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Risk Assessment

Frequent Questions

What is risk? What is risk assessment?

These issues are addressed in detail on the Basic Information page.

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What is risk management?

As described in EPA’s Risk Characterization Handbook (PDF) (89 pp, 8.9MB, about PDF), "Risk Management" is the process which evaluates how to protect public health. Examples of risk management actions include deciding how much of a substance a company may discharge into a river; deciding which substances may be stored at a hazardous waste disposal facility; deciding to what extent a hazardous waste site must be cleaned up; setting permit levels for discharge, storage, or transport; establishing national ambient air quality standards; and determining allowable levels of contamination in drinking water.

Risk assessment provides "INFORMATION" on potential health or ecological risks, and risk management is the "ACTION" taken based on consideration of that and other information, as follows:

  • Scientific factors provide the basis for the risk assessment, including information drawn from toxicology, chemistry, epidemiology, ecology, and statistics - to name a few.
  • Economic factors inform the manager on the cost of risks and the benefits of reducing them, the costs of risk mitigation or remediation options and the distributional effects.
  • Laws and legal decisions are factors that define the basis for the Agency’s risk assessments, management decisions, and, in some instances, the schedule, level or methods for risk reduction.
  • Social factors, such as income level, ethnic background, community values, land use, zoning, availability of health care, life style, and psychological condition of the affected populations, may affect the susceptibility of an individual or a definable group to risks from a particular stressor.
  • Technological factors include the feasibility, impacts, and range of risk management options.
  • Political factors are based on the interactions among branches of the Federal government, with other Federal, state, and local government entities, and even with foreign governments; these may range from practices defined by Agency policy and political administrations through inquiries from members of Congress, special interest groups, or concerned citizens.
  • Public values reflect the broad attitudes of society about environmental risks and risk management.

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How does EPA conduct risk assessments?

At EPA, environmental risk assessments typically fall into one of two areas: human health risk assessments or ecological risk assessments. These are described in steps or parts due to the differences in how each of these are conducted at EPA.

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Where do I find EPA risk assessments?

Because risk assessments are performed all over EPA (see the EPA Organization Chart for other EPA Offices and Regions), risk assessments are produced by many of EPA's Regions and Program Offices. Here is a list of primary risk assessment sources:

See Tools & Guidance for a list of more resources.

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Where can I find some general information on risk assessment?

EPA has posted a few citizen guides that may be of help for those new to risk assessment. Here is a list of available publications:

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What can I do? Participating in risk assessments

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How does EPA conduct a human health risk assessment? and Why does EPA evaluate whether children may be at greater health risks than adults?

These issues are addressed in detail on the human health risk assessment page.

How does EPA conduct an ecological risk assessment? How does EPA use these assessments?

These issues are addressed in detail on the ecological risk assessment page.

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What does EPA mean by "variability","uncertainty", and "probabilistic modeling"?

Consideration must be given to two important factors throughout the development of a risk assessment: variability and uncertainty.

Variability - Refers to the range of toxic response or exposure. For example, the dose that might cause a toxic response can vary from one person to the next depending on factors such as genetic differences, preexisting medical conditions, etc. Exposure may vary from one person to the next depending on factors such as where one works, time spent indoors or out, where one lives, how much people eat or drink, etc.

Uncertainty - Refers to our inability to know for sure - it is often due to incomplete data. For example, when assessing the potential for risks to people, toxicology studies generally involve dosing of sexually mature test animals such as rats as a surrogate for humans. Since we don't really know how differently humans and rats respond, EPA often employs the use of an uncertainty factor to account for possible differences. Additional consideration may also be made if there is some reason to believe that the very young are more susceptible than adults, or if key toxicology studies are not available.

Probabilistic Modeling, a related term, is a technique that utilizes the entire range of input data to develop a probability distribution of exposure or risk rather than a single point value. The input data can be measured values and/or estimated distributions. Values for these input parameters are sampled thousands of times through a modeling or simulation process to develop a distibution of likely exposure or risk. Probabilistic models can be used to evaluate the impact of variability and uncertainty in the various input parameters, such as environmental exposure levels, fate and transport processes, etc.

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