Experimental Determination of the Deposition of Aerosol Particles in the Human Respiratory Tract

Sammanfattning: BACKGROUND: Aerosol particles have, since the antiquity, been linked to adverse effects on human health. It is estimated that the particles in urban air pollution cause at least 100,000 deaths in Europe each year, whereof 5,000 in Sweden. These figures do not include the outcomes of indoor sources or smoking, which shortens the lives of millions of people worldwide. During recent years especially the ultrafine particles (<0.1 µm), typically originating from combustion sources, have been a major concern. The deposition in the respiratory tract of these particles is one important factor determining their health effects. Limited data is available, especially for real-world aerosols. The objective of this thesis was to experimentally study the respiratory tract deposition of submicrometer aerosol particles. METHODS: A novel method (RESPI) was developed for investigation of fine and ultrafine particle deposition in the respiratory tract. It was designed to be used for human subjects in exposure studies and in typical ambient and indoor environments. RESPI was used in measurements of respiratory tract deposition for in total 50 subjects inhaling five aerosols (particles from NaCl, DEHS oil, two types of biomass combustion and from a busy street) during rest and exercise. RESULTS: It was shown that the probability of aerosol particles to deposit in the respiratory tract is altered by a factor 2-8 depending on particle size, particle solubility and individual breathing patterns. For particles in the studied size interval (10-600 nm), deposition probability was not, or only marginally, influenced by gender, level of exercise, particle shape and particle density. However, these factors altered the total amount of particles deposited. For example male and exercising subjects inhaled larger volumes of air, which increased the total number of deposited particles. Measurements of biomass combustion and street particles illustrated that the combined effects of physical and chemical properties of aerosols (particle size, density and solubility) may result in substantial differences in deposition. At the same mass exposure, the dose of traffic exhaust particles deposited in the respiratory tract was 16 times higher by number and 3 times higher by surface compared to those for biomass combustion particles. CONCLUSION: The results suggest that parts of the variations in toxicity of different aerosols could be explained by the amount of particles deposited in the respiratory tract. Furthermore, some individuals may be more susceptible to effects from air pollution due to a higher dose to the lungs.