Human Health

Human Health Chapter

HD Chapter Highlights

Chapter Leader

Danelle Lobdell
Office of Research and Development

Chapters

The 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 throughout the ROE, 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, are 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 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.

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.

Exhibit 5-1. Environmental Public Health Paradigm

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 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 other ROE chapters 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.

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.

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

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.