Short-term inhalation exposure of healthy and compromised rats and mice to fine and ultrafine carbon particles

Epidemiological studies have consistently shown associations between acute pulmonary effects and relatively low levels of ambient particulate matter (PM). The present study was carried out to examine the pulmonary toxicity of inhaled fine (FCB) and ultrafine carbon (UFC) particles as model compounds for carbonaceous (primary) PM, and to identify whether particle sizer particle number, and/or mass could be critical in inducing the deleterious effects. Healthy and compromised rats and mice were exposed for 4 h/day during 3 consecutive days to 10(4) or 10(5) fine carbon black (similar to 300-500 nm), or 10(5) or 10(6) ultrafine carbon (similar to 30-60 nm) particles/cm(3), covering a mass range of about 10 to 10,000 mu g/m(3). Separate groups of rats were also exposed to a combination of FCB and fine ammonium nitrate at similar number and mass concentrations. Animals were sacrificed the day after the last exposure to determine their pulmonary responses using bronchoalveolar lavage fluid (BALF) analysis and lung histopathology. Exposure to FCB resulted in early signs of lung injury. Effects were not enhanced in compromised animals when compared to healthy animals. Exposure to UFC particles at similar and higher number concentrations did not induce any biologically relevant changes. These data may indicate that at number concentrations occurring in ambient air, the size of the particles (in air) is more important than their number.