Generation of radiolabeled "soot-like" ultrafine aerosols suitable for usein human inhalation studies

We have developed a method for radiolabeling ultrafine carbon particle aggr egates with technetium-99m. The carbon aggregate aerosol was chosen to mimi c the physical properties of urban combustion or "soot-like" particulate, T he radioisotope is a short lived (t(1/2) = 6.02 h) gamma emitter commonly u sed in human studies where scintigraphic methods are employed. Primary carb on particles, the aggregation of which is controlled by concentration and t ime, were produced by arcing between graphite electrodes under an argon atm osphere. Radiolabeling of particles was accomplished by applying a pertechn etate solution onto the tips of electrodes prior to arcing. The activity me dian diameter of experimental aerosols could be varied from 50 to 150 nm. T he specific activity of aerosols increased with the amount of activity appl ied to the electrodes and decreased with time of generator operation. In-vi tro leaching of the radioisotope from particles into solution was also meas ured. Leaching appeared to increase with the specific activity of the aeros ol but was not affected by particle size.