We exposed groups of healthy and asthmatic volunteers to
sulfuric acid aerosols with volume median droplet diameters of approximately 20, 10, and 1 microns, at nominal concentrations of 2,000 micrograms/m3, and exposed them similarly to
aerosols of purified water as a control. Exposures lasted 1 h each, and included three 10-min periods of exercise (ventilation rate typically 40 to 45 L/min). Exposures occurred in randomized order 7 days apart. Temperature was 10 degrees C, relative humidity was approximately 100% in 20- and 10-microns (fog) exposures, and approximately 75 to 80% in 1-micron
aerosol exposures. Healthy subjects showed no statistically significant changes in lung function or in bronchial reactivity to
methacholine attributable to
acid exposures. They showed significant increases in lower and upper respiratory
irritant symptoms when exposed to 20- or 10-microns
acid fog, but not when exposed to 1-micron
acid aerosol. Asthmatics showed significant excess decreases in forced expiratory performance, increases in airway resistance, and increases in
irritant symptoms during
acid exposures, relative to control conditions. Lung function changes in asthmatics tended to increase with time during exposure; they did not vary significantly with
acid droplet size. Symptoms in asthmatics were slightly worse with 10- or 20-microns fog as compared with 1-micron
aerosol. In a few instances, symptoms and lung function decrements necessitated stopping exercise or terminating the exposure early. Thus,
asthma is a risk factor for unfavorable physiologic response to
sulfuric acid at occupational exposure concentrations. Large droplet size (i.e., fog) tends to exacerbate short-term symptomatic response, but we have not been able to demonstrate a consistent effect of droplet size on physiologic response.