Unit 6: Risk, Exposure, and Health // Section 2: Risk Assessment
Risk assessment is the process of establishing risks to humans and the environment from chemicals, radiation, technologies, or other contaminants and agents that can affect health and well-being. It is part of a broader process called risk analysis that also includes developing policies to manage risks once they are identified and quantified.
As summarized by the Society for Risk Analysis, a professional association of experts, "Risk analysis uses observations about what we know to make predictions about what we don't know. Risk analysis is a fundamentally science-based process that strives to reflect the realities of Nature in order to provide useful information for decisions about managing risks . . . . [It] seeks to integrate knowledge about the fundamental physical, biological, social, cultural, and economic processes that determine human, environmental, and technological responses to a diverse set of circumstances" (footnote 4).
Health and environmental experts use risk analysis to assess many types of threats, from infectious agents to noise pollution. The process has several components (Fig. 4).
- Risk assessment: Scientists identify hazards, determine dose-response relationships, and estimate actual or projected exposures. These steps lead to an estimate of overall risk to the general population or target groups.
- Risk management: Experts develop options for limiting estimated risk. Unlike risk assessment, which is based on scientific findings, risk management takes political and economic factors into account along with technical considerations.
- Risk communication: Policy makers discuss the problem and options for addressing it with the public, then incorporate the feedback that they receive into their decisions. As discussed below in section 7, "Benefit-Cost Analysis and Risk Tradeoffs," effective risk communication helps to ensure that decisions will be broadly acceptable.
Figure 4. The risk assessment/risk management paradigm
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Source: Courtesy United States Environmental Protection Agency, Office of Research and Development.
Risk assessment has been in use since the 1950s but has become more sophisticated and accurate over the past several decades, due in large part to increasing interest from government regulators. In the 1960s and 1970s, federal authority to regulate threats to health, safety, and the environment expanded dramatically with the creation of new oversight agencies such as the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA), along with adoption of numerous laws regulating environmental hazards. At the same time, improved testing methods and better techniques for detecting contaminants made it easier to study relationships between exposure and health effects.
These developments made it easier in some ways to protect public health and the environment, since regulators at the new agencies had broad mandates for action and abundant data about potential threats. But regulators had to allocate their resources among many competing issues, so they needed tools to help them focus on the most dangerous risks. Former EPA administrator William K. Reilly recalls, "Within the space of a few years, we went to the possibility of detecting not just parts per million but parts per billion and even, in some areas, parts per quadrillion . . . . That forces you to acknowledge that what you need is some reasonable method for predicting levels of real impact on humans so that you can protect people to an adequate standard" (footnote 5).
As an illustration of the power of modern analytical methods, Figure 5 shows results from a X-ray analysis of a strand of composer Ludwig van Beethoven's hair performed in the year 2000 by the U.S. Department of Energy's Argonne National Laboratory. The experiment found lead levels of about 60 parts per million in Beethoven's hair, compared to less than six parts per million for an average U.S. human hair today, indicating that some of Beethoven's lifelong illnesses may have been due to lead poisoning.
Figure 5. X-ray fluorescence intensity from Pb in hair
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Source: Courtesy United States Department of Energy, Argonne National Lab.
Risk analysis gave scientists and regulators a way to sort through the vast amounts of health information provided by methods like that illustrated in Fig. 5, compare relative risks from various contaminants, and set priorities for action. By the mid-1970s a number of federal agencies were carrying out risk assessments, each using its own procedures and standards.
To address concerns about inconsistencies among agencies, Congress requested a study from the National Academy of Sciences, which in 1983 published a seminal report, Risk Assessment in the Federal Government: Managing the Process (often referred to as the "Red Book") (footnote 6). This study provided a general framework for cancer risk assessment and recommended developing uniform risk assessment guidelines for agencies. Although no government-wide guidelines have been produced, EPA has produced numerous assessments of human health risks from exposure to substances such as air pollutants and drinking water contaminants. The Office of Management and Budget, which oversees U.S. regulatory policies, requires EPA and other federal agencies to submit comprehensive risk assessments and benefit-cost analyses along with proposed rule makings and regulations.
Following a model outlined in the Red Book, environmental risk assessments typically include four steps.
- Hazard identification: Determining whether or not exposure to an agent causes health problems. Researchers often address this question by testing the agent to see whether it causes cancer or other harmful effects in laboratory animals.
- Dose-response assessment: Characterizing the relationship between receiving a dose of the agent and experiencing adverse effects. Analysts often have to extrapolate from high laboratory doses to low actual doses and from laboratory animals to humans.
- Exposure assessment: Measuring or estimating how often humans are exposed to the agent, for how long, and the intensity of exposure. This can involve methods such as asking subjects about their lifestyles and habits; taking environmental samples; and screening subjects' blood, urine, hair, or other physical samples to measure concentrations of the agents in their bodies (Fig. 6).
- Risk characterization: Combining exposure and dose-response assessments to estimate health impacts on subjects.
Figure 6. Backpack system for measuring exposure to fine particulate air pollution
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Source: © John Spengler, Harvard School of Public Health.