over the past three 

decades. Reversing declines of species such as the brown 

pelican (caused by pesticides) and brook trout (caused by 

acid rain), replacing nuisance algal blooms caused by excess 

nutrients with balanced communities of phytoplankton, 

replacing beds of sludge worms below wastewater discharges 

with balanced communities of benthic invertebrates, and 

restoring biological communities previously decimated by 

improper handling of toxic and hazardous wastes are wellknown examples.

The significance of biological diversity also stems from the fact 

that, for many people, biological diversity contributes to the 

quality of life.19 Everyone recognizes the importance of species 

as commodities (if those species produce products that can 

be bought and sold), and some argue that species have moral 

value in and of themselves. 

Diversity and biological balance are also of interest because 

of how they may influence the functioning and stability 

of ecological systems.20,21 While scientists debate the exact 

relationship between the diversity and the functioning and 

17 Klein, R.D. 1979. Urbanization and stream water quality impairment. Water 

Resour. Bull. 15(4):948-963.

18 USDA Forest Service. 2004. National report on sustainable forests—2003. 

<http://www.fs.fed.us/research/sustain/>

19 Norton, B. 1988. Commodity, amenity, and morality: The limits of quantification in valuing biodiversity. In: Wilson, E.O., ed. Biodiversity. Washington, DC: 

National Academies Press.

20 Chapin III, F.S., B.H. Walker, R.J. Hobbs, D.U. Hooper, J.H. Lawton, O.E. 

Sala, and D. Tilman. 1997. Biotic control over the functioning of ecosystems. 

Science 277(5325):500-504.

21 Wilson, E.O. 1992. The diversity of life. Cambridge, MA: Belknap Press.
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-19

stability of ecological systems, it is generally agreed that as 

the number of species in any particular type of ecological 

system declines, there is a potential loss of resilience within 

that system.22 It is also recognized that these relationships are 

not straightforward and can vary in degree depending on the 

types of species introduced to or removed from a system.23

Diversity and balance have important time and space components. Diversity arises over time as adaptation results in new 

species that fill available niches in the environment. This is a 

dynamic process involving colonization, evolution of species 

adapted to new conditions, and extinction of species that are 

less well adapted to a changing environment. This process 

has occurred over thousands or millions of years over large 

geographic areas, punctuated occasionally by events such 

as large meteor impacts, periods of intense volcanism, and 

ice ages. Ecological systems that are stable in the short term 

evolve into different systems in the long term. Disturbances 

that reduce biological diversity or disrupt balance on a small 

scale may not have an effect on a larger scale or over longer 

time periods. 

Changes (decreases and increases) in biological diversity have 

likely occurred throughout the history of the U.S. in response 

to regional land use changes, water management, intentional 

and unintentional introductions of species, and environmental 

pollution. Other changes in diversity and the composition of the 

biological community can be rapid and dramatic. Introduced 

plants and plant pathogens can rapidly transform landscapes 

as some species, such as the American chestnut, are lost and 

others, such as kudzu, thrive. Introduction of the sea lamprey 

to the Great Lakes led to sweeping changes in the entire food 

chain, from lake trout all the way down to the phytoplankton.24 Declining sea otter populations led to loss of kelp forests, 

as sea urchins formerly preyed upon by otters grazed the kelp 

down to the sea floor.25 The decimation of grazers such as the 

American Bison or predators such as grizzly bear or wolves has 

had cascading impacts on upland vegetation, wetlands, fish, and 

other species.26 Toxic chemical pollution can create wastelands 

where only the most resistant species can survive, and nutrients 

and acid rain have had indirect effects on diversity and balance 

by causing sweeping changes in the chemical habitat. 

Indicators of diversity and biological balance incorporate 

information about primary producers and invertebrate and 

vertebrate consumers, especially keystone species that play 

critical roles in structuring habitat or serve major roles as 

primary producers, top predators, or important prey species. 

Indicators of invasive species are also important with respect 

to assessing trends in diversity and biological balance because 

these species can alter the nation’s ecological systems by displacing indigenous species, potentially changing the structure 

of biological communities. 

6.3.2 ROE Indicators

Trends in diversity and balance are evaluated using four 

National Indicators and two Regional Indicators (Table 6-3). 

The focus for this question is on national- or regional-scale 

trends in biological diversity or balance over time spans of 

one to three decades. The data on biological diversity and 

22 McCann, K.S. 2000. The diversity-stability debate. Nature 405(11):228-233.

23 Srivastava, D.S., and M. Vellend. 2005. Biodiversity-ecosystem function 

research: Is it relevant to conservation? Annu. Rev. Ecol. Syst. 36:267-294.

24 Eck, G.W., and L. Wells. 1987. Recent changes in Lake Michigan’s fish community and their probable causes, with emphasis on the role of the alewife 

(Alosa pseudoharengus). Can. J. Fish. Aquat. Sci. 44(Suppl. 2):53-60.

25 Estes, J.A., and J.F. Palmisano. 1974. Sea otters: Their role in structuring nearshore communities. Science 185:1058-1060.

26 Pritchard, J.A. 1999. Preserving Yellowstone’s natural conditions: Science and 

the perception of nature. Lincoln, NE: University of Nebraska Press. 

Table 6-3. ROE Indicators of Trends in Diversity and 

Biological Balance of the Nation’s Ecological Systems 

National Indicators Section Page

Coastal Benthic Communities (N/R) 3.5.2 3-44

Benthic Macroinvertebrates in Wadeable Streams 3.2.2 3-21

Bird Populations 6.2.2 6-20

Fish Faunal Intactness 6.2.2 6-21

Regional Indicators Section Page

Submerged Aquatic Vegetation in the Chesapeake Bay 3.5.2 3-46

Non-Indigenous Benthic Species in the Estuaries of the Pacific Northwest 6.2.2 6-23

N/R = National Indicator displayed at EPA Regional scale
ECOLOGICAL CONDITION

6-20 EPA’s 2008 Report on the Environment

balance come from a variety of sources, including both systematic monitoring and ad hoc data collection.27 Systematic 

probability surveys are now providing national pictures of 

the biological diversity of benthic communities in estuaries and in rivers and streams. The Breeding Bird Survey is a 

private sector effort that provides valuable national-level data 

on trends in bird populations. 

Trends involving longer-term effects associated with climate 

change are not included. Many issues regarding biodiversity at 

subregional and local scales (e.g., tall-grass prairie or the Okefenokee Swamp) that cannot be covered here are no less important.

INDICATOR | Bird Populations

Bird populations are among the most visible biological components of ecological systems, supporting a 

number of important ecological functions including seed 

dispersal, plant pollination, and pest control. Some birds 

migrate over entire continents, while others have more 

restricted ranges and habitats, but in all cases trends in bird 

populations and in the abundance of species integrate the 

influences of changes in landscape and habitat, the availability and quality of food, toxic chemicals, and climate. 

The North American Breeding Bird Survey (BBS) began 

in 1966 with approximately 600 surveys conducted in the 

U.S. and Canada east of the Mississippi River. Today there 

are approximately 3,700 active BBS routes across the continental U.S. and southern Canada (Sauer et al., 1997). 

Trends have been computed for observed population sizes 

of 418 bird species for the 1966-2003 period (Sauer et al., 

2004). The Audubon Society (2004) categorized each species according to its primary habitat: grassland, shrubland, 

woodland, urban, and water and wetlands. This indicator 

reflects the number of species with “substantial” increases 

or decreases in the number of observations (not a change in 

the number of species) for which adequate trend data exist 

between 1966 and 2003. Substantial increases or decreases 

were defined for this study as those in which the observed 

populations on BBS routes increased or decreased by more 

than two-thirds between 1966 and 2003; this designation 

does not necessarily imply a statistically significant trend.

What the Data Show

The results point to dynamic changes in observed bird 

populations in all habitat types (Exhibit 6-9), although 

there were no consistent increases or decreases. 

•	 Of 27 grassland species for which adequate data are 

available, only two species (7 percent) showed substantial observed population increases and 19 species (70 

percent) showed substantial decreases.

•	 Of 78 shrubland species for which adequate data are 

available, 11 species (14 percent) showed substantial 

increases, while 28 species (36 percent) showed substantial declines. 

•	 Of 164 woodland species for which adequate data are 

available, 48 species (29 percent) showed substantial 

observed population increases and 42 species (26 percent) showed substantial decreases.

•	 Of 43 primarily urban species for which adequate data 

are available, 17 species (40 percent) showed substantial 

observed population increases and 10 species (23 percent) had substantial decreases.

•	 Of 106 water and wetland bird species for which adequate data are available, 40 species (38 percent) showed 

substantial observed population increases and 14 species 

(13 percent) showed substantial decreases.

Indicator Limitations

•	 The BBS produces an index of relative abundance rather 

than a complete count of breeding bird populations. The 

Exhibit 6-9. Changes in bird populations in the

contiguous U.S. and southern Canada, by

habitat type, 1966-2003a

Habitat type

Number of species a

Coverage: 418 bird species studied as part 

of the North American Breeding Bird Survey

(BBS), which covers the contiguous U.S. 

and southern Canada.

b

Increases or decreases are considered 

“substantial” if the observed population on 

BBS routes increased or decreased by more 

than two-thirds from 1966 to 2003.

Data source: Audubon Society, 2004

0

25

50

75

100

125

150

175

200

Substantial 

increase

Substantial

decrease

No substantial

change

Population 

change:b

Grassland Shrubland Woodland Urban Water/

wetland

27 There are no systematic national efforts to quantify trends in the diversity of 

other vertebrate, invertebrate, plant, or microbial species, but a private sector 

organization, NatureServe, working in concert with state Natural Heritage 

Programs, has done much to assimilate and integrate data from ad hoc and 

systematic studies to assess the status of nearly 40,000 U.S. species and to 

quantify populations of more than 20,000 at-risk species.
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-21

INDICATOR | Bird Populations (continued)

data analyses assume that fluctuations in these indices of 

abundance are representative of the population as a whole.

•	 The BBS data do not provide an explanation for the 

causes of observed population trends. To evaluate population changes over time, BBS indices from individual 

routes are combined to obtain regional and continental 

estimates of trends. Although some species have consistent trends throughout the history of the BBS, most 

do not. For example, populations of permanent resident 

and short-distance migrant species (birds wintering primarily in the U.S. and Canada) are adversely affected by 

periodic episodes of unusually harsh winter weather. 

•	 Few species have consistent observed population trends 

across their entire ranges, so increases or decreases in 

this indicator may not reflect the situation across the 

entire range of the species.

Data Sources

Trend data were obtained from the Audubon Society’s 

2004 State of the Birds report (Audubon Society, 2004). 

Audubon’s analysis used raw data from the National Breeding Bird Survey (USGS, 2004), which can be downloaded 

from http://www.pwrc.usgs.gov/bbs/retrieval/menu.cfm. 

References

Audubon Society. 2004. State of the birds USA 2004. 

Audubon Magazine September-October. <http://www.

audubon.org/bird/stateofthebirds/>

Sauer, J.R., J.E. Hines, and J. Fallon. 2004. The North 

American Breeding Bird Survey, results and analysis 

1966-2003. Version 2004.1. Laurel, MD: USGS Patuxent 

Wildlife Research Center. 

<http://www.mbr-pwrc.usgs.gov/bbs/bbs.html>

Sauer, J.R., J.E. Hines, G. Gough, I. Thomas, and B.G. 

Peterjohn. 1997. The North American Breeding Bird Survey, results and analysis. Version 96.4. Laurel, MD: USGS 

Patuxent Wildlife Research Center. 

<http://www.mbr-pwrc.usgs.gov/bbs/genintro.html>

USGS (United States Geological Survey). 2004. North 

American Breeding Bird Survey. Laurel, MD: USGS 

Patuxent Wildlife Research Center. Accessed 2004.

<http://www.pwrc.usgs.gov/bbs/index.html> v

INDICATOR | Fish Faunal Intactness

I

ntactness, the extent to which ecological communities 

have retained their historical composition, is a critical 

aspect of the biological balance of the nation’s ecological 

systems (NRC, 2000). It is of particular importance in 

freshwater systems that are impacted by pollution, habitat 

alteration, fisheries management, and invasive species. 

This indicator tracks the intactness of the native freshwater 

fish fauna in each of the nation’s major watersheds by comparing the current faunal composition of those watersheds 

with their historical composition. In this case, historical data 

are based on surveys conducted prior to 1970. The indicator 

specifically measures the reduction in native species diversity 

in each 6-digit U.S. Geological Survey hydrologic unit code 

(HUC) cataloguing unit in the 48 contiguous states. Intactness is expressed as a percent based on the formula: 

reduction in diversity = 1 – # of current native species

# of historical native species 

The native species diversity indicator proposed by 

the National Research Council (NRC, 2000) compared expected native species diversity (projected from 

species-area-curve models) with observed diversity. This 

“Fish Faunal Intactness” indicator makes use of empirical, 

rather than modeled, data sets and focuses on a well-known 

group of organisms with a fairly strong historical record. 

Reductions in watershed diversity may be due either to the 

overall extinction of a species (at least 12 U.S. freshwater fish 

species are known to be extinct and another three species are 

known only from historical records and may be extinct) or, 

more commonly, to the extirpation of a species from selected 

watersheds. In the case of regional extirpations, opportunities may exist for restoring a species to watersheds in its 

historical range.

The fish distributional data underlying this indicator were gathered by NatureServe, a nonprofit research 

organization, and are derived from a number of sources, 

including species occurrence data from state Natural Heritage Programs, a broad array of relevant scientific literature 

(e.g., fish faunas), and expert review in nearly every state. 

These data were assembled during the 1997-2003 period. 

The underlying data include distributions for 782 native 

freshwater fish species across small watersheds (8-digit 

HUC). For this indicator, data were pooled and reported 

by larger 6-digit HUCs to reduce potential errors of omission in the smaller watersheds.

What the Data Show

Watersheds 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 

( )
ECOLOGICAL CONDITION

6-22 EPA’s 2008 Report on the Environment

INDICATOR | Fish Faunal Intactness (continued)

fish species that were present before 1970 (Exhibit 6-10). 

Watersheds covering nearly a quarter (24 percent) of the 

area, however, have lost 10 percent or more of their native 

fish species. Reductions in diversity are especially severe in 

the Southwest (e.g., the lower Colorado River watershed) 

and the Great Lakes, with eight major watersheds (representing 2 percent of total area) having lost at least half of 

their native fish species.

Some watersheds are naturally more species-rich than 

others, and for those with greater historical diversity, 

even a small percentage reduction may mean the loss of 

numerous species in absolute terms. Although the greatest diversity of fish species is found in the Southeast, the 

greatest reduction in numbers has occurred in portions of 

the Midwest and the Great Lakes, where several watersheds 

have lost more than 20 species (Exhibit 6-11). In contrast, 

southwestern HUCs have all lost 10 or fewer species, but 

because these watersheds historically supported fewer species, on a percentage basis their fish faunas are regarded as 

less intact.

Indicator Limitations

•	 The incomplete historical record for freshwater fish 

distributions and inconsistent inventory records for contemporary fish distributions are sources of uncertainty. 

•	 Although NatureServe has attempted to compile the 

most complete distributional information possible for 

these species at the 8-digit HUC level, these data are 

dynamic; new records frequently are added and existing 

records are revised as new information is received and as 

taxonomic changes occur.

Data Sources

This indicator presents a summary of data available from the 

NatureServe Explorer database (NatureServe, 2006) (http://

www.natureserve.org/getData/dataSets/watershedHucs/

index.jsp). The identity and status (current vs. historical) 

of all native fish species recorded in each 8-digit HUC are 

available from this database, along with species-by-species 

distribution maps at the 8-digit HUC level. Analyses based 

on these data have previously been reported in Master et al. 

(1998, 2003) and Stein et al. (2000).

References

Master, L., A. Olivero, P. Hernandez, and M. Anderson. 

2003. Using small watershed fish, mussel, and crayfish historical and current presence data to describe aquatic biogeography and inform its conservation. Abstract #PO67. 

Society for Conservation Biology Annual Meeting, 

Duluth, Minnesota. 

Master, L.L, S.R. Flack, and B.A. Stein. 1998. Rivers of life: 

Critical watersheds for protecting freshwater biodiversity. 

Arlington, VA: The Nature Conservancy. 

<http://www.natureserve.org/publications/riversOflife.jsp>

a

Data are displayed by 6-digit hydrologic unit code (HUC) watershed. Percent reduction is based on the number of 

native species present during the period 1997-2003, compared with historical numbers documented prior to 1970. A 

species is considered “present” if there is at least one record of its presence in any 8-digit HUC within the 6-digit HUC. 

Data source: NatureServe, 2006

0%

Percent reduction 

in species:

Percent of area 

in each category

>0 to <10%

10 to <25%

25 to <50%

50%

Fishless

Exhibit 6-10. Percent reduction in native fish species diversity in the contiguous U.S. from 

historical levels to 1997-2003a

7% 

2% 

55% 

15% 

21%
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-23

INDICATOR | Fish Faunal Intactness (continued)

NatureServe. 2006. NatureServe explorer. Accessed 2006.

<www.natureserve.org/explorer>

NRC (National Research Council). 2000. Ecological 

indicators for the nation. Washington, DC: National 

Academies Press. 

<http://www.nap.edu/openbook/0309068452/html/>

Stein, B.A., L.S. Kutner, and J.S. Adams. 2000. Precious 

heritage: The status of biodiversity in the United States. 

New York, NY: Oxford University Press. <http://www.

natureserve.org/publications/preciousHeritage.jsp> 

v

a

Data are displayed by 6-digit hydrologic unit code (HUC) watershed. Reduction is based on the number of native 

species present during the period 1997-2003, compared with historical numbers documented prior to 1970. A 

species is considered “present” if there is at least one record of its presence in any 8-digit HUC within the 6-digit HUC.

Data source: NatureServe, 2006

4%

2% 

0

Number of 

species lost:

Percent of area 

in each category

1-5

6-10

11-20

>20

Fishless

Exhibit 6-11. Reduction in native fish species diversity in the contiguous U.S. from historical 

levels to 1997-2003a

60% 

13% 

21%

INDICATOR Non-Indigenous Benthic Species in the Estuaries of the 

Pacific Northwest

Non-indigenous species (NIS) are one of the greatest threats to aquatic ecosystems and can impact local 

and regional economies (Lowe et al., 2000). The number 

of invasive species in estuaries of the Pacific Northwest 

(including Puget Sound, Columbia Estuary, and Coos Bay) 

is rising, and these areas can become sources of invasives to 

other locales. Coastal waters are particularly vulnerable to 

NIS transported in ballast water and introduced via aquaculture (Puget Sound Action Team, 2002). It is becoming 

apparent that NIS are capable of impacting estuaries along 

the Pacific coast, even though they are rarely addressed in 

routine monitoring studies. One limitation is the lack of 

standardized invasion metrics and threshold values.

This indicator focuses on estuarine soft-bottom communities of the Columbian Biogeographic Province located 

along the Pacific coast from Cape Mendocino, California, 

north to the Strait of Juan de Fuca at the entrance to Puget 

Sound, Washington. It is limited to sites with salinities of 

5 parts per thousand or higher. The indicator is based on 

the percent abundance of NIS individuals relative to the 

combined abundance of native and NIS individuals in a 

benthic grab sample. 

The data for this indicator were collected by EPA’s Environmental Monitoring and Assessment Program (EMAP) 

using a probability survey over the 1999-2001 period (Nelson et al., 2004, 2005) and by a special probabilistic study 
ECOLOGICAL CONDITION

6-24 EPA’s 2008 Report on the Environment

INDICATOR Non-Indigenous Benthic Species in the Estuaries of the 

Pacific Northwest (continued)

focusing on estuaries not exposed to ballast water or aquaculture. Probability sampling provides unbiased estimates 

of the percent abundance of natives and NIS in all estuaries 

in the study area, but because the data for the special study 

have not yet been statistically expanded, data for this indicator are based on stations sampled rather than area. 

Interpretation of this indicator requires threshold values to distinguish among different levels of invasion. To 

determine the lowest expected level of invasion within the 

Columbian Biogeographic Province, EPA examined the 

extent of invasion in estuaries with minimal exposure to 

ballast water discharges and aquaculture of exotic oysters, 

which are the primary invasion vectors in the region. 

Using observed percentages of NIS at the minimally 

exposed estuaries as a reference, the threshold for “minimally invaded” survey sites was set at 10 percent NIS (i.e., 

sites were classified as minimally invaded if NIS constituted 0 to 10 percent of the individuals collected). Survey 

sites were classified as “highly invaded” if NIS were more 

abundant than native species (more than 50 percent NIS) 

and as “moderately invaded” if NIS constituted 10 to 50 

percent of the individuals.

What the Data Show

Approximately 15 percent of the stations in the Columbian 

Province were highly invaded (i.e., abundance of NIS was 

greater than abundance of natives) and another 20 percent were moderately invaded (Exhibit 6-12). The EMAP 

survey showed that NIS were among the most frequently 

occurring anthropogenic stressors in this biogeographic 

region when compared to indicators of sediment contamination or eutrophication (Nelson et al., 2004). 

The extent of invasion was not uniform, however, 

among exposed and minimally exposed estuaries. Estuaries with greater exposure to these invasion vectors were 

more invaded; 44 percent of the stations in the exposed 

estuaries were moderately to highly invaded compared 

to only 21 percent of the stations in minimally exposed 

estuaries (Exhibit 6-12). Nonetheless, the observation that 

21 percent of the stations in these “pristine” estuaries were 

at least moderately invaded indicates that NIS can disperse 

widely once they are introduced into a region, so even 

estuaries with no direct exposure to ballast water or aquaculture are at risk of invasion. 

Indicator Limitations

•	 This indicator presents baseline data only; trend 

information is not yet available.

•	 Studies in the San Francisco Estuary (Lee et al., 2003) 

and in Willapa Bay, Washington (Ferraro and Cole, 

in progress) have shown that the percent of NIS can 

vary substantially among different types of soft-bottom 

communities—e.g., unvegetated sediment versus sea 

grass beds. Thus, regional background values for the 

Columbian Province as a whole may not be appropriate 

for specific community types. 

•	 This indicator represents percent NIS in individual 

benthic grabs of the soft-bottom community, but does 

not characterize the total number of NIS in the estuaries. It does not include benthic NIS not subject to grab 

sampling, particularly hard substrate organisms. 

•	 The data for the indicator were only collected during 

a summer index period and thus do not capture 

seasonal variations.

Minimalc Moderated Highe

Extent of invasion:

Percent of estuarine sites in each category:

65.7

56.1

79.4

19.9

28.6

7.4

14.5

15.3

13.2

All 

estuaries

Exposed 

estuaries

f

Minimally

exposed 

estuaries

f 

Exhibit 6-12. Relative abundance of 

non-indigenous benthic species in estuaries of 

the Pacific Northwest, 1999-2001a,b

a

Coverage: Soft-bottom estuaries 

between Cape Mendocino, CA, and 

the Strait of Juan de Fuca, WA 

(limited to sites with salinity 5 

parts per thousand). 

b

Totals may not add to 100% due to 

rounding.

c

Minimally invaded: 0-10% 

of benthic organisms belong to 

non-indigenous species

d

Moderately invaded: >10-50% of 

benthic organisms belong to non-indigenous species

e

Highly invaded: >50% of benthic organisms belong to 

non-indigenous species

f

“Exposed” estuaries have been exposed to ballast water 

discharges from international shipping and/or aquaculture of 

exotic oysters. “Minimally exposed” estuaries have not.

Data source: U.S. EPA, 2006

 Study 

area

Oregon

Washington

California
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-25

6.3.3 Discussion

What These Indicators Say About Trends in 

the Diversity and Biological Balance of the 

Nation’s Ecological Systems 

Few national programs track diversity and biological balance. 

However, there are ROE indicators available for invertebrate 

communities and select vertebrates (birds and fish) and regionally for invasive species (as these can be important disruptors of 

ecosystem balance) and important communities of submerged 

aquatic vegetation (SAV). Some of these indicators show 

reduced or declining diversity for particular groups of animals 

and plants, but this is not consistent across all the ROE indicators. The particular trends of available ROE indicators are 

discussed below by plant and animal groupings, followed by the 

limitations of the available information and future challenges.

Primary Producers 

Primary producers range from the microscopic plants of 

the oceans to the giant redwoods of California. The types 

of plants and the biomass they produce are fundamental to 

ecological systems. For example, SAV is an important biological component of aquatic systems, contributing to diversity 

and balance by providing habitat and food. While there is no 

National Indicator of trends in SAV, the SAV in Chesapeake 

Bay indicator (p. 3-46) provides data on trends in an important regional ecosystem. SAV has increased in the Bay over 

the past 25 years, but remains below its historical coverage. 

Contributing factors in the Bay include excessive nutrients, 

sediment loads, diseases, and physical disturbance. 

Invertebrates 

Invertebrates such as worms, insects, and crustaceans are 

among the most diverse group of organisms. Collectively 

they make up the largest component of animal biomass on the 

planet and are critical components of aquatic and terrestrial 

food webs. Trends in the composition of invertebrate communities can reflect important environmental changes. 

In the nation’s coastal systems, baseline measures of invertebrate biodiversity and species composition indicate that about 

one-fifth of estuarine area exhibits low biological condition 

INDICATOR Non-Indigenous Benthic Species in the Estuaries of the 

Pacific Northwest (continued)

•	 The threshold values for “minimally invaded,” “moderately invaded,” and “highly invaded” are preliminary 

and require further research in order to establish their 

ecological significance. Specific values may differ in 

other biogeographic provinces.

Data Sources

Data for this indicator were collected by two different 

studies: EPA’s National Coastal Assessment (NCA) and a 

special EPA study of minimally exposed estuaries. The 

complete results from these studies were not publicly 

available at the time this report went to press, but summary data from the 1999 NCA are available from Nelson 

et al. (2004, 2005), and the underlying sampling data can 

be obtained from EPA’s NCA database (U.S. EPA, 2007) 

(http://www.epa.gov/emap/nca/html/data/index.html). 

Results from the special study of minimally exposed 

estuaries will be published in the near future. Until then, 

data for this indicator can be obtained from EPA’s Western 

Ecology Division (U.S. EPA, 2006).

References

Lee II, H., B. Thompson, and S. Lowe. 2003. Estuarine 

and scalar patterns of invasion in the soft-bottom benthic 

communities of the San Francisco Estuary. Biol. Invasions 

5:85-102.

Lowe, S., M. Browne, S. Boudjelas, and M. De Poorter. 

2000. 100 of the world’s worst invasive alien species—a 

selection from the Global Invasive Species Database. 

Auckland, New Zealand: International Union for the 

Conservation of Nature, Invasive Species Specialist Group. 

<http://www.issg.org/booklet.pdf>

Nelson, W.G., H. Lee II, and J. Lamberson. 2005. Condition of estuaries of California for 1999: A statistical summary. EPA/620/R-05/004. 

<http://www.epa.gov/wed/pages/publications/authored/

EPA620R-05004ConditionOfEstuariesOfCANelson.pdf>

Nelson, W.G., H. Lee II, J.O. Lamberson, V. Engle, L. 

Harwell, and L.M. Smith. 2004. Condition of estuaries of 

the western United States for 1999: A statistical summary. 

EPA/620/R-04/200. 

<http://www.epa.gov/wed/pages/publications/authored/

EPA620R-04200ConditionOfEstuariesOfThe

WesternUSNelson.pdf>

Puget Sound Action Team. 2002. Puget Sound update: 

The eighth report of the Puget Sound Ambient Monitoring Program (PSAMP). Olympia, WA: Puget Sound 

Water Quality Action Team. <http://www.psat.wa.gov/

Publications/update_02/ps_update_2002-sec.pdf>

U.S. EPA (United States Environmental Protection Agency). 

2007. National Coastal Assessment. Accessed 2007. 

<http://www.epa.gov/emap/nca/index.html>

U.S. EPA. 2006. Data provided to ERG (an EPA 

contractor) by Henry Lee, EPA Western Ecology Division. 

August 7, 2006.

v
ECOLOGICAL CONDITION

6-26 EPA’s 2008 Report on the Environment

(see the Coastal Benthic Communities indicator, p. 3-44). 

Because benthic invertebrates live on or in sediments, it is not 

surprising that many of these areas also exhibit low sediment 

and/or water quality. For small streams, the benthic macroinvertebrate Index of Biological Integrity exhibits a broad 

distribution from low to high values (see the Benthic Macroinvertebrates in Wadeable Streams indicator, p. 3-21). 

Vertebrates

The biodiversity of fish, amphibians, reptiles, birds, and 

mammals is influenced by available food resources, the size 

and arrangement of suitable habitats, influxes of new species, 

climate and weather, and the presence of contaminants. Vertebrates often receive much attention because they are highly 

visible and are often near the top of the food chain.

Among vertebrates the most reliable indicator of national 

trends is for birds, which have been tracked since 1966 (see the 

Bird Populations indicator, p. 6-20). Bird populations are in 

dynamic flux. There appears to be a net decline of observed 

populations most commonly found in grasslands and shrublands, comparable increases and decreases in observed populations in woodlands, and some gains in observed populations 

inhabiting urban and water/wetlands areas. 

Fish are distributed throughout most of the nation’s aquatic 

and marine ecological systems. Comparisons between current 

and historical species compositions (see the Fish Faunal Intactness indicator, p. 6-21) indicate that one-fifth of the watersheds of the contiguous 48 states retain their full complement 

of fish species, while about a quarter have experienced a loss 

in species of 10 percent or more. Absolute losses have occurred 

primarily in the Midwest and the Great Lakes, while on a 

percentage basis, losses have been highest in the Great Lakes 

and the Southwest. 

Invasive Species

The infiltration of new species into areas is a natural phenomenon but can be accelerated through intentional and 

unintentional introductions. Introduction of species such as 

kudzu, zebra mussels, grass carp, starlings, and nutria have 

had profound effects on ecological systems.28 Many newly 

introduced species may lack predators or parasites that kept 

these species under control in their native habitats, allowing them to out-compete resident species and even dominate 

entire systems. While national data are lacking, the NonIndigenous Estuarine Species in Pacific Northwest indicator (p. 6-23) shows that in the Columbian Biogeographic 

Province (from California to Washington), about one-third 

of the stations sampled were highly or moderately invaded 

with non-indigenous invertebrates. 

Limitations, Gaps, and Challenges

A number of additional ROE indicators would help EPA better address the question of trends in diversity and biological 

balance. While there are ROE indicators for the extent and 

distribution of vegetation types, there remain gaps with respect 

to indicators of plant biodiversity in terrestrial and aquatic ecological systems, including both vascular and non-vascular plants. 

There is no ROE indicator for threatened and endangered 

species. Also, there are no ROE indicators for algal blooms in 

coastal waters, nor are there any comparable indicators for freshwater systems—e.g., the extent of nuisance aquatic plants such 

as the prolific growths of Eurasian milfoil and water chestnut in 

lakes and ponds, which continue to create water management 

problems.29,30 ROE indicators of climate-related vegetation 

changes also are lacking (e.g., fluctuations in the extent of kelp 

beds along the Pacific coast related to El Niño events).31

There are no ROE indicators for major groups of vertebrate 

biota including amphibians, reptiles, and mammals. Because 

amphibians live both on land and in the water, their diversity 

and trends in their abundance could be influenced by a wide 

range of stressors to air, water, and land. Recent reported 

declines in amphibian populations worldwide indicate that 

losses are attributable in some areas primarily to overharvesting, in others to loss of habitat, and in still others to unknown 

causes,32 but at this time there is no National Indicator that 

meets the criteria for this report. There also are no ROE indicators for trends in important insect and freshwater shellfish 

species, coastal fish and shellfish communities, microbial communities in soil and water, or genetic diversity in plant and 

animal populations, which could affect their viability when 

stressed by contaminants or habitat alteration.

Modern transportation and international trade in biota for 

food have caused invasive species to remain a potentially 

important but poorly quantified source of stress to the diversity and balance of native species. While the Non-Indigenous 

Estuarine Species in Pacific Northwest indicator (p. 6-23) provides some insight into the potential importance of invasive 

species, the full significance of accelerated species introductions is not captured by any ROE indicator. 

In addition to indicator gaps and limitations, there are challenges to developing indicators of biological diversity and 

balance even if the data were available. For example, establishing an appropriate time scale for assessing trends in diversity 

and balance poses a major challenge. Biological variation is 

expected at annual, decadal, and even longer time scales. 

Because of the limited time frames over which observations 

have been made, parsing normal fluctuations in diversity and 

balance from longer-term trends is difficult. In addition, the 

level of interest and care of observation can change with time, 

confounding the determination of actual trends. 

28 Lowe, S., M. Browne, S. Boudjelas, and M. De Poorter. 2000. 100 of the 

world’s worst invasive alien species: A selection from the Global Invasive Species Database. Auckland, New Zealand: World Conservation Union, Invasive 

Species Specialist Group.

29 Madsen, J.D., J.W. Sutherland, J.A. Bloomfield, L.W. Eichler, and C.W. Boylen. 

1991. The decline of native vegetation under dense Eurasian water-milfoil 

canopies. J. Aquat. Plant Manage. 29:94-99. 

30 Lake Champlain Basin Program Federal Agencies Work Group. 2005. 

Opportunities for federal action: Managing aquatic non-native nuisance plants 

and animals. <http://nh.water.usgs.gov/champlain_feds/nonnative.htm>

31 Dayton, P.K., and M. Tegner. 1984. Catastrophic storms, El Niño, 

and patch stability in a southern California kelp community. Science 

224(4646):283-285.

32 Stuart, S.N., J.S. Chanson, N.A. Cox, B.E. Young, A.S.L. Rodrigues, D.L. 

Fischman, and R.W. Waller. 2004. Status and trends of amphibian declines and 

extinctions worldwide. Science 306(5702):1783-1786.
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-27

Appropriate spatial scales are equally important. Regional Indicators provide helpful insights into stressors affecting diversity 

and biological balance in some kinds of ecological systems 

for which there are no National Indicators. In fact, because 

many ecological systems vary so much by geographic region, 

compilations of Regional Indicators may provide the only 

rational approach for identifying meaningful trends. Especially 

important examples for biological diversity are unique ecosystems such as the Arctic and Pacific islands. Trends in physical 

characteristics and processes can have far-reaching effects. For 

example, polar bears represent important keystone species in 

the nation’s Arctic regions, where they are stressed by warming of coastal waters that limit the duration of ice formation. 

Pacific island biota are stressed by invasive species and a number of other stressors.

6.4 What Are the 

Trends in the Ecological 

Processes That Sustain 

the Nation’s Ecological 

Systems?

6.4.1 Introduction

Ecological systems are sustained by a number of biological, 

physical, and chemical processes. Collectively, these processes 

produce organic matter using energy (photosynthesis and 

chemosynthesis), transfer carbon and nutrients (through food 

webs and through decomposition), drive soil formation, and 

enable the reproduction of organisms (e.g., through pollination 

of plants by insects). Ecological processes also play an important 

role in providing ecological services such as the provision of 

natural resources and regulation of air and water quality.33

Ecological processes influence the extent, distribution, and 

biodiversity of systems. If primary production declines, energy 

flow to higher trophic levels is diminished, potentially compromising the sustainability of animal populations dependent 

on plants for food. Primary production is influenced by the 

availability of nutrients. Decreases and increases in nutrients 

can affect the amounts of primary production as well as the 

types of plants that grow, with subsequent effects on animals. 

The successful reproduction of plants and animals depends on 

the physical and chemical regimes of their environment. 

Too much primary production can also cause problems, such 

as those that occur in eutrophic lakes that experience an 

overload of nutrient inputs. Eutrophic conditions can alter 

the composition of animal and plant life and result in reduced 

oxygen levels due to decomposition of organic matter. For 

these reasons, management of nutrient inputs is commonly 

driven by the potential for excessive plant growth.

Primary production and associated carbon cycling (which 

form the base of food webs), nitrogen cycling (e.g., ammonification and nitrification), nutrient cycling (e.g., phosphorous 

and other essential elements for sustainability of carbon-based 

life), and hydrogen/oxygen cycles (implicating hypoxic/anoxic 

conditions) are fundamental ecological processes within 

systems. Processes related to the production, transfer, and loss 

of biomass and the reproduction and death rates of individuals within populations are reflected in various “end states” in 

time, snapshots of the outcomes of integrated processes. The 

standing stock of a population or the amounts and types of 

carbon stored within an ecological system are measures of 

these end states. While not processes themselves, trends in end 

states provide some insight into the relative balance among 

processes. Carbon storage in forests, discussed in this section, 

is an example of such an end state.

EPA has long been concerned with the impacts of human 

activities that can affect the rates, types, and timing of 

ecological processes. In particular, activities that upset the 

balance between primary production and respiration (e.g., 

biochemical oxygen demand, nutrients from fertilizers and 

human waste, and the effects of ultraviolet radiation) and 

activities that affect sediment erosion and transport are 

important factors in water quality management. Many pesticides, chemicals used in industry, pollutants, and waste products have the potential to interfere with species reproduction 

(one of the most important of ecological processes). At local 

and regional scales, changes in land use that alter the extent 

and distribution of ecological systems (Section 6.2) directly 

affect ecological processes within and adjacent to particular 

areas. Concomitant changes often occur in primary production, nutrient cycling, and erosion and sediment transport. 

For example, shifts from forested to urban or agricultural 

lands influence the amounts and types of primary producers, the infiltration of water into soils, and the storage and 

cycling of carbon and nutrients. 

Table 6-4. ROE Indicators of Trends in the Ecological Processes 

That Sustain the Nation’s Ecological Systems

National Indicators Section Page

Carbon Storage in Forests 6.4.2 6-28

33 Millennium Ecosystem Assessment. 2005. Ecosystems and human well-being: 

Current state and trends. Washington, DC: Island Press.
ECOLOGICAL CONDITION

6-28 EPA’s 2008 Report on the Environment

INDICATOR | Carbon Storage in Forests

After carbon dioxide is converted into organic matter by photosynthesis, carbon is stored in forests for a period 

of time in a variety of forms before it is ultimately returned 

to the atmosphere through the respiration and decomposition of plants and animals, or harvested from forests for use 

in paper and wood products. A substantial pool of carbon 

is stored in woody biomass (roots, trunks, and branches). 

Another portion eventually ends up as organic matter in 

forest floor litter and the upper soil horizons. Carbon storage in forest biomass and forest soils is an essential physical 

and chemical attribute of stable forest ecosystems, and a 

key link in the global carbon cycle.

This indicator, developed by the U.S. Department of 

Agriculture (USDA) Forest Service, tracks decadal changes 

in net carbon storage rates in the pools of living and dead 

biomass in forests in the contiguous 48 states. The carbon 

pools for this indicator are estimated using USDA Forest 

Service Forest Inventory and Analysis (FIA) data from five 

historical periods (circa 1953, 1963, 1977, 1987, and 1997). 

These data cover forest classified as “timberland” under 

FIA data collection procedures—that is, forests capable of 

producing at least 20 cubic feet per acre per year of industrial 

wood and not withdrawn from timber utilization by statute 

or regulation. Timberland makes up roughly two-thirds of 

U.S. forest land. Alaska and Hawaii are not included because 

of limited historical data. The FIA program estimates 

carbon storage using on-the-ground measurements of tree 

trunk size from many forest sites; statistical models that 

show the relationship between trunk size and the weight of 

branches, leaves, coarse roots (greater than 0.1 inch in diameter), and forest floor litter; and estimates of forest land area 

obtained from aerial photographs and satellite imagery. Values are converted into carbon storage based on coefficients 

derived from previous field studies (Smith and Heath, 2002; 

Smith et al., 2003; Birdsey, 1996). Forest floor litter is composed of dead organic matter above the mineral soil horizons, including litter, humus, and fine woody debris. Larger 

branches and logs on the ground are counted as “down dead 

wood.” Organic carbon in soil is not included. 

What the Data Show

The change in carbon inventories from year to year—i.e., 

net storage—reflects increases in growth as well as decreases 

due to harvesting, land use change, and disturbances such 

as fire, insects, and disease. Overall, net carbon storage in 

forests of the contiguous 48 states has been positive since 

1953 (Exhibit 6-13), indicating that over at least the last 

half-century, forests have served as a sink rather than a 

source of carbon. The average rate of net carbon storage in 

forests increased between the 1950s and the 1980s, peaking 

at 210 million metric tons of carbon per year (MtC/yr) from 

1977 to 1986. The rate declined to 135 MtC/yr for the last 

period of record (1987-1996), with declining storage evident 

in live, dead, and understory pools. This decline is thought 

Exhibit 6-13. Average annual net carbon 

storage in forests of the contiguous U.S., by 

forest component, 1953-1996a

a

Coverage: Forest land 

classified as “timberland,” 

which accounts for 

approximately two-thirds

of the forest land of the 

contiguous 48 states. 

These data do not include 

carbon stored in forest soil.

Data source: USDA Forest 

Service, 2004a,b

Aboveground live trees

Understory vegetation

Forest floor litter

Aboveground standing

dead trees

Down dead wood 

(including stumps)

Belowground dead wood

Belowground live trees (roots)

0

50

100

150

200

250

1953-1962 1963-1976 1977-1986 1987-1996

Reporting period

Average annual net carbon storage 

(million metric tons/yr)

6.4.2 ROE Indicators

This section uses one National Indicator (Table 6-4) to 

examine trends in the ecological processes that sustain ecological systems. Information for this indicator comes from satellite 

remote sensing, geographic information systems, and independent field studies conducted as part of the USDA Forest 

Service Forest Inventory and Analysis. It is important to note 

that the data presented for carbon storage in forests include 

only forests classified as “timberland,” which excludes about 

one-third of U.S. forest land cover. Timberland is defined as 

forests capable of producing at least 20 cubic feet per acre per 

year and not withdrawn from timber utilization by regulation 

or statute. This is an important distinction between previously 

illustrated trends in forest extent and type and the following 

discussion of carbon storage. 
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-29

INDICATOR | Carbon Storage in Forests (continued)

to be due to a combination of increased harvests relative 

to growth, more accurate data, and better accounting of 

emissions from dead wood (USDA Forest Service, 2004b). 

The rate of storage over this period is equivalent to approximately 9 to 10 percent of U.S. carbon dioxide emissions 

over a comparable period (U.S. EPA, 2005).

Carbon storage trends vary among regions of the country, depending on land use patterns and factors such as 

climate and soil quality. In three of the four major regions, 

net storage was positive throughout the period of record, 

with the North generally showing the largest net storage 

rates (Exhibit 6-14). The exception was the Pacific Coast 

region, which experienced net losses of forest carbon during two of the four reporting periods. Rates of net carbon 

storage appear to have decreased over time in the South; 

this trend is thought to be due to an increase in harvesting 

relative to growth (USDA Forest Service, 2004b). Some of 

the harvested carbon is sequestered in wood products.

Indicator Limitations

•	 The data include only forest classified as “timberland,” 

which excludes about one-third of U.S. forest land 

cover. Historical data from Alaska and Hawaii are insufficient for inclusion in this indicator.

•	 Data are derived from state inventories that do not correspond exactly to the years identified in Exhibits 6-13 

and 6-14.

•	 Carbon stored in forest soil is not 

included.

•	 Carbon pools are not measured, but are 

estimated based on inventory-to-carbon 

coefficients developed with information 

from ecological studies. These coefficients 

may change over time as new ecological studies are conducted, which could 

change storage rate estimates.

These limitations are discussed in detail 

in Heath and Smith (2000) and Smith and 

Heath (2000, 2001).

Data Sources

Exhibits 6-13 and 6-14 were previously published in the data supplement to USDA Forest Service (2004b). The numbers depicted 

in these figures have not been published, but 

were provided by the USDA Forest Service 

(2004a). The physical measurements used 

as inputs in the carbon storage models can 

be obtained from the FIA database (USDA 

Forest Service, 2005) (http://fia.fs.fed.us/

tools-data/).

References

Birdsey, R.A. 1996. Carbon storage for 

major forest types and regions in the conterminous United 

States. In: Sampson, R.N., and D. Hair, eds. Forests and 

global change, volume 2: Forest management opportunities 

for mitigating carbon emissions. Washington, DC: American Forests. pp. 1-25, 261-308.

Heath, L.S., and J.E. Smith. 2000. An assessment of uncertainty in forest carbon budget projections. Environ. Sci. 

Policy 3:73-82.

Smith, J.E., and L.S. Heath. 2002. Estimators of forest 

floor carbon for United States forests. Res. Pap. NE-722. 

Newtown Square, PA: USDA Forest Service, Northeastern 

Research Station. 37 pp.

Smith, J.E., and L.S. Heath. 2001. Identifying influences 

on model uncertainty: An application using a forest carbon 

budget model. Environ. Manage. 27:253-267.

Smith, J.E., and L.S. Heath. 2000. Considerations for 

interpreting probabilistic estimates of uncertainty of 

forest carbon. In: Joyce, L.A., and R. Birdsey, eds. The 

impact of climate change on America’s forests. General 

Technical Report RMRS-59. Fort Collins, CO: USDA 

Forest Service, Rocky Mountain Research Station. 

pp. 102-111.

Smith, J.E., L.S. Heath, and J.C. Jenkins. 2003. Forest 

volume-to-biomass models and estimates of mass for live 

Exhibit 6-14. Average annual net carbon storage in forests of 

the contiguous U.S. by region, 1953-1996a

a

Coverage: Forest land classified as 

“timberland,” which accounts for 

approximately two-thirds of the forest land 

of the contiguous 48 states. These data do 

not include carbon stored in forest soil.

Data source: USDA Forest Service, 

2004a,b

Reporting period

Average annual net carbon storage 

(million metric tons per year)

-25

0

25

50

75

100

1953-1962 1963-1976 1977-1986 1987-1996

North

South

Rocky 

Mountains

Pacific 

Coast

Rocky

Mountains

North

South

Pacific 

Coast
ECOLOGICAL CONDITION

6-30 EPA’s 2008 Report on the Environment

6.4.3 Discussion

What This Indicator Says About Trends in 

the Ecological Processes That Sustain the 

Nation’s Ecological Systems

The ROE indicator provides data on trends in primary production and carbon cycles for terrestrial systems.34 Primary 

producers capture, store, and supply solar-derived energy to 

other species in the system. In the forest, the energy currency is organic matter. Primary producers convert carbon 

dioxide into organic matter, which is then available to species throughout the ecological system as an energy resource 

and ultimately returns to the atmosphere (see the Carbon 

Storage in Forests indicator, p. 6-28). For forests, the stability of the system may depend on the balance between carbon 

stored in standing stock and carbon lost from the system due 

to harvesting. Net carbon storage has been positive for the 

last half-century, reflecting an overall gain in forest biomass. 

The rate of net storage increased between the 1950s and the 

1980s, then declined through the mid-1990s. During the 

1987-1996 time period, the greatest carbon storage occurred 

in the North and Rocky Mountain regions where there is 

more tree growth relative to harvesting, while the greatest 

decline in storage rates occurred in the South where harvesting has been increasing relative to growth. The distribution of carbon has received much attention, not only from a 

biological point of view but also with respect to global cycles 

of carbon. Increases and decreases in carbon storage suggest that other pools of carbon (e.g., within the aquatic and 

atmospheric environments) are also changing. The distribution of carbon among all these pools reflects a combination 

of processes and can also influence other chemical, physical, 

and biological processes.

Limitations, Gaps, and Challenges

Carbon storage trends are important for assessing the future 

viability of ecological systems, and they have increasing utility 

in evaluating global carbon cycles and potential climate change. 

At this time, however, ROE indicators are not available for carbon storage in systems other than forests (e.g., grasslands), and 

the indicator presented here is restricted to timberland (versus 

all forest) and does not include carbon storage in soil. Direct 

measurement can pose a challenge; in this case, statistical models must be employed to estimate carbon storage relationships 

among different components of the forest ecosystem.

A further limitation of the indicator presented here is that 

it provides very little insight into other ecological processes 

across the nation. Indicators are lacking for primary production, nutrient cycling (e.g., nitrogen fixation and denitrification), secondary production, and reproduction and growth 

rates of populations. Indicators also are lacking for processes 

such as pollination, decomposition, and removal of contaminants from air and water. EPA recognizes this as a gap in 

understanding trends in ecological processes. To some degree, 

information presented in Sections 6.2 and 6.3 gives insight 

into the net result of ecological processes. Trends in the extent 

and distribution of ecological systems and in the biodiversity and balance of those systems reflect underlying processes 

that produce food, cycle nutrients, and sustain populations of 

plants and animals. Sections 6.2 and 6.3 can be thought of as 

addressing “end states” that indicate the results of underlying ecological processes. Trends in these end states may or 

may not pick up important trends in the underlying processes 

because systems are dynamic and internal relationships are 

rarely linear. Indicators of ecosystem stability or resilience are 

potentially important gaps in this regard.

34 Whitmarsh, J., and Govindjee. 1999. The photosynthetic process. In: Singhal, 

G.S., G. Renger, S.K. Sopory, K.D. Irrgang, and Govindjee, eds. Concepts in 

photobiology: Photosynthesis and photomorphogenesis. New Delhi, India: 

Narosa Publishers; Dordrecht, The Netherlands: Kluwer Academic Publishers. 

pp. 11-51.

INDICATOR | Carbon Storage in Forests (continued)

and standing dead trees of U.S. forests. General Technical Report NE-298. Newtown Square, PA: USDA Forest 

Service, Northeastern Research Station. 57 pp.

USDA Forest Service. 2005. Forest Inventory and Analysis 

(FIA) database. Accessed 2005. 

<http://fia.fs.fed.us/tools-data/>

USDA Forest Service. 2004a. Data provided to ERG (an 

EPA contractor) by Linda Heath, USDA Forest Service. 

December 23, 2004.

USDA Forest Service. 2004b. National report on sustainable forests—2003. <http://www.fs.fed.us/research/

sustain/> (main site); <http://www.fs.fed.us/research/

sustain/one_pagers/indicator%2027.pdf> (data supplement: summary); <http://www.fs.fed.us/research/sustain/

documents/Indicator%2027/c5i27.pdf> (data supplement: 

graphics and metadata)

U.S. EPA (United States Environmental Protection 

Agency). 2005. Inventory of U.S. greenhouse gas emissions 

and sinks: 1990-2003. EPA/430/R-05/003.

v
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-31

6.5 What Are the 

Trends in the Critical 

Physical and Chemical 

Attributes of the Nation’s 

Ecological Systems?

6.5.1 Introduction

Physical and chemical attributes influence and sustain ecological systems. Critical physical attributes include temperature, 

light, and hydrology (rainfall, soil moisture, flow rates, and 

sea level), as well as infrequent physical events that reshape 

ecological systems, such as fires, floods, and storms. Examples 

of critical chemical attributes include oxygen, nutrients, pH, 

salinity, and the presence of other chemicals in the environment.35 Together, these attributes have driven the evolutionary 

history of species, and they continue to drive ecological processes, shape the conditions in which species live, and govern 

the very nature of ecological systems. 

Species have evolved within particular physical and chemical 

environments. These are characterized by mean (i.e., longterm average) conditions as well as by fluctuations on time 

scales of a day (e.g., tidal and light/dark cycles), seasons (e.g., 

temperature and hydrological cycles), years (e.g., periodic 

climatic and fire events), and longer time scales. The occurrence of ice ages every 40,000 to 100,000 years reflects one 

of the longer time scales. Because critical physical and chemical attributes influence so many aspects of ecological systems, 

small changes in average conditions or changes in temporal 

variations can potentially have large effects on the extent and 

distribution of ecological systems and on the biodiversity of 

these systems. 

Average conditions and the degree and periodicity of fluctuations in physical and chemical attributes vary over the 

surface of the globe, and species have evolved with specific 

niche requirements that reflect the physical and chemical 

states of the ecological systems in which they live. For this 

reason, a species that has evolved in tropical waters would 

have temperature requirements that are higher and narrower (the species is less able to tolerate fluctuations) than a 

species that has evolved in temperate waters where temperatures are lower and more variable. Reproduction and other 

activity patterns of species are often related to physical 

and chemical cues such as temperature, light, and salinity. 

Because species have evolved coincident with the presence 

(or absence) of physical disturbances, reproductive strategies 

may be linked with the occurrence of events that otherwise 

appear destructive. Thus, disturbances such as periodic fires 

or flooding may be essential for sustaining certain species 

and ecological systems where these disturbances have been 

present over evolutionary time scales. 

Critical physical attributes reflect, in part, the influence of 

solar radiation. Solar radiation warms land and water masses 

and drives hydrologic cycles. The amount of light reaching the surface of the Earth and penetrating into its waters 

determines levels of photosynthesis, which is essential to the 

support of biological systems. Other examples of physical, 

chemical, and biological processes that are influenced by the 

amount and periodicity of light include temperature and 

weather conditions, photoactivation of chemicals, mutations, and the timing of reproductive cycles. Solar radiation 

can also have potentially harmful effects on some species. Light regimes can be influenced by changes in solar 

energy reaching the earth, changes in the transparency of 

water, and changes in sea level, which in turn can change 

the degree of light penetration reaching the sea floor, coral 

reefs, and kelp forests. The implication of climate change for 

changes in many aspects of ecological condition has received 

broad attention.36,37

EPA has been actively involved over its three decades in 

assessing and managing factors that alter the critical chemical and physical characteristics of ecological systems (e.g., 

temperature, pH, electrochemical [redox] potential, and the 

transparency of air and water). For example, the use of water 

for cooling purposes can result in temperature increases in 

receiving waters of a river, acid rain can lower the pH levels 

of lakes in sensitive regions, and wastewater and fertilizer can 

lead to low redox potentials, which affect biological communities and the cycling of both toxic and non-toxic materials. Although EPA is not directly involved in the control of 

hydrology—an important physical factor in the environment—hydrology greatly influences the fate and transport of 

pollutants in aquatic ecosystems. Changes in such factors as 

the amount of runoff or snowpack can affect ground water 

levels as well as flows into streams and rivers. Flood control 

efforts can alter flooding and sedimentation processes that 

sustain particular types of systems. Because ground water is 

a primary source to surface water bodies in many parts of 

the nation, changes in the quantity (water level) and quality 

of ground water influence ecological conditions not only in 

the hyporheic zone (below and adjacent to the stream bed) 

but also in surface waters. The potential impacts of climate 

change (whether natural or human-induced) have important 

consequences for virtually every aspect of ecological structure and function.

35 Information on nutrients and potentially toxic chemicals is presented in 

Chapters 2, 3, and 4 of the ROE.

36 Millennium Ecosystem Assessment Board. 2005. Living beyond our means: 

Natural assets and human well being. <http://www.maweb.org/documents/

document.429.aspx.pdf>

37 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

Impacts, adaptation and vulnerability. Contribution of Working Group II 

to the fourth assessment report of the Intergovernmental Panel on Climate 

Change. Cambridge, UK: Cambridge University Press. <http://www.ipcc.

ch/ipccreports/ar4-wg2.htm>
ECOLOGICAL CONDITION

6-32 EPA’s 2008 Report on the Environment

6.5.2 ROE Indicators

The evaluation of trends in the critical physical and chemical 

attributes of the nation’s ecological systems relies primarily on nine National Indicators and one Regional Indicator 

(Table 6-5). Information comes from a variety of sources, 

including satellite remote sensing, geographic information 

systems, monitoring programs, visual surveys, and independent 

field studies. Indicator data in this section are drawn from a 

variety of programs such as EPA’s Wadeable Streams Assessment (WSA), National Aeronautics and Space Administration 

(NASA) remote sensing, the National Oceanic and Atmospheric Administration’s (NOAA’s) National Climatic Data 

Center and tidal gauge network, and the U.S. Geological Survey’s (USGS’s) National Water Quality Assessment (NAWQA) 

program and stream gauge network.

Table 6-5. ROE Indicators of Trends in the Critical 

Physical and Chemical Attributes of the Nation’s Ecological Systems

National Indicators Section Page

U.S. and Global Mean Temperature and Precipitation 6.5.2 6-32

Sea Surface Temperature 6.5.2 6-37

Streambed Stability in Wadeable Streams 3.2.2 3-11

High and Low Stream Flows 3.2.2 3-8

Sea Level 6.5.2 6-39

Nitrogen and Phosphorus Loads in Large Rivers 3.2.2 3-17

Nitrogen and Phosphorus in Wadeable Streams 3.2.2 3-13

Nitrogen and Phosphorus in Streams in Agricultural Watersheds 3.2.2 3-15

Lake and Stream Acidity 2.2.2 2-42

Regional Indicators Section Page

Hypoxia in the Gulf of Mexico and Long Island Sound 3.5.2 3-48

INDICATOR | U.S. and Global Mean Temperature and Precipitation

Air temperature and precipitation are two important properties of climate and are the most widely measured 

variables. Changes in these indicators may have wideranging direct or indirect effects on ecological condition 

and human health. These impacts may be positive or negative, depending on the effect, the magnitude of change, 

and the location. For example, changes in temperature can 

affect heat- and cold-related mortality and illness due to 

altered frequency and magnitude of heat waves and cold 

spells. Changes in temperature may also change the range 

and distribution of animal and plant species. Precipitation 

changes affect water availability and quality, which can 

have important effects on agricultural, forest, animal, and 

fisheries productivity, as well as human nutrition. Indirect 

effects of temperature and precipitation changes include 

changes in the potential transmission of vector-borne 

infectious diseases. These may result from alterations in the 

ranges and seasons of animals that carry disease or from 

accelerated maturation of certain infectious parasites. 

This indicator shows trends in temperature and precipitation based on instrumental records from 1901 to 2006 

(except for Alaska and Hawaii, where records begin in 

1918 and 1905, respectively). Air temperature and precipitation trends are summarized for the contiguous U.S., as 

well as for 11 climate regions of the U.S., including Alaska 

and Hawaii (these climate regions are different from the 

ten EPA Regions). For context, this indicator also shows 

trends in global temperature (over land and sea) and global 

precipitation (over land) from 1901 to 2006.

Temperature and precipitation data are presented as 

trends in anomalies. An anomaly represents the difference 

between an observed value and the corresponding value 

from a baseline period. This indicator uses a 30-year baseline period of 1961 to 1990. To generate the temperature 

time series, measurements were converted into monthly 

anomalies, in degrees Fahrenheit. The monthly anomalies 

then were averaged to get an annual temperature anomaly 

for each year. Precipitation trends were calculated in 

similar fashion, starting with anomalies for total monthly 

precipitation, in millimeters. Monthly anomalies were 

added to get an annual anomaly for each year, which was 

then converted to a percent anomaly—i.e., the percent 
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-33

INDICATOR | U.S. and Global Mean Temperature and Precipitation (continued)

departure from the average annual precipitation during the 

baseline period. Trends in temperature and precipitation 

were calculated from the annual time series by ordinary 

least-squares regression. For each of the 11 climate regions, 

this indicator also shows a smoothed time series, which was 

created from the annual series using a nine-point binomial filter (4 years on each side, averaged with decreasing 

weights further from the center year).

What the Data Show

Since 1901, temperatures have risen across the contiguous U.S. at an average rate of 0.12°

F per decade (1.2°F per 

century) (Exhibit 6-15, panel A). Over the past 30 years, 

average temperatures rose at an increased rate of 0.59°

F 

per decade, and 5 of the top 10 warmest years on record 

for the contiguous U.S. have occurred since 1990. The 

overall warming trend is not confined to just a few anomalous years, as the last eight 5-year periods (2002-2006, 

2001-2005, ...1995-1999) were the eight warmest 5-year 

periods on record (NOAA, 2007a). Warming occurred 

throughout the U.S., with all but three of the 11 climate 

regions (all but the Central, South, and Southeast) showing an increase of more than 1°

F since 1901 (Exhibit 6-16). 

The greatest temperature increase occurred in Alaska 

(3.3°F per century). 

Trends in global temperature and precipitation provide a 

context for interpreting trends in temperature and precipitation in the U.S. Instrumental records from land stations and 

ships indicate that global mean surface temperature rose by 

about 1.2°F during the 20th century (Exhibit 6-15, panel B), 

similar to the rate of warming within the contiguous U.S. 

During the last three decades, however, the U.S. warmed at 

nearly twice the global rate.

As global mean temperatures have risen, global mean 

precipitation also has increased (Exhibit 6-17, panel B). 

This is expected because evaporation increases with 

increasing temperature, and there must be an increase in 

precipitation to balance the enhanced evaporation (IPCC, 

2007). Globally, precipitation over land increased at a 

rate of 1.7 percent per century since 1901, but the trends 

vary spatially and temporally. Over the contiguous U.S., 

total annual precipitation increased at an average rate of 

6.5 percent per century since 1901 (Exhibit 6-17, panel 

A), although there was considerable regional variability 

(Exhibit 6-18). The greatest increases came in the East 

North Central climate region (11.2 percent per century) 

and the South (10.5 percent). Hawaii was the only region 

to show a decrease (-7.2 percent).

Indicator Limitations

•	 Biases may have occurred as a result of changes over time 

in instrumentation, measuring procedures (e.g., time of 

day), and the exposure and location of the instruments. 

Where possible, data have been adjusted to account for 

changes in these variables. 

•	 Uncertainties in both the temperature and precipitation 

data increase as one goes back in time, as there are fewer 

stations early in the record. However, these uncertainties 

are not sufficient to mislead the user about fundamental 

trends in the data.

Data Sources

Anomaly data were provided by the National Oceanic and 

Atmospheric Administration’s (NOAA’s) National Climatic 

Data Center (NCDC), which calculated global, U.S., and 

regional temperature and precipitation time series based 

on monthly values from a network of long-term monitoring stations (NOAA, 2007b). Data from individual stations 

were obtained from the U.S. Historical Climate Network 

(USHCN version 1) and the Global Historical Climate 

Network (GHCN), which are NCDC’s online databases 

(NOAA, 2007c).

Year

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

A. Contiguous U.S. temperature anomalies

a

Anomalies are calculated with respect to the 1961-1990 mean.

Data source: NOAA, 2007b Anomaly (°F)

Exhibit 6-15. Annual temperature anomalies in 

the contiguous U.S. and worldwide, 1901-2006a

-3

-2

-1

0

1

2

3

-3

-2

-1

0

1

2

3

Year

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

B. Global temperature anomalies

Anomaly (°F)

1901-2006 trend: +1.16°F per century

1977-2006 trend: +3.05°F per century

1901-2006 trend: +1.17°F per century

1977-2006 trend: +5.92°F per century
ECOLOGICAL CONDITION

6-34 EPA’s 2008 Report on the Environment

INDICATOR | U.S. and Global Mean Temperature and Precipitation (continued)

-3 -2 -1 0123

Exhibit 6-16. Annual temperature anomalies in the U.S. by region, 1901-2006a

1900 1920 1940 1960 1980 2000

-5 -5

1900 1920 1940 1960 1980 2000

-5

-4 -4 -4

-3 -3 -3

-2 -2 -2

-1 -1 -1

0 0 0

1 1 1

2 2 2

3 3 3

4 4 4

5 5 5

1900 1920 1940 1960 1980 2000

1900 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000 1900

-5 -5 -5

1920 1940 1960 1980 2000

-4 -4 -4

-3 -3 -3

-2 -2 -2

-1 -1 -1

0 0 0

1 1 1

2 2 2

3 3 3

4 4 4

5 5 5

1900 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000 1900

-5 -5 -5

1920 1940 1960 1980 2000

-4 -4 -4

-3 -3 -3

-2 -2 -2

-1 -1 -1

0 0 0

1 1 1

2 2 2

3 3 3

4 4 4

5 5 5

1900 1920 1940 1960 1980 2000 1900

-5 -5

1920 1940 1960 1980 2000

-4 -4

-3 -3

-2 -2

-1 -1

0 0

1 1

2 2

3 3

4 4

5 5

Anomaly (°F)

Year

Temperature change (°F per century):

a

Anomalies are calculated with respect to the 1961-1990 mean. 

b

Time series were smoothed using a 9-point binomial filter.

Data source: NOAA, 2007b

J. Alaska

A. Northeast

1901-2006 trend: +1.79°F per century 1901-2006 trend: no change

1901-2006 trend: +0.17°F per century 1901-2006 trend:

+1.76°F per century

1901-2006 trend: +1.81°F per century

1901-2006 trend: +1.69°F per century 1901-2006 trend: +2.11°F per century 1901-2006 trend: +1.73°F per century

1918-2006 trend: +3.25°F per century 1905-2006 trend: +1.15°F per century

G. Southwest

D. South

C. Central

F. West North Central

I. Northwest

K. Hawaii

B. Southeast

H. West

E. East North Central

Annual anomaly

Smoothed trendb

1901-2006 trend: +0.24°F per century

Gray interval: -0.1 to 0.1°F

Southeast

Hawaii

Alaska

East

North Central

Central

South

West 

North Central

Southwest

Northwest

West

Northeast
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-35

INDICATOR | U.S. and Global Mean Temperature and Precipitation (continued)

References

IPCC (Intergovernmental Panel on Climate Change). 

2007. Climate change 2007: The physical science basis. 

Contribution of Working Group I to the fourth assessment 

report of the Intergovernmental Panel on Climate Change. 

Cambridge, UK: Cambridge University Press. <http://

www.ipcc.ch/ipccreports/ar4-wg1.htm>

NOAA. 2007a. 2006 annual climate review: U.S. summary. June 21, 2007, edition. <http://www.ncdc.noaa.gov/

oa/climate/research/2006/ann/us-summary.html>

NOAA. 2007b. Data provided to ERG (an EPA contractor) by Jay Lawrimore and David Wuertz, NOAA. October 12-November 16, 2007.

NOAA. 2007c. National Climatic Data Center. Accessed 

October-November 2007. <http://www.ncdc.noaa.gov/

oa/ncdc.html> (NCDC home page); <http://www.ncdc.

noaa.gov/oa/climate/research/ushcn/ushcn.html> (U.S. 

Historical Climate Network version 1); <http://www.

ncdc.noaa.gov/oa/climate/research/ghcn/ghcn.html> 

(Global Historical Climate Network)

Year

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

A. Contiguous U.S. precipitation anomalies

a

Anomalies and percent change are calculated with respect to the 

1961-1990 mean.

Data source: NOAA, 2007b Percent anomaly

Exhibit 6-17. Annual precipitation anomalies in 

the contiguous U.S. and worldwide, 1901-2006a

-20

-15

-10

-5

0

5

10

15

20

Year

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

B. Global precipitation anomalies

Percent anomaly

-20

-15

-10

-5

0

5

10

15

20

1901-2006 trend: +6.46% per century

1901-2006 trend: +1.74% per century
ECOLOGICAL CONDITION

6-36 EPA’s 2008 Report on the Environment

INDICATOR | U.S. and Global Mean Temperature and Precipitation (continued)

1900 1920 1940 1960 1980 2000

100

-60

-40

-20

0

20

40

60

80

100

-60

-40

-20

0

20

40

60

80

100

-60

-40

-20

0

20

40

60

80

100

-60

-40

-20

0

20

40

60

80

100

-60

-40

-20

0

20

40

60

80

100

100

-60 -60 -60

-40 -40 -40

-20 -20 -20

0 0 0

20 20 20

40 40 40

60 60 60

80 80 80

100

1900 1920 1940 1960 1980 2000

1900 1920 1940 1960 1980 2000

Exhibit 6-18. Annual precipitation anomalies in the U.S. by region, 1901-2006a Percent anomaly

Year

Northeast

Southeast

Hawaii

Alaska

East

North Central

Central

South

West 

North Central

Southwest

Northwest

West

-60 -60 -60

-40 -40 -40

-20 -20 -20

0 0 0

20 20 20

40 40 40

60 60 60

80 80 80

100 100 100

1900 1940 1960 1980 2000 1920

1900 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000

1900 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000

1900 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000

a

Anomalies and percent change are calculated with respect to the 

1961-1990 mean. 

b

Time series were smoothed using a 9-point binomial filter.

Data source: NOAA, 2007b

1900 1920 1940 1960 1980 2000

J. Alaska

A. Northeast

1901-2006 trend: +8.26% per century

1901-2006 trend: +11.23% per century

1901-2006 trend: +1.28% per century

1918-2006 trend: +5.92% per century

Annual anomaly

Smoothed trendb

G. Southwest

D. South

C. Central

F. West North Central

I. Northwest

K. Hawaii

B. Southeast

H. West

E. East North Central

1901-2006 trend: +8.13% per century

1901-2006 trend: +10.51% per century 1901-2006 trend: +1.91% per century

1901-2006 trend: 

+9.13% per century

1901-2006 trend: +5.97% per century

1905-2006 trend: -7.16% per century

-35 -28 -21 -14 -7 0 7 14 21 28 35

Change in precipitation (% per century):

Gray interval: -2 to 2%

1901-2006 trend: +1.87% per century

v
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-37

INDICATOR | Sea Surface Temperature

Sea surface temperature (SST) is a critical physical attribute of the oceans and coastal 

ecological systems. Water temperature directly 

affects biological and physical process rates, 

water column stability, and the presence and 

functioning of species of plants (e.g., algae, 

sea grasses, marsh plants, and mangroves) and 

animals (e.g., microscopic animals, larger 

invertebrates, fish, and mammals). Increases 

in temperature have been associated with the 

timing of breeding in sea turtles (Weishampel et al., 2004), stress and bleaching of coral 

reefs (Brown, 1997; Woodbridge and Done, 

2004), alteration of species migration patterns, 

changes in ecological system extent and composition (Helmuth et al., 2002), and changes in 

the frequency or extent of blooms of harmful 

algae (Ostrander et al., 2000). On longer time 

scales (decades to centuries), rising SST may 

result in decreases in the supply of nutrients 

to surface waters from the deep sea, which could trigger a 

cascade of effects leading to decreases in primary production 

and declines in fish production (Pratchett et al., 2004), wetland loss, reductions in coastal storm buffering, and losses of 

local tourism. SST is both an indicator of, and a profound 

influence on, the climate system. Changes in SST may result 

from long-term cycles in ocean circulation, climate variability, or secular trends in climate (Committee on the Bering 

Sea Ecosystem et al., 1996).

This SST indicator, developed by the National Climatic 

Data Center (NCDC) of the National Oceanic and Atmospheric Administration (NOAA) and the National Center 

for Atmospheric Research, describes the long-term variability and change in global mean SST for the 1880-2006 

period. This reconstruction provides consistent spatial and 

temporal data with their associated 95 percent confidence 

intervals. The data are compiled from in situ measurements 

from the International Comprehensive Ocean-Atmosphere 

Data Set (ICOADS) release 2 (Slutz et al., 2002) and—in 

recent years—from satellite imagery. Data are available 

from multiple sources (e.g., ship reports, buoy monitors, 

oceanographic profiles) from as early as 1854 (Woodruff 

et al., 1998). By filtering and blending data sets that use 

alternative measurement methods and include redundancies in space and time, this reconstruction is able to fill 

spatial and temporal data gaps and correct for biases in the 

different measurement techniques (e.g., uninsulated buckets, intakes near warm engines, uneven spatial coverage). 

The extended reconstructed data are shown as anomalies, 

or differences, from the “normal” (i.e., average) SST from 

1971 to 2000. The long-term average change obtained by 

this method is very similar to those of the “unanalyzed” 

measurements and reconstructions developed by other 

researchers (e.g., Rayner et al., 2003).

What the Data Show

The reconstruction of SST anomalies over all latitudes 

indicates that the highest SSTs during the period of record 

occurred over the last three decades (Exhibit 6-19). Warming has occurred through most of the twentieth century and 

appears to be independent of measured inter-decadal and 

short-term variability (Smith and Reynolds, 2005). The SST 

warming occurred in two parts, the first between 1910 and 

1940 and the second after 1970, with a roughly stationary 

period between 1940 and 1970. SST appears to have cooled 

between 1880 and 1910, although confidence intervals are 

wider over the early period of record. Despite that uncertainty, warming for the entire period of the indicator and for 

the period from 1900 forward is statistically significant.

Indicator Limitations

•	The 95 percent confidence interval is wider than other 

methods for long-term reconstructions; in mean SSTs, 

this interval tends to dampen anomalies. 

•	The geographic resolution is coarse for ecosystem 

analyses but reflects long-term and global changes as 

well as variability. 

•	 The reconstruction methods used to create this indicator 

remove almost all random “noise” in the data. However, 

the anomalies are also dampened when and where data 

are too sparse for a reliable reconstruction. The 95 percent 

Exhibit 6-19. Annual global sea surface temperature anomaly, 

1880-2006a 

a

Coverage: Anomaly with respect to the 1971-2000 climate normal, which is plotted 

as zero.

Data source: NOAA, 2007b

Year

Temperature anomaly (°F)

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

-1.5

-1

-0.5

0

0.5

1

1.5

1971-2000 

climate normal

Annual

anomaly

Upper 95% confidence interval

Lower 95% confidence interval
ECOLOGICAL CONDITION

6-38 EPA’s 2008 Report on the Environment

INDICATOR | Sea Surface Temperature (continued)

confidence interval reflects this “damping” effect as well as 

uncertainty caused by possible biases in the observations.

•	 Data screening results in loss of many observations at latitudes higher than 60 degrees north or south. Although 

the effects of screening at high latitudes are extremely 

small on the global average, the main effect is to lessen 

anomalies and widen the confidence intervals. 

Data Sources

This extended reconstruction of SST, called ERSST.v3, 

was recently described in Smith et al. (in press). NCDC 

(NOAA, 2007b) provides access to monthly and annual 

SST and error data from this reconstruction (http://www.

ncdc.noaa.gov/oa/climate/research/sst/ersstv3.php), as well 

as a mapping utility that allows the user to calculate average 

anomalies over time and space (http://nomads.ncdc.noaa.

gov/#climatencdc). The ERSST.v3 reconstruction is based 

on in situ measurements and satellite data, both of which 

are available from online databases. In situ measurements 

are available from NOAA (2007a) (http://icoads.noaa.gov/

products.html), and satellite data from NASA (2007) (http://

podaac.jpl.nasa.gov/DATA_PRODUCT/SST/index.html).

References

Brown, B. 1997. Coral bleaching: Causes and consequences. 

Coral Reefs 16:S129-S138.

Committee on the Bering Sea Ecosystem, Polar Research 

Board, Commission on Geosciences, Environment and 

Resources, and National Research Council. 1996. The 

Bering Sea ecosystem. Washington, DC: National Academies Press. pp. 196-237.

Helmuth, B., C.D.G. Harley, P.M. Halpin, M. O’Donnell, 

G.E. Hofmann, and C.A. Blanchette. 2002. Climate 

change and latitudinal patterns of intertidal thermal stress. 

Science 298:1015-1017.

NASA (National Aeronautics and Space Administration). 

2007. Physical Oceanography Distributed Active Archive 

Center (PO.DAAC), sea surface temperature products. Jet 

Propulsion Laboratory. Accessed 2007. <http://podaac.jpl.

nasa.gov/DATA_PRODUCT/SST/index.html>

NOAA (National Oceanic and Atmospheric Administration). 2007a. International Comprehensive OceanAtmosphere Data Sets (ICOADS). Accessed 2007. 

<http://icoads.noaa.gov/>

NOAA. 2007b. Sea surface temperature (SST) datasets. 

National Climatic Data Center. Accessed October 2007. 

<http://www.ncdc.noaa.gov/oa/climate/research/sst/sst.

html#grid>

Ostrander, G.K., K.M. Armstrong, E.T. Knobbe, D. Gerace, 

and E.P. Scully. 2000. Rapid transition in the structure 

of a coral reef community: The effects of coral bleaching and physical disturbance. Proc. Natl. Acad. Sci. USA 

97(10):5297-5302.

Pratchett, M.S., S.K. Wilson, M.L. Berumen, and M.I. 

McCormick. 2004. Sublethal effects of coral bleaching 

on an obligate coral feeding butterflyfish. Coral Reefs 

23(3):352-356. 

Rayner, N.A., D.E. Parker, E.B. Horton, C.K. Folland, 

L.V. Alexander, D.P. Rowell, E.C. Kent, and A. Kaplan. 

2003. Global analyses of sea surface temperature, sea ice, 

and night marine air temperature since the late nineteenth 

century. J. Geophys. Res. 108:4407.

Slutz, R.J., S.J. Lubker, J.D. Hiscox, S.D. Woodruff, R.L. 

Jenne, D.H. Joseph, P.M. Steurer, and J.D. Elms. 2002. 

Comprehensive ocean-atmosphere data set; release 1. 

NTIS PB86-105723. Boulder, CO: NOAA Environmental Research Laboratories, Climate Research Program. 

<http://icoads.noaa.gov/Release_1/coads.html#abstract>

Smith, T.M., R.W. Reynolds, T.C. Peterson, and J. 

Lawrimore. In press. Improvements to NOAA’s Historical 

Merged Land-Ocean Surface Temperature Analysis 

(1880-2006). J. Climate. <http://www.ncdc.noaa.gov/

oa/climate/research/sst/papers/Merged.Recon.v8.pdf> 

(preprint) 

Smith, T.M., and R.W. Reynolds. 2005. A global merged 

land air and sea surface temperature reconstruction 

based on historical observations (1880-1997). J. Climate 

18(12):2021-2036. 

<http://www.ncdc.noaa.gov/gcag/merge.pdf>

Weishampel, J.F., D.A. Bagley, and L.M. Erhart. 2004. 

Earlier nesting by loggerhead sea turtles following sea surface warming. Glob. Change Biol. 10(8):1424-1427.

Woodbridge, S., and T. Done. 2004. Learning to predict 

large-scale coral bleaching from past events: A Bayesian 

approach using remotely sensed data, in-situ data, and 

environmental proxies. Coral Reefs 23(1):96-108. 

Woodruff, S.D., H.F. Diaz, J.D. Elms, and S.J. Worley. 

1998. COADS release 2 data and metadata enhancements 

for improvements of marine surface flux fields. Phys. 

Chem. Earth 23(5-6):517-526. <http://icoads.noaa.gov/

egs_paper.html>

v
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-39

INDICATOR | Sea Level

Sea level is an indicator of global and local change and a factor that affects human welfare and coastal ecosystem conditions. Coastal areas host a rich set of natural and 

economic resources and include some of the most developed 

and rapidly growing population centers in the nation. More 

than 100 million people globally live within 1 meter of the 

mean sea level and more than 40 percent of the U.S. population lives in watersheds along U.S. ocean coasts (NOAA, 

2005). Changing sea levels can inundate low-lying wetlands 

and dry lands (Burkett et al., 2005), erode beaches (USGS, 

1998), change rates of sedimentation (Olff et al., 1997), 

and increase the salinity of marshes, estuaries, and aquifers 

(Condrey et al., 1995; Williams et al., 1999). Documented 

consequences of sea level rise include loss of buffering 

against storms and floods (Burkett et al., 2005), changes in 

bird populations (Erwin, 2005) and land cover (Williams et 

al., 1999), property losses (Burkett et al., 2005), and infrastructure damage (Theiler and Hammar-Klose, 1999; U.S. 

Department of Transportation, 2003).

Approximately 58,000 square kilometers of land in the 

contiguous U.S. lie less than 1.5 meters above sea level; 

80 percent of this land is in Louisiana, Florida, Texas, 

and North Carolina (Titus and Richman, 2001). Almost 

half of the shoreline studied along the U.S. Atlantic Coast 

was determined to be highly to very highly vulnerable 

to effects of sea level rise (Theiler and Hammar-Klose, 

1999). The areas of highest vulnerability are high-energy 

coastlines where the coastal slope is low and the major 

landform type is a barrier island. The risks may be minimal if wetlands accretion can match or outpace sea level 

rises, but accretion rates vary widely (Hartig et al., 2000, 

Table 3). 

A number of factors affect sea level, including, but not 

limited to, changes in sea temperature, salinity, and total 

water volume and mass (e.g., from melting glaciers or 

changes in the amount of water stored on land). Sea level 

rises with warming sea temperatures and falls with cooling. Changes in the total volume and mass of ocean water 

also result from the melting or accumulation of Antarctic and Greenland ice sheets and non-polar glaciers and 

changes in the amount of water stored in lakes, rivers, and 

ground water. As such, global average sea level change is 

Exhibit 6-20. Changes in relative sea level along U.S. coasts, 1950-1999a

a

Trends are based on tidal gauge measurements. Each dot represents a tidal gauge 

station that operated during the period 1950-1999.

Data source: NOAA, 2006

180° 165°W 150°W 135°W 120°W 105°W 90°W 75°W 60°W

15°N

30°N

45°N

60°N

75°N

Mean relative sea level change (mm per year):

-18 to -15

-14.99 to -12

-11.99 to -9

-8.99 to -6

-5.99 to -3

-2.99 to 0

0.01 to 3

3.01 to 6

6.01 to 9

9.01 to 12
ECOLOGICAL CONDITION

6-40 EPA’s 2008 Report on the Environment

INDICATOR | Sea Level (continued)

an indicator of the physical and climatic stability of the 

global environment. 

Temporal scale is an important factor in interpreting sea 

level trends. Sea level changes may reflect factors such as 

seasonality, inter-annual to decadal scale variability such 

as El Niño, and/or long-term climate change (decades to 

centuries). Spatial scale also is important because absolute 

sea height does not change uniformly around the globe. 

This indicator presents trends in absolute and relative 

sea level. Absolute sea level represents only the sea height, 

whereas relative sea level change is defined as sea height 

change plus land height changes (due to subsidence or 

uplift and changes in natural land accretion). Relative sea 

level data are from the tidal gauge measurements of the 

National Water Level Observation Network, composed 

of approximately 175 long-term, continuously operating stations located along the U.S. coast, including the 

Great Lakes and islands in the Atlantic and Pacific Oceans 

(Smith, 1980; Gill and Schultz, 2001). Tidal gauge data 

are presented from 1950 to 1999, although a few locations have been monitoring since the mid-1800s (NOAA, 

2001). Absolute sea level data are from satellite measurements from NASA’s TOPEX/Poseidon spacecraft, which 

uses radar to map the precise features of the ocean surface, 

and the “Jason” satellite, which monitors ocean circulation 

(Leuliette et al., 2006). The two satellites use radar altimetry to collect sea level data globally. These data have been 

available since 1993. 

What the Data Show

Relative sea levels (combined land and sea movement) in 

many locations rose from 1950 to 1999, typically at rates 

of 0-3 millimeters per year (mm/yr) (up to 1 foot per century) (Exhibit 6-20). Relative sea level has risen more rapidly (3-6 mm/yr) along the mid-Atlantic coast from North 

Carolina to New Jersey and at rates as high as 9-12 mm/

yr at two stations in Louisiana. Other locations, such as the 

southern coast of Alaska, show relative sea level drop, with 

a maximum decrease of 16 mm/yr. Average relative sea 

level rise for all U.S. coasts was not calculated because the 

distribution of tidal gauge stations is not spatially representative of aggregate trends, but for reference, an analysis 

of tidal gauge data worldwide estimated that on average, 

relative sea level rose between 1.5 and 2.0 mm/yr during 

the 20th century (Miller and Douglas, 2004).

The satellite record shows that global mean absolute sea 

level (i.e., independent of land movements) has increased 

at a rate of 3 mm (0.12 inches) per year since 1993 (Exhibit 

6-21). Absolute sea levels do not change uniformly around 

the Earth, however. Around the U.S., areas with increasing absolute sea level include the Gulf coast and portions of 

the Atlantic coast (Exhibit 6-22). Areas showing a decrease 

include the southern part of the Pacific coast and the western Gulf of Alaska. 

Indicator Limitations

•	An estimated 50 to 60 years of data are required to 

obtain linear mean sea level trends having a 1 mm/yr 

precision with a 95 percent statistical confidence interval. 

•	Tidal gauge measurements do not represent more generalized (i.e., average) relative sea level change along U.S. 

coasts (or globally).

•	 Most local tidal gauge measurements cannot indicate 

whether changes in relative sea level are due to changes 

in absolute sea level or changes in land elevation. 

•	 Satellite data are not available for a multi-decadal time 

series needed to separate out medium-term variability 

from long-term change. 

•	 Satellite data are not horizontally precise enough to 

resolve sea level trends for small water bodies (such as 

many estuaries) or for localized interests (such as a particular harbor or beach). 

Data Sources

Exhibit 6-20 is based on a map and corresponding trend 

data published by the National Oceanic and Atmospheric 

Administration’s (NOAA’s) National Oceans Service 

(NOAA, 2006) (http://tidesandcurrents.noaa.gov/sltrends/

sltrends.shtml). These data were previously published in 

Year

a

Values are reported as anomalies with 

respect to the 1993-1997 mean. 

b

Data were collected by the 

TOPEX/Poseidon and Jason 1 satellite 

altimeters. Data were adjusted by 

applying an inverse barometer (air pressure) correction and removing 

seasonal signals.

Data source: Leuliette et al., 2006 Mean sea level anomaly (mm)

Exhibit 6-21. Global mean sea level, 1993-2006a,b

TOPEX measurements

Jason measurements

60-day smoothing

-20

-10

0

10

20

30

40

1992 1994 1996 1998 2000 2002 2004 2006

Trend: +3.0 mm per year

1993-1997 mean
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-41

INDICATOR | Sea Level (continued)

NOAA (2001), along with a list of station coordinates 

(NOAA, 2001, Appendix I). Individual station measurements are accessible through NOAA (2006).

Exhibits 6-21 and 6-22 were produced using data provided by Leuliette et al. (2006) (time series at http://sealevel.

colorado.edu/results.php; map at http://sealevel.colorado.

edu/maps.php). Leuliette et al.’s analysis was based on measurements from NASA’s Ocean Topography Experiment 

(TOPEX) and Jason satellite altimeters; results were calibrated using a model documented in Leuliette et al. (2004). 

Satellite measurements can be obtained from NASA’s online 

database (NASA, 2006) (http://topex-www.jpl.nasa.gov/

science/data.html).

References

Burkett, V.R., D.B. Zilkoski, and D.A. Hart. 2005. Sealevel rise and subsidence: Implications for flooding in New 

Orleans, Louisiana. In: Subsidence observations based on 

traditional geodetic techniques, and numerical models. U.S. 

Geological Survey, National Wetlands Research Center. 

<http://www.nwrc.usgs.gov/hurricane/Sea-Level-Rise.pdf>

Condrey, R., P. Kemp, J. Visser, J. Gosselink, D. Lindstedt, 

E. Melancon, G. Peterson, and B. Thompson. 1995. Status, 

trends, and probable causes of change in living resources in 

the Barataria and Terrebonne estuarine systems. Thibodaux, 

LA: Barataria-Terrebonne National Estuary Program.

Erwin, R.M. 2005. Atlantic sea level rise, lagoonal marsh 

loss, and wildlife habitat implications. U.S. Geological 

Survey. Accessed December 29, 2005. <http://www.pwrc.

usgs.gov/resshow/erwin1rs/erwin1rs.htm>

Gill, S.K., and J.R. Schultz. 2001. Tidal datums and 

their applications. NOAA Special Publication NOS 

CO-OPS 1.

Hartig, E.K., F. Mushacke, D. Fallon, and A. Kolker. 

2000. A wetlands climate change impact assessment for the 

metropolitan East Coast region. Draft for public review. 

<http://metroeast_climate.ciesin.columbia.edu/reports/

wetlands.pdf>

Leuliette, E.W., R.S. Nerem, G.T. Mitchum, and D.P. 

Chambers. 2006. Sea level change: 2006 release #3. 

Accessed October 2006. <http://sealevel.colorado.edu/>

Leuliette, E.W., R.S. Nerem, and G.T. Mitchum. 2004. 

Calibration of TOPEX/Poseidon and Jason altimeter data 

to construct a continuous record of mean sea level change. 

Mar. Geod. 27(1-2):79-94. 

<http://sealevel.colorado.edu/MG_Leuliette2004.pdf>

Exhibit 6-22. Changes in absolute sea level along U.S. coasts, 1993-2006a

a

Trends are based on satellite measurements. Data were adjusted by 

applying an inverse barometer (air pressure) correction.

Data source: Leuliette et al., 2006

Mean absolute sea level change (mm per year):

-15 -10 -5 0 5 10 15

165°W 150°W 135°W 120°W 105°W 90°W 75°W 60°W

15°N

30°N

45°N

60°N

75°N

No data

180°
ECOLOGICAL CONDITION

6-42 EPA’s 2008 Report on the Environment

INDICATOR | Sea Level (continued)

Miller, L., and B.C. Douglas. 2004. Mass and volume 

contributions to twentieth-century global sea level rise. 

Nature 428:406-409. <http://www.grdl.noaa.gov/SAT/

pubs/papers/2004nature.pdf>

NASA (National Aeronautics and Space Administration). 

2006. Ocean surface topography from space. Updated 

January 2006. 

<http://topex-www.jpl.nasa.gov/science/data.html>

NOAA (National Oceanic and Atmospheric Administration). 2006. Sea levels online. Accessed October 6, 2006. 

<http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml> 

(home page); <http://tidesandcurrents.noaa.gov/sltrends/

msltrendstable.htm> (data table)

NOAA. 2005. Population trends along the coastal United 

States: 1980-2008. <http://www.oceanservice.noaa.gov/

programs/mb/supp_cstl_population.html>

NOAA. 2001. Sea level variations of the United States 

1854-1999. NOAA Technical Report NOS CO-OPS 36.

<http://tidesandcurrents.noaa.gov/publications/

techrpt36.pdf>

Olff, H., J. De Leeuw, J.P. Bakker, R.J. Platerink, H.J. Van 

Wijnen, and W. De Munck. 1997. Vegetation succession 

and herbivory in a salt marsh: Changes induced by sea level 

rise and silt deposition along an elevational gradient. J. 

Ecol. 85:799-814.

Smith, R.A. 1980. Golden Gate tidal measurements. J. 

Waterw. Port C. Div. 106(WW3):407-410.

Thieler, E.R., and E.S. Hammar-Klose. 1999. National 

assessment of coastal vulnerability to sea-level rise: preliminary results for the U.S. Atlantic coast. U.S. Geological 

Survey Open-File Report 99-593. 

<http://pubs.usgs.gov/of/of99-593/index.html>

Titus, J., and C. Richman. 2001. Maps of lands vulnerable 

to sea level rise: modeled elevations along the U.S. Atlantic 

and Gulf coasts. Climate Res. 18:205-228. 

<http://yosemite.epa.gov/oar/globalwarming.nsf/

UniqueKeyLookup/SHSU5C3J4E/$File/maps.pdf>

U.S. Department of Transportation. 2003. Does sea level 

rise matter to transportation along the Atlantic coast? In: 

U.S. Department of Transportation, Center for Climate 

Change and Environmental Forecasting. The potential 

impacts of climate change on transportation. <http://

yosemite.epa.gov/oar/globalwarming.nsf/UniqueKeyLookup/JSAW672M6T/$File/Transportation_Paper.pdf>

USGS (United States Geological Survey). 1998. The 

Chesapeake Bay: Geologic product of rising sea level. Fact 

Sheet 102-98. <http://pubs.usgs.gov/fs/fs102-98/>

Williams, K., K.C. Ewel, R.P. Stumpf, F.E. Putz, and T.W. 

Workman. 1999. Sea-level rise and coastal forest retreat on 

the west coast of Florida, USA. Ecology 80(6):2045-2063.

v

6.5.3 Discussion

What These Indicators Say About Trends in 

Critical Physical and Chemical Attributes of 

the Nation’s Ecological Systems

Critical Physical Attributes 

Information is available on trends in temperature and precipitation (see the Temperature and Precipitation indicator, 

p. 6-32). Across the contiguous U.S., mean temperature 

increased over the past century. The rate of increase in the past 

30 years was higher than in the previous part of the century, 

amounting to more than 0.5oF per decade. Some regional 

trends in temperature are evident, with Alaska and the western part of the contiguous 48 states exhibiting a greater warming trend than the rest of the country. This overall warming 

trend is consistent with the latest findings of the Intergovernmental Panel on Climate Change (IPCC), which concluded 

that “Warming of the climate system is unequivocal, as is now 

evident from observations of increases in global average air 

and ocean temperatures, widespread melting of snow and ice, 

and rising global average sea level.”38

These general warming trends have occurred concurrently 

with rising atmospheric concentrations of greenhouse gases 

(see the Greenhouse Gas Concentrations indicator, p. 2-66). 

The IPCC confirms a connection, concluding that “Most of 

the observed increase in global average temperatures since the 

mid-20th century is very likely [defined by IPCC as greater 

than 90 percent probability] due to the observed increase in 

anthropogenic greenhouse gas concentrations.”39

Temperature changes can influence the physical aspects of 

ecological systems, including regional and global weather and 

oceanographic patterns. Observed impacts associated with 

warming include the global retreat of mountain glaciers, 

reduction in snow-cover extent, earlier spring melting of ice 

on rivers and lakes, and increases in sea surface temperatures 

38 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

The physical science basis. Contribution of Working Group I to the fourth 

assessment report of the Intergovernmental Panel on Climate Change. 

Cambridge, UK: Cambridge University Press. <http://www.ipcc.ch/ipccreports/ar4-wg1.htm>

39 Ibid.
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-43

and ocean heat content.40 For example, global sea surface 

temperature increased throughout the past century, with the 

greatest increases occurring in the past three decades (see the 

Sea Surface Temperature indicator, p. 6-37).

The potential ecological implications of a gradual warming 

trend have received much attention.41,42,43 Virtually every ecological system in the U.S. is potentially vulnerable to changes 

in temperature regimes that might affect physical (and in turn, 

biological) conditions, including coastal and marine areas,44,45

inland freshwater and wetland systems,46 and terrestrial systems.47 All species have preferred ranges of temperature for 

survival, growth, and reproduction as well as lower and upper 

thermal tolerance limits. Mean temperature, seasonal changes, 

and other temporal fluctuations constitute species’ temperature 

regimes. As these regimes change, several types of stresses are 

placed on a species. First, a species may not be well adapted 

to the new regime and may not be able to sustain its population. Second, other species may be better adapted and able to 

extend their ranges into new areas. Finally, because temperature can affect other biological and physical attributes of 

systems, the ecological system itself may change in a way that 

is not favorable for the species. 

Temperature patterns are interlinked with air and water circulation patterns, which are critical to the dispersal of organisms, the movement of nutrients, and many other processes 

important to sustaining ecological systems. The replenishment of water over land surfaces is particularly critical, as it 

is a major determinant of the sustainability of the varied ecological systems that exist along a gradient of moisture from 

wetlands to deserts. For example, in areas where precipitation is reduced, droughts can have a pronounced and rapid 

influence on vegetation.48

Overall, precipitation increased in the U.S. over the past 

century (see the Temperature and Precipitation indicator, p. 

6-32). Regional differences are apparent, however, with the 

greatest increases in the East North Central climate region and 

the South, very small increases in other regions, and a decrease 

in Hawaii. It is difficult to assign causes to such local and 

regional changes in precipitation because of natural climate 

variability (e.g., oscillations such as El Niño and others), complex interactions between aerosols (from natural and industrial 

processes) and clouds, and the effects of urban and rural land 

use on evaporation and transpiration.

Stream flows are another physical attribute that shapes and 

sustains ecological systems. Whether by moving sediment 

under high flow regimes or fostering sedimentation in lower 

flow regimes, stream flows impact ecological communities 

by forming aquatic habitats and defining habitat boundaries. 

Streambed stability is an important variable in this regard (see 

the Streambed Stability indicator, p. 3-11). Cycles of high and 

low flow are particularly important for species that depend on 

specific conditions. For example, streambeds may require an 

annual high flow event to restore habitat that had been filled 

with debris and sediment during lower flow periods. The 

timing of seasonal flows also coincides with the reproductive 

cycles of some species. Data from stream gauges indicate that 

over the last half-century, high flow volumes have increased 

substantially in many streams compared to the previous 20 

years, but they have decreased in just as many (see the Stream 

Flows indicator, p. 3-8). Meanwhile, low flow volume appears 

to have increased in many streams, while variability of flow 

has generally decreased—indicating a smaller difference 

between high and low flows. Among streams in grassland and 

shrubland areas, the number and duration of no-flow periods 

also has decreased since the 1960s. While weather patterns 

naturally vary from year to year, trends revealing broader 

shifts in high and low flows and changes in no-flow periods 

may forewarn of instability in ecological systems. 

In many locations along the U.S. coast, sea level has risen 

steadily, reflecting changes in water levels as well as subsidence in land in some areas (see the Sea Level indicator, p. 

6-39). These changes can alter the ecological conditions in 

coastal areas, especially where land elevations are low. The 

rise of sea levels results in increased flooding that can be 

exacerbated during storm events. Rising sea level also can 

result in increased salinity levels in coastal inland waters and 

soils, thereby changing the chemical condition of habitats. 

Freshwater ecological systems are progressively lost as they 

are transformed into more saline inland waters or into open 

coastal waters. 

Critical Chemical Attributes

Dissolved oxygen is critical to the support of aerobic animals 

and plants. In aquatic systems, dissolved oxygen levels reflect a 

balance between that produced by plants, consumption by all 

biota, and physical mixing processes. The spatial extent and 

timing of reduced oxygen conditions (hypoxia) and no oxygen 

40 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

Impacts, adaptation and vulnerability. Contribution of Working Group II 

to the fourth assessment report of the Intergovernmental Panel on Climate 

Change. Cambridge, UK: Cambridge University Press. <http://www.ipcc.

ch/ipccreports/ar4-wg2.htm>

41 National Research Council. 2001. Climate change science: An analysis of 

some key questions. Committee on the Science of Climate Change. Washington, DC: National Academies Press.

42 Millennium Ecosystem Assessment Board. 2005. Living beyond our means: 

Natural assets and human well being. <http://www.maweb.org/documents/

document.429.aspx.pdf>

43 Intergovernmental Panel on Climate Change. 2007. Climate change 2007: 

Impacts, adaptation and vulnerability. Contribution of Working Group II 

to the fourth assessment report of the Intergovernmental Panel on Climate 

Change. Cambridge, UK: Cambridge University Press. <http://www.ipcc.

ch/ipccreports/ar4-wg2.htm>

44 Barry, J.P., C.H. Baxter, R.D. Sagarin, and S.E. Gilman. 1995. Climate-related, 

long-term faunal changes in a California rocky intertidal community. Science 

267:672-675.

45 Kennedy, V.S., R.R. Twilley, J.A. Kleypas, J.H. Cowan, Jr., and S.R. Hare. 2002. 

Coastal and marine ecosystems and global climate change: Potential effects on 

U.S. resources. Arlington, VA: Pew Center on Global Climate Change. 

46 Poff, N.L., M.M. Brinson, and J.W. Day, Jr. 2002. Aquatic ecosystems and 

global climate change: Potential impacts on inland freshwater and coastal wetland ecosystems in the United States. Arlington, VA: Pew Center on Global 

Climate Change.

47 Malcolm, J., and L. Pitelka, 2000. Ecosystems and global climate change: A 

review of potential impacts on U.S. terrestrial ecosystems and biodiversity. 

Washington, DC: Pew Center on Global Climate Change.

48 Allen, C., and D. Breshears. 1998. Drought-induced shift of a forestwoodland ecotone: Rapid landscape response to climate variation. PNAS 

95(25):14839-14842.
ECOLOGICAL CONDITION

6-44 EPA’s 2008 Report on the Environment

conditions (anoxia) affects the distribution and sustainability 

of populations of aerobic organisms. As hypoxic and anoxic 

areas increase in size and persistence, animals such as mollusks 

(snails and clams), arthropods (e.g., crabs and shrimp), and fish 

have proportionally less habitat within which they can thrive. 

For these reasons, trends in oxygen affects the sustainability of 

populations as well as the overall biodiversity of aquatic and 

marine systems.

Regional information is available on hypoxic conditions in 

the Gulf of Mexico and Long Island Sound (see the Hypoxia 

in Gulf of Mexico and Long Island Sound indicator, p. 3-48). 

The size of the hypoxic zones in both the Gulf of Mexico 

and Long Island Sound has been highly variable since the 

mid-1980s, with no discernable trend in either area. In both 

cases, there remain substantial areas in the latest year of record 

(2007) where low dissolved oxygen concentrations make the 

waters unsuitable to support most fish and shellfish species. 

Nutrient levels are tightly interwoven into ecological condition. Aquatic systems are strongly influenced by nutrient 

levels, and nutrient inputs within a watershed may impact 

ecological systems far from the origin of the input (e.g., input 

occurs upstream, but impact occurs at the mouth of a river). 

Indicators focusing on the most active nutrients in aquatic 

systems—nitrogen and phosphorus—provide insights into 

trends in nutrient loads, cycles, and transport. 

Nutrient loads have been examined for the Mississippi, 

Columbia, St. Lawrence, and Susquehanna Rivers (see the N 

and P Loads in Large Rivers indicator, p. 3-17). The largest 

of the monitored rivers, the Mississippi River, carries more 

than 15 times the nitrate load of the other rivers. The nutrient 

loads in this river more than doubled from the 1950s to the 

present. In contrast to the overall upward trend of nitrate loads 

in the Mississippi River, nitrate loads in the Columbia River 

nearly doubled in the 1990s compared to historical loads, but 

returned to historical levels by 2002. Nitrate loads increased in 

the St. Lawrence but did not exhibit a particular trend in the 

Susquehanna. Trends in phosphorus loads are variable in the 

Mississippi and Columbia Rivers, and show a decrease in the 

St. Lawrence and Susquehanna Rivers, likely due to phosphorus controls.

Baseline information on nitrogen and phosphorus concentrations is available for two sets of streams: wadeable streams 

and streams in agricultural watersheds. Among wadeable 

streams, a recent nationwide survey found that for both 

of these nutrients, roughly one-third of wadeable stream 

miles had concentrations that were substantially higher than 

regionally appropriate reference levels (see the N and P in 

Wadeable Streams indicator, p. 3-13). Agriculture-dominated 

watersheds are often characterized by higher loads of applied 

nitrogen and phosphorus fertilizers to optimize crop development. Streams located within these areas provide an indication of the extent of nutrient inputs. Baseline studies confirm 

that levels of nitrogen and phosphorus are elevated in many of 

these water bodies (see the N and P in Agricultural Streams 

indicator, p. 3-19).

The pH of air masses and waters is critical to biological functions, can directly affect the viability of species, and can affect 

the bioavailability of chemicals (both nutrients and potential 

toxics). There has been a decrease in wet deposition of sulfur 

and nitrogen compounds over the past 15 years, as discussed 

in Chapter 2. Associated with the decrease in deposition has 

been an increase in the acid neutralizing capability of water 

bodies (see the Lake and Stream Acidity indicator, p. 2-42). 

In one sensitive region, however (the Blue Ridge), fresh water 

bodies have yet to show recovery from acidification. 

Limitations, Gaps, and Challenges

There are ROE indicators for only a few of the critical 

physical and chemical attributes of ecological systems. EPA 

would like to have ROE indicators for solar radiation over 

land and water as well as penetration into the nation’s waters. 

In addition, there are no ROE indicators of disturbance 

regimes associated with flooding and fire. Other important 

gaps include water levels in lakes, the amount of snowpack 

or ground water available to support base flow in rivers and 

streams, and indicators of soil quality such as salinity or base 

cation saturation. Still, information is available for a few of 

the most critical attributes. Trends in temperature provide 

insight into other trends that have important biological and 

physical ramifications.

The indicators of trends in chemical and physical life-sustaining 

parameters are influenced by uncertainty. As technology 

changes, biases develop for data collected over long periods of 

time. Data collection tools may improve, creating new uncertainties when comparing recent data to historical trend data. 

In historical trend analyses, gaps in the record may emerge. 

Bridging the gaps between data series may require use of estimation or interpolation methods, or those time periods may 

be excluded altogether. All indicators of long-term trends are 

susceptible to changes in monitoring technology and historical 

data gaps. However, the increase in temperature and precipitation is occurring, and with the collection of additional data sets, 

longer-term trends can be confirmed or refuted.

Measuring trends in physical and chemical attributes is subject 

to a number of limitations. For the assessment of the indicator 

for stream flow, the U.S. Geological Survey gauging stations 

that generate the data for this parameter are placed on the 

larger tributaries and may miss trends in the smaller waterways. However, this indicator does provide valuable trend 

information regarding high and low flows for larger waterways. For the assessment of acidification, the focus is largely 

on areas where previous studies revealed an impact. This may 

exclude areas that are impacted to a lesser extent by acid rain.

While the large river surveys provide trend data for a watershed, it is not possible to identify the relative contributions 

of different land uses in the river basin. More detailed studies 

focus on the most common land uses contributing to nutrient 

runoff. Each provides useful information regarding trends in 

the specific system.

Information contained in the indicators represents baseline, 

decadal, and even century-level trends. However, for hydrologic and temperature patterns, these time periods may be 

too short to assess long-term changes. The field of paleoclimatology offers some promise for extending information to 
ECOLOGICAL CONDITION

EPA’s 2008 Report on the Environment 6-45

larger time frames.49 In addition, the predictive capability of 

forecasting the extent of dissolved oxygen deficits in regional 

and coastal water bodies is increasing.50 Information is also 

available on the distribution of solar energy over the surface of 

the U.S. Over time, such information could be used to evaluate trends in this physical attribute.

6.6 What Are the 

Trends in Biomarkers 

of Exposure to 

Common Environmental 

Contaminants in Plants 

and Animals?

6.6.1 Introduction

Chemicals can be introduced to the environment intentionally 

(e.g., fertilizers, pesticides, and herbicides), or unintentionally 

through accidental spillage or leaks of chemicals used in home 

and commercial applications (e.g., in wastes from municipal 

and industrial operations). The extent to which the presence 

of mixtures of chemicals influences human health and the 

environment has long been a focus of EPA assessments. 

Biomarkers of exposure can include measures of chemical 

concentrations in plant and animal tissue. Such measures 

provide insight into the magnitude of chemical exposure 

that organisms receive from their environment. Measures of 

biological response such as biochemical concentrations (e.g., 

enzymes and ligands) that respond to chemical exposures 

can also serve as biomarkers of exposure. Examples include 

histopathological anomalies such as plant tissue damage from 

ozone or tumors in fish exposed to sediment contaminated 

with polycyclic aromatic hydrocarbons (PAHs). This evaluation examines the trends in biomarkers of exposures to common environmental contaminants in plants and animals as 

presented in the ROE indicators. It also discusses challenges 

in assessing trends in these biomarkers.

Chemical stressors can have a detrimental effect on plant 

and animal communities. Exposure of plants and animals to 

chemical stressors can lead to increases in tissue concentrations of the chemical stressor in the plants and animals. Once 

stressor concentrations are above threshold levels, they can 

affect physiological systems within the plants and animals 

and can begin to have toxic effects on individuals within 

the population. These individual effects can lead to changes 

in plant and animal community structure when chemical stressor concentrations in the environment reach levels 

that can affect one or more species, or when the population 

numbers of a key species are detrimentally affected. Biomarkers of exposure, including concentrations of chemical 

stressors or key biomarkers collected over time within plant 

and animal tissues, can help to gauge the health of plant and 

animal communities over time. These biomarkers of chemical exposure, when coupled with other information (e.g., 

toxicity testing results), can provide a basis for estimating 

what levels of a chemical stress can and cannot be tolerated 

in the environment by plant and animal communities. These 

biomarkers also help explain the recovery of certain animal populations (e.g., brown pelican) that were once nearly 

driven to extinction by specific chemical stressors. Tissue 

levels of pesticides, PCBs, and mercury have been used 

for many years to evaluate exposures to such species as the 

brown pelican, bald eagle, and lake trout and a host of other 

fish and wildlife. The Mussel Watch program relies on sampling lower-trophic-level organisms (mussels and clams) for 

a broad range of chemicals to evaluate exposures in coastal 

areas. As these examples demonstrate, measures of bioaccumulative compounds in animal tissues provide an indication 

of exposure levels throughout food webs. 

6.6.2 ROE Indicators

Although trends in specific contaminants of concern in 

environmental media (e.g., sediments or air) have been available for specific locations, the indicators to evaluate trends in 

biomarkers of exposure to common environmental contaminants in plants and animals are mainly focused on national or 

regional programs that have been measuring chemical stressor 

concentrations in fish tissue in lakes and coastal regions of the 

U.S. over less than a decade. An example of such biomonitoring efforts is summarized in the National Coastal Condition Report II,51 which was completed as a collaborative 

effort between EPA, the National Oceanic and Atmospheric 

Administration, the U.S. Fish and Wildlife Service, and the 

U.S. Geological Survey.52

Trends in biomarkers of exposure to common environmental 

contaminants in plants and animals are evaluated using three 

National Indicators (Table 6-6). The focus of this question is 

on national- or regional-scale trends in biomarkers of exposure over the period in which measurements have occurred 

(i.e., the last one to three decades, depending upon the biomarkers of exposure). While other subregional or local-scale 

efforts concerning monitoring of biomarkers of exposure cannot be covered here, they are no less important. 

49 National Oceanic and Atmospheric Administration. 2003. North American 

drought: A paleo perspective. <http://www.ngdc.noaa.gov/paleo/drought/

drght_home.html>

50 Longstaff, B.J., D. Jasinski, and P. Tango. 2005. Ecological forecast—summer 

2005. Monitoring and Analysis Subcommittee. Chesapeake Update. 

51 U.S. Environmental Protection Agency. 2002. EMAP research strategy. 

EPA/620/R-02/002.

52 Within the U.S. Geological Survey, the Biomonitoring of Environmental 

Status and Trends (BEST) Program is another example of a national program 

mandated to collect biomarkers of common contaminant exposure. Although 

monitoring of fish contaminant concentrations is a focus of this program, this 

program also monitors common pollutants in many other aquatic and terrestrial receptors, such as upper trophic level receptors (fish-eating birds like the 

bald eagle), and catalogues biomarker data collected from many sources into 

an online database. 
ECOLOGICAL CONDITION

6-46 EPA’s 2008 Report on the Environment

6.6.3 Discussion

What These Indicators Say About Trends 

in Biomarkers of Exposure to Common 

Environmental Contaminants in Plants 

and Animals

The ROE indicators provide a baseline of recent conditions 

against which future trends can be assessed. Lipophilic chemicals such as polychlorinated biphenyls (PCBs), DDT, and 

methylmercury are present in fish tissues throughout most of 

the nation’s freshwater lakes and coastal systems (Coastal Fish 

Tissue indicator, p. 3-61; Lake Fish Tissue indicator, p. 3-63), 

which shows widespread exposure to these bioaccumulative 

compounds. Some judgment concerning these levels can be 

made by reference to benchmarks that relate to tissue residues. 

For example, approximately one-fifth of estuarine fish samples 

were found to have at least one contaminant at levels that 

exceed commonly used benchmarks. Differences are apparent 

across EPA Regions. The contaminants most responsible for 

exceedances were PCBs, mercury, DDT, and PAHs.

Foliar injury from ozone pollution disrupts plant/tree physiology. Baseline data indicate that exposure of forests to ozone 

levels varies geographically, with more severe injury generally 

occurring in the eastern U.S. than in the West (Ozone Injury 

to Forest Plants indicator, p. 2-24). Up to 7 percent of sites 

had severe foliar injury in some EPA Regions, while no injury 

was observed at sites in Regions 8 and 10.

Limitations, Gaps, and Challenges 

Few national programs involve unbiased assessment that 

can support indicators of trends in national conditions in 

biomarkers of exposure. While there are tissue-level ROE 

indicators for fish, there are no similar indicators for plants 

(either aquatic or terrestrial) or wildlife species. This represents a gap in EPA’s ability to identify trends in biomarkers of 

exposure to common environmental contaminants in plants 

and animals.

Among the primary challenges relating to monitoring biomarkers of exposure are the following:

•	 To monitor a single biomarker of exposure on a national or 

regional scale requires a great deal of planning, coordination, and resources. Biomarkers are more costly and timeconsuming to measure than chemical concentrations in 

other media (e.g., water, sediment, air), because the living 

things that require measurement are more difficult to collect and/or analyze for the chemical stressors.

•	 The biomarkers of exposure need to be clearly linked to 

biomarkers of effects to be useful for predicting whether the 

function of plant or animal communities is being affected 

by the concentrations of chemical in the environment. In 

many cases, capabilities are currently lacking to link biomarkers of exposure with biomarkers of effects. In addition, 

most monitoring focuses on the media within which plants 

and animals live (i.e., air and water), and does not address 

the body burden of the chemical in the plant or animal or 

biomarkers of effects.

•	 With a myriad of environmental contaminants in the 

environment, it is difficult to prioritize which contaminants 

should be monitored in biological tissues. Classically, the 

organochlorine pesticides (e.g., DDT), PCBs, and mercury 

have been monitored in fish tissues in the aquatic environment. However, in the future, new chemicals may emerge 

as equally or more important (see Chapter 7). 

Table 6-6. ROE Indicators of Trends in Biomarkers of Exposure to 

Common Environmental Contaminants in Plants and Animals

National Indicators Section Page

Coastal Fish Tissue Contaminants (N/R) 3.8.2 3-61

Contaminants in Lake Fish Tissue 3.8.2 3-63

Ozone Injury to Forest Plants 2.2.2 2-24

N/R = National Indicator displayed at EPA Regional scale
EPA’s 2008 Report on the Environment 7-1

Next Steps

The Report on the Environment represents a commitment by 

EPA to continually improve the quality and quantity of information available to understand the condition of human health 

and the environment and how they are changing over time. 

The results of these improvements will be communicated to 

the public via regular updates of the ROE. Specific plans for 

updating the report include: 

•	 EPA’s 2008 ROE: Revised editions of this report will 

be produced at a frequency that will provide input to the 

Agency’s strategic planning process. New editions will 

reflect revisions or additions to the ROE questions, updates 

and revisions of the indicators in this report, addition of 

new indicators, and revisions to the “Introduction” and 

“Discussion” sections that accompany each question.

•	 EPA’s 2008 ROE: Highlights of National Trends: This 

document, which communicates key information from the 

ROE to the interested public, will be updated periodically.

•	 Electronic version of the ROE (http://www.epa.

gov/roe): EPA will present the ROE and ROE Highlights in electronic form on the Internet so people can 

navigate and query the ROE content. This “e-ROE” will 

be updated on an ongoing basis to enable users to obtain 

indicator revisions as soon as they are available. 

To strengthen its ability to answer the ROE questions, the 

Agency will work to overcome some of the important challenges identified by public comments and by EPA’s Science 

Advisory Board in its review of the 2008 ROE.

7. Afterword

Chapter 7
CHAPTER 7

7-2 EPA’s 2008 Report on the Environment

Challenges

Throughout this report, EPA uses indicators to answer what 

it believes are among the most important questions about the 

environment and human health. For many of these questions, 

the answers are incomplete. Three important challenges affect 

EPA’s ability to answer these questions: 

•	 Synthesizing and integrating information from multiple 

indicators to obtain a coherent understanding of their 

interrelationships, as relevant to the ROE questions. 

•	 Filling gaps and reducing limitations in the 2008 ROE 

indicators.

•	 Addressing emerging issues that suggest potential new areas 

of concern for which indicators are not yet available.

All three areas offer opportunities for improvement in future 

editions of this report.

Synthesis and Integration

Synthesizing and integrating information across multiple 

indicators is a major challenge for several reasons: 

•	 There currently are no “meta-indicators” that can provide 

an integrated, comprehensive measure of trends in human 

health or the environment to answer any of the ROE 

questions. Instead, the available indicators provide in-depth 

coverage of particular aspects of the environment or health 

that are relevant to answer the questions. 

•	 Differences in the spatial and temporal coverage of indicator 

data make it difficult to compare trends among indicators. 

•	 In many cases, it is not clear whether a trend in one ROE 

indicator is directly linked to trends in other, potentially 

related ROE indicators. 

These types of challenges preclude EPA from being able, at 

present, to fully respond to the individual ROE questions or 

to make an integrated or “bottom line” statement in response 

to any of the questions. EPA will strive to address these challenges in future reports by working to fill gaps and reduce 

indicator limitations, as described below.

Indicator Gaps and Limitations

Each ROE question focuses on a set of interrelated environmental issues (described in the “Introduction” to the question) 

about which there is a good scientific understanding. In general, there are ROE indicators that describe status and trends 

relating to some but not all of these issues. The “Discussion” 

section for each question describes the limitations in the current indicators and their underlying data, as well as gaps where 

no appropriate indicators are available to answer important 

parts of the questions. EPA is working to strategically analyze 

gaps and limitations in order to identify priorities for developing additional indicators and improving existing indicators. 

This work will: 

•	 Expand EPA’s ability to present indicators and supporting 

data at variable geographic scales. This will likely involve 

scaling National Indicators in a way that recognizes important natural boundaries in air, land, and water, while at the 

same time presenting the data in a way that is meaningful 

and useful to EPA’s Regions and other stakeholders, and 

developing a strategy for the incorporation of many more 

regional and sub-regional indicators consistent with the 

hierarchical framework described above in the “Synthesis 

and Integration” section.

•	 Strengthen existing indicators, both by resolving their limitations and by incorporating statistical analysis in order to 

quantify the uncertainty in current status and trends. 

•	 Identify what indicators are most needed to answer the 

ROE questions, taking into consideration new or emerging 

technologies and research needs to support future development of these indicators.

•	 Utilize improved research, science, and technology to 

develop new indicators.

•	 Work with the scientific community to ensure that the 

information reported continues to meet EPA’s high standards for science. EPA’s Science Advisory Board has recommended that EPA revisit the indicator criteria to achieve a 

better balance between inclusiveness and sound science.

Partnerships with federal, state, and non-governmental organizations to support indicator development and improvement 

through coordinated research, monitoring, and data sharing 

will be critical to fulfilling this commitment.

Emerging Issues

In this report, “emerging issues” are issues whose potential to 

affect human health and the environment is not well understood. Emerging issues pose different challenges to EPA’s ability 

to answer the ROE questions than do indicator gaps and limitations. For example, many emerging issues have only recently 

been described in the scientific literature and popular press. 

Therefore, the current state of scientific understanding makes 

it unclear whether indicators are needed, and if so, how they 

should be constructed and tracked. Areas where issues potentially relevant to the ROE questions are emerging include:

•	 New technologies, contaminants, or environmental effects potentially related to such contaminants.

Examples include brominated flame retardants;1,2 residues of 

pharmaceuticals and personal care products;3,4,5 air pollutants 

1 Rayne, S., M.G. Ikonomou, and B. Antcliffe. 2003. Rapidly increasing polybrominated diphenyl ether concentrations in the Columbia River system 

from 1992 to 2000. Environ. Sci. Technol. 37(13):2847-2854.

2 Birnbaum, L.S., and D.F. Staskal. 2004. Brominated flame retardants: Cause for 

concern? Environ. Health Perspect. 112(1):9-17.

3 Daughton, C.G., and T.A. Ternes. 1999. Pharmaceuticals and personal care 

products in the environment: Agents of subtle change? Environ. Health 

Perspect. 107(Suppl 6):907-944. <http://www.epa.gov/ppcp/pdf/errata.pdf> 

4 Koplin, D.W., E.T. Furlong, M.T. Meyer, E.M. Thurman, S.D. Zaugg, L.B. 

Barber, and H.T. Buxton. 2002. Pharmaceuticals, hormones, and other 

organic wastewater contaminants in U.S. streams, 1999-2000: A national 

reconnaissance. Environ. Sci. Technol. 36:1202-1211. <http://pubs.acs.org/

journals/esthag/36/i06/pdf/es011055j.pdf>

5 Lindsey, M.E., M.T. Meyer, and E.M. Thurman. 2001. Analysis of trace levels of 

sulfonamide and tetracycline antimicrobials in groundwater and surface water 

using solid-phase extraction and liquid chromatography/mass spectrometry. 

Anal. Chem. 73(19):4640-4646.
CHAPTER 7

EPA’s 2008 Report on the Environment 7-3

related to the use of alternative fuels (e.g., biodiesel);6 new 

chemicals and new uses for existing chemicals;7 wastes that 

contain multiple materials that are challenging to separate, 

particularly for recycling and reuse;8 the growing field of 

nanotechnology and the potential release of engineered 

nanomaterials (e.g., nanoparticles) to the environment;9 and 

diseases and conditions for which there is emerging evidence 

that exposure to environmental contaminants may be a risk 

factor (see Section 5.4.3). 

•	 Issues for which the inherent complexity of the interactions between pollutants, environmental media, 

and ecological systems makes it unclear what should 

be measured. Examples include (1) interactions between 

changing climate and feedback mechanisms and the effects of 

a wide range of pollutants on human health, water resources, 

ecosystems, coastal areas, and other valued resources,10,11,12,13

including the distribution and occurrence of harmful algal 

blooms or other pathogens;14 and (2) loss of genetic diversity, 

which may result in the loss of an entire species if that species 

becomes less able to adapt to changing conditions.15

These examples are neither definitive nor prioritized, but 

offered simply to illustrate the types of challenges that lie ahead.

6 Morris, R.E., A.K. Pollack, G.E. Mansell, C. Lindhjem, Y. Jia, and G. Wilson. 

2003. Impact of biodiesel fuels on air quality and human health. National 

Renewable Energy Laboratory. NREL/SR-540-33793. <http://www.nrel.

gov/docs/fy03osti/33793.pdf>

7 U.S. Department of Energy. 2000. Energy and environmental profile of the 

U.S. chemical industry. Report prepared by Energetics Incorporated. Columbia, MD. <http://www.eere.energy.gov/industry/chemicals/>

8 U.S. Environmental Protection Agency. 2001. Electronics: A new opportunity 

for waste prevention, reuse, and recycling. EPA/530/F-01/006. <http://

www.epa.gov/epaoswer/osw/elec_fs.pdf> 

9 Oberdörster, G., E. Oberdörster, and J. Oberdörster. 2005. Nanotoxicology: 

An emerging discipline evolving from studies of ultrafine particles. Environ. 

Health. Perspect. 113:823-839.

10 Foley, J. 2005. Atmospheric science: Tipping points in the tundra. Science 

310(5,748):627-628.

11 Milkov, A.V. 2004. Global estimates of hydrate-bound gas in marine 

sediments: How much is really out there? Earth Sci. Rev. 66(3-4):183-197. 

12 Faeth, P., and S. Greenhalgh. 2000. A climate and environmental strategy for 

U.S. agriculture. WRI Issue Brief, World Resources Institute, Washington, DC, 

November 2000.

13 Harrison, J., and P. Matson. 2003. Patterns and controls of nitrous oxide 

emissions from waters draining a subtropical agricultural valley. Global 

Biogeochem. Cycles 17(3):1080.

14 Daniels, N.A., and A. Shafaie. 2000. A review of pathogenic Vibrio infections 

for clinicians. Infect. Med. 17(10):665-685. <http://www.issc.org/client_

resources/Education/PathogenicVibrioInfections.pdf>

15 Bagley, M.J., S.E. Franson, S.A. Christ, E.R. Waits, and G.P. Toth. 2003. 

Genetic diversity as an indicator of ecosystem condition and sustainability: 

Utility for regional assessments of stream condition in the eastern United 

States. U.S. Environmental Protection Agency. EPA/600/R-03/056.
APPENDIX A

EPA’s 2008 Report on the Environment A-1

T

his glossary provides definitions for a limited set of 

terms. Most of these terms are included because they 

have a particular usage or meaning either within EPA 

or in the context of this report. A few others are included to 

ensure understanding of intended meaning because they are 

key terms within this report. This glossary does not include 

other scientific terms for which standard definitions are 

readily available.

Appendix A:

Acronyms and Glossary

Acronyms

AAPCC American Association of Poison Control Centers

ADHD attention-deficit/hyperactivity disorder

ANC acid neutralizing capacity

AQI Air Quality Index

AQS Air Quality System

ARMS Agricultural Resources Management Survey

AWQC-AL ambient water-quality criterion for the 

protection of aquatic life

BBS Breeding Bird Survey

C-CAP Coastal Change Analysis Program

CDC Centers for Disease Control and Prevention

CERCLIS Comprehensive Environmental Response, 

Compensation, and Liability Information System

CFC chlorofluorocarbon

CH4 methane

CO carbon monoxide

CO2 carbon dioxide

CWS community water system

DDE dichlorodiphenyldichloroethane

DDT dichlorodiphenyltrichloroethane

DO dissolved oxygen

ECI Ecological Connectivity Indicator

EECl effective equivalent troposphere chlorine

EESC effective equivalent stratospheric chlorine

EMAP Environmental Monitoring and Assessment 

Program

EPA Environmental Protection Agency

ERS Economic Research Service

ETS environmental tobacco smoke

FIA Forest Inventory and Analysis

FY fiscal year

GHG greenhouse gas

GI gastrointestinal

GIS geographic information system

GOME Global Ozone Monitoring Experiment

GWP global warming potential

HAP hazardous air pollutant

HCB hexachlorobenzene

HCFC halogenated fluorocarbon

HFC hydrofluorocarbon

HUC hydrologic unit code

IBI Index of Biological Integrity

ICD International Classification of Diseases

IMPROVE Interagency Monitoring of Protected Visual 

Environments

K potassium

LBW low birthweight

LOD level of detection

LTM Long-Term Monitoring

LUMCON Louisiana Universities Marine Consortium

MCL Maximum Contaminant Level

km kilometer

μeq/L microequivalents per liter

μg/dL micrograms per deciliter

μg/L micrograms per liter

μg/m3 micrograms per cubic meter

μm micron

mm/yr millimeters per year

MT million tons

MtC/yr metric tons of carbon per year

ng/g nanograms per gram

ng/mL nanograms per milliliter

pg/g picograms per gram

ppb parts per billion

ppm parts per million

ppt parts per trillion

Units of Measure
APPENDIX A

A-2 EPA’s 2008 Report on the Environment

MDL method detection limit

MMT methylcyclopentadienyl manganese tricarbonyl

MRLC Multi-Resolution Land Characteristics

MSA metropolitan statistical area

N nitrogen

N2O nitrous oxide

NAAQS National Ambient Air Quality Standards

NASA National Air and Space Administration 

NASS National Agricultural Statistics Service

NATA National-Scale Air Toxics Assessment

NAWQA National Water-Quality Assessment

NCA National Coastal Assessment

NCDC National Climatic Data Center

NCHS National Center for Health Statistics

NCI National Cancer Institute

NEDS National Emissions Data System

NEI National Emissions Inventory

NHANES National Health and Nutrition Examination 

Survey

NHIS National Health Interview Survey

NIS non-indigenous species

NIWA National Institute of Water and Atmospheric 

Research

NLCD National Land Cover Database or National Land 

Cover Dataset

NNDSS National Notifiable Diseases Surveillance System

NOAA National Oceanic and Atmospheric 

Administration

NO nitric oxide

NO2 nitrogen dioxide

NOx nitrogen oxides 

NPL National Priorities List

NRC National Research Council

NRCS Natural Resources Conservation Service

NRI National Resources Inventory

NVSS National Vital Statistics System

O3 ozone

ODS ozone-depleting substance

O/E observed/expected

OMB Office of Management and Budget

OP organophosphate

OSWER Office of Solid Waste and Emergency Response

P phosphorus

PAH polycyclic aromatic hydrocarbon

PAN peroxyacetyl nitrate

PBDE polybrominated diphenyl ether

PBT persistent, bioaccumulative, and toxic

PCB polychlorinated biphenyl

PCC Poison Control Center

PDP Pesticide Data Program

PFC perfluorinated carbon

PM particulate matter

PM2.5 particles with aerodynamic diameters less than or 

equal to 2.5 microns

PM10 particles with aerodynamic diameters less than or 

equal to 10 microns

RBS Relative Bed Stability

RCRA Resource Conservation and Recovery Act

RfC reference concentration

ROE Report on the Environment

SAB Science Advisory Board

SAV submerged aquatic vegetation

SBUV Solar Backscatter Ultraviolet

SEER Surveillance, Epidemiology, and End Results

SEF Southeastern Ecological Framework

SF6 sulfur hexafluoride

SO2 sulfur dioxide

SST sea surface temperature

TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin

TEQ toxic equivalency quotient

TESS Toxic Exposure Surveillance System

TIME Temporally Integrated Monitoring of Ecosystems

TOMS Total Ozone Mapping Spectrometer

TRI Toxics Release Inventory

TSDF treatment, storage, and disposal facility

TSP total suspended particulates

TT Treatment Technique

USDA United States Department of Agriculture

USGS United States Geological Survey

UV ultraviolet

VOC volatile organic compound

WBDO waterborne disease outbreak

WISCARS Web-Based Injury Statistics Query and 

Reporting System

WSA Wadeable Streams Assessment
APPENDIX A

EPA’s 2008 Report on the Environment A-3

YPLL years of potential life lost

Glossary

A

advisory: A nonregulatory document that communicates 

risk information to those who may have to make risk 

management decisions. For example, a fish consumption 

advisory may recommend that people limit or avoid eating 

certain species of fish caught from certain lakes, rivers, 

or coastal waters. In some cases, advisories may include 

recommendations for specific groups (such as infants, 

children, the elderly, or women who are pregnant or may 

become pregnant). 

agricultural and animal waste: Waste generated by the 

production and harvest of crops or trees or the rearing of 

animals. Animal waste is a subset of agricultural waste and 

includes waste (e.g., feed waste, bedding and litter, and feedlot 

and paddock runoff) from livestock, dairy, and other animalrelated agricultural and farming practices.

air pollutant: Any substance in air that could, in high enough 

concentration, harm humans, animals, vegetation, or material. 

Air pollutants can include almost any natural or artificial 

composition of matter capable of being airborne—solid 

particles, liquid droplets, gases, or a combination thereof. 

Air pollutants are often grouped in categories for ease in 

classification; some of the categories are sulfur compounds, 

volatile organic compounds, particulate matter, nitrogen 

compounds, and radioactive compounds.

Air Quality Index (AQI): An index for reporting daily air 

quality that characterizes air pollution levels and associated 

health effects that might be of concern. EPA calculates the 

AQI for five criteria pollutants. AQI values range from 0 to 

500; the higher the AQI value, the greater the level of air 

pollution and the greater the health concern. AQI values 

below 100 are generally thought of as satisfactory. When 

AQI values are above 100, air quality is considered to be 

unhealthy—at first for certain sensitive groups of people, 

then for everyone as AQI values get higher. Refer to EPA’s 

AIRNOW Web site (http://www.epa.gov/airnow) for more 

information on the AQI and how it is calculated. 

Air Quality System (AQS): EPA’s electronic repository of 

ambient air monitoring data collected by EPA, state, local, 

and tribal air pollution control agencies from thousands of 

monitoring stations. The AQS contains monitoring data, 

descriptive information about monitoring stations, and data 

quality assurance and quality control information. 

air toxics: Air pollutants that cause or may cause cancer or 

other serious health effects, such as reproductive effects or 

birth defects, or adverse environmental and ecological effects. 

Examples of toxic air pollutants include benzene (found in 

gasoline), perchloroethylene (emitted from some dry cleaning 

facilities), and methylene chloride (used as a solvent by a 

number of industries). Air toxics are also known as hazardous 

air pollutants. 

anthropogenic: Originating from humans; not naturally 

occurring. 

area source: A source of air pollution that is released over an 

area that cannot be classified as a point source. Area sources 

can include vehicles and other small engines, small businesses 

and household activities, or biogenic sources such as a forest 

that releases hydrocarbons.

B

baseline: A reference condition against which changes or 

trends are judged—usually a set of conditions that exist at a 

particular point in time.

benchmark: A concentration or other accepted measure 

against which environmental conditions are compared.

bioaccumulative compound: A compound that tends 

to accumulate in tissues and build up in food webs. Some 

bioaccumulative compounds can potentially have adverse 

effects on ecosystems or human health.

biogenic source: An air emissions source created by some 

sort of biological activity. Examples include emissions resulting 

from microbial activity in soils and emissions from trees and 

other vegetation. Emissions from biogenic sources are a subset 

of emissions from natural sources (see natural source). 

biological balance: The interrelationships among organisms, 

including the structure of food webs and the ability of 

ecological systems to maintain themselves over time. Balance 

is a dynamic characteristic, rather than a fixed state.

biological diversity: The variety and variability among 

living organisms and the ecological complexes in which 

they occur. Though it most often refers to the numbers of 

species, the term can apply to levels of organization ranging 

from genes to ecosystems. 

biomarker: A molecular or cellular indicator (or “marker”) 

of an event or condition (exposure, effect, susceptibility) in a 

biological system or sample. It is the product of an interaction 

between a contaminant and some target molecule or cell. 

biomarker of effect: A measure of disease progression, 

representing a measurable alteration at the molecular, 

cellular, or some other structural level in the body that can 

be recognized as a potential or established adverse health 

effect. Such a biomarker can indicate a biological response or 

health effect related to a chemical or other stressor; however, 

it is not always possible to link a biomarker with exposure to 

a single substance. 
APPENDIX A

A-4 EPA’s 2008 Report on the Environment

biomarker of exposure: The level of a contaminant or 

its metabolite collected from the body or from substances 

produced or excreted within biological systems. In humans, 

this measurement can reflect the amount of the contaminant 

that is stored in the body, and is sometimes referred to as the 

body burden. It indicates the level of exposure. 

biomarker of susceptibility: A measurement of individual 

factors that can affect response to environmental agents. 

Examples include enzymes whose presence or absence may 

reflect a particular genetic condition. 

biomonitoring: The measurement of human tissues or 

excreta from biological systems for direct or indirect evidence 

of exposure to chemical, biological, or radiological substances. 

biotic environment: The biological component of an 

ecosystem, including plants and animals.

C

cleanup: Action taken to deal with a release (or threat of 

release) of a hazardous substance that could affect humans 

and/or the environment. This term is sometimes used 

interchangeably with the terms “remedial action,” “removal 

action,” “response action,” and “corrective action.”

climate change: A term sometimes used to refer to all forms 

of climatic inconsistency; because the Earth’s climate is never 

static, the term is more properly used to imply a significant 

change from one climatic condition to another. In some cases, 

“climate change” has been used synonymously with “global 

warming.” Scientists, however, tend to use “climate change” 

in the wider sense to also include natural changes in climate. 

coastal waters: Waters at the interface between terrestrial 

environments and the open ocean. Many unique habitats lie 

in coastal waters—for example, estuaries, coastal wetlands, 

seagrass meadows, coral reefs, mangrove and kelp forests, and 

upwelling areas. 

community: In ecology, an assemblage of populations of 

different species within a specified location in space and 

time. Sometimes, a particular subgrouping may be specified, 

such as the fish community in a lake or the soil arthropod 

community in a forest. 

community water system: A water system that supplies 

drinking water to 25 or more of the same people year-round 

in their residences. 

condition: The state of a resource, generally reflecting 

a combination of physical, chemical, and biological 

characteristics such as temperature, water clarity, chemical 

composition, or the status of biological communities. ROE 

questions address the condition of fresh surface waters, ground 

water, wetlands, coastal waters, recreational waters, and 

consumable fish and shellfish. (Also see ecological condition.)

construction and demolition debris: Waste materials 

generated during the construction, renovation, and demolition 

of buildings, roads, and bridges. Construction and demolition 

debris often contains bulky, heavy materials such as concrete, 

wood (from buildings), asphalt (from roads and roofing 

shingles), gypsum (from drywall), metals, bricks, glass, plastics, 

building components (doors, windows, plumbing fixtures), 

and trees, stumps, earth, and rock from clearing sites. 

contaminant: Any physical, chemical, biological, or 

radiological substance or matter that has an adverse effect on 

air, water, or soil. 

contaminated land: Land that has been polluted with 

hazardous materials and requires cleanup or remediation. 

Contaminated lands include sites contaminated as a result of 

improper handling or disposal of toxic and hazardous wastes, 

sites where improper handling or accidents released toxic or 

hazardous materials that are not wastes, and sites where toxics 

may have been deposited by wind or flooding.

criteria pollutants: A group of six widespread and common 

air pollutants that EPA regulates on the basis of standards 

set to protect public health or the environment (see National 

Ambient Air Quality Standards). The six criteria pollutants are 

carbon monoxide, lead, nitrogen dioxide, ozone, particulate 

matter, and sulfur dioxide. 

D

deleted NPL site: A site that has been deleted from the 

Superfund National Priorities List because its cleanup goals 

have been met and there is no further need for federal action. 

(See Superfund and National Priorities List.)

drinking water quality: Refers to whether contaminants are 

present in water that people drink—including water from the 

tap, private wells, hauled water, untreated surface water sources, 

and bottled water—at levels that could affect human health. 

drinking water standards: Regulations that EPA sets to 

control the level of contaminants in the nation’s drinking 

water. Enforceable standards include Maximum Contaminant 

Levels (MCLs) and Treatment Techniques (TTs) (see separate 

entries for each). Drinking water standards apply to all public 

water systems (see public water system). 

E

ecological condition: A term referring to the state of 

the physical, chemical, and biological characteristics of 

the environment, and the processes and interactions that 

connect them.

ecological connectivity: A term referring to the connected 

system of open space throughout an ecosystem and adjacent 

ecosystems. Includes the presence of ecotones, the transitional 

regions between ecosystems.

ecological processes: The metabolic functions of 

ecosystems—energy flow, elemental cycling, and the 

production, consumption, and decomposition of organic matter. 

ecological system: A hierarchically nested area that 

includes all living organisms (people, plants, animals, and 

microorganisms), their physical surroundings (such as soil, 

water, and air), and the natural cycles that sustain them. 
APPENDIX A

EPA’s 2008 Report on the Environment A-5

ecoregion: An area within which the ecosystems—and the 

type, quality, and quantity of environmental resources—

are generally similar. An ecoregion can serve as a spatial 

framework for the research, assessment, management, and 

monitoring of ecosystems and ecosystem components. Several 

different classification schemes have been developed, at various 

resolutions. For more information about EPA’s ecoregion 

designations for North America, visit http://www.epa.gov/

wed/pages/ecoregions/ecoregions.htm. 

ecosystem: The interacting system of a particular biological 

community and its non-living environmental surroundings, or 

a class of such systems (e.g., forests or wetlands). 

emission factor: The relationship between the amount of 

pollution produced by a particular source and the amount of 

raw material processed. For example, an emission factor for 

a blast furnace making iron might be pounds of particulates 

emitted per ton of raw materials processed. 

emission inventory: A listing, by source and pollutant, of 

the amount of air pollutants discharged into the atmosphere. 

Emission inventories can be based on emissions estimates, 

emissions measurements, or both. 

endpoint: A biological or ecological characteristic that is the 

basis for evaluation or measurement.

end state: Any one of a number of ecosystem characteristics 

observed at a point in time. The term is commonly used to 

represent the results of ecological processes.

EPA Region: One of ten EPA geographic divisions, each 

responsible for executing the Agency’s programs within a 

specific group of states and territories. A map of the EPA 

Regions is provided in Chapter 1, Exhibit 1-2.

ephemeral waters: Water bodies (e.g., streams or wetlands) 

that contain water for brief periods, usually in direct response 

to a precipitation event. Ephemeral waters generally flow for a 

shorter time period than intermittent waters, although in some 

cases the terms are used interchangeably (see intermittent waters). 

exposure: For humans, the amount of a chemical, physical, 

or biological contaminant at the outer boundary of the body 

available for exchange or intake via inhalation, ingestion, or 

skin or eye contact. 

extent: The amount and distribution of a resource, which 

may be measured in terms of spatial area, volume, depth, or 

flow (e.g., for water resources). ROE questions address the 

extent of fresh surface waters, ground water, wetlands, and 

coastal waters.

extraction and mining waste: Soil and rock generated 

during the process of gaining access to the ore or mineral 

body, as well as water that infiltrates the mine during the 

extraction process. This category also includes certain wastes 

associated with the beneficiation of ores and minerals, 

including wastes from the following activities: crushing, 

grinding, washing, dissolution, crystallization, filtration, 

sorting, sizing, drying, sintering, pelletizing, briquetting, 

calcining to remove water and/or carbon dioxide, roasting in 

preparation for leaching (except where the roasting/leaching 

sequence produces a final or intermediate product that does 

not undergo further beneficiation or processing), gravity 

concentration, magnetic separation, electrostatic separation, 

floatation, ion exchange, solvent extraction, electrowinning, 

precipitation, amalgamation, and heap, dump, vat, tank, and 

in situ leaching. 

F

final NPL site: A site that has been formally added to the 

Superfund National Priorities List. (See Superfund and National 

Priorities List.)

finished water: Water that has been treated and is ready to be 

delivered to customers. 

fossil fuel combustion waste: Waste from the combustion 

of oil, natural gas, or petroleum coke; the combustion of coal 

at electric utilities and independent power-producing facilities, 

non-utilities, and facilities with fluidized bed combustion 

technology; or the combustion of mixtures of coal and other 

fuels (i.e., coburning of coal with other fuels) where coal is at 

least 50 percent of the total fuel.

G

global climate change: See climate change.

greenhouse gas: Any gas that absorbs infrared radiation 

in the atmosphere. Greenhouse gases include water vapor, 

carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), 

halogenated fluorocarbons (HCFCs), ozone (O3), perfluorinated 

carbons (PFCs), and hydrofluorocarbons (HFCs). 

H

hazardous air pollutants: See air toxics. 

hazardous waste: Waste with properties that make it 

dangerous or potentially harmful to human health or 

the environment. The universe of hazardous wastes is 

large and diverse. Hazardous wastes can be liquids, solids, 

contained gases, or sludges. They can be the byproducts of 

manufacturing processes or simply discarded commercial 

products, like cleaning fluids or pesticides. Hazardous waste 

is regulated under the Resource Conservation and Recovery 

Act (RCRA) Subtitle C (see RCRA hazardous waste for the 

regulatory definition). States can identify additional wastes as 

hazardous beyond those identified by EPA. 

health-based standards: Standards based on contaminant 

concentrations in environmental media or exposure doses that 

are likely to be without an appreciable risk of adverse health 

effects in humans. (Some health-based standards allow for 

consideration of technological and cost limitations.)

hypoxia: The occurrence of low dissolved oxygen 

concentrations in water. Hypoxia is generally defined with 

respect to saturation; because saturation levels vary with 

temperature and salinity, the concentration that defines 

hypoxia may vary seasonally and geographically. In practice, 
APPENDIX A

A-6 EPA’s 2008 Report on the Environment

scientists often use a threshold of 2 parts per million, the 

generally accepted minimum required for most marine life to 

survive and reproduce. 

I

impervious surface: A hard surface area that either prevents 

or retards the entry of water into the soil mantle or causes 

water to run off the surface in greater quantities or at an 

increased rate of flow. Common impervious surfaces include 

rooftops, walkways, patios, driveways, parking lots, storage 

areas, concrete or asphalt paving, and gravel roads. 

index: A single number, derived from two or more 

environmental variables, that is intended to simplify complex 

information. For example, the Index of Biological Integrity 

combines several metrics of benthic community condition 

into a single index score. 

index period: In EPA’s aquatic resource monitoring, a 

term used to describe the portion of the year when data 

are collected. The index period is often selected based on 

ecological considerations. 

indicator: A numerical value 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. 

industrial non-hazardous waste: Waste generated from 

processes associated with the production of goods and 

products, such as electric power generation and manufacturing 

of materials such as pulp and paper, iron and steel, glass, and 

concrete. This waste usually is not classified as municipal solid 

waste by the federal government, but some states may classify 

it as such if it enters the municipal solid waste stream.

industrial source: A term used in this report to describe 

air emissions sources of industrial origin. The report breaks 

industrial sources down into contributions from selected 

industries, as appropriate. 

intermittent waters: Water bodies (e.g., streams or wetlands) 

that contain water for part of each year, due to precipitation 

events and some ground water contributions. Intermittent 

streams and wetlands typically contain water for weeks or 

months, while “ephemeral” streams and wetlands contain 

water for briefer periods—but in some cases these terms are 

used interchangeably (see ephemeral waters). 

invasive species: A non-indigenous plant or animal species 

that can harm the environment, human health, or the economy. 

L

land treatment unit: A site where physical, chemical, 

and biological processes occurring in the topsoil layers (e.g., 

naturally occurring soil microbes and sunlight) are used to 

treat and contain waste. Hazardous waste is applied directly 

to the soil surface or incorporated into the upper layers of 

the soil, where its constituents are degraded, transformed, 

or immobilized. Liner systems or leachate collection and 

removal systems are not required for land treatment units. 

Closure consists primarily of placing a vegetative cover over 

the unit and certifying that hazardous constituent levels in the 

treatment zone do not exceed background levels. 

landfill: A disposal site for solid wastes spread in layers, 

compacted to the smallest practical volume, and covered by 

material (e.g., soil). Landfills are designed to isolate waste 

from the surrounding environment (e.g., ground water, 

rain, air). Landfills are subject to requirements that include 

installing and maintaining a final cover, operating leachate 

collection and removal systems, maintaining and monitoring 

the leak detection system, ground water monitoring, 

preventing storm water run-on and -off, and installing and 

protecting surveyed benchmarks. 

M

Maximum Contaminant Level (MCL): The highest level 

of a contaminant that EPA allows in drinking water. MCLs 

are enforceable standards that ensure that drinking water does 

not pose either a short-term or long-term health risk. EPA 

sets MCLs at levels that are economically and technologically 

feasible. Some states set MCLs that are more strict than EPA’s. 

medical waste: Any solid waste generated in the diagnosis, 

treatment, or immunization of human beings or animals, in 

research pertaining thereto, or in the production or testing 

of biologicals, excluding hazardous waste identified or listed 

under 40 CFR Part 261 or any household waste as defined in 

40 CFR Sub-Section 261.4(b)(1). 

metal mining sector: Metal mining facilities that fall 

within Standard Industrial Classification Code 10 and must 

report to the Toxics Release Inventory in accordance with 

Section 313 of the Emergency Planning and Community 

Right to Know Act.

mobile source: A term used to describe a wide variety of 

vehicles, engines, and equipment that generate air pollution 

and that move, or can be moved, from place to place. 

“On-road” sources are vehicles used on roads to transport 

passengers or freight. “Nonroad” sources include vehicles, 

engines, and equipment used for construction, agriculture, 

transportation, recreation, and many other purposes. 

municipal solid waste: Waste from homes, institutions, 

and commercial sources consisting of everyday items such as 

product packaging, grass clippings, furniture, clothing, bottles 

and cans, food scraps, newspapers, appliances, consumer 

electronics, and batteries. (Excluded from this category are 

municipal wastewater treatment sludges, industrial process 

wastes, automobile bodies, combustion ash, and construction 

and demolition debris.)

N

National Ambient Air Quality Standards (NAAQS): 

Standards established by EPA that apply to outdoor air 
APPENDIX A

EPA’s 2008 Report on the Environment A-7

throughout the country. The Clean Air Act established two 

types of national air quality standards. Primary standards 

set limits to protect public health, including the health of 

“sensitive” populations such as asthmatics, children, and 

the elderly. Secondary standards set limits to protect public 

welfare, including protection against decreased visibility and 

damage to animals, crops, vegetation, and buildings. EPA has 

set NAAQS for the six criteria pollutants. 

National Indicator: An ROE indicator for which nationally 

consistent data are available, and which helps to answer an 

ROE question at a national scale. Some National Indicators also 

present data broken down by EPA Region. (See ROE indicator.)

National Priorities List (NPL): EPA’s list of the most 

serious uncontrolled or abandoned hazardous waste sites 

identified for possible long-term remedial action under 

Superfund. (See Superfund.)

natural source: A term used in this report to describe any 

air emissions source of natural origin. Examples include 

volcanoes, wild fires, wind-blown dust, and releases due to 

biological processes (see biogenic source).

non-indigenous species: A species that has been 

introduced by human action, either intentionally or by 

accident, into an area outside its natural geographical range; 

also called an alien, exotic, introduced, or non-native species. 

Certain non-indigenous species are considered “invasive.” 

(See invasive species.) 

non-production-related waste: Waste that is not 

production-related; for example, waste associated with 

catastrophic events and cleanup actions. Toxic chemicals in 

non-production-related waste must be reported to the Toxics 

Release Inventory (see Toxics Release Inventory). 

non-transient non-community water system: A type of 

public water system that supplies water to 25 or more of the 

same people at least 6 months per year in places other than 

their residences. Some examples are schools, factories, office 

buildings, and hospitals that have their own water systems. 

(See public water system.) 

nonpoint source: A diffuse source of pollution, having no 

single point of origin. This term is commonly used to describe 

water pollution caused by rainfall or snowmelt moving over 

and through the ground and carrying natural and humanmade contaminants into lakes, rivers, streams, wetlands, 

estuaries, other coastal waters, and ground water. Atmospheric 

deposition and hydrologic modification are also sources of 

nonpoint water pollution. 

non-public water system: A water system that does not 

provide water for human consumption through at least 15 

service connections, or regularly serve at least 25 individuals, 

for at least 60 days per year. 

nutrient: Any substance assimilated by living things that 

promotes growth. The term is generally applied to nitrogen 

and phosphorus but is also applied to other essential and trace 

elements.

O

oil and gas production waste: Gas and oil drilling muds, 

oil production brines, and other waste associated with 

exploration for, or development and production of, crude oil 

or natural gas. 

onsite treatment: See treatment.

ozone-depleting substance: Any compound that 

contributes to stratospheric ozone depletion (see ozone 

depletion). 

ozone depletion: Destruction of the stratospheric ozone 

layer, which shields the Earth from ultraviolet radiation 

harmful to life. This destruction of ozone is caused by the 

breakdown of certain chlorine- and/or bromine-containing 

compounds (chlorofluorocarbons or halons). These 

compounds break down when they reach the stratosphere and 

then catalytically destroy ozone molecules. 

P

point source: A fixed location or facility that discharges 

pollution—for example, a factory smokestack, a ship, an ore 

pit, a ditch, or a pipe discharging treated industrial wastewater 

or treated sewage into a waterway. 

pollutant: Any substance introduced into the environment 

that may adversely affect the usefulness of a resource or 

the health of humans, animals, or ecosystems. For most 

environmental media, this term is commonly understood to 

refer to substances introduced by human activities. In the case 

of air, the convention is to include substances emitted from 

natural sources as well (see air pollutant). 

population: In ecology, a group of interbreeding organisms 

occupying a particular space. In other contexts, including 

human health, this term generally refers to the number of 

humans living in a designated area. 

precursor: In photochemistry, any compound antecedent 

to a pollutant. For example, volatile organic compounds 

(VOCs) and nitrogen oxides react in sunlight to form 

ozone or other photochemical oxidants. As such, VOCs and 

nitrogen oxides are precursors. 

primary pollutant: Any pollutant that is emitted into the 

atmosphere directly from its source and that retains the same 

chemical form. An example of a primary pollutant is dust that 

blows into the air from a landfill. 

Priority Chemicals: A set of chemicals, found in the nation’s 

products and wastes, that EPA targets for voluntary reduction 

(or recovery and recycling if they cannot be eliminated 

or reduced at the source). The list of Priority Chemicals 

is available at http://www.epa.gov/epaoswer/hazwaste/

minimize/chemlist.htm. 

production-related waste: The sum of a facility’s 

production-related onsite waste releases, onsite waste 

management (recycling, treatment, and combustion for 

energy recovery), and offsite transfers for disposal, treatment, 
APPENDIX A

A-8 EPA’s 2008 Report on the Environment

recycling, or energy recovery. Toxic chemicals in productionrelated waste must be reported to the Toxics Release Inventory 

(see Toxics Release Inventory). 

public water system: A system that provides water for 

human consumption through at least 15 service connections, 

or regularly serves at least 25 individuals, for at least 60 days 

per year. Public water systems are divided into three categories 

(see community water system, non-transient non-community water 

system, and transient non-community water system). Examples 

of public water systems include municipal water companies, 

homeowner associations, schools, businesses, campgrounds, 

and shopping malls. 

R

radioactive waste: Waste containing substances that 

emit ionizing radiation. Radioactive waste is classified by 

regulation according to its source and/or content. The types 

of waste that are typically considered “radioactive waste” 

include high-level waste, low-level waste, mixed low-level 

waste, transuranic waste (i.e., elements heavier than uranium), 

and certain wastes from the extraction and processing 

of uranium or thorium ore. Spent nuclear fuel, which is 

produced as a result of the controlled nuclear fission process in 

nuclear reactors, is considered a nuclear material rather than 

radioactive waste. 

RCRA Cleanup Baseline: A priority subset of the universe 

of facilities that are subject to cleanup under the Resource 

Conservation and Recovery Act (RCRA) due to past or 

current treatment, storage, or disposal of hazardous wastes, 

and that have historical releases of contamination.

RCRA hazardous waste: A national regulatory designation 

for certain wastes under the Resource Conservation 

and Recovery Act (RCRA). Some wastes are given this 

designation because they are specifically listed on one of 

four RCRA hazardous waste lists (see http://www.epa.

gov/epaoswer/osw/hazwaste.htm). Other wastes receive 

this designation because they exhibit at least one of four 

characteristics—ignitability, corrosivity, reactivity, or toxicity. 

Regional Indicator: An ROE indicator that helps to answer 

an ROE question on a smaller-than-national geographic scale. 

A Regional Indicator may cover a topic for which nationally 

consistent data are unavailable, or it may present an issue that 

is of particular concern within a certain geographic area. (See 

ROE indicator.)

risk factor: A characteristic (e.g., race, sex, age, obesity) or 

variable (e.g., smoking, occupational exposure level) associated 

with increased probability of an adverse effect. 

ROE indicator: An indicator that meets the ROE criteria (see 

Box 1-1, p. 1-8) and has been peer-reviewed. (See indicator.)

S

secondary pollutant: Any pollutant that is formed by 

atmospheric reactions of precursor or primary emissions. An 

example of a secondary pollutant is ground-level ozone, which 

forms from chemical reactions involving airborne nitrogen 

oxides, airborne volatile organic compounds, and sunlight.

sewage sludge: A semi-solid residue from any of a number of 

air or water treatment processes. When treated and processed, 

sewage sludge becomes a nutrient-rich organic material called 

biosolids. 

stratosphere: The layer of the atmosphere that starts about 6 

to 9 miles above the Earth’s surface at mid-latitudes and lies 

atop the troposphere. The stratosphere contains small amounts 

of gaseous ozone, which filters out about 99 percent of the 

incoming ultraviolet radiation. 

stressor: A physical, chemical, or biological entity that can 

induce adverse effects on ecosystems or human health. 

Superfund: A program, operated under the legislative 

authority of the Comprehensive Environmental Response, 

Compensation, and Liability Act and the Superfund 

Amendments and Reauthorization Act, that funds and carries 

out EPA solid waste emergency and long-term removal and 

remedial activities. These activities include establishing the 

National Priorities List, investigating sites for inclusion on 

the list, determining their priority, and conducting and/or 

supervising cleanup and other remedial actions. (See National 

Priorities List.)

T

toxic chemical: A chemical that can produce injury if 

inhaled, swallowed, or absorbed through the skin.

Toxics Release Inventory (TRI): A database containing 

detailed information on nearly 650 chemicals and chemical 

categories that over 23,000 industrial and other facilities 

manage through disposal or other releases, recycling, 

combustion for energy recovery, or treatment. 

Toxics Release Inventory (TRI) chemicals: The 

chemicals and chemical categories that appear on the current 

TRI toxic chemical list. As of December 2007, the TRI toxic 

chemical list contains 581 individually listed chemicals and 

30 chemical categories (including three delimited categories 

containing 58 chemicals). The list of TRI chemicals is 

available at http://www.epa.gov/tri/chemical/index.htm.

Toxics Release Inventory (TRI) facilities: The facilities 

that are required by Section 313 of the Emergency Planning 

and Community Right to Know Act to report to the TRI. 

In the 2005 reporting year, approximately 23,500 facilities 

reported to the TRI.

transient non-community water system: A type of 

public water system that provides water in a place—such as 

a gas station or campground—where people do not remain 

for long periods of time. These systems do not have to test or 

treat their water for contaminants that pose long-term health 

risks, because fewer than 25 people drink the water over a 

long period. They still must test their water for microbes and 

several chemicals. (See public water system.) 
APPENDIX A

EPA’s 2008 Report on the Environment A-9

treatment: Any process that changes the physical, chemical, 

or biological character of a waste to make it less of an 

environmental threat. Treatment can neutralize the waste, 

recover energy or material resources from it, render it less 

hazardous, or make it safer to transport, store, or dispose of. 

Treatment Technique (TT): A required process intended 

to reduce the level of a contaminant in drinking water. 

troposphere: The layer of the atmosphere closest to the 

Earth’s surface. The troposphere extends from the surface up 

to about 6 to 9 miles. 

U

underground injection: The technology of placing fluids 

underground in porous formations of rocks, through wells or 

other conveyance systems. The fluids may be water, wastewater, 

or water mixed with chemicals. Regulations for disposing 

of waste this way vary depending on type of waste. RCRA 

hazardous waste is placed in highly regulated (Class 1) wells. 

urbanization: The concentration of development in 

relatively small areas (cities and suburbs). The U.S. Census 

Bureau defines “urban” as referring to areas with more than 

1.5 people per acre.

W

wadeable stream: A stream, creek, or small river that is 

shallow enough to be sampled using methods that involve 

wading into the water. Wadeable streams typically include 

waters classified as first through fourth order in the Strahler 

Stream Order classification system. 

wetland: An area that is inundated or saturated by surface 

or ground water at a frequency and duration sufficient to 

support, and that under normal circumstances does support, a 

prevalence of vegetation typically adapted for life in saturated 

soil conditions. Wetlands generally include swamps, marshes, 

bogs, and similar areas. 
APPENDIX B

EPA’s 2008 Report on the Environment B-1

T

he 2008 ROE was developed by EPA’s Office of 

Research and Development, working in collaboration 

with EPA’s program and Regional offices as well as external partners. This appendix describes the key elements of the 

2008 ROE development process. 

Laying the Foundation

EPA published its Draft Report on the Environment in June 

2003 and invited feedback. The Agency received comments 

from several sources:

•	The Science Advisory Board (SAB) reviewed the 2003 Draft 

ROE Technical Document in March 2004, issuing draft 

comments shortly afterwards and publishing final comments 

in December 2004.1

•	Through February 2004, the public provided comments on 

the 2003 Draft ROE Technical Document via EPA’s online 

public comment system.2

•	Stakeholders commented on the 2003 Draft ROE Public 

Report during six dialogue sessions across the nation in 

2003 and early 2004.3

In January 2004, the EPA Administrator requested that work 

begin to develop the next version of the ROE. Exhibit B-1 

shows the organizational structure for development of EPA’s 

2008 ROE.4 A standing ROE Work Group took the lead in 

all phases of development. The group included five theme 

leads, each responsible for development of a particular chapter 

of the 2008 ROE, plus representatives of EPA Regions and 

other relevant EPA offices. During the development process, 

the theme leads coordinated with other federal agencies and 

organizations involved in indicator development or data collection. An Environmental Indicators Steering Committee, 

composed of senior managers from across the Agency, oversaw 

development of the ROE. The Steering Committee reviewed 

Work Group activities and draft products.

Environmental Indicators

Steering Committee

ROE Work Group

Chapter Leads

• Office of Research and

Development 

• Office of Air and Radiation

• Office of Water

• Office of Solid Waste and

Emergency Response 

Other Participants

• Office of Prevention, Pesticides 

and Toxic Substances

Office of Policy, Economics 

and Innovation 

•

Office of the Chief Financial 

Officer 

•

• Office of Environmental 

Information 

• EPA Regions

Exhibit B-1. Organizational structure for development of EPA’s 2008 ROE

Other federal agencies 

and organizations 

involved in indicator or 

data development

Appendix B:

Development of EPA’s 2008 ROE

1 U.S. Environmental Protection Agency. 2004. EPA’s Draft Report on the 

Environment (ROE) 2003: An advisory by the ROE Advisory Panel of the 

EPA Science Advisory Board. Science Advisory Board. EPA/SAB/05/004. 

<http://yosemite.epa.gov/sab/sabproduct.nsf/18246BED9FB52FE085256F

6A006BC3C1/$File/SAB-05-004_unsigned.pdf>

2 U.S. Environmental Protection Agency. 2004. E-docket for Draft 

Report on the Environmental Technical Document. Docket Number: 

OEI-2003-0030. <http://www.regulations.gov/fdmspublic/component/

main?main=DocketDetail&d=EPA-HQ-OEI-2003-0030>

3 U.S. Environmental Protection Agency. 2004. Summary report of the 

National Dialogue on the EPA Draft Report on the Environment 2003. 

Office of Environmental Information. <http://www.epa.gov/Envindicators/

docs/National_Dialogue_Summary_Report.pdf>

4 An additional organizational element, the Indicators Work Group, was 

added to the process as the indicators were being finalized for the July 

2005 peer review. The Indicators Work Group provided coordination 

between the ROE Work Group and the Environmental Indicators Steering 

Committee.
APPENDIX B

B-2 EPA’s 2008 Report on the Environment

The ROE is based on three components:

•	A series of fundamental questions about the condition of 

the nation’s air, water, and land; about human exposure and 

health; and about the condition of ecological systems. These 

are questions that the Agency considers to be of critical 

importance to its mission. 

•	An indicator definition. 

•	Criteria against which indicators are evaluated to ensure 

that they are useful, objective, transparent, and scientifically reliable.

The first step in developing the 2008 ROE was to review and 

refine the 2003 Draft ROE version of these components:

•	Questions. Over 100 EPA specialists from across the 

Agency were convened in the five ROE theme areas: air, 

water, land, human exposure and health, and ecological 

condition. Each theme team was charged with considering 

feedback and refining the ROE questions. The questions 

were finalized after review by the Environmental Indicators 

Steering Committee in 2004.

•	Indicator definition and criteria. The 2003 Draft ROE 

indicator definition and criteria were refined for the 2008 

ROE using an iterative process that included input from 

EPA specialists and review by the Environmental Indicators Steering Committee. Care was taken to ensure that 

the criteria were consistent with requirements of EPA’s 

Information Quality Guidelines. 

Indicator Development

Once the questions, definition, and criteria were refined, the 

next step was to identify and develop indicators to answer 

the questions.

•	2003 Draft ROE indicators were screened against the 2008 

ROE indicator definition and criteria. Many 2003 Draft 

ROE indicators were proposed for the 2008 ROE; some 

were withdrawn; and some were combined into other indicators (see Appendix C for details).

•	Ideas for new indicators were solicited from across EPA, 

other federal agencies, and organizations. Newly proposed 

indicators were screened for their ability to meet the indicator definition and criteria and for their value in answering 

the ROE questions. 

For each indicator that passed screening, three components 

were developed: text describing the indicator, a graphic or 

table displaying the indicator data, and a metadata form that 

documents the data source and quality (see Box B-1).

The 2008 ROE development team worked with staff at other 

departments, agencies, and private organizations that originally 

developed indicators or provided indicator data to ensure that 

indicator graphics, data, and quality assurance information were 

up to date and accurate. Indicators were reviewed by the Environmental Indicators Steering Committee.

•	Describe the physical, chemical, or biological measurements upon which this indicator is based. Are these measurements widely accepted as scientifically and technically 

valid? Explain. 

•	Describe the sampling design and/or monitoring plan 

used to collect the data over time and space. Is it based on 

sound scientific principles? Explain.

•	Describe the conceptual model used to transform these 

measurements into an indicator. Is this model widely 

accepted as a scientifically sound representation of the 

phenomenon it indicates? Explain. 

•	For which ROE question(s) is this indicator used? 

To what extent is the indicator sampling design and 

monitoring plan appropriate for answering the relevant 

question(s) in the ROE? 

•	To what extent does the sampling design represent sensitive populations or ecosystems? 

•	What, if any, are the established reference points, thresholds, or ranges of values for this indicator that unambiguously reflect the state of the environment? 

•	What documentation clearly and completely describes the 

underlying sampling and analytical procedures used? 

•	To what extent is the complete data set accessible, including metadata, data-dictionaries, and embedded definitions? Are there confidentiality issues that may limit 

accessibility to the complete data set? 

•	Are the descriptions of the study or survey design clear, 

complete, and sufficient to enable the study or survey to 

be reproduced? Explain. 

•	To what extent are the procedures for quality assurance and quality control of the data documented and 

accessible? 

•	What statistical methods, if any, have been used to generalize or portray data beyond the time or spatial locations 

where measurements were made (e.g., statistical survey 

inference, no generalization is possible)? Are these methods scientifically appropriate? 

•	What uncertainty measurements or estimates are available 

for the indicator and/or the underlying data set? 

•	To what extent do uncertainty and variability impact the 

conclusions that can be inferred from the data and the 

utility of the indicator?

•	Describe any limitations, or gaps in the data that may mislead a user about fundamental trends in the indicator over 

space or over the time period for which data are available.

Box B-1. Questions Addressed in the 2008 ROE Metadata Forms
APPENDIX B

EPA’s 2008 Report on the Environment B-3

•	Indicate the extent to which you think the proposed 

indicator is appropriate, adequate, and useful for evaluating

______.a

•	Indicate the extent to which you think the proposed indicator makes an important contribution to answering the 

specific ROE question it is intended to answer.

•	To what extent do you think the indicator meets the 

indicator definition?

•	To what extent do you think the indicator meets each of 

the indicator criteria? 

•	Do you have any suggestions for more effective graphic 

presentation of the data? Provide any additional comments,

suggestions, or concerns regarding the indicator that you 

have not already noted earlier. In particular, note any limitations to the indicator. 

•	Select one: Overall, this indicator (1) ___ should be 

included in the ROE; (2) ___ should be included in the 

ROE with the modifications identified above; or (3) ___ 

should not be included in the ROE.

•	Do any of the proposed indicators clearly seem to be 

more appropriate, adequate, or useful for evaluating 

______a than others? Do any seem to be more important 

than the others for answering the question(s) they are 

intended to answer?

•	Are there any additional national-level indicators that 

make an important contribution to answering one of 

the ROE questions in your topic area, but were not 

proposed for the ROE, that you would recommend? As 

you consider this question, consider the list of indicators 

presented in ROE03 that EPA does not intend to carry 

forward to the 2008 ROE, along with EPA’s rationale 

for withdrawing them. If you disagree with EPA’s rationale and feel any of these indicators should be included 

in the ROE, please so indicate in your response to this 

question, along with your rationale for why they should 

be included. 

Indicator Peer Review and Public Comment

Once the full suite of proposed indicators was assembled, 

all indicators were independently peer-reviewed by nationally recognized experts to ensure that they were scientifically 

sound and properly documented, met the indicator definition 

and criteria, and were useful for answering the questions posed 

in the ROE. Two rounds of review were conducted:

•	At a workshop in July 2005, 21 experts reviewed the initial 

set of 88 proposed indicators.

•	In November 2005, nine experts reviewed 11 indicators 

that were new or had been substantially revised since the 

July 2005 review.

The peer review, organized by a contractor, was conducted 

following the Office of Management and Budget’s (OMB’s) 

specifications for peer review of “Highly Influential Scientific 

Assessments” as specified in OMB’s “Final Information Quality 

Bulletin for Peer Review.”5 The reviewer selection criteria, list 

of reviewers, charge to reviewers, and reviewer comments can 

be found in the peer review summary report.6

 EPA announced 

the peer reviews in the Federal Register and also posted the 

proposed indicators on a Web site for public comment. Key 

questions addressed during the review are listed in Box B-2. 

After the peer review and public comment period, EPA revised 

and finalized the indicators. EPA’s responses to reviewer and 

public comments are available at EPA’s ROE Web site: http://

www.epa.gov/roe.

ROE Review

Concurrent with indicator development, EPA’s ROE team, 

working with specialists across the Agency, developed the 

text elements of the 2008 ROE. The final indicators were 

incorporated into the text to produce the full 2008 ROE. 

This draft document was reviewed internally at EPA, externally by other federal agencies and OMB, and externally by 

SAB (including public comment on the federal docket). EPA 

revised the document based on comments and, after the third 

review, finalized it for publication. 

Box B-2. Charge Questions for Peer Review of the Proposed 2008 ROE Indicators

a This part of the charge varied according to theme area as follows:

•	Air: “our nation’s air and therefore useful for contributing to an overall 

picture of our nation’s air”

•	Water: “our nation’s waters and for contributing to an overall picture of 

our nation’s waters”

•	Chemicals on land: “trends in chemicals used on land and their effects 

on human health and the environment”

•	Land wastes: “trends in wastes and their effects on human health and 

the environment”

•	Human health: “human health and for contributing to an overall picture of human health”

•	Ecological condition: “ecological conditions and therefore useful for 

contributing to an overall picture of ecological conditions”

5 Office of Management and Budget. 2004. Final information quality bulletin for peer review. December 16, 2004. <http://www.whitehouse.gov/

omb/memoranda/fy2005/m05-03.pdf>

6 U.S. Environmental Protection Agency. 2006. Report of the peer review 

of proposed ROE07 indicators. Office of Research and Development. 

<http://cfpub.epa.gov/eroe/index.cfm?fuseaction=main.peerReview> 
APPENDIX C

EPA’s 2008 Report on the Environment C-1

•	Indicators new to the 2008 report are listed in bold font. 

•	Indicators in the 2003 report but withdrawn in 2008 are 

highlighted in gray.

•	The rationale for withdrawing indicators is explained at the 

end of this appendix.

•	Some indicators are used to answer more than one ROE 

question; indicators are listed in the table below only 

where they are first used to answer an ROE question in the 

2008 report. 

Appendix C:

Comparison of Indicators Used in 

EPA’s 2008 ROE and the 2003 Draft ROE

Outdoor Air Quality

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Lead Emissions Lead Emissions

Ambient Concentrations of Lead Ambient Concentrations of Lead

Nitrogen Oxides Emissions Emissions: Particulate Matter (PM2.5 and PM10),

Sulfur Dioxide, Nitrogen Oxides, and Volatile Organic 

Compounds

Emissions (Utility): Sulfur Dioxide and Nitrogen Oxides

Volatile Organic Compounds Emissions Emissions: Particulate Matter (PM2.5 and PM10),

Sulfur Dioxide, Nitrogen Oxides, and Volatile Organic 

Compounds

Ambient Concentrations of Ozone Ambient Concentrations of Ozone: 8-hour and 1-hour

Ozone Injury to Forest Plants Ozone Injury to Trees (from the ecological condition 

chapter)

Particulate Matter Emissions Emissions: Particulate Matter (PM2.5 and PM10),

Sulfur Dioxide, Nitrogen Oxides, and Volatile Organic 

Compounds

Ambient Concentrations of Particulate Matter Ambient Concentrations of Particulate Matter: PM2.5

and PM10

Regional Haze Visibility

Sulfur Dioxide Emissions Emissions: Particulate Matter (PM2.5 and PM10),

Sulfur Dioxide, Nitrogen Oxides, and Volatile Organic 

Compounds

Emissions (Utility): Sulfur Dioxide and Nitrogen Oxides

Acid Deposition Deposition: Wet Sulfate and Wet Nitrogen

Atmospheric Deposition of Nitrogen (from the water 

chapter)

Air Chapter
APPENDIX C

C-2 EPA’s 2008 Report on the Environment

Outdoor Air Quality

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Lake and Stream Acidity Acid Sensitivity in Lakes and Streams (from the water 

chapter)

Percent of Days with Air Quality Index Values Greater 

Than 100 

Number and Percentage of Days That Metropolitan 

Statistical Areas (MSAs) Have Air Quality Index (AQI) 

Values Greater Than 100

Air Toxics Emissions Air Toxics Emissions

Ambient Concentrations of Benzene Ambient Concentrations of Selected Air Toxics

Concentrations of Ozone-Depleting Substances Concentrations of Ozone-Depleting Substances (Effective 

Equivalent Chlorine)

Ozone Levels over North America Ozone Levels over North America

Carbon Monoxide Emissions 

Ambient Concentrations of Carbon Monoxide 

Ambient Concentrations of Nitrogen Dioxide

Mercury Emissions 

Ozone and Particulate Matter Concentrations for U.S. 

Counties in the U.S./Mexico Border Region

Ambient Concentrations of Manganese Compounds in EPA 

Region 5

Withdrawn Worldwide and U.S. Production of Ozone-Depleting 

Substances (ODSs)

Withdrawn Number of People Living in Areas with Air Quality Levels 

Above the NAAQS for Particulate Matter (PM) and Ozone

Greenhouse Gases

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

U.S. Greenhouse Gas Emissions 

Atmospheric Concentrations of Greenhouse Gases 

Indoor Air Quality

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

U.S. Homes Above EPA’s Radon Action Level U.S. Homes Above EPA’s Radon Action Levels

Blood Cotinine Level Blood Cotinine Level; Blood Cotinine Level in Children 

(from the human health chapter)

Withdrawn Percentage of Homes Where Young Children Are Exposed 

to Environmental Tobacco Smoke
APPENDIX C

EPA’s 2008 Report on the Environment C-3

Ground Water

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Nitrate and Pesticides in Shallow Ground Water in 

Agricultural Watersheds

Pesticides in Farmland Streams and Ground Water

Nitrate in Farmland, Forested, and Urban Streams and 

Ground Water (partially replaced, partially withdrawn)

Withdrawn Nitrate in Farmland, Forested, and Urban Streams and 

Ground Water (partially withdrawn)

Fresh Surface Waters

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

High and Low Stream Flows Changing Stream Flows

Number/Duration of Dry Stream Flow Periods in

Grassland/Shrublands

Nitrogen and Phosphorus in Streams in Agricultural 

Watersheds

Nitrate in Farmland, Forested, and Urban Streams and 

Ground Water (partially replaced, partially withdrawn)

Phosphorus in Farmland, Forested, and Urban Streams 

(partially replaced, partially withdrawn)

Nitrogen and Phosphorus Loads in Large Rivers Partly new information and partly from indicator: Movement 

of Nitrogen (from the ecological condition chapter)

Pesticides in Streams in Agricultural Watersheds Pesticides in Farmland Streams and Ground Water 

Benthic Macroinvertebrates in Wadeable Streams Macroinvertebrate Biotic Integrity Index for Streams

Streambed Stability in Wadeable Streams 

Nitrogen and Phosphorus in Wadeable Streams

Withdrawn Altered Fresh Water Ecosystems 

Withdrawn Lake Trophic State Index

Withdrawn Percent Urban Land Cover in Riparian Areas 

Withdrawn Agricultural Lands in Riparian Areas 

Withdrawn Sedimentation Index

Withdrawn Nitrate in Farmland, Forested, and Urban Streams and 

Ground Water (partially withdrawn)

Withdrawn Phosphorus in Farmland, Forested, and Urban Streams 

(partially withdrawn)

Withdrawn Phosphorus in Large Rivers

Withdrawn Atmospheric Deposition of Mercury 

Withdrawn Chemical Contamination in Streams and Ground Water 

Withdrawn Sediment Contamination of Inland Waters 

Withdrawn Fish Index of Biotic Integrity in Streams

Water Chapter
APPENDIX C

C-4 EPA’s 2008 Report on the Environment

Wetlands

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Wetland Extent, Change, and Sources of Change Wetland Extent and Change

Sources of Wetland Change/Loss

Drinking Water

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Population Served by Community Water Systems with No 

Reported Violations of Health-Based Standards

Population Served by Community Water Systems That 

Meet All Health-Based Standards

Recreational Waters

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Withdrawn Number of Beach Days That Beaches Are Closed or Under 

Advisory

Coastal Waters 

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Trophic State of Coastal Waters Water Clarity in Coastal Waters 

Dissolved Oxygen in Coastal Waters 

Chlorophyll Concentrations

Total Nitrogen in Coastal Waters

Total Phosphorus in Coastal Waters

Coastal Sediment Quality Sediment Contamination of Coastal Waters 

Sediment Toxicity in Estuaries

Coastal Benthic Communities Benthic Community Index (for Coastal Waters) (presented 

in both the water and ecological condition chapters)

Submerged Aquatic Vegetation in the Chesapeake Bay Submerged Aquatic Vegetation (changed to a Regional 

Indicator; from the ecological condition chapter)

Hypoxia in the Gulf of Mexico and Long Island Sound 

Withdrawn Total Organic Carbon in Sediments

Withdrawn Population Density in Coastal Areas 
APPENDIX C

EPA’s 2008 Report on the Environment C-5

Consumable Fish and Shellfish

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Coastal Fish Tissue Contaminants Chemical Contamination (from the ecological condition 

chapter) (partially withdrawn)

Contaminants in Lake Fish Tissue Contaminants in Fresh Water Fish

Withdrawn Percent of River Miles and Lake Acres Under Fish 

Consumption Advisories

Withdrawn Number of Watersheds Exceeding Health-Based National 

Water Quality Criteria for Mercury and PCBs in Fish Tissue

Land Cover

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Land Cover Extent of Grasslands and Shrublands

Extent of Forest Area, Ownership, and Management

Patches of Forest, Grassland, Shrubland, and Wetland 

in Urban/Suburban Areas (from the ecological condition 

chapter)

Ecosystem Extent (from the ecological condition chapter)

Land Cover in the Puget Sound/Georgia Basin 

Land Use

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Land Use Extent of Urban and Suburban Lands

Extent of Agricultural Land Uses

Urbanization and Population Change Extent of Developed Lands (plus land chapter introduction 

from 2003 Draft ROE)

Withdrawn The Farmland Landscape

Withdrawn Sediment Runoff Potential from Croplands and Pasturelands

Land Chapter
APPENDIX C

C-6 EPA’s 2008 Report on the Environment

Wastes

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Quantity of Municipal Solid Waste Generated and Managed Quantity of Municipal Solid Waste (MSW) Generated and 

Managed

Number and Location of Municipal Solid Waste (MSW) 

Landfills 

Quantity of RCRA Hazardous Waste Generated and 

Managed 

Quantity of RCRA Hazardous Waste Generated and 

Managed

Number and Location of RCRA Hazardous Waste 

Management Facilities (partially replaced, partially 

withdrawn)

Withdrawn Quantity of Radioactive Waste Generated and in Inventory

Withdrawn Number and Location of Municipal Solid Waste (MSW) 

Landfills (partially withdrawn)

Withdrawn Number and Location of RCRA Hazardous Waste 

Management Facilities (partially withdrawn)

Withdrawn Number and Location of Superfund National Priorities List 

(NPL) Sites

Withdrawn Number and Location of RCRA Corrective Action Sites

Chemicals Used on the Land

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Fertilizer Applied for Agricultural Purposes Fertilizer Use 

Toxic Chemicals in Production-Related Wastes Combusted 

for Energy Recovery, Released, Treated, or Recycled

Quantity and Type of Toxic Chemicals Released and 

Managed

Number and Location of RCRA Hazardous Waste 

Management Facilities (partially replaced, partially 

withdrawn)

Pesticide Residues in Food Pesticide Residues in Food

Reported Pesticide Incidents 

Withdrawn Agricultural Pesticide Use

Withdrawn Potential Pesticide Runoff from Farm Fields

Withdrawn Risk of Nitrogen Export

Withdrawn Risk of Phosphorus Export

Withdrawn Pesticide Leaching Potential (from the ecological condition 

chapter)
APPENDIX C

EPA’s 2008 Report on the Environment C-7

Contaminated Land

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Current Human Exposures Under Control at High-Priority 

Cleanup Sites

Migration of Contaminated Ground Water Under Control at 

High-Priority Cleanup Sites 

Exposure to Environmental Contaminants

2008 ROE Indicator Title Corresponding 2003 Draft ROE Indicator Title

Blood Lead Level Blood Lead Level

Blood Lead Level in Children 

Blood Mercury Level Blood Mercury Level

Blood Mercury Level in Children

Blood Cadmium Level Blood Cadmium Level

Urinary Pesticide Level Urine Organophosphate Levels to Indicate Pesticides

Blood Persistent Organic Pollutants Level

Urinary Phthalate Level

Withdrawn Urine Arsenic Level

Withdrawn Blood Volatile Organic Compound Levels

Human Exposure and Health Chapter

Health Status

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

Life Expectancy at Birth Life Expectancy

Infant Mortality Infant Mortality

General Mortality (partially based on “Leading Causes of Death” in the 

contextual information provided in the 2003 Draft ROE 

human health chapter)
APPENDIX C

C-8 EPA’s 2008 Report on the Environment

Disease and Conditions

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

Cancer Incidence Cancer Incidence

Childhood Cancer Incidence Childhood Cancer Incidence

Cardiovascular Disease Prevalence and Mortality Cardiovascular Disease Mortality

Cardiovascular Disease Prevalence

Chronic Obstructive Pulmonary Disease Prevalence and 

Mortality 

Chronic Obstructive Pulmonary Disease Mortality

Asthma Prevalence Asthma Prevalence

Childhood Asthma Prevalence

Infectious Diseases Associated with Environmental 

Exposures or Conditions

(with the following new additions: Giardiasis, Lyme 

Disease, Rocky Mountain Spotted Fever, West Nile Virus, 

Legionellosis) 

Cholera Prevalence

Cryptosporidiosis Prevalence

E. coli O157:H7 Prevalence

Hepatitis A Prevalence

Salmonellosis Prevalence

Shigellosis Prevalence

Typhoid Fever Prevalence

Birth Defects Prevalence and Mortality Deaths Due to Birth Defects

Birth Defect Incidence

Low Birthweight Low Birthweight Incidence

Preterm Delivery 

Withdrawn Cancer Mortality

Withdrawn Asthma Mortality 

Withdrawn Childhood Cancer Mortality

Withdrawn Childhood Asthma Mortality
APPENDIX C

EPA’s 2008 Report on the Environment C-9

Extent and Distributon

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

Forest Extent and Type Extent of Area by Forest Type

Forest Fragmentation Forest Pattern and Fragmentation

Ecological Connectivity in EPA Region 4 

Relative Ecological Condition of Undeveloped Land in EPA 

Region 5

Withdrawn Forest Age Class

Withdrawn Extent of Ponds, Lakes, and Reservoirs

Withdrawn Extent of Estuaries and Coastline

Diversity and Biological Balance

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

Bird Populations 

Fish Faunal Intactness 

Non-Indigenous Benthic Species in the Estuaries of the 

Pacific Northwest

Withdrawn At-Risk Native Forest Species

Withdrawn Populations of Representative Forest Species

Withdrawn Tree Condition

Withdrawn At-Risk Native Grassland and Shrubland Species

Withdrawn Population Trends of Invasive and Native Non-Invasive 

Bird Species

Withdrawn At-Risk Native Fresh Water Species

Withdrawn Non-Native Fresh Water Species

Withdrawn At-Risk Fresh Water Plant Communities

Withdrawn Coastal Living Habitats

Withdrawn Shoreline Types

Withdrawn Fish Diversity

Withdrawn At-Risk Native Species

Withdrawn Bird Community Index

Ecological Condition Chapter
APPENDIX C

C-10 EPA’s 2008 Report on the Environment

Explanation of Indicators Used in the 2003 

Draft ROE But Not in the 2008 ROE

A number of indicators were included in EPA’s 2003 Draft 

ROE that are not included in the 2008 ROE. The general 

reasons for these changes are described below, followed by 

indicator-specific explanations. 

•	Members of the independent scientific review panel that 

reviewed the draft indicators for the 2008 ROE recommended their withdrawal.

•	The EPA Science Advisory Board Committee review of the 

2003 Draft ROE recommended EPA develop and utilize 

a more precise definition of “indicator” than was used for 

2003 Draft ROE.

•	EPA developed a set of specific indicator criteria to provide 

a more precise conformance to Office of Management and 

Budget and EPA Information Quality Guidelines. 

•	The 2008 ROE introduced a Regional Pilot Project and 

developed and implemented a relevant process. SubNational or Regional Indicators that were included in the 

2003 Draft ROE but did not go through this pilot are not 

included in the 2008 ROE. 

A small number of the indicators in 2003 Draft ROE did not 

conform to one or more of these requirements. Explanations 

for not including these indicators were peer-reviewed by an 

independent scientific panel along with the indicators in this 

report. Broadly speaking, the explanations for withdrawal fall 

into five categories, coded as follows:

•	(D) Definition. The indicator fails to meet the improved 

indicator definition for the 2008 ROE.

•	(C) Criteria. The indicator fails to meet one of the six 

indicator criteria that were established to conform to EPA 

Information Quality Guidelines. 

Ecological Processes

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

Carbon Storage in Forests Carbon Storage

Withdrawn Forest Disturbance: Fire, Insects, and Disease

Ecological Exposure to Contaminants

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

Withdrawn Animal Deaths and Deformities

Withdrawn Fish Abnormalities

Withdrawn Unusual Marine Mortalities

Physical and Chemical Attributes

ROE 2008 Indicator Title Corresponding 2003 Draft ROE Indicator Title

U.S. and Global Mean Temperature and Precipitation 

Sea Surface Temperature 

Sea Level 

Withdrawn Soil Compaction

Withdrawn Soil Erosion (Forests)

Withdrawn Soil Erosion (Farmland)

Withdrawn Processes Beyond the Range of Historic Variation

Withdrawn Soil Quality Index

Withdrawn Terrestrial Plant Growth Index

Withdrawn Chemical Contamination (partially withdrawn)
APPENDIX C

EPA’s 2008 Report on the Environment C-11

•	(N) New indicator. The indicator is replaced by a “new” 

and superior indicator that was not available for the 2003 

Draft ROE.

•	(R) Regional. The indicator is not national in scope and is 

not part of the 2008 ROE Regional Pilot Project.

•	(P) Peer review. The independent peer review panel recommended withdrawing the indicator from the 2008 ROE.

The following information briefly explains the rationale for 

withdrawing specific indicators from the 2008 ROE. Each 

indicator is categorized as D, C, N, R, or P. The indicators are 

organized by chapter.

Air Chapter

Worldwide and U.S. Production of 

Ozone-Depleting Substances (ODSs)—C

This 2003 Draft ROE indicator presented estimates of the 

amount of ODSs produced worldwide in 1986 and 1999, and 

annual U.S. production from 1958 to 1993. This indicator was 

withdrawn because of issues concerning data reliability and 

relevance. Global ODC production data are not reliable with 

respect to comparability among reporting countries. The U.S. 

estimates are more reliable because of legal reporting requirements and the small number of sources. However, the data set 

fails to account for imports, and annual production is not a 

good surrogate for emissions of ODCs into the environment 

because the time between production and eventual entry into 

the environment is highly variable among the various products 

and recovery systems.

Number of People Living in Areas with Air Quality Levels 

Above the NAAQS for Particulate Matter (PM) and Ozone—C

This 2003 Draft ROE indicator conveyed how many people 

(based on census data) lived in counties where air pollutant 

levels at times were above the level of the NAAQS during the 

year stated. It was intended to give the reader some indication 

of the number of people potentially exposed to unhealthy air. 

Because of changing populations and air quality standards, 

however, this indicator masks actual trends in the levels of air 

pollutants. It is not a valid exposure indicator for the ROE 

because it is not based on measurement of an actual marker of 

exposure measured on or in individuals. 

Percentage of Homes Where Young Children Are Exposed 

to Environmental Tobacco Smoke—D

This 2003 Draft ROE indicator portrayed the percentage of 

homes in the U.S. in which young children were exposed 

to tobacco smoke in 1998 versus 1957. The survey was based 

on a questionnaire (do children live in the home, and does 

someone who smokes regularly live in the home), rather than 

on measurements of the amount of smoke actually present or 

the degree to which children were exposed to the resulting 

smoke. This indicator violates the ROE indicator definition, 

which requires that indicators be based on actual measurements; furthermore, the 2008 ROE’s Blood Cotinine indicator better indicates children’s exposure to smoke.

Water Chapter

Altered Fresh Water Ecosystems—C

Percent Urban Land Cover in Riparian Areas—C

Agricultural Lands in Riparian Areas—C

These 2003 Draft ROE indicators were based on the percentage of land within 30 meters of the edge of a stream or lake 

that is classified as urban or agriculture based on 1991 satellite 

data (NLCD). Baseline data are incomplete, there are no reference points for the appropriate percentage of such cover, and it 

is not clear that the indicators could be reproduced with newer 

satellite data. There are no data for other alterations such as 

damming, channelization, etc.

Lake Trophic State Index—R, C

This 2003 Draft ROE indicator was based on phosphorus data 

collected in a one-time statistical sample of lakes in the northeastern U.S. during 1991-1994. It is not included in the 2008 

ROE Regional Pilot Project. 

Sedimentation Index—R, C, N

This 2003 Draft ROE indicator was based on data collected 

on freshwater streams in the Mid-Atlantic Highlands Region 

during a one-time 1993-1994 statistical survey. It is not 

included in the 2008 ROE Regional Pilot Project. The 2008 

ROE’s Streambed Stability in Wadeable Streams indicator 

provides a more complete nationwide picture of sedimentation 

in streams.

Nitrate in Farmland, Forested, and Urban Streams and 

Ground Water (partially withdrawn)—N

Phosphorus in Farmland, Forested, and Urban Streams 

(partially withdrawn)—N

These 2003 Draft ROE indicators were replaced by two new 

indicators, “Nitrogen and Phosphorus in Streams in Agricultural Watersheds” and “Nitrate and Pesticides in Shallow 

Ground Water in Agricultural Watersheds.” The NAWQA 

streams in forested and urban watersheds were based on a 

small sample size, and may not be representative of forested 

and urban streams in general.

Phosphorus in Large Rivers—C

The indicator was based on phosphorus concentrations in large 

rivers sampled periodically by the USGS National Stream 

Quality Accounting Network (NASQAN). Monitoring at 

many of the large river NASQAN sites has been discontinued. 

Information on phosphorus loads in four major rivers has been 

incorporated into the new 2008 ROE indicator, Nitrogen and 

Phosphorus Loads in Large Rivers. 

Atmospheric Deposition of Mercury—C

This indicator was withdrawn following peer review of the 

indicators because trend data could not be analyzed in time to 

revise it.

Chemical Contamination in Streams and Ground Water—C

This 2003 Draft ROE indicator was based on data from a 

large number of USGS National Water Quality Assessment 
APPENDIX C

C-12 EPA’s 2008 Report on the Environment

(NAWQA) watersheds. The sampling and analytical protocols 

(including the analytes measured) are not comparable across all 

NAWQA watersheds. 

Sediment Contamination of Inland Waters—C

This 2003 Draft ROE indicator was based on reported concentrations of sediment contaminants collected by a large 

number of organizations focusing particularly on places where 

sediment contamination is perceived to be a problem (the 

EPA National Sediment Inventory). The database suffers from 

a number of limitations: the data are heavily biased toward 

sites at which there is a known or suspected toxicity problem and to particular geographic areas (non-representative of 

the nation), the data cover different dates in different locations (making estimation of trends difficult), and the data and 

procedures used to assign sites to a toxicity category are not 

uniform from watershed to watershed. It is unsuitable for 

trend estimation. 

Fish Index of Biotic Integrity in Streams—R, C

This 2003 Draft ROE indicator was based on fish community 

data collected on freshwater fish in the Mid-Atlantic Highlands Region during a one-time 1993-1996 statistical survey. 

Condition cannot be assessed in streams where no fish were 

caught, because data were insufficient to indicate whether the 

stream had poor quality or simply no fish. It is not included in 

the 2008 ROE Regional Pilot Project. 

Total Organic Carbon in Sediments—R

This 2003 Draft ROE indicator was based on data collected 

in a survey of Mid-Atlantic estuaries during a one-time 

1997-1998 statistical survey. It is not included in the 2008 ROE 

Regional Pilot Project. Also, total organic carbon in sediments is useful in understanding sediment toxicity, but there 

are unlikely to be trends in sediment total organic carbon, and 

therefore it would be of limited value as an ROE indicator.

Population Density in Coastal Areas—D

Discussion of population density in coastal areas was moved 

to the introduction of the water chapter section responding to 

the question, “What are the trends in the extent and condition of coastal waters and their effects on human health and 

the environment?”

Number of Beach Days That Beaches Are Closed or 

Under Advisory—D

Percent of River Miles and Lake Acres Under Fish 

Consumption Advisories—D

These 2003 Draft ROE indicators were based on the frequency of beach closures or fish consumption advisories as 

reported to EPA voluntarily by states and local government 

organizations. The data are not nationally or temporally 

consistent because of different and changing criteria for 

closing beaches or issuing fish consumption advisories in the 

different states, many of which do not involve actual water 

quality measurements. They are therefore administrative 

indicators (based on administrative action rather than actual 

physical measurements) and fail to meet the definition for 

ROE indicators. 

Number of Watersheds Exceeding Health-Based 

National Water Quality Criteria for Mercury and PCBs in 

Fish Tissue—C

This 2003 Draft ROE indicator was based on voluntary 

reporting of mercury contamination using data that had not 

undergone formal QA/QC review. It is not representative of 

the nation, or suitable for trend monitoring. 

Land Chapter

The Farmland Landscape—C

This 2003 Draft ROE indicator represented croplands and the 

forests, woodlots, wetlands, grasslands, and shrublands that 

surround or are intermingled with them, and the degree to 

which croplands dominate the landscape. The indicator relied 

on data generated using early 1990s satellite data, and it is 

unclear whether the definition of “farmland landscape” is sufficiently precise to be replicated independently, especially with 

respect to any future satellite data availability. 

Sediment Runoff Potential from Croplands and 

Pasturelands—C

This 2003 Draft ROE indicator represented the estimated 

sediment runoff potential for croplands and pasturelands based 

on topography; weather patterns; soil characteristics; land use, 

land cover, and cropping patterns; and the Universal Soil Loss 

equation. The indicator addressed “potential” and not actual/

current condition, and relied on a model (the Soil and Water 

Assessment Tool: http://www.brc.tamus.edu/swat) to predict 

ambient characteristics based on pressure/stressor measurements, which violates a fundamental ROE protocol on the use 

of models in indicators. Trends in this indicator would likely 

be associated only with trends in land cover, cropping practices, and weather (topography and soil type are unlikely to 

change). No reliable spatial trend data at the appropriate scale 

exist for either cropping practices or land cover, and consequently trends in this indicator would be difficult to calculate. 

Agricultural Pesticide Use—C

Agricultural pesticide usage data, measured at the national 

aggregate level for all pesticides, are very difficult to interpret. From one time period to another, the mix of pesticides 

changes, pest pressures change, agricultural practices change, 

agricultural acreage changes, regulatory status of key uses 

changes, and many other important variables change. Moreover, the effects of pesticide usage are encountered at three 

levels of the product’s life cycle: production, usage, and 

residues on foods. The geographic distribution of those effects 

renders difficult the interpretation of national usage levels for 

all pesticides, taken as a group. While it is of course possible to 

compare magnitudes of aggregates at different times, the real 

significance for the environment is in the differences in the 

content and geographic distribution of the aggregates, not in 

the magnitude of the aggregate.

Potential Pesticide Runoff from Farm Fields—C

Pesticide Leaching Potential—C

These 2003 Draft ROE indicators represented the potential 

movement of agricultural pesticides from the site of application 
APPENDIX C

EPA’s 2008 Report on the Environment C-13

to ground and surface waters, based on estimates of pesticide 

leaching and runoff losses derived from soil properties, field 

characteristics, management practices, pesticide properties, 

and climate for 243 pesticides applied to 120 specific soils in 

growing 13 major agronomic crops. The indicators address 

“potential” and not actual/current condition, and rely on 

models to predict ambient characteristics based on measurements of pressures/stressors. This violates a fundamental ROE 

protocol on the use of models in indicators.

Risk of Nitrogen Export—C

Risk of Phosphorus Export—C

These 2003 Draft ROE indicators represented the potential 

movement of nitrogen and phosphorus from the site of application to surface waters, based on a large empirical dataset 

relating land use to nitrogen and phosphorus observed in 

receiving streams over several decades at a variety of locations. 

The indicators address “potential” and not actual/current 

conditions, and rely on statistical models to predict ambient 

characteristics based on measurements of pressures/stressors. 

This violates a fundamental ROE protocol on the use of models in indicators.

Quantity of Radioactive Waste Generated and 

in Inventory—C

This 2003 Draft ROE indicator was based on production 

and inventory data collected by the Department of Energy. 

Although the data continue to be collected, they are no longer 

publicly available post-September 11, 2001; therefore, ongoing 

data trends are not and will not be available for this indicator 

in the future. Moreover, the earlier data reflected two distinct 

periods in the history of waste generation in the nuclear weapons complex. The first reflected a period during which wastes 

and other materials were being generated as an integral part of 

the production of weapons-grade nuclear materials and components. The period after 1989 reflected the cessation of largescale production of such materials and the initiation of cleanup 

activities and wastes from those initiatives. Thus, even before 

the truncation of data in the post-9/11 period, there were significant issues with the comparability of the data over time.

Number and Location of Municipal Solid Waste (MSW) 

Landfills—D, N

This 2003 Draft ROE indicator represents an administrative 

count of landfills, rather than an amount of waste produced, 

and therefore does not meet the 2008 ROE indicator definition. The indicator was replaced by a new and superior indicator that tracks the quantity of municipal solid waste generated 

and how it is managed.

Number and Location of RCRA Hazardous Waste 

Management Facilities (partially withdrawn)—D, N

This 2003 Draft ROE indicator, by itself, represents an 

administrative decision to force a cleanup, rather than an 

amount of waste present or removed, and therefore does not 

meet the 2008 ROE indicator definition. The data were combined into a new indicator, Quantity of RCRA Hazardous 

Waste Generated and Managed, which combines information 

from several 2003 Draft ROE indicators.

Number and Location of Superfund National Priorities List 

(NPL) Sites—D

This 2003 Draft ROE indicator represented an administrative 

decision to force a cleanup, rather than an amount of waste 

present or removed, and therefore does not meet the 2008 

ROE indicator definition. 

Number and Location of RCRA Corrective Action Sites—D

This 2003 Draft ROE indicator represented an administrative 

decision to force a cleanup, rather than an amount of waste 

present or removed, and therefore does not meet the 2008 

ROE indicator definition.

Human Exposure and Health Chapter

Urine Arsenic Level—R

This 2003 Draft ROE indicator was based on data from EPA 

Region 5 only, and is not part of the 2008 ROE Regional Pilot. 

Blood Volatile Organic Compound Levels—C

This 2003 Draft ROE indicator was based on a convenience 

sample whose representativeness cannot be determined or 

necessarily used as a baseline for future sampling. The indicator is based on detects only, so there is no reference level. Also, 

volatile organic compounds are cleared from the bloodstream 

rapidly (about 1 hour), so there is a significant possibility of 

false negatives, considering that exposure tends to be associated with occupational and indoor settings. 

Cancer Mortality—P

Childhood Cancer Mortality—P

Asthma Mortality—P

Childhood Asthma Mortality—P

The independent peer review panel recommended the 

removal of the cancer and asthma mortality indicators because 

trends in these indicators are less likely to be due to changes in 

environmental factors than to changes in social factors such as 

availability/access to healthcare.

Ecological Condition Chapter

Forest Age Class—N

While forest age class has implications for biodiversity and 

ecological function, this indicator was withdrawn in favor of 

indicators of forest extent and type and forest fragmentation.

Extent of Ponds, Lakes, and Reservoirs—C

This 2003 Draft ROE indicator was based on data from the 

USGS National Wetlands Inventory. While these data are 

based on a valid statistical sampling design, the total amount 

of surface water is less than half the area of lakes, reservoirs, 

and ponds greater than 6 acres in size in the USGS National 

Hydrography Data Set. Until this discrepancy is resolved, the 

indicator may not satisfy the ROE criteria. 

Extent of Estuaries and Coastline—C

This 2003 Draft ROE indicator was based on remote sensing 

data, but is unlikely to show trends unrelated to sea level rise 

and changing tides, so it is not a very useful indicator for trends.
APPENDIX C

C-14 EPA’s 2008 Report on the Environment

At-Risk Native Species—C

At-Risk Native Grassland and Shrubland Species—C

At-Risk Native Forest Species—C

Populations of Representative Forest Species—C

Non-Native Fresh Water Species—C

At-Risk Native Fresh Water Species—C

At-Risk Fresh Water Plant Communities—C

The ecological condition chapter was restructured from the 

2003 Draft ROE organization per the recommendation of 

EPA’s Science Advisory Board and numerous stakeholders. As 

such, the chapter no longer requires that the above indicators 

be broken out by ecosystem. In addition, the ability to track 

trends of many of these indicators is questionable.

Tree Condition—C

This 2003 Draft ROE indicator was based on an ongoing 

statistical sample of forests across the contiguous U.S. and 

comprises components that relate to crown (tree canopy) condition, the ratio of dead to live wood, and the fire class. This 

indicator likely relates more to forest management practices 

than to environmental condition, and for this reason has low 

relevance value to EPA.

Population Trends of Invasive and Native Non-Invasive Bird 

Species—R

This 2003 Draft ROE indicator was based on an analysis of 

USGS Breeding Bird Survey data in grassland and shrubland 

ecosystems for 5-year periods ranging from the late 1960s 

to 2000. Because the ecological condition questions are no 

longer directed at specific ecosystem types, this appears to be 

a Regional Indicator. Also, it is not clear at this time that the 

data for this indicator will be collected in the future.

Coastal Living Habitats—C

This 2003 Draft ROE indicator was based on remote sensing 

data of coastal wetlands, mudflats, sea-grass beds, etc., but the 

only system for which a National Indicator has been developed is coastal vegetated wetlands, which already is covered in 

another indicator (the 2008 ROE’s Wetlands indicator).

Shoreline Types—C

This 2003 Draft ROE indicator was based on NOAA’s Environmental Sensitivity Index. The index is based on a standardized mapping approach, but coverage is not complete for large 

parts of the coastline and the data in some of the atlases are 

more than 15 years old. Consequently, this indicator is not 

appropriate for measurement of representative, national trends.

Fish Diversity—R

This 2003 Draft ROE indicator was based on a statistical sample of fish trawls in Mid-Atlantic estuaries during 1997-1998. 

This indicator is not part of the 2008 ROE Regional Pilot 

Project, and EPA’s Environmental Monitoring and Assessment 

Program (EMAP) is no longer collecting fish samples to support this indicator.

Bird Community Index—R

This 2003 Draft ROE indicator was not national in scope or 

part of the ROE EPA Regional Pilot.

Forest Disturbance: Fire, Insects, and Disease—P

The independent peer review panel recommended that this 

indicator be withdrawn because it was “limited in many 

aspects of its coverage: temporally, spatially, and in types of 

disturbance...Ecological interpretation of disturbance patterns 

is difficult...For example, the lack of fire may actually represent an ecological disturbance, while fire suppression can lead 

to overcrowded forests that are more conducive to insect and 

disease outbreaks.” The reviewers also commented that the 

data were questionable and that the interdependence among 

the disturbance categories could result in significant doublecounting. Finally, timber harvest was not included even 

though it disturbs more acres than fires, insects, or disease.

Soil Compaction—C

Soil Erosion—C

These 2003 Draft ROE indicators are based on an ongoing 

statistical sample of soils in forests across the contiguous U.S., 

but the actual indicators are based on models rather than measurement. This violates a fundamental ROE protocol on the 

use of models in indicators. 

Processes Beyond the Range of Historic Variation—C

This 2003 Draft ROE indicator was based on an analysis of 

recent Forest Inventory and Analysis data on climate events, 

fire frequency, and forest insect and disease outbreaks, which 

were then compared to anecdotal data for the 1800-1850 

period. Because the early data are anecdotal, and because the 

data mostly relate to forest management practices, etc., it is 

proposed that this indicator has low relevance to EPA and that 

trend data are of questionable utility as an ROE indicator.

Soil Quality Index—R

This 2003 Draft ROE indicator was based on a survey of soils 

in the Mid-Atlantic region during the 1990s; that survey was 

not repeated and is not part of the Regional Pilot Project for 

the 2008 ROE.

Terrestrial Plant Growth Index—P

The independent peer review panel recommended that this 

indicator be withdrawn because “The results are too ambiguous and not explained, or perhaps, unexplainable...NDVI is 

a crude measure of growth. [Also,] The relative deviation of 

the Plant Growth Index (20-40%) without explanation during 

the period of analysis suggests that the indicator might lack the 

precision needed to assess national trends in productivity.”

Chemical Contamination (partially withdrawn)—C

This 2003 Draft ROE indicator combined data from the 

NAWQA program that are not consistent in terms of sampling 

frequency or analytical protocols. The part of this indicator 

presenting contaminant levels in coastal fish as measured by 

EMAP was moved to a separate indicator in the water chapter 

of the 2008 ROE: Coastal Fish Tissue Contaminants.
APPENDIX C

EPA’s 2008 Report on the Environment C-15

Animal Deaths and Deformities—C

This 2003 Draft ROE indicator was based on data reported by 

a number of different organizations to USGS on incidences of 

death or deformities in waterfowl, fish, amphibians, and mammals. Trends are available only for waterfowl, and because data 

reporting is voluntary rather than systematic, the data are not 

adequate to determine actual trends versus trends in reporting.

Fish Abnormalities—C

This 2003 Draft ROE indicator was based on a statistical 

sample of fish trawls in estuaries in the Atlantic and Gulf, but 

the data are no longer being collected by EMAP to support 

this indicator. 

Unusual Marine Mortalities—C

This 2003 Draft ROE indicator was based on voluntary 

reporting of unusual mortality events to NOAA. Because 

there is no systematic requirement to report, these data are not 

suitable to support national trends in the indicator.