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Appendix B: EPA Memorandum from Henry Habicht
Pages 351-374

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From page 351...
... The guidance addresses a problem that affects public perception regarding the reliability of EPA's scientific assessments and related regulatory decisions. EPA has talented scientists, and public confidence in the quality of our scientific output will be enhanced by our visible interaction with peer scientists and through presentation of risk assessments and underlying scientific data.
From page 352...
... In order to make these decisions, mangers need to understand the strengths and limitations of the assessment. On this point, the guidance emphasizes that informed EPA risk assessors
From page 353...
... EPA's newly revised Exposure Assessment Guidelines provide standard descriptors of exposure and risk. Use of these terms in all Agency risk assessments
From page 354...
... For example, an emergency telephone inquiry does not require a full written risk assessment, but the caller must be told that EPA comments are based on a `'back-of-the-envelope" calculation and, like other preliminary or simple calculations, cannot be regarded as a risk assessment. GUIDANCE PRINCIPLES Guidance principles for developing, describing, and using EPA risk assessments are set forth in the Appendix.
From page 355...
... 3. Regarding exposure and risk characterization, it is Agency policy to present information on the range of exposures derived from exposure scenarios and on the use of multiple risk-descriptors (i.e., central tendency, high end of individual risk, population risk, important subgroups, if known)
From page 356...
... The Administrator and I believe that this effort is very important. It furthers our goals of rigor and candor in the preparation, presentation, and use of EPA risk assessments.
From page 357...
... Environmental Protection Agency Risk Assessment Council November, 1991 357
From page 358...
... Risk Assessment One group generates the risk assessment by collecting, analyzing, and synthesizing scientific data to produce the hazard identification, doseresponse, and exposure assessment portion of the risk assessment and to characterize risk. This group relies in part on Agency risk assessment guidelines to address science policy issues and scientific uncertainties.
From page 359...
... They do not make decisions on the acceptability of any risk level for protecting public health or selecting procedures for reducing risks. For users of the assessment and for decision-makers who integrate these assessments into regulatory decisions, the distinction between risk assessment and risk management means refraining from influencing the risk description through consideration of non-scientific factors-e.g., the regulatory outcome and from attempting to shape the risk assessment to avoid statutory constraints, meet regulatory objectives, or serve political purposes.
From page 360...
... Thus, regulatory decisions are usually based on a combination of the technical analysis used to develop the risk assessment and information from other fields. For this reason, risk assessors and managers should understand that the regulatory decision is usually not determined solely by the outcome of the risk assessment.
From page 361...
... The 1983 NRC report carefully distinguished qualitative risk assessment from quantitative assessments, preferring risk statements that are not strictly numerical. The term risk assessment is often given narrower and broader meanings than we have adopted here.
From page 362...
... 1. The risk assessment process calls for characterizing risk as a combination of qualitative information, quantitative information, and information regarding uncertainties.
From page 363...
... Methods for establishing dose-response relationships often depend on various assumptions used in lieu of a complete data base and the method chosen can strongly influence the overall assessment.. This relationship means that careful attention to the choice of a high-to-low dose extrapolation procedure is very important.
From page 364...
... The exposure assessment examines a wide range of exposure parameters pertaining to the "real world" environmental scenarios of people who may be exposed to the agents under study. The data considered for the exposure assessment range from monitoring studies of chemical concentrations in environmental media, food, and other materials to information on activity patterns of different population subgroups.
From page 365...
... Qualitative descriptions of this kind provide crucial information that augments understanding of numerical risk estimates. Uncertainties such as these are
From page 366...
... The risk assessment process calls for identifying and highlighting significant risk conclusions and related uncertainties partly to assure full communication among risk assessors and partly to assure that decision-makers are fully informed. Issues are identified by acknowledging noteworthy qualitative and quantitative factors that make a difference in the overall assessment of hazard and risk, and hence in the ultimate regulatory decision.
From page 367...
... Because different assessments presented different descriptors of risk without always making clear what was being described, the RAC discussed the advisability of using separate descriptors for population risk, individual risk, and identification of sensitive or highly exposed population segments. The RAC also discussed the need for consistency across programs and the advisability of requiring risk assessments to provide roughly comparable information to risk managers and the public through the use of a consistent set of risk descriptors.
From page 368...
... This analysis, in turn, allows risk managers to identify populations at greater and lesser risk and to shape regulatory solutions accordingly. EPA risk assessments will be expected to address or provide descriptions of (1)
From page 369...
... This conceptual range is not meant to precisely define the limits of this descriptor, but should be used by the assessor as a target range for characterizing "high end risk." Bounding estimates and worst case scenarios should not be termed high end risk estimates. The high end risk descriptor is a plausible estimate of the individual risk for those persons at the upper end of the risk distribution.
From page 370...
... Obviously, this method results in a large uncertainty and requires explanation. The risk descriptor addressing central tendency may be either the arithmetic mean risk (Average Estimate)
From page 371...
... Population risk refers to an assessment of the extent of harm for the population as a whole. In theory, it can be calculated by summing the individual risks for all individuals within the subject population.
From page 372...
... For non-linear cancer models, an estimate of population risk must be calculated by summing individual risks. For non-cancer effects, we generally have not developed the risk assessment techniques to the point of knowing how to add risk probability, so a second descriptor, below, is more appropriate.
From page 373...
... Generally, selection of the population segments is a matter of either a priori interest in the subgroup, in which case the risk assessor and risk manager can jointly agree on which subgroups to highlight, or a matter of discovery of a sensitive or highly exposed subgroup during the assessment process. In either case, once identified, the subgroup can be treated as a population in itself, and characterized the same way as the larger population using the descriptors for population and individual risk.
From page 374...
... persons might be subjected to the calculated exposure or risk in the real world. A calculation of risk based on specific hypothetical or actual combinations of factors postulated within the exposure assessment can also be useful as a risk descriptor.


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