Science and Judgment in Risk Assessment (1994) / Chapter Skim
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5 Risk Characterization
5 Risk Characterization
Pages 68-78
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From page 68... ...
to characterize the public-health risk associated with an emission source. In risk characterization, the assessor takes the exposure information from the exposure-assessment stage (discussed in Chapter 3)
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From page 69... ...
This value is usually expressed as a population risk, such as 1 x 10-6, which means that no more than one in 1 million exposed persons is expected to develop cancer. Risk estimates obtained in this way are not scientific estimates of actual cancer risk; they are upper bounds on actual cancer risk that are useful to regulators for setting priorities and for setting exposure limits.
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From page 70... ...
Uncertainty analysis can take place at the time of each of those analyses, but because it affects the eventual risk estimate, it is considered part of the final step of risk assessment risk characterization. Several recent documents illustrate EPA's current approach to the analysis of uncertainty associated with health risk assessment, including the Superfund document (EPA, 1989a)
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From page 71... ...
For individual risk, information such as the people at highest risk, the risk levels these individuals are subject to, the activities putting them at higher risk, and the average risk for individuals in the population of interest should be addressed. For population risk, information as to the number of cases of a particular health effect that might be probabilistically estimated in this population for a specific time period, the portion of the population that are within a specified range of some benchmark level for non-carcinogens; and, for carcinogens, the number of persons above a certain risk level should be included.
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From page 72... ...
. Section 8.4 of the document "discusses practical approaches to assessing uncertainty in Superfund site risk assessments and describes ways to present key information bearing on the level of confidence in quantitative risk estimates for a site." The document considers three categories of uncertainty associated with site risk assessments: selection of substances, toxicity values, and exposure assessments.
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From page 73... ...
, and any special considerations; the potential for synergistic or antagonistic interactions with other substances affecting the same individuals; and calculation of lifetime cancer risks on the basis of less-than-lifetime exposures. For each substance not included in the quantitative risk assessment because of inadequate toxicity information, list: · possible health effects; and · possible consequences of exclusion on final risk estimates.
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From page 74... ...
, distinguishing between known effects in humans and those that are predicted to occur based on animal experiments; · level of confidence in the quantitative toxicity information used to estimate risks and . presentation of qualitative information on the toxicity of substances not included in the quantitative assessment; level of confidence in the exposure estimates for key exposure pathways and related exposure parameter assumptions; the magnitude of the cancer risks and noncancer hazard indices relative to the Superfund site remediation goals in the NCP (e.g., the cancer risk range of 10 - to 10-7 and noncancer hazard index of 1.0)
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From page 75... ...
or over some shorter period sampled randomly from the distribution used to characterize home-residence time. The resulting charactenzation obtained for uncertainty in estimated total increased fatal-cancer risk associated with potential maximal exposure to all radionuclides for an exposure scenario involving a uranium-m~ll tailings pile is shown in Figure 5-1.
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From page 76... ...
Besides the exposure guidelines described above, the risk-characterization memorandum (Appendix B) provides guidance on risk characterization and uncertainty analysis for EPA risk managers and risk assessors.
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From page 77... ...
- c7 rig r Full Characterization of Risk: A full and open discussion of uncertainties in the body of each EPA risk assessment, including prominent display of critical uncertainties in the risk characterization. Numerical risk estimates should always be accompanied by descriptive information carefully selected to ensure an objective and balanced characterization of risk in risk assessment reports and regulatory documents.
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From page 78... ...
Communication of Risk Risk communication consists of two parts: communication between the risk assessor and the risk manager and communication between the risk-assessment management team and the public. The risk manager often receives the individual and population risk estimates (generally point estimates but occasionally ranges of these estimates)
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