NUMBER CONCENTRATION AND MASS CONCENTRATION AS DETERMINANTS OF BIOLOGICAL RESPONSE TO INHALED IRRITANT PARTICLES

Particulate pollutants are mixtures of a variety of chemical species. Sulfuric acid aerosol is a highly irritating component of particulate matter less than 10 mu m (PM-10) that can produce adverse health effec ts at current peak ambient concentrations in the United States. We hyp othesized that, in addition to the mass concentration of sulfuric acid , the number of sulfuric acid droplets was also an important factor af fecting lung injury. To test this hypothesis, guinea pigs were exposed for 3 h to either filtered air; inert carbon particles at 10(8) parti cles/ml; sulfuric acid at 350 mu g SO42-/m(3) layered on 10(8), 10(7), or 10(6) carbon particles/ml; sulfuric acid at 50, 100, 200, and 300 mu g SO42-/m(3) layered on 10(8) carbon particles/ml. Alterations in p hagocytic capacity (PC), intracellular pH (pH(i)), and intracellular f ree calcium concentration ([Ca2+](i)) of harvested macrophages were us ed as indices of irritant potency. At a fixed number concentration of particles (10(8) particles/ml), there was a sulfuric acid concentratio n-dependent decrease in PC, pH(i) and [Ca2+](i). Furthermore, at a fix ed mass concentration (350 mu g SO42-/m(3)), sulfuric acid layered car bon particles at 10(8) particles/ml but not at other number concentrat ions decreased pH(i) of macrophages. The number concentration of sulfu ric acid layered carbon particles did not affect PC or [Ca2+](i). Thes e results suggest that there is a threshold for both number concentrat ion and mass concentration for the aerosols to produce a biological re sponse, and that epidemiologic studies should consider other aerosol c haracteristics in addition to mass when attempting to relate health en dpoints to ambient pollutant exposures.