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Region 8

Risk Assessment Overview

Risk assessment is the process used by EPA and many other regulatory agencies to characterize the nature and magnitude of health risks to humans (e.g., residents, workers, recreational visitors) and ecological receptors (e.g., birds, mammals, fish, plants) from chemical contaminants that may be present in the environment at a site. This information is used by risk managers to help decide what actions are needed at the site to ensure that humans and ecological receptors are adequately protected from toxic chemicals that have been released into the environment.

For a more general overview of the risk assessment process, visit the following EPA sites:

Risk assessment is, to the maximal extent possible, a scientific process. In general terms, risk depends on the following factors:

  • How much of a chemical is present in an environmental medium (e.g., soil, water, air).
  • How much contact (exposure) a person or ecological receptor has with the contaminated environmental medium.
  • The inherent toxicity of the chemical.

The risk assessment process usually begins by collecting measurements that characterize the nature and extent of chemical contamination in the environment, as well as information needed to predict how the contamination may behave in the future. Based on this information, the risk assessor evaluates the frequency and magnitude of human and ecological exposures that may occur as a consequence of contact with the contaminated medium, both now and in the future. This evaluation of exposure is then combined with information on the inherent toxicity of the chemical (that is, the expected response to a given level of exposure) to predict the probability, nature, and magnitude of the adverse health effects that may occur.

In the ideal, all risk assessments would be based on a very strong knowledge base (i.e., reliable and complete data on the nature and extent of contamination, fate and transport processes, the magnitude and frequency of human and ecological exposure, and the inherent toxicity of all of the chemicals). However, in real life, information is usually limited on one or more of these key data requirements needed for risk assessment calculations. This means that risk assessors often have to make estimates and use judgment when performing risk calculations, and consequently all risk estimates are uncertain to some degree. For this reason, a key part of all good risk assessments is a fair and open presentation of the uncertainties in the calculations and a characterization of how reliable (or how unreliable) the resulting risk estimates really are.

More information on these key components of performing risk assessments in Region 8, as well as relevant guidance documents and resources, are provided on the following pages:

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