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.

Sulfur dioxide and ammonium sulfate effects on pulmonary function and bronchial reactivity in human subjects.

The effect of exposures to 1 ppm sulfur dioxide (SO2) and 500 micrograms/m3 respirable ammonium sulfate [(NH4)2SO4] was studied in 20 nonsmoking subjects to determine if a response can be measured at these atmospheric levels and if the response is additive or synergistic. Four-hour separate and combined exposures were employed. Each subject acted as his or her own control and performed two light-to-moderate exercise stints (612 kg-m/min) for 15 minutes on each day's confinement in the environmental chamber. Pulmonary function tests (body plethysmography and spirometry) and bronchial reactivity to methacholine were performed to assess the response of these exposures. No significant changes in pulmonary function or bronchial reactivity were observed in the individual exposures [(NH4)2SO4 or SO2], the combined exposure [(NH4)2SO4 and SO2], or 24 hours post-exposure. This study design and the observed results did not demonstrate any readily apparent risk to healthy subjects with these exposures. Since no significant changes were measured, it was not possible to conclude if these two pollutants in combination produce an additive or synergistic response.