Respiratory Tract Deposition of Inhaled Wood Smoke Particles in Healthy Volunteers

Background: Respiratory tract deposition of air pollution particles is a key to their adverse health effects. This study was aimed to determine the size-resolved deposition fraction (DF) of sooty wood smoke particles in the lungs of healthy subjects. The type of wood smoke investigated is typical for household air pollution from solid fuels, which is among the largest environmental health problems globally. Methods: Twelve healthy volunteers inhaled diluted wood smoke from incomplete soot-rich combustion in a common wood stove. The DF of smoke particles (10-500nm) was measured during three 15-min exposures in each subject during spontaneous breathing. Lung function was measured using standard spirometry. Results: The total DFs by particle number concentration were 0.340.08. This can be compared with DFs of 0.21-0.23 in healthy subjects during previous experiments with wood pellet combustion. For particle mass, the total DFs found in this study were 0.22 +/- 0.06. DF and breathing frequency were negatively correlated as expected from model calculations (p<0.01). Conclusions: The DF of the investigated sooty wood smoke particles was higher than for previously investigated particles generated during more efficient combustion of biomass. Together with toxicological studies, which have indicated that incomplete biomass combustion particles rich in soot and polycyclic aromatic hydrocarbons (PAHs) are especially harmful, these data highlight the health risks of inadequate wood combustion.