Effect of TLV Levels of SO2and H2SO4on Bronchial Clearance in Exercising Man

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Abstract
Pulmonary mucociliary function was assessed following exposure to industrial threshold limit values (TLV) of sulfur dioxide (5 ppm) SO2 ) and sulphuric acid mist (1 mg/m3 H2 SO4 ). Bronchial clearance was measured in two sets of ten healthy exercising non-smoking adults under control and exposure conditions. A 99m Tc-albumen saline aerosol (MMD 3 μm) was inhaled as a bolus in late inspiration under controlled conditions to produce reproducible deposition in large airways. Lung retention of radioactivity was quantified using a gamma camera and computer analysis. Clearance was significantly faster (P < .05) on exposure to both SO2 and H2 SO4 compared to control values. Maximum mid-expiratory flow rates (MMFR) were significantly reduced (P < .01) on exposure to SO2 (mean decrease 8.5%), but only slightly reduced for H2 SO4 (1.4%). The speeding in clearance was probably an irritant response in both cases. For SO2 the response appeared predominantly reflex, while H2 SO4 showed evidence of a direct effect.