Respiratory dose of inhaled ultrafine particles in healthy adults

Ultrafine particles (less than 0.10 mum in diameter) are ubiquitous in the atmosphere and possess unique physicochemical characteristics that may pose a potential health risk. To help elucidate the potential health risk, we measured respiratory dose of ultrafine particles (0.04, 0.06, 0.08 and 0.10 mum in diameter) in healthy young adults using a novel serial bolus-delivery method. Under normal breathing conditions (i.e. tidal volume of 500 mi and respiratory flow rate of 250 ml s(-1)), bolus aerosols were delivered sequentially to a lung depth ranging from 50-500 mi in 50 mi increments and deposition was measured for each of ten equal-volume compartments. Results show that regional deposition varies widely along the depth of the lung regardless of the particle sizes used. Peak deposition was found in the lung regions situated between 150 and 200 mi from the mouth. Sites of peak deposition shifted proximally with a decrease in particle size. Deposition dose per unit surface area was largest in the proximal lung regions and decreased rapidly with an increase in lung depth. Peak surface dose was 5-7 times greater than the average lung dose. The results indicate that local enhancement of dose occurs in normal lungs, and such a dose enhancement may play an important role in the potential health effects of ultrafine aerosols.