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

We have developed a method for radiolabeling ultrafine carbon particle aggregates with technetium-99m. The carbon aggregate aerosol was chosen to mimic the physical properties of urban combustion or "soot-like" particulate, The radioisotope is a short lived (t(1/2) = 6.02 h) gamma emitter commonly used in human studies where scintigraphic methods are employed. Primary carbon particles, the aggregation of which is controlled by concentration and time, were produced by arcing between graphite electrodes under an argon atmosphere. Radiolabeling of particles was accomplished by applying a pertechnetate solution onto the tips of electrodes prior to arcing. The activity median diameter of experimental aerosols could be varied from 50 to 150 nm. The specific activity of aerosols increased with the amount of activity applied to the electrodes and decreased with time of generator operation. In-vitro leaching of the radioisotope from particles into solution was also measured. Leaching appeared to increase with the specific activity of the aerosol but was not affected by particle size.