Pulmonary effects of sulfur dioxide and respirable carbon aerosol

Four-hour individual and combined exposures to 1.0 ppm sulfur dioxide (SO2) and 0.5 mg/m3 (1.5 micron mass median diameter) activated carbon aerosol (ACA) were studied in 20 healthy nonsmoking subjects to determine if activated carbon as a "carrier" aerosol can augment the pulmonary response to SO2. Fifteen-minute exercise stints (VE = 35 liters/min) were performed at commencement and completion of each 4-hr period. Significant increases in nose or throat irritation occurred with the SO2 and SO2 + ACA exposures and in eye irritation with the SO2 + ACA exposure. Small, statistically significant decrements in spirometric function were observed following the first exercise (t = 17 min) for both the SO2 and SO2 plus ACA exposures; no significant changes were associated with the ACA exposure. Comparing function changes between the SO2 and the SO2 + ACA exposures demonstrated no statistically significant differences, thus a lack of SO2 response enhancement by the carbon aerosol. The determination that the activated carbon sorbed only 1% of the SO2 challenge concentration could explain the observed lack of SO2 response enhancement.