Introduction

Through the performance of risk assessments, researchers seek to understand the fundamental processes that underlie human health problems that are caused by pollutants in the environment. Risk assessments address questions of exposure and the adverse outcomes associated with exposure. The health risks assessed by the risk assessment disciplines include: cancer, birth defects, developmental disorders, and other serious health problems that can be caused by exposure to chemical or biological agents in the environment. In ecological risk assessments, risk practitioners address concerns about the effects of pollution on organisms and ecosystems.

There are four steps in the process of risk assessment (whether oriented toward human health or toward environmental stressors): hazard identification, dose-response assessment, exposure assessment, and risk characterization. In each step, scientists address key questions, with the goal of formulating a complete understanding of the seriousness and scope of a hazard. Additionally, due to the complexity of the process, the work is completed by a wide range of scientific and technical disciplines and levels of expertise.

The approach to risk assessment described here is that associated with the federal government in the United States, as well as some other agencies within the U.S. (state, local and regional), as well as other countries and some international organizations. This is the approach used for environmental and occupational health, and differs from, for example, engineering or actuarial risk assessment.

Risk Assessment Four-Step Process

Hazard Identification

• Does exposure to a certain substance cause injury or disease in humans or to the environment?
• Are certain subgroups more at risk than others?
• What are the conditions under which these ill effects are caused?
• Are the ill affects observed in experimental settings likely to be observed in real-world settings?

Dose-Response Assessment

• What is the relationship between the amount of exposure (or dose) and the incidence and severity of the adverse health effect?
• How is this relationship influenced by factors such the pattern of exposure or age and lifestyle?
• How can extrapolations be made between animal responses (observed through experiments) and human responses (resulting from real-life exposures) or between high-dose responses (observed in the laboratory) and low-dose responses (resulting from environmental exposures)?

Exposure Assessment

• What is the intensity, frequency, and duration of individuals' exposure to a substance?
• What ecosystem components are at risk? Is the risk mainly to aquatic organisms, to insects and insect-eating birds, to sediment-dwelling organisms, or to mammals and game such as deer?

Risk Characterization

• How much of a pollutant can individuals be exposed to before their health is affected?
• How likely is it that people or other living things in the environment will suffer the ill effects?
• How certain is this information? What questions and uncertainties remain?
• What is the risk to people who are exposed the most?

Further Reading

• Ecological Risk Analysis: Guidance, Tools, and Applications, Oak Ridge National Laboratory, Environmental Sciences Division
• EPA's Research on Risk Assessment, U.S. EPA National Center for Environmental Assessment
• ''Human and Ecological Risk Assessment'': A Journal, The Association for Environmental Health and Sciences (AEHS)
• Issues in Risk Assessment, National Academies Press
• National Research Council's Committee on Emerging Issues and Data on Environmental Contaminants, National Academies
• Risk Assessment in the Federal Government, National Academies Press
• Risk Assessment Basics, U.S. Environmental Protection Agency
• Science and Judgment in Risk Assessment, National Academies Press
• Strengthening Science at the U.S. Environmental Protection Agency: Research-Management and Peer-Review Practices, National Academies Press
• Understanding Risk: Informing Decisions in a Democratic Society, National Academies Press