The Importance of Population Susceptibility for Air Pollution Risk Assessment: A Case Study of Power Plants near Washington, DC
Levy, Jonathan I., Greco, Susan L., Spengler, John D., Environmental Health Perspectives
In evaluating risks from air pollution, health impact assessments often focus on the magnitude of the impacts without explicitly considering the distribution of impacts across subpopulations. In this study, we constructed a model to estimate the magnitude and distribution of health benefits associated with emission controls at five older power plants in the Washington, DC, area. We used the CALPUFF atmospheric dispersion model to determine the primary and secondary fine-particulate-matter (< 2.5 [micro]m in aerodynamic diameter) concentration reductions associated with the hypothetical application of "Best Available Control Technology" to the selected power plants. We combined these concentration reductions with concentration-response functions for mortality and selected morbidity outcomes, using, a conventional approach as well as considering susceptible subpopulations. Incorporating susceptibility had a minimal effect on total benefits, with central estimates of approximately 240 fewer premature deaths, 60 fewer cardiovascular hospital admissions (CHA), and 160 fewer pediatric asthma emergency room visits (ERV) per year. However, because individuals with lower education appear to have both higher background mortality razes and higher relative for air-pollution-related mortality, stratifying by educational attainment implies that 51% of the mortality benefits accrue among the 25% of the population with less high school education. Similarly, diabetics and African Americans bear disproportionate shares of the CHA and ERV benefits, respectively. Although our ability to characterize subpopulations is constrained by the available information, our analysis demonstrates that incorporation of susceptibility information significantly affects demographic and geographic patterns of health benefits and enhances our understanding of individuals likely to benefit from emission controls. Key words: asthma emergency department visits, cardiovascular hospital admissions, diabetes, education, mortality, particulate matter, power plant, risk assessment, susceptibility. Environ Health Perspect 110:1253-1260 (2002). [Online 29 October 2002]
The issue of subpopulation susceptibility to fine particulate matter (< 2.5 pm in aerodynamic diameter; P[M.sub.2.5]) has been given increased attention by researchers in recent years, motivated in part by the research priorities articulated by the National Academy of Sciences (1). Understanding patterns of susceptibility not only would help identify and protect sensitive subpopulations, but also would contribute to the understanding of mechanisms by which P[M.sub.2.5] might influence human health.
Often, air pollution policies are informed by risk assessments or benefit-cost analyses, which generally focus on the total health benefits of alternative emission control strategies (2-5). Because relevant susceptibility evidence is limited, differential effects on susceptible subpopulations are rarely incorporated. Typically, the same relative risks are applied to all individuals in an "at-risk" age group, and baseline rates of disease or health care use are assumed to be uniform across large geographic areas (often national averages).
However, it is likely that the effects of air pollution vary widely across subpopulations, depending on demographics, behavior patterns, income, access to health care, and other factors. Differences could exist either in relative risks (if an increment of air pollution yields a different percentage increase in different populations) or in absolute risks (if there are differences in baseline disease patterns by subpopulation, independent of air pollution). For a benefits assessment, if policy makers were concerned about distributional issues or if the ultimate valuation of benefits depended on population characteristics, the incorporation of susceptibility could potentially influence the conclusions. …