Acute exposure to sulfur dioxide and mortality: a case-crossover analysis of power plant emissions

Abstract

Purpose: Short-term exposure to sulfur dioxide has been associated with mortality; however, most studies have been conducted in metropolitan areas and do not account for point source emissions (e.g., proximity to power plants). During a three-year period, an administratively ordered air quality monitoring program captured sulfur dioxide (SO2) and particulate matter (PM2.5) emissions in communities within close proximity to a coal-fired power plant. This offered a unique opportunity to assess the health impacts in non-urban communities from this point source. Methods: We used a time-stratified case-crossover design to examine the impact of short-term exposure to SO2 on all-cause, respiratory, circulatory, stroke, and COPD mortality. Conditional logistic regression models were adjusted for PM2.5 exposure, daily average temperature, daily average dew point temperature, weekdays vs. weekends, and holidays. We assessed the influence of wind direction and peak exposures on mortality. Results: 4,693 deaths were included in our analysis. A one-unit increase in SO2 on the preceding day was associated with an increased risk in all-cause mortality [OR=1.03 (95% CI: 1.004,1.06)] and circulatory mortality [OR=1.05 (95% CI: 1.004,1.09)] during the summer season. However, after restricting the analysis to days when the wind trajectory blew from the power plant to impacted communities, SO2 exposure on the day of death and preceding day were significantly associated with all-cause, circulatory, respiratory, and stroke mortality during spring, summer, and winter. Persons over age 65 were more susceptible to these effects than those 65 and under. Conclusions: Communities in non-urban and rural areas can sustain significant health impacts from point source emissions of SO2, such as coal-fired power plants. Epidemiology studies of such sources should account for meteorological conditions, including wind direction.