An Assessment of Potential Impacts of SO2 on Mild or Moderate Exercising Asthmatics. L. R. Shull, K. J. Yost, M. K. Jones, R. Bates, and B. Pugh, EMCON, 1433 N. Market Blvd., Sacramento, CA 95834; EMCON 15055 SW Sequoia Pkwy, Suite 140, Portland, OR 97224; and EMCON 6 Riverside Drive, Suite 101, Andover, MA 01810
The U.S. EPA recently recommended a revision to the National Ambient Air Quality Standard for sulfur dioxide (SO2). In a proposed rulemaking published in the Federal Register, EPA recommended a 5-minute standard of 6 ppm. This concentration may only be exceeded during one 5-minute interval per year. The basis for this criterion is the protection of mild and moderate asthmatics who exercise outside, a sensitive sub-population identified by EPA. Dose-response data clearly support the hypothesis that asthmatics who are exercising and are exposed to SO2 are at an increased risk of having an asthma attack. Many facilities that emit SO2 are concerned with EPA's proposed rulemaking. One such facility is a copper smelter in a small town in Arizona. The company performed a survey of the community to determine how many residents were asthmatic, what their exercise habits were, and when during the day their symptoms were worse. Out of 4,009 residents, 1,400 individuals were contacted through a random-dial phone survey. Air monitoring data were also collected at various locations around the town, allowing the number of 5-minute exceedances of 0.6 ppm to be quantified. The purpose of the study was two fold. The first objective was to determine the probability that a mild or moderate asthmatic will have an asthma attack while exercising due to exposure to SO2. The expected number of asthma attacks that would occur per year was calculated based on this probability. The second objective was to identify any correlation between being an asthmatic and the other variables measured in the study, such as gender, age, smoking status, number of years spent in the town, and presence of respiratory allergies. Another comparison of interest was between the time of day when asthma symptoms are worse and measured SO2 concentrations during those times. Results of the study indicate that the probability that a mild or moderate asthmatic who exercises outside will experience an asthma attack due to exposure to SO2 is extremely small (0.0117% chance per person per year). The only significant correlation identified was an inverse relationship between the time of day when symptoms are worse and SO2 concentrations.