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Human Health Risk Assessment
Human health risk assessment seeks to estimate the nature and probability of adverse health effects in humans who may be exposed to chemicals in contaminated environmental media, now or in the future. The key components of the human health risk assessment process are outlined below; click on a topic for more detailed information and related resources and guidance documents. Examples of completed EPA Region 8 human health risk assessments are provided at the bottom of this page.
Note: Different methods are used to characterize human exposure to lead and risks from lead than those used for most other chemicals. Relevant guidance and tools for evaluating lead risks to children and adults can be found on the Evaluation of Risks from Lead page.
Site Conceptual Model: In this step, the risk assessor prepares a schematic diagram identifying the primary contamination sources and the potential exposure pathways (e.g., ingestion of contaminated water, inhalation of chemicals in air) by which different types of human populations (e.g., resident, workers, recreational visitors) might come into contact with contaminated media. This conceptual model is used to plan the human health risk assessment and associated data collection activities.
Exposure Assessment: The risk assessor identifies who is likely to be exposed at a site, the contaminants of potential concern (COPCs), the pathways by which exposure may occur, and the magnitude of the exposure (i.e., the dose). In some cases, exposure assessment may involve the use of probabilistic risk assessment (PRA) methods and/or biomonitoring.
Toxicity Assessment: The risk assessor compiles information on the types of adverse effects that each chemical of potential concern can cause, and how those effects depend on exposure amount (dose), route of exposure (oral, inhalation, dermal), and exposure duration. Note that adjusting toxicity values based on the site-specific bioavailability of chemicals is discussed in a separate section, Bioavailability.
Risk Characterization: The risk assessor combines the information on exposure and toxicity to predict the types of effects that may occur and to provide information on the probability or severity of those effects. Note that human exposure to and risk from lead and asbestos are characterized using a somewhat different approach than described above and are discussed in separate independent sections: Evaluation of Risks from Lead and Evaluation of Risks from Asbestos.
Uncertainty Analysis: The risk assessor identifies the main sources of uncertainty in the risk estimates presented in the risk characterization step and evaluates the likely direction and magnitude of the error that may be introduced by the uncertainties. This may be done either in a qualitative discussion or may be performed quantitatively.
Risk Assessment Guidance for Superfund (RAGS), Volume 1
Human Health Evaluation Manual
EPA developed detailed guidance for use at Superfund sites starting in 1989. The basic concepts of risk assessment and recommended strategies and approaches are presented in Risk Assessment Guidance for Superfund Volume I, Part A (usually referred to as RAGS A).
Since that time, EPA has issued a series of additional guidance documents that provide more specialized guidance of various aspects of the risk assessment process, including:
- Supplement to Part A: Community Involvement in Superfund Risk Assessments
- RAGS I Part B: Development of Risk-based Preliminary Remediation Goals
- RAGS I Part C: Risk Evaluation of Remedial Alternatives
- RAGS I Part D: Standardized Planning, Reporting, and Review of Superfund Risk Assessments
- RAGS I Part E: Supplemental Guidance for Dermal Risk Assessment, Final
EPA’s Framework for Human Health Risk Assessment to Inform Decision Making
As part of an agency-wide program by EPA’s Risk Assessment Forum, the Final Framework for Human Health Risk Assessment to Inform Decision Making was released in April 2014 to describe a framework for conducting human health risk assessments that are responsive to the needs of EPA’s decision making process.
Examples of Completed Region 8 Human Health Risk Assessments
Note: The strategies employed in the risk assessments below are based on site-specific considerations and may not be applicable to all sites.
- Baseline Human Health Risk Assessment - Vasquez Boulevard and I-70 Superfund Site (Denver, Colo., August 2001)
- Baseline Human Health Risk Assessment for the Ogden Railyard Site (Ogden, Utah, January 2003)
- Baseline Human Health Risk Assessment - Davenport and Flagstaff Smelter: Risks to Residents from Arsenic and Lead in Soil (Salt Lake Valley, Utah, February 2001)
- Baseline Human Health Risk Assessment - Eureka Mills (Eureka, Utah, September 2002)
- Baseline Human Health Risk Assessment for the Intermountain Waste Oil Refinery Site (Bountiful, Utah, May 2002)