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 (SO42-) 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/m(3) 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 SO42- occurred. The results suggest that Fine carbon particles are an effective vector for the delivery of toxic amounts of SO42- to the periphery of the lung under conditions of elevated RH.