Factors governing the mass loading of aerosolized carbon black particles with acid sulfates, inhalation exposure, and alveolar macrophage phagocytic function

A flow-past nose-only inhalation system is described for the coexposure of animals to carbon black aerosols (CBA) and sulfur dioxide (SO₂) at varying relative humidities (RH). The conversion of SO₂ to sulfate (SO₄/^2-) on the CBA, at a fixed aerosol concentration, was dependent on RH and SO₂ concentration. The effect of the aerosol gas mixture on alveolar macrophage (AM) phagocytosis was assessed 3 days following nose-only exposure of mice for 4 h. Exposure to 10 mg/m³ CBA alone at low RH (10%) and high RH (85%), to 10 ppm SO₂ alone at both RH, and to the mixture at low RH had no effect on AM phagocytosis. In contrast, AM phagocytosis was significantly suppressed following coexposure at 85% RH, the only circumstance in which significant chemisorption of the gas and oxidation to SO₄/^2- occurred. The results suggest that fine carbon particles are an effective vector for the delivery of toxic amounts of SO₄/^2- to the periphery of the lung under conditions of elevated RH.